Fluororesin particles and method for producing fluororesin particles

Abstract

The present invention relates to fluororesin particles comprising a first fluororesin having a thermal history of having been heated to the melting point or higher and a second fluororesin having no thermal history of having been heated to the melting point or higher, wherein the first fluororesin and the second fluororesin are non-melt-moldable fluororesins, the 50% cumulative particle size of the fluororesin particles in terms of mass is 500-900 μm, the amount of fluororesin particles having a particle size of 250 μm or less with respect to the total mass of the fluororesin particles is 4.0 mass% or less, and the amount of fluororesin particles having a particle size of from more than 1180 μm to 1680 μm with respect to the total mass of the fluororesin particles is 6.0 mass% or less.

Description

Fluororesin particles and method for producing fluororesin particles

[0001] The present invention relates to fluororesin particles and a method for producing fluororesin particles. This application claims priority to Japanese Patent Application No. 2024-037642, filed on March 11, 2024, the contents of which are incorporated herein by reference.

[0002] Polytetrafluoroethylene resin (molding powder) obtained by suspension polymerization of tetrafluoroethylene is compression molded and then sintered to form a molded body. The molded body obtained by sintering is processed into a molded product of the desired shape by cutting or other processes. However, once-sintered polytetrafluoroethylene resin (sintered PTFE) such as cutting chips generated during processing is hard, and even if it is crushed and compressed, it does not come together and cannot be molded. For this reason, it is difficult to reuse it.

[0003] Patent Document 1 discloses a molded body obtained by mixing sintered PTFE powder with PTFE fine powder obtained by emulsion polymerization of tetrafluoroethylene, compression molding the mixed powder, and sintering the mixture. The molded body has a PTFE fine powder content of 50%, and it is disclosed that the strength and elongation of the molded body are about 74% and about 94%, respectively, of the molded body having a PTFE fine powder content of 100% (i.e., 0% sintered PTFE powder).

[0004] Patent No. 6612001

[0005] However, it has been confirmed that the mixed powder used in the method described in Patent Document 1 has low fluidity, is difficult to handle, and has poor productivity during molding. It has also been confirmed that the mixed powder is easily pulverized by vibration during transportation and other factors, which further reduces the fluidity.

[0006] An object of the present invention is to provide fluororesin particles that have high fluidity even when made from a fluororesin that has a thermal history of being heated to above its melting point, and a method for producing such fluororesin particles.

[0007] The present invention has the following aspects. [1] Fluororesin particles comprising a first fluororesin that has a thermal history of being heated to or above its melting point and a second fluororesin that does not have a thermal history of being heated to or above its melting point, wherein the first fluororesin and the second fluororesin are non-melt-formable fluororesins, the 50% cumulative particle diameter based on mass of the fluororesin particles is 500 to 900 μm, the content of the fluororesin particles having a particle diameter of 250 μm or less is 4.0 mass% or less relative to the total mass of the fluororesin particles, and the content of the fluororesin particles having a particle diameter of more than 1180 μm and 1680 μm or less is 6.0 mass% or less relative to the total mass of the fluororesin particles. [2] The fluororesin particles according to [1], wherein the first fluororesin has tetrafluoroethylene units, and the content of the tetrafluoroethylene units relative to the total mass of the first fluororesin is 99 mass% or more. [3] The fluororesin particles according to [1] or [2], wherein the second fluororesin has tetrafluoroethylene units, and the content of the tetrafluoroethylene units relative to the total mass of the second fluororesin is 99 mass% or more. [4] The fluororesin particles according to any of [1] to [3], wherein the content of the first fluororesin relative to the total mass of the first fluororesin and the second fluororesin is 10 mass% or more. [5] The fluororesin particles according to any of [1] to [4], wherein the 50% cumulative particle diameter based on mass of the fluororesin particles is 520 to 900 μm, 550 to 880 μm, or 580 to 850 μm. [6] The fluororesin particles according to any one of [1] to [5], wherein the content of the fluororesin particles having a particle size of 250 μm or less relative to the total mass of the fluororesin particles is 3.8 mass% or less, 3.5 mass% or less, 0.01 to 4.0 mass%, 0.1 to 3.8 mass%, or 0.15 to 3.5 mass%. [7] The fluororesin particles according to any one of [1] to [6], wherein the content of the fluororesin particles having a particle size of more than 1180 μm and 1680 μm or less relative to the total mass of the fluororesin particles is 5.5 mass%, 5.0 mass% or less, 0.1 to 6.0 mass%, 0.3 to 5.5 mass%, or 0.5 to 5.0 mass%.[8] The fluororesin particles according to any one of [1] to [7], wherein the combined content of fluororesin particles having a particle size of 250 μm or less and fluororesin particles having a particle size of more than 1180 μm and 1680 μm or less relative to the total mass of the fluororesin particles is 9.2 mass% or less, 9.0 mass% or less, 8.5 mass% or less, 0.1 to 9.2 mass%, 0.4 to 9.0 mass%, or 0.6 to 8.5 mass%. [9] The fluororesin particles according to any one of [1] to [8], wherein the content of the first fluororesin relative to the total mass of the first fluororesin and the second fluororesin is 10 to 90 mass%, 15 to 85 mass%, or 20 to 80 mass%.

[10] The method for producing fluororesin particles according to any one of [1] to [9], comprising granulating a powder of the first fluororesin and a powder of the second fluororesin in water.

[0008] According to the present invention, it is possible to provide fluororesin particles that have high fluidity even when using a fluororesin that has a thermal history of being heated to a temperature equal to or higher than its melting point, and a method for producing the fluororesin particles.

[0009] FIG. 2 is an explanatory diagram of a method for evaluating the fluidity of fluororesin particles.

[0010] The following definitions of terms apply throughout the present specification and claims. "Monomer-based unit" is a collective term for an atomic group formed directly by polymerization of one monomer molecule and an atomic group obtained by chemically converting a portion of the atomic group. In this specification, a monomer-based unit is also simply referred to as a monomer unit. "Monomer" refers to a compound having a polymerizable carbon-carbon double bond. "Melting point" refers to the temperature corresponding to the maximum value of the melting peak measured by differential scanning calorimetry (DSC). The "to" symbol indicating a range of values ​​means that the values ​​before and after it are included as the lower and upper limits. "Average particle size" refers to the 50% cumulative value in the number-based particle size distribution determined using a laser diffraction / scattering particle size distribution analyzer (e.g., HORIBA, Ltd., LA-920 measuring instrument). "Particle size" refers to a value measured by sieving. Particles having a particle size of x μm or less refer to particles that have passed through a sieve with an opening of x μm. Particles with a particle size of more than y μm refer to particles that did not pass through a sieve with a mesh size of y μm. "50% cumulative particle size by mass" refers to the 50% cumulative value calculated from the mass-based particle size distribution of the fluororesin particles. The 50% cumulative particle size by mass can be calculated, for example, by stacking sieves with mesh sizes of 1680 μm, 1180 μm, 1000 μm, 850 μm, 600 μm, 425 μm, 355 μm, 250 μm, and 150 μm, calculating the mass of the fluororesin particles remaining on each sieve and the mass of the fluororesin particles that passed through the 150 μm sieve, plotting the particle size on the horizontal axis and the cumulative mass on the vertical axis, and using a logarithmic probability chart. The particle size on the horizontal axis is the mesh size of the sieve that did not pass through. For example, the mass of fluororesin particles that passed through an 1180 μm sieve but not a 1000 μm sieve is plotted on the horizontal axis at 1000 μm. The mass of fluororesin particles that passed through a 150 μm sieve is plotted on the horizontal axis at 0 μm. Excel may be used instead of the logarithmic probability paper. Furthermore, when each plot is connected by a straight line and the vertical axis is 50 mass%, the horizontal axis may represent the 50% cumulative particle size based on mass. "Bulk density" can be measured in accordance with JIS K6891:1995. Note that bulk density refers to the apparent density described in JIS K6891:1995.The "angle of repose" can be measured in accordance with Part 2: Physical Property Measurement Methods-2 of JIS R 9301-2-2:1999 (ISO 920:1976). "Melt-moldable" means that the material exhibits melt fluidity. "Exhibiting melt fluidity" means that there exists a temperature at which the melt flow rate is 0.1 to 1,000 g / 10 min at a temperature 20°C or more higher than the melting point of the resin under a load of 49 N. "Melt flow rate" refers to the melt mass-flow rate (MFR) defined in JIS K 7210:1999 (ISO 1133:1997). "Non-melt-moldable" means that the material does not exhibit melt fluidity. "Standard specific gravity (hereinafter also referred to as "SSG")" is a value that serves as an index of average molecular weight; a higher value indicates a smaller molecular weight. It can be measured in accordance with ASTM D1457-91a and D4895-91a.

[0011] <Fluororesin Particles> The fluororesin particles of this embodiment include a first fluororesin (hereinafter also referred to as "fluororesin 1") that has a thermal history of being heated to or above its melting point, and a second fluororesin (hereinafter also referred to as "fluororesin 2") that does not have a thermal history of being heated to or above its melting point. Fluororesin 1 and fluororesin 2 are non-melt-formable fluororesins. The 50% cumulative particle size, based on mass, of the fluororesin particles is 500 to 900 μm. The content of the fluororesin particles having a particle size of 250 μm or less relative to the total mass of the fluororesin particles is 4.0 mass% or less. The content of the fluororesin particles having a particle size of more than 1180 μm and 1680 μm or less relative to the total mass of the fluororesin particles is 6.0 mass% or less.

[0012] The 50% cumulative particle diameter based on the mass of the fluororesin particles (hereinafter referred to as "D ５０ ") is 500 to 900 μm, preferably 520 to 900 μm, more preferably 550 to 880 μm, and even more preferably 580 to 850 μm. D ５０ When the value is equal to or greater than the lower limit, the powder particles are less likely to clump together, resulting in excellent handling properties. ５０ When the value is equal to or less than the upper limit, the fluidity is likely to be improved.

[0013] The content of fluororesin particles having a particle size of 250 μm or less relative to the total mass of the fluororesin particles is 4.0% by mass or less, preferably 3.8% by mass or less, and more preferably 3.5% by mass or less. The lower limit of the content of fluororesin particles having a particle size of 250 μm or less is not particularly limited, but may be 0.01% by mass or more, 0.1% by mass or more, or 0.15% by mass or more. The content of fluororesin particles having a particle size of 250 μm or less is preferably 0.01 to 4.0% by mass, more preferably 0.1 to 3.8% by mass, and even more preferably 0.15 to 3.5% by mass. When the content of the fluororesin particles having a particle size of 250 μm or less is equal to or less than the above upper limit, the uniformity of the particle size distribution is high and fluidity is likely to be improved.

[0014] The content of fluororesin particles having a particle size of more than 1180 μm and not more than 1680 μm relative to the total mass of the fluororesin particles is 6.0% by mass or less, preferably 5.5% by mass or less, and more preferably 5.0% by mass or less. The lower limit of the content of fluororesin particles having a particle size of more than 1180 μm and not more than 1680 μm is not particularly limited, but may be 0.1% by mass or more, 0.3% by mass or more, or 0.5% by mass or more. The content of fluororesin particles having a particle size of more than 1180 μm and not more than 1680 μm is preferably 0.1 to 6.0% by mass, more preferably 0.3 to 5.5% by mass, and even more preferably 0.5 to 5.0% by mass. When the content of the fluororesin particles having a particle size of more than 1180 μm and not more than 1680 μm is not more than the above upper limit, the uniformity of the particle size distribution is high and fluidity is likely to be improved.

[0015] The total content of fluororesin particles having a particle size of 250 μm or less and fluororesin particles having a particle size of more than 1180 μm and less than 1680 μm is preferably 9.2 mass% or less, more preferably 9.0 mass% or less, and even more preferably 8.5 mass% or less, relative to the total mass of the fluororesin particles. The lower limit of the total content of fluororesin particles having a particle size of 250 μm or less and fluororesin particles having a particle size of more than 1180 μm and less than 1680 μm is not particularly limited, but may be 0.1 mass% or more, 0.4 mass% or more, or 0.6 mass% or more. The total content of fluororesin particles having a particle size of 250 μm or less and fluororesin particles having a particle size of more than 1180 μm and less than 1680 μm is preferably 0.1 to 9.2 mass%, more preferably 0.4 to 9.0 mass%, and even more preferably 0.6 to 8.5 mass%. When the total content of the fluororesin particles having a particle size of 250 μm or less and the fluororesin particles having a particle size of more than 1180 μm and 1680 μm or less is equal to or less than the upper limit, the particle size distribution is highly uniform and the flowability is likely to be improved.

[0016] The combined content of fluororesin particles having a particle size of 425 μm or less and fluororesin particles having a particle size of more than 1000 μm and 1680 μm or less relative to the total mass of the fluororesin particles is preferably 5 to 25 mass%, more preferably 7 to 25 mass%, and even more preferably 10 to 23 mass%. When the combined content of fluororesin particles having a particle size of 425 μm or less and fluororesin particles having a particle size of more than 1000 μm and 1680 μm or less falls within the above range, the particle size distribution is highly uniform and the flowability is likely to be improved.

[0017] The content of the fluororesin particles having a particle size of more than 1000 μm and not more than 1680 μm is preferably 1 to 22 mass%, more preferably 2 to 15 mass%, and even more preferably 3 to 12 mass%, relative to the total mass of the fluororesin particles. When the content of the fluororesin particles having a particle size of more than 1000 μm and not more than 1680 μm is within the above range, the flowability is likely to be improved.

[0018] The content of the fluororesin particles having a particle size of more than 850 μm and not more than 1680 μm relative to the total mass of the fluororesin particles is preferably 8 to 54 mass%, more preferably 10 to 52 mass%, and even more preferably 12 to 50 mass%. When the content of the fluororesin particles having a particle size of more than 850 μm and not more than 1680 μm is within the above range, the flowability is likely to be improved.

[0019] The content of fluororesin particles having a particle size of 425 μm or less relative to the total mass of the fluororesin particles is preferably 0.5 to 21 mass%, more preferably 0.8 to 20 mass%, and even more preferably 1 to 15 mass%. When the content of fluororesin particles having a particle size of 425 μm or less is within the above range, the flowability is likely to be improved.

[0020] The content of fluororesin particles having a particle size of 355 μm or less relative to the total mass of the fluororesin particles is preferably 0.1 to 10 mass%, more preferably 0.1 to 8 mass%, and even more preferably 0.3 to 7 mass%. When the content of fluororesin particles having a particle size of 355 μm or less is within the above range, the flowability is likely to be improved.

[0021] The content of fluororesin particles having a particle size of more than 1680 μm relative to the total mass of the fluororesin particles is preferably 2.0 mass% or less, more preferably 1.0 mass% or less, and even more preferably 0.5 mass% or less. The lower limit of the content of fluororesin particles having a particle size of more than 1680 μm is not particularly limited, but may be 0.03 mass% or more, 0.01 mass% or more, or 0 mass% or more. The content of fluororesin particles having a particle size of more than 1680 μm is preferably 0.01 to 2.0 mass%.

[0022] The angle of repose of the fluororesin particles is preferably less than 50°, more preferably less than 45°, and even more preferably less than 40°. The lower limit of the angle of repose is not particularly limited, but may be 10° or more, 15° or more, or 20° or more. The angle of repose is preferably 10° or more and less than 50°, more preferably 15° or more and less than 45°, and even more preferably 20° or more and less than 40°. When the angle of repose is equal to or less than the above upper limit, the fluidity is likely to be improved.

[0023] The bulk density of the fluororesin particles is preferably 0.50 to 0.95 g / mL, more preferably 0.58 to 0.90 g / mL, and even more preferably 0.60 to 0.80 g / mL. When the bulk density of the fluororesin particles is equal to or greater than the above lower limit, productivity in producing a molded product tends to be improved.

[0024] <Non-melt-formable fluororesin> Both fluororesin 1 and fluororesin 2 are non-melt-formable fluororesins. Fluororesin 1 and fluororesin 2 may be the same or different. Fluororesin 1 and fluororesin 2 may each independently be one type of fluororesin, or two or more types of fluororesins may be used in combination. When two or more types of fluororesins are used in combination, it is sufficient that the mixture of the two or more types of fluororesins is non-melt-formable.

[0025] As the fluororesin 1 and the fluororesin 2, a polymer having a tetrafluoroethylene unit (hereinafter also referred to as a "TFE unit") is preferable, and examples thereof include polytetrafluoroethylene (PTFE), a tetrafluoroethylene-ethylene copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, a tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer, a tetrafluoroethylene-chlorotrifluoroethylene copolymer, a tetrafluoroethylene-ethylene-hexafluoropropylene copolymer, and a tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymer.

[0026] Preferably, fluororesin 1 and fluororesin 2 are each independently PTFE. PTFE refers to a resin in which the content of TFE units relative to the total mass of the fluororesin is 99% by mass or more. The content of TFE units relative to the total mass of PTFE is preferably 99.5% by mass or more, and may be 100% by mass.

[0027] Examples of the monomer units other than the TFE units include the above-mentioned ethylene units, hexafluoropropylene units, perfluoro(alkyl vinyl ether) units, chlorotrifluoroethylene units, vinylidene fluoride units, as well as monomer units based on perfluoro(2,2-dimethyl-1,3-dioxole), perfluoro(4-methoxy-1,3-dioxole), perfluoroalkylethylene, etc. The monomer units other than the TFE units may be one type or two or more types. By including monomer units other than the TFE units, the crystallization of PTFE is suppressed to some extent, and the tensile strength, tensile elongation, dielectric breakdown resistance, creep resistance, etc. are improved.

[0028] (Fluororesin 1) Fluororesin 1 has a thermal history of being heated to or above its melting point at least once. Fluororesin 1 can be obtained by pulverizing cuttings generated when a primary molded body produced by heating to or above its melting point is processed into a secondary molded body such as an industrial part of a desired shape, or by pulverizing an unnecessary secondary molded body. The pulverization can be performed using a pulverizer or the like. After coarse pulverization, the material may be pulverized into fine particles. An example of the heating is heating by baking required for producing a molded body. By heating to or above its melting point, the melting point of fluororesin 1 is lowered below the melting point of fluororesin 1 before being heated to or above its melting point.

[0029] The melting point of fluororesin 1 before being heated to or above its melting point is preferably 360°C or lower, more preferably 355°C or lower, and even more preferably 350°C or lower. There are no particular restrictions on the lower limit of the melting point, but it is preferably 100°C or higher, and more preferably 150°C or higher. The melting point is preferably 100 to 360°C, more preferably 100 to 355°C, and even more preferably 150 to 350°C. When the melting point is within the above range, the mechanical strength of the resulting molded article is likely to be improved.

[0030] The melting point of fluororesin 1 is preferably 335°C or lower, more preferably 330°C or lower. There is no particular limitation on the lower limit of the melting point, but it is preferably 100°C or higher, more preferably 150°C or higher. The melting point is preferably 100 to 335°C, more preferably 150 to 330°C. When the melting point is within the above range, the mechanical strength of the obtained molded article is likely to be improved.

[0031] The fluororesin 1 may be, for example, crushed pieces of a molded product obtained by a method including a step of heating a molding material containing a fluororesin (e.g., "PTFE") obtained by suspension polymerization to above its melting point. Fluororesin obtained by suspension polymerization has an extremely high melt viscosity and exhibits non-melt moldability, meaning that it cannot be molded by typical thermoplastic resin molding methods such as extrusion molding and injection molding. Therefore, when molding a fluororesin produced by suspension polymerization (hereinafter also referred to as "molding powder"), a method is used in which the molding powder is filled into a mold, compression molded, and then fired.

[0032] Specifically, the molding powder is molded by first filling a mold with the molding powder at room temperature and compression-molding it to form a preform, which is then heated to or above the melting point of PTFE for sintering to form a primary molded body. The molding powder may be granulated as needed and used as a granulated product. During granulation, inorganic fillers and other optional components may be added. The primary molded body is then machined, such as by cutting, to form a secondary molded body of the desired shape. Examples of secondary molded bodies include industrial components such as gaskets, linings, and insulating films, and square tanks that are subjected to strong acids and strong alkalis in the semiconductor industry. Powders such as shavings, scraps, etc. (hereinafter also referred to as "shavings, etc.") generated when cutting a primary molded body to form a secondary molded body, as well as powders obtained by crushing the shavings, etc., and powders obtained by crushing unwanted secondary molded bodies can be used as the fluororesin 1. In this specification, the shavings, etc. and powders are collectively referred to as "crushed material." The secondary molded body or shavings, etc. can be crushed using a crusher or the like. After the coarse crushing, it may be further pulverized. The volume of each crushed material is, for example, 50 cm ３ The following is the result.

[0033] (Fluororesin 2) Fluororesin 2 does not have a thermal history of being heated to or above its melting point. The melting point of fluororesin 2 is preferably 360°C or lower, more preferably 355°C or lower, and even more preferably 350°C or lower. The lower limit of the melting point is not particularly limited, but is preferably 100°C or higher, and more preferably 150°C or higher. The melting point is preferably 100 to 360°C, more preferably 100 to 350°C, and even more preferably 150 to 350°C. When the melting point is within the above range, the mechanical strength of the obtained molded product is likely to be improved.

[0034] The fluororesin 2 may be, for example, the above-mentioned molding powder or a fluororesin produced by emulsion polymerization (hereinafter also referred to as "fine powder").

[0035] The suspension polymerization can be carried out by a method known in the art. Examples of such methods include the method described in Japanese Patent No. 6256355. More specifically, examples of such methods include the methods described in Example 1 and Comparative Example 1 of Japanese Patent No. 6256355.

[0036] The emulsion polymerization method is a polymerization method in which a monomer is polymerized in an aqueous medium containing water to obtain a dispersion containing particles of the fluororesin 2. In general, emulsion polymerization is performed by a method in which a reaction liquid containing water, a polymerization initiator, and a surfactant is polymerized in the reaction liquid while the reaction liquid is stirred.

[0037] From the viewpoint of suppressing coloration of the resulting molded article, the content of the nonionic surfactant is preferably 2 parts by mass or less, more preferably 1 part by mass or less, and even more preferably 0.1 parts by mass or less, relative to 100 parts by mass of the fluororesin in the dispersion. When a fine powder is used, 0% by mass is preferred. Examples of nonionic surfactants will be described later.

[0038] The content of the fluororesin 2 in the dispersion is preferably from 5 to 40% by mass, more preferably from 7 to 35% by mass, and even more preferably from 10 to 30% by mass.

[0039] The average particle size of the fluororesin 2 contained in the dispersion is preferably 0.05 to 0.5 μm, more preferably 0.08 to 0.45 μm, and even more preferably 0.10 to 0.35 μm. When the average particle size is within this range, the emulsion stability is excellent.

[0040] The fluororesin 2 preferably contains either a molding powder or a fine powder, or both. In the method for producing PTFE by emulsion polymerization, a TFE monomer is homopolymerized in the reaction solution, or a TFE monomer is copolymerized with a monomer other than the TFE monomer in the reaction solution to obtain a dispersion in which the fluororesin is dispersed in a dispersion medium. For example, in the presence of an aqueous medium, a polymerization initiator, an anionic fluorine-containing emulsifier, and a stabilizing aid, the TFE monomer is emulsion-polymerized, preferably for 1 to 20 hours, at a pressure of preferably 0.5 to 3.0 MPa, to obtain a dispersion. The nonionic surfactant may also be blended. Alternatively, a dispersion may be obtained without using a fluorosurfactant by the methods described in WO 2021 / 085470, WO 2022 / 181662, etc.

[0041] Examples of the anionic fluorine-containing emulsifier will be described later. The amount of the anionic fluorine-containing emulsifier used in the emulsion polymerization step of TFE monomer is preferably 0.15 to 2.0 parts by mass, more preferably 0.2 to 1.0 part by mass, and even more preferably 0.2 to 0.5 part by mass, per 100 parts by mass of the PTFE to be produced.

[0042] As the stabilizing aid, paraffin wax, fluorine-based oil, fluorine-based solvent, silicone oil, etc. are preferred, with paraffin wax being more preferred. One stabilizing aid may be used alone, or two or more may be used in combination. Paraffin wax may be liquid, semi-solid, or solid at room temperature, with saturated hydrocarbons having 12 or more carbon atoms being preferred. The melting point of paraffin wax is preferably 40 to 65°C, more preferably 50 to 65°C. The amount of stabilizing aid used is preferably 0.1 to 12 parts by mass, more preferably 0.1 to 8 parts by mass, per 100 parts by mass of the aqueous medium used.

[0043] As the polymerization initiator, a water-soluble radical initiator or a water-soluble oxidation-reduction catalyst is preferably used. As the water-soluble radical initiator, persulfates such as ammonium persulfate and potassium persulfate; and water-soluble organic peroxides such as disuccinic acid peroxide, bisglutaric acid peroxide, and tert-butyl hydroperoxide are preferred. The polymerization initiator may be used alone or in combination of two or more. Oil-soluble initiators can also be used. As the polymerization initiator, disuccinic acid peroxide is more preferred. The amount of the polymerization initiator used is preferably 0.01 to 0.20 parts by mass, more preferably 0.01 to 0.15 parts by mass, per 100 parts by mass of the PTFE to be produced.

[0044] The standard specific gravity (SSG) of the fluororesin contained in the dispersion is an index of the average molecular weight of the fluororesin, and it can be conceptually classified as a high molecular weight PTFE when the SSG is 2.14 or more and less than 2.22, and a low molecular weight fluororesin when the SSG is 2.22 to 2.4. Since the physical properties of the fluororesin decrease when the molecular weight is low, the SSG is preferably 2.14 or more and less than 2.22, and more preferably 2.14 to 2.21.

[0045] (Anionic Fluorine-Containing Emulsifier) ​​Examples of the anionic fluorine-containing emulsifier used in emulsion polymerization include fluorine-containing emulsifiers represented by general formula 1 (hereinafter also referred to as "fluorine-containing emulsifier 1"). General formula 1: XCF ２ CF ２ (O) ｍ CF ２ CF ２ OCF ２ COOA (wherein X is a hydrogen atom or a fluorine atom, and A is a hydrogen atom, an alkali metal, or NH ４ and m is 0 or 1. Fluorine-containing emulsifier 1 is preferred in that it has a good effect of stabilizing the polymerization of PTFE particles.

[0046] The X is preferably a fluorine atom in terms of polymerization stability. The m is preferably 1 in terms of polymerization stability and mechanical stability of the dispersion. Specific examples of A include H, Li, Na, K, and NH. ４ The fluorine-containing emulsifier 1 has good solubility in water and metal ion components are unlikely to remain as impurities, and therefore, NH ４ A particularly preferred example of the fluorine-containing emulsifier 1 is CF ３ CF ２ CF ２ CF ２ OCF ２ COONH ４ , C ２ F ５ OCF ２ CF ２ OCF ２ COONH ４ (hereinafter referred to as EEA), with EEA being more preferred.

[0047] The fluorine-containing emulsifier 1 can be produced by fluorinating an ester of a corresponding non-fluorine-containing carboxylic acid or partially fluorinated carboxylic acid by a known fluorination method such as a liquid-phase fluorination method in which the ester is reacted with fluorine in a liquid phase, a fluorination method using cobalt fluoride, or an electrochemical fluorination method, hydrolyzing the ester bond of the obtained fluorinated ester, purifying the ester, and then neutralizing the ester with ammonia.

[0048] (Nonionic surfactant) Examples of the nonionic surfactant to be blended in the aqueous emulsion obtained by emulsion polymerization include a nonionic surfactant represented by general formula 2 (hereinafter also referred to as "nonionic surfactant 2") and a nonionic surfactant represented by general formula 3 (hereinafter also referred to as "nonionic surfactant 3"). General formula 2: R １ -ODH (wherein R １ is an alkyl group having 8 to 18 carbon atoms, O is an oxygen atom, and D is a polyoxyalkylene chain consisting of 5 to 20 oxyethylene groups and 1 to 2 oxypropylene groups.) General Formula 3: R ２ -O-E-G (wherein R ２ is an alkyl group having 6 to 18 carbon atoms, O is an oxygen atom, E is a polyoxyalkylene chain consisting of 1 to 3 oxybutylene groups and 5 to 20 oxyethylene groups, and G is a hydrogen atom or a methyl group.) One type of nonionic surfactant may be used alone, or two or more types may be used in combination.

[0049] The nonionic surfactant contained in the dispersion is preferably one or more selected from the group consisting of nonionic surfactant 2 and nonionic surfactant 3, and two or more may be used in combination. Nonionic surfactant 2 and nonionic surfactant 3 may also be used in combination.

[0050] Note that nonionic surfactants are mixtures of multiple molecules with a certain chain length distribution and a mixture of isomers, and the chain length of the polyoxyalkylene chain represents the average chain length of the multiple molecules. The number of oxyethylene groups and oxypropylene groups in the polyoxyalkylene chain is an average value. Also, when multiple types of nonionic surfactants are mixed and used, it is sufficient that the average number of oxyalkylene groups in each nonionic surfactant is within the above-mentioned range. Furthermore, each numerical value is not limited to an integer.

[0051] In the nonionic surfactant 2, R １ The number of carbon atoms in the alkyl group represented by R is preferably in the range of 8 to 18, and more preferably 10 to 16. １When the number of carbon atoms is equal to or greater than the lower limit of the above range, the surface tension of the dispersion is likely to be low and the wettability is likely to be improved. When the number of carbon atoms is equal to or less than the upper limit, the storage stability of the dispersion is excellent. When the alkyl group, which is the hydrophobic group, has a branched structure in which it branches off midway, this is preferred in that it is easier to improve the wettability of the dispersion. The alkyl group having a branched structure is preferably an alkyl group branched in the range from the carbon atom at the base of the alkyl group to the fifth carbon atom, and more preferably an alkyl group branched in the range from the carbon atom at the base of the alkyl group to the third carbon atom. In addition, the branched carbon atom may be a secondary carbon atom or a tertiary carbon atom, and a secondary carbon atom is preferred. The alkyl group having a branched structure includes, for example, C １０ H ２１ CH (CH ３ ) CH ２ -, C ９ H １９ CH(C ３ H ７ ) -, C ６ H １３ CH(C ６ H １３ )- and the like can be exemplified.

[0052] In the nonionic surfactant 2, the hydrophilic group D is a polyoxyalkylene chain consisting of 5 to 20 oxyethylene groups and 1 to 2 oxypropylene groups. In particular, when the polyoxyalkylene chain is consisting of 7 to 12 oxyethylene groups and 1 to 2 oxypropylene groups, the properties of the second dispersion become favorable. When D contains an oxypropylene group, the defoaming property is likely to be improved. Having 2 or fewer oxypropylene groups is preferable in that it reduces the surface tension, making it easier to enhance wettability and reducing the risk of repellency during recoating. Furthermore, in D, the oxypropylene group may be present between the polyoxyethylene groups or may be bonded to the end of the polyoxyethylene chain. Bonding an oxypropylene group to the end of the polyoxyethylene chain tends to enhance the defoaming property. In particular, bonding an oxypropylene group to the molecular terminal of the polyoxyethylene chain tends to further enhance the defoaming property.

[0053] In the nonionic surfactant 2, the average number of oxyethylene groups per molecule is preferably 5 to 20, more preferably 7 to 12. When the average number of oxyethylene groups per molecule is equal to or greater than the lower limit of the above range, good storage stability is likely to be obtained. When the average number of oxyethylene groups per molecule is equal to or less than the upper limit of the above range, good wettability is likely to be obtained. As the nonionic surfactant 2, C １３ H ２７ O (C ２ H ４ O) ８ C ３ H ６ OH, C １３ H ２７ O (C ２ H ４ O) ９ C ３ H ６ OH, C １３ H ２７ O (C ２ H ４ O) １０ (C ３ H ６ O) ２ H, C １６ H ２７ O (C ２ H ４ O) １２ (C ３ H ６ O) ２ Commercially available nonionic surfactants having an average molecular structure such as H can be used.

[0054] The content of nonionic surfactant 2 is preferably 2 to 12 parts by mass, more preferably 4 to 12 parts by mass, per 100 parts by mass of the fluororesin in the dispersion. When the content is equal to or greater than the lower limit of the above range, good storage stability is likely to be obtained. A high content of nonionic surfactant 2 is suitable for applications requiring thick application, but no improvement in performance is observed even when the content exceeds the upper limit of the above range, and therefore, for economic reasons, it is preferably equal to or less than the upper limit of the above range.

[0055] In the nonionic surfactant 3, R ２The number of carbon atoms in the alkyl group represented by the formula (I) is preferably in the range of 6 to 18, more preferably 8 to 16, and even more preferably 10 to 14. When the number of carbon atoms in the alkyl group is equal to or greater than the lower limit of the above range, the surface tension of the dispersion tends to be low and wettability tends to be increased. When the number of carbon atoms in the alkyl group is equal to or less than the upper limit of the above range, the dispersion tends to have excellent storage stability. When the number of carbon atoms in the alkyl group is within the above range, the wettability and storage stability are good.

[0056] R ２ The alkyl group represented by the formula (I) preferably has a branched structure, since it is easier to increase the wettability of the dispersion. The branched carbon atom may be a secondary carbon atom or a tertiary carbon atom, and a secondary carbon atom is preferred. The alkyl group having a branched structure is preferably a C １０ H ２１ CH (CH ３ ) CH ２ -, C ９ H １９ CH(C ３ H ７ ) -, C ６ H １３ CH(C ６ H １３ ) -, CH(CH ３ ) ２ CH ２ CH (CH ３ ) ２ CH ２ CH (CH (CH ３ ) ２ CH ２ - etc. can be exemplified. ２ In the alkyl group represented by the formula (I), 10% or less of the hydrogen atoms in the alkyl group may be substituted with a halogen atom such as a fluorine atom, a chlorine atom, a bromine atom, etc. The alkyl group may also contain one or two unsaturated bonds.

[0057] E in general formula 3 is a polyoxyalkylene chain consisting of 1 to 3 oxybutylene groups and 5 to 20 oxyethylene groups. The number of oxybutylene groups is preferably 1 to 2.5, more preferably 1 to 2. When it is equal to or greater than the lower limit of the above range, the defoaming properties, wettability, and viscosity properties tend to be good. When it is equal to or less than the upper limit, the viscosity increase of the dispersion is suppressed, and good stability is likely to be obtained. When it is within the above range, properties such as viscosity, stability, defoaming properties, and wettability are good, which is preferable. The oxybutylene group may be branched or linear, with branched being preferred.

[0058] The oxybutylene group is —CH ２ -CH(C ２ H ５ )-O-,-CH(C ２ H ５ ) CH ２ -O-, -CH(CH ３ )-CH(CH ３ ) —O—, —CH ２ CH ２ -CH(CH ３ ) —O—, —CH ２ CH ２ CH ２ CH ２ Among them, —CH ２ -CH(C ２ H ５ )-O-,-CH(C ２ H ５ ) CH ２ —O—, —CH ２ CH ２ -CH(CH ３ )-O- is preferred. Examples of raw materials for the oxybutylene group include various butylene oxides, and specific examples include 1,2-butylene oxide, 2,3-butylene oxide, tetrahydrofuran, and methyloxetane.

[0059] In the nonionic surfactant 3, the number of oxyethylene groups in the polyoxyalkylene chain is 5 to 20, preferably 6 to 15, and more preferably 7 to 13. When the number is equal to or greater than the lower limit of the above range, the storage stability of the dispersion tends to be good. When the number is equal to or less than the upper limit, the wettability tends to be good. When the number is within the above range, properties such as viscosity, stability, defoaming property, and wettability are good, which is preferable. The oxybutylene groups in the polyoxyalkylene chain may have a block structure or a random structure.

[0060] The oxybutylene group may be present at any position in the polyoxyalkylene chain, but R ２ It is preferable that the —O— group is present in the range up to 70% of the total length of the polyoxyalkylene chain, and R ２ It is more preferable that the R of the polyoxyalkylene chain is present in the range from the —O— group side to 50% of the total length of the polyoxyalkylene chain. ２ The portion bonded to the -O- group is preferably an oxybutylene group, more preferably a polyoxybutylene chain consisting of 1 to 2 oxybutylene groups. Furthermore, the portion of the polyoxyalkylene chain bonded to the G group is preferably an oxyethylene group, more preferably a polyoxyethylene chain consisting of 5 to 20 oxyethylene groups. Polyoxyalkylene chains having these preferred structures are preferred because they have better properties such as viscosity, stability, defoaming properties, and wettability. G in general formula 3 is a hydrogen atom or a methyl group, preferably a hydrogen atom.

[0061] The nonionic surfactant 3 can be obtained by addition reaction of butylene oxide and ethylene oxide with a higher alcohol by a known method. Butylene oxide and ethylene oxide may be mixed and reacted simultaneously, or butylene oxide may be reacted first and then ethylene oxide, or ethylene oxide may be reacted first and then butylene oxide. The method of reacting butylene oxide first and then ethylene oxide is preferred.

[0062] As the nonionic surfactant 3, C １３ H２７ OCH ２ CH(C ２ H ５ )O(C ２ H ４ O) ８ H、C １０ H ２１ HH(H) ３ )CH ２ OCH ２ CH(C ２ H ５ )O(C ２ H ４ O) ８ H、C １０ H ２１ HH(H) ３ )CH ２ OCH(C ２ H ５ )CH ２ O(C ２ H ４ O) ８ H、C １２ H ２５ OCH ２ CH(C ２ H ５ )O(C ２ H ４ O) ８ H、C ８ H １７ OCH ２ CH(C ２ H ５ )O(C ２ H ４ O) １０ H、C １２ H ２５ OCH ２ CH(C ２ H ５ )O(C ２ H ４ O) １０ H、C １３ H ２７ OCH ２ CH(C ２ H ５ )O(C ２ H ４ O) １１ H、C １３ H ２７ OCH ２ CH ２ OCH ２ CH(C２ H ５ )O(C ２ H ４ O) ８ H、C １２ H ２５ O(CH ２ CH(C ２ H ５ )O) ２ (C ２ H ４ O) ８ H、C １０ H ２１ CH(CH ３ )CH ２ O(C ２ H ４ O) ９ CH ２ CH(C ２ H ５ )OH、C １６ H ３３ OC ２ H ４ OCH(C ２ H ５ )CH ２ O(C ２ H ４ O) ９ H、C １２ H ２５ SO ２ CH(C ２ H ５ )O(C ２ H ４ O) ８ CH ２ CH(C ２ H ５ )OH、C １３ H ２７ OCH(CH ３ )CH(CH ３ )O(C ２ H ４ O) ８ H、C １０ H ２１ CH(CH ３ )CH ２ OCH(CH ３ )CH(CH ３ )O(C ２ H ４ O) ８ H、C １０ H ２１ CH(CH ３)CH ２ OCH(CH) ３ )CH(CH ３ )O(C ２ H ４ O) ８ H、C １２ H ２５ OCH(CH) ３ )CH(CH ３ )O(C ２ H ４ O) ８ H、C ８ H １７ OCH(CH) ３ )CH(CH ３ )O(C ２ H ４ O) １０ H、C １２ H ２５ OCH(CH) ３ )CH(CH ３ )O(C ２ H ４ O) １０ H、C １３ H ２７ OCH(CH) ３ )CH(CH ３ )O(C ２ H ４ O) １１ H、C １３ H ２７ O(CH ２ ) ４ O(C ２ H ４ O) ８ H、C １２ H ２５ O(CH) ２ ) ４ O(C ２ H ４ O) ８ H、C ８ H １７ O(CH) ２ ) ４ O(C ２ H ４ O) １０ H、C １２ H ２５ O(CH) ２ ) ４ O(C ２ H ４ O) １０ H、C １３ H２７ O(CH ２ ) ４ O(C ２ H ４ O) １１ H, C １３ H ２７ O(CH ２ ) ２ CH(CH ３ )O(C ２ H ４ O) ８ H, C １２ H ２５ O(CH ２ ) ２ ​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​When the dispersion contains nonionic surfactant 3, the content of nonionic surfactant 3 is preferably 0.1 to 12 parts by mass, more preferably 0.5 to 11 parts by mass, and even more preferably 1 to 10 parts by mass, per 100 parts by mass of the fluororesin in the dispersion. When the content is equal to or greater than the lower limit of the above range, good storage stability is likely to be obtained. In addition, cracks are less likely to occur in the fluororesin coating film, and repellency is less likely to occur. A high content of nonionic surfactant 3 is suitable for applications requiring thick coating, but no improvement in performance is observed even if the content exceeds the upper limit of the above range, and therefore, for economic reasons, it is preferable that the content be equal to or less than the upper limit of the above range.

[0064] When nonionic surfactant 2 and nonionic surfactant 3 are used in combination as the nonionic surfactant, the average number of oxybutylene groups per molecule of the nonionic surfactant as a whole is preferably 0.5 to 2, more preferably 0.7 to 1.7, and even more preferably 0.9 to 1.5. Nonionic surfactant 2 and nonionic surfactant 3 may be added separately. A mixture containing nonionic surfactant 3 and nonionic surfactant 2 that is a by-product during the preparation of nonionic surfactant 3 may also be used.

[0065] The dispersion contains water as a dispersion medium for the fluororesin particles. This water may be water contained in the aqueous emulsion obtained by emulsion polymerization, or water prepared separately from the water in the aqueous emulsion. The dispersion may optionally contain one or more of a pH adjuster (e.g., ammonia), an anionic surfactant, a polyethylene oxide thickener, a polyurethane thickener, a thixotropic agent, a silicone wettability improver, a fluorine wettability improver, a preservative, etc. Furthermore, the dispersion may contain one or more of a water-soluble organic solvent, an organic solvent (e.g., toluene, xylene, etc.), a pigment (e.g., carbon black, etc.), a glass powder, hollow glass beads, and a colorant (e.g., graphite particles, silica particles, mica, etc.).

[0066] The fine powder can be recovered from the dispersion by a known method, such as that described in paragraphs

[0061] to

[0067] of Japanese Patent No. 5949883.

[0067] (Composition) In addition to fluororesin 1 and fluororesin 2, the fluororesin particles may contain one or more other solid components other than fluororesin 1 and fluororesin 2. Examples of other solid components include solid components used in the production process of fluororesin 1, solid components used in the production process of fluororesin 2, and solid components added after the production of fluororesin 1 and fluororesin 2. Specific examples include inorganic fillers, pigments (e.g., carbon black), colorants (e.g., graphite particles, silica particles, mica), and the above-mentioned additives. Examples of inorganic fillers include reinforcing fibers (glass fiber, carbon fiber, etc.), glass powder, bronze powder, graphite powder, hollow glass beads, etc. The content of other solid components is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less, relative to the total mass of the fluororesin particles. It may be zero.

[0068] The total content of Fluororesin 1 and Fluororesin 2 relative to the total mass of the fluororesin particles is preferably from 30 to 100 mass%, more preferably from 40 to 100 mass%, and even more preferably from 50 to 100 mass%.

[0069] The content of fluororesin 1 relative to the total mass of fluororesin 1 and fluororesin 2 is preferably 10% by mass or more, more preferably 10 to 90% by mass, even more preferably 15 to 85% by mass, and particularly preferably 20 to 80% by mass. When the content of fluororesin 1 is equal to or greater than the lower limit of the above range, recycling efficiency is improved when fluororesin 1 originates from cuttings or the like during production of the above-mentioned secondary molded body (in the case of recycled fluororesin). When the content of fluororesin 1 is equal to or less than the upper limit of the above range, the compressive strength of the obtained molded body is likely to be improved.

[0070] When fluororesin 2 contains molding powder, the content of fluororesin 2 relative to the total mass of fluororesin 1 and fluororesin 2 is preferably 10 to 95 mass%, more preferably 15 to 90 mass%, and even more preferably 20 to 80 mass%. When the content of fluororesin 2 is at least the lower limit of the above range, the compressive strength of the obtained molded body is likely to be improved. When the content of fluororesin 2 is at most the upper limit of the above range, recycling efficiency is improved when fluororesin 1 is derived from cuttings or the like during production of the above-mentioned secondary molded body (in the case of recycled fluororesin).

[0071] When fine powder is included as fluororesin 2, the content of fluororesin 2 relative to the total mass of fluororesin 1 and fluororesin 2 is preferably 10 to 95 mass%, more preferably 15 to 90 mass%, and even more preferably 20 to 80 mass%. When the content of fluororesin 2 is at least the lower limit of the above range, the compressive strength of the obtained molded body is likely to be improved. When the content of fluororesin 2 is at most the upper limit of the above range, recycling efficiency is improved when fluororesin 1 is derived from cuttings or the like during production of the above-mentioned secondary molded body (in the case of recycled fluororesin).

[0072] When the fluororesin 2 contains molding powder and fine powder, the ratio of the molding powder content to the fine powder content is preferably 0.1 to 10, more preferably 0.1 to 5, and even more preferably 0.5 to 4.

[0073] The fluororesin particles may be of one type or two or more types. When two or more types of fluororesin particles are used, the average content and ratio of the entire fluororesin particles may be within the above-mentioned ranges.

[0074] <<Method for Producing Fluororesin Composition>> As a method for producing the fluororesin particles of this embodiment, methods known in the art can be used. Among them, as a method for producing the fluororesin particles, it is preferable to granulate a powder of the first fluororesin and a powder of the second fluororesin. The granulation method will be described below.

[0075] The granulation method of the present embodiment preferably includes a dry mixing step of dry-mixing a powder of the first fluororesin and a powder of the second fluororesin to obtain a mixture, a granulation step of adding a liquid medium to the obtained mixture and stirring the mixture in the liquid medium to obtain granules, and a separation step of separating the liquid medium from the granules.

[0076] The bulk density of the powder of fluororesin 1 is preferably 0.100 g / mL or more, more preferably 0.105 g / mL or more, and even more preferably 0.110 g / mL or more. When the bulk density is equal to or greater than the lower limit, less air is carried over during the production of a molded body, resulting in excellent deaeration properties and good fusion between powder particles. Furthermore, voids are less likely to remain in the resulting molded body, and the uniformity of the molded body is also likely to be improved.

[0077] The average particle size of the powder of fluororesin 1 is preferably 1 to 500 μm, more preferably 5 to 300 μm, even more preferably 5 to 100 μm, and particularly preferably 10 to 70 μm. When the average particle size of fluororesin 1 is within the above range, the uniformity of the obtained molded product is improved.

[0078] When the fluororesin 2 is a molding powder, the bulk density is preferably 0.1 g / mL or more, more preferably 0.2 g / mL or more, and even more preferably 0.3 g / mL or more. When the fluororesin 2 is a fine powder, the bulk density is preferably 0.2 g / mL or more, more preferably 0.3 g / mL or more, and even more preferably 0.4 g / mL or more. When the bulk density is equal to or greater than the lower limit, less air is carried over during the production of a molded body, resulting in excellent deaeration properties and good fusion between powder particles. Furthermore, voids are less likely to remain in the resulting molded body, and the uniformity of the molded body is also likely to be improved.

[0079] When the fluororesin 2 is a molding powder, the average particle size is preferably 15 to 600 μm, more preferably 20 to 550 μm, even more preferably 25 to 500 μm, particularly preferably 25 to 450 μm, and most preferably 25 to 400 μm. When the fluororesin 2 is a fine powder, the 50% cumulative particle size on a mass basis is preferably 100 to 600 μm, more preferably 300 to 550 μm, and even more preferably 350 to 550 μm. When the average particle size of the fluororesin 2 is within the above range, the uniformity of the obtained molded body is improved.

[0080] The dry mixing step can be carried out by a method known in the art. When producing fluororesin particles containing the above-mentioned other solid components such as an inorganic filler, it is preferable to dry-mix the first fluororesin powder, the second fluororesin powder, and the other solid components in the dry mixing step to obtain a mixture containing the first fluororesin powder, the second fluororesin powder, and the other solid components.

[0081] Examples of the liquid medium used in the granulation step include an organic solvent and water, and the liquid medium preferably contains water. More preferably, the liquid medium contains both water and an organic solvent that is poorly soluble in water.

[0082] The boiling point of the poorly water-soluble organic solvent is preferably 30 to 150°C, more preferably 70 to 130°C. Specific examples include hydrocarbon organic solvents such as hexane, heptane, octane, nonane, decane, dodecane, gasoline, kerosene, and toluene; chlorinated hydrocarbon organic solvents such as carbon tetrachloride and trichloroethylene; and fluorinated hydrocarbon organic solvents such as trichlorotrifluoroethane, trichlorodifluoroethane, and trichlorofluoromethane. Among these, hydrocarbon organic solvents are preferred, with hexane, heptane, nonane, n-decane, dodecane, gasoline, kerosene, and toluene being more preferred, and nonane, n-decane, and dodecane being even more preferred. One type of poorly water-soluble organic solvent may be used alone, or two or more types may be used in combination.

[0083] The content of the slightly water-soluble organic solvent relative to the total mass of the liquid medium is preferably from 1 to 30 mass %, more preferably from 2 to 20 mass %, and even more preferably from 3 to 10 mass %.

[0084] The amount of the liquid medium used relative to 100 parts by mass of the mixture is preferably 100 to 3,000 parts by mass, more preferably 200 to 2,000 parts by mass, and even more preferably 300 to 1,000 parts by mass.

[0085] As the stirring method in the granulation step, a stirring method known in the art can be used. The stirring vessel can be one having a baffle and equipped with an agitator. Examples of the agitator include a propeller blade, a flat blade, a 45° pitch flat blade, a turbine blade, an agitator with a pitched or non-pitched curved blade, a spiral band agitator, and a comb agitator.

[0086] The stirring speed is preferably 100 to 5000 rpm, more preferably 200 to 4000 rpm, and even more preferably 300 to 3000 rpm. The stirring peripheral speed is preferably 1 to 30 m / s, more preferably 1 to 20 m / s, and even more preferably 1 to 10 m / s. When the stirring speed and stirring peripheral speed are within the above ranges, fluororesin particles having excellent bulk density and flowability are likely to be obtained.

[0087] The stirring time is preferably from 10 seconds to 40 minutes, more preferably from 10 seconds to 30 minutes, and even more preferably from 10 seconds to 20 minutes. The temperature of the liquid medium during stirring is preferably from 20 to 80°C, more preferably from 30 to 80°C, and even more preferably from 40 to 80°C.

[0088] The separation step can be carried out by a method known in the art, such as decantation, centrifugation, or filtration. The separated wet fluororesin particles are preferably dried. Drying is carried out in a state where the wet fluororesin particles are not fluidized much, preferably by leaving them to stand. Drying methods include vacuum drying, high-frequency drying, and hot air drying. The drying temperature is preferably 30 to 330°C, and more preferably 100 to 330°C.

[0089] <Molded body> The molded body of this embodiment can be obtained by compression molding the above-mentioned fluororesin particles and firing them. Specifically, the fluororesin particles are placed in a mold and compression molded under pressure to obtain a preform, and the obtained preform is fired to obtain a primary molded body. The shape of the primary molded body is not particularly limited. For example, it may be a block shape such as a cylindrical or polygonal pillar shape.

[0090] When compressing fluororesin particles, the pressure is 100 to 600 kg / cm ２ The firing temperature after the preforming is preferably 360 to 390° C. When cooling the compact, particularly if the compact is large, it is preferable to reduce the cooling rate and carefully lower the temperature over a sufficient period of time in order to prevent distortion or cracking of the compact.

[0091] The obtained primary molded article may be processed by cutting or the like to produce a secondary molded article of a desired shape. Examples of uses of the secondary molded article include seals, packings, rollers, sockets, and joints.

[0092] The molded article of this embodiment may be the primary molded article or the secondary molded article.

[0093] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples. In the following examples, Examples 1 to 6 are working examples, Examples 7 to 14 are comparative examples, and Example 15 is a reference example.

[0094] <Evaluation Method> (Melting Point) Using a differential scanning calorimeter (DSC 8500, manufactured by Perkin Elmer), the fluororesin was heated to 380° C. at a rate of 10° C. / min in an air atmosphere, and the melting point was determined from the endothermic peak. When there were multiple endothermic peaks, the peak temperature of the largest endothermic peak was used.

[0095] (Average Particle Diameter) Fluororesin powder was dispersed in water and the particle size distribution was measured and calculated on a number basis using a laser diffraction / scattering particle size distribution measuring device (LA-920 measuring device, manufactured by Horiba, Ltd.).

[0096] (Particle size, D ５０) Sieves with openings of 1680 μm, 1180 μm, 1000 μm, 850 μm, 600 μm, 425 μm, 355 μm, 250 μm, and 150 μm were stacked, and the mass of the fluororesin particles remaining on each sieve and the fluororesin particles that passed through the 150 μm sieve was determined. The total mass of the fluororesin particles remaining on the 150 μm sieve and the fluororesin particles that passed through the 150 μm sieve was taken as the mass of the fluororesin particles having a particle size of 250 μm or less. The mass of the fluororesin particles that passed through the 1680 μm sieve and remained on the 1180 μm sieve was taken as the mass of the fluororesin particles having a particle size of more than 1180 μm and 1680 μm or less. From the mass of the fluororesin particles that passed through the 150 μm sieve and the fluororesin particles remaining on each of the above sieves, D ５０ The particle size on the horizontal axis was the mesh size of the sieve that did not pass through. For example, the mass of fluororesin particles that passed through the 1180 μm sieve but did not pass through the 1000 μm sieve was plotted on the horizontal axis at 1000 μm. The mass of fluororesin particles that passed through the 150 μm sieve was plotted on the horizontal axis at 0 μm.

[0097] (Standard Specific Gravity) Measured in accordance with ASTM D1457-91a and D4895-91a.

[0098] (Bulk Density) The bulk density of the fluororesin particles was measured in accordance with JIS K6891: 1995. Specifically, a sample was dropped into a stainless steel weighing bottle having an internal volume of 100 mL through a funnel attached to the top, and the sample that had risen from the bottle was scraped off with a flat plate. The weight of the sample remaining in the weighing bottle was then divided by the internal volume of the bottle to obtain the bulk density.

[0099] (Fluidity: Slit Flow) The fluidity of the fluororesin particles was measured in a measurement chamber adjusted to 25±2° C. using the device shown in FIG. 1. 100 g of the fluororesin particles was placed in a first hopper 1. The lower end door 2 of the first hopper 1 was opened in one go, and H was poured into the opening at the lower end of the first hopper 1. １ The sample was filled into a second hopper 3 having an opening 4 at a distance of 60 mm. ２The second hopper 3 has a first plate 3a inclined 30° from the vertical and a second plate 3b inclined 30° from the vertical in the opposite direction to the first plate 3a, forming a 60° angle between the first plate 3a and the second plate 3b. The second hopper 3 also has a front plate (not shown) and a back plate (not shown) arranged parallel to and facing the front plate. The front ends of the first plate 3a and the second plate 3b in the figure are closed by the front plate, and the rear ends of the first plate 3a and the second plate 3b in the figure are closed by the back plate. The second plate 3b is movable and moves when a connecting rod 7 connected to the second plate 3b is moved in the direction of the arrow in the figure. Specifically, by moving the connecting rod 7 upward along the arrow in the figure, the second plate 3b also moves, opening the slit portion 5 at the bottom end of the second hopper 3. After filling the second hopper 3 with the sample, the connecting rod 7 was moved upward along the arrow at 12 mm / min to open the slit portion 5 of the second hopper 3, allowing the fluororesin particles to fall into the receiver 8. Then, when 50 g of the sample had fallen into the receiver 8, the value displayed on the scale 6 indicating the opening width of the slit portion 5 (opening width, unit: mm) was read. This value was used as an index of fluidity. The smaller the value displayed on the scale 6, the better the fluidity. The opening at the bottom of the first hopper 1 was 58 mm long in the left-right direction and 22 mm long in the depth direction (58 mm x 22 mm). The opening 4 at the top of the second hopper 3 was 104 mm long in the left-right direction and 63 mm long in the depth direction (104 mm x 63 mm). Measurement samples were the fluororesin particles produced in the examples described below and the fluororesin particles after shaking for 30 minutes with a YAMATO SHAKER MODEL SA-31 (manufactured by Yamato Scientific Co., Ltd.) In Table 1, "Slit flow (initial)" means the result for the fluororesin particles immediately after production, and "Slit flow (30 min)" means the result for the fluororesin particles after shaking for 30 min.

[0100] (Aggregation) The fluororesin particles produced in the examples described below were shaken for 30 minutes using a YAMATO SHAKER MODEL SA-31 (manufactured by Yamato Scientific Co., Ltd.), and then the presence or absence of aggregation was observed. Specifically, the presence or absence of lumps was observed. Table 1 shows the presence or absence of lumps.

[0101] (Angle of repose) For the fluororesin particles produced in Examples 3 and 6 described below, the angle of repose was measured in accordance with Part 2: Measurement of physical properties-2 of JIS R 9301:1999 (ISO 920:1976). Specifically, 100 g of the fluororesin particles were dropped from a funnel onto a horizontal plate, and the base angle was calculated from the diameter and height of the resulting cone-shaped drop, and this base angle was taken as the angle of repose. The distance from the bottom of the funnel to the horizontal plate was 100 mm.

[0102] [Production Example 1] A powder (molding powder) of fluororesin 2A consisting only of TFE units was produced by suspension polymerization. The melting point of the resulting fluororesin 2A was 345°C, and the average particle size was 25 μm. The resulting fluororesin 2A was not melt-moldable, as there was no temperature at which the melt flow rate was 0.1 to 1000 g / 10 min at a temperature 20°C or more higher than the melting point of the resin under a load of 49 N. Fluororesin 2A was a fluororesin that had no thermal history of being heated above its melting point.

[0103] [Production Example 2] Fluororesin 2A was preformed and then fired at or above its melting point to produce a primary molded body. Offcuts and scraps obtained when a secondary molded body was cut out of the resulting primary molded body were pulverized to obtain powder of Fluororesin 1 having an average particle size of 36 μm. Fluororesin 1 is a fluororesin with a thermal history of being heated to or above its melting point. The melting point of the resulting Fluororesin 1 was 329°C. The resulting Fluororesin 1 was not melt-moldable, as there was no temperature at which the melt flow rate was 0.1 to 1,000 g / 10 min at temperatures 20°C or more higher than the melting point of the resin under a load of 49 N.

[0104] [Production Example 3] A 100 L stainless steel autoclave equipped with a baffle and a stirrer was charged with 36 g of EEA, 555 g of paraffin wax (melting point 55 ° C), and 61.3 L of deionized water. After the interior of the autoclave was purged with nitrogen and reduced pressure, TFE was introduced and the temperature was raised to 62 ° C with stirring. TFE was further injected until the internal pressure reached 1.765 MPa, and 26.3 g of disuccinic acid peroxide (concentration 80 mass%, remainder water) was dissolved in 1 L of warm water at about 70 ° C and injected. After about 3 minutes, the internal pressure of the autoclave dropped to 1.716 MPa, so TFE was injected to maintain the internal pressure at 1.765 MPa, and polymerization was allowed to proceed. During the polymerization, EEA was dissolved in warm water and a total of 53 g of EEA was injected in two batches. The autoclave temperature was gradually increased to 72°C, and when the amount of TFE injected reached 22 kg, the reaction was terminated and the TFE in the autoclave was released into the atmosphere. The polymerization time was 105 minutes. After cooling, the solidified paraffin wax on top was removed, yielding a dispersion containing fluororesin 2B composed solely of TFE units produced by emulsion polymerization. The content of fluororesin 2B relative to the total mass of the dispersion was approximately 25.0 mass%, and the EEA concentration was 0.40 mass parts per 100 mass parts of fluororesin 2B. The average particle size of fluororesin 2B in dispersion C was 0.26 μm. The standard specific gravity (SSG) of fluororesin 2B was 2.21. The melting point of fluororesin 2B was 337°C. The obtained fluororesin 2B was not melt-moldable, since there was no temperature at which the melt flow rate was 0.1 to 1000 g / 10 min at a temperature 20°C or more higher than the melting point of the resin under a load of 49 N. An 8-L stainless steel coagulation tank equipped with a baffle and a stirrer was charged with 7.3 kg of an aqueous emulsion adjusted and diluted with pure water to a concentration of 10% by mass, the temperature inside the tank was adjusted to 20°C, and the mixture was stirred and coagulated at 427 rpm, followed by filtration to obtain a wet powder. The obtained wet powder was dried at 200°C for 7 hours, and then dried. ５０ Thus, a powder (fine powder) of fluororesin 2B having a particle size of 550 μm was obtained.

[0105] [Examples 1 to 6] A total of 1 kg of fluororesin 1 powder and either or both of fluororesin 2A powder and fluororesin 2B powder was placed in a 9 L stainless steel vessel equipped with a baffle plate and a stirrer (propeller stirrer blades with a blade length of 100 mm). The mixture was stirred for 90 seconds at a stirring peripheral speed of 40 m / s to obtain a mixed powder. 3 L of water and a predetermined amount of n-decane were added to the mixed powder, and the mixture was stirred for 1 minute at 600 rpm (stirring peripheral speed of 3 m / s) to granulate. The solids were then separated into water and n-decane and dried at 150°C for 7 hours to obtain fluororesin particles. The amounts of fluororesin 1 powder, fluororesin 2A powder, and fluororesin 2B powder used, as well as the amount of n-decane used, are shown in Table 1. The "-" symbol for n-decane in Table 1 indicates that n-decane was not used. Using the obtained fluororesin particles, the bulk density, flowability, and cohesion were measured. The results are shown in Table 1. The angles of repose of Examples 3 and 6 were measured to be 38° and 39°, respectively.

[0106] [Examples 7 to 12] A total of 1 kg of fluororesin 1 powder and either or both of fluororesin 2A powder and fluororesin 2B powder was placed in a 9 L stainless steel vessel equipped with a baffle plate and a stirrer (propeller stirring blade with a blade length of 100 mm), and stirred for 90 seconds at a stirring peripheral speed of 40 m / s to obtain a mixed powder. The obtained powder was used to measure bulk density, flowability, and cohesion. The results are shown in Table 1. Note that the fluororesin particles in Examples 7 to 12 were fine powders, and most of the fine powder passed through the sieve with the above openings, and D ５０ Furthermore, in Examples 7 to 12, aggregation of the fluororesin particles was observed after shaking for 30 minutes, and it was not possible to measure the "slit flow (30 minutes)."

[0107] [Examples 13-14] A total of 1 kg of fluororesin 1 powder and fluororesin 2A powder or fluororesin 2B powder was placed in a pan granulator with a diameter of 600 mm, and a predetermined amount of n-decane was added, followed by tumbling and sizing at 20 rpm for 15 minutes. The amounts of fluororesin 1 powder, fluororesin 2A powder, and fluororesin 2B powder used are shown in Table 1. The resulting fluororesin particles were used to measure bulk density, flowability, and cohesiveness. The results are shown in Table 1.

[0108] [Example 15] Granulation was carried out by a conventional method using only the powder of fluororesin 2A. Specifically, fluororesin particles were produced by referring to the production method in Example 1 (Example) of Japanese Patent No. 5691160. The bulk density, flowability, and cohesiveness of the obtained fluororesin particles were measured. The results are shown in Table 1.

[0109]

[0110] As shown in Table 1, the fluororesin particles of Examples 1 to 6 produced by granulation were found to have extremely high initial fluidity compared to the fluororesin particles of Examples 7 to 12. Aggregation was particularly observed in the fluororesin particles of Examples 7 to 12. Furthermore, the fluororesin particles of Examples 1 to 6 produced by granulation in water were found to have high initial fluidity and fluidity after 30 minutes of shaking compared to the fluororesin particles of Examples 13 and 14 produced by granulation other than in water. Furthermore, the fluororesin particles of Examples 1 to 6 exhibited fluidity very close to that of the fluororesin particles of Example 15 that did not contain a fluororesin having a thermal history of being heated above its melting point (fluororesin particles made only from conventional, new molding powder).

[0111] REFERENCE SIGNS LIST 1...first hopper, 2...lower end door, 3...second hopper, 3a...first plate, 3b...second plate, 4...opening, 5...slit portion, 6...scale, 7...connecting rod, 8...receiver

Claims

1. Fluororesin particles comprising a first fluororesin that has a thermal history of being heated to or above its melting point, and a second fluororesin that does not have a thermal history of being heated to or above its melting point, wherein the first fluororesin and the second fluororesin are non-melt-formable fluororesins, the 50% cumulative particle size based on mass of the fluororesin particles is 500 to 900 μm, the content of the fluororesin particles having a particle size of 250 μm or less relative to the total mass of the fluororesin particles is 4.0 mass% or less, and the content of the fluororesin particles having a particle size of more than 1180 μm and 1680 μm or less relative to the total mass of the fluororesin particles is 6.0 mass% or less.

2. Fluororesin particles according to claim 1, wherein the first fluororesin has tetrafluoroethylene units, and the content of the tetrafluoroethylene units relative to the total mass of the first fluororesin is 99 mass% or more.

3. Fluororesin particles according to claim 2, wherein the second fluororesin has tetrafluoroethylene units, and the content of the tetrafluoroethylene units relative to the total mass of the second fluororesin is 99 mass% or more.

4. Fluororesin particles according to any one of claims 1 to 3, wherein the content of the first fluororesin relative to the total mass of the first fluororesin and the second fluororesin is 10 mass% or more.

5. A method for producing fluororesin particles according to any one of claims 1 to 3, comprising granulating the first fluororesin powder and the second fluororesin powder in water.

6. A method for producing fluororesin particles according to claim 4, comprising granulating the first fluororesin powder and the second fluororesin powder in water.

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