WO2025197709A1 - Fluorine-containing copolymer composition and method for producing same, and crosslinked rubber article and method for producing same - Google Patents

Abstract

Provided is a fluorine-containing copolymer composition, etc., with which it is possible to obtain a crosslinked rubber article that has low compression set and is unlikely to break even when used for a long period of time in a compressed state at high temperatures of 325°C or higher. This fluorine-containing copolymer composition contains a fluorine-containing copolymer (A) that has a unit based on a nitrile-group-containing monomer and a unit based on tetrafluoroethylene, and a crosslinking agent (B) that has two or more amino groups. The amount of units based on the nitrile-group-containing monomer is at least 0.80 mol% and less than 1.00 mol% in 100 mol% of all the monomer units in the fluorine-containing copolymer (A), and the amount of the crosslinking agent (B) is 0.80-1.30 parts by mass per 100 parts by mass of the fluorine-containing copolymer (A).

Description

Fluorine-containing copolymer composition and method for producing the same, crosslinked rubber article and method for producing the same

The present invention relates to a fluorocopolymer composition and a method for producing the same, as well as a crosslinked rubber article and a method for producing the same. In particular, the present invention relates to a fluorocopolymer composition that can produce crosslinked rubber articles with excellent heat resistance and a method for producing the same, as well as a crosslinked rubber article obtained from the fluorocopolymer composition and a method for producing the same.

Crosslinked rubber articles made by crosslinking fluorine-containing copolymers have excellent heat resistance, chemical resistance, oil resistance, and weather resistance, and are therefore widely used as sealing materials (e.g., O-rings, packings, oil seals, gaskets), cushioning materials, etc. in fields such as vehicles, ships, aircraft, general machinery, and construction.

For example, Patent Document 1 discloses a fluorine-containing copolymer having units based on tetrafluoroethylene, units based on perfluoro(alkyl vinyl ether), units based on a monomer having a fluorine atom and two or more polymerizable unsaturated bonds, and units based on a monomer having a nitrile group and a fluorine atom, wherein, when the storage moduli of the fluorine-containing copolymer at frequencies of 0.3 rad/s and 0.03 rad/s determined by dynamic viscoelasticity measurement at 140°C are G' _0.3 and G' _0.03 , G' _0.3 /G' _0.03 is 1.00 to 1.45; and also discloses a fluorine-containing copolymer composition containing the fluorine-containing copolymer and a crosslinking agent.
Patent Document 2 discloses a fluorine-containing copolymer composition comprising: a fluorine-containing copolymer (A) having units having a nitrile group and units based on tetrafluoroethylene; a fluorine-containing copolymer (B) having units having at least one functional group selected from the group consisting of a group having a carbonyl group, a hydroxy group, an epoxy group and an isocyanate group and units based on tetrafluoroethylene; and a crosslinking agent.
Patent Document 3 discloses a fluorine-containing copolymer composition containing a fluorine-containing copolymer having nitrile groups, a phosphorus compound having a melting point of 60° C. or less, and a crosslinking agent.

International Publication No. 2022/220180 International Publication No. 2021/210502 International Publication No. 2021/210503

Crosslinked rubber articles obtained from the compositions described in Patent Documents 1 to 3 have excellent heat resistance. However, in recent years, there has been a demand for even greater heat resistance. For example, there is a demand for crosslinked rubber articles that have low compression set and are less likely to crack, even when used in a compressed state at high temperatures of 325°C or higher for long periods of time.

The present invention has been made in light of these circumstances, and aims to provide a fluorocopolymer composition and a method for producing the same that can yield crosslinked rubber articles that have small compression set and are less likely to crack, even when used in a compressed state for long periods of time at temperatures of 325°C or higher, as well as crosslinked rubber articles obtainable from the fluorocopolymer composition and a method for producing the same.

The present invention is based on the discovery that crosslinked rubber articles obtained by crosslinking a fluorocopolymer composition containing a fluorocopolymer having a specific amount of specific monomer units and containing a specific type of crosslinking agent in a specific ratio relative to the fluorocopolymer have small compression set and are resistant to cracking, even when used in a compressed state for long periods of time at temperatures of 325°C or higher.

The present invention is as follows.
[1] A polymerizable composition comprising: a fluorine-containing copolymer (A) having units based on a monomer having a nitrile group and units based on tetrafluoroethylene; and a crosslinking agent (B) having two or more amino groups;
the content of units based on the monomer having a nitrile group in 100 mol % of all monomer units in the fluorine-containing copolymer (A) is 0.80 mol % or more and less than 1.00 mol %,
The fluorine-containing copolymer composition, wherein the content of the crosslinking agent (B) is 0.80 to 1.30 parts by mass per 100 parts by mass of the fluorine-containing copolymer (A).
[2] The fluorine-containing copolymer (A) has units based on perfluoro(alkyl vinyl ether),
the content of units based on tetrafluoroethylene in 100 mol% of all monomer units in the fluorine-containing copolymer (A) is 67.0 mol% or more and less than 71.5 mol%,
The fluorine-containing copolymer composition according to the above-mentioned [1], wherein the content of units based on the perfluoro(alkyl vinyl ether) in 100 mol% of all monomer units in the fluorine-containing copolymer (A) is 27.0 to 32.0 mol%.
[3] The fluorine-containing copolymer composition according to the above [1] or [2], wherein the fluorine-containing copolymer (A) has a carboxy terminal group, and the ratio of the integrated peak intensity of absorbance in the range of 1700 to 1850 cm ⁻¹ to the integrated peak intensity of absorbance in the range of 2210 to 2700 cm ⁻¹ in the spectrum obtained by measuring the fluorine-containing copolymer (A) by infrared spectroscopy is 0.7 or more.
[4] The fluorine-containing copolymer composition according to any one of the above [1] to [3], wherein the crosslinking agent (B) is 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane.
[5] The fluorine-containing copolymer composition according to any one of the above [1] to [4], which contains a filler (C).
[6] The fluorine-containing copolymer composition according to the above-mentioned [5], wherein the content of the filler (C) is 1 to 20 parts by mass per 100 parts by mass of the fluorine-containing copolymer (A).
[7] The fluorine-containing copolymer composition according to the above [5] or [6], wherein the filler (C) is carbon black.
[8] The fluorocopolymer composition according to any one of the above [1] to [7], wherein the torque difference (M _H −M _L ) of the fluorocopolymer composition measured by the following measurement method is 60 to 90 dN·m.
[Measurement method: Using a crosslinking property measuring device in accordance with JIS K6296-1:2023, the maximum torque M H and minimum torque M _L of the fluorocopolymer composition are measured under the conditions of a measurement temperature of 180°C, a measurement time of 30 minutes, a vibration frequency of 100 cpm, and an angle of 3.00 _deg .]
[9] The method for producing the fluorine-containing copolymer composition according to any one of the above [1] to [8], which comprises kneading the fluorine-containing copolymer (A) and the crosslinking agent (B).
[10] A crosslinked rubber article obtained by crosslinking the fluorocopolymer (A) in the fluorocopolymer composition according to any one of the above [1] to [8].
[11] A method for producing a crosslinked rubber article, which comprises crosslinking the fluorocopolymer (A) in the fluorocopolymer composition according to any one of the above [1] to [8].

The present invention provides a fluorocopolymer composition and a method for producing the same that can produce crosslinked rubber articles that have small compression set and are resistant to cracking, even when used in a compressed state for long periods of time at temperatures of 325°C or higher, and a crosslinked rubber article obtained from the fluorocopolymer composition and a method for producing the same.

The present invention will be described in detail below.
In this specification, the preferred definitions can be adopted arbitrarily, and it can be said that a combination of preferred definitions is more preferred.
In this specification, the expression "XX to YY" as a range of values means "XX or more and YY or less."
In this specification, for preferred numerical ranges (e.g., ranges of content, etc.), the lower and upper limits described in stages can be independently combined. For example, the description "preferably 10 to 90, more preferably 30 to 60" can be combined with the "preferable lower limit (10)" and the "more preferable upper limit (60)" to form "10 to 60." Furthermore, in the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in the examples.
"Room temperature" means 20-25°C.
The term "unit" refers collectively to an atomic group derived from one molecule of the monomer that is formed directly by polymerizing the monomer, and an atomic group obtained by chemically converting a part of the atomic group. Hereinafter, "a unit based on a monomer" may be simply referred to as "unit."
"Rubber" means rubber exhibiting properties defined by JIS K 6200:2008, and is distinguished from "resin."
"Melting point" means the temperature corresponding to the maximum value of the melting peak as measured by differential scanning calorimetry (DSC).
In this specification, the content (mol %) of each unit in the fluorine-containing copolymer was calculated by nuclear magnetic resonance (NMR) analysis as described in the Examples section.

[Fluorine-containing copolymer composition]
The fluorine-containing copolymer composition according to an embodiment of the present invention (hereinafter sometimes simply referred to as "the fluorine-containing copolymer composition of the present embodiment") comprises a fluorine-containing copolymer (A) having units based on a monomer having a nitrile group and units based on tetrafluoroethylene, and a crosslinking agent (B) having two or more amino groups, wherein the content of units based on the monomer having a nitrile group in 100 mol% of all monomer units in the fluorine-containing copolymer (A) is 0.80 mol% or more and less than 1.00 mol%, and the content of the crosslinking agent (B) is 0.80 to 1.30 parts by mass per 100 parts by mass of the fluorine-containing copolymer (A).

The fluorocopolymer composition of this embodiment provides a crosslinked rubber article that has small compression set and is resistant to cracking, even when used for long periods in a compressed state at high temperatures of 325°C or higher. Note that "small compression set and resistance to cracking, even when used for long periods in a compressed state at high temperatures of 325°C or higher" is sometimes simply referred to as "excellent heat resistance."

The reason why crosslinked rubber articles having excellent heat resistance can be obtained from the fluorocopolymer composition of this embodiment is not clear in detail, but is presumed to be as follows.
The fluorine-containing copolymer composition of the present embodiment comprises
(i) the content of units based on monomers having a nitrile group in 100 mol% of all monomer units in the fluorine-containing copolymer (A) is 0.80 mol% or more and less than 1.00 mol%;
(ii) the content of the crosslinking agent (B) having two or more amino groups is 0.80 to 1.30 parts by mass per 100 parts by mass of the fluorine-containing copolymer (A);
The combination of the above features (i) and (ii) makes it possible to achieve a uniform crosslink density when crosslinking the nitrile groups and the crosslinking agent (B), thereby reducing the occurrence of excessive stress concentration and shear force, thereby reducing the probability of molecular chain breakage and maintaining rubber elasticity. As a result, it is presumed that a crosslinked rubber article can be obtained that has a small compression set and is less likely to crack, even when used in a compressed state for a long period of time at temperatures of 325°C or higher.

The fluorine-containing copolymer composition of this embodiment is not particularly limited as long as it contains the fluorine-containing copolymer (A) and the crosslinking agent (B), and may or may not contain a filler (C), a crosslinking aid, other components, etc., as necessary.

<Fluorine-containing copolymer (A)>
The fluorine-containing copolymer (A) has units based on a monomer having a nitrile group and tetrafluoroethylene (hereinafter sometimes simply referred to as "TFE") units.

The content of the fluorocopolymer (A) relative to the total mass of the fluorocopolymer composition is not particularly limited, but from the viewpoint of heat resistance, it is preferably from 60.00 to 98.70 mass%, more preferably from 65.00 to 98.30 mass%, particularly preferably from 70.00 to 98.00 mass%.
The content of the fluorine-containing copolymer (A) relative to the total mass of the polymers contained in the fluorine-containing copolymer composition is not particularly limited, but from the viewpoint of heat resistance, it is preferably from 80 to 100 mass%, more preferably from 90 to 100 mass%, particularly preferably from 95 to 100 mass%.

(Units based on a monomer having a nitrile group)
The fluorine-containing copolymer (A) has units based on a monomer having a nitrile group (hereinafter, sometimes simply referred to as "R _CN ").
R 3 _CN preferably contains a fluorine atom, and more preferably is a unit based on a monomer represented by general formula (1), in order to obtain better effects of the present invention.
CR ¹¹ R ¹² =CR ¹³ -R ¹⁴ -CN...General formula (1)

In general formula (1), R ¹¹ , R ¹² and R ¹³ each independently represent a hydrogen atom, a fluorine atom or a methyl group, and R ¹⁴ represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms or a group having an etheric oxygen atom at the end of the perfluorohydrocarbon group or between carbon-carbon bonds.
R ¹¹ , R ¹² and R ¹³ are preferably fluorine atoms or hydrogen atoms in terms of excellent polymerization reactivity of R _CN , more preferably all fluorine atoms or all hydrogen atoms, and particularly preferably all fluorine atoms in terms of excellent mold releasability and heat resistance of the crosslinked rubber article.
R ¹⁴ may be linear, branched, or cyclic, but is preferably linear or branched. R ¹⁴ may or may not have an unsaturated bond, but preferably does not have one from the viewpoint of heat resistance.
The number of carbon atoms in R ¹⁴ is not particularly limited, but is preferably 2 to 8, more preferably 3 to 7, even more preferably 3 to 6, and particularly preferably 3 to 5, from the viewpoints of reactivity and availability.
R ¹⁴ may or may not have an etheric oxygen atom, but preferably has an etheric oxygen atom in view of better rubber properties.
The number of etheric oxygen atoms in R ¹⁴ is not particularly limited, but is preferably 1 to 3, more preferably 1 or 2, from the viewpoints of reactivity and availability.

Specific examples of the monomer represented by general formula (1) include the following. The description after the formula is the abbreviation of the compound. These may be used alone or in combination of two or more.
_CF2 = _CFOCF2CF ( _CF3 ) _OCF2CF2CN : _8CNVE
CF2 =CFO( _CF2 ) _5CN :MV5CN
_{CF2 = CFOCF2CF2CF2OCF ( CF3} )CN
_CF2 =CFO( _CF2 ) _3CN
Among these, 8CNVE and MV5CN are preferred because they provide crosslinked rubber articles with better mold releasability and heat resistance.

From the viewpoint of obtaining crosslinked rubber articles with excellent heat resistance, the content of units based on the monomer having a nitrile group in 100 mol% of all monomer units in the fluorine-containing copolymer (A) is 0.80 mol% or more and less than 1.00 mol%. From this viewpoint, the content is preferably 0.80 to 0.95 mol%, more preferably 0.85 to 0.95 mol%, particularly preferably 0.85 to 0.93 mol%, and even more preferably 0.85 to 0.90 mol%.

(Units based on TFE)
TFE is a monomer represented by CF ₂ ═CF ₂ .
The content of the tetrafluoroethylene-based unit (TFE unit) in 100 mol% of all monomer units of the fluorine-containing copolymer (A) is preferably 67.0 mol% or more and less than 71.5 mol%. When the TFE unit is 67.0 mol% or more, the heat resistance is improved. When the TFE unit is less than 71.5 mol%, the crosslinked rubber article having high rigidity can be obtained.
From these viewpoints, the content of TFE units in 100 mol % of all monomer units in the fluorine-containing copolymer (A) is more preferably from 67.0 to 70.5 mol %, particularly preferably from 67.0 to 70.0 mol %.

From the viewpoint of obtaining crosslinked rubber articles with excellent heat resistance, the total content of units based on the monomer having a nitrile group and units based on tetrafluoroethylene in 100 mol% of all monomer units in the fluorine-containing copolymer (A) is preferably 67.8 mol% or more and less than 72.5 mol%, more preferably 67.8 to 71.0 mol%, and particularly preferably 67.0 to 70.0 mol%.

(units based on PAVE)
The fluorine-containing copolymer (A) may or may not have units based on perfluoro(alkyl vinyl ether) (hereinafter, sometimes simply referred to as "PAVE") (PAVE units), but it is preferable that it has such units.
As the PAVE, a monomer represented by the following general formula (2) is preferred.
CF ₂ =CF-O-R ^f1 ...General formula (2)
In general formula (2), R ^f1 is a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms in R ^f1 is not particularly limited as long as it is 1 to 10, but is preferably 1 to 8, more preferably 1 to 6, and particularly preferably 1 to 5.

Specific examples of PAVE include the following (i) to (iv):
(i) CF ₂ ═CFOCF ₃ : perfluoro(methyl vinyl ether) (hereinafter, sometimes simply referred to as “PMVE”)
(ii) CF ₂ ═CFOCF ₂ CF ₃ : perfluoro(ethyl vinyl ether)
(iii) CF ₂ ═CFOCF ₂ CF ₂ CF ₃ : perfluoro(propyl vinyl ether) (hereinafter, sometimes simply referred to as “PPVE”)
(iv) CF ₂ = CFOCF ₂ CF ₂ CF ₂ CF ₃
These may be used alone or in combination of two or more.
Among these, PMVE and PPVE are preferred from the viewpoints of reactivity and availability.

The content of units based on perfluoro(alkyl vinyl ether) (PAVE units) in 100 mol% of all monomer units in the fluorine-containing copolymer (A) is not particularly limited, but from the viewpoint of heat resistance and chemical resistance, it is preferably 27.0 to 32.0 mol%, more preferably 29.0 to 32.0 mol%, and particularly preferably 29.5 to 32.0 mol%.

From the viewpoint of obtaining crosslinked rubber articles with excellent heat resistance, the total content of units based on the monomer having a nitrile group, units based on tetrafluoroethylene, and units based on PAVE in 100 mol% of all monomer units in the fluorine-containing copolymer (A) is preferably 75 to 100 mol%, more preferably 80 to 100 mol%, even more preferably 90 to 100 mol%, and particularly preferably 95 to 100 mol%, and may be 98 to 100 mol%, 99 to 100 mol%, or even 100 mol%.

(units based on other monomers)
The fluorine-containing copolymer (A) may or may not have units other than units based on a monomer having a nitrile group, TFE units and PAVE units.
Incidentally, monomers other than the monomer having a nitrile group, TFE, and PAVE may be simply referred to as "other monomers." Furthermore, units other than units based on the monomer having a nitrile group, TFE units, and PAVE units may be simply referred to as "units based on other monomers" or "other units."
Specific examples of units based on other monomers include vinylidene fluoride (hereinafter sometimes simply referred to as "VdF") units, units based on monomers having two or more polymerizable unsaturated bonds, units based on monomers represented by the following general formula (3) (hereinafter sometimes simply referred to as "formula (3) units"), units based on hexafluoropropylene (hereinafter sometimes simply referred to as "HFP units"), units based on chlorotrifluoroethylene, etc. These may be used alone or in combination of two or more.

The total content of units based on other monomers in all units constituting the fluorinated copolymer (A) is not particularly limited, but from the viewpoint of heat resistance and chemical resistance, it is preferably 0 to 20 mol %, more preferably 0 to 10 mol %, and particularly preferably 0 to 1 mol %. It is most preferable that the copolymer (A) does not contain any units based on other monomers.

-Copolymer containing VdF units-
VdF is a monomer represented by CF ₂ ═CH ₂ .

There are no particular restrictions on the proportion of VdF units in all units constituting the fluorinated copolymer (A), but from the viewpoint of suppressing sticking, it is preferably 0.1 to 5 mol%, more preferably 0.1 to 3 mol%, and particularly preferably 0.1 to 1 mol%.

- Units based on monomers having two or more polymerizable unsaturated bonds -
The unit based on a monomer having two or more polymerizable unsaturated bonds preferably has a fluorine atom, and is preferably a unit based on a fluorine-containing monomer having two or more polymerizable unsaturated bonds.
When units based on a fluorine-containing monomer having two or more polymerizable unsaturated bonds are copolymerized, the polymerizable double bonds at the ends of the units based on the fluorine-containing monomer having two or more polymerizable unsaturated bonds react during polymerization to give a copolymer having a branched chain.
Examples of the polymerizable unsaturated bond include a carbon-carbon double bond (C═C) and a triple bond (C≡C), etc. These may be used alone or in combination of two or more.
Among these, double bonds are preferred from the viewpoint of heat resistance. The number of polymerizable unsaturated bonds is not particularly limited, but is preferably 2 to 6, more preferably 2 or 3, and particularly preferably 2, from the viewpoint of heat resistance.
As the fluorine-containing monomer having two or more polymerizable unsaturated bonds, a compound represented by the following general formula (4) is preferred, since the fluorine-containing copolymer (A) has excellent rubber properties when made into a crosslinked rubber article:

(CR ³¹ R ³² =CR ³³ ) _a3 R ³⁴ ...General formula (4)
In general formula (4), R ³¹ , R ³² and R ³³ each independently represent a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group. In general formula (4), R ³⁴ represents a trivalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end of the perfluorohydrocarbon group or between carbon-carbon bonds. In general formula (4), a3 represents an integer of 2 to 6, preferably 2 or 3, and more preferably 2. In general formula (4), multiple R ^{31 s} , multiple R ^{32 s} , and multiple R ^{33 s} may be the same or different, and are preferably the same.

R ³¹ , R ³² and R ³³ are preferably fluorine atoms or hydrogen atoms in order to improve the polymerization reactivity of the fluorine-containing monomer having two or more polymerizable unsaturated bonds, more preferably all fluorine atoms or all hydrogen atoms, and particularly preferably all fluorine atoms in order to improve the heat resistance and chemical resistance of the crosslinked rubber article.
R ³⁴ may be linear, branched, or cyclic, preferably linear or branched, and more preferably linear. R ³⁴ preferably has 2 to 10 carbon atoms, more preferably 3 to 8, even more preferably 3 to 6, and particularly preferably 3 to 5.
R ³⁴ may or may not have an etheric oxygen atom, but preferably has an etheric oxygen atom in view of better crosslinking reactivity and rubber physical properties.
The number of etheric oxygen atoms in R ³⁴ is preferably 1 to 6, more preferably 1 to 3, and particularly preferably 1 or 2. The etheric oxygen atom in R ³⁴ is preferably present at the terminal of R ³⁴ .

Specific examples of suitable monomers represented by formula (4) include monomers represented by general formula (4-1) and general formula (4-2).

(CF ₂ =CF) ₂ R ⁴¹ ...General formula (4-1)
In general formula (4-1), R ⁴¹ represents a divalent perfluorohydrocarbon group having 2 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of the perfluorohydrocarbon group.
Specific examples of the monomer represented by general formula (4-1) include the following. The description after the formula is the abbreviation of the compound. One type may be used alone, or two or more types may be used.
_CF2 =CFO( _CF2 ) _2OCF = _CF2
CF2 =CFO( _CF2 ) _3OCF = _CF2 :C3DVE
CF ₂ =CFO(CF ₂ ) ₄ OCF = CF ₂ :C4DVE
_CF2 =CFO( _CF2 ) ₆ OCF= _CF2
CF2 =CFO( _CF2 ) ₈ OCF= _CF2
CF2 =CFO( _CF2 ) _2OCF ( _CF3 ) _CF2OCF = _CF2
CF2 =CFO( _CF2 ) _2O (CF( _CF3 ) _CF2O ) _2CF = _CF2
CF2 = _{CFOCF2O ( CF2CF2O} ) _2CF = _CF2
CF2 =CFO( _CF2O ) _3O (CF( _CF3 ) _CF2O ) _2CF = _CF2
CF2 = _CFOCF2CF ( _CF3 )O( _CF2 ) _2OCF ( _CF3 ) _CF2OCF = _CF2
CF2 = _{CFOCF2CF2O ( CF2O ) 2CF2CF2OCF = CF2}
As the monomer represented by the general formula (4-1), C3DVE and C4DVE are preferred since they provide even better rubber properties when the fluorocopolymer composition is made into a crosslinked rubber article.

(CH ₂ =CH) ₂ R ⁵¹ ...General formula (4-2)
In general formula (4-2), R ⁵¹ represents a divalent perfluorohydrocarbon group having 2 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of the perfluorohydrocarbon group.
Specific examples of the monomer represented by general formula (4-2) include the following. The description after the formula is the abbreviation of the compound. One type may be used alone, or two or more types may be used.
_CH2 =CH( _CF2 ) _2CH = _CH2
CH ₂ =CH(CF ₂ ) ₄ CH=CH ₂ :C4-DV
CH ₂ =CH(CF ₂ ) ₆ CH=CH ₂ :C6-DV
The monomer represented by formula (4-2) is preferably C6-DV.

Among all the units constituting the fluorine-containing copolymer (A), the proportion of units based on a fluorine-containing monomer having two or more polymerizable unsaturated bonds is not particularly limited, but from the viewpoint of heat resistance, it is preferably 0.1 to 5 mol %, more preferably 0.3 to 3 mol %, and particularly preferably 0.3 to 1 mol %.

-Formula (3) unit-
The general formula (3) is as follows:
CF ₂ =CF-O-R ^f4 ...General formula (3)
In general formula (3), R ^f4 is a group having an etheric oxygen atom between the carbon-carbon bond of a perfluorohydrocarbon group having 1 to 8 carbon atoms. The number of carbon atoms in R ^f4 is preferably 1 to 7, more preferably 1 to 6, in terms of excellent low-temperature properties.
Specific examples of the monomer represented by general formula (3) include the following. The description after the formula is the abbreviation of the compound. These may be used alone or in combination of two or more.
CF ₂ =CF-OCF ₂ CF ₂ -OCF ₂ -OCF ₂ -OCF ₂ -OCF ₂ -OCF ₃ :C9PEVE
CF ₂ =CF-OCF ₂ CF ₂ -OCF ₂ -OCF ₂ -OCF ₃ :C7PEVE
CF ₂ =CF-OCF ₂ CF ₂ -OCF ₂ CF ₂ -OCF ₂ CF ₃ :EEAVE
_CF2 =CF- _OCF2 - _OCF3
CF ₂ = CF-OCF ₂ -OCF ₂ CF _3
CF2 =CF-O( _{CF2CF ( CF3} ) _{O ) 2CF2CF2CF3}
CF ₂ =CF-OCF ₂ -OCF ₂ -OCF ₃
Among these, C9PEVE, C7PEVE and EEAVE are preferred because they provide better low-temperature properties when the fluorocopolymer (A) is made into a crosslinked rubber article.

There are no particular restrictions on the proportion of units of formula (3) in all units constituting the fluorinated copolymer (A), but in terms of excellent low-temperature properties, it is preferably 0.1 to 5 mol %, more preferably 0.1 to 3 mol %, and particularly preferably 0.1 to 1 mol %.

- Units based on other monomers than those mentioned above -
The fluorine-containing copolymer (A) may have units based on other monomers than those mentioned above. Examples of other monomers include other fluorine-containing monomers and non-fluorine-containing monomers.
Specific examples of other fluorine-containing monomers include vinyl fluoride; pentafluoropropylene; perfluorocyclobutene; (perfluoroalkyl)ethylenes _such as CH ₂ ═CHCF ₃ , CH ₂ ═CHCF ₂ CF ₃ , CH 2 ═CHCF _{2 CF 2 CF 3 , CH 2 ═CHCF 2 CF 2 CF 2 CF 3 , CH 2} ═CHCF ₂ CF ₂ CF ₂ CF ₃ ; and the like.
Specific examples of non-fluorine-containing monomers include α-olefins such as isobutylene and pentene; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether and butyl vinyl ether; and vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caproate and vinyl caprylate.
The content of units based on monomers other than those mentioned above in all units constituting the fluorinated copolymer (A) is not particularly limited, but in terms of excellent heat resistance and chemical resistance, it is preferably from 0.1 to 1 mol %, more preferably from 0.1 to 0.5 mol %, particularly preferably 0.1 to 0.3 mol %.

As the other monomer, a monomer having at least one atom selected from the group consisting of a chlorine atom, a bromine atom, and an iodine atom may be used. When a monomer having at least one atom selected from the group consisting of a chlorine atom, a bromine atom, and an iodine atom is copolymerized, at least one of a chlorine atom, a bromine atom, and an iodine atom can be introduced into the side chain of the fluorine-containing copolymer (A).
Suitable examples of the monomer having at least one of a chlorine atom, a bromine atom, and an iodine atom include Compound A represented by General Formula (5) and Compound B represented by General Formula (6).

CR ²¹ R ²² =CR ²³ R ²⁴ ...General formula (5)
CR ²¹ R ²² -R ²⁵ -CR ²³ R ²⁴ ...General formula (6)
However, compound A and compound B each have one or more chlorine atoms, bromine atoms, and iodine atoms.
In the general formula (5) and the general formula (6), R ²¹ , R ²² and R ²³ each independently represent a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom or an iodine atom.
In general formula (5) and general formula (6), ^R24 is an alkyl group, a group having an etheric oxygen atom at the terminal of an alkyl group or between carbon-carbon bonds, a fluoroalkyl group, or a group having an etheric oxygen atom at the terminal of a fluoroalkyl group or between carbon-carbon bonds. ^R24 may have at least one of a chlorine atom, a bromine atom, and an iodine atom. ^R24 may be linear or branched.
R ²⁵ in general formula (6) is a group having one or more polymerizable unsaturated bonds. The polymerizable unsaturated bond may be bonded to an alkyl group, a group having an etheric oxygen atom at the terminal of an alkyl group or between a carbon-carbon bond, a fluoroalkyl group, or a group having an etheric oxygen atom at the terminal of a fluoroalkyl group or between a carbon-carbon bond. R ²⁵ may have at least one of a chlorine atom, a bromine atom, and an iodine atom. R ²⁵ may be linear or branched.

Specific examples of the monomer having a bromine atom include bromotrifluoroethylene, 4-bromo-3,3,4,4-tetrafluorobutene-1, vinyl bromide, 1-bromo-2,2-difluoroethylene, perfluoroallyl bromide, 4-bromo-1,1,2-trifluorobutene-1, 4-bromo-1,1,3,3,4,4-hexafluorobutene, 4-bromo-3-chloro-1,1,3,4,4-pentafluorobutene, 6-bromo-5,5,6,6-tetrafluorohexene, 4-bromoperfluorobutene-1, 3,3-difluoroallyl bromide, 2-bromo-perfluoroethyl perfluorovinyl ether, CF ₂ ═CFOCF ₂ CF ₂ CF ₂ OCF ₂ CF ₂ Br, CF ₂ BrCF ₂ O—CF═CF ₂ , CH ₃ OCF=CFBr, CF ₃ CH ₂ OCF=CFBr, etc. These may be used alone or in combination of two or more.

Specific examples of the monomer having an iodine atom include iodoethylene, 4-iodo-3,3,4,4-tetrafluoro-1-butene, 2-iodo-1,1,2,2-tetrafluoro-1-vinyloxyethane, 2-iodoethyl vinyl ether, allyl iodide, 1,1,2,3,3,3-hexafluoro-2-iodo-1-(perfluorovinyloxy)propane, 3,3,4,5,5,5-hexafluoro-4-iodopentene, iodotrifluoroethylene, 2-iodoperfluoro(ethyl vinyl ether), CF ₂ ═CFOCF(CF ₃ )CF ₂ OCF ₂ CF ₂ CH ₂ I, CF ₂ ═CFOCF ₂ CF ₂ CH ₂ I, CH ₂ ═CHCF ₂ CF ₂ I, and the like. These may be used alone or in combination of two or more.

Specific examples of monomers containing iodine atoms and bromine atoms include 3-bromo-4-iodoperfluorobutene-1 and 2-bromo-4-iodoperfluorobutene-1. These may be used alone or in combination of two or more.

<Ratio of Carboxy Terminal Group Content>
It is preferable that the fluorocopolymer (A) has carboxy terminal groups, and that the ratio of the integrated peak intensity of absorbance at 1700 to 1850 cm-1 to the integrated peak intensity of absorbance at 2210 to 2700 cm ^{- 1} in the spectrum obtained by measuring the fluorocopolymer (A) by infrared spectroscopy is 0.7 or more. In other words, the content ratio of carboxy terminal groups in the fluorocopolymer (A) measured by infrared spectroscopy is preferably 0.7 or more. When the content ratio of carboxy terminal groups is 0.7 or more, the polarity of the molecular terminals of the fluorocopolymer is increased, thereby improving adhesion to crosslinking agents and fillers. As a result, vulcanization efficiency is improved, and the heat resistance of crosslinked rubber articles is improved.
The content ratio of the carboxy terminal groups is preferably not more than 5.0. When the content ratio of the carboxy terminal groups is not more than 5.0, decomposition of the fluorocopolymer (A) caused by the carboxy terminal groups when exposed to high temperatures is reduced.
The content ratio of the carboxy terminal group is preferably 0.7 to 2.0, more preferably 0.7 to 1.0, and even more preferably 0.7 to 0.9. The content ratio of the carboxylic acid may be more than 0.7, and the content ratio of the carboxy terminal group may be more than 0.7 and not more than 2.0, more than 0.7 and not more than 1.0, or more than 0.7 and not more than 0.9.
In particular, the fluorine-containing copolymer composition according to the present embodiment is
(i) the content of units based on monomers having a nitrile group in 100 mol% of all monomer units in the fluorine-containing copolymer (A) is 0.80 mol% or more and less than 1.00 mol%;
(ii) the content of the crosslinking agent (B) having two or more amino groups is 0.80 to 1.30 parts by mass per 100 parts by mass of the fluorine-containing copolymer (A);
The above combination of configurations is provided.
It is believed that some intermolecular interaction resulting from this combination of configurations improves the adhesion between the fluorocopolymer (A) and the crosslinking agent due to the carboxy terminal groups, thereby improving the reaction efficiency with the crosslinking agent. Therefore, it is believed that by providing the above configurations (i) and (ii) and setting the content of carboxy terminal groups in the fluorocopolymer (A) to 0.7 or more, preferably 0.7 to 5.0, more preferably 0.7 to 2.0, and even more preferably 0.7 to 1.4, it is possible to obtain crosslinked rubber articles with excellent heat resistance.

<<Method for producing fluorine-containing copolymer (A)>>
An example of the method for producing the fluorine-containing copolymer (A) is a method in which the above-mentioned monomers are copolymerized in the presence of a radical polymerization initiator.
When the above-mentioned monomers are copolymerized in the presence of a radical polymerization initiator, a carboxyl terminal group is generated at the end of the polymer due to a radical reaction caused by the radical polymerization initiator.
Incidentally, the content of carboxy terminal groups in the fluorocopolymer (A) tends to increase as the ratio of the radical polymerization initiator to the fluorocopolymer (A) increases.
The radical polymerization initiator is preferably a water-soluble polymerization initiator, a redox polymerization initiator, or the like.

Specific examples of water-soluble polymerization initiators include persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate, and organic polymerization initiators such as disuccinic acid peroxide and azobisisobutylamidine dihydrochloride. Of these, persulfates are preferred, and ammonium persulfate is more preferred.

Redox polymerization initiators include polymerization initiators that combine persulfates and reducing agents. Of these, polymerization initiators that can polymerize each monomer at a polymerization temperature in the range of 0 to 85°C are preferred. Specific examples of persulfates that make up redox polymerization initiators include alkali metal salts of persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate, with ammonium persulfate being preferred. Specific examples of reducing agents that can be combined with persulfates include thiosulfates, sulfites, hydrogen sulfites, pyrosulfites, and hydroxymethanesulfinates, with hydroxymethanesulfinates being preferred, and sodium hydroxymethanesulfinate being particularly preferred.

In the process for producing the fluorine-containing copolymer (A), the above-mentioned monomers may be copolymerized together with a radical polymerization initiator in the presence of a chain transfer agent.
The chain transfer agent is preferably an iodine compound, and particularly preferably an iodine compound represented by formula RI _2. In the above formula, R represents an alkylene group having 3 or more carbon atoms (preferably 3 to 8 carbon atoms) or a perfluoroalkylene group.
Specific examples of the iodo compound represented by formula RI ₂ include 1,3-diiodopropane, 1,4-diiodobutane, 1,6-diiodohexane, 1,8-diiodooctane, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane, 1,6-diiodoperfluorohexane, and 1,8-diiodoperfluorooctane.
As the iodine compound, an iodine compound having a perfluoroalkylene group is preferred, and 1,4-diiodoperfluorobutane is particularly preferred.
When the above-mentioned monomers are copolymerized in the presence of these iodine compounds, iodine atoms can be introduced into the fluorine-containing copolymer (A).
For details of the components other than those mentioned above used in producing the fluorine-containing copolymer (A) and the production method, reference can be made to the method described in paragraphs 0019 to 0034 of WO 2010/082633.

<Crosslinking agent (B)>
The fluorocopolymer composition of the present embodiment contains a crosslinking agent (B) having two or more amino groups, whereby the fluorocopolymer (A) is crosslinked by the crosslinking agent (B), thereby giving a crosslinked rubber article having excellent heat resistance.
Specific examples of the crosslinking agent (B) having two or more amino groups include hexamethylenediamine, hexamethylenediamine carbamate, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis(3-amino-4-hydroxyphenyl)propane, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (hereinafter sometimes simply referred to as "BOAP", also known as bisaminophenol AF), 2,2-bis(3,4-diaminophenyl)propane, 2,2-bis(3,4-diaminophenyl)hexafluoropropane, 2,2-bis(3-amino-4-(N-phenylamino)phenyl)hexafluoropropane, 4,4'-methylenedianiline, m-phenylenediamine, adipic acid dihydrazide, and the compound represented by formula (XII) of Japanese Patent No. 5,833,657. These may be used alone or in combination of two or more.
Among these, BOAP is preferred because it provides a more excellent effect of the present invention.

The content of the crosslinking agent (B) is from 0.80 to 1.30 parts by mass per 100 parts by mass of the fluorocopolymer (A) from the viewpoint of heat resistance.
The content of the crosslinking agent (B) is preferably 0.80 to 1.25 parts by mass, more preferably 0.80 to 1.22 parts by mass, and particularly preferably 0.80 to 1.20 parts by mass, relative to 100 parts by mass of the fluorocopolymer (A). When the amount of the crosslinking agent blended is within the above range, the crosslinked rubber article will have an excellent balance between strength and elongation.

The fluorine-containing copolymer composition of the present embodiment comprises
(i) the content of units based on monomers having a nitrile group in 100 mol% of all monomer units in the fluorine-containing copolymer (A) is 0.80 mol% or more and less than 1.00 mol%;
(ii) the content of the crosslinking agent (B) having two or more amino groups is 0.80 to 1.30 parts by mass per 100 parts by mass of the fluorine-containing copolymer (A);
It is presumed that this combination of configurations results in improved crosslink density without excessive stress concentration when crosslinking occurs at the nitrile groups and the crosslinking agent (B) as crosslinking points, resulting in a crosslinked rubber article with high heat resistance.

When the content of units based on monomers having a nitrile group in 100 mol% of all monomer units in the fluorine-containing copolymer (A) is 0.80 mol% or more and less than 1.00 mol%, the content of the crosslinking agent (B) is preferably 0.80 to 1.25 parts by mass, more preferably 0.80 to 1.22 parts by mass, particularly preferably 0.80 to 1.20 parts by mass, per 100 parts by mass of the fluorine-containing copolymer (A).
When the content of units based on a monomer having a nitrile group in 100 mol% of all monomer units in the fluorine-containing copolymer (A) is 0.80 to 0.95 mol%, the content of crosslinking agent (B) is preferably 0.80 to 1.25 parts by mass, more preferably 0.80 to 1.22 parts by mass, and particularly preferably 0.80 to 1.20 parts by mass, relative to 100 parts by mass of the fluorine-containing copolymer (A). For example, the content of units based on a monomer having a nitrile group in 100 mol% of all monomer units in the fluorine-containing copolymer (A) may be 0.80 to 0.95 mol%, and the content of crosslinking agent (B) may be 0.80 to 1.25 parts by mass, relative to 100 parts by mass of the fluorine-containing copolymer (A).
When the content of units based on a monomer having a nitrile group in 100 mol% of all monomer units in the fluorine-containing copolymer (A) is 0.85 to 0.95 mol%, the content of crosslinking agent (B) is preferably 0.80 to 1.25 parts by mass, more preferably 0.80 to 1.22 parts by mass, and particularly preferably 0.80 to 1.20 parts by mass, relative to 100 parts by mass of the fluorine-containing copolymer (A). For example, the content of units based on a monomer having a nitrile group in 100 mol% of all monomer units in the fluorine-containing copolymer (A) may be 0.85 to 0.95 mol%, and the content of crosslinking agent (B) may be 0.80 to 1.22 parts by mass, relative to 100 parts by mass of the fluorine-containing copolymer (A).
When the content of units based on a monomer having a nitrile group in 100 mol% of all monomer units in the fluorine-containing copolymer (A) is 0.85 to 0.90 mol%, the content of crosslinking agent (B) is preferably 0.80 to 1.25 parts by mass, more preferably 0.80 to 1.22 parts by mass, and particularly preferably 0.80 to 1.20 parts by mass, relative to 100 parts by mass of the fluorine-containing copolymer (A). For example, the content of units based on a monomer having a nitrile group in 100 mol% of all monomer units in the fluorine-containing copolymer (A) may be 0.85 to 0.90 mol%, and the content of crosslinking agent (B) may be 0.80 to 1.20 parts by mass, relative to 100 parts by mass of the fluorine-containing copolymer (A).

<Other crosslinking agents>
The fluorocopolymer composition of this embodiment may or may not contain other crosslinking agents. However, since the fluorocopolymer composition of this embodiment contains the crosslinking agent (B), it is preferable that it does not contain other crosslinking agents.
The other crosslinking agent is used to crosslink the fluorine-containing copolymer (A), and examples thereof include organic peroxides, polyols, triazines, etc. These may be used alone or in combination of two or more.
Among these, organic peroxides are preferred in view of the superior crosslinking reactivity of the fluorocopolymer (A), productivity of the crosslinked rubber article, heat resistance of the crosslinked rubber article, and chemical resistance of the crosslinked rubber article.

The total content of the crosslinking agent (B) and the other crosslinking agents is preferably from 0.80 to 1.25 parts by mass, more preferably from 0.80 to 1.22 parts by mass, and particularly preferably from 0.80 to 1.20 parts by mass, per 100 parts by mass of the fluorine-containing copolymer (A).
The content of the crosslinking agent (B) in 100% by mass of the total amount of crosslinking agents contained in the fluorinated copolymer composition is preferably from 60 to 100% by mass, more preferably from 80 to 100% by mass, particularly preferably from 90 to 100% by mass, and may be 100% by mass.

<Filler (C)>
The fluorine-containing copolymer composition may or may not contain a filler (C), but it is preferable that it contains a filler (C) in view of excellent releasability.
Examples of the filler (C) include carbon black, barium sulfate, calcium metasilicate, calcium carbonate, titanium oxide, silicon dioxide, aromatic polyester, polyamideimide, thermoplastic polyimide, clay, and talc.
Of these fillers (C), carbon black is preferred from the viewpoint of excellent releasability.
In the fluorine-containing copolymer composition, the content of the filler (C) per 100 parts by mass of the fluorine-containing copolymer (A) is not particularly limited, but from the viewpoint of heat resistance and chemical resistance, it is preferably from 1 to 20 parts by mass, more preferably from 5 to 20 parts by mass, particularly preferably from 10 to 20 parts by mass.

<Crosslinking aid (co-crosslinking agent)>
The fluorine-containing copolymer composition of the present embodiment may or may not contain a crosslinking aid (co-crosslinking agent).
The crosslinking aid is suitably used to improve crosslinking efficiency when the fluorine-containing copolymer (A) is crosslinked with an organic peroxide.
After the crosslinking reaction is completed, the crosslinking aid bonds with the fluorine-containing copolymer (A) and becomes part of the crosslinked structure.
The crosslinking aid is preferably a compound having two or more reactive functional groups in the same molecule. Specific examples of the reactive functional group include an unsaturated bond, a halogen atom, an acid anhydride residue, a carboxy group, an amino group, a cyano group, and a hydroxyl group. The multiple reactive functional groups present in the same molecule of the crosslinking aid may be the same or different.
The unsaturated bond may, for example, be a carbon-carbon double bond-containing group. Specific examples of the carbon-carbon double bond-containing group include alkenyl groups such as a vinyl group, an allyl group, and a methallyl group; unsaturated acyl groups such as an acryloyl group and a methacryloyl group; and a maleimide group. The carbon-carbon double bond-containing group is preferably an alkenyl group having 2 to 4 carbon atoms, and more preferably an allyl group.

When the fluorine-containing copolymer composition contains a crosslinking aid, the mass ratio of the content of the crosslinking agent to the content of the crosslinking aid in the fluorine-containing copolymer composition (content of crosslinking agent/content of crosslinking aid) is not particularly limited, but is preferably from 0.2 to 7.0, more preferably from 0.4 to 5.0, particularly preferably from 0.5 to 2.0, in terms of preventing unreacted crosslinking aid from remaining and allowing the crosslinking reaction to proceed well.
In the fluorine-containing copolymer composition, the total content of the crosslinking agent and crosslinking aid per 100.00 parts by mass of the fluorine-containing copolymer (A) is not particularly limited, but is preferably 0.80 to 5.00 parts by mass, more preferably 0.80 to 4.00 parts by mass, and particularly preferably 0.80 to 3.00 parts by mass. When the total content of the crosslinking agent and crosslinking aid is not less than the lower limit, the hardness of the crosslinked rubber article tends to be excellent. When the total content of the crosslinking agent and crosslinking aid is not more than the upper limit, the crosslinking reactivity is excellent.

When the fluorine-containing copolymer composition contains a cross-linking aid, the content of the cross-linking aid relative to the total mass of the fluorine-containing copolymer composition is not particularly limited, but from the viewpoint of heat resistance and chemical resistance, it is preferably 0.30 to 10.00 mass%, more preferably 0.30 to 5.00 mass%, and particularly preferably 0.31 to 1.00 mass%.

<Other ingredients>
The fluorine-containing copolymer composition may or may not contain components other than those described above, provided that the effects of the present invention are not impaired.
Examples of other components include processing aids (for example, acid acceptors such as fatty acid esters (glycerin monooleate, etc.), fatty acid metal salts (sodium stearate, calcium stearate, etc.), and oxides of divalent metals (magnesium oxide, calcium oxide, zinc oxide, lead oxide, etc.), synthetic waxes (polyethylene wax, etc.), and fluorine-containing copolymers other than the above-mentioned fluorine-containing copolymer (A) (hereinafter also referred to as "other fluorine-containing copolymers")), vulcanizing agents, scorch retarders (for example, phenolic hydroxyl group-containing compounds such as bisphenol A, quinones such as hydroquinone, and α-methylstyrene dimers such as 2,4-di(3-isopropylphenyl)-4-methyl-1-pentene), crown ethers (for example, 18-crown-6), and pigments.

There are no particular restrictions on the content of other components relative to the total mass of the fluorocopolymer composition, but from the viewpoint of heat resistance and chemical resistance, it is preferably 0 to 30 mass%, more preferably 0 to 20 mass%, and particularly preferably 0 to 10 mass%.

[Method for producing fluorine-containing copolymer composition]
The method for producing the fluorine-containing copolymer composition of the present invention is a method in which the fluorine-containing copolymer (A) and the crosslinking agent (B) are kneaded together.
The above-mentioned kneading can be achieved by kneading the fluorocopolymer (A), the crosslinking agent (B), and, if necessary, other components by a kneading method using a known rubber kneading apparatus such as a two-roll mill, a kneader, a Banbury mixer or an extruder.
Alternatively, the components may be kneaded together to obtain a mixture, which may then be molded. That is, the fluorine-containing copolymer composition may be a molded product. Specific examples of methods for molding the mixture include compression molding, injection molding, extrusion molding, calendar molding, or a method in which the mixture is dissolved in a solvent and then dipped or coated to form a molded product.

<Torque of Fluorine-Containing Copolymer Composition>
The torque difference (M _H −M _L ) of the fluorocopolymer composition measured by the following measurement method is preferably from 60 to 90 dN·m.
[Measurement method: Using a crosslinking property measuring device in accordance with JIS K6296-1:2023, the maximum torque M H and minimum torque M _L of the fluorocopolymer composition are measured under the conditions of a measurement temperature of 180°C, a measurement time of 30 minutes, a vibration frequency of 100 cpm, and an angle of 3.00 _deg .]
When the torque difference (M _H -M _L ) is 60 dN·m or more, sufficient crosslink density can be ensured and the compression set at 325° C. or higher is improved. When the torque difference (M _H -M _L ) is 90 dN·m or less, cracking of the test piece at 325° C. or higher can be suppressed. From these viewpoints, the torque difference (M _H -M _L ) is preferably 60 to 90 dN·m, more preferably 65 to 85 dN·m, and even more preferably 67 to 83 dN·m.

The torque M _H is preferably 68 to 96 dN·m. When the torque M _H is 68 dN·m or more, sufficient crosslink density can be ensured and the compression set at 325°C or higher is improved. When the torque M _H is 96 dN·m or less, cracking of the test piece at 325°C or higher can be suppressed. From these viewpoints, the torque M _H is preferably 70 to 95 dN·m, more preferably 71 to 90 dN·m, and even more preferably 73 to 89.0 dN·m.

The torque M _L is preferably 5.0 to 7.0 dN·m. When the torque M _L is 5.0 dN·m or more, sufficient crosslink density can be ensured and cracking of the test piece can be suppressed at 325°C or higher. When the torque M _L is 7.0 dN·m or less, cracking of the test piece can be suppressed at 325°C or higher. From these viewpoints, the torque M _L is preferably 5.5 to 6.5 dN·m, more preferably 5.7 to 6.3 dN·m, and even more preferably 5.8 to 6.1 dN·m.

[Crosslinked rubber article]
The crosslinked rubber article of the present invention is obtained by crosslinking the fluorocopolymer (A) in the fluorocopolymer composition of the present invention.

[Method for producing crosslinked rubber articles]
The process for producing a crosslinked rubber article of the present invention is a process for crosslinking the fluorocopolymer (A) in the fluorocopolymer composition.
The method for producing a crosslinked rubber article of the present invention is preferably a method in which the fluorocopolymer composition is primarily heated at 100 to 400°C for 1 second to 24 hours and, after the primary heating, is secondarily heated at 80 to 400°C for 30 minutes to 48 hours.
The crosslinked rubber article can be obtained by crosslinking the fluorocopolymer (A) in the fluorocopolymer composition.
Examples of the method for crosslinking the fluorine-containing copolymer (A) in the fluorine-containing copolymer composition include a method in which the fluorine-containing copolymer composition is crosslinked by heating, and a method in which the fluorine-containing copolymer composition is crosslinked by irradiation with ionizing radiation.
Specific examples of the crosslinking method by heating include heat press crosslinking, steam crosslinking and hot air crosslinking, from which an appropriate method may be selected taking into consideration the shape and application of the fluorocopolymer composition.

Examples of molding methods include injection molding, extrusion molding, co-extrusion molding, blow molding, compression molding, inflation molding, transfer molding, and calendar molding.
Examples of the extrusion molding method include (i) a method in which a suspension solution prepared by dissolving and dispersing the fluorine-containing copolymer (A) or the fluorine-containing copolymer composition in a suitable solvent is applied and dried to form a coating film, and (ii) a method in which the fluorine-containing copolymer (A) or the fluorine-containing copolymer composition is extruded and molded into the shape of a hose or an electric wire.

The fluorine-containing copolymer (A) is preferably crosslinked by heating.
A specific example of a method for producing a crosslinked rubber article by thermal crosslinking is hot press molding, which uses a heated mold, fills a cavity of the mold having a desired shape with a fluorocopolymer composition, and heats the composition to crosslink the composition simultaneously with molding (hot press crosslinking), thereby obtaining a crosslinked rubber article.
The heating temperature is not particularly limited, but is preferably 100 to 400° C., more preferably 130 to 220° C., even more preferably 140 to 200° C., and particularly preferably 150 to 180° C. The heating time is not particularly limited, but is preferably 1 second to 24 hours, more preferably 1 minute to 1 hour, and particularly preferably 5 minutes to 40 minutes.

When the hot press molding method is used, it is also preferable to further heat the crosslinked rubber article obtained by hot press crosslinking (sometimes referred to as primary crosslinking or primary heating) in an oven or the like using electricity, hot air, steam or the like as a heat source, as necessary, to advance the crosslinking (sometimes referred to as secondary crosslinking or secondary heating).
The temperature during secondary crosslinking is not particularly limited, but is preferably 80 to 400°C, more preferably 80 to 350°C, even more preferably 150 to 350°C, even more preferably 180 to 350°C, and particularly preferably 200 to 320°C. The secondary crosslinking time is not particularly limited, but is preferably 30 minutes to 48 hours, more preferably 1 hour to 48 hours, and particularly preferably 4 hours to 24 hours. By achieving sufficient secondary crosslinking, the rubber physical properties (mechanical properties, compression set, and other properties) of the crosslinked rubber article are improved. In addition, peroxide residues contained in the crosslinked rubber article are decomposed, volatilized, and reduced. The hot press molding method is preferably applied to molding sealing materials, etc.

Examples of the ionizing radiation in the method of irradiating with ionizing radiation include electron beams, ultraviolet rays, gamma rays, etc. When crosslinking is carried out by irradiation with ionizing radiation, a preferred method is to previously mold the fluorine-containing copolymer (A) or the fluorine-containing copolymer composition into a desired shape and then irradiate it with ionizing radiation to crosslink it.
The dose of ionizing radiation is appropriately set, preferably 1 to 300 kGy, more preferably 10 to 200 kGy.

<Physical properties>
The compression set CS of the crosslinked rubber article at 325°C for 70 hours is not particularly limited, but is preferably 40% or less, more preferably 25% or less, particularly preferably 22% or less, in view of the fact that the fluorocopolymer (A) is well crosslinked and the crosslinked rubber article has better shape recovery after being pressurized.
The compression set CS of the crosslinked rubber article at 325°C for 168 hours is not particularly limited, but from the same viewpoint, it is preferably 55% or less, more preferably 39% or less, and particularly preferably 36% or less.
The compression set CS of the crosslinked rubber article at 340° C. for 70 hours is not particularly limited, but from the same viewpoint, it is preferably 53% or less, more preferably 42% or less, and particularly preferably 39% or less.
The compression set CS of the crosslinked rubber article at 340° C. for 168 hours is not particularly limited, but from the same viewpoint, it is preferably 80% or less, more preferably 65% or less, and particularly preferably 64% or less.
The compression set of the crosslinked rubber article is measured by the method described in the Examples section below.

<Application>
The crosslinked rubber article is suitable for use as a material for O-rings, sheets, gaskets, oil seals, diaphragms, V-rings, and the like. The crosslinked rubber articles can also be used in semiconductor manufacturing equipment parts, heat-resistant and chemical-resistant sealing materials, heat-resistant and oil-resistant sealing materials, wire coating materials, sealing materials for liquid crystal display panel manufacturing equipment, sealing materials for light-emitting diode manufacturing equipment, corrosion-resistant rubber paints, sealing materials for urea-resistant grease, rubber paints, adhesive rubbers, hoses, tubes, calendered sheets (rolls), sponges, rubber rolls, oil drilling components, heat-dissipating sheets, solution-crosslinked products, rubber sponges, bearing seals (urea-resistant grease and the like), linings (chemical-resistant), insulating sheets for automobiles, insulating sheets for electronic devices, rubber bands for watches, endoscope packings (amine-resistant), bellows hoses (processed from calendered sheets), water heater packings/valves, fenders (offshore civil engineering, ships), fibers and nonwoven fabrics (protective clothing and the like), board sealing materials, rubber gloves, stators for uniaxial eccentric screw pumps, parts for urea SCR systems, vibration isolators, vibration dampers, sealants, additives for other materials, and toys.
Examples of semiconductor manufacturing equipment parts using crosslinked rubber articles include sealing materials (O-rings, square rings, gaskets, packings, oil seals, bearing seals, lip seals, etc.), tubes, hoses, various rubber rolls, diaphragms, linings, etc.
Examples of semiconductor manufacturing equipment include etching equipment (dry etching equipment, plasma etching equipment, reactive ion etching equipment, reactive ion beam etching equipment, sputter etching equipment, ion beam etching equipment, wet etching equipment, ashing equipment, etc.), cleaning equipment (dry etching cleaning equipment, UV/ _O3 cleaning equipment, ion beam cleaning equipment, laser beam cleaning equipment, plasma cleaning equipment, gas etching cleaning equipment, extraction cleaning equipment, Soxhlet extraction cleaning equipment, high temperature and high pressure extraction cleaning equipment, microwave extraction cleaning equipment, supercritical extraction cleaning equipment, etc.), exposure equipment (stepper, coater developer, etc.), polishing equipment (CMP equipment, etc.), film formation equipment (CVD equipment, sputtering equipment, etc.), diffusion/ion implantation equipment (oxidation diffusion equipment, ion implantation equipment, etc.), etc.

The present invention will be specifically described below based on examples, but the present invention is not limited to the following examples, and various modifications are possible within the scope of the gist of the present invention.
Examples 1 and 2 are working examples, and Examples 3 to 8 are comparative examples.

<Measurement of Fluorine-Containing Copolymer Composition>
The content (mol %) of each unit in Fluorocopolymer 1 and Fluorocopolymer 2 was calculated by ¹⁹ F-nuclear magnetic resonance (NMR) analysis, except that the content of propylene units was calculated from ¹ H and ¹³ C-nuclear magnetic resonance (NMR) analysis.

<Identification of Carboxy Terminals in Fluorinated Copolymers>
The carboxyl end group ratio was quantified by the integrated absorbance from 1700 to 1850 cm ⁻¹ . To quantitatively compare the carboxyl end group ratio between different samples, the integrated absorbance ratio was normalized by taking the ratio to the integrated absorbance from 2210 to 2700 cm ⁻¹ .
The obtained fluorocopolymer was press-molded at 100°C to obtain a sheet. The obtained sheet was measured with a transmission Fourier transform infrared spectrophotometer to obtain an infrared absorption spectrum. From the obtained spectrum, the carboxy terminal group amount ratio was calculated.

<Measurement of Torque Difference (M _H -M _L )>
The obtained fluorine-containing copolymer composition was cut into 10 g pieces to obtain cut pieces. The obtained cut pieces were sandwiched between two polyester films (manufactured by ALFA Technologies, PART#F0311-S, 130 mm × 130 mm × 24 μm) on both main surfaces to obtain a measurement sample. The measurement sample was placed on a die.
Next, torque (dNm) was measured in accordance with a method in accordance with JIS K6296-1:2023 under the conditions of a measuring device: PREMER RPA (manufactured by Alpha Technologies), die shape: D0380, 180°C (test temperature), 30 minutes (vulcanization time), vibration frequency: 100 cpm, and angle: 3.00 deg., and a torque-vulcanization time curve was obtained.
From the obtained torque-vulcanization time curve, the minimum torque value (M _L ) and the maximum torque value (M _H ) were identified, and the torque difference (M _H -M _L ) was calculated from these values.

<Measurement of compression set, etc.>
The compression set of the obtained crosslinked rubber article (O-ring) was measured with reference to JIS K 6262:2013.
The O-rings (original thickness (wire diameter) of the test specimen = 3.5 mm) produced in each example were compressed to a compression rate of 18% using a compression device.
Next, the compression device with the compressed O-ring fixed thereto was placed in an electric furnace and left standing at 325°C for 70 hours (compression treatment 1), 325°C for 168 hours (compression treatment 2), 340°C for 70 hours (compression treatment 3), or 340°C for 168 hours (compression treatment 4). Thereafter, the compression device was removed from the electric furnace, and the O-ring was immediately removed from the compression device.
The removed O-ring was placed in a constant temperature room and left at 23°C for 30 minutes. Thereafter, the thickness of the O-ring (thickness after compression treatment) was measured. The test was performed using two test pieces, and the arithmetic average of the measured values of the two test pieces was used.
The compression set was calculated using the following formula: The closer the compression set is to 0%, the better the result is.
Compression set rate (%) = {original thickness of test piece (wire diameter) - thickness of test piece 30 minutes after removal from compression device (thickness after compression treatment)} ÷ (original thickness of test piece - thickness of spacer) x 100
The test pieces were also evaluated for the presence or absence of cracks according to the following criteria.
0/2: Neither of the two pieces broke.
1/2: One of the two pieces broke.
2/2: 2 out of 2 pieces were broken.

<Compounds used>
Details of the various compounds used and explanations of their abbreviations are given below.
(1) Monomers: TFE: tetrafluoroethylene; PMVE: CF ₂ ═CFOCF ₃ : perfluoro(methyl vinyl ether)
・8CNVE: CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ CN
(2) Polyamine compound (crosslinking agent)
BOAP: 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (3) Emulsifier C ₂ F ₅ OCF ₂ CF ₂ OCF ₂ COONH ₄
(4) Polymerization initiator: APS: ammonium persulfate (5) Filler: CB: carbon black (manufactured by Cancarb Limited, grade: N990, particle size (D50): 450 nm)
(6) pH adjuster: disodium hydrogen phosphate dodecahydrate (7) coagulant: nitric acid, manufactured by Kanto Chemical Co., Ltd.

[Production of Fluorine-Containing Copolymer]
Fluorine-containing copolymers 1 and 2 were produced as follows.

<Fluorine-containing copolymer 1>
After degassing a 20 L stainless steel pressure reactor equipped with anchor blades, 9795 g of ultrapure water, 1194 g of a 30 mass% solution of C ₂ F ₅ OCF ₂ CF ₂ OCF ₂ COONH ₄ as an emulsifier, 50.0 g of 8CNVE, and 21.5 g of a 5 mass% aqueous solution of disodium hydrogen phosphate dodecahydrate were charged, and the gas phase was replaced with nitrogen. While stirring at a speed of 180 rpm using anchor blades, 118 g of TFE and 545 g of PMVE were pressed into the vessel, and the internal temperature was then raised to 80 ° C. The internal pressure of the reactor was 0.90 MPa [gauge]. 100 mL of a 3 mass% aqueous solution of ammonium persulfate (APS) was added to initiate polymerization. The molar ratio of the monomers injected before the start of polymerization (hereinafter also referred to as "initial monomers") was TFE:PMVE:8CNVE=23.6:73.6:2.8.
After the initiation of polymerization, as the polymerization progressed, monomers were injected as follows. Hereinafter, injection of a monomer after the initiation of polymerization will also be referred to as "post-addition," and a monomer injected after the initiation of polymerization will also be referred to as "post-added monomer."

When the pressure inside the reactor dropped to 0.89 MPa [gauge], TFE was injected and the pressure inside the reactor was increased to 0.90 MPa [gauge]. This process was repeated, and every time 153 g of TFE was injected, 10.1 g of 8CNVE and 113 g of PMVE were injected in this order.
When the cycle was completed and the total added mass of TFE reached 1071 g, 153 g of TFE was injected. When the total added mass of post-added TFE reached 1224 g, the addition of the post-added monomer was stopped, the reactor internal temperature was cooled to 10 ° C., and the polymerization reaction was stopped to obtain a latex containing a fluorine-containing copolymer. The polymerization time was 273 minutes. The total added masses of the post-added monomers were 1224 g of TFE, 791 g of PMVE, and 70.6 g of 8CNVE, which was converted into a molar ratio of TFE:PMVE:8CNVE = 71.2:27.7:1.1.

The latex was added to a 5% by mass aqueous solution of nitric acid to coagulate and separate the fluorocopolymer. The fluorocopolymer was filtered, washed with ultrapure water, and vacuum dried at 100°C to obtain a white fluorocopolymer 1. The content (molar ratio) of each unit in the obtained fluorocopolymer 1 was TFE unit:PMVE unit:8CNVE unit = 68.6:30.5:0.9.
The amount of carboxyl terminal groups in the resulting fluorocopolymer 1 was measured by the above-mentioned method and was found to be 0.88.

<Fluorine-containing copolymer 2>
After degassing a 20 L stainless steel pressure reactor equipped with anchor blades, 7.2 L of ultrapure water, 880 g of a 30 mass% solution of C ₂ F ₅ OCF ₂ CF ₂ OCF ₂ COONH ₄ as an emulsifier, 7.3 g of 8CNVE, and 15.9 g of a 5 mass% aqueous solution of disodium hydrogen phosphate dodecahydrate were charged, and the gas phase was replaced with nitrogen. While stirring at a speed of 375 rpm using anchor blades, 137 g of TFE and 635 g of PMVE were pressed into the vessel, and the internal temperature was then raised to 80 ° C. The internal pressure of the reactor was 0.90 MPa [gauge]. 28 mL of a 3 mass% aqueous solution of ammonium persulfate (APS) was added to initiate polymerization. The molar ratio of the initially added monomers was TFE:PMVE:8CNVE=26.3:73.3:0.4.

After the initiation of polymerization, as the polymerization progressed, the monomers were injected as follows.
When the pressure inside the reactor dropped to 0.89 MPa [gauge], TFE was injected and the pressure inside the reactor was increased to 0.90 MPa [gauge]. This was repeated, and every time 119.3 g of TFE was injected, 3.7 g of 8CNVE, 74 g of PMVE, and 3.7 g of 8CNVE were injected in this order.
When the polymerization rate began to decrease, a 3% by mass aqueous solution of APS was appropriately added. The total amount of the 3% by mass aqueous solution of APS added after the start of polymerization was 35 mL.
When the cycle was completed and the total added mass of TFE reached 1073.7 g, 119.3 g of TFE was injected. When the total added mass of post-added TFE reached 1193 g, the addition of the post-added monomer was stopped, the reactor internal temperature was cooled to 10 ° C., and the polymerization reaction was stopped to obtain a latex containing a fluorine-containing copolymer. The polymerization time was 375 minutes. The total added masses of the post-added monomers were 1193 g of TFE, 666 g of PMVE, and 66.6 g of 8CNVE, which was converted into a molar ratio of TFE:PMVE:8CNVE=74.0:25.0:1.0.

The latex was added to a 5% by mass aqueous solution of aluminum potassium sulfate, and the fluorocopolymer was coagulated and separated. The fluorocopolymer was filtered, washed with ultrapure water, and vacuum dried at 50°C to obtain a white fluorocopolymer 2. The content (molar ratio) of each unit in the obtained fluorocopolymer 2 was TFE unit:PMVE unit:8CNVE unit=70.9:28.6:0.5.
The amount of carboxyl terminal groups in the resulting fluorocopolymer 2 was measured by the above-mentioned method and found to be 0.66.

[Examples 1 to 8]
(1) Production of Fluorocopolymer Composition The components shown in Table 1 were mixed in the amounts (parts by mass) shown in Table 1 and kneaded with a two-roll mill at room temperature for 10 minutes to obtain a mixed fluorocopolymer composition.
The above-mentioned physical properties of the obtained fluorocopolymer composition were measured. The measurement results are shown in Table 1.

(2) Production of Crosslinked Rubber Article (O-Ring) The obtained fluorocopolymer composition was hot-pressed at 180°C for 30 minutes using a hydraulic press (model: SA-301 50T type, manufactured by Tester Sangyo Co., Ltd., ram diameter: 180 mm) to obtain an O-ring (P-26 (standard specified in JIS B2401:2012)) (primary crosslink).
Immediately after molding, the mold releasability was evaluated.
A: The O-ring could be removed from the mold.
B: The O-ring was stuck to the mold and could not be removed.
Samples that could not be removed during the mold releasability evaluation were cooled sufficiently, and after the samples had thermally shrunk, they were removed from the mold.
The O-ring was then heated in an oven under a nitrogen atmosphere under the following conditions (secondary crosslinking).
Secondary crosslinking conditions: After heating at 90°C for 2 hours, the temperature was increased to 200°C over 2 hours and maintained at 200°C for 4 hours. The temperature was then increased to 305°C over 2 hours and further heated at 305°C for 13 hours.

Thereafter, the O-rings were cooled to room temperature to obtain the O-rings of Examples 1 to 8, which were crosslinked rubber articles.
The above-mentioned physical properties of the resulting crosslinked rubber article were measured. The measurement results are shown in Table 1.

As can be seen from the evaluation results shown in Table 1, crosslinked rubber articles (Examples 1 and 2) obtained by crosslinking a fluorocopolymer of a fluorocopolymer composition of the present invention had smaller compression set after compression treatment at high temperatures of 325°C and 340°C, and were less likely to crack due to the compression treatment, compared to crosslinked rubber articles (Examples 3 to 8) obtained by crosslinking a fluorocopolymer of a fluorocopolymer composition not of the present invention.

Claims (11)

A fluorine-containing copolymer (A) having units based on a monomer having a nitrile group and units based on tetrafluoroethylene, and a crosslinking agent (B) having two or more amino groups,
the content of units based on the monomer having a nitrile group in 100 mol % of all monomer units in the fluorine-containing copolymer (A) is 0.80 mol % or more and less than 1.00 mol %,
The fluorine-containing copolymer composition, wherein the content of the crosslinking agent (B) is 0.80 to 1.30 parts by mass per 100 parts by mass of the fluorine-containing copolymer (A). the fluorine-containing copolymer (A) has units based on perfluoro(alkyl vinyl ether),
the content of units based on tetrafluoroethylene in 100 mol% of all monomer units in the fluorine-containing copolymer (A) is 67.0 mol% or more and less than 71.5 mol%,
The fluorine-containing copolymer composition according to claim 1, wherein the content of units based on said perfluoro(alkyl vinyl ether) in 100 mol% of all monomer units in said fluorine-containing copolymer (A) is 27.0 to 32.0 mol%. 2. The fluorine-containing copolymer composition according to claim 1, wherein said fluorine-containing copolymer (A) has a carboxy terminal group, and the ratio of the integrated peak intensity of absorbance at 1700 to 1850 cm ^{−1 to the integrated peak intensity of absorbance at 2210 to 2700 cm −1 in} the spectrum obtained by measuring said fluorine-containing copolymer (A) by infrared spectroscopy is 0.7 or more. The fluorine-containing copolymer composition according to claim 1, wherein the crosslinking agent (B) is 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane. The fluorinated copolymer composition according to claim 1, which contains a filler (C). The fluorocopolymer composition according to claim 5, wherein the content of the filler (C) is 1 to 20 parts by mass per 100 parts by mass of the fluorocopolymer (A). The fluorine-containing copolymer composition according to claim 6, wherein the filler (C) is carbon black. 2. The fluorocopolymer composition according to claim 1, wherein the torque difference (M _H −M _L ) of said fluorocopolymer composition measured by the following measurement method is from 60 to 90 dN·m.
[Measurement method: Using a crosslinking property measuring device in accordance with JIS K6296-1:2023, the maximum torque M H and minimum torque M _L of the fluorocopolymer composition are measured under the conditions of a measurement temperature of 180°C, a measurement time of 30 minutes, a vibration frequency of 100 cpm, and an angle of 3.00 _deg .] The method for producing the fluorocopolymer composition according to any one of claims 1 to 8, comprising kneading the fluorocopolymer (A) and the crosslinking agent (B). A crosslinked rubber article obtained by crosslinking the fluorocopolymer (A) in the fluorocopolymer composition according to any one of claims 1 to 8. A method for producing a crosslinked rubber article, comprising crosslinking the fluorocopolymer (A) in the fluorocopolymer composition according to any one of claims 1 to 8.