JP2003026820A - Carbon fiber-reinforced composite material, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon fiber-reinforced composite material comprising a matrix resin having high elongation and excellent heat resistance, and having excellent characteristics such as fatigue resistance, resistance to thermal crack, and heat resistance, and to provide a method for producing the composite material. SOLUTION: This method for producing the carbon fiber-reinforced composite material comprises a liquid epoxy resin composition capable of providing a cured product having >=4% tensile elongation at a room temperature when the composition is cured a the same condition as the molding condition of the carbon fiber-reinforced composite material, and having the glass transition temperature >=10 deg.C higher than the curing temperature. The carbon fiver- reinforced composite material is produced by using the method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon fiber reinforced composite material suitably used for aircraft members, automobile members, ship members, sports equipment members and the like, and a method for producing the same.

[0002]

2. Description of the Related Art A fiber-reinforced composite material composed of a reinforcing fiber and a matrix resin is lightweight and has excellent mechanical properties such as strength, rigidity and impact resistance. Therefore, it is used as an aircraft member, an automobile member, a ship member, a sports equipment member. It has been applied to many fields such as.

Among these, the carbon fiber reinforced composite material having carbon fiber excellent in specific strength and specific elastic modulus as a reinforcing fiber has a large weight saving effect and is particularly applicable to a wide range of fields.

The matrix resin of the carbon fiber reinforced composite material is an epoxy resin which is a thermosetting resin which has excellent mechanical properties, heat resistance, chemical resistance, adhesion to carbon fibers, and has a small polymerization shrinkage and a small linear expansion coefficient. (Cured product) is widely used. In particular, an epoxy resin (cured product) using a polyamine curing agent is often used because of its excellent adhesion to carbon fiber.

For the production of a fiber-reinforced composite material composed of carbon fibers and an epoxy resin, a method in which a prepreg, which is an intermediate body composed of carbon fibers and an uncured epoxy resin, is prepared, laminated and heat-cured is widely used. Has been.

However, this method is not necessarily excellent in productivity because an intermediate called prepreg must be produced.

On the other hand, an RTM method (resin transf) for injecting a liquid thermosetting resin into a reinforced fiber base material placed in a mold and curing it by heating to obtain a fiber reinforced composite material.
In recent years, erMolding) has attracted attention as a method for producing a carbon fiber reinforced composite material which is more excellent in productivity.

In particular, in order to obtain a carbon fiber reinforced composite material having a high volume fiber content and superior mechanical properties by the RTM method, the epoxy resin having a low viscosity is used in order to improve the impregnation property into the reinforcing fiber base material. It is necessary to use a resin composition (composition comprising an epoxy resin and a curing agent).

However, when using a low-viscosity epoxy resin composition, there is a limitation of low viscosity, so that the raw materials and the compounding ratio which can be used are largely restricted as compared with the conventional epoxy resin composition for prepreg. Therefore, it is difficult to satisfy various desired characteristic values at the same time.

At the same time, one of the characteristics that is desired to be satisfied is compatibility between the elongation of the matrix resin (that is, the cured product of the epoxy resin) and the heat resistance (that is, high glass transition temperature). When the elongation of the matrix resin is low, the tensile strength of the fiber-reinforced composite material is low,
It has disadvantageous properties such as low fatigue property and impact resistance, cracking due to thermal stress during molding and cracking due to thermal cycle (low thermal cracking resistance). In addition, when the glass transition temperature of the matrix resin is exceeded during molding, the heat resistance of the carbon fiber reinforced composite material is significantly reduced, so the glass transition temperature of the matrix resin is a controlling factor of the heat resistance of the carbon fiber reinforced composite material. , It is desired to be as high as possible. Generally, the glass transition temperature of a cured product of a thermosetting resin has a positive correlation with the curing temperature. However, the difference between the glass transition temperature and the curing temperature greatly depends on the chemical composition of the resin used.

To increase the elongation of the cured epoxy resin,
Techniques such as flexible chains (polyoxyalkylene, long-chain alkylene, polysiloxane, etc.) that reduce the crosslink density are effective, but when these techniques are used, the glass transition temperature of the cured product is relative to the curing temperature. Will be low. Furthermore, the elastic modulus of the cured product also becomes low. When the elastic modulus of the matrix resin is low, the mechanical properties of the fiber-reinforced composite material, especially the compressive strength and bending strength, are low.

For the above reasons, it has been difficult to obtain a carbon fiber reinforced composite material having satisfactory performance with the existing liquid epoxy resin composition.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is a carbon fiber which is composed of a matrix resin having high elongation and excellent heat resistance, and which has both heat resistance and characteristics such as fatigue resistance and thermal crack resistance. It is to provide a reinforced composite material and a manufacturing method thereof.

[0014]

In order to solve the above problems, the method for producing a carbon fiber reinforced composite material of the present invention is a cured product obtained by curing under the same curing conditions as the molding conditions of the carbon fiber reinforced composite material. A method comprising using a liquid epoxy resin composition having a room temperature tensile elongation of 4% or more and a glass transition temperature of 10 ° C. or more higher than a curing temperature. A liquid epoxy resin composition having a room temperature tensile elongation of 5% or more is preferably used.

The carbon fiber reinforced composite material according to the present invention produced by such a method has both excellent mechanical properties and heat resistance, and is particularly suitable for automobile members and the like.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below along with preferred embodiments. In the method for producing a carbon fiber reinforced composite material according to the present invention, a liquid epoxy resin composition is used. As the liquid epoxy resin composition, a polyamine-curable epoxy resin resin composition and an acid anhydride-curable epoxy resin composition are often used in the production of fiber-reinforced composite materials. A composition composed of an epoxy resin and a polyamine curing agent is preferable because of excellent adhesion between the cured product and the carbon fiber.

In the present invention, a liquid epoxy resin composition having excellent elongation and heat resistance of the cured product is selected and used.

The term "liquid" as used herein means a viscosity such that the reinforcing fibers can be easily impregnated at the injection temperature, specifically 500 mPa.
-It means a liquid of s or less. Normal impregnation temperature is 10
Since the temperature is often 0 ° C. or lower, the liquid epoxy resin composition used in the present invention preferably has a viscosity at 100 ° C. of 500 mPa · s or lower. Alternatively, the temperature at which the viscosity reaches 500 mPa · s is preferably 100 ° C. or lower. In the case of a normal liquid, the viscosity increases monotonically with temperature, and therefore both can be considered to be equivalent. Or the viscosity
It is more preferable that the temperature of 500 mPa · s be 70 ° C. or lower because low temperature injection becomes possible.

Regarding the elongation of the cured product of the liquid epoxy resin composition, only the liquid epoxy resin composition is produced under the same curing conditions as in the production (molding) of the carbon fiber reinforced composite material, that is, at the same curing temperature and the same curing time. It is necessary that the room temperature tensile elongation of the cured product sample obtained by curing the above is 4% or more. More preferably, the room temperature tensile elongation is 5% or more. At this time, it is preferable that the room temperature tensile elastic modulus is at least 3.2 GPa.

At the same time, the cured product is 1
It is essential to have a glass transition temperature higher than 0 ° C. The glass transition temperature of the cured product can be known by performing differential scanning calorimetry on the above-mentioned cured product.

When such an epoxy resin composition is designed, it contains many rigid skeletons such as a benzene ring and a cyclohexane ring, and a long-chain alkylene, polyoxyalkylene,
It is effective to design the molecular skeleton of the cured product so as to increase the molecular weight between cross-linking points by avoiding long chains of single bonds such as polysiloxane as much as possible.

The method for producing a carbon fiber reinforced composite material according to the present invention can be applied to any method for producing a fiber reinforced composite material using a known liquid resin.

The RTM method can be used as one of preferred manufacturing methods. The RTM method is a method of injecting a liquid thermosetting resin into a reinforcing fiber base material placed in a mold and curing the resin to obtain a fiber-reinforced composite material. Above all, it is suitable for the vacuum RTM method in which the inside of the mold cavity is depressurized and the resin is injected by utilizing the pressure difference between the inside and the outside.

The reinforcing fiber substrate is a woven fabric made of carbon fiber,
A blade or the like may be used as it is, or a woven fabric or the like may be laminated and shaped, and the form may be fixed by a means such as a binder or a stitch to form a preform. Further, reinforcing fibers other than carbon fibers, for example, glass fibers, aramid fibers, metal fibers and the like may be used in combination.
Examples of the combination method include a method in which one of the warp and weft of the woven fabric is a reinforcing fiber other than carbon fiber, a method in which a carbon fiber woven fabric and a woven fabric or mat of other reinforcing fibers are laminated, and the like.

A closed mold made of a rigid body may be used as the mold, and a method using a rigid one-sided mold and a flexible film (bag material) is also possible. In the latter case, the reinforcing fiber substrate is placed between the rigid one-sided mold and the flexible film.

As the rigid mold material, various existing materials such as metal (steel, aluminum, etc.), FRP, wood, gypsum, etc. can be used. As the flexible film, a film of nylon, fluororesin, or silicone resin is used.

When a rigid closed mold is used, the liquid epoxy resin composition is usually injected by pressurizing and clamping the liquid epoxy resin composition. At this time, a suction port may be provided separately from the injection port and connected to a vacuum pump for suction. It is also possible to inject the liquid epoxy resin only by the atmospheric pressure without performing a suction and using a special pressurizing means.

When using a rigid one-sided type and a flexible film, suction and injection at atmospheric pressure are usually used. In order to achieve good impregnation by injection at atmospheric pressure, it is effective to use a resin diffusion medium as shown in US Pat. No. 4,902,215.

It is also possible to install a foam core, a honeycomb core, metal parts, etc. in the mold in addition to the reinforcing fiber base material to obtain a composite material integrated with these. In particular, the sandwich structure obtained by arranging and molding the carbon fiber base material on both sides of the foam core is lightweight and has a large bending rigidity, and is therefore useful as an outer plate material.

Further, prior to the installation of the reinforcing fiber base material,
It is also preferable to apply a gel coat to the rigid body type surface.

After the resin injection is completed, heat curing is carried out by using an appropriate heating means. The curing temperature at this time is
As described above, the heat resistance of the carbon fiber reinforced composite material is correlated with the glass transition temperature of the matrix resin.
C is preferred. If you set the curing temperature to an unnecessarily high temperature,
Since adverse effects such as long molding time and high cost of the mold, heat medium, and auxiliary materials used occur, 60 to 150 ° C. is preferable unless particularly high heat resistance is required. The curing time is usually 10 minutes to 3 hours.

Since the RTM method is a method particularly suitable for manufacturing a plate member having a curved surface, the method for manufacturing a carbon fiber reinforced composite material according to the present invention can be applied to an outer plate of an aircraft, a railway vehicle, an automobile, a ship, etc. It is particularly preferably used for manufacturing. Among them, it is suitable for manufacturing automobile members that require mass production in a short molding cycle.

As another manufacturing method, there is a filament winding method. The filament winding method is a method in which a mandrel is wound with a strand of reinforcing fiber in which a liquid resin is impregnated and then heated and cured. The filament winding method is suitable for manufacturing members having rotational symmetry, and is therefore suitable for manufacturing pressure vessels, flywheels, automobile propeller shafts, and the like.

In the carbon fiber reinforced composite material obtained by the present invention, the volume content of the reinforcing fibers is preferably 50% or more in order to effectively utilize the excellent specific strength and specific elastic modulus of the carbon fibers. . At this time, by using the preferable liquid epoxy resin composition of the present invention, desired heat resistance can be obtained at the same time.

[0035]

The present invention will be described in more detail with reference to the following examples. (1) Example 1 (Evaluation of Liquid Epoxy Resin Composition) Polyamine-curable liquid epoxy resin composition TR-C32 manufactured by Toray Industries, Inc. was preheated to 50 ° C. and molded from aluminum having a plate-like cavity with a thickness of 2 mm. It was poured into a mold, heated at 1 ° C./min in an oven, and when the temperature reached 90 ° C., this temperature was maintained for 2 hours, and then the mold was removed to obtain a plate of a cured epoxy resin.
Dumbbell-shaped test pieces (small size 1 (1 /
2) No.) was obtained and room temperature (23 ° C) according to JIS K7113
The tensile test was conducted at. The tensile elongation was 5.8% and the tensile elastic modulus was 3.3 GPa. Using a differential scanning calorimeter TA3000 (manufactured by Mettler), a small piece sample cut out from the same cured product plate was subjected to temperature rise measurement at a temperature rise rate of 40 ° C / min, and the glass transition temperature was measured from the midpoint of the glass transition region. Was 113 ° C.

Further, the viscosity of TR-C32 at 50 ° C.
It was 140 mPa · s when measured with a flat plate rotational viscometer.

(Production of fiber-reinforced composite material) Length 300 mm,
It has a rectangular parallelepiped cavity with a width of 300 mm and a height of 1.3 mm.
A mold release agent was applied to the inner surface of the cavity of a steel mold having an upper mold and a lower mold, a resin injection port provided at the center of the lower mold, and resin injection ports at the four corners of the upper mold. .

Carbon fiber plain weave cloth CF6273H (T700GC-12K
Using, 190 g / m ² basis weight, manufactured by Toray Industries, Inc., and cutting into a square of 280 mm on each side so that one side is the warp direction, 6 sheets were stacked in the cavity.

The mold is clamped using a press and the mold temperature is 50 ° C.
The temperature was raised to. The outlet was connected to a vacuum pump via a trap, and the pressure inside the mold was reduced to 0.5 kPa or less. Then, Toray Industries, Inc. polyamine curable liquid epoxy resin composition TR-C
32 was injected into the cavity at an injection pressure of 300 kPa. Injection was completed when almost no bubbles were found in the epoxy resin flowing out to the trap. Heat the mold at 1 ° C per minute,
When the temperature reached 90 ° C., this temperature was maintained for 2 hours, and then the mold was removed to obtain a fiber reinforced composite material.

When the surface of the fiber-reinforced composite material and the cross section after cutting and polishing were microscopically observed, defects such as voids and cracks were not observed.

According to ASTM-D3039, Instron 420
The tensile strength of the fiber-reinforced composite material was measured using an 8-type tensile tester (manufactured by Instron). The test piece dimensions are
The width was 25.4 mm, the length was 229 mm, the environmental temperature was 23 ° C, and the crosshead speed was 1.27 mm / s. Tensile strength is 871MP
It was a.

[0042]

As described above, according to the carbon fiber reinforced composite material and the method for producing the same of the present invention, since molding is performed using a specific liquid epoxy resin composition, the resulting molded article has excellent mechanical properties. And heat resistance can be compatible.

Continued front page    F-term (reference) 4F072 AA01 AA07 AB06 AB09 AB10                       AB11 AB28 AD23 AE01 AF28                       AK03 AK11 AK14 AK20 AL01                       AL02

Claims (9)

[Claims] 1. The room temperature tensile elongation of the cured product is 4% when cured under the same curing conditions as the molding conditions of the carbon fiber reinforced composite material.
Above, a method for producing a carbon fiber reinforced composite material, characterized in that a liquid epoxy resin composition having a glass transition temperature higher than the curing temperature by 10 ° C. or more is used. 2. The room temperature tensile elongation of the cured product is 5% when cured under the same curing conditions as the molding conditions of the carbon fiber reinforced composite material.
The method for producing a carbon fiber reinforced composite material according to claim 1, wherein the liquid epoxy resin composition as described above is used. 3. A liquid epoxy resin having a room temperature tensile elastic modulus of 3.2 GPa or more when cured by applying the same temperature history as the molding conditions of the carbon fiber reinforced composite material. 1. The method for producing a carbon fiber reinforced composite material according to 1 or 2. 4. The curing temperature of the liquid epoxy resin is 60 to 1
The method for producing a carbon fiber-reinforced composite material according to any one of claims 1 to 3, which is within a range of 50 ° C. 5. The method for producing a carbon fiber reinforced composite material according to claim 1, wherein the liquid epoxy resin composition comprises an epoxy resin and a polyamine curing agent. 6. The method for producing a carbon fiber reinforced composite material according to claim 1, wherein the carbon fiber reinforced composite material after molding has a volume fiber content of 50% or more. 7. The pressure inside the cavity of the mold in which the carbon fiber base material is arranged is reduced, and the liquid epoxy resin composition is injected into the cavity by utilizing the reduced pressure difference between the internal pressure of the cavity and the external pressure. The method for producing a carbon fiber reinforced composite material according to any one of claims 1 to 6, which uses a vacuum RTM method of impregnating a carbon fiber base material. 8. A carbon fiber reinforced composite material produced by the method according to claim 1. 9. The carbon fiber reinforced composite material according to claim 8, which is a member for automobiles.