EP1688230B1 - Method for continuous manufacturing of fiberboards from wood - Google Patents

Abstract

Method involves fibers, glued with adhesive containing mainly phenolic components. Dosage of solid resin applied on dry wood is less than 5 percent. Pressed material mat (8) is inserted in continuously working press (6) and compressed at start with maximum specific pressure from 2.5 to 5.5 N>mm2> and hardened to fiber board (11). Fiber boards are warm stacked and supplied to heat treatment at over 60[deg]C. An independent claim is also included for the equipment for execution of the method.

Description

The invention relates to a method for the continuous production of wood-based panels according to the preamble of claim 1.

A process for the continuous production of wood-based panels, in particular plates with a closed plate surface on both sides in the thickness range of 1.5 - 6 mm in the dry process is known. For this purpose, a mat formed from a spreading station is sprayed with water after the pre-pressing and the mat trimming on the top of the mat. Often, the molding tape on which the mat is scattered, sprayed with water. The lignocellulosic particles have a moisture content below 15%, as a rule, the moisture content of the mat is around 9%. A higher humidity can not be adjusted, otherwise it will burst in the hot press. The Platzer are caused by a high vapor pressure, which in turn has its cause in the high humidity. At a higher humidity than 15% a sieve would have to be used in the hot press for evaporation. The associated screenprint is disturbing and must be sanded. By spraying it is achieved that in the hot press a closed plate surface of high density is formed, wherein the density maximum is close to the plate surface. The water on the mat is partly taken up by the lignocellulosic particles which are in the outermost layer of slabs. The bound moisture of these particles increases. Due to the increase in humidity, the particles during hot pressing after heating to just over 100 ° C are very soft and flow under the specific pressure. So that the lignocellulose particles do not stick to the sprayed forming tape, release agent is added to the spray water or the release agent is sprayed directly onto the forming belt. The release agent makes it possible to spray a larger amount of water onto the forming belt without the particles sticking to the forming belt. The cost of the release agent per m ² produced plate are significant.

Dry-process adhesive consumption is significantly higher than in semi-dry and wet processes, as dry-bonded hydrogen bonds can not be used in the same way. In the case of the production of fibreboards with a moisture content of more than 15% and a maximum of 35% - the so-called semi-dry process - the mat is introduced on a wire belt in the press. The upper side of the mat and partly the sieve is additionally sprayed with water to a to obtain a closed plate surface. Unpolished fibreboards with densities above 800 kg / m ³ and thicknesses below 6 mm from the semi-dry and wet process can be directly painted on the top of the board, without a very large amount of paint per m ² plate is necessary. The cause of the low paint consumption lies in the closed disk surface. The closed plate surface also improves the leveling properties of the paint on the plate surface. However, plates from the semi-dry and wet process can only be produced to a maximum thickness of 6 mm and are characterized by a very low adhesive consumption in addition to the closed surface.

With the generic DE-A-100 24 543 is a process for the production of wood-based panels, such as chipboard and fiberboard, especially fiberboard made of wood and other lignocellulosic materials according to the dry process has become known. It is formed from a scattering station on a continuously moving mold belt offset with a binder Pressgutmatte which is cured after introduction between a continuously operating press using pressure and heat to form a strand of board or an endless wood-based panel. Due to the special construction of the pressed material mat, it is possible to save adhesive and to improve the deaeration of the pressed material mat during compaction.

With CA-A-12 13 707 has become known a method for the production of material plates, in which the material plates are suitable after production in damp or inappropriate environment compared to the conventional material plates less swell. For this purpose, in the production of the material plate with a phenol-formaldehyde glue or with an isocyanate glue, it is subjected to a second temperature application after the usual temperature treatment at about 210 ° C. for producing a material plate. In this case, temperatures of 230 ° to 270 ° Celsius apply, which is introduced into at least one surface side and / or on the narrow sides. Among other things, this treatment ensures that the material plate has improved strength values.

With EP 0 365 708 A1 For example, there has been known a method of producing wood-based or fibrous articles in which the articles are stored at elevated temperature for a period of time after hot pressing and before cooling to reduce the level of free formaldehyde. The application of the method makes it possible to produce articles bound with formaldehyde, which no longer emit harmful gases after the heat treatment.

The object of the present invention is to provide a method by which dry-process wood-based panels are manufacturable, and with this method, the semi-dry and wet processes of fiberboard manufacture can be replaced by a more environmentally friendly and less costly dry process with low adhesive usage.

The solution to this problem is that the fibers glued with an adhesive containing predominantly phenolic components in a blowpipe and / or in a mixer, wherein the dosage is less than 5% of solid resin atro wood, the mat is introduced into the continuous press and at the beginning with maximum specific Pressure of 2.5 N / mm ² to 5.5 N / mm ² compacted and cured to a fiber board with double-sided closed surfaces and the finished plates are warm stacked and fed to a heat treatment at about 60 ° C.

It has now surprisingly been found that in a continuous press plates with surfaces closed on both sides and low adhesive consumption can be produced.

As a particularly favorable in terms of adhesive consumption, a combination of Blasrohrbeleimung and mixer gluing has been found. In the blowpipe gluing and / or in the mixer, formaldehyde - a crosslinking agent - can be added to the wood particles, which react with the formed bondable substances and thus also contribute to the reduction of the adhesive. Surprisingly, it has now been found that in a gluing of the fibers thus produced with phenol condensation adhesive, a particularly low dosage is possible. By the above measures, it is thus succeeded the dosage of Condensation adhesives, which is usually more than 10% of solid resin based on atro pulp to reduce to less than 5%.

The pressing time must be extended by at least 15% compared to the conventional drying process due to the longer curing time of the adhesive, the time-consuming activation of the bondable substances and the prolonged devolatilization. In order to avoid a large extension of the pressing time, a high hotplate temperature at the beginning of the hot pressing has proven to be favorable. When hot pressing must be noted that the maximum specific pressure above 2.5 N / mm ^2, preferably 5 N / mm ² as soon as possible after mat contact with the steel strip of the hot press is applied to the mat. This ensures that the fibers of the mat surface are compacted during the passage of an optimum softening state, whereby a closed plate surface is formed.

With this method, it is now possible to produce panels with a very well-closed surface on the top and a well-closed surface on the bottom. It is possible to produce sheets without applying release agent to the forming belt, which significantly reduces the production cost of the equipment. The panels can even be painted directly on both sides without having to sand them first. Due to the high specific pressure at the beginning of the hot pressing from 2.5 to 5 N / mm ² , a closed plate surface is achieved. In addition, the density maximum is increased by the moistening by up to 150 kg / m ³ and the density maximum is closer to the plate surface (lower pressing skin). The increased density maximum improves the bending properties of the plate.

In the drawing, the system for carrying out the method is shown in side view. It is now possible to limit the press length to less than 15 m. By using a very short continuous press 5 under 15 m in length, no pre-press of the usual kind is necessary due to the low feed rate below 200 mm / s for plates 10 thicker than 10 mm and waiving a width adjustment. Instead, in the production of fiberboard 11 with the moistening apparatus 1, 3, 4 and 10 is very easily pre-compacted and moistened the upper mat half. The pre-compaction should be carried out with fibers to a density of about 70 kg / m ³ , ie about 30% of the original bed height. For this purpose, only a specific pressure of a maximum of 0.3 N / mm ^{2 is} necessary, so that the precompacting and preheating 4 can be performed in cost-effective lightweight construction.

By these measures, it is possible to produce a thin HDF boards and on the other hand, thick MDF boards, the investment amount for the plant compared to a conventional MDF plant with prepress and star turners is very low. The pressing factor of very thin plates 11 is significantly higher for long presses due to the limitation in the feed rate than for short presses. For long continuous presses 6, the feed is limited by the final production and by the risk of blowers in the press inlet.

When adding the Phenolleims in the blowpipe must be taken into account that Phenolleim, unlike Aminoplastharzen at the end of the blowpipe (not shown) must be planned shortly before the dryer in the pipe. The Phenolleim leads to caking on the inner wall of the blower tube, which can only be removed mechanically. In Aminoplastleimen the caking is degraded by hydrolysis with time during operation, without mechanical removal is necessary. It has also proven advantageous for trouble-free operation that a switch is installed shortly after dosing so that it is possible to clean one pipe and guide the fiber flow through the other.

The dark plates thus produced must be thermally treated after the hot pressing. In particular, the plates are passed through a heat channel or stacked warm in a heated hall. By the heat treatment of the fiberboard 11 at temperatures between 110 ° C and 200 ° C after the continuous press, the bonding of the individual fibers is increased, whereby the bending properties and the swelling values improved become. To carry out the heat treatment, the fiber plates 11 are warmly stacked or pulled as a package through a heat channel.

The device for introducing steam in each case consists of a steam box 5 and 10, are introduced to the mat side openings, for example in slot shape. The steam boxes 5 and 10 can be additionally heated to avoid condensate or a condensate separator is connected. The steam boxes 10 are installed in the wire 9 directly in front of the inlet of the continuous press 6. The steam box 10 should be installed as close as possible in front of the continuous press 6 to avoid precuring of the adhesive. If the moistening is to take place also on the upper side of the mat 8, an upper steam box 5 with a further circulating screen belt must be used. In addition, if the system is still running without pre-press, then must be precompressed before the steam box 5 on a short distance with a Vorverdichtungs- and preheating 4. For this, the sieve can be guided over rollers.

List of Reference Numerals: DP 1327EP

1.

Water spray

Second

spreader

Third

Water spray

4th

Pre-compression and preheating device

5th

A steamer

6th

Continuously working press

7th

forming belt

8th.

mat

9th

screen belt

10th

A steamer

11th

fibreboard

Claims (6)

1. Method for the continuous manufacture of wood material boards, such as chip and fibre boards (11), in particular fibre boards made of wood and other lignocellulose-containing materials, using the drying method in which there is formed from a scattering station (2) onto a continuously moving shaping belt (7) a pressed material mat which is mixed with binder and cured, after insertion between the steel strips, which are guided so as to encircle an upper and lower frame part, of a continuously operating press (6) and with the application of pressure and heat, to form a train of boards or an endless wood material board, characterised by the combination of the following method steps:

   1.1 the fibres are glued using an adhesive containing predominantly phenolic components, less than 5 % solid resin being added based on absolutely dry wood,

   1.2 the pressed material mat is introduced into a continuously operating press (6) and initially compacted with maximum specific pressure of from 2.5 N/mm² to 5.5 N/mm² and cured to form a fibre board, and

   1.3 the fibre boards (11) are stacked warm and supplied to a heat treatment at above 60 °C.
2. Method according to claim 1, characterised in that the fibre boards (11) are heat-treated preferably at above 100 °C.
3. Method according to either claim 1 or claim 2, characterised in that the stacked fibre boards (11) are drawn through a heating channel during the heat treatment.
4. Method according to either claim 1 or claim 2, characterised in that the stacked fibre boards (11) are subjected to the heat treatment in a heated hall.
5. Method according to claim 1, characterised in that the fibre boards (11) are destacked after leaving the continuously operating press without passing through a cooling star turner.
6. Method according to claim 1, characterised in that the fibres are glued preferably with an addition of less than 2 % solid resin based on absolutely dry wood.

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