Fluorine resin

Abstract

To provide a fluororesin having an oxolane ring, which is suppressed in yellowing after heating and melting and which is reduced in coloring especially in the molding of a thick wall product, and a method for producing the same.SOLUTION: Provided is a fluororesin which contains a residue unit represented by the following formula (1) and, when dissolved in perfluorohexane to make a 10 wt.% perfluorohexane solution, has a transmittance of 50% or more as measured with an optical path length of 10 mm and a wavelength of 275 nm. (In formula (1), Rf1, Rf2, Rf3, and Rf4 each independently represent one selected from the group consisting of a fluorine atom, C1-7 linear perfluoroalkyl groups, C3-7 branched perfluoroalkyl groups, and C3-7 cyclic perfluoroalkyl groups. The perfluoroalkyl group may have an ethereal oxygen atom. Further, Rf1, Rf2, Rf3, and Rf4 may be linked to each other to form a C4-8 ring and the ring may be one containing an ethereal oxygen atom).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a fluororesin and a method for producing the same. [Background technology]

[0002] Fluorine resins have excellent heat resistance, electrical properties, chemical resistance, waterproofing, liquid and oil repellency, and optical properties, and are therefore used in protective films for semiconductors and other electronic components, water-repellent films for inkjet printer heads, waterproof and oil-resistant coatings for filters, and optical components.

[0003] Among these, fluororesins containing oxolane rings have a bulky ring structure, making them amorphous and highly transparent and heat-resistant. Furthermore, because they are composed only of carbon, fluorine, and oxygen, they have excellent electrical properties, chemical resistance, waterproofness, and liquid and oil repellency. Furthermore, because they are amorphous, they can be melt-molded.

[0004] Non-Patent Document 1 describes the synthesis and properties of a polymer (polyPFMMD) obtained by polymerizing perfluoro-2-methylene-4-methyl-1,3-dioxolane (PFMMD), a type of fluororesin containing an oxolane ring, using perfluorobenzoyl peroxide as a radical polymerization initiator. PolyPFMMD has excellent heat resistance. However, according to the inventors' investigations, the polyPFMMD described in Non-Patent Document 1 exhibits significant yellowing after hot-melt molding, particularly in thick molded articles. Therefore, there is a strong demand for technology that can achieve low coloration and high transparency even in thick molded articles of polyPFMMD.

[0005] Furthermore, a method for producing fluororesin containing oxolane rings that suppresses yellowing after heat-melt molding, has excellent yield and productivity, and has a narrow molecular weight distribution Mw / Mn has not been clarified. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Macromolecules 2005,38,4237-4245 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made with the aim of solving the problems associated with fluororesins containing oxolane rings. Specifically, the object is to provide a fluororesin containing oxolane rings that is inhibited from yellowing after heat melting, and that exhibits reduced coloring even when molded into thick-walled products, and a method for producing the same. [Means for solving the problem]

[0008] As a result of extensive research, the present inventors have found that a fluororesin that has low light absorption and high transmittance at a wavelength of 275 nm can solve the above problems, and have thus completed the present invention.

[0009] That is, the present invention relates to a fluororesin that contains a residue unit represented by the following formula (1), and that, when dissolved in perfluorohexane to form a 10 wt % perfluorohexane solution, has a transmittance of 50% or more as measured at an optical path length of 10 mm and a wavelength of 275 nm.

[0010] [ka]

[0011] (In formula (1), Rf1, Rf2, Rf3, and Rf4 each independently represent one of the group consisting of a fluorine atom, a linear perfluoroalkyl group having 1 to 7 carbon atoms, a branched perfluoroalkyl group having 3 to 7 carbon atoms, or a cyclic perfluoroalkyl group having 3 to 7 carbon atoms, and the perfluoroalkyl group may have an etheric oxygen atom, and Rf1, Rf2, Rf3, and Rf4 may be linked together to form a ring having 4 to 8 carbon atoms, and the ring may contain an etheric oxygen atom.) [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a fluororesin containing an oxolane ring that is inhibited from yellowing when subjected to melt molding into a thick molded article, and a method for producing the same. [Brief explanation of the drawings]

[0013] [Figure 1] 1 shows transmission spectra for a 10 wt % fluororesin-perfluorohexane solution at an optical path length of 10 mm in Examples 1 and 2 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0014] The fluororesin according to one embodiment of the present invention will be described in detail below.

[0015] The fluororesin of the present invention contains a residue unit represented by the following formula (1), and when dissolved in a perfluorohexane solution to form a 10 wt % perfluorohexane solution, the transmittance measured at an optical path length of 10 mm and a wavelength of 275 nm is 50% or more.

[0016] [ka]

[0017] (In formula (1), Rf1, Rf2, Rf3, and Rf4 each independently represent one of the group consisting of a fluorine atom, a linear perfluoroalkyl group having 1 to 7 carbon atoms, a branched perfluoroalkyl group having 3 to 7 carbon atoms, or a cyclic perfluoroalkyl group having 3 to 7 carbon atoms, and the perfluoroalkyl group may have an etheric oxygen atom, and Rf1, Rf2, Rf3, and Rf4 may be linked together to form a ring having 4 to 8 carbon atoms, and the ring may contain an etheric oxygen atom.) The fluororesin of the present invention is amorphous and has high transparency and heat resistance due to the bulky ring structure contained in the specific formula (1). Furthermore, because it is composed only of carbon, fluorine, and oxygen, it has excellent electrical properties, chemical resistance, waterproofness, and liquid and oil repellency.

[0018] In formula (1), Rf1, Rf2, Rf3, and Rf4 each independently represent one of the group consisting of a fluorine atom, a linear perfluoroalkyl group having 1 to 7 carbon atoms, a branched perfluoroalkyl group having 3 to 7 carbon atoms, or a cyclic perfluoroalkyl group having 3 to 7 carbon atoms. The perfluoroalkyl group may have an etheric oxygen atom. Furthermore, Rf1, Rf2, Rf3, and Rf4 may be bonded to each other to form a ring having 4 to 8 carbon atoms, and the ring may contain an etheric oxygen atom.

[0019] Examples of the linear perfluoroalkyl group having 1 to 7 carbon atoms include a trifluoromethyl group, a pentafluoroethyl group, a heptafluoropropyl group, a nonafluorobutyl group, an undecafluoropentyl group, a tridecafluorohexyl group, and a pentadecafluoroheptyl group.

[0020] Examples of the branched perfluoroalkyl group having 3 to 7 carbon atoms include a heptafluoroisopropyl group, a nonafluoroisobutyl group, a nonafluorosec-butyl group, and a nonafluorotert-butyl group.

[0021] Examples of the cyclic perfluoroalkyl group having 3 to 7 carbon atoms include a heptafluorocyclopropyl group, a nonafluorocyclobutyl group, and a tridecafluorocyclohexyl group.

[0022] Examples of the linear perfluoroalkyl group having 1 to 7 carbon atoms which may have an etheric oxygen atom include a -CF2OCF3 group, a -(CF2)2OCF3 group, and a -(CF2)2OCF2CF3 group.

[0023] Examples of cyclic perfluoroalkyl groups having 3 to 7 carbon atoms which may have an etheric oxygen atom include a 2-(2,3,3,4,4,5,5,6,6-decafluoro)-pyrinyl group, a 4-(2,3,3,4,4,5,5,6,6-decafluoro)-pyrinyl group, and a 2-(2,3,3,4,4,5,5-heptafluoro)-furanyl group.

[0024] At least one of Rf1, Rf2, Rf3, and Rf4 is preferably a fluororesin that is one type of group consisting of a linear perfluoroalkyl group having 1 to 7 carbon atoms, a branched perfluoroalkyl group having 3 to 7 carbon atoms, or a cyclic perfluoroalkyl group having 3 to 7 carbon atoms, thereby allowing the fluororesin of the present invention to exhibit excellent heat resistance.

[0025] A specific example of the residue unit represented by formula (1) is a residue unit represented by the following formula (2).

[0026] [ka]

[0027] Among these, fluororesins containing a residue unit represented by the following formula (3) are preferred because they have excellent heat resistance and moldability, and fluororesins containing a perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit are more preferred.

[0028] [ka]

[0029] The fluororesin of the present invention contains a residue unit represented by the formula (1) and, when dissolved in perfluorohexane to form a 10 wt % perfluorohexane solution, has a transmittance of 50% or more as measured at an optical path length of 10 mm and a wavelength of 275 nm.

[0030] When the fluororesin of the present invention is dissolved in a perfluorohexane solution to prepare a 10 wt% perfluorohexane solution, the transmittance measured at 275 nm over a 10 mm optical path length is 50% or more. Herein, the transmittance at a 10 mm optical path length may refer to either the value obtained when light actually passes through the solution for 10 mm, or the value calculated for 10 mm assuming light passes through the solution for 10 mm. In the latter case, it can also be referred to as the transmittance when the optical path length is converted to 10 mm. Hereinafter, a 10 wt% fluororesin-perfluorohexane solution of the present invention will be simply referred to as the "measurement solution." A measurement solution with a transmittance of 50% or more suppresses yellowing during melt molding of a thick molded article using the fluororesin of the present invention. According to the present inventors, when the measurement solution has high light absorption and low transmittance at the wavelength of 275 nm, which is in the ultraviolet region, significant yellowing occurs during melt molding of a thick molded article using the fluororesin of the present invention. On the other hand, it has been found that when the measurement solution has low light absorption and high transmittance at a wavelength of 275 nm, yellowing is suppressed when the fluororesin of the present invention is used to melt-mold a thick molded product.

[0031] The transmittance of the measurement solution at a wavelength of 275 nm is preferably 70% or more, more preferably 80% or more, even more preferably 85% or more, even more preferably 90% or more, and even more preferably 95% or more, which further suppresses yellowing after heat melting.

[0032] It is also preferable that the measurement solution does not exhibit a minimum peak in the transmission spectrum at an optical path length of 10 mm and a wavelength of 250 to 300 nm.

[0033] The fluororesin of the present invention is capable of suppressing yellowing during melt molding of thick molded articles, and therefore is suitable for solid 19 It is preferable that there is no peak in the range of −150 to 170 ppm in F-NMR.

[0034] The fluororesin of the present invention has a weight average molecular weight Mw of 5×10 4 ~3×10 5It is preferable that the weight average molecular weight Mw is in this range. When the weight average molecular weight Mw is in this range, the melt molding processability and defoaming property when melted are excellent. Furthermore, when the weight average molecular weight Mw is in this range, the occurrence of cracks during heating and cooling is reduced. From the viewpoint of excellent melt molding processability and excellent defoaming property when melted, the fluororesin of the present invention more preferably has a weight average molecular weight Mw of 5×10 4 ~2×10 5 It is preferable that the range is:

[0035] The weight-average molecular weight Mw of the fluororesin of the present invention can be calculated using gel permeation chromatography (GPC), for example, by using a standard polymethyl methacrylate of known molecular weight as the standard sample and a solvent capable of dissolving both the standard sample and the fluororesin as the eluent, from the elution times of the sample and the standard sample and the molecular weight of the standard sample. An example of the solution is Asahiklin AK-225 (manufactured by Asahi Glass Co., Ltd.) to which 10 wt % of 1,1,1,3,3,3-hexafluoro-2-propanol (manufactured by Wako Pure Chemical Industries, Ltd.) has been added.

[0036] The molecular weight distribution Mw / Mn, which is the ratio of the weight average molecular weight Mw to the number average molecular weight Mn of the fluororesin of the present invention, is not particularly limited, but from the viewpoints of suppressing yellowing after heating and melting, providing excellent melt molding processability, excellent defoaming properties during melting, and reducing the occurrence of cracks during heating and cooling, the molecular weight distribution Mw / Mn is preferably 1.2 to 8, more preferably 1.2 to 5, and even more preferably 1.5 to 3. The number average molecular weight Mn can be measured in the same manner as the above-mentioned method for measuring the weight average molecular weight Mw, and the molecular weight distribution Mw / Mn can be calculated by dividing the weight average molecular weight Mw by the number average molecular weight Mn.

[0037] The fluororesin of the present invention preferably has a yellowness index (YI) of 10 or less, more preferably 4 or less, and even more preferably 3 or less, measured in the diameter direction on a thick-walled melt-molded article (a cylindrical molded article 10 mm in diameter and approximately 17 mm in height, melt-molded in a test tube at 280°C for 24 hours). According to the present inventors, yellowing of the fluororesin after melt-molding is more pronounced when melt-molded into a thick article in a closed environment than when heated in an open environment. For example, one method for evaluating the yellowness and coloration of a thick melt-molded article is to heat 3 g of the fluororesin of the present invention in a test tube with an outer diameter of 13 mm at 280°C for 24 hours, melt-molding the resulting cylindrical article (10 mm in diameter and approximately 17 mm in height), and then evaluate the yellowness index (YI) measured in the diameter direction. Here, the diameter direction refers to the vertical direction when the test tube is placed on its side on a desk or similar surface. The yellowness was measured by placing the obtained resin molded product in a test tube on its side on a piece of white paper, taking a digital photograph from above, and reading the RGB values ​​of the molded product from the obtained image using software. The read RGB values ​​were calculated using the following formula: X=0.4124R+0.3576G+0.1805B Y=0.2126R+0.7152G+0.0722B Z=0.0193R+0.1192G+0.9505B The tristimulus values ​​X, Y, and Z of the XYZ color system are calculated using the above formula, and the yellowness index (YI) under illuminant C (auxiliary illuminant C) is calculated from X, Y, and Z in accordance with the method of JIS K7373.

[0038] The fluororesin of the present invention preferably has a yellowness index (YI) of not more than 1 in a thin melt-molded product (3 mm thick, molded by heating and melting in a petri dish at 280°C for 24 hours). The molding method and evaluation method can be those described in the examples.

[0039] The fluororesin of the present invention may contain other monomer residue units, and examples of other monomer residue units include tetrafluoroethylene (TFE), hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE), trifluoroethylene, hexafluoroisobutylene, perfluoroalkylethylene, fluorovinyl ether, vinyl fluoride (VF), vinylidene fluoride (VDF), perfluoro-2,2-dimethyl-1,3-dioxole (PDD), perfluoro(allyl vinyl ether), and perfluoro(butenyl vinyl ether).

[0040] Although there are no particular limitations on the particle size of the fluororesin of the present invention, the volume average particle size is preferably 1 to 1000 μm, more preferably 1 to 500 μm, and even more preferably 1 to 300 μm, because this provides high fluidity to the resin powder, enabling continuous supply to a molding machine or the like, suppressing residual solvent in the resin, increasing bulk density and packing properties, and providing excellent handleability during molding processing.

[0041] The volume average particle size of the fluororesin of the present invention 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 measured by dispersing resin particles in water or an organic solvent such as methanol and measuring the particle size distribution. An example of a laser scattering meter is the Microtrac manufactured by Microtrac Bell Co., Ltd.

[0042] The volume average particle size, also known as the mean volume diameter, is the average particle size expressed on a volume basis and is expressed as Σ(vd) / Σ(v) when the particle size distribution is divided into each particle size channel, d is the representative particle size value for each particle size channel, and v is the volume-based percentage for each particle size channel.

[0043] The fluororesin of the present invention is in powder form, and preferably has a volume average particle size of 1 to 1000 μm.

[0044] The method for producing a fluororesin according to one embodiment of the present invention will be described in detail below.

[0045] The fluororesin of the present invention can be produced by polymerizing a mixture containing a radical polymerization initiator represented by the following formula (4) and a monomer represented by the following formula (5).

[0046] [ka]

[0047] (In formula (4), Rf 9 , Rf 10 , Rf 11 , Rf 12 each independently represents a perfluoroalkyl group having 1 to 20 carbon atoms, and the perfluoroalkyl group may have an etheric oxygen atom; and Rf 9 and Rf 10 may be linked together to form a ring having 4 to 8 carbon atoms, and Rf 11 and Rf 12 may be linked to each other to form a ring having 4 to 8 carbon atoms, and the ring may contain an etheric oxygen atom.

[0048] [ka]

[0049] (In formula (5), Rf5, Rf6, Rf7, and Rf8 each independently represent one of the group consisting of a fluorine atom, a linear perfluoroalkyl group having 1 to 7 carbon atoms, a branched perfluoroalkyl group having 3 to 7 carbon atoms, or a cyclic perfluoroalkyl group having 3 to 7 carbon atoms, and the perfluoroalkyl group may have an etheric oxygen atom, and Rf5, Rf6, Rf7, and Rf8 may be linked to each other to form a ring having 4 to 8 carbon atoms, and the ring may contain an etheric oxygen atom.) Rf5, Rf6, Rf7, and Rf8 in formula (5) have the same meanings as Rf1, Rf2, Rf3, and Rf4 in formula (1), respectively.

[0050] In the method for producing a fluororesin of the present invention, the use of a radical polymerization initiator represented by formula (4) makes it possible to obtain a fluororesin that exhibits reduced yellowing during melt molding of a thick molded article. Furthermore, the use of a radical polymerization initiator represented by formula (4) allows the production of a fluororesin with superior yield and productivity compared to the use of a linear perfluorodiacyl peroxide. Furthermore, a fluororesin with a narrow molecular weight distribution Mw / Mn can be obtained. The narrow molecular weight distribution Mw / Mn improves the thermal melt moldability. Furthermore, the use of a radical polymerization initiator represented by formula (4) decarboxylates the radical polymerization initiator before adding it to the polymer, resulting in a polymer that contains almost no carbonyl groups. This is believed to result in a structure in which the terminal represented by formula (6) below is directly added to the polymer, which is advantageous for obtaining a fluororesin that exhibits reduced yellowing during melt molding of a thick molded article.

[0051] [ka]

[0052] (In formula (6), Rf 15 , Rf 16 each independently represents a perfluoroalkyl group having 1 to 20 carbon atoms, and the perfluoroalkyl group may have an etheric oxygen atom; and Rf 15 and Rf 16 may be linked to each other to form a ring having 4 to 8 carbon atoms, and the ring may contain an etheric oxygen atom. In formula (4), Rf 9 , Rf 10 , Rf 11 , Rf 12 Rf each independently represents a perfluoroalkyl group having 1 to 20 carbon atoms, and the perfluoroalkyl group may have an etheric oxygen atom. 9 and Rf 10 may be linked together to form a ring having 4 to 8 carbon atoms, and Rf 11 and Rf 12may be linked to each other to form a ring having 4 to 8 carbon atoms, and the ring may contain an etheric oxygen atom.

[0053] Examples of the perfluoroalkyl group having 1 to 20 carbon atoms in the formula (4) include linear perfluoroalkyl groups having 1 to 20 carbon atoms, such as trifluoromethyl, pentafluoroethyl, heptafluoropropyl, nonafluorobutyl, undecafluoropentyl, tridecafluorohexyl, pentadecafluoroheptyl, and perfluorohexadecyl; branched perfluoroalkyl groups having 3 to 7 carbon atoms, such as heptafluoroisopropyl, nonafluoroisobutyl, nonafluorosec-butyl, and nonafluorotert-butyl; cyclic perfluoroalkyl groups, such as nonafluorocyclobutyl and tridecafluorocyclohexyl; and perfluoroalkyl groups having an etheric oxygen atom, such as -OCF, -OCFCF, and -OCF. Furthermore, when these groups are linked together to form a ring having 4 to 20 carbon atoms, examples of the ring include a perfluorocyclobutyl group, a perfluorocyclopentyl group, a perfluorocyclohexyl group, a perfluoropentyl group, a perfluorooctyl group, a perfluorooxolane group, and a perfluorodioxolane group.

[0054] An example of the radical polymerization initiator represented by formula (4) is a radical polymerization initiator represented by the following formula (7).

[0055] [ka]

[0056] In the method for producing a fluororesin of the present invention, it is more preferable to use a radical polymerization initiator represented by the following formula (8). By using a radical polymerization initiator represented by formula (8), it is possible to obtain a fluororesin that is further prevented from yellowing when melt-molding a thick molded product. Furthermore, it is possible to obtain a fluororesin with a narrow molecular weight distribution Mw / Mn. A narrow molecular weight distribution Mw / Mn improves the hot melt moldability. Furthermore, it is possible to obtain a fluororesin with excellent yield and productivity.

[0057] [ka]

[0058] (In formula (8), Rf 13 , Rf 14 each independently represents a perfluoroalkyl group having 3 to 20 carbon atoms, and the perfluoroalkyl group may have an etheric oxygen atom. Examples of the perfluoroalkyl group having 3 to 20 carbon atoms in the formula (8) include a -CF2CF2CF2- group, a -CF2CF2CF2CF2CF2- group, a -CF2CF2CF2CF2CF2CF2- group, a -CF2CF2CF2CF2CF2CF2CF2- group, a -CF2CF2CF2CF2CF2CF2- group, a -CF2CF2CF(CF3)CF2CF2- group, a -CF2CF2OCF2CF2- group, and a -OCF2CF2CF2O- group.

[0059] In the method for producing a fluororesin of the present invention, it is more preferable to use a radical polymerization initiator represented by the following formula (9) or (10). By using a radical polymerization initiator represented by formula (9) or (10), yellowing after heat melting is further suppressed, and a fluororesin can be obtained that exhibits further suppressed yellowing when melt-molded into a thick molded product in a closed environment such as a test tube. Furthermore, a fluororesin with a narrow molecular weight distribution Mw / Mn can be obtained. A narrow molecular weight distribution Mw / Mn improves heat melt moldability. Furthermore, the fluororesin can be obtained with excellent yield and productivity. In this specification, the radical polymerization initiator represented by formula (10) is sometimes referred to as bis(perfluorocyclohexylcarbonyl) peroxide.

[0060] [ka]

[0061] (In formula (9), j is an integer of 3 to 20.)

[0062] [ka]

[0063] Bis(perfluorocyclohexylcarbonyl) peroxide can be obtained by methods such as those described in Japanese Patent Application Laid-Open No. 11-49749 and J. App. Polym. Sci., 1999, 72, 1101-1108. In this case, perfluorohexane (FC-72, manufactured by 3M Japan) or the like can be used as a solvent instead of AK-225. The bis(perfluorocyclohexylcarbonyl) peroxide of the present invention may be synthesized by methods other than those described in the above-mentioned literature. For example, Chem. Rev., 1996, 96, 1779-1808, describes a method for synthesizing fluorinated peroxides. Examples of such methods include reacting an acid fluoride with hydrogen peroxide, reacting an acid chloride with hydrogen peroxide, and reacting an acid anhydride with hydrogen peroxide. In this case, the presence of a base such as sodium hydroxide in the system promotes the reaction.

[0064] In the method for producing a fluororesin of the present invention, a chain transfer agent may be used to adjust the molecular weight. Examples of chain transfer agents include organic compounds having 1 to 20 carbon atoms and containing at least one atom selected from the group consisting of hydrogen atoms and chlorine atoms. Specific examples of chain transfer agents include organic compounds having 1 to 20 carbon atoms and containing hydrogen atoms, such as toluene, acetone, ethyl acetate, tetrahydrofuran, methyl ethyl ketone, methanol, ethanol, and isopropanol; and organic compounds having 1 to 20 carbon atoms and containing chlorine atoms, such as chloroform, dichloromethane, tetrachloromethane, chloromethane, dichloroethane, trichloroethane, tetrachloroethane, pentachloroethane, hexachloroethane, benzyl chloride, pentafluorobenzyl chloride, and pentafluorobenzoyl chloride. Among these, organic compounds having 1 to 20 carbon atoms and containing chlorine atoms are preferred from the viewpoint of suppressing yellowing after heat melting, and organic compounds having 1 to 20 carbon atoms and containing hydrogen atoms and chlorine atoms are more preferred. The amount of the chain transfer agent is, for example, 0.01 to 50% by weight based on the total amount of the monomer and the chain transfer agent.

[0065] In the method for producing the resin of the present invention, the polymerization method is not limited, and examples thereof include solution polymerization, precipitation polymerization, bulk polymerization, emulsion polymerization, and suspension polymerization.

[0066] In the production method of the present invention, it is preferable to further mix an organic solvent into the mixture during the polymerization step. In the resin production method of the present invention, the resin powder has high fluidity, allowing continuous supply to molding machines and the like, reducing residual solvent in the resin, resulting in a powder with high bulk density, increased packing properties, and excellent handleability during molding. Therefore, it is preferable to use an organic solvent that dissolves at least the monomer represented by formula (5) but does not dissolve at least a portion of the resin containing the residue unit represented by formula (1) produced by polymerization, resulting in precipitation of the resin, and the resin produced by polymerization precipitates as particles in the organic solvent. In the resin production method of the present invention, the organic solvent may be referred to as a "precipitation polymerization solvent." Using the precipitation polymerization solvent allows the resin produced by the polymerization reaction to precipitate as particles having a specific volume average particle size, resulting in the production of resin particles with excellent moldability and packing properties. Furthermore, because no polymerization aids such as emulsifiers and dispersants are used, resin particles can be produced that do not contain emulsifiers or dispersants, which can cause impairments in transparency and heat resistance.

[0067] Here, the precipitation polymerization solvent means a solvent in which resin particles containing a residue unit represented by formula (1) remain after being immersed in the organic solvent for a long period of time. Specifically, the precipitation polymerization solvent means a solvent in which resin particles remain after being immersed in the organic solvent for a long period of time. 4 ~70×10 4When the resin particles are immersed in an organic solvent in an amount 10 times (w / w) the amount of the resin particles at 50°C for 5 hours or more and the remaining resin particles can be confirmed with the naked eye in the organic solvent, the organic solvent can be regarded as precipitation polymerization solvent A. Precipitation polymerization solvent A is preferably an organic solvent in which the weight loss of the resin sample is less than 20 wt% when the solution is cooled to 25°C after immersion for 5 hours or more at 50°C and the remaining resin sample in a solid state is recovered. The weight loss of the resin sample is more preferably less than 12 wt%, and even more preferably less than 10 wt%.

[0068] The resin weight loss rate can be measured by the following method. After filtering the cooled solution, the solid on the filter is rinsed with the solvent, washed several times with acetone, and then dried to recover the resin sample on the filter. The weight of the recovered resin is measured, and the weight of the recovered resin is subtracted from the amount of resin immersed in the organic solvent. The percentage of this value divided by the amount of resin immersed in the organic solvent is used as the resin weight loss rate.

[0069] Precipitation polymerization solvents include non-halogen organic solvents such as acetone, methyl ethyl ketone, hexane, and butyl acetate, chlorine-containing organic solvents such as dichloromethane and chloroform, and organic solvents containing a fluorine atom in the molecule.

[0070] 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 yield, and is easy to obtain a high molecular weight substance.Specific examples of the precipitation polymerization solvent 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, 1,2,2,3,3,4,4-heptafluorocyclopentane, 1H,1H-pentafluoropropanol, 1H,1H-heptafluorobutanol, 2-perfluorobutylethanol, 4,4,4-trifluorobutanol, 1H,1H,3H-tetrafluoropropanol, 1H,1H,5H-octafluoropropanol, 1H,1H,7H-dodecafluoroheptanol, 1H,1H,3H-hexafluorobutanol, 2 , 2,3,3,3-pentafluoropropyl difluoromethyl ether, 2,2,3,3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, hexafluoroisopropyl methyl ether, 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, 2,2,3,4,4,4-hexafluorobutyl difluoromethyl ether, and the like.

[0071] Among these, 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 are preferred, with 1,2,2,3,3,4,4-heptafluorocyclopentane being preferred due to its excellent polymerization yield and ease of obtaining high molecular weight polymers. The ratio of fluorine atoms to hydrogen atoms in the precipitation polymerization solvent molecule is preferably 1:9 to 9:1, more preferably 1:9 to 7:3, and even more preferably 4:6 to 7:3, in terms of the number of atoms, due to its excellent polymerization yield. The precipitation polymerization solvent contains fluorine atoms and hydrogen atoms in the molecule, and the hydrogen atom content in the solvent is preferably 1 wt% or more, more preferably 1.5 wt% or more, based on the weight of the solvent molecule, due to its excellent polymerization yield. In addition, the concentration is preferably 1% by weight or more and 5% by weight or less, and more preferably 1.5% by weight or more and 4% by weight or less, in order to provide a high polymerization yield and easily obtain a high molecular weight product. In addition, the precipitation polymerization solvent is preferably one that does not contain a chlorine atom in the molecule in order to provide a high polymerization yield and easily obtain a high molecular weight product.

[0072] The ratio of the monomer represented by formula (5) to the precipitation polymerization solvent is preferably monomer:precipitation polymerization solvent=1:99 to 50:50 by weight, more preferably 5:95 to 40:60, and even more preferably 5:95 to 30:70, because this provides excellent productivity and particles with excellent flow properties.

[0073] In the production method of the present invention, it is preferred that the monomer represented by formula (5) is perfluoro(4-methyl-2-methylene-1,3-dioxolane) represented by formula (11), and the residue unit represented by formula (1) is a perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit represented by formula (3).

[0074] [ka]

[0075] By producing a fluororesin according to the method of the present invention, it is possible to obtain a fluororesin that is suppressed from yellowing during melt molding into a thick molded article. Furthermore, it is possible to obtain a fluororesin with a narrow molecular weight distribution Mw / Mn while exhibiting the above properties. Furthermore, it is possible to obtain a fluororesin with excellent yield and productivity while exhibiting the above properties. [Example]

[0076] The present invention will be described in more detail below with reference to examples. However, the examples are merely illustrative of the present invention and are not intended to limit the present invention.

[0077] [Measurement of weight average molecular weight Mw and molecular weight distribution Mw / Mn] Measurements were performed using gel permeation chromatography equipped with a Tosoh Corporation TSKgel SuperHZM-M column and an RI detector. The eluent used was Asahiklin AK-225 (Asahi Glass Co., Ltd.) with 10 wt% 1,1,1,3,3,3-hexafluoro-2-propanol (Wako Pure Chemical Industries, Ltd.). Agilent standard polymethyl methacrylate was used as the standard sample. The weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) calculated in terms of polymethyl methacrylate were calculated from the elution times of the sample and standard sample.

[0078] [solid 19 F-NMR measurements] Using a Varian VNMRS-400, magnetic field strength was 376.18 MHz (19F), a 1.6 mm FAST MAS probe was used, and the hahn-echo method was used with a pulse width of 1.3 μs, a spectrum width of 250 kHz (664.6 ppm), a spectrum center: -120 ppm, a waiting time of 10 seconds, a MAS rotation speed of 39 kHz, and an accumulation count of 2048. Approximately 10 mg of fluororesin was used as a solid sample, with PTFE (-122.0 ppm) as the standard. 19 F-NMR measurements were carried out.

[0079] [Transmittance measurement of polymer solution] A fluororesin-perfluorohexane solution with a 10 wt% concentration was prepared by dissolving the fluororesin in perfluorohexane (FC-72, 3M Japan). Using a Hitachi UH5300 UV-Vis spectrophotometer and a quartz cell with a 10 mm optical path length, the quartz cell containing the polymer solution was placed on the sample side of the spectrophotometer, and a quartz cell containing perfluorohexane (FC-72) was placed on the reference side. The transmittance of the polymer solution was measured over a wavelength range of 190 to 700 nm, at a scan speed of 400 nm / min and intervals of 1 nm. The transmittance value obtained at a wavelength of 275 nm was taken as the transmittance of a 10 wt% perfluorohexane solution of the fluororesin at a 10 mm optical path length at a wavelength of 275 nm. A graph of the relationship between wavelength and transmittance was also used to determine whether a minimum peak was present at wavelengths of 250 to 300 nm.

[0080] [Measurement of yellowness index (YI) of thick-walled melt-molded product (φ10mm x H17mm, in a test tube at 280℃ for 24 hours)] 3.0 g of fluororesin was placed in a glass test tube (Nichiden Rika Glass, ST-13M) with an outer diameter of 13 mm and a total length of 100 mm. The test tube was covered with aluminum foil and an aluminum cap (Maruem, M-1), placed in a test tube stand, and placed in an oven. The tube was heated at 280°C for 24 hours, and then allowed to cool, yielding a cylindrical resin molded product (diameter: 10 mm, height: approximately 17 mm) inside the test tube. The resulting resin molded product was placed on its side on a piece of white paper, and a digital photograph was taken from above under white fluorescent light using a PowerShot SX620HS (Canon). The RGB values ​​of the molded product were then read from the image using Paint (Microsoft image processing software). The RGB values ​​were calculated using the following formula: X=0.4124R+0.3576G+0.1805B Y=0.2126R+0.7152G+0.0722B Z=0.0193R+0.1192G+0.9505B The tristimulus values ​​X, Y, and Z of the XYZ color system were calculated using the above formula. The yellowness index (YI) for light source C (auxiliary illuminant C) was calculated from X, Y, and Z according to the method of JIS K7373, and the yellowness index (YI) of a thick melt-molded product (φ10 mm x H17 mm, in a test tube at 280°C for 24 hours) was then calculated.

[0081] [Yellowness index (YI) of thin melt-molded product (3 mm thick, in a petri dish at 280°C for 24 hours)] 2.0 g of fluororesin was weighed into a 26.4 mm inner diameter Petri dish (a flat Petri dish with a lid and a receiver, manufactured by Flat Corporation; the receiver only, with a 1 mm thick glass bottom). The dish was placed in an inert oven (Yamato Scientific DN411I) and left at room temperature for 30 minutes under an air flow (20 L / min). The temperature was then raised to 280 °C over 30 minutes and heated at 280 °C for 24 hours. The oven door was then closed while maintaining the air flow (20 L / min). The oven was then turned off and the sample was allowed to cool for 12 hours. The sample was then removed and a 3 mm thick, 26.4 mm diameter fluororesin melt-molded product was obtained on the Petri dish. The air used was compressed air passed through a dehumidifier (dew point temperature: -20 °C or lower). The resulting fluororesin melt-molded product was measured for transmittance at wavelengths from 200 nm to 1500 nm at 1 nm intervals using a spectrophotometer (Hitachi High-Tech Science U-4100). Data at 5 nm intervals from 380 nm to 780 nm were extracted from the measured transmittance data, and the tristimulus values ​​X, Y, and Z of the XYZ color system were calculated according to the method of JIS Z8701. Furthermore, according to the method of JIS K7373, the yellowness index (YI) under illuminant C (auxiliary illuminant C) was calculated to determine the yellowness index (YI) of the fluororesin melt-molded product with the Petri dish. The yellowness index (YI) of the Petri dish alone (receiver only) was measured, and the yellowness index (YI) of the fluororesin melt-molded product with a thickness of 3 mm was calculated by subtracting the yellowness index (YI) of the Petri dish alone (receiver only) from the yellowness index (YI) of the fluororesin molded product with the Petri dish. The yellowness index (YI) of the petri dish alone (receiver only) was 0.21.

[0082] [Volume average particle size measurement] The volume average particle size (unit: μm) was measured using a Microtrac MT3000 manufactured by Microtrac Bell Co., Ltd., and methanol as the dispersion medium.

[0083] [Example 1] A 75 mL glass ampoule was charged with 0.133 g (0.000205 mol) of bis(perfluorocyclohexylcarbonyl) peroxide as initiator, 10.0 g (0.0410 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as monomer, and 40.0 g of FC-72 as polymerization solvent. The ampoule was repeatedly subjected to nitrogen substitution and depressurization via freeze degassing, and then sealed under reduced pressure (monomer / solvent = 20 / 80 (wt / wt)). The ampoule was placed in a thermostatic chamber at 55 °C and held for 24 hours to carry out radical solution polymerization. A viscous resin solution was obtained. After cooling to room temperature, the ampoule was opened, and the resin solution was diluted with 50 g of FC-72 to adjust the viscosity. 240 g of Zeorora H (1,2,2,3,3,4,4-heptafluorocyclopentane, manufactured by Nippon Zeon Co., Ltd.) was placed in a beaker equipped with a stirrer, and the diluted resin solution was added to the beaker under stirring to precipitate the resin. The precipitated resin was recovered by filtration, washed twice with acetone, and vacuum dried to obtain powdered perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin (yield: 93%). The weight-average molecular weight of the resulting fluororesin was 8.6 × 10 4 The molecular weight distribution Mw / Mn was 3.5. 19 F-NMR showed no peaks between -150 and 170 ppm, and no fluorine-containing aromatic rings such as pentafluorophenyl groups were detected. The evaluation results of the obtained fluororesin are shown in Table 1 and Figure 1.

[0084] [Example 2] A 30 mm diameter glass ampoule equipped with a magnetic stirrer was charged with a solution of 0.0266 g (0.000041 mol) of bis(perfluorocyclohexylcarbonyl) peroxide as an initiator dissolved in 2.7 g of FC-72, 10.0 g (0.0410 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as a monomer, 37.3 g of Zeorora-H (manufactured by Nippon Zeon Co., Ltd., 1,2,2,3,3,4,4-heptafluorocyclopentane) as a polymerization solvent, and 1.111 g (0.00931 mol) of chloroform (manufactured by Wako Pure Chemical Industries, Ltd.) as a chain transfer agent. The ampoule was then repeatedly subjected to nitrogen substitution and depressurization, and then sealed under reduced pressure (amount of chain transfer agent: 10 wt % of the total weight of the monomer and chain transfer agent). Precipitation polymerization was carried out by holding the ampoule upright at 40°C for 24 hours while stirring with a magnetic stirrer. The mixture became cloudy, and a slurry of resin precipitated in the polymerization solvent was obtained. After cooling to room temperature, the ampoule was opened, and the liquid containing the generated resin particles was filtered, washed with acetone, and vacuum dried to obtain powdered perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin (yield: 90%). The weight-average molecular weight of the resulting fluororesin was 9.2 x 10 4 The molecular weight distribution Mw / Mn was 2.7. The volume average particle size of the obtained fluororesin was 18 μm, and the powder had excellent fluidity, which was superior to that of Example 1. Solid 19 F-NMR showed no peaks between -150 and 170 ppm, and no fluorine-containing aromatic rings such as pentafluorophenyl groups were detected. The evaluation results of the obtained fluororesin are shown in Table 1 and Figure 1.

[0085] [Comparative Example 1] A 30 mm diameter glass ampoule equipped with a magnetic stirrer was charged with 0.0865 g (0.000205 mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator, 10.0 g (0.0205 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as a monomer, 40.0 g of Zeorora-H (manufactured by Nippon Zeon Co., Ltd., 1,2,2,3,3,4,4-heptafluorocyclopentane) as a polymerization solvent, and 1.111 g (0.00931 mol) of chloroform (manufactured by Wako Pure Chemical Industries, Ltd.) as a chain transfer agent. The ampoule was repeatedly subjected to nitrogen substitution by freeze degassing and depressurization, and then sealed under reduced pressure (amount of chain transfer agent: 10 wt % of the total weight of the monomer and chain transfer agent). Precipitation polymerization was carried out by holding the ampoule upright at 55°C for 24 hours while stirring with a magnetic stirrer. The resulting slurry became cloudy and contained resin precipitated in the polymerization solvent. After cooling to room temperature, the ampoule was opened, and the liquid containing the resulting resin particles was filtered, washed with acetone, and vacuum dried to obtain particulate perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin (yield: 81%). The weight-average molecular weight of the resulting fluororesin was 9.8 x 10 4 The molecular weight distribution Mw / Mn was 2.6. 19 F-NMR confirmed a peak at -163 ppm derived from a pentafluorophenyl group (fluorine-containing aromatic ring). The evaluation results of the obtained fluororesin are shown in Table 1 and Figure 1.

[0086] Comparative Example 2 A polymerization tube equipped with a stir bar was charged with 4.8 g (0.020 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as the monomer, 3 mL of dichloropentafluoropropane (AGC, AK-225) as the solvent, 0.21 g of ammonium perfluorooctanoate as the emulsifier, 0.24 g of NaHPO·7H O as the pH adjuster, 0.15 g of (NH) SO as the initiator, and 50 mL of distilled water degassed with N. The headspace above the solution was purged with N and then slightly overpressurized with N. The contents of the tube were then heated at 75 °C for 5 h while stirring with a stir bar. The resulting reaction mixture was treated with 80 mL of 6.3 M aqueous HCl to precipitate the polymer. The polymer was washed three times with 200 mL of distilled water and three times with 200 mL of acetone. Next, this polymer was placed in a vacuum oven and dried at 150°C under vacuum (150 mmHg) for 24 hours, yielding a white powdery polymer (yield: 3%). The above procedure from polymerization to drying was repeated two more times, and the resulting polymers were mixed to obtain a polymer for evaluation. The evaluation results of the resulting polymer are shown in Table 2. The weight-average molecular weight of the resulting fluororesin was 34 x 10 4 The molecular weight distribution Mw / Mn was 25. The yield was very low and the molecular weight distribution was very wide.

[0087] Comparative Example 3 A 75 mL glass ampoule was charged with 10.0 g (0.041 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as a monomer, 35 g of AK-225 as a solvent, and 0.02 g of 4,4-bis(t-butylcyclohexyl) peroxydicarbonate (NOF Corp., Perloyl TCP) as an initiator. After repeated nitrogen substitution and depressurization by freeze degassing, the ampoule was sealed under reduced pressure. The ampoule was heated at 60°C for 3 hours while shaking in a thermostatic shaker. The polymer removed from the ampoule was dried at 100°C under vacuum (150 mmHg) for 24 hours to obtain a polymer (yield: 76%). The above procedures from polymerization to drying were repeated two more times, and the resulting polymers were mixed to obtain a polymer for evaluation. The evaluation results of the resulting polymer are shown in Table 2. The weight-average molecular weight of the resulting fluororesin was 12 × 10 4 The molecular weight distribution Mw / Mn was 1.8.

[0088] [Table 1]

[0089] [Table 2]

[0090] [Reference example 1] A 75 mL glass ampoule was charged with a solution of 0.52 g (0.0012 mol) of (CFCFCOO) as initiator diluted with 52 g of FC-72 and 30.0 g (0.12 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as monomer. The ampoule was repeatedly subjected to nitrogen substitution and depressurization by freeze degassing, and then sealed under reduced pressure. Radical polymerization was carried out by holding the ampoule at 25°C for 24 hours. The ampoule was opened, and the contents were poured into a beaker containing 600 g of hexane under stirring. The solid was recovered by filtration, washed twice with acetone, and vacuum dried to obtain a bulk perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin (17% yield). The weight-average molecular weight of the resulting fluororesin was 83 × 10 4The molecular weight distribution Mw / Mn was 25. The yield was very low and the molecular weight distribution was very wide.

[0091] [Reference example 2] The resin particles obtained in Example 2 were immersed in 10 times the amount of each of the solvents at 50° C. for 5 hours, and the presence or absence of remaining resin particles was observed with the naked eye.

[0092] The organic solvents in which residual resin particles were visible to the naked eye are as follows: 1,1,2,2-Tetrafluoroethyl-2,2,2-trifluoroethyl ether, 2,2,2-trifluoroethanol, 1,1,1,3,3,3-hexafluoroisopropanol, 1,2,2,3,3,4,4-heptafluorocyclopentane, chloroform.

[0093] The mixture was then cooled to 25°C, filtered, and rinsed with the solvent to remove the resin particles. The resin particles were then washed twice with 10 times the amount of acetone and vacuum dried. The recovery rate was calculated from the dry weight, and in all cases the recovery rate was 90% or higher. The filtrate obtained above was distilled off, and the solid content in the filtrate was determined. The solid content in the filtrate was less than 10% of the resin particles used. From these results, it was confirmed that the weight loss rate of the resin weight was less than 10% by weight.

[0094] As shown in Examples 1 and 2, the fluororesin of the present invention has a lower yellowness in thick-walled melt-molded articles (φ10 mm × H17 mm, in a test tube at 280°C for 24 hours) than Comparative Example 1, and yellowing during melt molding of thick molded articles is suppressed.

[0095] The method for producing a fluororesin of the present invention has a higher yield than the method of Reference Example 1, and as shown in Examples 1 and 2, a fluororesin can be produced in a yield of 80% or more, and depending on the conditions, a fluororesin can be produced in a yield of 85% or more, or even 90% or more.

[0096] The fluororesin obtained by the method for producing a fluororesin of the present invention has an improved yellowness when heated in a test tube at 280°C for 24 hours, and has a narrower molecular weight distribution than the method of Reference Example 1, with a molecular weight distribution Mw / Mn of 5 or less, and depending on the conditions, 4 or less, or even 3 or less. [Industrial Applicability]

[0097] The fluororesin of the present invention is useful in fields related to fluororesins.

Claims

1. A fluororesin containing a residue unit represented by the following formula (1), having a molecular weight distribution Mw / Mn of 1.2 to 8, and having an end represented by the following formula (6) directly attached to the polymer, which, when dissolved in perfluorohexane to form a 10 wt % perfluorohexane solution, has a transmittance of 50% or more as measured at an optical path length of 10 mm and a wavelength of 275 nm: A thick-walled melt-molded product of the fluororesin (a cylindrical molded body having a diameter of 10 mm and a height of approximately 17 mm, molded by heating and melting in a test tube at 280°C for 24 hours) has a yellowness index of 4 or less. 【Chemical 1】 (In formula (1), Rf １ , Rf ２ , Rf ３ , Rf ４ each independently represents one of the group consisting of a fluorine atom, a linear perfluoroalkyl group having 1 to 7 carbon atoms, a branched perfluoroalkyl group having 3 to 7 carbon atoms, or a cyclic perfluoroalkyl group having 3 to 7 carbon atoms, wherein the perfluoroalkyl group may have an etheric oxygen atom, and Rf １ , Rf ２ , Rf ３ , Rf ４ may be linked to each other to form a ring having 4 to 8 carbon atoms, and the ring may contain an etheric oxygen atom. 【Chemistry 2】 (In formula (6), Rf １５ , Rf １６ each independently represents a perfluoroalkyl group having 1 to 20 carbon atoms, and the perfluoroalkyl group may have an etheric oxygen atom; and Rf １５ and Rf １６ may be linked to each other to form a ring having 4 to 8 carbon atoms, and the ring may contain an etheric oxygen atom.

2. 2. The fluororesin according to claim 1, which, when dissolved in perfluorohexane to form a 10 wt % perfluorohexane solution, does not show a minimum peak in the transmission spectrum at an optical path length of 10 mm and a wavelength of 250 to 300 nm.

3. 3. The fluororesin according to claim 1, wherein the fluororesin is in powder form and has a volume average particle size of 1 to 1000 μm.

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