JP2010111026A - Method of manufacturing foam molded article using porous material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a foamed molded article having good dimension stability by manufacturing the foamed molded article incorporated with a fiber reinforcing material by irradiation with a microwave, wherein bending strength is excellent and reinforcing effect by a fiber reinforcing material is sufficiently demonstrated by setting forth a fiber reinforcing material around a surface layer of a foamed molded article. <P>SOLUTION: A method of manufacturing the foamed molded article includes a first process of preparing wet porous material, a second process of impregnating a thermosetting resin into the wet porous material, a third process of sealing the porous material 5 impregnated with the thermosetting resin and fiber reinforcing materials 3a, 3b into a molding die, a fourth process of irradiating a microwave from an outside of the molding die so as to foam, cure and mold the thermosetting resin to form a foamed molded article after the third process, and a fifth process of taking out the foamed molded article from the molding die. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a foamed molded product by foaming, curing and molding a thermosetting resin in a mold by irradiating microwaves, and a foamed molded product obtained thereby.

  Phenolic resins or fiber-reinforced phenolic resins are used in various applications such as vehicle members and building materials due to their excellent heat resistance and versatility, and their demand is increasing. As such a structural material, a material superior in lightness, mechanical strength, flame retardancy, heat insulation, durability, etc. is required. As a central material, a sandwich structure is provided in which an outer skin member such as a fiber reinforced plastic sheet, a resin decorative board, a wood veneer, or a plywood is bonded to the surface thereof with an adhesive or the like. Furthermore, there is a demand for the development of materials that make use of design for high added value, and it is also considered to bond fabrics and leathers with excellent design properties to the surface of the molded body.

  However, the foamed phenol resin used as the central material is usually weak in mechanical strength and is brittle. If it is directly bonded to the outer skin member, adhesion failure may occur or the mechanical strength may be reduced due to the difference in properties between the central material and the outer skin member. There was a problem that physical properties deteriorated. In addition, since a separate bonding step is required, the manufacturing process is complicated. Further, when the molded product has a curved surface shape, there is a problem that a high technical force is required for the bonding operation.

  In Patent Document 1, an outer skin layer such as a fiber reinforced plastic layer, a wood veneer, or a resin decorative board is arranged in advance on the inner surface of a mold, and a paste-like resin containing a phenol resin is applied to the inside to tighten the mold. Thereafter, there is described a method of irradiating microwaves to foam and cure the paste resin to form a foamed phenol molded product having a skin layer on the surface.

  In Patent Document 2, a planar fiber reinforcing material is placed in a mold, a phenol resin mixture is poured into the mold, and then the mold is clamped, and the phenol resin mixture is foamed by microwave heating. Is described in which a foamed phenol molded product is integrally formed by infiltrating into a planar fiber reinforcement and curing it together with a foamed layer.

  These methods change the water contained in the resin to water vapor in a very short time by internal heating by microwave irradiation, thereby foaming with water vapor and simultaneously curing the resin with the heat to produce a molded product. Is. The obtained molded article has a porous structure having countless bubbles of about 1 μm, and is a material that is lightweight and excellent in heat insulation.

  The above manufacturing process can be completed in just a few minutes to 10 minutes, and the process proceeds in a very short time compared to the conventional foaming method using a heat conduction method by external heating, enabling foaming molding at low energy and cost. Become. Moreover, since it is a foaming type using water, the material can be made porous without using a foaming agent having environmental problems such as chlorofluorocarbon gas or hydrocarbon gas. Furthermore, even a material having a thickness of 15 cm or more can be molded, and a complex shape can be easily molded.

  The fiber reinforcing material described in Patent Document 2 itself has a high tensile strength, and exhibits a high reinforcing effect by impregnating resin inside. Moreover, a foam molded product having higher rigidity can be obtained by arranging the fiber reinforcement in the surface layer so as to follow the outer shape of the foam molded product. However, since there is no continuity with respect to the thickness direction of the fiber reinforcement, there is a drawback in that when a large bending load is applied to the foamed molded product, it cracks in the horizontal direction and is easily broken.

  In addition, because the internal pressure suddenly rises in the internal heating by microwave irradiation, the fiber reinforcement may meander, or may be molded in a state where it is placed inside instead of the surface layer of the foam molded product, In this case, a sufficient reinforcing effect cannot be exhibited. Furthermore, when manufacturing a molded product having a curved shape, there is also a problem that the fiber reinforcement is easily molded without following the shape of the curved portion of the mold. This problem is particularly likely to occur when using rigid fiber reinforcements such as glass cloth and glass mats. Where the fiber reinforcing material does not follow the shape of the curved surface portion, reinforcement with the reinforcing material is insufficient, so that the fiber reinforcing material is easily broken and cracks are likely to occur on the surface.

Furthermore, the internal pressure at the time of foaming / curing does not increase uniformly inside the mold, but tends to increase non-uniformly. There is also a problem that the deformation causes a problem in the dimensional stability of the foam molded product.
Japanese Patent Laid-Open No. 7-148851 Japanese Patent Laid-Open No. 11-20029

  In view of the above situation, the present invention is superior in bending strength in producing a foam molded product integrated with a fiber reinforcement by irradiating microwaves, and the fiber reinforcement is in the vicinity of the surface layer of the foam molded product. An object of the present invention is to produce a foamed molded article that sufficiently exhibits the reinforcing effect of the fiber reinforcing material and has good dimensional stability.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by impregnating a porous material with a thermosetting resin and integrally molding this with a fiber reinforcing material. It came to complete.

  That is, the present invention includes a first step of preparing a wet porous material, a second step of impregnating the wet porous material with a thermosetting resin, and impregnating the thermosetting resin in a mold. After the third step and the third step of encapsulating the porous material and the fiber reinforcement, by applying microwaves from the outside of the mold, the thermosetting resin is foamed, cured and molded. And a fourth step of forming the foam molded product, and a fifth step of taking out the foam molded product from the mold.

  The present invention is also a foam molded article obtained by the above production method.

  According to the production method of the present invention, in producing a foam molded product integrated with a fiber reinforcement by irradiating microwaves, the bending strength is excellent, and the fiber reinforcement is in the vicinity of the surface layer of the foam molded product. By arranging the foamed molded article, the reinforcing effect of the fiber reinforcement can be sufficiently exerted, and good dimensional stability can be produced.

  Hereinafter, the present invention will be described in detail.

  The manufacturing method according to the present invention includes a first step of preparing a wet porous material, a second step of impregnating the wet porous material with a thermosetting resin, and a thermosetting resin in the mold. After the third step and the third step of encapsulating the porous material impregnated with the fiber reinforcing material, the microwave is irradiated from the outside of the molding die to foam, cure and mold the thermosetting resin. It includes a fourth step of forming a foamed molded product and a fifth step of taking out the foamed molded product from the mold.

  The porous material in the present invention is a flexible material having a large number of pores inside, and can absorb the liquid in such a way that it is substituted for the air in the pores by being immersed in the liquid. Water-absorbing materials can be used. Moreover, since it is calculated | required to have resistance to the high heat at the time of foam molding, the material which has heat resistance is preferable. Specific examples include a sponge, a three-dimensional woven fabric, and a three-dimensional knitted fabric. A sponge is preferred, and among them, a cellulose sponge, which is a 100% natural material produced by combining pulp-derived cellulose with natural fibers such as flax and cotton, is most preferred. This is because the impregnation property of the thermosetting resin is good, the ability to absorb microwaves is high, and the heat resistance and strength are also excellent.

  As the porous material, a material formed into an appropriate shape in consideration of the shape of the desired foamed molded product is used.

  In the first step, a porous material in a wet state is prepared. The porous material in a wet state may be any material as long as the porous material contains water. Water is a component that plays a role as a foaming agent by being heated by microwave irradiation and changing to water vapor. By impregnating the porous material in a wet state, not a dry state, with the thermosetting resin, the porous material can be uniformly impregnated with the thermosetting resin. This is presumably because when the porous material is in a wet state, the resin can easily move into the fibers in the porous material because of the osmotic pressure.

  In order to prepare a porous material in a wet state, the water absorption amount may be adjusted by squeezing water after water is absorbed into the porous material in a dry state. The smaller the amount of water used, the higher the heating rate after microwave irradiation, which is preferable.

  In the second step, the wet porous material prepared in the first step is impregnated with a thermosetting resin.

  As the thermosetting resin, a resin that can be foamed by a gas such as water vapor generated by microwave irradiation and can be cured at an internal temperature at that time can be used. Specifically, liquid resins with a large loss factor such as phenol resin, epoxy resin, vinyl ester resin, urea resin, etc. are mentioned, but phenol resin is preferred because of excellent physical properties of the obtained foamed molded product, In particular, a resol type phenol resin is preferred.

  Along with the thermosetting resin, components necessary for the curing, for example, a curing agent and a curing catalyst are appropriately blended. For example, when a phenol resin is used, it is preferable to use a curing agent (specifically, an acid) dedicated to the phenol resin.

  In addition, a conventionally known foam stabilizer and a foaming agent other than water (for example, chlorofluorocarbon gas or hydrocarbon gas) can be appropriately blended. When a foam stabilizer is blended, the shape of bubbles at the time of foaming is adjusted, the number of closed cells increases, and the bulk specific gravity decreases, thereby improving the heat insulation and mechanical strength. In the present invention, it is not necessary to add a foaming agent, but it is preferable to use a foaming agent when producing a molded article having a small bulk specific gravity.

  In addition, in order to improve the impregnation property of the thermosetting resin (penetration into gaps in the fiber reinforcement), the viscosity of the thermosetting resin is decreased by adding water to the thermosetting resin in advance. It is preferable to keep it. However, the amount of water can be adjusted according to the type and viscosity of the resin. However, if the amount of water is too large, the foaming efficiency tends to decrease. About 20% by weight.

  The above mixture is a mixture of a thermosetting resin and water, a foam stabilizer, and a foaming agent as necessary, and is stirred using an appropriate machine. Finally, a curing agent and a curing catalyst are added and further stirred. Can be prepared.

  When the porous material is impregnated with the thermosetting resin, a roller or the like may be used so that the thermosetting resin uniformly penetrates into the porous material. The excessively impregnated thermosetting resin may be removed by squeezing. The impregnation amount of the thermosetting resin can be appropriately adjusted in consideration of the bulk specific gravity of the final foamed molded product.

  Next, in the third step, the porous material impregnated with the thermosetting resin obtained in the second step and the fiber reinforcing material are enclosed in a mold.

  The fiber reinforcing material used in the present invention has a sheet-like shape, and exhibits a high reinforcing effect by being impregnated with a thermosetting resin through a gap in the fiber. Specifically, glass fibers such as glass mats and glass cloth, natural fibers such as hemp, cotton, and wool, and woven fabrics, knits, nonwoven fabrics, and the like made of synthetic fibers such as polyester fibers and acrylic fibers can be used. Glass fiber is preferred because of its high reinforcing effect. These are cut into an appropriate size and used. In foam molding by an internal heating method using microwave irradiation, an extremely high internal pressure is generated, so that the thermosetting resin impregnated in the porous material penetrates into the gaps of the fiber reinforcing agent and is cured there. A molded product having high strength can be obtained. The fiber reinforcing material is preferably a material having a coarse density so that the resin can be easily impregnated.

  The mold used in the present invention is preferably made of a material that does not reflect microwaves and is difficult to absorb and transmit. Further, a material having strength and elastic modulus that can withstand high internal pressure during foaming / curing is preferable. Specifically, a mold made of FRP (fiber reinforced plastic) is preferable. Metals cannot be used because they reflect microwaves. Further, in order to pass a gas such as water vapor generated by microwave irradiation, the mold is provided with a vent.

  When the mold has the desired shape of the molded product, foaming and curing can be performed by laying a release film inside the mold. In addition, when using a mold that is large enough to contain a molded product, a silicone rubber mold having the shape of the molded product is placed inside the mold and foamed and molded. It can also be done. Since silicone rubber is excellent in elasticity, it is possible to manufacture a molded product that faithfully reproduces the shape of a very complicated and fine curved surface shape such as a grain pattern. The silicone rubber mold can be easily manufactured by using a commercially available curing silicone resin or a curing agent thereof, and curing the resin in an appropriate mold.

  In the molding die, the porous material impregnated with the thermosetting resin and the fiber reinforcing material are arranged so as to be laminated, and then the molding die is clamped.

  A specific procedure in the third step will be described with reference to FIG.

  First, in the FRP mold 1, a release film (not shown) is laid or a silicone rubber mold (not shown) is placed, and then the lower fiber reinforcement 3a is placed. The porous material 5 impregnated with it and impregnated with the thermosetting resin is arranged, and further laminated thereon, and another fiber reinforcing material 3b is arranged. In FIG. 1, the fiber reinforcements 3 are arranged one by one up and down, but may be arranged only on one side.

  Although FIG. 1 illustrates the case where a plate-shaped molded product is molded, a molded product having a curved shape can be manufactured by placing a silicone rubber mold having a curved shape inside. It is.

  After clamping the mold 1 so as to withstand high internal pressure due to rapid water vapor generation, by irradiating microwaves from the outside of the mold, foaming / curing and molding the thermosetting resin, A fourth step of forming the foam molded product is performed. That is, the microwave is irradiated to the whole mold 1 for several minutes to 10 minutes using a microwave irradiation apparatus. During this short period of time, foaming / curing and molding of the thermosetting resin, penetration and curing of the thermosetting resin into the gaps of the fiber reinforcement, and adhesion between the porous material and the fiber reinforcement are simultaneously performed. Will progress.

  When irradiating the mold with the microwave, it is radiated as uniformly as possible. Generally, the frequency of microwaves used industrially is 2450 MHz, and the wavelength is about 12 cm. Therefore, there is a possibility of causing uneven heating due to the wavelength. Therefore, the object is irradiated as uniformly as possible by rotating the object or rotating the metal fan for diffusing the microwave.

  As the output power of the microwave increases, the foaming / curing reaction proceeds faster, so that molding in a short time becomes possible. On the contrary, since it becomes difficult to control foaming, it may be adjusted in association with the irradiation time. Further, the adjustment is performed in consideration of the shape and size of the molded product, the type of the thermosetting resin, the amount of the curing agent, the type of the reinforcing fiber material, and the like.

  After irradiation is performed as necessary after irradiation, the obtained molded product is taken out of the mold. Even when a silicone rubber mold is used without using a release film, the mold can be easily released.

  In the obtained molded product, the center material is a foamed cured product composed of a porous material and a cured thermosetting resin, and a fiber reinforcing material impregnated with the cured thermosetting resin is bonded to the cured product. Has the structure. In the present invention, since a high internal pressure is generated with foaming / curing, the stretchable fiber reinforcing material is firmly and evenly adhered even to a molded product having a curved shape.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

(Example 1 and Comparative Example 1)
The following materials were mixed to prepare a thermosetting resin mixture.
・ Resol type phenol resin: BRL-191 (viscosity (25 ° C.): 2750-3750 mPa · s, non-volatile content: 76-80 wt%, approximately 15 wt% of volatile content is water, remaining as Showa High Polymer Co., Ltd. Is free phenol)
-Phenolic resin curing agent: Resinol PS-63 manufactured by Daiichi Kogyo Seiyaku Co., Ltd. (Phenolsulfonic acid is about 63% by weight, free sulfuric acid is 1% by weight or less, free phenol is 5% by weight, and the rest is water): 8 % By weight (The amount of each component is shown as a weight ratio to the phenol resin. The same applies hereinafter.)
・ Bamboo powder: 2% by weight
-Foam stabilizer: Flotia K-54 manufactured by Daiichi Kogyo Seiyaku Co., Ltd. (a blend of castor oil alkylene oxide adduct and bisphenol A formaldehyde condensate): 2% by weight
-Foaming agent: diethyl ether (boiling point 35 ° C.): 3% by weight
The amount of resin used was adjusted so that the bulk specific gravity of the foamed molded product was within the range of 400 to 450 kg / m ³ .

As the fiber reinforcement, a continuous mat CSM (weight per unit: 300 g / m ² ) manufactured by Asahi Fiber Glass Co., Ltd., which is a glass mat, was used, and two sheets were used so that they could be laminated on the top and bottom of the molded product.

  As the porous material, cellulose sponge (thickness: about 7 mm) manufactured by Toray Fine Chemical Co., Ltd. was used.

  As the mold, an FRP mold formed by laminating a plurality of glass fabrics and an unsaturated polyester resin was used.

  As the microwave heating device, a household microwave oven RO-BV6 manufactured by Mitsubishi Electric Corporation was used.

  Microwave irradiation was performed at 200 W for 5 minutes. After the microwave irradiation, after-curing was performed by maintaining at 60 ° C. for 3 hours. What was fully cooled was subjected to a bending test.

  In Example 1, in accordance with the above-described procedure, a fiber reinforcing material is disposed in the vicinity of the surface layers on both sides, and the inner member is a flat foam molded product (thickness: about 1 cm) made of cellulose sponge and a cured phenol resin. ) Was manufactured.

In Comparative Example 1, the procedure of Example 1 was repeated without using a cellulose sponge to produce a flat foam-molded product (thickness: about 1 cm).
(1) Bending strength test A three-point bending test was performed under the following conditions to calculate the maximum bending strength.
1. Testing machine: Material testing machine (A & D Tensilon RTF1325)
2. 2. Deflection speed: 5 mm / min Distance between fulcrums: 100mm
4). Test sample: thickness t = 8-12 mm, width b = 24.5-25.5 mm, length L = 270-275 mm
5). Formula for calculating maximum bending strength: Maximum bending strength = 3 * Pmax (maximum bending load) * L / 2 * b * t ²
Several test samples were prepared and tested, and the average values are shown in the following table.

  The results of measuring the bending strength and bulk specific gravity are shown in Table 1.

  From the results in Table 1, it can be seen that the bending strength was improved by about 80% by using cellulose sponge.

  Furthermore, when the external appearance after the bending test of the foam molded article of Example 1 was observed, cracks were observed only in the longitudinal direction (thickness direction) at the center of the sample. On the other hand, in the foam molded product of Comparative Example 1, a large crack was observed in the horizontal direction in the material. When the above-mentioned three-point bending is performed, the maximum bending moment is applied to the central portion, which is the load point, but in the foamed molded product without the cellulose sponge of Comparative Example 1, the cracks generated at the central portion greatly expand in the horizontal direction. It is thought.

  A photograph (150 magnifications) of the inside of the cellulose sponge that has absorbed water before impregnating the resin and observed with a microscope is shown in FIG. 2, and the inside of the foamed molded product of Example 1 is microscope (500 times magnification). FIG. 3 shows a photograph taken by observation. In this foam-molded product, the resin is impregnated into the inside of the small cell in the cellulose sponge and the wall surface of the cell to express high strength, and the cell in the cellulose sponge is connected to prevent the progress of cracks. It is thought that bending strength was obtained.

  FIG. 4 shows the relationship between the amount of deflection and the bending strength when the foam molded products of Example 1 and Comparative Example 1 were subjected to a bending test. In both Example 1 and Comparative Example 1, a decrease in load is observed when the amount of deflection reaches about 3 mm. In Comparative Example 1, the amount of decrease in load is large, and cracks spread all at once, leading to destruction. It is done. On the other hand, in Example 1, although the crack occurred, it did not spread and an increase in the load was observed even after the load once decreased.

(2) Stability of the fiber reinforcement in the foam molded product When the cross sections of the foam molded products of Example 1 and Comparative Example 1 were confirmed, in Example 1, the glass mat was placed on the surface layer of the molded product on the plane. And was impregnated with resin. Therefore, in addition to the effect of preventing crack growth due to cell connection in the cellulose sponge, a high reinforcing effect can be exhibited. On the other hand, in Comparative Example 1, the glass mat meanders and is disposed inside the molded product. For this reason, the reinforcing effect is not sufficient.

(3) Dimensional Stability of Foam Molded Product The thicknesses of the foam molded products of Example 1 and Comparative Example 1 were measured, and the relationship between the distance from the center of the molded product and the difference from the average thickness was shown in FIG. It was shown to. These foam-molded products were molded so as to have a uniform thickness, but in Comparative Example 1, there was a tendency that the central portion was thicker and thinner as it approached both ends. On the other hand, in Example 1, it turns out that there is little variation from an average value and the dimension (thickness) is stabilized as a whole. That is, it was found that the use of cellulose sponge improves the dimensional stability. This is probably because the cellulose sponge contributes to uniform internal pressure generated by microwave irradiation.

The conceptual diagram which shows the state which has arrange | positioned the material before microwave irradiation in the type | mold by the shaping | molding method of this invention Magnified photo of the inside of a cellulose sponge that has absorbed water before impregnation with resin Photomicrograph in which the inside of the foam molded product of Example 1 was enlarged The graph which shows the relationship between the bending amount at the time of using the foaming molded article of Example 1 and Comparative Example 1 for a bending test, and bending strength. The graph which shows the relationship between the distance from the center part in the foaming molded product of Example 1 and Comparative Example 1, and the difference from the average value of thickness.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 FRP mold 3a, 3b Fiber reinforcement 5 Porous material impregnated with thermosetting resin

Claims (5)

A first step of preparing a wet porous material;
A second step of impregnating the wet porous material with a thermosetting resin;
A third step of enclosing a porous material impregnated with a thermosetting resin and a fiber reinforcing material in a mold;
After the third step, a fourth step of forming a foamed molded product by irradiating microwaves from the outside of the mold and performing foaming / curing and molding of the thermosetting resin, and
A method for producing a foam molded product, comprising a fifth step of taking out the foam molded product from the mold.   The manufacturing method according to claim 1, wherein the porous material is at least one selected from the group consisting of a sponge material, a three-dimensional woven fabric, and a three-dimensional knitted fabric.   The manufacturing method according to claim 1, wherein the thermosetting resin is a phenol resin.   The manufacturing method according to claim 1, wherein the fiber reinforcing material is glass fiber.   A foam-molded article obtained by the production method according to claim 1.