JP7566085B2 - Fluorine resin and its manufacturing method - Google Patents

Description

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

Fluorine-based resins have traditionally been used in protective films for semiconductors and other electronic components, water-repellent films for inkjet printing, waterproof and oil-resistant coatings for filters, and optical components due to their excellent electrical and optical properties, chemical resistance, waterproofness, and oil-repellent properties.

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

Non-Patent Document 1 describes a fluororesin containing an oxolane ring, and notes that the transparency of the resin decreases when stored in air for more than two weeks, and that it turns yellow when heated at 260-290°C. It describes that by re-precipitating and purifying this resin, impurities with carboxylic acid groups generated in a side reaction during polymerization are removed, and transparency does not decrease even when stored in air, but there is no description of coloring when heated. According to the inventors, when the fluororesin is re-precipitated, the metal components contained in the resin cannot be sufficiently removed, and there is an issue that coloring occurs when heated.

Patent Document 1 also describes that it is possible to obtain fluororesin particles by means of suspension polymerization, emulsion polymerization, or the like. However, the dispersant and emulsifier used as polymerization aids remain inside the resin particles and cause discoloration when heated, impairing the transparency and heat resistance that are the characteristics of this resin. According to the inventors, there was also the problem that discoloration occurs when heated due to the fluororesin containing a specific metal.

Since the molding process requires heating, there is a possibility that the above-mentioned fluororesin processed products may become discolored. Therefore, from the perspective of using them in optical applications, there was a demand for fluororesins that would reduce discoloration when heated.

WO2014/156996 Public Relations Macromolecules, 2005, 38, 4237-4245

The present invention was made in consideration of the above problems, and aims to provide a fluororesin that reduces coloration when heated and a method for producing the same.

The inventors discovered 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 exhibits little coloration when heated, leading to the completion of the present invention.

(In formula (1), Rf ₁ , Rf ₂ , Rf ₃ , and Rf ₄ each independently represent a group selected from the group consisting of linear, branched, or cyclic perfluoroalkyl groups which may have a fluorine atom or an etheric oxygen atom having 1 to 7 carbon atoms. Rf ₁ , Rf ₂ , Rf ₃ , and Rf ₄ may be bonded to each other to form a ring having 4 to 8 carbon atoms.)

The invention is described in detail below.

The present invention is a resin that contains a residue unit represented by general formula (1) and has a total content of chromium, iron, and nickel metals of 500 mass ppb or less.

The fluororesin of the present invention has a bulky ring structure contained in the general formula (1), and is therefore amorphous, highly transparent, and highly heat resistant. In addition, being composed only of carbon, fluorine, and oxygen, it has excellent electrical properties, chemical resistance, waterproofness, and liquid and oil repellency.

In the present invention, Rf ₁ , Rf ₂ , Rf ₃ , and Rf ₄ groups in the residue unit represented by general formula (1) each independently represent one type 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. Rf ₁ , Rf ₂ , Rf ₃ , and Rf ₄ may be bonded to each other to form a ring having 4 to 8 carbon atoms. Examples of linear perfluoroalkyl groups 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, and a pentadecafluoroheptyl group. Examples of branched perfluoroalkyl groups having 3 to 7 carbon atoms include a heptafluoroisopropyl group, a nonafluoroisobutyl group, a nonafluorosec-butyl group, and a nonafluorotert-butyl group. Examples of cyclic perfluoroalkyl groups having 3 to 7 carbon atoms include a heptafluorocyclopropyl group, a nonafluorocyclobutyl group, and a tridecafluorocyclohexyl group. Examples of linear perfluoroalkyl groups having 1 to 7 carbon atoms which may have an etheric oxygen atom include, for example, _{-CF2OCF3 group} , -( _CF2 ) _{2OCF3 group} , and -( _CF2 ) _2OCF2CF3 group. Examples of _{cyclic perfluoroalkyl} groups having 3 to 7 carbon atoms which may have an etheric oxygen atom include, for example, 2-(2,3,3,4,4,5,5,6,6-decafluoro)-pyrinyl group, 4-(2,3,3,4,4,5,5,6,6-decafluoro)-pyrinyl group, and 2-(2,3,3,4,4,5,5-heptafluoro)-furanyl group.

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

Specific examples of residue units represented by general formula (1) include the following residue units:

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.

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 when heated. The content is preferably 300 ppb by mass or less, and more preferably 120 ppb by mass or less. This further reduces discoloration when heated. Usually, the content is expressed as 5 ppb by mass or more, but this is due to the lower analytical limit, and may be less than 5 ppb by mass if measurable.

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

Furthermore, since a fluororesin with reduced coloration can be obtained, it is more preferable that the metal contents of chromium and nickel are each 100 ppb by mass or less.

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

The resin of the present invention has excellent fluidity and moldability, and is therefore preferably in a particulate form, and more preferably has a volume average particle diameter of 5 μm or more and 500 μm or less. This is preferable because it allows for continuous supply to molding machines and the like when the resin is processed. A volume average particle diameter of 5 μm or more makes the resin less likely to be scattered by air currents, improving handleability. Furthermore, when the volume average particle diameter is 500 μm or less, the resin has high fluidity, allowing for continuous supply to molding machines and the like, improving handleability.

When the resin of the present invention has a particulate shape, the volume average particle size 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 quantified with good reproducibility by dispersing the resin particles in water, and measuring after subjecting the resin particles to a process of homogenizing the dispersion state of the crystal particles using an ultrasonic homogenizer. An example of a laser scattering meter is the MT3000 manufactured by Microtrac.

When the resin of the present invention has a particulate shape, it is preferably a precipitation polymer, since it does not contain an emulsifier or dispersant and has excellent transparency and heat resistance.

When the resin of the present invention has a particulate 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 packing properties.

The resin of the present invention may contain other monomer residue units, such as 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, there is no limitation on the molecular weight of the resin, and examples of the molecular weight include a weight average molecular weight of 2,500 to 2,000,000 in terms of PMMA as measured by gel permeation chromatography (GPC). From the viewpoint of the melt viscosity and mechanical strength of the resin, it is preferably 10,000 to 1,000,000 (g/mol).

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

Here, yellowness can be measured using a common spectrophotometer.

Next, we will explain the method for producing the resin of the present invention.

As a first aspect of the method for producing a resin of the present invention,
An example of the method for producing a fluororesin includes a precipitation polymerization step in which precipitation polymerization is carried out 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 1,000 ppm by mass or less.

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

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

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

In the resin manufacturing method of the present invention, by using an organic solvent (hereinafter referred to as "precipitation polymerization solvent") as the polymerization solvent that dissolves the monomer represented by general formula (4) and precipitates a resin containing a residue unit represented by general formula (5), the resin produced by the polymerization reaction can be precipitated as particles having a specific volume average particle size, and as a result, a resin with a particle shape that is excellent in moldability and filling properties can be produced. In addition, since no polymerization aids such as emulsifiers and dispersants are used, resin particles that do not contain emulsifiers and dispersants that cause a loss of transparency and heat resistance can be produced.

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

The Hansen solubility parameters are the solubility parameters introduced by Hildebrand, which Hansen divided into three components, the dispersion term δD, the polar term δP, and the hydrogen bonding term δH, and displayed in three-dimensional space. The dispersion term δD indicates the effect of dispersion forces, the polar term δP indicates the effect of dipole-dipole forces, and the hydrogen bonding term δH indicates the effect of hydrogen bonding forces. In three-dimensional space, the greater the distance between the coordinates of a resin and the coordinates of an organic solvent, the more likely the resin is to precipitate in that organic solvent.

The definition and calculation method of the Hansen solubility parameter are described in the following literature: Charles M. Hansen, "Hansen Solubility Parameters: A Users Handbook", CRC Press, 2007. In addition, for organic solvents for which literature values are not known, the Hansen solubility parameter can be easily estimated from the chemical structure by using computer software (Hansen Solubility Parameters in Practice (HSPiP)).

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

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 with established Hansen solubility parameters 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 shown in three-dimensional space, a sphere (solubility sphere) is found in which the coordinates of the organic solvents that dissolved resin A are all contained inside the sphere and the coordinates of the organic solvent to be precipitated are on the outside, and the central coordinates of the solubility sphere are taken as the Hansen solubility parameter of the resin.

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

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

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

As the precipitation polymerization solvent in the present invention, it is preferable to select an organic solvent having a resin solubility index R of 4 or more, calculated from the Hansen solubility parameter according to formula (7).
R=4×{(δD ₁ - δD ₂ ) ² + (δP ₁ - δP ₂ ) ² + (δH ₁ - δH ₂ ) ² } ^0.5 ...(7)
Here, δD ₁ , δP ₁ and δH ₁ are the dispersion term, polar term and hydrogen term of the Hansen solubility parameter of the resin particles, respectively, and δD ₂ , δP ₂ and δH ₂ are the dispersion term, polar term and hydrogen term of the Hansen solubility parameter of the organic solvent, respectively.

For example, examples of organic solvents that have an affinity Ra of 4 or more with a resin containing perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue units include the organic solvents listed in Table 1 below.

Furthermore, as the precipitation polymerization solvent, an organic solvent containing fluorine atoms and hydrogen atoms in the molecule is preferred because it is less likely to cause chain transfer reactions in radical polymerization, has excellent polymerization yields, and is easy to obtain high molecular weight substances. Specific examples of precipitation polymerization solvents containing fluorine atoms and hydrogen atoms 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, and 1,2,2,3,3,4,4-heptafluorocyclopentane.

Examples of radical polymerization initiators for radical polymerization include organic peroxides such as benzoyl peroxide, lauryl peroxide, octanoyl peroxide, acetyl peroxide, di-tetr-butyl peroxide, tetr-butylcumyl peroxide, dicumyl peroxide, tetr-butyl peroxyacetate, perfluoro(di-tetr-butyl peroxide), bis(2,3,4,5,6-pentafluorobenzoyl) peroxide, tetr-butyl peroxybenzoate, and tetr-butyl perpivalate; and azo 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).

In the manufacturing 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).

As a second aspect of the method for producing a 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 with a water content in the reaction system of 1,000 ppm by mass or less, and a precipitation step of contacting a solution containing the fluororesin obtained by the solution polymerization with a poor solvent to precipitate the fluororesin while maintaining the water content in the system at 100 ppm or less.

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

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.

In the manufacturing 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.

The present invention provides a fluororesin with reduced coloration and a method for producing the fluororesin.

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

<Volume average particle size>
The volume average particle size (unit: μm) was measured using MT3000 manufactured by Microtrac and methanol as the dispersion medium.
<Metal component content>
The fluororesin was dissolved in hexafluorobenzene and then extracted with a dilute acid aqueous solution, and the metal components (unit: ppb) were measured using ELAN DRC II manufactured by Perkin Elmer.
<Yellowness Index (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.

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 inlet tube, and a thermometer was replaced with nitrogen. 1.215 g (0.00288 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator, 140.0 g (0.574 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as a monomer, and 1250 g of Asahiklin AE-3000 (manufactured by Asahi Glass Co., Ltd., 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether) as a precipitation polymerization solvent were added, and the mixture was kept at 55° C. with stirring for 24 hours to carry out 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.

Comparative Example 1: Production of Perfluoro(4-methyl-2-methylene-1,3-dioxolane) Resin A fluororesin was produced in accordance with Non-Patent Document 1 below. The inside of a 1 L SUS316 autoclave equipped with a SUS316 paddle-type stirring blade, a nitrogen inlet 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, 140.0 g (0.574 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as a monomer, and 230 g of hexafluorobenzene as a polymerization solvent were added, and radical solution polymerization was carried out by holding at 55°C for 24 hours under stirring, and a viscous liquid in which the resin was dissolved was obtained. The solution was cooled to room temperature, and the resin solution was diluted with 1000 g of hexafluorobenzene to adjust the viscosity, to prepare a diluted resin solution. 3 L of hexane was added to the vat, and the diluted resin solution was extruded into the hexane with a syringe to precipitate the resin, yielding perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin (yield: 68%).

Because the resin obtained was amorphous, the volume average particle size could not be measured. The metal content and yellowness of the resin obtained are shown in Table 2. The resin particles obtained were poor in fluidity and filling properties, and had a problem with transparency due to the high metal content and high yellowness. In addition, water droplets that had aggregated due to the heat of vaporization of the poor solvent were found in the poor solvent used in the precipitation process, and the moisture 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 SUS316 paddle-type stirring blade, a nitrogen inlet tube, and a thermometer was replaced with nitrogen. 0.775 g (0.00184 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator, 5.289 g of Newcol 714SN (manufactured by Nippon Nyukazai Co., Ltd., polyoxyethylene polycyclic phenyl ether sulfate ester salt) 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 were added, and the mixture was kept at 55° C. for 24 hours under stirring to perform 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 have a problem with transparency due to the large amount of metal content and high yellowness.

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 SUS316 paddle-type stirring blade, a nitrogen inlet tube, and a thermometer was replaced with nitrogen. 1.190 g (0.00282 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator, 140.0 g (0.574 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as a monomer, and 1250 g of Asahiklin AE-3000 (manufactured by Asahi Glass Co., Ltd., 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether) as a precipitation polymerization solvent were added, and the mixture was kept at 55° C. with stirring for 24 hours to carry out 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 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, 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 SUS316 paddle-type stirring blade, a nitrogen inlet tube, and a thermometer was replaced with nitrogen. 0.726 g (0.00172 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator, 5.314 g of Newcol 714SN (manufactured by Nippon Nyukazai Co., Ltd., polyoxyethylene polycyclic phenyl ether sulfate ester salt) as a dispersion stabilizer, 16.280 g of methanol as a chain transfer agent, 140.0 g (0.573 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as a monomer, and 186.7 g of ion-exchanged water as a suspension polymerization solvent were added, and the mixture was kept at 55° C. for 24 hours under stirring 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 have a problem with transparency due to the large amount of metal content and high yellowness.

The present invention can provide a fluororesin that reduces discoloration when heated and a method for producing the fluororesin.

Claims (4)

Fluororesin particles comprising a residue unit represented by the following general formula (1), a total content of chromium, iron and nickel being 120 mass ppb or less, a volume average particle diameter of 5 μm or more and 500 μm or less, and a yellowness index of a hot press molded product (thickness 200 nm) at 230° C. for 50 minutes being 1.0 or less :
(In formula (1), Rf ₁ , Rf ₂ , Rf ₃ and Rf ₄ 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, and at least one of them is a group selected from the group consisting of linear, branched or cyclic perfluoroalkyl groups having 1 to 7 carbon atoms. Rf ₁ , Rf ₂ , Rf ₃ and Rf ₄ may be linked together to form a perfluoroaliphatic ring which may have an etheric oxygen atom having 4 to 8 carbon atoms.) 2. The fluororesin particles according to claim 1, wherein the total content of chromium, iron and nickel is from 5 ppb to 120 ppb by mass. 3. The fluororesin particles according to claim 1, having a sodium content of 1000 ppb by mass or less. 4. The fluororesin particles according to claim 1, having a volume average particle size of 5 μm or more and 64 μm or less and a particulate shape.