JPH03130104A - Production of acetylated fiber plate - Google Patents

Abstract

PURPOSE:To enhance production efficiency and to promote curing reaction by utilizing an adhesive having such a type wherein curing is promoted in the presence of acid. CONSTITUTION:Organic fiber is impregnated with acetic anhydride and they are allowed to react with each other, and thereby hydroxyl group in the organic fiber is acetylated. As adhesive having such a type wherein curing is promoted in the presence of acid is added to acetylated organic fiber. Furthermore the mixture is made airborne by hot air and thereafter foaming is performed. This mixture is thermally pressed and molded. As the utilized organic fiber, the chips of e.g. conifer such as pine, japanese cryptomeria and cypress or broad- leaved tree material such as lauan, kapok, chestling tree and poplar are fibfillated according to an ordinary method and this fibrillated fiber is dried. The obtained organic fiber is preferably utilized. Thereby an organic fiber plate can be efficiently produced which is excellent in dimension stability for absorption and discharge of moisture.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing an acetylated fiberboard, and particularly to a novel method capable of producing an acetylated fiberboard with excellent dimensional stability.

<Prior Art> It has been known to manufacture organic fiberboards by compression molding organic fibers obtained by cutting various softwood or hardwood materials into chips and defibrating them.

However, as the organic fiberboard expands or contracts as moisture absorbs and dries into the organic fibers, it lacks dimensional stability, causing warping and cracking. This has led to problems such as corrosion occurring from inside the fiberboard due to contaminants entering the fiberboard.

As a final method to solve this problem, an acetylated organic material is produced by coating a wood fiber mat with acetic anhydride, acetylating the wood fiber mat by heating it in a sealed space, and removing the by-product acetic acid and residual acetic anhydride. It has been proposed to produce a thermoplastic fiberboard by producing a fiber mat and heat-pressing this mat (Japanese Patent Publication No. 1987-
501915).

<Problems to be Solved by the Invention> According to the method for manufacturing a thermoplastic fiberboard described above, the effect of preventing expansion of the fiberboard due to moisture absorption is improved compared to an untreated fiberboard. According to the inventor's experiments, the water resistance against long-term immersion was not necessarily fully satisfactory. In addition, the fiberboard manufactured by this method is obtained by simply heating and pressing an acetylated wood fiber mat without using an adhesive, so the temperature, pressure, time, etc. It is necessary to strictly control the heating and compacting conditions, making the operation complicated.

Means for Solving the Problems> In view of the current situation, the present inventor has conducted extensive research in order to provide a method for industrially manufacturing organic fiberboard with excellent dimensional stability against moisture absorption and release. As a result of repeated efforts, the present invention was completed.

That is, the present invention acetylates the hydroxyl groups in the organic fiber by impregnating the organic fiber with acetic anhydride and causing the reaction, and then adding an adhesive whose curing is accelerated by the presence of an acid to the acetylated organic fiber. This method of manufacturing an acetylated fiberboard is characterized in that the fiberboard is further blown with hot air, subjected to 7 ohming, and then hot-press molded.

Examples of organic fibers used in the present invention include pine,
Organic fibers obtained by defibrating chi-nobu of softwood such as cedar, cypress, or hardwood such as lauan, capor, chestnut, poplar, etc. according to a conventional method and drying to a moisture content of 20% or less, preferably 10% or less. Suitably used. Most of these organic fibers have a length of 1 to 30 mm and a diameter of 2 to 300 μm. These organic fibers are shaped like a bundle of conduits, tracheids, or cells, and the cell walls around the fiber periphery are often torn or cracked.

In order to produce the acetylated fiberboard according to the present invention, the above-mentioned organic fibers are impregnated with an aqueous solution of metal acetate such as sodium acetate or potassium acetate without any catalyst or as a catalyst, dried, and then dried with acetic anhydride. , immersed in an acetic anhydride reaction solution bath such as chloroacetic anhydride. Next, the organic fiber impregnated with acetic anhydride is taken out from the reaction liquid tank or the acetic anhydride is discharged from the reaction liquid tank, thereby impregnating the organic fiber with about 50 to 80% by weight of acetic anhydride. As a method for impregnating acetic anhydride, it is also possible to add acetic anhydride to organic fibers by spraying or the like, and mix and impregnate the organic fibers.

Organic fibers impregnated with acetic anhydride in this way are
Acetylation in which hydroxyl groups in organic fibers are replaced with acetyl groups by heating in a separate reactor or mixer at 70 to 150°C for several minutes to several hours and reacting while removing by-product acetic acid. You can sell textiles. At this time, the weight increase rate due to acetylation is about 15 to 25%. At the end of the acetylation reaction, most of the by-product acetic acid has been discharged from the system, and unreacted acetic anhydride remains.

This remaining unreacted acetic anhydride (and some amount of acetic acid) is put into a mixer (blender) without being removed,
A urea resin adhesive or a phenol adhesive is added and mixed as an adhesive whose curing is accelerated by the presence of an acid. As a result, the adhesive is sufficiently attached to each acetylated organic fiber. The amount of adhesive added is preferably 2 to 15% by weight based on the organic fiber, and the resin percentage is preferably 30 to 60%.

Generally, the lower the resin ratio, the more uniformly the resin can be mixed into the organic fibers. The adhesive added to organic fibers is of a type whose curing is accelerated by the presence of acid.
Gradual hardening occurs after addition due to the presence of acetic anhydride (and some by-product acetic acid) remaining after the acetylation process.

The acetylated organic fibers to which the adhesive has been attached are then placed into a hot air duct and dried by blowing air.

The air blowing speed at this time is generally about 15 to 20 m/sec, but it can be appropriately adjusted within a wide range depending on the specific gravity of the organic fiber, the feeding amount, the processing capacity of the previous and subsequent steps, etc. The organic fibers are dried to a moisture content of 6 to 8% by blowing with this hot air.

The dried organic fibers are subjected to 7 ohms in a conventional manner to form a fiber mat of a constant thickness, and then inserted into a hot press. During hot press molding, the added adhesive is further hardened to obtain the desired acetylated organic fiberboard.

<Function> A small amount of acetic acid, which is a by-product, and a considerable amount of acetic anhydride remain in the acetylation process of organic fibers, but this is a type of adhesive whose curing is accelerated by the presence of acid on acetylated fibers. The curing of the adhesive is accelerated by the action of acetic acid and acetic anhydride. Therefore, there is no need to remove acetic acid and acetic anhydride.

<Example> Radiata pine chips at 160℃, 7kg/cm
2 for 3 minutes, defibrated using a defibrator refiner, and then immersed the dried wood fibers in a liquid acetic anhydride reaction tank for 2 minutes, and then removed from the reaction tank to remove excess acetic anhydride from the wood fibers. They were drained alternately for 5 minutes. This wood fiber is heated at 120°C while emitting the by-product acetic acid.
Acetylation treatment was performed by heating and reacting for a period of time. After the reaction was completed, the mixture was cooled to 50'C, and a urea resin adhesive having a resin solid content of 45% was added and mixed in an amount of 6% to the fibers in a blender. Next, it was placed in a hot air duct and dried to a moisture content of 6 to 8% while blowing air. The dried wood fibers were subjected to 7 ohms according to a conventional method and heat-pressed at 125°0 for 6 minutes to obtain an acetylated organic fiberboard with a thickness of 5 mm.

This acetylated organic fiberboard exhibited extremely excellent water resistance even when immersed in water for a long period of time, and had good dimensional stability.

<Effects of the Invention> According to the method of the present invention, since a type of adhesive whose curing is accelerated by the presence of acid is used as an adhesive for manufacturing fiberboard, acetic acid and residual acetic acid produced as by-products due to the acetylation reaction are The anhydride can be effectively used as a curing agent for the adhesive. Therefore, there is no need for a step for removing reaction by-products and residues after the acetylation reaction, resulting in excellent production efficiency. Moreover, in thermoforming the fiberboard, in addition to the curing mechanism by heating, the curing accelerating function by the acid is added, so that the curing reaction is accelerated. Furthermore, the method of the present invention can be implemented by simply adding an acetylation treatment step to the conventional fiberboard manufacturing process, and is extremely useful industrially.

Claims (1)

[Claims] (1) acetylating the hydroxyl groups in the organic fiber by impregnating the organic fiber with acetic anhydride and causing the reaction; adding an adhesive whose curing is accelerated by the presence of an acid to the acetylated organic fiber; A method for producing an acetylated fiberboard, which comprises further blowing with hot air, followed by forming and thermopressing.