JP7770615B1 - Wood composite material, air conditioner, and method for manufacturing wood composite material - Google Patents

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

This disclosure relates to a wood composite material using wood and resin, an air conditioner, and a method for manufacturing the wood composite material.

In recent years, efforts have been made to reduce carbon dioxide emissions against the backdrop of annual increases in atmospheric carbon dioxide concentrations. For example, in the materials field, efforts are being made to utilize natural wood as a raw material to reduce carbon dioxide emissions when producing materials. Patent Document 1 discloses material technology related to a colorless, optically transparent wood composite material, which is made by removing the lignin from the 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.

International Publication No. 2017/136714 Japanese Patent Application Laid-Open No. 2023-93543

However, with the material configuration of Patent Document 1, although the resin impregnation into the gaps in the wood suppresses light scattering within the wood, there is a risk of light being diffused at 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 thicker. 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 dirt and the wood become integrated, making cleaning difficult and further reducing light transmittance. Patent Document 2 also describes a layered structure created by lamination, but this requires a separate lamination process, complicating the manufacturing process.

This disclosure has been made to solve the above-mentioned problems, and aims to provide a wood composite material, an air conditioner, and a method for manufacturing a wood composite material with good light transmittance.

The wood composite material according to the present disclosure comprises an inner layer containing wood and resin, a surface layer formed on the surface of the inner layer and containing wood and resin, and a back layer formed on the back surface of the inner layer and containing wood and resin, wherein the total filling rate of the surface layer and the back layer is half or less of the overall wood filling rate, and further comprises a stress relief layer formed between the surface layer, the back layer and the inner layer and containing wood and 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 uses a material that has been treated with sunlight for a longer time than the inner layer, thereby increasing the amount of lignin removed from the wood .

According to the present disclosure, the total filling rate of the surface layer and the back layer is less than half of the overall wood filling rate. This means that there is less wood in the outermost layers, the surface and back layers. This reduces the occurrence of diffused light reflection and splinters. This allows for the production of a wood composite with good light transmittance.

1 is a top view showing a wood composite material according to embodiment 1. FIG. 1 is a cross-sectional view showing a wood composite material according to a first embodiment. 1 is a cross-sectional view showing a wood composite material according to a modified example of the first embodiment. FIG. 6 is a cross-sectional view showing a wood composite material according to a second embodiment. A cross-sectional view showing a wood composite material according to a first modified example of embodiment 2. A cross-sectional view showing a wood composite material according to a second modified example of embodiment 2. A cross-sectional view showing a wood composite material according to a third modified example of embodiment 2. A cross-sectional view showing a wood composite material according to a fourth modified example of embodiment 2. A cross-sectional view showing a wood composite material according to a fifth modified example of embodiment 2. A cross-sectional view showing a wood composite material according to a sixth modified example of embodiment 2. 10 is a graph showing the measurement results of the molecular structure of a wood composite material according to embodiment 3. FIG. 10 is a perspective view showing an air conditioner according to a fourth embodiment.

The following describes embodiments of the wood composite material, air conditioner, and method for manufacturing the wood composite material of the present disclosure, with reference to the drawings. Note that the present disclosure is not limited to the embodiments described below. Furthermore, in the following drawings, including Figure 1, the size relationships between the components may differ from the actual size. Furthermore, in the following description, terms indicating directions are 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," or "rear."

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 a 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 manner that entangles cellulose fibers. Lignin is a complex and diverse aromatic compound that acts as a binder to secure cellulose fibers together.

The wood composite material 1 according to this embodiment 1 focuses on lignin, and is a material in which the lignin is modified and then composited with resin 12. Various types of coniferous or broadleaf trees can be used as the wood 11. Examples of coniferous trees include cedar, cypress, red pine, Edo pine, larch, and Douglas fir, while examples of broadleaf trees include balsa, beech, white oak, zelkova, and chestnut teak. From the perspective of providing a wide path for impregnation with resin 12, wood 11 with a low density is better, and it is desirable to use balsa.

A variety of thermosetting and thermoplastic resins can be used for the resin 12. Thermosetting resins include epoxy resin, unsaturated polyester resin, phenolic resin, and urea resin. Thermoplastic resins include polycarbonate, acrylic, polyvinyl chloride, polystyrene, and acrylonitrile-butadiene-styrene copolymer. These are used in a liquid state, such as a molten state or 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 wood 11 structure. Therefore, a thermosetting resin with a small molecular size before hardening is desirable for the resin 12, and epoxy resin is preferable considering the 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 Corporation, curing agent: HY951 manufactured by Nagase ChemteX Corporation) is used for the resin 12.

The wood composite material 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 a bleaching solution 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 solution such as sodium hydroxide. In this state, the wood is exposed to sunlight for at least one hour. The exposure time varies depending on the intensity of the sunlight and the thickness of the wood 11. For example, in summer, a 1 mm thick wood 11 can be treated in one hour. It is desirable to adjust the exposure time depending on the conditions, and exposure may be carried out over two days or more. It is also possible to reapply hydrogen peroxide during exposure, which allows for more effective treatment. The treated wood 11 has changed from its original brown color to white. This indicates that the color of the wood 11 is due to the aromatic chromophores in lignin, but this treatment has rendered the chromophores colorless and modified the wood. 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.

Next, the treated modified wood is washed. Washing is performed by immersing the wood in various alcohols, such as ethanol or isopropyl alcohol, and vibrating the immersed state. From the perspectives of safety and versatility, ethanol is the preferred alcohol. Next, the washed wood 11 is immersed in toluene, allowing the toluene to penetrate the gaps in the wood 11. While toluene and other good solvents for low-molecular-weight resin 12, such as xylene, can also be used, in this embodiment 1, toluene is used for versatility. Next, the wood 11 is immersed in resin 12 to impregnate it. The base resin and curing agent are mixed in a specified ratio in advance to create a mixture. 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 is 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 the additional pressurized impregnation compresses the air remaining in the wooden piece 11, further promoting impregnation of the resin 12.

Finally, the resin 12 is hardened on the wood 11 impregnated with resin 12. For example, if wood 11 is 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 in 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 beforehand, and the resin 12 is 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 sandwich structure of "resin 12 - wood 11 impregnated with resin 12 - resin 12." A glass plate is then 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 will flow out from the front and back surfaces of the wood 11 impregnated with the resin 12, 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.

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 back layer 4 form the outermost layers of the wood composite material 1. The inner layer 2 comprises wood 11 and resin 12. The surface layer 3 is provided on the surface of the inner layer 2 and comprises wood 11 and resin 12. The back layer 4 is provided on the back surface of the inner layer 2 and comprises 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. All of the wood A111 is oriented in a regular direction relative to the thickness direction, and all of the wood B112 is also oriented in a regular direction relative to the thickness direction.

The surface layer 3 and back layer 4 are resin-rich layers, and the total wood 11 filling rate of the surface layer 3 and the back layer 4 is less than half the wood 11 filling rate of 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 wood 11 filling rate 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. As a result, the thickness of the resin-rich layer is only a small portion of the thickness of the wood 11 used, making it thinner than the overall thickness of the wood 11. Furthermore, the above manufacturing method allows the wood 11 filling rate of the inner layer 2 to be higher than that of the outermost layer. Furthermore, when using cypress, which has a strong grain, a material that transmits light while retaining the wood grain can be obtained. Conventionally, it was necessary to stack multiple layers with different wood 11 filling rates. However, in this embodiment 1, the wood composite material 1 can be manufactured without a lamination process.

The cellulose fibers in 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 in diameter due to the diameter of the wood 11 fiber will occur, 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, because the structure is less susceptible to splinters, diffuse reflection of light due to splinters can be suppressed.

In this way, the material configuration of 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, 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. 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.

Figure 3 is a cross-sectional view showing a wood composite material 1 according to a modified example of embodiment 1. As shown in Figure 3, in this modified example, 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 C113. All of the wood A111 is oriented in a regular direction relative to the thickness direction, but wood C113 is oriented in an irregular direction relative to the thickness direction. As in this modified example, the fiber axes of the fibers of the wood 11 may be oriented in different directions.

Next, we will provide a detailed explanation of materials in which resin 12 is impregnated into the gaps in wood 11 through examples and comparative examples. Balsa wood 11 was used, and epoxy resin 12 was used. Materials were produced by varying the presence or absence of a resin 12 sandwich structure, the wood 11 filling rate in each layer and the ratio of wood 11 filling rate in the outermost layer (surface layer 3, back layer 4) to the entire material, surface irregularities, and the manufacturing method, including 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 expressed in volume, and surface irregularities are expressed in arithmetic mean surface roughness. Light transmittance was measured at a wavelength of 600 nm. The results are shown in Table 1.

Examples 1, 2, and 3 have a resin 12 sandwich structure. While the overall wood 11 filling rate is the same, the wood 11 filling rates in the outermost layer and inner layer 2 are different. As a result, the wood 11 filling rate 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 wood 11 filling rate 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, exceeding half of the total. The light transmittance was significantly reduced, at 42.6% in Comparative Example 1 and 29.8% in Comparative Example 2.

Examples 4, 5, and 6 differ in the overall wood 11 filling rate. When the filling rate of the outermost wood 11 in 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 wood 11 in the entire material exceeded 50%, the light transmittance was significantly worse, at 39.2% in Comparative Example 3 and 36.4% in Comparative Example 4.

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. As such, the smaller the surface irregularities, the greater the light transmittance. Comparative Example 5 did 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.

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 relief layer 5. In this embodiment 2, parts that are common to embodiment 1 are given the same reference numerals and their description will be omitted, and the following description will focus on the differences from embodiment 1.

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 of the materials obtained in example 1 are used. Below, we will explain an example of a wood composite material 1 that uses all of the wood 11 obtained in example 1 for the laminate, and that is composed of an inner layer 2, a stress relief layer 5, a surface layer 3, and a back layer 4. 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 relief layer 5. The filling rate of wood 11 in the stress relief layer 5 is different from the filling rate of wood 11 in the inner layer 2.

In embodiment 1, the filling rate of 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 resin 12 impregnation, increasing the amount of resin 12, and ultimately resulting in materials with different filling rates of wood 11. Alternatively, wood 11 may be compressed before being composited with resin 12 to reduce the air volume within the wood 11. The material with a longer sunlight exposure time serves as the stress relief layer 5, while the material with a shorter sunlight exposure time serves as the inner layer 2. The laminate is then placed on glass plates, as in embodiment 1. 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 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 inner layer 2 and the stress relief layer 5, the same conditions as in embodiment 1 can be used. Depending on the type of resin 12, pressure may be applied while the resin is heated. As a result, a laminate consisting of the inner layer 2, the stress relaxation layer 5, the surface layer 3, and the back layer 4 can be obtained.

The wood 11 filling rate in the stress relief layer 5 is between that of the inner layer 2 and those of the surface layer 3 and back layer 4. By providing the stress relief layer 5, the wood 11 filling rate gradually decreases from the inner layer 2. This reduces the difference in thermal expansion coefficient between layers, thereby reducing the stress generated between layers and suppressing the occurrence of delamination, which impairs light transmittance. As in embodiment 1, the wood 11 filling rate in the surface layer 3 and back layer 4 is composed of a composition that is less than half the filling rate of the entire wood 11. Here, the wood 11 filling the inner layer 2 is referred to as wood D114, the wood 11 filling the stress relief layer 5 is referred to as wood E115, and the wood 11 filling the surface layer 3 and back layer 4 is referred to as wood F116. Both wood D114 and wood E115 are regularly oriented in the thickness direction. The wood F116 also has a regular orientation in the thickness direction.

Figure 5 is a cross-sectional view showing a wood composite material 1 according to a first variant of embodiment 2. As shown in Figure 5, in the first variant, the wood 11 filled in the inner layer 2 is referred to as wood D114, the wood 11 filled in the stress relief layer 5 is referred to as wood E115, and the wood 11 filled in the front layer 3 and back layer 4 is referred to as wood G117. Wood D114 and wood E115 are both 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 variant, the fiber axes of the fibers of wood 11 may be oriented in different directions.

Figure 6 is a cross-sectional view showing a wood composite material 1 according to a second variant of embodiment 2. As shown in Figure 6, in this second variant, the wood composite material 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. 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 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, wood 11 with the amount of lignin removed adjusted as described above may be used, or wood 11 obtained by compressing the wood 11 before compounding with the resin 12 to reduce the air volume within 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 the back layer 4 are resin-rich layers, the layers can be bonded together without gaps when stacked, and the occurrence of gaps due to insufficient adhesion can also be suppressed.

The stress relief layer 5 has been described as being a composite of wood 11 and resin 12, but it need not be a composite of wood 11 and resin 12. It need only be a material with 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 relief 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 may be mixed with the plastic, or a filler 7 such as silicon oxide may be mixed with the plastic. The thermal expansion coefficient of the stress relief 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. If the thermal expansion coefficients are between these, the material is not limited.

Figure 7 is a cross-sectional view showing a wood composite material 1 according to a third variant of embodiment 2. As shown in Figure 7, in the third variant, short fibers 6 are filled into the stress relief layer 5. The wood composite material 1 comprises an inner layer 2, a surface layer 3, a back layer 4, and a stress relief layer 5. The wood 11 filled into the inner layer 2 is referred to as wood D114, and the wood 11 filled into the surface layer 3 and back layer 4 is referred to as wood G117. As described above, the stress relief 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 relief layer 5 is the same as the thermal expansion coefficient between the inner layer 2 and the surface layer 3 and back layer 4.

Figure 8 is a cross-sectional view showing a wood composite material 1 according to a fourth variant of embodiment 2. As shown in Figure 8, in this fourth variant, the stress relief layer 5 is filled with filler 7. The wood composite material 1 includes an inner layer 2, a surface layer 3, a back layer 4, a stress relief layer 5, and an outer stress relief 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 relief 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, the stress relief layer 5 is filled with filler 7, and the filling rate of the wood 11 is controlled so that the thermal expansion coefficient of the stress relief layer 5 is equal to the thermal expansion coefficients of the inner layer 2, the surface layer 3, and the back layer 4.

Figure 9 is a cross-sectional view showing a wood composite material 1 according to a fifth variant of embodiment 2. As shown in Figure 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.

Figure 10 is a cross-sectional view showing a wood composite material 1 according to a sixth variant of embodiment 2. As shown in Figure 10, in the sixth variant, the wood composite material 1 obtained in embodiment 1 is laminated with each fiber direction changed. For example, the fiber axis of the stress relief 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°. This also makes it possible to disperse stress generated by shrinkage of the wood 11.

Embodiment 3.
FIG. 11 is a graph showing the results of measuring the molecular structure of the wood composite 1 according to the third embodiment. In this third embodiment, the molecular structure of the wood composite 1 was investigated using a Fourier transform infrared spectrophotometer (FTIR) as an infrared spectroscopy method. As shown in FIG. 11 , in the FTIR, the extreme value near 1030 cm ⁻¹ (hereinafter, intensity A) represents vibrations resulting from the carbon-oxygen bond of cellulose in the wood 11. The extreme value near ^{1595 cm −1} (hereinafter, 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, in order to obtain a material that can be impregnated with the resin 12 and that is easy to handle, the strength ratio B/A is preferably 0.05 or more and 0.7 or less, and more preferably 0.2 or more and 0.5 or less.

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 includes 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. The air conditioner 8 may include multiple air outlets 82; FIG. 12 illustrates an example in which two airflow direction louvers are provided. The air conditioner may also include multiple airflow direction louvers 83; FIG. 10 illustrates an example in which one airflow direction louver 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.

The housing 81, which is partially composed of 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, which 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 panel. On the other hand, materials that do not transmit light cannot display colors. Therefore, adjustable light transmittance is desirable. As described above, the materials of Embodiments 1 to 3 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 achieved. While the fourth embodiment uses 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.

1 Wood composite material, 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 (7)

an inner layer having 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,
A wood composite material in which the stress relief layer is made of a material that has been treated with sunlight for a longer period of time than the inner layer, thereby increasing the amount of lignin removed from the wood . The wood composite material according to claim 1 , wherein the surface layer and the back layer are resin-rich layers. The wood composite material according to claim 1 or 2, 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, which is the diameter of the wood fiber. The wood composite material according to claim 1 or 2, wherein the wood filling rate 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, wherein, 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. An air conditioner comprising a housing in which the wood composite material according to claim 1 or 2 constitutes a part. 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 an inner layer, a surface layer, a back layer, and a stress relaxation layer, each having a different wood filling rate, and then pressing the laminate.