JPS637123B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention involves drying wood fibers to a moisture content of 7% or less,
While the material is still warm (30°C or higher), a mixture of polyisocyanate and dimethylformamide is sprayed onto the wood fibers, and this is permeated into the wood fibers.Water is further sprayed, and then these sprays are sprayed. A method for producing a structural board from wood fibers, which is characterized by thermoforming wood fibers at a temperature higher than the boiling point of dimethylformamide, the purpose of which is to evaluate the physical properties of the wood fiberboard, among other things:
The object of the present invention is to provide a wood fiberboard with significantly improved bending strength and water resistance. 2. Description of the Related Art Conventionally, wood fiberboards such as fiber boards and particle boards are products made by forming wood fibers such as fibers and particles into boards using heat pressure and chemical bonding agents. Binding agents for such wood fiberboards include urea-formalin,
Urea melamine - formalin type, resorcinol -
There are formalin-based, phenol-formalin-based, and formalin-free polyisocyanates, which have been commonly used. Among these, as a binder for structural boards, polyisocyanate has superior physical properties of the board compared to other binders. However, compared to structural board materials such as plywood, it is inferior in bending strength and water resistance, so it is currently used for limited purposes. Furthermore, since polyisocyanate is currently more expensive than other binders, there is a limit to the rate at which it can be added to wood fiberboard economically. There is a strong need for a manufacturing method that improves strength and water resistance while minimizing increases in manufacturing costs. Traditionally, wood fiberboards are manufactured by spraying polyisocyanate binders onto wood fibers such as fibers and particles and then forming them under heat and pressure.Since the polyisocyanate is a solvent type, there is no moisture introduced into the mat. In consideration of the stiffness of the board, wood fibers with a relatively high moisture content (13 to 25%) are usually used as raw materials. When polyisocyanate is sprayed onto such moisture-rich wood fibers, the isocyanate groups of the polyisocyanate react with the water in the wood fibers to produce polyurea, but the produced polyurea is It only works as a filler. Furthermore, the produced polyurea is a crystalline solid having a low molecular weight, and is powder-like and brittle rather than resin-like. It is also known to spray a mixture of polyisocyanate and a solvent onto wood fibers to produce a resinous polyurea through the reaction of the isocyanate groups with the water in the wood fibers in the solvent.
Even with this type of wood fiberboard, it cannot be expected to have a high bonding strength between wood fibers, and the water absorption of wood fibers has not been essentially improved, so the manufactured wood fiberboard has a high bending strength and It had physical properties with poor water resistance. In addition, in order to improve the above-mentioned physical properties of wood fiberboard, it is possible to improve the physical properties by increasing the addition rate of polyisocyanate or increasing the specific gravity of the board.
The price of the manufactured wood fiberboard increases significantly, and the board becomes heavy, which is undesirable from both an economical and processability standpoint. In order to achieve the object of the present invention, the inventors of the present invention have conducted various studies on the reaction process of polyisocyanate in wood fibers and the physical properties of the reaction products and wood fiber boards, and have found that wood fibers such as fibers and particles The material is dried to a moisture content of 7% or less, and the material temperature is
By spraying a mixture of polyisocyanate and dimethylformamide onto the wood fibers while still warm at 30°C or higher and allowing the mixture to penetrate into the wood fibers, the isocyanate groups of the polyisocyanate transform into cellulose, a component of the wood fibers. discovered that urethane bonds are formed by reacting with hydroxyl groups in lignin molecules, creating strong bonds between wood fibers. They also found that the water absorption of wood fibers was significantly improved because the isocyanate groups blocked hydrophilic hydroxyl groups in cellulose and lignin molecules. Next, the above-mentioned wood fibers are further sprayed with water, and then the sprayed wood fibers are heat-pressed at a temperature higher than the boiling point of dimethylformamide (153°C), and the dimethylformamide is expelled from the wood fiber board during the heat-pressing process. It is something that can be evaporated. The wood fiberboard obtained by the present invention has significantly improved bending strength and water resistance, and can be used as a structural board material for applications where plywood is used. It has high commercial value as it can reduce the Next, preferred specific examples of the present invention will be described. The wood fiber board of the present invention is a board manufactured from wood fibers such as fibers and particles. However, the following description will specifically relate to the manufacture of dry fiberboard. Wood chips are inserted into a digester and steamed under conditions of a steam pressure of 8 kg/cm ² and a steaming time of 4 minutes, and then defibrated with a refiner to obtain wet fibers. This fiber is dried in a tube dryer in hot air with an inlet temperature of 260° C. and an outlet temperature of 90° C. to a moisture content of 7% or less, preferably 5% or less. Immediately after drying the parched fiber, or at least while it is still warm at a temperature of 30°C or higher,
A mixture of polyisocyanate and dimethylformamide as a catalyst or a solvent inert to the isocyanate groups is sprayed to infiltrate the fiber. The standing time is 15-30 minutes. The isocyanate groups of the infiltrated polyisocyanate react with the hydroxyl groups in the cellulose and lignin molecules, which are the components of the fiber, to form urethane bonds using a dimethylformamide catalyst. Polyisocyanates used as binders include polyfunctional isocyanates having at least two isocyanate groups in one molecule, such as phenylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate,
Examples include hexamethylene diisocyanate, triphenylmethane 4,4',4'' triisocyanate, etc. The reaction between this polyisocyanate and an active hydrogen compound is greatly promoted by the catalyst of dimethylformamide. It has the effect of promoting the reaction between the isocyanate groups of isocyanate and the hydroxyl groups in the cellulose and lignin molecules, which are the components of the fiber.The point to be careful of is the amount of water in dimethylformamide, and usually the amount of water in dimethylformamide is 0.2
~0.3%, but if it exceeds 0.8%, carbon dioxide gas is emitted during mixing with polyisocyanate, and the isocyanate groups may partially react with water, resulting in some isocyanate groups being consumed. It is necessary to manage this properly. Here, in addition to the above-mentioned catalytic effect, dimethylformamide has the effect of swelling the fiber, and has the effect of promoting the penetration of polyisocyanate into the fiber. On the other hand, in the present invention, if the viscosity of the mixture of the polyisocyanate and dimethylformamide as a catalyst is appropriate, the intended purpose can be achieved without using a solvent, but if the viscosity is too high, the isocyanate It is desirable to dilute with a solvent that is inert to the group. Examples of solvents that are inert to isocyanate groups include acetone, ethyl acetate, methyl acetate, methyl ethyl ketone, toluene, carbon tetrachloride, and dioxane. By adding this solvent to the binder, it becomes a diluent for the polyisocyanate and dimethylformamide, and has the effect of uniformly permeating and diffusing into the polyisocyanate and fiber, as well as adjusting the catalytic action of dimethylformamide. In the production of dry fiberboard, solvents with high boiling points are good as solvents that are inert to isocyanate groups; acetone (boiling point
56.6℃) than methyl ethyl ketone (boiling point 79.6
℃), dioxane (boiling point 101.0℃) is preferred. The use of dioxane will be described below. Unless otherwise indicated, percentages are expressed as weight percent based on bone-dry fiber. The addition rate of polyisocyanate as a binder is 2
~8%, and 3% is preferable in order to obtain a cost advantage over plywood, which is a structural board material. The addition rate of dimethylformamide is preferably in the range of 0.5 to 4%; if it is less than 0.5%, the effect will be weak, and if it is more than 4%, dimethylformamide itself is extremely hygroscopic, so a large amount remains in the wood fiberboard, resulting in water resistance. You get a bad board. The addition rate of dimethylformamide is preferably 2%. The addition rate of dioxa varies depending on the board manufacturing process and the shape of the wood fibers, but is preferably about 3%, which is equivalent to the addition rate of polyisocyanate. Polyisocyanate, dimethylformamide, and dioxane were uniformly mixed in amounts of 3%, 2%, and 3%, respectively, based on the weight of the bone-dry fiber, and this mixture was heated to the water content of 5%.
Spray with a spray gun on the following fibers that are still warm and have a temperature of 30℃ or higher. When the fiber is dry, the polyisocyanate penetrates deeply into the fiber due to the swelling action of dimethylformamide, which has a greater swelling power on wood than water. Polyisocyanate is also adsorbed between the segments of cellulose and lignin molecules, which are the components of the fiber. Thereafter, a reaction occurs between the isocyanate groups of the polyisocyanate and the hydroxyl groups in the cellulose and lignin molecules, and the reaction is promoted by the dimethylformamide catalyst to generate urethane bonds. When there is a large amount of water in the fiber, there is little reaction between isocyanate groups and hydroxyl groups in cellulose and lignin molecules, and the isocyanate groups mainly react with water to produce polyurea. In order to generate urethane bonds, it is necessary to sufficiently evaporate the moisture in the fiber using a dryer, and the moisture content must be kept at 7% or less, preferably at 5% or less. In addition, since the reaction between isocyanate groups and hydroxyl groups in cellulose and lignin molecules tends to occur in an atmosphere at a temperature of about 40° to 50°C, it is necessary to use a material with high fiber quality that has been dried with a dryer. That is, it is necessary to spray the polyisocyanate at least while the fiber is still warm (at least 30°C). If polyisocyanate is sprayed after the material temperature has cooled to below 30℃, isocyanate groups and cellulose,
Reaction with hydroxyl groups in lignin molecules is difficult to occur, and boards manufactured using this method have high bending strength,
It had poor water resistance. As mentioned above, urethane bonds are generated by the reaction between polyisocyanate, isocyanate groups, and the hydroxyl groups in the cellulose and lignin molecules, which are the components of the fibers. An adhesive layer with strong bonding strength is formed. Furthermore, since hydrophilic hydroxyl groups in cellulose and lignin molecules are blocked, a dry fiberboard with extremely low water absorption can be obtained. Next, the fiber sprayed with the binder is further sprayed with water using a spray gun. The reason for spraying water here is that the added water plasticizes the fibers and improves the firmness of the board due to the hot pressure of the hot press. That is, it also increases the mechanical strength of the board. The binder and water sprayed fibers are formed into a fiber mat by a forming machine. The formed fiber mat is inserted into a hot press and hot pressed. The pressing temperature is heated at a temperature higher than the boiling point of dimethylformamide (153℃),
It is necessary to volatilize the dimethylformamide during hot pressure. As mentioned above, dimethylformamide has a very high hygroscopicity, so if a large amount remains inside the board, the water resistance of the fiberboard will be significantly reduced. When hot-pressing at a temperature below the boiling point of dimethylformamide (153°C), the hot-pressing time takes a very long time, which increases the manufacturing cost of dry fiberboard. The pressing temperature is preferably 180°C to 210°C. Press pressure is 50
〜70Kg/cm ² , press time is 2 to 10 minutes, and the board specific gravity is 0.4 to 0.8, the board thickness is 2 to
Obtain 25mm dry fiberboard. The bonding force between the fibers was further increased and tightened during the hot pressing process, making it possible to manufacture a strong dry fiberboard with great elasticity. As described above, the wood fiberboard obtained by the present invention generates strong urethane bonds through the reaction between the isocyanate groups of polyisocyanate and the hydroxyl groups in the cellulose and lignin molecules, which are components of wood fibers, and during hot pressure, macromolecules By gradually increasing the cohesive force, the bending strength of the formed board becomes significantly higher. It was also found that because the hydrophilic hydroxyl groups in the cellulose and lignin molecules were blocked by isocyanate groups, water resistance was significantly improved, and the dimensional stability of the wood fiberboard was improved. Furthermore, the wood fiberboard of the present invention can reduce the addition rate of polyisocyanate as a binder, and has high commercial value economically. Therefore, it is possible to obtain a high level of bending strength and excellent water resistance that could not have been expected in the past, and it can be used as a structural board material such as plywood. A more specific explanation will be given below using Examples, but it goes without saying that the present invention is not limited to the methods and numerical values of the Examples below. Example 1 According to the usual dry fiber board manufacturing method, lauan wood chips were inserted into a digester and boiled under conditions of a steam pressure of 8 kg/cm ² and a steaming time of 4 minutes, and then defibrated with a refiner. A wet fiber was obtained. This fiber was dried in a tube dryer in hot air with an input temperature of 260°C and an exit temperature of 90°C to reduce the moisture content to 5% or less. As binders, 3% diphenylmethane diisocyanate, 2% dimethylformamide, and 3% dioxane were used, based on the weight of the bone-dry fiber.
% of the three components were thoroughly stirred. This binder is used at a material temperature of approximately 40°C to 60°C with a moisture content of 5% or less.
The still warm fiber was sprayed with an air spray gun. After standing for 20 to 25 minutes, water was further sprayed with an air spray gun so that the moisture content of the fiber mat was about 18%. Next, a fiber mat is layered using a forming machine using these sprayed fibers, and this fiber mat is layered for 10 minutes.
After pre-pressing at a pressure of Kg/ ^cm2 , the product was then inserted between the hot plates of a hot press at a hot plate temperature of 200℃ and a pressure of
The wood fiberboard of the present invention was obtained by hot-pressing molding under conditions of 50 kg/cm ² and a hot-pressing time of 3 minutes. Example 2 According to the normal particle board production method, lauan wood chips were made into the same size as the chips for particle board, and then the chips were dried in hot air at 180°C using a jet dryer. The moisture content was reduced to 4% or less. As a binder,
7% diphenylmethane diisocyanate and 3% dimethylformamide based on the weight of bone dry chips.
% and dioxane of 3% were thoroughly stirred. This binder was sprayed with an air spray gun onto the chips that had a moisture content of 4% or less and were still warm at a material temperature of approximately 40°C to 60°C. After standing for 20 to 25 minutes, water was further sprayed with an air spray gun so that the moisture content of the chips was about 15%. Next, these sprayed chips are used to layer a chip mat using a forming machine, and this chip mat is pre-pressed at a pressure of 10 kg/cm ² , and then inserted between the hot plates of a hot press, at a hot plate temperature of 190°C.
The wood fiberboard of the present invention was obtained by hot-pressing molding under conditions of a pressure of 25 kg/cm ² and a hot-pressing time of 5 minutes. Example 3 In accordance with the usual method for producing dry fiberboard, red pine wood chips were inserted into a digester, steamed under conditions of a steam pressure of 8 kg/cm ² and a steaming time of 4 minutes, and then defibrated using a refiner. A wet fiber was obtained. This fiber was dried in a tube dryer in hot air with an inlet temperature of 260°C and an outlet temperature of 90°C to obtain a fiber with a water content of 5% or less. The binder used was a sufficiently stirred mixture of 3% diphenylmethane diisocyanate and 3% dimethylformamide based on the weight of the bone-dry fiber. This binder has a water content of 5% above.
The following fibers were sprayed with an air spray gun when they were still warm and had a temperature of approximately 40 to 60 degrees Celsius. 20-25
After standing for a minute, water was further sprayed with an air spray gun so that the moisture content of the fiber mat was about 20%. Next, a fiber mat is layered using a forming machine using these sprayed fibers.
After pre-pressing this fiber mat at a pressure of 10 kg/cm ² , it was then inserted between the hot plates of a hot press at a temperature of 200°C, a pressure of 50 kg/cm ² , and a hot pressing time of 3.
The wood fiberboard of the present invention was obtained by hot-pressing molding under conditions of 1 minute. Comparative Example 1 According to the usual dry fiberboard manufacturing method, lauan wood chips were inserted into a digester and boiled under conditions of a steam pressure of 8 Kg/cm ² and a steaming time of 4 minutes, and then defibrated with a refiner. A wet fiber was obtained. This fiber was dried in a tube dryer in hot air with an input temperature of 260°C and an exit temperature of 90°C to obtain a fiber with a moisture content of about 18%. Next, the binder shown in Example 1 was sprayed onto the still warm fiber having a moisture content of about 18% and a material temperature of about 40° C. to 60° C. using an air spray gun. Next, a fiber mat is layered using a forming machine using the sprayed fibers, and the fiber mat is pre-pressed at a pressure of 10 kg/cm ² .
Then, insert it between the hot plates of the hot press to adjust the hot plate temperature.
A wood fiberboard was obtained by hot-pressing molding at 200° C., pressure of 50 kg/cm ² , and hot-pressing time of 3 minutes. Comparative Example 2 In Example 2, the chips used as the raw material for particle board had a moisture content of 4% or less and a material temperature of approximately 18°C.
A wood fiberboard was obtained in exactly the same manner as in Example 2 except that the chips were used. Comparative Example 3 In Example 3, the same procedure as in Example 3 was used except that the binder used was a sufficiently stirred mixture of 3% diphenylmethane diisocyanate and 3% dioxane based on the weight of the bone-dry fiber. A wood fiber board was obtained in the same manner. Various physical properties of the wood fiberboards obtained in the Examples and Comparative Examples were measured and shown in Table 1. From the results in Table 1, it can be seen that the wood fiberboard obtained by the present invention has excellent physical properties. 【table】

Claims (1)

[Claims] 1. Dry the wood fibers to a moisture content of 7% or less and reduce the material temperature.
A mixture of polyisocyanate and dimethylformamide is sprayed onto the wood fibers while still warm at 30°C or higher, and after this is permeated into the wood fibers, water is further sprayed, and then the sprayed wood fibers are sprayed with a mixture of polyisocyanate and dimethylformamide. 1. A method for producing wood fiberboard, which comprises thermoforming fibers at a temperature higher than the boiling point of dimethylformamide.