JP2020070517A - Sizing agent composition, method for producing carbon fiber, and carbon fiber with sizing agent adhered thereto - Google Patents

Abstract

To provide a sizing agent composition providing a carbon fiber allowing for formation of a carbon fiber-reinforced composite material which is excellent in adhesion property between a matrix resin and a carbon fiber and is excellent in mechanical strength.SOLUTION: The sizing agent composition is provided that includes an oxazoline compound (A) and an aliphatic compound (B) having a hydrocarbon group in its side chain. The sizing agent composition further preferably includes an epoxy compound (C). In the present invention, a mixing ratio (mass ratio) of the oxazoline compound (A) is preferably 5-95 wt.%. In addition, the oxazoline compound (A) is preferably water-soluble.SELECTED DRAWING: None

Description

  The present invention relates to a sizing agent composition used for carbon fibers, a method for producing carbon fibers using the sizing agent composition, and sizing agent-attached carbon fibers.

  Carbon fiber is lightweight, has excellent specific strength and specific elastic modulus, and is also excellent in heat resistance and chemical resistance. Therefore, as a fiber reinforced composite material combined with various matrix resins, aircraft members, spacecraft members, It is used in many fields such as automobile parts, ship parts, civil engineering and construction materials, and sports equipment. With such a wide range of applications, there is an increasing demand for higher performance of carbon fibers. Particularly, carbon fibers for sports and aircraft are required to have higher strength and higher elastic modulus. There is.

  In the composite material using carbon fibers, it is important that the adhesiveness between the carbon fibers and the matrix resin is excellent in order to utilize the excellent properties of the carbon fibers. However, the carbon fiber does not necessarily have sufficient adhesiveness with the matrix resin, and in order to activate the surface thereof, surface oxidation treatment such as chemical oxidation treatment, gas phase oxidation treatment and electrolytic oxidation treatment is performed. However, as the elastic modulus of the carbon fiber increases, the activation reaction of the surface of the carbon fiber due to such surface oxidation treatment tends to occur less easily, and improvement of the adhesiveness between the carbon fiber and the matrix resin is required. ing. Further, since carbon fibers have a small elongation and a brittle property, carbon fiber bundles, which are aggregates of long carbon fibers, tend to cause fuzz due to mechanical friction or the like.

  Therefore, in order to suppress the occurrence of such fluff and to improve the adhesiveness between the carbon fiber and the matrix resin, in the manufacturing process of the carbon fiber reinforced composite material, a sizing treatment for imparting a sizing agent to the carbon fiber is performed. A study is underway.

  In order to improve the adhesiveness between the carbon fiber and the matrix resin, for example, Patent Document 1 uses a compound having both a terminal unsaturated group and a polar group as a sizing agent, and Patent Document 2 uses an epoxy group and a vinyl group. It has been proposed to use a compound contained in one molecule. However, even if these compounds are used, the adhesiveness between the carbon fiber and the matrix resin is not sufficiently satisfactory. Further, Patent Document 3 proposes a sizing agent using an oxazoline compound, but the effect of suppressing the generation of fluff is insufficient, and the adhesiveness is not satisfactory. Therefore, there is a demand for a sizing agent that can improve the adhesion between the carbon fiber and the matrix resin and at the same time suppress the generation of fluff.

JP, 2004-300267, A JP, 2000-355884, A JP, 2017-203236, A

  The object of the present invention is to improve the above-mentioned drawbacks of the prior art and to provide a sizing agent composition which provides a carbon fiber capable of forming a carbon fiber reinforced composite material having excellent adhesion between a matrix resin and carbon fiber and excellent mechanical strength There is something to do.

  The sizing agent composition of the present invention is a sizing agent composition containing (A) an oxazoline compound and (B) an aliphatic compound having a hydrocarbon group in a side chain. The sizing agent composition of the present invention preferably further contains (C) an epoxy compound. In the present invention, the mixing ratio (mass ratio) of the (A) oxazoline compound is preferably 5 to 95 wt%. Further, in the present invention, the (A) oxazoline compound is preferably water-soluble.

  The present invention includes a method for producing carbon fibers by applying the sizing agent of the present invention to carbon fibers, carbon fibers obtained thereby, and a carbon fiber composite material comprising such carbon fibers and a matrix resin.

  When the sizing agent composition of the present invention is used, the adhesion between the fiber and the matrix resin is improved, and a fiber-reinforced composite material having excellent mechanical strength can be obtained.

  The sizing agent composition of the present invention is a sizing agent composition containing at least (A) an oxazoline compound and (B) an aliphatic compound having a hydrocarbon group in a side chain.

  In the present invention, the oxazoline compound is a compound containing an oxazoline group. The oxazoline group does not react with water or an alcoholic hydroxyl group, but can react with a carboxyl group, a phenolic hydroxyl group, an aromatic thiol or the like to form a covalent bond. Therefore, the oxazoline compound has sufficient storage stability as a sizing agent composition, while the functional group contained in the surface of the fiber or the matrix resin, particularly the phenolic hydroxyl group or the carboxylic acid reacts with the oxazoline group to give the fiber. The adhesiveness between the matrix resin and the matrix resin can be improved. Therefore, when the fiber provided with the sizing agent of the present invention is used in a composite material, a fiber reinforced composite material having excellent mechanical strength can be obtained.

  Furthermore, the sizing agent composition of the present invention contains (B) an aliphatic compound having a hydrocarbon group in the side chain. By including (B) the aliphatic compound having a hydrocarbon group in the side chain, it is possible to improve the scratch resistance of the fiber bundle and suppress the generation of fluff. Therefore, by providing the sizing agent of the present invention, it is possible to obtain a fiber bundle that is excellent in adhesiveness with the matrix resin and has less fuzz. When such a fiber bundle is used in a composite material, a fiber reinforced composite material having excellent mechanical strength can be obtained.

  The oxazoline compound (A) used in the present invention is not particularly limited as long as it is a compound containing an oxazoline group, but is preferably a compound having two or more oxazoline groups. Further, it is preferably a polymer having an oxazoline group in its side chain. By having many oxazoline groups, the adhesiveness between the fiber and the matrix resin can be further improved. From the viewpoint of the adhesiveness between the fiber and the matrix resin, the amount of the oxazoline group contained in the (A) oxazoline compound is preferably 0.01 to 13 mmol / g, and more preferably 0.1 to 10 mmol / g. preferable.

  When a polymer having an oxazoline ring in its side chain is used, its number average molecular weight is preferably 500 or more, more preferably 800 to 100,000, further preferably 1,000 to 50,000, and more preferably 5,000 to 30,000. Is particularly preferable. The main skeleton is not particularly limited, but is preferably a vinyl polymer such as an olefin polymer, an acrylic polymer, or a styrene polymer, and above all, a fat such as an olefin polymer or an acrylic polymer. A vinyl group-based polymer is preferable because it is easy to obtain a fiber bundle with less fuzz.

  In the present invention, the mixing ratio (mass ratio) of the (A) oxazoline compound is preferably 1 to 95 wt%, and preferably 5 to 30 wt% with respect to the total amount of the nonvolatile components contained in the sizing agent composition. Is more preferable.

In the present invention, the (A) oxazoline compound is preferably water-soluble. When a water-soluble compound is used, the sizing agent solution can be more uniformly adhered to the fiber, and the oxazoline compound can react more uniformly with the carboxyl groups and phenolic hydroxyl groups on the fiber surface, so the adhesion of the fiber and the sizing agent Is improved, and as a result, the adhesiveness between the fiber and the matrix resin is also improved, which is preferable. Further, when the glass transition temperature (T _g ) of the oxazoline compound (A) does not have a glass transition temperature (T _g ), its melting temperature is preferably 200 ° C. or lower. It is preferable that the temperature is 200 ° C. or lower, because after the sizing agent is applied to the fibers, it can be liquefied by the heat applied during the drying of the fiber bundle and more uniformly adhered to the fibers.

  The (A) oxazoline compound used in the present invention is not particularly limited, but more specifically, it is a water-soluble oxazoline-based reactive polymer Epocros WS series, WS-300, WS-500 manufactured by Nippon Shokubai Co., Ltd. , WS-700 and the like.

  In the present invention, the aliphatic compound having a hydrocarbon group in the side chain (B) is not particularly limited, but for example, a polyoxyalkylene compound having a hydrocarbon in the side chain, an aliphatic polyester compound, a polyolefin compound Etc. Among these, polyoxyalkylene compounds having a hydrocarbon in the side chain are preferable. The aliphatic compound having a hydrocarbon group on its side chain is not particularly limited in molecular weight, but a polymer is preferably used. When a polymer is used as the aliphatic compound having a hydrocarbon group in the side chain, it may be a homopolymer of a monomer having a hydrocarbon group in the side chain, or a monomer having a hydrocarbon group in the side chain. And a copolymer of monomers having no hydrocarbon group. A copolymer of a monomer having a hydrocarbon group in the side chain and a monomer having no hydrocarbon group is more preferable. When using a copolymer, either a random copolymer or a block copolymer can be used as the copolymer.

  The aliphatic compound having a hydrocarbon group in the side chain (B) used in the present invention is not particularly limited, but specifically, Daipan Kogyo Seiyaku Co., Ltd., Epan 410, Epan 420, Epan 450. , Epan 485, Epan 680, Epan 710, Epan 720, Epan 740, Epan 750, Epan 785, Epan U-103, Epan U-105, Epan U-108, Pronon # 102, Pronon # 104 manufactured by NOF CORPORATION, Pronon # 201, Pronon # 202B, Pronon # 204, Pronon # 208, Unilube 70DP-600B, Unilube 70DP-950B, Sanyo Kasei Kogyo New Pole PE-61, New Pole PE-62, New Pole PE-64, New Pole PE-68, New Pole PE-71, New Pole PE-74 New Pole PE-75, New Pole PE-78, New Pole PE-108, by Matsumoto Yushi Co., Ltd. Uporu U, Tomenorin F, and the like.

  In the present invention, the mixing ratio (mass ratio) of the aliphatic compound (B) having a hydrocarbon group in the side chain is 1 to 99 wt% with respect to the total amount of the nonvolatile components contained in the sizing agent composition. It is more preferably from 5 to 95 wt%.

  The sizing agent composition of the present invention preferably further contains (C) an epoxy compound. The epoxy compound has a high affinity with the fiber surface and the (A) oxazoline compound, and can enhance the impregnation of the sizing agent composition into the fiber bundle. Therefore, the sizing agent solution can be more uniformly adhered to the fibers, the adhesion between the fibers and the sizing agent is improved, and as a result, the adhesion between the fibers and the matrix resin is also improved, which is preferable. Further, by containing an epoxy group, the adhesiveness between the carbon fiber and the resin is improved by the reaction with the functional group on the carbon fiber or the functional group contained in the matrix resin. In the present invention, the mixing ratio (mass ratio) of the (C) epoxy compound is preferably 95 wt% or less, and preferably 20 to 90 wt% with respect to the total amount of the nonvolatile components contained in the sizing agent composition. Is more preferable.

  It is preferable to use a liquid epoxy compound as the (C) epoxy compound used in the present invention. When a liquid compound is used, it is easy to uniformly apply the sizing agent to the fiber bundle. Further, the epoxy compound (C) preferably has an aliphatic skeleton. By using the epoxy compound having an aliphatic skeleton, the friction can be further reduced and the abrasion resistance of the fiber bundle can be improved. The (C) epoxy compound is not particularly limited, but for example, Denacol EX-611, EX-612, EX-614, EX-614B, EX-622, EX-512, manufactured by Nagase Chemtex Co., Ltd., EX-521, EX-411, EX-421, EX-313, EX-314, EX-321, EX-811, EX-851, EX-821, EX-832, EX-841, EX-861, EX-. Specific examples thereof include 911, EX-941, EX-920, and EX-931.

  As the epoxy compound (C), not only a compound containing only an epoxy group as a functional group but also a modified product such as a urethane-modified epoxy compound may be used. When the modified product is used as the epoxy compound, it is preferable to use the urethane-modified epoxy compound. When a urethane-modified epoxy compound is used as the epoxy compound, the flexibility of the urethane can relieve the stress applied to the yarn and similarly impart rubbing resistance. The urethane-modified epoxy compound is a compound obtained by reacting a compound having an epoxy group and a hydroxyl group with an isocyanate compound, and for example, EPU-6, EPU-7N, EPU-11F, EPU-15F manufactured by ADEKA CORPORATION. Specific examples thereof include EPU-1395, EPU-1527, EPU-1753, EPU-73B, EPU-17, EPU-17T-6, EPU-80, and HYDRAN N320 manufactured by DIC Corporation.

  In the present invention, the sizing agent composition may contain auxiliary components such as a dispersant and a surfactant in order to improve the handling property of the carbon fiber, scratch resistance, fluff resistance and impregnation property.

  When the sizing agent composition of the present invention as described above is used, the adhesiveness between the fiber and the matrix resin is improved, and a fiber-reinforced composite material having excellent mechanical strength can be obtained.

  The reinforcing fiber to which the sizing agent composition of the present invention is attached is not particularly limited, but a particularly remarkable effect is obtained when used as a fiber bundle in which a plurality of filaments (single yarns) are aggregated. In the present invention, the number of filaments constituting the fiber bundle is defined as a fiber bundle state if it is 10 or more, but it is preferably 100 or more, and more preferably 1,000 to 100,000. Is preferred. When the sizing agent-attached fibers are carbon fibers, from the viewpoint of productivity, the number is preferably 3,000 to 80,000, and more preferably 6,000 to 50,000. preferable. When the number of filaments constituting the fiber bundle is small, the flexibility of the fiber bundle tends to increase and the handling property tends to improve, while the productivity of the reinforcing fiber tends to decrease. On the other hand, when the number of fibers is large, it may be difficult to produce fiber bundles, and the sizing agent tends to be insufficiently treated.

  The overall shape of the fiber bundle is preferably a flat fiber bundle. When the fiber bundle is a flat fiber bundle, the sizing agent applied even to the inside of the fiber bundle and the matrix resin used in the subsequent composite material are more likely to diffuse. The flatness of the fiber bundle (width / thickness of the fiber bundle) is preferably 10 times or more, particularly preferably 50 to 400 times.

  The width of such a fiber bundle is preferably 5 mm or more, and particularly preferably in the range of 10 to 100 mm. The length of the fiber bundle is not particularly limited, and may be continuous fibers or discontinuous fibers. When used as a discontinuous fiber, its fiber length is preferably in the range of 1 to 100 mm. More preferably, it is in the range of 5 to 50 mm.

  The average diameter of the fibers (single yarn) used in the present invention is preferably in the range of 0.001 to 100 μm, more preferably in the range of 3 to 20 μm. A more preferable average diameter range is 4 to 15 μm, and a particularly preferable range is 5 to 10 μm. If the fiber diameter is too small, the fiber component becomes bulky, and it tends to be difficult to increase the volume fraction of the fiber. On the other hand, if the fiber diameter is too large, it tends to be difficult to obtain fibers having high strength. When the fiber diameter is in the above range, a composite material having excellent mechanical strength can be obtained.

  The method of attaching the sizing agent composition of the present invention to the reinforcing fibers is not particularly limited, but a method of preparing a sizing agent solution and attaching the sizing agent solution to the fibers (sizing treatment) is preferable. The solvent for diluting the sizing agent composition is not particularly limited, but water is preferable. A method of emulsifying with a surfactant to prepare an aqueous dispersion of sizing agent (emulsion solution) and sizing is also preferable.

  When preparing the aqueous dispersion of the sizing agent, the surfactant is not particularly limited, and anionic, cationic, nonionic surfactants and the like can be used. Of these, nonionic surfactants are preferable from the viewpoint of emulsification performance and stability of the dispersion liquid.

  As the nonionic surfactant, polyethylene glycol type (higher alcohol ethylene oxide adduct, alkylphenol ethylene oxide adduct, fatty acid ethylene oxide adduct, polypropylene glycol ethylene oxide adduct, etc.), polyhydric alcohol type (fatty acid ester of glycerin, Surfactants such as sorbitol fatty acid ester and fatty acid alkanolamide).

  Examples of the emulsification method include a method using a batch equipped with a stirring blade, a method using a ball mill, a method using a shaker, and a method using a high shear emulsifier such as a Gaulin homogenizer.

  The amount of the surfactant added is not particularly limited as long as it can emulsify the sizing agent composition, and it is usually about 0.1 to 30% by mass.

  As an example of the method of sizing treatment, a method of bringing fibers into contact with a sizing agent liquid can be mentioned. Specifically, after a part of the roll is immersed in the sizing agent liquid and surface-transferred, a touch roll type in which fibers are brought into contact with the roll to adhere the sizing agent aqueous solution, and the fibers are directly immersed in the sizing agent liquid, Then, a dipping method in which the amount of the sizing agent liquid deposited is controlled by passing it through a nip roll as needed is mentioned.

  Further, the method of removing the solvent from the fiber is not limited, and various means such as heat treatment, air drying, and centrifugation may be used in combination. From the viewpoint of cost, heat treatment is preferable, and as the heating means for heat treatment, for example, hot air, hot plate, roller, infrared heater or the like can be used.

  Examples of fibers to which the sizing agent composition of the present invention is attached include various reinforcing fibers capable of reinforcing the matrix resin. Specifically, various inorganic fibers such as carbon fiber, glass fiber, ceramic fiber, silicon carbide fiber, aromatic polyamide fiber (aramid fiber), polyethylene fiber, polyethylene terephthalate fiber, polybutylene terephthalate fiber, polyethylene naphthalate fiber, poly Various organic transitions such as arylate fibers, polyacetal fibers, polybenzoxazole fibers, polyphenylene sulfide fibers, polyketone fibers, and polybenzimidazole fibers can be preferably mentioned. Among them, the sizing agent composition of the present invention can be preferably used for carbon fibers, glass fibers and aromatic polyamide fibers, and when used for carbon fibers, it exhibits a particularly excellent effect.

  A method for producing a carbon fiber according to another aspect of the present invention is a method for producing a carbon fiber by applying the sizing agent composition to a carbon fiber, and the sizing agent-attached carbon fiber according to a further aspect of the present invention is It is a carbon fiber to which the sizing agent composition of the present invention is attached. The carbon fiber constituting the carbon fiber of the present invention is not particularly limited, and any carbon fiber such as pitch-based, rayon-based, polyacrylonitrile (PAN) -based can be used, but operability, process passability, mechanical strength, etc. In view of this, the PAN system is preferable. The characteristics such as fineness and strength of the carbon fiber are not particularly limited, and any known carbon fiber can be used without limitation. The PAN-based carbon fiber can be produced, for example, by the following method.

<Precursor fiber>
The precursor fiber used in the method for producing a carbon fiber of the present invention contains acrylonitrile in an amount of 90% by mass or more, preferably 95% by mass or more, and a monomer containing 10% by mass or less of other monomers alone or in combination. Acrylic precursor fibers produced by spinning a polymerized spinning solution are preferred. Examples of the other monomer include itaconic acid and (meth) acrylic acid ester. The precursor fiber is obtained by washing the raw material fiber after spinning with water, drying, stretching and oiling. At this time, steam drawing is performed so that the total draw ratio becomes 5 to 15 times. From the viewpoint of production efficiency, the number of filaments of the precursor fiber is preferably 1000 filaments or more, more preferably 6000 filaments or more.

<Flame resistance treatment>
The obtained precursor fiber is preheated at 200 to 260 ° C and a draw ratio of 0.90 to 1.00 before flameproofing, and subsequently subjected to flameproofing treatment in heated air at 200 to 260 ° C for 10 to 100 minutes. The treatment at this time is generally performed at a draw ratio in the range of 0.85 to 1.15, but 0.95 or more is more preferable in order to obtain a carbon fiber having high strength and high elastic modulus. In this flameproofing treatment, the precursor fiber is an oxidized fiber, and the tension (stretch distribution) at the time of flameproofing is not particularly limited. In the flameproofing process, it is preferable to carry out the flameproofing process until the fiber density of the precursor fiber becomes 1.34 to 1.38 g / cm ³ .

<First carbonization treatment>
The flame resistant fiber can be carbonized by adopting a conventionally known method. For example, the temperature is gradually increased in a first carbonization furnace at 300 to 800 ° C. under a nitrogen atmosphere, and the tension of the flameproof fiber is controlled to perform the first carbonization in the first stage under tension.

<Second carbonization treatment>
In order to further promote carbonization and graphitization (higher crystallization of carbon), the temperature is gradually increased in a second carbonization furnace at 800 to 1600 ° C. in an atmosphere of an inert gas such as nitrogen, and the first carbonization is performed. Firing is performed by controlling the tension of the fiber.

  In each carbonization furnace, it is not preferable to drastically change the temperature near the entrance of the furnace, for example, to rapidly introduce the fiber to the maximum temperature because many surface defects and internal defects are generated. Further, if the residence time becomes longer than necessary in the high temperature portion of the furnace, graphitization will proceed excessively and brittle carbon fibers will be obtained, which is not preferable. In the first carbonization process to the second carbonization process, the tension may be controlled and, if necessary, a process may be performed in a plurality of furnaces so that the physical properties are predetermined. When a higher elastic modulus is required, the graphitization treatment may be further performed at a high temperature of 2000 to 3000 ° C.

<Surface oxidation treatment>
The carbon fiber is preferably subjected to surface oxidation treatment in an electrolytic solution. By performing the surface treatment, a functional group can be introduced on the surface of the carbon fiber, and the adhesiveness with the sizing agent and the matrix resin can be enhanced.

  The amount of electricity applied to the carbon fibers by the surface treatment may be adjusted appropriately so as to obtain the desired amount of surface functional groups, but it is preferably in the range of 10 to 500 coulombs per 1 g of the carbon fibers. When the amount of electricity applied to 1 g of carbon fiber is adjusted within this range, it is easy to obtain carbon fiber having excellent mechanical properties as a fiber and having improved adhesiveness with resin. On the other hand, when the amount of electricity applied to 1 g of carbon fiber is less than 10 coulombs, the adhesiveness to the resin tends to be lowered, and when it exceeds 500 coulombs, the fiber strength tends to be lowered due to excessive treatment.

  As the electrolytic solution, it is preferable to use an aqueous solution of an inorganic acid or an inorganic base and inorganic salts. It is preferable to use a strong acid such as sulfuric acid or nitric acid as the electrolyte because the surface treatment is efficient. Further, it is preferable to use, for example, an inorganic salt such as ammonium sulfate or sodium hydrogencarbonate as the electrolyte because the risk of the electrolytic solution is lower than that when an inorganic acid or an inorganic base is used.

  The electrolyte concentration of the electrolytic solution is preferably 0.1 N or higher, more preferably 0.1 to 1 N. If the electrolyte concentration is less than 0.1, it tends to be unsuitable for electrolysis due to its low electrical conductivity, while if the electrolyte concentration is too high, the electrolyte will precipitate and the stability of the concentration will become low. Tend.

  The higher the temperature of the electrolytic solution is, the higher the electric conductivity is, so that the treatment can be accelerated. On the other hand, when the temperature of the electrolytic solution exceeds 40 ° C., it is difficult to provide uniform conditions without time fluctuations due to fluctuations in concentration due to evaporation of water and the like.

<Sizing process>
The surface-treated carbon fiber is passed through a sizing liquid, and the above sizing agent composition is applied thereto. The concentration of the sizing agent in the sizing liquid is preferably 10 to 25% by mass, and the amount of the sizing agent deposited is preferably 0.1 to 10% by mass, more preferably 0.2 to 5% by mass, and further preferably It is 0.5 to 2 mass%. In the sizing agent application treatment, it is preferable to apply the sizing solution such as a sizing solution in which a sizing agent is dissolved in a solvent or an aqueous emulsion solution obtained by using an emulsifier to carbon fibers. The solvent of the sizing solution is not particularly limited, but water is preferable. The application method is not particularly limited, and an immersion method in which carbon fibers are immersed in a sizing solution, a spray method in which a carbon fiber is sprayed, a contact method using a kiss touch roller, or the like is used. Above all, it is preferable to use the dipping method in which the carbon fiber is dipped in the sizing solution. In addition, auxiliary components such as a dispersant and a surfactant may be added to the sizing agent in order to improve the handleability, abrasion resistance, fluff resistance and impregnation of the carbon fiber.

<Drying process>
The carbon fiber after the sizing treatment is subjected to a drying treatment in order to evaporate water, which was a solvent or a dispersion medium at the time of the sizing treatment, to obtain a carbon fiber to which a sizing agent is added. It is preferable to use an air dryer for drying. The drying temperature is not particularly limited, but it is usually set to 100 to 180 ° C. in the case of a general-purpose aqueous emulsion. Such a drying treatment may also serve as a heat treatment after removing the dispersion medium, and in the present invention, a heat treatment step may be performed after the drying step. By performing a heat treatment after drying (dispersion medium removal), it is possible to react the oxazoline group of the compound (A) with the functional group on the fiber surface to form a crosslinked structure, and to strengthen the fiber surface and the sizing agent more strongly. Can be glued. Drying temperature of the heat treatment after (dispersion medium removed) is a glass transition temperature (T _g), glass transition temperature (T _g) of the case not having its melting temperature (T _m) or more temperatures (A) oxazoline compound It is preferable that it is in the range of T _g or T _m + 10 ° C. to T _g or T _m + 300 ° C., particularly preferably in the range of T _g or T _m + 20 ° C. to T _g or T _m + 200 ° C. ..

  The carbon fiber thus obtained is used in combination with a matrix resin to obtain a composite material by known means / methods such as autoclave molding, press molding, resin transfer molding, and filament winding molding.

  A carbon fiber composite material which is a further embodiment of the present invention is a carbon fiber composite material comprising the above-mentioned carbon fibers and a matrix resin.

The carbon fiber used in the carbon fiber composite material of the present invention is preferably used as a sheet-shaped reinforcing fiber material. Examples of the sheet-shaped material include a material obtained by aligning a fiber material in a sheet shape in one direction, a material obtained by molding the fiber material into a fabric such as a woven or knitted fabric or a non-woven fabric, and a multiaxial woven fabric. When used as a non-woven fabric, it may be a non-woven fabric composed of continuous fibers or a non-continuous fiber. When used as a sheet-shaped reinforcing fiber material, the basis weight is preferably 25 to 10,000 g / m ² .

  A thermosetting resin or a thermoplastic resin is used as the matrix resin. Specific examples of the thermosetting matrix resin include epoxy resin, unsaturated polyester resin, phenol resin, vinyl ester resin, cyanate ester resin, urethane acrylate resin, phenoxy resin, alkyd resin, urethane resin, maleimide resin and cyanate ester resin. Examples of the prepolymerized resin, bismaleimide resin, acetylene-terminated polyimide resin and polyisoimide resin, and nadic acid-terminated polyimide resin. These may be used alone or as a mixture of two or more. Of these, epoxy resins and vinyl ester resins having excellent heat resistance, elastic modulus, and chemical resistance are particularly preferable. In addition to the curing agent and the curing accelerator, these thermosetting resins may contain a commonly used coloring agent, various additives, and the like.

  Examples of the thermoplastic resin include polypropylene, polysulfone, polyether sulfone, polyether ketone, polyether ether ketone, aromatic polyamide, aromatic polyester, aromatic polycarbonate, polyetherimide, polyarylene oxide, thermoplastic polyimide, polyamide. , Polyamideimide, polyacetal, polyphenylene oxide, polyphenylene sulfide, polyarylate, polyacrylonitrile, polyaramid, polybenzimidazole and the like.

  The sizing agent composition of the present invention can further improve the adhesiveness between the carbon fiber and the matrix resin, particularly when a thermosetting resin such as unsaturated polyester, vinyl ester resin, or epoxy resin is combined as the matrix resin. It is possible to obtain a carbon fiber composite material excellent in mechanical strength.

  The content of the resin composition in the composite material is 10 to 90% by weight, preferably 20 to 60% by weight, and more preferably 25 to 45% by weight.

  The carbon fiber-reinforced composite material of the present invention thus obtained is a fiber-reinforced composite material having excellent adhesiveness between fibers and matrix resin and excellent mechanical strength.

  The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The physical properties of each carbon fiber were measured by the following methods.

(1) Evaluation of sizing agent adhesion amount The sizing agent adhesion amount was obtained by collecting two treated 1.0 m sizing agent adhesion fiber bundles and heating them to 550 ° C. at 10 ° C./min in a nitrogen atmosphere. After that, it was baked at the same temperature for 10 minutes, and the weight reduction amount was calculated as the amount of the sizing agent attached by the following formula.
Adhesion amount of sizing agent = (ab) / b × 100 [%]
a: fiber weight before firing [g]
b: Fiber weight after firing [g]

(2) Evaluation of MPF
The sizing agent-attached carbon fiber bundle was run at a speed of 50 ft / min for 2 minutes between the five pin guides while applying a tension of 200 g, and then passed through a urethane sheet carrying a weight of 125 g to carry out urethane. The amount of carbon fibers retained in the sheet was measured and calculated by the following formula. The MPF value is preferably 60 or less, more preferably 30 or less.
MPF value (μg / ft) = supplementary fluff amount (μg) / evaluated fiber bundle length (ft)

(3) Interfacial shear strength (microdroplet method)
As a vinyl ester resin, 100 parts by weight of a vinyl ester resin Lipoxy H-600 (product name) manufactured by Showa Denko KK, 1 part by weight of a peroxide curing agent, and 0.5 parts of cobalt naphthenate as a catalyst are prepared as matrix resins. Was used to measure the interfacial shear strength by the microdroplet method.

[Sizing agent composition]
The sizing agent composition was prepared by appropriately mixing the following compounds as described below.
Compound (A) Oxazoline compound-Epocros: Epocros WS-700 (product name) manufactured by Nippon Shokubai Co., Ltd., oxazoline ring-containing polymer having an acrylic main chain skeleton, oxazoline group amount: 4.5 mmol / g, T _g : 50 ° C., Number average molecular weight (M _n ) 20000
Compound (B) Aliphatic compound having a hydrocarbon group in the side chain-Woopol U: Matsumoto Yushi-Seiyaku Co., Ltd. Wopol U (product name), polyoxyethylene polyoxypropylene glycol random polymer-Tomenoline F: Matsumoto Yushi-Seiyaku Co., Ltd. Tomenorin F (product name), polyoxyethylene polyoxypropylene glycol block polymer-Epan U-103: Daipan Kogyo Co., Ltd. Epan U-103 (product name), polyoxyethylene polyoxypropylene glycol compound (C) Epoxy compound-N320: HYDRAN N320 (product name) manufactured by DIC Corporation, urethane-modified epoxy compound-EX-931: Denacol EX-931 (product name) manufactured by Nagase Chemtex Corporation, polypropylene glycol diglycidyl ether-EX -321: Denacol EX-321 (product name) manufactured by Nagase Chemtex Co., Ltd., trimethylolpropane polyglycidyl ether

[Example 1]
(A) Epocros WS-700 as the oxazoline compound, (B) Wopol U as the aliphatic compound having a hydrocarbon group in the side chain, and (C) the urethane-modified epoxy compound N320 as the epoxy compound are effective component ratios (mass ratio). Mixed at 10/10/80 to obtain a sizing solution.

  The polyacrylonitrile fiber was subjected to flameproofing treatment at 250 ° C. in air and then carbonized at a maximum temperature of 650 ° C. in a nitrogen gas atmosphere. Then, the carbon fiber produced by high-temperature carbonization at 1300 ° C. in a nitrogen atmosphere is subjected to surface treatment by electrolytic oxidation using a 10 wt% ammonium sulfate aqueous solution, and an unsized carbon fiber bundle (tensile strength: 4300 MPa, tensile elastic modulus: 240 GPa, number of filaments: 24000) was obtained. The obtained unsized carbon fiber was continuously immersed in a sizing bath prepared by diluting the above sizing agent with water, and the sizing agent was applied so that the amount of the sizing agent deposited was 1 wt%. After that, water was removed and heat treatment was performed with a hot air dryer having an ambient temperature of 160 ° C. to obtain a sizing agent-attached carbon fiber. The attached amount of the sizing agent was 1.14%. The obtained carbon fiber had very little fluff and was excellent in handleability. In addition, the adhesiveness with resin was also very high, and a composite material with very excellent properties was obtained.

[Example 2]
(A) Epocros WS-700 as an oxazoline compound, (B) Woopol U as an aliphatic compound having a hydrocarbon group in a side chain, and (C) N320 as an epoxy compound at an effective component ratio (mass ratio) of 5/10/85. A sizing treatment was performed in the same manner as in Example 1 except that the sizing solution was mixed. The amount of the sizing agent attached was 1.05%. In Example 2 in which the ratio of the (A) oxazoline compound was 5%, the carbon fiber had few fluffs and was excellent in handleability. Further, a composite material having high adhesiveness with a resin and excellent characteristics was obtained.

[Example 3]
(A) Epocros WS-700 is used as the oxazoline compound, and (B) Tomenolin F is used as the aliphatic compound having a hydrocarbon group in the side chain at an active ingredient ratio (mass ratio) of 90/10 to prepare a sizing solution. Sizing treatment was performed in the same manner as in Example 1. The attached amount of the sizing agent was 1.22%. The obtained carbon fiber had few fluff and was excellent in handleability. Moreover, the adhesiveness with resin was also high, and a composite material having excellent characteristics was obtained.

[Example 4]
(A) Epocros WS-700 as an oxazoline compound, (B) Epan U-103 as an aliphatic compound having a hydrocarbon group in the side chain, and (C) an EX-931 as an epoxy compound in an effective component ratio (mass ratio). The sizing treatment was performed in the same manner as in Example 1 except that the sizing solution was mixed at 75/25 / 56.25. The amount of the sizing agent attached was 0.7%. In Example 4 in which the proportion of the oxazoline compound (A) was 18.75%, a composite material having a high amount of fluff but high adhesiveness with the resin and excellent characteristics was obtained.

[Example 5]
(A) Epocros WS-700 as an oxazoline compound, (B) Epan U-103 as an aliphatic compound having a hydrocarbon group in the side chain, (C) EX-931, EX-321 as an epoxy compound are effective component ratios (mass). The sizing treatment was performed in the same manner as in Example 1 except that the sizing solution was prepared by mixing the components at a ratio of 18.75 / 25 / 37.5 / 3.75. The amount of the sizing agent attached was 0.76%. In Example 5 in which the ratio of the (A) oxazoline compound was 18.75%, a composite material having a high amount of fluff but high adhesiveness and excellent properties was obtained.

[Comparative Example 1]
(A) Oxazoline compound is not used as the sizing agent, and (B) Upol U is used as the aliphatic compound having a hydrocarbon group in the side chain, and (C) The epoxy compound N320 of the urethane-modified epoxy compound is used as an effective component ratio (mass ratio). The mixture was mixed at a ratio of 90/10 to obtain a sizing solution. The carbon fiber obtained in Comparative Example 1 which did not use the (A) oxazoline compound as a sizing agent had a microdroplet value of 46 MPa, which was lower than that in Example 1, and had insufficient adhesiveness with a resin. The composite material had inferior properties.

[Comparative example 2]
Without using the (A) oxazoline compound as the sizing agent, (B) Epan U-103 as the aliphatic compound having a hydrocarbon group in the side chain, (C) the epoxy compound EX-931, EX-321 as the active ingredient ratio ( (Mass ratio) 25/45/30 were mixed to obtain a sizing solution. In Comparative Example 2 in which the (A) oxazoline compound was not used as the sizing agent, the convergence was poor and the handleability was poor, and the value of the microdroplet was 49 MPa, which was lower than that in Example 1, and the adhesiveness to the resin was poor. It was enough.

[Comparative Example 3]
(A) Only Epocros WS-700, which is an oxazoline compound, was used as a sizing solution. In Comparative Example 3 in which the (B) aliphatic compound having a hydrocarbon group in the side chain was not used as the sizing agent and only the (A) oxazoline compound was used, the adhesiveness was lower than in the Examples, and the yarn was hard and handled. The carbon fiber was inferior in properties and had a very high MPF value of 200 μg / ft and was fluffy and poor in quality.

  Since the carbon fiber-reinforced composite material produced by using the carbon fiber to which the sizing agent of the present invention is applied has excellent adhesiveness with the matrix resin, it is possible to obtain a carbon fiber-reinforced composite material having excellent mechanical properties.

Claims (8)

  A sizing agent composition comprising at least (A) an oxazoline compound and (B) an aliphatic compound having a hydrocarbon group in a side chain.   The sizing agent composition according to claim 1, further comprising (C) an epoxy compound.   The sizing agent composition according to claim 1 or 2, wherein the ratio of the (A) oxazoline compound is 5 to 95 wt%.   The sizing agent composition according to claim 1, wherein the (A) oxazoline compound is water-soluble.   A method for producing carbon fibers, which comprises applying the sizing agent according to any one of claims 1 to 4 to carbon fibers.   A carbon fiber to which the sizing agent according to any one of claims 1 to 4 is attached.   The carbon fiber according to claim 6, wherein the amount of the sizing agent attached is 0.1 to 10 mass% with respect to the carbon fiber.   A carbon fiber composite material comprising the carbon fiber according to claim 6 and a matrix resin.