Sound-absorbing hollow structure

Abstract

To provide a sound-absorbing hollow structure that maintains sound absorption while being flame-retardant. [Solution] The sound-absorbing hollow structure 1 comprises a base layer 2 having a plurality of internal spaces, cells S1 and S2, and a metal layer 6 provided on at least one surface of the base layer 2. The base layer 2 contains a resin and a flame retardant, and the base layer 2 and the metal layer 6 are provided with communication holes 7 that connect the inside and outside of the cells S. The flame retardant is, for example, an inorganic flame retardant, and the flame retardant content is 5% by mass or more relative to the total mass of the base layer.

Description

[Technical Field]

[0001] The present invention relates to a sound-absorbing hollow structure having a plurality of cells. [Background technology]

[0002] Conventionally, hollow structures are known in which multiple cells having a polygonal prism or cylindrical shape are arranged side by side inside. For example, the hollow structure described in Patent Document 1 has a resin core layer formed by folding a textured sheet material molded into a predetermined shape, and a resin sheet-like skin layer joined to both the upper and lower surfaces of the core layer. In Patent Document 1, a communication hole is provided on one side of the hollow structure to connect the inside and outside of the cells, thereby improving sound absorption. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2017-65026 [Overview of the project] [Problems that the invention aims to solve]

[0004] Incidentally, the applications of the hollow structures described above are wide-ranging, and they are used as various soundproofing materials for vehicles, buildings, and other structures. For example, they are envisioned for use as paneling for walls and ceilings to improve sound insulation in rooms. In such applications, in addition to sound absorption, the hollow structure itself may need to be flame-retardant.

[0005] For example, Patent Document 1 does not consider the hollow structure from this perspective. Furthermore, since the hollow structure in Patent Document 1 has communication holes, it is conceivable that at high temperatures or during combustion, material could enter the core layer inside the hollow structure through these communication holes and burn from the inside, thus working to one's disadvantage.

[0006] This invention has been made in view of these circumstances, and aims to provide a sound-absorbing hollow structure that is flame-retardant while maintaining sound absorption properties. [Means for solving the problem]

[0007] The sound-absorbing hollow structure of the present invention is a sound-absorbing hollow structure having a base layer having a plurality of cells that form internal spaces, and a metal layer provided on at least one surface of the base layer, wherein the base layer contains a resin and a flame retardant, and the base layer and the metal layer are provided with communication holes that connect the inside and outside of the cells.

[0008] The above-mentioned flame retardant is characterized by being an inorganic flame retardant.

[0009] The above-mentioned flame retardant is characterized by being a dehydrating or degassing flame retardant at high temperatures or during combustion.

[0010] The above-mentioned flame retardant is characterized by being a hydrated metal.

[0011] The amount of the above-mentioned flame retardant is 5% by mass or more relative to the total mass of the above-mentioned base material layer.

[0012] The above-mentioned base material layer comprises a core layer made of synthetic resin on which the cells are provided, and a skin layer made of synthetic resin disposed on the surface of the core layer and on which the metal layer is provided, and each layer of the core layer and the skin layer contains the flame retardant.

[0013] The above-mentioned base material layer contains inorganic clay minerals, and the amount of inorganic clay minerals is characterized by being 30% by mass or more of the total mass of the base material layer.

[0014] The above-mentioned communication hole is a communication hole formed by piercing through the base layer and the metal layer from the side of the metal layer toward the inside of the cell in the base layer, and the opening edge of the communication hole is located on the inside of the cell.

[0015] On the tip side of the opening edge of the above communication hole, the above base material layer is exposed, which is a characteristic.

[0016] The above communication holes are provided so that at least one or more are arranged in each of the above cells, and are characterized by satisfying the following formula (1). Total number of the above cells ≤ Total number of the above communication holes ≤ Total number of the above cells × 1.5 ··· (1)

[0017] Regarding the hole diameter of the opening edge of the above communication hole, when the average hole diameter is D, the above communication hole is characterized by satisfying the following formula (2). 0.2 mm ≤ D ≤ 1.0 mm ··· (2)

[0018] In the heat generation test compliant with ISO5660-1, the total heat generation amount in a test time of 20 minutes is 8 MJ / m Hereinafter, and the heat generation rate does not exceed 200 kW / m continuously for 10 seconds or more 2 which is a characteristic.

Effect of the Invention

[0019] The sound-absorbing hollow structure of the present invention has a base material layer having a plurality of cells and a metal layer, and the base material layer contains a resin and a flame retardant. Therefore, the metal layer blocks radiant heat and protects the base material layer from external heat, while the flame retardant can make the base material layer itself difficult to burn. Also, in such a hollow structure, at high temperature or during combustion, the air in the cells (including the combustible gas generated by the thermal decomposition of the resin) expands and the structure deforms, and combustion progresses from the gap at its end. However, since the communication holes are provided, the expanded air is discharged through the communication holes, so that the deformation of the structure due to expansion can be suppressed, and as a result, it leads to the suppression of combustion. Furthermore, since the communication holes are also provided in the metal layer, the communication holes are difficult to be blocked even when heated. As a result, a sound-absorbing hollow structure with flame retardancy while maintaining sound absorption is obtained.

[0020] Since the flame retardant is an inorganic flame retardant, it is possible to reduce the elongation of the base material layer provided with the communication holes and make it difficult to deform. For example, at the opening edge of the communication holes, deformation over time (recovery) and deformation during gas escape due to the expansion of air or gas during combustion can be suppressed. In addition, since it contains an inorganic material, the base material layer becomes harder, and when forming the communication holes, the hole diameters can vary, and due to this variation, a sound absorption effect can be exhibited in a wide frequency band.

[0021] Also, since the flame retardant exhibits dehydration or degassing properties at high temperatures or during combustion and generates water vapor gas, etc., the air in the cell may expand more. However, since the expanded air is discharged through the communication holes, deformation of the structure due to expansion can be suppressed.

[0022] Also, since the flame retardant is a hydrated metal compound (and also a dehydrating flame retardant), the water generated at high temperatures or during combustion volatilizes, suppressing the temperature rise in the surroundings and making it difficult to catch fire. In addition to suppressing the temperature rise, the flame retardant can also reduce the concentration of combustible gas.

[0023] Since the content of the flame retardant is 5% by mass or more based on the total mass of the base material layer, the structure itself becomes more difficult to burn.

[0024] The base material layer has a core layer made of synthetic resin and a skin layer made of synthetic resin. Since each of the core layer and the skin layer contains a flame retardant, it is more difficult to burn than when only one of the core layer and the skin layer contains a flame retardant, and the flame retardancy can be improved.

[0025] The above-mentioned base material layer contains inorganic clay minerals, with an inorganic clay mineral content of 30% by mass or more relative to the total mass of the base material layer. A higher inorganic clay mineral content reduces the amount of resin, which is a combustion component, making it easier to maintain the shape when the temperature rises. Furthermore, depending on the type of flame retardant, water and gas may be generated when the temperature rises, making it difficult to maintain the shape, but this can be avoided. In addition, the high content of inorganic clay minerals provides excellent flame retardancy and makes it easier to maintain the structure. Moreover, the inclusion of 30% by mass or more inorganic clay minerals suppresses shrinkage during molding and use of the hollow structure.

[0026] If a communication hole is provided, it is possible that the opening edge of the communication hole could trigger a fire, which could be disadvantageous in terms of flame retardancy. In this regard, the above-mentioned communication hole is formed by piercing through the base layer and the metal layer from the metal layer side toward the inside of the base layer cell, and since the opening edge of the communication hole is located on the inside of the cell, the metal layer is present at the opening edge and its surroundings in the communication hole formed by piercing, preventing the end face of the resin portion from being exposed and suppressing fire from this opening edge.

[0027] At the tip of the opening edge of the communication hole, the base material layer is exposed. In this case, the amount of resin at the tip of the opening edge of the communication hole is less than in other parts (horizontal parts), so it does not affect the flame retardancy.

[0028] In cells without communication holes, there is a risk of deformation due to the expansion of air inside the cell. However, since communication holes are provided so that at least one is placed in each cell, a passage can be secured to discharge the expanded air inside each cell during high temperatures or combustion, thereby suppressing deformation of the structure. Furthermore, by satisfying the above formula (1), it is possible to avoid adverse effects on sound absorption and flame retardancy that would occur if there were many communication holes.

[0029] By setting the average hole diameter of the opening edge of the communication hole within the range of formula (2) above, a good balance between flame retardancy and sound absorption can be achieved.

[0030] The above sound-absorbing hollow structure exhibited a total heat generation of 8 MJ / m³ over a 20-minute test period in a heat generation test compliant with ISO 5660-1. 2 The following conditions must be met, and the heat generation rate must be 200 kW / m² for at least 10 seconds. 2 Since it does not exceed a certain limit, it has excellent fire-retardant properties. [Brief explanation of the drawing]

[0031] [Figure 1] This is a perspective view showing a schematic configuration of one embodiment of the sound-absorbing hollow structure of the present invention. [Figure 2] Figure 1 is a partial cross-sectional view of the sound-absorbing hollow structure. [Figure 3] This is a partially enlarged cross-sectional view of Figure 2. [Figure 4] This is a schematic diagram illustrating the process of forming communication holes. [Modes for carrying out the invention]

[0032] Hereinafter, embodiments of the sound-absorbing hollow structure of the present invention will be described with reference to the drawings.

[0033] Figure 1 shows a schematic configuration of one embodiment of the sound-absorbing hollow structure of the present invention. As shown in Figure 1, the sound-absorbing hollow structure 1 is configured as a plate-like member comprising a base layer 2 having a plurality of cells S that form internal spaces, and a metal layer 6 provided on one side of the base layer 2. Note that the cross-section of the base layer 2 is shown schematicly in Figure 1, and the details will be explained in Figures 2 and 3.

[0034] In Figure 1, the metal layer 6 is provided so as to cover the upper surface of the base layer 2. The material of the metal layer 6 is not particularly limited, but it is preferable to use aluminum, which has excellent ability to shield from thermal radiation (reflect heat rays). The thickness of the metal layer 6 is, for example, 5 μm to 100 μm. A larger thickness of the metal layer 6 makes it easier to suppress deformation of the hollow structure at high temperatures, and consequently makes it easier to suppress ignition. On the other hand, a thinner metal layer can reduce weight. The metal layer 6 may be, for example, a metal plate or metal foil, or it may be a metal vapor-deposited layer provided on the base layer 2.

[0035] The metal layer 6 is preferably aluminum foil, with a thickness of 7 μm to 50 μm, and more preferably 20 μm to 40 μm.

[0036] In the sound-absorbing hollow structure 1, the base material layer 2 and the metal layer 6 are provided with communication holes 7 that connect the inside and outside of the cell S. In Figure 1, one communication hole 7 is provided in each cell S. Note that there may be cells in the sound-absorbing hollow structure that do not have communication holes. When used as a soundproofing material, sound pressure enters the internal space of each cell S through these communication holes 7, and the sound pressure can be effectively reduced in that internal space. In other words, each cell can function as a Helmholtz resonator, and the sound absorption coefficient can be improved compared to a hollow structure without communication holes.

[0037] Furthermore, the communication holes 7 also function as exhaust paths for heated air within the cell S, especially at high temperatures. At first glance, it might seem that the presence of communication holes 7 would be disadvantageous in terms of flame retardancy, as the opening edges of the communication holes 7 could trigger a fire. However, if communication holes 7 are not formed, at high temperatures, the air within the core layer expands, causing the plate-like member to deform significantly, exposing the edges of the plate material and leading to combustion. By forming communication holes, the heated air within the core layer is expelled to the outside, suppressing the expansion of the plate-like member and thus preventing combustion caused by it. Details of the communication holes 7 will be described later.

[0038] As shown in Figure 1, cell S has a first cell S1 and a second cell S2 with different configurations. The first cells S1 are arranged in a row along the X direction, and two adjacent first cells S1 in the X direction in a plan view share one side of a hexagon. The second cells S2 are similarly arranged in a row along the X direction. Furthermore, the rows of first cells S1 and rows of second cells S2 are arranged alternately along the Y direction, which is perpendicular to the X direction. With this arrangement of first cells S1 and second cells S2, the base layer 2 as a whole forms a honeycomb structure.

[0039] The thickness T of the base material layer 2 is not particularly limited, but is, for example, 5 mm to 30 mm. From the viewpoint of combustion resistance performance, it is preferable that the thickness T of the base material layer 2 is smaller, and it may be 5 mm to 20 mm, or 5 mm to 15 mm. In the sound-absorbing hollow structure 1, for example, when comparing 5 mm and 30 mm, at high temperatures or the like, the base material layer 2 melts and the honeycomb structure collapses. However, if the thickness T is large, the deformation amount of the sound-absorbing hollow structure 1 increases significantly as it becomes thinner by that amount. As a result, the ends are likely to be exposed, which is likely to have an adverse effect. Also, when it catches fire or the like, since the amount of resin is also large due to the large thickness T, it is easier to burn.

[0040] The weight (g / m 2 ) of the base material layer 2 is, for example, 2000 g / m 2 ~5000 g / m 2 and may be 3000 g / m 2 ~4000 g / m 2 .

[0041] Next, FIG. 2(a) shows a cross-sectional view (cross-sectional view along line A-A) along the column of the first cell S1, and FIG. 2(b) shows a cross-sectional view (cross-sectional view along line B-B) along the column of the second cell S2. As shown in FIG. 2, the base material layer 2 has a core layer 3 in which cells S1 and S2 are provided, a skin layer (upper skin layer) 4 disposed on the upper surface of the core layer 3 and provided with a metal layer 6, and a skin layer (lower skin layer) 5 disposed on the lower surface of the core layer 3.

[0042] The core layer 3 is formed from a flat sheet material having a predetermined sheet thickness. Specifically, after the sheet material is formed into a concavo-convex sheet material having a predetermined concavo-convex shape, it is formed by folding. The core layer 3 is composed of an upper wall portion 3a, a lower wall portion 3b, and side wall portions 3c erected between the upper wall portion 3a and the lower wall portion 3b to partition the cell S into a hexagonal prism shape.

[0043] As shown in Figure 2(a), in the first cell S1, a two-layer upper wall 3a is provided above the side wall 3c. A single-layer lower wall 3b is provided below the side wall 3c. On the other hand, as shown in Figure 2(b), in the second cell S2, a single-layer upper wall 3a is provided above the side wall 3c, and a two-layer lower wall 3b is provided below the side wall 3c. Furthermore, adjacent first cells S1 and second cells S2 are separated by two-layer side wall 3c.

[0044] The skin layers 4 and 5 are formed from a flat sheet material having a predetermined sheet thickness. The skin layers 4 and 5 may use sheet materials with different compositions or layer structures than the core layer 3, or they may use the same sheet material as the core layer 3. It is preferable that the sheet materials on which skin layers 4 and 5 are formed are the same. The skin layers 4 and 5 are bonded to the upper or lower surface of the core layer 3, respectively.

[0045] In the sound-absorbing hollow structure 1, the base layer 2 contains a flame retardant in the resin to reduce flammability. In the embodiment shown in Figure 2, it is sufficient that at least one of the core layer 3, skin layer 4, and skin layer 5 constituting the base layer 2 contains the flame retardant. For example, only the core layer 3 may contain the flame retardant, or only the skin layer 4 and skin layer 5 may contain the flame retardant. From the viewpoint of flame resistance, it is preferable that all of the core layer 3, skin layer 4, and skin layer 5 contain the flame retardant.

[0046] The resin used in the base layer 2 can be a synthetic resin, a natural resin, a natural rubber, or the like. The synthetic resin is not particularly limited and includes polyethylene resin, polyolefin resins such as polypropylene resin, polyamide resin, polyethylene terephthalate resin, and polystyrene resin. These resins may be used individually or in combination of two or more. Thermoplastic resins are preferred as synthetic resins, and polypropylene resin is more preferred among them.

[0047] The resin content is preferably 20% to 90% by mass, and more preferably 30% to 80% by mass, relative to the total mass of the base layer 2 (in Figure 2, the total mass of the core layer 3, skin layer 4, and skin layer 5; the same applies hereinafter). As will be described later, the amount of resin can be relatively reduced by adding inorganic substances in addition to the flame retardant. For example, the resin content may be 30% to less than 50% by mass, or 30% to less than 40% by mass, relative to the total mass of the base layer 2.

[0048] As flame retardants, hydrated metal compounds, nitrogen-based compounds, silicon-based compounds, etc., can be used, and well-known inorganic and organic flame retardants can be used. For example, nitrogen-based compounds include melamine compounds (melamine cyanurate, etc.), guanidine compounds, and triazine compounds. However, halogen-based compounds are preferably not used from an environmental perspective.

[0049] It is preferable to use an inorganic flame retardant as the flame retardant. By using an inorganic flame retardant, the elongation of the base layer 2 is reduced and deformation is minimized when forming the communication holes 7. Furthermore, although the inorganic flame retardant is dispersed in the base layer 2, its non-uniformity makes it easy for variations in the diameter of the communication holes 7 to occur. As a result, in terms of sound absorption, the variation in diameter allows for sound absorption across a wide frequency range. Moreover, in the plate material, by actively creating variations in the diameter of the communication holes, sound absorption can be achieved across an even wider frequency range.

[0050] Preferably, the flame retardant exhibits dehydrating or degassing properties at high temperatures or during combustion. For example, a dehydrating flame retardant exhibits flame retardant properties by lowering the ambient temperature through the desorption of hydrates, which generates water or water vapor gas. A degassing flame retardant can suppress combustion by blocking oxygen through the generation of inert gases such as nitrogen gas. When using these flame retardants, the inside of the cell S may expand due to the generated gases, but the expanded air is discharged through the communication holes 7, thereby suppressing deformation of the hollow structure due to expansion.

[0051] Among the flame retardants mentioned above, it is more preferable to use hydrated metal compounds that are dehydrating and inorganic flame retardants. Examples of hydrated metal compounds include aluminum hydroxide, magnesium hydroxide, and various hydrates. The decomposition temperatures of aluminum hydroxide and magnesium hydroxide are sufficiently lower than the material temperature during combustion, and they also have a large heat absorption capacity, resulting in excellent flame retardant performance.

[0052] The flame retardant content is preferably 5% by mass or more, more preferably 10% by mass or more, and may be 20% by mass or more, or 30% by mass or more, based on the total mass of the base layer 2. On the other hand, in order to ensure moldability, the flame retardant content is preferably 80% by mass or less based on the total mass of the base layer 2.

[0053] Furthermore, the base layer 2 may contain additives other than flame retardants. Preferably, the additives are metal salts (such as magnesium stearate or calcium stearate) or inorganic substances such as inorganic clay minerals. Hereinafter, in this specification, "inorganic substance" refers to substances other than flame retardants. The inorganic substance may be used alone or in combination of two or more. The inorganic substance may be untreated or surface-treated.

[0054] As for inorganic materials, inorganic clay minerals are preferred due to their heat resistance and ability to maintain structure. For example, when hydrated metals are used as flame retardants, decomposition begins during combustion, releasing water vapor, which can lead to voiding of the structure and reduced rigidity. Therefore, it is preferable to use inorganic clay minerals to maintain rigidity. Examples of inorganic clay minerals include talc, mica, kaolin, smectite, vermiculite, zeolite, and sepiolite, and among these, talc is preferred. For example, comparing the residues after the exothermic test in the examples, talc, an inorganic clay mineral, leaves more residue than calcium carbonate, indicating better shape retention.

[0055] The shape of the inorganic material is not particularly limited, and particulate, flaky, or fibrous forms can be used. The average particle size (D50) of the inorganic material is, for example, 0.5 μm to 50 μm, preferably 1 μm to 20 μm. This average particle size is calculated from the volume-based particle size distribution measured using a laser diffraction / scattering particle size analyzer.

[0056] The inorganic substance content is preferably 20% by mass or more, more preferably 30% by mass or more, and may be 40% by mass or more, or 50% by mass or more, based on the total mass of the base layer 2. On the other hand, in order to ensure moldability, the inorganic substance content is preferably 70% by mass or less, based on the total mass of the base layer 2.

[0057] When the base layer 2 contains an inorganic substance along with a flame retardant, the total amount of the flame retardant and inorganic substance is preferably 40% by mass or more, more preferably 50% by mass or more, and may be 60% by mass or more, based on the total mass of the base layer 2. By increasing the total amount of the flame retardant and inorganic substance, the amount of easily combustible resin can be relatively reduced. Furthermore, from the viewpoint of maintaining the structure of the hollow structure at high temperatures, it is preferable that the amount of inorganic substance is greater than the amount of flame retardant. Specifically, the mass ratio of (flame retardant content):(inorganic substance content) may be (1:2) to (1:4).

[0058] Furthermore, it is preferable that each of the core layer 3, skin layer 4, and skin layer 5 in the base material layer 2 contains a flame retardant and an inorganic substance.

[0059] In addition, while the above describes the content of resin, flame retardant, and inorganic substances in the base layer 2, the content of resin, flame retardant, and inorganic substances in each of the layers 3, 4, and 5 that make up the base layer 2 can be appropriately changed within a range that satisfies the numerical range of the content of each in the base layer 2 as described above.

[0060] Furthermore, the numerical ranges for each content in the base layer 2 may be appropriately applied to each of the layers 3, 4, and 5. For example, the flame retardant content in the core layer 3 is preferably 5% by mass or more, more preferably 10% by mass or more, and may be 20% by mass or more, 30% by mass or more, and preferably 80% by mass or less of the total mass of the core layer 3. The same applies to the content of skin layer 4, skin layer 5, and other components.

[0061] Here, we will further describe the layer structure of the core layer and skin layer in a form in which each contains a flame retardant. Figure 3 shows an enlarged view of section C in Figure 2. In Figure 3, the upper wall portion 3a of the core layer has a three-layer structure, and the skin layer 4 has a two-layer structure. These layer structures originate from the sheet materials that serve as raw materials. The sheet thickness of the sheet material forming the core layer is T. a This corresponds to the sheet thickness of the sheet material forming the skin layer 4, which is T b It corresponds to this.

[0062] As shown in Figure 3, the upper wall portion 3a of the core layer is composed of a main layer 31 which is an intermediate layer, a surface layer 32 welded to the upper surface of the main layer 31, and a surface layer 33 welded to the lower surface of the main layer 31. In this configuration, the main layer 31 contains resin, a flame retardant, and an inorganic substance as needed, in predetermined proportions. On the other hand, the surface layers 32 and 33 are mainly composed of resin, and may be composed of resin only (100%). It is preferable that the resins constituting the main layer 31, surface layer 32, and surface layer 33 are the same resin, for example, polypropylene resin is used. The thickness of the main layer 31 is thickness T. a It accounts for, for example, 80% or more of the total thickness of the main layer 31, surface layer 32, and surface layer 33.

[0063] The skin layer 4 is composed of a main layer 41 and a surface layer 42 welded to the lower surface of the main layer 41. In this configuration, the main layer 41 contains resin, a flame retardant, and an inorganic substance as needed in predetermined proportions. On the other hand, the surface layer 42 is mainly composed of resin, and may be composed of resin only (100%). It is preferable that the resins constituting the main layer 41 and the surface layer 42 are the same resin, and for example, polypropylene resin can be used. The thickness of the main layer 41 is thickness T. b It accounts for, for example, 80% or more of the total thickness of the main layer 41 and the surface layer 42.

[0064] In this way, the upper wall portion 3a of the core layer 3 and the skin layer 4 are joined to each other via the surface layer, thereby ensuring sufficient interlayer bonding strength while incorporating a certain amount of flame retardants and inorganic substances in the core layer 3 and the skin layer 4. Although Figure 3 shows the upper wall portion 3a of the core layer 3, the lower wall portion 3b and the side wall portion 3c of the core layer 3 have a similar layer structure. Furthermore, the skin layer 5 has a layer structure similar to that of the skin layer 4.

[0065] Also, the sheet thickness (T) that forms the core layer a (equivalent to), sheet thickness (T) that forms the skin layer b These correspond to 0.1 mm to 1.0 mm, and may also be 0.2 mm to 0.6 mm.

[0066] Returning to Figure 2, in the sound-absorbing hollow structure 1, the communication holes 7 are formed by piercing the base layer 2 from the side of the metal layer 6 toward the interior of the cells S1 and S2 of the base layer 2. The opening edge of the communication hole 7 is located on the interior side of the cells S1 and S2. In Figure 2, the communication holes 7 are formed at equal intervals along the X direction. Specifically, the distance between the centers of adjacent cells S1 and S2 in the X direction (cell pitch) P1 is equal to the distance between adjacent communication holes 7 in the X direction P2 (distance P=P1=P2), and one communication hole is formed in each cell S. When there is one communication hole in each cell S at high temperature or during combustion, the expanded air is uniformly dispersed from the entire surface and gradually discharged. It is also possible to ensure that one or more communication holes are formed in each cell S by making the pitch P2 that forms the communication holes shorter than the cell pitch P1 (P1>P2).

[0067] Next, Figure 4 shows a schematic diagram of the process for forming the communication hole shown in Figure 2(b). As shown in Figure 4, the communication hole is made by passing a needle member 8 through. The needle member 8 is formed to become thinner towards the tip, and as a whole it has a needle shape with a pointed tip. Multiple needle members 8 are arranged at predetermined intervals in the X direction, and the interval is equal to the distance between the centers of adjacent second cells S2 in the X direction.

[0068] In this communication hole formation process, the needle member 8 is lowered into the hollow structure fixed below it, penetrating while pushing and widening the upper wall portions 3a of the metal layer 6, skin layer 4, and core layer 3. Due to friction with the circumferential surface of the needle member 8, the upper wall portions 3a of the metal layer 6, skin layer 4, and core layer 3 deform as the needle member 8 descends, extending inward towards the inside of the cell S2. After penetration, the needle member 8 is raised and removed from the hollow structure, completing the communication hole formation process. The result is then the state shown in Figure 2(b).

[0069] In this process, when the needle member 8 is inserted through the hollow structure, the metal layer 6 stretches less than the upper wall portion 3a of the skin layer 4 and core layer 3. As a result, the base material layer 2 is exposed at the tip 7a of the opening edge of the communication hole 7, and the metal layer 6 is not actually visible when the communication hole 7 is observed from inside the cell. Consequently, the density of the flame retardant at the tip of the opening edge of the communication hole 7 may be higher than in other parts (horizontal parts), making it difficult to burn despite its thinness, and suppressing the spread of fire starting from the hole, even with the communication hole 7 provided. Furthermore, when the upper wall portion 3a of the skin layer 4 and core layer 3 has the configuration shown in Figure 3, each main layer (flame retardant layer) and each surface layer (resin layer) stretches more easily than the metal layer. Therefore, the tip 7a of the opening edge of the communication hole 7 does not have a metal layer 6 and is composed of a surface layer and a main layer or a surface layer, and in this case as well, the density of the flame retardant may be relatively higher.

[0070] As shown in Figure 2, at least one communication hole is provided in each cell. The relationship between the total number of cells and the total number of communication holes preferably satisfies the following equation (1). Total number of cells ≤ Total number of connecting holes ≤ Total number of cells × 1.5 ... (1)

[0071] In the configuration shown in Figure 2, one communication hole 7 is formed in each cell S1 and S2, and the total number of cells is equal to the total number of communication holes (total number of cells = total number of communication holes).

[0072] Furthermore, the total number of connecting holes may be greater than the total number of cells (the relationship is: total number of cells < total number of connecting holes). This configuration can be formed, for example, by making the spacing P2 between adjacent connecting holes in the X direction shorter than the spacing P1 between the centers of adjacent cells in the X direction. For example, by adjusting the spacing P2 to 0.7 to 0.9 times the spacing P1, the total number of connecting holes can be kept within the upper limit of equation (1) above.

[0073] In configurations where the total number of communication holes exceeds the total number of cells, some cells will have two communication holes. Such cells are thought to allow for smoother air expulsion from within the cell, especially at high temperatures, and are less prone to deformation. Furthermore, when forming this configuration, the tip of the needle member may come into contact with the side wall of the cell. However, since the base layer containing a predetermined amount of inorganic flame retardant or inorganic substance is rigid, it becomes easier to stably form communication holes. On the other hand, the rigidity of the hollow structure tends to decrease as the total number of communication holes increases, and when the total number of communication holes is about twice the total number of cells, it may become difficult to maintain the structure of the intermediate structure at high temperatures.

[0074] Furthermore, regarding the diameter of the opening edge of the communication hole, if the average diameter D is 2.0 mm or less, it is preferable that the following formula (2) is satisfied. By keeping it within this range, a good balance between flame retardancy and sound absorption can be achieved. 0.2mm ≦ D ≦ 1.0mm (2)

[0075] The method for manufacturing the sound-absorbing hollow structure of the present invention will be described in general terms below.

[0076] First, sheet materials for forming the core layer and sheet materials for forming each skin layer are prepared. Each sheet material can be obtained, for example, by a molding process. For a sheet material forming a three-layer core layer, it can be obtained by bonding the upper surface layer and the lower surface layer to the main layer, respectively.

[0077] Next, the core layer is formed using a sheet material that forms the core layer. Specifically, a textured sheet material having a predetermined uneven shape is formed from the sheet material (textured sheet forming step), and then the core layer is formed by folding the textured sheet material (folding step). Sheet materials forming each skin layer are welded to both sides of the obtained core layer (welding step). For example, the upper surface of the core layer and the upper skin layer are welded together by heat welding of the resins of each surface layer. After welding the upper and lower skin layers, an adhesive is applied to the surface of one of the skin layers, and a metal layer is formed by attaching, for example, metal foil. Finally, the sound-absorbing hollow structure is obtained by performing the communication hole formation step described above.

[0078] Furthermore, the core layer may not be formed through a folding process, but rather by methods such as expanding a plastic sheet material.

[0079] Furthermore, the sound-absorbing hollow structure of the present invention is not limited to the configuration described above.

[0080] For example, the shape of the cells within the core layer may be polygonal, such as a rectangular prism or an octagonal prism, or cylindrical. Different shaped cells may be mixed within the core layer. Also, gaps (spaces) may exist between cells.

[0081] In the above, the upper and lower skin layers were assumed to have the same composition, but they may have different compositions. For example, different thermoplastic resins may be used for the upper and lower skin layers, or one of the skin layers (for example, the skin layer on the side without the metal layer) may be made of a thermoplastic resin that does not contain a flame retardant. Also, in the above, the base layer was assumed to have a core layer and a skin layer, but the skin layer is not an essential component, and the base layer may consist only of a core layer.

[0082] In a hollow structure, the metal layer may be provided on both sides of the base material layer.

[0083] In a hollow structure, communication holes may be provided on both sides of the base material layer. For example, metal layers may be provided on both sides of the base material layer, and communication holes may be provided so as to penetrate the metal layers on both sides of the cell.

[0084] In this embodiment, one or more additional layers may be welded to the upper surface of the metal layer or the lower surface of the lower skin layer. For example, a layer may be welded to the outer surface of the sound-absorbing hollow structure to impart specific chemical and physical properties such as water repellency and light shielding, or a layer printed with a predetermined pattern or color may be welded. The layer to be welded is not limited to a resin layer; it may be made of any material that can be molded to be relatively thin, such as a paper layer or a wood layer. [Examples]

[0085] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0086] [Example 1, Reference Examples 1-3] A 0.3 mm thick sheet material was used for the core layer, and a 0.6 mm thick sheet material was used for the skin layer. After fabricating a honeycomb-shaped substrate layer (see Figure 2) consisting of the core layer and skin layers bonded to both sides thereof, a 7 μm thick aluminum foil was attached to one of the skin layers via an adhesive. The composition and thickness of the substrate layers for each test example are shown in Table 1. Calcium carbonate was used as the inorganic substance in these test examples.

[0087] In Reference Example 2 and Example 1, each cell was processed to form at least one connecting hole. The average hole diameter D of the connecting holes was approximately 0.8 mm.

[0088] Each test specimen was subjected to a heat generation test in accordance with ISO 5660-1. Each test specimen (plate-shaped member; 100 mm x 100 mm) was placed horizontally on a cone calorimeter with the metal layer side (the side with the communication holes) facing the cone heater. The gas generated by heating with the cone heater was ignited and burned using a spark igniter. The heat output and heat generation rate were measured, and the specimens were evaluated as "flame-retardant equivalent," "semi-noncombustible equivalent," or "noncombustible equivalent" based on the standards shown in Table 2. "Semi-noncombustible equivalent" and "noncombustible equivalent" were deemed acceptable. The results are shown in Table 1.

[0089] [Table 1]

[0090] [Table 2]

[0091] As shown in Table 1, when comparing Reference Examples 1 and 2, which do not contain flame retardants, the addition of connecting holes resulted in a near-noncombustible level, although a slight decrease in flame resistance was observed. On the other hand, when comparing Reference Example 3, which contains magnesium hydroxide as a flame retardant, with Example 1, the noncombustible level could be maintained even when connecting holes were added.

[0092] In all test cases, deformation was observed after the start of the test. Specifically, the center of each test specimen bulged, while the edges sank. It was found that ignition progressed starting from this deformation of the surface material. Furthermore, in test specimens with communication holes (Reference Example 2, Example 1), the degree of deformation tended to be suppressed, confirming that the communication holes are effective not only for sound absorption but also for preventing flammability caused by the deformation.

[0093] [Examples 2-6, Comparative Example 1] A honeycomb-shaped substrate layer (see Figure 2) consisting of a core layer and skin layers bonded to both sides was fabricated. Then, a 40 μm thick aluminum foil was attached to one of the skin layers via an adhesive. Subsequently, the substrate layer was processed to form at least one interconnected hole in each cell. The average hole diameter D of the interconnected holes was approximately 0.8 mm. The composition of the substrate layer, the thickness of the core layer sheet material, and the thickness of the skin layer sheet material for each test example are shown in Table 3. Note that interconnected holes were formed in all the test examples shown in Table 3.

[0094] The exothermic test described above was performed on each of the obtained test specimens. The results are shown in Table 3.

[0095] [Table 3]

[0096] As shown in Table 3, Examples 2-4, consisting only of PP resin and magnesium hydroxide, were equivalent to non-combustible. In contrast, Comparative Example 1, which contained no flame retardant and consisted only of PP resin and talc (an inorganic substance), was equivalent to flame-retardant. Since talc alone does not have any element to lower the temperature during combustion, it was observed that the resin on the side walls of the cell melted and collapsed due to the weight of the skin layer, causing ignition from the gaps in the skin layer.

[0097] Examples 5 and 6 included talc in addition to the flame retardant, and the results of the exothermic reaction test were equivalent to non-combustibility. Compared to Examples 2 to 4, there was not much difference in the exothermic reaction test between Examples 5 and 6, but the talc contributed to maintaining the rigidity of the structure during combustion, and a good trend was observed in terms of structural retention. [Industrial applicability]

[0098] The sound-absorbing hollow structure of the present invention is given flame retardancy while maintaining sound absorption, and can therefore be widely used as various soundproofing materials. In particular, it is suitable as a panel material for walls, ceilings, and other surfaces where flame resistance is required. [Explanation of Symbols]

[0099] 1 Sound-absorbing hollow structure 2 Base material layer 3 Core Layers 31 Main layer 32 Surface layer 33 Surface layer 4 Skin Layers 41 Main layer 42 Surface layer 5 Skin Layers 6 metal layer 7 Communication hole 8 Needle member S cell S1 Cell 1 S2 Cell 2

Claims

1. A sound-absorbing hollow structure comprising a base layer having multiple cells that form internal spaces, and a metal layer provided on at least one surface of the base layer, The aforementioned substrate layer comprises a resin and a flame retardant. The sound-absorbing hollow structure is characterized in that the base layer and the metal layer are provided with communication holes that connect the inside and outside of the cell.

2. The sound-absorbing hollow structure according to claim 1, characterized in that the flame retardant is an inorganic flame retardant.

3. The sound-absorbing hollow structure according to claim 1 or 2, characterized in that the flame retardant is a flame retardant that is dewatering or degassing at high temperatures or during combustion.

4. The sound-absorbing hollow structure according to claim 1 or 2, characterized in that the flame retardant is a hydrated metal.

5. The sound-absorbing hollow structure according to claim 1 or 2, characterized in that the content of the flame retardant is 5% by mass or more with respect to the total mass of the base material layer.

6. The substrate layer comprises a core layer made of synthetic resin on which the cells are provided, and a skin layer made of synthetic resin disposed on the surface of the core layer and on which the metal layer is provided. The sound-absorbing hollow structure according to claim 1 or 2, characterized in that each of the core layer and the skin layer contains the flame retardant.

7. The aforementioned substrate layer contains inorganic clay minerals, The sound-absorbing hollow structure according to claim 1 or 2, characterized in that the content of the inorganic clay mineral is 30% by mass or more relative to the total mass of the base material layer.

8. The sound-absorbing hollow structure according to claim 1 or 2, characterized in that the communication hole is formed by piercing the base material layer and the metal layer from the side of the metal layer toward the inside of the cell in the base material layer, and the opening edge of the communication hole is located on the inside of the cell.

9. The sound-absorbing hollow structure according to claim 8, characterized in that the base material layer is exposed at the tip side of the opening edge of the communication hole.

10. The communication holes are provided such that at least one is located in each of the cells. The sound-absorbing hollow structure according to claim 1 or 2, characterized in that it satisfies the following formula (1). Total number of cells ≤ Total number of connecting holes ≤ Total number of cells × 1.5 ... (1)

11. The sound-absorbing hollow structure according to claim 1 or 2, characterized in that the communication hole satisfies the following formula (2) when the average diameter of the opening edge of the communication hole is D. 0.2mm ≦ D ≦ 1.0mm・・・(2) 【Request Item 12】 In a heat generation test compliant with ISO 5660-1, the total heat generated over a 20-minute test period was 8 MJ / m³. ２ The following conditions must be met, and the heating rate must remain at 200 kW / m² for at least 10 seconds. ２ A sound-absorbing hollow structure according to claim 1 or 2, characterized in that it does not exceed [a certain value].

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