EP2216149A1 - Method for manufacturing chipboards - Google Patents

Abstract

The method involves forming chipping for an intermediate layer (4) and chipping for covering layers of a chip tray (1) separately. The chipping is formed from the fresh wood for external covering layer (2). The chipping is formed from the matured timber for internal covering layer (3).

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to a method for the production of chipboard using waste wood and fresh wood with the features of the preamble of independent claim 1.

The suitable resources for fresh wood for the production of wood-based materials are limited. It is therefore necessary to resort increasingly to the production of wood-based products on recycled or recycled wood, here and in the following the term waste wood for wood is used, which was previously processed once to a product.

The invention is concerned with the widest possible use of waste wood for the production of chipboard, without affecting their technological properties.

STATE OF THE ART

In the chipboard industry, a so-called two-strand chip preparation is known. In this case, chips from fresh wood, usually cutting chips and / or Gatterspäne, and chips from waste wood are dried in separate lines and then fractionated in separate screening devices. The chips are divided into four fractions in both lines: (1) oversized chips returned to comminution, (2) chips for the middle layer of chipboard, (3) chips for the chipboard cover layers and (4) dust, which can be added to the outer layers to a limited extent and otherwise burned. The yield of the individual fractions in addition to the type of Generation of chips can be influenced by the mesh size of Siebbespannungen. In any case, coarse chips are created in both lines, which can be used in the middle layer of chipboard, and fine chips for the surface layers of chipboard. If there are insufficient chips for the cover layers in the sieves of fraction (3), shavings of fraction (2) of the middle layer are comminuted to cover shavings. In the known two-strand chip preparation the chips are fractionally joined after the individual preparation of chips from fresh wood and chips from waste wood, glued and then sprinkled with a scattering unit for the lower cover layer, the middle layer and the upper cover layer. As a scattering units typically either Windstreukammern (Absetzkammern) or roller screens are used. Windscrew chambers fractionate according to the flight characteristics of the chips, that is, their size and weight. Large, but also small heavy parts fall out of the air stream in front of the small, light parts. Roller screens with a roller bed fractionate according to the size of the chips. This creates a layered structure from fine to coarse. Even if the fraction (3) of the waste wood line, ie the top layer fraction of chips from waste wood, is cleaned after sieving, for example, in a climatic sifter, can not be prevented from finding in the top layers impurities from the waste wood to which, for example, minerals, finer Sand, glass and plastics count. These contaminants hinder the grinding of the surfaces of the chipboard. They produce cutouts at cut edges when dividing the chipboard into smaller formats. Furthermore, the plate surface does not reach the quality of a Feinstschichtoberfläche a chipboard made entirely of fresh wood due to the impurities. Experience has shown that the service lives of the sanding belts are also considerably shorter if there are a lot of waste wood in the cover layers. The described defects are particularly evident when the cover layers of the chipboard are manufactured with roller screens.

From the DE 197 51 326 A1 a method for the production of wood-based materials, including chipboard, using waste wood and fresh wood with the features of the preamble of independent claim 1 is known. In particular, aminoplas-containing waste wood is to be used. The shredded waste wood is mixed with the fresh chips shaved with aminoplast in customary quantities and thus used as cover layer or middle layer material in the customary production of chipboard.

From the DE 196 22 421 A1 is a method for the treatment of waste wood known to win wood chips for the production of chipboard.

From the DE 29 34 212 A1 is a combination plate known in the cover layers of wood and a middle layer of other types of materials such. As hemp, flax, bagasse, rice straw, straw, etc., possibly with the addition of wood, are formed to use instead of scarce raw material wood waste in the middle class. The preparation of the wood chips for the outer layers and the materials for the middle layer is carried out in separate chip processing lines.

OBJECT OF THE INVENTION

The invention has for its object to provide a method having the features of the preamble of independent claim 1, with the best possible use of waste wood high quality chipboard with the best technological properties and high quality surface can be produced.

SOLUTION

According to the invention the object is achieved by a method having the features of independent claim 1. The dependent claims 2 to 12 relate to preferred embodiments of the new method. The claim 13 is directed to a chipboard produced by the new method.

DESCRIPTION OF THE INVENTION

In the new process for producing chipboard using waste wood and fresh wood, in addition to the chips for the middle layer and the chips for each two outer layers are processed separately on each side of the chipboard. That is, on each side of the chipboard there is an outer cover layer, for which the chips are at least predominantly processed from fresh wood, and an inner cover layer, for which the chips are at least predominantly processed from waste wood. The chips for the outer and inner cover layers are kept separated from each other during production of the chipboard and glued and sprinkled separately. Thus, the chips of fresh wood are concentrated in the outer cover layers, while the chips of waste wood are concentrated in the inner cover layers and in the middle layer. In this way, the maximum possible benefit is drawn from the fresh wood used. Both the positive Effects of fresh wood on the technological properties of chipboard as well as on their surface quality have maximum effect in the outer cover layers. Thus, the quality of the plate surface of a chipboard produced according to the invention corresponds to the quality of the surface of a chipboard, which is entirely made exclusively of fresh wood. Fresh wood chips can be made much longer and leaner than old wood shavings. As a result, less binder can be used in the outer cover layers to achieve the same strength values. The strength of a chipboard is essentially determined by its flexural strength. In turn, the bending strength is determined by the chip quality, ie the degree of slimming, and the degree of gluing, in particular of the outer cover layers. For these reasons, the shavings of waste wood in the inner cover layers, which lie below the flexurally resistant outer cover layers in the case of a chipboard produced according to the invention, can be glued with less binder while achieving comparable strength properties. As is well known, fine chips made of waste wood have an approximately cubic structure and therefore a much larger surface area in terms of weight than chips made of fresh wood and therefore normally require correspondingly more binder. As a result, a part of the cost advantage of waste wood over fresh wood, which is more expensive as such and requires more energy to dry, is usually compensated. In the method according to the invention, however, a maximum cost advantage can be achieved by the use of waste wood, since it is used with a relatively low binder content. For example, panels with a very high proportion of waste wood can be produced whose surfaces can be directly painted and printed.

Although only a small amount of fresh wood is used in the method according to the invention, the outer cover layers are preferably composed only of fresh wood in order to maximize their surface quality. In this case, grinding dust can be recycled from the grinding of the chipboard produced according to the invention and added to the cover layers. In the present case, this sanding dust is to be evaluated as fresh wood, since it is produced by sanding the cover layers consisting exclusively of fresh wood and accordingly contains no impurities.

In contrast, in the new method, the inner cover layers as well as the middle layer of the chipboard can be composed exclusively of waste wood. Accordingly, in the new process, it is preferable to crush all the chips obtained from the fresh wood to a size that they are suitable for use in the outside Makes cover layers suitable. In principle, in the method according to the invention, the middle layer can also be sprinkled from chips from waste wood and chips from fresh wood.

Because the chips made of fresh wood according to the invention only or at least largely used for the outer layers, only a relatively small drying device is required for their drying.

The completely separate preparation of the chips for the inner and outer cover layers also makes it possible to optimize the gluing of the various cover layers with regard to the chips contained and their function. For this purpose, different binder amounts or binder compositions may be used.

In order to keep the binder requirement in the new method as small as possible without disadvantages for the chipboard produced, the chips for the inner cover layers can be formed in principle coarser than the chips for the outer cover layers.

Concretely, the chips for the outer cover layers may pass through a sieve of mesh size in the range of 1.3 to 1.6 mm and be substantially retained by a sieve of 0.3 to 0.6 mm mesh while the chips for the inner cover layers, pass through a sieve with a mesh size in the range of 1.6 to 1.8 mm and can be substantially retained by a sieve with a mesh size of 0.5-0.75 mm.

Preferably, the chips for the outer cover layers have a relatively high degree of slimming of 1: 2.5 to 5.

Furthermore, it is preferred if no separating layers are provided between the inner and outer cover layers and also towards the middle layer, as formed by large cracks in the chip sizes at the edges of the layers. The Spangrößenverlauf within the individual layers is adjustable by the design and the setting of the scatterers.

How little fresh wood is required for the production of chipboard according to the invention, it is clear that the thickness of the inner cover layers can be greater than that of the outer cover layers. Thus, the thickness of the inner cover layers can be set to 1 to 3 mm, while a thickness of the outer cover layers of only 0.5 to 1.5 mm is sufficient. However, this specification refers to the thickness of the outer cover layers after sanding.

In a chipboard produced according to the invention, the at least five-layer structure of outer cover layers, inner cover layers and middle layer, wherein only the outer cover layers predominantly consist of fresh wood, is easily detectable.

Advantageous developments of the invention will become apparent from the claims, the description and the drawings. The advantages of features and of combinations of several features mentioned in the introduction to the description are merely exemplary and can come into effect alternatively or cumulatively, without the advantages having to be achieved by embodiments according to the invention. Further features are the drawings - in particular the illustrated geometries and the relative dimensions of several components to each other and their relative arrangement and operative connection - refer. The combination of features of different embodiments of the invention or of features of different claims is also possible deviating from the chosen relationships of the claims and is hereby stimulated. This also applies to those features which are shown in separate drawings or are mentioned in their description. These features can also be combined with features of different claims. Likewise, in the claims listed features for further embodiments of the invention can be omitted.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1

ist ein Querschnitt durch den Schichtaufbau einer erfindungsgemäß hergestellten Spanplatte.

Fig. 2

gibt den Verlauf der mittleren Spangröße über die Dicke einer ersten Ausführungsform der erfindungsgemäß hergestellten Spanplatte wieder, und

Fig. 3

gibt den Verlauf der mittleren Spangröße über die Dicke einer zweiten Ausführungsform einer erfindungsgemäß hergestellten Spanplatte wieder.

The invention will be explained and described in more detail below with reference to specific embodiments with reference to the accompanying drawings.

Fig. 1

is a cross section through the layer structure of a chipboard produced according to the invention.

Fig. 2

shows the course of the average chip size across the thickness of a first embodiment of the particle board according to the invention, and

Fig. 3

gives the course of the average chip size over the thickness of a second embodiment of a particle board according to the invention again.

The figures are to be understood expressly as schematic representations and not necessarily to scale.

DESCRIPTION OF THE FIGURES

A chipboard 1 according to the invention produced according to Fig. 1 has two outer cover layers 2, two inner cover layers 3 and a middle layer 4. The middle layer 4 can additionally be subdivided into further partial layers. The outer cover layers 2 consist exclusively of chips of fresh wood and sanding dust from surface grinding of previously manufactured chipboard 1. For this purpose, fresh wood is treated separately to obtain chips of a single sieve fraction, typically through a sieve with a mesh size of 1.3 to 1.6 mm but is retained by a screen with a mesh size of 0.3 to 0.6 mm. Coarse chips are recalculated. Finer chips can be used to a limited extent as the previously mentioned fine grinding as a filler for the outer layers 2. Otherwise they will be burned. The chips of fresh wood of the sieve fraction described preferably have a high degree of slimming of about 1: 2.5 to 5, which allows to set a high bending strength of the particle board 1 on the outer cover layers 2 with a relatively low binder content. Moreover, the outer cover layers 2, which are made exclusively of fresh wood, are free of contaminants. Your plan grinding is therefore easy, as well as a division of the chipboard 1 in desired formats. Outside the outer cover layers 2, the chipboard 1 can be completely formed on the basis of waste wood. For this purpose, wood chips from two sieve fractions for the inner cover layers 3 on the one hand and the middle layer 4 on the other hand are processed from comminuted waste wood. The chips made of waste wood of the inner cover layers 3 are typically somewhat coarser than those of the outer cover layers 2. Despite the typically cubic dimensions of these chips from waste wood, they can be glued with comparatively little binder even with high technological requirements for the particle board 1, because they flexural strength the chipboard 1 is provided by the outer cover layers 2. Even in the middle layer 4 of even coarser chips from waste wood, a comparatively low binder content is sufficient. In this case, the binder can basically be the same over all layers two to four of the chipboard 1. But it is also possible to use different binders and, for example, in the outer cover layers 2 and possibly also in the inner cover layers 3 in contrast to the middle layer 4 to use a formaldehyde-free binder. Here, the person skilled in the art has optimization options in which he sensibly also takes into account the different compositions of the outer cover layers 2 on the one hand and the inner cover layers 3 and the middle layer 4 on the other hand from chips made of fresh wood or waste wood.

Fig. 2 outlines a possible distribution of the mean chip size G over the thickness d of a chipboard 1 produced according to the invention Fig. 1 , The chips for the outer cover layers 2 are typically sprinkled with shavings becoming coarser towards the middle of the plate. The chips for the inner cover layers 3 and the middle layer 4 can, as indicated here, also be scattered with a homogeneous distribution over the thickness d.

However, preferred is an in Fig. 3 indicated Spangrößenverteilung G over the thickness d, are selectively avoided in the jumps in the chip sizes between the individual layers 2 to 4. Smaller jumps in the chip size distribution are not critical. However, larger jumps may act as interfaces or interfaces at which there is an increased risk of dissolution of the composite of layers 2 to 4.

The table below gives possible dimensions of the various layers 2 to 4 of a chipboard 1 according to Fig. 1 for different thicknesses of chipboard 1 again. It follows that the cover layers 1 are produced with a typical grinding allowance of 0.3 mm. In addition, the average densities of the individual layers are given, which correlate with the chip size in the individual layers. <b><u> Table 1 </ u></b> ca.mm about kg / m ³ ca.mm about kg / m ³ ca.mm about kg / m ³ ca.mm about kg / m ³ Plate thickness unpolished 8th 10.6 703 13.6 16.6 Abschliff 0.6 0.6 0.6 0.6 Plate thickness ground 8th 10 692 13 16 DS outside unpolished 0.85 860 0.85 850 0.85 830 0.9 820 DS ground outside 0.55 860 0.55 850 0.55 830 0.60 820 DS inside 1.2 810 1.3 805 1.8 790 1.75 775 middle class 4.5 650 6.3 640 8.3 625 11.3 615 DS inside 1.2 810 1.3 805 1.8 790 1.75 775 DS ground outside 0.55 860 0.55 850 0.55 830 0.60 820 DS outside unpolished 0.85 860 0.85 850 0.85 830 0.9 820 ca.mm about kg / m ³ ca.mm about kg / m ³ ca.mm about kg / m ³ Plate thickness unpolished 18.6 28.6 38.6 Abschliff 0.6 0.6 0.6 Plate thickness ground 18 28 38 DS outside unpolished 0.9 815 1.1 795 1.35 785 DS ground outside 0.60 815 0.80 795 1.05 785 DS inside 1.9 770 2.55 750 2.7 730 middle class 13 610 21.3 580 30.5 565 DS inside 1.9 770 2.55 750 2.7 730 DS ground outside 0.60 815 0.80 795 1.05 785 DS outside unpolished 0.9 815 1.1 795 1.35 785

In order to carry out the new process for producing a chipboard from fresh wood and waste wood, in addition to at least three preparation lines for the chips from fresh wood for the outer cover layers 2, for the chips from waste wood for the inner cover layers 3 and for the chips from waste wood for the middle layer. 4 a total of five scattering units needed. With a scattering unit, the chips are sprinkled from fresh wood for the outer layers 2. With two further scattering units, the chips from waste wood for the inner cover layers 3 are scattered; and with at least one further scattering unit, the chips from waste wood for the middle layer 4 are scattered. If a symmetrical distribution of the chip sizes is to be achieved also over the middle layer, as in Fig. 3 is shown, two in different orientation sequentially switched scattering units must be used for the middle layer.

The scattering units for the outer cover layers may be Windstreukammern or roller screens. For the production of the inner cover layers roll gripper heads are preferably used with two superimposed roller beds. With appropriate adjustment, these devices can be used to produce homogeneous layers, layers with a "fine / coarse" selection and also combinations from "homogeneous to fine". For a homogeneous Spangrößenverteilung in the middle layer can scattering heads with so-called fan-rollers (cage-former) or Roller screens are used with two superimposed roller beds. Also a Spangrößenverteilung, which is a combination of in the FIGS. 2 and 3 shown Spangrößenverteilungen is possible. Thus, although the chip sizes of the middle layer 4 according to the symmetrical distribution Fig. 3 but the chip sizes of the inner cover layers 3 are homogeneously distributed. As a result, as a rule, there are no such large jumps in the chip sizes at the junctions to the middle layer 4 and the outer cover layers 2 that separating layers would be formed as a result.

The machine investments required for the implementation of the present invention are quickly compensated by the fact that high-quality chipboard, especially with high-quality surface using only a small proportion of fresh wood and, accordingly, relatively low cost of the wood and its drying can be produced.

LIST OF REFERENCE NUMBERS

1

chipboard

2

outer cover layer

3

inner cover layer

4

middle class

Claims (13)

Process for the production of chipboard (1) using waste wood and fresh wood, wherein chips for a middle layer (4) and chips for cover layers (2, 3) of the chipboard (1) are treated separately, characterized in that the chips for outer cover layers (2) are processed at least predominantly from the fresh wood, that the chips for inner cover layers (3) are at least predominantly recycled from the waste wood and that the chips for the outer cover layers (2) and the inner cover layers (3) are scattered separately. A method according to claim 1, characterized in that the outer cover layers (2) are sprinkled only from chips of fresh wood. A method according to claim 1 or 2, characterized in that the chips of fresh wood for the outer cover layers (2) grinding dust is added. Method according to one of claims 1 to 3, characterized in that the inner cover layers (3) are scattered only from chips from waste wood. Method according to one of claims 1 to 4, characterized in that the middle layer (4) is scattered only from chips from waste wood. Method according to one of claims 1 to 5, characterized in that the chips for the inner cover layers (3) and the outer cover layers (2) are glued differently. Method according to one of claims 1 to 6, characterized in that the chips for the inner cover layers (3) are processed so that they are coarser than the chips for the outer cover layers (2). Method according to one of claims 1 to 7, characterized in that the chips for the outer cover layers (2) through a sieve with a mesh size in the range from 1.3 to 1-6 mm and substantially retained by a sieve of 0.3 to 0.6 mm mesh size. Method according to one of the preceding claims, characterized in that the chips for the outer cover layers (2) have a slenderness ratio of 1: 2.5 to 5. Method according to one of the preceding claims, characterized in that between the inner cover layers (3) and the outer cover layers (2) and the middle layer (4) no separating layers are formed, at which the size of the chips changes abruptly. Method according to one of the preceding claims, characterized in that the thickness of the inner cover layers (3) is adjusted to 1 to 3 mm. Method according to one of the preceding claims, characterized in that the thickness of the outer cover layers (2) is adjusted to 0.5 to 1.5 mm after the grinding. Wood panel produced by the method according to one of the preceding claims, 1 to 12.

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