EP1323509A1 - Method for continuous manufacturing of fiberboards from wood - Google Patents

Abstract

Continuous production of woodchip or woodfiber panels, involves application of adhesive to boiled wood fibers and compression of a mat of scattered and wetted fibers on a conveyer belt. <??>Woodchips are boiled at NOTLESS 12bar, preferably NOTLESS 16bar for NOTLESS 3min. ≤ 5% of phenolic based adhesive is then applied to the chips in a blowing tube and/or in a mixer and the chips scattered(2) onto a conveyer belt(7) to form a mat(8). The mat, with a moisture content of ≤ 15% just prior entering a continuously working heated press, is sprayed(3) with 5-80g/sq m water on the upper side while being steamed(10) on the lower side. Initial pressure on the mat in the press(6) is 2.5-5.5m/sq mm so that the mat is compressed to form a panel(11) with densified faces on both sides. <??>An Independent claim is made for a the process plant which comprises a woodchip boiler, an adhesive applicator with blowing tube and/or mixer, a water spray unit(1), chip scattering machine(2) to form a mat on a conveyer belt(7), a water spray unit(3) for wetting the upper side of the mat, precompressor and preheater(4), a steamer(5) with or without a filter ribbon, a steamer(10) and circulating filter ribbon(9) on the mat lower side and a continuously working press(6).

Description

The invention relates to a method for the continuous production of Wood-based panels according to the preamble of claim 1 and a plant for performing the method according to claim 17.

A process for the continuous production of wood-based panels, especially of plates with a closed plate surface on both Pages in the thickness range of 1.5 - 6 mm in the dry process are known. For this purpose, a mat is formed from a scattering station after the pre-pressing and sprayed the mat trimming with water on the mat top. Often, the ribbon on which the mat is sprinkled is also watered sprayed. The lignocellulosic particles have a moisture content below 15% As a rule, the mat's moisture content is around 9%. A higher humidity can must not be set, otherwise the hot press will burst. The Blowouts are caused by a high vapor pressure, which in turn has its cause in the high humidity. At a humidity higher than 15% a sieve in the hot press would have to be used for evaporation. The associated screen print is annoying and must be sanded become.

The spraying ensures that a closed one in the hot press High density plate surface is formed, the density maximum is close to the plate surface. The water on the mat will partly from the lignocellulosic particles, which are in the outermost Plate layer are included. The bound moisture of these particles increases. Due to the increase in moisture, the particles become hot pressed after heating to just over 100 ° C very soft and flow under the specific pressure.

To prevent the lignocellulosic particles from sticking to the sprayed forming belt, 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 of} plate produced is considerable. However, the amount of spray that is absorbed by the forming belt through the particles lying on the forming belt is limited. The water has to be drawn into the mat against gravity by capillary forces. This different application quantity at the top and bottom often causes the plates to bend after leaving the hot press. In order to avoid this curvature, it is then necessary to spray less onto the upper mat surface. So far, it has not been possible to produce boards with a comparable closed board surface as in the semi-dry and wet process in the dry process. The plates often have to be reground to remove the press skin. So much must be sanded from the plate that the maximum density is close to the surface. On the one hand, grinding causes very high operating costs and, on the other hand, considerably more material has to be used to produce the same plate.

The adhesive consumption in the dry process is much higher than in Semi-dry and wet processes, since the hydrogen bonds in Drying processes cannot be used in the same way. The The boiler temperature in today's systems is below 190 ° C (12 bar Vapor pressure) to prevent the plates from having a dark color.

In the case of the production of fiberboard with a moisture content of over 15% and a maximum of 35% - the so-called semi-dry process - the mat is introduced into the press on a screen belt. The upper side of the mat and partly also the sieve is additionally sprayed with water in order to obtain a closed plate surface. Ungrinded fiberboard with densities over 800 kg / m ³ and thicknesses under 6 mm from the semi-dry and wet processes can be coated directly on the top of the board without the need for a very high amount of paint per m ^{2 of} board. The reason for the low paint consumption is the closed plate surface. The closed surface of the board also improves the flow properties of the paint on the board surface. Sheets from the semi-dry and wet processes can only be produced in a maximum thickness of up to 6 mm and are characterized by a very low adhesive consumption in addition to the closed surface.

The object of the present invention is now to specify a method and a To create plant with the wood-based panels with closed Surface can be produced using the dry process and with this process the semi-dry and wet process of fibreboard production by one more environmentally friendly and cheaper drying process is to be replaced.

The solution to this problem for the method is that the wood chips are cooked at over 12 bar, preferably at 16 bar, with a residence time of more than 3 minutes. The fibers are then glued with an adhesive containing predominantly phenolic components in a blowpipe and / or in a mixer, the dosage being below 5% solid resin based on dry wood, the scattered mat with a moisture content of ≤ 15% is immediately before the continuously working Press is moistened by water spraying from 5 to 80 g / m ² on the top of the mat and by steam in an appropriate amount on the underside of the mat and the mat thus prepared is introduced into the continuously operating press and at the beginning with a maximum specific pressure of 2.5 N / mm ² to 5.5 N / mm ² compressed and cured to a fiberboard with surfaces closed on both sides.

The solution for a system according to the method is characterized by following combination arranged in the working direction: on Wood chip cooker, a gluing device made from a blowpipe and / or mixer, a ribbon water sprayer, a spreader to form a Mat on a continuously moving forming belt, one Water spray device for moistening the top of the mat, if necessary a pre-compression and preheating device, an evaporation device with or without sieve belt for the top of the mat, a steaming device for the underside of the mat, with one running around as a mat feed path Screen belt is steamed and a continuously working press.

It has now surprisingly been found that through a targeted Pretreatment of the wood chips in combination with a water spray and steam moistening the mat as well as the pressing pressure in a continuous working press plates with surfaces closed on both sides and low adhesive consumption can be produced.

The process must be carried out so that the wood chips at high temperature in the cooker (190 to 230 ° C, steam pressure 12 to 16 bar) and long dwell times (greater than 3 minutes) are pretreated thermally that glucinable substances arise from the hemicelluloses, the lignin the fiber surface is activated and a very open pulp without a large proportion of coarse fiber bundles. Through this Pretreatment creates dark fibers and is therefore independent of the Use a dark glue on dark sheets. The wood chips are steamed in the cooker preferably at 200 to 210 ° C for 4 minutes. With this combination, on the one hand, it becomes sufficiently bondable Substances are formed and the lignin is activated and secondly the The strength of the fiber is not reduced too much. The addition of acid in the Cooker for surface activation of the fibers has proven beneficial to the Gluing exposed. After defibration in the refiner, the Wood particles in the blowpipe glued and dried to moisture below 15%. As one has been particularly favorable in terms of adhesive consumption Combination of blowpipe glueing and mixer gluing highlighted. In The blower tube glue and / or in the mixer can formaldehyde - a crosslinker - The wood particles are added, which with the formed stickable substances reactions and thus also to Adhesive reduction contributes. Surprisingly, it has now been shown that when the fibers thus produced are glued with phenol condensation adhesive a particularly low dosage is possible. By the above measures have thus succeeded in dosing Condensation adhesives, usually based on over 10% solid resin atro fiber is to reduce to less than 5%.

It has proven to be another advantage of the higher cooker temperature that the fibers thus produced tend to be closed when hot-pressed Plate surface run as fibers that are cooked at low temperature provided the fibers are sufficiently moistened before hot pressing become. The moistening is according to the invention on the top of the mat with a water spray and on the bottom with a Steam humidification performed. The closed surfaces achieved is based on the combination of very well-digested fiber and Humidification returned. The fibrous material contains hardly any fiber bundles. Fiber bundles are more rigid than individual fibers. You can do not nestle into individual cavities as well as individual fibers. By pretreatment at high temperature will also increase the rigidity of the individual fibers reduced, so that the individual fiber at the Hot press softens more easily.

The mat is moistened on the underside with a targeted, flat introduction of steam immediately before the hot press. The steam should have a pressure of 1.01 to 1.3 bar (absolute), preferably 1.01 bar and should be as saturated or as little as possible overheated. The steam pressure must not be too high, otherwise the mat will lift off the sieve belt due to the steam. The amount of steam introduced is measured and regulated. Due to the condensation of the steam, the mat moisture is increased by approx. 5% - depending on the initial moisture of the mat and the mat temperature. If, for example, a 3 mm thick fiberboard with a density of 1000 kg / m ^{3 is to be} produced, the top of the mat can be sprayed with 20 g / m ^{2 of} water and the same amount of moisture is applied to the underside with the introduction of 20 g / m ^{2 of} steam fed. 400 g of wood are moistened by the steam and heated from 35 ° C to almost 100 ° C. About 13% of the total mat thickness is therefore moistened by the steam. This means that the moisture is still limited to the outer area of the mat. To avoid bending, the amount of steam can be increased slightly compared to the amount of water sprayed. Due to the high temperature of the wood particles, the condensed water is absorbed by the wood extremely quickly, so that an almost similarly closed surface is created on the underside as on the top, the density maximum is also increased and the density maximum is closer to the plate surface.

In the course of the method according to the invention, the moisture content must be higher than that in the conventional drying method, preferably 12 to 14%. Due to the higher humidity, the fibers are less stiff during hot pressing, which increases the contact area between the fibers. The larger contact area is important in order to obtain an adhesive connection over the activated fiber surface and also promotes the formation of hydrogen bonds. Compared to the conventional drying process, the pressing time must be extended by at least 15% due to the longer curing time of the adhesive, the time-consuming activation of the adhesive substances and the longer evaporation. In order to avoid a large extension of the pressing time, a high heating plate temperature at the beginning of the hot pressing has proven to be favorable. During hot pressing, it must be ensured that the maximum specific pressure above 2.5 N / mm ^2, preferably 5 N / mm ² , is applied to the mat as quickly as possible after contact with the steel strip of the hot press. The result of this is that the fibers of the mat surface are compacted while passing through an optimal softening state, as a result of which a closed plate surface is created.

• Partikel an der Oberfläche mehr plastifiziert und zerflossen
• Dichtemaximum ist größer
• Dichtemaximum liegt näher an der Plattenoberfläche
• Presszeit wird verkürzt
• Stahlband wird eher sauber

Due to the high specific pressure at the beginning of the hot pressing of 2.5 to 5 N / mm ² and the moistening, a very closed plate surface is achieved. In addition, the maximum density is increased by the moistening by up to 150 kg / m ³ and the maximum density is closer to the surface of the plate (less pressing skin). The bending properties of the plate are improved by the increased density maximum. The spraying also has the effect that the pressing time is shortened by 2 - 10% due to the steam boost effect. The steel strip is also kept clean by spraying. In summary, 5 effects can be demonstrated:

• Particles on the surface more plasticized and melted away
• Maximum density is larger
• The maximum density is closer to the plate surface
• Pressing time is reduced
• Steel band is rather clean

The steam is passed through a sieve belt, which consists of a steam-resistant Material such as steam-resistant plastic should consist of a steam box into the mat. The transfer belt should be in the Press to be run as a screen belt. On this transfer belt, the Mat transported into the press.

This process can now be used to close panels with a very good seal Surface on the top and well closed surface on the Bottom are produced. It is possible to produce plates without that release agent is applied to the forming belt, which is the Production costs of the plant significantly reduced. The plates can even can be painted directly on both sides without having to sand them beforehand.

A combination of spraying and subsequent dampening with steam on the top and bottom of the mat is also possible. For example, the invention can be carried out in such a way that 20 g / m ^{2 of} water are sprayed on the top and 15 g / m ^{2 of} steam is introduced and on the underside 5 g / m ^{2 of} water are sprayed onto the forming belt and 30 g / m ^{2 of} steam are introduced becomes. The more steam is moistened and preheated, the more the pressing speed can be increased. Depending on the requirements of the surface, an optimal compromise between moistening by spraying and steam introduction must be found for each plate range. In addition, the hot press can be designed in such a way that the press plate temperature for the upper and lower heating plate can be set differently, which means that with only steam humidification from below and one-sided spraying from above, uniform heating through a higher upper press plate temperature can be achieved.

It has now surprisingly been found that the wood particles or the fibers do not stick to the plastic sieve belt. In the The sieve belt was installed immediately before the steam box preheated to over 100 ° C so that no steam condenses in the sieve belt. Probably due to the heating of the sieve belt and that Blow through the steam and glue the wood particles with the sieve belt avoided.

In the drawing, the plant for performing the method is shown in side view. An advantage with regard to the system is that the press length can be limited to less than 15 m. By using a very short continuous press 5 of less than 15 m in length, a pre-press of the usual type is not necessary due to the low feed rate of less than 200 mm / s for plates 10 thicker than 10 mm and the absence of a width adjustment. Instead, in the production of fiberboard 11, the dampening apparatus 1, 3, 4 and 10 is very slightly pre-compressed and the upper half of the mat is also moistened. In the case of fibers, the pre-compression should take place to a density of about 70 kg / m ³ , that is about 30% of the original bed height. This only requires a specific pressure of a maximum of 0.3 N / mm ² , which means that the pre-compression and preheating apparatus 4 can be designed in an inexpensive, lightweight construction.

These measures make it possible, on the one hand, to thin HDF panels and on the other hand also to produce thick MDF boards, whereby the Investment amount for the plant compared to a conventional one MDF system with pre-press and star turner is very low. The press factor is very thin plates 11 in long presses due to the limitation in the Feed speed significantly higher than with short presses. At long continuously operating presses 6 is the feed through the final production and limited by the risk of blowouts in the press inlet.

When adding phenol glue in the blowpipe it must be taken into account that Phenol glue in contrast to aminoplast resins at the end of the blowpipe (not shown) must be injected into the tube shortly before the dryer. The Phenol glue leads to caking on the inner wall of the blowpipe, which only can be removed mechanically. With aminoplast glue, the Caking by hydrolysis with time reduced during operation without that mechanical removal is necessary. Beneficial for one Trouble-free operation has also been shown to occur shortly after dosing a switch is installed so that there is the possibility of a pipe clean and pass the fiber stream through the other.

The dark panels produced in this way must be thermally after hot pressing be treated. In particular, the plates are replaced by a Run heat channel or piled warm in a heated hall. Through 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 increased, which improves the bending properties and the swelling values become. The fibreboards are used to carry out the heat treatment 11warm piled up or pulled as a package through a heat channel.

The device for introducing steam each consists of a steam box 5 and 10, on which openings, for example in the form of slots, are introduced on the mat side. 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 screen belt 9 directly before the inlet of the continuous press 6. The steam box 10 should be installed as close as possible in front of the continuously operating press 6 in order to prevent the adhesive from pre-curing. If moistening is also to take place on the top of the mat 8, an upper steam box 5 with a further rotating sieve belt must be used. If the system is also executed without a pre-press, then the steam box 5 must be pre-compressed over a short distance using a pre-compression and preheating device 4. To do this, the sieve can be guided over rollers.
A typical system with a spreading machine 2, pre-press, a continuously operating press with a length greater than 15 m, cooling star turner and stacking requires high investment costs.

Reference symbol list: DP 1272 EP

1.

Water spray

Second

spreader

Third

Water spray

4th

Pre-compression and pre-heating device

5th

A steamer

6th

Continuously working press

7th

forming belt

8th.

mat

9th

screen belt

10th

A steamer

11th

fibreboard

Claims (20)

Process for the continuous production of wood-based panels, such as chipboard and fiberboard, in particular fiberboard made of wood and other lignocellulosic materials, using the dry process, in which a spreading station is formed from a scattering station onto a continuously moving forming belt an upper and lower frame part of the continuously guided steel strips of a continuously operating press is hardened to a sheet strand or an endless wood-based panel using pressure and heat, characterized by the combination of the following process steps: 1.1 the chips are cooked at over 12 bar, preferably at 16 bar, with a dwell time of more than 3 minutes, 1.2 the fibers are glued with an adhesive containing predominantly phenolic components in a blowpipe and / or in a mixer, the dosage being less than 5% solid resin based on dry wood, 1.3 the scattered mat with a moisture content of ≤ 15% is moistened immediately in front of the continuously operating press by water spraying from 5 to 80 g / m ² onto the upper side of the mat and by steam in an appropriate amount onto the underside of the mat 1.4 the mat prepared in this way is introduced into the continuously operating press and initially compressed with a maximum specific pressure of 2.5 N / mm ² to 5.5 N / mm ² and cured to form a fiberboard with surfaces closed on both sides. A method according to claim 1, characterized in that the mat has a moisture content of 12 to 14%. Method according to claims 1 and 2, characterized in that the mat on the top and or the forming belt is sprayed with water and then moistened with steam from both sides. Process according to claims 1 to 3, characterized in that 20 g / m ^{2 of} water is sprayed onto the top of the mat and 5 g / m ^{2 of} water is sprayed onto the shaping belt and 30 g / m ^{2 of} steam are introduced into the mat on both sides becomes. Method according to one or more of claims 1 to 4, characterized in that the wood chips are steamed in the cooker from 16 bar to 19 bar over a period of 4 minutes. Process according to one or more of Claims 1 to 5, characterized in that steam is introduced into the mat at a pressure of 1.01 to 1.3 bar, preferably 1.01 bar. Method according to one or more of claims 1 to 6, characterized in that the steam to be introduced into the mat is as saturated or as little as possible heated. Method according to one or more of claims 1 to 7, characterized in that acid is fed into the cooker when the wood chips are cooked. Method according to one or more of claims 1 to 8, characterized in that formaldehyde is added to the wood particles as crosslinking agent during the gluing. Method according to one or more of claims 1 to 9, characterized in that the mat is sprayed with 20 g / m ^{2 of} water on the upper side and 15 g / m ^{2 of} steam is introduced and 5 g / m ^{2 of} water on the underside onto the forming belt sprayed and 30 g / m ² steam is introduced into the mat. Method according to one or more of claims 1 to 10, characterized in that the screen belt is heated to over 100 ° C before the steam is introduced. Method according to one or more of claims 1 to 11, characterized in that additionally the outer outer mat layer is specifically moistened with steam within a light pre-compression and preheating device. Method according to one or more of claims 1 to 12, characterized in that the forming belt is sprayed with water and / or release agent. Method according to one or more of claims 1 to 13, characterized in that phenol-formaldehyde resin with a dosage of 4% solid resin based on dry fibrous material is used as the adhesive. Method according to one or more of claims 1 to 14, characterized in that the adhesive is added to the end of the blowpipe just before the dryer and that two blowpipes are used via a switch. Method according to one or more of claims 1 to 15, characterized in that the finished panels are stacked warm and additionally stored at above 60 ° C, preferably above 100 ° C. Plant for performing the method according to claims 1 to 16, arranged in the working direction, comprising one Wood chip cooker (not shown), a gluing device Blower tube and / or mixer (not shown), a ribbon water spray device (1), spreader (2) to form a Mat (8) on a continuously moving forming belt (7), one Water spray device (3) for moistening the top of the mat, if necessary, a pre-compression and preheating device (4), a steaming device (5) with or without a sieve for Mat top, an evaporation device (10) for the mat underside, whereby through a sieve belt running as a mat feed belt (9) is steamed and a continuously operating press (6). Installation according to claim 17, characterized in that the press length of the continuously operating press (6) is less than 15 m and the installation is carried out without a pre-press. Installation according to claims 17 and 18, characterized in that the plates (11) can be stacked after leaving the continuously operating press (6) with a pressing length of less than 15 m without having to pass through a cooling star turner. Plant according to claims 17 to 19, characterized in that a different press plate temperature is set in the continuously operating press (6) above and below.

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