Tow prepreg and method for manufacturing the same

Abstract

To provide a tow prepreg which has shape retention in addition to a balance between unwindability and adhesion, and considers a difference between matrix resins in the tow prepreg wound around a bobbin, and a resin flow in a heating and curing step.SOLUTION: There is provided a tow prepreg in which a reinforcement fiber bundle is impregnated with a matrix resin that is a reaction product of a resin composition containing a bifunctional epoxy resin (A), a bifunctional compound (B) having reactivity with an epoxy group, and a curing catalyst (C) selected from the group consisting of an amine-based curing catalyst, a phosphorus curing catalyst and an imidazole-based curing catalyst, wherein the matrix resin has a weight average molecular weight of 300 to 2,000 and a glass transition point of 15 to 35°C, unwinding tension at an atmospheric temperature of 20 to 50°C of the tow prepreg is 6.9 N or less, and a tensile shear peeling load under a predetermined condition of two tow prepregs is 1.0 to 24.5 N / mm.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a tow prepreg and a method for producing the same. [Background technology]

[0002] Fiber-reinforced plastics (FRP), which are made of reinforcing fibers such as glass fiber or carbon fiber and matrix resin, are lightweight and have excellent mechanical properties, and are therefore widely used in a wide range of applications from the consumer sector to industrial applications. For example, pressure vessels with tank liners (hereafter referred to as "liners") reinforced with FRP are used in storage tanks for natural gas and hydrogen gas.

[0003] Tow prepreg is known as an intermediate material for manufacturing fiber-reinforced plastics. Tow prepreg is made by impregnating bundles of reinforcing fibers (called "tow") made of carbon fibers or glass fibers with a matrix resin.

[0004] Tow prepregs have various uses. For example, a tow prepreg wound on a bobbin such as a paper tube is unwound and wound around a rotating mandrel at a specified tension and angle. Then, a molding method (filament winding: FW) is used to harden the matrix resin impregnated in the reinforcing fiber bundles, which allows the production of a lightweight molded product with excellent pressure resistance, etc.

[0005] In addition to the tackiness required for preventing slippage when wound around a mandrel, the unwinding property required for unwinding from a bobbin is also important for a tow prepreg. When manufacturing tow prepregs with an epoxy resin matrix, the viscosity of the matrix resin is adjusted by using a low-viscosity raw material or adding a solvent to achieve a balance between tackiness and releasability. Recently, the following methods have also been proposed:

[0006] Patent Document 1 proposes a tow prepreg in which a thermoplastic resin blended into an epoxy resin matrix is ​​dissolved and the environmental temperature and the viscosity at the start of curing are controlled, thereby improving releasability, processability, and shape retention. Patent Document 2 proposes a tow prepreg that has improved tack and releasability by making the matrix resin reactive through irradiation with energy rays such as UV rays, thereby promoting a reaction on the matrix resin surface. Patent Document 3 proposes a tow prepreg in which vinyl copolymer particles are placed between carbon fibers to hold the resin in the interfiber voids, thereby reducing the amount of matrix resin composition exposed on the surface and suppressing tack.

[0007] Furthermore, as a material similar to tow prepregs, Patent Document 4 proposes a tape-shaped unidirectional prepreg that contains opened reinforcing fibers and a polymer of a bisphenol A type epoxy compound and a bisphenol compound, the polymer having a weight-average molecular weight of 5,000 to 25,000 and an average number of reinforcing fibers in the thickness direction of 10 or less. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2019-089951 A [Patent Document 2] JP 2019-218483 A [Patent Document 3] Patent No. 6720508 [Patent Document 4] Patent No. 6895682 Summary of the Invention [Problem to be solved by the invention]

[0009] When a tow prepreg is unwound from a bobbin, the matrix resin content (content rate) of the tow prepreg at the start of unwinding is different from that at the end of unwinding. That is, when a tow prepreg is manufactured, it is usually wound around a bobbin such as a paper tube with a tension of several hundred grams to 1 kg. In this case, especially when the tow prepreg is wound for 300 meters or more, the matrix resin composition is squeezed out of the tow prepreg, and the tow prepreg located on the other side (outer circumference side) has a higher matrix resin content than the tow prepreg located on the paper tube side. If the difference in the matrix resin content is large like this, it will cause uneven thickness and variations in physical properties when the tow prepreg is wound around a liner or the like and heat-cured to manufacture a molded body (composite material).

[0010] Tow prepreg is wound around a bobbin such as a paper tube, and is unwound from the wound state when used. To improve productivity, however, in order to unwind at high speed, it is necessary for the tow prepreg to have low tack (adhesiveness). On the other hand, if the tackiness of the tow prepreg is too low, the tow prepreg wrapped around the liner in the FW process will slip, causing processing problems and adversely affecting the performance and quality of the molded product. Therefore, it is important to strike a balance between releasability and tackiness.

[0011] Furthermore, if the shape retention of the tow prepreg is poor, problems such as the tow prepreg being wound around the liner in a folded state during the FW process are likely to occur.

[0012] In addition, if the viscosity of the matrix resin excessively decreases in the process of heating and curing the matrix resin composition contained in the tow prepreg after the tow prepreg is wound around the mandrel (heat curing process), the resin will flow out of the reinforcing fiber bundle due to gravity or the tension of winding the tow prepreg around the liner (also called "resin flow"). If such a resin flow occurs, the matrix resin in the tow prepreg wound around the liner will be insufficient, causing many voids to occur in the molded product (fiber reinforced composite material) or changing the amount of the matrix resin composition in the fiber reinforced composite material, adversely affecting the performance and quality of the composite material reinforced pressure vessel obtained. Conversely, if the resin viscosity during heat curing is too high, the air layers remaining between the tow prepregs when the tow prepregs are wound will not be completely removed due to insufficient resin fluidity, and the molded product will have many voids remaining inside, adversely affecting the performance and quality of the composite material reinforced pressure vessel obtained.

[0013] For example, as disclosed in Patent Documents 1 to 4, various tow prepregs or materials similar to tow prepregs have been proposed. However, in addition to the balance between releasability and adhesion, it is desirable to take into consideration shape retention, the difference in the matrix resin content in the tow prepreg wound around a bobbin, and the resin flow during the heat curing process.

[0014] Therefore, an object of the present disclosure is to provide a tow prepreg that has a balance between unwinding ability and adhesion, as well as shape retention, and takes into consideration the difference in matrix resin content in the tow prepreg wound around a bobbin and the resin flow during the heat curing process. [Means for solving the problem]

[0015] Means for solving the above problems include the following aspects. <1> A tow prepreg in which a matrix resin, which is a reaction product of a resin composition containing a bifunctional epoxy resin (A), a bifunctional compound (B) reactive with an epoxy group, and a curing catalyst (C) selected from the group consisting of an amine-based curing catalyst, a phosphorus-based curing catalyst, and an imidazole-based curing catalyst, is impregnated into a reinforcing fiber bundle, The matrix resin has a weight average molecular weight of 300 to 2000 and a glass transition point of 15 to 35° C., The tow prepreg has an unwinding tension of 8.0 N / mm or less at an ambient temperature of 20 to 50°C, and a tensile shear peel load of 1.0 to 24.5 N / mm at an ambient temperature of 23°C after a 10 mm long overlapping portion of two of the tow prepregs is crimped at 40°C with a load of 9.8 N for 3 seconds. <2> After 300 m or more is wound around a bobbin with a winding tension of 9.8 N or more, the difference between the matrix resin content (mass%) at the start of winding and the matrix resin content (mass%) at the end of winding is less than 2%. <1> The tow prepreg according to claim 1, <3> After the tow prepreg is heated at 160°C for 60 minutes and cured, the matrix resin has a weight average molecular weight of 45,000 or more, a glass transition point of 80 to 160°C, and a minimum viscosity of 0.1 to 3.0 Pa s when the matrix resin is heated at a heating rate of 2°C / min and then cured. <1> or <2> The tow prepreg according to claim 1, <4> The bifunctional compound (B) reactive with an epoxy group is at least one of a phenol compound and an acetyl compound. <1> ~ <3> 13. A tow prepreg according to claim 12. <5> The content of the matrix resin in the tow prepreg is 20 to 40 mass %. <1> ~ <4> 13. A tow prepreg according to claim 12. <6> The resin composition further contains a plasticizer (D). <1> ~ <5> 2. A tow prepreg according to claim 1 , <7> <1> ~ <6> 2. A fiber-reinforced composite material obtained by curing the tow prepreg according to any one of claims 1 to 11. <8> <1> ~ <6> 2. A composite material having a layer of a cured product of the tow prepreg according to claim 1. <9> <1> ~ <6> A method for producing a tow prepreg according to any one of the above claims, A step (a) of preparing a reinforcing fiber bundle; (b) obtaining a precursor of the matrix resin from a resin composition comprising a bifunctional epoxy resin (A), a bifunctional compound (B) reactive with an epoxy group, and a curing catalyst (C) selected from the group consisting of an amine-based curing catalyst, a phosphorus-based curing catalyst, and an imidazole-based curing catalyst; (c) impregnating the precursor into the reinforcing fiber bundle to obtain a precursor-impregnated reinforcing fiber bundle; (d) a step of heating the precursor-impregnated reinforcing fiber bundle to heat-polymerize the precursor into the matrix resin, thereby obtaining the tow prepreg; A method for producing a tow prepreg comprising the steps of: <10> In the step (b), the glass transition point of the precursor is TgA, and the glass transition point of the matrix resin contained in the tow prepreg is TgB. In the step (d), the precursor is heat-polymerized so that TgA / TgB=0.85 to 1.40. <9> A method for producing a tow prepreg according to claim 1. Effect of the Invention

[0016] According to the present disclosure, there is provided a tow prepreg that takes into consideration not only the balance between unwinding ability and adhesion, but also shape retention, the difference in matrix resin content in the tow prepreg wound around a bobbin, and resin flow during the heat curing process. [Brief description of the drawings]

[0017] [Figure 1] FIG. 2 is a schematic diagram illustrating a method for measuring the unwinding tension of a tow prepreg according to the present disclosure. [Diagram 2] FIG. 2 is a schematic diagram illustrating a method for measuring a shear peel load when a tow prepreg according to the present disclosure is compressed. [Diagram 3] FIG. 2 is a schematic diagram showing an example of a method for producing a tow prepreg according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment that is an example of the present disclosure will be described. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In the present specification, the upper limit of a certain numerical range may be replaced by the upper limit of another numerical range, or may be replaced by a value shown in an example. The lower limit of a certain numerical range may be replaced by the lower limit of another numerical range, or may be replaced by a value shown in an example.

[0019] [Tow prepreg] The tow prepreg according to the present disclosure is formed by impregnating reinforcing fiber bundles with a matrix resin which is a reaction product of a resin composition comprising a bifunctional epoxy resin (A), a bifunctional compound (B) reactive with an epoxy group, and a curing catalyst (C) selected from the group consisting of an amine-based curing catalyst, a phosphorus-based curing catalyst, and an imidazole-based curing catalyst. The matrix resin contained in the tow prepreg according to the present disclosure has a weight average molecular weight of 300 to 2000 and a glass transition point of 15 to 35°C. Furthermore, the tow prepreg according to the present disclosure has an unwinding tension of 8.0 N / mm or less at an ambient temperature of 20 to 50°C, and a tensile shear peel load of 1.0 to 24.5 N / mm at an ambient temperature of 23°C after a 10 mm long overlapping portion of two of the tow prepregs is crimped at 40°C with a load of 9.8 N for 3 seconds.

[0020] The reinforcing fiber bundles, matrix resin, characteristics, production method, etc. of the tow prepreg according to the present disclosure will be described below.

[0021] <Reinforced fiber bundle> The reinforcing fiber bundle is composed of several thousand to several tens of thousands of continuous reinforcing fibers, also called filaments, each having a diameter of 5 to 10 μm. The reinforcing fibers constituting the reinforcing fiber bundle are not particularly limited, but from the viewpoints of strength, affinity with the matrix resin, and the like, for example, carbon fiber, boron fiber, silicon carbide fiber, glass fiber, aramid fiber, etc. are preferable, and carbon fiber is more preferable. Carbon fibers are generally classified into PAN-based fibers made from polyacrylonitrile and pitch-based fibers made from coal tar pitch or petroleum pitch. The carbon fibers that can be used as the reinforcing fiber bundle in the tow prepreg according to the present disclosure can be either PAN-based or pitch-based, and these may be used alone or in combination depending on the purpose and application.

[0022] <Matrix resin> The matrix resin is a reaction product of a resin composition containing a difunctional epoxy resin (A) (sometimes referred to as component (A)), a difunctional compound (B) (sometimes referred to as component (B)) reactive with epoxy groups, and a curing catalyst (C) (sometimes referred to as component (C)) selected from the group consisting of an amine-based curing catalyst, a phosphorus-based curing catalyst, and an imidazole-based curing catalyst. Hereinafter, each component contained in the resin composition for forming the matrix resin will be described.

[0023] Component (A): Difunctional epoxy resin Examples of bifunctional epoxy resins include bisphenol type epoxy resins such as bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, bisphenolacetophenone type epoxy resins, diphenyl sulfide type epoxy resins, diphenyl ether type epoxy resins, and bisphenol fluorene type epoxy resins; biphenol type epoxy resins, diphenyldicyclopentadiene type epoxy resins, alkylene glycol type epoxy resins, dihydroxynaphthalene type epoxy resins, dihydroxybenzene type epoxy resins, and methyl group-substituted products thereof; and bisphenol type epoxy resins, biphenol type epoxy resins, and methyl group-substituted products thereof are preferred. These difunctional epoxy resins may be used alone or in combination of two or more.

[0024] Component (B): Bifunctional compound reactive with epoxy groups The bifunctional compound reactive with epoxy groups is not particularly limited as long as it is a bifunctional compound reactive with the epoxy groups of the bifunctional epoxy resin of component (A), but is preferably at least one of a dihydric phenol compound and an acetyl compound.

[0025] (Phenol compounds) Examples of dihydric phenol compounds are shown below, but are not limited to those shown below as long as they are bifunctional. Examples include bisphenols such as bisphenol A, bisphenol F (all manufactured by Nippon Steel Chemical & Material Co., Ltd.), bisphenol fluorene, biscresol fluorene (all manufactured by Osaka Gas Chemical Co., Ltd.), Bis-E, Bis-Z, BisOC-FL, BisP-AP, BisP-CDE, BisP-HTG, BisP-MIBK, BisP-3MZ, SBOC, Bis25X-F (all manufactured by Honshu Chemical Industry Co., Ltd.), and bisphenol S; benzene diols such as hydroquinone, methyl hydroquinone, dibutyl hydroquinone, resorcin, methyl resorcin, catechol, and methyl catechol; naphthalenediols such as naphthalenediol; and biphenols such as biphenol, dimethyl biphenol, and tetramethyl biphenol. Among these, bisphenol compounds or biphenol compounds are preferred. These dihydric phenol compounds may be used alone or in combination of two or more.

[0026] (Acetyl compounds) The acetyl compound that can be used as component (B) in the present disclosure is a bifunctional compound having two acetyl groups in one molecule.

[0027] A bifunctional acetyl compound can be easily obtained by reacting a bifunctional phenol compound such as a bisphenol compound or a biphenol compound with acetic anhydride. Examples of bisphenol compounds that can be used as raw materials include bisphenol A, bisphenol F (all manufactured by Nippon Steel Chemical & Material Co., Ltd.), bisphenol fluorene (manufactured by Osaka Gas Chemical Co., Ltd.), Bis-E, Bis-Z, BisOC-FL, BisP-AP, BisP-CDE, BisP-HTG, BisP-MIBK, BisP-3MZ, S-BOC (all manufactured by Honshu Chemical Industry Co., Ltd.), and bisphenol S. Examples of biphenol compounds that can be used as raw materials include biphenol, dimethylbiphenol, tetramethylbiphenol, etc. Examples of other bifunctional phenol compounds include benzenediols such as hydroquinone, methylhydroquinone, dibutylhydroquinone, resorcin, methylresorcin, catechol, and methylcatechol, and naphthalenediols such as naphthalenediol. The bifunctional acetyl compound may be one obtained by acetylating the above-mentioned phenolic compounds, or one synthesized by other methods.

[0028] Component (C): A curing catalyst selected from the group consisting of an amine-based curing catalyst, a phosphorus-based curing catalyst, and an imidazole-based curing catalyst. The curing catalyst is contained in the resin composition in order to promote the reaction (polymerization) between the difunctional epoxy resin (A) and the difunctional compound (B) having reactivity with an epoxy group. When, for example, a divalent phenol compound is used as component (B), the curing catalyst (C) may be an amine-based curing catalyst, a phosphorus-based curing catalyst, or an imidazole-based curing catalyst, as long as it has catalytic ability to promote the reaction between an epoxy group and a phenolic hydroxyl group. Examples of such compounds include tertiary amines, quaternary ammonium salts, cyclic amines, organic phosphorus compounds, imidazoles, etc. Among these, it is preferable to use organic phosphorus compounds such as triphenylphosphine (TPP), tri-o-tolylphosphine (TOTP), tris(p-methoxyphenyl)phosphine (TPAP), and imidazoles such as 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole (TB-Z). These catalysts may be used alone or in combination of two or more kinds.

[0029] Plasticizer (D) The resin composition may contain a plasticizer. The resin composition may contain a plasticizer to improve the flexibility of the tow prepreg. The plasticizer is preferably one that is compatible with the bifunctional epoxy resin (A), and examples of the plasticizer include monofunctional epoxy compounds, monofunctional phenol compounds, aromatic hydrocarbon formaldehyde resins, and styrene. There are no particular limitations on the use of plasticizers as long as they do not cause a decrease in the mechanical properties of the tow prepreg or the CFRP molded from the tow prepreg, but the amount is preferably 0.1 to 10 parts by mass.

[0030] (Other Ingredients) The resin composition may contain, for example, a reaction retarder. When mixing the two liquids, the precursor composition is often heated because it is necessary to make the precursor composition homogeneous and to reduce the viscosity as much as possible. Therefore, it is preferable to delay the reaction to maintain a low viscosity state, and trialkyl borates such as tri-n-butyl borate, tri-n-octyl borate, and tri-n-dodecyl borate, and triaryl borates such as triphenyl borate are used as reaction retarders. These are used alone or in combination of two or more.

[0031] Although both components (A) and (B) are bifunctional compounds, the inclusion of a trifunctional or higher compound causes three-dimensional crosslinking, which inhibits thermoplasticity during heat curing. Therefore, it is preferable that the resin composition does not contain a trifunctional or higher compound, or if it does contain a trifunctional or higher compound, the amount of the trifunctional or higher compound is 1 mass% or less of the entire resin composition.

[0032] (Weight average molecular weight of matrix resin) The matrix resin has a weight-average molecular weight of 300 to 2000. If the weight-average molecular weight of the matrix resin is 300 or more, the matrix resin exhibits high shape retention when the tow prepreg is wound around a mandrel or the like at an ambient temperature of 20 to 50°C, and if the weight-average molecular weight is 2000 or less, the matrix resin exhibits high drapeability when the tow prepreg is wound. From this viewpoint, the weight average molecular weight of the matrix resin is preferably 500-1,500, and more preferably 900-1,200.

[0033] (Glass transition temperature of matrix resin) The glass transition point of the matrix resin is 15 to 35° C. If the glass transition point of the matrix resin is 15° C. or higher, the tackiness at an ambient temperature of 20 to 50° C. is not excessive, and no poor unwinding of the tow prepreg occurs. If the glass transition point of the matrix resin is 35° C. or lower, the appropriate tackiness prevents the tow prepreg from slipping when it is wound around a mandrel or a liner. From this viewpoint, the glass transition point of the matrix resin is preferably from 15 to 30°C, and more preferably from 20 to 25°C.

[0034] (Physical properties of matrix resin when heat cured at 160℃ for 60 minutes) In the tow prepreg according to the present disclosure, after being heated and cured at 160°C for 60 minutes, the matrix resin preferably has a weight average molecular weight of 45,000 or more and a glass transition point of 80 to 160°C. When the matrix resin is heated at a heating rate of 2°C / min and the viscosity is measured, the minimum viscosity (sometimes referred to as the "minimum melt viscosity of the matrix resin") is 0.1 to 3.0 Pa s. When the tow prepreg according to the present disclosure is heated under the above conditions (160°C x 60 minutes), the viscosity of the matrix resin decreases once and then hardens. However, since the weight-average molecular weight and glass transition point of the hardened matrix resin, as well as the minimum melt viscosity of the matrix resin, are all within the above-mentioned ranges, resin flow can be effectively suppressed when the matrix resin is heated and hardened to form a composite material (molded body), and the generation of voids between the tow prepregs due to excessive flow or insufficient fluidity of the resin can be suppressed.

[0035] (Measurement of matrix resin temperature rise viscosity) The minimum melt viscosity of the matrix resin is determined by measuring it using an Anton Pear MCR 102 or equivalent device under the following conditions: measurement frequency 3 Hz, load strain 1%, flat plate with a diameter of 20 mm, plate gap 0.5 mm, and heating rate 2°C / min in the temperature range of 30°C to 140°C.

[0036] The matrix resin contained in the tow prepreg according to the present disclosure is preferably a phenoxy resin. Here, the "phenoxy resin" is a linear polymer obtained by a condensation reaction between a dihydric phenol compound and an epihalohydrin, or a polyaddition reaction between a dihydric phenol compound and a difunctional epoxy resin, and is an amorphous thermoplastic resin.

[0037] The average molecular weight of the phenoxy resin is, for example, in the range of 10,000 to 200,000 as the weight average molecular weight (Mw) after heat curing, but from the viewpoint of the strength, workability, and processability of the composite material, it is preferably in the range of 20,000 to 100,000, and more preferably in the range of 30,000 to 80,000. If the Mw of the phenoxy resin is too low, the strength of the composite material is inferior, and if it is too high, the workability and processability are likely to be inferior. Note that Mw is a value measured by gel permeation chromatography (GPC) and converted using a standard polystyrene calibration curve.

[0038] Phenoxy resins are produced by known methods from raw material compounds in solution or without solvent. Among the phenoxy resins produced without solvent, those obtained by polymerizing raw material compounds in situ are also called "in situ polymerized phenoxy resins" or "thermoplastic epoxy resins."

[0039] Phenoxy resin and in situ polymerization type phenoxy resin are both linear polymers made from difunctional phenol compounds and difunctional epoxy resins, but the difference is that the molecular weight and molecular weight distribution of phenoxy resin are controlled within a certain range, and polymerization does not proceed further even when heated, whereas an increase in the molecular weight of in situ polymerization type phenoxy resin can be confirmed by heating. In the present disclosure, the matrix resin may be any of the phenoxy resins prepared in solution, those prepared without solvent, and those polymerized in situ.

[0040] When the phenoxy resin is produced in a solution, the reaction solvent is not particularly limited as long as it does not inhibit the reaction, and examples thereof include organic solvents such as benzene, toluene, xylene, methanol, alcohol, butyl alcohol, methyl ethyl ketone, cyclopentanone, cyclohexanone, butyrolactone, dioxane, tetrahydrofuran, acetophenone, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and sulfolane. A combination of two or more of these, or a mixed solvent of an organic solvent and an inorganic solvent (such as water) may also be used.

[0041] The polymerization reaction is carried out at a temperature at which the catalyst used does not decompose. The reaction temperature is 50 to 240°C, and the reaction pressure is usually normal pressure. When it is necessary to remove the reaction heat, the reaction is carried out by flash evaporation and condensation reflux method of the solvent used, indirect cooling method, or a combination of these. When a low boiling point solvent such as methyl ethyl ketone is used, the reaction temperature can be ensured by carrying out the reaction under high pressure using an autoclave.

[0042] The phenoxy resin obtained by this method can be used as a varnish as it is, or can be converted into a solvent-free solid resin by subjecting it to a solvent removal treatment using an evaporator or the like.

[0043] The lower the glass transition point (Tg) of the matrix resin, the better the moldability of the composite material, but the excessive tackiness causes poor unwinding of the tow prepreg. On the other hand, when the Tg is high, the unwinding property is improved, but the tackiness is too small, which causes slippage during winding of the tow prepreg and reduces drapeability, so a high-temperature process above the Tg is required. From this perspective, the Tg of the matrix resin is preferably in the range of 15 to 35°C. The Tg of the matrix resin is measured using a differential scanning calorimeter at a temperature rise rate of 10°C / min at a temperature range of -20 to 100°C, and is calculated from the peak value of the first scan.

[0044] If the phenoxy resin is in a varnish state, it is directly impregnated into a reinforcing fiber bundle and then dried to form a prepreg. If the phenoxy resin is in a solid state, it is impregnated into a reinforcing fiber substrate in a molten state using an impregnation die or the like to form a prepreg. Furthermore, the solid resin may be made into fibers, films, or powder and woven together with reinforcing fiber bundles (commingled method), or a film and reinforcing fiber bundles may be layered and pressurized and impregnated using a roll press or the like (film stack method), or a powder coating method may be used to coat reinforcing fiber bundles to form a tow prepreg.

[0045] On the other hand, when the phenoxy resin is produced without a solvent, the raw material compound and the reaction catalyst are mixed to form a precursor composition, which is then subjected to a polyaddition reaction by heating. In this case, the raw materials may be mixed after being preliminarily heated and melted in order to optimize the mixed state of the raw materials and the reaction catalyst, or a solvent such as cyclohexanone or methyl ethyl ketone may be added in an amount of up to about 10% by mass.

[0046] The conditions for producing phenoxy resin without a solvent are not significantly different from those for producing phenoxy resin in a solvent. However, in situ polymerization type phenoxy resin, which can be obtained in situ without using a reactor or the like, is a preferred phenoxy resin because the degree of polymerization can be adjusted within a desired range and it can be impregnated into reinforcing fiber bundles in the oligomer state to produce tow prepregs. Generally, high temperatures and pressures are required to impregnate high molecular weight materials (polymers) into reinforcing fiber bundles, which can easily result in voids due to poor impregnation or breakage of the reinforcing fibers. When a solvent is used, voids are likely to occur due to residual solvent. However, oligomers have a lower melt viscosity than polymers, so they can be easily impregnated into reinforcing fiber bundles by heating and melting.

[0047] The thickness of the tow prepreg according to the present disclosure is not particularly limited and can be selected depending on the application, the required mechanical properties, etc., and is, for example, 0.05 to 0.2 mm.

[0048] (Matrix resin content) The content of the matrix resin in the tow prepreg according to the present disclosure is preferably 20 to 40% by mass. If the content of the matrix resin in the entire tow prepreg is 20% by mass or more, the generation of voids in the molded article due to an insufficient amount of matrix resin can be suppressed, and if it is 40% by mass or less, a molded article with a high fiber volume content and excellent mechanical properties can be obtained. From this viewpoint, the content of the matrix resin in the tow prepreg is preferably 25 to 40 mass %, and more preferably 30 to 35 mass %.

[0049] (Unwinding tension) The tow prepreg according to the present disclosure has an unwinding tension of 8.0 N / mm or less at an ambient temperature of 20 to 50°C. Since the tow prepreg according to the present disclosure has an unwinding tension of 8.0 N / mm or less at the above-mentioned ambient temperature, the fibers are less likely to tear or break when the tow prepreg is unwound, and the tow prepreg can be easily unwound from the bobbin. From this viewpoint, the unwinding tension is preferably 6.5 N / mm or less, and more preferably 5.4 N / mm or less. Fig. 1 is a schematic diagram for explaining a method for measuring the unwinding tension of a tow prepreg according to the present disclosure. As shown in Fig. 1, the tow prepreg 22 wound around a bobbin 24 is pulled horizontally from the bobbin 24 to measure the load when unwinding. The load when unwinding is the unwinding tension.

[0050] (shear peeling load) The tow prepreg according to the present disclosure has a tensile shear peel load (sometimes simply referred to as "shear peel load" in the present disclosure) of 1.0 to 24.5 N / mm at an ambient temperature of 23°C after two tow prepregs are laminated at a length of 10 mm under a load of 9.8 N at 40°C for 3 seconds. When the tow prepreg according to the present disclosure has a shear peel load of 1.0 N / mm or more, slippage can be suppressed when the tow prepreg is wound around a liner, etc., and when the shear peel load is 24.5 N / mm or less, the unwinding force of the tow prepreg is reduced, thereby suppressing the occurrence of unwinding defects. From this viewpoint, the shear peel load of the tow prepreg according to the present disclosure is preferably 2.9 to 19.6 N / mm, and more preferably 4.9 to 14.7 N / mm.

[0051] Fig. 2 is a schematic diagram for explaining a method for measuring the shear peel load when the tow prepregs according to the present disclosure are crimped. As shown in Fig. 2(A), the ends of two tow prepregs 22A and 22B in the longitudinal direction are overlapped by 10 mm, and the overlapped portions are crimped by hot plates 30A and 30B at 40°C and a load of 9.8 N for three seconds. Next, as shown in Fig. 2(B), the other ends of the two tow prepregs 22A and 22B are pulled in opposite directions so as to be separated, and the shear peel load of the overlapping portions is measured.

[0052] [Method of manufacturing tow prepreg] The method for producing the tow prepreg according to the present disclosure is not particularly limited, but for example, the tow prepreg can be suitably produced by the following production method.

[0053] That is, a preferred method for producing a tow prepreg according to the present disclosure is as follows: A step (a) of preparing a reinforcing fiber bundle; (b) obtaining a precursor of the matrix resin from a resin composition comprising a bifunctional epoxy resin (A), a bifunctional compound (B) reactive with an epoxy group, and a curing catalyst (C) selected from the group consisting of an amine-based curing catalyst, a phosphorus-based curing catalyst, and an imidazole-based curing catalyst; (c) impregnating the precursor into the reinforcing fiber bundle to obtain a precursor-impregnated reinforcing fiber bundle; (d) a step of heating the precursor-impregnated reinforcing fiber bundle to heat-polymerize the precursor into the matrix resin, thereby obtaining the tow prepreg; Includes. Each step will now be described in detail.

[0054] Step (a): Prepare a reinforcing fiber bundle. When manufacturing the tow prepreg according to the present disclosure, as the reinforcing fiber bundle to be used, a commercially available reinforcing fiber bundle that has been opened can be used. Examples of commercially available products of reinforcing fibers include, but are not limited to, the following carbon fibers.

[0055] <Pitch-based carbon fiber> Pitch-based carbon fiber (“GRANOC (registered trademark)” XN-60-60S, manufactured by Nippon Graphite Fiber Corporation, tensile elastic modulus: 620 GPa, tensile strength: 3430 MPa, density: 2.12 g / cm 3 ) Pitch-based carbon fiber (“DIALEAD (registered trademark)” K63712, manufactured by Mitsubishi Chemical Corporation, tensile elastic modulus: 640 GPa, tensile strength: 2600 MPa, density: 2.12 g / cm 3 )

[0056] <PAN-based carbon fiber> PAN-based carbon fiber (“TORAYCA (registered trademark)” T700SC-12000, manufactured by Toray Industries, Inc., tensile elastic modulus: 230 GPa, tensile strength: 4900 MPa, density: 1.8 g / cm 3 ) PAN-based carbon fiber (“PYROFIL (registered trademark)” TR50S12L, manufactured by Mitsubishi Chemical Corporation, tensile elastic modulus: 235 GPa, tensile strength: 4900 MPa, density: 1.8 g / cm 3 ) PAN-based carbon fiber (“TENAX (registered trademark)” HTS40, manufactured by Teijin Limited, tensile elastic modulus: 240 GPa, tensile strength: 4400 MPa, density: 1.8 g / cm 3 )

[0057] The tow prepreg of the present disclosure does not essentially require the opening treatment of the carbon fiber bundles, but the opening treatment may be performed depending on the type of reinforcing fiber bundles used, the number of filaments, etc. The method for opening the carbon fiber bundles is not particularly limited, and for example, known methods such as a vibration opening method in which a vibration roll is brought into contact with the fiber bundles, or an air opening method in which air is blown onto the fiber bundles can be used.

[0058] Step (b): A precursor of a matrix resin (matrix resin precursor) is obtained from a resin composition containing a bifunctional epoxy resin (A), a bifunctional compound (B) reactive with an epoxy group, and a curing catalyst (C) selected from the group consisting of an amine-based curing catalyst, a phosphorus-based curing catalyst, and an imidazole-based curing catalyst.

[0059] The components (A), (B), and (C) are the same as those described above for the tow prepreg, and other components that may be contained in the resin composition are also the same as those described above. The content of each component in the resin composition varies depending on the compound used, but examples of the content include the following. Bifunctional epoxy resin (A): For 1 mole, Bifunctional compound (B) reactive with epoxy groups: 0.95 to 1.05 mol Curing catalyst (C): 0.05 to 5 parts by mass based on the total amount of the bifunctional epoxy resin (A) and the bifunctional compound (B) As described above, it is preferable to use a resin composition for forming a phenoxy resin, particularly an in-situ polymerization type phenoxy resin (thermoplastic epoxy resin), as the matrix resin.

[0060] The components (A) to (C) can be mixed using any conventionally known device, such as a planetary mixer or kneader, but it is preferable to use a device equipped with a temperature control function. As for the order of mixing the components, the components (A) to (C) may be mixed all at once or in any order.

[0061] A resin composition containing each component is cured to partially react (polymerize) the bifunctional epoxy resin (A) with the bifunctional compound (B) reactive with epoxy groups, thereby obtaining a precursor of the matrix resin (matrix resin precursor) for impregnating the reinforcing fiber bundles. The matrix resin precursor is preferably cured to proceed with polymerization until the weight average molecular weight (Mw) reaches a range of about 300 to 6000. The curing is carried out by leaving the mixture at rest at any temperature in the range of 23 to 40° C. for 24 to 216 hours.

[0062] In addition, since the reinforcing fiber bundles are impregnated with a matrix resin precursor in the next step (c), it is preferable to adjust the viscosity of the precursor.

[0063] Step (c): The reinforcing fiber bundle is impregnated with the matrix resin precursor to obtain a precursor-impregnated reinforcing fiber bundle.

[0064] The impregnation of the matrix resin precursor into the reinforcing fiber bundle is carried out after polymerizing a matrix resin precursor composition obtained by mixing a matrix resin raw material compound containing a bifunctional epoxy resin (A) and a bifunctional compound (B) reactive with an epoxy group with a curing catalyst (C) using a mixer or kneader until the weight average molecular weight (Mw) reaches a range of, for example, about 300 to 6,000.

[0065] The method of impregnating the resin precursor into the reinforcing fiber bundles involves directly impregnating the reinforcing fiber bundles with the precursor composition in a heated and molten state at 40 to 80° C. using an impregnation die, a resin bath, etc. The tow prepreg of the present disclosure can also be produced by the so-called “wet method”, in which the reinforcing fiber bundles are immersed in the matrix resin precursor composition diluted with a solvent to impregnate the reinforcing fiber bundles with the resin.

[0066] After the prepreg has been impregnated, excess precursor resin is removed using a touch roll or the like, and the prepreg is then moved to step (d). The cross-sectional shape of the prepreg after impregnation may be adjusted using a grooved roll, etc. The cross-sectional shape is not particularly limited and may be any shape, such as round, elliptical, spindle-shaped, rectangular, or flat.

[0067] Step (d): The precursor-impregnated reinforcing fiber bundle is heated to heat-polymerize the precursor into a matrix resin, thereby obtaining a tow prepreg. When the glass transition point of the matrix resin precursor in step (b) is TgA and the glass transition point of the matrix resin contained in the tow prepreg is TgB, it is preferable to heat-polymerize the matrix resin precursor in step (d) so that TgA / TgB=0.85 to 1.40, more preferably 0.90 to 1.30, and further preferably 0.95 to 1.20.

[0068] 3 is a schematic diagram showing an example of a method for producing a tow prepreg according to the present disclosure, in which 100 is a tow prepreg production apparatus, 10 is a bobbin-wound reinforcing fiber, 12 is a reinforcing fiber bundle, 14 is a resin bath, 16 is a free roll, 18 is a drive roll, 20 is a drying furnace, and 22 is a tow prepreg.

[0069] The reinforcing fiber bundle 12 unwound from the bobbin 10 is guided to a resin bath 14 by a free roll 16 and a drive roll 18, and is impregnated with a resin composition (a precursor of a matrix resin). At this time, the viscosity of the resin composition is preferably 50 to 3,000 mPa s as measured by a rotational viscometer, and the viscosity is adjusted as necessary using an organic solvent such as MEK. In the case of the wet method, the viscosity is adjusted by diluting the matrix resin precursor to a solids concentration of 30 to 50%.

[0070] Next, the reinforcing fiber bundles impregnated with the resin composition are heated and dried continuously for 0.5 minutes or more while being applied with a certain tension in a drying furnace 20 adjusted to 130 to 160°C after removing excess resin composition. In the drying furnace, the solvent contained in the precursor impregnated in the reinforcing fiber bundles is removed and a polymerization reaction proceeds to form a matrix resin. This allows the production of a tow prepreg 22 in which the reinforcing fiber bundles are impregnated with the matrix resin.

[0071] Thereafter, the tow prepreg 22 is wound around a bobbin with a winding tension of 9.8 to 39.2 N to an arbitrary length within a range of 300 to 3000 m while being allowed to cool.

[0072] By using this method, it is possible to produce a tow prepreg according to the present disclosure, which has an unwinding tension of 8.0 N / mm or less at an ambient temperature of 20 to 50°C, and a tensile shear peel load of 1.0 to 24.5 N / mm at an ambient temperature of 23°C after a 10 mm long overlapping portion of two tow prepregs is crimped at 40°C with a load of 9.8 N for 3 seconds.

[0073] (Difference in matrix resin content) The tow prepreg according to the present disclosure can have a difference in matrix resin content (mass %) between the start and end of winding of less than 2% after 300 m or more have been wound around a bobbin with a winding tension of at least 9.8 N. If the difference in matrix resin content in the tow prepreg wound around a bobbin is less than 2%, then when the tow prepreg unwound from the bobbin is wound around a liner or the like and heat cured, unevenness due to differences in matrix resin content will be reduced, and a molded product with high uniformity in strength, etc. can be obtained.

[0074] [Application] The use of the tow prepreg according to the present disclosure is not particularly limited, and the tow prepreg may be used as a fiber-reinforced composite material in which the tow prepreg is cured, or as a composite material having a layer of the cured tow prepreg. For example, the tow prepreg according to the present disclosure may be wound around an object requiring reinforcement (such as a tank) and then heat-cured to produce a fiber-reinforced composite material, or the tow prepreg may be wound around a mandrel, heat-cured, and then pulled out to produce a pipe-shaped fiber-reinforced composite material. In addition, the tow prepreg according to the present disclosure may be cut to an appropriate length, stacked, and then compressed and cured using a hot press or the like to form a layered cured product. A composite material having layers of such cured products may be produced. Furthermore, the tow prepreg according to the present disclosure may be twisted into a string-like shape such as a twisted yarn, and then heat-cured to form a thermoplastic strand, which may be used as a reinforcing material or a material for a 3D printer. EXAMPLES

[0075] The composite member according to the present disclosure will be described in more detail below with reference to examples, although the present disclosure is not limited to the following examples. First, the materials used in the examples will be described.

[0076] [Epoxy resin] A1: Bisphenol A type liquid epoxy resin (YD-128, manufactured by Nippon Steel Chemical & Material Co., Ltd.) [Phenol compounds] B1: Bisphenol A (manufactured by Nippon Steel Chemical & Material Co., Ltd.) [Polymerization catalyst] C1: Tri-o-tolylphosphine (manufactured by Hokko Chemical Industry Co., Ltd., trade name: "TOTP") [Reinforced fiber base material] E1: PAN-based carbon fiber (Toray Industries, Inc., T700SC-12K-60E)

[0077] Example 1 (Production of tow prepreg) A solution of 3 parts by mass of C1 in 3 parts by mass of methyl ethyl ketone (MEK) was added to a mixture of 188 parts by mass of A1 and 112 parts by mass of B1, and the mixture was uniformly kneaded using a planetary mixer, and then cured at 23°C for 144 hours to obtain precursor composition (F1). The glass transition temperature (TgA) and weight average molecular weight of precursor composition (F1) are shown in Table 1.

[0078] The reinforcing fiber bundle was then passed through a resin bath containing a precursor composition (F1) diluted with MEK to a solid content concentration of 40%, to impregnate the bundle with the precursor composition (F1). After the precursor impregnation, excess resin was removed with a touch roll, and the solvent was removed in a drying oven adjusted to 140°C while the precursor was heat-polymerized, and the bundle was wound around a bobbin with a winding tension of 19.6 N, to produce a tow prepreg in which the reinforcing fiber bundle was impregnated with the matrix resin. Through such continuous processes, a tow prepreg with a total length of 1000 m was wound around a bobbin.

[0079] [Examples 2 to 7 and Comparative Examples 1 to 4] A tow prepreg was produced in the same manner as in Example 1, except that the production conditions were changed to those shown in Table 1.

[0080] [evaluation] The produced tow prepregs were evaluated for releasability, adhesion, drapeability, and shape retention at an ambient temperature of 23°C. The unwinding force (unwinding tension) was measured by the method shown in Figure 1, and the adhesive strength (tensile shear peel load) was measured by the method shown in Figure 2. Each tow prepreg was measured four times, and the average values ​​were taken as the unwinding force and adhesive strength of the tow prepreg. The drapeability was evaluated by wrapping the tow prepreg around a stainless steel rod with a diameter of 10 mm. The shape retention was evaluated based on the change in tow width when both ends of a tow prepreg cut to 1 m were pulled with a tension of 29.4 N at an ambient temperature of 23°C. The evaluation criteria for adhesion, releasability, drapeability, and shape retention were as follows. (1) Adhesiveness 〇: Moderate adhesiveness (not too sticky, adhesiveness recovers at body temperature) △: Slightly too sticky (can be unwound but has strong tack) ×: Excessive adhesion (very strong adhesion and poor releasability) ××: No tuck

[0081] (2) Unravelability 〇: Easy to unwind △: Unwinding itself is possible, but the unwinding force is high. ×: Difficult to unwind

[0082] (3) Drapability 〇: Flexible and easy to wrap and stack △: It is possible to wrap and laminate by heating, but it is a little stiff. ×: Quite hard and stiff, flexibility does not return with body heat

[0083] (4) Shape retention 〇: The change in toe width before and after applying a tension of 29.4 N is less than 1.5 mm △: The change in toe width before and after applying a tension of 29.4 N is 1.5 mm or more and less than 3.0 mm. ×: The change in toe width before and after applying a tension of 29.4 N is 3.0 mm or more.

[0084] The composition of the tow prepreg, the production conditions and the evaluation results are shown in Table 1. The underlines indicate that they are outside the scope of this disclosure. In Table 1, the weight loss rate is the weight loss rate of the tow prepreg before and after wrapping the tow prepreg (1 m) around a stainless steel rod and heat curing it at 180°C for 30 minutes. The larger the weight loss rate, the more likely it is that air bubbles will form during heat curing, so the smaller the weight loss rate, the more preferable it is.

[0085] [Table 1] [Explanation of symbols]

[0086] 10 Bobbin-wound reinforcement fiber 12 Reinforced fiber bundle 14 Resin bath 16 Freerolls 18 Driving Roll 20 Drying oven 22 Tow prepreg 100 Tow prepreg manufacturing equipment

Claims

1. A tow prepreg comprising a reinforcing fiber bundle impregnated with a matrix resin which is a reaction product of a resin composition comprising a bifunctional epoxy resin (A), a bifunctional compound (B) reactive with an epoxy group, and a curing catalyst (C) selected from the group consisting of an amine-based curing catalyst, a phosphorus-based curing catalyst, and an imidazole-based curing catalyst, The matrix resin has a weight average molecular weight of 300 to 2000 and a glass transition point of 15 to 35° C., The tow prepreg has an unwinding tension of 8.0 N / mm or less at an ambient temperature of 20 to 50° C., and a tensile shear peel load of 1.0 to 24.5 N / mm at an ambient temperature of 23° C. after a 10 mm long overlapping portion of two of the tow prepregs is pressure-bonded at 40° C. with a load of 9.8 N for 3 seconds.

2. 2. The tow prepreg according to claim 1, wherein after 300 m or more of the tow prepreg has been wound around a bobbin with a winding tension of 9.8 N or more, a difference in the matrix resin content (mass %) at the start of winding and the end of winding is less than 2%.

3. 3. The tow prepreg according to claim 1 or 2, wherein, after the tow prepreg is heated and cured at 160° C. for 60 minutes, the matrix resin has a weight average molecular weight of 45,000 or more, a glass transition point of 80 to 160° C., and a minimum viscosity of 0.1 to 3.0 Pa s when the matrix resin is heated at a heating rate of 2° C. / min and cured.

4. The tow prepreg according to any one of claims 1 to 3, wherein the bifunctional compound (B) reactive with an epoxy group is at least one of a phenol compound and an acetyl compound.

5. The tow prepreg according to any one of claims 1 to 4, wherein a content of the matrix resin in the tow prepreg is 20 to 40 mass%.

6. The tow prepreg according to any one of claims 1 to 5, wherein the resin composition further contains a plasticizer (D).

7. A fiber-reinforced composite material obtained by curing the tow prepreg according to any one of claims 1 to 6.

8. A composite material having a layer of the cured tow prepreg according to any one of claims 1 to 6.

9. A method for producing a tow prepreg according to any one of claims 1 to 6, comprising the steps of: A step (a) of preparing a reinforcing fiber bundle; (b) obtaining a precursor of the matrix resin from a resin composition comprising a bifunctional epoxy resin (A), a bifunctional compound (B) reactive with an epoxy group, and a curing catalyst (C) selected from the group consisting of an amine-based curing catalyst, a phosphorus-based curing catalyst, and an imidazole-based curing catalyst; A step (c) of impregnating the precursor into the reinforcing fiber bundle to obtain a precursor-impregnated reinforcing fiber bundle; (d) a step of heating the precursor-impregnated reinforcing fiber bundle to heat-polymerize the precursor into the matrix resin, thereby obtaining the tow prepreg; A method for producing a tow prepreg comprising the steps of:

10. 10. The method for producing a tow prepreg according to claim 9, wherein, in the step (d), the precursor is heat-polymerized so that TgA / TgB=0.85 to 1.40, where TgA is a glass transition point of the precursor in the step (b) and TgB is a glass transition point of the matrix resin contained in the tow prepreg.

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