JP5458275B2 - Manufacturing method of high-strength particle board - Google Patents

Description

  The present invention relates to a method for manufacturing a particle board for hot pressing after adhering an adhesive to a wood chip.

Wood particle board (hereinafter simply referred to as “particle board”) is made by cutting raw material such as demolition materials for houses, waste materials (waste wood), small diameter trees, tree branches, etc. with a knife ring flaker or hammer mill. Manufactured from the obtained wood chips (wood pieces), it is used as a core material for furniture, etc., a wall material for a house, a floor base material, a core material for housing equipment such as a kitchen cabinet.
For the production of particle board, a method is adopted in which an adhesive is applied to a dried wood chip by spraying, etc., formed into a mat shape, inserted into a hot press, heated and pressed to form a plate shape, etc. .
As shown in FIG. 1, many particle boards are composed of a surface layer 1 and a back layer 2 using small-sized (fine-grained) wood chips, and a core layer 3 using large-sized (coarse-grained) wood chips. It consists of three layers.
Typical particle board adhesives include urea resin, melamine resin, urea melamine co-condensation resin, phenol resin, isocyanate low polymer, etc., depending on the application of particle board and required performance such as water resistance and durability. They are properly used (see, for example, Patent Document 1).

Recently, it has been difficult to obtain plywood logs to protect the global environment and forest resources, and due to problems such as rising plywood prices and supply shortages, it would be desirable to use particleboard for applications where plywood has been used in the past. There is a need. However, conventional particle boards are inferior to plywood in strength and performance, and their alternative use has not progressed much.
In particular, floor materials for truck bodies and transportation containers are loaded with heavy objects and may be exposed to rainwater, etc., so the surface is hard and strong, and the bending strength is high. In addition to a high so-called Young's modulus that does not flex much, it also has high performance requirements for water resistance and durability. For this reason, conventionally, plywood made of hard and strong wood, such as Apiton and Kluin, has been used. However, the timbers of those tree species are particularly difficult to obtain, and alternative materials are being sought.

Further, Patent Document 2 discloses a mold plate that can replace a plywood for a mold, in which a single plate from which raw wood is peeled is bonded and reinforced to one or both sides of a particle board.
However, in the case of a particle board (base particle board) using only a wood chip as a wood material without using a wood veneer, the current Japanese Industrial Standard (JIS A5908) has the strongest “18” the type "any bending strength in the longitudinal and lateral directions is 18N / mm ² or more (in the lateral bending Young's coefficient 3000N / mm ² or higher).

On the other hand, first-class structural plywood of Japanese agricultural and forestry standards for plywood (February 27, 2003, Ministry of Agriculture, Forestry and Fisheries Notification No. 233) has a display thickness of 15.0 mm or more and less than 18.0 mm and 18.0 mm. In the range below 21.0 mm, it is specified that the bending strength should be 24.0 N / mm ² or more and the bending Young's modulus should be 5000 N / mm ² or more.
There is still no known method that can produce a particleboard with high bending strength and bending Young's modulus that can withstand use as a flooring material for truck bodies and shipping containers.

JP 2002-200608 A JP 2001-90339 A

  The present invention has been made in view of the above circumstances, and provides a method capable of producing a particle board capable of expressing a high bending strength and a bending Young's modulus even with a particle board composed of only wood chips. This is the issue.

In order to solve the above problems, the present invention includes an impregnation step of impregnating a wood chip with an aqueous solution of a resol-type phenol resin to obtain a resin-impregnated chip, and a three-layer structure in which a surface layer and a back layer are combined with a core layer from the resin-impregnated chip. A method for producing a particle board comprising laminating layer mats to each other and forming a plate by heating and pressurizing, wherein in the impregnation step, the resin impregnated chips of the front layer and the back layer have a resin solid An aqueous solution of a phenol resin having a content of 55 to 75% by mass, a resin viscosity of 50 to 200 mPa · s, and a weight average molecular weight of 300 to 700 is supplied to 100 parts by mass of the dryness of the wood chip. Thus, a method for producing a particle board characterized by obtaining a resin-impregnated chip containing 15 to 80 parts by mass of a resin solid content is provided.
In addition, the present invention can be implemented more easily and efficiently by providing a preliminary drying step of preliminary drying the resin-impregnated chips of the front layer and the back layer prior to the molding step.

According to the present invention,
Even a particle board composed only of wood chips can produce a particle board that can withstand use as a floor material for a truck body or a transportation container and that can exhibit high bending strength and bending Young's modulus.

It is a schematic sectional view showing an example of a three-layer particle board.

Hereinafter, the present invention will be described based on preferred embodiments.
The particle board manufacturing method of this embodiment includes at least (1) an impregnation step of impregnating a wood chip with an aqueous resin solution to obtain a resin-impregnated chip, and (2) combining the surface layer and the back layer from the resin-impregnated chip with the core layer. (3) A step of laminating the three layers of mats (forming) and (3) a step of forming a plate by heating and pressing in the order of (1) to (3). In addition, when drying the resin-impregnated chip obtained in the step (1) before molding, a preliminary drying step is provided between (1) and (2).
In the following description, “front and back layers” is an abbreviation for “surface and back layers”.

According to the particle board manufacturing method described later, a particle board having a bending strength of 24.0 N / mm ² or more at a thickness of 9 mm to 50 mm and a bending Young's modulus of 5000 N / mm ² or more (in the present invention, “high strength Particle board ").

<Wooden chips>
Wood chips are manufactured as usual. That is, the material is house dismantling material, plywood lumbering, building material manufacturing waste, thinning lumber, etc., and can be made into chips using ordinary chipper equipment such as a hammer mill or knife ring flaker. Removal of foreign matters such as metal during chip manufacture and drying of the chip are performed as usual.

The wood chip used for the front and back layers has a length of 5 mm or less, a thickness of 1 mm or less, and a width of 2 mm or less, and the wood chip used for the core layer has a length of 40 mm or less, a thickness of 2 mm or less, and a width of 30 mm or less. Adjust the shifter.
Even if the wood chip is adjusted to a predetermined size, 100% is not controlled because it is a wood counterpart, so if 90% or more in terms of mass falls within the specified range, there is no practical problem.

The wood chips of the front and back layers have a length of 5 mm or less, a thickness of 1 mm or less, and a width of 2 mm or less, thereby forming a dense plate surface as if the front and back layers impregnated with resin were coated with resin, Durable particle board can be obtained without being caught. If the chip is larger than this, the penetration of the resin does not reach the inside, and the chip is not sufficiently strengthened, and a small dent is generated on the surface, resulting in inconveniences such as a drop in the performance of the particle board and catching luggage. If the chip is smaller than this, the bending strength of the particle board is lowered.
Although the wood chip of the core layer has a length of 40 mm or less, a thickness of 3 mm or less, and a width of 5 mm or less, although it is strong, it has an appropriate gap and can reduce the specific gravity of the entire particle board.

<Adhesive resin for front and back layers>
Adhesive used to bond wood chips on the front and back layers, from the viewpoint of durability and water resistance, phenolic resins are used. Thereby, the particle board excellent in durability and water resistance can be obtained.

  The phenol resin adhesive used for bonding the wood chips of the front and back layers in the present invention is a resol type phenol resin (initial condensate), and is prepared as an aqueous formulation to which a small amount of wax emulsion is added. The phenol resin is preferably a condensate of phenol and formaldehyde (phenol-formaldehyde).

  In the case of the present invention, the average molecular weight of a normal phenol resin for particleboard is about 800 to 7000, whereas in the case of the present invention, the front and back layers have a phenol resin adhesive having a weight average molecular weight of 300 to 700. Is used. When the adhesive resin used for the front and back layers is within the above range, the resin penetrates into the interior of the wood chip, reinforces the wood chip from the inside, and the adhesion between the wood chips becomes stronger.

  In addition, the weight average molecular weight of a phenol resin shows the molecular weight converted into polystyrene (PS) with a known molecular weight by GPC (gel permeation chromatography). Specifically, the following conditions can be used as GPC measurement conditions. The measuring device is “HLC-8220GPC” manufactured by Tosoh Corporation, the column is two “KF-802” and one “KF-803” manufactured by Showa Denko KK, and the detector is a differential refractometer. The treatment is “GPC-8020 Model II version 4.30” manufactured by Tosoh Corporation, the solvent is tetrahydrofuran, the flow rate is 1.0 ml / min, and the column temperature is 40 ° C. As a standard, the following monodisperse polystyrene having a known molecular weight was used in accordance with the measurement manual of “GPC-8020 model II version 4.30”. The polystyrene used was “A-500”, “A-1000”, “A-2500”, “A-5000”, “F-1”, “F-2”, “F-4” manufactured by Tosoh Corporation. , "F-10", "F-20", "F-40", "F-80", "F-128". The sample was obtained by filtering a 0.5 mass% tetrahydrofuran solution in terms of resin solids with a microfilter (50 μl).

For normal particle board adhesives, it is desirable that the content of resin solids (non-volatile content) be as high as possible from the viewpoint of production, but from the viewpoint of adhesive strength, condensation was advanced to some extent before the step of impregnating wood chips. Since an initial condensate is used, there are limitations on resin viscosity and storage stability. For this reason, generally, the adhesive for particle board has a resin viscosity in the range of 50 to 200 mPa · s , and the resin solid content is in the range of 40 to 50 mass% with phenol resin.
However, in the present invention, the function of the resin adhesive for the front and back layers is not only the adhesion between the wooden chips, but also the penetration into the wooden chips. In order to maximize both functions, the average molecular weight of the phenolic resin adhesive for the front and back layers is made smaller than usual as described above. As a result, the degree of condensation of the adhesive resin is low, the resin viscosity is low, and the storage stability is greatly increased. Therefore, the phenol resin adhesive has the same viscosity (50 to 200 mPa · s) as the general adhesive. It is possible to increase the content of resin solids to 55 to 75 % by mass.
And by supplying high concentration adhesive resin to the wood chip, even if a part of the adhesive penetrates into the wood chip, there is no shortage of adhesive to bond between the wood chips, and further comparison There is a merit that there is no puncture at the time of hot press decompression because there is little target moisture.

When the average molecular weight of the adhesive resin used for the front and back layers exceeds the above range, the penetration of the resin into the chip is not sufficient, so that the chip is not sufficiently reinforced, and the performance of the obtained particle board is that of the present invention. The value is not reached. Inevitably, the non-volatile content of the resin liquid must be lowered, and as a result, a lot of moisture is given to the chip together with the resin, and the chip adheres to the inner wall of the plant due to the wet and sticky adhesive. In other words, the chips do not move smoothly inside the plant due to agglomeration, and a uniform mat cannot be formed even in the forming process, and a good product cannot be obtained. In drying the resin-impregnated chip, too much energy is required to evaporate, and the drying equipment becomes large and economically expensive.
When the average molecular weight of the adhesive resin used for the front and back layers is lower than the above range, sufficient condensation cannot be obtained due to insufficient condensation of the resin, and the performance of the obtained particle board reaches the value of the present invention. do not do. In addition, the amount of unreacted formaldehyde is large, and the amount of formaldehyde emitted from the obtained particle board is large and harmful.

  In the production of a phenol resin adhesive, the molar ratio of formaldehyde to phenol (hereinafter referred to as F / P molar ratio) is preferably 1.4 to 3.0, and more preferably 1.6 to 2.5. As the catalyst used for the condensation reaction, an inorganic strong alkali such as sodium hydroxide or sodium carbonate is used. The reaction temperature is preferably 80 to 95 ° C. The end point of the reaction can be determined by whether or not a predetermined viscosity has been reached using a conversion table of molecular weight and viscosity prepared in advance by determining the F / P molar ratio and the type and amount of the catalyst.

  As for the viscosity of the adhesive resin composition for the front and back layers, the viscosity (25 ° C.) measured by a B-type viscometer is preferably in the range of 50 to 200 mPa. Thereby, when supplying to the chip (such as spraying or coating), the handling property of conveyance through the pipeline is excellent.

<Adhesive resin for core layer>
Examples of the adhesive resin used for the core layer include phenol resin adhesives, melamine resin adhesives, isocyanate adhesives, and the like, and each can be used alone or in a mixed state as in a conventional method. Thereby, as mentioned above, the relatively large wood chip for the core layer can be firmly bonded.

The phenol resin adhesive and melamine resin adhesive for the core layer are phenol resins used for ordinary particle boards (resin non-volatile content: 40-50 mass%, resin viscosity: 50-200 mPa · s, weight average molecular weight: 800-7000) or melamine resin (resin nonvolatile content 60 to 70 wt%, resin viscosity 50 to 200 MPa · s), even better, it may be the same phenolic resins as used for the front and back layers.

As the isocyanate-based adhesive, polyisocyanate such as diphenylmethane diisocyanate (MDI) dinuclear (monomer) or tetranuclear (dimer), or an initial condensate of these polyisocyanate and polyol may be used. it can. Examples of the polyol include various alkylene glycols, triols, and other various polyols.
The isocyanate-based adhesive does not contain moisture, but rather has a property of taking up moisture during the curing process. For this reason, when used alone for the core layer, the isocyanate-based adhesive has a ratio of the adhesive resin of the front and back layers that is higher than usual and tends to cause a puncture phenomenon at the time of hot press, A suitable adhesive.
When using an isocyanate adhesive mixed with a phenol resin adhesive or a melamine resin adhesive, it is preferable to add a small amount of a wax emulsion to form an aqueous formulation.
From using phenolic resin adhesive on both layers in the present invention, whether to use a phenolic resin adhesive to the core layer alone, or phenol resin adhesive and an isocyanate-based adhesive and an aqueous formulation containing a small amount of wax emulsion Is preferred .

<Impregnation step and coating step>
The front and back layers are separately subjected to an impregnation step of impregnating the wood chip with an adhesive resin, and the core layer is separately subjected to an application step of applying the adhesive resin to the wood chip.
As will be described in detail later, the amount of resin solids with respect to the wood chips is 15 to 80 parts by mass of resin solids with respect to 100 parts by mass of the wood chips in the front and back layers, and the wood chips are absolutely dry in the core layer. It is preferable to make resin solid content into 6-16 mass parts with respect to 100 mass parts of quantity. In the front and back layers, the solid resin content is 18 to 70 parts by mass with respect to 100 parts by mass of the dryness of the wood chips, and in the core layer, the resin solids content is 8 to 12 with respect to 100 parts by mass of the absolute dryness of the wood chips. It is more preferable to set it as a mass part.

<Impregnation step>
For the front and back layers, the above-mentioned aqueous adhesive composition for the front and back layers is used so that the resin solid content (grease content) in the resin-impregnated chip is within the range of 15 to 80% by mass with respect to the chip dry weight. To do. This makes it possible to sufficiently reinforce the wood chips by infiltrating a sufficient amount of resin and sufficiently bond the wood chips to make the surface of the particle board dense, and has high durability and water resistance. Can be obtained.
If the resin solid content (grease content) in the resin-impregnated chips for the front and back layers exceeds 80%, the performance of the particle board will not improve much, but the cost will be high and it will not be economical. Is too large to be practical.

<Application process>
The core layer adhesive resin is applied to the core layer so that the resin solid content in the resin-coated chip is in the range of 6 to 16% by mass relative to the chip dry weight. Thereby, it is possible to firmly bond the core layer chip larger than the front and back layer chip.

When phenol resin adhesive or melamine resin adhesive is used for the core layer, if the resin solid content in the resin-coated chip exceeds 16% by mass, the puncture phenomenon during hot-pressure molding due to excessive moisture in the mat (water vapor during decompression) The pressure of the particle board swells up and does not become a product), and the chip's cohesive force becomes too strong, and the chip does not move smoothly through the plant, and the forming does not work well and the particle board can withstand use It is difficult to manufacture.
When an isocyanate-based adhesive is used for the core layer, if the resin solid content in the resin-coated chip exceeds 16% by mass, the performance of the particle board is not improved so much, but the cost increases and is not economical. Chips spilled on the hot plate adhere to the hot plate, and in some cases, the particle board cannot be removed from the hot plate.

<Preliminary drying process>
As described above, the adhesive resin used for the front and back layers has a lower degree of condensation (average molecular weight is smaller) than that of a normal adhesive, has less tackiness, and has less caking force of the resin-impregnated chip. In the present invention, since the resin-impregnated chip contains a large amount of adhesive resin, the resin-impregnated chip is added to the device particularly in operation in a forming system of a method in which the chip particle size is continuously changed by blowing the chip with wind power. In some cases, the resin-impregnated chips adhere to each other, and the resin-impregnated chips are difficult to smoothly transport and form. Therefore, in the present invention, it is preferable to pre-dry the resin-impregnated chips for the front and back layers prior to forming from the viewpoint that smooth forming without adhesion to equipment can be achieved.

Such a method of pre-drying the resin-impregnated chip for the front and back layers may be performed under a temperature condition of 100 ° C. or less. When the drying temperature exceeds 100 ° C., the above-mentioned adhesive resin used for the front and back layers undergoes a condensation reaction during the preliminary drying, so that the chip is not sufficiently impregnated and the adhesive force is also likely to be reduced. Further, if the drying temperature is low, the influence on the resin is small even if the drying time is 30 minutes or longer, but it is preferable to perform the preliminary drying within 30 minutes from the viewpoint of particle board production efficiency. Thus, from the viewpoint of drying efficiency and productivity, the resin-impregnated chips of the front and back layers are preferably dried by heating so that the moisture content is 5 to 20% at 60 to 100 ° C.
In addition, the resin-coated chip for the core layer does not need to be pre-dried since an adhesive does not contain moisture particularly when an isocyanate adhesive is used.

  For the preliminary drying, an airflow dryer using hot air, a rotary dryer, a tunnel dryer, or other high-frequency or microwave dryer is used. If hot air is used, dry the chip with sufficient agitation to avoid uneven chip temperature.

<Forming process>
The resin-impregnated chip for the front and back layers and the resin-coated chip for the core layer, in which the wood chip and the resin are kneaded, are formed into a mat shape with a predetermined thickness in the order of the back layer, the core layer, and the surface layer, and stacked in three layers To go. This process is called forming, and each layer is called a mat. The thickness of the surface layer and the back layer is preferably about 0.5 to 2.0 mm after hot pressing, for example.

  Forming is performed by a normal method, and a method of dropping a resin-impregnated chip or a resin-coated chip onto a conveyor while leveling a conventional group of pins, or a resin-impregnated chip or a resin-coated chip A method is usually used in which the wind is blown by wind and dropped onto the conveyor.

What is formed on the three-layer mat is heated and pressurized (hot pressure) to form a particle board. The hot platen of the hot press makes contact with the mat of the front and back layers on a smooth surface, and forms the front and back layers smoothly. In the present invention, the hot press can use either a multistage hot platen system or a continuous press system. Since the resin content of the front and back layers is large, the multi-stage heating plate method has the effect of improving the product yield without deterioration of the particle board surface, which is caused by leaving it on the heating plate for a certain period of time without pressure. The continuous press method can be produced without any problem as in the case of normal particle board. The hot pressure condition is 160 to 230 ° C., 25 to 50 kgf / cm ² (where 1 kgf is about 9.8 N), and the time is suitably in the range of 10 to 25 seconds per 1 mm of the thickness of the particle board. When releasing the pressure, gradually decrease the pressure as usual to prevent puncture.

Although the performance of the particle board and its specific gravity are closely related, it is desirable that the density of the particle board is 0.8 to 1.0 g / cm ^{3 in} order to achieve the object of the present invention.
After hot pressing, processes such as ear trimming (trimming) and inspection are performed as usual. The surface of the front and back layers that are strongly impregnated with the resin is dense and hard, so surface polishing (sanding) is not necessary, but it can also be performed when precise thickness adjustment or the like is required.

According to the present invention, a high-strength particle board having a high bending strength (24.0 N / mm ² or more) and a bending Young's modulus (5000 N / mm ² or more) comparable to a structural plywood can be produced.
The high-strength particle board obtained by the present invention can be suitably used for applications in which plywood is conventionally used, such as a truck body or a flooring material for a transport container, on which heavy objects are loaded. .

  Hereinafter, the present invention will be specifically described with reference to examples. The physical properties of the particle board were evaluated according to JIS A5908 except for the bending Young's modulus, and the bending Young's modulus was evaluated according to Japanese Agricultural Standard for plywood (first grade bending test using a small test piece of structural plywood).

Example 1
As wood chips for the front and back layers, 90% or more of wood chips having a length of 4 mm or less, a thickness of 0.3 mm or less, and a width of 1 mm or less were produced. In addition, as an adhesive composition for the front and back layers, a phenol resin having a nonvolatile content of 60% by mass, a viscosity of 100 mPa · s, and a weight average molecular weight of 500 and a commercially available wax emulsion (Diaproof WY-4, solid content 45%, A mixture of Dainippon Color Materials Co., Ltd.) was prepared.
The above-mentioned adhesive composition for the front and back layers was kneaded with the wood chip for the front and back layers using a blender to produce a resin-impregnated chip for the front and back layers.
In the resin-impregnated chips for the front and back layers, the resin solid content of the phenol resin (non-volatile content of the condensate) is 20 parts by mass and the wax solid content is 0.5 parts by mass with respect to 100 parts by mass of the dryness of the chip. It is blended with.
The resin-impregnated chips for the front and back layers were dried with a hot air dryer at 80 ° C. for 30 minutes until the moisture content with respect to the resin solid content became 15%.

On the other hand, as a wood chip for the core layer, a wood chip having a size of 90% or more of a length of 30 mm or less, a thickness of 1 mm or less, and a width of 2 mm or less was produced. In addition, as the adhesive composition for the core layer, a commercially available phenol resin (nonvolatile content: 45 mass%, viscosity: 100 mPa · s) and MDI (Millionate MR-100, Nippon Polyurethane Industry Co., Ltd.) is 9: 1. A mixture prepared by mixing in a weight ratio and further mixed with a commercially available wax emulsion (Diaproof WY-4, solid content 45%, Dainippon Color Industry Co., Ltd.) was prepared.
A resin coating chip for the core layer was manufactured by kneading the core layer adhesive compound into the core chip for the core layer using a blender.
In the resin-coated chip for the core layer, the resin solid content of the phenol resin (the total of the solid content of the phenol resin and MDI) is 10 parts by mass and the solid content of the wax is 1 part by mass with respect to 100 parts by mass of the absolutely dry amount of the chip. It is blended in the ratio.

The resin-impregnated chip for the front and back layers and the resin-coated chip for the core layer are respectively weighed, formed into a three-layer mat as usual, and hot-pressed at 200 ° C. and 35 kgf / cm ² for 6 minutes. (Thickness 15 mm, specific gravity 0.88) was produced.
The physical properties of the obtained particle board were evaluated as shown in Table 1 and corresponded to the high-strength particle board.

(Example 2)
In the resin-impregnated chip for the front and back layers, a particle board was produced in the same manner as in Example 1 except that the resin solid content of the phenol resin was 70 parts by mass with respect to 100 parts by mass of the dryness of the chip (thickness) 15 mm, specific gravity 0.88).
The physical properties of the obtained particle board were evaluated as shown in Table 1 and corresponded to the high-strength particle board.

The evaluation results of Examples 1 and 2 are summarized in Table 1. Here, the “grease content” refers to the ratio of the resin solid content to 100 parts by mass of the absolutely dry amount of the wood chip.

(Comparative Example 1)
In the resin-impregnated chip for the front and back layers, the production of the particle board was tried in the same manner as in Example 1 except that the resin solid content of the phenol resin was changed to 90 parts by mass with respect to 100 parts by mass of the absolutely dry amount of the chip. However, the viscosity of the resin-impregnated chips for the front and back layers was so great that the mat could not be formed.

(Comparative Example 2)
In the resin-impregnated chip for the front and back layers, a particle board was produced in the same manner as in Example 1 except that the resin solid content of the phenol resin was 13 parts by mass with respect to 100 parts by mass of the dryness of the chip (thickness) 15 mm, specific gravity 0.88).
The physical properties of the obtained particle board were evaluated as shown in Table 2. The bending strength satisfied the requirements for the high strength particle board, but the bending Young's modulus did not satisfy the requirements for the high strength particle board.

(Comparative Example 3)
A particle board was produced in the same manner as in Example 1 except that a phenol resin having a nonvolatile content of 78% by mass, a viscosity of 100 mPa · s, and a weight average molecular weight of 200 was used for the adhesive composition used for the front and back layers.
When the physical properties of the obtained particle board were evaluated, it was as shown in Table 2 and did not satisfy the requirements of the high-strength particle board.

(Comparative Example 4)
Example, except that the weight average molecular weight of the phenol resin used for the front and back layers is 800, and the resin solid content of the phenol resin in the resin-impregnated chip for the front and back layers is 30 parts by mass with respect to 100 parts by mass of the absolutely dry amount of the chip In the same manner as in No. 1, a particle board was produced. The viscosities of the resin-impregnated chips for the front and back layers were large, and it was difficult to form a mat.
The physical properties of the obtained particle board were evaluated as shown in Table 2. The bending strength satisfied the requirements for the high strength particle board, but the bending Young's modulus did not satisfy the requirements for the high strength particle board.

  The evaluation results of Comparative Examples 1 to 4 are summarized in Table 2.

1 ... surface layer, 2 ... back layer, 3 ... core layer, 4 ... particle board.

Claims (4)

An impregnation step of impregnating a wood chip with an aqueous solution of a resol type phenolic resin to obtain a resin-impregnated chip, and a three-layer mat including a surface layer and a back layer from the resin-impregnated chip and a core layer are laminated to each other, A method for producing a particle board comprising a molding step of pressing and molding into a plate shape,
In the impregnation step, the resin impregnated chips of the front layer and the back layer have a resin solid content of 55 to 75% by mass and a resin viscosity of 50 to 200 mPa · s, and a weight average molecular weight of 300 to 700. A method for producing a particle board, comprising supplying an aqueous solution of a phenol resin in a range to obtain a resin-impregnated chip containing 15 to 80 parts by mass of a resin solid content with respect to 100 parts by mass of an absolutely dry amount of a wooden chip. Prior to the molding step, a pre-drying step for pre-drying the resin-impregnated chips for the front layer and the back layer is provided, and the resin-impregnated chips for the front layer and the back layer so that the moisture content is 5 to 20% at an atmospheric temperature of 60 to 100 ° C. The method for producing a particle board according to claim 1, wherein: The method for producing a particle board according to claim 1 or 2, wherein the resin-impregnated chip used for the core layer is a resin-impregnated chip containing 8 to 12 parts by mass of a resin solid content with respect to 100 parts by mass of an absolutely dry amount of the wood chip. . For the surface layer and the back layer, use wood chips of length 5 mm or less, thickness 1 mm or less, width 2 mm or less, and for the core layer, wood chips 40 mm or less, thickness 3 mm or less, width 5 mm or less. The manufacturing method of the particle board as described in any one of Claims 1-3 used.

Images