Fluorine resin manufacturing method

Abstract

To provide a fluorine resin reduced in coloration when heating, and a production method of a fluorine resin.SOLUTION: A fluorine resin includes a residue unit represented by the following general formula (1), where a total of contents of chromium, iron, and nickel is 500 mass ppb or less. In the formula (1), Rf1, Rf2, Rf3, and Rf4 are each independently a linear, branched, or cyclic perfluoroalkyl group which may have a fluorine atom, or a C1-7 ethereal oxygen atom. Further, Rf1, Rf2, Rf3, and Rf4 may be combined with each other to form a perfluoro aliphatic ring which may have a C4-8 ethereal oxygen atom.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a fluororesin with few impurities and excellent optical properties, and a method for producing the same.

Background Art

[0002] Conventionally, fluororesins have been used for protective films for electronic components such as semiconductors, water-repellent films for inkjet printing, waterproof and oil-repellent coatings for filters, and members in the optical field because of their excellent electrical properties, optical properties, chemical resistance, waterproofness, and liquid-repellent and oil-repellent properties.

[0003] Among them, fluororesins containing an oxolane ring have an amorphous structure due to their bulky ring structure, and have high transparency and high heat resistance. In addition, since it is composed only of carbon, fluorine, and oxygen, it has high optical properties, electrical properties, chemical resistance, waterproofness, and liquid-repellent and oil-repellent properties. Furthermore, since it is amorphous, it can be melt-molded.

[0004] Non-Patent Document 1 describes a fluororesin containing an oxolane ring, stating that when stored in the air for more than two weeks, the transparency of the resin decreases, and it turns yellow when heated at 260 to 290°C. Although it is described that by reprecipitating and purifying this resin, impurities with carboxylic acid groups generated by side reactions during polymerization can be removed and the transparency does not decrease even when stored in the air, there is no description about coloring during heating. According to the present inventors, when the above-mentioned fluororesin is produced by reprecipitation, there is a problem that the metal components contained in the resin cannot be sufficiently removed, resulting in coloring during heating.

[0005] Also, Patent Document 1 describes that it is possible to obtain fluororesin particles by means such as suspension polymerization or emulsion polymerization. However, the dispersant and emulsifier used as polymerization aids remain inside the resin particles, causing coloring during heating, thus impairing the transparency and heat resistance, which are the characteristics of this resin. In addition, according to the present inventors, there is a problem that coloring also occurs during heating when the fluororesin contains a specific metal.

[0006] Since it is necessary to heat during the shaping process, the processed products of the above-mentioned fluororesin may be colored. Therefore, a fluororesin with reduced coloring during heating has been desired from the viewpoint of use in optical applications.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention has been made in view of the above problems, and provides a fluororesin with reduced coloring during heating and a method for producing the same.

Means for Solving the Problems

[0009] The inventors of the present invention have found that a fluororesin containing a residue unit represented by the following general formula (1) and having a total content of chromium, iron, and nickel of 500 mass ppb or less has little coloring during heating, and have completed the present invention.

[0010]

Chemical Formula

[0011] (In formula (1), Rf1, Rf2, Rf3, and Rf4 each independently represent a group selected from the group consisting of a fluorine atom or a linear, branched, or cyclic perfluoroalkyl group which may have an etheric oxygen atom having 1 to 7 carbon atoms. Further, Rf1, Rf2, Rf3, and Rf4 may be linked to each other to form a ring having 4 or more and 8 or less carbon atoms.)

[0012] The invention will be described in detail below.

[0013] The present invention relates to a resin containing a residue unit represented by the general formula (1), and having a total content of metals such as chromium, iron, and nickel of 500 mass ppb or less.

[0014] The fluororesin of the present invention has a bulky ring structure contained in the general formula (1), and thus is amorphous and has high transparency and high heat resistance. Further, since it is composed only of carbon, fluorine, and oxygen, it has high electrical properties, chemical resistance, waterproofness, and oil and liquid repellency.

[0015] In the residue unit represented by the general formula (1) in the present invention, the Rf1, Rf2, Rf3, and Rf4 groups each independently represent one kind of a group consisting of a linear, branched, or cyclic perfluoroalkyl group which may have a fluorine atom or an etheric oxygen atom having 1 to 7 carbon atoms. Further, Rf1, Rf2, Rf3, and Rf4 may be connected to each other to form a ring having 4 to 8 carbon atoms. Examples of the linear perfluoroalkyl group having 1 to 7 carbon atoms include a trifluoromethyl group, a pentafluoroethyl group, a heptafluoropropyl group, a nonafluorobutyl group, an undecafluoropentyl group, a tridecafluorohexyl group, a pentadecafluoroheptyl group, etc. Examples of the branched perfluoroalkyl group having 3 to 7 carbon atoms include a heptafluoroisopropyl group, a nonafluoroisobutyl group, a nonafluoro sec-butyl group, a nonafluoro tert-butyl group, etc. Examples of the cyclic perfluoroalkyl group having 3 to 7 carbon atoms include a heptafluorocyclopropyl group, a nonafluorocyclobutyl group, a tridecafluorocyclohexyl group, etc. Examples of the linear perfluoroalkyl group which may have an etheric oxygen atom having 1 to 7 carbon atoms include a -CF2OCF3 group, a -(CF2)2OCF3 group, a -(CF2)2OCF2CF3 group. Examples of the cyclic perfluoroalkyl group which may have an etheric oxygen atom having 3 to 7 carbon atoms 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, a 2-(2,3,3,4,4,5,5-heptafluoro)-furanyl group, etc.

[0016] For excellent heat resistance, it is preferable that at least one of Rf1, Rf2, Rf3, and Rf4 is a group selected from the group consisting of linear, branched, or cyclic perfluoroalkyl groups having 1 to 7 carbon atoms.

[0017] Specific examples of the residue unit represented by general formula (1) include the following residue units.

[0018] [ka]

[0019] Among these, resins containing the following residue units are preferred because they have excellent heat resistance and moldability, and resins containing perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue units represented by general formula (3) are more preferred.

[0020] [ka]

[0021] The resin of the present invention has a total content of chromium, iron, and nickel metals of 500 ppb by mass or less. This results in a fluororesin with reduced discoloration upon heating. The content is preferably 300 ppb by mass or less, and more preferably 120 ppb by mass or less. This further reduces discoloration upon heating. While the content is usually expressed as 5 ppb by mass or more, this is due to the lower analytical limit, and may be less than 5 ppb by mass if measurable.

[0022] Here, the contents of the metals chromium, iron, and nickel can be measured by general composition analysis, such as IPC-MS.

[0023] Furthermore, since a fluororesin with even lower coloring can be obtained, it is more preferable that the chromium and nickel metal contents are each 100 mass ppb or less.

[0024] The resin of the present invention preferably has a sodium content of 1000 mass ppb or less.

[0025] Since the resin of the present invention is excellent in fluidity and moldability, it is preferably in the form of particles, and more preferably has a volume average particle diameter of 5 μm or more and 500 μm or less. This is preferable because it enables continuous supply to a molding processing machine or the like when processing the resin. When the volume average particle diameter is 5 μm or more, it is difficult to scatter by an air current, and the handleability is improved. Also, when the volume average particle diameter is 500 μm or less, the fluidity is high, continuous supply to a molding processing machine or the like becomes possible, and the handleability is improved.

[0026] When the resin of the present invention has a particle shape, the volume average particle diameter can be evaluated by measuring the particle size distribution (volume distribution) by the laser diffraction scattering method. The particle size distribution by the laser diffraction scattering method can be quantified with good reproducibility by dispersing resin particles in water and subjecting them to a treatment to homogenize the dispersion state of crystal particles with an ultrasonic homogenizer, and then measuring. As a laser scattering meter, MT3000 manufactured by Microtrac can be exemplified.

[0027] When the resin of the present invention has a particle shape, it preferably is a precipitated polymer because it does not contain an emulsifier or a dispersant and is excellent in transparency and heat resistance.

[0028] The bulk density of the resin of the present invention when it has a particle shape is preferably 0.2 g / cm 3 or more and 1.5 g / cm 3 or less from the viewpoint of filling properties.

[0029] The resin of the present invention may contain other monomer residue units. Examples of other monomer residue units include tetrafluoroethylene (TFE), hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE), trifluoroethylene, hexafluoroisobutylene, perfluoroalkyl ethylene, fluorovinyl ether, vinyl fluoride (VF), vinylidene fluoride (VDF), perfluoro-2,2-dimethyl-1,3-dioxole (PDD), perfluoro(allyl vinyl ether), and perfluoro(butenyl vinyl ether).

[0030] In the present invention, there is no restriction on the molecular weight of the resin. For example, the weight average molecular weight in terms of PMMA measured by gel permeation chromatography (GPC) may be 2,500 to 2,000,000. From the viewpoints of the melt viscosity and mechanical strength of the resin, it is preferably 10,000 to 1,000,000 (g / mol).

[0031] The yellowness of the fluororesin of the present invention is preferably 3.0 or less, more preferably 1.0 or less. Thereby, the molded article can be more suitably used for optical applications. The yellowness can be measured, for example, by press molding the fluororesin into a desired shape.

[0032] Here, the yellowness can be measured by a general spectrophotometer colorimeter.

[0033] Next, the manufacturing method of the resin of the present invention will be described.

[0034] As a first aspect of the manufacturing method of the resin of the present invention, a method for producing a fluororesin having a precipitation polymerization step of performing precipitation polymerization in the presence of a monomer represented by the following general formula (4), a radical polymerization initiator, and an organic solvent with the water content in the reaction system being 1000 mass ppm or less can be mentioned.

[0035] In addition, since a particulate resin having excellent flowability and moldability can be obtained, the organic solvent is preferably an organic solvent that dissolves a monomer represented by the following general formula (4) and precipitates a resin containing a residue unit represented by the following general formula (5).

[0036] [ka]

[0037] (In formula (4), Rf5, Rf6, Rf7, and Rf8 each independently represent a group selected from the group consisting of a fluorine atom or a linear, branched, or cyclic perfluoroalkyl group having 1 to 7 carbon atoms, which may have an etheric oxygen atom. Rf5, Rf6, Rf7, and Rf8 may be linked to each other to form a ring having 4 to 8 carbon atoms.)

[0038] [ka]

[0039] (In formula (5), Rf5, Rf6, Rf7, and Rf8 each independently represent a group selected from the group consisting of a fluorine atom or a linear, branched, or cyclic perfluoroalkyl group having 1 to 7 carbon atoms, which may have an etheric oxygen atom. Rf5, Rf6, Rf7, and Rf8 may be linked to each other to form a ring having 4 to 8 carbon atoms.)

[0040] In the resin production method of the present invention, an organic solvent (hereinafter referred to as a "precipitation polymerization solvent") is used as a polymerization solvent to dissolve a monomer represented by general formula (4) and precipitate a resin containing a residue unit represented by general formula (5). This allows the resin produced by the polymerization reaction to be precipitated as particles having a specific volume average particle size, resulting in the production of a resin with a particle shape that is excellent in moldability and packing properties. Furthermore, because no polymerization aids such as emulsifiers and dispersants are used, resin particles that do not contain emulsifiers or dispersants, which can impair transparency and heat resistance, can be produced.

[0041] Whether a certain organic solvent is an organic solvent that precipitates a certain resin can be determined by whether the polarity of the organic solvent is within a specific range. In the present invention, it is preferable to select an organic solvent having a polarity within a specific range as the precipitation polymerization solvent based on the Hansen solubility parameters.

[0042] The Hansen solubility parameter is obtained by dividing the solubility parameter introduced by Hildebrand into three components: the dispersion term δD, the polar term δP, and the hydrogen bonding term δH by Hansen and representing them in three-dimensional space. The dispersion term δD represents the effect of the dispersion force, the polar term δP represents the effect of the dipole-dipole force, and the hydrogen bonding term δH represents the effect of the hydrogen bonding force. In three-dimensional space, the farther the coordinates of a resin and the coordinates of an organic solvent are apart, the easier it is for the resin to precipitate in the organic solvent.

[0043] The definition and calculation method of the Hansen solubility parameter are described in the following literature. Charles M. Hansen, "Hansen Solubility Parameters: A User's Handbook", CRC Press, 2007. For organic solvents whose literature values are unknown, the Hansen solubility parameter can be easily estimated from its chemical structure by using computer software (Hansen Solubility Parameters in Practice (HSPiP)).

[0044] In the present invention, HSPiP 5th Eddition is used, and the values of the organic solvents registered in the database are used, and the estimated values are used for the organic solvents not registered.

[0045] The Hansen solubility parameter of a resin is usually determined by conducting a solubility test in which the resin is dissolved in a number of different organic solvents for which the Hansen solubility parameter has been established and the solubility is measured. Specifically, when the coordinates of the Hansen solubility parameters of all the organic solvents used in the solubility test are plotted in three-dimensional space, a sphere (solubility sphere) is found such that the coordinates of the organic solvents that dissolved resin A are all contained inside the sphere and the coordinates of the organic solvents that precipitate the resin are on the outside, and the central coordinates of the solubility sphere are taken as the Hansen solubility parameter of the resin.

[0046] If the coordinates of the Hansen solubility parameters of an organic solvent not used in the solubility test are (δD, δP, δH), and the coordinates are contained within the solubility sphere, the organic solvent is considered to dissolve the resin. On the other hand, if the coordinates are outside the solubility sphere, the organic solvent is considered to precipitate the resin.

[0047] In the present invention, the Hansen solubility parameter of the resin was the value of the Hansen solubility parameter of the compound represented by the following general formula (6) (pentamer of the compound represented by general formula (5)), which was estimated using HSPiP. By this method, for example, the Hansen solubility parameters δD, δP, and δH of resin particles containing perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue units represented by general formula (3) were calculated to be 11.6, 3.5, and 1.4 (MPa 1 / 2 )

[0048] [ka]

[0049] (In formula (6), Rf9, Rf 10 , Rf 11 , Rf 12 Rf9 and Rf10 each independently represent a group selected from the group consisting of a fluorine atom or a linear, branched, or cyclic perfluoroalkyl group having 1 to 7 carbon atoms, which may have an etheric oxygen atom. 10 , Rf 11 , Rf12 may be connected to each other to form a ring having 4 to 8 carbon atoms.

[0050] As the precipitation polymerization solvent in the present invention, it is preferable to select an organic solvent in which the resin dissolution index R calculated by the formula (7) from the Hansen solubility parameter is 4 or more. R = 4 × {(δD1 - δD2) 2 + (δP1 - δP2) 2 + (δH1 - δH2) 2} 0.5 ···(7) Here, δD1, δP1, and δH1 are the dispersion term, polar term, and hydrogen term of the Hansen solubility parameter of the resin particles, respectively, and δD2, δP2, and δH2 are the dispersion term, polar term, and hydrogen term of the Hansen solubility parameter of the organic solvent, respectively.

[0051] For example, organic solvents described in Table 1 below can be mentioned as organic solvents having an affinity Ra of 4 or more with a resin containing a perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit.

[0052]

Table 1

[0053] Furthermore, as the precipitation polymerization solvent, an organic solvent containing a fluorine atom and a hydrogen atom in the molecule is preferable because a chain transfer reaction hardly occurs in radical polymerization, the polymerization yield is excellent, and a high molecular weight substance is easily obtained. Specific precipitation polymerization solvents containing a fluorine atom and a hydrogen atom in the molecule 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, and the like.

[0054] As the radical polymerization initiator used in radical polymerization, for example, organic peroxides such as benzoyl peroxide, lauryl peroxide, octanoyl peroxide, acetyl peroxide, di-tetr-butyl peroxide, tetr-butyl cumyl peroxide, dicumyl peroxide, tetr-butyl peroxyacetate, perfluoro(di-tetr-butyl peroxide), bis(2,3,4,5,6-pentafluorobenzoyl) peroxide, tetr-butyl peroxybenzoate, tetr-butyl perpivalate; azo initiators such as 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-butyronitrile), 2,2'-azobisisobutyronitrile, dimethyl-2,2'-azobisisobutyrate, 1,1'-azobis(cyclohexane-1-carbonitrile) and the like can be mentioned.

[0055] In the production method of the present invention, it is preferable that the monomer represented by the general formula (4) is perfluoro(4-methyl-2-methylene-1,3-dioxolane) represented by the following general formula (8), and the residue unit represented by the general formula (5) is a perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit represented by the following general formula (9).

[0056]

Chemical formula

[0057]

Chemical formula

[0058] As a second aspect of the method for producing the resin of the present invention, The fluororesin can be produced by a method for producing the fluororesin, which comprises a solution polymerization step of carrying out solution polymerization in the presence of a monomer represented by the following general formula (4), a radical polymerization initiator, and an organic solvent at a water content of 1,000 mass ppm or less in the reaction system, and a precipitation step of contacting a solution containing the fluororesin obtained by solution polymerization with a poor solvent to precipitate the fluororesin while maintaining the water content in the system at 100 ppm or less.

[0059] The poor solvent here is preferably the same solvent as the organic solvent in the first embodiment of the resin production method of the present invention.

[0060] The organic solvent in the second embodiment may be either a good solvent or a poor solvent for the fluororesin of the present invention, but is preferably a good solvent.

[0061] In the production method of the present invention, in common with the first and second aspects, it is preferable to carry out polymerization after purifying at least one of the monomer represented by the general formula (4), the initiator, and the organic solvent with at least one of a filtration filter, an ion exchange resin, a metal ion removal filter, and a metal ion remover. [Effects of the Invention]

[0062] According to the present invention, it is possible to provide a fluororesin with reduced coloration and a method for producing the fluororesin. [Example]

[0063] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0064] <Volume average particle size> The volume average particle size (unit: μm) was measured using MT3000 manufactured by Microtrac and methanol as a dispersion medium. <Metal component content> The fluororesin was dissolved in hexafluorobenzene and then extracted with a dilute acid solution, and the metal components (unit: ppb) were measured using ELAN DRC II manufactured by Perkin Elmer. <Yellowness (YI)> The fluororesin was hot-pressed at 230° C. for 50 minutes in a nitrogen atmosphere to prepare a pressed sheet having a thickness of 200 nm, and the yellowness index (YI) was measured using SD5000 manufactured by Nippon Denshoku Industries Co., Ltd.

[0065] (Example 1) Preparation of perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles A 1-L SUS316 autoclave equipped with a SUS316 paddle-type stirring blade, a nitrogen inlet tube, and a thermometer was purged with nitrogen. 1.215 g (0.00288 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide (initiator), 140.0 g (0.574 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) (monomer), and 1250 g of Asahiklin AE-3000 (Asahi Glass Co., Ltd., 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether) (precipitation polymerization solvent) were added and stirred at 55°C for 24 hours to conduct precipitation polymerization. After cooling to room temperature, the liquid containing the purified resin particles was filtered and washed with acetone to obtain perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles (Resin A) (yield: 63%). The volume average particle size, metal content and yellowness of the obtained resin particles are shown in Table 2. The obtained resin particles had excellent fluidity and filling properties, low metal content, low yellowness and good transparency.

[0066] [Table 2]

[0067] (Comparative Example 1) Preparation of perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin Next, a fluororesin was produced in accordance with Non-Patent Document 1. The inside of a 1-L SUS316 autoclave equipped with a paddle-type stirring blade made of SUS316, a nitrogen introduction tube, and a thermometer was purged with nitrogen. 0.476 g (0.00113 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide was used as an initiator, 140.0 g (0.574 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) was used as a monomer, and 230 g of hexafluorobenzene was used as a polymerization solvent. Radical solution polymerization was carried out by holding the mixture at 55°C for 24 hours under stirring, and a viscous liquid in which the resin was dissolved was obtained. After cooling to room temperature, the resin solution was diluted with 1000 g of hexafluorobenzene to prepare a resin-diluted solution for viscosity adjustment. 3 L of hexane was added to the vat, and the resin was precipitated by extruding the above resin-diluted solution into the hexane with a syringe to obtain a perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin (yield: 68%).

[0068] Since the obtained resin was amorphous, the volume-average particle diameter could not be measured. The metal components and yellowness of the obtained resin are shown in Table 2. The obtained resin particles were inferior in fluidity and fillability, had a large amount of metal components, and had a high yellowness, so there were also problems with transparency. In addition, water droplets aggregated by the heat of vaporization of the poor solvent were confirmed in the poor solvent used in the precipitation step, and the moisture in the system was 100 ppm or more.

[0069] (Comparative Example 2) Production of perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles The interior of a 1-L SUS316 autoclave equipped with a SUS316 paddle-type stirring blade, a nitrogen inlet tube, and a thermometer was purged with nitrogen. Suspension polymerization was carried out by adding 0.775 g (0.00184 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator, 5.289 g of Newcol 714SN (Nippon Nyukazai Co., Ltd., polyoxyethylene polycyclic phenyl ether sulfate) as a dispersion stabilizer, 16.300 g of methanol as a chain transfer agent, 140.0 g (0.574 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as a monomer, and 190.0 g of ion-exchanged water as a suspension polymerization solvent. The mixture was stirred at 55°C for 24 hours to carry out suspension polymerization. After cooling to room temperature, the liquid containing the purified resin particles was filtered and washed with acetone to obtain perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles (yield: 85%). The volume average particle size, metal content, and yellowness of the obtained resin particles are shown in Table 2. The obtained resin particles have excellent fluidity and packing properties, but the high metal content and high yellowness pose a transparency issue.

[0070] (Example 2) Preparation of perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles A 1-L glass autoclave equipped with a SUS316 paddle-type stirring blade, a nitrogen inlet tube, and a thermometer was purged with nitrogen. 1.190 g (0.00282 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide (initiator), 140.0 g (0.574 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) (monomer), and 1250 g of Asahiklin AE-3000 (Asahi Glass Co., Ltd., 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether) (precipitation polymerization solvent) were added and stirred at 55°C for 24 hours to conduct precipitation polymerization. After cooling to room temperature, the liquid containing the purified resin particles was filtered and washed with acetone to obtain perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles (Resin A) (yield: 66%). The volume average particle size, metal content and yellowness index of the obtained resin particles are shown in Table 2. The obtained resin particles had a small amount of metal content and were excellent in yellowness index, fluidity and filling property.

[0071] (Comparative Example 3) Preparation of perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles A 1-L glass autoclave equipped with a SUS316 paddle-type stirring blade, a nitrogen inlet tube, and a thermometer was purged with nitrogen. Suspension polymerization was carried out by adding 0.726 g (0.00172 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide as initiator, 5.314 g of Newcol 714SN (Nippon Nyukazai Co., Ltd., polyoxyethylene polycyclic phenyl ether sulfate ester salt) as dispersion stabilizer, 16.280 g of methanol as chain transfer agent, 140.0 g (0.573 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as monomer, and 186.7 g of ion-exchanged water as suspension polymerization solvent. The mixture was stirred at 55°C for 24 hours and cooled to room temperature. The purified resin particles were filtered and washed with acetone to obtain perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles (yield: 85%). The volume average particle size, metal content, and yellowness of the obtained resin particles are shown in Table 2. The obtained resin particles have excellent fluidity and filling properties, but have a problem with transparency due to the high metal content and high yellowness. [Industrial Applicability]

[0072] The present invention can provide a fluororesin that is less discolored when heated and a method for producing the fluororesin.

Claims

1. A solution polymerization step of solution polymerizing in the presence of a monomer represented by the following general formula (2), a radical polymerization initiator, and an organic solvent with the water content in the reaction system being 1000 ppm by mass or less, and a precipitation step of contacting a solution containing the fluororesin obtained by solution polymerization with a poor solvent to precipitate the fluororesin while maintaining the water content in the system at 100 ppm by mass or less, wherein the poor solvent is an organic solvent containing a fluorine atom and a hydrogen atom in the molecule, and a method for producing a fluororesin containing a residue unit represented by the following general formula (1) and having a total content of chromium, iron, and nickel of 500 ppb by mass or less. 【Chemical 1】 (In formula (1), Rf １ , Rf ２ , Rf ３ , Rf ４ each independently represents a group selected from the group consisting of a linear, branched or cyclic perfluoroalkyl group which may have a fluorine atom or an etheric oxygen atom having 1 to 7 carbon atoms. Also, Rf １ , Rf ２ , Rf ３ , Rf ４ may be linked to each other to form a perfluoroaliphatic ring which may have an etheric oxygen atom having 4 to 8 carbon atoms.) [Chemical Formula 2] (In formula (2), Rf ５ , Rf ６ , Rf ７ , Rf ８ each independently represents a linear, branched or cyclic perfluoroalkyl group which may have a fluorine atom or an etheric oxygen atom having 1 to 7 carbon atoms. Further, Rf ５ , Rf ６ , Rf ７ , Rf ８ may be linked to each other to form a perfluoroaliphatic ring which may have an etheric oxygen atom having 4 to 8 carbon atoms.)

2. The method for producing a fluororesin according to claim 1, wherein at least one of the monomer represented by the general formula (2), the initiator, and the organic solvent in the solution polymerization step is purified with at least one of a filtration filter, an ion exchange resin, a metal ion removal filter, or a metal ion remover, and then polymerization is carried out.

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