Patent Publication Number: US-2005126851-A1

Title: Molded sonic absorber

Description:
FIELD OF THE INVENTION  
      The present invention relates to a molded sonic absorber, a laminated sonic absorber, and an interior material for an automobile and the like using the absorbers.  
     PRIOR ART  
      Conventional sound absorption/sound-insulating material for a vehicle or a dwelling house and the sound absorption material for a sound-insulating wall in freeway, are principally glass wool, rock wool, aluminum fiber, lightweight foamcrete, porous ceramic or the like as an inorganic substance. As the organic material, a laminate of polymer foam such as foamed urethane with an adhesive such as isocyanate is used for automobile ceiling as sound absorption/sound insulating material. Sound absorption panel with fibrous body composed of an organic material is put to practical use, too.  
      However, a satisfactory sound absorption material could not be obtained in terms of an improvement in workability, prevention of an obstacle to the human body, environmental protection, and easy processing and potential for recycling of waste for efficient utilization of resources. The range of 400-1000 Hz is included in the range of human voice. The sense of hearing is more sensible to this range than the normal sound area. A person feels fatigued to noise including this range tiring. Therefore, a material that efficiently absorbs a noise in the above-mentioned frequency range has been demanded, but there has been no material that can satisfy the demand.  
      JP08-87278A, JP08-87279A, JP10-77562A, and JP10-110370 A have been known as the related prior arts.  
      JP 08-87278 A discloses a sound absorption sheet structured by a porous sound absorption body in which a porosity of a sound absorption layer increases as the layer approaches an outer surface. This invention enhances a sound absorption effect. However, a constitution of this invention is complicated, leading to poor practicability.  
      JP 08-87279 A discloses a method of uniformizing a sound absorption frequency range by laminating sound absorption materials of different sound absorption frequency ranges. However, this invention requires the following steps of: producing sound absorption materials of different sound absorption frequency ranges; and laminating the sound absorption materials, and therefore results in poor productivity.  
      JP 10-77562 A and JP 10-110370 A each disclose a manufacturing technique for a sound absorption material made of a fibrous body. Those inventions each disclose a sound absorption material which is structured by two or more kinds of fibers and in which a part of the constituent fibers are thermally fused. However, in order to adopt such a structure, the fibers must adopt a two-layer structure (a core/sheath structure) made up of a center layer and a surface layer. Therefore, a special apparatus is needed in producing the fibers. None of those inventions is general.  
      None of the above four inventions discloses use of a wate material or the like.  
      JP 08-84982 A discloses a method of recycling waste including: crushing discarded materials generated from automobiles and buildings into fine pieces; mixing the fine pieces with a binder; clamping the mixture by using a net-shaped material (for instance, a metal gauze or a punching metal) through which air can permeate; and molding the mixture under heating by allowing hot air to pass through the net-shaped material, so that the molded object is applicable to the sound absorption material or the like. However, a mesh in the metal gauze or the punching metal for clamping the finely crushed pieces is extremely small, and sound absorption performance is anticipated to deteriorate. The publication discloses nothing about a specific sound absorption effect.  
      JP 07-205169 A discloses a method of producing a molded soundproof material including: crushing discarded materials generated from automobiles and buildings; mixing the crushed product with a fibrous binder; evenly dispersing the mixture in water; subjecting the dispersion to dehydration and heating; and molding the resultant product under heating and pressure into a molded soundproof material. However, this method involves a problem in that the production process is complicated. The publication discloses nothing about a specific soundproofing effect of the resultant molded soundproof material.  
      JP03-7739A discloses a technique in which a ground material of polyurethane scrap is added and mixed with a prepolymer composed of a diol and an isocyanate using a binder, and in which the whole is subjected to molding under heating and pressure. However, the publication discloses nothing about a sound absorption effect.  
     DISCLOSURE OF THE INVENTION  
      A purpose of the present invention is to provide a sound absorption material and a laminated sonic absorber each of which is excellent in sound absorption property particularly in a human audible frequency range, and an interior material for an automobile and the like using the absorbers.  
      As means for solving the above problems, the present invention provides a molded sonic absorber containing (A) a chip of an organic or inorganic fibrous body and (B) a chip of an organic or inorganic porous body.  
      The phrase “fibrous body” as used herein refers to a molded object containing an organic or inorganic fiber, and the shape, size, or the like of the molded object is not particularly limited.  
      The term “chip” as used herein as against fibrous body includes: a ground, cut, cracked, or crushed product obtained by application of a mechanical means; one originally present as a chip in a fibrous body such as a fragment generated during the production processing; and a fibrous body molded into a chip. The shape and size of a chip are not particularly limited, but the chip preferably has a maximum length of 20 mm or less.  
      As other solving means, the present invention provides a laminated sonic absorber having two or more layers including the above molded sonic absorber and a foam in the form of a laminate.  
      The above molded sonic absorber or laminated sonic absorber is applicable to an interior material for an automobile, to a building material, and to a sound absorption structure. The term “structure” in the phrase “sound absorption structure” means a structure having a flat or solid shape in accordance with its application, and includes a structure of a desired shape such as a panel-like shape or a cabinet-like shape.  
      The phrase “sound absorption” as used herein refers to a property that acts to reduce the loudness level, and differs from a sound insulating action only for insulating a sound.  
      Examples of the chip of an organic fibrous body as the component (A) in the molded sonic absorber of the present invention include chips made from a thermoplastic resin, a thermosetting resin, a natural polymer, and a semisynthetic polymer.  
      Examples of the thermoplastic synthetic polymer include: polyolefin made of polyethylene, polypropylene, poly-4-methylpentene-1, and the like; ethylene-based copolymers such as an ionomer, an ethylene-vinyl acetate copolymer, an ethylene-methyl methacrylate copolymer, an ethylene-ethyl acrylate copolymer, and an ethylene-acrylic acid copolymer; halogen copolymers such as polyvinyl chloride or polyvinylidene chloride; an AS resin; an ABS resin; and polystyrene.  
      Examples of the thermosetting synthetic polymer include an epoxy resin and an unsaturated polyester resin. Examples of the natural polymer include cellulose, cotton, silk, wool, and hemp. Examples of a semisynthetic fiber include cellulose nitrate, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, and ethyl cellulose.  
      Examples of the chip of an inorganic fibrous body include chips made from glass wool, rock wool, an aluminum fiber, and a boron fiber.  
      In the case where a thermoplastic synthetic polymer is used as the component (A), a thermoplastic synthetic polymer having a high melting point is preferable. Many thermoplastic synthetic polymers have low melting points, and deform when heated in compression molding or the like treatment upon molding. Therefore, the shape of the fibrous body may not remain as it is, which may adversely affect the sound absorption performance.  
      In the case where a thermoplastic synthetic polymer is used as the component (A), preferable is a thermoplastic synthetic polymer provided with heat resistance comparable to that of a polyethylene terephthalate resin or a nylon 6 resin. However, a thermoplastic polymer compound having a lower melting point (for example, a polyethylene or an ethylene-based copolymer) can be used from the standpoint of utilizing waste as a raw material. In that case, it is desirable to adjust the melting point of the thermoplastic polymer compound and the content of the component (A).  
      In the case where a thermoplastic polymer compound having a low melting point is used, a thermoplastic polymer having a melting point in the temperature range of 80 to 110° C. is used. In addition, the content of the thermoplastic polymer compound in the component (A) is 20% by mass or less, preferably 15% by mass or less, more preferably 10% by mass or less, still more preferably 5% by mass or less, and particularly preferably 3% by mass or less.  
      In the case where a thermoplastic polymer compound having a low melting point is used as the component (A), it is desirable to adjust the heating temperature and heating time of the polymer compound in compression molding treatment according to the melting point and content of the polymer compound. If a thermoplastic polymer compound having a low melting point is used as the component (A), and the heating temperature and heating time of the polymer compound in compression molding treatment are adjusted, the polymer compound fuses to act as a binding agent or an adhesive. Therefore, a binding agent as a component (C) can be unnecessary, or the usage amount of the binding agent can be reduced. Furthermore, the sound absorption performance is not damaged by virtue of the action of the component (A) as the residue.  
      The component (A) preferably has high hardness to enhance the sound absorption performance. From such a point of view, cellulose acetate fibers, which are semisynthetic polymers, are preferable.  
      The cellulose acetate fibers are classified into a cellulose diacetate fiber and a cellulose triacetate fiber. Among them, the cellulose diacetate fiber is preferable. The cellulose diacetate fiber has higher hydrophobicity than that of a natural fiber, has lower hydrophobicity than that of a synthetic fiber, and thus has appropriate hygroscopicity and hydrophobicity. Therefore, moisture itself of the fiber which has appropriately taken up moisture acts to enhance the sound absorption performance, which is preferable.  
      In the case where a cellulose acetate fiber is used as the component (A), preferable is a cellulose acetate fiber containing an acetate filament (continuous fiber), an acetate tow obtained by bundling the acetate filament, or an acetate staple (short fiber). Those fibers may be crimped or may not be crimped. However, a crimped acetate staple is preferable in terms of air permeability and moisture retention.  
      A waste material such as a scrap fiber generated in a staple factory or the like or a scrap filter generated in a cigarette filter factory can be used as the cellulose acetate fiber. Among them, the scrap filter is preferable because every filter is cut into an equal fiber length and the cellulose diacetate fiber is used as a raw material. Those cellulose acetate fibers are preferably well disentangled before use by using a card or the like to enhance dispersibility in the molded sonic absorber.  
      In the case where a scrap filter for a cigarette is used, paper forming the filter (cigarette filter roll paper) is included in the component (A). Such a paper component accounts for less than 80% by mass, preferably 50% by mass or less, more preferably 40% by mass or less, still more preferably 30% by mass or less, particularly preferably 10 to 20% by mass, and most preferably 12 to 18% by mass of the component (A).  
      In the case where the paper content resulting from the raw material is great, a paper removing operation may be performed, or the component (A) containing no paper may be added separately. However, from the viewpoint of reducing waste and effectively utilizing resources, such a material may be applied as a production raw material for use in an application where the sound absorption performance is not required to a large extent. For example, such a material may be applied as a production raw material for use in an application where a heat insulating property is highly required rather than the sound absorption property.  
      The component (A) may be one containing a short fiber, a continuous fiber, or a mixture thereof.  
      With regard to the size (for a fiber, a fiber length) of the chip as the component (A), its maximum length is preferably 20 mm or less, more preferably 1 to 20 mm, still more preferably 5 to 20 mm, particularly preferably 10 to 20 mm, and most preferably 10 to 15 mm in order to enhance the dispersibility and the sound absorption performance.  
      The maximum length as used herein refers to a maximum value for a major axis of an island part (a domain) in the case where an area that has been subjected to molding under heating is taken with a known image capturing device, and is subjected to two-dimensional processing with an image processing device or the like.  
      A degree of fineness of the component (A), which is not particularly limited, is selected preferably from the range of 1.5 to 10 deniers, more preferably from the range of 2 to 8 deniers, and still more preferably from the range of 2.5 to 5 deniers. Fibers of different degrees of fineness may be mixed and used.  
      A sectional form of the component (A) is not particularly limited, but is preferably of a Y shape in terms of sound absorption performance and use of a cigarette filter provided as waste.  
      The component (A) may contain a component originating from a raw material. For instance, the component (A) may contain industrial waste such as rag opening, waste cotton, or a scrap fiber of a natural fiber to be disposed of as industrial waste or the like. As a matter of course, the component (A) may contain a scrap fiber of a synthetic fiber.  
      The component (B) in the molded sonic absorber of the present invention is an organic or inorganic porous body. Pores in the porous body may be independent of or continuous with each other. Examples of the inorganic porous body as the component (B) include activated carbon including charcoal, pumice, foamcrete, and sintered clay. Examples of the organic porous body include foams such as a polyethylene foam, a polystyrene foam, and a polypropylene foam.  
      A porous foam of the component (B) preferably uses at least an organic foam, in particular a polymeric foam rather than be composed only of an inorganic foam. A porous foam composed only of an inorganic foam makes it difficult to integrate the component (A) and the component (B), with the result that the strength of the resulting molded sonic absorber deviates from a practical range.  
      In the case where a mixture of an inorganic foam and an organic foam is used as the component (B), it is advantageous to set the content of the inorganic foam to be 20% by mass or less of the entire foam in terms of integration.  
      A thermoplastic polymeric foam such as a polyethylene foam or a polystyrene foam can be used as the polymeric foam. However, using a foam composed of a thermosetting resin provides a more preferable effect in terms of sound absorption performance. When a thermoplastic polymer foam is heated in compression molding, it may be deformed and a void ratio rate thereof may decrease. Sound absorption ability over the whole sound wave region may be easily lost. This case, however, is not so bad as the fibrous body.  
      A polyurethane foam (a urethane foam) can be given as a particularly preferable thermosetting polymeric foam, and particularly, a thermosetting polymeric foam composed of a soft polyurethane foam that is a foam obtained via a reaction between a polyol and an isocyanate. In the case where an adhesive is used to strongly integrate the component (A) with the component (B), the polyurethane foam is excellent in affinity with the adhesive and wettability. In addition, the polyurethane foam imparts strength, hardness, and durability to the molded sonic absorber, and is thus preferable.  
      The polyurethane foam serving as a raw material for the component (B) may be, for example, a scrap generated in a foaming process, a trim of urethane foaming, one used as a buffer material for baggage or the like, or one used as a filler for furniture or the like. A ground product of urethane and a compressed urethane chip which have been recovered from waste products such as home appliances, in particular a refrigerator, may be also used. For example, in the case of a refrigerator, a heat insulating material is sorted out through manual disassembly, urethane is sorted out by means of wind force, and urethane is ground into chips with a crusher. Each of these ground products may be used as a polyurethane foam. Alternatively, compressed urethane chips obtained by appropriately compressing those ground products may be used.  
      A density of the component (B) is preferably in the range of 0.015 to 0.03 g/cm 3 , more preferably in the range of 0.015 to 0.025 g/cm 3 , and still more preferably in the range of 0.015 to 0.02 g/cm 3 .  
      In the case where a polyurethane foam is employed as the component (B), a polyurethane foam molded product mechanically formed in to a chip through cutting, grinding, cracking, crushing, or the like may be used. In addition, a polyurethane foam molded product molded into a chip may be used.  
      The shape of the chip of the component (B) is not particularly limited, but the chip has a maximum length of preferably 20 mm or less, more preferably 5 to 20 mm, and still more preferably 10 to 15 mm.  
      A maximum length of 20 mm or less not only enhances the dispersibility of the component (B) in the molded sonic absorber but also reduces a restoring property thereof upon molding. As a result, mold ability increases, and maldistribution of the sound absorption performance on completion of a molded object reduces. Setting the lower limit to 5 mm or more results in a good mixing property of the component (A) and the component (B) and a reduction in maldistribution of the sound absorption performance, and is thus preferable.  
      In order to enhance the sound absorption performance, the content of the component (A) is preferably 80 to 20% by mass, more preferably 70 to 30% by mass, still more preferably 60 to 40% by mass, and particularly preferably 45 to 55% by mass, whereas the content of the component (B) is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, still more preferably 40 to 60% by mass, and particularly preferably 55 to 45% by mass.  
      If the content of the component (A) is 80% by mass or less and the content of the component (B) is 20% by mass or more, the component (A) and the component (B) can be mixed uniformly and a mixing property with a binding agent is satisfactory. As a result, moldability increases. If the content of the component (A) is 20% by mass or more and the content of the component (B) is 80% by mass or less, the sound absorption performance can be enhanced. Therefore, suitable performance for a sound absorption material can be maintained. If the contents of the component (A) and the component (B) are within the above ranges, a balance among the sound absorption property, strength, and hardness of the molded object obtained from those materials can be established.  
      In the molded sonic absorber of the present invention, the component (A) and the component (B) are integrated, and a binding agent as the component (C) can be used in combination with these components as a material making up for the integration. The binding agent is not particularly limited as long as the binding agent has tackiness, but an adhesive is particularly preferable.  
      Examples of the adhesive include hydrophilic polymer-based and hydrophobic polymer-based adhesives such as a vinyl acetate-based adhesive, a polyvinyl alcohol-based adhesive, a cellulose-based adhesive, an olefin resin-based adhesive, an epoxy resin-based adhesive, a nitrile rubber-based adhesive, and a urethane resin-based adhesive.  
      Of those, in order to obtain sufficient tensile and flexural strengths and appropriate hardness on completion of a molded object, hydrophobic polymer-based adhesives such as an epoxy resin-based adhesive, a nitrile rubber-based adhesive, and a urethane resin-based adhesive are preferable, and a urethane resin-based adhesive is the most preferable.  
      Examples of the polyol used for synthesizing a urethane resin-based adhesive include a polyether polyol and a polyester polyol, the polyether polyol is preferred. The polyether polyol to be used is prepared as follows. First, a polyhydric alcohol such as polypropylene glycol, glycerin, diglycerin or pentaerythritol, or an amine such as ethylenediamine or ethanolamine is provided as the starting material. Then, the starting material is subjected to ring-opening polymerization with an alkylene oxide such as ethylene oxide or propylene oxide. A polyol with a number average molecular weight in the range of 200 to 10,000 is preferable. Examples of the isocyanate used for synthesizing a urethane resin-based adhesive include aromatic isocyanates typified by tolylene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI).  
      The content of the binding agent (adhesive) is preferably 10 to 30 parts by mass, more preferably 15 to 30 parts by mass, and still more preferably 20 to 25 parts by mass with respect to 100 parts by mass of the total of the component (A) and the component (B). A content of the binding agent of 10 parts by mass or more can maintain a sufficient bond strength between the component (A) and the component (B). A content of the binding agent of 30 parts by mass or less can maintain excellent sound absorption performance.  
      A porous granular material such as activated carbon or a natural fiber chip such as a paper piece or a non-woven fabric piece can be added as an auxiliary if required to the molded sonic absorber of the present invention. In the case where a cigarette filter contains activated carbon, its filter scrap can be used as it is. In particular, addition of a paper piece can increase the volume of the molded object without affecting the sound absorption performance.  
      A blending amount of the auxiliary is preferably 5 to 20 parts by mass, more preferably 7 to 18 parts by mass, and still more preferably 10 to 15 parts by mass with respect to 100 parts by mass of the total of the component (A) and the component (B)  
      The molded sonic absorber of the present invention can be obtained via the following procedure. A fibrous body as the component (A) and a porous body as the component (B) are separately formed into chips, followed by mixing. Alternatively, both components are mixed and are then formed into chips through grinding or the like. Subsequently, the resulting mixture of chips is mixed with an adhesive or other auxiliary if required, and the whole is molded into a desired shape.  
      Available crushers for forming the component (A) and the component (B) into chips include a rotary crusher and a rag opening crusher.  
      A method in which molding materials composed of the component (A), the component (B), and, if required, the component (C) are mixed and placed in a vessel of a desired shape, or a method in which molding materials are subjected to compression molding to provide a desired shape can be applied to the molding.  
      The vessel of a desired shape is not particularly limited. For instance, a wood vessel, a plastic vessel, a metallic vessel, and a ceramic vessel can be used. Furthermore, one obtained from the above molding materials containing the component (A) and the component (B) may be used.  
      Conditions for applying the compression molding method vary slightly depending on the ratio between the component (A) and the component (B), on the size, thickness, or the like of the molded object, and on the kind of adhesive. For example, for a molded object measuring approximately 30 cm by 30 cm by 10 cm, the molding is carried out at a temperature of 80 to 110° C. and under a pressure of 98 to 980 kPa (1 to 10 kg/cm 2 ) for 3 to 10 minutes.  
      The molded object has a density preferably in the range of 0.05 to 0.2 g/cm 3 , more preferably in the range of 0.08 to 0.18 g/cm 3 , and still more preferably in the range of 0.12 to 0.18 g/cm 3 . A density within the above range can satisfy the sound absorption performance, the strength, and the hardness as well as the lightweight property.  
      The molded object may be of a desired shape such as a sheet, a plate, a cube, a rectangular parallelopiped, a columnar, or a spherical according to an application.  
      A molding method or a slicing method can be applied as a method of producing the molded sonic absorber of the present invention. However, a molded object obtained by the molding method offers a good sound absorption coefficient in the frequency range not lower than 600 Hz if the molded object has a high specific gravity.  
      The reason why the molded sonic absorber of the present invention exerts excellent sound absorption performance particularly for a sound in a human audible range is probably as follows. The shapes of the component (A) and the component (B) constituting the molded sonic absorber are not uniform, resulting in poor uniform dispersibility compared to that of a powder. In other words, the components are partly randomly dispersed in a state where one of the components is slightly unevenly distributed. Therefore, contrarily, the randomly dispersed states of the component (A) and the component (B) synergistically interact in absorbing acoustic wave energy in the human audible range and converting the acoustic wave energy into heat energy, to thereby enhance a sound absorption ability for the acoustic wave energy. As a result, the sound absorption performance is enhanced.  
      The molded sonic absorber of the present invention can provide a vertical incidence sound absorption coefficient of 0.2 or more, preferably 0.4 or more, at 400 Hz measured according to the vertical incidence sound absorption measurement method (JIS A1405). Moreover, the molded sonic absorber can provide a vertical incidence sound absorption coefficient of 0.4 or more in the frequency range of 400 to 1,000 Hz. Preferably, the molded sonic absorber can provide a vertical incidence sound absorption coefficient of 0.4 or more in the frequency range of 400 to 550 Hz.  
      The laminated sonic absorber of the present invention is obtained by laminating two or more layers including the above molded sonic absorber and a foam. Adjacent layers are bonded to each other with the adhesive or the like.  
      The foam in the laminate may be one composed of a component identical to the component (B). The shapes and sizes of the molded sonic absorber and the foam can be determined depending on applications. Two or more foams different from each other in thickness and density may be combined and laminated.  
      The order in which the molded sonic absorber and the foam are laminated may be regular or random. In addition, one or two or more molded sonic absorber layers may be laminated, and similarly, one or two or more foam layers may be laminated. For example, a molded sonic absorber and a foam may be alternately laminated. Alternatively, a foam may serve as an intermediate layer with molded sonic absorbers laminated on its both sides. Contrarily, a molded sonic absorber may serve as an intermediate layer with foams laminated on its both sides.  
      A support layer and/or a protective layer may be laminated on one or both faces of the laminate.  
      The support layer is made from a metallic plate, a plastic plate, a wood plate, a ceramic plate, a woven fabric, a non-woven fabric, cardboard, paper, or the like. When mounting a laminate on an automobile ceiling face, an interior wall surface, or the like, the support layer forms a bonding layer between the laminate and the automobile ceiling face, the interior wall surface, or the like.  
      When mounting a laminate on an automobile ceiling face, an interior wall surface, or the like, for example, the protective layer faces the interior. The protective layer can be made from the same material as that for the support layer. However, the protective layer is preferably made from a woven fabric, a non-woven fabric, or the like from the viewpoint of enhancing the sound absorption performance.  
      Examples of the laminated sonic absorber include one with a molded sonic absorber having a density of approximately 0.10 g/cm 3  arranged on its sound absorption face side and with a molded sonic absorber having a density lower than the above density assembled on its back face side. In this case, the lower the density of the latter layer, the more excellent the sound absorption performance.  
      For example, a laminated sonic absorber with a molded sonic absorber having a thickness of approximately 10 mm and a density of 0.10 g/cm 3  arranged on its sound absorption face side and with a molded sonic absorber having a thickness of 25 mm and a density of 0.15 g/cm 3  arranged on its back face side is compared with an entire molded sonic absorber having a thickness of 35 mm and a density of 0.10 g/cm 3 . In this case, the laminated sonic absorber is superior in strength and hardness to the entire molded sonic absorber. Therefore, the laminate of two or more layers different from each other in density is preferable because of its application to a wider range of use.  
      The molded sonic absorber or laminated sonic absorber of the present invention is applicable to an interior material for an automobile, a building material, a sound absorption structure, or the like.  
      In the case where the molded sonic absorber or laminated sonic absorber of the present invention is used for a ceiling material for an automobile, the molded sonic absorber or the laminated sonic absorber is placed on an automobile ceiling face. Then, a hot melt powder or a hot melt film is applied onto the surface of the molded sonic absorber. Furthermore, a material to serve as a protective layer such as a non-woven fabric or a textile is laminated on the surface, followed by molding under heating. As a result, a desired deep drawing shape (having a depth of about 150 mm) can be obtained. In this case, a woven fabric or a non-woven fabric is suitable for the protective layer. A synthetic leather such as vinyl chloride imparts the sound absorption performance.  
      In addition, the molded sonic absorber or laminated sonic absorber of the present invention is applicable to, for example, a wall surface, a ceiling material, a partition wall, a partition, or an interior decorative material in a house, an office, a factory, a laboratory, a compressor, a motor, or an outdoor heat exchanger of an air conditioner. The molded sonic absorber or laminated sonic absorber of the present invention provides not a sound insulating action but a sound absorption action. Therefore, the molded sonic absorber or laminated sonic absorber of the present invention can exert excellent sound absorption performance even when used in a partition form as mentioned above.  
      When the molded sonic absorber or laminated sonic absorber of the present invention is used outdoors, or is used in a factory, a laboratory, or the like, the molded sonic absorber or laminated sonic absorber is expected to often contact a hard substance. Therefore, a punching metal maybe used as the protective layer. In the case where a punching metal is used, a punch (hole) area preferably accounts for 40% or more, more preferably 60% or more of the whole punching metal area. This is because both the protective function and the sound absorption performance can be obtained. In such a case, additionally affixing a dimple sheet on the support layer side enhances the sound absorption performance in a frequency range near 500 Hz, and also enhances the sound absorption performance in a high frequency range not lower than 1.5 kHz.  
      A molded sonic absorber constituted by a cellulose acetate fiber is suitable for an interior application requiring hygroscopicity because cellulose acetate does not swell even if the cellulose acetate absorbs water. For example, in the case where a molded sonic absorber constituted by a cellulose acetate fiber is applied to a ceiling material for a vehicle or an interior, the molded sonic absorber does not deform when in use, and is capable of absorbing moisture in the air and keeping the absorbed moisture. Therefore, the molded sonic absorber can serve as an absorbent to exert a condensation preventing function, a moisture conditioning function, and the like. Moreover, the molded sonic absorber can further enhance its sound absorption performance owing to moisture absorption itself, in other words, by keeping moisture.  
      The molded sonic absorber of the present invention may contain some degree of impurities unless the impurities contain a toxic substance, as its raw material. Therefore, waste can be used for a raw material for the molded sonic absorber. Furthermore, it is not necessary to dispose of the molded sonic absorber of the present invention after the use. The molded sonic absorber of the present invention can be recycled as follows. The molded sonic absorber is washed, is formed into chips with a crusher or the like, and is added with an adhesive if required, followed by remolding. Therefore, the molded sonic absorber of the present invention is excellent in terms of both a reduction in rubbish and recycling of resources.  
      Furthermore, the molded sonic absorber and laminated sonic absorber of the present invention can be used for heat insulating materials in various applications because the molded sonic absorber and laminated sonic absorber of the present invention can exert a heat insulating action as well as the sound absorption action.  
      The molded sonic absorber and laminated sonic absorber of the present invention are excellent in sound absorption performance particularly in the range of 400 to 1,000 Hz in the human audible range. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       FIG. 1  is a diagram for illustrating an air permeability-measuring apparatus. 
    
    
     EXAMPLES  
      Hereinafter, the present invention is described in more detail by way of Examples. However, the present invention is not limited to those Examples. Measurement methods in the following Examples and Comparative Examples are as follows.  
      (1) Sound Absorbing Performance  
      Molded objects obtained in Examples and Comparative Examples were measured in accordance with JIS A1405:1998 Acoustics-Determination of sound absorption coefficient and impedance in impedance tubes-Method using standing wave ratio.  
      The size of a sample was pursuant to the description in the section 6.1.2 Reference of JIS A1405. A sample cut into a circular form with a diameter of 100 mm and a thickness of 35 mm was used for lower frequencies (operating frequency of 100 to 800 Hz). Similarly, a sample cut into a circular form with a diameter of 29 mm and a thickness of 35 mm was used for higher frequencies (operating frequency of 800 to 5,000 Hz or more). A sample was cut in such a manner that a pressurizing direction when molding a molded sonic absorber would be an incidence direction of an acoustic wave.  
      A sound absorption coefficient, which corresponded to a defined in the section 3.1 Vertical incidence sound absorption coefficient of JIS A1405:1998, was determined in accordance with a method of calculating α of JIS. The sound absorption coefficient was measured at 23° C. and 60% RH. The measurement was performed three times, and the three measured values were averaged. The results are shown in Table 1.  
      (2) Air Permeability  
      Each of the molded objects obtained in the examples and comparative examples was cut into a disk with a thickness of 3 mm and a diameter of 100 mm. The disk was sandwiched between upper and lower transparent plastic tubes as shown in  FIG. 1  to prepare a measuring apparatus. A smoked cigarette was inserted into a hole drilled in the lower transparent plastic tube of the measuring apparatus to measure a time period (second) from the insertion to leak of smoke from the upper transparent plastic tube. Transparent and waterproof adhesive tape was wound around the side surface including a connection part between a circumference of the molded object and each of the upper and lower transparent plastic tubes to prevent smoke leak. The results are shown in Table 1.  
     Example 1  
      Used for the component (A) was a ground scrap of a plain cigarette filter (cigarette filter free of activated carbon) of a crimped diacetate tow with a degree of fineness of 3 deniers. The filter had 0.09 g of paper (filter roll paper) and 0.55 g of diacetate tow per cigarette. The roll paper had a weight ratio of 14% by mass.  
      Mixed were 50% by mass of the component (A) and 50% by mass of a soft polyurethane foam molded object (measuring 5 cm×10 cm×20 cm and having a density of 0.020 g/cm 3 ) produced from a propyleneoxide adduct of glycerin (having a molecular weight of 3,500) and tolylene diisocyanate (TDI) as the component (B). Then, the mixture was ground into chips with a rotary crusher (manufactured by Asai Seisakusho Co., Ltd.) having a blade length of 600 mm in such a manner that the maximum length of the chips would be 20 mm or less.  
      To 1,480 g of the mixture were added 220 g of a moisture curing type polyurethane-based adhesive (trade name Ribbon Decks, manufactured by Token Resin Chemistry Co., Ltd.) produced from a propyleneoxide adduct of glycerin (having a molecular weight of 3,500) and diphenylmethane diisocyanate (MDI). Then, the whole was uniformly mixed to provide a sound absorption material.  
      The sound absorption material was loaded into a compression molding machine with a molding capacity measuring 30 cm×30 cm×3.5 cm. Then, water vapor was added to the material, and the whole was molded for 2 minutes at a temperature of 105° C. and under a pressure of 392 kPa (4 kg/cm 2 ) into a molded sonic absorber of the present invention having a density of 0.10 g/cm 3  and a thickness of 35 mm. The sound absorption coefficient and air permeability of the molded sonic absorber were measured.  
     Example 2  
      Used for the component (A) was a diacetate staple, a scrap of a crimped cellulose diacetate tow for a cigarette with a degree of fineness of 3 deniers. Then, mixed were 70% by mass of the component (A) and 30% by mass of a soft polyurethane foam molded object (measuring 5 cm×10 cm×20 cm and having a density of 0.020 g/cm 3 ) produced from a propyleneoxide adduct of glycerin (having a molecular weight of 3,500) and tolylene diisocyanate (TDI) as the component (B). Then, the mixture was ground into chips with a rotary crusher (manufactured by Asai Seisakusho Co., Ltd.) having a blade length of 600 mm in such a manner that the maximum length of the chips would be 20 mm or less.  
      To 1480 g of the mixture were added 220 g of a moisture curing type polyurethane-based adhesive (trade name Ribbon Decks, manufactured by Token Resin Chemistry Co., Ltd.) produced from a propyleneoxide adduct of glycerin (having a molecular weight of 3,500) and diphenylmethane diisocyanate (MDI). Then, the whole was uniformly mixed to provide a sound absorption material.  
      The sound absorption material was loaded into a compression molding machine with a molding capacity measuring 30 cm×30 cm×10 cm. Then, water vapor was added to the material, and the whole was molded for 2 minutes at a temperature of 105° C. and under a pressure of 490 kPa (5 kg/cm 2 ) into a molded sonic absorber of the present invention having a density of 0.20 g/cm 3 . The sound absorption coefficient and air permeability of the molded sonic absorber were measured.  
     Example 3  
      50% by mass of the component (A) and 50% by mass of the component (B), the component (A) and the component (B) being the same as those of Example 1, were separately ground into chips with a rotary crusher. The average of the maximum length of the chips from the component (A) and the maximum length of the chips from the component (B) was 7 mm. Subsequently, the chips were mixed.  
      5 parts by mass of paper pieces crushed to have a maximum length of 7 mm were added to 100 parts by mass of the mixture, followed by uniform mixing. Then, 135 g of the same moisture curing type polyurethane-based adhesive as that of Example 1 was added to 1,215 g of the resultant mixture to provide a sound absorption material.  
      The sound absorption material was molded under conditions identical to those of Example 1 into a molded sonic absorber of the present invention (density: 0.15 g/cm 3 ). The sound absorption coefficient and air permeability of the molded sonic absorber were measured.  
     Example 4  
      30 parts by mass of an epoxy-based adhesive (trade name Epikote, manufactured by Shell Chemical Co., Ltd.) blended with a curing agent was added to 100 parts by mass of a mixture of 50% by mass of the component (A) and 50% by mass of the component (B), the component (A) and the component (B) being the same as those of Example 1. Then, the whole was uniformly mixed to provide a sound absorption material. After that, the sound absorption material was molded into a molded sonic absorber of the present invention having a density of 0.20 g/cm 3  in the same manner as in Example 2. The sound absorption coefficient and air permeability of the molded sonic absorber were measured.  
     Example 5  
      The molded sonic absorber obtained in Example 1 was cut into pieces each having a thickness of 15 mm. Subsequently, each of those pieces was cut into a circular form having a diameter of 100 mm or 29 mm. Then, a sound absorption performance test was carried out on each of the pieces. The sound absorption coefficient and air permeability of the molded sonic absorber were measured.  
     Example 6  
      A molded sonic absorber of the present invention was obtained in the same manner as in Example 1 except that 50% by mass of the same diacetate staple as that of Example 1 and 50% by mass of a polystyrene foam molded object (measuring 5 cm×10 cm×20 cm) having a density of 0.02 g/cm 3  were used. The molded sonic absorber had a density of 0.10 g/cm 3 . The sound absorption coefficient and air permeability of the molded sonic absorber were measured.  
     Example 7  
      The molded sonic absorber of Example 1 (having a density of 0.10 g/cm 3 ) was cut into a layer having a thickness of 10 mm. Similarly, the molded sonic absorber of Example 2 (having a density of 0.20 g/cm 3 ) was cut into a layer having a thickness of 25 mm. Those layers were integrated with an adhesive to provide a laminated sonic absorber (having an overall thickness of 35 mm). The sound absorption coefficient of the laminated sonic absorber was measured with the layer having a density of 0.10 g/cm 3  being the sound absorption face. The sound absorption coefficient of the laminated sonic absorber was measured. The sound absorption coefficient and air permeability of the laminated sonic absorber were measured.  
     Example 8  
      The molded sonic absorber of Example 1 (having a density of 0.10 g/cm 3 ) was cut into a layer having a thickness of 10 mm. Similarly, the molded sonic absorber of Example 3 (having a density of 0.15 g/cm 3 ) was cut into a layer having a thickness of 25 mm. Those layers were integrated with an adhesive to provide a laminated sonic absorber (having an overall thickness of 35 mm). The sound absorption coefficient of the laminated sonic absorber was measured with the layer having a density of 0.10 g/cm 3  being the sound absorption face. The sound absorption coefficient of the laminated sonic absorber was measured.  
     Comparative Example 1  
      Only the same component (A) as that of Example 1 was used and ground to have a maximum length of about 12 mm in the same manner as in Example 1. The ground material and the same moisture curing type polyurethane-based adhesive as that of Example 1 were used to provided a molded object in the same manner as in Example 2. The molded object had a density of 0.10 g/cm 3 . The sound absorption coefficient and air permeability of the molded object were measured.  
     Comparative Example 2  
      The diacetate staple of Example 2 was used, and was pressurized with triacetin to provide a compressed molded object having a density of 0.1 g/cm 3  and a thickness of 10 mm. The molded object was laminated on and integrated with a polystyrene foam (having a density of 0.02 g/cm 3  and a thickness of 25 mm) to serve as a support layer. The sound absorption coefficient of the resultant laminate was measured.  
                           TABLE 1                                          Comparative           Example   Example                                                             1   2   3   4   5   6   7   8   1   2                                                                         (A)   cigarette filter   50   70   50   50   50   50   50   50   —   100                                                         % by mass of paper in   14   0   14   0   14   14   14   14   —   0       component (A)                                                             (B)   soft polyurethane   50   30   50   50   50   —   —   —   100   —           foam           polystyrene foam   —   —   —   —   —   50   —   —   —   —                                                         maximum length of   20   20   7   20   20   20   —   —   12   —       components (A) and (B) after       manufacturing method   molding   slicing   molding   slicing   slicing   molding   slicing/   slicing/   slicing   molding                                   laminating   laminating                                                             molded   density (g/cm 3 )   0.10   0.20   0.15   0.20   0.10   0.10   0.10/0.20   0.10/0.15   0.10   0.10       object   thickness (mm)   35   35   35   35   15   35   35   35   35   35       sound    400 Hz   0.50   0.30   0.30   0.20   0.10   0.20   0.45   0.35   0.10   0.06       adsorption    630 Hz   0.70   0.65   0.65   0.50   0.20   0.50   0.70   0.68   0.10   0.20       coefficicent   1000 Hz   0.80   0.75   0.75   0.60   0.40   0.60   0.80   0.84   0.20   0.35                                                         air permeability (second)   55   80   72   78   58   80   —   —   220   —                 Each of Examples 7 and 8 is a laminate of sliced products and a density in each of Examples 7 and 8 is a density for each layer of the two-layer laminate.             
 
      The molded sonic absorbers and laminated sonic absorbers of Examples 1 to 8 were excellent in sound absorption performance in the frequency range of 400 to 1,000 Hz. Moreover, the molded sonic absorbers in Examples 1 to 6 showed very good air permeability despite their densities equal to or greater than each of the densities of Comparative Examples 1 and 2.