JPH0226573B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to modified wood that has particularly excellent dimensional stability and stain resistance, and more specifically, the present invention relates to modified wood that has excellent dimensional stability and stain resistance, and more specifically, the acetylation treatment of amorphous regions of cellulose such as the micellar spaces of wood, and the properties of the treated wood thus obtained. The present invention relates to a method for producing modified wood particularly excellent in dimensional stability and stain resistance, which is obtained by filling and curing a hydrophobic synthetic resin into wood voids including cellulose amorphous regions such as micellar spaces. Wood has been used for a long time as a building material, furniture material, and for a wide range of other purposes, but it has the drawbacks of being susceptible to decay due to attack by various fungi and insects such as termites, as well as being easily contaminated. To,
Through repeated absorption and dissipation of water, moisture, etc.
It has a decisive defect as a structural material and a surface material: it is susceptible to deformation such as warping, cracking, twisting, and expansion/contraction. This is due to the fact that fine voids in the wood structure, that is, areas where cellulose is highly amorphous, particularly microscopic voids such as micellar spaces within cell walls, are expanded by the intrusion of water vapor and the like. As a means to improve such staining properties and dimensional instability, wood is treated with acylating agents, urethanizing agents,
It is already known to treat wood with etherifying agents, especially acetylating agents, and to impregnate and harden wood with resins. However, it is difficult to say that either method is satisfactory for the reasons described below. That is, the former attempts to alleviate the above defects by treating wood with an acylating agent, urethanizing agent, or etherifying agent to chemically modify the hydroxyl groups of wood components, especially cellulose, and bulking the wood. However, under mild conditions, the hydroxyl groups in the wood components remain and sufficient chemical modification cannot be achieved. Measures have been taken to increase the efficiency of chemical modification by making it amorphous. Although this method increases the chemical modification rate, at the same time, the essential characteristics of wood, such as lightness, toughness, workability, specific strength, and natural beauty of the grain, are impaired by the action of the strong acid used. There will be a disadvantage of being exposed. Furthermore, it was not possible to prevent contaminants from entering the wood. On the other hand, wood is impregnated with resin and hardened.
Even when impregnated with a large amount of resin, dimensional stability and stain resistance are not significantly improved. This is because the resin liquid only enters large voids in the wood, especially into the cell lumens, and the resins simply homopolymerize with each other. In other words, it is expected that the dimensional stability and contamination resistance will be significantly improved only when the resin penetrates into minute voids such as micellar gaps in the cell wall and adheres closely to the inner wall surface of the cell wall. However, there were gaps between the cell wall and the resin, and the adhesion was poor, allowing water and contaminants to easily penetrate, making it impossible to achieve the intended purpose. The present inventors have combined two of the optimal conditions of the above-mentioned conventional techniques, and by their close interaction, we have developed a system that prevents aqueous substances from easily penetrating into minute voids such as micellar gaps within the cell walls of wood. By doing so, we succeeded in obtaining modified wood with excellent dimensional stability and stain resistance, and completed the present invention. That is, in the present invention, cellulose amorphous regions such as micellar spaces within the cell wall of a thin wood board are acetylated, and a hydrophobic synthetic resin is filled and hardened into the wood voids including the micelle spaces. Since the product obtained by the present invention does not amorphize the cellulose crystalline region, the wood does not become brittle, and by acetylating the cellulose hydroxyl groups, hydrophobic synthesis is achieved in minute voids such as micellar gaps in the wood. Since the affinity is increased without creating any obstacles during impregnation with the resin liquid, not only the resin liquid impregnates the cell lumen of the wood, but also the minute voids such as micellar gaps are hydrophobically synthesized. It is spread out by the resin liquid, allowing the hydrophobic synthetic resin to easily penetrate. In addition, because the anchoring effect on the inner wall surface of the cell wall and the affinity with the hydrophobic synthetic resin are enhanced, the hydrophobic synthetic resin hardens within the cell wall and on the inner wall surface of the cell wall, reducing the intrusion of water and pollutants. Dimensional stability and stain resistance can be significantly improved without compromising the essential properties of wood. The present invention will be explained in more detail below. There are no particular restrictions on the species of wood that can be used in the present invention, and there is no need to perform any special pretreatment before subjecting it to the treatment process of the present invention. However, in order to facilitate acetylation or impregnation with resin liquid, soluble components may be removed in advance by boiling or steaming, or with an alkaline aqueous solution or hot water. A known method may be used to acetylate the cellulose amorphous region in the wood component. That is, acetic anhydride or a mixture of acetic anhydride and fatty acids (e.g.
A mixture of chloroacetic anhydride and acetic acid) is chemically reacted with the hydroxyl groups in the wood components, particularly in the amorphous region of cellulose. A catalyst may be added to the above acetylating agent to promote the reaction with wood components and/or a catalyst to promote the penetration of the acetylating agent into minute voids such as micellar gaps within the wood cell wall. Good, but
For the reasons already mentioned, the use of strong catalysts that would amorphize the crystalline regions of the wood should be avoided. Therefore, when using acetic anhydride, a typical acetylating agent, it is preferable to use sodium acetate or potassium acetate as a catalyst and to treat under mild conditions in the presence or absence of a solvent. In order to bring the above-mentioned acetylating agent into contact with wood, for example, the wood may be immersed in the reactant, or the reactant may be vaporized and the wood may be exposed to this. 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 acetylating agent into the wood. This reaction is
In order to prevent significant strength reduction and thermoplasticization of the wood, it is preferable to adjust the weight increase rate of the treated wood obtained by acetylating the amorphous region of cellulose so that it does not exceed 30%. The wood thus treated with the reactant is washed with water or a suitable solvent, dried, and subjected to the next step of filling and hardening with a hydrophobic synthetic resin. This process mainly consists of immersing the treated wood in a resin solution mainly composed of a hydrophobic polymerizable monomer alone or a hydrophobic polymerizable prepolymer, or applying or injecting this resin solution onto the treated wood. Become,
This operation can be carried out under reduced pressure, increased pressure, or reduced pressure. Hydrophobic polymerizable monomers used in this step include styrene monomer, methyl methacrylate, styrene oxide, epichlorohydrin,
Examples include divinylbenzene. Examples of the polymerizable prepolymer include vinyl polymerized acrylate, melamine polymerized acrylic prepolymer, unsaturated polyester prepolymer, acrylic urethane prepolymer, and epoxy prepolymer. A reaction initiator, plasticizer, colorant and/or flame retardant may be added to the resin liquid as appropriate. Treated wood impregnated with resin liquid by the above method,
Subjected to the next curing process. This step consists of heating the wood under pressure at 80 to 250°C, if necessary, or wrapping the wood to prevent the resin liquid from scattering and heating it under normal pressure. Through this treatment, hydrophobic polymerizable monomers and polymerizable prepolymers that have penetrated into minute voids such as micelle gaps inside the cell walls of the wood polymerize with each other, or depending on the type of resin, wood components and graft polymers may form. It comes to form. Through the above series of operations, the modified material has significantly improved not only dimensional stability and stain resistance, but also desirable properties as a structural material and surface material, such as water resistance, corrosion resistance, strength, and hardness. You can get quality wood. Example 1 A 0.6 mm thick hemlock thin board was immersed in acetic anhydride at 130°C containing 5% by weight of sodium acetate for 10 minutes to obtain an acetylated veneer with a weight increase rate (absolute dry weight ratio) of 20%. Ta. On this acetylated veneer, oligoester acrylate: methyl methacrylate =
A solution prepared by adding a small amount of a polymerization initiator (benzoyl peroxide) to a 50:50 mixture was injected under reduced pressure. After injection, heat and pressure curing was performed at 130° C. for 30 minutes to obtain a modified veneer A. Example 2 Modified veneer B was obtained by carrying out the same operation as in Example 1, except that general-purpose saturated polyester:styrene=50:50 was used instead of oligoester acrylate. Example 3 A modified veneer C was obtained in the same manner as in Example 2, except that methyl methacrylate was used alone instead of the polymerizable prepolymer. Test Example 1 When the acetylated veneer, which is the intermediate material of Example 1, was immersed in various solvents at room temperature for 24 hours, the elongation rate was compared with that of the untreated one. The results are shown in Table 1 below.

[Table] After immersion Before immersion
*Elongation rate (%) = −
length length

Claims (1)

[Claims] 1. By acetylating a thin wood board under mild conditions, the cellulose amorphous region of the thin wood board is acetylated, and the resulting treated thin wood board is treated with a hydrophobic synthetic resin liquid to contain the amorphous region. A method for producing modified wood, which comprises filling a wood cavity with a hydrophobic synthetic resin and then curing the filled resin.