JPH0367601B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing a plastic-like wood-based molded board with significantly improved water resistance and weather resistance. [Prior Art] There is currently a strong desire for an effective method of utilizing forest resources, which are renewable resources, and in particular, unused wood such as small-diameter trees and thinned wood. Furthermore, there is an urgent need to establish a more effective method for using small pieces of wood, which are produced as industrial waste in industries that use wood. In view of the above-mentioned circumstances, the present inventors developed a wood-based molded product with a plastic-like appearance using small pieces of wood as the main raw material, and filed a patent application (Japanese Unexamined Patent Application Publication No. 1983-1993).
152837). This method focuses on esterified wood pieces, which are made by reacting dibasic acid anhydrides with small wood pieces to introduce carboxyl groups into the wood.The esterified wood pieces are mixed with an epoxy compound, and the mixture is hot-press-molded. This can be obtained by The resulting wood-based molded product has a plasticized wood piece that makes up the molded product, and has a smooth, shiny, plastic-like appearance, even though the wood component is the main component. It has excellent dimensional stability against water, mechanical strength, hardness, and heat distortion temperature. However, the above-mentioned wood-based molded products have the following problems, and have had the disadvantage that their uses must be limited. That is, when the above-mentioned wood-based molded product is immersed in water, it has good dimensional stability, but there is a problem that the surface smoothness and gloss deteriorate. In addition, there was a drawback in terms of weather resistance, such as whitening and deterioration of the surface of the wood-based molded product. [Problems to be Solved by the Invention] Accordingly, the present invention provides a method that shows no deterioration in surface smoothness and gloss even when immersed in water.
Another object of the present invention is to provide a method for obtaining a wood-based molded board with excellent weather resistance. [Means for Solving the Problems] The present inventors have studied to solve the problems of the above-mentioned wood-based molded products, and found that by interposing a resin film during hot-press molding and laminating and adhering these at the same time, the above-mentioned problems can be solved. It has been found that a molded article can be obtained in which the problems of the above are largely solved. That is, the present invention provides carboxyl group-containing esterified wood pieces obtained by reacting polybasic acid anhydrides with hydroxyl groups in wood, or carboxyl group-containing esterified wood pieces containing unreacted polybasic acid anhydrides. In a method for obtaining a wood-based molded board by hot-pressing a mixture of a compound containing two or more epoxy groups in the molecule, a thermoplastic resin film is applied to one or both sides of the mixture during hot-pressing, and 140 This is a method for producing a wood-based molded board with excellent water resistance and weather resistance, which is characterized by integral molding by hot pressing at a temperature of 60 kg/cm ² or higher at a temperature of 60 kg/cm 2 or higher. The carboxyl group-containing esterified wood chips used in the present invention are chips, fibers, or powdered wood chips that are reacted with a polybasic acid anhydride to produce cellulose, hemicellulose, lignin, etc. contained in the wood tissue. A carboxyl group is chemically introduced into a small piece of wood by esterifying the hydroxyl group in the chemical component of the wood, and it is easily produced according to the method of the present inventors (Japanese Patent Application Laid-open No. 152837/1983). be able to. In this case, there is no problem even if it contains unreacted polybasic acid anhydride. That is, in the present invention, either the carboxyl group-containing esterified wood pieces or the carboxyl group-containing esterified wood pieces containing unreacted polybasic acid anhydride may be used. Examples of compounds containing two or more epoxy groups in the molecule include bisphenol type epoxy compounds obtained from bisphenol A and epichlorohydrin, liborac type epoxy compounds obtained from phenolic resin and epichlorohydrin, and halogenated bisphenol A and epichlorohydrin. and polyalkylene ether type epoxy compounds obtained from polyalkylene glycol and epichlorohydrin. In particular, it is industrially produced in large quantities,
Bisphenol type epoxy compounds, which are also available at low cost, are preferred. The amount of these epoxy compounds to be used is 0.3 to 2 equivalents of epoxy groups per equivalent of carboxyl group in the mixture or, if unreacted polybasic acid anhydride is present, 1 equivalent of carboxyl group and anhydride group in total. The amount is preferably 0.8 to 1.2 equivalents. In the present invention, the thermoplastic resin film is strongly bonded and integrated with the base material by thermoforming, and serves to significantly improve the water resistance and weather resistance of the resulting wood-based molded board. In particular, a film with good water resistance is preferred, and its moisture permeability is 140g/m ² , 24
The effect is remarkable for films with performance below 40℃ and 90%RH. Examples of such thermoplastic films include methacrylic resin, acrylonitrile resin, polyacetal resin, styrene resin,
Examples include films made of polyester resins, polyamide resins, etc., and laminate films mainly made of these materials. However, for films such as polyamide resins, which have some moisture permeability due to the characteristics of the resin, the moisture permeability can be adjusted by adjusting the thickness. It is preferable to use one within this range. In addition, from the viewpoint of adhesion to the base material, a film formed of methacrylic resin, polycarbonate resin, acrylonitrile resin, styrene resin, etc. among the above resins is preferable. Most preferred is a film made of methacrylic resin or polycarbonate resin, which is superior in terms of transparency, water resistance, and weather resistance. Next, the manufacturing method of the present invention will be explained step by step. First, the carboxyl group-containing esterified wood pieces or the carboxyl group-containing esterified wood pieces containing the unreacted polybasic acid anhydride are thoroughly mixed with a compound containing two or more epoxy groups in the molecule. At this time, if necessary, in order to accelerate the curing reaction by addition reaction between epoxy groups and carboxyl groups, and depending on the composition, acid anhydride groups, conventional polyhydric carboxylic acids and acid anhydrides are used in curing epoxy resins. Catalysts such as metal salts of carboxylic acids, tertiary amines, etc. may be added.
In addition, glass fibers are added to further improve the mechanical strength of the resulting wood-based molded board, and halogen-containing compounds such as tetrabromobisphenol A, tetrachlorbisphenol A, hexachlorobenzene are added to impart flame retardancy. A dye or a pigment may be simultaneously added and mixed as a coloring agent. The mixing method can be carried out using a blender, kneader, mixing roll, or the like. Note that, in some cases, by providing a heating step during mixing, mixing can be performed more efficiently. Next, a thermoplastic resin film is applied to one or both sides of the mixture obtained as described above, and the mixture is hot-pressed. Although any method may be used as the hot-press molding method, for example, the following method can be used using a hot press. First, the mixture is formed to form a mat either directly on the caul board or on a thermoplastic resin film applied on the caul board. Next, a thermoplastic resin film is applied on top of the mat, and a smooth mirror plate or an embossed plate having an uneven pattern is applied thereon, and heat and pressure are applied for a required period of time. The heat pressure must meet the temperature and pressure conditions that plasticize the wood chips in the mixture and bond the resulting base material and film.
Kg/ ^cm2 or more is required. Pressures and temperatures that do not satisfy these conditions are not preferred because the wood particles in the mixture become difficult to plasticize or, even if plasticized, the adhesion between the resulting substrate and the film deteriorates. The upper limit of the heat pressure is not particularly limited, but generally it is preferably within a range in which the thermoplastic resin film does not melt and flow. If the film melts during hot pressing, it may be mixed into the base material, which is being plasticized at the same time, and may not be able to achieve its original purpose. Under the above conditions, the mixture undergoes an addition esterification reaction between the carboxyl groups in the esterified wood chips and the epoxy groups in the epoxy compound, which are then crosslinked to form a tough wood-based molded board. The thus obtained wood-based molded board has small pieces of wood that have been plasticized, and has a smooth, glossy, plastic-like appearance. In addition, it has been observed that the thermoplastic resin film is integrated with the base material and strongly bonded, but this is because the entire mixture, including the wood chips of the base material, melts and flows under hot pressure molding and is fully bonded to the film surface. This is thought to be due to the fact that it acted as an adhesive on the film during the process of contact with the film and subsequent solidification. Under high temperature and high pressure, the epoxy compound or acid anhydride in the mixture sufficiently wets the film, and microscopically, after partially dissolving or swelling the surface of the film, it reacts and hardens. It is thought that this made the bond strong. Therefore, hot pressing of a film onto a substrate at a stage where the curing reaction is far advanced or complete does not result in a good adhesive. As described above, one of the features of the present invention is that there is no need to use an adhesive for laminating the base material and the film. [Effects of the Invention] As described above, in the present invention, when a mixture of esterified wood pieces and an epoxy compound is hot-pressed to form a dense plastic-like wood-based molded board in which the wood pieces are plasticized, It has been found that by interposing a thermoplastic resin film, the film can effectively adhere to the surface of the base material and can be integrally molded at the same time. As a result, the denseness, gloss, and other excellent characteristics of the wood-based molded board are not impaired, and even when immersed in water, the surface smoothness and gloss do not deteriorate, and the surface also has excellent weather resistance. No whitening or deterioration, water resistance,
We were able to significantly improve weather resistance. As described above, the wood-based molded board having excellent properties obtained by the manufacturing method of the present invention is suitable in many fields such as building materials, electrical insulation materials, industrial parts materials, etc. Hereinafter, the present invention will be explained in more detail using production examples, examples, and comparative examples, but the present invention is not limited thereto. Production example Production example of carboxyl group-containing esterified wood Production example 1 Dried wood flour of red pine wood passed through a 24-mesh sieve
400 g, 102 g of phthalic anhydride, and 2.1 g of sodium carbonate as a catalyst were added into a kneader with a capacity of 5.
The esterification reaction was carried out at 170°C for 2 hours with stirring.
After the reaction, the reaction product was taken out and used as esterified wood flour without washing.
The addition rate of phthalic anhydride added to the wood flour in this esterified wood flour was 15.8% by weight based on the wood flour. Production Example 2 Esterified wood flour with a phthalic anhydride addition rate of 14.2% by weight was obtained in the same manner as Production Example 1 except that the reaction time was 1 hour. Example 1 29 g of diglycidyl ether of bisphenol A (EPOMIK R-139 manufactured by Mitsui Petrochemical Epoxy Co., Ltd., epoxy equivalent 180-190) was added to 66 g of the esterified wood flour obtained in Production Example 1, and the mixture was mixed with a mixing roll. 170 in a kneader with a capacity of 5.
The mixture was heated and stirred at ℃ for 25 minutes. Next, the mixture was formed onto a 40 μm thick methacrylic resin film placed on a caul board to form a mat. Next, the same film as above was applied on top of the mat, and a mirror plate was placed on top of it.
These were inserted between the hot plates of a press machine and hot-press molded. Heat and pressure conditions are temperature 180℃, pressure 150Kg/cm ² ,
It took 30 minutes. After hot-press molding, a wood-based molded board with a thickness of 3.6 mm was obtained. Example 2 Molding was carried out in the same manner as in Example 1 except that the temperature of the heat and pressure condition in Example 1 was changed from 180°C to 145°C, and the thickness was
A 3.6 mm wood-based molded board was obtained. Comparative Example 1 Molding was carried out in the same manner as in Example 1 except that the temperature of 180°C in the heat and pressure conditions in Example 1 was changed to 130°C, and the thickness was
A 3.6 mm wood-based molded board was obtained. Comparative Example 2 The pressure of 150Kg/cm 2 in the heat pressure condition in Example 1 was changed to 50Kg/cm ²
A wood-based molded board with a thickness of 4.8 mm was obtained by molding in the same manner as in Example 1 except for changing the size to cm ² . Comparative Example 3 In Example 1, the mixture obtained by mixing in a kneader was directly formed on a coal board,
A pine tree was formed. Next, a mirror plate was placed on top of the mat, and these were inserted between the hot plates of a press to perform hot-press molding. The heat and pressure conditions were a temperature of 180° C., a pressure of 150 Kg/cm ² and a time of 30 minutes. The molded plate thus obtained was again placed on a methacrylic resin film with a thickness of 40μ applied on the coal board, and then the same film as above was applied on the molded plate, and then A mirror plate was applied, and then it was inserted between the hot plates of a press machine and hot-press molded. The heat and pressure conditions were a temperature of 180° C., a pressure of 150 Kg/cm ² and a time of 30 minutes. After hot-press molding, a wood-based molded board with a thickness of 3.7 mm was obtained.

[Table] In the wood-based molded boards obtained in Examples 1 and 2 and Comparative Examples 1 to 3, the plasticity of the molded board, the adhesion between the base material and the methacrylic resin film, the water resistance,
and weather resistance. Plasticity was evaluated from the state of plasticization on the surface of the wood-based molded board. The adhesion test was carried out using a cross-cut sellotape peel test as follows. That is, 100 goblets were formed within a 1.5 cm square on the surface of the molded plate using steel, and Cellotape was further adhered to the surface. Thereafter, the adhered cellophane tape was peeled off at once, and the ratio of the film remaining adhered to the goblets, that is, the adhesion rate was determined. The water resistance test was conducted as follows. 23 test pieces
After being immersed in water at 60°C for 1 month, the specimens were dried at 60°C for 2 hours, and the reduction in gloss on the surface of the test piece and the state of adhesion between the base material and the thermoplastic resin film were observed. Further, the weather resistance test was conducted as follows. Using a sunshine weather meter, the condition of the surface of the test piece was observed depending on the elapsed test time. These results are shown in Table-1. Examples 1 and 2 from Table-1
It is recognized that the wood-based molded board manufactured by the manufacturing method of the present invention has excellent adhesion between the base material and the methacrylic resin film, as well as water resistance and weather resistance, as compared to the comparative example. Example 3 47 g of diglycidyl ether of bisphenol A was added to 143 g of esterified wood flour obtained in Production Example 2, mixed with a mixing roll, and further mixed with a volume of 5
The mixture was heated and stirred at 170°C for 30 minutes in a kneader. Next, the mixture was formed onto a 40 μm thick methacrylic resin film placed on a caul board to form a mat. Next, the same film as above was applied on top of the mat, a mirror plate was placed on top of the film, and these were inserted between the hot plates of a press to perform hot pressure forming. Heat pressure condition is temperature
The temperature was 170°C, the pressure was 150 kg/cm ² , and the time was 30 minutes. After hot-press molding, a wood-based molded board with a thickness of 6.4 mm was obtained. Example 4 A wood-based molded board with a thickness of 6.4 mm was obtained by molding in the same manner as in Example 3, except that the methacrylic resin film with a thickness of 40 μm used in Example 3 was replaced with a polycarbonate resin film with a thickness of 35 μm. Ta. Example 5 A wood-based molded board with a thickness of 6.4 mm was obtained by molding in the same manner as in Example 3 except that the 40 μ thick methacrylic resin film used in Example 3 was replaced with a 40 μ thick polyacrylonitrile film. Ta. Example 6 A 6.4 mm thick wood-based molded board was molded in the same manner as in Example 3 except that the 40 μ thick methacrylic resin film used in Example 3 was replaced with a 40 μ thick unstretched nylon film. Obtained. Comparative Example 4 A wood-based molded board with a thickness of 6.3 mm was obtained by molding in the same manner as in Example 3, except that the methacrylic resin film with a thickness of 40 μm used in Example 3 was not used.

【table】

[Table] Table 2 shows the test results for adhesion, water resistance, and weather resistance of the wood molded boards obtained in Examples 3 to 6 and Comparative Example 4. Note that each molded plate had good plasticity. In addition, as a result of evaluating the adhesion between the base material and the thermoplastic resin film using the cellophane tape peeling test described above, all of Examples 3 to 6 were found to be good. Repeated 20 times at Goban's location. As is clear from Table 2, the wood-based molded boards manufactured by the manufacturing method of the present invention in Examples 3 to 6 have better water resistance and It is recognized that it has excellent weather resistance.

Claims (1)

[Scope of Claims] 1. Pieces of carboxyl group-containing esterified wood obtained by reacting hydroxyl groups in wood with a polybasic acid anhydride, or said carboxyl group-containing esterified wood containing unreacted polybasic acid anhydride. A method for obtaining a wood-based molded board by hot-pressing a mixture of small pieces and a compound containing two or more epoxy groups in the molecule, in which a thermoplastic resin film is applied to one or both sides of the mixture during hot-pressing. 140℃ or higher,
A method for manufacturing a wood-based molded board, characterized by integrally molding it by hot pressing at 60 kg/cm ² or more. 2. The method for producing a wood-based molded board according to claim 1, wherein the thermoforming is performed under molding conditions in which the thermoplastic resin film does not melt and flow. 3 The thermoplastic resin film has a moisture permeability of 140g/ ^m2 ,
The method for producing a wood-based molded board according to claim 1 or 2, wherein the film is kept at 40° C. and 90% RH or less for 24 hours. 4. The method for manufacturing a wood-based molded board according to any one of claims 1 to 3, wherein the thermoplastic resin film is a film formed of methacrylic resin or polycarbonate resin.