Wood composite material, air conditioner, and method for manufacturing wood composite material

Abstract

The wood composite material comprises an inner layer containing wood and resin, a surface layer containing wood and resin provided on the surface of the inner layer, and a back layer containing wood and resin provided on the back surface of the inner layer, and the total filling rate of the surface layer and the back layer is less than half of the overall wood filling rate.

Description

[Technical Field]

[0001] The present disclosure relates to a wood composite material using wood and resin, an air conditioner, and a method for manufacturing the wood composite material. [Background technology]

[0002] In recent years, efforts have been made to reduce carbon dioxide emissions against the backdrop of the yearly increase in atmospheric carbon dioxide concentration. For example, in the field of materials, efforts have been made to utilize natural wood as a raw material to reduce carbon dioxide emissions when producing materials. Patent Document 1 discloses a material technology related to a wood composite material that is colorless and optically transparent, which is obtained by removing lignin from wood and then impregnating it with a resin whose refractive index is close to that of cellulose, the main component of wood. Furthermore, Patent Document 2 discloses a technology for laminating composites of compressed wood and resin. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2017 / 136714 [Patent Document 2] Japanese Patent Publication No. 2023-93543 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the material configuration of Patent Document 1, although the resin impregnation into the gaps in the wood suppresses light scattering inside the wood, there is a risk of light being diffused on the surface of the wood. In this case, the diffused reflection of light reduces the amount of light that penetrates into the material, resulting in reduced light transmittance. Light transmittance is further impaired when the wood is made into a thick board. Furthermore, because the outermost surface of the material is wood, friction with other components can cause the wood to rub against other components, resulting in splinters, which can roughen the surface and increase the amount of diffused light reflection. Furthermore, because the outermost surface of the material is wood, when dirt adheres to the wood, the wood and the dirt become integrated, making cleaning difficult and further reducing light transmittance. Furthermore, Patent Document 2 describes a layered structure created by lamination, but the manufacturing process is complicated because a separate lamination process is required.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a wood composite material with good light transmittance, an air conditioner, and a method for manufacturing a wood composite material. [Means for solving the problem]

[0006] The wood composite material according to the present disclosure comprises an inner layer containing wood and resin, a surface layer provided on the surface of the inner layer and containing wood and the resin, and a back layer provided on the back surface of the inner layer and containing wood and the resin, wherein the total filling rate of the surface layer and the back layer is half or less of the filling rate of the entire wood, and the wood composite material further comprises a stress relief layer provided between the surface layer, the back layer and the inner layer and containing wood and the resin, wherein at least one of the fiber axes of the wood fibers in the inner layer, the surface layer, the back layer and the stress relief layer are oriented in a different direction, and the stress relief layer is more resistant to sunlight irradiation than the inner layer. Processing by Long time This increased the amount of lignin removed from the wood. materials are used. [Effects of the Invention]

[0007] According to the present disclosure, the total filling rate of the surface layer and the back layer is less than half of the total filling rate of the wood. Therefore, the amount of wood in the outermost layers, the surface and back layers, is small. This reduces the occurrence of diffused reflection of light and splinters. Therefore, a wood composite with good light transmittance can be obtained. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a top view showing a composite wood material according to a first embodiment. [Figure 2] 1 is a cross-sectional view showing a wood composite material according to a first embodiment. [Figure 3] FIG. 3 is a cross-sectional view showing a wood composite material according to a modified example of the first embodiment. [Figure 4] FIG. 6 is a cross-sectional view showing a wood composite material according to a second embodiment. [Figure 5] FIG. 10 is a cross-sectional view showing a wood composite material according to a first modified example of the second embodiment. [Figure 6] FIG. 10 is a cross-sectional view showing a wood composite material according to a second modified example of the second embodiment. [Figure 7] FIG. 10 is a cross-sectional view showing a wood composite material according to a third modified example of the second embodiment. [Figure 8] FIG. 10 is a cross-sectional view showing a wood composite material according to a fourth modified example of the second embodiment. [Figure 9] FIG. 10 is a cross-sectional view showing a wood composite material according to a fifth modified example of the second embodiment. [Figure 10] FIG. 10 is a cross-sectional view showing a wood composite material according to a sixth modified example of the second embodiment. [Figure 11] 10 is a graph showing the measurement results of the molecular structure of a wood composite material according to the third embodiment. [Figure 12] FIG. 10 is a perspective view showing an air conditioner according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the wood composite material, air conditioner, and method for manufacturing the wood composite material of the present disclosure will be described with reference to the drawings. Note that the present disclosure is not limited to the embodiments described below. Furthermore, in the following drawings, including FIG. 1, the size relationships between the components may differ from the actual size. Furthermore, in the following description, terms indicating directions will be used as appropriate to facilitate understanding of the present disclosure, but these terms are for the purpose of explaining the present disclosure and do not limit the present disclosure. Examples of terms indicating directions include "up," "down," "right," "left," "front," and "rear."

[0010] Embodiment 1 FIG. 1 is a top view of a wood composite material 1 according to a first embodiment. As shown in FIG. 1, the wood composite material 1 is a composite of wood 11 and resin 12, with the resin 12 impregnated into the gaps in the wood 11. Wood 11 is one of the most abundant polymers on Earth and has attracted attention as a material with low environmental impact. Wood 11 has a structure in which three components, cellulose, hemicellulose, and lignin, are intertwined. Cellulose has a linear β-glucose structure and has long been a material that has attracted attention for its potential to enhance the functionality of resin 12. Cellulose in fibrous form is sometimes extracted and used as a material. Hemicellulose has a branched β-glucose structure and exists in a state where cellulose fibers are intertwined with each other. Lignin is a complex and diverse aromatic compound that acts as a binder to fix cellulose fibers.

[0011] The wood composite material 1 according to the first embodiment focuses on lignin, and is a material obtained by modifying the lignin and then compounding it with resin 12. Various types of coniferous or broad-leaved trees can be used as the wood 11. Coniferous trees include cedar, cypress, red pine, Edo pine, larch, Douglas fir, etc., and broad-leaved trees include balsa, beech, white oak, zelkova, chestnut teak, etc. From the viewpoint of providing a wide path for impregnation with resin 12, a wood 11 with a low density is better, and it is desirable to use balsa.

[0012] Various types of thermosetting resins and thermoplastic resins can be used as the resin 12. Examples of thermosetting resins include epoxy resin, unsaturated polyester resin, phenolic resin, and urea resin. Examples of thermoplastic resins include polycarbonate, acrylic, polyvinyl chloride, polystyrene, and acrylonitrile-butadiene-styrene copolymer. These resins are used in a liquid state, such as a molten state or a state dissolved in a solvent. During impregnation, it is desirable for the resin 12 to have a small molecular size and a refractive index close to that of the structure of the wood 11. Therefore, a thermosetting resin with a small molecular size before hardening is desirable for the resin 12, and epoxy resin is desirable in terms of refractive index and versatility. In the first embodiment, balsa wood is used for the wood 11, and epoxy resin (main agent: CY230 manufactured by Nagase ChemteX Corporation, curing agent: HY951 manufactured by Nagase ChemteX Corporation) is used for the resin 12.

[0013] The wood composite 1, consisting of wood 11 and resin 12, is produced, for example, by the following manufacturing method. First, the wood 11 is coated with or immersed in an aqueous solution with a bleaching effect, such as hydrogen peroxide. To enhance the effectiveness of the hydrogen peroxide, the wood 11 may be pre-coated with or pre-immersed in an alkaline aqueous solution, such as sodium hydroxide. In this state, the wood 11 is irradiated with sunlight for at least one hour. The irradiation time varies depending on the intensity of the sunlight and the thickness of the wood 11. For example, if the wood 11 is 1 mm thick in summer, treatment can be completed in one hour. It is desirable to adjust the irradiation time depending on the conditions, and irradiation may be carried out for two or more days. It is also possible to reapply hydrogen peroxide during irradiation, which allows for more effective treatment. The treated wood 11 has changed from its original brown color to white. The wood 11 is colored by the aromatic chromophores of lignin, but this treatment decolorizes the chromophores, indicating that the wood 11 has been modified. Depending on the type of wood 11, a brown color may remain. This indicates a strong chromophore, and although the color approaches white with extended sunlight exposure, it is also possible to leave the brown color. This ultimately results in a brown, light-transmitting material. Furthermore, treatment is not limited to sunlight; it is also possible to use artificial lamps, such as ultraviolet light, for this purpose.

[0014] Next, the treated modified wood is washed. This washing is performed by immersing the wood in various alcohols, such as ethanol or isopropyl alcohol, and vibrating the wood while immersed. From the viewpoints of safety and versatility, ethanol is the preferred alcohol. Next, the washed wood 11 is immersed in toluene, allowing the toluene to penetrate into the gaps in the wood 11. While toluene and xylene, other good solvents for low-molecular-weight resin 12, are also available, in this embodiment, toluene is used for versatility. Next, the wood 11 is immersed in resin 12 to perform impregnation. A mixture of the base resin and the curing agent is prepared in advance in a specified ratio. A third component, such as a reactive diluent, which is incorporated into the molecular structure of the epoxy resin 12, may be added to adjust the viscosity. Impregnation is performed in a vacuum atmosphere. The wood 11 is immersed in resin 12 under vacuum, and the resin 12 is impregnated into the wood 11 while removing any air bubbles in the wood 11. Although it depends on the size of the wooden piece 11, for example, if the wooden piece 11 is 50 mm x 50 mm x 1 mm thick, vacuum impregnation will be completed in 30 minutes. After vacuum impregnation, a pressurized impregnation process may be performed using an autoclave or similar device. It has been confirmed that adding pressurized impregnation compresses the air remaining in the wooden piece 11, further promoting impregnation of the resin 12.

[0015] Finally, the resin 12 is hardened on the wood 11 impregnated with resin 12. For example, when using wood 11 measuring 50 mm x 50 mm x 1 mm thick, hardening is performed as follows: Two 100 mm x 100 mm x 5 mm thick glass plates are prepared, and the wood 11 impregnated with resin 12 is placed at the center of the glass plates. The same volume of resin 12 as the wood 11 is poured onto the surface of the glass plates and laid on top of the glass plates. The wood 11 impregnated with resin 12 is then placed on top of the resin 12, and another piece of wood 11 impregnated with resin 12 is poured on top of it. This creates a "resin 12-wood 11 impregnated with resin 12-resin 12-resin 12" sandwich structure. Next, a glass plate is placed on top, sandwiching the wood 11 between the glass plates. The wood 11 is subjected to the weight of the glass plates and pressure corresponding to the area of ​​the wood 11. If the pressure is too small, the wood 11 will deform due to hardening shrinkage. If the pressure is too great, the resin 12 on the front and back surfaces of the wood 11 impregnated with the resin 12 will flow out, and no resin 12 will remain on the outermost surface. By leaving the wood 11 in a sandwiched state for 12 hours or more and hardening the resin 12, a material in which the resin 12 has been impregnated into the gaps in the wood 11 can be obtained.

[0016] FIG. 2 is a cross-sectional view showing a wood composite material 1 according to the first embodiment. As shown in FIG. 2, the wood composite material 1 includes an inner layer 2, a surface layer 3, and a back layer 4. The surface layer 3 and the back layer 4 form the outermost layers of the wood composite material 1. The inner layer 2 contains wood 11 and resin 12. The surface layer 3 is provided on the surface of the inner layer 2 and contains wood 11 and resin 12. The back layer 4 is provided on the back surface of the inner layer 2 and contains wood 11 and resin 12. Here, the wood 11 filled in the inner layer 2 is referred to as wood A111, and the wood 11 filled in the surface layer 3 and back layer 4 is referred to as wood B112. The wood A111 is oriented in a regular direction in the thickness direction, and the wood B112 is also oriented in a regular direction in the thickness direction.

[0017] The surface layer 3 and the back layer 4 are resin-rich layers, and the total filling rate of the wood 11 in the surface layer 3 and the back layer 4 is less than half the filling rate of the wood 11 in the entire material. This allows for a light-transmitting material that suppresses diffuse reflection at the outermost surface. If the total filling rate exceeds half, the filling amount of wood 11 at the outermost surface is high, and the wood 11 may protrude to the outermost surface. The wood 11 used is 1 mm thick, but the resin-rich layer is formed by splinters on the surface of the wood 11. Therefore, the thickness of the resin-rich layer is only a small portion of the thickness of the wood 11 used, and is thinner than the overall thickness of the wood 11. Furthermore, the above manufacturing method allows the inner layer 2 to have a higher filling rate of wood 11 than the outermost layer. Furthermore, when cypress, which has a strong grain, is used, a material that transmits light while retaining the grain can be obtained. Conventionally, it was necessary to stack multiple layers with different filling rates of wood 11, but in this embodiment 1, the wood composite material 1 can be manufactured without a lamination process.

[0018] The cellulose fibers of wood 11 are known to be approximately 50 μm in diameter. If there is no resin-rich layer between the top layer 3 and the bottom layer 4, the outermost surface will be wood 11 fiber. As a result, irregularities of approximately 50 μm will occur due to the diameter of the wood 11 fiber, causing diffuse reflection of light. Furthermore, if the outermost surface is wood 11 fiber, rubbing the surface will cause splinters in the wood 11, roughening the surface. This also increases the amount of diffuse reflection of light. Diffuse reflection on the outermost surface can be suppressed by reducing the surface irregularities. By having a resin-rich layer and a total filling rate that is less than half the filling rate of the entire wood 11, the outermost surface will become resin 12. The pressure from the glass plate and the leveling effect of the resin 12 further reduce the irregularities, resulting in a material with an irregular structure of 50 μm or less. Furthermore, since the structure is less prone to splinters, diffuse reflection of light due to splinters can be suppressed.

[0019] Thus, the material configuration of the wood composite material 1 has a layer structure that suppresses diffuse reflection and the occurrence of splinters. To suppress diffuse reflection and the occurrence of splinters, the wood composite material 1 has a layer structure with a distribution of wood filling amount between the inner layer 2 of the material and the outermost layer, which is the surface layer 3 and back layer 4. The wood composite material 1 is made using a simple process without laminating a structure in which the wood filling rate of the outermost layer is lower than that of the inner layer 2. This material structure suppresses the occurrence of unevenness on the outermost surface caused by wood and the exposure of wood to the outermost surface, making it possible to consistently obtain a light-transmitting material with suppressed diffuse reflection.

[0020] Figure 3 is a cross-sectional view of a wood composite material 1 according to a modification of the first embodiment. As shown in Figure 3, in this modification, the wood material 11 filled in the inner layer 2 is referred to as wood material A111, and the wood material 11 filled in the front layer 3 and back layer 4 is referred to as wood material C113. While the wood material A111 is oriented in a regular direction relative to the thickness direction, the wood material C113 is oriented in an irregular direction relative to the thickness direction. As in this modification, the fiber axes of the fibers of the wood material 11 may be oriented in different directions.

[0021] Next, materials in which resin 12 is impregnated into gaps in wood 11 will be described in detail using examples and comparative examples. Balsa was used for the wood 11, and epoxy was used for the resin 12. Materials were produced by varying the presence or absence of a sandwich structure of resin 12, the wood 11 filling rate in each layer and the ratio of the wood 11 filling rate of the outermost layer (surface layer 3, back layer 4) to the entire material, the surface irregularities, and the manufacturing method, the pressure applied when the resin 12 hardened. Performance was then examined for light transmittance and the presence or absence of surface splinters. The wood 11 filling rate is shown by volume, and the surface irregularities are shown by arithmetic mean surface roughness. Light transmittance was measured at a wavelength of 600 nm. The results are shown in Table 1.

[0022] [Table 1]

[0023] Examples 1, 2, and 3 have a sandwich structure of resin 12, and the overall wood 11 filling rate is the same, but the filling rates of wood 11 in the outermost layer and the inner layer 2 are different. As a result, the filling rate of wood 11 in the outermost layer relative to the entire material was 17.3% in Example 1, 42.0% in Example 2, and 50.0% in Example 3. The light transmittance was 63.6% in Example 1, 63.8% in Example 2, and 64.4% in Example 3, and no surface splintering occurred in any of these examples. On the other hand, Comparative Examples 1 and 2 have the same overall wood 11 filling rate, but the filling rate of wood 11 in the outermost layer relative to the entire material exceeds 50%, at 55.2% in Comparative Example 1 and 67.9% in Comparative Example 2, which is more than half of the total filling rate. The light transmittance in this case was significantly reduced to 42.6% in Comparative Example 1 and 29.8% in Comparative Example 2.

[0024] Examples 4, 5, and 6 differ in the filling rate of the entire wooden piece 11. When the filling rate of the wooden piece 11 in the outermost layer relative to the entire material was 50% or less, the light transmittance was 62.9% in Example 4, 64.2% in Example 5, and 63.0% in Example 6. When the filling rate of the wooden piece 11 in the outermost layer relative to the entire material exceeded 50%, the light transmittance was 39.2% in Comparative Example 3 and 36.4% in Comparative Example 4, which were significantly worse.

[0025] Examples 7, 8, 9, and 10 differ in the size of the surface irregularities. They were produced by varying the pressure when sandwiched between the aforementioned glass plates. Compared to Example 1, Example 7 had a surface irregularity of 50 μm, Example 8 had a surface irregularity of 40 μm, Example 9 had a surface irregularity of 30 μm, and Example 10 had a surface irregularity of 20 μm. The light transmittance was 70.2% for Example 7, 71.8% for Example 8, 74.4% for Example 9, and 77.0% for Example 10. Thus, the smaller the surface irregularities, the higher the light transmittance. Comparative Example 5 does not have a sandwich structure of resin 12. In this case, burrs occurred on the surface, and the light transmittance was 42.2%, which was worse than Example 1.

[0026] Embodiment 2 4 is a cross-sectional view showing a wood composite material 1 according to embodiment 2. This embodiment 2 differs from embodiment 1 in that the wood composite material 1 includes a stress relaxation layer 5. In this embodiment 2, parts that are common to embodiment 1 are given the same reference numerals and their explanations are omitted, and the following description will focus on the differences from embodiment 1.

[0027] The wood composite material 1 according to the second embodiment is a laminate using the composite material of the first embodiment. In the second embodiment, one or more of the materials obtained in the first embodiment are used. Below, an example will be described in which the wood composite material 1 uses the wood 11 obtained in the first embodiment for the entire laminate, and is composed of an inner layer 2, a stress relaxation layer 5, a surface layer 3, and a back layer 4. As shown in FIG. 4, the wood composite material 1 comprises the inner layer 2, the surface layer 3, the back layer 4, and the stress relaxation layer 5. The filling rate of the wood 11 in the stress relaxation layer 5 is different from the filling rate of the wood 11 in the inner layer 2.

[0028] In the first embodiment, the filling rate of the wood 11 can be changed by extending the sunlight exposure time to further modify the lignin and increasing the amount of lignin removed. Increasing the amount of lignin removed creates space for impregnation with the resin 12, increasing the amount of resin 12, resulting in materials with different filling rates of the wood 11. Alternatively, wood 11 may be compressed before being composited with the resin 12 to reduce the air volume within the wood 11. The material with a longer sunlight exposure time is used as the stress relief layer 5, and the material with a shorter sunlight exposure time is used as the internal layer 2, and these are laminated together. The laminate is then placed on glass plates, as in the first embodiment. Resin 12 is poured onto the top and bottom surfaces of the laminate in an amount equal to the volume of the laminate. The laminate is then sandwiched between the glass plates and pressure is applied to produce the material. The pressure is adjusted depending on the number of layers, but as long as there are a total of three layers, including the internal layer 2 and the stress relief layer 5, the same conditions as in the first embodiment can be used. Depending on the type of resin 12, pressure may be applied in a heated state. This allows for a laminate consisting of the internal layer 2, the stress relief layer 5, the surface layer 3, and the back layer 4 to be obtained.

[0029] The packing rate of the wood 11 in the stress relaxation layer 5 is between that of the inner layer 2, the surface layer 3, and the back layer 4. By providing the stress relaxation layer 5, the packing rate of the wood 11 gradually decreases from the inner layer 2. This reduces the difference in thermal expansion coefficient between the layers, thereby reducing the stress generated between the layers and suppressing the occurrence of delamination, which inhibits light transmittance. As in the first embodiment, the packing rate of the wood 11 in the surface layer 3 and the back layer 4 is less than half the packing rate of the entire wood 11. Here, the wood 11 filled in the inner layer 2 is referred to as wood D114, the wood 11 filled in the stress relaxation layer 5 is referred to as wood E115, and the wood 11 filled in the surface layer 3 and the back layer 4 is referred to as wood F116. Both wood D114 and wood E115 are regularly oriented in the thickness direction. In addition, the wood F116 also has a regular orientation in the thickness direction.

[0030] Fig. 5 is a cross-sectional view of a wood composite material 1 according to a first variation of the second embodiment. As shown in Fig. 5, in the first variation, the wood material 11 filled in the inner layer 2 is referred to as wood D114, the wood material 11 filled in the stress relaxation layer 5 is referred to as wood E115, and the wood material 11 filled in the front layer 3 and back layer 4 is referred to as wood G117. Both wood D114 and wood E115 are oriented in a regular direction relative to the thickness direction, while wood G117 is oriented in an irregular direction relative to the thickness direction. As in the first variation, the fiber axes of the fibers of the wood material 11 may be oriented in different directions.

[0031] FIG. 6 is a cross-sectional view showing a wood composite 1 according to a second modification of the second embodiment. As shown in FIG. 6, in this second modification, the wood composite 1 further includes an outer stress relief layer 51, resulting in a five-layer structure consisting of an inner layer 2, two stress relief layers 5, and two outer stress relief layers 51. A laminate with more than three layers is significantly affected by stress. Here, the wood 11 filled in the inner layer 2 is referred to as Wood H118, and the wood 11 filled in the stress relief layer 5 is referred to as Wood I119. The wood 11 filled in the outer stress relief layer 51 is referred to as Wood J120, and the wood 11 filled in the top layer 3 and bottom layer 4 is referred to as Wood K121. Regarding the filling rate of the wood 11, the wood 11 may be used after adjusting the amount of lignin removed as described above. Alternatively, the wood 11 may be compressed before being composited with the resin 12 to reduce the air volume within the wood 11. Furthermore, in the composite material of wood 11 and resin 12 obtained in embodiment 1, the surface layer 3 and the back layer 4 are resin-rich layers, so that the layers can be bonded together without gaps when stacked, and the occurrence of gaps due to insufficient adhesion can also be suppressed.

[0032] Although the stress relaxation layer 5 has been described as being a composite of wood 11 and resin 12, it need not be a composite of wood 11 and resin 12. For example, any material may be used as long as it has a thermal expansion coefficient between that of the inner layer 2 and that of the surface layer 3 and back layer 4. Furthermore, the stress relaxation layer 5 does not have to be made of a single material, but may be a composite material made by mixing two or more materials. When made of a single material, various plastic materials are used. When mixing two or more materials, short fibers 6 such as glass or a filler 7 such as silicon oxide may be mixed with the plastic. The thermal expansion coefficient of the stress relaxation layer 5 is determined by the thermal expansion coefficients of the inner layer 2 and that of the surface layer 3 and back layer 4. As long as the thermal expansion coefficients are between these, the material is not limited.

[0033] Figure 7 is a cross-sectional view of a wood composite material 1 according to a third variation of the second embodiment. As shown in Figure 7, in this third variation, short fibers 6 are filled into the stress relaxation layer 5. The wood composite material 1 includes an inner layer 2, a surface layer 3, a back layer 4, and a stress relaxation layer 5. The wooden material 11 filled into the inner layer 2 is referred to as wood D114, and the wooden material 11 filled into the surface layer 3 and back layer 4 is referred to as wood G117. As described above, the stress relaxation layer 5 is filled with short fibers 6, and the filling rate of the wooden material 11 is controlled so that the thermal expansion coefficient of the stress relaxation layer 5 is the same as that between the inner layer 2 and the surface layer 3 and back layer 4.

[0034] FIG. 8 is a cross-sectional view of a wood composite material 1 according to a fourth variation of the second embodiment. As shown in FIG. 8, in this fourth variation, the stress relaxation layer 5 is filled with a filler 7. The wood composite material 1 includes an inner layer 2, a surface layer 3, a back layer 4, a stress relaxation layer 5, and an outer stress relaxation layer 51. The wooden piece 11 filled in the inner layer 2 is referred to as wood H118, the wooden piece 11 filled in the outer stress relaxation layer 51 is referred to as wood J120, and the wooden piece 11 filled in the surface layer 3 and back layer 4 is referred to as wood L122. As described above, the stress relaxation layer 5 is filled with the filler 7, and the filling rate of the wooden piece 11 is controlled so that the thermal expansion coefficient of the stress relaxation layer 5 is equal to the thermal expansion coefficients of the inner layer 2, the surface layer 3, and the back layer 4.

[0035] Fig. 9 is a cross-sectional view showing a wood composite material 1 according to a fifth variation of embodiment 2. As shown in Fig. 9, the wood composite material 1 may have a layered structure that is not symmetrical in the thickness direction with respect to the inner layer 2.

[0036] Fig. 10 is a cross-sectional view of a wood composite material 1 according to a sixth variation of the second embodiment. As shown in Fig. 10, in the sixth variation, the wood composite material 1 obtained in the first embodiment is laminated with the fiber directions changed. For example, the fiber axis of the stress relaxation layer 5 is rotated 45° relative to the fiber axis of the inner layer 2, and the fiber axes of the outer surface layer 3 and back layer 4 are rotated 90° relative to the fiber axis of the inner layer 2. This also makes it possible to disperse stress generated by shrinkage of the wood material 11.

[0037] Embodiment 3 Fig. 11 is a graph showing the measurement results of the molecular structure of the wood composite material 1 according to the third embodiment. In this third embodiment, the molecular structure of the wood composite material 1 was investigated using a Fourier transform infrared spectrophotometer (FTIR) as an infrared spectroscopy method. As shown in Fig. 11, in the FTIR, -1 The extreme value around 1595 cm (hereinafter referred to as intensity A) represents the vibration originating from the bond between carbon and oxygen in cellulose in wood 11. -1 The extreme value near B / A (hereinafter referred to as intensity B) represents vibrations resulting from the aromatic ring structure of lignin. The smaller the intensity ratio B / A, the more modified the lignin is, and zero indicates complete modification. Because lignin functions as a binder that fixes cellulose fibers, excessive modification of the wood 11 makes it prone to crumbling and difficult to handle. On the other hand, if the intensity ratio B / A is large, the lignin is not modified, resulting in insufficient impregnation with the resin 12. Therefore, to obtain a material that can be impregnated with the resin 12 and is easy to handle, the intensity ratio B / A is preferably between 0.05 and 0.7, and more preferably between 0.2 and 0.5.

[0038] Embodiment 4 FIG. 12 is a perspective view showing an air conditioner 8 according to a fourth embodiment. In this fourth embodiment, a wood composite material 1 is used in the air conditioner 8. The air conditioner 8 comprises a housing 81, an air outlet 82, airflow direction louvers 83 for adjusting the airflow direction, a first display panel 841, and a second display panel 842. A plurality of air outlets 82 may be provided; FIG. 12 illustrates an example in which two air outlets 82 are provided. A plurality of airflow direction louvers 83 may also be provided; FIG. 10 illustrates an example in which one air outlet 82 is provided for each air outlet 82, for a total of two louvers. The first display panel 841 and the second display panel 842 differ only in size, and any number of panels may be provided. The first display panel 841 and the second display panel 842 may be, for example, lamps that indicate the operating status with different colors, or panels that display the temperature, etc.

[0039] The housing 81, which is partially constituted by the wood composite material 1, is light-transmitting. The wood composite material 1 does not need to be used for the entire housing 81; it can be used only for the first display panel 841 and the second display panel 842, which are part of the housing 81. The first display panel 841 and the second display panel 842 each contain optical elements such as LEDs and display colors through the display panel. Because the display panel also functions as a light diffuser, using a material with nearly 100% light transmittance is undesirable because light is perpendicular to the display panel. On the other hand, a material that does not transmit light cannot display colors. For this reason, it is desirable that the light transmittance be adjustable. As described above, the materials of the first to third embodiments allow for control of light transmittance. Therefore, by using a material with high light transmittance in areas where light transmittance is desirable and a material with low light transmittance in areas where light transmittance is undesirable, an air conditioner 8 with a unique design can be obtained. Although the fourth embodiment has been described using an air conditioner 8 as an example, the material can also be used in the housing 81 of various home appliances such as refrigerators and rice cookers. In this case too, by using a material with high light transmittance in areas where light transmission is desired and a material with low light transmittance in areas where light transmission is not desired, it is possible to obtain a device with a unique design. [Explanation of symbols]

[0040] 1 wood composite, 2 inner layer, 3 surface layer, 4 back layer, 5 stress relief layer, 6 short fiber, 7 filler, 8 air conditioner, 11 wood, 12 resin, 51 outer stress relief layer, 81 housing, 82 air outlet, 83 air direction louver, 111 wood A, 112 wood B, 113 wood C, 114 wood D, 115 wood E, 116 wood F, 117 wood G, 118 wood H, 119 wood I, 120 wood J, 121 wood K, 122 wood L, 841 first display panel, 842 second display panel.

Claims

1. an inner layer comprising wood and resin; a surface layer provided on a surface of the inner layer and including the wood and the resin; a back layer provided on the back surface of the internal layer and including the wood and the resin; The total filling rate of the surface layer and the back layer is half or less of the filling rate of the entire wood, a stress relaxation layer provided between the surface layer, the back layer and the inner layer, the stress relaxation layer including the wood and the resin; At least one of the fiber axes of the wood fibers in the inner layer, the surface layer, the back layer, and the stress relaxation layer are oriented in different directions, The stress relaxation layer is made of a material that has been treated with sunlight for a longer period of time than the inner layer, resulting in a greater amount of lignin being removed from the wood. wood composite.

2. The surface layer and the back layer are resin-rich layers. The wood composite of claim 1.

3. The arithmetic mean surface roughness of the surface layer and the arithmetic mean surface roughness of the back layer are 50 μm or less, which is the diameter of the fiber of the wood.

3. The wood composite material according to claim 1 or 2.

4. The filling rate of the wood of the stress relaxation layer is between the filling rate of the inner layer, the filling rate of the surface layer, and the filling rate of the back layer.

3. The wood composite material according to claim 1 or 2.

5. In infrared spectroscopy, the intensity ratio B / A of the vibration A of carbon and oxygen in cellulose in the wood to the vibration B of the aromatic ring of lignin is 0.05 or more and 0.7 or less.

3. The wood composite material according to claim 1 or 2.

6. A housing comprising the wood composite material of claim 1 or 2 as a part thereof. Air conditioner.

7. A step of obtaining modified wood by modifying the chromophores of lignin in the wood; impregnating the modified wood with resin; A step of hardening the resin-impregnated modified wood while applying pressure to the resin-sandwiched modified wood; and a step of laminating the inner layer, the surface layer, the back layer, and the stress relaxation layer, each having a different wood filling rate, and then pressing the laminate. Manufacturing methods for wood composites.

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