Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
  • B27N—MANUFACTURE BY DRY PROCESSES OF ARTICLES, WITH OR WITHOUT ORGANIC BINDING AGENTS, MADE FROM PARTICLES OR FIBRES CONSISTING OF WOOD OR OTHER LIGNOCELLULOSIC OR LIKE ORGANIC MATERIAL
  • B27N3/00—Manufacture of substantially flat articles, e.g. boards, from particles or fibres
  • B27N3/06—Making particle boards or fibreboards, with preformed covering layers, the particles or fibres being compressed with the layers to a board in one single pressing operation

Definitions

• the present invention relates to a three-layer particle board and a method for manufacturing a three-layer particle board.
• Patent Document 1 discloses that particleboard, which is made by applying adhesive to crushed wood chips, is piled up in a mat shape and hot-pressed with a hot plate, is used as an alternative material to plywood.
• Patent Document 1 also discloses a three-layer particleboard in which crushed wood chips are classified, and coarse crushed wood chips are used as the core material and fine crushed wood chips are used as the surface layer.
• Particleboard can be made relatively inexpensively because crushed pieces of waste materials and recycled materials can be used as constituent materials. Even if waste materials and recycled materials are not used, three-layer particleboard can be made relatively inexpensively because all of the crushed wood chips made by crushing wood materials are used without waste. Thus, three-layer particleboard is excellent as an alternative to plywood because it can be made relatively inexpensively.
• three-layer particleboard uses fine crushed wood chips for the surface layer, it has improved surface properties (smoothness) compared to single-layer particleboard made of coarse crushed wood chips, but its bending strength is lower. Increasing the density of the surface layer to ensure a certain level of bending strength in three-layer particleboard creates the problem of increased weight and the need for more adhesive. Particleboard also has low screw pull-out strength, meaning it cannot be used as a load-bearing surface material for screw installation, and it also has the problem of lacking dimensional stability due to moisture absorption.
• the present invention was made in consideration of these points, and its purpose is to provide a three-layer particle board that has excellent surface properties, bending strength, and screw pull-out strength, and has little dimensional change, without increasing cost or weight.
• the present invention involves incorporating a large number of extremely thin wood shavings into the core layer of a three-layer particle board.
• the first invention is based on a three-layer particleboard in which the surface layer is made of finer wood chips than the core layer.
• the first invention is characterized in that the core layer contains numerous thin wood chips with a uniform thickness of 0.05 mm or more and 0.35 mm or less.
• ground wood chips refer to wood chips of various shapes and of non-uniform thickness, which are formed by finely grinding wood material with a known grinding device until it passes through a sieve with a specified mesh size installed at the discharge outlet of the grinding device.
• shaved wood chips refer to thin, flake-like wood chips of uniform thickness, which are formed by cutting wood material into a thin, uniform thickness with a known cutting device having a blade that cuts material into a thin, uniform thickness. Note that "shaved wood chips have a uniform thickness” allows for thickness variations due to processing errors of the cutting device, for example, a thickness variation of about ⁇ 20% is allowed.
• the core layer of the three-layer particle board contains not only the crushed wood chips that are usually included, but also wood chips that have an extremely thin and uniform thickness of 0.05 mm to 0.35 mm, which are produced by cutting.
• This configuration increases the bending strength of the core layer of the particle board. 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.
• the presence of the thin-flaky wood chips makes it easier to bond the wood chips (crushed wood chips and wood chips) together with a small amount of adhesive. Therefore, with the three-layer particle board of the first invention, it is possible to reduce the amount of adhesive used while maintaining the same bending strength as before.
• the particle board according to the first invention has an excellent surface property (smoothness) because the surface layer is made up of relatively fine wood chips, just like conventional particle boards with a three-layer structure.
• the core layer when some of the crushed wood chips in the core layer are replaced with wood shavings that are thinner than the crushed wood chips, the core layer contains more wood shavings than the crushed wood chips before replacement.
• the wood shavings have a uniform thickness and a flat surface. Therefore, when a large number of wood shavings are included in the core layer (when some of the crushed wood chips in the core layer are replaced with wood shavings), the total surface area of the many wood chips that make up the core layer increases significantly, making it more difficult for screws to come out than in a conventional three-layer particleboard in which the core layer is composed only of crushed wood chips.
• the core layer is reinforced and the screw pull-out strength (wood screw holding power) is significantly improved, making it suitable for a load-bearing subsurface material to be installed with screws.
• the inventors of the present application conducted a test to verify the effect of including extremely thin flake-like wood chips with a thickness of 0.05 mm to 0.35 mm in the core layer of a three-layer particleboard.
• particleboard containing wood chips in the core layer had improved normal bending strength (MOR), water absorption length change rate (LE), and wood screw holding strength (WS) compared to conventional particleboard that did not contain wood chips in the core layer, and that while there was no significant improvement in water absorption thickness expansion rate (TS), there was some improvement, and that the absolute value of water absorption thickness expansion rate (TS) fully met the standard (12% or less) required for structural particleboard.
• MOR normal bending strength
• LE water absorption length change rate
• WS wood screw holding strength
• the first invention it is possible to provide a three-layer particle board that has excellent surface properties, bending strength, and screw pull-out strength, and has little dimensional change, without increasing cost or weight.
• the second invention is the first invention, characterized in that the surface layer contains a large number of the wood cuttings.
• extremely thin flake-like wood chips with a thickness of 0.05 mm to 0.35 mm are included not only in the core layer of a three-layer particle board but also in the surface layer.
• the bending strength of not only the core layer but also the surface layer of the particle board is increased. Therefore, there is no need to increase the density of the surface layer or use a large amount of adhesive to ensure the bending strength of the particle board.
• the amount of adhesive used can be further reduced compared to when they are included only in the core layer.
• the wood chips are extremely thin, with a thickness of 0.05 mm to 0.35 mm, so even if they are included in the surface layer, they are unlikely to cause unevenness on the surface. Therefore, the surface properties (smoothness) are excellent, just like conventional particle boards.
• the particleboard according to the second invention by including wood chips not only in the core layer but also in the surface layer, the screws are less likely to come loose. Therefore, with the second invention, it is possible to provide a three-layer particleboard with superior screw pull-out strength (wood screw holding power).
• the particleboard according to the second invention is more resistant to moisture penetration and has excellent water resistance compared to conventional particleboards whose surface layer is composed only of ground wood chips.
• the crushed wood chips which are not cut to a thin thickness, are crushed during press molding, and when moisture penetrates the interior, the crushed wood chips absorb the moisture and tend to swell, resulting in large changes in dimensions (changes in length and thickness).
• the particle board of the second invention as described above, has a structure that makes it more difficult for moisture to penetrate into the interior than conventional particle boards, and since the many replaced wood cutting pieces are cut to a thin thickness, there is no large change in dimensions (length and thickness) due to absorption of moisture.
• the inventors of the present application conducted a test to verify the effect of including extremely thin flake-like wood chips with a thickness of 0.05 mm to 0.35 mm in both the core and surface layers of a three-layer particleboard.
• particleboards containing wood chips in both the core and surface layers have improved normal bending strength (MOR), wet bending strength (wet MOR), moisture absorption length change (LE), moisture absorption and release length change (HLE) and wood screw holding strength (WS) compared to conventional particleboards that do not contain wood chips in either the core or surface layers, and that while there was no significant improvement in moisture absorption thickness expansion (TS), there was some improvement, and the absolute value of moisture absorption thickness expansion (TS) fully meets the standard (12% or less) required for structural particleboards.
• MOR normal bending strength
• wet MOR wet bending strength
• LE moisture absorption length change
• HLE moisture absorption and release length change
• WS wood screw holding strength
• the second invention it is possible to provide a three-layer particleboard that has excellent surface properties, bending strength, screw pull-out strength, and water resistance, and has little dimensional change, without increasing cost or weight.
• the third invention is the first or second invention, characterized in that the core layer contains first wood chips as the wood pulverized pieces for the core layer, which pass through a first sieve with a mesh size of 16 mm or less, but do not pass through a second sieve with a mesh size of 0.5 mm or more and smaller than the first sieve, and the surface layer contains second wood chips as the wood pulverized pieces for the surface layer, which pass through both the first and second sieves.
• the core layer uses a large number of first wood chips that pass through a first sieve with a mesh size of 16 mm or less but do not pass through a second sieve with a mesh size of 0.5 mm or more that is smaller than the first sieve, and the surface layer uses fine second wood chips that pass through both the first and second sieves.
• the surface layer uses fine second wood chips that pass through both the first and second sieves.
• the fourth invention is the first or second invention, characterized in that in the core layer, the wood cuttings are mixed in a ratio of 20% by weight to 90% by weight of the total weight of the wood pieces for the core layer, which is composed of the crushed wood pieces and the wood cuttings contained in the core layer.
• the inventors of the present application have found from the results of the above verification tests that by mixing multiple wood chips for the core layer with wood chips in a ratio of 20% by weight to 90% by weight of the total weight of the core layer, the normal bending strength (MOR), water absorption length change (LE) and wood screw retention strength (WS) are improved, and that the higher the mixing ratio of wood chips in the core layer, the greater the improvement rate of normal bending strength (MOR) and water absorption length change (LE).
• MOR normal bending strength
• LE water absorption length change
• WS wood screw retention strength
• wood chips are mixed into the numerous core layer wood chips at a ratio of 20% to 90% by weight of the total weight.
• the fifth invention is a method for manufacturing a particleboard having a three-layer structure in which fine wood chips are used for the surface layer than for the core layer, comprising a first crushing step in which a first wood material is crushed to produce a large number of wood chips, and a second sieve in which the large number of wood chips are sieved using a first sieve having a mesh size of 16 mm or less and a second sieve having a mesh size of 0.5 mm or more and smaller than the first sieve to produce a large number of first wood chips that pass through the first sieve but not the second sieve, a large number of second wood chips that pass through both the first and second sieves, and a large number of wood chips that pass through the first and second sieves.
• a first classification step in which the first wood chips are classified into a number of pulverized wood chips for a core layer and a number of pulverized wood chips for a surface layer, the first wood chips being classified into a number of pulverized wood chips for a core layer and a number of pulverized wood chips for a surface layer; a cutting step in which the second wood material is cut so that the fibers are linearly present on the surface to produce a number of thin wood flakes having a uniform thickness of 0.05 mm to 0.35 mm; and a second crushing step in which the number of thin wood flakes and the number of thin wood flakes are crushed so that they are broken along the fiber direction to produce a number of small wood flakes having an elongated shape, and a number of small wood flakes produced by the above-mentioned number of thin wood flakes and the number of small wood flakes.
• crushing the first wood material means using a known crushing device to crush the first wood material finely until it passes through a sieve with a specified mesh size installed at the discharge outlet of the crushing device, and crushing forms wood chips of various shapes with non-uniform thickness.
• cutting the second wood material means cutting the second wood material thinly and uniformly by a known cutting device having a blade that cuts material thinly and uniformly, and cutting forms flake-like wood cutting pieces with uniform thickness. Note that "wood cutting pieces with uniform thickness” means that thickness variations due to processing errors are allowed, for example, thickness variations of about ⁇ 20% are allowed.
• the fifth invention makes it possible to provide a three-layer particleboard that has excellent surface properties, bending strength, and screw pull-out strength, and has little dimensional change, without increasing cost or weight.
• the sixth invention is the fifth invention, characterized in that the cutting process, the second crushing process, and the second classification process are included in a manufacturing method for a wood board in which a large number of the first small wood flakes that pass through the third sieve but not the fourth sieve are glued together in a collective state.
• the seventh invention is the sixth invention, characterized in that in the selection process, the numerous first woody thin pieces are selected as the numerous woody cutting pieces for the core layer.
• the eighth invention is the sixth invention, characterized in that in the selection process, the numerous second small wood flakes that pass through both the third and fourth sieves and the numerous third small wood flakes that do not pass through both the third and fourth sieves are selected as wood cutting pieces for the core layer.
• the wood shavings produced when the second wood material is processed to form another wood board are used as the wood shavings in the particle board. Therefore, even if a material (wood shavings) different from the material (ground wood chips) used in normal particle boards is used, it can be easily procured because the different material is the one produced when processing the material for the other wood board. Therefore, according to the sixth to eighth inventions, a three-layer particle board with excellent surface properties, bending strength, and screw pull-out strength and little dimensional change can be easily and relatively inexpensively provided.
• the wood chips contained in at least the core layer are made of materials other than the first small wood chips that are selected by classifying the small wood chips.
• waste material that is generated during the formation of other wood boards and is not used in other wood boards is used as wood chips for the core layer of the three-layer particle board, making it possible to form the three-layer particle board more inexpensively.
• the second wood material of the other wood boards is used without waste, this leads to the effective use of wood resources.
• the ninth invention is any one of the fifth to eighth inventions, characterized in that in the wood chip mixing step, the multiple core layer crushed wood chips and the multiple core layer wood chips are mixed so that the multiple core layer wood chips make up 20% to 90% by weight of the total weight of the multiple core layer wood chips.
• wood chips are mixed with a large number of core layer wood chips in a ratio of 20% by weight to 90% by weight of the total weight of the core layer.
• the core layer of a three-layer particleboard contains numerous flaky wood chips with an extremely thin and uniform thickness, making it possible to provide a three-layer particleboard with excellent surface properties, bending strength, and screw pull-out strength, and with little dimensional change, without increasing cost or weight.
• FIG. 1 is a cross-sectional view showing a part of a particle board according to a first embodiment.
• FIG. 2 is a diagram showing the process of producing ground wood pieces.
• FIG. 3 is a diagram showing the process of producing wood cutting pieces.
• FIG. 4 is an enlarged perspective view showing a first small wood piece.
• FIG. 5 is a diagram showing the manufacturing process of particle board.
• 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.
• FIG. 7 shows the results of an experiment to verify the effects of the first embodiment.
• FIG. 8 is a cross-sectional view showing a part of a particle board according to the second embodiment.
• FIG. 9 shows the results of an experiment to verify the effect of the second embodiment.
• 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.
• the particle board 10 is a board in which a large number of wood pieces 1, ..., 1 are bonded together in a collective state.
• the particle board 10 contains a large number of wood pieces 1, ..., 1 and an adhesive.
• the feature of the present invention is the constituent material (wood pieces 1) of the particle board 10, and the thickness and density are not particularly limited.
• the particle board 10 can be configured, for example, as a particle board specified in JIS A5908, so that it has a thickness of 5 mm to 40 mm and a density of 400 kg/m 3 to 900 kg/m 3.
• the bending strength is superior to that of conventional particle boards containing only wood crushed pieces 2, ..., 2. Therefore, for example, even if the thickness is 3 mm or more but less than 5 mm, sufficient bending strength can be ensured, and even if the density is less than 400 kg/m 3 , sufficient bending strength and peeling strength can be ensured.
• 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 core layer 11 and the surface layer 12 differ in the configuration of the wood pieces 1, 1 that they contain.
• Both the core layer 11 and the surface layer 12 contain numerous 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 are different in size, with the surface layer 12 using wood pulverized chips 2, ..., 2 that are finer than the core layer 11.
• the core layer 11 also contains not only numerous wood pulverized chips 2, ..., 2, but also numerous wood cutting chips 3, ..., 3.
• 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 wood pulverized chips 2, ..., 2 that are finer than the core layer 11.
• the wood crushed chips 2,...,2 are used as wood chips in conventional particle boards, while the wood shavings 3,...,3 used in the core layer 12 are used as a constituent material of another wood board 50, which will be described later.
• the core layer 11 uses a mixture of the wood crushed chips 2,...,2 used in conventional particle boards and the wood shavings 3,...,3 used as a constituent material of another wood board 50 as a number of wood chips 1,...,1, and the surface layer 12 uses the wood crushed chips 2,...,2 used in conventional particle boards as a number of wood chips 1,...,1.
• the wood shavings 3,...,3 are mixed at a ratio of 10% by weight to 90% by weight of the total weight of the wood chips 1,...,1.
• the wood pulverized pieces 2, 2 are obtained by finely pulverizing the wood material A with a known pulverizing device such as a crusher, hammer mill, pin mill, jet mill, ring flaker, cutter mill, etc. until it passes through a sieve with a predetermined mesh size provided at the outlet of the pulverizing device.
• a known pulverizing device such as a crusher, hammer mill, pin mill, jet mill, ring flaker, cutter mill, etc.
• wood chips 2a, 2a obtained by pulverizing the wood material A are classified using two types of sieves, one large and one small.
• a first sieve with a mesh size of 16 mm or less and a second sieve with a mesh size of 0.5 mm or more and smaller than the first sieve are used.
• the first wood chips 2b, ..., 2b that have been selected by classification i.e., pass through the first sieve but not the second sieve
• the second wood chips 2c, ..., 2c that have passed through both the first and second sieves i.e., are finer than the first wood chips 2b, ..., 2b
• a sieve having a mesh size of 16 mm or less for example, a sieve having a nominal mesh size of 2 mm or more and 16 mm or less as specified in JIS Z8801-1:2019 can be used, preferably a sieve having a nominal mesh size of 2.8 mm or more and 8 mm or less, and particularly preferably a sieve having a nominal mesh size of 4 mm or more and 5.6 mm or less.
• a sieve having a mesh size of 0.5 mm or more and smaller than the first sieve for example, a sieve having a nominal mesh size of 0.5 mm or more and 2 mm or less as specified in JIS Z8801-1:2019 can be used, preferably a sieve having a nominal mesh size of 0.5 mm or more and 1.4 mm or less, and particularly preferably a sieve having a nominal mesh size of 0.5 mm or more and 1 mm or less.
• the wood chips 2a, ..., 2a are classified and sorted using a sieve (first sieve) with a nominal mesh size of 4 mm and a sieve (second sieve) with a nominal mesh size of 1 mm (i.e., the chips pass through the first sieve but do not pass through the second sieve) and are used as the first wood chips 2b, ..., 2b.
• first sieve first sieve
• second sieve second sieve
• the third wood chips 2d, ..., 2d that do not pass through both types of sieves are not used as wood pulverized pieces 2, ..., 2 but are returned to the pulverizing device and pulverized again.
• the species of wood material A is not particularly limited, and any species of wood can be used as wood material A.
• fir wood such as cedar, cypress, and Douglas fir, acacia, aspen, poplar, pine (hard pine, soft pine, radiata pine, etc.), birch, rubber (rubber tree), etc. can be used as wood material A.
• 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.
• other imported materials such as balsa, cedar, mahogany,
• the wood cutting pieces 3, 3 used in the core layer 11 are produced from the wood material B when a wood board 50 different from the particle board 10 according to the present invention is formed.
• the wood board 50 is formed by cutting the wood material B into a thin and uniform thickness using a known cutting device having a blade for cutting the material into a thin and uniform thickness, and then crushing the resulting wood flakes 3a, 3a with a uniform thickness t (0.05 mm to 0.35 mm) into a thin and uniform thickness using a known crushing device to form a thin and uniform thickness of many wood flakes 3b, 3b, which are then classified using two types of sieves, large and small, and the first wood flakes 3c, 3c selected by the classification are bonded together in a collective state.
• a third sieve with a mesh size of 35 mm or less and a fourth sieve with a mesh size of 0.5 mm or more and smaller than the third sieve are used.
• a large number of first small wood flakes 3c, ..., 3c are selected, and also the third small wood flakes 3e, ..., 3e that pass through both the third and fourth sieves (i.e., the second small wood flakes 3d, ..., 3d that are finer than the first small wood flakes 3c, ..., 3c) and the third small wood flakes 3e, ..., 3e that do not pass through both the third and fourth sieves (i.e., the first small wood flakes 3c, ..., 3c) are obtained.
• the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e that are not selected by this classification are used as the wood cutting pieces 3, ..., 3 to be included in the core layer 11.
• the small wood pieces 3b, ..., 3b obtained by cutting and crushing the wood material B those that are not classified and are not used in the wood board 50 can be used as the wood cutting pieces 3, ..., 3 to be included in the core layer 11.
• a sieve with a mesh size of 35 mm or less for example, a sieve with a nominal mesh size of 5.6 mm or more and 31.5 mm or less as specified in JIS Z8801-1:2019 can be used, preferably a sieve with a nominal mesh size of 5.6 mm or more and 16 mm or less, and particularly preferably a sieve with a nominal mesh size of 5.6 mm or more and 8 mm or less.
• a sieve with a mesh size of 0.5 mm or more and smaller than the third sieve for example, a sieve with a nominal mesh size of 0.5 mm or more and 2 mm or less as specified in JIS Z8801-1:2019 can be used, preferably a sieve with a nominal mesh size of 0.5 mm or more and 1.4 mm or less, and particularly preferably a sieve with a nominal mesh size of 0.5 mm or more and 1 mm or less.
• the second woody flakes 3d, ..., 3d and the third woody flakes 3e, ..., 3e that were not selected by classification using a sieve (third sieve) with a nominal mesh size of 5.6 mm and a sieve (fourth sieve) with a nominal mesh size of 0.5 mm among the small woody flakes 3b, ..., 3b are used as the woody cutting pieces 3, ..., 3 to be included in the core layer 11.
• the thickness t of the wood flakes 3a is 0.05 mm or more and 0.35 mm or less, preferably 0.10 mm or more and 0.30 mm or less, more preferably 0.15 mm or more and 0.25 mm or less, and even more preferably 0.15 mm or more and 0.20 mm or less.
• the thickness t of the wood flakes 3a can be changed by changing the thickness setting (e.g., the speed at which the material is fed) of a known cutting device.
• the wood flakes 3a cut by the cutting device will have a uniform thickness t.
• multiple wood flakes 3a, ..., 3a cut by a cutting device whose thickness setting e.g., the speed at which the material is fed
• a cutting device whose thickness setting (e.g., the speed at which the material is fed) is set so that the thickness of the wood flakes 3a is t will have the same thickness t.
• the small wood flakes 3b and the first to third small wood flakes 3c to 3e that are obtained by classifying the small wood flakes 3b are crushed wood flakes 3a, they have a uniform thickness t, just like the wood flakes 3a.
• the numerous small wood flakes 3b, ..., 3b, the numerous small wood flakes 1 to 3c, ..., 3c, the numerous small second wood flakes 3d, ..., 3d, and the numerous small third wood flakes 3e, ..., 3e each have the same thickness t.
• the wood flakes 3a (as well as the smaller wood flakes 3b, the first smaller wood flakes 3c, the second smaller wood flakes 3b and the third smaller wood flakes 3e) have a uniform thickness t" means that thickness variations due to processing errors of the cutting device are allowed, for example, a thickness variation of about ⁇ 20% is allowed.
• the numerous woody flakes 3a, ..., 3a (as well as the numerous smaller woody flakes 3b, ..., 3b, the numerous first to third smaller woody flakes 3c, ..., 3c, the numerous second smaller woody flakes 3d, ..., 3d, and the numerous third smaller woody flakes 3e, ..., 3e) have the same thickness t" does not only mean that all of the woody flakes 3a, ..., 3a actually have the same thickness, but also means that cutting is performed using a cutting device in which the thickness setting (e.g., the material feeding speed) is adjusted so that the numerous woody flakes 3a, ..., 3a have the same thickness t, and the thickness varies by, for example, about ⁇ 20% due to biological variations in the wood material B and processing errors in the cutting device.
• the thickness setting e.g., the material feeding speed
• the wood material B is a natural material
• the biological characteristics of the wood material B such as the part (heartwood or sapwood), specific gravity (hardness), and fiber direction, affect (varies) the thickness of the numerous woody slices 3a, ..., 3a formed by contact with the blade. Therefore, the variation in thickness of the numerous woody slices 3a, ..., 3a can occur not only due to processing errors, but also due to the biological characteristics of the wood material B.
• the first small woody flakes 3c used to form the wood board 50 will now be described in detail.
• the first small woody flakes 3c have an elongated (striped) 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.
• the fiber direction dimension d1 is the length and the fiber orthogonal direction dimension d2 is the width
• the length d1 is 40 mm or less, preferably 35 mm or less, more preferably 30 mm or less, even more preferably 25 mm or less, and even more preferably 10 mm to 20 mm.
• the width d2 is 35 mm or less, preferably 15 mm or less, and more preferably 0.5 mm to 5 mm.
• the length d1 and width d2 of the first small woody flakes 3c are both average values.
• the length d1 and width d2 (both average values) of the first woody flakes 3c are calculated by photographing a large number of the first woody flakes 3c, ..., 3c, approximating the image of each of the first woody flakes 3c into an ellipse using known image analysis software, and averaging the length of the long side of the approximated ellipse as the dimension in the fiber direction and the short side as the dimension d perpendicular to the fiber.
• the first small wood flakes 3c, ..., 3c of such thickness, shape and size are selected by classifying the numerous small wood flakes 3b, ..., 3b using two appropriately selected large and small sieves (third and fourth sieves) as described above, and this classification also results in the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e to be used in the core layer 11.
• the wood cutting pieces 3, ..., 3 in the core layer 11 of the particle board 10 are not limited to those described above.
• the first small wood flakes 3c, ..., 3c used in the wood board 50 may be used as the wood cutting pieces 3, ..., 3 that constitute the core layer 11.
• wood flakes 3a, ..., 3a before crushing after cutting and the numerous small wood flakes 3b, ..., 3b before classification after crushing may be used as the wood cutting pieces 3, ..., 3 that constitute the core layer 11.
• all, 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 core layer 11.
• 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 core layer 11. All the flakes 3a to 3e selected as the woody cutting pieces 3 have a uniform thickness t, and the core layer 11 includes a large number of woody cutting pieces 3, ..., 3 having the same thickness t.
• the species of wood material B is not particularly limited, and any species of wood can be used as wood material B.
• fir materials such as cedar, cypress, and Douglas fir, acacia, aspen, poplar, pine (hard pine, soft pine, radiata pine, etc.), birch, rubber (rubber tree), etc. can be used as wood material B.
• 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.
• other imported materials such as balsa, cedar, mahogany,
• the numerous wood pieces 1, ..., 1 that make up the particle board 10 are made up of the crushed wood pieces 2, ..., 2 and shaved wood pieces 3, ..., 3 as described above.
• the density is preferably 250 kg/m 3 or more and 800 kg/m 3 or less, more preferably 300 kg/m 3 or more and 500 kg/m 3 or less. If the density is less than 250 kg/m 3 , it is possible to form a particle board 10 with the same density and bending strength by increasing the mixing ratio of wood flakes, but stable production becomes difficult.
• the density of the wood pieces 1 may exceed 800 kg/m 3 , but it is difficult to easily obtain such wood pieces 1. In other words, as long as wood pieces 1 exceeding 800 kg/m 3 can be easily obtained, the upper limit of the density is not limited to 800 kg/m 3 , and may be even higher.
• the moisture content of the wood pieces 1 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 during the hot press process in the press molding process, 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 during the hot press process, and the hardening of the adhesive may be inhibited, which may reduce the bending strength.
• the adhesive used for the particle board 10 is not particularly limited as long as it is a thermosetting adhesive.
• an isocyanate-based adhesive can be used.
• amine-based adhesives such as phenolic resin, urea resin, and melamine resin, and natural adhesives can also be used.
• 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.
• 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 hot pressing step S4.
• 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.
• the wood chip preparation process S11 includes a material preparation process S111, a crushing process S112, and a classification process S113.
• (Material preparation step S111) First, prepare a wooden material A. When using raw wood such as logs or thinned wood, the logs are cut into short pieces and the bark is removed to prepare the wooden material A. When using scraps or waste materials generated at construction sites, waste pallet materials, recycled materials, etc., the logs are cut into short pieces to prepare the wooden material A.
• the prepared wood material A is finely crushed into small pieces using a known crusher such as a crusher, hammer mill, pin mill, jet mill, ring flaker, cutter mill, etc., until it passes through a sieve with a predetermined mesh size provided at the outlet of the crusher.
• Wood chips 2a, ..., 2a are obtained by crushing the wood material A.
• the wood chips 2a, ..., 2a may have various shapes, such as powder, granules, rods, columns, fibers, flakes, etc.
• the wood chips 2a, ..., 2a obtained by crushing are classified into three sizes using two types of sieves (first and second sieves), one large and one small. Specifically, the wood chips 2a, ..., 2a are divided into first wood chips 2b, ..., 2b of a desired size that pass through the first coarse sieve but not through the second fine sieve, second wood chips 2c, ..., 2c that are finer than the first wood chips 2b, ..., 2b that have passed through both the first and second sieves, and third wood chips 2d, ..., 2d that are coarser than the first wood chips 2b, ..., 2b that do not pass through both the first and second sieves.
• first and second sieves two types of sieves
• the first wood chips 2b, ..., 2b thus classified and selected are used as the ground wood chips 2, ..., 2 for the core layer 11, and the second wood chips 2c, ..., 2c obtained at the same time are used as the ground wood chips 2, ..., 2 for the surface layer 12.
• the third wood chips 2d, ..., 2d are not used as the ground wood chips 2, ..., 2 but are returned to the grinding device and ground again.
• the wood cutting piece production process S12 includes a material preparation process S121, a cutting process S122, a crushing process S123, and a classification process S124.
• the second woody small slices 3d, ..., 3d and the third woody small slices 3e, ..., 3e generated during the formation of the wood board 50 are used as the woody cutting pieces 3, ..., 3 for the core layer 11. Therefore, the woody cutting piece production process S12 is a part of the process of the manufacturing method of the wood board 50.
• (Material preparation step S121) First, prepare a wood material B. When logs, thinned wood, or other raw wood are used, they are cut into short pieces and the bark is removed to prepare the wood material B. When scraps or waste wood generated at construction sites, waste pallet materials, recycled materials, or the like are used, they are cut into short pieces to prepare the wood material B.
• the prepared wood material B is cut into thin, uniform pieces 3a, ..., 3a with a uniform thickness t by a known cutting device having a blade for cutting the material into thin, uniform pieces using a known cutting device having a blade for cutting the material into thin, uniform pieces 3a, ..., 3a with a uniform thickness t.
• the thickness setting of the cutting device e.g., the speed at which the wood material B is fed
• the thickness setting of the cutting device is adjusted to form a large number of wood flakes 3a, ..., 3a with a uniform thickness t and with fibers a appearing linearly on the surface.
• the thickness of the small wood pieces 3b, ..., 3b obtained in the next crushing process will also be thickness t.
• the wood flakes 3a, ..., 3a When force is applied to the wood flakes 3a, ..., 3a in a random direction, the wood flakes 3a, ..., 3a usually break from the parts where the force is weak (they tend to break in the direction of the weak force). Since the force connecting the fibers 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 broken in the fiber direction by the above-mentioned crushing device (when force is applied), the wood flakes 3a, ..., 3a break along the fiber direction and shorten in the fiber direction, resulting in elongated small wood flakes 3b, ..., 3b.
• the woody flakes 3b, ..., 3b obtained by pulverization are classified into three sizes using two types of sieves (third and fourth sieves), large and small. Specifically, the woody flakes 3b, ..., 3b are divided into first woody flakes 3c, ..., 3c of desired size that pass through the coarse third sieve and do not pass through the fine fourth sieve, second woody flakes 3d, ..., 3d that pass through both the third and fourth sieves (i.e., finer than the first woody flakes 3c, ..., 3c), and third woody flakes 3e, ..., 3e that do not pass through both the third and fourth sieves (i.e., coarser than the first woody flakes 3c, ..., 3c).
• the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e other than the first small wood flakes 3c, ..., 3c classified and selected in this manner are used as the wood cutting pieces 3, ..., 3 for the core layer 11.
• wood piece production process S1 the above-mentioned wood crushed piece production process S11, wood cutting piece 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 the first wood chips 2b, ..., 2b and the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e) and wood pieces 1, ..., 1 for the surface layer 12 (the second wood chips 2c, ..., 2c).
• ⁇ Adhesive application step 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 be coated with adhesive.
• 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.
• ⁇ Mat forming process S3> In the mat forming process S3, as shown in 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.
• 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.
• 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 surface layer 12 to the entire particle board 10.
• the mats 9 are formed so that the thickness (height) of the first and third mats 9a, 9c that will become the surface layer 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.
• the ratio of the thickness of the core layer 11 and each surface layer 12 to the entire particle board 10 is not limited to the above ratio, and may be any ratio.
• ⁇ Heat pressing step S4> The mat 9 formed in the mat forming process S3 is carried into a hot press device and set between hot plates, where the mat 9 is compressed by hot pressing at a predetermined pressure and temperature. At this time, the adhesive hardens, bonding the numerous wood pieces 1, 1 together to form a single particle board 10, as shown on the right side of Fig. 6.
• the above-mentioned mat 9 having a thickness of about 90 mm is compressed to, for example, 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/ mm2 , and the pressing time is, for example, 1.5 to 3 minutes (for example, 10 to 20 seconds per mm 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.
• a preliminary heating process using a heating device may be performed before the hot press process using the hot press device.
• the core layer 11 of the particle board 10 having a three-layer structure contains not only the wood crushed pieces 2, ..., 2 (first wood chips 2b, ..., 2b) that are usually contained, but also wood cutting pieces 3, ..., 3 having a very thin and uniform thickness of 0.05 mm or more and 0.35 mm or less by cutting processing.
• 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.
• the core layer 11 is composed of only the wood crushed pieces 2, ..., 2, the presence of the thin wood cutting pieces 3, ..., 3 makes it easier to bond the wood pieces 1, ..., 1 (the wood crushed pieces 2, ..., 2 and the wood cutting pieces 3, ..., 3) to each other with a small amount of adhesive. Therefore, according to the particle board 10 having a three-layer structure of the first embodiment, it is possible to reduce the amount of adhesive used while maintaining the same bending strength as conventional particle boards.
• the surface layer 12 is composed of relatively fine wood pulverized pieces 2, ..., 2 (second wood chips 2c, ..., 2c), so that the surface properties (smoothness) are excellent.
• the core layer 11 contains more wood shavings 3, ..., 3 than the wood pulverized chips 2, ..., 2 before replacement.
• the wood shavings 3, ..., 3 have a uniform thickness and a flat surface.
• the core layer 11 contains a large number of wood shavings 3, ..., 3 (when some of the wood pulverized chips 2, ..., 2 contained in the core layer 11 are replaced with the wood shavings 3, ..., 3), the total surface area of the many wood pieces 1, ..., 1 that make up the core layer 11 increases significantly, and the screws become less likely to come loose compared to a conventional three-layer particle board in which the core layer is composed only of granular wood pulverized chips. Therefore, according to the particle board 10 of this embodiment 1, by including wood cuttings 3, ..., 3 in the core layer 11, the core layer 11 is reinforced and the screw pull-out strength (wood screw holding power) is significantly improved, making it suitable as a load-bearing sub-surface material for screw installation.
• the inventors of the present application conducted a test to verify the effect of including extremely thin, flaky wood shavings 3, ..., 3 with a thickness of 0.05 mm to 0.35 mm in the core layer 11 of a three-layer particleboard 10.
• the particleboard 10 including the thin wood shavings 3, ..., 3 in the core layer 11 had improved normal bending strength (MOR), water absorption length change rate (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 expansion rate (TS) was somewhat improved, although not significantly improved, and that the absolute value of the water absorption thickness expansion rate (TS) fully met the standard (12% or less) required for structural particleboard.
• MOR normal bending strength
• LE water absorption length change rate
• WS wood screw holding strength
• the core layer 11 uses a large number of first wood chips 2b, ..., 2b that pass through a first sieve with a mesh size of 16 mm or less but do not pass through a second sieve with a mesh size of 0.5 mm or more and smaller than the first sieve, and the surface layer 12 uses fine second wood chips 2c, ..., 2c that pass through both the first and second sieves.
• first wood chips 2b, ..., 2b that pass through a first sieve with a mesh size of 16 mm or less but do not pass through a second sieve with a mesh size of 0.5 mm or more and smaller than the first sieve
• the surface layer 12 uses fine second wood chips 2c, ..., 2c that pass through both the first and second sieves.
• the inventors of the present application have found that by mixing wood cutting pieces 3, ..., 3 (second small wood slices 3d, ..., 3d and third small wood slices 3e, ..., 3e) with a large number of wood cutting pieces 1, ..., 1 for the core layer 11 in a ratio of 20% by weight or more and 90% by weight or less of the total weight of the core layer 11, the normal bending strength (MOR), water absorption length change rate (LE) and wood screw holding strength (WS) are improved, and that the higher the mixing ratio of the wood cutting pieces 3, ..., 3 in the core layer 11, the greater the improvement rate of the normal bending strength (MOR) and water absorption length change rate (LE).
• MOR normal bending strength
• LE water absorption length change rate
• WS wood screw holding strength
• the wood shavings 3, ..., 3 are produced 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 in normal particle boards is used, it can be easily procured because the different material is the material produced during material processing of the other wood board 50. Therefore, according to the manufacturing method of this embodiment 1, a three-layer particle board 10 with excellent surface properties, bending strength, and screw pull-out strength and little dimensional change can be easily and relatively inexpensively provided.
• the wood chips 3, ..., 3 contained in at least the core layer 11 are those other than the first wood chips 3c, ..., 3c (the second wood chips 3d, ..., 3d and the third wood chips 3e, ..., 3e) selected by classifying the wood chips 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 as the wood chips 3, ..., 3 for the core layer 11 of the three-layer particle board 10, making it possible to form the three-layer particle board 10 more inexpensively.
• the wood material B of the other wood boards 50 is used without waste, this leads to effective use of wood resources.
• test specimen X0 was constructed in the same manner as a conventional particle board that does not include the wood cuttings 3, ..., 3, and the test specimens X1 to X4 have different mixing ratios of the wood cuttings 3, ..., 3 in the core layer 11, but are otherwise constructed in the same manner as the particle board 10 of the first embodiment.
• FIG. 7 also shows the test results of each of the test specimens X1 to X4 in relative proportions, with the test result of the test specimen X0 being set at 100.
• Specimen X0 The mixture ratio of the wood cuttings 3, ..., 3 in the core layer 11 is 0% by weight.
• Specimen X1 The mixture ratio of the wood cuttings 3, ..., 3 in the core layer 11 is 20% by weight.
• Specimen X2 The mixture ratio of the wood cuttings 3, ..., 3 in the core layer 11 is 40% by weight.
• Specimen X3 The mixture ratio of the wood cuttings 3, ..., 3 in the core layer 11 is 60% by weight.
• Specimen X4 The mixture ratio of the wood cuttings 3, ..., 3 in the core layer 11 is 80% by weight.
• particle boards 10 (specimens X2 to X4) containing 40% or more by weight of wood shavings 3, ..., 3 in the core layer 11 had improved normal bending strength (MOR) compared to a conventional particle board (specimen X0) that did not contain wood shavings 3, ..., 3 in the core layer 11. Furthermore, the higher the mixing ratio of wood shavings 3, ..., 3 in the core layer 11, the higher the normal bending strength (MOR).
• the particleboards 10 (test specimens X1 to X4) containing wood shavings 3, ..., 3 in the core layer 11 showed some improvement in water absorption thickness expansion (TS) compared to the conventional particleboard (test specimen X0) not containing wood shavings 3, ..., 3 in the core layer 11, although not a large improvement was observed, and the absolute value of the water absorption thickness expansion (TS) fully met the standard (12% or less) required for structural particleboards.
• the particleboards 10 (test specimens X1 to X4) containing wood shavings 3, ..., 3 in the core layer 11 showed an improvement in water absorption length change (LE) compared to the conventional particleboard (test specimen X0) not containing wood shavings 3, ..., 3 in the core layer 11. Also, the higher the mixing ratio of wood shavings 3, ..., 3 in the core layer 11, the higher the improvement rate of water absorption length change (LE).
• the particle boards 10 (test specimens X1 to X4) that contain wood shavings 3, ..., 3 in the core layer 11 also showed improved wood screw holding power (WS) compared to the conventional particle board (test specimen X0) that does not contain wood shavings 3, ..., 3 in the core layer 11. Furthermore, when the mixture ratio of wood shavings 3, ..., 3 in the core layer 11 was 40% by weight or more, the improvement rate of wood screw holding power (WS) was 40% or more.
• the particleboard 10 (specimens X2 to X4) containing wood shavings 3, ..., 3 in the core layer 11 had higher normal bending strength (MOR) and wood screw holding power (WS) and lower water absorption length change rate (LE) compared to the conventional particleboard (specimen X0) that does not contain wood shavings 3, ..., 3 in the core layer 11.
• MOR normal bending strength
• WS wood screw holding power
• LE water absorption length change rate
• 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.
• the ones not classified for use in the wood board 50 were used as the wood cutting pieces 3, ..., 3 to be included in the core layer 11, but in the second embodiment, the first small wood flakes 3c, ..., 3c used in the wood board 50 are used as the wood cutting pieces 3, ..., 3 that constitute the core layer 11. Also, in the second embodiment, the first small wood flakes 3c, ..., 3c used in the wood board 50 are used as the wood cutting pieces 3, ..., 3 used in the surface layer 12, similar to the wood cutting pieces 3, ..., 3 used in the core layer 11.
• the wood cutting pieces 3, ..., 3 used in the particle board 10 are not limited to those described above.
• the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e not used in the wood board 50 may be used as the wood cutting pieces 3, ..., 3 used in the particle board 10.
• the wood flakes 3a, ..., 3a before crushing after cutting and the numerous small wood flakes 3b, ..., 3b before classification after crushing may be used as the wood cutting pieces 3, ..., 3 used in the particle board 10.
• all or 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 used in the particle board 10.
• 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 used in the particle board 10.
• the manufacturing method for particle board 10 differs from embodiment 1 only in the wood chip mixing step S13, and the other steps are the same as in embodiment 1.
• wood crushed pieces 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.
• the wood pieces 1, ..., 1 for the core layer 11 are produced by mixing a large number of wood pulverized pieces 2, ..., 2 (first wood chips 2b, ..., 2b) for the core layer 11 produced in the wood pulverized piece production step with a large number of wood shavings 3, ..., 3 (first wood thin pieces 3c, ..., 3c) for the core layer 11 produced in the wood shavings production step at a desired mixing ratio (the wood shavings 3, ..., 3 relative to the total weight of the wood pieces 1, ..., 1 is 10% by weight or more and 90% by weight or less).
• the wood chips 1, ..., 1 for the surface layer 12 are produced by mixing a large number of wood pulverized chips 2, ..., 2 for the surface layer 12 (second wood chips 2c, ..., 2c) produced in the wood pulverized chip production process with a large number of wood shavings 3, ..., 3 for the surface layer 12 (first wood chips 3c, ..., 3c) produced in the wood shavings production process at a desired mixing ratio (the proportion of the wood shavings 3, ..., 3 to the total weight of the wood chips 1, ..., 1 is 10% by weight or more and 90% by weight or less).
• the wood chips 3 are extremely thin, with a thickness of 0.05 mm or more and 0.35 mm or less, so that even if they are included in the surface layer 12, unevenness is unlikely to occur on the surface. Therefore, the surface properties (smoothness) are excellent, just like conventional particle boards.
• the wood shavings 3, ..., 3 are included not only in the core layer 11 but also in the surface layer 12 (part of the wood crushed pieces 2, ..., 2 included in the surface layer 12 is replaced with the wood shavings 3, ..., 3).
• part of the wood crushed pieces 2, ..., 2 (second wood crushed pieces 2c, ..., 2c) for the surface layer 12, which are finer than the wood crushed pieces 2, ..., 2 (first wood crushed pieces 2b, ..., 2b) for the core layer 11, with the wood shavings 3, ..., 3 having a uniform thickness and a flat surface the total surface area of the many wood pieces 1, ..., 1 that make up the surface layer 12 is significantly increased. Therefore, according to the particle board 10 of the second embodiment, the screws are more difficult to pull out. 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).
• the particleboard 10 of the second embodiment by replacing some of the relatively fine wood crushed chips 2,...,2 of the surface layer 12 with wood cutting chips 3,...,3 having a uniform thickness and flat surfaces, the total surface area of the numerous wood chips 1,...,1 that make up the surface layer 12 is significantly increased.
• the bonding area between the numerous wood chips 1,...,1 increases, and the number of bonding points increases and the bonding points are uniformly distributed. Therefore, the particleboard 10 of the second embodiment is more resistant to moisture penetration and has excellent water resistance compared to conventional particleboards whose surface layer 12 is composed only of the wood crushed chips 2,...,2.
• the crushed wood chips which are not cut to a thin thickness, are crushed during press molding, and when moisture penetrates the interior, the crushed wood chips are more likely to absorb the moisture, which can cause significant dimensional changes (changes in length and thickness).
• the particle board 10 of this embodiment 2 has a structure that makes it more difficult for moisture to penetrate into the interior compared to conventional particle boards, and because the numerous replaced wood cutting pieces 3, ..., 3 are cut to a thin thickness, there is no significant change in the dimensions (length and thickness) due to absorption of moisture.
• the second embodiment it is possible to provide a three-layer particle board 10 that has excellent surface properties, bending strength, screw pull-out strength, and water resistance, and has little dimensional change, without increasing cost or weight.
• the first small wood flakes 3c, ..., 3c selected by classifying the small wood flakes 3b, ..., 3b are used as the wood cutting pieces 3, ..., 3 contained in the core layer 11 and the surface layer 12.
• the first small wood flakes 3c, ..., 3c selected by classification for use in other wood boards 50 have smaller variations in dimensions (length and width) than the second small wood flakes 3d, ..., 3d and the third small wood flakes 3e, ..., 3e used as the wood cutting pieces 3, ..., 3 in embodiment 1.
• Specimen X10 was constructed in the same manner as a conventional particle board that does not include wood cuttings 3, ..., 3, and specimens X11 and X12 were constructed in the same manner as the particle board 10 of embodiment 2, except that the mixture ratio of wood cuttings 3, ..., 3 in the core layer 11 and the surface layer 12 was different.
• FIG. 9 shows the test results of specimens X10, X11, and X12 in relative proportions when the test results of specimen X10 were set to 100.
• Specimen X10 The mixture ratio of the wood cuttings 3, ..., 3 in the core layer 11 and the surface layer 12 is 0% by weight.
• Specimen X11 The mixture ratio of the wood cuttings 3, ..., 3 in the core layer 11 is 40% by weight, and the mixture ratio of the wood cuttings 3, ..., 3 in the surface layer 12 is 0%.
• Specimen X12 The mixture ratio of the wood cuttings 3, ..., 3 in the core layer 11 is 40% by weight, and the mixture ratio of the wood cuttings 3, ..., 3 in the surface layer 12 is 40%.
• specimen X12 had significantly improved MOR and wet MOR compared to specimens X10 and X11. Furthermore, the improvement rates of specimen X12 over specimen X11 were 48% for MOR and 51% for wet MOR, which were significantly higher than the improvement rates of specimen X11 over specimen X10 (MOR 28%, wet MOR 26%).
• specimen X12 showed some improvement in water absorption thickness swelling (TS) compared to specimens X10 and X11, although not a large improvement, and the absolute value of water absorption thickness swelling (TS) fully met the standard required for structural particleboard (12% or less).
• specimen X12 showed an improvement in water absorption length change (LE) compared to specimens X10 and X11.
• the moisture absorption/desorption length change rate (HLE) of specimen X12 was significantly improved compared to specimens X10 and X11.
• the improvement rate of specimen X12 over specimen X11 was 26%, which was higher than the improvement rate of specimen X11 over specimen X10 (22%).
• the particleboard 10 (specimen X12) containing wood shavings 3, ..., 3 in the surface layer 12 showed an improved water resistance index (wet bending strength (wet MOR) / normal bending strength (MOR)) compared to the particleboards (specimens X10 and X11) that did not contain wood shavings 3, ..., 3 in the surface layer 12.
• the particleboard 10 (specimen X12) containing the wood shavings 3, ..., 3 in the core layer 11 and surface layer 12 had higher normal bending strength (MOR), wet bending strength (wet MOR), wood screw holding power (WS) and water resistance, and lower water absorption length change rate (LE) and moisture absorption/desorption length change rate (HLE), compared to the conventional particleboard (specimen X10) not containing the wood shavings 3, ..., 3.
• MOR normal bending strength
• wet MOR wet bending strength
• WS wood screw holding power
• HLE moisture absorption/desorption length change rate
• the particleboard 10 (specimen X12) containing the wood shavings 3, ..., 3 in the surface layer 12 had similar root mean square height Sq and arithmetic mean height Sa (indicators of surface properties) to the conventional particleboard (specimen X10) not containing the wood shavings 3, ..., 3 in the surface layer 12.
• the particleboard 10 in which the core layer 11 and surface layer 12 contain the wood shavings 3, ..., 3 has higher normal bending strength (MOR), wet bending strength (wet MOR) and water resistance, and lower water absorption length change rate (LE) and moisture absorption/desorption length change rate (HLE), compared to the particleboard 10 (specimen X11) in which the core layer 11 only contains the wood shavings 3, ..., 3.
• MOR normal bending strength
• wet MOR wet bending strength
• HLE moisture absorption/desorption length change rate
• the two surface layers 12, 12 are configured to be thinner (height) than the core layer 11, but the two surface layers 12, 12 may also be thicker than the core layer 11.
• wood cuttings generated during material processing of another wood board 50 are used as the wood cuttings 3, ..., 3.
• the wood cuttings 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.
• the present invention is useful for three-layer particle boards and methods for manufacturing three-layer particle boards.

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