Particle board and method for manufacturing particle board

Abstract

To provide a particle board that exhibits excellent screw withdrawal strength.SOLUTION: A particle board 10 has a three-layer structure, in which a middle layer 11 is a flaky cut wood piece layer comprising wood pieces 1,...,1 that consist solely of flaky cut wood pieces 3,...,3 having a thickness of 0.05-0.35 mm, and the two surface layers 12,12 are crushed wood piece layers comprising wood pieces 1,...,1 that are crushed wood pieces 2,...,2.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to particle board. [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 particleboard, which is made by applying adhesive to crushed wood chips and piling them into a mat shape and hot pressing them with a hot platen, is used as an alternative to plywood. Particleboard can be made from waste materials and recycled materials, and since wood can be used without waste by changing the size of the crushed wood chips used in the core layer and surface layer, it is an excellent alternative to plywood in that it can be made 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 particle board uses finely crushed pieces, there is a problem that it lacks screw pull-out strength when used as a replacement for structural plywood used as a load-bearing base material for load-bearing walls and the like.

[0006] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a particle board having excellent screw pull-out strength. [Means for solving the problem]

[0007] In order to achieve the above object, in the present invention, the particle board has a multi-layer structure, and at least one layer is constructed as a wood shavings layer that contains only extremely thin wood shavings as wood pieces.

[0008] Specifically, the first invention is premised on a particle board having a multi-layer structure in which a large number of wood pieces are glued together in a collective state.

[0009] The first invention is characterized in that at least one layer is a wood cuttings layer containing only wood cuttings having a thickness of 0.05 to 0.35 mm as the wood pieces, and the layers other than the wood cuttings layer are wood ground pieces layers containing wood ground pieces as the wood pieces.

[0010] In the first invention, the particle board has a multi-layer structure, and at least one layer is a wood chip layer containing only extremely thin wood chips with a thickness of 0.05 to 0.35 mm. Thin wood chips have a larger area than granular wood chips obtained by crushing a wood material. Therefore, by forming at least one layer from the wood chip layer, screws are less likely to come out than in particle boards composed only of wood chips. Therefore, according to the first invention, a particle board with excellent screw pull-out strength (wood screw holding power) can be provided, and the particle board can be used as a substitute for structural plywood used in load-bearing base materials.

[0011] The second invention is characterized in that, in the first invention, it has two surface layers and at least one intermediate layer provided between the two surface layers, and the surface layers are the wood shavings layer.

[0012] In the second aspect of the present invention, the two surface layers are made of wood chip layers. This configuration makes it possible to provide a particle board that has excellent pull-out strength even when screws are driven into the particle board from either side in the thickness direction.

[0013] Furthermore, according to the second invention, a large number of extremely thin wood shavings are folded over the surface of the particle board, which makes it difficult for unevenness to occur on the surface, resulting in excellent surface properties (smoothness).

[0014] In addition, in the second invention, the two surface layers are made of a wood chip layer in which many extremely thin wood chips are folded and glued together, which makes it more difficult for water to penetrate inside than conventional particle boards that are made only of a ground wood chip layer made of granular ground wood chips. In other words, the second invention makes it possible to provide a particle board that has excellent water resistance as well as screw pull-out strength.

[0015] Meanwhile, the inventors of the present application conducted a test to verify the effect of forming the two surface layers of a multi-layered particleboard from a wood shavings layer that contains only extremely thin wood shavings with a thickness of 0.05 to 0.35 mm as wood pieces. As a result, it was found that the particleboard whose surface layer is formed from a wood shavings layer has improved normal bending strength (MOR), wet bending strength (wetMOR), water absorption length change rate (LE), wood screw holding strength (WS) and peel strength (IB) compared to a conventional particleboard whose surface layer is formed from a ground wood piece layer.

[0016] In conventional multi-layer particle boards, the surface layer is made of finely ground wood chips to improve the surface properties, but such a structure results in a lower bending strength than single-layer particle boards. Therefore, it is possible to ensure a certain degree of bending strength in multi-layer particle boards by increasing the density of the surface layer, but increasing the density of the surface layer creates problems such as increased weight and increased use of adhesive.

[0017] In contrast, in the second invention, rather than increasing the density of the two surface layers, the wood pieces that make up the two surface layers are changed from crushed wood chips to shaved wood chips, thereby improving bending strength without increasing cost and weight.

[0018] As described above, according to the second invention, it is possible to provide a multi-layer particle board that is excellent not only in screw pull-out strength but also in surface properties, water resistance, bending strength and peel strength, and that exhibits little dimensional change, without increasing cost or weight.

[0019] The third invention is characterized in that, in the first invention, it has two surface layers and at least one intermediate layer provided between the two surface layers, and at least one of the intermediate layers is the wood shavings layer.

[0020] In the third invention, at least one of the intermediate layers is made of a wood shavings layer. With this configuration, the intermediate layer made of the wood shavings layer stably holds the screws, making them difficult to pull out. Therefore, the third invention can provide a particle board with excellent screw pull-out strength.

[0021] Meanwhile, the inventors of the present application conducted a test to verify the effect of forming at least one intermediate layer of a multi-layered particleboard from a wood shavings layer that contains only extremely thin wood shavings with a thickness of 0.05 to 0.35 mm as wood chips. As a result, it was found that a particleboard having at least one intermediate layer formed from a wood shavings layer has improved normal bending strength (MOR), wet bending strength (wetMOR), water thickness swelling rate (TS), water length change rate (LE), wood screw holding strength (WS) and peel strength (IB) compared to a conventional particleboard in which all intermediate layers are formed from pulverized wood chip layers.

[0022] In conventional multi-layer particle boards, the surface layer is made of finely ground wood chips to improve the surface properties, but such a structure results in a lower bending strength than single-layer particle boards. Therefore, it is possible to ensure a certain degree of bending strength in multi-layer particle boards by increasing the density of the surface layer, but increasing the density of the surface layer creates problems such as increased weight and increased use of adhesive.

[0023] In contrast, in the third invention, rather than increasing the density of the surface layer, the wood pieces constituting at least one intermediate layer are changed from crushed wood chips to shaved wood chips, thereby making it possible to improve bending strength without increasing cost and weight.

[0024] As described above, according to the third invention, a multi-layer particle board that is excellent not only in screw pull-out strength but also in bending strength and peel strength and that exhibits little dimensional change can be provided without increasing cost or weight.

[0025] A fourth invention is the second invention, characterized in that at least one of the intermediate layers is the wood shavings layer.

[0026] In the fourth aspect of the present invention, not only the two surface layers but also at least one of the middle layers is made of wood chip layers. With this configuration, a particle board with even better screw pull-out strength can be provided.

[0027] A fifth aspect of the present invention is the third aspect of the present invention, characterized in that the intermediate layer, which is the wood cuttings layer, is provided in plurality.

[0028] According to the fifth aspect of the present invention, by providing a plurality of intermediate layers which are layers of wood shavings, it is possible to provide a particle board which is superior in screw pull-out strength.

[0029] A sixth invention is any one of the second to fifth inventions, characterized in that at least one of the ground wood chip layers is a mixed layer containing a large number of the wood cuttings.

[0030] In the sixth invention, at least one of the wood shavings layers is a mixed layer containing a large number of wood shavings. A mixed layer containing wood shavings has higher rigidity than a non-mixed layer that does not contain wood shavings and is composed only of granular wood shavings, and the wood pieces can be bonded together with a small amount of adhesive. Therefore, with the particle board, the amount of adhesive used can be reduced while maintaining bending strength.

[0031] The seventh invention is characterized in that, in any one of the second to fifth inventions, at least one of the wood fragment layers is a mixed layer containing a large number of the wood cuttings, and the mixed layer is provided between the wood fragment layer and a non-mixed layer that does not contain the wood cuttings.

[0032] In the seventh aspect of the present invention, a mixed layer containing wood crushed chips and wood cuttings is provided between a non-mixed layer containing only wood crushed chips as wood chips and a wood cuttings layer containing only wood cuttings as wood chips. By providing a mixed layer between the non-mixed layer and the wood cuttings layer in this way, the difference in size of the wood chips (wood crushed chips, wood cuttings) between the layers is reduced, and peeling between the layers can be suppressed.

[0033] The eighth invention is characterized in that, in the first invention, the wood cutting pieces are produced from the wood material during the formation of a wood board, which is made by gluing together a large number of first small wood flakes selected by classification from a large number of small wood flakes obtained by cutting a wood material and grinding a large number of wood flakes having a thickness of 0.05 to 0.35 mm.

[0034] The ninth invention is characterized in that, in the second invention, the wood cutting pieces are produced from the wood material when a wood board is formed by gluing together a large number of first small wood flakes selected by classification from a large number of small wood flakes obtained by cutting a wood material and crushing a large number of wood flakes having a thickness of 0.05 to 0.35 mm, and that the wood cutting pieces used for at least the surface layer are other than the first small wood flakes selected by classification from the small wood flakes.

[0035] In the eighth and ninth inventions, wood shavings are produced when wood materials are processed to form other wood boards. Therefore, even if a material (wood shavings) different from the material (crushed wood chips) used in normal particle boards is used to improve the screw pull-out strength, it can be easily procured because the different material is the one produced during the processing of materials for other wood boards. Therefore, according to the eighth and ninth inventions, particle boards with excellent screw pull-out strength can be provided easily and at a relatively low cost.

[0036] In particular, in the eighth invention, the wood chips contained in at least the surface layer are other than the first small wood chips selected by classifying the small wood chips. In this way, by using waste wood that is generated during the formation of other wood boards and is not used for other wood boards as the wood chips for the surface layer of the particle board, the particle board can be formed more inexpensively. In addition, since the wood material of other wood boards is used without waste, it leads to effective use of wood resources. Effect of the Invention

[0037] As described above, according to the present invention, a particle board has a multi-layer structure in which at least one layer is a wood shavings layer that contains only extremely thin wood shavings as wood pieces, thereby making it possible to provide a particle board with excellent screw pull-out strength. [Brief description of the drawings]

[0038] [Figure 1] FIG. 1 is a cross-sectional view showing a part of the particle board according to the first embodiment. [Diagram 2] FIG. 2 is a diagram showing the process of producing ground wood pieces. [Diagram 3] FIG. 3 is a diagram showing the process of producing wood cutting pieces. [Figure 4] FIG. 4 is an enlarged perspective view showing a first small wood piece. [Diagram 5] FIG. 5 is a diagram showing the manufacturing process of particle board. [Figure 6] FIG. 6 is a partially enlarged cross-sectional view showing in comparison the mat before the hot pressing step and the particle board formed after the hot 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 is a cross-sectional view showing a part of the particle board according to the third embodiment. [Figure 10] FIG. 10 is a cross-sectional view showing a part of the particle board according to the fourth embodiment. [Figure 11] FIG. 11 is a cross-sectional view showing a part of the particle board according to the fifth embodiment. [Figure 12] FIG. 12 shows the results of an experiment to verify the effects of the fifth embodiment. [Figure 13] FIG. 13 is a cross-sectional view showing a part of the particle board according to the sixth embodiment. [Figure 14] FIG. 14 is a cross-sectional view showing a part of the particle board according to the seventh embodiment. [Figure 15] FIG. 15 is a cross-sectional view showing a part of the particle board according to the eighth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. The following description of the embodiments is merely illustrative in nature and is not intended to limit the present invention, its application, or its uses.

[0040] First Embodiment of the Invention -Composition of particle board- 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.

[0041] Particleboard 10 is made up of numerous wood pieces 1, ..., 1 glued together in a collected state. Particleboard 10 contains numerous wood pieces 1, ..., 1 and an adhesive. The feature of the present invention lies in the constituent material (wood pieces 1) of particleboard 10, and there are no particular limitations on the thickness or density, but particleboard 10 may, for example, have a thickness of 3 mm to 25 mm and a density of 500 kg / m 3 More than 800kg / m 3 It is configured as follows:

[0042] <Wood piece> In this embodiment 1, the numerous wood pieces 1, ..., 1 that make up the particle board 10 are made up of numerous crushed wood pieces 2, ..., 2 and numerous shaved wood pieces 3, ..., 3. The particle board 10 has a three-layer structure, including a middle layer 11 and two surface layers 12, 12 that sandwich the middle layer 11 and form the surface. The middle layer 11 and the surface layers 12 differ in the configuration of the wood pieces 1, ..., 1 that they contain.

[0043] The surface layer 12 contains many wood shavings 2, ..., 2 as wood pieces 1, ..., 1, as in a normal particle board, while the middle layer 11 contains many wood shavings 3, ..., 3 as wood pieces 1, ..., 1. That is, in the present embodiment 1, the middle layer 11 is configured as a wood shavings layer in which the wood pieces 1, ..., 1 are composed only of the wood shavings 3, ..., 3, and many wood shavings 3, ..., 3 are bonded together in a collective state. On the other hand, the surface layer 12 is configured as a wood shavings layer in which the wood pieces 1, ..., 1 are composed only of the wood shavings 2, ..., 2, and many wood shavings 2, ..., 2 are bonded together in a collective state.

[0044] In this embodiment 1, the ground wood chips 2, ..., 2 used in the surface layer 12 are the same as those used as wood chips in conventional particle boards, while the shaved wood chips 3, ..., 3 used in the middle layer 11 are the same as those used as constituent materials for another wood board 50, which will be described later. That is, in this embodiment 1, the ground wood chips 2, ..., 2 used in conventional particle boards are used as the numerous wood chips 1, ..., 1 in the surface layer 12, and the shaved wood chips 3, ..., 3 used as constituent materials for another wood board 50 are used as the numerous wood chips 1, ..., 1 in the middle layer 11.

[0045] The ground wood chips 2, . . . , 2 and shaved wood chips 3, . . . , 3 used in the particle board 10 will be described in detail below.

[0046] [Crushed wood chips] As shown in Fig. 2, the wood pulverized pieces 2, ..., 2 are obtained by pulverizing the wood material A into granules using a known pulverizing device (chipper) such as a hammer mill, a pin mill, or a jet mill. In the particle board 10 of the present embodiment 1, as shown in Fig. 2, the wood granular pieces 2a, ..., 2a obtained by pulverizing the wood material A are classified using two types of sieves, large and small, and the second wood granular pieces 2c, ..., 2c that are finer than the first wood granular pieces 2b, ..., 2b that have passed through both types of sieves are used as the wood pulverized pieces 2, ..., 2 for the surface layer 12, rather than the first wood granular pieces 2b, ..., 2b selected by classification. For example, granular pieces with a particle size (maximum diameter) of 0.5 mm or more and 5 mm or less are selected as the first wood granular pieces 2b, ..., 2b.

[0047] As shown in Figure 2, as a result of the above classification, the third wood granules 2d, ..., 2d which are coarser than the first wood granules 2b, ..., 2b and do not pass through both types of sieves are not used as wood crushed pieces 2, ..., 2 but are returned to the chipper device and crushed again.

[0048] The species of the wood material A is not particularly limited, and any species of tree can be used as the wood material A. For example, fir materials such as cedar, cypress, and Douglas fir, acacia, aspen, poplar, pine (hard pine, soft pine, radiata pine, etc.), birch, rubber (rubber tree), and the like can be used as the wood material A. In addition, domestic materials such as Abies sachalinensis, larch, Yezo spruce, sawara, hiba, kaya, tsuga, cypress, various pines, paulownia, maple, birch (white birch), shiitake, beech, oak, fir, Japanese oak, camphor, and zelkova; North American materials such as American cypress, American hiba, American cedar, American fir, spruce, American tsuga, and redwood; South Sea materials such as agathis, terminalia, lauan, meranti, junkon, chamerele, carampayan, amberoi, melina, teak, apitong, and sengon laut; and other foreign materials such as balsa, cedar, mahogany, lignum vitae, acacia mangium, Mediterranean pine, sorghum, and chamerele. In addition to logs and thinned wood, scraps and waste materials generated at construction sites, waste pallet materials, recycled materials, and the like may be used as the wood material A.

[0049] [Wood cuttings] The wood shavings 3, ..., 3 used in the intermediate layer 11 are produced from a wood material B when a wood board 50 different from the particle board 10 according to the present invention is formed. As shown in Fig. 3, the wood board 50 is produced by cutting a wood material B with a known cutting device (strander) to produce a large number of wood flakes 3a, ..., 3a having a thickness of 0.05 to 0.35 mm, which are then crushed with a known crushing device to form a large number of small wood flakes 3b, ..., 3b, which are then classified using two types of sieves, large and small, and the first small wood flakes 3c, ..., 3c selected by the classification are bonded together in an aggregated state.

[0050] In the particle board 10 of the present embodiment 1, when forming the above-mentioned wood board 50, among the many small wood flakes 3b, ..., 3b obtained by further crushing the many wood flakes 3a, ..., 3a having a thickness of 0.05 to 0.35 mm obtained by cutting the wood material B, the many first small wood flakes 3c, ..., 3c selected by classification are used as the wood cutting pieces 3, ..., 3 to be included in the intermediate layer 11. Specifically, by classifying the many small wood flakes 3b, ..., 3b using two appropriately selected large and small sieves, the many first small wood flakes 3c, ..., 3c that pass through the coarse sieve but do not pass through the fine sieve are selected. Through classification, a large number of small wood flakes 3b, ..., 3b are selected, and also second small wood flakes 3d, ..., 3d which are finer than the first small wood flakes 3c, ..., 3c which have passed through both types of sieves, and third small wood flakes 3e, ..., 3e which are coarser than the first small wood flakes 3c, ..., 3c which have not passed through both types of sieves are obtained.

[0051] 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 is an average value. Since the small wood flakes 3b are obtained by pulverizing the wood flakes 3a, the small wood flakes 3b also have the same thickness t as the wood flakes 3a.

[0052] The first small woody flakes 3c will be described in detail. As shown in an enlarged view in FIG. 4, the first small woody flakes 3c have a long and slender shape (strip shape) in which the fiber direction dimension d1 in the direction along the fibers a of vessels, tracheids, etc. is longer than the fiber orthogonal direction dimension d2 in the direction 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 or more and 20 mm or less. The width d2 is 35 mm or less, preferably 15 mm or less, and more preferably 0.5 mm or more and 5 mm or less. The length d1 and width d2 of the first small woody flakes 3c are both average values.

[0053] 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 sieves, one large and one small, as described above.

[0054] In the first embodiment, as described above, after the numerous woody flakes 3a, ..., 3a are crushed, the first small woody flakes 3c, ..., 3c selected by classification can be used as the woody shavings 3, ..., 3 in the intermediate layer 11 of the particle board 10. However, the woody flakes 3, ..., 3 constituting the intermediate layer 11 of the particle board 10 are not limited to those described above. Other than the first small woody flakes 3c, ..., 3c (the second small woody flakes 3d, ..., 3d and the third small woody flakes 3e, ..., 3e) may be used as the woody shavings 3, ..., 3 constituting the intermediate layer 11. In addition, the woody flakes 3a, ..., 3a before crushing after cutting and the numerous small woody flakes 3b, ..., 3b before classification after crushing may be used as the woody shavings 3, ..., 3 constituting the intermediate layer 11. Furthermore, all, any two, three or four of the wood flakes 3a, ..., 3a, the small wood flakes 3b, ..., 3b, the first small wood flakes 3c, ..., 3c, the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e may be combined and used as the wood cutting pieces 3, ..., 3 constituting the intermediate layer 11. In other words, at least one of the wood flakes 3a, ..., 3a, the small wood flakes 3b, ..., 3b, the first small wood flakes 3c, ..., 3c, the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e may be used as the wood cutting pieces 3, ..., 3 constituting the intermediate layer 11.

[0055] The species of the wood material B is not particularly limited, and any species of tree can be used as the wood material B. For example, fir materials such as cedar, cypress, and Douglas fir, acacia, aspen, poplar, pine (hard pine, soft pine, radiata pine, etc.), birch, rubber (rubber tree), and the like can be used as the wood material B. In addition, domestic materials such as Abies sachalinensis, larch, Yezo spruce, sawara, hiba, kaya, tsuga, cypress, various pines, paulownia, maple, birch (white birch), shiitake, beech, oak, fir, Japanese oak, camphor, and zelkova; North American materials such as American cypress, American hiba, American cedar, American fir, spruce, American tsuga, and redwood; South Sea materials such as agathis, terminalia, lauan, meranti, junkon, chamerele, carampayan, amberoi, melina, teak, apitong, and sengon laut; and other imported materials such as balsa, cedar, mahogany, lignum vitae, acacia mangium, Mediterranean pine, sorghum, and chamerele. In addition to logs and thinned wood, scraps and waste materials generated at construction sites, waste pallet materials, recycled materials, etc. may also be used as the wood material B.

[0056] The numerous wood pieces 1, . . . , 1 constituting the particle board 10 are constituted by the crushed wood pieces 2, . . . , 2 and the shaved wood pieces 3, .

[0057] 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 preferably, 300 kg / m 3 More preferably, it is 800 kg / m 3 Less than or equal to 500 kg / m 3 Less than 400 kg / m, more preferably 400 kg / m 3 Density is 250kg / m or less. 3 If the density of the wood piece 1 is less than 800 kg / m, the thickness of the mat required to form the particle board 10 having the same density and bending strength becomes large, and the pressing pressure in the hot pressing process in the press molding step must be increased. 3 However, it is difficult to obtain such a wood piece 1. 3If it is easy to obtain wood chips 1 exceeding this value, the upper limit of density is 800 kg / m 3 It is not limited to this and may be a higher value.

[0058] 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 in the hot press process in the press molding step, which may lengthen 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 in the hot press process, and furthermore, the hardening of the adhesive may be inhibited, which may reduce the bending strength.

[0059] <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.

[0060] -Manufacturing method of particle board- 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 preparation step S1, an adhesive application step S2, a mat forming step S3, and a heat pressing step S4.

[0061] <Wood piece production process S1> The wood piece producing process S1 includes a wood crushed piece producing process S11 and a wood cutting piece producing process S12.

[0062] [Wood chip production process S11] The wood pulverized piece preparation process S11 includes a material preparation process S111, a pulverization process S112, and a classification process S113.

[0063] (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 prepare wood material A. When using scraps or waste wood generated at construction sites, waste pallet materials, recycled materials, etc., cut them into short pieces to prepare wood material A.

[0064] (Crushing process S112) Next, the prepared wood material A is crushed into granules by a known crushing device (chipper) such as a hammer mill, a pin mill, a jet mill, etc. By crushing the wood material A, wood granule pieces 2a, ..., 2a are obtained.

[0065] (Classification process S113) The wood grain pieces 2a, ..., 2a obtained by crushing are classified into three sizes using two types of sieves, large and small. Specifically, the wood grain pieces 2a, ..., 2a are divided into first wood grain pieces 2b, ..., 2b of a desired particle size (for example, 0.5 mm or more and 5 mm or less) that pass through a coarse sieve but not through a fine sieve, second wood grain pieces 2c, ..., 2c that are finer than the first wood grain pieces 2b, ..., 2b that pass through both types of sieves, and third wood grain pieces 2d, ..., 2d that are coarser than the first wood grain pieces 2b, ..., 2b that do not pass through both types of sieves. The second wood grain pieces 2c, ..., 2c obtained at the same time, rather than the first wood grain pieces 2b, ..., 2b classified and selected in this way, are used as the wood crushed pieces 2, ..., 2 for the surface layer 12.

[0066] [Wood cutting piece production process S12] The wood cutting piece preparation 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 present embodiment 1, the first wood thin pieces 3c, ..., 3c generated during the formation of the wood board 50 are used as the wood cutting pieces 3, ..., 3 for the intermediate layer 11. Therefore, the wood cutting piece preparation process S12 is a part of the method for manufacturing the wood board 50.

[0067] (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 prepare wood material B. When using scraps or waste wood generated at construction sites, waste pallet materials, recycled materials, etc., cut them into short pieces to prepare wood material B.

[0068] (Cutting process S122) Next, the prepared wood material B is cut by a known cutting device (strander) of outer blade type or inner blade type to form a large number of wood flakes 3a, ..., 3a of the desired thickness t. Specifically, the direction and speed at which the wood material B is fed into the cutting device are adjusted to form a large number of wood flakes 3a, ..., 3a of the desired thickness t with fibers a appearing linearly on the surface.

[0069] In addition, by producing the wood flakes 3a, ..., 3a having a thickness t in this cutting step S122, the smaller wood flakes 3b, ..., 3b obtained in the subsequent crushing step will have a desired thickness t.

[0070] (Crushing process S123) Next, the woody flakes 3a, ..., 3a obtained by cutting are crushed using a known crushing device such as a hammer, a blade (knife flaker), a hammer mill, a pin mill, a jet mill, etc., to make them smaller than the size immediately after cutting. At this time, if the woody flakes after cutting are crushed in the width direction so as to break along the fiber direction (length direction), it is possible to create small woody flakes 3b, ..., 3b with elongated shapes. In other words, if a force (impact) is applied to the woody flakes 3a, ..., 3a along the fiber orthogonal direction perpendicular to the fiber direction, they are difficult to break, but if a force is applied parallel to the fiber direction, they are easily broken. Even if the woody flakes 3a, ..., 3a are curled, they are divided into flat shapes by crushing. The direction of the force applied to the woody flakes 3a, ..., 3a is not limited to the direction parallel to the fiber direction. If a force is applied to the woody flakes 3a, ..., 3a in a random direction, the woody flakes 3a, ..., 3a usually break from the part where the force is weak (they are easily broken in the direction of the weak force). Since the force connecting each fiber of the wood flakes 3a, ..., 3a (force perpendicular to the fibers) is overwhelmingly weaker than the force in the fiber direction, if the wood flakes 3a, ..., 3a are crushed in random directions using the above-mentioned crushing device (force is applied), the wood flakes 3a, ..., 3a will split along the fiber direction and shorten in the direction perpendicular to the fibers, resulting in small, elongated wood flakes 3b, ..., 3b.

[0071] Furthermore, even if the wood flakes 3a, . . . , 3a contain knots, the knots are more brittle than other parts, so the knots are turned into powder by crushing and are removed in the subsequent classification process.

[0072] In this way, by adding the crushing step S123 after the cutting step S122 rather than using only one cutting step S122, a two-step processing process can be carried out, making it possible to easily produce small, knot-free, high-strength wood flakes 3b, ..., 3b of the required size.

[0073] (Classification process S124) The woody small flakes 3b, ..., 3b obtained by crushing are classified into three sizes using two types of sieves, large and small. Specifically, the woody small flakes 3b, ..., 3b are divided into first woody small flakes 3c, ..., 3c of desired size that pass through a coarse sieve but not through a fine sieve, second woody small flakes 3d, ..., 3d that are finer than the first woody small flakes 3c, ..., 3c that pass through both types of sieves, and third woody small flakes 3e, ..., 3e that are coarser than the first woody small flakes 3c, ..., 3c that do not pass through both types of sieves. The first woody small flakes 3c, ..., 3c classified and selected in this way are used as woody cutting pieces 3, ..., 3 for the intermediate layer 11.

[0074] In the wood piece production process S1, wood pieces 1, ..., 1 (first wood thin pieces 3c, ..., 3c) for the intermediate layer 11 and wood pieces 1, ..., 1 (second wood granular pieces 2c, ..., 2c) for the surface layer 12 are produced through the above-mentioned wood crushed piece production process S11 and wood shavings production process S12.

[0075] <Adhesive application process S2> The wood pieces 1, ..., 1 for the intermediate layer 11 and the wood pieces 1, ..., 1 for the surface layer 12 produced in the wood piece production process S1 are each carried into an adhesive applicator to apply adhesive. As the adhesive, for example, an isocyanate-based adhesive can be used, and other adhesives such as amine-based adhesives such as phenolic resin, urea resin, and melamine resin, and natural wood (tannin)-based adhesives may also be used. A commonly used water repellent may also be used together with the adhesive.

[0076] <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 is applied are piled up in a state of being gathered 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 intermediate layer 11 to which adhesive is applied are piled up on the first mat 9a in a state of being gathered 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 is applied are piled up on the second mat 9b in a state of being gathered 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 mat 9 having a three-layer structure is formed.

[0077] At this time, the thicknesses of the first to third mats 9a to 9c are adjusted to obtain the desired ratio of thickness of the intermediate layer 11 and each of the surface layers 12 to the entire particleboard 10. For example, when forming a particleboard 10 having a thickness of 9 mm in which the thickness of the surface layer 12 accounts for 15% of the entire particleboard 10 (surface layer 12: intermediate 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 become the surface layers 12 is about 13.5 mm, and the thickness (height) of the second mat 9b that will become the intermediate layer 11 is about 63 mm.

[0078] <Heat pressure process S4> The mat 9 formed in the mat forming process S3 is carried into a hot press device and set between hot platens, where the mat 9 is hot pressed and compressed at a predetermined pressure and temperature by the hot press device. 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 Fig. 6 is formed.

[0079] At this time, as shown in FIG. 6, the above-mentioned mat 9 having a thickness of about 90 mm is compressed, for example, into a particle board 10 having a thickness of 9 mm, and the thickness is compressed to 1 / 10. The pressing temperature in the hot press process is not particularly limited, but is, for example, 160 to 220° C. The pressing pressure in the hot press 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 process using a heating device may be performed prior to the hot pressing process using the hot pressing device.

[0080] -Effects of embodiment 1- In the first embodiment, the particle board 10 has a multi-layer structure (three-layer structure), and at least one layer is composed of a wood chip layer containing only very thin wood chips 3, ..., 3 with a thickness of 0.05 to 0.35 mm as the wood chips 1, ..., 1. The flaky wood chips 3, ..., 3 have a larger area than the granular wood chips 2, ..., 2 obtained by crushing the wood material A. Therefore, by forming at least one layer from the wood chip layer, screws are less likely to come out than in the particle board 10 composed only of the wood chips 2, ..., 2. Therefore, according to the first embodiment, a particle board 10 with excellent screw pull-out strength (wood screw holding power) can be provided, and the particle board 10 can be used as a substitute for structural plywood used in load-bearing base materials.

[0081] Moreover, in this embodiment 1, the intermediate layer 11 is composed of a wood shavings layer. With this configuration, the intermediate layer 11 made of the wood shavings layer stably holds the screws, making them difficult to pull out. Therefore, this embodiment 1 can provide a particle board 10 with excellent screw pull-out strength.

[0082] In addition, in this embodiment 1, the wood shavings 3, ..., 3 produced when the wood material B is processed to form the other wood board 50 are used as the wood shavings 3, ..., 3 for the intermediate layer 11. Therefore, even if a material (wood shavings 3, ..., 3) different from the material (ground wood chips 2, ..., 2) used in the normal particle board 10 is used to improve the screw pull-out strength, it can be easily procured because the different material is the one produced during the material processing of the other wood board 50. Therefore, according to this embodiment 1, a particle board 10 with excellent screw pull-out strength can be provided easily and at a relatively low cost.

[0083] In particular, in the first embodiment, when the wood cutting pieces 3, ..., 3 contained in the intermediate layer 11 are other than the first small wood flakes 3c, ..., 3c selected by classifying the small wood flakes 3b, ..., 3b, waste material that is generated during the formation of the other wood boards 50 and is not used for the other wood boards 50 is used, so the particle board 10 can be formed more inexpensively. Also, since the wood material B of the other wood boards 50 is used without waste, this leads to effective use of wood resources.

[0084] As described later, the inventors of the present application conducted tests to verify the effects of constructing the intermediate layer 11 of the particleboard 10 with a wood shavings layer that contains only wood shavings 3, ..., 3 with a thickness of 0.05 to 0.35 mm as the wood pieces 1, ..., 1. As a result, it was found that the particleboard 10 having the intermediate layer 11 constructed with the wood shavings layer has improved normal bending strength (MOR), wet bending strength (wetMOR), water absorption thickness swelling rate (TS), water absorption length change rate (LE), wood screw holding strength (WS) and peel strength (IB) compared to a conventional particleboard having an intermediate layer not constructed with a wood shavings layer.

[0085] In conventional three-layer particleboards, the surface layer is made of finely ground wood chips to improve the surface quality, but this structure results in lower bending strength compared to single-layer particleboards. Therefore, it is possible to ensure a certain degree of bending strength in conventional three-layer particleboards by increasing the density of the surface layer, but increasing the density of the surface layer creates problems such as increased weight and increased use of adhesive.

[0086] In contrast, in the first embodiment, the density of the surface layer is not increased, and the wood pieces 1, ..., 1 constituting the middle layer 11 of the particle board 10 having a three-layer structure are composed of many thin wood shavings 3, ..., 3 having a larger area than the wood shavings 2, ..., 2, instead of granular wood pulverized pieces 2, ..., 2. With this configuration, the particle board 10 according to the first embodiment has a higher bending strength of the middle layer 11 than conventional particle boards. Therefore, even if the surface layer 12 is composed of wood pulverized pieces 2, ..., 2 having small grain size in order to improve the surface property (smoothness), 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, and the bending strength can be improved without increasing the cost and weight. Furthermore, compared to when the middle layer 11 is composed of wood pulverized pieces 2, ..., 2, the thin wood shavings 3, ..., 3 can be bonded and integrated with a small amount of adhesive. Therefore, according to the particle board 10 of the first embodiment, it is possible to reduce the amount of adhesive used while ensuring bending strength.

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

[0088] As described above, according to this embodiment 1, a particle board 10 having a laminated structure that is excellent not only in screw pull-out strength but also in surface properties, bending strength, and peel strength, and that has little dimensional change, can be provided without increasing cost or weight.

[0089] -Verification of effectiveness- In order to verify the above-mentioned effect of forming the intermediate layer 11 of the particleboard 10 from a wood shavings layer containing only wood shavings 3, ..., 3 with a thickness of 0.05 to 0.35 mm as the wood pieces 1, ..., 1, the inventors of the present application prepared a test specimen X0 in which the intermediate layer 11 was formed from a wood shavings layer containing only a large number of wood shavings 2, ..., 2 as the wood pieces 1, ..., 1, as in the case of a conventional particleboard, and a test specimen X1 in which the intermediate layer 11 was formed from a wood shavings layer in which a large number of wood shavings 3, ..., 3 were bonded together in a collective state, and the test specimens were measured according to JIS A5908 and JIS According to A5905, bending strength test, wet bending strength test, water absorption thickness swelling rate test, water absorption length change rate test, wood screw holding strength test, and peel strength test were performed to determine normal bending strength (MOR), wet bending strength (wetMOR), water absorption thickness swelling rate (TS), water absorption length change rate (LE), wood screw holding strength (WS), and peel strength (IB), with the results shown in Fig. 7. The specimen X1 has the same structure as the particleboard 10 of the first embodiment. Fig. 7 also shows the results of each test of specimen X1 in relative proportion to the results of each test of specimen X0, which are set to 100.

[0090] As shown in FIG. 7, the particle board 10 (specimen X1) in which the intermediate layer 11 is composed of wood shavings 3, ..., 3 has improved modulus of resistance (MOR) and wet MOR compared to the conventional particle board (specimen X0) in which the intermediate layer 11 is composed of ground wood chips 2, ..., 2. The wet MOR was improved by a remarkable 67%.

[0091] In addition, with regard to dimensional change, the particleboard 10 (specimen X1) in which the intermediate layer 11 is composed of wood shavings 3, ..., 3 showed a decrease (improvement) in both water absorption thickness expansion rate (TS) and water absorption length change rate (LE) compared to the conventional particleboard (specimen X0) in which the intermediate layer 11 is composed of ground wood chips 2, ..., 2, and the water absorption length change rate (LE) improved significantly by 38%.

[0092] In addition, with regard to the wood screw holding strength (WS), the particle board 10 (specimen X1) in which the middle layer 11 was composed of wood shavings 3, ..., 3 showed a significant improvement of 40% compared to the conventional particle board (specimen X0) in which the middle layer 11 was composed of ground wood chips 2, ..., 2.

[0093] Furthermore, in terms of peel strength (IB), the particle board 10 (specimen X1) in which the middle layer 11 was composed of wood shavings 3, ..., 3 showed a significant improvement of 99% compared to the conventional particle board (specimen X0) in which the middle layer 11 was composed of ground wood chips 2, ..., 2.

[0094] As described above, the particleboard 10 (specimen X1) in which the intermediate layer 11 is made of the wood shavings 3, ..., 3 has higher (improved) bending strength under normal conditions (MOR), wet bending strength (wetMOR), wood screw holding power (WS) and peel strength (IB) than the conventional particleboard (specimen X0) in which the intermediate layer 11 is made of the wood crushed pieces 2, ..., 2. The results show that by making the intermediate layer 11 of the particleboard 10 of the particleboard 10 of the wood shavings layer containing only the wood shavings 3, ..., 3 having a thickness of 0.05 to 0.35 mm as the wood pieces 1, ..., 1, it is possible to provide a particleboard 10 that has excellent surface properties like the conventional ones, excellent bending strength and peel strength as well as screw pull-out strength, and small dimensional change without increasing cost and weight.

[0095] Second Embodiment of the Invention The particle board 10 according to the second embodiment is a part of the particle board 10 according to the first embodiment, with the structure changed. Specifically, as shown in Fig. 8, in the particle board 10 according to the second embodiment, the surface layer 12 formed of the ground wood chip layer contains wood shavings 3, ..., 3. That is, in the second embodiment, the surface layer 12 contains not only a large number of ground wood chips 2, ..., 2, but also a large number of ground wood chips 3, ..., 3 as wood chips 1, ..., 1. That is, in the second embodiment, the surface layer 12 is a ground wood chip layer formed by bonding and integrating a large number of ground wood chips 2, ..., 2 in a collective state, and is formed as a mixed layer containing a large number of ground wood chips 3, ..., 3.

[0096] The wood cutting pieces 3, ..., 3 used for the surface layer (mixed layer) 12 are wood flakes 3b, ..., 3b formed by cutting and crushing the wood material B to form the wood board 50, which are not classified for use in the wood board 50 (second wood flakes 3d, ..., 3d and third wood flakes 3e, ..., 3e).

[0097] The wood cutting pieces 3, ..., 3 constituting the surface layer (mixed layer) 12 are not limited to those described above. The first small wood slices 3c, ..., 3c used in the wood board 50 may be used as the wood cutting pieces 3, ..., 3 constituting the surface layer (mixed layer) 12. Also, the wood slices 3a, ..., 3a before grinding after cutting or the many small wood slices 3b, ..., 3b before classification after grinding may be used as the wood cutting pieces 3, ..., 3 constituting the surface layer (mixed layer) 12. Furthermore, all or any two, three or four of the wood slices 3a, ..., 3a, the small wood slices 3b, ..., 3b, the first small wood slices 3c, ..., 3c, the second small wood slices 3d, ..., 3d and the third small wood slices 3e, ..., 3e may be used as the wood cutting pieces 3, ..., 3 constituting the surface layer (mixed layer) 12. In other words, at least one of the wood flakes 3a, ..., 3a, the small wood flakes 3b, ..., 3b, the first small wood flakes 3c, ..., 3c, the second small wood flakes 3d, ..., 3d, and the third small wood flakes 3e, ..., 3e can be used as the wood cutting pieces 3, ..., 3 that constitute the surface layer (mixed layer) 12.

[0098] The other configurations are the same as those in the first embodiment.

[0099] The method for producing the particle board 10 differs from that of the first embodiment only in that the wood piece producing step S1 includes a wood piece mixing step S13, and the other steps are the same as those of the first embodiment.

[0100] [Wood piece mixing process S13] In the wood piece mixing process S13, a large number of ground wood chips 2, ..., 2 (second wood granular chips 2c, ..., 2c) for the surface layer (mixed layer) 12 produced in the ground wood chip production process and a large number of wood cutting chips 3, ..., 3 (second small wood chips 3d, ..., 3d and third small wood chips 3e, ..., 3e) for the surface layer (mixed layer) 12 produced in the wood cutting chip production process are mixed to a desired mixing ratio (the wood cutting chips 3, ..., 3 relative to the total weight of the wood chips 1, ..., 1 is 10 to 90% by weight).

[0101] In the wood piece production process S1 of embodiment 2, wood pieces 1, ..., 1 (first small wood flakes 3c, ..., 3c) for the intermediate layer 11 and wood pieces 1, ..., 1 (a mixture of second wood granular pieces 2c, ..., 2c and second small wood flakes 3d, ..., 3d and third small wood flakes 3e, ..., 3e) for the surface layer (mixed layer) 12 are produced by the same wood crushed piece production process S11 and wood shavings production process S12 as in embodiment 1, and the above-mentioned wood piece mixing process S13.

[0102] The second embodiment can achieve the same effect as the first embodiment. In the second embodiment, the intermediate layer 11 is not only made of the wood cuttings 3, ..., 3, but also the surface layer 12, which is a wood pulverized chip layer containing the wood pulverized chips 2, ..., 2, is made of a mixed layer containing the wood cuttings 3, ..., 3. The mixed layer containing the wood cuttings 3, ..., 3 has higher rigidity than a non-mixed layer containing only the granular wood pulverized chips 2, ..., 2 and not containing the wood cuttings 3, ..., 3, and can bond and integrate the wood pieces 1, ..., 1 with a small amount of adhesive. Therefore, the particle board 10 of the second embodiment can reduce the amount of adhesive used while maintaining bending strength.

[0103] Furthermore, in the particle board 10 of the second embodiment, the extremely thin wood shavings 3, ..., 3 having a thickness of 0.05 to 0.35 mm get into the gaps between the relatively fine wood pulverized pieces 2, ..., 2 (second wood granular pieces 2c, ..., 2c) in the surface layer 12, making it difficult for unevenness to occur on the surface. In particular, if the thin wood shavings 3, ..., 3 are folded over on the surface of the particle board 10, the surface becomes smoother and has excellent surface properties (smoothness).

[0104] As described above, according to the second embodiment, a particle board 10 having superior surface properties and bending strength compared to the first embodiment can be provided without increasing costs and weight.

[0105] Furthermore, in the particle board 10 according to the second embodiment, the surface layer 12 contains wood shavings 3, ..., 3, which makes it more difficult for screws to come out than in the first embodiment. Therefore, the second embodiment can provide a three-layer particle board 10 that is not only excellent in surface properties and bending strength, but also has excellent screw pull-out strength (wood screw holding power).

[0106] In addition, according to the particle board 10 of the second embodiment, if the surface layer 12 is formed only of the ground wood chips 2, ..., 2, many gaps are formed between the ground wood chips 2, ..., 2, but since the flaky wood cutting chips 3, ..., 3 are mixed in, the flaky wood cutting chips 3, ..., 3 enter the many gaps, making the gaps smaller and fewer. Therefore, the particle board 10 of the second embodiment is less susceptible to moisture penetration than a conventional particle board made only of granular ground wood chips. In other words, according to the second embodiment, a particle board 10 that is excellent not only in surface properties, bending strength, and screw pull-out strength, but also in water resistance, can be provided without increasing cost and weight.

[0107] Furthermore, in conventional particle boards made only of granular wood fragments, the wood fragments are crushed during press molding, and when moisture penetrates into the interior, the wood fragments are easily absorbed, which may result in large dimensional changes (changes in length and thickness). In contrast, the particle board 10 of the second embodiment has a structure that makes it difficult for moisture to penetrate into the interior compared to conventional particle boards, as described above, so that the dimensions (length and thickness) do not change significantly due to absorption of moisture. In other words, according to the second embodiment, a particle board 10 that is excellent in surface properties, bending strength, screw pull-out strength, and water resistance and has small dimensional changes can be provided without increasing costs and weight.

[0108] In the second embodiment, the wood chips 3, ..., 3 to be included in the surface layer 12 are selected from the small wood chips 3b, ..., 3b and classified to be other than the first small wood chips 3c, ..., 3c (the second small wood chips 3d, ..., 3d and the third small wood chips 3e, ..., 3e). In this way, the particle board 10 can be formed more inexpensively by using the waste material that is not used in the other wood boards 50 and is generated during the formation of the other wood boards 50 as the wood chips 3, ..., 3 for the surface layer 12. In addition, the wood material B of the other wood boards 50 is used without waste, which leads to effective use of wood resources.

[0109] Third Embodiment of the Invention The particle board 10 according to the third embodiment is obtained by modifying a part of the configuration of the particle board 10 according to the first embodiment.

[0110] Specifically, as shown in Fig. 9, the particle board 10 of the third embodiment has three intermediate layers 11a-11c and two surface layers 12, 12 that sandwich the three intermediate layers 11a-11c and form the surface. That is, in the third embodiment, the particle board 10 has three intermediate layers and is configured as a five-layer structure.

[0111] The three intermediate layers 11a to 11c are composed of first to third intermediate layers 11a to 11c laminated in order between two surface layers 12, 12. The first and third intermediate layers 11a, 11c have the same configuration, while the second intermediate layer 11b has a different configuration from the first and third intermediate layers 11a, 11c.

[0112] Specifically, the second intermediate layer 11b is configured with wood pieces 1, ..., 1 consisting only of wood cutting pieces 3, ..., 3, as in the intermediate layer 11 of the first embodiment. On the other hand, the first and third intermediate layers 11a, 11c are configured with wood pieces 1, ..., 1 consisting of a mixture of wood pulverized pieces 2, ..., 2 and wood cutting pieces 3, ..., 3. That is, the second intermediate layer 11b is configured as a wood cutting piece layer in which a large number of wood cutting pieces 3, ..., 3 are bonded together in a collective state, and the first and third intermediate layers 11a, 11c are configured as a mixed layer containing a large number of wood cutting pieces 3, ..., 3, which is a wood pulverized piece layer in which a large number of wood pulverized pieces 2, ..., 2 are bonded together in a collective state.

[0113] In the third embodiment, the first and third intermediate layers 11a, 11c, which are mixed layers, are provided between the two surface layers 12, 12, which are wood pulverized chip layers (non-mixed layers) that do not contain a large number of wood shavings 3, ..., 3, and the second intermediate layer 11b, which is a wood shavings layer. In other words, a mixed layer (the first and third intermediate layers 11a, 11c) consisting of a mixture of the wood pulverized chips 2, ..., 2 and the wood shavings 3, ..., 3 is provided between the non-mixed layer (surface layer 12) consisting of only the wood pulverized chips 2, ..., 2, and the wood shavings layer (the second intermediate layer 11b) consisting of only the wood shavings 3, ..., 3.

[0114] The first and third intermediate layers (mixed layers) 11a, 11c use first wood granules 2b, ..., 2b as the ground wood pieces 2, ..., 2 which are coarser than the second wood granules 2c, ..., 2c used as the ground wood pieces 2, ..., 2 for the surface layer 12.

[0115] In addition, the first and third intermediate layers (mixed layers) 11a, 11c use, as wood cutting pieces 3, ..., 3, the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e, which are not classified and are not used for the wood board 50, among the small wood flakes 3b, ..., 3b formed by cutting and crushing the wood material B to form the wood board 50.

[0116] The wood cutting pieces 3, ..., 3 constituting the first and third intermediate layers (mixed layers) 11a, 11c are not limited to those described above. The first small wood pieces 3c, ..., 3c used in the wood board 50 may be used as the wood cutting pieces 3, ..., 3 constituting the first and third intermediate layers (mixed layers) 11a, 11c. Also, the wood cutting pieces 3a, ..., 3a before crushing after cutting or the numerous small wood pieces 3b, ..., 3b before classification after crushing may be used as the wood cutting pieces 3, ..., 3 constituting the first and third intermediate layers (mixed layers) 11a, 11c. Furthermore, all or any two, three or four of the woody flakes 3a, ..., 3a, the small woody flakes 3b, ..., 3b, the first small woody flakes 3c, ..., 3c, the second small woody flakes 3d, ..., 3d and the third small woody flakes 3e, ..., 3e may be combined and used as the woody cutting pieces 3, ..., 3 constituting the first and third intermediate layers (mixed layers) 11a, 11c. In other words, at least one of the woody flakes 3a, ..., 3a, the small woody flakes 3b, ..., 3b, the first small woody flakes 3c, ..., 3c, the second small woody flakes 3d, ..., 3d and the third small woody flakes 3e, ..., 3e may be used as the woody cutting pieces 3, ..., 3 constituting the first and third intermediate layers (mixed layers) 11a, 11c.

[0117] As described above, the second intermediate layer 11b is configured similarly to the intermediate layer 11 of embodiment 1, and the surface layer 12 is configured similarly to the surface layer 12 of embodiment 1. The other configurations are the same as those of embodiment 1.

[0118] The manufacturing method of the particle board 10 differs from that of embodiment 1 in that the wood piece production process S1 includes a wood piece mixing process S13, and the adhesive application process S2 and the mat forming process S3 differ from those of embodiment 1, but the other processes are similar to those of embodiment 1.

[0119] [Wood piece mixing process S13] In the wood piece mixing process S13, a large number of ground wood pieces 2, ..., 2 (first wood granular pieces 2b, ..., 2b) for the first and third intermediate layers (mixed layers) 11a, 11c produced in the ground wood piece production process S11 and a large number of wood cutting pieces 3, ..., 3 (second small wood pieces 3d, ..., 3d and third small wood pieces 3e, ..., 3e) for the first and third intermediate layers (mixed layers) 11a, 11c produced in the wood cutting piece production process S12 are mixed to a desired mixing ratio (the wood cutting pieces 3, ..., 3 relative to the total weight of the wood pieces 1, ..., 1 is 10 to 90% by weight).

[0120] In the wood piece production process S1 of embodiment 3, the same wood crushed piece production process S11 and wood shavings production process S12 as in embodiment 1 and the above-mentioned wood piece mixing process S13 are carried out to produce wood pieces 1, ..., 1 for the first and third intermediate layers (mixed layers) 11a, 11c (a mixture of first wood granular pieces 2b, ..., 2b and second small wood pieces 3d, ..., 3d and third small wood pieces 3e, ..., 3e), wood pieces 1, ..., 1 for the second intermediate layer 11b (first small wood pieces 3c, ..., 3c), and wood pieces 1, ..., 1 for the surface layer 12 (second wood granular pieces 2c, ..., 2c).

[0121] <Adhesive application process S2> In embodiment 3, wood pieces 1, ..., 1 for the first and third intermediate layers (mixed layers) 11a, 11c, wood pieces 1, ..., 1 for the second intermediate layer 11b, and wood pieces 1, ..., 1 for the surface layer 12, which are prepared in the wood piece preparation process S1, are each transported to an adhesive application device and adhesive is applied thereto.

[0122] <Mat forming process S3> In the third embodiment, to form a particleboard 10 having a five-layer structure, wood pieces 1,...,1 for the surface layer 12 (non-mixed layer), wood pieces 1,...,1 for the first middle layer (mixed layer) 11a, wood pieces 1,...,1 for the second middle layer 11b (wood cutting piece layer), wood pieces 1,...,1 for the third middle layer (mixed layer) 11c, and wood pieces 1,...,1 for the surface layer 12 (non-mixed layer) are piled up in this order in a state where they are gathered in the thickness direction until they reach a predetermined thickness (height). In this manner, a mat 9 having a five-layer structure is formed.

[0123] The third embodiment can achieve the same effect as the first embodiment. In the third embodiment, the first and third intermediate layers 11a, 11c, which are wood pulverized chip layers, are configured as mixed layers containing a large number of wood shavings 3, ..., 3. The mixed layer containing the wood shavings 3, ..., 3 has higher rigidity than a non-mixed layer that does not contain wood shavings 3, ..., 3 and is composed only of granular wood pulverized chips 2, ..., 2, and can bond and integrate the wood pieces 1, ..., 1 with a small amount of adhesive. Therefore, the particle board 10 of the third embodiment can reduce the amount of adhesive used while maintaining bending strength.

[0124] In the third embodiment, a mixed layer (first and third intermediate layers 11a, 11c) including the wood pulverized chips 2, ..., 2 and the wood shavings 3, ..., 3 is provided between a non-mixed layer (two surface layers 12, 12) including only the wood pulverized chips 2, ..., 2 as the wood pieces 1, ..., 1 and a wood shavings layer (second intermediate layer 11b) including only the wood shavings 3, ..., 3 as the wood pieces 1, ..., 1. By providing a mixed layer between the non-mixed layer and the wood shavings layer in this way, the difference in size of the wood pieces 1, ..., 1 (the wood pulverized chips 2, ..., 2 and the wood shavings 3, ..., 3) between the layers is reduced, and peeling between the layers can be suppressed.

[0125] In the third embodiment, the wood chips 3, ..., 3 to be included in the first and third intermediate layers (mixed layers) 11a, 11c are selected by classifying the wood chips 3b, ..., 3b and are other than the first wood chips 3c, ..., 3c (the second wood chips 3d, ..., 3d and the third wood chips 3e, ..., 3e). In this way, the particle board 10 can be formed more inexpensively by using the waste wood that is not used in the other wood board 50 generated during the formation of the other wood board 50 as the wood chips 3, ..., 3 for the first and third intermediate layers (mixed layers) 11a, 11c. In addition, the wood material B of the other wood board 50 is used without waste, which leads to effective use of wood resources.

[0126] Fourth embodiment of the invention The particle board 10 according to the fourth embodiment is obtained by modifying a part of the configuration of the particle board 10 according to the first embodiment.

[0127] Specifically, as shown in Figure 10, the particle board 10 of the fourth embodiment has five middle layers 11a-11e and two surface layers 12, 12 that sandwich the five middle layers 11a-11e and form the surface. That is, in the fourth embodiment, the particle board 10 has five middle layers and is configured as a seven-layer structure.

[0128] The five intermediate layers 11a to 11e are composed of first to fifth intermediate layers 11a to 11e laminated in order between two surface layers 12, 12. The first, third and fifth intermediate layers 11a, 11c and 11e are composed in the same manner. The second and fourth intermediate layers 11b and 11d are composed in the same manner. The first, third and fifth intermediate layers 11a, 11c and 11e are composed differently from the second and fourth intermediate layers 11b and 11d.

[0129] Specifically, in the first, third and fifth intermediate layers 11a, 11c and 11e, the wood pieces 1, ..., 1 are composed only of wood cutting pieces 3, ..., 3, like the intermediate layer 11 in the first embodiment. On the other hand, in the second and fourth intermediate layers 11b and 11d, the wood pieces 1, ..., 1 are composed only of ground wood pieces 2, ..., 2. In other words, the first, third and fifth intermediate layers 11a, 11c and 11e are composed of wood cutting piece layers formed by bonding a large number of wood cutting pieces 3, ..., 3 together in a collective state, and the second and fourth intermediate layers 11b and 11d are composed of wood ground wood pieces layers formed by bonding a large number of ground wood pieces 2, ..., 2 together in a collective state.

[0130] The first, third and fifth intermediate layers 11a, 11c and 11e use first wood granules 2b, ..., 2b as the ground wood pieces 2, ..., 2 which are coarser than the second wood granules 2c, ..., 2c used as the ground wood pieces 2, ..., 2 for the surface layer 12.

[0131] The other configurations are the same as those in the first embodiment.

[0132] The manufacturing method of particle board 10 differs from embodiment 1 in that three types of wood pieces 1, ..., 1 are produced in wood piece production process S1, and also in adhesive application process S2 and mat forming process S3, but the other processes are similar to embodiment 1.

[0133] <Wood piece production process S1> In embodiment 4, wood pieces 1, ..., 1 (first wood thin pieces 3c, ..., 3c) for the first, third and fifth intermediate layers 11a, 11c and 11e, wood pieces 1, ..., 1 (first wood granular pieces 2b, ..., 2b) for the second and fourth intermediate layers 11b and 11d, and wood pieces 1, ..., 1 (second wood granular pieces 2c, ..., 2c) for the surface layer 12 are produced.

[0134] <Adhesive application process S2> In embodiment 4, wood pieces 1, ..., 1 for the first, third and fifth intermediate layers 11a, 11c, 11e, wood pieces 1, ..., 1 for the second and fourth intermediate layers 11b, 11d, and wood pieces 1, ..., 1 for the surface layer 12, which are prepared in the wood piece preparation process S1, are each transported to an adhesive application device and adhesive is applied thereto.

[0135] <Mat forming process S3> In the fourth embodiment, to form a particleboard 10 having a seven-layer structure, wood pieces 1, ...,1 for the surface layer 12, wood pieces 1, ...,1 for the first intermediate layer 11a, wood pieces 1, ...,1 for the second intermediate layer 11b, wood pieces 1, ...,1 for the third intermediate layer 11c, wood pieces 1, ...,1 for the fourth intermediate layer 11d, wood pieces 1, ...,1 for the fifth intermediate layer 11e, and wood pieces 1, ...,1 for the surface layer 12 are piled up in this order in a state where they are gathered in the thickness direction until they reach a predetermined thickness (height). In this manner, a mat 9 having a seven-layer structure is formed.

[0136] The fourth embodiment can achieve the same effects as the first embodiment. Moreover, the fourth embodiment has a plurality of intermediate layers (first, third and fifth intermediate layers 11a, 11c and 11e) which are wood cutting chip layers, thereby providing a particle board 10 having superior screw pull-out strength.

[0137] Fifth embodiment of the invention The particle board 10 according to the fifth embodiment is obtained by modifying a part of the configuration of the particle board 10 according to the first embodiment.

[0138] Specifically, as shown in FIG. 11, the particle board 10 of embodiment 5 is constructed with a three-layer structure like embodiment 1, but in embodiment 5, the middle layer 11 is constructed as a ground wood piece layer formed by gluing together a large number of ground wood pieces 2, ..., 2 in a collective state, and the surface layers 12, 12 are constructed as ground wood piece layers formed by gluing together a large number of shaved wood pieces 3, ..., 3 in a collective state.

[0139] In the fifth embodiment, the intermediate layer 11 uses, as the ground wood pieces 2, ..., 2, first wood grain pieces 2b, ..., 2b which are coarser than the second wood grain pieces 2c, ..., 2c used in the surface layer 12 of the first embodiment.

[0140] On the other hand, for the surface layer 12, out of the small wood flakes 3b, ..., 3b formed by cutting and crushing the wood material B to form the wood board 50, those that are not classified and are not used for the wood board 50 (the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e) are used as the wood cutting pieces 3, ..., 3.

[0141] The wood cutting pieces 3, ..., 3 constituting the surface layer 12 are not limited to those described above. The first small wood slices 3c, ..., 3c used in the wood board 50 may be used as the wood cutting pieces 3, ..., 3 constituting the surface layer 12. Also, the wood slices 3a, ..., 3a before grinding after cutting or the many small wood slices 3b, ..., 3b before classification after grinding may be used as the wood cutting pieces 3, ..., 3 constituting the surface layer 12. Furthermore, all or any two, three or four of the wood slices 3a, ..., 3a, the small wood slices 3b, ..., 3b, the first small wood slices 3c, ..., 3c, the second small wood slices 3d, ..., 3d and the third small wood slices 3e, ..., 3e may be used as the wood cutting pieces 3, ..., 3 constituting the surface layer 12. In other words, at least one of the wood flakes 3a, ..., 3a, the small wood flakes 3b, ..., 3b, the first small wood flakes 3c, ..., 3c, the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e can be used as the wood cutting pieces 3, ..., 3 that constitute the surface layer 12.

[0142] The other configurations are the same as those of embodiment 1. Moreover, the manufacturing method of the particle board 10 is also the same as that of embodiment 1, except that the wood pieces 1, ..., 1 that make up each layer are different.

[0143] The fifth embodiment can achieve the same effects as the first embodiment. Moreover, according to the fifth embodiment, by forming the two surface layers 12, 12 from wood shavings layers, it is possible to provide a particle board 10 that has excellent pull-out strength even when screws are driven into it from either side in the thickness direction.

[0144] Furthermore, since the wood pieces 1, ..., 1 of the surface layer 12 are composed only of wood shavings 3, ..., 3, the thin flake-like wood shavings 3, ..., 3 are overlapped on the surface of the particle board 10, so that the surface is less prone to unevenness than the particle board 10 of embodiment 1, resulting in excellent surface properties (smoothness).

[0145] Furthermore, in the particleboard 10 of the fifth embodiment, the two surface layers 12, 12 are made of wood shavings layers in which many extremely thin wood shavings 3, ..., 3 are bonded together in a folded state, making it more difficult for water to penetrate inside than conventional particleboards in which the two surface layers 12, 12 are made only of granular wood crushed chips 2, ..., 2. In other words, the fifth embodiment can provide a particleboard 10 that has excellent water resistance as well as screw pull-out strength.

[0146] As described later, the inventors of the present application conducted tests to verify the effects of constructing the two surface layers 12, 12 of the particleboard 10 from a wood shavings layer that contains only extremely thin wood shavings 3, ..., 3 with a thickness of 0.05 to 0.35 mm as the wood pieces 1, ..., 1. As a result, it was found that the particleboard 10 having the surface layer 12 constructed from a wood shavings layer has improved normal bending strength (MOR), wet bending strength (wetMOR), water absorption length change rate (LE), wood screw holding strength (WS) and peel strength (IB) compared to a conventional particleboard having the surface layer 12 formed from a pulverized wood piece layer.

[0147] In conventional three-layer particleboards, the surface layer is made of finely ground wood chips to improve the surface quality, but this structure results in lower bending strength compared to single-layer particleboards. Therefore, it is possible to ensure a certain degree of bending strength in conventional three-layer particleboards by increasing the density of the surface layer, but increasing the density of the surface layer creates problems such as increased weight and increased use of adhesive.

[0148] In contrast, in the fifth embodiment, the density of the two surface layers 12, 12 is not increased, but the wood pieces 1, ..., 1 constituting the two surface layers 12, 12 of the three-layer particle board 10 are not granular wood crushed pieces 2, ..., 2, but are composed of a large number of thin wood cutting pieces 3, ..., 3 having a larger area than the wood crushed pieces 2, ..., 2, thereby improving the bending strength without increasing the cost and weight. Also, compared to when the surface layer 12 is composed of the wood crushed pieces 2, ..., 2, the thin wood cutting pieces 3, ..., 3 can be bonded and integrated with a small amount of adhesive. Therefore, according to the particle board 10 of the fifth embodiment, the amount of adhesive used can be reduced while maintaining the bending strength.

[0149] As described above, according to the fifth embodiment, a multi-layer particle board 10 having excellent screw pull-out strength, surface properties, water resistance, bending strength and peel strength, and small dimensional change can be provided without increasing cost or weight.

[0150] -Verification of effectiveness- In order to verify the above-mentioned effect of forming the two surface layers 12, 12 of the particleboard 10 from a wood shavings layer containing only extremely thin wood shavings 3, ..., 3 having a thickness of 0.05 to 0.35 mm as the wood pieces 1, ..., 1, the inventors of the present application prepared a test specimen X0 in which the two surface layers 12, 12 were formed from a wood shavings layer containing only a large number of wood shavings 2, ..., 2 as the wood pieces 1, ..., 1, as in the case of a conventional particleboard, and a test specimen X1 in which the two surface layers 12, 12 were formed from a wood shavings layer in which a large number of wood shavings 3, ..., 3 were bonded together in a collective state, and the test specimens were measured according to JIS A5908 and JIS A bending strength test, a wet bending strength test, a water absorption thickness expansion rate test, a water absorption length change rate test, a wood screw holding strength test, and a peel strength test were performed in accordance with A5905, and the normal bending strength (MOR), wet bending strength (wetMOR), water absorption length change rate (LE), wood screw holding strength (WS), and peel strength (IB) were obtained, with the results shown in Fig. 12. The specimen X2 has the same structure as the particleboard 10 of the fifth embodiment. Fig. 12 also shows the results of each test of specimen X2 in relative proportion to the results of each test of specimen X0, which are set to 100.

[0151] As shown in FIG. 12, the particle board 10 (specimen X2) in which the two surface layers 12, 12 are made of wood shavings 3, ..., 3 has improved modulus of resistance (MOR) and wet modulus of resistance (wetMOR) compared to the conventional particle board (specimen X0) in which the two surface layers 12, 12 are made of ground wood chips 2, ..., 2, with both improvement rates exceeding 100%, resulting in a significant improvement.

[0152] In addition, with regard to dimensional change, the particleboard 10 (specimen X2) in which the two surface layers 12, 12 are made up of wood shavings 3, ..., 3 showed a decrease (improvement) in the water absorption length change rate (LE) compared to the conventional particleboard (specimen X0) in which the two surface layers 12, 12 are made up of ground wood chips 2, ..., 2, with the improvement rate being a remarkable 46%.

[0153] In addition, with regard to the wood screw holding strength (WS), the particle board 10 (specimen X2) in which the two surface layers 12, 12 are composed of shaved wood chips 3, ..., 3 showed an improvement over the conventional particle board (specimen X0) in which the two surface layers 12, 12 are composed of crushed wood chips 2, ..., 2, with the improvement rate being 20%.

[0154] Furthermore, with regard to the peel strength (IB), the particle board 10 (specimen X2) in which the two surface layers 12, 12 are composed of wood shavings 3, ..., 3 showed an improvement over the conventional particle board (specimen X0) in which the two surface layers 12, 12 are composed of ground wood chips 2, ..., 2, with the improvement rate being 19%.

[0155] As described above, the particleboard 10 (specimen X2) in which the two surface layers 12, 12 are made of wood shavings 3, ..., 3 has higher (improved) bending strength under normal conditions (MOR), wet bending strength (wetMOR), wood screw retention (WS) and peel strength (IB) and lower (improved) water absorption length change rate (LE) compared to the conventional particleboard (specimen X0) in which the two surface layers 12, 12 are made of wood crushed pieces 2, ..., 2. From these results, it is found that by forming the two surface layers 12, 12 of the particleboard 10 from wood shavings layers containing only wood shavings 3, ..., 3 with a thickness of 0.05 to 0.35 mm as the wood pieces 1, ..., 1, it is possible to provide a multi-layered particleboard 10 that is excellent not only in screw pull-out strength but also in surface properties, water resistance, bending strength and peel strength, and has small dimensional change, without increasing cost or weight.

[0156] Sixth embodiment of the invention The particle board 10 according to the sixth embodiment is a particle board 10 according to the fifth embodiment, with a part of the structure changed. Specifically, as shown in Fig. 13, in the particle board 10 according to the sixth embodiment, the intermediate layer 11 formed in the ground wood chip layer contains wood shavings 3, ..., 3. That is, in the sixth embodiment, the intermediate layer 11 contains not only a large number of ground wood chips 2, ..., 2, but also a large number of ground wood chips 3, ..., 3 as wood chips 1, ..., 1. That is, in the sixth embodiment, the intermediate layer 11 is a ground wood chip layer formed by bonding and integrating a large number of ground wood chips 2, ..., 2 in a collective state, and is formed as a mixed layer containing a large number of ground wood chips 3, ..., 3.

[0157] The wood cutting pieces 3, ..., 3 used in the middle layer (mixed layer) 11 are made from small wood flakes 3b, ..., 3b formed by cutting and crushing wood material B to form a wood board 50, which are not classified for use in the wood board 50 (second small wood flakes 3d, ..., 3d and third small wood flakes 3e, ..., 3e).

[0158] The wood cutting pieces 3, ..., 3 constituting the intermediate layer (mixed layer) 11 are not limited to those mentioned above. The first small wood slices 3c, ..., 3c used in the wood board 50 may be used as the wood cutting pieces 3, ..., 3 constituting the intermediate layer (mixed layer) 11. Also, the wood slices 3a, ..., 3a before grinding after cutting or the many small wood slices 3b, ..., 3b before classification after grinding may be used as the wood cutting pieces 3, ..., 3 constituting the intermediate layer (mixed layer) 11. Furthermore, all or any two, three or four of the wood slices 3a, ..., 3a, the small wood slices 3b, ..., 3b, the first small wood slices 3c, ..., 3c, the second small wood slices 3d, ..., 3d and the third small wood slices 3e, ..., 3e may be used as the wood cutting pieces 3, ..., 3 constituting the intermediate layer (mixed layer) 11. In other words, at least one of the wood flakes 3a, ..., 3a, the small wood flakes 3b, ..., 3b, the first small wood flakes 3c, ..., 3c, the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e can be used as the wood cutting pieces 3, ..., 3 that constitute the intermediate layer (mixed layer) 11.

[0159] The other configurations are the same as those in the fifth embodiment.

[0160] The method for producing the particleboard 10 differs from that of the fifth embodiment only in that the wood piece producing step S1 includes a wood piece mixing step S13, and the other steps are the same as those of the fifth embodiment.

[0161] [Wood piece mixing process S13] In the wood piece mixing process S13, a large number of wood crushed pieces 2, ..., 2 (first wood granular pieces 2b, ..., 2b) for the middle layer (mixed layer) 11 produced in the wood crushed piece production process and a large number of wood cutting pieces 3, ..., 3 (second wood small pieces 3d, ..., 3d and third wood small pieces 3e, ..., 3e) for the surface layer (mixed layer) 12 produced in the wood cutting piece production process are mixed to a desired mixing ratio (the wood cutting pieces 3, ..., 3 relative to the total weight of the wood pieces 1, ..., 1 is 10 to 90% by weight).

[0162] In the wood piece production process S1 of embodiment 6, the same wood crushed piece production process S11 and wood shavings production process S12 as in embodiment 5 and the above-mentioned wood piece mixing process S13 are carried out to produce wood pieces 1, ..., 1 (a mixture of first wood granular pieces 2b, ..., 2b and second small wood flakes 3d, ..., 3d and third small wood flakes 3e, ..., 3e) for the intermediate layer (mixed layer) 11 and wood pieces 1, ..., 1 (second wood granular pieces 2c, ..., 2c) for the surface layer 12.

[0163] The sixth embodiment can achieve the same effect as the fifth embodiment. In the sixth embodiment, the surface layers 12, 12 are not only made of the wood cuttings 3, ..., 3, but also the middle layer 11, which is a wood pulverized chip layer containing the wood pulverized chips 2, ..., 2, is made of a mixed layer containing the wood cuttings 3, ..., 3. The mixed layer containing the wood cuttings 3, ..., 3 has higher rigidity than a non-mixed layer containing only the granular wood pulverized chips 2, ..., 2 and does not contain the wood cuttings 3, ..., 3, and the wood pieces 1, ..., 1 can be bonded together with a small amount of adhesive. Therefore, the particle board 10 of the sixth embodiment can reduce the amount of adhesive used while maintaining bending strength.

[0164] Furthermore, in the particle board 10 of embodiment 6, the intermediate layer 11 contains wood shavings 3, ..., 3, which makes it more difficult for the screws to come out than in embodiment 5. Therefore, embodiment 6 can provide a three-layer particle board 10 that is not only excellent in surface properties and bending strength, but also in screw pull-out strength (wood screw holding power).

[0165] In the sixth embodiment, the wood chips 3, ..., 3 to be included in the intermediate layer 11 are selected from the small wood chips 3b, ..., 3b and classified to be other than the first small wood chips 3c, ..., 3c (the second small wood chips 3d, ..., 3d and the third small wood chips 3e, ..., 3e). In this way, the particle board 10 can be formed more inexpensively by using the waste wood that is not used in the other wood boards 50 and is generated during the formation of the other wood boards 50 as the wood chips 3, ..., 3 for the intermediate layer 11. In addition, the wood material B of the other wood boards 50 is used without waste, which leads to effective use of wood resources.

[0166] Seventh embodiment of the invention The particle board 10 according to the seventh embodiment is obtained by modifying a part of the configuration of the particle board 10 according to the fifth embodiment.

[0167] Specifically, as shown in Figure 14, the particle board 10 of the seventh embodiment has three intermediate layers 11a-11c and two surface layers 12, 12 that sandwich the three intermediate layers 11a-11c and form the surface. That is, in the third embodiment, the particle board 10 has three intermediate layers and is configured as a five-layer structure.

[0168] The three intermediate layers 11a to 11c are composed of first to third intermediate layers 11a to 11c laminated in order between two surface layers 12, 12. The first and third intermediate layers 11a, 11c have the same configuration, while the second intermediate layer 11b has a different configuration from the first and third intermediate layers 11a, 11c.

[0169] Specifically, the second intermediate layer 11b is composed of wood pieces 1, ..., 1 only consisting of wood pulverized pieces 2, ..., 2, like the intermediate layer 11 of the fifth embodiment. On the other hand, the first and third intermediate layers 11a, 11c are composed of wood pieces 1, ..., 1 consisting of a mixture of wood pulverized pieces 2, ..., 2 and wood cutting pieces 3, ..., 3. That is, the second intermediate layer 11b is composed of a wood pulverized piece layer formed by bonding and integrating a large number of wood pulverized pieces 2, ..., 2 in a collective state, and is composed of a non-mixed layer that does not contain a large number of wood cutting pieces 3, ..., 3, while the first and third intermediate layers 11a, 11c are composed of a wood pulverized piece layer formed by bonding and integrating a large number of wood pulverized pieces 2, ..., 2 in a collective state, and is composed of a mixed layer that contains a large number of wood cutting pieces 3, ..., 3.

[0170] In the seventh embodiment, the second intermediate layer 11b is an unmixed layer consisting of only the ground wood chips 2, ..., 2, and the two surface layers 12, 12 are wood cuttings layers consisting of only the wood cuttings 3, ..., 3. In other words, the first and third intermediate layers 11a, 11c are mixed layers consisting of a mixture of the ground wood chips 2, ..., 2 and the wood cuttings 3, ..., 3, and are provided between the unmixed layer (surface layer 12) consisting of only the ground wood chips 2, ..., 2 and the wood cuttings layer (second intermediate layer 11b) consisting of only the ground wood chips 3, ..., 3.

[0171] In the first to third intermediate layers 11a to 11c, the first wood grain pieces 2b, ..., 2b are used as the ground wood pieces 2, ..., 2, as in the intermediate layer 11 of the fifth embodiment.

[0172] In addition, the first and third intermediate layers (mixed layers) 11a, 11c use, as wood cutting pieces 3, ..., 3, the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e, which are not classified and are not used for the wood board 50, among the small wood flakes 3b, ..., 3b formed by cutting and crushing the wood material B to form the wood board 50.

[0173] The wood cutting pieces 3, ..., 3 constituting the first and third intermediate layers (mixed layers) 11a, 11c are not limited to those described above. The first small wood pieces 3c, ..., 3c used in the wood board 50 may be used as the wood cutting pieces 3, ..., 3 constituting the first and third intermediate layers (mixed layers) 11a, 11c. Also, the wood cutting pieces 3a, ..., 3a before crushing after cutting or the numerous small wood pieces 3b, ..., 3b before classification after crushing may be used as the wood cutting pieces 3, ..., 3 constituting the first and third intermediate layers (mixed layers) 11a, 11c. Furthermore, all or any two, three or four of the woody flakes 3a, ..., 3a, the small woody flakes 3b, ..., 3b, the first small woody flakes 3c, ..., 3c, the second small woody flakes 3d, ..., 3d and the third small woody flakes 3e, ..., 3e may be combined and used as the woody cutting pieces 3, ..., 3 constituting the first and third intermediate layers (mixed layers) 11a, 11c. In other words, at least one of the woody flakes 3a, ..., 3a, the small woody flakes 3b, ..., 3b, the first small woody flakes 3c, ..., 3c, the second small woody flakes 3d, ..., 3d and the third small woody flakes 3e, ..., 3e may be used as the woody cutting pieces 3, ..., 3 constituting the first and third intermediate layers (mixed layers) 11a, 11c.

[0174] The other configurations are the same as those in the fifth embodiment.

[0175] The manufacturing method of the particle board 10 differs from that of embodiment 5 in that the wood piece production process S1 includes a wood piece mixing process S13, and the adhesive application process S2 and the mat forming process S3 differ from those of embodiment 1, but the other processes are the same as those of embodiment 5.

[0176] [Wood piece mixing process S13] In the wood piece mixing process S13, a large number of ground wood pieces 2, ..., 2 (first wood granular pieces 2b, ..., 2b) for the first and third intermediate layers (mixed layers) 11a, 11c produced in the ground wood piece production process S11 and a large number of wood cutting pieces 3, ..., 3 (second small wood pieces 3d, ..., 3d and third small wood pieces 3e, ..., 3e) for the first and third intermediate layers (mixed layers) 11a, 11c produced in the wood cutting piece production process S12 are mixed to a desired mixing ratio (the wood cutting pieces 3, ..., 3 relative to the total weight of the wood pieces 1, ..., 1 is 10 to 90% by weight).

[0177] In the wood piece production process S1 of embodiment 7, the same wood crushed piece production process S11 and wood shavings production process S12 as in embodiment 5 and the above-mentioned wood piece mixing process S13 are carried out to produce wood pieces 1, ..., 1 for the first and third intermediate layers (mixed layers) 11a, 11c (a mixture of first wood granular pieces 2b, ..., 2b with second wood small flakes 3d, ..., 3d and third wood small flakes 3e, ..., 3e), wood pieces 1, ..., 1 (first wood granular pieces 2b, ..., 2b) for the second intermediate layer 11b, and wood pieces 1, ..., 1 for the surface layer 12 (second wood small flakes 3d, ..., 3d and third wood small flakes 3e, ..., 3e).

[0178] <Adhesive application process S2> In embodiment 7, the wood pieces 1, ..., 1 for the first and third intermediate layers (mixed layers) 11a, 11c, the wood pieces 1, ..., 1 for the second intermediate layer 11b, and the wood pieces 1, ..., 1 for the surface layer 12, which are prepared in the wood piece preparation process S1, are each transported to an adhesive application device and adhesive is applied thereto.

[0179] <Mat forming process S3> In the seventh embodiment, to form a particleboard 10 having a five-layer structure, wood pieces 1,...,1 for the surface layer 12 (wood shavings layer), wood pieces 1,...,1 for the first intermediate layer (mixed layer) 11a, wood pieces 1,...,1 for the second intermediate layer (non-mixed layer) 11b, wood pieces 1,...,1 for the third intermediate layer (mixed layer) 11c, and wood pieces 1,...,1 for the surface layer 12 (wood shavings layer) are piled up in this order in a state where they are gathered in the thickness direction until they reach a predetermined thickness (height). In this manner, a mat 9 having a five-layer structure is formed.

[0180] The seventh embodiment can achieve the same effect as the fifth embodiment. In the seventh embodiment, the first and third intermediate layers 11a, 11c, which are wood pulverized chip layers, are configured as mixed layers containing a large number of wood shavings 3, ..., 3. The mixed layer containing the wood shavings 3, ..., 3 has higher rigidity than a non-mixed layer that does not contain wood shavings 3, ..., 3 and is composed only of granular wood pulverized chips 2, ..., 2, and can bond and integrate the wood pieces 1, ..., 1 with a small amount of adhesive. Therefore, the particle board 10 of the seventh embodiment can reduce the amount of adhesive used while maintaining bending strength.

[0181] In the seventh embodiment, a mixed layer (first and third intermediate layers 11a, 11c) including the wood pulverized chips 2, ..., 2 and the wood shavings 3, ..., 3 is provided between a non-mixed layer (second intermediate layer 11b) including only the wood pulverized chips 2, ..., 2 as the wood pieces 1, ..., 1 and a wood shavings layer (two surface layers 12, 12) including only the wood shavings 3, ..., 3 as the wood pieces 1, ..., 1. By providing a mixed layer between the non-mixed layer and the wood shavings layer in this way, the difference in size of the wood pieces 1, ..., 1 (the wood pulverized chips 2, ..., 2 and the wood shavings 3, ..., 3) between the layers is reduced, and peeling between the layers can be suppressed.

[0182] In the seventh embodiment, the wood chips 3, ..., 3 to be included in the first and third intermediate layers (mixed layers) 11a, 11c are selected by classifying the wood chips 3b, ..., 3b and are other than the first wood chips 3c, ..., 3c (the second wood chips 3d, ..., 3d and the third wood chips 3e, ..., 3e). In this way, the particle board 10 can be formed more inexpensively by using the waste material that is not used in the other wood board 50 and is generated during the formation of the other wood board 50 as the wood chips 3, ..., 3 for the first and third intermediate layers (mixed layers) 11a, 11c. In addition, the wood material B of the other wood board 50 is used without waste, which leads to effective use of wood resources.

[0183] Eighth embodiment of the invention The particle board 10 according to the eighth embodiment is a particle board 10 according to the fifth embodiment, with a partial configuration changed.

[0184] Specifically, as shown in Figure 15, the particle board 10 of embodiment 8 has seven middle layers 11a-11g and two surface layers 12, 12 that sandwich the seven middle layers 11a-11g and form the surface. That is, in embodiment 8, the particle board 10 has seven middle layers and is configured as a nine-layer structure.

[0185] The seven intermediate layers 11a-11g are composed of first to seventh intermediate layers 11a-11g laminated in order between two surface layers 12, 12. The first, third, fifth and seventh intermediate layers 11a, 11c, 11e and 11g are composed in the same manner. The second and sixth intermediate layers 11b and 11f are composed in the same manner. The first, third, fifth and seventh intermediate layers 11a, 11c, 11e and 11g are composed differently from the second and sixth intermediate layers 11b and 11f and the fourth intermediate layer 11d.

[0186] Specifically, in the eighth embodiment, the first, third, fifth and seventh intermediate layers 11a, 11c, 11e and 11g are configured as mixed layers including not only a large number of ground wood chips 2, ..., 2 but also a large number of wood cutting chips 3, ..., 3 as the wood chips 1, ..., 1. The second and sixth intermediate layers 11b and 11f are configured as non-mixed layers including only the wood cutting chips 3, ..., 3 as the wood chips 1, ..., 1. The fourth intermediate layer 11d is configured as a wood cutting chip layer including only the wood cutting chips 3, ..., 3 as the wood chips 1, ..., 1.

[0187] In the seventh embodiment, the first to third and fifth to seventh intermediate layers 11a to 11c and 11e to 11g, which are wood pulverized layers, use the first wood grain pieces 2b, ..., 2b as the wood pulverized pieces 2, ..., 2. In addition, the fourth intermediate layer 11d, which is a wood cutting piece layer, and the first, third, fifth and seventh intermediate layers 11a, 11c, 11e and 11g, which are mixed layers, use the wood small flakes 3b, ..., 3b formed by cutting and pulverizing the wood material B to form the wood board 50, which are not classified and are not used for the wood board 50 (the second wood small flakes 3d, ..., 3d and the third wood small flakes 3e, ..., 3e) as the wood cutting pieces 3, ..., 3.

[0188] The wood cutting pieces 3, ..., 3 constituting the fourth intermediate layer (wood cutting piece layer) 11d and the first, third, fifth, seventh intermediate layers (mixed layers) 11a, 11c, 11e, 11g are not limited to those described above. The first small wood pieces 3c, ..., 3c used in the wood board 50 may be used as the wood cutting pieces 3, ..., 3 constituting the wood cutting piece layer and the mixed layer. Also, the wood cutting pieces 3a, ..., 3a before crushing after cutting and the numerous small wood cutting pieces 3b, ..., 3b before classification after crushing may be used as the wood cutting pieces 3, ..., 3 constituting the wood cutting piece layer and the mixed layer. Furthermore, all or any two, three or four of the wood slices 3a, ..., 3a, the small wood slices 3b, ..., 3b, the first small wood slices 3c, ..., 3c, the second small wood slices 3d, ..., 3d and the third small wood slices 3e, ..., 3e may be combined and used as the wood cuttings 3, ..., 3 constituting the wood cuttings layer and the mixed layer. In other words, at least one of the wood slices 3a, ..., 3a, the small wood slices 3b, ..., 3b, the first small wood slices 3c, ..., 3c, the second small wood slices 3d, ..., 3d and the third small wood slices 3e, ..., 3e may be used as the wood cuttings 3, ..., 3 constituting the wood cuttings layer and the mixed layer.

[0189] The other configurations are the same as those in the fifth embodiment.

[0190] The manufacturing method of the particle board 10 differs from that of embodiment 5 in that the wood piece production process S1 includes a wood piece mixing process S13, and the adhesive application process S2 and the mat forming process S3 differ from those of embodiment 1, but the other processes are the same as those of embodiment 5.

[0191] [Wood piece mixing process S13] In the wood piece mixing process S13, a large number of wood crushed pieces 2, ..., 2 (first wood granular pieces 2b, ..., 2b) for the 1st, 3rd, 5th, 7th intermediate layers (mixed layers) 11a, 11c, 11e, 11g produced in the wood crushed piece production process S11 and a large number of wood cutting pieces 3, ..., 3 (second wood small pieces 3d, ..., 3d and third wood small pieces 3e, ..., 3e) for the 1st, 3rd, 5th, 7th intermediate layers (mixed layers) 11a, 11c, 11e, 11g produced in the wood cutting piece production process S12 are mixed to a desired mixing ratio (the wood cutting pieces 3, ..., 3 relative to the total weight of the wood pieces 1, ..., 1 is 10 to 90% by weight).

[0192] In the wood piece production process S1 of embodiment 8, the same wood crushed piece production process S11 and wood shavings production process S12 as in embodiment 5 and the above-mentioned wood piece mixing process S13 are carried out to produce wood pieces 1, ..., 1 for the first, third, fifth and seventh intermediate layers (mixed layers) 11a, 11c, 11e, 11g (a mixture of the first wood granular pieces 2b, ..., 2b and the second wood small flakes 3d, ..., 3d and the third wood small flakes 3e, ..., 3e), wood pieces 1, ..., 1 for the fourth intermediate layer 11d (the second wood small flakes 3d, ..., 3d and the third wood small flakes 3e, ..., 3e), and wood pieces 1, ..., 1 for the surface layer 12 (the second wood small flakes 3d, ..., 3d and the third wood small flakes 3e, ..., 3e).

[0193] <Adhesive application process S2> In embodiment 8, wood pieces 1, ..., 1 for the first, third, fifth, seventh intermediate layers (mixed layers) 11a, 11c, 11e, 11g, wood pieces 1, ..., 1 for the fourth intermediate layer 11d, and wood pieces 1, ..., 1 for the surface layer 12, which are prepared in the wood piece preparation process S1, are each transported to an adhesive application device and adhesive is applied thereto.

[0194] <Mat forming process S3> In the eighth embodiment, in order to form a particle board 10 having a nine-layer structure, the wood pieces 1, ..., 1 for the surface layer 12 (wood shavings layer), the wood pieces 1, ..., 1 for the first intermediate layer (mixed layer) 11a, the wood pieces 1, ..., 1 for the second intermediate layer (non-mixed layer) 11b, the wood pieces 1, ..., 1 for the third intermediate layer (mixed layer) 11c, the wood pieces 1, ..., 1 for the fourth intermediate layer (wood shavings layer) 11d, the wood pieces 1, ..., 1 for the fifth intermediate layer (mixed layer) 11e, the wood pieces 1, ..., 1 for the sixth intermediate layer (non-mixed layer) 11f, the wood pieces 1, ..., 1 for the seventh intermediate layer (mixed layer) 11g, and the wood pieces 1, ..., 1 for the surface layer 12 (wood shavings layer) are piled up in this order in a state where they are gathered in the thickness direction until they reach a predetermined thickness (height). In this manner, a mat 9 having a nine-layer structure is formed.

[0195] The eighth embodiment can achieve the same effect as the fifth embodiment. In the particle board 10 of the eighth embodiment, not only the two surface layers 12, 12 but also the fourth intermediate layer 11d are made of wood shavings layers. In addition, the multiple intermediate layers (the first, third, fifth, seventh intermediate layers 11a, 11c, 11e, 11g) which are wood pulverized chip layers are made of mixed layers containing wood shavings 3, ..., 3. Therefore, the particle board 10 of the eighth embodiment is less likely to have screws come out than the particle board 10 of the fifth embodiment. Therefore, according to the eighth embodiment, it is possible to provide a particle board 10 with a multi-layer structure which is not only excellent in surface properties and bending strength but also has excellent screw pull-out strength (wood screw holding power).

[0196] In the present embodiment 8, in the wood cutting piece layer (two surface layers 12, 12) and the mixed layer (first, third, fifth, seventh middle layers 11a, 11c, 11e, 11g), wood cutting pieces 3, ..., 3 are made of wood cutting pieces 3, ..., 3 other than the first wood cutting pieces 3c, ..., 3c (second wood cutting pieces 3d, ..., 3d and third wood cutting pieces 3e, ..., 3e) that are selected by classifying the wood cutting pieces 3b, ..., 3b. In this way, the particle board 10 can be formed more inexpensively by using waste wood that is not used in the other wood boards 50 generated during the formation of the other wood boards 50 as the wood cutting pieces 3, ..., 3. In addition, the wood material B of the other wood boards 50 is used without waste, which leads to effective use of wood resources.

[0197] Other Embodiments In the above-mentioned embodiments 1 to 8, the two surface layers 12, 12 are configured to be thinner (higher) than the intermediate layer 11. However, the two surface layers 12, 12 may be thicker than the intermediate layer 11.

[0198] In addition, in the present embodiments 1 to 8, an example has been described in which wood shavings generated during material processing of another wood board 50 are used as the wood shavings 3, ..., 3. However, the wood shavings 3, ..., 3 may not be generated during material processing of another wood board 50, but may be procured for the purpose of forming the above-mentioned particle board 10. [Industrial Applicability]

[0199] The present invention is useful for particle boards having a multi-ply structure. [Explanation of symbols]

[0200] 1 wood piece 2 Crushed wood chips 3 wood cuttings 3a wood flakes 3b Small wood flakes 3c 1st woody flake 3d. Secondary woody flakes (other than the first secondary woody flakes) 3e. Third woody flakes (other than first woody flakes) 10. Particleboard 11 Middle Class 12 Surface layer 50 Wood Board

Claims

1. A particle board with a multi-layer structure in which a large number of wood pieces are glued together in a collective state, At least one layer is a wood shavings layer containing only wood shavings having a thickness of 0.05 to 0.35 mm as the wood pieces; The layer other than the wood cutting chip layer is a wood pulverized chip layer containing wood pulverized chips as the wood chips. A particle board characterized by:

2. 2. The particle board according to claim 1, The present invention comprises two surface layers and at least one intermediate layer provided between the two surface layers, The surface layer is the wood shavings layer. A particle board characterized by:

3. 2. The particle board according to claim 1, The present invention comprises two surface layers and at least one intermediate layer provided between the two surface layers, At least one of the intermediate layers is the wood shavings layer. A particle board characterized by:

4. 3. The particle board according to claim 2, At least one of the intermediate layers is the wood shavings layer. A particle board characterized by:

5. 4. The particle board according to claim 3, The intermediate layer is a plurality of layers of wood chips. A particle board characterized by:

6. A particle board according to any one of claims 2 to 5, At least one of the wood chip layers is a mixed layer containing a large number of the wood chips. A particle board characterized by:

7. A particle board according to any one of claims 2 to 5, At least one of the wood chip layers is a mixed layer containing a large number of the wood chips; The mixed layer is provided between the non-mixed layer, which is the wood chip layer and does not contain the wood chips, and the wood chip layer. A particle board characterized by:

8. The particle board according to claim 1, The wood chips are produced from the wood material when a wood board is formed by bonding together a number of first small wood chips selected by classification from a number of small wood chips obtained by cutting a wood material and crushing the resulting number of thin wood chips having a thickness of 0.05 to 0.35 mm. A particle board characterized by:

9. The particle board according to claim 2, The wood cutting pieces are produced from the wood material when a wood board is formed by bonding together a number of first small wood flakes selected by classification from a number of small wood flakes obtained by cutting a wood material and crushing the resulting number of thin wood flakes having a thickness of 0.05 to 0.35 mm, The wood cutting pieces used for at least the surface layer are those other than the first wood small pieces selected by classification from among the wood small pieces. A particle board characterized by:

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