EP3181315A1 - Method for producing an osb with a smooth surface - Google Patents

Abstract

The invention relates to a method for producing an OSB board (10) in which long, wood chips coated with an adhesive are scattered oriented in at least three layers (1, 2, 3), the alignment of the wood chips in adjacent layers (1, 2 , 3) and then the scattered layers (1, 2, 3) are pressed under high pressure and temperature to a plate (10) of desired thickness, whereby the adhesive melts and cures, which is characterized by the following steps: Spreading a mixture (4) of wood flour and a synthetic resin powder on an upper side (5), Stripping or shaking off the spread mixture (4) so that unevenness is filled to a depth of 4 mm, Curing the mixture under the influence of pressure and temperature, whereby the synthetic resin melts and forms a uniform surface layer, wherein the synthetic resin is melamine or phenolic resin and the mixture (4) is sprinkled in an amount of at least 80 g / m 2.

Description

The invention relates to a method for producing an OSB in which long, glued with an adhesive wood chips (strands) are oriented oriented in at least three layers, wherein the orientation of the wood chips offset in adjacent layers and then the scattered layers under high pressure and temperature a plate desired thickness are pressed, wherein the adhesive hardens.

Such a plate is for example from the EP 1 136 636 A1 known. An OSB is characterized by the fact that it has an intersecting, alternating longitudinally and transversely of the ground plan, layer by layer. The strands have a length of 70 to 200 mm, a width of 6 to 30 mm and a thickness of 0.3 to 1.2 mm. The material used is softwood or hardwood, the wood content in the finished board being between 90% and 98%. The orientation of the chips in the individual layers is realized by successive scattering units.

The well-known OSB (Oriented Strand Board) is used as formwork panel. In order to achieve a smooth surface, fibers or shavings are sprinkled on the last layer of the beach, which are intended to compensate for the unevenness of the surface of the core, in order to achieve as flat a surface as possible. This fine cover layer consists of a wood fines material, which after a Siebmaschenweite that is smaller than 0.5 mm, was obtained. On the fine chip layer, a paper layer is placed and in a short-cycle press all layers are pressed together, wherein under pressure and heat, a flow of the core is achieved and thus a bond between the phenolic paper and the core.

The fact that the scattering direction of the strands is rotated by 90 ° from one layer to the next results in a high flexural strength of OSB, which makes OSB interesting for many applications in the construction sector. Another advantage is that an OSB, especially when using softwoods, has a lower bulk density compared to other wood-based materials. This makes OSB the product of choice for automotive applications as well. In addition, OSB can be produced in lengths and widths that, for example, minimizes the effort involved in manufacturing a truck bed.

Due to the geometry of the strands and their scattering, there is no smooth or even closed surface on the finished OSB, but the OSB has a surface structure with many depressions, in some cases up to about 4 mm. This surface structure prevents coating of OSB with commonly used technologies in other wood-based materials, such as laminating urea / and / or melamine resin impregnated papers, laminating finish foils, etc. Thus, OSBs are closed to many applications that would be economically attractive. Conceivable here are applications for concrete formwork, floors, vehicle floors and side panels of cargo areas of trucks and transport vehicles.

The easiest way to create a smooth surface on an OSB would be to sand, but this will result in material losses of more than 10%. This is not sensible not only in terms of costs, but also in terms of the environment.

Another way to create a smooth surface is to incorporate additional fine chip spreaders onto an OSB line. However, this entails a substantial investment in chip production, chip preparation and chip sizing. In existing factories, there is no room for such installations in many OSB lines, so this option is eliminated for most manufacturers. Even with new plants, it is unclear how many percent of the entire production should be provided with such an optimized cover layer, so that a considerable investment must be considered as a significant investment.

In the US 4,364,984 A discloses an OSB having a five-layered structure wherein the lower and upper cover layers have substantially finer chips relative to the strands of the core.

The DE 25 13 764 A1 discloses a method for producing a wood-based panel, wherein a mixture of adhesive, plastic and wood flour powder is applied to the sides of the wood-based panel to be coated and then pressed with the wood-based panel. Such a plate can then be coated with a decorative paper, a PVC film or a veneer to find use as a furniture board.

Another way of smoothing the top is to fill the holes with the help of a paint. This requires a Lackierlinie with several commissioned works. Since the order quantities must be at some 100 g / m ² , this process is very costly. In addition, a subsequent coating with melamine resin-impregnated papers on a short-cycle press is not readily possible, since there is regularly between the painted OSB surface and melamine to adhesion problems. Also, the equipment of the paint with suitable fillers, such as wood flour, etc., apparently does not solve this problem. In addition, it may interfere with the curing of the paint, at least if the imperfections in the surface of the OSB are particularly deep.

Another approach is the use of relatively thick phenol resin-impregnated kraft papers, which often come to a final weight of more than 400 g / m ² . These are pressed onto the surface in a short-cycle press. Although this covers the existing holes visually, the indentation resistance remains low in the areas in which there is a typical defect in the surface of the OSB under coating. Thus, there is a very high risk that if such a coated OSB is used, for example, as a cargo area in a truck, punctiform loads cause damage. Later, water can penetrate into these damages and lead to swelling of the plate, which leads to large-scale material destruction. Compared to commonly used materials (plywood), this would result in a shorter cycle to replace the cargo bed, which increases the cost to the user. Within the inhomogeneity below the coating already described, a cloudiness that results from light and dark areas and a slight waviness is often observed. This results in no high-quality appearance of the product.

On this basis, the invention is based on the object to provide an alternative method for producing an OSB with a smooth surface, which can be provided with a coating.

• Aufstreuen eines Gemisches aus Holzmehl und einem Kunstharzpulver auf eine Oberseite,
• Abstreifen oder Abrütteln des aufgestreuten Gemisches, sodass Unebenheiten bis zu einer Tiefe von 4 mm verfüllt werden,
• Aushärten des Gemisches unter Druck- und Temperatureinfluss, wobei das Kunstharz aufschmilzt und eine gleichmäßige Oberflächenschicht ausbildet,

wobei das Kunstharz Melamin- oder Phenolharz ist und das Gemisch in einer Menge von mindestens 80 g/m² aufgestreut wird.To solve the problem, the generic method is characterized by the following steps:

• Sprinkling a mixture of wood flour and a synthetic resin powder on top,
• Stripping or shaking off the spread mixture so that unevenness is filled to a depth of 4 mm,
• Curing of the mixture under pressure and temperature influence, whereby the synthetic resin melts and a uniform surface layer forms,

wherein the synthetic resin is melamine or phenolic resin and the mixture is sprinkled in an amount of at least 80 g / m ² .

The active kneading / shaking of the mixture into the wells later gives a first-class surface which is easy to coat. For example, a paper or a foil can be applied. The refined OSB can preferably be used as a concrete formwork panel or as a loading area of a truck. The mixture may be sprinkled on top of an already compressed OSB or sprinkled onto the last scattered layer of long chips, a chip cake consisting of at least three scattered layers of long chips.

The mixture is preferably sprinkled with a basis weight of at least 100 g / m ² . In particular, preferably with a basis weight of 200 g / m ^{2 is} scattered.

The mixture may preferably consist of 50% by weight of wood flour and 50% by weight of synthetic resin powder.

The long wood chips are scattered on a circulating in a transport direction T conveyor belt. If a smooth underside is also to be produced, a mixture of wood flour and synthetic resin powder is first sprinkled onto a paper layer and then the first layer of long wood chips is sprinkled on it. In this case, the compression of the layer structure is later preferably carried out in a short-cycle press, because the technological structure of a short-cycle press would be very expensive for this purpose.

In principle, it would also be conceivable to press the layer structure continuously.

A phenolic resin-impregnated soda kraft paper can preferably be applied to the upper mixture layer before the layer structure consisting of the layers lying on top of one another is pressed.

It is advantageous if the mixture is sprinkled by means of an anilox roller. But it can also be sprinkled very easily via a funnel-shaped container arranged above the conveyor belt. Milling dust is well suited for use as wood flour in the mixture. At the same time recycling aspects are considered.

In order to stabilize the mixture, wood or cellulose fibers with a proportion of 5 to 20% by weight can additionally be added for the reinforcement. Also, wetting agents, hardeners, etc. may be added to the mixture as adjuvants that positively affect the process.

An OSB comprising at least three layers of strands is characterized by a layer applied from the visible side of the first and / or last layer of a mixture of wood flour and synthetic resin and a coating applied to the mixture layer, in particular a paper layer.

On the layer of wood flour and resin, a paper covering this covering can be laminated. The paper layer is preferably a phenol resin-impregnated soda kraft paper. The synthetic resin is preferably melamine or phenolic resin.

Figur 1 -

die schematische Darstellung einer OSB-Plattenherstellungsanlage;

Figur 2 -

die vergrößerte Darstellung gemäß Sichtpfeil II aus Figur 1;

With the help of a drawing, the invention will be described in more detail below. Show it:

FIG. 1 -

the schematic representation of an OSB board manufacturing plant;

FIG. 2 -

the enlarged view according to viewing arrow II FIG. 1 ;

First, long wood chips (strands) having a length of 150 to 300 mm, preferably at most 200 mm, a width of 10 to 2 mm and a thickness of less than 1 mm, on a in a direction of transport T circulating - not shown here - Scattered conveyor belt and scattered to a lower cover layer 1. On this layer 1, a middle layer 2 of long chips is scattered, wherein the chips are offset in the middle layer 2 with respect to the lower cover layer 1 by substantially 90 °. That is, when the chips are oriented in the lower cover layer 1 in the longitudinal direction (transporting direction T), the strands in the middle layer 2 are oriented transversely thereto, that is, they run in the transverse direction. On the middle layer 2, an upper cover layer 3 of long wood chips is scattered, which have the same orientation as the strands in the lower cover layer 1. The wood chips are glued with an adhesive.

Suitable adhesives are phenol-formaldehyde binders (PF), urea-formaldehyde binders (MF), melamine-urea-formaldehyde binders (MUF) or melamine-urea-phenol-formaldehyde binders (MUPF). PDMI is also suitable as an adhesive. Within an OSB, two different binders can also be used as an adhesive. In the middle layer, the chips can be glued, for example, with PDMI and in the outer layers with MUF or MUPF binder. Preferably, PMDI is used as the adhesive.

On the upper cover layer 3, a layer 4 of a mixture 4 is made Wood flour and a synthetic resin powder (melamine resin or phenolic resin) sprinkled. By means of a stripping device 6, the mixture layer 4 is stripped, so that the mixture 4 of wood flour and synthetic resin powder is actively rubbed in the located in the upper side 5 of the upper cover layer 3 holes. The consisting of the layers 1, 2, 3, 4 cake 8 is transported in a double belt press 20. At a pressing temperature of 260 ° C, a pressure of up to 300 N / cm ² , the layer structure is pressed to form an OSB 10 of desired thickness.

As FIG. 2 shows the compressed mixture 4 in the layer 4, the spaces between the wood chips in the upper cover layer 3 from. Due to the different thicknesses and lengths or widths of the strands, cavities are formed in the individual layers 1, 2, 3 which leave on the upper side 5 of the upper cover layer 3 recesses of up to 4 mm, which may also have undercuts in which the mixture 4 of wood flour and synthetic resin powder of the layer 4 is pressed in, so that the in FIG. 2 shown smooth surface 7 on the compressed OSB 10 sets.

On the smooth surface 7 of the OSB 10, a coating, preferably made of paper or foil is then laminated. The paper can also be placed on the doctored or shaken layer 4 before the chip cake 8 is pressed.

Embodiment 1

On the top side 5 of an OSB 10 (22 mm), a mixture 4 of wood flour and melamine resin powder (100 g / m ² ) was spread in a ratio of 1: 1 with a spreader. For spreading a TPS machine is used, whose essential components are a storage hopper, underneath a rotating screen roller and a stripper. Due to the rotational speed of the anilox roller, the order quantity per square meter established. Behind the spreader is a device with which the scattered powder is doctored into the recesses by a puller. On the sprinkled surface 7 a phenol resin-impregnated sodium kraft paper was applied. The impregnate had a final weight of about 450 g / m ² . The assembly was pressed in a short-cycle press at a pressing temperature of 200 ° C, a pressure of 20 bar and a pressing time of 35 sec. For comparison, OSB 10 with no sprinkled powder was pressed with the same phenolic resin impregnate. When compared visually, a significantly greater ripple and cloudiness was observed on the comparison plate. Some of the strands under the coating are still clearly visible or palpable. On the two samples, the indentation strength was tested by means of a ball drop test. For this an iron ball was dropped on the surface 7 from different heights. For each height five drop tests were carried out. The test for the appropriate height is passed if none of the five tests show mechanical damage. variant OSB with powder and impregnated rhino TEG OS 400 OSB without powder with impregnated rhino TEG OS 400 Fall height ball drop test 1500 mm 900 mm

Embodiment 2

On an OSB line, a mixture 4 of grinding dust and melamine resin powder (200 g / m ² ) in the ratio 1: 1 is sprinkled onto the uppermost beach layer 3 of a chip cake 8 with the aid of a spreading device. With the increased amount while still lying loose on the conveyor belt beach is taken into account, which have even larger spaces to be filled. For spreading a TPS machine is used, whose essential components are a storage hopper, underneath a rotating anilox roller and a stripping device. Due to the rotational speed of the anilox roll the order quantity per square meter is determined. On the sprinkled surface 7 phenol resin-impregnated sodium kraft paper was placed in a pattern. The impregnate had a final weight of about 210 g / m ² . The assembly was pressed in a short-cycle press at a pressing temperature of 200 ° C, a pressure of 20 bar and a pressing time of 35 sec.

For comparison, OSB 10 having no powder sprinkled on it was pressed with the phenolic resin impregnate of Embodiment 1. On the two samples, the indentation strength was tested by means of a ball drop test. For this an iron ball was dropped on the surface 7 from different heights. For each height five drop tests were carried out. The test for the appropriate height is passed if none of the five tests show mechanical damage.

Here it can be seen that the spread mixture 4 of wood flour and melamine resin powder makes it possible to use thinner phenol resin-impregnated soda paper with the same indentation strengths. variant OSB with powder 1x impregnate per TEG 827 OSB without powder 1x impregnated Rhino TEG OS 400 Fall height ball drop test 900 mm 900 mm

In the mixture 4 of wood flour or milling dust, of course, other thermosetting binders or binder mixtures can be used as a powder resins (phenol-formaldehyde resin, melamine-phenol-formaldehyde resin). Also wood or cellulose fibers can be added to the reinforcement (5 to 20% by weight). The powder resins can be added to other auxiliaries that positively influence the process (wetting agents, hardeners, etc.)

The chip cake can be sprinkled 3 or 5 layers. Also more than five layers of glued chips are possible.

LIST OF REFERENCE NUMBERS

1

lower cover layer

2

middle class

3

upper cover layer

4

Layer / mixture

5

top

6

stripper

7

surface

8th

chip cake

10

plate

20

Short-cycle press

Claims (21)

Method for producing an OSB (10) in which long, glued with an adhesive wood chips in at least three layers (1, 2, 3) are scattered oriented, wherein the alignment of the wood chips in adjacent layers (1, 2, 3) is offset and then the scattered layers (1, 2, 3) are pressed under high pressure and temperature to a plate (10) of desired thickness, whereby the adhesive melts and cures, characterized by the following steps: Spreading a mixture (4) of wood flour and a synthetic resin powder on an upper side (5) Stripping or shaking off the spread mixture (4) so that unevenness is filled to a depth of 4 mm, Curing the mixture under the influence of pressure and temperature, whereby the synthetic resin melts and forms a uniform surface layer, wherein the synthetic resin is melamine or phenolic resin and the mixture (4) is sprinkled in an amount of at least 80 g / m ² . A method according to claim 1, characterized in that the mixture (4) on a top (5) of an already compressed OSB (10) is scattered. A method according to claim 1, characterized in that the mixture on the top (5) of the last scattered layer (3) of long wood chips of at least three scattered layers (1, 2, 3) existing chip cake (8) is scattered. Method according to one of the preceding claims, characterized in that the mixture (4) is sprinkled with a basis weight of at least 100 g / m ² . A method according to claim 4, characterized in that the mixture (4) is sprinkled with a basis weight of 200 g / m ² . Method according to one of the preceding claims, characterized in that the mixture (4) consists of 50% by weight of wood flour and 50% by weight of synthetic resin powder. Method according to one of the preceding claims, characterized in that the mixture (4) is actively scribed into the recesses. Method according to one of the preceding claims, characterized in that the long wood chips are scattered on a circulating in a direction of transport conveyor belt. Method according to one of the preceding claims, characterized in that initially on a paper layer, a mixture (4) of wood flour and synthetic resin powder is scattered and then the first layer of long wood chips is scattered. Method according to one of the preceding claims, characterized in that an impregnated sodium kraft paper is applied to the mixture layer before the layer structure is pressed. A method according to claim 10, characterized in that the soda kraft paper is impregnated with phenolic resin. Method according to one of claims 2 to 7, characterized in that the layer structure is compressed in a short-cycle press at a temperature of 200 ° C, a pressure of 20 bar and a pressing time of 35 sec. Method according to one of the preceding claims, characterized in that the mixture (4) is scattered by means of an anilox roller. Method according to one of the preceding claims, characterized in that milling dust is used as wood flour. Method according to one of the preceding claims, characterized in that the mixture (4) for reinforcing additional wood or cellulose fibers are added. A method according to claim 15, characterized in that the reinforcement has a proportion of 5 to 20% by weight. Method according to one of the preceding claims, characterized in that wetting agents and / or hardeners are added to the mixture (4). OSB board (10) consisting of at least three layers (1, 2, 3) of strands and on the visible side of the first and / or the last layer (3) applied layer (4) of a mixture of wood flour and resin characterized by a the mixture layer (4) covering coating. OSB board (10) according to claim 18, characterized in that the coating is an impregnated paper layer. OSB board (10) according to one of claims 17 to 19, characterized in that the synthetic resin is melamine or phenolic resin. OSB board (10) according to claim 19 or 20, characterized in that the paper layer is a soda kraft paper.

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