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 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 that is formed in an uneven shape for controlling the 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 frequencies of <NUM> to <NUM> noise causes annoyance 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 a sound absorbing structure including: a first sound absorbing portion formed of a material having an acoustic impedance substantially equal to or slightly greater than the acoustic impedance of air; and a second sound absorbing portion formed of a material having an acoustic impedance greater than that of the first sound absorbing portion. This patent document states that: if the acoustic impedance of a sound absorbing layer is significantly different from the acoustic impedance of air, most of incident sound waves are reflected at the interface between the sound absorbing layer and the air layer, that is, the surface of the sound absorbing layer; but a first sound absorbing layer configuring the interface with the air layer is made to have the above acoustic impedance, so that most of the incident sound waves reach a second sound absorbing layer without being reflected by the surface of the first sound absorbing layer; and the acoustic impedance discontinuity is made relatively small between the first sound absorbing layer and the second sound absorbing layer, so that it is possible to minimize partial reflection of the incident sound waves due to the difference in acoustic impedance at the interface between the first sound absorbing layer and the second sound absorbing layer.

<CIT> discloses hollow structure plates, methods and apparatuses for manufacturing the same, and sound absorbing structure plates.

Preferred embodiments are subject of the dependent claims.

As described above, sound-insulation materials for vehicles reflect the incident sound waves to block the sound by increasing the difference in acoustic impedance between air and the layer, or between the layers. Acoustic impedances greatly vary depending on layer configurations. For example, those of fiber layers are relatively small and those of rubber layers are relatively large. Therefore, a rubber layer can be used as a sound-insulation material to improve sound insulation properties, but the weight of the sound-insulation material increases, which is a problem for vehicles.

Therefore, an object of the present invention is to provide a sound-insulation material for a vehicle capable of reducing weight thereof while maintaining high rigidity thereof, and capable of exhibiting sufficient sound insulation performance, especially against noise having frequencies of <NUM> to <NUM> generated in vehicles.

In order to achieve the object, the present invention provides a sound-insulation 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, wherein 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; a first airflow-blocking resin film layer provided on at least one surface of the core layer; and a decoupling layer provided on a surface of the first airflow-blocking resin film layer, the surface being opposite to the core layer; wherein 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, and wherein: an average specific acoustic impedance ratio is <NUM> < (P/v)/Za < <NUM> between <NUM> and <NUM>, where: P and v are respectively a sound pressure and a particle velocity on a surface of the first airflow-blocking resin film layer provided on the core layer, the surface being opposite to the core layer; and Za is an acoustic impedance of the decoupling 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 sound-insulation material for a vehicle, of the present invention preferably has a configuration such that a thickness of the first airflow-blocking resin film layer on the core layer is <NUM> to <NUM>.

Alternatively, the sound-insulation 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.

A pitch Pcy between the cells in the direction in which the cells in the core layer are adjacent to each other to form a row is preferably <NUM> or less.

The first airflow-blocking resin film layer may have a structure in which a plurality of different materials are laminated.

The sound-insulation material for a vehicle, according to the present invention includes: a core layer having tubular cells, the tubular cells being arranged in a plurality of rows; a first airflow-blocking resin film layer provided on at least one surface of the core layer; and a decoupling layer provided on a surface of the first airflow-blocking resin film layer, the surface being opposite to the core layer; wherein: an average specific acoustic impedance ratio is <NUM> < (P/v)/Za < <NUM> between <NUM> and <NUM>, where: P and v are respectively a sound pressure and a particle velocity on a surface of the first airflow-blocking resin film layer provided on the core layer, the surface being opposite to the core layer; and Za is an acoustic impedance of the decoupling layer. This configuration makes it possible: to reduce the weight of the sound-insulation material for a vehicle while maintaining high rigidity; and to reflect most of sound waves having frequencies of <NUM> to <NUM> generated in vehicles after incidence on the decoupling layer, at the interface with the first airflow-blocking resin film layer to exhibit sufficient sound insulation performance against noise generated in a vehicle.

The configuration, in which the thickness of the first airflow-blocking resin film layer is <NUM> to <NUM>, makes it possible to reduce the weight thereof while maintaining the abovementioned sound insulation performance.

A resin film layer having a plurality of apertures is provided on the core surface opposite to the first airflow-blocking resin film layer. With this configuration, an aperture pattern preformed in the resin film layer having a plurality of apertures enables the degree of blockage of the open end to be readily adjusted and stably maintained on at least one surface of the core layer. This makes it possible to control the peak of the sound absorption coefficient of the sound-insulation material for a vehicle, and thus, to exhibit the excellent sound absorption performance as well as the abovementioned sound insulation performance.

The first airflow-blocking resin film layer has a structure in which a plurality of different materials are laminated. This configuration makes it possible to facilitate the design for making the specific acoustic impedance ratio (P/v)/Za within a predetermined range.

The core layer has a configuration such that: each of 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. This configuration ensures that the closed surfaces of the cells in the core layer serve as a surface for adhering the first airflow-blocking resin film layer and the core layer, and can improve adhesiveness between the first airflow-blocking resin film layer and the core layer since the closed surfaces of the cells are arranged in every other row.

An embodiment of a sound-insulation 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-insulation 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 that is to be 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 of 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.

A 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. A 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-insulation 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-insulation 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 cells <NUM> of substantially hexagonal tubular shape 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 walls 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 ends 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 ends 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 ends 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 ends 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 specific acoustic impedance ratios between an airflow-blocking resin film layer and a decoupling 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> generally tends to be higher.

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> in 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>. In particular, in order to control the specific acoustic impedance ratio between the airflow-blocking resin film layer and the decoupling layer to be described below, within a predetermined range, the pitch Pcy between the cells <NUM> is still more preferably <NUM> or less.

Next, individual embodiments of the sound-insulation material 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-insulation 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 decoupling layer <NUM> further provided on the resin film layer <NUM>. Note that the sound-insulation material for a vehicle, of the present invention, is used so that the decoupling layer <NUM> side is located on the side of a noise generating source.

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.

Although the thickness of the airflow-blocking resin film layer <NUM> depends on a specific acoustic impedance ratio between the airflow-blocking resin film layer and the decoupling layer to be described below, for example, the lower limit thereof is 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.

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 decoupling 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 decoupling layer <NUM>, and the temperature for thermoforming into a predetermined shape of the sound-insulation material for a vehicle are set to about <NUM> to <NUM>. This configuration and process enables the adhesive layer only to melt to firmly adhere to the core layer <NUM> and the decoupling layer <NUM>, while not melting the central layer. A resin having a melting point higher than that of polyethylene for the adhesive layer is polypropylene as well as polyamide.

The decoupling layer <NUM> is a layer generally used as a layer for decoupling (breaking) vibration transmission in the sound-insulation material for a vehicle. The material of the decoupling layer <NUM> is not particularly limited if it is a material used for decoupling layers of sound-insulation materials for a vehicle. However, from the viewpoint of reducing the weight of the sound-insulation material for a vehicle, it is preferable to use polyester fibers, synthetic fibers such as nylon fibers and acrylic fibers, inorganic fibers such as glass wool and rock wool, and metal fibers such as aluminum fibers. In addition, it is also preferable to use foam of thermoplastic resin, thermosetting resin, or the like such as urethane foam, polyethylene foam, and nylon foam. In addition, the fibers and the foam may be combined. In particular, the decoupling layer <NUM> is preferably felt, and is preferably formed of a polyester fiber such as a low melting point polyester fiber or a material such as glass wool. In addition, the felt manufacturing method is preferably a manufacturing method such as needle punching, thermal bonding, or spunlacing.

The basis weight of the decoupling layer <NUM> depends on a specific acoustic impedance ratio between the airflow-blocking resin film layer and the decoupling layer to be described below, so it is not limited to the following, but for example, the lower limit thereof is 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 basis weight is not limited to these, but it is preferably <NUM>/m<NUM> or less, more preferably <NUM>/m<NUM> or less, and still more preferably <NUM>/m<NUM> or less.

In this embodiment, an average specific acoustic impedance ratio (P/v)/Za (unit: dimensionless) is in the range of <NUM> to <NUM> between <NUM> and <NUM>, where: P and v are respectively a sound pressure and a particle velocity on a surface of the airflow-blocking resin film layer <NUM> provided on the core layer <NUM>, the surface being opposite to the core layer <NUM>; and Za is an acoustic impedance of the decoupling layer <NUM>. Setting the average specific acoustic impedance ratio (P/v)/Za to <NUM> or more enables sufficiently reflecting sound waves having frequencies of <NUM> to <NUM> incident on the decoupling layer <NUM> at the interface between the decoupling layer <NUM> and the airflow-blocking resin film layer <NUM>. In addition, reducing the average specific acoustic impedance ratio (P/v)/Za to <NUM> or less enables sufficiently exhibiting the above-mentioned sound insulation performance while maintaining the weight reduction of the sound-insulation material for a vehicle. The lower limit of the average specific acoustic impedance ratio (P/v)/Za is preferably <NUM> or more, and more preferably <NUM> or more. In addition, the upper limit of the average specific acoustic impedance ratio (P/v)/Za is preferably <NUM> or less, and more preferably <NUM> or less.

The average specific acoustic impedance ratio (P/v)/Za can be obtained by the following method. Specific acoustic impedance ratios (P/v)/Z<NUM> between air and the airflow-blocking resin film <NUM> provided on one surface of the core layer <NUM>, on the surface opposite to the core layer, are measured over a frequency range of <NUM> to <NUM>. Here, the acoustic impedance of air is represented by Z<NUM>. P/v is also called the specific acoustic impedance. On the other hand, the specific acoustic impedance ratios Za/Z<NUM> between air and the decoupling layer <NUM>, on the surface thereof without the core layer <NUM> and the airflow-blocking resin film <NUM>, are measured over a frequency range of <NUM> to <NUM>. Then, (P/v)/Za can be obtained from the measured values of (P/v)/Z<NUM> and Za/Z<NUM> at each frequency by the following expression.

The average specific acoustic impedance ratio (P/v)/Za may be a simple average of the ratios measured in the frequency range of <NUM> to <NUM> and at least a frequency interval of <NUM> or less. Both (P/v)/Z<NUM> and Za/Z<NUM> described above can be measured by a method conforming to ISO <NUM>-<NUM> (<NUM>-microphone transfer function method). For example, they can be measured with a commercially available impedance tube (model number <NUM> manufactured by Brüel & Kjær Sound & Vibration Measurement (B & K)).

The sound pressure P and the particle velocity v differ depending on the configuration of the airflow-blocking resin film layer <NUM> (for example, material, thickness, and so on). The sound pressure P and the particle velocity v are also affected by the configuration of the core layer <NUM> (for example, the material, the arrangement of the core, the thickness of the entire core layer, the pitch of the core, the thickness of the core wall surface, and so on) provided with the airflow-blocking resin film layer <NUM>, and the adhesive strength between the airflow-blocking resin film layer <NUM> and the core layer <NUM>. The specific acoustic impedance ratio (P/v)/Z<NUM> between air and the airflow-blocking resin film layer <NUM> provided on the core layer <NUM> is not particularly limited, but for example, in the frequency range of <NUM> to <NUM>, the upper limit of the average thereof is preferably <NUM> or less, more preferably <NUM> or less, and still more preferably <NUM> or less. In addition, the lower limit of the average specific acoustic impedance ratio (P/v)/Z<NUM> is not particularly limited, but it is preferably <NUM> or more, and more preferably <NUM> or more.

The specific acoustic impedance ratio Za/Z<NUM> between the decoupling layer <NUM> and air differs depending on the configuration of the decoupling layer <NUM> (for example, the type of material, the basis weight, and so on). The specific acoustic impedance ratio Za/Z<NUM> is not particularly limited, but for example, in the frequency range of <NUM> to <NUM>, the upper limit of the average thereof is preferably <NUM> or less, more preferably <NUM> or less, and still more preferably <NUM> or less. In addition, the lower limit of the average specific acoustic impedance ratio Za/Z<NUM> is not particularly limited, but it is preferably <NUM> or more.

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, a decoupling layer <NUM> is further provided on the airflow-blocking resin film layer <NUM>, and the specific acoustic impedance ratio (P/v)/Za is made within the above-mentioned numerical range. This configuration makes it possible: to reduce the weight of the sound-insulation material for a vehicle while maintaining high rigidity; and to exhibit sufficient sound insulation performance against noise having a frequency of <NUM> to <NUM> generated in the vehicle.

As shown in <FIG>, a sound-insulation material for a vehicle, of a second embodiment, includes: a core layer <NUM> described above, a first airflow-blocking resin film layer 40a provided on one surface thereof, a decoupling layer <NUM> provided on the first airflow-blocking resin film layer 40a, and a second airflow-blocking resin film layer 40b provided on the other surface of the core layer <NUM>. 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.

The first airflow-blocking resin film layer 40a has the same configuration (resin film material, thickness, and so on) as the one described in the first airflow-blocking resin film layer <NUM>. In addition, the second airflow-blocking resin film layer 40b is also preferably the one having the same performance as the first airflow-blocking resin film layer 40a, although the decoupling layer is not further provided thereon. That is, the average specific acoustic impedance ratio is preferably <NUM> < (P/v)/Z2a < <NUM> between <NUM> and <NUM>, where: P and v are respectively a sound pressure and a particle velocity on a surface of the second airflow-blocking resin film layer 40b, the surface being opposite to the core layer <NUM>; and if the core layer <NUM> is filled with a sound absorbing material, Z2a is the acoustic impedance on the surface of the sound absorbing material.

Note that when the first and second airflow-blocking resin film layers 40a and 40b are provided on both sides of the core layer <NUM> in this way, the specific acoustic impedance ratios (P/v)/Z<NUM> between air and the first airflow-blocking resin film layer 40a are measured, without the decoupling layer <NUM>, on a surface of the first resin film layer 40a, the surface being opposite to the core layer <NUM>, and the specific acoustic impedance ratios (P<NUM>/v<NUM>)/Z<NUM> between air and the second airflow-blocking resin film layer 40b are measured on a surface of the second airflow-blocking resin film layer 40b, the surface being opposite to the core layer <NUM>. The specific acoustic impedance ratios Za/Z<NUM> between air and the decoupling layer <NUM> on the surface thereof are measured without the core layer <NUM> and the first airflow-blocking resin film layer 40a, as in the first embodiment. The specific acoustic impedance ratios Z2a/Z<NUM> between air and the sound absorbing material inside the core layer <NUM> on the surface thereof are measured without the second airflow-blocking resin film layer 40b.

According to the second embodiment, the first and second airflow-blocking resin film layers 40a and 40b are provided on both surfaces of the core layer <NUM> in which the open ends and the closed surfaces are arranged in every other row. Also, with this configuration, since the second airflow-blocking resin film layer 40b has the same performance as the first airflow-blocking resin film layer 40a, the same effect as that of the first embodiment can be obtained. In addition, providing the second airflow-blocking resin film layer 40b closes the open end <NUM> of at least one surface of the core layer <NUM> to enable further improving the sound transmission loss of the sound-insulation material for a vehicle.

As shown in <FIG>, a sound-insulation material for a vehicle, of the third embodiment, includes: a core layer <NUM> described above; an airflow-blocking resin film layer <NUM> provided on one surface thereof; a decoupling layer <NUM> provided on the airflow-blocking resin film layer <NUM>; and a resin film layer <NUM> having a plurality of apertures on a surface of the core layer <NUM>, the surface being opposite to the first airflow-blocking resin film layer <NUM>. 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 being adhered 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> in 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> in 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> in 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 a surface of the core layer <NUM>, the surface being opposite to the airflow-blocking resin film layer <NUM>, the same effect as that of the first embodiment can be obtained. In addition, the aperture pattern preformed in the apertured film layer <NUM> enables the degree of blockage of the open end <NUM> to be readily adjusted and stably maintained on at least one surface of the core layer <NUM>. This makes it possible to control the ratio of sound insulation and sound absorption of the sound-insulation material for a vehicle. Therefore, with respect to the first airflow-blocking resin film layer 40a and the decoupling layer <NUM>, it is possible to more readily control the value of the specific acoustic impedance ratio (P/v)/Za described above and the sound insulation performance of the sound-insulation material for a vehicle.

As shown in <FIG>, a sound-insulation material for a vehicle, of a fourth embodiment, includes: a core layer <NUM> described above; a plurality of airflow-blocking resin film layers 40a and 40b provided on one surface thereof; and a decoupling layer <NUM> provided on the airflow-blocking resin film layer 40b. 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 plurality of airflow-blocking resin film layers 40a and 40b to be used may have the same configuration (the material, thickness, and the like of the resin film) or may have different configurations from each other. When the plurality of airflow-blocking resin film layers 40a and 40b are provided between the core layer <NUM> and the decoupling layer <NUM> in this way, the sound pressure P and the particle velocity v are measured on the outermost surface of the airflow-blocking resin film layer 40b, out of the plurality of airflow-blocking resin film layers 40a and 40b provided on the core layer <NUM>.

According to the fourth embodiment, also with the plurality of airflow-blocking resin film layers 40a and 40b provided between the core layer <NUM> and the decoupling layer <NUM>, the same effect as that of the first embodiment can be obtained. In addition, the plurality of airflow-blocking resin film layers 40a and 40b may have different configurations from each other, so that it is possible to increase the degree of freedom in design when adjusting the value of the specific acoustic impedance ratio (P/v)/Za described above, and to more readily control the sound insulation performance of the sound-insulation material for a vehicle.

Examples and a comparative example of the present invention are described below.

As Example <NUM>, a sound-insulation material for a vehicle having a multilayer structure shown in <FIG> and <FIG> was produced. First, an airflow-blocking resin film (material: polyethylene/polyamide/polyethylene <NUM>-layer film) with a thickness of <NUM> was adhered to one surface of the core layer having the structure of <FIG> (material: polypropylene resin, pitch Pcy between cells: <NUM>, thickness of core layer: <NUM>), and the specific acoustic impedance ratios (P/v)/Z<NUM> between air and this airflow-blocking resin film on the surface thereof were measured over a frequency range of <NUM> to <NUM> with an impedance tube (model number <NUM>, φ29 manufactured by B & K). Next, felt (material: miscellaneous fibers, manufacturing method: needle punching, basis weight: <NUM> / m<NUM>) was adhered to the airflow-blocking resin film as a decoupling layer. Here, the specific acoustic impedance ratios Za/Z<NUM> between air and the felt on the surface thereof were measured over a frequency range of <NUM> to <NUM> with the impedance tube. The specific acoustic impedance ratios (P/v)/Za were calculated from these measured values. The average specific acoustic impedance ratio (P/v)/Za of Example <NUM> was <NUM> in the frequency range of <NUM> to <NUM>. In addition, the surface density of the sound-insulation material for a vehicle, of Example <NUM>, was <NUM>/m<NUM>.

In the same manner as in Example <NUM>, as shown in Table <NUM> below, the sound-insulation materials for a vehicle, of Examples <NUM> to <NUM>, were produced in which the materials, basis weights, thicknesses, and the like of the airflow-blocking resin film and the decoupling layer were changed. Then, the specific acoustic impedance ratios (P/v)/Z<NUM> and Za/Z<NUM>, and the surface density thereof were measured. In addition, as a comparative example, the specific acoustic impedance ratio and the surface density were also measured for a rubber sheet with the same size (material: ethylene propylene diene rubber (EPDM)). The results including Example <NUM> are shown in Table <NUM> and <FIG>.

As shown in Table <NUM> and <FIG>, it was confirmed that, as compared with the comparative example of the rubber sheet having a surface density of <NUM>/m<NUM>, all the examples successfully obtained great specific acoustic impedance ratios with respect to the surface densities, and thus exhibited high sound insulation properties while reducing the weight of the sound-insulation materials for a vehicle. A graph showing this more clearly is in <FIG> shows the results of measuring the sound transmission loss (dB) between frequencies of <NUM> and <NUM> with respect to Example <NUM> and Comparative Example. Here, the sound transmission loss was measured by measuring sound intensity in combination with a reverberation room and an anechoic room. The relationship between the sound transmission loss and each measured value is shown in the following expression. The size of each measurement sample was <NUM> × <NUM>. <MAT> where:.

As shown in <FIG>, Example <NUM> has a mass of about <NUM>/<NUM> of that of Comparative Example and has sound transmission loss about <NUM> dB higher than that of Comparative Example over frequencies of <NUM> to <NUM>, and thus this can maintain high sound insulation properties while significantly reducing the weight of the sound-insulation material for a vehicle.

Claim 1:
A sound-insulation 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 (<NUM>) of the cells (<NUM>) are arranged on both sides of the core layer (<NUM>) such that rows of the open ends (<NUM>) of the cells (<NUM>) are in every other row;
a first airflow-blocking resin film layer (<NUM>) provided on at least one surface of the core layer (<NUM>) and
a decoupling layer (<NUM>) provided on a surface of the first airflow-blocking resin film layer (<NUM>), the surface being opposite to the core layer (<NUM>),
characterized in that
the closed surfaces (<NUM>) of the cells (<NUM>) arranged in every other row serve as a surface for adhering the first airflow-blocking resin film layer (<NUM>) and the core layer (<NUM>), and
an average specific acoustic impedance ratio is <NUM> < (P/v)/Za < <NUM> between <NUM> and <NUM>, where P and v are, respectively, a sound pressure and a particle velocity on a surface of the first airflow-blocking resin film layer (<NUM>) provided on the core layer (<NUM>), the surface being opposite to the core layer (<NUM>), and Za is an acoustic impedance of the decoupling layer (<NUM>).