KR20210099703A - Acoustic absorber having stack structure for automobile - Google Patents

Abstract

The present invention relates to a sound absorbent material with a laminated structure for vehicles. A conventional sound absorbent material for vehicles is a sound insulation structure using a heavy-duty sound-insulating material sheet called a heavy layer, thereby having problems, such as heavy overall weight, an increase in manufacturing cost, environmental pollution due to difficulty in recycling, and the like although sound insulation property is excellent. In addition, even in the case of a conventional fiber material multi-layer sound absorbent material formed of a high-density layer and a low-density layer (the entire area is a laminated structure of the high-density layer and the low-density layer), the high-density sound absorbent material layer becomes harder after molding, so workability, transportation and installation, and the like, was poor. To solve these problems, the sound absorbent material has a structure of more than a double layer formed of a high-density layer and a low-density layer and is formed in a partial lamination structure intensively arranging the high-density layer in only areas with a large contribution to improvement instead of a structure formed of the high-density layer and the low-density layer as in the prior art, thereby providing effects of increasing recycling properties, sound absorption performance, and weight reduction in comparison with the conventional heavy layer application structure and acquiring weight reduction and workability improvement in comparison with a sound insulation material of a laminated structure in which the entire part is formed of a high-density layer and a low-density layer.

Description

Acoustic absorber having stack structure for automobile

The present invention relates to a sound absorbing material for automobiles, which has a structure of more than double layers consisting of a high-density layer and a low-density layer. By configuring it as a partial lamination structure intensively placed in a portion with a large contribution, it is possible to obtain the effect of recycling, sound absorption performance improvement and weight reduction compared to the conventional heavy layer application structure, and the whole is a laminate structure of a high density layer and a low density layer It relates to a sound-absorbing material for automobiles that can reduce weight and improve workability compared to the sound-insulating material used in the present invention.

In general, typical noise introduced into the interior of a vehicle includes engine penetration noise generated from an engine and transmitted through a vehicle body or air. An engine cover or hood insulator is used to suppress the engine noise, but the effect of actually removing the noise is insignificant, and the dash outer attached to the exterior of the vehicle and the dash inner attached to the interior inner) plays a role in removing most of the noise.

Therefore, in order to block noise from entering the interior of the vehicle, in the case of the dash inner, as shown in FIG. 1, in the related art, most of the sound insulation layer (heavy layer) (a heavy-duty sound insulation sheet; 3) is coated with polyurethane ( polyurethane, PU) foam or poly

A sound absorbing and insulating material attached by bonding or heat-sealing polyethylene terephthalate (PET; 2) to the dash panel 1 has been used. However, in this case, although the sound insulation performance is excellent, the assembly weight is heavy at 6 ~ 9Kg per unit, there are problems such as an increase in manufacturing cost and environmental pollution due to the difficulty of recycling, and the sound insulation material is attached to the interior of the vehicle Therefore, there has been a problem that there is almost no sound absorption performance for noise in the room. In addition, as shown in FIG. 2 , a sound absorbing and insulating material in which a sound absorbing and insulating material 3 of a separate heavy layer is attached to a sound absorbing material of a dual structure in which a high density material 2b is attached to a low density material 2a is applied to the dash panel 1 ) is introduced, but even in this case, the effect of weight reduction and sound absorption was insufficient. In addition, when using the heavy layer as described above, there is a limit to weight improvement, and the smell of the heavy layer has also been pointed out as a problem.

As another method, a method of manufacturing a product by adding a predetermined binder fiber after crushing the waste yarn is used. In this case, since it is difficult to manage the dead, there is a large variation in sound absorption, and problems such as deterioration of workability due to dust generation during processing, investment cost burden due to the installation of dust collectors, etc. In addition, as a method that has been widely used recently, a non-woven fabric layer obtained by thermally bonding a binder fiber such as polyolefin or polyester having a relatively low melting point and a synthetic fiber having a high melting point is heat-bonded in place of a heavy sound insulating material layer with a difference in density (low-density fiber material). and high-density fiber material), or a method of reducing the weight of parts by constructing and manufacturing two or more multiple layers with different airflow differences, is disclosed in Korean Patent Application Laid-Open No. 10-2003-0000746, sound absorbing and insulating materials for automobiles, (Published date: January 06, 2003). However, these methods can achieve the effect of reducing the weight of parts by simply arranging the nonwoven fabric in a plurality of layers, but there is a limit to reducing it to the same level as the present invention.

More specifically, in the case of a sound absorbing and insulating material to which a heavy layer sound insulating material sheet is attached and a sound absorbing material composed of a fiber material, a sound transmission mechanism from the engine to the interior of the vehicle is different. In other words, in the case of the conventional sound absorbing and insulating material specification to which the heavy layer sound insulating material sheet is attached, as shown in FIG. 3 , the noise generated from the engine primarily passes through the dash panel 1 of the vehicle body, and the passed noise is reflected from the crash pad 4 inside the vehicle and transmitted back to the heavy layer sound insulating material sheet 3 . After that, the sound reflected from the sound insulating material sheet 3 is finally introduced into the vehicle. , When analyzing the frequency of the incoming noise, it is mostly rough and loud high-frequency sounds over 1000Hz.

In addition, in the actual dash inner product, the portion with a thickness of 15mm or more accounts for around 50%, and the fact that leakage noise through the air conditioner pipe or brake booster hole is not absorbed and transmitted to the room is also pointed out as a problem. is becoming

In addition, when analyzing the distribution of sound pressure generated when the noise emitted from the engine comes into contact with the dash panel, the center of the noise is the largest, and the sound pressure decreases toward the outside. In other words, it means that the portion adjacent to the engine among the dash panels has the greatest contribution to noise improvement of the sound absorbing material in the dash inner, and the contribution decreases as the distance increases. there will be no However, in the prior art, the sound absorbing material of the same structure is attached to the entire site, in this case, it is difficult to achieve a satisfactory weight reduction, and also many problems are occurring in terms of workability. In other words, in the case of multiple sound-absorbing materials made of fiber material in which the high-density layer and the low-density layer have the same area, the high-density sound-absorbing material layer has an excessively hard surface strength after molding. Problems such as poor mountability such as detachment occur frequently.

Patent Publication No. 10-2003-0000746, sound absorbing and insulating materials for automobiles, (published on January 06, 2003)

Therefore, the present invention was invented to solve the above problems, and it is composed of a double-layer or more structure consisting of a high-density layer and a low-density layer. By configuring the layers in a partially laminated structure in which the layers are intensively arranged in areas with a high contribution to noise improvement of the body panel, it is possible to obtain the effects of recyclability, sound absorption performance improvement and weight reduction compared to the conventional heavy layer application structure, and the entire high-density layer An object of the present invention is to provide a sound absorbing material for automobiles that can reduce weight and improve workability compared to a sound insulating material having a laminated structure of a low-density layer.

As an embodiment, in a sound absorbing material for automobiles in which a low-density sound-absorbing material having a relatively low areal density and a relatively high-density sound-absorbing material are stacked in a double-layer or more structure, some areas with a relatively large contribution to indoor noise that require vibration damping performance and low frequency sound absorption and insulation performance Only the high-density sound-absorbing material is laminated, and the rest part includes a single-layer structure made of only the low-density sound-absorbing material, and the high-density sound-absorbing material is laminated on the center part of the sound-absorbing material corresponding to the dash panel center part, and between the high-density sound-absorbing material and the low-density sound-absorbing material It further includes a nonwoven fabric.

The high-density sound-absorbing material is made of a sound-absorbing material having an areal density of 500 to 2000g/m2, and the low-density sound-absorbing material includes a sound-absorbing material having an areal density of 500 to 2000g/m2.

As an embodiment, the lamination area of the high-density sound-absorbing material is 20 to 90% of the area of the low-density sound-absorbing material.

In one embodiment, the lamination area of the high-density sound-absorbing material is 30 to 80% of the area of the low-density sound-absorbing material.

In one embodiment, the lamination area of the high-density sound-absorbing material is 40 to 60% of the area of the low-density sound-absorbing material.

The sound absorbing material for automobile according to the present invention greatly improves the problem of weight increase due to the insertion of the heavy layer, which is a problem of the existing sound absorbing material, so that the fuel efficiency of the vehicle can be improved, and additional weight reduction compared to the sound absorbing material of the existing entire double-layer structure It has the effect of reducing the manufacturing cost as well as the effect of improving workability, such as portability and mountability. In addition, since it is manufactured from a material that can be recycled, it has the effect of reducing problems such as environmental pollution.

1 is a cross-sectional view of a conventional sound absorbing material using a heavy layer sound insulating material sheet.
2 is a cross-sectional view showing a sound absorbing material of a conventional double-layer structure in which a high-density material is attached to a low-density material.
3 is a view for explaining a noise transmission mechanism by the sound absorbing and insulating material of the heavy layer sound insulating material sheet.
4 is a cross-sectional view showing a sound absorbing material of a partial double-layer sound absorbing structure according to the present invention.
FIG. 5A is a view showing the center part requiring vibration damping performance and low frequency sound absorption and insulating performance in a dash panel for explaining the present invention.
Figure 5b is a view showing the divided double-layer structure region and the single-layer structure region in the sound absorbing material of the partial double-layer sound-absorbing structure according to the present invention.
6 is a view for explaining a noise transmission mechanism by the sound absorbing material of the present invention.
7A and 7B are diagrams showing the results of evaluating the sound absorbing and insulating performance and sound absorbing performance of the sound absorbing material of the present invention and the sound absorbing material of the conventional heavy layer sound insulating material sheet, respectively.

The present invention described below can apply various transformations and can have various embodiments, and specific embodiments are illustrated in the drawings and described in detail in the detailed description.

However, this is not intended to limit the present invention to specific embodiments, and it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. In describing the present invention, if it is determined that a detailed description of a related known technology may obscure the gist of the present invention, the detailed description thereof will be omitted.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as “comprise” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Also, terms such as first, second, etc. may be used to distinguish and describe various components, but the components should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another.

In addition, when at least two different embodiments are described in the present application, all or part of the components may be used by merging and mixing with each other even if there is no particular description within the scope not departing from the technical spirit of the present invention. .

The present invention relates to a sound absorbing material for automobiles, which can improve indoor noise by preventing deterioration of sound absorption while remarkably reducing weight, which is a problem in the prior art, and having an effect of improving workability such as transportability and mountability. In the case of the existing sound absorbing material, it was attempted to improve the indoor noise by using the same structure material for part or all of the noise part to shield the transmitted noise from the engine, etc., but in this case, the transportability is poor because the surface of the product is hardened after molding, There was a problem in that it was easily removed when it was installed on the fixing pin at the end of the body panel.

Accordingly, the sound-absorbing material for automobiles of the present invention is disclosed to solve the above-described problems, and the sound-absorbing material for automobiles of the present invention will be described in more detail with the drawings, taking the dash inner sound-absorbing material as an example.

The sound-absorbing material of the present invention does not use a heavy-duty sound-insulating material sheet, which accounts for 80% of the weight, but in the double sound-absorbing basic structure of 'hard-layer sound-absorbing material + soft-layer sound-absorbing material'. A double sound-absorbing structure is applied to the part where the low-frequency sound absorption and insulation performance is important to simultaneously achieve solid transmission sound in the low-frequency region and high-frequency sound absorption performance. It has a partial double-layer sound-absorbing structure.

That is, it is composed of a sound-absorbing material of a double-layer structure consisting of a high-density layer and a low-density layer, but a high-density layer is selectively placed on the part where the engine of the dash panel that directly receives the noise generated from the engine is located, and the part where the fan and belt are located. At the same time, by arranging a low-density layer throughout the noise area, while maintaining the effect of improving indoor noise, the original purpose of the sound-absorbing material, the weight is reduced compared to the existing sound-absorbing material, and workability such as transport and installation is dramatically improved made to be

In addition, in the transmission noise of the engine, the present invention was completed in the direction of improving the indoor noise by effectively removing the high-frequency noise of 1000 Hz or more, particularly, the high-frequency noise in the range of 1000 to 4000 Hz among the noise introduced into the room. Here, the 1000 to 4000 Hz section is generally a frequency section that can be most sensitively detected by humans. Below or above this section, human hearing responds insensitively. Therefore, the present invention was evaluated mainly on sound absorption, and the evaluation by the test piece was evaluated using Apamat, a sound absorbing and insulating performance test equipment for sound absorbing and insulating materials, and α-Cabin, a sound absorption performance test equipment. Based on the evaluation results by It was possible to provide a sound absorbing material for automobiles that was superior to the material and reduced in weight by up to 60% or more.

Hereinafter, the sound absorbing material for a dash inner for a vehicle according to the present invention will be described in more detail as follows.

4 is a cross-sectional view showing a sound-absorbing material of a partial double-layer sound-absorbing structure according to the present invention, and Fig. 5a is a part where vibration damping performance and low-frequency sound absorption and insulation performance are important in the dash panel for the explanation of the present invention, and sound absorption performance improvement except this It is a view showing the required parts separately, and FIG. 5b is a view showing the double-layer structure area and the single-layer structure area separately in the sound-absorbing material of the partial double-layer sound-absorbing structure according to the present invention.

First, as shown in FIG. 4, the sound absorbing material for the dash panel 1 according to the present invention is constructed by laminating a high-density material (hard felt layer; 13) on a low-density material (soft felt layer; 12), but vibration damping performance and It has a partial double-layer sound-absorbing structure made by laminating high-density materials only in a predetermined area in the center where low-frequency sound absorbing and insulating performance is required. That is, in FIG. 5B , the central part is configured as a double-layer structure by stacking the high-density material 13 , but the rest of the periphery except for this is configured as a single-layer structure made of only the low-density material 12 . In other words, in the dash panel 1 of FIG. 5A , the center part 1a is a part that directly receives the noise generated by the engine, which corresponds to the part where the engine is located and the part where the fan and the belt are located. Performance and low-frequency sound absorbing and insulating performance are important parts, therefore, the central part of the sound absorbing material corresponding to this center part 1a is composed of a double-layer structure, and the sound absorbing material corresponding to the remaining parts (which is a part requiring improvement in sound absorbing performance) except for this The part is to be composed of a single-layer structure. The center part 1a of the dash panel 1 is a part through which the air conditioner hose and accelerator pedal cable connected from the engine side to the inside of the crash pad pass, and since the hose or cable acts as a solid transmission excitation source to the dash panel, In the center part 1a, the low-frequency vibration damping performance of 500 Hz or less and the sound absorption performance are simultaneously improved by the double structure of the 'soft felt layer + hard felt layer' of the sound absorbing material. At the same time, the portion other than the center portion 1a is composed of only a single layer of the soft felt layer to maximize the sound absorption performance of the high frequency region of 500 Hz or more to improve the engine tone at the same time. After all, the sound absorbing material of the present invention has a structure that is strong against noise defects due to work errors because the double structure in the center absorbs noise leaking through various holes, and the vibration damping performance and sound absorption performance are optimally according to the acoustic characteristics of the dash panel. It has been improved to make it work.

This partial double-layer sound-absorbing structure becomes a more improved structure that simultaneously satisfies the sound-absorbing and insulating performance advantages of the existing sound-insulating structure and the sound-absorbing performance advantages of the entire double sound-absorbing structure. As in the present invention, when the sound absorbing material of the partial double-layer sound absorbing structure composed only of fiber material is applied, as shown in FIG. 6 , the noise generated from the engine passes through the dash panel 11 of the vehicle body and crashes After being reflected by the pad (4), it is transmitted to the sound absorbing material and the sound is absorbed by the sound absorbing material. ) is improved (see FIG. 7b).

In order to find out the degree of improvement in sound absorbing and insulating performance and sound absorbing performance of the sound absorbing material of the present invention, a comparative test was conducted with a conventional sound absorbing and insulating material having a 'heavy layer sound insulating sheet + polyurethane (PU)' structure. is shown in the accompanying Figures 7a and 7b. At this time, the evaluation was performed using Apamat, a sound absorption and insulating performance testing equipment for sound absorbing and insulating materials, and α-Cabin, a sound absorption performance testing equipment. The indoor noise was evaluated by the simulation program AutoSEA (Statistical Energy Analysis), and as a result, it was confirmed that the indoor noise was superior to that of the conventional sound absorbing and insulating materials.

When explaining the configuration example of the sound absorbing material according to the present invention in more detail, in the case of the hard layer (high-density material), the surface density is 500 ~ 2000 g / m 2 , and the weight is high compared to the thickness, so the surface is relatively hard, and the solid transmission sound In order to improve the vibration damping performance and sound absorption and insulation performance of low frequencies (500 Hz or less), it can be implemented as a needle type PET instead of the existing layer type. The composition is LM(Low Melt)-PET 4De' 30% by weight + R(Regular)-PET 6De' 70% by weight.

In addition, the soft layer has an areal density of 500 ~ 2000g/m2, and the content of lowdenia, which is superior in sound absorption performance than the existing DASH ISO-PAD, was increased to maximize the sound absorption performance of high frequency (500Hz or more). The composition is 30% by weight of LM-PET 4De' + 50% by weight of R-PET 3De' + 20% by weight of R-PET 6De'.

In addition, the sound-absorbing material of the present invention is composed of a partial double-layer sound-absorbing structure, based on the sound pressure distribution of each part generated when the transmitted noise generated from the engine passes through the dash panel. By analyzing the main noise parts according to the results, a double sound absorbing structure is applied to the parts where the vibration damping performance and low frequency sound absorption and insulation performance of the dash panel are important, and only the soft layer sound absorbing material is applied to the parts where the high frequency sound absorption and insulation performance is important. Preferably, in the molding process, the application area of the high-density sound-absorbing material of the hard layer, which is the second layer, is about 20 to 90% of the application area of the low-density sound-absorbing material of the soft layer, which is the first layer, so that the sound absorption and insulation performance, which is the original purpose of the sound absorption material, is sufficiently exhibited. However, it was possible to bring the effect of weight reduction. Here, preferably, the application area of the high-density sound-absorbing material is arranged in the main noise section to be 30 to 80% of the application area of the low-density sound-absorbing material, and more preferably, the application area of the high-density sound-absorbing material is 40 to 60% of the application area of the low-density sound-absorbing material It is better to place it so that

At this time, when the high-density material of the second layer is disposed in less than 20% of the area of the low-density material of the first layer, the original purpose of sound absorbing and insulating performance, especially the sound insulating performance, is significantly lowered, making it unsuitable. Although it is not a problem in terms of sound insulation performance, it is not preferable because the surface is too hard, which causes problems in transport and mountability, and the effect of reducing weight is insufficient.

On the other hand, as a sound absorbing material applied to the high-end specifications of large vehicles, for better tone tuning, it is also possible to configure by interposing a heavy nonwoven fabric between the soft felt layer and the hard felt layer, in this case low frequency absorption It is also possible to improve the sound insulation performance.

The difference in sound absorption performance between the structure and structure of the sound-absorbing material according to the present invention as described above and the composition of the existing material will become more apparent from the examples to be described later.

Hereinafter, the present invention will be described in more detail based on the following examples, but the present invention is not limited to the following examples.

(Examples and Comparative Examples)

As Examples and Comparative Examples of the present invention, 30% by weight of a sheath-core low-melting polyester fiber having a melting point of 120° C., a length of 51 mm, and a shortness of 4 denier, a melting point of 255° C., a length of 51 mm, and a shortness of 6 After mixing 70% by weight of polyester staple fibers of denier, a high-density sound absorbing material for the second layer was prepared to have a thickness of 5mm and an areal density of 800g/m2 through a needle punching process, melting point 120℃, length 51mm, shortness 30% by weight of 4-denier ciscoa-type low-melting polyester fiber, 50% by weight of polyester staple fiber having a melting point of 255°C, a length of 51 mm, and a short fineness of 3 denier, and a polyester having a melting point of 255°C, a length of 51 mm, and a short fineness of 6 denier. A low-density layer sound absorbing material for the first layer was prepared by mixing 20% by weight of staple fibers to have a thickness of 15 mm and an areal density of 1200 g/m 2 .

After laminating the low-density sound-absorbing material of the first layer and the high-density sound-absorbing material of the second layer prepared in this way, for each Example and Comparative Example, Apamat and α-Cabin were used to absorb and insulate the specimen. Performance was evaluated, and after comparative analysis of indoor virtual noise using AutoSEA, the results are shown in Table 2. After that, it was put into the molding process to produce a product for actual vehicle evaluation, and it was applied to the actual vehicle and evaluated. At the time of molding, the high-density sound-absorbing material of the second layer prepared first is molded through a preheating and foaming starting mold through a preheating oven, and then the application area of the second layer is different for each Example and Comparative Example as shown in Table 1 below. The trimming (trimming) starting mold was used and cut, and then placed on the starting mold for forming again, and then the preheated first layer low-density sound absorbing material was laminated on the upper part and pressed to adhere and mold. The sound absorbing material for actual vehicle evaluation manufactured in this way was applied to an actual vehicle and evaluated, and the results are shown in Table 2.

Examples 1 to 8 were all the same except that the application area of the second layer high-density sound-absorbing material was changed as in Table 1 compared to the application area of the low-density sound-absorbing material. In addition, Comparative Example 1 is prepared in the same manner as in Example, except that the application area of the second layer high-density sound-absorbing material is 100% of the application area of the first-layer low-density sound-absorbing material (the entire double-layer sound-absorbing structure), and Comparative Example 2 shows that the application area of the second-layer high-density sound-absorbing material is 10% of the application area of the first-layer low-density sound-absorbing material outside the range suggested in the present invention. In addition, Comparative Example 3 was the same as in Example, except that a separate EVA layer was attached, and polyurethane foam was used as a sound absorbing material. However, in the actual vehicle interior noise evaluation, a product molded by foaming urethane foam on the EVE layer was used. The sound absorption performance of the samples of the sound absorbing material of the above Examples and Comparative Examples was measured using a reverberation room test equipment, and the sound source generated after placing a sound absorbing material of 0.7 to 1.44 m 2 in the reverberation room with a test equipment that reduced the existing reverberation room was generated by the wall. The sound absorption rate of the sound absorbing material is measured by the intrusive incident reflected from the sound absorbing material. At this time, the sound absorption coefficient is better as the value is higher.

Looking at the results of Table 2, in the case of Example, compared to the case of Comparative Example 1, the weight reduction and sound absorption and insulation performance of 90% to 100% was shown, and in particular, the sound quality was improved. However, in the case of Example, compared to Comparative Example 1, since the dual structure is partially applied, it is judged to be advantageous in terms of workability such as portability and mountability. In addition, Comparative Example 2 showed the worst result, and in the case of Example, although the overall weight was significantly lowered compared to Comparative Example 3, it was evaluated as equal or superior in terms of performance results.

As described in detail above, according to the sound absorbing material for automobiles according to the present invention, the problem of weight increase due to the insertion of the heavy layer, which is a problem of the existing sound absorbing material, is greatly improved, so that the fuel efficiency of the automobile can be improved, and the existing entire double layer Compared to the sound-absorbing material of the structure, there is an effect of additional weight reduction as well as the effect of reducing manufacturing cost and improving workability such as transportability and mountability. In addition, since it is manufactured from a material that can be recycled, it has the effect of reducing problems such as environmental pollution.

On the other hand, the embodiments disclosed in the drawings are merely presented as specific examples to aid understanding, and are not intended to limit the scope of the present invention. It is apparent to those of ordinary skill in the art to which the present invention pertains that other modifications based on the technical spirit of the present invention can be implemented in addition to the embodiments disclosed herein.

1: dash panel 1a: center part
4: crash pad 12: low-density sound absorbing material
13: high-density sound-absorbing material

Claims (5)

In the sound-absorbing material for automobiles in which a low-density sound-absorbing material having a relatively low surface density and a relatively high-density sound-absorbing material are laminated in a double-layer or more structure,
The high-density sound absorbing material is laminated only in some areas with a relatively large contribution to indoor noise that require vibration damping performance and low-frequency sound absorbing and insulating performance, and the remaining portion includes a single-layer structure made of only the low-density sound absorbing material,
The high-density sound-absorbing material is laminated on the center portion of the sound-absorbing material corresponding to the dash panel center portion,
A sound-absorbing material for automobiles having a laminated structure further comprising a nonwoven fabric between the high-density sound-absorbing material and the low-density sound-absorbing material. According to claim 1,
The high-density sound-absorbing material is made of a sound-absorbing material having an areal density of 700 to 1800 g/m2, and the low-density sound-absorbing material is a sound-absorbing material for automobiles having a laminated structure made of a sound-absorbing material having an areal density of 700 to 1800 g/m2. The method according to any one of claims 1 to 2,
A sound absorbing material for automobiles having a laminated structure in which the lamination area of the high-density sound-absorbing material is 30 to 80% of the area of the low-density sound-absorbing material. 4. The method of claim 3,
A sound absorbing material for automobiles having a laminated structure in which the lamination area of the high-density sound-absorbing material is 40 to 70% of the area of the low-density sound-absorbing material. 4. The method of claim 3,
A sound absorbing material for automobiles having a laminated structure in which the lamination area of the high-density sound-absorbing material is 50 to 60% of the area of the low-density sound-absorbing material.

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