WO2010084386A2

WO2010084386A2 - Methods for manufacturing panels and panel obtained herewith

Info

Publication number: WO2010084386A2
Application number: PCT/IB2009/055706
Authority: WO
Inventors: Laurent Meersseman
Original assignee: Flooring Industries Limited, Sarl
Priority date: 2009-01-20
Filing date: 2009-12-11
Publication date: 2010-07-29
Also published as: WO2010084386A3; BE1018630A5

Abstract

Method for manufacturing panels of the type which is at least composed of a substrate (2) and a top layer (3) provided on this substrate (2), said top layer comprising a printed decor (4), wherein the method comprises at least a step (S1 ) wherein said decor (4) is formed directly on the panel (1) by means of a print performed with a digital printing device, characterized in that the method also comprises a drying treatment (15A-15B-15C-15D), in which the print is at least partially dried in a forced manner, wherein the step (S1) of forming the decor (4) comprises at least applying a first print portion and applying a second print portion at the location of the first print portion, wherein the first print portion is exposed to the drying operation (15A) before the second print portion is applied.

Description

Methods for manufacturing panels and panel obtained herewith.

This invention relates to methods for manufacturing panels, as well as to panels which can be obtained by such methods.

More particularly, the invention relates to methods for manufacturing panels of the type which is at least composed of a substrate and a top layer provided on this substrate, said top layer comprising a printed decor. Herein, this may relate, for example, to furniture panels, ceiling panels, floor panels or the like, which substantially consist of a MDF or HDF (Medium or High Density Fiberboard) basic panel or substrate and a top layer provided thereon. In particular, this relates to a method in which one or more material layers are provided on the substrate, wherein at least one of these material layers is provided by means of a print performed directly on the panel or the substrate, wherein this print then forms at least a portion of said printed decor.

Such panels are known as such, for example, from US 1 ,971 ,067 or DE 195 32 819 A1. In particular, the invention relates to a method which comprises at least a step in which said decor is formed directly on the panel by a print by means of two or more digital printing units. The use of digital printing techniques for forming such decor is known as such, for example, of WO 01/48333 or EP 1 872 959.

From the aforementioned documents, it is also known that said material layers may comprise one or more basic layers, wherein these basic layers substantially extend underneath said print, and/or may comprise one or more finishing layers which substantially extend above said print. Such finishing layers may comprise, for example, transparent or translucent synthetic material layers, which form a protective layer above the printed decor and may comprise, for example, wear- resistant particles, such as aluminum oxide. It is not excluded that this protective layer comprises a material sheet, such as a paper sheet.

The inventor has found that the use of a suitable basic layer is important in particular for digital printing techniques, as such basic layer, on the one hand, must have sufficient affinity for the adherence of the applied colorants or inks, however, on the other hand, may not be too porous in order to avoid that the applied colorants or inks might be absorbed in an excessive manner by this underlying layer or the substrate. These difficulties may lead to a sub-optimal printing quality. Moreover, these difficulties are still more prominently present when water-based inks are used. However, from an economical point of view, working with water- based inks is more advantageous than working with solvent-based inks. It is evident that these problems will occur in particular when working with porous substrates, such as MDF or HDF (Medium or High Density Fiberboard), and/or when working with porous basic layers, such as basic layers comprising one or more paper sheets. When working with not or less porous substrates and/or basic layers, another phenomenon will arise. In such case, point-wise applied ink droplets, as this may be the case with digital printing techniques, due to their high surface tension may have the tendency of flowing into each other, such that in such case, too, a reduced printing quality will be noticed.

The herein above-mentioned phenomena and problems may also lead to that the amount of ink, which can be deposited on the panel in one step without a loss of printing quality, is restricted, such that these phenomena may lead to insufficient covering and/or to an unjust color rendition. Namely, the print heads may be adjusted, with the intention of limiting the total amount of ink, for depositing only a limited amount of basic color. For example, in the case that wood patterns are printed, this, compared to the other colors, may lead to an irregular deficit of basic color with red pigment. In the case of an arrangement with the basic colors cyan, magenta, yellow and black (CMYK), such adjustment thus may lead to an irregular deficit of magenta. Namely, wood patterns comprise many red and/or brown tints, and the required amount of magenta ink may reach the maximum adjusted amount earlier than the required amount of ink of the other colors, which results in an unjust color rendition.

The present invention in first instance relates to an alternative method for manufacturing panels, which method, according to various preferred embodiments thereof, allows obtaining a better printing quality without necessitating a modification of the basic layer which possibly has to be applied.

To this aim, the invention relates to a method for manufacturing panels of the type which is at least composed of a substrate and a top layer provided on this substrate, said top layer comprising a printed decor, wherein the method comprises at least a step in which said decor is formed directly on the panel by a print by means of two or more digital printing units, with the characteristic that the method also comprises a drying treatment, in which the print or the obtained print portion is at least partially dried in a forced manner, wherein the print portion provided by a first of said two digital printing units is exposed to the drying operation and herein is at least partially dried before a second of said two digital printing units is active at the location of this print portion concerned. The drying may lead, for example, to a fixation of the applied print portion. Preferably, said digital printing techniques are of the type which can deposit ink droplets in a point- wise manner, such as this is the case, for example, with Drop-on-Demand (DOD) inkjet systems.

By "in a forced manner", it is meant that the respective drying operation is not performed by a mere exposition to the surrounding air, but is performed, for example, by means of heated air, forced air flow, radiation heat and/or heat supplied to the panel in another manner and/or created in the panel.

By "at the location of, it is not necessarily meant that the respective print portions are provided on identically the same place, however, it is meant that the surface covered by said second digital printing unit is at least partially overlapping the surface covered by said first digital printing unit. In the case of point-wise deposited ink droplets, the individual ink droplets of the respective print portions, however, possibly may be completely separated from each other. It is also possible that the ink droplets of the respective print portions overlap each other.

According to the invention, so-called single-pass inkjet systems as well as so- called multi-pass inkjet systems may be applied. With so-called single-pass inkjet systems, a print is realized by a single movement or pass of one or more print heads relative to the surface to be printed. Preferably, the print heads are stationary during printing, whereas the surface to be printed will pass underneath the print heads, and such preferably in a continuous manner. In so-called multipass inkjet systems, a print is realized in multiple movements or passes of one or more print heads relative to the surface to be printed. The print portions realized in each of these passes may be performed with a shifting in mutual respect. Preferably, the panel to be printed will be stationary during such pass while the print head or print heads move thereover. Between two passes, said shifting may be performed, for example, in that the print head or print heads are adjusted transversely to the printing direction.

It is clear that the two or more printing units^{^}of the invention in the case of a multi- pass inkjet system may relate to one and the same print head forming said decor in at least two passes directly on the panel, as well as to two separate print heads printing the panel one after the other. According to the invention, then at least a partial drying is performed, in the first case preferably before the same print head is a second time active at the location of an earlier provided print portion, and in the second case preferably before the second print head is active at the location of an earlier provided print portion. Of course, it is not excluded that these two cases will occur together.

For achieving said forced drying, for example, a drying unit may be positioned between said two printing units, and/or both printing units may be positioned in a common drying unit. According to still another example, at least the first of said two print units can be provided with a drying unit and/or said forced drying can be performed with a separate drying unit. This example is particularly interesting when working with a multi-pass inkjet system. When use is made of a separate drying unit, the board can be provided in such drying unit or can be transported there through, or such drying unit can be moved relative to the board.

As a drying unit, for example, one or more hot-air ovens, UV radiators or IR radiators can be applied.

According to another possibility for achieving forced drying, whether or not combined with the aforementioned drying units, it is possible that the drying operation is performed by heat or energy which has been supplied to the panel prior to realizing the respective print portion. For example, according to a preferred embodiment, printing may be performed on heated substrates or panels. It is noted that realizing a print or a print portion on heated substrates or panels as such forms an independent inventive aspect of the invention, irrespective of the fact whether a digital or an analogous printing technique is applied. The temperature of the panels may be, for example, between 20⁰C and 55°C or may even rise to 80⁰C or more. Possibly, in the case of particle board, MDF or HDF boards, use can be made of boards which are still warm from a press treatment having taken place during their manufacture. Of course, it is also possible that the respective substrates, panels or boards, prior to being printed, are fed into an oven or are heated in another manner. For example, they may be supplied by means of a heated transport device and/or they may be provided on a heated table during printing.

According to still another possibility, drying may be caused by a chemical reaction, whether or not taking place as a consequence of applying the respective print portion. To this aim, for example, inks may be used which are modified with an agent which can react with the respective basic layer and/or the substrate, which as such also forms an independent aspect of the invention, irrespective of the fact whether a digital or analogous printing technique is applied. Such drying by means of a chemical reaction may take place, for example, when the chemical reaction as such is exothermic, or when the chemical reaction results in reaction products which are less moist than the reagents, or even are solid.

By drying the applied print portion between two drying operations, or drying it at least partially, a relatively fast fixation of the colorant or ink at the surface of the panel is obtained, such that the risk of a possible absorption into the basic layer and/or substrate or a possible flowing together of a plurality of ink droplets can be minimized. In this manner, the resolution of the print and/or the quality thereof can be kept better under control. By means of the method of the first aspect, it can also be achieved by means of these drying treatments that the maximally deposited amount of ink can be increased.

From the above, it is clear that the inventive idea of the method of the first aspect also can be formulated in another manner and that the invention thus in fact relates to a method for manufacturing panels of the type which is at least composed of a substrate and a top layer provided on this substrate, said top layer comprising a printed decor, wherein the method comprises at least a step wherein said decor is formed directly on the panel by means of a print performed with a digital printing device, with the characteristic that the method also comprises a drying treatment, in which the print is at least partially dried in a forced manner, wherein the step of forming the decor comprises at least applying a first print portion and applying a second print portion at the location of the first print portion, wherein the first print portion is exposed to said drying operation before the second print portion is applied. It is clear that the print portion can cover any surface. This may relate, for example, to one or more printed points, or, for example, to a monochromatic print portion covering approximately the entire panel.

It is evident that the print portion provided by each digital printing unit is subjected to such forced drying operation preferably immediately after the application thereof. It is clear that such embodiment of the present method can be obtained by providing a drying unit after each printing unit and/or by performing the printing respectively on heated panels and/or by working with heated inks. In the case of a multi-pass inkjet system, this can be performed by providing one or more or all print heads with a drying device or by interposing a drying treatment after each printing pass, for example, by means of a drying unit which moves over the panel.

Preferably, according to the invention inkjet printing units are applied as digital printing units, which preferably as such respectively form a monochromatic print portion. This means that each printing unit or print head solely works with ink of one color. In the case of a multi-color print, for example, at least use can be made of standard colors which, by means of the principle of color addition or color subtraction, allow forming a large variety of different colors, and still better allow forming substantially all colors, such as it may be the case with printing units respectively forming cyan, magenta, yellow and possibly black monochromatic print portions. Also, the combination of at least red, green, blue and possibly black may be chosen.

In a first preferred embodiment, said digital printing units are of the type which is stationary, wherein said printing then is performed as the panel moves along the printing units. Herein, preferably one or more printing units cover the entire surface to be printed of the respective panel, such that this surface can be provided with the printed decor concerned in a single movement along the printing units. Such "single-pass" arrangement of printing units is known as such, for example, from the aforementioned document EP 1 872 959.

In an arrangement according to the above first preferred embodiment, it is preferred that said printing is performed in a single movement along the respective digital printing units. In case this relates to printing units which each apply a monochromatic print portion, to this aim preferably per color a number of print heads, possibly only one, are arranged, which allow covering the entire surface to be printed.

According to said first preferred embodiment, the panel, during printing, preferably has a speed of more than 30 m/min and still better of more than 80 m/min. Speeds up to 150 m/min are not excluded.

Generally, it is noted that for obtaining a good drying at high speeds, it is recommended in between printings to enlarge the distance over which the drying operation is performed, and/or to modify the applied inks in order to obtain faster drying. For example, in the case of solvent-based inks, solvents may be chosen having a relatively low evaporation temperature. In the case of water-based inks, the inks may be heated beforehand, such that less energy has to be added for obtaining the evaporation temperature. It is noted that working with inks having a temperature of more than 20⁰C, and still better of more than 25°C or even more than 40⁰C, as such relates to an inventive aspect of the present invention, irrespective of the fact whether a digital printing technique or an analogous printing technique is applied for forming a printed decor on a panel. Of course, higher temperatures are not excluded. In the case of solvent-based inks, too, a higher application temperature may have advantages. When the temperature of the inks is high enough, the printing line possibly may be run without drying units. Such arrangement is advantageous in respect to energy consumption. The heating of inks may be performed such that it always consumes less energy than keeping a hot-air oven or the like on its operating temperature.

In a second preferred embodiment, said digital printing units form part of a multipass printing device. Preferably, each of said printing units performs a print consisting of 6 to 32 print portions performed in respective passes, or still better between 8 and 24 print portions in respective passes. As aforementioned, it is possible to perform the invention by means of only one printing unit, wherein then drying is performed between two passes, for example, by means of a drying device provided on the print head concerned, such as a drying device comprising one or more UV lamps.

In a preferred embodiment of the present invention, preferably at least four digital printing units or print heads are applied, wherein these printing units as such each form a monochromatic print portion. Whether or not in combination therewith, said digital printing units preferably form a multi-colored print, for example, at least on the basis of the colors cyan, magenta, yellow and black. According to a particular embodiment, at least a fifth color is used in addition to the colors cyanrmagenta, yellow and black. Preferably, this fifth color is adapted to the tint of the print to be formed. Preferably, these five colors, as aforementioned, respectively are provided by at least one printing unit, which, by means of the respective color, as such forms a monochromatic print portion.

Preferably, in a step preceding the printing, the substrate is provided with one or more material layers, which form a basic layer for the print. To this aim, the material layers known as such may be used. Such basic layer may be of uniform or at least quasi-uniform color. Possibly, in this manner a basic layer may be formed having the basic color of the printed decor to be formed thereon. Prior to applying such material layers, unevennesses at the surface of the substrate possibly may be filled with a material layer comprising a filler. At the surface of the substrate, also a sealing material layer can be used, and/or a material layer serving as a primer for retaining the colorants, such as inks and paints, which are to be applied at a later moment. So, for example, one or more ink-receptive layers can be applied.

It is noted that said material layers, such as filling material layers, basic layers, sealing layers or primer layers, can be applied simpler, more precisely and/or smoothly on larger surfaces than on the surfaces of smaller panels. Thus, it is possible that, for example, in the case that the method of the invention is applied for manufacturing floor, wall or ceiling panels of restricted surface, it is started from larger boards of substrate material, wherein one or more of said material layers are provided on the surface of these larger boards, these larger boards are subdivided into smaller panels and said print is performed at least partially on those smaller panels. Preferably, said larger board, during said subdividing, is divided into panels having a size which corresponds, or at. least approximately corresponds, to the final panels. It is also possible that subdividing is performed only after completing the printing. Preferably, such basic layers or other material layers are applied in liquid form. As aforementioned, said first material layer preferably relates to a basic layer or primer layer. For application in liquid form, one or more rollers can be applied, and/or jetting or spraying devices can be used. However, it is not excluded that said material layers comprise a material sheet, such as a paper layer or a foil. In this case, this can be provided by means of a press treatment. Such material sheet can be provided with synthetic material, for example, with a synthetic material which can realize the bonding with the-board surface: For example, use can be made of an amino resin, such as melamine formaldehyde resin. However, also a glue may be used, such as phenol glue. However, an amino resin, such as melamine formaldehyde resin, also can be provided in liquid form on the board surface without using such material sheets. When working with one or more material layers comprising material sheets, best one or more or still better all such material sheets are provided on the surface of a larger board. Application techniques, which are suitable for applying material layers, are more advantageous when being utilized on larger surfaces.

Preferably, water-based inks are applied in said digital printing units. As mentioned above, these inks are less expensive than solvent-based inks. However, it is not excluded that solvent-based inks would be applied in said digital printing units.

Preferably, in the case that drying units are applied for forced drying, at least an infrared or an UV radiator are used, for example, in the form of one or more lamps.

According to a second independent aspect, the present invention also relates to a method for manufacturing panels, wherein more lively decors can be obtained. To this aim, the invention relates to a method for manufacturing panels of the type which is at least composed of a substrate and a top layer provided on this substrate, said top layer comprising a printed decor, wherein the method comprises at least a step in which said decor is formed directly on the panel by a print by means of digital printing units, with the characteristic that at least five digital printing units are used, wherein each of these five digital printing units respectively forms a monochromatic print portion of different color.

Preferably, said five different colors comprise at least cyan, magenta, yellow and black. These colors as such already allow forming a large variety of different colors.

Preferably, said five colors comprise at least two different colors which are obtained on the basis of an ink comprising red pigment. Except possibly magenta, one may work, for example, with at least one other color, which is obtained on the basis of an ink comprising red pigment. For example, the color concerned may relate to a red or brown tint. Red pigment is of particular importance when forming printed decors with a wood pattern. It is clear that according to the invention, it is not required that said two colors, which comprise red pigment, should at least comprise magenta. It is noted that applying at least two inks comprising red pigment, as such also forms an independent aspect of the invention, irrespective of the fact whether still one or more other inks or colors are applied, wherein this aspect then substantially aims at realizing prints, which represent a wood pattern, directly on panels.

According to all aspects of the invention, in the case of manufacturing floor panels, the method preferably further also comprises the step of forming profiled edge regions at the panels, wherein this step preferably is performed prior to applying a possible finishing layer. Such profiled edge regions preferably comprise coupling means allowing to interconnect two or more of such floor panels at their edges. Preferably, this relates to coupling means allowing for a glue-free connection, such as known as such, for example, from the document WO 97/47834. Also in the case of floor panels, these preferably have a surface of less than 0.5 m², or of even less than 0.3 m². The thickness of such floor panels may vary between 5 and 25 mm, or still better is situated between 6 and 15 millimeters.

As already mentioned above, according to all aspects to the invention it is preferred to perform the print directly on the surface of panels, said panels already having approximately or entirely the dimensions of the final panels. Providing the print as late as possible in the production chain reduces the required storage room and enables a smooth reaction to the demands of the market.

Preferably, above the print, according to all aspects of the invention at least a transparent finishing layer is provided. Such material layer possibly may comprise a material sheet, such as a paper sheet, however, may also substantially consist of synthetic material. For example, a lacquer, such as a UV-hardening or electron beam-hardening lacquer, may be applied, or a thermically hardening layer, such as a melamine-containing thermically hardening layer. Such transparent material layer preferably also comprises hard particles, for example, aluminum oxide particles. Preferably, the invention according to all of its aspects is applied for obtaining a printed decor representing a wood pattern. Other motifs, such as stone patterns or fantasy motifs, are not excluded. In the case of floor panels, preferably one plank is represented per panel.

According to all of its aspects, the invention preferably is applied for manufacturing floor panels and/or panels of which said substrate material substantially consists of MDF or HDF or another wood-based material.

It is noted that the technique of inkjet printing is well suited for performing prints on the surface of smaller panels, which already approximately show the dimensions of the final panels. However, it is not excluded that the print is performed on larger panels, which still have to be subdivided in order to arrive at the final panels. The inventor has found that it is particularly advantageous to apply multi-pass inkjet systems for printing such larger boards. Thus, according to a third aspect the invention in an independent manner relates to a method for manufacturing panels, wherein it is started from larger boards, with the characteristic that the method comprises at least a step in which a print is formed directly on the larger board, by means of a multi-pass inkjet system, and wherein the method also comprises a step in which the larger board provided with the print is subdivided into two or more smaller panels. Preferably, the invention of this independent aspect further also shows the characteristics of one or more of the above-mentioned aspects and/or the preferred embodiments thereof.

Due to the fact that a multi-pass inkjet system is applied for printing larger boards, the risk of defects in the print is minimized, such that less rejects can be produced. When in one of the passes the print head is malfunctioning or not functioning, in the subsequent passes, for example, after having cleaned the respective print head, still an acceptable result can be obtained, such contrary to a single-pass inkjet system, wherein malfunctioning or not functioning of one or more of the print heads in most cases leads to an unacceptable result. Preferably, between 6 and 32 passes are performed, and still better between 8 and 24 passes, wherein 16 passes already may offer a very good result.

Preferably, said print is performed after said boards are provided with one or more basic layers. Preferably, at least 2 basic layers are applied. Such basic layers preferably are white or beige. Preferably, said print is performed after the substrate and/or said basic layers are subjected to at least one grinding treatment. Preferably, grinding is performed at least once in longitudinal direction and at least once in transverse direction. In this manner, a very good basis for printing can be realized.

Preferably, such board, after printing has been accomplished, also is provided with one or more finishing layers, and preferably prior to said subdividing. Preferably, this relates to finishing layers on the basis of an amino resin, such as on the basis of melamine resin. As an alternative therefor, also translucent or transparent lacquers may be used. Preferably, the material of the finishing layers is brought onto the board without applying material sheets as carriers. For example, such material can be deposited in liquid form, for example, by means of one or more rollers. After this material possibly has dried, then, for example, in the case of an amino resin, also a press operation may be applied. By means of such press operation, a structure can be obtained at the surface of the respective board. Preferably, said subdividing is performed only after such drying operation and/or press operation has taken place. Said finishing layers further may also comprise hard particles, such as aluminum oxide, by which an improved wear resistance is obtained at the surface of the final panels. Preferably, such particles are provided on the still wet finishing layer or finishing layers by means of a strewing device.

According to a fourth aspect, the invention in an independent manner further also relates to a method for manufacturing panels, wherein the method comprises at least a step in which, by means of a multi-pass inkjet system, a print is formed directly on the panel or on a larger board, from which panels are obtained by subdividing, wherein said step of forming the print comprises at least applying a first print portion in a first pass and applying a second print portion in a second pass, with the characteristic that one or more ink droplets of the print portion provided in the second pass overlap with one or more ink droplets of the print portion provided in the first pass. Preferably, the majority of the ink droplets of the print portion provided in the second pass show an overlapping with one or more ink droplets of the print portion provided in the first pass. Preferably, at least 5 percent and still better at least 10 percent or at least 20 percent of the surface of an ink droplet of a print portion is made overlapping with ink droplets of print portions of preceding passes or subsequent passes. It is clear that the invention also relates to panels having a printed decor, wherein at least a part of the ink droplets forming said printed decor, and preferably at least 20% or 30% thereof, are made overlapping. Said overlaps may be present in printing direction and/or transverse to this printing direction.

The overlap realized according to the above fourth aspect of the invention preferably can be applied for realizing relatively dark printed decors, such as, for example, when imitating a tropical wood species, such as wenge, jatoba, merbau and the like. Such overlap namely has the advantage that a better covering degree of the print on the underlying layers and/or the substrate may be achieved, as a consequence of which more intense colors may be achieved.

The overlap of the fourth aspect also leads to minimizing the also above- mentioned risk of defects in the print. Namely, the absence of ink droplets during one or more of the passes is less visible.

As already mentioned above, the print portions realized in each of the passes can be realized with a shifting in mutual respect. Herein, said shifting preferably is smaller than the average diameter of the ink droplets which are provided in the subsequent step. Preferably, said shifting is minimum 60% or still better at least 75% of said average diameter of the ink droplets. It is clear that the invention according to a fifth aspect in an independent manner relates to a method for manufacturing panels, wherein the method comprises at least a step in which, by means of a multi-pass inkjet system, a print is formed directly on the panel or on a larger board, from which panels are obtained by subdividing, wherein said step of forming the print comprises at least applying a first print portion in a first pass and applying a second print portion in a second pass, with the characteristic that the print portions in the second pass are performed with a shifting in respect to said first pass, wherein said shifting is smaller than the average diameter of the ink droplets which are provided in said second pass. Herein, said first pass and second pass preferably follow each other. This means that they preferably are performed without performing other print portions in between. However, this is not necessarily the case.

The shifting which is applied according to the above-mentioned fifth aspect of the invention preferably can be applied for realizing relatively dark printed decors, such as, for example, when imitating a tropical wood species, such as wenge, jatoba, merbau and the like. Such shifting namely has the advantage that a better covering degree of the print on the underlying layers and/or the substrate can be achieved, by which more intense colors can be achieved.

The shifting of the fifth aspect also leads to minimizing the also above-mentioned risk of defects in the print. Namely, the absence of ink droplets during one or more of the passes will be less visible.

Preferably, between the passes mentioned in the fourth and the fifth aspect a drying treatment is performed at least on a portion of the print. Hereby, at least a partial fixation of the ink droplets applied in the respective pass can be obtained. It is clear that in this case an embodiment of the first aspect of the invention is obtained.

It is clear that in all aspects preferably use is made of prints or print portions which are composed point-wise, for example, by means of ink droplets forming the points of the print. Preferably, herein so-called drop-on-demand inkjet systems are applied.

It is clear that the invention also relates to a panel which is obtained by means of a method with the characteristics of any aspect of the invention, or combinations thereof. Preferably, this relates to a floor panel.

With the intention of better showing the characteristics of the invention, hereafter, as an example without any limitative character, several preferred embodiments are described, with reference to the accompanying drawings, wherein:

Figure 1 schematically represents some steps in a method with the characteristics of the invention;

Figure 2 represents a view according to the direction F2 represented in

Figure 1 ;

Figure 3 in perspective and schematically represents a step in a method with the characteristics of, amongst others, the third aspect of the invention;

Figure 4, at a larger scale, represents a view on the area F4 indicated in figure 3; and

Figure 5 in a similar view represents a variant.

Figure 1 schematically represents some steps S0-S1-S2 in a method for manufacturing panels, in this case, floor panels 1. The floor panel is of the type which is at least composed of a substrate 2, in this case a wood-based substrate 2, such as MDF or HDF, and a top layer 3 provided on this substrate 2.

Figure 2 represents that the top layer 3 of the manufactured floor panel 1 shows a decor 4, in this case a printed decor 4 with a wood pattern, more particularly a wood pattern representing only one wood part. Herein, this relates to oblong floor panels 1. As also mentioned above, such panels 1 also may be provided with coupling means at least at two opposite edges 5-6 and/or 7-8, said coupling means allowing to interconnect two or more of such floor panels. Herein, this may relate to a tongue and groove connection for gluing together, or to gluelessly connectable coupling profiles. Such coupling means are not represented here, however, they are known, for example, from the document WO 97/47834.

Figure 1 clearly shows that the method comprises at least a step S1 , wherein said decor 4 is formed directly on the panel 1 by a print by means of two or more digital printing units 9A-9B-9C-9D-9E.

Possibly, as represented here, the substrate 2 of the panel 1 can be provided with one or more material layers in a preceding step SO, wherein these material layers form a basic layer 10 for the print to be performed thereon. One or more of such layers may be applied in liquid form, for example, such as here by means of a roller 11. It is noted that also the underside 12 of the substrate 2 can be provided with a material layer, whether or not being applied in liquid form. As also mentioned in the introduction, it is possible to provide these material layers 10 on a larger board, which subsequently is subdivided into panels 1 , for example, by means of a sawing treatment.

The printing device 13 represented here makes use of at least four digital printing units 9A-9B-9C-9D, in this case, stationary inkjet print heads, which extend over the entire width B1 to be printed of the panel 1 concerned. Herein, each printing unit 9A-9B-9C-9D is intended for realizing a monochromatic print portion while the respective panel 1 moves along the printing units 9A-9B-9C-9D. Herein, the totality of the printed decor 4 is formed substantially or entirely during a single movement T along the inkjet print heads or printing units 9A-9B-9C-9D. This movement T preferably is continuous and may take place at a speed of more than=30 m/min or even up to 150 m/min. The higher speeds are of particular interest when the printed panels 1 in the same production line still have to be provided with profiled edge regions by means of, for example, a milling operation. These milling operations usually are performed at speeds higher than 100 m/min.

It is clear that also a plurality of stationary printing units 9A can be applied for providing the entire width B1 of the surface to be printed with a monochromatic print portion of the same color. As is clearly indicated in figure 2, the width B1 of the surface to be printed does not necessarily correspond to the width B2 of the panel 1 to be printed. In fact, as here, unprinted edges 5A-6A may be present at one or more sides 5-6 of this panel, said edges, for example, corresponding or approximately corresponding to material zones to be removed. In these material zones, for example, the also above-mentioned coupling means or other profiled edges regions may be formed.

By the combination of the four monochromatic print portions provided on top of each other, a multi-color printed decor 4 is obtained. To this aim, the inkjet print heads or printing units 9A-9B-9C-9D respectively apply a monochromatic print portion on the basis of cyan, magenta, yellow and black ink. Here, this thus relates to a so-called printing with CMYK colors.

In dashed line 14, it is represented that except printing units 9A-9B-9C-9D for the colors cyan, magenta, yellow and black, respectively, also at least a fifth printing unit 9E can be applied for forming a monochromatic print portion in a fifth color. Preferably, such fifth or further color then specifically is adapted to the decor 4 to be formed. In the case of a wood pattern, such as here, preferably a red tint or a brown tint is applied as the fifth color, or, in other words, in the extra printing unit 9E preferably an ink is applied which comprises red pigment, however, which differs from the ink forming said magenta.

When using a fifth printing unit 9E with another ink than the other four printing units 9A-9B-9C-9D, a method according to the second aspect of the invention is obtained.

The particularity of the invention according to its first aspect consists in that the method also comprises a drying treatment 15A, in which the print or the obtained print portion is at least partially dried in a forced manner. As clearly shown, in this case the print portion applied by a digital printing unit 9A-9B-9C-9D-9E respectively is exposed to a subsequent drying operation 15A-15B-15C-15D-15E, before a following digital printing unit is active at the location of this respective print portion. To this aim, a drying unit 16 is arranged after each printing unit 9A-9B-9C- 9D-9E. Herein, this may relate, for example, to hot-air ovens or UV lamps, depending on the applied inks.

According to the invention, it is, of course, not excluded that one or more print portions are not forcedly dried before a following digital printing unit 9B is active at the location of the respective print portion. In that a drying treatment 15A is provided at least on one location between the printing units 9A-9B, an improved printing quality can be obtained in comparison with the techniques of the state of the art.

It is also possible that, after printing is completed, also a drying treatment 15E is applied until, for example, a complete drying of the inks is achieved, or at least an acceptable drying, which allows that further treatments of the panel 1 and/or stacking the printed panels 1 is possible.

In figure 1 , it is also shown that in a further step S2 the printed panel 1 can be provided with one or more material layers, which form a transparent or translucent finishing layer 17 above the printed decor 4. For example, such finishing layer may be realized by means of a lacquer layer and/or melting glue (hot melt). Such lacquer may relate, for example, to an UV-hardening or electron beam-hardening lacquer, which, for example, comprises wear-protective particles, such as aluminum oxide. Figure 1 represents that such finishing layer 17 can be applied at least partially in liquid form. To this aim, rollers can be used, and/or, as represented, the technique of curtain pouring and/or the technique of vacuum coating.

Figure 3 schematically represents a variant for the step S1 represented in the figure. Herein, a multi-pass printing device 13 is applied for printing the substrate 2, which in this case comprises a larger board 18, from which, by subdividing, two or more floor panels or other panels 1 can be obtained. It is clear that such embodiment shows the characteristics of the third- aspect- of the invention mentioned in the introduction. Preferably, already one or more basic layers are situated on the substrate before printing is started.

Figure 3 represents that the printing device 13 comprises a plurality of printing units 9, which each in several passes perform a portion of the print. In the represented view, the second pass is performed. As indicated by arrow 19, the arrangement 20 of printing units 9 moves over the board 18, whereas this board 19 is stationary. Herein, the arrangement 20 of printing units is shifted in transverse direction over a distance D1 in comparison with its position during the first pass. Hereby, it is obtained that the first print portion 21 , applied in said first pass, and the second print portion 22, applied in said second pass, are performed with a shifting over a distance D1 in mutual respect.

Figure 4 clearly shows that the distance D1 of the shifting is smaller than the average diameter D2 of the ink droplets 23 of the print portions 21-22 provided in said first and/or second pass. Hereby, an embodiment is obtained with the characteristics of the fifth aspect of the invention mentioned in the introduction. Moreover, figure 4 also clearly shows that the ink droplets 23 provided during the respective passes overlap each other. In this case, the respective overlaps 24 are present in printing direction T as well as transverse to the printing direction T.

Figure 5 represents a variant in which the central points of the majority of the ink droplets 23 applied in the first and the second pass are shifted in mutual respect in the printing direction T. By applying this technique, by means of smaller ink droplets 23 still a complete covering of the substrate 2 can be obtained. In this example, too, overlaps 24 are present in the printing direction T as well as transverse to the printing direction T.

It is evident that the techniques of the fourth aspect and/or the fifth aspect, which are illustrated by means of the figures 4 and/or 5, also can be applied when the print or the respective portions of the print are performed on smaller panels. Figure 3 also represents an example of the first aspect of the invention. As the arrangement 20 of printing units 9 is provided with a drying device 15, the first print portion 21 can be subjected to a drying treatment prior to performing the second print portion 22.

It is also noted that, where in the previous description monochromatic print portions are mentioned, it is meant that these print portions are obtained by means of ink of a single color. As, for example, the density and/or the size of the printing points formed with this ink can be varied, however, still a difference in tint can be present in these print portions which are monochromatic as such.

The present invention is in no way limited to the herein above-described embodiments, however, such methods and panels may be realized according to various variants, without leaving the scope of the present invention.

Claims

Claims.

1.- Method for manufacturing panels of the type which is at least composed of a substrate (2) and a top layer (3) provided on this substrate (2), said top layer comprising a printed decor (4), wherein the method comprises at least a step (S1) wherein said decor (4) is formed directly on the panel (1) by means of a print performed with a digital printing device, characterized in that the method also comprises a drying treatment (15A-15B-15C-15D), in which the print is at least partially dried in a forced manner, wherein the step (S1) of forming the decor (4) comprises at least applying a first print portion and applying a second print portion at the location of the first print portion, wherein the first print portion is exposed to the drying operation (15A) before the second print portion is applied.

2.- Method according to claim 1 , characterized in that the step (S1) of forming the decor (4) is performed by means of two or more digital printing units (9A-9B- 9C-9D) and that said first print portion is provided by a first (9A) of said two digital printing units and this first print portion is exposed to the drying operation (15A) before a second (9B) of said two digital printing units (15B) is active at the location of this respective first print portion for providing said second print portion.

3.- Method according to claim 2, characterized in that said digital printing units (9A-9B-9C-9D) are inkjet printing units, which as such respectively form a monochromatic print portion.

4.- Method according to claim 3 or 4, characterized in that said digital printing units (9A-9B-9C-9D) are of the type which is stationary, wherein said print is performed while the panel (1) moves along the printing units (9A-9B-9C-9D) and wherein respectively one or more printing units (9A-9B-9C-9D) cover the entire surface to be printed of the panel (1) concerned.

5.- Method according to any of the claims 3 to 5, characterized in that said print is performed in a single movement (T) along the respective digital printing units (9A-9B-9C-9D).

6.- Method according to any of the preceding claims, characterized in that the panel (1) during printing has a speed of more than 30 m/min.

7.- Method according to any of the preceding claims, characterized in that at least four digital printing units (9A-9B-9C-9D) are applied, wherein these printing units (9A-9B-9C-9D) as such respectively form a monochromatic print portion.

8.- Method according to any of the preceding claims, characterized in that said digital printing device or printing units (9A-9B-9C-9D) form a multi-color print at least on the basis of the colors cyan, magenta, yellow and black.

9.- Method according to claim 8, characterized in that in addition to the colors cyan, magenta, yellow and black at least a fifth color is used, which is adapted to the print to be formed, and wherein these five colors respectively are provided by at least one printing unit (9A-9B-9C-9D-9E), which, by means of the respective color, as such forms a monochromatic print portion.

10.- Method according to any of the preceding claims, characterized in that the substrate (2), in a preceding step (SO), is provided with a basic layer (10).

11.- Method according to any of the preceding claims, characterized in that in said digital printing unit or in the printing units (9A-9B-9C-9D), water-based inks are applied.

12.- Method according to any of the preceding claims, characterized in that at least an infrared radiator is applied as said drying unit (15A-15B-15C-15D).

13.- Method according to any of the claims 1 to 10, characterized in that in said digital printing device or printing units (9A-9B-9C-9D), solvent-based inks are applied.

14.- Method according to any of the preceding claims, characterized in that at least a UV radiator is applied as said drying unit (15A-15B-15C-15D).

15.- Method for manufacturing panels of the type which is at least composed of a substrate (2) and a top layer (3) provided on this substrate (2), said top layer comprising a printed decor (4), wherein the method comprises at least a step (S1) in which said decor (4) is formed directly on the panel (1) by a print by means of digital printing units (9A-9B-9C-9D-9E), characterized in that at least five digital printing units (9A-9B-9C-9D-9E) are applied, wherein each of these five digital printing units respectively forms a monochromatic print portion of different color.

16.- Method for manufacturing panels, starting from larger boards (18), characterized in that the method comprises at least a step in which, by means of a multi-pass inkjet system (13), a print is formed directly on the larger board (18), and wherein the method also comprises a step in which the larger board (18) provided with the print is subdivided into two or more smaller panels (1).

17.- Method for manufacturing panels, wherein the method comprises at least a step (S1) in which, by means of a multi-pass inkjet system (13), a print is formed directly on the panel (1) or on a larger board (18), from which panels (1) are obtained by subdividing, wherein said step of forming the print comprises at least applying a first print portion (21) in a first pass and applying a second print portion (22) in a second pass, characterized in that one or more ink droplets (23) of the print portion (22) provided in the second pass overlap with one or more ink droplets (23) of the print portion (21) provided in the first pass.

18.- Method for manufacturing panels, wherein the method comprises at least a step (S1) in which, by means of a multi-pass inkjet system (13), a print is formed directly on the panel (1) or on a larger board (18), from which panels (1) are obtained by subdividing, wherein said step of forming the print comprises at least applying a first print portion (21) in a first pass and applying a second print portion (22) in a second pass, characterized in that the print portion (22) in the second pass is performed with a shifting in respect to said first pass, wherein said shifting (D1) is smaller than the average diameter (D2) of the ink droplets (23) which are applied in said second pass.

19.- Floor panel, characterized in that it is obtained by means of a method with the characteristics of any of the preceding claims.