WO2008071539A1 - Carrier board - Google Patents

Abstract

The invention relates to a process for producing a fibreboard as a carrier board for panels coated using the direct printing process, after the drying process. The process is essentially characterized in that the fibres are moistened after they have dried and before they are compressed. Furthermore, the invention relates to a fibreboard, in particular an MDF or HDF board, produced from wood fibres and serving as a carrier board for producing panels coated using the direct printing process, wherein the fibreboard has a moisture content of above 6%, preferably of above 6.5%, particularly preferably of above 7.0%, based on the dry weight of the fibreboard, and the invention also relates to the use of such a fibreboard for producing panels coated using the direct printing process.

Description

 SHELF

The invention relates to a method for producing a fiberboard as a carrier plate for direct-printing coated panels by the dry process. Furthermore, the invention relates to a fiber board made of wood fibers, in particular MDF or HDF board, as a support plate for the production of direct-coated coated panels.

For the production of panels for cladding ceilings, walls and floors have in recent years fiberboard produced by the dry process is particularly proven and therefore provide the majority of the support plates used for the panels.

Depending on the density, fibreboards produced by the dry process are classified into MDF and HDF boards. The term MDF stands for "Medium Density Fiberboard" and comprises boards with a density of up to 800 kg / m ^3. So-called HDF boards "High Density Fiberboard" have a density of more than 800 kg / m ³ . For floor panels to which special requirements with regard to dimensional stability and strength, only the use of HDF panels is required.

In order to give the panels the desired, decorative appearance and to give them an abrasion-resistant surface, as is required especially in the case of floor panels, various coating methods have been able to establish themselves. In this case, the laminate coating, which is usually realized using the DPL process, represents currently the most widely used variant. DPL stands for "direct pressure laminate" and includes a process for the usually resin impregnated, dried papers, ie at least one decor paper if necessary with an overlay paper, under high heat and pressure with a carrier plate is pressed. From the plates coated in this way, the desired panels are then produced in a downstream production process. In order to obtain an increased abrasion resistance of the decorative surface, hard particles, for example corundum or silicon carbide particles, are introduced into the layer structure.

In addition to the laminate coating, it is also possible to provide plates in a direct printing process with a decorative surface. For increased optical requirements are fine here in several stages sanded plates provided with a primer on which then the desired decor is applied. In order to obtain the desired gloss and the required abrasion resistance, the panels pretreated in this way are then sealed, which is generally accomplished by means of UV-curing lacquers, which in turn can be provided with hard particles.

Depending on the later intended use of the plates used, the quality of the optical quality and the required abrasion resistance are determined. A particularly high optical quality is in turn characterized by a high resolution of the decor print and by a constant gloss level. In the case of the direct or indirect gravure printing processes used for high feed rates and production widths, it is absolutely necessary to achieve an extremely regular substrate with a particularly low surface roughness in order to achieve these properties. It is therefore very important for the direct printing of a support plate on the quality of the substrate and thus on the quality of the provided support plate.

The invention thus sets itself the task of an improved fiber board, produced according to the Dry process, as a support plate for a panel coated by direct printing, as well as a method for its preparation to specify.

For the production of MDF and HDF boards, wood chips from deciduous and / or softwood are shredded after their washing and a hydrothermal digestion in refiners. These fibers produced in this way can be conveyed from there via the so-called blow-line, in which binders and auxiliaries and additives can be added, via a fiber dryer into a fiber bunker, from which the charge is then fed to a spreading station. This then forms a non-woven fabric, which is pressed in a cycle press or cut as an infinite strand in a continuous double belt press or a calender press. Depending on this, the desired plate formats are cut to length before or after the press. As auxiliaries and additives are understood, for example, hardeners and accelerators, water repellents or fire protection and fungicidal agents. In addition to the addition of binder and auxiliaries and additives in the blow-line, it is also possible to add these between the fiber dryer and the fiber bunker. According to the already dry state of the fibers one speaks then of a dry gluing. Significant importance in compressing the glued and provided with additives fibers is the moisture content of the fibers during pressing of the plates. Moisture accomplishes heat transfer from the heated press plates via the near-surface zones to the core zone of the plate. Accordingly, the added binder can then react here as well, with the result that the plate acquires its mechanical properties. At the commonly used pressing temperatures of about 100 ⁰ C to about 200 ⁰ C at pressures up to 500 N / cm ² , the moisture is in a vaporous state.

Although a too high moisture content of the fibers causes good heat transfer, but a very high vapor volume is formed, which in turn builds up such an increased pressure in the plate cross-section that the internal binding forces can not withstand this, so the plate when leaving the press in plate plane breaks -. it comes to so-called "bursting" in order to prevent this "Platzer ^Λ, only an extension of the pressing time in conjunction with a lower pressing temperature, would be possible in addition to reducing fiber moisture but this is to be avoided for considerations of economy, the moisture content. , determined by the Darrmethode, the dry-laid fiberboard is therefore usually in Range from 3.5 to 5.0%. The Darrmethode understood here as the determination of the moisture by reference the mass of the moisture to the dry mass of the plate, determined at 103 +/- 2 ⁰ C according to the equation; Moisture content in% = {wet weight - dry matter) / dry matter x 100. To achieve this, the fibers provided with the binder are usually dried to a moisture content in front of the press of less than 10%.

But even for the laminate coating, where also high temperatures and pressures must be applied, there is a risk of bursting of the plates, which is why here carrier plates are used with a humidity to about 5%.

However, such low plate wetness are disadvantageous when coating in direct printing in several respects.

The most significant disadvantage is the high degree of absorbency associated with low plate moisture, which causes the drying portions of the applied primer to diffuse very rapidly into the support plate and prevent regular film formation. Furthermore, it can be observed that at lower plate humidities, near-surface fibers are reinforced when a primer is applied get up and. so again prevent the formation of a continuous closed, smooth coating film. The consequence is that a repeated primer usually has to be combined with one or more intermediate sanding in order to achieve the necessary surface quality.

Another significant disadvantage of the prior art with a moisture content of only 3.5 to 5% available fiberboard as support plates for the direct printing process coated panels is that they are exposed in the intended, installed state a room climate, the leads to an increase in moisture in the support plates. With this increase in humidity inevitably a dimensional change and thus an unwanted, uncontrolled deformation of the support plate is connected, which in turn, in the case of floor panels can lead to heavy load and thus premature damage to the edge areas in turn.

Regardless of the type of coating of fiberboard their high electrical resistance. This has disadvantages in the use of the plates as floor panels, since the electrical charges of a user resulting from the passage are not dissipated via the covering, but abruptly in contact with a dissipative other surface, as typically a metallic door buckle, be dissipated. This is noticeable to the user in an unpleasant way in an electric shock. Since, however, the electrical resistance of a fiberboard is excessively dependent on its moisture, this problem occurs considerably less in the case of support plates according to the invention than in the case of the plate dampenings customary in the prior art of 3.5 to 5%.

It has been found that a support plate with a higher moisture content, which thus no longer has the disadvantages described, can be produced by adding moisture to the fibers after they have been dried and before being pressed into a fiber plate. Surprisingly, it was found that with an increase of the moisture to 12 to 20%, preferably to 13 to 18%, particularly preferably 14 to 16%, an impermissibly high internal vapor pressure is not created which "burst" in the compression of such pretreated fibers despite a increased moisture content ε fail and so economically HDF plates with a humidity of about about 6.0%, preferably of about about 6.5%, more preferably about about 7.0% can be prepared. The increase in fiber moisture should be as regular as possible over the entirety of the fibers. A mere, superficial spraying of the fibers in front of the press is not suitable for this purpose.

The use of steam, particularly preferably of steam-air mixture, has proved to be advantageous. If the steam or the steam-air mixture is passed through the pressed material mat, the mat temperature and the moisture content of the fiber mat are raised on the same side. The effect of increasing the temperature is used by methods for preheating a pressed material mat, in order to increase the capacity of a press by reducing the required pressing time. However, in order to prevent the risk of bursting of plates here, the fibers are always dried well below 8% to the total moisture content, ie fiber moisture and introduced via the steam or the steam-air mixture moisture, below 10% based on to keep the dry weight of the fibers. At the latest in order to avoid bursting in the laminate coating of the plates, this is necessary.

For plates which are coated by the direct printing method, however, this is not necessary, for reasons described such as coatability or electrical conductivity even disadvantageous.

Claims

PATENT APPLICATIONS 1. A process for producing a fiberboard as a support plate for the direct-printing coated panels by the dry process, characterized in that the fibers are moistened after drying and prior to compression. 2. The method according to claim 1, characterized in that by moistening a moisture content of the finished plate of about about 6%, preferably of about about 6.5%, more preferably of about about 7.0%, based on the dry weight of the plate , is achieved. 3. The method according to claim 1, characterized in that adjusted by moistening the moisture content of the fibers prior to their compression to 12 to 20%, preferably to 13 to 18%, particularly preferably to 14 to 16%, based on the dry weight of the fibers becomes. 4. The method according to any one of the preceding claims, characterized in that the moistening by the application of the Pressgutmatte before the press with steam and / or a vapor-air mixture. 5. fiber board made of wood fibers, in particular MDF or HDF board, as a support plate for the production of direct-coated coated panels, characterized in that the fiberboard a moisture content of about 6%, preferably of more than 6.5%, more preferably of more than 7.0%, based on the dry weight of the fiberboard. 6. Use of a fiber board made of wood fibers, in particular MDF or HDF board as a carrier plate for the production of direct-coated coated panels, the fiberboard having a moisture content of more than 6%, preferably more than 6.5%, more preferably more than 7, 0%, based on the dry weight of the fiberboard.