RU2266196C2 - Method for decreasing the content and emission of formaldehyde intended for fiber boars - Google Patents

Abstract

FIELD: wood-working industry, in particular, methods for decreasing the content and emission of formaldehyde intended for fiber boards.

SUBSTANCE: the process of production of fiber boards is conducted with employment of aminated adhesive resins with an addition of substances binding the formaldehyde by compacting in running presses or continuous-action presses and by cooling. After compacting, but before cooling the fiber board is subjected to a short-time curing at 80 to 100C during 6 to 16 hours, depending an the expected level of decrease and emission of formaldehyde and used parameters of the process of production.

EFFECT: reduced content and emission of formaldehyde in the fiber board.

5 cl, 3 dwg, 3 ex

Description

FIELD OF THE INVENTION

The subject of the invention is a method for producing a plate and, in particular, a method for reducing the content and emission (i.e. emission) of formaldehyde in the case of a particle board. The method is intended for use in the manufacturing process of these plates, pressed in running presses and continuous presses, using aminated adhesive resins (adhesive aminopolymers).

State of the art

A method of manufacturing a panel according to the invention is known from GB 2354482. This document is incorporated herein by reference.

At the moment, there are many methods for particle board to reduce formaldehyde content and emissions. The main ones are:

- modification of adhesive resins, usually carried out by reducing the molar level of formaldehyde with respect to urea, which in most cases leads to a decrease in the reactivity of the resin, but often also weakens the strength of adhesive joints and their resistance to water;

- the addition of formaldehyde binding agents; however, such substances can often adversely affect the physical and chemical properties of particle board;

- mixing urea-formaldehyde resins with other resins, for example, resorcinol or phenolic; this, in turn, is accompanied by a significant increase in the cost of production;

- an increase in the time of pressing a chipboard, which results in a decrease in production;

- drying of wood particles to a state with extremely low moisture content; this direction is limited by technical conditions and precautions due to possible fire in the drying device;

- processing chipboard with gaseous ammonia; for reasons related to safety, this method requires special tight chambers;

- processing of particle boards in their final form with hot air in special chambers with forced intensive air exchange; this method, taking into account the real productivity of the production line, may require additional special production equipment to ensure uniform flow of products;

- surface treatment of particle boards in their final form through solutions of substances that react with formaldehyde; in this case, special equipment is needed, and, on the other hand, there is a risk of deterioration of the surface quality of such a plate.

Thus, currently existing common methods for reducing the content and emission of formaldehyde in relation to a particleboard either require significant financial costs and involve additional devices and installations, or, in some cases, can adversely affect production efficiency by lowering the productivity of the process and / or deterioration in the quality of a particleboard made according to such methods.

SUMMARY OF THE INVENTION

The present invention is directed to solving the technical problem of reducing the content and emission of formaldehyde in relation to a particle board and, in one aspect, provides a method for reducing formaldehyde in a particle board and releasing it from a particle board, carried out in the process of manufacturing a particle board . The method includes the use of aminated adhesive resins, the addition of curing agents, pressing the plate in presses of continuous or continuous type, and cooling the plate. A distinctive feature of the method is that the particle board after pressing, but before cooling, is subjected to short-term aging at a temperature of from 80 to 100 ° C for a period of time from 6 to 16 hours, depending on the expected level of reduction in the content and emission of formaldehyde and used manufacturing process parameters.

In a preferred embodiment of the process, formaldehyde binding agents are added.

In another aspect, the invention provides a method for manufacturing a particle board, including a step of heating and pressing, the distinguishing feature of which is that the particle board after pressing, but before cooling, is subjected to aging at a temperature of from 80 to 100 ° C for a period of time from 6 to 16 hours.

Preferably, a laminate system having a base plate and a film-like layer impregnated with resin with temperature and pressure on both sides is treated in a pressing device so that the laminate system is thereby adhered together.

From a particle board, panels can be produced that are provided with a groove or protrusion at each of the outer edges.

Currently, common methods for the manufacture of particle boards using aminated resins require cooling of such a board immediately after pressing, before aging. The cooling process takes place on rotary coolers, where the particle board is located for a period of time from several minutes to several tens of minutes, most often during the time required to reduce the temperature of the outer layer of the particle board to 45-60 ° C.

It turned out unexpectedly that the heat accumulated in the chipboard during its pressing can be used to deepen the polycondensation of the adhesive resin, which, as far as one can judge, cannot be completely completed in the press due to the very short pressing cycles of the boards. Incomplete hardening of the adhesive can cause the formaldehyde to split off and, consequently, in the case of chipboard, increase its content and excretion. The selection can be very long-lasting, especially under storage and use conditions, leading to a significant increase in the moisture content in the chipboard.

The short-term curing of the chipboard after pressing provided according to the invention to some extent replaces the extension of the pressing time of such a board. The positive effect of the specified time extension on the hygienic properties of the board has already become a general rule of technology for the manufacture of chipboards. However, it is also known that for economic reasons the practical application of this technique is limited. On the other hand, an increase in the reactivity of resins is one of the conditions for realizing the technical advantages provided by the system of continuous pressing of particle boards, which has been proposed over the past two years. This is an additional confirmation of the importance of curing.

To date, in order to avoid hydrolysis of the adhesive joints and, therefore, weakening the strength of the chipboard, the cooling and curing processes of such boards have been accompanied by control of the temperature reached before curing. The temperature actually achieved by cooling was not controlled. It was believed that in this case, the most desirable temperature, the lowest of all possible. For this reason, in modern installations, instead of single devices, systems of rotary coolers are used, for example, three rotary coolers, to which chipboards are fed in series.

In relation to a particleboard, the invention allows to radically reduce the content and emission of formaldehyde without resorting to significant changes in the actual technical and technological conditions common in factories for the manufacture of such boards. The specified result is achieved regardless of the equipment of the production line, the parameters of the pressing process, timber and chemicals. The solution to the problem described above allows you to stabilize the hygienic quality of particle board. Due to the possibility of using resins characterized by an increased molar ratio of formaldehyde to urea, this solution provides the production of a plate of the indicated type, characterized by special hygienic quality, as well as higher efficiency in the production of particle boards. Compared to particle boards made in the usual way, i.e. with cooling after pressing, the technical applications of the present invention during testing and testing under conditions similar to industrial, showed a decrease in the content and emission of formaldehyde, including even by 70%. Short-term holding parameters before cooling, i.e. temperature and time are set depending on the expected level of formaldehyde content and emission, taking into account the characteristics of the adhesive resin and the purpose of the products.

List of drawings

Next will be presented several practical examples of the invention, illustrated by drawings.

Figure 1-3 shows a comparable diagram of the hygienic properties of particle boards made in the usual way and by the method according to the invention.

Information confirming the possibility of carrying out the invention

Example 1

Urea-formaldehyde adhesive resin with a molar ratio of urea to formaldehyde of 1.0: 1.5 was used for the manufacture of particle board. The curing agent was ammonium nitrate. The pressing temperature of the chipboard was 205 ° C with a specific pressing time of 6 s / 1 mm of the thickness of the specified board.

For a plate of the type under discussion, cooled, as usual, after pressing, the formaldehyde content and emission were 10.3 mg / 100 mg of a fully dried plate (p.p.p.) and approximately 14.9 mg / 1 kg of completely dried, respectively slabs. In the method of the invention, the curing agent addition to the adhesive on the surface layers was reduced by 50%.

According to the invention, the plate was kept for 16 hours before cooling; the temperature in the inner layer of the chipboard during picking for short-term aging was 95-100 ° C. The formaldehyde content and emission decreased, respectively, to 4.1 mg / 100 mg of the completely dried plate and 8.1 mg / 1 kg of the completely dried plate. Thus, the content and emission of formaldehyde after aging changed for the better, and other properties of particle board remained at the same level as in conventional products. This is illustrated in figure 1, where "1" and "2" characterize the values, respectively, for a plate, aged before cooling, and for a plate made in the usual way (cooled after pressing).

Example 2

An adhesive resin with a urea to formaldehyde ratio of 1.0: 1.2 was used for sizing wood particles. The curing agent used contained known formaldehyde binding agents. Pressing was carried out at 218 ° C and a specific pressing time of 11 s / 1 mm of the thickness of the chipboard. For a particle board manufactured in the usual way, the formaldehyde content and emission were respectively 4.50 mg / 100 mg of a fully dried board and 6.8 mg / 1 kg of a fully dried board. In the case of short-term aging for 8 hours following pressing, but before cooling, with the temperature of the inner layer of the particleboard 80-85 ° C, the content and emission of formaldehyde decreased, respectively, to 2.0 mg / 100 mg of a completely dried plate and 5.6 mg / 1 kg of a fully dried plate. The degree of swelling of the chipboard after soaking in water decreased by about 25%. The hygienic quality of a particleboard made according to the described example is illustrated in FIG.

Example 3

Urea-formaldehyde-melamine resin with ammonium chloride was used as a curing agent. The plate was pressed at 185 ° C and a specific pressing time of 80 s / 1 mm plate thickness. In a plate chilled prior to normal aging, the formaldehyde content and emission were respectively 8.4 mg / 100 mg of a fully dried plate and 12 mg / 1 kg of a completely dried plate. In the case of short-term curing for 6 hours, after pressing, but before cooling, with a temperature of the inner layer of the plate 90 ° C, the content and emission of formaldehyde decreased, respectively, to 5.9 mg / 100 mg of completely dried plate and 9.7 mg / 1 kg of completely dried plate. Other properties, including the results of the V 100 water resistance test, have not changed. The hygienic quality of the slab made according to the described example is illustrated in FIG.

Claims (5)

1. A method of manufacturing a particleboard, including the step of heating and pressing, characterized in that the particleboard after pressing, but before cooling, is subjected to aging at a temperature of from 80 to 100 ° C for a period of time from 6 to 16 hours 2. The method according to claim 1, characterized in that in the pressing device, a layered system is processed having a base plate and a film-like layer impregnated with resin, with temperature and pressure on both sides so that the layered system is thereby glued together. 3. The method according to claim 1 or 2, characterized in that the panels are produced from chipboard with a groove or protrusion at each of the outer edges. 4. A method of reducing the formaldehyde content in a particle board and separating it from a particle board, carried out in the process of manufacturing a particle board, including the use of aminated adhesive resins, adding curing agents, pressing the plate in presses of continuous or continuous type and cooling the plate characterized in that the chipboard after pressing, but before cooling, is subjected to short-term aging at a temperature of from 80 to 100 ° C for a period of time from 6 up to 16 hours, depending on the expected level of reduction in the content and emission of formaldehyde and the used parameters of the manufacturing process. 5. The method according to claim 4, characterized in that add substances that bind formaldehyde.

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