Sound absorber and vehicle member

Abstract

To provide a novel sound absorber capable of developing superior sound absorption characteristics in a wide frequency band even when thin.SOLUTION: The present invention relates to a sound absorber that comprises a porous layer 1 formed of an impermeable material and a porous layer 2 formed of a permeable material. The porous layer 1 comprises a base part having a plurality of pores and a hollow neck part extending at least some of pores into the porous layer 2, and two or more kinds of Helmholtz resonance box structures which resonate to sound made incident from the pores and differ in resonance frequency are formed when the porous layer 2 side is arranged facing an object member.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a sound-absorbing material and a vehicle member.

Background Art

[0002] As a soundproofing material for the purpose of preventing noise in the engine room of an automobile from propagating into the passenger compartment, etc., a soundproofing material is known in which a first breathable sound-absorbing layer, an airtight resin film layer, and a second breathable sound-absorbing layer are adhered in this order from the passenger compartment side (see, for example, Patent Document 1). In this document, a mixture of urethane foam and fibers is used for the first and second breathable sound-absorbing layers, and a laminate of a plurality of resin films is used for the airtight resin film layer.

[0003] Also, as a single-layer felt for dealing with sounds in a wide frequency band, an inclined air flow resistance sound-absorbing felt having a high air flow resistance value portion and a low air flow resistance value portion between layers is known (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the prior art, there is still room for improvement with respect to exhibiting excellent sound absorption characteristics in a wide frequency band even if it is thin. Such an expectation for improvement is particularly remarkable in sound-absorbing materials for vehicles such as automobiles.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a new sound-absorbing material capable of exhibiting excellent sound-absorbing characteristics in a wide frequency band even if it is thin. Another object of the present invention is to provide a vehicle member including the sound-absorbing material.

Means for Solving the Problems

[0007] One aspect of the present invention includes a porous layer composed of a non-breathable material and a porous layer composed of a breathable material. The porous layer includes a base portion having a plurality of holes and a hollow neck portion extending from at least some of the holes into the porous layer. When the porous layer side is arranged facing the target member, two or more Helmholtz resonance box structures having different resonance frequencies that resonate with the sound incident from the holes are formed, thereby providing a sound-absorbing material. Such a sound-absorbing material has an unprecedented structure and can exhibit excellent sound-absorbing characteristics in a wide frequency band even if it is thin.

[0008] In one embodiment, the Helmholtz resonance box structure may include a Helmholtz resonance box structure having a resonance frequency of less than 2000 Hz and a Helmholtz resonance box structure having a resonance frequency of 2000 Hz or more.

[0009] In one embodiment, the Helmholtz resonance box structure may include a Helmholtz resonance box structure having a resonance frequency of less than 2000 Hz, a Helmholtz resonance box structure having a resonance frequency of 2000 to 3000 Hz, and a Helmholtz resonance box structure having a resonance frequency of more than 3000 Hz.

[0010] In one embodiment, adjacent Helmholtz resonance box structures may have different resonance frequencies.

[0011] In one embodiment, the sound-absorbing material may include a porous layer, a porous layer, and a backing layer composed of a non-breathable material in this order.

[0012] In one embodiment, the aperture ratio of the base portion may be 1 to 20%.

[0013] In one aspect, the thickness of the sound-absorbing material may be 15 mm or less.

[0014] In one aspect, the porous layer may contain rubber and the porous layer may contain a non-woven fabric.

[0015] In one aspect, the porous layer may contain a composite material including rubber and a non-woven fabric.

[0016] In one aspect, the air permeability resistance of the porous layer may be 1 - 4 kPa·sec / m.

[0017] One aspect of the present invention provides a vehicle member including the above-described sound-absorbing material.

Effects of the Invention

[0018] According to the present invention, a new sound-absorbing material capable of exhibiting excellent sound-absorbing characteristics in a wide frequency band even with a thin thickness can be provided. Further, according to the present invention, a vehicle member including the sound-absorbing material can be provided.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0020] Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In this specification, the term "step" includes not only an independent step but also a step in which the intended action of the step is achieved even if it cannot be clearly distinguished from other steps. In this specification, the term "layer" includes not only a structure formed over the entire surface when observed as a plan view but also a structure formed partially.

[0021] In this specification, a numerical range indicated using "~" indicates a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively. In a numerical range described stepwise in this specification, the upper limit value or the lower limit value of a numerical range at a certain step may be replaced with the upper limit value or the lower limit value of a numerical range at another step. Also, in the numerical range described in this specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples.

[0022] When referring to the amount of each component in a composition in this specification, when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified, it means the total amount of the plurality of substances present in the composition.

[0023] <Sound-absorbing material> FIG. 1 is a schematic cross-sectional view of a sound-absorbing material according to an embodiment. The sound-absorbing material 10 includes a porous layer 1 made of a non-venting material and a porous layer 2 made of a venting material. The porous layer 1 includes a (planar) base portion 1a having a plurality of holes h and a hollow neck portion 1b extending from at least a part of the holes h into the porous layer 2. The porous layer 1 may include a hollow neck portion 1b extending from all of the holes h into the porous layer 2. The porous layer 2 has holes that communicate with the holes h and have the same depth as the extension length of the neck portion 1b into the porous layer 2. The space inside the holes h may be a cavity or may be filled with a porous material described later.

[0024] The sound-absorbing material 10 can be used by arranging the porous layer 1 side as the sound incident side and the porous layer 2 side as the side of another member (target member) to be sound-absorbed. The sound-absorbing material 10 and the target member may or may not be in contact with each other. The target member may be made of an airtight material, specifically, automotive members, particularly body panels such as wheelhouse panels, door panels, floor panels, and cover parts such as undercovers and wheelhouse covers. When the sound-absorbing material 10 has a backing layer described later, the target member may be made of a breathable material. From the viewpoint of improving the sound absorption characteristics of other members, the sound-absorbing material 10 can also be referred to as a sound absorption characteristic improving member. Further, the structure including the sound-absorbing material 10 and the target member can also be referred to as a sound absorption structure.

[0025] In the sound-absorbing material 10, when the porous layer 2 side is arranged facing the target member, a Helmholtz resonance box structure that resonates with the sound incident from the hole h is formed. The hollow neck portion 1b extending in the porous layer 2 can reduce the resonance frequency of the hole h, making it easier to obtain better sound absorption performance at lower frequencies. The sound-absorbing material 10 has two or more types of Helmholtz resonance box structures with different resonance frequencies. The sound (acoustic energy) incident from the porous layer 1 side is considered to resonate in the sound-absorbing material 10 and dissipate as heat energy. As a result, sound attenuation is observed.

[0026] Figs. 2 to 5 are schematic cross-sectional views of sound-absorbing materials according to other embodiments. The sound-absorbing materials shown in Figs. 2 to 4 are provided with a backing layer made of an airtight material on the entire surface opposite to the sound incident side. In this case, a Helmholtz resonance box structure can be formed independently without arranging the target member as described above.

[0027] As shown in Fig. 2, the sound-absorbing material 11 includes a porous layer 1, a porous layer 2, and a backing layer 3 made of an airtight material in this order. As shown in Fig. 3, the sound-absorbing material 12 includes a porous layer 1, a porous layer 2, and a backsheet layer 3 made of an airtight material in this order. In the figure, the porous layer 2 has holes (through-holes) that communicate with the holes h and have the same depth as the thickness of the porous layer 2. As shown in Fig. 4, the sound-absorbing material 13 includes a porous layer 1, a porous layer 2, and a backsheet layer 3 made of an airtight material in this order. In the figure, no holes are formed in the porous layer 2, and the hollow neck portion 1b is buried in the porous layer 2. As shown in Fig. 5, the sound-absorbing material 14 includes a porous layer 1, a porous layer 2, and a backsheet layer 3 made of an airtight material in this order. In the figure, the porous layer 2 has holes (through-holes) that communicate with the holes h and have the same depth as the thickness of the porous layer 2, and the backsheet layer 3 also has holes that communicate with those holes.

[0028] From the viewpoint of sound absorption performance, the thickness of the sound-absorbing material can be 5 mm or more, and may be 8 mm or more. Also, since it has excellent sound absorption characteristics even when thin, it can be 30 mm or less, may be 25 mm or less, may be 20 mm or less, may be 15 mm or less, may be 13 mm or less, or may be 12 mm or less.

[0029] The side surface of the sound-absorbing material may be in a state where the end surfaces of the porous layer and the porous layer are exposed, or the end surface of the porous layer may be covered with a material (coating material) for forming the porous layer. By forming this coating material not only to cover the end surface of the porous layer but also in excess, it is possible to perform hole processing for attaching the sound-absorbing material to other members on the excess portion.

[0030] (Porous layer) The porous layer is made of an airtight material. Here, the fact that the porous layer is an airtight layer, that is, an airtight layer, means a layer with few continuous pores and high air flow resistance. Specifically, the airtight layer may be a layer in which, when observing the cross section of the layer, the continuous pores leading from the sound wave incident side to the side opposite to the sound wave incident side are 10% or less in area.

[0031] The specific method for confirming continuous pores is as follows. That is, the porous layer to be observed is cast using an embedding epoxy resin (product names Epomount 27-771, 27-772, manufactured by Refine Tech Co., Ltd.), and using a diamond cutter, cutting is performed such that the diamond cutter is perpendicular to the surface of the porous layer and passes through the center of the pores on the surface of the porous layer. The cut cross-section is polished using a liquid compound (product name L120P, manufactured by Sankyo Corporation), and cross-section observation is performed using a digital microscope (product name VHX-100F, manufactured by Keyence Corporation). From the cross-section observation photograph, the area S1 of the void portion that continuously passes from the sound wave incident side to the side opposite the sound wave incident side of the porous layer filled with the embedding epoxy resin, and the area S2 of the cross-section of the porous layer are obtained, and the area ratio of the continuous pores is calculated from S1 / S2.

[0032] As the non-porous material constituting the porous layer, there is no limitation as long as it is a material with a high air permeability resistance confirmed as described above. For example, plastics, rubbers, metals, and composite materials thereof can be mentioned. As the base, examples include films made of these materials with a thickness of less than 200 μm, soft sheets with a thickness of 200 μm or more, and rigid plates with a thickness exceeding 1 mm (which can be referred to as porous films, porous sheets, porous plates, etc.). Regarding the neck portion, it may be formed using these materials, or it may be formed using tubes made of these materials. In addition, as the non-porous material constituting the porous layer, a composite material containing rubber or a composite of rubber and non-woven fabric can be mentioned. In the manufacturing process of the sound-absorbing material, the porous layer (base portion and neck portion) may contain a material in which the material forming the porous layer and the porous material are combined, for example, a composite material containing rubber and non-woven fabric. The porous layer may be composed of the composite material.

[0033] Examples of plastics include polyesters such as polyethylene terephthalate (PET), polyolefins such as polypropylene (PP), high-density polyethylene (HDPE), and low-density polyethylene (LDPE), ethylene-vinyl acetate copolymer resin (EVA), ABS, AES, ASA, and polyphenylene ether (PPE). Examples of the rubber include urethane rubber (PU), silicone rubber, natural rubber (NR), butyl rubber, styrene-butadiene rubber (SBR), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), ethylene-propylene-diene rubber (EPDM), fluororubber (FKM), etc. Examples of the metal include stainless steel, aluminum, copper, etc. Examples of the composite material include fiber-reinforced rubber (FRR), fiber-reinforced plastic (FRP), etc. From the viewpoint of workability when integrating with the porous layer as a molded product with a complex shape, the material for forming the porous layer is preferably rubber or plastic. From the viewpoint that a non-ventilated layer (the layer that becomes the porous layer) can be easily formed on the porous layer by coating and drying on the porous layer, rubbers such as natural rubber, acrylonitrile-butadiene rubber, styrene-butadiene rubber, chloroprene rubber, urethane rubber, and fluororubber that can be used in the form of latex are more preferable.

[0034] From the viewpoint of durability, the thickness of the base portion can be 50 μm or more, and may be 100 μm or more. From the viewpoints of weight reduction and thinning, etc., it can be 5 mm or less, and may be 2 mm or less.

[0035] The thickness of the base portion can be measured as follows. That is, the base portion to be observed is cast using an embedding epoxy resin, and cutting is performed using a diamond cutter so that the diamond cutter is perpendicular to the surface of the porous layer. The cut cross-section is polished using a liquid compound, and the cross-section is observed with a digital microscope. The thickness of the base portion is measured from the cross-sectional observation photograph.

[0036] From the viewpoint of allowing sound waves to sufficiently enter the sound-absorbing material, the porosity of the base portion can be 1% or more, and may be 2% or more. From the viewpoint of suitably generating Helmholtz resonance, it can be 20% or less, and may be 15% or less. The porosity can be calculated by dividing the area of the pores when the porous layer of the sound-absorbing material is viewed in the thickness direction by the area of the porous layer (base portion).

[0037] The shape of the holes in the base may be circular, elliptical, rectangular, polygonal, irregular, etc., and a shape suitable for adjusting the aperture ratio and construction convenience can be adopted. By adjusting the hole diameter, pitch, etc., the resonance frequency during sound absorption can be adjusted. From the perspective of workability, the shape of the holes is preferably circular.

[0038] The hole diameter (aperture diameter), that is, the inner diameter of the hollow neck portion, can be 0.5 mm or more from the perspective of obtaining an appropriate aperture ratio, and may be 2 mm or more. Also, from the perspective of suppressing the intrusion of foreign substances into the sound-absorbing material, it can be 10 mm or less, and may be 5 mm or less. The hole diameter can be measured as follows. That is, the base to be observed is cast using embedding epoxy resin, and cutting is performed using a diamond cutter so that the diamond cutter is perpendicular to the porous layer surface and passes through the center of the hole on the base surface. The cut cross-section is polished using a liquid compound, and the cross-section is observed with a digital microscope. The hole diameter is measured from the cross-section observation photo. The hole diameter is obtained as the average value of the measured values for 5 holes.

[0039] When the porous layer of the sound-absorbing material is viewed in the thickness direction, from the perspective of obtaining excellent sound-absorbing characteristics, the holes may be arranged in a lattice pattern, and may be arranged in a rhombic lattice pattern (oblique lattice pattern), hexagonal lattice pattern (triangular lattice pattern), square lattice pattern, rectangular lattice pattern, skewed lattice pattern, etc. The pitch of the holes can be 1 mm or more from the perspective of workability, and may be 5 mm or more. Also, from the perspective of improving the aperture ratio, it can be 30 mm or less, and may be 20 mm or less. The pitch of the holes refers to the center-to-center distance between adjacent holes, as shown by P in FIG. 6 described later. The pitch of the holes is obtained as the average value of the measured values for 5 holes.

[0040] From the perspective of further improving the sound absorption characteristics, the length of the neck portion can be 5% or more of the thickness of the porous layer, and may be 10% or more, 30% or more, or 50% or more. From the perspective of ensuring the gap between the back surface of the sound-absorbing material (the surface on the opposite side of the sound wave incident side) and the tip of the neck portion, the length of the neck portion can be 90% or less of the thickness of the porous layer, and may be 80% or less.

[0041] The length of the neck portion varies depending on the thickness of the porous layer and the like and is not particularly limited, but can be 1 mm or more, and may be 3 mm or more, or 5 mm or more. Similarly, the length of the neck portion can be 9 mm or less, and may be 8 mm or less.

[0042] The thickness of the neck portion, that is, the difference between the inner diameter and the outer diameter of the hollow structure, can be 50 μm or more, and may be 100 μm or more, from the perspective of making the neck portion rigid and obtaining better durability against vibration. The thickness of the neck portion can be 5 mm or less, and may be 2 mm or less, from the perspective of ensuring the volume of the porous layer and particularly improving the low-frequency sound absorption performance.

[0043] The length and thickness of the neck portion can be measured from a cross-sectional observation photograph by performing a cross-sectional observation in the same manner as the aforementioned base portion. The length and thickness of the neck portion are obtained as the average value of the measured values for 5 neck portions.

[0044] From the perspective of durability, the porous layer and the porous layer may be adhered or integrated. This makes it easier to prevent the porous layer and the porous layer from peeling off due to vibration or the like, or the neck portion from vibrating independently and breaking. The adhesion or integration of the two may be performed using an adhesive, or may be performed by impregnating at least a part of the material constituting the porous layer into the porous layer and drying it.

[0045] In the method using an adhesive, an adhesive layer can be provided between the porous layer and the porous layer. Examples of the adhesive layer include layers containing adhesive components such as vinyl acetate resin, polyolefin resin, ethylene-vinyl acetate copolymer resin, isobutene-maleic anhydride copolymer resin, acrylic copolymer resin, acrylic monomer, acrylic oligomer, styrene-butadiene rubber, vinyl chloride resin, chloroprene rubber, nitrile rubber, urethane resin, silylated urethane resin, epoxy resin, modified epoxy resin, polyethylene resin, ionomer resin, silicone resin, modified silicone resin, water glass, silicate, etc., or laminates (e.g., double-sided tape) having layers containing these adhesive components on both sides of a support composed of paper, cloth, resin film, metal tape, etc. The thickness of the adhesive is not particularly limited, but can be 0.01 to 500 μm, and may be 1 to 250 μm.

[0046] In the impregnation method, the porous layer (base portion and neck portion) can include, for example, a composite material containing rubber and non-woven fabric. The porous layer may, for example, be provided with a layer of the composite material (composite material layer) on the porous layer side, or may be the composite material layer. Examples of the advantages of using such a composite material for the porous layer include the following. · By adjusting the solid content concentration of the latex rubber solution to be impregnated, the rubber amount can be partially increased or decreased, and it is easy to control the structure of the non-ventilation layer / ventilation layer. · Since the non-ventilation layer / ventilation layer is firmly integrated, it has excellent durability. · The ventilation resistance of the ventilation layer can be controlled by the rubber amount, and it is easy to adjust the sound absorption performance and density. · A vibration damping effect can be imparted by the viscoelasticity of the rubber.

[0047] (porous layer) The porous layer is composed of a breathable material. The porous layer refers to a layer containing a breathable porous material, specifically, a layer with an air permeability resistance of 4 kPa·sec / m or less. From the perspective of easily maintaining the viscous loss of the air of the sound wave incident on the porous layer, the air permeability resistance of the porous layer can be 1 kPa·sec / m or more, and may be 2 kPa·sec / m or more. Also, from the perspective of easily making the sound wave incident on the porous layer, it can be 4 kPa·sec / m or less, and may be 3 kPa·sec / m or less. The specific method for confirming the air permeability resistance is as follows. That is, it can be measured with a breathability tester (KES-F8) manufactured by Kato Tech Co., Ltd., sample size: 50 mm × 50 mm to 100 mm × 100 mm (thickness: 1 mm or less), Φ40 mm (thickness: 1 mm to 50 mm). The porous layer may be obtained by mechanically removing the porous layer from the sound-absorbing material. Also, in the case of a three-dimensionally formed porous layer, it can be measured by deforming the curved surface into a plane.

[0048] As the breathable material constituting the porous layer, there is no limitation as long as it is a material with a low air permeability resistance confirmed as described above, and examples include non-woven fabrics, foamed foams, etc.

[0049] Examples of non-woven fabrics include non-woven fabrics composed of fibers such as glass, silica, rock wool, plastics (PET, PP, nylon, cellulose, natural fibers, or composites thereof). As non-woven fabrics, those capable of imparting shape containing a binder inside, those with an adjusted air permeability resistance containing inorganic particles, elastomers, rubber, etc. inside can also be used. Examples of foamed foams include urethane foam, polyethylene foam, melamine foam, rubber sponge, etc.

[0050] As the material of the porous layer, from the perspective of easily adjusting the air permeability resistance and easily imparting three-dimensional formability by compounding with rubber (rubber latex), resin, particle material, etc. separately from forming the porous layer, it is preferably a non-woven fabric. The porous layer can include a composite material containing a porous material and rubber. The composite of the porous material and rubber can be achieved by impregnating a material containing rubber into the porous material and then drying it. The composite of the porous material and rubber means, for example, that the surface of the material (fiber) constituting the nonwoven fabric is coated with rubber while maintaining the air permeability as the porous layer.

[0051] The average fiber diameter of the fibers constituting the nonwoven fabric is not particularly limited, but from the viewpoint of obtaining better sound absorption characteristics, it can be, for example, 1 to 30 μm, and may be 5 to 15 μm. The average fiber diameter is obtained by taking the average of the fiber diameters of individual fibers measured from a photograph taken at 1000 times magnification with an electron microscope. Specifically, the average fiber diameter is obtained by measuring the fiber diameters of a total of 100 fibers arbitrarily selected from 10 photographs and averaging them.

[0052] From the viewpoint of sound absorption performance especially at low frequencies, the thickness of the porous layer can be 5 mm or more, and may be 8 mm or more. Also, from the viewpoint of applications for automotive parts where a thin thickness is required, it can be 15 mm or less, and may be 12 mm or less.

[0053] When the porous layer has holes communicating with the holes of the porous layer, the depth of the holes can be equal to or greater than the extension length of the neck portion from the viewpoint that it is easy in terms of the manufacturing method to form a neck portion after drilling the holes, and it may be the same as the thickness of the porous layer (even if the porous layer has through holes). The porous layer may not have holes, and in that case, the neck portion may be buried in the porous layer. That is, the hollow portion of the neck portion may contain (be filled with) the material of the porous layer.

[0054] (Lining layer) The lining layer is composed of a non - breathable material. The lining layer can improve the durability, rigidity, etc. of the sound - absorbing material. The lining layer may be formed on the entire surface of the porous layer, and may have holes communicating with the holes of the porous layer and the porous layer. For the specific form of the lining layer, the form of the porous layer (especially the base) can be referred to.

[0055] Further, as the backing layer, an adhesive sheet or film for adhering to the sound absorption target, or a damping sheet or film for imparting damping properties can also be used.

[0056] From the viewpoints of improving durability, rigidity, etc., the thickness of the backing layer can be 50 μm or more, and may be 100 μm or more. From the viewpoint of applications for automotive parts where thinness is required, the thickness can be 5 mm or less, and may be 2 mm or less.

[0057] Thus, in addition to the porous layer and the porous medium layer, the sound absorption material can include other layers (such as sheets, films, etc.). These other layers can be attached via an adhesive layer or the like. As the layer that can be provided on the sound incident side, that is, the porous layer side, there can be mentioned a breathable layer (a layer having an air permeability resistance of 4 kPa·sec / m or less), or a non-breathable layer having holes at the same positions as the holes of the porous layer (a layer that does not prevent the incidence of sound). On the side opposite to the sound incident side, that is, the porous medium layer side, in addition to the above-mentioned backing layer, a breathable layer can be provided. Examples of the breathable layer include porous sound absorption materials (such as foamed foams, non-woven fabrics, felts, etc.), porous films, etc., for the purpose of improving sound absorption characteristics, covering holes, improving design properties, etc. Examples of the non-breathable layer having holes at the same positions as the holes of the porous layer include porous metal plates, porous plastic sheets, etc., for the purpose of surface protection on the sound incident side, improving durability, improving rigidity, improving mechanical strength, etc.

[0058] (Helmholtz resonance box structure) In the sound absorption material, when the porous medium layer side is arranged facing the target member, two or more types of Helmholtz resonance box structures having different resonance frequencies and resonating with the sound incident from the holes are formed. Thereby, the sound absorption material can exhibit high sound absorption characteristics in a wide range from the low frequency side to the high frequency side. The Helmholtz resonator box structure has components of a Helmholtz resonator, namely an opening (holes in the porous layer), a neck (the thickness of the porous layer, or the thickness of the porous layer and the length of the neck portion), and a body (the porous layer), and is a structure that theoretically functions as a Helmholtz resonator box.

[0059] From the perspective of broadening the sound absorption frequency range, the Helmholtz resonator box structure preferably includes a Helmholtz resonator box structure having a resonance frequency of less than 2000 Hz and a Helmholtz resonator box structure having a resonance frequency of 2000 Hz or more, and more preferably includes a Helmholtz resonator box structure having a resonance frequency of less than 2000 Hz, a Helmholtz resonator box structure having a resonance frequency of 2000 - 3000 Hz, and a Helmholtz resonator box structure having a resonance frequency of more than 3000 Hz. At this time, it is more preferable that adjacent Helmholtz resonator box structures have different resonance frequencies. That is, by having holes (holes with different sound absorption frequency ranges) that exhibit different resonance frequencies adjacent to each other, sound waves are more likely to diffract and enter each hole, making it easier to broaden the sound absorption frequency range.

[0060] Figure 6 is a diagram schematically showing the arrangement of holes in the sound absorption material. This figure shows a preferred arrangement of holes A - C that exhibit different resonance frequencies when the porous layer of the sound absorption material is viewed from the thickness direction. In Figure 6(a), holes A and C are arranged in a square lattice, and holes that exhibit different resonance frequencies are adjacent to each of holes A and C. In Figure 6(b), holes A - C are arranged in a triangular lattice (regular triangular lattice), and holes that exhibit different resonance frequencies are adjacent to each of holes A - C. For example, around hole A, the same number of holes B and C are adjacent, and holes A are not adjacent to each other.

[0061] Figure 7 is a diagram showing a method for calculating the resonance frequency of the Helmholtz resonator box structure. In this figure, the portions surrounded by dashed lines each indicate a Helmholtz resonator box unit. The resonance frequency of the Helmholtz resonator box structure that resonates with the sound incident from each hole can be adjusted from various dimensions of the sound absorption material according to this calculation method.

[0062] In FIG. 7, V is the volume of the porous layer when the porous layer is divided into Helmholtz resonance box units. When the holes are arranged in a lattice pattern with a certain period, V is calculated as the volume of a rectangular parallelepiped or cube obtained by multiplying the thickness T of the porous layer by a square or rectangle (see the dashed line portion in FIG. 6) starting from the centers of adjacent holes and passing through the midpoints between the holes. When there are multiple ways to draw a rectangle passing through the midpoints between the holes, draw them so that adjacent rectangles do not overlap and the area is maximized. Also, when the holes are arranged randomly at unspecified pitch intervals without a certain period, V is calculated as the volume of a prism obtained by multiplying the thickness T of the porous layer by a polygon with the midpoints between adjacent holes as vertices. In any case, when a neck portion extends within the porous layer, the volume V is the volume obtained by subtracting the volume of the neck portion. δ is the end correction. For example, when the shape of the hole is circular, δ can be calculated as 0.8 times the diameter of the hole. When the shape of the hole is not circular, δ can be calculated as 0.8 times the diameter of a perfect circle having the same area as the area of the hole.

[0063] <Method for manufacturing sound-absorbing material> The method for manufacturing the sound-absorbing material 10 shown in FIG. 1 will be described below, but the method for manufacturing the sound-absorbing material is not particularly limited.

[0064] (First manufacturing method) Prepare a latex rubber solution with a low solid content and a latex rubber solution with a high solid content. The solid content in the latex rubber solution with a low solid content can be 15 to 35% by mass, and the solid content in the latex rubber solution with a high solid content can be 40 to 70% by mass.

[0065] Each latex rubber solution can contain one or more of the rubbers exemplified above. Further, various additives generally used according to the purpose can be blended in each latex rubber solution. Examples of the additives include wetting agents or viscosity modifiers for adjusting the impregnation property into the nonwoven fabric, colorants (such as carbon black) for coloring, vulcanizing agents (such as sulfur or zinc oxide) for improving heat resistance and durability, vulcanization accelerators, antioxidants, inorganic fillers (such as talc or clay), heat-sensitive materials for improving the cohesiveness and preventing segregation during heat drying, stabilizers (such as surfactants or pH adjusters) for improving the stability of the solution, and the like.

[0066] The porous layer is impregnated with a latex rubber solution having a low solid content concentration. Examples of the impregnation method include a method of spraying the latex rubber solution onto the porous layer, a method of immersing the porous layer in the latex rubber solution, and the like. At this time, the amount of the latex rubber is adjusted so that the air permeability resistance of the porous layer does not exceed 4 kPa·sec / m. The nonwoven fabric coated with the latex rubber solution having a low solid content concentration is heated and dried to cause the latex rubber to agglomerate and cure. Thereby, a porous layer made of a composite material containing the nonwoven fabric and the rubber is formed.

[0067] For the nonwoven fabric in which the latex rubber has been agglomerated and cured, holes having a desired arrangement and depth are formed using a pointed member as needed. Examples of the pointed member include needle pins and punches. The shape of the pointed member (the shape of the tip) can be appropriately adjusted so that the formed holes have a desired shape. Further, in order to form a plurality of holes simultaneously, the pointed member may be a member in which a plurality of pointed protrusions are arranged on a plane.

[0068] A latex rubber solution having a high solid content concentration is applied to the porous layer in which the holes are formed. Examples of the application method include spray coating, dip coating, coating with a brush, roller coating, and the like. Thereby, the latex rubber solution having a high solid content concentration penetrates near the surface of the porous layer and near the inner wall surface of the holes. At this time, the application amount and the application method are adjusted so that the holes are not blocked and the latex rubber solution is not applied to the bottom of the holes.

[0069] A nonwoven fabric coated with a latex rubber solution having a high solid content is heated and dried to cause the latex rubber to agglomerate and cure. Due to this agglomeration and curing, the portion where the latex rubber with a high solid content exists becomes airtight. As a result, a sound-absorbing material 10 shown in FIG. 1 can be obtained, which includes a porous layer composed of an airtight material and a porous layer, and the porous layer includes a base portion having a plurality of holes and a hollow neck portion extending into the porous layer from at least a part of the holes.

[0070] The heating and drying can be performed, for example, at 60 to 100°C, but appropriate equipment and conditions should be set as appropriate according to the formulation of the latex rubber. For heating and drying, in addition to a hot press, an atmosphere furnace, a microwave heating device, etc. can be used. By performing a hot press using a mold or the like during heating and drying, a shape can be imparted to the nonwoven fabric.

[0071] Other layers such as the backing layer may be laminated together and integrally molded before the hot press, or may be separately molded and bonded to the sound-absorbing material.

[0072] (Second manufacturing method) Holes having a desired arrangement are formed in a plastic film, which is an airtight material, using a pointed member. A rubber tube, which is an airtight material and has the same inner diameter as the holes, is adhered to the holes using an adhesive. Examples of the adhesive include an agent that forms an adhesive layer between the porous layer and the porous layer. Holes having a desired arrangement and depth are formed in a nonwoven fabric, which is the porous layer, using a pointed member. The arrangement of the holes is made to coincide with the arrangement of the rubber tube. Also, the diameter of the holes is adjusted to be the same as the outer diameter of the rubber tube. The plastic film with the rubber tube prepared as described above is laminated so that the rubber tube fits into the holes of the nonwoven fabric, and the plastic film and the nonwoven fabric are adhered using an adhesive. As a result, a sound-absorbing material 10 shown in FIG. 1 can be obtained, which includes a porous layer composed of an airtight material and a porous layer, and the porous layer includes a base portion having a plurality of holes and a hollow neck portion extending into the porous layer from at least a part of the holes.

[0073] The sound-absorbing material thus obtained may be used in the form of a flat plate as a sound-absorbing sheet, or may be used in a three-dimensional shape as a three-dimensionally molded article. This sound-absorbing material in which the above-described characteristic Helmholtz resonance box structure is formed absorbs noise in a wide frequency range from low frequencies to high frequencies. Therefore, it can be suitably used as a sound-absorbing material for automotive components, etc., and can be particularly suitably used for applications such as fender liners or undercovers that require sound absorption of low-frequency road noise. The wide frequency range referred to here can be a range where the frequency is 500 to 6000 Hz, and the above sound-absorbing material has excellent sound-absorbing characteristics in the frequency range of 800 to 5000 Hz, particularly 1000 to 4000 Hz.

[0074] <Vehicle component> The vehicle component includes the above-described sound-absorbing material. Examples of the vehicle component include the following aspects. The vehicle component may be an automotive component. Exterior: A vehicle component that is a sound-absorbing member of a vehicle exterior material, a vehicle exterior material. Examples of the exterior include (vehicle) undercovers or under protectors, wheelhouse covers, soundproof covers, body panels, etc. Specifically, engine undercovers, floor undercovers, rear undercovers, transmission covers, fender liners / protectors or mudguards, wheelhouse panels, door panels, floor panels, etc. are included. Interior: A vehicle component that is a sound-absorbing member of a vehicle interior material, a vehicle interior material. Examples of the interior include vehicle silencers, vehicle soundproof bodies, etc. Specifically, ceiling materials (roof silencers), dash silencers, floor silencers, floor carpets, hood silencers, etc. are included. Others: Sound-absorbing materials for tires. Examples of the sound-absorbing material for tires include sound-absorbing structures in which vehicle covers, cases, etc. are combined with the above-described sound-absorbing material.

Example

[0075] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

[0076] <Materials Used> · PET film: Φ29 mm (for high-frequency side measurement) or Φ98 mm (for low-frequency side measurement), thickness 0.1 mm · Silicone tube: length 7 mm or 1 mm, outer diameter 3 mm, inner diameter 2 mm · Glass nonwoven fabric: Φ29 mm (for high-frequency side measurement) or Φ98 mm (for low-frequency side measurement), thickness 12 mm, air permeability resistance 2.0 kPa·sec / m · Polypropylene-polyester mixed fiber nonwoven fabric (trade name Sinsulate (manufactured by 3M)): Φ29 mm (for high-frequency side measurement) or Φ98 mm (for low-frequency side measurement), thickness 13 mm · Chloroprene rubber (CR) latex: Showprene 671A (manufactured by Showa Denko K.K.) The air permeability resistance of the glass nonwoven fabric was measured using an air permeability tester (KES-F8) manufactured by Kato Tech Co., Ltd. after processing the glass nonwoven fabric into a size of Φ40 mm using a punch.

[0077] (Example 1) Circular holes with a diameter of Φ2 mm were punched in the PET film using a punch. Then, for some of the holes, the inner diameter of the silicone rubber tube (length 7 mm) was aligned with the holes in the PET film, and the silicone rubber tube was adhered. For adhesion, an adhesive for plastic and synthetic rubber (trade name Semedain UT110 (urethane-based adhesive), manufactured by Semedain Co., Ltd.) was used. As a result, a hole A part (a hole with a neck part) provided with a silicone rubber tube and a hole C part (a hole without a neck part) not provided with it were formed. The holes were arranged in a square lattice (see Fig. 6(a)) with a pitch of 8 mm so that the same type of hole parts (for example, hole A parts) did not adjacent to each other. The aperture ratio of the PET film after hole formation was 5%. An adhesive for metal and plastic (trade name Spray glue 77 (styrene-butadiene rubber-based adhesive), manufactured by 3M) was applied to the surface of the silicone rubber tube and the PET film in contact with the glass nonwoven fabric. At the location corresponding to the hole A part of the glass nonwoven fabric, a hole with a diameter of Φ3 mm and a depth of 7 mm was made using a punch. Then, a silicone rubber tube of PET film was inserted into the hole, and the PET film and the glass nonwoven fabric were laminated and adhered. Thus, a sound-absorbing material (thickness 12.1 mm) was produced.

[0078] (Example 2) Circular holes with a diameter of Φ2 mm or Φ3 mm were made in the PET film using a punch. Also, silicone rubber tubes with lengths of 7 mm and 1 mm were used in combination as the silicone rubber tubes. Then, in the same manner as in Example 1, hole A part and hole B part (holes having neck parts with lengths of 7 mm and 1 mm respectively, Φ2 mm) provided with silicone rubber tubes, and hole C part (hole having no neck part, Φ3 mm) not provided with them were formed. The holes were arranged in a regular triangular lattice (see Fig. 6(b)) with a pitch of 8 mm so that the same type of hole parts did not adjacent to each other. The aperture ratio of the PET film after hole formation was 8%. An adhesive for metal / plastic was applied to the surfaces of the silicone rubber tube and the PET film in contact with the glass nonwoven fabric in the same manner as in Example 1. At the locations corresponding to the hole A part and hole B part of the glass nonwoven fabric, holes with a diameter of Φ3 mm and a depth of 7 mm or 1 mm were made respectively using a punch. Then, a silicone rubber tube of PET film was inserted into the hole, and the PET film and the glass nonwoven fabric were laminated and adhered. Thus, a sound-absorbing material (thickness 12.1 mm) was produced.

[0079] (Example 3) The glass nonwoven fabric was impregnated with a first CR latex solution having a solid content concentration of 20 mass% by spray coating. The impregnation amount was 6000 g / m 2 It was heated in an atmosphere furnace at 90 °C to remove moisture and aggregate and cure the first CR latex. The air permeability resistance of the glass nonwoven fabric after the first CR latex was cured was 2.4 kPa·sec / m. For the glass nonwoven fabric obtained by aggregating and curing the first CR latex, through holes with a diameter of Φ2 mm or Φ3 mm were formed in a desired arrangement using a punch. The holes were circular and arranged in a regular triangular lattice (see Fig. 6(b)) with a pitch of 8 mm. The surface of the glass nonwoven fabric with the through holes formed and the surface of the holes were coated with a second CR latex solution having a solid content concentration of 50% by mass by spray coating. The coating amount was 2000 g / m 2 This was used. At this time, the coating method was adjusted so that holes with different neck lengths of 7 mm (hole A part, Φ2 mm), 1 mm (hole B part, Φ2 mm), or 0 mm (hole C part, Φ3 mm: no neck part formed) were formed, and the same type of hole parts were not adjacent to each other. By heating this in an atmosphere furnace at 90 °C, moisture was removed and the second CR latex was aggregated and cured. Due to the curing of the second CR latex, a porous layer having a base part and a neck part was formed on the glass nonwoven fabric which is a porous layer. The porous layer (base part and neck part) was made of a composite material (non - breathable material) containing chloroprene rubber and glass nonwoven fabric, and the thickness of each of the base part and the neck part was 1 mm. The porosity of the porous layer was 8%. The porous layer was made of a composite material (breathable material) containing glass nonwoven fabric and chloroprene rubber. In this way, a sound - absorbing material (thickness 12 mm) was produced.

[0080] (Comparative Example 1) A single - layer polypropylene - polyester mixed fiber nonwoven fabric was used as the sound - absorbing material (thickness 13 mm).

[0081] (Comparative Example 2) In the same manner as in Example 3, a glass nonwoven fabric obtained by aggregating and curing the first CR latex was produced. This was used as the sound - absorbing material (thickness 12 mm).

[0082] (Comparative Example 3) In the same manner as in Example 1, holes with a diameter of Φ2 mm were made in the PET film. Then, for all the holes, the inner diameter of the silicone rubber tube (length 7 mm) was aligned with the holes in the PET film, and the silicone rubber tube was adhered. As a result, a PET film having only the hole A portion (a hole having a neck portion) provided with the silicone rubber tube was produced. Except for this, a PET film and a glass nonwoven fabric were laminated and adhered in the same manner as in Example 1 to produce a sound-absorbing material (thickness 12.1 mm).

[0083] <Confirmation of Helmholtz resonance box structure> According to the calculation method shown in FIG. 7, the resonance frequency in the Helmholtz resonance box structure of each sound-absorbing material was calculated. The results are shown in Table 1.

[0084]

Table 1

[0085] <Measurement of sound absorption rate of sound-absorbing material> The normal incidence sound absorption rate of each produced sound-absorbing material was measured according to the following. For those provided with a porous layer, sound was incident from the porous layer side. The results are shown in Table 2. According to Table 2, it can be seen that the sound-absorbing materials of the examples are excellent in sound absorption characteristics in a wide frequency range. Device name: Type 4206 impedance tube (Brüel & Kjær) Measurement method: Normal incidence sound absorption rate (conforming to JIS A 1405-1) Measurement range: 50 to 3500 Hz Measurement sample size: Φ29 mm (for high-frequency side measurement: measurement range 500 to 6500 Hz), Φ98 mm (for low-frequency side measurement: measurement range 125 to 1600 Hz)

[0086]

Table 2

Explanation of symbols

[0087] 1…porous layer, 1a…base portion, 1b…neck portion, 2…porous layer, 3…lining layer, 10, 11, 12, 13, 14…sound absorbent material.

Claims

1. A sound-absorbing material comprising a porous layer made of a non-ventilating material and a porous layer made of a ventilating material, wherein the porous layer includes a base portion having a plurality of holes and a hollow neck portion extending from at least some of the holes into the porous layer, and when the porous layer side is arranged facing a target member, a Helmholtz resonator structure having two or more types of holes with different resonance frequencies that resonate with sound incident from the holes is formed.

2. The sound-absorbing material according to claim 1, wherein the Helmholtz resonator structure includes a Helmholtz resonator structure having a resonance frequency of less than 2000 Hz and a Helmholtz resonator structure having a resonance frequency of 2000 Hz or more.

3. The sound-absorbing material according to claim 1 or 2, wherein the Helmholtz resonator structure includes a Helmholtz resonator structure having a resonance frequency of less than 2000 Hz, a Helmholtz resonator structure having a resonance frequency of 2000 to 3000 Hz, and a Helmholtz resonator structure having a resonance frequency of more than 3000 Hz.

4. The sound-absorbing material according to any one of claims 1 to 3, wherein adjacent Helmholtz resonator structures have different resonance frequencies.

5. The sound-absorbing material according to any one of claims 1 to 4, further comprising a backing layer made of a non-ventilating material, the porous layer, and the porous layer in this order.

6. The sound-absorbing material according to any one of claims 1 to 5, wherein the aperture ratio of the base portion is 1 to 20%.

7. The sound-absorbing material according to any one of claims 1 to 6, having a thickness of 15 mm or less.

8. The sound-absorbing material according to any one of claims 1 to 7, wherein the porous layer contains rubber and the porous layer contains non-woven fabric.

9. The sound-absorbing material according to claim 8, wherein the porous layer includes a composite material containing the rubber and the non-woven fabric.

10. The sound-absorbing material according to any one of claims 1 to 9, wherein the air permeability resistance of the porous layer is 1 to 4 kPa·sec / m.

11. A vehicle member including the sound-absorbing material according to any one of claims 1 to 10.

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