JPH03182309A - Heating of fiber reinforced composite material - Google Patents

Abstract

PURPOSE:To heat a block-shaped preform material uniformly in a short period of time and manufacture an FRP molded form having a high strength efficiently by a method wherein a dielectric loss improving agent is blended in the block-shaped preform material of a composite material, in which reinforcing fibers are blended into a plastic material, at a rate of a specified weight % to effect microwave heating. CONSTITUTION:Dielectric loss improving agent is blended into a block-shaped preform material, in which glass fibers, carbon fibers or the like are blended into a plastic material as reinforcing fibers. The dielectric loss improving agent is a substance having a high dielectric loss angle or a high dielectric loss factor of itself and shows a high dielectric loss factor while the same agent is silicon carbide, carbon black, various rubber materials and the like, for example. The blending amount of the dielectric loss improving agent is 0.1-4.5weight% with respect to the total weight of the block- shaped preform material. The block-shaped preform material 1a, supplied into an iron tube 2a, is inserted into a heating furnace 3 and is heated by microwave introduced from the direction of an arrow sign C in a diagram whereby the microwave is absorbed into the dielectric loss improving agent and internal heating progresses thereby increasing the temperature of the whole of the block-shaped preform material uniformly in a short period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for efficiently heating a fiber-reinforced composite material formed into a lump by microwave heating.

[Prior art] As one of the FRP molding methods, pre-molded material (
It is known to use a preformed material (herein referred to as a preformed material) and further mold it into a desired final shape by compression molding or other methods.

In manufacturing such preforming materials, the main components are plastic materials and reinforcing fibers, and if necessary, a curing agent (if a thermosetting resin is used as the plastic material), a filler, a coloring agent, a binder, Preforming is performed by blending the lot number type additives, etc., and heating is performed at the final stage of preforming to prepare for main molding.

On the other hand, the form of the preforming material is sheet-like or lump-like (
(including bulk or block-shaped ones), but thin sheet-shaped ones are preferable in terms of achieving uniform heating with less temperature gradient, and the idea is to uniformly heat bulk preformed material. was unknown.

However, sheet-like materials are expensive to manufacture and require complicated lamination molding to form the final shape.

It is known that prior to the preforming step, shearing force is applied to the raw materials by heating them while kneading, but this method has the problem that the reinforcing fibers are cut and the reinforcing effect is insufficient. occurs.

[Problem to be Solved by the Invention J The present invention has been made in view of the above-mentioned circumstances, and aims to provide a method that can efficiently and uniformly heat even bulk preformed materials. It is something to do.

[Means for Solving the Problems] The present invention includes a dielectric loss improver in a proportion of 0.1 to 4.5% by weight in a bulk preformed material of a composite material made by blending reinforcing fibers with a plastic material. The main feature of this method is that it uses microwave heating using microwave irradiation as a heating means.

[Function] The present inventors came up with the idea of adopting microwave heating as a uniform heating means for the above-mentioned bulk preformed material, and conducted a comparative study between external heating using an electric heater and external heating using infrared rays. According to this, in the latter two cases, heating is performed only from the outside, so in order to achieve internal specific heating, heating must be started at a relatively low temperature and gradually raised over a long period of time, and that bulk preforming is required. It was found that in order to prevent temperature gradients from occurring inside the material, it was necessary to ripen it for a very long time.

In contrast, microwave heating relies heavily on the dielectric loss of the non-heated body, and even if microwave heating is suddenly applied to a preformed material using conventional general-purpose materials, the plastic material itself and the material blended into it will be damaged. It has been found that there is a problem in that the heating effect is affected by the electrical properties of the reinforcing fibers and other various compounded materials, and that it lacks versatility. Furthermore, even if the material properties happen to match well and the effect of microwave heating appears, it does not mean that the optimal material selection has taken the microwave heating effect into consideration. It is recommended that improvement measures be taken to further improve performance.

Therefore, in the present invention, with the aim of always exhibiting a stable microwave heating effect regardless of the raw material used for manufacturing the bulk preform material, various methods have been developed for the purpose of increasing the dielectric loss of the bulk preform material. After considering additives, we came to the conclusion that a dielectric loss improver should be added. A dielectric loss improver is a substance that has its own dielectric properties or a high dielectric constant, and thereby exhibits a high dielectric loss factor. Typical examples include silicon carbide, silicon carbide, Examples include carbon black, various rubber materials, marble, soda glass water, ethylene glycol, and glycerin.

The blending amount of the dielectric loss improver must be 0.1% by weight or more based on the total weight of the bulk preform material, thereby increasing the dielectric loss of the bulk preform material to the extent that the microwave heating effect is sufficiently exhibited. becomes possible. But 4
．． If the amount exceeds 5% by weight, the strength of the bulk preformed material will decrease, so in the present invention, the content is 0.1 to 4.5% by weight.Other raw materials used in the present invention are FRP.
You can choose from a wide variety of general-purpose materials as long as it does not go against the purpose of manufacturing.For example, plastic materials can be thermoplastic or thermosetting, and reinforcing fibers can be selected from a wide variety of materials, including glass fiber and carbon fiber. fibers can be used. As other additives, binders, curing agents, plasticizers, fillers, antioxidants, pigments, etc. may be blended as necessary, and all conventionally known additives can be blended.

When microwaves (usually 300 MHz to 30 GHz) are irradiated to the bulk preform material manufactured using such raw materials, the microwaves are absorbed by the dielectric loss improver and internal heating progresses, causing the bulk preform to proceed. It becomes possible to achieve the desired purpose by raising the temperature of the entire material uniformly and within a short time.

[Example] FIG. 1 is an overall conceptual diagram showing an apparatus for carrying out the present invention,
FIG. 2 is a sectional view of the main part, in which iron pipes 2a and 2b are connected to a heating furnace 3 having a built-in quartz tube passage 4 and a fan 6, and a waveguide 5 is connected to the upper part. The bulk preformed material 1a fed into the iron pipe 2a in the direction of arrow A enters the heating furnace 3 and is heated by microwaves introduced from the direction of arrow C.

The microwaves are diffusely reflected by the fan 6 and irradiated onto the preformed material 1a from all angles. When the bulk preformed material 1a is rotated, vibrated, or moved up and down, the surface receiving the microwave irradiation changes and more uniform heating is achieved.

At this time, since the quartz tube passage 4 does not absorb microwaves, the microwaves are directly irradiated onto the bulk preformed material. It is recommended that the inside of the heating furnace 3 be replaced with an inert gas such as N2 to prevent oxidative deterioration of various compounds including plastic materials.

As an experiment, carbon black was added as a dielectric loss improver to a composite material consisting of polypropylene powder and glass fiber at a ratio of 0.51i%, and 200rAII
A cylindrical preformed material of I x 200 mm (I amount: 3 kg) was produced and irradiated with microwaves of 2450 MHz x 8 KW. At this time, the pre-forming material can be heated to 220 mm in just 3 minutes.
The temperature distribution inside the preformed material showed excellent uniformity of ±5°C. Heated preformed material 1
b is carried out in the direction of arrow B through the iron pipe 2b, and then molded by a compression molding machine. The mechanical strength of the final molded product showed a higher value than that of a molded product using a comparative amount of kneaded and heated material.

In addition, in this microwave heating, the heating time (unit: 2 minutes)
When the relationship between the temperature and the temperature at the center of the bulk preformed material at that time was determined, the results shown in FIG. 3 were obtained. As can be seen in Figure 3, a positive linear function is established between the heating time and the core temperature, indicating that the present invention provides a heating method that is extremely stable and has good controllability. I understand. Therefore, when adopting a method of heating a lump preformed material using a device such as that shown in Fig. 1, for example, the heating time obtained by calculating from the reached temperature is set as the furnace passage time, and the arrow of each molded body All that is required is to set the moving speed in the A and B directions.

Fig. 4 is a plan view of the microwave heating device designed based on the concept of Fig. 1.2, and Fig. 5 is a side view. In addition to providing a quartz tube passage 4, there are 10 tubes on the entrance side (2 tiers above and below, 5 tubes in each tier)
A charging air cylinder 11 and one in each charging header 10.
Arranging cylinders 12 for arranging 0 pieces of bulk preforming material are provided in each of the upper and lower two stages. On the other hand, on the exit side, there are provided two horizontal discharge cylinders 21 and two longitudinal discharge cylinders 22, one each in upper and lower stages, for sequentially discharging the bulk preformed material discharged and inserted into the outlet header 20. Therefore, the ten bulk preforms inserted into the inlet header 10 by the arranging cylinder 12 are inserted in groups of ten into the quartz tube passage 4 by the charging cylinder 11, and then passed through the waveguide 5. It is heated by being irradiated with microwaves. Thereafter, this operation is repeated to sequentially charge the subsequent lumpy preformed material, but the preceding lumpy preformed material, which is moved to the left in the drawing by this charging, is subjected to microwave heating for a predetermined period of time during this transition process. When the desired temperature is reached, one group is discharged into the outlet header 20 at once. Then, until the next discharge is carried out, it is conveyed in the direction of arrow Z by the time difference cooperative play of the horizontal cylinder 21 and the longitudinal cylinder 22. When one group of lump preformed material is discharged and conveyed in this way, it is arranged A new group of 10 bulk preforms is charged from the right side of the figure by the time-lag coordinated play of the loading cylinder 12 and the charging cylinder 11, and their extrusion force extrudes the most advanced bulk preform material on the left. Ru. By repeating this operation, the bulk preformed material is heated continuously.

[Effects of the Invention] Since the present invention is configured as described above, the bulk preformed material containing the plastic material and reinforcing fibers is uniformly heated in a short time, which prevents the reinforcing fibers from breaking. However, it has become possible to manufacture high-strength FRP shape-retaining bodies at a high rate.

4. I-JJIL explanation of the drawings Fig. 1 is an explanatory diagram conceptually showing a heating device for carrying out the heating method of the present invention, Fig. 2 is its cross-sectional view, and Fig. 3 shows the heating time and reach. A graph showing the temperature relationship, FIG. 4 is an explanatory plan view showing a specific example of the heating device, and FIG. 5 is an explanatory side view.

1...Bulk preforming material 3...Heating furnace 4...Quartz tube passage 5...Waveguide X Thermal darkness (child) Fig. 4

Claims (1)

[Claims] In a method of heating a bulk preformed material of a composite material made of a plastic material mixed with reinforcing fibers, a dielectric loss improver is blended into the bulk preformed material at a ratio of 0.1 to 4.5% by weight. A heating method for a fiber-reinforced composite material, characterized in that microwave heating is performed by irradiating microwaves.