JPH04316801A - Manufacture of improved wood based board - Google Patents

Abstract

PURPOSE:To reduce the dimensional change due to deaeration, enhance the rigidity under wet state and consequently prevent the strength of the board concerned from lowering, by a method wherein formaldehyde source is mixed with board stock to attain a uniform formalization under catalyst by making contact with wooden fiber having a great surface area and combination with cellulose. CONSTITUTION:Board stock, which is prepared by splitting or crushing wood such as broad leaved wood material, after being applied with urea resin-based adhesive, is formed under heat and pressure into sheet in order to obtain porous board. In this case, the sheet is formed under the condition that formaldehyde source is added to the board stock and kneaded together. Under the state that the board is placed in the reaction device of gas circulating system so as to traverse the direction of gas flow, sulfurous acid gas as catalyst is introduced in the reaction device so as to pierce the board at 120 deg.C to circulate for about 60min in order to formalize the interior of the board.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a new and improved wood board that exhibits little dimensional change due to water absorption and dehydration, and that has increased rigidity when wet to prevent a decrease in strength.

0002

[Prior Art and its Problems] Generally, fiberboard or particle board (hereinafter simply referred to as "board") with a medium specific gravity expands, swells, or shrinks due to humidity, water, or dryness, resulting in its size increasing. The strength and physical properties of the board were significantly reduced, especially when wet.

[0003] For this reason, when using this type of board, problems often occur due to these problems or the use of the board is restricted.

Conventionally, attempts have been made to solve this problem by adding water repellents such as wax during board manufacture and using adhesives with good water resistance, but these methods have not been effective. In the former case, adding a large amount of water repellent agent actually inhibits adhesion and significantly reduces the strength of the board, while in the latter case, it causes discoloration and a significant increase in cost. It was seen.

On the other hand, although formalization treatment has been attempted as a means of stabilizing the dimensions of lumber and paper, it is difficult to penetrate the chemical deeply into the treated material with simple gas treatment. However, even after a long period of time, only the surface was treated, and its use was limited to some extremely thin wooden boards, paper, or cloth.

[0006]

[Means for Solving the Problems] In view of the above-mentioned circumstances, the present invention is capable of uniformly and efficiently formalizing the inside of a porous wooden board in a short period of time to prevent deterioration of physical properties when wet. Furthermore, the present invention aims to provide a board that can reliably improve the dimensional stability of the board against discoloration, absorption of water, and dehydration.

That is, a board material obtained by defibrating or crushing wood is coated with an adhesive and hot-pressed to a density of 0.2 to
To obtain a porous board of 0.9 g/cm3, a formaldehyde source was added and mixed with the above board raw material to form a board, and this board was set in a reaction device of a gas circulation system so as to cross the gas flow direction. Then, a method was used in which a catalyst such as sulfur dioxide was introduced into the device and circulated through the board in the thickness direction to efficiently formalize the inside of the board.

[0008] Furthermore, when manufacturing a board using the same material as in the above example, a formaldehyde source is added and mixed into the board raw material to form a board, and this board is set in the gas flow direction in a reaction device of a gas circulation system. Another method was used in which a catalyst such as sulfur dioxide was introduced into the apparatus and infiltrated while being circulated to formalize the front and back layers of the board.

[0009]

[Operation] The present invention is applied to porous wooden boards that maintain a large surface area by reacting with a formaldehyde source mixed in the board raw material in advance and a catalyst such as sulfur dioxide in the gas circulation system, and penetrating the interior of the board. Or, by penetrating it, the cellulose in the wood that comes into contact with it easily binds, and it has a special effect that the board can be formalized in a short time and without any unevenness.

0010

EXAMPLES The production method of the present invention will be explained in more detail below based on 1 and 2 examples.

Example 2 A urea resin adhesive was applied to a fiber obtained by defibrating hardwood, and tetraoxane was further mixed in, and the fiber was hot-pressed to a density of 0.67 g/cm3 and a thickness of 9 mm using a conventional method. The board was set in a gas circulation system reaction device across the gas flow direction, sulfur dioxide gas was introduced into the reaction device as a catalyst, and the board was penetrated at a temperature of 120°C for about 60 minutes. The above gas is circulated to formalize the inside of the board.

Example ■ Fibers made from defibrated hardwood are coated with a urea resin adhesive and then hot-pressed. Trioxane is mixed into the raw material of the board and the density is 0.65 g/min by a conventional method. cm3
A board formed to a thickness of 9 mm was set in the gas flow direction in a reaction device of a gas circulation system, and a mixed gas of sulfur dioxide and ferric chloride was introduced as a catalyst into the device.
The above gas is circulated and permeated on the front and back surfaces of the board at a temperature of 0.degree. C. for about 60 minutes to formalize the front and back layers of the board.

[0013] The formaldehyde source in the above embodiments is particularly important when the adhesive is a urea resin, melamine resin, phenol resin, or a co-condensed resin adhesive thereof, and is a formalin-based resin containing an excessive amount of formaldehyde. No need to add.

[0014] Furthermore, the concentration of formaldehyde in the method of the present invention is 1 as an integrated amount relative to the weight of the board.
% or more, and it is desirable that the concentration of sulfur dioxide as a catalyst is always maintained at 1/20 or more of the formaldehyde concentration. The reason for this is that although formalization treatment is possible even if the concentrations of formaldehyde and sulfur dioxide are lower than the above concentrations, the object of the present invention cannot be fully achieved.

[0015] In addition, the temperature of formalization treatment is 60°C.
A temperature range of ~200°C is appropriate; even if the temperature is higher than 200°C, no significant improvement in the effect can be expected; on the contrary, physical properties will deteriorate due to high-temperature treatment, and if the temperature is lower than 60°C, the reaction will be slow and the treatment will be difficult. It was disadvantageous because it took too much time.

[0016] As the formaldehyde source to be mixed with the above-mentioned board raw material, in addition to formalin, paraformaldehyde, trioxane, tetraoxane, etc., glyoxal and other substances that become aldehyde gas when heated are preferable, and each may be used alone or in combination. It is free to use any metal salt catalyst, and in addition to sulfur dioxide, metal salt catalysts such as ferric chloride, ferric sulfate, and zinc chloride may be used alone or in combination.

[0017]Although each of the above embodiments has been described using wood fiber as a raw material, the method for producing a board according to the present invention can be applied to any board that uses wood fiber as a raw material, whether it is in the form of flakes or powder.
The desired formalization process can be achieved with a porous board formed to a certain density.

[0018] Furthermore, the tree species used as the raw material may be either commonly obtained broad-leaved trees or coniferous trees, or they may be mixed, or some vegetable materials or mineral materials other than wood may be mixed. There is no problem. Furthermore, in addition to this,
Regarding the adhesive used for forming the board, any adhesive commonly used for this type of board can be used.

In summary, the formalization treatment of the board of the present invention is carried out by setting a board made by mixing a liquid or powder formaldehyde source into a board raw material and hot-pressing the board in advance in a circulation system, and then By penetrating or infiltrating the gaseous catalyst into the board, the aim is to promote contact between the fibers and chips that make up the porous board and formaldehyde and the catalyst, thereby achieving efficient formalization. The processing gas pressure inside is usually 0.
．． About 5 kg/cm2 is sufficient.

[0020]

[Effects of the Invention] Next, the effects of the present invention will be described.
The dimensional stability (thickness and Table 1 shows the comparison of the expansion coefficients according to length.

[0021] In the board of the present invention, the formaldehyde source and catalyst easily enter the inside of the board, come into contact with wood fibers having a large surface area, and combine with cellulose, thereby proceeding with the formalization process efficiently and uniformly throughout the board. Therefore, if you compare this with an untreated board, the difference is obvious at a glance from the table above. That is, according to the same table, it can be seen that the treated board of the present invention has significantly reduced dimensional changes due to absorption and dehydration. In addition, in the processing means of the present invention,
It maintains high rigidity even when the board is immersed in water, increases the weight of the board extremely little compared to other chemical treatments, and provides remarkable effects such as almost no discoloration of the board due to treatment. It is.

[Brief explanation of the table]

Table 1 is a comparison table of water absorption and expansion rates between a conventional board and a board produced by the method of the present invention.

[Table 1]

Claims (2)

[Claims] Claim 1: When applying an adhesive to a board material obtained by defibrating or crushing wood to obtain a porous wood board, a formaldehyde source is mixed in the wood board material and the board is hot-pressed. , this board is set in a reaction device of a gas circulation system so as to cross the gas flow direction, and a catalyst such as sulfur dioxide is introduced and circulated into the device, and penetrates the board in the thickness direction. A method for producing an improved wood board characterized by formalizing it. [Claim 2] When applying an adhesive to a board material obtained by defibrating or crushing wood to obtain a porous wood board, a formaldehyde source is mixed in the wood board material and the board is hot-pressed. This board is set in the gas flow direction in a reaction device of a gas circulation system, and a catalyst such as sulfur dioxide is introduced into the device and permeated while being circulated, thereby formalizing the front and back layers of the board. A method for manufacturing improved wooden boards.