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

Abstract

This wood composite material comprises: an inner layer that includes wood and resin; an obverse layer provided on the obverse surface of the inner layer, the obverse layer including wood and resin; and a reverse layer provided on the reverse surface of the inner layer, the reverse layer including wood and resin. The total of the filling rate of the obverse layer and the filling rate of the reverse layer is no greater than half the filling rate of the wood overall.

Description

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

[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.

[0002] In recent years, against the background of the increasing concentration of carbon dioxide in the atmosphere year by year, efforts have been made to reduce carbon dioxide emissions. For example, in the field of materials, efforts have been made to utilize natural wood as a raw material and reduce the carbon dioxide emissions when making materials. Patent Document 1 discloses a material technology related to a colorless and light-transmissive wood composite material by removing lignin in wood and then impregnating resin having a refractive index close to that of cellulose, which is the main component of wood. Patent Document 2 discloses a technique for laminating a composite of compressed wood and resin.

[0003] International Publication No. 2017 / 136714, Japanese Unexamined Patent Application Publication No. 2023 - 93543

[0004] However, in the material configuration of Patent Document 1, although the resin impregnates the gaps in the wood to suppress the scattering of light inside the wood, there is a risk of irregular reflection of light on the surface of the wood. In this case, due to the irregular reflection of light, the amount of light transmitted into the material decreases, resulting in a decrease in light transmittance. In particular, when the wood is made into a thick plate, the light transmittance is further impaired. In addition, since the outermost surface of the material is wood, the wood may be rubbed and chipped due to friction with other members, etc., and the surface may become rough, increasing the amount of irregular reflection of light. Furthermore, since the outermost surface of the material is wood, when dirt adheres, the wood and the dirt are integrated, making cleaning difficult, which further reduces the light transmittance. In addition, although Patent Document 2 has a layer structure formed by lamination, a separate process for lamination is required, which complicates the manufacturing process.

[0005] The present disclosure has been made to solve the above problems, and an object thereof is to provide a wood composite material with good light transmittance, an air conditioner, and a method for manufacturing the wood composite material.

[0006] The wood composite material according to this disclosure comprises an inner layer having wood and resin, a surface layer provided on the surface of the inner layer and having wood and resin, and a back layer provided on the back surface of the inner layer and having wood and resin, wherein the combined filling rate of the surface layer and the back layer is half or less of the total filling rate of the wood.

[0007] According to this disclosure, the combined filling rate of the surface layer and the back layer is less than half of the total filling rate of the wood. Therefore, there is less wood in the outermost layers, the surface and back. As a result, diffuse reflection of light and the occurrence of splintering can be suppressed. Consequently, a wood composite material with good light transmittance can be obtained.

[0008] This is a top view showing a wood composite material according to Embodiment 1. This is a cross-sectional view showing a wood composite material according to Embodiment 1. This is a cross-sectional view showing a modified version of a wood composite material according to Embodiment 1. This is a cross-sectional view showing a wood composite material according to Embodiment 2. This is a cross-sectional view showing a wood composite material according to the first modified version of Embodiment 2. This is a cross-sectional view showing a wood composite material according to the second modified version of Embodiment 2. This is a cross-sectional view showing a wood composite material according to the third modified version of Embodiment 2. This is a cross-sectional view showing a wood composite material according to the fourth modified version of Embodiment 2. This is a cross-sectional view showing a wood composite material according to the fifth modified version of Embodiment 2. This is a cross-sectional view showing a wood composite material according to the sixth modified version of Embodiment 2. This is a graph showing the measurement results of the molecular structure of a wood composite material according to Embodiment 3. This is a perspective view showing an air conditioner according to Embodiment 4.

[0009] Embodiments of the wood composite material, air conditioner, and method for manufacturing the wood composite material described herein will be explained below with reference to the drawings. However, this disclosure is not limited to the embodiments described below. Also, the relationships of the sizes of the components in the following drawings, including Figure 1, may differ from those of the actual components. Furthermore, in the following description, terms indicating direction will be used as appropriate to facilitate understanding of this disclosure, but these terms are for illustrative purposes only and do not limit this disclosure. Examples of terms indicating direction include "up," "down," "right," "left," "front," or "back."

[0010] Embodiment 1. Figure 1 is a top view showing a wood composite material 1 according to Embodiment 1. As shown in Figure 1, the wood composite material 1 is a composite of wood 11 and resin 12 into a single material, with the resin 12 impregnating the gaps in the wood 11. Wood 11 is one of the most abundant polymers on Earth and is attracting 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 structure of β-glucose and has been a material that has attracted attention in the past for its ability to enhance the functionality of resin 12. Sometimes only fibrous cellulose is extracted and used as a material. Hemicellulose has a branched structure of β-glucose and exists in a way that it intertwines with the cellulose fibers. Lignin is a complex and diverse aromatic compound and plays the role of a binder that fixes the cellulose fibers.

[0011] The wood composite material 1 according to this embodiment 1 focuses on lignin, and is a material formed by modifying lignin and then compounding it with resin 12. Various types of coniferous or hardwoods can be used as the wood 11. Examples of coniferous trees include Japanese cedar, Japanese cypress, Japanese red pine, Japanese pine, Japanese larch, and Douglas fir, while examples of hardwoods include balsa, beech, Japanese white oak, zelkova, and chestnut teak. From the viewpoint of providing a wide pathway for impregnation of the resin 12, wood 11 with a lower density is preferable, and the use of balsa is desirable.

[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, while examples of thermoplastic resins include polycarbonate, acrylic, polyvinyl chloride, polystyrene, and acrylonitrile-butadiene-styrene copolymer. These are used in a liquid state, either molten or dissolved in a solvent. When impregnating, it is desirable that the molecular size of the resin 12 is small and that its refractive index is close to that of the wood 11 structure. For this reason, a thermosetting resin with a small molecular size before curing is desirable for the resin 12, and epoxy resin is preferable when considering refractive index and versatility. In this embodiment 1, balsa wood is used for the wood 11, and epoxy resin (main agent: CY230 manufactured by Nagase ChemteX Co., Ltd., curing agent: HY951 manufactured by Nagase ChemteX Co., Ltd.) is used for the resin 12.

[0013] The wood composite material 1, consisting of wood 11 and resin 12, is manufactured, for example, by the following manufacturing method. First, the wood 11 is coated or immersed in an aqueous solution having a bleaching effect, such as hydrogen peroxide. In this case, an alkaline aqueous solution such as sodium hydroxide may be pre-coated or pre-immersed to enhance the effect of the hydrogen peroxide. In this state, sunlight is irradiated for one hour or more. The irradiation time varies depending on the intensity of sunlight or the thickness of the wood 11. For example, if the wood 11 is 1 mm thick in the summer, it can be treated in one hour. Depending on the conditions, it is desirable to adjust the irradiation time, and irradiation may be carried out over two days or more. It is also possible to reapply hydrogen peroxide during irradiation, which can effectively advance the treatment. The treated wood 11, which was originally brownish-red, has changed to white. The wood 11 is colored by the aromatic chromophore of lignin, but this treatment indicates that the chromophore has been decolorized and modified. Depending on the type of wood 11, some brownish-red color may remain. This indicates a strong chromophore, and while extending the sunlight treatment time will bring it closer to white, it is also possible to intentionally retain a brownish color. This ultimately results in a brownish, light-transmitting material. Furthermore, treatment is not limited to sunlight; it is also possible to use artificial lamps such as ultraviolet light.

[0014] Next, the treated modified wood is washed. Washing is carried out by immersing it in various alcohols such as ethanol and isopropyl alcohol, and vibrating it while it is immersed. From the viewpoint of safety and versatility, the use of ethanol is preferable as the alcohol. Subsequently, the washed wood 11 is immersed in toluene, allowing the toluene to penetrate into the gaps in the wood 11. In addition to toluene, other low molecular weight solvents that are good for resin 12, such as xylene, can also be used, but in this embodiment 1, toluene is used from the viewpoint of versatility. Next, the wood 11 is impregnated by immersing it in resin 12. The main agent and the hardener are mixed in a specified ratio in advance to make a mixture. At this time, a third component that is incorporated into the molecular structure of the epoxy resin 12, such as a reactive diluent, may be added to adjust the viscosity. Impregnation is carried out in a vacuum atmosphere, and the wood 11 is immersed in resin 12 under vacuum, and the resin 12 is impregnated while removing air bubbles in the wood 11. Depending on the size of the wood 11, for example, if a piece of wood 11 measuring 50 mm x 50 mm x 1 mm thick is used, vacuum impregnation is completed in 30 minutes. After vacuum impregnation, a pressure impregnation process may be performed using an autoclave or the like. It has been confirmed that by adding pressure impregnation, the air components remaining in the wood 11 are compressed, and the impregnation of the resin 12 progresses further.

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

[0016] Figure 2 is a cross-sectional view showing a wood composite material 1 according to Embodiment 1. As shown in Figure 2, the wood composite material 1 comprises an inner layer 2, a surface layer 3, and a back layer 4. The surface layer 3 and the back layer 4 constitute the outermost layer of the wood composite material 1. The inner layer 2 has wood 11 and resin 12. The surface layer 3 is provided on the surface of the inner layer 2 and has wood 11 and resin 12. The back layer 4 is provided on the back surface of the inner layer 2 and has 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 the back layer 4 is referred to as wood B112. Both wood A111 and wood B112 are oriented in a regular direction with respect to the thickness direction.

[0017] The surface layer 3 and the back layer 4 are resin-rich layers, and the combined filling rate of the wood 11 in the surface layer 3 and the back layer 4 is composed of a composition that is less than half of the total filling rate of the wood 11 in the entire material. This makes it possible to obtain a light-transmitting material that suppresses diffuse reflection at the outermost surface. If the total filling rate exceeds half, the amount of wood 11 at the outermost surface is large, and the wood 11 may protrude from the outermost surface. The wood 11 used is 1 mm thick, but the resin-rich layer is formed from the splinters on the surface of the wood 11. Therefore, the thickness of the resin-rich layer is only a small part of the thickness of the wood 11 used, and is thinner relative to the total thickness of the wood 11. Furthermore, with the above manufacturing method, the filling rate of the wood 11 is higher in the inner layer 2 than in the outermost layer. Also, if cypress with a strong grain is used, a material that transmits light while retaining the grain can be obtained. Conventionally, it was necessary to laminate multiple layers with different filling rates of wood 11, but in this embodiment 1, the wood composite material 1 can be manufactured without going through a lamination process.

[0018] The cellulose fibers of wood 11 are known to be about 50 μm in diameter. When there is no resin-rich layer on the surface layer 3 and back layer 4, the outermost surface becomes the wood fibers 11. This results in irregularities of about 50 μm due to the diameter of the wood fibers 11, causing diffuse reflection of light. Furthermore, when the outermost surface is the wood fibers 11, friction on the surface causes splintering of the wood 11, making the surface rough. This also increases the amount of diffuse reflection of light. Diffuse reflection of the outermost surface can be suppressed by reducing the surface irregularities. When a resin-rich layer is present, and the total filling rate is less than half of the total filling rate of wood 11, the outermost surface becomes resin 12. Due to the pressure from the glass plate and the leveling effect with the resin 12, the irregularities are further reduced, and a material with an irregular structure of 50 μm or less can be obtained. Furthermore, since the structure is less prone to splintering, diffuse reflection of light caused by splintering can be suppressed.

[0019] Thus, the material composition of the wood composite material 1 has a layered structure that suppresses diffuse reflection and splintering. To suppress diffuse reflection and splintering, the wood composite material 1 has a layered structure in which the amount of wood filling is distributed between the inner layer 2, the outermost layer which is the surface layer 3, and the back layer 4. The wood composite material 1 is manufactured using a simple process without laminating a structure in which the wood filling ratio of the outermost layer is smaller than that of the inner layer 2. This material structure suppresses the occurrence of surface irregularities caused by wood and suppresses the exposure of wood to the outermost surface, thereby enabling the stable acquisition of a light-transmitting material with suppressed diffuse reflection.

[0020] Figure 3 is a cross-sectional view showing a modified wood composite material 1 according to Embodiment 1. As shown in Figure 3, in the modified example, the wood 11 filling the inner layer 2 is referred to as wood A111, and the wood 11 filling the surface layer 3 and back layer 4 is referred to as wood C113. Wood A111 is oriented in a regular direction with respect to the thickness direction, but wood C113 is oriented in an irregular direction with respect to the thickness direction. As in the modified example, the fiber axes of the wood 11 fibers may be oriented in different directions.

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

[0022]

[0023] Examples 1, 2, and 3 have a resin 12 sandwich structure, and the overall wood 11 filling rate is the same, but the filling rate of wood 11 in the outermost layer and the inner layer 2 is different. As a result, the ratio of the outermost layer's wood 11 filling rate to the total 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 them. On the other hand, in Comparative Examples 1 and 2, the overall wood 11 filling rate is the same, but the filling rate of the outermost layer's wood 11 to the total 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. In this case, the light transmittance deteriorated significantly, to 42.6% in Comparative Example 1 and 29.8% in Comparative Example 2.

[0024] Examples 4, 5, and 6 differ in the overall filling rate of the wood 11. When the filling rate of the outermost layer of wood 11 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 outermost layer of wood 11 relative to the entire material exceeded 50%, the light transmittance was 39.2% in Comparative Example 3 and 36.4% in Comparative Example 4, showing a significant deterioration.

[0025] Examples 7, 8, 9, and 10 differ in the size of the surface irregularities. They were produced by changing the pressure when the glass plates were sandwiched together as described above. 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 was the case without the resin 12 sandwich structure. In this case, splinters occurred on the surface, and the light transmittance was 42.2%, which was worse than that of Example 1.

[0026] Embodiment 2. Figure 4 is a cross-sectional view showing a wood composite material 1 according to Embodiment 2. Embodiment 2 differs from Embodiment 1 in that the wood composite material 1 is provided with a stress relaxation layer 5. In Embodiment 2, parts common to Embodiment 1 are denoted by the same reference numerals and their descriptions are omitted, and the differences from Embodiment 1 will be the focus of the explanation.

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

[0028] In Embodiment 1, the filling rate of the wood 11 can be changed by extending the sunlight irradiation time to further modify the lignin and increasing the amount of lignin removed. By increasing the amount of lignin removed, space is created for impregnation with resin 12, increasing the amount of resin 12, and as a result, materials with different amounts of wood 11 filling can be obtained. Alternatively, the wood 11 may be compressed before compounding with resin 12 to reduce the volume of air inside the wood 11 beforehand. Materials with longer sunlight irradiation times are used as the stress relaxation layer 5, and materials with shorter irradiation times are used as the inner layer 2, and these are laminated. Then, the laminated material is placed on a glass plate in the same manner as in Embodiment 1, and with the same volume of resin 12 as the laminate flowing on the upper and lower surfaces of the laminate, it is sandwiched between glass plates and pressure is applied to produce the material. The pressure is adjusted according to the number of layers, but if there are a total of three layers (inner layer 2 and stress relaxation layer 5), it can be carried out under the same conditions as in Embodiment 1. Also, depending on the type of resin 12, pressure may be applied while it is heated. This makes it possible to obtain a laminate consisting of an inner layer 2, a stress relaxation layer 5, a surface layer 3, and a back layer 4.

[0029] The filling rate of the wood 11 in the stress relaxation layer 5 is between the filling rate of the inner layer 2 and the filling rates of the surface layer 3 and the back layer 4. By providing the stress relaxation layer 5, the filling rate of the wood 11 gradually decreases from the inner layer 2. This reduces the difference in thermal expansion coefficients between layers, thereby reducing the stress generated between layers and suppressing the occurrence of delamination that hinders light transmission. Also, similar to Embodiment 1, the filling rate of the wood 11 in the surface layer 3 and the back layer 4 is composed of a composition that is less than half of the total filling rate of the wood 11. Here, the wood 11 filling the inner layer 2 is referred to as wood D114, the wood 11 filling the stress relaxation layer 5 is referred to as wood E115, and the wood 11 filling the surface layer 3 and the back layer 4 is referred to as wood F116. All of the wood D114 and wood E115 are oriented in a regular direction with respect to the thickness direction. Furthermore, all of the wood F116 pieces are oriented in a regular direction relative to their thickness.

[0030] Figure 5 is a cross-sectional view showing a wood composite material 1 according to a first modification of Embodiment 2. As shown in Figure 5, in the first modification, the wood 11 filling the inner layer 2 is called wood D114, the wood 11 filling the stress relaxation layer 5 is called wood E115, and the wood 11 filling the surface layer 3 and back layer 4 is called wood G117. Both wood D114 and wood E115 are oriented in a regular direction with respect to the thickness direction, but wood G117 is oriented in an irregular direction with respect to the thickness direction. As in the first modification, the fiber axes of the wood 11 fibers may be oriented in different directions.

[0031] Figure 6 is a cross-sectional view showing a wood composite material 1 according to a second modified example of Embodiment 2. As shown in Figure 6, in the second modified example, the wood composite material 1 further has an outer stress relaxation layer 51, and has a five-layer structure consisting of an inner layer 2, two stress relaxation layers 5, and two outer stress relaxation layers 51. Laminates with more than three layers are 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 relaxation layer 5 is referred to as wood I119. The wood 11 filled in the outer stress relaxation layer 51 is referred to as wood J120, and the wood 11 filled in the surface layer 3 and back layer 4 is referred to as wood K121. Regarding the filling rate of the wood 11, as described above, wood 11 with the amount of lignin removed may be used, or wood 11 that has been compressed before compounding with resin 12 to reduce the volume of air in the wood 11 may be used. Furthermore, in the composite material of wood 11 and resin 12 obtained in Embodiment 1, since the surface layer 3 and back layer 4 are resin-rich layers, the layers can be bonded together without gaps during lamination, and the occurrence of gaps due to insufficient bonding can be suppressed.

[0032] The stress relaxation layer 5 has been described using the example of a composite material of wood 11 and resin 12, but it does not have to be a composite material of wood 11 and resin 12. For example, any material that has a thermal expansion coefficient between the inner layer 2 and the surface layer 3 and back layer 4 is acceptable. 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 can be used. When mixing two or more materials, short fibers 6 such as glass or fillers 7 such as silicon dioxide may be mixed into the plastic. The thermal expansion coefficient of the stress relaxation layer 5 is determined by the thermal expansion coefficient between the inner layer 2 and the surface layer 3 and back layer 4, and the material is not limited if the thermal expansion coefficients are in between.

[0033] Figure 7 is a cross-sectional view showing a wood composite material 1 according to a third modification of Embodiment 2. As shown in Figure 7, in the third modification, short fibers 6 are filled in the stress relaxation layer 5. The wood composite material 1 comprises an inner layer 2, a surface layer 3, a back layer 4, and a stress relaxation layer 5. The wood 11 filled in the inner layer 2 is referred to as wood D114, and the wood 11 filled in 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 wood 11 is controlled so that the thermal expansion coefficient of the stress relaxation layer 5 becomes the thermal expansion coefficient between the inner layer 2 and the surface layer 3 and back layer 4.

[0034] Figure 8 is a cross-sectional view showing a wood composite material 1 according to a fourth modification of Embodiment 2. As shown in Figure 8, in the fourth modification, filler 7 is filled in the stress relaxation layer 5. The wood composite material 1 comprises 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 wood 11 filled in the inner layer 2 is referred to as wood H118, the wood 11 filled in the outer stress relaxation layer 51 is referred to as wood J120, and the wood 11 filled in the surface layer 3 and back layer 4 is referred to as wood L122. As described above, filler 7 is filled in the stress relaxation layer 5, and the filling rate of wood 11 is controlled so that the thermal expansion coefficient of the stress relaxation layer 5 becomes the thermal expansion coefficient between the inner layer 2 and the surface layer 3 and back layer 4.

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

[0036] Figure 10 is a cross-sectional view showing a wood composite material 1 according to a sixth modification of Embodiment 2. As shown in Figure 10, in the sixth modification, the wood composite material 1 obtained in Embodiment 1 is laminated with the respective fiber directions changed. For example, the fiber axis of the stress relaxation layer 5 is rotated by 45° with respect 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 by 90°. This also allows for the dispersion of stress generated by the shrinkage of the wood 11.

[0037] Embodiment 3. Figure 11 is a graph showing the measurement results of the molecular structure of the wood composite material 1 according to Embodiment 3. In Embodiment 3, the molecular structure of the wood composite material 1 was investigated using infrared spectroscopy, specifically with a Fourier transform infrared spectrophotometer (FTIR). As shown in Figure 11, the FTIR measured at 1030 cm⁻¹. －１ The extreme values ​​in the vicinity (hereinafter referred to as intensity A) represent vibrations originating from the carbon-oxygen bonding of cellulose in the wood 11. 1595 cm －１ The extreme value in the vicinity (hereinafter referred to as intensity B) represents vibrations originating from the ring (aromatic ring) structure of the aromatic group of lignin. A smaller intensity ratio B / A indicates that the lignin has been modified, and a value of zero indicates that it has been completely modified. Since lignin functions as a binder that fixes cellulose fibers, if it is modified too much, the wood 11 will easily crumble and become difficult to handle. On the other hand, if the intensity ratio B / A is large, the lignin is not modified, and the impregnation of the resin 12 becomes insufficient. For this reason, in order to obtain a material that can be impregnated with resin 12 and has good handling properties, an intensity ratio B / A of 0.05 or more and 0.7 or less is desirable, and 0.2 or more and 0.5 or less is more desirable.

[0038] Embodiment 4. Figure 12 is a perspective view showing an air conditioner 8 according to Embodiment 4. In Embodiment 4, the case in which a wood composite material 1 is used in the air conditioner 8 will be described. The air conditioner 8 consists of a housing 81, air outlets 82, air direction louvers 83 for adjusting the direction of air discharge, a first display panel 841, and a second display panel 842. Multiple air outlets 82 may be provided, and Figure 12 illustrates the case where two are provided. Multiple air direction louvers 83 may also be provided, and Figure 10 illustrates the case where one is provided for each air outlet 82, for a total of two. The only difference between the first display panel 841 and the second display panel 842 is their size, and any number of them may be provided. The first display panel 841 and the second display panel 842 may be, for example, lamps that indicate the operating status by color, or panels that display temperature, etc.

[0039] The housing 81 is partially composed of wood composite material 1 and has light transmittance. The wood composite material 1 does not need to be used for the entire housing 81; it can also be used only for the first display panel 841 and the second display panel 842, which are parts of the housing 81. The first display panel 841 and the second display panel 842 are equipped with optical elements such as LEDs inside, and display colors through the display panels. Since the display panels also serve as light diffusers, using materials with near 100% light transmittance is undesirable because the light will be perpendicular. On the other hand, materials that do not transmit light cannot display colors. For this reason, it is desirable that the light transmittance be adjustable. As described above, the materials of these embodiments 1 to 3 can control the light transmittance. Therefore, by using a material with high light transmittance in parts where light transmission is desirable and a material with low light transmittance in parts where light transmission is undesirable, an air conditioner 8 with a unique design can be obtained. Although the air conditioner 8 was described as an example in embodiment 4, it can also be used for the housing 81 of various home appliances such as refrigerators and rice cookers. In this case as well, by using a material with high light transmittance in areas where light transmission is desirable and a material with low light transmittance in areas where light transmission is undesirable, it is possible to obtain equipment with a unique design.

[0040] 1 Wood composite material, 2 Inner layer, 3 Surface layer, 4 Back layer, 5 Stress relief layer, 6 Short fibers, 7 Filler, 8 Air conditioner, 11 Wood, 12 Resin, 51 Outer stress relief layer, 81 Housing, 82 Air outlet, 83 Air direction louvers, 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. A wood composite material comprising: an inner layer having wood and resin; a surface layer provided on the surface of the inner layer and having wood and resin; and a back layer provided on the back surface of the inner layer and having wood and resin, wherein the combined filling rate of the surface layer and the back layer is half or less of the total filling rate of wood.

2. The wood composite material according to claim 1, wherein the arithmetic mean surface roughness of the surface layer and the arithmetic mean surface roughness of the back layer are 50 μm or less of the diameter of the wood fibers.

3. The wood composite material according to claim 1 or 2, further comprising a stress-relieving layer provided between the surface layer, the back layer and the internal layer, and having the wood and the resin.

4. The wood composite material according to claim 3, wherein the filling rate of the wood in the stress relaxation layer is between the filling rate of the internal layer, the filling rate of the surface layer, and the filling rate of the back layer.

5. The wood composite material according to claim 3 or 4, 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 relaxation layer is oriented in different directions.

6. The wood composite material according to any one of claims 1 to 5, wherein, in infrared spectroscopy, the intensity ratio B / A of the vibration A of carbon and oxygen in cellulose in the wood and the vibration B of the aromatic ring of lignin is 0.05 or more and 0.7 or less.

7. An air conditioner comprising a housing in which a wood composite material described in any one of claims 1 to 6 is partially formed.

8. A method for manufacturing a wood composite material, comprising the steps of: obtaining modified wood in which the chromophore of lignin in the wood has been modified; impregnating the modified wood with a resin; and hardening the resin-impregnated modified wood while pressing it while sandwiched between layers of resin.

9. The method for manufacturing a wood composite material according to claim 8, further comprising the step of laminating an inner layer, a surface layer, a back layer, and a stress relaxation layer with different wood filling ratios, and then applying pressure.

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