Sizing agents for reinforcing fibers, reinforcing fibers, and fiber composite materials

Abstract

This invention provides a sizing agent for reinforcing fibers that offers emulsion stability while improving the penetration rate when impregnating reinforcing fibers with matrix resin. Furthermore, it enables the creation of reinforcing fibers to which this sizing agent adheres, and fiber composite materials using these reinforcing fibers as reinforcing materials. [Solution] The sizing agent for reinforcing fibers contains a resin and a nonionic surfactant containing a benzylated phenol derivative (A), which is an alkylene oxide adduct of benzylated phenols having at least one benzyl group, wherein the benzylated phenol derivative (A) contains a dibenzylated phenol derivative (A2), which is an adduct in which a total of 1 to 100 moles of alkylene oxide are added to 1 mole of dibenzylated phenol. In the case of reinforcing fibers, the sizing agent for reinforcing fibers is attached to the fiber material. In the case of fiber composite materials, the matrix resin is impregnated into the reinforcing fibers.

Description

Technical Field

[0001] The present invention relates to a sizing agent for reinforcing fibers, reinforcing fibers, and fiber composite materials.

Background Art

[0002] Fiber composite materials obtained by impregnating reinforcing fibers such as carbon fibers and glass fibers with a matrix resin such as an epoxy resin are widely used in fields such as machinery, construction materials, and transportation equipment. Before impregnating the reinforcing fibers used in the fiber composite material with the matrix resin, a treatment is performed to attach a sizing agent (also referred to as a sizing agent) for the purpose of suppressing damage to the reinforcing fibers and enhancing the bundling property of the reinforcing fibers.

[0003] As this type of sizing agent, for example, Japanese Patent Application Laid-Open No. 2019-99942 (Patent Document 1) discloses a sizing composition for carbon fibers containing a sizing agent and a nonionic surfactant, wherein the nonionic surfactant contains an alkylene oxide adduct of distyrenated phenol and an alkylene oxide adduct of tristyrenated phenol.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The sizing composition (sizing agent) for carbon fibers of Patent Document 1 is said to be able to improve the wettability of the reinforcing fibers with respect to the matrix resin and the bundling property of the carbon fiber strands by containing the above-described specific nonionic surfactant. However, there was room for improvement in the impregnability (i.e., penetration rate) of the matrix resin with respect to the reinforcing fibers to which the sizing agent of Patent Document 1 was applied.

[0006] Therefore, there is a need to realize a sizing agent for reinforcing fibers that combines emulsion stability and the impregnation properties of the matrix resin into the fiber material, reinforcing fibers to which this agent has been applied, and fiber composite materials using these reinforcing fibers as a reinforcing material. [Means for solving the problem]

[0007] The present invention has been made in view of the above-mentioned problems, and the sizing agent for reinforcing fibers according to the present invention contains a resin and a nonionic surfactant containing a benzylated phenol derivative (A), which is an alkylene oxide adduct of benzylated phenols having at least one benzyl group, wherein the benzylated phenol derivative (A) contains a dibenzylated phenol derivative (A2), which is an adduct in which a total of 1 to 100 moles of alkylene oxide are added to 1 mole of dibenzylated phenol.

[0008] The reinforced fiber according to the present invention is characterized in that the above-mentioned sizing agent for reinforced fibers is attached to the fiber material.

[0009] Furthermore, the fiber composite material according to the present invention is characterized in that the reinforcing fibers are impregnated with a matrix resin.

[0010] With these configurations, since the sizing agent for reinforcing fibers contains the specific dibenzylated phenol derivative (A2) described above, the penetration rate of the reinforcing fibers to the matrix resin after the sizing agent is attached to the fiber material can be improved. As a result, it is easier to improve the physical properties such as the strength of the fiber composite material. Furthermore, the sizing agent for reinforcing fibers of the present invention also has good emulsion stability and can suppress the generation of scum in the sizing treatment solution, thus providing excellent operational stability.

[0011] Preferred embodiments of the present invention will be described below. However, the scope of the present invention is not limited by the examples of preferred embodiments described below.

[0012] In one embodiment, the sizing agent for reinforcing fibers according to the present invention preferably contains at least ethylene oxide and propylene oxide in the dibenzylated phenol derivative (A2).

[0013] This configuration makes it easier to achieve both emulsion stability of the sizing agent for reinforcing fibers and impregnation of the matrix resin into the reinforcing fibers.

[0014] In one embodiment, the sizing agent for reinforcing fibers according to the present invention preferably further comprises a tripenzylated phenol derivative (A3), which is an adduct in which a total of 1 to 100 moles of alkylene oxide are added to 1 mole of tripenzylated phenol.

[0015] With this configuration, the sizing agent for reinforcing fibers contains multiple types of benzyl phenol derivatives, which further improves the stability of the emulsion and makes it easier to suppress the generation of scum.

[0016] In one embodiment, the sizing agent for reinforcing fibers according to the present invention preferably contains the dibenzylated phenol derivative (A2) and the tripenzylated phenol derivative (A3) in a mass ratio of dibenzylated phenol derivative (A2) / tribenzyllated phenol derivative (A3) = 10 / 90 to 80 / 20.

[0017] This configuration makes it easier to achieve both emulsion stability of the sizing agent for reinforcing fibers and impregnation properties of the matrix resin into the reinforcing fibers.

[0018] The sizing agent for reinforcing fibers according to the present invention preferably contains at least one of a monobenzylated phenol derivative (A1) which is an adduct obtained by adding a total of 1 to 100 moles of an alkylene oxide to 1 mole of monobenzylated phenol, and a polybenzylated phenol derivative (A4) which is an adduct obtained by adding a total of 1 to 100 moles of an alkylene oxide to 1 mole of polybenzylated phenol having four or more benzyl groups.

[0019] According to this configuration, since the sizing agent for reinforcing fibers contains a plurality of types of benzylated phenol derivatives, it is easier to further suppress the generation of scum.

[0020] The sizing agent for reinforcing fibers according to the present invention preferably contains the benzylated phenol derivative (A) in a proportion of 5 to 50% by mass in the non-volatile content.

[0021] According to this configuration, it is easier to further balance the emulsion stability of the sizing agent for reinforcing fibers and the impregnability of the matrix resin to the reinforcing fibers.

[0022] The sizing agent for reinforcing fibers according to the present invention preferably contains at least one selected from the group consisting of an epoxy resin, a vinyl ester resin, a polyolefin resin, a polyurethane resin, an acrylic resin, and a polyester resin as the resin.

[0023] According to this configuration, it is easy to realize the sizing agent for reinforcing fibers of the present invention.

[0024] Further features and advantages of the present invention will become more apparent from the following description of exemplary and non-limiting embodiments.

Embodiments for Carrying out the Invention

[0025] Embodiments of the sizing agent for reinforcing fibers, reinforcing fibers, and fiber composite materials according to the present invention will be described.

[0026] [1]Sizing Agent for Reinforcing Fibers The sizing agent for reinforcing fibers according to this embodiment (hereinafter, also simply referred to as a sizing agent) contains at least a resin and a nonionic surfactant.

[0027] (1) Resin The resin is not limited in type as long as it is a resin that is dispersed or dissolved in the sizing agent. As the resin, for example, it preferably contains at least one selected from the group consisting of epoxy resins, vinyl ester resins, polyolefin resins, polyurethane resins, acrylic resins, and polyester resins.

[0028] As the epoxy resin, known epoxy resins can be used without particular limitation. The epoxy resin may be a commercially available product, and non-limiting examples include Epotope (registered trademark) series (manufactured by Nippon Steel Chemical & Material Co., Ltd.), Denacol (manufactured by Nagase ChemteX Corporation), KER series (manufactured by Kumho P&B Chemicals, Inc.), etc.

[0029] The vinyl ester resin is, for example, a thermosetting resin obtained by the reaction of an epoxy resin and an unsaturated monocarboxylic acid. As the vinyl ester resin, known vinyl ester resins can be used without particular limitation. The vinyl ester resin may be a commercially available product, and non-limiting examples include those obtained by reacting a commercially available epoxy resin with an unsaturated monocarboxylic acid.

[0030] As the polyolefin resin, known polyolefin resins, modified polyolefin resins, etc. can be used without particular limitation. The polyolefin resin (especially the modified polyolefin resin) may be a commercially available product, and non-limiting examples include the MGP series (manufactured by Maruho Chemical Co., Ltd.), the High-Tech P series (manufactured by Toho Chemical Industry Co., Ltd.), the Sumikaflex series (manufactured by Sumitomo Chemical Co., Ltd.), etc.

[0031] Any known urethane resin can be used without particular limitation. The urethane resin may be a commercially available product, and examples of such products include, but are not limited to, the Superflex® series (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Dispacol® series (manufactured by Sumika Covestro Urethane Co., Ltd.), Bibond® series (manufactured by Sumika Covestro Urethane Co., Ltd.), Bihydrol® series (manufactured by Sumika Covestro Urethane Co., Ltd.), ETERNACOLL® series (manufactured by UBE Corporation), Adekabonditer® HUX series (manufactured by ADEKA Corporation), and MELUSI® series (manufactured by Toyo Polymer Co., Ltd.).

[0032] Any known acrylic resin can be used without particular restriction. The acrylic resin may be a commercially available product, and examples include the Acryset series (manufactured by Nippon Shokubai Co., Ltd.) and Nikazol (manufactured by Nippon Carbide Industries Co., Ltd.), among others.

[0033] Any known polyester resin can be used without particular limitation. The polyester resin may be a commercially available product, and examples include the Hi-Tech PE series (manufactured by Toho Chemical Industry Co., Ltd.), which are not limited to this.

[0034] The resin may be provided as a liquid resin and used by incorporating it into the sizing agent. Alternatively, the resin 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 resin in the mixture (such as solvents and dispersants) may be included in the sizing agent without being removed. Furthermore, the resin may consist of one type of component or may be a mixture of multiple types of resins.

[0035] In the sizing agent of the embodiment, the resin is preferably contained in an amount of 45% by mass or more, and more preferably 50% by mass or more, in the non-volatile content of the sizing agent. Furthermore, it is preferably contained in an amount of 90% by mass or less, and more preferably 85% by mass or less. If multiple types of resins are included, this resin content represents the total content of those resins. Here, non-volatile content refers to the components that remain without volatilizing after the sizing agent is heated in a hot air dryer at 105°C for 2 hours.

[0036] (2) Nonionic surfactants The nonionic surfactant of the present invention comprises a benzylated phenol derivative (A), and optionally comprises other nonionic surfactants other than the benzylated phenol derivative (A).

[0037] (2-1) Benzylated phenol derivative (A) The benzylated phenol derivative (A) is an alkylene oxide adduct of a benzylated phenol, which is a phenol-substituted compound having at least one benzyl group. Specifically, benzylated phenols include monobenzyl phenols, dibenzyl phenols, tripenzylated phenols, and polybenzyl phenols having four or more benzyl groups, and the benzylated phenol derivative (A) is an adduct obtained by adding an alkylene oxide to the benzylated phenol. The benzylated phenol derivative (A) may be one type or multiple types.

[0038] (2-1-1) Dibenzylated phenol derivative (A2) The sizing agent according to the present invention includes a dibenzyl phenol derivative (A2) as a benzylated phenol derivative (A), which is an adduct obtained by adding a total of 1 to 100 moles of alkylene oxide to 1 mole of dibenzyl phenol.

[0039] The sizing agent described in Patent Document 1, mentioned above, contains an alkylene oxide adduct of distyrenelated phenol and an alkylene oxide adduct of tristyrenelated phenol, which is thought to improve the stability of the emulsion, thereby improving the wettability to the matrix resin and the flocculation of the carbon fiber strands. However, the inventors have found that reinforcing fibers using a sizing agent containing both an alkylene oxide adduct of distyrenelated phenol and an alkylene oxide adduct of tristyrenelated phenol do not easily improve the penetration rate of the matrix resin. Therefore, the inventors conducted diligent research and found that by incorporating an alkylene oxide adduct (A2) of a specific dibenzyl phenol as a nonionic surfactant, it is possible to achieve both emulsion stability and a high penetration rate of the matrix resin into the reinforcing fibers, leading to the present invention.

[0040] The sizing agent according to this embodiment contains the aforementioned specific dibenzylated phenol derivative (A2) as a nonionic surfactant, resulting in good emulsion stability and improved penetration rate of the matrix resin into the reinforcing fibers while suppressing scum formation.

[0041] In the dibenzylated phenol derivative (A2), the number of carbon atoms in the alkylene oxide (AO) added to the dibenzylated phenol is not particularly limited, but for example, an alkylene oxide having 2 to 4 carbon atoms is preferably used. The alkylene oxide (AO) may contain not just one but multiple types of alkylene oxides, and it is preferable that it contains at least one of ethylene oxide and propylene oxide, and more preferably both ethylene oxide and propylene oxide. The number of carbon atoms in the alkylene oxide (AO) and the number of moles added are the same for the alkylene oxide (AO) in the monobenzylated phenol derivative (A1), tripenzylated phenol derivative (A3), and polybenzylated phenol derivative (A4) described later.

[0042] The dibenzylated phenol derivative (A2) according to this embodiment may include a compound represented by one of the structural formulas of formula (1) and formula (2) below. [ka] [ka] In formulas (1) and (2), AO represents an alkylene oxide group. In formulas (1) and (2), "m" represents the number of added alkylene oxide groups. m is, for example, an integer from 1 to 100, but the dibenzylated phenol derivative (A2) of the present invention is an adduct obtained by adding a total of 1 to 100 moles of alkylene oxide to 1 mole of dibenzylated phenol, and it is not prevented that dibenzylated phenol derivatives (A2) with more than 100 alkylene oxide groups as individual molecules are included, nor is it prevented that dibenzylated phenol with 0 alkylene oxide groups is included.

[0043] As shown in formulas (1) and (2) above, the dibenzylated phenol that serves as the raw material for the dibenzylated phenol derivative (A2) according to this embodiment only needs to have two benzyl groups introduced to the phenol skeleton, and the positions in which the benzyl groups are introduced are not particularly limited. It may be a dibenzylphenol in which two benzyl groups are directly introduced as substituents to the aromatic ring of the phenol skeleton as shown in formula (1) above, or a second benzyl group may be introduced to the aromatic ring of the first benzyl group directly introduced as a substituent to the phenol skeleton as shown in formula (2) above.

[0044] The sizing agent according to this embodiment preferably contains 2 to 30% by mass of dibenzylated phenol derivative (A2) in the nonvolatile content of the sizing agent. Setting the concentration range of dibenzylated phenol derivative (A2) within the above range makes it easier to further achieve both suppression of scum generation and improvement of the penetration rate of the matrix resin into the reinforcing fibers. The sizing agent according to this embodiment is even more preferably containing 3 to 20% by mass of dibenzylated phenol derivative (A2) in the nonvolatile content.

[0045] (2-1-2) Tribenzylated phenol derivative (A3) In this embodiment, the sizing agent preferably includes a benzylated phenol derivative (A) that, in addition to a dibenzylated phenol derivative (A2), further contains a tripenzylated phenol derivative (A3), which is an adduct obtained by adding a total of 1 to 100 moles of alkylene oxide to 1 mole of tripenzylated phenol.

[0046] Similar to the dibenzylated phenol derivative (A2) described above, the tripenzylated phenol used as a raw material for the tripenzylated phenol derivative (A3) according to this embodiment only needs to have three benzyl groups introduced to the phenol skeleton, and the positions in which the benzyl groups are introduced are not particularly limited. For example, it may be tripenzylphenol in which three benzyl groups are directly introduced to the phenol skeleton as substituents, or the second and third benzyl groups may be introduced to the aromatic ring of the first benzyl group directly introduced to the phenol skeleton, or a third benzyl group may be introduced to any of the aromatic rings of the two benzyl groups directly introduced to the phenol skeleton as substituents. Thus, if the sizing agent according to this embodiment contains multiple types of benzylated phenol derivatives, it is easier to suppress the generation of scum. It is preferable that the tripenzylated phenol derivative (A3) is included in the non-volatile content of the sizing agent at a concentration of 2 to 30% by mass.

[0047] The sizing agent according to this embodiment preferably contains the above-mentioned dibenzylated phenol derivative (A2) and tripenzylated phenol derivative (A3) in a mass ratio of dibenzylated phenol derivative (A2) / tribenzylated phenol derivative (A3) = 10 / 90 to 80 / 20. When the mass ratio of dibenzylated phenol derivative (A2) / tribenzylated phenol derivative (A3) is 10 / 90 or higher, the penetration rate of the matrix resin into the reinforcing fibers tends to improve. Also, when the mass ratio of dibenzylated phenol derivative (A2) / tribenzylated phenol derivative (A3) is 80 / 20 or lower, the generation of scum in the sizing solution tends to be suppressed.

[0048] (2-1-3) Monobenzyl phenol derivatives (A1) and polybenzyl phenol derivatives (A4) The sizing agent for reinforcing fibers according to this embodiment preferably contains at least one of the following: a monobenzyl phenol derivative (A1), which is an adduct obtained by adding a total of 1 to 100 moles of alkylene oxide to 1 mole of monobenzyl phenol; and a polybenzyl phenol derivative (A4), which is an adduct obtained by adding a total of 1 to 100 moles of alkylene oxide to 1 mole of polybenzyl phenol having four or more benzyl groups. It is preferable that at least one of the monobenzyl phenol derivative (A1) and the polybenzyl phenol derivative (A4) is contained in the nonvolatile content of the sizing agent at a concentration of 1 to 15% by mass.

[0049] The monobenzyl phenol used as a raw material for the monobenzyl phenol derivative (A1) is a compound in which one benzyl group is directly introduced into the phenol skeleton, and the position where the benzyl group is introduced (meta, para, ortho) is not particularly limited. Furthermore, the polybenzyl phenol used as a raw material for the polybenzyl phenol derivative (A4) is a compound in which four or more benzyl groups are introduced into the phenol skeleton, and the position where the benzyl groups are introduced is not limited, similar to the dibenzyl phenol derivative (A2) and tripenzylate phenol derivative (A3). With this configuration, the sizing agent for reinforcing fibers contains multiple types of benzyl phenol derivatives, making it easier to suppress the generation of scum.

[0050] As described above, the sizing agent according to the present invention contains a dibenzylated phenol derivative (A2) as an essential component of the benzylated phenol derivative (A), and optionally contains a monobenzylated phenol derivative (A1), a tripenzylated phenol derivative (A3), and a polybenzylated phenol derivative (A4). The sizing agent according to this embodiment preferably contains the benzylated phenol derivative (A) containing these components in a proportion of 5 to 50% by mass in the non-volatile content of the sizing agent. Including the benzylated phenol derivative (A) in a proportion of 5% by mass or more in the non-volatile content of the sizing agent suppresses the generation of scum and facilitates the penetration rate of the matrix resin into the reinforcing fibers. Furthermore, the sizing agent according to this embodiment can be given a concentration suitable for a sizing agent by including the benzylated phenol derivative (A) in a proportion of 50% by mass or less in the non-volatile content.

[0051] Furthermore, a preferred embodiment of the sizing agent according to this embodiment includes a dibenzyl phenol derivative (A2) as an essential component, and also includes at least one of monobenzyl phenol derivative (A1), tripenzylate phenol derivative (A3), and polybenzyl phenol derivative (A4). In this case, when the mass ratio of dibenzyl phenol derivative (A2) is set to 1, it is preferable that the total mass ratio of monobenzyl phenol derivative (A1), tripenzylate phenol derivative (A3), and polybenzyl phenol derivative (A4) is 0.3 or more. Also, when the mass ratio of the resin is set to 1, it is preferable that the ratio of benzyl phenol derivative (A) is 1 to 10.

[0052] Furthermore, various benzylated phenols (monobenzylated phenol, dibenzylated phenol, tripenzylated phenol, polybenzylated phenol), which are phenol-substituted products having at least one benzyl group and serve as raw materials for the benzylated phenol derivative (A) mentioned above, can be produced by conventionally known synthesis methods. For example, they can be produced by purifying a reaction solution obtained by reacting phenol and benzyl alcohol in a predetermined molar ratio under a Lewis acid catalyst (e.g., aluminum chloride, γ-alumina, etc.).

[0053] (3) Other nonionic surfactants Other than the benzylated phenol derivative (A), known nonionic surfactants can be used without particular limitation. Non-limiting examples of other nonionic surfactants include nonionic surfactants such as alkylene oxide adducts of styrenated phenol, alkylene oxide adducts of distyrenated phenol, alkylene oxide adducts of tristyrenated phenol, alkylene oxide adducts of distyrenated cumylphenol, and alkylene oxide adducts of nonylphenol; alkylene oxide adducts of higher alcohols such as tetradecyl alcohol, dodecyl alcohol, and isotridecyl alcohol; alkylene oxide adducts of vegetable oils; and sorbitan monooleate. Preferably, the alkylene oxide contains at least one of ethylene oxide and propylene oxide. The content of other nonionic surfactants is not particularly limited, and for example, it is preferably 30% by mass or less, more preferably 20% by mass or less, in the nonvolatile content of the sizing agent.

[0054] (4) Other ingredients The sizing agent may contain, as an optional component, components other than resins and nonionic surfactants (hereinafter referred to as "other components"). Examples of such other components include, but are not limited to, surfactants other than nonionic surfactants (such as anionic surfactants), smoothing agents, solvents, dispersants, silane coupling agents, preservatives, antistatic agents, antioxidants, UV absorbers, and defoaming agents.

[0055] The smoothing agent preferably contains at least one selected from the group consisting of a predetermined ester compound and a predetermined hydrocarbon compound. When the smoothing agent contains an ester compound, the abrasion resistance of the reinforcing fiber tends to improve. However, there is no prejudice against the smoothing agent containing both an ester compound and a hydrocarbon compound.

[0056] The ester compound preferably contains at least one selected from the group consisting of linear ester compounds with 10 to 50 total carbon atoms that are liquid at 45°C, and branched ester compounds with 10 to 50 total carbon atoms that are liquid at 45°C. The linear ester compound may be a single compound or a mixture of multiple compounds. It is preferable that a portion of the linear ester compound be a linear monoester compound, and more preferably that all of it be a linear monoester compound, as this makes it easier to obtain a stable sizing agent solution. The branched ester compound may be a single compound or a mixture of multiple compounds. It is preferable that a portion of the branched ester compound be a branched monoester compound, and more preferably that all of it be a branched monoester compound, as this makes it easier to obtain a stable sizing agent solution. In the ester compound, it is preferable that the total amount of linear monoester compounds and branched monoester compounds accounts for 20% by mass or more, as this tends to increase the stability of the sizing agent solution. It is more preferable that the total amount of linear monoester compounds and branched monoester compounds accounts for 40% by mass or more of the ester compound.

[0057] Examples of linear ester compounds with a total of 10 to 50 carbon atoms that are liquid at 45°C include nonyl acetate (11 total carbon atoms), ethyl oleate (20 total carbon atoms), decyl oleate (28 total carbon atoms), lauryl oleate (30 total carbon atoms), oleyl oleate (36 total carbon atoms), octyl palmitate (16 total carbon atoms), and myristyl myristate (28 total carbon atoms) (these are examples of linear monoester compounds with a total of 10 to 50 carbon atoms that are liquid at 45°C), as well as dilauryl succinate (28 total carbon atoms) (this is an example of a linear diester compound with a total of 10 to 50 carbon atoms that is liquid at 45°C), but are not limited to these. Preferably, the total number of carbon atoms in the linear ester compound is 11 to 36.

[0058] Examples of branched-chain ester compounds with a total of 10 to 50 carbon atoms that are liquid at 45°C include 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) (these are examples of branched-chain monoester compounds with a total of 10 to 50 carbon atoms that are liquid at 45°C), as well as diisodecyl adipate (26 total carbon atoms) (this is an example of a branched-chain diester compound with a total of 10 to 50 carbon atoms that is liquid at 45°C), but are not limited to these. Preferably, the total number of carbon atoms in the branched-chain ester compound is 18 to 31.

[0059] The hydrocarbon compounds include 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. Examples of poly-α-olefins that are liquid at 45°C include hydrogenated oligomers of 1-decene. Examples of synthetic paraffins that are liquid at 45°C include the Shell® GTL series (manufactured by Shell Lubricants Japan Co., Ltd.) and the Isane® Biolife series (manufactured by Total Energy Lubricants Japan Co., Ltd.). Examples of mineral oils that are liquid at 45°C include 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 Co., Ltd.).

[0060] The sizing agent according to this embodiment may contain ester compounds other than those mentioned above as a smoothing agent. For example, it may contain an ester compound in which a polyhydric alcohol and a fatty acid are ester-bonded (e.g., pentaerythritol tetraoleate). Furthermore, it may contain an aliphatic alcohol having 2 to 24 carbon atoms (e.g., isostearyl alcohol) as an emulsifying modifier, or a polyhydric alcohol such as ethylene glycol or polyethylene glycol.

[0061] [2] Method for manufacturing sizing agent for reinforcing fibers The sizing agent according to this embodiment can be obtained, for example, by dissolving and dispersing the components (1) to (4) described above in a solvent. The solvent may be an organic solvent such as water or acetone. The apparatus, conditions, and methods for dissolving components such as resins in the solvent are arbitrary. As an example, the sizing agent according to this embodiment can be obtained by preparing a uniform dispersion or solution by placing each pre-weighed component in a beaker at a temperature of 10°C to 90°C, and gradually adding deionized water while stirring.

[0062] The concentration of nonvolatile components in a sizing agent diluted with a diluent is not particularly limited, but may be, for example, 10% by mass or more and 60% by mass or less. As mentioned above, the nonvolatile components of a sizing agent refer to the components that remain without volatilizing after heating the sizing agent in a hot air dryer at 105°C for 2 hours, and the concentration refers to the ratio of the mass of nonvolatile components in the sizing agent to the mass of the sizing agent. From an economic standpoint, the nonvolatile components are preferably 20% or more, more preferably 30% or more, and particularly preferably 40% or more. Furthermore, if an organic solvent is included as a solvent, considering the impact on the working environment, the amount of the organic solvent relative to the nonvolatile components is preferably 10% or less, more preferably 5% or less, and particularly preferably 1% or less.

[0063] Furthermore, each raw material may be a commercially available product sold in the form of a mixture, and in this case, it is not essential to remove the resin and nonionic surfactant, as well as any other nonionic surfactants and other components that may be added, before use. For example, a raw material containing urethane resin may be a commercially available product sold in the form of a solution or dispersion, and the solvents and dispersants contained in such commercial products may be mixed without being removed. Therefore, the sizing agent may contain these solvents and dispersants.

[0064] [3] Reinforced fiber When the sizing agent according to this embodiment is applied to a fiber material by impregnation or other means, reinforced fibers with the sizing agent attached to the fiber material are obtained. These reinforced fibers are an example of the reinforced fibers according to the present invention. The fiber material is preferably an inorganic fiber, and in this case, the reinforced fibers are inorganic fibers to which the sizing agent is attached. Furthermore, it is more preferable that the inorganic fiber is a carbon fiber or a glass fiber.

[0065] As a method for manufacturing reinforced fibers, methods commonly used in this field for applying this type of sizing agent to fiber materials can be applied. Specifically, immersion lubrication, spray lubrication, roller lubrication, and guide lubrication methods may be employed. When applying each method, the sizing agent may be appropriately diluted with a solvent such as water.

[0066] In the reinforcing fibers according to this embodiment, the amount of sizing agent attached is not particularly limited. For example, it is preferable that the amount of sizing agent attached is 0.1% by mass or more and 3% by mass or less of the total amount of sizing agent attached to the reinforcing fibers.

[0067] [4] Fiber composite materials The resulting reinforcing fibers can be used as a reinforcing material to reinforce composite materials that use resin or the like as a matrix. A fiber composite material characterized by containing the above-mentioned reinforcing fibers and a matrix resin which is a thermosetting resin is one embodiment of the present invention.

[0068] The matrix resin of the fiber composite material is not particularly limited, but epoxy resins, unsaturated polyester resins, and the like are preferably used.

[0069] With regard to other configurations, the embodiments disclosed herein are illustrative in all respects, and it should be understood that the scope of the present invention is not limited thereto. Those skilled in the art will readily understand that modifications can be made as appropriate without departing from the spirit of the invention. Therefore, other embodiments modified without departing from the spirit of the invention are naturally included within the scope of the present invention. [Examples]

[0070] The present invention will be further described below with reference to examples. However, the following examples are not limiting to the present invention.

[0071] [Preparation of sizing agents for reinforcing fibers] The sizing agents for the examples and comparative examples were obtained by combining the components shown in Tables 2 to 4 below using the following method.

[0072] [1] Preparation of each component (1) Nonionic surfactants The nonionic surfactants used in the examples and comparative examples are described below. While examples of manufacturing methods are sometimes shown for each compound, each manufacturing method is merely an example, and the results of the examples and comparative examples will not change even if the compound is manufactured using a method different from those exemplified below.

[0073] (1-1) Benzylated phenol derivative (A) (1-1-1) Dibenzylated phenol derivative (A2) In Tables 2 and 3, A2-1 to A2-4 represent the dibenzylated phenol derivatives (A2) shown below. • The dibenzylated phenol derivative (A2-1) is an adduct obtained by randomly adding 30 moles of ethylene oxide and 5 moles of propylene oxide to 1 mole of dibenzylated phenol. • The dibenzylated phenol derivative (A2-2) is an adduct obtained by adding 5 moles of propylene oxide to 1 mole of dibenzylated phenol, and then adding 20 moles of ethylene oxide to this adduct. • Dibenzylated phenol derivatives (A2-3) are adducts obtained by randomly adding 10 moles of ethylene oxide and 2 moles of propylene oxide to 1 mole of dibenzylated phenol, and then adding 15 moles of ethylene oxide to the adduct. • The dibenzylated phenol derivative (A2-4) is an adduct obtained by adding 25 moles of ethylene oxide to 1 mole of dibenzylated phenol.

[0074] (1-1-2) Tribenzylated phenol derivative (A3) A3-1 to A3-4 represent the following tripenzylated phenol derivatives (A3). • Tribenzylated phenol derivative (A3-1) is an adduct obtained by randomly adding 30 moles of ethylene oxide and 5 moles of propylene oxide to 1 mole of tribenzylated phenol. Tribenzylated phenol derivative (A3-2) is an adduct obtained by adding 5 moles of propylene oxide to 1 mole of tribenzylated phenol, and then adding 20 moles of ethylene oxide to this adduct. • The tripenzylated phenol derivative (A3-3) is an adduct obtained by randomly adding 10 moles of ethylene oxide and 2 moles of propylene oxide to 1 mole of tripenzylated phenol, and then adding 15 moles of ethylene oxide to this adduct. • Tribenzylated phenol derivatives (A3-4) are adducts obtained by adding 25 moles of ethylene oxide to 1 mole of tribenzylated phenol.

[0075] (1-1-3) Monobenzylated phenol derivative (A1) A1-1 to A1-2 represent the monobenzylated phenol derivative (A1) shown below. The monobenzyl phenol derivative (A1-1) is an adduct obtained by randomly adding 30 moles of ethylene oxide and 5 moles of propylene oxide to 1 mole of monobenzyl phenol. The monobenzyl phenol derivative (A1-2) is an adduct obtained by adding 5 moles of propylene oxide to 1 mole of monobenzyl phenol, and then adding 20 moles of ethylene oxide to this adduct.

[0076] (1-1-4) Polybenzylated phenol derivative (A4) A4-1 to A4-2 represent the polybenzylated phenol derivatives (A4) shown below. Polybenzyl phenol derivative (A4-1) is an adduct obtained by randomly adding 30 moles of ethylene oxide and 5 moles of propylene oxide to 1 mole of polybenzyl phenol. • Polybenzyl phenol derivative (A4-2) is an adduct obtained by adding 5 moles of propylene oxide to 1 mole of polybenzyl phenol, and then adding 20 moles of ethylene oxide to this adduct.

[0077] The benzylated phenols used as starting materials for the various benzylated phenol derivatives (A) described above are shown below. As explained earlier, the position of the benzyl group in the benzylated phenols is irrelevant. Dibenzylated phenol: A phenol-substituted compound in which 2 moles of benzyl groups are introduced to 1 mole of phenol. Tribenzylated phenol: A phenol-substituted compound in which 3 moles of benzyl groups are introduced to 1 mole of phenol. Monobenzylated phenol: A phenol-substituted compound in which 1 mole of benzyl groups are introduced to 1 mole of phenol. Polybenzylated phenol: A phenol-substituted compound in which 4 moles of benzyl groups are introduced to 1 mole of phenol. These benzylated phenols can be obtained by reacting phenol with benzyl alcohol under a Lewis acid catalyst (e.g., aluminum chloride, γ-alumina) and separating the reaction product by column chromatography.

[0078] (1-2) Other nonionic surfactants B-1 to B-14 are nonionic surfactants other than benzylated phenol derivatives (A), and represent the following compounds. • B-1: This is an adduct obtained by randomly adding 30 moles of ethylene oxide and 5 moles of propylene oxide to 1 mole of distyrenated phenol. B-2: This is an adduct obtained by adding 5 moles of propylene oxide to 1 mole of distyrenated phenol, and then adding 20 moles of ethylene oxide to that adduct. B-3: This adduct is obtained by randomly adding 10 moles of ethylene oxide and 2 moles of propylene oxide to 1 mole of distyrenated phenol, and then adding 15 moles of ethylene oxide to the adduct. • B-4: This is an adduct obtained by adding 25 moles of ethylene oxide to 1 mole of distyrenated phenol. B-5: This is an adduct obtained by randomly adding 30 moles of ethylene oxide and 5 moles of propylene oxide to 1 mole of tristylenide. B-6: This is an adduct obtained by randomly adding 30 moles of ethylene oxide and 5 moles of propylene oxide to 1 mole of monostyrene-modified phenol. • B-7: This is an adduct obtained by randomly adding 30 moles of ethylene oxide and 5 moles of propylene oxide to 1 mole of distyrenate cumylphenol. • B-8: This is an adduct obtained by adding 20 moles of ethylene oxide to 1 mole of nonylphenol. B-9: This is an adduct obtained by randomly adding 25 moles of ethylene oxide and 5 moles of propylene oxide to 1 mole of tetradecyl alcohol. B-10: This is an adduct obtained by adding 5 moles of ethylene oxide to 1 mole of dodecyl alcohol. B-11: This is an adduct obtained by adding 5 moles of propylene oxide to 1 mole of isotridecyl alcohol, and then adding 20 moles of ethylene oxide to that adduct. B-12: This is an adduct obtained by adding 25 moles of ethylene oxide to 1 mole of hydrogenated castor oil. B-13: This product is obtained by esterifying PEG600 and oleic acid in a molar ratio of (PEG600:oleic acid) = 1:1.5. B-14: This is Sorbitan Monooleart.

[0079] (2) Resin The resins C1-1 to C6-3 shown in Tables 2 to 4 are composed of 100% of the resins listed below, or are resin compositions containing the resins listed below. Of these, C1-1 to C1-5 are epoxy resins, C3-1 and C3-2 are polyolefin resins, and C4-1 to C4-3 are polyurethane resins, all of which are commercially available products as shown in Table 1. The product names, distributors, and non-volatile content concentrations of each are shown in Table 1. These commercially available products may contain organic solvents, but these organic solvents are removed during the drying process after the sizing agent is applied to the fiber material and do not exert their effect on the fiber material; therefore, the amount of these additives is not listed in Tables 2 to 4 below.

[0080] [Table 1]

[0081] Please note that Epotote, Denacol, Superflex, Adekabon Titer, and MELUSI, as listed in Table 1, are registered trademarks. Furthermore, the symbols in the "Distributor" column of Table 1 represent the following companies. *1: Nippon Steel Chemical & Material Co., Ltd. *2: Kumho P&B Chemicals, Inc. *3: Nagase ChemteX Corporation *4: Maruyoshi Chemical Co., Ltd. *5: Toho Chemical Industry Co., Ltd. *6: Daiichi Kogyo Seiyaku Co., Ltd. *7: ADEKA Corporation *8: Toyo Polymer Co., Ltd.

[0082] In Table 1, the component of C1-5 is diglycerol polyglycidyl ether. C3-1 is a modified polypropylene resin emulsion, and C3-2 is mainly composed of a modified polypropylene wax emulsion. The polyolefin resin and polyurethane resin content in Tables 2-4 does not include the content of solvents, etc., contained in C3-1, C3-2, and C4-1-C4-3.

[0083] The resins other than those listed in Table 1 have the following components. The vinyl ester resin C2-1 is a reaction compound (bisphenol A diglycidyl ether methacrylic acid adduct) of epoxy resin (product name: "jER(registered trademark) 828" (manufactured by Mitsubishi Chemical Corporation)) and methacrylic acid. The non-volatile content concentration of C2-1 is 100% by mass. The vinyl ester resin C2-2 is an ethylene oxide 2-mol addition bisphenol A acrylic acid adduct. The non-volatile content concentration of C2-2 is 100% by mass. The vinyl ester resin C2-3 is 2-acryloyloxyethyl-2-hydroxyethyl-phthalic acid. The non-volatile content concentration of C2-3 is 100% by mass. Acrylic resin C5-1 is a 23% aqueous solution of ammonia neutralized copolymer of maleic anhydride and n-butyl methacrylate in a mass ratio of 60 / 40 (maleic anhydride / n-butyl methacrylate). The non-volatile content concentration of C5-1 is 23% by mass. Acrylic resin C5-2 is a 30% aqueous solution of sodium neutralized acrylic acid and 2-hydroxyethylacrylamide in a mass ratio of 15 / 85 (polymer of acrylic acid / 2-hydroxyethylacrylamide). The non-volatile content concentration of C5-2 is 30% by mass. Polyester resin C6-1 is a polyester resin that has been esterified by adding a 2-mol ethylene oxide adduct of bisphenol A (product name "Newport® BPE-20", manufactured by Sanyo Chemical Industries, Ltd.) and maleic acid in a molar ratio of hydroxyl value / acid value = 4 / 3. The non-volatile content concentration of C6-1 is 100% by mass. Polyester resin C6-2 is a polyester resin that has been esterified by adding bisphenol A ethylene oxide 4-mol adduct (product name "Newport® BPE-40", manufactured by Sanyo Chemical Industries, Ltd.) and fumaric acid in a molar ratio of hydroxyl value / acid value = 5 / 4. The non-volatile content concentration of C6-2 is 100% by mass. Polyester resin C6-3 is a polyester resin that has been esterified by adding a 10-mol ethylene oxide adduct of bisphenol A (product name "Newport® BPE-100", manufactured by Sanyo Chemical Industries, Ltd.) and adipic acid in a molar ratio of hydroxyl value / acid value = 6 / 5. The non-volatile content concentration of C6-3 is 100% by mass.

[0084] (3) Other ingredients The other components used in the examples and comparative examples are as follows: D-1 is sodium secondary alkanesulfonate (secondary alkanes with 11-14 carbon atoms). D-2 is Octylpalmitate. D-3 is pentaerythritol tetraoleate. D-4 is isostearyl alcohol.

[0085] [2] Preparation of sizing agent For each example and comparative example, components (1) to (3) were weighed to the proportions of parts by mass shown in Tables 2 to 4 below. The values ​​of parts by mass for each component are equivalent to mass%, as the total content of nonionic surfactants, resins, and other components is set to 100 parts by mass. The values ​​of parts by mass for resins in Tables 2 to 4 indicate the mass ratio (mass%) of the resin, so the amount of resin used is the amount obtained by dividing the listed parts by mass by the non-volatile content concentration of each resin. For example, in Example 7, the parts by mass for C3-1 was 68 parts by mass (68% by mass), but the non-volatile content concentration of polyolefin resin composition C3-1 is 30% by mass, so the weighed mass of C3-1 corresponds to 226 parts by mass (68% by mass ÷ 30% by mass).

[0086] First, each component (resin, nonionic surfactant, and other components) was weighed and placed in a beaker. Deionized water was added little by little while stirring to prepare a homogeneous dispersion. Then, deionized water was gradually added to the resulting dispersion while stirring to achieve a non-volatile content of 3% by mass, and sizing agents (treatment solutions) for each example of the diluted form were prepared.

[0087] [Evaluation of sizing agents for reinforcing fibers] (1) Manufacturing of reinforcing fibers Reinforced fibers were manufactured using the sizing agents from each example and comparative example. The sizing agents from each example and comparative example were evaluated based on the condition of each part of the manufacturing equipment during production, as well as the physical properties of the resulting reinforced fibers.

[0088] (1-1) Production of carbon fiber strands treated with sizing agent Commercially available carbon fiber strands without sizing agents (unsizing carbon fibers obtained from polyacrylonitrile-based fibers; tensile strength 3500 MPa, tensile modulus 2.3 × 10⁻¹⁰) 5For carbon fibers (MPa, 12000 filaments), dispersions of the sizing agents from each example and comparative example were supplied by immersion method to achieve a sizing agent adhesion amount of 2% by mass (excluding solvent). The carbon fibers coated with the sizing agent were passed through an electric furnace to remove the solvent. The heating conditions at this time were 120°C for 5 minutes. After drying, the carbon fibers were wound onto a thread tube to obtain carbon fiber strands coated with the sizing agent.

[0089] (1-2) Manufacturing of glass fiber strands to which sizing agents have been applied. Commercially available glass fiber strands without sizing agents were treated with the sizing agents specified in each example and comparative example by immersion. The concentration of the sizing agent dispersion in the oiling bath was set to 3% by mass, and oil was supplied so that the amount of sizing agent attached was 2% by mass (excluding solvent). The glass fibers with the sizing agents attached were passed through an electric furnace to remove the solvent. The heating conditions at this time were 120°C for 5 minutes. After drying, the glass fibers were wound onto a thread tube to obtain glass fiber strands with the sizing agents attached.

[0090] The sizing agents for each example and comparative example, and the reinforcing fibers (reinforcing fiber strands) to which the sizing agents for each example and comparative example were attached, were evaluated by the following tests.

[0091] (2) Evaluation of the penetration rate A chrome-plated, matte pin with a diameter of 1 cm was used as a fiber-splitting bar to split the reinforcing fiber strands into 1 cm wide strips. 0.06 g of epoxy resin (manufactured by Mitsubishi Chemical Corporation, product name "jER828") was dropped onto the split reinforcing fiber strands as a matrix resin using a metal hypodermic needle (inner diameter × outer diameter: 1.25 × 1.65 mm) in a 25°C atmosphere, and the maximum diameter of the epoxy resin 40 seconds after dropping was measured.

[0092] Based on the measurement results of the maximum diameter, the penetration rate was evaluated by classifying it into the following four levels. Of these, levels C and above are considered practical. A: The maximum diameter of the epoxy resin is 5 mm or more. B: Maximum diameter of epoxy resin is 4mm or more but less than 5mm. C: Maximum diameter of epoxy resin is 3.5 mm or more and less than 4 mm. D: Maximum diameter of epoxy resin is less than 3.5 mm

[0093] (3) Stability evaluation A 3% by mass solution of the sizing agent for each example and comparative example (solvent: deionized water) was circulated in an oil bath using a pump, and the state of the solution was observed visually.

[0094] Based on the observation results, the stability of the sizing agent was evaluated by classifying the results into the following four levels. Of these, levels C and above are considered practical. A: After 7 days, the pump circulation was stopped and observation was made, but no scum formation was observed. B: After 7 days, when the pump circulation was stopped and observation was made, a small amount of scum was observed that was visible to the naked eye, but the sizing agent appeared to be dispersed fairly uniformly. C: After 7 days, when the pump circulation was stopped and observation was made, a small amount of scum was observed, but when the pump circulation was restarted, the sizing agent appeared to be uniformly dispersed. D: After 7 days, a visible amount of scum was observed while pump circulation was running. When the pump circulation was stopped and observation was made, precipitate was confirmed in the dispersion.

[0095] Tables 2 to 4 show the formulations of the sizing agents and evaluation results for each example in the examples and comparative examples.

[0096] Table 2: Examples [Table 2]

[0097] Table 3: Examples [Table 3]

[0098] Table 4: Comparative Examples [Table 4]

[0099] The sizing agent in the example containing the dibenzyl phenol derivative (A2) exhibited both penetration rate and stability at level C or higher, confirming that both penetration rate and stability can be achieved. In contrast, the sizing agent in the comparative example without the dibenzyl phenol derivative (A2) exhibited at least one of either penetration rate or stability at level D, failing to achieve both penetration rate and stability. In particular, comparative examples 4-6 (corresponding to Patent Document 1), which contained both the alkylene oxide adduct of distyrenated phenol and the alkylene oxide adduct of tristyrenated phenol, exhibited a penetration rate at level D, indicating that the penetration rate of the matrix resin into the reinforcing fibers was inferior to that of each example. [Industrial applicability]

[0100] This invention can be used in the production of reinforcing fibers such as carbon fibers and glass fibers.

Claims

1. resin and A nonionic surfactant containing a benzylated phenol derivative (A) which is an alkylene oxide adduct of benzylated phenols that are phenol-substituted products having at least one benzyl group, A sizing agent for reinforcing fibers, characterized in that the benzylated phenol derivative (A) contains a dibenzylated phenol derivative (A2) which is an adduct obtained by adding a total of 1 to 100 moles of alkylene oxide to 1 mole of dibenzylated phenol.

2. The sizing agent for reinforcing fibers according to claim 1, wherein the alkylene oxide in the dibenzylated phenol derivative (A2) comprises at least ethylene oxide and propylene oxide.

3. The sizing agent for reinforcing fibers according to claim 1, further comprising a tripenzylated phenol derivative (A3) in which the benzylated phenol derivative (A) is an adduct obtained by adding a total of 1 to 100 moles of alkylene oxide to 1 mole of tripenzylated phenol.

4. The sizing agent for reinforcing fibers according to claim 3, comprising the dibenzylated phenol derivative (A2) and the tripenzylated phenol derivative (A3) in a mass ratio of dibenzylated phenol derivative (A2) / tripenzylated phenol derivative (A3) = 10 / 90 to 80 / 20.

5. The sizing agent for reinforcing fibers according to claim 1, wherein the benzylated phenol derivative (A) comprises at least one of the following: a monobenzylated phenol derivative (A1), which is an adduct obtained by adding a total of 1 to 100 moles of alkylene oxide to 1 mole of monobenzylated phenol; and a polybenzylated phenol derivative (A4), which is an adduct obtained by adding a total of 1 to 100 moles of alkylene oxide to 1 mole of polybenzylated phenol having four or more benzyl groups.

6. The sizing agent for reinforcing fibers according to claim 1, comprising the benzylated phenol derivative (A) in a proportion of 5 to 50% by mass in the nonvolatile content.

7. The sizing agent for reinforcing fibers according to claim 1, wherein the resin comprises at least one selected from the group consisting of epoxy resin, vinyl ester resin, polyolefin resin, polyurethane resin, acrylic resin, and polyester resin.

8. A reinforced fiber characterized in that the sizing agent for reinforcing fibers described in any one of claims 1 to 7 is attached to the fiber material.

9. A fiber composite material comprising reinforcing fibers as described in claim 8, impregnated with a matrix resin.

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