Conductive fluororesin composition and method for producing the same, and tube

Abstract

To provide a fluorine-containing resin composition having conductivity.SOLUTION: A conductive fluorine-containing resin composition comprises: a fluorine-containing copolymer having a unit based on tetrafluoroethylene and a unit based on perfluoro(alkyl vinyl ether); and a conductive metal oxide, wherein the conductive metal oxide has a major axis of less than 4 μm and an aspect ratio of 10 or more, the conductive metal oxide has a refractive index of 1.0 to 3.0, a content of the conductive metal oxide is 10 mass% or more and less than 40 mass% with respect to a total mass of the conductive fluorine-containing resin composition, and a total light transmittance in a 0.1 mm thick film made of the conductive fluorine-containing resin composition exceeds 5%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a conductive fluororesin composition, a method for producing a conductive fluororesin composition, and a tube using a conductive fluororesin composition. [Background technology]

[0002] Patent Document 1 describes, for example, a fluorine-containing resin composition obtained by melt-kneading a fluorine-containing copolymer having a specific functional group with nanodiamonds whose surface has been chemically modified, as a material for forming an insulating layer that covers electric wires. Patent Document 2 describes a composition for forming the surface layer of a printer's transfer belt, which is a mixture of a dispersion of fine powder of a fluororesin in water and a conductive agent such as a metal oxide. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 6455367 [Patent Document 2] Japanese Patent Publication No. 2007-212740 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Depending on the intended use of articles manufactured using fluororesin compositions, it may be required that they be less prone to static electricity for reasons such as preventing dust adhesion or explosion prevention. Furthermore, it is desirable that the surface smoothness of the molded product not be impaired even when conductive agents are added. The present invention aims to provide a fluororesin composition that can improve conductivity without impairing the surface smoothness of a molded product. [Means for solving the problem]

[0005] The present invention has the following aspects. [1] A conductive fluorine-containing resin composition comprising a fluorine-containing copolymer having units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), and a conductive metal oxide, where the major axis of the conductive metal oxide is less than 4 μm and the aspect ratio is 10 or more, where the refractive index of the conductive metal oxide is 1.0 to 3.0, where the content of the conductive metal oxide is 10% by mass or more and less than 40% by mass based on the total mass of the conductive fluorine-containing resin composition, a conductive fluorine-containing resin composition having a total light transmittance of more than 5% in a film with a thickness of 0.1 mm made of the conductive fluorine-containing resin composition. [2] The conductive fluorine-containing resin composition according to [1], wherein the conductive metal oxide is antimony-doped tin oxide. [3] A tube having a conductive layer made of the conductive fluorine-containing resin composition according to [1] or [2]. [4] The tube according to [3], wherein the thickness in the radial direction of the conductive layer is less than 300 μm. [5] The tube according to [3] or [4], further having a layer made of a fluorine-containing copolymer having units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether). [6] The tube according to [5], wherein the outermost layer is the conductive layer and the innermost layer is a layer made of the fluorine-containing copolymer. [7] A kneading step of kneading a raw material containing a fluorine-containing copolymer having units derived from tetrafluoroethylene and units derived from perfluoroalkyl vinyl ether, and a conductive metal oxide, using a biaxial melt kneading extruder, where the content of the conductive metal oxide is 10% by mass or more and less than 40% by mass based on the total mass of the raw material, where the major axis of the conductive metal oxide is less than 4 μm and the aspect ratio is 10 or more, where the refractive index of the conductive metal oxide is 1.0 to 3.0, In the kneading step, the ratio L / D representing the ratio of the length L of the kneading element or the mixing element to the barrel inner diameter D of the twin-screw melt kneading extruder is set to be more than 3, and the shear rate γ represented by the following formula (a) is set to be more than 40 sec -1 -1, a method for producing a conductive fluororesin composition. γ = π × D × N / 60 …(a) In formula (a), γ is the shear rate (unit: sec -1 -1), π is 3.14 (pi), D is the barrel inner diameter (unit: mm), N represents the screw rotation speed (unit: rpm).

Advantages of the Invention

[0006] According to the present invention, a fluororesin composition having enhanced conductivity can be obtained without impairing the surface smoothness of the molded product. According to the present invention, a tube having a conductive layer with good surface smoothness can be obtained.

Modes for Carrying Out the Invention

[0007] The following definitions of terms apply throughout this specification and the claims. A numerical range represented by "~" means a numerical range having the numerical values before and after ~ as the lower limit value and the upper limit value, respectively. A "unit" in a polymer means a atomic group derived from one molecule of the monomer formed by polymerization of the monomer. The unit may be an atomic group directly formed by a polymerization reaction, or may be an atomic group in which a part of the atomic group has been converted to another structure by treating the polymer obtained by the polymerization reaction. An "etheric oxygen atom" means an oxygen atom forming an ether bond (-O-) between carbon atoms. A "perfluoroalkyl group" means a group in which all hydrogen atoms covalently bonded to carbon atoms of an alkyl group are substituted with fluorine atoms. "(Meth)acrylate" is a general term for acrylate and methacrylate. The "melting point" is the temperature corresponding to the maximum value of the melting peak measured by differential scanning calorimetry (DSC). The "melt flow velocity" is the melt mass flow rate (MFR) as defined in JIS K 7210-1:2014 (corresponding international standard ISO 1133-1:2011). The measurement conditions for MFR are a temperature of 372°C and a load of 49N or a temperature of 230°C and a load of 21N. The refractive index of fluorine-containing copolymers and conductive metal compounds are measured according to the method specified in JIS K 7142:2014.

[0008] The following measurement methods are used in this specification. <Aspect ratio of conductive metal compounds> Conductive metal compound particles are observed using a transmission electron microscope (TEM), and their major and minor axes are measured. The average major axis (average major axis) and average minor axis (average minor axis) are determined for 100 ± 10 particles, and the ratio of the average major axis to the average minor axis (average major axis / average minor axis) is calculated to determine the aspect ratio.

[0009] <Total light transmittance of a film made of a conductive fluororesin composition> The conductive fluororesin composition to be measured is formed into a 0.1 mm thick (tolerance 0.05 mm) film by press molding. The press molding conditions are a temperature of 350°C and a pressure of 5 MPa, and the film dimensions are 130 mm (length) x 130 mm (width) x 0.1 mm (thickness). The obtained film is cut into 50 mm (length) x 50 mm (width) pieces to be used as measurement samples. The total light transmittance of the sample for measurement is measured according to the method in accordance with JIS K 7361-1:1997.

[0010] <Volume resistivity of conductive fluororesin composition> The volume resistivity of the film used for the measurement of total light transmittance described above is measured according to the method compliant with JIS K 7194:1994.

[0011] ≪Electroconductive fluorine-containing resin composition E≫ The conductive fluororesin composition E of this embodiment comprises a fluoropolymer A and a conductive metal oxide B. It may also contain an optional component C.

[0012] <Fluorine-containing copolymer A> The following (1) to (6) are possible units that constitute fluorine-containing copolymer A. Fluorine-containing copolymer A contains at least the following TFE units and the following PAVE units. Furthermore, it may contain one or more selected from the following HFP units, other fluorine-containing units, and other non-fluorine units. The fluorine-containing copolymer A may have the following functional group i. Embodiments having functional group i will be described later.

[0013] (1) TFE unit: A unit based on tetrafluoroethylene (hereinafter also referred to as "TFE"). (2) PAVE unit: A unit based on perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE"). (3) HFP unit: A unit based on hexafluoropropylene (hereinafter also referred to as "HFP"). (4) Other fluorine-containing units: Units based on fluorine-containing monomers other than TFE, PAVE, and HFP (excluding those containing the functional group i below; hereinafter also referred to as "other fluorine-containing monomers"). (5) Other nonfluorine units: Nonfluorine monomers that do not contain a fluorine atom (excluding those containing the functional group i below; hereinafter also referred to as "other nonfluorine monomers"). (6) Unit i: A unit based on monomer i having a functional group i selected from the group consisting of carbonyl group-containing groups, hydroxyl groups, epoxy groups, and isocyanate groups. Functional group i contributes to improved adhesion.

[0014] As for the aforementioned PAVE, CF2 = CFOR f1 (However, R f1 This refers to a perfluoroalkyl group having 1 to 10 carbon atoms, or a perfluoroalkyl group having 2 to 10 carbon atoms having an etheric oxygen atom. Examples include R. f1The perfluoroalkyl group in [the compound] may be linear or branched. R f1 The number of carbon atoms of R is preferably 1 to 6, more preferably 1 to 3. CF2=CFOR f1 Examples thereof include CF2=CFOCF3, CF2=CFOCF2CF3, CF2=CFOCF2CF2CF3 (hereinafter also referred to as "PPVE"), CF2=CFOCF2CF2CF2CF3, CF2=CFO(CF2)8F, etc., and PPVE is preferred. The PAVE units contained in the fluorine-containing copolymer A may be one type or two or more types.

[0015] As the other fluorine-containing monomer, a fluorine-containing compound having one or two polymerizable double bonds is preferred, such as fluoroolefins (excluding TFE and HFP) such as vinyl fluoride, vinylidene fluoride (hereinafter also referred to as "VdF"), trifluoroethylene, chlorotrifluoroethylene (hereinafter also referred to as "CTFE"), etc., CF2=CF(CF2) p OCF=CF2 (where p is 1 or 2), CH2=CX 2 (CF2) q X 3 (where X 2 is a hydrogen atom or a fluorine atom, q is an integer of 2 to 10, and X 3 is a hydrogen atom or a fluorine atom.). Examples thereof include perfluoro(2-methylene-4-methyl-1,3-dioxolane).

[0016] As the other fluorine-containing monomer, monomers selected from the group consisting of VdF, CTFE, and CH2=CX 2 (CF2) q X 3 are preferred. CH2=CX 2 (CF2) q X 3 Examples thereof include CH2=CH(CF2)2F, CH2=CH(CF2)3F, CH2=CH(CF2)4F, CH2=CF(CF2)3H, CH2=CF(CF2)4H, etc., and CH2=CH(CF2)4F and CH2=CH(CF2)2F are preferred. The other fluorine-containing units in fluorine-containing copolymer A may be one type or two or more types.

[0017] As other non-fluorinated monomers, compounds having one polymerizable double bond and no fluorine atoms are preferred, and examples include olefins with three or fewer carbon atoms, such as ethylene and propylene. Other non-fluorinated monomers include ethylene and propylene, with ethylene being particularly preferred. The other non-fluorinated units contained in fluorine-containing copolymer A may be one type or two or more types.

[0018] Preferably, the content of TFE units is 90 to 99.9 mol%, the content of PAVE units is 0.1 to 10 mol%, and the total content of TFE units and PAVE units is 90.1 to 100 mol% relative to the total number of units of fluorine-containing copolymer A. When the TFE unit content is above the lower limit of the range, the fluorine-containing copolymer A exhibits excellent heat resistance, chemical resistance, etc., and when it is below the upper limit, the fluorine-containing copolymer A exhibits excellent stress crack resistance. The TFE unit content is more preferably 95 to 99.5 mol%, and particularly preferably 96 to 99 mol%. When the PAVE unit content is within the aforementioned range, the fluorine-containing copolymer A exhibits excellent moldability. The PAVE unit content is more preferably 0.5 to 5 mol%, and particularly preferably 1 to 4 mol%.

[0019] The total content of HFP units, other fluorine-containing units, and other non-fluorine units in fluorine-containing copolymer A is preferably 9.9 mol% or less, more preferably 4.5 mol% or less, and particularly preferably 3 mol% or less. It may also be zero. The proportion of each unit in fluorine-containing copolymer A can be measured by NMR analysis such as molten nuclear magnetic resonance (NMR) analysis, fluorine content analysis, infrared absorption spectroscopy, etc.

[0020] [A form in which fluorine-containing copolymer A has a functional group i] If the fluorine-containing copolymer A has a functional group i, the fluorine-containing copolymer A may have i units based on monomer i having the functional group i, or it may have terminal groups having the functional group i, or it may have both.

[0021] Monomer i has one or more functional groups i. If monomer i has two or more functional groups i, these two or more functional groups i may be the same or different. The monomer i is preferably a compound having one functional group i and one polymerizable double bond. Monomer i may be a fluorine-containing monomer or a non-fluorine monomer that does not contain fluorine atoms. A non-fluorine monomer is preferred.

[0022] There are no particular restrictions on the carbonyl group-containing group, which is functional group i, as long as it contains a carbonyl group. Examples include groups having carbonyl groups between carbon atoms of a hydrocarbon group, carbonate groups, carboxyl groups, haloformyl groups, alkoxycarbonyl groups, acid anhydride residues, polyfluoroalkoxycarbonyl groups, and fatty acid residues. In a group having carbonyl groups between carbon atoms of a hydrocarbon group, examples of hydrocarbon groups include alkylene groups having 2 to 8 carbon atoms. The alkylene group may be linear or branched. Note that the number of carbon atoms in the alkylene group does not include the carbon atoms of the carbonyl group. A haloformyl group is a group represented by -C(=O)-X (where X is a halogen atom). Examples of halogen atoms in a haloformyl group include fluorine atoms and chlorine atoms, with fluorine atoms being preferred. In other words, a fluoroformyl group (also called a carbonyl fluoride group) is preferred as the haloformyl group. The alkoxy group in the alkoxycarbonyl group may be linear or branched. The alkoxy group is preferably an alkoxy group having 1 to 8 carbon atoms, and a methoxy group or an ethoxy group is particularly preferred.

[0023] Among the carbonyl group-containing groups, from the viewpoint of improving adhesion to the substrate, groups selected from the group consisting of groups having carbonyl groups between carbon atoms of a hydrocarbon group, carbonate groups, carboxyl groups, haloformyl groups, alkoxycarbonyl groups, and acid anhydride residues are preferred, with carboxyl groups and acid anhydride residues being more preferred.

[0024] Monomer i having a carbonyl group-containing group as functional group i includes cyclic hydrocarbon compounds having an acid anhydride residue and a polymerizable unsaturated bond (hereinafter also referred to as "monomer i-1"), monomers having a carboxyl group (hereinafter also referred to as "monomer i-2"), vinyl esters, (meth)acrylates, and CF2=CFOR f3 COOX 4 (However, R f3 X is a perfluoroalkylene group having 1 to 10 carbon atoms, or a perfluoroalkylene group having 2 to 10 carbon atoms with an etheric oxygen atom, 4 This is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. Examples include: Examples of monomer i-1 include acid anhydrides of unsaturated dicarboxylic acids. Examples of acid anhydrides of unsaturated dicarboxylic acids include itaconic anhydride (hereinafter also referred to as "IAH"), citraconic anhydride (hereinafter also referred to as "CAH"), 5-norbornene-2,3-dicarboxylic anhydride (also known as hymic anhydride; hereinafter also referred to as "NAH"), and maleic anhydride. Examples of monomer i-2 include unsaturated dicarboxylic acids such as itaconic acid, citraconic acid, 5-norbornene-2,3-dicarboxylic acid, and maleic acid; and unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid. Examples of the vinyl ester include vinyl acetate, vinyl chloroacetate, vinyl butanoate, vinyl pivalate, vinyl benzoate, and vinyl crotate. Examples of the (meth)acrylate include (polyfluoroalkyl)acrylate and (polyfluoroalkyl)methacrylate.

[0025] Examples of monomer i having a hydroxyl group as functional group i include vinyl esters, vinyl ethers, allyl ethers, or (meth)acrylates having one or more hydroxyl groups at the terminal or side chain, crotonic acid-modified compounds such as hydroxyethyl crotate, and allyl alcohols.

[0026] Examples of monomer i having an epoxy group as functional group i include unsaturated glycidyl ethers (e.g., allyl glycidyl ether, 2-methylallyl glycidyl ether, vinyl glycidyl ether, etc.) and unsaturated glycidyl esters (e.g., glycidyl acrylate, glycidyl methacrylate, etc.).

[0027] Examples of monomer i having an isocyanate group as functional group i include 2-(meth)acryloyloxyethyl isocyanate, 2-(2-(meth)acryloyloxyethoxy)ethyl isocyanate, and 1,1-bis((meth)acryloyloxymethyl)ethyl isocyanate.

[0028] Fluorine-containing copolymer A may have one i-unit or two or more i-units. From the viewpoint of improving adhesion to the substrate, it is preferable that the i unit has at least a carbonyl group-containing group as the functional group i. A monomer having a carbonyl group-containing group is preferred as the monomer i.

[0029] Of the monomers i having a carbonyl group-containing group as functional group i, monomer i-1 is preferred from the viewpoint of improved thermal stability and adhesion to the substrate. As monomer i-1, monomers selected from the group consisting of IAH, CAH, and NAH are particularly preferred. By using at least one selected from the group consisting of IAH, CAH, and NAH, fluorine-containing copolymer A having acid anhydride residues can be easily produced without using the special polymerization method required when maleic anhydride is used as monomer i-1 (see Japanese Patent Publication No. 11-193312). Among IAH, CAH, and NAH, NAH is more preferred because it has better adhesion to the substrate.

[0030] If functional group i is present in the terminal group of the main chain of fluorine-containing copolymer A, then the terminal group having functional group i is a terminal group derived from polymerization initiators, chain transfer agents, etc., used in the production of fluorine-containing copolymer A. The fluorine-containing copolymer A may contain both i-units having a functional group i and terminal groups having a functional group i. It is more preferable that the fluorine-containing copolymer A has i-units.

[0031] When fluorine-containing copolymer A has i units, the content of i units relative to the total units of fluorine-containing copolymer A is preferably 0.01 to 3 mol%, more preferably 0.02 to 2 mol%, and particularly preferably 0.05 to 1.5 mol%. When the content of i units is above the lower limit of the range, the adhesion improvement effect is excellent. When the content of i units is below the upper limit of the range, the heat resistance and color of fluorine-containing copolymer A are good. The ratio of i units to the total units of fluorine-containing copolymer A can be determined, for example, using methods such as infrared absorption spectroscopy, as described in Japanese Patent Application Publication No. 2007-314720.

[0032] When the fluorine-containing copolymer A has i units, the total content of HFP units, other fluorine-containing units, other non-fluorine units, and i units relative to the total units of the fluorine-containing copolymer A is preferably 9.9 mol% or less, more preferably 4.5 mol% or less, and particularly preferably 3 mol% or less. When the fluorine-containing copolymer A has i units, the content of TFE units relative to the total units of the fluorine-containing copolymer A is preferably 90 to 99.9 mol%, more preferably 95 to 99.5 mol%, and particularly preferably 96 to 99 mol%. When the fluorine-containing copolymer A has i units, the PAVE unit content is preferably 0.1 to 10 mol%, more preferably 0.5 to 5 mol%, and particularly preferably 1 to 4 mol% relative to the total units of the fluorine-containing copolymer A.

[0033] The melting point of fluorine-containing copolymer A is preferably 260 to 320°C, more preferably 280 to 315°C, and even more preferably 295 to 310°C. If the melting point of fluorine-containing copolymer A is above the lower limit of the aforementioned range, it exhibits excellent heat resistance; if it is below the upper limit, it exhibits an excellent balance between heat resistance and processability. The melting point of fluorine-containing copolymer A can be adjusted by the types of units that make up fluorine-containing copolymer A, the proportion of each unit, the molecular weight, etc. For example, the melting point tends to increase as the proportion of TFE units increases.

[0034] The melt flow rate (MFR) of fluorine-containing copolymer A is preferably 0.1 to 1000 g / 10 min, more preferably 0.5 to 100 g / 10 min, even more preferably 1 to 50 g / 10 min, and particularly preferably 5 to 40 g / 10 min. When the MFR is above the lower limit of the above range, the processability is excellent. When the MFR is below the upper limit of the above range, good mechanical strength is easily obtained in the conductive fluorine-containing resin composition E. MFR is an indicator of the molecular weight of fluorine-containing copolymer A; a higher MFR indicates a lower molecular weight, while a lower MFR indicates a higher molecular weight. The molecular weight and MFR of fluorine-containing copolymer A can be adjusted by the manufacturing conditions of fluorine-containing copolymer A. For example, when producing fluorine-containing copolymer A by polymerizing monomers, shortening the polymerization time tends to increase the MFR.

[0035] The refractive index of fluorine-containing copolymer A is preferably 1.1 to 2.5, more preferably 1.2 to 3.0, and particularly preferably 1.3 to 2.0. When the refractive index of fluorine-containing copolymer A is within the above range, it exhibits excellent transparency. The refractive index of fluorine-containing copolymer A can be adjusted by its degree of crystallinity. For example, lowering the degree of crystallinity tends to increase the refractive index.

[0036] <Conductive metal oxide B> Conductive metal oxide B is particulate with an aspect ratio of 10 or more and a major axis of less than 4 μm. Using such needle-shaped fine particles makes it easier to enhance the conductivity of conductive fluororesin composition E. The aspect ratio is preferably 15 or higher, and more preferably 20 or higher. There is no particular upper limit, but in terms of flexibility, it is preferably 50 or lower, and more preferably 30 or lower. The longest diameter is preferably 3 μm or less, and more preferably 2 μm or less. The lower limit is not particularly limited, but in terms of strength, it is preferably 0.1 μm or more, and more preferably 0.2 μm or more.

[0037] The conductive metal oxide B used has a refractive index of 1.0 to 3.0. Having a refractive index within this range makes it easier to minimize the refractive index difference between the fluorine-containing copolymer A and the conductive metal oxide B. The refractive index of conductive metal oxide B is preferably 1.2 to 2.8, and more preferably 1.3 to 2.5.

[0038] Examples of conductive metal oxide B include tin oxide (SnO2, refractive index 2.0), antimond-doped tin oxide (ATO, refractive index 2.0) obtained by doping indium oxide (In2O3) with pentavalent antimony, and tin-doped indium oxide (ITO, refractive index 2.0) obtained by doping In2O3 with tetravalent tin. Antimond-doped tin oxide is more preferred in terms of conductivity.

[0039] The content of conductive metal oxide B in the conductive fluororesin composition E is 10% by mass or more and less than 40% by mass, preferably 15 to 35% by mass, and more preferably 20 to 30% by mass, relative to the total mass. When the content of conductive metal oxide B is above the lower limit of the above range, the conductivity imparting effect is excellent. When it is below the upper limit, the surface smoothness of the molded product of the conductive fluororesin composition E is excellent. In addition, it is easy to increase the total light transmittance.

[0040] <Optional component C> The conductive fluororesin composition E of this embodiment may also contain any component C other than the fluoropolymer A and the conductive metal oxide B. Optional component C can be any known additive such as fillers, plasticizers, or flame retardants. These additives may be used individually or in combination of two or more. The content of optional component C in the conductive fluororesin composition E is preferably within a range that ensures the transparency of the film made from the conductive fluororesin composition E.

[0041] <Physical properties of conductive fluororesin composition E> The conductive fluororesin composition E exhibits a total light transmittance of over 5% for a 0.1 mm thick film made from the conductive fluororesin composition E. As shown in the examples described later, good conductivity can be obtained when the conductive fluororesin composition E contains 10% by mass or more of conductive metal oxide B and the total light transmittance exceeds 5%. For example, if the volume resistivity of the conductive fluororesin composition E is 2.0 × 10⁻⁶ 14 A value of Ω·cm or less can be achieved. The volume resistivity is 2.0 × 10⁻⁶. 14 When the value is Ω·cm or less, for example, it has excellent dust adhesion prevention effects due to static electricity suppression.

[0042] The total light transmittance is preferably 6% or more, more preferably 7% or more, and particularly preferably 8% or more. There is no particular upper limit, but from the viewpoint of transparency, it is preferably 90% or less, and more preferably 80% or less. The aforementioned volume resistivity is 1.0 × 10⁻⁶ 15 Ω·cm or less is more preferable, and 1.0 × 10 8 A value of Ω·cm or less is even more preferable.

[0043] The total light transmittance can be adjusted by the kneading strength during the production of the conductive fluororesin composition E. For example, when the composition of the conductive fluororesin composition E is constant, increasing the kneading strength during production tends to increase the total light transmittance. This is thought to be because the conductive metal oxide B is more uniformly dispersed in the conductive fluororesin composition. Furthermore, the total light transmittance can be adjusted by the MFR (molecular weight) of the fluorine-containing copolymer A. For example, when the content of conductive metal oxide B and the kneading strength are constant, lowering the MFR of the fluorine-containing copolymer A tends to increase the total light transmittance. This is thought to be because the fluidity of the conductive fluorine-containing resin composition E increases, and the conductive metal oxide B is dispersed more uniformly.

[0044] Furthermore, when the conductive fluororesin composition consists solely of fluoropolymer A, the total light transmittance is generally about 6-50%, preferably 6-30%, and more preferably 8-20%. Furthermore, when the conductive fluororesin composition consists only of fluoropolymer A, the volume resistivity is approximately 1.0 × 10⁻⁶. 5 ~1.0×10 16 It is approximately Ω·cm, and 1.0 × 10 8 ~5.0×10 14 Ω·cm is preferred, and 1.0 × 10 14 ~5.0×10 14 Ω·cm is preferable.

[0045] Method for producing conductive fluororesin compositions The method for producing the conductive fluororesin composition of this embodiment includes a kneading step of kneading raw materials containing a fluororesin copolymer A and a conductive metal oxide B. The composition of the raw materials, including in preferred embodiments, is the same as that of conductive fluororesin composition E. The kneaded material (conductive fluororesin composition E) obtained in the kneading process is preferably molded as needed. For example, it may be extruded into pellets.

[0046] In the mixing process, the raw materials are mixed using a twin-screw fused compounding extruder (hereinafter also referred to as a "twin-screw extruder"). A twin-screw extruder comprises two screws, a barrel containing the two screws, a raw material supply port in the barrel, and a die located at the downstream end of the barrel. The extruder may be a twin-screw extruder with two screws rotating in the same direction, which are passed through a cylinder of a barrel with through holes, or it may be a twin-screw extruder with two screws rotating in opposite directions. A twin-screw extruder with two screws rotating in the same direction is more preferred. The meshing of the two screws may be non-meshing, partially meshing, or fully meshing.

[0047] The screw used consists of multiple screw elements mounted on a shaft. The screw elements have the same cross-sectional shape perpendicular to the axis. Examples of screw elements, categorized by function, include rotary elements, kneading elements, and mixing elements. The rotary element has a twist angle that allows it to rotate continuously around the shaft, and is used for conveying. It is a capable screw element. A kneading element is a screw element composed of multiple plate-shaped discs with no torsional angle. The mixing element is a screw element formed by creating a notch in a right-hand threaded full-flight element, or a screw element formed by creating a notch in a left-hand threaded full-flight element. The mixing element may or may not have self-cleaning properties.

[0048] The twin-screw extruder in this embodiment has one or more melting zones in which at least one of the mixing elements and kneading elements of the screw elements is arranged in a continuous manner. A barrel is made up of multiple barrel blocks connected in series. The barrel block has through holes formed in it that correspond to the cross-sectional shape of the screw. When forming a conductive fluororesin composition E into pellets, the molten conductive fluororesin composition E is extruded from a die attached to the discharge port of a twin-screw extruder to form strands, which are then cut by a pelletizer to form pellets. The number of discharge ports in the die may be one or multiple.

[0049] The kneading conditions in the mixing process are as follows: L / D, which represents the ratio of the length of the kneading element or mixing element (i.e., the total length of the screw in the molten zone) L (mm) to the inner diameter D (mm) of the barrel, is greater than 3, and the shear rate γ, expressed by the following formula (a), is set to 40 sec. -1 Let's consider it to be greater than. γ = π × D × N / 60 …(a) In equation (a), γ is the shear rate (unit: sec). -1 ), π represents 3.14 (pi), D represents the barrel bore diameter (unit: mm), and N represents the screw rotation speed (unit: rpm).

[0050] L / D and shear rate γ are indicators of mixing strength. When L / D is constant, a higher shear rate γ results in higher mixing strength. When shear rate γ is constant, a higher L / D results in higher mixing strength. As shown in the examples described later, the raw material contains 10% by mass or more of conductive metal oxide B, the L / D ratio is greater than 3 in the kneading process, and the shear rate γ is 40 sec. -1 If the value is greater than 2.0 × 10⁻¹⁰, then good conductivity of the conductive fluororesin composition E can be obtained. For example, if the volume resistivity of the conductive fluororesin composition E is 2.0 × 10⁻¹⁰ 14 It is possible to achieve a value of Ω·cm or less.

[0051] The L / D ratio is preferably 20 or higher, more preferably 30 or higher, and particularly preferably 35 or higher. There is no particular upper limit, but from the viewpoint of thermal degradation due to retention, it is preferably 100 or lower, and more preferably 60 or lower. The shear rate γ is 45 sec. -1 The above is preferable, 50 seconds -1 The above is more preferable, 70sec -1The above is particularly preferable. While there is no particular upper limit, 500 seconds is preferable from the viewpoint of suppressing resin decomposition. -1 The following is preferable, 200 sec -1 The following is more preferable: The shear rate γ can be adjusted by the screw rotation speed N, as well as by changing the tip clearance between the barrel and the screw flight.

[0052] The barrel inner diameter D is preferably 10 to 100 mm, and more preferably 12 to 60 mm. The length L is preferably 200 to 5000 mm, and more preferably 400 to 2000 mm. The screw rotation speed N is preferably, for example, 50 to 800 rpm, and more preferably 70 to 300 rpm. The kneading temperature is set to be above the melting point of fluorine-containing copolymer A. The absolute value of the difference between the melting point of fluorine-containing copolymer A and the kneading temperature is preferably 0 to 200°C, and more preferably 10 to 100°C.

[0053] Molded body Various molded articles can be manufactured by molding the conductive fluororesin composition E. The molding method is not particularly limited, and known molding methods can be applied. For example, melt molding methods (extrusion molding, injection molding, press molding, etc.) can be used. Examples of extrusion molding methods include film sheet molding using a T-die, tube molding using a circular die, irregular shape extrusion molding, melt spinning, and blow molding for hollow parts. Multilayer molded products with two or more layers may also be manufactured by extrusion molding. A molded article obtained by molding conductive fluororesin composition E is electrically conductive. In addition, it is transparent and chemically resistant.

[0054] ≪Tube≫ As the molded body, a tube (annular molded body) is preferred, for example. The tube of this embodiment has a conductive layer E made of a conductive fluororesin composition E. Furthermore, it may have a layer A made of a fluoropolymer A. The conductive layer E is conductive, transparent, and chemical resistant. The surface made of the conductive fluororesin composition E is less prone to static electricity, providing a dust adhesion prevention effect. Layer A is transparent and chemical resistant, and good surface smoothness can be easily obtained. The tube of this embodiment is suitable, for example, as a tube for transporting chemical solutions.

[0055] A tube having conductive layers E and A is preferably a multilayer tube in which two or more layers are laminated in the radial direction. In a multilayer tube, it is preferable that the outermost layer is conductive layer E and the innermost layer is layer A. An intermediate layer may be present between the outermost and innermost layers. The intermediate layer is preferably made of a transparent resin composition.

[0056] The outer diameter of the single-layer tube made of conductive layer E is preferably 0.1 to 50 mm, and more preferably 0.05 to 5 mm. The radial thickness (wall thickness) of the single-layer tube is preferably 0.01 to 10 mm, and more preferably 0.05 to 1 mm.

[0057] In a multilayer tube having conductive layer E and layer A, the thickness of the conductive layer E in the radial direction is preferably less than 300 μm, preferably 200 μm or less, and more preferably 100 μm or less. When the thickness of the conductive layer E is less than 300 μm, the transparency is excellent. The lower limit of the thickness of the conductive layer E is not particularly limited, but from the viewpoint of strength, it is preferably 5 μm or more, and more preferably 20 μm or more. The outer diameter of the multilayer tube is preferably 0.5 to 100 mm, and more preferably 1 to 10 mm. The radial thickness (wall thickness) of the multilayer tube is preferably 0.02 to 10 mm, and more preferably 0.05 to 5 mm. [Examples]

[0058] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0059] [Raw materials] <Fluorine-containing copolymer A> Fluorine-containing copolymer A1: A copolymer consisting of 98 mol% TFE units and 2 mol% PPVE units, with a melting point of 310°C, a melting temperature of 35.9 g / 10 min, and a refractive index of 1.4. Fluorine-containing copolymer A2: A copolymer consisting of 98.5 mol% TFE units and 1.5 mol% PPVE units, with a melting point of 310°C, a melting temperature of 13 g / 10 min, and a refractive index of 1.4. <Conductive metal oxide B> Conductive metal oxide B1: Antimond-doped tin oxide (ATO), major axis 1.1 mm, aspect ratio 25, refractive index 2.0.

[0060] [Twin-screw fused compounding extruder] A twin-screw extruder (manufactured by Technovel, product name "KZW15TW-45HG1100", screw diameter: 15mmΦ, L / D: 45) was used.

[0061] Examples 1-4 below are examples, and Examples 5-7 are comparative examples. [Example 1] Using a twin-screw fusion extruder, conductive fluorine-containing copolymer A1 and conductive metal oxide B1 were melt-kneaded according to the formulations shown in Table 1 to produce pellets of conductive fluorine-containing resin composition. The kneading conditions are shown in Table 1. The kneading temperature was 370°C. Next, a film made of a conductive fluororesin composition was manufactured using a press molding machine under the above molding conditions, and the total light transmittance and volume resistivity were measured. The results are shown in Table 1. Furthermore, a 0.1 mm thick film consisting solely of fluorine-containing copolymer A1 has a total light transmittance of 95% and a volume resistivity of 1.0 × 10⁻⁶. 17 It had a density of Ω·cm and was insulating.

[0062] [Examples 2, 3, and 6] In Example 1, the content ratio of fluorine-containing copolymer A1 and conductive metal oxide B1 was changed as shown in Table 1. The conductive fluororesin composition was manufactured in the same manner as in Example 1, molded into a film, and its total light transmittance and volume resistivity were measured. The results are shown in Table 1.

[0063] [Example 4] In Example 2, fluorine-containing copolymer A1 was changed to fluorine-containing copolymer A2. The conductive fluororesin composition was manufactured in the same manner as in Example 2, molded into a film, and its total light transmittance and volume resistivity were measured. The results are shown in Table 1. Furthermore, a 0.1 mm thick film consisting solely of fluorine-containing copolymer A2 has a total light transmittance of 93% and a volume resistivity of 1.0 × 10⁻⁶. 17 It had a density of Ω·cm and was insulating.

[0064] [Example 5] In Example 1, the content ratio of fluorine-containing copolymer A1 and conductive metal oxide B1 was changed as shown in Table 1. Furthermore, the length L of the kneading element was changed from 173 mm to 45 mm, and the L / D ratio was changed to 3. The conductive fluororesin composition was manufactured in the same manner as in Example 1, molded into a film, and its total light transmittance and volume resistivity were measured. The results are shown in Table 1.

[0065] [Example 7] In Example 2, the screw rotation speed N was changed from 100 rpm to 45 rpm, and the shear rate γ was set to 35 sec. -1 I changed it to this. The conductive fluororesin composition was manufactured in the same manner as in Example 2, molded into a film, and its total light transmittance and volume resistivity were measured. The results are shown in Table 1.

[0066] [Evaluation of surface smoothness] Multilayer tubes having an outer layer made of the conductive fluororesin composition obtained in Examples 1-7 were manufactured, and their surface smoothness was evaluated. Specifically, multilayer extrusion molding was performed using a two-layer tube molding die, with the inner layer being a fluorine-containing copolymer A1 and the outer layer being the conductive fluorine-containing resin composition of each example. A 40mm diameter extruder was used for the inner layer, and the die temperature after the two resins were combined was set to 370°C. The cylinder temperature was set to 280-370°C. A 30mm diameter extruder was used for the outer layer, and the cylinder temperature was set to 280-370°C. The discharge volume of each extruder and the tube take-up speed were adjusted so that the final tube shape had an inner diameter of 6mm, an outer diameter of 8mm, an inner layer thickness of 0.9mm, and an outer layer thickness of 0.1mm. This resulted in a take-up speed of 6m / min. The tubes discharged from the die passed through a vacuum sizing section and were then cooled in a water tank to fix their final shape. The obtained tubes were visually inspected, and if irregularities originating from die slits were observed on the outer surface, it was determined that melt fracture had occurred. If no such irregularities were observed, it was determined that melt fracture had not occurred. The results are shown in Table 1.

[0067] [Table 1]

[0068] As shown in the results in Table 1, the conductive fluororesin compositions of Examples 1 to 4 exhibited good conductivity and surface smoothness. Examples 2, 4, and 7 all contained the same amount of conductive metal oxide B1, but examples 2 and 4, which had a total light transmittance exceeding 5%, had lower volume resistivity and superior conductivity compared to example 7. Examples 5 and 7 show that the conductive metal oxide B1 content is between 10% by mass and less than 40% by mass, but the total light transmittance is 5% or less, resulting in high volume resistivity and poor conductivity. Example 6 had a total light transmittance of 5% or less, but contained 40% by mass of conductive metal oxide B1, resulting in poor surface smoothness.

Claims

1. A conductive fluorine-containing resin composition comprising a fluorine-containing copolymer having units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), and a conductive metal oxide, The conductive metal oxide has a major axis of less than 4 μm and an aspect ratio of 10 or more. The refractive index of the conductive metal oxide is 1.0 to 3.

0. The content of the conductive metal oxide is 10% by mass or more and less than 40% by mass, relative to the total mass of the conductive fluororesin composition. A conductive fluororesin composition having a total light transmittance of more than 5% in a 0.1 mm thick film made of the conductive fluororesin composition.

2. The conductive fluororesin composition according to claim 1, wherein the conductive metal oxide is antimond-doped tin oxide.

3. A tube having a conductive layer made of the conductive fluororesin composition described in claim 1 or 2.

4. The tube according to claim 3, wherein the radial thickness of the conductive layer is less than 300 μm.

5. Furthermore, the tube according to claim 3, having a layer made of a fluorine-containing copolymer having units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether).

6. The tube according to claim 5, wherein the outermost layer is the conductive layer and the innermost layer is a layer made of the fluorine-containing copolymer.

7. A method for producing the conductive fluororesin composition described in Claim 1, The process includes a kneading step in which a raw material containing a fluorine-containing copolymer having units derived from tetrafluoroethylene and units derived from perfluoro(alkyl vinyl ether), and a conductive metal oxide, is kneaded using a twin-screw fusion kneading extruder. The content of the conductive metal oxide is 10% by mass or more and less than 40% by mass relative to the total mass of the raw materials. The conductive metal oxide has a major axis of less than 4 μm and an aspect ratio of 10 or more. The refractive index of the conductive metal oxide is 1.0 to 3.

0. In the kneading process, the ratio L / D, which represents the ratio of the length L of the kneading element or mixing element to the barrel inner diameter D of the twin-screw molten kneading extruder, is set to greater than 3, and the shear rate γ, represented by the following formula (a), is set to 40 sec. －１ A method for producing a conductive fluororesin composition. γ=π×D×N / 60…(a) In equation (a), γ is the shear rate (unit: sec) －１ ), π is 3.14 (the ratio of a circle's circumference to its diameter). D is the barrel inner diameter (unit: mm). N represents the screw rotation speed (unit: rpm).

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