Sizing agents for inorganic fibers, inorganic fibers, methods for producing the same and composite materials

Abstract

Sizing agent for inorganic fibers, comprising a resin and cellulose nanofibers, wherein the cellulose nanofibers are contained in a non-volatile content of the sizing agent of at least 10 ppm and less than 50,000 ppm, wherein the sizing agent further comprises a surfactant, wherein a proportion of the surfactant is 1 wt% or more and 50 wt% or less.

Description

TECHNICAL AREA

[0001] The present invention relates to a sizing agent for inorganic fibers containing cellulose nanofibers, an inorganic fiber, a method for producing the same, and a composite material. STATE OF THE ART

[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. To improve the adhesion between the inorganic fibers, such as carbon fibers, and the base material, such as a thermoplastic resin, a process is used to bond a sizing agent to the inorganic fibers.

[0003] A known sizing agent for inorganic fibers, used to reinforce a thermoplastic matrix resin, is disclosed, for example, in a patent document. Patent document 1 discloses a sizing agent-coated carbon fiber obtained by coating a carbon fiber with a sizing agent containing nanocellulose with a number-average fiber diameter of 1 nm to 1000 nm and a compound with an epoxy group. It is described that the nanocellulose is present in the sizing agent in an amount of 5% by weight or more, based on the total amount of the sizing agent. QUOTE LIST PATENT LITERATURE Patent literature 1: JP 2017 -119 936 A Patent literature 2: JP 2016 -79 507 A Patent literature 3: WO 2019 / 159 733 A OVERVIEW OF THE INVENTIONAL PROBLEM

[0004] However, the arbitrator of patent document 1 has the problem that the improvement of the adhesion of the inorganic fiber to the base material is not sufficient; its ability to prevent detachment from the inorganic fiber and its handling behavior are also insufficient. SOLUTION TO THE PROBLEM

[0005] As a result of research to solve the aforementioned problems, the inventors of the present invention have found that a sizing agent for inorganic fibers containing a predetermined amount of cellulose nanofibers and a resin is very suitable.

[0006] To solve the above problems, a sizing agent for inorganic fibers according to one aspect of the present invention comprises a resin and cellulose nanofibers, and the cellulose nanofibers are contained with a non-volatile content of the sizing agent of at least 10 ppm and less than 50000 ppm.

[0007] The sizing agent for inorganic fibers can contain cellulose nanofibers with a fiber diameter of at least 1 nm and at most 1000 nm. This means that at least some of the cellulose nanofibers can have a fiber diameter of at least 1 nm and at most 1000 nm.

[0008] The sizing agent for inorganic fibers may contain at least one resin selected from the group consisting of an epoxy resin, a vinyl ester resin, a polyamide resin, a polyolefin resin, a polyurethane resin, a polyester resin, a phenoxy resin, a polyimide resin and a polyimide resin precursor.

[0009] The sizing agent for inorganic fibers also contains a surfactant.

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

[0011] The resin in the sizing agent for inorganic fibers may contain at least one resin selected from the group consisting of an epoxy resin and a polyester resin, and in this case the sizing agent for inorganic fibers may be applied to a composite material in which a matrix resin is an epoxy resin, more precisely to an inorganic fiber that forms part of such a composite material.

[0012] The resin in the sizing agent for inorganic fibers may contain at least one selected from the group consisting of a polyamide resin, a polyurethane resin, a polyimide resin and a polyimide resin precursor, and in this case the sizing agent for inorganic fibers may be applied to a composite material in which a matrix resin is a polyamide resin, more precisely to an inorganic fiber forming part of such a composite material.

[0013] The resin in the sizing agent for inorganic fibers may contain a vinyl ester resin, and in this case, the sizing agent for inorganic fibers may be applied to a composite material in which a matrix resin is a vinyl ester resin, more specifically to an inorganic fiber that forms part of such a composite material.

[0014] The resin in the sizing agent for inorganic fibers may contain at least one selected from the group consisting of a polyolefin resin and a phenoxy resin, and in this case the sizing agent for inorganic fibers may be applied to a composite material in which a matrix resin is a polyolefin resin, more precisely to an inorganic fiber that forms part of such a composite material.

[0015] To solve the problems mentioned above, the sizing agent for inorganic fibers is attached to an inorganic fiber according to another aspect of the present invention.

[0016] To solve the aforementioned problems, a method for producing an inorganic fiber according to a further aspect of the present invention comprises the adhesion of the sizing agent for inorganic fibers to an inorganic fiber.

[0017] To solve the above problems, a composite material according to a further aspect of the present invention comprises the inorganic fiber and a matrix resin, wherein the resin in the sizing agent for inorganic fibers comprises at least one from the group consisting of an epoxy resin and a polyester resin, and the matrix resin is an epoxy resin.

[0018] To solve the above problems, a composite material according to a further aspect of the present invention comprises the inorganic fiber and a matrix resin, wherein the resin in the sizing agent for inorganic fibers comprises at least one selected from the group consisting of a polyamide resin, a polyurethane resin, a polyimide resin and a polyimide resin precursor, and the matrix resin is a polyamide resin.

[0019] To solve the above problems, a composite material according to a further aspect of the present invention comprises the inorganic fiber and a matrix resin, wherein the resin in the sizing agent for inorganic fibers contains a vinyl ester resin and the matrix resin is a vinyl ester resin.

[0020] To solve the above problems, a composite material according to a further aspect of the present invention comprises the inorganic fiber and a matrix resin, wherein the resin in the sizing agent for inorganic fibers comprises at least one from the group consisting of a polyolefin resin and a phenoxy resin, and the matrix resin is a polyolefin resin. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0021] The present invention makes it possible to improve the adhesion of an inorganic fiber to a base material of a composite material, the ability to prevent detachment from the inorganic fiber, and the handling behavior of a sizing agent. SHORT FIGURE DESCRIPTION

[0022] The Fig. Figure 1 is a schematic view of a device for evaluating the interface properties of a composite material for the evaluation of the adhesion properties listed in the section with examples. DESCRIPTION OF THE EXAMPLES OF EXECUTION<Erstes Ausführungsbeispiel>

[0023] First, a first embodiment is described in which a sizing agent for inorganic fibers (hereinafter also referred to as sizing agent) is implemented according to the present invention. The sizing agent contains a predetermined amount of cellulose nanofibers and a resin. (Cellulose nanofibers)

[0024] Cellulose nanofibers can improve the adhesion between an inorganic fiber and a matrix resin. Depending on their size, cellulose nanofibers can be classified into cellulose microfibrils (individual cellulose nanofibers) with a base fiber diameter of 3 nm to 4 nm, cellulose microfibril bundles with a width of 10 nm to 20 nm, obtained by bundling multiple cellulose microfibrils, microfibrillated cellulose, which forms a cobweb-like network with a width of several tens to several hundred nanometers and is obtained by further bundling of microfibril bundles, and so on; however, any of these can be used. The cellulose nanofibers can be produced by fiberization and micronization using a plant-based fiber material, such as...Pulp can be obtained as a raw material by a known manufacturing process, or a commercially available product can be used. The known manufacturing process is not particularly limited, and examples include a mechanical pulverization process such as a high-pressure homogenization process or an ultrasonic fiberization process, an underwater counter-collision process, a TEMPO oxidation process, and a micronization process using an enzyme such as cellulase.

[0025] The lower limit of the fiber diameter of the cellulose nanofiber is preferably at least 1 nm, particularly preferably at least 3 nm. The upper limit of the fiber diameter of the cellulose nanofiber is preferably at most 1000 nm, more preferably at most 800 nm. By defining the fiber diameter within such a range, the adhesion between the inorganic fiber and the matrix resin can be further improved. In addition, the dispersibility during solution preparation can be improved. The fiber diameter of the cellulose nanofiber was measured using a scanning electron microscope (SEM). First, an aqueous dispersion of cellulose nanofibers, which had been dried for 2 hours at 105 °C, was magnified to a level at which the fiber diameter could be measured as the fiber width using the SEM.Twenty non-overlapping cellulose nanofibers were randomly selected, and their fiber diameters were determined. The maximum and minimum values ​​of the obtained fiber diameters are referred to as the "fiber diameter (minimum - maximum)" of the measured cellulose nanofibers. Furthermore, the average value of the obtained fiber diameters is referred to as the "fiber diameter (average)" of the measured cellulose nanofibers. If the cellulose nanofiber was in powder form, it was dispersed in water to homogenize it and then used.

[0026] The sizing agent preferably contains cellulose nanofibers with a fiber diameter of at least 1 nm and at most 1000 nm, preferably contains the cellulose nanofibers in an amount of at least 50% by mass and particularly preferably contains the cellulose nanofibers in an amount of at least 80% by mass of all cellulose nanofibers.

[0027] These cellulose nanofibers can be used individually or in combination with two or more types of them.

[0028] The lower limit for the proportion of cellulose nanofibers in the non-volatile fraction of the sizing agent is at least 10 ppm, preferably at least 15 ppm. If the proportion is at least 10 ppm, the adhesion between the matrix resin and the inorganic fiber can be further improved. Furthermore, the upper limit of the proportion is less than 50,000 ppm, preferably at most 46,000 ppm. If the proportion is less than 50,000 ppm, the handling properties can be improved. The term "non-volatile fraction" as used here refers to the residue after a volatile substance has been sufficiently removed by a 2-hour heat treatment of an object at 105°C, i.e., to the absolute dry mass. (Resin)

[0029] The resin is selected from known resins according to the intended use of the inorganic fiber to which the sizing agent is applied. Specific examples of resins include an epoxy resin, a vinyl ester resin, a polyamide resin, a polyolefin resin, a polyurethane resin, a polycarbonate resin, a polyester resin, a PEEK resin, a fluorinated resin, a phenoxy resin, a phenolic resin, a BMI resin, a polyimide resin, a polyimide resin precursor, and a polyethersulfone resin. Among these, an epoxy resin, a vinyl ester resin, a polyamide resin, a polyolefin resin, a polyurethane resin, a polyester resin, a phenoxy resin, a polyimide resin, and a polyimide resin precursor are preferred.

[0030] Specific examples of the resin include, for example, an epoxy resin (manufactured by Mitsubishi Chemical Corporation: trade names jER828, jER1002), an epoxy resin (manufactured by Nagase ChemteX Corporation: trade name Denacol EX-521), a polyurethane resin (manufactured by DKS Co. Ltd.: trade name SUPERFLEX 500M), a modified polypropylene resin (manufactured by Maruyoshi Chemical Co., Ltd.: trade name MGP-1650), a modified polypropylene resin (manufactured by TOHO Chemical Industry Co., Ltd.: trade name Hitech P-9018), a modified polyester resin (manufactured by Toyobo Co., Ltd.: trade name Vylonal MD-1480), a phenoxy resin (manufactured by Nippon Steel Chemical & Materials Co., Ltd.: trade name YP-50S), and a polyimide resin precursor of 3,3',4,4'-biphenyltetracarboxylic anhydride and diaminodiphenyl ether. a polyamide resin (manufactured by Toray Industries, Inc.): Trade name AQ Nylon P-95), a polyester resin consisting of an ethylene oxide 2-mol adduct of bisphenol A and fumaric acid, and a vinyl ester resin consisting of an epoxy resin and methacrylic acid.

[0031] When the sizing agent is used for application to inorganic fibers that form part of a composite material with a matrix resin as the base material, the type of resin to be mixed into the sizing agent is preferably selected taking into account the type of matrix resin, for example, with regard to 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 at least one selected from an epoxy resin and a polyester resin. If the matrix resin is a polyamide resin, the resin in the sizing agent is preferably at least one 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 preferably at least one selected from a polyolefin resin and a phenoxy resin. (surfactant)

[0032] The sizing agent also contains a surfactant. By incorporating the surfactant into the sizing agent, the cellulose nanofiber is less likely to detach easily from the inorganic fiber after application of the sizing agent; that is, the ability to prevent detachment of the cellulose nanofiber is improved. Examples of surfactants include anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants. These surfactants can be used individually or in combination with two or more types.

[0033] Depending on the requirements, a known non-ionic surfactant can be used as the non-ionic surfactant. Specific examples of nonionic surfactants include (1) compounds in which an alkylene oxide having 2 to 4 carbon atoms is added to an organic acid, organic alcohol, organic amine and / or organic amide, for example, ether-type nonionic surfactants such as polyoxyethylene dilaurate, polyoxyethylene oleate, polyoxyethylene oleic acid diester, polyoxyethylene octyl ether, polyoxyethylene lauryl ether, polyoxyethylene lauryl ether methyl ether, polyoxyethylene polyoxypropylene lauryl ether, polyoxyethylene 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, compounds,in which ethylene oxide is added to a secondary dodecyl alcohol, polyoxyethylene tridecyl ether, polyoxyalkylene tetradecyl ether, polyoxyethylene laurylamino ether, polyoxyethylene lauramide ether and polyoxyalkylene tristyrene phenyl ether, (2) non-ionic surfactants of the polyhydric polyoxyalkylene alcohol fatty acid ester type, such as polyoxyalkylene sorbitan trioleate, polyoxyalkylene coconut oil, polyoxyalkylene castor oil, polyoxyalkylene hydrogenated castor oil, polyoxyalkylene hydrogenated castor oil triooctanoate, and maleic acid esters, stearic acid esters or oleic acid esters of polyoxyalkylene hydrogenated castor oil, (3) non-ionic surfactants of the alkylamide type, such as stearic acid diethanolamide and diethanolamine monolauramide, (4) non-ionic surfactants of the polyoxyalkylene fatty acid amide type, such as polyoxyethylene diethanolamine monolauramide, Polyoxyethylene laurylamine and polyoxyethylene talgamine, and (5) ether and ester compounds, such as copolymers of polyoxyethylene, dimethyl phthalate and lauryl alcohol.

[0034] Depending on the requirements, a known anionic surfactant can be used. Specific examples of the anionic surfactant include (1) phosphoric acid ester salts of aliphatic alcohols, such as lauryl phosphoric acid ester salts, cetyl phosphoric acid ester salts, octyl phosphoric acid ester salts, oleyl phosphoric acid ester salts, and stearyl phosphoric acid ester salts; (2) phosphoric acid ester salts of adducts of at least one alkylene oxide selected from ethylene oxide and propylene oxide with an aliphatic alcohol, such as polyoxyethylene lauryl ether phosphoric acid ester salts, polyoxyethylene oleyl ether phosphoric acid ester salts, and polyoxyethylene stearyl ether phosphoric acid ester salts; (3) aliphatic sulfonic acid salts or aromatic sulfonic acid salts, such as lauryl sulfonic acid salts, myristyl sulfonic acid salts, cetyl sulfonic acid salts, oleyl sulfonic acid salts, stearyl sulfonic acid salts, tetradecane sulfonic acid salts, dodecylbenzene sulfonic acid salts, and secondary alkyl (C13 to C15) sulfonic acid salts,(4) Sulfuric acid ester salts of aliphatic alcohols, such as lauryl sulfuric acid ester salts, oleyl sulfuric acid ester salts and stearyl sulfuric acid ester salts, (5) Sulfuric acid ester salts of adducts of at least one alkylene oxide selected from ethylene oxide and propylene oxide with an aliphatic alcohol, such as polyoxyethylene lauryl ether sulfuric acid ester salts, polyoxyalkylene (polyoxyethylene, polyoxypropylene) lauryl ether sulfuric acid ester salts and polyoxyethylene oleyl ether sulfuric acid ester salts, (6) Sulfuric acid ester salts of fatty acids, such as castor oil fatty acid sulfuric acid ester salts, sesame oil fatty acid sulfuric acid ester salts, tall oil fatty acid sulfuric acid ester salts, soybean oil fatty acid sulfuric acid ester salts, rapeseed oil fatty acid sulfuric acid ester salts, palm oil fatty acid sulfuric acid ester salts, Lard fatty acid sulfuric acid ester salts, beef tallow fatty acid sulfuric acid ester salts, and whale oil fatty acid sulfuric acid ester salts, (7) Sulfuric acid ester salts of oils and fats,such as sulfuric acid ester salts of castor oil, sulfuric acid ester salts of sesame oil, sulfuric acid ester salts of tall oil, sulfuric acid ester salts of soybean oil, sulfuric acid ester salts of rapeseed oil, sulfuric acid ester salts of palm oil, sulfuric acid ester salts of lard, sulfuric acid ester salts of beef tallow, and sulfuric acid ester salts of whale oil, (8) fatty acid salts, such as lauric acid salts, oleic acid salts, and stearic acid salts, and (9) sulfosuccinic acid ester salts of aliphatic alcohols, such as dioctylsulfosuccinic acid salts. Examples of a counterion of the anionic surfactant are alkali metal salts, such as a potassium salt and a sodium salt, an ammonium salt, and alkanolamine salts, such as triethanolamine.

[0035] Depending on the requirements, a known cationic surfactant can be used. Specific examples of cationic surfactants include lauryltrimethylammonium chloride, cetyltrimethylammonium chloride, stearyltrimethylammonium chloride, behenyltrimethylammonium chloride, didecyldimethylammonium chloride, 1,2-dimethylimidazole, and triethanolamine.

[0036] A known amphoteric surfactant can be used if necessary. Specific examples of amphoteric surfactants include an amphoteric betaine surfactant.

[0037] The lower limit of the surfactant content in the non-volatile portion of the sizing agent is at least 1% by mass, preferably at least 2% by mass. If the content is at least 1% by mass, the ability to prevent delamination can be further improved. The upper limit of the surfactant content is at most 50% by mass, preferably 40% by mass. If the content is at most 50% by mass, the adhesion properties can be further improved.

[0038] The action and effect of the sizing agent of the present embodiment are described below.

[0039] (1-1) The sizing agent according to the present embodiment contains a predetermined amount of cellulose nanofibers and a resin. When the sizing agent is applied to an inorganic fiber, the adhesion of the inorganic fiber to a substrate of the composite material and the ability to prevent detachment of a cellulose nanofiber from the inorganic fiber can be improved. In particular, when the sizing agent is applied directly to the surface of the inorganic fiber, irregularities originating from the cellulose nanofibers form on the fiber surface, thus improving the adhesion through the anchoring effect.Furthermore, when the matrix resin is impregnated with the inorganic fiber to which the sizing agent is adhered, in order to form a composite material, the propagation of cracks at the interface between the inorganic fiber and the matrix resin is prevented, thus improving the strength of the composite material.

[0040] (1-2) The proportion of cellulose nanofibers in the non-volatile fraction of the sizing agent is less than 50,000 ppm. Therefore, the flowability of a solution of the sizing agent can be improved, or a decrease in flowability can be suppressed. Furthermore, when the sizing agent is diluted with a solvent or when it is prepared, the sizing agent is readily miscible with the solvent. Therefore, the handling properties of the sizing agent can be improved. <Zweites Ausführungsbeispiel>

[0041] Next, a second embodiment is described, in which a method for producing an inorganic fiber according to the present invention is carried out. The second embodiment is the same as the first embodiment except for the following points.

[0042] The method 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. The amount applied (which does not contain a solvent) is not particularly limited, but the sizing agent is preferably applied to the inorganic fiber in an amount of at least 0.01% by mass and at most 10% by mass. By specifying the amount applied within such a range, the effect, such as the bundling properties of the inorganic fibers, can be further improved. (Inorganic fiber)

[0043] The type of inorganic fiber used in the present embodiment is not particularly limited, and examples include glass fiber, carbon fiber, ceramic fiber, metal fiber, mineral fiber, rock fiber, and slug fiber. Among these, glass fiber and carbon fiber are preferable from the point of view that they better exhibit the effects of the present invention. Examples of carbon fiber include PAN-based carbon fibers obtained from acrylic fibers as raw material, pitch-based carbon fibers obtained from pitch as raw material, and carbon fibers obtained from recycled carbon fibers, polyester fibers, polyethylene resins, phenolic resins, cellulose resins, or lignin resins as raw material.

[0044] To adhere the sizing agent to the inorganic fiber according to the first embodiment, a commonly used industrial method can be employed. Examples include roller dipping, roller contact, spraying, and papermaking processes. The inorganic fiber to which the sizing agent has adhered can then be subjected to a drying treatment according to a known method.

[0045] According to the method for producing an inorganic fiber according to the present embodiment, the following effects can be achieved in addition to the effects of the first embodiment.

[0046] (2-1) The method for producing an inorganic fiber according to the present embodiment comprises the adhesion of a sizing agent containing cellulose nanofibers and a resin to a carbon fiber. Therefore, in particular, the ability to prevent the detachment of the cellulose nanofiber from the inorganic fiber can be improved. Since the application of the sizing agent to the inorganic fiber is carried out in a single step, it is also efficient, i.e., the process efficiency can also be improved. <Drittes Ausführungsbeispiel>

[0047] A third embodiment is described below, in which a composite material according to the present invention is used. The third embodiment is the same as the first and second embodiments except for the following points.

[0048] The composite material is obtained by impregnating a matrix resin as the base material with the inorganic fiber to which the sizing agent is adhered according to the second embodiment. The form of the inorganic fiber for producing the composite material is not particularly restricted; for example, a long fiber form, a short fiber form, or a nonwoven form can be used. (Matrix resin)

[0049] The matrix resin is selected from known resins according to the purpose and use of the composite material. Specific examples of matrix resins include epoxy resin, vinyl ester resin, polyamide resin, polyolefin resin, polyurethane resin, polycarbonate resin, polyester resin, PEEK resin, fluorinated resin, phenoxy resin, phenolic resin, BMI resin, polyimide resin, polyimide resin precursor, and polyethersulfone resin.

[0050] The matrix resin can be selected taking into account the type of resin contained in the sizing agent, for example, with regard to improving adhesion to the inorganic fiber and improving recyclability. If the matrix resin is an epoxy resin, the resin in the sizing agent is preferably at least one of an epoxy resin and one of a polyester resin. If the matrix resin is a polyamide resin, the resin in the sizing agent is preferably at least one of 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 preferably at least one of a polyolefin resin and one of a phenoxy resin.

[0051] The following effects can be achieved with the composite material according to the present embodiment.

[0052] (3-1) A sizing agent containing a predetermined amount of cellulose nanofibers and a resin is pre-bonded to the inorganic fibers contained in the composite material according to the present embodiment. This results in a fiber-reinforced resin composite material which, due to the excellent adhesion between the inorganic fibers and the matrix resin, exhibits outstanding properties, particularly mechanical properties.

[0053] The embodiments described above can be modified as follows. The embodiments described above and the following modification examples can be combined within a technically consistent range. - From the point of view of maintaining the performance of the sizing agent and improving the application properties to the inorganic fiber, the sizing agent according to the embodiments described above is not incompatible with the addition of water or an organic solvent, a smoothing agent, an antioxidant, a preservative and the like as further components, insofar as the effect of the present invention is not impaired. - The area in which the sizing agent is applied according to the embodiments described above is not particularly limited. For example, the sizing agent according to the embodiments described above can be applied to a carbon fiber reinforced polymer (CFRP) material impregnated with a matrix resin, such as a polyimide resin, or to a reinforcing fiber for concrete. EXAMPLES

[0054] The following examples are 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 (Preparation of the sizing agent)

[0055] In the preparation of the sizing agent according to Example 1, the raw materials used were cellulose nanofibers (A-1) with a fiber diameter (minimum - maximum) of 20 nm - 300 nm and a fiber diameter (average) of 180 nm, as shown in Table 1; epoxy resins (B-1), as shown in Table 2, as resin (B); and random adducts (C-1) of 30 mol ethylene oxide and 5 mol propylene oxide of tristyrenized phenol (C-1), as shown in Table 3, as surfactant (C). Subsequently, a previously prepared resin emulsion, a previously prepared aqueous dispersion of cellulose nanofibers, and a surfactant were mixed to obtain an aqueous solution of the sizing agent from Example 1 with the proportions specified in Table 4.

[0056] For the preparation of the sizing agents of Examples 2 to 14 according to the invention, Example 15 not according to the invention, and Comparative Examples 1 to 5, cellulose nanofiber (A) from Table 1, resin (B) from Table 2, and surfactant (C) from Table 3 according to the invention were used as raw materials. Aqueous solutions of a sizing agent were then prepared according to one of the preparation methods specified in A to E.

[0057] A: A mixture of the respective raw materials was heated to 100°C and made uniform, then cooled to 70°C or less and water was gradually added to obtain an aqueous solution of a sizing agent.

[0058] B: A resin emulsion containing a previously prepared surfactant and a previously prepared aqueous dispersion of cellulose nanofibers were mixed to obtain an aqueous solution of a sizing agent.

[0059] C: A previously prepared resin emulsion, a previously prepared aqueous dispersion of cellulose nanofibers and a surfactant were mixed to obtain an aqueous solution of a sizing agent.

[0060] D: A previously prepared resin emulsion and a previously prepared aqueous dispersion of cellulose nanofibers were mixed to obtain an aqueous solution of a sizing agent.

[0061] E: An aqueous solution of a sizing agent was obtained using a previously prepared resin emulsion.

[0062] The type and content of cellulose nanofiber (A) contained in the aqueous solutions of the sizing agents thus obtained, the type and content of resin (B) as the non-volatile component, the type and content of surfactant (C), and the method for preparing the sizing agent are given in the columns "Cellulose nanofiber (A)," "Resin (B)," "Surfactant (C)," and "Mixing method used in production," respectively, of Table 4. The non-volatile component of the resin (B) was determined as the mass of the absolute dry matter from which volatile substances were sufficiently removed by a 2-hour heat treatment of an object at 105 °C. [Table 1] Classification Fiber diameter (minimum - maximum)[nm] Fiber diameter (average) [nm] A-1 20-300 180 A-2 100-500 250 A-3 50-300 200 A-4 30-200 90 A-5 3-4 3,5 A-6 3-4 3,3 [Table 2] Classification resin solids content 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 Maruyoshi Chemical Co., Ltd., trade name: MGP-1650 30% B-5 Modified polypropylene resin, manufactured by TOHO ChemicalIndustry 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 Phenoxy resin, manufactured by Nippon Steel Chemical & Materials Co., Ltd., trade name: YP-50S 100% B-8 Polyimide resin precursor of 3,3',4,4'-biphenyltetracarboxylic anhydride and diaminodiphenyl ether 10% B-9 Polyamide resin, manufactured by Toray Industries, Inc., trade name: AQ Nylon P-95 50% B-10 Polyester resin made from EO 2 mol adduct of bisphenol A and fumaric acid 100% B-11 Vinyl ester resin made from epoxy resin and methacrylic acid 100% B-12 Epoxy resin, manufactured by Nagase ChemteX Corporation, trade name: Denacol EX-521 100% [Table 3] Classification surfactant C-1 Random adduct of 30 mol ethylene oxide and 5 mol propylene oxide of tristyrolated phenol C-2 Compound obtained by adding 10 mol of ethylene oxide to dodecyl alcohol C-3 Compound obtained by adding 15 mol of ethylene oxide to isononyl alcohol C-4 Compound obtained by adding 10 mol of ethylene oxide and 5 mol of propylene oxide to tetradecyl alcohol C-5 Compound obtained by adding 7 moles of ethylene oxide 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

[0063] Details of the resins described in the column “Matrix resin used for the adhesion assessment” in Table 4, and the meanings represented by “*1)”, “*2)” and “*3)” in Table 4, are as follows. (Matrix resin used for the assessment of adhesion)

[0064] Epoxy resin: Trade name jER828, manufactured by Mitsubishi Chemical Corporation + Triethylenetetramine

[0065] Vinyl ester resin: Trade name Lipoxy R-804B, manufactured by Showa Denko KK (using a methyl ethyl ketone peroxide curing agent, manufactured by the same company)

[0066] Polyamide resin: UBE-Nylon 1011FB, manufactured by UBE Industries Ltd.

[0067] Polypropylene resin: 2 wt% maleic anhydride-modified polypropylene *1): Non-volatile salary standard *2): Parts by mass, based on 100 parts by mass of the total non-volatile content of resin (B) and surfactant (C) *3): Proportional content of the non-volatile component of the sedative (ppm) Experimental Part 2 (Evaluation) - Evaluation of adhesion capacity

[0068] The adhesion strength was assessed based on a stress measured using a microdroplet method with a commercially available device for evaluating the interfacial properties of a composite material. Fig. Figure 1 shows a schematic representation of the device for evaluating the interface properties of a composite material 10.

[0069] The aqueous solution of each example, prepared as described above, was further diluted with water to produce an aqueous solution with a solids content of 2 wt%. The aqueous solution was then applied by immersion to carbon or glass fiber strands at a solids content of 2 wt%, thus producing carbon or glass fiber strands onto which the sizing agent of the respective example was applied.

[0070] Next, a carbon or glass fiber strand was extracted from the carbon or glass fiber strands, and both ends of this fiber 12 were attached under tension to a plate-shaped, square frame holder 11 using an adhesive 14. The matrix resin of each example listed in Table 4 was then applied to the fiber 12 to form a resin droplet 13 with a diameter of approximately 70 µm and fixed in place.

[0071] Two plate-shaped blades 17 and 18, each with a vertical cross-section tapered on one side surface, are attached to a device body (not shown) in a state in which their tip sections 17a and 18a face each other.

[0072] The holder 11 was attached to a substrate 16, which was fixed to the device body at a point where the fiber 12, to which the resin droplet 13 was attached, was sandwiched between the tip sections 17a and 18a of the two blades 17 and 18. A load cell 15 is connected to the substrate 16, and a tensile force exerted on the substrate 16 is measured.

[0073] When the holder 11 was moved in the direction of the fiber axis at a speed of 5 mm / min, the maximum tensile force F generated when the resin droplet 13 was detached from the fiber 12 by the tip sections 17a and 18a of the blades 17 and 18 was measured by the load cell 15.

[0074] The interfacial shear strength τ was calculated from the measured values ​​using Formula 1 below. This process was repeated 20 times, and the average of the resulting interfacial shear strengths was determined. Furthermore, based on this average value, a rate of increase relative to the numerical reference value of the matrix resin used (shown below) was calculated, and the evaluation was performed according to the criteria listed below. The results are presented in Table 4 under "Adhesion." The type of inorganic fiber and the type of matrix resin used are indicated in the columns "Inorganic fiber used for the adhesion evaluation" and "Matrix resin used for the adhesion evaluation," respectively, in Table 4. τ=F / πDL

[0075] In Formula 1 F is the maximum tensile force (N) that arises when the resin droplet 13 is peeled off the fiber 12, D the diameter of the fiber 12 (m) and L is the diameter (m) in the direction of the resin droplet's pull. 13.

[0076] Numerical reference values ​​of the matrix resins used Epoxy resin: 60 MPa Vinyl ester resin: 40 MPa Polyamide resin: 50 MPa Polypropylene resin: 22 MPa

[0077] Assessment criteria for adhesion capacity ◯ (acceptable): The growth rate is at least 5%. × (bad): The rate of increase is less than 5%. - Assessment of the ability to prevent transfers

[0078] The occurrence or absence of detachment of the cellulose nanofiber from the inorganic fiber after passing through a sizing bath for the application of a sizing agent to the inorganic fiber was determined on a metal roller section after the drying step, and the detachment prevention capacity was evaluated according to the following criteria. The results are listed in the "Detachment Prevention Capacity" column in Table 4.

[0079] ⊚ (good): No detachment of the cellulose nanofiber was observed on the metal roller, and continuous operation for two weeks or longer was possible.

[0080] ◯ (acceptable): Detachment of the cellulose nanofiber was observed to a small extent on the metal roller, however continuous operation for two weeks or longer was possible.

[0081] × (bad): The detachment of the cellulose nanofiber was frequently observed on the metal roller, and it was necessary to stop production and clean the metal roller within less than two weeks. - Handling behavior

[0082] The handling characteristics of the arbitrator in each example were evaluated according to the following criteria. The results are listed in the "Handling Characteristics" column in Table 4.

[0083] ◯ (acceptable): When used as a one-component sizing agent in a process for the production of inorganic fibers, the sizing agent retained its flowability, making it easy to measure the weight and introduce the sizing agent into the process using a pump.

[0084] × (bad): When used as a one-component sizing agent in a process for the production of inorganic fibers, the sizing agent did not retain its flowability, making it difficult to measure the weight and introduce the sizing agent into the process using a pump. - Evaluation of process efficiency

[0085] The process efficiency of the mediation method in each example was evaluated based on the following criteria. The results are listed in the "Process Efficiency" column in Table 4.

[0086] ◯ (acceptable): The application of the cellulose nanofibers and the resin to the fiber is done in one step.

[0087] × (bad): In a two-stage process, the cellulose nanofibers are applied to the fiber and then the sizing agent, which contains the resin, is applied to the fiber.

[0088] As can be seen from the results in Table 4 above, the sizing agents of the respective examples were evaluated with regard to adhesion, peel-off resistance, handling, and process efficiency, which were acceptable or better in all cases. According to the present invention, an effect is produced to improve adhesion, peel-off resistance, handling, and process efficiency. REFERENCE MARK LIST 10 Device for evaluating the interface properties of a composite material 11 bracket 12 fibers 13 drops of resin 14 Adhesive 15 stress cell 16 Substrat 17, 18 blade

Claims

[1] Sizing agent for inorganic fibers comprising a resin and cellulose nanofibers, wherein the cellulose nanofibers are contained in a non-volatile content of the sizing agent of at least 10 ppm and less than 50000 ppm, wherein the sizing agent also contains a surfactant, wherein a proportion of the surfactant is 1 wt% or more and 50 wt% or less. [2] Sizing agent for inorganic fibers according to claim 1, wherein the cellulose nanofibers comprise cellulose nanofibers having a fiber diameter of at least 1 nm and at most 1000 nm. [3] Sizing agent for inorganic fibers according to claim 1 or 2, wherein the resin comprises at least one selected from the group consisting of an epoxy resin, a vinyl ester resin, a polyamide resin, a polyolefin resin, a polyurethane resin, a polyester resin, a phenoxy resin, a polyimide resin and a polyimide resin precursor. [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 a carbon fiber. [5] A sizing agent for inorganic fibers according to any one of claims 1 to 4, wherein the resin contains at least one selected from the group consisting of an epoxy resin and a polyester resin, and the sizing agent for inorganic fibers is applied to a composite material in which a matrix resin is an epoxy resin. [6] A sizing agent for inorganic fibers according to any one of claims 1 to 4, wherein the resin contains at least one selected from the group consisting of a polyamide resin, a polyurethane resin, a polyimide resin and a polyimide resin precursor, and the sizing agent for inorganic fibers is applied to a composite material in which a matrix resin is a polyamide resin. [7] Sizing agent for inorganic fibers according to any one of claims 1 to 4, wherein the resin contains a vinyl ester resin and the sizing agent for inorganic fibers is applied to a composite material in which a matrix resin is a vinyl ester resin. [8] A sizing agent for inorganic fibers according to any one of claims 1 to 4, wherein the resin contains at least one selected from the group consisting of a polyolefin resin and a phenoxy resin, and the sizing agent for inorganic fibers is applied to a composite material in which a matrix resin is a polyolefin resin. [9] Inorganic fiber to which the sizing agent for inorganic fibers according to any one of claims 1 to 4 is adhered. [10] Method for producing an inorganic fiber, comprising adhering the sizing agent for inorganic fibers according to any one of claims 1 to 8 to an inorganic fiber. [11] Composite material comprising the inorganic fiber according to claim 9 and a matrix resin, wherein the resin in the sizing agent for inorganic fibers contains at least one selected from the group consisting of an epoxy resin and a polyester resin, and the matrix resin is an epoxy resin. [12] Composite material comprising the inorganic fiber according to claim 9 and a matrix resin, wherein the resin in the sizing agent for inorganic fibers contains at least one selected from the group consisting of a polyamide resin, a polyurethane resin, a polyimide resin and a polyimide resin precursor, and the matrix resin is a polyamide resin. [13] Composite material comprising the inorganic fiber according to claim 9 and a matrix resin, wherein the resin in the sizing agent for inorganic fibers contains a vinyl ester resin and the matrix resin is a vinyl ester resin. [14] Composite material comprising the inorganic fiber according to claim 9 and a matrix resin, wherein the resin in the sizing agent for inorganic fibers contains at least one selected from the group consisting of a polyolefin resin and a phenoxy resin, and the matrix resin is a polyolefin resin.

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