EP1690603B1 - Fiberboard comprising a coating deposited on at least a section of its surface - Google Patents

Abstract

One or more layers of liquid plastic resin blended with fibers, is coated onto the wooden panel. The resin is a thermoset, especially an aminoplastic, particularly melamine resin. The fibers are cellulose, viscose, other synthetics, glass, ceramic or their mixtures. Preferably 5-20 wt% of fibers are employed, based on the weight of resin used. Once the composite is hardened, the fibers are transparent. Corundum is included in the layer. An independent claim is included for the corresponding coating method.

Description

The invention relates to a wood-based panel having an at least partially applied surface coating and a method for applying the coating.

Wood-based panels with a surface coating, which is usually applied to the top, possibly also the underside and the side surfaces, are known for many purposes. Increasingly important floor panels made of wood materials, but also ceiling and wall panels, wood-based panels for room dividers and the like. In order to obtain a durable surface coating which is also abrasion-resistant in the case of floors, the use of impregnates is customary.

Impregnates are special papers impregnated with synthetic resin. The resins incorporated in the paper are cured to such an extent that the papers are dry and storable. After application to the wood-based panels, the impregnates are cured under the action of pressure and temperature. Pressure and temperature are usually applied in presses. The softening prior to the final curing resin flows through the paper framework through to a layer which, where the impregnate is applied, the surface of the wood-based panel coated.

The impregnate may include, as required, a paper printed with a decor. It may be incorporated corundum as a means against the abrasion in the impregnate.

The production of impregnates is complex and expensive, especially because of the expensive special papers that serve as a carrier material for synthetic resin, decor and corundum if necessary.

Therefore, techniques have been developed to apply decors without backing paper directly to the surface of wood-based materials, as well as synthetic resins and possibly corundum. Typical examples are the DE 27 18 705 A1 , the US2001 / 0006704 and the GB1 579 661 in which the application of melamine resin is described on a wood-based panel. The melamine resin may be provided with pigments or fillers.

In detail, however, difficulties arose when applying the most thermosetting synthetic resins, especially in the processing of the well-suited and inexpensive aminoplasts. Heretofore, the synthetic resin, e.g. a melamine resin, applied to the special paper and precondensed. Drying of the impregnate resulted in shrinkage due to a reaction of the synthetic resin. The special paper has undergone this change in shape. When the impregnate was pressed onto the wood-based panel, no significant changes in shape were observed.

When the synthetic resin is applied directly to a wood-based material surface, the synthetic resin itself can be applied sparingly depending on the desired layer thickness. With a relatively thin, direct application, however, it is disadvantageous that the synthetic resins do not always form the desired, uniform layer on the surface of the wood-based material board. The surface coating has an uneven layer thickness.

In addition, the shrinkage of synthetic resins proves to be problematic during curing. The thermosetting resins exert a strong tensile force in the plane of the coated surface of the wood-based panel due to the large shrinkage stress arising on emergence, which in part lead to deformations which make further processing of the coated panel impossible. The high shrinkage stress, in conjunction with the relatively low adhesive force of the thermosetting synthetic resins on the plate also causes flaking occur. The lack of film formation, which is particularly observed in melamine resins, leads to the immediate Application to the surface of a wood-based panel to allow parts of the resin to dissolve from the wood-based panel during curing.

The invention is therefore based on the object to propose a directly applied surface coating for a wood-based panel, which avoids the disadvantages described above.

The object is achieved with a wood-based panel according to claim 1.

The liquid-applied synthetic resin layer is cured under the action of elevated temperature and / or elevated pressure.

The addition of cellulose fibers, viscose fibers, synthetic fibers or fibers of glass or a mixture of at least two of the aforementioned fibers in the direct application of the resin to a Holzwerkstoffbberfläche has unexpectedly proved to be very suitable to a uniform layer thickness of the resin on the surface of the wood-based panel guarantee.

Furthermore, the addition of cellulose fibers, viscose fibers, synthetic fibers or fibers of glass or a mixture of at least two of the aforementioned fibers causes the shrinkage of the resin during curing greatly reduces the stresses occurring in the surface of the coated wood material and especially the deformations caused thereby , In order to ensure that no undesirable deformations of the wood-based panel occur, can be applied to the opposite surface of the wood-based panel, in the position of use usually the bottom, a so-called balance of the same resin or a material with comparable properties in order to equalize the stresses occurring.

Such a synthetic resin layer mixed with cellulose fibers, viscose fibers, synthetic fibers or fibers made of glass or a mixture of at least two of the aforementioned fibers does not require paper as a carrier material and is therefore much less expensive and less energy-consuming to produce than known coatings.

The addition of such fibers improves the cohesion and in particular the adhesion of layers of synthetic resin, which are applied to wood-based surfaces, in particular thermosetting resins. Particularly suitable is the addition of fibers has proven in aminoplasts, especially in melamine resins.

The invention comprises both typical fibers whose diameter is small in relation to the length, and particles which are cuboidal or spherical, so have approximately the same dimensions in length, height and width, for example crystalline cellulose particles. Suitable cellulose fibers, whether in the form of natural cotton fibers such. As linters, as particles of crystalline cellulose or in the form of synthetically produced fibers such as viscose, Tencel or the like .. But also synthetic fibers or fibers made of glass are suitable, provided that they are compatible with the selected resin. Mixtures of at least two of the aforementioned fibers, which are added to a synthetic resin for coating the surface of a wood-based panel, have proved to be particularly advantageous.

The diameter of the fibers may typically be between 10 μm and 150 μm, preferably between 15 μm and 40 μm. The length of the fibers may be 10 .mu.m to 100 .mu.m, preferably 10 .mu.m to 80 .mu.m. The fibers used according to the invention need not have a large degree of slimming, they can also be used as cubic fibers with approximately the same edge length or as roundish particles.

Even small amounts of fibers are sufficient to achieve the purpose desired according to the invention. Already 5 percent by weight (% by weight) of fibers based on the weight of the synthetic resin used are sufficient for the film formation z. As a melamine resin on a wood-based material surface significantly, in particular to improve uniform and at the same time the adhesion of the resin to the wood-based panel. According to a preferred embodiment of the invention, 1 to 40% by weight of fibers are based on the weight of the synthetic resin used used, more preferably 5 to 20% by weight.

The addition of fibers to the applied resin is technically possible without further difficulties. As the proportion of fibers in the synthetic resin to be applied increases and / or as the length or size of the fibers increases, the viscosity of the synthetic resin to be applied may increase. However, this is acceptable in many areas.

According to a further preferred embodiment of the invention, the fibers are transparent after curing of the synthetic resin layer on the wood-based panel. As a result, the visibility of a decoration already applied to the surface of the wood-based material remains unimpaired.

The addition of corundum to the fiber-reinforced synthetic resin layer according to the invention on the surface of the wood material is readily possible. If the corundum is applied homogeneously with the fiber-reinforced synthetic resin, it is not effectively shielded by the fibers, which can lead to increased wear of the press plates. To remedy this problem, it may prove useful, above the existing, fiber-reinforced synthetic resin layer according to the invention at least one further layer of a synthetic resin or a synthetic resin mixture, for. B. a further layer of synthetic resin, which is optionally mixed with fibers to apply.

According to an advantageous embodiment, the fiber-added layer of synthetic resin, which is at least partially applied to the surface of a wood-based panel, part of a multi-layer surface coating. So z. As decorative color layers, wear layers with corundum portions, elastically deformable, soft layers or topcoat layers follow each other to wear the surface of a wood-based panel to be committed wear-resistant. According to a preferred embodiment of the invention, these layers are all applied directly to the surface, for example by spraying, rolling or knife coating. If corundum is used, it can be applied by a litter device. It can be sprinkled directly into the fiber-reinforced resin layer.

• Einmischen von Fasern oder Partikeln in ein flüssiges Kunstharz
• Aufstreichen, Aufwalzen, Aufgießen, Aufrakeln oder Aufsprühen des Kunstharz-Fasergemisches auf die Holzwerkstoffplatte
• Trocknen des Kunstharz-Fasergemisches.

The invention further relates to a method for applying a liquid resin-fiber mixture to a wood-based panel according to claim 8. The method has the steps

• Mixing of fibers or particles in a liquid synthetic resin
• Brushing, rolling, pouring, knife coating or spraying the resin-fiber mixture on the wood-based panel
• Drying of the synthetic resin-fiber mixture.

If, according to the invention, a surface coating of a plurality of layers is applied, the layer of liquid synthetic resin provided with fibers can readily be arranged as one of several layers at any point of the multilayer surface structure.

As far as it concerns layers whose material must dry or harden, it is possible according to an advantageous development of the invention to dry or harden the layer just applied so far that the application of the next layer is possible. Only when all layers are applied, the simultaneous and complete curing of all layers takes place. This multi-section drying makes sense in terms of cost and interconnection of the various layers.

Details of the invention will be explained in more detail with reference to the following exemplary embodiments:

example 1

On the top and bottom of a medium-density fiberboard 65 g / m ^{2 of} a melamine resin are applied, which has a solids content of about 58%. In the melamine resin 20 wt% crystalline cellulose particles are mixed. The cellulose particles have a diameter of 100 μm. The job is done by means of rollers.

The thus applied melamine resin layer is precondensed in a hot air oven to a residual moisture content of the melamine resin of 6 wt .-%. The final curing of the melamine resin is carried out in a short-cycle press at 165 ° C for 20 seconds. The both sides equally coated wood-based panel is evenly coated after curing of the melamine resin coating without defects and unchanged flat.

Example 2

80 g / m ^{2 of} a mixture of melamine resin, which has a solids content of about 58%, are applied to the top of a medium-density fibreboard (MDF) previously printed with decor. The melamine resin is blended with 20 g / m ^{2 of} cellulose particles with a diameter of 80 to 100 microns. Furthermore, 20 g / m ^{2 of} corundum in the form of cubic particles with 40 to 60 μm edge length are mixed into the melamine resin. The term "g / m ² " refers in each case to the amount that is applied to one square meter surface of the wood-based panel.

After the intermediate drying of the corundum-containing layer, another layer of melamine resin and cellulose is applied. The melamine resin is applied in an amount of 30 g / m ² , and the cellulose blended in the melamine resin in an amount of 10 g / m ² . The cellulose particles in this layer have a diameter of 10 .mu.m to 20 .mu.m.

On the underside of the MDF board, a balance bar of 50 g / m ² melamine resin and 10 g / m ² cellulose particles is applied.

These fiber-reinforced melamine resin layers are pre-dried in the hot air stream to a residual moisture content of 6% water content in the synthetic resin layer.

The final processing of the fiber-reinforced melamine resin coated MDF boards is carried out in short-cycle presses at 165 ° C for 20 sec to plates which have on the decor-printed top highly abrasive properties, and which are used as floor laminate panels.

Claims (11)

1. A derived timber board with a surface coating applied at least in parts with at least one coating of a synthetic resin applied in a liquid state, characterized in that the at least one coating of a synthetic resin applied in a liquid state is reinforced with particles of cellulose.
2. The derived timber board according to claim 1, characterized in that the particles of cellulose are present in the form of natural cotton fibres, such as linters, as particles of crystalline cellulose or in the form of synthetically manufactured cellulose as viscose, TENCEL.
3. The derived timber board according to claims 1 or 2, characterized in that the particles of cellulose are cellulose fibres with a diameter between 10 µm and 150 µm, preferably between 15 µm and 40 µm and that the length of these fibres is between 10 µm and 100 µm, preferably 10 µm to 80 µm.
4. The derived timber board according to claim 1, 2 or 3, characterized in that the particle-reinforced synthetic resin coating comprises a thermosetting synthetic resin, in particular an aminoplastic, specifically a melamine resin.
5. The derived timber board according to at least one of the preceding claims, characterized in that the concentration of particles amounts to at least 5 weight percent, preferably 5 to 40 weight percent, particularly preferably 5 to 20 weight percent with reference to the weight of the synthetic resin used.
6. The derived timber board according to at least one of the preceding claims, characterized in that the particles added to the synthetic resin are transparent after the synthetic resin has cured.
7. The derived timber board according to at least one of the preceding claims, characterized in that the synthetic resin coating reinforced with particles contains corundum.
8. The derived timber board according to at least one of the preceding claims, characterized in that the particle-reinforced synthetic resin coating is a component of a multi-layered surface coating.
9. A method for applying a liquid synthetic resin-particle mixture to a derived timber board, comprising the steps of:

   - mixing particles of cellulose into a liquid synthetic resin

   - painting, rolling, pouring, application by squeegee or spraying the synthetic resin-particle mixture to the derived timber board

   - drying the synthetic resin-particle mixture.
10. The method according to claim 9, characterized in that the particles of up to 40 weight percent with reference to the weight of the synthetic resin used are mixed into the synthetic resin.
11. The method according to claim 10, characterized in that the synthetic resin-particle mixture is dried in a plurality of stages.