Sizing agents, sized fibers, prepregs and dispersions

Abstract

Provided are a specific sizing agent, sized fibers, and a prepreg that make it possible to suppress foaming during hot forming and to form a molded object that has an excellent appearance, including smoothness, and, in a laminate, has excellent adhesion and water resistance. Also provided is a dispersion that contains a tetrafluoroethylene polymer powder and has excellent dispersion stability, even when the amount of surfactant is reduced.　A sizing agent that contains a heat-fusible tetrafluoroethylene polymer powder that has an average particle size of 0.1–200 μm. Sized fibers, and a prepreg that includes the fibers and a matrix resin. A dispersion that includes a heat-fusible tetrafluoroethylene polymer powder that has an average particle size of 10–100 μm, a surfactant, and a liquid dispersion medium, the dispersion containing no more than 0.01 parts by mass of the surfactant per 1 part by mass of the heat-fusible tetrafluoroethylene polymer powder.

Description

[Technical Field]

[0001] The present invention relates to a sizing agent containing a tetrafluoroethylene-based polymer, sized fibers, prepregs, and dispersions containing tetrafluoroethylene-based polymer powder. [Background technology]

[0002] Fiber-reinforced plastics are lightweight and durable, and the reinforcing fibers used include inorganic fibers such as glass fiber, carbon fiber, boron fiber, and metal fiber, as well as organic fibers such as highly impact-resistant aramid fiber, Zylon fiber (poly(paraphenylene benzobisoxazole)), and polyethylene fiber. Carbon fiber in particular has excellent mechanical properties, so carbon fiber-reinforced composite materials, in which matrix resins are reinforced with carbon fiber, are widely used as composite materials to replace metals in a variety of applications, including aircraft components, spacecraft components, automobile components, and ship components, as well as in sports applications such as golf shafts and fishing rods, office equipment applications, and computer applications (IC trays, laptop computer housings, etc.).

[0003] Various sizing agents have been investigated to improve the strength of composite materials by increasing the affinity between the matrix resin and reinforcing fibers and improving interfacial adhesion, as well as to cover and converge the fibers, reducing damage and making them easier to handle. Thermosetting resins such as phenolic resin, melamine resin, bismaleimide resin, unsaturated polyester resin, and epoxy resin are used as sizing agents, and epoxy resin is generally the main component. Patent Document 1 discloses a prepreg obtained by impregnating carbon fibers to which a sizing agent containing an aliphatic epoxy compound and an aromatic epoxy compound has been attached with a specific epoxy resin composition as a matrix resin. Patent Document 2 discloses carbon fibers coated with a sizing agent containing a polymer having one of ester, urethane, and carbonate bonds in the main chain, and discloses that such carbon fibers can be used to obtain composite materials with excellent mechanical properties.

[0004] Furthermore, tetrafluoroethylene polymers have low surface energy, and powders thereof tend to aggregate easily, so that dispersion stability of the dispersions thereof tends to become a problem. Patent Document 3 discloses an aqueous dispersion containing a powder of a tetrafluoroethylene-based polymer. Typically, dispersions contain surfactants to enhance the dispersion stability of tetrafluoroethylene-based polymer powders. However, even after the dispersion is applied to a substrate and dried, the surfactant remains on the substrate surface, which can cause roughness on the substrate surface and deteriorate the appearance. Furthermore, the residual surfactant on the substrate surface can deteriorate the electrical properties of the molded product and its adhesion to other substrates. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-40566 [Patent Document 2] Japanese Patent Publication No. 2020-23770 [Patent Document 3] Japanese Patent Application Publication No. 2019-52211 Summary of the Invention [Problem to be solved by the invention]

[0006] When molding a fiber-reinforced composite material containing an ultra-heat-resistant resin, such as super engineering plastics, as a matrix resin, the molding temperature becomes higher than conventional ones. In such cases, the sizing agents described in Patent Documents 1 and 2 thermally decompose during heat molding to generate volatile components, which cause foaming in the molded product, thereby affecting the appearance, such as smoothness, and the adhesion / peel strength of the resulting molded product.

[0007] As a result of extensive research, the present inventors have found that a sizing agent containing a heat-fusible tetrafluoroethylene-based polymer having a specific particle size has excellent interfacial adhesion with ultra-heat-resistant resins, and that if such a sizing agent is applied to fibers, preferably as a dispersion in a liquid dispersion medium, the heat resistance of the tetrafluoroethylene-based polymer can suppress foaming during heat molding, allowing the formation of molded articles with excellent appearance, such as smoothness. Furthermore, they have found that such molded articles have particularly excellent adhesion and water resistance when formed into laminates.

[0008] The present inventors have discovered that a dispersion having excellent dispersion stability can be obtained even with a reduced amount of surfactant, as long as it contains a tetrafluoroethylene-based polymer powder having an average particle size within a predetermined range, and that such a dispersion is useful as a sizing agent, which led to the completion of the present invention. The present invention aims to provide a sizing agent that is inhibited from foaming when heated, sized fibers, prepregs, and a dispersion containing a tetrafluoroethylene-based polymer powder with excellent dispersion stability and a small amount of a surfactant. [Means for solving the problem]

[0009] The present invention has the following aspects. <1> A sizing agent containing a powder of a heat-fusible tetrafluoroethylene polymer having an average particle size of 0.1 to 200 μm. <2> The melting temperature of the tetrafluoroethylene-based polymer is 280 to 325°C. <1> Sizing agent. <3> The 5% weight loss temperature of the tetrafluoroethylene-based polymer is 360°C or higher. <1> or <2> Sizing agent. <4> the tetrafluoroethylene-based polymer is a tetrafluoroethylene-based polymer having a unit based on perfluoro(alkyl vinyl ether) and a polar functional group, or a tetrafluoroethylene-based polymer containing 2.0 to 5.0 mol % of a unit based on perfluoro(alkyl vinyl ether) based on all units and having no polar functional group; <1> ~ <3> Any of the sizing agents.

[0010] <5> The tetrafluoroethylene polymer having a polar functional group is a tetrafluoroethylene polymer having a carbonyl group-containing group, and the number of the carbonyl group-containing groups is 1×10 6 10 to 5,000 pieces per piece, <4> Sizing agent. <6> a dispersion liquid containing the tetrafluoroethylene-based polymer powder and a liquid dispersion medium; <1> ~ <5> Any of the sizing agents. <7> The dispersion medium comprises a powder of the tetrafluoroethylene-based polymer having an average particle size of 10 to 100 μm, a surfactant, and a liquid dispersion medium, and the content of the surfactant is 0.01 parts by mass or less per part by mass of the tetrafluoroethylene-based polymer powder. <6> Sizing agent.

[0011] <8> A sized fiber with a heat-fusible tetrafluoroethylene polymer attached to its surface. <9> The amount of the tetrafluoroethylene polymer attached is 0.1 to 10 parts by mass per 100 parts by mass of the fibers. <8> Sizing treated fiber. <10> <8> or <9> A prepreg comprising the sized fibers according to claim 1 and a matrix resin.

[0012] <11> A dispersion comprising a powder of a heat-fusible tetrafluoroethylene-based polymer having an average particle size of 10 to 100 μm, a surfactant, and a liquid dispersion medium, wherein the content of the surfactant is 0.01 parts by mass or less per part by mass of the tetrafluoroethylene-based polymer powder. <12> The surfactant has a surface tension of 28 mN / m or less. <11> Dispersion of. <13> the surfactant is a silicone surfactant, a fluorine-based surfactant, a glycol surfactant, or an alkylamide ether surfactant; <11> or <12> Dispersion of. <14> The content of the tetrafluoroethylene-based polymer is 25 to 60 parts by mass relative to 100 parts by mass of the liquid dispersion medium. <11> ~ <13> A dispersion of either <15> <11> ~ <14> A sizing agent comprising a dispersion of any one of the above. [Effects of the Invention]

[0013] A prepreg containing fibers treated with the sizing agent of the present invention and a matrix resin exhibits excellent adhesion between the fibers and the matrix resin. Furthermore, the prepreg of the present invention exhibits excellent adhesion between the fibers and the matrix resin during molding, and foaming during heat molding is suppressed, resulting in molded articles that are excellent in appearance (e.g., smoothness) and water resistance. The present invention also provides a dispersion containing a tetrafluoroethylene-based polymer powder and a small amount of surfactant, which exhibits excellent dispersion stability. The coated substrate obtained from the dispersion exhibits minimal surface roughness and an excellent appearance. Furthermore, when the coated substrate is bonded to another material, the adhesion is excellent. In particular, when fibers are used as the substrate, a prepreg with excellent adhesion to the matrix resin can be obtained by treating the fibers with a sizing agent comprising the dispersion of the present invention and then impregnating the sized fibers with a matrix resin. DETAILED DESCRIPTION OF THE INVENTION

[0014] The following terms have the following meanings: The "average particle size" of a powder is the cumulative 50% diameter of the target particle by volume, defined as "D50" below. "D50" is the volume-based cumulative 50% diameter of an object determined by laser diffraction / scattering. In other words, particle size distribution is measured by laser diffraction / scattering, and a cumulative curve is calculated with the total volume of the particle group as 100%. D50 is the particle diameter at the point on that cumulative curve where the cumulative volume is 50%. "D90" is the volume-based cumulative 90% diameter of the object, measured in the same manner. The D50 and D90 of an object are determined by dispersing the particles in water and analyzing them using the laser diffraction / scattering method with a laser diffraction / scattering particle size distribution analyzer (LA-920, manufactured by Horiba, Ltd.).

[0015] The "melting temperature (melting point) of a polymer" is the temperature corresponding to the maximum value of the melting peak measured by differential scanning calorimetry (DSC). The "5% weight loss temperature of a polymer" is the temperature at which a 5% weight loss is observed when the temperature is increased at a rate of 20°C / min in a temperature range of 23 to 900°C in a nitrogen gas atmosphere using a TGA measuring device in accordance with JIS K7120. The "glass transition temperature (Tg) of a polymer" is a value measured by analyzing a polymer using dynamic mechanical analysis (DMA).

[0016] The "viscosity of the dispersion" is the viscosity measured using a Brookfield viscometer at 25° C. and 30 rpm. The measurement is repeated three times, and the average value of the three measurements is used. The "thixotropy ratio" is a value calculated by dividing the viscosity η1 of a liquid composition measured at a rotation speed of 30 rpm by the viscosity η2 measured at a rotation speed of 60 rpm. Each viscosity measurement is repeated three times, and the average value of the three measurements is used. The "sedimentation rate of components" is a value calculated by the following formula from the height of the entire dispersion in the screw tube and the height of the sedimented layer (dispersed layer) before and after standing when 18 mL of dispersion is placed in a screw tube with an internal volume of 30 mL and left to stand at 25°C for 14 days. If no sedimented layer is observed after standing and there is no change in the state, it is assumed that there is no change in the height of the entire dispersion, and the sedimentation rate of components is 100%. The higher the sedimentation rate, the better the dispersion stability. Component sedimentation rate (%) = (height of sedimented layer) / (height of total dispersion) x 100

[0017] The term "unit" in a polymer refers to an atomic group based on one molecule of a monomer formed by polymerization of the monomer. The unit may be a unit formed directly by a polymerization reaction, or may be a unit in which a portion of the unit is converted into a different structure by processing the polymer. Hereinafter, a unit based on monomer A will also be simply referred to as a "monomer A unit." "Tetrafluoroethylene-based polymer" means a polymer containing units based on tetrafluoroethylene.

[0018] The sizing agent of the present invention (hereinafter also referred to as "the present sizing agent") contains a powder (hereinafter also referred to as "F powder") of a heat-fusible tetrafluoroethylene-based polymer (hereinafter also referred to as "F polymer") having an average particle size of 0.1 to 200 μm. By disposing the sizing agent on fibers and heat treating them, sized fibers, preferably sized carbon fibers, can be produced. The resulting sized fibers have the F polymer attached to their surfaces.

[0019] Fibers sized with this sizing agent are less likely to generate decomposition products and are less likely to foam during heat molding, even when used to mold prepregs or fiber-reinforced composite materials containing ultra-heat-resistant resins as matrix resins. This allows for the formation of molded products that are particularly excellent in appearance, such as smoothness, adhesion, and water resistance. Although its mechanism of action is unclear, it is generally assumed as follows: This sizing agent contains F polymer, which is thought to be more likely to be distributed densely and uniformly on the surface of the sized fibers obtained by treatment with this sizing agent. Furthermore, F polymer is likely to form microspherulites, which tends to enhance adhesion between the sized fibers and the matrix resin. Furthermore, because the F polymer itself has excellent heat and water resistance, it is less likely to decompose even when molded at high temperatures, which is thought to contribute to improving the properties of the resulting molded products.

[0020] The average particle size (D50) of the F powder in the present sizing agent is 0.1 to 200 μm. The D50 of the F powder is preferably 50 μm or less, more preferably 30 μm or less. The D50 of the F powder is preferably 0.03 μm or more, more preferably 0.1 μm or more. Furthermore, the D90 of the F powder is preferably 10 μm or less. With D50 and D90 in this range, the flowability of the F powder is good, and the F powder is easily distributed uniformly on the fiber surface. In addition, the heat resistance and electrical properties (low dielectric constant, etc.) of the F polymer are most easily exhibited.

[0021] In this sizing agent, the bulk density of the F powder is set to 0.15 g / m in order to distribute the F powder uniformly on the fiber surface. 2 The bulk density of the F powder is preferably 0.50 g / m or more. 2 The following is preferred:

[0022] The F powder in the present sizing agent may contain resins other than the F polymer or inorganic compounds, but preferably contains the F polymer as the main component. The content of the F polymer in the F powder is preferably 80% by mass or more, more preferably 100% by mass. Examples of the resin include heat-resistant resins such as aromatic polyester, polyamideimide, thermoplastic polyimide, polyphenylene ether, and polyphenylene oxide. Examples of the inorganic compound include silica and boron nitride. The F powder may form a core-shell structure with an F polymer as the core and a resin or inorganic compound other than an F polymer as the shell, or may form a core-shell structure with an F polymer as the shell and a resin or inorganic compound other than an F polymer as the core.

[0023] The F polymer in the present invention is a heat-meltable polymer containing units (hereinafter also referred to as TFE units) based on tetrafluoroethylene (hereinafter also referred to as TFE). The fluorine content of the F polymer is preferably 70 to 76 mass %.

[0024] The melting temperature of the F polymer is preferably 180°C or higher, more preferably 200°C or higher, even more preferably 260°C or higher, and particularly preferably 280°C or higher. The melting temperature of the F polymer is preferably 325°C or lower, more preferably 320°C or lower. The melting temperature of the F polymer is preferably 180 to 325°C, more preferably 260 to 325°C, and even more preferably 280 to 325°C. In such cases, the heat resistance of molded articles formed from the present composition tends to be excellent. The glass transition point of the F polymer is preferably 50° C. or higher, more preferably 75° C. or higher, and is preferably 150° C. or lower, more preferably 125° C. or lower. The glass transition point of the F polymer is preferably 75 to 125° C., more preferably 80 to 100° C.

[0025] Examples of F polymers include polymers containing TFE units and units based on perfluoro(alkyl vinyl ether) (PAVE) (PAVE units) (PFA), polymers containing TFE units and units based on hexafluoropropene (HFP) (FEP), polymers containing TFE units and units based on ethylene (ETFE), and hot-melt polytetrafluoroethylene (PTFE), with PFA and FEP being preferred, and PFA being more preferred. The polymers may further contain units based on other comonomers. As PAVE, CF2=CFOCF3, CF2=CFOCF2CF3 and CF2=CFOCF2CF2CF3 (hereinafter also referred to as PPVE) are preferred, and PPVE is more preferred.

[0026] The F polymer preferably has a polar functional group, more preferably an atomic group containing an oxygen atom. The polar functional group may be contained in a unit in the F polymer or in a terminal group of the polymer main chain. Examples of the latter include F polymers having a polar functional group as an end group derived from a polymerization initiator, a chain transfer agent, etc., and F polymers having a polar functional group obtained by treating an F polymer with plasma or ionizing radiation. Preferred polar functional groups having an atomic group containing an oxygen atom include hydroxyl-containing groups, carbonyl-containing groups, and phosphono-containing groups. From the viewpoint of dispersion stability when the sizing agent is used as a dispersion during fiber sizing treatment, hydroxyl-containing groups and carbonyl-containing groups are more preferred, and carbonyl-containing groups are even more preferred. When the F polymer has a carbonyl group-containing group, the number of carbonyl group-containing groups in the F polymer is 1×10 6 The number per unit is preferably 10 to 5000, more preferably 100 to 3000. The number of carbonyl group-containing groups in the F polymer can be quantified based on the polymer composition or the method described in WO 2020 / 145133.

[0027] As the hydroxyl group-containing group, a group containing an alcoholic hydroxyl group is preferred, and -CF2CH2OH, -C(CF3)2OH and a 1,2-glycol group (-CH(OH)CH2OH) are more preferred. The carbonyl group-containing group is a group containing a carbonyl group (>C(O)). Preferred carbonyl group-containing groups include a carboxyl group, an alkoxycarbonyl group, an amide group, an isocyanate group, a carbamate group (-OC(O)NH), an acid anhydride residue (-C(O)OC(O)-), an imide residue (-C(O)NHC(O)-, etc.), and a carbonate group (-OC(O)O-), with an acid anhydride residue being more preferred.

[0028] As the F polymer, a polymer (1) having a polar functional group containing TFE units and PAVE units, and a polymer (2) having no polar functional group containing TFE units and PAVE units and containing 2.0 to 5.0 mol % of PAVE units based on all units are preferred. These F polymers not only have excellent dispersion stability when dispersed in the sizing agent, but also tend to distribute more densely and uniformly on the surface of sized fibers obtained by treatment with the sizing agent. They also tend to form microspherulites in molded articles, which tends to enhance adhesion between the sized fibers and the matrix resin. Furthermore, their excellent heat resistance makes it easier to obtain molded articles with excellent appearance (surface smoothness).

[0029] The polymer (1) is preferably a polymer containing TFE units, PAVE units, and units based on a monomer having a polar functional group, and more preferably a polymer containing these units in the amounts of 90 to 99 mol%, 0.5 to 9.97 mol%, and 0.01 to 3 mol%, in this order, based on all units. Moreover, as the monomer having a polar functional group, itaconic anhydride, citraconic anhydride, and 5-norbornene-2,3-dicarboxylic anhydride (hereinafter also referred to as "NAH") are preferred. Specific examples of polymer (1) include the polymers described in WO 2018 / 16644.

[0030] Polymer (2) is composed only of TFE units and PAVE units, and preferably contains 95.0 to 98.0 mol% of TFE units and 2.0 to 5.0 mol% of PAVE units based on all units. The content of PAVE units in polymer (2) is preferably 2.1 mol% or more, more preferably 2.2 mol% or more, based on all units. Such polymers have a higher degree of freedom in molecular conformation and tend to enhance the above-mentioned mechanism of action. The term "polymer (2) has no polar functional group" means that the number of carbon atoms constituting the polymer main chain is 1 × 10 6 This means that the number of polar functional groups possessed by the polymer is less than 500 per unit area. The number of polar functional groups is preferably 100 or less, and more preferably less than 50. The lower limit of the number of polar functional groups is usually 0. Polymer (2) may be produced using a polymerization initiator or chain transfer agent that does not generate a polar functional group as the terminal group of the polymer chain, or may be produced by fluorinating an F polymer having a polar functional group (such as an F polymer having a polar functional group derived from a polymerization initiator at the terminal group of the polymer main chain). Fluorination methods include methods using fluorine gas (see, for example, JP 2019-194314 A).

[0031] In the present sizing agent, it is preferable to use an F polymer that is persistent even at high temperatures. Specifically, the 5% weight loss temperature of the F polymer is preferably 360°C or higher, more preferably 400°C or higher. The 5% weight loss temperature of the F polymer is preferably 600°C or lower. By using F polymer, which is persistent even at such high temperatures, foaming can be suppressed when molding a molded article from the prepreg described below, and the molded article tends to have excellent appearance such as smoothness.

[0032] This sizing agent can be used as a sizing agent for glass fibers such as E glass, D glass, L glass, S glass, T glass, Q glass, UN glass, and NE glass, which are used as reinforcing fibers in the technical field of fiber-reinforced plastics; organic fibers such as aramid fibers, polyolefin fibers, modified polyphenylene ether fibers, vinylon fibers, rayon fibers, polyester fibers, and natural fibers; boron fibers, carbon fibers, and metal fibers. The shape of the fibers may be any of chopped strands, surfacing, roving, or mats thereof, woven fabric, nonwoven fabric, etc. There are also no particular limitations on the fiber length or cross-sectional shape of the fibers. Among these, it is preferable to use the present sizing agent as a sizing agent for carbon fibers.

[0033] The carbon fiber may be a pitch-based, rayon-based, polyacrylonitrile (PAN)-based, single-walled carbon nanotube, multi-walled carbon nanotube, carbon nanofiber, etc. There are no particular limitations on the fineness, strength, and other properties of the carbon fiber. Among these, acrylonitrile (PAN)-based carbon fibers are preferred from the viewpoints of operability, processability, and mechanical properties. PAN-based carbon fibers can be obtained, for example, by subjecting a carbon fiber precursor fiber made of a PAN-based polymer to flame retardation treatment in an oxidizing atmosphere at 200 to 300°C, followed by preliminary carbonization treatment in an inert atmosphere at 500 to 1200°C, and then carbonization treatment in an inert atmosphere at 1200 to 2000°C.

[0034] The present sizing agent may be in powder form or liquid form. The present liquid sizing agent comprises a dispersion containing an F polymer powder having an average particle size of 0.1 to 200 μm and a liquid dispersion medium (hereinafter also referred to as "the present dispersion (1)"). A preferred method for disposing the present sizing agent on fibers is to prepare the present dispersion (1), apply it to fibers, and then heat-treat the fibers to cause the F polymer to adhere to the surface of the fibers.

[0035] The liquid dispersion medium for dispersing the F powder in this dispersion liquid (1) is preferably an aprotic compound that is liquid at 25°C under atmospheric pressure and is classified as polar, and more preferably a polar compound selected from amides, ketones, and esters. When such a liquid dispersion medium is used, the dispersion stability of the F powder in the dispersion liquid is excellent. The boiling point of the liquid dispersion medium is preferably in the range of 50 to 240° C. Two or more types of liquid dispersion medium may be used in combination.

[0036] Examples of liquid dispersion media include water, N,N-dimethylformamide, N,N-dimethylacetamide, 3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, N-methyl-2-pyrrolidone, γ-butyrolactone, cyclohexanone, cyclopentanone, butyl acetate, methyl isopropyl ketone, and methyl ethyl ketone. In the present invention, the content of the liquid dispersion medium in the present dispersion (1) is preferably from 30 to 90% by mass, more preferably from 50 to 80% by mass. In the present invention, the content of F powder in the present dispersion (1) is preferably 1% by mass or more, more preferably 5 to 50% by mass, based on the total mass of the present dispersion (1).

[0037] The present dispersion (1) may further contain various surfactants added to impart dispersibility. When the present dispersion (1) contains a surfactant, the content thereof is preferably 1 to 15% by mass based on the total mass of the present dispersion (1). However, in the present invention, since F powder has excellent dispersion stability, the present dispersion (1) having excellent dispersion stability and handleability can be produced without necessarily using a surfactant. Therefore, when the dispersion (1) is applied to fibers, the sizing agent is easily dispersed uniformly on the fiber surface, and after heat treatment, the F polymer is easily distributed densely and uniformly on the fiber surface.

[0038] As the surfactant, anionic, cationic, nonionic surfactants and the like can be used, and among them, nonionic surfactants are preferred. The hydrophilic portion of the surfactant is preferably a polyoxyethylene group or an alcoholic hydroxyl group. The hydrophobic portion of the surfactant is preferably an acetylene group, a polysiloxane group, a fluorine-containing organic group (such as a perfluoroalkyl group), or a polyoxyalkylene group consisting of an oxyalkylene group having 3 or more carbon atoms. Preferred surfactants are acetylene-based surfactants, silicone-based surfactants, fluorine-based surfactants, alkylamide ether-based surfactants, and glycol-based surfactants. Two or more of these surfactants may be used. When two types of surfactants are used, the surfactants are preferably a silicone-based surfactant and a glycol-based surfactant. The silicone surfactant is preferably the same as the silicone surfactant in the present dispersion (2) described below. Specific examples of such surfactants include the "Ftergent" series (manufactured by Neos Corporation), the "Surflon" series (manufactured by AGC Seimi Chemical Co., Ltd.), the "Megafac" series (manufactured by DIC Corporation), and the "Unidyne" series (manufactured by Daikin Industries, Ltd.).

[0039] In addition to the above components, the dispersion (1) may further contain other components such as a thixotropic agent, a viscosity modifier, an antifoaming agent, a silane coupling agent, a dehydrating agent, a plasticizer, a weathering agent, an antioxidant, a heat stabilizer, a lubricant, an antistatic agent, a brightener, a colorant, a conductive agent, a release agent, a surface treatment agent, a flame retardant, various inorganic fillers, and various organic fillers, as long as the effects of the present invention are not impaired. Specific examples of the inorganic filler include the same inorganic fillers as those that may be contained in the present dispersion (2) described below.

[0040] Furthermore, the present dispersion (1) may further contain a resin material other than the F polymer, from the viewpoint of improving the adhesiveness between the sizing agent and the matrix resin. Such resin materials may be thermosetting or thermoplastic, may be modified, and may be dissolved or dispersed in the present dispersion (1). Examples of such resin materials include tetrafluoroethylene polymers other than F polymers, polyimide resins, polyamic acids (polyimide precursors), polyamideimide resins, maleimide resins, acrylic resins, phenolic resins, liquid crystalline polyester resins, liquid crystalline polyesteramide resins, polyolefin resins, modified polyphenylene ether resins, polyfunctional cyanate ester resins, polyfunctional maleimide-cyanate ester resins, polyfunctional maleimide resins, vinyl ester resins, urea resins, diallyl phthalate resins, melamine resins, guanamine resins, melamine-urea co-condensation resins, styrene resins, aromatic elastomers, polycarbonate resins, polyarylate resins, polysulfones, polyarylsulfones, aromatic polyamide resins, aromatic polyetheramides, polyphenylene sulfides, polyaryl ether ketones, polyamideimides, polyphenylene ethers, and epoxy resins. As the tetrafluoroethylene polymer other than the F polymer, non-thermofusible polytetrafluoroethylene is preferred from the viewpoint of improving the electrical properties of the sized fiber. When the present dispersion (1) contains a resin material, the content thereof is preferably 40% by mass or less based on the total amount of the present dispersion (1).

[0041] The non-thermofusible polytetrafluoroethylene is preferably contained in the present dispersion (1) as a non-thermofusible polytetrafluoroethylene powder. The ratio of the content of such powder in the present dispersion (1) to the content of the F powder is preferably 1 or more, more preferably 2 or more. The ratio is preferably 10 or less, more preferably 5 or less. The D50 of such powder is preferably 0.1 to 1 μm.

[0042] The viscosity of the present dispersion (1) is preferably 75 to 10,000 mPa·s. In this case, the present dispersion (1) has excellent dispersion stability, and the handling property and the uniformity of the sizing treatment of the fibers are easily improved. Furthermore, the present dispersion (1) has improved miscibility with varnishes of different resin materials. The thixotropy ratio of the present dispersion (1) is preferably 1.0 to 2.2, more preferably 1.5 to 2.0. In this case, the present dispersion (1) has excellent dispersion stability and good handleability, and the uniformity of the sizing treatment of the fibers is likely to be improved. In addition, the present dispersion (1) has improved miscibility with varnishes of different resin materials.

[0043] Examples of a method for disposing the sizing agent on fibers (a method for performing a sizing treatment) include a roller sizing method in which a part of a roll is immersed in the dispersion (1) to adhere the dispersion (1) to the surface of the roller, and then the fibers are brought into contact with the roll to adhere the dispersion (1); a roller immersion method in which fibers are directly immersed in the dispersion (1) and then passed through a nip roll as necessary to control the amount of the dispersion (1) adhered; and a spray method in which the dispersion (1) is atomized and sprayed onto a fiber bundle. Among these, the roller immersion method is preferred, because it is easy to uniformly apply the present dispersion (1) even to fiber bundles having a large number of single fibers per bundle. Furthermore, the amount of the sizing agent applied can be adjusted by adjusting the amount of the present dispersion (1) squeezed out after the application of the present dispersion (1).

[0044] The amount of the sizing agent (1) attached to the fiber is preferably in the range of 0.1 to 10 parts by mass, more preferably 0.2 to 5 parts by mass, per 100 parts by mass of the fiber in the sized fiber after the heat treatment described below, as the amount of F polymer attached. The sizing agent may be applied to the fibers by either a batch method or a continuous method, but the continuous method is preferred from the viewpoint of easily suppressing uneven application of the sizing agent to the fibers and improving productivity. The fibers may be ultrasonically vibrated during application of the sizing agent.

[0045] It is preferable to heat-treat the fibers having the present dispersion (1) disposed thereon to evaporate the dispersion medium and obtain sized fibers having an F polymer attached to the surface. The F polymer attached to the surface of the fibers is more preferably a baked F polymer. The sized fibers having a baked F polymer attached to the surface can be obtained by evaporating the dispersion medium from the fibers having the present dispersion (1) disposed thereon and further heat-treating the fibers to bake the F polymer. The heat treatment for evaporating the dispersion medium is carried out by holding the fibers containing the dispersion liquid (1) at the volatilization temperature of the dispersion medium to dry the liquid coating on the fibers. The heat treatment for baking the F polymer is carried out by holding the dried coating at a temperature above the melting temperature of the F polymer. In this way, a baked F polymer is formed on the fiber surface. Note that the temperature during drying usually refers to the temperature of the drying atmosphere. During drying, the dispersion medium does not necessarily have to be completely evaporated. Specifically, the amount of dispersion medium to be evaporated is preferably 50% by mass or more of the liquid dispersion medium contained in the present dispersion liquid (1).

[0046] Drying may be carried out in one stage at a constant temperature, or in two or more stages at different temperatures. Drying methods include a method using an oven, a method using a ventilation drying furnace, and a method using heat rays such as infrared rays, and either a contact method or a non-contact method may be used. Drying may be carried out under either normal pressure or reduced pressure, and the drying atmosphere may be any of an oxidizing gas atmosphere (oxygen gas, etc.), a reducing gas atmosphere (hydrogen gas, etc.), and an inert gas atmosphere (helium gas, neon gas, argon gas, nitrogen gas, etc.). The drying temperature is preferably 50 to 280° C. The drying time is preferably 0.1 to 30 minutes.

[0047] The F polymer can be baked using an oven, a ventilation oven, or by irradiating it with heat rays such as infrared rays. A combination of infrared heating and hot air heating may also be used.

[0048] The F polymer may be baked under either atmospheric pressure or reduced pressure. The baking atmosphere may be any of an oxidizing gas atmosphere, a reducing gas atmosphere, and an inert gas atmosphere. The baking temperature is preferably equal to or higher than the melting temperature of the F polymer and equal to or lower than the temperature at which the F polymer loses 5% weight, and is usually 300 to 380°C. The baking time is preferably 30 seconds to 30 minutes, more preferably 1 to 15 minutes. If the F polymer is baked under such conditions, productivity is increased and the generation of hydrofluoric acid due to decomposition of the F polymer is easily suppressed.

[0049] After distributing the dispersion liquid (1) on the fibers, the carbon fibers may be contact-dried by contact drying, for example, by contacting the fibers with a heated roller to evaporate the dispersion medium, and then the F polymer may be baked. The fibers introduced into the heated roller are pressed against the heated roller by tension and rapidly dried, so that the flattened shape of the fibers expanded by the heated roller is easily fixed by the sizing agent. The flattened fibers have a small contact area between the individual fibers, and therefore tend to have high openability.

[0050] The sized fiber of the present invention is a fiber having an F polymer attached to its surface. The definition and scope of the F polymer, including preferred embodiments thereof, are the same as those of the F polymer in the present sizing agent described above. The amount of F polymer attached to the sized fibers is preferably 0.1 to 10 parts by mass, more preferably 0.2 to 5 parts by mass, per 100 parts by mass of the fibers. The sized fibers of the present invention are preferably obtained from the sizing agent in a manner similar to that described above. The sized fibers of the present invention have excellent adhesion to matrix resins and also have high impregnation of the matrix resin into the fiber bundles, so that prepregs and fiber-reinforced composite materials having excellent mechanical properties can be easily obtained from such fibers. Hereinafter, the prepreg (hereinafter also referred to as "the present prepreg") containing the sized fiber (hereinafter also referred to as "sized fiber") of the present invention will be described.

[0051] The prepreg contains the sized fibers and a matrix resin, and is typically obtained by impregnating the sized fibers with the matrix resin. The prepreg can be produced, for example, by impregnating the sized fibers with the matrix resin or a matrix resin composition, followed by drying and semi-curing. Specifically, it can be produced by a wet method in which the matrix resin or matrix resin composition is dissolved in a solvent such as methyl ethyl ketone or methanol to reduce the viscosity and then impregnated, or by a hot melt method in which the viscosity is reduced by heating and then impregnated.

[0052] In the wet method, prepreg can be produced by immersing sized fibers in a liquid containing a matrix resin, then removing the fibers and evaporating the solvent using an oven or the like. In the hot melt method, prepregs can be produced by directly impregnating sized fibers with a matrix resin or matrix resin composition that has been reduced in viscosity by heating, or by first preparing a film by coating the matrix resin or matrix resin composition on release paper or the like, then placing the film on one or both sides of sized fibers and heating and pressurizing the resulting mixture to impregnate the sized fibers with the matrix resin. The hot melt method is preferred because it leaves no residual solvent in the prepreg.

[0053] The sizing-treated fibers may be used as a fiber bundle or as a sheet-like reinforcing fiber material. Examples of sheet-like materials include fibers aligned in one direction in a sheet form, fiber materials formed into woven or knitted fabrics or nonwoven fabrics, and multiaxial woven fabrics. The sizing-treated fibers may be used as continuous fibers or discontinuous fibers. When discontinuous fibers are used, they may be a mixture of fibers in the form of single yarns that have been completely opened and reinforcing fibers in the form of incompletely opened fiber bundles. The fibers may be aligned in the same direction, or a random mat oriented in random directions is also preferably used. When the fibers are formed into a sheet, there are no particular limitations on the thickness, but for laminate applications, a thickness in the range of 0.01 to 0.2 mm is preferred, and woven fabrics that have been subjected to ultra-opening or tight-weighing treatments are suitable from the standpoint of dimensional stability.

[0054] The matrix resin may be a thermosetting resin or a thermoplastic resin. Examples of thermosetting resins include epoxy resins, unsaturated polyester resins, phenolic resins, vinyl ester resins, cyanate ester resins, urethane acrylate resins, phenoxy resins, alkyd resins, urethane resins, prepolymerized resins of maleimide resins and cyanate ester resins, bismaleimide resins, polyimide resins and polyisoimide resins having acetylene terminals, and polyimide resins having Nadic acid terminals. These thermosetting resins may be used alone or in combination of two or more. Furthermore, the thermosetting resin may be a thermosetting resin composition containing various additives in addition to a curing agent and a curing accelerator.

[0055] Examples of thermoplastic resins include polysulfone, polyphenylsulfone, polyethersulfone, aromatic polyetherketones (such as polyetherketone, polyetheretherketone, polyetherketoneketone, and polyetheretherketoneketone), polyamide, aromatic polyester, aromatic polycarbonate, polyetherimide, polyarylene oxide, thermoplastic polyimide, polyamideimide, polyacetal, polyphenylene oxide, polyphenylene sulfide, liquid crystal polyester, polyarylate, polyacrylonitrile, and polybenzimidazole. These thermoplastic resins may be used alone or in combination of two or more. Furthermore, the thermoplastic resin may be a thermoplastic resin composition containing various additives. When the thermosetting resin or thermoplastic resin is a resin composition, examples of various additives include plasticizers, weathering agents, antioxidants, heat stabilizers, lubricants, antistatic agents, brighteners, colorants, conductive agents, mold release agents, surface treatment agents, flame retardants, various inorganic fillers, and various organic fillers.

[0056] Among these, the matrix resin is preferably a heat-resistant resin selected from the group consisting of polysulfone, polyphenylsulfone, polyethersulfone, aromatic polyetherketone, polyetherimide, polyphenylene sulfide, and liquid crystal polyester. These are classified as ultra-heat-resistant resins known as super engineering plastics, and are more likely to exhibit the effects of the present sizing-treated fiber. When the matrix resin has a polar functional group such as a carbonyl group, a sulfonic group, or an ester group in its structure and the F polymer of the present invention also has a polar functional group, it is presumed that the polar functional group in the matrix resin and the polar functional group in the F polymer interact with each other, resulting in high adhesiveness, which is preferable.

[0057] The fiber mass fraction in the prepreg is preferably 40 to 90 mass%, more preferably 50 to 80 mass%. Within this range, the mass of the resulting fiber-reinforced composite material is not excessively large, and the advantages of the fiber-reinforced composite material, such as excellent specific strength and specific modulus, can be utilized. Prepregs containing fibers sized with this sizing agent can be easily impregnated with the matrix resin used for compounding, and are high-quality materials with minimal unevenness in mechanical properties. Such prepregs containing reinforcing fibers may contain various additives within the range that does not impair the original purpose.

[0058] The prepreg of the present invention containing sized fibers and a matrix resin has excellent adhesion to the matrix resin and also has high impregnation of the matrix resin into the fibers, and therefore, when molded, a fiber-reinforced composite material with excellent mechanical properties can be obtained.

[0059] To mold a fiber-reinforced composite material using this prepreg, a method can be applied in which the prepregs are laminated, and then the matrix resin is heated while applying pressure to the laminate to form a laminate. Methods for applying heat and pressure include press molding, autoclave molding, bagging molding, wrapping tape molding, and internal pressure molding, with wrapping tape molding and internal pressure molding being preferred, particularly for sporting goods. Autoclave molding is preferred for aircraft applications, which require higher quality and performance laminated composite materials. Press molding is preferred for various vehicle exteriors. In addition, when molding a fiber reinforced composite material using this prepreg, resin transfer molding, filament winding molding, sheet winding molding, etc. can also be applied.

[0060] Furthermore, a metal-clad laminate can be obtained by stacking the above-described prepregs, disposing a metal substrate on one or both sides of the prepregs, and laminating and molding the prepregs. Specifically, a metal-clad laminate can be produced by stacking one or more of the above-described prepregs, disposing a metal substrate on one or both sides of the prepregs, and laminating and molding the prepregs. Examples of metals that can be used as the metal substrate include iron, stainless steel, aluminum, copper, brass, nickel, zinc, titanium, and alloys of these metals.

[0061] The molding conditions are the same as those for ordinary laminates and multilayer boards for printed wiring boards. For example, a multi-stage press, multi-stage vacuum press, continuous molding machine, autoclave molding machine, etc. are used, and the temperature is 180 to 350°C, the heating time is 100 to 300 minutes, and the surface pressure is 20 to 100 kg / cm. 2 By laminating and molding the metal clad laminate, a metal clad laminate can be produced.

[0062] The fiber composite material may be further laminated with another substrate, such as a heat-resistant resin film or a prepreg, which is a precursor of a fiber-reinforced resin plate, and examples of such a fiber composite material include a fiber-reinforced composite material having a heat-resistant resin film layer and a fiber-reinforced composite material having a prepreg layer. The heat-resistant resin film is a film containing one or more types of heat-resistant resin, and examples of the heat-resistant resin include the resins described above.

[0063] As a lamination method, a method in which prepregs are laminated and heated to obtain a laminate and then hot-pressed with another substrate can be mentioned. When the other substrate is a prepreg, the conditions for the hot pressing are preferably a temperature of 120 to 400° C., a vacuum atmosphere of 20 kPa or less, and a pressing pressure of 0.2 to 10 MPa.

[0064] The fiber-reinforced composite material of the present invention is suitable for use in applications requiring strength, abrasion resistance, chemical resistance, and flame retardancy, such as exteriors and interiors of transportation equipment such as automobiles, motorcycles, and aircraft, sliding parts such as gears and bearings, insulating parts, sporting goods such as rackets and bats, industrial machinery, robots, parts of medical equipment, oil drilling equipment, oil transport hoses, hydrogen tanks, hydrogen tank pressure vessels, and wind turbine blades. The fiber-reinforced composite material and the laminate of the present invention can also be used as low-vibration components, such as rotating parts of motors, compressors, and machine tools (such as lathes and milling cutters), as well as the interior and exterior of transportation equipment such as automobiles, motorcycles, and aircraft. Furthermore, since the fiber-reinforced composite material of the present invention has excellent mechanical properties at low temperatures, it can be used for components to be used at extremely low temperatures, such as liquid hydrogen tanks.

[0065] The average particle size of the F powder in the present sizing agent is more preferably 10 to 100 μm. A dispersion containing F powder with this average particle size, a surfactant, and a liquid dispersion medium, in which the surfactant content is 0.01 parts by mass or less per part by mass of F powder with this average particle size (hereinafter also referred to as the present dispersion (2)), has particularly excellent dispersion stability and is suitable as the present sizing agent. Furthermore, due to its characteristics, the present dispersion (2) can also be used for purposes other than the present sizing agent.

[0066] The average particle size (D50) of the F powder in the present dispersion (2) is preferably 50 μm or less, more preferably 40 μm or less, and is preferably 20 μm or more. Furthermore, from the viewpoint of the dispersibility of the present dispersion (2), the D90 of the F powder in the present dispersion (2) is preferably 40 μm or more, more preferably 60 μm or more, and is preferably 100 μm or less, more preferably 90 μm or less.

[0067] Since F powder has low surface energy and tends to aggregate, this dispersion (2) contains a surfactant. The surfactant content is 0.01 or less per part by mass of F powder. Since the F powder in this dispersion (2) has a relatively large average particle size and a small surface area, it is highly stabilized by a small amount of surfactant and dispersed in the dispersion medium, so this dispersion (2) has excellent dispersion stability.

[0068] Furthermore, since the surfactant content of this dispersion (2) is smaller than that of the F powder, when it is used to produce a coated substrate (described later), the surface of the resulting coated substrate is less rough and has an excellent appearance. Furthermore, when the resulting coated substrate is bonded to other materials, the adhesion is excellent. In particular, when fibers are used as the substrate, a prepreg with excellent adhesion can be obtained by treating the fibers with a sizing agent made from this dispersion (2) and then impregnating the sized fibers with a matrix resin. From the viewpoint of the appearance of the surface of the obtained coated substrate, the content of the surfactant in the dispersion (2) is preferably 0.008 or less, more preferably 0.005 or less, per part by mass of the F powder, and from the viewpoint of dispersibility, the content of the surfactant is preferably 0.0001 or more, per part by mass of the F powder.

[0069] The surfactant is preferably the silicone surfactant, fluorine surfactant, glycol surfactant, or alkylamide ether surfactant described above. Two or more of these surfactants may be used. When two or more surfactants are used, the total content thereof may be within the above range. When two surfactants are used, the surfactants are preferably a silicone surfactant and a glycol surfactant. The surfactant preferably has a surface tension of 28 mN / m or less, more preferably 26 mN / m or less. The surfactant preferably has a surface tension of 20 mN / m or more. The surfactant is preferably nonionic.

[0070] Silicone surfactants are surfactants in which hydrophilic substituents have been introduced into a portion of a silicone whose main skeleton is a siloxane bond in which silicon and oxygen are alternately linked by chemical bonds. Examples include organopolysiloxanes, polyether-modified polysiloxanes, polyester-modified polysiloxanes, aralkyl-modified polysiloxanes, and acrylic-modified polysiloxanes.

[0071] Fluorine-based surfactants are surfactants having a hydrophilic portion having a hydroxyl group, a carboxyl group, a sulfo group, or a group derived from these groups, and a hydrophobic portion having a fluorine-containing organic group. Examples include the "Ftergent" series (manufactured by Neos Corporation, Ftergent is a registered trademark), the "Surflon" series (manufactured by AGC Seimi Chemical Co., Ltd., Surflon is a registered trademark), the "Megafac" series (manufactured by DIC Corporation, Megafac is a registered trademark), and the "Unidyne" series (manufactured by Daikin Industries, Ltd., Unidyne is a registered trademark).

[0072] Glycol surfactants are surfactants made of glycol derivatives in which a hydrophilic moiety such as a hydroxyl group or an ester group is bonded to a hydrophobic moiety such as a hydrocarbon group. Examples of glycol surfactants include glycol monoalkyl ethers, glycol monoaryl ethers, glycol monoalkyl ether acetates, and glycol monoaryl ether acetates.

[0073] Alkylamide ether surfactants are nonionic surfactants in which a carboxylic acid and a polyoxyalkylamine are bonded by an amide bond, such as polyoxyethylene alkylamide and polyoxyethylene oleic acid amide.

[0074] Among the surfactants, silicone surfactants are more preferred from the viewpoint of the dispersion stability of the present dispersion. Among the silicone surfactants, organopolysiloxanes are preferred, and polyether-modified polysiloxanes, polyester-modified polysiloxanes, aralkyl-modified polysiloxanes, or acrylic-modified polysiloxanes are preferred. The organopolysiloxane may have an organopolysiloxane structure in the main chain, in the side chain, or in both the main chain and the side chain. The organopolysiloxane is preferably a linear polymer. The organopolysiloxane is more preferably a polydiorganosiloxane.

[0075] Organopolysiloxanes include those containing dimethylsiloxane units ((CH3)2SiO 2 / 2 ) is preferred, and organopolysiloxanes containing dimethylsiloxane units in the main chain and having polyoxyalkylene at the main chain terminals are preferred. 1 )(R 2 )SiO 2 / 2 More preferred is an organopolysiloxane (2) containing diorganosiloxane units represented by the formula: 1 represents an alkyl group, preferably a methyl group. 2 represents a group having polyoxyalkylene, and the formula -X 2 -OY 2 -Z 2 (wherein, X 2 represents an alkylene group, and Y 2 represents a polyoxyalkylene group, Z 2 represents a hydrogen atom, an alkyl group or an acyl group.

[0076] The polyoxyalkylene contained in organopolysiloxane (1) or (2) may consist of only one type of oxyalkylene group, or may consist of two or more types of oxyalkylene groups. In the latter case, the different types of oxyalkylene groups may be linked randomly or in blocks. The oxyalkylene group in the polyoxyalkylene is preferably an oxyethylene group or an oxypropylene group. The number of oxyalkylene group units (degree of polymerization) in the polyoxyalkylene is preferably 2 or more. The number of oxyalkylene group units is preferably 100 or less, more preferably 50 or less, and even more preferably 20 or less.

[0077] The degree of polymerization of the organopolysiloxane is preferably at least 2. The degree of polymerization of the organopolysiloxane is preferably 1,000 or less, more preferably 100 or less, and even more preferably 50 or less. In the organopolysiloxane (2), the ratio of the number of dimethylsiloxane units to the number of diorganosiloxane units (degree of polymerization) is preferably greater than 1. This ratio is preferably 20 or less.

[0078] The weight average molecular weight of the organopolysiloxane is preferably from 300 to 100,000, more preferably from 500 to 10,000, and even more preferably from 500 to 2,000. The organopolysiloxane preferably has an HLB of 8 to 18. The HLB value is calculated by the Griffin equation and is the sum of the formula weights of the hydrophilic moieties divided by the molecular weight multiplied by 20. In the case of organopolysiloxane (1) or (2), the HLB value is calculated by dividing the molecular weight of the polyoxyalkylene in the organopolysiloxane by the molecular weight of the organopolysiloxane, with the polyoxyalkylene being the hydrophilic moiety, and multiplying the result by 20. Specific examples of organopolysiloxanes include "BYK-347," "BYK-349," "BYK-378," "BYK-3450," "BYK-3451," "BYK-3455," and "BYK-3456" (manufactured by BYK Japan), and "KF-6011" and "KF-6043" (manufactured by Shin-Etsu Chemical Co., Ltd.).

[0079] The boiling point of the liquid dispersion medium in the present dispersion liquid (2) is preferably 75° C. or higher, more preferably 100° C. or higher, and preferably 300° C. or lower, more preferably 250° C. or lower. The liquid dispersion medium may be water or a non-aqueous liquid dispersion medium, and is preferably a liquid dispersion medium selected from the group consisting of water, alcohols, amides, ketones, esters, and hydrocarbons. The non-aqueous liquid dispersion medium may be fluorinated or not. Preferred alcohols include methanol, ethanol, isopropanol, butanol, and hexanol. Preferred amides include dimethylformamide, acetanilide, and N-methyl-2-pyrrolidone. Preferred ketones include acetone, methyl ethyl ketone, diisobutyl ketone, and methyl isobutyl ketone. Preferred esters include ethyl acetate, butyl acetate, ethyl benzoate, and butyl benzoate. Preferred hydrocarbons include pentane, hexane, heptane, octane, toluene, and xylene. The liquid dispersion medium may be a mixture of two or more kinds. The liquid dispersion medium is preferably degassed to prevent a decrease in uniformity of the component distribution in a molded product obtained using the present dispersion liquid (2) and to prevent voids. Of these liquid dispersion media, water is more preferred.

[0080] From the viewpoint of efficiently coating a substrate with a large amount of F powder during the production of a coated substrate described below, the amount of F powder in Dispersion (2) is preferably 25 to 100 parts by mass per 100 parts by mass of the liquid dispersion medium. Typically, F powder has low surface energy and tends to aggregate, so the amount of F powder in a dispersion can be kept low. However, Dispersion (2) has excellent dispersion stability even when the amount of F powder is increased. Therefore, even when the amount of F powder in the dispersion is increased, the dispersion stability, substrate impregnation, and coatability are excellent, and a substrate with excellent surface appearance can be obtained even when a large amount of F powder is applied to or impregnated into the substrate. From the above viewpoints, the amount of F powder in Dispersion (2) is more preferably 40 parts by mass or more per 100 parts by mass of the liquid dispersion medium.

[0081] This dispersion (2) is obtained by mixing F powder with a predetermined amount of surfactant and dispersion medium. The mixing method may include mixing F powder with a predetermined amount of surfactant and dispersion medium together, or mixing a predetermined amount of surfactant and dispersion medium in advance and then adding F powder to the mixture. The addition may be all at once, continuously, or intermittently. Examples of the mixer used for mixing include a mixer with stirring blades, a Henschel mixer, a ribbon blender, a rocking mixer, and a vibration mixer. The mixing method may be either a batch method or a continuous method. Mixers used for batch mixing are preferably a Henschel mixer, a pressure kneader, a Banbury mixer, or a planetary mixer.

[0082] The temperature at which the F powder, a predetermined amount of surfactant, and the dispersion medium are mixed is not particularly limited as long as the F powder is uniformly dispersed, but is usually 20°C or higher. The mixing is also carried out at a temperature lower than the boiling point of the dispersion medium, preferably 100°C or lower.

[0083] The dispersion (2) may further contain at least one component selected from the group consisting of inorganic fillers and aromatic polymers (hereinafter also referred to as the third component). When the dispersion (2) contains an inorganic filler, the molded article obtained by applying the dispersion (2) to a substrate tends to have excellent electrical properties and low linear expansion. When the dispersion (2) contains an aromatic polymer, the molded product obtained by applying the dispersion (2) to a substrate tends to have excellent adhesiveness and UV processability. From the above viewpoint, preferred inorganic fillers are nitride fillers and inorganic oxide fillers, with silicate fillers such as boron nitride filler, aluminum nitride filler, beryllia filler (beryllium oxide filler), silica filler, wollastonite filler, and talc filler, and metal oxide fillers such as cerium oxide, aluminum oxide, magnesium oxide, zinc oxide, and titanium oxide being more preferred, with silica filler being even more preferred. The inorganic filler is preferably surface-treated with a silane coupling agent.

[0084] The inorganic filler preferably has a D50 of 20 μm or less, more preferably 10 μm or less, and preferably has a D50 of 0.01 μm or more, more preferably 0.1 μm or more. The shape of the inorganic filler may be any of granular, needle-like (fibrous), and plate-like. Specific shapes of the inorganic filler include spherical, scale-like, layer-like, leaf-like, apricot-like, columnar, cockscomb-like, equiaxed, leaf-like, micaceous, block-like, flat, wedge-like, rosette-like, net-like, and prismatic shapes.

[0085] Specific examples of suitable inorganic fillers include silica fillers (such as the "Admafine (registered trademark)" series manufactured by Admatechs Co., Ltd.), zinc oxide surface-treated with an ester such as propylene glycol dicaprate (such as the "FINEX (registered trademark)" series manufactured by Sakai Chemical Industry Co., Ltd.), spherical fused silica (such as the "SFP (registered trademark)" series manufactured by Denka Co., Ltd.), titanium oxide coated with a polyhydric alcohol and an inorganic substance (such as the "Tipaque (registered trademark)" series manufactured by Ishihara Sangyo Kaisha, Ltd.), and rutile-type titanium oxide surface-treated with alkylsilane (such as the "Teikai (registered trademark)" series manufactured by Teika Co., Ltd.). "JMT (registered trademark)" series, etc.), hollow silica filler ("E-SPHERES" series manufactured by Taiheiyo Cement Corporation, "Silinax" series manufactured by Nittetsu Mining Co., Ltd., "Ecocospher" series manufactured by Emerson & Cumming Co., Ltd., etc.), talc filler ("SG" series manufactured by Nippon Talc Co., Ltd., etc.), steatite filler ("BST" series manufactured by Nippon Talc Co., Ltd., etc.), boron nitride filler ("UHP" series manufactured by Showa Denko KK, "Denka Boron Nitride" series ("GP", "HGP" grades), etc. manufactured by Denka Co., Ltd.).

[0086] As the aromatic polymer, aromatic polyimide, aromatic polyamide, aromatic polyamideimide, aromatic maleimide, aromatic elastomer such as styrene elastomer, and aromatic polyamic acid are preferred, aromatic polyimide, aromatic polyamideimide, aromatic maleimide, polyphenylene ether, aromatic elastomer such as styrene elastomer are more preferred, and aromatic polyimide, aromatic polyamideimide, and aromatic polyamic acid are even more preferred. The aromatic polyimide may be thermoplastic or thermosetting. Thermoplastic polyimide means a polyimide in which imidization is complete and no further imidization reaction occurs.

[0087] Specific examples of aromatic polyimides include the "Neoprim (registered trademark)" series (manufactured by Mitsubishi Gas Chemical Company, Inc.), the "Spixeria (registered trademark)" series (manufactured by Somar), the "Q-PILON (registered trademark)" series (manufactured by PI Technical Research Institute), the "WINGO" series (manufactured by Wingo Technology Co., Ltd.), the "Tomide (registered trademark)" series (manufactured by T&K TOKA Corporation), the "KPI-MX" series (manufactured by Kawamura Sangyo Co., Ltd.), and the "UPIA (registered trademark)-AT" series (manufactured by Ube Industries, Ltd.). Specific examples of aromatic polyamideimides include HPC-1000 and HPC-2100D (both manufactured by Showa Denko Materials Co., Ltd.).

[0088] Examples of styrene elastomers include styrene-butadiene copolymers, hydrogenated styrene-butadiene copolymers, hydrogenated styrene-isoprene copolymers, styrene-butadiene-styrene block copolymers, styrene-isoprene-styrene block copolymers, hydrogenated styrene-butadiene-styrene block copolymers, and hydrogenated styrene-isoprene-styrene block copolymers.

[0089] The present dispersion (2) may further contain a non-thermofusible polytetrafluoroethylene powder as a third component. In this case, a molded product formed from the present dispersion (2) is likely to have excellent electrical properties. The mass ratio of the content of this powder in the present dispersion (2) relative to the content of the F powder is preferably 0.5 or more, more preferably 1 or more. The above ratio is preferably 10 or less, more preferably 5 or less. The D50 of such powder is preferably 0.1 to 1 μm.

[0090] When the third component is mixed, the mixing method may be the same as the above-mentioned mixing method. When the third component is mixed, it may be added at any stage during the preparation of the dispersion. For example, the third component may be mixed in advance with the F powder and / or a predetermined amount of surfactant, or the third component may be added when mixing the F powder with a predetermined amount of surfactant and dispersion medium. Alternatively, a mixture of the F powder, a predetermined amount of surfactant, and dispersion medium may be mixed in advance with a mixture of the third component and dispersion medium, or the third component may be added to the dispersion after the dispersion is obtained. The third component may be added all at once or in portions, continuously, or intermittently.

[0091] The component sedimentation rate of the present dispersion (2) obtained as described above is preferably 60% or more, more preferably 70% or more. The upper limit of the component sedimentation rate is 100%. Due to the above-mentioned mechanism of action, the present dispersion (2) tends to have excellent dispersion stability.

[0092] The viscosity of the dispersion (2) obtained as described above is preferably 10 mPa·s or more, more preferably 20 mPa·s or more, from the viewpoint of coatability or impregnation onto a substrate when producing a coated substrate, as described below. The viscosity of the dispersion (2) is preferably 100,000 mPa·s or less, more preferably 10,000 mPa·s or less, and even more preferably 2,000 mPa·s or less. The viscosity of the dispersion (2) can be adjusted to the desired range by controlling the amount of F powder and the type and amount of the dispersion medium.

[0093] The thixotropy ratio of the present dispersion (2) is preferably 1.0 to 2.2. The present dispersion (2) having such a thixotropy ratio is excellent in coatability, impregnation, and homogeneity. The thixotropy ratio is calculated by dividing the viscosity of the present dispersion (2) measured at a rotation speed of 30 rpm by the viscosity of the present dispersion (2) measured at a rotation speed of 60 rpm. From the viewpoint of preventing a decrease in uniformity of component distribution and voids in the molded product obtained from the present dispersion (2), the foam volume ratio in the present dispersion (2) is preferably less than 10%, more preferably less than 5%, and is preferably 0% or more. The foam volume ratio is calculated by dividing the volume (V N) and the combined volume of the bubbles when it is decompressed to 0.003 MPa (V V ) and the value is calculated using the following formula. Foam volume ratio [%] = 100 × (V V -V N ) / V N is.

[0094] When the solid content of the present dispersion (2) contains the third component, the third component is also included in the solid content. The solid content of the present dispersion (2) also includes other components insoluble in the present dispersion (2) other than the F powder. The solid content concentration is preferably 25% by mass or more, and more preferably 50% by mass or more, based on 100% by mass of the total mass of the dispersion. From the viewpoint of the dispersibility of the present dispersion (2), the solid content concentration is preferably 80% by mass or less, and more preferably 60% by mass or less. The amount of F powder in the solid content is preferably 50% by mass or more, and more preferably 70% by mass or more, based on 100% by mass of the total mass of the solid content. The amount of F powder in the solid content is preferably 99% by mass or less.

[0095] In addition to the above components, the dispersion (2) may further contain other components such as a thixotropic agent, a viscosity modifier, an antifoaming agent, a silane coupling agent, a dehydrating agent, a plasticizer, a weathering agent, an antioxidant, a heat stabilizer, a lubricant, an antistatic agent, a brightener, a colorant, a conductive agent, a release agent, a surface treatment agent, a flame retardant, and various organic fillers.

[0096] A coated substrate in which the substrate is coated with the F layer can be produced by contacting the present dispersion (2) with a substrate and baking the substrate to form a layer made of the F polymer (hereinafter also referred to as "F layer"). Examples of contacting methods include a method of applying the present dispersion (2) to the surface of the substrate, a method of immersing the substrate in the present dispersion (2) to impregnate the substrate with the present dispersion (2), and a method of spraying the present dispersion (2) onto the substrate.

[0097] Examples of the substrate include metal foil, resin film, woven fabric, nonwoven fabric, and fiber. Suitable embodiments of the coated substrate include a metal-clad laminate having a metal foil and an F layer formed on at least one surface thereof, a multilayer film having a resin film and an F layer formed on at least one surface thereof, and a coated woven fabric obtained by impregnating a woven fabric or nonwoven fabric with the present dispersion (2) and coating the fibers in the woven fabric or nonwoven fabric with the F layer. Alternatively, the present dispersion (2) may be directly brought into contact with fibers and baked to coat the fibers with the F polymer. The F layer may cover the entire surface of the substrate or may cover only a part of it, as long as the F polymer is attached to the surface of the substrate. The F layer may have holes.

[0098] Examples of metal foils include metal substrates such as copper, nickel, aluminum, titanium, and alloys thereof. Examples of resin films include polyimide, polyarylate, polysulfone, polyarylsulfone, polyamide, polyetheramide, polyphenylene sulfide, polyaryletherketone, polyamideimide, liquid crystalline polyester, liquid crystalline polyesteramide, F polymer, non-thermofusible tetrafluoroethylene-based polymer, and prepreg, which is a precursor for fiber-reinforced resin substrates. Preferred examples of F polymer and non-thermofusible tetrafluoroethylene-based polymer in the resin film include PTFE, PFA, and FEP. The shape of these metal foils or resin films may be flat, curved, or irregular, and may also be foil, plate, film, or fiber. Specific examples of coated substrates include metal-clad laminates having a metal foil and an F layer on at least one surface of the metal foil, and multilayer films having a polyimide film and an F layer on both surfaces of the polyimide film. These laminates have excellent physical properties such as electrical properties and are suitable as printed circuit board materials. Specifically, these laminates can be used to produce flexible printed circuit boards and rigid printed circuit boards.

[0099] The metal foil is preferably a copper foil. A metal clad laminate having a copper foil substrate is particularly useful as a printed circuit board material. The ten-point average roughness of the surface of the metal foil is preferably 0.01 to 0.05 μm. The resin film is preferably a polyimide film or an F polymer film. A multilayer film having such a film as the substrate is useful as a wire covering material or a printed circuit board material.

[0100] In producing a metal clad laminate or a multilayer film having an F layer, it is sufficient that the F layer is formed on at least one surface of the substrate, and the F layer may be formed on only one surface of the substrate, or on both surfaces of the substrate. The surface of the substrate may be surface-treated with a silane coupling agent or the like. When applying the dispersion, coating methods such as spraying, roll coating, spin coating, gravure coating, microgravure coating, gravure offset coating, knife coating, kiss coating, bar coating, die coating, fountain-meyer bar coating, and slot die coating can be used.

[0101] When the present dispersion (2) is impregnated into a woven fabric and dried by heating, the woven fabric is coated with an F layer, and a sized coated woven fabric is obtained. As the woven fabric, glass fiber woven fabric, carbon fiber woven fabric, aramid fiber woven fabric, and metal fiber woven fabric are preferred, and glass fiber woven fabric and carbon fiber woven fabric are more preferred. Methods for impregnating the woven fabric with the present dispersion (2) include a method of immersing the woven fabric in the present dispersion (2) and a method of applying the present dispersion to the woven fabric.

[0102] The dispersion (2) is brought into contact with the surface of a fiber, followed by baking to adhere an F layer to the surface of the fiber, thereby obtaining a coated fiber in which the fiber is coated with an F layer. Examples of the fiber include the same reinforcing fibers as those for which the sizing agent can be used.

[0103] By covering the above-mentioned fibers with the F layer, a sizing effect is obtained that suppresses fiber breakage and fluffing. When the present dispersion (2) is used as a sizing agent, additives may be added to the present dispersion (2) as needed depending on the fiber used. Fibers sized with the present dispersion (2) have excellent heat resistance and adhesiveness to other polymers.

[0104] The surface tension of the substrate is preferably greater than that of the surfactant. In this case, the substrate is more easily wetted by the dispersion (2), and the surface of the coated substrate is less likely to become rough. The surface tension of the substrate is preferably at least 5 mN / m greater than that of the surfactant, and more preferably at least 10 mN / m greater. For example, when the surface tension of the surfactant is 28 mN / m or less, the surface tension of the substrate is particularly preferably 35 mN / m or more.

[0105] The F layer is preferably formed by removing the dispersion medium by heating and then baking the F polymer. The temperature for removing the dispersion medium is preferably a temperature below the boiling point of the dispersion medium, more preferably a temperature 50 to 150°C lower than the boiling point. For example, when N-methyl-2-pyrrolidone, which has a boiling point of approximately 200°C, is used, heating is preferably at 150°C or lower, preferably 100 to 120°C. For example, when water, which has a boiling point of approximately 100°C, is used, heating is preferably at 90°C or lower, preferably 70 to 80°C. It is preferable to blow air in the step of removing the dispersion medium.

[0106] After removing the dispersion medium, the substrate is preferably heated to a temperature range in which the F polymer is baked to form an F layer, and the polymer is preferably baked, for example, in the range of 300 to 400° C. The F layer preferably contains a baked product of the F polymer. As described above, the F layer is formed through the steps of contacting the present dispersion (2) with the substrate, removing the dispersion medium, and baking the F polymer. These steps may be performed once or twice or more times. For example, the present dispersion (2) is applied to the substrate, and the dispersion medium is removed by heating to form a film. The present dispersion (2) may be further applied to the formed film, the dispersion medium is removed by heating, and the F polymer is baked by further heating to form the film. From the viewpoint of easily obtaining a thick film with excellent appearance, the steps of applying the present dispersion (2), drying, and baking may be performed twice.

[0107] The thickness of the F layer is preferably 0.1 μm or more, more preferably 1 μm or more. The upper limit of the thickness is 200 μm. Within this range, an F layer with excellent crack resistance can be easily formed. The peel strength between the F layer and the substrate is preferably 10 mN / m or more, more preferably 15 mN / m or more. The peel strength is preferably 100 mN / m or less. By using the dispersion (2), such a laminate can be easily formed without impairing the physical properties of the F polymer in the F layer. The porosity of the F layer is preferably 20% or less, more preferably 10% or less. The porosity is preferably 0.1% or more. The porosity is determined by determining the void areas of the F layer through image processing of an SEM photograph of the cross section of a molded product observed using a scanning electron microscope (SEM), and then dividing the area occupied by the void areas by the area of the F layer (%). The area occupied by the void areas is determined by approximating the void areas as circles.

[0108] Examples of the configuration of the metal clad laminate or multilayer film include substrate / F layer / substrate / F layer / substrate, substrate / substrate / F layer / substrate / substrate, etc. The substrates may be the same or different, and the substrate or F layer may further contain glass cloth or a filler. Such metal clad laminates are useful as antenna parts, printed circuit boards, aircraft parts, automobile parts, sporting goods, food industry supplies, heat dissipation parts, paints, cosmetics, and the like; specifically, they are useful as wire coating materials for aircraft electric wires and the like, enameled wire coating materials used in motors of electric vehicles and the like, electrical insulating tape, insulating tape for oil drilling, materials for printed circuit boards, separation membranes such as microfiltration membranes, ultrafiltration membranes, reverse osmosis membranes, ion exchange membranes, dialysis membranes, and gas separation membranes, electrode binders for lithium secondary batteries, fuel cells, and the like, copy rolls, covers for furniture, automobile dashboards, and home appliances, sliding members such as load bearings, sliding shafts, valves, bearings, gears, cams, belt conveyors, and food transport belts, tools such as shovels, files, saws, and the like, boilers, hoppers, pipes, ovens, baking molds, chutes, dies, toilets, container coating materials, power devices, transistors, thyristors, rectifiers, transformers, power MOS FETs, CPUs, heat dissipation fins, and metal heat sinks. More specifically, the material is useful as a sealing material for processing machines, vacuum ovens, plasma processing equipment, etc. that are heat-treated under low-oxygen conditions, such as housings for personal computers and displays, electronic device materials, and the interior and exterior of automobiles, as well as heat-dissipating parts in processing units such as sputtering and various dry etching equipment.

[0109] Furthermore, the dispersion (2) can be used for applications such as impregnating an insulating layer of a printed wiring board, a thermal interface material, a substrate for a power module, or a coil used in a power device such as a motor, and drying the impregnated material to form a thermally conductive heat-resistant coating layer, bonding ceramic parts or metal parts together in an automotive engine, or imparting corrosion resistance to a heat exchanger or the fins or tubes that constitute the heat exchanger.

[0110] Furthermore, the present dispersion (2) is suitable as a present sizing agent. When the present dispersion (2) is used as a sizing agent, the appearance of the fibers coated with the F layer is excellent, and therefore, in fiber-reinforced plastics containing the reinforcing fibers and the matrix resin, the adhesion between the reinforcing fibers and the matrix resin is improved. Therefore, a prepreg containing fibers and a matrix resin that has been sized by contacting the present dispersion (2) with the fibers has excellent mechanical properties. Furthermore, because the F layer has excellent heat resistance, such a prepreg tends to have excellent surface smoothness even when processed at high temperatures.

[0111] Examples of reinforcing fibers include the same fibers as those mentioned above, and among these, carbon fiber, glass fiber, aramid fiber and boron fiber are preferred. The matrix resin may be the same as the matrix resin in the present prepreg. Because the F layer has excellent heat resistance, it is not easily decomposed even when heated when using such heat-resistant resin as a matrix resin to mold a prepreg or when further processing the prepreg, and the prepreg and its processed products tend to have excellent surface smoothness.

[0112] The production method for obtaining the prepreg from the present dispersion (2) may be the same as the production method for obtaining the present prepreg from the present dispersion (1) described above. The prepreg obtained from the dispersion (2) can be further molded into a fiber-reinforced composite material in the same manner as the above-mentioned method for molding the prepreg into a fiber-reinforced composite material.

[0113] As described above, the dispersion (2) has excellent dispersion stability, and a coated substrate coated with an F layer using the dispersion (2) has excellent surface appearance and excellent adhesion to other substrates. In particular, coating fibers with an F layer using the dispersion (2) provides a sizing effect that suppresses fiber breakage and fuzzing. Therefore, the dispersion (2) is preferably used as a sizing agent. When the dispersion (2) is used as a sizing agent, the appearance of fibers coated with the F layer is excellent, and in fiber-reinforced plastics containing the reinforcing fibers and a matrix resin, the adhesion between the reinforcing fibers and the matrix resin is improved. Therefore, a prepreg containing fibers and a matrix resin that has been sized by contacting the fibers with the dispersion (2) has excellent mechanical properties.

[0114] The present sizing agent, the present dispersion (1), the sized fibers, and the present dispersion (2) have been described above, but the present invention is not limited to the configurations of the above-described embodiments. For example, the present sizing agent, the present dispersion (1), the sized fibers, and the present dispersion (2) may be added to any other components in the configuration of the above embodiment, or may be replaced with any components that exhibit similar functions. [Example]

[0115] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. Details of each component are shown below. Example 1 1-1. Preparation of each ingredient [F Powder] F Powder 11: A polymer containing 97.9 mol% of TFE units, 0.1 mol% of NAH units, and 2.0 mol% of PPVE units, in that order, with an acid anhydride residue having a main chain carbon number of 1 x 10 6 Powder (average particle size 2 μm, bulk density 0.18 g / m) made of polymer (melting temperature 300°C, 5% weight loss temperature: 400°C or higher) with 1000 particles per particle 2 ) F Powder-12: A powder (average particle size 2 μm, bulk density 0.19 g / m) consisting of a polymer (melting temperature 305°C, 5% weight loss temperature: 400°C or higher) containing 97.5 mol% of TFE units and 2.5 mol% of NAH units, in that order, and no polar functional groups. 2 ) [Epoxy resin] Epoxy resin 1: Epicoat 828 manufactured by Japan Epoxy Resin Co., Ltd. The polymer of F Powder 11 has a carbonyl group with a main chain carbon number of 1 × 10 6 There are 1000 per piece. [Surfactants] Surfactant A: Polyoxyethylene / polyoxypropylene / polyoxyethylene triblock copolymer ("Pluronic F88" manufactured by Asahi Denka Co., Ltd.) [Carbon fiber] Carbon fiber 1: Mitsubishi Chemical "MR50R" [Liquid dispersion medium] NMP: N-methyl-2-pyrrolidone [film] Film 1: A film (thickness: 15 μm) obtained by melt-extruding polyether ketone ketone ("Kepstan 7003" manufactured by Arkema France)

[0116] 1-2. Preparation of sizing agent dispersion and placement on carbon fiber [Example 1-1] (1) First, F Powder 11 (10 parts by mass) and NMP (90 parts by mass) were placed in a pot, followed by the addition of zirconia balls. The pot was then rolled at 150 rpm for 1 hour to obtain Dispersion Liquid 11 (viscosity: 400 mPa s). (2) The dispersion liquid 11 obtained in (1) above was applied to carbon fibers by a roller immersion method, and then the fibers were passed through a drying oven at 120°C for 5 minutes to be heated and dried. Thereafter, the fibers were baked in a far-infrared oven at 340°C for 10 minutes to obtain sized carbon fibers (hereinafter referred to as carbon fibers T1) having a baked product of F powder 11 attached to the surface of the carbon fibers. (3) Carbon fiber T1 oriented in one direction, with a weight of 75 g / m 2The film 1 was placed on both sides of the sheet-like carbon fiber substrate, and the two films 1 were heated and melted to impregnate the carbon fiber substrate, thereby producing a prepreg 1. Prepreg 1 was cut to a predetermined size and then laminated in a steel mold so that the fiber axis direction of each prepreg was aligned in one direction. The mold with the laminate placed in it was compressed at 380°C and 5 MPa for 30 minutes in a two-stage heating and cooling press (50-ton press, manufactured by Shinto Metal Industries Co., Ltd.), and the temperature was then lowered to 200°C over several minutes to obtain Laminate 1 with a thickness of approximately 2 mm. Laminate 1 and 18 μm-thick copper foil were then laminated and compressed under the same conditions to obtain Molded Product 1.

[0117] [Example 1-2] A molded body 2 was obtained in the same manner as in Example 1-1, except that F powder 12 was used instead of F powder 11. [Example 1-3] Epoxy resin 1 (80 parts by mass) and surfactant A (20 parts by mass) were mixed and subjected to phase inversion emulsification to obtain dispersion 12. A molded body 3 was obtained in the same manner as in Example 1-1, except that dispersion 12 was used instead of dispersion 11. 1-3.Evaluation The appearance, peel strength and water resistance of the molded articles 1 to 3 were evaluated according to the following criteria.

[0118] <Appearance of molded product> The surface of the molded article was visually observed and evaluated as follows. ◯: No bubbles are observed on the surface of the molded product, and it is smooth ×: Foaming was observed on the surface of the molded article, and it was not smooth. <Peel strength of molded product> The molded body was cut into a rectangular shape (length: 100 mm, width: 10 mm) to prepare a sample. Next, the sample was fixed at a position 50 mm from one end in the longitudinal direction, and the maximum load (N / cm) applied when peeling the copper foil and the laminate at an angle of 90° to the sample from one end in the longitudinal direction at a pulling rate of 50 mm / min was measured. Based on the measured values, the peel strength was evaluated according to the following criteria. 〇:10N / cm or more ×: Less than 10N / cm <Water resistance of molded body> The peel strength of the molded body after water absorption was measured in the same manner as in the above <Peel strength of molded body>, except that the molded body was kept in an atmosphere of 85°C and 85% relative humidity for 72 hours before preparing the sample. For each molded body, the ratio of the peel strength of the molded body after water absorption to the peel strength of the molded body measured in the above <Peel strength of molded body> was calculated and evaluated according to the following criteria. 〇: 90% or more ×: Less than 90% The evaluation results of molded bodies 1 to 3 are shown in Table 1.

[0119] [Table 1] <Example 2> 2-1. Preparation of each ingredient [F Powder] F Powder 21: Powder (D50: 25 μm) consisting of a polymer containing TFE units, NAH units, and PPVE units in the order of 97.9 mol%, 0.1 mol%, and 2.0 mol%, respectively, and having polar functional groups (melting temperature: 300°C, 5% weight loss temperature: 400°C or higher). F Powder 22: Powder (D50: 28 μm) consisting of a polymer containing 97.5 mol% TFE units and 2.5 mol% PPVE units, in that order (melting temperature: 305°C, 5% weight loss temperature: 400°C or higher). F Powder 23: Powder (D50: 2 μm) consisting of a polymer containing 97.5 mol% TFE units and 2.5 mol% PPVE units, in that order (melting temperature: 305°C, 5% weight loss temperature: 400°C or higher). The polymer of F Powder 21 has a carbonyl group-containing group with a main chain carbon number of 1 × 10 6 The polymers of F Powder 22 and F Powder 23 have no polar functional groups.

[0120] [Surfactants] Surfactant 1: Polyoxyalkylene-modified polydimethylsiloxane (surface tension: 26 mN / m) Surfactant 2: Polyoxyalkylene-modified polyorganosiloxane (surface tension: 30 mN / m) [Liquid dispersion medium] Water (Surface tension: 72mN / m) [Base material] Substrate 1: Carbon fiber (surface tension: 38 mN / m) Substrate 2: Hydrophilic resin fiber (surface tension: 25 mN / m)

[0121] 2-2. Dispersion liquid manufacturing example [Example 2-1] First, powder 21, surfactant 1, and water as a liquid dispersion medium were placed in a pot, followed by the addition of zirconia balls. The pot was then rolled at 150 rpm for 1 hour to obtain dispersion 21 (viscosity: 30 mPa s) containing powder 21 (50 parts by mass), surfactant 1 (0.2 parts by mass), and water (49.8 parts by mass). [Example 2-2 to Example 2-6] Dispersions 22 to 26 were prepared in the same manner as Dispersion 21, except that the types of F powder, surfactant, and liquid dispersion medium and the amount of surfactant were changed as shown in Table 2.

[0122] The components of the dispersions 21 to 26 obtained above are summarized in Table 2. In addition, coated substrates were prepared using dispersions 21 to 26 by the following method and evaluated according to the evaluation criteria. The coated substrates obtained from each dispersion were evaluated according to the evaluation criteria below, and the results are also summarized in Table 2.

[0123] 2-3. Example of manufacturing coated substrate The dispersion liquid 21 was applied to the surface of a long copper foil (thickness 18 μm) using a bar coater to form a wet film. Next, the metal foil on which this wet film was formed was passed through a drying oven at 120°C for 5 minutes and dried by heating to obtain a dry film. Thereafter, the dry film was heated at 380°C for 3 minutes in a nitrogen oven. In this way, a coated substrate 1 was produced, which had a metal foil and a polymer layer (thickness 5 μm) as a molded product containing a molten and baked product of the powder 21 on its surface. Coated substrates 2 to 6 were produced in the same manner as coated substrate 1, except that dispersion 21 was changed to dispersions 22 to 26, respectively.

[0124] 2-4.Evaluation 2-4-1. Evaluation of dispersion stability of dispersion liquid After each dispersion was stored in a container at 25°C, its dispersibility was visually confirmed and the dispersion stability was evaluated according to the following criteria.

[0125] [Evaluation criteria] ◯: No aggregates are visible. △: Fine aggregates were visible on the side wall of the container. Upon gentle stirring, the mixture was uniformly redispersed. ×: Agglomerates are visible at the bottom of the container. They are uniformly redispersed when stirred with shear.

[0126] 2-4-2. Evaluation of component sedimentation rate Each dispersion (18 mL) was placed in a screw tube (internal volume: 30 mL) and left to stand at 25°C for 14 days. The component sedimentation rate was calculated from the height of the entire dispersion in the screw tube and the height of the sedimentation layer (dispersion layer) before and after standing, according to the following formula. If no sedimentation layer was observed after standing and there was no change in the state, it was assumed that there was no change in the height of the entire dispersion, and the component sedimentation rate was set to 100%. Component sedimentation rate (%) = (height of sedimented layer) / (height of total dispersion) x 100 [Evaluation criteria] ◯: The component sedimentation rate measured by the above method is 70% or more. △: The component sedimentation rate measured by the above method is less than 70% and 60% or more. ×: The component sedimentation rate measured by the above method is less than 60%.

[0127] 2-4-3.Evaluation of the surface coating condition of coated substrates The surface smoothness of each coated substrate was visually inspected and evaluated according to the following criteria.

[0128] [Evaluation criteria] ◯: The entire surface of the polymer layer is smooth. Δ: Irregularities due to agglomerates or missing powder are visible at the edges of the surface of the polymer layer. ×: Irregularities due to agglomerates or powder omissions are visible over the entire surface of the polymer layer.

[0129] [Table 2] [Industrial Applicability]

[0130] The sizing agent, sized fibers, and prepregs formed from the fibers of the present invention can suppress foaming during heat molding, and can form molded articles that have excellent appearance, such as smoothness, and when laminated, are particularly excellent in adhesion and water resistance. The resulting molded articles are suitable for use in many fields, such as printed circuit boards, aircraft components, spacecraft components, automobile components, ship components, civil engineering and construction materials, oil drilling components, hydrogen tanks, hydrogen tank pressure vessels, wind turbine blades, and sporting goods. Furthermore, as is clear from the above results, Dispersion (2) has excellent dispersibility and dispersion stability. Furthermore, the surface of a substrate coated with Dispersion (2) has excellent uniformity and excellent appearance. Therefore, it is believed that the coated substrate obtained by coating a substrate with Dispersion (2) exhibits the properties of the F polymer to a high degree. Furthermore, it is believed that a sizing effect can be obtained when Dispersion (2) is used as a sizing agent. It is believed that a prepreg containing fibers sized with Dispersion (2) and a matrix resin has excellent mechanical properties. The entire contents of the specifications, claims and abstracts of Japanese Patent Application No. 2020-118558 filed on July 9, 2020, and Japanese Patent Application No. 2020-148433 filed on September 3, 2020, are hereby incorporated by reference as the disclosure of the specification of the present invention.

Claims

1. A sizing agent comprising a dispersion containing a powder of a heat-fusible tetrafluoroethylene-based polymer having an average particle size of 10 to 100 μm, a surfactant, and a liquid dispersion medium, wherein the content of the surfactant is 0.01 parts by mass or less per part by mass of the powder of the tetrafluoroethylene-based polymer.

2. 2. The sizing agent according to claim 1, wherein the melting temperature of the tetrafluoroethylene-based polymer is 280 to 325°C.

3. 3. The sizing agent according to claim 1, wherein the 5% weight loss temperature of the tetrafluoroethylene-based polymer is 360°C or higher.

4. The sizing agent according to any one of claims 1 to 3, wherein the tetrafluoroethylene-based polymer is a tetrafluoroethylene-based polymer having units based on perfluoro(alkyl vinyl ether) and polar functional groups, or a tetrafluoroethylene-based polymer containing 2.0 to 5.0 mol% of units based on perfluoro(alkyl vinyl ether) based on all units and having no polar functional groups.

5. The tetrafluoroethylene-based polymer having a polar functional group is a tetrafluoroethylene-based polymer having a carbonyl group-containing group, and the number of the carbonyl group-containing groups is 1×10 ６ The sizing agent according to claim 4, wherein the number of particles per particle is 10 to 5,000.

6. A dispersion comprising a powder of a heat-fusible tetrafluoroethylene-based polymer having an average particle size of 10 to 100 μm, a surfactant, and a liquid dispersion medium, wherein the content of the tetrafluoroethylene-based polymer is 25 to 60 parts by mass per 100 parts by mass of the liquid dispersion medium, and the content of the surfactant is 0.01 part by mass or less per part by mass of the tetrafluoroethylene-based polymer powder.

7. 7. The dispersion of claim 6, wherein the surfactant has a surface tension of 28 mN / m or less.

8. 8. The dispersion according to claim 6, wherein the surfactant is a silicone-based surfactant, a fluorine-based surfactant, a glycol-based surfactant, or an alkylamide ether-based surfactant.

9. A sizing agent comprising the dispersion according to any one of claims 6 to 8.

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