Abstract:
The present invention relates to a sound absorbing and insulating material with improved heat resistance and moldability and a method for manufacturing the same, more particularly to a sound absorbing and insulating material having, as a surface layer, a heat-resistant material prepared by impregnating a binder into a nonwoven fabric formed of a heat-resistant fiber stacked on one side of a base layer formed of a conventional sound absorbing and insulating material, and a method for manufacturing the same. 
     The sound absorbing and insulating material of the present invention is a conventional sound absorbing and insulating material has improved sound-absorbing property, flame retardancy, heat-insulating property and heat resistance as compared to the conventional sound absorbing and insulating material, is applicable to parts maintained at high temperatures of 200° C. or higher due to the surface layer and is moldable into a desired shape during the curing of the binder impregnated into the surface layer. Therefore, the sound absorbing and insulating material of the present invention can be widely used in industrial fields requiring sound absorbing and insulating materials, including electric appliances such as an air conditioner, a refrigerator, a washing machine, a lawn mower and the like, transportation such as an automobile, a ship, an airplane and the like, construction materials such as a wall material, a flooring material and the like, and so forth.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims, under 35 U.S.C. §119, the priority of Korean Patent Application No. 10-2013-0159411, filed on Dec. 19, 2013, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
       BACKGROUND 
       [0002]    (a) Technical Field 
         [0003]    The present invention relates to a sound absorbing and insulating material with improved heat resistance and moldability and a method for manufacturing the same, more particularly to a sound absorbing and insulating material having, as a surface layer, a heat-resistant material prepared by impregnating a binder into a nonwoven fabric formed of a heat-resistant fiber stacked on one side of a base layer formed of a conventional sound absorbing and insulating material, which has improved sound-absorbing property, flame retardancy, heat-insulating property and heat resistance as compared to the conventional sound absorbing and insulating material, is applicable to parts maintained at high temperatures of 200° C. or greater due to the surface layer and is moldable into a desired shape during the curing of the binder impregnated into the surface layer, and a method for manufacturing the same. 
         [0004]    (b) Background Art 
         [0005]    Noise, as an unwanted side effect of industrial development, causes gradually more damages. Accordingly, various methods have been provided to prevent noise. As a way of such noise prevention, researches for developing new sound absorbing and insulating materials capable of arresting, absorbing or insulating sound have been conducted in various ways. 
         [0006]    Representative industrial sectors requiring sound absorbing and insulating materials include electric appliances such as an air conditioner, a refrigerator, a washing machine, a lawn mower and the like, transportation such as an automobile, a ship, an airplane and the like, construction materials such as a wall material, a flooring material and the like, and so forth. The sound absorbing and insulating material is required in other various industrial fields, too. In general, the sound absorbing and insulating materials used in industries require, in addition to good sound-absorbing property, reduced weight, flame retardancy, heat resistance and heat-insulating property, depending on their applications. Especially, flame retardancy and heat resistance may be further required for sound absorbing and insulating materials used in engines, exhaust systems and the like maintained at high temperatures of 200° C. or greater. At present, an aramid fiber is gaining attentions for sound absorbing and insulating materials having superior heat resistance. 
         [0007]    In addition, in order to provide functionalities such as flame retardancy, water repellency and the like to a sound absorbing and insulating material, many sound absorbing materials wherein a nonwoven fabric containing aramid fibers and a functional skin material are stacked have been developed. 
         [0008]    For example, Korean Patent Publication No. 2007-0033310 discloses a flame-retardant sound absorbing material wherein a nonwoven fabric layer in which a heat-resistant short aramid fiber and a short thermoplastic polyester fiber are bridged and a skin material layer formed of a wetlaid nonwoven fabric consisting of a short aramid fiber are stacked. 
         [0009]    In addition, Japanese Patent Publication No. 2007-0039826 discloses a water-repellent sound absorbing material wherein a nonwoven fabric layer of a heat-resistant short aramid fiber or a blend of a short aramid fiber and a short thermoplastic polyester fiber and a skin material layer treated with a water repellent are stacked. 
         [0010]    Further, Japanese Patent Publication No. 2007-0138953 discloses a heat-resistant sound absorbing material wherein a nonwoven fabric layer consisting of a heat-resistant aramid fiber and a skin material layer formed of a fiber sheet containing a heat-resistant aramid fiber are stacked. 
       SUMMARY 
       [0011]    In order solve the above-described problem of the existing art, the inventors of the present invention have researched for a long time to develop a new sound absorbing and insulating material having superior sound-absorbing property, flame retardancy, heat-insulating property and heat resistance. As a result, they have developed a sound absorbing and insulating material with a new structure wherein a surface layer formed of a heat-resistant material is stacked on the surface of a conventional sound absorbing and insulating material. Since a binder of the surface layer penetrates into a nonwoven fabric having irregular micro cavities with a complicated three-dimensional labyrinth structure without blocking the micro cavities, the three-dimensional structure inside the nonwoven fabric is maintained during curing of the heat-resistant material. 
         [0012]    The present invention is directed to providing a sound absorbing and insulating material having superior sound-absorbing property, flame retardancy, heat-insulating property and heat resistance and being moldable into a desired shape during the curing of the binder included in the surface layer. 
         [0013]    The present invention is also directed to providing a method for manufacturing a sound absorbing and insulating material with improved heat resistance and moldability, by stacking a heat-resistant material prepared by impregnating a binder into a nonwoven fabric formed of a heat-resistant fiber and then drying the same so as to control the binder content on one side of a base layer formed of a conventional sound absorbing and insulating material. 
         [0014]    The present invention is also directed to providing a method for reducing noise by using the sound absorbing and insulating material in a noise-generating device. 
         [0015]    In one aspect, the present invention provides a sound absorbing and insulating material including: a base layer formed of a conventional sound absorbing and insulating material; and a surface layer containing a nonwoven fabric containing 30-100 wt % of a heat-resistant fiber and a binder present in the same layer as the nonwoven fabric and maintaining a three-dimensional structure inside the nonwoven fabric, wherein the surface layer is stacked on one side of the base layer. 
         [0016]    In another aspect, the present invention provides a method for manufacturing a sound absorbing and insulating material according, including: a) a step of immersing a nonwoven fabric containing 30-100 wt % of a heat-resistant fiber in a binder solution; b) a step of forming a surface layer by drying the nonwoven fabric; and c) a step of stacking the surface layer on one side of a base layer formed of a conventional sound absorbing and insulating material. 
         [0017]    In another aspect, the present invention provides a method for reducing noise of a noise-generating device, including: i) a step of checking a three-dimensional shape of a noise-generating device; ii) a step of preparing and molding the above-described sound absorbing and insulating material so as to correspond to the three-dimensional shape of the device partially or entirely; and iii) a step of bringing the sound absorbing and insulating material adjacent to the noise-generating device. 
         [0018]    The sound absorbing and insulating material of the present invention, wherein the heat-resistant material in which the binder is impregnated into the nonwoven fabric formed of the heat-resistant fiber is stacked as the surface layer, is advantageous in that the sound-absorbing property, flame retardancy, heat-insulating property and heat resistance of the base layer are improved and the sound absorbing and insulating material can be shaped into a three-dimensional shape due to the binder. 
         [0019]    In addition, the sound absorbing and insulating material of the present invention is advantageous in that functionality can be provided to the sound absorbing and insulating material by further including a functional additive in the binder solution. 
         [0020]    The sound absorbing and insulating material of the present invention is also advantageous in that, since flame retardancy, heat-insulating property and heat resistance are superior in addition to sound-absorbing property, the sound absorbing and insulating material is not deformed or denatured even when used in a noise-generating device maintained at high temperatures of 200° C. or greater. 
         [0021]    Further, the sound absorbing and insulating material of the present invention is advantageous in that, if a thermosetting resin is used as the binder, molding into a desired shape is possible during the curing of the thermosetting resin. That is to say, the overall process can be simplified since the curing and molding of the thermosetting resin are achieved simultaneously. 
         [0022]    In addition, the sound absorbing and insulating material of the present invention is advantageous in that, since a nonwoven fabric formed of a heat-resistant fiber is used, thermal deformation of the nonwoven fabric due to the reaction heat of thermal curing does not occur even when a thermosetting resin is used as the binder. 
         [0023]    Also, sound absorbing and insulating material of the present invention is advantageous in that, since the heat-resistant fiber is used intensively at high amounts only in the surface layer, the desired heat-resistant effect can be ensured with minimized use of the expensive heat-resistant fiber. 
         [0024]    Accordingly, the sound absorbing and insulating material of the present invention is useful as a sound absorbing and insulating material in applications requiring arresting, absorbing or insulating of sound, including electric appliances such as an air conditioner, a refrigerator, a washing machine, a lawn mower and the like, transportation such as an automobile, a ship, an airplane and the like, construction materials such as a wall material, a flooring material and the like, and so forth. The sound absorbing and insulating material of the present invention is useful as a sound absorbing and insulating material for a noise-generating device maintained at high temperatures of 200° C. or greater. In particular, when the sound absorbing and insulating material of the present invention is used in an automobile, it may be closely attached to a noise-generating device of the automobile such as an engine, an exhaust system and the like, provided with a distance from the noise-generating device, or molded as a part of the noise-generating device. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0025]      FIG. 1  schematically shows the cross-sectional structure of a sound absorbing and insulating material of the present invention, wherein a surface layer 2 of a nonwoven fabric in which a binder is uniformly impregnated is stacked on one side of a base layer 1 formed of a conventional sound absorbing and insulating material by an adhesive 3. 
           [0026]      FIGS. 2A-2C  show electron microscopic images (×300) of a nonwoven fabric constituting a surface layer.  FIG. 2A  is an image of a nonwoven fabric before impregnation of a binder,  FIG. 2B  is an image of a nonwoven fabric in which 20 parts by weight of a binder has been impregnated based on 100 parts by weight of the nonwoven fabric, and  FIG. 2C  is an image of a nonwoven fabric in which 50 parts by weight of a binder has been impregnated based on 100 parts by weight of the nonwoven fabric. 
           [0027]      FIGS. 3A-3B  schematically show an example of a sound absorbing and insulating material applied to a noise-generating device of an automobile after molding as a part.  FIG. 3A  is an image of a sound absorbing and insulating material molded for use in an automobile engine, and  FIG. 3B  shows an example wherein a sound absorbing and insulating material is applied in a part of an automobile engine. 
           [0028]      FIGS. 4A-4B  schematically show an example wherein a sound absorbing and insulating material is applied to noise-generating device of an automobile with some distance.  FIG. 4A  is an image of a sound absorbing and insulating material molded for use in a lower part of an automobile, and  FIG. 4B  shows an example wherein a sound absorbing and insulating material is attached to a lower part of an automobile. 
           [0029]      FIG. 5  is a graph comparing the sound-absorbing performance of a surface layer depending on the density of a nonwoven fabric. 
           [0030]      FIG. 6  is a graph comparing the heat-insulating performance of an aluminum heat-insulating plate with that of a sound absorbing and insulating material of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF MAIN ELEMENTS 
       [0000]    
       
         
           
               1 : base layer formed of conventional sound absorbing and insulating material 
               2 : surface layer formed of binder-impregnated nonwoven fabric 
               3 : adhesive layer 
           
         
       
     
       DETAILED DESCRIPTION 
       [0034]    The present invention relates to a sound absorbing and insulating material with improved heat resistance and moldability and a method for manufacturing the same. The sound absorbing and insulating material of the present invention, which is obtained by stacking a surface layer formed of a specific heat-resistant material on a base layer formed of a conventional sound absorbing and insulating material, is advantageous in that it has improved sound-absorbing property, flame retardancy, heat-insulating property and heat resistance and is moldable into a desired three-dimensional shape using a binder impregnated in the surface layer. 
         [0035]    In an aspect, the present invention provides a sound absorbing and insulating material including: a base layer formed of a conventional sound absorbing and insulating material; and a surface layer containing a nonwoven fabric containing 30-100 wt % of a heat-resistant fiber and a binder present in the same layer as the nonwoven fabric and maintaining a three-dimensional structure inside the nonwoven fabric, wherein the surface layer is stacked on one side of the base layer. 
         [0036]    In an exemplary embodiment of the present invention, the stacking between the base layer and the surface layer may be performed by an adhesive, heat or pressure. 
         [0037]    In an exemplary embodiment of the present invention, the adhesive used for the stacking between the base layer and the surface layer may be a binder included in the surface layer. More specifically, the adhesive may be a thermosetting resin. 
         [0038]    In an exemplary embodiment of the present invention, each of the base layer and the surface layer may be formed of a single layer or multiple layers. The base layer may have a thickness of 5-50 mm and the surface layer may have a thickness of 0.1-5 mm. 
         [0039]    In an exemplary embodiment of the present invention, the base layer may be formed of a conventional sound absorbing and insulating material formed of at least one material selected from a group consisting of a polyethylene terephthalate fiber, a polypropylene fiber, a polyethylene fiber, a polyamide fiber, a glass wool, a polyurethane fiber and a melamine fiber. 
         [0040]    In an exemplary embodiment of the present invention, the heat-resistant fiber constituting the nonwoven fabric may have a limiting oxygen index (LOI) of 25% or greater and a heat resistance temperature of 150° C. or greater. 
         [0041]    In an exemplary embodiment of the present invention, the heat-resistant fiber may be one or more selected from a group consisting of an aramid fiber, a polyphenylene sulfide (PPS) fiber, an oxidized polyacrylonitrile (oxi-PAN) fiber, a polyimide (PI) fiber, a polybenzimidazole (PBI) fiber, a polybenzoxazole (PBO) fiber, a polytetrafluoroethylene (PTFE) fiber, a polyketone (PK) fiber, a metallic fiber, a carbon fiber, a glass fiber, a basalt fiber, a silica fiber and a ceramic fiber. 
         [0042]    In another exemplary embodiment of the present invention, the heat-resistant fiber may be an aramid fiber. 
         [0043]    In an exemplary embodiment of the present invention, the nonwoven fabric may be formed of an aramid fiber having a fineness of 1-15 denier and may be a single-layered nonwoven fabric having a thickness of 3-20 mm. 
         [0044]    In an exemplary embodiment of the present invention, the nonwoven fabric may have a density of 100-2000 g/m 2 , more specifically 200-1200 g/m 2 . 
         [0045]    In an exemplary embodiment of the present invention, the binder may be a thermosetting resin. 
         [0046]    In another exemplary embodiment of the present invention, the thermosetting resin may be an epoxy resin capable of forming a three-dimensional network structure in the internal structure of the nonwoven fabric. 
         [0047]    In another exemplary embodiment of the present invention, the epoxy resin may be one or more epoxy resin selected from a group consisting of bisphenol A diglycidyl ether, bisphenol B diglycidyl ether, bisphenol AD diglycidyl ether, bisphenol F diglycidyl ether, bisphenol S diglycidyl ether, polyoxypropylene diglycidyl ether, a bisphenol A diglycidyl ether polymer, phosphazene diglycidyl ether, bisphenol A novolac epoxy, a phenol novolac epoxy resin and an o-cresol novolac epoxy resin. 
         [0048]    The structure of the sound absorbing and insulating material according to the present invention is described in more detail referring to  FIG. 1  and  FIG. 2A-2C . 
         [0049]      FIG. 1  schematically shows the cross-sectional structure of the sound absorbing and insulating material of the present invention. Referring to  FIG. 1 , the sound absorbing and insulating material according to the present invention has a surface layer 2 of a nonwoven fabric in which a binder is uniformly impregnated stacked on one side of a base layer 1 formed of a conventional sound absorbing and insulating material. 
         [0050]    The technical feature of the sound absorbing and insulating material of the present invention lies in the surface layer. The surface layer contains a nonwoven fabric containing 30-100 wt % of a heat-resistant fiber and a binder present in the same layer as the nonwoven fabric and maintaining a three-dimensional structure inside the nonwoven fabric. Although the surface layer has a small thickness as compared to the base layer and contains the heat-resistant fiber with an extremely low content based on the total weight of the fiber materials used to prepare the sound absorbing and insulating material, stacking of the surface layer formed of a heat-resistant material significantly improves sound-absorbing property, flame retardancy, heat-insulating property and heat resistance and enables molding into a desired three-dimensional shape using the binder. 
         [0051]    The internal structure of the surface layer 2 is described in more detail referring to  FIGS. 2A-2C . 
         [0052]      FIGS. 2A-2C  show electron microscopic images showing the three-dimensional structure inside the nonwoven fabric before and after impregnation of the binder. 
         [0053]      FIG. 2A  is an electron microscopic image showing the internal structure of the nonwoven fabric before impregnation of the binder. It can be seen that heat-resistant fiber yarns cross each other to form irregular micro cavities.  FIGS. 2B and 2C  are electron microscopic images after impregnation of the binder into the nonwoven fabric. It can be seen that the binder is finely and uniformly distributed and attached to the heat-resistant fiber yarns. Also, it can be seen that the content of the binder on the yarn surface increases as the content of the binder increases. 
         [0054]    Although there may be differences depending on the preparation method, fibers are randomly arranged three-dimensionally in a nonwoven fabric. Accordingly, the pore structure inside a nonwoven fabric tends to be a very complicated labyrinth structure (labyrinth system) wherein regularly or irregularly arranged fibers are three-dimensionally interconnected rather than bundles of independent capillary tubes. That is to say, the nonwoven fabric used in the surface layer has irregular micro cavities formed as the yarns formed of the heat-resistant fiber loosely cross each other. 
         [0055]    When the binder is impregnated into the nonwoven fabric, the binder is finely and uniformly distributed and attached to the surface of the nonwoven fabric yarns formed of the heat-resistant fiber, thereby forming much finer micro cavities than before the impregnation. The formation of fine micro cavities in the internal structure of the nonwoven fabric means increased resonance of noise and thus improved sound-absorbing property. If the binder forms a three-dimensional network structure as it is cured, the sound-absorbing property can be further improved since more fine micro cavities can be formed inside the nonwoven fabric. 
         [0056]    Accordingly, since the nonwoven fabric can maintain the intrinsic three-dimensional structure as the binder is uniformly impregnated into the nonwoven fabric and, additionally, since more fine micro cavities can be formed as the binder is cured, the surface layer has remarkably improved sound-absorbing performance due to the maximized noise absorption through increased resonance in the nonwoven fabric. 
         [0057]    As seen from the electron microscopic images of  FIGS. 2A-2C , the surface layer has an internal structure in which the binder is uniformly dispersed and distributed on the surface of the heat-resistant fiber yarns constituting the nonwoven fabric. 
         [0058]    Hereinafter, the components of the surface layer having such an internal structure are described in more detail. 
         [0059]    A heat-resistant fiber is used as the main fiber constituting the nonwoven fabric. The heat-resistant fiber may be any one having superior durability and capable of enduring high-temperature and ultrahigh-temperature conditions. Specifically, the heat-resistant fiber may be one having a limiting oxygen index (LOI) of 25% or greater and a heat resistance temperature of 150° C. or greater. More specifically, the heat-resistant fiber may be one having a limiting oxygen index (LOI) of 25-80% and a heat resistance temperature of 150-30000° C. Most specifically, the heat-resistant fiber may be one having a limiting oxygen index (LOI) of 25-70% and a heat resistance temperature of 200-1000° C. And, the heat-resistant fiber may have a fineness of 1-15 denier, specifically 1-6 denier and a yarn length of 20-100 mm, specifically 40-80 mm. 
         [0060]    The heat-resistant fiber may be a ‘super fiber’ as commonly called in the related art. Specifically, the super fiber may be one or more selected from a group consisting of an aramid fiber, a polyphenylene sulfide (PPS) fiber, an oxidized polyacrylonitrile (oxi-PAN) fiber, a polyimide (PI) fiber, a polybenzimidazole (PBI) fiber, a polybenzoxazole (PBO) fiber, a polytetrafluoroethylene (PTFE) fiber, a polyketone (PK) fiber, a metallic fiber, a carbon fiber, a glass fiber, a basalt fiber, a silica fiber, a ceramic fiber and the like. 
         [0061]    Specifically, an aramid fiber may be used as the heat-resistant fiber in the present invention. More specifically, meta-aramid, para-aramid or a mixture thereof may be used as the heat-resistant fiber in the present invention. The aramid fiber used as the yarn of the nonwoven fabric in the present invention may have a fineness of 1-15 denier, specifically 1-6 denier, and a yarn length of 20-100 mm, specifically 40-80 mm. If the yarn length is too short, bridging of yarns may be difficult during needle punching. As a result, cohesion of the nonwoven fabric may be weak. And, if the yarn length is too long, cohesion of the nonwoven fabric may be superior but movement of yarns may be difficult during carding. 
         [0062]    The aramid fiber is an aromatic polyamide fiber wherein aromatic rings such as benzene ring are bonded with each other by amide groups. To distinguish from an aliphatic polyamide (e.g., nylon), the aromatic polyamide fiber is called ‘aramid’. The aramid fiber is prepared by spinning of aromatic polyamide and is classified into meta-aramid and para-aramid depending on the location of the amide bonds. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0063]    The meta-aramid (m-aramid) represented by Chemical Formula 1 is prepared by dry spinning after dissolving isophthaloyl chloride and m-phenylenediamine in a dimethylacetamide (DMAc) solvent. The meta-aramid has a relatively high elongation at break of 22-40% due to the uneven polymer structure, is dyeable and can be easily prepared into fiber. The meta-aramid is commercially available under the trade names Nomex™ (DuPont) and Conex™ (Teijin). 
         [0064]    The para-aramid (p-aramid) represented by Chemical Formula 2 is prepared by wet spinning after dissolving terephthaloyl chloride and p-phenylenediamine in an N-methylpyrrolidone (NMP) solvent. The para-aramid has high strength due to its highly oriented linear molecular structure. Being stronger than meta-aramid about 3-7 times, it is used for reinforcement or protection materials. Also, the para-aramid exhibits strong chemical resistance, less thermal shrinkage and superior dimensional stability as well as high tensile strength, flame resistance and self-extinguishing property. The para-aramid is commercially available under the trade names Kevlar™ (DuPont), Twaron™ (Teijin) and Technora™ (Teijin). 
         [0065]    The aramid is provided in the form of filament, staple, yarn and the like and is used for reinforcing materials (transformer, motor and the like), insulating materials (insulating paper, insulating tape and the like), heat-resistant fibers (fireproof clothing, gloves and the like), high-temperature filters, or the like. 
         [0066]    Although the nonwoven fabric constituting the surface layer in the present invention is practically prepared from the heat-resistant fiber yarn, nonwoven fabrics prepared by further adding other fibers to the heat-resistant fiber yarn, to reduce cost or provide lightweightness, functionality and the like to the nonwoven fabric, may also be included in the scope of the present invention. That is to say, although the nonwoven fabric of the present invention is prepared from the heat-resistant fiber yarn, the present invention is not limited to the nonwoven fabric formed only of the heat-resistant fiber. The nonwoven fabric of the present invention may include the heat-resistant fiber yarn in an amount of 30-100 wt %, more specifically 60-100 wt %, based on the weight of the nonwoven fabric. 
         [0067]    Further, the surface layer includes the binder impregnated therein, which is present in the same layer as the nonwoven fabric and maintains the three-dimensional structure inside the nonwoven fabric. The binder used in the present invention may be any one capable of maintaining the three-dimensional structure inside the nonwoven fabric. The expression ‘maintaining the three-dimensional structure inside the nonwoven fabric’ means that the binder, which has been impregnated into the nonwoven fabric, is uniformly distributed and attached to the surface of the fiber yarn of the nonwoven fabric and maintains or further forms irregular micro cavities, thereby maintaining the original three-dimensional structure inside the nonwoven fabric. 
         [0068]    Although a binder generally refers to a material used to adhere or join two materials, the term binder used in the present invention refers to a material impregnated into the nonwoven fabric formed of the heat-resistant fiber. 
         [0069]    Many materials can be used as the binder impregnated into the nonwoven fabric. First, a thermoplastic resin or a thermosetting resin may be considered as the binder material. 
         [0070]    The thermoplastic resin which is represented by a polyamide-based resin has crystalline polar groups like the aramid fiber as a representative heat-resistant fiber. As such, if a thermoplastic binder is impregnated into the nonwoven fabric formed of the thermoplastic heat-resistant fiber, a strong interfacial layer is formed between them by face-to-face contact between the similar crystalline polar groups, which partially blocks the micro cavities of the nonwoven fabric. That is to say, if a thermoplastic resin is used as the binder impregnated into the nonwoven fabric formed of the thermoplastic heat-resistant fiber, sound-absorbing performance is decreased due to the partial blocking of the micro cavities of the nonwoven fabric. At a glimpse, it may be thought that the sound-absorbing performance would be improved if the micro cavities are blocked. But, since noise is not extinguished inside the nonwoven fabric but is transmitted via other routes, improvement of sound-absorbing performance cannot be expected if the thermoplastic binder is impregnated. And, if the thermoplastic binder is impregnated into a nonwoven fabric formed of the inorganic-based heat-resistant fiber, an adhesive additive has to be further added because of weak binding. 
         [0071]    In contrast, a thermosetting binder has totally different physical and chemical properties from the thermoplastic heat-resistant fiber. Accordingly, if a thermosetting binder is impregnated into the nonwoven fabric formed of the thermoplastic heat-resistant fiber, an interfacial layer is formed by edge-to-edge contact because of the difference in characteristics. As a result, the micro cavities of the nonwoven fabric remain open. That is to say, if a thermosetting resin is used as the binder impregnated into the nonwoven fabric formed of the heat-resistant fiber, the three-dimensional structure inside the nonwoven fabric can be maintained. Accordingly, a thermosetting resin may be used preferably as the binder in the present invention. 
         [0072]    Furthermore, the thermosetting resin has the characteristics that it is curable with light, heat or a curing agent and its shape is not deformed even at high temperatures. Accordingly, by using the heat-resistant fiber and the thermosetting binder with a specific condition, the present invention is advantageous in that the shape of the sound absorbing and insulating material can be maintained even at high temperatures. Therefore, if a thermosetting resin is used as the binder impregnated into the nonwoven fabric, molding into a desired shape can be achieved during the curing of the resin and the resulting shape can be maintained even at high temperatures. 
         [0073]    As described above, if a thermosetting resin is used as the binder impregnated into the nonwoven fabric formed of the heat-resistant fiber, the effects of maintaining the three-dimensional structure inside the nonwoven fabric and molding into a desired shape during the curing of the binder resin can be expected. 
         [0074]    More specifically, an epoxy resin may be used as the binder. The epoxy resin is a kind of a thermosetting resin and is curable into a polymer material having a three-dimensional network structure. Accordingly, since the epoxy resin can form a network structure and thus micro cavities when cured inside the nonwoven fabric, more fine micro cavities can be formed inside the nonwoven fabric and the sound-absorbing performance can be further improved. 
         [0075]    Further, since a more advanced three-dimensional network structure can be formed if the curing is carried out in the presence of a curing agent, the sound-absorbing effect can be further improved. That is to say, a three-dimensional network-structured polymer is formed as the epoxy groups or hydroxy groups of the epoxy resin react with the functional groups of the curing agent such as amine groups or carboxylic acid groups to form covalent crosslinkages. The curing agent not only serves as a catalyst that catalyzes curing reaction but also is directly involved in the reaction and is linked in the molecule of the epoxy resin. Accordingly, the size and physical properties of the micro cavities can be controlled by selecting different curing agents. 
         [0076]    The epoxy resin may be one or more selected from a group consisting of bisphenol A diglycidyl ether, bisphenol B diglycidyl ether, bisphenol AD diglycidyl ether, bisphenol F diglycidyl ether, bisphenol S diglycidyl ether, polyoxypropylene diglycidyl ether, bisphenol A diglycidyl ether polymer, phosphazene diglycidyl ether, bisphenol A novolac epoxy, phenol novolac epoxy resin, o-cresol novolac epoxy resin and the like. The epoxy resin may be one having an epoxy equivalent of 70-400. If the epoxy equivalent is too low, intermolecular binding may be too weak to form a three-dimensional network structure or the physical properties of the sound absorbing and insulating material may be unsatisfactory because of weak adhesion with the heat-resistant fiber. And, if the epoxy equivalent is too high, the physical properties of the sound absorbing and insulating material may be unsatisfactory because a very dense network structure is formed. 
         [0077]    If a thermosetting resin is used as the binder in the present invention, the curing agent may be included in a binder solution. The curing agent may be one having functional groups that can react readily with the functional groups of the binder such as epoxy groups or hydroxy groups. As the curing agent, an aliphatic amine, an aromatic amine, an acid anhydride, urea, an amide, imidazole and the like may be used. Specifically, the curing agent may be one or more selected from a group consisting of diethyltoluenediamine (DETDA), diaminodiphenylsulfone (DDS), boron trifluoride-monoethylamine (BF 3 .MEA), diaminocyclohexane (DACH), methyltetrahydrophtalic anhydride (MTHPA), methyl-5-norbornene-2,3-dicarboxylic anhydride (NMA), dicyandiamide (Dicy), 2-ethyl-4-methylimidazole and the like. More specifically, an aliphatic amine- or amide-based curing agent may be used because they have relatively good crosslinking ability and very superior chemical resistance and weather resistance. Most specifically, dicyandiamide (Dicy) may be used in consideration of crosslinking ability, flame retardancy, heat resistance, storage stability, processability and the like. Because dicyandiamide (Dicy) has a high melting point above 200° C., it retains superior storage stability after being mixed with the epoxy resin and can ensure sufficient processing time for curing and molding. 
         [0078]    Further, a catalyst that facilitates the curing of the thermosetting resin used as the binder may be used in the present invention. The catalyst may be one or more selected from a group consisting of urea, dimethylurea, a tetraphenylborate salt of quaternary DBU, quaternary phosphonium bromide and the like. The catalyst may be included in the binder-containing solution. 
         [0079]    In addition, various additives, e.g., a flame retardant, a heat resistance improver, a water repellent and the like, may be used to provide functionalities to the sound absorbing and insulating material. The additive is included in the binder solution and no additional skin material for providing functionalities to the sound absorbing and insulating material is necessary. 
         [0080]    The flame retardant may be melamine, a phosphate, a metal hydroxide and the like Specifically, one or more selected from a group consisting of melamine, melamine cyanurate, melamine polyphosphate, phosphazene, ammonium polyphosphate and the like may be used as the flame retardant. More specifically, the flame retardant may be melamine, which can enhance flame retardancy and heat resistance at the same time. 
         [0081]    The heat resistance improver may be alumina, silica, talc, clay, glass powder, glass fiber, metal powder and the like 
         [0082]    One or more fluorine-based water repellent may be used as the water repellent. 
         [0083]    In addition, additives commonly used in the art may be selected and used depending on purposes. 
         [0084]    As described above, the sound absorbing and insulating material of the present invention has a structure in which a surface layer formed of a specific heat-resistant material is stacked on one side of a base layer formed of a conventional sound absorbing and insulating material. The base layer and the surface layer may be stacked by bonding using an adhesive or using heat or pressure. For example, when the stacking is performed using an adhesive, an adhesive may be coated on one side of the base layer or the surface layer and then the two layers may be stacked. The adhesive may be any one commonly used in the art. Because the binder impregnated into the surface layer in the present invention also has adhesive property, the binder may also be used as the adhesive. Specifically, when the binder is used as the adhesive, a thermosetting resin may be used because stronger adhesive effect is expected since the thermosetting resin is cured by the heat applied during molding. More specifically, an epoxy resin may be used as the adhesive. The amount of the adhesive used is not particularly limited in the present invention. The amount can be controlled within a range allowed for the adhesion of the two layers. 
         [0085]    In the sound absorbing and insulating material of the present invention, each of the base layer and the surface layer may be formed of a single layer or multiple layers. When the base layer or the surface layer is formed of multiple layers, the individual layers may be formed of the same or different materials. Because the present invention is directed to improving sound-absorbing property, flame retardancy, heat-insulating property, heat resistance and moldability by further stacking the surface layer to a conventional sound absorbing and insulating material, the material, layer structure and the like of the base layer are not particularly limited. That is to say, any conventional sound absorbing and insulating material may be used as the base layer of the present invention to achieve the effect desired by the present invention. Examples of the conventional sound absorbing and insulating material may include a polyethylene terephthalate fiber, a polypropylene fiber, a polyethylene fiber, a polyamide fiber, a glass wool, a polyurethane fiber, a melamine fiber and the like. 
         [0086]    In another aspect, the present invention provides a method for manufacturing a sound absorbing and insulating material, including: a) a step of immersing a nonwoven fabric containing 30-100 wt % of a heat-resistant fiber in a binder solution; b) a step of forming a surface layer by drying the nonwoven fabric; and c) a step of stacking the surface layer on one side of a base layer formed of a conventional sound absorbing and insulating material. 
         [0087]    Hereinafter, the steps of the method for manufacturing a sound absorbing and insulating material according to the present invention are described in detail. 
         [0088]    In the step a), a nonwoven fabric formed of a heat-resistant fiber is immersed in a binder solution. 
         [0089]    In the present invention, the nonwoven fabric is immersed in the binder solution so as to improve sound-absorbing and sound-insulating performance and to allow molding of the sound absorbing and insulating material into a desired shape. The binder solution in which the nonwoven fabric is immersed contains, in addition to a binder resin, a curing agent, a catalyst, commonly used additives and a solvent. 
         [0090]    The binder, the curing agent, the catalyst and the commonly used additives contained in the binder solution are the same ad described above. The solvent used to prepare the binder solution may be one or more selected from a group consisting of a ketone, a carbonate, an acetate, a cellosolve and the like. Specifically, the solvent may be one or more selected from acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), dimethyl carbonate (DMC), ethyl acetate, butyl acetate, methyl cellosolve, ethyl cellosolve, butyl cellosolve and the like. 
         [0091]    Specifically, the binder solution used in the present invention may contain 1-60 wt % of a binder and a solvent as the remainder. The binder solution used in the present invention may further contain a curing agent and other additives including a catalyst. In this case, the binder solution may contain 1-60 wt % of a binder, 0.1-10 wt % of a curing agent, 0.01-5 wt % of a catalyst, 1-40 wt % of additives and a solvent as the remainder. More specifically, the binder solution may contain 1-30 wt % of a binder, 0.1-10 wt % of a curing agent, 0.01-5 wt % of a catalyst, 1-30 wt % of a flame retardant as an additive and 40-95 wt % of a solvent. 
         [0092]    The degree of impregnation into the nonwoven fabric may be controlled by controlling the concentration of the binder solution of the present invention. Specifically, the binder solution may be prepared to have a solid content of 1-60 wt %, more specifically 20-50 wt %. If the binder solution is too thin, the purpose of the present invention cannot be accomplished because the content of the binder impregnated into the nonwoven fabric is small. And, if the binder solution is too thick, the nonwoven fabric may become hard and may not serve as a sound absorbing and insulating material. 
         [0093]    If the content of the curing agent contained in the binder solution is too low, molding into a desired shape may be difficult because complete curing of the binder cannot be expected. As a result, the effect of improving the mechanical strength of the sound absorbing and insulating material may be unsatisfactory. And, if the content is too high, the sound absorbing and insulating material may become hard and storage stability and the like may be unsatisfactory. If the content of the catalyst is too low, the effect of facilitating reaction may be insignificant. And, if the content of the catalyst is too high, storage stability and the like may be unsatisfactory. The additives may be one or more additive(s) commonly used in the art, including a flame retardant, a heat resistance improver, a water repellent and the like. The content of these additives may be adjusted adequately depending on the purpose of addition. If the addition amount is too small, the desired effect may not be achieved. And, too large an addition amount may be economically unfavorable and may cause undesired side effects. 
         [0094]    In the step b), a surface layer is prepared by drying the nonwoven fabric. 
         [0095]    The drying in the present invention is carried out by taking out the nonwoven fabric from the binder solution and removing the solvent. The drying may be carried out at appropriate temperatures under pressure. Specifically, the drying process may include a process of taking out the nonwoven fabric and controlling the binder content in the nonwoven fabric by compressing at a pressure of 1-20 kgf/cm 2 . Also, the drying process may include a process of taking out the nonwoven fabric and evaporating the solvent by heating at a temperature of 70-200° C. Also, the drying process may include a process of compressing the nonwoven fabric at a pressure of 1-20 kgf/cm 2  and then heating at a temperature of 70-200° C. after taking out the nonwoven fabric. 
         [0096]    The drying in the present invention is a process whereby the content of the binder in the nonwoven fabric is controlled. With this, the physical properties of the sound absorbing and insulating material can be controlled. The content of the binder included in the nonwoven fabric after the drying is an important factor determining the size, shape and distribution of micro cavities inside the sound absorbing and insulating material. Accordingly, the sound-absorbing property and mechanical property of the sound absorbing and insulating material may be controlled therewith. In the present invention, the drying may be carried out such that the final content of the binder included in the nonwoven fabric is 1-300 parts by weight, more specifically 30-150 parts by weight, based on 100 parts by weight of the nonwoven fabric. 
         [0097]    In the step c), the surface layer prepared in the step b) is stacked on one side of a base layer formed of a conventional sound absorbing and insulating material. 
         [0098]    The stacking may be accomplished by bonding using an adhesive or using heat or pressure. For example, when the stacking is performed using an adhesive, an adhesive may be coated on one side of the base layer or the surface layer and then the two layers may be stacked. 
         [0099]    The method for manufacturing a sound absorbing and insulating material according to the present invention may further include, after the step c), d) a step of molding the sound absorbing and insulating material at high temperature. 
         [0100]    Specifically, the method for manufacturing a sound absorbing and insulating material including the step d) may include: a) a step of immersing a nonwoven fabric containing 30-100 wt % of a heat-resistant fiber in a binder solution; b) a step of forming a surface layer by drying the nonwoven fabric; c) a step of stacking the surface layer on one side of a base layer formed of a conventional sound absorbing and insulating material; and d) a step of molding the sound absorbing and insulating material at high temperature. 
         [0101]    In the step d), the sound absorbing and insulating material formed by stacking the base layer and the surface layer is molded at high temperature. The molding at high temperature considers also the curing of the thermosetting binder and is carried out at a temperature of 150-300° C., more specifically at a temperature of 170-230° C. 
         [0102]    The method for manufacturing a sound absorbing and insulating material according to the present invention may further include, before the step a), a step of forming a nonwoven fabric by a needle punching process using a heat-resistant fiber. For example, in the step a-1), an aramid nonwoven fabric having a thickness of 3-20 mm may be formed by a needle punching process of a heat-resistant aramid fiber having a fineness of 1-15 denier. 
         [0103]    For example, the method for manufacturing a sound absorbing and insulating material according to the present invention including the step a-1) may include: a-1) a step of forming a nonwoven fabric having a thickness of 3-20 mm by a needle punching process using a heat-resistant fiber having a fineness of 1-15 denier; a) a step of immersing the nonwoven fabric containing 30-100 wt % of a heat-resistant fiber in a binder solution; b) a step of forming a surface layer by drying the nonwoven fabric; and c) a step of stacking the surface layer on one side of a base layer formed of a conventional sound absorbing and insulating material. 
         [0104]    For example, the method for manufacturing a sound absorbing and insulating material according to the present invention including the step a-1) may also include: a-1) a step of forming a nonwoven fabric having a thickness of 3-20 mm by a needle punching process using a heat-resistant fiber having a fineness of 1-15 denier; a) a step of immersing the nonwoven fabric containing 30-100 wt % of a heat-resistant fiber in a binder solution; b) a step of forming a surface layer by drying the nonwoven fabric; c) a step of stacking the surface layer on one side of a base layer formed of a conventional sound absorbing and insulating material; and d) a step of molding the sound absorbing and insulating material at high temperature. 
         [0105]    The step a-1) of forming the nonwoven fabric includes a needle punching process using a heat-resistant fiber. The sound-absorbing property may vary depending on the thickness and density of the nonwoven fabric. It is expected that the sound-absorbing property will improve as the thickness and density of the nonwoven fabric are increased. 
         [0106]    The nonwoven fabric used in the present invention may have a thickness of 3-20 mm when considering the industrial field and the like where the sound absorbing and insulating material is used. When the thickness of the nonwoven fabric is smaller than 3 mm, the durability and moldability of the sound absorbing and insulating material may be unsatisfactory. When the thickness exceeds 20 mm, productivity may decrease and production cost may increase. Further, the density of the nonwoven fabric may be 100-2000 g/m 2 , preferably 200-1200 g/m 2 , more preferably 300-800 g/m 2 , when considering performance and cost. 
         [0107]    The aramid nonwoven fabric is formed by stacking a web of 30-100 g/m 2  formed by carding two- to 12-fold and continuously performing up-down preneedling, down-up needling and up-down needling, thereby forming physical bridges that provide the necessary thickness, binding strength and other desired physical properties. The needle used to perform the needling may be a barb-type needle, having a working blade of 0.5-3 mm and a needle length (the distance from crank outside to point) of 70-120 mm Preferably, the needle stroke may be 30-350 times/m 2 . 
         [0108]    More specifically, the fineness of yarn for the nonwoven fabric may be 1.5-8.0 denier, the thickness of the pile layer may be 6-13 mm, the needle stroke may be 120-250 times/m 2 , and the density of the nonwoven fabric may be 300-800 g/m 2 . 
         [0109]    The internal structure of the sound absorbing and insulating material manufactured by the method described above may be confirmed using an electron microscope. When observed with an electron microscope, the sound absorbing and insulating material of the present invention has 1-100 μm-sized micro cavities distributed inside thereof. The micro cavities are distributed regularly or irregularly with a spacing of 0.1-500 μm. 
         [0110]    In another aspect, the present invention provides a method for reducing noise of a noise-generating device, including: i) checking a three-dimensional shape of a noise-generating device; ii) preparing and molding a sound absorbing and insulating material so as to correspond to the three-dimensional shape of the device partially or entirely; and iii) bringing the sound absorbing and insulating material adjacent to the noise-generating device. 
         [0111]    The device refers to a noise-generating device including a motor, an engine, an exhaust system and the like. However, the scope of the device is not limited to the motor, engine and exhaust system. The sound absorbing and insulating material may be manufactured to correspond to the three-dimensional shape of the device partially or entirely. Since the sound absorbing and insulating material of the present invention is moldable during curing of the binder, the sound absorbing and insulating material may be molded to correspond to the three-dimensional shape of the device partially or entirely. 
         [0112]    The expression “adjacent” means closely attaching the sound absorbing and insulating material to the noise-generating device, providing it with a distance from the noise-generating device, or molding it as a part of the noise-generating device. The expression adjacent also includes mounting the sound absorbing and insulating material to a member connected to the noise-generating device (e.g., another sound absorbing and insulating material). 
         [0113]      FIGS. 3A-3B  and  FIGS. 4A-4B  schematically show representative examples wherein the sound absorbing and insulating material of the present invention is applied to a noise-generating device of an automobile. 
         [0114]      FIGS. 3A-3B  schematically shows an example wherein a sound absorbing and insulating material is molded as a part and applied to a noise-generating device of an automobile.  FIG. 3A  is an image of a sound absorbing and insulating material molded to be used in an automobile engine, and  FIG. 3B  shows an example wherein the sound absorbing and insulating material is applied in a part of an automobile engine. 
         [0115]      FIGS. 4A-4B  schematically shows an example wherein a sound absorbing and insulating material is applied to a noise-generating device of an automobile.  FIG. 4A  is an image of a sound absorbing and insulating material molded to be used in a lower part of an automobile, and  FIG. 4B  shows an example wherein the sound absorbing and insulating material is attached to a lower part of an automobile. 
         [0116]    As described above, the sound absorbing and insulating material of the present invention, wherein the surface layer formed of the binder-impregnated nonwoven fabric, the binder being impregnated to maintain the three-dimensional structure inside the nonwoven fabric, is stacked on one side of the conventional sound absorbing and insulating material, exhibits improved sound-absorbing property, flame retardancy, heat-insulating property and heat resistance and can exhibit the desired sound-absorbing performance without deformation when directly applied to a noise-generating device maintained at high temperatures of 200° C. or above. 
       EXAMPLES 
       [0117]    Hereinafter, the present invention is described in more detail through examples. However, the scope of the present invention is not limited by the examples. 
       Examples 
     Preparation of Sound Absorbing and Insulating Material 
     Example 1 
     Preparation of Sound Absorbing and Insulating Material 
       [0118]    1) Preparation of Surface Layer Formed of Epoxy Resin-Impregnated Aramid Nonwoven Fabric 
         [0119]    A meta-aramid short fiber having a limiting oxygen index (LOI) of 40%, a heat resistance temperature of 300° C., a fineness of 2 denier and a length of 51 mm was air blown and formed into a web of 30 g/m 2  through carding. The web was stacked by overlapping 10-fold on a conveyor belt operated at 5 m/min using a horizontal wrapper. An aramid nonwoven fabric having a density of 300 g/m 2  and a thickness of 6 mm was prepared by continuously performing up-down needling, down-up needling and up-down needling with a needle stroke of 150 times/m 2 . 
         [0120]    The prepared nonwoven fabric was immersed in a binder solution with 1 dip 1 nip (pick-up 300%). The binder solution contained 8 wt % of bisphenol A diglycidyl ether, 2 wt % of bisphenol A diglycidyl ether polymer, 0.2 wt % of dicyandiamide, 0.02 wt % of dimethylurea, 10 wt % of melamine cyanurate and 79.78 wt % of dimethyl carbonate. 
         [0121]    The nonwoven fabric was taken out from the binder solution and dried at a temperature of 150° C. The dried nonwoven fabric contained 50 parts by weight of a binder based on 100 parts by weight of the nonwoven fabric. 
         [0122]    2) Preparation of Sound Absorbing and Insulating Material Wherein Surface Layer is Stacked on Base Layer 
         [0123]    After sequentially stacking a polyethylene nonwoven fabric having a density of 100 g/m 2  and a glass wool having a density of 700 g/m 2 , the 6-mm thick surface layer prepared in 1) was stacked thereon. Then, a sound absorbing and insulating material was prepared by thermal molding for 2 minutes in a mold of a desired shape at a temperature of 250° C. by compressing at a pressure of 8 kgf/cm 2 . 
       Comparative Example 1 
     Preparation of Sound Absorbing and Insulating Material Formed of Aramid Nonwoven Fabric 
       [0124]    An aramid nonwoven fabric having a density of 300 g/m 2  and a thickness of 6 mm was prepared by needle punching as described in Example 1 for use as a sound absorbing and insulating material. 
       Comparative Example 2 
     Preparation of Sound Absorbing and Insulating Material Formed of Epoxy Resin-Coated Aramid Nonwoven Fabric 
       [0125]    An aramid nonwoven fabric having a density of 300 g/m 2  and a thickness of 6 mm was prepared by needle punching as described in Example 1. Subsequently, a coating solution containing an epoxy resin was coated on the surface of the nonwoven fabric so that the content of a binder was 50 parts by weight based on 100 parts by weight of the nonwoven fabric. Then, the nonwoven fabric was molded after drying at a temperature of 150° C. 
         [0126]    The coating solution contained 8 wt % of bisphenol A diglycidyl ether, 2 wt % of bisphenol A diglycidyl ether polymer, 0.2 wt % of dicyandiamide, 0.02 wt % of dimethylurea, 10 wt % of melamine cyanurate and 79.78 wt % of dimethyl carbonate. 
       Comparative Example 3 
     Preparation of Sound Absorbing and Insulating Material Formed of Thermoplastic Resin-Impregnated Aramid Nonwoven Fabric 
       [0127]    An aramid nonwoven fabric having a density of 300 g/m 2  and a thickness of 6 mm was prepared by needle punching as described in Example 1. The nonwoven fabric was immersed in a binder solution, dried and then molded. 
         [0128]    The binder solution was a thermoplastic resin solution containing 10 wt % of polyethylene resin, 10 wt % of melamine cyanurate and 80 wt % of dimethyl carbonate (DMC). 
       Comparative Example 4 
     Preparation of Sound Absorbing and Insulating Material Formed of Epoxy Resin-Impregnated PET Nonwoven Fabric 
       [0129]    A polyethylene terephthalate (PET) nonwoven fabric having a density of 300 g/m 2  and a thickness of 6 mm was prepared by needle punching as described in Example 1. The nonwoven fabric was immersed in a binder solution, dried and then molded. 
         [0130]    The PET nonwoven fabric prepared in Comparative Example 4 was thermally deformed due to the reaction heat produced during the curing of epoxy and could not be molded into a desired shape because it was completely thermally deformed during the drying and thermal molding processes. 
       Test Example 
     Evaluation of Physical Properties of Sound Absorbing and Insulating Materials 
       [0131]    The physical properties of the sound absorbing and insulating materials were measured and compared as follows. 
         [0132]    1. Evaluation of heat resistance 
         [0133]    To evaluate heat resistance, the sound absorbing and insulating material was aged in an oven at a temperature of 260° C. for 300 hours. After keeping at standard state (temperature 23±2° C., 50±5% relative humidity) for at least 1 hour, appearance was inspected and tensile strength was measured. It was visually inspected whether there were shrinkage or deformation, surface peeling, fluffing and cracking. The tensile strength was measured using a dumbbell-type No. 1 for randomly selected five sheets of test samples at a speed of 200 mm/min under a standard condition. 
         [0134]    2. Evaluation of thermal cycle 
         [0135]    The durability of the sound absorbing and insulating material was evaluated by the thermal cycle test method. The durability was determined after performing five cycles under the following conditions. 
         [0136]    1) Condition of one cycle 
         [0137]    Room temperature→high temperature (150° C.×3 hr)→room temperature→low temperature (−30° C.×3 hr)→room temperature→humid condition (50° C.×95% RH). 
         [0138]    2) Durability evaluation standard 
         [0139]    After the thermal cycle test, the change in appearance was inspected. For example, surface damage, swelling, breaking and discoloring were inspected. If there was no change in appearance, the sound absorbing and insulating material was evaluated as ‘no abnormality’. 
         [0140]    3. Evaluation of flame retardancy 
         [0141]    The flame retardancy of the sound absorbing and insulating material was measured according to the ISO 3795 flammability test method. 
         [0142]    4. Evaluation of nonflammability 
         [0143]    The nonflammability of the sound absorbing and insulating material was measured according to the UL94 vertical burn test. 
         [0144]    5. Evaluation of sound-absorbing property 
         [0145]    The sound-absorbing property of the sound absorbing and insulating material was measured according to the ISO 354 method. 
         [0146]    6. Evaluation of air permeability 
         [0147]    1) Evaluation method 
         [0148]    The test sample was mounted on a Frazier-type tester and the amount of air flowing through the sample vertically was measured. The area of the test sample through which the air passed was 5 cm 2  and the applied pressure was set to 125 pascal (Pa). 
       Test Example 1 
     Comparison of Properties of Sound Absorbing and Insulating Materials Depending on Heat-Resistant Fibers 
       [0149]    In Test Example 1, the physical properties of sound absorbing and insulating materials prepared with different heat-resistant fiber yarns were compared. Sound absorbing and insulating materials were prepared as described in Example 1 by preparing a surface layer and a base layer, stacking them and then molding. The nonwoven fabrics used to prepare the surface layer were prepared using yarns having a fineness of 2 denier and a length of 51 mm, which are described in Table 1. The physical properties of the prepared sound absorbing and insulating materials were measured as described above. The result of measuring the properties of the sound absorbing and insulating materials prepared with different heat-resistant fibers is shown in Table 1 and Table 2. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Physical properties of sound absorbing and insulating materials 
               
             
          
           
               
                   
                 Yarn 1 
                 Yarn 2 
                 Yarn 3 
                 Yarn 4 
                 Yarn 5 
                 Yarn 6 
                 Yarn 7 
               
               
                   
                   
               
             
          
           
               
                 Yarn 
                 Yarn 
                 Aramid 
                 PPS 
                 PI 
                 PBI 
                 PBO 
                 oxi-PAN 
                 PK 
               
               
                   
                 material 
               
               
                   
                 Limiting 
                 40 
                 30 
                 50 
                 40 
                 60 
                 65 
                 30 
               
               
                   
                 oxygen 
               
               
                   
                 index 
               
               
                   
                 Heat 
                 300 
                 230 
                 300 
                 300 
                 300 
                 300 
                 300 
               
               
                   
                 resistance 
               
               
                   
                 temperature 
               
               
                   
                 (° C. × 1 hr) 
               
               
                 Heat 
                 Appearance 
                 No 
                 No 
                 No 
                 No 
                 No 
                 No 
                 No 
               
               
                 resistance 
                   
                 abnormality 
                 abnormality 
                 abnormality 
                 abnormality 
                 abnormality 
                 abnormality 
                 abnormality 
               
               
                   
                 Tensile 
                 200 
                 180 
                 220 
                 200 
                 210 
                 210 
                 200 
               
               
                   
                 strength 
               
               
                   
                 (Kgf/cm 2 ) 
               
               
                 Thermal 
                 Appearance 
                 No 
                 No 
                 No 
                 No 
                 No 
                 No 
                 No 
               
               
                 cycle 
                   
                 abnormality 
                 abnormality 
                 abnormality 
                 abnormality 
                 abnormality 
                 abnormality 
                 abnormality 
               
             
          
           
               
                 Flame 
                 Self- 
                 Self- 
                 Self- 
                 Self- 
                 Self- 
                 Self- 
                 Self- 
               
               
                 retardancy 
                 extinguishing 
                 extinguishing 
                 extinguishing 
                 extinguishing 
                 extinguishing 
                 extinguishing 
                 extinguishing 
               
               
                 Nonflammability 
                 Nonflammable 
                 Nonflammable 
                 Nonflammable 
                 Nonflammable 
                 Nonflammable 
                 Nonflammable 
                 Nonflammable 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 Sound-absorbing rate of sound 
                   
               
               
                   
                 absorbing and insulating materials 
               
             
          
           
               
                 Fre- 
                 Yarn 
                 Yarn 
                 Yarn 
                 Yarn 
                   
               
               
                 quency 
                 1 
                 2 
                 6 
                 7 
                 Base 
               
               
                 (Hz) 
                 (aramid) 
                 (PPS) 
                 (oxi-PAN) 
                 (PK) 
                 layer* 
               
               
                   
               
             
          
           
               
                 400 
                 0.08 
                 0.05 
                 0.08 
                 0.05 
                 0.08 
               
               
                 500 
                 0.10 
                 0.06 
                 0.09 
                 0.06 
                 0.09 
               
               
                 630 
                 0.16 
                 0.09 
                 0.13 
                 0.08 
                 0.18 
               
               
                 800 
                 0.23 
                 0.15 
                 0.22 
                 0.19 
                 0.25 
               
               
                 1000 
                 0.35 
                 0.30 
                 0.35 
                 0.26 
                 0.39 
               
               
                 1250 
                 0.44 
                 0.39 
                 0.45 
                 0.37 
                 0.52 
               
               
                 1600 
                 0.59 
                 0.49 
                 0.57 
                 0.31 
                 0.66 
               
               
                 2000 
                 0.70 
                 0.66 
                 0.68 
                 0.48 
                 0.74 
               
               
                 2500 
                 0.79 
                 0.71 
                 0.80 
                 0.67 
                 0.79 
               
               
                 3150 
                 0.83 
                 0.80 
                 0.85 
                 0.78 
                 0.83 
               
               
                 4000 
                 0.86 
                 0.83 
                 0.88 
                 0.84 
                 0.89 
               
               
                 5000 
                 0.99 
                 0.95 
                 0.92 
                 0.83 
                 0.96 
               
               
                 6300 
                 0.98 
                 0.96 
                 0.98 
                 0.89 
                 0.97 
               
               
                 8000 
                 0.99 
                 0.95 
                 0.89 
                 0.95 
                 0.98 
               
               
                 10000 
                 0.98 
                 0.97 
                 0.99 
                 0.95 
                 0.95 
               
               
                   
               
               
                 *Base layer: the base layer used in 2) of Example 1; prepared by stacking a glass wool having a density of 700 g/m 2  and a polyethylene nonwoven fabric having a density of 100 g/m 2 ; thickness = 10 mm. 
               
             
          
         
       
     
         [0150]    As seen from Table 1 and Table 2, all the sound absorbing and insulating materials prepared using heat-resistant fibers having a limiting oxygen index of 25% or greater and a heat resistance temperature of 150° C. or greater as presented by the present invention exhibited satisfactory heat resistance, durability, flame retardancy, nonflammability and sound-absorbing property. Accordingly, it was confirmed that conventional heat-resistant fibers known as super fiber can be used as the material of the nonwoven fabric of the sound absorbing and insulating material according to the present invention. 
       Test Example 2 
     Comparison of Properties of Sound Absorbing and Insulating Materials Depending on Density of Nonwoven Fabric 
       [0151]    In Test Example 2, sound absorbing and insulating materials were prepared in the same manner as in Example 1 using nonwoven fabrics having different densities in surface layers. The sound-absorbing performance of the prepared sound absorbing and insulating materials is shown in  FIG. 5 . 
         [0152]    As seen from  FIG. 5 , the sound-absorbing performance of the sound absorbing and insulating material was superior when a nonwoven fabric having a density of 600 g/m 2  was used than when a nonwoven fabric having a density of 300 g/m 2  was used. 
       Test Example 3 
     Evaluation of Physical Properties of Sound Absorbing and Insulating Materials 
       [0153]    In Test Example 3, the properties of sound absorbing and insulating materials depending on the method by which a thermosetting binder was applied to a nonwoven fabric used in a surface layer were compared. 
         [0154]    That is to say, the sound-absorbing rate of the sound absorbing and insulating materials prepared by impregnating (Example 1) and coating (Comparative Example 2) the thermosetting binder was compared. The result of measuring the sound-absorbing rate of the sound absorbing and insulating material formed of a nonwoven fabric (Comparative Example 1), the sound absorbing and insulating material on which the thermosetting binder was coated (Comparative Example 2), the sound absorbing and insulating material wherein the thermosetting binder was impregnated into the nonwoven fabric (surface layer of Example 1) and the sound absorbing and insulating material wherein a nonwoven fabric impregnated with the thermosetting binder was stacked as a surface layer (sound absorbing and insulating material of Example 1) is shown in Table 3. 
         [0000]    
       
         
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
             
             
               
                   
                   
               
               
                   
                 Sound-absorbing rate 
               
             
          
           
               
                   
                   
                   
                   
                 Sound absorbing 
               
               
                 Fre- 
                   
                   
                 Surface 
                 and insulating 
               
               
                 quency 
                 Comparative 
                 Comparative 
                 layer of 
                 material of 
               
               
                 (Hz) 
                 Example 1 
                 Example 2 
                 Example 1 
                 Example 1 
               
               
                   
               
             
          
           
               
                 400 
                 0.01 
                 0.02 
                 0.08 
                 0.10 
               
               
                 500 
                 0.03 
                 0.03 
                 0.10 
                 0.14 
               
               
                 630 
                 0.12 
                 0.05 
                 0.16 
                 0.19 
               
               
                 800 
                 0.16 
                 0.08 
                 0.23 
                 0.32 
               
               
                 1000 
                 0.26 
                 0.12 
                 0.35 
                 0.52 
               
               
                 1250 
                 0.32 
                 0.15 
                 0.44 
                 0.69 
               
               
                 1600 
                 0.39 
                 0.22 
                 0.59 
                 0.72 
               
               
                 2000 
                 0.48 
                 0.29 
                 0.70 
                 0.77 
               
               
                 2500 
                 0.64 
                 0.40 
                 0.79 
                 0.78 
               
               
                 3150 
                 0.63 
                 0.57 
                 0.83 
                 0.84 
               
               
                 4000 
                 0.72 
                 0.68 
                 0.86 
                 0.88 
               
               
                 5000 
                 0.80 
                 0.77 
                 0.99 
                 0.99 
               
               
                 6300 
                 0.78 
                 0.82 
                 0.98 
                 0.99 
               
               
                 8000 
                 0.89 
                 0.98 
                 0.99 
                 0.99 
               
               
                 10000 
                 0.90 
                 0.98 
                 0.98 
                 0.99 
               
               
                   
               
             
          
         
       
     
         [0155]    The sound absorbing and insulating material presented by the present invention has a structure in which the thermosetting binder-impregnated nonwoven fabric is stacked as the surface layer on the base layer formed of a conventional sound absorbing and insulating material. As seen from Table 3, the sound absorbing and insulating material according to the present invention showed superior sound-absorbing rate in all frequency ranges as compared to Comparative Example 1 (nonwoven fabric) and Comparative Example 2 (binder-coated nonwoven fabric). From Table 3, it can be seen that the thermosetting binder-impregnated nonwoven fabric layer (corresponding to the surface layer of the sound absorbing and insulating material of the present invention) shows superior sound-absorbing effect as compared to Comparative Example 1 and Comparative Example 2 and the sound-absorbing effect is remarkably improved when it is stacked on the base layer (conventional sound absorbing and insulating material). 
         [0156]    In contrast, the sound absorbing and insulating material of Comparative Example 2 wherein the nonwoven fabric on which the thermosetting binder was coated was used showed lower sound-absorbing rate than the nonwoven fabric (Comparative Example 1) in the frequency range of 400-5000 Hz. 
       Test Example 4 
     Evaluation of Heat-Insulating Performance of Sound Absorbing and Insulating Materials 
       [0157]    In Test Example 4, the heat-insulating performance of the surface layer of Example 1 (binder-impregnated aramid nonwoven fabric) and the sound absorbing and insulating materials prepared in Comparative Example 1 (aramid nonwoven fabric) and Comparative Example 3 (thermoplastic resin-impregnated aramid nonwoven fabric) was evaluated. After applying heat at a temperature of 1000° C. from one side of a 25-mm thick sample of each sound absorbing and insulating material for 5 minutes, temperature was measured on the opposite side of the sample. 
         [0158]    The temperature measured on the opposite side of the sound absorbing and insulating material was at a temperature of 250° C. for the surface layer of Example 1 and at a temperature of 350° C. for the sound absorbing and insulating material of Comparative Example 1. Accordingly, it was confirmed that the sound absorbing and insulating material of the present invention wherein the thermosetting resin was impregnated exhibits improved heat-insulating performance. In contrast, the thermoplastic resin-impregnated sound absorbing and insulating material of Comparative Example 3 melted down and deformed as soon as the heat at a temperature of 1000° C. was applied. 
         [0159]    Accordingly, it can be seen that the sound absorbing and insulating material of the present invention has very superior heat-insulating property. 
       Test Example 5 
     Comparison of Heat-Insulating Performance with Aluminum Heat-Insulating Plate 
       [0160]    In Test Example 5, the heat-insulating performance of the sound absorbing and insulating material of Example 1 was compared with that of an aluminum heat-insulating plate. While applying the same heat from one side of the sound absorbing and insulating material and the heat-insulating plate at a temperature of 250° C., the temperature at the opposite side was measured with time. The result is shown in  FIG. 6 . 
         [0161]    As seen from  FIG. 6 , the sound absorbing and insulating material according to the present invention showed better heat-insulating performance with the heat resistance temperature at least 11° C. lower as compared to the aluminum heat-insulating plate. 
       Test Example 6 
     Comparison of Properties of Sound Absorbing and Insulating Material Depending on Binder Content 
       [0162]    Surface layers of sound absorbing and insulating materials were prepared in the same manner as in Example 1. The epoxy resin-impregnated aramid nonwoven fabric was dried to have different final binder contents. The binder content was represented as parts by weight of the binder included in the sound absorbing and insulating material based on 100 parts by weight of the dried nonwoven fabric. 
         [0163]    The result of comparing the mechanical properties and sound-absorbing rate of the sound absorbing and insulating materials prepared with different binder contents is shown in Table 4 and Table 5. 
         [0000]    
       
         
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
             
             
               
                   
                   
               
               
                   
                 Physical properties of sound absorbing and 
               
               
                   
                 surface layers with different binder contents 
               
               
                   
                 Binder content (parts by weight) 
               
             
          
           
               
                   
                 0 
                 10 
                 50 
                 100 
                 200 
               
               
                   
                   
               
             
          
           
               
                 Air 
                 500 
                 380 
                 350 
                 320 
                 210 
               
               
                 permeability 
               
               
                 (mL/cm 2  · s) 
               
               
                 Tensile 
                 40 
                 60 
                 200 
                 240 
                 310 
               
               
                 strength 
               
               
                 (kg/cm 2 ) 
               
               
                 Nonflam- 
                 Nonflam- 
                 Nonflam- 
                 Nonflam- 
                 Nonflam- 
                 Nonflam- 
               
               
                 mability 
                 mable 
                 mable 
                 mable 
                 mable 
                 mable 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 5 
               
             
             
               
                   
                   
               
               
                   
                 Sound-absorbing rate of surface 
                   
               
               
                   
                 layers with different binder contents 
               
             
          
           
               
                 Fre- 
                 0 
                 10 
                 50 
                 100 
                 200 
               
               
                 quency 
                 parts by 
                 parts by 
                 parts by 
                 parts by 
                 parts by 
               
               
                 (Hz) 
                 weight 
                 weight 
                 weight 
                 weight 
                 weight 
               
               
                   
               
             
          
           
               
                 400 
                 0.01 
                 0.01 
                 0.08 
                 0.06 
                 0.02 
               
               
                 500 
                 0.03 
                 0.04 
                 0.10 
                 0.09 
                 0.04 
               
               
                 630 
                 0.12 
                 0.14 
                 0.16 
                 0.15 
                 0.09 
               
               
                 800 
                 0.16 
                 0.17 
                 0.23 
                 0.25 
                 0.11 
               
               
                 1000 
                 0.26 
                 0.26 
                 0.35 
                 0.30 
                 0.14 
               
               
                 1250 
                 0.32 
                 0.34 
                 0.44 
                 0.42 
                 0.17 
               
               
                 1600 
                 0.39 
                 0.41 
                 0.59 
                 0.54 
                 0.22 
               
               
                 2000 
                 0.48 
                 0.55 
                 0.70 
                 0.58 
                 0.35 
               
               
                 2500 
                 0.64 
                 0.68 
                 0.79 
                 0.67 
                 0.44 
               
               
                 3150 
                 0.63 
                 0.69 
                 0.83 
                 0.72 
                 0.52 
               
               
                 4000 
                 0.72 
                 0.77 
                 0.86 
                 0.75 
                 0.53 
               
               
                 5000 
                 0.80 
                 0.83 
                 0.99 
                 0.79 
                 0.57 
               
               
                 6300 
                 0.78 
                 0.88 
                 0.98 
                 0.80 
                 0.63 
               
               
                 8000 
                 0.89 
                 0.91 
                 0.99 
                 0.90 
                 0.70 
               
               
                 10000 
                 0.90 
                 0.92 
                 0.98 
                 0.92 
                 0.71 
               
               
                   
               
             
          
         
       
     
         [0164]    As seen from Table 4 and Table 5, the sound-absorbing rate was improved as the binder was impregnated into the nonwoven fabric when compared with the nonwoven fabric not impregnated with the binder. Also, it was confirmed that the sound-absorbing rate of the sound absorbing and insulating material could be controlled with the binder content. 
       Test Example 7 
     Comparison of Properties of Sound Absorbing and Insulating Material Depending on Binders 
       [0165]    Surface layers of sound absorbing and insulating materials wherein 50 parts by weight of a binder was impregnated based on 100 parts by weight of an aramid nonwoven fabric were prepared in the same manner as in Example 1. The resins described in Table 6 were used as the binder. 
         [0166]    The result of comparing the mechanical properties and sound-absorbing rate of the surface layers of the sound absorbing and insulating materials prepared with different binders is shown in Table 6. 
         [0000]    
       
         
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 6 
               
             
             
               
                   
                   
               
               
                   
                 Physical properties of sound absorbing and 
               
               
                   
                 insulating materials with different binders 
               
               
                   
                 Binder resin 
               
             
          
           
               
                   
                   
                   
                   
                   
                 Polyure- 
               
               
                   
                 Epoxy 
                 Phenol 
                 Urea 
                 Melamine 
                 thane 
               
               
                   
                   
               
             
          
           
               
                 Heat 
                 300 
                 260 
                 190 
                 300 
                 200 
               
               
                 resistance 
               
               
                 temperature 
               
               
                 (° C. × 1 hr) 
               
               
                 Tensile 
                 200 
                 165 
                 180 
                 180 
                 170 
               
               
                 strength 
               
               
                 (kg/cm 2 ) 
               
               
                 Flame 
                 Self- 
                 Self- 
                 Self- 
                 Self- 
                 Self- 
               
               
                 retardancy 
                 extin- 
                 extin- 
                 extin- 
                 extin- 
                 extin- 
               
               
                   
                 guishing 
                 guishing 
                 guishing 
                 guishing 
                 guishing 
               
               
                 Nonflam- 
                 Nonflam- 
                 Nonflam- 
                 Nonflam- 
                 Nonflam- 
                 Nonflam- 
               
               
                 mability 
                 mable 
                 mable 
                 mable 
                 mable 
                 mable