JPH04268342A - Production of carbon fiber-reinforced composite material - Google Patents

Abstract

PURPOSE:To impart excellent mechanical strengths to a carbon fiber-reinforced composite material produced by the prior art techniques. CONSTITUTION:A prepreg sheet prepared by impregnating a carbon fiber with an epoxy resin and curing the resin into a tack-free srate is cut in consideration of the shape, size and number of laminated of the member to be made. The cut prepreg sheets are coated with an uncured epoxy resin containing a flexibilizer such as polyethylene glocol, polypropylene glycol or liquid rubber. They are laminated, subjected to vacuum bag molding, placed in an autoclave and cured under elevated pressure and temperature. A technique such as press molding can be employed in the same way.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a carbon fiber reinforced composite material particularly useful for structures such as space structures, aircraft, automobiles, and leisure equipment.

0002

[Prior Art] Fiber-reinforced composite materials (CFRP) based on carbon fibers are characterized by their specific strength and specific modulus. It is superior to other materials and has come to be widely used as a structural material for aviation, space, automobiles, leisure goods, etc. Currently, the main manufacturing method for CFRP is a composite material in which unidirectional or crossed carbon fibers are solidified with epoxy resin. CFRP using epoxy resin is in a flexible semi-hardened state, and the resin is laminated and hardened, and has features such as being able to be integrally molded into complex shapes.

0003

[Problems to be Solved by the Invention] As the performance of carbon fiber itself increases, the brittle characteristics of epoxy resin become a problem. The epoxy resin conventionally used in CFRP is brittle, so when tensile, repeated, or compressive loads are applied, it breaks before the reinforcing fibers. C
The destruction of the entire FRP was triggered by the destruction of the fibers. Furthermore, the brittle characteristics of the epoxy resin increase the variation in the strength characteristics of the CFRP, which has the disadvantage of increasing the safety factor when designing a structure. Therefore, thermoplastic resins such as polyetheretherketone (PEEK) are expected to be used to change the toughness of resins. However, it has the disadvantage that the molding temperature is much higher than that of epoxy resin, and it cannot be manufactured using existing equipment.

The object of the present invention is to solve the problems of carbon fiber reinforced composite materials produced by such conventional techniques and to provide a technique for imparting excellent mechanical strength.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the method for producing a carbon fiber reinforced composite material according to the present invention includes a coating step and a heating/pressure treatment step. In the manufacturing method, the coating process involves applying uncured epoxy to which a flexibility imparting agent such as polyethylene glycol, polypropylene glycol, or liquid rubber is added to a prepreg sheet in which carbon fibers are impregnated with semi-cured thermosetting resin. A resin is applied, and the heat/pressure treatment step is to harden the prepreg sheet coated with an epoxy resin by heat/pressure.

[0006]

[Operation] In the production method of the present invention, a prepreg sheet,
The uncured epoxy resin (hereinafter referred to as modified epoxy resin) coated with a flexibility imparting agent such as polyethylene glycol, polypropylene glycol, or liquid rubber is cured under heat and pressure. A fiber-reinforced composite material with integrated lamination can be realized. The modified epoxy resin exhibits a larger elongation at break than the epoxy resin used for the matrix resin due to the addition of a flexibility imparting agent. Therefore, it becomes possible to increase interlaminar fracture toughness, suppress the progress of damage such as interlaminar delamination, and improve mechanical properties such as tensile strength and fatigue strength.

[0007] The modified epoxy resin layer used in the present invention may be any material as long as it has good adhesion to the prepreg sheet and high toughness.

[0008]For molding, it is preferable to laminate prepreg sheets coated with the above-mentioned epoxy resin and heat and pressure mold them.

[0009]

[Example] As an example of the present invention, a case where heat and pressure curing was carried out in an autoclave will be described below. FIG. 1 shows a flow diagram of the fabrication method of the present invention. In the figure, the prepreg sheet is cut in consideration of the size, shape, number of laminated sheets, etc. of the member to be manufactured (step S1).

[0010] The prepreg sheet and modified epoxy resin are applied according to the required lamination order (step S2).
), which are stacked (step S3).

[0011] A release film, a pressure sheet, or the like is placed on the laminate and covered with a vacuum bag to perform a bagging process (step S4).

[0012] Putting the composition into an autoclave,
It is heated and cured under pressure (step S5).

[0013] In this example, heat and pressure curing was carried out in an autoclave, but methods such as press molding can be similarly used.

The modified epoxy resin used here was #25
00 epoxy resin (Toray Industries, Inc.) filled with 60 parts by weight of polyethylene glycol, a flexibility imparting agent.

FIG. 2 shows a cross-sectional view of a carbon fiber reinforced composite material manufactured using the manufacturing method of the embodiment shown in FIG. In this example, a composite material layer 3 made of a hardened prepreg sheet,
It has a structure in which modified epoxy resin layers 4 applied between 0°/45° layers are laminated and integrated.

FIG. 3 shows a 45°/90° interlayer, and FIG. 4 shows a 90° interlayer.
Figure 5 shows a cross-sectional view of a carbon fiber reinforced composite material in which a modified epoxy resin is applied between all layers.

FIG. 6 shows the tensile breaking loads of the carbon fiber reinforced composite materials of the examples shown in FIGS. 2 to 5 and the conventional composite material without a modified epoxy resin layer. All test pieces were in the form of strips with a width of 25 mm. From this result, greater breaking strength was obtained compared to the conventional one. It can also be seen that the coefficient of variation, which represents variations in strength, has become smaller, indicating that reliability has improved.

[0018]

[Effects of the Invention] As described above, according to the present invention, it is possible to realize a carbon fiber reinforced composite material with excellent mechanical strength, and the variation in strength can be reduced. This has the effect of improving reliability.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the flow of the manufacturing method of the present invention.

FIG. 2 is a cross-sectional view of a composite material manufactured using the manufacturing method of the example.

FIG. 3 is a cross-sectional view of a composite material manufactured using the manufacturing method of the example.

FIG. 4 is a cross-sectional view of a composite material manufactured using the manufacturing method of the example.

FIG. 5 is a cross-sectional view of a composite material manufactured using the manufacturing method of the example.

FIG. 6 is a diagram showing the tensile strength and coefficient of variation of the composite material of the example of FIGS. 2 to 5 and a conventional composite material that does not have a modified epoxy resin layer of the same shape.

[Explanation of symbols]

3 Composite material layer 4 Modified epoxy resin layer

Claims (1)

[Claims] 1. A method for producing a carbon fiber reinforced composite material comprising a coating step and a heating/pressure treatment step, the coating step comprising preparing a prepreg sheet in which carbon fibers are impregnated with a thermosetting resin in a semi-cured state. An uncured epoxy resin to which flexibility imparting agents such as polyethylene glycol, polypropylene glycol, and liquid rubber have been added is applied to the epoxy resin. In the heat and pressure treatment process, the prepreg sheet coated with the epoxy resin is heated and A method for producing a carbon fiber reinforced composite material, characterized in that the material is cured under pressure.