JP7292718B2 - Compressed wood and its manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a compressed lumber obtained by compressing a plate-shaped lumber and a method for producing the same.

Conventionally, conifers such as Japanese cedar and Japanese cypress grow quickly and are more readily available in Japan than broad-leaved trees such as lauan, and are therefore widely used as furniture and building materials.

However, since coniferous trees are softer and less strong than hardwoods, the surface of softwood is easily damaged when used in furniture, and there are concerns about insufficient strength when used in building materials. be.

In order to solve such problems, conventionally, as described in Patent Document 1, compression processing is performed on lumber to increase the strength of the lumber.

Specifically, first, moisture is added to both surfaces (front surface and back surface) of the wood to soften the surface layers on both surfaces of the wood. Due to this softening treatment, the surface layers on both sides of the lumber in the thickness direction become more susceptible to compressive deformation than the inner layer between them. After that, the lumber is heated and compressed in the thickness direction. Compressed lumber manufactured in this way has a three-layer structure having hard surface layers with high compressibility on both sides in the thickness direction, and a soft inner layer with low compressibility between these surface layers. have.

Compressed lumber produced in this way has a higher material density and higher strength than uncompressed lumber of the same thickness.

Patent No. 6450489

In general, when compressed wood used for furniture and building materials is processed into a product shape such as a table, the surface layer is cut for the purpose of adjusting the surface shape and improving the appearance, and the surface layer is cut. The thickness may be reduced, or the surface layer may be scraped off to expose the inner layer. Further, when joining compressed lumber pieces by using a screw or a dowel, a screw hole or a dowel hole is formed in the surface of the compressed lumber from which the surface layer is cut.

However, when a screw hole or dowel hole is formed in an area where the surface layer is thin or in an area where the inner layer is exposed, most of the hole exists in the soft inner layer, and the screw or dowel is inserted. In such a case, the shape of the hole may be deformed, and there is a risk that the screw or dowel may fall out of the hole.

Therefore, there has been a demand for the development of a compressed lumber that can maintain a hard layer on the surface side that is thick enough to withstand joining with screws and dowels even when the surface layer is cut.

The present invention has been made in view of the above problems, and provides a compressed lumber that can maintain a hard, highly compressed layer on the surface side even when the surface layer of the compressed lumber is cut, and a method for producing the same. intended to

In order to achieve the above object, a compressed lumber according to the present invention is a compressed lumber having a plurality of layers with different compression ratios in the thickness direction of the lumber , wherein one surface in the thickness direction of the compressed lumber is The first layer portion to be formed, the second layer portion adjacent to the inside of the first layer portion in the thickness direction, and the first layer portion of the second layer portion are on the opposite side in the thickness direction. a third layer forming the central region in the thickness direction adjacent to the third layer; and a fourth layer forming the other surface adjacent to the third layer, wherein the second and the fourth layer have higher compressibility than the first layer and the third layer, respectively.

According to this configuration, the compressed wood has a higher compressibility than these layers between the first layer forming the surface and the third layer forming the central region in the thickness direction. That is, since it has a hard second layer, when the compressed wood is processed into a product shape, the first layer, which will be the surface layer, is cut, and the thickness of the first layer is reduced. Even if the thickness is reduced or the inner layer is exposed, the hardest layer remains at or near the surface, ensuring a hard layer. Therefore, the second layer can firmly hold the shapes of the screw holes and dowel holes formed in the surface of the compressed lumber, thereby preventing the screws and dowels from coming off.

The present invention also provides a method for producing compressed lumber, comprising a softening step of applying moisture to the surface of a plate-like lumber to soften both surface regions of the lumber, and after the softening step, , a drying treatment step of heating one surface side of the wood to reduce moisture in a region of a predetermined thickness on the outer surface side of the softened surface layer region, and drying the wood after the drying treatment step and a compression step of compressing in the thickness direction.

According to this configuration, first, by applying water to the surface of the plate-like wood, the surface layer region of the wood absorbs the water and softens more than the inner inner layer. After that, by heating the lumber from the surface side, only moisture in a predetermined thickness region on the outer surface side of the softened surface layer region evaporates and decreases. Therefore, the inner layer has a small amount of moisture and is not softened, the predetermined thickness region on the outer surface side is once softened and then hardened by evaporation of moisture, and the inner layer and the outer surface side have a predetermined thickness Between the regions, there is an intermediate layer that remains softened due to the presence of moisture. In this state, when the lumber is compressed in the thickness direction, the soft intermediate layer containing a large amount of moisture is compressed at a higher compressibility than the other layers. Thereby, in the compressed lumber, the second layer having a higher compressibility than the first layer and the third layer can be formed. It should be noted that it is easy to adjust the amount of moisture remaining in the predetermined thickness region on the outer surface side by adjusting the heat treatment, and the adjustment of the compression rate after compression of the three layers can be adjusted as desired. be.

Further, according to the present invention, in the method for producing compressed lumber, the softening treatment step is performed by steaming the lumber.

According to this structure, the lumber is also softened by the application of heat. Therefore, by heating the lumber with steam, heat is applied to the lumber together with the moisture, and the predetermined thickness region and the intermediate layer on the outer surface side are softened. can be sufficiently softened. Thereby, the compressibility of the second layer portion can be improved, and the second layer portion can be made harder.

Further, according to the present invention, in the method for manufacturing compressed lumber, the drying treatment step is performed by bringing a heated press plate into contact with the surface of the lumber for a predetermined time in an uncompressed state, and the compression step comprises the It is characterized by heating and compressing the lumber with a press plate.

According to this configuration, by applying heat to the wood in the compression process, the compressibility of the wood can be increased, and the strength of each layer can be increased. Further, by using the press plate used in the drying treatment step for heating and compression in the compression step, the processing time can be shortened.

According to the compressed wood of the present invention, between the third layer forming the central region in the thickness direction and the first layer positioned on the outermost side in the thickness direction, the compressibility is higher than those of these layers. Since the second layer has a high compressibility, even if the first layer is cut when processing the compressed wood into a product shape, the second layer having a high compressibility and a hard surface can be used. The second layer can hold the shapes of the screw holes and dowel holes formed in the surface of the compressed lumber to prevent the screws and dowels from coming off.

Further, according to the method for producing compressed lumber of the present invention, after softening the surface layer side region of the lumber with water, the lumber is heated from the surface side to reduce the water content in the predetermined thickness region on the outer surface side. By compressing the wood in this state, a high compressibility can be formed between the first layer and the third layer. can efficiently produce a compressed lumber having a second layer of

(a) is a perspective view of a compressed lumber that is an embodiment of the present invention, and (b) is an enlarged view of a cross-sectional area surrounded by b in (a). FIG. 2 is a perspective view of wood that is a material for compressed wood. It is a flow chart of a manufacturing method of compressed lumber. It is a sectional view showing a compression device typically. It is explanatory drawing of the drying process process using a compression apparatus. It is explanatory drawing of the heating compression process and cooling process using a compression apparatus. Fig. 3 is a graph showing the relationship between density and position from the first surface of compressed wood; 4 is a graph showing test results of a tapping screw pull-out test.

FIG. 1(a) is a perspective view of a compressed lumber 10 which is one embodiment of the present invention, and FIG. 1(b) is an enlarged view of a cross-sectional area surrounded by b in (a). FIG. 2 is a perspective view of a piece of wood 20 as a material for the compressed wood 10. As shown in FIG.

As the wood 20 that is the material of the compressed wood 10, both coniferous trees such as Japanese cedar and Japanese cypress and broad-leaved trees such as oak and lauan can be used, but coniferous trees are preferred. As the plate-like wood 20 used as a material, a flat-grained material having a flat grain on the surface or a straight-grained material having a straight-grained surface can be used. Wood can also be used, but if straight-grained timber is used, shearing may occur at tree ring boundaries during compression, resulting in a decrease in yield. It is particularly preferred to use eye material. In the present invention, the cross-grained lumber refers to a lumber obtained by sawing raw wood in the direction of the tangential line of the annual rings, which is a so-called core-removed lumber in which the centers of the annual rings are removed. This is because if a cored material having a center of annual rings is used, the annual rings near the core may be bent and cracked when the cross-grained material is heated and compressed. In addition, straight grain refers to wood grain with parallel annual rings that appear when a log is sawed toward the center, and wood obtained by sawing in this way is called straight grain wood.

In the present embodiment, a cross-grain material of coniferous trees is used as the wood 20, and the first surface 20a, which is the upper surface in FIG. The second surface 20b is the surface of the back side of the wood 20 (the side close to the center of the annual ring).

Compressed lumber 10 has a plurality of layers with different compressibility in thickness direction D. A first surface layer portion (first layer portion) 12, a first intermediate layer portion (second layer portion) 14, and an inner layer It has a five-layer structure including a portion (third layer portion) 15 , a second intermediate layer portion (second layer portion) 16 and a second surface layer portion (first layer portion) 18 . In addition, in FIG. 1, the first intermediate layer portion 14 and the second intermediate layer portion 16 are painted out for easy understanding of each layer portion.

The first surface layer portion 12 is a layer forming the first surface 10a, and the second surface layer portion 14 is a layer forming the second surface 10b.

The inner layer portion 15 is a layer including a central region in the thickness direction D of the compressed wood 10 and has a thickness greater than that of the other layer portions 12 , 14 , 16 and 18 .

The first intermediate layer portion 14 is located between the inner layer portion 15 and the first surface layer portion 12 , and the second intermediate layer portion 16 is located between the inner layer portion 15 and the second surface layer portion 18 . The first and second intermediate layer portions 14 and 16 have a higher compressibility than the first surface layer portion 12, the second surface layer portion 18 and the inner layer portion 15, so that the first and second surface layer portions 12 , 18 and the inner layer portion 15, the air-dried specific gravity and fiber density are higher. As shown in FIG. 1(b), in the first and second intermediate layers 14 and 16 with high compressibility, the width of the wood grain 30 of annual rings is narrow, and the boundary between the adjacent layers is The wood grain 30 is bent.

The thickness ratio of each layer is, for example, when the thickness of the compressed wood 10 is 30 to 35 mm, the first surface layer 12 and the second surface layer 18 are 5 to 15%, and the first intermediate layer 14 is 5 to 15%. and the second intermediate layer portion 16 can be 10 to 15%, and the inner layer portion 15 can be 40 to 70%. It should be noted that these ratios can be appropriately changed depending on the thickness of the wood 20 as a material and the degree of softening and drying of the wood 20 in the softening treatment process and the drying treatment process described below. For example, it is possible to make the thickness of the first surface layer 12 larger than that of the second surface layer 18, or make the thicknesses of the first and second intermediate layers 14 and 16 substantially equal. The thicknesses of the first surface layer portion 12 and the first intermediate layer portion 14 are each preferably 1 mm or more, and more preferably 1 mm to 7 mm.

Next, a method for manufacturing the compressed lumber 10 will be described. As shown in FIG. 3, the compressed lumber 10 of this embodiment is manufactured through a softening treatment step S10, a drying treatment step S12, a heat compression step (compression step) S14, and a cooling step S16. In the drying treatment step S12, the heating compression step S14 and the cooling step S16, the compression device 50 shown in FIG. 4 is used.

FIG. 4 is a sectional view schematically showing the compression device 50 as well. The compression device 50 includes a box-shaped lower die 52 having a bottom portion 52a in which the wood 20 is placed and having an open top surface, and a plate-shaped upper die 54 that constitutes a lid portion of the lower die 52. It has a basic configuration comprising a compression mold 56 consisting of. The upper mold 54 is movable in a direction (arrow Y direction) toward and away from the lower mold 52, and when it comes into contact with the lower mold 52, the compression mold 56 is closed, and the space inside the mold is sealed. 58 are configured. The plate-like member forming the bottom portion 52 a of the lower mold 52 and the plate-like upper mold 54 constitute a press plate for compressing the wood 20 . An O-ring 53 is fitted in a groove provided in the upper edge of the lower die 52, and the O-ring 53 is in close contact with the upper die 54, thereby sealing the space 58 within the die.

The upper die 54 is provided with a pipeline 62 for circulating steam 60 and a pipeline 72 for circulating cooling water 70 . Further, the lower die 52 is provided with a pipeline 64 for circulating the steam 60 and a pipeline 74 for circulating the cooling water 70 . Furthermore, the lower mold 52 has a pipeline 66 for introducing the steam 60 into the space 58 in the mold, a pipeline 68 for discharging the steam 60 from the space 58 in the mold, and water in the space 58 in the mold. A conduit 78 is provided for.

Upstream of the upper die 54 and the lower die 52, an introduction side steam path 61 for introducing the steam 60 into the pipeline 62, the pipeline 64 and the pipeline 66 is provided. A discharge side steam path 69 for discharging the steam 60 from the pipelines 62 , 64 and 68 is provided downstream.

Further, upstream of the upper mold 54 and the lower mold 52, a cooling water path 71 for introducing cooling water 70 into the pipe 72 and the pipe 74 is provided, and downstream of the upper mold 54 and the lower mold 52. is provided with a drainage path 79 for draining water from the conduits 72, 74 and 78;

Valves 81, 82 and 83, which are capable of opening and closing the paths, respectively, are provided in the introduction side steam path 61 of the compression die 56 before reaching the pipelines 62, 64 and 66, respectively. 69 are provided with valves 86, 87 and 88, respectively, which can open and close the passages downstream of the lines 62, 64 and 68, respectively.

The cooling water path 71 of the compression mold 56 is provided with valves 91 and 92 that can open and close the paths before reaching the pipes 72 and 74, respectively. , lines 72, 74 and 78 are provided with valves 96, 97 and 98 which can open and close the paths respectively. A pressure gauge 85 is provided between the valve 83 and the conduit 66 .

Each step of the method for manufacturing the compressed lumber 10 will be described in detail below.

[1. Softening process]
In the softening treatment step S10, moisture is applied to the first surface 20a and the second surface 20b of the wood 20 to soften the surface layer region of the wood 20. As shown in FIG. The thickness of the surface layer region to be softened is preset in consideration of the thickness of the first and second surface layer portions 12, 18 and the thickness of the first and second intermediate layer portions 14, 16 of the compressed wood 10 after completion. can do. In this embodiment, the wood 20 is steamed and softened. Steaming treatment of the wood 20 can be performed using, for example, a well-known steaming can. The steaming time can be, for example, at 95° C. to 100° C. for about 5 minutes to 30 minutes. A steaming time of 15 minutes or more is more preferable from the viewpoint of locating the first intermediate layer portion 14 and the second intermediate layer portion 16, which will be described later, on the center side in the thickness direction of the compressed lumber.

FIG. 5(a) shows a state in which the wood 20 after the softening treatment is placed on the compression device 50, the softened surface layer regions 21 and 29 are painted over, and the softened surface layer regions 21 and 29 are positioned between the surface layer regions 21 and 29, and these The inner layer portion 25 having a lower moisture content than the inner layer portion 25 is shown without filling. Due to the softening treatment, the surface layer region 21 on the first surface 20 a side and the surface layer region 29 on the second surface 20 b side of the wood 20 absorb moisture and become softer than the inner layer 25 .

In the softening treatment step S10, instead of the steaming treatment, for example, the lumber 20 may be softened by adding moisture by immersing the lumber 20 in a water tank. Since the lumber 20 is softened not only by the addition of moisture but also by heat, the surface layer region of the lumber 20 can be sufficiently softened in a short time by applying heat together with moisture in the softening treatment step S10 as in the present embodiment. can be made In addition, as a result, the degree of softening of the surface layer region of the wooden piece 20 is increased, the compressibility of the first and second intermediate layer portions 14 and 16 in the compressed wooden piece 10 is improved, and the first and second intermediate layer portions 14 are softened. , 16 can be made more rigid.

[2. Drying process]
FIG. 5(b) is an explanatory view of the drying treatment process, showing a state in which the upper mold 54 and the lower mold 52, which are the press plates of the compression device 50, are brought into contact with the lumber 20 in a heated state and in a non-compressed state. showing. In the drying treatment step S12, the first surface 20a side and the second surface 20b side of the wood 20 are heated to reduce moisture in the predetermined thickness areas 22 and 28 on the outer surface side of the softened surface layer areas 21 and 29. to cure the predetermined thickness regions 22 and 28 .

Specifically, the first surface 20a and the second surface 20b of the wood 20 are brought into contact with the upper mold 54 and the lower mold 52 of the compression device 50 for a predetermined time in a heated and uncompressed state. The temperature rise of the upper die 54 and the lower die 52 causes the valves 86 and 87 downstream of the compression die 56 to close, the valves 81 and 82 upstream of the compression die 56 to gradually open, and the hot steam 60 to gradually flow into the upper die 54 . and by introducing it into the lower mold 52 (see FIG. 4). Further, the temperature of the upper die 54 and the lower die 52 can be kept constant by adjusting the opening degrees of the valves 81 and 82 that feed the steam 60 and the opening degrees of the valves 86 and 87 that discharge the steam 60. can be done. Further, in the drying treatment step S12, the valve 83 of the compression mold 56 is closed to prevent the steam 60 from being introduced into the internal space of the upper mold 54 and the lower mold 52. The time for which the upper mold 54 and the lower mold 52 are brought into contact with the wood 20 is, for example, about 5 minutes to 15 minutes while the upper mold 54 and the lower mold 52 are heated to about 150° C. to 180° C. can be done.

By this drying process, moisture in the predetermined thickness regions 22 and 28 on the outer surface side of the wood 20 evaporates, dries and hardens. FIG. 5(b) shows the state of the lumber 20 after the drying treatment, and shows the areas 22 and 28 in which the water content has decreased in the surface layer areas 21 and 29 without filling. Intermediate layers 24 and 26, which are located between the regions 22 and 28 and the inner layer 25 and have a high moisture content, are shown by filling in. FIG. The intermediate layers 24 and 26 retain moisture and are in a softer state than the regions 22 and 28 and the inner layer 25 . In addition, the predetermined thickness regions 22 and 28 on the outer surface side can be easily adjusted for remaining moisture by adjusting the heat treatment (that is, adjusting the heating temperature, heating time, etc.). and 28, the middle layers 24 and 26, and the adjustment of the compression ratio after compression of the inner layer 25 can be adjusted as desired.

[3. Heating compression step]
In the heating and compressing step S14, as shown in FIG. 6A, the upper mold 54 is slowly moved until it comes into contact with the lower mold 52, thereby compressing the wood 20 in the thickness direction. During the heat compression process, the upper mold 54 and the lower mold 52 are maintained at approximately 150.degree. C. to 180.degree. At this time, the valves 83, 88 and 98 can be closed to make the space 58 in the mold completely closed. In this state, the heated and compressed state is maintained for about 20 to 120 minutes. By maintaining the heated and compressed state, the air in the mold internal space 58 thermally expands, and the moisture in the wood 20 evaporates to generate water vapor, thereby increasing the pressure in the mold internal space 58 . The compressed wood 20 under this elevated pressure is treated with hot steam, which significantly relieves the stress accumulated inside the wood 20 in a short time and fixes the compressed shape. In the wood 20, the wet, soft intermediate layers 24 and 26 are more compressible than the other layers. Compressed with high compression ratio.

In addition, when the amount of steam is insufficient only by evaporation of the moisture from the wood 20, or when the pressure in the mold internal space 58 is low, the amount of opening of the valve 83 can be increased to increase the amount of steam and the pressure. . Conversely, when the pressure in the mold internal space 58 is high, the valve 88 can be opened to reduce the pressure. The pressure in the mold internal space 58 can be monitored by a pressure gauge 85.

The compression rate of the wood 20 is adjusted by changing the thickness of the wood 20 before compression and the height of the O-ring 53, or by placing a flat metal plate (not shown) on the bottom 52a of the lower die 52. It is possible, and if it is a coniferous wood 20, it can be done up to about 70%. The compressibility of 70% means that the wood 20 with a thickness of 10 cm is compressed to a total thickness of 3 cm. The compressibility is preferably between 30% and 50%.

The compression of the wood 20 does not have to be accompanied by heating, but by compressing while applying heat as in the present embodiment, the compression rate of the wood 20 can be increased, and the compressed wood 10 after production can be obtained. The strength of each layer can be increased. Furthermore, in the present embodiment, the press plate used in the drying treatment process is used in the heating and compression process, thereby shortening the processing time.

[4. Cooling process]
In the cooling step S14, the temperature of the upper mold 54 and the lower mold 52 is lowered to about 20-40° C. and maintained for 30-60 minutes to cool the compressed wood 20 (ie, the compressed wood 10). For cooling, the valves 81, 82 and 83 of the compression device 50 are closed, the valves 86, 87 and 88 are opened to discharge the steam 60 from the upper mold 54, the lower mold 52 and the mold inner space 58, and the valves 91, 92, This is done by opening the 96 and 97 and allowing the cooling water 70 to flow through the upper die 54 and the lower die 52 . Thereafter, as shown in FIG. 6(b), the upper die 54 is moved away from the lower die 52, and the compressed lumber 10 is taken out.

As an example of the compressed wood 10 formed by the above-described manufacturing method, when the heating time in the drying process is 10 minutes and the compression ratio in the heat compression process is 30%, the thickness of the compressed wood 10 is about 32 mm. The thickness of the first surface layer 12, the first intermediate layer 14 and the second intermediate layer 16 is approximately 4 mm, the thickness of the inner layer 15 is approximately 17 mm, and the thickness of the second surface layer 18 is approximately 3 mm. can be done. Moreover, even when the compression ratio is 40% or 50%, when the heating time for the drying treatment is set to 10 minutes, the thickness of each layer of the compressed wood 10 having a thickness of about 32 mm is compressed. The same can be done for the 30% ratio.

As another example of the compressed wood 10, when the heating time in the drying process is set to 5 minutes and the compression rate is set to 30%, 40% or 50%, the compressed wood 10 having a thickness of about 32 mm has the first The thickness of the surface layer portion 12 is approximately 2 to 3 mm, the thickness of the first intermediate layer portion 14 is approximately 4 mm, the thickness of the inner layer portion 15 is approximately 20 mm, the thickness of the second intermediate layer portion 16 is approximately 4 mm, and the thickness of the second intermediate layer portion 16 is approximately 4 mm. The thickness of the surface layer 16 can be about 1-2 mm.

The compressed lumber 10 manufactured in this way has a density distribution in the thickness direction D as shown in FIG. FIG. 7 is a graph showing the relationship between the position in the thickness direction D from the first surface 10a of the compressed wood 10 and the density. The dashed line indicates the compressed lumber that was subjected to the heat compression process without performing the process.

As shown in the graph, in compressed wood that has not been dried, the compressibility is highest in the outermost surface layer in the thickness direction, and the density gradually decreases toward the central region in the thickness direction. there is In contrast, in the compressed lumber 10 of the present embodiment, the densities of the first and second intermediate layer portions 14 and 16 are higher than the densities of the first and second surface layer portions 12 and 18 and the density of the inner layer portion 15. It's becoming The density distribution in the thickness direction D gradually increases from the first surface layer portion 12 toward the first intermediate layer portion 14 and gradually decreases from the first intermediate layer portion 14 toward the inner layer portion 15. The density gradually increases from the inner layer portion 15 toward the second intermediate layer portion 16 , and the density gradually decreases from the second intermediate layer portion 16 toward the second surface layer portion 18 . The density ratio of the first intermediate layer portion 14 to the first surface layer portion 12 (ratio of the average values of the densities of the respective layer portions) and the density ratio of the second intermediate layer portion 16 to the second surface layer portion 18 are respectively 1.2. It is preferable that it is above.

In the above-described compressed lumber 10, the first and second intermediate layer portions 14 and 16 having high compressibility are formed adjacent to each other with the inner layer portion 15 having low compressibility sandwiched therebetween. 14 and 16 are adjacent to the inner side in the thickness direction of the first and second surface layer portions 12 and 18, respectively, which have a low compressibility. is cut, the first surface layer portion 12 and/or the second surface layer portion 18 is cut, the thickness of the first surface layer portion 12 and the second surface layer portion 18 is reduced, or the inner first intermediate layer portion is cut. Even when the layer portion 14 and the second intermediate layer portion 16 are exposed, the hard first intermediate layer portion 14 and the second intermediate layer portion 16 are maintained on the first surface 10a side and the second surface 10b side. can do. The first and second intermediate layer portions 14 and 16 can firmly retain the shapes of the screw holes and dowel holes formed in the surface of the compressed wood 10, and can prevent the screws and dowels from coming off. .

Further, when manufacturing the compressed wood 10, it is possible to apply the same treatment to both surface layer regions in the thickness direction D to form a five-layer structure having two intermediate layer portions 14 and 16 with a high compressibility. Since it can be manufactured, it is excellent in manufacturability.

The present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the scope of the invention.

For example, the compressed wood according to the present invention has only one surface side (that is, only the first surface 10a side of the compressed wood 10 or only the second surface 10b side) between the inner layer portion and the surface layer portion. , any structure having an intermediate layer portion with a higher compressibility than these. Therefore, for example, in order from one surface side in the thickness direction, a low compressibility surface layer (first layer), a high compressibility intermediate layer (second layer), and a low compressibility inner layer It may be a four-layer structure having a (third layer), an inner layer, and a surface layer (fourth layer) having a higher compressibility than the surface layer which is the first layer. This four-layer compressed lumber structure can be formed, for example, by drying one surface side of the lumber 20 in the thickness direction in a drying process and compressing the other surface side without drying treatment. Alternatively, softening treatment and drying treatment may be performed only on one surface side, and compression may be performed without performing these treatments on the other surface side.

In order to confirm the effect of the present invention, compressed lumber according to the invention example and the comparative example were produced experimentally, and a tapping screw pull-out test was conducted. As shown in Table 1, the material type of the experimentally produced compressed lumber was Japanese cedar, and the compression rate of each compressed lumber was set to 50%, and a lumber having a thickness of 56 mm was compressed to a thickness of 28 mm. The steaming treatment time was 20 minutes, and the drying treatment time was 20 minutes for the invention examples and 0 minutes for the comparative examples (no drying treatment).

The test piece used for the pull-out test had a size of 20 mm x 45 mm x 80 mm by cutting 3 mm from both surfaces in the thickness direction of the compressed lumber. A tapping screw pull-out test was carried out on five specimens each of the inventive examples and the comparative examples. According to JIS B 1122:2015, the dimensions of the tapping screw were set to φ4 mm×35 mm, the pilot hole size of the tapping screw was set to φ2 mm×15 mm, and the embedding depth was set to 15 mm. The test surface was the surface on the front side of the wood, and the test speed was 2 mm/min. A desktop precision universal testing machine (type name: AGS-10kNX, manufacturer: Shimadzu Corporation) was used for the test.

The test results are shown in FIG. Each bar graph shows the average value of 5 specimens. As shown in FIG. 8, it was found that the compressed lumber of the invention example can withstand a load about 20% greater than that of the compressed lumber of the comparative example. The holding force of a tapping screw tends to increase as the density increases, and this is because in the manufacturing process of compressed wood, the middle layer inside the thickness direction is more likely to be loosened than the surface layer by applying a drying treatment after the softening treatment. becomes a high compressibility, and after cutting the surface, the density of the present invention is higher than that of the comparative example.

Specifically, according to FIG. 8, in the inventive example, the surface was cut by 3 mm, and the average value of the load measured by the above-mentioned pull-out test was 1.85 kN, and the lowest value was 1.7 kN. (average value = 1.51 kN), a significant improvement in the pull-out load was observed. In addition, the compressed wood of the present invention showed an average of more than 5 specimens when subjected to a pull-out test under the same conditions with the surface cut by 3 mm compared to that produced at the same compression rate without the drying process. It is preferable to form the intermediate layer so as to withstand a load of 1.1 times or more, particularly a load of 1.2 times or more.

10 Compressed wood 10a First surface 10b Second surface 12 First surface layer (first layer)
14 First intermediate layer (second layer)
15 inner layer (third layer)
16 Second intermediate layer (second layer)
18 Second surface layer (first layer)
20 wood 50 compression device D thickness direction

Claims (4)

Compressed wood having a plurality of layers with different compression ratios in the thickness direction of the wood,
a first layer forming one surface in the thickness direction of the compressed lumber;
a second layer portion adjacent to the inner side in the thickness direction of the first layer portion;
a third layer portion forming a central region in the thickness direction adjacent to the first layer portion of the second layer portion on the opposite side in the thickness direction;
a fourth layer forming the other surface adjacent to the third layer;
has
The compressed lumber, wherein the second layer and the fourth layer have higher compressibility than the first layer and the third layer, respectively. A method for producing compressed wood according to claim 1 ,
a softening treatment step of applying moisture to the surface of a plate-shaped piece of wood to soften both surface regions of the piece of wood;
After the softening treatment step, a drying treatment step of heating one surface side of the wood to reduce moisture in a region of a predetermined thickness on the outer surface side of one of the softened surface layer regions;
A compression step of compressing the wood in the thickness direction after the drying treatment step;
A method for producing compressed wood, comprising: 3. The method for producing compressed lumber according to claim 2 , wherein said softening treatment step is carried out by steaming said lumber. The drying treatment step is performed by bringing a heated press plate into contact with the surface of the wood for a predetermined time in an uncompressed state,
4. The method of manufacturing compressed lumber according to claim 2 , wherein said compressing step is performed by thermally compressing said lumber with said press plate.

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