Method for printing a wood material board and wood material board with printed decorative layer

Abstract

Disclosed is a method for printing a wood material board, in particular a wood fiber material board, by means of a digital printing process. The method includes the steps of (a) printing at least one side of a wood material board by means of digital printing technology, forming a decorative layer; (b) applying a protective layer containing at least one resin, at least one radiation-curable varnish and/or at least one polyurethane to the decorative layer of the wood material board; and (c) pre-drying and/or pre-gelling the protective layer applied to the decorative layer of the wood material board.

Claims

1. A method for printing a wood material board by means of a digital printing process, comprising the steps of: a) applying at least one pre-coating or priming layer comprising at least one aqueous resin solution to at least one side of the wood material board that is to be printed, wherein the aqueous resin solution has a solid content between 30 and 80% by weight based upon total weight of the aqueous resin solution and is applied in an amount of between 10 and 80 g/m.sup.2, and after application is dried to a moisture content of 10% or less; b) applying at least one layer of water-based pigmented primer that is dried after application; c) printing the at least one side of the wood material board by means of digital printing technology, forming a decorative layer, wherein the amount of digital printing ink used is between 5 and 10 g/m.sup.2; d) applying a protective layer containing at least one resin to the decorative layer, wherein the amount of protective layer applied is between 5 and 50 g/m.sup.2; and e) pre-drying the protective layer applied to the decorative layer, wherein the protective layer is pre-dried to the extent that it is still free-flowing and cross-linkable, such that intermediate storage of the printed board is possible before application of further wear protection or other finishing layers and such that the protective layer acts as a primer between incompatible layers, wherein the pre-drying of the at least one resin used as the protective layer is performed for 5 to 15 seconds depending on the application quantity.

2. The method as claimed in claim 1, wherein, the at least one pre-coating or priming layer further comprises at least one radiation-curable mastic compound.

3. The method as claimed in claim 1, wherein, before the printing of the at least one side of the wood material board, at least one layer of a water-based, pigmented printing ink is applied to the at least one side of the wood material board that is to be printed.

4. The method as claimed in claim 1, wherein a water-based digital printing ink is used to print the at least one side of the wood material board.

5. The method as claimed in claim 1, wherein the at least one resin, which forms the protective layer to be applied to the decorative layer of the wood material board comprises at least one water-compatible resin.

6. The method as claimed in claim 1, wherein the protective layer to be applied to the decorative layer of the wood material board further comprises at least one radiation-curable varnish chosen from the group of acrylates, modified acrylates, epoxies, and mixtures thereof.

7. The method as claimed in claim 1, wherein the protective layer to be applied to the decorative layer of the wood material board further comprises at least one polyurethane containing an aliphatic urethane.

8. The method as claimed in claim 7, wherein the protective layer to be applied to the decorative layer of the wood material board comprises a mixture of at least one radiation-curable varnish and the at least one polyurethane.

9. The method as claimed in claim 1, wherein the protective layer further comprises at least one radiation-curable varnish and/or at least one polyurethane and step e) is followed by the application and pre-drying of at least one second protective layer made of at least one water-compatible resin that is applied to the pre-gelled protective layer.

10. The method as claimed in claim 1, wherein the wood material board printed and provided with a protective layer is fed to a short-cycle press for further processing.

11. The method as claimed in claim 1, wherein the protective layer applied is between 8 and 30 g/m.sup.2.

12. The method as claimed in claim 1, wherein the protective layer applied is between 10 and 20 g/m.sup.2.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention will be explained in more detail on the basis of a number of exemplary embodiments, with reference to the FIGURES of the drawing, in which:

(2) FIG. 1 shows a perspective view of a cross section of a printed wood material board according to one embodiment.

DETAILED DESCRIPTION OF THE INVENTION

(3) FIG. 1 shows the cross section of a wood material board printed by means of the present method. Firstly, a priming layer 2 made of an aqueous resin solution or a curable mastic compound was applied to the upper side of the wood material board 1, in order to eliminate irregularities in the surface of the wood material board and to provide an improved surface for the subsequent digital printing.

(4) The decorative layer 3 is then printed onto the priming layer 2, and is subsequently provided with a protective layer 4 made of a water-compatible resin or a radiation-curable varnish. In general, it is also possible for the protective layer 4 to be composed of a first partial layer 4a in the form of a radiation-curable varnish and a second partial layer 4b in the form of a water-compatible resin, which have been applied to the decorative layer 3 one after the other with intermediate drying.

(5) The protective layer 4 is adjoined by a wear layer 5, which consists of a binder and abrasion-resistant particles.

Exemplary Embodiment 1

(6) An HDF board (fiber board with increased bulk density) is firstly pre-coated with an aqueous synthetic resin (melamine-formaldehyde resin). The application quantity is around 20-50 g liquid resin/m.sup.2 (solids content: about 55%). The resin contains the usual additives such as wetting agents, hardeners, release agents and defoamers. After that, the applied resin is dried to a moisture content of about 6% in a convection dryer or a near-infrared oven. Then, a plurality of layers of a water-based, pigmented primer is applied (5-8). After each application, the primer is dried with the aid of a convection dryer or a near-infrared dryer. The primed board is then printed with a motif by using a digital printer. About 6-8 g/m.sup.2 of water-based digital printing ink are used.

Primer/Protective Alternative 1a

(7) A layer of melamine-formaldehyde resin is then applied and pre-dried as already described above. The pre-drying is carried out only up to the point at which the resin is still free-flowing and cross-linkable. As a result, sticking of the resin-coated boards is prevented. As a result of the incomplete cross-linking of the synthetic resin, it is also ensured that an application of further liquid or powdery resin layers (e.g. melamine resin) or resin-impregnated papers and subsequent pressing in short-cycle further processing is possible without any impairment to the adhesion of the layers subsequently applied taking place. The application quantities of the resins (liquid, powdery or on paper) can quite possibly be several hundred grams, depending on the desired structure and structure depth. As mentioned, the boards treated in this way can be fed to a short-cycle press for further processing.

Primer/Protective Alternative 1b

(8) A layer based on UV varnishes (1- or 2-component) or polyurethane or mixtures thereof is applied to the digital print, by which means the adhesion to the printing ink and to the further layers is improved, and which layer serves as a protective layer. Any other desired primers can likewise be used, however. The combined protective and primer layer is applied in a quantity of 8-30 g primer/m.sup.2. The primer can be pre-gelled by a UV lamp, an ESH emitter or NIR. After that, the boards can be stacked and can subsequently be further processed. This can be done, for example, by means of the application of a plurality of layers of UV or ESH varnishes, which, as individual functional layers, prevent the tendency to wear or scratching. The boards treated in this way can then be fed to a short-cycle press for further processing and finishing.

Exemplary Embodiment 2

(9) An HDF board (fiber board with increased bulk density) is firstly pre-coated with a UV or ESH mastic. The application quantity is around 50-100 g varnish/m.sup.2 (100%). The UV/ESH mastic is pigmented and can be applied in a plurality of layers. In each case, drying with the aid of UV or ESH emitters is carried out between the individual applications. If required, after each application/curing, intermediate grinding is carried out. The primed board is then printed with a motif by using a digital printer. About 6-8 g/m.sup.2 UV digital printing ink is used.

Primer/Protective Alternative 2a

(10) A primer based on UV varnishes (1- or 2-component) or polyurethane or mixtures thereof is applied to the digital print, which improves the adhesion to the printing ink and to the further layers and serves as a protective layer. Any other primers desired can likewise be used, however. The combined protective and primer layer is applied in a quantity of 8-30 g primer/m.sup.2. The primer can be pre-gelled by means of a UV lamp, an ESH emitter or NIR. After that, the boards can be stacked and can subsequently be further processed. A layer of melamine-formaldehyde resin is then applied and pre-dried as already described above. The pre-drying is carried out only up to the point at which the resin is still free-flowing and cross-linkable. As a result of the incomplete cross-linking of the synthetic resin, it is ensured that an application of further liquid or powdery resin layers (e.g. melamine resin) or resin-impregnated papers and subsequent pressing in short-cycle further processing is possible without any impairment to the adhesion of the layers subsequently applied taking place. The application quantities of the resins (liquid, powdery or on paper) can quite possibly be several hundred grams, depending on the desired structure and structure depth.

Primer/Protective Alternative 2b

(11) Applied to the digital print, for example, is a UV varnish which contains a primer that improves the adhesion to the printing ink and to the further layers. In addition, the primer is also intended to prevent the occurrence of gas bubbles. These frequently occur during the direct application of a varnish to the UV ink. Surprisingly, this no longer occurs after the primer application. The combined protective and primer layer is applied in a quantity of 8-30 g primer/m.sup.2. This can be, for example, a primer based on a polyurethane. Any other desired primers can likewise be used, however. The varnish can be pre-gelled by a UV lamp or ESH emitter. After that, the boards can be stacked and can subsequently be further processed. This can be done, for example, by means of the application of a plurality of layers of UV or ESH varnishes, which, as individual functional layers, prevent the tendency to wear or scratching. The boards treated in this way can then be fed to a short-cycle press for further processing and finishing.