RS63670B1 - PROCEDURE FOR THE PRODUCTION OF PRINTED AND DIGITALLY PRINTED BASES - Google Patents

Description

Description

[Technical field of the invention]

[0001] This invention deals with a process for the production of embossed decorative substrates, especially panels and plates, especially based on wood fibers such as MDF (medium density fiberboard) or HDF (high density fiberboard) substrates on which the decor is formed by digital printing.

[Background of the invention]

[0002] Digital printing refers to the process of printing from a digital image directly onto a substrate. It usually refers to professional printing where small jobs from desktop publishing and other digital sources are printed using large format and/or high volume laser or inkjet printers. Digital printing has a higher cost per printed item than traditional offset printing processes, although this cost is usually offset by the savings gained by avoiding all the technical intermediate steps required to produce the printing plates. It also allows for print-on-demand, short rotation, and even image modification with each printed copy. Labor savings and the increased capability of digital editions mean that digital printing is reaching a point where it can match or surpass offset printing technology's ability to produce larger print runs of a few thousand copies at low cost.

[0003] However, when using digital printing on substrates such as high density fiberboard, the decor is generally still printed on a separate backing of paper or fleece that is applied to the substrate. In fact, while a base coat may be applied to ensure sufficient adhesion of applied inks, such base coats may affect print quality. Actually a porous layer can absorb the ink leading to insufficient coverage while a non-porous base layer can cause them to stick together and can affect the color quality. The use of a separate printing substrate, however, makes the process more expensive and complex.

[0004] Usually, the production of floors or similar products includes an embossing phase that is carried out after printing (for example digital printing) the decor on wood-based panels and panels such as wood particle boards, MDF or HDF panels. Therefore, the embossed reliefs are directly transferred to the top coating (varnish, liquid...) when using engraved rollers, or to the top layer (melamine, paper, foil...) when using a short cycle press. Therefore, the embossed reliefs are not transferred directly to the substrate but to the top coat/top layer. As a consequence, known floors, such as standard laminates, show reliefs of maximum depth limited to the thickness of the mentioned top coating/top layer, which is about 30-300 µm.

[0005] Document US 2007/283648 describes a procedure for modifying the beveled edges of a laminate floor panel.

[0006] WO 03/084760 describes a method of printing an image on an object, which comprises the steps of providing an object with an outer surface having a flat part and a channel drawn from the flat part; applying the first primer on the outer surface; drying of the first primer; and spraying droplets to form an image.

[0007] WO 2009/013580 describes a process for the production of a panel comprising at least a substrate and a printed decor with relief performed on this substrate.

[0008] Therefore, there is a need for alternative methods that enable obtaining floors with deeper embossed surfaces.

[0009] The present invention aims to provide a method for the production of substrates comprising a decor formed by digital printing, which exhibits deep embossed reliefs/embossed prints.

[0010] The present invention also aims to provide a process for the production of such substrates that enables good image quality.

[0011] The present invention also aims to provide a process for the production of such substrates that demonstrate an improved natural appearance.

[Detailed description of the invention]

[0012] This invention relates to the method according to patent claim 1.

[0013] Substrates can especially be selected from the group consisting of panels and plates.

[0014] Boards based on wood, especially boards based on wood fibers are preferred for use.

[0015] In one embodiment, the substrates are selected from the group consisting of HDF, MDF, cardboard and WPC (wood plastic composite). More specifically, the substrate is HDF.

[0016] In the case of floor panels, the printed fiberboards obtained in the process are cut so as to form the final floor panel which preferably has an area of less than 0.5 m<2>, or even less than 0.3 m<2>.

[0017] In the process of the invention, phase a) is performed with engraved embossing rollers or pressure plates.

[0018] For example, the embossing phase (a) is carried out with hot or cold embossing rollers. More specifically, hot embossing rollers can be rollers that are heated to a temperature of 120°C to 170°C, preferably up to 150°C. More specifically, cold embossing rollers may be rollers with a temperature of 20°C to 35°C.

[0019] Preferably, both hot and cold embossing rollers transfer the relief to the substrate without reverse deformation of the substrate.

[0020] Usually, the embossing rollers can be engraved embossing rollers that allow the relief of said rollers to be transferred to the substrate. Those embossing rollers can have a surface structure relief of up to 12 mm, preferably up to 1.5 mm.

[0021] Preferably, when embossing rollers are used, the mechanical embossing phase (a) is carried out at a transfer speed of the substrate between 5 and 20 m/min, preferably at 8 m/min.

[0022] In one embodiment, phase (a) is performed with pressure plates, for example with a short cycle press.

[0023] Preferably, the short cycle press is heated to a temperature in the range of 30°C to 300°C, preferably in the range of 120°C to 250°C.

[0024] Preferably, the heating period is between 2 seconds to 10 minutes, preferably 2 to 30 seconds is sufficient.

[0025] In the process of the present invention, the embossing step (a) is performed directly on the substrate and not on any top coating/top layer on the substrate. Therefore, the imprinted surface is located directly on the substrate.

[0026] In the process of the present invention, the embossing phase (a) is therefore performed before the digital printing phase.

[0027] Phase (a) is performed on at least one main side of the substrate. The embossed surface is therefore present on at least one main side of the substrate.

[0028] In one embodiment, the primer is selected from the group consisting of transparent or slightly colored UV varnish, transparent or slightly colored UV oil, water-based stains, and mixtures thereof.

[0029] The UV-priming material preferably consists essentially of a UV-curing varnish, pigments, a curing agent, reactive diluents or radical-forming agents such as a chain-initiating agent.

[0030] Pigmented water-based primer preferably contains at least one light-colored pigment, more specifically, preferably at least one white pigment. Preferably, that primer is a white colored UV varnish.

[0031] More specifically, that primer is a transparent UV varnish known under the trade name UV BASE COAT marketed by Akzo Nobel, or that primer is a slightly colored UV varnish known under the trade name UV BASE COAT WHITE marketed by Akzo Nobel.

[0032] More specifically, the primer is a water-based stain known under the trade name AQUA PIGMENTS STAIN NORDIC WHITE marketed by Akzo Nobel, or a transparent UV oil known as OIL BASE COAT marketed by Osmo Polyx.

[0033] The applied amount of primer used in the process of this invention can be in the range between 5 and 50 g/m<2>, preferably between 25 and 30 g/m<2>.

[0034] Preferably, the primer allows a good transfer of the decor within the imprints, such as the cavities of the imprinted surface. In addition, the primer also preferably achieves adhesion between the embossed surface and the digitally printed decor.

[0035] In one example, in step (c), the coated substrate with the UV-priming material is pregelatinated by UV radiation.

[0036] In one example, a coated substrate with a pigmented water-based primer is dried in a convection dryer by heating the coated substrate to a temperature in the range of 50°C to 90°C, preferably to a temperature in the range of 60°C to 80°C.

[0037] In one example, a substrate coated with a pigmented water-based primer is dried with an infrared dryer.

[0038] In phase (d), the substrate coated with the base layer is subjected to digital printing in order to form the decor.

[0039] Generally, printed decor is a wooden pattern. Other patterns such as stone patterns, parquet imitations or fictional patterns are however also possible. As digital printing is very versatile, any pattern can be printed, even for small quantities and in a short period of time and without the need for an external supplier such as a printing house.

[0040] In step (d), the liquid ink may be water-based ink or UV ink. Water-based inks cost less than solvent-based inks. Therefore, water-based inks are preferred for digital printing.

[0041] Preferably, said preferred digital printing techniques are those that can deposit ink droplets in the form of dots, as is the case, for example, with Drop-on-Demand (DOD) inkjet systems.

[0042] In one example, the substrate during printing has a speed of more than 10 m/min and preferably greater than 80 m/min, or more specifically up to 150 m/min.

[0043] In another example, the substrate stands still and the printer head of the inkjet system passes over the substrate.

[0044] In stage (e), the ink that makes the printed decor dries or hardens. Drying of water-based inks can be carried out under ambient conditions or can optionally be accelerated by conventional means such as a heater, hair dryer or infrared dryer. The time required for the ink to dry depends on numerous factors such as the composition of the ink, its water content, the size of the droplets, and of course, the temperature of the surface, the temperature and humidity of the surrounding air, and the amount of air circulation in the immediate environment of the printed decoration.

[0045] More specifically, UV inks are cured by UV radiation.

[0046] The amount of ink for digital printing can be between 5 and 15 g/m<2>, preferably between 6 and 8 g/m<2>.

[0047] Preferably, the digital printing is a direct digital printing, and does not require the use of a special backing paper or fleece that is applied to the substrate.

[0048] According to the present invention, the decor is digitally printed on the base layer, wherein the base layer lies on the embossed surface of the substrate. More specifically, the resulting decorative substrates include an embossed surface formed directly on the substrate, wherein the embossed surface is below the base layer and the decorative layer (digitally printed decor).

[0049] In one embodiment, the method of the invention further comprises a phase consisting of: f) coating the digitally printed decor with a top coat or a final layer.

[0050] Preferably, the top coating is selected from the group consisting of varnishes, oils and resins. Among the oils, for example, UV or oxidative oils can be mentioned.

[0051] Preferably, the topcoat is based on an amine resin, such as melamine provided in resin or sheet form. As an alternative, clear or transparent varnishes can also be used.

[0052] Preferably, the topcoat is applied to the board in liquid form, for example, by means of one or more rollers. Alternatively, the top coat is applied to the board using melamine sheets.

[0053] Said top coating can further also include solid particles, such as aluminum oxide, which provides better wear resistance on the surface of the final substrate. This topcoat exhibits improved abrasion resistance compared to lacquer. Preferably, such particles are formed on a still wet topcoat.

[0054] The final thickness of the top coating is generally between 30 and 300, preferably between 50 and 220 µm.

[0055] According to one example, in order to improve the abrasion resistance of the upper smooth surface (walking area), a polyurethane topcoat is applied according to the Kleiberit HotCoating<®> technology, and a UV varnish is applied, especially with a sponge roller, deep into the imprinted area. According to this embodiment, the hot coating is not applied to the embossed areas in order not to lose the embossed structure.

[0056] Kleiberit HotCoating<®> technology consists of applying KLEIBERIT PUR HC 717 to the surface. KLEIBERIT PUR HC 717 is solid at room temperature.

[0057] In one embodiment, the process of the invention further includes a phase consisting of: g) drying or hardening of the top coating.

[0058] More specifically, the top coating with UV material is cured by UV radiation.

[0059] The conditions required to ensure the curing of the top coating substantially based on melamine sheets include, in particular, temperature range, duration and pressure. The suitable temperature range, duration and pressure for curing the topcoat may vary as they depend primarily on the specific polymer and curing agent used. However, generally a suitable temperature is in the range of 100 to 300°C, preferably 120°C to 250°C. Warming up for 2 seconds to 10 minutes, preferably 2 to 30 seconds is generally sufficient. Furthermore, a pressure of 20 to 60 kg/cm<2> is desirable.

[0060] In one embodiment, the method of the invention further includes a phase consisting of: h) placing the rear side of the substrate with balance paper or a layer of varnish.

[0061] More specifically, the varnish layer is selected from the group consisting of: slightly colored UV varnish, transparent UV varnish, slightly colored UV oil, transparent UV oil, water-based stains, and mixtures thereof.

[0062] For example, phase h) consists of laying the back of the substrate with PES needle felted fleece with a woven substrate (PP). Such a phase is carried out to improve the grounding properties of the surface and water resistance.

[0063] Currently, during the installation of standard laminate and/or parquet, the foil is placed between the "floor" and the substrate. According to this example, PES needle fleece with a woven backing replaces the foil.

[0064] In one embodiment, the imprinted surface includes imprints that extend to the maximum depth to the thickness of the substrate, for example up to 12 mm especially when the substrate is HDF.

[0065] Preferably, the imprints are selected from the group consisting of holes, cracks, pores, and mixtures thereof.

[0066] According to the present invention, the decor is digitally printed on an embossed surface covered with a base layer.

[0067] In one embodiment, the digitally printed decor corresponds to the embossed prints.

More specifically, during the digital printing stage, the imprinted surface is positioned under the print heads to apply the digitally printed decor in precise positions on the imprints.

[0068] The inventors have found that the method according to the present invention preferably enables the preparation of floors with deeply impressed surfaces, and more specifically with deeper impressed surfaces compared to existing known floors.

[0069] More specifically, the process according to the present invention preferably enables the creation of an embossed surface directly on the substrate, and not on a top coat or top layer as in conventional known processes. Therefore, the imprints of the imprinted surface of the substrate have a maximum depth limited to the thickness of the substrate and are not limited to the thickness of the top layer. More specifically, the process of the invention allows obtaining a substrate with prints of a maximum depth of up to 12 mm (HDF thickness), preferably between 0.8 mm and 12 mm, more preferably between 1 mm and 12 mm.

[0070] The process also preferably allows obtaining floors with good picture quality, and which looks more natural than existing products. More specifically, the process allows for good transfer of decor onto/into the imprints of the imprinted surface. An extremely realistic imitation of a wooden template is preferably achieved.

[0071] As used herein, "wood fiber substrate" means a wood fiber substrate that includes an embossed surface, wherein the embossed surface includes at least one relief print.

[0072] The embossed surface is directly present on the surface of the substrate and not on the topcoat/top layer.

[0073] In one embodiment, the substrate is pressed to the maximum depth to the thickness of the substrate. More specifically, the substrate is pressed to a maximum depth of 12 mm.

[0074] Preferably, the imprinted surface of the substrate comprises at least one imprint of a depth of 1 mm to 12 mm, preferably of 1 mm or 1.5 mm.

[0075] Preferably, the substrate, at the place of the imprints, is at least imprinted over 0.5 mm, preferably over 0.8 mm. More specifically, that substrate, at the place of the imprints, is imprinted to a depth of 1 mm to 12 mm, preferably to a depth of 1 mm or 1.5 mm.

[Brief description of the drawing]

[0076]

Fig. 1 schematically shows a substrate produced by a preferred method of realizing the method according to the present invention.

The primer can be applied in the form of a filler, and cover and fill the imprints of the imprinted surface, as particularly shown in Fig.1. Actually in Fig.1, the base layer 3 covers the entire imprinted surface S, and in particular fills the imprints E such as holes, cracks, pores, and their mixtures.

Fig. 2 schematically shows a substrate produced by means of another method of realizing the method according to the present invention. In this fig.2, the base coat 3 preferably covers but does not fill the imprints E of the imprinted surface S. Preferably, the primer is applied with a soft rubber roller (25 ShA).

[0077] According to the preferred way of realizing the method of the invention shown in Fig. 1, the panel 1 is produced in the following way.

[0078] The substrate 2 made of high density fiberboard (HDF) is particularly embossed with engraved rollers or a short cycle press, in order to create an embossed surface on the substrate. The stamped surface is coated with a reactive composition such as transparent or slightly colored UV varnish, transparent or slightly colored UV oil, water-based stains, and their mixtures, which form the base layer 3.

[0079] More specifically, the reactive composition is then applied in one application phase to the substrate 2 by appropriate means, for example by a roller.

[0080] The applied amount of primer used in the process of this invention can be between 5 and 50 g/m<2>, preferably between 25 and 30 g/m<2>. In one method of realization, the coated substrate with material for UV-initial coating is pregelatinized by UV radiation. In one embodiment, the coated substrate with a pigmented water-based primer is dried in a convection dryer by heating the coated substrate to a temperature in the range of 50°C to 90°C, preferably to a temperature in the range of 60°C to 80°C. In one embodiment, the coating coated with a pigmented water-based primer is dried with an infrared dryer.

[0081] On the imprinted surface of the substrate 2 thus coated with the base layer 3, the decor 4 is then performed by digital printing and water-based ink or UV ink, using for example a Drop-on-Demand (DOD) inkjet system. The specific properties of the base layer 3 improve the adhesion of the ink to the substrate 2, preventing excessive absorption or otherwise coalescing of the ink drops that make up the decor 4.

[0082] In one method of realization, after printing the decor 4 with water-based ink, the panel 1 is introduced into the oven and heated to a temperature of 70 to 250°C, for a period of 2 to 30 seconds in order to dry and/or harden the ink droplets, which creates the decor 4. In one way of realization, UV inks are cured by UV radiation.

[0083] After that, the decor applied to the panel 1 is protected by applying a top coating 5, mainly based on amine resin, more specifically melamine resin. Such resin may be spread on the panel 1 in liquid form, generally by means of one or more rollers. Alternatively, this coating is performed on panel 1 in a solid form, generally using one or more sheets. The dimensions of the coating sheet are chosen according to the panel dimensions. For example, the coating sheet is 2620 mm long, 2070 mm wide and has a weight of 150 gr/m<2>.

[0084] After drying, if resin is used, the top coat is subjected to a pressing operation under

Claims (14)

by a pressure of about 60 kg/cm<2> at a temperature between 100 and 300 °C for a period of 10 seconds. If necessary, the water-based ink can also harden during this stage. After curing, the base layer 3 has significant adhesive properties but retains its elasticity and flexibility. Therefore, the cohesion between the different layers of panel 1 is strengthened and the risk of delamination is reduced, especially under stress. [0085] More specifically, the top coating with UV material is performed by UV radiation. [0086] The final thickness of the top coating 5 is generally between 2 and 100, preferably between 5 and 50 µm. In the case of the production of floor panels, regions of profiled edges can be created on the panels, either before or after applying the method of the present invention. [0087] The rear part of the panel can additionally be protected by applying a suitable protective layer 6 such as a balance paper or a suitable varnish. Patent claims 1. The procedure for the production of decorative substrates based on wood fibers, which includes the following stages: a) mechanical embossing at least on one main side of the substrate (2) which is different from the edge of the substrate so that an imprinted surface (S) is formed, whereby this imprinted surface (S) is present on at least this main side of the substrate (2); b) applying primer (3) to the stamped surface of the substrate (2); c) drying or curing the primer applied to the imprinted surface to form the base layer; d) digital printing of the decor (4) on the base layer using liquid ink; and e) drying or hardening of the liquid ink that forms the digitally printed decor, wherein step (a) is performed directly on the substrate (2) and not on any topcoat/top layer present on the substrate (2), and wherein step a) is performed with engraved embossing rollers or pressure plates. 2. The method according to claim 1, in which the substrate (2) has a back side, an embossed surface (S), a primer (3), and a decor (4) extending parallel to the back side. 3. The method according to claim 1 or 2, in which the substrates are floor panels, wherein the method further includes the phase of forming profiled edge regions on the floor panels after phases a) to e). 4. The method according to claim 1, wherein the substrates are selected from the group consisting of panels and plates. 5. The method according to any one of claims 1 to 4, wherein the substrates are selected from the group consisting of HDF, MDF, cardboard and WPC. 6. The method according to any one of claims 1 to 5, wherein the primer is selected from the group consisting of transparent or slightly colored UV varnish, transparent or slightly colored UV oil, water-based stains, and mixtures thereof. 7. The method according to any one of claims 1 to 6, wherein the digital printing in step d) is performed using a Drop-on-Demand inkjet system. 8. The method according to any one of claims 1 to 7, in which step d) is performed using UV ink or water-based ink. 9. The method according to any one of claims 1 to 8, further comprising the step of: f) coating the digitally printed decor (4) with a top coat (5). 10. The method according to claim 9, wherein the top coating (5) is selected from the group consisting of varnishes, oils and resins. 11. The method according to any one of claims 9 or 10, further comprising the step of: g) drying or hardening of the top coating (5). 12. The method according to any one of claims 1 to 11, further comprising a step consisting of: h) placing the back side of the substrate (2) with balance paper (6) or a layer of varnish. 13. The method according to any one of claims 1 to 12, wherein the imprinted surface (S) includes imprints extending to a maximum depth of the thickness of the substrate (2). 14. The method according to any one of claims 1 to 13, wherein the digitally printed decor (4) is consistent with the imprints. 1