JP7624760B2 - Sound absorbing material and its manufacturing method - Google Patents

Description

The present invention relates to sound-absorbing materials used in automobiles, trains, and other vehicles, aircraft, ships, and building materials for buildings and civil engineering structures, and to methods for manufacturing the same.

Sound-absorbing materials are used in vehicles such as automobiles and trains, aircraft, ships, and building materials for buildings and civil engineering structures to prevent the intrusion of external noise. Main materials for sound-absorbing materials include fiber assemblies such as woven or nonwoven fabrics made of natural fibers such as cotton, wool, and hemp, synthetic fibers such as polyester, polyamide, acrylic, polyolefin, and polyurethane, inorganic fibers such as glass fiber, rock wool, carbon fiber, and metal fiber, and synthetic resin foams such as polyurethane foam, polyester foam, and polyethylene foam.
Normally, sound-absorbing materials made of fiber assemblies or synthetic resin foams can improve their sound-absorbing performance by increasing their thickness. However, as the thickness of the sound-absorbing material increases, its bulk and weight also increase, making it difficult to mount the material on vehicles such as automobiles and trains, aircraft, ships, etc., or to install the material on buildings and civil engineering structures, etc. In particular, recent automobiles and building materials are required to be lightweight, and the space for mounting and installing the material is limited, making it very difficult to increase the thickness of the sound-absorbing material to improve its sound-absorbing performance.

Therefore, sound-absorbing materials have been proposed that aim to improve sound-absorbing performance without increasing the thickness, as disclosed in Patent Documents 1 to 3.
The adhesive sound-absorbing sheet described in Patent Document 1 contains 90% by mass or more of porous pulp fibers having a degree of beating in the range of 350 to 650 ml (CSF) and a large number of pores opening to the surface, and has non-breathable adhesive layers scattered in the form of dots on one or both sides of a fiber sheet base material having an air flow resistance of 0.07 to 2.00 kPa·s/m, and the total area ratio of the non-breathable adhesive layers is set to 5 to 95% of the surface area of the fiber sheet base material, thereby setting the air flow resistance to 0.30 to 2.50 kPa·s/m.
The soundproof covering material described in Patent Document 2 is characterized in that it comprises a first elastic porous body, a porous film having an open porosity of 0.1 to 5% and an open pore size of 50 to 500 μm, and a second elastic porous body, which are laminated in this order.
The sheet-shaped low-frequency sound-absorbing material described in Patent Document 3 comprises sound-absorbing layers 1 and 3 made of fibers or a porous material, and a thin film layer 2 having melting properties and disposed between the sound-absorbing layers 1 and 3.

International Publication No. 2011/013427 JP 2018-141432 A JP 2019-2996 A

The above-mentioned conventional sound-absorbing materials are provided with layers such as non-breathable adhesive layers, porous films, and meltable thin film layers in order to improve their sound-absorbing performance, but there is a problem in that the process of providing such layers is complicated.
Furthermore, in order to improve the sound absorption performance of conventional sound-absorbing materials, adjustment of the area ratio is required in the case of a non-breathable adhesive layer, or adjustment of the aperture rate and aperture diameter is required in the case of a porous film, and there was a problem in that the adjustment work required to improve the sound absorption performance was complicated.
Furthermore, in conventional sound-absorbing materials, the fiber assemblies used in the elastic porous bodies, skin materials, and sound-absorbing layers are prone to uneven fiber density due to uneven distribution of fibers. This uneven fiber density makes it extremely difficult to precisely control the sound-absorbing performance, and there is a problem that even if the above-mentioned troublesome work is carried out, the manufactured fiber assemblies may not have the desired sound-absorbing performance.
In other words, the conventional sound-absorbing materials described above have problems in that the manufacturing process is complicated and the degree of freedom in sound-absorbing performance is smaller than expected.

The present invention was made with a focus on the problems existing in the conventional technology. The purpose is to provide a sound-absorbing material that allows a high degree of freedom in sound-absorbing performance, and to provide a method for manufacturing the sound-absorbing material that allows easy manufacturing operations.

As a means for solving the above-mentioned problems in the conventional art, the invention of the sound-absorbing material described in claim 1 is a sound-absorbing material having a base layer made of melamine foam and a skin layer made of nonwoven fabric laminated to the base layer, and a ventilation adjustment section for adjusting the ventilation resistance of the sound-absorbing material is provided between the base layer and the skin layer, and the ventilation adjustment section is formed in a spotted pattern using a hot melt adhesive.
The invention described in claim 2 is the sound-absorbing material described in claim 1, wherein the sound-absorbing material has an air flow resistance of 0.2 to 2 kPa·s.
The invention described in claim 3 is the sound-absorbing material described in claim 1 or 2, wherein the surface density of the ventilation adjustment portion is 1 to 20 g/ ^m2 .
The invention described in claim 4 is the invention of a sound-absorbing material described in any one of claims 1 to 3, wherein the sound-absorbing material has a sound absorption coefficient of 70% or more for a sound with a frequency of 3150 Hz measured by a normal incidence method.
The invention of a method for manufacturing a sound-absorbing material described in claim 5 is a sound-absorbing material described in any one of claims 1 to 4, which comprises a first step of laminating a nonwoven fabric coated with a hot melt adhesive on a surface of a melamine foam to obtain a laminate, and a second step of heating the laminate, and the hot melt adhesive used is in powder form with a particle size of 80 to 500 μm as determined by a sieving method.
The invention described in claim 6 is the invention for the manufacturing method of the sound-absorbing material described in claim 5, wherein the density of the melamine foam in the first step is 6 to 11 kg/ ^m3 .
The invention described in claim 7 is the invention of the manufacturing method of the sound-absorbing material described in claim 5 or claim 6, wherein the basis weight of the nonwoven fabric in the first step is 15 to 150 g/ ^m2 .
The invention of the method for manufacturing a sound-absorbing material described in claim 8 is the invention of the method for manufacturing a sound-absorbing material described in any one of claims 5 to 7, wherein in the second step, the heating temperature is 180 to 230°C.

[Action]
The sound-absorbing material of the present invention has an airflow adjustment section between a base layer made of melamine foam and a surface layer made of nonwoven fabric, for adjusting the airflow resistance of the sound-absorbing material. This airflow adjustment section is formed in a spotted shape with hot melt adhesive, and has air permeability due to the gaps between the hot melt adhesive spots. Therefore, by adjusting the airflow resistance of the airflow adjustment section, the sound-absorbing material can have a desired airflow resistance without being affected by the base layer or the surface layer, and since the airflow resistance of the airflow adjustment section can be freely adjusted, the sound-absorbing performance can be made highly flexible.
In addition, the above-mentioned spotted shape is not necessarily limited to a shape in which the dots of hot melt adhesive are all scattered apart from each other, but also includes a shape in which the dots of hot melt adhesive are partially connected to each other.
When the air flow resistance of the sound-absorbing material is 0.2 to 2 kPa·s, the sound-absorbing material can be particularly suitable as a sound-absorbing material for use in automobiles, vehicles such as automobiles and railways, aircraft, ships, or building materials for buildings and civil engineering structures.
When the surface density of the ventilation adjustment portion is 1 to 20 g/ ^m2 , the ventilation resistance of the sound absorbing material can be stably adjusted.
A sound absorbing material can be considered to be a good sound absorbing material, particularly for use in automobiles, if its sound absorption coefficient for a sound of frequency 3150 Hz measured by the normal incidence method is 70% or more.

The method for producing a sound-absorbing material of the present invention includes a first step of applying a hot melt adhesive to the surface of a melamine foam, a second step of laminating a nonwoven fabric on the surface of the melamine foam to obtain a laminate, and a third step of heating the laminate. In the first step, a powdered hot melt adhesive having a particle size of 80 to 500 μm as determined by a sieving method is used, so that the ventilation adjustment portion made of the hot melt adhesive can be made into a spotted shape having suitable ventilation properties, making it easy to adjust the ventilation resistance of the sound-absorbing material.
When the density of the melamine foam in the first step is 6 to 11 kg/ ^m3 , it is possible to suppress the penetration of the molten hot melt adhesive into the melamine foam and to obtain suitable sound absorbing performance.
When the weight per unit area of the nonwoven fabric is 15 to 150 g/ ^m2 , it is possible to suppress the penetration of the molten hot melt adhesive into the nonwoven fabric and to obtain suitable sound absorbing performance.
When the heating temperature in the second step is 180 to 230°C, the hot melt adhesive melts suitably, thereby suitably bonding the melamine foam and the nonwoven fabric while forming the ventilation adjustment portion into a spotted shape suitable for the sound-absorbing material.

〔effect〕
According to the present invention, it is possible to provide a sound-absorbing material that has a high degree of freedom in terms of sound-absorbing performance, and also to provide a method for manufacturing the sound-absorbing material that facilitates the manufacturing operations.

4A is a front cross-sectional view showing the sound-absorbing material of the embodiment, and FIG. 4B is a plan cross-sectional view of the ventilation adjustment portion. FIG. FIG. FIG. 2 is an explanatory diagram showing a manufacturing apparatus for a sound-absorbing material according to an embodiment. FIG. 2 is an explanatory diagram showing a case where melamine foam is compressed. Graph showing sound absorption coefficient for melamine foam having a thickness of 10 mm in an example. Graph showing sound absorption coefficient for a melamine foam having a thickness of 20 mm in an example. Graph showing sound absorption coefficient for melamine foam having a thickness of 40 mm in an example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.
As shown in FIG. 1( a ), the sound-absorbing material 10 has a base layer 11 and a skin layer 12 laminated on one side of the base layer 11, and an airflow adjustment section 13 is provided between the base layer 11 and the skin layer 12 to adjust the airflow resistance of the sound-absorbing material 10.
In the sound absorbing material 10, the base layer 11 is made of melamine foam, the surface layer 12 is made of nonwoven fabric, and the ventilation adjustment portion 13 is made of a hot melt adhesive.
1B, in the ventilation adjustment portion 13, the hot melt adhesive 13A is dot-like in plan view, and the ventilation adjustment portion 13 has a plurality of dot-like hot melt adhesive 13A, so that the ventilation adjustment portion 13 is formed in a spot-like shape in plan view. The ventilation adjustment portion 13 formed in a spot-like shape has gaps 13B between the dot-like hot melt adhesive 13A.

The sound-absorbing material 10 has breathability in the base layer 11 and the surface layer 12, and the ventilation adjustment portion 13 also has breathability due to the gaps 13B between the multiple dots of hot melt adhesive 13A, so that the ventilation resistance acts as a buffer against noise passing through the interior, thereby demonstrating sound-absorbing performance.
The uses of the sound-absorbing material 10 are not particularly limited, and may be, for example, for vehicles such as automobiles and trains, for aircraft, for ships, or as building materials for buildings and civil engineering structures. However, the sound-absorbing material 10 of the present application is preferably used in automobiles, from the viewpoints that it has a large degree of freedom in sound-absorbing performance, is thin and lightweight due to the use of melamine foam, which will be described later, for the base material layer 11, and has excellent flame retardancy.

The airflow resistance of the sound-absorbing material 10 is not particularly limited, since it is set according to the frequency of the noise to be absorbed depending on the application. For example, if the application of the sound-absorbing material 10 is for automobiles, sounds with frequencies of 2000 to 6000 Hz are considered to be noise, and if the application of the sound-absorbing material 10 is for building materials, sounds with frequencies of 400 to 2000 Hz are considered to be noise, and the airflow resistance of the sound-absorbing material 10 is appropriately set according to these noise frequencies.
Typically, if the sound-absorbing material 10 is not limited to a specific application but is intended for a wide range of use in vehicles such as automobiles and trains, aircraft, ships, or building materials for buildings and civil engineering structures, the air resistance is set in the range of 0.2 to 4.0 kPa·s.
As described above, the sound-absorbing material 10 is preferably used in automobiles. From the viewpoint of use in automobiles, the air flow resistance is preferably 0.2 to 2.0 kPa·s, more preferably 0.3 to 2.0 kPa·s, and even more preferably 0.3 to 1.95 kPa·s/m so that the sound-absorbing material 10 can exhibit sound-absorbing performance favorably against noise having a frequency of 2000 to 6000 Hz.
If the sound-absorbing material 10 is used as a building material, the air flow resistance is preferably 0.8 to 4.0 kPa·s, more preferably 0.8 to 3.8 kPa·s, and even more preferably 0.9 to 3.0 kPa·s/m so that the sound-absorbing material 10 can exhibit sound-absorbing performance effectively against noise with a frequency of 400 to 2000 Hz.
The airflow resistance (kPa·s/m) in the present invention refers to a value measured using an air permeability tester (product name: KES-F8-AP1, manufactured by Kato Tech Co., Ltd., steady flow differential pressure measurement method).

The sound absorbing performance of the sound absorbing material 10 can be expressed by a sound absorption coefficient measured by a normal incidence method specified in or conforming to JIS A 1405-2.
The sound absorption coefficient of the sound-absorbing material 10 is not particularly limited, since the desired value varies depending on the application. However, from the viewpoint of exhibiting suitable sound absorption performance as a sound-absorbing material used in vehicles such as automobiles and trains, aircraft, and ships, or as building materials for buildings and civil engineering structures, if the sound absorption coefficient for sounds with frequencies of 2000 to 2500 Hz is 50% or more, then the sound-absorbing material will exhibit suitable sound absorption performance for noises with frequencies of 400 to 6000 Hz.
In particular, when the sound absorbing material 10 is used in an automobile, the sound absorption coefficient of the sound absorbing material 10 is preferably 70% or more for a sound with a frequency of 3150 Hz, and more preferably 80% or more for a sound with a frequency of 4000 Hz.

When the sound absorbing material 10 is used in an automobile, in particular, the flame retardancy according to the UL94 standard is preferably V-0 or higher.
As shown in FIG. 2 , the sound-absorbing material 10 has a structure including a base layer 11 and two skin layers 12 laminated on both sides of the base layer 11, and an airflow adjustment section 13 for adjusting the airflow resistance of the sound-absorbing material 10 can be provided between the base layer 11 and each skin layer 12.
The shape of the sound-absorbing material 10 is not particularly limited as long as it is suitable for the intended use.
Furthermore, the manner in which the sound-absorbing material 10 is used is not particularly limited, and it may be used alone or in combination with a general sound-insulating material or other sound-absorbing materials.

The base layer 11 constitutes the main portion of the sound-absorbing material 10, and is made of melamine foam, which makes the sound-absorbing material 10 thin and lightweight. In particular, melamine foam has excellent flame retardancy, rated V-0 in the UL94 standard, and is suitable for use in automobiles.
The melamine foam used for the base layer 11 is not particularly limited to being a multi-layered one having two or more layers, or a single layered one, but a single layered one is preferred from the viewpoint of facilitating production by eliminating the need to bond the layers together.

The air flow resistance of the melamine foam used in the base layer 11 is not particularly limited as long as it can exhibit sound absorption performance according to the application, but from the viewpoint of exhibiting suitable sound absorption performance in applications such as automobiles, railways, and other vehicles, aircraft, ships, or building materials for buildings and civil engineering structures, it is preferably 0.05 to 2.0 kPa·s, more preferably 0.1 to 1.0 kPa·s, and even more preferably 0.1 to 0.5 kPa·s.
In particular, when the application is for automobiles, the air flow resistance of the melamine foam is preferably 0.05 to 1.0 kPa·s, more preferably 0.1 to 0.5 kPa·s, and even more preferably 0.1 to 0.3 kPa·s, from the viewpoint of suitably exhibiting sound absorption performance for sounds having frequencies of 2500 to 6000 Hz.

The thickness of the melamine foam is not particularly limited as long as it can exhibit sound absorbing performance appropriate for the application, but it is preferably 10 to 60 mm from the viewpoint of exhibiting suitable sound absorbing performance for applications such as automobiles, railways, and other vehicles, aircraft, ships, or building materials for buildings and civil engineering structures.
Melamine foam has the property that as it becomes thinner, its sound absorption coefficient for high frequency sounds increases, while as it becomes thicker, its sound absorption coefficient for low frequency sounds increases.
Therefore, in the case of a sound-absorbing material 10 for an automobile that generates noise with a frequency of 2500 to 6000 Hz, it is preferable that the thickness of the melamine foam be thin; specifically, the thickness is preferably 10 to 40 mm, more preferably 10 to 30 mm, and even more preferably 10 to 20 mm.

The density of the melamine foam is not particularly limited since it varies depending on the above-mentioned air resistance and thickness, but is preferably 6 to 11 kg/ ^m3 from the viewpoint of exhibiting suitable sound absorbing performance in applications such as automobiles, railways, and other vehicles, aircraft, ships, or building materials for buildings and civil engineering structures.
In addition, when the base layer 11 is formed of compressed melamine foam as described later, the airflow resistance, thickness and density of the melamine foam are the values before compression. The airflow resistance, thickness and density of the melamine foam after compression are not particularly limited because they change depending on the compression ratio described later.

The base layer 11 is made of melamine foam compressed by applying pressure in the thickness direction, thereby improving the sound absorbing performance of the sound absorbing material 10 .
In other words, melamine foam is a foam with an open-cell structure having a large number of uniform, fine pores inside, and has the physical property that when it is compressed by pressure in the thickness direction, depending on the manufacturing conditions, the effect of the pressure force is limited to the upper and lower layers in the thickness direction, making it possible to locally compress the upper and lower layers.
By taking advantage of the physical properties of this melamine foam and using a single layer of melamine foam, it is possible to form an upper layer 14A, a middle layer 15, and a lower layer 14B, each having different densities, in the base layer 11, as shown in Figure 3.

The upper layer 14A, the middle layer 15, and the lower layer 14B are integrated in the base material layer 11, and the boundaries between the respective parts are difficult to define, particularly when a single layer of melamine foam is used for the base material layer 11. However, in a base material layer 11 using melamine foam, the upper layer 14A, the middle layer 15, and the lower layer 14B each have approximately the same thickness in an attempt to balance the stress generated inside.
For this reason, in the sound-absorbing material 10 of the present application, the base layer 11 is divided into three equal parts in the thickness direction, and the respective parts are designated, in order from the surface side, as an upper layer 14A, a middle layer 15, and a lower layer 14B.

In the base material layer 11 using a single layer of melamine foam, the densities of the upper layer 14A, the middle layer 15, and the lower layer 14B are higher than the density of the middle layer 15. This is because, when the melamine foam is compressed by pressure in the thickness direction, the upper layer 14A and the lower layer 14B are compressed by the effect of the pressure force and the density increases locally, whereas the middle layer 15 is hardly affected by the pressure force and compression is suppressed.
The upper layer 14A, the intermediate layer 15, and the lower layer 14B have different densities, and therefore have different airflow resistances, so that the base material layer 11 formed with the upper layer 14A, the intermediate layer 15, and the lower layer 14B having different densities exhibits suitable sound absorbing performance against noise over a wide range of frequencies.
As described above, in the sound-absorbing material 10 of the present application, the base layer 11 is divided into three equal parts in the thickness direction, and the respective parts are, in order from the surface side, the upper layer part 14A, the middle layer part 15, and the lower layer part 14B. Therefore, the densities of the upper layer part 14A, the middle layer part 15, and the lower layer part 14B in the present application refer to the average densities measured in each of the three parts obtained by dividing the base layer 11 into three equal parts in the thickness direction.

The density of the intermediate layer 15 is not particularly limited as long as it is suitable for the application of the sound-absorbing material 10. From the viewpoint of use in automobiles or building materials, however, it is preferably not more than 1.10 times, more preferably not more than 1.08 times, and even more preferably not more than 1.05 times the density of the melamine foam before compression.
The densities of the upper layer 14A and the lower layer 14B depend on the application of the sound-absorbing material 10 and are not particularly limited as long as they are higher than the density of the middle layer 15. However, from the viewpoint of use in automobiles or building materials, the density is 1.10 to 1.63 times the density of the middle layer 15.
The densities of the upper layer 14A and the lower layer 14B can be appropriately set according to the application of the sound-absorbing material 10 by adjusting the compression ratio described below. When the application is for automobiles, the densities of the upper layer 14A and the lower layer 14B are preferably 1.10 to 1.40 times the density of the intermediate layer 15. When the application is for building materials, the densities of the upper layer 14A and the lower layer 14B are preferably 1.35 to 1.63 times the density of the intermediate layer 15.
Furthermore, the densities of the upper layer 14A and the lower layer 14B can be made approximately equal or different, for example by appropriately adjusting the heating temperature during compression of the melamine foam on the upper layer 14A side and the lower layer 14B side. However, from the perspective of ease of manufacture, it is preferable that the densities of the upper layer 14A and the lower layer 14B be approximately equal.

The skin layer 12 is intended to protect the surface of the base layer 11 in the sound-absorbing material 10. In particular, when the base layer 11 is formed of compressed melamine foam, the upper layer 14A and the lower layer 14B, which have increased density, may become brittle due to their increased hardness. Therefore, it is preferable that at least one surface of the base layer 11 (upper layer 14A) is protected by the skin layer 12.
The material of the skin layer 12 is not particularly limited as long as it can protect the surface of the base material layer 11, and sheets such as woven fabrics and nonwoven fabrics, films made of synthetic resins, etc. can be used. Among these materials for the skin layer 12, nonwoven fabrics are preferred from the viewpoints of availability and sound absorption performance. In particular, when the sound absorbing material 10 is used for automobiles or building materials, the use of nonwoven fabrics as the material for the skin layer 12 can improve the appearance quality of the sound absorbing material 10, and the sound absorbing material 10 can also be used as a conspicuous member such as an interior material for automobiles or an interior wall material for building materials.

The fibers of the nonwoven fabric are not particularly limited as long as they can protect the surface of the base layer 11, and examples thereof include synthetic fibers such as polyester fibers, polyethylene fibers, polypropylene fibers, polyamide fibers, acrylic fibers, urethane fibers, polyvinyl chloride fibers, polyvinylidene chloride fibers, and acetate fibers, biodegradable fibers (polylactic acid fibers) made of starch extracted from plants such as corn and sugar cane, natural fibers such as pulp, cotton, palm fibers, hemp fibers, bamboo fibers, and kenaf fibers, inorganic fibers such as glass fibers, carbon fibers, ceramic fibers, and asbestos fibers, and regenerated fibers obtained by defibrating scraps of textile products using these fibers, and one or more of these are used. Among these fibers, polyester fibers are preferred in terms of availability, moldability, and flame retardancy.
The method for producing the nonwoven fabric is not particularly limited as long as it can protect the surface of the base material layer 11, and examples of the method include a spunbond method, a needle punching method, a thermal bond method, a chemical bond method, a stitch bond method, a spunlace method, etc. Among these methods, the spunbond method is a preferred method from the viewpoints of ease of production and that the resulting nonwoven fabric is thin and has high strength.

The airflow resistance of the skin layer 12 is not particularly limited as long as it does not affect the adjustment of the airflow resistance of the sound-absorbing material 10 by the airflow adjustment unit 13. Not affecting the adjustment of the airflow resistance of the sound-absorbing material 10 by the airflow adjustment unit 13 means that the airflow resistance of the skin layer 12 is sufficiently lower than the airflow resistance of the airflow adjustment unit 13. If the airflow resistance of the skin layer 12 is the same as or higher than the airflow resistance of the airflow adjustment unit 13, there is a high possibility that the sound absorption performance of the sound-absorbing material 10 will be determined by the airflow resistance of the skin layer 12.
Specifically, from the viewpoint of improving sound absorption performance while maintaining strength and durability capable of protecting the surface of the base layer 11, the air flow resistance of the surface layer 12 is preferably 0.01 to 0.1 kPa·s/m, more preferably 0.015 to 0.08 kPa·s/m, and even more preferably 0.015 to 0.04 kPa·s/m.
When a nonwoven fabric is used for the surface layer 12, the basis weight is preferably 10 g/m ² to 120 g/m ² , more preferably 15 g/m 2 to 110 g/m 2, and even more preferably 15 g/m ² to 100 g/m ² , from the viewpoint of keeping the air ^flow resistance of the surface layer 12 in the ^above range.

When a nonwoven fabric is used for the skin layer 12, it can be impregnated with a synthetic resin such as a thermoplastic resin or a thermosetting resin in order to maintain the strength and durability required to protect the surface of the base material layer 11, to be used for joining to the base material layer 11, to prevent fiber loss, to improve the appearance quality, etc.
The amount of synthetic resin impregnated into the nonwoven fabric is not particularly limited as long as the airflow resistance of the nonwoven fabric can be maintained lower than the airflow resistance of the base layer 11. Specifically, the amount of synthetic resin impregnated is preferably 50 g/m2 or ^less , more preferably 10 to 50 g/ ^m2 .

The synthetic resin with which the nonwoven fabric is impregnated is preferably a thermosetting resin, since the melamine foam is heated when the base layer 11 is formed, and the sound-absorbing material 10 is hot-press molded depending on the application.
Examples of thermosetting resins include urethane-based resins, melamine-based resins, thermosetting acrylic resins, particularly thermosetting acrylic resins which harden by forming ester bonds when heated, urea-based resins, phenol-based resins, epoxy-based resins, and thermosetting polyester-based resins.
In addition, it is preferable to use the thermosetting resin in the form of an aqueous solution, an aqueous emulsion, or an aqueous dispersion, because these are easy to handle.

The thermosetting resin is preferably a phenolic resin, more preferably a phenol-alkylresorcinol co-condensate, from the viewpoints of easy availability, ease of preparation into an aqueous solution, aqueous emulsion, or aqueous dispersion, adhesiveness, and flame retardancy. Phenol-alkylresorcinol co-condensates have the advantage that the aqueous solution of the initial condensate is stable and can be stored for a long period of time at room temperature compared to initial condensates consisting of phenol alone.
In particular, by impregnating a nonwoven fabric with an aqueous solution of a phenol-alkylresorcinol co-condensate and bringing it into a semi-cured state (B stage), the stability is improved and moldability can be maintained even after long-term storage.

The ventilation adjustment portion 13 is a main portion for adjusting the overall ventilation resistance of the sound-absorbing material 10. The ventilation adjustment portion 13 is formed in a spotted shape by thermally melting the hot melt adhesive 13A in a dotted state on the surface of the base material layer 11, and has many gaps 13B (see FIG. 1(b)).
In more detail, the surface of the base layer 11 formed by the melamine foam is very smooth because it does not have unevenness caused by uneven fiber density, such as that of nonwoven fabric, and the air bubbles in the melamine foam are very dense and fine, so the unevenness caused by the air bubbles is also very dense and fine. Therefore, the hot melt adhesive is heat-melted in a substantially uniformly dispersed state on the surface of the melamine foam (base layer 11), without being unevenly scattered or melted by heat and penetrating the surface. The hot melt adhesive that is heat-melted in a substantially uniformly dispersed state on the surface of the melamine foam exerts an appropriate adhesive force even in a small amount, and makes the ventilation adjustment portion 13 into a thin film having substantially uniform gaps 13B.
The thin-film airflow adjustment portion 13 having substantially uniform gaps 13B allows sound to pass through the base layer 11 only when it passes through the gaps 13B, and prevents sound from passing through the portions other than the gaps 13B (the portions of the dots of hot melt adhesive 13A). As a result, the overall airflow resistance of the sound-absorbing material 10 becomes higher than the airflow resistance of the base layer 11, and the sound-absorbing performance of the sound-absorbing material 10 is improved.
It should be noted that the air permeability adjustment section 13 is bonded to the base material layer 11 and integrated therewith, and it is difficult to measure the air permeability resistance of only the air permeability adjustment section 13. However, from the viewpoint that the overall air permeability resistance of the sound-absorbing material 10 is adjusted and determined by this air permeability adjustment section 13, the air permeability resistance of the air permeability adjustment section 13 is considered to be approximately equal to the air permeability resistance of the sound-absorbing material 10.
In addition, the ventilation adjustment section 13 is formed in a spotted manner using hot melt adhesive 13A that has been heat-melted in a scattered dot-like state, but the hot melt adhesive 13A that has been heat-melted in a scattered dot-like state does not necessarily have to be all separated from each other, and may be partially connected.

The type of hot melt adhesive is not particularly limited, and examples include one or more types selected from polyethylene-based, polyester-based, polyamide-based, ethylene-vinyl acetate copolymer-based, acrylic-based, synthetic rubber-based, etc. Among these, polyamide-based hot melt adhesives have suitable flame retardancy and are suitable when the sound absorbing material 10 is used in particular for automotive applications.
The form of the hot melt adhesive is not particularly limited and may be a powder, an aqueous emulsion, or the like. From the viewpoints of ease of use and ease of adjusting the air resistance, a powder form is preferred.
The method of applying the powdered hot melt adhesive is not particularly limited, and examples include a method of applying the powdered material as it is, such as electrostatic spray application, or a method of dispersing the powdered material in water or the like to prepare a dispersion and applying the dispersion by a spray method, a roll method, a spin method, a dip method, etc. Among these, the method of applying a dispersion containing a powdered hot melt adhesive by a spray method is a preferred application method from the viewpoints of simplicity, short working time, and ease of adjustment of the amount of hot melt adhesive applied.
The particle size of the powdered hot melt adhesive is not particularly limited as long as it can bond the base layer 11 and the surface layer 12 together. From the viewpoint of making the ventilation adjustment portion 13 speckled and suitably forming the gaps 13B, the particle size determined by a sieving method is preferably 80 to 500 μm, more preferably 100 to 300 μm, and even more preferably 100 to 150 μm.

The adjustment of the overall airflow resistance of the sound-absorbing material 10 by the airflow adjustment section 13 can be achieved by adjusting the surface density of the airflow adjustment section 13. In other words, as the surface density of the airflow adjustment section 13 increases, the overall airflow resistance of the sound-absorbing material 10 increases, and as the surface density of the airflow adjustment section 13 decreases, the overall airflow resistance of the sound-absorbing material 10 decreases.
The surface density of the ventilation adjustment portion 13 is not particularly limited as long as the ventilation resistance of the sound-absorbing material 10 can be adjusted to a value appropriate for the application. However, from the viewpoint of exhibiting suitable sound absorbing performance particularly for automotive applications, the surface density is preferably 1 to 20 g/ ^m2 , and more preferably 5 to 10 g/ ^m2 .

The surface density of the ventilation adjustment portion 13 can be adjusted by the amount of hot melt adhesive applied per unit area. In other words, as the amount of hot melt adhesive applied per unit area increases, the surface density of the ventilation adjustment portion 13 increases, thereby increasing the airflow resistance of the sound-absorbing material 10, and as the amount of adhesive applied per unit area decreases, the surface density of the ventilation adjustment portion 13 decreases, thereby decreasing the airflow resistance of the sound-absorbing material 10.
Specifically, the amount of hot melt adhesive applied per unit area corresponds to the surface density of the ventilation adjustment portion 13, and is preferably 1 to 20 g/ ^m2 , more preferably 5 to 10 g/m2, in terms of the amount applied per unit area on the surface of the base layer 11 (melamine foam 11A) or the surface of the skin layer 12 (nonwoven fabric ^12A) .
Furthermore, the object to which the hot melt adhesive is applied may be either melamine foam or nonwoven fabric, and is not particularly limited, but it is preferable to use nonwoven fabric from the viewpoint of preventing the heat-molten hot melt adhesive from penetrating the surface of the melamine foam and blocking the air bubbles in the melamine foam.
In particular, when applying a powdered hot melt adhesive to a nonwoven fabric, the hot melt adhesive is spread at the above-mentioned surface density and then heated, so that the hot melt adhesive is pre-fused to the surface of the nonwoven fabric, thereby preventing the hot melt adhesive from seeping into the melamine foam surface while maintaining the surface density, which is more preferable.

The above-mentioned sound-absorbing material 10 is manufactured using an apparatus 20 as shown in FIG. 4 through a first step S1 in which a nonwoven fabric 12A coated with a hot melt adhesive 13A is laminated on the surface of a melamine foam 11A to obtain a laminate 10A, and a second step S2 in which the laminate 10A is heated.
In the device 20, a nonwoven fabric 12A coated with a predetermined amount of hot melt adhesive 13A is prepared in advance in a separate process, and this nonwoven fabric 12A is placed on a conveyor 21 with the surface coated with the hot melt adhesive 13A facing upward, and is transported from the upstream side to the downstream side.
In the first step S1, a melamine foam 11A is laminated on the surface of the nonwoven fabric 12A on which the hot melt adhesive 13A is applied, to obtain a laminate 10A.
In the second step S2, the laminate 10A is transported onto a base 24, and a heating plate 25 disposed above the base 24 heats the laminate 10A on the base 24, thereby producing the sound-absorbing material 10.

In the second step S2, the heating temperature is not particularly limited as long as it is less than 240°C, which is the heat resistance temperature of the melamine foam 11A. However, from the viewpoint of preventing the melamine foam 11A from returning to its original density due to elasticity, etc., the heating temperature is preferably 180 to 230°C, more preferably 180 to 220°C, and even more preferably 200 to 220°C.
In the second step S2, when the laminate 10A is hot-pressed by the heating platen 25 for a predetermined pressing time, the melamine foam 11A is compressed in the thickness direction as described above, thereby improving the sound absorbing performance. This pressing time is not particularly limited as long as the base layer 11 can be formed from the melamine foam 11A, but is preferably 1 second to 1 minute from the viewpoint of keeping the compression ratio within the range described later and improving the working efficiency.

In the second step S2, when the melamine foam 11A is compressed in the thickness direction as described above to form a base layer 11 having an upper layer 14A, a middle layer 15 and a lower layer 14B, it is necessary to adjust the pressure applied by the heating plate 25.
The pressure can be adjusted by adjusting the compression ratio of the melamine foam 11A. The compression ratio of the melamine foam 11A can be calculated by the formula: (1-T/T0) x ₁₀₀ , where _T0 is the thickness of the melamine foam 11A before compression (see FIG. 5) and T is the thickness of the melamine foam 11A after compression, i.e., the thickness of the base layer 11 (see FIG. 5).
The compression ratio of the melamine foam 11A is preferably 10 to 30% from the viewpoint of suitably forming the upper layer portion 14A, the intermediate layer portion 15 and the lower layer portion 14B.

EXAMPLES Hereinafter, examples that further embody the present invention will be described, but the present invention is not limited to these examples.
[Sample Preparation]
Three types of melamine foam were used: one with a thickness of 10 mm and an airflow resistance of 0.11 kPa·s/m (Sample No. 1), one with a thickness of 20 mm and an airflow resistance of 0.12 kPa·s/m (Sample No. 7), and one with a thickness of 40 mm and an airflow resistance of 0.18 kPa·s/m (Sample No. 13).
The hot melt adhesive used was made of a polyamide copolymer, had a particle size of 100 to 150 μm as determined by a sieving method, and had a softening temperature of 150° C.
The nonwoven fabric used was made of polyester fibers and had a basis weight of 20 g/ ^m2 produced by the spunbond method.

The hot melt adhesive was sprayed onto one side of the nonwoven fabric so that the application amount (area density of the ventilation adjustment part) was 1 g/ ^m2 , 5 g/ ^m2 , 10 g/ ^m2 , 20 g/ ^m2 , or 30 g/ ^m2, and then the nonwoven fabric was heated in a heating furnace at 160°C to temporarily fuse the hot melt adhesive to the nonwoven fabric, thereby obtaining a nonwoven fabric coated with the hot melt adhesive.
Next, the nonwoven fabric coated with the hot melt adhesive was laminated on the surface of the melamine foam of Sample Nos. 1, 7, and 13 so that the surface coated with the hot melt adhesive was in contact with the surface, thereby obtaining a laminate.
The laminate was then heated at 180° C., and the nonwoven fabric and the melamine foam were bonded together with a hot melt adhesive to obtain Samples Nos. 2 to 6, 8 to 12, and 14 to 18.

[Sound absorption test]
The airflow resistance of each of Samples No. 1 to 18 was measured using an air permeability tester (product name: KES-F8-AP1, manufactured by Kato Tech Co., Ltd., steady flow differential pressure measurement method). The results are shown in Table 1.
In addition, the sound absorption coefficient of each of Sample Nos. 1 to 18 was measured by the normal incidence method in accordance with JIS A 1405-2. The results are shown in the graph of Figure 6 for Sample Nos. 1 to 6 with a melamine foam thickness of 10 mm, in the graph of Figure 7 for Sample Nos. 7 to 12 with a melamine foam thickness of 20 mm, and in the graph of Figure 8 for Sample Nos. 13 to 18 with a melamine foam thickness of 40 mm.

As a result of the sound absorption test, samples No. 2 to ^No. 5, which have a surface density of 1 to 20 g/m2 in the ventilation adjustment portion, have clearly improved sound absorption performance in almost the entire frequency range in which the sound absorption coefficient was measured, compared to sample No. 1, which does not have a ventilation adjustment portion, and the sound absorption coefficient was approximately 80% or more in the frequency range of 2000 to 5000 Hz in particular.
Similarly, Samples No. 8 to 11, in which the surface density of the ventilation adjustment portion was set ^to 1 to 20 g/m2, showed clearly improved sound absorption performance in almost the entire frequency range in which the sound absorption coefficient was measured, compared to Sample No. 7, in which the ventilation adjustment portion was not formed, and in particular, the sound absorption coefficient was approximately 85% or more at frequencies of 2000 to 5000 Hz.
Similarly, in samples No. 14 to 17 in which the surface density of the ventilation adjustment portion was ^set to 1 to 20 g/m2, the sound absorption performance was clearly improved in almost the entire frequency range in which the sound absorption coefficient was measured, compared to sample No. 13 in which the ventilation adjustment portion was not formed, and the sound absorption coefficient was approximately 90% or more in the frequency range of 2000 to 5000 Hz in particular.
From the above, it was shown that when the surface density of the ventilation adjustment portion is set ^to 1 to 20 g/m2, it is a sound absorbing material that is particularly suitable for automobiles.

In addition, sample No. 6, in which the surface density of the ventilation adjustment portion was set to 30 g/ ^m2 , had a higher sound absorption coefficient for sounds in the range of 1000 to 1500 Hz than sample No. 1.
Similarly, sample No. 12, in which the surface density of the ventilation adjustment portion was 30 g/ ^m2 , had a higher sound absorption coefficient for sounds of 1000 to 1500 Hz than sample No. 7.
Similarly, sample No. 18, in which the surface density of the ventilation adjustment portion was set to 30 g/ ^m2 , had a higher sound absorption coefficient for sounds of 1000 to 1500 Hz than sample No. 13.
From the above, when the surface density of the ventilation adjustment portion is set to 30 g/ ^m2 , it is not suitable for automotive applications, but it is suitable for applications requiring sound absorption performance against noise of 1000 to 1500 Hz, such as building materials.

The sound-absorbing material and manufacturing method of the present invention can produce a sound-absorbing material with a high degree of freedom in sound-absorbing performance, and the density and air resistance of the sound-absorbing material can be easily adjusted, making it industrially applicable.

REFERENCE SIGNS LIST 10 Sound absorbing material 10A Laminate 11 Base layer 11A Melamine foam 12 Skin layer 12A Nonwoven fabric 13 Ventilation adjustment section 13A Hot melt adhesive 13B Gap 14A Upper layer section 14B Lower layer section 15 Intermediate layer section 20 Apparatus 21 Conveyor 24 Base 25 Heating platen S1 First step S2 Second step

Claims (8)

A sound-absorbing material having a base layer made of melamine foam and a surface layer made of a nonwoven fabric laminated on the base layer,
a ventilation adjustment portion for adjusting the ventilation resistance of the sound absorbing material is provided between the base material layer and the surface layer,
The ventilation adjustment portion is formed in a dotted shape using a hot melt adhesive,
The hot melt adhesive is a polyamide-based hot melt adhesive,
The surface density of the ventilation adjustment portion is 1 to 20 g/ ^m2 ,
The melamine foam has an air resistance of 0.1 to 0.5 kPa s,
A sound-absorbing material characterized in that the overall airflow resistance of the sound-absorbing material is 0.2 to 2.0 kPa·s (however, this ^does not include a composite sound-absorbing material obtained by bonding a nonwoven fabric facing material containing at least one melt-blown ultrafine fiber layer having an average fiber diameter of 0.3 to 7 μm and a basis weight of 1 to 40 g/m2 and an open-cell melamine resin foam layer by applying a copolymer polyester-based hot melt powder). The sound-absorbing material according to claim 1, wherein the airflow resistance of the surface layer is 0.01 to 0.1 kPa·s. The sound-absorbing material according to claim 1 or 2, wherein the thickness of the melamine foam is 10 to 30 mm. The sound absorbing material according to any one of claims 1 to 3 has a sound absorption coefficient of 70% or more for a sound with a frequency of 3150 Hz measured by the normal incidence method. A method for manufacturing a sound-absorbing material according to any one of claims 1 to 4,
A first step of laminating a nonwoven fabric coated with a hot melt adhesive on a surface of a melamine foam to obtain a laminate;
A second step of heating the laminate,
A method for producing a sound-absorbing material, characterized in that the hot melt adhesive used is in powder form with a particle size of 80 to 500 μm as determined by a sieving method. The method for manufacturing a sound-absorbing material according to claim 5, wherein the density of the melamine foam in the first step is 6 to 11 kg/ ^m3 . The method for manufacturing a sound-absorbing material according to claim 5 or 6, wherein the basis weight of the nonwoven fabric in the first step is 15 to 150 g/ ^m2 . The method for manufacturing a sound-absorbing material according to any one of claims 5 to 7, wherein in the second step, the heating temperature is 180 to 230°C.

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