JP2870994B2 - Fiber reinforced composite and molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] An improved method for forming a fiber-reinforced composite used for structural members such as aircraft, ships, vehicles, and buildings is provided.

[Prior art] Fiber reinforced composites used in the above application fields are usually prepared by impregnating a thermosetting matrix resin into a woven fabric composed of long fibers having high strength and high elastic modulus, and initially curing under a predetermined condition. It is obtained by laminating a plurality of so-called “prepregs” and curing by heating and pressurizing. However, this method has weak points in physical properties perpendicular to the laminating surface (in the thickness direction), In view of the fact that a three-dimensional fiber skeleton structure (having a reinforcing component in the thickness direction) can be obtained, such a three-dimensional fiber skeleton structure is set as a core in a molding die. In recent years, a method of directly injecting a matrix resin into a resin and impregnating and curing by heating (RI method) has been attempted.

The three-dimensional fiber skeleton structure used herein is generally referred to as a “preform”. In the impregnation molding method as described above, the preform placed in the molding die is formed by the inherent drapability of the fiber structure, or It is known that the desired shape may not be maintained due to deformation due to the resin injection pressure at the time of impregnation, and as a result, poor quality of molded products is likely to occur.

In the RI molding method, a preform set in a mold is usually a high-density woven or knitted fabric made of a fiber material having a high strength elastic modulus, and originally has some drapability. Further, since the resin is a viscous fluid and has a flow velocity and a flow pressure, it is inevitable that the preform is deformed at the time of injection or the mold is partially separated.

Various methods have been studied and implemented to reduce this, such as increasing the rigidity of the fiber material, improving the weaving and knitting structure, lowering the viscosity of the resin, and improving the injection conditions. In some cases, deformation troubles are likely to occur.

As described above, since the preform is a three-dimensional fiber structure, each of the constituent fiber materials has a sufficient resistance to the tensile external force in the axial direction, but has poor form retention to the external force in the compressive direction. This is a fundamental problem. The present invention pays attention to such problems of the preform, and aims to improve it while utilizing the characteristics as a fiber structure.

[Problem to be Solved by the Invention] The present invention has been made to solve such a problem of the RI method.
It is an object of the present invention to provide a molding method which prevents deformation by giving an appropriate structural rigidity to a preform before resin injection in advance and enables production of a high-quality composite member.

Means for Solving the Problems In order to solve the above problems, the invention according to claim 1 mainly includes a three-dimensional fiber skeleton material and a thermosetting matrix resin. In the fiber reinforced composite used as the element, the three-dimensional fiber skeleton material is formed by blending, knitting or weaving a heat-resistant fiber material and a thermoplastic fiber material, and reducing the heat deformation temperature of the thermoplastic fiber material. The thermosetting matrix resin is heated to a temperature higher than the substantial curing reaction temperature, and the three-dimensional fiber skeleton material is subjected to heat treatment at a temperature higher than the heat deformation temperature of the thermoplastic fiber material to form the thermosetting matrix material. Impregnated with resin,
It is cured and molded.

According to the invention described in claim 2, in the fiber reinforced composite having a three-dimensional fiber skeleton material and a thermosetting matrix resin as main components, the three-dimensional fiber skeleton material is a heat-resistant fiber material And a thermoplastic fiber material mixed, twisted or interwoven, and the heat deformation temperature of the thermoplastic fiber material is higher than the substantial curing reaction temperature of the thermosetting matrix resin, and the three-dimensional The fiber skeleton is stretched by applying a tensile force to heat it to a temperature higher than the thermal deformation temperature of the thermoplastic fiber material to shape it. Thereafter, a thermosetting matrix resin is introduced to impregnate and cure.

[Action]

In other words, a preform is prepared by mixing and knitting a thermoplastic fiber material having an appropriate heat distortion temperature with a heat-resistant fiber material, which is the main material constituting the preform, by blending, kneading, and aligning. Alternatively, the thermoplastic material is melted and impregnated by applying heat while being stretched by applying a tensile force, thereby imparting a preform with a preferable three-dimensional shape and shape retention in advance. The preform thus shaped is set during molding, a thermosetting matrix resin is injected, and then heated and cured, but the substantial curing temperature of the matrix resin is reduced by the heat of the thermoplastic material. By selecting the material so that the temperature is lower than the deformation temperature, the hardening molding is performed without impairing the three-dimensional shape of the preform formed earlier.

Here, "mixed fiber" is a so-called comingdled yarn state in which two or more fiber materials are mixed at a single fiber level, and "mixed twist" is a state in which two or more fiber materials are twisted at a yarn level. It means the state of twine. However, since it is a requirement that the heat-resistant fiber material and the thermoplastic fiber material coexist at a substantially constant ratio in the length direction, the number of twists may be small or large.

As described above, many woven fabrics obtained by mixing and weaving a heat-resistant fiber material and a thermoplastic fiber material have already been proposed in the form of the prepreg. However, in these cases, the thermoplastic fiber material itself melts and permeates to perform the function of the matrix resin. Needless to say, it is basically different from the holding material.

The heat-resistant fiber material constituting the present invention is at least
A multifilament fiber made of an inorganic or organic polymer material having a high strength and a high elastic modulus that is stable at a temperature of 250 ° C or higher. For example, carbon fiber, glass fiber, alumina fiber, aramid fiber and the like correspond to this. The thermoplastic fiber material is a multifilament fiber which is made of a fiber-forming thermoplastic material and can be plasticized and fluidized at a specific thermoforming temperature, such as aliphatic polyamide, polybutylene terephthalate, polyethylene terephthalate, and copolyester. Such fibers include fibers made of so-called super engineering plastics such as polyetherimide, polyphenylene sulfide, and polyetheretherketone. Further, as the thermosetting matrix resin, any resin such as epoxy, unsaturated polyester, phenol resin or the like which can be impregnated into a fiber preform and then cured under appropriate temperature and pressure conditions to form a uniform molding surface can be used. However, in the present invention, it is necessary to select a molding temperature of the thermosetting matrix resin that is substantially lower than a thermal deformation temperature of the thermoplastic fiber material.

In the above, the composition ratio (Vf) of the fiber material and the matrix resin depends on the required physical properties of the obtained composite product, but the ratio of the heat-resistant fiber material, which is a substantial aggregate, is 15 to
It is considered that 50% vol is preferable from a practical viewpoint. On the other hand, the mixing ratio of the thermoplastic fiber material to the heat-resistant fiber material is preferably 15 to 40% wt from the viewpoint of shape retention of the preform.

[Example] Example 1 Commercially available PAN-based carbon fiber 6K yarn and fiber obtained by melt-spinning polybutylene terephthalate at a take-up speed of 2500 m / min.
This fiber was twisted with 600D (melting point of the fiber was 225 ° C as measured by DSC) to produce a filament yarn having an apparent fineness of 4400D.

Using this filament yarn, a three-dimensional woven fabric consisting of three components of warp, weft and vertical yarn was prepared by a manual weaving device created by the inventor based on the method shown in JP-B-54-38673. The ratio of warp: weft: vertical yarn is 25:25:
The apparatus conditions were adjusted to 10 so that the number of threads per inch in each axial direction of each thread was ± 1 shown in Table 1. Approximately 50 mm wide and 25 mm thick obtained in this way
The preform 8 was obtained by cutting the three-dimensional fabric of Example 1 into a length of about 200 mm.

The test preform 8 is stretched by applying a tensile force to each fiber in the axial direction using a jig 11 as shown in FIG. 1, placed in a hot-air dryer as close to a rectangular parallelepiped as possible,
Hold for 2 seconds. After the polybutylene terephthalate component melted and penetrated between the carbon fibers, it was taken out and cooled at room temperature.

Here, the jig 11 in FIG. 1 has a plurality of rods 12 assembled so as to form each side of the rectangular parallelepiped, and holes 13 provided at each corner of the rectangular parallelepiped. Then, the preform 8 is disposed inside the jig 11, a wire 14 such as a wire is connected to each angle of the preform 8, and one end of the wire 14 is passed through the hole 13. By applying tension, the corners of each preform 8 are pulled and the preform 8 is spread.

FIG. 2 is a conceptual diagram of a molding die used for the RI molding method.
The sample chamber 9 has an inner dimension of 50 mm × 25 mm × 200 mm, and is made of chrome-plated SS steel material and provided with a resin inlet 2 and a vent 3. The test preform 8 was set in the sample chamber 9 after the inside of the sample chamber 9 was treated with a fluorocarbon release agent and subjected to the above-mentioned stretching heat treatment. After the main body 1a and the main body 1b of the mold 1 are sealed together, the vent port 3 is connected to a vacuum pump system to eliminate air in the mold, and an epoxy resin having the composition shown in Table 2 is introduced from the inlet port 2. After that, the mold was filled in the mold, and then the mold 1 was returned to the hot air drier again and subjected to the heat curing treatment according to the program shown in Table 3. The practical curing temperature of this resin is 90 ~
120 ° C. After completion of the treatment, the molded product was gradually cooled at −30 ° C./hr and taken out to obtain a test sample [1].

Comparative Example 1 A three-dimensional fabric was prepared using a commercially available PAN-based carbon fiber 6K yarn and the method and apparatus used in Example 1. The device conditions were adjusted so that the configuration of the warp: weft: vertical yarn was the same as in Example 1. The preform 8 was obtained by cutting the three-dimensional woven fabric thus obtained having a width of about 50 mm and a thickness of about 25 mm into a length of about 200 mm. Except that the test preform 8 was not stretched and heat-treated by a jig, the test sample [2] was produced by resin injection and heat curing using the mold 1 of FIG. 2 in exactly the same manner as in Example 1.

For the test samples [1] and [2], the parallelism and orthogonality of the carbon fiber components observed on the molding surface are visually observed.
Comparative evaluation was performed.

In the sample [1] of the example, there is almost no disturbance of the preform weave structure on each surface, but in the sample [2] of the comparative example, the component yarns are slackened at the ridge of the rectangular parallelepiped and dropped into the inner layer. At a portion near the resin injection port 2 of the molding die 1, a slight arc-shaped deformation (bowing) was observed in the (weft) yarn component orthogonal to the resin flow.

The test samples [1] and [2] were cut along the center line connecting the resin injection port 2 and the vent port 3 of the mold 1 (in the warp direction), and the vertical thread pitch of the cross section was observed. As shown in Table 4, the pitch of the vertical yarn in the sample [1] hardly fluctuated, but in the sample [2], the pitch of the vertical yarn was clearly non-uniform around the portion near the resin injection port 2 of the mold 1. Sex was observed.

In the present embodiment, the polybutylene terephthalate, which is a thermoplastic fiber material, was melt-infiltrated between carbon fibers, which are heat-resistant fiber materials, while applying tensile tension in the axial direction of each fiber using the jig 11 and expanding the fibers. However, the thermoplastic fiber material may be melted and infiltrated between the heat-resistant fiber materials without applying tensile tension in the axial direction of each fiber. According to this, although there is a slight deformation due to the inherent characteristics of the fiber structure such as deflection, the deformation due to the resin injection pressure can be prevented as in the above-described embodiment.

That is, by melting and infiltrating the thermoplastic fiber material between the heat-resistant fiber materials, an appropriate structural rigidity is imparted to the three-dimensional fiber skeleton material in advance, and the heat deformation temperature of the thermoplastic fiber material is set to the thermosetting matrix. Since the temperature is higher than the substantial curing reaction temperature of the resin, the thermoplastic fiber material is not thermally deformed even during the injection and curing of the matrix resin, and the structural rigidity of the three-dimensional fiber skeleton material is maintained.

In the above-described embodiment, in addition to the above, the polybutylene terephthalate, which is a thermoplastic fiber material, is melted between carbon fibers, which is a heat-resistant fiber material, while applying tensile tension in each fiber direction using a jig 11 and expanding the fiber. The infiltration also prevents the deformation of the three-dimensional fiber skeleton material due to the inherent characteristics of the fiber structure, such as deflection, which can occur before the melt infiltration.

[Effects] As described above, according to the first aspect of the present invention, the thermoplastic fiber material is dissolved and infiltrated between the heat-resistant fiber materials, whereby the structural rigidity suitable for the three-dimensional fiber skeleton material is previously obtained. Is added, and the thermal deformation temperature of the thermoplastic fiber material is higher than the substantial curing reaction temperature of the thermosetting matrix resin, so the thermoplastic resin material is not thermally deformed during the matrix resin injection and curing. The structural rigidity of the three-dimensional fiber skeleton is maintained. Therefore, it is possible to prevent deformation of the three-dimensional fiber skeleton material due to the thermosetting matrix resin injection pressure and deformation during subsequent thermosetting.

According to the second aspect of the present invention, in addition to the effects of the first aspect, deformation of the three-dimensional fiber skeleton material due to the inherent characteristics of the fiber structure such as flexure. Can be prevented.

[Brief description of the drawings]

 1 and 2 are schematic diagrams of the present invention. 1a Mold main body (split) 1b Mold main body (split) 2 ... Resin injection port, 3 ... Vent port 8 ... Preform 11 ... Expansion processing jig, 12 ... Rod 13 ... ... holes, 14 ... linear bodies

Claims (2)

(57) [Claims] 1. A fiber reinforced composite comprising a three-dimensional fiber skeleton material and a thermosetting matrix resin as main components, wherein the three-dimensional fiber skeleton material comprises a heat-resistant fiber material and a thermoplastic fiber material. The thermoplastic fiber material has a heat deformation temperature higher than a substantial curing reaction temperature of the thermosetting matrix resin, and the three-dimensional fiber skeleton is a thermoplastic fiber material. A fiber-reinforced composite, which is shaped by heat treatment at a temperature not lower than the heat distortion temperature, and thereafter, is impregnated with a thermosetting matrix resin, and is cured and molded. 2. A fiber reinforced composite comprising a three-dimensional fiber skeleton and a thermosetting matrix resin as main components, wherein the three-dimensional fiber skeleton comprises a heat-resistant fiber material and a thermoplastic fiber material. The thermoplastic fiber material has a heat deformation temperature higher than a substantial curing reaction temperature of the thermosetting matrix gin, and the three-dimensional fiber skeleton is subjected to tensile tension. 2. The method according to claim 1, wherein the heat treatment is performed by heating at a temperature higher than the heat deformation temperature of the thermoplastic fiber material while being stretched, followed by shaping, followed by impregnation by introducing a thermosetting matrix resin. Fiber reinforced composite.