EP3181315B1 - Method for producing an osb with a smooth surface - Google Patents

Description

The invention relates to a method for producing an OSB in which long wood chips (strands) glued with an adhesive are scattered in at least three layers, the orientation of the wood chips being offset in adjacent layers and then the scattered layers under high pressure and temperature desired thickness can be pressed onto a plate, whereby 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 intersecting beaches that run alternately in the longitudinal direction as well as in the transverse direction of the floor plan. The strands are 70 to 200 mm long, 6 to 30 mm wide and 0.3 to 1.2 mm thick. Softwood or hardwood is used as the material, with the proportion of wood in the finished board between 90% and 98%. The chips are oriented in the individual layers using scattering units arranged one behind the other.

The well-known OSB (Oriented Strand Board) is used as formwork panel. In order to achieve a smooth surface, fibers or chips are sprinkled on the last beach layer, which should compensate for the unevenness of the surface of the core in order to achieve a surface that is as flat as possible. This fine surface layer consists of a fine wood material, which after a Sieve mesh size, which is smaller than 0.5 mm, was obtained. A layer of paper is placed on the fine chip layer and all layers are pressed together in a short-cycle press, whereby the core flows under pressure and heat and thus there is an adhesive bond between the phenolic paper and the core.

The fact that the direction of the strands is rotated by 90 ° from one layer to the next results in a high bending strength of OSB, which makes OSB interesting for many applications in the construction sector. Another advantage is that an OSB, especially when using softwood, has a lower bulk density than other wood-based materials. This also makes OSB the product of choice for applications in vehicle construction. In addition, OSB can be produced in lengths and widths, which, for example, minimizes the effort required for assembly when manufacturing a truck loading area.

Due to the geometry of the beaches 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, sometimes up to about 4 mm. This surface structure prevents OSB from being coated with technologies commonly used in other wood-based materials, such as the lamination of paper impregnated with urea and / or melamine resin, the lamination of finish foils, etc. This closes many applications that would be economically interesting. Applications for concrete formwork, floors, vehicle floors and side panels of loading areas of trucks and transport vehicles are conceivable here.

The easiest way to create a smooth surface on an OSB would be grinding, but this leads to material losses of more than 10%. This does not make sense not only from a cost perspective, but also from an ecological perspective.

Another way to create a smooth surface is to install additional spreading devices for fine chips in an OSB production line. However, this entails an extensive investment in chip production, chip preparation and chip gluing. In existing manufacturing plants, there is no space for such installations in many OSB lines, so this option is ruled out for most manufacturers. Even with new plants, it is unclear what percentage of the entire production should be provided with such an optimized top layer, so that a considerable investment must be seen as a risk.

In the US 4,364,984 A discloses an OSB with a five-layer structure, the lower and upper cover layers having significantly finer chips than the core strands.

The DE 25 13 764 A1 discloses a method for producing a wood-based panel, in which a mixture of adhesive, plastic and wood flour is applied as a powder 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 in order to be used as a furniture plate.

Another way of smoothing the top is to fill the holes with a varnish. This requires a painting line with several application units. Since the application quantities must also be around 100 g / m ² , this process is very cost-intensive. In addition, subsequent coating with papers impregnated with melamine resin on a short-cycle press is not readily possible, since adhesion problems regularly arise between the coated OSB surface and melamine. Equipping the paint with suitable fillers, such as wood flour, etc., obviously does not solve this problem. In addition, there may be problems with the hardening of the paint, at least when the imperfections in the surface of the OSB are particularly deep.

The EP 1 749 587 A1 discloses a building board made of wood-based material and a method for its production, in which an OSB board is produced from at least three layers of compressed, resin-glued chips. A coating of a water-based varnish is applied to these pressed chips, which is then dried and a flat surface can be achieved. Wood flour can be added to the water-based varnish.

Another solution is the use of relatively thick phenolic resin-impregnated sodium kraft papers, which often have a final weight of more than 400 g / m ² . These are pressed onto the surface in a short-cycle press. This does cover the existing holes optically, but the resistance to indentation remains low in the areas in which a typical flaw in the surface of the OSB is under coating. There is therefore a very high risk that if such an OSB is used, for example, as a loading area in a truck, punctiform loads will cause damage. Water can later penetrate into this damage and lead to swelling of the plate, which results in extensive material destruction. Compared to the materials usually used for this (plywood), this would result in a shorter cycle for replacing the loading area, which increases the costs for the user. Within the inhomogeneity already described below the coating, a cloudiness that results from light and dark areas and a slight ripple can often be observed. This does not result in a high-quality appearance of the product.

In the EP 2 027 979 A1 Another problem of coating wood-based panels is addressed. For environmental reasons, a wood-based panel should be powder-coated. For powder coating, an electrostatically charged paint powder is evenly distributed on the surface to be painted using an electric field, then melted onto this surface and bonded to form a homogeneous paint layer that adheres firmly to the surface. To make the powder coating too the plate must be correspondingly conductive so that the electrical field can be applied. For this purpose, it is proposed to use conductive salts in the manufacture of phenolic adhesive-bound plates.

Proceeding from this, the object of the invention is to create 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 (5) der oberen Deckschicht (3),
• Abstreifen oder Abrütteln des aufgestreuten Gemisches, sodass Unebenheiten bis zu einer Tiefe von 4 mm verfüllt werden,
• Aushärten des Gemisches (4) unter Druck- und Temperatureinfluss indem das Gemisch (4) in die Vertiefungen in der oberen Deckschicht (3) hineingepresst wird, 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 an upper side (5) of the upper cover layer (3),
• Scraping or shaking off the sprinkled mixture so that unevenness is filled to a depth of 4 mm,
• Hardening of the mixture (4) under the influence of pressure and temperature by pressing the mixture (4) into the depressions in the upper cover layer (3), whereby the synthetic resin melts and a uniform surface layer trains,

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

By actively scraping / shaking the mixture into the wells, a first-class surface is obtained that is easy to coat. For example, paper or foil can be applied. The OSB finished in this way can preferably be used as a concrete formwork panel or as a loading area for a truck. The mixture can be sprinkled on top of an already pressed OSB or sprinkled on 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 . It is particularly preferably sprinkled with a weight per unit area of 200 g / m ² .

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

The long wood chips are scattered on a conveyor belt rotating in a transport direction T. If a smooth underside is also to be created, a mixture of wood flour and synthetic resin powder is first sprinkled on a paper layer and the first layer of long wood chips is sprinkled on it. In this case, the layer structure is later preferably pressed in a short-cycle press, because the technological structure of a short-cycle press would be very complex for this.

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

A phenolic resin-impregnated sodium kraft paper can preferably be placed on 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 on using an anilox roller. However, it can also be sprinkled very simply over a funnel-shaped container arranged above the conveyor belt. Milling dust is well suited for use as wood flour in the mixture. This also takes recycling aspects into account.

To stabilize the mixture, wood or cellulose fibers with a proportion of 5 to 20% by weight can also be added to the reinforcement. Wetting agents, hardeners etc. can also be added to the mixture as auxiliaries which have a positive effect on the process.

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

A paper layer covering this can be laminated onto the layer of wood flour and synthetic resin. The paper layer is preferably a phenolic resin impregnated sodium 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;

The invention will be described in more detail below with the aid of a drawing. Show it:

Figure 1 -

the schematic representation of an OSB board manufacturing plant;

Figure 2 -

the enlarged view according to arrow II Figure 1 ;

First, long wood shavings (strands), which have a length of 150 to 300 mm, preferably a maximum of 200 mm, a width of 10 to 2 mm and a thickness of less than 1 mm, on a circumferential in a transport direction T - not shown here - Scattered conveyor belt and scattered to a lower cover layer 1. A middle layer 2 of long chips is scattered onto this layer 1, the chips in the middle layer 2 being offset by essentially 90 ° with respect to the lower cover layer 1. This means that if the chips in the lower cover layer 1 are oriented in the longitudinal direction (transport direction T), the strands in the middle layer 2 are oriented transversely thereto, that is to say they run in the transverse direction. An upper cover layer 3 of long wood chips is sprinkled on the middle layer 2, 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. Two different binders can also be used as adhesives within an OSB. In the middle layer, the chips can be glued with PDMI, for example, and in the outer layers with MUF or MUPF binders. PMDI is preferably used as an adhesive.

A layer 4 made of a mixture 4 is made from the top cover layer 3 Wood flour and a synthetic resin powder (melamine resin or phenolic resin) sprinkled on. The mixture layer 4 is stripped off by means of a stripping device 6, so that the mixture 4 of wood flour and synthetic resin powder is actively rubbed into the holes in the top 5 of the top cover layer 3. The cake 8 consisting of layers 1, 2, 3, 4 is transported into 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 an OSB 10 of the desired thickness.

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

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

Embodiment 1

A mixture 4 of wood flour and melamine resin powder (100 g / m ² ) in a ratio of 1: 1 was sprinkled onto the top 5 of an OSB 10 (22 mm) using a scattering device. A machine from TPS is used for spreading, the essential components of which are a hopper, a rotating anilox roller underneath and a stripping device. The application rate per square meter is determined by the rotation speed of the anilox roller fixed. Behind the spreader is a device with which the sprinkled powder is doctored into the recesses by a pulling device. A phenolic resin-impregnated sodium kraft paper was placed on the sprinkled surface 7. The impregnate had a final weight of approx. 450 g / m ² . The structure was pressed in a short cycle press at a press temperature of 200 ° C, a pressure of 20 bar and a press time of 35 seconds. For comparison, an OSB 10 without the sprinkled powder was pressed with the same phenolic resin impregnate. In the visual comparison, a significantly stronger ripple and cloudiness was observed on the comparison plate. In some cases, the beaches under the coating can still be clearly recognized or felt. The indentation strength of the two samples was tested using a ball drop test. For this purpose, an iron ball was dropped onto surface 7 from different heights. Five drop tests were carried out for each height. The test for the corresponding height is passed if no mechanical damage is observed in any of the five tests. 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 ) is sprinkled on the top beach layer 3 of a chip cake 8 with the aid of a scattering device in a ratio of 1: 1. The increased quantity takes into account the beaches still lying loosely on the conveyor belt, which have even larger gaps to be filled. A machine from TPS is used for spreading, the main components of which are a hopper and a rotating anilox roller underneath and are a scraper. The application rate per square meter is determined by the rotation speed of the anilox roller. Phenol resin-impregnated sodium kraft paper was placed on the sprinkled surface 7. The impregnate had a final weight of approx. 210 g / m ² . The structure was pressed in a short cycle press at a press temperature of 200 ° C, a pressure of 20 bar and a press time of 35 seconds.

For comparison, an OSB 10 without powder sprinkled on was pressed with the phenolic resin impregnate from embodiment 1. The indentation strength of the two samples was tested using a ball drop test. For this purpose, an iron ball was dropped onto surface 7 from different heights. Five drop tests were carried out for each height. The test for the corresponding height is passed if no mechanical damage is observed in any of the five tests.

This shows that the sprinkled mixture 4 of wood flour and melamine resin powder enables the use of thinner phenolic resin-impregnated soda paper with the same indentation strength. 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 it is of course also possible to use thermosetting binders or binder mixtures other than powder resins (phenol-formaldehyde resin, melamine-phenol-formaldehyde resin). Wood or cellulose fibers can also be added for reinforcement (5 to 20% by weight). Additional auxiliaries that positively influence the process (wetting agents, hardeners etc.) can be added to the powder resins.

The chip cake can be sprinkled in 3 or 5 layers. More than five layers of glued chips are also possible.

Reference symbol list

1

lower cover layer

2nd

Middle class

3rd

upper cover layer

4th

Layer / mixture

5

Top

6

Scraper

7

surface

8th

Chip cake

10th

plate

20th

Short cycle press

Claims (17)

1. Method for producing an OSB (10), in which long wood strands coated with an adhesive are scattered in an oriented manner in at least three layers (1, 2, 3), wherein the wood strands in adjoining layers (1, 2, 3) are aligned in an offset manner and then the scattered layers (1, 2, 3) are compressed under high pressure and temperature to form a board (10) of the desired thickness, as a result of which the adhesive melts and cures, comprising the following steps:

   - scattering a mixture (4) of wood flour and a synthetic resin powder onto an upper side (5) of the top cover layer (3),

   - stripping or shaking off the scattered-on mixture (4) so that unevennesses to a depth of 4 mm are filled,

   - curing the mixture (4) under the influence of pressure and temperature by pressing the mixture (4) into the depressions in the top cover layer (3), wherein the synthetic resin melts and a uniform surface layer forms,

   wherein the synthetic resin is melamine resin or phenolic resin and the mixture (4) is scattered on in an amount of at least 80 g/m².
2. Method according to Claim 1, characterized in that the mixture (4) is scattered onto an upper side (5) of an already pressed OSB (10).
3. Method according to Claim 1, characterized in that the mixture is scattered onto the upper side (5) of the last scattered layer (3) of long wood strands of a strand cake (8) consisting of at least three scattered layers (1, 2, 3).
4. Method according to one of the preceding claims, characterized in that the mixture (4) is scattered on with a weight per unit area of at least 100 g/m².
5. Method according to Claim 4, characterized in that the mixture (4) is scattered on with a weight per unit area of 200 g/m².
6. Method according to one of the preceding claims, characterized in that the mixture (4) consists of 50% by weight wood flour and 50% by weight synthetic resin powder.
7. Method according to one of the preceding claims, characterized in that the mixture (4) is actively introduced into the depressions by a doctor blade.
8. Method according to one of the preceding claims, characterized in that the long wood strands are scattered onto a conveyor belt circulating in a transporting direction.
9. Method according to one of the preceding claims, characterized in that first a mixture (4) of wood flour and synthetic resin powder is scattered onto a paper layer and, after that, the first layer of long wood strands is scattered on.
10. Method according to one of the preceding claims, characterized in that an impregnated soda kraft paper is placed onto the mixture layer before the layer structure is compressed.
11. Method according to Claim 10, characterized in that the soda kraft paper is impregnated with phenolic resin.
12. 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 for a pressing time of 35 sec.
13. Method according to one of the preceding claims, characterized in that the mixture (4) is scattered on by means of an anilox roll.
14. Method according to one of the preceding claims, characterized in that milling dust is used as wood flour.
15. Method according to one of the preceding claims, characterized in that wood fibres or cellulose fibres are additionally added to the mixture (4) for reinforcement.
16. Method according to Claim 15, characterized in that the reinforcement comprises a proportion of 5 to 20% by weight.
17. Method according to one of the preceding claims, characterized in that wetting agents and/or curing agents are added to the mixture (4).

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