JP7756759B2 - Particle board and its manufacturing method - Google Patents

Description

The present invention relates to particle boards thermocompressed from wood chips and methods for manufacturing the same.

As an example of this type of technology, Patent Document 1 proposes a particle board having a pair of surface layers made up of fine chips and an inner layer arranged between the pair of surface layers and made up of coarse chips.

Japanese Patent Application Laid-Open No. 2002-86421

However, the particle board disclosed in Patent Document 1 is not intended to be fastened with nails for use as a wall material or floor material, etc. Therefore, it is difficult to say that such particle board has high nail resistance, such as nail lateral resistance and nail head penetration strength.

The present invention has been made in view of the above points, and its object is to provide a particle board having high nail resistance, such as nail lateral resistance and nail head penetration strength.

In view of the above problems, the particle board of the present invention is a particle board comprising a pair of surface layers arranged on both sides, an internal layer arranged between the pair of surface layers, and a pair of intermediate layers arranged between each of the surface layers and the internal layer, characterized in that the size of the wood chips in the surface layer is smaller than the size of the wood chips in the internal layer and the internal layer, and the size of the wood chips in the intermediate layer is larger than the size of the wood chips in the internal layer.

According to the present invention, by satisfying this range of wood chip sizes, it is possible to increase the particle board's resistance to nail head penetration force (hereinafter referred to as "nail head penetration force").
Specifically, the wood chips in the surface layer are smaller than those in the other layers, and because they are densely packed in the surface layer, the surface layer has a greater resistance to the force acting from the nail head than the other layers. Furthermore, because the wood chips in the middle layer are larger than those in the other layers, the wood chips overlap each other over a larger area in the in-plane direction of the particle board.
Therefore, the force acting from the nail head can be received over a wide area of the middle layer, including the adjacent wood chips, and the particle board according to the present invention can therefore have a higher nail head penetration force than conventional particle boards.

Furthermore, because the wood chips in the middle layer are larger than those in the inner layer, the binding force between the wood chips in the middle layer can be increased. The inner layer is sandwiched between these middle layers, allowing the inner layer to withstand the force from the sides of the nails. Furthermore, because the wood chips in the inner layer are smaller than those in the middle layer, the wood chips in the inner layer can be denser than those in the middle layer. As a result, the particle board of the present invention can achieve higher lateral nail resistance than ever before.

In a more preferred embodiment, the proportion of the wood chips in each of the intermediate layers relative to the total mass of the wood chips in the inner layer and the pair of intermediate layers is 15.5 mass % or more and 25.0 mass % or less.

According to this aspect, by satisfying these ranges, the nail head penetration strength and nail lateral resistance of the particle board can be further increased. Here, if the proportion of wood chips in each intermediate layer is less than 15.5 mass%, the effect of the intermediate layer on nail resistance is small,
The nail head penetration force and nail side resistance may not be sufficiently increased. On the other hand, even if the proportion of wood chips in each intermediate layer exceeds 25.0 mass%, the effect of nail resistance of the intermediate layer cannot be expected to be any greater.

In a more preferred embodiment, the thickness of the wood chips in the inner layer and each intermediate layer is 0.6 mm or more and 1.0 mm or less. By satisfying this range of wood chip thickness, a particle board with high lateral nail resistance can be obtained.
It is difficult to produce wood chips that are less than 6 mm thick, and if the thickness exceeds 1.0 mm, the binding force between the chips that make up the middle layer decreases, and it may not be possible to increase the particle board's lateral nail resistance.

In a more preferred embodiment, the ratio of the total mass of the inner layer and the pair of intermediate layers to the total mass of the inner layer and the pair of intermediate layers is:
The proportion of the adhesive applied to the inner layer and the pair of intermediate layers is 5% by mass or more and 15% by mass or less.

According to this embodiment, by setting the proportion of adhesive within this range, as the proportion of adhesive in the inner layer and the intermediate layer increases, the peel strength of the test specimen also increases, and as a result, the nail lateral resistance and nail head penetration force also increase. Here, if the proportion of adhesive is less than 5 mass%, it may be impossible to obtain sufficient nail lateral resistance and nail head penetration force.
Even if it exceeds this value, further improvement in nail side resistance and nail head penetration force cannot be expected.

In a more preferred embodiment, the ratio of the total mass of the inner layer and the pair of intermediate layers to the total mass of the wood chips of the inner layer, the pair of intermediate layers, and the surface layers on both sides is:
The content is 40% by mass or more and 80% by mass or less.

According to this aspect, by setting the proportion of the adhesive in this range, it is possible to ensure the productivity of the particle board and the quality of the surface of the particle board.
If this ratio is less than 40% by mass, it is difficult to obtain wood chips for the surface layer from one piece of wood, while if this ratio exceeds 80% by mass, it is difficult to ensure the quality of the particle board surface.

The particle board according to the present invention has higher nail resistance, such as nail lateral resistance and nail head penetration strength, than conventional particle boards.

1 is a schematic cross-sectional view of a particle board according to an embodiment of the present invention. FIG. 2 is a flow chart for explaining a method for manufacturing the particle board shown in FIG. 1. 2 is a schematic conceptual diagram for explaining the steps from the mat production step to the board formation step shown in FIG. 1. [0023]FIG. FIG. 1A is a side view for explaining a nail lateral resistance test, and FIG. 1B is a front view of FIG. FIG. 1A is a cross-sectional view for explaining a nail head penetration test, and FIG. 1B is a top view of FIG.

Hereinafter, a particle board according to an embodiment and a method for manufacturing the same will be described with reference to FIGS. 1 to 3.

1. Particle Board 10 First, the particle board 10 according to this embodiment will be described with reference to Figure 1. Figure 1 is a schematic cross-sectional view of the particle board according to this embodiment. As shown in Figure 1, the particle board 10 according to this embodiment is a particle board including a pair of surface layers 13 disposed on both sides, an internal layer 11 disposed between the pair of surface layers 13, and a pair of intermediate layers 12, 12 disposed between each of the surface layers 13 and the internal layer 11.

Wood chips are made from pieces of wood made from coniferous trees such as pine, cedar, and cypress, or broad-leaved trees such as lauan, capol, and poplar. Wood chips are made by crushing or cutting wood or other materials into small pieces using a crusher or cutter.

In this embodiment, the size of the wood chips 13a of the surface layer 13 is the same as that of the inner layer 11 and the intermediate layer 1.
The size of the wood chips 12a in the intermediate layer 12 is smaller than the size of the wood chips 11a in the inner layer 11.
The size of 3a is determined by classification using a sieve.

The wood chips 11a to 13a are bonded together via an adhesive. In this embodiment, the adhesive is preferably a thermosetting resin adhesive. Examples of thermosetting resin adhesives include urethane adhesives, urea resin adhesives, melamine resin adhesives, urea-melamine co-condensation resin adhesives, and phenolic resin adhesives. Urethane adhesives include mixtures of isocyanate monomers or isocyanates with active hydrogen compounds such as polyols, urethane prepolymers, and polyurethanes.

In addition to MDI (diphenylmethane diisocyanate), TD is also used as an isocyanate.
Examples of the isocyanate include tolylene diisocyanate (MDI), MDI prepolymer, TDI prepolymer, and a mixture of two or more of these.

Since urethane adhesives are moisture-curing adhesives that cure upon reaction with moisture, the moisture contained in the wood chips evaporates during board formation, accelerating the curing of the adhesive. This improves the adhesion between the wood chips. From this perspective, it is particularly preferable to use a mixture of an isocyanate such as MDI and an active hydrogen compound such as a polyol for the inner layer 11 and middle layer 12, which also use large wood chips for the surface layer.

Furthermore, because the wood chips 12a in the intermediate layer 12 are larger than the wood chips 11a in the inner layer 11, the binding force between the wood chips 12a in the intermediate layer 12 along the thickness direction of the particle board 10 can be increased. The inner layer 11 is sandwiched between these intermediate layers 12, allowing the intermediate layers 12 on both sides to withstand force from the side of a nail. Furthermore, because the wood chips 11a in the inner layer 11 are smaller than the wood chips 12a in the intermediate layer 12, the wood chips in the inner layer 11 can be denser than those in the intermediate layer 12. As a result, the particle board 10 according to this embodiment can achieve higher lateral nail resistance than ever before.

In this way, according to this embodiment, it is possible to increase the nail head penetration force of the particle board 10. Specifically, the size of the wood chips 11a in the surface layer 13 is smaller than that of the other layers,
Since the wood chips 11a are densely arranged in the surface layer 13, the surface layer 13 has a greater resistance to the force acting from the nail head than the other layers.

Furthermore, because the wood chips 12a in the middle layer 12 are larger than those in the other layers, the wood chips 12a overlap over a wider area in the in-plane direction of the particle board 10. This allows the force acting from the nail head to be absorbed over a wider area in the middle layer 12, including the adjacent wood chips 12a. As a result, the particle board 10 according to this embodiment can achieve a higher nail head penetration force than ever before.

From this perspective, in this embodiment, it is preferable that the proportion of the wood chips 12a in each intermediate layer 12, 12 to the total mass of the wood chips 11a, 12a in the inner layer 11 and the pair of intermediate layers 12, 12 is 15.5 mass% or more and 25.0 mass% or less.

Meeting these ranges further increases the nail head penetration strength and lateral nail resistance of the particle board 10. If the proportion of wood chips 12a in each intermediate layer 12 is less than 15.5% by mass, the nail head penetration strength and lateral nail resistance due to the intermediate layer 12 may not be sufficiently increased. On the other hand, even if the proportion of wood chips 12a in each intermediate layer 12 exceeds 25.0% by mass, the nail resistance of the intermediate layer 12 cannot be expected to be any greater.

Furthermore, the thickness of the wood chips 11a and 12a of the inner layer 11 and each intermediate layer 12 is 0.6
It is preferable that the wood chips 11a have a diameter of 1.0 mm or more and 1.0 mm or less.
By satisfying the above-mentioned thickness of 1.0 mm, the particle board 10 has high nail head penetration strength and high nail lateral resistance.
The binding force between the wood chips 12a, 12a constituting the particle board 10 is reduced, and the lateral nail resistance of the particle board 10 cannot be increased.

In this embodiment, the thicknesses of the wood chips 11a, 12a in the inner layer 11 and each intermediate layer 12 are set within the above-mentioned range, but the thickness of the wood chips 13a in the surface layer 13 may be within the same range because they have a low contribution to the nail head penetration force and nail lateral resistance force, and is not particularly limited as long as the size of the wood chips 13a in the surface layer 13 is smaller than those in the other layers.

Furthermore, the proportion of adhesive applied to the inner layer 11 and the pair of intermediate layers 12, 12 relative to the total mass of the inner layer 11 and the pair of intermediate layers 12, 12 is preferably 5% by mass or more and 15% by mass or less. By setting the proportion of adhesive within this range, the peel strength of the particle board 10 increases as the proportion of adhesive in the inner layer 11 and the pair of intermediate layers 12, 12 increases, and as a result, the nail lateral resistance and nail head penetration strength of the particle board 10 also increase. Here, if the proportion of adhesive is less than 5% by mass, it may be impossible to obtain sufficient nail lateral resistance and nail head penetration strength for the particle board 10. If the proportion of adhesive is 15% by mass or more, the particle board 10 may not be able to obtain sufficient nail lateral resistance and nail head penetration strength.
Even if it exceeds this value, further improvement in nail side resistance and nail head penetration force cannot be expected.

Furthermore, the ratio of the total mass of the wood chips in the inner layer 11 and the pair of middle layers 12, 12 to the total mass of the wood chips in the inner layer 11, the pair of middle layers 12, 12, and both surface layers 13, 13 is preferably 40% by mass or more and 80% by mass or less. By setting the adhesive ratio within this range, the productivity of the particle board 10 and the surface quality of the particle board 10 can be ensured. If this ratio is less than 40% by mass, it is difficult to obtain the wood chips 13a for the surface layer 13 from a single piece of wood. On the other hand, if this ratio exceeds 80% by mass, it is difficult to ensure the surface quality of the particle board 10.

2. Particle Board Manufacturing Method Hereinafter, a particle board manufacturing method according to this embodiment will be described with reference to Fig. 2 and Fig. 3. Fig. 2 is a flow diagram for explaining the particle board manufacturing method shown in Fig. 1. Fig. 3 is a schematic conceptual diagram for explaining the steps from the mat manufacturing step to the board forming step shown in Fig. 1.

[Chip manufacturing process S1]
This manufacturing method begins with the chip preparation step S1 shown in Figure 2. In this step, wood chips are prepared from wood. Wood chips are pieces of wood made from coniferous trees such as pine, cedar, and cypress, or broad-leaved trees such as lauan, capol, and poplar. Wood chips are prepared by crushing or cutting wood or other materials into small pieces using a crusher or cutter. The thickness of the wood chips can be adjusted by adjusting the cutting length of the flaker blade of the cutter.

[Classification process S2]
Next, a classification step S2 shown in FIG. 2 is performed. In this step, the fragmented wood chips are classified into desired sizes using a sieve. In this embodiment, the fragmented wood chips are classified into three size ranges. In this classification, two sieves with different mesh sizes are prepared. First, the fragmented wood chips are passed through the sieve with the larger mesh size, and the wood chips remaining on this sieve are collected as an intermediate layer 12.
Next, the wood chips that have passed through the sieve with large openings are subjected to the following steps:
The wood chips remaining on the sieve are used as the wood chips 11 for the inner layer 11.
a, and the wood chips that pass through this sieve are referred to as wood chips 13a for the surface layer 13.

[Adhesive application step S3]
Next, the adhesive application step S3 shown in Figure 2 is performed. The above-mentioned adhesive is applied to the classified wood chips 11a, 12a, and 13a. In the adhesive application step S3, the adhesive may be applied to the wood chips by spraying, by brushing, or by mixing the wood chips 11a, 12a, and 13a with the adhesive; the application method is not particularly limited. Furthermore, during the mat preparation step S4 described below, the adhesive may be applied while the wood chips are being stacked in layers.

[Mat production step S4]
Next, a mat preparation step S4 shown in Fig. 2 is carried out. In this step, a forming mat 10' is prepared from the wood chips coated with adhesive. In this embodiment, the wood chips 11a, 12a, and 13a are placed on a base 51 of a press device shown in Fig. 3, and then formed into a mat (formed into a forming mat). Specifically, the mat layer 13 that becomes the surface layer 13 is formed.
3, a mat layer 12' serving as the intermediate layer 12, and a mat layer 11' serving as the inner layer are laminated in the order shown in FIG. 3 to produce a forming mat 10'.

[Board forming step S5]
Next, the board forming step S5 shown in Figure 2 is performed. In this step, the particle board 10 is formed by hot pressing the produced forming mat 10'. Specifically, as shown in Figure 3, the particle board 10 is manufactured by hot pressing the forming mat 10' with a heated pressing member 52 of a hot press device. At this time, both the base 51 and the pressing member 52 are heated. The temperature (heating temperature) at which the forming mat 10' is formed into a board shape is, for example, in the range of 120 to 220°C, depending on the type of adhesive, and the pressure during hot pressing is, for example, about 2 to 5 MPa.

In this way, the particle board 10 shown in Figure 1 can be obtained. The particle board 10 can be used, for example, as a building material such as a wall material, floor material, or ceiling material, or as a base material for fittings or storage furniture.

The present invention will be described below with reference to examples.
1. Relationship between the sizes of wood chips in each layer [Example 1-1]
In Example 1-1, a particle board was manufactured that had a pair of surface layers arranged on both sides, an internal layer arranged between the pair of surface layers, and a pair of intermediate layers arranged between each of the surface layers and the internal layer.

Specifically, the cutting length of the flaker blade was adjusted to cut wood (cedar) so that the wood chips were 1.5 mm thick, and the wood chips were then classified as follows: The wood chips were classified so that the size of the wood chips in the surface layer was smaller than the size of the wood chips in the inner and middle layers, and the size of the wood chips in the middle layer was larger than the size of the wood chips in the inner layer.

Specifically, wood chips that pass through a 2.00 mm mesh sieve were used for the surface layer. Wood chips that do not pass through a 2.00 mm mesh sieve but pass through a 5.66 mm mesh sieve were used for the inner layer. Wood chips that do not pass through a 5.66 mm mesh sieve were used for the middle layer. Here, mesh size is defined as the mesh size specified in JIS Z 8800-1 (2006).
The nominal opening size is specified in the JIS. Adhesive was added to these classified wood chips so that the amount was 5% by mass of the total mass of each layer. Phenol resin was used as the adhesive for the surface layer, and diphenylmethane diisocyanate (MD
I) was used.

Here, a forming mat was prepared with the composition of each layer set as follows: The ratio of wood chips in each surface layer was 30% by mass relative to the total amount of wood chips in the particle board.
(60% by mass in total). The total ratio of wood chips in the inner layer and the intermediate layer is:
The wood chips in each intermediate layer accounted for 40% by mass of the total amount of wood chips in the particle board. The wood chips in each intermediate layer accounted for 15.5% by mass of the wood chips in the inner and intermediate layers (total of 31% by mass).

The obtained forming mat was subjected to heat pressing under the conditions of a heat plate temperature of 180°C, a pressure of 25 kf/ ^cm2 , and a heat pressing time of 3 minutes so as to have a thickness of 9 mm and ^a set density of 0.75 g/cm3.
Particle boards were produced by hot pressing.

[Comparative Example 1-1]
A commercially available particle board was prepared having the same thickness as that of Example 1. The difference from the particle board of Example 1-1 is that no intermediate layer was provided.

[Comparative Example 1-2]
A particle board was produced in the same manner as in Example 1. The difference from Example 1 is that the size of the wood chips in the middle layer was smaller than the size of the wood chips in the inner layer.
The wood chips used in the intermediate layer of Example 1 were used in the inner layer, and the wood chips used in the inner layer of Example 1 were used in the intermediate layer.

<Nail lateral resistance test>
In accordance with JIS A 5908:2015, a nail lateral resistance test was performed on the test specimens 60 that were the particle boards of Example 1 and Comparative Examples 1 and 2. Specifically, as shown in FIG.
As shown in (a) and (b), a N50 nail 62 was driven partway into a test piece 60, and both sides of the nail 62 were engaged with the device body 61. In this state, a load was applied in a direction that pulled the device body 61 and the test piece 60 apart, and the load at which the test piece 60 broke was taken as the nail side resistance force. The results are shown in Table 1 below.

<Nail head penetration test>
In accordance with ASTM D1037 and JIS A 5908:2015, a nail head penetration test was performed on test specimens 70, which were particle boards of Example 1 and Comparative Examples 1 and 2. Specifically, as shown in Figures 5(a) and 5(b), a nail 72 of N50 was driven into test specimen 70 until the head of the nail 72 contacted the test specimen 70, and the tip of the nail 72 penetrated into groove 7 of device body 71.
The test piece 70 was fixed to the device body 71 so that the nail 72 protruded from the test piece 70. In this state, a load was applied to the nail 72 so as to pull the nail 72 away from the side of the test piece 70.
The load when the head of nail 2 penetrated was taken as the nail head penetration force. The results are shown in Table 1.

[Results and Discussion]
As shown in Table 1, the specimen of Example 1-1 had higher nail side resistance and nail head penetration force than those of Comparative Examples 1-1 and 1-2.
This is thought to be because, unlike Comparative Example 1-1, an intermediate layer was provided, and further, Comparative Example 1-2 differs in that the size of the wood chips in the intermediate layer was made larger than the size of the wood chips in the inner layer.

Specifically, in Example 1-1, compared to Comparative Example 1-2, the wood chips in the middle layer are larger and have a stronger binding force than the wood chips in the inner layer, so that the inner layer is sandwiched between the middle layers on both sides and can withstand the force from the side of the nail, which is thought to have increased the nail side resistance.
Furthermore, because the wood chips that make up the middle layer are larger than those in the other layers, the wood chips overlap over a wider area in the in-plane direction of the particle board, allowing the force acting from the nail head to be absorbed over a wider area, including adjacent wood chips. This is thought to be why Example 1-1 had a greater nail head penetration force than Comparative Examples 1-1 and 1-2.

2. Optimum Ratio of Each Intermediate Layer In order to evaluate the optimum ratio of each intermediate layer in the particle board, particle board specimens of Examples 2-1 to 2-4 were prepared in the same manner as in Example 1-1.

[Examples 2-1 to 2-4]
Examples 2-1 to 2-4 differ from Example 1-1 in that the proportion of wood chips in each intermediate layer relative to the total amount of wood chips in the inner layer and the pair of intermediate layers is set to 12.5% by mass (Example 2-1), 15.5% by mass (Example 2-2), 25.0% by mass (Example 2-3), and 30.0% by mass (Example 2-4), respectively.
This test specimen was manufactured under the same conditions as -1.

Similar to Example 1-1, nail side resistance tests and nail head penetration tests were conducted on these test specimens to measure the nail side resistance and nail head penetration force. The results are shown in Table 2 below. In Table 2, the measurement results of Comparative Example 1-1 are also shown to clarify the superiority of the nail resistance performance of Examples 2-1 to 2-4.

[Results and Discussion]
As shown in Table 2, the test specimens of Examples 2-2 and 2-3 had higher nail side resistance and nail head penetration force than those of Example 2-1.
This is because the proportion of each intermediate layer is lower than in Examples 2-2 to 2-4. On the other hand, even if the proportion of each intermediate layer is set to 30.0% by mass as in Example 2-4, it is difficult to obtain a greater effect. Therefore, it is preferable to set the proportion of the intermediate layer in Example 2-2 as the lower limit and the proportion of the intermediate layer in Example 2-3 as the upper limit. In other words, it is preferable that the proportion of wood chips in each intermediate layer relative to the total amount of wood chips in the internal layer and the pair of intermediate layers be 15.5% by mass or more and 25.0% by mass or less.

3. Regarding the thickness of wood chips In order to evaluate the optimum ratio of wood chip thickness in particle boards, particle board specimens of Examples 3-1 to 3-4 were prepared in the same manner as in Example 1-1.

[Examples 3-1 to 3-4]
Specifically, Examples 3-1 to 3-4 differ from Example 1-1 in that the cutting length of the flaker blade is adjusted to reduce the thickness of the wood chips in the inner layer and the pair of intermediate layers by 0.8 mm.
(Example 3-1), 1.0 mm (Example 3-2), 1.5 mm (Example 3-3), and 1.8 mm (Example 3-4). Note that Example 3-3 is a test specimen manufactured under the same conditions as Example 1-1, and the thickness of the wood chips on the surface layer is also the same.

Similar to Example 1-1, nail side resistance tests and nail head penetration tests were conducted on these test specimens to measure the nail side resistance and nail head penetration force. The results are shown in Table 3 below. In addition, Table 3 also shows the measurement results of Comparative Example 1-2 to clarify the superiority of the nail resistance performance of Examples 3-1 to 3-4.

[Results and Discussion]
As shown in Table 3, the test specimens of Examples 3-1 and 3-2 had higher nail side resistance and nail head penetration force than those of Examples 3-3 and 3-4.
This is thought to be because the wood chips in Example 3-2 were thinner than those in Examples 3-3 and 3-4, and therefore the wood chips were densely stacked in the thickness direction. When the thickness of the wood chips in each intermediate layer exceeded 1.0 mm, as in Examples 3-3 and 3-4, the binding force between the wood chips that make up the intermediate layer decreased, making it impossible to increase the nail side resistance and nail head penetration force.

Therefore, it is preferable to set the thickness of the wood chips in Example 3-1 as the lower limit and the thickness of the wood chips in Example 3-2 as the upper limit. That is, the thickness of the wood chips in the inner layer and each of the intermediate layers relative to the total amount of wood chips in the inner layer and the pair of intermediate layers is 0.8 mm or more, and 1.0 mm or more.
It is preferable that the thickness of the wood chips is 0.0 mm or less. Although the thinner the thickness of the wood chips, the more preferable it is, from the viewpoint of manufacturing, the thickness of the wood chips is preferably 0.6 mm or more.

4. Optimum Amount of Adhesive In order to evaluate the optimum amount of adhesive in the middle layer and inner layer of particle board and the effect of adhesive on the surface layer, Examples 4-1 to 4-4 were prepared in the same manner as in Example 1-1.
-7 particle board specimens were prepared.

[Examples 4-1 to 4-7]
Specifically, Examples 4-1 to 4-4 differ from Example 1-1 in that the ratio (addition rate) of the adhesive in the inner layer and the pair of inner layers to the total amount of the inner layer and the pair of inner layers is 3 mass % (Example 4-1), 5 mass % (Example 4-2), and 10 mass % (Example 4-3), respectively.
), and 15 mass % (Example 4-4). Example 4-2 is a test specimen manufactured under the same conditions as Example 1-1. The total amount of the intermediate layer and the pair of inner layers is
This is the sum of the mass of the wood chips in these layers and the mass of the adhesive added to these layers.
The ratio of the intermediate layer and the pair of inner layers is the mass of the adhesive of the intermediate layer and the pair of inner layers divided by the total mass calculated above.

Furthermore, Examples 4-5 to 4-7 differ from Example 1-1 in that the proportion (addition rate) of the adhesive in the surface layer relative to the total amount of the surface layer is 10 mass %, and the adhesive in the surface layer is 10 mass % (Example 4-5), 15 mass % (Example 4-6), and 20 mass % (Example 4-7), respectively.
) is the key point.

[Comparative Examples 4-1 and 4-2]
As Comparative Example 4-1, a plywood specimen having the same thickness as that of Example 4-1 was prepared. As Comparative Example 4-1, a particle board specimen similar to that of Comparative Example 1-2 was prepared.

The nail side resistance test and nail head penetration test were carried out on these test specimens in the same manner as in Example 1-1, and the nail side resistance and nail head penetration force were measured.
The peel strength of the surface layer of these test specimens was measured in accordance with JIS No. 015. Specifically, a peeling tool was attached to the surface of the test specimen, and the peel strength of the test specimen near the intermediate layer was measured. The results are shown in Table 4 below.

[Results and Discussion]
As shown in Table 3, it was found that in the test specimens of Examples 4-1 to 4-4, the peel strength of the test specimens increased as the proportion of adhesive in the internal layer and intermediate layer increased.
As the peel strength increases, the nail lateral resistance and nail head penetration force also increase.

Furthermore, the test specimens of Examples 4-2 to 4-4 had higher nail lateral resistance and nail head penetration strength than those of Comparative Example 4-1, Comparative Example 4-2, and Example 4-1. Therefore, it is preferable to set the adhesive ratio of Example 4-3 as the lower limit and the adhesive ratio of Example 4-4 as the upper limit. In other words, it is preferable that the ratio (addition rate) of the adhesive applied to the inner layer and the pair of intermediate layers relative to the total mass of the inner layer and the pair of intermediate layers is 5% by mass or more and 15% by mass or less.

Furthermore, in the test specimens of Examples 4-5 to 4-7, even when the proportion of adhesive in the surface layer was changed, there was no change in the nail lateral resistance and nail head penetration force. Therefore, since the effect of the adhesive addition rate in the surface layer on the nail lateral resistance and nail head penetration force is small, it is considered that for the nail lateral resistance and nail head penetration force, it is preferable that the proportion (addition rate) of adhesive applied to the surface layer is smaller than the proportion (addition rate) of adhesive applied to the inner layer and the pair of intermediate layers.

5. Optimum Amount of Wood Chips in Inner and Middle Layers In order to confirm the optimum amount of wood chips in the inner and middle layers of particle boards, test specimens of particle boards of Examples 5-1 to 5-3 and Comparative Examples 5-1 and 5-2 were prepared in the same manner as in Example 1-1.

[Examples 5-1 to 5-3]
Specifically, Examples 5-1 to 5-3 differ from Example 1-1 in that the ratio of the total mass of the wood chips in the inner layer and the pair of intermediate layers to the total mass of the wood chips in the inner layer, the pair of intermediate layers, and the surface layers on both sides is 40% by mass (Example 5-1), 60% by mass (Example 5-2), and
), and 80 mass (Example 5-3), and Example 5-1 is a specimen manufactured under the same conditions as Example 1-1. The ratio of the total mass of the wood chips in the inner layer and the pair of middle layers is the value obtained by dividing the mass of the wood chips in these layers by the total mass of the wood chips used in the particle board.

[Comparative Examples 5-1 and 5-2]
As Comparative Example 5-1, the ratio of the total mass of the wood chips in the inner layer and the pair of intermediate layers was 30
We attempted to produce particle boards with a surface layer ratio of 90% by mass, but found it difficult to obtain the surface layer ratio when cutting from a single piece of wood and classifying the resulting wood chips. Furthermore, as Comparative Example 5-2, we attempted to produce particle boards with a total mass ratio of wood chips in the inner layer and a pair of middle layers of 90% by mass, but found it difficult to obtain a sufficient surface layer thickness. In particular, we found that polishing the surface layer could expose the middle layer. These test specimens were subjected to nail lateral resistance tests and nail head penetration tests in the same manner as in Example 1-1, and the nail lateral resistance and nail head penetration force were measured. We found it difficult to obtain the surface layer ratio when cutting from a single piece of wood and classifying the resulting wood chips.

[Results and Discussion]
From the results of Comparative Examples 5-1 and 5-2, when taking into consideration the productivity of the particle board and the surface quality of the particle board, it is preferable that the ratio of the total mass of the wood chips in the inner layer and the pair of intermediate layers to the total mass of the wood chips in the inner layer, the pair of intermediate layers, and the surface layers on both sides is 40% by mass or more and 80% by mass or less.

Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment, and various design modifications can be made within the scope of the spirit of the present invention as set forth in the claims.

1: particle board, 11: inner layer, 13: surface layer, 12: middle layer, 11a: wood chips in inner layer, 12a: wood chips in middle layer, 13a: wood chips in surface layer

Claims (5)

A pair of surface layers arranged on both sides,
an inner layer disposed between a pair of outer layers;
A method for manufacturing a particle board comprising: a pair of intermediate layers disposed between each of the surface layers and the inner layer;
a classifying step of classifying wood chips made from wood into surface layer wood chips, inner layer wood chips, and middle layer wood chips so that the size of the surface layer wood chips is smaller than the size of the inner layer wood chips and the middle layer wood chips, and the size of the middle layer wood chips is larger than the size of the inner layer wood chips;
an adhesive application step of applying an adhesive to the classified surface layer wood chips, the inner layer wood chips, and the middle layer wood chips;
a mat preparation step of preparing a forming mat so that a pair of surface mat layers made of the surface wood chips as layers on both sides, an inner mat layer made of the inner wood chips arranged between the pair of surface mat layers, and a pair of intermediate mat layers made of the intermediate wood chips arranged between each of the surface mat layers and the inner mat layer;
a board forming step of forming the particle board by hot pressing the forming mat;
A method for producing particle board, comprising at least 2. The method for manufacturing particle board according to claim 1, wherein in the mat manufacturing process, the forming mat is manufactured so that the ratio of the wood chips for the intermediate layer of each of the intermediate layer mat layers to the total mass of the wood chips for the inner layer mat layer and the wood chips for the intermediate layer of the pair of intermediate layer mat layers is 15.5 mass% or more and 25.0 mass% or less. 3. The method for manufacturing particle board according to claim 1 , wherein the thickness of the classified inner layer wood chips and each of the classified intermediate layer wood chips is 0.6 mm or more and 1.0 mm or less in the classification step. 4. The method for manufacturing a particle board according to claim 1, wherein in the adhesive application step, the ratio of the adhesive applied to the mat layer for the inner layer and the pair of mat layers for the intermediate layer to the total mass of the mat layer for the inner layer and the pair of mat layers for the intermediate layer is 5% by mass or more and 15% by mass or less. 5. The method for manufacturing a particle board according to claim 1, wherein in the mat production process, the ratio of the total mass of the inner layer wood chips of the inner layer mat layer and the intermediate layer wood chips of the pair of intermediate layer mat layers to the total mass of the inner layer wood chips of the inner layer mat layer, the intermediate layer wood chips of the pair of intermediate layer mat layers, and the surface layer wood chips of the pair of surface layer mat layers is 40 % by mass or more and 80% by mass or less.