Particle board and manufacturing method thereof

Abstract

To manufacture a three-layered structure particle board having excellent surface properties, bending strength and screw pull-out strength and small dimensional change without increasing cost and weight.SOLUTION: In a particle board 10 according to the present invention having a three-layered structure in which wood pulverized pieces 2, ..., 2 finer than a core layer 11 are used in a surface layer 12, the core layer 11 includes many wood cut pieces 3, ..., 3 having a thickness of 0.05 to 0.35 mm.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a particle board having a three-ply structure. [Background technology]

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

[0003] Patent Document 1 discloses that particleboard, which is formed by depositing adhesive on crushed wood chips in a mat shape and hot pressing with a hot plate, is used as an alternative material to plywood. Patent Document 1 also discloses a three-layer particleboard in which wood chips are classified, and coarse wood chips are used as the core material and fine wood chips are used as the surface layer. Since crushed pieces of waste materials and recycled materials can be used as constituent materials for particleboard, it can be formed relatively inexpensively. Furthermore, even if waste materials and recycled materials are not used, three-layer particleboard can be formed relatively inexpensively because all of the wood chips produced by crushing wood materials are used without waste. Thus, three-layer particleboard is excellent as an alternative to plywood in that it can be formed relatively inexpensively. [Prior art documents] [Patent documents]

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

[0005] However, because three-layer particleboard uses fine crushed wood chips for the surface layer, it has better surface properties (smoothness) than single-layer particleboard made of coarse crushed wood chips, but its bending strength is lower. In three-layer particleboard, if the density of the surface layer is increased to ensure a certain level of bending strength, the weight increases and the amount of adhesive used increases. In addition, particleboard has low screw pull-out strength, making it unusable as a load-bearing surface material for screw installation, and it also has the problem of lacking dimensional stability due to moisture absorption.

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

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

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

[0009] The first invention is characterized in that the core layer contains a large number of wood shavings having a thickness of 0.05 to 0.35 mm.

[0010] Here, crushed wood chips refer to granular wood chips formed by crushing a wood material, and shaved wood chips refer to thin flake-like wood chips formed by cutting a wood material.

[0011] In the first invention, the core layer of the three-layer particle board contains not only ground wood chips, which are usually contained, but also extremely thin wood shavings with a thickness of 0.05 to 0.35 mm. With this configuration, the bending strength of the core layer of the particle board is increased. Therefore, it is not necessary to increase the density of the surface layer or use a large amount of adhesive to ensure the bending strength of the particle board. Furthermore, compared to when the core layer is composed of ground wood chips only, the presence of the thin-flaky wood shavings makes it easier to bond the wood pieces (ground wood chips and wood shavings) together with a small amount of adhesive. Therefore, the three-layer particle board according to the first invention can reduce the amount of adhesive used while maintaining the bending strength of the conventional one.

[0012] In addition, in the particle board according to the first invention, like conventional three-layer particle boards, the surface layer is composed of relatively fine granular wood fragments, and therefore has excellent surface properties (smoothness).

[0013] Furthermore, the particleboard according to the first invention contains in its core layer many thin wood shavings that have a larger surface area than granular crushed wood chips, so screws are less likely to come out than in conventional three-layer particleboards whose core layer is made only of crushed wood chips. Therefore, by including wood shavings in the core layer, the particleboard according to the first invention reinforces the core layer and significantly improves the screw pull-out strength (wood screw holding power), making it suitable for use as a load-bearing surface material for base construction with screws.

[0014] Meanwhile, the inventors of the present application conducted a test to verify the effect of including extremely thin wood shavings with a thickness of 0.05 to 0.35 mm in the core layer of a three-layer particleboard. As a result, it was found that the particleboard containing wood shavings in the core layer had improved normal bending strength (MOR), linear expansion coefficient (LE) and wood screw holding strength (WS) compared to a conventional particleboard not containing wood shavings in the core layer, and that the thickness swelling coefficient (TS) was improved to some extent, although not significantly, and that the absolute value of the thickness swelling coefficient (TS) fully met the standard (12% or less) required for structural particleboard.

[0015] As described above, according to the first aspect of the present invention, a three-layer particle board that is excellent in surface properties, bending strength, and screw pull-out strength and that exhibits little dimensional change can be provided without increasing cost or weight.

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

[0017] In the second invention, extremely thin wood shavings having a thickness of 0.05 to 0.35 mm are included not only in the core layer of a three-layer particle board but also in the surface layer. With this configuration, the particle board increases the bending strength of not only the core layer but also the surface layer. Therefore, it is not necessary to increase the density of the surface layer or use a large amount of adhesive to ensure the bending strength of the particle board. Also, by including wood shavings in not only the core layer but also the surface layer, the amount of adhesive used can be further reduced compared to when the adhesive is included only in the core layer.

[0018] In addition, in the particleboard according to the second aspect of the invention, extremely thin wood chips having a thickness of 0.05 to 0.35 mm are inserted into the gaps between the relatively fine wood chips in the surface layer, so that the surface is less prone to unevenness. In particular, when the thin wood chips are folded over on the surface of the particleboard, the surface becomes smoother and has excellent surface properties (smoothness).

[0019] Furthermore, according to the particleboard of the second invention, by including wood shavings not only in the core layer but also in the surface layer, screws are less likely to come out than when they are included only in the core layer. Therefore, according to the second invention, it is possible to provide a three-layer particleboard with superior screw pull-out strength (wood screw holding power).

[0020] Furthermore, in the particleboard according to the second invention, if the surface layer were made only of crushed wood chips, many gaps would be formed between the crushed wood chips, but because flaky wood shavings are mixed in, the flaky wood shavings fill the many gaps, making the gaps smaller and fewer. Therefore, the particleboard according to the second invention is more resistant to moisture penetration and has excellent water resistance than conventional particleboards whose surface layer is made only of crushed wood chips.

[0021] Furthermore, in conventional particleboards whose surface layer is made only of crushed wood chips, the crushed wood chips are crushed during press molding, and when moisture penetrates the inside of the particleboard, it becomes more likely to absorb moisture, which may result in significant dimensional changes (changes in length and thickness).In contrast, the particleboard according to the second invention has a structure that makes it more difficult for moisture to penetrate into the inside than conventional particleboards, as described above, and therefore does not absorb moisture and therefore does not undergo significant changes in dimensions (length and thickness).

[0022] As described above, according to the second invention, a three-layer particle board that is excellent in surface properties, bending strength, screw pull-out strength and water resistance and has little dimensional change can be provided without increasing cost or weight.

[0023] The third invention is characterized in that, in the first or second 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.

[0024] The fourth 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 the wood cutting pieces contained in at least the surface layer are other than the first small wood flakes selected by classification from the small wood flakes.

[0025] In the third and fourth inventions, the wood shavings are generated when wood materials are processed to form other wood boards. Therefore, even if a material (wood shavings) different from the material (ground wood chips) used for normal particle boards is used, it can be easily procured because it is a different material generated during the processing of materials for other wood boards. Therefore, according to the third and fourth inventions, it is possible to easily and relatively inexpensively provide a three-layer particle board that has excellent surface properties, bending strength, and screw pull-out strength, and has little dimensional change.

[0026] In particular, in the fourth 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, waste wood that is generated during the formation of other wood boards and is not used for other wood boards is used as the wood chips for the surface layer of the three-layer particle board, making it possible to form the three-layer particle board more inexpensively. In addition, since the wood material of the other wood boards is used without waste, this leads to effective use of wood resources. Effect of the Invention

[0027] As described above, according to the present invention, the core layer of a three-layer particle board contains a large number of extremely thin wood shavings, making it possible to provide a three-layer particle board that has excellent surface properties, bending strength, and screw pull-out strength and is less susceptible to dimensional change, without increasing cost or weight. [Brief description of the drawings]

[0028] [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. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] 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.

[0030] 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.

[0031] 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:

[0032] <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 core layer 11 and two surface layers 12,12 that sandwich the core layer 11 and form the surface. The wood pieces 1,...,1 that the core layer 11 and the surface layers 12 contain are different in configuration.

[0033] Both the core layer 11 and the surface layer 12 contain a large number of wood pulverized chips 2, ..., 2 as wood pieces 1, ..., 1, but the wood pulverized chips 2, ..., 2 used in the core layer 11 and the surface layer 12 have different particle sizes, and finer wood pulverized chips 2, ..., 2 are used in the surface layer 12 than in the core layer 11. Also, the core layer 11 contains not only a large number of wood pulverized chips 2, ..., 2 but also a large number of wood cutting chips 3, ..., 3. That is, in this embodiment 1, the wood pieces 1, ..., 1 of the core layer 11 are composed of the wood pulverized chips 2, ..., 2 and the wood cutting chips 3, ..., 3, and the wood pieces 1, ..., 1 of the surface layer 12 are composed only of the wood pulverized chips 2, ..., 2 that are finer than the core layer 11.

[0034] In the present embodiment 1, the wood crushed pieces 2, ..., 2 are used as wood pieces in conventional particle boards, while the wood shavings 3, ..., 3 used in the surface layer 12 are used as a constituent material of another wood board 50, which will be described later. That is, in the present embodiment 1, the wood crushed pieces 2, ..., 2 used in conventional particle boards are mixed with the wood shavings 3, ..., 3 used as a constituent material of another wood board 50, and used as a number of wood pieces 1, ..., 1 in the core layer 11, and the wood crushed pieces 2, ..., 2 used in conventional particle boards are used as a number of wood pieces 1, ..., 1 in the surface layer 12. In the core layer 11, the wood shavings 3, ..., 3 are mixed at a ratio of 10 to 90% by weight with respect to the total weight of the wood pieces 1, ..., 1.

[0035] The ground wood chips 2, . . . , 2 and shaved wood chips 3, . . . , 3 used in the particle board 10 will be described in detail below.

[0036] [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, wood granular pieces 2a, ..., 2a obtained by pulverizing the wood material A are classified using two types of sieves, large and small, and the first wood granular pieces 2b, ..., 2b selected by classification are used as the wood pulverized pieces 2, ..., 2 for the core layer 11, and the second wood granular pieces 2c, ..., 2c that are finer than the first wood granular pieces 2b, ..., 2b that have passed both types of sieves are used as the wood pulverized pieces 2, ..., 2 for the surface layer 12. 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.

[0037] 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.

[0038] 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.

[0039] [Wood cuttings] The wood shavings 3, ..., 3 used in the core layer 11 are produced from a wood material B during the formation of a wood board 50 different from the particle board 10 according to the present invention. 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.

[0040] In the particle board 10 of this embodiment 1, when forming the above-mentioned wood board 50, of the numerous small wood flakes 3b, ..., 3b obtained by cutting the wood material B to obtain numerous wood flakes 3a, ..., 3a having a thickness of 0.05 to 0.35 mm and further crushing these, the wood flakes other than the numerous first small wood flakes 3c, ..., 3c selected by classification are used as the wood cutting pieces 3, ..., 3 to be included in the core layer 11. Specifically, by classifying a large number of small wood flakes 3b, ..., 3b using two types of sieves, large and small, appropriately selected, a large number of small wood flakes 3b, ..., 3b are selected, and second small wood flakes 3d, ..., 3d that are finer than the first small wood flakes 3c, ..., 3c that have passed through both types of sieves, and third small wood flakes 3e, ..., 3e that are coarser than the first small wood flakes 3c, ..., 3c that have not passed through both types of sieves are also obtained. In this embodiment 1, the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e that have not been selected by this classification are used as the wood cuttings 3, ..., 3 to be included in the core layer 11. In other words, in this embodiment 1, among the small wood flakes 3b, ..., 3b obtained by cutting and crushing the wood material B, those that are not classified and are not used for the wood board 50 can be used as the wood cutting pieces 3, ..., 3 to be included in the core layer 11.

[0041] 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.

[0042] The first small woody flakes 3c used to form the wood board 50 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 due to 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.

[0043] 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, and this classification also produces the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e to be used in the core layer 11.

[0044] In the first embodiment, as described above, after the numerous woody flakes 3a, ..., 3a are crushed, the woody flakes other than the first woody flakes 3c, ..., 3c selected by classification (the second woody flakes 3d, ..., 3d and the third woody flakes 3e, ..., 3e) can be used as the woody shavings 3, ..., 3 in the core layer 11 of the particle board 10. However, the woody flakes 3, ..., 3 constituting the core layer 11 of the particle board 10 are not limited to those described above. The first woody flakes 3c, ..., 3c used in the wood board 50 may be used as the woody shavings 3, ..., 3 constituting the core layer 11. Also, the woody flakes 3a, ..., 3a before crushing after cutting and the numerous woody flakes 3b, ..., 3b before classification after crushing may be used as the woody shavings 3, ..., 3 constituting the core 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 core 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 core layer 11.

[0045] 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.

[0046] 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, .

[0047] 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.

[0048] 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 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 in the hot press process, and furthermore, the hardening of the adhesive may be inhibited, which may reduce the bending strength.

[0049] <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.

[0050] -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.

[0051] <Wood piece production process S1> The wood piece producing process S1 includes a wood crushed piece producing process S11, a wood cutting piece producing process S12, and a wood piece mixing process S13.

[0052] [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.

[0053] (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.

[0054] (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.

[0055] (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 to 5 mm) 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 first wood granules 2b, ..., 2b classified and selected in this manner are used as wood crushed pieces 2, ..., 2 for the core layer 11, and the second wood granules 2c, ..., 2c obtained at the same time are used as wood crushed pieces 2, ..., 2 for the surface layer 12.

[0056] [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 second wood thin pieces 3d, ..., 3d and the third wood thin pieces 3e, ..., 3e generated during the formation of the wood board 50 are used as the wood cutting pieces 3, ..., 3 for the core layer 11. Therefore, the wood cutting piece preparation process S12 is a part of the method for manufacturing the wood board 50.

[0057] (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.

[0058] (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.

[0059] 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.

[0060] (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.

[0061] 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.

[0062] 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.

[0063] (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 the first woody small flakes 3c, ..., 3c of the desired size that pass through the coarse sieve but not the fine sieve, the 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 the 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 second woody small flakes 3d, ..., 3d and the third woody small flakes 3e, ..., 3e other than the first woody small flakes 3c, ..., 3c classified and selected in this way are used as the woody cutting pieces 3, ..., 3 for the core layer 11.

[0064] [Wood piece mixing process S13] In the wood piece mixing process S13, the numerous wood crushed pieces 2, ..., 2 (first wood granular pieces 2b, ..., 2b) for the core layer 11 produced in the wood crushed piece production process and the numerous wood cutting pieces 3, ..., 3 (second wood small slices 3d, ..., 3d and third wood small slices 3e, ..., 3e) for the core layer 11 produced in the wood cutting piece production process are mixed at the desired mixing ratio (the wood cutting pieces 3, ..., 3 are 10 to 90% by weight relative to the total weight of the wood pieces 1, ..., 1).

[0065] In the wood piece production process S1, the above-mentioned wood crushed piece production process S11, wood shavings production process S12, and wood piece mixing process S13 are carried out to produce wood pieces 1, ..., 1 for the core layer 11 (a mixture of first wood granular pieces 2b, ..., 2b and second small wood pieces 3d, ..., 3d and third small wood pieces 3e, ..., 3e) and wood pieces 1, ..., 1 for the surface layer 12 (second wood granular pieces 2c, ..., 2c).

[0066] <Adhesive application process S2> The wood pieces 1, ..., 1 for the core layer 11 and the wood pieces 1, ..., 1 for the surface layer 12 produced in the wood piece production 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.

[0067] <Mat forming process S3> In the mat forming process S3, as shown on the left side of FIG. 6, first, a 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 number of wood pieces 1, ..., 1 for the core 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 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.

[0068] At this time, the thicknesses of the first to third mats 9a to 9c are adjusted to obtain the desired ratio of the thickness of the core 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 (skin layer 12: core layer 11: surface layer 12 = 15:70:15), the mats 9 are formed so that the thickness (height) of the first and third mats 9a, 9c that will become the surface layers 12 is about 13.5 mm, and the thickness (height) of the second mat 9b that will become the core layer 11 is about 63 mm.

[0069] <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.

[0070] 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.

[0071] -Effects of embodiment 1- In the present embodiment 1, the core layer 11 of the particle board 10 with a three-layer structure contains not only the wood pulverized pieces 2, ..., 2 (first wood granular pieces 2b, ..., 2b) that are usually contained, but also the wood shavings 3, ..., 3 that are extremely thin, with a thickness of 0.05 to 0.35 mm. With this configuration, the bending strength of the core layer 11 of the particle board 10 is increased. Therefore, in order to ensure the bending strength of the particle board 10, it is not necessary to increase the density of the surface layer 12 or use a large amount of adhesive. Furthermore, compared to when the core layer 11 is composed of only the wood pulverized pieces 2, ..., 2, the presence of the thin wood shavings 3, ..., 3 makes it easier to bond the wood pieces 1, ..., 1 (the wood pulverized pieces 2, ..., 2 and the wood shavings 3, ..., 3) to each other with a small amount of adhesive. Therefore, according to the particle board 10 with a three-layer structure of the present embodiment 1, it is possible to reduce the amount of adhesive used while ensuring the bending strength of the conventional one.

[0072] 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).

[0073] Furthermore, according to the particleboard 10 of this embodiment 1, the core layer 11 contains many thin wood shavings 3, ..., 3 which have a larger area than the granular wood crushed chips 2, ..., 2, so screws are less likely to come out than in a conventional three-layer particleboard whose core layer is made only of granular wood crushed chips. Therefore, according to the particleboard 10 of this embodiment 1, by including the wood shavings 3, ..., 3 in the core layer 11, the core layer 11 is reinforced and the screw pull-out strength (wood screw holding power) is significantly improved, making it suitable for use as a load-bearing subsurface material to which screws are applied.

[0074] As described later, the inventors of the present application conducted a test to verify the effect of including extremely thin wood shavings 3, ..., 3 having a thickness of 0.05 to 0.35 mm in the core layer 11 of a three-layer particleboard 10. As a result, it was found that the particleboard 10 including the thin wood shavings 3, ..., 3 in the core layer 11 had improved normal bending strength (MOR), linear expansion coefficient (LE) and wood screw holding strength (WS) compared to a conventional particleboard not including the thin wood shavings 3, ..., 3 in the core layer 11, and that the water absorption thickness swelling coefficient (TS) was somewhat improved, although not significantly improved, and that the absolute value of the water absorption thickness swelling coefficient (TS) fully met the standard (12% or less) required for structural particleboard.

[0075] As described above, according to the first embodiment, it is possible to provide a three-layer particle board 10 that is excellent in surface properties, bending strength, and screw pull-out strength and that is small in dimensional change, without increasing cost or weight.

[0076] In addition, in this embodiment 1, the wood shavings 3, ..., 3 are generated when the wood material B is processed to form the other wood board 50. Therefore, even if a material (wood shavings 3, ..., 3) different from the material (ground wood chips 2, ..., 2) used for normal particle boards is used, it can be easily procured because the different material is generated during material processing of the other wood board 50. Therefore, according to this embodiment 1, it is possible to easily and relatively inexpensively provide a three-layer particle board 10 that has excellent surface properties, bending strength, and screw pull-out strength and has little dimensional change.

[0077] -Verification of effectiveness- In order to verify the above-mentioned effect of including the wood shavings 3, ..., 3 in the core layer 11 of the particleboard 10, the inventors prepared the following five types of particleboard 10 (test specimens X0 to X4) and conducted bending strength tests, water absorption thickness expansion coefficient tests, and wood screw retention tests in accordance with JIS A5908 to obtain normal bending strength (MOR), water absorption thickness expansion coefficient (TS), water absorption linear expansion coefficient (LE), and wood screw retention strength (WS), and obtained the results shown in Fig. 7. Note that the test specimens X0 to X4 have different mixing ratios of the wood shavings 3, ..., 3 in the core layer 11, and are otherwise configured similarly to the particleboard 10 of the first embodiment. Fig. 7 also shows the test results of the test specimens X1 to X4 in relative proportions when the test results of the test specimen X0 are set to 100. Test specimen X0: The mixture ratio of wood cutting pieces 3, ..., 3 in the core layer 11 is 0% by weight. Specimen X1: The mixture ratio of wood cuttings 3, ..., 3 in the core layer 11 is 20% by weight. Specimen X2: The mixture ratio of wood cuttings 3, ..., 3 in the core layer 11 is 40% by weight. Specimen X3: The mixture ratio of wood cutting pieces 3, ..., 3 in the core layer 11 is 60% by weight. Specimen X4: The mixture ratio of wood cutting pieces 3, ..., 3 in the core layer 11 is 80% by weight.

[0078] As shown in Fig. 7, the particle boards 10 (specimens X2 to X4) in which the core layer 11 contains 40% or more by weight of wood shavings 3, ..., 3 have improved normal bending strength (MOR) compared to the conventional particle board (specimen X0) that does not contain wood shavings 3, ..., 3 in the core layer 11. In addition, the higher the mixing ratio of the wood shavings 3, ..., 3 in the core layer 11, the higher the normal bending strength (MOR).

[0079] Regarding dimensional change, the particleboards 10 (specimens X1 to X4) containing the wood shavings 3, ..., 3 in the core layer 11 showed some improvement in water absorption thickness expansion coefficient (TS) compared to the conventional particleboard (specimen X0) not containing the wood shavings 3, ..., 3 in the core layer 11, although there was no significant improvement. The absolute value of the water absorption thickness expansion coefficient (TS) fully satisfied the standard (12% or less) required for structural particleboards. On the other hand, the particleboards 10 (specimens X1 to X4) containing the wood shavings 3, ..., 3 in the core layer 11 showed an improvement in water absorption linear expansion coefficient (LE) compared to the conventional particleboard (specimen X0) not containing the wood shavings 3, ..., 3 in the core layer 11. Also, the higher the mixing ratio of the wood shavings 3, ..., 3 in the core layer 11, the higher the improvement rate of the water absorption linear expansion coefficient (LE).

[0080] Also, the particle boards 10 (specimens X1 to X4) in which the core layer 11 contained the wood shavings 3, ..., 3 showed improved wood screw holding strength (WS) compared to the conventional particle board (specimen X0) in which the core layer 11 did not contain the wood shavings 3, ..., 3. When the mixing ratio of the wood shavings 3, ..., 3 in the core layer 11 was 40% by weight or more, the improvement rate of wood screw holding strength (WS) was 40% or more.

[0081] As described above, the particleboards 10 (specimens X2 to X4) having the wood shavings 3, ..., 3 in the core layer 11 had higher normal bending strength (MOR) and wood screw holding power (WS) and lower coefficient of linear water expansion (LE) compared to the conventional particleboard (specimen X0) that did not have the wood shavings 3, ..., 3 in the core layer 11. These results show that by having the wood shavings 3, ..., 3 in the core layer 11 of the three-layer particleboard 10, it is possible to provide a three-layer particleboard 10 that not only has excellent surface properties like the conventional ones, but also has excellent bending strength and screw pull-out strength and has little dimensional change, without increasing cost or weight.

[0082] Second Embodiment of the Invention The particle board 10 according to the second embodiment is a modified version of the particle board 10 according to the first embodiment. Specifically, as shown in Fig. 8, the particle board 10 according to the second embodiment contains wood shavings 3, ..., 3 not only in the core layer 11 but also in the surface layer 12. That is, in the second embodiment, both the core layer 11 and the surface layer 12 contain not only a large number of pulverized wood chips 2, ..., 2 but also a large number of wood shavings 3, ..., 3.

[0083] Like the wood shavings 3, ..., 3 used in the core layer 11, the wood shavings 3, ..., 3 used in the surface layer 12 are made of small wood flakes 3b, ..., 3b formed by cutting and crushing the wood material B to form the wood board 50, and those that are not classified and are not used in the wood board 50 (second small wood flakes 3d, ..., 3d and third small wood flakes 3e, ..., 3e) are used as the wood shavings 3, ..., 3 to be included in the surface layer 12.

[0084] In addition, like the wood cutting pieces 3, ..., 3 used in the core layer 11, 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 crushing after cutting or the many small wood slices 3b, ..., 3b before classification after crushing 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 combination. 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.

[0085] The other configurations are the same as those in the first embodiment.

[0086] The method for producing the particleboard 10 is different from that of the first embodiment only in the wood chip mixing step S13, and the other steps are the same as those of the first embodiment.

[0087] In embodiment 2, in the wood piece mixing process S13, wood fragments 2, ..., 2 and wood cutting pieces 3, ..., 3 are mixed to produce wood pieces 1, ..., 1 for the core layer 11 and wood pieces 1, ..., 1 for the surface layer 12.

[0088] Specifically, the wood pieces 1, ..., 1 for the core layer 11 are produced in the same manner as in the wood piece mixing step S13 of embodiment 1. The wood pieces 1, ..., 1 for the core layer 11 are produced by mixing a large number of wood pulverized pieces 2, ..., 2 for the core layer 11 (first wood grain pieces 2b, ..., 2b) produced in the wood pulverized piece production step with a large number of wood shavings 3, ..., 3 for the core layer 11 (second wood small flakes 3d, ..., 3d and third wood small flakes 3e, ..., 3e) produced in the wood shavings production step at a desired mixing ratio (the wood shavings 3, ..., 3 relative to the total weight of the wood pieces 1, ..., 1 is 10 to 90% by weight).

[0089] On the other hand, the wood pieces 1, ..., 1 for the surface layer 12 are produced by mixing a large number of ground wood pieces 2, ..., 2 for the surface layer 12 (second wood granular pieces 2c, ..., 2c) produced in the ground wood piece production process with a large number of wood cutting pieces 3, ..., 3 for the surface layer 12 (second small wood pieces 3d, ..., 3d and third small wood pieces 3e, ..., 3e) produced in the wood cutting piece production process, at 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).

[0090] -Effects of embodiment 2- In the second embodiment, the three-layer particleboard 10 includes extremely thin wood shavings 3, ..., 3 having a thickness of 0.05 to 0.35 mm not only in the core layer 11 but also in the surface layer 12. This configuration increases the bending strength of the particleboard 10 not only in the core layer 11 but also in the surface layer 12. Therefore, there is no need to increase the density of the surface layer 12 or use a large amount of adhesive in order to ensure the bending strength of the particleboard 10. Furthermore, by including the wood shavings 3, ..., 3 in not only the core layer 11 but also the surface layer 12, the amount of adhesive used can be further reduced compared to the particleboard 10 of the first embodiment, in which the wood shavings 3, ..., 3 are included only in the core layer 11.

[0091] 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).

[0092] Furthermore, according to the particle board 10 of the second embodiment, by including the wood shavings 3, ..., 3 not only in the core layer 11 but also in the surface layer 12, the screws are less likely to come out compared to the first embodiment, in which the wood shavings are included only in the core layer 11. Therefore, according to the second embodiment, it is possible to provide a three-layer particle board 10 with superior screw pull-out strength (wood screw holding power).

[0093] Furthermore, according to the particle board 10 of the second embodiment, if the surface layer 12 were formed only from the crushed wood chips 2, ..., 2, many gaps would be formed between the crushed wood chips 2, ..., 2, but because the flaky wood shavings 3, ..., 3 are mixed in, the flaky wood shavings 3, ..., 3 fill the many gaps, making the gaps smaller and fewer. Therefore, the particle board 10 of the second embodiment is more resistant to moisture penetration and has excellent water resistance compared to conventional particle boards whose surface layer is composed only of crushed wood chips.

[0094] Furthermore, in conventional particle boards whose surface layer is made only of crushed wood chips, the crushed wood chips are crushed during press molding, and when moisture penetrates the inside, the moisture is 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 inside compared to conventional particle boards, as described above, and therefore does not absorb moisture and therefore does not undergo large changes in dimensions (length and thickness).

[0095] As described above, according to the second embodiment, a three-layer particle board 10 having excellent surface properties, bending strength, screw pull-out strength and water resistance and small dimensional change can be provided without increasing cost and weight.

[0096] In the second embodiment, the wood chips 3, ..., 3 contained in the core layer 11 and the surface layer 12 are selected from the wood chips 3b, ..., 3b and classified to be 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 waste wood that is not used in the other wood board 50 and is generated during the formation of the other wood board 50 is used as the wood chips 3, ..., 3 for the core layer 11 and the surface layer 12 of the three-layer particle board 10, so that the three-layer particle board 10 can be formed more inexpensively. In addition, the wood material B of the other wood board 50 is used without waste, which leads to effective use of wood resources.

[0097] Other Embodiments In the above-mentioned first and second embodiments, the two surface layers 12, 12 are configured to be thinner (higher) than the core layer 11. However, the two surface layers 12, 12 may be thicker than the core layer 11.

[0098] In addition, in the above embodiments 1 and 2, examples have been described in which wood shavings generated during material processing of other wood boards 50 are used as the wood shavings 3, ..., 3. However, the wood shavings 3, ..., 3 may not be generated during material processing of other wood boards 50, but may be procured for the purpose of forming the above-mentioned particle board 10. [Industrial Applicability]

[0099] The present invention is useful for particleboards having a three-ply structure. [Explanation of symbols]

[0100] 2 crushed wood pieces 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 Core layer 12 Surface layer 50 Wood Board

Claims

1. A three-layer particle board in which the surface layer uses finer wood chips than the core layer, The core layer contains numerous wood chips having a thickness of 0.05 to 0.35 mm. A particle board characterized by:

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

3. The particle board according to claim 1 or 2, 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:

4. 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 contained at least in 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:

Images