JPH0677921B2 - Method for producing acetylated fiberboard - Google Patents

Description

The present invention relates to a method for producing an acetylated fiber board, and more particularly to a novel method capable of producing an acetylated fiber board having excellent dimensional stability.

<Prior Art> It has been conventionally known to produce an organic fiber board by compression-molding an organic fiber obtained by disintegrating various softwood or hardwood materials into chips and then defibrating the chips.

However, dimensional stability is lacking due to the expansion or contraction of the organic fiber board that accompanies the absorption and absorption of water in the organic fiber and its drying, resulting in warping and cracking, and the permeation of this water. Therefore, there is a problem that corrosion is generated from the inside of the fiberboard due to the ingress of contaminants.

As a method for solving this problem, an acetylated organic substance obtained by coating a wood fiber mat with acetic anhydride and acetylating the wood fiber mat by heating in a sealed space to remove by-product acetic acid and residual acetic anhydride. It has been proposed to manufacture a fiber mat and then to heat and press the mat to manufacture a thermoplastic fiber board (Tokuhyo Sho 57-50).
1915 publication).

<Problems to be Solved by the Invention> According to the method for producing a thermoplastic fiber board described above, the effect of preventing expansion of the fiber board due to absorption of water is improved as compared with an untreated fiber board. According to the experiments conducted by the present inventor, the water resistance against long-term water immersion was not always sufficiently satisfactory. In addition, the fiber board produced by this method is obtained by simply heating and pressing an acetylated wood fiber mat without using an adhesive. It is necessary to strictly control the heating and pressing conditions of, and the operation is complicated.

<Means for Solving the Problems> In view of the present situation as described above, the present inventors have earnestly studied to provide a method for industrially producing an organic fiber board having excellent dimensional stability against absorption and release of water. As a result of the repetition, the present invention has been completed.

That is, the present invention is to acetylate the hydroxyl groups in the organic fibers by impregnating the organic fibers with acetic anhydride and reacting them, and adding an adhesive to the acetylated organic fibers, the curing of which is accelerated by the presence of an acid. In addition, the method for producing an acetylated fiber board is characterized in that it is formed by hot air blowing, forming, and hot pressing.

Examples of the organic fiber used in the present invention include pine,
Moisture content is obtained by defibrating softwood chips such as cedar and cypress, or hardwood chips such as rawan, capol, chestnut, and poplar, according to the standard method.
Organic fibers obtained by drying to 20% or less, preferably 10% or less are suitably used. This organic fiber has a length of 1-30
Most of them have a diameter of 2 to 300 μm. The organic fibers are in the form of bundles of conduits and temporary conduits or cells, and the cell walls on the outer periphery of the fibers are often torn or cracked.

In order to produce an acetylated fiber board according to the present invention, the organic fiber is impregnated with or without a catalyst as an aqueous solution of a metal acetate such as sodium acetate or potassium acetate, followed by drying, and then acetic anhydride. Immerse in a reaction solution tank of acetic anhydride such as chloroacetic anhydride. Next, the organic fiber impregnated with acetic anhydride is taken out from the reaction solution tank or is discharged from the reaction solution tank to impregnate the organic fiber with about 50 to 80% by weight of acetic anhydride. The acetic anhydride may be impregnated by adding acetic anhydride to the organic fibers by spraying or the like and mixing and impregnating them.

In this way, the organic fiber impregnated with acetic anhydride,
Acetylation in which the hydroxyl group in the organic fiber is replaced with an acetyl group by reacting while heating in another reactor or a mixer at 70 to 150 ° C for several minutes to several hours to remove by-product acetic acid. You can sell the fiber. At this time, the weight increase rate due to acetylation is about 15 to 25%. By the time the acetylation reaction is completed, most of the by-product acetic acid has been discharged out of the system, and unreacted acetic anhydride remains. The residual unreacted acetic anhydride (and a small amount of acetic acid) is put into a mixer (blender) without being removed, and a urea resin adhesive or phenol is used as an adhesive whose curing is accelerated by the presence of acid. Add the system adhesive and mix. As a result, the adhesive is sufficiently attached to each of the acetylated organic fibers. The amount of adhesive added is 2 for organic fibers
It is preferable that the resin content is 30% by weight and the resin ratio is 30%.
It is preferably -60%. Generally, a resin having a low resin content can be more uniformly mixed with the organic fibers. Since the adhesive added to the organic fiber is of a type in which curing is accelerated by the presence of an acid, after the addition due to the presence of acetic anhydride (and a small amount of by-product acetic acid) remaining after the acetylation treatment, It hardens gradually.

The acetylated organic fiber to which the adhesive is attached is then put into a hot air duct and air-dried. The air blowing speed at this time is generally about 15 to 20 m / sec, but the specific gravity of the organic fiber,
It is appropriately adjusted in a wide range depending on the feed amount, the processing capacity of the preceding and succeeding processes, and the like. By blowing with the hot air, the organic fibers are dried to a water content of 6 to 8%.

The dried organic fiber is formed into a fiber mat having a predetermined thickness by a conventional method, and then inserted into a hot press. At the time of hot pressing by hot pressing, the added adhesive is further hardened to obtain a desired acetylated organic fiber board.

<Action> In the acetylation treatment of the organic fiber, a small amount of acetic acid, which is a by-product, and a considerable amount of acetic anhydride remain, but an adhesive of a type in which curing is accelerated by the presence of an acid with respect to the acetylated fiber. The curing of the adhesive is accelerated by the action of these acetic acid and acetic anhydride. Therefore, it is not necessary to remove these acetic acid and acetic anhydride.

<Examples> Radiata pine chips were boiled at 160 ° C and 7 kg / cm ² for 3 minutes, defibrated with a defibrillator refiner, and dried wood fibers were immersed in a liquid acetic anhydride reaction solution tank for 2 minutes. Then, it was taken out of the reaction solution tank, and excess acetic anhydride was discharged from the wood fiber over 5 minutes. Against this wood fiber
Acetylation was carried out by heating the mixture at 120 ° C. for 1 hour while discharging the by-product acetic acid. After completion of the reaction, the mixture was cooled to 50 ° C., and 6% of a urea resin adhesive having a resin solid content of 45% was added and mixed to the fiber in a blender. Then, it was put into a hot air duct and dried while being blown to a water content of 6 to 8%. Forming dried wood fiber according to the usual method,
A 6 mm thick acetylated organic fiber board was obtained by hot pressing at 125 ° C. for 6 minutes. This acetylated organic fiber board exhibited extremely excellent water resistance even with long-term water immersion, and had good dimensional stability.

<Effects of the Invention> According to the method of the present invention, since an adhesive whose curing is promoted by the presence of an acid is used as an adhesive for producing a fiberboard, acetic acid produced by the acetylation reaction and residual Acetic anhydride can be effectively used as a curing agent for the adhesive. Therefore, the step of removing the reaction by-product and the residue after the acetylation reaction is not required, and the production efficiency is excellent. Moreover, in the heat molding of the fiberboard, the curing promotion function by the acid is added in addition to the curing mechanism by heating, so that the curing reaction is accelerated. Furthermore, the method of the present invention can be carried out only by adding an acetylation treatment step to the conventional fiber board production step, and is industrially extremely useful.

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Claims (1)

[Claims] 1. An organic fiber is impregnated with acetic anhydride to react therewith to acetylate the hydroxyl groups in the organic fiber, and an adhesive is added to the acetylated organic fiber to accelerate the curing due to the presence of an acid. The method for producing an acetylated fiber board is characterized in that it is formed by hot air blowing, forming and hot pressing.