Decking material

Abstract

To provide a deck material capable of reducing upward warping that occurs when placed outdoors.SOLUTION: Since a lower core layer is thinner than an upper core layer, the upper core layer is more likely to expand due to water absorption, on the other hand, the lower core layer is less likely to expand due to water absorption. In addition, since a thickness of an upper surface layer portion is equal to or less than a thickness of a lower surface layer portion, shrinkage of the upper surface layer portion is suppressed. As a result, contraction of the upper surface layer and expansion of the lower core layer of the deck material are suppressed, and thus, upward warping of the deck material is reduced.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to decking materials installed outdoors.

Background Art

[0002] Conventionally, in outdoor structures such as terraces, verandas, boardwalks, and benches, plate-shaped decking materials made of materials such as wood and synthetic resin have been used.

[0003] For example, in Patent Document 1 below, a decking material is provided with a base material, an upper surface layer portion covering the upper surface of the base material, and a lower surface layer portion covering the lower surface of the base material. The base material and the upper surface layer portion are made of a wood powder-containing resin in which wood powder is blended, while the lower surface layer portion is made of a synthetic resin not containing wood powder, and the blending ratio of wood powder in the upper surface layer portion is smaller than the blending ratio of wood powder in the base material.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When a decking material such as that in Patent Document 1 above is installed outdoors, the upper surface portion of the decking material may shrink in the longitudinal and width directions due to the heat influence from sunlight. In addition, the lower surface portion of the decking material may expand in the longitudinal and width directions by absorbing moisture derived from water contained in or on the ground. When at least one of these occurs, there is a risk that the decking material will curve such that both ends in the longitudinal and width directions of the decking material are displaced upward with respect to the central portion, that is, the decking material may warp upward.

[0006] This invention has been made in view of the above circumstances, and aims to provide a decking material that can reduce the upward warping that occurs when placed outdoors. [Means for solving the problem]

[0007] To solve the aforementioned problems, the present invention provides a plate-shaped decking material that is placed outdoors and extends in the longitudinal direction, comprising a base material, an upper surface layer portion that covers the upper surface of the base material, and a lower surface layer portion that covers the lower surface of the base material, wherein the base material and the upper surface layer portion are composed of a compound resin containing a resin material and a specific component that exhibits a greater dimensional change in response to water absorption than the resin material, and the base material includes an upper core layer portion covered by the upper surface layer portion, a lower core layer portion covered by the lower surface layer portion, and a plurality of partition walls interposed between the upper core layer portion and the lower core layer portion, forming a space between the upper core layer portion and the lower core layer portion and partitioning the space, wherein the thickness of the lower core layer portion is formed to be thinner than the thickness of the upper core layer portion, and the thickness of the upper surface layer portion is formed to be less than or equal to the thickness of the lower surface layer portion.

[0008] According to the present invention, since the thickness of the lower core layer is thinner than the thickness of the upper core layer, the upper core layer is more prone to expansion due to water absorption, while the lower core layer is less prone to expansion due to water absorption. As a result, the shrinkage of the upper surface layer can be canceled out by the expansion of the upper core layer due to water absorption, and the expansion of the lower core layer due to water absorption is also suppressed. Furthermore, since the thickness of the upper surface layer is less than or equal to the thickness of the lower surface layer, the shrinkage of the upper surface layer is suppressed. In addition, as the thickness of the lower surface layer increases, it becomes more difficult for moisture to reach the lower core layer from the bottom, thus suppressing the expansion of the lower core layer due to water absorption. As a result, the shrinkage of the upper surface layer and the expansion of the lower core layer of the decking material are suppressed, thereby reducing the upward warping of the decking material.

[0009] In the present invention, preferably, the interface between the upper surface layer and the upper core layer is formed in a wavy shape. With this configuration, the contact area between the upper surface layer and the upper core layer is increased, thereby suppressing delamination between the upper surface layer and the upper core layer. Furthermore, because the interface is formed in a wavy shape, a portion of the upper surface layer becomes even thinner, thus further suppressing shrinkage of the upper surface layer.

[0010] Preferably, the thickness of the lower core layer is set to a range of 0.2 to 0.6 times the thickness of the upper core layer, and the thickness of the upper surface layer is set to a range of 0.5 to 1.0 times the thickness of the lower surface layer. With this configuration, the thickness of the lower core layer becomes relatively thinner than the thickness of the upper core layer within the above range, and the thickness of the upper surface layer becomes relatively thinner than the thickness of the lower surface layer within the above range, thereby effectively suppressing the shrinkage of the upper surface layer and the expansion of the lower core layer.

[0011] Preferably, the thickness of the upper surface layer is thinner than the thickness of the upper core layer, and the thickness of the lower surface layer is greater than or equal to the thickness of the lower core layer. With this configuration, the shrinkage of the upper surface layer can be suitably counteracted by the expansion of the upper core layer. In addition, by preventing moisture from reaching the lower core layer from the bottom surface with the lower surface layer, the expansion of the lower core layer due to water absorption can be suitably suppressed.

[0012] Preferably, the thickness of the upper surface layer is set to a range of 0.3 to 0.6 times the thickness of the upper core layer, and the thickness of the lower surface layer is set to a range of 1.0 to 2.0 times the thickness of the lower core layer. With this configuration, by setting the thickness of each part within the above range, shrinkage of the upper surface layer and expansion of the lower core layer can be effectively suppressed.

[0013] Furthermore, preferably, the lower surface layer does not contain the specified component. This configuration suppresses swelling of the lower surface layer due to water absorption. [Effects of the Invention]

[0014] As described above, the decking material of the present invention can reduce upward warping of the decking material caused by shrinkage of the upper surface layer and expansion of the lower core layer. [Brief explanation of the drawing]

[0015] [Figure 1] This is a perspective view showing the deck structure according to one embodiment of the present invention. [Figure 2] This is a perspective view showing the decking material used in the above deck structure, individually. [Figure 3] This is a cross-sectional view of the decking material shown above. [Figure 4] These are experimental results showing the dimensions and warp of the decking material of this embodiment and conventional decking material. [Modes for carrying out the invention]

[0016] [Explanation of deck structure] Figure 1 shows a deck structure according to one embodiment of the present invention. The deck structure shown in this figure is used, for example, outdoors as a terrace or boardwalk, and comprises a plurality of decking materials 1 that constitute the floor surface, a support frame 40 that supports the decking materials 1 from below, and a plurality of base portions 50 that support the support frame 40 in the ground E.

[0017] [Description of decking materials] Next, the detailed structure of the decking material 1 will be described, mainly using Figures 2 and 3. Figure 2 shows a perspective view of the decking material 1, and Figure 3 shows a cross-sectional view of the decking material. As shown in these figures, the decking material 1 is a hollow plate-like member having internal spaces (multiple closed spaces S, which will be described later), and its cross-section as a whole is a flattened rectangle.

[0018] The decking material 1 has a multi-layer structure and comprises a base material 2, a first surface layer material 3 that covers the top surface and part of the sides of the base material 2, and a second surface layer material 4 that covers the bottom surface and part of the sides of the base material 2.

[0019] The base material 2 is a hollow member having a ladder-shaped cross section. That is, the base material 2 includes an upper core layer portion 10 extending along the horizontal plane, a lower core layer portion 11 extending parallel to the upper core layer portion 10 at a position spaced downward from the upper core layer portion 10, a pair of left and right side walls 12A and 12B connecting both ends in the width direction of the upper core layer portion 10 and the lower core layer portion 11 in the vertical direction, and a plurality of partition walls 13 connecting the upper core layer portion 10 and the lower core layer portion 11 in the vertical direction between the pair of side walls 12A and 12B. As shown in FIG. 2, the upper core layer portion 10, the lower core layer portion 11, the side walls 12, and the partition walls 13 all extend along the longitudinal direction X.

[0020] Concave groove portions V recessed toward the center in the width direction of the deck material 1 are respectively formed in the left and right side walls 12A and 12B of the base material 2.

[0021] The first surface layer material 3 integrally includes an upper surface layer portion 20 covering the upper core layer portion 10 (upper surface) of the base material 2, and a pair of left and right side surface layer portions 21A and 21B covering portions above the concave groove portions V in the left and right side walls 12A and 12B of the base material 2. The first surface layer material 3, the upper core layer portion 10, and the side walls 12A and 12B are integrally formed by multi-color extrusion molding. In particular, the interface between the upper core layer portion 10 and the upper surface layer portion 20 is formed in a fine wave shape, and the contact area between the upper core layer portion 10 and the upper surface layer portion 20 is increased by that amount. As a result, the upper core layer portion 10 and the upper surface layer portion 20 are firmly joined, and peeling between them is preferably suppressed. The amplitude of the wave is set to about 0.2 [mm], for example, and the wavelength of the wave is set to about 1.0 [mm], for example.

[0022] The second surface layer material 4 integrally includes a lower surface layer portion 30 covering the lower core layer portion 11 (lower surface) of the base material 2, and a pair of left and right side surface layer portions 31A and 31B covering portions below the concave groove portions V in the left and right side walls 12A and 12B of the base material 2. The second surface layer material 4, the lower core layer portion 11, and the side walls 12A and 12B are integrally formed by multi-color extrusion molding. On the other hand, both end faces in the longitudinal direction X of the base material 2 and the left and right concave groove portions V of the base material 2 are not covered by either the first surface layer material 3 or the second surface layer material 4.

[0023] Both the base material 2 and the first surface layer material 3 (top surface layer 20 and side surface layer 21) are composed of a wood powder-blended resin containing a resin material and wood powder. For example, a styrene-based resin blended with wood powder can be suitably used as the first surface layer material 3. Similarly, a polyvinyl chloride (PVC) resin or ABS resin blended with wood powder can be suitably used as the base material 2. Of course, the types of synthetic resins listed here are merely preferred examples, and various other synthetic resins can be used. For example, polyethylene, polypropylene, EVA resin, and polystyrene can be used. As for wood powder, any type of finely ground wood can be used. Note that the wood powder corresponds to the "specific component with large dimensional changes due to water absorption" in the claim.

[0024] However, the wood powder content differs between the base material 2 and the first surface material 3, with the wood powder content in the first surface material 3 being set to a lower value than that in the base material 2. Specifically, the wood powder content in the base material 2 is set to approximately 30%, while the wood powder content in the first surface material 3 is set to approximately 10%.

[0025] In addition to wood powder, various other components may be incorporated into the base material 2 and the first surface material 3. For example, various additives such as coloring pigments to create a wood-like texture, foaming agents, UV absorbers, flame retardants, or antistatic agents may be incorporated.

[0026] Unlike the base material 2 and the first surface material 3 described above, the second surface material 4 (bottom surface portion 30 and side surface portion 31) is made of a synthetic resin (resin material) that does not contain wood powder. For example, polyvinyl chloride (PVC) resin can be suitably used as the second surface material 4. Of course, the synthetic resin that can be used as the second surface material 4 is not limited to this, and various synthetic resins can be used as long as they are compatible with the base material 2 and do not contain wood powder. In addition, the second surface material 4 may contain components other than wood powder, such as pigments, foaming agents, ultraviolet absorbers, flame retardants, fillers, or antistatic agents.

[0027] In the deck material 1, the thickness TC2 of the lower core layer 11 is formed to be thinner than the thickness TC1 of the upper core layer 10 (TC1 > TC2). Specifically, the thickness TC1 of the upper core layer 10 is set to 4.2 [mm], and the thickness TC2 of the lower core layer 11 is set to 1.5 [mm]. In relation to this, the thickness TC2 of the lower core layer 11 is 0.357 times the thickness TC1 of the upper core layer 10. However, not limited to the above dimensions, it is preferable that the thickness TC2 of the lower core layer 11 be set in the range of 0.2 times or more and 0.6 times or less the thickness TC1 of the upper core layer 10, within the range of 1.0 [mm] to 2.0 [mm] and the thickness TC1 of the upper core layer 10 to 2.0 [mm]. This is preferable in terms of reducing the upward warping of the deck material 1, which will be discussed later. The thickness TC1 of the upper core layer 10 is calculated based on the average height of the corrugated interface (corrugated interface) formed between it and the upper surface layer 20. In other words, the thickness TC1 of the upper core layer 10 is the average of the distance from the bottom surface of the upper core layer 10 to the peak of the corrugated interface and the distance from the bottom surface of the upper core layer 10 to the trough of the corrugated interface.

[0028] Furthermore, the thickness TL1 of the upper surface layer 20 is formed to be less than or equal to the thickness TL2 of the lower surface layer 30 (TL1 ≤ TL2). Specifically, the thickness TL1 of the upper surface layer 20 is set to 1.5 [mm], and the thickness TL2 of the lower surface layer 30 is set to 2.0 [mm]. In connection with this, the thickness TL1 of the upper surface layer 20 is 0.75 times the thickness TL2 of the lower surface layer 30. However, not limited to the above dimensions, it is preferable that the thickness TL1 of the upper surface layer 20 be set in the range of 0.4 [mm] to 4.0 [mm], and the thickness TL2 of the lower surface layer 30 be set in the range of 1.0 [mm] to 4.0 [mm], and that the thickness TL1 of the upper surface layer 20 be set in the range of 0.5 times to 1.0 times the thickness TL2 of the lower surface layer 30, in order to reduce the upward warping of the deck material 1, which will be described later.

[0029] Furthermore, the thickness TL1 of the upper surface layer 20 is formed to be thinner than the thickness TC1 of the upper core layer 10. Specifically, the thickness TL1 of the upper surface layer 20 is set to 1.5 [mm], and the thickness TC1 of the upper core layer 10 is set to 4.2 [mm]. In connection with this, the thickness TL1 of the upper surface layer 20 is approximately 0.357 times the thickness TC1 of the upper core layer 10. However, not limited to the above dimensions, it is desirable for the thickness TL1 of the upper surface layer 20 to be set to 0.3 times or more and 0.6 times or less the thickness TC1 of the upper core layer 10, in the range of 0.4 [mm] to 4.0 [mm] and the range of 2.0 [mm] to 8.0 [mm], in order to reduce the upward warping of the deck material 1, which will be discussed later.

[0030] Furthermore, the thickness TL2 of the lower surface layer 30 is formed to be greater than or equal to the thickness TC2 of the lower core layer 11. Specifically, the thickness TL2 of the lower surface layer 30 is set to 2.0 [mm], and the thickness TC2 of the lower core layer 11 is set to 1.5 [mm]. In connection with this, the thickness TL2 of the lower surface layer 30 is approximately 1.33 times the thickness TC2 of the lower core layer 11. However, not limited to the above dimensions, it is desirable that the thickness TL2 of the lower surface layer 30 be set to 1.0 times or more and 2.0 times or less the thickness TC2 of the lower core layer 11, within the range of 1.0 [mm] to 4.0 [mm] and the thickness TC2 of the lower core layer 11, in order to reduce the upward warping of the deck material 1, which will be discussed later.

[0031] [Effect, etc.] Generally, decking materials, which are formed by covering the top and bottom surfaces of a base material with top and bottom surface layers respectively, are placed outdoors. As a result, the top surface layer that constitutes the top surface of the decking material is prone to shrinkage due to the heat effects of sunlight. In other words, the top surface layer is more likely to shrink due to cooling when sunlight stops reaching it than to expand due to heating from sunlight. Thus, the top surface layer tends to shrink when placed outdoors. Furthermore, the bottom surface of the decking material is close to the ground and is therefore prone to absorbing moisture (hereinafter referred to as water absorption) from water contained in or on the ground. When the bottom surface layer absorbs water, that moisture can reach the lower core layer located beneath the base material. If wood powder is mixed into the lower core layer, when moisture reaches the lower core layer from the bottom surface layer or end faces and the lower core layer absorbs water, the lower core layer expands in the longitudinal and width directions. Furthermore, since wood powder undergoes greater dimensional changes in response to water absorption than resin materials, the lower core layer containing wood powder tends to expand in the longitudinal and lateral directions when it absorbs water. As described above, conventional decking materials inherently tend to shrink in the upper surface layer and expand in the lower core layer. These phenomena can cause the decking material to warp, where both ends in the longitudinal and lateral directions are displaced upward relative to the center, in other words, it can cause the decking material to warp upwards.

[0032] In contrast, the deck material 1 of this embodiment reduces upward warping of the deck material 1 by adopting the dimensional relationship described above. Specifically, in the deck material 1 of this embodiment, the thickness TC2 of the lower core layer 11 is thinner than the thickness TC1 of the upper core layer 10. As a result, the upper core layer 10 is prone to expansion due to water absorption, while the lower core layer 11 is less prone to expansion due to moisture absorption. Consequently, the shrinkage of the upper surface layer 20 can be offset by the expansion of the upper core layer 10 due to water absorption, and as the lower core layer 11 becomes thinner, the expansion due to water absorption is also suppressed. Furthermore, since the thickness TL1 of the upper surface layer 20 is less than or equal to the thickness TL2 of the lower surface layer 30, the shrinkage of the upper surface layer 20 is suppressed. Moreover, as the thickness TL2 of the lower surface layer 30 increases, it becomes more difficult for moisture to reach the lower core layer 11 from the bottom, thus suppressing the expansion of the lower core layer 11 due to water absorption. These measures suppress the shrinkage of the upper surface layer 20 and the expansion of the lower core layer 11, thereby reducing the upward curvature of the deck material 1.

[0033] Figure 4 shows experimental results of measuring the dimensions and warp amount MC [mm] of the deck material 1 of this embodiment and the conventional deck material (hereinafter referred to as the conventional product). In Figure 4, the warp amount MC [mm] corresponds to the amount of dimensional change in the direction perpendicular to the longitudinal direction X per 2m in the longitudinal direction X of the deck material. In other words, the smaller the warp amount MC, the smaller the upward warp. Note that the deck material 1 of this embodiment and the conventional product use the same material and processing method, differing only in dimensions.

[0034] As shown in Figure 4, the deck material 1 of this embodiment has a warp amount MC of 0.7 [mm], while the conventional product has a warp amount MC of 13.8 [mm]. In other words, the upward warp of the deck material 1 is significantly reduced compared to the conventional product.

[0035] Comparing decking material 1 with conventional products, both have the same characteristic of having a lower core layer 11 thickness TC2 that is thinner than the upper core layer 10 thickness TC1. However, decking material 1 differs from conventional products in that the upper surface layer 20 thickness TL1 is less than or equal to the lower surface layer 30 thickness TL2. As a result, decking material 1 tends to have a thinner upper surface layer 20 thickness TL1, thus weakening the effect of shrinkage of the upper surface layer 20 due to thermal changes. Also, because the lower surface layer 30 tends to have a thicker thickness TL2, moisture from the underside of decking material 1 is prevented by the lower surface layer 30, reducing the amount of moisture that reaches the lower core layer 11. Consequently, expansion of the lower core layer 11 due to water absorption is suppressed. Furthermore, since the lower surface layer 30 does not contain wood powder, there is almost no expansion due to water absorption. Thus, the deck material 1 achieves a significant reduction in upward warping compared to conventional products by simultaneously satisfying two conditions: the thickness TC2 of the lower core layer 11 is thinner than the thickness TC1 of the upper core layer 10, and the thickness TL1 of the upper surface layer 20 is less than or equal to the thickness TL2 of the lower surface layer 30.

[0036] Furthermore, a numerical comparison shows that in the conventional product, the thickness TC2 of the lower core layer 11 is 0.714 times that of the upper core layer 10 (corresponding to RC in Figure 4), while in the deck material 1, the thickness TC2 of the lower core layer 11 is 0.357 times that of the upper core layer 10 (corresponding to RC in deck material 1). In other words, deck material 1 tends to have a thinner thickness TC2 of the lower core layer 11 and a thicker thickness TC1 of the upper core layer 10 compared to the conventional product. Consequently, deck material 1 is less prone to expansion of the lower core layer 11 compared to the conventional product, and the effect of canceling out the contraction of the upper surface layer 20 with the expansion of the upper core layer 10 can be suitably obtained.

[0037] Here, in the deck material 1, the thickness TC2 of the lower core layer 11 is 0.357 times the thickness TC1 of the upper core layer 10, which falls within the preferred range (0.2 to 0.6 times) described above. The above range is a value that has been determined in advance experimentally or analytically. Specifically, the above range is one in which the effects of shrinkage of the upper surface layer 20 and expansion of the lower core layer 11 are suitably obtained, and the strength of the deck material 1 can be ensured.

[0038] Furthermore, while conventional products have a thickness TL1 of the upper surface layer 20 that is 2.0 times (corresponding to RL in Figure 4) greater than 1.0 times the thickness TL2 of the lower surface layer 30, deck material 1 has a thickness TL1 of the upper surface layer 20 that is 0.75 times (corresponding to RL in Figure 4) less than 1.0 times the thickness TL2 of the lower surface layer 30. In other words, deck material 1 shows a pronounced tendency for the thickness TL1 of the upper surface layer 20 to be thinner and the thickness TL2 of the lower surface layer 30 to be thicker. As a result, shrinkage of the upper surface layer 20 is suitably suppressed, and the lower surface layer 30 suitably prevents moisture from reaching the lower core layer 11.

[0039] Here, the deck material 1 has a thickness TL1 of the upper surface layer 20 that is 0.75 times the thickness TL2 of the lower surface layer 30, which falls within the aforementioned preferred range (0.5 to 1.0 times). The above range is a value that has been determined in advance experimentally or analytically. Specifically, the above range is one in which the shrinkage of the upper surface layer 20 and the expansion of the lower core layer 11 are suitably suppressed, and in which the thickness TL1 of the upper surface layer 20 and the thickness TL2 of the lower surface layer 30 are ensured to be equal to or greater than the respective specified dimensions even after roughening the surface of the deck material 1.

[0040] Furthermore, when comparing deck material 1 with conventional products, the conventional product has a lower surface layer 30 with a thickness TL2 (0.5 mm) that is thinner than the lower core layer 11 with a thickness TC2 (2.5 mm), whereas deck material 1 has a lower surface layer 30 with a thickness TL2 (2.0 mm) that is greater than or equal to the lower core layer 11 with a thickness TC2 (1.5 mm). As a result, deck material 1 tends to have a thicker lower surface layer 30 with a thickness TL2, which effectively prevents moisture from reaching the lower core layer 11 from the lower surface of deck material 1. In other words, the expansion of the lower core layer 11 due to water absorption is effectively suppressed.

[0041] Here, the deck material 1 has a thickness TL2 of the lower surface layer 30 which is approximately 1.33 times the thickness TC2 of the lower core layer 11 (corresponding to R2 in Figure 4), and falls within the aforementioned suitable range (1.0 to 2.0 times or less). The above range is a value that has been determined in advance experimentally or analytically. Specifically, the above range is one in which the expansion effect of the lower core layer 11 can be obtained while ensuring the strength of the base material 2 of the deck material 1.

[0042] Furthermore, as is common with conventional products, the deck material 1 is formed with a thickness TL1 of the upper surface layer 20 that is thinner than the thickness TC1 of the upper core layer 10. This allows the shrinkage of the upper surface layer 20 to be suitably canceled out by the expansion of the upper core layer 10. Specifically, because the upper core layer 10 is formed to be relatively thicker than the upper surface layer 20, the upper core layer 10 has higher rigidity and is more prone to expansion due to water absorption. Therefore, the shrinkage of the upper surface layer 20 can be canceled out by the expansion of the upper core layer 10 due to water absorption, thereby suppressing the shrinkage of the upper surface layer 20. Here, although the upper core layer 10 is less prone to water absorption because it is covered by the upper surface layer 20, the thinness of the upper surface layer 20 makes it easier for moisture to reach the upper core layer 10. Furthermore, since the upper core layer 10 has a higher wood powder content than the upper surface layer 20, the upper core layer 10 expands more easily than the upper surface layer 20. Therefore, even if the amount of moisture reaching the upper core layer 10 is small, the upper core layer 10 can expand efficiently, counteracting the shrinkage of the upper surface layer 20.

[0043] Furthermore, a difference between deck material 1 and conventional products is that the interface between the upper surface layer 20 and the upper core layer 10 is formed in a wave shape. As a result, the upper surface layer 20 and the upper core layer 10 are firmly bonded together, thereby suppressing delamination between the upper surface layer 20 and the upper core layer 10. In addition, in the upper surface layer 20, areas where the thickness TL1 is thinner according to the wave shape are partially formed, which also has the effect of further suppressing the shrinkage of the upper surface layer 20.

[0044] Furthermore, the deck material 1 has a top surface layer 20 thickness TL1 that is approximately 0.357 times the thickness TC1 of the upper core layer 10 (corresponding to R1 in Figure 4), which falls within the aforementioned preferred range (0.3 to 0.6 times). This range is a value that has been determined in advance experimentally or analytically. Specifically, this range allows the shrinkage of the top surface layer 20 to be suitably suppressed by the expansion of the upper core layer 10, and ensures that the thickness TL1 of the top surface layer 20 is greater than or equal to the specified dimension even after roughening.

[0045] [Differentiation] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above and may be modified as appropriate without departing from the spirit of the invention. For example, in the above embodiments, wood powder was blended into the base material 2 and the first surface layer material 3 as a specific component that undergoes a greater dimensional change in response to water absorption than the resin material, but the invention is not necessarily limited to wood powder. For example, any material that undergoes a greater dimensional change in response to water absorption than the resin material, such as calcium carbonate, may be used. [Explanation of Symbols]

[0046] 1: Decking material 2: Base material 10: Upper core layer 11: Lower core layer 13: Partition Wall 20:Top surface layer 30: Bottom surface layer

Claims

1. A decking material in the shape of a board, which is placed outdoors and extends in the longitudinal direction, Substrate and The upper surface layer portion covers the upper surface of the substrate, The substrate comprises a lower surface layer portion that covers the lower surface of the substrate, The substrate and the upper surface layer are composed of a compound resin containing a resin material and a specific component that exhibits a greater dimensional change in response to water absorption than the resin material. The aforementioned substrate is The upper core layer is covered above by the upper surface layer, A lower core layer is located below the upper surface layer and its lower part is covered by the lower surface layer, It includes a plurality of partition walls interposed between the upper core layer and the lower core layer, which divide the space while forming a space between the upper core layer and the lower core layer, The thickness of the lower core layer is formed to be thinner than the thickness of the upper core layer, and the thickness of the upper surface layer is formed to be less than or equal to the thickness of the lower surface layer. A decking material characterized by the following features.

2. The interface between the upper surface layer and the upper core layer is formed in a wavy shape. The decking material according to feature 1.

3. The thickness of the lower core layer is set to a range of 0.2 times or more and 0.6 times or less the thickness of the upper core layer, and The thickness of the upper surface layer is set to be between 0.5 and 1.0 times the thickness of the lower surface layer. The decking material according to feature 1 or 2.

4. The thickness of the upper surface layer is formed to be thinner than the thickness of the upper core layer. The thickness of the lower surface layer is formed to be greater than or equal to the thickness of the lower core layer. The decking material according to feature 1 or 2.

5. The thickness of the upper surface layer is set to a range of 0.3 times or more and 0.6 times or less the thickness of the upper core layer. The thickness of the lower surface layer is set to be between 1.0 and 2.0 times the thickness of the lower core layer. The decking material according to feature 4.

6. The aforementioned lower surface layer does not contain the aforementioned specific component. The decking material according to feature 1.

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