JP2007230130A - Sound absorption laminate structure using foam honeycomb core - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a honeycomb sound-absorption laminate structure employing a compound foam sheet which is produced by imparting stiffness to a foam material made of a soft thermoplastic resin having high sound-absorbing performance but poor stiffness and is available as a sound absorption material for e.g. various industrial materials. <P>SOLUTION: The sound absorption laminate structure is a laminate consisting of a compound foam sheet 1 in which cells of a honeycomb-structured core made of foam of a thermoplastic resin (A) are filled with foam of another thermoplastic resin (B) and a sheet which has a large number of pores and is laminated on the compound foam sheet. The sheet having a large number of pores 7 is arranged on the side facing a sound source. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sound-absorbing laminated structure using a foamed honeycomb core. More specifically, the present invention relates to two or more types of thermoplastics in which the material forming the honeycomb structure core and the material filled in each cell of the honeycomb structure core are different. The present invention relates to a sound-absorbing laminated structure using a foamed honeycomb core having a high sound-absorbing performance and rigidity, in which a sheet having holes formed thereon is laminated on a honeycomb core formed of a resin foam.

In recent years, noise problems are often highlighted, and sound absorption is attracting attention from the viewpoint of comfort, and sound absorption materials are widely used for building materials, automobile interior materials, and the like. As one of the sound-absorbing materials, there is a resin foam material, which is excellent in lightness, heat insulation, flexibility, floatability and moldability, and uses of the material using the foam material are expanding.
However, the sound absorption performance is that, when sound is applied to the substrate, the vibration of the air is transmitted to the air in the pores inside the substrate, causing viscous friction of the air in the pores, and a part of the sound energy is thermal energy. It is known that the resin foam having sound absorbing performance needs to be breathable because the sound must be penetrated into the material without being reflected by the material surface. ing. That is, the foam bubbles need to communicate. For this reason, a foamed foam is used by embossing or the like on a closed cell foam of a thermoplastic resin that is difficult to construct a continuous foamed urethane foam that is a thermosetting resin. . For example, a thermoplastic resin foam material to which sound absorbing performance is added by creating a gap in the foam material to be foam-molded and having an air flow resistance value in a specific range (see, for example, Patent Document 1) has an area. Examples thereof include a foamed plastic resin foam material (see, for example, Patent Document 2) that has been provided with sound absorbing performance that is formed so that holes of 1 mm ² or more have a hole area ratio of 3% or more.

On the other hand, the present inventors have already shown that a foam having a closed cell structure made of a flexible material has a characteristic sound absorption peak in a frequency range of 800 to 5000 Hz, which is not found in a hard material, and has a high sound absorption performance. The honeycomb sound-absorbing structure in which a high-stiffness thermoplastic resin and a foam of a flexible material are combined, which can be used for building materials and automotive applications by adding rigidity to the material (see, for example, Patent Document 3) ) Was developed, but there was a problem that the rigidity required for vehicle interior materials was slightly inferior.
JP 2003-25362 A JP 2003-25361 A Japanese Patent Application No. 2005-110750

  In view of the above problems, the object of the present invention is to provide a composite foam that can be used as a sound-absorbing material for various industrial materials by imparting rigidity to a flexible material foam of a thermoplastic resin that has high sound-absorbing performance but is inferior in rigidity. An object of the present invention is to provide a honeycomb sound-absorbing laminated structure using a sheet.

  As a result of intensive studies to solve the above problems, the present inventors have found that a flexible material foam made of a thermoplastic resin having high sound absorption performance but poor rigidity, and a honeycomb made of a lightweight and rigid thermoplastic resin foam A structure in which a sheet with holes formed on a composite foam sheet obtained by combining structural cores is laminated in a honeycomb structure core with a foam made of a flexible material having a sound absorbing action by Helmholtz resonance and a high sound absorbing performance. Therefore, it can be used as a sound-absorbing structure because it has sound absorption performance and can form a sandwich panel structure by laminating sheets. As a result, the present invention was completed.

  That is, according to the first aspect of the present invention, the composite foam sheet in which each cell of the honeycomb structure core made of the foam of the thermoplastic resin (A) is filled with the foam of another thermoplastic resin (B). A sound-absorbing laminate structure in which a sheet having a plurality of holes formed thereon is laminated, wherein the sheet having the plurality of holes is provided on a side facing a sound source. Provided.

  According to the second invention of the present invention, in the first invention, the sound absorbing material is characterized in that a hole is formed in the foamed body of the other thermoplastic resin (B) filled in the honeycomb structure core cell. A laminated structure is provided.

  Further, according to the third invention of the present invention, in the second invention, the opening area of the hole formed in the foam of another thermoplastic resin (B) filled in the honeycomb core cell is thermoplastic. There is provided a sound-absorbing laminated structure characterized by being smaller than the area of a honeycomb structure core made of a foam of the resin (A).

  According to the fourth invention of the present invention, in any one of the first to third inventions, the foam of the other thermoplastic resin (B) filled in the honeycomb core cell has an open cell structure. A sound-absorbing laminated structure is provided.

  According to the fifth invention of the present invention, in any one of the first to fourth inventions, the holes provided in the sheet laminated on the side facing the sound source are formed on the foam of the thermoplastic resin (B). A sound-absorbing laminated structure is provided, which is characterized in that the sound-absorbing laminated structure is disposed.

According to the sixth invention of the present invention, in any one of the first to fifth inventions, the bending elastic modulus of the thermoplastic resin (A) forming the foam of the honeycomb structure core is filled in the core cell. There is provided a sound-absorbing laminated structure characterized by being larger in flexural modulus of the other thermoplastic resin (B) forming the foam.

According to the seventh invention of the present invention, in any one of the first to sixth inventions, the flow resistance value of the foam of the thermoplastic resin (B) is 1.0 × 10 ^{3 to} 1.0 ×. There is provided a sound-absorbing laminated structure characterized by being 10 ⁶ Pa · S / m ² .

  According to the eighth invention of the present invention, in any one of the first to seventh inventions, the thermoplastic resin (A) forming the foam of the honeycomb structure core is polypropylene or high-density polyethylene, and A sound-absorbing laminated structure is provided in which the other thermoplastic resin (B) forming the foam filled in the core cell is an ethylene-vinyl acetate copolymer or low-density polyethylene.

  The sound-absorbing laminated structure of the present invention is obtained on a composite foam sheet filled in a honeycomb core made of a thermoplastic resin foam that is different from the thermoplastic resin and preferably made of a thermoplastic resin foam having a higher rigidity. In order to obtain a honeycomb sound-absorbing structure having high rigidity and excellent sound-absorbing function, it is used as a sound-absorbing structure for automobile interior materials. Can do.

  In the present invention, a foam of a thermoplastic resin (B) different from the thermoplastic resin (A) is formed in a cell of a honeycomb honeycomb core composed of a foam made of the thermoplastic resin (A). This is a honeycomb sound-absorbing laminated structure in which a sheet having holes formed thereon is laminated on a filled composite foam sheet. Hereinafter, the present invention will be described in detail with respect to the structure, material resin, manufacturing method and the like.

1. Composite Foam Sheet The composite foam sheet used in the sound-absorbing structure of the present invention has a structure in which the foam of the thermoplastic resin (B) is filled in the cells of the honeycomb structure core made of the foam of the thermoplastic resin (A). It is a sheet to have.

(1) Honeycomb structure core (i) Thermoplastic resin (A)
The thermoplastic resin (A) forming the honeycomb structure core foam is used for imparting rigidity to the thermoplastic resin foam filled in the honeycomb structure core. The thermoplastic resin (A) is not particularly limited as long as it is a foamable thermoplastic resin, but the bending elastic modulus of the thermoplastic resin (A) is that of the thermoplastic resin (B) to be filled. A resin having a flexural modulus or higher is preferable. If the flexural modulus of the thermoplastic resin (A) is smaller than that of the thermoplastic resin (B) to be filled, rigidity cannot be imparted, which is not preferable.
Specific examples of the thermoplastic resin (A) include, for example, low density polyethylene, high density polyethylene (HDPE), linear low density polyethylene, ethylene-vinyl acetate copolymer (EVA), random polypropylene, homopolypropylene, block Olefin resins such as polypropylene (hereinafter, “polypropylene (PP)” means random polypropylene, homopolypropylene, block polypropylene, or a mixture thereof); polyvinyl chloride, chlorinated polyvinyl chloride, ABS resin, polystyrene , Polycarbonate, polyamide, polyvinylidene fluoride, polyphenylene sulfide, polysulfone, polyether ether ketone, and copolymers thereof. Among these thermoplastic resins, crystalline PP and HDPE are preferably used from the viewpoint of the rigidity of the obtained foam.

  Further, the thermoplastic resin (A) forming the honeycomb core is used as a sheet that forms the honeycomb core by foaming and at the same time coats the surface of the foam filled in the cells of the honeycomb structure core. Therefore, a thermoplastic resin having a large MI, which is an indicator of fluidity, is preferable because it can reduce the time required for coating.

The thermoplastic resin (A) may be cross-linked as necessary. By using a crosslinked thermoplastic resin, the expansion ratio can be improved. Weight reduction of the obtained foam can be achieved by increasing the expansion ratio, and from this point of view, it is preferable to use a crosslinked product. Examples of the crosslinking method include a method in which a peroxide is melt-kneaded in a thermoplastic resin at a temperature lower than the decomposition temperature of the peroxide, and then heated to a temperature higher than the decomposition temperature of the peroxide for crosslinking.
The peroxide used in this method is not particularly limited, and examples thereof include dibutyl peroxide, dicumyl peroxide, tertiary butyl cumyl peroxide, diisopropyl peroxide, and the like, since the decomposition temperature is in an appropriate temperature range. Dicumyl peroxide and tertiary butyl cumyl peroxide are preferable, and dicumyl peroxide is particularly preferable.

  The added amount of the peroxide is preferably 0.5 to 5 parts by weight, particularly preferably 1 to 3 parts by weight with respect to 100 parts by weight of the thermoplastic resin. If the amount is too large, the resin decomposition reaction tends to proceed, and the resulting foam is colored. If the amount is too small, crosslinking of the thermoplastic resin may be insufficient, which is not preferable.

(Ii) Foam of the thermoplastic resin (A) In the present invention, the foam of the thermoplastic resin (A) is obtained by adding a foaming agent to the thermoplastic resin and foaming it. As the foaming agent, a thermal decomposition type chemical foaming agent that generates a decomposition gas by heating can be suitably used. Specific examples of the thermally decomposable chemical blowing agent are not particularly limited as long as they have a decomposition temperature higher than the melting temperature of the thermoplastic resin used. For example, sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, azide Inorganic thermal decomposition type foaming agents such as compounds and sodium borohydride; azodicarbonamide, azobisisobutyronitrile, N, N′-dinitrosopentamethylenetetramine, P, P′-dinitrosopentamethylenetetramine, P , P′-oxybisbenzenesulfonylhydrazide, barium azodicarboxylate, trihydrazinotriazine and the like. Among them, azodicarbonamide, which is easy to adjust the decomposition temperature and decomposition rate, has a large amount of gas generation, and is excellent in hygiene, is preferable.

The amount of the pyrolytic chemical foaming agent added is preferably 1 to 25 parts by weight per 100 parts by weight of the thermoplastic resin (A). If the amount of the pyrolytic foaming agent added is too large, bubbles are broken and uniform cells are not formed. Conversely, if the amount is too small, foaming may not be sufficiently achieved.
The expansion ratio of the thermoplastic resin (A) foam is preferably 2 to 60 times, more preferably 5 to 40 times. When the expansion ratio is less than 2, sufficient lightness cannot be obtained, and the sound absorbing performance of the obtained foam is also lowered. On the other hand, if the expansion ratio exceeds 60 times, uniform cells cannot be formed, and it is difficult to obtain a good foam.
The foaming ratio is a value expressed as the reciprocal of the specific gravity.

(2) Core filler (i) Thermoplastic resin (B)
The foamed thermoplastic resin (B) filled in the honeycomb structure core is not particularly limited as long as it is a foamable thermoplastic resin, but the foam has flexibility and a flexural modulus. Is preferably 1 to 100 MPa. Examples of such thermoplastic resins include low density polyethylene, high density polyethylene, linear low density polyethylene, ethylene-vinyl acetate copolymer (EVA), ethylene / propylene / diene copolymer rubber (EPDM), and the like. Olefin-based resin. Among these, linear low density polyethylene and EVA are particularly desirable.
In the present invention, the flexibility of the thermoplastic resin is based on the value of the flexural modulus of the resin, and refers to that having a flexural modulus of 1 to 100 MPa.

The density of the linear low-density polyethylene preferably used is preferably 0.860 to 0.920 g / cm ³ . When the density is less than 0.860 g / cm ³ , the productivity decreases with a decrease in moldability, and when it exceeds 0.920 g / cm ³ , the foamability decreases and a good foam is obtained. I can't.

  Moreover, the vinyl acetate (VA) content of EVA preferably used is preferably 40% or less. When the VA content of EVA is 40% or more, the foamability is remarkably lowered and a good foam cannot be obtained.

Furthermore, the range of MI of the thermoplastic resin (B) is preferably 0.1 to 10 g / 10 min. When MI is less than 0.1 g / 10 min, productivity is lowered along with a decrease in moldability, and when it exceeds 10 g / 10 min, foamability is lowered. Among the thermoplastic resins, EVA is particularly preferable from the viewpoint of increasing the flexibility of the foam obtained.
The flexibility of the foam resin is defined using the flexural modulus of the resin forming the foam (JIS K7106), and MI is a value measured at 230 ° C. and 21.18 N load according to JIS K7210. It is.

The thermoplastic resin (B) may be cross-linked as necessary. By using a cross-linked thermoplastic resin, it is preferable to use a cross-linked one because the expansion ratio can be improved and the weight of the resulting foam can be reduced. Examples of the crosslinking method include a method in which a peroxide is melt-kneaded in a thermoplastic resin at a temperature lower than the decomposition temperature of the peroxide, and then heated to a temperature higher than the decomposition temperature of the peroxide for crosslinking.
The peroxide used in this method is not particularly limited, and examples include dibutyl peroxide, dicumyl peroxide, tertiary butyl cumyl peroxide, diisopropyl peroxide, and the like, since the decomposition temperature is in an appropriate temperature range. Dicumyl peroxide and tertiary butyl cumyl peroxide are preferable, and dicumyl peroxide is particularly preferable.

  The added amount of the peroxide is preferably 0.5 to 5 parts by weight, particularly preferably 1 to 3 parts by weight with respect to 100 parts by weight of the thermoplastic resin (B). If the amount is too large, the resin decomposition reaction tends to proceed, and the resulting foam is colored. If the amount is too small, crosslinking of the thermoplastic resin may be insufficient, which is not preferable.

(Ii) Foam of thermoplastic resin (B) In the present invention, a foaming agent is added to the thermoplastic resin (B) in order to obtain a foam of the thermoplastic resin (B). As the foaming agent contained in the foamed layer resin, a thermally decomposable chemical foaming agent that generates a decomposition gas by heating can be suitably used. The pyrolytic foaming agent is not particularly limited as long as it has a decomposition temperature higher than the melting temperature of the thermoplastic resin used. For example, sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, azide compound, Inorganic thermal decomposition foaming agent such as sodium hydride; azodicarbonamide, azobisisobutyronitrile, N, N′-dinitrosopentamethylenetetramine, P, P′-dinitrosopentamethylenetetramine, P, P ′ -Oxybisbenzenesulfonyl hydrazide, barium azodicarboxylate, trihydrazinotriazine, etc. are mentioned, and azodicarbonamide is preferred because it is easy to adjust the decomposition temperature and decomposition rate, has a large amount of gas generation, and is excellent in hygiene.

The amount of the pyrolytic chemical foaming agent added is preferably 1 to 25 parts by weight per 100 parts by weight of the thermoplastic resin (B). If the amount of the pyrolytic foaming agent added is too large, bubbles are broken and uniform cells are not formed. Conversely, if the amount is too small, foaming may not be sufficiently achieved.
The foam of the present invention is obtained by foaming the above thermoplastic resin using the above foaming agent. By setting the amount of the foaming agent within the above range, the foaming ratio is preferably 2 to 60 times. More preferably, a foam of 5 to 40 times is obtained. If the expansion ratio is less than 2 times, sufficient lightness cannot be obtained, and the sound absorption performance of the resulting foam is also deteriorated. If it exceeds 60 times, uniform cells cannot be formed, and good foaming is achieved. It is difficult to get a body. In particular, when the expansion ratio is 5 or less, it is difficult to obtain light weight and it is difficult to obtain sufficient sound absorption.
The foaming ratio is a value expressed as the reciprocal of the specific gravity.

Note that the cell structure of the foam of the thermoplastic resin (B) filled in the honeycomb cell may be an open cell structure. The flow resistance value of the foam of the thermoplastic resin (B) having an open cell structure is preferably 1.0 × 10 ^{3 to} 1.0 × 10 ⁶ Pa · S / m ² , more preferably 5 0.0 × 10 ^{4 to} 5.0 × 10 ⁵ Pa · S / m ² . When the flow resistance value is less than 1.0 × 10 ³ Pa · S / m ² , sound waves easily enter the material, energy loss of sound waves is reduced, sound absorption performance is impaired, and 1.0 × 10 ⁷ Pa. · S / m ² and is poor ventilation exceeds, because sound waves from entering the material, sound absorbing performance is impaired.
The flow resistance value is a value measured according to the measurement of ISO 9053.

(3) Composite Foamed Sheet Structure An example of the composite foamed sheet structure used in the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view in the thickness direction of a composite foam sheet used in the present invention, and FIG. 2 is a cross-sectional view in the XX ′ direction of FIG. 1 and 2, a composite foam sheet 1 is formed of honeycomb core partition walls 2 and honeycomb cells 3 formed therefrom. The honeycomb core partition walls 2 are made of a foam of thermoplastic resin (A). It has a shape filled with a foam of the thermoplastic resin (B).

The honeycomb structure core of the composite foam sheet of the present invention has a shape in which a so-called honeycomb core is formed of the thermoplastic resin foam, and the thickness of the partition wall 2 of the honeycomb structure core is not particularly limited. .1 to 4.0 mm is preferable. The size of the cells 3 formed in the honeycomb structure core is preferably 6.0 to 20.0 mm. Furthermore, the total thickness of the honeycomb structure sheet 1 is preferably 4.0 to 20.0 mm. If each of these is out of the above range, it is not preferable in terms of flexibility, rigidity, and sound absorption.
The honeycomb cell size refers to the width d shown in FIG. 2 when the cell shape is hexagonal.

  Further, in order to increase the rigidity of the entire composite foam sheet, as shown in FIG. 3, the thickness of the composite foam sheet of the honeycomb structure core partition wall 2 of the high rigidity material is inclined to approach the outer surface of the composite foam sheet. Accordingly, it is possible to adopt a structure in which the cross-sectional area of the cell 3 formed of the foam of the thermoplastic resin (B), which is a flexible material, is increased.

  Furthermore, as shown in FIG. 4, holes 4 can be formed in the foam of the thermoplastic resin (B) filled in the honeycomb core of the composite foam sheet of the present invention. The size of the hole 4 to be opened is not particularly limited, but is preferably smaller than the size (surface area) of the honeycomb structure core defined above. When it becomes larger than the honeycomb core, the honeycomb core is scraped, and the partition walls of the honeycomb structure core become thin, leading to a decrease in rigidity.

2. Laminated perforated sheet The perforated sheet used in the sound-absorbing laminated structure of the present invention is laminated on a composite foam sheet to form a sandwich panel structure and used for imparting rigidity.
The material of the perforated sheet is not particularly limited, but from the viewpoint of imparting rigidity, the material preferably has a flexural modulus of 500 MPa (JIS K-6922-2) or higher. If the flexural modulus of the material is less than 500 MPa, rigidity cannot be imparted, which is not preferable.

  The size of the hole in the perforated sheet is not particularly limited, but is preferably smaller than the honeycomb core from the viewpoint of obtaining a sound absorbing action by Helmholtz resonance. If the pores of the perforated sheet are larger than the honeycomb core, the sound absorption performance is lowered. Also, the number of holes is not particularly limited, but is preferably the same as the number of cells of the composite foam sheet, and particularly when the cells are perforated, it is the same as the number of holes. Is preferred.

  Moreover, it is desirable that the holes in the perforated sheet are arranged on the foam of the thermoplastic resin (B) filled in the honeycomb core cell in the composite foam sheet. If the holes are not arranged on the thermoplastic resin (B), the sound absorbing action by the flexible material foam and the sound absorbing action by Helmholtz resonance cannot be obtained, so that the sound absorbing performance is lowered.

3. Sound absorbing laminated structure using foamed honeycomb core
The sound absorbing laminated structure of the present invention is obtained by laminating the perforated sheet on the composite foam sheet.
An example of the sound-absorbing laminated structure of the present invention will be described with reference to the drawings. FIG. 5 is a cross-sectional view of the sound absorbing laminated structure of the present invention. In FIG. 5, the sound absorbing structure 5 is formed by laminating a sheet 6 provided with a large number of holes 7 on the composite foam sheet 1 formed from the honeycomb core partition walls 2 and the honeycomb cells 3. The side on which the stacked sheets 6 are laminated is the side facing the sound source. FIG. 6 is an example in which holes 4 are provided in the foam 3 constituting the cell, and FIG. 7 is an example in which the holes 4 are provided in the foam 3 constituting the cell and the honeycomb structure core partition walls 2 are arranged in the thickness direction. This is an example with an inclination.

  The sound-absorbing laminated structure of the present invention is, for example, a structure as shown in FIGS. 5 to 7, on a composite foam sheet in which rigidity is imparted to a flexible material foam having sound-absorbing characteristics by a honeycomb structure core of a highly rigid material. Further, by laminating perforated sheets, a highly rigid sandwich panel structure is formed, and sound absorption by a flexible material and sound absorption action by Helmholtz resonance can be used, resulting in a structure that achieves both sound absorption performance and rigidity. Such a structure having both rigidity and sound absorbing performance can be effectively used as a sound absorbing material in the field of automobile interior materials where high rigidity and sound absorbing performance are particularly required.

4). Production method of sound-absorbing laminated structure using foamed honeycomb core The sound-absorbing laminated structure of the present invention is produced by producing a composite foam sheet and laminating a perforated sheet on the composite foam sheet. Each of these will be described below.

(1) Production method of composite foam sheet The composite foam sheet of the present invention comprises a step (i) of forming a foamable thermoplastic resin sheet having a plurality of foamable thermoplastic resins (B) granules connected to the surface thereof, It comprises a step (ii) of coating the surface of the granular material side of the sheet with a foamable thermoplastic resin (A), followed by a step of foaming the whole (iii), and if necessary, a perforating step (iv). Each step will be described in detail.

(I) Forming process of foamable thermoplastic resin sheet The first process of producing the composite foamed sheet of the present invention is to form a foamable thermoplastic resin sheet having a plurality of foamable thermoplastic resin granules connected to the surface. It is a process to do. The sheet having a plurality of foamable thermoplastic resin granules connected to the surface is, for example, a sheet having a cross section shown in FIG. In FIG. 8, a foamable thermoplastic resin sheet 10 is a sheet having a shape in which a plurality of foamable resin granules 12 are connected to the surface of a foamable thermoplastic resin thin film 11.
The foamable thermoplastic resin thin film is melt-kneaded at a temperature lower than the decomposition temperature of the thermally decomposable foaming agent by supplying the thermoplastic resin (B) with a thermally decomposable foaming agent and, if necessary, a crosslinking agent. The foamable thermoplastic resin composition obtained is extruded from a T die or the like. The thickness of the thin film is preferably 0.1 to 0.6 mm, more preferably 0.3 to 0.5 mm. If the thickness of the foamable thermoplastic resin thin film is too thick, the foamable thermoplastic resin sheet is likely to be corrugated during heating, and if it is too thin, the foamable thermoplastic resin thin film is easily broken when producing the foamable thermoplastic resin sheet. .

  The method of connecting the foamable thermoplastic resin granules to the surface of the thin film is not particularly limited, but there is a method in which a fluororesin sheet having a plurality of recesses or a mold is hot-pressed on the thin film obtained above. Can be mentioned. Examples of the method of hot pressing a fluorine resin sheet having a plurality of recesses include a method of hot pressing a fluorine resin sheet having a plane shown in FIG. 9 on the thin film. In FIG. 9, the fluororesin sheet 14 has a plurality of holes 15, and the shape of the foamable granular material 12 on the thin film 11 depends on the shape of the holes 14. The shape of the foamable thermoplastic resin granular material 12 is not particularly limited, and can be, for example, a hexagonal shape, a cylindrical shape, etc., and can be easily foamed uniformly when the foamable thermoplastic resin granular material 12 is foamed. Since the ratio of the area of the foam portion of the thermoplastic resin (B) on the foam surface side can be increased, it is preferable to make a truncated cone shape with high sound absorption performance.

The arrangement and size of the expandable granular material 12 on the thin film 11 can be changed by adjusting the recesses of the fluororesin sheet and the mold, and this arrangement and size can be used to increase the honeycomb structure after foaming described later. The shape and size of the core is determined.
Further, the shape of the pores 15 and the arrangement method can change the shape of the honeycomb core after foaming into a polygon such as a triangle, a quadrangle, a hexagon, and an octagon. It is desirable to make it square. Further, a method of controlling the shape, arrangement, and expansion ratio of the holes so that the size of the honeycomb core is 5 to 20 mm from the viewpoint of rigidity is preferable. Here, the size of the honeycomb core indicates, for example, the distance d shown in FIG. 2 when the honeycomb core is a hexagon.

(Ii) Step of coating the foamable thermoplastic resin (A) on the surface of the foamable sheet on the granule side Foam melted on the surface of the foamable thermoplastic resin (B) sheet obtained as described above on the granule side The composite thermoplastic resin (A) is coated to form a composite foamable thermoplastic sheet. The foamable thermoplastic resin (A) is supplied to the thermoplastic resin (A) by supplying a pyrolytic foaming agent and, if necessary, a cross-linking agent to an extruder, at a temperature lower than the decomposition temperature of the pyrolytic foaming agent. It can be melt-kneaded. As a coating method of the foamable thermoplastic resin (A), the foamable resin sheet to be coated is laminated on the foamable thermoplastic resin (B) sheet, and the temperature is lower than the decomposition temperature of the pyrolytic foaming agent. And it processes at the temperature more than melting | fusing point of resin to coat. The heat treatment method is not particularly limited. For example, a heating method using an electric heater, a far infrared heater, a heating device in which a heating medium such as heated oil or air is circulated, or the like is used. Can be mentioned.

  As another method for producing a composite foamable thermoplastic resin sheet, a foamable thermoplastic resin (A) sheet to be coated and a foamable thermoplastic resin (B) sheet that forms a foam layer in a cell are laminated. As mentioned above, there is a method in which a fluororesin sheet or a mold having a concave portion is stacked and hot pressed. In this method, since the coating time is not required, productivity is improved.

  A method for producing a composite foamable thermoplastic resin sheet by hot pressing the laminated sheet will be described with reference to FIG. Laminate the foamable thermoplastic resin (A) sheet to be coated and the foamable thermoplastic resin (B) sheet that forms a foam layer in the cell (FIG. 10 (a)), and then stack the fluororesin sheet and mold. The composite sheet (FIG. 10 (b)) in which the foamable thermoplastic resin (B) is coated on the surface of the foamable thermoplastic resin (A) sheet on the particulate side can be obtained.

(Iii) Foaming step A honeycomb sound-absorbing structure is manufactured by foaming the composite foamable thermoplastic resin sheet obtained above. The heating method for foaming the composite foamable thermoplastic resin sheet is not particularly limited as long as it can be heated above the decomposition temperature of the contained pyrolytic foaming agent. Examples of the heating method include an infrared heater and a heating device in which a heating medium such as heated oil or air is circulated.
In particular, as a continuous foaming device, in addition to a take-off type foamer that foams while taking out foam on the outlet side of the heating furnace, a belt-type foamer, a vertical or horizontal foaming furnace, a hot air thermostat, or an oil bath, a metal bath A heat bath such as a salt bath is used.
By heating, the foamable thermoplastic resin (B) granules are foamed so as to fill the gaps between the foams of the thermoplastic resin (A). As a result, a honeycomb-like cell is formed so that the foam of the thermoplastic resin (A) forms a columnar structure between the granular foams of the flexible material, and after foaming of the foamable thermoplastic resin (B) granules The shape becomes a honeycomb structure such as a regular hexagon, and the rigidity can be increased.

(Iv) Hole making step Holes are made in the thermoplastic resin (B) foam which is the flexible material portion of the composite foam sheet obtained above. The method for forming a hole is not particularly limited, and examples thereof include a laser method and a drill method.

(2) Lamination of perforated sheet The honeycomb sound-absorbing laminated structure of the present invention is obtained by laminating a perforated sheet on the composite foam sheet.
The composite foam sheet forms a honeycomb structure having a specific shape. Depending on the shape, holes are created in the perforated sheet and disposed so that the holes of the perforated sheet can be disposed on the thermoplastic resin (B) foam filled in the honeycomb core.
The method for laminating the perforated sheet on the composite foam sheet may be a conventionally known laminating method.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to an Example. The measurement methods used in the examples are as follows.
(1) Foaming ratio: Measured according to JIS K6767.
(2) Foam thickness: measured with calipers.
(3) Flexural modulus: measured in accordance with JIS K7106.
(4) Compressive strength: measured in accordance with JIS K6767.
(5) Peak sound absorption rate: measured in accordance with JIS A1405.

Example 1
(1) Manufacture of a composite foamable thermoplastic sheet As a foamable thermoplastic resin filled in a cell, an ethylene-vinyl acetate copolymer (EVA; H1011 (trade name) manufactured by Sumitomo Chemical Co., Ltd.) Flexural modulus = 48 MPa, MI = 0.6 g / 10 min, VA content = 15%), dicumyl peroxide (Park Mill D (trade name) manufactured by NOF Corporation) as a crosslinking agent, and azodicarbonamide (Otsuka Chemical) as a foaming agent SO-20 (trade name) manufactured by the company was supplied to a twin screw extruder, melted and kneaded at 130 ° C., and extruded into a sheet form with a T-die having a surface length of 300 mm and a lip of 1.5 mm.
On the other hand, as the foamable thermoplastic resin forming the honeycomb core, polypropylene (PP; MA3 (trade name) manufactured by Nippon Polypro Co., Ltd.) and quinone dioxime (manufactured by Ouchi Shinsei Chemical Co., Ltd.) as the cross-linking agent in the proportions shown in Table 1. Azodicarbonamide (SO-20 (trade name) manufactured by Otsuka Chemical Co., Ltd.) as a foaming agent is supplied to a twin screw extruder, melt-kneaded at 130 ° C., and sheeted with a T-die having a surface length of 300 mm and a lip of 1.5 mm. Extruded.
The two foamed thermoplastic resin sheets obtained above are laminated, a fluorine resin sheet having a hole with a diameter of 4.0 mm as shown in FIG. 9 is laminated, and the top of the fluorine resin sheet is laminated. A heat press was performed at 170 ° C. to perform crosslinking and shaping. Next, it cooled by the 25 degreeC cooling press, and obtained the composite foamable thermoplastic resin sheet of the shape shown in FIG.10 (b). Table 1 shows the physical properties.

(2) Manufacture of honeycomb structure The composite foamable thermoplastic resin sheet obtained above is placed on a fluororesin sheet, the fluororesin sheet is overlaid thereon, and heated for 10 minutes using a 230 ° C hand press. And foamed. Then, it moved to the 25 degreeC cooling press, and obtained the composite foam sheet by cooling for 10 minutes.
As shown in FIGS. 1 and 2, the obtained composite foamed sheet is foamed by heating so that the foamable thermoplastic resin granules fill the gaps of the thermoplastic resin foam forming the core partition walls. The foamed body had a regular hexagonal honeycomb structure, and the polypropylene resin foam formed honeycomb cells between the foams.

(3) Production of sound-absorbing laminated structure A hole having a diameter of 2 mm and a depth of 4 mm was drilled in the flexible foam portion (EVA foam) of the obtained composite foam sheet.
Next, a hole with a diameter of 0.5 mm is drilled on a 1 mm thick sheet made of polypropylene (PP; MA3 (trade name) manufactured by Nippon Polypro Co., Ltd.) directly above the hole formed in the composite foam sheet. The sheet was pasted with an adhesive such as hot melt so that the holes of the sheet and the holes of the composite foamed sheet overlapped to create a laminated structure. The resulting laminate structure was measured for foaming ratio, foam thickness, compressive strength, and sound absorption coefficient. The results are shown in Table 1 and FIG.

(Example 2)
Example 1 A laminated structure was obtained in the same manner as in Example 1 except that 100-mm holes having a diameter of 0.1 mm were randomly opened per honeycomb cell in the flexible foam part (EVA foam) of the obtained composite foam sheet. Created. The resulting laminate structure was measured for foaming ratio, foam thickness, compressive strength, and sound absorption coefficient. The results are shown in Table 1 and FIG.

(Comparative Example 1)
The sound absorbing performance was measured using an ethylene-vinyl acetate copolymer foam in which the raw material resin had a flexural modulus of 48 MPa. The results are shown in Table 1 and FIG.

(Comparative Example 2)
The sound absorption performance was measured using a polypropylene foam having a flexural modulus of the raw material resin of 1500 MPa. The results are shown in Table 1 and FIG.

(Comparative Example 3)
The sound absorption performance was measured using a composite foam sheet in which the honeycomb core was not foamed. The results are shown in Table 1 and FIG.

  As is apparent from the results of Table 1 and FIG. 11, the sound-absorbing laminated structures obtained in Examples 1 and 2 according to the present invention are excellent in 50% compressive strength and have an excellent sound absorption coefficient. I understand.

  The laminated structure of the present invention is excellent in rigidity and sound absorbing performance, and can be used in various material fields as a sound absorbing material, and can be particularly effectively used as a sound absorbing material in the automotive field.

It is sectional drawing of an example of the composite foam sheet used by this invention. It is sectional drawing of the X-X 'direction of FIG. It is sectional drawing of the other example of the composite foam sheet used by this invention. It is sectional drawing of the other example of the composite foam sheet used by this invention. It is sectional drawing of an example of the sound absorption laminated structure of this invention. It is sectional drawing of the other example of the sound absorption laminated structure of this invention. It is sectional drawing of the other example of the sound absorption laminated structure of this invention. It is sectional drawing of an example of the foamable thermoplastic resin sheet used by this invention. It is a top view of an example of the fluorine resin sheet used by the present invention. It is a figure explaining an example of the manufacturing method of the composite foam sheet of this invention. It is a sound-absorption measurement result of the laminated structure of an Example and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Composite foam sheet 2 Honeycomb core partition 3 Honeycomb cell 4 Hole 5 Sound absorption laminated structure 6 Perforated sheet 7 Hole 10 Expandable thermoplastic resin sheet 11 Expandable thermoplastic resin thin film 12 Expandable resin granular material 14 Fluorine-based resin sheet 15 Hole

Claims (8)

  A sheet having a large number of holes is laminated on a composite foam sheet in which each cell of a honeycomb structure core made of a foam of the thermoplastic resin (A) is filled with a foam of another thermoplastic resin (B). A sound-absorbing laminated structure, characterized in that the laminated sheet is provided on the side facing the sound source.   2. The sound-absorbing laminated structure according to claim 1, wherein the foam of the other thermoplastic resin (B) filled in the honeycomb core cell has a hole.   The hole area of the hole formed in the foam of the other thermoplastic resin (B) filled in the honeycomb structure core cell is smaller than the area of the honeycomb structure core made of the foam of the thermoplastic resin (A). The sound-absorbing laminated structure according to claim 2, wherein   The sound absorbing laminated structure according to any one of claims 1 to 3, wherein the foam of the other thermoplastic resin (B) filled in the honeycomb structure core cell has an open cell structure.   The sound absorption according to any one of claims 1 to 4, wherein the hole provided in the sheet laminated on the side facing the sound source is disposed on the foam of the thermoplastic resin (B). Laminated structure.   The bending elastic modulus of the thermoplastic resin (A) forming the foam of the honeycomb core is larger than the bending elastic modulus of the other thermoplastic resin (B) forming the foam filled in the core cell. The sound-absorbing laminated structure according to any one of claims 1 to 5. The flow resistance value of the foam of the thermoplastic resin (B) is 1.0 × 10 ^{3 to} 1.0 × 10 ⁶ Pa · S / m ^2. The sound-absorbing laminated structure according to item.   The thermoplastic resin (A) forming the foam of the honeycomb structure core is polypropylene or high-density polyethylene, and the other thermoplastic resin (B) forming the foam filled in the core cell is ethylene. The sound-absorbing laminated structure according to claim 1, which is a vinyl acetate copolymer or low-density polyethylene.

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