Method for purifying fluororesin, method for producing purified fluororesin, fluororesin, optical material, electronic material, and plastic optical fiber

Abstract

One of the technologies provided by the present invention is a method for purifying a fluororesin, the method including bringing a fluororesin that includes a fluorine-containing alicyclic structure in the molecular chain into contact with a fluorinating agent to decrease the amount of fluorine compounds having a molecular weight of 300 or less contained in the fluororesin. This technology makes it possible to produce a fluororesin that includes a fluorine-containing alicyclic structure in the molecular chain and is suitable for use in plastic optical fibers. The fluorine compounds may be compounds represented by formula (1A). In formula (1A), R1 and R2 each independently represent a fluorine atom or a C1-4 perfluoroalkyl group.

Description

Method for refining fluororesin, method for producing refined fluororesin, fluororesin, optical material, electronic material, and plastic optical fiber

[0001] The present invention relates to a method for purifying a fluororesin, a method for producing the purified fluororesin, and a fluororesin. The present invention also relates to an optical material, an electronic material, and a plastic optical fiber containing the fluororesin.

[0002] Fluorine resins containing a fluorinated alicyclic structure in the molecular chain are generally amorphous and have excellent transparency, as well as various excellent properties such as liquid repellency, durability, and electrical properties, and are therefore used in a variety of applications including optical and electronic applications. One example of an optical application is plastic optical fiber. Non-Patent Document 1 discloses poly(perfluoro-2-methylene-4-methyl-1,3-dioxolane) as a fluororesin containing a fluorinated alicyclic structure in the molecular chain.

[0003] Macromolecules,2005,38,4237-4245

[0004] An object of the present invention is to provide a technique for producing a fluororesin containing a fluorine-containing alicyclic structure in the molecular chain, which is suitable for use in a plastic optical fiber.

[0005] The present invention provides a method for purifying a fluororesin, the method comprising contacting a fluororesin containing a fluorinated alicyclic structure in its molecular chain with a fluorinating agent to reduce the content of fluorine compounds having a molecular weight of 300 or less in the fluororesin.

[0006] From another aspect, the present invention provides a method for producing a purified fluororesin, wherein the fluororesin contains a fluorinated alicyclic structure in a molecular chain, the method comprising purifying the fluororesin by the above-mentioned method for purifying a fluororesin of the present invention.

[0007] From another aspect, the present invention provides a fluororesin having a structural unit containing a fluorinated aliphatic ring structure, wherein the content of fluorine compounds having a molecular weight of 300 or less is 1 ppm (by mass) or less.

[0008] From another aspect, the present invention provides an optical material comprising the fluororesin of the present invention.

[0009] From another aspect, the present invention provides an electronic material comprising the fluororesin of the present invention.

[0010] From another aspect, the present invention provides a plastic optical fiber comprising a layer containing the fluororesin of the present invention.

[0011] According to the present invention, a technique can be provided that can produce a fluororesin that contains a fluorine-containing alicyclic structure in the molecular chain and is suitable for use in a plastic optical fiber.

[0012] FIG. 1 is a cross-sectional view schematically showing an example of a plastic optical fiber containing a fluororesin obtained through the method for purifying a fluororesin of the present invention.

[0013] A method for purifying a fluororesin according to a first aspect of the present invention includes contacting a fluororesin containing a fluorinated alicyclic structure in its molecular chain with a fluorinating agent to reduce the content of fluorine compounds having a molecular weight of 300 or less in the fluororesin.

[0014] In a second aspect of the present invention, for example, in the purification method according to the first aspect, the fluorine compound is at least one selected from a compound represented by the following formula (1A) and a compound represented by the following formula (1B): In formula (1A) and formula (1B), R 1 and R 2 each independently represents a fluorine atom or a perfluoroalkyl group having 1 to 4 carbon atoms.

[0015] In a third aspect of the present invention, for example, in the purification method according to the first or second aspect, the fluorine compound is hexafluoroacetone.

[0016] In a fourth aspect of the present invention, for example, in the purification method according to any one of the first to third aspects, the fluororesin is brought into contact with the fluorinating agent in a particulate state.

[0017] In a fifth aspect of the present invention, for example, in the purification method according to any one of the first to fourth aspects, the fluororesin is contacted with the fluorinating agent at a temperature of (Tg1-20)°C or higher, where Tg1 is the glass transition temperature of the fluororesin.

[0018] In a sixth aspect of the present invention, for example, in the purification method according to any one of the first to fifth aspects, the fluorinating agent is fluorine gas.

[0019] In a seventh aspect of the present invention, for example, in the purification method according to any one of the first to sixth aspects, the fluorine-containing alicyclic structure has a dioxolane skeleton.

[0020] In an eighth aspect of the present invention, for example, in the purification method according to any one of the first to seventh aspects, the fluororesin has a constitutional unit (A) represented by the following formula (2): In formula (2), Rf 1 ~Rf 4 Rf each independently represents a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms. 1 and Rf 2 , and Rf 3 and Rf 4 may be linked to form a ring.

[0021] In a ninth aspect of the present invention, for example, in the purification method according to the eighth aspect, the structural unit (A) is a unit derived from 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole.

[0022] In a tenth aspect of the present invention, for example, in the purification method according to the eighth or ninth aspect, the fluororesin further has tetrafluoroethylene units.

[0023] In an eleventh aspect of the present invention, for example, in the purification method according to any one of the first to tenth aspects, the content of the fluorine compounds in the fluororesin is set to 1 ppm (by mass) or less by reducing the fluorine compounds.

[0024] A production method according to a twelfth aspect of the present invention is a method for producing a purified fluororesin, wherein the fluororesin contains a fluorinated alicyclic structure in a molecular chain, and the production method includes purifying the fluororesin by the purification method for a fluororesin according to any one of the first to eleventh aspects.

[0025] In a thirteenth aspect of the present invention, for example, in the production method according to the twelfth aspect, the fluororesin is purified to obtain the fluororesin having a content of the fluorine compound of 1 ppm (by mass) or less.

[0026] A fluororesin according to a fourteenth aspect of the present invention has a constitutional unit containing a fluorinated alicyclic structure, and has a content of fluorine compounds having a molecular weight of 300 or less of 1 ppm (by mass) or less.

[0027] In the fifteenth aspect of the present invention, for example, the fluororesin according to the fourteenth aspect has a structural unit (A) represented by the following formula (2): In formula (2), Rf 1 ~Rf 4 Rf each independently represents a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms. 1 and Rf 2 , and Rf 3 and Rf 4 may be linked to form a ring.

[0028] In a sixteenth aspect of the present invention, for example, in the fluororesin according to the fifteenth aspect, the structural unit (A) is a unit derived from 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole.

[0029] In a seventeenth aspect of the present invention, for example, in the fluororesin according to the fifteenth or sixteenth aspect, the fluororesin further has tetrafluoroethylene units.

[0030] An optical material according to an eighteenth aspect of the present invention includes the fluororesin according to any one of the fourteenth to seventeenth aspects.

[0031] An electronic material according to a nineteenth aspect of the present invention includes the fluororesin according to any one of the fourteenth to seventeenth aspects.

[0032] A plastic optical fiber according to a twentieth aspect of the present invention comprises a layer containing a fluororesin according to any one of the fourteenth to seventeenth aspects.

[0033] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following description of the preferred embodiments of the present invention is not intended to limit the present invention to the specific embodiments.

[0034] [Fluororesin Purification Method] The purification method of this embodiment includes contacting a fluororesin containing a fluorinated alicyclic structure in its molecular chain with a fluorinating agent to reduce the content of fluorine compounds with a molecular weight of 300 or less in the fluororesin. When a fluororesin containing a fluorinated alicyclic structure in its molecular chain is used in a plastic optical fiber, coloration may occur. The inventors' studies have revealed that fluororesins containing a fluorinated alicyclic structure in their molecular chain contain low-molecular-weight fluorine compounds such as hexafluoroacetone (HFA) as impurities, and that the low-molecular-weight fluorine compounds tend to aggregate during molding at a relatively low temperature (e.g., approximately 200°C, close to the glass transition temperature of the resin) to form a plastic optical fiber, which can cause coloration. The purification method of this embodiment is suitable for reducing the content of the above-mentioned low-molecular-weight fluorine compounds.

[0035] The molecular weight of the fluorine compound may be 270 or less, 250 or less, 220 or less, or even 200 or less. The lower limit of the molecular weight is, for example, 50 or more.

[0036] The fluorine compound may be an organic compound.

[0037] The fluorine compound is, for example, at least one selected from a compound represented by the following formula (1A) and a compound represented by the following formula (1B). The fluorine compound may be the compound represented by formula (1A). The compound represented by formula (1B) is a hydrate of the compound represented by formula (1A). In formula (1A) and formula (1B), R 1 and R 2each independently represents a fluorine atom or a perfluoroalkyl group having 1 to 4 carbon atoms. The number of carbon atoms in the perfluoroalkyl group may be 1 to 3, 1 or 2, or 1. The perfluoroalkyl group may be linear, branched, or cyclic. The compounds of formulas (1A) and (1B) are HFAs or structures similar to HFAs.

[0038] The fluorine compound may be at least one selected from HFA and a hydrate of HFA, or may be HFA itself. HFA is a compound represented by the following formula (3A). A hydrate of HFA is a compound represented by the following formula (3B).

[0039] The fluororesin may be contacted with the fluorinating agent in a particulate state. Contact in a particulate state may contribute to the diffusion of the fluorinating agent into the fluororesin. The particle size, expressed in terms of median diameter (d50), may be, for example, 20 mm or less, 15 mm or less, 10 mm or less, 5 mm or less, 1 mm or less, 800 μm or less, 500 μm or less, 300 μm or less, or even 100 μm or less. The lower limit of the particle size, expressed in terms of d50, may be, for example, 10 μm or more, 20 μm or more, or even 30 μm or more. The d50 of the particles may be 10 μm to 20 mm. The d50 of the particles can be evaluated, for example, by particle size distribution measurement using a laser diffraction method, an automatic image processing method (particle image imaging method), or the like.

[0040] The fluororesin may be contacted with the fluorinating agent at a temperature of (Tg1 - 20)°C or higher, where Tg1 is the glass transition temperature of the fluororesin. The contact with the fluorinating agent may be carried out at (Tg1 - 15)°C or higher, or even (Tg1 - 10)°C or higher. The contact with the fluorinating agent may also be carried out at (Tg1 + 40)°C or lower, (Tg1 + 35)°C or lower, (Tg1 + 30)°C or lower, (Tg1 + 25)°C or lower, (Tg1 + 20)°C or lower, (Tg1 + 15)°C or lower, or even (Tg1 + 10)°C or lower, or may be carried out within a temperature range of (Tg1 ± 20)°C. The contact at each of the above temperatures (purification temperatures) can contribute to the diffusion of the fluorinating agent into the fluororesin and, when the fluororesin is in the form of particles, is particularly suitable for preventing adhesion of the particles to each other. The Tg1 of the fluororesin is the midpoint glass transition temperature (T mg )

[0041] The Tg1 of the fluororesin is, for example, 100°C to 220°C, and may be 125°C or higher, 140°C or higher, or even 150°C or higher.

[0042] The fluorinating agent is typically a gas. Contact with a gaseous fluorinating agent can contribute to the diffusion of the fluorinating agent into the fluororesin. Furthermore, contact with a gaseous fluorinating agent is also suitable for purifying fluororesins that are difficult to dissolve in a solvent. An example of a gaseous fluorinating agent is fluorine gas (F2). The gaseous fluorinating agent may be contacted with the fluororesin alone or as a mixed gas with another gas. Examples of other gases include inert gases such as nitrogen and argon. The proportion of fluorine gas contained in the mixed gas is, for example, 5 to 95% by volume, 10 to 90% by volume, 15 to 85% by volume, or even 20 to 80% by volume. The proportion may be 70% by volume or less, 60% by volume or less, 50% by volume or less, 40% by volume or less, or even 30% by volume or less.

[0043] The time for contacting the fluororesin with the fluorinating agent (purification time) is, for example, 5 hours or more, and may be 10 hours or more, 20 hours or more, 30 hours or more, 40 hours or more, 50 hours or more, or even 60 hours or more. The upper limit of the purification time is, for example, 120 hours or less.

[0044] When the fluorinating agent is gaseous, the pressure of the atmosphere in which the fluororesin and the fluorinating agent are brought into contact (purification pressure) is expressed as absolute pressure (the same applies hereinafter to pressure) and is, for example, 10 kPa to 3 MPa. The upper limit of the purification pressure may be 1 MPa or less, 500 kPa or less, 200 kPa or less, or even 100 kPa or less (atmospheric pressure or less). The purification pressure may be the pressure of the mixed gas.

[0045] The contact between the fluororesin and the fluorinating agent can be carried out, for example, by introducing the fluorinating agent into a chamber containing the fluororesin. However, the method and mode of contact are not limited to the above examples. The introduction of the fluorinating agent may be carried out multiple times depending on, for example, the volume of the chamber and / or the amount of the fluororesin.

[0046] (Fluororesin) The fluororesin contains a fluorinated alicyclic structure. The fluorinated alicyclic structure may be contained in the main chain or a side chain of the fluororesin. The fluororesin may have a structural unit containing the fluorinated alicyclic structure.

[0047] An example of the fluorine-containing alicyclic structure has a dioxolane skeleton, but the fluorine-containing alicyclic structure is not limited to the above example.

[0048] An example of a fluororesin containing a fluorinated alicyclic structure having a dioxolane skeleton (polymer (P)) will be described below, although the fluororesin is not limited to the example shown below.

[0049] The polymer (P) has, for example, a structural unit (A) represented by the following formula (2). In formula (2), Rf 1 ~Rf 4 Rf each independently represents a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms. 1 and Rf2 , and Rf 3 and Rf 4 may be linked to form a ring. "Perfluoro" means that all hydrogen atoms bonded to a carbon atom are replaced with fluorine atoms.

[0050] The perfluoroalkyl group of formula (2) may be linear, branched, or cyclic. The linear perfluoroalkyl group may have 1 to 5 carbon atoms, 1 to 3 carbon atoms, or even 1 carbon atom. Examples of linear perfluoroalkyl groups include trifluoromethyl, pentafluoroethyl, heptafluoropropyl, nonafluorobutyl, undecafluoropentyl, tridecafluorohexyl, and pentadecafluoroheptyl groups. The branched perfluoroalkyl group may have 3 to 7 carbon atoms. Examples of branched perfluoroalkyl groups include heptafluoroisopropyl, nonafluoroisobutyl, nonafluorosec-butyl, and nonafluorotert-butyl groups. The cyclic perfluoroalkyl group may have 3 to 7 carbon atoms. Examples of cyclic perfluoroalkyl groups include heptafluorocyclopropyl, nonafluorocyclobutyl, and tridecafluorocyclohexyl groups.

[0051] The perfluoroalkyl ether group of formula (2) may be linear, branched, or cyclic. The linear perfluoroalkyl ether group may have 1 to 5 carbon atoms, or even 1 to 3 carbon atoms. Examples of linear perfluoroalkyl ether groups are -OCF3, -CF2OCF3, -(CF2)2OCF3, and -(CF2)2OCF2CF3. The branched perfluoroalkyl ether group may have 3 to 7 carbon atoms. The cyclic perfluoroalkyl ether group may have 3 to 7 carbon atoms. Examples of cyclic perfluoroalkyl ether groups are 2-(2,3,3,4,4,5,5,6,6-decafluoro)-pyrinyl, 4-(2,3,3,4,4,5,5,6,6-decafluoro)-pyrinyl, and 2-(2,3,3,4,4,5,5-heptafluoro)-furanyl.

[0052] Rf 1 ~Rf4 At least one selected from the above may be a perfluoroalkyl group having 1 to 7 carbon atoms or a perfluoroalkyl ether group having 1 to 7 carbon atoms.

[0053] Rf 1 and Rf 2 , and / or Rf 3 and Rf 4 When these are linked to form a ring, the number of carbon atoms in the ring is, for example, 4 to 8. The ring may be a 5-membered ring or a 6-membered ring.

[0054] Specific examples of the structural unit (A) are represented by the following formulas (4) and (5). The structural unit (A) of formula (4) is a unit derived from 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole. The structural unit of formula (5) is a unit derived from 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole.

[0055]

[0056]

[0057] The structural unit (A) may be a structural unit of formula (4), that is, a unit derived from 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole.

[0058] The polymer (P) may have one or more types of structural unit (A). The content of the structural unit (A) in the polymer (P) may be, for example, 20 mol% or more, 40 mol% or more, 50 mol% or more, 60 mol% or more, or even 80 mol% or more, relative to the total of all structural units. When the structural unit (A) is contained in 20 mol% or more, the polymer (P) tends to have higher heat resistance. When the structural unit (A) is contained in 40 mol% or more, the polymer (P) tends to have higher transparency and high mechanical strength in addition to high heat resistance. In the polymer (P), the content of the structural unit (A) may be 95 mol% or less, or may be 90 mol% or less, relative to the total of all structural units.

[0059] The structural unit (A) is derived from, for example, a compound represented by the following formula (6): 1 ~Rf 4 is the same as equation (2).

[0060] The polymer (P) may further include a structural unit other than the structural unit (A). An example of the structural unit is the structural unit (B) represented by the following formula (7).

[0061]

[0062] In formula (7), R 5 ~R 8 each independently represents a fluorine atom or a perfluoroalkyl group having 1 to 7 carbon atoms. The perfluoroalkyl group may be linear, branched, or cyclic. Some of the fluorine atoms may be substituted with halogen atoms other than fluorine atoms. Some of the fluorine atoms in the perfluoroalkyl group may be substituted with halogen atoms other than fluorine atoms.

[0063] The polymer (P) may have one or more types of structural unit (B). The content of the structural unit (B) in the polymer (P) is, for example, 5 to 80 mol %, or may be 10 to 60 mol %, or may be 50 mol % or less, 40 mol % or less, or even 20 mol % or less, relative to the total of all structural units.

[0064] The structural unit (B) is derived from, for example, a compound represented by the following formula (8): 5 ~R 8 is the same as formula (7). The compound represented by formula (8) is a fluorine-containing olefin such as tetrafluoroethylene or chlorotrifluoroethylene.

[0065] The structural unit (B) may be a tetrafluoroethylene unit; in other words, the polymer (P) having the structural unit (A) may further have a tetrafluoroethylene unit.

[0066] More specific examples of polymer (P) are 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole / tetrafluoroethylene copolymer and 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole / tetrafluoroethylene copolymer. The above copolymers are also commercially available as Teflon AF (trade name) and Hyflon AD (trade name), respectively.

[0067] The polymer (P) may further contain other structural units besides the structural units (A) and (B). An example of such other structural units is a hexafluoropropane unit. The polymer (P) may be substantially free of other structural units than the structural units (A) and (B). The phrase "the polymer (P) is substantially free of other structural units than the structural units (A) and (B)" means that the total of the structural units (A) and (B) is 95 mol % or more, preferably 98 mol % or more, of the total of all structural units in the polymer (P).

[0068] It is preferable that the fluororesin is substantially free of hydrogen atoms. In this specification, "the fluororesin is substantially free of hydrogen atoms" means that the content of hydrogen atoms in the fluororesin is 1 mol % or less.

[0069] The fluororesin can typically be formed by radical polymerization, and known polymerization methods such as solution polymerization and bulk polymerization can be used for the polymerization of the fluororesin.

[0070] For the polymerization of the fluororesin, additives such as a polymerization initiator and a chain transfer agent may be used. Examples of the polymerization initiator include organic peroxides such as benzoyl peroxide, lauryl peroxide, octanoyl peroxide, acetyl peroxide, di-tert-butyl peroxide, tert-butylcumyl peroxide, dicumyl peroxide, tert-butyl peroxyacetate, perfluoro(di-tert-butyl peroxide), bis(2,3,4,5,6-pentafluorobenzoyl) peroxide, tert-butyl peroxybenzoate, and tert-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). The additive may be a perfluorinated compound.

[0071] The weight average molecular weight (Mw) of the fluororesin is, for example, 10,000 to 1,000,000. Mw can be evaluated by gel permeation chromatography (GPC).

[0072] In the purification method of this embodiment, by reducing the fluorine compounds, the content (residual amount) of the fluorine compounds in the fluororesin may be 1 ppm or less, 0.8 ppm or less, 0.5 ppm or less, 0.3 ppm or less, 0.2 ppm or less, or even 0.1 ppm or less. In this specification, all ppm is based on mass. Among the fluorine compounds, the ACGIH (American Conference of Governmental Industrial Hygienists) has determined that the permissible concentration of HFA and HFA-like structures for short-term exposure to the human body is 0.4 ppm or less. The purification method of this embodiment is also suitable for reducing the content of HFA and HFA-like structures in the fluororesin to the above-mentioned permissible concentration or less. Meanwhile, because HFA and HFA-like structures tend to form hydrates, purification using heated steam is also considered, but according to the inventors' studies, sufficient reduction using this method is difficult.

[0073] In the purification method of the present embodiment, by reducing the fluorine compounds, the content of the fluorine compounds in the fluororesin may be set to 1 / 10 or less, 1 / 25 or less, 1 / 50 or less, 1 / 75 or less, or even 1 / 100 or less of the content before purification.

[0074] The content of the fluorine compound in the purified fluororesin can vary depending on, for example, the shape of the fluororesin, the median diameter if it is particulate, the type and concentration of the fluorinating agent, and the purification conditions (temperature, pressure, time, etc.).

[0075] The purification method of this embodiment may include additional steps. An example of such additional step is a drying step in which the fluororesin, particularly particles, are dried before purification. Drying of the fluororesin can be performed, for example, by vacuum drying, reduced-pressure drying, atmospheric pressure drying, blowing drying, shaking drying, hot air drying, or heat drying. Another example of such additional step is a step in which the purified fluororesin is subjected to vacuum devolatilization and / or heating to remove any remaining fluorinating agent. In one example of a heating step (annealing step), the fluororesin that has been contacted with the fluorinating agent is maintained at a predetermined temperature in an atmosphere of an inert gas such as nitrogen. The annealing step is also suitable for reducing the amount of fluorine-based gas (e.g., F gas, HF gas) contained in the fluororesin. The temperature in the annealing step may be selected from the range exemplified above for the temperature at which the fluororesin is contacted with the fluorinating agent. The duration of the annealing step is, for example, 1 to 20 hours. The annealing step can be performed, for example, by discharging the fluorinating agent from a chamber containing the fluororesin and then introducing an inert gas into the chamber. The method and mode of the annealing step are not limited to the above examples.

[0076] [Method for producing fluororesin] The purification method of the present embodiment can produce, for example, a purified fluororesin containing a fluorinated alicyclic structure in the molecular chain. In this aspect, the method for producing a fluororesin of the present embodiment is a method for producing a purified fluororesin, in which the fluororesin contains a fluorinated alicyclic structure in the molecular chain, and the production method includes purifying the fluororesin by the purification method of the present embodiment.

[0077] In the production method of this embodiment, the fluororesin may be purified as described above to obtain a fluororesin having a fluorine compound content of 1 ppm or less.

[0078] [Fluororesin] The fluororesin of this embodiment has a structural unit containing a fluorinated alicyclic structure. Furthermore, in the fluororesin of this embodiment, the content of fluorine compounds having a molecular weight of 300 or less is 1 ppm or less. The content may be 0.8 ppm or less, 0.5 ppm or less, 0.3 ppm or less, 0.2 ppm or less, or even 0.1 ppm or less. Examples of fluorine compounds, fluorinated alicyclic structures, and fluororesins are as described above in the description of the purification method of this embodiment.

[0079] The fluororesin of the present embodiment may have a structural unit (A) represented by the following formula (2).

[0080] In formula (2), Rf 1 ~Rf 4 Rf each independently represents a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms. 1 and Rf 2 , and Rf 3 and Rf 4 may be linked to form a ring.

[0081] The structural unit (A) may be a unit derived from 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole.

[0082] The fluororesin of the present embodiment having the structural unit (A) may further have a tetrafluoroethylene unit.

[0083] The fluororesin of this embodiment may have the same structure as the purified fluororesin described above in the description of the purification method of this embodiment.

[0084] The fluororesin of the present embodiment can be produced, for example, through the purification method of the present embodiment or by the production method of the present embodiment, although the production method of the fluororesin of the present embodiment is not limited to the above examples.

[0085] The fluororesin of this embodiment can be used, for example, as an optical material or an electronic material. An example of an optical component is a plastic optical fiber (POF). The POF can include a layer containing the fluororesin of this embodiment. However, the uses of the fluororesin of this embodiment are not limited to the above examples.

[0086] [POF] FIG. 1 shows an example of a POF containing a fluororesin according to this embodiment. The POF 1 in FIG. 1 is composed of multiple layers including a core 2 and a clad (first clad) 3. The core 2 is a layer located at the center of the POF 1 and transmits light. The first clad 3 is a layer located outward of the core 2 with respect to the central axis of the POF 1 and covers the core 2. The core 2 has a relatively high refractive index, and the first clad 3 has a relatively low refractive index. The POF 1 in FIG. 1 further includes a second clad (double clad) 4 covering the outer periphery of the first clad 3, and a coating layer (overclad) 5 covering the outer periphery of the second clad 4. The POF 1 may be a graded index (GI) type.

[0087] The fluororesin of this embodiment may be contained in at least one layer constituting the POF 1. The fluororesin of this embodiment may be contained in at least one selected from the core 2, the first clad 3, and the second clad 4, more preferably in the second clad 4. The core 2, the first clad 3, the second clad 4, and the coating layer 5 may contain a resin that may be contained in the corresponding layer of a known POF. Examples of resins that may be contained in the core 2, the first clad 3, and the second clad 4 include fluorine-containing resins, acrylic resins such as methyl methacrylate, styrene-based resins, and carbonate-based resins. Examples of resins that may be contained in the coating layer 5 include polycarbonate, various engineering plastics, cycloolefin polymers, polytetrafluoroethylene (PTFE), modified PTFE, and perfluoroalkoxyalkane (PFA). Each layer may contain an additive such as a refractive index adjuster.

[0088] The POF 1 can be manufactured by, for example, a melt spinning method, in which raw resin is melt-extruded to form the layers that make up the optical fiber.

[0089] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0090] [Glass transition temperature Tg1] The Tg1 of the fluororesin was measured by the above-mentioned method under the following conditions: Measurement device: Q-2000 manufactured by TA Instruments Temperature program: temperature increase from 30°C to 200°C (temperature increase rate 10°C / min) Atmospheric gas: nitrogen (flow rate 50 mL / min) Measurement rate: 10°C / min Sample amount: 5 mg

[0091] [HFA Content] The HFA content of the fluororesin was determined from the mass spectrum obtained by subjecting the resin to the following GC-MS: The ion mass of the peak derived from HFA was m / z=166.

[0092] [GC-MS] GC-MS for the fluororesin was carried out under the following conditions: Thermal desorption apparatus: TDS / CIS manufactured by Gerstel GC / MS apparatus: 6980plus / 5973N manufactured by Agilent Technologies GC column: HP-5ms UI, 30 m x 0.25 mm, id x 0.25 μm manufactured by Agilent Technologies Sample amount: 10 mg (contained in a glass tube) Sample heating conditions: temperature increased from 20°C to 300°C (rate 60°C / min) and held for 30 minutes Other: gas generated by heating the sample was cold trapped and analyzed.

[0093] [Heating Test] A heating test of a fluororesin simulating molding processing was carried out as follows. 10 g of the fluororesin to be evaluated was placed in a PFA tube with an inner diameter of 10 mm, one end of which was sealed with a PTFE stopper. Next, the fluororesin in the tube was heated to 270°C for 20 hours to melt, and then allowed to cool to room temperature to form a rod. After allowing to cool, the removed rod was observed under an optical microscope (magnification 20x) to check for the presence or absence of coloration. Observation was carried out at 10 random locations.

[0094] Example 1 1 kg of particles of 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole / tetrafluoroethylene copolymer (Teflon AF 1600X, manufactured by Mitsui Chemours Fluoro Products) were spread evenly across a PFA tray (internal dimensions: length 287 mm, width 382 mm, depth 48 mm) and placed in a chamber. The median diameter (d50) of the particles was 800 μm. The copolymer had a Tg1 of 163°C. Next, the chamber was purged with nitrogen gas several times to create a nitrogen gas atmosphere, and then the temperature was raised to 180°C. Once the temperature reached 180°C, a fluorine gas / nitrogen gas mixture (volume ratio 20:80) was introduced into the chamber as a fluorinating agent (flow rate 10.50 L / min) while the pressure in the chamber was adjusted to 90 kPa. After maintaining the treatment conditions of 180°C and 90 kPa for about 65 hours, the atmosphere in the chamber was replaced with nitrogen to stop exposing the copolymer to the fluorinating agent, and the chamber was cooled to room temperature to complete the purification.

[0095] The HFA content in the copolymer before purification was 15 ppm. On the other hand, the content after purification was 0.1 ppm or less (below the detection limit). Furthermore, no HFA-related structures were detected in the ion mass m / z range of 166-200 in the GC-MS mass spectrum. No coloration was observed in the rods formed from the copolymer after purification.

[0096] (Example 2) The purification of the copolymer was completed in the same manner as in Example 1, except that the fluorinating agent was changed to a single gas of fluorine gas. The HFA content after purification was 0.1 ppm or less (below the detection limit), and no HFA-related structures were detected. Furthermore, no coloration was observed in the rods formed from the purified copolymer.

[0097] (Example 3) Copolymer purification was completed in the same manner as in Example 1, except that the temperature of exposure to the fluorinating agent was changed to 170°C. The HFA content after purification was 0.1 ppm or less (below the detection limit), and no HFA-related structures were detected. Furthermore, no coloration was observed in the rods formed from the purified copolymer.

[0098] Comparative Example 1 In Comparative Example 1, purification was carried out by exposure to heated steam rather than by using a fluorinating agent.

[0099] 1 kg of particles of the copolymer used in Example 1 was spread evenly on a SUS tray (inner dimensions: length 287 mm, width 382 mm, depth 48 mm) and placed in a chamber. Next, heated steam (265 ° C) was introduced into the chamber and held at 100 kPa (normal pressure) for 40 minutes, after which the chamber was opened and cooled to room temperature to complete the purification. The HFA content after purification was 4.1 ppm, and HFA-related structures were also detected. In addition, coloration was confirmed in the rods formed from the copolymer after purification.

[0100] (Comparative Example 2) Copolymer purification was completed in the same manner as in Comparative Example 1, except that the temperature of the introduced heated steam was changed to 220°C. The HFA content after purification was 1.5 ppm, and HFA-related structures were also detected. In addition, coloration was confirmed in the rods formed from the copolymer after purification.

[0101] The purification conditions and evaluation results are summarized in Table 1 below.

[0102]

[0103] The fluororesin obtained through the purification method of the present invention can be used, for example, as an optical material or an electronic material. One example of an optical material is POF.

Claims

1. a step of contacting a fluororesin, in a particulate state, which contains a fluorinated alicyclic structure in its molecular chain, with a fluorinating agent at a temperature of (Tg1±20)°C, where Tg1 is the glass transition temperature of the fluororesin, and cooling the fluororesin after contact with the fluorinating agent to reduce the content of fluorine compounds having a molecular weight of 300 or less contained in the fluororesin to 1 ppm (by mass) or less, A method for purifying fluororesin. wherein R 1 is a primary fluoroalkyl group having 1 to 5 carbon atoms; R 2 OCF=CF 2 wherein R 2 is R 1 or a primary fluoroalkyl group containing an ether oxygen and 4 to 12 carbon atoms; and 1. A method for improving the high temperature stability of a melt-processible copolymer of at least two comonomers selected from the group consisting of fluorodioxoles having the formula: wherein each one of R and R' is independently fluorine or a trifluoromethyl group, the method comprising the steps of: a) adding the copolymer to at least a stoichiometric amount of a hydroxybenzoate, based on the concentration of —COOH and —COF groups, (1) a base selected from organic amines and ammonia having a boiling point of at most about 130°C at atmospheric pressure; and (2) Tertiary alcohols containing up to 8 carbon atoms with an anhydrous or aqueous stabilizer selected from the group consisting of: b) isolating and drying the intermediate at a temperature between about 70°C and 150°C; c) converting the dried intermediate to a copolymer having improved thermal stability by contacting the intermediate with fluorine at a temperature between 20°C and the lowest temperature at which the copolymer exhibits a solid-state phase transition, whether first order or second order; and d) removing excess fluorine and volatile by-products from the reaction product and recovering the copolymer; The method includes at least one cycle of

2. 2. The method for purifying a fluororesin according to claim 1, wherein the fluorine compound is at least one selected from the group consisting of compounds represented by the following formula (1A) and compounds represented by the following formula (1B): 【Chemical 1】 【Chemistry 2】 In formula (1A) and formula (1B), R 1 and R 2 each independently represents a fluorine atom or a perfluoroalkyl group having 1 to 4 carbon atoms.

3. 2. The method for purifying a fluororesin according to claim 1, wherein the fluorine compound is hexafluoroacetone.

4. 2. The method for purifying a fluororesin according to claim 1, wherein the fluororesin is contacted with the fluorinating agent in a gaseous state in a gaseous atmosphere.

5. A method for purifying a fluororesin according to claim 4, wherein the fluororesin is contacted with the fluorinating agent in a gas atmosphere having an absolute pressure of 90 kPa or more and 100 kPa or less.

6. The fluororesin is treated so that the glass transition temperature of the fluororesin is Tg 1 as (Tg 1 2. The method for purifying a fluororesin according to claim 1, wherein the fluororesin is contacted with the fluorinating agent at a temperature of 0.5°C or lower.

7. The method for purifying a fluororesin according to claim 1, wherein the fluororesin is contacted with the fluorinating agent for 30 hours or more and 120 hours or less.

8. 2. The method for purifying a fluororesin according to claim 1, wherein the fluorinating agent is fluorine gas.

9. The method for purifying a fluororesin according to claim 1 , wherein the fluorine-containing alicyclic structure has a dioxolane skeleton.

10. 2. The method for purifying a fluororesin according to claim 1, wherein the fluororesin has a structural unit (A) represented by the following formula (2): 【Chemistry 3】 In formula (2), Rf 1 ~Rf 4 Rf each independently represents a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms. 1 and Rf 2 , and Rf 3 and Rf 4 may be linked to form a ring.

11. The method for purifying a fluororesin according to claim 10, wherein the structural unit (A) is a unit derived from 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole.

12. The method for purifying a fluororesin according to claim 10, wherein the fluororesin further contains tetrafluoroethylene units.

13. The method for purifying a fluororesin according to claim 1, wherein the fluororesin after contacting with the fluorinating agent is cooled under a gas atmosphere.

14. The method for purifying a fluororesin according to claim 1, wherein the fluororesin after contact with the fluorinating agent is cooled under a nitrogen atmosphere.

15. A method for producing a purified fluororesin, comprising: The fluororesin contains a fluorine-containing alicyclic structure in a molecular chain, The production method includes purifying the fluororesin by the method for purifying a fluororesin according to any one of claims 1 to 14 to obtain the fluororesin having a content of the fluorine compound of 1 ppm (by mass) or less. Manufacturing method.

16. having a structural unit containing a fluorinated aliphatic ring structure, The content of fluorine compounds having a molecular weight of 300 or less is 1 ppm (by mass) or less. Fluorine resin.

17. The fluororesin according to claim 16, having a structural unit (A) represented by the following formula (2): 【Chemistry 4】 In formula (2), Rf 1 ~Rf 4 Rf each independently represents a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms. 1 and Rf 2 , and Rf 3 and Rf 4 may be linked to form a ring.

18. The fluororesin according to claim 17, wherein the structural unit (A) is a unit derived from 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole.

19. The fluororesin according to claim 17, wherein the fluororesin further comprises tetrafluoroethylene units.

20. An optical material comprising the fluororesin according to any one of claims 16 to 19.

21. An electronic material comprising the fluororesin according to any one of claims 16 to 19.

22. A layer containing the fluororesin according to any one of claims 16 to 19 is provided. Plastic optical fiber.

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