TW202340333A - Method for purifying fluororesin, method for producing purified fluororesin, fluororesin, optical material, electronic material, and plastic optical fiber - Google Patents

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

Purification method of fluororesin, manufacturing method of purified fluororesin, fluororesin, optical materials, electronic materials and plastic optical fibers

The present invention relates to a method for purifying fluororesin, a method for producing purified fluororesin, and fluororesin. Furthermore, the present invention relates to optical materials, electronic materials and plastic optical fibers containing the above-mentioned fluororesin.

Fluororesins containing a fluorine-containing alicyclic structure in their molecular chains are generally amorphous and have excellent transparency, as well as excellent various properties such as liquid repellency, durability, and electrical properties. Therefore, they are used in optical applications and electronic applications. Various uses. An example of optical applications is plastic optical fiber. Non-patent Document 1 discloses poly(perfluoro-2-methylene-4-methyl-1,3-dioxolane) as a fluororesin whose molecular chain contains a fluorine-containing alicyclic structure. Prior technical literature non-patent literature

Non-patent literature 1: Macromolecules, 2005, 38, 4237-4245

[Problem to be solved by the invention]

The purpose of the present invention is to provide a technology that can produce fluororesin whose molecular chain contains a fluorine-containing aliphatic ring structure and is suitable for use in plastic optical fibers. [Technical means to solve problems]

invention supply A method for purifying fluororesin, It includes the following steps: contacting a fluororesin whose molecular chain contains a fluorine-containing aliphatic ring structure with a fluorinating agent to reduce the content of fluorine compounds with a molecular weight of less than 300 contained in the above fluororesin.

According to another aspect, the invention supply A method for manufacturing purified fluororesin, The molecular chain of the above-mentioned fluororesin contains a fluorine-containing aliphatic ring structure, The above-mentioned manufacturing method includes the following steps: purifying the above-mentioned fluororesin using the above-mentioned purification method of the fluororesin of the present invention.

According to another aspect, the invention supply A fluororesin, It has a structural unit containing a fluorine-containing aliphatic ring structure, and The content of fluorine compounds with a molecular weight of 300 or less is 1 ppm (mass basis) or less.

According to another aspect, the invention supply An optical material containing the above-mentioned fluororesin of the present invention.

According to another aspect, the invention supply An electronic material containing the above-mentioned fluororesin of the present invention.

According to another aspect, the invention supply A plastic optical fiber, It is provided with a layer containing the fluororesin of the present invention. [Effects of the invention]

According to the present invention, a technology can be provided that can produce a fluororesin whose molecular chain contains a fluorine-containing aliphatic ring structure and is suitable for use in plastic optical fibers.

The purification method of the fluororesin of the first aspect of the present invention includes the following steps: A fluororesin containing a fluorine-containing aliphatic ring structure in its molecular chain is brought into contact with a fluorinating agent to reduce the content of fluorine compounds with a molecular weight of 300 or less contained in the fluororesin.

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

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

In a fourth aspect of the present invention, for example, in the purification method of any one of the first to third aspects, the fluororesin is brought into contact with the fluorinating agent in the form of particles.

In the fifth aspect of the present invention, for example, in the purification method of any one of the first to fourth aspects, the above-mentioned fluororesin is mixed with the above-mentioned fluorinating agent at a temperature above (Tg ₁ -20)°C Contact, Tg ₁ is the glass transition temperature of the above-mentioned fluororesin.

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

In the seventh aspect of the present invention, for example, in the purification method of any one of the first to sixth aspects, the above-mentioned fluorine-containing aliphatic ring structure has a dioxolane skeleton.

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

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

In a tenth aspect of the present invention, for example, in the purification method of the eighth or ninth aspect, the above-mentioned fluororesin further has a tetrafluoroethylene unit.

In an eleventh aspect of the present invention, for example, in the purification method of any one of the first to tenth aspects, the content of the above-mentioned fluorine compound in the above-mentioned fluororesin is 1 ppm by reducing the above-mentioned fluorine compound. (quality standard) or less.

Manufacturing method of the twelfth aspect of the present invention It is a method for manufacturing purified fluororesin. The molecular chain of the above-mentioned fluororesin contains a fluorine-containing aliphatic ring structure, The above-mentioned manufacturing method includes the step of purifying the above-mentioned fluororesin by using the fluororesin purification method of any one of the first to eleventh aspects.

In the thirteenth aspect of the present invention, for example, in the manufacturing method of the twelfth aspect, the above-mentioned fluororesin in which the content of the above-mentioned fluorine compound is 1 ppm (mass basis) or less is obtained by purifying the above-mentioned fluororesin.

Fluororesin according to the fourteenth aspect of the present invention Has a structural unit containing a fluorine-containing aliphatic ring structure, and The content of fluorine compounds with a molecular weight of 300 or less is 1 ppm (mass basis) or less.

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

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

In a seventeenth aspect of the present invention, for example, in the fluororesin of the fifteenth or sixteenth aspect, the fluororesin further has a tetrafluoroethylene unit.

Optical material according to the eighteenth aspect of the present invention Contains fluororesin in any one of the 14th to 17th aspects.

Electronic material according to the nineteenth aspect of the present invention Contains fluororesin in any one of the 14th to 17th aspects.

Plastic optical fiber according to the twentieth aspect of the present invention It is provided with a layer including the fluororesin of any one of the 14th to 17th aspects.

Hereinafter, embodiments of the present invention will be described. The following description is not intended to limit the invention to specific embodiments.

[Purification method of fluororesin] The purification method of this embodiment includes the following steps: contacting a fluororesin whose molecular chain contains a fluorine-containing aliphatic ring structure with a fluorinating agent to reduce the content of fluorine compounds with a molecular weight of less than 300 contained in the fluororesin. When a fluororesin whose molecular chain contains a fluorine-containing aliphatic ring structure is used in a plastic optical fiber, coloring may sometimes be observed. According to the research of the present inventors, it was clarified that the fluororesin whose molecular chain contains a fluorine-containing aliphatic ring structure contains low-molecular fluorine compounds such as hexafluoroacetone (HFA) as impurities, and is suitable for forming plastic optical fibers at relatively low temperatures (such as , close to the glass transition temperature of the resin (approximately 200°C), low molecular fluorine compounds tend to agglomerate, which may cause coloring. The purification method of this embodiment is suitable for reducing the content of the above-mentioned low molecular fluorine compounds.

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

The fluorine compound may also be an organic compound.

The fluorine compound is, for example, at least one selected from the group consisting of the compound represented by the following formula (1A) and the compound represented by the formula (1B). The fluorine compound may be a compound represented by formula (1A). The compound represented by formula (1B) is a hydrate of the compound represented by formula (1A). [Chemistry 5] [Chemical 6] In formula (1A) and formula (1B), R ¹ and R ² each independently represent 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, or may be 1 or 2, or may be 1. The perfluoroalkyl group may be linear, branched, or cyclic. The compounds of formula (1A) and (1B) are HFA or similar structures of HFA.

The fluorine compound may be at least one selected from HFA and hydrates of HFA, or may be HFA. HFA is a compound represented by the following formula (3A). The hydrate of HFA is a compound represented by the following formula (3B). [Chemical 7] [Chemical 8]

Fluorine resin can come into contact with the fluorinating agent in the form of particles. Contact in the form of particles facilitates the diffusion of the fluorinating agent into the fluororesin. If the size of the particles is expressed by the median diameter (d50), for example, it is 20 mm or less, or it can be 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, And then below 100 μm. If the lower limit of the particle size is represented by d50, it may be, for example, 10 μm or more, 20 μm or more, and further 30 μm or more. The d50 of the particles can be 10 μm ~ 20 mm. The d50 of 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.

Fluorine resin can come into contact with fluorinating agents at temperatures above (Tg ₁ -20)°C. Tg ₁ is the glass transition temperature of fluorine resin. Contact with the fluorinating agent can also be carried out at a temperature above (Tg ₁ -15)°C, and further above (Tg ₁ -10)°C. In addition, the contact with the fluorinating agent can be below (Tg ₁ + 40) ℃, (Tg ₁ + 35) ℃ below, (Tg ₁ + 30) ℃ below, (Tg ₁ + 25) ℃ below, (Tg ₁ + 20) ℃ below, It can be implemented at a temperature below (Tg ₁ +15)°C, and further below (Tg ₁ +10)°C, or within a temperature range of (Tg ₁ ±20)°C. Contact at each of the above temperatures (purification temperature) can help the diffusion of the fluorinating agent into the fluororesin, and is particularly suitable for preventing the particles from adhering to each other when the fluororesin is particles. In addition, Tg ₁ of fluororesin is the mid-point glass transition temperature (T _mg ) calculated based on the provisions of Japanese Industrial Standard (former Japanese Industrial Standard: JIS) K7121:1987.

The Tg ₁ of the fluororesin is, for example, 100°C to 220°C, and may be 125°C or higher, 140°C or higher, or 150°C or higher.

Fluorinating agents are typically gases. Contact with the fluorinating agent as a gas helps the diffusion of the fluorinating agent into the fluororesin. In addition, contact with a fluorinating agent as a gas is also suitable for the purification of fluororesins that are difficult to dissolve in solvents, for example. An example of a gas as a fluorinating agent is fluorine gas (F ₂ ). The fluorinating agent as a gas can be in contact with the fluororesin alone or in the form of a mixed gas with other gases. Examples of other gases are inert gases such as nitrogen and argon. The ratio of fluorine gas contained in the mixed gas is, for example, 5 to 95 volume %, or may be 10 to 90 volume %, 15 to 85 volume %, or further 20 to 80 volume %. The above-mentioned ratio may be 70 volume % or less, 60 volume % or less, 50 volume % or less, 40 volume % or less, and further, 30 volume % or less.

The time for bringing the fluororesin and the fluorinating agent into contact (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, and further 60 hours or more. The upper limit of the purification time is, for example, 120 hours or less.

When the fluorinating agent is a gas, the pressure (purification pressure) of the atmosphere in which the fluororesin and the fluorinating agent are brought into contact is expressed in terms of absolute pressure (the same applies to pressure below), 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 100 kPa or less (normal pressure or less). The purification pressure can be the pressure of the mixed gas.

The contact between the fluororesin and the fluorinating agent can be implemented, for example, by introducing the fluorinating agent into a chamber containing the fluororesin. However, the method and form of contact are not limited to the above examples. For example, the introduction of the fluorinating agent can be performed multiple times according to the volume of the chamber and/or the amount of fluororesin.

(Fluororesin) Fluorine resin contains a fluorine-containing aliphatic ring structure. The fluorine-containing aliphatic ring structure may be included in the main chain of the fluororesin or in the side chain of the fluororesin. The fluororesin may have a structural unit containing a fluorine-containing aliphatic ring structure.

An example of the fluorine-containing aliphatic ring structure has a dioxolane skeleton. However, the fluorine-containing aliphatic ring structure is not limited to the above example.

Hereinafter, an example of a fluororesin (polymer (P)) containing a fluorine-containing aliphatic ring structure having a dioxolane skeleton will be described. However, the fluororesin is not limited to the examples shown below.

The polymer (P) has, for example, a structural unit (A) represented by the following formula (2). [Chemical 9] In formula (2), Rf ¹ to Rf ⁴ each independently represent a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms. Rf ¹ and Rf ² , and Rf ³ and Rf ⁴ can be connected to form a ring. The so-called "perfluorinated" means that all hydrogen atoms bonded to carbon atoms have been replaced by fluorine atoms.

The perfluoroalkyl group of formula (2) may be linear, branched, or cyclic. The carbon number of the linear perfluoroalkyl group may be 1 to 5, 1 to 3, or even 1. Examples of linear perfluoroalkyl groups are trifluoromethyl, pentafluoroethyl, heptafluoropropyl, nonafluorobutyl, undecafluoropentyl, tridecafluorohexyl, and pentadecafluoroheptyl. The number of carbon atoms in the branched perfluoroalkyl group may be 3 to 7. Examples of branched perfluoroalkyl groups are heptafluoroisopropyl, nonafluoroisobutyl, nonafluorosecondbutyl, and nonafluorotertiarybutyl. The number of carbon atoms in the cyclic perfluoroalkyl group may be 3 to 7. Examples of cyclic perfluoroalkyl groups are heptafluorocyclopropyl, nonafluorocyclobutyl, and tridecafluorocyclohexyl.

The perfluoroalkyl ether group of formula (2) may be linear, branched, or cyclic. The number of carbon atoms in the linear perfluoroalkyl ether group may be 1 to 5, or further 1 to 3. Examples of linear perfluoroalkyl ether groups are -OCF ₃ group, -CF ₂ OCF ₃ group, -(CF ₂ ) ₂ OCF ₃ group, and -(CF ₂ ) ₂ OCF ₂ CF ₃ group. The carbon number of the branched perfluoroalkyl ether group may be 3 to 7. The carbon number of the cyclic perfluoroalkyl ether group may be 3 to 7. 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)-furyl.

At least one selected from Rf ¹ to Rf ⁴ may be a perfluoroalkyl group having 1 to 7 carbon atoms or a perfluoroalkyl ether group having 1 to 7 carbon atoms.

When Rf ¹ and Rf ² and/or Rf ³ and Rf ⁴ are connected to form a ring, the number of carbon atoms in the ring is, for example, 4 to 8. The ring can be a 5-member ring or a 6-member ring.

Specific examples of the structural unit (A) are represented by the following formulas (4) and (5). 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.

[Chemical 10]

[Chemical 11]

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

The polymer (P) may have one or more types of structural units (A). The content of the structural unit (A) in the polymer (P) relative to the total of all structural units may be, for example, 20 mol% or more, or it may be 40 mol% or more, 50 mol% or more, or 60 mol% or more. , and then more than 80 mol%. By containing more than 20 mol% of the structural unit (A), the polymer (P) tends to have higher heat resistance. When the polymer (P) contains 40 mol% or more of the structural unit (A), the polymer (P) tends to have not only higher heat resistance but also higher transparency and higher mechanical strength. In the polymer (P), the content of the structural unit (A) may be 95 mol% or less or 90 mol% or less relative to the total of all structural units.

The structural unit (A) is derived from a compound represented by the following formula (6), for example. In the formula (6), Rf ¹ to Rf ⁴ are the same as the formula (2). [Chemical 12]

The polymer (P) may further have other structural units in addition to the structural unit (A). Examples of other structural units are structural unit (B) represented by the following formula (7).

[Chemical 13]

In formula (7), R ⁵ to R ⁸ each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 7 carbon atoms. The perfluoroalkyl group may be linear, branched, or cyclic. Part of the fluorine atoms may be substituted by halogen atoms other than fluorine atoms. Part of the fluorine atoms in the perfluoroalkyl group may be replaced by halogen atoms other than fluorine atoms.

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

The structural unit (B) is derived from a compound represented by the following formula (8), for example. In the formula (8), R ⁵ to R ⁸ are the same as the formula (7). The compound represented by formula (8) is a fluorine-containing olefin such as tetrafluoroethylene and chlorotrifluoroethylene. [Chemical 14]

The structural unit (B) may also be a tetrafluoroethylene unit. In other words, the polymer (P) having the structural unit (A) may further have a tetrafluoroethylene unit.

More specific examples of the 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. Each of the above copolymers is also commercially available as TEFLON AF (trade name) and HIFLON AD (trade name).

The polymer (P) may further contain other structural units in addition to the structural units (A) and (B). Examples of other structural units are hexafluoropropane units. The polymer (P) may substantially contain no other structural units other than the structural units (A) and (B). Furthermore, the so-called polymer (P) does not substantially contain other structural units other than the structural units (A) and (B). It means that the total of the structural units (A) and (B) in the polymer (P) is It means that the total of all structural units is 95 mol% or more, preferably 98 mol% or more.

The fluororesin preferably contains substantially no hydrogen atoms. In this specification, the term "fluororesin substantially does not contain hydrogen atoms" means that the content of hydrogen atoms in the fluororesin is 1 mol% or less.

Typically, fluororesins are formed by free radical polymerization. For the polymerization of fluororesin, known polymerization methods such as solution polymerization and block polymerization can be applied.

Additives such as polymerization initiators or chain transfer agents can also be used in the polymerization of fluororesin. Examples of polymerization initiators are benzoyl peroxide, lauryl peroxide, octyl peroxide, acetyl peroxide, di-tert-butyl peroxide, tert-butyl cumene peroxide, diisopropyl peroxide. Propylbenzene, tert-butyl peracetate, perfluoro(di-tert-butyl peroxide), bis(2,3,4,5,6-pentafluorobenzoyl peroxide), benzoyl peroxide Organic peroxides such as tributyl ester and tert-butyl perpivalate; 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2- Butyronitrile), 2,2'-azobisisobutyronitrile, 2,2'-azobisisobutyric acid dimethyl ester, and 1,1'-azobis(cyclohexane-1-carbonitrile) and other azo starters. Additives may also be perfluorinated compounds.

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

In the purification method of this embodiment, by reducing the above-mentioned fluorine compound, the content (residual amount) of the above-mentioned fluorine compound in the fluororesin is 1 ppm or less, and may also be 0.8 ppm or less, 0.5 ppm or less, 0.3 ppm or less, 0.2 ppm or less, and further 0.1 ppm or less. In this manual, ppm is the quality standard. Furthermore, among the above-mentioned fluorine compounds, regarding HFA and similar structures of HFA, the ACGIH (American Conference of Industrial Hygiene Experts) has decided that the allowable concentration for short-term human exposure is 0.4 ppm or less. The purification method of this embodiment is also suitable for controlling the content of HFA and HFA-like structures in the fluororesin to be below the above-mentioned allowable concentration. On the other hand, since HFA and similar structures of HFA easily form hydrates, purification by heating water vapor is also considered. However, according to the research of the present inventors, this method is difficult to achieve sufficient reduction.

In the purification method of this embodiment, by reducing the above-mentioned fluorine compound, the content of the above-mentioned fluorine compound in the fluororesin is 1/10 or less of that before purification, and may also be 1/25 or less, 1/50 or less, or 1/75. below, and further below 1/100.

The content of the fluorine compound in the purified fluororesin may depend on, for example, the shape of the fluororesin, the state of the particles, the median diameter, the type or concentration of the fluorinating agent, and the purification conditions (temperature, pressure, time, etc.) And changes occur.

The purification method of this embodiment may also include further steps. An example of a further step is a drying step in which the fluororesin, especially the particles, are dried before purification. Drying of the fluororesin can be carried out, for example, by vacuum drying, reduced pressure drying, normal pressure drying, air supply drying, shaking drying, hot air drying, heating drying, or the like. Another example of further steps is the following step: vacuum devolatilization and/or heating of the purified fluororesin to remove residual fluorinating agent. In one example of the heating step (annealing step), the fluororesin in contact with the fluorinating agent is maintained at a predetermined temperature in an inert gas atmosphere such as nitrogen. The implementation of the annealing step is also suitable for reducing the fluorine-based gas (F _gas , HF gas, etc.) contained in the fluororesin. The temperature of the annealing step can be selected from the range exemplified above as the temperature for bringing the fluororesin into contact with the fluorinating agent. The time 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 the chamber containing the fluororesin and then introducing an inert gas into the chamber. The method and aspect of the annealing step are not limited to the above examples.

[Method for manufacturing fluororesin] Using the purification method of this embodiment, for example, a purified fluororesin whose molecular chain contains a fluorine-containing aliphatic ring structure can be produced. According to this aspect, the method for manufacturing a fluororesin of this embodiment is a method for manufacturing a purified fluororesin. The molecular chain of the fluororesin contains a fluorine-containing aliphatic ring structure. The above-mentioned manufacturing method includes the following steps: using the purification method of this embodiment. Method to purify fluororesin.

In the manufacturing method of this embodiment, by purifying the fluororesin as described above, a fluororesin having a fluorine compound content of 1 ppm or less can also be obtained.

[Fluororesin] The fluororesin of this embodiment has a structural unit containing a fluorine-containing aliphatic ring structure. Furthermore, in the fluororesin of this embodiment, the content of the fluorine compound with a molecular weight of 300 or less is 1 ppm or less. The content may also be 0.8 ppm or less, 0.5 ppm or less, 0.3 ppm or less, 0.2 ppm or less, and further 0.1 ppm or less. Examples of the fluorine compound, the fluorine-containing alicyclic structure, and the fluororesin are as described above in the description of the purification method of this embodiment.

The fluororesin of this embodiment may have a structural unit (A) represented by the following formula (2).

[Chemical 15] In formula (2), Rf ¹ to Rf ⁴ each independently represent a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms. Rf ¹ and Rf ² , and Rf ³ and Rf ⁴ can be connected to form a ring.

Structural unit (A) may also be a unit derived from 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole.

The fluororesin of this embodiment having the structural unit (A) may further have a tetrafluoroethylene unit.

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

The fluororesin of this embodiment can be produced by, for example, the purification method of this embodiment, or can be produced by the production method of this embodiment. However, the manufacturing method of the fluororesin of this embodiment is not limited to the above example.

The fluororesin of this embodiment can be used for optical materials or electronic materials, for example. An example of an optical component is plastic optical fiber (POF). POF may be provided with a layer containing the fluororesin of this embodiment. However, the use of the fluororesin according to this embodiment is not limited to the above examples.

[POF] An example of the POF containing the fluororesin of this embodiment is shown in FIG. 1 . POF1 in Figure 1 is composed of a plurality of layers including a core 2 and a cladding layer (first cladding layer) 3. Core 2 is located in the center of POF1 and is the layer that transmits light. The first cladding layer 3 is a layer arranged outside the core 2 with respect to the central axis of the POF 1 and covering the core 2 . The core 2 has a relatively high refractive index, and the first cladding 3 has a relatively low refractive index. The POF 1 in FIG. 1 further includes a second cladding layer (double cladding layer) 4 covering the outer periphery of the first cladding layer 3, and a coating layer (cladding layer) 5 covering the outer periphery of the second cladding layer 4. POF1 can also be of the refractive index profile (GI) type.

The fluororesin of this embodiment may be included in at least one layer constituting POF1. The fluororesin of this embodiment is preferably contained in at least one selected from the core 2 , the first cladding 3 and the second cladding 4 , and is more preferably contained in the second cladding 4 . The core 2 , the first cladding layer 3 , the second cladding layer 4 and the covering layer 5 may contain resins that can be contained in the corresponding layers in known POF. Examples of resins that can be included in the core 2, the first cladding layer 3, and the second cladding layer 4 are fluorine-containing resins, acrylic resins such as methyl methacrylate, styrene-based resins, and carbonate-based resins. Examples of resins that the coating layer 5 may include include polycarbonate, various engineering plastics, cyclic olefin polymers, polytetrafluoroethylene (PTFE), modified PTFE, and perfluoroalkoxyalkanes (PFA). Each layer may also contain additives such as refractive index modifiers.

POF1 can be produced by a melt spinning method, for example. In the melt spinning method, the raw material resin is melted and extruded to form the layers constituting the optical fiber. [Example]

Hereinafter, the present invention will be further described in detail through examples. The present invention is not limited to the following examples.

[Glass transition temperature Tg ₁ ] The Tg ₁ of the fluororesin was measured under the following conditions using the above method. Measuring device: Q-2000 manufactured by TA Instruments Temperature control program: heating from 30°C to 200°C (heating rate 10°C/min) Atmospheric gas: nitrogen (flow rate 50 mL/min) Measurement speed: 10°C/min Sample size: 5 mg

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

[GC-MS] GC-MS for fluororesin was performed under the following conditions. Thermal desorption device: TDS/CIS manufactured by Gerstel GC/MS device: 6980plus/5973N manufactured by Agilent Technologies GC column: HP-5ms UI, 30 m×0.25 mm, id×0.25 μm manufactured by Agilent Technologies Sample size: 10 mg (contained in glass tube) Sample heating conditions: heating from 20°C to 300°C (speed 60°C/min) and holding for 30 minutes Others: Cool, capture and analyze the gas generated by heating the sample.

[Heating test] The heating test of the fluororesin that has been subjected to molding processing is carried out as follows. 10 g of the fluororesin to be evaluated was contained in a PFA tube with an inner diameter of 10 mm, one side of which was sealed with a plug made of PTFE. Then, the fluororesin in the tube was heated at 270° C. for 20 hours to melt, and then naturally cooled to room temperature to form a rod. After natural cooling, the taken-out rod was observed with an optical microscope (magnification: 20 times) to confirm whether there was coloration. Observations were conducted at any 10 locations.

(Example 1) 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole/tetrafluoroethylene copolymer (manufactured by Chemours-Mitsui Fluoroproducts, TEFLON AF 1 kg of particles of 1600X) are spread evenly on a PFA tray (internal dimensions: 287 mm in length, 382 mm in width, 48 mm in depth) and contained in the chamber. The particle median diameter (d50) is 800 μm. In addition, Tg ₁ of the polymer is 163°C. Next, the chamber was replaced with nitrogen several times to bring it into a nitrogen atmosphere, and then the temperature was raised to 180°C. At the time when it reaches 180°C, a mixed gas of fluorine/nitrogen (volume ratio 20:80) flows into the chamber as a fluorinating agent (flow rate 10.50 L/min), and at the same time, the pressure in the chamber is 90 kPa. After maintaining the treatment conditions of 180°C and 90 kPa for about 65 hours, the chamber was replaced with nitrogen to stop the copolymer from being exposed to the fluorinating agent and the chamber was cooled to room temperature to complete the purification.

The HFA content in the copolymer before purification was 15 ppm. On the other hand, the content after purification is 0.1 ppm or less (below the detection limit). In addition, the HFA-like structure confirmed in the GC-MS mass spectrum in the range of ion mass m/z=166 to 200 was not detected. No coloring was observed in the rods formed from the purified copolymer.

(Example 2) Except that the fluorinating agent was changed to a single gas of fluorine gas, the same operation was carried out as in Example 1 to complete the purification of the copolymer. The content of HFA after purification was below 0.1 ppm (below the detection limit), and no HFA-like structures were detected. Moreover, coloring was not confirmed in the rod formed from the purified copolymer.

(Example 3) Except that the exposure temperature in the fluorinating agent was changed to 170°C, the same operation was performed as in Example 1 to complete the purification of the copolymer. The content of HFA after purification was below 0.1 ppm (below the detection limit), and no HFA-like structures were detected. Moreover, coloring was not confirmed in the rod formed from the purified copolymer.

(Comparative example 1) In Comparative Example 1, purification was performed by exposure to heated vapor instead of a fluorinating agent.

1 kg of particles of the copolymer used in Example 1 was spread evenly on a SUS (Steel Use Stainless, stainless steel) tray (internal dimensions: 287 mm in length, 382 mm in width, and 48 mm in depth). and contain it in the chamber. Then, heated steam (265°C) was introduced into the chamber, and after maintaining it at 100 kPa (normal pressure) for 40 minutes, the chamber was opened and cooled to room temperature to complete purification. The content of HFA after purification was 4.1 ppm, and HFA-like structures were also detected. Moreover, coloring was confirmed in the rod formed from the purified copolymer.

(Comparative example 2) The purification of the copolymer was completed in the same manner as in Comparative Example 1, except that the temperature of the heated water vapor introduced was changed to 220°C. The content of HFA after purification was 1.5 ppm, and HFA-like structures were also detected. Moreover, coloring was confirmed in the rod formed from the purified copolymer.

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

[Table 1] Example 1 Example 2 Example 3 Comparative example 1 Comparative example 2 Purification conditions Fluorine gas concentration (volume %) 20 100 20 0 0 Use of heated water vapor without without without have have Exposure time (hours) 65 65 65 0.67 0.67 Temperature(℃) 180 180 170 265 220 Evaluation HFA content (ppm) 0.1 or less 0.1 or less 0.1 or less 4.1 1.5 Detection of HFA similar structures without without without have have Coloring without without without have have [Industrial availability]

The fluororesin obtained through the purification method of the present invention is considered to be used in optical materials or electronic materials, for example. An example of optical materials is POF.

1: Plastic optical fiber (POF) 2: Core body 3: 1st cladding 4: 2nd cladding (double cladding) 5: Covering layer (cladding layer)

FIG. 1 is a cross-sectional view schematically showing an example of a plastic optical fiber containing a fluororesin obtained by the fluororesin purification method of the present invention.

1: Plastic optical fiber (POF)

2: Core body

3: 1st cladding

4: 2nd cladding (double cladding)

5: Covering layer (cladding layer)

Claims (20)

A method for purifying fluororesin, It includes the following steps: contacting a fluororesin whose molecular chain contains a fluorine-containing aliphatic ring structure with a fluorinating agent to reduce the content of fluorine compounds with a molecular weight of less than 300 contained in the above fluororesin. The purification method of fluororesin according to claim 1, wherein the above-mentioned fluorine compound is at least one selected from the group consisting of the compound represented by the following formula (1A) and the compound represented by the formula (1B); [Chemical 1] [Chemicalization 2] In formula (1A) and formula (1B), R ¹ and R ² each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 4 carbon atoms. The method for purifying fluororesin of claim 1, wherein the fluorine compound is hexafluoroacetone. The method for purifying fluororesin according to claim 1, wherein the fluororesin is brought into contact with the fluorinating agent in the form of particles. The purification method of fluororesin according to claim 1, wherein the fluororesin is contacted with the fluorinating agent at a temperature above (Tg ₁ - 20)°C, and Tg ₁ is the glass transition temperature of the fluororesin. The purification method of fluororesin of claim 1, wherein the above-mentioned fluorinating agent is fluorine gas. The purification method of fluororesin according to claim 1, wherein the above-mentioned fluorine-containing aliphatic ring structure has a dioxolane skeleton. The method for purifying fluororesin of claim 1, wherein the above fluororesin has a structural unit (A) represented by the following formula (2): [Chemical 3] In formula (2), Rf ¹ to Rf ⁴ each independently represent a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms; Rf ¹ and Rf ² , and Rf ³ and Rf ⁴ can be connected to form a ring. The purification method of fluororesin of claim 8, wherein the above structural unit (A) is derived from 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole unit. The purification method of fluororesin of claim 8, wherein the fluororesin further has a tetrafluoroethylene unit. The method for purifying fluororesin according to claim 1, wherein the content of the fluorine compound in the fluororesin is reduced to 1 ppm (mass basis) or less by reducing the fluorine compound. A method for manufacturing purified fluororesin, wherein The molecular chain of the above-mentioned fluororesin contains a fluorine-containing aliphatic ring structure, The above-mentioned manufacturing method includes the following steps: purifying the above-mentioned fluororesin using the purification method of the fluororesin according to any one of claims 1 to 11. The manufacturing method of Claim 12, wherein the fluororesin having a content of the fluorine compound of 1 ppm (mass basis) or less is obtained by purifying the fluororesin. A fluororesin, It has a structural unit containing a fluorine-containing aliphatic ring structure, and The content of fluorine compounds with a molecular weight of 300 or less is 1 ppm (mass basis) or less. The fluororesin of claim 14 has a structural unit (A) represented by the following formula (2): [Chemical 4] In formula (2), Rf ¹ to Rf ⁴ each independently represent a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms; Rf ¹ and Rf ² , and Rf ³ and Rf ⁴ can be connected to form a ring. The fluororesin of claim 15, wherein the structural unit (A) is a unit derived from 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole. The fluororesin of claim 15, wherein the fluororesin further has a tetrafluoroethylene unit. An optical material comprising the fluororesin according to any one of claims 14 to 17. An electronic material containing the fluororesin according to any one of claims 14 to 17. A plastic optical fiber, It has a layer containing the fluororesin according to any one of claims 14 to 17.

Images