Method for producing polytetrafluoroethylene fine powder, and polytetrafluoroethylene powder

Abstract

Provided are: a method for producing a polytetrafluoroethylene fine powder, which enables a clean working environment; and a polytetrafluoroethylene powder. The present invention pertains to a method for producing a polytetrafluoroethylene fine powder having an average particle diameter of 20 [mu] m or less, the method comprising a step for irradiating a polytetrafluoroethylene powder having an average particle diameter of 700 [mu] m or more with ionizing radiation to obtain a polytetrafluoroethylene fine powder having an average particle diameter of 20 [mu] m or less.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing polytetrafluoroethylene fine powder and polytetrafluoroethylene powder. Background Art

[0002] A method of irradiating a fluororesin such as polytetrafluoroethylene (PTFE) with ionizing radiation and then pulverizing it to micronize the fluororesin is well known (see, for example, Patent Document 1).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Laid-Open No. 2-139204 Summary of the Invention

[0006] Technical Problem to be Solved by the Invention

[0007] In Patent Document 1, regarding the fluororesin irradiated with ionizing radiation, it is only described that "it may be any one of powdery, granular, fibrous, preformed fluororesin, etc.", and no sufficient research has been conducted.

[0008] An object of the present invention is to provide a method for manufacturing polytetrafluoroethylene fine powder and polytetrafluoroethylene powder that can achieve a clean working environment.

[0009] Means for Solving the Technical Problem

[0010] The present invention (1) is a method for manufacturing polytetrafluoroethylene fine powder (hereinafter also referred to as "the manufacturing method of the present invention"), wherein, through the step of irradiating polytetrafluoroethylene powder with an average particle size of 700 μm or more with ionizing radiation, polytetrafluoroethylene fine powder with an average particle size of 20 μm or less is obtained.

[0011] The present invention (2) is the method for manufacturing polytetrafluoroethylene fine powder according to the present invention (1), wherein the melt viscosity of the above polytetrafluoroethylene fine powder at 380 °C is 1×10 1 ~7×10 5 Pa·s.

[0012] The present invention (3) is the method for manufacturing polytetrafluoroethylene fine powder according to the present invention (1) or (2), wherein the apparent density of the above polytetrafluoroethylene powder is 0.40 g / ml or less.

[0013] The present invention (4) is the method for manufacturing polytetrafluoroethylene fine powder according to any one of the present invention (1) to (3), wherein the above polytetrafluoroethylene powder is obtained by sieving using a sieve with a mesh size of 700 μm to 2 mm.

[0014] The manufacturing method of the polytetrafluoroethylene fine powder according to any one of the present inventions (1) to (4), wherein the powder raising induction index of the above-mentioned polytetrafluoroethylene powder in the powder raising induction test carried out under the following conditions is 2 or less.

[0015] (Powder raising induction test)

[0016] The polytetrafluoroethylene powder scooped up with a stainless steel measuring spoon having a width of 133 mm, a length of 205 mm, and a depth of 70 mm is dropped from a height of 1.2 mm into an 18 L plastic container, and the amount of powder raised at this time is compared; the comparison is visually performed by 3 people, and indexing (powder raising induction index) is carried out according to the following procedures.

[0017] 1: It is clearly seen that no powder is raised.

[0018] (Within 5 seconds after the polytetrafluoroethylene powder is dropped into an 18 L plastic container (height 32 cm), the state of powder-like polytetrafluoroethylene powder particles cannot be visually confirmed in the upper part of the upper surface (the part at a height of 32 cm) of the plastic container.)

[0019] 2: Powder is raised, but it is a trace amount.

[0020] (Within 5 seconds after the polytetrafluoroethylene powder is dropped into an 18 L plastic container (height 32 cm), powder-like polytetrafluoroethylene powder particles can be visually confirmed in the upper part of the upper surface (the part at a height of 32 cm) of the plastic container, but cannot be visually confirmed after 5 seconds, and it is such a state of trace powder raising.)

[0021] 3: Powder is raised and may adhere to the operator's clothes.

[0022] (Within 5 seconds after the polytetrafluoroethylene powder is dropped into an 18 L plastic container (height 32 cm), powder-like polytetrafluoroethylene powder particles can be visually confirmed in the upper part about 5 cm above the upper surface (the part at a height of 32 cm) of the plastic container, and the state of accumulation of fine powder of polytetrafluoroethylene powder is confirmed on the floor surface where the plastic container is placed, although the accumulation amount is very small. The polytetrafluoroethylene powder may adhere to the operator's clothes and shoes. The accumulation amount is a small amount that is difficult to measure.)

[0023] 4: It is clearly seen that powder is raised.

[0024] (Within 5 seconds after the polytetrafluoroethylene powder is dropped into an 18 L plastic container (height 32 cm), the state of powder-like polytetrafluoroethylene powder particles can be visually confirmed in the upper part about 10 cm above the upper surface (the part at a height of 32 cm) of the plastic container.)

[0025] The present invention (6) is a polytetrafluoroethylene powder (hereinafter also referred to as "the first PTFE powder of the present invention"), wherein the apparent density is 0.40 g / ml or less and the average particle diameter is 700 μm or more.

[0026] The present invention (7) is the polytetrafluoroethylene powder described in the present invention (6), wherein the powder lifting induction index in the powder lifting induction test conducted under the following conditions is 2 or less.

[0027] (Powder lifting induction test)

[0028] The polytetrafluoroethylene powder scooped up with a stainless steel measuring spoon having a width of 133 mm, a length of 205 mm, and a depth of 70 mm is dropped from a height of 1.2 mm into an 18 L plastic container, and the amount of powder lifted at this time is compared. The comparison is visually performed by 3 persons, and indexing is performed according to the following procedures (powder lifting induction index).

[0029] 1: No powder lifting is clearly visible.

[0030] (Within 5 seconds after the polytetrafluoroethylene powder is dropped into an 18 L plastic container (height 32 cm), the state of powdery polytetrafluoroethylene powder particles cannot be visually confirmed in the upper part of the upper surface (the part at a height of 32 cm) of the plastic container.)

[0031] 2: There is powder lifting, but it is trace amount.

[0032] (Within 5 seconds after the polytetrafluoroethylene powder is dropped into an 18 L plastic container (height 32 cm), powdery polytetrafluoroethylene powder particles can be visually confirmed in the upper part of the upper surface (the part at a height of 32 cm) of the plastic container, but cannot be visually confirmed after 5 seconds, and this is a state of trace powder lifting.)

[0033] 3: There is powder lifting, and it may adhere to the operator's clothes.

[0034] (Within 5 seconds after the polytetrafluoroethylene powder is dropped into an 18 L plastic container (height 32 cm), powdery polytetrafluoroethylene powder particles can be visually confirmed in the upper part about 5 cm above the upper surface (the part at a height of 32 cm) of the plastic container, and the accumulation of fine powder of polytetrafluoroethylene powder is confirmed on the floor surface where the plastic container is placed, although the accumulation amount is small. The polytetrafluoroethylene powder may adhere to the operator's clothes and shoes. The accumulation amount is a small amount that is difficult to measure.)

[0035] 4: Powder lifting is clearly visible.

[0036] (Within 5 seconds after the polytetrafluoroethylene powder falls into an 18 L plastic container (height 32 cm), the state of the powdery polytetrafluoroethylene powder particles can be visually confirmed in the upper part about 10 cm above the upper surface of the plastic container (the part at a height of 32 cm).)

[0037] The present invention (8) is a polytetrafluoroethylene powder (hereinafter also referred to as "the second PTFE powder of the present invention"), wherein the average particle size is 700 μm or more, and it contains 3% by weight or less of fine powder with a mesh size of 42 or less.

[0038] The present invention (9) is the polytetrafluoroethylene powder described in the present invention (8), wherein the apparent density is 0.40 g / ml or less.

[0039] The present invention (10) is the polytetrafluoroethylene powder described in the present invention (8) or (9), and it is a fine polytetrafluoroethylene powder.

[0040] The present invention (11) is a polytetrafluoroethylene powder (hereinafter also referred to as "the third PTFE powder of the present invention"), which is used as a raw material for polytetrafluoroethylene fine powder, and the average particle size is 700 μm or more.

[0041] Effects of the Invention

[0042] According to the present invention, a method for manufacturing polytetrafluoroethylene fine powder and a polytetrafluoroethylene powder that can achieve a clean working environment can be provided. Detailed Embodiments

[0043] In this specification, an "organic group" refers to a group containing one or more carbon atoms, or a group formed by removing one hydrogen atom from an organic compound.

[0044] Examples of such "organic groups" include:

[0045] An alkyl group that may have one or more substituents,

[0046] An alkenyl group that may have one or more substituents,

[0047] An alkynyl group that may have one or more substituents,

[0048] A cycloalkyl group that may have one or more substituents,

[0049] A cycloalkenyl group that may have one or more substituents,

[0050] A cyclo-dienyl group that may have one or more substituents,

[0051] An aryl group that may have one or more substituents,

[0052] An aralkyl group that may have one or more substituents,

[0053] A non-aromatic heterocyclic group which may have one or more substituents,

[0054] A heteroaryl group which may have one or more substituents,

[0055] Cyano group,

[0056] Formyl group,

[0057] RaO-,

[0058] RaCO-,

[0059] RaSO2-,

[0060] RaCOO-,

[0061] RaNRaCO-,

[0062] RaCONRa-,

[0063] RaOCO-,

[0064] RaOSO2-, and

[0065] RaNRbSO2-

[0066] (In these formulas, Ra is independently

[0067] An alkyl group which may have one or more substituents,

[0068] An alkenyl group which may have one or more substituents,

[0069] An alkynyl group which may have one or more substituents,

[0070] A cycloalkyl group which may have one or more substituents,

[0071] A cycloalkenyl group which may have one or more substituents,

[0072] A cyclo-dienyl group which may have one or more substituents,

[0073] An aryl group which may have one or more substituents,

[0074] An aralkyl group which may have one or more substituents,

[0075] A non-aromatic heterocyclic group which may have one or more substituents, or

[0076] A heteroaryl group which may have one or more substituents,

[0077] Rb is independently H or an alkyl group which may have one or more substituents).

[0078] As the organic group, an alkyl group which may have one or more substituents is preferred.

[0079] The present invention is described in detail below.

[0080] <Production method of the present invention>

[0081] In the production method of the present invention, PTFE fine powder having an average particle size of 20 μm or less is obtained by irradiating PTFE powder having an average particle size of 700 μm or more with ionizing radiation.

[0082] In the method disclosed in Patent Document 1, when irradiating ionizing radiation to PTFE powder, the PTFE powder needs to be filled into a special container for irradiating ionizing radiation. Generally, the average particle size of PTFE powder used as a raw material for PTFE micropowder is 300 to 650 μm. If the average particle size is within this range, when the PTFE powder is filled into the container, the working environment sometimes deteriorates due to the lifting of the PTFE powder. In contrast, in the manufacturing method of the present invention, by making the average particle size of the PTFE powder irradiated with ionizing radiation be 700 μm or more, the lifting of the PTFE powder can be reduced, thereby achieving a clean working environment.

[0083] In addition, when the PTFE fine powder obtained by the production method of the present invention is compared with the PTFE fine powder produced from PTFE powder having an average particle size of 300 to 650 μm, no substantial difference is found in properties. Therefore, the PTFE fine powder can be used in the same applications as the existing PTFE fine powder.

[0084] In addition, PTFE powder is roughly divided into a powder called PTFE fine powder and a powder called PTFE molding powder. PTFE fine powder is known as a raw material for high-function products such as the coating layer of special porous membranes, pipes, and electric wires. In such high-function products, in order to suppress the occurrence of cavities, coarse particles with an average particle size of more than 700 μm are usually removed from the PTFE fine powder for use. That is, the commodity value of the PTFE fine powder with an average particle size of more than 700 μm is small. The manufacture method of the present invention also has the advantage of being able to effectively utilize the PTFE fine powder with an average particle size of more than 700 μm.

[0085] In addition, PTFE molding powder is known as a raw material for special gaskets and also as a raw material for special high-function products such as rods, tubes, and sheets. In such high-function products, in order to suppress the occurrence of voids, coarse particles are usually removed from PTFE molding powder before use. However, the size of the coarse particles varies depending on the product form of PTFE molding powder, so it is difficult to define it fundamentally.

[0086] The average particle size of the above-mentioned PTFE powder may be 700 μm or more, preferably 850 μm or more, more preferably 900 μm or more, further preferably 940 μm or more, and particularly preferably 1000 μm or more. There is no particular limitation on the upper limit, and it is preferably 10000 μm or less.

[0087] It should be noted that as the PTFE powder, the average particle size may be 700 μm or more, and it may also contain fine powder with a particle size less than 700 μm.

[0088] The average particle size of the above-mentioned PTFE powder can be measured by the following method.

[0089] Stack 10, 20, 32, 48, 60, and 83 mesh (inch mesh) standard sieves in order from above. Place the PTFE powder on the 10-mesh sieve, vibrate the sieve to make the fine PTFE powder fall downward in turn, and after obtaining the proportion of the PTFE powder remaining on each sieve in %, mark the cumulative % of the remaining proportion (vertical axis) on the logarithmic probability paper with respect to the mesh size of each sieve (horizontal axis), connect these points with a straight line, and find the particle size at which the proportion reaches 50% on this straight line, and take this value as the average particle size.

[0090] The above-mentioned PTFE powder is obtained, for example, by sieving using a sieve with a mesh size of 700 μm to 2 mm. Examples of such a sieve include 8 to 24 mesh sieves. From the perspective of the yield, 8 mesh and 10 mesh are preferred.

[0091] In this specification, the mesh size of the sieve is the nominal size in JIS Z8801-1:2019.

[0092] The content of fine powder with 42 mesh or less (such as 48 mesh, etc.) in the above-mentioned PTFE powder is preferably 3% by weight or less relative to the total amount of the PTFE powder. When the content of fine powder with 42 mesh or less relative to the total amount of the PTFE powder is in such a range, the effects of the present invention can be obtained better. As this content, relative to the total amount of the PTFE powder, it is preferably 2.5% by weight or less, more preferably 2.0% by weight or less, further preferably 1.5% by weight or less, and particularly preferably 1.0% by weight or less.

[0093] The content of the fine powder with 42 mesh or less can be measured by, for example, the method described in the following examples.

[0094] It should be noted that in this specification, "fine powder with 42 mesh or less" refers to the fine powder that passes through the mesh when classified with a mesh of 42 mesh or less.

[0095] The apparent density of the above-mentioned 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 preferably 0.40 g / ml or less.

[0096] The apparent density of the PTFE powder is measured in accordance with JIS K 6892.

[0097] The standard specific gravity (SSG) of the above PTFE powder is preferably 2.130 to 2.280. The above standard specific gravity is measured by the water displacement method in accordance with ASTM D 792 using a sample molded in accordance with ASTM D4895 89.

[0098] The powder lift induction index of the above PTFE powder in the powder lift induction test conducted under the following conditions is preferably 2 or less, more preferably 1. When the powder lift induction index in the powder lift induction test conducted under the following conditions is in such a range, the lift of the PTFE powder is suppressed, and a clean working environment can be achieved.

[0099] (Powder lift induction test)

[0100] The polytetrafluoroethylene powder scooped up with a stainless steel measuring spoon with a width of 133 mm, a length of 205 mm, and a depth of 70 mm is dropped from a height of 1.2 mm into an 18 L plastic container, and the amount of powder lift generated at this time is compared. The comparison is visually made by 3 people, and the indexation (powder lift induction index) is carried out according to the following procedure.

[0101] 1: No powder lift is clearly visible.

[0102] (Within 5 seconds after the polytetrafluoroethylene powder is dropped into an 18 L plastic container (height 32 cm), the state where powdery polytetrafluoroethylene powder particles cannot be visually confirmed in the upper part of the upper surface (the part at a height of 32 cm) of the plastic container.)

[0103] 2: There is powder lift, but it is in a very small amount.

[0104] (Within 5 seconds after the polytetrafluoroethylene powder is dropped into an 18 L plastic container (height 32 cm), powdery polytetrafluoroethylene powder particles can be visually confirmed in the upper part of the upper surface (the part at a height of 32 cm) of the plastic container, but they cannot be visually confirmed after 5 seconds, and it is in a state of such a very small amount of powder lift.)

[0105] 3: There is powder lift, and it may adhere to the operator's clothes.

[0106] (Within 5 seconds after the polytetrafluoroethylene powder fell into an 18L plastic container (32cm in height), powdered polytetrafluoroethylene powder particles could be visually confirmed in the upper portion of about 5cm from the upper surface of the plastic container (the portion at a height of 32cm), and fine accumulation of polytetrafluoroethylene powder was confirmed on the floor surface where the plastic container was placed, although the accumulation amount was very small. The polytetrafluoroethylene powder may adhere to the clothes and shoes of the operator. The accumulation amount was a small amount that was difficult to measure.)

[0107] 4: Powder is clearly seen rising.

[0108] (Within 5 seconds after the polytetrafluoroethylene powder fell into the 18L plastic container (32cm in height), the state of the powdered polytetrafluoroethylene powder particles could be visually confirmed in the upper portion of about 10cm from the upper surface of the plastic container (the portion with a height of 32cm).)

[0109] The PTFE of the above-mentioned PTFE powder can be a homopolymer of tetrafluoroethylene (TFE), or can be a modified PTFE comprising a polymerized unit based on TFE (TFE unit) and a polymerized unit based on a modified monomer (hereinafter also referred to as "modified monomer unit"). The above-mentioned modified PTFE can comprise a TFE unit of more than 99.0 mass % and a modified monomer unit of less than 1.0 mass %. In addition, the above-mentioned modified PTFE can be composed only of a TFE unit and a modified monomer unit.

[0110] In the above-mentioned modified PTFE, the content of the modified monomer unit is preferably in the scope of 0.00001~1.0 mass % relative to all polymerized units. As the lower limit of the content of the modified monomer unit, it is more preferably 0.0001 mass %, more preferably 0.001 mass %, and further preferably 0.005 mass %, and especially more preferably 0.010 mass %. As the upper limit of the content of the modified monomer unit, it is preferably 0.90 mass %, more preferably 0.50 mass %, further preferably 0.40 mass %, and further more preferably 0.30 mass %, and further more preferably 0.20 mass %, especially more preferably 0.15 mass %, and particularly preferably 0.10 mass %.

[0111] In the present specification, the modified monomer unit refers to a part of the molecular structure of PTFE, and is a part derived from a modified monomer.

[0112] The content of each polymerized unit can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and fluorescent X-ray analysis according to the type of monomer.

[0113] As the above-mentioned modified monomer, there is no particular limitation as long as it can copolymerize with TFE. Examples thereof include perfluoroolefins such as hexafluoropropylene [HFP]; hydrogen-containing fluorinated olefins such as trifluoroethylene and vinylidene fluoride [VDF]; perhaloolefins such as chlorotrifluoroethylene; perfluoro vinyl ethers: perfluoroallyl ethers; (perfluoroalkyl)ethylene, ethylene, etc. In addition, the modified monomer used may be one kind or two or more kinds.

[0114] There is no particular limitation on the above-mentioned perfluoro vinyl ether. For example, it may include those represented by the following general formula (A)

[0115] CF2=CF-ORf (A)

[0116] (In the formula, Rf represents a perfluoro organic group) and other perfluoro unsaturated compounds. In this specification, the above-mentioned "perfluoro organic group" refers to an organic group in which all hydrogen atoms bonded to carbon atoms are replaced by fluorine atoms. The above-mentioned perfluoro organic group may also have an ether oxygen.

[0117] As the above-mentioned perfluoro vinyl ether, for example, perfluoro(alkyl vinyl ether) [PAVE] in which Rf in the above general formula (A) is a perfluoroalkyl group having 1 to 10 carbon atoms can be cited. The number of carbon atoms of the above-mentioned perfluoroalkyl group is preferably 1 to 5.

[0118] As the perfluoroalkyl group in the above-mentioned PAVE, for example, perfluoromethyl, perfluoroethyl, perfluoropropyl, perfluorobutyl, perfluoropentyl, perfluorohexyl, etc. can be cited.

[0119] As the above-mentioned perfluoro vinyl ether, more preferably, perfluoro vinyl ether in which Rf in the above general formula (1) is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, Rf is a group represented by the following formula:

[0120] [Chemical formula 1]

[0121]

[0122] (In the formula, m represents an integer of 0 or 1 to 4), perfluoro vinyl ether in which Rf is a group represented by the following formula:

[0123] [Chemical formula 2]

[0124]

[0125] (In the formula, n represents an integer of 1 to 4), and other perfluoro vinyl ethers.

[0126] As (perfluoroalkyl)ethylene (PFAE), there is no particular limitation. For example, (perfluorobutyl)ethylene (PFBE), (perfluorohexyl)ethylene, etc. can be cited.

[0127] As perfluoroallyl ether, for example, the general formula (B) can be cited:

[0128] CF2=CF-CF2-ORf 1 (B)

[0129] (wherein, Rf 1 represents a perfluoro organic group) the fluorine-containing monomer represented.

[0130] Said Rf 1 is preferably a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoroalkoxyalkyl group having 1 to 10 carbon atoms. As the above-mentioned perfluoroallyl ether, 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 is preferred, and 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 is more preferred, and CF2=CF-CF2-O-CF2CF2CF3 is further preferred.

[0131] As the above-mentioned modified monomer, at least one selected from the group consisting of PAVE and HFP is preferred, and at least one selected from the group consisting of perfluoro(methyl vinyl ether) (PMVE) and HFP is more preferred.

[0132] In the heat of fusion curve of the above-mentioned PTFE when heated at a rate of 10 °C / minute using a differential scanning calorimeter [DSC], one or more endothermic peaks appear in the range of 325 to 347 °C, and the heat of fusion in the range of 290 to 350 °C calculated from the above-mentioned heat of fusion curve is preferably 62 mJ / mg or more.

[0133] The above-mentioned PTFE can be produced by, for example, emulsion polymerization or suspension polymerization, the above-mentioned PTFE fine powder can be produced by, for example, emulsion polymerization, and the above-mentioned PTFE molding powder can be produced by, for example, suspension polymerization.

[0134] The above-mentioned emulsion polymerization can be carried out by a known method. For example, in the presence of an anionic fluorinated surfactant and a polymerization initiator, emulsion polymerization of the monomers required to form the above-mentioned PTFE is carried out in an aqueous medium to obtain an aqueous dispersion containing the above-mentioned PTFE particles (primary particles). In the above-mentioned emulsion polymerization, a chain transfer agent, a buffer, a pH regulator, a stabilization aid, a dispersion stabilizer, a radical scavenger, etc. can be used as needed.

[0135] The above suspension polymerization can be carried out by known methods. For example, in the presence of water and a polymerization initiator, polymerization of the monomers required to form the above PTFE is carried out, whereby particles of the above PTFE are obtained. In the above suspension polymerization, a chain transfer agent, a buffer, a pH regulator, a stabilization aid, a dispersion stabilizer, a radical scavenger, etc. can be used as needed.

[0136] The ionizing radiation irradiated onto the above PTFE powder is not particularly limited, and examples thereof include electron beams, ultraviolet rays, γ-rays, X-rays, neutron rays, high-energy ions, etc., and electron beams or γ-rays are preferred.

[0137] As the radiation dose of the above ionizing radiation, 1 to 2500 kGy is preferred, more preferably 1000 kGy or less, and still more preferably 750 kGy or less. Additionally, more preferably 10 kGy or more, and still more preferably 100 kGy or more.

[0138] As the irradiation temperature of the above ionizing radiation, there is no particular limitation as long as it is 5°C or higher and below the melting point of PTFE. It is also known that the molecular chains of PTFE crosslink near the melting point. In order to obtain low-molecular-weight PTFE, it is preferably 320°C or lower, more preferably 300°C or lower, and still more preferably 260°C or lower. From an economic perspective, irradiation at room temperature is preferred.

[0139] The irradiation of the above ionizing radiation can be carried out in any atmosphere, for example, it can be carried out in air, an inert gas, a vacuum, etc. From the aspect of being able to be carried out at low cost, irradiation in air is preferred.

[0140] In the manufacturing method of the present invention, through the process of irradiating the above PTFE powder with ionizing radiation, PTFE fine powder with an average particle size of 20 μm or less is obtained.

[0141] The above PTFE fine powder is obtained, for example, by pulverizing after irradiating the above PTFE powder with ionizing radiation.

[0142] As the method of the above pulverization, there is no particular limitation, and examples thereof include a method of pulverizing using a pulverizer. The above pulverizer includes impact pulverizers such as a planetary pulverizer, a hammer mill, a pin mill, a jet mill, etc., and attrition pulverizers such as a cutting pulverizer that pulverizes using the shearing force caused by the unevenness between a rotating blade and an outer peripheral stator, etc.

[0143] The pulverization temperature is preferably -200°C or higher and less than 50°C. Pulverization can be carried out at a temperature near room temperature (10 to 30°C), or it can be cryogenic pulverization at -200 to -100°C.

[0144] After the above-mentioned pulverization, coarse particles can be removed by further classification after removing particulate and fibrous particles by air classification.

[0145] The average particle size of the above-mentioned PTFE fine powder is preferably 20 μm or less, more preferably 15 μm or less, still more preferably 10 μm or less. In addition, it is preferably 1 μm or more.

[0146] The above-mentioned average particle size is measured using a laser diffraction particle size distribution measuring device (HELOS&RODOS) manufactured by JEOL Ltd., and the average particle size is set to the particle size corresponding to 50% of the integral of the particle size distribution.

[0147] The melt viscosity of the above-mentioned PTFE fine powder at 380 °C is preferably 1×10 1 Pa·s or more, more preferably 5×10 2 Pa·s or more. In addition, it is preferably 7×10 5 Pa·s or less, more preferably 2×10 5 Pa·s or less, still more preferably 1×10 5 Pa·s or less.

[0148] The above-mentioned melt viscosity is the value measured as follows: According to ASTM D 1238, using an elevated flow tester (manufactured by Shimadzu Corporation) and a die head, a 2 g sample preheated at 380 °C for 5 minutes is held at the above temperature under a load of 0.7 MPa for measurement.

[0149] <The first PTFE powder of the present invention>

[0150] The apparent density of the first PTFE powder of the present invention is 0.40 g / ml or less, and the average particle size is 700 μm or more.

[0151] The first PTFE powder of the present invention can preferably be used as the PTFE powder in the manufacturing method of the present invention. That is, it can preferably be used as the raw material of the PTFE fine powder. The preferred modes of the PTFE powder described in the manufacturing method of the present invention can also be applied to the first PTFE powder of the present invention.

[0152] <The second PTFE powder of the present invention>

[0153] The average particle size of the second PTFE powder of the present invention is 700 μm or more, and it contains 3% by weight or less of fine powder with a mesh size of 42 or less.

[0154] The second PTFE powder of the present invention can preferably be used as the PTFE powder in the manufacturing method of the present invention. That is, it can preferably be used as the raw material of PTFE fine powder. The preferred manner of the PTFE powder described in the manufacturing method of the present invention can also be applied to the second PTFE powder of the present invention.

[0155] <The third PTFE powder of the present invention>

[0156] The third PTFE powder of the present invention is used as the raw material of PTFE fine powder and has an average particle size of 700 μm or more.

[0157] The above-mentioned PTFE fine powder is the same as the PTFE fine powder in the manufacturing method of the present invention, and the preferred manner is also the same.

[0158] The third PTFE powder of the present invention can preferably be used as the PTFE powder in the manufacturing method of the present invention. The preferred manner of the PTFE powder described in the manufacturing method of the present invention can also be applied to the third PTFE powder of the present invention.

[0159] The embodiments have been described above, but it can be understood that various changes can be made to the manner and details without departing from the spirit and scope of the claims.

[0160] Examples

[0161] Next, examples are given to explain the present invention in more detail, but the present invention is not limited to these examples.

[0162] Various physical properties were measured by the following methods.

[0163] Apparent density of PTFE powder

[0164] Measured according to JIS K6892.

[0165] Average particle size of PTFE powder and PTFE fine powder

[0166] Standard sieves of 10, 20, 32, 48, 60, and 83 mesh (inch mesh) were overlapped in order from above. The PTFE powder was placed on the 10-mesh sieve, and the sieve was vibrated to make the fine PTFE powder fall downward in turn. After obtaining the proportion of the PTFE powder remaining on each sieve in %, the cumulative % of the remaining proportion (vertical axis) was marked on the logarithmic probability paper with respect to the mesh of each sieve (horizontal axis), and these points were connected with a straight line. The particle size at which the proportion reached 50% was obtained on this straight line, and this value was taken as the average particle size.

[0167] The average particle size of the PTFE fine powder was measured using a laser diffraction particle size distribution measuring device (HELOS&RODOS) manufactured by JEOL Ltd., and the average particle size was set to be equal to the particle size corresponding to 50% of the particle size distribution integral.

[0168] The proportion of micro powder in PTFE powder

[0169] The PTFE powder was sieved with a 48-mesh (inch mesh) sieve, and the undersize ratio (ratio of the powder passing through the sieve to the total amount of the PTFE powder) at this time was measured (passing 48 mesh).

[0170] Lifting induction test of PTFE fine powder

[0171] The PTFE fine powder scooped with a stainless steel measuring spoon of 133 mm wide, 205 mm long and 70 mm deep was dropped from a height of 1.2 mm into an 18L plastic container, and the amount of powder flying generated was compared. The comparison was made by 3 people visually, and the index (powder flying sensitivity index) was calculated according to the following method.

[0172] 1: No powder is obviously seen to be raised.

[0173] (Within 5 seconds after the PTFE fine powder was dropped into the 18L plastic container (32cm in height), the state of the powdered PTFE fine powder particles could not be visually confirmed on the upper part of the upper surface (32cm in height) of the plastic container.)

[0174] 2: Powder is raised, but it is very small.

[0175] (Within 5 seconds after the PTFE fine powder was dropped into the 18L plastic container (32cm in height), powdered PTFE fine powder particles could be visually confirmed on the upper part of the upper surface of the plastic container (the part with a height of 32cm), but after 5 seconds, they could not be visually confirmed, indicating that a small amount of powder was flying.)

[0176] 3: Powder is raised and may adhere to the worker's clothes.

[0177] (Within 5 seconds after the PTFE fine powder was dropped into the 18L plastic container (32cm in height), powdered PTFE fine powder particles were visually confirmed in the upper portion of about 5cm from the upper surface of the plastic container (the portion at the height of 32cm), and the accumulation of fine PTFE fine powder was confirmed on the floor surface where the plastic container was placed, although the accumulation amount was very small. The PTFE fine powder may adhere to the clothes and shoes of the workers. The accumulation amount was a small amount that was difficult to measure.)

[0178] 4: Powder is clearly seen rising.

[0179] (Within 5 seconds after the PTFE fine powder fell into the 18L plastic container (32cm in height), the state of the powdered PTFE fine powder particles could be visually confirmed in the upper portion of about 10cm from the upper surface of the plastic container (the portion with a height of 32cm).)

[0180] Melting Viscosity of PTFE Fine Powder

[0181] The value obtained by measuring according to ASTM D 1238, using an elevated flow tester (manufactured by Shimadzu Corporation) and a die of 2φ - 8L, and holding a 2g sample pre-heated at 380°C for 5 minutes at the above temperature under a load of 0.7MPa.

[0182] Examples 1 - 11 (Table 1)

[0183] The commercially available homopolymer PTFE fine powder (standard specific gravity: 2.175) was sieved with a 10-mesh (mesh size 1.7mm) sieve. The sieve residue rate (the ratio of the residue on the sieve to the total amount of PTFE fine powder) at this time is shown in Table 1.

[0184] In Examples 1 - 8, in air at room temperature, the sieve residue (the residue on the sieve) was irradiated with cobalt - 60 γ-rays under the conditions shown in Table 1 to obtain low-molecular-weight PTFE powder.

[0185] In addition, in Examples 9 - 11, after appropriately mixing the sieve-through powder (the powder that passed through the sieve) with the sieve residue (the residue on the sieve), it was irradiated with cobalt - 60 γ-rays in air at room temperature under the conditions shown in Table 1 to obtain low-molecular-weight PTFE powder.

[0186] The low-molecular-weight PTFE powder was pulverized at normal temperature and dry using a free mill (Mill) of Nara Machinery Co., Ltd. to obtain PTFE fine powder.

[0187] Comparative Examples 1 - 8 (Table 2)

[0188] Using the sieve-through powder (the powder that passed through the sieve) instead of the sieve residue, and in other respects, PTFE fine powder was obtained by the same method as in Examples 1 - 8.

[0189] It should be noted that before using the sieve-through powder, it was sieved with a 10-mesh (mesh size 1.7mm) sieve, but no residue was found on the sieve (the sieve residue rate was 0wt%).

[0190]

[0191]

Claims

1. A manufacturing method of polytetrafluoroethylene fine powder, wherein, By subjecting polytetrafluoroethylene powder with an average particle size of 700 μm or more to a process of irradiating ionizing radiation, polytetrafluoroethylene fine powder with an average particle size of 20 μm or less is obtained.

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

3. The manufacturing method of polytetrafluoroethylene micropowder according to claim 1 or 2, wherein, The apparent density of the polytetrafluoroethylene powder is 0.40 g / ml or less.

4. The manufacturing method of polytetrafluoroethylene fine powder according to any one of claims 1 to 3, wherein, The polytetrafluoroethylene powder is obtained by sieving using a sieve with a mesh size of 700 μm to 2 mm.

5. The manufacturing method of polytetrafluoroethylene fine powder according to any one of claims 1 to 4, wherein, The powder lift induction index of the polytetrafluoroethylene powder in a powder lift induction test conducted under the following conditions is 2 or less. Powder lift induction test The polytetrafluoroethylene powder scooped up with a stainless steel measuring spoon with a width of 133 mm, a length of 205 mm, and a depth of 70 mm is dropped from a height of 1.2 mm into an 18 L plastic container, and the amount of powder lift generated at this time is compared; the comparison is visually made by 3 people and indexed according to the following criteria to obtain the powder lift induction index. 1: Powder lift is not visibly seen. Within 5 seconds after the polytetrafluoroethylene powder is dropped into an 18 L plastic container (height 32 cm), the state of powder-like polytetrafluoroethylene powder particles cannot be visually confirmed in the upper part of the upper surface (the part at a height of 32 cm) of the plastic container. 2: There is powder lift, but it is in a very small amount. Within 5 seconds after the polytetrafluoroethylene powder is dropped into an 18 L plastic container (height 32 cm), powder-like polytetrafluoroethylene powder particles can be visually confirmed in the upper part of the upper surface (the part at a height of 32 cm) of the plastic container, but cannot be visually confirmed after 5 seconds. This is a state of very small amount of powder lift. 3: There is powder lift and it may adhere to the operator's clothes. Within 5 seconds after the polytetrafluoroethylene powder is dropped into an 18 L plastic container (height 32 cm), powder-like polytetrafluoroethylene powder particles can be visually confirmed in the upper part approximately 5 cm above the upper surface (the part at a height of 32 cm) of the plastic container, and the state of accumulation of fine powder of polytetrafluoroethylene powder can be confirmed on the floor where the plastic container is placed, although the accumulated amount is very small; the polytetrafluoroethylene powder may adhere to the operator's clothes and shoes; the accumulated amount is a small amount that is difficult to measure. 4: Powder lift is visibly seen. Within 5 seconds after the polytetrafluoroethylene powder is dropped into an 18 L plastic container (height 32 cm), the state of powder-like polytetrafluoroethylene powder particles can be visually confirmed in the upper part approximately 10 cm above the upper surface (the part at a height of 32 cm) of the plastic container.

6. A polytetrafluoroethylene powder, wherein, The apparent density is 0.40 g / ml or less and the average particle size is 700 μm or more.

7. The polytetrafluoroethylene powder according to claim 6, wherein The powder lift induction index in a powder lift induction test conducted under the following conditions is 2 or less. Powder lift induction test The polytetrafluoroethylene powder scooped up with a stainless steel measuring spoon with a width of 133 mm, a length of 205 mm, and a depth of 70 mm is dropped from a height of 1.2 mm into an 18 L plastic container, and the amount of powder lift generated at this time is compared; the comparison is visually made by 3 people and indexed according to the following criteria to obtain the powder lift induction index. 1: Powder lift is not visibly seen. Within 5 seconds after the polytetrafluoroethylene powder falls into an 18L plastic container (32cm in height), the state of the powdered polytetrafluoroethylene powder particles cannot be visually confirmed on the upper part of the upper surface (32cm in height) of the plastic container; 2: Powder is raised, but it is very small. Within 5 seconds after the polytetrafluoroethylene powder fell into an 18L plastic container (32cm in height), powdered polytetrafluoroethylene powder particles could be visually confirmed on the upper part of the upper surface of the plastic container (the part with a height of 32cm), but after 5 seconds, they could not be visually confirmed, indicating that a small amount of powder was raised; 3: Powder is raised and may adhere to the worker's clothes. Within 5 seconds after the polytetrafluoroethylene powder fell into an 18L plastic container (32cm in height), powdered polytetrafluoroethylene powder particles could be visually confirmed in the upper part of about 5cm from the upper surface of the plastic container (the part at the height of 32cm), and the accumulation of fine polytetrafluoroethylene powder was confirmed on the floor surface where the plastic container was placed, although the accumulation amount was very small; the polytetrafluoroethylene powder may adhere to the clothes and shoes of the operator; the accumulation amount was a small amount to the extent that it was difficult to measure; 4: Powder is clearly seen rising. Within 5 seconds after the polytetrafluoroethylene powder fell into an 18 L plastic container (32 cm in height), the state of powdered polytetrafluoroethylene powder particles could be visually confirmed in the upper portion of about 10 cm from the upper surface of the plastic container (the portion at a height of 32 cm).

8. A polytetrafluoroethylene powder, wherein, The average particle size is 700 μm or more, and contains 3% by weight or less of fine powder with a size of 42 mesh or less.

9. The polytetrafluoroethylene powder according to claim 8, wherein, The apparent density is below 0.40 g / ml.

10. The polytetrafluoroethylene powder according to claim 8 or 9, which is polytetrafluoroethylene fine powder.

11. A polytetrafluoroethylene powder used as a raw material for polytetrafluoroethylene fine powder, the average particle size of which is 700 μm or more.

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