JP2023125627A - Laminate sound absorbing body - Google Patents

Abstract

To obtain a laminate sound absorbing body which is thinner and has especially high sound absorbency in a low-frequency band.SOLUTION: A laminate sound absorbing body containing an A layer constituting an outermost layer of one of surfaces of the laminate sound absorbing body, a C layer constituting an outermost layer of the other of the surfaces, and a B layer being a porous layer provided inside, each of the A layer and the C layer being a resin foam layer, a surface in contact with the B layer being smooth, a sound absorption coefficient of a sound at 300 Hz of the laminate sound absorbing body being more than or equal to 0.50, and a minimum sound absorption coefficient of a sound in a range of 1,000 Hz to 5,000 Hz being more than or equal to 0.60.SELECTED DRAWING: Figure 1

Description

The present invention relates to a laminated sound absorber.

A sound absorber is a product that has the function of absorbing sound, and is widely used in the fields of architecture and automobiles. The sound absorbing body is desired to have sound absorbing performance over a wide range of frequencies in order to be applicable to a wide range of uses.
As described in Patent Document 1, it is said that a laminated sound absorber with a normal incidence sound absorption coefficient of more than α=0.5 has good sound absorption performance in that frequency band. However, in order to improve the sound absorption performance in a wide frequency range, the laminated sound absorber must be made thicker, which poses a problem in that the applications and/or locations of the laminated sound absorber are restricted.

As described in Patent Document 2, it is known that the combination of a resin foam and a specific thin film layer improves sound absorption for sounds of 1000 to 2000 Hz, but it does not target even lower frequencies.
There is also another method using a membrane vibration type material. However, when membrane vibration type materials are used, it is possible to make the laminated sound absorber thinner, but it is only effective in a certain narrow range of frequencies, and clearly absorbs sound in low frequency bands and other frequency bands. It has the characteristic that the rate decreases (see FIG. 8).
Therefore, there is a strong desire for a laminated sound absorber that can achieve both excellent sound absorption performance and a reduction in thickness.

JP2003-41528A JP 2019-2996 Publication

An object of the present invention is to obtain a laminated sound absorber that is thinner and has particularly high sound absorbing properties in a low frequency band.

In order to solve the above problem, the present inventor invented the following method.
1. Containing layer A constituting the outermost layer on one side of the laminated sound absorber, layer C constituting the outermost layer on the other side, and layer B which is a porous layer provided inside,
Each of the A layer and the C layer is a resin foam layer, and the surface in contact with the B layer is smooth,
The laminated sound absorber has a sound absorption coefficient of 0.50 or more for sounds of 300Hz and a minimum sound absorption coefficient of 0.60 or more for sounds in the range of 1000Hz to 5000Hz.
Laminated sound absorber.
2. The A layer and the C layer are urethane resin foam and/or melamine resin foam having an air permeability of 1.0 cm ³ /cm ² sec or more,
2. The laminated sound absorber according to 1, wherein layer B is a porous layer having a density of 70 kg/m ³ or more and smooth on both sides.
3. The total thickness of the laminated sound absorber is 90 mm or less, and the thickness of the A layer and the C layer are the same, and/or the thickness of the C layer constituting the outermost layer on one side is 40 to 60 mm, and the C layer is the same. 3. The laminated sound absorber according to 1 or 2, wherein the layer is thicker than the A layer.
4. 4. The laminated sound absorber according to any one of 1 to 3, which has two or more B layers, and has an A layer or a C layer between the B layers.
5. 5. The laminated sound absorber according to any one of 1 to 4, wherein layer B is a layer impregnated with a liquid.

According to the present invention, it is possible to obtain a laminated sound absorbing body that is thinner and has higher sound absorbing properties in a low frequency band.

Diagram showing measurement results for layer B Diagram showing measurement results considering layer A and layer C Diagram showing the measurement results of an example in which layer B is sandwiched between different materials Diagram showing measurement results of 7-layer structure Diagram showing measurement results for layer B Diagram showing measurement results for layer A Diagram showing the measurement results of an example of examining the thickness of layer A and layer C Diagram showing measurement results of membrane vibration type Diagram showing measurement results when layer B was not provided

The present invention
Containing layer A constituting the outermost layer on one side of the laminated sound absorber, layer C constituting the outermost layer on the other side, and layer B provided inside,
The surfaces of each of the A layer and the C layer in contact with the B layer are smooth,
The laminated sound absorber is basically a laminated sound absorber that has a sound absorption coefficient of 0.50 or more for sounds of 300 Hz and a minimum sound absorption coefficient of 0.60 or more for sounds in the range of 1000 Hz to 5000 Hz.

[Overall structure of the laminated sound absorber of the present invention]
The laminated sound absorber of the present invention includes the following A layer constituting the outermost layer on one side, and the C layer constituting the outermost layer on the other side, that is, the opposite side when viewed from the one side, and the A layer. It consists of the following B layer sandwiched between the C layer. The A layer and the C layer may have the same thickness, or the C layer may be thicker than the A layer. and a layer B (with a density of 70 kg/m ³ or more) which is sandwiched between the layer A and does not constitute the outermost layer of the laminated sound absorber, and the surface of the layer A and the layer C that is in contact with the layer B. is smooth.
In the present invention, it is preferable that the A layer, the B layer, and the C layer all contain resin, and it is more preferable that they are resin foams.
The laminated sound absorber of the present invention has a total thickness that is thinner than conventional sound absorbers. The total thickness is preferably 90 mm or less, more preferably 85 mm or less, even more preferably 83 mm or less, and most preferably 82 mm or less.
Moreover, it is preferable that the above-mentioned layer B is one or more types selected from porous layers such as foam layers having smooth surfaces on both sides.
The air permeability in the present invention is calculated by converting the air permeability resistance measured by an air permeability tester (product name: KES-F8-API, Kato Tech Co., Ltd., steady flow differential pressure measurement method) for a sample with a thickness of 40 mm. Obtained. (Pass through a constant flow rate V (m ³ / (m ² sec), measure the pressure difference ΔP (kPA) at this time, find the ventilation resistance R = ΔP / V, and further calculate the ventilation resistance = 12.5 / R. demand).
The air permeability referred to here is the air permeability of each layer alone when the thickness of each layer is 40 mm. Since the thicker the film, the lower the air permeability, the air permeability itself, which changes depending on the thickness, was taken into consideration.
Here, it is preferable that one surface of the laminated sound absorber made of layer A constituting the outermost layer is a surface facing the sound source side of the sound to be absorbed when the laminated sound absorber is installed. It is preferable that the A layer is on the opposite surface to the other surface of the layered sound absorbing body constituted by the B layer. The layers constituting the outermost layer of the laminated sound absorber are the layer facing the sound source side and the layer forming the surface of the sound absorber through which sound passes and exits.
The overall shape can be any shape known as a laminated sound absorber, such as a flat plate, a plate with a curved surface, a cylinder, or a rod.
Further, the outer surfaces of the A layer and the C layer constituting the outer surface of the laminated sound absorbing body of the present invention may be smooth or may have an uneven shape.
The sound absorption coefficient in the present invention is measured according to JIS A1405-2.

[Detailed structure of the laminated sound absorber of the present invention]
A laminated sound absorber may be formed of three layers in total, including one layer A and one layer B sandwiched between one layer C and one layer C.
Then, a five-layer structure having two A layers, two B layers, and one C layer, laminated in the order of A layer/B layer/A layer/B layer/C layer, and one layer A. A five-layer structure may be used in which a layer A/layer B/layer C/layer B/layer C is laminated in the order of layer B, two layers B, and two layers C. Furthermore, there is a seven-layer structure laminated in the order of A layer/B layer/C layer/B layer/A layer/B layer/C layer, A layer/B layer/A layer/B layer/A layer/B layer/ 7-layer structure laminated in the order of C layer, A layer / B layer / A layer / B layer / C layer / B layer / C layer, 7 layer structure laminated in the order A layer / B layer / C layer A seven-layer structure may be used, in which the structure is stacked in the following order: /B layer/C layer/B layer/C layer. Or it may consist of more layers.

At this time, from the viewpoint of improving sound absorption, when a plurality of A layers are included, it is preferable that all the A layers have the same thickness and/or are made of the same material. In addition, in the case of having a plurality of C layers, it is preferable that all the C layers have the same thickness and/or are made of the same material. Further, it is preferable that all the A layers and C layers are made of the same material. When having multiple B layers, it is preferable that all B layers have the same thickness.
All A layers and all C layers may have the same thickness, or the C layer may be thicker than the A layer.
Among them, it is preferable that all A layers have the same thickness, all C layers have the same thickness, and A layers and C layers have the same thickness.

In the present invention, it is preferable that the A layer and the C layer constituting both sides of the laminated sound absorber have the same thickness. When the laminated sound absorber has an A layer or C layer that is not a surface layer, this layer may have the same thickness as the A layer and C layer that constitute the surface, or may be a layer thicker than the A layer and C layer. On the contrary, it may be a thin layer.
Moreover, in one laminated sound absorber, all the A layers may be made of the same resin or may be made of different resins. Further, when there are two or more B layers, these B layers may be made of the same resin or may be made of different resins.

In the case of a structure in which only one layer A and one layer B are laminated, the sound absorption coefficient on the lower frequency side becomes higher, but the sound absorption coefficient on the higher frequency side may particularly decrease. Alternatively, the change in sound absorption coefficient with respect to frequency may not be particularly different from the case where the B layer is not provided.
Further, when the B layer is provided as the outermost layer in the direction of sound incidence, the sound absorption coefficient on the low frequency side increases, but the sound absorption coefficient on the high frequency side tends to particularly decrease. Conversely, when the B layer is provided as the outermost layer on the opposite side to the direction of sound incidence, the effect of providing the B layer tends to decrease.
In order to obtain a smooth surface in the present invention, known means such as forming by ordinary cutting or forming by using the inner surface of a mold are adopted as means for forming the surface of layer A and the surface of layer B. No measures are taken to intentionally create rough or uneven surfaces.

[Sound absorption performance of the laminated sound absorber of the present invention]
The laminated sound absorber of the present invention has excellent sound absorption performance, and has a sound absorption coefficient of 300 Hz sound of 0.50 or more, more preferably 0.60 or more, and even more preferably 0.70 or more. Note that the "sound absorption coefficient" hereinafter refers to the "sound absorption coefficient of sound transmitted in the thickness direction of the laminated sound absorber".
The minimum sound absorption coefficient of sound in the entire range of 1000Hz to 5000Hz (the lowest sound absorption coefficient in the frequency range (the same applies hereinafter)) is 0.60 or more, preferably 0.70 or more, more preferably 0.75 or more, More preferably 0.80 or more, most preferably 0.85 or more.
The minimum sound absorption coefficient in the frequency band of 400 to 5000 Hz is preferably 0.70 or more, more preferably 0.75 or more, and even more preferably 0.80 or more.
Regarding the sound absorption coefficient of the present invention when the thickness of the B layer per layer is 3.0 mm, the sound absorption coefficient for 300 Hz sound is 0.55 or more, preferably 0.57 or more, and 0.55 or more. It is more preferably 60 or more, even more preferably 0.63 or more, and most preferably 0.65 or more. Furthermore, in addition to the above sound absorption coefficient, when the thickness of layer B per layer is 3.0 mm, the thickness direction of the laminated sound absorber of the present invention in the entire frequency range of 1000Hz to 5000Hz The minimum sound absorption coefficient of sound transmitted through the fiber is 0.60 or more, preferably 0.70 or more, more preferably 0.75 or more, even more preferably 0.80 or more, and most preferably 0.90 or more.
Alternatively, the minimum sound absorption coefficient in the frequency band of 400 to 5000 Hz is 0.70 or more, preferably 0.80 or more.

<A layer and C layer>
[Common matters for A layer and C layer]
The A layer and the C layer are made of a resin foam layer with a smooth surface in contact with the B layer below, and examples of the resin foam material include polyethylene resin, polypropylene resin, polyurethane resin, polyester resin, acrylic resin, and polystyrene. Examples include resin, melamine resin, silicone resin, natural rubber, and synthetic rubber. Among these, a melamine resin foam layer and a urethane resin foam layer are preferred. In the laminated sound absorber of the present invention, the materials constituting the plurality of A layers may be the same material or different materials. Among these, it is preferable that both the A layer and the C layer are foam layers of melamine resin, and it is more preferable that the A layer and the C layer have air permeability.
In order to exhibit sufficient sound absorption, the total thickness of the one or more layers A and C that the laminated sound absorber of the present invention has is preferably 50.0 mm or more, and 60.0 mm or more. is more preferable, 70.0 mm or more is even more preferable, and 75.0 mm or more is most preferable. Further, in consideration of the balance between sound absorption properties and the thickness of the entire layer, the thickness is preferably 90.0 mm or less, more preferably 85.0 mm or less, even more preferably 83.0 mm or less, and most preferably 80.0 mm or less. This total thickness is the total thickness of the three or more layers, for example, even when the A layer and the C layer are three or more layers in total.
The thicknesses of layer A and layer C may be the same, or layer C may be thicker than layer A.
For example, when there is one A layer and one C layer, it is preferable that the A layer and the C layer independently have a thickness of 20 mm to 60 mm.

Of both surfaces of layer A and layer C, at least the surface in contact with layer B needs to be smooth. The term "smooth" as used herein means that although the surface of the foam layer of layer A has fine irregularities due to the openings of the pores, no irregularities other than the fine irregularities are intentionally formed. These include a surface obtained by cutting with a straight blade, a surface formed by a mold with a smooth surface, etc. Therefore, it is assumed that the surface is smooth even due to the presence of the fine irregularities. In other words, the smoothness of the surface means, for example, that the surface is not processed to have an uneven shape, or that the surface is not provided with convex portions or concave portions by molding.
The air permeability of layer A and layer C is independently preferably 1.0 cm ³ /cm ² sec or more, more preferably 5.0 cm ³ /cm ² sec or more, even more preferably 10.0 cm ³ /cm ^{2 or} more. , 15.0 cm ³ /cm ² or more is most preferable, and 25.0 cm ³ /cm ² or more is particularly preferable. Moreover, it is preferably 100.0 cm ³ /cm ² sec or less, more preferably 50.0 cm ³ /cm ² sec or less, and even more preferably 40.0 cm ³ /cm ² sec or less.

(Melamine resin foam layer)
The melamine resin foam layer used in the A-layer and the C-layer is a foam having open cells that is foamed from a melamine resin as a raw material. Melamine resin foam is produced by blending melamine with additives such as formaldehyde, a blowing agent, a catalyst, and an emulsifier, and then foaming and curing the mixture. It can be obtained by a known method such as blending, foaming and curing. It may or may not contain resins other than melamine resin. Preferably, it does not contain any inorganic or organic fibrous substances, and the inside of the foam layer does not have any pores or processed structures other than the porous structure formed during manufacturing, and the entire layer has no pores. Preferably, it consists of a dispersed, uniform layer.
The density measured according to JIS K 7222 is preferably 4.0 kg/m ³ or more, more preferably 5.0 kg/m ³ or more, and even more preferably 6.0 kg/m ³ or more. Further, the weight is preferably 15.0 kg/m ³ or less, more preferably 13.0 kg/m ³ or less, and even more preferably 11.0 kg/m ³ or less.
In particular, the air permeability of the melamine resin foam layer is preferably 10.0 cm ³ /cm ² sec or more, more preferably 13.0 cm ³ /cm ² sec or more, and even more preferably 15.0 cm ³ /cm ² sec or more. Moreover, it is preferably 100.0 cm ³ /cm ² sec or less, more preferably 50.0 cm ³ /cm ² sec or less, and even more preferably 35.0 cm ³ /cm ² sec or less.

(Urethane resin foam layer)
The urethane resin foam layer is a foam having open cells obtained by foaming the urethane resin during synthesis.
Urethane resin foam is obtained by reacting an isocyanate compound with a component that reacts with isocyanate, and at the same time adding or acting on additives such as a blowing agent, and is obtained by known means as foamed polyurethane resin. be able to. It may or may not contain resins other than urethane resins. Preferably, it does not contain any inorganic or organic fibrous substances, and the inside of the foam layer does not have any pores or processed structures other than the porous structure formed during manufacturing, and the entire layer has no pores. Preferably, it consists of a dispersed, uniform layer.
The density measured according to JIS K 7222 is preferably 15.0 kg/m ³ or more, more preferably 18.0 kg/m ³ or more, and even more preferably 20.0 kg/m ³ or more. Further, the weight is preferably 30.0 kg/m ³ or less, more preferably 27.0 kg/m ³ or less, and even more preferably 25.0 kg/m ³ or less.
In particular, the air permeability of the urethane resin foam layer is preferably 1.0 cm ³ /cm ² sec or more, more preferably 1.5 cm ³ /cm ² sec or more, and even more preferably 1.7 cm ³ /cm ² sec or more. Further, the speed is preferably 30.0 cm ³ /cm ² sec or less, more preferably 20.0 cm ³ /cm ² sec or less, and even more preferably 18.0 cm ³ /cm ² sec or less.

<B layer>
[Matters common to B layer]
Each material that can be used for the B layer is a porous layer with a density of 70 kg/m ³ or more, preferably 100 kg/m ³ or more, more preferably 150 kg/m 3 or more, even more preferably 200 kg/m ³ or more, and 210 kg/m 3 or more. ³ or more is most preferable. Among these, one or more selected from a polyvinyl alcohol resin layer, a polyurethane resin layer, a chloroprene rubber layer, a polyethylene resin layer, and a polyester nonwoven fabric layer are preferred. Among these, foams with a polyurethane resin layer are preferred.
Further, in order to exhibit sufficient sound absorption, the total thickness of the one or more B layers included in the laminated sound absorbing body of the present invention is preferably 1.0 mm or more, more preferably 1.5 mm or more, and 1.0 mm or more, more preferably 1.5 mm or more. More preferably, the diameter is .8 mm or more. Further, in consideration of sound absorption properties, the thickness is preferably 10.0 mm or less, more preferably 6.0 mm or less, even more preferably 4.0 mm or less, and most preferably 3.0 mm or less. For example, when there are two B layers, each B layer is independently 1.0 mm to 10.0 mm, each B layer preferably has the same thickness, and the total thickness of each B layer is 3 mm. Preferably, the thickness is from .0 mm to 6.0 mm.

Further, it may be non-air permeable or may be air permeable. When having air permeability, the air permeability may be lower or higher than that of the A layer. The air permeability here is not the air permeability per unit thickness, but the air permeability of each B layer reflecting the thickness of each B layer. Even if the same material is thicker, the air permeability decreases, so the air permeability itself, which changes depending on the thickness, is taken into consideration. Note that the air permeability was measured using the same method as the method for measuring the air permeability of layer A and layer C, except for the thickness of the sample.
Further, by impregnating only the B layer with the liquid, the sound absorption coefficient of the laminated sound absorber can be improved. The liquid in this case includes a liquid that does not dissolve the B layer.
As for the degree of impregnation, the upper limit of the amount that can be impregnated into layer B may be impregnated, and even if it does not reach the upper limit, it is preferably 0.10 g or more, and 0.20 g per 1000 mm ³ of dry layer B. The amount is more preferably 0.30 g or more, and even more preferably 0.30 g or more. Further, the impregnable amount is preferably below the upper limit and 0.60 g or less, more preferably 0.50 g or less, and even more preferably 0.40 g or less.
By impregnating the B layer with the liquid in this way, the sound absorption performance of the entire laminated sound absorber can be improved.

(Polyvinyl alcohol resin layer)
Polyvinyl alcohol resin is usually produced by saponifying polyvinyl acetate resin. The degree of saponification of the polyvinyl alcohol resin is preferably 30 mol% or more, more preferably 50 mol% or more. Moreover, 99.9 mol% or less is preferable, and 99.3 mol% or less is more preferable. If the degree of saponification of the polyvinyl alcohol resin is less than 30 mol%, the mechanical strength may be poor, and if it exceeds 99.9 mol%, it may be difficult to impregnate the resin with liquid.

The degree of polymerization of the polyvinyl alcohol resin is preferably 500 or more, more preferably 1000 or more. Further, it is preferably 5,000 or less, more preferably 4,000 or less. If the degree of polymerization of the polyvinyl alcohol resin is less than 500, the mechanical strength of the polyvinyl alcohol resin layer may decrease, and if the degree of polymerization exceeds 5000, it may be difficult to form the polyvinyl alcohol resin layer. .
When layer B is a polyvinyl alcohol resin layer, it does not need to be impregnated with a liquid, but it may be impregnated with a liquid. As liquids which may be impregnated, water, polyhydric alcohols such as ethylene glycol, propylene glycol and glycerin can be chosen, in particular. By selecting and impregnating these materials, the sound absorption performance of the polyvinyl alcohol resin layer after impregnation is improved.

The content of water and the polyhydric alcohol in the polyvinyl alcohol resin layer is not particularly limited, but the preferable lower limit is 20 parts by weight and the preferable upper limit is 150 parts by weight based on 100 parts by weight of the polyvinyl alcohol resin. If the content of the polyhydric alcohol is less than 20 parts by weight, the interlayer film for laminated glass may become too hard, resulting in problems in handling. If it exceeds 150 parts by weight, the interlayer film for laminated glass may become too hard. Penetration resistance may decrease. A more preferable lower limit of the content of the polyhydric alcohol is 30 parts by weight, and a more preferable upper limit is 100 parts by weight.

(Polyurethane resin layer)
The polyurethane resin layer that can be used as layer B is a foam obtained by foaming the polyurethane resin during synthesis. Although it is not necessary to impregnate the polyurethane resin layer with a liquid, it may be impregnated with a liquid.
Polyurethane resin foam is obtained by reacting an isocyanate compound with a component that reacts with isocyanate, and at the same time adding or acting on additives such as a blowing agent, and is obtained by known means as foamed polyurethane resin. be able to.
The density measured according to JIS K 7222 is preferably 20.0 kg/m ³ or more, more preferably 50.0 kg/m ³ or more, even more preferably 100.0 kg/m ³ or more, and 200.0 kg/m ³ or more. is even more preferable.
When the polyurethane resin layer has air permeability, the air permeability per polyurethane resin layer is preferably 1.00 cm ³ /cm ² sec or more, and may be 0.150 cm ³ /cm ² sec or more. Further, it is preferably 2000.00 cm ³ /cm ² sec or less, more preferably 1200.00 cm ³ /cm ² sec or less, even more preferably 10.00 cm ³ /cm ² sec or less, and 5.00 cm ³ /cm ² sec or less. Most preferred.

(chloroprene rubber layer)
Any chloroprene rubber layer that can be used as layer B can be used as long as it has a density of 50 kg/m ³ or more. Then, it can be obtained by adding a foaming agent to chloroprene rubber mixed with a crosslinking agent and the like as necessary, and foaming the foaming agent.

(Ethylene vinyl acetate resin foam layer)
As the ethylene vinyl acetate resin foam layer that can be used as layer B, any known ethylene vinyl acetate resin having a density of 50 kg/m ³ or more can be employed.

[Manufacturing method of laminated sound absorber]
As a method for manufacturing the laminated sound absorbing body of the present invention, any known method for manufacturing a laminate can be selected and employed.
It is possible to prepare the required number of A layers and B layers, and while laminating these layers one by one, the layers can be bonded with an adhesive or welded. Alternatively, a method can be adopted in which the layers are simply stacked one on top of the other and mechanically fixed in a state in which these layers are in close contact with each other. In addition, when using an adhesive or welding, it is necessary to take into consideration so as not to impede the improvement of sound absorption properties.
When obtaining a laminated sound absorber having a B layer impregnated with a liquid, the B layer may be impregnated with the liquid in advance and lamination may be performed using this as described above.

In addition, in the laminated sound absorbing body of the present invention, both the A layer and the B layer contain known additives that can be contained in the resin, such as pigments, plasticizers, ultraviolet stabilizers, and antioxidants, to the extent that the effects of the present invention are not impaired. can.

[Applications of laminated sound absorbers]
The laminated sound absorber of the present invention can be used in buildings that require soundproofing to prevent internal noise from going out, and conversely, buildings that require soundproofing to prevent external noise from entering the interior, as well as automobiles and trains. It can be used for installation on structural materials, walls, ceilings, under floors, etc. of transportation means that generate noise that should be reduced. As for the installation method, the same means as the installation of known laminated sound absorbers and soundproofing materials can be adopted.

EXAMPLES Examples and comparative examples of the present invention will be shown and explained below.
The materials listed in Tables 1 to 3 below were used as layers A, B, and C, and the thicknesses were adjusted to desired thicknesses to obtain materials for the laminated sound absorbers used in each of the Examples and Comparative Examples. These laminated sound absorbers are obtained by stacking the respective materials without gluing them together.

Melamine foam 1: Basotect UF (BASF, air permeability 31.09 cm ³ /cm ² sec, density 6.2 kg/m ³ )
Melamine foam 2: Basotect G (BASF, air permeability 19.60 cm ³ /cm ² sec, density 10.3 kg/m ³ )
EVA (ethylene vinyl acetate) foam: EVA60-0.20 (Glory Sangyo Co., Ltd., density 210 kg/m ³ )
EPDM (ethylene propylene diene rubber) foam: Lucilla (Toyo Quality One Co., Ltd., air permeability 0.39 cm ³ /cm ² sec)
Urethane foam 1: Ruby cell (Toyo Polymer Co., Ltd., density 250 kg/m ³ )
Urethane foam 2: Sofras (Aion Co., density 210 kg/m ³ )
Urethane foam 3: AC sponge (AC Chemical Co., density 250 kg/m ³ )
Urethane foam 4: HDZ (Toyo Quality One Co., Ltd., air permeability 1.81 cm ³ /cm ² sec, density 23.2 kg/m ³ )
Urethane foam 5: NH (Toyo Quality One Co., Ltd., air permeability 16.49 cm ³ /cm ² sec, density 23.2 kg/m ³ )
Membrane vibration type material: J-700 (Nittobo Materials, thickness 1mm, density 2100kg/ ^m3 )
Polystyrene: Styrofoam (registered trademark) (DuPont Styro) (density 27 kg/m ³ )
PVA (polyvinyl alcohol resin) foam: PVA water absorption cloth (Daiso, density 320 kg/m ³ ) (diameter 39.5 mm, impregnated with 0.4 g of water per 2 mm thickness)
Polyethylene foam: PE Lite A-8 (INOAC Corporation, density 70 kg/m ³ )
Chloroprene rubber foam: C-4205 (INOAC Corporation, density 180 kg/m ³ )
The above air permeability is the air permeability when the thickness is 40 mm.

Changes in sound absorption coefficient with respect to frequency of each example and comparative example were measured, and the results are shown in FIGS. 1 to 9. Sample No. Sample Nos. 1 to 6 and 10 to 20 are examples based on a three-layer structure of A layer/B layer/C layer. Sample No. 7 is an example of a seven-layer structure consisting of A layer/B layer/C layer/B layer/A layer/B layer/C layer. 8 and 9 are examples consisting of only one layer.
The laminated sound absorbers used in all Examples and Comparative Examples had a cylindrical shape with a diameter of 39.5 mm.
Further, each cylindrical laminated sound absorber was installed so that sound was incident from layer A to layer C, and the sound absorption coefficient was measured according to JIS A1405-2.

Sample No. Sample Nos. 1 to 3 are examples in which the A layer and C layer are common and each B layer is changed. 4 is sample No. This is an example in which the A layer and C layer of Sample No. 1 are changed. 5 and 6 are sample nos. This is an example in which only one of the A layer and C layer of No. 1 is changed.
Sample No. 7 is an example in which the laminated sound absorber has a structure consisting of seven layers. The total thickness of layer B in the table is 6 mm. Since there are three B layers each having a thickness of 2 mm, the total thickness is 6 mm.
Sample No. Sample Nos. 8 and 9 are examples consisting of only one layer. Sample No. 10 is an example in which the density of the B layer is low. No. 11 is an example in which the air permeability of layer A is low.
Sample No. 12 is an example in which the PVA layer of layer B contained water as described above,
Sample No. Sample No. 13 is an example in which urethane foam is used for the A layer and C layer. Sample No. 14 has layer A made of urethane foam and layer C made of melamine foam. No. 15 is an example in which the A layer is made of melamine foam and the C layer is made of urethane foam.
Sample No. Sample No. 16 is an example in which the A layer is a 20 mm thick melamine foam and the C layer is a 60 mm thick melamine foam. No. 17 is an example in which the A layer is made of 60 mm thick melamine foam, and the C layer is made of 20 mm thick melamine foam.
Sample No. 18 to 20 are all sample Nos. This is an example in which the B layer in 1 is changed.

Examples and comparative examples will be confirmed below along with each figure.
Sample No. If the A layer and C layer are made common as in 1 to 3, and each B layer is changed, the transition of the sound absorption coefficient depending on the frequency will also change. No. According to No. 1 and No. 2, the sound absorption coefficient at 300 Hz exceeds 0.60, but No. In the case of No. 3, the sound absorption coefficient was particularly high at high frequencies.
Sample No. No. 1, in which layer A and layer C of the laminated sound absorber of No. 1 are made of different melamine foams. 4. Sample No. No. 1, in which either layer A or layer C of the laminated sound absorber No. 1 is made of a different melamine foam. In samples No. 5 and No. 6, the sound absorption coefficient at 300 Hz could be improved. Furthermore, by using a laminated sound absorbing body consisting of seven layers, the sound absorption coefficient at 300 Hz could be improved.

Sample No. No. 1 in which layer B of the laminated sound absorber in No. 1 was replaced with a PVA foam impregnated with water. In No. 12, the minimum sound absorption coefficient was particularly improved at frequencies of 1000 Hz or higher.
Sample No. No. 1 in which the A and C layers of the laminated sound absorber of No. 1 are made of urethane foam. 13, and sample No. No. 1, in which only the A layer of the laminated sound absorber of No. 1 is made of another urethane foam. In No. 14, the sound absorption coefficient at 300 Hz and the minimum sound absorption coefficient at 1000 Hz or higher were improved. Then, sample No. No. 1, in which only the C layer of the laminated sound absorber of No. 1 is made of another urethane foam. In sample no. The sound absorption coefficient at 300 Hz was comparable to that of Laminated Sound Absorber No. 1, and the lowest sound absorption coefficient at 1000 Hz or higher was comparable.

Sample No. In No. 1, the thickness of layer A of the laminated sound absorber was 20 mm, and the thickness of layer C was 60 mm. In Sample No. 16, the sound absorption coefficient was particularly improved at 300 Hz, but in Sample No. No. 1 is a comparative example in which the thickness of layer A of the laminated sound absorber No. 1 is 60 mm, and the thickness of layer C is 20 mm. In No. 17, the sound absorption coefficient at 300 Hz decreased.
Sample No. No. 1 in which layer B of the laminated sound absorber of No. 1 was changed. 18 and 19, sample no. The results were not significantly different from, or were slightly inferior to, the sound absorption coefficient at 300 Hz of No. 1 and the lowest sound absorption coefficient at the same level of 1000 Hz or higher.
Sample No. No. 1 in which layer B of the laminated sound absorber of No. 1 was changed. In No. 20, the sound absorption coefficient was particularly improved at 300 Hz.

In contrast to these examples, No. 1, which is a comparative example consisting of only one layer, No. 8 and 9 could not give sufficient results.
Furthermore, No. 2 has a lower density of layer B. 10. No. 1 with low air permeability of layer A. Even with 11, sufficient results could not be obtained.

Claims (5)

Containing layer A constituting the outermost layer on one side of the laminated sound absorber, layer C constituting the outermost layer on the other side, and layer B which is a porous layer provided inside,
Each of the A layer and the C layer is a resin foam layer, and the surface in contact with the B layer is smooth,
The laminated sound absorber has a sound absorption coefficient of 0.50 or more for sounds of 300Hz and a minimum sound absorption coefficient of 0.60 or more for sounds in the range of 1000Hz to 5000Hz.
Laminated sound absorber. The A layer and the C layer are urethane resin foam and/or melamine resin foam having an air permeability of 1.0 cm ³ /cm ² sec or more,
The laminated sound absorber according to claim 1, wherein layer B is a porous layer having a density of 70 kg/m ³ or more and smooth on both sides. The total thickness of the laminated sound absorber is 90 mm or less, and the thickness of the A layer and the C layer are the same, and/or the thickness of the C layer constituting the outermost layer on one side is 40 to 60 mm, and the C layer is the same. The laminated sound absorber according to claim 1 or 2, wherein the layer is thicker than the A layer. The laminated sound absorber according to any one of claims 1 to 3, which has two or more B layers, and has an A layer or a C layer between the B layers. The laminated sound absorber according to any one of claims 1 to 4, wherein layer B is a layer impregnated with a liquid.