WO2024257865A1 - Copolymer, composition, and molded body - Google Patents

Abstract

The present invention provides: a copolymer which is capable of forming a molded body that is excellent in terms of the degree of yellowing, the elongation and the non-defective rate; a composition; and a molded body.　A copolymer according to the present invention contains a unit based on tetrafluoroethylene, a unit based on ethylene, and one or both of a unit based on a compound represented by formula (1) and a unit based on a compound represented by formula (2). The total content of the unit based on tetrafluoroethylene and the unit based on ethylene is 80% by mole to 96.8% by mole with respect to all units contained in the copolymer. The content of the unit based on tetrafluoroethylene is not less than 49.0% by mole but less than 56.0% by mole with respect to the total content of the unit based on tetrafluoroethylene and the unit based on ethylene. The content of the unit based on a compound represented by formula (1) or a compound represented by formula (2) is 3.2% by mole to 4.0% by mole with respect to all units contained in the copolymer. The melt flow rate of the copolymer is 25-50 g/10 minutes as measured under the conditions of a temperature of 297°C and a load of 49 N in accordance with ASTM D3159.　Formula (1): CZ₂=CX(CF₂)_mY Formula (2): CF₂=CF-O-(CF₂)_nF

Description

Copolymer, composition and molded article

The present invention relates to a copolymer, a composition, and a molded article.

Ethylene/tetrafluoroethylene copolymer (hereinafter also referred to as "ETFE") is excellent in heat resistance, weather resistance, electrical insulation, non-adhesiveness, water repellency, oil repellency, etc., and is characterized by high moldability and mechanical strength among fluororesins. Therefore, a variety of molded products such as electric wire coverings, tubes, sheets, films, filaments, pump casings, joints, packings, linings, coatings, etc. are manufactured by melt molding methods such as extrusion molding, blow molding, injection molding, and rotational molding.
For example, Patent Document 1 discloses a polymer composition containing a copolymer having ethylene repeating units, tetrafluoroethylene repeating units, and other repeating units.

Chinese Patent Publication No. 104151754

When ETFE is used as a constituent material of a molded article, it is required that it has excellent properties such as mechanical strength, heat resistance, and chemical resistance, as well as excellent appearance and quality stability of the molded article.
The present inventors have evaluated a molded article formed using the ETFE described in Patent Document 1 and have found that there is room for improvement in terms of yellowness, elongation and yield rate.

The present invention aims to provide a copolymer capable of forming a molded article having excellent yellowness, elongation, and yield rate. It also aims to provide a composition containing the copolymer, and a molded article obtained by molding the copolymer.

As a result of extensive research into the above-mentioned problems, the present inventors discovered that a molded article with excellent yellowness, elongation and yield rate can be formed by using a copolymer containing units based on tetrafluoroethylene, units based on ethylene, and units based on a compound represented by formula (1) or a compound represented by formula (2) described below, in which the content of each unit is within a specified range and the copolymer has a melt flow rate of 25 to 50 g/10 min, and thus arrived at the present invention.

That is, the inventors discovered that the above problems can be solved by the following configuration.
[1]
A copolymer comprising units based on tetrafluoroethylene, units based on ethylene, and either or both of units based on a compound represented by formula (1) described later and units based on a compound represented by formula (2) described later, wherein the total content of the units based on tetrafluoroethylene and the units based on ethylene is 80.0 to 96.8 mol % relative to the total content of the units based on tetrafluoroethylene and the units based on ethylene, the content of the units based on tetrafluoroethylene is 49.0 mol % or more and less than 56.0 mol % relative to the total content of the units based on tetrafluoroethylene and the units based on ethylene, the content of the units based on a compound represented by formula (1) described later or the compound represented by formula (2) described later is 3.2 to 4.0 mol % relative to the total units included in the copolymer, and the melt flow rate measured in accordance with ASTM D3159 under conditions of a temperature of 297°C and a load of 49 N is 25 to 50 g/10 min.
[2]
The copolymer according to [1], which comprises units based on the tetrafluoroethylene, units based on the ethylene, and units based on a compound represented by formula (1), and the content of the units based on the compound represented by formula (1) is 3.2 to 4.0 mol% based on all units contained in the copolymer.
[3]
A composition comprising the copolymer according to [1] or [2].
[4]
A solid composition comprising the copolymer according to [1] or [2], wherein the amount of TOC (total organic carbon) eluted is 1,000 to 63,000 μg/ ^cm2 .
[5]
A solid composition comprising the copolymer according to [1] or [2] and having a water content of 0.02 to 0.8% by mass.
[6]
A molded article obtained by molding the copolymer according to [1] or [2].
[7]
A molded article obtained by molding the composition according to [3].
[8]
A molded article obtained by molding the solid composition according to [4].

The present invention provides a copolymer capable of forming a molded article having excellent yellowness, elongation, and yield rate. The present invention also provides a composition containing the copolymer, and a molded article obtained by molding the copolymer.

The terms used in the present invention have the following meanings.
A numerical range expressed using "to" means a range that includes the numerical values before and after "to" as the lower and upper limits.

The term "unit" refers collectively to an atomic group derived from one molecule of the above-mentioned monomer that is formed directly by polymerization of the monomer, and an atomic group obtained by chemically converting a part of the above-mentioned atomic group. In the following, in some cases, a unit derived from an individual monomer will be referred to by the name of the monomer with "unit" added.
The "TFE unit" is a unit based on tetrafluoroethylene in the copolymer, the "E unit" is a unit based on ethylene in the copolymer, and the "A unit" is a unit based on a compound represented by formula (1) or (2) described below.

[Copolymer]
The copolymer of the present invention (hereinafter also referred to as "the present copolymer") contains E units, TFE units, and A units within respective predetermined ranges. The present copolymer has a melt flow rate of 25 to 50 g/10 min measured under conditions of a temperature of 297° C. and a load of 49 N in accordance with ASTM D3159.

The copolymer can form a molded article having excellent yellowness, elongation and yield rate. Although the details of the reason for this are not yet clear, it is presumed to be due to the following reasons.
One of the reasons why the present copolymer can form a molded article having excellent properties as described above is believed to be that a copolymer having a content of A units based on a compound represented by formula (1) or a compound represented by formula (2) described below of 3.2 to 4.0 mol % relative to all units contained in the copolymer and a melt flow rate of 25 to 50 g/10 min is used.
That is, it is presumed that by having a melt flow rate of 25 g/10 min or more, the melt flow rate is not too low, the flexibility is good, and cracks are unlikely to occur, so that the elongation of the molded article can be improved.
It is presumed that by having a melt flow rate of 50 g/10 min or less, the melt flow rate is not too high and the copolymer is less likely to decompose, thereby suppressing voids in the molded body and improving the yield rate of the molded body.
In addition, since the content of A units is 3.2 mol % or more based on the total units contained in the copolymer, the content of A units is not too small in a copolymer having a relatively high melt flow rate, so that it is presumed that the decrease in transparency due to milky white coloring of the molded body can be suppressed and the yellowness of the molded body can be suppressed low.
In addition, since the content of A units is 4.0 mol % or less based on the total units contained in the copolymer, the content of A units is not too high, and the copolymer constituting the molded body is less likely to undergo various decomposition reactions even at high temperatures, which is presumably why the yield rate of the molded body has been improved.
It is presumed that by specifying the content of A units and the melt flow rate in this way, molded articles excellent in yellowness index, elongation and non-defective product rate were obtained.

This copolymer contains TFE units based on tetrafluoroethylene, E units based on ethylene, and A units based on a compound represented by formula (1) or a compound represented by formula (2).

CZ ₂ =CX(CF ₂ ) _m Y Formula (1)
CF ₂ =CF-O-(CF ₂ ) _n F Formula (2)
In formula (1), X, Y and Z each independently represent a hydrogen atom or a fluorine atom, and m represents an integer of 2 to 6.
In formula (2), n represents an integer of 1 to 6.

In the compound represented by formula (1), X and Z are preferably a hydrogen atom in terms of polymerizability.
From the viewpoint of heat resistance, Y is preferably a fluorine atom.
m is preferably an integer of 2 to 6, and more preferably an integer of 4.

The compound represented by formula (1) is _{preferably CH2} =CH( _CF2 ) _2F , _CH2 =CH( _CF2 ) _4F , _CH2 =CH( _CF2 ) _6F , _CH2 =CF( _CF2 ) _4F , or _CH2 =CF( _CF2 ) _3H , and more preferably _CH2 =CH( _CF2 ) _4F (hereinafter also referred to as "PFBE").

Specific examples of the compound represented by formula (2) include CF ₂ ═CF-O-(CF ₂ ) F, CF ₂ ═CF-O-(CF ₂ ) ₂ F, CF ₂ ═CF-O-(CF ₂ ) ₃ F, CF ₂ ═CF-O-(CF ₂ ) ₄ F, CF ₂ ═CF-O-(CF ₂ ) ₅ F, and CF ₂ ═CF-O-(CF ₂ ) ₆ F. Among these, CF ₂ ═CF-O-(CF ₂ ) ₃ F, which corresponds to the compound in which n is 3, is preferred.

The present copolymer may contain, as A units, either a unit based on a compound represented by formula (1) (hereinafter also referred to as "A1 units") or a unit based on a compound represented by formula (2) (hereinafter also referred to as "A2 units"), or may contain both A1 units and A2 units.
That is, when the present copolymer contains both A1 units and A2 units, the "content of A units" means the total content of A1 units and the content of A2 units.

The content of A units is 3.2 to 4.0 mol % based on the total units contained in the copolymer.
When the content of A units is 3.2 mol % or more based on the total units contained in the copolymer, a molded article having excellent yellowness, elongation and haze can be formed.
In addition, by controlling the content of A units to 4.0 mol % or less based on the total units contained in the copolymer, a molded product having an excellent yield rate, suppressed deterioration at high temperatures, and excellent long-term mechanical stability can be formed.
The content of A units is preferably 3.4 to 3.9 mol % based on the total units contained in the copolymer, in that a well-balanced yellowness index and a good yield rate are obtained.

As the present copolymer, a copolymer containing TFE units, E units and A1 units, or a copolymer containing TFE units, E units and A2 units is preferred, and a copolymer having TFE units, E units and A1 units is more preferred from the viewpoint of excellent long-term bending resistance.
When the present copolymer is a copolymer containing TFE units, E units and A1 units, the content of A1 units is 3.2 to 4.0 mol% based on the total units contained in the present copolymer, and from the above-mentioned viewpoints, it is preferably 3.4 to 3.9 mol%.
When the present copolymer is a copolymer containing TFE units, E units, and A2 units, the content of the A2 units is 3.2 to 4.0 mol% based on the total units contained in the present copolymer, and from the above-mentioned viewpoints, it is preferably 3.3 to 3.8 mol%.

In the present copolymer, the total content of TFE units and E units is 80.0 to 96.8 mol % based on all units contained in the present copolymer.
The total content of TFE unit and E unit is preferably 85.0 mol% or more, more preferably 88.0 mol% or more, from the viewpoint of excellent durability against repeated load.The total content of TFE unit and E unit is preferably 96.6 mol% or less, from the viewpoint of excellent surface smoothness of molded article.

In the present copolymer, the content of the TFE units is 49.0 mol % or more and less than 56.0 mol % based on the total content of the TFE units and the E units.
The content of TFE units is preferably from 50.0 mol % to less than 56.0 mol %, and more preferably from 52.0 mol % to less than 56.0 mol %, based on the total content of TFE units and E units, from the viewpoint of excellent heat resistance.

The content of TFE units is preferably 40.0 to 54.0 mol%, more preferably 45.0 to 53.9 mol%, and particularly preferably 50.0 to 53.5 mol%, based on the total units contained in the copolymer. If the content is equal to or greater than the lower limit, the heat resistance of the molded article will be superior, and if the content is equal to or less than the upper limit, the mechanical properties of the molded article will be superior.

The content of E units is preferably 36.0 to 49.0 mol%, more preferably 40.0 to 48.0 mol%, and particularly preferably 42.0 to 47.0 mol%, based on the total units contained in the copolymer. If the content is equal to or greater than the lower limit, the mechanical properties of the molded article will be superior, and if the content is equal to or less than the upper limit, the heat resistance of the molded article will be superior.

The present copolymer may contain units based on other monomers than tetrafluoroethylene, ethylene, the compound represented by formula (1) and the compound represented by formula (2).
Specific examples of other monomers include:
Fluoroolefins (vinyl fluoride, vinylidene fluoride, trifluoroethylene, hexafluoropropylene, hexafluoroisobutylene, etc., excluding compounds represented by formula (1) and formula (2)); CF ₂ ═CFORf ¹ SO ₂ X ¹ (wherein Rf ¹ is a perfluoroalkylene group having 1 to 10 carbon atoms which may contain an oxygen atom between the carbon atoms, and X ¹ is a halogen atom or a hydroxyl group); CF ₂ ═CFORf ² CO ₂ X ² (wherein Rf ² is a perfluoroalkylene group having 1 to 10 carbon atoms which may contain an oxygen atom between the carbon atoms, and X ² is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms); CF ₂ ═CF(CF ₂ )pOCF═CF ₂ (wherein p is 1 or 2); fluorine-containing monomers having a ring structure (perfluoro(2,2-dimethyl-1,3-dioxole), 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole, perfluoro(2-methylene-4-methyl-1,3-dioxolane), etc.); and itaconic acid, itaconic anhydride, citraconic acid and citraconic anhydride.
When the present copolymer contains units based on other monomers, the content of the units based on other monomers is preferably 2.0 mol % or less, more preferably 1.0 mol % or less, based on all units contained in the present copolymer.
The present copolymer is preferably one comprising TFE units, E units and A units, and more preferably one comprising TFE units, E units and A1 units.

<Melt flow rate>
The melt flow rate (hereinafter, also referred to as "MFR") of the present copolymer is 25 to 50 g/10 min.
When the copolymer has an MFR of 25 g/10 min or more, it is possible to form a molded article which is excellent in elongation, light transmittance, yellowness index and yield rate.
Furthermore, since the copolymer has an MFR of 50 g/10 min or less, it is possible to form a molded article having an excellent yield rate and excellent high-temperature sealability.
The MFR of the present copolymer is preferably from 27 to 50 g/10 min in view of the good balance between elongation and the rate of non-defective products.
A specific example of a method for controlling the MFR of the present copolymer within the above range is a method for adjusting the molecular weight of the present copolymer. The higher the molecular weight of the present copolymer, the smaller the MFR.
The MFR of the present copolymer means the mass of the present copolymer flowing out of an orifice having a diameter of 2 mm and a length of 8 mm in 10 minutes, measured under conditions of a temperature of 297° C. and a load of 49 N in accordance with ASTM D3159.

<Melting Point>
The melting point of the present copolymer is preferably 220° C. or higher, more preferably 225° C. or higher, and particularly preferably 230° C. or higher, in view of superior durability against repeated load.
The melting point of the present copolymer is preferably 280° C. or lower, more preferably 270° C. or lower, and particularly preferably 260° C. or lower, in view of excellent moldability of the present copolymer.
Specific examples of the method for adjusting the melting point of the present copolymer to fall within the above range include a method of lowering the polymerization temperature during the production of the present copolymer, and a method of adjusting the content of A units in the present copolymer.
The melting point of the present copolymer is the temperature corresponding to the endothermic peak when the present copolymer is heated at a rate of 10° C./min in an air atmosphere using a differential scanning calorimeter.

<Production Method>
The present copolymer can be produced by using the above-mentioned monomers (ethylene, tetrafluoroethylene, and one or both of the compound represented by formula (1) and the compound represented by formula (2)) by a known method such as bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, etc., among which, it is preferably produced by solution polymerization.
In the production of the present copolymer, in addition to the above-mentioned monomers, a polymerization initiator, a polymerization medium, a chain transfer agent, etc. can be used.

The polymerization initiator is preferably a radical polymerization initiator having a half-life of 10 hours at a temperature of 0 to 100° C., and particularly preferably a radical polymerization initiator having a temperature of 20 to 90° C. Specific examples of the polymerization initiator include various polymerization initiators exemplified in WO 2013/015202.
The polymerization initiator may be used alone or in combination of two or more kinds.
The amount of the polymerization initiator used is preferably 0.01 to 0.9 parts by mass, particularly preferably 0.05 to 0.5 parts by mass, based on 100 parts by mass of the monomer used.

The polymerization medium may be a perfluorocarbon, a hydrofluorocarbon, a hydrofluoroether, etc. Specific examples of the polymerization medium include the polymerization media exemplified in WO 2013/015202.
The polymerization medium may be used alone or in combination of two or more kinds.
The amount of the polymerization medium used is preferably 5 times or more, more preferably 7 times or more, by mass ratio to the amount of the monomers used, and is preferably 20 times or less, more preferably 17 times or less.

As the chain transfer agent, from the viewpoint of a large chain transfer constant and a small amount to be added, preferred are alcohols such as methanol, ethanol, 2,2,2-trifluoroethanol, 2,2,3,3-tetrafluoropropanol, 1,1,1,3,3,3-hexafluoroisopropanol, 2,2,3,3,3-pentafluoropropanol, etc.; hydrocarbons such as n-pentane, n-hexane, cyclohexane, etc.; hydrofluorocarbons such as CF ₂ H _2, etc.; ketones such as acetone, etc.; mercaptans such as methyl mercaptan, etc.; esters such as methyl acetate, ethyl acetate, etc.; ethers such as diethyl ether, methyl ethyl ether, etc.
Among them, at least one selected from the group consisting of alcohols, hydrocarbons and hydrofluorocarbons is preferred from the viewpoint of higher chain transfer constant and higher stability of the end group of the copolymer, at least one selected from the group consisting of alcohols and hydrocarbons is more preferred, and alcohols are particularly preferred. Among the alcohols, methanol or ethanol is particularly preferred. Among them, methanol is particularly preferred from the viewpoint of reactivity and availability. Two or more chain transfer agents may be used.
The amount of the chain transfer agent used is preferably 0.001 times or more, more preferably 0.005 times or more, based on the amount of the monomer used, in terms of mass ratio, and is preferably 5 times or less, more preferably 4 times or less.

The polymerization temperature is preferably 15 to 60° C., more preferably 20 to 58° C., and particularly preferably 25 to 55° C. If the polymerization temperature is 15° C. or higher, the polymerizability is excellent. If the polymerization temperature is 60° C. or lower, the melting point of the present copolymer can be improved.
The polymerization pressure is preferably from 0.5 to 3.0 MPa, particularly preferably from 0.9 to 2.5 MPa.
The polymerization time is preferably from 1 to 12 hours.

[Composition]
The composition of the present invention (hereinafter, also referred to as "the present composition") contains the above-mentioned present copolymer. Since the present composition contains the present copolymer, by using the present composition, a molded article excellent in yellowness index, elongation and non-defective product rate can be formed.
The content of the present copolymer is preferably from 50% by mass to less than 100% by mass, more preferably from 70% by mass to less than 100% by mass, and particularly preferably from 90% by mass to less than 100% by mass, based on the total mass of the present composition.

[Solid Composition]
The solid composition of the present invention (hereinafter also referred to as "the solid composition") contains the copolymer, and the amount of TOC (total organic carbon) eluted relative to the surface area of the solid composition is 1,000 to 63,000 μg/ ^cm2 . Since the adhesive strength after a hot water resistance test is high, the amount of TOC eluted is preferably 50,000 μg/cm2 or ^less , and more preferably 30,000 μg/cm2 or ^less . Since the tensile strength after a heat aging test is high, the amount of TOC eluted is preferably 2,000 μg/ ^cm2 or more, and more preferably 5,000 μg/ ^cm2 or more.
Specific examples of methods for controlling the TOC elution amount of the present solid composition within the above range include methods of adjusting the purity of water used in granulating the present copolymer or the water content of the copolymer.

The solid composition contains the copolymer, and the water content relative to the mass of the solid composition is preferably 0.02 to 0.8% by mass. The water content is preferably 0.5% by mass or less, and more preferably 0.3% by mass or less, since the amount of TOC eluted is low. The water content is preferably 0.03% by mass or more, and more preferably 0.04% by mass or more, since the tensile strength after a heat aging test is high.
A specific example of a method for controlling the water content of the present solid composition to fall within the above range is to extend the time for which the present copolymer is kept at 100° C. or higher during drying after granulation.

<Other Ingredients>
The present composition may contain other components in addition to those described above. Specific examples of such other components include resins other than the present copolymer, heat stabilizers, antioxidants, colorants, ultraviolet absorbers, fillers, crosslinking agents, crosslinking assistants, and organic peroxides.
When the present composition contains other components, the content of the other components is preferably 0.0000001 to 70 parts by mass, more preferably 0.0000005 to 60 parts by mass, and particularly preferably 0.000001 to 50 parts by mass, per 100 parts by mass of the present copolymer in the present composition.

The method for producing this composition includes melt-kneading this copolymer with the above-mentioned components, which are used as necessary, by a known method.

[Molded body]
The molded article of the present invention is obtained by molding the present copolymer or the present composition. The present molded article contains the present copolymer and is therefore excellent in yellowness index, elongation and yield rate.
Specific examples of the molding method include injection molding, extrusion molding, blow molding, press molding, rotational molding, and electrostatic coating. As the molding method of the molded body, press molding or injection molding is preferable. Injection molding is more preferable because it can obtain an injection molded body with a beautiful appearance without corroding the mold used for molding.

Specific examples of molded articles of the present invention include nuts, bolts, joints, films, bottles, gaskets, wire coatings, tubes, hoses, pipes, valves, sheets, seals, packing, tanks, rollers, containers, cocks, connectors, filter housings, filter cages, flow meters, pumps, wafer carriers, and wafer boxes.

The present copolymer, the present composition or the above-mentioned molded article can be used for the following applications.
Food packaging films, lining materials for fluid transfer lines used in food manufacturing processes, packing materials, sealing materials, and fluid transfer components for food manufacturing equipment such as sheets;
Drug stoppers, packaging films, lining materials for fluid transfer lines used in drug manufacturing processes, packing materials, sealing materials, and drug transfer components such as sheets;
Inner lining components for chemical tanks and piping in chemical plants or semiconductor factories;
Fuel transfer components such as O-rings, square rings, tubes, packing, valve core materials, hoses, and seals used in automobile fuel systems and peripheral devices, as well as hoses and seals used in automobile AT devices;
Carburetor flange gaskets, shaft seals, valve stem seals, sealing materials, hoses, etc. used in automobile engines and peripheral devices, as well as other automobile parts such as automobile brake hoses, air conditioner hoses, radiator hoses, and electric wire covering materials;
Chemical liquid transfer components for semiconductor manufacturing equipment, such as O-rings, square rings, tubes, packings, valve core materials, hoses, seal materials, rolls, gaskets, diaphragms, and joints;
Paint and ink components such as paint rolls, hoses, tubes, and ink containers for painting equipment;
Tubes for food and beverages, hoses for food and beverages, and other tubes, hoses, belts, packings, and food and beverage transport components such as joints, food packaging materials, and glass cooking equipment;
Waste liquid transport components such as tubes and hoses for transporting waste liquid;
Components for transporting high-temperature liquids, such as tubes and hoses for transporting high-temperature liquids;
Steam piping components such as steam piping tubes and hoses;
Anticorrosive tapes for piping, such as tapes wrapped around piping on ship decks, etc.;
Various coating materials such as electric wire coating materials, optical fiber coating materials, transparent front coating materials and back coating materials provided on the light incident surface of photovoltaic elements of solar cells;
Sliding members such as diaphragms of diaphragm pumps and various packings;
Agricultural films, carrier films for fuel cells, and weather-resistant covers for various roofing materials and side walls;
Interior materials used in the building industry, and glass covering materials such as non-combustible fire-resistant safety glass;
Lining material for laminated steel sheets used in the home appliance field, etc.
Among these, the molded article of the present invention is particularly suitable for use as a chemical solution transport member and an industrial film because of its excellent yellowness index, elongation and yield rate.

The present invention will be described in detail below with reference to examples. Examples 1 to 11 are working examples, and Examples 12 to 18 are comparative examples. However, the present invention is not limited to these examples.
The various measurement and evaluation methods are as follows.

[Proportion of each unit]
The content (mol %) of each unit in the copolymer was calculated by ¹⁹ F-NMR measurement, except for the content of E units in the copolymer, which was calculated by ¹ H-NMR measurement and ¹³ C-NMR measurement.

[MFR (Melt Flow Rate)]
Using a melt indexer (manufactured by Technoseven Co., Ltd.), the mass (g) of the copolymer flowing out from an orifice having a diameter of 2 mm and a length of 8 mm in 10 minutes was measured under conditions of a temperature of 297° C. and a load of 49 N in accordance with ASTM D3159, and this was taken as MFR (g/10 min).

[Melting point]
The melting point (°C) of the copolymer was determined from the endothermic peak observed when the copolymer was heated to 300°C at a rate of 10°C/min in an air atmosphere using a differential scanning calorimeter (product name "DSC7020", manufactured by Hitachi High-Tech Science Corporation).

<Film Forming>
The copolymer obtained in each example was press molded at a temperature within the range of the melting point of the copolymer + 50°C ± 20°C (for example, 280°C to 320°C when the melting point of the copolymer is 250°C) to obtain a film having a thickness of 200 μm. The press molding was performed using a heated press machine ("SA-301" manufactured by Tester Sangyo Co., Ltd.).
The obtained films were subjected to the following evaluation tests (excluding the evaluation test for the non-defective product rate).

<Heat resistance>
A dumbbell -shaped test piece as defined in JIS K6301 No. 3 was cut out from the obtained film having a thickness of 1 mm. The tensile elongation (unit: %) of this test piece was measured in accordance with the method of ASTM D-3159 using a Strograph (manufactured by Toyo Seiki Seisakusho Co., Ltd.) by setting the distance between the gripping jigs to 35 mm and pulling the test piece at a pulling speed of 200 mm/min in a room temperature (temperature 23±2° C.) environment.

The test piece was placed in a gear oven (forced circulation air heating aging tester) (manufactured by Toyo Seiki Seisakusho Co., Ltd.) and subjected to heat exposure treatment. The temperature for the heat exposure treatment was set to 250°C, and heat treatment was performed for 24 hours after placement. The tensile elongation of the test piece after heat treatment was measured in the same manner as above. The tensile elongation percentage after heat treatment was calculated, assuming that the tensile elongation before heat treatment was 100%, and was evaluated according to the following criteria.

(Evaluation Criteria for Tensile Elongation)
○: Tensile elongation after heat aging test is 50% or more △: Tensile elongation after heat aging test is 15% or more and less than 50% ×: Tensile elongation after heat aging test is less than 15%

<Light transmittance>
The light transmittance of the film having a thickness of 200 μm was measured at a wavelength of 300 nm using a spectrophotometer (Shimadzu Corporation, "UV-2200").
From the measured light transmittance values, the light transmittance of each film was evaluated based on the following evaluation criteria.

(Light transmittance evaluation standard)
○: Light transmittance is more than 91%.
△: Light transmittance is 90% or more and 91% or less.
×: Light transmittance is less than 90%.

<Yellowness>
The YI (Yellow Index) value of a film having a thickness of 200 μm was measured using a color difference meter (ZE-2000 manufactured by Nippon Denshoku Industries Co., Ltd.).
From the measured YI value, the yellowness of each film was evaluated according to the following evaluation criteria: A larger YI value indicates a higher yellowness of the film.

(Yellowness Evaluation Criteria)
◯: YI value is less than 2.0.
×: YI value is 2.0 or more.

<HAZE>
The haze (cloudiness, unit: %) of a film having a thickness of 200 μm was measured using a haze meter (manufactured by Nippon Seimitsu Kogaku Co., Ltd., model: SEP-T) in accordance with JIS K7105.
From the measured haze value, the haze of each film was evaluated according to the following evaluation criteria.

(Haze evaluation criteria)
Good: Haze is less than 3.0%.
Δ: Haze is 3.0% or more and less than 4.0%.
×: Haze is 4.0% or more.

<Stretch>
A film having a thickness of 1 mm was press-molded according to the above molding method, and a dumbbell-shaped test piece defined in ASTM-D638 Type V was cut out from the obtained film. The obtained test piece was subjected to a tensile creep test in which the test piece was pulled under conditions of an initial gauge length of 25.4 mm and a tensile speed of 200 mm/min using a Strograph (manufactured by Toyo Seiki Seisakusho Co., Ltd.) in an environment of a temperature of 175°C. The tensile creep test was continued until the test piece broke, and the value of the gauge length (unit: mm) when the test piece broke was measured.
From the measured distance between the gauge marks at the time of breakage, the elongation of each film was evaluated based on the following evaluation criteria.

(Elongation Evaluation Criteria)
○: The distance between the gauge lines at the time of breakage is 190 mm or more. ×: The distance between the gauge lines at the time of breakage is less than 190 mm.

<Folding resistance>
According to ASTM D2176, a folding fatigue test was carried out by the MIT method, which is known as a method for evaluating stress crack resistance. First, a film having a thickness of 0.23 mm was press-molded according to the above molding method, and a rectangular test piece having a width of 12.5 mm and a length of 130 mm was cut out from the obtained film. The obtained test piece was mounted on an MIT folding fatigue tester (manufactured by Toyo Seiki Seisakusho Co., Ltd.), and the test piece was bent under the conditions of a load of 1.25 kg, a bending angle of 135 degrees on the left and right, and a bending frequency of 175 times/min, and the number of times the test piece was bent until it was broken (folding endurance number) was measured.
The folding resistance of each film was evaluated based on the measured number of folding times and in accordance with the following evaluation criteria. A higher number of folding times indicates better folding resistance.

(Evaluation Criteria for Folding Endurance)
○: The number of times that the folding can be performed is 200,000 or more. △: The number of times that the folding can be performed is 100,000 or more and less than 200,000. ×: The number of times that the folding can be performed is less than 100,000.

<Quality rate>
An injection molding machine ("ROBOSHOT α-50C" manufactured by FANUC) was prepared for producing an injection molded article. As the mold for the injection molding machine, a mold engraved to obtain a cylindrical molded article with design dimensions of an outer diameter of 25 mm, an inner diameter of 20 mm, and a height of 20 mm was used, and as the gate, a tunnel gate with a gate tip diameter of 1.0 mm was used.
Using the above-mentioned injection molding machine, the copolymers obtained in each example were injection molded to obtain molded bodies under molding conditions of a cylinder temperature of 350°C, a mold temperature of 150°C, an injection speed of 20 mm/sec, a dwell pressure of 78.4 MPa, a dwell time of 3 sec, and a cooling time of 30 sec.
The surfaces of the obtained molded bodies were visually observed, and molded bodies in which neither irregularities nor holes were found on the surface were judged to be good products, while molded bodies in which at least one of irregularities and holes was found on the surface were judged to be defective products.
The above injection molding was performed 1000 shots, and the above visual observation and judgment were performed on the resulting 1000 evaluation injection molded bodies. The ratio of the number of molded bodies judged to be defective to the total number of evaluation injection molded bodies (non-defective product rate, unit: %) was calculated, and the non-defective product rate was evaluated based on the following criteria.

(Evaluation criteria for non-defective product rate)
Good: The rate of good products is 97% or more. Good: The rate of good products is 95% or more but less than 97%. Bad: The rate of good products is less than 95%.

<TOC elution amount>
The amount of TOC (total organic carbon) eluted was measured in accordance with SEMI F57 "Specification for polymeric materials and components for use in ultrapure water and chemical supply systems."
30 g of a sample (solid composition obtained in the Example) and a PFA container to be used were pre-washed with ultrapure water in accordance with SEMI F40.
30 g of the pre-washed sample was placed in a pre-washed PFA container, 100 mL of ultrapure water was poured into it to completely immerse it, and the container was sealed and subjected to elution at 85° C.±3° C. for 7 days.
The concentration of each component in the eluate was measured using a TOC-L CPH (manufactured by Shimadzu Corporation) to determine the amount of elution relative to the surface area.

<Moisture content>
The moisture content was measured by the following procedure.
Using an infrared moisture meter "FD610" (Kett Electric Laboratory), the moisture content was measured from the mass loss rate before and after the test under conditions of a drying temperature of 140°C, a time static mode of 10 minutes, and a sample (solid composition obtained in the Examples) mass of 100 g.

[Evaluation test]
<Production of Painted Test Pieces>
A SUS304 stainless steel plate measuring 50 mm in length, 150 mm in width and 2 mm in thickness was baked at 400°C for 1 hour, and then its surface was sandblasted with alumina particles ("White Fused Alumina 50A (product name)" manufactured by Pacific Random Co., Ltd.) and the blasted powder was removed with an air gun to obtain a substrate. The copolymer obtained in the examples was pulverized to an average particle size of 80 to 120 μm, electrostatically coated on the substrate, and baked in an oven at 275°C for 15 minutes. The coating process and the baking process were each performed four times, and a coated article was obtained in which a coating layer made of powder with a thickness of about 250 μm was formed on the substrate.

<Hot water resistance test (PCT peel test)>
The coating film formed on the coating test piece was cut with a cutter knife in a lateral direction at intervals of 10 mm. At one end of the coating test piece where there was no primer layer, the outermost layer and the topcoat layer were peeled off from the substrate to obtain a gripping area. After treating for 24 hours at 130°C in a pressure cooker (high-temperature steam pressure cooker), the gripping area was fixed to the chuck of a tensile tester, and the 90° peel strength (unit: N/cm) was measured at a pulling speed of 50 mm/min.
Based on the measured value, the adhesive strength was evaluated according to the following criteria.

(Adhesive Strength Evaluation Criteria)
○: 1.5 N/cm or more ×: less than 1.5 N/cm

[Example 1]
1,167 g of a fluorine-based organic solvent (ASAHIKLIN (registered trademark) AE-3000, manufactured by AGC Corporation, CF ₃ CH ₂ OCF ₂ CF ₂ H), 12.8 g of CH ₂ ═CH(CF ₂ ) ₄ F (PFBE), and 1.8 g of methanol were charged into a pre-degassed polymerization tank equipped with a stirrer and having an internal volume of 1.2 L. The solution in the polymerization tank was heated to 72° C. (polymerization temperature), and 180 g of a mixed gas of TFE/ethylene=89/11 (molar ratio) was then charged, after which the pressure in the polymerization tank was increased to 1.5 MPa [gauge].
A polymerization initiator solution of 12.2 mL of tert-butyl peroxypivalate dissolved in AE-3000 at a concentration of 1% by mass was initially charged, and polymerization was carried out. In addition, a mixed gas of TFE/ethylene = 54/46 (molar ratio) was continuously charged so that the pressure in the polymerization tank during the polymerization reaction was maintained at 1.5 MPa [gauge]. In addition, PFBE was continuously charged in an amount equivalent to 3.9 mol% relative to the total mole number of TFE and ethylene charged during polymerization.
When the amount of TFE/ethylene introduced reached 110 g, the polymerization was terminated to obtain Copolymer 1 of Example 1.
The composition of copolymer 1 was TFE unit/E unit/PFBE unit (molar ratio) = 52.4/43.7/3.9. The "PFBE unit" is a unit based on _CH2 =CH( _CF2 ) _4F of each copolymer. The MFR of copolymer 1 was 25g/10min, and the melting point was 234°C.
Pure water was added to the obtained copolymer 1, and the mixture was heated with stirring to remove the solvent. Next, water was removed from the mixture of pure water and copolymer 1, and the mixture was dried at a drying temperature of 100° C. or higher for 3.0 hours to obtain solid composition 1. The TOC elution amount of solid composition 1 after drying was 8,300 μg/cm ² , and the water content was 0.08 mass%.

[Example 2]
Copolymer 2 of Example 2 was obtained in the same manner as in Example 1, except that the amount of PFBE and the amount of methanol initially charged into the polymerization tank were changed to 11.5 g and 2.7 g, respectively, the amount of the polymerization initiator solution initially charged was changed to 10.3 mL, and the amount of PFBE continuously charged during polymerization was changed to an amount equivalent to 3.3 mol % based on the total moles of TFE and ethylene.
The composition of copolymer 2 was TFE unit/E unit/PFBE unit (molar ratio)=52.7/44.0/3.3. The MFR of copolymer 2 was 27 g/10 min and the melting point was 240° C.
Drying was carried out in the same manner as in Example 1, except that the drying was carried out by maintaining a state of 100° C. or higher for 2.3 hours, to obtain Solid Composition 2. The TOC elution amount of the solid composition after drying was 11,700 μg/cm ² , and the water content was 0.13 mass %.

[Example 3]
Copolymer 3 of Example 3 was obtained in the same manner as in Example 1, except that the amount of PFBE and the amount of methanol initially charged into the polymerization tank were changed to 12.4 g and 2.4 g, respectively, the amount of the polymerization initiator solution initially charged was changed to 11.6 mL, and the amount of PFBE continuously charged during polymerization was changed to an amount equivalent to 3.7 mol % based on the total moles of TFE and ethylene.
The composition of copolymer 3 was TFE unit/E unit/PFBE unit (molar ratio)=53.0/43.3/3.7. The MFR of copolymer 3 was 30 g/10 min, and the melting point was 236° C.
Drying was carried out in the same manner as in Example 1, except that the drying was carried out so as to maintain a state of 100° C. or higher for 2.4 hours, to obtain Solid Composition 3. The TOC elution amount of the solid composition after drying was 11,100 μg/cm ² , and the water content was 0.12 mass %.

[Example 4]
Copolymer 4 of Example 4 was obtained in the same manner as in Example 1, except that the amount of PFBE and the amount of methanol initially charged into the polymerization tank were changed to 11.7 g and 3.1 g, respectively, the amount of the polymerization initiator solution initially charged was changed to 10.6 mL, and the amount of PFBE continuously charged during polymerization was changed to an amount equivalent to 3.4 mol % based on the total moles of TFE and ethylene.
The composition of copolymer 4 was TFE unit/E unit/PFBE unit (molar ratio)=53.1/43.5/3.4. The MFR of copolymer 4 was 34 g/10 min and the melting point was 239° C.
Drying was carried out in the same manner as in Example 1, except that the drying was carried out by maintaining a state of 100° C. or higher for 2.7 hours, to obtain Solid Composition 4. The TOC elution amount of the solid composition after drying was 9,600 μg/cm ² , and the water content was 0.10 mass %.

[Example 5]
Copolymer 5 of Example 5 was obtained in the same manner as in Example 1, except that the amount of PFBE and the amount of methanol initially charged into the polymerization tank were changed to 11.2 g and 3.5 g, respectively, the amount of the polymerization initiator solution initially charged was changed to 10.0 mL, and the amount of PFBE continuously charged during polymerization was changed to an amount equivalent to 3.2 mol % based on the total moles of TFE and ethylene.
The composition of copolymer 5 was TFE unit/E unit/PFBE unit (molar ratio)=53.0/43.8/3.2. The MFR of copolymer 5 was 38 g/10 min and the melting point was 241° C.
Drying was carried out in the same manner as in Example 1, except that the drying was carried out so as to maintain a state of 100° C. or higher for 2.8 hours, to obtain Solid Composition 5. The TOC elution amount of the solid composition after drying was 8,900 μg/cm ² , and the water content was 0.09 mass %.

[Example 6]
Copolymer 6 of Example 6 was obtained in the same manner as in Example 1, except that the amount of PFBE and the amount of methanol initially charged into the polymerization tank were changed to 12.8 g and 2.5 g, respectively, the amount of the polymerization initiator solution initially charged was changed to 12.2 mL, and the amount of PFBE continuously charged during polymerization was changed to an amount equivalent to 3.9 mol % based on the total moles of TFE and ethylene.
The composition of copolymer 6 was TFE unit/E unit/PFBE unit (molar ratio)=52.8/43.3/3.9. The MFR of copolymer 6 was 36 g/10 min, and the melting point was 234° C.
Drying was carried out in the same manner as in Example 1, except that the drying was carried out so as to maintain a state of 100° C. or higher for 2.0 hours, to obtain Solid Composition 6. The TOC elution amount of the solid composition after drying was 13,700 μg/cm ² , and the water content was 0.16 mass %.

[Example 7]
Copolymer 7 of Example 7 was obtained in the same manner as in Example 1, except that the amount of PFBE and the amount of methanol initially charged into the polymerization tank were changed to 12.7 g and 3.0 g, respectively, the amount of the polymerization initiator solution initially charged was changed to 11.9 mL, and the amount of PFBE continuously charged during polymerization was changed to an amount equivalent to 3.8 mol % based on the total moles of TFE and ethylene.
The composition of copolymer 7 was TFE unit/E unit/PFBE unit (molar ratio)=52.8/43.4/3.8. The MFR of copolymer 7 was 45 g/10 min and the melting point was 235° C.
Drying was carried out in the same manner as in Example 1, except that the drying was carried out by maintaining a state of 100° C. or higher for 3.2 hours, to obtain Solid Composition 7. The TOC elution amount of the solid composition after drying was 7,600 μg/cm ² , and the water content was 0.07 mass %.

[Example 8]
Copolymer 8 of Example 8 was obtained in the same manner as in Example 1, except that the amount of PFBE and the amount of methanol initially charged into the polymerization tank were changed to 12.2 g and 3.1 g, respectively, the amount of the polymerization initiator solution initially charged was changed to 11.3 mL, and the amount of PFBE continuously charged during polymerization was changed to an amount equivalent to 3.6 mol % based on the total moles of TFE and ethylene.
The composition of copolymer 8 was TFE unit/E unit/PFBE unit (molar ratio)=53.1/43.3/3.6. The MFR of copolymer 8 was 41 g/10 min, and the melting point was 237° C.
Drying was carried out in the same manner as in Example 1, except that the drying was carried out so as to maintain a state of 100° C. or higher for 2.1 hours, to obtain a solid composition 8. The TOC elution amount of the solid composition after drying was 13,000 μg/cm ² , and the water content was 0.15 mass %.

[Example 9]
Copolymer 9 of Example 9 was obtained in the same manner as in Example 1, except that the amount of PFBE and the amount of methanol initially charged into the polymerization tank were changed to 11.2 g and 4.1 g, respectively, the amount of the polymerization initiator solution initially charged was changed to 10.0 mL, and the amount of PFBE continuously charged during polymerization was changed to an amount equivalent to 3.2 mol % based on the total moles of TFE and ethylene.
The composition of copolymer 9 was TFE unit/E unit/PFBE unit (molar ratio)=53.2/43.6/3.2. The MFR of copolymer 9 was 50 g/10 min and the melting point was 241° C.
Drying was carried out in the same manner as in Example 1, except that the drying was carried out by maintaining a state of 100° C. or higher for 2.3 hours, to obtain Solid Composition 9. The TOC elution amount of the solid composition after drying was 11,700 μg/cm ² , and the water content was 0.13 mass %.

[Example 10]
1,167 g of a fluorinated organic solvent (ASAHIKLIN (registered trademark) AE-3000, manufactured by AGC Corporation, CF ₃ CH ₂ OCF ₂ CF ₂ H), 124.6 g of CF ₂ ═CFO(CF ₂ ) ₂ F (PPVE), and 8.4 g of methanol were charged into a pre-degassed polymerization tank equipped with a stirrer and having an internal volume of 1.2 L. The solution in the polymerization tank was heated to 66° C. (polymerization temperature), and TFE/ethylene=76/24 (molar ratio) was added until the pressure in the polymerization tank reached 1.5 MPa [gauge].
A polymerization initiator solution of 12.0 mL of tert-butyl peroxypivalate dissolved in AE-3000 at a concentration of 1% by mass was initially charged, and polymerization was carried out. In addition, a mixed gas of TFE/ethylene = 54/46 (molar ratio) was continuously charged so that the pressure in the polymerization tank during the polymerization reaction was maintained at 1.5 MPa [gauge]. In addition, PPVE was continuously charged in an amount equivalent to 3.2 mol% with respect to the total mole number of TFE and ethylene charged during polymerization.
When the amount of TFE/ethylene introduced reached 110 g, the polymerization was terminated to obtain Copolymer 10 of Example 10.
The composition of copolymer 10 was TFE unit/E unit/PPVE unit (molar ratio) = 52.6/44.2/3.2. The "PPVE unit" is a unit based on _CF2 =CFO( _CF2 ) _2F of each copolymer. The MFR of copolymer 12 was 45g/10min, and the melting point was 253°C.
Pure water was added to the obtained copolymer 10, and the mixture was heated with stirring to remove the solvent in the same manner as in Example 1. Next, water was removed from the mixture of pure water and copolymer 10, and drying was performed by maintaining a drying temperature of 100° C. or higher for 3.2 hours. The TOC of solid composition 10 after drying was 7,700 μg/cm ² , and the water content was 0.07 mass%.

[Example 11]
Copolymer 11 of Example 11 was obtained in the same manner as in Example 10, except that the amount of PPVE and the amount of methanol when initially charged into the polymerization tank were changed to 135.2 g and 7.8 g, respectively, the amount of the polymerization initiator solution initially charged was changed to 13.0 mL, and the amount of PPVE continuously charged during polymerization was changed to an amount equivalent to 3.5 mol % based on the total moles of TFE and ethylene.
The composition of copolymer 11 was TFE unit/E unit/PPVE unit (molar ratio)=52.4/44.1/3.5. The MFR of copolymer 11 was 35 g/10 min and the melting point was 252° C.
Drying was carried out in the same manner as in Example 1, except that the drying was carried out so as to maintain a state of 100° C. or higher for 2.8 hours, to obtain a solid composition 11. The TOC elution amount of the solid composition after drying was 88.00 μg/cm ² , and the water content was 0.09 mass %.

[Example 12]
Copolymer 12 of Example 12 was obtained in the same manner as in Example 1, except that the amount of PFBE and the amount of methanol initially charged into the polymerization tank were changed to 12.2 g and 3.0 g, respectively, the amount of the polymerization initiator solution initially charged was changed to 11.3 mL, and the amount of PFBE continuously charged during polymerization was changed to an amount equivalent to 3.6 mol % based on the total moles of TFE and ethylene.
The composition of copolymer 12 was TFE unit/E unit/PFBE unit (molar ratio)=52.8/43.6/3.6. The MFR of copolymer 12 was 23 g/10 min and the melting point was 237° C.
Drying was carried out in the same manner as in Example 1, except that the drying was carried out so as to maintain a state of 100° C. or higher for 3.7 hours, to obtain a solid composition 12. The TOC elution amount of the solid composition after drying was 6,280 μg/cm ² , and the water content was 0.05 mass %.

[Example 13]
Copolymer 13 of Example 13 was obtained in the same manner as in Example 1, except that the amount of PFBE and the amount of methanol initially charged into the polymerization tank were changed to 10.4 g and 3.1 g, respectively, the amount of the polymerization initiator solution initially charged was changed to 9.1 mL, and the amount of PFBE continuously charged during polymerization was changed to an amount equivalent to 2.9 mol % based on the total moles of TFE and ethylene.
The composition of copolymer 13 was TFE unit/E unit/PFBE unit (molar ratio)=53.1/44.0/2.9. The MFR of copolymer 13 was 29 g/10 min, and the melting point was 243° C.
Drying was carried out in the same manner as in Example 1, except that the drying was carried out so as to maintain a state of 100° C. or higher for 4.5 hours, to obtain a solid composition 13. The TOC elution amount of the solid composition after drying was 4,900 μg/cm ² , and the water content was 0.03 mass %.

[Example 14]
Copolymer 14 of Example 14 was obtained in the same manner as in Example 1, except that the amount of PFBE and the amount of methanol initially charged into the polymerization tank were changed to 9.8 g and 3.9 g, respectively, the amount of the polymerization initiator solution initially charged was changed to 8.4 mL, and the amount of PFBE continuously charged during polymerization was changed to an amount equivalent to 2.7 mol % based on the total moles of TFE and ethylene.
The composition of copolymer 14 was TFE unit/E unit/PFBE unit (molar ratio)=53.5/43.8/2.7. The MFR of copolymer 14 was 38 g/10 min, and the melting point was 245° C.
Drying was carried out in the same manner as in Example 1, except that the drying was carried out so as to maintain a state of 100° C. or higher for 3.7 hours, to obtain a solid composition 14. The TOC elution amount of the solid composition after drying was 6,300 μg/cm ² , and the water content was 0.05 mass %.

[Example 15]
Copolymer 15 of Example 15 was obtained in the same manner as in Example 1, except that the amount of PFBE and the amount of methanol initially charged into the polymerization tank were changed to 13.2 g and 4.6 g, respectively, the amount of the polymerization initiator solution initially charged was changed to 13.2 mL, and the amount of PFBE continuously charged during polymerization was changed to an amount equivalent to 3.2 mol % based on the total moles of TFE and ethylene.
The composition of copolymer 15 was TFE unit/E unit/PFBE unit (molar ratio)=53.2/43.6/3.2. The MFR of copolymer 15 was 65 g/10 min, and the melting point was 241° C.
Drying was carried out in the same manner as in Example 1, except that the drying was carried out so as to maintain a state of 100° C. or higher for 2.5 hours, to obtain a solid composition 15. The TOC elution amount of the solid composition after drying was 10,000 μg/cm ² , and the water content was 0.11 mass %.

[Example 16]
Copolymer 16 of Example 16 was obtained in the same manner as in Example 1, except that the amount of PFBE and the amount of methanol initially charged into the polymerization tank were changed to 14.9 g and 14 g, respectively, the amount of the polymerization initiator solution initially charged was changed to 15.6 mL, and the amount of PFBE continuously charged during polymerization was changed to an amount equivalent to 5.0 mol % based on the total moles of TFE and ethylene.
The composition of copolymer 16 was TFE unit/E unit/PFBE unit (molar ratio)=52.5/42.5/5.0. The MFR of copolymer 16 was 36.0 g/10 min, and the melting point was 224° C.
Drying was carried out in the same manner as in Example 1, except that the drying was carried out so as to maintain a state of 100° C. or higher for 2.4 hours, thereby obtaining a solid composition 16. The TOC elution amount of the solid composition after drying was 11,000 μg/cm ² , and the water content was 0.12 mass %.

[Example 17]
Copolymer 17 of Example 17 was obtained in the same manner as in Example 1, except that the amount of PFBE and the amount of methanol initially charged into the polymerization tank were changed to 12.2 g and 3.0 g, respectively, the amount of the polymerization initiator solution initially charged was changed to 11.3 mL, and the amount of PFBE continuously charged during polymerization was changed to an amount equivalent to 3.6 mol % based on the total moles of TFE and ethylene.
The composition of copolymer 17 was TFE unit/E unit/PFBE unit (molar ratio)=53.0/43.4/3.6. The MFR of copolymer 17 was 40 g/10 min, and the melting point was 237° C.
Drying was carried out in the same manner as in Example 1, except that the drying was carried out so as to maintain a state of 100° C. or higher for 0.5 hours, to obtain a solid composition 17. The TOC elution amount of the solid composition after drying was 66,000 μg/cm ² , and the water content was 0.98 mass %.

[Example 18]
Copolymer 18 of Example 18 was obtained in the same manner as in Example 1, except that the amount of PFBE and the amount of methanol initially charged into the polymerization tank were changed to 12.2 g and 3.1 g, respectively, the amount of the polymerization initiator solution initially charged was changed to 11.3 mL, and the amount of PFBE continuously charged during polymerization was changed to an amount equivalent to 3.6 mol % based on the total moles of TFE and ethylene.
The composition of copolymer 18 was TFE unit/E unit/PFBE unit (molar ratio)=53.2/43.1/3.6. The MFR of copolymer 18 was 41 g/10 min, and the melting point was 237° C.
Drying was also carried out in the same manner as in Example 1, except that the drying was carried out so as to maintain a state of 100° C. or higher for 6.1 hours, to obtain a solid composition 18. The TOC elution amount of the solid composition after drying was 960 μg/cm ² , and the water content was 0.01 mass %.

Table 1 shows the composition of the copolymer in each example, as well as the measurement and evaluation results of the copolymer.
In the table, the column "TFE units (mol %)" indicates the content (unit: mol %) of TFE units relative to all units contained in the copolymer.
The column "E units (mol %)" indicates the content (unit: mol %) of E units relative to all units contained in the copolymer.
The column "TFE/(TFE+E) (mol %)" indicates the content of TFE units relative to the total content of TFE units and E units (unit: mol %).
The column "A units (mol %)" indicates the content (unit: mol %) of A units relative to all units contained in the copolymer.

As shown in Table 1, it was confirmed that by using a copolymer that contains TFE units, E units, and A units, in which the total content of TFE units and E units is 80.0 to 96.8 mol% based on the total content of all units contained in the copolymer, the content of TFE units is 49.0 mol% or more and less than 56.0 mol% based on the total content of TFE units and E units, the content of A units is 3.2 to 4.0 mol% based on the total content of all units contained in the copolymer, and the MFR is 25 to 50 g/10 min, it is possible to form a molded product that is excellent in yellowness, elongation, and yield rate (Examples 1 to 11).

Table 2 shows the measurement results and evaluation results of the solid compositions of each example.
In the table, the column "TFE units (mol %)" indicates the content (unit: mol %) of TFE units relative to all units contained in the copolymer.
The column "E units (mol %)" indicates the content (unit: mol %) of E units relative to all units contained in the copolymer.
The column "TFE/(TFE+E) (mol %)" indicates the content of TFE units relative to the total content of TFE units and E units (unit: mol %).
The column "A units (mol %)" indicates the content (unit: mol %) of A units relative to all units contained in the copolymer.

The entire contents of the specification, claims and abstract of Japanese Patent Application No. 2023-098962, filed on June 16, 2023, are hereby incorporated by reference as the disclosure of the present invention.

Claims (8)

A copolymer comprising a unit based on tetrafluoroethylene, a unit based on ethylene, and either or both of a unit based on a compound represented by formula (1) and a unit based on a compound represented by formula (2),
the total content of the units based on tetrafluoroethylene and the units based on ethylene is 80.0 to 96.8 mol % based on all units contained in the copolymer,
the content of the units based on tetrafluoroethylene is 49.0 mol % or more and less than 56.0 mol % with respect to the total content of the units based on tetrafluoroethylene and the units based on ethylene,
the content of units based on the compound represented by formula (1) or the compound represented by formula (2) is 3.2 to 4.0 mol % based on all units contained in the copolymer,
A copolymer having a melt flow rate of 25 to 50 g/10 min, as measured in accordance with ASTM D3159 under conditions of a temperature of 297° C. and a load of 49 N.
CZ ₂ =CX(CF ₂ ) _m Y Formula (1)
CF ₂ =CF-O-(CF ₂ ) _n F Formula (2)
In formula (1), X, Y and Z each independently represent a hydrogen atom or a fluorine atom, and m represents an integer of 2 to 6.
In formula (2), n represents an integer of 1 to 6. A copolymer comprising a unit based on the tetrafluoroethylene, a unit based on the ethylene, and a unit based on the compound represented by formula (1),
The copolymer according to claim 1, wherein the content of units based on the compound represented by formula (1) is 3.2 to 4.0 mol % based on all units contained in the copolymer. A composition comprising the copolymer according to claim 1 or 2. A solid composition comprising the copolymer according to claim 1 or 2, and having an elution amount of TOC (total organic carbon) of 1,000 to 63,000 μg/ ^cm2 . A solid composition comprising the copolymer according to claim 1 or 2, the water content of which is 0.02 to 0.8% by mass. A molded article obtained by molding the copolymer according to claim 1 or 2. A molded article obtained by molding the composition according to claim 3. A molded body obtained by molding the solid composition according to claim 4.