JPH083335A - Unidirectional carbon fiber prepreg stabilized in shape and its production - Google Patents

Abstract

PURPOSE:To obtain the prepreg economically stabilized in the adhesivity of a matrix resin by preventing the spring back of the carbon fiber. bundle. CONSTITUTION:This unidirectional carbon fiber prepreg contains carbon fiber bundles having 0.5-10.0wt.% of a shape-stabilizing agent adhered thereto and having a torsional strength of 5-40 deg.C and an epoxy resin composition as essential components, and the method for producing the unidirectional carbon fiber prepreg having characteristics comprising having 0.5-10.0wt.% of the epoxy resin composition cured product adhered to the carbon fibers and having a carbon fiber torsional strength of 5-40 comprise thermally impregnating the carbon fiber bundles having (A) a low temperature-curing agent adhered thereto with the epoxy resin composition under a pressure and curing a part of the epoxy resin composition with (A) the curing agent in the impregnation process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a unidirectional carbon fiber prepreg. More specifically, the present invention relates to a unidirectional carbon fiber prepreg which has excellent surface smoothness and is capable of giving a carbon fiber reinforced composite material (hereinafter, abbreviated as CFRP) having high internal denseness and having good adhesiveness.

[0002]

CFRP obtained from a prepreg made of carbon fiber and a matrix resin is particularly excellent in mechanical properties. Therefore, CFRP is used for sports such as golf clubs, tennis rackets, and fishing rods, as well as aircraft and space vehicles. It has been applied to a wide range of applications including cutting-edge fields such as structural materials.

Such CFRP can be produced by stacking a plurality of prepregs, which are intermediate base materials, in the laminating step and then heating and curing the matrix resin in the molding step. At this time, in order to obtain a dense molded product in which the reinforcing fibers are accurately aligned in a certain direction and have few voids, the prepreg may have appropriate tackiness and drapeability and good handling property. is necessary.

The prepreg used to make CFRP can be manufactured by impregnating carbon fibers with a thermosetting resin such as an epoxy resin. Since the epoxy resin itself has originally excellent adhesiveness, the prepreg obtained by impregnating the reinforcing fiber with the epoxy resin also has adhesiveness. However, so-called springback occurs in which the carbon fiber bundle crushed in the process of manufacturing the prepreg tries to return to the form before crushing with time, so that the resin on the surface portion of the prepreg sneaks into the inside of the prepreg. As a result, the resin layer on the surface of the prepreg becomes thin, and the adhesiveness of the prepreg decreases over time. Further, in order to further reduce the weight of the composite material, it is often performed to increase the fiber content in the prepreg, but in such a prepreg, since the resin content is originally low, the phenomenon described above is caused. Appears more prominently.

Further, when a thermoplastic resin such as polyether sulfone or polyimide is blended in order to improve the toughness of an epoxy resin cured product or to optimize the resin viscosity, the adhesiveness of the resin itself is significantly reduced. In order to
The tackiness of the obtained prepreg is also significantly reduced. Therefore, in order to increase the tackiness of the resin itself, a method of blending a tacky substance into the resin to improve the tackiness of the resin itself, a method of applying the tacky substance to the prepreg surface, etc. have been considered. In the former method, it is necessary to blend a large amount of sticky substance into the resin, and in the latter method, the brittle layer is interposed between the prepreg layers of the molded product. In reality, it is unavoidable that physical properties deteriorate.

On the other hand, an epoxy resin or a thermoplastic resin is added to the carbon fiber as a sizing agent in order to bundle the fiber bundle, prevent fluff, and improve the handleability. For example, JP-B-57-49675 and JP-B-62-56.
JP-A-266 discloses that an epoxy resin or the like is applied to the surface of a carbon fiber bundle as a sizing agent for carbon fibers. Further, for example, Japanese Patent Publication No. 2-2990 discloses a carbon fiber bundle sized with a polyetherimide resin.
The publication describes a carbon fiber bundle sized with a polyamide resin. However, although these techniques can prevent the fluff of the carbon fiber to improve the handling property and the adhesion between the carbon fiber and the matrix resin in the composite material, they prevent the springback of the carbon fiber bundle. The reality is that we could not do this.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks of the prior art and provides a carbon fiber prepreg having excellent adhesive stability, which is suitable for obtaining a molded article having excellent surface smoothness. With the goal.

[0008]

In order to solve the above problems, the prepreg of the present invention has the following constitution. That is, a unidirectional carbon fiber prepreg containing a carbon fiber having a morphological stabilizer attached in an amount of 0.5 to 10.0% by weight and a strand torsion hardness of 5 to 40 ° and an epoxy resin composition as essential components. Is.

In order to solve the above problems, the method of manufacturing a prepreg of the present invention has the following constitution. That is, in a solution of a morphological stabilizer dissolved in an organic solvent, soak the carbon fiber, then after removing the solvent, impregnated with an epoxy resin composition, a method for producing a unidirectional carbon fiber prepreg, Alternatively, the epoxy resin composition is heated and pressed to impregnate the carbon fiber bundle to which the low temperature type curing agent for epoxy resin (A) is attached, and a part of the epoxy resin composition is cured with the curing agent (A) in the impregnation step. It is a method for producing a unidirectional carbon fiber prepreg, which is characterized in that

The present invention will be described in detail below.

The matrix epoxy resin suitable for the present invention is particularly preferably an epoxy resin containing an amine, a phenol, or a compound having a carbon-carbon double bond as a precursor. Specifically, examples of epoxy resins having amines as precursors include various isomers of tetraglycidyldiaminodiphenylmethane, triglycidyl-p-aminophenol, triglycidyl-m-aminophenol, and triglycidylaminocresol. Tetraglycidyldiaminodiphenylmethane is preferable as a resin for composite materials as aircraft structural materials because it has excellent heat resistance.

Examples of the epoxy resin containing phenol as a precursor include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, and resorcinol type epoxy resin. Can be mentioned. Liquid bisphenol A type epoxy resins and bisphenol F type epoxy resins have low viscosities, and therefore are preferably used for blending with other epoxy resins and additives to adjust the tackiness and viscosity of the epoxy resin composition. .

These epoxy resins may be used alone or in an appropriate combination. A combination of a glycidyl amine type epoxy resin and a glycidyl ether type epoxy resin is preferably used because it has both heat resistance, water resistance and workability.

The epoxy resin is used as an epoxy resin composition in combination with a curing agent for epoxy resin. As the curing agent for epoxy resin, any compound having an active group capable of reacting with an epoxy group can be used. A compound having an amino group, an acid anhydride group or an azido group is preferable. For example, dicyandiamide, various isomers of diaminodiphenyl sulfone, aminobenzoic acid esters, various acid anhydrides, phenol novolac resin, and cresol novolac resin can be mentioned. Dicyandiamide is preferably used because it is excellent in the storage stability of the prepreg. When an aromatic diamine is used as a curing agent, an epoxy resin cured product having good heat resistance can be obtained.
In particular, various isomers of diaminodiphenyl sulfone are most suitable for the present invention because they give a cured product having good heat resistance. The addition amount is preferably such that the epoxy groups of the epoxy resin and the active hydrogen of diaminodiphenyl sulfone are approximately equivalent in stoichiometry.

It is also possible to blend and use a thermoplastic resin such as polyether sulfone, polyether imide or polyvinyl formal, or a polymer compound such as an elastomer such as nitrile rubber in these epoxy resin compositions. .

In the present invention, since the morphological stabilizer is added to the carbon fiber bundle, the spring back of the carbon fiber bundle in the prepreg is suppressed, and the matrix resin on the surface of the prepreg becomes less likely to settle inside the carbon fiber bundle. , The adhesiveness of the prepreg is maintained for a long time.

The amount of the morphological stabilizer attached is 0.5 to
It must be in the range of 10.0% by weight. If the adhesion amount is less than 0.5%, the morphological stability of the carbon fiber bundle will be insufficient, and the adhesiveness of the prepreg and the surface smoothness of the molded product will be poor. On the other hand, if the adhered amount exceeds 10.0%,
The carbon fiber bundle becomes rigid, and the drape property of the obtained prepreg is impaired.

Further, it is necessary that the torsional hardness of the carbon fiber bundle to which the morphological stabilizer is attached is in the range of 5 to 40 °. The torsional hardness of the carbon fiber bundle is measured as follows. A carbon fiber bundle of 2000 to 4000 filaments is cut out by about 15 cm, a load of 25 g is applied thereto, a twist of 10 rotations is applied thereto, and the mixture is left to stand, and a twist angle with respect to before the twist is measured. The larger the twist angle, the lower the flexibility of the carbon fiber bundle. The torsional hardness measured in this way is a characteristic that affects the drape property when used as a prepreg. If this value is too large, the drape property of the prepreg is impaired. Stability becomes insufficient. That is, when the torsional hardness of the carbon fiber bundle is less than 5 °, the morphological stability becomes insufficient, the adhesiveness of the prepreg becomes poor, and the surface smoothness of the obtained molded product also becomes poor. On the other hand, if the torsional hardness of the carbon fiber bundle is larger than 40 °, the carbon fiber bundle becomes rigid and the drape property of the obtained prepreg is impaired.

Therefore, the use of a carbon fiber bundle having a morphological stabilizer of 0.5 to 10.0% by weight and a torsional hardness in the range of 5 to 40 ° results in good adhesion stability of the prepreg. It is necessary in order to be compatible with the drape property of the prepreg.

As the morphological stabilizer, the same epoxy resin composition as described above used as the matrix resin for the composite material can be used. In this case, the epoxy resin composition used as the morphological stabilizer can achieve the purpose as the morphological stabilizer because the curing reaction is more advanced than that of the epoxy resin composition used as the matrix resin. Specifically, the epoxy resin composition used as a morphological stabilizer has a glass transition temperature of 70.
It is preferable that the curing is advanced until the temperature reaches ℃ or higher. From the viewpoint of heat resistance, it is preferable to use, as the morphological stabilizer, a composition containing an epoxy resin and a curing agent shown below as main components. That is, as the epoxy resin suitable for the morphological stabilizer of the present invention, amines, phenols, and the above-mentioned epoxy resins having a compound having a carbon-carbon double bond as a precursor are particularly preferable. Further, as the curing agent for epoxy resin in this case, the curing agent for epoxy resin used as the matrix can be used.

In general, a cured epoxy resin has a high cross-linking density, so that when the epoxy resin composition is used as a morphological stabilizer, the torsional hardness of the carbon fiber bundle may be significantly increased too much. For example, when an epoxy resin composition containing an amine such as a tetraglycidyl diamine type epoxy resin as a precursor and a curing agent such as diaminodiphenyl sulfone as a main component is used as a morphological stabilizer, carbon fiber The torsional hardness of the bundle is generally high. On the other hand, when an epoxy resin composition containing a phenol type epoxy resin such as bisphenol A type epoxy resin or bisphenol F type epoxy resin and a curing agent such as dicyandiamide as a main component is used as a morphological stabilizer, or an elastomer such as nitrile rubber. When the epoxy resin composition containing is used as a morphological stabilizer, the torsional hardness of the carbon fiber bundle is generally low. Therefore, the twist hardness of the carbon fiber bundle should be adjusted by devising the blending amount of the epoxy resin and the curing agent, adding a third component such as an elastomer or thermoplastic resin, or adjusting the amount of adhesion to the carbon fiber bundle. Should be within the above range.

Further, various thermoplastic resins can be used as the morphological stabilizer used in the present invention. When the thermoplastic resin is used as the morphological stabilizer, the glass transition temperature of the thermoplastic resin is preferably 70 ° C. or higher. If the glass transition temperature is lower than 70 ° C, the morphological stability of the carbon fiber bundle may be impaired due to the heat history during prepreg formation. Specifically, heat-resistant engineering plastics such as polyetherimide, polysulfone, and polyethersulfone can be preferably used.

The method for attaching the morphological stabilizer is not particularly limited, but its preferred embodiment will be described below. One of the methods is a method of immersing carbon fibers in a solution in which a morphological stabilizer is dissolved in an organic solvent, removing the solvent, and attaching the morphological stabilizer. For example, for a system containing an epoxy resin and a curing agent as the main components, a low boiling point solvent such as methyl ethyl ketone or acetone is preferably used, and after the solvent is removed or the solvent is removed and heat curing treatment is performed. When an engineering plastic such as polyether imide is used as a morphological stabilizer, a chlorine-based solvent such as methylene chloride, a polar aprotic solvent such as dimethylacetamide or N-methyl-2-pyrrolidone, or the like. A mixed solvent is preferably used. The amount of the morphological stabilizer attached can be adjusted by using a doctor knife, a squeeze roll, or the like after the solution concentration or the immersion. When the morphological stabilizer contains a thermosetting resin component, the torsional hardness of the carbon fiber bundle can be adjusted by selecting the heating temperature and time during the heat curing treatment. In any case, it is important to set the torsional hardness of the carbon fiber bundle within the above range.

A morphologically stabilized carbon fiber can also be produced by using an emulsion obtained by adding an emulsifier to the morphological stabilizer. For example, an emulsion obtained by adding polyvinyl alcohol to a system of an epoxy resin and a curing agent is preferably used. According to this method, since the finely divided stabilizer is present between the fibers and a fine gap can be formed between the fibers, it is possible to achieve both the morphological stabilization and the impregnation property of the prepreg.

The prepreg of the present invention comprises the above-mentioned carbon fiber and an epoxy resin composition. As a method for producing such a prepreg, except that a carbon fiber whose morphology is stabilized is used, by a conventional method, a matrix resin is impregnated under heating and pressure, a so-called hot melt method,
Alternatively, any of the so-called wet methods of impregnation using a solution of a matrix resin dissolved in an organic solvent can be applied.

Another method suitable for producing the prepreg of the present invention will be described below. That is, when a prepreg is produced by impregnating a carbon fiber bundle to which the curing agent (A) for low temperature curing type epoxy resin is attached by heating and pressurizing the epoxy resin composition, the epoxy resin in the vicinity of the carbon fiber is impregnated in the impregnation step. In this method, a part of the resin composition is cured with the curing agent (A).

According to this method, a prepreg having an excellent impregnating property can be produced under a milder impregnation temperature or pressure condition as compared with a method of impregnating an epoxy resin composition with a fiber whose form is stabilized beforehand. It is possible.

In this case, the epoxy resin curing agent (A) previously attached to the carbon fiber is a low temperature curing agent which can cure the epoxy resin at a lower temperature than the curing agent contained in the epoxy resin composition as the matrix resin. It is necessary to use a mold hardener. When a curing agent that cures the epoxy resin at a high temperature is used, a heat treatment at a higher temperature or for a longer time than the usual conditions for producing a prepreg is required to cure the matrix resin near the carbon fiber. As a result, the curing agent contained in the matrix resin simultaneously cures the entire matrix resin, which impairs the drapability of the prepreg.

The low temperature type curing agent used in the present invention is a curing agent which cures an epoxy resin at a temperature of room temperature or more and 100 ° C. or less, and typical examples thereof include aliphatic amines such as hexamethylenediamine and diethylenetriamine. , Xylylenediamine, piperazine, imidazole compounds and the like. The amount of these low temperature type curing agents with respect to the carbon fibers is adjusted depending on the type of the curing agent and the desired degree of performance of the prepreg, but is usually 0.1 to 1.0% by weight.
The degree is appropriate.

[0030]

The present invention will be described in more detail with reference to the following examples.

Example 1 "Epicoat 828" 18.9 manufactured by Yuka Shell Epoxy Co., Ltd. as an epoxy resin
g, 4.3 g of piperazine as a curing agent, 90% saponification degree
Was added to 1200 g of a 2% aqueous solution of polyvinyl alcohol and vigorously stirred with a homomixer to obtain a morphological stabilizer emulsion having a concentration of 1.9%. Carbon fiber "T300B-3K-40B" manufactured by Toray Industries, Inc.
After immersing (a carbon fiber strand of 3000 filaments), it was dried with a hot air dryer at 150 ° C. for 10 minutes. At this time, the emulsion adhesion amount and the torsional hardness are 2.
It was 1% and 10 °.

Next, an epoxy resin composition comprising the following epoxy resin and curing agent was prepared with a kneader.

<Epoxy resin> ELM434 (tetraglycidyldiaminodiphenylmethane) 40 parts by weight EPC830 (bisphenol F type epoxy) 20 parts by weight EPC152 (brominated bisphenol A type epoxy) 63 parts by weight EP828 (bisphenol A type epoxy) 127 parts by weight <Hardener>4,4'-DDS(4,4'-diaminodiphenyl sulfone) 80 parts by weight This resin composition was heated to 80 ° C and coated on release paper to form a resin film.

The resin film thus produced was set in a prepreg machine, and resin was impregnated from both sides of the above-mentioned morphologically stabilized carbon fibers aligned in one direction (impregnation temperature 100 ° C., impregnation pressure 4 kgf / cm. ² and the resin content rate is 38%).

Next, the tackiness of the prepreg was measured as follows. After leaving the prepreg in an atmosphere of 25 ° C. and RH of 40% for 10 days, the prepreg was applied to a steel cylinder having a diameter of 10 mm so that the fiber direction of the prepreg was 2 to 3 layers such that the fiber direction of the prepreg was at an angle of 45 ° with respect to the longitudinal direction of the cylinder. Wrapped around. When this was left in an atmosphere of 25 ° C. and RH of 40% and the winding state of the prepreg after 24 hours was observed, it was confirmed that the prepreg was completely adhered and had good adhesiveness.

(Example 2) A prepreg was produced in the same manner as in Example 1 except that 25 parts by weight of polyether sulfone "5003P" manufactured by Mitsui Toatsu was added to the resin composition.
When the tackiness of the prepreg was measured in the same manner as in Example 1, it was found to be good.

(Example 3) Carbon fiber "T300B-3K" manufactured by Toray Industries, Inc. was added to an aqueous solution in which 0.5% by weight of piperazine was dissolved.
-40B ″ was dipped, and then dried with a hot air drier to attach piperazine to the fiber surface. Using the epoxy resin film produced in Example 1 or 2, one of the above carbon fibers was aligned in one direction. It was laminated on both upper and lower sides and impregnated using a prepreg apparatus at a temperature of 100 ° C. and an impregnation pressure of 4 kgf / cm ^2. The carbon fiber content of the obtained prepreg was 5.
It was 8% by weight, and had appropriate drapeability and tackiness. This prepreg retains its drape property and tackiness even after being left in an atmosphere of 25 ° C. and a relative humidity of 40% for 10 days. When a columnar winding test was conducted in the same manner as in Example 1, it was found to be good. It showed tackiness.

When the epoxy resin composition of this prepreg was extracted and removed with methyl ethyl ketone,
A carbon fiber bundle to which a cured product of some epoxy resin compositions was attached was obtained. To measure the amount of this cured product,
When a carbon fiber bundle having a length of 15 cm was treated in an electric furnace in a nitrogen atmosphere at 500 ° C. for 30 minutes to decompose and remove the cured product, the weight loss was 2.1%. Furthermore, the torsional hardness of this carbon fiber bundle was 30 °.

(Comparative Example 1) "T" was carried out in the same manner as in Example 1 except that the concentration of the morphological stabilizer emulsion was 0.2%.
When 300B-3K-40B ″ was treated, the amount of the morphological stabilizer and the torsional hardness were 0.3% and 4 °, respectively. Then, a prepreg was prepared in the same manner as in Example 1. The tackiness of the obtained prepreg was insufficient, and when a cylinder winding test was conducted in the same manner as in Example 1, the prepreg was almost peeled from the cylinder.

(Comparative Example 2) A "T" was prepared in the same manner as in Example 1 except that the concentration of the morphological stabilizer emulsion was 6.0%.
When 300B-3K-40B "was treated, the amount of the morphological stabilizer and the torsional hardness were 12.2% and 55%, respectively.
It was °. Then, a prepreg was prepared in the same manner as in Example 1. The obtained prepreg lacked drapability, and a cylinder winding test was conducted in the same manner as in Example 1. As a result, the prepreg was almost peeled from the cylinder.

[0041]

EFFECT OF THE INVENTION In the prepreg of the present invention, by preventing the springback of the carbon fiber bundle, the adhesiveness of the matrix resin is reflected in the adhesiveness of the prepreg,
Also, the tackiness of the prepreg is stable over time.
Further, the prepreg manufacturing method of the present invention makes it possible to manufacture the prepreg having the above-described excellent tackiness under a milder impregnation temperature or pressure condition. further,
By using the prepreg of the present invention, a carbon fiber reinforced composite material having excellent surface smoothness and internal denseness can be produced.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuaki Oki 1515 Tsutsui, Matsumae-cho, Iyo-gun, Ehime Prefecture Toray Co., Ltd. Ehime Plant

Claims (11)

[Claims] 1. A carbon fiber bundle having a morphological stabilizer attached in an amount of 0.5 to 10.0% by weight and a torsional hardness in the range of 5 to 40 °, and an epoxy resin composition as essential components. Direction carbon fiber prepreg. 2. The unidirectional carbon fiber prepreg according to claim 1, wherein the morphological stabilizer contains a thermoplastic resin as a main component. 3. The unidirectional carbon fiber prepreg according to claim 2, wherein the thermoplastic resin has a glass transition temperature of 70 ° C. or higher. 4. The unidirectional carbon fiber prepreg according to claim 1, wherein the morphological stabilizer is a cured product containing an epoxy resin and a curing agent as main components. 5. The unidirectional carbon fiber prepreg according to claim 4, wherein the glass transition temperature of the cured product is 70 ° C. or higher. 6. A carbon fiber is dipped in a solution of a morphological stabilizer dissolved in an organic solvent, and then the solvent is removed.
A method for producing a unidirectional carbon fiber prepreg, which comprises impregnating an epoxy resin composition. 7. The method for producing a unidirectional carbon fiber prepreg according to claim 6, wherein the morphological stabilizer contains a thermoplastic resin as a main component. 8. The method for producing a unidirectional carbon fiber prepreg according to claim 7, wherein the thermoplastic resin has a glass transition temperature of 70 ° C. or higher. 9. A morphological stabilizer comprising an epoxy resin and a curing agent as main components, which is heat-cured after or after removing the solvent.
A method for producing the unidirectional carbon fiber prepreg described. 10. The method for producing a unidirectional carbon fiber prepreg according to claim 9, wherein the glass transition temperature of the cured product after the heat curing treatment is 70 ° C. or higher. 11. An epoxy resin composition is heated and pressed to impregnate a carbon fiber bundle to which a low temperature type curing agent (A) for epoxy resin is attached, and a part of the epoxy resin composition is cured in the impregnation step ( A method for producing a unidirectional carbon fiber prepreg, which comprises curing in A).