JP7531039B1 - Particleboard and manufacturing method thereof - Google Patents

Abstract

[Problem] To manufacture a three-layer particleboard with excellent surface properties, water resistance, bending strength, and peel strength, and with little dimensional change, without increasing cost or weight. [Solution] In a three-layer particleboard 10 using fine wood pulverized pieces 2, ..., 2 in the surface layer 12, which is finer than the core layer 11, the surface layer 12 contains a large number of wood shavings 3, ..., 3 with a thickness of 0.05 to 0.35 mm. [Selected Figure] Figure 1

Description

The present invention relates to a particleboard having a three-layer structure and a method for manufacturing a particleboard having a three-layer structure .

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.

Patent Document 1 discloses that particleboard, which is made by applying adhesive to crushed wood chips, piling them into a mat shape and hot pressing them 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 made relatively inexpensively. Even if waste materials and recycled materials are not used, three-layer particleboard can be made relatively inexpensively because all of the wood chips made by crushing wood materials are used without waste. Thus, three-layer particleboard is excellent as an alternative to plywood in that it can be made relatively inexpensively.

International Publication No. 2005/115705

However, because three-layer particleboard uses fine ground wood chips for the surface layer, it has improved surface properties (smoothness) compared to single-layer particleboard made of coarse ground wood chips, but its bending strength is low. Increasing the density of the surface layer of three-layer particleboard to ensure a certain level of bending strength poses the problem of increased weight and increased use of adhesive. Three-layer particleboard also has the problem of low peel strength, and poor water resistance and 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, water resistance, bending strength, and peel strength, and has little dimensional change, without increasing cost or weight.

To achieve the above objective, the present invention uses a surface layer made of finely ground wood chips that are smaller than the core layer of a three-layer particle board, and contains a large number of extremely thin shaved wood chips.

Specifically, 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 surface layer contains numerous wood chips with a thickness of 0.05 to 0.35 mm.

Here, crushed wood chips refer to granular wood chips formed by crushing wood material, and shaved wood chips refer to thin pieces of wood formed by cutting wood material.

In the first invention, the surface layer of the three-layer particle board contains not only the fine wood chips that are usually included, but also extremely thin wood chips with a thickness of 0.05 to 0.35 mm. This configuration increases the bending strength of the surface 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. Furthermore, compared to when the surface layer is composed only of wood chips, the presence of thin wood chips makes it easier to bond the wood pieces (wood chips and wood chips) together with a small amount of adhesive. Therefore, with the three-layer particle board according to the first invention, it is possible to reduce the amount of adhesive used while ensuring bending strength.

In addition, with the particleboard according to the first invention, extremely thin wood chips, 0.05 to 0.35 mm thick, fill the gaps between the relatively fine wood chips on the surface, making it difficult for unevenness to form on the surface. In particular, when the thin wood chips are folded over on the surface of the particleboard, the surface becomes smoother, resulting in excellent surface properties (smoothness).

In addition, according to the particleboard of the first invention, if the surface layer is formed only from crushed wood chips, many gaps will be formed between the crushed wood chips, but because flaky wood chips are mixed in, the flaky wood chips get into the many gaps, making the gaps smaller and fewer. Therefore, the particleboard of the first invention is more resistant to moisture penetration and has excellent water resistance than conventional particleboards whose surface layer is composed only of crushed wood chips.

The inventors of the present application conducted a test to verify the effect of including extremely thin wood chips with a thickness of 0.05 to 0.35 mm in the surface layer of a three-layer particleboard. As a result, it was found that particleboard containing wood chips in the surface layer has improved normal bending strength (MOR), wet bending strength (wet MOR), water absorption length change (LE), and peel strength (IB) compared to conventional particleboard that does not contain wood chips in the surface layer.

As described above, according to the first invention, it is possible to provide a three-layer particle board that has excellent surface properties, water resistance, bending strength, and peel strength, and has little dimensional change, without increasing cost or weight.

The second invention is the first invention, characterized in that the above-mentioned 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 crushing a large number of thin wood flakes having a thickness of 0.05 to 0.35 mm obtained by cutting the wood material.

The third invention is the second invention, characterized in that the wood cutting pieces are the small wood flakes other than the first small wood flakes selected by classification.

In the second and third 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 material processing for other wood boards. Therefore, according to the second and third inventions, a three-layer particle board with excellent surface properties, water resistance, bending strength, and peel strength and small dimensional change can be easily and relatively inexpensively provided.

In particular, in the third invention, wood chips other than the first small wood chips that are selected by classifying the small wood chips are used as the 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 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 the effective use of wood resources.

As explained above, according to the present invention, the surface layer of the three-layer particle board is made of finer ground wood chips than the core layer, and contains a large number of extremely thin shaved wood chips. This makes it possible to provide a three-layer particle board with excellent surface properties, water resistance, bending strength, and peeling 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.

The following describes in detail the embodiments of the present invention with reference to the drawings. The following description of the embodiments is merely exemplary in nature and is in no way intended to limit the present invention, its applications, or its uses.

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.

Particleboard 10 is made up of a large number of wood pieces 1, 1 glued together in a collected state. Particleboard 10 contains a large number of 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 although there are no particular limitations on the thickness or density, particleboard 10 is configured to have a thickness of 3 mm to 25 mm and a density of 500 kg/ ^m3 to 800 kg/ ^m3 , for example.

<Wood chips>
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 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 chips 1, ..., 1, but the wood pulverized chips 2, ..., 2 used in the core layer 11 and the surface layer 12 have different particle sizes, with the surface layer 12 using wood pulverized chips 2, ..., 2 that are finer than the core layer 11. The surface layer 12 also contains not only numerous wood pulverized chips 2, ..., 2 but also numerous wood shavings 3, ..., 3. In other words, in this embodiment 1, the wood chips 1, ..., 1 of the core layer 11 are composed only of the wood pulverized chips 2, ..., 2, and the wood chips 1, ..., 1 of the surface layer 12 are composed of the wood pulverized chips 2, ..., 2 that are finer than the core layer 11 and the wood shavings 3, ..., 3.

In this embodiment 1, the wood crushed pieces 2, ..., 2 are used as wood pieces in conventional particle boards, while the wood cutting pieces 3, ..., 3 used in the surface layer 12 are used as a constituent material of another wood board 50, which will be described later. In other words, in this embodiment 1, the core layer 11 uses the wood crushed pieces 2, ..., 2 used in conventional particle boards as the numerous wood pieces 1, ..., 1, and the surface layer 12 uses a mixture of the wood crushed pieces 2, ..., 2 used in conventional particle boards and the wood cutting pieces 3, ..., 3 used as a constituent material of another wood board 50 as the numerous wood pieces 1, ..., 1. In the surface layer 12, the wood cutting pieces 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.

The following provides a detailed explanation of the wood crushed pieces 2, ..., 2 and wood shavings 3, ..., 3 used in the particle board 10.

[Wood chips]
As shown in Fig. 2, the wood pulverized pieces 2, ..., 2 are obtained by pulverizing the wood material A into granules using a known pulverizing device (chipper) such as a hammer mill, a pin mill, or a jet mill. In the particle board 10 of the present embodiment 1, as shown in Fig. 2, the wood granular pieces 2a, ..., 2a obtained by pulverizing the wood material A are classified using two types of sieves, large and small, and the 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 finer than the first wood granular pieces 2b, ..., 2b that passed through 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.

As shown in FIG. 2, the third wood grains 2d, ..., 2d, which are coarser than the first wood grains 2b, ..., 2b and do not pass through either of the two sieves as a result of the above classification, are not used as wood crushed pieces 2, ..., 2, but are returned to the chipper device and crushed again.

There are no particular limitations on the species of wood material A, and any species of tree can be used as wood material A. For example, fir wood such as cedar, cypress, and Douglas fir, acacia, aspen, poplar, pine (hard pine, soft pine, radiata pine, etc.), birch, rubber (rubber tree), etc. can be used as wood material A. In addition, domestic 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 wood material A.

[Wood cuttings]
The wood cutting pieces 3, 3 used in the surface layer 12 are produced from a wood material B when a wood board 50 different from the particle board 10 according to the present invention is formed. As shown in Fig. 3, the wood board 50 is formed by cutting a wood material B with a known cutting device (strander) to obtain 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, one large and one small, and the first small wood flakes 3c, 3c selected by the classification are bonded together in an aggregated state.

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 further crushing the numerous thin wood flakes 3a, ..., 3a having a thickness of 0.05 to 0.35 mm obtained by cutting the wood material B, the only ones used as the wood cutting pieces 3, ..., 3 to be included in the surface layer 12 are the numerous first small wood flakes 3c, ..., 3c selected by classification. 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 cutting pieces 3, ..., 3 to be included in the surface layer 12. In other words, in this embodiment 1, among the small wood flakes 3b, ..., 3b obtained by cutting and crushing the wood material B, those that are not classified and are not used in the wood board 50 can be used as the wood cutting pieces 3, ..., 3 to be included in the surface layer 12.

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 crushing the wood flakes 3a, the small wood flakes 3b also have the same thickness t as the wood flakes 3a.

The first small woody pieces 3c used to form the wood board 50 will now be described in detail. As shown enlarged in FIG. 4, the first small woody pieces 3c have an elongated (striped) shape in which the fiber direction dimension d1 along the fiber a of vessels, tracheids, etc. is longer than the fiber orthogonal direction dimension d2 perpendicular to the fiber direction. If the fiber direction dimension d1 is the length and the fiber orthogonal direction dimension d2 is the width, the length d1 is 40 mm or less, preferably 35 mm or less, more preferably 30 mm or less, even more preferably 25 mm or less, and even more preferably 10 mm 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 pieces 3c are both average values.

The first small wood flakes 3c, ..., 3c having such thickness, shape and size are selected by classifying the numerous small wood flakes 3b, ..., 3b using two types of sieves, large and small, appropriately selected 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 surface layer 12.

In this embodiment 1, as described above, after grinding a large number of woody flakes 3a, ..., 3a, the ones other than the first small woody flakes 3c, ..., 3c selected by classification (the second small woody flakes 3d, ..., 3d and the third small woody flakes 3e, ..., 3e) can be used as the woody cutting pieces 3, ..., 3 in the surface layer 12 of the particle board 10. However, the woody cutting pieces 3, ..., 3 constituting the surface layer 12 of the particle board 10 are not limited to those described above. The first small woody flakes 3c, ..., 3c used in the wood board 50 may be used as the woody cutting pieces 3, ..., 3 constituting the surface layer 12. In addition, the woody flakes 3a, ..., 3a before grinding after cutting and the large number of small woody flakes 3b, ..., 3b before classification after grinding may be used as the woody cutting pieces 3, ..., 3 constituting the surface layer 12. Furthermore, all or any two, three or four of the woody flakes 3a, ..., 3a, the small woody flakes 3b, ..., 3b, the first small woody flakes 3c, ..., 3c, the second small woody flakes 3d, ..., 3d and the third small woody flakes 3e, ..., 3e may be combined and used as the woody cutting pieces 3, ..., 3 that constitute the surface layer 12. In other words, at least one of the woody flakes 3a, ..., 3a, the small woody flakes 3b, ..., 3b, the first small woody flakes 3c, ..., 3c, the second small woody flakes 3d, ..., 3d and the third small woody flakes 3e, ..., 3e can be used as the woody cutting pieces 3, ..., 3 that constitute the surface layer 12.

There are no particular limitations on the species of wood material B, and any species of tree can be used as wood material B. For example, fir wood such as cedar, cypress, and Douglas fir, acacia, aspen, poplar, pine (hard pine, soft pine, radiata pine, etc.), birch, rubber (rubber tree), etc. can be used as wood material B. In addition, domestic 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 wood material B.

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

Regarding the physical properties of the wood pieces 1 (ground wood pieces 2, wood cutting pieces 3), the density is preferably 250 kg/m ³ or more, more preferably 300 kg/m ³ or more, and also preferably 800 kg/m ³ or less, more preferably 500 kg/m ³ or less, and even more preferably 400 kg/m ³ or less. If the density is less than 250 kg/m ³ , the thickness of the mat required to form a particle board 10 with the same density and bending strength becomes large, and the pressing pressure for the hot pressing process in the press molding process needs to be increased. In addition, 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, if 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 (ground wood pieces 2, shaved wood pieces 3) is preferably 2% to 20%, and more preferably 2% to 8%. 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.

<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. In addition, other 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.

- 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 hot pressing step S4.

<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.

[Wood chip production process S11]
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 logs or thinned wood are used, they are cut into short pieces and the bark is removed to prepare the wooden material A. When using recycled materials, etc., cut them into short pieces to form wood material A.

(Crushing step 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.

(Classification step S113)
The wood grain pieces 2a, ..., 2a obtained by crushing are classified into three sizes using two types of sieves, one large and one small. The first wood grain pieces 2b, ..., 2b having a desired particle size (for example, 0.5 mm or more and 5 mm or less) that pass through the sieve and do not pass through the fine sieve, and the first wood grain pieces 2b, ..., 2b that pass through both the two types of sieves. Second wood grain pieces 2c, ..., 2c which are finer than the grain pieces 2b, ..., 2b, and third wood grain pieces 2d which are coarser than the first wood grain pieces 2b, ..., 2b and do not pass through both of the two types of sieves. , ..., 2d. The first wood granule pieces 2b, ..., 2b thus classified and selected are used as the wood pulverized pieces 2, ..., 2 for the core layer 11, and the second wood granule pieces 2c, ..., 2c obtained at the same time are used as the wood pulverized pieces 2, ..., 2 for the core layer 11. , 2 for the surface layer 12.

[Wood cutting piece production process S12]
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. 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 surface layer 12. Therefore, the wood 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 wooden material B. When logs or thinned wood are used, they are cut into short pieces and the bark is removed to prepare the wooden material B. When using recycled materials, etc., cut them into short pieces to form wood material B.

(Cutting process S122)
Next, the prepared wood material B is cut by a known cutting device (strander) of an outer blade type or an inner blade type to form a large number of wood slices 3a, . . . , 3a having a 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 a desired thickness t with fibers a appearing linearly on the surface.

In addition, in this cutting process S122, by producing thin wood pieces 3a, ..., 3a with a thickness of t, the thickness of the small wood pieces 3b, ..., 3b obtained in the next crushing process will be the desired thickness t.

(Crushing step 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 will not break easily, but if a force is applied parallel to the fiber direction, they will break easily. Even if the woody flakes 3a, ..., 3a are curled, they will be 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 will usually break from the part where the force is weak (they are more likely to break 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 become shorter in the direction perpendicular to the fibers, resulting in small, elongated wood flakes 3b, ..., 3b.

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

In this way, by adding the crushing process S123 after the cutting process S122, rather than using only one cutting process S122, and going through two processing steps, it is possible to easily produce small wood flakes 3b, ..., 3b of the required size that are free of knots and have high strength.

(Classification step S124)
The small wood flakes 3b, ..., 3b obtained by crushing are classified into three sizes using two types of sieves, one large and one small. The first small woody pieces 3c, ..., 3c of the desired size pass through the first sieve and do not pass through the fine sieve, and the second small woody pieces 3c, ..., 3c that are finer than the first small woody pieces 3c, ..., 3c that pass through both of the two types of sieves. The second woody small slices 3d, ..., 3d are separated into the third woody small slices 3e, ..., 3e which are coarser than the first woody small slices 3c, ..., 3c which do not pass through both of the two types of sieves. The second woody small pieces 3d, ..., 3d and the third woody small pieces 3e, ..., 3e other than the first woody small pieces 3c, ..., 3c that have been classified and selected are used as the wood cutting pieces 3, …, let’s say 3.

[Wood piece mixing step S13]
In the wood chip mixing step S13, a large number of wood chips 2, ..., 2 for the surface layer 12 produced in the wood chip production step (second wood grain pieces 2c, ..., 2c) and wood cuttings produced in the wood chip production step are mixed. The produced numerous wood cutting pieces 3, ..., 3 for the surface layer 12 (second wood thin pieces 3d, ..., 3d and third wood thin pieces 3e, ..., 3e) are mixed in a desired mixing ratio (wood chips The wood cutting pieces 3, ..., 3 are mixed so that the ratio of the wood cutting pieces 3, ..., 3 to the total weight of 1, ..., 1 is 10 to 90% by weight.

In the 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 (first wood granular pieces 2b, ..., 2b) for the core layer 11 and wood pieces 1, ..., 1 (a mixture of second wood granular pieces 2c, ..., 2c and second small wood pieces 3d, ..., 3d and third small wood pieces 3e, ..., 3e) for the surface layer 12.

<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. 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.

<Mat forming process S3>
In the mat forming process S3, as shown in the left side of Fig. 6, first, a large number of wood pieces 1, ..., 1 for the surface layer 12 to which adhesive is applied are piled up in a state of being gathered in the thickness direction until they reach a predetermined thickness (height), forming a first mat 9a of wood pieces 1, ..., 1. Next, a large number of wood pieces 1, ..., 1 for the 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 large number of wood pieces 1, ..., 1 for the surface layer 12 to which adhesive is applied are piled up on the second mat 9b in a state of being gathered in the thickness direction until they reach a predetermined thickness (height), forming a third mat 9c of wood pieces 1, ..., 1. In this manner, a mat 9 having a three-layer structure is formed.

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 surface layer 12 to the entire particle board 10. For example, when forming a particle board 10 with a thickness of 9 mm, in which the surface layer 12 accounts for 15% of the thickness of the entire particle board 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 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.

<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 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.

At this time, as shown in FIG. 6, the mat 9 having a thickness of about 90 mm is compressed to a particle board 10 having a thickness of 9 mm, for example, 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. In addition, a preliminary heating process using a heating device may be performed before the hot press process using the hot press device.

--Effects of the First Embodiment--
In the present embodiment 1, the surface layer 12 of the particle board 10 having a three-layer structure contains not only the fine wood pulverized pieces 2, ..., 2 (second wood granular pieces 2c, ..., 2c) that are usually contained, but also extremely thin wood shavings 3, ..., 3 having a thickness of 0.05 to 0.35 mm. With this configuration, the bending strength of the surface layer 12 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. In addition, compared to when the surface layer 12 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 having a three-layer structure of the present embodiment 1, it is possible to reduce the amount of adhesive used while ensuring bending strength.

In addition, according to the particle board 10 of this embodiment 1, the extremely thin wood shavings 3, ..., 3, with a thickness of 0.05 to 0.35 mm, penetrate 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).

In addition, according to the particle board 10 of this embodiment 1, if the surface layer 12 is formed only from granular wood crushed pieces 2, ..., 2, many gaps will be formed between the wood crushed pieces 2, ..., 2. However, since the flaky wood cutting pieces 3, ..., 3 are mixed in, the flaky wood cutting pieces 3, ..., 3 enter the many gaps, making the gaps smaller and fewer. Therefore, the particle board 10 of this embodiment 1 is more resistant to moisture penetration and has excellent water resistance compared to conventional particle boards in which the surface layer 12 is composed only of granular wood crushed pieces.

As described below, the inventors of the present application conducted a test to verify the effect of including extremely thin wood shavings 3, ..., 3 with a thickness of 0.05 to 0.35 mm in the surface layer 12 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 surface layer 12 has improved normal bending strength (MOR), wet bending strength (wet MOR), water absorption length change (LE), and peel strength (IB) compared to a conventional particleboard not including the thin wood shavings 3, ..., 3 in the surface layer 12.

As described above, according to this embodiment 1, it is possible to provide a three-layer particle board 10 that has excellent surface properties, water resistance, bending strength, and peel strength, and has little dimensional change, without increasing cost or weight.

In addition, in this embodiment 1, the wood shavings 3, ..., 3 are generated when the wood material B is processed to form another wood board 50. Therefore, even if a material (wood shavings 3, ..., 3) different from the material (ground wood pieces 2, ..., 2) used for normal particle boards is used, it can be easily procured because the different material is generated during the processing of the material for the other wood board 50. Therefore, according to this embodiment 1, a three-layer particle board 10 with excellent surface properties, water resistance, bending strength, and peel strength and small dimensional change can be easily and relatively inexpensively provided.

In particular, in this embodiment 1, wood chips 3, ..., 3 for the surface layer 12 are used that are not the first wood chips 3c, ..., 3c (the second wood chips 3d, ..., 3d and the third wood chips 3e, ..., 3e) that are obtained by classifying and selecting the small wood chips 3b, ..., 3b. In this way, waste wood that is not used for the other wood boards 50 and is generated during the formation of the other wood boards 50 is used as the wood chips 3, ..., 3 for 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, since the wood material B of the other wood boards 50 is used without waste, this leads to effective use of wood resources.

-Verification of effectiveness-
In order to verify the above-mentioned effect of including the wood cuttings 3, ..., 3 in the surface layer 12 of the particle board 10, the inventors prepared the following five types of particle board 10 (test specimens X0 to X4) and performed bending strength tests, wet bending strength tests, water absorption length change tests, and peel strength tests in accordance with JIS A5908 and JIS A5905 to obtain normal bending strength (MOR), wet bending strength (wet MOR), water absorption length change (LE), and peel strength (IB), and the results are shown in Figure 7. Note that the test specimens X0 to X4 have different mixing ratios of the wood cuttings 3, ..., 3 in the surface layer 12, and are otherwise configured in the same manner as the particle board 10 of embodiment 1. Also, Figure 7 shows the test results of the test specimens X1 to X4 in relative proportions when the test result of the test specimen X0 is set to 100.

Specimen X0: The mixture ratio of the wood cuttings 3, ..., 3 in the surface layer 12 is 0% by weight. Specimen X1: The mixture ratio of the wood cuttings 3, ..., 3 in the surface layer 12 is 20% by weight. Specimen X2: The mixture ratio of the wood cuttings 3, ..., 3 in the surface layer 12 is 40% by weight. Specimen X3: The mixture ratio of the wood cuttings 3, ..., 3 in the surface layer 12 is 60% by weight. Specimen X4: The mixture ratio of the wood cuttings 3, ..., 3 in the surface layer 12 is 80% by weight.

As shown in Figure 7, the particle boards 10 (test specimens X1 to X4) containing wood shavings 3, ..., 3 in the surface layer 12 had improved normal bending strength (MOR) and wet bending strength (wet MOR) compared to the conventional particle board (test specimen X0) that did not contain wood shavings 3, ..., 3 in the surface layer 12. Furthermore, the higher the mixing ratio of wood shavings 3, ..., 3 in the surface layer 12, the higher the normal bending strength (MOR) and wet bending strength (wet MOR).

In addition, with regard to dimensional change, the particleboards 10 (test specimens X1 to X4) that contain wood shavings 3, ..., 3 in the surface layer 12 showed a lower (improved) water absorption length change rate (TS) compared to the conventional particleboard (test specimen X0) that does not contain wood shavings 3, ..., 3 in the surface layer 12. Also, the higher the mixing ratio of wood shavings 3, ..., 3 in the surface layer 12, the higher the improvement rate of water absorption length change rate (TS).

In addition, the particle boards 10 (test specimens X1 to X4) that contain wood shavings 3, ..., 3 in the surface layer 12 also showed improved peel strength (IB) compared to the conventional particle board (test specimen X0) that does not contain wood shavings 3, ..., 3 in the surface layer 12.

As described above, the particleboard 10 (specimens X1 to X4) containing the wood shavings 3, ..., 3 in the surface layer 12 had higher normal bending strength (MOR), wet bending strength (wet MOR) and peel strength (IB) and lower water absorption length change (LE) compared to the conventional particleboard (specimen X0) that did not contain the wood shavings 3, ..., 3 in the surface layer 12. These results show that by including the wood shavings 3, ..., 3 in the surface layer 12 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 water resistance, bending strength and peel strength and exhibits little dimensional change, without increasing cost or weight.

Other Embodiments
In the above embodiment 1, 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.

In addition, in the above embodiment 1, an example was described in which wood cuttings generated during material processing of another wood board 50 are used as the wood cuttings 3, ..., 3, but the wood cuttings 3, ..., 3 may not be generated during material processing of another wood board 50, but may be procured for forming the above-mentioned particle board 10.

INDUSTRIAL APPLICABILITY The present invention is useful for a three-ply particleboard and a method for producing a three-ply particleboard .

2. Wood chips
3 Wood chips
3a Wood slices
3b Small wood flakes
3c First woody flake
3d. Second woody flakes (other than the first woody flakes)
3e. Class 3 woody flakes (other than Class 1 woody flakes)
10. Particleboard
11 Core layer
12 Surface
50 Wood Board

Claims (6)

A three-layer particle board in which the surface layer uses finer granular wood chips than the core layer,
The core layer is a plurality of core layer wood pieces, each of which is composed only of wood pulverized pieces for the core layer, each of which is made of a first wood granular piece having a maximum particle size of 0.5 mm or more and 5 mm or less, and which are bonded together with a thermosetting adhesive;
The surface layer is made of a number of surface layer wood pieces, which are composed of second wood granules finer than the first wood granules, and a number of thin wood cutting pieces having a thickness of 0.05 mm to 0.35 mm , and are bonded together with a thermosetting adhesive.
A particle board characterized by: The particle board according to claim 1,
In the surface layer, the wood cutting pieces are mixed in a ratio of 20% by weight to 90% by weight based on the total weight of the plurality of surface layer wood pieces.
A particle board characterized by: A method for manufacturing a three-layer particle board using finer granular wood chips in the surface layer than in the core layer,
A first crushing step of crushing the first wood material into granules to produce a large number of wood granule pieces;
a first classification step in which the numerous wood granular pieces are classified using two types of sieves, large and small, into numerous first wood granular pieces that pass through the first sieve with a coarse mesh but do not pass through the second sieve with a fine mesh, numerous second wood granular pieces that pass through both the first and second sieves, and numerous third wood granular pieces that do not pass through both the first and second sieves, and the first wood granular pieces are used as wood pulverized pieces for the core layer and the second wood granular pieces are used as wood pulverized pieces for the surface layer;
A cutting process for cutting the second wood material so that the fibers are linearly exposed on the surface to produce a large number of thin wood flakes having a thickness of 0.05 mm to 0.35 mm;
a selection process for selecting at least one of the numerous wood flakes, the numerous thin wood flakes having an elongated shape produced by a second crushing process in which the numerous wood flakes are crushed so as to break them along the fiber direction, or the numerous first to third thin wood flakes obtained by a second classification process in which the numerous thin wood flakes are classified using two types of sieves, large and small, as wood cutting pieces for the surface layer;
a wood chip mixing step of mixing the plurality of wood pulverized chips for the surface layer and the plurality of wood cutting chips for the surface layer to obtain a plurality of wood chips for the surface layer;
An adhesive application step of applying an adhesive to each of the multiple core layer wood pieces consisting of only the multiple core layer wood pulverized pieces and the multiple surface layer wood pieces;
a mat forming process in which a three-layer mat is formed by piling up the numerous adhesive-coated wood pieces for the surface layer to form a first mat, piling up the numerous adhesive-coated wood pieces for the core layer on the first mat to form a second mat, and piling up the numerous adhesive-coated wood pieces for the surface layer on the second mat to form a third mat;
and a hot pressing process for forming the particle board by subjecting the three-layer mat to a hot pressing process to harden the adhesives of the first to third mats.
A method for producing particle board. In the method for producing particle board according to claim 3,
The cutting step, the second crushing step, and the second classification step are included in a method for manufacturing a wood board in which the large number of first woody thin pieces are bonded together in a collective state,
In the selection step, at least one of the first to third small wood pieces is selected as the wood cutting piece for the surface layer.
A method for producing particle board. In the method for producing particle board according to claim 4,
In the selection step, the second and third small wood pieces other than the first small wood pieces are selected as wood cutting pieces for the surface layer.
A method for producing particle board. In the method for producing particle board according to at least one of claims 3 to 5,
In the wood chip mixing step, the multiple wood pulverized chips for the surface layer and the multiple wood chips for the surface layer are mixed so that the multiple wood chips for the surface layer account for 20% by weight or more and 90% by weight or less of the total weight of the multiple wood chips for the surface layer.
A particle board characterized by: