JP2003337588A - Sound absorbing body and sound absorbing structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sound absorbing body with which both of sound absorbing performance and sound insulating performance are assured by integral molding without laminating a plurality of materials and a sound absorbing structure. <P>SOLUTION: The sound absorbing body 40 has a molding 44 having two unfoamed layers 41 and 42 and a foamed layer 43 which is held between these unfoamed layers 41 and 42 and has a number of gaps. A plurality of holes 41A of the depth at which the holes penetrate the unfoamed layer 41 and do not arrive at the unfoamed layer 42 are formed at arbitrary points of the molding 44. The sectional area of the holes 41A is 0.7 to 400 mm<SP>2</SP>and the pitch thereof is ≥1 mm. The foamed layer 43 is provided with the gaps formed by decompression of a molding material including a supercritical fluid. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a sound absorbing body and a sound absorbing structure. More specifically, the present invention relates to a sound absorbing body having a sound insulating property and a sound absorbing structure using the sound absorbing body that requires sound absorbing properties.

[0002]

BACKGROUND ART A sound insulating material and a sound absorbing material have hitherto been used to shield noise and noise. Among these, as the sound absorbing material, it is common to use a soft non-woven fabric or a foam molded article that absorbs sound waves well. Such a sound absorbing material does not have rigidity, and normally sound insulation performance cannot be expected. On the other hand, as the sound insulating material, it is general to use a member that has high density and high rigidity and is hard to vibrate by sound waves. Since such a sound insulating material reflects and blocks sound waves, it does not absorb the sound waves, and normally sound absorbing performance cannot be expected.

[0003]

However, the conventional sound absorbing material and sound insulating material as described above cannot secure both sound absorbing performance and sound insulating performance, and are members having both sound absorbing performance and sound insulating performance. In order to secure the above, a complicated process such as attaching a sound absorbing material and a sound insulating material is required, and there is a problem that the manufacturing becomes complicated. Also, if it is attempted to secure both sound absorbing performance and sound insulating performance by bonding sound absorbing material and sound insulating material, one of product characteristics such as heat resistance, rigidity, light weight and shape may be sacrificed. There is also a problem in that it is necessary to optimize the material forming the sound absorbing material and the sound insulating material, which makes the selection of the material complicated.

An object of the present invention is to provide a sound absorbing body and a sound absorbing structure in which both sound absorbing performance and sound insulating performance are secured by integral molding without laminating a plurality of materials.

[0005]

In order to achieve the above object, the sound absorbing body of the present invention comprises a molded article having two unfoamed layers and a foamed layer sandwiched between these unfoamed layers and having a large number of voids. And a plurality of holes having a depth that penetrates the one unfoamed layer and does not reach the other unfoamed layer are formed at any location of the molded body, and the cross-sectional area of the hole is 0. .7-
It is 400 mm ² , the pitch is 1 mm or more, and the foamed layer is provided with voids generated by depressurizing the molding material containing the supercritical fluid.

The unfoamed layer is formed, for example, by the molding material filled in the cavity of the mold of the injection molding machine contacting the cavity surface of the mold and rapidly cooling before foaming. The foam layer, for example, in the cylinder of the injection molding machine,
Generated by depressurizing the inside of the mold by a method such as expanding the cavity volume after injecting and filling a molding material in which a supercritical fluid is mixed and / or dissolved in a thermoplastic resin or thermoplastic elastomer into the mold. To do.

As a molding material, a supercritical fluid is dissolved,
Alternatively, it is not particularly limited as long as it contains a thermoplastic material that can be mixed with the supercritical fluid. Examples of the thermoplastic material include thermoplastic resins and thermoplastic elastomers. As the thermoplastic resin, for example, homopolypropylene, propylene-ethylene block copolymer, propylene-ethylene random copolymer, polyolefin resin such as polyethylene,
Alternatively, polystyrene resin, ABS (acrylonitrile-butadiene-styrene) resin, polyvinyl chloride resin, polyamide resin, polyester resin, polyacetal resin, polycarbonate resin, polyaromatic ether or thioether resin, polyaromatic Ester-based resins, polysulfone-based resins, acrylate-based resins, etc. can be adopted.

In order to impart impact resistance, a thermoplastic elastomer such as ethylene-propylene rubber (EPR), ethylene-butene copolymer elastomer (EBR), styrene-ethylene butylene styrene block copolymer (SEBS) is used in combination. You may. These thermoplastic materials may be used alone, or two or more kinds may be used in combination. In addition to these thermoplastic materials, other fillers such as glass fiber and talc, and
Various polymer materials that can be injection-molded, such as those containing various additives, can be adopted.

Here, the supercritical fluid is a fluid having an intermediate property between a gas state and a liquid state, and becomes a supercritical state when the temperature and pressure (critical point) determined by the type of fluid are exceeded. Say. Such a supercritical fluid has a stronger osmotic force (dissolving power) into the inside of the thermoplastic resin and the like than that in a liquid state and is uniform. In the present invention, as the supercritical fluid, for example, an inert gas such as carbon dioxide, nitrogen, air, oxygen, hydrogen and helium can be used as a fluid, but carbon dioxide and nitrogen are particularly preferable.

For example, when a thermoplastic resin in which a supercritical fluid is mixed and / or dissolved is filled in a mold / cavity of an injection molding machine and then the volume of the cavity is expanded, the internal pressure of the cavity is reduced to a supercritical state. Is released and becomes a normal gas state, the foaming pressure becomes high, and foaming is performed so as to have an expanded cavity volume. This foaming does not expand the cavity volume so much, that is, in the case of a low expansion ratio, it is easy to form a foamed layer having a so-called microcell structure with an average cell diameter of 50 μm or less. It tends to be a foam layer having coarser voids than the microcell structure.

The hole may have any shape such as a cylindrical shape, an elliptic cylindrical shape, a polygonal cylindrical shape, and a conical shape. This hole
It does not have to penetrate one unfoamed layer and penetrate the other unfoamed layer. If this hole penetrates both of these unfoamed layers, sound absorption may not be exhibited. Here, the cross-sectional area of the holes means the area of the holes on the surface of the one unfoamed layer. The cross-sectional area of this hole is 0.7-400 m
It is within the range of m ² . If the cross-sectional area of this hole is less than 0.7 mm ² , it becomes difficult to absorb high-frequency sound, and 400 mm
^If it exceeds ² , it may be difficult to absorb low-frequency sound. When the cross-sectional shape of the hole is circular, the inner diameter of the hole is preferably in the range of 1 to 20 mm, and particularly 2-1.
0 mm is more preferable.

Here, the pitch means that the distance between adjacent holes is
The shortest distance between the outer peripheral portions of the holes. That is, the pitch is not limited to the interval in which holes are regularly formed at regular intervals, and may be the interval between adjacent holes formed in an irregular pattern. This pitch is preferably 1 mm or more, more preferably 10 to 100 mm. If this pitch is less than 1 mm, high-frequency sound may not be absorbed. If necessary, one sound absorbing body may be provided with a plurality of types of holes having different cross-sectional areas and / or pitches.

As a method for manufacturing the above-mentioned sound absorbing body, for example, the following method may be mentioned. (1) Mixing and / or dissolving a supercritical fluid in a thermoplastic resin or a thermoplastic elastomer in a cylinder of an injection molding machine using a mold provided with a movable mold that can move forward and backward with respect to an internal cavity. The molding material thus obtained is injection-filled in a mold. (2) After the molding material is filled in the mold, a portion of the molding material which is in contact with the inner surface of the mold / cavity is cooled to form an unfoamed layer, and the inside is in a molten state at any time. By retreating the movable mold, expanding the cavity volume, and depressurizing the inside of the cavity, a molded body having a foamed layer with a large number of voids inside and an unfoamed layer on the outer periphery is obtained (in the thickness direction The cross section is unfoamed layer / foamed layer / unfoamed layer).

(3) On one surface of the molded body obtained in (2),
The cross-sectional area is 0.7 to 400 mm ² , and the pitch is 1
Make a hole of mm or more in the place where you want to absorb sound. As a method for making a hole, a known method such as making a hole with a drill or a heated pin may be used. In addition, a sword mountain-shaped punching device that slides freely with respect to one mold is provided, and (2)
After foaming with, before taking out the molded body from the mold, advance the knife-shaped hole punching device in the direction of the inside of the cavity to penetrate one unfoamed layer to the unfoamed layer on the other side. You may make holes that have not been reached. The diameter and pitch of the pin of the device can be appropriately set according to the hole diameter and pitch required for the sound absorbing body.

The injection molding machine, mold and the like that can be used for manufacturing the above-mentioned sound absorbing body are capable of injection compression molding, can introduce a high-pressure fluid into a cylinder for injection molding, and heat a supercritical fluid. There is no particular limitation as long as it is a device that can be mixed and / or dissolved in a plastic material. For example, a molding method and a manufacturing apparatus such as US Pat. No. 5,158,986 and JP-A-10-230528 (FIG. 5 of the publication is a typical example) can be used. In addition, the injection molding die described in the above-mentioned two patents is disclosed in Japanese Patent Laid-Open No. 8-244081 and Japanese Patent No. 288008.
6, the mold disclosed in Japanese Patent Laid-Open No. 2000-6213 (including its movement control mechanism) may be used.

According to the present invention described above, an unfoamed layer,
By including the foamed layer, the non-foamed layer has a sound insulating property, and the foamed layer has a large number of voids inside, and thus has a sound absorbing property. Therefore, it is possible to secure both sound absorbing performance and sound insulating performance by integrally molding without laminating a plurality of materials. In addition, the foam layer includes voids generated by depressurizing a molding material containing a supercritical fluid. By reducing the pressure of this supercritical fluid, it changes from the supercritical state to a normal gas state. Therefore, since the volume expands to form voids in the normal gas state, the foamed layer can be formed without using a normal chemical foaming agent.

The sound absorbing body of the present invention has a molded body having two unfoamed layers and a foamed layer sandwiched between these unfoamed layers and having a large number of voids. A plurality of holes having a depth that does not reach the other unfoamed layer is formed through the one unfoamed layer, and the cross-sectional area of the hole is
0.7-400 mm ² , the pitch is 1 mm or more, and the foam layer has voids generated by depressurizing a molding material containing a supercritical fluid and fibers having a weight average fiber length of 1 mm or more. It is characterized by being provided.

Here, the magnifications of the non-foamed layer, the holes and the foamed layer are as described above. The molding material is not particularly limited as long as it includes a thermoplastic material and a fibrous filler and has a weight average fiber length of 1 mm or more after molding. For example, a fiber-containing thermoplastic resin containing reinforcing fibers having an average fiber length in the range of 2 to 100 mm may be used alone as a resin pellet, or the resin pellet and another molding material may be used. Mixtures may be used. The blending amount of the fiber-containing thermoplastic resin is preferably 40% by mass or more and 98% by mass or less of the thermoplastic resin and 2% by mass or more and 60% by mass or less of the fiber filler.

If the amount of the thermoplastic resin is less than 40% by mass, the fluidity may be deteriorated and the molding operation may be complicated. On the other hand, when the thermoplastic resin is more than 98% by mass,
In some cases, the amount of fiber filler becomes small, sufficient strength cannot be obtained, and properties such as vibration damping are impaired. If the average fiber length is less than 2 mm, the average fiber length in the obtained sound absorbing body will be less than 1 mm, which may reduce the strength and rigidity. If it exceeds 100 mm, injection molding will be difficult.

More preferably, the rod in which the fibrous filler is bundled is provided with the thermoplastic material, and the reinforcing fiber is provided in an amount of 10% by mass or more and 90% by mass or more.
After impregnating so as to have a ratio of less than or equal to mass%, the reinforcing fibers are arranged in a state substantially parallel to the length direction of the pellet obtained by cutting so that the length dimension is from 2 mm to 100 mm. The fiber-reinforced resin pellets are preferably used alone or diluted with another thermoplastic material so as to have the above-mentioned fiber amount.

Examples of the thermoplastic material include a thermoplastic resin and a thermoplastic elastomer, which are as described above. Examples of the fibrous filler include reinforcing fibers. Examples of reinforcing fibers include ceramic fibers such as rock wool and boron fibers, inorganic fibers such as glass fibers and carbon fibers, metal fibers such as aluminum fibers and copper fibers, ultra high molecular weight polyethylene fibers, aramid fibers and polyarylate fibers. Any of organic fibers can be adopted. In particular, it is preferable to use glass fiber. In the foam layer, the average cell diameter is 50 μm because the voids due to the spring back of the fibrous filler and the voids generated when the above-mentioned supercritical fluid becomes a normal gas state are easily mixed.
The following foamed layer tends to have coarser voids than the so-called microcell structure.

As a method for manufacturing the above-mentioned sound absorbing body, for example, the following method may be mentioned. (1) A supercritical fluid is mixed and / or melted with a thermoplastic material in a cylinder of an injection molding machine using a mold provided with a movable mold that can move forward and backward with respect to an internal cavity. (2) The fiber-containing thermoplastic material is supplied into the cylinder by side feed from a direction downstream of the cylinder portion where the step (1) is performed from a direction orthogonal to the flow direction of the supercritical fluid, and (1) Inject and fill the mold together with the molding material of.

(3) After the fiber-containing thermoplastic material and the molding material are filled together in the mold, the portion of the molding material in the cavity which is in contact with the inner surface of the cavity is cooled to form an unfoamed layer. At any time when is in a molten state, the movable die is moved in a direction in which the volume of the cavity is expanded to reduce the pressure in the cavity. By this operation. A molded product having a large number of voids inside and an unfoamed layer on the outer periphery can be obtained (the cross section in the thickness direction is unfoamed layer / foamed layer / unfoamed layer). (4) A hole is formed in a portion of the molded body obtained in (3) where sound absorption is desired. The method of forming the holes may be the same as that of the invention of claim 1 described above.

Instead of the above (2), (2 ') an injection molding machine for dissolving or mixing a supercritical fluid in a thermoplastic material is used, and a fiber-reinforced thermoplastic material is prepared by using another injection molding machine. It may be filled in the cavity. In that case, the filling of (1) and (2 ′) may be completed before the step (3) starts at the latest.

In the above (2), the reason for side-feeding the fiber-reinforced thermoplastic material is that the reinforcing fiber is broken at the cylinder portion into which the supercritical fluid is injected, and the weight average fiber length in the molded body is less than 1 mm. This is because it is preferable to prevent In (2 '), the reason why the fiber-reinforced thermoplastic material is filled in another injection molding machine is that the cylinder of the injection molding machine that mixes and / or dissolves the supercritical fluid into the thermoplastic material, that is, the shear pressure. This is because it is advantageous to prevent the weight average fiber length in the molded body from becoming less than 1 mm, rather than supplying the fiber reinforced thermoplastic material into a cylinder having a high temperature and being easily cut into fibers.

According to this, the same operation and effect as described above can be obtained. Further, the foam layer has voids generated by decompressing a molding material containing a supercritical fluid and fibers having a weight average fiber length of 1 mm or more, so that the supercritical fluid becomes a normal gas state. Since the voids generated in 1 and the voids formed by springback containing fibers having a weight average fiber length of 1 mm or more are mixed voids, high rigidity,
A sound absorber having high impact resistance can be obtained.

In the sound absorber of the present invention, the thickness of at least one of the unfoamed layers is preferably 0.5 to 2.0 mm, more preferably 0.5 to 1.0 mm. Here, the thickness of at least one of the unfoamed layer,
If it is less than 0.5 mm, practical sound insulation performance may not be obtained. If the thickness of at least one of the unfoamed layers exceeds 2.0 mm, sufficient sound absorbing performance may not be exhibited.

In the sound absorbing body of the present invention, the expansion ratio of the foam layer is preferably 1.2 to 5 times, and more preferably 2.0 to 4 times. When the expansion ratio is less than 1.2 times, the sound absorbing performance is deteriorated, and when it exceeds 5 times, the strength of the sound absorbing body is decreased, and for example, the sound absorbing body may be damaged during use or mounting, or mounting may be difficult. is there.

In the sound absorbing body of the present invention, it is preferable that the foaming layer includes a high foaming region having a foaming ratio of 2.0 to 5.0 times. Here, the sound absorbing body of the present invention may include a plurality of foam layers having different foaming ratios. Generally, when the foaming rate is different, the foaming layer also has different sound absorbing performance and strength. Therefore, according to this configuration, the strength and rigidity of the sound absorber as a whole can be improved by forming the sound absorbing portion in the foam layer having a high expansion ratio and the other portion in the solid portion or the low foam portion. Can be held.

In the case of the sound absorbing body having a plurality of foam layers having different expansion ratios, the expansion ratio is 2 to 5 times, preferably 2.5.
It is preferable that a high foaming region having a foaming ratio of up to 4 times and a portion other than that having a high foaming ratio be solid or have a low expansion region having a foaming ratio of less than 2 times, preferably less than 1.2 times. In such a sound absorbing body, it is preferable that the hole is formed in the highly foamed region.

The sound absorbing structure of the present invention is a sound absorbing structure used in applications requiring sound absorbing properties, and includes the above-mentioned sound absorbing body, and includes a timing belt cover, an air cleaner cover, an air duct, an engine cover, and an exhaust gas. It is characterized by being used as any one of a vehicle resonator, an intake manifold, a shield plate for an engine room and a room, a trunk room, an automobile ceiling material, and a door panel. According to this, if the characteristic performance of each component, for example, the luggage compartment is taken as an example, the capacity for storing spare tires and luggage can be secured, and the load applied when storing luggage can be withstood and the sound absorption described above can be achieved. It can be a component with good sound and sound insulation performance.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. [First Embodiment] A first embodiment of the present invention will be described. FIG. 1A is a plan view of the sound absorber 40 according to the first embodiment of the present invention. FIG. 1B is a cross-sectional view of the sound absorbing body 40. The sound absorbing body 40 has a molded body 44. Molded body 4
4 is two unfoamed layers 41, 42 and these unfoamed layers 4
A foam layer 43 sandwiched between 1 and 42 and having a large number of voids. The unfoamed layers 41 and 42 are layers having high density and high rigidity by hardening a molten resin or the like without foaming. Here, the unfoamed layer 4
The thickness of 1 is substantially the same as that of the unfoamed layer 42.

The unfoamed layers 41, 42 have a thickness of 0.5 to
It is 2.0 mm, preferably 0.5 to 1.0 mm. If the thickness of the unfoamed layers 41 and 42 is less than 0.5 mm, practical sound insulation performance may not be obtained. If the thickness of at least one of the unfoamed layers exceeds 2.0 mm, sufficient sound absorbing performance may not be exhibited.

On the other hand, the foam layer 43 has a large number of voids as described above. The expansion ratio of the foam layer 43 is 1.2 to
It is preferably 5 times, more preferably 2.0 to
4 times. When the expansion ratio is less than 1.2 times, the sound absorbing performance is deteriorated, and when it exceeds 5 times, the strength of the sound absorbing body 40 is decreased, and for example, it is damaged during use or mounting, or when mounting becomes difficult. There is.

Further, the sound absorbing body 40 may include a plurality of foam layers 43 having different foam expansion ratios, for example, a high foam region having a foam expansion ratio of 2.0 to 5.0 times. Good. Generally, when the foaming rate of the foamed layer 43 is different, the sound absorbing performance and the strength are also different. Therefore, according to this configuration, the sound absorbing body 40 as a whole is made strong and rigid by forming the sound absorbing portion in a foam layer having a high expansion ratio and the other portions in the solid portion or the low foam portion. Can hold.

In the case of the sound absorbing body 40 having a plurality of foam layers having different expansion ratios, the expansion ratio is 2 to 5 times, preferably 2.5.
It is preferable that a high foaming region having a foaming ratio of up to 4 times and a portion other than that having a high foaming ratio be solid or have a low expansion region having a foaming ratio of less than 2 times, preferably less than 1.2 times. In such a sound absorber 40, it is preferable that a hole 41A described later is formed in a highly foamed region. The unfoamed layer 41 is formed at an arbitrary position of the molded body 44.
A plurality of circular holes 41 </ b> A having a depth that penetrates through and does not reach the unfoamed layer 42. In the present embodiment, the holes 41A are formed at the depth of the unfoamed layer 41.

The cross-sectional area of the hole 41A is 0.7 to 400 mm.
It is within the range of ² . The cross-sectional area of this hole 41A is 0.7 mm ^2.
If less than 400, it becomes difficult to absorb high-frequency sound, and 400
If it exceeds mm ² , it may be difficult to absorb low-frequency sound. In addition, when the cross-sectional shape of the hole 41A is circular, the inner diameter of the hole 41A is preferably in the range of 1 to 20 mm, and more preferably 2 to 10 mm. The pitch of the holes 41A is 1 mm or more, and the preferable pitch of the holes 41A is 10 to 100 mm. The pitch of the holes 41A is 1
If it is less than mm, it may not be possible to absorb high-frequency sound.

FIG. 2 shows an injection molding apparatus 50 for molding a molded body according to this embodiment. FIG. 3 shows the molding machine 1 of the injection molding device 50. The injection molding device 50 includes a gas cylinder 51 and a booster pump 5.
2, valve 53, variable valve 54, valve 55
And an injection machine 60 and a molding machine 1. The gas cylinder 51 stores a gas that becomes a supercritical fluid, and a known gas cylinder can be used. In addition,
In this embodiment, the gas used is nitrogen gas. The booster pump 52 boosts the pressure of the gas supplied from the gas cylinder 51 into high-pressure gas.

The valve 53 is provided between the gas cylinder 51 and the booster pump 52 and regulates the flow rate of gas from the gas cylinder 51. The variable valve 54 and the valve 55 are
It is provided between the booster pump 52 and the injector 60 and adjusts the flow rate of gas from the gas cylinder 51. In addition, valve 5
As the variable valve 54 and the valve 55, known valves can be used.

The injection machine 60 is equipped with an injection cylinder 61, a screw 62, a hopper 63, a drive unit 64, and a nozzle 65, and heats and melts a molding material containing a thermoplastic material to plasticize and knead it. Is to do. The injection cylinder 61 is a substantially cylindrical member into which a molding material is placed. The injection cylinder 61 includes an electric heater (not shown), and heats and melts the molding material inside.

The side from which the molding material of the injection cylinder 61 is injected is a front end portion 61A, and the other is a base end portion 61B. The inner space of the tip portion 61A is thinner than the other inner space of the injection cylinder 61. A charging port A for charging the gas from the gas cylinder 51 is formed in a substantially middle portion of the injection cylinder 61 in the longitudinal direction. Further, at a substantially middle portion in the longitudinal direction of the injection cylinder 61, a charging port B for charging a fiber reinforcing material or the like is formed on the tip end 61A side of the charging port A.

The screw 62 is provided along the central axis of the injection cylinder 61 and rotates to knead the heated and melted molding material. By the rotation of the screw 62, the kneaded molding material moves toward the tip portion 61A. The hopper 63 is for charging the molding material into the injection cylinder 61, and is connected to the side surface on the base end 61B side.
The drive part 64 is for rotating the screw 62, and is provided in the base end part 61B. Drive unit 64
A known drive means such as a motor can be used for the. The nozzle 65 is connected to the molding machine 1 and is for injecting the kneaded molding material into the molding machine 1.

Next, the molding machine 1 is the one shown in FIG. 3, and performs molding by injecting the molten molding material into the mold 10. The mold 10 is divided into a fixed mold 10A and a movable mold 10B. This mold 10
Inside the moving mold 10B, the cavity 1 of the mold 10 is
Movable core 12 that can move forward and backward with respect to 1
Is provided. By moving the movable core 12, the cavity 11 of the mold 10 has a variable volume.

Further, the fixed mold 10A of the mold 10 is provided with a passage 13 such as a sprue or a runner for introducing the molten resin therein. A strip-shaped electric heating body 14 is provided around the passage 13. As a result, the passage 13
Form a so-called hot runner that does not cure the molten resin flowing inside the passage 13.

Further, the fixed mold 10A and the movable core 1
Each of the two has an electric heating element 1 embedded in the vicinity of each molding surface.
5, 16 are provided. These electric heating elements 15, 16
The temperature of each molding surface of the fixed mold 10A and the movable core 12 is controlled to be a predetermined temperature by appropriately adjusting the amount of heat generated by. A gas pin (not shown) for injecting a pressurized gas into the molten resin injected into the cavity 11 is provided in the fixed mold 10 </ b> A so as to be able to project into and retract from the cavity 11.

In the molding machine 1, the fixed die plate 3 to which the fixed die 10A is attached, the moving die plate 4 to which the moving die 10B is attached, and the moving die plate 4 are advanced toward the fixed die plate 3. There are provided a mold clamping device 5 for moving the mold, and a mold moving device 20 for moving the movable core 12 of the mold 10 to an arbitrary position within a predetermined range and stopping the movable core 12 at the position.

The movable die plate 4 is slidably provided along a tie bar 8 spanned between a fixed plate 7 to which a hydraulic cylinder device 6 for mold clamping is fixed and a fixed die plate 3. is there. The mold clamping device 5 has a toggle mechanism 9 to which the piston rod 6A of the hydraulic cylinder device 6 is connected, and the pressing force of the hydraulic cylinder device 6 is increased by the toggle mechanism 9 to move the movable die plate 4 forward. The moving mold 10B is brought into close contact with the fixed mold 10A to close the mold 10.

The mold moving device 20 advances the movable core 12 with respect to the cavity 11 to move the cavity 11 into the cavity 11.
The cavity 11 is expanded by applying a compressive force to the molten molding material injected into the mold and retracting the movable core 12, and the movable die plate 4 and the movable mold 10 are expanded.
It is interposed between B and. Further, the mold moving device 20
By moving the movable core 12 back and forth,
It is also a cavity clearance changing means capable of arbitrarily changing the clearance between the second molding surface and the molding surface of the fixed mold 10A.

The mold moving device 20 has inclined surfaces 21A and 22A which are inclined with respect to the moving direction of the movable core 12, and a pair of inclined members 21 in which these inclined surfaces 21A and 22A are in contact with each other. , 22, a base plate 23 having a flat surface orthogonal to the moving direction of the movable core 12, a mold mounting base 24 for connecting the movable die plate 4 and the movable mold 10B, and the movable core 1
2 and a compression plate 25 connecting the inclined member 22.

Of these, the inclined member 21 is slidable along the surface of the base plate 23 attached to the moving die plate 4, and the hydraulic cylinder device 26 is also provided.
Thus, the movable core 12 is driven in a direction orthogonal to the moving direction. Here, the tilting member 22
At both edges of the inclined surface 22A, rising portions 22B along the moving direction of the inclined member 21 are provided. A groove 22C extending in the longitudinal direction of the rising portion 22B is provided inside the rising portion 22B. On the other hand, on the side surface of the inclined member 21 that is in contact with the inner side surface of the rising portion 22B, a protrusion 21B that fits into the groove 22C of the inclined member 22 is provided.

As a result, when the piston rod 26A of the hydraulic cylinder device 26 is advanced, the tilting member 21 presses the tilting member 22 and the movable core 12 moves forward, while the piston rod 26A of the hydraulic cylinder device 26 moves backward. The tilting member 21 draws the tilting member 22 so that the movable core 12 retracts. A hydraulic unit 30 is provided to supply hydraulic pressure to the mold moving apparatus 20. Further, the control unit 31 for controlling the hydraulic unit 30 and causing the mold moving apparatus 20 to perform a desired operation. Is provided.

The control device 31 has a sequence control circuit such as a digital sequencer, and moves the movable core 12 forward and backward stepwise with respect to the cavity 11,
It is possible to set such that arbitrary different operations such as retreating after being temporarily stopped at a predetermined position are continuously performed. Although not shown in the figure, a gas pin (not shown) provided in the fixed mold 10A is provided with a pressurized gas supply device such as a gas cylinder for supplying a pressurized gas in the vicinity of the molding machine 1. .

Next, the molding procedure of the molded body 44 of this embodiment will be described with reference to FIGS. The injection machine 6 of FIG.
The injection cylinder 61 of 0 is heated to the molding temperature of a predetermined molding material by an electric heater (not shown). Then the hopper 63
Then, the molding material is put into the injection cylinder 61 and the screw 62 is rotated to start plasticization and kneading of the molding material. In the present embodiment, the molding material is a pellet made of a thermoplastic material.

The molding material is not particularly limited as long as it contains a thermoplastic material in which the supercritical fluid can be dissolved or mixed with the supercritical fluid. Examples of the thermoplastic material include thermoplastic resins and thermoplastic elastomers. Examples of the thermoplastic resin include homopolypropylene, propylene-ethylene block copolymer, propylene-ethylene random copolymer, polyolefin resin such as polyethylene, or polystyrene resin, ABS (acrylonitrile-butadiene-styrene) resin, Polyvinyl chloride resin, polyamide resin, polyester resin, polyacetal resin, polycarbonate resin,
A polyaromatic ether or thioether resin, a polyaromatic ester resin, a polysulfone resin, an acrylate resin, etc. can be adopted.

In order to impart impact resistance, a thermoplastic elastomer such as ethylene-propylene rubber (EPR), ethylene-butene copolymer elastomer (EBR), styrene-ethylene butylene styrene block copolymer (SEBS) is used in combination. You may. These thermoplastic materials may be used alone, or two or more kinds may be used in combination. In addition to these thermoplastic materials, other fillers such as glass fiber and talc, and
Various polymer materials that can be injection-molded, such as those containing various additives, can be adopted.

The booster pump 52 pumps nitrogen gas from the gas cylinder 51 through the valve 53, the variable valve 54 and the valve 55.
After the pressure is raised to a critical pressure or higher by the valve 55, the valve 55 is opened and introduced from the injection port A of the injection cylinder 61.

The nitrogen gas introduced into the injection cylinder 61 is heated by the thermoplastic material in the injection cylinder 61 to become a supercritical fluid, and is mixed and / or dissolved in the molding material. The supercritical fluid is preferably mixed and / or dissolved in the molding material in an amount of at least 0.1% by weight or more, preferably 0.3% by weight or more. The molding material in which the supercritical fluid is mixed and / or melted is filled into the cavity 11 of FIG. 3 through the nozzle 65 (injection step).

As shown in FIG. 3, the mold 10 operates the electric heating elements 15 and 16 so that the temperature of the molding surface of the movable core 12 becomes higher than that of the fixed mold 10A. After placing, the mold clamping device 5 is operated to move the movable die plate 4 toward the fixed die plate 3, and the movable die 10B is brought into contact with the fixed die 10A as shown in FIG. While closing, the mold moving device 20 is operated to move the movable core 1 to the position S as shown in FIG. 4 (A).
2 is moved, and the thickness dimension of the cavity 11 is set to t1.
In this state, a molding material in which a supercritical fluid is mixed and / or dissolved is injected and filled.

Here, the thickness t1 of the cavity 11 formed by the movable core 12 stationary at the position S is such that the volume of the cavity 11 having the thickness t1 is larger than the amount of the molten resin injected. Is set to.

After the injection of the molding material in which the supercritical fluid is mixed and / or dissolved is started, the mold moving device 20 is operated to move the movable core 12 to the position T as shown in FIG. 4 (B). Move forward and set the thickness of the cavity 11 to t2.
To This reduces the volume of the cavity 11,
The molding material injected into the cavity 11 is compressed.
If necessary, in order to prevent appearance defects due to silver etc.,
You may apply counter pressure.

Here, the non-foamed layers 41, 42 of the molded body 44.
Can be adjusted by adjusting the elapsed time from the start of injection of the molten resin to the start of the retreat of the movable core 12. In other words, if the above-mentioned elapsed time is made longer, the unfoamed layer 4
Since Nos. 1 and 42 become thicker, the above-mentioned elapsed time is set so that the thickness of the non-foamed layers 41 and 42 becomes a desired dimension.

After the movable core 12 reaches the position T, the mold moving device 20 is operated in the reverse direction, and as shown in FIG. 4 (C), the cavity 11 has a volume U corresponding to the molded body. The movable core 12 is retracted to the cavity 1
By setting the thickness dimension of 1 to t3, the cavity internal pressure is reduced. When the internal pressure of the cavity 11 is reduced, the supercritical fluid returns to a normal gas state, so that a large number of voids are generated and the foam layer 43 is formed.

The retracting speed Vr of the movable core 12 is 0.05
In the range of up to 100 mm / sec, preferably 0.05 to 50 mm
It can be set in the range of / second. When a predetermined time required to sufficiently cool the molded body has elapsed, the mold clamping device 5 is operated to retract the movable die plate 4 and open the mold 10. Then, the molded body is taken out of the mold 10 and the molding is completed (molding step). After that, the above-described molding operation is repeated as necessary.

After that, as shown in FIG. 1, a circular shape having a depth that penetrates the unfoamed layer 41 and does not reach the unfoamed layer 42 by a heated pin or the like as shown in FIG. A plurality of holes 41A are formed (hole forming step). The sound absorbing body 40 is completed by forming the aforementioned holes in the molded body 44.

The sound absorbing structure of the present embodiment includes a sound absorbing body 40. For example, although not shown, a timing belt cover, an air cleaner cover, an air duct, an engine cover, an intake / exhaust resonator, an intake manifold, an engine room, and the like. Indoor shielding plate, trunk room,
It is used as either an automobile ceiling material or a door panel.

According to this embodiment as described above, the following effects can be obtained. (1) Since the unfoamed layers 41 and 42 and the foamed layer 43 are provided, the unfoamed layers 41 and 42 have sound insulation performance, and the foamed layer 43 has a large number of voids inside, and thus the sound absorption performance. Have. Therefore, it is possible to secure both sound absorbing performance and sound insulating performance by integrally molding without laminating a plurality of materials.

(2) The foam layer 43 has voids formed by decompressing the molding material containing the supercritical fluid. By reducing the pressure of this supercritical fluid, it changes from the supercritical state to a normal gas state. Therefore, since the volume expands to form voids in the normal gas state, the foam layer 43 can be formed without using a normal chemical foaming agent.

(3) By using a supercritical fluid, the expansion ratio can be made higher than in the case of using an ordinary chemical foaming agent, so that it is possible to improve the sound absorbing property.

(4) By utilizing the supercritical fluid, the mold transfer property can be improved even if the expansion ratio is increased, so that the sound absorbing body 40 having a good appearance can be obtained.

[Second Embodiment] Next, a second embodiment of the present invention will be described. In the following description, the same parts and members as those already described are designated by the same reference numerals to simplify the description. In the injection step in the first embodiment, no fibrous filler or the like was added, but in the second embodiment, a fibrous filler or the like is added in addition to the molding material containing the thermoplastic material. .

As the fibrous filler, for example, a fiber-containing thermoplastic resin containing reinforcing fibers having an average fiber length of 2 to 100 mm may be used alone as resin pellets, or A mixture of this resin pellet and another molding material may be used. The blending amount of the fiber-containing thermoplastic resin is 40% by mass or more of the thermoplastic resin.
8 mass% or less and fiber filler 2 mass% or more and 60 mass%
It is preferable to contain the following.

If the content of the thermoplastic resin is less than 40% by mass, the fluidity may be deteriorated and the molding operation may be complicated. On the other hand, when the thermoplastic resin is more than 98% by mass,
In some cases, the amount of fiber filler becomes small, sufficient strength cannot be obtained, and properties such as vibration damping are impaired. If the average fiber length is less than 2 mm, the average fiber length in the obtained sound absorbing body will be less than 1 mm, which may reduce the strength and rigidity. If it exceeds 100 mm, injection molding will be difficult.

More preferably, the rod in which the fibrous filler is bundled is made of a thermoplastic material and the reinforcing fiber is at least 10% by mass.
After impregnating so as to have a ratio of 0 mass% or less, the reinforcing fibers are arranged in a state substantially parallel to the length direction of the pellet obtained by cutting so that the length dimension is from 2 mm to 100 mm. , Use fiber reinforced resin pellets alone,
It is preferable to use it by diluting it with another thermoplastic resin or the like so that the above-mentioned fiber amount is obtained.

Specific examples of the fibrous filler include reinforcing fibers. Examples of reinforcing fibers include ceramic fibers such as rock wool and boron fibers, inorganic fibers such as glass fibers and carbon fibers, metal fibers such as aluminum fibers and copper fibers, ultra high molecular weight polyethylene fibers, aramid fibers and polyarylate fibers. Any of organic fibers can be adopted. In particular, it is preferable to use glass fiber.

Next, the molding procedure of the molded body 44 of this embodiment will be described with reference to FIGS. The device used is the same as in the first embodiment. The injection cylinder 61 of the injection machine 60 of FIG. 2 is heated to a predetermined molding temperature of a molding material by an electric heater (not shown). Then, the molding material is put into the injection cylinder 61 from the hopper 63, and the screw 62 is rotated to start plasticization and kneading of the molding material. In this embodiment, the molding material is a pellet made of a thermoplastic material containing no fibrous filler. Materials such as thermoplastic materials other than the fibrous filler are the same as those in the first embodiment.

The booster pump 52 pumps nitrogen gas from the gas cylinder 51 through the valve 53, the variable valve 54 and the valve 55.
After the pressure is raised to a critical pressure or higher by the valve 55, the valve 55 is opened and introduced from the injection port A of the injection cylinder 61.

The nitrogen gas introduced into the injection cylinder 61 is heated by the molding material in the injection cylinder 61 to become a supercritical fluid, which is mixed and / or dissolved in the molding material. next,
Using a known thermoplastic material supply device not shown in FIG. 2, the thermoplastic material pellets containing the fibrous filler are side-fed from the charging port B of FIG. 2, that is, orthogonal to the flowing direction of the supercritical fluid. It is supplied from the above direction and introduced into the injection cylinder 61.

After that, in the injection cylinder 61, the molding material from the hopper 63 and the thermoplastic material pellets containing the fibrous filler from the charging port B are melted and mixed. After the melting and mixing, the mixed molding material and the like are filled into the cavity 11 of FIG. 3 through the nozzle 65.

The supercritical fluid is at least 0.1% by weight, preferably 0.3% by weight, based on the thermoplastic material pellets containing the molding material from the hopper 63 and the fibrous filler from the charging port B. Above, it is preferable to mix and / or dissolve. The thermoplastic material pellets containing the fibrous filler, which are side-fed from the charging port B, are appropriately adjusted so as to have the required glass fiber amount (injection step).

The reason for side-feeding the thermoplastic material pellets containing the fibrous filler is that the reinforcing fiber is broken at the charging port A into which the supercritical fluid is injected, and the weight average fiber in the formed product is formed. This is to prevent the length from becoming less than 1 mm.

After the injection process described above, the sound absorbing body and the sound absorbing structure are obtained through the molding process, hole forming process and the like similar to the first embodiment. In the molding step, the molded body 44 is molded using the same molding machine 1 as in the first embodiment. However, when the supercritical fluid becomes a normal gas state, voids are generated and A void is generated inside the molded body 44 by simultaneously generating a void due to so-called springback due to a rapid expansion of the volume between the mold 10 and the cavity 11.

According to this embodiment as described above, the following effects are obtained in addition to the effects of the first embodiment described above. (5) The foam layer 43 has a supercritical fluid and a weight average fiber length of 1
By including a void generated by depressurizing a molding material containing a fiber of mm or more, a void generated when the supercritical fluid becomes a normal gas state and a fiber having a weight average fiber length of 1 mm or more are included. Since the voids formed by spring back are mixed voids, the sound absorber 40 having high rigidity and high impact resistance can be obtained.

The present invention is not limited to the above-mentioned embodiment, and modifications and improvements within a range in which the object of the present invention can be achieved are included in the present invention. For example, although nitrogen is used as the supercritical fluid in the above embodiments, the invention is not limited to this, and for example, an inert gas such as carbon dioxide, air, oxygen, hydrogen, or helium can be used as the fluid.

In the second embodiment, the molding cylinder and the thermoplastic material pellets containing the fibrous filler are put into the injection cylinder 61 of the same injection machine 60, but the present invention is not limited to this. Another injection molding machine may be used to fill the cavity 11 with the thermoplastic material pellets containing the fibrous filler. In that case, before the molten molding material is filled into the cavity 11 at the latest, the filling of the thermoplastic material pellets or the like containing the fibrous filler from another injection molding machine may be completed.

As described above, the reason for filling the thermoplastic material pellets containing the fibrous filler with another injection molding machine is as follows.
A thermoplastic material containing a fiber reinforcing material is fed into an injection cylinder 61 of an injection machine 60 for mixing and / or dissolving a supercritical fluid in a thermoplastic material, that is, an injection cylinder 61 having a high shear pressure and capable of easily cutting fibers. This is because it is more advantageous for preventing the weight average fiber length in the molded body 44 from becoming less than 1 mm.

In each of the above-described embodiments, the method of forming the hole 41A is a method of forming the hole with a heated pin, but the method is not limited to this, and a known method such as a drill may be used. In addition, a piercing tool having a sword shape is provided so as to freely slide on one of the molds, and after the foaming is performed in the molding step, before the molded body 44 is taken out of the mold 10, the sword shape is removed. The punching device may be advanced toward the inside of the cavity 11 so as to punch a hole that penetrates one unfoamed layer and does not reach the unfoamed layer on the opposite side. The diameter and pitch of the pin of the device can be appropriately set based on the hole diameter and pitch required for the sound absorbing body 40.

[0087]

EXAMPLES The present invention will be described in more detail with reference to examples. The present invention is not limited to the contents of the embodiment. [Example 1] Hereinafter, the present invention will be described more specifically by way of examples. With respect to the first embodiment, a sound absorber was manufactured under the following specific conditions.

1. Sound Absorber Manufacturing Method (1) The injection molding apparatus 50 shown in FIG. 2 was used. In the injection cylinder 61 of the injection molding device 50, the resin temperature of the molding material 21
Mosttron L (made by Idemitsu Petrochemical Co., Ltd., reinforced polypropylene containing 40% by weight of glass fiber) at 0 ° C was used as resin back pressure 12
While melting and kneading at MPa, nitrogen gas pressurized to 13 MPa was introduced from the gas cylinder 51 into the injection cylinder 61 so as to be 0.6% by weight with respect to Mosttron L.

After the high-pressure nitrogen is heated to the resin temperature to become a supercritical fluid, and mixed and / or dissolved with Mosttron L,
At a mold temperature of 80 ° C., a filling speed of 40 mm was set in a disk-shaped cavity having a t1 of 5 mm and a diameter of 250 mm in FIG. 4 (A).
1 second before the completion of the filling by injection filling at the speed of 1 / sec.
The moving mold was advanced until 2 became 3 mm (the resin filling amount was a cavity wall thickness of 3 mm).

One second after the completion of filling, move the moving mold to 2
The cavity wall thickness was expanded to 9 mm at a retreat speed of mm / sec. After cooling, the disk-shaped molded product was taken out, and 30 circular holes shown in the following A were drilled on one surface of the molded product with a drill. A: Inner diameter 1.5 mm, pitch (distance between centers of adjacent holes) 20 mm, depth 3 mm Further, when the cross section in the thickness direction of the sound absorbing body 40 was observed after the evaluation of the sound absorbing characteristics described later, the unfoamed layer was It was 2.0 mm.

(2) The same procedure as (1) was performed except that the circular holes were changed to B and C described below. B: inner diameter 3.0 mm, pitch 20 mm C: inner diameter 6.0 mm, pitch 20 mm

2. Measurement of Sound Absorption Characteristics The sound absorption characteristics were measured according to the vertical incident sound absorption coefficient measurement by the in-pipe method of JIS A1405. The measurement results are shown below. Sound absorber with circular holes A: 600 Hz has the highest sound absorption (sound absorption rate 30%). Sound absorber with a circular hole B: 1000 Hz has the highest sound absorption (sound absorption rate 50%). Sound absorber with a circular hole of C: 1200 Hz has the highest sound absorption (sound absorption rate 60%).

Example 2 Regarding the second embodiment,
A sound absorber was manufactured under the following specific conditions. 1. Sound Absorber Manufacturing Method (1) The injection molding apparatus 50 shown in FIG. 2 was used. In the injection cylinder 61 of the injection molding device 50, the resin temperature of the molding material 21
0 ° C polypropylene (made by Idemitsu Petrochemical Co., Ltd. [MI =
30 g / 10 min (measured by the method according to JIS K 7210), homopolypropylene, grade name J300
0 GV]) with a resin back pressure of 12 MPa,
Nitrogen gas pressurized to 13 MPa was introduced into the injection cylinder 61.

Mosttron L (40% by weight glass fiber reinforced polypropylene manufactured by Idemitsu Petrochemical Co., Ltd.) was side-fed from the inlet B. Nitrogen gas is gas cylinder 5
From 1 to the injection cylinder 61, 0.6 wt% was supplied to the total amount of Mostron L and the polypropylene, and Mosttron L was supplied so that the glass fiber amount was 25% with respect to the total amount.

The high-pressure nitrogen is heated to the resin temperature to become a supercritical fluid, and is mixed and / or dissolved with Mostron L and the polypropylene, and then, in the disk-shaped cavity having a t1 of 5 mm and a diameter of 250 mm in FIG. 4 (A). And filling speed 40m
Injection filling at m / sec, 1 sec before the filling is completed,
The moving mold was advanced and shaped until t2 of (B) was 3 mm (resin filling amount is a cavity wall thickness of 3 mm). 1 second after the completion of filling, move the moving mold to 2 mm /
The cavity wall thickness was expanded to 9 mm at a retreat speed of 2 seconds.

After cooling, the disk-shaped molded product was taken out, and 25 circular holes shown in the following D were drilled on one surface of the molded product with a drill. D: Inner diameter 6.0 mm, pitch 20 mm, depth 3 mm After evaluating the sound absorbing characteristics described later, when the cross section in the thickness direction of the sound absorber was observed, the unfoamed layer was 2.0 mm. Also,
Ash remaining after ashing the sound absorber (mainly glass fiber)
Was measured with a microscope and the average fiber length was measured by a method in which the fiber length was 1.8.
It was mm.

2. Measurement of Sound Absorption Characteristics The sound absorption characteristics were measured according to the vertical incident sound absorption coefficient measurement by the in-pipe method of JIS A1405. Measurement result: 1200 Hz has the highest sound absorption (sound absorption rate 60%).

According to Examples 1 and 2, it is understood that by forming holes having various hole diameters and pitches in the sound absorbing body, it is possible to efficiently absorb sounds in a wide range of frequencies.

[0099]

According to the present invention, both sound absorbing performance and sound insulating performance can be secured by integrally molding without laminating a plurality of materials, and only unpleasant sound can be selectively absorbed. A sound absorbing body and a sound absorbing structure can be provided.

[Brief description of drawings]

FIG. 1 is a plan view (A) and a sectional view (B) of a sound absorbing body of the present invention.
Is.

FIG. 2 is a schematic view of an injection molding apparatus used when manufacturing the sound absorbing body of the present invention.

FIG. 3 is a schematic view of a molding machine used when manufacturing the sound absorbing body of the present invention.

FIG. 4 is a diagram for explaining a procedure for molding the sound absorbing body of the present invention.

[Explanation of symbols]

40 sound absorber 41, 42 unfoamed layer 41A hole 43 foam layer 44 molded body

Front page continuation (51) Int.Cl. ⁷ identification code FI theme code (reference) C08J 9/12 CEZ C08K 7/02 4J002 C08K 7/02 C08L 101/00 5D061 C08L 101/00 E04B 1/82 M E04B 1 / 82 E06B 5/20 E06B 5/20 G10K 11/16 EF term (reference) 2E001 DF04 GA01 GA82 HD11 HE01 JA22 JA28 JA29 JB07 2E039 BB03 3D023 BA02 BA03 BB21 BB30 BC00 BD02 BD03 BD04 BD18 BD21 BE02 BE04 BE24 4F074 A07 A4A97A AE04 AG01 BA31 BA33 CA26 DA20 DA35 DA57 DA59 4F100 AK01A AK01B AK01C AT00C BA03 BA07 DC11A DJ01B EH36 GB32 JH01 JL02 4J002 AA011 BB031 BB121 BB121 BN01 DF01A06A00 BN01A6A6A0B01B01B01B01B01B01B01B01B01B01B01B01B01B01B01B01B01B01B01A0101

Claims (5)

[Claims] 1. A molded article comprising two unfoamed layers and a foamed layer sandwiched between these unfoamed layers and having a large number of voids, wherein the one unfoamed layer is present at any location of the molded article. A plurality of holes that penetrate the layer and have a depth that does not reach the other unfoamed layer are formed, the cross-sectional area of the holes is 0.7 to 400 mm ² , and the pitch thereof is 1 mm or more, and The sound absorbing body is characterized in that the foam layer has voids generated by depressurizing a molding material containing a supercritical fluid. 2. A molded body having two unfoamed layers and a foamed layer sandwiched between these unfoamed layers and having a large number of voids, wherein the one unfoamed layer is present at an arbitrary position of the molded body. A plurality of holes that penetrate the layer and have a depth that does not reach the other unfoamed layer are formed, the cross-sectional area of the holes is 0.7 to 400 mm ² , and the pitch thereof is 1 mm or more, and The sound absorbing body is characterized in that the foam layer has voids generated by decompressing a molding material containing a supercritical fluid and fibers having a weight average fiber length of 1 mm or more. 3. The sound absorbing body according to claim 1 or 2, wherein the thickness of at least one of the unfoamed layers is 0.5 to 2.
A sound absorbing body characterized by being 0 mm. 4. The sound absorbing body according to claim 1, wherein the foaming layer includes a high foaming region having a foaming ratio of 2.0 to 5.0 times. . 5. A sound absorbing structure used for applications requiring sound absorption, comprising the sound absorbing body according to any one of claims 1 to 4, a timing belt cover, an air cleaner cover, an air duct. , Engine cover, intake / exhaust resonator, intake manifold, engine room and indoor shielding plate,
A sound absorbing structure characterized by being used as either a trunk room, an automobile ceiling material, or a door panel.