Particle board and method for manufacturing particle board

Abstract

In a particle board 10 which has a three-layer structure in which wood crushed pieces 2, ..., 2 finer than a core layer 11 are used for surface layers 12, a large number of flaky wood cut pieces 3, ..., 3 having a uniform thickness of 0.05-0.35 mm are included in the core layer 11.

Description

[Technical Field]

[0001] The present invention relates to a particle board having a three-layer structure and a method for manufacturing a particle board having a three-layer structure. [Background technology]

[0002] Traditionally, tropical plywood such as lauan plywood has been widely used. However, in recent years, tropical plywood has become difficult to obtain due to the depletion of raw materials and concerns about environmental destruction, and efforts are being made to replace it with other wood boards.

[0003] Patent Document 1 discloses that particle board, formed by applying adhesive to crushed wood chips and piling them into a mat-like shape and then hot-pressing them with a hot platen, can be used as an alternative to plywood. Patent Document 1 also discloses a three-layer particle board in which crushed wood chips are classified, and coarse crushed wood chips are used as the core material and fine crushed wood chips are used as the surface layer. Particle boards can be manufactured relatively inexpensively because crushed pieces of waste wood, recycled materials, etc. can be used as components. Furthermore, even if no waste wood, recycled materials, etc. are used, three-layer particle boards can be manufactured relatively inexpensively because all of the crushed wood chips produced by crushing wood materials are used without waste. Thus, three-layer particle boards are excellent as an alternative to plywood because they can be manufactured relatively inexpensively. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2005 / 115705 Summary of the Invention [Problem to be solved by the invention]

[0005] However, because three-layer particleboard uses fine ground wood chips for the surface layer, it has improved surface smoothness compared to single-layer particleboard made of coarse ground wood chips, but its bending strength is lower. Increasing the density of the surface layer to ensure a certain level of bending strength in three-layer particleboard creates the problem of increased weight and adhesive usage. Furthermore, particleboard has low screw pull-out strength, making it unsuitable for use as a load-bearing surface material for screw installation, and it also suffers from poor dimensional stability due to moisture absorption.

[0006] The present invention has been made in consideration of these points, and its object is to provide a three-layer particle board that has excellent surface properties, bending strength, and screw pull-out strength, and that exhibits little dimensional change, without increasing cost or weight. [Means for solving the problem]

[0007] In order to achieve the above object, in the present invention, a core layer of a particle board having a three-layer structure contains a large number of extremely thin wood shavings.

[0008] Specifically, the first invention is based on a particle board having a three-layer structure in which the surface layer is made of finer pulverized wood chips than the core layer.

[0009] The first invention is characterized in that the core layer contains a large number of thin wood shavings having a uniform thickness of 0.05 mm or more and 0.35 mm or less.

[0010] Here, "ground wood chips" refers to wood chips of various shapes and of non-uniform thickness, formed by finely grinding wood material using a known grinding device until the material passes through a sieve with a specified mesh size installed at the outlet of the grinding device. Also, "wood shavings" refers to thin, uniformly thick wood chips formed by cutting wood material into a thin, uniform thickness using a known cutting device with a blade that cuts the material into a thin, uniform thickness. Note that "wood shavings having a uniform thickness" allows for thickness variations due to processing errors in the cutting device, for example, a thickness variation of about ±20%.

[0011] In the first invention, the core layer of a three-layer particleboard contains not only the usual crushed wood chips, but also wood shavings with an extremely thin, uniform thickness of 0.05 mm to 0.35 mm, which are produced by cutting. This configuration increases the bending strength of the core layer of the particleboard. Therefore, it is not necessary to increase the density of the surface layer or use a large amount of adhesive to ensure the particleboard's bending strength. Furthermore, compared to when the core layer is composed solely of crushed wood chips, the presence of thin wood shavings makes it easier to bond the wood chips (crushed wood chips and wood shavings) together with a small amount of adhesive. Therefore, the three-layer particleboard according to the first invention can reduce the amount of adhesive used while maintaining bending strength comparable to that of conventional particleboards.

[0012] Furthermore, in the particle board according to the first aspect of the invention, the surface layer is made up of relatively fine pulverized wood chips, just like conventional particle boards with a three-layer structure, and therefore has excellent surface properties (smoothness).

[0013] Furthermore, in the particleboard according to the first aspect of the present invention, if some of the crushed wood chips in the core layer are replaced with thinner wood chips, the core layer will contain more wood chips than the original crushed wood chips. Wood chips have a uniform thickness and a flat surface. Therefore, if the core layer contains a large number of wood chips (if some of the crushed wood chips in the core layer are replaced with wood chips), the total surface area of ​​the numerous wood chips that make up the core layer will increase significantly, making screws less likely to come out than in a conventional three-layer particleboard whose core layer is composed solely of crushed wood chips. Therefore, in the particleboard according to the first aspect of the present invention, the inclusion of wood chips in the core layer reinforces the core layer and significantly improves the screw pull-out strength (wood screw holding power), making it suitable for use as a load-bearing subfloor surface material for screws.

[0014] The inventors of the present application conducted a test to verify the effect of incorporating extremely thin wood shavings, between 0.05 mm and 0.35 mm thick, into the core layer of a three-layer particleboard. The results showed that particleboard containing wood shavings in the core layer had improved bending strength (MOR), length change (LE) and wood screw holding strength (WS) compared to conventional particleboard that did not contain wood shavings in the core layer, and that water thickness swelling (TS) was somewhat improved, although not significantly, and that the absolute value of TS fully met the standard (12% or less) required for structural particleboard.

[0015] As described above, according to the first invention, a three-layer particle board having excellent surface properties, bending strength, and screw pull-out strength and small dimensional change can be provided without increasing cost or weight.

[0016] A second invention is characterized in that in the first invention, the surface layer contains a large number of the wood cuttings.

[0017] In the second invention, extremely thin wood shavings, measuring between 0.05 mm and 0.35 mm in thickness, are incorporated into not only the core layer but also the surface layers of a three-layer particle board. This configuration increases the bending strength of both the core layer and the surface layers of the particle board. Therefore, there is no need to increase the density of the surface layers or use large amounts of adhesive to ensure the particle board's bending strength. Furthermore, by incorporating wood shavings into both the core layer and the surface layers, the amount of adhesive used can be further reduced compared to when wood shavings are incorporated only into the core layer.

[0018] Furthermore, in the particle board according to the second invention, the wood chips are extremely thin, between 0.05 mm and 0.35 mm, so even if they are included in the surface layer, they are unlikely to cause irregularities on the surface, resulting in excellent surface properties (smoothness) similar to those of conventional particle boards.

[0019] Furthermore, in the particle board according to the second invention, by including wood chips not only in the core layer but also in the surface layer, screws become more difficult to pull out. Therefore, the second invention can provide a particle board with a three-layer structure that has excellent screw pull-out strength (wood screw holding power).

[0020] Furthermore, in the particleboard according to the second invention, by replacing some of the relatively fine wood chips in the surface layer with wood shavings of uniform thickness and flat surfaces, the total surface area of ​​the numerous wood chips that make up the surface layer is significantly increased. A significantly increased total surface area of ​​the numerous wood chips that make up the surface layer increases the bonding area between the numerous wood chips, and also increases the number of bonding points and makes them more evenly distributed. Therefore, the particleboard according to the second invention is more resistant to moisture penetration and has excellent water resistance compared to conventional particleboards whose surface layer is made up solely of wood chips.

[0021] Furthermore, in conventional particle boards whose surface layer is made only of crushed wood chips, the crushed wood chips, which are not cut to a thin thickness, are crushed during press molding, and when moisture penetrates the interior, the crushed wood chips absorb the moisture and tend to swell, resulting in significant dimensional changes (changes in length and thickness).In contrast, the particle board of the second invention, as described above, has a structure that makes it more difficult for moisture to penetrate the interior than conventional particle boards, and because the numerous replaced wood chips are cut to a thin thickness, they do not absorb moisture and therefore do not undergo significant dimensional changes (changes in length and thickness).

[0022] The inventors of the present application conducted tests to verify the effects of incorporating extremely thin wood shavings, between 0.05 mm and 0.35 mm thick, into both the core and surface layers of a three-layer particleboard. The results showed that particleboard containing wood shavings in both the core and surface layers exhibited improved modulus of resistance (MOR), wet modulus of resistance (wet MOR), moisture absorption length change (LE), moisture absorption length change (HLE), and wood screw holding strength (WS) compared to conventional particleboard containing no wood shavings in either the core or surface layers. The inventors also found that the moisture thickness swelling (TS) showed some improvement, although not a significant improvement, and that the absolute value of TS fully met the standard (12% or less) required for structural particleboard.

[0023] As described above, according to the second invention, a three-layer particle board having excellent surface properties, bending strength, screw pull-out strength, and water resistance, and having little dimensional change, can be provided without increasing cost or weight.

[0024] The third invention is characterized in that, in the first or second invention, the core layer contains first wood chips as the wood pulverized pieces for the core layer, which pass through a first sieve with a mesh size of 16 mm or less but do not pass through a second sieve with a mesh size of 0.5 mm or more and smaller than the first sieve, and the surface layer contains second wood chips as the wood pulverized pieces for the surface layer, which pass through both the first and second sieves.

[0025] In the third invention, the core layer uses a large number of first wood chips that pass through a first sieve with a mesh size of 16 mm or less but do not pass through a second sieve with a mesh size of 0.5 mm or more and smaller than the first sieve, and the surface layer uses finer second wood chips that pass through both the first and second sieves. By using finer ground wood chips than the core layer in the surface layer and including wood shavings in the core layer, it is possible to provide a three-layer particleboard that has excellent surface properties, bending strength, and screw pull-out strength, and that exhibits little dimensional change, without increasing cost or weight.

[0026] The fourth invention is characterized in that, in the first or second invention, the wood cutting chips in the core layer are mixed in a ratio of 20% by weight to 90% by weight of the total weight of the wood chips for the core layer, which is composed of the wood crushed chips and the wood cutting chips contained in the core layer.

[0027] Based on the results of the above-mentioned verification tests, the inventors of the present application have found that by mixing wood chips into a large number of core layer wood chips in a proportion of 20% by weight to 90% by weight of the total weight of the core layer wood chips, the normal bending strength (MOR), water absorption length change (LE) and wood screw holding strength (WS) are improved, and that the higher the proportion of wood chips mixed in the core layer, the greater the improvement in normal bending strength (MOR) and water absorption length change (LE).

[0028] Therefore, in the fourth invention, wood shavings are mixed into the numerous core wood pieces at a ratio of 20% to 90% by weight of the total weight of the core wood pieces. By mixing the numerous core wood pieces with wood shavings at such a ratio, it is possible to provide a three-layer particleboard with excellent surface properties, bending strength, and screw pull-out strength, and with little dimensional change, without increasing cost or weight.

[0029] The fifth invention is a method for manufacturing a particle board with a three-layer structure in which finer wood pulverized chips are used in the surface layer than in the core layer, and includes a first crushing step in which a first wood material is crushed to produce a large number of wood chips, and a second crushing step in which the large number of wood chips are sieved using a first sieve with a mesh size of 16 mm or less and a second sieve with a mesh size of 0.5 mm or more and smaller than the first sieve to produce a large number of first wood chips that pass through the first sieve but not the second sieve, a large number of second wood chips that pass through both the first and second sieves, and a large number of wood chips that pass through the first and second sieves. and a large number of third wood chips that do not pass through either of the first and second wood chips, and the first wood chips are used as wood pulverized pieces for the core layer and the second wood chips are used as wood pulverized pieces for the surface layer. A cutting process is performed to cut the second wood material so that the fibers appear linearly on the surface to produce a large number of thin wood flakes with a uniform thickness of 0.05 mm to 0.35 mm. A second crushing process is performed to crush the large number of wood flakes and the large number of wood flakes so that they are broken along the fiber direction, thereby producing a large number of thin, elongated small wood flakes, and a second crushing process is performed to crush the large number of small wood flakes. a selection step of selecting at least one type of the numerous first to third small wood pieces obtained by the second classification step using a third sieve and a fourth sieve smaller than the third sieve as numerous core layer wood shavings; a wood piece mixing step of mixing the numerous core layer pulverized wood pieces with the numerous core layer wood shavings to form numerous core layer wood pieces; an adhesive application step of applying adhesive to the numerous surface layer wood pieces including the numerous surface layer pulverized wood pieces and the numerous core layer wood pieces; and a process of applying adhesive to the numerous surface layer wood pieces to which adhesive has been applied. The method is characterized by comprising a mat-forming process in which a three-layer mat is formed by piling wood chips to form a first mat, piling the numerous wood chips for the core layer coated with adhesive on the first mat to form a second mat, and piling the numerous wood chips for the surface layer coated with adhesive on the second mat to form a third mat, and a hot pressing process in which the three-layer mat is subjected to a hot pressing process to harden the adhesive of the first to third mats, thereby forming the particle board.

[0030] Here, "crushing the first wood material" refers to using a known crushing device to finely crush the first wood material until it passes through a sieve with a specified mesh size installed at the outlet of the crushing device, and wood chips of various shapes and varying thicknesses are formed by the crushing. Furthermore, "cutting the second wood material" refers to using a known cutting device with a blade that cuts material to a thin, uniform thickness to cut the second wood material to a thin, uniform thickness, and thin wood chips of uniform thickness are formed by the cutting. Note that "wood chips of uniform thickness" allows for thickness variations due to processing errors, for example, a thickness variation of about ±20%.

[0031] According to the fifth aspect of the present invention, a particle board with a three-layer structure that is excellent in surface properties, bending strength, and screw pull-out strength and that is small in dimensional change can be provided without increasing cost or weight.

[0032] The sixth invention is characterized in that, in the fifth invention, the cutting process, the second crushing process, and the second classification process are included in a method for manufacturing a wood board in which a large number of first small wood flakes that pass through the third sieve but do not pass through the fourth sieve are glued together in a collective state.

[0033] A seventh aspect of the present invention is the sixth aspect of the present invention, characterized in that in the selection step, the large number of first small wood slices are selected as the large number of wood cuttings for the core layer.

[0034] The eighth invention is characterized in that, in the sixth invention, in the selection process, the numerous second small wood flakes that pass through both the third and fourth sieves and the numerous third small wood flakes that do not pass through both the third and fourth sieves are selected as wood cutting pieces for the core layer.

[0035] In the sixth to eighth inventions, the wood shavings produced when a second wood material is processed to form another wood board are used as the wood shavings for the particle board. Therefore, even if a material (wood shavings) different from the material (ground wood chips) used in ordinary particle boards is used, it can be easily procured because it is the material produced when processing the material for the other wood board. Therefore, according to the sixth to eighth inventions, it is possible to easily provide a three-layer particle board that has excellent surface properties, bending strength, and screw pull-out strength, and that has little dimensional change, at a relatively low cost.

[0036] In particular, in the eighth invention, the wood shavings contained in at least the core layer are made of materials other than the first small wood flakes selected by classifying the small wood flakes. In this way, waste wood generated during the formation of other wood boards that is not used in other wood boards is used as the wood shavings for the core layer of the three-layer particle board, making it possible to form the three-layer particle board more inexpensively. In addition, since the second wood material of the other wood boards is used without waste, this leads to the effective use of wood resources.

[0037] The ninth invention is characterized in that, in any one of the fifth to eighth inventions, in the wood piece mixing process, the numerous core layer wood crushed pieces and the numerous core layer wood cutting pieces are mixed so that the numerous core layer wood cutting pieces account for 20% by weight or more and 90% by weight or less of the total weight of the numerous core layer wood cutting pieces.

[0038] In the ninth invention, in the wood chip mixing step, wood chips are mixed with a large number of core wood chips at a ratio of 20% to 90% by weight of the total weight of the core wood chips. By mixing wood chips with a large number of core wood chips at such a ratio, a three-layer particle board with excellent surface properties, bending strength, and screw pull-out strength, and with little dimensional change can be provided without increasing cost or weight. [Effects of the Invention]

[0039] As explained above, according to the present invention, the core layer of a three-layer particle board contains a large number of thin, uniformly thick wood shavings, making it possible to provide a three-layer particle board that has excellent surface properties, bending strength, and screw pull-out strength, and that exhibits little dimensional change, without increasing cost or weight. [Brief explanation of the drawings]

[0040] [Figure 1] FIG. 1 is a cross-sectional view showing a part of the particle board according to the first embodiment. [Figure 2] FIG. 2 is a diagram showing the process of producing pulverized wood chips. [Figure 3] FIG. 3 is a diagram showing the process of producing wood cuttings. [Figure 4] FIG. 4 is an enlarged perspective view schematically showing the first small woody slice. [Figure 5] FIG. 5 is a diagram showing the particle board manufacturing process. [Figure 6] FIG. 6 is a partially enlarged cross-sectional view showing a comparison between the mat before the heat-pressing step and the particle board formed after the heat-pressing step. [Figure 7] FIG. 7 shows the results of an experiment to verify the effects of the first embodiment. [Figure 8] FIG. 8 is a cross-sectional view showing a part of the particle board according to the second embodiment. [Figure 9] FIG. 9 shows the results of an experiment to verify the effects of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0041] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following description of the embodiments is merely exemplary in nature and is not intended to limit the present invention, its applications, or its uses.

[0042] First Embodiment of the Invention -Particle board composition- 1 shows a particle board 10 according to a first embodiment of the present invention. The particle board 10 can be used, for example, as a base material for building materials such as flooring, or as a component material for furniture.

[0043] Particle board 10 is made up of a large number of wood pieces 1, ..., 1 glued together in a collected state. Particle board 10 contains a large number of wood pieces 1, ..., 1 and an adhesive. The feature of the present invention is the constituent material (wood pieces 1) of particle board 10, and there are no particular limitations on thickness or density. However, particle board 10 is, for example, a particle board specified in JIS A5908 with a thickness of 5 mm to 40 mm and a density of 400 kg / m 3 More than 900kg / m 3 As will be described in detail below, in this embodiment 1, by using not only pulverized wood chips 2, ..., 2 but also shaved wood chips 3, ..., 3 as the numerous wood chips 1, ..., 1, the particle board has superior bending strength to conventional particle boards that contain only pulverized wood chips 2, ..., 2. For example, even if the thickness is 3 mm or more but less than 5 mm, sufficient bending strength can be ensured, and the density can be increased to 400 kg / m 3 Even if the thickness is less than this, sufficient bending strength and peel strength can be ensured.

[0044] <Wood piece> In this embodiment 1, the numerous wood pieces 1,...,1 that make up the particle board 10 are made up of numerous pulverized wood pieces 2,...,2 and numerous shaved wood pieces 3,...,3. The particle board 10 has a three-layer structure, including a core layer 11 and two surface layers 12,12 that sandwich the core layer 11 and form the surface. The core layer 11 and the surface layers 12 differ in the composition of the wood pieces 1,...,1 that they contain.

[0045] Both the core layer 11 and the surface layer 12 contain a large number of pulverized wood chips 2,...,2 as wood chips 1,...,1, but the pulverized wood chips 2,...,2 used in the core layer 11 and the surface layer 12 are different in size, with the surface layer 12 using finer pulverized wood chips 2,...,2 than those in the core layer 11. The core layer 11 also contains not only a large number of pulverized wood chips 2,...,2 but also a large number of wood shavings 3,...,3. In other words, in this embodiment 1, the wood chips 1,...,1 in the core layer 11 are made up of pulverized wood chips 2,...,2 and shavings 3,...,3, and the wood chips 1,...,1 in the surface layer 12 are made up only of pulverized wood chips 2,...,2 that are finer than those in the core layer 11.

[0046] In this embodiment 1, the ground wood chips 2 are the same as those used in conventional particle boards, while the wood shavings 3 used in the core layer 12 are used as a constituent material for another wood board 50, which will be described later. That is, in this embodiment 1, the core layer 11 uses a large number of wood chips 1, which are a mixture of the ground wood chips 2 used in conventional particle boards and the ground wood chips 3 used as a constituent material for another wood board 50, and the surface layer 12 uses the ground wood chips 2 used in conventional particle boards as a large number of wood chips 1, 1. In the core layer 11, the ground wood chips 3 are mixed in a ratio of 10% by weight to 90% by weight of the total weight of the wood chips 1, 1.

[0047] The ground wood chips 2, . . . , 2 and shaved wood chips 3, . . . , 3 used in the particle board 10 will be described in detail below.

[0048] [Crushed wood chips] As shown in Fig. 2, the pulverized wood pieces 2, ..., 2 are obtained by finely pulverizing wood material A using a known pulverizing device such as a crusher, hammer mill, pin mill, jet mill, ring flaker, or cutter mill until the wood passes through a sieve with a specified mesh size installed at the outlet of the pulverizing device. In the particle board 10 of the first embodiment, as shown in Fig. 2, wood chips 2a, ..., 2a obtained by pulverizing wood material A are classified using two sieves, one large and one small. For classification, a first sieve with a mesh size of 16 mm or less and a second sieve with a mesh size of 0.5 mm or more but smaller than the first sieve are used. The first wood chips 2b,...,2b that have been sorted by classification (i.e., they pass through the first sieve but not the second sieve) are used as the ground wood pieces 2,...,2 for the core layer 11, and the second wood chips 2c,...,2c that have passed through both the first and second sieves (i.e., they are finer than the first wood chips 2b,...,2b) are used as the ground wood pieces 2,...,2 for the surface layer 12.

[0049] As the first sieve having a mesh size of 16 mm or less, for example, a sieve having a nominal mesh size of 2 mm to 16 mm as specified in JIS Z8801-1:2019 can be used, preferably a sieve having a nominal mesh size of 2.8 mm to 8 mm, and particularly preferably a sieve having a nominal mesh size of 4 mm to 5.6 mm. As the second sieve having a mesh size of 0.5 mm or more and smaller than the first sieve, for example, a sieve having a nominal mesh size of 0.5 mm to 2 mm as specified in JIS Z8801-1:2019 can be used, preferably a sieve having a nominal mesh size of 0.5 mm to 1.4 mm, and particularly preferably a sieve having a nominal mesh size of 0.5 mm to 1 mm. In this embodiment 1, the wood chips 2a, ..., 2a are sorted by classifying them using a sieve (first sieve) with a nominal mesh size of 4 mm and a sieve (second sieve) with a nominal mesh size of 1 mm (i.e., the chips pass through the first sieve but do not pass through the second sieve), and the resulting chips are used as the first wood chips 2b, ..., 2b.

[0050] As shown in Figure 2, the third wood chips 2d,...,2d that do not pass through both types of sieves (i.e., are coarser than the first wood chips 2b,...,2b) due to the above classification are not used as wood pulverized pieces 2,...,2 but are returned to the pulverizing device and pulverized again.

[0051] The species of wood material A is not particularly limited, and any species of tree can be used as wood material A. For example, fir wood such as cedar, cypress, and Douglas fir, acacia, aspen, poplar, pine (hard pine, soft pine, radiata pine, etc.), birch, rubber (rubber tree), etc. can be used as wood material A. In addition, domestic timber such as todomatsu (Japanese Sakhalin fir), larch, Yezo spruce, sawara (Japanese sawara), hiba (Japanese cypress), kaya (Japanese tortoiseshell), tsuga (Japanese larch), cypress, cypress (Japanese laurel), various pines, paulownia (Japanese paulownia), maple, birch (white birch), shiitake (Japanese chestnut), beech, oak, fir, oak, camphor, and zelkova; North American timber such as American cypress, American cypress, American cedar, American fir, spruce, American larch, and redwood; South Sea timber such as agathis, terminalia, lauan, meranti, Junkon (Japanese cedar), camellere, karampayan, ambeloi, melina, teak, apitong, and sengonlaut; and other imported timber such as balsa, cedarwood, mahogany, lignum vitae, acacia mangium, Mediterranean pine, sorghum, and camellere. In addition to logs and thinned wood, scraps and waste wood generated at construction sites, waste pallet materials, recycled materials, etc. may also be used as the wood material A.

[0052] [Wood cuttings] The wood shavings 3, 3 used in the core layer 11 are produced from a wood material B during the formation of a wood board 50 different from the particle board 10 of the present invention. As shown in Fig. 3, the wood board 50 is made by cutting a wood material B into a thin, uniform thickness using a known cutting device with a blade that cuts the material into a thin, uniform thickness, resulting in a large number of wood flakes 3a, 3a having a uniform thickness t (0.05 mm to 0.35 mm). These wood flakes are then crushed using a known crushing device to form a large number of small wood flakes 3b, 3b, which are then classified using two sieves, one large and one small, and the first small wood flakes 3c, 3c selected by the classification are glued together in a consolidated state.

[0053] In the particle board 10 of the first embodiment, when forming the wood board 50, a number of wood flakes 3a, ..., 3a having a uniform thickness t (thickness of 0.05 mm or more and 0.35 mm or less) are cut from the wood material B and further crushed to produce a number of small wood flakes 3b, ..., 3b. Of these, an appropriate amount of wood flakes other than the number of first small wood flakes 3c, ..., 3c selected by classification are used as the wood shavings 3, ..., 3 to be included in the core layer 11. For classification, a third sieve with a mesh size of 35 mm or less and a fourth sieve with a mesh size of 0.5 mm or more and smaller than the third sieve are used. By classifying the numerous small wood flakes 3b, 3b using the third and fourth sieves, numerous first small wood flakes 3c, 3c are selected, and also the third small wood flakes 3e, 3e that pass through both the third and fourth sieves (i.e., the second small wood flakes 3d, 3d that are finer than the first small wood flakes 3c, 3c) and the third small wood flakes 3e, 3e that do not pass through both the third and fourth sieves (i.e., the first small wood flakes 3c, 3c) are obtained. In the present embodiment 1, the second small wood flakes 3d, 3d and the third small wood flakes 3e, 3e that are not selected by this classification are used as the wood shavings 3 to be included in the core layer 11. In other words, in this embodiment 1, among the small wood flakes 3b, ..., 3b obtained by cutting and crushing the wood material B, those that are not classified and are not used in the wood board 50 can be used as wood cutting pieces 3, ..., 3 to be included in the core layer 11.

[0054] As the third sieve having a mesh size of 35 mm or less, for example, a sieve having a nominal mesh size of 5.6 mm to 31.5 mm as specified in JIS Z8801-1:2019 can be used, preferably a sieve having a nominal mesh size of 5.6 mm to 16 mm, and particularly preferably a sieve having a nominal mesh size of 5.6 mm to 8 mm. As the fourth sieve having a mesh size of 0.5 mm or more and smaller than the third sieve, for example, a sieve having a nominal mesh size of 0.5 mm to 2 mm as specified in JIS Z8801-1:2019 can be used, preferably a sieve having a nominal mesh size of 0.5 mm to 1.4 mm, and particularly preferably a sieve having a nominal mesh size of 0.5 mm to 1 mm. In this embodiment 1, of the small wood flakes 3b, ..., 3b, the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e that were not selected by classification using a sieve with a nominal mesh size of 5.6 mm (third sieve) and a sieve with a nominal mesh size of 0.5 mm (fourth sieve) are used as the wood cutting pieces 3, ..., 3 to be included in the core layer 11.

[0055] The thickness t of the wood flakes 3a is 0.05 mm or more and 0.35 mm or less, preferably 0.10 mm or more and 0.30 mm or less, more preferably 0.15 mm or more and 0.25 mm or less, and even more preferably 0.15 mm or more and 0.20 mm or less. The thickness t of the wood flakes 3a can be changed by changing the thickness setting (e.g., the material feed speed) of a known cutting device. Wood flakes 3a cut by a cutting device will have a uniform thickness t. Furthermore, multiple wood flakes 3a, ..., 3a cut by a cutting device whose thickness setting (e.g., the material feed speed) is set so that the thickness of the wood flakes 3a becomes t will have the same thickness t. Furthermore, since the small wood flakes 3b and the first to third small wood flakes 3c to 3e that are classified from them are crushed wood flakes 3a, they have a uniform thickness t, just like the wood flakes 3a, and the numerous small wood flakes 3b, ..., 3b, the numerous first to third small wood flakes 3c, ..., 3c, the numerous second small wood flakes 3d, ..., 3d and the numerous third small wood flakes 3e, ..., 3e each have the same thickness t.

[0056] In addition, "the wood flakes 3a (similarly the small wood flakes 3b, the first small wood flakes 3c, the second small wood flakes 3b and the third small wood flakes 3e) have a uniform thickness t" means that thickness variations due to processing errors of the cutting device are allowed, for example, a thickness variation of about ±20% is allowed. Furthermore, "the numerous wood flakes 3a, ..., 3a (as well as the numerous small wood flakes 3b, ..., 3b, the numerous first to third small wood flakes 3c, ..., 3c, the numerous second small wood flakes 3d, ..., 3d, and the numerous third small wood flakes 3e, ..., 3e) have the same thickness t" does not only mean that all wood flakes 3a, ..., 3a actually have the same thickness, but also includes cases where cutting is performed using a cutting device in which the thickness setting (for example, the material feeding speed) is adjusted so that the numerous wood flakes 3a, ..., 3a have the same thickness t, and where there is variation in thickness of, for example, about ±20% due to biological variation in the wood material B and processing errors in the cutting device. Since wood material B is a natural material, biological characteristics such as the part of wood material B (heartwood or sapwood), specific gravity (hardness), and fiber direction affect (variation in) the thickness of the numerous wood flakes 3a, ..., 3a formed by contact with the blade. Therefore, thickness variation in the numerous wood flakes 3a, ..., 3a can be caused not only by processing errors but also by the biological characteristics of wood material B.

[0057] The first small wood flakes 3c used to form the wood board 50 will now be described in detail. As shown enlarged in FIG. 4, the first small wood flakes 3c have an elongated (striped) shape in which the fiber direction dimension d1 along the fibers a of vessels, tracheids, etc. is longer than the fiber-orthogonal direction dimension d2 perpendicular to the fiber direction. If the fiber direction dimension d1 is the length and the fiber-orthogonal direction dimension d2 is the width, the length d1 is 40 mm or less, preferably 35 mm or less, more preferably 30 mm or less, even more preferably 25 mm or less, and even more preferably 10 mm to 20 mm. The width d2 is 35 mm or less, preferably 15 mm or less, and more preferably 0.5 mm to 5 mm. The length d1 and width d2 of the first small wood flakes 3c are both average values. The length d1 and width d2 (both average values) of the first wood flakes 3c are calculated by photographing a large number of first wood flakes 3c, ..., 3c, approximating the image of each first wood flake 3c to an ellipse using publicly known image analysis software, and averaging the length of the long side of the approximated ellipse as the fiber direction dimension and the short side as the fiber perpendicular direction dimension d.

[0058] As described above, the first small wood flakes 3c, ..., 3c of such thickness, shape and size are selected by classifying a large number of small wood flakes 3b, ..., 3b using two appropriately selected large and small sieves (third and fourth sieves), and this classification also produces the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e to be used in the core layer 11.

[0059] In the first embodiment, as described above, after the numerous wood flakes 3a, ..., 3a are crushed, the wood flakes other than the first small wood flakes 3c, ..., 3c (the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e) selected by classification can be used as the wood shavings 3, ..., 3 in the core layer 11 of the particle board 10. However, the wood shavings 3, ..., 3 that make up the core layer 11 of the particle board 10 are not limited to those described above. The first small wood flakes 3c, ..., 3c used in the wood board 50 may also be used as the wood shavings 3, ..., 3 that make up the core layer 11. Furthermore, the wood flakes 3a, ..., 3a after cutting and before crushing, or the numerous small wood flakes 3b, ..., 3b after crushing and before classification, may also be used as the wood shavings 3, ..., 3 that make up the core layer 11. Furthermore, all, two, three, or four of the wood flakes 3a, ..., 3a, small wood flakes 3b, ..., 3b, first small wood flakes 3c, ..., 3c, second small wood flakes 3d, ..., 3d, and third small wood flakes 3e, ..., 3e may be combined and used as the wood cuttings 3 that make up the core layer 11. In other words, at least one type of wood flakes 3a, ..., 3a, small wood flakes 3b, ..., 3b, first small wood flakes 3c, ..., 3c, second small wood flakes 3d, ..., 3d, and third small wood flakes 3e, ..., 3e can be used as the wood cuttings 3 that make up the core layer 11. Each of the thin pieces 3a to 3e selected as the wood shavings 3 has a uniform thickness t, and the core layer 11 contains a large number of wood shavings 3, ..., 3 having the same thickness t.

[0060] The species of wood material B is not particularly limited, and any species of tree can be used as wood material B. For example, fir wood such as cedar, cypress, and Douglas fir, acacia, aspen, poplar, pine (hard pine, soft pine, radiata pine, etc.), birch, rubber (rubber tree), etc. can be used as wood material B. In addition, domestic timber such as todomatsu (Japanese Sakhalin fir), larch, Yezo spruce, sawara (Japanese sawara), hiba (Japanese cypress), kaya (Japanese tortoiseshell), tsuga (Japanese larch), cypress, cypress (Japanese laurel), various pines, paulownia (Japanese paulownia), maple, birch (white birch), shiitake (Japanese chestnut), beech, oak, fir, oak, camphor, and zelkova; North American timber such as American cypress, American cypress, American cedar, American fir, spruce, American larch, and redwood; South Sea timber such as agathis, terminalia, lauan, meranti, Junkon (Japanese cedar), camellere, karampayan, ambeloi, melina, teak, apitong, and sengonlaut; and other imported timber such as balsa, cedarwood, mahogany, lignum vitae, acacia mangium, Mediterranean pine, sorghum, and camellere. In addition to logs and thinned wood, scraps and waste wood generated at construction sites, waste pallet materials, recycled materials, etc. may also be used as the wood material B.

[0061] The numerous wood pieces 1, . . . , 1 that make up the particle board 10 are made up of the above-described crushed wood pieces 2, . . . , 2 and shaved wood pieces 3, .

[0062] Regarding the physical properties of the wood pieces 1 (ground wood pieces 2, wood cutting pieces 3), their density is preferably 250 kg / m 3 More than 800kg / m 3 More preferably, it is 300 kg / m or less. 3 More than 500kg / m 3 Density is 250 kg / m or less. 3 If the density of the wood chips 1 is less than 800 kg / m, it is possible to form particle boards 10 with the same density and bending strength by increasing the mixing ratio of wood chips, but stable production becomes difficult. 3 However, it is difficult to obtain such a wood piece 1. 3 If it is possible to easily obtain wood chips 1 exceeding this value, the upper limit of density is 800 kg / m 3It is not limited to this and may be a higher value.

[0063] Furthermore, the moisture content of the wood pieces 1 (ground wood pieces 2, shaved wood pieces 3) is preferably 2% or more and 20% or less, and more preferably 2% or more and 8% or less. If the moisture content is less than 2%, it may take a long time to soften the wood pieces during the hot pressing process in the press molding step, which may increase the pressing time and reduce the bending strength. On the other hand, if the moisture content of the wood pieces 1 exceeds 20%, it may take a long time to heat and compress the wood pieces during the hot pressing process, and furthermore, the hardening of the adhesive may be inhibited, which may reduce the bending strength.

[0064] <Adhesive> The adhesive used for the particle board 10 is not particularly limited as long as it is a thermosetting adhesive. For example, an isocyanate-based adhesive can be used. Other adhesives that can be used include amine-based adhesives such as phenolic resin, urea resin, and melamine resin, and natural adhesives. The adhesive is applied to the wood pieces 1,...,1 before they are piled up, and hardens when the mat on which the wood pieces 1,...,1 are piled up is hot-pressed. This causes the numerous wood pieces 1,...,1 to be bonded together in a collective state.

[0065] -Particle board manufacturing method- Next, a description will be given of a method for manufacturing the particle board 10. The method for manufacturing the particle board 10 includes a wood piece manufacturing step S1, an adhesive application step S2, a mat forming step S3, and a heat pressing step S4.

[0066] <Wood piece production process S1> The wood piece producing step S1 includes a wood crushed piece producing step S11, a wood shavings producing step S12, and a wood piece mixing step S13.

[0067] [Wood chip production process S11] The wood pulverized piece preparation step S11 includes a material preparation step S111, a pulverization step S112, and a classification step S113.

[0068] (Material preparation process S111) First, prepare wood material A. When using logs, thinned wood, or other raw wood, cut them into short pieces and remove the bark to create wood material A. When using scraps or waste wood generated at construction sites, waste pallet material, recycled wood, etc., cut them into short pieces to create wood material A.

[0069] (Crushing process S112) Next, the prepared wood material A is finely crushed into small pieces using a known crusher such as a crusher, hammer mill, pin mill, jet mill, ring flaker, or cutter mill until it passes through a sieve with a specified mesh size installed at the outlet of the crusher. By crushing the wood material A, wood chips 2a, ..., 2a are obtained. The wood chips 2a, ..., 2a may have various shapes, such as powder, granules, rods, columns, fibers, or flakes.

[0070] (Classification process S113) The wood chips 2a, ..., 2a obtained by grinding are classified into three sizes using two types of sieves (first and second sieves), one large and one small. Specifically, the wood chips 2a, ..., 2a are divided into first wood chips 2b, ..., 2b of a desired size that pass through the first coarse sieve but not the second fine sieve, second wood chips 2c, ..., 2c that are finer than the first wood chips 2b, ..., 2b and pass through both the first and second sieves, and third wood chips 2d, ..., 2d that are coarser than the first wood chips 2b, ..., 2b and do not pass through either the first or second sieve. The first wood chips 2b, ..., 2b classified and selected in this way are used as the wood pulverized pieces 2, ..., 2 for the core layer 11, and the second wood chips 2c, ..., 2c obtained at the same time are used as the wood pulverized pieces 2, ..., 2 for the surface layer 12. The third wood chips 2d, ..., 2d are not used as the wood pulverized pieces 2, ..., 2 but are returned to the crushing device and crushed again.

[0071] [Wood cutting piece production process S12] The wood shavings production process S12 includes a material preparation process S121, a cutting process S122, a crushing process S123, and a classification process S124. As described above, in the first embodiment, the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e generated during the formation of the wood board 50 are used as the wood shavings 3, ..., 3 for the core layer 11. Therefore, the wood shavings production process S12 is a part of the method for manufacturing the wood board 50.

[0072] (Material preparation process S121) First, prepare wood material B. When using logs, thinned wood, or other raw wood, cut them into short pieces and remove the bark to create wood material B. When using scrap wood, waste wood, waste pallet wood, recycled wood, or other materials generated at construction sites, cut them into short pieces to create wood material B.

[0073] (Cutting process S122) Next, the prepared wood material B is cut into a thin, uniform thickness using a known cutting device having a blade that cuts the material into a thin, uniform thickness to form a large number of wood flakes 3a, ..., 3a with a uniform thickness t. Specifically, the thickness setting of the cutting device (for example, the speed at which the wood material B is fed) is adjusted to form a large number of wood flakes 3a, ..., 3a with a uniform thickness t and with linear fibers a appearing on the surface.

[0074] In this cutting step S122, by producing the thin wood pieces 3a, ..., 3a having a thickness of t, the thickness of the small thin wood pieces 3b, ..., 3b obtained in the subsequent crushing step will also be thickness t.

[0075] (Crushing process S123) Next, the wood flakes 3a, ..., 3a obtained by cutting are crushed using a known crushing device such as a crusher, hammer mill, pin mill, jet mill, ring flaker, or cutter mill to reduce the size to a size smaller than that immediately after cutting. For example, if the wood flakes 3a, ..., 3a after cutting are crushed widthwise using a jet mill so as to split along the fiber direction (lengthwise), thin, elongated wood flakes 3b, ..., 3b can be produced. In other words, applying a force (impact) to the wood flakes 3a, ..., 3a in a direction perpendicular to the fiber direction makes them less likely to split, but applying a force parallel to the fiber direction makes them more easily split. Even if the wood flakes 3a, ..., 3a are curled, they can be split into flat pieces by crushing. The direction of the force applied to the wood flakes 3a, ..., 3a is not limited to the direction parallel to the fiber direction. When force is applied to the wood flakes 3a, ..., 3a in a random direction, the wood flakes 3a, ..., 3a usually crack from the part where the force is weaker (they tend to crack in the direction of the weaker force). Because the force connecting the fibers of the wood flakes 3a, ..., 3a (the force perpendicular to the fibers) is overwhelmingly weaker than the force in the fiber direction, if the wood flakes 3a, ..., 3a are crushed in a random direction using the crushing device (when force is applied), the wood flakes 3a, ..., 3a will crack along the fiber direction and shorten in the direction perpendicular to the fiber, resulting in long, thin wood flakes 3b, ..., 3b.

[0076] Furthermore, even if the wood slices 3a, . . . , 3a contain dead knots, the dead knots are more brittle than the other parts, so the dead knots are turned into powder by crushing and are removed in the subsequent classification process.

[0077] In this way, by adding the crushing step S123 after the cutting step S122, rather than using only one step, and going through a two-step processing process, it is possible to easily produce high-strength small wood flakes 3b,...,3b of the required size without dead knots.

[0078] (Classification process S124) The wood flakes 3b, ..., 3b obtained by pulverization are classified into three sizes using two sieves (third and fourth sieves), one large and one small. Specifically, the wood flakes 3b, ..., 3b are divided into first wood flakes 3c, ..., 3c of desired size that pass through the coarse third sieve but not the fine fourth sieve, second wood flakes 3d, ..., 3d that pass through both the third and fourth sieves (i.e., finer than the first wood flakes 3c, ..., 3c), and third wood flakes 3e, ..., 3e that do not pass through either the third or fourth sieve (i.e., coarser than the first wood flakes 3c, ..., 3c). The second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e other than the first small wood flakes 3c, ..., 3c that have been classified and selected in this manner are used as the wood cutting pieces 3, ..., 3 for the core layer 11.

[0079] [Wood piece mixing process S13] In the wood piece mixing process S13, the numerous wood pulverized pieces 2,...,2 (first wood chips 2b,...,2b) for the core layer 11 produced in the wood pulverized piece production process are mixed with the numerous wood shavings 3,...,3 (second wood flakes 3d,...,3d and third wood flakes 3e,...,3e) for the core layer 11 produced in the wood shavings production process to achieve the desired mixing ratio (the wood shavings 3,...,3 are 10% by weight or more and 90% by weight or less of the total weight of the wood pieces 1,...,1).

[0080] In the wood piece production process S1, the above-mentioned wood crushed piece production process S11, wood shavings production process S12, and wood piece mixing process S13 are carried out to produce wood pieces 1,...,1 for the core layer 11 (a mixture of first wood chips 2b,...,2b and second wood flakes 3d,...,3d and third wood flakes 3e,...,3e) and wood pieces 1,...,1 for the surface layer 12 (second wood chips 2c,...,2c).

[0081] <Adhesive application process S2> The wood pieces 1,...,1 for the core layer 11 and the wood pieces 1,...,1 for the surface layer 12 produced in the wood piece production step S1 are each carried into an adhesive applicator and adhesive is applied. For example, an isocyanate-based adhesive can be used as the adhesive, but other adhesives that can be used include amine-based adhesives such as phenolic resin, urea resin, and melamine resin, and natural wood (tannin) adhesives. A commonly used water repellent agent can also be used together with the adhesive.

[0082] <Mat forming process S3> In the mat-forming process S3, as shown on the left side of FIG. 6, first, a large number of wood pieces 1,...,1 for the surface layer 12, to which adhesive has been applied, are piled up in a state where they are gathered together in the thickness direction until they reach a predetermined thickness (height), forming a first mat 9a of wood pieces 1,...,1. Next, a large number of wood pieces 1,...,1 for the core layer 11, to which adhesive has been applied, are piled up on the first mat 9a in a state where they are gathered together in the thickness direction until they reach a predetermined thickness (height), forming a second mat 9b of wood pieces 1,...,1. Furthermore, a large number of wood pieces 1,...,1 for the surface layer 12, to which adhesive has been applied, are piled up on the second mat 9b in a state where they are gathered together in the thickness direction until they reach a predetermined thickness (height), forming a third mat 9c of wood pieces 1,...,1. In this manner, a three-layered mat 9 is formed.

[0083] At this time, the thicknesses of the first to third mats 9a to 9c are adjusted to achieve the desired ratio of the thickness of the core layer 11 and each surface layer 12 to the overall particleboard 10. For example, when forming a particleboard 10 with a thickness of 9 mm, in which the surface layer 12 accounts for 15% of the overall thickness of the particleboard 10 (surface layer 12:core layer 11:surface layer 12 = 15:70:15), the mats 9 are formed so that the thickness (height) of the first and third mats 9a, 9c that will form the surface layers 12 is approximately 13.5 mm, and the thickness (height) of the second mat 9b that will form the core layer 11 is approximately 63 mm. Note that the thickness ratio of the core layer 11 and each surface layer 12 to the overall particleboard 10 is not limited to the above ratio and may be any ratio.

[0084] <Heat pressure process S4> The mat 9 formed in the mat forming step S3 is carried into a hot press machine and set between heating platens, where it is compressed by hot pressing at a predetermined pressure and temperature. At this time, the adhesive hardens, bonding and integrating the numerous wood pieces 1, 1. As a result, the particle board 10 shown on the right side of Figure 6 is formed.

[0085] At this time, as shown in FIG. 6, the mat 9 having a thickness of about 90 mm as exemplified above is compressed into a particle board 10 having a thickness of, for example, 9 mm, and the thickness is compressed to 1 / 10. The pressing temperature in the hot pressing process is not particularly limited, but is, for example, 160 to 220°C. The pressing pressure in the hot pressing process is, for example, 2 to 4 N / mm 2 The pressing time is, for example, 1.5 to 3 minutes (for example, 10 to 20 seconds per mm of thickness). The pressing time varies depending on the thickness of the particle board 10, and may be completed in less than 1 minute or may require more than 3 minutes. Furthermore, a preliminary heating treatment using a heating device may be performed before the hot pressing treatment using the hot pressing device.

[0086] -Effects of the first embodiment- In this first embodiment, the core layer 11 of the three-layer particle board 10 contains not only the usual wood pulverized chips 2 (first wood chips 2b), but also wood shavings 3 (3) with an extremely thin, uniform thickness of 0.05 mm to 0.35 mm, which are obtained by cutting. This configuration increases the bending strength of the core layer 11 of the particle board 10. Therefore, it is not necessary to increase the density of the surface layer 12 or use a large amount of adhesive to ensure the bending strength of the particle board 10. Furthermore, compared to when the core layer 11 is composed only of the wood pulverized chips 2, the presence of the thin wood shavings 3 makes it easier to bond the wood pieces 1 (the wood pulverized chips 2 and the wood shavings 3) together with a small amount of adhesive. Therefore, according to the particle board 10 having a three-layer structure of the first embodiment, it is possible to reduce the amount of adhesive used while maintaining bending strength comparable to that of conventional particle boards.

[0087] Furthermore, in the particle board 10 of this embodiment 1, as with conventional three-layer particle boards, the surface layer 12 is composed of relatively fine wood pulverized pieces 2, ..., 2 (second wood chips 2c, ..., 2c), and therefore has excellent surface properties (smoothness).

[0088] Furthermore, in the particle board 10 of the first embodiment, if some of the ground wood chips 2,...,2 in the core layer 11 are replaced with wood shavings 3,...,3 that are thinner than the ground wood chips 2,...,2, the core layer 11 will contain more wood shavings 3,...,3 than the ground wood chips 2,...,2 before replacement. The wood shavings 3,...,3 have a uniform thickness and flat surfaces. Therefore, if the core layer 11 contains many wood shavings 3,...,3 (if some of the ground wood chips 2,...,2 in the core layer 11 are replaced with wood shavings 3,...,3), the total surface area of ​​the many wood chips 1,...,1 that make up the core layer 11 will increase significantly, making it more difficult for screws to slip out than in a conventional three-layer particle board whose core layer is composed only of granular ground wood chips. Therefore, according to the particle board 10 of this embodiment 1, by including wood shavings 3, ..., 3 in the core layer 11, the core layer 11 is reinforced and the screw pull-out strength (wood screw holding power) is significantly improved, making it suitable as a load-bearing subfloor surface material for screw installation.

[0089] As will be described later, the inventors of the present application conducted tests to verify the effects of including extremely thin, flaky wood shavings 3, ..., 3 with a thickness of 0.05 mm to 0.35 mm in the core layer 11 of a three-layer particle board 10. As a result, it was found that particle board 10 including the thin wood shavings 3, ..., 3 in the core layer 11 had improved bending strength (MOR), water absorption length change (LE), and wood screw holding strength (WS) compared to conventional particle board not including the thin wood shavings 3, ..., 3 in the core layer 11, and that water absorption thickness swelling (TS) showed some improvement, although not a significant improvement, and that the absolute value of water absorption thickness swelling (TS) fully met the standard (12% or less) required for structural particle board.

[0090] As described above, according to the first embodiment, it is possible to provide a three-layer particle board 10 that is excellent in surface properties, bending strength, and screw pull-out strength and that undergoes little dimensional change, without increasing cost or weight.

[0091] In this embodiment 1, the core layer 11 uses a large number of first wood chips 2b...2b that pass through a first sieve with a mesh size of 16 mm or less but do not pass through a second sieve with a mesh size of 0.5 mm or more and smaller than the first sieve, and the surface layer 12 uses finer second wood chips 2c...2c that pass through both the first and second sieves. In this way, by using finer wood pulverized chips 2...2 than the core layer 11 for the surface layer 12 and including wood shavings 3...3 in the core layer 11, a three-layer particleboard 10 with excellent surface properties, bending strength, and screw pull-out strength and minimal dimensional change can be provided without increasing cost or weight.

[0092] By the way, based on the results of the above verification tests, the inventors of the present application have found that by mixing wood cutting pieces 3, ..., 3 (second wood thin pieces 3d, ..., 3d and third wood thin pieces 3e, ..., 3e) into the numerous wood pieces 1, ..., 1 for the core layer 11 at a ratio of 20% by weight or more and 90% by weight or less of the total weight of the core layer 11, the normal bending strength (MOR), water absorption length change (LE) and wood screw holding power (WS) are improved, and that the higher the mixing ratio of wood cutting pieces 3, ..., 3 in the core layer 11, the greater the improvement rate of normal bending strength (MOR) and water absorption length change (LE). Therefore, by mixing wood cuttings 3, ..., 3 with a large number of wood pieces 1, ..., 1 for the core layer 11 in a ratio of 20% by weight to 90% by weight of the total weight, it is possible to provide a three-layer particle board with excellent surface properties, bending strength, and screw pull-out strength, and with little dimensional change, without increasing cost or weight.

[0093] Furthermore, in this embodiment 1, the wood shavings 3, ..., 3 are produced when wood material B is processed to form another wood board 50 and are used in the particle board 10. Therefore, even if a material (wood shavings 3, ..., 3) different from the material (ground wood chips 2, ..., 2) used in ordinary particle boards is used, it can be easily procured because the different material is produced when processing the material for the other wood board 50. Therefore, according to the manufacturing method of this embodiment 1, it is possible to easily and relatively inexpensively provide a three-layer particle board 10 that has excellent surface properties, bending strength, and screw pull-out strength and exhibits little dimensional change.

[0094] In particular, in this first embodiment, the wood shavings 3, ..., 3 contained in at least the core layer 11 are those other than the first small wood flakes 3c, ..., 3c (the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e) selected by classifying the small wood flakes 3b, ..., 3b. In this way, waste wood that is not used in the other wood boards 50 and is generated during the formation of the other wood boards 50 is used as the wood shavings 3, ..., 3 for the core layer 11 of the three-layer particle board 10, thereby making it possible to form the three-layer particle board 10 more inexpensively. Furthermore, since the wood material B of the other wood boards 50 is used without waste, this leads to the effective use of wood resources.

[0095] -Verification of effectiveness- To verify the above-mentioned effects of including the wood shavings 3 in the core layer 11 of particle board 10, the inventors prepared the following five types of particle board 10 (specimens X0 to X4) and conducted bending strength tests, water absorption thickness swelling tests, water absorption length change tests, and wood screw holding strength tests in accordance with JIS A5908 and JIS A5905. The normal bending strength (MOR), water absorption thickness swelling (TS), water absorption length change (LE), and wood screw holding strength (WS) were determined, and the results are shown in Figure 7. Specimen X0 was constructed similarly to a conventional particle board that did not include the wood shavings 3, while specimens X1 to X4 differed in the mixing ratio of the wood shavings 3 in the core layer 11, but were otherwise constructed similarly to the particle board 10 of embodiment 1. FIG. 7 also shows the test results of each of the specimens X1 to X4 as a relative ratio when the test result of the specimen X0 is set to 100. Test specimen X0: The mixing ratio of wood chips 3, ..., 3 in the core layer 11 is 0% by weight Specimen X1: The mixture ratio of wood chips 3, ..., 3 in the core layer 11 is 20% by weight Specimen X2: The mixture ratio of wood chips 3, ..., 3 in the core layer 11 is 40% by weight Specimen X3: The mixture ratio of wood chips 3, ..., 3 in the core layer 11 is 60% by weight Specimen X4: The mixture ratio of wood chips 3, ..., 3 in the core layer 11 is 80% by weight

[0096] As shown in Figure 7, particle boards 10 (specimens X2 to X4) containing 40% by weight or more of wood shavings 3, ..., 3 in the core layer 11 showed improved normal bending strength (MOR) compared to the conventional particle board (specimen X0) that did not contain wood shavings 3, ..., 3 in the core layer 11. Furthermore, the normal bending strength (MOR) increased as the mixing ratio of wood shavings 3, ..., 3 in the core layer 11 increased.

[0097] Furthermore, with regard to dimensional change, particleboards 10 (specimens X1-X4) containing wood shavings 3 in the core layer 11 showed some improvement in water absorption thickness swelling (TS) compared to a conventional particleboard (specimen X0) that did not contain wood shavings 3 in the core layer 11, although not significantly improved. The absolute value of TS fully satisfied the standard (12% or less) required for structural particleboards. Meanwhile, particleboards 10 (specimens X1-X4) containing wood shavings 3 in the core layer 11 showed an improvement in water absorption length change (LE) compared to a conventional particleboard (specimen X0) that did not contain wood shavings 3 in the core layer 11. Furthermore, the improvement in water absorption length change (LE) increased with the proportion of wood shavings 3 in the core layer 11.

[0098] Furthermore, the particle boards 10 (specimens X1 to X4) containing wood shavings 3, ..., 3 in the core layer 11 also showed improved wood screw holding strength (WS) compared to the conventional particle board (specimen X0) that did not contain wood shavings 3, ..., 3 in the core layer 11. When the mixing ratio of wood shavings 3, ..., 3 in the core layer 11 was 40% by weight or more, the improvement rate of wood screw holding strength (WS) was 40% or more.

[0099] As described above, particle boards 10 (specimens X2 to X4) containing wood shavings 3,...,3 in the core layer 11 had higher bending strength under normal conditions (MOR) and wood screw holding power (WS) and lower water absorption length change (LE) compared to conventional particle boards (specimen X0) that did not contain wood shavings 3,...,3 in the core layer 11. These results show that by including wood shavings 3,...,3 in the core layer 11 of three-layer particle board 10, it is possible to provide a three-layer particle board 10 that not only has excellent surface properties like conventional particle boards, but also has excellent bending strength and screw pull-out strength and little dimensional change, without increasing cost or weight.

[0100] Second Embodiment of the Invention The particle board 10 according to the second embodiment is a modified version of the particle board 10 according to the first embodiment. Specifically, as shown in Fig. 8, the particle board 10 according to the second embodiment contains wood shavings 3, ..., 3 not only in the core layer 11 but also in the surface layer 12. In other words, in the second embodiment, both the core layer 11 and the surface layer 12 contain not only a large number of pulverized wood chips 2, ..., 2 but also a large number of wood shavings 3, ..., 3.

[0101] In the first embodiment, among the small wood flakes 3b, ..., 3b formed by cutting and crushing the wood material B to form the wood board 50, those not classified for use in the wood board 50 (the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e) were used as the wood shavings 3, ..., 3 to be included in the core layer 11, but in the second embodiment, the first small wood flakes 3c, ..., 3c used in the wood board 50 are used as the wood shavings 3, ..., 3 that make up the core layer 11. Furthermore, in the second embodiment, the first small wood flakes 3c, ..., 3c used in the wood board 50 are also used as the wood shavings 3, ..., 3 used in the surface layer 12, just like the wood shavings 3, ..., 3 used in the core layer 11.

[0102] As in the first embodiment, the wood shavings 3, ..., 3 used in the particle board 10 (core layer 11 and surface layer 12) are not limited to those described above. The second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e not used in the wood board 50 may be used as the wood shavings 3, ..., 3 used in the particle board 10. Furthermore, the wood flakes 3a, ..., 3a after cutting and before crushing, and the numerous small wood flakes 3b, ..., 3b after crushing and before classification may be used as the wood shavings 3, ..., 3 used in the particle board 10. Furthermore, all, two, three, or four of the wood flakes 3a, ..., 3a, small wood flakes 3b, ..., 3b, first small wood flakes 3c, ..., 3c, second small wood flakes 3d, ..., 3d, and third small wood flakes 3e, ..., 3e may be combined and used as the wood shavings 3 to be used in the particle board 10. In other words, at least one of the wood flakes 3a, ..., 3a, small wood flakes 3b, ..., 3b, first small wood flakes 3c, ..., 3c, second small wood flakes 3d, ..., 3d, and third small wood flakes 3e, ..., 3e may be used as the wood shavings 3 to be used in the particle board 10.

[0103] The other configurations are the same as those in the first embodiment.

[0104] The method for producing the particle board 10 is different from that of the first embodiment only in the wood chip mixing step S13, and the other steps are the same as those of the first embodiment.

[0105] In embodiment 2, in the wood piece mixing process S13, wood fragments 2, ..., 2 and wood cutting pieces 3, ..., 3 are mixed to produce wood pieces 1, ..., 1 for the core layer 11 and wood pieces 1, ..., 1 for the surface layer 12.

[0106] Specifically, the production of the wood pieces 1,...,1 for the core layer 11 is almost the same as the wood piece mixing step S13 in embodiment 1. The wood pieces 1,...,1 for the core layer 11 are produced by mixing a large number of wood pulverized pieces 2,...,2 (first wood chips 2b,...,2b) for the core layer 11 produced in the wood pulverized piece production step with a large number of wood shavings 3,...,3 (first wood thin pieces 3c,...,3c) for the core layer 11 produced in the wood shavings production step at a desired mixing ratio (the wood shavings 3,...,3 relative to the total weight of the wood pieces 1,...,1 is 10% by weight or more and 90% by weight or less).

[0107] On the other hand, the wood pieces 1,...,1 for the surface layer 12 are produced by mixing a large number of wood crushed pieces 2,...,2 (second wood chips 2c,...,2c) for the surface layer 12 produced in the wood crushed piece production process with a large number of wood cutting pieces 3,...,3 (first small wood flakes 3c,...,3c) for the surface layer 12 produced in the wood cutting piece production process to achieve the desired mixing ratio (the wood cutting pieces 3,...,3 are 10% by weight or more and 90% by weight or less of the total weight of the wood pieces 1,...,1).

[0108] -Effects of the second embodiment- In the second embodiment, extremely thin wood shavings 3, ..., 3 with a thickness of 0.05 mm to 0.35 mm are included not only in the core layer 11 of the three-layer particle board 10 but also in the surface layer 12. This configuration increases the bending strength of not only the core layer 11 but also the surface layer 12 of the particle board 10. Therefore, it is not necessary to increase the density of the surface layer 12 or use a large amount of adhesive to ensure the bending strength of the particle board 10. Furthermore, by including the wood shavings 3, ..., 3 in both the core layer 11 and the surface layer 12, the amount of adhesive used can be further reduced compared to the particle board 10 of the first embodiment, in which the wood shavings are included only in the core layer 11.

[0109] Furthermore, in the particle board 10 according to the second embodiment, the wood shavings 3 are extremely thin, with a thickness of 0.05 mm to 0.35 mm, and therefore do not easily cause irregularities on the surface even when included in the surface layer 12. As a result, the surface properties (smoothness) are as excellent as those of conventional particle boards.

[0110] Furthermore, in the particle board 10 according to the second embodiment, wood shavings 3 are included not only in the core layer 11 but also in the surface layer 12 (part of the ground wood shavings 2 included in the surface layer 12 are replaced with wood shavings 3). By replacing part of the ground wood shavings 2 (second ground wood shavings 2c) for the surface layer 12, which are finer than the ground wood shavings 2 (first ground wood shavings 2b) for the core layer 11, with wood shavings 3 having a uniform thickness and flat surfaces, the total surface area of ​​the numerous wood shavings 1 making up the surface layer 12 is significantly increased. Therefore, the particle board 10 according to the second embodiment makes screws less likely to come out. Therefore, the second embodiment can provide a three-layer particle board 10 with superior screw pull-out strength (wood screw holding power).

[0111] Furthermore, in the particle board 10 of the second embodiment, some of the relatively fine wood pulverized chips 2,...,2 of the surface layer 12 are replaced with wood shavings 3,...,3 of uniform thickness and flat surfaces, thereby significantly increasing the total surface area of ​​the numerous wood pulverized chips 1,...,1 that make up the surface layer 12. A significant increase in the total surface area of ​​the numerous wood pulverized chips 1,...,1 that make up the surface layer 12 increases the bonding area between the numerous wood pulverized chips 1,...,1, and also increases the number of bonding points and makes them more evenly distributed. Therefore, the particle board 10 of the second embodiment is more resistant to moisture penetration and has excellent water resistance compared to conventional particle boards whose surface layer 12 is composed only of wood pulverized chips 2,...,2.

[0112] Furthermore, in conventional particle boards whose surface layers are made only of crushed wood chips, the crushed wood chips, which are not cut to a thin thickness, are crushed during press molding. When moisture penetrates the interior, the crushed wood chips are more likely to absorb moisture, which can result in significant dimensional changes (changes in length and thickness). In contrast, the particle board 10 of the second embodiment, as described above, has a structure that makes it more difficult for moisture to penetrate the interior than conventional particle boards, and because the numerous replaced wood chippings 3,...,3 are cut to a thin thickness, they do not absorb moisture and therefore do not undergo significant changes in dimension (length and thickness).

[0113] As described above, according to the second embodiment, a three-layer particle board 10 having excellent surface properties, bending strength, screw pull-out strength, and water resistance, and small dimensional change, can be provided without increasing cost or weight.

[0114] In the second embodiment, the first small wood flakes 3c, ..., 3c selected by classifying the small wood flakes 3b, ..., 3b are used as the wood shavings 3, ..., 3 contained in the core layer 11 and the surface layer 12. The first small wood flakes 3c, ..., 3c selected by classification for use in other wood boards 50 have smaller dimensional (length and width) variations than the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e used as the wood shavings 3, ..., 3 in the first embodiment. Therefore, by using such first small wood flakes 3c, ..., 3c as the wood shavings 3, ..., 3, it is possible to provide a three-layer particle board 10 that has excellent surface properties, bending strength, and screw pull-out strength and that experiences less dimensional change.

[0115] -Verification of effectiveness- To verify the above-mentioned effect of incorporating extremely thin wood shavings 3, ..., 3 with a thickness of 0.05 mm to 0.35 mm not only in the core layer 11 but also in the surface layer 12 of a three-layer particle board 10, the inventors prepared the following three types of particle board 10 (specimens X10, X11, and X12). They conducted bending strength tests, wet bending strength tests, water absorption thickness swelling tests, water absorption length change tests, and wood screw holding strength tests in accordance with JIS A5908 and JIS A5905 to determine the normal bending strength (MOR), water absorption thickness swelling (TS), water absorption length change (LE), and wood screw holding strength (WS). They also conducted a moisture absorption and desorption test to determine the moisture absorption and desorption length change (HLE). The results are shown in Figure 9. In the moisture absorption / desorption test, three types of particle boards 10 (specimens X10, X11, and X12) were placed under conditions of 20°C and 65% relative humidity, high temperature and high humidity, and high temperature and low humidity. The length change under the high temperature and high humidity conditions was measured, with the length under the 20°C and 35% relative humidity condition used as the reference. The difference in length change was calculated as the moisture absorption / desorption length change (HLE). Specimen X10 was constructed similarly to a conventional particle board that did not contain wood shavings 3,...,3. Specimens X11 and X12 differed in the mixing ratio of wood shavings 3,...,3 in the core layer 11 and surface layer 12, but were otherwise constructed similarly to the particle board 10 of the second embodiment. Figure 9 shows the test results for specimens X10, X11, and X12, expressed as a relative ratio when the test result for specimen X10 was set to 100. Specimen X10: The mixture ratio of wood chips 3, ..., 3 in the core layer 11 and the surface layer 12 is 0% by weight Specimen X11: The mixture ratio of wood shavings 3, ..., 3 in the core layer 11 is 40% by weight, and the mixture ratio of wood shavings 3, ..., 3 in the surface layer 12 is 0%. Specimen X12: The mixture ratio of wood shavings 3, ..., 3 in the core layer 11 is 40% by weight, and the mixture ratio of wood shavings 3, ..., 3 in the surface layer 12 is 40%.

[0116] As shown in Figure 9, specimen X12 had significantly improved MOR and wet MOR compared to specimens X10 and X11. The improvement rates of specimen X12 over specimen X11 were 48% for MOR and 51% for wet MOR, which were significantly higher than the improvement rates of specimen X11 over specimen X10 (MOR 28%, wet MOR 26%).

[0117] Regarding dimensional change, the water absorption thickness swelling (TS) of specimen X12 was not significantly improved compared to specimens X10 and X11, but there was some improvement, and the absolute value of TS fully met the standard required for structural particleboard (12% or less).On the other hand, the water absorption length change (LE) of specimen X12 was improved compared to specimens X10 and X11.

[0118] Furthermore, the wood screw holding strength (WS) of specimen X12 was improved compared to specimen X10, and the improvement rate was the same as that of specimen X11 compared to specimen 10.

[0119] Furthermore, the moisture absorption / desorption length change rate (HLE) of specimen X12 was significantly improved compared to specimens X10 and X11. The improvement rate of specimen X12 over specimen X11 was 26%, which was higher than the improvement rate of specimen X11 over specimen X10 (22%).

[0120] Furthermore, with regard to water resistance, the particle board 10 (specimen X12) containing wood shavings 3, ..., 3 in the surface layer 12 showed an improved water resistance index (wet bending strength (wet MOR) / normal bending strength (MOR)) compared to the particle boards (specimen X10 and specimen X11) that did not contain wood shavings 3, ..., 3 in the surface layer 12.

[0121] Furthermore, although not shown in Figure 9, the root mean square height Sq and arithmetic mean height Sa (indicators of surface quality) of the surfaces of specimens X10 and X12 were measured and compared, and the results showed that both were almost the same, with only a difference of about 1 to 4 μm.

[0122] As described above, particleboard 10 (specimen X12) containing wood shavings 3,...,3 in the core layer 11 and surface layer 12 had higher normal bending strength (MOR), wet bending strength (wet MOR), wood screw holding strength (WS), and water resistance, and lower water absorption length change (LE) and moisture absorption / desorption length change (HLE), compared to conventional particleboard (specimen X10) that did not contain wood shavings 3,...,3. Furthermore, particleboard 10 (specimen X12) containing wood shavings 3,...,3 in the surface layer 12 had similar root mean square height Sq and arithmetic mean height Sa (indicators of surface texture) to conventional particleboard (specimen X10) that did not contain wood shavings 3,...,3 in the surface layer 12. These results show that according to embodiment 2, in which wood shavings 3, ..., 3 are included in the core layer 11 and surface layer 12 of the particle board 10, it is possible to provide a three-layer particle board 10 that not only has excellent surface properties like conventional particle boards, but also has excellent bending strength, screw pull-out strength, and water resistance, and exhibits little dimensional change, without increasing cost or weight.

[0123] Furthermore, particleboard 10 (specimen X12) containing wood shavings 3 in both core layer 11 and surface layer 12 exhibited higher modulus of resistance (MOR), wet MOR, and water resistance, and lower moisture absorption length change (LE) and moisture absorption / desorption length change (HLE), compared to particleboard 10 (specimen X11) containing wood shavings 3 only in core layer 11. These results demonstrate that embodiment 2, in which the core layer 11 and surface layer 12 of particleboard 10 contain wood shavings 3, 3, can provide a three-layer particleboard 10 with superior bending strength, screw pull-out strength, and water resistance, and with less dimensional change, without increasing cost or weight, compared to embodiment 1, in which the core layer 11 of particleboard 10 contains wood shavings 3, 3.

[0124] Other Embodiments In the first and second embodiments, the two surface layers 12, 12 are configured to be thinner (higher) than the core layer 11, but the two surface layers 12, 12 may be thicker than the core layer 11.

[0125] Furthermore, in the above embodiments 1 and 2, examples have been described in which wood shavings generated during material processing of other wood boards 50 are used as wood shavings 3, ..., 3, but the wood shavings 3, ..., 3 may not be generated during material processing of other wood boards 50, but may be procured to form the above-mentioned particle board 10. [Industrial Applicability]

[0126] INDUSTRIAL APPLICABILITY The present invention is useful for a particle board having a three-layer structure and a method for manufacturing a particle board having a three-layer structure. [Explanation of symbols]

[0127] 2 crushed wood pieces 3 wood cuttings 3a wood flakes 3b Small wood flakes 3c 1st woody flake 3d 2nd woody flakes 3e 3rd woody flake 10. Particle board 11 Core layer 12 Surface layer 50 wood boards

Claims

1. A three-layer particle board with a surface layer made of finer wood chips than the core layer, The core layer contains a large number of thin wood chips having a uniform thickness of 0.05 mm or more and 0.35 mm or less. A particle board characterized by:

2. The particle board according to claim 1, The surface layer contains a large number of wood chips. A particle board characterized by:

3. The particle board according to claim 1 or 2, The core layer contains first wood chips as the wood pulverized pieces for the core layer, which pass through a first sieve with a mesh size of 16 mm or less and do not pass through a second sieve with a mesh size of 0.5 mm or more and smaller than that of the first sieve, The surface layer contains second wood chips that pass through both the first and second sieves as the wood pulverized pieces for the surface layer. A particle board characterized by:

4. The particle board according to claim 1 or 2, In the core layer, the wood shavings are mixed in a ratio of 20% by weight to 90% by weight of the total weight of the wood pieces for the core layer, which are composed of the wood crushed pieces and the wood shavings contained in the core layer. A particle board characterized by:

5. A method for manufacturing a three-layer particle board using finer wood chips in the surface layer than in the core layer, a first crushing step of crushing the first wood material to produce a large number of wood chips; a first classification step in which the numerous wood chips are classified using a first sieve with a mesh size of 16 mm or less and a second sieve with a mesh size of 0.5 mm or more and smaller than the first sieve into numerous first wood chips that pass through the first sieve but not the second sieve, numerous second wood chips that pass through both the first and second sieves, and numerous third wood chips that do not pass through both the first and second sieves, and the first wood chips are used as wood pulverized pieces for the core layer and the second wood chips are used as wood pulverized pieces for the surface layer; a cutting step of cutting the second wood material so that the fibers are linearly exposed on the surface to produce a large number of thin wood flakes having a uniform thickness of 0.05 mm to 0.35 mm; a selection process for selecting at least one type of wood chips for the core layer from the numerous wood flakes, the numerous thin, elongated wood flakes produced by a second crushing process in which the numerous wood flakes are crushed so as to split along the fiber direction, and the numerous first to third small wood flakes obtained by a second classification process in which the numerous small wood flakes are classified using a third sieve and a fourth sieve smaller than the third sieve; a wood chip mixing step of mixing the plurality of pulverized wood chips for the core layer with the plurality of shaved wood chips for the core layer to form a plurality of wood chips for the core layer; an adhesive application step of applying an adhesive to each of the numerous surface layer wood pieces including the numerous surface layer pulverized wood pieces and the numerous core layer wood pieces; a mat-forming process in which a three-layered mat is formed by stacking the numerous adhesive-coated wood pieces for the surface layer to form a first mat, stacking the numerous adhesive-coated wood pieces for the core layer on the first mat to form a second mat, and stacking the numerous adhesive-coated wood pieces for the surface layer on the second mat to form a third mat; and a hot pressing step of subjecting the three-layered mat to hot pressing to harden the adhesives of the first to third mats, thereby forming the particle board. A method for manufacturing particle board.

6. The particle board manufacturing method according to claim 5, The cutting step, the second crushing step, and the second classification step are included in a method for manufacturing a wood board in which a large number of first small wood flakes that pass through the third sieve but do not pass through the fourth sieve are glued together in a collective state. A method for manufacturing particle board.

7. The method for manufacturing particle board according to claim 6, In the selection step, the plurality of first small wood pieces are selected as the plurality of wood cutting pieces for the core layer. A method for manufacturing particle board.

8. The method for manufacturing particle board according to claim 6, In the selection step, the second wood chips that pass through both the third and fourth sieves and the third wood chips that do not pass through both the third and fourth sieves are selected as the wood chips for the core layer. A method for manufacturing particle board.

9. In the method for manufacturing particle board according to any one of claims 5 to 8, In the wood chip mixing step, the wood chips for the core layer are mixed with the wood chips for the core layer so that the proportion of the wood chips for the core layer is 20% by weight or more and 90% by weight or less with respect to the total weight of the wood chips for the core layer. A method for manufacturing particle board.

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