EP3059020A1 - Method for manufacturing a composite wood board, in particular a composite wood board with a decoration layer - Google Patents

Abstract

The present invention relates to a method for producing a wood-based panel, in particular provided with a decorative layer wood material panel, comprising the steps of providing at least one wood fiber support plate, moistening at least a portion of a surface of the at least one wood fiber support plate with aqueous vapor, grinding the at least partially moistened surface of Wood fiber support plate, and applying at least one decorative layer on the at least partially moistened and ground surface of the wood fiber support plate.

Description

The present invention relates to a method for producing a wood-based panel according to the preamble of claim 1 and an apparatus for carrying out this method according to claim 13.

description

Wood-based panels as support materials are used in various fields, such as used as floor panels in the form of laminate floors, as insulation panels for indoor and outdoor use or as wall panels. Such material plates are usually made of wood fibers, wood shavings or strands, e.g. In the case of wood fiber laminate floors, HDF (High Density HDF) panels are used with a variety of decors.

For decoration of such wood-based panels there are several approaches. So there is a possibility in the coating of wood-based panels with a decorative paper, the variety of differently patterned decorative papers are no limits. As an alternative to the use of decorative papers on wood-based panels, the possibility of direct printing of the wood-based panels has increasingly developed, with a printing of paper and its subsequent lamination or direct coating is omitted on the wood-based panels. The printing techniques mainly used here are gravure printing and digital printing. The gravure printing process is a printing technique in which the elements to be imaged are formed as depressions in a printing form, e.g. in a printing roller, which is colored before printing. Digital printing makes it possible to produce a print image with particularly high quality through a higher resolution and also allows a wider range of applications with high flexibility.

In recent years, the printing of wood-based panels from simple two-color printing in the gravure printing process for furniture backs on the four-color printing in the gravure printing for example laminate flooring products to digital printing for high-quality applications has developed. The use of medium-density fiberboard (MDF) or fiberboards with increased density (HDF boards) proves to be particularly advantageous for direct printing, as they ensure a good print image due to the smooth and fine surface. The pressure is usually carried out on a primer, in particular a pigment-containing primer, which is applied during the preparation of the surface of the wood fiber board for printing usually several times by Walzenauftragswerke. To improve the surface quality, one or more sanding units can also be positioned before and / or between the commissioned works. With their help height irregularities can be eliminated and thus the quality of the surface to be printed on the wood fiber board can be improved. On the one hand, the primer should produce a uniform surface; on the other hand, the pigmentation of the primer layer should cover the inherent color of the wood material.

A basic prerequisite for even priming of the wood fiber boards is as uniform as possible moist level of wood fiber board used as a support plate, wherein the most uniform possible moisture level should not be too low. So the moisture should be above about 4% for a wood fiber board.

Due to the specific manufacturing process of wood fiber boards, which includes a hot pressing of glued wood fibers, however, considerable moisture differences in the boards in cross section and in the general moisture distribution can occur after production during the cooling process and during storage of the wood fiber boards. Thus, in the course of the production process of wood fiber support plates, the fibers are transported under pressure and high temperatures of press belts by so-called Kontipressen. Here, the outer layers of the later wood fiber boards are strongly dried, whereas the middle layers are moistened. After cooling the plates, for example in so-called star walls, in which also a loss of moisture occurs, the still warm plates are stacked and stored in stacks. In the course of the storage process, a drying of the plate edges initially occurs, whereas in the middle of the plate stack a uniform distribution or equalization of the temperature and the moisture takes place. After complete cooling, rewetting of the edges of the plates takes place from the outside to the inside, with cooling and rewetting taking place faster or even slower, depending on the storage temperature and relative humidity. As an empirical value can be said that the cooling takes longer in the summer, whereas the rewetting is faster because of the typically higher moisture content of the air in the summer. By contrast, cooling takes place more quickly in winter, but the return air conditioning or rewetting of the panels takes longer due to the reduced supply of moisture in the air.

This different drying and moisture behavior of wood fiber boards leads to considerable problems in the primer or the subsequent printing. A fiberboard that has not yet cooled or is not on a uniform wet level, can be poor or even not printed at all. The wood fiber boards are too dry especially in the edge area and can therefore only conditionally or poorly wet by water-based primers. This circumstance manifests itself in reduced orders and uneven jobs in the typically light to white primer. Due to the lack of primer in a range of 20 to 40 g primer / m ^{2 also} results in a primed area, which has considerable unevenness. These unevenness in the primer can not be completely printed by the pressure rollers in the gravure printing later. This then leads to bright imperfections in the print, which are caused by the still visible light primer. The problem is that the moisture responsible for this or the uneven distribution of moisture in the surface of a wood fiber board can not be determined exactly, since only the moisture in the uppermost layer of the wood fiber board is responsible for the quality of wetting the surface of the wood fiber board.

To reduce this problem, the wood fiber boards are first stored in a conventional manner after production over a defined period of time to adjust a uniform moist distribution in the plates. However, it can always be due to a variety of causes such. Standstill of the production plant or periods of heat come to operational bottlenecks that do not allow a defined Reklimatisierung the wood fiber boards, not the wood fiber boards in time. This can then lead to certain plate batches can only be processed at reduced speed or not at the primer and printing line. Both are associated with additional costs and delays in further processing and delivery to customers.

One approach to solving this problem is to completely air-condition the storage room or wood pulp maturing warehouse. However, this means significant additional costs for storage quantities of several 10,000 m ³ wood fiber boards.

Thus, the conventional methods have a number of disadvantages. The conventional process for direct printing of fiberboard is highly dependent on climatic conditions. Moreover, this process does not allow any reaction possibilities in the case of short-term investment scenarios on the fiberboard line and there is a reduced or Inferior quality during priming and printing up to increased rejects.

The present invention is therefore based on the technical problem of solving the problems described with the least possible technical effort and to be able to further process wood fiber boards under moisture fluctuations. In addition, an increase in costs should be avoided and, if possible, the costs should be reduced.

The stated object is achieved by a method having the features of claim 1.

• Bereitstellen von mindestens einer Holzfaserträgerplatte,
• Befeuchten von zumindest einem Abschnitt einer Oberfläche der mindestens einen Holzfaserträgerplatte mit wasserhaltigen Dampf,
• Schleifen der zumindest abschnittsweise befeuchteten Oberfläche der Holzfaserträgerplatte, und
• Auftragen von mindestens einer Dekorschicht auf die zumindest abschnittweise befeuchtete Oberfläche der Holzfaserträgerplatte.

Accordingly, a method for producing a wood-based panel, in particular provided with a decorative layer wood-based panel is provided. The present method comprises the following steps:

• Providing at least one wood fiber support plate,
• Wetting at least a portion of a surface of the at least one wood fiber support plate with aqueous vapor,
• Grinding the at least partially moistened surface of the wood fiber support plate, and
• Applying at least one decorative layer on the at least partially moistened surface of the wood fiber support plate.

Accordingly, a process is provided with the present method, in which a targeted moistening (steaming or spraying) with water-containing steam, preferably water, is carried out by not yet re-climate-treated wood fiber support plates. According to the method, after separating the wood fiber support plates, eg from a stack of plates, either part / section or the entire surface of the wood fiber support plate is increased by steaming or spraying with water-containing steam in the wet level in front of the printing line. Since the primary objective of the present method is to moisten the surface of the wood fiber support plate, just a few grams of water-containing steam per square meter surface suffice. By limiting the moistening or evaporation amount is also avoided that it comes in the surface of the wood fiber support plates to eventual fiber swelling, which could cause an impairment of the surface or surface unrest.

The present method provides significant benefits in terms of cost reduction, inventory reduction, and quality improvement

As mentioned, after the moistening device, a first grinding machine will be positioned so that slight swelling can be removed immediately if necessary.

Furthermore, the humidification can be adjusted depending on the existing problem or problem by failure of a corresponding program. Thus, it is possible to perform by targeted shutdown and control a vapor deposition only in the edge region of the wood fiber boards, whereas in full-surface problems, the entire surface of the wood fiber board can be moistened.

The application of an aqueous liquid on wood fibers during the production process of wood fiber boards is eg from the DE 10 2008 008 240 B4 or even the DE 10 2008 049 132 A1 known, with significant differences to the present method.

So will in the DE 10 2008 240 B4 Water applied to the top of a wood-based panel in an amount between 10 ml / m ² and 40 ml / m ² , which also moves into the wood-based panel. The amounts of water described herein are well above the amounts of hydrous vapor used in the present process, as will be explained in more detail later.

In the DE 10 2008 049 132 A1 For example, applying an aqueous liquid to one side of a raw wood fiberboard and simultaneously applying a vacuum to the second side of the raw wood fiberboard opposite the first side so that the aqueous liquid is drawn into and / or through the raw wood fiberboard. Such moisture penetration of the raw wood fiber board can, for example, prevent dimensional changes of the fiberboard. However, a complete moisture penetration of a fiberboard leads to a swelling of the surface of the fiberboard, which just precludes a uniform priming and printing of the fiberboard.

In one embodiment of the present method, the water-containing vapor used for at least partially moistening the surface of the wood fiber support plate consists of at least 95%, preferably at least 98%, particularly preferably 100% water. It is conceivable to add hydrous steam additives to the To improve the properties of the fiberboard. For example, biocides or surfactants to improve the wetting properties of the water vapor can be added to the same. The additives may be added to the steam or water-containing steam at 0 to 5% by weight, preferably 0 to 2% by weight.

It is further preferred that the water-containing vapor used for at least partially wetting the surface of the wood fiber support plate has a droplet size between 5 and 50 μm, preferably 10 and 40 μm, particularly preferably between 20 and 30 μm. Typically, the present process uses a water vapor having a droplet size of 30 microns.

The temperature of the water-containing vapor, in particular of the water vapor, can be up to 60 °, with temperatures between 30 and 60 ° C, in particular 40 and 50 ° C are preferred.

In a further embodiment of the present method, the water-containing vapor used for at least partially wetting the surface of the wood fiber support plate in an amount between 1 to 10 g / m ² wood fiber support plate, preferably between 2 to 8 g / m ² , particularly preferably 3 to 5 g / m ² applied. This corresponds to about a volume amount of aqueous vapor of 1 to 10 ml / m ² , preferably 2 to 8 ml / m ² , particularly preferably 3 to 5 ml / m ² .

According to the present method, the at least partially moistened surface of the wood fiber support plate is subjected to at least one grinding operation after the step of sputtering. During the grinding process, a part of the moistened surface of the wood fiber support plate is abraded, yet surprisingly - as explained later in the embodiment, a significant improvement in the surface quality of the wood fiber support plate for the subsequent application of the decorative layer. The process of grinding after wetting the surface of the wood fiber support plate can be repeated as often as desired.

In a further embodiment of the present method, the at least partially moistened surface and possibly ground surface of the wood fiber support plate is at least partially dried. The intermediate drying of the moistened and ground wood fiber support plate can be done eg in an IR dryer.

In a next step of the present process, at least one resin layer can be applied to the at least partially moistened, ground and subsequently dried surface of the wood fiber support plate. This resin layer is also referred to as rolling base and serves to improve the adhesion of the primer layer on the support plate. The rolling base preferably comprises a formaldehyde resin, e.g. Melamine-formaldehyde resin, melamine-urea-formaldehyde resin or urea-formaldehyde resin. This resin layer can be applied one or more times and accordingly consist of several layers. Preferably, the resin layer (rolling base) after application, e.g. dried in a convection dryer.

In a further preferred embodiment of the present method, in a next step, at least one primer layer is applied to the at least one resin layer.

The primer layer preferably used in the present method comprises a composition of casein as a binder and inorganic pigments, especially inorganic color pigments. As color pigments, white pigments such as titanium dioxide TiO ₂ can be used. Other color pigments may be calcium carbonate, barium sulfate or barium carbonate. The primer contains, in addition to the color pigments such as titanium dioxide and casein, water as a solvent.

It is likewise preferred if the applied pigmented base layer comprises at least one, preferably at least two, more preferably at least four successively applied layers or jobs, wherein the application quantity between the layers or jobs can be the same or different, ie the applied quantity every single layer can vary. Thus, the application amount of a layer or an order of the primer layer between 1 to 50 g / m ² , preferably between 2 to 30 g / m ² , more preferably between 5 and 15 g / m ² wood fiber support plate amount.

The total amount of the applied pigmented base layer, in particular in the form of a liquid application, may be between 5 and 200 g / m ² , preferably between 10 and 150 g / m ² , particularly preferably between 20 and 100 g / m ² wood fiber board.

After application of the primer layer, the same is dried in at least one convection dryer. In the case of application of several primer layers or primer layers, a respective drying step takes place after application of the respective primer layer or primer layer. It is also conceivable that one or more grinding units are provided after each drying step of a primer layer for grinding the primer layers.

In the present case, in a further embodiment, in the case of the application of at least one primer layer to the carrier plate, then to the same at least one primer layer, e.g. be applied in the form of a UV or ESH spatula.

In a further variant of the present method, the at least one decorative layer is applied by gravure printing or digital printing. In the case of a printed decor, a water-based pigmented ink can be gravure coated or digital-printed. This water-based pigmented ink can also be applied in more than one layer, for example two to ten layers, preferably three to eight layers.

As mentioned, the application of the at least one decorative layer preferably takes place by means of an analog gravure printing method and / or a digital printing method. The gravure printing process is a printing technique in which the elements to be imaged are in the form of depressions in a printing form which is inked before printing. The ink is predominantly in the recesses and is due to contact pressure of the printing plate and adhesion forces on the object to be printed, such. a wood fiber support plate, transferred. On the other hand, in digital printing, the print image is transferred directly from a computer to a printing press, such as a press. a laser printer or ink jet printer. This eliminates the use of a static printing form. Both methods allow the use of aqueous inks and inks or UV-based colorants.

It is also conceivable to combine the mentioned printing techniques from gravure and digital printing. A suitable combination of the printing techniques can be done either directly on the support plate or the layer to be printed or even before printing by adjusting the electronic records used.

In a further preferred variant of the present method, at least one wearing or covering layer is applied to the at least one decorative layer, which after the Order is subjected to at least one drying step, for example in a convection dryer.

The at least one wear layer may be formed in different ways. In a first variant a) the wear layer comprises natural or synthetic fibers, at least one binder, abrasion-resistant particles, pigments and / or at least one additive. In a further variant b), the at least one wear layer consists of a UV-curable and / or electron beam-curable (ESH) protective layer. According to another variant c), the wear layer may be formed in the form of a thermosetting protective layer.

The individual possible variants of the wear layer are explained in more detail below.

The wear layer of variant a) of fibers, binders, particles, pigments and / or additive is applied in the form of a powder to the upper side of the fiber carrier plate, in particular to the decorative layer of the fiber carrier plate. The composition according to a) is composed of 30 to 65% by weight, preferably 40 to 60% by weight of fibers, 20 to 45% by weight, preferably 30 to 40% by weight of binder, 5 to 25% by weight, preferably 10 to 20% by weight of abrasion-resistant particles and 0 to 8 wt%, preferably 0.5 to 6 wt% additive together.

The thickness of the wear layer a) can be between 0.05 and 10 mm, in particular between 0, 1 and 5 mm. In this case, this wear layer a) may be divided at least into an upper and a lower layer, wherein the upper layer may have a thickness between 0.05 and 7 mm, whereas the lower layer has a preferred thickness between 0.5 and 3 mm. In particular, a thickness of one of the two layers of 0.7 mm is preferred.

The upper layer may preferably contain a proportion of between 0 and 1% by weight of the additive, while the proportion of the additive in the lower layer is advantageously between 0.5 and 5% by weight. It is also conceivable that the lower layer has no abrasion-resistant particles. These are preferably added to increase the wear resistance of the surface layer in the upper layer.

The at least one additive is advantageously selected from the group comprising conductive substances, flame retardants, luminescent substances and metals. The conductive substances may be selected from the group comprising carbon black, carbon fibers, Metal powders and nanoparticles, in particular carbon nanotubes. As flame retardants phosphates, borates, in particular ammonium polyphosphate, tris (tri-bromneopentyl) phosphate, zinc borate or boric acid complexes of polyhydric alcohols can be used. The use of flame retardants leads to a reduction in flammability and is therefore of particular importance in laminate floors, which are used in closed rooms with special requirements for fire protection or in escape routes.

The luminescent substances used are preferably fluorescent and / or phosphorescent substances based on inorganic or organic substances, in particular zinc sulfide and alkaline earth aluminates. The luminescent substances can be applied to the surface in geometric shapes by means of templates. By incorporating these dyes into the surface of material panels, which can be used as floor or wall panels, for example, in closed rooms, a reference to escape routes and escape direction is thus possible in case of failure of the lighting.

The natural or synthetic fibers used are preferably selected from the group consisting of wood fibers, cellulose fibers, partially bleached cellulose fibers, wool fibers, hemp fibers and organic or inorganic polymer fibers.

The binder used is advantageously a binder selected from the group comprising melamine, acrylate and polyurethane resins.

The abrasion-resistant particles are preferably selected from the group consisting of aluminum oxides, corundum, boron carbides, silicon dioxides, silicon carbides and glass beads.

According to the further variants b) and c), the wear layer can also be present as a UV-curable and / or electron beam-curable (ESH) protective layer or as a thermosetting resin layer (liquid overlay).

Radiation-curable acrylate-containing paints can be used in particular for variant b) of the present protective layer. Typically, the radiation-curable coatings used for this purpose contain methacrylates, such as, for example, polyester (meth) acrylates, polyether (meth) acrylates, epoxy (meth) acrylates or urethane (meth) acrylates. It is also conceivable that the acrylate or acrylate-containing lacquer used substituted or unsubstituted monomers, oligomers and / or polymers, in particular in the form of Acrylic acid, acrylic ether and / or acrylic acid ester monomers, oligomers or polymers. The acrylates mentioned allow crosslinking in the presence of UV or electron beams in the curing or drying process.

In one embodiment, preferably more than one radiation-curable protective layer, preferably two or three radiation-curable protective layers are applied, which are each arranged or applied to one another. Also, the at least one radiation-curable protective layer may contain chemical crosslinkers, e.g. Isocyanate-based, whereby the intermediate adhesion of the individual superimposed layers is increased.

In the radiation-curable wear layer, which is arranged on the printed decorative layer, the above-mentioned abrasion-resistant particles, fibers and other additives, such as flame retardants, conductive substances and / or luminescent substances may be added.

The heat-curable resin layer used as wear layer according to variant c) preferably comprises a formaldehyde-containing resin, in particular a melamine-formaldehyde resin and / or melamine-urea-formaldehyde resin. Like the other protective layer variants already mentioned, the thermosetting resin layer may also contain abrasion-resistant particles, natural and / or synthetic fibers and other additives. Such a thermosetting resin layer is also called a liquid overlay. It is also possible to use a plurality of thermosetting resin layers, which are arranged one above the other and are applied in succession. In addition, wetting agents and release agents are preferably used in such a liquid overlay layer. A process for the preparation of the described liquid overlay layer is disclosed in US 5,348,859 EP 233 86 93 A1 described.

The wood fiber board provided with a wearing layer or covering layer of the variant a (powder), variant b (UV or ESH layer) and variant c (liquid overlay layer) can likewise be provided with a 3D embossing structure, the surface structure preferably being optional in a short-cycle press imprinted synchronously with the decor. The 3D structure is preferably embossed or impressed by means of suitable embossing structures. The structuring can be carried out using structured paint rollers, structured calenders or structured press plates.

The at least one wood fiber support plate is selected from the group consisting of chipboard, high density wood fiber board (HDF), medium density wood fiber board (MDF), OSB board and WPC board. The wood board used as a support plate has a maximum density of 1400 kg / m ³ , preferably 1200 kg / m ³ , a minimum density of 750 kg / m ³ , preferably 800 kg / m ³ , and a gross density of 850 kg / m ³ on.

The present method thus enables the production of a wood-based panel with the following layer structure: Wood fiber support plate - resin layer (rolling base) - primer layers - primer layer - decorative layer - wear layer. Each of these layers may be present in one or more layers. It is generally possible that e.g. multiple primer layers and a primer layer are present. On the back of the wood fiber support plate a Gegenzugpapier and other sound insulating layers can be applied.

The present method for producing a wood-based panel is carried out in a device or production line which has at least one device for moistening at least a portion of a surface of the at least one wood fiber support plate with aqueous vapor and at least one device for applying at least one decorative layer to the at least partially moistened Surface of the wood fiber support plate comprises, wherein the at least one application device is arranged in the processing direction after the moistening device.

In a variant of the present device, the moistening device allows a spray application of water, optionally with additives in aqueous solution or dispersion, an automatic adjustment of the spray rate to the speed and automatic cleaning cycles. The spray liquid is applied at a temperature of up to 60 ° C, a pH between 2 to 8 and a viscosity of up to 200 mPa · s. The spray widths achievable with the moistening or spraying device are between 180 to 5,700 mm and the spraying amounts are between 10 to 4,000 ml / (m • min), i. up to 10 ml / m2 at a feed rate of 400 m / min.

To carry out the present method, it is likewise advantageous if at least one grinding device for grinding the at least partially moistened surface of the wood fiber support plate is provided in the production line. The at least one grinding device is arranged downstream of the moistening device in the processing direction.

In a further variant, the present device comprises a device for applying a resin layer (rolling base) to the moistened and ground carrier plate and a device for drying the resin layer (eg in the form of a convection dryer), both devices being arranged downstream of the moistening device and the grinding machine are.

In a further embodiment, the present device comprises at least one device for applying a pigmented layer, e.g. a primer layer on a backing plate and a device for drying the primer layer, e.g. a convection dryer. Depending on requirements, more than primer layer can be applied, so that more than one application device for the primer layer, each with a subsequent convection dryer can be provided in the production line. The number of application devices for the primer layer with subsequent convection dryer is arbitrarily variable and easily adaptable to the given production conditions.

In a further embodiment variant of the present production line, the application device for the primer is followed by at least one application device for a primer layer followed by convection dryer followed by at least one application device, preferably two to three application devices for the decorative layer and at least one final application device for a cover or wear layer including convection dryer on.

The application devices for the various layers to be applied can be in the form of a roller, spray device or pouring device, and the drying devices respectively arranged downstream of the application devices can be in the form of a convection dryer, IR and / or NIR drier.

1. a) mindestens eine Befeuchtungsvorrichtung zum Befeuchten von zumindest einem Abschnitt einer Oberfläche einer Holzfaserträgerplatte mit wasserhaltigen Dampf;
2. b) mindestens eine Schleifmaschine zum Schleifen der Oberfläche der zumindest abschnittsweise befeuchteten Oberfläche der Holzfaserträgerplatte und mindestens ein in Verarbeitungsrichtung hinter der Schleifmaschine angeordnetes IR-Aggregat (wobei das IR-Aggregat insbesondere eine Erzeugung einer vorbestimmten Mindestoberflächentemperatur und Vergleichmäßigung der Oberflächentemperatur dient);
3. c) eine erste Auftragsvorrichtung zum Auftragen von mindestens einer ersten Harzschicht (Walzgrund) auf die Holzfaserträgerplatte;
4. d) eine in einer Verarbeitungsrichtung hinter der ersten Auftragsvorrichtung angeordnete erste Trocknungsvorrichtung (z.B. Konvektionstrockner) zum Trocknen der mindestens einen ersten Harzschicht (Walzgrund);
5. e) eine in Verarbeitungsrichtung hinter der ersten Auftragsvorrichtung angeordnete zweite Auftragsvorrichtung zum Auftragen von mindestens einer Grundierungsschicht auf die Holzfaserträgerplatte, wobei die zweite Auftragsvorrichtung mindestens eine, bevorzugt zwei, insbesondere bevorzugt vier Auftragswerke umfasst;
6. f) eine in Verarbeitungsrichtung hinter der zweiten Auftragsvorrichtung angeordnete zweite Trocknungsvorrichtung (z.B. Konvektionstrockner) zum Trocknen der mindestens einen Grundierungsschicht;
7. g) eine in Verarbeitungsrichtung hinter der zweiten Trocknungsvorrichtung zum Trocknen der mindestens einen Grundierungsschicht angeordnete dritte Auftragsvorrichtung zum Auftragen von mindestens einer Primerschicht auf die Holzfaserträgerplatte;
8. h) eine in Verarbeitungsrichtung hinter der dritten Auftragsvorrichtung angeordnete dritte Trocknungsvorrichtung (z.B. Konvektionstrockner) zum Trocknen der mindestens einen Primerschicht;
9. i) eine in Verarbeitungsrichtung hinter der dritten Trocknungsvorrichtung zum Trocknen der Primerschicht angeordnete vierte Auftragsvorrichtung zum Auftragen von mindestens einer Dekorschicht, wobei die vierte Auftragsvorrichtung mehrere Druckwalzen zum Tiefdruck (z.B. Drei- oder Vierdruckwalzen) umfassen kann;
10. j) eine in Verarbeitungsrichtung hinter der vierten Auftragsvorrichtung zum Auftragen der Dekorschicht angeordnete fünfte Auftragsvorrichtung zum Auftragen von mindestens einer Schutzschicht; und
11. k) eine in Verarbeitungsrichtung hinter der fünften Auftragsvorrichtung zum Auftragen der mindestens einen Schutzschicht angeordnete vierte Trocknungsvorrichtung (z.B. Konvektionstrockner) zum Trocknen der mindestens einen Schutzschicht.

In a preferred embodiment, the construction of an assembly line is as follows:

1. a) at least one moistening device for moistening at least a portion of a surface of a wood fiber support plate with aqueous vapor;
2. b) at least one grinding machine for grinding the surface of the at least partially moistened surface of the wood fiber support plate and at least one in Processing direction behind the grinding machine arranged IR aggregate (the IR unit is in particular a generation of a predetermined minimum surface temperature and equalization of the surface temperature);
3. c) a first application device for applying at least a first resin layer (rolling ground) to the wood fiber support plate;
4. d) a first drying device arranged in a processing direction behind the first application device (eg convection dryer) for drying the at least one first resin layer (rolling base);
5. e) a second application device arranged behind the first application device in the processing direction for applying at least one primer layer to the wood fiber support plate, the second application device comprising at least one, preferably two, particularly preferably four, applicators;
6. f) a second drying device arranged downstream of the second application device in the processing direction (eg convection dryer) for drying the at least one primer layer;
7. g) a third application device arranged behind the second drying device for drying the at least one primer layer in the processing direction for applying at least one primer layer to the wood fiber carrier plate;
8. h) a third drying device arranged downstream of the third application device in the processing direction (eg convection dryer) for drying the at least one primer layer;
9. i) a fourth application device arranged behind the third drying device for drying the primer layer, for applying at least one decorative layer, wherein the fourth application device may comprise a plurality of gravure printing rollers (eg, three- or four-pressure rollers);
10. j) a fifth application device arranged behind the fourth application device for applying the decorative layer in the processing direction for applying at least one protective layer; and
11. k) a downstream in the processing direction behind the fifth application device for applying the at least one protective layer arranged fourth drying device (eg convection dryer) for drying the at least one protective layer.

The application devices used are preferably applicator rollers which allow the layers to be applied to the upper side of the wood-based panels.

Depending on the requirements of the production line, it is of course possible to vary the number of application device and drying devices. So it is e.g. conceivable and possible, a production line of two units comprising application device and drying device or even more than two such. use three, four or five units of application device and drying device.

Figur 1

eine schematische Darstellung einer Fertigungslinie einer Holzwerkstoffplatte unter Anwendung des erfindungsgemäßen Verfahrens.

The invention will be explained in more detail with reference to the figures of the drawings of an embodiment. Show it:

FIG. 1

a schematic representation of a production line of a wood-based panel using the method according to the invention.

The present method using the example of a printing plant, the FIG. 1 is shown schematically explained.

The press will process 2.07 m wide and 2.80 m long HDF boards with a plate thickness of 6 to 12 mm at speeds of up to 85 m / min. First, the HDF raw plates are separated and steamed in a moistening device 1A 3.5 g of water vapor / m ² and a droplet size of about 30 microns.

After moistening, the moistened surface is sanded in a grinding machine 1. After grinding, the plates are preheated in an IR dryer 2 to a temperature of about 45 ° C.

This is followed by a first application of resin (rolling base) in the first coater 3 with subsequent drying by hot air in a convection dryer 4. The coating resin used is an aqueous melamine-formaldehyde resin having a solids content of 60% by weight.

Then, a water-based white primer based on casein and inorganic pigments is applied by means of four application units 5 and dried by hot air after each application in a convection dryer 6. The individual commissioned works 5 apply different amounts of primer. The total white application varies depending on the pressure requirement between 20 g / m ² and 30 g / m ² .

This is followed by a primer application 7 followed by drying in a further convection dryer 8. This is followed by printing 9 (decoration) of the plates in indirect gravure printing. After printing, the plates are coated with melamine-formaldehyde resin 10 (protective layer) and also dried in a convection dryer 11. Then the plates are stored for a few days before being processed further.

The primer process is particularly important as it has a significant impact on the color print quality of the coated HDF plates. For a particular color pattern also a constant amount of white order must be guaranteed, otherwise it may come to different brightnesses of the primer and thus also to different colors within a color pattern over several plates.

Exemplary embodiment :

Large-format HDF boards (2,500 mm x 2007 mm x 7 mm) were separated from a stack and given a primer and a decorative print at a production speed of 85 m / min. After cleaning, a transparent primer based on a thermosetting resin was used. (Application amount: approx. 20 g liquid / m ² ) for use. After intermediate drying with hot air, the application of a pigmented primer with casein as binder followed. The application of the pigmented primer was repeated four times after intermediate drying. The total order amount was about 25 g liquid / m ² . After a further primer application (order quantity: approx. 10 g liquid / m ² ), the decor printing was carried out by gravure printing.

After the decor pressure, flaws caused by uneven primer were seen. They could be observed especially in the front and rear of the plate in the feed direction. When viewed under the microscope, the undercoat not covered by ink could be observed in these defects. To eliminate these defects was behind the plate separation humidification of the affected plate parts z. B. made with a rotor spray system from Ahlbrandt. The "order quantity" was about 3.5 g of water vapor per square meter. The droplet size was about 30 microns. The flap system on the humidification system was controlled by photocells.

The fiberboard showed less defects after printing (fewer unprinted areas) and this less pronounced than the standard plate. An evaluation of the defects with the help of software should confirm the visually obtained result. As a result, the percentage of the unprinted area in the standard plate was found to be 7.17%. In the case of the moistened fibreboard, the unprinted area was only 6.18%.

This is surprising since the previously moistened surfaces are sanded off again during the cleaning procedure and the exposure time of the water mist to the surface of the plate is only about 5 seconds.

In a further experiment, the same amount of water was applied after grinding. An unprinted area of 9.71% was determined. In that regard, moistening before grinding is surprisingly effective.

Claims (15)

Method for producing a wood-based panel, in particular a wood-based panel provided with a decorative layer,
comprising the steps Providing at least one wood fiber support plate, Moistening at least a portion of a surface of the at least one wood fiber support plate with aqueous vapor, - Sanding the at least partially moistened surface of the wood fiber support plate, and - Applying at least one decorative layer on the at least partially moistened and ground surface of the wood fiber support plate. A method according to claim 1, characterized in that the water-containing vapor used for at least partially wetting the surface of the wood fiber support plate consists of at least 95%, preferably from at least 98%, particularly preferably 100% of water. A method according to claim 1 or 2, characterized in that the water-containing vapor used for at least partially wetting the surface of the wood fiber support plate has a droplet size between 5 and 50 microns, preferably 10 and 40 microns, more preferably between 20 and 30 microns, Method according to one of the preceding claims, characterized in that the water-containing vapor used for at least partially wetting the surface of the wood fiber support plate in an amount between 1 to 10 g / m ² , preferably between 2 to 8 g / m ² , particularly preferably 3 to 5 g / m ^{2 is} applied. Method according to one of the preceding claims, characterized in that after the step of moistening the at least partially moistened surface of the wood fiber support plate is at least partially dried. Method according to one of the preceding claims, characterized in that at least one resin layer is applied to the at least partially moistened and ground surface of the wood fiber support plate. A method according to claim 6, characterized in that at least one primer layer is applied to the at least one resin layer. A method according to claim 7, characterized in that at least one primer layer is applied to the at least one primer layer. Method according to one of the preceding claims, characterized in that the at least one decorative layer is applied by gravure printing or digital printing. A method according to claim 9, characterized in that at least one decorative layer is applied to the at least one decorative layer. Method according to one of the preceding claims, characterized in that the at least one wood fiber support plate is selected from the group comprising chipboard, high-density wood fiber board (HDF), medium-density wood fiber board (MDF), OSB board and WPC board. Apparatus for carrying out a method according to at least one of the preceding claims at least one device for moistening at least a portion of a surface of the at least one wood fiber support plate with aqueous vapor, at least one grinding device for grinding the at least partially moistened surface of the wood fiber support plate, which is arranged in the processing direction after the moistening device, and - At least one device for applying at least one decorative layer on the at least partially moistened surface of the wood fiber support plate Apparatus according to claim 12, characterized in that the moistening device is designed as a spraying device. Apparatus according to claim 12 or 13, characterized by at least one device for applying at least one primer layer. Device according to one of claims 12 to 14, characterized by at least one device for applying the decorative layer.

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