Sizing agent for reinforcing fibers and reinforcing fibers

Abstract

It combines at a high level the functions of impregnation of the matrix resin into the reinforcing fibers, abrasion resistance of the reinforcing fibers, openability of the reinforcing fibers, and stability of the sizing agent solution. [Solution] A sizing agent for reinforcing fibers containing a urethane resin (A) and a smoothing agent (B), wherein the smoothing agent (B) contains at least one compound selected from the group consisting of an ester mixture (B1) which is a mixture of a linear ester compound that is liquid at 45°C and has 10 to 50 total carbon atoms and a branched ester compound that is liquid at 45°C and has 10 to 50 total carbon atoms, and a hydrocarbon compound (B2) which contains at least one compound selected from the group consisting of poly-alphaolefins that are liquid at 45°C, synthetic paraffins that are liquid at 45°C, and mineral oils that are liquid at 45°C.

Description

[Technical Field]

[0001] The present invention relates to a sizing agent for reinforcing fibers and reinforcing fibers. [Background technology]

[0002] Fiber-reinforced resins, which are composites of reinforcing fibers such as carbon fiber and glass fiber with resin materials, are widely used as lightweight, high-strength materials. To improve the performance and productivity of fiber-reinforced resins, various agents that can be added to the reinforcing fibers have been investigated.

[0003] A commonly used sizing agent (also called a sizing agent) containing a urethane resin is applied to reinforcing fibers, and this type of sizing agent is called a urethane-based sizing agent. Urethane-based sizing agents are generally formulated with the technical idea that the urethane resin function allows the matrix resin to impregnate the reinforcing fibers, while the combined use of a smoothing agent provides abrasion resistance to the reinforcing fibers. For example, Japanese Patent Laid-Open Publication No. 7-173769 (Patent Document 1) discloses a urethane-based sizing agent containing an ester compound as a smoothing agent. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 7-173769 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional urethane-based sizing agents are designed to achieve impregnation through urethane resin and abrasion resistance through smoothing agents, resulting in a trade-off between impregnation and abrasion resistance. Furthermore, conventional urethane-based sizing agents have room for improvement in terms of the openability of the reinforcing fibers to which they are applied and the stability of the sizing agent solution.

[0006] Therefore, it is desired to realize a sizing agent for reinforcing fibers that combines high levels of matrix resin impregnation of reinforcing fibers, abrasion resistance of reinforcing fibers, openability of reinforcing fibers, and stability of the sizing agent solution, and reinforcing fibers to which the sizing agent is applied. [Means for solving the problem]

[0007] The sizing agent for reinforcing fibers according to the present invention contains a urethane resin (A) and a smoothing agent (B). and is applied to inorganic fibers containing at least one of carbon fibers and glass fibers. The sizing agent for reinforcing fibers is characterized in that the smoothing agent (B) contains at least one compound selected from the group consisting of: an ester mixture (B1) which is a mixture of a linear ester compound that is liquid at 45°C and has 10 to 50 total carbon atoms and a branched ester compound that is liquid at 45°C and has 10 to 50 total carbon atoms; and a hydrocarbon compound (B2) which contains at least one compound selected from the group consisting of poly-α-olefins that are liquid at 45°C, synthetic paraffins that are liquid at 45°C, and mineral oils that are liquid at 45°C.

[0008] The reinforcing fiber according to the present invention is characterized in that the above-mentioned sizing agent for reinforcing fiber Inorganic fibers containing at least one of carbon fibers and glass fibers It is characterized by being attached to

[0009] These configurations make it possible to achieve high levels of impregnation of the matrix resin into the reinforcing fibers, abrasion resistance of the reinforcing fibers, openability of the reinforcing fibers, and stability of the sizing agent solution.

[0010] Preferred embodiments of the present invention will be described below, but the scope of the present invention is not limited to the preferred embodiments described below.

[0011] In one embodiment of the sizing agent for reinforcing fibers according to the present invention, the smoothing agent (B) preferably contains the ester mixture (B1).

[0012] This configuration tends to make the reinforcing fibers particularly resistant to abrasion.

[0013] In one embodiment of the sizing agent for reinforcing fibers according to the present invention, it is preferred that in the ester mixture (B1), at least a part of the linear ester compounds are linear monoester compounds, and at least a part of the branched ester compounds are branched monoester compounds.

[0014] This configuration tends to improve the stability of the sizing agent solution.

[0015] In one embodiment of the sizing agent for reinforcing fibers according to the present invention, the linear monoester compound and the branched monoester compound preferably account for 20 mass % or more in total in the ester mixture (B1).

[0016] This configuration particularly tends to improve the stability of the sizing agent solution.

[0017] In one embodiment, the sizing agent for reinforcing fibers according to the present invention preferably contains the urethane resin (A) in an amount of 60% by mass or more but less than 100% by mass, where the total content of the urethane resin (A) and the smoothing agent (B) is 100% by mass.

[0018] This configuration tends to increase the impregnation of the matrix resin.

[0019] In one embodiment, the sizing agent for reinforcing fibers according to the present invention preferably further contains a nonionic surfactant (C).

[0020] This configuration tends to improve the stability of the sizing agent solution.

[0021] In one embodiment, the sizing agent for reinforcing fibers according to the present invention preferably contains the urethane resin (A) in an amount of 60% by mass or more but less than 100% by mass, where the total content of the urethane resin (A), the smoothing agent (B), and the nonionic surfactant (C) is 100% by mass.

[0022] This configuration tends to increase the impregnation of the matrix resin.

[0023] Further features and advantages of the present invention will become more apparent from the following description of illustrative and non-limiting embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0024] An embodiment of the sizing agent for reinforcing fibers and reinforcing fibers according to the present invention will be described.

[0025] [Configuration of sizing agent for reinforcing fibers] The sizing agent for reinforcing fibers according to this embodiment (hereinafter simply referred to as "sizing agent") contains a urethane resin (A) and a smoothing agent (B). The sizing agent may also contain a nonionic surfactant (C).

[0026] (urethane resin) As the urethane resin (A), known urethane resins can be used without particular limitation. The urethane resin may be a commercially available product, and non-limiting examples include the Superflex (registered trademark) series (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), the Dispercol (registered trademark) series (manufactured by Sumika Covestro Urethane Co., Ltd.), the Baybond (registered trademark) series (manufactured by Sumika Covestro Urethane Co., Ltd.), the Bayhydrol (registered trademark) series (manufactured by Sumika Covestro Urethane Co., Ltd.), the ETERNACOLL (registered trademark) series (manufactured by UBE Corporation), and the Adekabontitor (registered trademark) HUX series.

[0027] The urethane resin (A) may be provided as a mixture such as a solution or dispersion when preparing the sizing agent, and the commercially available products exemplified above may be such mixtures. In this case, components other than the urethane resin (A) in the mixture (such as the solvent and dispersant) may be included in the sizing agent without being removed.

[0028] (smoothing agent) The lubricant (B) contains at least one selected from the group consisting of a predetermined ester mixture (B1) and a predetermined hydrocarbon compound (B2). When the lubricant (B) contains the ester mixture (B1), the abrasion resistance of the reinforcing fibers tends to be improved. However, the lubricant (B) may contain both the ester mixture (B1) and the hydrocarbon compound (B2).

[0029] The ester mixture (B1) is a mixture of a linear ester compound that is liquid at 45°C and has a total carbon number of 10 to 50, and a branched ester compound that is liquid at 45°C and has a total carbon number of 10 to 50. The linear ester compound may be a single compound or a mixture of multiple compounds. Since a stable sizing solution is easily obtained, it is preferable that some of the linear ester compounds are linear monoester compounds, and more preferably that all of the linear ester compounds are linear monoester compounds. The branched ester compound may be a single compound or a mixture of multiple compounds. Since a stable sizing solution is easily obtained, it is preferable that some of the branched ester compounds are branched monoester compounds, and more preferably that all of the branched ester compounds are branched monoester compounds. It is preferable that the linear monoester compound and the branched monoester compound account for a total of 20% by mass or more of the ester mixture (B1), because this tends to particularly enhance the stability of the sizing solution. It is more preferable that the total amount of the linear monoester compound and the branched monoester compound account for 40% by mass or more of the ester mixture (B1).

[0030] Examples of linear ester compounds having a total carbon number of 10 to 50 and liquid at 45°C include, but are not limited to, nonyl acetate (total carbon number of 11), ethyl oleate (total carbon number of 20), decyl oleate (total carbon number of 28), lauryl oleate (total carbon number of 30), oleyl oleate (total carbon number of 36), and myristyl myristate (total carbon number of 28) (the above are examples of linear monoester compounds having a total carbon number of 10 to 50 and liquid at 45°C), and dilauryl succinate (total carbon number of 28) (an example of a linear diester compound having a total carbon number of 10 to 50 and liquid at 45°C). The linear ester compound preferably has a total carbon number of 11 to 36.

[0031] Examples of branched-chain ester compounds having a total of 10 to 50 carbon atoms that are liquid at 45°C include, but are not limited to, isononyl isononanoate (18 total carbon atoms), 2-ethylhexyl palmitate (24 total carbon atoms), isotridecyl palmitate (29 total carbon atoms), 2-ethylhexyl stearate (26 total carbon atoms), isotridecyl stearate (31 total carbon atoms), and isotridecyl oleate (31 total carbon atoms) (the above are examples of branched-chain monoester compounds having a total of 10 to 50 carbon atoms that are liquid at 45°C), and diisodecyl adipate (26 total carbon atoms) (an example of a branched-chain diester compound having a total of 10 to 50 carbon atoms that is liquid at 45°C). The total carbon atoms of the branched-chain ester compound are preferably 18 to 31.

[0032] The hydrocarbon compound (B2) includes at least one compound selected from the group consisting of polyalphaolefins that are liquid at 45°C, synthetic paraffins that are liquid at 45°C, and mineral oils that are liquid at 45°C. Examples of polyalphaolefins that are liquid at 45°C include, but are not limited to, hydrogenated 1-decene oligomers. Examples of synthetic paraffins that are liquid at 45°C include, but are not limited to, the Shell® GTL series (manufactured by Shell Lubricants Japan Co., Ltd.) and the Isane® Biolife series (manufactured by Total Energies Lubricants Japan Co., Ltd.). Examples of mineral oils that are liquid at 45°C include, but are not limited to, the Cosmo Pure Spin® series (manufactured by Cosmo Oil Lubricants Co., Ltd.), the Diana Fresia® series (manufactured by Idemitsu Kosan Co., Ltd.), and the Ultra series (manufactured by S-OIL).

[0033] (nonionic surfactants) As the nonionic surfactant (C), known nonionic surfactants can be used without particular limitation. Non-limiting examples of the nonionic surfactant (C) include oxypropylene-based nonionic surfactants and secondary alcohol-based nonionic surfactants.

[0034] (Other ingredients) The sizing agent may contain components other than the urethane resin (A), the smoothing agent (B), and the nonionic surfactant (C) (hereinafter referred to as "other components"). Examples of such other components include, but are not limited to, resins other than the urethane resin (A) (such as butadiene resins, epoxy resins, and polyester resins), solvents, dispersants, silane coupling agents, preservatives, antistatic agents, antioxidants, UV absorbers, antifoaming agents, and surfactants other than the nonionic surfactant (C).

[0035] (Content of each ingredient) The sizing agent preferably contains 60% by mass or more, and more preferably 80% by mass or more, of urethane resin (A), where the total content of urethane resin (A) and smoothing agent (B) is 100% by mass. The content of urethane resin (A) may be less than 100% by mass, and is preferably 99% by mass or less, and more preferably 97% by mass or less, where the total content of urethane resin (A) and smoothing agent (B) is 100% by mass. That is, the content of smoothing agent (B) is preferably 1% by mass or more, and more preferably 3% by mass or more, where the total content of urethane resin (A) and smoothing agent (B) is 100% by mass.

[0036] When the sizing agent contains a nonionic surfactant (C), the urethane resin (A) is preferably contained in an amount of 60% by mass or more, and more preferably 80% by mass or more, based on the total content of the urethane resin (A), the smoothing agent (B), and the nonionic surfactant (C) being 100% by mass. The content of the urethane resin (A) may be less than 100% by mass, based on the total content of the urethane resin (A), the smoothing agent (B), and the nonionic surfactant (C) being 100% by mass, and is preferably 99% by mass or less, and more preferably 96% by mass or less. The content of the smoothing agent (B) is not limited as long as the total content including the nonionic surfactant (C) is greater than 0% by mass and is between 40% and 40% by mass, but is preferably 1% by mass or more, and more preferably 3% by mass or more. The content of the nonionic surfactant (C) is not limited as long as the total content together with the content of the smoothing agent (B) is more than 0 mass% and 40 mass%, but it is preferably 0.1 mass% or more, and more preferably 0.5 mass% or more.

[0037] [Method for producing a sizing agent for reinforcing fibers] The sizing agent according to this embodiment can be obtained, for example, by dissolving the urethane resin (A), the smoothing agent (B), and optionally the nonionic surfactant (C) and other components in a solvent. The solvent can be, for example, water. The apparatus, conditions, and method for dissolving the urethane resin (A) and other components in the solvent are optional. For example, the sizing agent according to this embodiment can be obtained by placing pre-weighed components other than the urethane resin (A) in a beaker at a temperature of 10°C to 90°C, gradually adding ion-exchanged water while stirring to prepare a uniform dispersion, and then gradually adding the urethane resin (A) dispersion. The urethane resin (A) dispersion used in this case may be a commercially available dispersion or may be prepared in advance.

[0038] Each raw material may be a commercially available product sold in the form of a mixture. In this case, it is not necessary to remove components other than the urethane resin (A), the smoothing agent (B), and the optionally added nonionic surfactant (C) before use. For example, a raw material containing the urethane resin (A) may be a commercially available product sold in the form of a solution or dispersion, and the solvent, dispersant, etc. contained in the commercially available product may be mixed without removing them. Therefore, the sizing agent may contain these solvents, dispersants, etc.

[0039] [Reinforced fiber] The reinforcing fiber according to this embodiment is characterized in that the sizing agent is attached to a fiber material. The fiber material may be any fiber material, such as carbon fiber. It is preferable to produce a fiber-reinforced resin using the fiber material to which the sizing agent according to this embodiment is attached as the reinforcing fiber, since this facilitates impregnation of the matrix resin into the reinforcing fiber.

[0040] The method for attaching the sizing agent to the fiber material can be any method commonly used in the art for attaching this type of sizing agent to fiber materials. That is, the immersion oiling method, the spray oiling method, the roller oiling method, the guide oiling method, etc. can be used. When applying each method, the sizing agent can be appropriately diluted with a solvent such as water.

[0041] The amount of sizing agent attached to the reinforcing fiber according to this embodiment is not particularly limited. For example, it is preferable that the amount of sizing agent attached is 0.3 mass % to 3 mass % of the total reinforcing fiber to which the sizing agent is attached.

[0042] Other Embodiments One aspect of the present invention is a sizing agent for reinforcing fibers containing a urethane resin (A) and a smoothing agent (B), wherein the smoothing agent (B) contains at least one compound selected from the group consisting of: an ester mixture (B1) which is a mixture of a linear ester compound that is liquid at 45°C and has 10 to 50 total carbon atoms and a branched ester compound that is liquid at 45°C and has 10 to 50 total carbon atoms; and a hydrocarbon compound (B2) which contains at least one compound selected from the group consisting of poly-α-olefins that are liquid at 45°C, synthetic paraffins that are liquid at 45°C, and mineral oils that are liquid at 45°C.

[0043] One aspect of the present invention may be a reinforcing fiber, characterized in that the above-mentioned sizing agent for reinforcing fibers is adhered to a fiber material. In one aspect of this reinforcing fiber, the fiber material is preferably an inorganic fiber.

[0044] These configurations make it possible to achieve high levels of impregnation of the matrix resin into the reinforcing fibers, abrasion resistance of the reinforcing fibers, openability of the reinforcing fibers, and stability of the sizing agent solution.

[0045] Regarding other configurations, it should be understood that the embodiments disclosed in this specification are illustrative in all respects and that the scope of the present invention is not limited thereby. Those skilled in the art will easily understand that appropriate modifications are possible without departing from the spirit of the present invention. Therefore, other embodiments modified without departing from the spirit of the present invention are naturally included in the scope of the present invention. [Example]

[0046] The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

[0047] [Preparation of sizing agent for reinforcing fibers] The sizing agents of the examples and comparative examples shown in Tables 5 to 9 below were obtained by the following method.

[0048] (1) Reagents (1-1) Urethane resin composition The urethane resin compositions used in the examples and comparative examples will be explained in order. Urethane resin compositions A-1 to A-14 are all aqueous dispersions of urethane resin, and all contain a urethane resin corresponding to the urethane resin (A) according to this embodiment. Urethane resin compositions A-1 to A-13 are commercially available products shown in Table 1, and their respective trade names, distributors, and solid content concentrations are also shown in Table 1. Urethane resin compositions A-1 to A-13 may contain an organic solvent, but since this organic solvent is removed in the drying process after the application of a sizing agent to the fibrous material and does not exert any effect on the fibrous material, the amount of this additive is not shown in Tables 5 to 9 below.

[0049] Table 1: Urethane resin composition (commercially available product) [Table 1]

[0050] Note that Superflex, Dispercol, Baybond, Bayhydrol, ETERNACOLL, and Adekabontiter listed in Table 1 are registered trademarks. Also, the symbols in the distributor section of Table 1 represent the following companies. *1: Daiichi Kogyo Seiyaku Co., Ltd. *2: Sumika Covestro Urethane Co., Ltd. *3: UBE Corporation *4:ADEKA Corporation

[0051] Urethane resin composition A-14 is an aqueous dispersion of a copolymer of hexanemethylene diisocyanate, polyethylene oxide, and polypropylene oxide. The number average molecular weight of the copolymer is 12,000, and the solids concentration of the composition is 4%.

[0052] The urethane resin contents shown in Tables 5 to 9 below are values ​​that do not include the contents of solvents and the like contained in urethane resin compositions A-1 to A-14.

[0053] (1-2) Smoothing agent The lubricants used in the examples and comparative examples will be explained in order.

[0054] The ester compounds used as smoothing agents are shown in Table 2. Of the ester compounds shown in Table 2, ester compounds B1-1 to B1-6 and B1-13 are linear ester compounds that are liquid at 45°C and have a total of 10 to 50 carbon atoms, and ester compounds B1-1 to B1-6 are linear monoester compounds that are liquid at 45°C and have a total of 10 to 50 carbon atoms. Ester compounds B1-7 to B1-12 and B1-14 are branched ester compounds that are liquid at 45°C and have a total of 10 to 50 carbon atoms, and ester compounds B1-7 to B1-12 are branched monoester compounds that are liquid at 45°C and have a total of 10 to 50 carbon atoms.

[0055] Table 2: Ester compounds [Table 2]

[0056] Among the examples and comparative examples, examples containing at least one selected from ester compounds B1-1 to B1-6 and B1-13 and at least one selected from ester compounds B1-7 to B1-12 and B1-14 correspond to examples containing an ester mixture (B1) as a smoothing agent.

[0057] The hydrocarbon compounds used as lubricants are shown in Table 3. Of the hydrocarbon compounds shown in Table 3, hydrocarbon compounds B2-1 to B2-3 are synthetic paraffins that are liquid at 45°C, B2-4 to B2-9 are mineral oils that are liquid at 45°C, and B2-10 and B2-11 are poly-α-olefins that are liquid at 45°C.

[0058] Table 3: Hydrocarbon compounds [Table 3]

[0059] Shell, Isane, Purespin, and Diana Fresia listed in Table 3 are registered trademarks. The symbols in the Sellers section of Table 3 represent the following companies. *1: Shell Lubricants Japan Co., Ltd. *2: Total Energies Lubricants Japan Co., Ltd. *3: Cosmo Oil Lubricants Co., Ltd. *4: Idemitsu Kosan Co., Ltd. *5:S-OIL Co., Ltd. *6: Nippon Seiro Co., Ltd.

[0060] (1-3) Nonionic surfactants The nonionic surfactants used in the examples and comparative examples will be explained in order. Note that although examples of the manufacturing method for each compound may be shown below, each manufacturing method is only an example, and even if the compound is manufactured by a method different from the method exemplified below, the results of the examples and comparative examples will not change.

[0061] Nonionic surfactant C-1 is an adduct of 10 moles of ethylene oxide with 1 mole of lauric acid. Nonionic surfactant C-1 was obtained by reacting lauric acid with ethylene oxide in a molar ratio of 1:10.

[0062] Nonionic surfactant C-2 is an adduct of 1 mole of oleic acid and 3 moles of ethylene oxide. Nonionic surfactant C-2 was obtained by reacting oleic acid and ethylene oxide in a molar ratio of 1:3.

[0063] Nonionic surfactant C-3 is an adduct of 1 mole of oleic acid and 13 moles of ethylene oxide. Nonionic surfactant C-3 was obtained by reacting oleic acid and ethylene oxide in a molar ratio of 1:13.

[0064] Nonionic surfactant C-4 is an adduct of 10 moles of ethylene oxide with 1 mole of lauryl alcohol. Nonionic surfactant C-4 was obtained by reacting lauryl alcohol with ethylene oxide in a molar ratio of 1:10.

[0065] As the nonionic surfactant C-5, Softanol (registered trademark) 50 (manufactured by Nippon Shokubai Co., Ltd.) was used.

[0066] As the nonionic surfactant C-6, Softanol (registered trademark) 90 (manufactured by Nippon Shokubai Co., Ltd.) was used.

[0067] Nonionic surfactant C-7 is an adduct of 1 mole of tristyrenated phenol and 20 moles of ethylene oxide. Tristyrenated phenol and ethylene oxide were reacted in a molar ratio of 1:20 to obtain nonionic surfactant C-7.

[0068] Nonionic surfactant C-8 is an adduct of 1 mole of 12-hydroxystearic acid triglyceride and 8 moles of ethylene oxide. Nonionic surfactant C-8 was obtained by reacting 12-hydroxystearic acid triglyceride with ethylene oxide in a molar ratio of 1:8.

[0069] Nonionic surfactant C-9 is an adduct of 12 moles of ethylene oxide with 1 mole of 12-hydroxystearic acid triglyceride. Nonionic surfactant C-9 was obtained by reacting 12-hydroxystearic acid triglyceride with ethylene oxide in a molar ratio of 1:12.

[0070] Nonionic surfactant C-10 is an adduct of 12 moles of ethylene oxide with 1 mole of oleyl alcohol. Nonionic surfactant C-10 was obtained by reacting oleyl alcohol with ethylene oxide in a molar ratio of 1:12.

[0071] (1-4) Other ingredients Table 4 shows the urethane resin, smoothing agent, nonionic surfactant and other components used in the examples and comparative examples.

[0072] Table 4: Other ingredients [Table 4]

[0073] PYRATEX, jER, and Finetex listed in Table 4 are registered trademarks. The symbols in the Sellers section of Table 4 represent the following companies. *1: Nippon A&L Co., Ltd. *2: Kumho P&B Chemicals, Inc. *3: Mitsubishi Chemical Corporation *4:Synthomer USA LLC *5:DIC Corporation *6: Shin-Etsu Chemical Co., Ltd.

[0074] (2) Preparation of sizing agent For each of the Examples and Comparative Examples, the components were weighed out in the mass ratios shown in Tables 5 to 9 below. The mass ratios of the urethane resins in Tables 5 to 9 indicate the mass ratios of the urethane resin components, and the corresponding amounts of urethane resin compositions used are calculated by dividing the mass ratios by the solids concentration of the urethane resin composition. For example, in Example 1, the mass ratio of urethane resin composition A-1 was 80 mass%, but the solids concentration of urethane resin composition A-1 was 50 mass%, so the weighed mass of urethane resin composition A-1 was equivalent to 160 mass% (80 mass% ÷ 50 mass%). The mass ratios of the components are calculated relative to the total content of the urethane resin, smoothing agent, and nonionic surfactant, which is 100 mass%.

[0075] First, all components other than the urethane resin composition were weighed and placed in a beaker, and ion-exchanged water was added little by little while stirring to prepare a uniform dispersion. Next, the urethane resin composition (all of urethane resin compositions A-1 to A-14 are dispersions) was added little by little to the dispersion. Thereafter, ion-exchanged water was gradually added to the resulting solution while stirring to adjust the nonvolatile content to 4% by mass, thereby preparing the sizing agent for each example.

[0076] [Evaluation of sizing agents for reinforcing fibers] (1) Reinforced fiber manufacturing Reinforcing fibers were produced using the sizing agents of each of the Examples and Comparative Examples. The sizing agents of each of the Examples and Comparative Examples were evaluated based on the state of each part of the production equipment during production and the physical properties of the resulting reinforcing fibers. In Tables 5 to 9 below, carbon fiber is abbreviated as CF and glass fiber is abbreviated as GF.

[0077] (1-1) Production of strand-shaped carbon fiber A 2% dispersion of the sizing agent of each of the Examples and Comparative Examples was applied to commercially available strand-shaped carbon fiber without any sizing agent by immersion so that the amount of sizing agent attached was 2% by mass (excluding the solvent). The carbon fiber with the sizing agent attached was passed through an electric furnace to remove the solvent. The heating conditions were 120°C and 5 minutes. The dried carbon fiber was wound around a bobbin to obtain a strand-shaped carbon fiber with a sizing agent attached.

[0078] (1-2) Production of nonwoven carbon fiber The sizing agent of each of the Examples and Comparative Examples was applied to commercially available nonwoven carbon fiber fabrics to which no sizing agent had been applied by spraying. The spray liquid was sprayed to a concentration of 2%, and the amount of sizing agent applied was 2% by mass (excluding the solvent). The carbon fiber to which the sizing agent had been applied was heated in an electric furnace to remove the solvent. The heating conditions were 120°C and 5 minutes.

[0079] (1-3) Production of strand-shaped glass fibers The sizing agent of each of the Examples and Comparative Examples was applied to commercially available strand-shaped glass fibers to which no sizing agent had been applied by immersion. The concentration of the sizing agent dispersion in the oil bath was set to 2%, and oil was added so that the amount of sizing agent attached was 2% by mass (excluding solvent). The glass fibers to which the sizing agent had been applied were passed through an electric furnace to remove the solvent. The heating conditions were 120°C and 5 minutes. The dried glass fibers were wound around a bobbin to obtain glass fibers to which the sizing agent had been applied.

[0080] (1-4) Manufacturing of nonwoven glass fiber The sizing agent of each of the Examples and Comparative Examples was applied to commercially available nonwoven glass fiber fabrics to which no sizing agent had been applied by spraying. The spray liquid was sprayed to a concentration of 2%, and the amount of sizing agent applied was 2% by mass (excluding the solvent). The glass fiber to which the sizing agent had been applied was heated in an electric furnace to remove the solvent. The heating conditions were 120°C and 5 minutes.

[0081] (2) Stability evaluation A 4% dispersion of each sizing agent from each of the Examples and Comparative Examples was circulated in an oil bath using a pump, and the state of the dispersion was visually observed. The results were classified into the following five levels. Of these, level D and above are practical. A: After 14 days, no gel formation was observed and smooth continuous operation was possible. B: No gel formation was observed after 7 days. After 14 days, when the pump circulation was stopped and observation was made, a visible amount of gel formation was observed, but it did not interfere with continuous operation. C: After 7 days, the pump circulation was stopped and observation revealed that a visible amount of gel had formed, but this did not interfere with continuous operation. D: After 7 days, a visible amount of gel was observed while the pump was circulating, but this did not interfere with continuous operation. E: Within 7 days, visible amounts of gel were observed while the pump was circulating, hindering continuous operation.

[0082] (3) Abrasion evaluation The carbon fiber and glass fiber strands obtained by the above method were used as samples to evaluate their abrasion resistance. Five 2mm diameter chrome-plated stainless steel rods were arranged in a zigzag pattern at 15mm intervals. The strands unwound from the rolls were stretched so that they contacted the stainless steel rods at a contact angle of 120° and were wound up under a tension of 1kg. Just before the winding roll, the strands were sandwiched between two 10cm square pieces of urethane foam with a 1kg load applied, and rubbed at a speed of 1m / min for 5 minutes. The mass of fluff adhering to the sponge was measured, and the samples were classified into the following three levels based on that mass. Of these, level C or higher was deemed practical. A: The fuzz was less than 0.15 mg per meter of strand. C: The amount of fluff per 1 m of strand was 0.15 mg or more but less than 0.20 mg. E: The amount of fluff per 1 m of strand was 0.20 mg or more.

[0083] (4) Spreadability evaluation The carbon fiber strands and glass fiber strands obtained by the above method were used as samples to evaluate their spreadability. The strands were spread while being transported by rollers, and the state after spreading was visually observed. Based on the observed state, the samples were classified into the following two levels: Level A is practically usable, and Level E is difficult to use. A: There were no gaps between the fiber bundles after spreading, and they were spread evenly. E: The fiber bundles were not sufficiently opened.

[0084] (5) Impregnation evaluation The carbon fiber nonwoven fabric and glass fiber nonwoven fabric obtained by the above method were used as samples to evaluate impregnation. Two 10 cm square test sheets were cut from each nonwoven fabric. 0.5 g of polyamide 6 (Amilan CM1017, manufactured by Toray) pellets were sandwiched between the two test sheets, and the two test pieces were then sandwiched between a polytetrafluoroethylene sheet (Teflon® sheet, manufactured by DuPont) from the outside to form a test piece. The test pieces were pressed for 30 seconds at 300°C and 1 MPa using a hot press (AS ONE, high-temperature hot press 0-1t H400-01). After pressing, the test pieces were disassembled, the test sheets were peeled off from the polytetrafluoroethylene sheet, and the surface facing the polytetrafluoroethylene sheet (observation surface) was visually observed. Based on the results of the visual evaluation, the test pieces were classified into the following three levels. Of these, level C or higher was considered practical. A: For both test sheets, it was clearly possible to see that the polyamide 6 reached the observation surface. C: For one or both of the two test sheets, it was possible to slightly observe that the polyamide 6 had reached the observation surface. E: For both test sheets, the polyamide 6 did not appear to have reached the observation surface.

[0085] 〔result〕 Tables 5 to 9 show the formulation of the sizing agent and the evaluation results for each of the examples and comparative examples.

[0086] Table 5: Examples [Table 5]

[0087] Table 6: Examples [Table 6]

[0088] Table 7: Comparative Examples [Table 7]

[0089] Table 8: Examples [Table 8]

[0090] Table 9: Comparative Examples [Table 9] [Industrial Applicability]

[0091] The present invention can be used for the production of reinforcing fibers such as carbon fibers and glass fibers.

Claims

1. A sizing agent for reinforcing fibers, comprising a urethane resin (A) and a smoothing agent (B), and applied to inorganic fibers including at least one of carbon fibers and glass fibers, The smoothing agent (B) an ester mixture (B1) which is a mixture of a linear ester compound having a total carbon number of 10 to 50 and which is liquid at 45°C, and a branched ester compound having a total carbon number of 10 to 50 and which is liquid at 45°C; and a hydrocarbon compound (B2) containing at least one compound selected from the group consisting of polyalphaolefins that are liquid at 45°C, synthetic paraffins that are liquid at 45°C, and mineral oils that are liquid at 45°C; A sizing agent for reinforcing fibers, comprising at least one selected from the group consisting of:

2. 2. The sizing agent for reinforcing fibers according to claim 1, wherein the smoothing agent (B) contains the ester mixture (B1).

3. 3. The sizing agent for reinforcing fibers according to claim 2, wherein in the ester mixture (B1), at least a part of the linear ester compounds is a linear monoester compound, and at least a part of the branched ester compounds is a branched monoester compound.

4. The sizing agent for reinforcing fibers according to claim 3, wherein the linear monoester compound and the branched monoester compound account for 20 mass% or more in total in the ester mixture (B1).

5. 2. The sizing agent for reinforcing fibers according to claim 1, wherein the urethane resin (A) is contained in an amount of 60% by mass or more and less than 100% by mass, where the total content of the urethane resin (A) and the smoothing agent (B) is 100% by mass.

6. The sizing agent for reinforcing fibers according to claim 1, further comprising a nonionic surfactant (C).

7. 7. The sizing agent for reinforcing fibers according to claim 6, wherein the urethane resin (A) is contained in an amount of 60% by mass or more and less than 100% by mass, where the total content of the urethane resin (A), the smoothing agent (B), and the nonionic surfactant (C) is 100% by mass.

8. A reinforcing fiber comprising inorganic fibers including at least one of carbon fibers and glass fibers, and the sizing agent for reinforcing fibers according to any one of claims 1 to 7 attached to the reinforcing fiber.

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