JPS6047290B2 - Prepreg manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high quality carbon fiber prepreg by a hot melt method using an epoxy resin composition having a specific composition.

Carbon fiber has attracted attention as a reinforcing material for composite materials because it is lightweight, has high strength, and high elasticity.
Carbon fiber reinforced composite materials using this material are becoming widely used in sports, leisure goods, aircraft, etc.

Conventionally, one method of manufacturing molded products using a thermosetting composite reinforced with carbon fibers is to make a so-called prepreg in which carbon fibers arranged in one direction are impregnated with a thermosetting resin such as an epoxy resin. A method is known in which these materials are laminated at a predetermined angle and cured by heating and pressing to form a molded product.

There are two methods for producing prepreg: the so-called solvent method, in which a resin composition is dissolved in a solvent and impregnated with carbon fibers, and the so-called hot-melt method, in which the resin composition is heated and melted without using a solvent and impregnated into carbon fibers. However, the method using a solvent deteriorates the working environment due to the evaporation and diffusion of the solvent, and increases the equipment cost due to the equipment to protect it.
Disadvantages in terms of disaster prevention due to the flammability of the solvent, increased equipment costs due to solvent recovery equipment, and trace amounts of solvent remaining in the prepreg after the solvent evaporates can cause molded boards to deteriorate, resulting in poor manufacturing process and economic efficiency. , has some fundamental drawbacks in terms of prepreg quality.

However, the hot melt method has the advantage of overcoming these drawbacks of the solvent method. The various properties required of this prepreg include, of course, excellent physical properties of the molded product1, but also a long pot life as long as possible at room temperature, a low curing temperature, and a fast curing speed. It will be done.

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 prepreg and other materials,
For example, when simultaneously bonding and curing metals (Coke Air), reducing residual stress due to thermal expansion between carbon fiber composite materials and metals is an essential requirement depending on the application, and curing speed directly affects productivity. It is something.

In order to obtain a carbon fiber prepreg that satisfies these conditions, the present inventors studied a resin composition and a prepreg manufacturing method using the same, and as a result, they arrived at the present invention.

That is, the present invention is a method for producing carbon fiber prepreg using a hot melt method, which is as follows.

Dicyandiamide with a particle size of 100 p or less per 100 parts by weight of a phenol-novolak type and bisphenol A-type epoxy resin mixture containing at least % by printed weight of a phenol-novolac type epoxy resin and having a viscosity of 30 to 300 poise at 80°C. 3-(3
．． A method for producing a carbon fiber prepreg using an epoxy resin composition containing 0.5 to 6 parts by weight of 4-dichlorophenyl)-1,1-dimethylurea, the method comprising: applying the epoxy resin composition to a release paper; Carbon fibers are arranged on the coating box, a release paper is introduced on top of it, and then the viscosity of the resin is lowered by passing it over a heated heating plate, and then a linear pressure of 0.1 to 100 k9 is applied using a heated press roller.
/Cm is used to spread the carbon fibers at the same time as impregnating them with resin.

The prepreg obtained by the present invention has no cracks and no internal cavities, has a long pot life, and has good storage stability. In addition, this prepreg can be molded under mild conditions of low temperature and low pressure, and the resulting molded product is The deposit characteristics are good. First, the epoxy resin composition used in the present invention will be explained.

The resin composition includes [A] phenol/novolac type epoxy resin [B] bisphenol A type epoxy resin [C]
] The resin mixture of didiandiamide [D] 3-(3.4 dichlorophenyl)-1,1-dimethylurea and [A] and [B] has a viscosity of 30 to 300 poise at 80°C and contains phenol. Contains at least 80% by weight of novolac type epoxy resin 4, and contains 0.5 to 6 parts by weight of [C] and [D] each based on 100 parts by weight of the resin mixture of [A] + [B]. It is.

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. When formed into a composite quickly, high interlaminar shear strength (ILSS) can be obtained.

As the phenol-novolac 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 EPNll38, EPNll39 (
Ciba Geigy), Tauepoxy DEN43l, DE
N438, DEN439 (manufactured by Dow Chemical Company), EPP
Examples include N2Ol (manufactured by Nippon Kayaku Co., Ltd.), Epiclon N74O (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, Piconote 1004
, Epikote 1007, Epikote 1009 (manufactured by Shell Chemical Co., Ltd.), Araldite CY2O5, CY23O, CY
232, CY22l, GY257, GY252, GY2
55, GY25O, GY26O, GY28O, Araldite 60711 Araldite 7071, Araldite 7
072 (manufactured by Ciba Geigy), Dowepoxy DER33
l, DER332, DER662, DER663U, .
DER662U (manufactured by Dow Chemical Company) Epicron 840
1850, 855, 8601105013050, 40
50170501 (manufactured by Dainippon Ink and Chemicals), Epotote YD-115, YD-115CA, . YD-11
7, YD-121, YD-127, YD-128, YD
-128CA. ．． YD-12? , YD-134, YD-
001Z. ．． YD-011, YD-012, YD-01
4, YD-014ES. ．． YD-017, YD-019
, YD-020. ．． Examples include YD-002 (manufactured by Tobu 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, a high ILSS value cannot be obtained. Note hardening agent:
Dicyandiamide 3PHR curing accelerator: 3-
(3.4 dichlorophenyl) -1,1-dimethylurea 5P1 (R unidirectional carbon fiber prepreg, 1
30° C19 powder, 7k9/C [PHR: Addition rate to 10 parts of resin] As is clear from Table 1, the higher the content of phenol novolac type resin, the higher the ILSS.
However, since the impact resistance is poor when using this resin alone, it is necessary to include a bisphenol A type resin.

The upper limit of the content of phenol/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 prepreg tanks (food Ck). In the present invention, the viscosity of the epoxy resin mixture is 30 to 300 poise (80°C). When molding using prepreg, defoaming is performed in the so-called precure stage at 60 to 90°C, but if the melt viscosity exceeds 300 poise (80°C), defoaming is difficult and voids remain and composite performance deteriorates.

Further, prepreg impregnated with such a high viscosity resin is hard, has a weak tank, 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, making 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 is 30 poise (80'
If it is less than C), the prepared prepreg tank will be too strong, the handleability will be poor, and the resin will often be washed away during molding, resulting in a decrease in composite performance.

When the viscosity of the resin is in the range of 30 to 300 poise (80° C.), this together with the effect of pulverization of dicyandiamide, which will be described later, contributes to improving composite performance.

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

Dicyandiamide (hereinafter referred to as DICY) as a curing agent
, 3-(3.4dichlorophenyl)- as a curing accelerator
1. By using 1-dimethylurea (hereinafter referred to as DMU), it has a pot life of 2 months at room temperature (20'C),
And at a relatively low temperature of 120-135°C
9 times to completely harden.

Previously, prepregs that had a long pot life (1 month or more) had a high curing temperature (150 to 200 degrees Celsius), whereas prepregs that cured at low temperatures (100 to 150 degrees Celsius) had a short pot life. (within one week), but the prepreg using the composition of the present invention has the characteristics of a low curing temperature and a long pot life.

The DICY or dicyandiamide used in this invention must have a particle size of less than 100 microns. In the hot melt method of the present invention, heating and spreading of the resin composition is performed using DIC.
D
ICY is dispersed in the prepreg as a solid, but DIC
It has been found that when the particle size of Y is large, the curing reaction becomes non-uniform and voids are likely to occur in the molded product, which affects the properties of the composite.

If a large amount of particles with a DICY particle size exceeding 100 μm is present, the quality of the prepreg and further the physical properties of the composite will deteriorate. If a large amount of DICY crystals exceeding 100μ are present in the prepreg, many cavities will be formed in the prepreg, and many hoids will also be present in the low-pressure molded product.
I? S decreases. The cause of these problems is that during the prepreg manufacturing process, when carbon fibers are impregnated with resin, impregnation and defoaming do not go smoothly due to large crystals of DICY, and in addition, large crystals of DICY occur during the process of laminating and curing Pre7 Preg. This is thought to be the result of increasing the non-uniformity of the curing reaction and inhibiting defoaming of air that has entered between the layers during lamination. However, the DIC is less than 100μ, particularly preferably less than 10μ.
When the Y crystals were crushed into fine particles, the cavities in the prepreg and the voids in the low-pressure molded product were almost eliminated, and the physical properties of the composite were improved. DICY in prepreg
The crystal size, voids in the prepreg and low-pressure molded product, and ILSS are shown below. As curing accelerators, monochlorophenyl-1.1-dimethylurea, imidazole compounds (e.g., 2-ethyl-4-methylimidazole, 2-methylimidazole), benzyldimethylamine, etc. are known, but they are low-temperature curable and usable. 3-(3.4dichlorophenyl)-1.1- of the present invention in terms of time
Dimethylurea is the best. In the present invention, DI
CY 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. 0.5 each
If the amount is less than 6 parts by weight, the curing speed will be slow and molding will take time, and if it exceeds 6 parts by weight, the composite performance will deteriorate. This is shown in the table below. *Vf: Fiber volume % Epoxy resin Arartite EPNll38 (manufactured by Ciba Geigy)
7 Shojubu Epicoat 10
02 (manufactured by Shell Chemical Co., Ltd.) 20 parts by weight Epicoat 838 (
(manufactured by Shell Chemical Co.) 1 part curing condition: 130℃, 7kg
/All9 powder The weight ratio of DICY and DMU also affects composite performance.

In terms of composite performance, the inventors have confirmed that better results can be obtained with larger amounts of DMU. That is, when DICY/DMU=3/5, there are almost no voids in the molded product obtained even by the low pressure molding method (1k9/CIL), and the composite performance is excellent. The presence or absence of voids in FRP molded products is an extremely important factor in the reliability of the performance of the molded product, and is one of the most important items in quality inspection. Its detection is carried out using DICY
(By making the blending amount and blending ratio of 5DMU and the crystals of DICY finer, and by further regulating the melt viscosity of the resin composition at the pre-cure stage, we can improve the prepreg quality and composite performance and increase the reliability of the molded product. Therefore, the significance of the present invention is extremely large.The method for producing unidirectional carbon fiber prepreg by the hot melt method of the present invention will be specifically explained.

Phenol Novolac type epoxy resin (4) Weight 7
% or more, and has a melt viscosity of 30 to 3 at 80°C.
First, AICY, which has been pulverized to 100p or less, particularly preferably 10μ or less, is added to a resin mixture whose composition has been adjusted to give 00 poise, and the mixture is kneaded with a roll mill or kneader while heating. Add DMU and mix thoroughly. At this time, it is not preferable to add DICY and DMU at the same time and knead because the pot life will be shortened due to thermal history. The kneaded resin composition is coated on release paper (paper coated with silicone) using a film coater. Google. Carbon fibers are introduced in parallel at regular intervals onto this resin-coated release paper, the release paper is introduced on top of this, and the carbon fibers are placed on a heating plate heated to 80 to 150°C, preferably 100 to 130C, for 5 to 12 hours. ) to pass. 80' at this time
If the temperature is below 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 sufficiently spread, 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. After lowering the viscosity of the resin by passing it over a heating plate, the temperature is 40 to 150° C1, preferably 50 to 9
0.1-100k9 with a breath roller heated to 0℃
/Cml Preferably, a sheet-like prepreg is produced by pressing with a linear pressure of 2 to 6k9/Cm to impregnate the fibers, and simultaneously spreading the fibers. The most difficult aspect of sheet prepreg quality is the absence of cracks. In particular, cracks are likely to occur when manufacturing extremely thin Prible sheets with a carbon fiber basis weight of 80 g/d or less.

The inventors of the present invention have intensively investigated a method for stably manufacturing these thin prepreg sheets without cracks, and found that by using carbon fibers with good spreadability, the carbon fibers can be impregnated with resin and the carbon fibers can be spread out. This process was carried out smoothly, and it became possible to stably produce prepreg sheets with no cracks due to sufficient adhesion, bonding, and overlapping of adjacent carbon fiber yarns under milder production conditions. Next, the present invention will be explained in detail by way of examples.

Example 1 Araldite EPNll38 (phenol novolac type epoxy resin, manufactured by Ciba Geigy) 7 parts by weight, Epicote 1002 (bisphenol A type epoxy resin, manufactured by Shell Chemical Co., Ltd.) 20 parts by weight, Epicote 828 (
Bisphenol A type epoxy resin manufactured by Shell Chemical Co., Ltd.) 10
The epoxy resin mixture consisting of parts by weight was kneaded in a kneader at 90'C. The resulting resin mixture had a viscosity of 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, 5 parts by weight of a curing accelerator 3-(3.4-dichlorophenyl)-1.1-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 (Beshuite HTA-7-6000, manufactured by Toho Veslon Co., Ltd.) were arranged on this at equal intervals and in parallel, and the release paper was placed on top of it. After lowering the viscosity of the resin by pressing it lightly with a roller on a heating plate heated to 120'C for 3 minutes, 4 kg was placed on a heated plate heated to 90'C.
A sheet prepreg was produced by pressing with a linear pressure of /Cm. As a result of electron microscopic observation of this prepreg sheet, no cavities were observed inside, and the pot life was 2 months (20°C).

This product was molded under curing conditions of 130° C17k9/c scraps and 9 gin, and the physical properties of the molded product were as follows.
Bending strength: 168kg/TrIlL Bending modulus: 13.5T/D ILSS9.9kg/i (room temperature) ILSS7.6k9/Tf7lt (80 Vf6O%) In addition, this prepreg sheet was heated to 708C1 under vacuum of approximately 1k9
/Cdl3O min, then 1300C1 pressurized 1kg/Cl
As a result of electron microscopic observation, almost no voids were observed in the molded product molded under the low pressure curing condition of tl9O, and the physical properties were almost the same as those of the high-pressure molded molding as described below.

Bending strength 165k9/TiTlL bending modulus
12.8T/I LSS9.8k9/d (room temperature) ILSS7.4k9/Tn! t(80°C)Vf6O%
Example 2 25 parts by weight of DEN438 (phenol/novolac type epoxy resin, manufactured by Dow Chemical Company), DEN43
9 (Phenol Novolak type epoxy resin, manufactured by Dow Chemical Company) 7 weighing parts, DER33L (Bisphenol A
To a resin mixture (viscosity 110 poise at 80'C) consisting of 5 parts by weight of epoxy resin (manufactured by Dow Chemical Company), 3 parts by weight of dicyandiamide having a particle size of 2 to 50 µm, and 3 parts by weight of 3-(3.
5 parts by weight of 4-dichlorophenyl)-1,1-dimethylurea was added to obtain a resin composition.

Using this resin composition, a prepreg sheet in the saw direction was manufactured by the hot melt method in the same manner as in Example 1. The pot life of this sheet was 2 months (20'C), and no cavities were observed in the cross section of the sheet. This one at 135°C, 7k
The physical properties of the molded product molded under the curing conditions of 9/CIL19Gin were as follows. Bending strength 172k9/
i Flexural modulus 13.1T/D ILSSIO. 2k9/Mlt (room temperature) ILSS8.2k9/i (80'C) ノ ■F6l% In addition, this prepreg sheet was heated at 70℃ and vacuum approximately 1k9/Mlt.
C, 30 minutes, then 135℃, pressurization 1k9/CTll
The physical properties of the molded product molded at a low pressure of 9O were almost the same as those of the high pressure molded case as described below.

No voids were found inside. Bending strength 1
71kg/i Flexural modulus 13.1T/I ILSSIO. lk9/i (room temperature) ILSS8. Ok9/Tnli (80.

C) Vf 59% Comparative Example 1 (Phenol Novolac type epoxy resin not used) Epicoat 828 (bisphenol A type epoxy resin, manufactured by Shell Chemical Co., Ltd.) 6 parts, Epicoat 1002 (same as above) 4
An epoxy resin mixture consisting of parts by weight was kneaded in a kneader at 90°C, and then 3 parts by weight of dicyandiamide ground to 10 μm or less was added and kneaded in a roll mill.

Next, 5 parts by weight of 3-(3.4-dichlorophenyl)-1.1-dimethylurea was added and kneaded, and a unidirectional prepreg was produced in the same manner as in Example 1. Heat this to 135°C
The physical properties of the molded product molded under the curing conditions of 17k9/Dl9O were as follows. Bending strength 158kg/
i Flexural modulus 12. '7T/Tlui ILSS8.4k,/D ILSS5. Okg/Tr! i ■F6O% I? S value is low.

Comparative Example 2 (Using dicyandiamide with a particle size exceeding 100μ)
The same resin composition as in Example 1 (Araldite EPNll
70 parts by weight of 38, 20 parts by weight of Epicote 1002,
After kneading 1 part by weight of Epikote 828 in a kneader at 90°C, 3 parts by weight of dicyandiamide containing crystals with a particle size exceeding 100p were added and kneaded on a roll mill.

At this time, the distance between the rolls was slightly increased so that a large amount of dicyandiamide particles with a particle size exceeding 100 μm remained.
Next, 5 parts by weight of 3-(3.4-dichlorophenyl)-1.1-dimethylurea was added and kneaded, and then a unidirectional prepreg was produced in the same manner as in Example 1. A large number of cavities were observed in this prepreg sheet, and a large number of voids were present in the molded product that was low-pressure molded under the same conditions as in Example 1, and the physical properties of the low-pressure molded product were also deteriorated as shown below. bending strength
160k9/d Flexural modulus 12.8T/I ILSS8.9k9/m! FL ■F6l%

Claims (1)

[Claims] 1 A mixture of a phenol novolac type epoxy resin and a bisphenol A type epoxy resin containing at least 50% by weight of a phenol novolac type epoxy resin and having a viscosity of 30 to 300 poise at 80°C.A particle size of 100μ per 100 parts by weight of the resin mixture. A release paper is coated with an epoxy resin composition containing 0.5 to 6 parts by weight of each of the following didiandiamide and 3-(3.4 dichlorophenyl)-1,1-dimethylurea, and then A hot-melt type carbon fiber prepreg characterized by arranging carbon fibers, introducing a release paper thereon, and then passing it over a heated heating plate and pressing it with a post-press roller that lowers the viscosity of the resin. Manufacturing method.