JP3148298B2 - Manufacturing method of lightweight composite molding - Google Patents

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 lightweight fiber-reinforced resin composite molding containing a porous core. More specifically, it relates to an improved method for producing the above-mentioned composite molded article using a multi-layered fibrous web containing special particles.

[0002]

2. Description of the Related Art Porous resin moldings such as foams and syntactic foams are used as lightweight materials, as they are or as sandwich materials combined with other materials, as aerospace materials, vehicle structural materials, sporting goods, etc. Are widely used in the field.

[0003] Such a porous resin molded product is usually molded (foam molding) using a foamable resin. Are roughly classified into the method, a method of molding (1) heating or a resin or its raw material is foamed and depressurizing placed in a mold, (2)
There is a method in which a specific one of these resins is foam-molded into particles (primary foam), which is then placed in a mold and further expanded (secondary foam).

[0004] As a method of making this into a lightweight structure such as a sandwich material, a foamed molded product is used as a skin material, and a fiber-reinforced resin molded product (hereinafter referred to as F if necessary) is molded in advance.
RP), foam molding is covered with a prepreg or the like, or foaming is performed by injecting a foaming resin into a previously formed hollow outer shell.

[0005] In recent years, as a method of improving these methods, a method of using an internal pressure molding using foaming / expansion or a thermally expandable molded product as a material of a porous body has been proposed (for example, JP-A-1-255530, JP-A-63-162207
issue). As a further improvement of these methods, the present inventors have previously proposed a novel method of forming a sandwich material using thermally expandable resin particles and a liquid curable resin together with a reinforcing fiber material (European Patent Published application No. 0407996
No., Japanese Patent Publication No. Hei 7-12613 ).

According to this method, there is an advantage that a sandwich material having a porous core (syntactic foam core) can be formed in one step, but at the time of heat molding, the resin particles which have been expanded and reduced in weight are raised. It is easy to be unevenly distributed,
In addition, when the layer to be the porous core is thick, especially when foaming starts in the middle of molding, heat transfer is poor due to the heat insulating effect of the foamed and expanded particles, making it difficult to heat and radiate heat. There's a problem.

[0007] From another viewpoint, in the molded product using the foam core or the syntactic core, the strength and adhesiveness of the core generally affect the physical properties of the molded product, and the problem may remain depending on the shape of the molded product. Are known. (For example, Japanese Patent Laid-Open No. 1-1
No. 10943, No. 1-1110944, No. 2-10
No. 4226).

[0008]

SUMMARY OF THE INVENTION The present invention solves various problems in the molding method using the thermally expandable resin particles and the like previously proposed by the present inventors. It is an object of the present invention to provide a method for obtaining a molded article having good physical properties, which is difficult, can prevent unnecessary uneven distribution of particles that expand and expand, and has a reinforced porous core. More specifically, when forming a syntactic foam or a sandwich material containing the same using hollow particles and particles capable of being heat-expanded and expanded, it is relatively easy to generate heat transfer problems even with a thick molded product. can be molded, it can suppress the foam floating of the particles, consisting of syntactic foam at the same time co-in
It is an object of the present invention to provide a method for molding a novel lightweight composite molded article whose part is fiber reinforced.

As already mentioned, it is well known to form lightweight molded articles using hollow particles or particles that expand and expand upon heating. However, hollow particles or particles that have been expanded and reduced in weight are likely to float during molding and are often not evenly distributed or settled at the intended position. They also hinder heat transfer during heat molding , making it difficult and sometimes impossible to control the temperature during molding.

The present invention is intended to solve such a problem. In order to solve the former problem , it is an object of the present invention to determine the position of the foamed particles by laminating near the filling and inhibiting the movement of the particles by the web. and for the latter problem is to attempt to localize the site of foamed and expanded to (close to the mold surface) molding surface. At the same time, the syntactic foam core formed by short fibers, fibrils, or the like is effectively reinforced.

[0011]

SUMMARY OF THE INVENTION According to the present invention, the above-mentioned object is achieved in that both outer layers mainly contain expandable particles (a) which can be expanded and expanded by heating, and the intermediate layer contains substantially non-expandable particles. By impregnating or injecting a resin into a substantially multilayered fibrous web (W) mainly containing expandable hollow particles (b) and heating the resin, the expandable particles (a) in the web (W) are heated. ) Is formed by foaming and expanding the compound.

The fibrous web (W) having a substantially multilayer structure used in the method of the present invention is mainly composed of expandable particles (a).
Hints hollow particles (b) becomes from the outer layer (A) containing little, predominantly hollow particles (b) a wherein expandable particles (a) does not include almost intermediate layer (B), and these are the thickness direction To
(A) / (B) / (A) .

That is, the expandable particles (a) are unevenly distributed in the outer layer (front and back) of the fibrous web (W), and the hollow particles (b) are unevenly distributed in the intermediate layer (core). The type, amount, and the like of the intrinsic particles change in the thickness direction of (W). The state of this change may be discontinuous or continuous.

The fibrous web (W) may be any material that can contain the above-mentioned particles (a) and (b) substantially in layers, and is understood to include a nonwoven fabric and a synthetic paper-like material. Should be. Such a fibrous web (W) can be manufactured, for example, by the following method.

[0015] (i) the method according to the wet web 2 sheets of the multilayer: using the expandable particles as fine particles (a) and hollow particles (b), these were dispersed in water together with short fibers or fibrils slurry, wet method And the lower layer (filter media side)
There are mainly expandable particles (a) having a large specific gravity in the upper layer, and hollow particles (b) mainly having a small specific gravity in the upper layer (surface side).
A fibrous web (synthetic paper) in which is present is produced, and two fibrous webs are put on top of each other (including hollow particles (b)).
(Layer) is laminated back to back so that the layer is located on the inner side, to obtain the above fibrous web (W).

(Ii) A method of laminating three dry webs: By a dry method, a fibrous web (A) containing expandable particles (a) and a fibrous web (B) containing hollow particles (b) are Each of these fibrous webs is manufactured separately.
(A) Two sheets and a fibrous web (B), (A) / (B)
/ (A) are laminated in this order to obtain the above fibrous web (W).

As the expandable particles (a) constituting the fibrous web (W), at least 5% or more, preferably 10% or more, more preferably 2% or more by heating during molding.
Particles having a volume expansion of 0% or more are used, and foamable particles are particularly preferably used.

Examples of the expandable particles include polymer particles mainly composed of polyvinylidene chloride, polyacrylonitrile, polyphenylene oxide and the like containing hydrocarbons and halogen compounds. "EXPANCEL" of Pancel, "Slens Beads" of Sekisui Plastics Co., Ltd., which comprises polystyrene and a foaming agent, and the like. A pulverized product of a resin containing an organic or inorganic foaming agent (for example, powder of “Polythrene” manufactured by Kyowa Kasei Co., Ltd. obtained by adding a foaming agent to an ABS resin) may be used.

On the other hand, substantially non-expandable hollow particles (b)
As light-weight particles containing one or many air bubbles therein, those which do not substantially cause volume expansion by heating during molding are used.

Examples of such hollow particles (b) include inorganic hollow particles such as hollow glass beads and silica beads, and polymer particles mainly containing polyvinylidene chloride and the like, and particles containing hydrocarbons and halogen compounds are foamed. Expanded particles (for example, “Expancel DE” manufactured by Expancel, etc.), particles containing fine bubbles (for example, shirasu balloon), or foam-like fine particles of polyurethane, polyolefin, or the like can be used.

Short fibers or fibrils are usually used as a fibrous material to be used for web production together with these particles. The short fibers or fibrils to be used as the web include polyester, polyamide, especially aramid, polyacrylonitrile, polyolefin, and the like, and natural fibers, etc., and so-called polymerized fibrils (fibrils are obtained during polymerization). ), Those made of polyolefin, especially polyethylene, aramid, especially polyparaphenylene terephthalamide. Of course, these mixtures may be used.

The short fibers used in the method of the present invention are ordinary short fibers having a length and a diameter suitable for forming a web. The appropriate length and diameter vary depending on the web forming method to be employed, but usually, the diameter is 1 to 50 μm, particularly 4 to 50 μm.
It is preferably about 20 μm. The fiber length is preferably 1 to 50 mm, particularly preferably 5 to 20 mm.

The fibrils used in the method of the present invention are:
Branched short fibers, beaten and split fibers, and fine film-like materials are also included. These are, for example,
The method described in Japanese Patent Application No. 1-42004 or U.S. Pat. No. 4,511,623 is preferred.
And fibrils according to the method of JP-A-37-5732 and natural pulp-like particles are also used.

When using these fibrils, it is preferable to employ a wet method. The fibril has a beating degree (freeness) of 50 ° SR or less, preferably 30 ° SR or less based on the Shopper-Rigler method. Those having a higher freeness are often difficult to handle as raw materials for the method of the present invention. In the wet method, short fibers and fibrils can be used in combination.

In the method of the present invention, using these raw materials,
Preferably, the web is produced by a wet method. A typical example of the wet method is a slurry method. In this method, each raw material is dispersed in water to make a dilute slurry, and then filtered and precipitated in a papermaking manner to form a web. The expansive particles (a) and the hollow particles (b) are suitably added during slurrying. When a web is formed by sedimentation filtration from a slurry in which these are mixed, the expandable particles (a) having a large specific gravity settle before the hollow particles (b), and the hollow particles (b) having a small specific gravity are formed.
These form a substantially stratified web with the short fibers or fibrils as they later precipitate . In the web thus obtained, the expandable particles (a) are unevenly distributed in the lower layer, and the hollow particles (b) are unevenly distributed in the upper layer. Therefore, when the two webs are stacked back-to-back so that the upper layers are in contact with each other, the above-described state is obtained. It becomes a fibrous web (W) having a multilayer structure.

The lamination may be performed at any stage after the web is manufactured by the wet method.
It may be performed when each web is put into a mold during molding.

On the other hand, in the case of producing a web by a dry method, usually, fibrils are not used, but short fibers are used to form a web by means such as a card or land webber. Needle punching or the like may be further performed on this.

At this time, a web (A) containing the expandable particles (a) and a web (B) containing the hollow particles (b) are separately manufactured, and the web (A) is interposed between the two webs (A). When the web (B) is sandwiched and laminated as (A) / (B) / (A), the above-mentioned fibrous web (W) is obtained. The lamination in this case may be performed at any stage, for example, may be performed at the time of needle punching, or may be performed in a mold at the time of molding.

In the method of the present invention, a fibrous web (W) having a multilayer structure as described above is impregnated with a resin and is heat-molded.
At this time, it is preferable to mold using a mold. When a mold is used, the fibrous web (W) may be impregnated with a resin in advance, or after the fibrous web (W) is put in the mold, the resin may be injected into the mold. .

In any case, if the expandable particles (a) in the fibrous web (W) are heated to a temperature equal to or higher than the expansion start temperature of the expandable particles (a) during heat molding, the expandable particles (a) in the fibrous web (W) expand in volume, and And the resin penetrates into various parts including the fibrous web (W) by the pressure, so-called internal pressure molding is performed. Thus, a resin molded article containing a lightweight syntactic foam reinforced with short fibers and / or fibrils is obtained.

In the present invention, at the time of molding, a sheet-like reinforcing fiber material (R) such as a reinforcing fiber woven fabric or prepreg can be used together with the above fibrous web (W), and it is more preferable. For example, if a sheet-like reinforcing fiber material (R) is laminated on one side or both sides of a fibrous web (W) and placed in a mold, and molded in the same manner, a syntactic foam reinforced with short fibers and / or fibrids With the core as the core, F
A good sandwich material having RP as a surface layer can be integrally formed.

The sheet-like reinforcing fiber material (R) used in combination with the fibrous web (W) at the time of molding includes polyesters, especially polyarylate fibers, polyamides, especially aramid fibers, polyacrylonitrile fibers, and polyolefins, especially fibers called high-polymerized polyethylene. Synthetic fiber, cotton, etc.
A woven fabric, a knitted fabric, a web, a nonwoven fabric, or the like of a natural fiber such as hemp, an inorganic fiber such as a glass fiber, a carbon fiber, an alumina fiber, and a silicon carbide fiber, and a mixture thereof are used. It is particularly preferable that these have excellent elastic modulus and strength.

The resin used for molding can be either a thermosetting resin or a thermoplastic resin, but in many cases, an uncured thermosetting resin is preferable. Examples of such a thermosetting resin include an epoxy resin, an unsaturated polyester resin, a vinyl ester resin, a phenol resin, a curable polyurethane resin, and a curable cycloolefin resin (for example, those known under the trademark “METON”). Can be

The term "resin" as used herein has a broad meaning including raw materials and precursors that are converted into resin by a reaction during molding, and includes reactive monomers and the like. Further, the "mold" here is not limited to a metal mold, and may be a molding mold made of resin, ceramics, wood, or the like. The mold is preferably a closed mold, but a non-closed mold can also be used.

In the method of the present invention, the above-mentioned fibrous web (W) having a multilayer structure is impregnated with an uncured resin in advance to form an intermediate material, which is then formed into a sheet-like reinforcing fiber material such as glass cloth.
It is also possible to adopt a method in which the resin contained in the intermediate material is permeated into the reinforcing fiber material while the particles in the intermediate material are heated and foamed, and molded at a stretch, while being placed in a mold with (R) and the like.

For example, a glass cloth impregnated with a soft resin (for example, an uncured unsaturated polyester resin) is adhered to the inner surface of a mold, the above-mentioned intermediate material is laminated thereon, and then the resin-impregnated glass cloth is laminated. Alternatively, a method may be used in which the mold is closed, heated, and cured by repeating the above process. In this case, the intermediate material and the glass cloth may be laminated and placed in a mold, and then resin may be injected into the mold and heat-molded.

At this time, a non-woven fabric with a small opening that allows the liquefied resin to pass through but does not allow particles to pass between the fibrous web (W) and the sheet-like reinforcing fiber material (R) can be used. In this way, a molded article having particularly good surface properties and appearance without particles near the surface of the molded article can be obtained.

[0038]

According to the method of the present invention as described above, since the expandable particles (a) confined by fibers or fibrils are present only in the portion near the surface layer of the molded product, even when the molded product is thick, it is heated during molding. Thereby, the particles expand and expand satisfactorily, and form a lightweight syntactic foam in combination with the hollow particles (b) at the center. Thus, it is relatively easy and inexpensive to obtain light-weight structural materials reinforced with short fibers and fibrils, especially thick lightweight structural materials with a sandwich structure having a syntactic foam core reinforced with short fibers and fibrils. I can do it. In addition, when performing die molding, a kind of internal pressure molding can be performed, and when the above fibrous web (W) is made into an intermediate material, when the sheet-like reinforcing fiber material is added to the intermediate material, the intermediate material is formed. The resin can be permeated into the reinforcing fiber material and molded at once.

Since the molded product obtained by the method of the present invention is excellent in lightness and excellent in mechanical properties and appearance, it can be effectively used in the fields of various structural materials, parts, sports goods and the like.

[0040]

Next, the present invention will be described in detail with reference to examples. These are for explanation of the present invention and do not limit the present invention. In the following examples, “parts” means “parts by weight” unless otherwise specified.

Example 1 A mold was made from two aluminum plates and “Teflon”.
A "Teflon" spacer is sandwiched between two aluminum plates, approximately 180 mm x 200 mm, 3 mm thick
(Depending on the spacer thickness). A nozzle was provided on one side of the mold.

On the other hand, a polymetaphenylene isophthalamide-based fiber (“CONEX” manufactured by Teijin Limited) was 20 mm thick.
A card web of 100 g / m ² was prepared using short fibers cut into a long length.

On this card web, "Microsphere F-" manufactured by Matsumoto Yushi Seiyaku Co., Ltd. was added at a rate of 100 g / m ^2.
50D "was evenly sprayed, and the above card web was overlaid and needle punched to obtain a web A. Similarly, a glass balloon M-28 manufactured by Asahi Glass Co., Ltd. was uniformly sprayed on the card web at a rate of 70 g / m ² , and the card web was overlaid and needle punched to obtain a web B. Two pieces of this web A are slightly smaller than the mold,
One web B was cut. Each of the cut webs was immersed in a mixed resin composed of 100 parts of an epoxy resin “Epicoat 807” and 31 parts of “Epomate YLH006” made of an oiled shell, and the mixed resin was sufficiently impregnated.

Further, a glass cloth (MS253-1040-2NT-10FS manufactured by Asahi Fiberglass Co., Ltd .;
00g / m ² ), and two pieces of this glass cloth were similarly cut slightly smaller than the above-mentioned mold. This glass cloth was also immersed in the above mixed resin to sufficiently impregnate the mixed resin.

Two webs A impregnated with a resin are sandwiched between two glass cloths impregnated with a resin, and one web B is further sandwiched between the two webs A and laminated. I put it in the mold. The mold was closed and placed in a 105 ° C. oil bath and removed from the oil bath after about one hour. At this time, the excess resin was discharged from the nozzle. However, the nozzle was closed halfway.

After cooling, the molded product was taken out of the mold. The resulting molded article had a good appearance and a corresponding strength.
The specific gravity of the molded product is 0.78, and the bending strength is 12.4 kg / m.
m ² and the elastic modulus were 630 kg / mm ² .

Example 2 Web A and Web B in Example 1 were formed in the same manner as Example 1 without using a glass cloth. That is, the web A and the web B impregnated with the resin were placed in a mold in the same manner as in Example 1 , placed in an oil bath at 105 ° C, and taken out of the oil bath after about 1 hour. At this time, excess resin is discharged from the nozzle and the nozzle is closed halfway. After cooling, the mold was opened and the molded product was taken out.

The specific gravity of the obtained molded product was about 0.58, the bending strength was 4.2 kg / mm ² , and the elastic modulus was 119 kg / mm ^2.
Met.

Example 3 An aramid fibrid mainly composed of polymetaphenylene isophthalamide was experimentally produced using an apparatus disclosed in Japanese Patent Publication No. 59-47695. This fibrid
-11851, and 37-5732. The degree of beating of the obtained fibrid is 51 ° SR.
Met.

50 parts of this fibrid, 50 parts of "Microsphere F-30D" manufactured by Matsumoto Yushi-Seiyaku Co., Ltd. and 25 parts of glass balloon M-28 manufactured by Asahi Glass Co., Ltd. were mixed to form a slurry. Papermaking was performed using a tappy standard machine to obtain a synthetic paper web of 150 g / m ² . This
The synthetic paper web of the above, the glass balloon M on the top (front) side
-28 is unevenly distributed and “My”
"Crossphere F-30D" was unevenly distributed.

On the other hand, in the same manner as in Example 1, a mold was made from two aluminum plates and “Teflon”. A Teflon spacer is interposed between two aluminum plates and has a size of approximately 180 mm × 200 mm and a thickness of 3 mm (depending on the spacer thickness). A nozzle was provided in one mold.

Two pieces of the synthetic paper web were cut slightly smaller than this mold. Then, it was immersed in the same mixed resin as in Example 1 to sufficiently impregnate the mixed resin. Then, two synthetic paper-like webs impregnated with a resin were overlapped so that the surface (lower surface) in contact with the surface of the filter material was outside during papermaking, and was placed in a mold. The mold was closed and placed in an oil bath at 85 ° C. and removed from the oil bath after about one hour. At this time, excess resin was discharged from the nozzle. However, the nozzle was closed halfway.

After cooling, the molded product was taken out of the mold. The resulting molded article had a good appearance and a corresponding strength.
The specific gravity of the molded product is about 0.60, and the bending strength is 4.4 kg / m
^{2. The} elastic modulus was 280 kg / mm ² .

Example 4 50 parts of an aramid fibrid (having a degree of beating of 45 ° SR) mainly composed of polymetaphenylene isophthalamide produced according to Example 3 and “Micro by Matsumoto Yushi Pharmaceutical Co., Ltd. 50 parts of "Sphere F-30D" and 50 parts of a glass balloon M-28 made by Asahi Glass were mixed and paper-made with a tappy standard machine to obtain a synthetic paper web similar to that of Example 3 .

As in Example 1, two aluminum plates and “Teflon” were approximately 180 mm × 200 mm in size.
A mold having a thickness of 3 mm (depending on the thickness of the spacer) was prepared, and a nozzle was provided on one of the molds.

Two pieces of the synthetic paper web were cut slightly smaller than the mold. Two pieces of the same glass cloth as in Example 1 were cut out according to the mold.

On both sides of this glass cloth, Unicell Corporation
And the same mixed resin as in Example 1, that is, a resin obtained by mixing 100 parts of “Epicoat 807” and 31 parts of “Epomate YLH006” was applied.

The web impregnated with the two resins is laminated between two glass cloths impregnated with the resin so that the surface (lower surface) that is in contact with the surface of the filter medium becomes outside during papermaking.
I put it in the mold. Close the mold and put in an oil bath at 85 ° C.
After an hour, it was removed from the oil bath. At this time, the excess resin was discharged from the nozzle. However, the nozzle was closed halfway.

After cooling, the molded product was taken out of the mold. The resulting molded article had a good appearance and a corresponding strength. Its specific gravity is about 1.02, and as a result of the bending test, the strength is 1
2.4 kg / mm ² , elastic modulus 572 kg / mm ² , tensile test result: strength 5.1 kg / mm ² , elastic modulus 13
It was 6 kg / mm ² .

Example 5 An ultra-drawn fiber of polyamide made of terephthalic acid and paraphenylenediamine / 3,4'-diaminodiphenyl ether ("Technola" manufactured by Teijin Limited) was cut into 2 mm, and the length was cut to 2 mm. According to the above method, the mixture was beaten in an aqueous solution of n-mermethyl-2-pyrrolidone to obtain fibrils.
The degree of beating of this fibril is 1 by the shopper Wrigler method.
It was 4.1 ° SR.

In the production of the fibrils, when concentrated after filtration and collected by filtration, 100 parts of the fibrils were mixed with "Microsphere F-3" manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.
OD ”(25 parts) was added and mixed. It was pressed and squeezed, but the apparent specific gravity was about 0.2. This is about 1m thick
m of web. This is called an intermediate material web A.

Similarly, as a separate batch, in the production of fibrils, when beating, concentrating and collecting by filtration, 10 parts of glass balloon M-28 manufactured by Asahi Glass Co., Ltd. was added to 100 parts of the fibrils. Mixing was performed. The web was squeezed and squeezed to obtain a web having a thickness of about 2 mm, but the apparent specific gravity was about 0.2. This is called an intermediate material web B.

In the same manner as in Example 1, a mold was made from two aluminum plates and “Teflon”. Teflon spacer is sandwiched between two aluminum plates.
× 200 mm, thickness 3 mm (depending on spacer thickness). A nozzle was provided in one mold.

Two intermediate material webs A and one intermediate material web B were cut slightly smaller than the mold. In addition, the same glass cloth (MS
253-1040-2NT-10FS) and two nonwoven fabrics (Unicell BT0404).

One intermediate material web B is sandwiched between the two intermediate material webs A , a nonwoven fabric (Unicell BT0404) is laminated on both surfaces thereof, and a glass cloth is attached to the outside thereof, respectively. It was placed in the above mold.

The mold was closed while compressing the web and the like placed in the mold, and a resin obtained by mixing 100 parts of “Epicoat-807” and 31 parts of “Epomate YLH-006” was injected into the mold. At this time, the inside of the mold was evacuated by evacuating using one nozzle of the mold, and the resin was injected while the evacuation was continued. It was confirmed that the resin was full and reached the exhaust nozzle. With one nozzle closed and the other open, the mold was closed and placed in an oil bath at 85 ° C. and removed from the oil bath after about one hour. At this time, excess resin was discharged from the nozzle. However, the nozzle was closed halfway.

After cooling, the mold was opened and the molded product was taken out. The resulting molded article had a good appearance and a corresponding strength. The specific gravity of the molded product is about 0.85. As a result of the bending test,
Strength is 11.7 kg / mm ² and elastic modulus is 547 kg / m
m ² .

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Claims (6)

(57) [Claims] 1. An outer layer which mainly contains expandable particles (a) which can be foamed and expanded by heating and an intermediate layer which mainly contains substantially non-expandable hollow particles (b). By impregnating or injecting a resin into a fibrous web (W) having a multilayer structure, and heating the resin, the expandable particles (a) in the fibrous web (W) are molded while being foamed and expanded. Manufacturing method of lightweight composite molding. Wherein said fibrous web (W) is produced by a wet process expandable particles (a) and hollow particles and (b) from the short fibers and / or slurry dispersed in water together with fibrils mainly expansion The two webs consisting of the lower layer containing the conductive particles (a) and the upper layer mainly containing the hollow particles (b) are placed such that the upper layers containing the hollow particles (b) are located inside each other.
2. The method according to claim 1, wherein the layers are laminated. 3. The fibrous web (W) is separately provided
Prepared people, the two webs containing expandable particles (a)
(A) and a web (B) containing hollow particles (b),
The method according to claim 1, wherein the layers are laminated in the order of (A) / (B) / (A) . 4. The fibrous web (W) is put into a mold together with a resin, and heated to expand and expand the expandable particles (a) contained in the fibrous web (W) in the mold. 4. The method according to claim 1, wherein the inner pressure is formed. 5. The method according to claim 1, wherein a sheet-like reinforcing fiber material (R) is further laminated on one or both surfaces of the fibrous web (W) and molded. 6. The method according to claim 1, wherein an uncured thermosetting resin is used as the resin.