ES2744807T3 - Method for making digitally printed substrates - Google Patents

Abstract

Process for the manufacture of decorative substrates based on wood fiber or mineral fiber, comprising the steps of: (a) coating a substrate (2) with a liquid reactive composition that can be digitally printed after drying; (b) drying the reactive composition coating the substrate to form a base layer (3) having a permeability such that it can adsorb and release any condensation products formed during step (d) and (e); (c) digitally printing a decoration (4) on the base layer using a liquid ink; (d) drying or curing the liquid ink that forms the digitally printed decoration; and (e) coating the digitally printed decoration with an overlay (5) under conditions that ensure curing of both the base layer and the overlay.

Description

DESCRIPTION

Method for manufacturing digitally printed substrates

[Technical field of the invention]

[0001] The present invention relates to a process for manufacturing decorative substrates, in particular panels and boards, in particular based on wood fibers or mineral fibers such as wood particle boards, MDF substrates (medium density fiber board ) or HDF (high density fiber board) in which a decoration is formed by digital printing.

[Background of the invention]

[0002] The use of digital printing to apply a decoration to wood-based panels and boards such as wood particle boards, MDF or HDF panels is known.

[0003] Digital printing refers to printing procedures of a digital image directly to the substrate. Usually, it refers to professional printing in which small works of electronic publishing and other digital sources are printed using large format and / or large volume laser or inkjet printers. Digital printing has a higher cost per printed object than traditional offset printing procedures, but this price is generally offset by the cost savings achieved by avoiding all the technical steps necessary to make printing plates. It also allows printing on demand, less time and even a modification of the image with each printed copy. The labor savings and the greater capacity of digital presses means that digital printing is reaching a point where it could match or replace the ability of offset printing technology to produce larger runs of several thousand copies at a low price

[0004] However, when digital printing is used on substrates such as high density fiber boards, the decoration is generally still printed on a separate paper or fleece holder that is applied on the substrate. In fact, although a basic layer can be applied to ensure sufficient adhesion of the inks applied, said basic layers can affect the print quality. In fact, a porous layer can absorb the ink resulting in insufficient coverage, while a non-porous basic layer can lead to its coalescence and affect the color quality. However, the use of a separate support for printing makes the process more expensive and complex.

[0005] International patent application WO 2010/084386 therefore proposes using several printing devices and exposing the printing portion deposited by a printing unit to forced drying before activating the next printing unit. Such a procedure is expensive since it requires special equipment. In addition, the quality of the decoration depends on the accuracy of the alignment of the printing unit.

[0006] US 2004/0086678 describes a process for the manufacture of decorative substrates based on wood fiber, in which a substrate is coated with a liquid reactive composition that can be digitally printed after drying. Said reactive composition is dried to form a basic layer on which a decoration is digitally printed using a liquid ink, which is subsequently dried or cured. The digitally printed decoration is then coated with an overlay.

[0007] Another problem encountered with the production of laminates is that multilayer laminates tend to delaminate under tension due to insufficient cohesion between the different layers.

[0008] The technical problem underlying the present invention is, therefore, to provide a process for the manufacture of substrates comprising a decoration formed directly on the substrate by digital printing that overcomes one or more of the drawbacks indicated above.

[0009] In particular, the invention aims to provide a process for the manufacture of said substrates that allows for good image quality.

[0010] In addition, the invention aims to provide such a procedure that does not require the acquisition of special equipment.

[0011] Furthermore, the object of the invention is to provide such a method that produces substrates that show improved resistance to delamination under stress.

[0012] The invention resides in particular in the finding that a basic layer coating made using a liquid reactive composition as specified below forms, after evaporation of volatile components such as solvents, a coating with such porosity. than any product Condensation, such as water, formed later, after curing the ink, or the subsequent layers, can be adsorbed without forming bubbles, which could alter the print quality and / or cohesion between the different layers, thus acting as a suitable primer For this application. Finally, after curing, the composition reinforces the cohesion between the decoration and the substrate, acting as well as an adhesive and avoiding delamination under stress.

[Summary of the invention]

[0013] According to a first aspect, the invention therefore relates to a process for the manufacture of decorative substrates based on wood fiber or mineral fiber, comprising the steps of:

a) coating a substrate with a liquid reactive composition that can be digitally printed after drying; b) drying the reactive composition that covers the substrate to form a basic layer that has a permeability such that it can adsorb and release any condensation product formed during step (d) and (e); c) digitally print a decoration on the basic layer using a liquid ink;

d) dry or cure the liquid ink that forms the digitally printed decoration; Y

e) Coating the digitally printed decoration with an overlap in conditions that ensure the curing of both the basic layer and the overlay.

[0014] The substrates can be, in particular, panels or boards, and more specifically, wood particle boards such as MDF or HDF panels or mineral fiber boards such as calcium silicate boards or fiber cement boards.

[0015] The liquid reactive composition may be formulated as a monocomponent composition or a bicomponent composition. The liquid reactive composition may be water based or may contain organic solvents.

[0016] In some embodiments, it may be preferred if the liquid reactive composition is a bicomponent composition.

[0017] The first component of such bicomponent composition may comprise acrylates functionalized with amine, hydroxy or carboxy, polyester, polyether polyols or vinyl polymers.

[0018] The second component of such bicomponent composition may comprise hardeners of isocyanate and / or aziridine.

[0019] According to a preferred embodiment, the liquid reactive composition is water based.

[0020] The reactive composition preferably has a viscosity in the range of 1 to 3 Pas.

[0021] Advantageously, the reactive composition is applied in step (a) using a roller, an injection device or a spray device.

[0022] Step (b) can be performed remarkably by heating the coated substrate at a temperature of 50 to 80 ° C.

[0023] Preferably, step (c) is performed using water-based ink. Advantageously, the digital printing in step (c) is performed using a drop-on-demand inkjet (DOD) system.

[0024] Step (d) can be performed by heating the substrate having the digitally printed printed decoration thereon at a temperature of 70 to 250 ° C, preferably for a period of 2 to 30 seconds.

[0025] According to a preferred embodiment of the invention, the superposition applied in step (e) is transparent. Preferably, it is in the form of a melamine resin or a sheet or melamine paper.

[0026] Preferably, step (e) is performed by pressing at a temperature in the range of 100 to 300 ° C, with a pressure between 20 and 60 kg / cm2 and / or for a period of 2 to 30 seconds.

[0027] The process of the invention can also further comprise the step of providing a balancing paper or a layer of lacquer to the back of the panel.

[0028] The process according to the invention will be described in more detail below. [Detailed description of the invention]

[0029] The method of the invention aims to manufacture decorative substrates based on wood fiber, especially for use as soil.

[0030] The substrates used in this procedure can be mainly high density fiber boards (HDF). However, the substrates used in this procedure can be based, alternatively, on solid, sheet, plywood, particle or MDF boards.

[0031] In the case of floor panels, the printed fiber boards obtained in the process are cut to form a final floor panel that preferably has an area of less than 0.5 m2, or even less than 0.3 m2 . The thickness of said floor panels can vary between 4 and 25 mm, or even better between 6 and 15 mm. Before applying the process according to the invention, the surface of the substrates can be filled with a layer of material comprising a load to obtain a uniform surface.

[0032] In step (a) of the process according to the invention, the substrate is coated with a liquid reactive composition to form a basic layer.

[0033] The liquid reactive composition preferably used in the process of the invention is a two-component system, in particular a two-component water-based system.

[0034] The first component of the bicomponent composition may include acrylates functionalized with OH, polyester, polyether polyols or vinyl polymers.

[0035] The second component of the bicomponent composition may include isocyanate or aziridine hardeners.

[0036] The reactive composition, with the two components described above combined, typically has an active ingredient content between 50 and 70% by weight.

[0037] The pH of the reactive composition, with the two components mixed, is typically in the range of 6 to 10.5. In some embodiments, the pH is in the range of 7.0 to 9.9. A pH adjuster (for example, acids or bases) can be added to the composition to obtain the desired pH; Typically, the composition is inherently acidic, whereby the pH is raised. The pH can be adjusted using various bases or buffering agents. Suitable bases or buffering agents include, for example, borax, sodium hydroxide, alkaline phosphates, alkali silicates, alkali carbonates, ammonia and amines such as diethanolamine or triethanolamine.

[0038] In addition to the active ingredients, the individual components may also contain other ingredients such as polyvalent metal compounds, alkali soluble resins, solvents, waxes, reactive or non-reactive acrylic compositions, reactive or non-reactive polyester compositions (such as polyester -polyols), surfactants, permanent and fugitive plasticizers, defoamers, wetting agents and biocides. Additionally, or as an alternative, optional ingredients may be added after the reactive composition has been formed by mixing the two individual components. The polyvalent metal compound provides crosslinking of the polymers in the film and increases the detergent resistance of the finish. Plasticizers or coalescing agents can be added to decrease the film formation temperature. Surfactants can be added to help level and moisten. Solvents can be added to aid the coating capacity of the reactive composition. Biocides help minimize mold or fungus formation in the coating. Defoamers and defoamers minimize the formation of bubbles in the coating.

[0039] Bicomponent water-based reactive compositions useful in the process according to the invention are commercially available, for example, from Friedrich Klumpp GmbH, Germany, under the trade name Hydroplast® Printing Sealer.

[0040] The two components can be mixed using conventional means such as manual pneumatic stirrer.

[0041] After mixing the two components, the resulting reactive composition can be applied to the substrate. The reactive composition is formulated as a liquid. It can be applied using conventional means such as one or more rollers, and / or injection or spray devices.

[0042] The reactive liquid composition typically has a viscosity of 1-3 Pas, and usually 1.5-2.5 Pa s. The composition is usually easy to apply and flows easily to match the low points. Reactive composition It typically provides a thin and easy to handle coating.

[0043] After coating, the reactive composition covering the substrate is dried in step (b) to evaporate any volatile component. Said volatile components may, in particular, be any solvent such as water or organic solvents. Drying in step (b) is simply a physical procedure and chemical curing of the reactive composition should be avoided as much as possible.

[0044] Drying can be performed under ambient conditions or optionally accelerated using conventional means such as a heater or fan. The time required for the basic layer to dry depends on several factors, such as the specific individual components used in the composition, its water content, the thickness of the coating and, of course, the surface temperature, the temperature and the humidity of the surrounding air, and the amount of air circulation in the immediate area of the applied reactive composition.

[0045] However, it is preferred that any heat applied during the drying stage be moderate, that it is less than 80 ° C and better than 50 ° C, to avoid or reduce the curing of the basic layer at this stage.

[0046] The thickness of the coated reactive composition after drying is usually between 25 and 150 pm, preferably between 50 and 100 pm.

[0047] After drying, the formed basic layer can be printed digitally. Before curing, the basic layer preferably has a permeability that allows adsorption and release of products such as water that can be formed later, especially after curing the overlay.

[0048] The dry basic layer has a good affinity towards most inks, especially water-based inks, and therefore ensures good adhesion of the ink. In addition, it has a porosity that guarantees that the ink is not absorbed in notable amounts while preventing the drops from bonding.

[0049] In step (c), the substrate coated with a basic layer is subjected to digital printing to form the decoration.

[0050] Generally, the printed decoration represents a wooden pattern. However, other patterns, such as stone patterns or fantasy patterns, are also possible. Since digital printing is very versatile, any pattern can be printed, even in small quantities and in a short time and without the need of an external provider such as a printing company.

[0051] The dry reactive composition provides a particularly good adhesion for water-based inks. Water based inks are also less expensive than solvent based inks. Therefore, water-based inks are preferred for such digital printing. However, solvent-based inks are not excluded.

[0052] Preferably, said digital printing techniques are of the type that can deposit ink droplets in a timely manner, as is the case, for example, with drop-on-demand inkjet (DOD) systems.

[0053] In a preferred embodiment, the substrate has, during printing, a speed of more than 30 m / min and better than more than 80 m / min or, in particular, up to 150 m / min.

[0054] In another preferred embodiment, the substrate is stopped and the print head of the inkjet system passes over the substrate.

[0055] In step (d), the ink forming the printed decoration is dried or cured. The drying of the ink can be carried out under ambient conditions or optionally accelerated using conventional means such as a heater or a fan. The time required for the ink to dry depends on several factors, such as the composition of the ink, its water content, the size of the drop and, of course, the surface temperature, the temperature and the humidity of the air surrounding, and the amount of air circulation in the immediate area of the printed decoration.

[0056] The suitable temperature range for drying or curing the ink may vary with the ink used. However, generally, a temperature in the range of 70 to 250 ° C is generally appropriate. A heating for a period between 2 and 30 seconds is generally sufficient to induce drying and the degree of crosslinking required.

[0057] While it is possible to apply heat to accelerate drying and induce curing of the ink at this stage, the ink can also be dried under ambient conditions and the curing of the ink can be performed during step (e) in which the overlay is applied at a temperature suitable for curing the basic layer and the overlap.

[0058] In step (e), the printed substrate is covered with an overlay or topcoat at a temperature that ensures curing of the overlay, as well as possibly of the ink. Heat also cures the basic layer, essentially by cross-linking reactions of the remaining reactive groups in the basic layer.

[0059] The conditions required to ensure the curing of the basic layer and the overlay include, in particular, the temperature range, duration and pressure. The temperature range, the duration and the pressure suitable for curing the reactive composition and the superposition may vary, since they are particularly dependent on the specific polymer and hardener used. However, generally, a temperature in the range of 100 to 300 ° C, preferably 120 ° C to 250 ° C, is appropriate. A heating for a period between 2 seconds and 10 minutes, preferably 2 to 30 seconds, is generally sufficient to induce the degree of crosslinking required. In addition, a pressure of 20 to 60 kg / cm2 is preferred.

[0060] Curing gives the basic layer novel properties. In particular, it provides the layer with durable elastic and adhesive properties. Therefore, the basic layer can contribute to guarantee the mechanical stability of the substrate. In particular, the adhesive properties of the cured basic layer reinforce the cohesion between the different layers of the panel and, therefore, reduce the risk of delamination of the substrate when subjected to external forces. Advantageously, the basic layer has a permeability with respect to liquids, especially water, which allows the diffusion of products such as water formed during curing. In this way, the accumulation of said products in the form of bubbles can be avoided, and the cohesion between the overlay and the printed substrate is improved.

[0061] Preferably, the overlay is based on an amino resin, such as a melamine provided in the form of a resin or sheet. Alternatively, translucent or transparent lacquers can also be used.

[0062] Preferably, the overlay covers the board in liquid form, for example, by means of one or more rollers. As an alternative, the overlay covers the board using melamine sheets. After this material has possibly dried, then, for example, in the case of an amino resin, a pressing operation can also be applied. By means of said pressing operation, a structure can be obtained on the surface of the respective board. Preferably, the pressed design is combined with the printing operation to obtain an embossed design in the register (EIR).

[0063] Said overlay may also comprise hard particles, such as aluminum oxide, whereby an improved wear resistance is obtained on the surface of the final substrate. This overlay shows better abrasion resistance than a lacquer. Preferably, said particles are provided in the still wet superimposed layer.

[0064] The final thickness of the overlay is generally between 2 and 100, preferably between 5 and 50 pm.

[0065] The back of the substrate may be protected by a balancing paper or a layer of lacquer.

[0066] The invention is preferably directed to the manufacture of substrates such as floor panels or boards and / or panels or boards of which said substrate material substantially comprises or consists of wood particle board, MDF or HDF material. In the case of the manufacture of floor substrates such as panels or boards, the process according to the invention can also comprise the step of forming profiled edge regions in the panels; said profiled edge regions preferably comprise coupling means that allow the interconnection of two or more of said floor panels at their edges.

[Brief description of the drawings]

[0067] Figure 1 schematically represents a substrate manufactured using a preferred embodiment of the process according to the invention.

[0068] According to a preferred embodiment of the process of the invention shown in Figure 1, a panel 1 is manufactured as follows.

[0069] A substrate 2 made of a high density fiberboard (HDF) is coated on top with a reactive composition such as Hydroplast® Printing Sealer (manufactured and sold by Friedrich Klumpp GmbH, Germany) that forms a basic layer 3. More specifically, the two components are mixed in a 95: 5 ratio and then applied in three stages of application on the substrate 2 by a suitable means, for example, by means of a roller. After drying each applied layer for 1 minute at 70 ° C, the basic layer 3 has a preferred thickness of 20 to 40 pm.

[0070] Therefore, the substrate 2 coated with a basic layer 3 is then then provided with a decoration 4 using digital printing and water-based ink, using, for example, a drop-on-demand inkjet system ( DOD) The specific properties of the basic layer 3 improve the adhesion of the ink on the substrate 2 while avoiding excessive absorption or, on the contrary, the coalescence of the ink drops that form the decoration 4.

[0071] After printing the decoration 4, the panel 1 is placed in an oven and heated to a temperature of 70 to 250 ° C, for a period of 2 to 30 seconds in view of the drying and / or curing of the drops of ink that form the decoration 4.

[0072] Subsequently, the decoration applied on the panel 1 is protected by the application of an overlay 5, in particular, based on an amino resin, in particular a melamine resin. Said resin may cover the panel 1 in liquid form, especially by means of one or more rollers. Alternatively, the overlay is provided on the panel 1 in solid form, in particular by means of one or more sheets. The dimensions of the superimposed sheet are chosen according to the dimensions of the panel. As an example, the superimposed sheet has a length of 2620 mm, a width of 2070 mm and a weight of 150 g / m2.

[0073] After drying, if a resin is used, the overlay is subjected to a pressing operation at a pressure of approximately 60 kg / cm 2 at a temperature between 100 and 300 ° C for a period of 10 seconds. This step induces curing of the basic layer 3 and layer 5 by crosslinking the polymers. If necessary, water-based ink can also be cured during this stage. After curing, the basic layer 3 has remarkable adhesive properties and yet maintains its elasticity and flexibility. In this way, cohesion between the different layers of panel 1 is reinforced and the risk of delamination is reduced, especially under tension.

[0074] The final thickness of the superposition 5 is generally between 2 and 100, preferably between 5 and 50 pm. In the case of the manufacture of floor panels, profiled edge regions can be formed in the panels, either before or after applying the process of the invention.

[0075] The back of the panel can be further protected by applying a suitable protective layer 6 such as a balancing paper or a suitable lacquer.

Claims (14)

I. Procedure for the manufacture of decorative substrates based on wood fiber or mineral fiber, comprising the steps of: (a) coating a substrate (2) with a liquid reactive composition that can be digitally printed after drying; (b) drying the reactive composition that covers the substrate to form a basic layer (3) that has a permeability such that it can adsorb and release any condensation product formed during step (d) and (e); (c) digitally print a decoration (4) on the basic layer using a liquid ink; (d) dry or cure the liquid ink that forms the digitally printed decoration; Y (e) coating the digitally printed decoration with an overlay (5) in conditions that ensure the curing of both the basic layer and the overlay. 2. The method according to claim 1, wherein the substrates are panels or boards. 3. The method according to claim 1, wherein the substrates are based on HDF. 4. A method according to any one of claims 1 to 3, wherein the liquid reactive composition is formulated as a bicomponent composition. 5. A method according to any one of claims 1 to 4, wherein the liquid reactive composition is water based. 6. The method according to claim 4 or 5, wherein the first component comprises hydroxyfunctional polymers. 7. A method according to any of claims 4 to 6, wherein the second component of the bicomponent composition comprises hardeners of isocyanate and / or aziridine. 8. Method according to any of claims 1 to 7, wherein the reactive composition has a viscosity between 1 and 3 Pas at 20 ° C. 9. The method according to any one of claims 1 to 8, wherein step (d) is performed by heating the substrate having the digitally printed decoration printed thereon at a temperature of 70 to 250 ° C, preferably during a period of 2 to 30 seconds 10. A method according to any one of claims 1 to 9, wherein step (c) is performed using water-based ink. I I. Method according to any one of claims 1 to 10, wherein the digital printing in step (c) is performed using a drop-on-demand inkjet (DOD) system. 12. A method according to any one of claims 1 to 11, wherein the superposition applied in step (e) comprises a melamine resin. 13. A method according to any one of claims 1 to 12, wherein step (e) is performed by pressing at a temperature in the range of 100 to 300 ° C, with a pressure of 20 to 60 kg / cm2 and / or during a period of 2 to 30 seconds. 14. A method according to any one of claims 1 to 13, further comprising the step of providing a balancing paper or a layer of lacquer to the back of the panel.