EP1059152B1 - Process for producing a workpiece from cellulose fibers, especially in the form of a fibre board - Google Patents

Abstract

Water is added to lignocellulose containing fibers(2) to effect swelling and until the weight ratio of water to fibers is 1:1. The wet fibers(9) are scattered to form a preform(11) which is calibrated and then dried without any external deformation to avoid relative movement of fibers.

Description

The invention relates to the production of a shaped body based on lignocellulose-containing fibers. In particular, the invention relates to a method for producing a fiberboard from wood fibers, wherein the fiberboard may have a low density. Such a fiberboard can be used in particular as insulating material. But it is also not excluded to use them as a construction element. A typical representative of fiberboards to which the invention relates are so-called wood soft fiberboards.

For the production of soft wood fiber boards, the so-called wet process is known. Wood fibers produced by grinding, grinding or squeezing force are converted into an aqueous suspension, which typically contains only 2 to 3% by weight of wood fibers. This suspension with the maximum swollen wood fibers is applied to a sieve belt, through the drainage first by gravity and then via various suction and Vorpreßeinrichtungen done. The thereby achievable degree of dewatering is limited by the water storage capacity of the swollen wood fibers and the only small permissible compressive forces down, as an insulating material is to be produced with low density. The obtained from the pre-dewatering of the suspension mat of wet wood fibers as a preform of soft wood fiber boards is then dried without pressure. During drying, the individual wood fibers shrink to each other, even if no binder was added. If a binder is added, make sure that this fixes to the wood fibers, since it is otherwise sucked or pressed with the water of the starting suspension.

A wet process as described above is known from GB 1006293 A. Furthermore, a so-called dry process for the production of wood fiber boards is known. The fibers for this are obtained in the same way as for the wet process. Subsequently, however, they are not transferred to a suspension, but in current dryers, ie in flight, dried down to a level which later allows easier drying. The moisture of the wood fibers are typically less than 10%. Before or after drying, a binder is added to the wood fibers, which glues the individual wood fibers together after the subsequent forming of the wood fibers into a mat as preform fiber boards and when pressing the mat to a fiberboard. These dry-process fibreboards, in a density range of 900 to 450 kg / m ^{3, are} referred to as High Density Fiberboard (HDF), Medium Density Fiberboard (MDF), Lightweight and Ultralight Fiberboard (ULF). Characteristic of fibreboards after the dry process is that even with ultra-light fiberboard due to the still relatively high density no good insulation effects are achieved.

Furthermore, a so-called semi-dry process is known in which the initially dried fibers are moistened again after the formation of a mat and then hot-pressed.

In this way, a smooth surface is achieved in the fiberboards produced. Another method for the production of fiberboard is known from DE 196 74 240 A1. Here, a wood fiber board having good insulating properties is prepared by mixing wood fibers whose moisture content remains unchanged after a refining process subsequent to a defibration process, with a binder and spreading with a spreader on a forming station to form a mat as a preform of the fiberboard. The mat is preformed in width and basis weight to be formed and cured in thickness after activation of the binder to form a fiberboard. The activation of the binder is effected by heat, for example by hot steam. The binder should be added to the moist wood fibers in a dry state. Disadvantages of the known method are that by the thickness deformation of the mat during curing to the fiberboard, the natural Aneinanderfestschrumpfen the wood fibers, which is utilized in the wet process, can not take place by changing relative to the change in thickness relative allocation of the individual wood fibers. For this reason, binders must be added in the known method. However, the addition of the binder in dry form is unfavorable, since with light fiberboard, i. H. in the case of fibreboards having a large free volume, the binder which can be added in dry form can be arranged in the free volume and is thus available only to a small extent for an effective bonding of the wood fibers at their points of contact.

The invention has the object of demonstrating an economically feasible process for the production of moldings based on lignocellulose-containing fibers, in particular usable as insulating fiber boards, which specifically exploits the solid shrinkage of the lignocellulose-containing fibers during drying.

According to the invention, this object is achieved by a method for Production of a molded article based on lignocellulose-containing fibers, in particular a fiber board, with the features of claim 1.

Advantageous embodiments of the method are described in the subclaims 2 to 9.

The new process uses wet, swollen lignocellulosic fibers as the starting material and forms a preform therefrom. In this case, the intermediate step is not passed over an aqueous suspension of the fibers. Rather, the wet fibers are scattered directly into a preform. This wet fiber preform is then calibrated, i. H. also adjusted in terms of their thickness. Only then does the drying of the already calibrated preform take place. In this case, the preform is no longer deformed in order to avoid a relative displacement of the individual wood fibers and thus to allow a butting shrinkage of the wood fibers during drying. The strengths of finished fibreboards achieved in this way are quite comparable to those of fibreboards which were produced by the wet process. At the same densities, they can even be significantly superior to those of wet-process wood fiber boards.

The fibers are brought to a maximum swollen state prior to molding the preform. This condition is a prerequisite for being able to fully exploit the firm shrinkage of the fibers during drying. The moisture of the fibers is thereby adjusted prior to molding to the preform so that upon preform molding there is a slight over-dampening above the fiber saturation point. The maximum weight ratio of fibers to water is 1: 1. However, it is ideal that the fibers are only slightly over-moisturized when forming the preform, in particular because the thermal drying effort for the formed and calibrated preform is thereby kept to a minimum.

In the practical implementation of the new method, the Moisture of the fibers can be adjusted before shaping the preform in a refiner downstream blowpipe. Here, the term blowpipe also includes a water vapor separator in the form of a cyclone. Thermal drying of the fibers is not provided in the new method prior to calibrating the preform.

In the new process, no binders need to be added to the fibers to obtain a stable shaped article. Alone the shrinkage of the fibers while drying ensures a stable connection of the fibers with each other.

However, to achieve improved strength values for the molded articles produced by the novel process, binders may be added to the wet fibers prior to molding to the preform. Preference is given to dispersion adhesives and natural adhesives such as starch solutions or degraded and modified starch solutions, so generally first liquid adhesives, which concentrate in particular when drying the initially over-moistened wood fibers at the contact points of the wood fibers with each other and these glue together in addition to the solid shrinkage, whereby by Harden dehydration. The concentration of such adhesives at the crossing points of the individual fibers, the efficiency based on the amount of adhesive used is very large. In particular, no adhesive is lost in the free volume of the molding or its underlying preform.

In a concrete implementation of the new process, the liquid adhesive is added to the wet fibers prior to molding to the preform in a refiner downstream blower tube.

As already indicated, the adhesive is applied in liquid form to the moist fibers. Preferably, it is sprayed onto the wet fibers.

In addition to the liquid adhesive or even in the production of moldings without binder can be added to the wet fibers prior to molding to the preform a flame retardant, a fungicidal and / or a hydrophobizing agent to adjust the properties of the molded body produced in a desired manner.

The achievable with the new method range of average apparent density is 80 to 300 kg / m ³ . The average density of the molded body is set when calibrating the preform from the wet fibers. It should be noted that the preform shrinks by the drying of the initially swollen wet fibers in their outer dimensions. That is, when calibrating the wet fiber preform, it must be calibrated to an excess that shrinks to the desired size later when the preform is being dried.

The drying of the preform from the wet fibers can be achieved by flowing in particular with hot air, which extracts the excess moisture from the preform. Heat for drying the preform may also be supplied to the preform through contact sheets. However, these contact sheets should contain openings for the removal of the vaporized moisture. Furthermore, it is necessary for a good heat transfer from the sheets to the wet preform pressing the sheets to the preform. In this case, however, the preform must not be deformed, otherwise the desired Zusammeneinanderfestschrumpfen the fibers is prevented. However, there is nothing against it if, after drying the preform for refining the surface of the shaped body, it is moistened again or moistened with a low-concentration binder solution, in order subsequently to be smoothed under the action of heat.

The invention will be explained in more detail below with reference to an embodiment and described. The figure shows a greatly simplified overview diagram of the sequence of the individual process steps in the manufacture of a fiberboard as a shaped body based on lignocellulose-containing fibers.

In a first process step 1 wood chips 2 are thermally digested with the addition of water 3 and subjected to mechanical comminution under pressure and temperature. Then a defibration in a refiner 4. The refiner 4 is followed by a blowpipe 5, in which optionally a liquid and drying by dewatering adhesive 6 can be sprayed onto the wet wood fibers. In a cyclone 7 then excess water vapor 8 is deposited. A thermal drying of the wood fibers does not initially. The wood fibers retain a slight over-moisture. However, the moist wood fibers 9 can also be scattered directly onto a belt 10 to a preform 11, which is referred to as a mat in fiberboard. The preform 11 from the moist and possibly offset with adhesive 6 wood fibers 9 is first calibrated, which is indicated by a pair of rollers 12. Subsequently, the calibrated preform 11 is dried by passing through hot air 13, which removes the moisture 14 from the preform 11. When drying the preform 11, the individual wood fibers shrink possibly together with additional bonding by the adhesive 6 to each other. Here, the outer dimensions of the preform 11 are still decreasing, so that the set by the pair of rollers 12 thickness of the preform 11 must be greater than the desired thickness of a later fiberboard 15, which is separable after drying of the endless strand of the preform 11. It is understood that the band 10, which is formed here over two rollers 16 circumferentially, must have openings to allow the flow through the hot air 13. The preform 11 may also be guided at its top by a further band 16 with openings. The bands 16 may also be heated to transfer heat to the preform 11 by contact, so that their drying is accelerated. The average bulk density of the finished fiberboard 15 is typically between 100 and 200 kg / m ³ . As starting material next to wood chips 2, which lead to a wood fiber board, all other materials can be used, which consist of lignocellulosic Fibers are constructed. Application can experience the fiberboard 15 in particular as insulating material. But it can also be used as a construction element at low stress. As insulating both applications for thermal insulation and impact sound insulation come into question.

Other shaped bodies based on lignocellulose-containing fibers than fiberboards can be produced in a corresponding manner. This also applies to three-dimensionally structured shaped bodies. When using natural fibers and a biodegradable adhesive, for example a starch solution, they can be used as biodegradable packaging materials.

LIST OF REFERENCE NUMBERS

1 -

step

2 -

wood chips

3 -

water

4 -

refiner

5 -

blowpipe

6 -

adhesive

7 -

cyclone

8th -

Steam

9 -

fibers

10 -

tape

11 -

preform

12 -

roller pair

13 -

hot air

14 -

humidity

15 -

fibreboard

16 -

role

Claims (9)

1. Method of producing a shaped body on the basis of lingo-cellulose containing fibres (9), particularly a fibre board (15),

   - wherein the lingo-cellulose containing fibres (9) are transferred into a state in which they are swollen to a maximum extent, and the moisture of the fibres (9) is adjusted to an over-moisture up to a ratio by weight of fibres to water of 1:1;

   - wherein the wet fibres (9) are spread out to make a preform (11),

   - wherein the preform (11) made of the wet fibres (9) is calibrated, and

   - wherein the calibrated preform (11) is dried, without the preform (11) being deformed from outside after calibrating and during drying.
2. Method of claim 1, characterized in that the moisture of the fibres (9) is adjusted in a cyclone (7) arranged downstream of a refiner (4) prior to forming the preform.
3. Method of claim 1 or 2, characterized in that no binder is added to the fibres (9).
4. Method of claim 1 or 2, characterized in that a liquid binder (6) curing through loss of water, particularly a dispersion binder, is added to the wet fibres (9) prior to forming the mat (11).
5. Method of claim 4, characterized in that the binder (6) is added to the wet fibres (9) prior to forming the preform (11) in a blow line arranged downstream of a refiner (4).
6. Method of claim 5, characterized in that the binder (3) is prayed onto the wet fibres (9).
7. Method of any of the claims 1 to 6, characterized in that a fire retardant, a fungicide and/or a hydrophobing agent is added to the wet fibres (9) prior to forming the preform (11).
8. Method of any of the claims 1 to 7, characterized in that the preform (11) made of the wet fibres (9) is calibrated in such a way, that the fibre board (15) displays and average raw density of 80 to 300 kg/m³.
9. Method of any of the claims 1 to 8, characterized in that the preform (11) made of the wet fibres (9) is dried by a stream going through.

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