JPH06226874A - Molding method for resin composite material - Google Patents

Abstract

(57) [Summary] [Purpose] Excellent mechanical bond strength between layers even when formed by simple press molding without deteriorating the properties of the reinforced fiber base material that is responsible for basic strength. To be able to [Constitution] The laminated body in which the prepreg is kept below the tack-free temperature of the resin in the prepreg is covered with a vacuum bag, and at that temperature, the air inside the vacuum bag is sucked to reduce the pressure, and then the vacuum bag The temperature of the vacuum bag is raised to room temperature while maintaining the reduced pressure state, the inside of the vacuum bag is set to normal pressure, and then the laminated body is pressurized and cured by heating. By sucking in a tack-free state, there is no sticking at the stacking interface and an air discharge passage is secured, so voids are prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding a void-free molded body from a resin-based composite material comprising a prepreg laminate.

[0002]

2. Description of the Related Art Fiber-reinforced resin composite materials have the advantages of excellent strength and rigidity and light weight, and are widely used for structural members such as aircraft and automobiles. As a method for forming this fiber reinforced resin composite material, SMC (Sheet Mold
ing Compound), BMC (Bulk Molding Compound),
FW (Filament Winding), RIM (Reaction Injecti)
on Molding), various molding methods such as continuous molding method are known (Refer to the revised supplement “FRP molding processing technology” edited by the Industrial Research Committee).

For example, in the SMC method, a prepreg in which a reinforcing fiber base material such as glass fiber is impregnated with an epoxy resin is used as a resin-based composite material, and the prepreg is laminated to a predetermined thickness and then heat-pressed. And made into a fiber reinforced resin composite material. However, in the obtained molded body, the strength of the laminated interface between the prepregs was weak, and the mechanical strength as a whole such as the interlaminar shear strength and the bending strength was insufficient.

Therefore, in recent years, in order to improve the mechanical strength of the fiber-reinforced resin composite material, means such as a method using a three-dimensional woven fabric or a stitched preform as the reinforcing fiber base material, an interlayer reinforcement molding method using whiskers, etc. Has been adopted. According to these means, the fiber-reinforced resin composite material in which the reinforcing fiber base material is three-dimensionally oriented is obtained, so that the interlaminar shear strength and the peel strength are significantly improved.

Further, as seen in Japanese Patent Laid-Open No. 4-4112, by pressurization (hydrostatic pressure) accompanied by decompression assist,
An autoclave molding method is also known in which the resin-rich layer at the lamination interface is controlled or voids are removed to enhance the strength.

[0006]

However, when the above means is adopted to improve the mechanical strength of the fiber-reinforced resin composite material, there are various problems such as productivity and cost, and it can be said that the method is satisfactory. Absent. For example, in the method using a three-dimensional woven fabric, the amount of warp and weft is restricted in order to maintain its shape, and depending on the direction in which the load acts, when a reinforced fiber base material with a uniform fiber filling amount such as a mat is used. It is considered that the strength is inferior to that of. Further, there is a problem that productivity is poor and cost is high due to the limitation of weaving technology.

In the method using the stitched preform, the reinforcing fiber base material may be damaged due to friction with the stitch yarn or stitch needle. Further, warp yarns and weft yarns cannot be present in the portion where the stitch yarn (vertical yarn) is present, and the vicinity of the portion becomes a defect, which causes concentration of stress and lowers the strength. Furthermore, in the inter-layer reinforcement molding method using whiskers, pretreatment (metal coating) for orienting the whiskers vertically between the layers and molding equipment (magnetic field orientation equipment) are required, and orientation is possible depending on the filling amount of reinforcing fibers. There is a problem that the amount of whiskers is limited.

In the autoclave molding method, outflow of resin is indispensable for removing voids. Therefore, a complicated mechanism for adjusting the outflow amount of resin is required, and it is difficult to adjust the timing of pressurization / decompression / pressurization. Further, there are problems in terms of cost and productivity, such as the need for auxiliary materials that are discarded after each molding, the long molding cycle, and the need for molding know-how according to the shape of the molded body.

The present invention has been made in view of the above circumstances, and bonds between layers even when formed by simple press molding without impairing the characteristics of the reinforcing fiber base material that has basic strength. The purpose is to provide excellent mechanical strength and high mechanical strength.

[0010]

A method of molding a resin-based composite material according to the present invention, which solves the above-mentioned problems, comprises a step of laminating a prepreg in a state of being maintained below a tack-free temperature of a resin in the prepreg to form a laminate. And a step of covering the laminated body with a vacuum bag to suck air in the vacuum bag to bring it into a depressurized state, and maintaining the depressurized state in the vacuum bag to raise the temperature to room temperature and then making the inside of the vacuum bag into a normal pressure. Then, a step of subsequently pressurizing and heat curing the laminated body is performed.

The tack-free temperature of the resin in the prepreg means the temperature at which the tackiness of the resin disappears. If the temperature during prepreg lamination is higher than this tack-free temperature,
Removal of voids during vacuum suction becomes insufficient. On the other hand, if the temperature is lower than the tack-free temperature, the rigidity of the prepreg itself is increased, and the prepreg is less likely to be deformed during vacuum suction, making it difficult to remove voids. Therefore, the temperature during vacuum suction is
It is desirable to set the temperature so that the rigidity does not become too high below the tack-free temperature. -5 for general prepreg
The optimum range is 5 ° C to 5 ° C.

[0012]

In the molding method of the present invention, first, the prepregs are laminated while maintaining the temperature below the tack-free temperature of the resin in the prepregs to form a laminate. At this time, since the tackiness of the resin has disappeared, the prepregs are prevented from sticking to each other at the lamination interface. Next, the laminated body is covered with a vacuum bag, and the air inside is sucked to bring it into a depressurized state. At this time, the air present at the laminated interface is removed,
If the pressure is simply reduced, the prepregs adjacent to each other may adhere to each other at the lamination interface, and the existence of the adhered portion may block the air discharge passage, causing the residual air to cause voids.

However, in the molding method of the present invention, cooling to a tack-free temperature or lower prevents the prepregs from sticking to each other at the lamination interface, and the pressure is reduced in that state. Therefore, a discharge passage for the air existing at the stacking interface is secured, and the air is reliably discharged during vacuum suction. After the pressure is sufficiently reduced, the temperature is raised to room temperature while maintaining the reduced pressure. At this time, if the temperature rises after the depressurized state is released, the temperature is still sufficiently low in the initial stage of the depressurized state release and air does not stick to the laminating interface, so that air enters the laminating interface. However, in the molding method of the present invention, the resin in the prepreg becomes tacky as the temperature rises in a depressurized state, and the prepregs are closely adhered to each other when pressed by the atmospheric pressure. Therefore, even if the atmospheric pressure is applied thereafter, air is prevented from entering the lamination interface.

After the inside of the vacuum bag is kept at normal pressure, the laminated body is pressed and heated by a pressing device or the like to be cured to be a molded body. That is, since the air is prevented from entering the lamination interface and the prepregs adjacent to each other are intimately adhered to each other, voids are prevented in the obtained molded body, and the prepregs have high bonding strength. can get.

Further, since there is no outflow of resin as in the autoclave molding method, the initial fiber content (Vf) etc. is maintained as it is.

[0016]

EXAMPLES Hereinafter, examples and comparative examples will be specifically described. (Example) A unidirectionally strengthened prepreg (a fiber basis weight of 300 g) obtained by impregnating an epoxy resin into a glass fiber base material ("T glass" manufactured by Nitto Boseki Co., Ltd.) having a diameter of 14 μm of an elementary fiber.
/ M ² , resin content RC = 35 wt%, plate thickness 6 mm, 2
26 sheets of 5 cm × 25 cm) were prepared.

Each of the prepregs was -5 ° C to 5 ° C.
Then, the prepreg laminate 1 was obtained by laminating on a lower press mold 2 while changing the fiber direction one by one as shown in FIG. 1 in an ambient temperature of −5 ° C. to 5 ° C. Next, -5 ° C to 5
Prepreg laminate 1 with vacuum bag 3 at ambient temperature of ℃
And was sealed airtight with a seal member 30.

Then, in an ambient temperature of −5 ° C. to 5 ° C., a tube 32 is passed through the pressure reducing port 31 provided in the vacuum bag 3.
Through the vacuum pump 33, and the pressure inside the vacuum bag 3 was set to 50 to 76 cmHg. 5-10 in that state
After holding for a minute, the atmosphere temperature is brought to room temperature (25 to 30 ° C.) while maintaining the reduced pressure state, and after the entire prepreg laminate 1 reaches room temperature, the reduced pressure state is released and the inside of the vacuum bag 3 is returned to normal pressure. It was

The vacuum bag 3 is removed from the obtained prepreg laminate 1, the press upper die 4 is lowered, and the prepreg laminate 1 is pressed and heated at 120 ° C. for 2 hours under a molding pressure of 5 atm. It was cured to form a fiber reinforced resin composite material.
The void amount of the obtained fiber-reinforced resin composite material was measured by an optical microscope photograph, and the interlaminar shear strength was measured by ILSS (short beam three-point bending test L / n = 5).
The results are shown in Table 1. Also, an optical micrograph of the cross section (×
54) is shown in FIG. (Comparative Example) Using the same prepreg as in the example, fiber reinforced in the same manner as in the example except that the prepreg thawed at room temperature (20 ° C to 25 ° C) for 24 hours was laminated and depressurized in a room temperature atmosphere. A resin composite was molded.

With respect to the obtained fiber-reinforced resin composite material, the void amount and the interlaminar shear strength were measured in the same manner as in Examples, and the results are shown in Table 1. An optical micrograph (× 54) of the cross section is shown in FIG.

[0021]

[Table 1] (Evaluation) From Table 1, in the molded products obtained by the molding method of the example, the void amount is reduced by 75% as compared with the comparative example, and thereby the interlaminar shear strength is improved by 40%. Further, the effect of reducing voids by the molding method of the example is apparent from the comparison between FIG. 2 and FIG.

[0022]

That is, according to the method for molding a resin-based composite material of the present invention, it is not necessary to reinforce with stitches or whiskers, and it is not necessary to perform autoclave treatment. Strength is surely improved. Therefore, the FRP that is obtained with good productivity
The cost of the molded body is also low.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a molding method according to an embodiment of the present invention.

FIG. 2 is a micrograph showing the internal structure of a molded body obtained in one example of the present invention.

FIG. 3 is a micrograph showing an internal structure of a molded body obtained in a comparative example.

[Explanation of symbols]

1: Prepreg laminate 2: Press lower mold
3: Vacuum bag 4: Press upper mold

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[Procedure amendment]

[Submission date] July 19, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a molding method according to an embodiment of the present invention.

FIG. 2 Granules inside a molded body obtained in one embodiment of the present invention
It is a microscope picture which shows a child structure.

FIG. 3 is a micrograph showing a particle structure inside a molded body obtained in a comparative example.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiro Yamada 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Masayoshi Ito 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Takeshi Yabuya 1 Toyota-cho, Toyota-shi, Aichi Toyota Motor Co., Ltd.

Claims (1)

[Claims] 1. A step of laminating a prepreg in a state of being maintained below a tack-free temperature of a resin in the prepreg to form a laminated body, and covering the laminated body with a vacuum bag to suck air in the vacuum bag. From the step of reducing the pressure, and the step of raising the temperature to room temperature while maintaining the reduced pressure inside the vacuum bag, then setting the inside of the vacuum bag to normal pressure, and then pressurizing and heat curing the laminate. A method for molding a resin-based composite material, comprising: