EP2480416B1 - Method for producing a digitally printed workpiece - Google Patents

Description

The invention relates to a method for producing a digitally printed flat, web-shaped or plate-shaped workpiece, for example a kitchen worktop, a furniture front or a laminate floor part with a decorative and resistant surface.

In order to accelerate the production of such a workpiece and to be able to react flexibly, digital printing processes, e.g. Inkjet printing process (inkjet) used. The difficulty with this ink jet printing process, however, is that the ink jet print heads used are difficult to handle in industrial printing with water-based inks. There are often blockages, the paint dries at the nozzles of the inkjet printheads, there are so-called nozzle misfires (nozzle errors).

The known use of radiation-hardening acrylate-containing printing inks also prevents subsequent impregnation with aqueous melamine resins due to the formation of a barrier layer and is therefore not possible.

The EP 1 858 244 discloses a method for producing a decor, in which a decor is printed on a carrier material and then covered with a synthetic resin layer. The unit made of carrier material and synthetic resin layer is then pressed so that the decor remains visible through an abrasion-resistant surface. An inkjet printer is used for printing, the printing fluid being suitable both for the inkjet printer and for a gravure printing process.

The WO 01/48333 discloses a method for producing a printed workpiece, in which a surface is printed with a decor and then coated with a translucent wear layer. As a result, the decor image is arranged protected under the wear layer.

It is therefore the object of the present invention to provide methods for producing a digitally printed flat, web-shaped or plate-shaped workpiece with a resistant surface, which avoids the disadvantages mentioned above and ensures high quality digital decor printing.

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

Advantageous embodiments of the invention are contained in the subclaims.

In the method according to the invention, a digitally printed flat, web-shaped or plate-shaped workpiece with an abrasion-resistant surface is produced, a digital data record for a decorative image being provided first, which is sent from a computer to a digital printing device. A printable workpiece is then fed to the printing device.

Subsequently, the digital printing of the respective workpiece by means of the printing device takes place exclusively using solvent-based printing inks. All printing inks that do not contain water as the main component are recorded as solvent-based printing inks. This includes, for example, all organic solvents such as alcohols and mixtures of different solvents. According to the invention, the digital printing is carried out using at least one solvent-based printing ink with a weight fraction of solvent 40-99%, preferably 65-92%, the solvent-based printing ink being a pigmented printing ink.

The printing is followed by a reduction in the solvent content to a defined residual moisture in the workpiece. The evaporation of the solvent can also be accelerated by heating the workpiece, for example by a hot air blower. The defined residual moisture describes a maximum content of solvent that remains in the workpiece.

The subsequent impregnation of the printed workpiece with a resin mixture can take place, for example, by coating, impregnating, wetting or spraying the workpiece with the respective solid or liquid resin mixture, the resin mixture then being cured in a heating press

The method has the advantage that the use of solvent-containing printing inks in the method according to the invention means that the nozzles of the print heads are not added to the printing device, which results in longer service lives of the printing device.

Compared to the use of radiation-hardening acrylate-containing printing inks, the use of solvent-containing printing inks according to the invention only enables the further process steps of impregnation by means of aqueous resins.

At the same time, the solvent content in the workpiece is reduced significantly faster, for example when using short-chain monohydric alcohols, than with water-based printing inks, which means that the printed workpiece can be dried with less energy consumption.

Finally, unlike water-based printing inks, the use of solvent-based printing inks in the method according to the invention does not cause the surface in the printing area of the workpiece to swell.

With the method according to the invention, decorative coated workpieces such as Kitchen worktops, kitchen furniture fronts, other furniture fronts or also laminate floors and similar workpieces with decorative surfaces of high quality. The reproduction of a wood structure or a stone structure, fantasy decors or other decors based on nature can be achieved, whereby the workpieces also have positive physical properties such as abrasion resistance, scratch resistance, heat resistance.

According to the invention, digital printing is carried out using at least one solvent-based printing ink with a solvent content of 40-99%, preferably 65-92%, the solvent-based printing ink being a pigmented printing ink.

After they have hardened, radiation-hardening printing inks can act as a barrier layer, for example by UV radiation, in the subsequent impregnation of a workpiece printed in this way with a water-based resin solution, thus preventing a permanent connection between the printed workpiece and underlying material layers. Due to the high proportion of solvent, the formation of a barrier layer from polymerized acrylates can be prevented particularly advantageously, since the solvent distributes the printing dyes on the surface and also transports them into the workpiece.

In a preferred method, one or more unprinted, resin-containing material layers are arranged above and / or below the printed workpiece before curing in the heating press, so that the resin flow from these material layers soaks the unheated, printed workpiece during the pressing process. Both material layers and the workpiece can consist of absorbent materials such as paper, for example.

After impregnating the printed workpiece or arranging a layer of material impregnated with a resin mixture on and / or below the printed workpiece, the workpiece can be applied to one or more layers of material and then joined together by pressing. For example, an impregnated and printed decorative paper can be applied to a wood-based board, preferably a chipboard, MDF or HDF board, which results in the lamination of a flex-resistant substrate.

By drying the workpiece to a residual moisture content of less than 4%, preferably less than 1.5%, swelling and lifting of the printed surface compared to the unprinted surface is advantageously prevented.

According to the invention, the solvent-based printing ink contains pigments, since pigments are colourfast and consequently there is no aging and decomposition of the printing inks by UV light. The use of a pigmented printing ink thus guarantees a high-quality print image over a long service life.

It is advantageous if after the impregnation of the printed workpiece with the resin mixture, the resin mixture is then predried. This enables pre-crosslinking of constituents of the resin mixture and a reduction in the water content to a residual moisture content of less than 10%, preferably less than 4%.

It is also advantageous if a resin mixture based on melamine resin is used, since this material penetrates the workpiece under pressure and can penetrate into an underlying material layer, for example a fiberboard, and after the resin mixture has hardened an inseparable connection has been established with the material layer. In addition, melamine resin has positive physical properties after curing, e.g. Moisture resistance, temperature resistance and scratch resistance.

In the case of aminoplasts, for example, the resin mixture is cured by crosslinking polymer strands as a result of a condensation reaction known per se at elevated pressure in the range 20-60bar, preferably 30-40bar and temperatures of 150-230 ° C, preferably 170-200 ° C using a heating press.

It is advantageous if the resin mixture is cured by means of a continuous double belt press. This press enables the processing of continuous material as well as piece material with a high processing speed. It is particularly advantageous if the double belt press is used to press further, non-printed, impregnated material layers, in particular paper layers, with the printed and impregnated workpiece. Since the material layers can be fed as continuous material, the double belt press offers a higher throughput due to its continuous mode of operation than, for example, a short cycle press. The surface can also be structured during the pressing process.

When a layer sequence of one or more unprinted, impregnated material layers, in particular paper layers, a layer of the previously printed and optionally impregnated workpiece and a further material layer, in particular a wood-based panel (13), is pressed into a solid, hardened unit, it is advantageous if this pressing is carried out in a pressing operation of a short-cycle press. This means that several layers can be pressed together.

Fig. 1:

Schematische Darstellung von drei erfindungsgemäßen Verfahrensschritten B), C) und D)

Fig. 2:

Schematische Darstellung eines erfindungsgemäßen Verfahrensschrittes E)

Fig. 3:

Schematische Darstellung von zwei erfindungsgemäßen Verfahrensschritten E) und F)

Fig. 4:

Schematische Darstellung von zwei alternativen erfindungsgemäßen Verfahrensschritten E) und F)

Fig. 5:

Schematische Darstellung der Schichtabfolge einer nach den erfindungsgemäßen Verfahren hergestellten Ausführungsvariante eines Werkstückes

Fig. 6:

Schematische Darstellung der Schichtabfolge einer weiteren nach den erfindungsgemäßen Verfahren hergestellten Ausführungsvariante eines Werkstückes

Fig. 7:

Schematische Darstellung der Schichtabfolge einer weiteren nach den erfindungsgemäßen Verfahren hergestellten Ausführungsvariante eines Werkstückes

Fig. 8:

Schematische Darstellung der Schichtabfolge einer weiteren nach den erfindungsgemäßen Verfahren hergestellten Ausführungsvariante eines Werkstückes

Exemplary embodiments according to the invention are described below with reference to the attached Figures 1-8 described in more detail. They show:

Fig. 1:

Schematic representation of three process steps B), C) and D)

Fig. 2:

Schematic representation of a method step E) according to the invention

Fig. 3:

Schematic representation of two process steps E) and F) according to the invention

Fig. 4:

Schematic representation of two alternative method steps E) and F)

Fig. 5:

Schematic representation of the layer sequence of a variant of a workpiece produced by the method according to the invention

Fig. 6:

Schematic representation of the layer sequence of a further embodiment variant of a workpiece produced by the method according to the invention

Fig. 7:

Schematic representation of the layer sequence of a further embodiment variant of a workpiece produced by the method according to the invention

Fig. 8:

Schematic representation of the layer sequence of a further embodiment variant of a workpiece produced by the method according to the invention

Fig. 1 schematically shows a feed station 102, with a roll 2 for decorative paper 3 to be printed, a printing station 103 for a decorative paper 3 and a station for reducing the solvent content 104 in the decorative paper 3 by means of a printing device 1. Printing in digital printing can also be carried out directly on decorative paper 3 on a surface of a workpiece, in particular an HDF or MDF board. The printing device 1 has a printer 4, which has four print heads 5. These release solvent-based printing ink 6 onto the surface of the decorative paper 3.

Following the printing of the workpiece, the printing ink is dried, if necessary using a schematically illustrated dryer 7. In the case of volatile solvents, the drying process can possibly also take place during printing without the aid of a dryer.

After the printing process, the decorative paper 3 can be rolled up onto a roll 8 for storage, transport and further processing.

The way of feeding a workpiece depends on its material properties. Sheets of paper can be clamped and unrolled, while wood-based panels are fed to the printing device on treadmills.

The print heads 5 can be arranged stationary in the printer 4 in order to implement a single-pass printing process. The print heads can advantageously extend across the entire width of the area to be printed. The individual print heads 5 have, for example, a width of 70 mm and are arranged next to one another in a print module, preferably with the solvent-containing printing inks black, mangenta, cyan and yellow. If several printing modules are arranged next to one another, workpieces can also be printed, for example with a width greater than 1 m. The arrangement of several print modules next to one another in a stationary manner enables a uniform multicolored print image on which no transitions between the individual print modules can be seen.

Alternatively, the print heads 5 can also be arranged on a movable carriage in the arrangement, so that printing on the workpiece can be carried out using the multi-pass method.

The stationary and movable printhead arrangement described above can also be arranged in several rows one behind the other in order to achieve a higher printing speed compared to a single-row arrangement. As an alternative to a printhead arrangement, nozzle bars can also be arranged.

Instead of four, six or more or fewer printing inks can also be used in printing device 1.

Fig. 2 shows a station for impregnating 105 the workpiece with a resin mixture 19, for example with an amino resin (melamine resin mixture). The previously printed decorative paper 3 is unwound from the roll 8, drawn through a resin bath 9 with the liquid resin, squeezed out excess resin by means of a squeeze roller 10 and then dried by a schematically illustrated dryer 11. This dryer 11 is designed such that it enables the resin to dry on. For example, the dryer 11 can be designed as a circulating air or warm air dryer. After the resin has dried, the workpiece can be wound onto another roll 12 for storage.

As an alternative to winding onto the roll 12, a cutting device (not shown) can also be provided in order to cut the impregnated and dried paper into sheets.

Fig. 3 shows a station 107 for arranging two unprinted paper layers 17, which are impregnated with a resin mixture 19, above and / or below a printed wooden workpiece 20.

In the station 107, a printed and impregnated decorative paper 3 can also be applied above or below a wood-based panel 13. In this case, the printed and impregnated decorative paper 3 is unwound above and below the wood-based panel 13 and this package, which has been brought together in this way, is then cured in a double belt press 14.

The resin mixture is then cured and the individual layers are connected to the respective printed workpiece in the double belt press 14 with two rollers 15 and a feed for the wood-based panel 13.

In an alternative embodiment, the printed decorative paper 3 is cured and bonded to the wood-based panel 13 ( Fig. 4 ) in a heated short cycle press 16.

Fig. 5 shows an exemplary structure of a product generated by the inventive method. A decorative paper 3 printed with the solvent-based printing ink 6, preferably the solvent-based digital printing ink, is applied to a wood-based panel 13. The decorative paper 3 has color pigments on, which are brought onto and into the decorative paper 3 during printing 103. A further resin-coated paper is arranged above this resin-coated decorative paper 3 provided with the color pigments, which paper is provided as an overlay paper 17 with a resin mixture 19 by impregnation 105.

At the in Fig. 6 The embodiment of a product shown is in addition to the product of Figure 5 a wear protection layer 21 is applied, which has corundum (aluminum oxide (Al ₂ O ₃ )) or another material to increase the abrasion resistance.

In a further embodiment variant after Fig. 7 Another resin-coated paper can be applied on the underside of the wood-based panel 13 as counter-pull paper. This can also be in the form of printed and impregnated decorative paper 18, as on the top, if the finished end product is to be coated from both sides, if necessary also as described above, by an overlay paper 17 made of aluminum oxide so that it is wear-resistant.

In an alternative embodiment, the overlay paper 17 can also be omitted or alternatively can be supplemented by two or more papers on the top, optionally also on the underside.

In a further variant according to Fig. 8 For example, a resin-coated paper 17 can be applied to the underside of a printed wooden workpiece plate 20.

In the method according to the invention, a digital data record for a decorative image, for example a wood structure replica or stone tile replica or another natural image or even a fantasy decor, is provided in the printing device 1 in a first method step. Furthermore, a material to be printed is fed to the printing device 1. A suitable material is, for example, a paper, preferably a non-resinated and uncoated decorative paper, which has a whitening agent, for example titanium dioxide (TiO ₂ ), applied to it and is absorbent. In an alternative embodiment, this decorative paper can also be provided with a melamine resin impregnation, so that in the dried state 5-40%, particularly preferably 10-20%, of the total weight of the paper is predetermined by the melamine content.

However, plastic materials and any other printable material can also be used as the printable workpiece. This includes also direct printing on a wood-based panel.

Then, in a further process step, the digital printing device is used to print on the decorative paper or the workpiece using inkjet print heads. The inkjet printheads used emit individual small droplets in the same or different droplet sizes. Suitable droplet sizes are between 3 and 100 pl per droplet, particularly preferably between 5 and 45 pl per droplet size. The droplets are discharged from a nozzle opening on the underside of the print heads. The size of the nozzle opening is between 10-100 µm, preferably 15-40 µm.

The digital printing ink used is preferably a pigmented ink in which solids (pigments) of a size between 0.01 μm and 5 μm, preferably 0.1-3 μm, are used as dyes. A mixture of pigments and liquid dyes is also possible. In a preferred embodiment, four printing inks with cyan, magenta, yellow and black pigments are used.

The printing ink used contains pigments, i.e. solids, which have a high to very high color stability. According to the known wool scale, this color stability is between 5-8, particularly preferably 6-8. The pigments that are used have an average particle size of 0.01-5 μm, particularly preferably 0.1-3 μm. The proportion of pigments based on the total weight of the digital printing ink used is 0.4-25%, particularly preferably 1-10%.

The other main component of the digital printing ink used according to the invention is a solvent which is not water, preferably an organic solvent. In a preferred embodiment, an alcohol, particularly preferably ethyl alcohol, is used here in a concentration of 40-99%, particularly preferably 65-92% (percent by weight).

Other constituents of the ink can be dispersants and a number of other additives. These additives influence the desired ones physical properties of the ink, such as viscosity, temperature stability, durability, pH, electrical conductivity, etc.

Reference numerals

1

Printing device

2nd

role

3rd

Decorative paper

4th

printer

5

Printheads

6

Printing ink

7

dryer

8th

role

9

Harzbad

10th

Nip roller

11

dryer

12th

role

13

Wood-based panel

14

Double belt press

15

role

16

Short cycle press

17th

Overlay paper

18th

Decorative paper

19th

Resin mixture

20th

Wood-based panel

21

Protective layer

102

Feeding station

103

Printing station

104

Drying station

105

Impregnation station

Claims (11)

1. Method for producing a digitally printed flat, web-shaped or plate-shaped workpiece (3, 20) with an abrasion-resistant surface, comprising the following steps:

   a) providing a digital data record for a decorative image for a digital printing device (1);

   b) feeding a printable workpiece (3, 20) to the printing device (1);

   c) digital printing by means of the printing device (1) by using at least one solvent-based printing ink (6);

   d) reducing the solvent content to a residual moisture in the workpiece (3, 20);

   e) impregnating the printed workpiece (3, 20) with a resin mixture (19); and

   f) curing the resin mixture (19) by means of a heating press (14, 15), wherein digital printing in step C) is carried out using at least one solvent-based printing ink (6) with a weight proportion of solvent of 40-99%, preferably 65-92%, and the solvent-based printing ink (6) is a pigmented printing ink.
2. Method according to claim 1, characterized in that one or more material layers (13) are applied to the workpiece (3, 20), which are firmly connected to the workpiece (3, 20) during the curing in step F).
3. Method according to claim 1 or 2, characterized in that at least one material layer (17) impregnated with a resin mixture (19) is applied to the workpiece (3, 20).
4. Method according to one of the preceding claims, characterized in that the reduction of the solvent content to a residual moisture in the workpiece (3, 20) of less than 4%, preferably less than 1.5%, is carried out.
5. Method according to one of the preceding claims, characterized in that after the step of reducing the solvent content to a residual moisture in the workpiece (3, 20), an arrangement of an unprinted material layer (17) containing a resin mixture is carried out, followed by a pressing in a heating press.
6. Method according to one of the preceding claims, characterized in that a resin mixture (19) based on melanin resin is used for impregnating the printed workpiece (3, 20) or the unprinted material layer (17).
7. Method according to one of the preceding claims, characterized in that the curing of the resin mixture (19) is carried out by a continuous double-belt press (14).
8. Method according to claim 7, characterized in that before curing, further unprinted, impregnated material layers (17), in particular paper layers, are arranged above and/or below the printed impregnated workpiece (3, 20) or the one or more material layers (13).
9. Method according to one of the preceding claims, characterized in that during or after the curing of the wetting-agent-containing resin mixture a surface treatment is carried out to produce a decorative laminate.
10. Method according to one of the preceding claims, characterized in that the curing of the resin mixture (19) is carried out by a short-cycle press (15).
11. Method according to claim 10, characterized in that for each pressing operation of the short-cycle press (15) the layer sequence of one or more unprinted, impregnated material layers, in particular paper layers (17), one layer of the previously printed and optionally impregnated workpiece (3, 20) and a further material layer, in particular a wood-based panel (13), are pressed to form a solid, cured unit.

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