hollow structure

Abstract

To provide a sound-absorbing hollow structure that is flame-retardant. [Solution] The hollow structure 1 is a hollow structure having a base layer 2 having a structure in which a plurality of cells S1, S2 are provided, and a metal layer 6 provided on the base layer 2, wherein the base layer 2 contains a resin and an additive which is at least one of an inorganic substance (excluding a flame retardant) and a flame retardant, and the content of the additive is 30% by mass or more of the total mass of the base layer, the inorganic substance is an inorganic clay mineral, and the content of the inorganic clay mineral relative to the total mass of the base layer is greater than the content of the flame retardant.

Description

Technical Field

[0001] The present invention relates to a hollow structure having a plurality of cells.

Background Art

[0002] Conventionally, a hollow structure in which a plurality of cells having a polygonal column shape or a cylindrical shape are arranged side by side inside is known. For example, the hollow structure described in Patent Document 1 has a resin core layer formed by folding a concavo-convex sheet material formed into a predetermined shape, and resin sheet-like skin layers joined to both upper and lower surfaces of the core layer. In Patent Document 1, a communication hole for communicating the inside and outside of the cell is provided on one surface of the hollow structure, and improvement in sound absorption is aimed at.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, the uses of the above-described hollow structures are wide-ranging and are applied to various soundproof materials such as vehicles and buildings. For example, in order to take soundproof measures for a room, it is also assumed to be used as a panel material for walls and ceilings. In such applications, there may be a case where it is required that the hollow structure itself is difficult to burn.

[0005] The present invention has been made in view of such circumstances, and an object thereof is to provide a hollow structure imparted with flame retardancy.

Means for Solving the Problems

[0006] The hollow structure of the present invention is a hollow structure having a base material layer with a structure provided with a plurality of cells and a metal layer provided on the base material layer, wherein the base material layer includes a resin, and an additive which is at least one of an inorganic substance (excluding a flame retardant; the same applies hereinafter) and a flame retardant, and the content of the additive is 30% by mass or more based on the total mass of the base material layer.

[0007] The base material layer includes the inorganic substance and the flame retardant as the additive, and the total content of the inorganic substance and the flame retardant is 50% by mass or more based on the total mass of the base material layer.

[0008] The inorganic substance is an inorganic clay mineral, and the content of the inorganic clay mineral based on the total mass of the base material layer is greater than the content of the flame retardant.

[0009] The base material layer has a resin core layer provided with the cells and a resin skin layer disposed on the surface of the core layer and provided with the metal layer, and each of the core layer and the skin layer includes the inorganic substance and the flame retardant.

[0010] The sheet thickness T

[0011] , b , a , , a , b , , a , for forming the core layer and the sheet thickness T b for forming the skin layer have a ratio of (T a :T b ) = (2:3 to 3:2).

[0011] The base material layer has a resin core layer provided with the cells and a resin skin layer disposed on the surface of the core layer and provided with the metal layer. When the sheet thickness for forming the core layer is T a , the content of the resin based on the total mass of the core layer is W a (mass%), the sheet thickness for forming the skin layer is T b , and the content of the resin based on the total mass of the skin layer is W b (mass%), it satisfies the following formula (1). (T a ×Wa )>(T b ×W b )···(1)

[0012] 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 heat generation rate must be 200 kW / m² for at least 10 seconds. 2 It is characterized by not exceeding a certain value.

[0013] 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 heat generation rate must be 200 kW / m² for at least 10 seconds. 2 The weight of the hollow structure shall not exceed 2000 g / m². 2 The following conditions must be met, and the bulk density of the hollow structure must be 0.1 to 0.7 g / cm³. 3 It is characterized by being such. [Effects of the Invention]

[0014] The hollow structure of the present invention comprises a base layer having multiple cells and a metal layer. The base layer contains a resin and at least one of an inorganic substance (excluding flame retardants) and a flame retardant as additives. The metal layer blocks radiant heat, protecting the base layer from external heat, while the additive, at least one of the inorganic substance and flame retardant, makes the base layer itself less flammable. Furthermore, since the additive is present in the base layer at a concentration of 30% by mass or more relative to the total mass of the base layer, the amount of easily combustible resin can be relatively reduced. This results in a hollow structure with flame retardancy.

[0015] The above-mentioned base layer contains inorganic substances and flame retardants as additives, and the total content of inorganic substances and flame retardants is 50% by mass or more of the total mass of the base layer. Therefore, the amount of easily combustible resin can be relatively reduced, and the base layer itself can be made even less combustible.

[0016] Furthermore, in hollow structures, the structure deforms at high temperatures or during combustion, and combustion tends to progress through gaps at the edges. However, by including inorganic clay minerals as an inorganic substance, it becomes easier to maintain the structure when the temperature rises, leading to improved combustion resistance. In addition, depending on the type of flame retardant, water and gas may be generated when the temperature rises, making it difficult to maintain the shape. However, since the inorganic clay mineral content is higher than the flame retardant content, this problem can be avoided. Moreover, the high content of inorganic clay minerals can suppress shrinkage, deformation, and warping during molding and use of hollow structures.

[0017] The above-mentioned base material layer has a resin core layer and a resin skin layer, and each layer of the core layer and skin layer contains inorganic substances and flame retardants. Therefore, compared to cases where, for example, the skin layer does not contain inorganic substances and only contains flame retardants, it is easier to maintain the structure of each layer itself, leading to improved flame resistance.

[0018] Sheet thickness T forming the above core layer a and the sheet thickness T that forms the skin layer b The ratio is (T a :T b The ratio is (2:3 to 3:2), and it is easier to improve flame resistance compared to cases where, for example, the skin layer is thicker and contains more resin than the core layer.

[0019] The sheet thickness forming the above core layer is T a The resin content relative to the total mass of the core layer is W a (mass%), the sheet thickness that forms the skin layer is T b The resin content relative to the total mass of the skin layer is W b When expressed as (mass %), the above equation (1) is satisfied, so the amount of resin in the skin layer can be relatively reduced compared to the core layer, making it easier to improve flame resistance to external heat.

[0020] The above hollow structure exhibited a total heat generation of 8 MJ / m³ over a 20-minute test period in accordance 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.

[0021] Furthermore, in a heat generation test conducted in accordance with ISO 5660-1, the above-mentioned hollow structure generated a total heat of 8 MJ / m³ over a 20-minute test period. 2 The following conditions must be met, and the heat generation rate must be 200 kW / m² for at least 10 seconds. 2 The weight of the hollow structure must not exceed 2000g / m². 2 The following conditions must be met, and the bulk density of the hollow structure must be 0.1-0.7 g / cm³. 3 Therefore, it is lightweight yet has excellent fire-resistant properties, making it useful as a soundproofing material for ceilings, for example. [Brief explanation of the drawing]

[0022] [Figure 1] This is a perspective view showing the schematic configuration of one embodiment of the hollow structure of the present invention. [Figure 2] This is a partial cross-sectional view of the hollow structure shown in Figure 1. [Figure 3] This is a partially enlarged cross-sectional view of Figure 2. [Figure 4] This is a schematic diagram showing a cell in a buckled state, etc. [Figure 5] This is a schematic diagram illustrating the process of forming communication holes. [Figure 6] This is a perspective view showing a schematic configuration of another embodiment of the hollow structure of the present invention. [Modes for carrying out the invention]

[0023] Hereinafter, embodiments of the hollow structure of the present invention will be described with reference to the drawings.

[0024] Figure 1 shows a schematic configuration of one embodiment of the hollow structure of the present invention. As shown in Figure 1, the hollow structure 1 is configured as a plate-like member comprising a base layer 2 having a plurality of internal cells S and a metal layer 6 provided on one surface 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.

[0025] 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.

[0026] 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.

[0027] In the 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 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.

[0028] Furthermore, these 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, by forming the communication holes 7, heated air within the core layer is expelled to the outside, which suppresses the expansion of the plate-like member and makes it easier to suppress combustion caused by this expansion.

[0029] 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.

[0030] The thickness T of the base layer 2 is not particularly limited, but is for example 5 mm to 30 mm. From the viewpoint of flame resistance, a smaller thickness T of the base layer 2 is preferable, and may be 5 mm to 20 mm or 5 mm to 15 mm. In the hollow structure 1, for example, comparing 5 mm and 30 mm, at high temperatures, the base layer 2 will melt and the honeycomb structure will collapse. However, if the thickness T is large, the hollow structure 1 will deform more due to the significantly thinner structure. As a result, the edges are more likely to be exposed, which is disadvantageous. Also, when ignited, a larger thickness T means a larger amount of resin, making it more flammable.

[0031] Weight of base layer 2 (g / m²) 2 ) For example, 1000g / m 2 ~5000g / m 2 It is 3000g / m 2 ~4000g / m 2 That's fine.

[0032] Also, the weight of the hollow structure 1 (g / m 2 ) For example, 1000g / m 2 ~5000g / m 2 It is 3000g / m² 2 ~4000g / m 2 It may also be the case that the bulk density of the hollow structure is 0.1 to 0.7 g / cm³. 3 It is preferable that this is the case. The "bulk density" referred to here is the density measured by considering the internal space of the cells S of the hollow structure 1 as part of the volume. For example, if the weight of the hollow structure 1 is 1600 g / m³ 2If the total thickness of the board is 5 mm, the bulk density is 0.32 g / cm³. 3 (=1600 ÷ (100 × 100 × 0.5)). Also, the weight of hollow structure 1 is 1600 g / m 2 If the total thickness of the sheet is 4 mm (for example, if 1 mm is compressed during molding), the bulk density is 0.4 g / cm³. 3 (=1600 ÷ (100 × 100 × 0.4)) and the weight of hollow structure 1 (g / m 2 If the values ​​are equal, a thinner overall plate thickness results in a higher bulk density.

[0033] Next, Figure 2(a) shows a cross-sectional view along the row of the first cell S1 (cross-sectional view along line AA), and Figure 2(b) shows a cross-sectional view along the row of the second cell S2 (cross-sectional view along line BB). As shown in Figure 2, the base layer 2 has a core layer 3 on which cells S1 and S2 are provided, a skin layer (upper skin layer) 4 which is placed on the upper surface of the core layer 3 and on which the metal layer 6 is provided, and a skin layer (lower skin layer) 5 which is placed on the lower surface of the core layer 3.

[0034] The core layer 3 is formed from a flat sheet material having a predetermined sheet thickness. Specifically, the sheet material is formed into an uneven sheet material having a predetermined uneven shape, and then folded to form the core layer 3. The core layer 3 consists of an upper wall portion 3a, a lower wall portion 3b, and a side wall portion 3c erected between the upper wall portion 3a and the lower wall portion 3b to divide the cell S into a hexagonal prism shape.

[0035] 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.

[0036] 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.

[0037] In the hollow structure 1, the base layer 2 contains a resin and at least one of an inorganic substance and a flame retardant as an additive, and the content of the additive is 30% by mass or more of 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). In the embodiment of Figure 2, the base layer 2 as a whole contains an additive (in any of the following forms: inorganic substance only, flame retardant only, or consisting of an inorganic substance and a flame retardant), and furthermore, the content of the additive is 30% by mass or more of the total mass of the base layer 2. From the viewpoint of relatively reducing the amount of resin, the content of the additive is preferably 50% by mass or more, and from the viewpoint of considering weight reduction, it is preferably 30% by mass to 55% by mass.

[0038] In the form in which the additive consists of an inorganic substance and a flame retardant, for example, the core layer 3 may contain an inorganic substance and a flame retardant, while the skin layers 4 and 5 may not contain either an inorganic substance or a flame retardant, or may contain only one of them. For example, the skin layers 4 and 5 may contain an inorganic substance and a flame retardant, while the core layer 3 may not contain either an inorganic substance or a flame retardant, or may contain only one of them. From the viewpoint of flame resistance, it is preferable that each of the core layer 3, skin layer 4, and skin layer 5 contains an inorganic substance and a flame retardant. Furthermore, in the form in which the additive consists of an inorganic substance and a flame retardant, it is more preferable that the total content of the inorganic substance and flame retardant be 50% by mass or more of the total mass of the base layer 2.

[0039] 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.

[0040] The resin content is, for example, 20% to 70% by mass relative to the total mass of the base layer 2. From the viewpoint of flame resistance, it is preferably 30% to 50% by mass, and from the viewpoint of weight reduction, it is preferably 45% to 70% by mass. From the viewpoint of flame resistance, the total mass of inorganic substances and flame retardants in the base layer 2 can be increased, and the amount of resin can be relatively reduced. For example, the resin content may be 30% or more and less than 40% by mass relative to the total mass of the base layer 2.

[0041] As the inorganic substance, it is preferable to use metal salts (such as calcium carbonate, magnesium stearate, or calcium stearate) or inorganic clay minerals. The inorganic substance may be used alone or in combination of two or more. The inorganic substance may be untreated or surface-treated.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] As a flame retardant, it is preferable to use an inorganic flame retardant. For example, in a configuration in which communication holes 7 are formed, using an inorganic flame retardant allows for less elongation and deformation of the base layer 2 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, for example in terms of sound absorption, the variation in diameter allows for sound absorption across a wide frequency range.

[0046] Preferably, flame retardants exhibit dehydrating or degassing properties at high temperatures or during combustion. For example, dehydrating flame retardants exhibit flame retardant properties by lowering the ambient temperature through the desorption of hydrates, which generates water or water vapor gas. Degassing flame retardants can suppress combustion by blocking oxygen through the generation of inert gases such as nitrogen gas. When using these flame retardants, the generated gas may cause the inside of the cell S to expand. However, in a configuration in which communication holes 7 are formed, for example, the expanded air is discharged through these communication holes 7, thereby suppressing deformation of the hollow structure due to expansion.

[0047] 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.

[0048] In the form where the additive consists of an inorganic substance and a flame retardant, the total content of the inorganic substance and flame retardant is, for example, 50% by mass or more, preferably 55% by mass or more, and may be 60% by mass or more, based on the total mass of the base layer 2. On the other hand, in order to ensure moldability, the total content of the inorganic substance and flame retardant is preferably 75% by mass or less, based on the total mass of the base layer 2.

[0049] 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, the inorganic substance content is preferably 70% by mass or less, based on the total mass of the base layer 2.

[0050] 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, the flame retardant content is preferably 60% by mass or less based on the total mass of the base layer 2.

[0051] From the viewpoint of maintaining the structure of the hollow structure at high temperatures, it is preferable that the amount of inorganic substance relative to the total mass of the base layer 2 is greater than the amount of flame retardant. Specifically, the mass ratio of (inorganic substance content):(flame retardant content) may be (1.5:1) to (9:1). More preferably, the ratio of (inorganic substance content):(flame retardant content) may be (2:1) to (4:1).

[0052] In the form in which the additive consists of an inorganic substance and a flame retardant, a particularly preferred form regarding the content of the inorganic substance and flame retardant is that in the base layer 2, the total content of the inorganic substance and flame retardant is 55% by mass or more and 75% by mass or less, with the inorganic substance content being 40% by mass or more and the flame retardant content being 10% by mass or more. Furthermore, it is preferable to use an inorganic clay mineral as the inorganic substance and a hydrated metal as the flame retardant.

[0053] In addition, while the above describes the contents of resin, inorganic substances, and flame retardants in the base layer 2, the contents of resin, inorganic substances, and flame retardants 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 contents for each component in the base layer 2 as described above.

[0054] Furthermore, the numerical ranges for each content in the base layer 2 may be appropriately applied to each layer 3, 4, and 5. For example, the inorganic substance content in core layer 3 is preferably 20% by mass or more, more preferably 30% by mass or more, and may be 40% by mass or more, 50% by mass or more, and preferably 70% by mass or less, relative to the total mass of core layer 3. Similarly, the flame retardant content in 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 60% by mass or less, relative to the total mass of core layer 3. The same applies to the content of skin layer 4, skin layer 5, and other components.

[0055] Here, we will further describe the layer structure of the core layer and skin layer in a form in which both contain inorganic substances and flame retardants. 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.

[0056] 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, an inorganic substance, and a flame retardant 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.

[0057] 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, an inorganic substance, and a flame retardant 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, 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.

[0058] In this way, by joining the upper wall portion 3a of the core layer 3 and the skin layer 4 to each other via the surface layer, sufficient interlayer bonding strength can be ensured in the core layer 3 and the skin layer 4 while still containing inorganic substances and flame retardants to a certain extent. 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.

[0059] Also, the sheet thickness (T) that forms the core layer a (equivalent to), sheet thickness (T) that forms the skin layer b(corresponding to) are 0.1 mm to 1.0 mm, and may also be 0.2 mm to 0.6 mm. Also, the ratio of these is (T a :T b It is preferable that the ratio of the core layer to the skin layer is (2:3 to 3:2), and having similar sheet thicknesses between the core layer and the skin layer helps prevent adverse effects on flammability compared to having a difference in sheet thickness between the core layer and the skin layer. Also, the sheet thickness T of the skin layer b The core layer sheet thickness T a The following is preferable:

[0060] The base layer 2 has a resin content of W relative to the total mass of the core layer 3. a (mass%), the resin content relative to the total mass of the skin layer 4 is W b When expressed as (mass%), it is preferable that the following formula (1) is satisfied. This makes it possible to relatively reduce the amount of resin in the skin layer relative to the core layer, and thus improves the flame resistance performance against external heat. (T a ×W a )>(T b ×W b )···(1)

[0061] When the additive is in the form of only an inorganic substance or only a flame retardant, a particularly preferred form of additive content is when the additive content in the base layer 2 is 30% to 55% by mass. When the additive is in the form of only an inorganic substance (preferably talc), flame retardancy can be easily imparted even without including a flame retardant by reducing the weight of the hollow structure. From the viewpoint of reducing weight, for example, the thickness T of the base layer 2 is preferably 5 mm to 15 mm, and more preferably 5 mm to 8 mm.

[0062] Furthermore, the weight of the hollow structure is 2000g / m 2 The following conditions must be met, and the bulk density of the hollow structure must be 0.1 to 0.7 g / cm³. 3 It is preferable that the bulk density is 0.1 to 0.4 g / cm³ when the cells are not buckled. 3 In the state where the cell is buckled, preferably 0.2 to 0.7 g / cm³ 3For example, hollow structures are sometimes manufactured by crushing them to a predetermined thickness during molding. In this case, the cells buckle, and as the plate thickness decreases, the bulk density increases (see Figure 4).

[0063] Returning to Figure 2, in the hollow structure 1, the communication holes 7 are formed by penetrating 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).

[0064] Next, Figure 5 shows a schematic diagram of the process for forming the communication hole shown in Figure 2(b). As shown in Figure 5, 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.

[0065] 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).

[0066] Here, during the process of penetrating the hollow structure with the needle member 8, 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 in fact, the metal layer 6 cannot be observed even when the communication hole 7 is observed from inside the cell. Consequently, the density of inorganic substances and flame retardants may be higher at the tip of the opening edge of the communication hole 7 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 and each surface layer stretches more easily than the metal layer, so 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 inorganic substances and flame retardants may be relatively higher.

[0067] The method for manufacturing the hollow structure of the present invention will be described in general terms below.

[0068] 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.

[0069] Next, the core layer is formed using a sheet material that will form 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 that will form 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, if necessary, the above-described process for forming connecting holes is performed to obtain a hollow structure.

[0070] Furthermore, the core layer may not be formed through a folding process, but rather by methods such as expanding a plastic sheet material.

[0071] Furthermore, the hollow structure of the present invention is not limited to the configuration described above.

[0072] 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.

[0073] 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 inorganic substances or flame retardants. 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.

[0074] In a hollow structure, the metal layer may be provided on both sides of the base material layer.

[0075] 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.

[0076] As shown in Figure 6, the structure may also be configured without communication holes connecting the inside and outside of the cells S. The hollow structure 1A in Figure 6 is configured as a plate-like member comprising a base layer 2 having multiple internal spaces (cells S) and a metal layer 6 provided on one side of the base layer 2. In this hollow structure 1A, no communication holes are provided to connect the inside and outside of the cells S. Sufficient flame resistance can be obtained even in this configuration.

[0077] 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 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]

[0078] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0079] [Examples 1-8, Comparative Example 1] A sheet material with a thickness of 0.3 mm to 0.4 mm was used for the core layer, and a sheet material with a thickness of 0.3 mm to 0.6 mm was used for the skin layer. After fabricating a honeycomb-shaped substrate layer (see Figure 2) consisting of a core layer and skin layers bonded to both sides thereof, a 40 μm thick aluminum foil was attached to one of the skin layers via an adhesive. The thickness of the substrate layer in each test example was 12 mm, and its composition is shown in Table 1. In these test examples, talc or calcium carbonate was used as the inorganic substance, and magnesium hydroxide was used as the flame retardant.

[0080] Furthermore, in each test example, the presence or absence of inorganic substances and flame retardants in the resin of the core layer sheet material and the skin layer sheet material is as shown in Table 1. For convenience, in Table 1, inorganic substances are written as "inorganic" and flame retardants as "flame retardant". As shown in Table 1, in Examples 4 and 7, the core layer sheet material contains inorganic substances and flame retardants, while the skin layer sheet material contains only inorganic substances, and the composition of each sheet material is shown in the margin. In the other examples, both the core layer and the skin layer sheet material contain inorganic substances and flame retardants, and the composition of each sheet material is similar to the composition of the entire base layer, so its description is omitted.

[0081] In Examples 1-7 and Comparative 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. On the other hand, no connecting holes were formed in Example 8.

[0082] 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. Specimens that did not meet the "flame-retardant equivalent" standard were classified as "combustible equivalent." The results are shown in Table 1.

[0083] [Table 1]

[0084] [Table 2]

[0085] As shown in Table 1, Comparative Example 1, in which the base layer consisted only of resin (PP resin), was equivalent to flammable, whereas Examples 1 to 8, in which the base layer contained resin (PP resin), an inorganic substance (talc or calcium carbonate), and a flame retardant (magnesium hydroxide), were equivalent to semi-noncombustible or noncombustible. Among these, Examples 1 and 2 in particular showed good reproducibility of the test results and suppressed the reduction in the thickness of the base layer after the 20-minute test.

[0086] In all of the test examples, deformation was observed after the start of the test. Specifically, the central part of each test specimen bulged, while the peripheral parts sank. It was found that ignition progressed starting from this deformation of the surface material. This suggests a correlation between structural integrity during combustion and combustion resistance in such hollow structures.

[0087] In Table 1, when comparing the examples, for example, the sheet thickness T of the skin layer b It was observed that increasing the thickness tended to decrease the flame resistance performance (Example 3). Note that in Example 3, the sheet thickness T b The layer is too thick and does not satisfy the relationship in equation (1) above. It is presumed that as the skin layer thickens, the amount of resin in the skin layer increases, which leads to an increase in the generation of flammable gas and has an adverse effect. Note that the sheet thickness T of the core layer a No such effect was observed in this test (Examples 2 and 6).

[0088] Furthermore, when the additive in the skin layer sheet material consisted solely of a flame retardant, a tendency for reduced combustion resistance was observed (Examples 4 and 7). In these cases, it is presumed that the skin layer contained a large amount of magnesium hydroxide, and the generation of water due to the rise in temperature made it difficult to maintain the structure. Comparing Examples 1-2 with Examples 5-6, there was not much difference between talc and calcium carbonate, but talc showed better reproducibility of test results and also tended to maintain its structure better during combustion.

[0089] [Examples 9-17] Next, tests were conducted on hollow structures in which the base layer contained resin and inorganic material, but did not contain flame retardants. In these test examples, talc was used as the inorganic material. A sheet material with a thickness of 0.3 mm to 0.4 mm was used for the core layer, and a sheet material with a thickness of 0.3 mm to 0.6 mm was used for the skin layer. After creating a honeycomb-shaped base layer (see Figure 2) consisting of a core layer and skin layers bonded to both sides thereof, aluminum foil was attached to one of the skin layers via adhesive. The thickness of the base layer in each test example was 5 mm or 12 mm, and its composition is shown in Table 3.

[0090] Furthermore, in each test example, inorganic substances are contained in the resin of the core layer sheet material and the skin layer sheet material, and the composition of each sheet material is similar to that of the entire base layer, so its description has been omitted. In Examples 9 to 13, no connecting holes were formed, while in Examples 14 to 17, each cell was processed to form at least one connecting hole.

[0091] Each obtained test specimen was subjected to a heat generation test in accordance with ISO 5660-1, as described above. The results are shown in Table 3.

[0092] [Table 3]

[0093] As shown in Table 3, even when the base layer contained resin and inorganic substances and did not contain flame retardants, results equivalent to semi-noncombustible or noncombustible were obtained. Comparing the examples in Table 3, the base layer thickness was relatively thin (less than 10 mm), and the weight of the hollow structure was 2000 g / m². 2 Examples 9-13, which are relatively lighter, yielded better results in combustion tests than Examples 14-17. It is thought that lighter hollow structures are less prone to deformation such as crushing at high temperatures, and consequently, less prone to ignition. [Industrial applicability]

[0094] Since the hollow structure of the present invention is flame-retardant, it is particularly suitable as a panel material for walls, ceilings, and other surfaces where fire resistance is required. [Explanation of Symbols]

[0095] 1, 1A 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 hollow structure comprising a base layer having a structure in which multiple cells are provided, and a metal layer provided on the base layer, The substrate layer comprises a resin and an additive which is at least one of an inorganic substance (excluding flame retardants) and a flame retardant. A hollow structure characterized in that the content of the additive is 30% by mass or more relative to the total mass of the base layer.

2. The hollow structure according to claim 1, wherein the base layer contains the inorganic substance and the flame retardant as additives, and the total content of the inorganic substance and the flame retardant is 50% by mass or more of the total mass of the base layer.

3. The hollow structure according to claim 1 or 2, characterized in that the inorganic substance is an inorganic clay mineral, and the content of the inorganic clay mineral relative to the total mass of the base material layer is greater than the content of the flame retardant.

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

5. Sheet thickness T forming the core layer ａ and the sheet thickness T that forms the skin layer ｂ The ratio of (T ａ : T ｂ The hollow structure according to claim 4, characterized in that ) = (2:3 to 3:2).

6. The substrate layer comprises a resin core layer on which the cells are provided, and a resin skin layer disposed on the surface of the core layer on which the metal layer is provided. The sheet thickness forming the core layer is T ａ The content of the resin relative to the total mass of the core layer is W ａ (mass%), the sheet thickness forming the skin layer is T ｂ The content of the resin relative to the total mass of the skin layer is W ｂ The hollow structure according to claim 1 or 2, characterized in that it satisfies the following formula (1) when expressed as (mass %). (T ａ ×W ａ )>(T ｂ ×W ｂ )・・・(1)

7. 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 hollow structure according to claim 1 or 2, characterized in that it does not exceed [a certain value].

8. 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 The weight of the hollow structure shall not exceed 2000 g / m². ２ The following conditions apply, and the bulk density of the hollow structure is 0.1 to 0.7 g / cm³. ３ The hollow structure according to claim 1 or 2, characterized in that it is the same as the one described in claim 1 or 2.

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