JPH0356642B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention particularly relates to a method for producing modified wood with excellent dimensional stability, and more specifically, the present invention relates to a method for producing modified wood having particularly excellent dimensional stability. Chemically treated with a reactant that can react with the hydroxyl groups of the components, the treated wood thus obtained is swollen with a polar liquid, and at the same time impregnated with a dehydration condensation type polymerizable substance dissolved in the polar liquid. The present invention relates to a method for producing modified wood having particularly excellent dimensional stability, which comprises removing the polar solvent that has permeated the wood under mild conditions, and then heating and curing the remaining polymeric material. Wood has been used as a building material, furniture material, and for a wide range of other purposes since ancient times, but it has the disadvantage of being susceptible to rot due to infiltration by various fungi and damage from insects such as termites, as well as being susceptible to water and moisture. absorption, such as
Due to repeated dissipation, warping, cracking, twisting,
It has a decisive defect as a structural material and surface material in that it is susceptible to deformation such as expansion and contraction.
This is mainly due to the property of wood components that easily absorb moisture. As a means to improve such dimensional instability,
Methods of treating wood with an acylating agent, particularly an acetylating agent, and methods of impregnating wood with a resin and curing it are already known. However, it is difficult to say that either method is satisfactory for the reasons described below. That is, the former method attempts to alleviate the above defects by treating wood with an acylating agent to acylate the hydroxyl groups of wood components, particularly cellulose, and reduce the hydrophilicity of the wood. Under mild conditions, the hydroxyl groups in the wood components remain and sufficient acylation cannot be achieved, so there is a limit to the dimensional stability that can be obtained (in the conventional example, anti-swelling coefficient (ASE)
Maximum efficiency is around 70)). Therefore, usually
Measures have been taken to increase the acylation efficiency by amorphizing cellulose crystalline regions using strong acids, aminos, amides, etc. Such a method increases the acylation rate, but at the same time,
The effect of the amorphizing agent used has the disadvantage that the essential features of wood, such as lightness, toughness, workability, and strength, are impaired. On the other hand, the method of impregnating and curing wood with a polymeric substance is widely used in the wood industry to make WPC-reinforced wood, but as seen in these examples, even if a large amount of polymeric substance is impregnated, cell membranes cannot be damaged. Although it can be filled, it does not efficiently penetrate into the wood cell walls.
Adsorption is impossible and dimensional stability usually does not improve much (ASE = 50% or less). There is also a known attempt to provide dimensional stability by impregnating a polymeric substance that can penetrate into the wood cell wall using an appropriate solvent, but in this case too, there is a limit to the dimensional stability that can be obtained. Yes (ASE=
60 to 70% is the maximum), and furthermore, if it is amorphized to advance impregnation, it becomes brittle as described above, which is not preferable. Exceptionally, high dimensional stability comparable to that obtained here (ASE = 80% or more) can be obtained when impregnated with a non-polymerizable material such as polyethylene glycol, which is easily oxidized by water. It is a soluble substance, and its high dimensional stability is significantly reduced by leaching into water and is not permanent, which greatly limits its range of application. Furthermore, JP-A No. 58-39405 discloses a non-fading wood obtained by acetylating wood, impregnating it with polyalkylene glycol or its vinyl derivative, and drying it. Even if the resin is treated, the resin will inevitably leach out even if it is filled into wood, similar to when it is injected into untreated wood, and the water resistance will not be improved. Furthermore, in order to improve water resistance, polyalkylene glycol is modified into a vinyl derivative and filled by radical polymerization, but this resin also has a molecular structure mainly composed of ether bonds, so it Parts other than radical polymerization are easily separated by heat, making it unstable, and even if it is temporarily modified, it cannot withstand long-term use around water or outdoors. By combining the above-mentioned conventional techniques under appropriate conditions, the present inventors succeeded in obtaining modified wood that is highly durable and excellent in dimensional stability, and have completed the present invention. That is, the present invention chemically modifies the hydroxyl groups of wood components under conditions that substantially leave the crystalline regions of the wood, swells the thus obtained treated wood with a polar liquid, and simultaneously dissolves it in the polar liquid. The method involves impregnating the wood with a dehydration condensation type polymerizable substance, then volatilizing the polar solvent from the wood under mild conditions, and finally heating and curing the polymerizable substance remaining in the wood. In other words, while the hydroxyl groups of wood components in the amorphous region, which are the main cause of dimensional changes, are chemically modified to make them less likely to absorb water, this treatment also removes the hydroxyl groups of remaining wood components that could not be chemically modified in the above treatment. A dehydration condensation type polymerizable substance dissolved in a polar solution that has a high affinity for hydroxyl groups is injected, and the dehydration condensation type polymeric substance is filled into the microscopic cavities of the swollen cell walls of wood and hardened to become insolubilized. It is. As a result, the dimensional stability, which could not be obtained only by chemically modifying the hydroxyl groups of wood components, can be significantly improved by filling with a dehydration condensation type polymeric substance. In addition, since dehydration condensation type thermosetting resins harden while being dehydrated, they have a very high affinity with the OH groups in the remaining wood components, and conversely, the parts that are chemically modified during pretreatment become hydrophobic. It remains because it has been preserved
Thermosetting resin is selectively filled around the OH group, reducing excess filling in areas that have little effect on modification, improving machinability, light weight,
It does not impair the essential characteristics of wood, such as its appearance. The present invention will be explained in more detail below. There are no particular restrictions on the species or shape of the wood that can be used in the present invention, and all kinds of wood, such as thin wood boards, thick boards, chips, and fibers, can be used. These woods do not require any special pretreatment before being subjected to the treatment steps of the present invention. However, in order to facilitate chemical modification or impregnation with a polymerizable substance, soluble components may be removed in advance by boiling, steaming, or an alkaline aqueous solution or hot water. The reactant used for chemical modification of wood components may be any substance as long as it chemically reacts with the hydroxyl group of the wood component to impart hydrophobicity, but it is usually an esterifying agent (acylating agent). agent) or etherification agent. Esterifying agents include organic acid anhydrides (for example, acid anhydrides such as acetic acid, propionic acid, and butyric acid), organic acid halides (for example, in addition to the above acids, acid halides such as caproic acid, lauric acid, stearic acid, and methacrylic acid). (in particular acid chlorides), and mixtures of organic acid anhydrides and fatty acids (for example mixtures of trifluoroacetic anhydride or chloroacetic anhydride with acetic acid, propionic acid, caproic acid or lauric acid, etc.). These esterifying agents can be used alone or in combination of two or more. A catalyst for promoting the reaction with the wood component and/or a solvent for promoting the penetration of the esterifying agent into the wood cell wall may be added to the above-mentioned esterifying agent, but for the reasons mentioned above. Therefore, it is preferable to avoid using strong catalysts that would amorphize the crystalline regions of the wood. Therefore, when acetic anhydride, which is a typical esterifying agent, is used, it is preferable to use sodium acetate or potassium acetate as a catalyst and to perform the treatment under mild conditions in the presence or absence of a solvent. Examples of the etherification agent include 1,2-epoxides such as ethylene oxide and propylene oxide, alkyl halides such as methyl chloride and ethyl chloride, aromatic halides such as benzyl chloride,
Dialkyl sulfates such as dimethyl sulfate, α-halogen acids such as monochloroacetic acid, vinyl compounds activated with negative groups such as vinyl cyanide, aldehydes such as formaldehyde, and the like can be used. In the case of an etherification agent, as in the case of an esterification agent, a catalyst and a solvent can be appropriately added, but as in the case of an esterification agent, it is desirable to avoid the use of strong reagents. In addition to the above-mentioned esterifying agents and etherifying agents, isocyanates (for example, methyl isocyanate, ethyl isocyanate, etc.) can also be used as the reactant to be reacted with the hydroxyl group. In order to bring the wood into contact with the reactant described above, the wood may be immersed in the reactant, or the wood may be exposed to the vaporized reactant. Further, such a method can be carried out under reduced pressure, under increased pressure, or by a reduced pressure method to promote impregnation of the reactant into the wood. This reaction is preferably controlled such that the weight gain of the treated wood obtained by treatment with the reactants does not exceed 30%. The wood thus treated with the reactant is washed with a suitable solvent if necessary and then dried, and subjected to the next step of swelling with a polar liquid and impregnation with a dehydration condensation type polymerizable substance. This process consists of immersing the treated wood in a solution of a polymerizable substance in a suitable polar liquid, or applying or injecting this solution onto the treated wood.
This operation can be carried out under reduced pressure, increased pressure, or reduced pressure. The polar liquids used in this process to swell the treated wood include water, methanol, cellosolve (ethylene glycol monoethyl ether), ethyl alcohol, n-propyl alcohol, iso-propyl alcohol, ethylene glycol, furfuryl alcohol, phenol, Formic acid, acetic acid, propionic acid, formamide, n-butylamine, diethylamine, morpholine, piperidine, dimethylformamide, dimethylacetamide, diethylformamide, dimethylsulfoxide, acetone, methylethylketone, dioxane, methyl acetate, ethyl acetate, and the like. On the other hand, dehydration condensation type polymerizable substances must be soluble in polar liquids, have a stereochemical structure that allows them to penetrate into cell walls, and after penetrating into wood, they must be able to penetrate into wood components. It must be capable of being converted into a resinous solid by an appropriate means that has an affinity for the hydroxyl groups in the resin. Examples of such dehydration condensation type polymerizable substances include initial condensates of amino and phenol resins, initial condensates of furan resins, and furan monomers. A catalyst, a curing agent, a plasticizer, a coloring agent, and/or a flame retardant can be added as appropriate to the solution in which the polymerizable substance is dissolved in a polar solvent. The treated wood impregnated with the polymerizable substance by the above method is subjected to the next solvent removal step. This step consists of maintaining the treated wood under a heated atmosphere (room temperature to about 150° C.) or under reduced pressure to gently volatilize the solvent from the wood. Through this process, the polar liquid that permeates into the microscopic cavities of the treated wood and contributes to the swelling is removed at the same time, leaving or replacing the impregnated polymerizable substance, so that it can be maintained in a swollen state. Generally, it is desirable to remove the solvent to below the fiber saturation point.
Specifically, when the polar liquid is water, it is 50 to 80 at normal pressure.
This can be achieved by keeping methanol and acetone indoors for 2 to 5 hours at ℃, and keeping dioxane at room temperature and under reduced pressure of 30 mmHg for 3 hours. The treated wood from which the solvent has been removed is then subjected to a final heat curing treatment. This step consists of heating the wood at room temperature to 250°C, optionally under normal pressure or pressure. Through this treatment, the polymerizable substances that had permeated the vicinity of the OH groups remaining from the chemical modification treatment in the fine structure of the wood dehydrate and condense with each other.
Alternatively, it forms a graft polymer with wood components, producing a bulking effect. As long as there is no outflow of the polymerizable substance, the solvent removal step and the curing step can also be carried out in parallel by leaving at room temperature and then gradually applying heat and pressure. Through the above series of operations, modified wood with significantly improved not only dimensional stability but also desirable properties as a structural material surface material, such as water resistance, stain resistance, and rot resistance, is obtained. be able to. Example 1 A 0.6 mm thick hemlock veneer was immersed in acetic anhydride at 130°C containing 5% by weight of sodium acetate for 10 minutes, resulting in an acetylated veneer with a weight increase rate (bone dry weight ratio) of 27%. Obtained. A mixed solution of phenolic resin initial condensate:water = 30:70 was injected into this acetylated veneer under reduced pressure. After injection, the veneer was kept at 60°C for 2 hours and the solvent was removed. Next, heat and pressure curing was performed at 130° C. for 30 minutes to obtain a modified veneer (A). Test Example 1 Modified veneer (A) treated by the method of the present invention, untreated veneer
(B) and the veneers (C), (D), and (E) treated in the following manner were once completely dried, allowed to absorb water for one hour under reduced pressure (5 mmHg), and then dried under pressure (10 Kg/cm ² ). The ASE
We compared and examined the values. The results are shown in Table 1.

[Table] From Table 1, it can be seen that the dimensional stability of the modified veneer according to the present invention is far superior to that of the modified veneer treated by a method corresponding to the conventional method. Furthermore, compared to the veneer (C) that was only subjected to acetylation treatment, the specific gravity increased by 0.07, and when the untreated veneer (B) was directly impregnated with a dehydration condensation type polymerizable substance and hardened, the specific gravity increased by 0.14. It can be seen that the filling is selective compared to the veneer (D). In addition, this modified veneer has excellent long-lasting dimensional stability, ease of processing, durability, and cosmetic properties.

Claims (1)

[Claims] 1. Treating wood with a reactant capable of reacting with hydroxyl groups of wood components under conditions that substantially leave cellulose crystalline regions in the wood to obtain treated wood in which the hydroxyl groups are chemically modified; The wood is swollen by swelling it with a polar liquid, impregnating it with a dehydration condensation type polymerizable substance dissolved in the polar liquid, volatilizing the polar solvent under mild conditions, and then curing the polymerizable substance by heating. A method for producing modified wood characterized by fixing it with.