Sheet, method for producing sheet, and crosslinked rubber article

Abstract

Provided is a sheet containing a fluorine-containing copolymer. The arithmetic mean surface roughness Ra of at least one surface of the sheet is 5.0 μm or less, and the thickness of the sheet is 4 mm or less. Also provided is a method for producing a sheet containing a fluorine-containing copolymer, in which method a raw material containing a fluorine-containing copolymer is wound around a roll by a roll kneader equipped with at least one pair of rolls to form a sheet, the maximum temperature of the raw material when forming the sheet is 60°C or more, and the thickness of the obtained sheet is 4 mm or less.

Description

Sheet, method for manufacturing the sheet, and crosslinked rubber article

[0001] The present invention relates to a sheet, a method for manufacturing a sheet, and a crosslinked rubber article. This application claims priority based on Japanese Patent Application No. 2024-197403, filed in Japan on November 12, 2024, the contents of which are incorporated herein by reference.

[0002] Crosslinked rubber articles, made by crosslinking fluorine-containing copolymers, are widely used in fields such as vehicles, ships, aircraft, general machinery, and construction as sealing materials (e.g., O-rings, packings, oil seals, gaskets), cushioning materials, etc., due to their excellent heat resistance, chemical resistance, oil resistance, and weather resistance.

[0003] As a fluorine-containing copolymer composition used to obtain such crosslinked rubber articles, Patent Document 1 discloses a fluorine-containing copolymer composition comprising a fluorine-containing copolymer, an organic peroxide, a compound having two or more polymerizable unsaturated bonds, and a phosphorus compound with a melting point of 60°C or lower. Patent Document 1 also describes obtaining a fluorine-containing copolymer composition by kneading the raw materials with two rolls at room temperature for 10 minutes.

[0004] International Publication No. 2020 / 184427

[0005] When raw materials are kneaded using two rollers, the kneaded material forms a sheet as it passes through the gap between the rollers, yielding a fluorine-containing copolymer composition sheet. However, conventional fluorine-containing copolymer composition sheets are prone to static electricity and easily attract foreign matter due to the presence of the fluorine copolymer. If a sealing material is made from a fluorine-containing copolymer composition sheet with foreign matter attached, there is a concern that the sealing material may become a source of contamination. Therefore, to prevent contamination, fluorine-containing copolymer composition sheets are sometimes inspected visually or mechanically to remove foreign matter. However, it is easy to overlook foreign matter in conventional fluorine-containing copolymer composition sheets.

[0006] The present invention provides a sheet with low electrostatic properties and a low rate of foreign matter detection, a method for manufacturing the same, and a crosslinked rubber article using the sheet.

[0007] The present invention has the following aspects. [1] A sheet containing a fluorine-containing copolymer, wherein the arithmetic mean surface roughness Ra of at least one surface is 5.0 μm or less and the thickness is 4 mm or less. [2] The sheet according to [1] above, which is a single-leaf sheet and has a polygonal shape in which all sides forming the outer edge are linearly formed in a plan view. [3] The sheet according to [1] or [2] above, wherein the root mean square height Rq of the surface is 10 μm or less. [4] The sheet according to any one of [1] to [3] above, wherein the maximum cross-sectional height Rt of the surface is 50 μm or less. [5] The sheet according to any one of [1] to [4] above, wherein the standard deviation of the thickness is 0.4 mm or less. [6] The sheet according to any one of [1] to [5] above, further containing a compound represented by the following formula (2). H ２ C=CH-R １ -R ３ -R ２ -CH=CH ２ ...(2) However, R １ and R ２ are each independently CH ２ or CF ２ and R ３This represents a divalent fluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end of the fluorohydrocarbon group or between carbon-carbon bonds. [7] A method for producing a sheet containing a fluorine-containing copolymer, comprising: forming a sheet by winding a raw material containing a fluorine-containing copolymer onto rolls in a roll kneading machine equipped with at least one pair of rolls, wherein the maximum temperature of the raw material when forming the sheet is 60°C or higher, and the thickness of the resulting sheet is 4 mm or less. [8] The method for producing a sheet according to [7], wherein the sheet wound onto the rolls is cut to a predetermined width in the circumferential direction of the rolls with a roll cutter, and the sheet cut to the predetermined width is cut to a predetermined length in the axial direction of the rolls to cut out a single sheet. [9] The method for producing a sheet according to [7] or [8], wherein the maximum temperature and the thickness of the sheet are adjusted so that the absolute value of the charge potential measured after placing the sheet on an antistatic mat for 5 minutes is 6 V or less.

[10] The method for producing a sheet according to any one of [7] to [9], wherein the raw material further comprises a compound represented by the following formula (2). H ２ C = CH - R １ -R ３ -R ２ -CH=CH ２ ... (2) However, R １ and R ２ Each is independent of CH ２ or CF ２ R ３ This represents a divalent fluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the terminal or between carbon-carbon bonds of the fluorohydrocarbon group.

[11] A crosslinked rubber article obtained by crosslinking the fluorine-containing copolymer in the sheet according to any one of [1] to [6] above.

[0008] According to the present invention, it is possible to provide a sheet with low electrostatic properties and a low rate of foreign matter detection, a method for manufacturing the same, and a crosslinked rubber article using the sheet.

[0009] This is a schematic side view showing an example of a roll mixer. This is a schematic front view of the roll mixer shown in Figure 1. This is a photograph of the sheet obtained in Example 1. This is a photograph of the sheet obtained in Example 3.

[0010] The meanings and definitions of terms used in this invention are as follows: "Unit" refers to a collective term for atomic groups derived from one monomer molecule directly formed by the polymerization of monomers, and atomic groups obtained by chemically transforming a part of the above atomic group. "Unit based on monomer" will also be simply referred to as "unit" below. "Rubber" refers to rubber exhibiting the properties defined by JIS K 6200:2008, and is distinguished from "resin." The "arithmetic mean surface roughness Ra," "root mean square height Rq," and "maximum cross-sectional height Rt" of the sheet surface, as well as the "thickness," "standard deviation of thickness," and "density" of the sheet, are measured by the methods described in the examples below. "Arithmetic mean surface roughness Ra," "root mean square height Rq," and "maximum cross-sectional height Rt" are also simply referred to as "Ra," "Rq," and "Rt," respectively. The "~" indicating a numerical range means that the values ​​written before and after it are included as the lower and upper limits.

[0011] [Sheet] The sheet according to one embodiment of the present invention includes a fluorine-containing copolymer. The fluorine-containing copolymer will be described in detail later.

[0012] The Ra of at least one surface of the sheet is 5.0 μm or less, preferably 3.0 μm or less, and more preferably 2.0 μm or less. If the sheet contains a compound represented by formula (2) described later, it is even more preferable to have a Ra of 1.0 μm or less. When Ra is below the above upper limit, the electrostatic charge and the rate of foreign matter detection are reduced. In terms of electrostatic charge and the rate of foreign matter detection, a lower Ra is preferable, and there is no particular lower limit, but in terms of adhesiveness when sheets are stacked, it is preferable to have a Ra of 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 0.7 μm or more. The above upper and lower limits can be combined as appropriate.

[0013] The Rq of at least one surface of the sheet is preferably 10 μm or less, more preferably 8.0 μm or less, and even more preferably 3.0 μm or less. If the sheet contains a compound represented by formula (2) described later, it is particularly preferably 2.0 μm or less. When Rq is below the above upper limit, the electrostatic charge and the rate of foreign matter detection are lower. In terms of electrostatic charge and the rate of foreign matter detection, a lower Rq is preferable, and there is no particular lower limit, but in terms of adhesiveness when sheets are stacked, it is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 0.8 μm or more. The above upper and lower limits can be combined as appropriate.

[0014] The Rt of at least one surface of the sheet is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less. If the sheet contains a compound represented by formula (2) described later, it is particularly preferably 10 μm or less. When Rt is below the above upper limit, the electrostatic charge and the rate of foreign matter detection are lower. In terms of electrostatic charge and the rate of foreign matter detection, a lower Rt is preferable, and there is no particular lower limit, but in terms of adhesiveness when sheets are stacked, it is preferably 1.0 μm or more, more preferably 5.0 μm or more, and even more preferably 7 μm or more. The above upper and lower limits can be combined as appropriate.

[0015] The sheet thickness is 4 mm or less, preferably 3.8 mm or less, and more preferably 3.6 mm or less. When the thickness is below the above upper limit, the transparency of the sheet improves, and the rate of missing foreign objects decreases. Also, the electrostatic properties tend to decrease. In terms of suppressing shrinkage and bending of the sheet, the sheet thickness is preferably 1.0 mm or more, more preferably 2 mm or more, and even more preferably 2.5 mm or more. The above upper and lower limits can be combined as appropriate.

[0016] The standard deviation of the sheet thickness is preferably 2.1 mm or less, more preferably 0.4 mm or less, even more preferably 0.1 mm or less, and particularly preferably 0.05 mm or less. When the standard deviation of thickness is below the above upper limit, the electrostatic charge and the rate of foreign matter detection are lower. In terms of electrostatic charge and the rate of foreign matter detection, a lower standard deviation of thickness is preferable, and there is no particular lower limit, but in terms of stable productivity, a standard deviation of 0.001 mm or more is preferable, and a standard deviation of 0.01 mm or more is more preferable. The above upper and lower limits can be combined as appropriate.

[0017] The density of the sheet is not particularly limited, but for example, 2.00 to 4.00 g / cm³. ３ Furthermore, 2.00 to 2.04 g / cm³ ３ Furthermore, 2.01 to 2.03 g / cm³ ３ That is the case.

[0018] The sheet may be a single sheet or a continuous strip. A single sheet is preferred in terms of ease of feeding into a roll machine. The shape of a single sheet in plan view is typically a roughly rectangular shape, but is not limited to this; other shapes, such as roughly polygonal shapes other than a rectangle, are also acceptable. A roughly rectangular shape means that at least some of the sides constituting the outer edge of the rectangle may be non-linear in plan view (e.g., irregularly curved shapes). The same applies to roughly polygonal shapes. An example of a roughly rectangular shape is one in which, of the four sides, two opposing sides in the first direction (e.g., the roll circumferential direction described later) are linear, and the remaining two sides are non-linear. A single sheet is preferable to have a polygonal shape in plan view, where all sides constituting the outer edge are linear, in order to reduce the rate of foreign matter being missed. Of the polygonal shapes, a rectangular shape is preferred in terms of ease of manufacturing. The end faces of the sheet in the in-plane direction are preferably two-dimensional planes in order to further reduce the rate at which foreign objects are missed.

[0019] <Fluorine-containing copolymers> Fluorine-containing copolymers are not particularly limited as long as they contain fluorine atoms and exhibit rubber properties through crosslinking, but those having monomer units containing fluorine atoms (hereinafter also referred to as "fluorine-containing monomers") are preferred, and perfluoropolymers are particularly preferred because they can reduce the compression set of the resulting crosslinked rubber articles. Fluorine-containing copolymers may also have units based on monomers other than those mentioned above (hereinafter also referred to as "other monomers").

[0020] A "perfluoropolymer" is a polymer that substantially does not contain hydrogen atoms bonded to carbon atoms, instead having fluorine atoms, and whose main chain consists of a chain of carbon atoms. The side chains of the perfluoropolymer may contain polyvalent atoms other than carbon atoms, and oxygen atoms are preferred as such polyvalent atoms. "Substantially free of hydrogen atoms" means that the hydrogen atom content in the perfluoropolymer is 0.5% by mass or less, preferably 0.1% by mass or less, more preferably 0.07% by mass or less, and particularly preferably 0.05% by mass or less. When the hydrogen atom content is within the above range, good heat resistance or chemical resistance is easily obtained.

[0021] Specific examples of fluorine-containing monomers include tetrafluoroethylene (hereinafter also referred to as "TFE"), perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE"), vinylidene fluoride (hereinafter also referred to as "VDF"), hexafluoropropylene (hereinafter also referred to as "HFP"), and chlorotrifluoroethylene (hereinafter also referred to as "CTFE").

[0022] As PAVE, the compound represented by formula (m1) is preferred due to its excellent polymerization reactivity and rubber properties. CF ２ =CF-O-R ｆ１ ... (m1) In equation (m1), R ｆ１ R represents a perfluoroalkyl group having 1 to 10 carbon atoms. ｆ１The number of carbon atoms is preferably 1 to 8, more preferably 1 to 6, even more preferably 1 to 5, and particularly preferably 1 to 3, from the viewpoint of superior polymerization reactivity. The perfluoroalkyl group may be linear or branched. Specific examples of PAVE include perfluoro(methyl vinyl ether) (hereinafter also referred to as "PMVE"), perfluoro(ethyl vinyl ether) (hereinafter also referred to as "PEVE"), and perfluoro(propyl vinyl ether) (hereinafter also referred to as "PPVE"), with PMVE or PPVE being preferred, and PMVE being more preferred.

[0023] Fluorine-containing copolymers are typically fluorine-containing elastomers. A "fluorine-containing elastomer" is a polymer having a glass transition temperature of 20°C or less and a melting peak (ΔH) of 4.5 [J / g] or less, and having at least one fluorine atom in the monomers constituting the polymer. The lower limit of the glass transition temperature is not particularly limited, but is, for example, 3°C. The glass transition temperature can be determined using a differential scanning calorimeter (e.g., "DSC600" manufactured by Hitachi High-Tech Science Corporation) to obtain a DSC curve by raising the temperature of 10 mg of the sample from -50°C at a rate of 10°C / min, and the temperature is the midpoint of the intersection of the extension of the baseline before and after the second-order transition of the DSC curve and the tangent line at the inflection point of the DSC curve.

[0024] Examples of fluorine-containing elastomers include FFKM, FEPM, and FKM. FFKM is a fluorine-containing copolymer that contains TFE units and PAVE units as essential units, with a total ratio of TFE units and PAVE units to the total of all units of 80 mol% or more. In FFKM, the molar ratio expressed as TFE units / PAVE units is preferably 60 / 40 to 20 / 80. FFKM may also contain other monomer units. FEPM is a fluorine-containing copolymer that contains TFE units and propylene (hereinafter also referred to as "P") units as essential units, with a total ratio of TFE units and P units to the total of all units of 50 mol% or more. In FEPM, the molar ratio expressed as TFE units / P units is preferably 80 / 20 to 20 / 80. FEPM may also contain other monomer units. FKM is a fluorine-containing copolymer containing VDF units and HFP units as essential units. In FKM, the total ratio of VDF units and HFP units to the total of all units is preferably 50 mol% or more. The molar ratio expressed as VDF units / HFP units is preferably 95 / 5 to 60 / 40. FKM may contain other monomer units. As the fluorine-containing copolymer, FFKM or FEPM is preferred, with FFKM being more preferred.

[0025] Other monomers include, for example, monomers having two or more polymerizable unsaturated bonds (hereinafter also referred to as "BO"), and monomers having one or more atoms selected from the group consisting of chlorine atoms, bromine atoms, and iodine atoms (hereinafter referred to as "R"). Ｈａｌ Also called "R ＣＮ This also refers to ), as well as the compound represented by formula (m6) described later (hereinafter also referred to as "POAVE").

[0026] BO is a monomer having two or more polymerizable unsaturated bonds. Examples of polymerizable unsaturated bonds include carbon-carbon double bonds (C=C) and carbon-carbon triple bonds (C≡C). The number of polymerizable unsaturated bonds in BO is preferably two or more and six or less, more preferably two or three, and even more preferably two, from the viewpoint of superior polymerization reactivity. BO preferably contains a fluorine atom from the viewpoint of reducing the compression set of the crosslinked rubber article at high temperatures.

[0027] As for BO, the compound represented by formula (m2) is preferred because it provides superior release properties for crosslinked rubber articles. (CR ２１ R ２２ =CR ２３ -) ａ１ R ２４ ... (m2) In equation (m2), R ２１ , R ２２ , and, R ２３ Each of these independently represents a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group, and a1 represents an integer from 2 to 6, R ２４ This represents a 1-valent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the terminal or between carbon-carbon bonds of a 1-valent perfluorohydrocarbon group having 1 to 10 carbon atoms. Multiple R ２１ , multiple R ２２ and multiple R ２３ Each of them may be the same or different from each other, but it is preferable that they be the same. a1 is preferably 2 or 3, and 2 is particularly preferred.

[0028] From the perspective that BO has superior polymerization reactivity, R ２１ , R ２２ and R ２３ It is preferable that R is a fluorine atom or a hydrogen atom. ２１ , R ２２ and R ２３ It is more preferable that all of them are fluorine atoms or all of them are hydrogen atoms, as this provides better release properties for the crosslinked rubber article. ２１ , R ２２ and R ２３It is particularly preferable that all of them are fluorine atoms. ２４ The chain may be linear, branched, or cyclic, with linear or branched being preferred, and linear being particularly preferred. ２４ The number of carbon atoms is preferably 2 to 8, more preferably 3 to 7, even more preferably 3 to 6, and particularly preferably 3 to 5.

[0029] R ２４ It may or may not have etheric oxygen atoms, but it is preferable to have etheric oxygen atoms because it provides superior crosslinking reactivity and rubber properties. ２４ The number of etheric oxygen atoms in is preferably 1 to 6, more preferably 1 to 3, and even more preferably 1 or 2. ２４ The etheric oxygen atom in R ２４ It is preferable that it be located at the terminal end.

[0030] Preferred examples of compounds represented by formula (m2) include the compounds represented by formula (m3) and the compounds represented by formula (m4). (CF ２ =CF-) ２ R ３１ ...(m3) In formula (m3), R ３１ This refers to a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the terminal or between carbon-carbon bonds of a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms. (CH ２ =CH-) ２ R ４１ ...(m4) In formula (m4), R ４１ This refers to a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the terminal or between carbon-carbon bonds of a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms.

[0031] A specific example of a compound represented by formula (m3) is CF ２ = CFO (CF ２ ) ２ OCF = CF ２ CF ２ = CFO (CF ２ ) ３ OCF = CF ２, CF ２ = CFO(CF ２ ) ４ OCF = CF ２ , CF ２ = CFO(CF ２ ) ６ OCF = CF ２、 CF ２ = CFO(CF ２ ) ８ OCF = CF ２ , CF ２ = CFO(CF ２ ) ２ OCF(CF ３ )CF ２ OCF = CF ２ , CF ２ = CFO(CF ２ ) ２ O(CF(CF ３ )CF ２ O) ２ CF = CF ２ , CF ２ = CFO CF ２ O(CF<00001​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​３ OCF = CF ２ (Hereafter also referred to as "C3DVE"), and CF ２ = CFO (CF ２ ) ４ OCF = CF ２ (Hereafter, this will also be referred to as "C4DVE") is one example.

[0032] A specific example of a compound represented by formula (m4) is CH ２ =CH(CF ２ ) ２ CH=CH ２ ,CH ２ =CH(CF ２ ) ４ CH=CH ２ , and, CH ２ =CH(CF ２ ) ６ CH=CH ２ Examples include: Among the compounds represented by formula (m4), a more preferred specific example is CH ２ =CH(CF ２ ) ６ CH=CH ２ (Hereafter also referred to as "C6DV") is one example. Among these, BO is preferably C3DVE or C4DVE.

[0033] R Ｈａｌ Examples include monomers containing a bromine atom and monomers containing an iodine atom. A specific example of a monomer containing a bromine atom is CF ２ = CFOCF ２ CF ２ CF ２ OCF ２ CF ２ Examples include Br, bromotrifluoroethylene, 4-bromo-3,3,4,4-tetrafluorobutene-1 (BTFB), 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, and 4-bromoperfluorobutene-1,3,3-difluoroallyl bromide.

[0034] Furthermore, specific examples of monomers containing a bromine atom include 2-bromo-perfluoroethyl perfluorovinyl ether and CF ２ Br-R ｆ２ -O -CF = CF ２ Fluorinated compounds such as CF ２ BrCF ２ O - CF = CF ２ , R １１ OCF = CFBr, and R １１ OCBr=CF ２ Fluorovinyl ethers such as CH ３ OCF = CFBr and CF ３ CH ２ OCF = CFBr can be cited. Here, R ｆ２ R is a perfluoroalkylene group, １１ R is a lower alkyl group or a lower fluoroalkyl group. １１ The number of carbon atoms is, for example, 1 to 10.

[0035] A specific example of a monomer containing an iodine atom is given by formula: CHR １２ = CH-Z-CH ２ CHR １２ -I iodized olefins are an example. In the formula, R １２ is H or CH ３ Z is a linear or branched (per)fluoroalkylene group having 1 to 18 carbon atoms, which may contain one or more etheric oxygen atoms, or a (per)fluoropolyoxyalkylene group as disclosed in U.S. Patent No. 5,674,959.

[0036] Furthermore, a specific example of a monomer containing an iodine atom is disclosed in U.S. Patent No. 5,717,036, which is of the formula: I(CH ２ CF ２ CF ２ ) ｐ OCF = CF ２ and ICH ２ CF ２ O[CF(CF ３ ) CF ２ O] ｐ CF = CF ２Examples of unsaturated ethers include those such as (wherein p is an integer from 1 to 3). Specific examples of monomers containing an iodine atom include iodoethylene, 4-iodo-3,3,4,4-tetrafluorobutene-1 (ITFB), 3-chloro-4-iodo-3,4,4-trifluorobutene, 2-iodo-1,1,2,2-tetrafluoro-1-(vinyloxy)ethane, 2-iodo-1-(perfluorovinyloxy)-1,1,-2,2-tetrafluoroethylene, 1,1,2,3,3,3-hexafluoro-2-iodo-1-(perfluorovinyloxy)propane, 2-iodoethyl vinyl ether, 3,3,4,5,5,5-hexafluoro-4-iodopentene, and iodotrifluoroethylene, all disclosed in U.S. Patent No. 4,694,045. Furthermore, specific examples of monomers containing an iodine atom include allyl iodide and 2-iodo-perfluoroethyl perfluorovinyl ether.

[0037] R ＣＮ From the viewpoint of polymerization reactivity, it is preferable that the material has polymerizable unsaturated bonds, and more preferably that it has one polymerizable unsaturated bond. Specific examples of polymerizable unsaturated bonds include carbon-carbon double bonds (C=C) and carbon-carbon triple bonds (C≡C). ＣＮ The compound represented by formula (m5) is preferred because it provides superior release properties and heat resistance for crosslinked rubber articles. CR ５１ R ５２ =CR ５３ -R ５４ -CN ... (m5) In equation (m5), R ５１ , R ５２ and R ５３ Each of these independently represents a hydrogen atom, a fluorine atom, or a methyl group, R ５４ This refers to a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the terminal or between carbon-carbon bonds of a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms.

[0038] R ＣＮ Due to its excellent polymerization reactivity, R ５１ , R ５２ and R ５３It is preferable that R is a fluorine atom or a hydrogen atom. ５１ , R ５２ and R ５３ It is more preferable that all of them are fluorine atoms or all of them are hydrogen atoms, as this provides better release properties and heat resistance for the crosslinked rubber article. ５１ , R ５２ and R ５３ It is particularly preferable that all of them are fluorine atoms. ５４ The chain may be linear, branched, or cyclic, with linear or branched being preferred. ５４ The number of carbon atoms is preferably 2 to 8, more preferably 3 to 7, even more preferably 3 to 6, and particularly preferably 3 to 5. ５４ It may or may not have etheric oxygen atoms, but it is preferable to have etheric oxygen atoms because it provides superior rubber properties. ５４ The number of etheric oxygen atoms in is preferably 1 to 3, and particularly preferably 1 or 2.

[0039] A specific example of a compound represented by formula (m5) is CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ CN (hereinafter also referred to as "8CNVE"), CF ２ = CFO (CF ２ ) ５ CN (hereinafter also referred to as "MV5CN"), CF ２ = CFOCF ２ CF ２ CF ２ OCF (CF ３ ) CN and CF ２ = CFO (CF ２ ) ３ CN is one example, and 8CNVE or MV5CN are preferred because they offer superior release properties and heat resistance for crosslinked rubber articles.

[0040] POAVE is a compound represented by formula (m6). CF ２ =CF(OCF) ２ CF ２ ) ｎ - (OCF２ ) ｍ -OR ｆ３ ...(m6) In formula (m6), R ｆ３ n represents a perfluoroalkyl group having 1 to 4 carbon atoms, n represents an integer from 0 to 3, m represents an integer from 0 to 4, and n+m represents an integer from 1 to 7.

[0041] R ｆ３ In this, the perfluoroalkyl group may be linear or branched. ｆ３ The number of carbon atoms is preferably 1 to 3. When n is 0, m is preferably 3 or 4. When n is 1, m is preferably an integer from 2 to 4. When n is 2 or 3, m is preferably 0. n is preferably an integer from 1 to 3. R ｆ３ When the number of carbon atoms, n, and m are within the above range, the low-temperature properties of the crosslinked rubber article are excellent, and the productivity of the crosslinked rubber article is improved.

[0042] Specific examples of POAVE are listed below. The abbreviations in parentheses after the formulas indicate the compounds. CF ２ = CF - OCF ２ CF ２ - (OCF ２ ) ４ -OCF ３ (C9PEVE) CF ２ = CF - OCF ２ CF ２ - (OCF ２ ) ２ -OCF ３ (C7PEVE) CF ２ =CF - (OCF ２ CF ２ ) ２ -OCF ２ CF ３ (EEAVE) CF ２ =CF - (OCF ２ CF ２ ) ３ -OCF ２ CF ３ (EEEAVE) CF ２ = CF - OCF ２ -OCF ３ CF ２ = CF - OCF ２-OCF ２ -OCF ３ As for POAVE, C9PEVE, C7PEVE, EEAVE, or EEEAVE are preferred due to their superior low-temperature properties and productivity of the cross-linked rubber articles. These compounds can be produced using the corresponding alcohol as a raw material by the method described in International Publication No. 00 / 056694.

[0043] The content of other monomer units in the fluorine-containing copolymer is preferably 0.01 to 30 mol%, more preferably 0.01 to 20 mol%, even more preferably 0.01 to 10 mol%, and most preferably 0.01 to 5 mol%, relative to the total content of all units. The preferred ranges for the content of other monomer units in FFKM, FEPM, and FKM are the same as described above.

[0044] Fluorine-containing copolymers preferably contain at least one selected from the group consisting of polymerizable unsaturated bonds, chlorine atoms, bromine atoms, iodine atoms, and nitrile groups, and more preferably contain at least one selected from the group consisting of chlorine atoms, bromine atoms, iodine atoms, and nitrile groups, in order to have superior crosslinking properties. In particular, it is preferable that the fluorine-containing copolymer has at least one of the above atoms or groups at the terminal and side chains.

[0045] When producing a fluorine-containing copolymer, polymerizable unsaturated bonds, chlorine atoms, bromine atoms, iodine atoms, and nitrile groups can be introduced to the side chains or terminals of the fluorine-containing copolymer by copolymerizing the other monomers mentioned above. Alternatively, iodine atoms can be introduced to the terminals of the fluorine-containing copolymer by polymerizing the monomers using a chain transfer agent containing iodine atoms. When the fluorine-containing copolymer contains iodine atoms, the iodine content is preferably 0.01 to 5.00% by mass, more preferably 0.01 to 2.00% by mass, and even more preferably 0.01 to 1.00% by mass, based on the total mass of the fluorine-containing copolymer.

[0046] (Method for producing fluorine-containing copolymers) One example of a method for producing fluorine-containing copolymers is a method of copolymerizing the above monomers in the presence of a radical polymerization initiator.

[0047] As radical polymerization initiators, water-soluble polymerization initiators and redox polymerization initiators are preferred. 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. Among these, persulfates are preferred, and ammonium persulfate is more preferred. As redox polymerization initiators, polymerization initiators combining persulfates and reducing agents are examples. Of these, polymerization initiators capable of polymerizing each monomer in the polymerization temperature range of 0 to 60°C are preferred. Specific examples of persulfates constituting 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 to be combined with persulfates include thiosulfates, sulfites, bisulfites, pyrosulfites, and hydroxymethanesulfinates, with hydroxymethanesulfinates being preferred, and sodium hydroxymethanesulfinate being particularly preferred.

[0048] In a method for producing a fluorine-containing copolymer, the monomer may be copolymerized in the presence of a chain transfer agent together with a radical polymerization initiator. The chain transfer agent is preferably an iodine compound, such as formula RI ２ An iodine compound represented by the formula RI is particularly preferred. In the above formula, R represents an alkylene group having 3 or more carbon atoms or a perfluoroalkylene group having 3 or more carbon atoms. The number of carbon atoms in R is preferably 3 to 8. Formula RI ２ Specific examples of iodine compounds represented by 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. By copolymerizing the above monomers in the presence of these iodine compounds, iodine atoms can be introduced into the fluorine-containing copolymer.

[0049] For details on components other than those mentioned above used in the production of fluorine-containing copolymers and the production method, refer to the method described in paragraphs 0019 to 0034 of International Publication No. 2010 / 082633.

[0050] The sheet of this embodiment may consist solely of a fluorine-containing copolymer, or it may consist of a composition containing a fluorine-containing copolymer and an additive. Hereinafter, the composition containing a fluorine-containing copolymer and an additive will also be referred to as a fluorine-containing copolymer composition. When manufacturing a crosslinked rubber article from the sheet of this embodiment, the sheet of this embodiment and the additive may be mixed to form a fluorine-containing copolymer composition. Examples of additives include crosslinking agents and crosslinking aids.

[0051] <Crosslinking Agents> Crosslinking agents are used to crosslink fluorine-containing copolymers. Examples of crosslinking agents include organic peroxides and compounds having two or more amino groups (hereinafter also referred to as "polyamine compounds"). Organic peroxides are preferred because they exhibit superior crosslinking reactivity of fluorine-containing copolymers.

[0052] Specific examples of organic peroxides include dialkyl peroxides, α,α'-bis(tert-butylperoxy)-p-diisopropylbenzene, α,α'-bis(tert-butylperoxy)-m-diisopropylbenzene, benzoyl peroxide, tert-butylperoxybenzene, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, tert-butylcumyl peroxide, and dicumyl peroxide. Of these, dialkyl peroxides, α,α'-bis(tert-butylperoxy)-p-diisopropylbenzene, and α,α'-bis(tert-butylperoxy)-m-diisopropylbenzene are preferred. Specific examples of dialkyl peroxides include 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethylhexane-2,5-dihydroxyperoxide, tert-butylperoxymaleic acid, tert-butylperoxysopropyl carbonate, ditert-butylperoxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, and 2,5-dimethyl-2,5-di(tert-butylperoxy)-3-hexine. Of these, dicumyl peroxide and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane are preferred.

[0053] The polyamine compound may be a compound in which a hydrogen atom of an aliphatic hydrocarbon is substituted with an amino group, or a compound in which a hydrogen atom of an aromatic hydrocarbon is substituted with an amino group. Compounds in which a hydrogen atom of an aromatic hydrocarbon is substituted with an amino group are preferred due to their excellent heat resistance. The polyamine compound preferably contains a fluorine atom. This results in a crosslinked rubber article with a smaller compression set at high temperatures. Specific examples of polyamine compounds 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 (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. 5833657. Among these, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane is preferred because it exhibits superior effects compared to the present invention. The crosslinking agent may consist of only one type or two or more types.

[0054] In the fluorine-containing copolymer composition, the crosslinking agent content is preferably 0.1 to 20 parts by mass, more preferably 0.1 to 10 parts by mass, and particularly preferably 0.1 to 5.0 parts by mass, per 100 parts by mass of the fluorine-containing copolymer. If the content is above the lower limit of the above range, the hardness of the crosslinked rubber article is better, and if it is below the upper limit of the above range, the transparency of the crosslinked rubber article is better.

[0055] <Crosslinking Aids> Crosslinking aids are used to improve the crosslinking reactivity of fluorine-containing copolymers. Preferred crosslinking aids are compounds having two or more reactive functional groups within the same molecule. Specific examples of reactive functional groups include carbon-carbon double bond-containing groups, halogen atoms, acid anhydride residues, carboxyl groups, amino groups, cyano groups, and hydroxyl groups. Specific examples of carbon-carbon double bond-containing groups include vinyl groups, alkenyl groups such as allyl and methallyl groups, unsaturated acyl groups such as acryloyl and methacryloyl groups, and maleimide groups. Carbon-carbon double bond-containing groups are preferably alkenyl groups having 2 to 4 carbon atoms, with allyl groups being particularly preferred. Multiple reactive functional groups present within the same molecule of a crosslinking aid may be identical or different from one another. Specific examples of crosslinking aids include the compound represented by formula (1) below, triallyl cyanurate, triallyl isocyanurate, trimethyl isocyanurate, 1,3,5-triacryloylhexahydro-1,3,5-triazine, triallyl trimellitate, m-phenylenediamine bismaleimide, p-quinone dioxime, p,p'-dibenzoylquinone dioxime, dipropargyl terephthalate, diallyl phthalate, N,N',N'',N'''-tetraallyl terephthalamide, and vinyl group-containing siloxane oligomers (polymethylvinylsiloxane, polymethylphenylvinylsiloxane, etc.). Among these, the compound represented by formula (1), triallyl cyanurate, triallyl isocyanurate, and trimethyl isocyanurate are preferred, the compound represented by formula (1), and triallyl isocyanurate are more preferred, and the compound represented by formula (1) is particularly preferred because it provides superior transparency of the crosslinked rubber. The crosslinking agent may contain only one type or two or more types.

[0056] Equation (1) is as follows: (CR ４ R ５ =CR ６ -) ２ R ７ ...(1) In formula (1), R ４ , R ５ and R ６Each of these independently represents a hydrogen atom, a fluorine atom, a C1-C5 alkyl group, or a C1-C5 fluoroalkyl group, and R ７ This represents a divalent fluorohydrocarbon group having 1 to 18 carbon atoms, or a group having an etheric oxygen atom at the terminal or between carbon-carbon bonds of the fluorohydrocarbon group. Multiple R ４ , multiple R ５ and multiple R ６ Each of them may be the same as or different from the others.

[0057] R ４ , R ５ and R ６ If R is an alkyl group or fluoroalkyl group, it may be linear or branched, but linear is preferred. ４ , R ５ and R ６ When is an alkyl group or fluoroalkyl group, the number of carbon atoms is 1 to 5, more preferably 1 to 3, and particularly preferably 1 or 2. From the viewpoint of superior polymerization reactivity, R ４ , R ５ and R ６ It is preferable that all of them are hydrogen atoms.

[0058] R ７ In this context, the fluorohydrocarbon group is preferably a perfluorohydrocarbon group because it offers superior heat resistance to the crosslinked rubber article. ７ The chain may be linear, branched, or cyclic, with linear or branched being preferred, and linear being particularly preferred. ７ The number of carbon atoms is 1 to 18, preferably 1 to 10, more preferably 2 to 8, and particularly preferably 3 to 7. ７ If it has an etheric oxygen atom, R ７ The number of etheric oxygen atoms in is preferably 1 to 6, more preferably 1 to 3, and particularly preferably 1 or 2. ７ If it has an etheric oxygen atom, the etheric oxygen atom is R ７ It is preferable that it be located at the terminal end.

[0059] Specific examples of compounds represented by formula (1) are the same as the specific examples of compounds represented by formula (m2) mentioned above.

[0060] Among the compounds represented by formula (1), the compound represented by formula (2) is preferred. When the compound represented by formula (2) is incorporated into the sheet, it functions as a plasticizer, improving the transparency of the sheet and reducing the rate of foreign matter detection. Furthermore, the heat resistance of the crosslinked rubber article is improved. H ２ C = CH - R １ -R ３ -R ２ -CH=CH ２ ...(2) In formula (2), R １ and R ２ Each is independent of CH ２ or CF ２ R ３ This represents a divalent fluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the terminal or between carbon-carbon bonds of the fluorohydrocarbon group.

[0061] In formula (2), R ２ In this context, the fluorohydrocarbon group is preferably a perfluorohydrocarbon group, as this provides superior heat resistance to the crosslinked rubber article. ３ The chain may be linear, branched, or cyclic, with linear or branched being preferred, and linear being particularly preferred. ３ The number of carbon atoms is 1 to 10, preferably 2 to 8, and particularly preferably 3 to 7. ３ If it has an etheric oxygen atom, R ３ The number of etheric oxygen atoms in is preferably 1 to 5, more preferably 1 to 3, and particularly preferably 1 or 2. ７ If it has an etheric oxygen atom, the etheric oxygen atom is R ７ It is preferable that it be located at the terminal end.

[0062] Because cross-linked rubber articles have superior heat resistance, R １ and R ２ ga CF ２ And R ３However, it is particularly preferable that the compound is a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the terminal or between carbon-carbon bonds of the perfluorohydrocarbon group. Specific examples of the compound represented by formula (2) are the same as those for the compound represented by formula (m4) described above. Among these, C6DV is preferred. The compound represented by formula (2) may be used in combination with other crosslinking aids.

[0063] In the fluorine-containing copolymer composition, the content of the crosslinking aid is preferably 0.1 to 20 parts by mass, more preferably 0.1 to 10 parts by mass, and particularly preferably 0.1 to 5.0 parts by mass, per 100 parts by mass of the fluorine-containing copolymer. If the content is above the lower limit of the above range, the hardness of the crosslinked rubber article is better, and if it is below the upper limit of the above range, the transparency of the crosslinked rubber article is better. When the crosslinking aid contains a compound represented by formula (2), the preferred range for the content of the compound represented by formula (2) is the same as the preferred range for the content of the crosslinking aid.

[0064] In the fluorine-containing copolymer composition, the mass ratio of the crosslinking agent content to the crosslinking aid content (crosslinking agent content / crosslinking aid content) is preferably 0.005 to 200, more preferably 0.01 to 100, and particularly preferably 0.02 to 50. Within this range, unreacted crosslinking aids are less likely to remain, the crosslinking reaction proceeds smoothly, and thus the transparency is superior.

[0065] In the fluorine-containing copolymer composition, the total content of the crosslinking agent and crosslinking aid is preferably 40 parts by mass or less, more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less, per 100 parts by mass of the fluorine-containing copolymer. If the values ​​are below the above, the transparency of the crosslinked rubber is better. In the fluorine-containing copolymer composition, the total content of the crosslinking agent and crosslinking aid is preferably 0.2 parts by mass or more, and particularly preferably 0.5 parts by mass or more, per 100 parts by mass of the fluorine-containing copolymer. If the values ​​are above the above, the hardness of the crosslinked rubber is better.

[0066] <Other Components> The fluorine-containing copolymer composition may contain other components not listed above, as long as the effects of the present invention are not impaired. Other components include fillers and reinforcing agents (e.g., carbon black, barium sulfate, calcium metasilicate, calcium carbonate, titanium dioxide, silicon dioxide, clay, talc, polytetrafluoroethylene, perfluoroalkoxyalkanes, and "fluorine-containing copolymer (X1-1)" as described in the examples section of International Publication No. 2016 / 017801, pulverized by a jet mill at a pressure of 0.55 MPa (hereinafter also referred to as "pulverized fluorine-containing copolymer (X1-1)"), metal oxides (e.g., oxides of divalent metals such as magnesium oxide, calcium oxide, zinc oxide, and lead oxide), scorch retarders (e.g., 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 (e.g., 18-crown-6), and release agents (e.g., fatty acid metal salts such as sodium stearate and calcium stearate). The aforementioned "fluorine-containing copolymer (X1-1)" will be described in detail below. The fluorine-containing copolymer (X1-1) comprises a unit (1) containing at least one functional group selected from the group consisting of a carbonyl group-containing group, a hydroxyl group, an epoxy group, and an isocyanate group, a unit (2) based on tetrafluoroethylene, and a unit (3-1) based on perfluoro(alkyl vinyl ether). This is a fluorine-containing copolymer in which the proportion of unit (1) to the total of all units is 0.01 to 3 mol% (preferably 0.03 to 2 mol%, more preferably 0.05 to 1 mol%), the proportion of unit (2) is 90 to 99.89 mol% (preferably 95 to 99.47 mol%, more preferably 96 to 98.95 mol%), the proportion of unit (3-1) is 0.1 to 9.99 mol% (preferably 0.5 to 9.97 mol%, more preferably 1 to 9.95 mol%), and the melting point is 260 to 320°C (preferably 260 to 320°C, more preferably 280 to 320°C, more preferably 295 to 315°C, and particularly more preferably 295 to 310°C).Specific examples of fluorine-containing copolymers (X1-1) include 5-norbornene-2,3-dicarboxylic acid anhydride (also known as Hymic anhydride (hereinafter also referred to as "NAH"), manufactured by Hitachi Chemical Co., Ltd.) as the monomer forming unit (1), and PPVE (CF) as the monomer forming unit (3-1). ２ = CFO (CF ２ ) ３A copolymer containing F (manufactured by AGC Inc.) (TFE / PPVE / NAH copolymer) is an example. The above-mentioned fluorine-containing copolymer (X1-1) can be produced by the following method, for example, as described in the Examples section of International Publication No. 2016 / 017801. First, 369 kg of 1,3-dichloro-1,1,2,2,3-pentafluoropropane (AK225cb, manufactured by AGC Inc.) (hereinafter referred to as "AK225cb") and 30 kg of PPVE are charged into a pre-degassed polymerization tank with a stirrer and an internal volume of 430 L. Next, the polymerization tank is heated to 50°C, and after charging another 50 kg of TFE, the pressure inside the polymerization tank is increased to 0.89 MPa [gauge]. Furthermore, a polymerization initiator solution was prepared by dissolving (perfluorobutyryl) peroxide at a concentration of 0.36% by mass and PPVE at a concentration of 2% by mass in AK225cb. Polymerization was carried out while continuously adding 3 L of this polymerization initiator solution to the polymerization tank at a rate of 6.25 mL per minute. In addition, TFE was continuously charged so that the pressure inside the polymerization tank was maintained at 0.89 MPa [gauge] during the polymerization reaction. Furthermore, a solution of NAH dissolved in AK225cb at a concentration of 0.3% by mass was continuously charged in amounts equivalent to 0.1 mol% of the number of moles of TFE charged during polymerization. Eight hours after the start of polymerization, when 32 kg of TFE had been charged, the temperature inside the polymerization tank was lowered to room temperature and the pressure was purged to atmospheric pressure. The resulting slurry was separated from AK225cb using solid-liquid separation, and then dried at 150°C for 15 hours to obtain granular fluorine-containing copolymer (X1-1). Based on the results of melt NMR analysis and infrared absorption spectroscopy analysis, the copolymer composition of this fluorine-containing copolymer (X1-1) is 0.1 / 97.9 / 2.0 (mol%) based on NAH / TFE / PPVE. Furthermore, the melting point of this fluorine-containing copolymer (X1-1) is 300°C, the dielectric constant is 2.1, and the MFR is 17.6 g / 10 min. The average particle size of the fluorine-containing copolymer (X1-1) is 1554 μm.

[0067] In the fluorine-containing copolymer composition, the total content of fillers and reinforcing agents is preferably 10 parts by mass or less, more preferably 1 part by mass or less, even more preferably 0.1 parts by mass or less, and particularly preferably 0.01 parts by mass or less, per 100 parts by mass of the fluorine-containing copolymer, from the viewpoint of superior transparency of the crosslinked rubber. However, when the aforementioned pulverized fluorine-containing copolymer (X1-1) is used as a filler, the amount is preferably 1 to 50 parts by mass, more preferably 2 to 40 parts by mass, even more preferably 3 to 30 parts by mass, and particularly preferably 5 to 25 parts by mass, per 100 parts by mass of the fluorine-containing copolymer.

[0068] In the fluorine-containing copolymer composition, the total content of components other than the fluorine-containing copolymer (if the fluorine-containing copolymer (X1-1) pulverized material is included, components other than the fluorine-containing copolymer and the fluorine-containing copolymer (X1-1) pulverized material), i.e., crosslinking agents, crosslinking aids, and other components, is preferably 0.5 to 2.0 parts by mass, more preferably 0.5 to 1.8 parts by mass, and particularly preferably 0.5 to 1.2 parts by mass, per 100 parts by mass of the fluorine-containing copolymer. If the content is above the lower limit of the above range, the hardness of the crosslinked rubber article is better, and if it is below the upper limit of the above range, the transparency of the crosslinked rubber article is better.

[0069] The composition of the sheet may be the same as or different from the final composition of the fluorine-containing copolymer composition, that is, the composition when the fluorine-containing copolymer is crosslinked to form a crosslinked rubber article.

[0070] The content of the fluorine-containing copolymer in the sheet is preferably 70% by mass or more, more preferably 90% by mass or more, particularly preferably 95% by mass or more, and especially preferably 98% by mass or more, and may also be 100% by mass, based on the total mass of the sheet. When the content of the fluorine-containing copolymer is above the lower limit of the above, the ability to wrap around the roll is improved.

[0071] When the sheet contains a compound represented by formula (2), the content of the compound represented by formula (2) is preferably 0.1 to 10% by mass, more preferably 0.1 to 5% by mass, even more preferably 0.1 to 3% by mass, and particularly preferably 0.5 to 2.5% by mass, based on the total mass of the sheet. If the content of the compound represented by formula (2) is above the lower limit, the rate of foreign matter detection is lower. If it is below the upper limit, the compression set is better.

[0072] The sheet may contain fillers and reinforcing agents, but the lower the content of fillers and reinforcing agents in the sheet, the higher the transparency of the sheet and the lower the rate of foreign matter detection tends to be. Therefore, it is preferable that the sheet is substantially free of fillers and reinforcing agents. When a fluorine-containing copolymer composition contains fillers or reinforcing agents, it is preferable to prepare the fluorine-containing copolymer composition by mixing the sheet with an additive containing the fillers or reinforcing agents. Here, "the sheet is substantially free of fillers and reinforcing agents" means that the total content of fillers and reinforcing agents in the sheet is 0.1 parts by mass or less per 100 parts by mass of fluorine-containing copolymer. The total content of fillers and reinforcing agents is preferably 0.01 parts by mass or less per 100 parts by mass of fluorine-containing copolymer, and particularly preferably 0 parts by mass.

[0073] [Method for Manufacturing a Sheet] A method for manufacturing a sheet according to one embodiment of the present invention involves forming a sheet by winding a raw material containing a fluorine-containing copolymer onto rolls in a roll kneading machine equipped with at least one pair of rolls (roll winding step). The raw material may also contain additives. The fluorine-containing copolymer and additives are as described above. The composition of the raw material is the same as the composition of the sheet to be manufactured.

[0074] A roll kneader only needs to have at least one pair of rolls and may be a kneader known for use in rubber compounding. From the viewpoint of workability and dispersion of raw materials, a two-roll open-roll kneader is preferred. Figures 1 and 2 show an example of a roll kneader. In this example, the roll kneader 1 is a two-roll open-roll kneader equipped with a pair of rolls 11 and 12. Reference numeral 2 in Figure 1 indicates the raw material. In Figure 2, the raw material 2 is omitted.

[0075] Rolls 11 and 12 are arranged with their roll shafts parallel to each other in the horizontal plane. The roll shafts of rolls 11 and 12 are connected to a drive mechanism (not shown) and are rotatable in the direction of the arrows in the figure. The size of the gap between rolls 11 and 12 (roll gap) can be adjusted by moving roll 12 in a direction perpendicular to the roll axis direction. The diameter of rolls 11 and 12 is preferably 6 to 28 inches, more preferably 8 to 20 inches, even more preferably 8 to 16 inches, and 16 inches is particularly preferred because the desired maximum temperature can be obtained without temperature control. The maximum height Rz (hereinafter simply referred to as "Rz") of the circumferential surface of each roll 11 and 12 is, for example, 0.2 μm or less. Rz is measured in accordance with JIS B 0601:2001 using a surface roughness measuring instrument (for example, Mitutoyo's compact surface roughness measuring instrument SURFTEST SJ-210 (standard drive, 0.75 mN type)).

[0076] The roll mixer 1 is equipped with a rubber aligning mechanism that regulates the width of the raw material (sheet) passing through the roll gap. The rubber aligning mechanism comprises a pair of plate-shaped rubber aligning members 13 and 14. For the sake of explanation, one of the rubber aligning members 14 is omitted in Figure 1. The rubber aligning members 13 and 14 are positioned above the rolls 11 and 12, spaced apart in the direction of the roll axis of the rolls 11 and 12. The rubber aligning members 13 and 14 are movable in the direction of the roll axis. The lower ends of the rubber aligning members 13 and 14 are formed in a shape that conforms to the circumferential surface of the rolls 11 and 12, so that the lower ends of the rubber aligning members 13 and 14 contact the circumferential surface of the rolls 11 and 12. The distance between the rubber aligning members 13 and 14 (rubber aligning width) only needs to be narrower than the width of the rolls 11 and 12, and can be appropriately set according to the width of the sheet to be manufactured (length in the direction of the roll axis), the amount of raw material to be prepared, etc.

[0077] The roll kneading machine 1 is equipped with a roll cutter that cuts the sheet wound around the roll 11 to a predetermined width in the circumferential direction of the roll. The roll cutter is equipped with a pair of cutters 15 and 16. For the sake of explanation, one of the cutters 16 is omitted in Figure 1. The cutters 15 and 16 are positioned below the roll 11, spaced apart by a predetermined width in the direction of the roll axis of the roll 11. The cutters 15 and 16 are attached to a cutter support base 17, and as the cutter support base 17 moves, the cutters 15 and 16 come into contact with the circumferential surface of the roll 11. The distance between the cutters 15 and 16 (the predetermined width) should be narrower than the rubber gathering width and can be appropriately set according to the width of the sheet to be manufactured (length in the direction of the roll axis).

[0078] The roll winding process is carried out, for example, as follows. First, as shown in Figure 1, the raw material 2 is supplied to the grooves on the roll gap while the rolls 11 and 12 are rotated. The rotation of the rolls 11 and 12 applies a shear force to the raw material 2, causing its temperature to rise. The raw material 2 gradually passes through the roll gap and becomes sheet-like. The sheet-like raw material 2 is taken up by the roll 11 and returned to the grooves on the roll gap. This series of steps is repeated until the temperature of the raw material 2 reaches a predetermined maximum temperature. As the above series of steps is repeated, the temperature of the raw material increases. Also, if the number of rotations per minute is the same, the larger the diameter of the rolls 11 and 12, the greater the shear heat generated by the longer distance the raw material travels, and the higher the temperature of the raw material tends to be. To adjust the temperature of the raw material, the surface temperature of the rolls may be adjusted using a water heater or the like. If the raw material contains additives, the raw material may be supplied all at once or added in stages. For example, the fluorine-containing copolymer may be supplied first, and the additives may be supplied later. To ensure uniform mixing of the raw materials, the sheet may be cut on the roll parallel to the roll axis, and the left and right sides of the sheet may be reversed from the cut point. Examples of cutting means in the direction of the roll axis include a roll knife, a cutter (ceramic cutter, etc.), and scissors (ceramic scissors, etc.). Before the temperature of the raw material 2 reaches a predetermined maximum temperature, the measured value of the roll gap is, for example, 0.1 to 5.0 mm, and more specifically, 0.2 to 1.0 mm. The roll gap before the temperature of the raw material 2 reaches a predetermined maximum temperature is typically set narrower than the final value in the roll winding process (hereinafter also referred to as the "predetermined value") from the viewpoint of ease of applying shear force. Before the temperature of the raw material 2 reaches a predetermined maximum temperature, the rotation speed of the rolls 11 and 12 per minute is, for example, 1 to 25 rpm, more specifically, 3 to 16 rpm, and particularly 5 to 15 rpm. The rotation speed may be changed when repeating the series of processes.

[0079] The maximum temperature of the raw material is 60°C or higher, preferably 65°C or higher, and particularly preferably 70°C or higher. The higher the maximum temperature, the lower the surface roughness (Ra, Rq, Rt, etc.) of the resulting sheet tends to be. There is no particular upper limit to the maximum temperature, but in terms of roll processability, it is preferably 100°C or lower, more preferably 90°C or lower, and particularly preferably 80°C or lower. The maximum temperature of the raw material is the surface temperature measured with a non-contact thermometer.

[0080] Once the raw material 2 reaches a predetermined maximum temperature, the roll gap is set to a predetermined value, and the raw material 2 is passed through it one or more times to obtain a sheet of a predetermined thickness. Before setting the roll gap to a predetermined value, the raw material 2 may be temporarily removed from the roll 11. The predetermined value of the roll gap is set according to the thickness of the sheet to be manufactured. The sheet thickness is as described above. When the sheet thickness is 1 to 4 mm, the measured value of the roll gap is typically 0.5 to 3.5 mm. After setting the roll gap to a predetermined value, the rotation speed of the rolls 11 and 12 per minute is, for example, 1 to 25 rpm, more specifically 3 to 16 rpm, and particularly 5 to 15 rpm. The rubber shaping width is, for example, 50 to 2500 mm, and more specifically 100 to 1500 mm. The number of rotations of rolls 11 and 12 after setting the roll gap to a predetermined value, that is, the number of times the raw material 2 passes through the roll gap after setting the roll gap to a predetermined value, is preferably 6 rotations or more, more preferably 10 rotations or more, and even more preferably 12 rotations or more, from the viewpoint of reducing the standard deviation of the sheet thickness. Furthermore, from the viewpoint of suppressing material deterioration, it is preferably 100 rotations or less, more preferably 50 rotations or less, and even more preferably 25 rotations or less.

[0081] In the roll winding process, it is preferable to adjust conditions such as the maximum temperature of the raw materials and the thickness of the sheet so that the absolute value of the charge potential measured after placing the resulting sheet on an anti-static mat for 5 minutes is 6V or less. The lower the absolute value of the charge potential, the more effectively static electricity can be removed, and the less likely foreign matter is to adhere after static removal. The absolute value of the charge potential is preferably 6.4V or less, and particularly preferably 6V or less. The higher the maximum temperature of the raw materials, the lower the absolute value of the charge potential tends to be. This is thought to be due to the reduction in surface roughness. Also, the thinner the sheet, the lower the absolute value of the charge potential tends to be. In addition, the absolute value of the charge potential can also be adjusted by the type of fluorine-containing copolymer, the type and amount of additives if additives are included, the temperature, humidity, water content, etc. The absolute value of the charge potential is measured by the method described in the Examples section below.

[0082] The sheet obtained in the roll winding process is peeled off the roll 11 and recovered. A single strip-shaped sheet may be obtained from the supplied raw material, or multiple sheets may be obtained. Sheets can be obtained, for example, by cutting the sheet wound on the roll to a predetermined length in the direction of the roll axis. The same means as described above can be used for cutting in the direction of the roll axis. Before cutting the sheet in the direction of the roll axis, it is preferable to cut the sheet to a predetermined width in the direction of the roll circumference with a roll cutter. This results in a sheet with a rectangular shape in which all sides constituting the outer edge in a plan view are formed to be straight.

[0083] [Crosslinked Rubber Article] A crosslinked rubber article according to one embodiment of the present invention is obtained by crosslinking the fluorine-containing copolymer in the sheet of the present invention.

[0084] A method for manufacturing the crosslinked rubber article of this embodiment includes, for example, a method of mixing the sheet of the present invention with a crosslinking agent and crosslinking the fluorine-containing copolymer in the resulting fluorine-containing copolymer composition. If the sheet is a sheet of a fluorine-containing copolymer composition containing a crosslinking agent, the step of mixing the crosslinking agent may be omitted.

[0085] The mixing of the sheet and the additive can be carried out using rubber mixing equipment such as a two-roll mixer, kneader, Banbury mixer, or extruder. A two-roll open mixer is preferred as the two-roll mixer. A pressure kneader, vacuum kneader, or internal mixer is preferred as the kneader. A pressure Banbury mixer or vacuum Banbury mixer is preferred as the Banbury mixer. A two-roll open mixer is particularly preferred as the rubber mixing equipment from the viewpoint of workability and dispersion. Furthermore, the fluorine-containing copolymer composition obtained after mixing may be molded. That is, the fluorine-containing copolymer composition may be a molded product. Specific examples of methods for molding the fluorine-containing copolymer composition include compression molding, injection molding, extrusion molding, calendering, or a method of dissolving in a solvent and then dipping or coating it before molding.

[0086] A preferred method for crosslinking a fluorine-containing copolymer in a fluorine-containing copolymer composition is by heating. Specific examples of heating-based crosslinking methods include hot press crosslinking, steam crosslinking, and hot air crosslinking. These methods can be appropriately selected considering the shape and application of the fluorine-containing copolymer composition. Preferred heating conditions are 100 to 400°C for 1 second to 24 hours.

[0087] A crosslinked rubber formed by primary crosslinking of a fluorine-containing copolymer composition by heating may be further heated to perform secondary crosslinking. By performing secondary crosslinking, the mechanical properties, compression set, and other properties of the crosslinked rubber can be stabilized or improved. The heating conditions for secondary crosslinking are preferably 100 to 300°C for 30 minutes to 48 hours.

[0088] Another method of crosslinking a fluorine-containing copolymer composition, other than by heating, is to irradiate the fluorine-containing copolymer composition with radiation. Specific examples of radiation used include electron beams and ultraviolet rays.

[0089] <Physical Properties> The compression set of the crosslinked rubber article at 200°C for 70 hours is preferably 55% or less, more preferably 50% or less, and particularly preferably 48% or less. When the compression set is below the above upper limit, the fluorine-containing copolymer is well crosslinked, and the shape recovery of the crosslinked rubber article after pressurization is better. The compression set is measured by the method described in the Examples section below.

[0090] <Applications> Cross-linked rubber articles are suitable for use as materials for O-rings, sheets, gaskets, oil seals, diaphragms, V-rings, and the like. Furthermore, it can be applied to heat-resistant and chemical-resistant sealants, heat-resistant and oil-resistant sealants, wire insulation materials, sealants for semiconductor manufacturing equipment, sealants for liquid crystal display panel manufacturing equipment, sealants for light-emitting diode manufacturing equipment, corrosion-resistant rubber paints, sealants for urea-based greases, rubber paints, adhesive rubber, hoses, tubes, calender sheets (rolls), sponges, rubber rolls, components for oil drilling, heat dissipation sheets, solution crosslinked materials, rubber sponges, bearing seals (urea-resistant, etc.), linings (chemical-resistant), automotive insulating sheets, insulating sheets for electronic equipment, rubber bands for watches, endoscope packings (amine-resistant), bellows hoses (processed from calender sheets), water heater packings / valves, fenders (marine civil engineering, ships), fibers and nonwoven fabrics (protective clothing, etc.), circuit board sealants, rubber gloves, stators for single-screw eccentric pumps, components for urea SCR systems, vibration dampers, vibration control agents, sealing agents, additives to other materials, and toys.

[0091] [Example of a Fluorine-Containing Copolymer Composition] A preferred example of a fluorine-containing copolymer composition obtained by mixing the sheet of this embodiment with an additive (hereinafter also referred to as "compound") will be described. The compound of this embodiment is a composition comprising the fluorine-containing copolymer crosslinked with a crosslinking agent and the pulverized fluorine-containing copolymer (X1-1) as a filler. As the fluorine-containing copolymer, the above-mentioned materials can be used, but the fluorine-containing elastomer is preferred, and the FFKM is more preferred. Furthermore, the fluorine-containing copolymer (A-1) obtained in Production Example 1, which will be described later, is particularly preferred. As the crosslinking agent, the above-mentioned materials can be used, but organic peroxides are preferred, dialkyl peroxides are more preferred, and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane is particularly preferred. As for the manufacturing method of the compound of this embodiment, a method can be adopted in which the sheet of this embodiment containing the fluorine-containing copolymer, the crosslinking agent, and the pulverized fluorine-containing copolymer (X1-1) are kneaded at room temperature (23°C) using two rolls or the like. Furthermore, the crosslinking aid and the mold release agent may be kneaded together as needed. In the compound manufacturing method of this embodiment, it is preferable to knead the additives such as the crosslinking agent, filler, crosslinking aid, and mold release agent after the sheet is formed, rather than incorporating them into the sheet beforehand. The amounts of the crosslinking agent, filler, crosslinking aid, and mold release agent per 100 mass of fluorine-containing copolymer are as described above. There are no particular restrictions on the kneading time, but 1 to 30 minutes is preferred, and 3 to 15 minutes is more preferred. Since the compound of this embodiment contains pulverized fluorine copolymer (X1-1), it is possible to improve plasma resistance without impairing heat resistance or chemical resistance.

[0092] The sheet of the present invention has a specific surface roughness on at least one surface, resulting in low electrostatic charge and a low rate of detecting foreign matter. Therefore, by using the sheet of the present invention, a cross-linked rubber article with fewer foreign matter can be obtained. Furthermore, by using the sheet of the present invention, the compression set of the cross-linked rubber article can also be reduced. The reason for the low electrostatic charge is thought to be that the small surface roughness and smoothness result in a large contact area with the static elimination mat during the measurement of the electrostatic potential described above, leading to good static elimination efficiency. The reason for the low rate of detecting foreign matter is thought to be that the small surface roughness and smoothness suppress light scattering due to surface irregularities, making it easier to detect foreign matter.

[0093] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples. Examples 1, 3, 5, 7, 9, 11, 13, 15, and 17 are examples, and Examples 2, 4, 6, 8, 10, 12, 14, 16, and 18 are comparative examples. "Parts" means parts by mass.

[0094] [Manufacturing Example 1: Fluorine-containing copolymer (A-1)] After degassing a 2100 mL stainless steel pressure reactor equipped with anchor blades, 804 g of ultrapure water and the emulsifier C were added. ２ F ５ OCF ２ CF ２ OCF ２ COONH ４ 80.1 g of a 30% by mass solution of [substance name], 0.72 g of C3DVE, 1.8 g of a 5% by mass aqueous solution of disodium hydrogen phosphate dodecahydrate, and 0.87 g of 1,4-diiodoperfluorobutane were charged, and the gas phase was purged with nitrogen. While stirring at a speed of 600 rpm using an anchor blade, 13 g of TFE and 65 g of PMVE were injected into the container under pressure once the internal temperature reached 80°C. The reactor pressure was 0.90 MPa [gauge]. 20 mL of a 1% by mass aqueous solution of ammonium persulfate was added to start polymerization. The initial monomer addition ratio, expressed as a molar ratio, was TFE:PMVE:C3DVE = 25:75:0.19.

[0095] As polymerization progressed, when the reactor pressure dropped to 0.89 MPa [gauge], TFE was injected to raise the reactor pressure to 0.90 MPa [gauge]. This was repeated, with 7 g of PMVE being injected each time 8 g of TFE was added. When the total added mass of TFE reached 80 g, the addition of the subsequent monomers was stopped, the reactor temperature was cooled to 10°C, the polymerization reaction was stopped, and a latex containing a fluorine-containing copolymer was obtained. The total added mass of the subsequent monomers was 80 g of TFE and 63 g of PMVE, which, when converted to a molar ratio, was TFE:PMVE = 65:35.

[0096] Nitric acid (manufactured by Kanto Chemical Co., Ltd., special grade) was dissolved in ultrapure water to prepare a 3% by mass aqueous solution of nitric acid. Latex was added to the aqueous nitric acid solution in a PFA (perfluoroalkoxyalkane) container to agglomerate the fluorine-containing copolymer. The amount of aqueous nitric acid solution was 150 parts for every 100 parts of fluorine-containing copolymer in the latex. The agglomerated fluorine-containing copolymer was recovered by filtration and added to ultrapure water in a PFA container, and washed by stirring at 200 rpm for 30 minutes. The amount of ultrapure water was 100 parts for every 100 parts of fluorine-containing copolymer. The above washing was repeated 10 times. The washed fluorine-containing copolymer was recovered by filtration and dried under reduced pressure at 50°C and 10 kPa to obtain a white fluorine-containing copolymer (A-1). The molar ratio of each unit in fluorine-containing copolymer (A-1) was TFE units:PMVE units:C3DVE units = 65.9:34.0:0.1. Furthermore, the iodine atom content was 0.15% by mass. The iodine atom content in the fluorine-containing copolymer was calculated using a combination of an automated sample combustion device, an ion chromatograph pretreatment system (Mitsubishi Chemical Analytec Co., Ltd., AQF-100 model), and an ion chromatograph.

[0097] [Manufacturing Example 2: Fluorine-containing copolymer (A-2)] After degassing a 20L stainless steel pressure reactor equipped with anchor blades, 7.2L of ultrapure water and the emulsifier C ２ F ５ OCF ２ CF ２ OCF ２ COONH ４880 g of a 30% by mass solution of [substance name], 7.3 g of 8CNVE, and 15.9 g of a 5% by mass aqueous solution of disodium hydrogen phosphate dodecahydrate were charged, and the gas phase was purged with nitrogen. While stirring at a speed of 375 rpm using an anchor blade, 137 g of TFE and 635 g of PMVE were injected into the container under pressure, and the internal temperature was raised to 80°C. The reactor internal pressure was 0.90 MPa [gauge]. 28 mL of a 3% by mass aqueous solution of ammonium persulfate (APS) was added, and polymerization was started. The molar ratio of the monomers injected under pressure before polymerization started (hereinafter also referred to as "initial added monomers") was TFE:PMVE:8CNVE = 26.3:73.3:0.4.

[0098] After polymerization began, monomers were injected as follows as polymerization progressed. Hereinafter, the injection of monomers after polymerization began will be called "post-addition," and the monomers injected after polymerization began will be called "post-added monomers." When the reactor pressure dropped to 0.89 MPa [gauge], TFE was injected to raise the reactor pressure to 0.90 MPa [gauge]. This was repeated, and each 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 that order. When the polymerization rate began to decrease, a 3% by mass aqueous solution of APS was added as appropriate. The total amount of 3% by mass aqueous solution of APS added after polymerization began was 35 mL. When the cycle in which the total amount of TFE added reached 1073.7 g was completed, 119.3 g of TFE was injected. When the total added mass of TFE reached 1193 g, the addition of the added monomers was stopped, the reactor 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 each added monomer were 1193 g for TFE, 666 g for PMVE, and 66.6 g for 8CNVE. Converting these to a molar ratio, the ratio was TFE:PMVE:8CNVE = 74.0:25.0:1.0. The latex was added to a 5% by mass aqueous solution of potassium aluminum sulfate to aggregate and separate the fluorine-containing copolymer. The fluorine-containing copolymer was filtered, washed with ultrapure water, and vacuum-dried at 50°C to obtain a white fluorine-containing copolymer (A-2). The content (molar ratio) of each unit in the obtained fluorine-containing copolymer (A-2) was TFE units:PMVE units:8CNVE units = 70.9:28.6:0.5.

[0099] [Production Example 3: Fluorine-containing copolymer (A-3)] Except for changing the amount of raw materials used, a fluorine-containing copolymer (A-3) was obtained using the same procedure as in Production Example 2 above. The content (molar ratio) of each unit in the obtained copolymer (A-3) was TFE units:PMVE units:8CNVE units = 64.4:35.1:0.5.

[0100] [Example 1] A sheet was prepared using a 16-inch roll (R-16, manufactured by Kansai Roll Co., Ltd., mirror-finish roll, Rz = 0.2 μm, 2 open rolls) following the procedure below. The roll temperature was not adjusted. 10 kg of fluorine-containing copolymer (A-1) was wound onto the roll. Then, the roll gap was set to 0 (measured value: 1 mm) and the rotation speed to 15 rpm, and sufficient shearing was applied to the wound fluorine-containing copolymer for 12 rotations. Immediately after the completion of the 12 rotations, the surface temperature of the fluorine-containing copolymer was measured with a non-contact thermometer (IT-545S, manufactured by Horiba, Ltd.) and was found to be 70°C. After that, the fluorine-containing copolymer was removed from the roll and wound onto the roll again with a roll gap of 1.8 (measured value: 3 mm), a rotation speed of 11 rpm, and a rubber backing width of 300 mm. After winding, both ends in the direction of the roll axis were cut in the direction of the roll circumference using a roll cutter (width: 120 mm). The sheet, with both ends cut off, was further cut in the direction of the roll axis using a roll knife and peeled off the roll to obtain a fluorine-containing copolymer sheet (sheet A).

[0101] [Example 2] A sheet was prepared using a 16-inch roll (R-16, manufactured by Kansai Roll Co., Ltd., mirror-finish roll, Rz = 0.2 μm, 2 open rolls) following the procedure below. The roll temperature was not adjusted. 10 kg of fluorine-containing copolymer (A-1) was wound onto the roll. Then, the roll gap was set to 1 (measured value: 2 mm) and the rotation speed to 15 rpm, and the wound fluorine-containing copolymer was sheared for 5 rotations. Immediately after the completion of the 5 rotations, the surface temperature of the fluorine-containing copolymer was measured with a non-contact thermometer (IT-545S, manufactured by Horiba, Ltd.) and was found to be 40°C. After that, the fluorine-containing copolymer was removed from the roll and wound onto the roll again with a roll gap of 1.8 (measured value: 3 mm), a rotation speed of 11 rpm, and a rubber backing width of 300 mm. After winding, both ends in the direction of the roll axis were cut in the direction of the roll circumference using a roll cutter (width: 120 mm). The sheet, with both ends cut off, was further cut in the direction of the roll axis using a roll knife and peeled off the roll to obtain a fluorine-containing copolymer sheet (sheet B).

[0102] [Example 3] A fluorine-containing copolymer sheet (sheet C) was prepared under the same conditions as in Example 1, except that the step of cutting both ends in the direction of the roll axis with a roll cutter (end trimming step) was omitted.

[0103] [Example 4] A fluorine-containing copolymer sheet (sheet D) was prepared under the same conditions as in Example 1, except that the roll gap was changed from 1.8 to 3.5 when the fluorine-containing copolymer was removed from the roll and then re-wound.

[0104] [Example 5] A fluorine-containing copolymer sheet (sheet E) was prepared under the same conditions as in Example 1, except that fluorine-containing copolymer (A-1) was changed to fluorine-containing copolymer (A-2). The surface temperature of the fluorine-containing copolymer immediately after the completion of 12 rotations was 75°C.

[0105] [Example 6] A fluorine-containing copolymer sheet (sheet F) was prepared under the same conditions as in Example 2, except that fluorine-containing copolymer (A-1) was changed to fluorine-containing copolymer (A-2). The surface temperature of the fluorine-containing copolymer immediately after the completion of 5 rotations was 50°C.

[0106] [Example 7] A fluorine-containing copolymer sheet (sheet G) was prepared under the same conditions as in Example 1, except that fluorine-containing copolymer (A-1) was changed to fluorine-containing copolymer (A-3). The surface temperature of the fluorine-containing copolymer immediately after the completion of 12 rotations was 73°C.

[0107] [Example 8] A fluorine-containing copolymer sheet (sheet H) was prepared under the same conditions as in Example 2, except that fluorine-containing copolymer (A-1) was changed to fluorine-containing copolymer (A-3). The surface temperature of the fluorine-containing copolymer immediately after the completion of 5 rotations was 45°C.

[0108] [Example 9] An 8-inch roll (Yamaguchi Steel Co., Ltd. test roll machine, mirror-finish roll, Rz = 0.2 μm, 2 open rolls) was used to produce a sheet using the following procedure. 2 kg of fluorine-containing copolymer (A-1) was wound onto the roll. At this time, the temperature of the roll was controlled using a water heater (WTC40, Nakamura Kagaku Kogyo Co., Ltd.). The water heater was set to 50°C. Then, the roll gap was set to 0 (measured value: 0.5 mm) and the rotation speed to 15 rpm, and sufficient shear was applied to the wound fluorine-containing copolymer for 12 rotations. Immediately after the completion of the 12 rotations, the surface temperature of the fluorine-containing copolymer was measured with a non-contact thermometer (IT-545S, Horiba, Ltd.) and was found to be 70°C. Subsequently, the fluorine-containing copolymer was removed from the roll and re-wound onto the roll with a roll gap of 2.5 mm (measured value: 3 mm), a rotation speed of 11 rpm, and a rubber graft width of 180 mm to produce a fluorine-containing copolymer sheet (sheet I).

[0109] [Example 10] A fluorine-containing copolymer sheet (sheet J) was prepared under the same conditions as in Example 9, except that the roll temperature was not controlled. The surface temperature of the fluorine-containing copolymer immediately after the completion of 12 rotations was 31°C.

[0110] [Example 11] A fluorine-containing copolymer sheet (sheet K) was prepared under the same conditions as in Example 9, except that the set temperature of the water heater for adjusting the roll temperature was changed to 40°C. The surface temperature of the fluorine-containing copolymer immediately after the completion of 12 rotations was 61°C.

[0111] [Example 12] A fluorine-containing copolymer sheet (sheet L) was prepared under the same conditions as in Example 9, except that the set temperature of the water heater for adjusting the roll temperature was changed to 30°C. The surface temperature of the fluorine-containing copolymer immediately after the completion of 12 rotations was 58°C.

[0112] [Example 13] A sheet was prepared using a 16-inch roll (R-16, manufactured by Kansai Roll Co., Ltd., mirror-finish roll, Rz = 0.2 μm, 2 open rolls) following the procedure below. The roll temperature was not adjusted. 6 kg of fluorine-containing copolymer (A-1) was wound onto the roll. Then, the roll gap was set to 0 (measured value: 1 mm) and the rotation speed to 5 rpm. C6DV (manufactured by Tosoh Finechem Co., Ltd.) was added while the roll was rotating to prepare the fluorine-containing copolymer composition. After that, the rotation speed was changed to 15 rpm, and sufficient shear was applied to the wound fluorine-containing copolymer composition for 12 rotations. Immediately after the completion of the 12 rotations, the surface temperature of the fluorine-containing copolymer composition was measured with a non-contact thermometer (IT-545S, manufactured by Horiba, Ltd.) and was found to be 70°C. Subsequently, the fluorine-containing copolymer composition was removed from the roll and re-wound onto the roll with a roll gap of 1.8 (measured value: 3 mm), a rotation speed of 11 rpm, and a rubber-covering width of 300 mm. After winding, both ends in the direction of the roll axis were cut in the direction of the roll circumference using a roll cutter (width: 120 mm). The sheet with both ends cut off was further cut in the direction of the roll axis using a roll knife and peeled off the roll to obtain a fluorine-containing copolymer composition sheet (sheet A-2).

[0113] [Example 14] A sheet was prepared using a 16-inch roll (R-16, manufactured by Kansai Roll Co., Ltd., mirror-finish roll, Rz = 0.2 μm, 2 open rolls) following the procedure below. The roll temperature was not adjusted. 6 kg of fluorine-containing copolymer (A-1) was wound onto the roll. Then, the roll gap was set to 1 (measured value: 2 mm) and the rotation speed to 5 rpm. C6DV (manufactured by Tosoh Finechem Co., Ltd.) was added while the roll was rotating to prepare the fluorine-containing copolymer composition. After that, the rotation speed was changed to 15 rpm, and sufficient shear was applied to the wound fluorine-containing copolymer composition for 3 rotations. Immediately after the completion of the 3 rotations, the surface temperature of the fluorine-containing copolymer composition was measured with a non-contact thermometer (IT-545S, manufactured by Horiba, Ltd.) and was found to be 35°C. Subsequently, the fluorine-containing copolymer composition was removed from the roll and re-wound onto the roll with a roll gap of 1.8 (measured value: 3 mm), a rotation speed of 11 rpm, and a rubber-covering width of 300 mm. After winding, both ends in the direction of the roll axis were cut in the direction of the roll circumference using a roll cutter (width: 120 mm). The sheet with both ends cut off was further cut in the direction of the roll axis using a roll knife to obtain a fluorine-containing copolymer composition sheet (sheet B-2).

[0114] [Measurement and Evaluation] The obtained sheets were evaluated as follows. The results are shown in Tables 1 and 2. In addition, photographs of the sheets obtained in Examples 1 and 3 are shown in Figures 3 and 4. In the figures, the left and right ends correspond to the ends in the direction of the roll axis.

[0115] <Surface Roughness> The surface roughness characteristics (arithmetic mean roughness Ra, maximum cross-sectional height Rt, root mean square height Rq) of the sheet surface for each example were determined using a surface roughness meter (SURFCOMNEX100 DX-12, manufactured by Tokyo Seimitsu Co., Ltd.) by the following method. Procedure (1): The reference height was calibrated using KS83 (LH=50, LV=-15.5, R=0.002). Thirty sheets were prepared using the above method, and two were randomly selected from them. Procedure (2): One of the two sheets was selected and placed on the measuring stand so that the edge (cut surface) of the sheet and the measuring stand were perpendicular, and the sheet and measuring stand were adhered with double-sided tape to prevent the sheet from moving. Procedure (3): Five locations were randomly selected from the surface of the sheet adhered to the measuring stand and measured under the measurement conditions shown below. Then the sheet was turned over, and five locations (a total of 10 locations) were measured using the same procedure. Procedure (4): For the remaining sheet, a total of 10 locations were measured using the same procedure as in Procedures (2) and (3). Procedure (5): The displacement y from the reference height was determined, and the arithmetic mean roughness Ra, root mean square height Rq, and maximum cross-sectional height Rt of the sheet surface were calculated. Ra and Rq were calculated using the formulas described in JIS B 0601:2013. The average of the 20 measurements taken in Procedures (3) and (4) was used as the arithmetic mean roughness Ra, root mean square height Rq, and maximum cross-sectional height Rt of the sheet.

[0116] [Measurement Conditions] Measuring probe: STYLUS DM8407 Measurement range: 2505.51 μm Stylus orientation: Downward Measurement length: 4 mm Movement method: Pre-drive length Return measurement Pre-drive length: 2 × cutoff wavelength / 2 Measurement speed: 0.6 mm / Cutoff: λc = 0.8 mm λc cutoff ratio: 300 Cutoff type: Gaussian Calculation standard: JIS-'01 / '13 standard

[0117] <Thickness> The thickness of the sheets was measured using a dial gauge. For each of the four sheets in each example, the thickness was measured at five different locations, and the average value of n=20 was adopted as the thickness. The standard deviation of the thickness was also calculated from the measured values.

[0118] <Absolute Value of Charge Potential> After obtaining each example sheet, it was placed on a table anti-static mat (manufactured by HOZAN) for 5 minutes. Then, the absolute value of the charge potential was measured using an electrostatic measuring instrument (SK-H050, manufactured by KEYENCE). An earth wire was installed on the table anti-static mat, and measurements were taken in an environment with a temperature of 23°C and a humidity of 50%. The absolute value of the charge potential was the average of the measurements taken from five sheets. The absolute value of the charge potential is an indicator of chargeability, and a lower value is preferable.

[0119] <Number of foreign objects> The tester visually inspected 30 sheets (10 kg) of each example, and found that 0.05 mm foreign objects were present in each sheet. ２ The above foreign matter was removed. At this time, the foreign matter measurement chart (0.05 mm in accordance with JIS P 8208) was used. ２ 1.5 mm ２ While checking the size of the foreign object (which is listed in the range up to), check the 0.05 mm inside the sheet. ２ The above foreign matter was removed. 0.05 mm ２ The following foreign objects were overlooked and not removed. When removing foreign objects, ceramic scissors (ceramic large scissors, manufactured by Slice) were used to remove only the foreign object portion. The number of pieces removed was counted as the number of foreign objects. However, the inspection time for foreign objects in one sheet was limited to 3 minutes, and if more than 3 minutes had passed, foreign objects were not removed even if they were present.

[0120] <Number of foreign objects missed> From the sheet from which foreign objects were removed in the above foreign object count test, another 0.05 mm ２ The above-mentioned foreign objects were removed. However, the inspection time for foreign objects on a single sheet was unlimited, and all other conditions were the same as those for the foreign object count test. The number of pieces removed in this test was counted as the number of foreign objects that were missed.

[0121] <Foreign Object Missed Rate> The foreign object missed rate was calculated from the number of foreign objects and the number of foreign objects missed in each of the above tests using the following formula: Foreign object missed rate = 100 × number of foreign objects missed / (number of foreign objects missed + number of foreign objects)

[0122] <Sheet Density> The density of the sheets was measured using Method A in accordance with JIS K 6268:1998.

[0123] <Compound Properties> [Compound Preparation and O-ring Preparation] "Examples 1-4, 9-12" 100 sheets prepared, 1 part of the crosslinking agent, 1 part of the crosslinking aid, 15 parts of the filler, and 1 part of the release agent were mixed together and kneaded for 10 minutes at room temperature (23°C) using a two-roller to obtain a compound. Crosslinking agent: Perhexa 25B (trade name, manufactured by Nippon Oil & Fats Co., Ltd., 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane) Crosslinking aid: TAIC (trade name, manufactured by Mitsubishi Chemical Corporation, triallyl isocyanurate) Filler: MT Carbon N990 (manufactured by Vanderbilt, carbon black) Release agent: sodium stearate

[0124] The obtained compound was heated and pressed at 170°C for 20 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 B 2401:2012)) (primary crosslinking). Then, the above O-ring was heated in an oven under the following conditions in an air atmosphere (secondary crosslinking). Secondary crosslinking was performed by heating at 250°C for 4 hours.

[0125] "Examples 5-8" 100 sheets prepared, 1 part of the crosslinking agent, 1.0 part of the crosslinking aid, and 20 parts of the filler were mixed and kneaded for 10 minutes at room temperature (23°C) using a two-roll mill to obtain a compound. Crosslinking agent: 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (BOAP) Filler: "Fluorine-containing copolymer (X1-1)" from the examples section of International Publication No. 2016 / 017801 was pulverized using a jet mill at a grinding pressure of 0.55 MPa. The particle size D90 was 4.5 μm and the particle size D50 was 1.7 μm.

[0126] The obtained compound was hot-pressed using a hydraulic press (model: SA-301 50T type, manufactured by Tester Sangyo Co., Ltd., ram diameter: 180 mm) under pressing conditions: 180°C for 20 minutes to obtain an O-ring (size: P-26) (primary crosslinking). Then, under a nitrogen atmosphere, the O-ring was heated at 90°C for 2 hours, then gradually increased to 200°C over 2 hours and held for 4 hours. Further heating was carried out over 2 hours to 305°C and heated at 305°C for 13 hours (secondary crosslinking). After that, it was cooled to room temperature to obtain the O-ring.

[0127] "Examples 13-14" 100 parts of the prepared sheet and 1.0 part of the crosslinking agent shown below were mixed and kneaded for 10 minutes at room temperature (23°C) using a two-roller to obtain a compound. Crosslinking agent: Perhexa 25B (trade name, manufactured by Nippon Oil & Fats Co., Ltd., 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane) O-rings were made from the obtained compound in the same manner as in Examples 1-4 and 9-12.

[0128] [Measurement of Compression Set] Using O-rings after secondary bridging as test specimens, the compression set was measured according to the following procedure, referencing JIS K 6262:2013. The test specimen (original thickness (wire diameter) = 3.5 mm) was compressed to a compressibility of 18% using a compression device. Next, the compression device with the compressed test specimen fixed in it was placed in an electric furnace and left at 200°C for 70 hours. After that, the compression device was removed from the electric furnace, the test specimen was immediately removed from the compression device, and the removed test specimen was placed in a constant temperature room and left at 23°C for 30 minutes, and the thickness of the test specimen (thickness after compression treatment) was measured. The test was performed using two test specimens, and the arithmetic mean of the measured values ​​of the two test specimens was used. The compression set was calculated using the following formula. Note that the closer the compression set is to 0%, the better the result. Compression set (%) = (Original thickness of the specimen - Thickness of the specimen after compression) ÷ (Original thickness of the specimen - Thickness of the spacer) × 100

[0129]

[0130]

[0131] Comparing Examples 1-4, Examples 1 and 3 showed lower absolute values ​​of charge potential and lower foreign object detection rates. They also exhibited lower compression set rates in the cross-linked rubber articles. In particular, Example 1, which underwent a trimming process to make the outer edges entirely straight, showed even lower absolute values ​​of charge potential and lower foreign object detection rates than Example 3. On the other hand, Example 2, with an Ra value exceeding 5.0 μm, and Example 4, with a sheet thickness exceeding 4 mm, both showed higher absolute values ​​of charge potential and higher foreign object detection rates. Similar trends were observed in the comparisons of Examples 5-6, 7-8, 9-12, and 13-14.

[0132] [Example 15] A fluorine-containing copolymer sheet (sheet M) was prepared under the same conditions as in Example 1, and the obtained sheet M was evaluated using the same method as in Example 1. The results are shown in Table 3. 100 parts of the prepared sheet M, 1 part of the crosslinking agent, 1 part of the crosslinking aid, 20 parts of the filler, and 1 part of the release agent were mixed and kneaded for 10 minutes at room temperature (23°C) using a two-roller to obtain a compound. Crosslinking agent: Perhexa 25B (trade name, manufactured by Nippon Oil & Fats Co., Ltd., 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane) Crosslinking aid: TAIC (trade name, manufactured by Mitsubishi Chemical Corporation, triallyl isocyanurate) Filler: "Fluorine-containing copolymer (X1-1)" from the Examples section of International Publication No. 2016 / 017801, pulverized using a jet mill at a grinding pressure of 0.55 MPa. The particle size D90 was 4.5 μm, and the particle size D50 was 1.7 μm. Release agent: Sodium stearate

[0133] The obtained compound was heated and pressed at 170°C for 20 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 B 2401:2012)) (primary crosslinking). The above O-ring was then heated in an oven under the following conditions in an air atmosphere (secondary crosslinking). Secondary crosslinking was performed by heating at 250°C for 4 hours. The O-ring after secondary crosslinking was used as a test piece, and the compression set was measured using the method and conditions described in [Measurement of Compression Set] above. The results are shown in Table 3.

[0134] [Example 16] A fluorine-containing copolymer sheet (sheet N) was prepared under the same conditions as in Example 2, and the obtained sheet N was evaluated using the same method as in Example 1. The results are shown in Table 3. A compound and an O-ring were obtained under the same conditions as in Example 15, except that sheet N was used instead of sheet M. The O-ring after secondary crosslinking was used as a test specimen, and the compression set was measured using the method and conditions described in [Measurement of Compression Set] above. The results are shown in Table 3.

[0135] [Example 17] A fluorine-containing copolymer sheet 1 (sheet P) was prepared under the same conditions as in Example 1, and the obtained sheet P was evaluated using the same method as in Example 1. The results are shown in Table 3. Using sheet P prepared in place of sheet M, a compound and an O-ring were obtained under the same conditions as in Example 15, except that the amount of filler (pulverized fluorine-containing copolymer (X1-1)) was 10 parts. The O-ring after secondary crosslinking was used as a test piece, and the compression set was measured using the method and conditions described in [Measurement of Compression Set] above. The results are shown in Table 3.

[0136] [Example 18] A fluorine-containing copolymer sheet 1 (sheet Q) was prepared under the same conditions as in Example 1, and the obtained sheet Q was evaluated using the same method as in Example 1. The results are shown in Table 3. Using sheet Q, which was prepared in place of sheet M, a compound and an O-ring were obtained under the same conditions as in Example 15, except that the amount of filler (pulverized fluorine-containing copolymer (X1-1)) was 10 parts. The O-ring after secondary crosslinking was used as a test piece, and the compression set was measured using the method and conditions described in [Measurement of Compression Set] above. The results are shown in Table 3.

[0137]

[0138] Comparing Examples 15 and 17 with Example 16, Examples 15 and 17 showed lower absolute values ​​of charge potential and lower foreign matter detection rates. Furthermore, the compression set rates of the cross-linked rubber articles were also lower.

[0139] 1... Roll mixing machine 11, 12... Rolls 13, 14... Rubber grafting components 15, 16... Cutter 17... Cutter support stand 2... Raw materials

Claims

1. A sheet containing a fluorine-containing copolymer, wherein the arithmetic mean surface roughness Ra of at least one surface is 5.0 μm or less, and the thickness is 4 mm or less.

2. The sheet according to claim 1, wherein the sheet is a single-leaf sheet and has a polygonal shape in which all sides constituting the outer edge in a plan view are formed in a straight line.

3. The sheet according to claim 1 or 2, wherein the root mean square height Rq of the surface is 10 μm or less.

4. The sheet according to claim 1 or 2, wherein the maximum cross-sectional height Rt of the surface is 50 μm or less.

5. The sheet according to claim 1 or 2, wherein the standard deviation of the thickness is 0.4 mm or less.

6. The sheet according to claim 1 or 2, further comprising a compound represented by the following formula (2). H ２ C=CH-R １ -R ３ -R ２ -CH=CH ２ ... (2) However, R １ and R ２ each independently represent CH ２ or CF ２ and R ３ represents a divalent fluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the terminal or between carbon-carbon bonds of the fluorohydrocarbon group.

7. A method for producing a sheet containing a fluorine-containing copolymer, comprising: using a roll kneading machine equipped with at least one pair of rolls, winding a raw material containing a fluorine-containing copolymer onto the rolls to form a sheet, wherein the maximum temperature of the raw material during the formation of the sheet is 60°C or higher, and the thickness of the resulting sheet is 4 mm or less.

8. The method for manufacturing a sheet according to claim 7, comprising cutting the sheet wound around the roll with a roll cutter to a predetermined width in the circumferential direction of the roll, and cutting the sheet cut to the predetermined width to a predetermined length in the direction of the roll axis to cut out a single sheet.

9. The method for manufacturing a sheet according to claim 7 or 8, wherein the maximum temperature and the thickness of the sheet are adjusted so that the absolute value of the charge potential measured after placing the sheet on an anti-static mat for 5 minutes is 6V or less.

10. The method for producing a sheet according to claim 7 or 8, wherein the raw material further comprises a compound represented by the following formula (2). ２ C = CH - R １ -R ３ -R ２ -CH=CH ２ ... (2) However, R １ and R ２ Each is independent of CH ２ or CF ２ R ３ This represents a divalent fluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the terminal or between carbon-carbon bonds of the fluorohydrocarbon group.

11. A crosslinked rubber article comprising the fluorine-containing copolymer in the sheet according to claim 1 or 2.

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