JPH0820706A - Epoxy resin composition and prepreg prepared therefrom - Google Patents

Abstract

PURPOSE:To obtain an epoxy resin composition which is properly handleable, is capable of controlling a resin flow at will upon molding, is free from difficulties in molding such as open molding and internal pressure molding, is capable of obtaining moldings having excellent impact resistance, and is very useful in improving the reliability of fiber reinforcing composites, in improving the characteristics and in improving the productivity, and a prepreg prepared therefrom. CONSTITUTION:This resin composition comprises an epoxy resin (A), a urethane- modified epoxy resin (B), a potential aminic curing agent (C), a curing accelerator (D), and a fibrous inorganic filler (E) having an aspect ratio of 3-500.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention is excellent in handling workability such as appropriate tackiness (adhesiveness) and drapeability (flexibility) of prepreg, storage stability at room temperature, and good impact resistance. Moreover, there is little resin flow at the time of molding, especially when molding tubular moldings made of fiber reinforced resin such as fishing rods and golf shafts, there is no furnace drop, and there are no defects such as scratches on the polished surface of these moldings. Excellent composite material. It relates to a fiber-reinforced composite material having properties.

[0002]

BACKGROUND OF THE INVENTION Fiber-reinforced composite materials such as carbon fibers are lightweight, have high strength and high elastic modulus, and are in the form of composites with resins, so-called prepregs, such as fishing rods, golf club shafts, and tennis. Sports / leisure fields such as rackets, industrial materials such as leaf springs and honeycomb structure materials, as well as automobile-related, aircraft materials, structural materials such as ships, electronic materials,
Widely used for various purposes such as civil engineering and building materials.

By the way, as a matrix resin for such a prepreg for a fiber-reinforced composite material, an epoxy resin is conventionally used (JP-A-62-127317 and JP-A-2-41314), and a urethane-modified epoxy resin. With the addition of (Japanese Patent Publication No. 62-44011,
JP-A-1-161041) has been proposed. However, these products have good workability in handling prepregs, for example, are free from defects such as scratches during polishing of the surface of tubular moldings, etc., and it is extremely difficult to obtain molded products with sufficient impact resistance. It was

Further, for the purpose of reducing the fluidity of the matrix resin at the time of molding the prepreg, a filler having a particle size of 10 times or less of the diameter of the reinforcing single fiber, such as graphite powder, carbon black or aluminum, is added to these matrix resins. Powder, silica powder, etc. added (JP-A-59-59)
No. 227931) is used for manufacturing a prepreg.

Particularly for tubular fiber-reinforced composite materials such as fishing rods and golf shafts, a sheet-shaped prepreg in which carbon fibers or glass fibers are aligned in one direction or a prepreg obtained by impregnating a woven fabric of the above-mentioned reinforcing fibers with a matrix resin is released. Wrap the taped mandrel coated with the agent in the longitudinal direction in the direction according to the desired design, and then wind the heat-shrinkable tape spirally using a tape winder, etc. while gradually overlapping it. Then, put it in a heating furnace, harden the matrix resin while applying tightening force with heat shrinkable tape, remove from the heating furnace and remove the tape after cooling, pull out the mandrel with a core removing machine etc. . However, the conventional prepreg has a drawback that the prepreg moves from the large diameter side of the mandrel toward the small diameter side during molding, that is, so-called furnace drop occurs. This is because heating causes the matrix resin to have low viscosity and to increase fluidity, so when the tightening force of the heat-shrinkable tape is applied in such a state, the mandrel has a taper, and the mandrel has a taper from the large diameter side to the small diameter side. A component force is generated and a so-called furnace drop occurs in which the prepreg moves in this direction. When this furnace drop occurs, the distribution of the matrix resin and the reinforcing fibers becomes uneven, and the desired physical properties of the composite material cannot be obtained, and it also causes defects in the molded product or warpage of the small diameter portion.

On the other hand, JP-A-57-22636 discloses that
Prior to winding the prepreg around the mandrel, a method has been proposed in which a thread or a thread impregnated with a thermosetting resin is spirally wound in the longitudinal direction of the mandrel and the friction thereof prevents the furnace from falling. However, in this method, not only the effect of preventing the furnace from falling is not sufficient, but also the yarn remains in the molded product, which is not preferable in terms of characteristics. Further, in Japanese Patent Laid-Open No. 59-159315, a temperature of 130 ° C. is applied to a matrix resin for prepreg before winding the prepreg around a mandrel.
There is proposed a method of preventing the furnace from falling by applying a thermosetting resin having a gel time of 80% or less of the above resin to the mandrel. However, this method requires a resin for undercoating whose gel time is adjusted by B-stage formation, and prior to molding, the step of applying this undercoating resin,
Air-drying is required, which significantly reduces productivity.

With regard to the handleability (tack and drape) of the prepreg during work, not only the productivity when the shaft is wound, but also a defect (scratch, etc.) on the surface of the molded product is required, so appropriate characteristics are required. To be done. If the tackiness is too strong, air is likely to be entrained at the time of winding, and if it is too low, workability such as laminating the prepreg deteriorates. In addition, when the drape property is insufficient, the prepreg is wound at the end portion of the winding, and particularly carbon fibers having a high elastic modulus may be broken. However, these factors appear on the surface as defects such as scratches at the time of polishing and coating after molding the shaft, causing defective products and deteriorating the physical properties, resulting in a significant reduction in yield.

As described above, the conventional prepreg using the matrix resin has appropriate workability and excellent composite material properties, does not fall down during molding, has no polishing on the molded product, and has no defects on the painted surface. It was extremely difficult to provide.

[0009]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned drawbacks of the conventional method and prevent the furnace from falling during molding without performing a pretreatment step. It is possible to obtain a fiber-reinforced composite material molded article which has excellent impact resistance and does not deteriorate other composite material properties, and which has desired properties. Further, the prepreg of the present invention has an appropriate winding workability at a normal winding temperature and can freely control the resin flow at the time of molding, so that defects (such as scratches) on the surface of the molded product after polishing can be obtained. ) Is provided.

[0010]

That is, the present invention provides an epoxy resin composition containing the following components (A), (B), (C), (D) and (E) (A) Epoxy resin (B) Urethane-modified epoxy resin (C) Latent amine-based curing agent (D) Curing accelerator (E) Fibrous inorganic filler with aspect ratio of 3 or more and 500 or less It exists in prepreg.

The present invention will be described in more detail below. The epoxy resin which is the component (A) used in the present invention is not particularly limited, and includes a bisphenol A type epoxy resin and other glycidyl ether type epoxy resins, for example,
Bisphenol F type epoxy resin, bisphenol S type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, glycidyl amine type epoxy resin, naphthalene type epoxy resin, brominated bisphenol A type epoxy resin, glycidyl ester type epoxy resin, Examples thereof include cycloaliphatic epoxy resins and heterocyclic epoxy resins. If desired, urethane-modified epoxy resin, rubber-modified epoxy resin, alkyd-modified epoxy resin, etc. may be used. Among these, bisphenol A type epoxy resin and novolac type epoxy resin are preferable from the viewpoint of balance of handling property, economical efficiency, and physical properties of composite material, but two or more kinds of these can be appropriately mixed and used according to required characteristics.

As the urethane-modified epoxy resin as the component (B), those obtained by reacting a urethane prepolymer having an isocyanate group at the molecular end with an epoxy resin having a hydroxyl group in the molecule are used. As a urethane prepolymer having an isocyanate group (hereinafter referred to as NCO group) at the molecular end, which is a raw material of the urethane-modified epoxy resin, diisocyanate and polyether polyol,
Examples thereof include various ones obtained by reacting a polyol such as a polyester polyol with a conventional method. Examples of the diisocyanate include tolylene 2,4-diisocyanate, tolylene 2,6-diisocyanate, 4,4′-
Examples thereof include diphenylmethane diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, xylylene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, and the like, but particularly preferred are tolylene diisocyanate and 4,4′-diphenylmethane diisocyanate. As the polyol, polyoxyethylene glycol, polyoxypropylene glycol, polyoxytetramethylene glycol, or glycerin, polyhydric alcohols such as trimethylolpropane or ethylene oxide of amines, alkylene oxide adducts such as propylene oxide, and the like, Polyether polyols with a molecular weight usually in the range of 500 to 3000; polyvalent polyols such as oxalic acid, succinic acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid and fumaric acid Carboxylic acid and ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-
Hexanediol, diethylene glycol, trimethylolpropane, glycerin, neopentyl glycol,
The polyhydric alcohol such as bis (hydroxymethylcyclohexane) has a molar ratio of hydroxyl group to carboxyl group of 1
Examples thereof include polyester polyols having a normal molecular weight in the range of 500 to 3000, which are obtained by condensation under the above conditions or obtained by ring-opening polymerization of a lactone such as caprolactone in the presence of a polyhydric alcohol.

The reaction of diisocyanate with polyols such as polyether polyols and polyester polyols is usually carried out under the condition that the molar ratio of NCO groups to hydroxyl groups is more than 1, preferably 1.05-2, and the temperature is from room temperature to 120 ° C. It is carried out in. The urethane prepolymer thus obtained preferably has an NCO group content of 0.5 to 5% by weight and a molecular weight of 1,000 to 10,000. The NCO group content and the molecular weight of the urethane prepolymer are the raw material composition, That is, it can be controlled by changing the molar ratio of the NCO group to the hydroxyl group.

The epoxy resin having a hydroxyl group in the molecule which is the other raw material of the urethane-modified epoxy resin is usually an epoxy resin having a molecular weight of 300 or more, particularly 350 or more. If the content of hydroxyl groups is too small, it is difficult to achieve the object of the present invention. Therefore, an epoxy resin having an average of 0.5 or more hydroxyl groups per epoxy resin molecule, for example, "E1001", "E1004", "E1009".
Bisphenol A type epoxy resin such as (made by Yuka Shell Co., Ltd.) or other hydroxyl group-containing epoxy resin used in the component (A), or hydroquinone, phenol novolac, cresol novolac, etc. are reacted with epichlorohydrin to give 1 in the molecule. It is preferable to use a hydroxyl group-containing epoxy resin having at least one epoxy group. The reaction between the urethane prepolymer having an NCO group at the molecular end and the epoxy resin having a hydroxyl group in the molecule has a molar ratio of the hydroxyl group of the epoxy resin to the NCO group of more than 1, preferably 3 to 40 at a room temperature. To 120 ° C., especially 60 to 100 ° C., until the NCO groups have completely disappeared. The urethane-modified epoxy resin of the present invention is preferably obtained by reacting the NCO group of the urethane prepolymer with the hydroxyl group of the epoxy resin.
At reaction temperatures below 00 ° C, unless there is a particular catalyst, NCO
The reaction between the group and the hydroxyl group in the epoxy resin proceeds preferentially, and the reaction between the NCO group and the epoxy group and the reaction between the NCO group and the urethane group do not substantially occur. This objective can be achieved.

The latent amine-based curing agent as the component (C) is one which functions as a curing agent at 50 ° C. or higher, and more preferably functions as a curing agent at 80 ° C. or higher.
Dicyandiamide (1-cyanoguanidine), methylguanidine, ethylguanidine, propylguanidine, butylguanidine, dimethylguanidine, trimethylguanidine, phenylguanidine, diphenylguanidine,
Guanidine-based curing agents such as triylguanidine, 2,3-guanylurea, benzoyldicyandiamide, 2,6-xylenylbiguanide, and phenylbiguanide can be mentioned. Further, for example, adipic acid dihydrazide, succinic acid dihydrazide, glutanoic acid dihydrazide, sebacic acid dihydrazide, oxalic acid dihydrazide, phthalic acid dihydrazide, isophthalic acid dihydrazide, terephthalic acid dihydrazide, p-oxybenzoic acid hydrazide, salicylic acid hydrazide, hydrazide hydrazide, Examples thereof include polyhydric carboxylic acid polyhydrazide-based curing agents such as acid dihydrazide and azelaic acid dihydrazide. These latent amine curing agents can be used alone or in combination of two or more depending on the required properties. However, dicyandiamide and adipic acid dihydrazide are preferable from the viewpoints of storage stability, economical efficiency, and physical properties of composite materials. If desired, another type of curing agent can be used in combination. Examples thereof include boron trifluoride amine complex, amine imide, diaminomaleonitrile, guanamines, phenol resin, melamine resin and urea resin. The amount of these curing agents used is usually such that the active hydrogen equivalent of the curing agent is around 0.2 to 1.2 equivalents relative to 1 equivalent of the epoxy group, although the physical properties of the cured product are good, but the storage stability is good. Etc. are adjusted as appropriate according to other required characteristics. Usually, 1 to 40 parts by weight, preferably 1 to 20 parts by weight is suitable for 100 parts by weight of the component (A). If the amount is less than 1 part by weight, curing will be insufficient,
If it is more than 40 parts by weight, the properties of the cured product are not deteriorated, which is not preferable.

Examples of the curing accelerator as the component (D) include imidazole derivatives and salts thereof (for example, Shikoku Kasei Co., Ltd., trade name Cureazole), amine adduct compounds (for example, Ajinomoto Co., trade name Amicure), microcapsules (for example, Asahi Kasei). Company name, Novacure), urea compounds (for example, 3- (3,4-dichlorophenyl) -1,1-N dimethylurea, 3-phenyl-1,1-dimethylurea, 3-
(4-chlorophenyl) -1,1-dimethylurea, 3-
(4-Methoxyphenyl) -1,1 dimethylurea, trimethylurea) and the like show excellent effects. The addition amount of these curing accelerators is 1 to 20 with respect to 100 parts by weight of the component (A).
Parts by weight are used, but preferably 1 to 10 parts by weight are used. If the amount is less than 1 part by weight, the curing acceleration effect is small,
If the amount is more than 20 parts by weight, the storage stability of the prepreg tends to decrease, which is not preferable.

As the fibrous inorganic filler as the component (E), those having an aspect ratio (fiber length / fiber diameter) of 3 or more and 500 or less, more preferably 3 or more and 450 or less are used. If the aspect ratio is less than 3, the resin flow at the time of molding will not be sufficiently low, and if the aspect ratio is more than 500, the impregnability into reinforcing fibers or the workability of prepreg and the moldability will be adversely affected. These fibrous inorganic fillers are not particularly limited,
In the natural product system, there are, for example, sepiolite, wollastonite, asbestos, slag fiber, etc., and in the artificial product system,
Examples thereof include zonolite, elestadite, gypsum fiber, and the like. Further, for example, aluminum borate, calcium carbonate, silicon carbonate, silicon nitride, potassium titanate, basic magnesium sulfate, zinc oxide, graphite, magnesia, calcium sulfate, magnesium borate. , Titanium diboride, α-alumina, chrysotile and the like. These fibrous inorganic fillers may be used alone or in combination of two or more. Of these, sepiolite, wollastonite or aluminum borate whiskers, calcium carbonate whiskers, and silicon carbide whiskers are particularly excellent in properties and economical efficiency. The amount of addition of these fibrous inorganic fillers is 0.
05 to 30 parts by weight, preferably 0.5 to 15 parts by weight are used. If the amount is less than 0.05 parts by weight, the flow does not sufficiently decrease at the time of molding, and if the amount is more than 30 parts by weight, the viscosity of the resin increases and the impregnability into the fiber in the prepreg-forming step does not decrease, which is not preferable.

In addition to the above components, if desired, an epoxide-reactive diluent may be added to the extent that reactivity, heat resistance, storage stability and the like are not deteriorated. Examples of reactive diluents include phenyl glycidyl ether, butyl glycidyl ether, alkyl glycidyl ether, styrene oxide, octylene oxide and mixtures thereof. In addition, coupling agents such as silane and titanate compounds, release agents such as higher fatty acids and waxes, flame retardants such as halogen and phosphorus compounds, defoaming agents,
Additives such as colorants can also be used if necessary.

The reinforcing fibers used in the production of these prepregs include carbon fibers, glass fibers, aramid fibers, polyester fibers, silicon carbide fibers, boron fibers,
Alumina fibers, polyethylene fibers, etc. may be mentioned, and one kind or two or more kinds of them may be appropriately used. To manufacture prepreg, general prepreg manufacturing methods can be applied,
The reinforcing substrate may be impregnated directly by the hot melt method or by the film method, or may be impregnated directly by the solvent impregnation method or after film formation. However, the solvent impregnation method requires a solvent distillation step. .

[0020]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples. The abbreviations of the compounds used in the examples and the test methods are as follows. <Raw material> “E828”: Bisphenol A type epoxy resin (made by Yuka Shell Co., Ltd.) “E1001”: Bisphenol A type epoxy resin (made by Yuka Shell Co., Ltd.) “EOCN102S”: Cresol novolac type epoxy resin (made by Nippon Kayaku Co., Ltd. ) "EPU-6": Urethane-modified epoxy resin (manufactured by Asahi Denka Co., Ltd.) DICY: Dicyandiamide (manufactured by Yuka Shell Co., Ltd.) DCMU: 3- (3,4-dichlorophenyl) -1,1
-N dimethyl urea (Hodogaya Chemical Co., Ltd.) "Milcon PS": Sepiolite (Showa Minerals Co., Ltd.) <Aspect ratio = 50>"NYAD325": Wollastonite (NYCO) <Aspect ratio = 5>" Arborex Y "," YS2 ": Aluminum borate whiskers (manufactured by Shikoku Chemicals Co., Ltd.) <Aspect ratio = 10 to 60>" Whiscals ": Calcium carbonate whiskers (manufactured by Shikoku Chemicals Co., Ltd.) <Aspect Ratio = 20-60>"R202": Fine silica, "Aerosil R202"
(Manufactured by Nippon Aerosil Co., Ltd.) "Talc SWB": Talc, average particle size 10 μm (manufactured by Nippon Talc Co., Ltd.)

<Measurement of resin flow> 10 prepregs
Cut to 0 x 100 mm and stack 4 plies,
After laminating a film with holes on the top and bottom and glass cloth on the outermost layer, press the resin at 120 ° C and 3.5 kg / cm ² with a heating press to measure the resin flow.

<Evaluation of Winding and Furnace Falling> A prepreg was formed in an oblique layer (± 45 °) 3 ply and a straight layer (0 °) 3
It was cut to be ply. The cut prepreg was wound on a mandrel coated with a release agent by a rolling table. The heat shrink tape was then wrapped with a tape rubbing device. Suspend in a heating furnace with the large diameter side up, 12
Cured at 0 ° C./2 hours. After cooling to room temperature, measure the furnace falling.

<Handling workability: tackiness, drapeability>
(Comprehensively judged from the laminated state of the oblique layer at 23 ° C., the possibility of correction, the hardness of the manual winding, the splash after rolling the rolling table, etc.) Good ... Good, Bad ...

<Bending test (3-point bending)> ASTM D7
According to 90, device: UTM-made by Toyo Baldwin
Using 5T, sample shape: (length 100 mm, width 10
mm, thickness 2 mm), span length: 80 mm, crosshead speed: 2 mm / min, and measured the strength in the 0 ° and 90 ° directions.

<ILSS> According to ASTM D2344, sample shape: (length 12 mm,
Width 10 mm, thickness 2 mm), span length: 8 mm, crosshead speed: 2 mm / min.

<Izod Impact Test> JIS K7110
According to the above, using a universal impact tester manufactured by Toyo Seiki Co., Ltd., sample shape: (length 70 mm, width 10 m
m, thickness 2 mm) to measure the strength in the 0 ° direction.

[Synthesis of Urethane Prepolymer] (Synthesis Example 1) 100 parts by weight of polyoxypropylene glycol having a molecular weight of 2000 and 26 parts by weight of tolylene diisocyanate (2,4 units 80%) were mixed in a flask purged with nitrogen. After the end of heat generation, the temperature was raised to 80 ° C. and the reaction was carried out for 3 hours to obtain a viscous urethane prepolymer having an NCO group content of 1.02% (hereinafter referred to as prepolymer [A]).

(Synthesis Example 2) 70 parts by weight of polyoxypropylene glycol having a molecular weight of 2000 and 30 parts by weight average molecular weight
30 parts by weight of propylene oxide adduct of trimethylol propane of 00 and 17 parts by weight of tolylene diisocyanate were mixed in a nitrogen-substituted flask and reacted at 90 ° C. for 4 hours to give a highly viscous NCO group content of 2.82%. Was obtained (hereinafter referred to as prepolymer [B]).

Example 1 14 parts by weight of "E828" (excluding the amount used for the masterbatch) and 4 parts of "E1001"
5 parts by weight, 25 parts by weight of "EOCN102S" were dissolved by stirring under nitrogen atmosphere at 100 ° C for 1 hour, and then 15 parts by weight of prepolymer [A] was added and uniformly mixed to obtain 2 parts at 100 ° C.
By reacting the NCO group in the urethane prepolymer with the hydroxyl group in the epoxy resin for a time, a base resin partially containing a urethane-modified epoxy resin was obtained. Note that N
The CO groups disappeared virtually completely under these conditions. This base resin was cooled to room temperature, 5 parts by weight of "Milcon PS" and 4 parts by weight of DICY were added in a master batch, and they were uniformly mixed with a stirrer at 70 ° C / 30 minutes. Then D
5 parts by weight of CMU was added and stirred for 10 minutes to obtain a resin composition of the present invention. The resin composition thus obtained and high-strength carbon fiber (“Torayca T700” manufactured by Toray Industries, Inc., elastic modulus 24 ton)
/ Mm ² ), a unidirectional prepreg was produced by a hot melt method to obtain a prepreg of the present invention. The carbon fiber areal weight of this prepreg was 125 g / m ² , and the resin amount was 35%. 16 plies of this prepreg are laminated in one direction and cured by an autoclave at 120 ° C for 2 hours to give about 2 mm.
A thick unidirectional laminate was formed. Table 1 shows the physical properties (Vf = 60% conversion value) of the obtained composite material. In particular, 90 ° bending strength and Izod impact strength showed excellent characteristics.

Further, this prepreg had very good handling workability (tacking and drapeability), and the 10 molded articles obtained had no furnace blowout at all. Furthermore, the surface of this molded product is polished using a polishing machine, and surface defects (scratches, etc.)
As a result, a good molded product having no defects was obtained.

(Examples 2, 3, 4, 5) The resin composition of the present invention was obtained by the same method as in Example 1 and the composition shown in Table 1. The workability of this prepreg is good, 90 °
Bending strength and Izod impact strength showed excellent properties. Further, the molded product did not fall down from the furnace, and no defect was observed on the polished surface.

(Comparative Examples 1, 2, 3) A prepreg was produced in the same manner as in Example 1 with the compositions shown in Table 1. The basis weight of the prepreg was 125 g / m ² , and the resin amount was 35%. This prepreg had high tackiness, large resin flow, and the furnace fell. Further, the occurrence of scratches after polishing the molded product was remarkable.

(Comparative Examples 4 and 5) Prepregs were produced in the same manner as in Example 1 except that "Aerosil R202" or "talc SWB" was used as the inorganic filler. The workability of this prepreg was relatively good, but the furnace fell down,
There was unevenness on the surface of the molded product, and scratches were observed on several of the 10 after polishing.

[0034]

[Table 1]

[0035]

EFFECTS OF THE INVENTION The prepreg manufactured from the matrix resin of the present invention can be appropriately adjusted in proper handling workability and resin flow at the time of molding, and is defective in molding methods such as oven molding and internal pressure molding. And a molded article having excellent impact resistance can be obtained, which is extremely useful for improving reliability, improving characteristics, and improving productivity of the fiber-reinforced composite material.

Claims (8)

[Claims] 1. An epoxy resin composition comprising the following components (A), (B), (C), (D) and (E): (A) epoxy resin (B) urethane-modified epoxy resin. (C) Latent amine-based curing agent (D) Curing accelerator (E) Fibrous inorganic filler having an aspect ratio of 3 or more and 500 or less. 2. The epoxy resin composition according to claim 1, wherein the latent amine curing agent (C) is dicyandiamide. 3. The epoxy resin composition according to claim 1, wherein the fibrous inorganic filler (E) is sepiolite. 4. The epoxy resin composition according to claim 1 or 2, wherein the fibrous inorganic filler (E) is wollastonite. 5. The epoxy resin composition according to claim 1, wherein the fibrous inorganic filler (E) is aluminum borate whiskers. 6. The fibrous inorganic filler (E) is calcium carbonate whiskers, wherein the fibrous inorganic filler is calcium carbonate whiskers.
The epoxy resin composition described in 1. 7. A prepreg obtained by impregnating reinforcing fiber with the epoxy resin composition according to claim 1. 8. The prepreg according to claim 7, wherein the reinforcing fibers are carbon fibers.