Fluorine resin

Abstract

To provide a fluorine resin containing an oxolane ring having a small haze value of a molding.SOLUTION: A fluorine resin includes a residue unit represented by general formula (1), and has yellowness of a heated, melted and molded article (thickness of 3 mm) at 280°C for 24 hours of 2 or less, wherein the fluorine resin has an insoluble content when the fluorine resin is dissolved in 1,1,1,2,3,4,4,5,5,5-decafluoro-3-methoxy-2-(trifluoromethyl)pentane of 0.2 wt.% or less. In the formula (1), Rf1, Rf2, Rf3 and Rf4 each independently represents one kind of the group consisting of a fluorine atom, a linear perfluoroalkyl group having 1 to 7 carbon atoms, a branched perfluoroalkyl group having 3 to 7 carbon atoms and a cyclic perfluoroalkyl group having 3 to 7 carbon atoms, the perfluoroalkyl group may have an ethereal oxygen atom, Rf1, Rf2, Rf3 and Rf4 may be bonded to each other to form a ring having 4 or more and 8 or less carbon atoms, and the ring may be a ring containing an ethereal oxygen atom.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a fluororesin and a method for producing the same. [Background technology]

[0002] Amorphous fluoropolymers are used in a variety of applications in the optical and electronic fields due to their excellent transparency, liquid repellency, durability, and electrical properties. In the optical field, amorphous fluoropolymers are used in optical components such as optical waveguides and pellicles, which are dust-proof films for semiconductor photomasks.

[0003] Among these, fluororesins containing oxolane rings have a bulky ring structure, making them amorphous and highly transparent and heat-resistant. Furthermore, because they are composed only of carbon, fluorine, and oxygen, they have excellent electrical properties, chemical resistance, waterproofness, and liquid and oil repellency. Furthermore, because they are amorphous, they can be melt-molded.

[0004] Non-Patent Document 1 describes the synthesis and properties of a polymer (polyPFMMD) of perfluoro-2-methylene-4-methyl-1,3-dioxolane (PFMMD), a type of fluororesin containing an oxolane ring. PolyPFMMD has excellent heat resistance. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Macromolecules 2005,38,4237-4245 Summary of the Invention [Problem to be solved by the invention]

[0006] According to the investigations of the present inventors, the resin produced by the method of Non-Patent Document 1 has a problem in that the haze value of the melt-molded product is high.

[0007] An object of the present invention is to solve the above-mentioned problems associated with fluororesins containing oxolane rings, and specifically to provide fluororesins containing oxolane rings that produce melt-molded products with a small haze value, and a method for producing the same. [Means for solving the problem]

[0008] The present invention is as follows. [1] A fluororesin containing a residue unit represented by the following general formula (1), and having a haze value of 2% or less when molded by hot press (thickness 1 mm). [ka] (In formula (1), Rf1, Rf2, Rf3, and Rf4 each independently represent one of the group consisting of a fluorine atom, a linear perfluoroalkyl group having 1 to 7 carbon atoms, a branched perfluoroalkyl group having 3 to 7 carbon atoms, or a cyclic perfluoroalkyl group having 3 to 7 carbon atoms, and the perfluoroalkyl group may have an etheric oxygen atom, and Rf1, Rf2, Rf3, and Rf4 may be linked to each other to form a ring having 4 to 8 carbon atoms, and the ring may contain an etheric oxygen atom.) [2] The fluororesin according to [1], wherein the amount of insoluble matter when the fluororesin is dissolved in 1,1,1,2,3,4,4,5,5,5-decafluoro-3-methoxy-2-(trifluoromethyl)pentane is 0.2% by weight or less based on the fluororesin. [3] The bulk density of the fluororesin is 0.1 to 1.5 g / cm 3 The fluororesin according to [1] or [2], [4] Fluororesin bulk density is 0.12 to 0.25 g / cm 3 The fluororesin according to [1] or [2], [5] The fluororesin according to any one of [1] to [4], wherein a melt-molded product (thickness: 3 mm) of the fluororesin after heating at 280° C. for 24 hours has a yellowness index of 4 or less. [6] The weight average molecular weight of the fluororesin is 5 x 10 4 ~3×10 5 The fluororesin according to any one of [1] to [5], wherein [7] a polymerization step (1) of polymerizing a monomer represented by the following general formula (4) in the presence of a radical polymerization initiator to obtain a fluororesin A containing a residue unit represented by the following general formula (5); an insoluble matter removal step (2) of removing insoluble matter from a mixture containing the fluororesin A containing the residue unit represented by general formula (5) obtained in the polymerization step and the solvent S2 to obtain a fluororesin A solution; A precipitation step (3) of precipitating fluororesin A from the fluororesin A solution obtained in the insoluble matter removal step, A manufacturing method for fluororesin that produces a hot press molded product (thickness 1 mm) with a haze value of 2% or less. [ka] (In formulas (4) and (5), Rf5, Rf6, Rf7, and Rf8 each independently represent one of the group consisting of a fluorine atom, a linear perfluoroalkyl group having 1 to 7 carbon atoms, a branched perfluoroalkyl group having 3 to 7 carbon atoms, or a cyclic perfluoroalkyl group having 3 to 7 carbon atoms, and the perfluoroalkyl group may have an etheric oxygen atom, and Rf5, Rf6, Rf7, and Rf8 may be linked to each other to form a ring having 4 to 8 carbon atoms, and the ring may contain an etheric oxygen atom.) [8] The production method according to [7], wherein the polymerization step (1) is any one of the following steps (1a), (1b), or (1c): (1a) a step of polymerizing a monomer represented by general formula (4) in the presence of a radical polymerization initiator and a good solvent b1 for the fluororesin A to obtain a mixture containing the fluororesin A and the good solvent b1; (1b) A step of polymerizing a monomer represented by general formula (4) in the presence of a radical polymerization initiator and a poor solvent c1 for fluororesin A to precipitate fluororesin A, recovering the precipitated fluororesin A, and mixing the recovered fluororesin A with a good solvent b1 for fluororesin A to obtain a mixture containing fluororesin A and the good solvent b1. (1c) A step of polymerizing a monomer represented by general formula (4) in the presence of a radical polymerization initiator and a poor solvent c1 for the fluororesin A to precipitate the fluororesin A, and mixing the precipitated fluororesin A with a good solvent b1 for the fluororesin A to obtain a mixture containing the fluororesin A, the good solvent b1, and the poor solvent c1. [9] The production method according to [8], wherein the step (1a) is carried out in the presence of a radical polymerization initiator, a good solvent b1 for the fluororesin A, and a poor solvent c1 for the fluororesin A.

[10] The production method according to any one of [7] to [9], wherein the insoluble matter removal step (2) is either the step (2a) or (2b) below: (2a) a step of filtering a mixture containing fluororesin A and solvent S2 through a filter to remove insoluble matter; (2b) A step of subjecting the mixture containing fluororesin A and solvent S2 to centrifugation to remove insoluble matter.

[11] The production method according to

[10] , wherein the solvent S2 is a good solvent b2 for the fluororesin A or a mixed solvent of the good solvent b2 and a poor solvent c2 for the fluororesin A.

[12] The method according to

[10] or

[11] , wherein the insoluble matter removal step (2) is (2a).

[13] The manufacturing method according to any one of

[10] to

[12] , wherein the filter is a filter having a 99% capture particle size of 10 μm or less or a screen filter having a pore size of 10 μm or less.

[14] The production method according to any one of [7] to

[13] , wherein the deposition step (3) is any one of the following steps (3a), (3b), (3c), or (3d): (3a) a step of lowering the temperature of the fluororesin A solution to precipitate the fluororesin A; (3b) adding the fluororesin A solution to a poor solvent c3 for the fluororesin A to precipitate the fluororesin A; (3c) A step of precipitating fluororesin A by adding a poor solvent c3 for the fluororesin A solution to the fluororesin A solution (3d) A step of precipitating fluororesin A by volatilizing the solvent from the fluororesin A solution.

[15] The method according to

[14] , wherein the solvent for the fluororesin A solution in the precipitation step (3a) is a mixed solvent of a good solvent b3 for the fluororesin A and a poor solvent c3 for the fluororesin A.

[16]

[14] or

[15] . The manufacturing method according to

[14] or

[15] , wherein, in the precipitation step (3a), when the solution temperature T1 before the temperature is lowered is 30°C or higher and the solution temperature after the temperature is lowered is T2, T1-T2 is 5°C or higher.

[17] The production method according to any one of [7] to

[16] , further comprising a separation step (5) of separating the fluororesin A from the solution in which the fluororesin A has precipitated obtained in the precipitation step (3) or from the solution to which the poor solvent c4 has been added in the poor solvent addition step (4), and a washing step (6) of washing the separated fluororesin A with the poor solvent c5.

[18] The polymerization step (1) is step (1b), and The method according to any one of

[14] to

[17] , wherein the deposition step (3) is step (3a), (3b), (3c) or (3d).

[19] The method according to any one of

[14] to

[18] , wherein the deposition step (3) is step (3a) or (3c).

[20] 18. The production method according to claim 14, wherein the deposition step (3) is any one of steps (3a), (3b) and (3c), and the solvent S2 is an aliphatic fluorine-containing solvent. [twenty one] 21. The method according to claim 7, wherein the insoluble matter removed in the insoluble matter removal step (2) comprises at least a fluororesin containing a residue unit represented by general formula (1). [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a fluororesin that contains a residue unit represented by general formula (1) and has a haze value of 2% or less when molded by hot press (thickness 1 mm). DETAILED DESCRIPTION OF THE INVENTION

[0010] <Fluoropolymer> The present invention relates to a fluororesin containing a residue unit represented by the following general formula (1), which has a haze value of 2% or less when molded by hot press (thickness 1 mm). [ka] (In formula (1), Rf1, Rf2, Rf3, and Rf4 each independently represent one of the group consisting of a fluorine atom, a linear perfluoroalkyl group having 1 to 7 carbon atoms, a branched perfluoroalkyl group having 3 to 7 carbon atoms, or a cyclic perfluoroalkyl group having 3 to 7 carbon atoms, and the perfluoroalkyl group may have an etheric oxygen atom, and Rf1, Rf2, Rf3, and Rf4 may be linked to each other to form a ring having 4 to 8 carbon atoms, and the ring may contain an etheric oxygen atom.) The invention will be described in detail below.

[0011] The present invention relates to a fluororesin containing a residue unit represented by a specific general formula (1). Because the fluororesin of the present invention has a bulky ring structure contained in the specific general formula (1), it is amorphous and exhibits high transparency and heat resistance. Furthermore, because it is composed only of carbon, fluorine, and oxygen, it exhibits excellent electrical properties, chemical resistance, waterproofness, and liquid and oil repellency.

[0012] In the present invention, Rf1, Rf2, Rf3, and Rf4 groups in the residue unit represented by general formula (1) each independently represent one of the group consisting of a fluorine atom, a linear perfluoroalkyl group having 1 to 7 carbon atoms, a branched perfluoroalkyl group having 3 to 7 carbon atoms, or a cyclic perfluoroalkyl group having 3 to 7 carbon atoms. The perfluoroalkyl group may have an etheric oxygen atom. Rf1, Rf2, Rf3, and Rf4 may be linked together to form a ring having 4 to 8 carbon atoms, and the ring may contain an etheric oxygen atom. Rf1, Rf2, Rf3, and Rf4 in general formula (1) are synonymous with Rf5, Rf6, Rf7, and Rf8 in general formulas (4) and (5) described below, respectively. Specific examples of Rf1, Rf2, Rf3, and Rf4 described below are also specific examples of Rf5, Rf6, Rf7, and Rf8.

[0013] Examples of linear perfluoroalkyl groups having 1 to 7 carbon atoms include trifluoromethyl, pentafluoroethyl, heptafluoropropyl, nonafluorobutyl, undecafluoropentyl, tridecafluorohexyl, and pentadecafluoroheptyl. Examples of branched perfluoroalkyl groups having 3 to 7 carbon atoms include heptafluoroisopropyl, nonafluoroisobutyl, nonafluorosec-butyl, and nonafluorotert-butyl. Examples of cyclic perfluoroalkyl groups having 3 to 7 carbon atoms include heptafluorocyclopropyl, nonafluorocyclobutyl, and tridecafluorocyclohexyl. Examples of linear perfluoroalkyl groups having 1 to 7 carbon atoms that may have an etheric oxygen atom include -CF2OCF3, -(CF2)2OCF3, and -(CF2)2OCF2CF3. Examples of cyclic perfluoroalkyl groups having 3 to 7 carbon atoms which may have an etheric oxygen atom include a 2-(2,3,3,4,4,5,5,6,6-decafluoro)-pyrinyl group, a 4-(2,3,3,4,4,5,5,6,6-decafluoro)-pyrinyl group, and a 2-(2,3,3,4,4,5,5-heptafluoro)-furanyl group.

[0014] A fluororesin in which at least one of Rf1, Rf2, Rf3, and Rf4 is a member of the group consisting of a linear perfluoroalkyl group having 1 to 7 carbon atoms, a branched perfluoroalkyl group having 3 to 7 carbon atoms, or a cyclic perfluoroalkyl group having 3 to 7 carbon atoms is preferred from the viewpoint of exhibiting excellent heat resistance.

[0015] Specific examples of the residue unit represented by general formula (1) include various residue units represented by the following formula (2).

[0016] [ka]

[0017] Among these, fluororesins containing a residue unit represented by the following general formula (3) are preferred because of their excellent heat resistance and moldability, and fluororesins containing a perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit are more preferred.

[0018] [ka]

[0019] The fluororesin of the present invention has a haze value of 2% or less in a melt-molded product (thickness 1 mm). A hot-press molded product (thickness 1 mm) with a haze value of 2% or less has the advantage that when used as an optical component, it has excellent transparency and can provide an optical component with excellent performance. A method for producing the fluororesin of the present invention, which has a haze value of 2% or less in a hot-press molded product (thickness 1 mm), will be described later. The haze value is measured by the following method. A 1 mm thick mold with a hollowed-out center was placed on a smooth metal plate with a polyimide film, and a fluororesin was placed in the hollowed-out area. The polyimide film and metal plate were then placed on top of the mold, sandwiched in a press, and heated at 280 ° C for 10 minutes without pressure. The mold was then heated and pressed at 280 ° C for 10 minutes under a pressure of 10 MPa in a press, followed by repeated depressurization and depressurization under a pressure of 10 MPa for 5 minutes. The molded product was then heated and pressed at 280 ° C for 10 minutes under a pressure of 10 MPa in a press, and then further cooled between cooling metal plates to obtain a heat-press molded product (1 mm thick). The haze (%) of the resulting heat-press molded product (1 mm thick) was measured according to JIS K7136 using a Nippon Denshoku Industries Co., Ltd. NDH5000 haze meter (light source: white LED).

[0020] The fluororesin of the present invention has a haze value of 2% or less, preferably 1% or less, more preferably 0.8% or less, and more preferably 0.5% or less, when hot-press molded (thickness: 1 mm). There is no lower limit to the haze value, and the lower the haze, the better; for example, 0.01% or more is an example.

[0021] The fluororesin of the present invention preferably has a yellowness index (hereinafter also referred to as "YI") of 6 or less when melt-molded at 280°C for 24 hours (thickness: 3 mm). A melt-molded product (thickness: 3 mm) with a yellowness index of 6 or less provides an optical component with excellent transparency and performance when used as such. The YI is preferably 4 or less, more preferably 3 or less, more preferably 2 or less, and even more preferably 1 or less. There is no lower limit for YI; the lower the better, but for example, it can be 0.01 or more. The YI is measured by the following method. First, the transmittance of a 3 mm-thick melt-molded fluororesin product is measured at wavelengths of 200 nm to 1500 nm using a spectrophotometer. Data for wavelengths of 380 nm to 780 nm are extracted from the measured transmittance data. From the transmittance data, tristimulus values ​​X, Y, and Z of the XYZ color system are calculated in accordance with JIS Z8701, and YI under illuminant C is calculated in accordance with JIS K7373.

[0022] The fluororesin of the present invention preferably has a bulk density of 0.1 to 1.5 g / cm in consideration of, for example, handleability and moldability. 3 The bulk density is 0.25 to 1.5 g / cm 3 More preferably, it is 0.25 to 1.0 g / cm 3 Furthermore, the inventors have found through their studies that the YI of the fluororesin of the present invention falls within a favorable range when the bulk density is within a specific range (see Examples 2, and 4 to 6). From this perspective, the bulk density is preferably 0.12 to 0.25 g / cm. 3 It is preferable that the density is 0.14 to 0.22 g / cm 3 It is even more preferable that the bulk density is measured as follows. Fluororesin A is weighed without vibration and placed in a 13.5 mL glass sample tube (the liquid level when 10 mL of water is placed in it is 2.8 cm) whose height per unit volume has been measured in advance, and the bulk density can be calculated from the powder height and weight at that time according to the following formula. The bulk density at this time is called loose bulk density. Bulk density = (weight of powder (g)) / (height of powder (cm) / 0.28 (cm / mL))

[0023] There is no limitation on the weight average molecular weight Mw, but for example, 1 × 10 3 ~5×10 7 The weight average molecular weight Mw is 5 × 10 because the haze value of the hot press molded product is excellent. 4 ~5×10 5 Furthermore, since the haze value of the hot press molded product is excellent, the weight average molecular weight Mw is preferably in the range of 5×10 4 ~3×10 5 When the weight average molecular weight Mw is in this range, the haze value of the hot press molded product is excellent, and the shear rate is 10 -2 s, melt viscosity at 250°C is 1×10 2 ~3×10 5 Pa·s, resulting in excellent melt molding processability. Furthermore, the defoaming property when melted is also excellent. Furthermore, when the weight average molecular weight Mw is in this range, cracks during heating and cooling are reduced. From the viewpoints of excellent haze value, excellent melt molding processability, and excellent defoaming property when melted, the fluororesin of the present invention preferably has a weight average molecular weight Mw of 5×10 4 ~2×10 5 The weight average molecular weight Mw is in this range, and the shear rate is 10 -2 s, melt viscosity at 250°C is 1×10 2 ~2×10 4 From the viewpoint of excellent haze value, excellent melt molding processability, and excellent defoaming property when melted, it is more preferable that the weight average molecular weight Mw is 5×10 4 ~1.5×10 5 From the viewpoint of reducing the occurrence of cracks during heating and cooling, it is more preferably in the range of 6×10 4 ~1.5×10 5 The range is.

[0024] The weight-average molecular weight Mw of the fluororesin of the present invention can be calculated using gel permeation chromatography (GPC), for example, by using a standard polymethyl methacrylate of known molecular weight as the standard sample and a solvent capable of dissolving both the standard sample and the fluororesin as the eluent, from the elution times of the sample and the standard sample and the molecular weight of the standard sample. An example of the solution is Asahiklin AK-225 (manufactured by Asahi Glass Co., Ltd.) to which 10 wt % of 1,1,1,3,3,3-hexafluoro-2-propanol (manufactured by Wako Pure Chemical Industries, Ltd.) has been added.

[0025] The molecular weight distribution Mw / Mn, which is the ratio of the weight average molecular weight Mw to the number average molecular weight Mn of the fluororesin of the present invention, is not particularly limited, but from the viewpoints of achieving an excellent haze value, suppressed yellowing after heating and melting, excellent melt-molding processability, excellent defoaming properties during melting, and reduced cracking during heating and cooling, the molecular weight distribution Mw / Mn is preferably 1.2 to 8, more preferably 1.2 to 5, even more preferably 1.5 to 3, and still more preferably 2.0 to 3. The number average molecular weight Mn can be measured in the same manner as the above-mentioned method for measuring the weight average molecular weight Mw, and the molecular weight distribution Mw / Mn can be calculated by dividing the weight average molecular weight Mw by the number average molecular weight Mn.

[0026] There is no particular limitation on the particle size of the fluororesin of the present invention, but in order to provide excellent handleability during molding processing, the volume average particle size is preferably 1 to 10,000 μm, more preferably 1 to 2,000 μm, more preferably 1 to 1,000 μm, and even more preferably 10 to 1,000 μm. The volume average particle size of the fluororesin of the present invention can be evaluated by particle size distribution measurement (volume distribution) using a laser diffraction scattering method. The particle size distribution using the laser diffraction scattering method can be measured by dispersing resin particles in water or an organic solvent such as methanol and measuring the particle size distribution. An example of a laser scattering meter is the Microtrac manufactured by Microtrac Bell Co., Ltd. The volume average particle size, also known as the mean volume diameter, is the average particle size expressed on a volume basis and is expressed as Σ(vd) / Σ(v) when the particle size distribution is divided into each particle size channel, d is the representative particle size value for each particle size channel, and v is the volume-based percentage for each particle size channel.

[0027] Since the fluororesin of the present invention has a low haze value, the amount of insoluble matter when dissolved in 1,1,1,2,3,4,4,5,5,5-decafluoro-3-methoxy-2-(trifluoromethyl)pentane (C2F5CF(OCH3)C3F7, manufactured by 3M Japan, Novec 7300) is preferably 0.2 wt% or less, more preferably 0.1 wt% or less, even more preferably 0.05 wt% or less, and even more preferably 0.01 wt% or less, based on the fluororesin. The amount of insoluble matter is measured as follows: 1,1,1,2,3,4,4,5,5,5-decafluoro-3-methoxy-2-(trifluoromethyl)pentane (C2F5CF(OCH3)C3F7, manufactured by 3M Japan, Novec 7300) is added to the fluororesin to adjust the solids concentration to 10 wt%. The solution is dissolved at 50°C for 5 hours and then shaken and stirred to prepare a fluororesin solution. The solution was pressure-filtered using a pressure filter equipped with a PTFE membrane filter with a pore size of 0.1 μm, the weight of which had been recorded in advance, and the Novec 7300 from which foreign matter had been removed using a pore size filter of 0.1 μm was placed in the pressure filter and pressure-filtered repeatedly to wash away the remaining fluororesin.The filter was then removed and vacuum-dried, and the weight of the resulting filter was subtracted by the weight of the filter before filtration to determine the amount of residue on the filter.The amount of residue on the filter was then divided by the weight of the resin used to determine the percentage, thereby determining the amount of insoluble matter (wt %).

[0028] <Fluororesin manufacturing method> The method for producing a fluororesin of the present invention is a method for producing a fluororesin whose melt-molded product (thickness: 1 mm) has a haze value of 10% or less, a polymerization step (1) of polymerizing a monomer represented by the following general formula (4) in the presence of a radical polymerization initiator to obtain a fluororesin A containing a residue unit represented by the following general formula (5); an insoluble matter removal step (2) of removing insoluble matter from a mixture of the fluororesin A containing the residue unit represented by general formula (5) obtained in the polymerization step and the solvent S2 to obtain a fluororesin A solution; and The method includes a precipitation step (3) of precipitating fluororesin A from the fluororesin A solution obtained in the insoluble matter removal step. [ka] [ka]

[0029] In formulas (4) and (5), Rf5, Rf6, Rf7, and Rf8 each independently represent a fluorine atom, a linear perfluoroalkyl group having 1 to 7 carbon atoms, a branched perfluoroalkyl group having 3 to 7 carbon atoms, or a cyclic perfluoroalkyl group having 3 to 7 carbon atoms, wherein the perfluoroalkyl group may have an etheric oxygen atom, and Rf5, Rf6, Rf7, and Rf8 may be linked together to form a ring having 4 to 8 carbon atoms, which ring may contain an etheric oxygen atom. Rf5, Rf6, Rf7, and Rf8 in formulas (4) and (5) are synonymous with Rf1, Rf2, Rf3, and Rf4 in formula (1), respectively.

[0030] Polymerization process (1) The polymerization step (1) is a step of polymerizing a monomer represented by general formula (4) in the presence of a radical polymerization initiator to obtain a fluororesin A containing a residue unit represented by general formula (5). There are no limitations on the polymerization method used in the polymerization step (1), and examples thereof include solution polymerization, precipitation polymerization, bulk polymerization, emulsion polymerization, and suspension polymerization.

[0031] In the production method of the present invention, it is particularly preferred that the monomer represented by general formula (4) is perfluoro(4-methyl-2-methylene-1,3-dioxolane) represented by general formula (8), and the residue unit represented by general formula (5) is a perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit represented by general formula (9).

[0032] [ka]

[0033] [ka]

[0034] Examples of radical polymerization initiators for radical polymerization include bis(perfluorobenzoyl)peroxide (PFBPO), (CF3COO)2, (CF3CF2COO)2, (C3F7COO)2, (C4F9COO)2, (C5F 11 COO)2, (C6F 13 COO)2, (C7F 15 COO)2, (C8F 17 perfluoroorganic peroxides such as benzoyl peroxide, lauryl peroxide, octanoyl peroxide, acetyl peroxide, di-tert-butyl peroxide, tert-butylcumyl peroxide, dicumyl peroxide, tert-butyl peroxyacetate, perfluoro(di-trt-butyl peroxide), bis(2,3,4,5,6-pentafluorobenzoyl) peroxide, tert-butyl peroxybenzoate, and tert-butyl perpivalate; and azo-based initiators such as 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-butyronitrile), 2,2'-azobisisobutyronitrile, dimethyl-2,2'-azobisisobutyrate, and 1,1'-azobis(cyclohexane-1-carbonitrile).

[0035] The radical polymerization initiator is preferably a perfluoroorganic peroxide, more preferably bis(perfluorobenzoyl)peroxide (PFBPO), from the viewpoints of small haze value, suppressed yellowing after heat melting, excellent melt molding processability, excellent defoaming properties during melting, and little cracking during heating and cooling. Here, the perfluoroorganic peroxide refers to a compound having a structure in which hydrogen atoms of an organic peroxide are substituted with fluorine atoms.

[0036] The polymerization step (1) is suitably carried out in the presence of a solvent, and depending on the type of solvent, it can be, for example, either the following step (1a) or (1b). (1a) a step of polymerizing a monomer represented by general formula (4) in the presence of a radical polymerization initiator and a good solvent b1 for the fluororesin A to obtain a mixture containing the fluororesin A and the solvent b1; (1b) A step of polymerizing a monomer represented by general formula (4) in the presence of a radical polymerization initiator and a poor solvent c1 for fluororesin A to precipitate fluororesin A, recovering the precipitated fluororesin A, and mixing the recovered fluororesin A with good solvent b1 to obtain a mixture containing fluororesin A and good solvent b1. (1c) A step of polymerizing a monomer represented by general formula (4) in the presence of a radical polymerization initiator and a poor solvent c1 for the fluororesin A to precipitate the fluororesin A, and mixing the precipitated fluororesin A with a good solvent b1 for the fluororesin A to obtain a mixture containing the fluororesin A, the good solvent b1, and the poor solvent c1.

[0037] In this specification, a good solvent for fluororesin A means an organic solvent that can dissolve fluororesin A at 50° C. The term "soluble" means that the weight average molecular weight Mw is 5 to 15×10 4 This means that at least a part of the fluororesin A dissolves in the organic solvent, and for example, when a sample of the fluororesin A is immersed in a 20-fold amount (w / w) of an organic solvent at 50°C for 5 hours or more, if 80% by weight or more of the sample of the fluororesin A dissolves in the solvent, the solvent can be considered a good solvent. Here, the fluororesin A can be a fluororesin containing a residue unit represented by the general formula (3) above.

[0038] A poor solvent for fluororesin A means a solvent that does not easily dissolve fluororesin A, for example, a solvent having a weight average molecular weight Mw of 5 to 15 × 10 4 A poor solvent can be a solvent in which the amount of fluororesin A dissolved in the solvent is less than 20 wt %, preferably less than 10 wt %, when a sample of fluororesin A is immersed in 20 times (w / w) the amount of solvent at 50°C for 5 hours or more and then cooled to 25°C. Furthermore, in the present invention, a poor solvent for fluororesin A is also a solvent that can precipitate fluororesin A from a solution of fluororesin A obtained by dissolving a fluororesin in a good solvent. The poor solvent is preferably a solvent that precipitates fluororesin A when a solution of fluororesin A dissolved in a certain good solvent is added dropwise to a solvent in an amount 10 times the amount of the good solvent at 25°C. Here, fluororesin A can be a fluororesin containing a residue unit represented by the general formula (3) above.

[0039] In this specification, solvents are designated by the symbol S, with the solvent used in step (1) being designated S1, the solvent used in step (2) being designated S2, the solvent used in step (3) being designated S3, the solvent used in step (4) being designated S4, and the solvent used in step (n) being designated Sn (where n is an integer). Good solvents are designated by the symbol b, with the good solvent used in step (1) being designated b1, the good solvent used in step (2) being designated b2, the good solvent used in step (3) being designated b3, the good solvent used in step (4) being designated b4, and the good solvent used in step (n) being designated bn (where n is an integer). Poor solvents are designated by the symbol c, with the poor solvent used in step (1) being designated c1, the poor solvent used in step (2) being designated c2, the poor solvent used in step (3) being designated c3, the poor solvent used in step (4) being designated c4, and the poor solvent used in step (n) being designated cn (where n is an integer).

[0040] The solvent that can serve as a good solvent is preferably at least one selected from the group consisting of aliphatic fluorine-containing solvents such as perfluorocarbons, hydrochlorofluorocarbons, hydrofluorocarbons, hydrofluoroethers and hydrofluoroolefins, or aromatic fluorine compounds, and is more preferably an aliphatic fluorine-containing solvent because it allows for the production of a fluororesin that exhibits good coloration when heated. Further preferred is at least one selected from the group consisting of perfluorohexane, perfluoro-N-methylmorpholine, perfluoro-N-propylmorpholine, perfluorotriethylamine, perfluoromethyldibutylamine, perfluorotributylamine, CF3CF2CHCl2, CF3CHFCHFCF2CF3, CF3CF2CF2CF2CF2CF2H, CF3(CF2)5CH2CH3, C4F9OCH3, C4F9OC2H5, 1,1,1,2,3,4,4,5,5,5-decafluoro-3-methoxy-2-(trifluoromethyl)pentane (C2F5CF(OCH3)C3F7), and hexafluorobenzene.

[0041] Examples of such solvents include perfluorocarbons such as Fluorinert FC-5052, FC-72, FC-770, FC-3283, FC-40, and FC-43 (all manufactured by 3M Japan); hydrochlorofluorocarbons such as Asahiklin AK-225 (manufactured by Asahi Glass Co., Ltd.); hydrofluorocarbons such as Vertrel XF (manufactured by Mitsui-Chemours), Asahiklin AC-2000, and AC-6000 (all manufactured by Asahi Glass Co., Ltd.); hydrofluoroethers such as Novec 7100, Novec 7200, and Novec 7300 (manufactured by 3M Japan); hydrofluoroolefins such as Opteon SF10 (manufactured by Mitsui-Chemours); and aromatic fluorine-containing solvents such as hexafluorobenzene. A preferred specific example of the good solvent is 1,1,1,2,3,4,4,5,5,5-decafluoro-3-methoxy-2-(trifluoromethyl)pentane (C2F5CF(OCH3)C3F7, manufactured by 3M Japan Ltd., Novec7300).

[0042] Since particles having a large bulk density and excellent powder handling properties can be obtained, the good solvent is preferably a fluorine-containing solvent, more preferably an aliphatic fluorine-containing solvent having a hydrogen atom in the molecule such as hydrofluorocarbon, hydrofluoroether, hydrochlorofluorocarbon, or hydrofluoroolefin; or an aromatic fluorine-containing solvent, even more preferably an aliphatic fluorine-containing solvent having a hydrogen atom in the molecule such as hydrofluorocarbon, hydrofluoroether, hydrochlorofluorocarbon, or hydrofluoroolefin, still more preferably a hydrofluorocarbon or hydrofluoroether, and particularly preferably a hydrofluoroether. Here, the aliphatic fluorine-containing solvent having a hydrogen atom may be saturated or unsaturated, and may be linear or cyclic.

[0043] Examples of solvents that can be poor solvents include 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 2,2,2-trifluoroethanol, 1,1,1,3,3,3-hexafluoroisopropanol, 1,2,2,3,3,4,4-heptafluorocyclopentane, 1H,1H-pentafluoropropanol, 1H,1H-heptafluorobutanol, 2-perfluorobutylethanol, 4, 4,4-trifluorobutanol, 1H,1H,3H-tetrafluoropropanol, 1H,1H,5H-octafluoropropanol, 1H,1H,7H-dodecafluoroheptanol, 1H,1H,3H-hexafluorobutanol, 2,2,3,3,3-pentafluoropropyl difluoromethyl ether, 2,2,3,3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2, Examples of the solvent include at least one selected from the group consisting of fluorine-containing solvents having a hydrogen atom in the molecule, such as 2-tetrafluoroethyl ethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, hexafluoroisopropyl methyl ether, 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, and 2,2,3,4,4,4-hexafluorobutyl difluoromethyl ether; and fluorine-free organic solvents, such as hexane, heptane, toluene, acetone, methanol, ethanol, isopropanol, ethyl acetate, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, chloroform, dichloromethane, dichloroethane, and trichloroethane.

[0044] The poor solvent is preferably a fluorine-containing solvent, more preferably a fluorine-containing solvent having a hydrogen atom in the molecule, and more preferably at least one selected from the group consisting of 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 2,2,2-trifluoroethanol, 1,1,1,3,3,3-hexafluoroisopropanol, and 1,2,2,3,3,4,4-heptafluorocyclopentane. From the viewpoint of economy, the poor solvent is preferably a fluorine-free organic solvent such as hexane, heptane, toluene, acetone, methanol, ethanol, isopropanol, ethyl acetate, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, chloroform, dichloromethane, dichloroethane, or trichloroethane. Furthermore, non-chlorine solvents are more preferred because they have excellent yellowness, and examples thereof include hexane, heptane, toluene, acetone, methanol, ethanol, isopropanol, ethyl acetate, methyl ethyl ketone, methyl isobutyl ketone, and tetrahydrofuran.

[0045] The polymerization step (1a) is a step in which polymerization is carried out in the presence of a good solvent b1 for the fluororesin A, and is preferably a step of solution polymerization in which the fluororesin A is dissolved in a solvent containing the good solvent b1.

[0046] In the polymerization step (1a), polymerization can also be carried out in the presence of a poor solvent c1 for the fluororesin A, in addition to a radical polymerization initiator and a good solvent b1 for the fluororesin A. The poor solvent c1 will be described later. Carrying out polymerization in the presence of the poor solvent c1 has the advantage of reducing the amount of poor solvent used in the precipitation step, which will be described later. The content of the poor solvent c1 is preferably set to an extent that the fluororesin produced by polymerization in the polymerization step does not precipitate, and the ratio of the good solvent b1 to the poor solvent c1 can be, for example, in the range of 1 to 50 wt % of the poor solvent c1 relative to the total of the good solvent b1 and the poor solvent c1.

[0047] The polymerization step (1b) is a step in which polymerization is carried out in the presence of a poor solvent c1 for the fluororesin A to precipitate the fluororesin A. The poor solvent c1 in the polymerization step (1b) can be water. When the poor solvent c1 is water, the polymerization is generally called suspension polymerization in the absence of an emulsifier, and emulsion polymerization in the presence of an emulsifier. In particular, it is preferable that the poor solvent c1 dissolves the monomer represented by general formula (4), and precipitation polymerization is more preferable, since this reduces the haze of the hot-press molded product. Here, precipitation polymerization refers to polymerization carried out in a solvent that dissolves the monomer and precipitates the polymer.

[0048] The poor solvent c1 is preferably a solvent that precipitates the fluororesin A dissolved in the good solvent b1 at the polymerization temperature (e.g., 30 to 70°C). The poor solvent c1 preferably has a solubility of the fluororesin A in a 20-fold amount of the solvent of less than 20 wt%, more preferably less than 10 wt%.

[0049] The conditions in the polymerization step (1), such as the polymerization temperature, polymerization time, radical polymerization initiator concentration, monomer concentration, initiator to monomer ratio, and solvent amount, can be appropriately determined taking into consideration the types of monomer, radical polymerization initiator, solvent, etc. used. Examples are as follows: The polymerization temperature is, for example, in the range of 30 to 70°C, and the polymerization time is, for example, in the range of 5 to 96 hours. The concentration of the radical polymerization initiator is, for example, in the range of 0.1 to 5 mol% relative to the monomer. The monomer concentration can be, for example, in the range of 5 to 40% by weight based on the total weight of the monomer and the solvent. However, these numerical ranges are merely examples and are not intended to be limiting. In particular, the monomer concentration is determined appropriately depending on the type of monomer and the type of solvent, and taking into consideration the solubility of the resulting polymer in the solvent.

[0050] In order to reduce the haze value of the hot-press molded product, it is preferable to use a chain transfer agent in addition to the monomer and radical polymerization initiator during polymerization. The chain transfer agent is not particularly limited, but examples include organic compounds having 1 to 20 carbon atoms and containing at least one atom selected from the group consisting of hydrogen and chlorine atoms. Here, the chain transfer agent refers to a substance that has the effect of reducing the molecular weight when present in the system during radical polymerization of the fluororesin. Specific examples of chain transfer agents include organic compounds having 1 to 20 carbon atoms and containing hydrogen atoms, such as toluene, acetone, ethyl acetate, tetrahydrofuran, methyl ethyl ketone, methanol, ethanol, and isopropanol; and organic compounds having 1 to 20 carbon atoms and containing chlorine atoms, such as chloroform, dichloromethane, tetrachloromethane, chloromethane, dichloroethane, trichloroethane, tetrachloroethane, pentachloroethane, hexachloroethane, benzyl chloride, pentafluorobenzyl chloride, and pentafluorobenzoyl chloride. Among these, from the viewpoints of suppressing the haze value of a hot press molded product, suppressing yellowing after heat melting, controlling the molecular weight of the fluororesin, providing excellent melt molding processability, excellent defoaming properties when melted, minimizing the occurrence of cracks when heated and cooled, and providing an excellent yield, it is preferable to use an organic compound having 1 to 20 carbon atoms and containing a chlorine atom, and more preferably one represented by general formula (A).

[0051] [ka]

[0052] (In formula (A), m is an integer of 0 to 3, n is an integer of 1 to 3, p is an integer of 0 to 1, q is an integer of 0 to 1, and m+n+p+q is 4. R 1 and R 2 R are each independently a hydrocarbon group having 1 to 19 carbon atoms or an oxygen atom, and the oxygen atom may form a double bond with the adjacent carbon atom. 1 and R 2The total number of carbon atoms in R is 1 to 19, and the hydrocarbon group may have one or more atoms selected from oxygen atoms, fluorine atoms, and chlorine atoms, and may not have any hydrogen atoms. The hydrocarbon group may be linear, branched, alicyclic, or aromatic. 1 and R 2 may be linked to each other to form a ring having 3 to 19 carbon atoms.)

[0053] Among these, organic compounds having 1 to 20 carbon atoms and containing hydrogen atoms and chlorine atoms are more preferred from the viewpoints of suppressing the haze value of hot-press molded products, suppressing yellowing after heat melting, controlling the molecular weight of the fluororesin, providing excellent melt molding processability, excellent defoaming properties when melted, minimizing cracking during heating and cooling, and providing excellent yields. Examples of organic compounds having 1 to 20 carbon atoms and containing hydrogen atoms and chlorine atoms include chloroform, dichloromethane, chloromethane, dichloroethane, trichloroethane, tetrachloroethane, pentachloroethane, benzyl chloride, and pentafluorobenzyl chloride. Furthermore, in an organic compound having 1 to 20 carbon atoms and containing hydrogen atoms and chlorine atoms, from the viewpoints of suppressing the haze value of a hot-press molded product, suppressing yellowing after heat melting, being able to control the molecular weight of the fluororesin, having excellent melt-molding processability, excellent defoaming properties during melting, minimal cracking during heating and cooling, and excellent yield, the number ratio of hydrogen atoms to chlorine atoms is preferably in the range of 1:9 to 9:1, and more preferably 1:9 to 5:5. Furthermore, from the viewpoints of suppressing the haze value of a hot-press molded product, suppressing yellowing after heat melting, being able to control the molecular weight of the fluororesin, having excellent melt-molding processability, excellent defoaming properties during melting, minimal cracking during heating and cooling, and excellent yield, the organic compound having 1 to 20 carbon atoms and containing hydrogen atoms and chlorine atoms is preferably represented by the following general formula (B) or (C), and more preferably represented by general formula (B):

[0054] [ka] (In formula (B), m and n each independently represent an integer of 1 to 3, p represents an integer of 0 to 1, q represents an integer of 0 to 1, and m+n+p+q represents 4. R 1 and R 2 are each independently a hydrocarbon group having 1 to 19 carbon atoms, and R 1 p and R 2 q The total number of carbon atoms in R is 0 to 19, and the hydrocarbon group may have one or more atoms selected from oxygen atoms, fluorine atoms, and chlorine atoms, and may not have any hydrogen atoms. The hydrocarbon group may be linear, branched, alicyclic, or aromatic. 1 and R 2 may be linked to each other to form a ring having 3 to 19 carbon atoms.)

[0055] [ka]

[0056] (In formula (C), m, n, u, and v each independently represent an integer of 0 to 3; m+u represents an integer of 1 to 5; n+v represents an integer of 1 to 5; p, q, r, s, and t each independently represent an integer of 0 to 1; m+n+p+q represents an integer of 3; r+s+u+v represents an integer of 3; and R 1 , R 2 , R 3 , R 4 , R 5 are each independently a hydrocarbon group having 1 to 18 carbon atoms, and R 1 , R 2 , R 3 , R 4 , R 5 The total number of carbon atoms in R is 0 to 18, and the hydrocarbon group may have one or more atoms selected from oxygen atoms, fluorine atoms, and chlorine atoms, and may not have any hydrogen atoms. The hydrocarbon group may be linear, branched, alicyclic, or aromatic. 1 , R 2 , R 3 , R 4 , R 5Two or more groups selected from may be linked to each other to form a ring having 3 to 19 carbon atoms, and there may be a plurality of such rings.)

[0057] Examples of organic compounds having 1 to 20 carbon atoms and containing a chlorine atom represented by general formula (A) include chloroform, dichloromethane, tetrachloromethane, chloromethane, dichloroethane, trichloroethane, tetrachloroethane, pentachloroethane, hexachloroethane, benzyl chloride, pentafluorobenzyl chloride, and pentafluorobenzoyl chloride. Examples of organic compounds having 1 to 20 carbon atoms and containing a hydrogen atom and a chlorine atom represented by general formula (B) include chloroform, dichloromethane, chloromethane, dichloroethane, trichloroethane, tetrachloroethane, pentachloroethane, benzyl chloride, and pentafluorobenzyl chloride. Examples of organic compounds having 1 to 20 carbon atoms and containing a hydrogen atom and a chlorine atom represented by general formula (C) include 1,1,1-trichloroethane.

[0058] Furthermore, in order to obtain a fluororesin that suppresses the haze value of a hot press molded product, suppresses yellowing after heat melting, achieves both defoaming properties and cracking during melting, has excellent defoaming properties and heat resistance during melting, has a low melt viscosity, and generates fewer cracks, and also has an excellent yield, the amount of the chain transfer agent is preferably 0.01 to 95% by weight, more preferably 1 to 50% by weight, and even more preferably 3 to 50% by weight, based on the total weight of the monomer and the chain transfer agent.

[0059] Insoluble matter removal process (2) The insoluble matter removal step (2) is a step of removing insoluble matter from a mixture containing fluororesin A containing a residue unit represented by general formula (5) obtained in the polymerization step (1) and solvent S2 to obtain a fluororesin A solution. By providing the insoluble matter removal step, the haze of the resulting hot-melt molded product (1 mm thick) of the fluororesin can be reduced to 2% or less. The presence of insoluble matter in a mixture containing fluororesin A and solvent S2 or a fluororesin A solution can be determined, for example, by visually observing the mixture or the solution, or by filtering the mixture or the solution under pressure through a PTFE membrane filter with a pore size of 0.1 μm whose weight has been recorded in advance, and then repeatedly filtering under pressure with a good solvent such as Novec 7300, which has been filtered to remove foreign matter through a pore size of 0.1 μm, to wash the remaining resin, removing the filter, vacuum drying, and calculating the amount of material remaining on the filter by subtracting the weight of the filter before filtration, or by observing the material remaining on the filter. The removal of at least a portion of the insoluble matter can be evaluated by, for example, visually observing the mixture or solution, or by a method in which fluororesin solution A is pressure-filtered through a PTFE membrane filter having a pore size of 0.1 μm and the weight of which has been recorded in advance, and then pressure-filtered using a good solvent such as Novec 7300 from which foreign matter has been removed using a pore size of 0.1 μm, and the good solvent is added and pressure-filtered repeatedly to wash away the remaining resin, followed by removing the filter and vacuum-drying it, and then calculating the amount of material remaining on the filter by subtracting the weight of the filter before filtration from the weight of the filter, or by observing the material remaining on the filter.

[0060] The fluororesin A solution is obtained by removing at least a portion of the insoluble matter in the insoluble matter removal step (2). It is preferable that at least a portion of the removed insoluble matter is a fluororesin containing a residue unit represented by general formula (1), from the viewpoint of reducing the haze value of the resulting fluororesin A of the present invention. In this case, the structure of the insoluble matter, i.e., the presence of a residue unit represented by general formula (1), can be confirmed by microscopic FT-IR or the like, and can be evaluated, for example, by the following method. A 0.1 μm PTFE filter used to filter the diluted resin solution is washed with 50 g of Novec 7300, and after drying, foreign matter on the filter is picked up and subjected to microscopic IR measurement. The results are compared with the IR chart of a fluororesin containing a residue unit represented by general formula (1). As shown in the examples, the insoluble matter removed in the insoluble matter removal step (2) was confirmed to be a resin containing a residue unit represented by general formula (1), and the fluororesin A of the present invention from which at least a portion of the insoluble matter was removed exhibited a reduced haze value.

[0061] The fluororesin A containing the residue unit represented by general formula (5) obtained in the polymerization step (1) is obtained as a mixture with different solvents depending on the type of polymerization step. In the case of the polymerization step (1a), the fluororesin A is, for example, a mixture with a good solvent b1 or a mixed solvent of a good solvent b1 and a poor solvent c1. In this case, in the insoluble matter removal step (2), these solvents can be used as solvent S2 as is. The good solvent b1 or the mixed solvent of a good solvent b1 and a poor solvent c1 can be used as is as good solvent b2 or a mixed solvent of a good solvent b2 and a poor solvent c2. Alternatively, solvent S2 can be obtained by further mixing another solvent.

[0062] In the case of the polymerization step (1b), the fluororesin A is obtained as a precipitate. The solvent S2 can be obtained by recovering the precipitate of the fluororesin A obtained in the polymerization step (1b) by solid-liquid separation or the like, and after washing and / or drying it as necessary, obtaining a mixture containing the good solvent b2 or a mixed solvent of the good solvent b2 and the poor solvent c2.

[0063] When the solvent S2 is a mixed solvent, the content of the poor solvent c2 is preferably set to a level that allows insoluble matter to coexist but does not cause precipitation of the fluororesin, taking into consideration the concentration of the fluororesin A, and the ratio of the good solvent b2 to the poor solvent c2 can be, for example, in the range of 1 to 50 wt % of the poor solvent c2 relative to the total of the good solvent b2 and the poor solvent c2.

[0064] In either case, the concentration of fluororesin A in the mixture of fluororesin A and solvent S2 to be subjected to the insoluble matter removal step is preferably 1 to 40% by weight, more preferably 5 to 30% by weight, from the viewpoint of effectively reducing haze in a hot-melt molded product of the fluororesin.

[0065] The insoluble matter removal step (2) can be, for example, either the following step (2a) or (2b). (2a) a step of filtering a mixture containing fluororesin A and solvent S2 through a filter to remove insoluble matter; (2b) A step of subjecting the mixture containing fluororesin A and solvent S2 to centrifugation to remove insoluble matter.

[0066] In the insoluble matter removal step (2a), the mixture containing fluororesin A and solvent S2 is filtered through a filter to remove insoluble matter. The filtration method is not particularly limited, but examples include pressure filtration, vacuum filtration, and centrifugal filtration. The particulate matter removal performance of the filter is not limited, but since this effectively reduces haze in a hot-melt molded product of fluororesin A, the 99% capture particle size of the filter is preferably 10 μm or less, more preferably 5 μm or less, more preferably 1 μm or less, more preferably 0.5 μm or less, even more preferably 0.2 μm or less, and even more preferably 0.1 μm or less. Here, the 99% capture particle size refers to the particle size of particles that the filter can capture at least 99% of. This is described in the filter's catalog or technical documentation, and can also be determined by examining the capture rate of standard particles of known particle sizes.

[0067] Examples of materials for the filter include resins such as polypropylene, polyethylene, polyethylene terephthalate, nylon, PTFE (polytetrafluoroethylene), PES (polyethersulfone), mixed cellulose esters, cellulose acetate, polycarbonate, cellulose, nylon, and polyamide; ceramics such as silica fiber and glass fiber; and metals such as stainless steel and Hastelloy, with PTFE being preferred because it can effectively reduce haze in hot-melt molded products of fluororesin A. The filter may be hydrophobic or hydrophilic.

[0068] Examples of the types of filters used include depth filters and screen filters. Examples of screen filters include mesh filters and membrane filters. Among these, screen filters are preferred because they can effectively reduce haze in hot-melt molded products of fluororesin A, and membrane filters are even more preferred, with PTFE membrane filters being even more preferred. Depth filters are filters that capture particles internally, while screen filters are filters that capture particles on their surface. Membrane filters are a type of screen filter. Furthermore, since excellent filtering performance can be achieved, multiple types of filters may be used in combination. For example, a combination of a depth filter and a screen filter, or a combination of screen filters with different particle capture sizes can be used. When a screen filter is combined with another filter such as a depth filter or a screen filter with a different particle capture size, the 99% particle capture size of the filter combined with the screen filter is preferably 1 to 10 μm, since excellent filtering performance can be achieved.

[0069] Since this effectively reduces haze in a hot-melt molded product of fluororesin A, it is preferable to use a screen filter with a pore size of 10 μm or less, more preferably a screen filter with a pore size of 5 μm or less, even more preferably a screen filter with a pore size of 1 μm or less, even more preferably a screen filter with a pore size of 0.5 μm or less, and even more preferably a screen filter with a pore size of 0.2 μm or less. Generally, when the pore size of a membrane filter is C μm, the 99% capture particle size is less than C μm, and depending on the product, it can capture 99.99% or more of C μm particles.

[0070] In the insoluble matter removal step (2b), the mixture containing the fluororesin A and the solvent S2 is centrifuged to remove the insoluble matter. There are no particular limitations on the centrifugation method, but examples include a method in which the mixture containing the fluororesin A and the solvent S2 is placed in a container, and centrifugal force is applied to the container to precipitate the insoluble matter, separating the solution and removing the insoluble matter. The centrifugation method may be a batch method, a continuous method, or an intermediate method between the batch method and the continuous method.

[0071] Precipitation process (3) In the precipitation step (3), fluororesin A is precipitated from the fluororesin A solution obtained in the insoluble matter removal step. As the solvent S3 for the fluororesin A solution, the solvent S2 used for removing the insoluble matter in the insoluble matter removal step (2) may be used as is, or a solvent of a different type or composition may be used depending on the method.

[0072] There are no particular limitations on the method for precipitating a polymer from the fluororesin A solution, but the precipitation step (3) can be, for example, any of the following steps (3a), (3b), (3c), or (3d): (3a) a step of lowering the temperature of the fluororesin A solution to precipitate the fluororesin A; (3b) adding the fluororesin A solution to a poor solvent c3 for the fluororesin A to precipitate the fluororesin A; (3c) A step of precipitating fluororesin A by adding a poor solvent c3 for the fluororesin A solution to the fluororesin A solution (3d) A step of precipitating fluororesin A by volatilizing the solvent from the fluororesin A solution.

[0073] The precipitation step (3a) is a step in which the temperature of the fluororesin A solution is lowered to precipitate the fluororesin A. As the solvent S3 for the fluororesin A solution, the solvent S2 used for insoluble matter removal in the insoluble matter removal step (2) may be used as is, or a solvent of a different type or composition may be used depending on the method. The good solvent b2 or a mixed solvent of the good solvent b2 and poor solvent c2 used for insoluble matter removal in the insoluble matter removal step (2) may be used as is as the solvent in the precipitation step (3a). That is, the good solvent b2 or the mixed solvent of the good solvent b2 and poor solvent c2 can be a good solvent b3 for the fluororesin A or a mixed solvent of the good solvent b3 for the fluororesin A and poor solvent c3 for the fluororesin A, respectively. The concentration of the fluororesin A in the fluororesin A solution is preferably 1 to 40 wt %, more preferably 1 to 30 wt %, and even more preferably 2 to 20 wt %, from the viewpoints of excellent productivity and obtaining particles that are easy to handle as a powder. From the viewpoint of achieving excellent productivity and obtaining particles that are easy to handle as a powder, it is preferable that the solvent S3 used in the precipitation step is a mixed solvent of a good solvent b3 and a poor solvent c3. When the solvent S3 used in the precipitation step is a mixed solvent of a good solvent b3 and a poor solvent c3, the weight ratio of the good solvent b3 to the poor solvent c3 is preferably 10:90 to 99:1, more preferably 20:80 to 95:5, even more preferably 30:70 to 95:5, even more preferably 30:70 to 90:10, and even more preferably 30:70 to 80:20, in order to achieve excellent productivity, obtain particles that are easy to handle as a powder, and reduce coloration of the heat-melted product.

[0074] In the precipitation step (3a), the solution temperature T1 before the temperature is lowered is, for example, preferably 30° C. or higher, more preferably 40° C. or higher, and even more preferably 50° C. or higher, and when the solution temperature after the temperature is lowered is T2, T1-T2 is preferably 5° C. or higher, more preferably 10° C. or higher, more preferably 15° C. or higher, and even more preferably 20° C. or higher. This allows the fluororesin A to be sufficiently precipitated.

[0075] In the precipitation step (3a), the temperature is preferably lowered over a period of 1 to 600 minutes, more preferably 5 to 300 minutes, because this provides excellent productivity, excellent powder handling, and reduces coloration of the heat-melted product.

[0076] In the precipitation step (3a), the temperature is preferably lowered at a rate of 0.05 to 20°C per minute, and particularly preferably at a rate of 0.1 to 5°C per minute, since this provides excellent productivity and particles that are easy to handle as a powder.

[0077] The precipitation step (3b) is a step of precipitating fluororesin A by adding a solution of fluororesin A to a poor solvent c3 for the fluororesin A, and the precipitation step (3c) is a step of precipitating fluororesin A by adding a poor solvent c3 for the fluororesin A solution to the solution of fluororesin A. Solvent S3 for the fluororesin A solution in the precipitation steps (3b) and (3c) may be solvent S2 used for removing insoluble matter in the insoluble matter removal step (2). However, from the viewpoint of facilitating precipitation of fluororesin A by mixing with poor solvent c3, it is preferable that solvent s2 used for removing insoluble matter in the insoluble matter removal step (2) is a mixed solvent of good solvent b2 and poor solvent c2. From the viewpoints of facilitating precipitation of fluororesin A and reducing coloration of the heat-melted product, the precipitation step (3b) in which fluororesin A is precipitated by adding a solution of fluororesin A to a poor solvent c3 for the fluororesin A is preferred. On the other hand, from the viewpoint of excellent powder handling, the precipitating step (3c) of precipitating fluororesin A by adding a poor solvent c3 for the fluororesin A solution to the fluororesin A solution is preferred.

[0078] In any of the steps, since excellent productivity is achieved, particles are prevented from adhering to each other, and particles that are easy to handle as a powder are obtained, the weight ratio of the good solvent to the poor solvent after mixing with the poor solvent c3 is preferably in the range of 10:90 to 90:10, more preferably 20:80 to 80:20, even more preferably 30:70 to 70:30, and even more preferably 30:70 to 60:40.

[0079] In the precipitation step (3d), solvent S3 is evaporated from the fluororesin A solution to precipitate fluororesin A. From the viewpoint of removing solvent S3 by evaporation, solvent S3 can be a solvent with a relatively low boiling point. The evaporation of solvent S3 can be carried out by a known method, such as a method of evaporating the solvent using a thin-film evaporator such as Exeva, a method of passing the solvent through a heated flash tank, a method of heating the solution in an extruder using a devolatilizing extrusion device to evaporate the solvent, a method of dispersing the fluororesin A solution in a solvent immiscible with the fluororesin A solution, such as water, and evaporating the solvent by heating or introducing steam (when steam is introduced, this method is generally called steam stripping), or a method of heating a fluororesin A solution containing a low-boiling-point good solvent and a high-boiling-point poor solvent and evaporating the low-boiling-point good solvent to precipitate fluororesin A. A combination of these methods may also be used. After removing the solvent by these methods, fluororesin A may be processed into pellets using a pelletizer or the like.

[0080] The precipitation steps (3a) to (3d) can also be used in combination as appropriate. For example, the fluororesin A solution obtained in the insoluble matter removal step can be subjected to the precipitation step (3b) or (3c), and the remaining fluororesin A solution can be further subjected to the precipitation step (3a) or (3d) to further recover the remaining fluororesin A.

[0081] In the precipitation step, it is preferable to stir the fluororesin A solution, as this provides excellent productivity and particles that are easy to handle as a powder, and examples of such methods include stirring with a stirring blade, stirring by vibration, etc. In any of the precipitation steps (3a) to (3d), it is preferable to stir the solution when precipitating the resin.

[0082] In the precipitation process, particles with excellent productivity and easy handling as powder are obtained, and the Pv value, which is the value of the agitator motor power per unit agitation capacity, is 0.05 to 50 kW / m 3 It is preferable to precipitate a particulate solid by lowering the temperature while stirring so that the Pv value is 0.2 to 50 kW / m 3 is more preferably 0.5 to 30 kW / m 3 is even more preferable, and 0.5 to 10 kW / m 3 is particularly preferable. Here, the Pv value (kW / m 3 ) can be calculated using the following formula (10).

[0083]

number

[0084] In equation (10), Np is a dimensionless number called the power number, which varies depending on the shape of the impeller. Np can be obtained from known sources, such as "Chemical Equipment, August 1995, pp. 71-79" or "Shinko-Faudler Technical Report, Vol. 28, No. 8 (October 1984), pp. 13-16." If the ratio b / d of the impeller width b to the impeller diameter d differs from that of the impellers described in the literature, it can be calculated using equation (11) below.

[0085] Actual Np = Literature Np × (actual b / d) / (literature b / d) (11) (Here, Np: power number, b: impeller width (mm), d: impeller diameter (mm).)

[0086] In the present invention, there is no particular limitation on the combination of the polymerization step (1), the insoluble matter removing step (2), and the precipitation step (3). However, from the viewpoint that including a step of precipitating the fluororesin as particles results in a fluororesin with fewer impurities and reduces discoloration of the heat-melted product, it is preferred that the polymerization step (1) is step (1a) or (1c) and the precipitation step (3) is step (3a), (3b), or (3c), or that the polymerization step (1) is step (1b) and the precipitation step (3) is step (3a), (3b), (3c), or (3d). More preferably, the polymerization step (1) is step (1a), the insoluble matter removal step (2) is step (2a), and the precipitation step (3) is step (3a), (3b), or (3c). It is also preferred that the polymerization step (1) is step (1b), the insoluble matter removal step (2) is step (2a), and the precipitation step (3) is step (3a), (3b), (3c), or (3d). The above combination of the polymerization step (1) and the precipitation step (3) is preferred because particulate fluororesin A can be obtained in either step, and further steps such as washing the particulate fluororesin A can be performed, making it easier to obtain a fluororesin with minimal coloration in the heat-melted product. Furthermore, the precipitation step is preferably step (3a) or (3c), because it results in particles with high bulk density and excellent powder handling properties. Furthermore, from the viewpoint of preventing torque increase and achieving excellent productivity in the particle precipitation step, the precipitation step is preferably step (3a).

[0087] In the fluororesin A solution from which the resin has been precipitated obtained in the precipitation step (3), it is preferable to carry out a poor solvent addition step (4) in which a poor solvent c4 is added, because this prevents the resulting resin from adhering to itself and results in a resin that is easy to handle as a powder. The amount of poor solvent c4 added in the poor solvent addition step (4) is preferably 0.1 times or more, and more preferably 0.5 to 1 times, the weight of the fluororesin A-containing solution obtained in the precipitation step, because this provides excellent productivity, prevents particles from adhering to each other, and results in a resin that is easy to handle as a powder.

[0088] In the present invention, any other steps may be added, and a separation step (5) of extracting a solid by solid-liquid separation may be included after the precipitation step (3) or the poor solvent addition step (4). The solid-liquid separation method is not particularly limited, and examples thereof include pressure filtration, vacuum filtration, centrifugation, and centrifugal filtration. The size of the filter used is not limited, and examples thereof include filters with a capture particle size of 30 μm or less. The material of the filter used is not limited, and examples thereof include polypropylene, polyethylene, polyethylene terephthalate, nylon, PTFE, and PES.

[0089] In the present invention, any other steps may be added, and the process may include a washing step of washing particles of fluororesin A and / or a drying step of drying particles of fluororesin A. In the washing step (6), it is preferable to use a poor solvent c6, which is an organic solvent that precipitates fluororesin A, preferably at 25° C. The drying method is not particularly limited, and examples thereof include vacuum drying, reduced-pressure drying, normal-pressure drying, air drying, shaking drying, warm-air drying, and heat drying.

[0090] In the present invention, it is preferable to further include a separation step (5) of separating the fluororesin A from the solution in which the fluororesin A has precipitated obtained in the precipitation step (3) or from the solution to which the poor solvent c4 has been added in the poor solvent addition step (4), and a washing step (6) of washing the separated fluororesin A with the poor solvent c6. This allows for the production of particles with even better yellowness.

[0091] Furthermore, it is preferable to use a solvent filtered through a filter with a 99% capture particle size of 5 μm or less or a screen filter with a pore size of 5 μm or less as the poor solvent c6, since this can effectively reduce haze in the hot-melt molded product. [Example]

[0092] The present invention will be described in more detail below with reference to examples. However, the examples are merely illustrative of the present invention and are not intended to limit the present invention.

[0093] <Physical property measurement method> (1) Weight average molecular weight Mw Measurements were performed using gel permeation chromatography equipped with a Tosoh Corporation TSKgel SuperHZM-M column and an RI detector. The eluent used was Asahiklin AK-225 (Asahi Glass Co., Ltd.) supplemented with 10 wt% 1,1,1,3,3,3-hexafluoro-2-propanol (Wako Pure Chemical Industries, Ltd.). Agilent standard polymethyl methacrylate was used as the standard sample, and the weight-average molecular weight (Mw) calculated in terms of polymethyl methacrylate was calculated from the elution times of the sample and standard sample.

[0094] (2) Measurement of volume average particle size The volume average particle size (unit: μm) was measured using a Microtrac MT3000 manufactured by Microtrac Bell, using methanol as the dispersion medium.

[0095] (3) Calculation of Pv value The Pv value, which is the value of the agitator motor power per unit agitation volume, was calculated using the following formula: Np was set to 4.2 when using four diagonal paddle agitators (blade diameter 50 mm, angled at 45°).

number

[0096] (4) Haze measurement A 1 mm thick mold with a hollowed-out center was placed on a smooth metal plate with a polyimide film, and a fluororesin was placed in the hollowed-out area. The polyimide film and metal plate were then placed on top of the mold, sandwiched in a press, and heated at 280 °C for 10 minutes without pressure. The mold was then heated and pressed at 280 °C for 10 minutes under a pressure of 10 MPa in a press, followed by repeated depressurization and depressurization under a pressure of 10 MPa for 5 minutes. The molded product was then heated and pressed at 280 °C for 10 minutes under a pressure of 10 MPa in a press, and then depressurized. The molded product sandwiched between the metal plates was further cooled between cooling metal plates to obtain a heat-press molded product (1 mm thick). The haze (%) of the resulting heat-press molded product (1 mm thick) was measured according to JIS K7136 using a Nippon Denshoku Industries Co., Ltd. NDH5000 haze meter (light source: white LED).

[0097] (5) Measurement of insoluble matter 1,1,1,2,3,4,4,5,5,5-Decafluoro-3-methoxy-2-(trifluoromethyl)pentane (CFCF(OCH)CF, manufactured by 3M Japan, Novec 7300) was added to the fluororesin to adjust the solids concentration to 10 wt%. The solution was dissolved at 50°C for 5 hours and shaken to prepare a fluororesin solution. The solution was pressure-filtered using a pressure filter equipped with a 0.1 μm pore size PTFE membrane filter, the weight of which had been recorded in advance. The pressure filter was then repeatedly filled with Novec 7300 that had previously been filtered to remove impurities using a 0.1 μm pore size filter, and the remaining fluororesin was washed away. The filter was then removed and vacuum-dried. The weight of the resulting filter was subtracted by the weight of the filter before filtration to determine the amount of residue on the filter. This amount was then divided by the weight of the resin used to determine the percentage of insoluble matter (wt%).

[0098] (6) Measurement of bulk density Fluororesin A is weighed without vibration and placed into a 13.5 mL glass sample tube (the liquid level is 2.8 cm when 10 mL of water is added) whose height per unit volume has been measured in advance, and the bulk density can be calculated from the powder height and weight at that time using the following formula. The bulk density at this time is called the loose bulk density. Bulk density = (weight of powder (g)) / (height of powder (cm) / 0.28 (cm / mL))

[0099] (7) Yellowness Index (YI) Measurement 2.0 g of fluororesin was weighed into a 26.4 mm inner diameter Petri dish (a flat Petri dish with a lid and a receiver, manufactured by Flat Corporation; the receiver only, with a 1 mm thick glass bottom). The dish was placed in an inert oven (Yamato Scientific DN411I) and left at room temperature for 30 minutes under an air flow (20 L / min). The temperature was then raised to 280 °C over 30 minutes and heated at 280 °C for 24 hours. The oven door was then closed while maintaining the air flow (20 L / min). The oven was then turned off and the sample was allowed to cool for 12 hours. The sample was then removed and a 3 mm thick, 26.4 mm diameter fluororesin melt-molded product was obtained on the Petri dish. The air used was compressed air passed through a dehumidifier (dew point temperature: -20 °C or lower). The resulting fluororesin melt-molded product was measured for transmittance at wavelengths from 200 nm to 1500 nm at 1 nm intervals using a spectrophotometer (Hitachi High-Tech Science U-4100). Data at 5 nm intervals from 380 nm to 780 nm were extracted from the measured transmittance data, and the tristimulus values ​​X, Y, and Z of the XYZ color system were calculated according to the method of JIS Z8701. The YI for illuminant C (auxiliary illuminant C) was calculated according to the method of JIS K7373 to determine the YI of the fluororesin melt-molded product with the Petri dish. The YI of the Petri dish alone (receiver only) was measured, and the YI of the fluororesin melt-molded product with a thickness of 3 mm was calculated by subtracting the YI of the Petri dish alone (receiver only) from the YI of the fluororesin molded product with the Petri dish. The YI of the Petri dish alone (receiver only) was 0.21.

[0100] Example 1 A 75 mL glass ampoule was charged with 0.173 g (0.000410 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide as initiator, 20.0 g (0.0820 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as monomer, 80.00 g of Novec 7300 (3M Japan, C2F5CF(OCH3)C3F7) as polymerization solvent, and 2.22 g (0.0186 mol) of chloroform (Wako Pure Chemical Industries, Ltd.) as chain transfer agent. The ampoule was repeatedly subjected to nitrogen substitution by freeze-degassing and depressurization, and then sealed under reduced pressure (monomer / solvent = 20 / 80 (wt / wt)). The ampoule was placed in a thermostatic bath at 55 °C and held for 24 hours to undergo radical solution polymerization, resulting in a viscous resin-dissolved liquid. After cooling to room temperature, the ampoule was opened, and the resin solution was diluted with 100 g of Novec 7300 to adjust the viscosity, producing a diluted resin solution (solids concentration: 10 wt%). The diluted resin solution was placed in a pressure filtration device (manufactured by ADVANTEC) equipped with a 0.1 μm pore size PTFE membrane filter (manufactured by ADVANTEC T010A), and pressure filtered to remove components insoluble in the solvent.

[0101] This solution was transferred to a 1000 mL separable flask equipped with a four-blade diagonal paddle stirring blade (blade diameter 50 mm, blade width 12 mm, tilted at 45°), a Three-One motor, and a water bath, which had been heated to 50°C. The flask was heated to 50°C with stirring at 200 rpm and held for 5 minutes. After this, 270 g of Zeorora H (manufactured by Zeon Corporation, 1,2,2,3,3,4,4-heptafluorocyclopentane) was added, and the mixture was stirred at 200 rpm and held at 50°C for 5 minutes (Zeorolla H / Novec 7300 = 60 / 40 (wt / wt)). The mixture was stirred at 600 rpm (PV value: 8.1 kW / m 3), the water bath was removed, and the mixture was allowed to cool in the air for approximately 30 minutes to 30°C, yielding a particulate solid. Subsequently, 150 g of Zeorora H was added while stirring at 600 rpm (Zeorolla H / Novec 7300 = 70 / 30 (wt / wt)). The mixture was subjected to suction filtration, washed twice with acetone, and vacuum dried under heat to yield particles of fluororesin A. The resulting resin had a weight-average molecular weight of 7.2 x 10 4 The resulting solution was fine particles with a volume average particle size of 88 μm, with almost no coarse particles. The acetone used here had been filtered through a 0.1 μm PTFE filter beforehand. The evaluation results for the fluororesin are shown in Table 1. Meanwhile, the PTFE filter used to filter the diluted resin solution was washed five times with 50 g of Novec 7300, and then dried. The insoluble matter on the resulting filter was confirmed by microscopic IR to contain a fluororesin component containing a perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit. By removing this resin component (unwanted material), the haze of the fluororesin was clearly reduced compared to Comparative Example 1.

[0102] Example 2 A 30 mm diameter glass ampoule equipped with a magnetic stirrer was charged with a solution of 0.0865 g (0.000205 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide as initiator dissolved in 0.260 g of hexafluorobenzene, 10.0 g (0.0205 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as monomer, 39.74 g of Zeorora-H (Nippon Zeon, 1,2,2,3,3,4,4-heptafluorocyclopentane) as polymerization solvent, and 1.111 g (0.00931 mol) of chloroform (Wako Pure Chemical Industries, Ltd.) as chain transfer agent. The ampoule was repeatedly subjected to nitrogen substitution by freeze-degassing and depressurization, and then sealed under reduced pressure (amount of chain transfer agent: 10 wt % of the total of the monomer and chain transfer agent). Precipitation polymerization was carried out by holding the ampoule upright at 55°C for 24 hours while stirring with a magnetic stirrer. The resulting solution became cloudy, and the resin precipitated in the polymerization solvent. After cooling to room temperature, the ampoule was opened. The resulting resin-containing solution was filtered, washed with acetone, and vacuum-dried to obtain particulate perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin with a volume average particle size of 95 μm. 90 g of Novec 7300 (3M Japan, C2F5CF(OCH3)C3F7) was added to 10.0 g of the resulting fluororesin, and the mixture was heated at 50°C for 4 hours to dissolve the resin, producing a diluted resin solution (solids concentration: 10 wt%). The diluted resin solution was placed in a pressure filtration apparatus (manufactured by ADVANTEC) equipped with a 0.1 μm pore size PTFE membrane filter (manufactured by ADVANTEC, T010A), and pressure-filtered to remove solvent-insoluble components. 2 L of acetone was placed in a plastic cup equipped with an anchor blade, and the pressure-filtered diluted resin solution was added to a beaker while stirring to precipitate the resin. The precipitated resin was recovered by filtration, washed once with acetone, and vacuum-dried to obtain powdered perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin. The weight-average molecular weight of the resulting fluororesin was 9.7 × 10 4The evaluation results of the fluororesin are shown in Table 1. The acetone used here had been previously filtered through a 0.1 μm PTFE filter. Meanwhile, the PTFE filter used to filter the diluted resin solution was washed five times with 50 g of Novec 7300, and then dried. The insoluble matter on the resulting filter was confirmed by micro-IR analysis to contain a fluororesin component containing a perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit. By removing this resin component (unwanted matter), the haze of the fluororesin was clearly reduced compared to Comparative Example 1.

[0103] Example 3 A 75 mL glass ampoule was charged with 0.173 g (0.000410 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide as initiator, 20.0 g (0.0820 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as monomer, 80.00 g of Novec 7300 (3M Japan, C2F5CF(OCH3)C3F7) as polymerization solvent, and 2.22 g (0.0186 mol) of chloroform (Wako Pure Chemical Industries, Ltd.) as chain transfer agent. The ampoule was repeatedly subjected to nitrogen substitution by freeze-degassing and depressurization, and then sealed under reduced pressure (monomer / solvent = 20 / 80 (wt / wt)). The ampoule was placed in a thermostatic bath at 55 °C and held for 24 hours to undergo radical solution polymerization, resulting in a viscous resin-dissolved liquid. After cooling to room temperature, the ampoule was opened, and the resin solution was diluted with 100 g of Novec 7300 to adjust the viscosity, producing a diluted resin solution (solids concentration: 10 wt%). The diluted resin solution was placed in a pressure filtration device (manufactured by ADVANTEC) equipped with a 0.1 μm pore size PTFE membrane filter (manufactured by ADVANTEC T010A), and pressure filtered to remove components insoluble in the solvent.

[0104] This solution was transferred to a 1000 mL separable flask equipped with four diagonal paddle stirring blades (blade diameter 50 mm, blade width 12 mm, tilted at 45°), a Three-One motor, and a water bath, which had been heated to 50°C, and stirred at 600 rpm (Pv value: 20.6 kW / m 3), and 420 g of Zeorora H (manufactured by Nippon Zeon, 1,2,2,3,3,4,4-heptafluorocyclopentane) was slowly added to obtain a particulate solid (Zeorolla H / Novec 7300 = 70 / 30 (wt / wt), Pv value after addition: 6.1 kW / m 3 The mixture was filtered by suction, washed twice with acetone, and vacuum dried under heat to obtain particles of fluororesin A. The resulting resin had a weight-average molecular weight of 7.9 × 10 4 The resulting particles had a volume average particle size of 87 μm and were almost free of coarse particles. Zeorora H, Novec 7300, and acetone used in the precipitation and subsequent steps had been filtered through a 0.1 μm PTFE filter. The evaluation results for the fluororesin are shown in Table 1. The PTFE filter used to filter the diluted resin solution was washed five times with 50 g of Novec 7300, and then dried. The insoluble matter on the resulting filter was examined using IR microscopy, and was confirmed to contain a fluororesin component containing a perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit. By removing this resin component (unwanted material), the haze of the fluororesin was clearly reduced compared to Comparative Example 1.

[0105] Example 4 A 75 mL glass ampoule was charged with 0.173 g (0.000410 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide as initiator, 20.0 g (0.0820 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as monomer, 80.00 g of Novec 7300 (3M Japan, C2F5CF(OCH3)C3F7) as polymerization solvent, and 2.22 g (0.0186 mol) of chloroform (Wako Pure Chemical Industries, Ltd.) as chain transfer agent. The ampoule was repeatedly subjected to nitrogen substitution by freeze-degassing and depressurization, and then sealed under reduced pressure (monomer / solvent = 20 / 80 (wt / wt)). The ampoule was placed in a thermostatic bath at 55 °C and held for 24 hours to undergo radical solution polymerization, resulting in a viscous resin-dissolved liquid. After cooling to room temperature, the ampoule was opened. To adjust the viscosity, the resin solution was diluted with 100 g of Novec 7300 to prepare a diluted resin solution (solids concentration: 10 wt%). The diluted resin solution was placed in a pressure filtration device (manufactured by ADVANTEC) equipped with a 0.1 μm pore size PTFE membrane filter (manufactured by ADVANTEC, T010A), and components insoluble in the solvent were removed by pressure filtration. 2 L of acetone was placed in a plastic cup equipped with an anchor blade, and the filtered diluted resin solution was added to a beaker while stirring to precipitate the resin. The precipitated resin was recovered by filtration, washed twice with acetone, and vacuum dried to obtain powdered perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin. The weight-average molecular weight of the resulting fluororesin was 5.7 × 10 4 The acetone used here was previously filtered through a 0.1 μm PTFE filter. The evaluation results of the fluororesin are shown in Table 1. Meanwhile, the PTFE filter used to filter the diluted resin solution was washed five times with 50 g of Novec 7300, and then dried. The insoluble matter on the resulting filter was confirmed by microscopic IR to contain a fluororesin component containing a perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit. By removing this resin component (unwanted matter), the haze of the fluororesin was clearly reduced compared to Comparative Example 1.

[0106] Example 5 A 75 mL glass ampoule was charged with 0.173 g (0.000410 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide as initiator, 20.0 g (0.0820 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as monomer, 80.00 g of Novec 7300 (3M Japan, C2F5CF(OCH3)C3F7) as polymerization solvent, and 2.22 g (0.0186 mol) of chloroform (Wako Pure Chemical Industries, Ltd.) as chain transfer agent. The ampoule was repeatedly subjected to nitrogen substitution by freeze-degassing and depressurization, and then sealed under reduced pressure (monomer / solvent = 20 / 80 (wt / wt)). The ampoule was placed in a thermostatic bath at 55 °C and held for 24 hours to undergo radical solution polymerization, resulting in a viscous resin-dissolved liquid. After cooling to room temperature, the ampoule was opened (solid content: 20 wt%). The resin solution was placed in a pressure filtration apparatus (manufactured by ADVANTEC) equipped with a 5 μm pore size PTFE membrane filter (manufactured by ADVANTEC T500A) and pressure filtered to remove solvent-insoluble components. To adjust the viscosity, the resin solution was diluted with 100 g of Novec 7300, which had previously been filtered through a 0.1 μm PTFE filter, to prepare a diluted resin solution (solid content: 10 wt%). 2 L of acetone was placed in a plastic cup equipped with an anchor blade, and the pressure-filtered diluted resin solution was added to a beaker while stirring to precipitate the resin. The precipitated resin was recovered by filtration, washed twice with acetone, and vacuum dried to obtain powdered perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin. The weight-average molecular weight of the resulting fluororesin was 5.5 × 10 4 The acetone used here was previously filtered through a 0.1 μm PTFE filter. The evaluation results of the fluororesin are shown in Table 1. Meanwhile, the PTFE filter used to filter the diluted resin solution was washed five times with 50 g of Novec 7300, and then dried. The insoluble matter on the resulting filter was confirmed by microscopic IR to contain a fluororesin component containing a perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit. By removing this resin component (unwanted matter), the haze of the fluororesin was clearly reduced compared to Comparative Example 1.

[0107] Example 6 A 75 mL glass ampoule was charged with 0.173 g (0.000410 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide as initiator, 20.0 g (0.0820 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane), 80.00 g of FC-72 (3M Japan, perfluorohexane) as polymerization solvent, and 2.22 g (0.0186 mol) of chloroform (Wako Pure Chemical Industries, Ltd.) as chain transfer agent. The ampoule was repeatedly subjected to nitrogen substitution and depressurization via freeze degassing, and then sealed under reduced pressure (monomer / solvent = 20 / 80 (wt / wt)). The ampoule was placed in a thermostatic chamber at 55 °C and held for 24 hours to undergo radical solution polymerization, resulting in a viscous resin-dissolved liquid. After cooling to room temperature, the ampoule was opened (solids concentration: 20 wt%). After cooling to room temperature, the ampoule was opened. The resin solution was diluted with 100 g of FC-72 to adjust the viscosity, producing a diluted resin solution (solids concentration: 10 wt%). The diluted resin solution was placed in a pressure filtration device (manufactured by ADVANTEC) equipped with a 0.1 μm pore size PTFE membrane filter (manufactured by ADVANTEC, T010A), and components insoluble in the solvent were removed by pressure filtration. 2 L of hexane was placed in a plastic cup equipped with an anchor blade, and the filtered diluted resin solution was added to a beaker while stirring to precipitate the resin. The precipitated resin was recovered by filtration, washed twice with acetone, and vacuum dried to obtain powdered perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin. The weight-average molecular weight of the resulting fluororesin was 7.2 × 10 4The hexane and acetone used here were previously filtered through a 0.1 μm PTFE filter. The evaluation results of the fluororesin are shown in Table 1. Meanwhile, the PTFE filter used to filter the diluted resin solution was washed five times with 50 g of Novec 7300, and then dried. The insoluble matter on the resulting filter was confirmed by micro-IR analysis to contain a fluororesin component containing a perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit. By removing this resin component (unwanted matter), the haze of the fluororesin was clearly reduced compared to Comparative Example 1.

[0108] Example 7 A 75 mL glass ampoule was charged with 0.173 g (0.000410 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide as initiator, 20.0 g (0.0820 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as monomer, 80.00 g of hexafluorobenzene (Tokyo Chemical Industry Co., Ltd.) as polymerization solvent, and 2.22 g (0.0186 mol) of chloroform (Wako Pure Chemical Industries, Ltd.) as chain transfer agent. The ampoule was repeatedly subjected to nitrogen substitution and depressurization via freeze degassing, and then sealed under reduced pressure (monomer / solvent = 20 / 80 (wt / wt)). The ampoule was placed in a thermostatic chamber at 55 °C and held for 24 hours to undergo radical solution polymerization, resulting in a viscous resin-dissolved liquid. After cooling to room temperature, the ampoule was opened (solids concentration: 20 wt%). After cooling to room temperature, the ampoule was opened, and the resin solution was diluted with 100 g of hexafluorobenzene to adjust the viscosity, producing a diluted resin solution (solids concentration: 10 wt%). The diluted resin solution was placed in a pressure filtration device (manufactured by ADVANTEC) equipped with a 0.1 μm pore size PTFE membrane filter (manufactured by ADVANTEC, T010A), and components insoluble in the solvent were removed by pressure filtration. 2 L of chloroform was placed in a plastic cup equipped with an anchor blade, and the filtered diluted resin solution was added to a beaker while stirring to precipitate the resin. The precipitated resin was recovered by filtration and then vacuum-dried to obtain powdered perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin. The weight-average molecular weight of the resulting fluororesin was 6.5 × 104 The evaluation results of the fluororesin are shown in Table 1. Meanwhile, the PTFE filter used to filter the diluted resin solution was washed by passing 50 g of Novec 7300 through it five times, and then dried. The insoluble matter on the obtained filter was confirmed by microscopic IR to contain a fluororesin component containing a perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit. By removing this resin component (unwanted matter), the haze of the fluororesin was clearly reduced compared to Comparative Example 1.

[0109] Comparative Example 1 The procedure was carried out according to the description of Sample 93 in Table 2 of Non-Patent Document 1. However, since the polymer concentration during reprecipitation purification was not specified, the polymer was diluted to 10 wt%. A 75 mL glass ampoule was charged with 0.0880 g (0.000209 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide as initiator, 20.0 g (0.0820 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as monomer, and 32.63 g of hexafluorobenzene as polymerization solvent. The ampoule was repeatedly subjected to nitrogen substitution by freeze degassing and depressurization, and then sealed under reduced pressure (monomer / solvent = 38 / 62 (wt / wt)). The ampoule was placed in a constant temperature bath at 60°C and held there for 24 hours to carry out radical solution polymerization, resulting in a viscous liquid containing the dissolved resin. After cooling to room temperature, the ampoule was opened, and the resin solution was diluted with 147 g of hexafluorobenzene to adjust the viscosity, producing a diluted resin solution. 1 L of chloroform was placed in a beaker equipped with an anchor blade, and the diluted resin solution was added to the beaker under stirring to precipitate the resin. The precipitated resin was recovered by filtration and then vacuum-dried to obtain amorphous perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin. After heating the resulting fluororesin for 24 hours at 280°C, the molded product contained numerous bubbles. However, visual observation revealed that the coloring was more intense than in Example 1, and was comparable to or slightly more intense than in Example 7. Furthermore, the average size of the resulting fluororesin was measured with a ruler, and the average size was approximately 10 mm. The weight-average molecular weight of the resulting fluororesin was 3.7 x 10 5The evaluation results of the fluororesin are shown in Table 1.

[0110] [Table 1]

[0111] Reference example 1 Fluorine resin A (weight average molecular weight Mw = 7.2 × 10) prepared in Example 1 4 ) was immersed in various organic solvents at 20 times the amount (w / w) of fluororesin A at 50°C for 5 hours or more, and the dissolution was confirmed visually, with the following results. Soluble in: FC-72, FC-770, Novec 7200, Novec 7300, and hexafluorobenzene. When the solutions dissolved in these solvents were cooled to 25°C, all of them remained dissolved. There was almost no residue left, and all of them had a solubility of 90 wt% or more. Insoluble: Zeorora H, AE-3000, trifluoroethanol, ethyl acetate, chloroform, acetone, hexane. In all cases, after cooling to 25°C, filtration, and drying, the recovery rate of fluororesin A exceeded 80%, and the solubility was less than 20 wt%.

[0112] Reference example 2 Fluorine resin A (weight average molecular weight Mw = 7.2 × 10 4 ) in Novec 7300 at a solids concentration of 10 wt %. A solution of fluororesin A was added dropwise at 25°C to the following organic solvent in an amount 10 times the amount of the fluororesin A solution. The precipitation of a solid was confirmed visually, and the results are as follows: No solid precipitated: FC-72, FC-770, Novec 7200, Novec 7300, hexafluorobenzene. All of them had no precipitate and a solubility of 90 wt% or more. Solids precipitated: Zeorora H, AE-3000, trifluoroethanol, ethyl acetate, chloroform, acetone, and hexane. In all cases, the recovery rate of fluororesin A after filtration and drying exceeded 80%, and the solubility was less than 20 wt%. [Industrial Applicability]

[0113] The present invention is useful in fields related to fluororesins.

Claims

1. A fluororesin containing a residue unit represented by the following general formula (1), which has a haze value of 2% or less when formed into a hot-press molded product (thickness 1 mm) and a yellowness index of 2 or less when formed into a hot-melt molded product (thickness 3 mm) at 280°C for 24 hours: The fluororesin has an amount of insoluble matter of 0.2% by weight or less when the fluororesin is dissolved in 1,1,1,2,3,4,4,5,5,5-decafluoro-3-methoxy-2-(trifluoromethyl)pentane. 【Chemistry 1】 (In formula (1), Rf １ , Rf ２ , Rf ３ and Rf ４ each independently represents one of the group consisting of a fluorine atom, a linear perfluoroalkyl group having 1 to 7 carbon atoms, a branched perfluoroalkyl group having 3 to 7 carbon atoms, or a cyclic perfluoroalkyl group having 3 to 7 carbon atoms, wherein the perfluoroalkyl group may have an etheric oxygen atom, and Rf １ , Rf ２ , Rf ３ and Rf ４ may be linked to each other to form a ring having 4 to 8 carbon atoms, and the ring may contain an etheric oxygen atom.

2. The bulk density of the fluororesin is 0.1 to 1.5 g / cm ３ 2. The fluororesin according to claim 1, wherein

3. The bulk density of the fluororesin is 0.12 to 0.25 g / cm ３ 2. The fluororesin according to claim 1, wherein

4. The weight average molecular weight of the fluororesin is 5 x 10 ４ ~3 x 10 ５ 4. The fluororesin according to claim 1, wherein

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