JP2006062326A - Manufacturing method of woody composite material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a woody composite material excellent in practical strength using a tannic adhesive without producing a harmful volatile substance. <P>SOLUTION: A woody molding material and a binder comprising the tannic adhesive composed of tannin and hexamethylenetetramine and adjusted to pH 7-13 are mixed to prepare an intimate mixture and this intimate mixture is laminated to form a woody laminated mat. High temperature steam is penetrated into the woody laminated mat and this woody laminated mat is heated and pressurized to cure the binder. By this method, the woody composite material wherein the woody molding material is bonded by the cured binder is obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a wood composite material in which wood-based molding materials are bound together by a binding material.

  The wood chip is formed from a long and slender wood chip that is crushed wood, and a binder is attached to the wood chip, and the wood chips are aligned and aligned in the longitudinal direction to form a laminated wood mat. A method of obtaining a wood composite material by heating and pressing a mat is known. The obtained wood composite material has high bending strength by orienting the wood chips (see, for example, Patent Document 1).

  Examples of wood composite materials made by joining the above wood chips with a binder are, for example, single plate laminate (LVL), particle board, medium density fiber board (MDF) (write Japanese name), hard board, etc. Is mentioned. However, the above-mentioned wood composite material is a renewable resource material in which the wood chip used is made of plant resources, but the binder is generally a petroleum-based material such as phenol resin, melamine resin, urea resin, isocyanate resin, etc. These petroleum materials are not renewable natural resources and cannot be said to be recyclable materials.

  A wood mat formed by laminating an elongated mixture of wood-based molding material and binder in one direction is placed on a conveyor such as a belt conveyor and conveyed to a press. However, there has been a problem that the orientation of the wood chips laminated on the wood laminate mat is disturbed by vibration during conveyance, or the laminate is broken, resulting in deterioration of physical properties of the molded product.

  As a method for solving such a problem, for example, an elongated wood chip obtained by crushing and classifying used waste wood by a crusher for recycling, and an adhesive mainly composed of tannin which is a natural component Natural type that uses renewable resources as a raw material by mixing with a binder containing tannin-based adhesive (hereinafter referred to as tannin-based adhesive), heating and curing the binder, and bonding wood chips with the cured binder A method for obtaining a woody composite material made of resources is known (for example, see Patent Document 2).

  The obtained wood composite material can have a strength enough to be used as a structural material. In addition, when the bonding material is made of a tannin adhesive and has a tackiness, when the mat of the wood-based molding material is conveyed to a press machine, noticeable disorder of orientation and collapse of the stacking of the end portion do not occur.

  On the other hand, in recent years, frequent occurrence of sick house syndrome caused by harmful volatile substances contained in housing members has become a social problem. Tannin-based adhesives are natural resources and are safer to humans than conventional petroleum-based materials such as phenolic resins, melamine resins, urea resins, and isocyanate resins. Depending on the type of curing agent, harmful can generate volatile substances.

  Depending on the application to be used, a low-cost wood composite material may be desired. Conventionally, improving the productivity as one method for reducing the cost has been studied, but there is a limit to improving the productivity with a thick plate in the conventional hot press machine that is heat-cured by heat conduction. It was. That is, in the case of a plate having a thickness of about 20 mm or more, it takes a very long time to heat the adhesive to a temperature at which the adhesive is sufficiently cured at the center of the plate, resulting in poor productivity and poor profitability. There was a problem.

  In general, tannin exhibits a liquidity of about pH 4 to 7 in an aqueous solution state, and is cured only by heating the aqueous solution as it is. Usually, there is a method for curing tannin, in addition to a method for curing by heating as it is, a method for mixing formaldehyde under an acidic condition and curing by heating. When using this curing reaction of tannin to produce a wood composite material, a mixed liquid of tannin and formaldehyde is adhered to the surface of a wood-based molding material that is a raw material, such as a wood chip crushed from wood. The wood composite material can be obtained by heating and pressing the wood chip to which the mixed solution is attached in a molding die to cure the tannin.

However, since the hemicellulose in the wood chips is not easily softened, the wood chips are not sufficiently consolidated by the above method, and the bending strength of the obtained wood composite material is insufficient or varies. There is a problem that practical strength may be low. In addition, if unreacted formaldehyde remains, it causes sick house syndrome and is harmful to the human body.
First page of JP-A-63-107507 Japanese Patent No. 3515099

  In view of the problems of the conventional method for producing a wood composite material using a tannin-based adhesive, the present invention uses a tannin-based adhesive and does not generate harmful volatile substances and has excellent practical strength. Another object of the present invention is to provide a method for producing a wood composite material.

  A method for producing a wood composite material according to claim 1 of the present invention (invention 1) for solving the above problems comprises a wood molding material and a binder comprising a tannin adhesive composed of tannin and hexamethylenetetramine. A wood-based laminated material is formed by mixing the admixture to form a wood-layered mat, and injecting high-temperature steam into the wood-layered mat and heating and pressing to cure the binder. It is characterized in that a wood composite material bonded with a hardened binder is obtained.

  The invention according to claim 2 (invention 2) is the method for producing a woody composite material according to invention 1, wherein the tannin-based adhesive has a pH of 7 to 13.

  In the invention 1, a tannin-based adhesive composed of tannin and hexamethylenetetramine is used as a binder for a wood-based molding material, and the binder is heated and cured with high-temperature steam to generate a harmful volatile substance. To obtain a wood composite material without any material.

  In addition, in the invention 2, by making the tannin-based adhesive alkaline, the hemicellulose in the wood chip is hydrolyzed and softened, the wood laminate mat is moderately compacted, there is no variation in strength, and it is safe for the human body, In addition, a wood composite material having sufficient practical strength is obtained.

  The tannin-based adhesive is an extracted component from natural wood, has good affinity with a wood-based molding material, has an appropriate tackiness, and further has a high strength when cured, and thus is preferable. The tree from which tannin is extracted is not particularly limited, but condensed tannin collected from radiata pine, mimosa (other names: wattle, acacia) and quebracho is preferable.

  The age of the tree from which the tannin is extracted is not particularly limited. For example, in the case of mimosa, a tree having an age of 8 to 10 years is preferable from the viewpoint of performance and productivity as an adhesive. There are no particular restrictions on the production area, but for example mimosa is preferably from South America or Africa, and quebracho is preferably from South America. Even if impurities such as sugar are mixed in tannin, there is no particular problem. However, when it is desired to make a high-strength wood composite material, it is better to have less impurities. The purity of tannin can be evaluated by, for example, Stiasny Value (SV). A preferred SV is 50 or more. More preferably, it is 70 or more.

For example, SV can be obtained as follows. About 100 mg of a pre-dried sample (bark extract or standard catechin) was weighed into a 25-ml round bottom flask, and 10 ml of distilled water, 2 ml of 37% formaldehyde aqueous solution, and 1 ml of hydrochloric acid (10 N) were added in this order. The flask is heated and boiled for 30 minutes. Immediately after the heating, the sample is filtered at once with a glass filter whose weight has been measured in advance, and washed with hot water and methanol sequentially. The glass filter is dried in an oven at 105 ° C. overnight, the weight is measured, and the residue weight is calculated. SV was calculated using the following equation. Standard catechin SV is also measured for value correction.
SV = (residue weight / sample weight) × (104.1 / SV of standard catechin) × 100

  Tannin may be used as it is extracted from wood, but it may be used after being modified by modification if it needs to be modified due to performance as an adhesive, viscosity, or the like. Tannin may be mixed with the wood-based molding material in the form of powder, but it is preferable to use it by dissolving or dispersing it in water or an organic solvent in view of ease of handling and the performance of the wood composite material. In this case, the tannin concentration is preferably 20% by weight to 70% by weight. The viscosity is preferably 10,000 cps or less, and is preferably 2,000 cps or less because it is easy to handle when mixing with the wood-based molding material by spray application of an adhesive.

  The aqueous solution of tannin is usually about pH 4-7. The tannin aqueous solution can adjust the reactivity and physical properties of the tannin adhesive by adjusting the pH. In the present invention, the pH is preferably alkaline. The pH is preferably 7 or more and 13 or less, more preferably 7 or more and 12 or less. By making the pH alkaline, the reaction rate of the tannin-based adhesive becomes moderately slow and suitable for the present invention, the adhesive is easy to handle, and the productivity and performance of the wood composite material are improved. In other words, since the reaction rate is moderate, the adhesive is not cured by the time it is put into the press machine after blending the adhesive, but is cured only when heated and pressed by the press machine.

  If the pH is acidic, the reaction may be too fast and harden before the press is charged. In addition, by making the pH alkaline, high-temperature steam acts during pressing to hydrolyze the hemicellulose in the wooden molding material, which softens the wooden molding material. However, hydrolysis is further accelerated by alkali. Is done. Due to this softening action, it is possible to consolidate the wood chips even at low pressing pressures, the density in the thickness direction of the product can be made uniform, the water resistance is improved, and the pressure during pressing is lowered. Is preferable. As a result, product performance such as strength and water resistance is improved.

  However, if the pH is higher than 13, the alkali is too strong and care must be taken, and the alkali is too strong and the wood component (for example, hemicellulose) is partially decomposed and modified through the softening. Since it may be colored black, it is not preferable. The pH of the tannin aqueous solution is preferably adjusted in advance before mixing with the curing agent. Although the kind of alkali which adjusts pH is not specifically limited, Sodium hydroxide, potassium hydroxide, etc. are mentioned.

  The hexamethylenetetramine acts as a curing agent for crosslinking and curing tannin. By using hexamethylenetetramine, the wood composite material can be made high in strength, excellent in productivity, no harmful volatile substances are generated, and the material cost is low. Hexamethylenetetramine may be in the form of powder or pellets. The amount of hexamethylenetetramine added is preferably 1% by weight to 20% by weight with respect to the tannin solid content. More preferably, it is 3 to 10% by weight. If it is less than 1% by weight, curing of tannin is difficult to proceed, and there is a possibility that a practically sufficient adhesive strength may not be exhibited. There is a possibility that it will end up, and the economy will become worse.

  Tannin and hexamethylenetetramine may be mixed in advance to form a binder containing a tannin-based adhesive, or may be separately mixed with a wood chip without mixing. Further, when tannin is used as an aqueous solution, hexamethylenetetramine can be used as a binder as it is in a solid form or as an aqueous solution and blended in advance with tannin.

  The present invention is most effective when the wood-based molding material is a wood chip. The shape of the elongated wooden chip is not particularly limited. Examples of the shape include block shape, flat plate shape, strand shape, flake shape, chip, wood flour, and fiber.

  The raw material species of wood chips include conifers such as cedar, cypress, pine, spruce, and fur; broad-leaved trees such as birch, apiton, sengonlaut, and aspen. Can also be included.

  Available forms include logs of the above tree species, raw materials such as thinned wood, scraps generated at factories and residential construction sites, waste pallet materials discarded after transporting parts, demolition waste generated at the time of building demolition, etc. . In particular, recycled materials such as demolition waste, waste pallet material, thinned wood, scraps generated during lumbering, and wood materials used as fuel and papermaking raw materials are preferred.

  Methods for processing the above raw materials into wood chips include a hammer mill, a uniaxial crusher that crushes wood by rotating a roll with a blade on the surface, a biaxial or multiaxial crusher with a structure in which rotating blades are engaged, etc. Although a crusher is used, a rotary cutter that cuts veneered material into a chopsticks shape to make a stick, a flaker that cuts a log with a rotary blade into a strand, and the like can also be used. In particular, when a recycled material is used as a raw material, foreign materials are likely to be mixed in, so that a crusher is preferable in consideration of the durability of the rotary blade.

  Since the wood chips obtained by the above method vary in size, the wood chips of a predetermined size are formed by a classification process. As a classification method at this time, there are a roller screen method, a vibrating mesh method, a wind selection method, and the like. The size of the wood chip is not particularly limited, but when strength and elastic modulus are required, the length is preferably 20 mm or more and 150 mm or less. If it is smaller than 20 mm, the strength and elastic modulus of the product will be low, and if it is larger than 150 mm, the variation in strength will be large.

  Further, when the length of the wood chip is 20 mm or more and 150 mm or less, the gap between the wood chips of the laminated wood mat is large, so that the wood chip is smaller than a particle board using a small wood chip having a length of less than 20 mm. The steam inside the mat is good and the wood mat can be heated in a very short time, and the features of the steam press can be effectively expressed.

  The wood chip is preferably adjusted to have a moisture content within a certain range. By making the water content constant, there is no variation in the quality of the molded product during production. A preferable water content is 0 to 14% by weight. When the tannin-based adhesive is used as an aqueous solution, the moisture content of the wood chip is preferably 0 to 10% by weight. If the water content exceeds 10% by weight, the water content of the woody composite material immediately after production becomes high, and it is necessary to cure for a long time before shipping.

  The wood chip adjusted in water content is mixed with the binder. The amount of the binder to be mixed depends on the density, shape and surface state of the wood-based molding material, but it is usually preferably 1% by weight to 20% by weight in terms of solid content of tannin with respect to the weight of the wood chip.

  Examples of the means for mixing the wood chips and the binder include a method in which the wood chips and the binder are put into a high speed mixer such as a Henschel mixer (high speed mixer manufactured by Henschel) and mixed to form a mixture. . When the binder is liquid, for example, an application means such as spray is used on the wood chip on a conveyor or in a drum blender to obtain an admixture in which the binder is attached to the surface of the wood chip. If this mixture is laminated and heated and pressed, a uniform and stable woody composite material can be obtained. When the wood chip is a plate material or a block-like member, it can be mixed by brush coating or roller coating.

  The mixture of the wood-based molding material and the binder laminates wood chips to form a wood laminate mat. Specifically, it can be carried out by putting a wood chip, that is, an admixture, to which a binder is attached, into a molding die and laminating it to form a wood laminate mat. When it is necessary to orient the wood chips in one direction, an orientation laminating apparatus such as a forming type divided at regular intervals or a disk orienter used in the manufacture of an oriented strand board (OSB) or the like is used.

  The above-mentioned wood laminate mat is placed between a press device for heating and pressurizing while allowing high temperature steam to penetrate into the wood mat, for example, a press plate of a general steam press device, and pressurizing and thermoforming. Heating and pressurization may be performed simultaneously, may be performed after pressurization, or may be performed after heating. The high temperature steam may be sprayed at any timing as long as the wood laminate mat is disposed between the pressurization panels of the steam press. The heating temperature is preferably 100 ° C. to 250 ° C. Therefore, the temperature of the high temperature steam is preferably 100 ° C. to 250 ° C. Moreover, the pressurizing pressure of the pressure plate is preferably 1 to 10 MPa. Further, the heating / pressurizing treatment time may be performed only for the time during which the binder is cured.

  In the invention 1, a wood-based molding material and a binder composed of a tannin-based adhesive composed of tannin and hexamethylenetetramine are mixed to form an admixture, and the admixture is laminated to form a wooden laminate mat. Recyclable because the wood-based molding material is bonded to the hardened binder by infiltrating the inside of the laminated mat with high-temperature steam and heating and pressing to cure the binder. Therefore, it is possible to obtain a wood composite material of a natural resource type using a natural resource as a raw material, and the wood composite material obtained does not use a harmful catalyst, so that no harmful volatile substances are generated.

  In the invention 2, by making the tannin aqueous solution alkaline, the above hemicellulose can be hydrolyzed and softened, so that the obtained wood composite material is moderately compacted and does not vary in strength and has sufficient practical use. This is a wood composite material having strength and water resistance.

  Examples of the present invention and examples carried out for comparison (hereinafter referred to as comparative examples) will be described below.

Example 1
The wood composite material was molded by the following manufacturing process. As a wood-based molding material, a wooden chip for boards (purchased from a wood waste disposal contractor), which is crushed wood waste with a uniaxial crusher, is a roller screen type wave roller screen device (manufactured by Taihei Co., Ltd.). ) Was used to classify wood chips having a thickness or width of 1 to 8 mm. The wood chip was adjusted to have a moisture content of 6% by weight.

  As tannin, SV82 mimosa tannin was used, and a tannin-based adhesive was prepared as follows. First, tannin powder was dissolved in hot water at about 40 ° C. to a concentration of 40% by weight. Thereafter, the pH was adjusted to 10 with an aqueous sodium hydroxide solution having a concentration of 50% by weight. A 40 wt% aqueous solution of hexamethylenetetramine was used as a curing agent, and a binder was prepared so that the hexamethylenetetramine solid content was 10 wt% with respect to the tannin solid content.

  The wood chip and the binder, that is, the tannin-based adhesive, are weighed so that the binder is 12 parts by weight with respect to 100 parts by weight of the wood-based molding material, put into a drum blender, and the binder is sprayed and mixed. An admixture with a binder attached to the chip surface was obtained. Next, this mixture was put into an OSL forming machine (manufactured by Taihei Co., Ltd.) and put into a forming die (length 2000 mm, width 500 mm, height 100 mm). In the forming mold, a metal partition plate (thickness 2 mm) was used which was divided into 10 equal parts at intervals of 50 mm, and the wood chips were aligned and laminated substantially in the length direction to obtain a wood laminate mat. The thickness of the wood laminate mat was about 100 mm.

  Next, the forming mold and the partition plate were removed from the mold, and the wood laminate mat was placed between the press plates of a steam press machine (Kawasaki Yuko Co., Ltd., 300-ton press machine). After placing the wood laminate mat, spray high-temperature steam at 0.9MPa and 180 ° C for 1 minute, then close the pressure plate so that the thickness of the wood laminate mat is 20mm, and hold it at 180 ° C for 5 minutes to keep the wood composite Obtained material.

  A sample was cut out from the wood composite material, and a bending test was performed according to JIS K 5908, and a water absorption thickness expansion coefficient (JIS K 5908) and a formaldehyde emission amount (JIS K 5908) were measured. (Write each measurement method. If there is JIS, that number is OK.)

(Example 2)
A wood composite material was obtained in the same manner as in Example 1 except that the pH was adjusted to 7, and the bending strength, water absorption thickness expansion rate, and formaldehyde emission were measured in the same manner.

(Comparative Example 1)
A wood composite material was obtained in the same manner as in Example 1 except that a tannin-based adhesive having a pH of 4 was used without adjusting the pH, and a bending test, a water absorption thickness expansion coefficient, and a formaldehyde emission amount were measured in the same manner.

(Comparative Example 2)
A woody composite material was obtained in the same manner as in Example 1 except that a formalin 37% by weight aqueous solution was used in place of hexamethylenetetramine and the binder was formulated so that the formalin was 10% by weight with respect to the tannin solid content. In the same manner, a bending test, a water absorption thickness expansion coefficient, and a formaldehyde emission amount were measured.

(Comparative Example 3)
A high-pressure steam is not sprayed onto the wood laminate mat, and a press machine that heats and pressurizes the pressurization panel is used, except that heating and pressurization are maintained at 180 ° C for 5 minutes. Obtained a wood composite material in the same manner as in Example 1, and the bending test, the water absorption thickness expansion coefficient, and the formaldehyde emission amount were measured in the same manner.

  Table 1 shows the measurement results of bending strength, water absorption thickness expansion rate, and formaldehyde emission.

Claims (2)

  A wood-based molding material and a binder composed of a tannin-based adhesive composed of tannin and hexamethylenetetramine are mixed to form an admixture, and this admixture is laminated to form a wooden laminate mat. A method for producing a wood composite material, characterized in that a wood composite material in which a wood-based molding material is bonded with a hardened binder is obtained by impregnating water vapor and heating and pressing to cure the binder. The method for producing a wood composite material according to claim 1, wherein the tannin-based adhesive has a pH of 7 to 13.