JP7714866B2 - Towpreg - Google Patents

Description

The present invention relates to towpregs that are particularly suitable for use in manufacturing hollow containers and cylinders made of fiber-reinforced composite materials. More specifically, the present invention relates to towpregs that provide fiber-reinforced composite materials that have an excellent balance between heat resistance and 0° tensile strength utilization rate and can improve the burst strength of pressure vessels.

Fiber-reinforced composite materials made with reinforcing fibers such as carbon fiber and glass fiber are used in a wide range of fields, including aerospace, automobiles, railway vehicles, ships, civil engineering and construction, and sporting goods, due to their excellent lightness. In particular, fiber-reinforced composite materials made with continuous reinforcing fibers are used in applications requiring high performance. Carbon fiber, which has excellent specific strength and specific modulus, is often used as the reinforcing fiber, and epoxy resin, which has excellent adhesion to carbon fiber, is often used as the thermosetting resin.

In response to the recent expansion of carbon fiber applications, molding methods are also expanding. Of these, filament winding is a method that is suitable for manufacturing hollow containers and cylinders, such as pressure vessels. From the standpoints of productivity and quality, in addition to the conventional wet method, attention is being paid to methods that use narrow intermediate substrates (hereinafter referred to as towpreg), such as tow prepreg, yarn prepreg, or strand prepreg, in which a bundle of reinforcing fibers is pre-impregnated with a thermosetting resin.

Towpregs are typically supplied in the form of bobbins, with hundreds to thousands of meters wound around a paper tube. They are unwound at high speed during the fiber-reinforced composite material molding process and used in filament winding molding. For this reason, it is necessary for the viscosity of the impregnated epoxy resin composition to increase little over time and for high-speed unwinding properties to be resistant to deterioration during the manufacturing, storage, and use of towpregs.

In pressure vessel applications where towpregs are suitable, there is a growing demand for further weight reduction in components, and technology is needed to reduce the amount of reinforcing fiber used by improving burst strength. Increasing the tensile strength in the fiber axis direction (0° tensile strength) of fiber-reinforced composite materials is effective in improving burst strength, and this can be achieved by either increasing the tensile strength of the reinforcing fibers or by increasing the 0° tensile strength utilization rate. The 0° tensile strength utilization rate is an indicator of how much of the strength of the reinforcing fibers a fiber-reinforced composite material utilizes; when the same type and amount of reinforcing fibers are used, a higher 0° tensile strength will be obtained with a higher 0° tensile strength utilization rate.

Pressure vessels also need to be sufficiently heat-resistant to the temperature rise that occurs when they are rapidly filled with high-pressure gas, and to have minimal performance degradation due to repeated use over long periods of time or use in high-temperature, high-humidity environments. To meet these performance requirements, it is useful to improve the elongation and toughness of the matrix resin, improve its heat resistance (glass transition temperature), and reduce its moisture absorption.

Patent Document 1 discloses an epoxy resin composition for wet filament winding molding that uses a liquid amine as a curing agent and has an excellent balance of heat resistance and 0° tensile strength utilization rate. While this type of epoxy resin composition can achieve a high 0° tensile strength utilization rate in fiber-reinforced composite materials, its viscosity stability over time (pot life) is insufficient for use as a towpreg.

Patent Document 2 discloses a towpreg that contains dicyandiamide as a curing agent and a large amount of core-shell rubber particles, which allows the production of pressure vessels with excellent drapeability, tackiness, and unwinding properties and high burst pressure. However, this type of towpreg is insufficient in terms of achieving both heat resistance and strength utilization.

International Publication No. 2016/208618 International Publication No. 2017/099060

In light of this background, the present invention aims to provide a towpreg that can produce a fiber-reinforced composite material with an excellent balance between heat resistance and 0° tensile strength utilization rate.

The present invention employs the following means to solve the above problems: The towpreg of the present invention is a towpreg obtained by impregnating reinforcing fibers with an epoxy resin composition that contains all of the following components [A] to [C] and satisfies conditions (I) and (II):
[A] A bifunctional epoxy resin that is liquid at 25°C; [B] At least one epoxy resin selected from the group consisting of biphenyl-type epoxy resins, biphenylaralkyl-type epoxy resins, dicyclopentadiene-type epoxy resins, and oxazolidone-type epoxy resins; [C] Dicyandiamide
(I) Contains 5 to 40 parts by mass of component [B] out of 100 parts by mass of the total epoxy resin
(II) The viscosity of the epoxy resin composition at 25°C is 1 to 150 Pa·s

The fiber-reinforced composite material obtained by molding and curing the towpreg of the present invention has an excellent balance of heat resistance and 0° tensile strength utilization rate, making it possible to obtain pressure vessels with excellent heat resistance and burst strength.

The present invention has the following configuration: The towpreg of the present invention is a towpreg obtained by impregnating reinforcing fibers with an epoxy resin composition that contains all of the following components [A] to [C] and satisfies conditions (I) and (II):
[A] A bifunctional epoxy resin that is liquid at 25°C; [B] At least one epoxy resin selected from the group consisting of biphenyl-type epoxy resins, biphenylaralkyl-type epoxy resins, dicyclopentadiene-type epoxy resins, and oxazolidone-type epoxy resins; [C] Dicyandiamide
(I) Contains 5 to 40 parts by mass of component [B] out of 100 parts by mass of the total epoxy resin
(II) The viscosity of the epoxy resin composition at 25°C is 1 to 150 Pa·s.

(Regarding component [A])
Component [A] in the present invention is a difunctional epoxy resin that is liquid at 25°C. Component [A] is necessary to adjust the viscosity of the epoxy resin composition to a level suitable for towpreg production without impairing the good balance between heat resistance and 0° tensile strength utilization. Here, "difunctional" means having two epoxy groups per molecule. Examples of such epoxy resins include bisphenol-type epoxy resins such as bisphenol A and bisphenol F, glycidylamine-type epoxy resins such as glycidylaniline, and aliphatic epoxy resins such as polyethylene glycol, polypropylene glycol, butanediol, neopentyl glycol, hexanediol, and cyclohexanedimethanol. These epoxy resins may be used alone or in appropriate mixtures.

Commercially available bisphenol-type epoxy resins include jER (registered trademark) 825 and jER (registered trademark) 828 (bisphenol A-type epoxy resins, manufactured by Mitsubishi Chemical Corporation), EPICLON (registered trademark) 830 and EPICLON (registered trademark) 807 (bisphenol F-type epoxy resins, manufactured by DIC Corporation), and jER (registered trademark) 806 (bisphenol F-type epoxy resin, manufactured by Mitsubishi Chemical Corporation).

Commercially available glycidylamine epoxy resins include GAN (N,N-diglycidylaniline, manufactured by Nippon Kayaku Co., Ltd.) and GOT (N,N-diglycidyl-o-toluidine, manufactured by Nippon Kayaku Co., Ltd.).

Commercially available aliphatic epoxy resins include "Denacol (registered trademark)" EX-821, "Denacol (registered trademark)" EX-850 (polyethylene glycol type epoxy resins, manufactured by Nagase ChemteX Corporation), "Denacol (registered trademark)" EX-920, "Denacol (registered trademark)" EX-941 (polypropylene glycol type epoxy resins, manufactured by Nagase ChemteX Corporation), "Denacol (registered trademark)" EX-214 (1,4-butanediol type epoxy resin, manufactured by Nagase ChemteX Corporation), "Araldite (registered trademark)" DY-026 (1,4-butanediol type epoxy resin, manufactured by Huntsman Japan Co., Ltd.), and "Denacol (registered trademark)" EX-212 (1,6 1,6-hexanediol type epoxy resin, manufactured by Nagase ChemteX Corporation), ADEKA Resin (registered trademark) ED-503 (1,6-hexanediol type epoxy resin, manufactured by ADEKA Corporation), DENACOL (registered trademark) EX-211 (neopentyl glycol type epoxy resin, manufactured by Nagase ChemteX Corporation), ADEKA Resin (registered trademark) ED-523 (neopentyl glycol type epoxy resin, manufactured by ADEKA Corporation), DENACOL (registered trademark) EX-216 (cyclohexanedimethanol type epoxy resin, manufactured by Nagase ChemteX Corporation), and RIKA Resin (registered trademark) DME-100 (cyclohexanedimethanol type epoxy resin, manufactured by New Japan Chemical Co., Ltd.).

In the present invention, component [A] preferably contains 3 to 20 parts by mass of aliphatic epoxy resin [A1] per 100 parts by mass of all epoxy resin components. Including component [A1] in this range effectively reduces the viscosity of the epoxy resin composition without compromising the good balance between heat resistance and 0° tensile strength utilization rate, enabling adjustment to a range suitable for towpreg production. Furthermore, when used in combination with components [D1] and [D2] (described below), it achieves a unique improvement in tensile elongation at break and toughness compared to the use of either component alone or the use of the two components in combination. While the reason for this effect is unclear, it is believed to be due to the cooperative action of the different mechanisms for improving tensile elongation at break and toughness that each of components [A1], [D1], and [D2] possess. Examples of such component [A1] include polyethylene glycol-type epoxy resins, polypropylene glycol-type epoxy resins, butanediol-type epoxy resins, neopentyl glycol-type epoxy resins, hexanediol-type epoxy resins, and cyclohexanedimethanol-type epoxy resins.

Furthermore, among component [A1], it is more preferable to include a bifunctional epoxy resin having an alkylene skeleton containing 4 to 10 carbon atoms, as this can suppress the moisture absorption of the matrix resin after curing. Examples of such bifunctional epoxy resins having an alkylene skeleton containing 4 to 10 carbon atoms include butanediol-type epoxy resins (alkylene skeleton carbon number: 4), neopentyl glycol-type epoxy resins (alkylene skeleton carbon number: 5), hexanediol-type epoxy resins (alkylene skeleton carbon number: 6), and cyclohexanedimethanol-type epoxy resins (alkylene skeleton carbon number: 8).

(Regarding component [B])
Component [B] in the present invention is at least one epoxy resin selected from the group consisting of biphenyl-type epoxy resins, biphenylaralkyl-type epoxy resins, dicyclopentadiene-type epoxy resins, and oxazolidone-type epoxy resins.

Commercially available biphenyl-type epoxy resins, component [B], include "jER (registered trademark)" YX4000, "jER (registered trademark)" YX4000H, and "jER (registered trademark)" YL6121H (all manufactured by Mitsubishi Chemical Corporation).

Commercially available biphenylaralkyl epoxy resins, which are a type of component [B], include NC-3000-L, NC-3000, and NC-3100 (all manufactured by Nippon Kayaku Co., Ltd.).

Commercially available dicyclopentadiene epoxy resins, which are a type of component [B], include "EPICLON (registered trademark)" HP-7200L, "EPICLON (registered trademark)" HP-7200, and "EPICLON (registered trademark)" HP-7200H (all manufactured by DIC Corporation), and XD-1000-2L, XD-1000, and XD-1000H (all manufactured by Nippon Kayaku Co., Ltd.).

Commercially available oxazolidone epoxy resins, which are a type of component [B], include "D.E.R. (registered trademark)" 858 (manufactured by Olin Corporation).

Among the components [B], dicyclopentadiene-type epoxy resin [B1] is more preferred because it provides the best balance between heat resistance and 0° tensile strength utilization, and it is even more preferred that component [B1] be a bifunctional type having two epoxy groups per molecule. Examples of commercially available products of such bifunctional component [B1] include "EPICLON (registered trademark)" HP-7200L (manufactured by DIC Corporation).

In the present invention, it is necessary to include 5 to 40 parts by mass of component [B], and preferably 5 to 30 parts by mass, out of 100 parts by mass of the total epoxy resin. By keeping the content of component [B] within this range, a good balance between heat resistance and 0° tensile strength utilization rate can be maintained, and the viscosity of the epoxy resin composition can be adjusted to a level suitable for towpreg production.

(Other epoxy resins)
Epoxy resins other than components [A] and [B] may be contained within the scope of the present invention, provided that the effects of the present invention are not impaired. Examples of such epoxy resins include, but are not limited to, solid bisphenol-type epoxy resins such as solid bisphenol A, solid bisphenol F, and solid bisphenol S; glycidyl amine-type epoxy resins such as diaminodiphenylmethane, diaminodiphenylsulfone, aminophenol, metaxylenediamine, and 1,3-bisaminomethylcyclohexane; and isocyanurate, hydantoin, phenol novolac, orthocresol novolac, bisnaphthalene, trishydroxyphenylmethane, and tetraphenylolethane epoxy resins. These epoxy resins may be used alone or in appropriate mixtures.

(Regarding component [C])
Component [C] of the present invention is dicyandiamide. Dicyandiamide is a heat-activated latent curing agent. That is, it is in a low-activity state below a certain temperature, but has the property of undergoing a phase change, chemical change, or the like to become highly active when subjected to a certain thermal history. Component [C] is a necessary component for imparting stability to the epoxy resin composition and for simultaneously preventing the epoxy resin composition from thickening during the epoxy resin composition preparation process, the towpreg production process, and the towpreg storage period, as well as for rapidly progressing the curing reaction under heated conditions.

Commercially available dicyandiamide products include "jER Cure (registered trademark)" DICY7 and "jER Cure (registered trademark)" DICY15 (both manufactured by Mitsubishi Chemical Corporation).

The content of dicyandiamide is preferably an amount such that the number of moles of active hydrogen in dicyandiamide is 0.3 to 1.2 equivalents, more preferably 0.4 to 0.9 equivalents, relative to the number of moles of epoxy groups in all epoxy resin components contained in the epoxy resin composition. That is, in the epoxy resin composition used in the towpreg of the present invention, the content of component [C] is preferably 2.5 to 20 parts by mass, more preferably 3.5 to 15 parts by mass, relative to 100 parts by mass of all epoxy resin components including component [A]. By keeping the content of component [C] within this range, deterioration in heat resistance and mechanical properties due to insufficient curing or excessive reaction heat generation can be prevented, and a good cured product can be obtained. Here, in the present invention, one molecule of dicyandiamide is interpreted as reacting with four epoxy groups, and the active hydrogen equivalent is treated as 21 g/eq.

(Regarding component [D])
The epoxy resin composition used in the towpreg of the present invention preferably contains a rubber component as component [D]. Here, the rubber component refers to a liquid or solid rubber component commonly used to enhance the toughness of cured epoxy resins. By including component [D], the toughness of the cured resin can be enhanced, resulting in a pressure vessel with minimal performance degradation with repeated use. Examples of such component [D] include rubber particulates such as acrylic rubber particulates, butadiene rubber particulates, butadiene-styrene rubber particulates, and silicone rubber particulates; core-shell rubber particulates having a core-shell structure in which rubber particulates are coated with a different polymer; liquid butadiene nitrile rubber; CTBN (carboxyl-terminated butadiene nitrile rubber); ATBN (amino-terminated butadiene nitrile rubber); and liquid rubbers such as butadiene nitrile rubber modified with carboxyl groups in the main chain. These rubber components may be used alone or in appropriate mixtures.

Commercially available products of such rubber components include "Kane Ace (registered trademark)" MX-125, "Kane Ace (registered trademark)" MX-150, "Kane Ace (registered trademark)" MX-154, "Kane Ace (registered trademark)" MX-257, "Kane Ace (registered trademark)" MX-267, "Kane Ace (registered trademark)" MX-416, "Kane Ace (registered trademark)" MX-451, "Kane Ace (registered trademark)" MX-EXP (HM5) (all manufactured by Kaneka Corporation), "PARALOID (registered trademark)" EXL-2655, "PARALOID (registered trademark)" EXL-2668 (all manufactured by Dow Examples include "Hypro (registered trademark)" 1300X31, "Hypro (registered trademark)" 1300X13, "Hypro (registered trademark)" 1300X13NA, and "Hypro (registered trademark)" 1300X8 (all manufactured by CVC Thermoset Specialties).

In the present invention, it is more preferable to include both the core-shell rubber particles [D1] and the carboxyl-terminated butadiene nitrile rubber [D2], as this provides a particularly excellent toughness improvement effect compared to when either component [D] is used alone.

Commercially available products of component [D1] include Kane Ace (registered trademark) MX-125, Kane Ace (registered trademark) MX-150, Kane Ace (registered trademark) MX-154, Kane Ace (registered trademark) MX-257, Kane Ace (registered trademark) MX-267, Kane Ace (registered trademark) MX-416, Kane Ace (registered trademark) MX-451, Kane Ace (registered trademark) MX-EXP (HM5) (all manufactured by Kaneka Corporation), PARALOID (registered trademark) EXL-2655, and PARALOID (registered trademark) EXL-2668 (all manufactured by The Dow Chemical Company).

Commercially available products of component [D2] include "Hypro(R)" 1300X31, "Hypro(R)" 1300X13, "Hypro(R)" 1300X13NA, and "Hypro(R)" 1300X8 (all manufactured by CVC Thermoset Specialties).

In the present invention, since it is possible to achieve both particularly excellent toughness improvement effects and heat resistance, when both core-shell rubber particles [D1] and carboxyl-terminated butadiene nitrile rubber [D2] are contained, the sum of the contents of component [D1] and component [D2] is preferably 5 to 45 parts by mass, more preferably 9 to 35 parts by mass, and even more preferably 9 to 20 parts by mass, per 100 parts by mass of all epoxy resin components. Furthermore, the content of component [D2] is preferably 0.5 to 15 parts by mass, more preferably 0.5 to 10 parts by mass, per 100 parts by mass of all epoxy resin components.

Furthermore, in the present invention, the mass ratio obtained by dividing the mass of component [D2] by the mass of component [D1] (mass of component [D2]/mass of component [D1]) is preferably 0.1 to 0.8. By setting the content of component [D2] relative to component [D1] within this range, it is possible to effectively obtain exceptionally excellent toughness while also achieving good heat resistance.

(Regarding component [E])
The epoxy resin composition used in the towpreg of the present invention preferably contains an aromatic urea as component [E]. By using component [E] in combination with component [C], a good balance between the viscosity stability over time and the curing rate of the epoxy resin composition can be achieved. Here, aromatic urea refers to a compound having a structure in which a urea group is bonded to an aromatic ring, and specific examples include 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), 3-(4-chlorophenyl)-1,1-dimethylurea, phenyldimethylurea (PDMU), and 2,4-toluenebis(3,3-dimethylurea) (TBDMU). These may be used alone or in appropriate mixtures.

Commercially available products of component [E] include DCMU99 (DCMU, manufactured by Hodogaya Chemical Co., Ltd.), "Omicure (registered trademark)" 24 (TBDMU, manufactured by Chori GLEX Co., Ltd.), and "Dyhard (registered trademark)" UR505 (4,4'-methylenebis(phenyldimethylurea), manufactured by AlzChem).

Among the components [E], it is preferable to use TBDMU, as this produces a cured resin with excellent heat resistance.

The content of component [E] is preferably 1.0 to 10 parts by mass, and more preferably 1.1 to 5.0 parts by mass, per 100 parts by mass of all epoxy resin components including component [A].

Furthermore, in the present invention, the molar ratio obtained by dividing the total number of moles of epoxy groups by the number of moles of urea groups (total number of moles of epoxy groups/number of moles of urea groups) is more preferably 15 to 55. By keeping the molar ratio of total epoxy groups to urea groups within this range, a good balance between rapid curing properties and heat resistance can be achieved.

(Other additives)
The epoxy resin composition used in the towpreg of the present invention can contain various additives, such as thermoplastic resins, viscosity modifiers such as thixotropic agents, antifoaming agents, stabilizers, flame retardants, and pigments, as long as the effects of the present invention are not impaired. The thermoplastic resin is preferably a thermoplastic resin soluble in epoxy resins. Examples of thermoplastic resins soluble in epoxy resins include polyvinyl acetal resins such as polyvinyl formal and polyvinyl butyral, polyvinyl alcohol, phenoxy resins, polyamides, polyimides, polyvinylpyrrolidone, and polysulfones. Examples of thixotropic agents include organic agents such as amide wax and hydrogenated castor oil, and inorganic agents such as silica, alumina, mixed oxides of aluminum and silicon, titanium oxide, precipitated calcium carbonate, smectite clay minerals (montmorillonite, beidellite, bentonite, hectorite, saponite, etc.), sepiolite, and carbon black. Examples of antifoaming agents include non-silicone polymer antifoaming agents and silicone antifoaming agents.

The epoxy resin composition to be impregnated into the towpreg of the present invention must have a viscosity at 25°C of 1 to 150 Pa·s, preferably 1 to 110 Pa·s, and more preferably 1 to 50 Pa·s. By achieving a viscosity within this range, the epoxy resin composition can be easily delivered during towpreg production, the reinforcing fibers can be impregnated, and the towpreg can be easily unwound.

In the present invention, the glass transition temperature of the cured resin is preferably 110 to 160°C, and more preferably 120 to 150°C. By setting the glass transition temperature of the cured resin in this range, a good balance between the heat resistance and toughness of the cured resin can be achieved. Here, the term "cured resin" refers to the product obtained by curing the epoxy resin composition of the present invention under heating conditions. There are no particular restrictions on the curing conditions for the epoxy resin composition; for example, the curing reaction can be completed by raising the temperature at a rate of 1 to 20°C/min, followed by heat treatment at 110 to 160°C for 0.5 to 8 hours.

A variety of known methods can be used to prepare the epoxy resin composition used in the towpreg of the present invention. For example, mixing can be performed using machines such as a kneader, planetary mixer, mechanical stirrer, dissolver, or three-roll mill, or by hand using a beaker and spatula.

The towpreg of the present invention is obtained by impregnating a reinforcing fiber bundle with the epoxy resin composition used in the towpreg of the present invention. The reinforcing fiber bundle typically used here is a bundle of 1,000 to 70,000 filaments with a diameter of 3 to 100 μm.

The reinforcing fiber bundles used in the towpreg of the present invention include fiber bundles made of glass fiber, carbon fiber, aramid fiber, boron fiber, alumina fiber, silicon carbide fiber, etc. Two or more of these fiber bundles may be mixed and used. Of these, it is preferable to use carbon fiber bundles, which can produce a lightweight, highly rigid fiber-reinforced composite material. Specific examples of such carbon fiber bundles include acrylic, pitch, and rayon carbon fiber bundles, with acrylic carbon fiber bundles, which have particularly high tensile strength, being preferred.

The mass content (Rc) of the epoxy resin composition in the towpreg of the present invention can be set without particular restrictions depending on the purpose, but is preferably 20 to 40%, more preferably 20 to 30%, and most preferably 22 to 28%. A mass content of 20% or more of the epoxy resin composition and the reinforcing fiber bundles can prevent defects such as unimpregnated areas and voids from occurring inside the resulting fiber-reinforced composite material. Furthermore, a mass content of 40% or less can increase the volume content of the reinforcing fiber bundles, thereby effectively developing the mechanical properties of the fiber-reinforced composite material and contributing to weight reduction.

The towpreg of the present invention can be produced by various known methods. Specifically, the epoxy resin composition used in the towpreg of the present invention can be heated without using an organic solvent to reduce its viscosity, and then the reinforcing fiber bundles are immersed in the composition to impregnate them. Alternatively, the epoxy resin composition, which has been heated to reduce its viscosity, can be coated onto a rotating roll or release paper, and then transferred to one or both sides of the reinforcing fiber bundles. The composition can then be passed through a bending roll or pressure roll to apply pressure and impregnate the bundles. Because this method produces high-quality towpregs, it is preferable that the towpreg production method of the present invention includes a step of contacting a rotating roll coated with the epoxy resin composition with at least one side of the reinforcing fiber bundles. Towpregs are typically supplied in the form of bobbins, with hundreds to thousands of meters wound around a paper tube.

The fiber-reinforced composite material of the present invention can be obtained by heat-curing the towpreg of the present invention. The towpreg of the present invention can be used in many fields, including aerospace, automobiles, railway vehicles, ships, civil engineering and construction, and sporting goods, and is particularly suitable for use in the manufacture of hollow containers such as pressure vessels and cylinders.

The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. The unit "parts" used in compositional ratios refers to parts by mass unless otherwise noted. Furthermore, measurements of various characteristics (physical properties) were carried out in an environment with a temperature of 23°C and a relative humidity of 50%, unless otherwise noted.

<Materials used in Examples and Comparative Examples>
(1) Reinforced fiber bundle: "TORAYCA (registered trademark)" T720SC-36K (tensile strength 5,880 MPa, number of filaments 36,000, total fineness 1,650 tex, density 1.8 g/cm ³ , manufactured by Toray Industries, Inc.).

(2) Component [A] (other than component [A1]): a bifunctional epoxy resin that is liquid at 25°C, "jER (registered trademark)" 828 (liquid bisphenol A epoxy resin, manufactured by Mitsubishi Chemical Corporation)
"jER (registered trademark)" 806 (liquid bisphenol F epoxy resin, manufactured by Mitsubishi Chemical Corporation)
GAN (N,N-diglycidylaniline, manufactured by Nippon Kayaku Co., Ltd.).

(3) Component [A1]: Aliphatic epoxy resin, "Denacol (registered trademark)" EX-821 (polyethylene glycol-type epoxy resin, manufactured by Nagase ChemteX Corporation)
"Denacol (registered trademark)" EX-211 (neopentyl glycol type epoxy resin, alkylene skeleton carbon number: 5, manufactured by Nagase ChemteX Corporation)
"Denacol (registered trademark)" EX-212 (1,6-hexanediol type epoxy resin, alkylene skeleton carbon number: 6, manufactured by Nagase ChemteX Corporation)
"Denacol (registered trademark)" EX-216 (cyclohexanedimethanol type epoxy resin, number of carbon atoms in alkylene skeleton: 8, manufactured by Nagase ChemteX Corporation).

(4) Component [B]: At least one epoxy resin selected from the group consisting of biphenyl-type epoxy resins, biphenylaralkyl-type epoxy resins, dicyclopentadiene-type epoxy resins, and oxazolidone-type epoxy resins. jER (registered trademark) YX4000 (biphenyl-type epoxy resin, manufactured by Mitsubishi Chemical Corporation)
NC-3000-L (biphenyl aralkyl epoxy resin, manufactured by Nippon Kayaku Co., Ltd.)
"EPICLON (registered trademark)" HP-7200L (dicyclopentadiene-type epoxy resin, manufactured by DIC Corporation)
"D.E.R. (registered trademark)" 858 (oxazolidone type epoxy resin, manufactured by Olin Corporation).

(5) Other epoxy resins: "Sumiepoxy (registered trademark)" ELM-434 (tetraglycidyldiaminodiphenylmethane, manufactured by Sumitomo Chemical Co., Ltd.).

(6) Component [C]: Dicyandiamide "jER Cure (registered trademark)" DICY7 (epoxy resin curing agent, dicyandiamide, manufactured by Mitsubishi Chemical Corporation).

(7) Other curing agents: "Seikacure (registered trademark)" S (epoxy resin curing agent, 4,4'-diaminodiphenyl sulfone, manufactured by Seika Corporation).

(8) Component [D1]: Core-shell rubber particles, Kane Ace (registered trademark) MX-150 (liquid bisphenol A type epoxy resin masterbatch containing 40% polybutadiene rubber type core-shell rubber particles, manufactured by Kaneka Corporation)
"Kane Ace (registered trademark)" MX-257 (liquid bisphenol A type epoxy resin masterbatch containing 37% polybutadiene rubber type core-shell rubber particles, manufactured by Kaneka Corporation).

(9) Component [D2]: Carboxyl group-terminated butadiene nitrile rubber "Hypro (registered trademark)" 1300X13NA (carboxyl group-terminated butadiene nitrile rubber, manufactured by CVC Thermoset Specialties).

(10) Component [E]: aromatic urea “Omicure” (registered trademark) 24 (TBDMU, manufactured by Chori GLEX Co., Ltd.).

(11) Other additives: BYK (registered trademark) 1790 (defoaming agent, manufactured by BYK Japan Co., Ltd.).

<Method for preparing epoxy resin composition>
All components except for component [C] and component [E] were placed in a beaker, which was then heated to 100°C and stirred until homogeneous. The resin temperature was then lowered to 25-60°C, after which component [C] and component [E] were added and stirred until homogeneous, yielding an epoxy resin composition. Whether component [B] was compatible with component [A] and homogeneous was determined visually. The component content ratios for the Examples and Comparative Examples are shown in Tables 1 to 3.

<Method for measuring viscosity of epoxy resin composition at 25°C>
In accordance with JIS Z8803 (2011), "Viscosity measurement method using a cone-plate rotational viscometer," measurements were performed using an E-type viscometer (TVE-30H, manufactured by Toki Sangyo Co., Ltd.) equipped with a standard cone rotor (1°34' x R24) at a rotation speed of 5 to 20 rpm. The temperature inside the sample cup was adjusted to the measurement temperature (25°C), and the epoxy resin composition was poured into the sample cup. The value was read when the displayed value stabilized after at least one minute had passed.

<Method for evaluating gelation onset time of epoxy resin composition>
Using a Cure Monitor LT-451 (manufactured by Lambient Technologies), the change in ionic viscosity of the epoxy resin composition over time at 150°C was measured. The ionic viscosity of the epoxy resin composition reaches a minimum value at the start of curing, increases as the curing reaction progresses, and then saturates upon completion. In the present invention, the percentage of the ionic viscosity value at a certain point in time relative to the ionic viscosity at the completion of the curing reaction (the highest value obtained by measurement) was calculated as the cure index (Cd), and the time required for Cd to reach 20% was defined as the gelation initiation time.

<Method for producing cured resin plate>
The epoxy resin composition was degassed in a vacuum and then poured into a mold set to a thickness of 2 mm or 6 mm using a Teflon (registered trademark) spacer. The temperature was then raised from room temperature to 150°C at a rate of 2.5°C per minute in a hot air oven, and the epoxy resin composition was cured by holding at that temperature for 1 hour. The temperature was then lowered to room temperature and the composition was demolded to produce a cured resin plate.

<Method for measuring glass transition temperature>
A test piece 12.7 mm wide and 45 mm long was cut out from a 2 mm thick cured resin plate, and DMA measurement was performed using a viscoelasticity measuring device (ARES, manufactured by TA Instruments) under conditions of a torsional vibration frequency of 1.0 Hz and a heating rate of 5.0°C/min in the temperature range of 30 to 250°C. The glass transition temperature (Tg) was defined as the temperature at the intersection of the tangent in the glassy state and the tangent in the transition state on the storage modulus G' curve.

<Method for measuring tensile elongation at break of cured epoxy resin>
A 1BA type dumbbell shape conforming to JIS K7161 (1994) was cut out from a 2 mm thick resin cured plate, and then a tensile test was carried out using an Instron universal testing machine (manufactured by Instron Corporation) with the chuck distance set to 58 mm and a test speed of 1 mm/min to measure the tensile elongation at break.

<Method for measuring fracture toughness of cured resin>
The test was performed according to the SENB (Single Edge Notched Bend) test method in accordance with ASTM D5045. A test piece 60 mm long and 12.7 mm wide was cut from a 6 mm thick resin-cured plate, and a pre-crack was introduced. Then, using an Instron universal testing machine (manufactured by Instron Corporation), the fracture toughness (K _IC ) was measured at a span of 50.8 mm, a crosshead speed of 10 mm/min, and six samples.

<Method for measuring water absorption of cured resin>
A cured resin plate processed to a thickness of 2 mm, length of 60 mm, and width of 10 mm was vacuum dried at 60°C for 24 hours, and then left to stand for 7 days under humid heat conditions at a temperature of 85°C and a humidity of 95% RH. The percentage of the mass change after exposure to the humid heat conditions relative to the dry mass of the test piece was taken as the water absorption rate.

<Method of manufacturing towpregs>
Using a towpreg manufacturing device equipped with a creel, kiss rolls, nip rolls, and a winder, an epoxy resin composition adjusted to a temperature of 20 to 60°C was applied to one side of Torayca (registered trademark) T720SC-36K carbon fiber, and the fiber bundle was then passed through nip rolls to impregnate the epoxy resin composition into the interior of the reinforcing fiber bundle, producing a towpreg with a resin content of 25%. The towpreg bobbin was wound up to 2,300 m onto a cardboard tube with an initial tension of 600 to 1,000 gf and a winding ratio of 6 to 10, to form a cylindrical shape with a winding width of 230 to 260 mm.

<Method for measuring the 0° tensile strength utilization rate of fiber-reinforced composite material>
The towpreg was sandwiched between metal plates with release films attached, and while applying a constant tension to the tow, the temperature was raised from room temperature to 150°C at a rate of 2.5°C per minute in a hot air oven, and then held at 150°C for 1 hour to cure the towpreg. Test specimens were prepared by bonding 14 mm wide, 50 mm long glass fiber reinforced plastic tabs to both ends of the cured towpreg so that the distance between the tabs was 150 mm. A tensile test was performed on this test specimen using an Instron universal testing machine (manufactured by Instron) at a crosshead speed of 3.0 mm/min to determine the breaking load per cross-sectional area in the fiber longitudinal direction (0° direction). The cross-sectional area of the test specimen was determined by dividing the mass per unit length of the reinforcing fiber by the density. The 0° tensile strength utilization factor was calculated using the average tensile strength of 10 test specimens. The 0° tensile strength utilization rate (%) was calculated by dividing the 0° tensile strength of the cured towpreg by the strand strength of the reinforcing fiber × 100.

<Method for measuring strand strength of reinforcing fiber>
The strand strength of the reinforcing fiber was determined according to the following procedure in accordance with JIS R7608:2007 "Test Method for Resin-Impregnated Strands." The resin-impregnated strands of the carbon fiber bundles to be measured were prepared by impregnating carbon fiber or graphitized fiber with a composition consisting of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylate (100 parts by mass), boron trifluoride monoethylamine (3 parts by mass), and acetone (4 parts by mass), followed by curing at a temperature of 125°C for 30 minutes. Six resin-impregnated carbon fiber strands were measured, and the average of the measurement results was used as the strand strength. The elongation range for measuring the tensile modulus was 0.3 to 0.7%. In this example, "Celloxide (registered trademark)" 2021P manufactured by Daicel Chemical Industries, Ltd. was used as the 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylate.

Example 1
An epoxy resin composition was prepared according to the above <Method for preparing epoxy resin composition> using 80 parts by mass of jER (registered trademark) 828 as component [A], 20 parts by mass of jER (registered trademark) YX-4000 as component [B], 6.3 parts by mass of jER Cure (registered trademark) DICY7 as component [C], 1.7 parts by mass of Omicure (registered trademark) 24 as component [E], and 0.5 parts by mass of BYK (registered trademark) 1790 as other additives. The viscosity of this epoxy resin composition at 25°C was 22 Pa·s, and the gel time at 150°C was 3.5 minutes. The cured resin had a glass transition temperature of 140°C, a tensile elongation at break of 5.5%, a fracture toughness (K _IC ) of 0.8 MPa·m ^0.5 , and a water absorption of 5.4%.

Next, this epoxy resin composition was used to produce a towpreg according to the above-mentioned <Towpreg Production Method>. The 0° tensile strength utilization rate obtained using this towpreg was 91%.

As mentioned above, good results were obtained in all tests.

Example 2
An epoxy resin composition and a towpreg were prepared and evaluated in the same manner as in Example 1, except that 20 parts by mass of NC-3000-L was used as component [B], as shown in Table 1. The evaluation results showed good results in all of the viscosity of the resin composition at 25°C, the gel time at 150°C, the glass transition temperature of the cured resin, the tensile elongation at break, the fracture toughness (K _IC ), the water absorption, and the 0° tensile strength utilization rate of the fiber-reinforced composite material.

Example 3
An epoxy resin composition and towpreg were prepared and evaluated in the same manner as in Example 1, except that 20 parts by mass of EPICLON (registered trademark) 7200-L was used as component [B], as shown in Table 1. The evaluation results showed good results in all of the viscosity of the resin composition at 25°C, the gel time at 150°C, the glass transition temperature of the cured resin, the tensile elongation at break, the fracture toughness (K _IC ), the water absorption, and the 0° tensile strength utilization rate of the fiber-reinforced composite material.

Example 4
As shown in Table 1, an epoxy resin composition and a towpreg were prepared and evaluated in the same manner as in Example 1, except that 20 parts by mass of "D.E.R. (registered trademark)" 858 was used as component [B]. The evaluation results showed that good results were obtained for all of the viscosity of the resin composition at 25°C, the gel time at 150°C, the glass transition temperature of the cured resin, the tensile elongation at break, the fracture toughness (K _IC ), the water absorption, and the 0° tensile strength utilization rate of the fiber-reinforced composite material.

(Examples 5 and 6)
As shown in Table 1, the resin composition was changed, and "hypro (registered trademark)" CTBN1300X13NA was used as component [D]. An epoxy resin composition and a towpreg were prepared and evaluated in the same manner as in Example 1. The results showed that the viscosity of the resin composition at 25°C, the gel time at 150°C, the glass transition temperature of the cured resin, the tensile elongation at break, the fracture toughness (K _IC ), the water absorption, and the 0° tensile strength utilization rate of the fiber-reinforced composite material all showed good results. In particular, component [D] showed an excellent value for K _IC .

(Examples 7 to 9)
As shown in Table 1, the resin composition was changed, and Kane Ace (registered trademark) MX-257 was used as component [D]. An epoxy resin composition and a towpreg were prepared and evaluated in the same manner as in Example 1. The results showed that the viscosity of the resin composition at 25°C, the gel time at 150°C, the glass transition temperature of the cured resin, the tensile elongation at break, the fracture toughness (K _IC ), the water absorption, and the 0° tensile strength utilization rate of the fiber-reinforced composite material all showed good results. In particular, component [D] showed an excellent value for K _IC .

Examples 10 to 13
As shown in Tables 1 and 2, the resin composition was changed, and Kane Ace (registered trademark) MX-150 was used as component [D1] and Hypro (registered trademark) CTBN1300X13NA was used as component [D2]. An epoxy resin composition and a towpreg were prepared and evaluated in the same manner as in Example 1. The resin composition's viscosity at 25°C, gel time at 150°C, glass transition temperature of the cured resin, tensile elongation at break, fracture toughness (K _IC ), water absorption, and 0° tensile strength utilization rate of the fiber-reinforced composite material all showed favorable results. In particular, the combined use of component [D1] and component [D2] showed particularly excellent K _IC values. Among these, Examples 10 to 12, in which the mass ratio of component [D2] to component [D1] was 0.1 to 0.8, achieved both excellent K _IC improvement and heat resistance.

(Examples 14 to 19)
As shown in Table 2, the resin composition was changed and component [A1] was used. Epoxy resin compositions and towpregs were prepared and evaluated using the same method as in Example 1. The resin compositions exhibited favorable results in terms of viscosity at 25°C, gelation time at 150°C, glass transition temperature, tensile elongation at break, fracture toughness (K _IC ), water absorption, and 0° tensile strength utilization rate of the fiber-reinforced composite material. Component [A1] effectively reduced the viscosity of the epoxy resin composition without compromising the favorable balance between heat resistance and 0° tensile strength utilization rate. Furthermore, its use in combination with components [D1] and [D2] significantly improved tensile elongation at break and toughness compared to the use of either component alone or the use of the two components in combination. Furthermore, Examples 15 to 19, which used a bifunctional epoxy resin having an alkylene skeleton containing 4 to 10 carbon atoms as component [A1], exhibited reduced moisture absorption of the cured resin compared to Example 14.

(Comparative Example 1)
As shown in Table 3, the resin composition was changed and component [B] was not used, but 20 parts by mass of Sumiepoxy (registered trademark) ELM-434 was used as another epoxy resin. An epoxy resin composition and towpreg were prepared and evaluated in the same manner as in Example 1. The glass transition temperature of the cured resin was a good 144°C, but the 0° tensile strength utilization rate of the fiber-reinforced composite material was an insufficient 84%.

(Comparative Example 2)
As shown in Table 3, the resin composition was changed; component [B] was not used, and 80 parts by mass of jER (registered trademark) 806 and 20 parts by mass of GAN were used as component [A]. An epoxy resin composition and towpreg were prepared and evaluated in the same manner as in Example 1. The 0° tensile strength utilization rate of the fiber-reinforced composite material was a good 93%, but the glass transition temperature of the cured resin was an insufficient 95°C.

(Comparative Examples 3 and 4)
As shown in Table 3, the resin composition was changed and the content of component [B] was reduced to 3 parts by mass, less than 5 parts by mass. An epoxy resin composition and a towpreg were prepared and evaluated in the same manner as in Example 1. As a result, the glass transition temperature of the cured resin was good, but the 0° tensile strength utilization rate of the fiber-reinforced composite material was insufficient, and the effect of component [B] was not fully obtained.

(Comparative Example 5)
As shown in Table 3, the resin composition was changed, and epoxy resin compositions and towpregs were produced and evaluated in the same manner as in Example 1. As a result, because the viscosity of the resin composition at 25°C was as high as 171 Pa s, the production equipment used required equipment for high heating conditions to transfer the epoxy resin composition, and the production efficiency of the towpreg was insufficient.

(Comparative Example 6)
As shown in Table 3, the resin composition was changed and component [A] was not used, but instead 80 parts by mass of Sumiepoxy (registered trademark) ELM-434 was used as another epoxy resin. An epoxy resin composition and towpreg were prepared and evaluated in the same manner as in Example 1. The glass transition temperature of the cured resin was a good 196°C, but the 0° tensile strength utilization rate of the fiber-reinforced composite material was an insufficient 77%.

(Comparative Example 7)
As shown in Table 3, the resin composition was changed and component [C] was not used, but instead "Seikacure (registered trademark)" S was used as another curing agent. An epoxy resin composition was prepared and evaluated in the same manner as in Example 1. As a result, it did not cure under the conditions of the above <Method for preparing cured resin board>, and the curing speed was insufficient.

Claims (6)

A towpreg obtained by impregnating reinforcing fibers with an epoxy resin composition that contains all of the following components [A], [B1], [C], [D1], and [D2] and satisfies conditions (I) and (II):
[A] A bifunctional epoxy resin that is liquid at 25°C. [B1] A dicyclopentadiene-type epoxy resin. [C] Dicyandiamide. [D1] Core-shell rubber particles. [D2] A carboxyl-terminated butadiene nitrile rubber. (I) A epoxy resin composition containing 5 to 40 parts by mass of component [B1] out of 100 parts by mass of the total epoxy resin. (II) A epoxy resin composition having a viscosity of 1 to 150 Pa·s at 25°C. 2. The towpreg according to claim 1, wherein the epoxy resin composition satisfies condition (III).
(III) Mass of component [D2]/mass of component [D1] = 0.1 to 0.8 3. The towpreg according to claim 1 or 2, wherein the epoxy resin composition satisfies the following condition (IV):
(IV) Glass transition temperature of 110 to 160°C The towpreg according to any one of claims 1 to 3, wherein the epoxy resin composition contains, as component [A], 3 to 20 parts by mass of the following component [A1] per 100 parts by mass of all epoxy resin components:
[A1] Aliphatic epoxy resin The towpreg according to claim 4, wherein the epoxy resin composition contains, as component [A1], a bifunctional epoxy resin having an alkylene skeleton containing 4 to 10 carbon atoms. A fiber-reinforced composite material obtained by curing the towpreg described in any one of claims 1 to 5.