JP2012214011A - Method for manufacturing woody board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a woody board that is increased in strength and dimension stability, especially in a dimension stability in a surface direction of the board against a variation in moisture content, on the premise of adding a polycarboxylic acid to a woody raw material.SOLUTION: The method for manufacturing a woody board includes at least the steps of: heating wood flakes under a humidified atmosphere, and then fibrillating the heated wood flakes into wet fiber; applying an aqueous solution dissolving a polycarboxylic acid or aqueous solution dissolving a polyvalent carboxylic acid anhydride to the fibrillated wet fiber to allow the polycarboxylic acid to adhere to the surface of the fibrillated wet fiber; and pressurizing and heating the wet fiber to which the polycarboxylic acid adheres, to form the woody board.

Description

  The present invention relates to a method for producing a wooden board excellent in strength and dimensional stability by adding a polyvalent carboxylic acid to a wooden raw material and hot pressing.

  Conventionally, a wooden board is manufactured by adding a synthetic resin as an adhesive to a wooden raw material such as flakes, chips, fibers, and the like, and hot-pressing them.

  However, a synthetic resin used as an adhesive is not necessarily preferable from the viewpoint of the global environment such as a problem of resource depletion. From this point of view, for example, there is a method of mixing a powdered or fragmented wood-derived material (wood material) and a polyvalent carboxylic acid such as citric acid, and heating and pressurizing the mixture to form a wood board. It has been proposed (see, for example, Patent Document 1).

  Also, as another manufacturing method, after adding a polyvalent carboxylic acid such as maleic acid to woody raw materials such as chips and flakes, the woody raw material is contacted with water vapor, and after sequentially treating these with drying and pulverization A method for producing a woody molded body by heating and pressurization has been proposed (see, for example, Patent Document 2).

International Publication 2001/1988 JP 2008-238448 A

  As described above, attempts have been made to produce a wooden board / molded body by adding a polyvalent carboxylic acid to a wooden raw material. However, these technologies focus on molding and bonding by adding carboxylic acid to the wood raw material. Even if the wood board is molded with the above-mentioned wood raw material, it is a practically important performance for the wood board. In some cases, sufficient strength and dimensional stability cannot be obtained.

  The present invention has been made in view of these points, and the object of the present invention is to provide strength and dimensional stability, particularly against moisture content changes, on the premise that a polyvalent carboxylic acid is added to the woody material. It is an object of the present invention to provide a method for manufacturing a wooden board with improved dimensional stability in the surface direction of the board.

  In view of the above problems, as a result of repeated studies by the inventors, in order to increase the strength of the wooden board, the wooden board is heated while actively contacting the lignin contained in the wood with the polyvalent carboxylic acid. It was found that molding by pressure was important.

  Therefore, the inventor cannot say that the surface of the above-mentioned wood powder is rich in lignin, or the chip-like and flake-like wood pieces are rich in lignin in the wood fibers inside. Therefore, regardless of the amount of polyvalent carboxylic acid added, it was thought that lignin contained in the woody material and polyvalent carboxylic acid would not come into positive contact.

  Then, the inventor conducted further experiments using various forms of wood raw materials to heat the wood pieces in an atmosphere containing moisture, and then defibrated the wood fibers (hereinafter, wet type). A layer rich in lignin is exposed on the surface of the fiber (referred to as “fiber”), and the woody raw material (wet fiber) in such a form positively contacts the lignin with the polyvalent carboxylic acid. I got new knowledge that I could do it.

  1st-3rd invention shown below is based on the said inventors' new said knowledge, The manufacturing method of the wooden board which concerns on 1st invention heated the wood chip in the atmosphere containing a water | moisture content Then, a step of defibrating the heated wood chip into wet fibers, and applying an aqueous solution in which polyvalent carboxylic acid is dissolved or an aqueous solution in which polyvalent carboxylic acid anhydride is dissolved to the defibrated wet fibers A step of attaching a polyvalent carboxylic acid to the surface of the defibrated wet fiber, and a step of forming a wooden board by pressurizing and heating the wet fiber to which the polyvalent carboxylic acid is attached. , At least.

  A method for producing a wooden board according to a second aspect of the present invention includes a step of heating a wood chip in an atmosphere containing moisture and then defibrating the heated wood chip into wet fibers, and the defibrated wet fibers A step of attaching a polyvalent ammonium carboxylate to the surface of the defibrated wet fiber by applying an aqueous solution in which the polyvalent carboxylate ammonium salt is dissolved, and a wet fiber to which the polyvalent carboxylic acid is adhered. And pressurizing and heating to form a wooden board.

  According to a third aspect of the present invention, there is provided a method for manufacturing a wood board, comprising: heating a wood piece in an atmosphere containing moisture; and then defibrating the heated wood piece into wet fibers; A step of attaching a polyvalent carboxylic acid powder or a polyvalent carboxylic acid anhydride powder to the surface of the substrate, a step of forming a wooden board by pressurizing and heating the wet fiber to which the powder is attached, It is characterized by including at least.

  Here, in the wood fiber that has been defibrated after heating the wood chip in an atmosphere containing moisture, a layer rich in lignin is exposed on the fiber surface. By using this lignin, even in the case of any of the first to third inventions, a small amount of polyvalent carboxylic acid can be used at the time of molding (at the time of hot pressing). The fluidity of the wet fiber is improved, and a wood board excellent in strength that the density of the surface of the wood board becomes high can be obtained. In addition, the strength of the wooden board and the dimensional stability in the surface direction during moisture absorption can be improved by generating a long fiber of the wooden material and generating an ester bond by adding a polyvalent carboxylic acid.

  Specifically, by heating and pressurizing (hot pressing) the wet fiber to which the polyvalent carboxylic acid or its powder is attached, the hydroxyl group on the wet fiber surface and the carboxyl group of the polyvalent carboxylic acid undergo a dehydration condensation reaction. Thereby, an ester bond is generated on the surface of the wet fiber. Here, since a plurality of carboxyl groups exist in the polyvalent carboxylic acid, the wet fibers are cross-linked through the ester bond of the polyvalent carboxylic acid.

  As a result, the wet fibers are bonded (restrained) to develop strength. This also restrains the movement of the fibers even when the fibers swell and contract as the moisture is absorbed and released, and suppresses the dimensional change of the wooden board. Furthermore, the wet fiber is hydrophobized by the formation of the ester bond, and the moisture content change of the wooden board can be suppressed.

  In the case of the first invention, when an aqueous solution in which a polyvalent carboxylic acid anhydride is dissolved is used, the polyvalent carboxylic acid anhydride is hydrolyzed to become a polyvalent carboxylic acid. Therefore, it is possible to attach the polyvalent carboxylic acid to the surface of the wet fiber regardless of whether the aqueous solution in which the polyvalent carboxylic acid is dissolved or the aqueous solution in which the polyvalent carboxylic acid anhydride is dissolved is used. The effects described above can be expected.

  In the case of the first invention, the polyvalent carboxylic acid is dissolved in the wet fiber by applying an aqueous solution in which the polyvalent carboxylic acid is dissolved or an aqueous solution in which the polyvalent carboxylic acid anhydride is dissolved to the wet fiber. Since the acid is adhered, the polyvalent carboxylic acid can be uniformly adhered to the surface of the wet fiber as compared with the one using these powders of the third invention.

  In the case of the second invention, the polyvalent carboxylic acid ammonium salt is ionized into a polyvalent carboxylic acid and ammonia in the state of an aqueous solution, and when further dried, becomes a polyvalent carboxylic acid ammonium salt. This adheres to the wet fiber. In the wood board molding process, the polyvalent ammonium carboxylate is thermally decomposed into polyvalent carboxylic acid and ammonia by hot pressure, and the ammonia attached to the surface of the wet fiber is volatilized by heating. As a result, the pH value of the board can be lowered and the wood board can be made acidic in the molding stage. Therefore, similar to the effect of the first invention (the invention described in claim 1), the reaction (esterification) of wood and carboxylic acid proceeds, and compared with the wooden board without polyvalent carboxylic acid, the strength and A wood board with excellent dimensional stability can be obtained.

  Further, in the case of the third invention, the polyvalent carboxylic acid in the powder state causes an esterification reaction with the wet fiber by the hot pressure in the molding step, as in the first invention. In addition, the polyvalent carboxylic acid anhydride in the powder state causes an esterification reaction with the wet fiber in the anhydrous state.

  Here, the wet fiber is, for example, heated in an atmosphere containing water such as water or water vapor to dissolve the wood fiber of the wood piece (soften the wood piece) and use the refiner or the like as the refined wood fiber. This refers to fibers that have been defibrated.

  As a defibrating method in the defibrating process of the first to third inventions, for example, boiled defibrating treatment in which wood chips are boiled in a boiling tank and boiled wood pieces are defibrated, steam disintegration using steam Examples include fiber processing. However, as a more preferable aspect, in the defibrating step, the wood pieces are steamed for 1 to 10 minutes under a steam pressure of 0.5 to 1.0 MPa, and the steamed wood pieces are subjected to the steam pressure. To defibrate the wet fiber.

  According to this aspect, by performing the defibrating process, longer wet fibers can be obtained without damaging the wet fibers as compared with the defibrated fibers after the boiling process. Thereby, the intensity | strength of a wooden board can be raised more.

  Furthermore, when the wet fiber is defibrated, the lignin on the surface of the wet fiber treated under the above-described steam pressure (ie, high temperature and high pressure) reacts with the polyvalent carboxylic acid during the molding of the wooden board. Since it softens, wet fibers flow easily during pressurization. Thereby, the wooden board from which the surface of a wooden board becomes high-density can be obtained.

  Here, when the steam pressure is less than 0.5 MPa, or when the steam treatment time is less than 1 minute, the wood fiber of the wood chip is difficult to be unraveled. May be difficult. On the other hand, if the steam pressure exceeds 1.0 MPa, or if the steam treatment time exceeds 10 minutes, the wood fiber of the wood chip may be damaged, and the fiber length of the boiled defibrated fiber May be equivalent or shorter.

  Moreover, as a more preferable aspect, in the defibrating step, the fiber length of the wet fiber is defibrated to at least 1 mm or more by selecting the vapor pressure and the steam treatment time within the above-mentioned ranges. According to this aspect, the strength of the wooden board can be improved by setting the fiber length of the wet fiber to 1 mm or more.

  In the case of the first and second inventions, after applying an aqueous solution to the wet fibers, the wet fibers may be dried, and the wood board may be formed with the dried wet fibers. Since wet fibers before being molded into a wooden board are dried in advance, the moisture content in the wooden board after molding can be suppressed and the dimensional stability of the wooden board can be achieved as compared with those without drying. .

  Further, in the step of attaching the polyvalent carboxylic acid according to the first invention, the polyvalent carboxylic acid or polyvalent carboxylic acid anhydride is not particularly limited as long as the above-described effects can be expected. Absent. However, in a more preferred embodiment, the polyvalent carboxylic acid includes a polyvalent carboxylic acid selected from at least one selected from the group consisting of citric acid, 1,2,3,4-butanetetracarboxylic acid, maleic acid, malic acid, and itaconic acid. A polyvalent carboxylic acid is used, and the selected polyvalent carboxylic acid anhydride is used as the polyvalent carboxylic acid anhydride.

  According to this aspect, the polyvalent carboxylic acid contained in these aqueous solutions can soften the lignin on the fiber surface of the wet fiber at least at 200 ° C. or higher. In particular, 1,2,3,4-butanetetracarboxylic acid and maleic acid can soften lignin at least 160 ° C. or more compared to other polyvalent carboxylic acids. It can be carried out.

  As a more preferred embodiment, citric acid or citric anhydride is used for the polyvalent carboxylic acid, and 2-15% by mass of the citric acid or citric anhydride is contained in the wet fiber. According to this aspect, it is possible to improve the bending strength of the wooden board and improve the dimensional stability during moisture absorption.

  That is, when the amount of citric acid or its anhydride to be contained is less than 2% by mass, there is a concern that the bending strength of the wooden board is lowered or the dimensional stability is lowered. On the other hand, even if the amount of citric acid or anhydride contained exceeds 15% by mass, no further effect can be expected, and discoloration (fading) of the wooden board may proceed.

  In another embodiment, maleic acid is used as the polyvalent carboxylic acid, maleic anhydride is used as the polyvalent carboxylic acid anhydride, and the maleic acid or the maleic anhydride is added to the wet fiber. 2-15 mass% of thing is contained.

  According to this aspect, it is possible to improve the bending strength and the dimensional stability of the wooden board. As described above, when maleic acid or maleic anhydride is used, a wood board can be formed at a lower heating temperature (160 ° C. or higher) than when citric acid or citric anhydride is used.

  Moreover, when the maleic acid or maleic anhydride to contain is less than 2 mass%, there exists a concern about the fall of bending strength and the fall of dimensional stability. On the other hand, even if the maleic acid or maleic anhydride to be contained exceeds 15% by mass, no further effect can be expected.

  The polyvalent carboxylic acid ammonium salt according to the second invention is not particularly limited as long as the above-described effects can be expected. However, as a more preferable embodiment, an ammonium maleate is used as the polyvalent carboxylic acid ammonium salt.

  According to this aspect, by using the maleic acid ammonium salt, as compared with the case of using maleic acid or maleic anhydride as in the first invention, moreover, the case of using ammonium citrate salt or the like. Also, the bending strength of the wooden board can be improved.

  According to the present invention, on the premise that a polyvalent carboxylic acid is added to a wood raw material, strength and dimensional stability, in particular, dimensional stability in the board surface direction against a change in moisture content can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS It is the photograph figure which observed the surface of the wet fiber which concerns on Example 1, 2 of this invention, the wood flour which concerns on the comparative example 1, the wooden board which concerns on Example 1, 2 and the comparative example 1, and (a) The photograph of the wet fiber which concerns on Example 1, (b) is the photograph figure of the surface of the wooden board which concerns on Example 1, (c) is the photograph figure of the wet fiber which concerns on Example 2, (d) is The photograph of the surface of the wooden board which concerns on Example 2, (e) is a photograph of the wood powder which concerns on the comparative example 1, (f) is the photograph of the surface of the wooden board which concerns on the comparative example 1. FIG.

  Embodiments according to the first to third inventions will be described below. Embodiments according to any of the inventions are methods for defibrating wood pieces into wood fibers and producing wood boards from the defibrated wood fibers, and producing dry wood boards such as medium fiber boards (MDF). It is a method to do.

  The manufacturing method of the wood board in these embodiments is shown below. Defibration treatment process, 2. 2. a polycarboxylic acid attaching step; It includes at least a molding step. Below, each process is demonstrated.

[1. Defibration process
First, a chip-shaped wood chip is prepared as a starting material of the wood board according to the first to third aspects of the invention. Examples of the wood chip include conifers such as cedar, pine and cypress, and generally known broad-leaved trees such as lauan.

  Next, after heating such a wood chip in an atmosphere containing moisture, the heated wood chip is defibrated into wet fibers. Specifically, the wood chip is put into a pressure vessel and steam-treated for 1 to 10 minutes under a steam pressure of 0.5 to 1.0 MPa (steam treatment). Thereafter, in the same pressure vessel, the wood chips after the steam treatment are defibrated into wet fibers of 1 mm or more by a refiner under the same steam pressure as the steam treatment.

  As another specific example, the above-described defibrating treatment may be performed under normal pressure. As yet another specific example, the wood chips are put into boiling water and boiled for 2 to 3 hours (boiling). Treatment), the wood chips after boiling may be defibrated by a refiner.

  Thus, the wood fiber (wet fiber) that has been defibrated after heating the wood chip in an atmosphere containing moisture can expose a layer rich in lignin on the fiber surface. Here, in the case of steam treatment, if the steam pressure is less than 0.5 MPa, or if the steam treatment time is less than 1 minute, the wood fiber of the wood chip is difficult to be unraveled, and thereafter It may be difficult to obtain wet fibers by treatment. On the other hand, when the steam pressure exceeds 1.0 MPa, or when the steam treatment time exceeds 10 minutes, the wood fiber of the wood chip may be damaged, and the fiber of the wet fiber after boiling treatment There is a possibility that it may be equal to or shorter than the length.

[2. (Polycarboxylic acid adhesion process)
In this way, the polyvalent carboxylic acid is attached to the surface of the defibrated wet fiber.
In the case of the embodiment according to the first invention, an aqueous solution in which a polyvalent carboxylic acid is dissolved in a wet fiber or an aqueous solution in which a polyvalent carboxylic acid anhydride is dissolved is applied, and the wet fiber after application is dried. By making it (water content 5-10%), the polyvalent carboxylic acid is adhered to the wet fiber. Thereby, polyvalent carboxylic acid can be uniformly adhered to the surface of the wet fiber.

  Here, as the polyvalent carboxylic acid, citric acid, malic acid, itaconic acid, succinic acid, maleic acid, fumaric acid, tartaric acid, adipic acid, 1,2,3,4-butanetetracarboxylic acid, malonic acid, glutaric acid An acid, an oxalic acid, a phthalic acid, a terephthalic acid, an isophthalic acid etc. can be mentioned, As a polyhydric carboxylic acid anhydride, the anhydride of these illustrated polyhydric carboxylic acid can be mentioned. Among these, according to the experiments by the inventors, it is more preferable to use citric acid, 1,2,3,4-butanetetracarboxylic acid, maleic acid, malic acid, itaconic acid, and the like as the polyvalent carboxylic acid. Even if these polycarboxylic acid anhydrides are used, substantially the same effect can be expected.

  And when using a citric acid or a citric acid anhydride, 2-15 mass% of citric acid or a citric acid anhydride is contained with respect to a wet fiber (added). When maleic acid or maleic anhydride is used, it is preferable to contain 2 to 15% by mass of maleic acid or maleic anhydride with respect to the wet fiber.

  As described above, in the present embodiment, even a slight amount of polyvalent carboxylic acid as shown in the lower limit of the addition amount of these polyvalent carboxylic acids or anhydrides of these acids is sufficiently formed as described later. Therefore, it is possible to obtain a wood board in which the improvement of the bending strength and the improvement of the dimensional stability of the wood board are compatible.

  Here, when the amount of citric acid or citric acid anhydride is less than 2% by mass, there is a concern that the bending strength of the wooden board is lowered or the dimensional stability is lowered. On the other hand, even if the amount of citric acid or citric anhydride contained exceeds 15% by mass, no further effect can be expected, and discoloration (fading) of the wooden board may proceed.

  When maleic acid or maleic anhydride is less than 2% by mass, there is concern about a decrease in bending strength and a decrease in dimensional stability. On the other hand, even if the maleic acid or maleic anhydride to be contained exceeds 15% by mass, no further effect can be expected.

  In the embodiment according to the second invention, an aqueous solution in which a polyvalent carboxylic acid ammonium salt is dissolved is used instead of the aqueous solution in which the polyvalent carboxylic acid is dissolved. In this embodiment, the polyvalent carboxylic acid ammonium salt is ionized into a polyvalent carboxylic acid and ammonia in the state of an aqueous solution, and further dried to form a polyvalent carboxylic acid ammonium salt, which adheres to the wet fiber. To do. And the polycarboxylic acid ammonium salt is thermally decomposed into polyvalent carboxylic acid and ammonia by the heat pressure in the molding step shown below, and the ammonia adhering to the surface of the wet fiber is volatilized by heating. As a result, the pH value of the board can be lowered and the wooden board can be made acidic in the molding stage. Therefore, similar to the effect of the first invention, the reaction (esterification) of wood and carboxylic acid proceeds, and the wood board superior in strength and dimensional stability compared to the wood board not added with polyvalent carboxylic acid. Is obtained.

  Examples of the polyvalent carboxylic acid ammonium salt include ammonium salts with the polyvalent carboxylic acid exemplified in the above-mentioned polyvalent carboxylic acid according to the first invention. More preferred polyvalent carboxylic acid ammonium salts are: And ammonium maleate. By using maleic acid ammonium salt, it is possible to improve the bending strength of the wooden board as compared with the case of using maleic acid or maleic anhydride, and further, when using ammonium citrate salt or the like. .

  In the embodiment according to the third invention, instead of the aqueous solution in which the polyvalent carboxylic acid is dissolved, a polyvalent carboxylic acid powder or a polyvalent carboxylic acid anhydride powder is used, and this powder is directly dissolved. Adhere to the surface of the wet fiber. Even in such a method, the esterification reaction with the wet fiber occurs due to the hot pressure of the molding step, so the wood board obtained through the molding step described later was obtained in the embodiment of the first invention. Bending strength and dimensional stability almost equal to those of a wood board can be obtained.

[3. Molding process]
The embodiments according to any of the first to third inventions also perform the following molding process. Specifically, the above-mentioned polyvalent carboxylic acid, polyvalent carboxylic acid anhydride, polyvalent carboxylic acid ammonium salt, polyvalent carboxylic acid powder, or wet fiber to which the polyvalent carboxylic acid anhydride powder is attached is mat-molded. Mold to wood mat using a machine. The formed wood mat is put into a press machine and pressed and heated (hot pressed) to form a wood board. Specifically, a wood mat made of wet fiber to which polyvalent carboxylic acid is attached is put into a molding device, and the heating temperature is 160 ° C. to 260 ° C., and the pressurizing condition is 0.2 MPa to 7 MPa. Hot press for 1-5 minutes. As another aspect, a wood mat is prepared with a predetermined thickness (for example, 3 mm) and a predetermined board density (for example, 0.8 kg / cm ³ ). For example, the wood mat may be pressurized up to 3 mm) at the above heating temperature and pressure holding time (holding time after reaching its thickness).

  Here, when 1,2,3,4-butanetetracarboxylic acid, maleic acid, or an anhydride of any of these acids shown in the embodiment according to the first invention is used, citric acid or Compared to the case where citric acid anhydride is used, the wood board can be molded at a lower heating temperature (160 ° C. or higher) in the following molding process.

  Thus, in these embodiments, the wood fiber that has been defibrated after heating the wood chip in an atmosphere containing moisture exposes a layer rich in lignin on the fiber surface. By using lignin, a small amount of polyvalent carboxylic acid can improve the fluidity of wet fibers during molding, and a wood board with excellent strength can be obtained. Furthermore, the strength and dimensional stability of the wood board can be improved by forming the ester bond by fiberizing the wood raw material and adding the polyvalent carboxylic acid.

  Examples of the present invention will be described below.

[Example 1]
As a wood chip, a few centimeters of softwood chips (cedar) were boiled in a boiling bath at 100 ° C. for 2 to 3 hours. Next, it was defibrated into wet fibers (boiling defibrated fibers) with a refiner at normal pressure. The average fiber length of the obtained wet fiber was measured with a microscope (average value of 100 samples). The results are shown in Table 1. The obtained wet fiber was observed with a microscope. The results are shown in FIG.

  Next, the citric acid aqueous solution is added to the wet fiber so that the ratio of citric acid shown in Table 2 as a polyvalent carboxylic acid is added to the wet fiber (dry mass) on the surface of the defibrated wet fiber. Applied (sprayed). Next, the wet fiber was dried to a moisture content of around 6% with a dryer (dryer), and the carboxylic acid was fixed (adhered) uniformly to the surface of the woody material.

Next, the wet fiber to which the citric acid was adhered was molded into a wood mat having a thickness of 70 mm using a mat molding machine. By putting this wood mat into a press machine and pressurizing it to a thickness of 3 mm (board density 0.8 g / cm ³ ) under heating conditions, that is, a hot pressing temperature of 220 ° C., a hot pressing time of 5 minutes, A wood board (wood fiber board) was obtained. The surface of the obtained wooden board was observed with a microscope. The result is shown in FIG.

[Example 2]
A wooden board was produced in the same manner as in Example 1. The difference from Example 1 is that the steam treatment and the defibration treatment of wood chips including cedar were performed in the same pressure vessel. Specifically, the above-mentioned several centimeters of coniferous chips are steamed under a vapor pressure of 0.5 to 1.0 MPa (specifically, 0.8 MPa) for 1 to 10 minutes (specifically, 5 minutes). Treated and steam-treated wood chips were defibrated to wet fibers (high-pressure defibrated fibers) with a refiner under the same steam pressure (0.5 to 1.0 MPa (specifically 0.8 MPa)). The point is different. The obtained wet fiber was observed with a microscope. The results are shown in FIG.

  And like Example 1, the citric acid of the ratio shown in Table 2 is added so that citric acid is attached to the wet fiber in the same manner, the wet fiber is dried, and this is formed into a wood mat, A wooden board was formed by pressurizing and heating the formed mat. In addition, it carried out similarly to Example 1, and measured the average fiber length of the obtained wet fiber with the microscope (average value of 100 samples). The results are shown in Table 1. The surface of the obtained wooden board was observed with a microscope. The results are shown in FIG.

[Comparative Example 1]
A wooden board was produced in the same manner as in Example 1. The difference from Example 1 is that a sander powder (wood powder) obtained by grinding softwood timber (cedar) with a belt sander (abrasive paper # 80) is used as the wood raw material. Then, in the same manner as in Example 1, citric acid was added to the wood flour in the same manner so that the citric acid in the ratio shown in Table 2 was added, and then the wood board was formed by applying pressure and heating. . In addition, similarly to Example 1, the average length of the obtained wood flour was measured with a microscope (average value of 100 samples). The results are shown in Table 1. The surface of the obtained wood powder and the molded wood board was observed with a microscope. The results are shown in FIGS. 1 (e) and (f).

<Measurement of bending strength of wood board>
As a wood board according to Examples 1 and 2 and Comparative Example 1, a test body (size 50 mm × 200 mm × thickness 3 mm) in a natural state (air-dried state: moisture content 5 to 9%) after hot pressing is prepared. did. In the test, a normal concentrated strength (N / mm ² ) was measured by applying a central concentrated load using a material testing machine and a load speed of 10 mm / min. The results are shown in Table 2. In addition, the air dry density of the wood board concerning Examples 1, 2 and Comparative Example 1 was measured. Specifically, the weight and volume of the air-dried wood board were calculated, and the weight was divided by the volume. The results are shown in parentheses in Table 2.

<Measurement of density distribution in wood board>
Furthermore, as a test body of the wood board according to Examples 1 and 2 and Comparative Example 1, 50 mm × 50 mm × 3 mm thickness was cut into a plurality of samples, and a density of 0.80 ± 0.01 g / cm from these test samples. A test specimen falling within the range of cm ³ was extracted, and the density distribution in the test specimen (wood board) was measured. Specifically, X-rays were irradiated in the thickness direction at a pitch of 0.02 mm, and the density distribution in the test body (wood board) along the thickness direction was measured from the transmittance of the X-rays. From the obtained density distribution, the difference between the maximum density value of the board surface layer and the minimum density value of the board inner layer (inner layer density difference) was calculated. The results are shown in Table 3.

[Result 1 and discussion]
As shown in Table 2, the wood boards of Examples 1 and 2 had higher bending strength than Comparative Example 1. There are two reasons for the high strength. One is that the fiber length of Examples 1 and 2 is longer than that of Comparative Example 1 as shown in Table 1 and FIG. This is because of the expression. Second, as shown in Table 3, the difference in the inner layer density of the wood board of Example 2 was larger than that of Comparative Example 1 and Example 1, and the board surface was densified.

<Board length change>
The wood boards according to Examples 1 and 2 and Comparative Example 1 (air-dried state: moisture content: 3 to 5%) were cut to a length of about 250 × width of about 50 mm to obtain a test body, and the test body was 40 ° C. and 90%. R. H. Was taken out after 2 weeks, which is a period in which the weight change almost settled, and the amount of change (%) in the length direction of the wood board before and after the test was measured. Here, the wood boards according to Examples 1 and 2 and Comparative Example 1 after the test in the thermo-hygrostat were dried at 105 ° C., and the moisture content (% ) Was calculated, and the moisture content change amount was calculated from the moisture content before and after the test in the thermo-hygrostat. The results are shown in parentheses in Table 4.

[Result 2 and discussion]
As shown in Table 4, compared with Comparative Example 1, the amount of change in length of the wood boards of Examples 1 and 2 was small. There are two reasons why dimensional stability is high. One is that, as shown in FIG. 1, the wood board raw materials of Examples 1 and 2 are in the form of long fibers. Second, as shown in Table 4, the wood board to which citric acid was added generated a new bond with hot pressing and a decrease in the moisture content change with hydrophobization.

[Comprehensive evaluation]
From the above, the wood fibers of Examples 1 and 2 have a longer fiber length than that of Comparative Example 1, and the layer rich in lignin is exposed on the fiber surface. It is thought that the wood board excellent in dimensional stability could be obtained.

  In particular, the wet fiber of Example 2 is longer than the fiber of Example 1, and the lignin on the surface of the wet fiber is treated at high temperature and high pressure during defibration, so that the lignin is reduced in molecular weight. As a result, it is considered that wet fibers easily flow during hot pressing. As a result, the inner layer density difference is also increased (the density of the surface layer is increased), and the bending strength of the wood board according to Example 2 is considered to be higher than the others.

  In addition, it is considered that the wet fiber was hydrophobized by the fiber formation of the wood raw material and the formation of the ester bond by the addition of citric acid, suppressing the change in the moisture content of the wood board and improving the dimensional stability. In the case of Examples 1 and 2, the wet fibers are intermingled in the wood board and act like a cross band effect of plywood, so that the swelling of the wood material at the time of moisture absorption is easily restrained. As a result, it is considered that the length change amount of the wood board according to Examples 1 and 2 is reduced, and the change in the dimension in the surface direction of the wood board with respect to the moisture content change is suppressed.

[Examples 3 to 7]
A wood board was produced under the production conditions described in Example 1 using the same wet fiber (high-pressure defibrated fiber) as in Example 2. The wooden board of Example 3 is a wooden board in which 15% by mass of citric acid is added to wet fibers, and Examples 4 to 7 are wooden boards in which an addition amount of 15% by mass of polyvalent carboxylic acid is added to wet fibers. In this case, maleic acid, 1,2,3,4-butanetetracarboxylic acid, itaconic acid, and malic acid are used as the polyvalent carboxylic acid.

  For these wooden boards, the bending strength and the inner layer density difference were measured in the same manner as in Example 2. The results are shown in Table 5. In addition, in the measurement of bending strength, the moisture content of the wooden boards of Examples 3 to 7 was 2 to 4% in an air-dried state.

  Further, in the same manner as in Example 2, the board length change amount and moisture content change amount of the wood board before and after moisture absorption according to Examples 3 to 7 were measured. The moisture content of the wood board before moisture absorption was 2 to 5% in the air-dried state. The results are shown in Table 6.

[Result 3 and discussion]
As shown in Tables 5 and 6, as in citric acid, polycarboxylic acid such as maleic acid, 1,2,3,4-butanetetracarboxylic acid, itaconic acid, malic acid was used. However, it was possible to increase the bending strength of the wooden board and ensure the dimensional stability of the wooden board during moisture absorption.

<Measures the relationship between hot-pressure temperature and inner layer density difference>
Under the board manufacturing conditions described in Example 1, the inner layer density difference of the wood board when the hot press temperature according to Examples 3 to 7 was changed was measured. The results are shown in Table 7.

[Result 4 and discussion]
As shown in Table 7, in the case of citric acid, the hot pressure temperature is 200 ° C. or higher, and in the case of maleic acid and 1,2,3,4-butanetetracarboxylic acid, the hot pressure temperature is 160 ° C. or higher. In the case of itaconic acid and malic acid, the hot-pressure temperature is 180 ° C. or higher and the inner layer density difference is 0.15 (g / cm ³ ) or higher. Under this hot-pressing condition, the bending strength of the wooden board can be increased. it can.

Example 8
A wood board was produced under the production conditions described in Example 1 using the same wet fiber (high-pressure defibrated fiber) as in Example 2. The wood board of Example 8 used maleic acid as the polyvalent carboxylic acid, and the performance of the wood board when the acid addition amount of maleic acid was changed as shown in Table 8 was evaluated in the same manner as in Example 2. . The results are shown in Table 8 (Example 8). In the measurement of bending strength, the moisture content of the wood board of Example 8 was 2 to 4% in an air-dried state.

[Result 5 and discussion]
As shown in Table 8, in the case of maleic acid, if it is added at least 2% by mass with respect to the wet fiber, the bending strength of the wooden board can be increased, and the dimensional stability in the surface direction of the wooden board during moisture absorption can be improved. It is thought that it can be secured.

[Examples 9-1 and 9-2]
A wood board was produced under the production conditions described in Example 1 using the same wet fiber (high-pressure defibrated fiber) as in Example 2.

  The wooden board of Example 9-1 is a wooden board in which 10% by mass of maleic acid is added to wet fiber using an aqueous maleic acid solution. The wood board of Example 9-2 is a wood board in which 10% by mass of ammonium maleate is added to wet fibers using an aqueous solution in which ammonium maleate is dissolved. These wooden boards are molded at a hot pressure temperature of 200 ° C., Example 9-1 corresponds to the first invention, and Example 9-2 corresponds to the second invention. The length change amount in the case of Example 2 was the length change amount (%) of the wood board when the wood board was moisture-absorbed for 2 weeks. Is the amount of change (%) in the length of the wooden board when the wooden board is absorbed for one week.

[Examples 10-1 and 10-2]
A wood board was produced under the production conditions described in Example 1 using the same wet fiber (high-pressure defibrated fiber) as in Example 2.

  The wooden board of Example 10-1 is a wooden board obtained by adding 10% by mass of citric acid to the wet fiber using an aqueous citric acid solution, and the wooden board of Example 10-2 is made of ammonium citrate salt. This is a wood board in which 10% by mass of ammonium citrate is added to wet fibers using a dissolved aqueous solution. These wooden boards are molded at a hot pressure temperature of 200 ° C., Example 10-1 corresponds to the first invention, and Example 10-2 corresponds to the second invention.

  The performance of each wooden board was evaluated in the same manner as in Example 2. Moreover, pH of aqueous solution and a wooden board was measured. The results are shown in Table 9.

[Comparative Examples 2 and 3]
A wood board was produced under the production conditions described in Example 1 using the same wet fiber (high-pressure defibrated fiber) as in Example 2.

  The wood board of Comparative Example 2 is a wood board in which 10% by mass of sodium maleate is added to wet fiber using a sodium maleate aqueous solution. The wood board of the comparative example 3 is a wood board which added sodium citrate 10 mass% with respect to the wet fiber using the sodium citrate aqueous solution. These wooden boards are molded at a hot pressure temperature of 200 ° C. The performance of each wooden board was evaluated in the same manner as in Example 2. Moreover, pH of aqueous solution and a wooden board was measured. The results are shown in Table 9. In addition, in Table 9, the result of the wooden board which did not add polyvalent carboxylic acid was also shown as a reference example.

[Result 6 and discussion]
As shown in Table 9, the wood boards of Examples 9-1, 9-2, 10-1, 10-2 (wood boards using maleic acid, ammonium maleate, citric acid, ammonium citrate) The bending strength was higher than those of Comparative Examples 2 and 3, and the Reference Example, and the length variation and the moisture content variation were small. Further, the bending strength of the wood board of Example 9-2 (wood board using ammonium maleate) was the highest.

  When using maleic acid ammonium salt or ammonium citrate salt as in Examples 9-2 and 10-2, these salts adhering to the wet fiber are decomposed ammonia due to the heat pressure at the time of wood board molding. Since it volatilizes, as shown in Table 9, the board pH value decreases with respect to the aqueous solution pH value, and the inside of the wooden board in the forming stage can be made acidic.

  Therefore, like the effect of 1st invention, reaction (esterification) of wood and carboxylic acid advances, and the wood board excellent in intensity | strength and dimensional stability is obtained compared with the wood board of a reference example. In addition, an aqueous solution in which an ammonium maleate salt or an ammonium citrate salt is dissolved is substantially neutral, so that it has excellent handling properties during production. In addition, it is considered that the reason why the wood board using the maleate ammonium salt has higher bending strength than the ammonium citrate salt is due to C = C contained in the maleate.

  On the other hand, as shown in Comparative Examples 2 and 3, when a polyvalent carboxylic acid sodium salt such as sodium maleate or sodium citrate is used, sodium remains regardless of the thermal pressure at the time of molding the wooden board. As shown in FIG. 4, the board pH value is difficult to decrease. As a result, the reaction (esterification) between the wood and the carboxylic acid does not proceed easily, and the obtained wooden board is considered to have strength and dimensional stability comparable to or lower than those of the reference example.

[Examples 11-1 to 11-4]
A wood board was produced under the production conditions described in Example 1 using the same wet fiber (high-pressure defibrated fiber) as in Example 2.

  The wood boards of Examples 11-1 to 11-4 are those using a maleic acid aqueous solution, an aqueous solution in which maleic anhydride is dissolved, maleic acid powder, and maleic anhydride powder. Examples 11-1, 11- 2 corresponds to the first invention, and Examples 11-3 and 11-4 correspond to the third invention.

  In each case, the addition amount of carboxylic acid is 10% by mass with respect to the wet fiber in both the aqueous solution and the powder (powder). In addition, the hot press temperature at the time of shaping | molding of a wooden board is 200 degreeC, and hot press time is 5 minutes. The performance of each wooden board was evaluated in the same manner as in Example 2. The results are shown in Table 10.

[Examples 12-1 to 12-4]
A wood board was produced under the production conditions described in Example 1 using the same wet fiber (high-pressure defibrated fiber) as in Example 2.

  The wood boards of Examples 12-1 to 12-4 are obtained by using an aqueous citric acid solution, an aqueous solution in which citric acid anhydride is dissolved, citric acid powder, and anhydrous citric acid powder. Examples 12-1, 12- 2 corresponds to the first invention, and Examples 12-3 and 12-4 correspond to the third invention.

  In each case, the addition amount of carboxylic acid is 10% by mass with respect to the wet fiber in both the aqueous solution and the powder (powder). In addition, the hot press temperature at the time of shaping | molding a wooden board and the hot press time are the same as Example 11-1. The performance of each wooden board was evaluated in the same manner as in Example 2. The results are shown in Table 10.

[Result 7 and discussion]
As shown in Table 10, the bending strength, length variation, and moisture content variation of the wood boards of Examples 11-1 to 11-4 are substantially the same, and the wood quality of Examples 12-1 to 12-4. The bending strength, length variation, and moisture content variation of the board were almost the same. As a result, substantially the same effect is exhibited even when a polyvalent carboxylic acid anhydride, a polyvalent carboxylic acid powder, or a polyvalent carboxylic acid anhydride powder is used instead of the aqueous solution in which the polyvalent carboxylic acid is dissolved. It is thought.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various designs can be made without departing from the spirit of the present invention described in the claims. It can be changed.

  In the present embodiment, a method for producing a dry wood board such as a medium fiber board (MDF) has been described as an example. For example, a dry wood board such as a hard board or a high density fiber board (HDF) is produced. For example, the wooden board may be manufactured by a method of manufacturing a wet wooden board such as an insulation board.

Claims (10)

A step of heating the wood pieces under an atmosphere containing moisture and then defibrating the heated wood pieces into wet fibers;
By applying an aqueous solution in which a polyvalent carboxylic acid is dissolved or an aqueous solution in which a polyvalent carboxylic anhydride is dissolved to the defibrated wet fiber, the polyvalent carboxylic acid is applied to the surface of the defibrated wet fiber. A step of attaching
A method for producing a wooden board, comprising: at least a step of forming a wooden board by pressing and heating the wet fiber to which the polyvalent carboxylic acid is attached.   In the defibrating step, the wood pieces are steamed for 1 to 10 minutes under a steam pressure of 0.5 to 1.0 MPa, and the wood pieces subjected to the steam treatment under the steam pressure are disassembled into wet fibers under the steam pressure. 2. The method for producing a woody board according to claim 1, wherein the wood board is fine.   The method for producing a wooden board according to claim 1 or 2, wherein in the step of attaching the polyvalent carboxylic acid, the wet fiber after the application of the aqueous solution is dried.   The polyvalent carboxylic acid is a polyvalent carboxylic acid selected from at least one of the group consisting of citric acid, 1,2,3,4-butanetetracarboxylic acid, maleic acid, malic acid, and itaconic acid. The method for producing a wooden board according to any one of claims 1 to 3, wherein an anhydride of the selected polyvalent carboxylic acid is used as the polyvalent carboxylic acid anhydride.   Citric acid or maleic acid is used as the polyvalent carboxylic acid, citric acid anhydride or maleic anhydride is used as the polyvalent carboxylic acid anhydride, and the citric acid and maleic acid are added to the wet fiber. The method for producing a woody board according to claim 1, further comprising 2 to 15% by mass of citric acid anhydride or maleic acid anhydride. A step of heating the wood pieces under an atmosphere containing moisture and then defibrating the heated wood pieces into wet fibers;
Applying an aqueous solution in which a polyvalent ammonium carboxylate is dissolved to the defibrated wet fiber to attach the polyvalent ammonium carboxylate to the surface of the defibrated wet fiber;
A method for producing a wooden board, comprising: at least a step of forming a wooden board by pressing and heating the wet fiber to which the polyvalent carboxylic acid is attached.   The method for producing a woody board according to claim 6, wherein an ammonium maleate is used as the polyvalent carboxylate ammonium salt. A step of heating the wood pieces under an atmosphere containing moisture and then defibrating the heated wood pieces into wet fibers;
Attaching a polyvalent carboxylic acid powder or a polyvalent carboxylic acid anhydride powder to the surface of the defibrated wet fiber;
A method for producing a wooden board, comprising: forming a wooden board by pressing and heating the wet fiber to which the powder is adhered.   In the defibrating step, the wood pieces are steamed for 1 to 10 minutes under a steam pressure of 0.5 to 1.0 MPa, and the wood pieces subjected to the steam treatment under the steam pressure are disassembled into wet fibers under the steam pressure. The method for producing a wooden board according to any one of claims 6 to 8, wherein the wood board is fine.   The method for producing a wooden board according to any one of claims 1 to 9, wherein in the defibrating step, the fiber length of the wet fiber is defibrated to at least 1 mm or more.

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