Sizing agent for inorganic fiber, inorganic fiber and manufacturing process for the same and composite material

Abstract

A sizing agent for inorganic fibers, comprising: at least one carbon nanostructure selected from a group consisting of carbon nanotubes and carbon nanofibers, a resin, and a surfactant;wherein, when the total content of a non-volatile component of resin and surfactant is assumed to be 100 parts by mass, the sizing agent for inorganic fibers contains the surfactant in a ratio of 2 to 50 parts by mass, wherein the resin comprises at least one substance selected from a group consisting of a vinyl ester resin, a polyamide resin, a polyolefin resin, a polyurethane resin, a polyester resin, a polyimide resin, and a polyimide resin precursor, wherein the surfactant is an ether-type nonionic surfactant, a polyoxyalkylene polyhydric alcohol fatty acid ester type nonionic surfactant, an alkylamide type nonionic surfactant, a polyoxyalkylene fatty acid amide type nonionic surfactant, or an ether-ester compound;

Description

TECHNICAL AREA

[0001] The present invention relates to a sizing agent for inorganic fibers having a carbon nanostructure, an inorganic fiber, a manufacturing process for an inorganic fiber and a composite material. TECHNICAL BACKGROUND

[0002] Fiber-reinforced thermoplastic resin composites are generally known as materials containing inorganic fibers, such as carbon fibers, and a matrix resin, such as a thermoplastic resin. This matrix resin serves as the base material and has diverse applications, for example, in the fields of building materials and transportation equipment. A treatment involving the application of a sizing agent to the inorganic fibers is carried out to improve the adhesion properties of the interface between the inorganic fibers, such as carbon fibers, and the base material, such as a thermoplastic resin.

[0003] For example, patent document 1 discloses a sizing agent for carbon fibers, which is used to reinforce a thermoplastic matrix resin. The carbon fiber sizing agent contains a polymer component that exhibits parameters such as a predetermined glass transition point. The mass ratio of the polymer component relative to the total non-volatile content of the sizing agent lies within a predetermined range. The polymer component is, for example, an aromatic polyester resin. Non-patent literature 1 describes polymer composites with carbon nanotube epoxies as reinforcing material. Non-patent literature 2 describes a method for dispersing single-walled carbon nanotubes in epoxy resins. Patent document 2 describes the production of epoxy polymer composites reinforced with carbon nanotubes. Non-patent literature 3 describes phenoxy resins.Patent document 3 describes a mesh element consisting of a mesh fabric and a coating formed on the surface of the mesh fabric, which contains carbon nanotubes and / or graphene. LIST OF COUNTER-POINTS PATENT LITERATURE Patent Publication 1: WO 2013 / 058 200 A1 Non-patent literature 1: Gong X. et al.: Surfactant-Assisted Processing of Carbon Nanotube / Polymer Composites. Chem. Mater. 2000, 12, 4, 1049-1052 Non-patent literature 2: SPINDLER-RANTA, Sean ; BAKIS, Charles, E.: Carbon nanotube reinforcement of a filament winding resin. In: 47th International SAMPE symposium, Vol. 47, 2002, pp. 1775-1787. - ISSN 0891-0138 Patent Publication 2: WO 2005 / 028 174 A2 Non-patent literature 3: Römpp: Phenoxy resins URL: https: / / roempp.thieme.de / lexicon / RD-16-01628 Patent Publication 3: WO 2019 / 176 933 A1 OVERVIEW OF THE INVENTIONAL PROBLEM

[0004] However, the improvement in adhesion properties achieved by the sizing agent according to patent specification 1 is not sufficient relative to the base material. SOLUTION TO THE PROBLEM

[0005] The inventors of the present application therefore carried out investigations aimed at solving the above-mentioned problem and found that a sizing agent for inorganic fibers, comprising a carbon nanostructure, for example a carbon nanotube, and a resin, is suitable and appropriate.

[0006] To solve the aforementioned problem and according to one aspect of the present invention, a sizing agent for inorganic fibers is provided, comprising: at least one carbon nanostructure selected from a group consisting of carbon nanotubes and carbon nanofibers, a resin, and a surfactant; and characterized in that, assuming the total content of a non-volatile component of the resin and surfactant to be 100 parts by mass, the sizing agent for inorganic fibers contains the surfactant in a ratio of 2 to 50 parts by mass. The resin comprises at least one substance selected from a group consisting of a vinyl ester resin, a polyamide resin, a polyolefin resin, a polyurethane resin, a polyester resin, a polyimide resin, and a polyimide resin precursor.The surfactant is an ether-like non-ionic surfactant, a non-ionic surfactant of the type of a polyoxyalkylene polyhydric alcohol and fatty acid ester, a non-ionic surfactant of the alkylamide type, a non-ionic surfactant of the polyoxyalkylene fatty acid amide type, or an ether-ester compound.

[0007] In the sizing agent for inorganic fibers, the carbon nanostructure can include carbon nanotubes, and the carbon nanotubes can comprise single-walled carbon nanotubes.

[0008] In the sizing agent for inorganic fibers, the proportion of carbon nanostructure in the non-volatile component of the resin can be at least 100 ppm and at most 50,000 ppm.

[0009] In the case of the sizing agent for inorganic fibers, the resin may contain a polyolefin resin in an embodiment not covered by the scope of protection.

[0010] The sizing agent for inorganic fibers can be applied to a glass fiber or a carbon fiber.

[0011] In an embodiment not covered by the scope of protection, the resin in the sizing agent for inorganic fibers may be an epoxy resin; if so, the sizing agent for inorganic fibers may be applied to a composite material in which the matrix resin is an epoxy resin, and also to an inorganic fiber that forms part of the composite material.

[0012] The resin in the sizing agent for inorganic fibers can be at least one substance selected from a group comprising: a polyamide resin, a polyurethane resin, a polyimide resin and a polyimide resin precursor, and if this is the case, the sizing agent for inorganic fibers can be used with a composite material in which the matrix resin is a polyamide resin, and also with an inorganic fiber that forms part of the composite material.

[0013] The resin in the sizing agent for inorganic fibers can be a vinyl ester resin; if so, the sizing agent for inorganic fibers can be used with a composite material in which a matrix resin is a vinyl ester resin, and also with an inorganic fiber that forms part of the composite material.

[0014] The resin in the sizing agent for inorganic fibers can be a polyolefin resin, and if so, the sizing agent for inorganic fibers can be used with a composite material in which a matrix resin is a polyolefin resin, and also with an inorganic fiber that forms part of the composite material.

[0015] Another aspect of the present invention provides an inorganic fiber to which the sizing agent for inorganic fibers is adhered.

[0016] Another aspect of the present invention provides a method for producing an inorganic fiber, which includes the adhesion of the sizing agent for inorganic fibers to an inorganic fiber.

[0017] Another aspect of an embodiment not covered by the scope of protection provides a composite material containing an inorganic fiber and a matrix resin, characterized in that the resin in the sizing agent for inorganic fibers is an epoxy resin and the matrix resin is an epoxy resin.

[0018] Another aspect of the invention provides a composite material containing the inorganic fiber and a matrix resin, characterized in that the resin in the sizing agent for inorganic fibers is at least one substance selected from a group comprising a polyamide resin, a polyurethane resin, a polyimide resin and a polyimide resin precursor, wherein the matrix resin is a polyamide resin.

[0019] Another aspect of the present invention provides a composite material comprising the inorganic fiber and a matrix resin, characterized in that the resin in the sizing agent for inorganic fibers is a vinyl ester resin, wherein the matrix resin is a vinyl ester resin.

[0020] Another aspect of the invention provides a composite material which contains the inorganic fiber and a matrix resin and is characterized in that the resin in the sizing agent for inorganic fibers is a polyolefin resin, wherein the matrix resin is a polyolefin resin. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0021] The present invention achieves an improvement in the adhesion properties of an inorganic fiber with respect to a base material in a composite material. BRIEF DESCRIPTION OF THE DRAWINGS The Fig.Figure 1 is a schematic representation of a device for evaluating a composite material interface characteristic for assessing an adhesion property in the sections with the examples. DESCRIPTION OF THE EXAMPLES OF EXECUTION <Erstes Ausführungsbeispiel

[0022] First, a first embodiment is described below, which is designed as a sizing agent for inorganic fibers according to the present invention (hereinafter also referred to as sizing agent). (Carbon nanostructure)

[0023] The sizing agent contains at least one carbon nanostructure selected from carbon nanotubes and carbon nanofibers, as well as a resin. Carbon nanotubes generally have a cylindrical structure in which a graphene layer is rolled around the center of a fiber. Carbon nanofibers generally have a layered structure of graphene layers that is either obliquely or perpendicularly layered relative to a fiber longitudinal direction, with the edge surfaces of the graphene layers exposed at the fiber surfaces.

[0024] The carbon nanotubes can be single-walled carbon nanotubes with a single layer, or they can be multi-walled carbon nanotubes with several layers, such as double-walled carbon nanotubes with two layers. Of these, single-walled carbon nanotubes are preferable insofar as the effect produced by the sizing agent can be further enhanced to improve the adhesion of an inorganic fiber to a substrate material of a composite.

[0025] Carbon nanotubes come in three types: zigzag, chair, and chiral, corresponding to differences in the geometric structure of carbon nanosheets. Any of these types can be used. It is also possible to use chemically modified carbon nanotubes, such as those modified with carboxyl groups.

[0026] Specific examples of carbon nanostructures include single-layer carbon nanotubes manufactured by Nanocyl SA, single-layer carbon nanotubes (trade name: TUBALL) manufactured by OCSiAL, two-layer carbon nanotubes manufactured by Nanocyl SA, multi-layer carbon nanotubes manufactured by Nanocyl SA, carboxyl group-modified multi-layer carbon nanotubes manufactured by Nanocyl SA, and reinforcing carbon nanofibers manufactured by ALMEDIO Inc. One type of such nanostructure can be used alone, or two or more types can be used in combination. (Resin)

[0027] The resin is selected appropriately from known resins, according to the application of the inorganic fiber for which the sizing agent is used. Specific examples of resins include epoxy resin, vinyl ester resin, polyamide resin, polyolefin resin, polyurethane resin, polycarbonate resin, polyester resin, PEEK resin, fluorinated resin, phenoxide resin, phenolic resin, BMI resin, polyimide resin, polyimide resin precursor, and polyethersulfone resin. Of these, epoxy resin, vinyl ester resin, polyamide resin, polyolefin resin, polyurethane resin, polyester resin, phenoxide resin, polyimide resin, and polyimide resin precursor are preferred.

[0028] Particularly specific examples of the resin are epoxy resins (manufactured by Mitsubishi Chemical Corporation under the trade names jER828 and jER1002), a polyurethane resin (manufactured by DKS Co., Ltd. under the trade name Superflex 500M), a modified polypropylene resin (manufactured by Maruyoshi Chemical Co., Ltd. under the trade name MGP-1650), a modified polypropylene resin (manufactured by TOHO Chemical Industry Co., Ltd. under the trade name Hitech P-9018), a modified polyester resin (manufactured by Toyobo Co., Ltd. under the trade name Vylonal MD-1480), a phenoxide resin (manufactured by NIPPON STEEL Chemical and Material Co., Ltd. under the trade name YP-50S), a polyimide resin precursor of 3,3',4,4'-biphenyltetracarboxylic anhydride and a diaminodiphenyl ether, and a polyamide resin (manufactured by Toray Industries Inc.).(trade name AQ Nylon P-95), a polyester resin consisting of a 2-mol ethylene oxide adduct of bisphenol A and fumaric acid, and a vinyl ester resin consisting of an epoxy resin and methacrylic acid.

[0029] If the sizing agent is used in an application where it is applied to an inorganic fiber that is part of a composite material which in turn has a resin matrix as its base material, the type of resin integrated into the sizing agent is preferably selected with respect to the type of matrix resin, for the purpose of improved adhesion of the inorganic fiber to the matrix resin and improved recyclability. If the matrix resin is an epoxy resin, the resin in the sizing agent is preferably also an epoxy resin. If the matrix resin is a polyamide resin, the resin in the sizing agent is preferably at least one substance selected from a polyamide resin, a polyurethane resin, a polyimide resin, and a polyimide resin precursor. If the matrix resin is a vinyl ester resin, the resin in the sizing agent is preferably a vinyl ester resin.If the matrix resin is a polyolefin resin, then the resin in the sizing agent is preferably at least one substance selected from a polyolefin resin and a phenoxide resin.

[0030] In the sizing agent, the proportion of carbon nanostructure in a non-volatile component of the resin is appropriately adjusted and is preferably at least 100 ppm and at most 50,000 ppm. Specifying this value further enhances the sizing agent's effectiveness in improving the adhesion of the inorganic fiber to the base material of the composite. As used here, the term "non-volatile component" refers to a residue remaining after volatile substances have been sufficiently removed by a two-hour heat treatment of the object at 105°C; that is, to an absolutely dry substance.

[0031] The ratio between the amount of carbon nanostructure contained in the sizing agent and the amount of the non-volatile component of the resin in the sizing agent may, for example, be at least 220 ppm, at least 400 ppm, at least 600 ppm, at least 700 ppm, at least 800 ppm, at least 1,000 ppm, at least 1,400 ppm, at least 1,500 ppm, at least 2,000 ppm, at least 2,500 ppm, at least 3,500 ppm, at least 4,000 ppm, at least 5,000 ppm, at least 10,000 ppm, at least 30,000 ppm, or at least 48,000 ppm, or this ratio may be at most 48,000 ppm, at most 30,000 ppm, at most 10,000 ppm, at most 5,000 ppm, at most 4,000 ppm, at most 3,500 ppm, at most 2,500 ppm, at most 2,000 ppm, at most 1,500 ppm, at most 1,400 ppm, at most 1,000 ppm, at most 800 ppm, at most 700 ppm, at most 600 ppm, at most 400 ppm or at most 220 ppm. (surfactant)

[0032] The sizing agent further comprises a surfactant. By integrating the surfactant into the sizing agent, the carbon nanostructure is formed in such a way that it cannot be readily detached from the inorganic fiber after application of the sizing agent; that is, the property of preventing detachment of the carbon nanostructure can be improved. According to the invention, the surfactant is an ether-like non-ionic surfactant, a non-ionic surfactant of the type of a polyoxyalkylene polyhydric alcohol and fatty acid ester, a non-ionic surfactant of the alkylamide type, a non-ionic surfactant of the polyoxyalkylene fatty acid amide type, or an ether-ester compound. Examples of the surfactant are, for example, an anionic surfactant, a cationic surfactant, a non-ionic surfactant, and an amphoteric surfactant. One type of such surfactant can be used alone, or two or more types can be used in combination. Specific examples of the non-ionic surfactant include, among others: (1) a compound in which an alkylene oxide having 2 to 4 carbon atoms is added to an organic acid, an organic alcohol, an organic amine and / or an organic amide, for example an ether-like non-ionic surfactant such as polyoxyethylene dialuric acid ester, polyoxyethylene oleic acid ester, polyoxyethylene oleic acid diester, polyoxyethylene octyl ether, polyoxyethylene lauryl ether, polyoxyethylene lauryl ether methyl ether, polyoxyethylene-polyoxypropylene lauryl ether, polyoxypropylene lauryl ether methyl ether, polyoxyethylene oleyl ether, polyoxybutylene oleyl ether, polyoxyethylene-polyoxypropylene nonyl ether, polyoxypropylene nonyl ether, polyoxyethylene-polyoxypropylene octyl ether, ethylene oxide adduct of 2-hexylhexanol, Polyoxyethylene 2-ethyl 1-hexyl ether, polyoxyethylene isononyl ether, polyoxyethylene dodecyl ether, a compound in which ethylene oxide is added to a secondary dodecyl alcohol, polyoxyethylene tridecyl ether, polyoxyalkylene tetradecyl ether,Polyoxyethylene laurylamino ether, polyoxyethylene lauramide ether or polyoxyalkylene tristyrene phenyl ether, (2) a non-ionic surfactant of the type of an ester of polyoxyalkylene polyhydric alcohol and fatty acid, such as polyoxyalkylene sorbitan trioleate, polyoxyalkylene coconut oil, polyoxyalkylene castor oil, polyoxyalkylene castor oil (hydrogenated), polyoxyalkylene castor oil (hydrogenated) trioctanoate or maleic acid esters, stearic acid esters or oleic acid esters of polyoxyalkylene castor oil (hydrogenated), (3) a non-ionic surfactant of the alkylamide type, such as stearic acid diethanolamide or diethanolamine monolauramide, (4) a non-ionic surfactant of the polyoxyalkylene fatty acid amide type, such as polyoxyethylene diethanolamine monooleylamide, polyoxyethylene laurylamine or polyoxyethylene bovine tallow, as well as (5) an ether-ester compound, such as a copolymer of polyoxyethylene, dimethyl phthalate and lauryl alcohol.

[0033] A known anionic surfactant can be used in a suitable manner in an embodiment not covered by the scope of protection. Specific examples of the anionic surfactant include, among others... (1) a phosphoric acid ester salt of an aliphatic alcohol, such as a lauryl phosphoric acid ester salt, a cetyl phosphoric acid ester salt, an octyl phosphoric acid ester salt, an oleyl phosphoric acid ester salt or a stearyl phosphoric acid ester salt, (2) a phosphoric acid ester salt of an adduct of at least one type of alkylene oxide (selected from ethylene oxide and propylene oxide) with an aliphatic alcohol, such as a polyoxyethylene lauryl ether phosphoric acid ester salt, a polyoxyethylene oleyl ether phosphoric acid ester salt or a polyoxyethylene stearyl ether phosphoric acid ester salt, (3) an aliphatic sulfonic acid salt or an aromatic sulfonic acid salt, such as a lauryl sulfonic acid salt, a myristyl sulfonic acid salt, a cetyl sulfonic acid salt, an oleyl sulfonic acid salt, a stearyl sulfonic acid salt, a tetradecane sulfonic acid salt, a dodecylbenzene sulfonic acid salt or a secondary alkyl (C13-C15) sulfonic acid salt, (4) a sulfuric acid ester salt of an aliphatic alcohol, such as a lauryl sulfuric acid ester salt, an oleyl sulfuric acid ester salt or a stearyl sulfuric acid ester salt, (5) a sulfuric acid ester salt of an adduct of at least one type of alkylene oxide (selected from ethylene oxide and propylene oxide) with an aliphatic alcohol, such as a polyoxyethylene lauryl ether sulfuric acid ester salt, a polyoxyalkylene (polyoxyethylene, polyoxypropylene) lauryl ether sulfuric acid ester salt or a polyoxyethylene oleyl ether sulfuric acid ester salt, (6) a sulfuric acid ester salt of a fatty acid, such as a castor oil fatty acid sulfuric acid ester salt, a sesame oil fatty acid sulfuric acid ester salt, a tall oil fatty acid sulfuric acid ester salt, a soybean oil fatty acid sulfuric acid ester salt, a rapeseed oil fatty acid sulfuric acid ester salt, a palm oil fatty acid sulfuric acid ester salt, a lard fatty acid sulfuric acid ester salt, a beef tallow fatty acid sulfuric acid ester salt or a fish oil fatty acid sulfuric acid ester salt, (7) a sulfuric acid ester salt of an oil or fat, such as a sulfuric acid ester salt of castor oil, a sulfuric acid ester salt of sesame oil, a sulfuric acid ester salt of tall oil, a sulfuric acid ester salt of soya oil, a sulfuric acid ester salt of rapeseed oil, a sulfuric acid ester salt of palm oil, a sulfuric acid ester salt of lard, a sulfuric acid ester salt of beef tallow or a sulfuric acid ester salt of fish oil, (8) a fatty acid salt, such as lauric acid salts, oleic acid salts, stearic acid salts, etc. and (9) a sulfosuccinic acid ester salt of an aliphatic alcohol, such as dioctyl sulfosuccinic acid ester salt.

[0034] Examples of a counterion of the anionic surfactant include: a potassium salt, a sodium salt and other alkali metal salts, an ammonium salt, triethanolamine and other alkanolamine salts.

[0035] A known cationic surfactant can be used in a suitable manner in an embodiment not covered by the scope of protection. Specific examples of the cationic surfactant include lauryl trimethylammonium chloride, cetyl trimethylammonium chloride, stearyl trimethylammonium chloride, behenyl trimethylammonium chloride, didecyl dimethylammonium chloride, 1,2-dimethylimidazole, and triethanolamine.

[0036] A known amphoteric surfactant can be used in a suitable manner in an embodiment not covered by the scope of protection. Specific examples of an amphoteric surfactant include a betaine-type amphoteric surfactant.

[0037] If the sizing agent contains the surfactant, the proportion of the carbon nanostructure in the total amount of the non-volatile component of resin and surfactant is specified accordingly and is preferably at least 50 ppm and at most 40,000 ppm. Specifying this value further enhances the sizing agent's effectiveness in improving the adhesion of the inorganic fiber to the base material of the composite.

[0038] The ratio of the amount of carbon nanostructure contained in the sizing agent relative to the total amount of non-volatile resin and surfactant can be, for example, at least 110 ppm, at least 240 ppm, at least 360 ppm, at least 595 ppm, at least 700 ppm, at least 750 ppm, at least 784 ppm, at least 950 ppm, at least 1,400 ppm, at least 1,470 ppm, at least 1,750 ppm, at least 1,900 ppm, at least 2,100 ppm, at least 3,000 ppm, at least 9,500 ppm, at least 19,500 ppm, or at least 33,600 ppm. or may be at most 33,600 ppm, at most 19,500 ppm, at most 9,500 ppm, at most 3,000 ppm, at most 2,100 ppm, at most 1,900 ppm, at most 1,750 ppm, at most 1,470 ppm, at most 1,400 ppm, at most 950 ppm, at most 784 ppm, at most 750 ppm, at most 700 ppm, at most 595 ppm, at most 360 ppm, at most 240 ppm or at most 110 ppm.

[0039] Assuming a total content of resin and surfactant in the non-volatile component of 100 parts by mass, the sizing agent contains the surfactant in a ratio of 2 to 50 parts by mass. This ratio can be, for example, at least 5 parts by mass, at least 15 parts by mass, at least 25 parts by mass, at least 30 parts by mass, at least 35 parts by mass, or at least 40 parts by mass, or it can be at most 40 parts by mass, at most 35 parts by mass, at most 30 parts by mass, at most 25 parts by mass, at most 15 parts by mass, or at most 5 parts by mass.

[0040] The following effects, for example, can be achieved with the slurry according to the present embodiment.

[0041] (1-1) The sizing agent according to the present embodiment comprises at least one carbon nanostructure selected from carbon nanotubes and carbon nanofibers, as well as a resin. When such a sizing agent is adhered to an inorganic fiber, the inorganic fiber can be improved with respect to its bundle properties and its adhesion properties to a substrate of a composite material. This improvement in adhesion is assumed to be based on an anchoring effect resulting from the formation of irregularities on the surface of the inorganic fiber, to which the sizing agent adheres, and from the transfer of part of the carbon nanostructure to the substrate. The property of preventing detachment of the carbon nanostructure from the inorganic fiber can also be improved. <Zweites Ausführungsbeispiel>

[0042] Next, a second embodiment is described, which is designed as a method for producing an inorganic fiber according to the present invention. Facts that differ from those described below with regard to the second embodiment correspond to the facts in the first embodiment.

[0043] The process for producing an inorganic fiber according to the present embodiment comprises the adhesion of the sizing agent according to the first embodiment to a carbon fiber. There is no specific limitation regarding the amount of sizing agent (apart from a solvent), and the adhesion is preferably carried out such that the amount of sizing agent is not less than 0.01% and not more than 10% by mass relative to the inorganic fiber. Due to the specification within such a numerical range, the effect on the bundle properties of the inorganic fiber can be further improved. (Inorganic fiber)

[0044] There is no specific restriction regarding the type of inorganic fiber that can be used with the present embodiment; it can therefore be glass fiber, carbon fiber, ceramic fiber, metal fiber, mineral fiber, rock fiber, or slag fiber. Of these, glass fiber and carbon fiber are preferred because the effects of the present invention can be implemented more effectively with them. Examples of carbon fiber types include, among others, a PAN-based carbon fiber obtained using an acrylic fiber as a starting material, a pitch-based carbon fiber obtained using pitch as a starting material, as well as a recycled carbon fiber and a carbon fiber obtained using a polyester fiber, a polyethylene resin, a phenolic resin, a cellulose resin, or a lignin resin as a starting material.

[0045] To adhere the sizing agent to the inorganic fiber according to the first embodiment, a commonly used industrial process can be employed. Examples include, but are not limited to, dip roller coating, contact roller coating, spray coating, and papermaking processes. The inorganic fiber to which the sizing agent has adhered can then be dried using a conventional method.

[0046] In addition to the effects of the first embodiment, the method for producing an inorganic fiber according to the present embodiment can achieve further effects, such as the following.

[0047] (2-1) The process for producing an inorganic fiber according to the present embodiment comprises the adhesion of a sizing agent comprising a carbon nanostructure and a resin to a carbon fiber. This improves the property of preventing the carbon nanostructure from detaching from the inorganic fiber. Furthermore, the application of the sizing agent to the inorganic fiber is carried out in a single step and is therefore efficient; in other words, process efficiency can also be improved. <Drittes Ausführungsbeispiel>

[0048] Next, a third embodiment is described, which is designed as a composite material according to the present invention. Any aspects that differ from those described below with regard to the third embodiment correspond to those in the first and second embodiments.

[0049] The composite material is obtained by impregnating the inorganic fiber, to which the sizing agent has been adhered using the second embodiment, with a resin matrix as the base material. There are no specific restrictions regarding the shape of the inorganic fiber in the production of the composite material; examples include long fibers, short fibers, and nonwoven fabrics. (Matrix resin)

[0050] The matrix resin is selected appropriately from known resins that are suitable for the intended purpose or application of the composite material. Specific examples of matrix resins include vinyl ester resin, polyamide resin, polyolefin resin, polyurethane resin, polycarbonate resin, polyester resin, PEEK resin, fluorinated resin, phenolic resin, BMI resin, polyimide resin, polyimide resin precursor, and polyethersulfone resin.

[0051] The matrix resin can be selected taking into account the type of resin contained in the sizing agent, for example, with regard to improved adhesion properties to the inorganic fiber and improved recyclability. In an embodiment not covered by the scope of protection, the matrix resin is an epoxy resin, and the resin in the sizing agent is preferably an epoxy resin. If the matrix resin is a polyamide resin, the resin in the sizing agent is preferably at least one substance selected from a polyamide resin, a polyurethane resin, a polyimide resin, and a polyimide resin precursor. If the matrix resin is a vinyl ester resin, the resin in the sizing agent is preferably a vinyl ester resin. If the matrix resin is a polyolefin resin, the resin in the sizing agent is a polyolefin resin.

[0052] The composite material according to the present embodiment can achieve, for example, the following effects.

[0053] (3-1) The inorganic fiber contained in the composite material according to the present embodiment has a sizing agent pre-bonded to it, which contains a carbon nanostructure and a resin. This results in a fiber-reinforced resin composite material, distinguished primarily by its mechanical properties and various other properties, due to the excellent adhesion properties of the inorganic fiber and the matrix resin.

[0054] The embodiments described above can be modified as follows. The embodiments described above and the following modifications are feasible by combining them within a technically reasonable range.

[0055] The sizing agent from the embodiments described above does not preclude the integration of a further component, such as water or an organic solvent, a smoothing agent, an antioxidant or a preservative, provided that this does not impair the effects of the present invention, for example with regard to the performance of the sizing agent to be maintained and with regard to improved application properties in relation to an inorganic fiber.

[0056] There is no specific restriction regarding the area in which the sizing agent from the embodiments described above is used. It can be used, for example, for a carbon fiber reinforced polymer (CFRP) impregnated with a matrix resin, such as a polyimide resin, as well as for a fiber used to reinforce concrete. EXAMPLES

[0057] The following are examples given to describe in more detail the features and effects of the present invention; however, the present invention is not limited to these examples. Experimental Part 1 (Production of sizing agents)

[0058] In the production of a non-protected sizing agent according to Example 1, the following starting materials were prepared: single-layer zigzag-type carbon nanotubes (A-1) listed in Table 1 as carbon nanostructure, an epoxy resin (B) listed in Table 2 as resin (B), and a random adduct of 30 mol ethylene oxide and 5 mol propylene oxide with tristyrene phenol (C1) listed in Table 3 as surfactant (C); A mixture obtained by mixing the same was heated to 100°C and made uniform, and then cooled to 70°C or less; then water was added stepwise to produce an aqueous solution of the sizing agent according to Example 1.

[0059] In the preparation of sizing agents according to the invention as shown in Examples 3, 5, 6, 14 and 15, the carbon nanostructures (A) from Table 1, the resins (B) from Table 2 and optionally the surfactants (C) from Table 3 were prepared as starting materials. Aqueous solutions of the sizing agents were then obtained using the preparation methods A to D listed below. A: A mixture of the respective starting materials was heated to 100°C and homogenized, then cooled to 70°C or less; then water was added stepwise to produce an aqueous solution of a sizing agent. B: An aqueous solution of a sizing agent was obtained by mixing a pre-prepared resin emulsion, a pre-prepared aqueous dispersion of a carbon nanostructure, and a surfactant. C: An aqueous solution of a sizing agent was obtained by mixing a pre-prepared resin emulsion and a surfactant. D: An aqueous solution of a sizing agent was obtained by gradually adding water to a mixture of a resin and a surfactant.

[0060] The type and proportion of carbon nanostructure (A), resin (B), and surfactant (C) contained in the respective aqueous solution of the sizing agent obtained in this way, as well as the manufacturing process for the sizing agent, are listed in Table 4 in the columns "Carbon Nanostructure (A)," "Resin (B)," "Surfactant (C)," and "Mixing Method During Production," respectively. The non-volatile fraction of the resin (B) was measured using the following method: 1 g of a sample was placed on an aluminum dish (whose mass had been measured beforehand) and subjected to a two-hour heat treatment at 105°C. The mass of the resulting completely dry substance was then measured, and the non-volatile fraction was calculated using the following formula: Non-volatile fraction (mass %) = (mass of absolutely dry substance after heat treatment / (mass of sample before heat treatment) × 100

[0057] Table 1 category Carbon nanostructure (A) A-1 Single-layer carbon nanotubes (zigzag type) A-2 Single-layer carbon nanotubes (chair type) A-3 Single-layer carbon nanotubes (chiral type) A-4 Single-layer carbon nanotubes (manufactured by Nanocyl SA; Aldrich product no. 755710) A-5 Single-layer carbon nanotubes SWCNT 80% (manufactured by OCSiAl; trade name: TUBALL) A-6 Single-layer carbon nanotubes SWCNT 93% (manufactured by OCSiAl; trade name: TUBALL) A-7 Two-layer carbon nanotubes (manufactured by Nanocyl SA; Aldrich product no. 755141) A-8 Multilayer carbon nanotubes (manufactured by Nanocyl SA; Aldrich product no. 755133) A-9 Carboxyl group-modified multilayer carbon nanotubes (manufactured by Nanocvl SA; Aldrich product no. 755125) A-10 Reinforcing carbon nanofibers (manufactured by ALMEDIO Inc.)

[0058] Table 2 category Harz (B) non-volatile fraction (mass%) B-1 Epoxy resin (manufactured by Mitsubishi Chemical Corporation; trade name: jER828) 100 B-2 Epoxy resin (manufactured by Mitsubishi Chemical Corporation; trade name: jER1002) 100 B-3 Polyurethane resin (manufactured by DKS Co., Ltd.; trade name: Superflex 500M) 45 B-4 Modified polypropylene resin (manufactured by Maruvoshi Chemical Co., Ltd.; trade name: MGP-1650) 30 B-5 Modified polypropylene resin (manufactured by TOHO Chemical Industry Co., Ltd.; trade name: Hitech P-9018) 35 B-6 Modified polyester resin (manufactured by Toyobo Co., Ltd.; trade name: Vylonal MD-1480) 25 B-7 Phenoxide resin (manufactured by NIPPON STEEL Chemical and Material Co., Ltd.; trade name YP-50S) 100 B-8 Polyimide resin precursor of 3,3',4,4'-biphenyltetracarboxylic anhydride and a diaminodiphenyl ether 10 B-9 Polyamide resin (manufactured by Toray Industries Inc.; trade name: AQ Nylon P-95) 50 B-10 Polyester resin consisting of a 2-mol ethylene oxide adduct of bisphenol A and fumaric acid 100 B-11 Vinyl ester resin made from an epoxy resin and methacrylic acid 100

[0059] Table 3 category Surfactant (C) C-1 Random adduct of 30 mol ethylene oxide and 5 mol propylene oxide with tristyrenephenol C-2 Compound in which 10 moles of ethylene oxide are added to dodecyl alcohol C-3 Compound in which 15 moles of ethylene oxide are added to isononyl alcohol C-4 Compound in which 10 moles of ethylene oxide and 5 moles of propylene oxide are added to tetradecimal alcohol C-5 Compound in which 7 moles of ethylene oxide are added to secondary dodecyl alcohol C-6 Sodium dodecylbenzenesulfonate C-7 1,2-Dimethylimidazol C-8 Triethanolamine C-9 Copolymer of polyethylene glycol with an average molecular weight of 2000, dimethyl terephthalate and lauryl alcohol

[0060] Table 4 Carbon nanostructure(A) Harz (B) Surfactant (C) Mixing method during production Inorganic fiber used to assess adhesion properties Matrix resin used to assess adhesion properties Evaluation type Amount added (ppm)*1 Amount added (ppm)*2 type Mass parts *3 type Mass parts Adhesion property Property of preventing detachment Process efficiency bundle property Example 1 A-1 1000 700 B-1 70 C-1 30 A carbon fiber epoxy resin ◯◯ ◯◯ ◯ ◯ Example 2 A-2 4000 3000 B-1B-2 4035 C-1 25 A carbon fiber epoxy resin ◯◯ ◯◯ ◯ ◯ Example 3 A-3 2000 1900 B-3 95 C-2 5 B carbon fiber Polyamide resin ◯◯ ◯◯ ◯ ◯ Example 4 A-4 700 595 B-1B-3 4540 C-1C-3 105 B carbon fiber epoxy resin ◯◯ ◯◯ ◯ ◯ Example 5 A-5 1500 1470 B-4 98 C-4 2 B carbon fiber Polypropylene resin ◯◯ ◯◯ ◯ ◯ Example 6 A-6 800 784 B-5 98 C-6 2 B fiber optics Polypropylene resin ◯◯ ◯◯ ◯ ◯ Example 7 A-5 1000 950 B-6 95 C-5 5 B carbon fiber epoxy resin ◯◯ ◯◯ ◯ ◯ Example 8 A-4A-6 5001000 250500 B-1B-7 4010 C-1 50 A carbon fiber epoxy resin ◯◯ ◯◯ ◯ ◯ Example 9 A-3 5000 3000 B-8 60 C-7 40 B carbon fiber er Polyamide resin ◯◯ ◯◯ ◯ ◯ Example 10 A-4 10000 9500 B-9 95 C-8 5 B carbon fiber Polyamide resin ◯◯ ◯◯ ◯ ◯ Example 11 A-5 2500 1750 B-1B-10 3040 C-1C-9 282 A carbon fiber epoxy resin ◯◯ ◯◯ ◯ ◯ Example 12 A-3 220 110 B-8 50 C-7 50 B carbon fiber Polyamide resin ◯◯ ◯◯ ◯ ◯ Example 13 A-5 48000 33600 B-1B-10 4030 C-1 30 A fiber optics epoxy resin ◯◯ ◯◯ ◯ ◯ Example 14 A-6 600 360 B-11 60 C-1 40 A carbon fiber Vinyl ester resin ◯◯ ◯◯ ◯ ◯ Example 15 A-7 400 240 B-11 60 C-1 40 A fiber optics Vinyl ester resin ◯ ◯◯ ◯ ◯ Example 16 A-8 3500 2100 B-1B-10 2040 C-1 40 A fiber optics epoxy resin ◯ ◯◯ ◯ ◯ Example 17 A-9 30000 19500 B-11 65 C-1 35 A carbon fiber Vinyl ester resin ◯ ◯◯ ◯ ◯ Example 18 A-10 400 240 B-11 60 C-1 40 A carbon fiber Vinyl ester resin ◯ ◯◯ ◯ ◯ Reference example 19 A-3 1400 1400 B-4 100 B carbon fiber Polypropylene resin ◯ ◯ ◯ ◯ Comparative example 1 B-6 95 C-5 5 C carbon fiber epoxy resin × ◯◯ ◯ ◯ Comparative example 2 B-3 90 C-3 10 C carbon fiber Polyamide resin × ◯◯ ◯ ◯ Comparative example 3 B-5 98 C-6 2 C fiber optics Polypropylene resin × ◯◯ ◯ ◯ Comparative example 4 B-11 65 C-1 35 D carbon fiber Vinyl ester resin × ◯◯ ◯ ◯

[0061] Further details regarding the resins listed in Table 4 in the column “Matrix resin used to assess adhesion properties” and the respective meanings expressed by “*1”, “*2” and “*3” are as follows: (Matrix resin used to assess adhesion properties)

[0062] Epoxy resin: manufactured by Mitsubishi Chemical Corporation; trade name jER828 + triethylenetetramine

[0063] Vinyl ester resin: manufactured by Showa Denko KK; trade name Ripoxy R-804B (using methyl ethyl ketone peroxide manufactured by the same company as a curing agent). Polyamide resin: manufactured by UBE Corporation; UBE Nylon; 1011FB. Polypropylene resin: 2 wt% maleic anhydride-modified polypropylene. * 1) Proportional content in relation to the non-volatile fraction of the resin (B) *2) Proportional content in relation to the total amount of the non-volatile fraction of resin (B) and surfactant *3) Based on the non-volatile fraction Experimental Part 2 (Evaluation) Assessment of the adhesion properties

[0064] The adhesion property was evaluated based on stress measured using a microdroplet method and a commercially available evaluation device for composite interface properties 10.

[0065] The aqueous solution of each example prepared as described above was further diluted in water to produce an aqueous solution with a solids content of 2% by mass. The aqueous solution was sprayed onto a carbon fiber or glass fiber nonwoven fabric to achieve a solids content of 2% by mass, thus producing a carbon fiber or glass fiber nonwoven fabric which was then treated with the sizing agent according to the respective example.

[0066] Next, a single carbon fiber or glass fiber was removed from the carbon fiber nonwoven or glass fiber nonwoven, and this fiber 12 was fixed at both ends to a holder 11 of the four-sided frame shape using an adhesive 14 while under tension. Then, the matrix resin was adhered to and fixed to the fiber as resin droplets 13 with a diameter of approximately 70 µm, according to each example listed in Table 4.

[0067] In a (not shown) device base body, two plate-shaped cutting edges 17 and 18, each having a vertical cross-section tapered on one side, are arranged in a position such that their tip areas 17a and 18a face each other.

[0068] In a position where the fiber 12 with the resin droplet 13 attached to it is sandwiched between the tip regions 17a and 18a of the two cutting edges 17 and 18, the holder 11 was mounted on a base plate 16, which is attached to the device body. The base plate 16 is connected to a load cell 15, and the stress exerted on the base plate 16 is measured.

[0069] The load cell 15 measured a maximum stress F which arises when the resin droplet 13 is peeled from the fiber by the tip areas 17a and 18a of the cutting edges 17 and 18 when the holder 11 is moved at a speed of 5 mm / minute in the direction of a fiber axis.

[0070] Based on the measured value, an interfacial shear strength τ was calculated using the numerical formula given below. The same procedure was performed 20 times, and an average value of the obtained interfacial shear strengths was determined. Furthermore, an increase relative to a numerical reference value for the matrix resin used, specified below, was calculated for the determined average value and evaluated according to the following criteria. The results are listed in Table 4 in the column "Adhesion Properties." Additionally, the types of inorganic fiber and matrix resin used are listed in Table 4 in the columns "Inorganic Fiber Used to Evaluate Adhesion Properties" and "Matrix Resin Used to Evaluate Adhesion Properties," respectively. τ=F / πDL

[0071] In the numerical formula 1 F is the maximum stress (N) generated when the resin droplet 13 is peeled from the fiber 12, D is the diameter (in meters) of the fiber 12 and L is the diameter (in m) of the resin droplet 13 in one direction of displacement.

[0072] Reference values ​​of the matrix resins used Epoxy resin: 60 MPa Vinyl ester resin: 40 MPa Polyamide resin: 50 MPa Polypropylene resin: 22 MPa Evaluation criteria for adhesion properties ◯◯ (satisfactory): The increase is at least 12%. ◯ (acceptable): The increase is at least 1%, but less than 12%. × (bad): The increase is less than 1%. • Evaluation of the property of preventing detachment

[0073] After a drying step, observations were made in a metal rolling area to determine whether the carbon nanostructure had detached from the inorganic fiber after it had passed through a sizing agent bath. The detachment resistance was then evaluated based on the following criteria. The results are listed in Table 4 under the column "Detachment Resistance".

[0074] ◯◯ (satisfactory): No detachment of the carbon nanostructure was visible on the metal roller and continuous operation for two weeks or more was possible. ◯ (acceptable): Although slight detachment of the carbon nanostructure on the metal roller was noticeable, continuous operation for two weeks or more was possible. × (bad): Considerable detachment of the carbon nanostructure was visible on the metal roller and production had to be stopped after less than two weeks to carry out cleaning. • Evaluation of process efficiency

[0075] Process efficiency was evaluated based on the following criteria. The results are listed in Table 4 in the column "Process efficiency". ◯ (satisfactory): Application of the carbon nanostructure and the resin is performed in one step. × (bad): There are two steps, namely the application of the carbon nanostructure and then the application of the resin-containing sizing agent. • Assessment of the bundle characteristic

[0076] The aqueous solution of each sample prepared as described above was further diluted with water to produce an aqueous solution with a solids content of 2% by mass. Uncoated carbon fiber strands derived from polyacrylonitrile were continuously immersed in the aforementioned aqueous solution. Using a roller whose wringing was adjusted to fix the amount of sizing agent (not including solvent) relative to the carbon fibers at 1% by mass, the aqueous solution adhered to the carbon fiber strands. This was followed by a drying process involving continuous, one-minute exposure to a 200°C oven, and then a pick-up process using a metal roller.

[0077] The condition of the carbon fiber strands after immersion in the aqueous solution for applying the sizing agent was observed after the drying step at the metal roller area, and the bundle properties were evaluated based on the following criteria. The results are listed in Table 4 in the column "Bundle Properties". ◯ (satisfactory): The carbon fiber strands passed through the metal roller in a well-bundled state and were easy to process. × (bad): The carbon fiber strands were not well bundled and tangling occurred in the area of ​​the metal roller.

[0078] The results listed in Table 4 above demonstrate that the present invention provides a sizing agent that exhibits excellent effectiveness in improving the adhesion properties of an inorganic fiber to a base material of a composite. The present invention also excels in terms of preventing delamination, process efficiency, and bundling properties.

[0079] The present invention also includes the following exemplary embodiments. (Additional embodiment 1)

[0080] A sizing agent for inorganic fibers comprising at least one carbon nanostructure selected from a group consisting of carbon nanotubes, carbon nanofibers and a resin. (Additional embodiment example 2)

[0081] The sizing agent for inorganic fibers according to additional embodiment 1, wherein the carbon nanostructure comprises carbon nanotubes and the carbon nanotubes comprise single-walled carbon nanotubes. (Additional embodiment example 3)

[0082] The sizing agent for inorganic fibers according to additional embodiment 1 or 2, wherein the proportion of the carbon nanostructure in the non-volatile component of the resin is at least 100 ppm and at most 50,000 ppm. (Additional embodiment 4)

[0083] The sizing agent for inorganic fibers according to one of the additional embodiments 1 to 3, wherein the resin contains at least one substance selected from the group comprising an epoxy resin, a vinyl ester resin, a polyamide resin, a polyolefin resin, a polyurethane resin, a polyester resin, a phenoxide resin, a polyimide resin and a polyimide resin precursor. (Additional embodiment 5)

[0084] The sizing agent for inorganic fibers according to one of the additional embodiments 1 to 4, which also comprises a surfactant. (Additional embodiment 6)

[0085] The sizing agent for inorganic fibers according to one of the additional embodiments 1 to 5, wherein the sizing agent for inorganic fibers is applied to a glass fiber or a carbon fiber. (Additional embodiment 7)

[0086] The sizing agent for inorganic fibers according to one of the additional embodiments 1 to 6, wherein the resin is an epoxy resin and the sizing agent for inorganic fibers is used with a composite material in which a matrix resin is an epoxy resin. (Additional embodiment 8)

[0087] The sizing agent for inorganic fibers according to one of the additional embodiments 1 to 6, wherein the resin is at least a substance selected from a group consisting of a polyamide resin, a polyurethane resin, a polyimide resin and a polyimide resin precursor, and wherein the sizing agent for inorganic fibers is used with a composite material in which a matrix resin is a polyamide resin. (Additional embodiment 9)

[0088] The sizing agent for inorganic fibers according to one of the additional embodiments 1 to 6, wherein the resin is a vinyl ester resin and the sizing agent for inorganic fibers is used with a composite material in which a matrix resin is a vinyl ester resin. (Additional embodiment example 10)

[0089] The sizing agent for inorganic fibers according to one of the additional embodiments 1 to 6, wherein the resin is at least a substance selected from a group consisting of a polyolefin resin and a phenoxide resin, and the sizing agent for inorganic fibers is used with a composite material in which a matrix resin is a polyolefin resin. (Additional embodiment example 11)

[0090] An inorganic fiber to which the sizing agent for inorganic fibers is adhered according to one of the additional embodiments 1 to 6. (Additional embodiment example 12)

[0091] A method for producing an inorganic fiber, comprising the adhesion of the sizing agent for inorganic fibers according to one of the additional embodiments 1 to 10 to an inorganic fiber. (Additional embodiment example 13)

[0092] A composite material comprising the inorganic fiber according to the additional embodiment 11 and a matrix resin, wherein the resin in the sizing agent for inorganic fibers is an epoxy resin and the matrix resin is an epoxy resin. (Additional embodiment 14)

[0093] A composite material comprising the inorganic fiber according to additional embodiment 11 and a matrix resin, wherein the resin in the sizing agent for inorganic fibers is at least one substance selected from the group comprising a polyamide resin, a polyurethane resin, a polyimide resin and a polyimide resin precursor, and wherein the matrix resin is a polyamide resin. (Additional embodiment example 15)

[0094] A composite material comprising the inorganic fiber according to additional embodiment 11 and a matrix resin, wherein the resin in the sizing agent for inorganic fibers is a vinyl ester resin and the matrix resin is a vinyl ester resin. (Additional embodiment 16)

[0095] A composite material comprising the inorganic fiber according to additional embodiment 11 and a matrix resin, wherein the resin in the sizing agent for inorganic fibers is at least one substance selected from a group consisting of a polyolefin resin and a phenoxide resin, and wherein the matrix resin is a polyolefin resin. REFERENCE MARK LIST 10 Evaluation device 10 for composite material interface properties 11 bracket 12 fibers 13 drops of resin 14 Adhesive 15 stress cell 16 Substrat 17, 18 cutting

Claims

[1] A sizing agent for inorganic fibers comprising: at least a carbon nanostructure selected from a group composed of carbon nanotubes and carbon nanofibers, a resin and a surfactant;wherein, if the total content of a non-volatile component of resin and surfactant is assumed to be 100 parts by mass, the sizing agent for inorganic fibers contains the surfactant in a ratio of 2 to 50 parts by mass, wherein the resin comprises at least one substance selected from the group consisting of a vinyl ester resin, a polyamide resin, a polyolefin resin, a polyurethane resin, a polyester resin, a polyimide resin, and a polyimide resin precursor, wherein the surfactant is an ether-like non-ionic surfactant, a non-ionic surfactant of the type of a polyoxyalkylene polyhydric alcohol and fatty acid ester, a non-ionic surfactant of the alkylamide type, a non-ionic surfactant of the polyoxyalkylene fatty acid amide type, or an ether-ester compound. [2] Sizing agent for inorganic fibers according to claim 1, wherein the carbon nanostructure comprises carbon nanotubes and the carbon nanotubes comprise single-walled carbon nanotubes. [3] Sizing agent for inorganic fibers according to claim 1 or 2, wherein the proportion of the carbon nanostructure in the non-volatile component of the resin is at least 100 ppm and at most 50,000 ppm. [4] Sizing agent for inorganic fibers according to any one of claims 1 to 3, wherein the sizing agent for inorganic fibers is applied to a glass fiber or to a carbon fiber. [5] Sizing agent for inorganic fibers according to any one of claims 1 to 4, wherein the resin is at least one substance selected from the group comprising: a polyamide resin, a polyurethane resin, a polyimide resin and a polyimide resin precursor, and wherein the sizing agent for inorganic fibers is used with a composite material wherein the matrix resin is a polyamide resin. [6] Sizing agent for inorganic fibers according to any one of claims 1 to 4, wherein the resin is a vinyl ester resin and the sizing agent for inorganic fibers is used with a composite material in which a matrix resin is a vinyl ester resin. [7] Sizing agent for inorganic fibers according to any one of claims 1 to 4, wherein the resin is a polyolefin resin, and wherein the sizing agent for inorganic fibers is used with a composite material in which a matrix resin is a polyolefin resin. [8] Inorganic fiber to which the sizing agent for inorganic fibers according to any one of claims 1 to 4 is adhered. [9] Method for producing an inorganic fiber, comprising the adhesion of the sizing agent for inorganic fibers according to any one of claims 1 to 7 to an inorganic fiber. [10] Composite material comprising the inorganic fiber according to claim 8 and a matrix resin, wherein the resin in the sizing agent for inorganic fibers is at least one substance selected from the group comprising a polyamide resin, a polyurethane resin, a polyimide resin and a polyimide resin precursor, wherein the matrix resin is a polyamide resin. [11] Composite material comprising the inorganic fiber according to claim 8 and a matrix resin, wherein the resin in the sizing agent for inorganic fibers is a vinyl ester resin and the matrix resin is a vinyl ester resin. [12] Composite material comprising the inorganic fiber according to claim 8 and a matrix resin, wherein the resin in the sizing agent for inorganic fibers is a polyolefin resin, and wherein the matrix resin is a polyolefin resin.

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