Sound-absorbing cover

Abstract

The sound-absorbing cover 1 includes a first sound-absorbing layer 10 and a second sound-absorbing layer 20 made of foam. The first skin layer 12 of the first sound-absorbing layer 10 and the second skin layer 22 of the second sound-absorbing layer 20 are stacked so as to face each other. An air layer 30 is provided between the facing surfaces of the first skin layer 12 and the second skin layer 22. The first skin layer 12 of the first sound-absorbing layer 10 and the second skin layer 22 of the second sound-absorbing layer 20 are set to different rigidities.

Description

Technical Field

[0001] The present invention relates to a sound absorbing cover to be disposed at a noise source such as a vehicle. Background Art

[0002] In vehicles such as automobiles, a sound absorbing cover is disposed around the noise source in order to reduce noise generated from the noise source such as an engine, a motor, an intake manifold, and an electric compressor.

[0003] Among them, hoods made of polyurethane foam have been used for automobile hoods, as exemplified in Patent Document 1. In recent years, the frequency band of noise to be absorbed has widened, and there is a demand for sound-absorbing hoods that absorb low-frequency noise below 1 kHz.

[0004] Therefore, Patent Document 2 discloses a laminated sound absorbing material which is formed by 2 / s or more porous body and a high ventilation layer composed of a ventilation volume greater than 0.05ml / cm 2 / s and 2ml / cm 2 The low-air permeability layer made of polyurethane foam with a density of 1 / s or less is formed into a laminated structure, thereby being able to effectively absorb noise in a frequency band below 1 kHz.

[0005] Patent Document 3 discloses an engine hood including a urethane foam resin layer, a PET nonwoven fabric layer, and an air layer therebetween, and having a sound absorbing effect also in the low frequency band of 500 to 1000 Hz.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2013-147939

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 2010-184655

[0010] Patent Document 3: Japanese Patent Application Laid-Open No. 2007-255189 Summary of the Invention

[0011] Problems to be solved by the invention

[0012] Patent Document 2 discloses a laminated sound-absorbing material method in which a low-air-permeability layer and a high-air-permeability layer are fixedly bonded together using an adhesive or the like, and a method in which the low-air-permeability layer and the high-air-permeability layer are simply overlapped and laminated. When the low-air-permeability layer and the high-air-permeability layer are fixedly bonded using an adhesive or the like, there is a possibility that air permeability will be impaired by the adhesive layer, reducing the sound absorption effect. Furthermore, when the low-air-permeability layer and the high-air-permeability layer are overlapped and laminated, although air permeability is not impaired in the overlapping region of the low-air-permeability layer and the high-air-permeability layer, the sound absorption performance at low frequencies depends on the performance of the low-air-permeability layer, leaving room for improvement in this respect.

[0013] Furthermore, the engine hood described in Patent Document 3 has a large difference in sound absorption effect between the frequency band of 800 to 1800 Hz and the frequency band below 800 Hz, and there is room for improvement in improving the sound absorption performance on the low-frequency side.

[0014] The present invention has been made in view of the above-mentioned actual situation, and an object of the present invention is to provide a sound absorbing cover capable of effectively absorbing low-frequency noise in a wider range.

[0015] Means used to solve problems

[0016] The inventors of the present invention focused on the stacking region of the two sound absorbing layers and discovered that by setting the structure and properties of the stacking region of the two sound absorbing layers within specific ranges, low-frequency noise can be effectively absorbed over a wider range, leading to the completion of the present invention.

[0017] In order to solve the above-mentioned problems, the sound-absorbing cover (1) of the present invention comprises: a first sound-absorbing layer, which has a first foam layer and a first skin layer formed integrally when the first foam layer is formed; and a second sound-absorbing layer, which has a second foam layer and a second skin layer formed integrally when the second foam layer is foamed, (2) the first skin layer of the first sound-absorbing layer has a rigidity different from the rigidity of the second skin layer of the second sound-absorbing layer, and (3) the first sound-absorbing layer and the second sound-absorbing layer are stacked in a state in which the first skin layer and the second skin layer are opposite to each other, and an air layer is provided between the opposing surfaces of the first skin layer and the second skin layer.

[0018] According to the sound absorbing cover of the present invention, low-frequency noise can be effectively absorbed in a wider range. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a top view of the sound absorbing cover which is the first embodiment of the present invention.

[0020] Figure 2 yes Figure 1 II-II sectional view.

[0021] Figure 3 yes Figure 1 Sectional view III-III.

[0022] Figure 4 It is a partial cross-sectional view of a sound absorbing cover according to a second embodiment of the present invention.

[0023] Figure 5 It is a partial cross-sectional view of a sound absorbing cover according to a third embodiment of the present invention.

[0024] Figure 6 This is a partially enlarged view of a sound absorbing cover according to a third embodiment of the present invention.

[0025] Figure 7 It is a partial cross-sectional view of a sound absorbing cover according to a fourth embodiment of the present invention.

[0026] Figure 8 It is a partial cross-sectional view of a sound absorbing cover according to a fourth embodiment of the present invention.

[0027] Figure 9 This is a graph comparing the frequency dependence of sound absorption.

[0028] Figure 10 This is a graph comparing the frequency dependence of sound absorption. DETAILED DESCRIPTION

[0029] <1. Application Examples of Sound-Absorbing Covers>

[0030] The sound-absorbing cover of the present invention is used to cover and absorb noise generated by noise sources such as engines, motors, intake manifolds, and electric compressors in automobiles. It is particularly suitable for use with noise sources that generate low-frequency noise. The sound-absorbing cover generally has a concave bottomed shape that opens toward the noise source and is secured to the noise source with bolts or other fastening members.

[0031] <2. Composition of the sound-absorbing cover>

[0032] This sound hood is constructed by stacking two foam sound-absorbing layers with skin layers, with the skin layers facing each other. One sound-absorbing layer is positioned toward the noise source, while the other is positioned away from the noise source, serving as a design surface. This sound hood has an air layer between the facing skin layers.

[0033] (First embodiment)

[0034] use Figure 1-Figure 3 The structure of the sound absorbing cover 1 as the first embodiment of the present invention will be described. Figure 1 、 Figure 2As shown, the sound absorbing cover 1 is a bottomed concave shape opened toward the noise source side (not shown). In addition, the sound absorbing cover 1 can be formed into any shape according to the outer shape of the noise source as a target.

[0035] In this embodiment, the cover body having a bottomed concave shape opened toward the noise source is formed by the second sound absorbing layer 20 , and the first sound absorbing layer 10 is arranged in a region of the concave portion facing the noise source.

[0036] like Figure 3 As shown, a first sound absorbing layer 10 and a second sound absorbing layer 20 are laminated in the area facing the noise source. The first sound absorbing layer 10 is a foamed sound absorbing layer comprising a first foam layer 11 and a first skin layer 12 integrally formed during the formation of the first foam layer 11. While the first skin layers 12, 12 are provided on both sides in the lamination direction in this embodiment, a configuration may also be employed in which the first skin layer 12 is provided only on the sides facing the second sound absorbing layer 20.

[0037] The second sound absorbing layer 20 is a sound absorbing layer made of foam and includes a second foam layer 21 and a second skin layer 22 integrally formed during the formation of the second foam layer 21. While the second skin layers 22, 22 are provided on both surfaces in the lamination direction in this embodiment, a configuration may also be employed in which the second skin layer 22 is provided only on the surface facing the first sound absorbing layer 10.

[0038] like Figure 2 、 Figure 3 As shown, the first skin layer 12 of the first sound absorbing layer 10 and the second skin layer 22 of the second sound absorbing layer 20 are stacked facing each other, with an air layer 30 provided between the facing surfaces of the first skin layer 12 and the second skin layer 22 .

[0039] like Figure 1 、 Figure 3 As shown, the first sound-absorbing layer 10 includes, in the plane direction of the surface layer on which the first skin layer 12 is formed, a first region 40 on which the first skin layer 12 is formed, and a second region 41 surrounding the first region 40. In this embodiment, the first region 40 is configured to have a rectangular shape when viewed from above. Furthermore, the first region 40 can be configured to any shape depending on the shape of the sound-absorbing object that serves as a noise source.

[0040] like Figure 3 As shown, when viewed in a cross-section along the thickness direction of the first sound absorbing layer 10, the upper surface of the second region 41 of the first sound absorbing layer 10 is positioned closer to the second sound absorbing layer 20 than the upper surface of the first region 40. In other words, the first region 40 is a recessed region formed inside the second region 41, and the first region 40 is positioned below the second region 41.

[0041] In addition, if Figure 1 As shown, six first engaging recesses 13 are formed in the second region 41 of the first sound absorbing layer 10 at intervals in the circumferential direction. In this embodiment, the first engaging recesses 13 are circular recesses connected to the outer edge of the first region 40 and recessed along the thickness direction of the first sound absorbing layer 10, forming a top view.

[0042] The first engaging recess 13 may be a rectangular recess in plan view, etc., and its shape is not limited. Alternatively, the first engaging recess 13 may be formed to have a step or an inclination when viewed in a cross section in the thickness direction of the first sound absorbing layer 10 .

[0043] Furthermore, the first engagement recess 13 may be an annular recess that is continuous in the circumferential direction so as to surround the entire periphery of the first region 40 , and may be set to any shape according to the shape of the first region 40 .

[0044] like Figure 2 、 Figure 3 As shown, the second sound absorbing layer 20 has six first engaging projections 23 projecting toward the first sound absorbing layer 10 at predetermined intervals in a region (second region 41 ) surrounding the second skin layer 22 disposed opposite the first skin layer 12 of the first sound absorbing layer 10 .

[0045] The first engaging protrusion 23 is formed at a position opposing the first engaging recess 13 of the opposing first sound absorbing layer 10. In this embodiment, the first engaging protrusion 23 is a circular (cylindrical) protrusion when viewed from above. Furthermore, the outer diameter of the first engaging protrusion 23 is slightly larger than the inner diameter of the first engaging recess 13 of the first sound absorbing layer 10.

[0046] Furthermore, when the first sound absorbing layer 10 is provided with an annular first engaging recess, the first engaging projection may be an annular projection corresponding to the first engaging recess and may be set to any shape depending on the shape of the first engaging recess.

[0047] The air layer 30 is formed by integrating the first sound absorbing layer 10 and the second sound absorbing layer 20. Specifically, when the first engaging recess 13 of the first sound absorbing layer 10 is engaged with the first engaging protrusion 23 of the second sound absorbing layer 20, the thickness of the first region 40 of the first sound absorbing layer 10 is smaller than the thickness of the second region 41. Figure 3 As shown, a gap is formed between the facing surfaces of the first skin layer 12 of the first sound absorbing layer 10 and the second skin layer 22 of the second sound absorbing layer 20 , and this gap serves as an air layer 30 .

[0048] In this embodiment, as will be described later, the second sound absorbing layer 20 has a greater hardness than the first sound absorbing layer 10. Furthermore, the outer diameter of the first engaging protrusion 23 of the second sound absorbing layer 20 is slightly larger than the inner diameter of the first engaging recess 13 of the first sound absorbing layer 10. Therefore, during engagement, deformation of the first engaging protrusion 23 is suppressed, and the first engaging protrusion 23 is pressed into and engaged with the first engaging recess 13 of the first sound absorbing layer 10. Consequently, the first sound absorbing layer 10 and the second sound absorbing layer 20 are integrated without interfering with operation.

[0049] Furthermore, in this embodiment, the first engaging recessed portion 13 is provided in the first sound absorbing layer 10, and the first engaging protruding portion 23 is provided in the second sound absorbing layer 20. However, a configuration may also be employed in which the engaging protruding portion is provided in the first sound absorbing layer 10 and the engaging recessed portion is provided in the second sound absorbing layer 20. Furthermore, the hardness of the second sound absorbing layer 20 may be lower than that of the first sound absorbing layer 10, within a range that does not hinder operation.

[0050] (Second embodiment)

[0051] In the first embodiment, the first sound absorbing layer 10 is provided with the first and second regions 40 and 41 having height differences in the thickness direction. In the second embodiment, the second sound absorbing layer 20 is provided with the third and fourth regions 50 and 51 having height differences in the thickness direction.

[0052] use Figure 4 The structure of the sound absorbing cover 1a of the second embodiment will be described. Components identical to those of the first embodiment are denoted by the same reference numerals as those of the first embodiment.

[0053] The second sound-absorbing layer 20 includes a third region 50, in which the second skin layer 22 is formed and arranged opposite the first skin layer 12 of the first sound-absorbing layer 10, and a fourth region 51 surrounding the third region 50. In this embodiment, the third region 50 is formed into a rectangular shape when viewed from above. Furthermore, the third region 50 can be formed into any shape depending on the shape of the sound-absorbing object that serves as the noise source.

[0054] like Figure 4 As shown, when viewed in a cross-section along the thickness direction of the second sound absorbing layer 20, the lower surface of the fourth region 51 of the second sound absorbing layer 20 is positioned closer to the first sound absorbing layer 10 than the lower surface of the third region 50. In other words, the third region 50 is a recessed region formed inside the fourth region 51, and the third region 50 is positioned above the fourth region 51.

[0055] In addition, if Figure 1 、 Figure 4As shown, six second engaging projections 24 are formed at intervals in the circumferential direction in the fourth region 51 of the second sound absorbing layer 20. In this embodiment, the second engaging projections 24 are circular (cylindrical) projections connected to the outer edge of the third region 50 and projecting in the thickness direction of the second sound absorbing layer 20 when viewed from above.

[0056] The second engaging projection 24 may be a rectangular projection in plan view, and its shape is not limited. Alternatively, the second engaging projection 24 may be a projection having a step or an inclination when viewed in a cross section in the thickness direction of the second sound absorbing layer 20 .

[0057] Furthermore, the second engaging projection 24 may be an annular projection that is continuous in the circumferential direction so as to surround the entire periphery of the third region 50 , and may be set to any shape according to the shape of the third region 50 .

[0058] The first sound absorbing layer 10 has six second engaging recesses 14 opened toward the second sound absorbing layer 20 at predetermined intervals in a region (fourth region 51 ) surrounding the first skin layer 12 disposed opposite the second skin layer 22 of the second sound absorbing layer 20 .

[0059] The second engaging recess 14 is formed at a position opposing the second engaging protrusion 24 of the second sound absorbing layer 20. In this embodiment, the second engaging recess 14 is circular in shape when viewed from above. Furthermore, in this embodiment, the outer diameter of the second engaging recess 14 is slightly smaller than the inner diameter of the second engaging protrusion 24 of the second sound absorbing layer 20.

[0060] Furthermore, when the second sound absorbing layer 20 is provided with an annular second engaging projection, the second engaging recess may be an annular recess corresponding to the second engaging projection and may be set to any shape depending on the shape of the second engaging projection.

[0061] The air layer 30 is formed by integrating the first sound absorbing layer 10 and the second sound absorbing layer 20. Specifically, when the second engaging recess 14 of the first sound absorbing layer 10 is engaged with the second engaging protrusion 24 of the second sound absorbing layer 20, the thickness of the third region 50 of the second sound absorbing layer 20 is smaller than the thickness of the fourth region 51. Figure 4 As shown, a gap is formed between the facing surfaces of the first skin layer 12 of the first sound absorbing layer 10 and the second skin layer 22 of the second sound absorbing layer 20 , and this gap serves as an air layer 30 .

[0062] In this embodiment, as will be described later, the density of the second sound absorbing layer 20 is greater than that of the first sound absorbing layer 10. Furthermore, the outer diameter of the second engaging protrusion 24 of the second sound absorbing layer 20 is slightly larger than the inner diameter of the second engaging recess 14 of the first sound absorbing layer 10. Therefore, during engagement, deformation of the second engaging protrusion 24 is suppressed, and the second engaging protrusion 24 is pressed into and engaged with the second engaging recess 14 of the first sound absorbing layer 10, thereby achieving integration without hindering operation.

[0063] Furthermore, in the second embodiment, the second engaging recessed portion 14 is provided in the first sound absorbing layer 10, and the second engaging protruding portion 24 is provided in the second sound absorbing layer 20. However, a configuration may be employed in which the engaging protruding portion is provided in the first sound absorbing layer 10, and the engaging recessed portion is provided in the second sound absorbing layer 20. Furthermore, the hardness of the second sound absorbing layer 20 may be lower than that of the first sound absorbing layer 10, within a range that does not hinder operation.

[0064] (Third embodiment)

[0065] In the third embodiment, the sound absorbing cover 1 according to the first embodiment is configured such that a plurality of protrusions 15 are further provided on the first sound absorbing layer 10 or the second sound absorbing layer 20. Figure 5 、 Figure 6 The structure of the sound absorbing cover 1b of the third embodiment will be described. Components identical to those of the first embodiment are denoted by the same reference numerals as those of the first embodiment.

[0066] The first skin layer 12 of the first sound absorbing layer 10 has a plurality of protrusions 15, 15, ... protruding toward the second sound absorbing layer 20. The plurality of protrusions 15, 15, ... are integrally formed with the first skin layer 12. In this embodiment, as shown in FIG. Figure 6 As shown, a conical protrusion 15 having a rounded tip is continuously formed.

[0067] Furthermore, the shape of the protrusions 15 may be non-uniform due to the nature of being integrally formed during foaming of the first sound-absorbing layer 10. The shape of the protrusions 15 is not limited as long as they protrude toward the second skin layer 22 of the opposing second sound-absorbing layer 20. Furthermore, any spacing may be provided between adjacent protrusions 15.

[0068] The air layer 30 is formed by integrating the first sound absorbing layer 10 and the second sound absorbing layer 20 in the same manner as in the first embodiment. Figure 6 As shown, a plurality of protrusions 15 , 15 , . . . of the first skin layer 12 are arranged in a gap formed between the facing surfaces of the first skin layer 12 of the first sound absorbing layer 10 and the second skin layer 22 of the second sound absorbing layer 20 .

[0069] In this embodiment, the protrusions 15 are arranged so that their protrusion height is slightly less than the length between the opposing surfaces of the first skin layer 12 of the first sound-absorbing layer 10 and the second skin layer 22 of the second sound-absorbing layer 20. These protrusions 15 are arranged with a slight gap between the tip of each protrusion 15 and the second skin layer 22 of the second sound-absorbing layer 20. With this configuration, the gaps between adjacent protrusions 15 and between each protrusion 15 and the second skin layer 22 form air layers 30.

[0070] By providing the plurality of protrusions 15, 15, ... on the first skin layer 12 of the first sound absorbing layer 10, the sound transmitted through the first skin layer 12 is diffused, and the sound absorbing area is increased, thereby improving the sound absorbing effect.

[0071] Furthermore, in this embodiment, the protrusions 15 are provided on the first skin layer 12 of the first sound absorbing layer 10. However, the protrusions may be provided on the second skin layer 22 of the second sound absorbing layer 20, or on both the first skin layer 12 and the second skin layer 22. Furthermore, the protrusions 15 of the first skin layer 12 may be arranged so that the tips of the protrusions 15 are in contact with the second skin layer 22 of the second sound absorbing layer 20.

[0072] (Fourth embodiment)

[0073] In the fourth embodiment, the sound absorbing cover 1 according to the first embodiment is configured such that the first concave engaging portion in the first sound absorbing layer 10 and the first convex engaging portion in the second sound absorbing layer 20 are not provided. Figure 7 The structure of the sound absorbing cover 1c of the fourth embodiment will be described. Components identical to those of the first embodiment are denoted by the same reference numerals as those of the first embodiment.

[0074] The first sound absorbing layer 10 is a plate-like member that is rectangular in shape when viewed from above. Figure 7 As shown, the first sound absorbing layer 10 includes a first recess 16 that opens from the inner edge of the second region 41 (the outer edge of the first region 40 ) toward the second sound absorbing layer 20 .

[0075] In this embodiment, the first recess 16 is a recess that is rectangular in shape when viewed from above. Figure 7 As shown, when viewed in a cross-section in the thickness direction, the first recess 16 positions the upper surface of the second region 41 of the first sound absorbing layer 10 closer to the second sound absorbing layer 20 than the upper surface of the first region 40 (the bottom surface of the first recess 16). Furthermore, the first skin layer 12 is formed on the bottom surface of the first recess 16.

[0076] like Figure 7As shown, when viewed in a cross-section along the thickness direction of the second sound absorbing layer 20, the second sound absorbing layer 20 includes a second recess 25 extending from the outer edge of the second region 41, which is a plate-shaped portion, toward the first sound absorbing layer 10. In this embodiment, the second recess 25 is a rectangular recess in a plan view corresponding to the outer diameter of the first sound absorbing layer 10. Furthermore, the depth of the second recess 25 is substantially the same as the thickness of the first sound absorbing layer 10.

[0077] In the second sound absorbing layer 20, the second skin layer 22 is formed in the region corresponding to the first region 40 on the bottom surface of the second recess 25. Alternatively, the second skin layer 22 may be formed on the entire bottom surface of the second recess 25, as long as it is provided at least on the surface facing the first skin layer 12 of the first sound absorbing layer 10.

[0078] The air layer 30 is formed by integrating the first sound absorbing layer 10 and the second sound absorbing layer 20. Specifically, when the first sound absorbing layer 10 is accommodated in the second recess 25 of the second sound absorbing layer 20, the thickness of the first region 40 of the first sound absorbing layer 10 is smaller than the thickness of the second region 41. Figure 7 As shown, a gap is formed between the facing surfaces of the first skin layer 12 of the first sound absorbing layer 10 and the second skin layer 22 of the second sound absorbing layer 20 , and this gap serves as an air layer 30 .

[0079] In this embodiment, the outer diameter of the first sound absorbing layer 10 is slightly smaller than the inner diameter of the second recess 25 of the second sound absorbing layer 20. Furthermore, the second sound absorbing layer 20 has a greater hardness than the first sound absorbing layer 10. Therefore, the first sound absorbing layer 10 is pressed into and accommodated in the second recess 25 of the second sound absorbing layer 20. As a result, the first and second sound absorbing layers 10, 20 are integrated without interfering with operation.

[0080] Alternatively, other fixing methods may be employed, such as fixing the outer side surface of the first sound absorbing layer 10 to the inner side surface of the second recess 25 of the second sound absorbing layer 20 using an adhesive, double-sided tape, or welding the areas excluding the facing surfaces of the first skin layer 12 of the first sound absorbing layer 10 and the second skin layer 22 of the second sound absorbing layer 20. Furthermore, as in the third embodiment, protrusions may be provided on the first skin layer 12 of the first sound absorbing layer 10 and the second skin layer 22 of the second sound absorbing layer 20.

[0081] (Fifth embodiment)

[0082] In the fifth embodiment, the sound absorbing cover 1a according to the second embodiment is configured such that the first concave engaging portion of the first sound absorbing layer 10 and the first convex engaging portion of the second sound absorbing layer 20 are not provided. Figure 8The structure of the sound absorbing cover 1d of the fifth embodiment will be described. Components identical to those of the second embodiment are denoted by the same reference numerals as those of the second embodiment.

[0083] The first sound-absorbing layer 10 is a plate-shaped member having a rectangular shape when viewed from above. The surface of the first sound-absorbing layer 10 facing the second sound-absorbing layer 20 is formed as a plane spanning the third region 50 and the fourth region 51. In this embodiment, the first skin layer 12 is formed on the surface of the third region 50 facing the second sound-absorbing layer 20. Alternatively, the first skin layer 12 may be formed on the entire surface of the surface facing the second sound-absorbing layer 20, including the fourth region.

[0084] like Figure 8 As shown, when viewed in a cross-section along the thickness direction of the second sound absorbing layer 20, the second sound absorbing layer 20 includes a second recess 25 extending from the outer edge of the fourth region 51, which is a plate-shaped portion, toward the first sound absorbing layer 10. In this embodiment, the second recess 25 is a rectangular recess in a plan view corresponding to the outer diameter of the first sound absorbing layer 10. Furthermore, the depth of the second recess 25 is substantially the same as the thickness of the first sound absorbing layer 10.

[0085] A third recess 26 is formed on the bottom surface of the second recess 25. The third recess 26 opens from the inner edge of the fourth region 51 (the outer edge of the third region 50) toward the first sound absorbing layer 10. In this embodiment, the third recess 26 is a rectangular recess in plan view.

[0086] like Figure 8 As shown, when viewed in a cross-section along the thickness direction of the second sound absorbing layer 20, the lower surface of the fourth region 51 of the second sound absorbing layer 20 is positioned closer to the first sound absorbing layer 10 than the lower surface of the third region 50 (the bottom surface of the third recess 26). Furthermore, the second skin layer 22 is formed on the bottom surface of the third recess 26 located in the third region 50.

[0087] The air layer 30 is formed by integrating the first sound absorbing layer 10 and the second sound absorbing layer 20. Specifically, when the first sound absorbing layer 10 is accommodated in the second recess 25 of the second sound absorbing layer 20, the thickness of the third region 50 of the second sound absorbing layer 20 is smaller than the thickness of the second region 51. Figure 8 As shown, a gap is formed between the facing surfaces of the first skin layer 12 of the first sound absorbing layer 10 and the second skin layer 22 of the second sound absorbing layer 20 , and this gap serves as an air layer 30 .

[0088] In this embodiment, the outer diameter of the first sound absorbing layer 10 is slightly smaller than the inner diameter of the second recess 25 of the second sound absorbing layer 20. Furthermore, the second sound absorbing layer 20 has a greater hardness than the first sound absorbing layer 10. Therefore, the first sound absorbing layer 10 is pressed into and accommodated in the second recess 25 of the second sound absorbing layer 20. As a result, the first and second sound absorbing layers 10, 20 are integrated without interfering with operation.

[0089] Alternatively, other fixing methods may be employed, such as using an adhesive, double-sided tape, or the like to accommodate the outer side surface of the first sound absorbing layer 10 and the inner side surface of the second recess 25 of the second sound absorbing layer 20, or fusing the areas excluding the facing surfaces of the first skin layer 12 of the first sound absorbing layer 10 and the second skin layer 22 of the second sound absorbing layer 20. Furthermore, as in the third embodiment, protrusions may be provided on the first skin layer 12 of the first sound absorbing layer 10 and the second skin layer 22 of the second sound absorbing layer 20.

[0090] (Other embodiments)

[0091] In the first to third embodiments described above, a convex engaging portion is provided on one side of the first sound absorbing layer 10 or the second sound absorbing layer 20, while a concave engaging portion is provided on the other side. These engaging portions are then engaged to integrate the first sound absorbing layer 10 and the second sound absorbing layer 20. However, the engaging method is not limited to the above embodiments. For example, engaging recessed portions may be provided on both the first sound absorbing layer 10 and the second sound absorbing layer 20, and separate engaging members may be pressed into each engaging recessed portion via a spacer that maintains a predetermined gap between the first sound absorbing layer 10 and the second sound absorbing layer 20 to achieve engagement. Alternatively, known engaging methods such as heat welding, engagement using adhesives, double-sided tape, or clamps may be employed.

[0092] <Sound Absorbing Layer Composition>

[0093] (First sound-absorbing layer)

[0094] The first sound-absorbing layer 10 is formed of urethane foam and includes a first foam layer 11 made of urethane foam and a first skin layer 12 integrally formed with the surface layer during the foaming process. Furthermore, the first sound-absorbing layer 10 is not limited to urethane foam; a foamed resin such as silicone foam may also be used.

[0095] The first foam layer 11 of the first sound absorbing layer 10 in the sound absorbing cover 1 of the first embodiment of the present invention has a thickness of 5 mm and a density of 0.14 g / cm 3 , ventilation resistance is 378000Ns / m 4 , ASKER C hardness is 22 degrees.

[0096] The airflow resistance is a value obtained by cutting out a sample having a diameter of 50 mm and a thickness of 4±2 mm from the portion of the first foam layer 11 excluding the first skin layer 12 in the first sound absorbing layer 10. The sample is measured using an airflow resistance measuring apparatus (Model: MFR-02) manufactured by Nihon Onkyo Engineering in accordance with the direct current method (DC method) specified in ISO 9053. The measured value is then divided by the sample thickness.

[0097] The ASKER C hardness is a value obtained by measuring a sample of the first sound absorbing layer 10 (including the first skin layers 12 on both sides) having a thickness of 5 mm using a rubber hardness tester (model: ASKER C type) manufactured by Kobunshi Keiki Co., Ltd. in accordance with JIS K 7312.

[0098] The density is a value obtained by cutting a sample with a diameter of 50 mm and a thickness of 5 mm from the first sound absorbing layer 10 (including the first skin layers 12 on both sides), measuring the mass using a Shimadzu scale (Model: TX3202N), and dividing the mass by the volume of the sample.

[0099] The first foam layer 11 of the first sound absorbing layer 10 has a thickness of 3 to 30 mm and a density of 0.06 to 0.2 g / cm3 depending on the characteristics, shape, and arrangement space of the noise source. 3 , Set the ventilation resistance to 1000~1000000Ns / m 4 , set the ASKERC hardness to 5-40 degrees.

[0100] Preferably, the thickness is set to 4 to 10 mm and the density is set to 0.10 to 0.16 g / cm2 from the viewpoint of effectively absorbing low-frequency noise in a wider range and achieving both space saving and light weight of the soundproof cover. 3 , set the ventilation resistance to 100000~1000000Ns / m 4 In addition, from the viewpoint of preventing sound leakage by closely adhering to a noise source with undulating surfaces and reducing secondary radiated sound from the surface of the sound absorbing cover caused by vibration transmission from a noise source accompanied by vibration, an ASKER C hardness of 10 to 30 degrees is preferred.

[0101] The thickness of the first skin layer 12 of the first sound absorbing layer 10 in the sound absorbing cover 1 of the first embodiment of the present invention is 10 μm, and the air flow resistance is 505000 Ns / m. 4 , ASKER C hardness is 22 degrees.

[0102] The airflow resistance is a value obtained by cutting a sample having a diameter of 50 mm and a thickness of 2±1 mm from the surface side including one of the first skin layers 12 of the first sound absorbing layer 10 (including the first skin layers 12 on both sides). The airflow resistance is measured from the side of the first skin layer 12 using a Nihon Onkyo Engineering airflow resistance measuring device (model: MFR-02) in accordance with the direct current method (DC method) specified in ISO 9053. The measured value is then divided by the sample thickness.

[0103] The ASKER C hardness is a value obtained by measuring the first sound absorbing layer 10 (including the first skin layers 12 on both sides) from the first skin layer 12 side on one side using a rubber hardness tester (model: ASKER C) manufactured by Kobunshi Keiki Co., Ltd. in accordance with JIS K 7312.

[0104] The first skin layer 12 of the first sound absorbing layer 10 has a thickness of 3 to 100 μm and an air flow resistance of 1000 to 10,000,000 Ns / m according to the frequency characteristics of the noise source. 4 , set the ASKER C hardness to the range of 5 to 40 degrees.

[0105] From the perspective of effectively absorbing low-frequency noise below 1000 Hz, it is preferable to set the ASKER C hardness to 10 to 30 degrees and the ventilation resistance to 100,000 to 1,000,000 Ns / m. 4 range.

[0106] (Second sound absorbing layer)

[0107] The second sound absorbing layer 20 is formed of urethane foam and includes a second foam layer 21 made of urethane foam and a second skin layer 22 integrally formed with the surface layer during foaming. Furthermore, the second sound absorbing layer 20 is not limited to urethane foam; foamed resins such as silicone foam may also be used.

[0108] The second foam layer 21 of the second sound absorbing layer 20 in the sound absorbing cover 1 of the first embodiment of the present invention has a thickness of 5 mm and a density of 0.12 g / cm 3 , ventilation resistance is 153000Ns / m 4 , ASKER C hardness is 76 degrees.

[0109] The airflow resistance is a value obtained by cutting out a sample having a diameter of 50 mm and a thickness of 4±2 mm from the portion of the second foam layer 21 in the second sound absorbing layer 20 excluding the second skin layer 22. The sample is measured using an airflow resistance measuring apparatus (Model: MFR-02) manufactured by Nihon Onkyo Engineering in accordance with the direct current method (DC method) specified in ISO 9053. The measured value is then divided by the sample thickness.

[0110] The ASKER C hardness is a numerical value obtained by measuring a sample of the second sound absorbing layer 20 (including the second skin layers 22 on both sides) having a thickness of 5 mm using a rubber hardness tester (model: ASKER C type) manufactured by Kobunshi Keiki Co., Ltd. in accordance with JIS K 7312.

[0111] The density is a value obtained by cutting a sample with a diameter of 50 mm and a thickness of 5 mm from the second foam layer 21 (including the second skin layers 22 on both sides), measuring the mass using a scale manufactured by Shimadzu Corporation (Model: TX3202N), and dividing the mass by the volume of the sample.

[0112] The second foam layer 21 of the second sound absorbing layer 20 is set to have a thickness of 3 to 30 mm and a density of 0.06 to 0.2 g / cm according to the characteristics, shape, and arrangement space of the noise source. 3 , Set the ventilation resistance to 1000~1000000Ns / m 4 , set the ASKERC hardness to 40~95 degrees.

[0113] Preferably, the thickness is set to 4 to 10 mm and the density is set to 0.10 to 0.16 g / cm2 from the viewpoint of effectively absorbing low-frequency noise in a wider range and achieving both space saving and light weight of the soundproof cover. 3 , set the ventilation resistance to 100000~1000000Ns / m 4 In addition, from the viewpoint of facilitating fixing of the soundproof cover to the object, the ASKER C hardness is preferably 60 to 90 degrees.

[0114] The second skin layer 22 of the second sound absorbing layer 20 in the sound absorbing cover 1 of the first embodiment of the present invention has a thickness of 10 μm and an air flow resistance of 584,000 Ns / m. 4 .

[0115] The airflow resistance is a value obtained by cutting a sample having a diameter of 50 mm and a thickness of 2±1 mm from the surface side including one of the second skin layers 22 of the second sound absorbing layer 20 (including the second skin layers 22 on both sides). The airflow resistance is measured from the side of the second skin layer 22 using a Nihon Onkyo Engineering airflow resistance measuring device (Model: MFR-02) in accordance with the direct current method (DC method) specified in ISO 9053. The measured value is then divided by the sample thickness.

[0116] The ASKER C hardness is a value obtained by measuring the hardness of a sample having a thickness of 5 mm of the second sound absorbing layer 20 (including the first skin layers 12 on both sides) from the first skin layer 12 side on one side using a rubber hardness tester (model: ASKER C rubber hardness tester) manufactured by Kobunshi Keiki Co., Ltd. in accordance with JIS K 7312.

[0117] The second skin layer 22 of the second sound absorbing layer 20 has a thickness of 3 to 100 μm and an air flow resistance of 1,000 to 1,000,000 Ns / m according to the frequency characteristics of the noise source. 4 , Set the ASKER C hardness to the range of 40 to 95 degrees.

[0118] From the perspective of effectively absorbing low-frequency noise below 1000 Hz, it is preferable to set the ASKER C hardness to 60 to 90 degrees and the ventilation resistance to 100,000 to 1,000,000 Ns / m. 4 range.

[0119] From the perspective of expanding the low-frequency absorption range of the membrane vibration-type sound absorbing structure described later, it is effective to differentiate the properties of the first skin layer 12 of the first sound absorbing layer 10 and the second skin layer 22 of the second sound absorbing layer 20. In particular, it is preferable that the hardness of the first skin layer 12 of the first sound absorbing layer 10, as measured using the aforementioned measurement method, be 5 to 40 degrees, and the hardness of the second skin layer 22 of the second sound absorbing layer 20 be 40 to 95 degrees. Furthermore, it is more preferable that the hardness of the first skin layer 12 of the first sound absorbing layer 10, as measured using the aforementioned measurement method, be 10 to 30 degrees, and the hardness of the second skin layer 22 of the second sound absorbing layer 20 be 60 to 90 degrees. Furthermore, depending on the required usage conditions, the first sound absorbing layer 10 may have the properties of the second sound absorbing layer 20, and the second sound absorbing layer 20 may have the properties of the first sound absorbing layer 10, as measured using the aforementioned measurement method.

[0120] <Method for Manufacturing Sound-Absorbing Cover>

[0121] When manufacturing the sound absorbing cover 1 of the present invention, only two foaming processes are required. First, a first foam body (first sound absorbing layer 10) consisting of a first foam layer 11 and a first skin layer 12 is formed. A release agent is applied to the inner surface of the upper mold and the inner surface of the lower mold of the forming mold. Next, the upper mold and the lower mold are combined, and a foamed urethane resin raw material is injected into the first cavity formed by the inner surface of the upper mold and the inner surface of the lower mold to perform foaming molding. At this time, the preferred temperature of the upper mold that forms the first skin layer 12 is 40 to 60°C. In addition, a wax-based release agent is preferably used, but its type is not limited.

[0122] Next, a second foamed body (second sound-absorbing layer 20) consisting of a second foam layer 21 and a second skin layer 22 is formed. Similarly, a release agent is applied to the inner surfaces of the upper and lower molds of the forming mold. Next, the upper and lower molds are clamped together, and a foamed urethane resin raw material is injected into the first cavity formed by the inner surfaces of the upper and lower molds to perform foam molding. At this time, the upper mold temperature for forming the second skin layer 22 is preferably between 40°C and 60°C. A wax-based release agent is preferably used, but its type is not limited.

[0123] When forming the plurality of protrusions 15 on the surface of the first skin layer 12 of the first sound absorbing layer 10 or the second skin layer 22 of the second sound absorbing layer 20 , a mold having a plurality of recesses formed on its inner surface is used as the upper mold.

[0124] <Effects of the sound-absorbing cover>

[0125] The effects of the sound absorbing cover 1 of this embodiment will be described. In the sound absorbing cover 1 of the present invention, the first sound absorbing layer 10 and the second sound absorbing layer 20 are stacked such that the first skin layer 12 of the first sound absorbing layer 10 faces the second skin layer 22 of the second sound absorbing layer 20. An air layer 30 is provided between the facing surfaces of the first skin layer 12 of the first sound absorbing layer 10 and the second skin layer 22 of the second sound absorbing layer 20. Here, a configuration in which the first sound absorbing layer 10 and the second sound absorbing layer 20 do not have the first skin layer 12 and the second skin layer 22 on their non-facing surfaces will be described.

[0126] When the first sound-absorbing layer 10 is positioned on the noise source side, the sound generated by the noise source first diffuses within the first foam layer 11 and is converted into heat energy. The sound then transmits through the first foam layer 11 and is released via the first skin layer 12. In this case, the first skin layer 12 and the air layer 30 form a first membrane vibration-type sound-absorbing structure. The numerous fine cells of the first foam layer 11 are sealed by the first skin layer 12. The rigidity of each cell membrane of the first skin layer 12 is low, thus reducing the natural vibration frequency and effectively absorbing low-frequency sound.

[0127] Furthermore, sound transmitted through the air layer 30 is released via the second skin layer 22 of the second sound-absorbing layer 20. The numerous tiny cells of the second foam layer 21 are sealed by the second skin layer 22. The cell membranes of the second skin layer 22 and the air within the cells form a second membrane vibration-type sound-absorbing structure. Similarly, due to the low rigidity of each cell membrane, the natural vibration is set to be low, effectively absorbing low-frequency sound. Furthermore, sound transmitted through the second skin layer 22 diffuses within the second foam layer 21 and is converted into heat energy.

[0128] Since the first skin layer 12 and the second skin layer 22 have different rigidities, the natural vibration frequency of the first membrane vibration type sound absorbing structure and the natural vibration frequency of the second membrane vibration type sound absorbing structure are in different ranges, thereby absorbing a wider range of low-frequency sounds.

[0129] Furthermore, by making the rigidity of the first skin layer 12 of the first sound absorbing layer 10 disposed on the noise source side smaller than the rigidity of the second skin layer 22 of the second sound absorbing layer 20 disposed on the non-noise source side, it is possible to absorb sounds starting from the first skin layer 12 toward the second skin layer 22 with lower frequencies.

[0130] In particular, by setting the ASKER C hardness of the first skin layer 12 of the first sound-absorbing layer 10 within the range of 5 to 40 degrees and the ASKER C hardness of the second skin layer of the second sound-absorbing layer 20 within the range of 40 to 95 degrees, respectively, based on the above-mentioned measurement method, it is possible to effectively absorb noise in the low-frequency band of 630 to 1000 Hz.

[0131] Furthermore, when the first sound absorbing layer 10 and the second sound absorbing layer 20 include the first skin layer 12 and the second skin layer 22 on the non-opposing surfaces of the first sound absorbing layer 10 and the second sound absorbing layer 20, respectively, the membrane vibration type sound absorbing structure formed by the first skin layer 12 on the non-opposing surface of the first sound absorbing layer 10 and the membrane vibration type sound absorbing structure formed by the second skin layer 22 on the non-opposing surface of the second sound absorbing layer 20 can achieve the same low-frequency sound absorption effect as described above.

[0132] <Evaluation Results of Sound-Absorbing Covers>

[0133] The effects of the present invention will be described with reference to examples.

[0134] (Example 1)

[0135] A polyether polyol (functional group number 3, molecular weight 6000) for soft polyurethane is mixed with a crosslinking agent, water as a foaming agent, a catalyst, and a foam stabilizer to prepare 60 parts by weight of a polyol raw material. This is then mixed with 40 parts by weight of a polyisocyanate raw material to form a foamed urethane resin raw material. Next, a wax-based release agent is applied to the inner surfaces of the upper and lower molds of a forming mold. The upper and lower molds are then closed together. While the upper and lower molds are maintained at 50°C, the foamed urethane resin raw material is injected into the mold cavity and foamed to form a first sound-absorbing layer 10a having a first foamed layer 11a and a first skin layer 12a. After foaming, the molds are removed to produce a rectangular plate-shaped sample measuring 500 mm in length, 600 mm in width, and 5 mm in thickness. After demolding, the sample is needle-punched to adjust the airflow resistance. Furthermore, the upper mold is provided with a predetermined convex portion, and the first sound-absorbing layer 10 is provided with a predetermined concave engagement portion.

[0136] The density of the first foamed layer 11a of this sample is 0.14 g / cm 3 , ASKER C hardness is 22 degrees, ventilation resistance is 378000Ns / m 4 In addition, the ventilation resistance of the surface layer side including the first skin layer 12a is 505000Ns / m 4 .

[0137] Next, after applying a wax-based release agent to the inner surfaces of the upper and lower molds of the forming mold, the upper and lower molds were clamped together. While the upper and lower molds were maintained at 50°C, a foamable urethane resin raw material was injected into the mold cavity of the forming mold for foaming, thereby forming a second sound-absorbing layer 20a having a second foamed layer 21a and a second skin layer 22a. For the second sound-absorbing layer, a polyol raw material was prepared by mixing a polyether polyol (functional group number 3, molecular weight 6000) for soft polyurethane, a crosslinking agent, water as a foaming agent, a catalyst, and a foam stabilizer. This was then mixed with 51 parts by weight of the polyol raw material and 49 parts by weight of the polyisocyanate raw material to form the foamable urethane resin raw material. To increase the hardness compared to the first sound-absorbing layer, a polyol raw material was used, a mixture of the polyether polyol (functional group number 3, molecular weight 6000) used in the first sound-absorbing layer and a lower molecular weight polyether polyol (functional group number 2, molecular weight 400) at a ratio of 70:30 parts by weight. After molding, the molds were removed to produce rectangular plate-shaped samples measuring 500 mm in length, 600 mm in width, and 5 mm in thickness. After demolding, the samples were needle-punched to adjust the airflow resistance. Furthermore, a predetermined recess was provided in the lower mold, and a predetermined convex engaging portion was formed in the second sound-absorbing layer 20.

[0138] Furthermore, the hardness of the second sound-absorbing layer can be adjusted by adjusting the mixing ratio of the polyether polyol and the low-molecular-weight polyether polyol. Furthermore, if the urethane foam moldability deteriorates by mixing the low-molecular-weight polyether polyol, the amount of crosslinking agent added can be adjusted.

[0139] The density of the second foamed layer 21a of this sample is 0.12 g / cm 3 , ASKER C hardness is 76 degrees, ventilation resistance is 153000Ns / m 4 In addition, the ventilation resistance of the surface layer side including the second skin layer 22a is 584000Ns / m 4 .

[0140] Next, the concave engaging portion of the first sound absorbing layer 10 is engaged with the convex engaging portion of the second sound absorbing layer 20. As in the first embodiment, the first sound absorbing layer 10 is positioned below the second sound absorbing layer 20. A 0.1 mm gap is formed between the facing surfaces of the first skin layer 12 and the second skin layer 22 to form an air layer 30.

[0141] (Example 2)

[0142] The first sound absorbing layer 10a and the second sound absorbing layer 20a were formed by the same method as in Example 1, and the second sound absorbing layer 20 was disposed below the first sound absorbing layer 10. That is, the first sound absorbing layer 10 and the second sound absorbing layer 20 in the first embodiment were disposed in reverse.

[0143] (Example 3)

[0144] The first sound absorbing layer 10b and the second sound absorbing layer 20b were formed using the same method as in Example 1, except for the amount of the foamed urethane resin raw material. The first sound absorbing layer 10b was positioned below the second sound absorbing layer 20b, and a 0.1 mm gap was formed between the opposing surfaces of the first skin layer 12b and the second skin layer 22b to serve as the air layer 30. Specifically, the first sound absorbing layer 10b was formed using the same foamed urethane resin raw material as that used in the first sound absorbing layer 10a of Example 1. Using the foamed urethane resin raw material used in Example 1 as the reference amount, the foamed urethane resin raw material was added in an amount 1.14 times the reference amount. Furthermore, the second sound absorbing layer 20b was formed using the foamed urethane resin raw material used in the second sound absorbing layer 20a of Example 1 as the reference amount.

[0145] The density of the first foamed layer 11b of this sample is 0.16 g / cm 3 , ASKER C hardness is 38 degrees, ventilation resistance is 639794Ns / m4 In addition, the ventilation resistance of the surface layer side including the first skin layer 12b is 130850Ns / m 4 In addition, the density of the second foaming layer 21b is 0.1g / cm 3 , ASKER C hardness is 59 degrees, ventilation resistance is 103000Ns / m 4 In addition, the ventilation resistance of the surface layer side including the second skin layer 22b is 379148Ns / m 4 .

[0146] (Example 4)

[0147] The first sound absorbing layer 10b and the second sound absorbing layer 20b are formed by the same method as in Example 3, and the second sound absorbing layer 20b is arranged below the first sound absorbing layer 10b. In other words, the first sound absorbing layer 10b and the second sound absorbing layer 20b of the third embodiment are arranged in reverse.

[0148] (Example 5)

[0149] The first sound absorbing layer 10c and the second sound absorbing layer 20c were formed using the same method as in Example 1, except for the amount and mix ratio of the foamed urethane resin raw material. The first sound absorbing layer 10c was positioned below the second sound absorbing layer 20c, and a 0.1 mm gap was formed between the opposing surfaces of the first skin layer 12c and the second skin layer 22c to serve as the air layer 30. Specifically, the first sound absorbing layer 10c was formed using the same foamed urethane resin raw material as that used in the first sound absorbing layer 10a of Example 1. Using the foamed urethane resin raw material used in the first sound absorbing layer of Example 1 as the reference amount, the foamed urethane resin raw material was added in an amount 0.85 times the reference amount. Furthermore, the second sound absorbing layer 20c was formed using 54 parts by weight of the polyol raw material and 46 parts by weight of the polyisocyanate raw material.

[0150] The density of the first foamed layer 11c of this sample is 0.12 g / cm 3 , ASKER C hardness is 23 degrees, ventilation resistance is 201098Ns / m 4 In addition, the ventilation resistance of the surface layer side including the first skin layer 12c is 438441Ns / m 4 In addition, the density of the second foaming layer 21c is 0.12g / cm 3 , ASKER C hardness is 63 degrees, ventilation resistance is 148029Ns / m 4 In addition, the ventilation resistance of the surface layer side including the second skin layer 22c is 713111Ns / m 4 .

[0151] (Example 6)

[0152] The first sound absorbing layer 10c and the second sound absorbing layer 20c were formed by the same method as in Example 5, and the second sound absorbing layer 20c was arranged below the first sound absorbing layer 10c. In other words, the first sound absorbing layer 10c and the second sound absorbing layer 20c in Example 5 were arranged in reverse.

[0153] (Example 7)

[0154] A first sound absorbing layer 10d and a second sound absorbing layer 20d were formed using the same method as in Example 1, except for the mixing ratio of the polyol raw material and the polyisocyanate raw material and the post-processing method. The first sound absorbing layer 10d was positioned below the second sound absorbing layer 20c, and a 0.1 mm gap was formed between the opposing surfaces of the first skin layer 12d and the second skin layer 22d to serve as the air layer 30. Specifically, the first sound absorbing layer 10d was formed using 63 parts by weight of the polyol raw material and 37 parts by weight of the polyisocyanate raw material. Furthermore, the second sound absorbing layer 20d was formed using the same foamed urethane resin raw material as that used for the second sound absorbing layer 20a in Example 1, and then needle punched to adjust the air flow rate.

[0155] The density of the first foamed layer 11d of this sample is 0.14 g / cm 3 , ASKER C hardness is 21 degrees, ventilation resistance is 281978Ns / m 4 In addition, the ventilation resistance of the surface layer side including the first skin layer 12d is 456171Ns / m 4 In addition, the density of the second foam layer 21d is 0.12g / cm 3 , ASKER C hardness is 67 degrees, ventilation resistance is 715612Ns / m 4 In addition, the ventilation resistance of the surface layer side including the second skin layer 22d is 504229Ns / m 4 .

[0156] (Example 8)

[0157] The first sound absorbing layer 10d and the second sound absorbing layer 20d were formed by the same method as in Example 7, and the second sound absorbing layer 20d was arranged below the first sound absorbing layer 10d. In other words, the first sound absorbing layer 10 and the second sound absorbing layer 20 in Example 7 were arranged in reverse.

[0158] (Comparative Example 1)

[0159] The first sound absorbing layer 10a and the second sound absorbing layer 20a were formed by the same method as in Example 1, and adhesive was applied to the entire surfaces of the first skin layer 12a and the second skin layer 22a to bond them together.

[0160] (Evaluation method)

[0161] The sound absorption coefficients of the samples of Examples 1 to 8 and Comparative Example 1 were measured according to the reverberation chamber method for measuring sound absorption coefficient in accordance with JIS A 1409. The surface opposite to the sound source was in contact with a rigid bottom plate during measurement.

[0162] In Examples 1, 3, 5, and 7, the first sound absorbing layer 10 is disposed on the sound source side, and in Examples 2, 4, 6, and 8, the second sound absorbing layer 20 is disposed on the sound source side. In Comparative Example 1, the first sound absorbing layer 10 is disposed on the sound source side.

[0163] like Figure 9 As shown in FIG. 1 , it can be confirmed that the sound absorption rate of Examples 1, 3, 5, and 7 is higher than that of Comparative Example 1 in the low frequency band of 800 to 1000 Hz. Figure 10 As shown, Examples 2, 4, 6, and 8 demonstrate higher sound absorption rates in the low-frequency band of 800 to 1000 Hz compared to Comparative Example 1. It is speculated that the dual-membrane vibration-type sound-absorbing structure described above can absorb a wider range of low-frequency noise. On the other hand, in Comparative Example 1, the low-frequency band of the membrane-vibration-type sound-absorbing structure is narrowed by forming a single, relatively rigid skin layer, integrating the first and second skin layers 12a and 22a. Furthermore, it is speculated that the pore membranes clogged with the adhesive increase the airflow resistance of the first and second skin layers 12a and 22a, reducing air permeability. This makes it difficult for noise to reach the second foamed layer 21a of the second sound-absorbing layer 20a, located farther from the sound source (the rigid base plate side). This reduces the proportion of high-frequency components absorbed by the porous sound-absorbing structure, resulting in a lower high-frequency sound absorption rate. Furthermore, Example 3 exhibits lower sound absorption rates in the low-frequency band compared to Examples 1, 5, and 7. This is believed to be because, in Example 3, the density, hardness, and airflow resistance of the first foam layer of the first sound-absorbing layer are higher than those of the other examples. Consequently, the energy of sound reaching the interface between the first skin layer and the second skin layer is reduced, and the sound absorption effect of the membrane-vibrating sound-absorbing structure cannot be fully exerted.

[0164] In addition, if Figure 10As shown, Examples 2, 4, 6, and 8 were found to have higher sound absorption rates in the low-frequency range of 800 to 1000 Hz compared to Comparative Example 1. Furthermore, Examples 2, 4, and 6 were found to have lower sound absorption rates in the low-frequency range of 630 to 1000 Hz compared to Examples 1, 3, and 5, respectively. This suggests that placing the first sound absorbing layer 10, which has a second skin layer 22 with greater rigidity (Asker C hardness) than the first skin layer 12, on the sound source side is effective in terms of sound absorption. This is believed to be because, as a sound absorption principle, a thicker layer from the skin layer on the sound source side to the rigid base plate shifts the sound absorption rate toward lower frequencies. However, placing the second sound absorbing layer (second skin layer), which has relatively greater rigidity, on the sound source side shifts the peak sound absorption rate of the second skin layer on the sound source side toward lower frequencies, thereby increasing the sound absorption rate around 630 Hz. However, no similar effect was observed in Examples 7 and 8. The reason for this is believed to be that the air permeability resistance of the second foam layer is higher than that of the first foam layer. Therefore, in the eighth embodiment, the energy of the sound reaching the interface between the first skin layer and the second skin layer is reduced, and the sound absorption effect of the membrane vibration type sound absorption structure cannot be fully exerted.

[0165] However, since the positional relationship of the first skin layer and the second skin layer, which are arranged to face each other with the air layer interposed therebetween, with respect to the rigid bottom plate remains almost unchanged, this effect remains unchanged, and the overall sound absorbing performance remains high compared to Comparative Example 1.

[0166] Furthermore, it was confirmed that in Examples 1, 2, 3, 5, 7, and 8, the first foam layer 11 of the first sound-absorbing layer 10 and the second foam layer 21 of the second sound-absorbing layer 20 exhibited noise absorption performance at mid- and high-frequency frequencies exceeding 1000 Hz. Furthermore, compared with Comparative Example 1, the sound absorption coefficient was higher over a wide frequency band of 630 to 5000 Hz.

[0167] Description of Reference Numerals

[0168] 1, 1a, 1b, 1c, 1d: sound-absorbing cover; 10: first sound-absorbing layer; 11: first foaming layer; 12: first surface layer; 13: first engaging recess; 14: second engaging recess; 15: protrusion; 16: first recess; 20: second sound-absorbing layer; 21: second foaming layer; 22: second surface layer; 23: first engaging protrusion; 24: second engaging protrusion; 25: second recess; 26: third recess; 30: air layer; 40: first area; 41: second area; 50: third area; 51: fourth area.

Claims

1. A sound-absorbing enclosure (1, 1a, 1b, 1c, 1d), wherein: The sound absorbing cover (1, 1a, 1b, 1c, 1d) comprises: A first sound absorbing layer (10) comprising a first foaming layer (11) and a first skin layer (12) formed integrally with the first foaming layer (11); as well as The second sound absorbing layer (20) comprises a second foaming layer (21) and a second skin layer (22) integrally formed during the foaming of the second foaming layer (21). The first skin layer (12) of the first sound absorbing layer (10) has a rigidity different from the rigidity of the second skin layer (22) of the second sound absorbing layer (20), The first sound absorbing layer (10) and the second sound absorbing layer (20) are stacked in a state where the first skin layer (12) and the second skin layer (22) are facing each other. An air layer (30) is provided between the opposing surfaces of the first surface layer (12) of the first sound absorbing layer (10) and the second surface layer (22) of the second sound absorbing layer (20). The second sound absorbing layer (20) is arranged on the noise source side. The rigidity of the first skin layer (12) of the first sound absorbing layer (10) is smaller than the rigidity of the second skin layer (22) of the second sound absorbing layer (20).

2. The sound absorbing cover (1, 1a, 1b, 1c, 1d) according to claim 1, wherein: The hardness of the first skin layer (12) of the first sound-absorbing layer (10) is ASKER C hardness 5 to 40 degrees, The hardness of the second skin layer (22) of the second sound-absorbing layer (20) is 40 to 95 degrees in ASKER C hardness.

3. The sound absorbing cover (1, 1a, 1b, 1c, 1d) according to claim 1, wherein: The hardness of the first skin layer (12) of the first sound-absorbing layer (10) is ASKER C hardness of 10 to 30 degrees, The hardness of the second skin layer (22) of the second sound-absorbing layer (20) is ASKER C hardness of 60 to 90 degrees.

4. The sound absorbing cover (1, 1a, 1b, 1c, 1d) according to any one of claims 1 to 3, wherein: The density of the first foaming layer (11) of the first sound-absorbing layer (10) is 0.06 to 0.2 g / cm 3 , The density of the second foaming layer (21) of the second sound-absorbing layer (20) is 0.06 to 0.2 g / cm 3 .

5. The sound absorbing cover (1, 1a, 1b, 1c, 1d) according to any one of claims 1 to 3, wherein: The density of the first foaming layer (11) of the first sound-absorbing layer (10) is 0.10 to 0.16 g / cm 3 , The density of the second foaming layer (21) of the second sound-absorbing layer (20) is 0.10 to 0.16 g / cm 3 .

6. The sound absorbing cover (1, 1a, 1b, 1c, 1d) according to any one of claims 1 to 3, wherein: The air permeability resistance of the first sound-absorbing layer (10) is 100,000 to 1,000,000 Ns / m 4 , The air permeability resistance of the second sound absorbing layer (20) is 100,000 to 1,000,000 Ns / m 4 .

7. The sound absorbing cover (1) according to any one of claims 1 to 3, wherein: The first sound absorbing layer (10) comprises: a first region (40) in which the first skin layer (12) is formed; a second region (41) surrounding the first region (40) and arranged on the second sound absorbing layer (20) side relative to the first region (40); and a plurality of first engaging recesses (13) opening toward the second sound absorbing layer (20) in the second region (41) and arranged at predetermined intervals in the circumferential direction of the second region (41). The second sound absorbing layer (20) includes a plurality of first engaging protrusions (23) engaging with the plurality of first engaging recesses (13) of the first sound absorbing layer (10). The air layer (30) is a gap formed between the opposing surfaces of the first skin layer (12) of the first sound absorbing layer (10) and the second skin layer (22) of the second sound absorbing layer (20) in a state where the plurality of the first engaging recesses (13) of the first sound absorbing layer (10) and the plurality of the first engaging protrusions (23) of the second sound absorbing layer (20) are respectively engaged.

8. The sound absorbing cover (1a) according to any one of claims 1 to 3, wherein: The second sound absorbing layer (20) comprises: a third region (50) in which the second skin layer (22) is formed; a fourth region (51) surrounding the third region (50) and arranged on the first sound absorbing layer (10) side relative to the third region (50); and a plurality of second engaging protrusions (24) projecting toward the first sound absorbing layer (10) in the fourth region (51) and arranged at predetermined intervals in a circumferential direction surrounding the third region (50). The first sound absorbing layer (10) has a plurality of second engaging recesses (14) engaging with the plurality of second engaging protrusions (24) of the second sound absorbing layer (20). The air layer (30) is a gap formed between the opposing surfaces of the first skin layer (12) of the first sound absorbing layer (10) and the second skin layer (22) of the second sound absorbing layer (20) in a state where the plurality of the second engaging recesses (14) of the first sound absorbing layer (10) and the plurality of the second engaging protrusions (24) of the second sound absorbing layer (20) are engaged.

9. The sound absorbing cover (1c) according to any one of claims 1 to 3, wherein: The first sound absorbing layer (10) includes a first recess (16) opening toward the second sound absorbing layer (20). The first skin layer (12) is formed on the bottom surface of the first recess (16), The second sound absorbing layer (20) has a second recess (25) opening toward the first sound absorbing layer (10). The second skin layer (22) is formed on the bottom surface of the second recess (25). The first sound absorbing layer (10) is formed into an outer diameter shape corresponding to the inner shape of the second recess (25) of the second sound absorbing layer (20), The air layer (30) is a gap formed between the opposing surfaces of the first surface layer (12) of the first sound absorbing layer (10) and the second surface layer (22) of the second sound absorbing layer (20) when the first sound absorbing layer (10) is accommodated in the second recess (25) of the second sound absorbing layer (20).

10. The sound absorbing cover (1d) according to any one of claims 1 to 3, wherein: The second sound absorbing layer (20) comprises a second recess (25) opening toward the first sound absorbing layer (10), and a third recess (26) opening toward the first sound absorbing layer (10) on the bottom surface of the second recess (25), wherein the second skin layer (22) is formed on the bottom surface of the third recess (26). The first sound absorbing layer (10) is formed into an outer diameter shape corresponding to the inner shape of the second recess (25) of the second sound absorbing layer (20), The air layer (30) is a gap formed between the opposing surfaces of the first surface layer (12) of the first sound absorbing layer (10) and the second surface layer (22) of the second sound absorbing layer (20) when the first sound absorbing layer (10) is accommodated in the second recess (25) of the second sound absorbing layer (20).

11. The sound absorbing cover (1, 1a, 1b, 1c, 1d) according to any one of claims 1 to 3, wherein: At least one of the first skin layer (12) of the first sound absorbing layer (10) and the second skin layer (22) of the second sound absorbing layer (20) has a plurality of protrusions (15) protruding toward the other side of the opposed arrangement.

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