JP2020122068A - Fluorine resin and method for producing the same - Google Patents

Abstract

To provide a fluorine resin having reduced coloration during heating and a method for producing a fluorine resin.SOLUTION: A fluorine resin has a residue unit represented by general formula (1), and a total content of chromium, iron and nickel is 500 mass ppb or less (where, Rf, Rf, Rf, Rfindependently represent a fluorine atom or a C1-7 linear, branched or cyclic perfluoroalkyl group, optionally having an ethereal oxygen atom; Rf, Rf, Rf, Rfmay be coupled to each other and form a C4-8 perfluoro aliphatic ring, optionally having an ethereal oxygen atom).SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a fluororesin containing few impurities and excellent in optical characteristics, and a method for producing the same.

Fluorine-based resins have traditionally been excellent in electrical characteristics, optical characteristics, chemical resistance, waterproofness, and liquid repellency and oil repellency. It is used as a coating and a member in the optical field.

Among them, a fluororesin containing an oxolane ring has a bulky ring structure 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 optical characteristics, electrical characteristics, chemical resistance, waterproofness, and liquid repellency and oil repellency. Furthermore, since it is amorphous, melt molding is possible.

Non-Patent Document 1 describes a fluororesin containing an oxolane ring, and when stored in the air for 2 weeks or more, the transparency of the resin decreases, and when heated at 260 to 290° C., it is colored yellow. By reprecipitation purification of this resin, it is described that impurities having a carboxylic acid group generated by a side reaction during polymerization are removed and the transparency does not decrease even if stored in the air, but regarding the coloring during heating, There is no description. According to the present inventors, when the fluororesin is reprecipitated, there is a problem that the metal component contained in the resin cannot be sufficiently removed and coloring occurs during heating.

Further, 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 the emulsifier used as the polymerization aid remain inside the resin particles and cause coloration during heating, which impairs the transparency and heat resistance of the resin. Further, according to the present inventors, there is a problem that coloring occurs during heating even when the fluororesin contains a specific metal.

Since it was necessary to overheat during the molding process, the processed product of the above-mentioned fluororesin was likely to be colored. Therefore, there has been a demand for a fluororesin having reduced coloring during heating from the viewpoint of being used for optical applications.

Publication of WO2014/156996 Macromolecules, 2005, 38, 4237-4245.

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.

The present inventors 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 is less colored when heated. This has led to the completion of the present invention.

(In the formula (1), Rf ₁ , Rf ₂ , Rf ₃ and Rf ₄ are each independently a straight chain, branched chain or branched chain which may have a fluorine atom or an etheric oxygen atom having 1 to 7 carbon atoms. A group selected from the group consisting of cyclic perfluoroalkyl groups, 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. )

The invention will be described in detail below.

The present invention is a resin containing a residue unit represented by the general formula (1) and having a total metal content of chromium, iron, and nickel of 500 mass ppb or less.

Since the fluororesin of the present invention has the bulky ring structure contained in the general formula (1), it is amorphous and has high transparency and high heat resistance. In addition, since it is composed only of carbon, fluorine, and oxygen, it has high electrical characteristics, chemical resistance, waterproofness, and liquid repellency.

The Rf ₁ , Rf ₂ , Rf ₃ , and Rf ₄ groups in the residue unit represented by the general formula (1) in the present invention each independently have a fluorine atom or an etheric oxygen atom having 1 to 7 carbon atoms. 1 group of a linear, branched or cyclic perfluoroalkyl group which may be present. 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. Examples of the linear perfluoroalkyl group having 1 to 7 carbon atoms include, for example, trifluoromethyl group, pentafluoroethyl group, heptafluoropropyl group, nonafluorobutyl group, undecafluoropentyl group, tridecafluorohexyl group, Examples thereof include a pentadecafluoroheptyl group, and examples of the branched perfluoroalkyl group having 3 to 7 carbon atoms include a heptafluoroisopropyl group, a nonafluoroisobutyl group, a nonafluorosec-butyl group, a nonafluorotert-butyl group, and the like. Examples of the cyclic perfluoroalkyl group having 3 to 7 carbon atoms include a heptafluorocyclopropyl group, a nonafluorocyclobutyl group, a tridecafluorocyclohexyl group, and the like. The etheric oxygen atom which may have a linear perfluoro alkyl group having 1 to 7 carbon atoms, _e.g., -CF 2 OCF _{3 group, - (CF 2) 2 OCF} 3 group, - (CF ₂ ) ₂ OCF ₂ CF ₃ groups and cyclic perfluoroalkyl groups having 3 to 7 carbon atoms and optionally having an etheric oxygen atom include, for example, 2-(2,3,3,4,4,5,5). 5,6,6-decafluoro)-pyrinyl group, 4-(2,3,3,4,4,5,5,6,6-decafluoro)-pyinyl group, 2-(2,3,3,3) 4,4,5,5-heptafluoro)-furanyl group and the like.

Since it has excellent heat resistance, at least one of Rf ₁ , Rf ₂ , Rf ₃ and Rf ₄ is selected from the group consisting of linear, branched or cyclic perfluoroalkyl groups having 1 to 7 carbon atoms. It is preferable that the group is

Then, examples of the specific residue unit represented by the general formula (1) include the following residue units.

Among these, a resin containing the following residue units is preferable because of its excellent heat resistance and moldability, and perfluoro(4-methyl-2-methylene-1,3-dioxolane) represented by the general formula (3) is preferable. Resins containing residue units are more preferred.

The resin of the present invention has a total content of chromium, iron and nickel metals of 500 mass ppb or less. As a result, a fluororesin with reduced coloring during heating can be obtained. The content is preferably 300 mass ppb or less, more preferably 120 mass ppb or less. As a result, coloring during heating is further reduced. Usually, the content is described as 5 mass ppb or more, but this is due to the lower limit of analysis, and if it can be measured, it may fall below 5 mass ppb.

Here, the contents of metals such as chromium, iron, and nickel can be measured by general composition analysis, and for example, IPC-MS can be exemplified.

Further, it is more preferable that the content of the chromium metal and the content of the nickel metal be 100 mass ppb or less, respectively, because a fluororesin with reduced coloring is obtained.

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

Since the resin of the present invention is excellent in fluidity and moldability, it is preferably in the form of particles, and more preferably, its volume average particle size is 5 μm or more and 500 μm or less. This is preferable because it enables continuous supply to a molding machine or the like when processing the resin. When the volume average particle diameter is 5 μm or more, it is less likely to be scattered by the air flow and the handleability is improved. Further, when the volume average particle size is 500 μm or less, the fluidity is high, continuous supply to a molding machine or the like is possible, and the handleability is improved.

The volume average particle diameter when the resin of the present invention has a particle shape can be evaluated by measuring a particle diameter distribution (volume distribution) by a laser diffraction scattering method. The particle size distribution by the laser diffraction scattering method is quantified with good reproducibility by measuring the resin particles dispersed in water and treated with an ultrasonic homogenizer to make the dispersed state of the crystal particles uniform. be able to. An example of the laser scatterometer is MT3000 manufactured by Microtrac.

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

When the resin of the present invention has a particle shape, the bulk density is preferably 0.2 g/cm ³ or more and 1.5 g/cm ³ or less from the viewpoint of filling property.

The resin of the present invention may contain other monomer residue units, and examples of the other monomer residue units include tetrafluoroethylene (TFE), hexafluoropropylene (HFP), chlorotrifluoroethylene. (CTFE), trifluoroethylene, hexafluoroisobutylene, perfluoroalkylethylene, 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).

In the present invention, the molecular weight of the resin is not particularly limited, and examples thereof include a weight average molecular weight in terms of PMMA measured by gel permeation chromatography (GPC) of 2,500 to 2,000,000. From the viewpoint of melt viscosity and mechanical strength of the resin, it is preferably 10,000 to 1,000,000 (g/mol).

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

Here, the degree of yellowness can be measured by a general spectral colorimeter.

Next, a method for producing the resin of the present invention will be described.

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

In addition, since a resin in the form of particles having excellent fluidity and moldability is obtained, the organic solvent dissolves the monomer represented by the following general formula (4) and leaves the residue represented by the following general formula (5). An organic solvent that precipitates a resin containing a group unit is preferable.

(In the formula (4), Rf ₅ , Rf ₆ , Rf ₇ , and Rf ₈ are each independently a straight chain, branched chain, or branched chain which may have a fluorine atom or an etheric oxygen atom having 1 to 7 carbon atoms. A group selected from the group consisting of cyclic perfluoroalkyl groups, and Rf ₅ , Rf ₆ , Rf ₇ and Rf ₈ may be linked to each other to form a ring having 4 to 8 carbon atoms. )

(In the formula (5), Rf ₅ , Rf ₆ , Rf ₇ , and Rf ₈ each independently have a fluorine atom or a linear, branched, or optionally substituted etheric oxygen atom having 1 to 7 carbon atoms. A group selected from the group consisting of cyclic perfluoroalkyl groups, and Rf ₅ , Rf ₆ , Rf ₇ and Rf ₈ may be linked to each other to form a ring having 4 to 8 carbon atoms. )

In the method for producing a resin of the present invention, an organic solvent that dissolves a monomer represented by the general formula (4) as a polymerization solvent and precipitates a resin containing a residue unit represented by the general formula (5) , "Precipitation polymerization solvent"), the resin produced by the polymerization reaction can be precipitated as particles having a specific volume average particle diameter, and as a result, a particle shape excellent in moldability and filling property. The resin can be manufactured. In addition, since no polymerization aid such as an emulsifier and a dispersant is used, it is possible to produce resin particles that do not contain an emulsifier and a dispersant that cause deterioration of transparency and heat resistance.

Whether or not a certain organic solvent is an organic solvent for precipitating a certain resin can be judged by whether or not the polarity of the organic solvent is within a specific range. In the present invention, it is preferable to select, as the precipitation polymerization solvent, an organic solvent having a polarity in a specific range based on Hansen solubility parameters.

The Hansen solubility parameter is a solubility parameter introduced by Hildebrand, which Hansen divides into three components of a dispersion term δD, a polar term δP, and a hydrogen bond term δH, and is shown in a three-dimensional space. is there. The dispersion term δD represents the effect of the dispersive force, the polar term δP represents the effect of the dipole-dipole force, and the hydrogen bond term δH represents the effect of the hydrogen bond force. In a three-dimensional space, the further the coordinates of a resin and the coordinates of an organic solvent are away from each other, the easier the resin is to precipitate in the organic solvent.

The definition and calculation method of the Hansen solubility parameter are described in the following documents. Charles M. Hansen, "HansenSolubilityParameters: AusersHandbook", CRC Press, 2007. For organic solvents for which literature values are unknown, Hansen solubility parameters can be easily estimated from their chemical structures by using computer software (HansenSolubilityParametersPractice (HSPiP)).

In the present invention, HSPiP 5th Edition is used, and the value is used for the organic solvent registered in the database, and the estimated value is used for the organic solvent not registered.

The Hansen solubility parameter of a resin is usually determined by dissolving the resin in a number of different organic solvents with established Hansen solubility parameters and conducting a solubility test to measure the solubility. Specifically, when the coordinates of the Hansen solubility parameters of all the organic solvents used in the solubility test are shown in the three-dimensional space, the coordinates of the organic solvent in which the resin A is dissolved are all included inside the sphere and are precipitated. A sphere (solubility sphere) whose solvent coordinates are outside the sphere is searched for, and the central coordinate of the solubility sphere is used as the Hansen solubility parameter of the resin.

When the coordinates of the Hansen solubility parameter of an organic solvent not used in the solubility test are (δD, δP, δH), if the coordinates are included inside the solubility sphere, the organic solvent is a resin. It is thought to dissolve. On the other hand, if the coordinates are outside the solubility sphere, the organic solvent is considered to precipitate the resin.

In the present invention, as the Hansen solubility parameter of the resin, the Hansen solubility parameter of the compound represented by the following general formula (6) (a pentamer of the compound represented by the general formula (5)) was estimated using HSPiP. Values were used. By this method, for example, the Hansen solubility parameters δD, δP, and δH of the resin particles containing the perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit represented by the general formula (3) are They are 11.6, 3.5, and 1.4 (MPa ^1/2 ), respectively.

(In the formula (6), Rf ₉ , Rf ₁₀ , Rf ₁₁ and Rf ₁₂ are each independently a straight chain, branched chain or branched chain which may have a fluorine atom or an etheric oxygen atom having 1 to 7 carbon atoms. A group selected from the group consisting of cyclic perfluoroalkyl groups is shown, and Rf ₉ , Rf ₁₀ , Rf ₁₁ and Rf ₁₂ may be linked to each other to form a ring having 4 to 8 carbon atoms. )

Then, as the precipitation polymerization solvent in the present invention, it is preferable to select an organic solvent having a solubility index R of the resin of 4 or more calculated by the formula (7) from the Hansen solubility parameter.
_{R = 4 × {(δD 1} -δD 2) 2 + (δP 1 -δP 2) 2 + (δH 1 -δH 2) 2} 0.5 ··· (7)
Here [delta] D _1, [delta] P _1, dispersion term of Hansen Solubility Parameter of each delta] H ₁ of the resin particles, the polarity term and hydrogen _{claim, δD 2, δP 2, δH} 2 is dispersion term of each Hansen solubility parameter of said organic solvent, It is a polar term and a hydrogen term.

For example, as an organic solvent having an affinity Ra with a resin containing a perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit of 4 or more, the organic solvents described in Table 1 below are listed. You can

Further, 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 does not easily occur in radical polymerization, the polymerization yield is excellent, and a high molecular weight polymer is easily obtained. Specific examples of the precipitation polymerization solvent containing a fluorine atom and a hydrogen atom in the molecule include 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether and 2,2,2-trifluoro. Examples include ethanol, 1,1,1,3,3,3-hexafluoroisopropanol, 1,2,2,3,3,4,4-heptafluorocyclopentane, and the like.

Examples of the radical polymerization initiator when performing radical polymerization include, for example, benzoyl peroxide, lauryl peroxide, octanoyl peroxide, acetyl peroxide, di-tetr-butyl peroxide, tetr-butyl cumyl peroxide, dicumyl peroxide. Oxide, tetr-butylperoxyacetate, perfluoro(di-tetr-butylperoxide), bis(2,3,4,5,6-pentafluorobenzoyl)peroxide, tetr-butylperoxybenzoate, tetr-butyl Organic peroxides such as perpivalate; 2,2′-azobis(2,4-dimethylvaleronitrile), 2,2′-azobis(2-butyronitrile), 2,2′-azobisisobutyronitrile, Examples thereof include azo initiators such as dimethyl-2,2'-azobisisobutyrate and 1,1'-azobis(cyclohexane-1-carbonitrile).

In the production method of the present invention, the monomer represented by the general formula (4) is perfluoro(4-methyl-2-methylene-1,3-dioxolane) represented by the following general formula (8). The residue unit represented by the general formula (5) is preferably a perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit represented by the following general formula (9). ..

As a second aspect of the resin production method of the present invention,
A solution polymerization step in which a monomer represented by the following general formula (4), a radical polymerization initiator, and a solvent in the reaction system in the presence of a water content of 1000 mass ppm or less in the presence of a solution are subjected to solution polymerization, and fluorine obtained by solution polymerization It can be produced by a method for producing a fluororesin, which comprises a deposition step of bringing a solution containing a resin into contact with a poor solvent to deposit the fluororesin while maintaining the system at 100 ppm or less.

Here, the poor solvent is preferably the same solvent as the organic solvent in the first aspect of the resin production method of the present invention.

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

The production method of the present invention has, in common with the first and second aspects, at least one of a monomer represented by the general formula (4), an initiator and an organic solvent, a filtration filter, It is preferable to carry out polymerization after purification with at least one of an ion exchange resin, a metal ion removing filter and a metal ion removing agent.

According to the present invention, it is possible to provide a fluororesin with reduced coloring and a method for producing the fluororesin.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

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

(Example 1) Production of perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles The inside of a 1 L SUS316 autoclave equipped with a SUS316 paddle type stirring blade, a nitrogen introducing tube and a thermometer was used. The atmosphere was replaced with nitrogen. 1.215 g (0.00288 mol) of bis(2,3,4,5,6-pentafluorobenzoyl)peroxide as an initiator and perfluoro(4-methyl-2-methylene-1,3-) as a monomer Dioxolane) 140.0 g (0.574 mol), Asahi Kulin AE-3000 (Asahi Glass, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether) 1250 g as a precipitation polymerization solvent. Was added, and precipitation polymerization was carried out by maintaining the mixture at 55° C. for 24 hours with stirring. After cooling to room temperature, the liquid containing the purified resin particles was filtered off and washed with acetone to obtain perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles (resin A) ( Yield: 63%). Table 2 shows the volume average particle diameter, metal component, and yellowness of the obtained resin particles. The obtained resin particles were excellent in fluidity and filling property, had low metal components, low yellowness, and good transparency.

(Comparative Example 1) Production of perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin Hereinafter, a fluororesin was produced according to Non-Patent Document 1. The inside of a 1 L SUS316 autoclave equipped with a SUS316 paddle type stirring blade, a nitrogen introduction tube and a thermometer was replaced with nitrogen. 0.476 g (0.00113 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator and perfluoro(4-methyl-2-methylene-1,3-) as a monomer. 140.0 g (0.574 mol) of dioxolane) and 230 g of hexafluorobenzene as a polymerization solvent were added, and the mixture was held at 55° C. for 24 hours under stirring to carry out radical solution polymerization, whereby a viscous liquid in which a resin was dissolved was obtained. Was given. After cooling to room temperature, the resin solution was diluted with 1000 g of hexafluorobenzene to adjust the viscosity to prepare a resin diluted solution. Hexane (3 L) was added to the vat, and the resin diluted solution was extruded into the hexane with a syringe to precipitate the resin, and a perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin was obtained ( Yield: 68%).

The volume average particle diameter could not be measured because the obtained resin was amorphous. Table 2 shows the metal components and yellowness of the obtained resin. The obtained resin particles were inferior in fluidity and filling property, contained a large amount of metal components, and had a high degree of yellowness. In the poor solvent used in the precipitation step, water droplets aggregated by the heat of vaporization of the poor solvent were confirmed, and the water content in the system was 100 ppm or more.

(Comparative Example 2) Production of perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles 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 used. The atmosphere was replaced with nitrogen. 0.775 g (0.00184 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator, and Newcol 714SN (manufactured by Nippon Emulsifier Co., Ltd., polyoxyethylene polycyclic phenyl) as a dispersion stabilizer. Ether sulfate ester salt) 5.289 g, methanol as a chain transfer agent 16.300 g, perfluoro(4-methyl-2-methylene-1,3-dioxolane) 140.0 g (0.574 mol) as a monomer, Ion-exchanged water (190.0 g) was added as a suspension polymerization solvent, and suspension polymerization was carried out by maintaining the mixture at 55° C. for 24 hours with stirring. After cooling to room temperature, the liquid containing the purified resin particles was filtered off and washed with acetone to obtain perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles (yield: 85 %). Table 2 shows the volume average particle diameter, metal component, and yellowness of the obtained resin particles. The obtained resin particles are excellent in fluidity and filling property, but have a large amount of metal components and a high degree of yellowness, which causes a problem in transparency.

(Example 2) Production of perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles The inside of a 1 L glass autoclave equipped with a paddle type stirring blade made of SUS316, a nitrogen introduction tube and a thermometer was used. The atmosphere was replaced with nitrogen. 1.190 g (0.00282 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator and perfluoro(4-methyl-2-methylene-1,3-) as a monomer Dioxolane) 140.0 g (0.574 mol), Asahi Kulin AE-3000 (Asahi Glass, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether) 1250 g as a precipitation polymerization solvent. In addition, precipitation polymerization was performed by maintaining the temperature at 55° C. for 24 hours with stirring. After cooling to room temperature, the liquid containing the purified resin particles was filtered off and washed with acetone to obtain perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles (resin A) ( Yield: 66%). Table 2 shows the volume average particle diameter, metal component, and yellowness of the obtained resin particles. The obtained resin particles contained few metal components and were excellent in yellowness, fluidity and filling property.

(Comparative Example 3) Production of perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles The inside of a 1 L glass autoclave equipped with a paddle type stirring blade made of SUS316, a nitrogen introduction tube and a thermometer was used. The atmosphere was replaced with nitrogen. 0.726 g (0.00172 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator, and Newcol 714SN (manufactured by Nippon Emulsifier Co., Ltd., polyoxyethylene polycyclic phenyl) as a dispersion stabilizer. Ether sulfate ester salt) 5.314 g, methanol as a chain transfer agent 16.280 g, perfluoro(4-methyl-2-methylene-1,3-dioxolane) 140.0 g (0.573 mol) as a monomer, Ion-exchanged water (186.7 g) was added as a suspension polymerization solvent, and suspension polymerization was carried out by maintaining the mixture at 55° C. for 24 hours with stirring. After cooling to room temperature, the liquid containing the purified resin particles was filtered off and washed with acetone to obtain perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles (yield: 85 %). Table 2 shows the volume average particle diameter, metal component, and yellowness of the obtained resin particles. The obtained resin particles are excellent in fluidity and filling property, but have a problem in transparency because they have many metal components and high yellowness.

INDUSTRIAL APPLICABILITY The present invention can provide a fluororesin with reduced coloring during heating and a method for producing a fluororesin.

Claims (10)

A fluororesin comprising 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.
(In the formula (1), Rf ₁ , Rf ₂ , Rf ₃ , and Rf ₄ are each independently a straight-chain, branched or Rf ₁ , Rf ₃ , Rf ₃ or Rf _{3 which} may have a fluorine atom or an etheric oxygen atom having 1 to 7 carbon atoms. A group selected from the group consisting of cyclic perfluoroalkyl groups, wherein Rf ₁ , Rf ₂ , Rf ₃ and Rf ₄ are linked to each other and have an etheric oxygen atom having 4 to 8 carbon atoms. Optionally, may form a perfluoroaliphatic ring.) The fluororesin according to claim 1, wherein the total content of chromium, iron, and nickel is 5 mass ppb or more and 500 mass ppb or less. Content of sodium is 1000 mass ppb or less, The fluororesin of Claim 1 or 2 characterized by the above-mentioned. The fluororesin according to any one of claims 1 to 3, which has a volume average particle diameter of 5 µm or more and 500 µm or less and has a particle shape. It is characterized by having a precipitation polymerization step in which precipitation polymerization is carried out in the presence of a monomer represented by the following general formula (2), a radical polymerization initiator, and an organic solvent at a water content of 1000 mass ppm or less in the reaction system. The method for producing the fluororesin according to claim 1.
(In the formula (2), Rf ₅ , Rf ₆ , Rf ₇ and Rf ₈ each independently have a fluorine atom or a linear, branched or optionally substituted etheric oxygen atom having 1 to 7 carbon atoms. Represents a cyclic perfluoroalkyl group, and Rf ₅ , Rf ₆ , Rf ₇ and Rf ₈ are linked to each other to form a perfluoroaliphatic ring which may have an etheric oxygen atom having 4 to 8 carbon atoms. May be formed.) The radical polymerization initiator, the monomer represented by the general formula (2) and the monomer represented by the general formula (2) are dissolved, and the residue unit represented by the general formula (1) is added. The method for producing a resin according to claim 5, comprising a step of polymerizing the resin containing the same in an organic solvent. 7. The method for producing a resin according to claim 5, wherein an organic solvent having a solubility index R with the resin calculated from the Hansen solubility parameter by the following formula (3) is 4 or more is used. ..
_{R = 4 × {(δD 1} -δD 2) 2 + (δP 1 -δP 2) 2 + (δH 1 -δH 2) 2} 0.5
...(3)
(Where [delta] D _1, [delta] P _1, dispersion term of Hansen Solubility Parameter of each delta] H ₁ wherein the resin particles, the polarity term and hydrogen term, [delta] D _2, [delta] P _2, dispersion term of Hansen Solubility Parameter of each delta] H ₂ is the organic solvent , And the polar and hydrogen terms.) The method for producing fluororesin particles according to any one of claims 5 to 7, wherein an organic solvent containing a fluorine atom and a hydrogen atom is used in the molecule. Solution polymerization step in which solution polymerization is carried out at a water content of 1000 mass ppm or less in the reaction system in the presence of the monomer represented by the general formula (2), a radical polymerization initiator, and an organic solvent, and fluorine obtained by solution polymerization 5. A precipitation step of bringing a solution containing a resin into contact with a poor solvent to precipitate a fluororesin while keeping the amount of water in the system at 100 mass ppm or less. A method for producing the fluororesin described. At least one of the monomer represented by the general formula (2), the initiator, and the organic solvent is purified with at least one of a filtration filter, an ion exchange resin, a metal ion removing filter, and a metal ion removing agent. The method for producing a fluororesin according to any one of claims 5 to 9, wherein the polymerization is carried out after the heating.