JP7577965B2 - Towpreg and fiber reinforced composites - Google Patents

Description

The present invention relates to a towpreg that is particularly suitable for use in manufacturing hollow containers and cylinders made of fiber-reinforced composite materials. More specifically, the present invention relates to a towpreg that is easy to handle and can produce high-quality molded products with few voids.

Fiber-reinforced composite materials using reinforcing fibers such as carbon fiber and glass fiber are used in many fields, such as aerospace, automobiles, railway vehicles, ships, civil engineering and construction, and sporting goods, due to their excellent lightness. In particular, fiber-reinforced composite materials using continuous reinforcing fibers are used in applications that require high performance. Carbon fiber, which has excellent specific strength and specific elastic 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 applications for carbon fiber, molding methods are also expanding. Among these, filament winding is a method that is preferably used for manufacturing hollow containers and cylinders such as pressure vessels. Instead of the conventional wet method in which a reinforced fiber bundle unwound from a bobbin is immersed in liquid thermosetting resin and then wound up on a mold, a method in which a narrow strip-shaped intermediate base material called a tow prepreg, yarn prepreg, or strand prepreg (hereinafter referred to as a tow prepreg) in which the reinforced fiber bundle is pre-impregnated with thermosetting resin is supplied and wound up on a mold is attracting attention from the standpoint of productivity and quality.

Towpregs are usually supplied in the form of bobbins, with hundreds to thousands of meters wound around a paper tube, and are unwound at high speed during the fiber-reinforced composite material molding process. In addition to being less likely to slip off the paper tube when the bobbin is stood upright and having good shape stability with less tightening during unwinding, it is also required that the tow spreads easily during filament winding molding and that gaps are less likely to form. In order to provide towpregs with stable quality, it is also required that the epoxy resin does not deteriorate much when stored for long periods of time before being impregnated into the tow.

In addition, in pressure vessel applications for which towpregs are suitable, they are required to have sufficient heat resistance against the temperature rise that occurs when high-pressure gas is rapidly filled, and to have little performance degradation due to repeated use over a long period of time. In order to satisfy these performance requirements, it is useful to improve the toughness and heat resistance (glass transition temperature) of the matrix resin.

Patent Document 1 discloses a method for manufacturing a composite container in which the towpreg is heated before being wrapped around the liner to reduce the viscosity of the matrix resin and suppress void formation, and then cooled after wrapping to increase the viscosity of the matrix resin and suppress tow slippage. However, this method is not economically satisfactory because it requires the installation of a heating and cooling mechanism in the manufacturing equipment for wrapping.

Patent Document 2 discloses a technology that strengthens tack and prevents tow slippage during filament winding molding by applying a high-viscosity, hardener-free second resin to the surface layer of a towpreg that has been impregnated with a low-viscosity first resin that contains a hardener. However, since the resin must be impregnated in two separate steps, this complicates the towpreg manufacturing process and is not economically satisfactory.

JP 2010-234658 A JP 2015-98556 A

In view of this background, the present invention aims to provide a towpreg that is unlikely to slip off the paper tube when the bobbin is set upright, has good shape stability for the bobbin with little tightening during unwinding, and has good tow spreadability during filament winding molding with little gap formation.

The present invention employs the following means to solve the above problems. That is, the towpreg of the present invention is a towpreg in which an epoxy resin composition having a viscosity of 5 to 150 Pa·s at 25°C is impregnated into a carbon fiber bundle having a fineness of 30 to 4000 g/1000 m, the resin content of the towpreg is 20 to 40 mass%, and when the surface of the towpreg is observed with an optical microscope at a magnification of 200 times, the ratio of the area of the part covered by solid components not dissolved in the epoxy resin to the visual area (coverage rate) is 0% or more and less than 2.5%, and further, the towpreg is laminated in three layers in the same direction, and the interlaminar friction coefficient measured by pulling out the central towpreg under conditions of a temperature of 25°C, a humidity of 50% RH, a speed of 1 mm/min, and a normal load of 20.6 N is 0.04 or more and less than 0.10.

The towpreg of the present invention satisfies the following requirements at the same time: the bobbin is less likely to slip off the paper tube when it is set upright; there is less tightening during unwinding, resulting in good shape stability for the bobbin; and the tow has good width expansion during filament winding molding, resulting in less gaps. This allows for easy handling when manufacturing hollow containers such as pressure vessels and cylinders using the filament winding method, and allows for the production of high-quality molded products with fewer voids.

FIG. 2A is a cross-sectional view showing the method for measuring the interlaminar friction coefficient of the present invention, and FIG. 2B is a plan view showing the method for measuring the interlaminar friction coefficient of the present invention. FIG. 1 is a schematic diagram illustrating a phenomenon in which a towpreg bobbin slips off a paper tube. FIG. 1 is a schematic diagram illustrating a phenomenon of tightening of a winding when a towpreg bobbin is unwound. 1 is an example of an image of a surface of a towpreg captured using an optical microscope at a magnification of 200 times. FIG. 2 is a front view showing a method for measuring the tightening speed of the present invention. FIG. 2A is a front view showing the method for measuring the width expansion ratio of the present invention, and FIG. 2B is a side view showing the method for measuring the width expansion ratio of the present invention.

The present invention has the following configuration. That is, the towpreg of the present invention is a towpreg in which an epoxy resin composition having a viscosity of 5 to 150 Pa·s at 25°C is impregnated into a carbon fiber bundle having a fineness of 30 to 4000 g/1000 m, the resin content (Rc) of the towpreg is 20 to 40 mass%, and when the surface of the towpreg is observed with an optical microscope at a magnification of 200 times, the ratio of the area of the part covered by solid components not dissolved in the epoxy resin to the visual area (coverage rate) is 0% or more and less than 2.5%, and further, the towpreg is laminated in three layers in the same direction, and the interlaminar friction coefficient measured by pulling out the central towpreg under conditions of a temperature of 25°C, a humidity of 50% RH, a speed of 1 mm/min, and a normal load of 20.6 N is 0.04 or more and less than 0.10.

In the present invention, the interlayer friction coefficient refers to the static friction coefficient in the friction phenomenon that occurs between layers of towpregs in a towpreg laminate in which towpregs are stacked. Here, the interlayer refers to the boundary region where the surfaces of the towpregs come into contact with each other, and in the present invention, it is referred to as interlayer even if it is not clearly observed with a microscope, etc.

In the present invention, the interlaminar friction coefficient is measured by the following method. First, as shown in FIG. 1, one towpreg 3 is sandwiched between two towpregs 4 with the same fiber direction, and a load of 20.6 N is applied vertically to the stacked towpregs using a pressure plate 1 (hereinafter referred to as vertical load). Next, the maximum load obtained when the sandwiched towpreg 3 is pulled out at a temperature of 25° C., a humidity of 50% RH, and a speed of 1 mm/min is read. The static friction coefficient obtained by dividing the maximum load read by twice the vertical load applied to the contact portion between the towpreg 3 and the towpreg 4 is defined as the interlaminar friction coefficient in the present invention. The reason for using a value twice the vertical load is that there are two surfaces of the towpreg that receive frictional resistance. More detailed test methods will be described in the examples below.

The interlaminar friction coefficient of the towpreg of the present invention measured by this method is 0.04 or more and less than 0.10. By satisfying this range, it is possible to obtain a towpreg that simultaneously satisfies the following: the bobbin is less likely to slip off the paper tube when it is erected, there is less tightening during unwinding, the bobbin has good shape stability, and the tow has good width expansion during filament winding molding, and gaps are less likely to form. In this way, by using a towpreg in which the occurrence of defects is suppressed, it is possible to improve the yield and the quality of the molded product.

Here, slipping off the paper tube when the bobbin is set up refers to the phenomenon in which, when a bobbin-shaped towpreg, in which several hundred to several thousand meters of towpreg are wound around a paper tube, is placed and left to rest with the longitudinal direction of the paper tube perpendicular to the surface of a workbench, the towpreg slips off and the bobbin shape collapses. A schematic diagram showing the slipping off phenomenon is shown in Figure 2. Once the slipping off phenomenon occurs, the yarn comes off at the end of the bobbin where the shape has collapsed (twill drop), making it impossible to unwind the tow.

Tightening during unwinding is a phenomenon that occurs when a bobbin-shaped towpreg, consisting of hundreds to thousands of meters of towpreg wound around a paper tube, is attached to the creel of a filament winding device and tension is applied to form the towpreg. The tension applied causes the bobbin to be squeezed and deformed, resulting in unevenness on the bobbin surface and bulging of the bobbin end face. A schematic diagram showing the tight winding phenomenon is shown in Figure 3. When tight winding occurs, the bulging bobbin end causes the yarn to come off, causing a "twill drop" phenomenon, making it impossible to unwind the towpreg.

In addition, tow widening during filament winding refers to the phenomenon in which the width of the towpreg expands due to the pressure applied when it is wound around the liner of a pressure vessel or a mandrel used to form a cylinder. If the towpreg does not have sufficient widening ability, voids will occur in the molded product, especially near the nozzle when manufacturing a pressure vessel, which will reduce the burst strength.

The interlaminar friction coefficient of the towpreg of the present invention can be adjusted to an appropriate range by adjusting the viscosity of the epoxy resin composition described below, the resin content (Rc) of the towpreg, the proportion of the area covered by the solid components not dissolved in the epoxy resin (coverage rate), and other factors.

The viscosity of the epoxy resin composition used in the towpreg of the present invention at 25°C must be 5 to 150 Pa·s, preferably 5 to 100 Pa·s, and more preferably 5 to 50 Pa·s. By setting the viscosity of the epoxy resin composition in this range, the interlaminar friction coefficient can be adjusted to an appropriate range. In the present invention, the lower the viscosity of the epoxy resin composition, the lower the resin content (Rc) of the towpreg can be and the higher the carbon fiber content, which can contribute to weight reduction of the fiber-reinforced composite material. In addition, the lower the viscosity of the epoxy resin composition, the simpler the mechanism for adjusting the viscosity by heating and adjusting the temperature of the epoxy resin composition in the towpreg manufacturing process can be, which is preferable from the viewpoint of suppressing equipment costs and energy consumption.

In addition, the epoxy resin composition used in the towpreg of the present invention preferably has a ratio (η 0.1 /η ₁₀ ) of the complex shear viscosity (η _0.1 ) measured at 25° C. and a frequency of 0.1 Hz using a parallel plate vibration rheometer to the complex shear viscosity (η ₁₀ ) measured at 25° C. and a frequency of 10 Hz using a parallel plate vibration rheometer, of 1.5 or more, _more preferably 3.0 or more. By satisfying this range for η _0.1 /η ₁₀ , it is possible to suppress slipping off the paper tube when the bobbin is erected, so that a good balance can be achieved between the effect of suppressing winding tightening during unwinding and the spreadability of the tow during filament winding molding. The upper limit of η _0.1 /η ₁₀ is not particularly limited, but is usually 300 or less. Means for controlling η _0.1 /η ₁₀ within this range include the addition of a viscosity modifier such as a thermoplastic resin or a thixotropic agent.

Specific examples of carbon fiber bundles used in the towpreg of the present invention include acrylic, pitch and rayon carbon fiber bundles, with acrylic carbon fiber bundles, which have particularly high tensile strength, being preferred.

The carbon fiber bundles used in the towpreg of the present invention must have a fineness of 30 to 4000 g/1000 m, and typically, carbon fiber bundles are used that are composed of 1,000 to 70,000 filaments with diameters of 3 to 100 μm. By setting the fineness of the carbon fiber bundles in this range, it is possible to obtain a towpreg that is easy to handle as a belt-shaped intermediate substrate and is uniformly impregnated with the epoxy resin composition all the way to the inside.

In addition, the carbon fiber bundle used in the towpreg of the present invention preferably has an arithmetic mean roughness (Ra) of the single fiber surface of the carbon fiber of 1 to 20 nm. By setting the arithmetic mean roughness (Ra) of the single fiber surface of the carbon fiber in this range, it becomes easy to adjust the interlaminar friction coefficient to an appropriate range. Here, the arithmetic mean roughness (Ra) of the single fiber surface is an index of the unevenness of the carbon fiber surface, and is the arithmetic mean roughness (Ra) calculated from the image of the three-dimensional surface shape obtained by measuring a three-dimensional surface shape of 600 nm x 600 nm using an atomic force microscope (AFM), with the roundness of the fiber approximated by a three-dimensional curved surface as the average line.

The resin content (Rc) of the towpreg of the present invention must be 20 to 40% by mass, preferably 20 to 36% by mass, and more preferably 20 to 30% by mass. Here, the resin content (Rc) of the towpreg is the mass ratio of the epoxy resin composition to the mass of the towpreg. By setting Rc in this range, the interlaminar friction coefficient can be adjusted to an appropriate range. In addition, when Rc is 20% by mass or more, it is possible to suppress the occurrence of defects such as unimpregnated parts and voids inside the obtained fiber-reinforced composite material, and when it is 40% by mass or less, it is possible to suppress the seepage of the resin composition from the towpreg bobbin and the scattering of the resin composition during the filament winding molding process. The smaller Rc is, the higher the carbon fiber content can be, which is preferable because it contributes to weight reduction of the fiber-reinforced composite material. Rc can be changed by controlling the mass of the epoxy resin composition impregnated into the carbon fiber bundle.

When the surface of the towpreg of the present invention is observed with an optical microscope at a magnification of 200 times, the ratio of the area of the portion covered by the solid components not dissolved in the epoxy resin to the area of the field of view (coverage rate) must be 0% or more and less than 2.5%.

In the present invention, the coverage is measured by the following method. First, the surface of the towpreg is imaged using an optical microscope at a magnification of 200 times while illuminating with a ring light, and a digital image as shown in FIG. 4 is obtained. By illuminating with a ring light, the reflection of light by the epoxy resin is canceled, and an image in which the solid components not dissolved in the epoxy resin are emphasized can be obtained. Next, the obtained digital image is binarized using image analysis software, and the parts covered by the solid components not dissolved in the epoxy resin are recognized and their area is calculated. The area of the parts covered by the solid components not dissolved in the epoxy resin obtained by the above method is divided by the actual area imaged, and the value expressed as a percentage is taken as the coverage. With this measurement method, it is possible to distinguish covered parts of a minimum size of about 1 μm.

When the coverage of the towpreg of the present invention measured by this method satisfies this range, the interlaminar friction coefficient can be adjusted to an appropriate range.

The materials that make up the towpreg of the present invention are described below.

(About epoxy resin)
The epoxy resin in the present invention can be used without any particular limitation, and examples thereof include bisphenol type epoxy resins such as bisphenol A type, bisphenol F type, and bisphenol S type, glycidyl amine type epoxy resins such as glycidyl aniline type, diaminodiphenylmethane type, diaminodiphenyl sulfone type, aminophenol type, metaxylenediamine type, and 1,3-bisaminomethylcyclohexane type, aliphatic epoxy resins such as polyethylene glycol type, polypropylene glycol type, butanediol type, neopentyl glycol type, hexanediol type, and cyclohexanedimethanol type, isocyanurate type, hydantoin type, phenol novolac type, orthocresol novolac type, dicyclopentadiene novolac type, biphenyl type, trishydroxyphenylmethane type, and tetraphenylolethane type epoxy resins. These epoxy resins may be used alone or in appropriate mixture.

Among these epoxy resins, it is preferable to include a glycidylamine type epoxy resin, since this has the effect of imparting stability to the epoxy resin composition and preventing thickening of the epoxy resin composition during the epoxy resin composition preparation process, the towpreg manufacturing process, and the towpreg storage period. By preventing thickening of the epoxy resin composition during these processes and periods, the impregnation state of the epoxy resin composition in the towpreg can be improved, and good unwinding properties during molding can be maintained. Examples of glycidylamine type epoxy resins include glycidylaniline type, diaminodiphenylmethane type, diaminodiphenylsulfone type, aminophenol type, metaxylenediamine type, and 1,3-bisaminomethylcyclohexane type. Commercially available products of such glycidylamine type epoxy resins include GAN (N,N-diglycidylaniline, manufactured by Nippon Kayaku Co., Ltd.), GOT (N,N-diglycidyl-o-toluidine, manufactured by Nippon Kayaku Co., Ltd.), "Sumiepoxy (registered trademark)" ELM-434 (tetraglycidyldiaminodiphenylmethane, manufactured by Sumitomo Chemical Co., Ltd.), "Araldite (registered trademark)" MY721 (tetraglycidyldiaminodiphenylmethane, manufactured by Huntsman Japan Co., Ltd.), and "ARALDITE (registered trademark)" MY0510 (tetraglycidyl-p-aminophenol, manufactured by Huntsman Japan Co., Ltd.).

Among these glycidylamine type epoxy resins, it is preferable to use tetraglycidyldiaminodiphenylmethane, as it has an excellent balance of heat resistance and mechanical properties.

Furthermore, because of its excellent effect of improving the pot life of the epoxy resin composition, it is more preferable to use tetraglycidyldiaminodiphenylmethane having a viscosity of 10 Pa·s or less at 50°C, even more preferable to use one having a viscosity of 9.0 Pa·s or less, and most preferable to use one having a viscosity of 6.0 Pa·s or less. Commercially available products of such tetraglycidyldiaminodiphenylmethane include "Sumiepoxy (registered trademark)" ELM-434L (viscosity at 50°C: 8.2 Pa·s, manufactured by Sumitomo Chemical Co., Ltd.), "Sumiepoxy (registered trademark)" ELM-434VL (viscosity at 50°C: 5.0 Pa·s, manufactured by Sumitomo Chemical Co., Ltd.), "Araldite (registered trademark)" MY721 (viscosity at 50°C: 3.6 to 5.0 Pa·s, manufactured by Huntsman Japan Co., Ltd.), "jER (registered trademark)" 604 (viscosity at 50°C: 5.0 to 10 Pa·s, manufactured by Mitsubishi Chemical Corporation), and YH-404 (viscosity at 50°C: 3.6 to 5.2 Pa·s, manufactured by Nippon Steel Chemical & Material Co., Ltd.).

The content of the glycidylamine type epoxy resin is preferably 10 parts by mass or more, more preferably 10 to 80 parts by mass, and even more preferably 20 to 60 parts by mass, per 100 parts by mass of epoxy resin. By setting the content of the glycidylamine type epoxy resin to 10 parts by mass or more per 100 parts by mass of epoxy resin, it is possible to obtain an effect of preventing thickening of the epoxy resin composition. In addition, by setting the content of the glycidylamine type epoxy resin to 80 parts by mass or less per 100 parts by mass of epoxy resin, it is possible to obtain an epoxy resin composition for towpregs that provides a fiber-reinforced composite material with an excellent balance between heat resistance and toughness.

(About the hardener)
The curing agent in the present invention can be used without any particular limitation, and examples thereof include dicyandiamide, cyanamide, aromatic amines such as diethyltoluenediamine, diaminodiphenylmethane, 3,3'-diethyl-4,4'-diaminodiphenylmethane, and diaminodiphenylsulfone, carboxylic anhydrides such as methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, and methylnadic anhydride, Lewis acids such as boron trifluoride amine complexes and boron trichloride amine complexes, and imidazoles such as 2-ethyl-4-methylimidazole, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, and 2-phenyl-4-methyl-5-hydroxymethylimidazole. These curing agents may be used alone or in appropriate mixtures.

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

Commercially available cyanamide products include "DYHARD (registered trademark)" Fluid 111 (manufactured by AlzChem).

Commercially available aromatic amines include "jER Cure (registered trademark)" WA (diethyltoluenediamine, manufactured by Mitsubishi Chemical Corporation), "KAYAHARD (registered trademark)" A-A (3,3'-diethyl-4,4'-diaminodiphenylmethane, manufactured by Nippon Kayaku Co., Ltd.), and "SEIKACURE (registered trademark)" S (epoxy resin hardener, 4,4'-diaminodiphenyl sulfone, manufactured by Seika Corporation).

Commercially available carboxylic acid anhydrides include HN-2200 (methyltetrahydrophthalic anhydride, manufactured by Hitachi Chemical Co., Ltd.), "RIKACID (registered trademark)" HH (hexahydrophthalic anhydride, manufactured by New Japan Chemical Co., Ltd.), and "KAYAHARD (registered trademark)" MCD (methylnadic anhydride, manufactured by Nippon Kayaku Co., Ltd.).

Commercially available boron halide amine complexes include Accelerator DY 9577 (boron trichloride amine complex, manufactured by Huntsman Japan Co., Ltd.) and LEECURE B-550 (boron trifluoride amine complex, manufactured by Leepoxy Plastics).

Commercially available imidazole products include "Curezol (registered trademark)" 2E4MZ, "Curezol (registered trademark)" 2MZA-PW, "Curezol (registered trademark)" 2MAOK-PW, and "Curezol (registered trademark)" 2P4MHZ-PW (all manufactured by Shikoku Chemicals Corporation).

Among such curing agents, it is preferable to use a curing agent that is compatible with the epoxy resin at 25°C, from the viewpoint of easily controlling the coverage rate to be small and adjusting the interlaminar friction coefficient to the appropriate range of the present invention. Here, being compatible with the epoxy resin means that the epoxy resin composition to be impregnated into the towpreg does not substantially contain a solid curing agent, and compatibility can be confirmed if no particle components derived from the raw material curing agent are detected by methods such as visual observation or optical microscope observation, or particle size distribution measurement by light scattering method. For this reason, the curing agent is preferably a solid curing agent that can be dissolved in the epoxy resin in a temperature range where a rapid reaction with the epoxy resin does not start and can maintain a compatible state at 25°C, or a liquid curing agent that can maintain a compatible state at 25°C, and more preferably a liquid curing agent.

Among these curing agents, aromatic amines are particularly preferred because they can provide an epoxy resin composition for towpregs that provides fiber-reinforced composite materials with an excellent balance of mechanical properties. Here, aromatic amine is a general term for compounds that have an amino group directly bonded to an aromatic ring. Examples of such aromatic amines include compounds with one aromatic ring, such as aminobenzylamine and diethyltoluenediamine, and compounds with two aromatic rings, such as 3,3'-diethyl-4,4'-diaminodiphenylmethane.

Among these aromatic amines, liquid aromatic amines that are liquid at 25°C are more preferred from the viewpoint of easily controlling the coverage rate to a small value and adjusting the interlayer friction coefficient to the appropriate range of the present invention.

Furthermore, among such liquid aromatic amines that are liquid at 25°C, it is more preferable to include a compound represented by the following chemical formula (1), since this provides excellent storage stability and heat resistance.

In the formula, R ¹ , R ² and R ³ are any one of hydrogen, an alkyl group having 1 to 4 carbon atoms, an alkoxy group and an alkylthio group, and R ¹ , R ² and R ³ may be the same or different.

Commercially available liquid aromatic amines that are liquid at 25°C and are represented by chemical formula (1) include "jER Cure (registered trademark)" WA (diethyltoluenediamine, manufactured by Mitsubishi Chemical Corporation) and "LONZACURE (registered trademark)" DETDA80 (diethyltoluenediamine, manufactured by Lonza Japan Co., Ltd.).

The content of such aromatic amine is preferably an amount that results in 0.7 to 2.0 equivalents of active hydrogen relative to the epoxy groups of the epoxy resin, and more preferably an amount that results in a range of 0.7 to 1.8 equivalents. By setting the content of aromatic amine within this range, it is possible to obtain an epoxy resin composition for towpregs that provides a fiber-reinforced composite material with an excellent balance of mechanical properties.

(Additives)
In the present invention, in order to adjust the interlayer friction coefficient and improve the performance such as the mechanical properties of the resin cured product, various additives such as viscosity modifiers such as thermoplastic resins and thixotropic agents, toughening agents such as rubber components, and other additives such as defoamers, stabilizers, flame retardants, and pigments can be contained. The thermoplastic resin is preferably a thermoplastic resin soluble in epoxy resin. Examples of the thermoplastic resin soluble in epoxy resin include polyvinyl acetal resins such as polyvinyl formal and polyvinyl butyral, polyvinyl alcohol, phenoxy resin, polyamide, polyimide, polyvinyl pyrrolidone, and polysulfone. Examples of the thixotropic agent include organic ones such as amide wax and hydrogenated castor oil, and inorganic ones such as silica, alumina, mixed oxides of aluminum and silicon, titanium oxide, light calcium carbonate, smectite clay minerals (montmorillonite, beidellite, bentonite, hectorite, saponite, etc.), sepiolite, and carbon black. The defoaming agent includes non-silicon polymer-based defoaming agents, silicone-based defoaming agents, and the like.

The epoxy resin composition used in the towpreg of the present invention preferably contains a toughening agent that is compatible with epoxy resins at 25° C. and/or a toughening agent having a particle size of 50 nm to 1 μm, and the toughness value K _Ic of the cured product obtained by curing the epoxy resin composition for 4 hours at 150° C. is 1.0 to 3.0 MPa·m ^0.5 . By satisfying these conditions, the toughness of the cured resin can be increased without an excessive increase in the interlaminar friction coefficient, and a fiber-reinforced composite material with little deterioration in performance due to repeated use can be obtained.

Here, being compatible with the epoxy resin at 25°C means that the epoxy resin composition impregnated into the towpreg does not contain substantially solid toughening agent components and does not cause gross liquid-liquid phase separation. Compatibility can be confirmed by mixing the epoxy resin and the toughening agent and visually observing them.

In addition, in the present invention, the particle size of the toughening agent refers to the volume average particle size, and can be measured by techniques such as laser diffraction/scattering and dynamic light scattering.

Examples of toughening agents that are compatible with epoxy resins at 25°C include liquid rubbers such as liquid butadiene nitrile rubber, CTBN (carboxyl-terminated butadiene nitrile rubber), ATBN (amino-terminated butadiene nitrile rubber), and butadiene nitrile rubber modified with carboxy groups in the main chain. These may be used alone or in appropriate mixtures. Commercially available liquid rubbers include "Hypro (registered trademark)" 1300X31, "Hypro (registered trademark)" 1300X13, "Hypro (registered trademark)" 1300X13NA, and "Hypro (registered trademark)" 1300X8 (all manufactured by CVC Thermoset Specialties).

Examples of toughening agents with particle sizes of 50 nm to 1 μm include rubber microparticles such as acrylic rubber microparticles, butadiene rubber microparticles, butadiene-styrene rubber microparticles, and silicone rubber microparticles, as well as core-shell rubber microparticles having a core-shell structure in which rubber microparticles are coated with a different polymer. These may be used alone or in an appropriate mixture.

Examples of commercially available products of such core-shell rubber microparticles 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, and "Kane Ace (registered trademark)" MX-EXP (HM5) (all manufactured by Kaneka Corporation).

The content of such toughening agent is preferably 5 parts by mass or more, and more preferably 5 to 30 parts by mass, per 100 parts by mass of epoxy resin. By setting the content of the toughening agent within this range, it is possible to increase the toughness of the cured resin without excessively increasing the interlaminar friction coefficient, and to obtain a fiber-reinforced composite material that exhibits little deterioration in performance due to repeated use.

In addition, in the present invention, the glass transition temperature of the cured product obtained by curing the epoxy resin composition at 150°C for 4 hours is preferably 120 to 160°C, and more preferably 120 to 150°C. By setting the glass transition temperature of the cured resin product in this range, it is possible to achieve a good balance between the heat resistance and toughness of the cured resin product.

In the towpreg of the present invention, it is preferable to contain 3 to 5 parts by mass of fumed silica having a primary particle diameter of 5 to 50 nm per 100 parts by mass of epoxy resin. By satisfying this condition, a better balance can be achieved between the effect of suppressing winding tightness during unwinding and the spreadability of the tow during filament winding molding. Here, fumed silica is fine particle silica with a primary particle diameter of several nanometers to several tens of nanometers, and is obtained by a combustion pyrolysis method or the like. The primary particle diameter of fumed silica refers to the average diameter of the primary particles, and can be measured by analyzing images observed with a transmission electron microscope, etc.

Among such fumed silicas, hydrophobic fumed silica that has been subjected to a hydrophobic surface treatment is more preferred because it is easy to adjust the η _0.1 /η ₁₀ to the preferred range of the present invention. Here, the hydrophobic surface treatment refers to a treatment in which a hydrophobic substituent such as an alkylsilyl group such as a dimethylsilyl group or a trimethylsilyl group, or a dimethylpolysiloxane is bonded to the silanol groups on the surface of the fine particle silica. Commercially available examples of such fumed silica include AEROSIL (registered trademark) R972 (average primary particle diameter: about 16 nm, manufactured by Nippon Aerosil Co., Ltd.), AEROSIL (registered trademark) R812 (average primary particle diameter: about 7 nm, manufactured by Nippon Aerosil Co., Ltd.), AEROSIL (registered trademark) RY200S (average primary particle diameter: about 16 nm, manufactured by Nippon Aerosil Co., Ltd.), and AEROSIL (registered trademark) R805 (average primary particle diameter: about 12 nm, manufactured by Nippon Aerosil Co., Ltd.).

In the towpreg of the present invention, it is preferable that the towpreg contains 0.5 to 2 parts by mass of particles that are insoluble in epoxy resin at 25°C and have a primary particle diameter of 0.5 to 150 μm per 100 parts by mass of epoxy resin, and that the Rc is 20 to 28%. By satisfying such conditions, a better balance can be achieved between the effect of suppressing winding tightening during unwinding and the spreadability of the tow during filament winding molding. Here, the particles that are insoluble in epoxy resin at 25°C can be used without any particular restrictions, and examples include particles of latent hardeners such as dicyandiamide and diaminodiphenyl sulfone, organic particles such as thermoplastic resins, and inorganic particles such as silica and carbon. The primary particle diameter of such particles can be measured by laser diffraction/scattering method, etc.

In the present invention, it is preferable that the particles that are insoluble in epoxy resin at 25°C and have a primary particle size of 0.5 to 150 μm contain dicyandiamide. Among the particles, dicyandiamide has the property of dissolving during the curing process and acting as an epoxy resin curing agent, and since solid content is unlikely to remain as defects in the cured product, it is possible to obtain an epoxy resin composition for towpregs that provides a fiber-reinforced composite material with excellent mechanical properties.

The primary particle diameter of dicyandiamide is preferably 0.5 to 150 μm, more preferably 0.5 to 100 μm, and even more preferably 0.5 to 10 μm. By setting the primary particle diameter in this range, it becomes easy to adjust the interlayer friction coefficient to an appropriate range, and the mechanical properties of the cured resin can be improved. Here, the primary particle diameter of dicyandiamide refers to the volume-based particle size distribution, and it is preferable that D10 is equal to or greater than the lower limit of the preferred range of primary particle diameters, and D90 is equal to or less than the upper limit of the preferred range of primary particle diameters. The primary particle diameter of dicyandiamide can be measured by laser diffraction/scattering methods, etc.

Various known methods can be used to prepare the epoxy resin composition used in the towpreg of the present invention. For example, the composition may be kneaded using a machine such as a kneader, planetary mixer, mechanical stirrer, dissolver, or three-roll mill, or it may be mixed by hand using a beaker and spatula, etc.

The towpreg of the present invention can be manufactured by various known methods. That is, the epoxy resin composition used in the towpreg of the present invention can be heated without using an organic solvent to reduce the viscosity, and the reinforcing fiber bundle is immersed in the epoxy resin composition and impregnated therewith; the epoxy resin composition having a low viscosity at room temperature or the epoxy resin composition having a low viscosity by heating can be coated on a rotating roll or release paper, and then transferred to one or both sides of the reinforcing fiber bundle, and then the reinforcing fiber bundle is pressed and impregnated by passing through a bending roll or a pressure roll. Since a high-quality towpreg can be manufactured, the manufacturing method of the towpreg of the present invention preferably includes a step of contacting at least one side of the reinforcing fiber bundle with a rotating roll coated with the epoxy resin composition. The towpreg is usually supplied in the form of a bobbin wound around a paper tube with several hundred to several thousand meters.

The fiber-reinforced composite material of the present invention can be obtained by heat curing the towpreg of the present invention. The intermediate substrate of the present invention can be used in many fields such as aviation and space, 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 detail below with reference to examples. However, the scope of the present invention is not limited to these examples. The unit of "parts" in the composition ratio means parts by mass unless otherwise noted. Furthermore, measurements of various characteristics (physical properties) were performed in an environment with a temperature of 23°C and a relative humidity of 50%, with the number of measurements being 1, unless otherwise noted.

Materials used in the Examples and Comparative Examples
(1) Carbon fiber bundle: Carbon fiber manufactured by Toray Industries, Inc. (fineness: 1645 g/1000 m, arithmetic average roughness (Ra): 2.1 nm of single fiber surface).

(2) Epoxy resin: "jER (registered trademark)" 807 (liquid bisphenol F type epoxy resin, manufactured by Mitsubishi Chemical Corporation)
- "jER (registered trademark)" 828 (liquid bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Corporation)
- "Sumiepoxy (registered trademark)" ELM-434VL (glycidylamine type epoxy resin, tetraglycidyldiaminodiphenylmethane, manufactured by Sumitomo Chemical Co., Ltd.)
"EPICLON (registered trademark)" HP-7200L (dicyclopentadiene type epoxy resin, manufactured by DIC Corporation).

(3) Curing agent: "jER Cure (registered trademark)" DICY7 (dicyandiamide (D10: 0.9 μm, D90: 7.4 μm), manufactured by Mitsubishi Chemical Corporation)
Accelerator DY 9577 (boron trichloride amine complex, manufactured by Huntsman Japan Co., Ltd.)
"DYHARD (registered trademark)" Fluid 111 (cyanamide, manufactured by AlzChem)
"KAYAHARD (registered trademark)" AA (liquid aromatic amine, 3,3'-diethyl-4,4'-diaminodiphenylmethane, liquid at 25°C, manufactured by Nippon Kayaku Co., Ltd.)
"jER Cure (registered trademark)" WA (liquid aromatic amine, diethyltoluenediamine, liquid at 25°C, manufactured by Mitsubishi Chemical Corporation).

(4) Additives: "AEROSIL (registered trademark)" RY200S (hydrophobic fumed silica, average primary particle diameter: about 16 nm, manufactured by Nippon Aerosil Co., Ltd.)
"Kane Ace (registered trademark)" MX-150 (liquid bisphenol A type epoxy resin masterbatch containing 40% polybutadiene rubber type core-shell rubber particles (particle size: 100 nm), manufactured by Kaneka Corporation)
"Kane Ace (registered trademark)" MX-267 (liquid bisphenol F type epoxy resin masterbatch containing 37% polybutadiene rubber type core-shell rubber particles (particle size: 100 nm), manufactured by Kaneka Corporation)
"Hypro (registered trademark)" 1300X13 (carboxyl-terminated butadiene nitrile rubber, manufactured by CVC Thermoset Specialties)
- "Vinylec" K (polyvinyl formal resin, manufactured by JNC Corporation).

<Method of measuring arithmetic mean roughness (Ra) of single fiber surface>
The carbon fibers were cut to a length of about several mm and fixed on a substrate (silicon wafer) using silver paste, and then an image of the three-dimensional surface shape at the center of each single fiber was obtained using an atomic force microscope (AFM). The atomic force microscope used was a NanoScope IIIa manufactured by Digital Instruments, Inc., with a Dimension 3000 stage system. The observation conditions were as follows:
Scanning mode: Tapping mode Probe: Silicon cantilever Scanning range: 0.6 μm x 0.6 μm
Scanning speed: 0.3Hz
- Number of pixels: 512 x 512
Measurement environment: room temperature, in air. For each sample, images were obtained by observing one spot on each single fiber, and the roundness of the fiber cross section was approximated by a cubic curve, and the arithmetic mean roughness (Ra) was calculated for the entire image. The average value of the values obtained for five single fibers was used.

<Method for preparing epoxy resin composition>
After the components other than the curing agent were put into a beaker, they were heated to 100°C and stirred until uniform. When fumed silica was used, the heated and stirred epoxy resin was cooled to 25-40°C and then dispersed using a three-roll mill. Next, the temperature of the epoxy resin was brought to 25-60°C, and the curing agent was added and stirred until uniform to obtain an epoxy resin composition. When a toughening agent compatible with the epoxy resin at 25°C was used, compatibility was confirmed by visual observation. The component content ratios of the examples and comparative examples are shown in Tables 1 to 3.

<Method for measuring viscosity of epoxy resin composition at 25°C>
According to JIS Z8803 (2011) "Viscosity measurement method using a cone-plate type 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 in, and the value was read when the displayed value stabilized after 1 minute or more had elapsed.

<Method of measuring _η0.1 / _η10 >
In accordance with JIS K 7244-10 (2005), the frequency dependence of the viscosity of the epoxy resin composition was measured under the conditions shown below, and the ratio of the complex shear viscosity (η _0.1 ) measured at a frequency of 0.1 Hz to the complex shear viscosity (η ₁₀ ) measured at a frequency of 10 Hz was calculated.
Apparatus: ARES-G2 (manufactured by TA Instruments)
Plate composition: Aluminum φ40mm disposable plate
Aluminum φ42mm disposable pull cup gap: 1.0mm
Temperature: 25°C
Measurement frequency: 0.1~10Hz
Distortion: 10%.

<Method of 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 maintaining the temperature for 4 hours. The temperature was then lowered to room temperature and the composition was removed from the mold to produce a cured resin plate.

<Method of measuring glass transition temperature>
A test piece having a width of 12.7 mm and a length of 45 mm was cut out from a 2 mm thick resin cured 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 temperature rise 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 in the storage modulus G' curve.

<Method for measuring fracture toughness of cured resin>
The test was carried out in accordance with 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 out from a 6 mm thick resin cured plate, and a pre-crack was then introduced. Then, using an Instron universal testing machine (manufactured by Instron Corporation), the span was set to 50.8 mm, the crosshead speed was set to 10 mm/min, and the number of samples was set to n=6, and the fracture toughness value (K _IC ) was measured.

<How to make a towpreg>
Using a towpreg manufacturing device equipped with a creel, kiss roll, nip roll, and winder, an epoxy resin composition adjusted to a temperature of 20 to 60°C was applied to one side of a carbon fiber bundle, and then the bundle was passed through a nip roll to impregnate the inside of the reinforced fiber bundle with the epoxy resin composition, thereby obtaining a towpreg. The towpreg bobbin was wound up to 2,300 m on a paper tube with an initial tension of 600 to 1,000 gf and a wind ratio of 6 to 10, to form a cylindrical shape with a winding width of 230 to 260 mm.

<Method of measuring Rc of towpreg>
The Rc of the towpreg was calculated from the towpreg bobbin mass (W _A ), the paper tube mass (W _B ), the carbon fiber mass per unit length (W _C ), and the length of the towpreg wound around the bobbin (W _D ) according to formula (1).

<Method for measuring interlayer friction coefficient>
The interlayer friction coefficient was measured by carrying out the following operations (a), (b), and (c) in this order.
(a) First, as shown in FIG. 1, a first layer towpreg 4 cut to a length of 150 mm was placed on a release paper 2 having a width of 40 mm and a length of 150 mm, and a second layer towpreg 3 cut to the same size was laminated on top of it so as to overlap by a length of 60 mm. Next, a towpreg for spacer 5 having a length of 20 mm was laminated on the first layer towpreg 4 so as to contact the overlapping portion of the second layer, and a third layer towpreg 4 having a length of 150 mm was laminated on top of it so as to overlap with the first layer to produce a towpreg laminate. Next, in order to prevent the towpreg laminate from being deformed more than necessary due to a vertical load, a spacer 6 having a thickness equivalent to that of the towpreg laminate by laminating cellophane tape was installed so as to contact the side of the towpreg laminate. Finally, a release paper 2 having a width of 40 mm and a length of 150 mm was attached so as to overlap with the release paper 2 of the lowest layer to produce a test sample.
(b) The test sample was placed in a sample chamber having a temperature of 25° C. and a humidity of 50% RH, and a constant vertical load of 20.6 N was applied by pressure plate 1 to the area from 60 mm of the overlap portion to 10 mm in the center of the spacer (area 10 mm wide and 70 mm long).
(c) 10 minutes after applying the vertical load, the second layer towpreg 3 was pulled out in the fiber direction at a tensile speed of 1 mm/min, and the pull-out load was measured. The maximum value of the pull-out load that appeared after the start of pulling was taken as the static friction force, and the static friction coefficient was calculated according to the following formulas (2) to (6). At this time, since the area of the overlap part where the second layer towpreg receives the vertical load decreases with pulling, the pull-out displacement at the time when the pull-out load becomes maximum was subtracted from the initial overlap part length, and the value obtained by dividing the pull-out load by twice the vertical load received by the area of the overlap part was taken as the static friction coefficient. In addition, at this time, since the towpreg 3 has slack immediately after the start of measurement, the pull-out displacement at the time when the pull-out load becomes maximum was corrected by subtracting the displacement until the slack was eliminated. The interlaminar friction coefficient in the present invention was determined by measuring this static friction coefficient three times and adopting the average value.

Here, the symbols in the formulas (2) to (6) have the following meanings.
F: Maximum pull-out load (static friction force)
N: Vertical load applied to the overlap portion of towpreg 3 and towpreg 4 at maximum load P: Vertical pressure applied to the overlap portion of towpreg 3 and towpreg 4 at maximum load _A34 : Area of the overlap portion of towpreg 3 and towpreg 4 at maximum load _As : Area of spacer 5 W: Width of towpreg _L34 : Length of the overlap portion of towpreg 3 and towpreg 4 at maximum load _L0 : Initial length of the overlap portion _L1 : Displacement until initial sagging of towpreg 3 is eliminated _Lt : Pull-out displacement at maximum load.

<Method of measuring coverage>
First, the towpreg was cut into a length of 10 mm and placed on a sample stage so that the surface coated with the epoxy resin composition could be observed. The surface of the towpreg was imaged at a magnification of 200 times using a Keyence digital microscope VHX-5000 while illuminating with a ring light, and a digital image as shown in FIG. 2 was obtained. By illuminating with a ring light, the reflection of light by the epoxy resin was canceled, and an image in which the solid components not dissolved in the epoxy resin were emphasized was obtained. The obtained digital image was then binarized using image analysis software ImageJ, and the parts covered by the solid components not dissolved in the epoxy resin were recognized and their areas were calculated. The area of the parts covered by the solid components not dissolved in the epoxy resin obtained by the above method was divided by the area actually captured, and the value expressed as a percentage was taken as the coverage rate.

<Method for evaluating towpreg slippage properties>
The towpreg bobbin obtained according to the above <Towpreg Manufacturing Method> was adjusted to 25°C, then placed so that the longitudinal direction of the paper tube was perpendicular to the surface of the workbench and left to stand for 10 minutes, and the amount of movement of the cylindrical bobbin bottom end was measured. When there was no movement of 10 mm or more and the shape stability of the bobbin was good, it was ranked as A, when the above abnormality occurred infrequently but was tolerable, it was ranked as B, and when the above abnormality occurred frequently and was not tolerable, it was ranked as C. The evaluation order was A was the best and C was the worst.

<Method for measuring towpreg tightening speed>
First, the towpreg bobbin obtained according to the above-mentioned <Towpreg manufacturing method> was rewound with a tension of 7 N to make the winding tension constant, and then a 5 kg weight was hung from the end of the towpreg using the device shown in FIG. 5. Next, the displacement of the weight after hanging was recorded with a displacement meter (laser reading type) to create a displacement curve (displacement vs. elapsed time). The tightening speed (mm/s) was calculated from the initial slope of the displacement curve. In the present invention, the tightening speed was the average value of four measurements. It can be said that the smaller this average value, the more difficult it is to tighten the towpreg.

<Method for evaluating towpreg spreadability>
First, a helical layer (±45°) was wound around a cylindrical liner (made of aluminum) having an outer diameter of 146 mm and a total length of 250 mm, using one towpreg obtained according to the above-mentioned <Towpreg manufacturing method>, with a creel tension of 30 N. Next, as shown in FIG. 6, the yarn width of the towpreg in the trunk and mirror parts of the second and subsequent helical layers was measured with a vernier caliper. The value obtained by dividing the yarn width of the mirror part of the helical layer by the yarn width of the trunk part of the helical layer was taken as the towpreg widening ratio. In the present invention, the yarn width was measured at seven points while changing the measurement points, and the average value of the calculated towpreg widening ratios was adopted. It can be said that the closer this average value is to 1.0, the better the widening property is.

Example 1
An epoxy resin composition was prepared according to the above <Method for preparing epoxy resin composition> using 100 parts by mass of "jER (registered trademark)" 828 as the epoxy resin and 1.0 part by mass of Accelerator DY 9577 as the curing agent. The viscosity of this resin composition at 25°C was 17 Pa·s. The cured resin obtained according to the above <Method for preparing cured resin plate> had a glass transition temperature of 108°C and a fracture toughness value (K _IC ) of 0.7 MPa·m ^0.5 .

Next, a towpreg was obtained using this epoxy resin composition according to the above-mentioned <Towpreg Production Method>. The Rc of this towpreg was 26.3 mass%, the coverage was 0%, and the interlaminar friction coefficient was 0.049. As a result of evaluating this towpreg, the slippage was rated B, the expansion ratio was 0.86, and the tightening speed was 18, and good results were obtained in all tests.

(Examples 2 to 3)
Except for changing the formulation of the epoxy resin composition as shown in Table 1, epoxy resin compositions and towpregs were prepared and evaluated in the same manner as in Example 1. The evaluation results showed that good results were obtained in all of the following: viscosity of the resin composition at 25°C, glass transition temperature of the cured resin, fracture toughness (K _IC ), Rc, coverage, interlaminar friction coefficient, slippage property, width expansion ratio, and tightening speed.

In Example 3, where the viscosity of the resin composition was relatively high, it was necessary to heat the epoxy resin composition during towpreg production to reduce the viscosity to an easy-to-apply level and to control the temperature so as to prevent viscosity increase due to the progress of the curing reaction. However, in Example 2, the viscosity was lower than 50 Pa·s, so simple temperature control was sufficient, and operability was excellent.

(Examples 4 to 6)
Except for changing the formulation of the epoxy resin composition as shown in Table 1, epoxy resin compositions and towpregs were prepared and evaluated in the same manner as in Example 1. The evaluation results showed that good results were obtained in all of the following: viscosity of the resin composition at 25°C, glass transition temperature of the cured resin, fracture toughness (K _IC ), Rc, coverage, interlaminar friction coefficient, slippage property, width expansion ratio, and tightening speed.

In all of Examples 4 to 6, the primary particle diameter of the toughening agent was 50 nm to 1 μm, and therefore excellent toughness was exhibited. In addition, the slippage property was rated A because the η _0.1 /η ₁₀ was 1.5 or more, and therefore the results were superior to those of Example 1.

Furthermore, in Example 6, which contains 3 to 5 parts by mass of fumed silica with a primary particle diameter of 5 to 50 nm per 100 parts by mass of epoxy resin, a better balance was achieved between the effect of suppressing tight winding during unwinding and the spreadability of the tow during filament winding molding.

(Examples 7 to 10)
Except for changing the composition of the epoxy resin composition as shown in Table 2 and using a liquid aromatic amine that is liquid at 25° C. as the curing agent, epoxy resin compositions and towpregs were prepared and evaluated in the same manner as in Example 1. The evaluation results showed good results in all of the viscosity of the resin composition at 25° C., the glass transition temperature of the cured resin, the fracture toughness value (K _IC ), Rc, coverage, interlaminar friction coefficient, slippage property, width expansion ratio, and tightening speed.

In Examples 7 to 10, by using a liquid aromatic amine that is liquid at 25°C, the coverage rate could be controlled to be small, and even when a solid epoxy ("EPICLON (registered trademark)" HP-7200L) that is prone to increasing viscosity or a large amount of toughening agent was mixed, it was easy to adjust the interlayer friction coefficient to the appropriate range of the present invention.

In addition, Examples 7 to 9 had higher Tg and better heat resistance than Example 10. Furthermore, since Examples 8 and 9 contain a glycidylamine type epoxy resin, the viscosity increase ratio after 24 hours at 25°C was smaller than that of Example 7, and storage stability was excellent.

(Examples 11 to 13)
Except for changing the composition of the epoxy resin composition as shown in Table 2, epoxy resin compositions and towpregs were prepared and evaluated in the same manner as in Example 1. The evaluation results showed good results in all of the viscosity of the resin composition at 25°C, the glass transition temperature of the cured resin, the fracture toughness value (K _IC ), Rc, coverage, interlaminar friction coefficient, slippage property, width expansion ratio, and tightening speed.

Even when solid components were included, the interlayer friction coefficient could be controlled within an appropriate range by setting the coverage rate to 0% or more and less than 2.5%. Furthermore, in Examples 11 and 13, which contain 0.5 to 2 parts by mass of particles that are insoluble in epoxy resin at 25°C and have a primary particle size of 0.5 to 150 μm per 100 parts by mass of epoxy resin and have an Rc of 20 to 28%, a better balance was achieved in the effect of suppressing winding tightness during unwinding and the spreadability of the tow during filament winding molding compared to Example 12.

(Comparative Example 1 and Comparative Example 2)
Except for changing the composition of the epoxy resin composition as shown in Table 3, epoxy resin compositions and towpregs were prepared and evaluated in the same manner as in Example 1. As a result of the evaluation, Comparative Examples 1 and 2, in which the coverage was 2.5% or more, had a large interlayer friction coefficient of 0.10 or more, and therefore had a small width expansion ratio, resulting in insufficient results.

(Comparative Example 3)
Except for changing the composition of the epoxy resin composition as shown in Table 3 and lowering the viscosity at 25°C to less than 5 Pa·s, an epoxy resin composition and a towpreg were prepared and evaluated in the same manner as in Example 1. As a result of the evaluation, the interlaminar friction coefficient was 0.021, which was smaller than 0.04, and therefore, although the expansion ratio was good at 0.93, the slippage property was rated C and the tightening speed was unsatisfactory at 89 mm/sec.

(Comparative Example 4)
Except for changing the composition of the epoxy resin composition as shown in Table 3 and increasing the viscosity at 25°C to more than 150 Pa·s, an epoxy resin composition and a towpreg were prepared and evaluated in the same manner as in Example 1. As a result of the evaluation, the interlayer friction coefficient was 0.11, which was greater than 0.10, so the slippage property was rated A and the tightening speed was 4.9 mm/sec, which was good, but the widening ratio was 0.70, which was unsatisfactory.

(Comparative Example 5)
An epoxy resin composition and a towpreg were prepared and evaluated in the same manner as in Example 1, except that the composition of the epoxy resin composition was changed as shown in Table 3 and Rc was set to 18.9%, which is smaller than 20%. As a result of the evaluation, the interlaminar friction coefficient was 0.64, which was larger than 0.10, so the slippage property was rated A and the tightening speed was 0.5 mm/sec, which was good, but the expansion ratio was 0.61, which was insufficient.

(Comparative Example 6)
An epoxy resin composition and a towpreg were produced and evaluated in the same manner as in Example 1, except that the composition of the epoxy resin composition was changed and Rc was increased to 42.5%, which is greater than 40%, as shown in Table 3. As a result of the evaluation, the interlaminar friction coefficient was 0.033, which was smaller than 0.04, and although the widening ratio was good at 0.97, the slippage was rated C and the tightening speed was unsatisfactory at 45 mm/sec. Furthermore, because Rc was large, there was a lot of seepage of the resin composition from the towpreg bobbin and a lot of scattering of the resin composition during the filament winding molding process, and the processability was insufficient.

The composition in the table is in parts by mass.

1: Pressure plate 2: Release paper 3: Second layer towpreg 4: First and third layer towpreg 5: Towpreg for spacer 6: Cellophane tape spacer 7: Towpreg 8: Paper tube 9: Weight 10: Movable weight base 11: Displacement meter 12: Towpreg 13: Liner 14: Yarn width of the trunk part of the helical layer 15: Yarn width of the mirror part of the helical layer

Claims (8)

an epoxy resin composition having a viscosity of 5 to 150 Pa s at 25°C, which contains as an epoxy resin a glycidylamine type epoxy resin selected from a glycidylaniline type, a diaminodiphenylmethane type, a diaminodiphenylsulfone type, an aminophenol type, and a metaxylenediamine type, and contains as a curing agent an aromatic amine which is liquid at 25°C and compatible with the epoxy resin ;
A towpreg impregnated with a carbon fiber bundle having a fineness of 30 to 4000 g/1000 m,
The content of the glycidylamine type epoxy resin is 10 to 60 parts by mass in 100 parts by mass of the epoxy resin,
The liquid aromatic amine contains a compound represented by the following chemical formula (1):
The resin content (Rc) of the towpreg is 20 to 40 mass%;
and when the surface of the towpreg is observed at a magnification of 200 times using an optical microscope, the ratio of the area of the portion covered by the solid component not dissolved in the epoxy resin to the area of the field of view (coverage rate) is 0% or more and less than 2.5%.
Furthermore, a towpreg is provided in which three layers of the towpreg are laminated in the same direction, and the central towpreg is pulled out under conditions of a temperature of 25° C., a humidity of 50% RH, a speed of 1 mm/min, and a normal load of 20.6 N, and the interlayer friction coefficient is measured to be 0.04 or more and less than 0.10.

In the formula, R ¹ , R ² and R ³ are any one of hydrogen, an alkyl group having 1 to 4 carbon atoms, an alkoxy group and an alkylthio group, and R ¹ , R ² and R ³ may be the same or different. 2. The towpreg according to claim 1, wherein a content of the glycidyl amine type epoxy resin is 20 to 60 parts by mass based on 100 parts by mass of the epoxy resin. 3. The towpreg according to claim 1 or 2, wherein the epoxy resin composition comprises a toughening agent that is compatible with epoxy resins at 25°C and/or a toughening agent having a primary particle size of 50 nm to 1 μm, and the toughness value KIc of a cured product obtained by curing the epoxy resin composition at ¹⁵⁰ °C for 4 hours is 1.0 to 3.0 MPa m. 4. The towpreg according to claim 1 , wherein the epoxy resin composition has a complex shear viscosity (η0.1) measured at 25° C. and a frequency of 0.1 Hz using a parallel plate oscillatory rheometer to a complex shear viscosity (η10) measured at 25° C. and a frequency of 10 Hz using a parallel plate oscillatory rheometer, the ratio ( ^η0.1 / ^η10 ) being 1.5 or more. The towpreg according to claim 4 , comprising 3 to 5 parts by mass of fumed silica having a primary particle diameter of 5 to 50 nm per 100 parts by mass of the epoxy resin. The towpreg according to any one of claims 1 to 5, wherein the content of the aromatic amine is an amount such that active hydrogen is 0.7 to 2.0 equivalents relative to epoxy groups of the epoxy resin. The towpreg according to any one of claims 1 to 6, further comprising a bisphenol F type epoxy resin. A fiber-reinforced composite material obtained by curing the towpreg according to any one of claims 1 to 7 .

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