JPS585925B2 - Epoxy resin composition for carbon fiber prepreg - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel epoxy resin composition for carbon fiber prepreg that has excellent composite pourability, cures at a relatively low temperature, and has a long pot life.

Because carbon fiber is lightweight, has high strength, and high elasticity, it has attracted attention as a reinforcing material for composite materials, and carbon fiber-reinforced composite materials using carbon fiber are being widely used in sports, leisure goods, aircraft, etc. .

Conventionally, one method of manufacturing molded products using a thermosetting resin composite reinforced with carbon fibers is to create a so-called prepreg in which carbon fibers arranged in one direction are impregnated with a thermosetting resin such as epoxy resin. A known method is to stack these materials at a predetermined angle and heat and press them to harden them to form a molded product.

The properties required of this prepreg include not only excellent physical properties of the molded product, but also a pot life as long as possible at room temperature, a low curing temperature, and a fast curing speed. .

That is, a long pot life at room temperature is a great advantage in terms of excellent storage stability and ease of handling.

In addition, the low curing temperature means that when simultaneously adhering and curing prepreg and other materials such as metal (cocure),
This is an essential condition for some applications, such as reducing residual stress due to thermal expansion between the carbon fiber reinforced composite material and the metal, and the curing speed directly leads to productivity.

Although it is extremely difficult to satisfy all of these conditions, the present inventors have arrived at the present invention as a result of intensive studies.

That is, the present invention covers the following [A] [B] [C] and CD
) An epoxy resin composition for carbon fiber prepreg, comprising (A) phenol-novolak type epoxy resin CB) bisphenol A type epoxy resin [C] dicyandiamide (D) 3-(3.4 dichlorophenyl)-1.1 -N dimethyl urea, [A] + [B] resin mixture has a viscosity of 30 to 300 poise at 80°C, contains at least 50% by weight of a phenolic novolac type epoxy resin, and [
[C] and [D] are each contained in an amount of 0.5 to 6 parts by weight per 100 parts by weight of the resin mixture of A]+[B].

Such a resin composition has a long pot life, moderate tackiness, and is suitable for handling when used as a prepreg for a composite reinforced with carbon fiber, and has a low curing temperature and a fast curing speed. is fast.

Furthermore, when made into a composite, it has high interlaminar shear strength (IL
SS) is obtained.

As the phenol-novolak type epoxy resin in the present invention, known ones can be used, and specifically, for example,
Epikote 152, Epicoat 154 (manufactured by Shell Chemical Co., Ltd.), Araldite EPN1138, EPN1139 (manufactured by Ciba Geigy), Dowepoxy DEN431, DEN
438, DEN439 (manufactured by Dow Chemical Company), EPPN
201 (manufactured by Nippon Kayaku Co., Ltd.), Epiclon N740 (manufactured by Dainippon Ink Chemical Industries, Ltd.), and the like.

In addition, known bisphenol A epoxy resins can be used, and specifically, for example, Epicoat 82
8, Epicote 834, Epicote 827, Epicote 1001, Epicote 1002, Epicote 1004,
Epicoat 1007, Epicoat 1009 (manufactured by Shell Chemical Co., Ltd.), Araldite CY205, CY230, CY232, C
Y221, GY257, GY252, GY255, GY
250, GY260, GY280, Araldite 607
1. Araldite 7071, Araldite 7072 (manufactured by Ciba Geigy), Dowepoxy DER331, DER
332, DER662, DER663U, DER662
U (manufactured by Dow Chemical Company), Epicron 840, 850,
855, 860, 1050, 3050, 4050705
0, (manufactured by Dainippon Ink and Chemicals), Epotote YD-
115, YD-115CA, YD-117, YD-12
1, YD-127, YD-128, YD-128CA,
YD-128S, YD-134, YD-001Z, YD
-011, YD-012, YD-014, YD-014
ES, YD-017, YD-019, YD-020, Y
Examples include D-002 (manufactured by Toto Kasei Co., Ltd.).

The above-mentioned phenol novolak type epoxy resin and bisphenol A type epoxy resin can each be used singly or in combination of two or more.

In the epoxy resin composition of the present invention, at least 50% by weight of the phenol-novolac type epoxy resin [A] is contained in the resin mixture of the phenol-novolac type epoxy resin [A] and the bisphenol A-type epoxy resin [B].
It is necessary to contain it.

As shown in the table below, if it is less than 50% by weight, the ILS is high.
S value cannot be obtained.

As is clear from Table 1, the ILSS improves as the content of the phenol novolak type resin increases, but since the impact resistance is poor with this resin alone, it is necessary to include a bisphenol A type resin.

The upper limit of the content of phenolic novolac type resin is usually 9
Up to about 5% by weight.

Bisphenol A type epoxy resins are available in various grades (solid, semi-solid, liquid with various viscosities) and are convenient for adjusting the tack (1ack) of prepregs.

In the present invention, the viscosity of the epoxy resin mixture is 30 to 30
It is 0 poise (80°C).

When molding using prepreg, defoaming is performed in a so-called precure step at 60 to 90°C, but if the melt viscosity exceeds 300 poise (80°C), defoaming is difficult, and DICY Regardless of particle size, voids remain in the molded product and composite performance deteriorates.

Further, prepreg impregnated with such a high viscosity resin is hard, has weak tack, lacks flexibility and is difficult to handle.

Furthermore, when such a resin is used to make a prepreg using a hot melt method, the fluidity of the resin is low, which makes it difficult to impregnate fibers, and the temperature and pressing force during impregnation must be increased.

On the other hand, the viscosity of the epoxy resin mixture was 30 poise (80°C
), the tack of the manufactured prepreg will be too strong, resulting in poor handling and resin loss during molding, resulting in poor composite performance.

Particularly preferred resin viscosity is 150 to 30 poise (80°C)
It is.

Disindiamide (hereinafter referred to as DICY) as a curing agent,
3-(3,4-dichlorophenyl)- as a curing accelerator
1. It has a pot life of 2 months at room temperature (20°C) by using 1-N dimethylurea (hereinafter referred to as DMU),
and 60-9 at a relatively low temperature of 120-135℃
Fully cure for 0 minutes.

Previously, prepregs that had a long pot life (1 month or more) had a high curing temperature (150-200℃), and conversely, prepregs that could be cured at low temperatures (100-150℃) had a short pot life ( prepregs using the compositions of the present invention have the advantage of low curing temperatures and long pot life.

As curing accelerators, monochlorophenyl-1.1-N dimethylurea, imidazole compounds (for example, 2-ethyl-
4-methylimidazole, 2-methylimidazole),
Although benzyldimethylamine and the like are known, the 3-(3.4-dichlorophenyl)-1.1-N dimethylurea of the present invention is the best in terms of low temperature curability and pot life.

In the present invention, DICY and DMU are each contained in an amount of 0.5 to 6 parts by weight per 100 parts by weight of the epoxy resin mixture.

If the amount is less than 0.5 parts by weight, the curing speed will be slow and it will take time to mold, and if it exceeds 6 parts by weight, the composite performance will deteriorate.

This is shown in the table below.

The weight ratio of DICY and DMU also affects composite pourability.

Regarding composite performance, the inventors have confirmed that better results can be obtained by using a larger amount of DMU.

In other words, when DICY/DMU=3/5, the low pressure molding method (1
kg/cm2), there are almost no voids in the molded product obtained, and the composite performance is excellent.

The epoxy resin composition of the present invention is used for producing carbon fiber prepreg.

Prepreg manufacturing methods include a solvent method and a hot melt method.

In the solvent method, a prepreg is manufactured by dissolving a resin composition in a solvent and impregnating carbon fibers with the resin solution.

On the other hand, the hot-melt method involves heating and melting a resin composition and impregnating it into carbon fibers in that state, without using a solvent.

As described below, the solvent method and the hot melt method each have their own characteristics, but carbon fiber prepregs can be suitably produced using either method using the epoxy resin composition of the present invention. .

When producing prepreg using the resin composition of the present invention by a solvent method, the particle size of DICY does not matter because DICY is dissolved in the solvent together with the resin, but when producing prepreg by a hot melt method, The particle size of DICY in the prepreg is composite.
Since the curing process is carried out at a temperature below 0° C., DICY is dispersed in the prepreg in a solid state. However, if the particle size of DICY is large, the curing reaction becomes uneven and voids are likely to occur in the molded product.

The particle size of DICY is 100μ or less, particularly preferably 10μ.
If the crystals of DICY are crushed into fine particles, the cavities in the prepreg and the voids in the low-pressure molded product will be almost eliminated, and the pourability of the composite will be further improved.

The presence or absence of voids in FRP molded products is an extremely important factor for reliability in the performance of the molded product, and is one of the most important items in quality inspection.
Detection is performed using lines, etc.

By making the blending amount and blending ratio of DICY and DMU fine, as well as the crystals of DICY, and further regulating the melt viscosity of the resin composition at the first stage of precure, we can improve prepreg quality and composite performance, and improve the reliability of molded products. Therefore, the significance of the present invention is extremely large.

Next, a method for producing carbon fiber prepreg using the resin composition of the present invention will be explained.

Prepreg manufacturing methods generally include the so-called solvent method, in which a resin composition is dissolved in a solvent and impregnated into carbon fibers, and the so-called solvent method, in which a resin composition is heated and melted without using a solvent and then impregnated into carbon fibers. There is a hot melt method.

Methods using solvents deteriorate the working environment due to evaporation and diffusion of the solvent, increase equipment costs due to protective equipment, drawbacks in terms of disaster prevention due to the flammability of the solvent, increase equipment costs due to solvent recovery equipment, and reduce prepreg after the solvent evaporates. The small amount of solvent remaining in the molded product causes voids in the molded product, resulting in deterioration of physical properties, and has some fundamental drawbacks from the aspects of the manufacturing process, economic efficiency, and prepreg quality.

However, the hot melt method has the advantage of overcoming these drawbacks of the solvent method.

However, at the same time, the solvent method is effective for manufacturing prepregs using highly viscous resin compositions that cannot be manufactured using the hot melt method, or for preparing prepregs for fibers that are difficult to impregnate with resin using the hot melt method, such as textiles. .

Therefore, it is appropriate to decide which method to use depending on the form of the fibers used and the properties of the resin.

When producing a prepreg by a solvent method using the resin composition of the present invention, the resin composition is added to a solvent such as acetone, methyl ethyl ketone, or methyl cellosolve at a concentration of 40 to
It is dissolved in 60% and impregnated into carbon fiber fabrics etc. using a conventional method.

A method for producing a unidirectional carbon fiber prepreg using a hot melt method will be specifically described.

Contains 50% by weight or more of phenolic novolac type epoxy resin and has a melt viscosity of 30 to 300 at 80°C
First, add a resin mixture that has been blended to make a poise.
DICY, which has been pulverized in advance to 100 μm or less, particularly preferably 10 μm or less, is added and kneaded in a roll mill or a twenty-one gourd while heating, and then a predetermined amount of DMU is added and thoroughly kneaded.

At this time, it is not preferable to add DICY and DMU at the same time and knead them because it will shorten the time required for the machining process.

The kneaded resin composition is coated with release paper (
coated on silicone-coated paper).

Carbon fibers were introduced in parallel at regular intervals onto this resin-coated release paper, and the release paper was introduced on top of the carbon fibers.
Pass over a hot plate heated to 150°C, preferably 100 to 130°C, for 5 to 120 seconds.

At this time, if the temperature is below 80°C, the resin will not be sufficiently softened and the carbon fibers will not be sufficiently impregnated with the resin in the next step, and the carbon fibers will not be able to be spread out sufficiently, resulting in adhesion between adjacent fibers. Cracks tend to exist in the manufactured prepreg due to insufficient bonding.

Moreover, at 150°C or higher, the viscosity of the resin is too low and it flows easily, which may not only cause trouble but also cause the curing reaction to proceed rapidly.

40-150℃ after passing over a heating plate to lower the viscosity of the resin
, preferably 0.1 to 100 kg/cm, preferably 2 to 6 kg/cm with a press roller heated to 50 to 90°C.
A sheet-like prepreg is produced by pressing with a linear pressure of cm to impregnate the fibers with resin and simultaneously pushing the fibers apart.

The most difficult aspect of sheet prepreg quality is the absence of cracks.

In particular, cracks are likely to occur when manufacturing very thin brippreg sheets with a carbon fiber basis weight of 80 g/m2 or less.

The inventors of the present invention have carefully investigated a method for stably manufacturing these thin Bripreg sheets without cracks, and found that by using carbon fibers with good opening properties, it is possible to impregnate carbon fibers with resin and to form carbon fibers. The spreading process was extremely smooth, and the adjoining carbon fiber yarns had sufficient adhesion, bonding, and overlapping, making it possible to stably produce a crack-free Bripreg sheet under milder production conditions.

The present invention will be explained in detail below using examples.

Actual winding example 1 [A] Araldite EPN1138 (phenol novolac type epoxy resin, manufactured by Ciba Geigy) 70 parts by weight, [B] Epicoat 1002 (bisphenol A type epoxy resin, manufactured by Shell Chemical Co., Ltd. 20 parts by weight, Epicoat 82)
8 (bisphenol A type epoxy resin, manufactured by Shell Chemical Co., Ltd.) to form a resin mixture (100 poise, 8
0°C) was obtained.

Add to this 3 parts by weight of the curing agent dicyandiamide and 3 parts by weight of the curing accelerator.
Five parts by weight of (3.4dichlorophenyl)-1.1-N dimethylurea was dissolved in a mixed solvent of acetone/ethylene glycol monomethyl ether=1/1 to form a 40% solution.

Carbon fiber fabric (#31 manufactured by Toho Bethlon Co., Ltd.) was added to this resin solution.
00) and impregnated with resin, the fabric was heated to 90 to 100°C to remove the solvent, thereby producing a fabric prepreg.

This fabric prepreg had a pot life of 2 months (20°C), and was molded under curing conditions of 130°C, 7 kg/cm2, and 90 minutes, and the physical properties of the molded product were as follows.

Note that when a woven prepreg is used, since the woven fabric is oriented in two directions, vertical and horizontal, the physical properties of the molded product are naturally much lower than in the case of a unidirectional prepreg.

Therefore, for example, the ILSS of 6.3 kg/mm2
is superior to the conventional case which does not contain a phenolic novolac type epoxy resin.

In particular, the improvement in ILSS at high temperatures is remarkable.

Example 2 CA) Araldite EPN1138 (phenol novolak type epoxy resin, manufactured by Ciba Geigy) 70 parts by weight, [B] Epicoat 1002 (bisphenol A type epoxy resin, manufactured by Shell Chemical Co., Ltd.) 20 parts by weight, Epicoat 8
An epoxy resin mixture consisting of 10 parts by weight of Bisphenol A epoxy resin No. 28 (bisphenol A type epoxy resin, manufactured by Shell Chemical Co., Ltd.) was kneaded in a kneader at 90°C.

The particle size of the resulting resin mixture was 100 poise (80°C).

To this was added 3 parts by weight of the curing agent dicyandiamide, which was pulverized to 100 μm or less, and kneaded on a roll mill.

Next, the curing accelerator 3-(3.4-dichlorophenyl)-1
．． 5 parts by weight of 1-N dimethylurea was added and kneaded to obtain an epoxy resin composition.

This composition was coated on a release paper using a film coater, and carbon fibers (Besphite HTA-7-6000, manufactured by Toho Beslon Co., Ltd.) were coated on this at equal intervals and in parallel. The viscosity of the resin is lowered by passing it on a heating plate heated to 120°C for 30 seconds while lightly pressing it with a roller, and then pressing it with a linear pressure of 4 kg/cm using a press roller heated to 90°C to produce a sheet prepreg. did.

As a result of electron microscopy observation of this Bripreg sheet, no cavities were observed inside, and the pot life was 2 months (20° C.).

This material was molded under curing conditions of 130° C., 7 kg/cm 2 and 90 minutes, and the physical properties of the molded product were as follows.

Bending strength 168kg/mm2 Bending modulus 13.5T/mm2 ILSS 9.9kg/mm2 (room temperature) ILSS
7.6kg/mm2 (80℃)Vf
60% In addition, this buripreg sheet was heated at 70°C in a vacuum at a rate of about 1 kg/kg.
cm2, 30 minutes, then 130℃, pressure 1kg/cm2
As a result of electron microscopy, almost no voids were observed in the molded product molded under low-pressure curing conditions of 90 minutes, and the physical properties were almost the same as in the case of high-pressure molding as described below.

Bending strength 165kg/mm2 Bending modulus 12.8T/mm2 ILSS 9.8kg/mm2 (room temperature) ILSS
7.4kg/mm2 (80℃)Vf
60% Example 3 25 parts by weight of DEN438 (phenol/novolac type epoxy resin, manufactured by Dow Chemical Company), 70 parts by weight of DEN439 (phenol/novolac type epoxy resin, manufactured by Dow Chemical Company), DER331 (bisphenol A type epoxy resin, manufactured by Dow Chemical Company) A resin mixture (viscosity at 80°C of 110 poise) consisting of 5 parts by weight (manufactured by Chemical Co., Ltd.) with a particle size of 2 to 5
A resin composition was obtained by adding 3 parts by weight of 0μ dicyandiamide and 5 parts by weight of 3-(3.4-dichlorophenyl)-1.1-N dimethylurea.

Using this resin composition, a unidirectional polyurethane sheet was manufactured by the hot melt method in the same manner as in Example 2.

The pot life of this sheet was 2 months (20° C.), and no cavities were observed in the cross section of the sheet.

This material was molded under curing conditions of 135°C, 7 kg/cm2, and 90 minutes, and the physical properties of the molded product were as follows.

Bending strength 172kg/mm2 Bending modulus 13.1T/mm2 ILSS 10.2kg/mm2 (room temperature) ILSS
8.2kg/mm2 (80℃)Vf
61% In addition, this buripreg sheet was heated at 70°C in a vacuum at a rate of about 1 kg/kg.
cm2, 30 minutes, then 135℃, pressure 1kg/cm2
The physical properties of the molded product molded under low pressure for 90 minutes were almost the same as those in the case of high pressure molding, as described below.

No voids were observed inside.

Bending strength 171kg/mm2 Bending modulus 13.1T/mm2 ILSS 10.1kg/mm2 (room temperature) ILSS
8.0kg/mm2 (80℃)Vf
59% Comparative Example 1 (No use of phenol/novolac type epoxy resin) Epicoat 828 (bisphenol A type epoxy resin,
After kneading an epoxy resin mixture consisting of 60 parts by weight of Epikote 1002 (manufactured by Ciel Kagaku Co., Ltd.) and 40 parts by weight of Epicoat 1002 (same as above) in a 21-glue at 90°C, 3 parts by weight of dicyandiamide pulverized to less than 10 μm was added and milled in a roll mill. Kneaded.

Then 3-(3.4-dichlorophenyl)-1.1-N
After adding and kneading 5 parts by weight of dimethyl urea, a unidirectional prepreg was produced in the same manner as in Example 2.

This material was molded under curing conditions of 135°C, 7 kg/cm2, and 90 minutes, and the physical properties of the molded product were as follows.

Bending strength 158kg/mm2 Bending modulus 12.7T/mm2 ILSS 8.4kg/mm2 ILSS 5.0kg/mm2 Vf 60% ILSS value compared to actual winding examples 2 and 3 in which phenol-novolac type epoxy resin was added is low.

Claims (1)

[Claims] 1. Dicyandiamide and 3-(3.
An epoxy resin composition for carbon fiber prepreg, characterized in that it contains 0.5 to 6 parts by weight of each of 4-dichlorophenyl-1.1-N dimethylurea.