Patent Description:
A typical structure of a vehicle has an engine compartment provided at the front, a trunk compartment provided at the rear, and a passenger compartment provided in the middle thereof. The passenger compartment is provided with seats such as a driver's seat, a front passenger seat, and a rear seat. The passenger compartment has a dash insulator, a floor carpet, a floor spacer, a trunk trim, and a trunk floor installed so that they cover the outside of the vehicle interior. These components are formed in an uneven shape according to shapes of vehicle bodies or designs of components. Furthermore, the exterior under a vehicle body has a front fender liner, a rear fender liner, and an undercover which is formed in an uneven shape for controlling air flow, installed thereon. For many of these components, a thermoplastic resin is used as a material, and each of the materials is heated and press-molded by a die having the shape of the component to be finished into an uneven-shaped component having a plurality of portions with different thicknesses.

As a recent trend in vehicle development, the quietness in the interior of a vehicle is emphasized. Noise transmitted to the interior of a vehicle includes noise from the windows, noise from the tires, noise from under the vehicle body, noise from engine sounds, and noise from motor sounds. It is said that particularly noise of frequencies of <NUM> to <NUM> is annoying to drivers and passengers. In addition, it is said that, in electric vehicles, even frequencies of <NUM> to <NUM>, to which annoyance has not been felt conventionally, would cause annoyance to drivers and passengers because electric vehicles have no engine. Therefore, the interior and exterior components of vehicles are required to have a function of absorbing noise in these frequency bands. On the other hand, it is also important to reduce fuel consumption, and it is also required to reduce weight of interior and exterior components of vehicles.

In addition, <CIT> discloses that, at both ends of a honeycomb core made of non-metal, frequency selection plates with apertures made of light metal are adhered via an adhesive, and fiber reinforced substrates are adhered outside the plates, in which the frequency selection plates transmit or block a specific frequency.

<CIT> discloses a multilayered hollow structure plate formed by attaching non-air-permeable sheets onto both the front and back of a core member obtained by fusing together hollow protrusions in two thermoplastic resin sheets. A sound absorbing material is provided on at least one of the front and back side thereof, and small holes opened in the multilayered hollow structure plate are formed in liner portions and the non-air permeable sheet only in the positions that matches the liner portions. <CIT> discloses a soundproofing structure that has an opening and two or more different types of resonance-type sound-absorbing cells. The opening is disposed at a position in which, out of the two or more different types of resonance-type sound-absorbing cells, two of the resonance-type sound-absorbing cells are in contact with each other, or is disposed at a position where two of the resonance-type sound-absorbing cells abut against each other so as to abut against at least one of these resonance-type sound-absorbing cells.

The frequency selection plate of <CIT> is made of light metal, so a sound damping effect is expected due to the friction of air passing through the aperture of the frequency selection plate, but there is no further effect. In addition, when a member having apertures is used, there is a problem in that dirt accumulates in the apertures, changing the frequency of transmission or blocking so that the desired sound absorption performance cannot be stably obtained.

Therefore, it is an object of the present invention to provide a sound-absorbing material for a vehicle, capable of stably yielding desired sound absorption performance while reducing the weight of the sound-absorbing material for a vehicle.

In order to achieve the object, the present invention provides a sound-absorbing material for a vehicle, having a multilayer structure, the material including: a core layer having tubular cells, the tubular cells being arranged in a plurality of rows; and a first airflow-blocking resin film layer adhered to one surface of the core layer, wherein a relationship between a Young's modulus E<NUM> (MPa) of the first airflow-blocking resin film layer and a surface density M<NUM> (g/m<NUM> ) of a layer structure on the first airflow-blocking resin film layer side with respect to the core layer is <NUM> < E<NUM>/M<NUM> < <NUM>. Each of the cells in the core layer has a closed surface at one end and an open end at another end, and the open ends of the cells are arranged on both sides of the core layer such that rows of the open ends of the cells are in every other row. The closed surfaces of the cells arranged in every other row serve as a surface for adhering the first airflow-blocking resin film layer and the core layer.

The tubular cell may have a polygonal tubular shape such as a substantially quadrangular tubular shape or a substantially hexagonal tubular shape, or may have a curved tubular shape such as a substantially circular tubular shape or a substantially elliptical tubular shape.

The open end, the one-side closed surface, and the other-side closed surface may have a polygonal shape such as a substantially quadrangular shape or a substantially hexagonal shape, or may have a curved shape such as a substantially circular shape or a substantially elliptical shape, according to the shape of the cell.

The first airflow-blocking resin film layer may have a structure in which a plurality of materials having different Young's modulus are laminated. The Young's modulus E<NUM> in this case is the Young's modulus of the entire first airflow-blocking resin film layer. In addition, the sound-absorbing material for a vehicle, of the present invention, may further include an inner surface layer on the surface of the first airflow-blocking resin film layer opposite to the core layer. The surface density M<NUM> in this case is the total surface density (mass per unit area) of the first airflow-blocking resin film layer and the inner surface layer. The inner surface layer is a layer of the surface facing the vehicle inner side, and may be, for example, a layer configured with fiber such as nonwoven fabric, plain needle punched fabric, or velour, a layer configured with a foamed resin such as urethane foam, polyethylene foam or nylon foam, or a layer in which these are combined.

The sound-absorbing material for a vehicle of the present invention may further include a second airflow-blocking resin film layer adhered to a surface of the core layer, the surface being opposite to the surface to which the first airflow-blocking resin film layer is adhered. In this case, a relationship between a Young's modulus E<NUM> (MPa) of the second airflow-blocking resin film layer and a surface density M<NUM> (g/m<NUM>) of a layer structure on the second airflow-blocking resin film layer side with respect to the core layer may satisfy <NUM> < E<NUM>/M<NUM> < <NUM> or need not satisfy it. In addition, the absolute value of the difference between.

E<NUM>/M<NUM> and E<NUM>/M<NUM> may be <NUM> or more. Furthermore, the sound-absorbing material for a vehicle of the present invention may further include an outer surface layer on the surface of the second airflow-blocking resin film layer opposite to the core layer. The surface density M<NUM> in this case is the total surface density of the second airflow-blocking resin film layer and the outer surface layer. The outer surface layer is a layer of the surface facing the vehicle outer side, and may be, for example, a layer configured with fiber such as nonwoven fabric, plain needle punched fabric, or velour, a layer configured with a foamed resin such as urethane foam, polyethylene foam or nylon foam, or a layer in which these are combined.

Alternatively, the sound-absorbing material for a vehicle, of the present invention, may further include a resin film layer having a plurality of apertures, the resin film layer being adhered to a surface of the core layer, the surface being opposite to the surface to which the first airflow-blocking resin film layer is adhered.

As described above, the sound-absorbing material for a vehicle, according to the present invention, includes: a core layer in which tubular cells are arranged in a plurality of rows; and a first airflow-blocking resin film layer adhered to one surface of the core layer. The sound-absorbing material for a vehicle has a configuration such that a relationship between a Young's modulus E<NUM> of the first airflow-blocking resin film layer and a surface density M<NUM> of a layer structure on the first airflow-blocking resin film layer side with respect to the core layer is <NUM> < E<NUM>/M<NUM> < <NUM>. With this configuration, when the airflow-blocking resin film layer has a Young's modulus E<NUM> significantly smaller than typical ones with respect to the surface density M<NUM>, use of an airflow-blocking resin film layer, which generally is not considered to contribute to sound absorption, also contributes to sound absorption from the relationship with the predetermined structure of the core layer. This makes it possible to obtain desired sound absorption performance having a peak of sound absorption coefficient in the frequency band of <NUM> to <NUM>, which causes annoying noise in vehicles. As described above, the predetermined structure of the core layer and the first airflow-blocking resin film layer enables high rigidity even with weight reduction of the vehicle component. The structure also enables exhibiting the desired sound absorption performance without using a member having a plurality of apertures, which can eliminate accumulation of dirt in the apertures to stably obtain the desired sound absorption performance.

The configuration, in which the first airflow-blocking resin film layer has a structure in which a plurality of materials having different Young's modulus are laminated, facilitates the design of the Young's modulus E<NUM> and the surface density M<NUM>. This can facilitate the control of the peak of the sound absorption coefficient.

The configuration, in which an inner surface layer is further provided on the surface of the first airflow-blocking resin film layer opposite to the core layer, makes it possible to protect the first airflow-blocking resin film layer having a Young's modulus less than general ones, and to stably obtain the desired sound absorption performance.

The configuration is such that: a second airflow-blocking resin film layer is adhered to the surface of the core layer opposite to the surface to which the first airflow-blocking resin film layer is adhered; and the absolute value of the difference between E<NUM>/M<NUM> and E<NUM>/M<NUM> is <NUM> or more, where E<NUM> is the Young's modulus of the second airflow-blocking resin film layer, and M<NUM> is the surface density of the layer structure on the second airflow-blocking resin film layer side with respect to the core layer. This configuration makes it possible to obtain a sound-absorbing material for a vehicle, having two peaks of sound absorption coefficient in a frequency band of <NUM> to <NUM>, which causes annoying noise in a vehicle, and thus, has excellent sound absorption performance with a wide frequency band of absorbing sound.

The sound-absorbing material for a vehicle may further include a resin film layer having a plurality of apertures, the resin film layer adhered to the surface of the core layer opposite to the surface to which the first airflow-blocking resin film layer is adhered. An aperture pattern preformed on the resin film layer having a plurality of apertures makes it possible to readily adjust and stably maintain the degree of blockage of the open end on at least one surface of the core layer. This enables controlling the peak of the sound absorption coefficient of the sound-absorbing material for a vehicle, and thus enables, together with the E/M values, more readily controlling the peak of the sound absorption coefficient of the sound-absorbing material for a vehicle into a desired frequency band.

A sound-absorbing material for a vehicle has a configuration such that: each of the cells in the core layer has a closed surface at one end and an open end at another end; the open ends of the cells allow an internal space of the cell to be in communication with an outside; and the open ends of the cells are arranged on both sides of the core layer such that rows of the open ends of the cells are in every other row. With this configuration, the closed surface of the cell in the core layer ensures that it serves as a surface for adhering the first airflow-blocking resin film layer and the core layer, and the closed surface of the cell is arranged in every other row. This can improve adhesiveness between the first airflow-blocking resin film layer and the core layer.

An embodiment of a sound-absorbing material for a vehicle, according to the present invention, is described below with reference to the accompanying drawings. Note that the drawings are not intended to be drawn to scale unless otherwise specified.

First, a core layer common to each embodiment of the sound-absorbing material for a vehicle, according to the present invention, is described below. <FIG> is a perspective view showing a manufacturing process of a core material which becomes the core layer. Note that a manufacturing method of this core material is described in detail in <CIT>.

As shown in <FIG>, a flat material sheet is thermoformed by a roller (not shown) having a predetermined die to be plastically deformed substantially without cutting the sheet, so that a core material <NUM> in the figure is formed. The material of the core material <NUM> to be used can include, for example, a thermoplastic resin such as polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), a composite material with fibers, paper, and metal, but it is not limited to these. In particular, a thermoplastic resin is preferable. In this embodiment, a case in which a thermoplastic resin is used is described below. The thickness of the material sheet is preferably in the range of <NUM> to <NUM>, for example, but it is not limited to this, and the thickness of the core material <NUM> after thermoforming is substantially the same.

The core material <NUM> has a three-dimensional structure in which ridge portions <NUM> and valley portions <NUM> are alternately arranged in a width direction X orthogonal to a manufacturing direction Y. The ridge portion <NUM> is configured with two side surfaces <NUM> and a top surface <NUM> between them, and the valley portion <NUM> is configured with two side surfaces <NUM> shared with the adjacent ridge portions <NUM> and a bottom surface <NUM> between them. In this embodiment, a case is described in which the shape of the ridge portion <NUM> is a trapezoid as shown in <FIG>, but the present invention is not limited to this. In addition to polygons such as triangles or rectangles, shapes may be curved shapes such as sine curves or bow shapes.

The core material <NUM> includes the three-dimensional structure continuously in the manufacturing direction Y. That is, as shown in <FIG>, a plurality of ridge portions 11a, 11b, 11c, and 11d are continuously formed in the manufacturing direction Y. The valley portions <NUM> are also formed continuously. The connection between the ridge portions <NUM> and the connection between the valley portions <NUM> are made by alternately repeating two types of connection methods.

The first connection method is such that, as shown in <FIG>, on a first folding line X1 in the width direction, top surfaces 17b and 17c of two adjacent ridge portions 11b and 11c are connected, via trapezoidal-shaped ridge portion connecting surfaces 15b and 15c, respectively. The ridge portion connecting surface <NUM> is formed at a right angle to the top surface <NUM>. On the first folding line X1 in the width direction, the bottom surfaces 14b and 14c of two adjacent valley portions are directly connected. The second connection method is such that, as shown in <FIG>, on a second folding line X2 in the width direction, bottom surfaces 14a and 14b (or 14c and 14d) of two adjacent valley portions are connected, via trapezoidal-shaped valley portion connecting surfaces 16a and 16b (or 16c and 16d), respectively. The valley portion connecting surface <NUM> is formed at a right angle to the bottom surface <NUM>. On the second folding line X2 in the width direction, top surfaces 12a and 12b (or 12c and 12d) of two adjacent ridge portions are directly connected.

Thus, the core material <NUM> has a plurality of three-dimensional structures (the ridge portions <NUM> and the valley portions <NUM>) connected via the connection regions (the ridge portion connecting surfaces <NUM> and the valley portion connecting surfaces <NUM>), and has the connection region folded to form a core layer of the sound-absorbing material for a vehicle, of the present invention. Specifically, the core material <NUM> is mountain-folded along the first folding line X1 such that the bottom surfaces 14b and 14c of two adjacent valley portions contact back-to-back with each other, and the angle formed by the ridge portion connecting surfaces 15b and 15c of two adjacent ridge portions increases to <NUM> degrees. In addition, the core material <NUM> is valley-folded along the second folding line X2 such that top surfaces 17a and 17b (or 17c and 17d) of two adjacent ridge portions contact face to face with each other, and the angle between the valley portion connecting surfaces 16a and 16b (or 16c and 16d) of two adjacent valley portions increases to <NUM> degrees. A core layer <NUM> of the sound-absorbing material for a vehicle, of the present invention, obtained by folding the core material <NUM> in this manner, is shown in <FIG> and <FIG>.

As shown in <FIG> and <FIG>, the core layer <NUM> includes substantially hexagonal tubular cells <NUM> arranged in a plurality of rows, and has cells 20A, 20C and 20E formed out of two adjacent ridge portions and cells 20B and 20D formed out of two adjacent valley portions, each arranged in every other row. A broken line <NUM> in <FIG> is the surface that has been the back surface of the core material, and generally indicates the inner wall of the cell <NUM> having the substantially hexagonal tubular shape.

The cells 20A, 20C, and 20E formed from the ridge portions includes six cell side walls each forming the substantially hexagonal tubular shape. Each of these cell side walls is formed out of the two top surfaces <NUM> and the four side surfaces <NUM> of the cell material. Furthermore, these cells 20A, 20C, and 20E include substantially hexagonal tubular-shaped closed surfaces 21A, 21C, and 21E, respectively, to close the cell ends at the cell end on one surface 10a (front surface in <FIG>) of the core layer <NUM>. Each of these closed surfaces <NUM> on one side is formed out of two trapezoidal ridge portion connecting surfaces <NUM> in the cell material. Furthermore, these cells 20A, 20C, and 20E include open ends 22A, 22C, and 22E that are opened in the substantially hexagonal shape at the cell ends on the other surface 10b which is at the opposite side of the core layer <NUM>. The open ends 22A, 22C, and 22E allow the respective internal spaces of the cells 20A, 20C, and 20E to be in communication with the outside.

The cells 20B and 20D formed from the valley portions also includes six cell side walls each forming the substantially hexagonal tubular shape. Each of these cell side walls is formed from two bottom surfaces <NUM> and four side surfaces <NUM> of the cell material. Furthermore, these cells 20B and 20D include open ends 22B and 22D that are opened in the substantially hexagonal shape at the cell ends on the one surface 10a of the core layer <NUM>. The open ends 22B and 22D allow the respective internal spaces of the cells 20B and 20D to be in communication with the outside. Furthermore, these cells 20B and 20D include substantially hexagonal tubular-shaped closed surfaces 21B and 21D that close the cell ends, respectively, at the cell end on the other surface 10b, which is at the opposite side of the core layer <NUM>. Each of these closed surfaces <NUM> on the other side is formed out of the two trapezoidal valley portion connecting surfaces <NUM> in the cell material.

In this way, the core layer <NUM> has the one-side closed surfaces 21A, 21C, and 21E formed out of the ridge portions of the cell material in every other row at the cell end on one surface 10a, and has the other-side closed surfaces 21B and 21D formed out of valley portions of the cell material in the different cell rows from the above at the cell end on the other surface 10b. However, unless otherwise stated, both the closed surface <NUM> on one side and the closed surface <NUM> on the other side perform substantially the same function.

The thickness of the entire core layer <NUM> varies depending on which component of the vehicle a multilayered structure is used for, so it is not limited to the following. However, it is preferably in the range of <NUM> to <NUM>, and is more preferably in the range of <NUM> to <NUM> from the viewpoint of controlling the peak of the sound absorption coefficient by the airflow-blocking resin film layer, to be described below, the sound absorption performance of the core layer <NUM> itself, and the strength and weight of the core layer <NUM>.

The basis weight (weight per unit area) of the core layer <NUM> varies depending on which component of the vehicle the multilayered structure is used for, so it is not limited to the following. However, it is preferably in the range of <NUM>/m<NUM> to <NUM>/m<NUM>, and is more preferably in the range of <NUM>/m<NUM> to <NUM>/m<NUM>. As the thickness of the core layer <NUM> is greater and the basis weight is greater, the strength of the core layer <NUM> tends to be higher, and the frequency at which the sound absorption coefficient is at the peak tends to be controllable at lower frequencies, in general.

The basis weight of the core layer <NUM> can be adjusted by the type of material of the core layer <NUM>, the thickness of the entire core layer <NUM> or the wall thickness of the cell <NUM> (thickness of the material sheet) as well as the pitches Pcx and Pcy between the cells <NUM> of the core layer <NUM> (distance between the central axes of the cells). In order to set the basis weight of the core layer <NUM> within the above range, for example, it is preferable that the pitch Pcy between the cells <NUM> be in the range of <NUM> to <NUM> in the direction in which the cells <NUM> are adjacent to each other to form a row, which is the core manufacturing direction Y, and it is more preferable that the pitch Pcy be in the range of <NUM> to <NUM>.

Next, individual embodiments of sound-absorbing materials for a vehicle, according to the present invention, are described below using the core layer <NUM> described above.

As shown in <FIG> and <FIG>, a sound-absorbing material for a vehicle, of a first embodiment, includes a core layer <NUM> described above, an airflow-blocking resin film layer <NUM> provided on one surface thereof, and a nonwoven fabric layer <NUM> being provided on the resin film layer <NUM> and serving as an inner surface layer.

The material of the airflow-blocking resin film layer <NUM> to be used may be, for example, resin films such as polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), and polyamide (PA), but it is not limited to these. In addition, the airflow-blocking resin film layer <NUM> may have a structure in which a plurality of layers of these different types of resins are laminated, or may have a structure in which a plurality of layers of materials, each having different Young's modulus, are laminated even if they are of the same type of resin.

The Young's modulus E of the airflow-blocking resin film layer <NUM> is not limited to the following because it depends on a ratio with a surface density E to be described below in detail, but it is lower than those to be used for general vehicle components, and for example, the upper limit thereof is preferably <NUM> MPa or less, more preferably <NUM> MPa or less, and still more preferably <NUM> MPa or less. In addition, the lower limit of the Young's modulus is preferably <NUM> MPa or more, and more preferably <NUM> MPa or more, but it is not limited to these. Note that the values of the Young's modulus in the direction in which the molten resin of the film flows (MD) and the Young's modulus in the direction perpendicular thereto (TD) differ depending on the type of resin and/or the manufacturing method of the film, but the Young's modulus of the lower value is used in calculating an E/M of the present invention.

The surface density (basis weight) of the airflow-blocking resin film layer <NUM> also depends on the total surface density E with the nonwoven fabric layer <NUM> to be described below, and it is not limited to the following, but the lower limit thereof is, for example, preferably <NUM>/m<NUM> or more, more preferably <NUM>/m<NUM> or more, and still more preferably <NUM>/m<NUM> or more. In addition, the upper limit of the surface density is preferably <NUM>/m<NUM> or less, more preferably <NUM>/m<NUM> or less, and still more preferably <NUM>/m<NUM> or less, but it is not limited to these.

The thickness of the airflow-blocking resin film layer <NUM> is not limited to the following, but the lower limit thereof is, for example, preferably <NUM> or more, more preferably <NUM> or more, and still more preferably <NUM> or more. In addition, the upper limit of the thickness is preferably <NUM> or less, more preferably <NUM> or less, and still more preferably <NUM> or less, but it is not limited to these.

The airflow-blocking resin film layer <NUM> may be adhered to the core layer <NUM> by heat-welding, or may be adhered thereto via an adhesive (not shown). The adhesive to be used is not particularly limited, but for example, it may be an epoxy-based or acrylic-based adhesive. In addition, in order to heat-weld the airflow-blocking resin film layer <NUM> with the core layer <NUM> and the nonwoven fabric layer <NUM>, for example, the airflow-blocking resin film layer <NUM> may have a three-layer structure including a central layer and two adhesive layers located on both side surfaces thereof. In this case, the material of the adhesive layers is a material having a melting point lower than the melting point of the material used for the central layer. For example, polyamide having a melting point of <NUM> to <NUM> is used for the central layer, and polyethylene having a melting point of <NUM> to <NUM> is used for the adhesive layer. Then, the temperature at the time of heating when the airflow-blocking resin film layer <NUM> is adhered to the core layer <NUM> and the nonwoven fabric layer <NUM>, and the temperature for thermoforming into a predetermined shape of the sound-absorbing material for a vehicle are set to about <NUM> to <NUM>. This configuration and process melts the adhesive layers to firmly adhere to the core layer <NUM> and the nonwoven fabric layer <NUM>, while not melting the central layer, so that the Young's modulus of the airflow-blocking resin film layer <NUM> is not significantly changed. This makes it possible to obtain desired sound absorption performance of the sound-absorbing material for a vehicle. As a resin having a melting point higher than that of polyethylene for the adhesive layer, there may be mentioned polypropylene, other than polyamide.

For the nonwoven fabric layer <NUM>, it is preferable to use various nonwoven fabrics such as spunbonded, spunlace, and needle punched nonwoven fabrics using a resin such as polyethylene terephthalate (PET), polypropylene (PP), or polyethylene (PE), but it is not limited to these.

The surface density (basis weight) of the nonwoven fabric layer <NUM> is not limited to the following because it depends on the total surface density E with the airflow-blocking resin film layer <NUM>, but the lower limit thereof is, for example, preferably <NUM>/m<NUM> or more, more preferably <NUM>/m<NUM> or more, and still more preferably <NUM>/m<NUM> or more. In addition, the upper limit of the surface density is preferably <NUM>/m<NUM> or less, more preferably <NUM>/m<NUM> or less, and still more preferably <NUM>/m<NUM> or less, but it is not limited to these.

In this embodiment, the Young's modulus of the airflow-blocking resin film layer <NUM> is defined as E, and the total surface density of the airflow-blocking resin film layer <NUM> and the nonwoven fabric layer <NUM> is defined as M. Here, E/M values are set to the range of <NUM> to <NUM> to enable the peak of the sound absorption coefficient of the sound-absorbing material for a vehicle to be controlled into the frequency band of <NUM> to <NUM>, which causes annoying noise in vehicles. Outside of this frequency band, when the peak of the sound absorption coefficient is to be provided in the band of <NUM> to <NUM>, the E/M value is preferably in the range of <NUM> to <NUM>, and furthermore, when the peak of the sound absorption coefficient is to be provided in the band of <NUM> to <NUM>, the E/M value is more preferably in the range of <NUM> to <NUM>. In addition, when the peak of the sound absorption coefficient is to be provided in the band of <NUM> to <NUM>, the E/M value is preferably in the range of <NUM> to <NUM>, and furthermore, when the peak of the sound absorption coefficient is to be provided in the band of <NUM> to <NUM>, the value of E/M is preferably in the range of <NUM> to <NUM>.

As described above, according to the first embodiment, an airflow-blocking resin film layer <NUM> is provided on at least one surface of the core layer <NUM> in which open ends and closed surfaces are arranged in every other row, and a nonwoven fabric layer <NUM> is further provided on the outside of the resin film layer <NUM>. This configuration enables high rigidity even with weight reduction of the sound-absorbing material for a vehicle. At the same time, the value of E/M, which is the ratio of Young's modulus E of the airflow-blocking resin film layer <NUM> to the total surface density M of the airflow-blocking resin film layer <NUM> and the nonwoven fabric layer <NUM>, is adjusted. This enables controlling the peak of the sound absorption coefficient of the sound-absorbing material for a vehicle in a desired frequency band.

Note that, although <FIG> and <FIG> show a case in which the nonwoven fabric layer <NUM> is provided on the outside of the airflow-blocking resin film layer <NUM>, the present invention is not limited to this. There may be a configuration such that no nonwoven fabric layer <NUM> is provided, and the Young's modulus E of the airflow-blocking resin film layer <NUM> and the surface density M of only the airflow-blocking resin film layer <NUM> is adjusted. This configuration enables the peak of the sound absorption coefficient of the sound-absorbing material for a vehicle to be controlled in a desired frequency band, similarly to the above.

As shown in <FIG>, a sound-absorbing material for a vehicle of a second embodiment includes: the core layer <NUM> described above; a first airflow-blocking resin film layer 40a provided on one surface thereof; a second airflow-blocking resin film layer 40b provided on the other surface thereof; and a first and a second nonwoven fabric layers 30a and 30b serving as an inner surface layer and an outer surface layer respectively and being provided on the respective airflow-blocking resin film layers. Note that the same configurations as those in the first embodiment are referred to by the same reference signs, and detailed descriptions thereof are omitted here.

Both the first and second airflow-blocking resin film layers 40a and 40b, and the first and second nonwoven fabric layers 30a and 30b, which are adhered on both side surfaces of the core layer <NUM>, may have the same configuration (the material and thickness of the resin film, the manufacturing method and basis weight of nonwoven fabric, or the like), or may have different configurations on the opposite side surfaces thereof.

Thus, when the airflow-blocking resin film layer <NUM> is provided on both sides of the core layer <NUM>, the value of E/M, which is the ratio of the Young's modulus E of the airflow-blocking resin film layer <NUM> to the total surface density M of the airflow-blocking resin film layer <NUM> and the nonwoven fabric layer <NUM>, is adjusted separately on the first airflow-blocking resin film layer 40a side and the second airflow-blocking resin film layer 40b side. That is, the Young's modulus of the first airflow-blocking resin film layer 40a is defined as E<NUM>, and the total surface density of the first airflow-blocking resin film layer 40a and the first nonwoven fabric layer 30a is defined as M<NUM>, and E<NUM>/M<NUM> values are set in the range of <NUM> to <NUM>. In addition, the Young's modulus of the second airflow-blocking resin film layer 40b is defined as E<NUM>, and the total surface density of the second airflow-blocking resin film layer 40b and the second nonwoven fabric layer 30b is defined as M<NUM>, and E<NUM>/M<NUM> values are set to the range of <NUM> to <NUM>. The value of E<NUM>/M<NUM> and the value of E<NUM>/M<NUM> are preferably different, and the absolute value of the difference between E<NUM>/M<NUM> and E<NUM>/M<NUM> is preferably <NUM> or more, more preferably <NUM> or more, and still more preferably <NUM> or more. Note that the upper limit of the absolute value of this difference is not particularly limited, but it is preferably <NUM> or less, for example.

According to the second embodiment, the sound-absorbing material for a vehicle is configured such that: the airflow-blocking resin film layer <NUM> and the nonwoven fabric layer <NUM> are provided on each of both surfaces of the core layer <NUM> in which the open ends and the closed surfaces are arranged in every other row; both the value of E<NUM>/M<NUM> on the first airflow-blocking resin film layer 40a side and the value of E<NUM>/M<NUM> on the second airflow-blocking resin film layer 40b side are set within the range of <NUM> to <NUM>; and furthermore, the values are made different from each other within this range. This configuration makes it possible to obtain the sound-absorbing material for a vehicle with excellent sound absorption performance having two peaks of sound absorption coefficient in a frequency band of <NUM> to <NUM>, which causes annoying noise in a vehicle. In particular, setting the absolute value of the difference between the values of E<NUM>/M<NUM> and E<NUM>/M<NUM> to <NUM> or more enables widening the frequency band of absorbing sound.

As shown in <FIG>, the sound-absorbing material for a vehicle of a third embodiment includes: the core layer <NUM> described above; an airflow-blocking resin film layer <NUM> provided on one surface thereof; a resin film layer <NUM> having a plurality of apertures on the surface of the core layer <NUM> opposite to the airflow-blocking resin film layer <NUM>; and a first and a second nonwoven fabric layers 30a and 30b serving as an inner surface layer and an outer surface layer respectively and being provided on the respective airflow-blocking resin film layers. Note that the same configurations as those in the first and second embodiments are referred to by the same reference signs, and detailed descriptions thereof are omitted here.

The resin film layer <NUM> having a plurality of apertures (hereinafter referred to as the apertured film layer <NUM>) has a plurality of holes <NUM> passing through the layer. The holes <NUM> are opened in advance before the adhesion to the core layer <NUM>, for example, by a hot needle or punching (punching using a male die and a female die). In order to prevent the holes from being closed, it is preferable to have a hole shape in which burrs of the holes are minimized.

The holes <NUM> do not have any particular limitation on their aperture pattern, but they are preferably arranged in a staggered arrangement or a lattice arrangement. The aperture rate of the apertured film layer <NUM> is not particularly limited, but it is preferably in the range of <NUM>% to <NUM>%. The diameter of the holes <NUM> is preferably in the range of <NUM> to <NUM>, and more preferably in the range of <NUM> to <NUM>.

Note that the pitches of the holes <NUM> of the apertured film layer <NUM> do not necessarily have to be the same as the pitches Pcx and Pcy of the cells <NUM> of the core layer <NUM> shown in <FIG>, and the holes <NUM> and the cells <NUM> do not necessarily have to be aligned when the apertured film layer <NUM> is adhered to the core layer <NUM>. This is because the positions of the holes <NUM> of the apertured film layer <NUM> and the open ends <NUM> of the cells <NUM> of the core layer <NUM> randomly overlap with each other to enable appropriate communication between the inside and outside. It is preferable that the pitch of the holes <NUM> of the apertured film layer <NUM> be smaller than the pitch of the cells <NUM> of the core layer <NUM> at least in either an X direction or a Y direction.

According to the third embodiment, also with the apertured film layer <NUM> provided on the surface of the core layer <NUM> opposite to the airflow-blocking resin film layer <NUM>, the same effect as in the first embodiment can be obtained. In addition, the aperture pattern preformed in the apertured film layer <NUM> can readily adjust and stably maintain the degree of blockage of the open ends <NUM> on at least one surface of the core layer <NUM>. This enables controlling the peak of the sound absorption coefficient of the sound-absorbing material for a vehicle, and thus enables, together with the E/M value on the airflow-blocking resin film layer <NUM> side, more readily controlling the peak of the sound absorption coefficient of the sound-absorbing material for a vehicle in a desired frequency band.

Examples of the present invention are described below.

As Example <NUM>, a sound-absorbing material for a vehicle, having a multilayer structure shown in <FIG> and <FIG>, was produced. A three-layered airflow-blocking resin film with a thickness of <NUM> (the material being polyethylene/polyamide/polyethylene, the Young's modulus of the film being <NUM> MPa) was adhered to one surface of the core layer having the structure of <FIG>. Furthermore, a spunbonded nonwoven fabric (the material being polyethylene terephthalate, the basis weight being <NUM>/m<NUM>) was adhered on the airflow-blocking resin film, as an inner surface layer. The total surface density of the airflow-blocking resin film and the nonwoven fabric was <NUM>/m<NUM>. Then, this multilayered structure was heated and pressed to obtain a sound-absorbing material for a vehicle in which the layers were adhered.

In order to evaluate the sound absorption performance of the sound-absorbing material for a vehicle of Example <NUM>, a cylindrical sample having a diameter of about <NUM> was taken from the sound-absorbing material for a vehicle of Example <NUM> according to a method conforming to ISO10534-<NUM> (JIS A <NUM>), and then the normal incident sound absorption coefficients at frequencies of <NUM> to <NUM> of this sample were measured. As a result, the peak frequency of the sound absorption coefficient was <NUM>.

In the same manner as in Example <NUM>, as shown in Table <NUM> below, sound-absorbing materials for a vehicle of Examples <NUM> to <NUM>, which vary in the materials, the basis weights, the thicknesses, and the like of the nonwoven fabrics and the airflow-blocking resin films, were produced, and the sound absorption performances thereof were measured. Table <NUM> and <FIG> show the results including Example <NUM>. Here, in any of the examples, the core layer used was made of a polypropylene resin and had a thickness of about <NUM> or less and a pitch Pcy between cells of about <NUM> or less.

As shown in Table <NUM> and <FIG>, the higher the value of E/M, which is the ratio of the Young's modulus E of the airflow-blocking resin film layer to the surface density M of the layer structure on the core layer, the higher the peak frequency of the sound absorption coefficient of the sound-absorbing material for a vehicle. Normally, it was generally thought that the airflow-blocking resin film layer does not contribute to sound absorption. It is however presumed that use of the airflow-blocking resin film layer having a Young's modulus E significantly smaller than that of general ones with respect to the surface density M contributes to sound absorption from the relationship with the predetermined structure of the core layer. In addition, as shown in <FIG>, the results of Examples <NUM> to <NUM> indicate that, with E/M values being set to the range of <NUM> to <NUM>, it is possible to produce sound-absorbing material for vehicles having desired sound absorption performance having a peak of sound absorption coefficient in the frequency band of <NUM> to <NUM>, which causes annoying noise in vehicles.

Claim 1:
A sound-absorbing material for a vehicle, having a multilayer structure, the material comprising:
a core layer (<NUM>) having tubular cells (<NUM>), the tubular cells (<NUM>) being arranged in a plurality of rows, wherein each of the cells (<NUM>) in the core layer (<NUM>) has a closed surface (<NUM>) at one end and an open end (<NUM>) at another end, and the open ends of the cells (<NUM>) are arranged on both sides of the core layer (<NUM>) such that rows of the open ends of the cells (<NUM>) are in every other row;
a first airflow-blocking resin film layer (<NUM>) adhered to one surface of the core layer (<NUM>), wherein a relationship between a Young's modulus E<NUM> in MPa of the first airflow-blocking resin film layer (<NUM>) and a surface density M<NUM> in g/m<NUM> of a layer structure (<NUM>,<NUM>) on the first airflow-blocking resin film layer side with respect to the core layer (<NUM>) is <NUM> < E<NUM>/M<NUM> < <NUM>/s<NUM>;
characterised in that:
the closed surfaces (<NUM>) of the cells arranged in every other row serve as a surface for adhering the first airflow-blocking resin film layer (<NUM>) and the core layer (<NUM>).