Process for the production of a multi-layer pressed board

The invention concerns a process for the production of a multi-layer pressed board which in the finished condition is made up at least from two layers of different pressed materials. The invention also concerns a manufacturing installation for the production of a multi-iayer pressed board. The invention further concerns such a manufactured pressed board.

Pressed boards are generally known, they are usually employed in interior building works for floors, walls or ceilings. Such boards comprise for example at least one HDF layer (high density fibreboard) and a layer consisting of a cork material. Usually in that case such a pressed board is made up from three layers, wherein either an HDF layer is arranged between two cork layers or a cork layer is arranged between two HDF layers. The HDF layer substantially achieves the hardness and stability for the pressed board whereas a cork layer has a certain elasticity and good insulating properties.

Accordingly a cork layer is used as the central layer in particular when surfaces which are as hard as possible are wanted, whereas the central layer is an HDF layer when a somewhat more yielding surface which has a warmer effect is desired.

Hitherto, to produce such a pressed board, the three respective layers are produced separately and pressed individually. The three resulting pressed layers are then ground at their surface in order to produce a respective smooth flat surface. In a further step the three boards are then placed one upon the other, with the contact surfaces provided having been previously coated with an adhesive after they had been cleaned. Those three layers with adhesive therebetween are then pressed so that the three layers firmly adhere to each other and thereby form a stable pressed board.

Such a process is complicated and expensive and in particular causes a large amount of grinding waste. Known processes are thus costly by virtue of the large number of processing steps and also by virtue of the large amount of material used.

Therefore the object of the invention is to improve a known process for the production of a multi-layer pressed board and in particular to reduce the above-indicated disadvantages.

In accordance with the invention therefore there is proposed a process as set forth in claim 1. Accordingly in a first step a first material is applied as uniformly as possible to a support base in order thus to form the first layer. In that case that first layer is initially left unpressed. A second material is next applied as uniformly as possible to that first unpressed layer in order thus to form a second layer on the first layer. That second layer is also initially left unpressed.

Those two layers which are disposed one upon the other and which are still unpressed are then usually pressed together with the action of heat thereon, possibly with one or more further layers, to afford the pressed board to be manufactured. That can be effected by a flat press so that at least those two specified layers are arranged flat between two pressing bodies of the flat press and then pressed. In the pressing operation on the one hand the two pressed layers are produced while on the other hand a

firm join is also made between those two layers in the pressing operation. In that respect a firm join between the two layers is important, in which respect there is no need for those two layers to be of a smooth and flat nature in their contact region. Rather the two layers can adapt to each other in the contact region and after the pressing operation a rather uneven contact region and thus joining region between those two layers is to be expected.

A cork material is used as the material for the first or second layer. The second or first layer respectively then correspondingly comprises a wood material. Both the cork material and also the wood material respectively correspond to a basically known material from which hitherto a respective individual pressed cork or pressed wood board was manufactured. Both the cork material and also the wood material have inter alia a bonding agent in order to guarantee the cohesion of the individual particles after the pressing operation. That bonding agent then serves also for joining the layers together in the joint pressing operation according to the invention for the two un- pressed layers.

Preferably prior to the pressing operation a third layer consisting of the first material is applied to the second layer. That therefore results in three layers which are applied one upon the other in an unpressed condition, of which the central one comprises the second material and the other two layers comprise the first material. In that respect there can basically be two variants, namely a variant in which the cork layer is arranged between two wood layers and another variant in which a wood layer is arranged between two cork layers. Those three unpressed layers are then jointly pressed preferably in a flat press and that correspondingly results in a triple-layer pressed board.

A triple-layer pressed board is also to be preferred in particular for the reason that such a pressed board comprising an odd number of layers has proven to be stable in respect of shape and in particular does not have any tendency to warp. It is desirable if the cork material is a mixture of cork grains and glue as the bonding agent. The cork grains involve a proportion of 75 - 95, in particular 82 - 92 percent by weight. The cork grains which can also be referred to as cork scrap provide that the layer to be produced has the properties which are generally known of cork and which are desired. In particular insulating and elasticity properties are desired in that respect. If that layer is

visible, the appearance of the cork is additionally to be borne in mind. The bonding agent provides that the cork constituents are fixedly joined so that the result is a layer which is as firm and strong as possible. In addition the bonding agent causes or at least promotes adhesion of the layers to each other.

The wood material used is preferably a mixture of 70 - 85, in particular 75 - 80 percent by weight of wood constituents, in particular wood fibres, and in addition glue as the bonding agent for the wood constituents. The wood constituents, in particular wood fibres, achieve stability for the layer in question, in particular in regard to breaking strength, that is to say in regard to tensile and thus flexural loadings. The glue provides for a strong firm join and thus makes it possible to produce a substantially firm layer. The wood material to be preferred corresponds to a material which is used in a manner that is already known for the production of HDF boards or individual HDF layers. Such a material for the production of an HDF layer has in particular a good price-yield ratio for the layer in question. Equally however it is possible to consider other compositions, such as for example the use of a material which is employed for the production of chipboard. In other words the wood constituents or wood fibres can be of differing degrees of fineness.

In accordance with a preferred configuration the layers are respectively applied with an applicator apparatus and the support base is moved in a conveyor direction during application of the layers relative to the applicator apparatuses in order to provide for uniform application of the layers. In that respect the applicator apparatuses can be stationary and the support base is moved under the applicator apparatuses in the conveyor direction. With continuous delivery of the respective material by the respective applicator apparatus and simultaneous continuous uniform movement of the support base in the conveyor direction, it is thus possible to achieve uniform application. In principle an absolute movement of the applicator apparatuses can also be effected. The movement of the support base is desirable however as that means that the finally completely applied layers- can be further conveyed to the pressing operation.

In accordance with a further configuration the process is such that a plurality of applicator apparatuses and in particular three applicator apparatuses are arranged in succession in the conveyor direction for the production of a triple-layer pressed board and each applicator apparatus has a substantially elongate delivery region for delivery of the respective material and each delivery region is oriented substantially transversely with respect to the conveyor direction. As viewed in the conveyor direction therefore at the beginning the material in question is delivered by a first delivery device substantially in the form of a wide strip on the support base and that strip forms the first layer and is further conveyed in the direction of the next applicator apparatus. The next applicator apparatus substantially also dispenses the material in question in the form of a strip, for the second layer, the material in strip form being disposed on the first and thus lowermost layer. In that way a layer or further layers can also be added.

For the application operation an applicator apparatus has a slit nozzle, the longitudinal direction of which is arranged substantially transversely with respect to the conveyor direction. In place of a slit nozzle it is also possible to use a plurality of individual applicator nozzles which apply the material in the form of a plurality of beads which then join together to form a layer on the support base.

In accordance with an embodiment there can additionally be provided one or more scrapers or smoothing devices which spread the respective layers of the first or second material to make them smooth before a further layer is applied.

The unpressed layers which are arranged one upon the other in the finished condition are then further conveyed to a pressing apparatus, in particular a flat press, The pressing operation is then effected there, preferably being effected with the application of heat. That provides for advantageous and also accelerated hardening of the materials used. Particularly when using materials with bonding agent that bonding agent is advantageously hardened as quickly as possible.

An embodiment involves a continuous pressing operation in which the unpressed layers are continuously guided to a pressing apparatus and there continuously pressed. In particular that continuous pressing operation is effected by means of a

calender press. Such a calender press has at least two pressing rollers, between which the layers are passed for the pressing procedure. In this connection a continuous process, in particular a pressing operation, means that the movement of the layers and the pressing operation take place simultaneously and substantially together and conveying and pressing do not alternate. Occasionally stopping the procedure for example in order to cut off the pressed layers or to cut them to size does not exclude the property of continuous pressing.

In accordance with the invention there is further proposed a manufacturing installation for the production of a multi-layer pressed board, wherein the manufacturing installation is adapted to carry out a process according to the invention. Further advantageous configurations of a manufacturing installation according to the invention are set forth in the appendant claims, in particular claims 11 to 16. The respective design configurations present themselves to the man skilled in the art on the basis of the respective configuration of the underlying processes in accordance with the foregoing description.

In accordance with the invention there is also proposed a multi-layer pressed board having at least one pressed cork layer and a pressed wood layer as set forth in claim 17. Such a pressed board according to the invention is produced by at least one un- pressed layer of a cork material as the starting material for the pressed cork layer and an unpressed layer of a wood material as the starting material for the pressed wood layer being pressed together to afford the pressed board. Such a multi-layer pressed board is frequently to be recognised by virtue of the fact that a somewhat uneven and/or irregular contact zone, in particular contact surface, is present between the pressed cork layer and the pressed wood layer. At any event there is frequently no flat contact surface which has been ground smooth, between those two layers. That uneven contact region can mostly already be recognised in a cross-section through the pressed board.

Preferably the pressed board has been produced by a process according to the invention. In accordance with an embodiment in that respect a central pressed cork layer is arranged between two pressed wood layers and in accordance with another configuration a central pressed wood layer is provided between two pressed cork layers. The

man skilled in the art will usually select the respective configuration in accordance with the intended purpose of use.

It is to be noted that the individual layers can be of different thicknesses. In the case of triple-layer pressed boards in which a cork layer is disposed between two wood layers it is also possible for the two wood layers to be of mutually different thicknesses. The same applies to triple-layer pressed boards in which a wood layer is arranged between two cork layers, in which case the two cork layers may be of mutually different thicknesses. In this connection the terms cork layer and wood layer do not mean a pure cork layer and a pure wood layer respectively, but a layer which has wood or cork respectively, in particular in the combination as described hereinbefore in relation to some embodiments, consisting of wood and cork constituents respectively and bonding agent.

The present invention is described in greater detail by way of example hereinafter by means of some embodiments with reference to the accompanying Figures in which:

Figure 1 diagrammatically shows a manufacturing installation according to the invention,

Figure 2 diagrammatically shows a triple-layer pressed board according to the invention with a central cork layer, and

Figure 3 diagrammatically shows a triple-layer pressed board with a central wood layer.

Figure 1 diagrammatically shows a manufacturing installation 2 comprising a first, a second and a third applicator apparatus 4, 6 and 8, a conveyor apparatus 10 and a flat press 12. It is to be noted in particular that the illustrated size relationships which have been adopted for illustrative purposes do not have to correspond to the actual size relationships of an embodiment.

As shown in Figure 1 therefore a production process takes place in such a way that a support base 14 is gradually moved in the conveyor direction 16 under the applicator apparatuses 4, 6 and 8 by means of the conveyor apparatus 10. In that case a cork material 24 is continuously applied to the support base 14 by the first applicator apparatus 4 and thus forms the first layer 34.

By virtue of the forward movement of the support base 14 by the conveyor apparatus 10 the first layer 34 which has begun is further moved to the second applicator apparatus 6 which delivers a wood material 26 as a second material in order to begin the second layer 36 on the first layer 34. Now, from the position of the second applicator apparatus, the first layer 34 and the second layer 36 are further conveyed to the third applicator apparatus 8 which delivers a cork material 28 as the third material, which is deposited as the third layer 38 on the second layer 36.

When the cork material 24 of the first layer has substantially covered the support base 14 or has substantially reached the desired area in plan of the pressed board to be produced, the first applicator apparatus 4 stops the delivery of the cork material 24. In that case the support base 14 is further conveyed until the wood material 26 has completely covered the cork material 24. The second applicator apparatus 6 then stops delivery of the wood material 26 and a short time later in the same fashions the third applicator apparatus 8 stops delivery of the cork material 28 as the third material. There are then three layers 34, 36 and 38 or 34', 36' and 38' respectively which are of substantially the same size with respect to the surface area of the pressed board, on the support base 14 or 14' respectively.

Those three layers which hitherto rest one upon the other only due to the force of gravity are then further conveyed by means of the support base 14 to the flat press 12. In the flat press 12 the support base 14' with the three layers 34', 36' and 38' then rests on a co-operating backing body 18 of the flat press 12. For pressing the hitherto un- pressed layers 34', 36' and 38' the pressing ram 20 is moved on to the uppermost layer 38' in the pressing direction 22 and the three layers 34', 36' and 38' are pressed together between the co-operating backing body 18 and the pressing ram 20 to form a pressed board according to the invention.

In the pressing operation the pressing pressure is maintained for a while and in that situation heating is also effected by way of the co-operating backing body and the pressing ram. The pressing ram 20 can then be lifted again and the pressed layers 34', 36' and 38' which are now firmly pressed together can be removed. After removal from the flat press 12 the process then comprises cutting the pressed board to size and possibly grinding the edges and/or surfaces.

It is also to be noted that, with reference to Figure 1 , basically a discontinuous production process has been described. That is appropriate in particular also by virtue of using a flat press. Nonetheless a continuous production process can also be considered at least in portion-wise fashion. By way of example, the applicator apparatuses 4, 6 and 8 as shown in Figure 1 could continuously apply the respective materials and instead of the support base 14 the conveyor apparatus 10 could itself form the support base and it would be possible to produce a multi-layer - triple-layer as shown in Figure 1 - endless web, from which then corresponding portions are cut prior to the respective pressing operation, and passed to a flat press.

In principle it is also possible to envisage a continuous production process in which operation is not effected with a flat press but with a kind of calender press. In that case the three layers are continuously fed to the pressing assembly and subsequently to the pressing operation individual boards of large format are cut off. Any type of press which can be used for the production of HDF and/or chipboards is also suitable for producing the pressed board according to the invention.

Figure 2 shows a triple-layer pressed board in which a central cork layer 46 is arranged between two wood layers 44 and 48 as the first and third layers. The surface 50 of the pressed board 42 has been ground substantially flat and smooth. The contact regions 45 and 47 respectively between the first and second layers 44 and 46 respectively and the second and third layers 46 and 48 respectively is in contrast of a less flat nature, due to the production process. In addition the surfaces in question were not ground smooth in the contact regions 45 and 47.

The pressed board 62 in Figure 3 comprises a wood layer 66 as the central layer and thus the second layer between two cork layers 64 and 68. In this case also the contact regions 65 and 67 between the first and second layers 64, 66 and between the second and third layers 66, 68 respectively are not entirely flat, due to the production process according to the invention.

It is to be noted that Figures 2 and 3 also show an only diagrammatic illustration of the pressed board 42 or 62 respectively. The views are not intended to give any indication of actual size relationships, either in respect of the cork board itself nor in respect of the layers relative to each other nor the diagrammatically illustrated particles of the cork layers 46, 64 and 68. The terms cork layer and wood layer used also do not necessarily describe a layer which consists exclusively of wood or cork, as has already been explained hereinbefore.