EP1923223A1 - Method for manufacturing decorative films - Google Patents

Abstract

Carrier paper (1) is fed to a lower end of printing rollers (3-5). Printing heads (6-8) on an ink-jet printer are aligned radially onto the upper end of each printing roller. The printing heads fire drops (10-12) of ink at the printing rollers at a speed of e.g. 6 milliseconds. The printing heads contain printing inks in basic colors like yellow, cyan or magenta so that the printing rollers are coated with drops of yellow, cyan or magenta ink, which are transferred from the printing rollers onto the carrier paper. An independent claim is also included for a device for carrying out the method of the present invention.

Description

The invention relates to a method for producing decorative films according to the preamble of claim 1. It also relates to the use of the decorative films thus produced.

To print smaller quantities of film, it is known to use the digital printing. For example, decorative films of melamine resin impregnated paper are used in large quantities to coat chipboard and other substrates, for example, to imitate a wood surface. Here, the gravure printing process for printing the paper for mass production of large quantities has proven itself. However, gravure printing machines are associated with significant initial costs (machine armor, pattern matching times, production of gravure cylinders, startup waste, etc.) and are therefore too costly for small quantities.

Often, however, the same decorative film must be produced on the one hand by gravure in large quantities, on the other hand, but also in small quantities. For example, in the mass production of a table top for the surface of the table top, although a deep-drawn in a large amount produced decorative film can be used, but not for the edges of the table top, because he is too little flexible or hard-wearing enough. In such a case, for the table edge, a series production for a more robust film (up to 3 times thicker film) with the same decor, but in a much smaller amount be set up. Even with the introduction of new decors or samples for customers, the initial cost of gravure printing are too high and expensive (engraving of the cylinder, etc.).

For smaller quantities, digital printing with an inkjet printer is suitable. However, as the decor made with gravure and the decor made with digital printing look exactly the same, there are significant problems.

In order to reproduce the gravure decoration as accurately as possible, inter alia, the printheads of the inkjet printer must be arranged as close as possible to the paper to be printed, so that the ink droplets impinge on the paper as accurately as possible.

Digital printing usually uses four printheads, three for the primary colors yellow, cyan, and magenta, and one for black. However, if the absorbent sheet is wetted with drops of paint from the first printhead, there is a risk of it becoming distorted by the moisture of the drops before being printed with the last printhead. This warping is particularly noticeable when using absorbent decorative papers which are later soaked in melamine resin or other resin blends. The papers have a high capillarity as a prerequisite for absorbing the corresponding resins. Due to the warping of the paper, however, the drops of color from the print heads no longer strike the intended places, which may, for example, result in a clearly visible line for the human eye.

Also, the primary colors do not mix so perfectly if the color drops are not positioned exactly to each other, which can cause unwanted color shifts.

Since with the inkjet printer at a greater distance no exactly reproducible storage of the ink droplets can be achieved on the film, there are also problems with metamerism. That is, the appearance of the gravure printed film and the printed with digital printing film may not or only slightly differ from one and the same light source, but large deviations occur in another light source, such as artificial light against daylight.

In addition, the ink is discharged from the ink jet printer at a very high speed of e.g. 6 m / s, so that it penetrates deep into the porous film. Through the capillary forces it is then sucked from the inside of the film to the surface. Not all fibers lying on the surface are wetted with paint on the visible side, which results in a gray haze and / or too low a color intensity.

With an inkjet printer can hardly produce decorative prints that have the same appearance as when produced by gravure printing or printed with other printing decor decorative prints.

The object of the invention is therefore to obtain by digital printing printed decorative films with maximum similarity to those that have been printed in gravure or in another process.

This is achieved according to the invention with the method characterized in claim 1. In claims 2 to 11 preferred embodiments of the method according to the invention and in claims 12 to 14 preferred uses of the decorative film produced according to the invention are given.

According to the absorbent sheet or film-like substrate is not printed directly with the inkjet printer, but a rotating, endless color carrier is used, which is printed with the inkjet printer and then transfers the color to the film-shaped substrate. The ink carrier is thus inked by the printheads of the inkjet printer ink droplets and then outputs the ink to the film-shaped substrate. Such printing devices are known per se (cf. DE 102 45 066 A1 ). It is surprising, however, that they can be used to produce decorative films which, in contrast to decorative films printed with a conventional inkjet printer, in which the ink droplets impinge directly on the printing material, have an appearance similar to that of the human eye of decorative films Gravure printing is made, indistinguishable.

The absorbent sheet-like printing material is preferably supplied from a supply roll. The absorbent sheet-like substrate can, for. As paper, cardboard or resin impregnated paper or cardboard.

To produce the decorative films, an unimpregnated paper, in particular decor paper, or pre-impregnated paper (pre-impregnate) is preferably used. The printed decor paper will normally be used by the user impregnated with melamine and applied to the surface of the object to be provided with it.

That is, according to the invention, printed decorative paper and printed decorative film can be produced. The printed decorative paper is unimpregnated paper that is impregnated after printing with resin, in particular melamine resin to melamine laminate or with resin mixtures and can then be painted to form a finish film. Instead, prepreg paper may be printed and subsequently painted to form a finish film.

In contrast to the direct inkjet printing, in which the ink is fired from the print head directly onto the absorbent sheet-like substrate, according to the invention also absorbent decorative paper with high capillarity is perfectly printable.

Since, according to the invention, the ink droplets are no longer fired directly from the print heads onto the paper but onto the ink carrier, the printed film also has no gray haze and / or no color shift. The airspeed of the paint drops may be as usual e.g. 3 to 10 m / s.

In addition, according to the invention, the printheads of the inkjet printer with a very short distance of z. B. 1 mm or less are arranged by the color carrier, since neither dusty paper, nor waves of paper require a greater distance required.

A line or other unwanted color effects are avoided, as well as contamination of the printheads through paper dust. Due to the small distance between the printheads of the ink carrier also an exact positioning of the color print applied by the respective print head on the ink carrier is possible.

Since, in contrast to conventional digital printing according to the invention no ink is injected from the printheads in the absorbent film, the invention requires less expensive digital ink. Also, a print run is generally sufficient. The ink discharged from the printheads remains completely on the surface of the absorbent substrate and does not penetrate it, as in conventional inkjet digital printing.

Also can be produced by the precise position of the drop of paint on the ink carrier according to the invention a decorative film, which has virtually no color deviations from a same produced by another printing process, especially gravure decorative printing. It is thus possible to fire the color drops exactly and reproducibly one above the other, side by side or in one another with the print heads on the color carrier. This can z. B. a hue can be made exactly and reproducibly. While printing with methods in which two primary colors are printed on top of each other, the hue of the mixed colors can be changed only by the order of printing, ie, when, for example, cyan and yellow printed on each other, only two green hues are possible, namely on the one hand printed on yellow Cyan and yellow printed on cyan on the other hand, the green color of cyan and yellow can be changed arbitrarily according to the invention by appropriate placement and size of the cyan and yellow drops on the color carrier.

The ink jet printer has at least one, but preferably at least three print heads each containing one of the three primary multicolor printing colors yellow, cyan or magenta. Also, another printhead may be provided which contains black color.

If the supplied absorbent film-shaped substrate is pre-colored, it is already possible to produce decorations.

It is advisable to use pre-inked substrates on a case-by-case basis in order to achieve the required depth effect of the décor. Pre-inking not only saves costly digital ink, but can also be colored with pigments, particularly natural color pigments (e.g., iron oxide), which can not be used in known digital printing processes.

Each printhead may have only a limited number of nozzle openings, the z. B. can be controlled with a PC. If only one such printhead is used, but one wants to print wide webs, such a printhead must be moved across the width of the substrate web to print one line, thereby significantly reducing the printing speed.

Preferably, so many printheads are used, so that the entire width of the printing material is covered, the z. B. can be selectively controlled by a PC with the inkjet printer, so that can form over the width of the printing substrate extending line of drops of ink on the ink carrier. This is the Printing speed at such in-line printing, where the entire line is printed at once, essentially only dependent on the drop-fire speed, so that the printing speed can be significantly increased.

Since premixed inks are also used in gravure printing, printheads with premixed colors are preferred per se in the production of decors in order to achieve the same color effect. However, when using pre-mixed colors, the printheads must be cleaned each time a different decor is to be printed. In addition, in such a case, it is impossible to perform dissimilar wood decals (e.g., a company logo).

When using printheads with the multi-color primary colors or black color eliminates such cleaning or even 4-color overlays are possible. Also, the colors with the three primary colors and black can be achieved by software with almost identical quality as with premixed colors.

In the production of decors, preferably translucent, ie translucent, colors are used for reasons of metamerism and depth effect in intaglio printing.

As printheads, binary print heads or gray scale print heads can be used.

In both types of printheads, a piezo element is provided per nozzle opening, which is driven by a PC or the like device. While with the binary print head, the drop size can only be controlled with 0 or 100% can, the grayscale print head, the size of the respective drops, for example, between 4 and 50 picoliters adjustable. However, even with a binary printhead, grayscale can be achieved, depending on whether only one drop or several drops are shot at a point on the color carrier.

For this purpose, the inkjet printer is provided with a drive of the ink carrier, such as a stepper motor, which is controlled such that the circulation of the ink carrier is interrupted for different lengths depending on the gray level. It is also possible, in the case of a gray level printer, to reduce the possible drop size by e.g. half, to increase the feed of the film.

The ink carrier preferably has a surface of rubber or a rubber-elastic material, which is printed with the inkjet printer. The surface may be smooth or structured and / or provided with a coating, such as a nano-coating to z. B. to influence the surface tension and thus the size of the ink drops deposited on the ink carrier.

The length of each step in which the color carrier is driven by the stepping motor corresponds to the distance between two lines which are printed with the print heads on the color carrier. In the case of a print head extending across the width of the film, the line spacing is as long as the distance of the nozzle openings of the print head from one another, so that a grid of square-shaped dots is formed for depositing the color drops on the color carrier.

The circulating, endless color carrier may be formed as a roller or as an endless belt.

In this case, each print head can be associated with a roller or an endless belt, which is printed by the print head with the relevant color, wherein the ink is successively transferred from the rollers to the printing material. Instead, only one roller may be provided for two, more or all print heads.

If rollers are used, the printheads must be aligned exactly radially. In contrast, in an endless belt as a color carrier, the print heads are preferably aligned perpendicular to the upper run of the endless belt, ie parallel to each other, which may be easier than the exact radial alignment of the print heads in a roller.

In order to mix the color drops which have been superimposed on or overlaid on the color carrier, a vibration device can be provided for mixing the color drops which are respectively emitted by the print heads of the inkjet printer on the color carrier. The vibration device can be driven by an ultrasonic generator, for example.

In order to adjust the printheads so that they place the drops of ink exactly at the predetermined location on the ink carrier, an image processing device, such as a camera can be provided, which accurately detects the point at which the ink droplet has been stored. In a deviation of the deposited ink droplet from the predetermined location of the respective printhead is readjusted automatically, for example, characterized in that the Printhead concerned fires the drop of paint sooner or later. The camera can z. B. be formed over the width of the ink carrier away slidably.

Grayscale printers are particularly suitable for adjustment with the image-processing device, since they allow a correspondingly precise adjustment by dispensing very small drops.

In order to prevent nozzle orifices of a printhead, which have not been used for a long time during printing, from clogging with dried ink, the inkjet printer is preferably controlled so as to emit a drop of paint through these orifices at predetermined intervals. Such z. B. every 10 to 60 minutes of fired paint drops has no effect on the appearance of the decor.

Under certain circumstances, it may be necessary to stop the printing process, although only a part of the film-shaped substrate from the supply roll of z. B. 500 meters has been printed, for example, to clean the printheads or the roller.

When stopping and when starting the printing device while extending over the width of the sheet-shaped substrate extending straight edge, so that the decor has a clear visible cross-hatch and thus the entire paper roll must be discarded, since in the series production a production cycle, for example, not broken by a piece can be.

Accordingly, the ink jet printer according to the invention is preferably designed controllable so that jagged edges are formed when stopping the ink carrier and subsequent restart on the film-shaped substrate, which engage complementary, whereby a straight line, which is immediately perceived by the human eye, is avoided. The serrated edges are preferably jagged irregular. That is, the prongs have a different width, length and / or shape.

When printing is finished, the ink droplets remaining on the ink carrier must still be transferred. For this purpose, in a roller, the initial section of the roller is unrolled with the remaining drops of paint on the paper. So that the ink carrier can be moved back to the starting position, according to the invention the drive of the ink carrier can be switched to reverse operation.

The ink carrier is preferably heatable. Thus, the viscosity of the ink droplets on the ink carrier can be controlled, decreasing with a short low heating and increasing with prolonged heating to a higher temperature by evaporation of the solvent of the ink.

In order to increase the viscosity of the ink droplets on the ink carrier, a drying path for the ink on the ink carrier is preferably provided on the ink carrier, which is formed by the fact that between the direction of rotation of the ink carrier last printhead on the one hand and the ink transfer point of the ink carrier on the film-shaped On the other hand, a printing material accordingly large distance is provided. This drying section can z. B. be at least a quarter of the circumference of the roller. Also, at least one drying device (eg infrared radiator) may be mounted on this route.

Furthermore, a device for forming a predetermined atmosphere in the region of the ink carrier between the print head (s) and the ink transfer point can be provided on the printing substrate. Even so, the process of drying the ink drops on the ink carrier and thus the viscosity of the drop of paint can be controlled during the transfer to the substrate. The given atmosphere can be moving air, so the device can be a fan. Also, the atmosphere may be formed, for example, by air of high or low humidity.

The device according to the invention can also have a cleaning device for the ink carrier. For this purpose, for example, a dirt-absorbing roller can roll on the ink carrier, which dips into a cleaning liquid.

Furthermore, a cleaning roller may be provided for cleaning the printheads, which corresponds to the size and optionally the shape of the pressure roller and can be pivoted or moved in the position of the pressure roller.

A further roller, which can be swiveled or brought into the position of the ink carrier in accordance with the shape and size of the pressure roller, can be provided for closing the print heads. This ensures that a longer downtime of the printing unit leads to no drying of the printheads.

Preferably, instead of or in addition to the supply roll with the film-shaped printing material to be printed, a roll with a film-shaped printing material for a proof print can be introduced. For visual inspection of the printed substrate or the Probeandrucks an optical device, such as a microscope, a stroboscope and / or a magnifying glass can be provided.

• Figur 1 eine Vorrichtung mit drei Druckköpfen, die jeweils eine Druckwalze bedrucken;
• Figur 2 eine Vorrichtung mit vier Druckköpfen, die ein- und dieselbe Druckwalze bedrucken;
• Figur 3 eine der Figur 2 entsprechende Vorrichtung mit zusätzlichen Einrichtungen;
• Figur 4 eine Vorrichtung mit einem Endlosband als Farbträger und vier Druckköpfen; und
• Figur 5 eine Vorrichtung mit vier Druckköpfen, die ein- und dieselbe Walze bedrucken, mit einer Papierrolle zum Probeandruck.

The invention is explained in more detail by way of example with reference to the accompanying drawing. In each case show schematically and in side view:

• Figure 1 shows a device with three printheads, each printing a pressure roller;
• Figure 2 shows a device with four printheads, the one and the same pressure roller print;
• FIG. 3 shows a device corresponding to FIG. 2 with additional devices;
• Figure 4 shows a device with an endless belt as a color carrier and four printheads; and
• Figure 5 shows a device with four printheads, the one and the same roller print, with a paper roll for Probeandruck.

According to FIG. 1, paper is fed as an absorbent film-shaped printing material 1 in the direction of the arrow 2 to the lower end of three printing rollers 3, 4, 5. On the upper end of each pressure roller 3, 4, 5, a print head 6, 7, 8 of an ink jet printer is radially aligned.

The print heads 6, 7, 8 fire paint drops 10, 11, 12 on the printing rollers 3, 4, 5 at a speed of e.g. 6 m / s from. The printheads 6, 7, 8 contain the multicolor primary colors yellow, cyan and magenta, respectively, so that the printing rollers 3, 4, 5 are printed with yellow, cyan or magenta ink drops 10, 11, 12, respectively, from the printing rollers 3, 4, 5 are transferred to the carrier paper 1, wherein the pressure rollers 3, 4, 5 rotate at the same speed in the direction of arrow 9.

Instead of the multicolor printing inks yellow, cyan, magenta, the print heads 6, 7, 8 may also contain, for example, premixed inks.

According to FIG. 2, four printing heads 14, 15, 16, 17 are radially aligned on the pressure roller 13. For example, while the printheads 14, 15, 16 include the multicolor primary, yellow, cyan, and magenta colors, the printhead 17 contains black color. Thereby, mixed color drops 18 of these colors can be formed on the pressure roller 13.

The peripheral portion A of the roller 13 between the last in the circumferential direction 10 print head 16 and the ink transfer point 20 on the paper to be printed 1 forms a drying section to increase the viscosity of the ink drops 18th

According to FIG. 3, the device according to FIG. 2 additionally has a pre-drier 21 on the drying section A and, in addition, a camera 22 as an image-processing device. Furthermore, a cleaning roller 23 settles on the roller 13.

As shown by the arrow 24, after pivoting out of the pressure roller 13, a roller for cleaning the print heads 14 to 17 or a roller for closing the print heads 14 to 17 can be pivoted.

According to Figure 4, an endless belt 25 is provided as a color carrier, which rotates about two rollers 26, 27, of which at least one is driven. The four printheads 14 to 17 arranged in parallel are aligned perpendicular to the upper run of the endless belt 25, while the lower run transfers the mixed color drops 18 onto the paper 1 to be printed.

According to Figure 5, a paper roll 28 is additionally provided for Probeandruck. Further, a guide roller 29 for the sample paper and a counter-pressure roller 31 at the ink transfer point 20 is provided. A stroboscope 32 and a microscope 33 serve to visually check the trial printing.

Claims (14)

Process for the production of decorative films by digital printing with an inkjet printer on an absorbent film-shaped printing substrate (1), characterized in that an inkjet printer is used, which prints a circulating endless ink carrier (3 to 5; 13; 25), which transfers the ink to the film-shaped substrate Substrate (1) transmits. A method according to claim 1, characterized in that the absorbent sheet-like printing material (1) is formed by a pre-impregnated with resin paper. A method according to claim 1 or 2, characterized in that the film-shaped printing material (1) is impregnated after printing with a resin. Method according to one of the preceding claims, characterized in that a pre-inked film-shaped printing material is used as the absorbent film-shaped printing substrate (1). Method according to one of the preceding claims, characterized in that translucent colors are used for printing. Method according to one of the preceding claims, characterized in that the print heads (6 to 8; 14 to 17) of the ink jet printer are positioned such that they respectively discharged color drops by depositing one above the other or into each other. Method according to one of the preceding claims, characterized in that an inkjet printer is used with at least one gray level print head for delivering color drops of different sizes to the color carrier. Method according to one of the preceding claims, characterized in that an image processing device (22) is used for adjusting the at least one print head (6 to 8; 14 to 17) of the inkjet printer. A method according to claim 7 and 8, characterized in that the grayscale printer is adjusted during the adjustment for dispensing small drops. Method according to one of the preceding claims, characterized in that the ink-jet printer is controlled such that when the ink carrier (3 to 5; 13; 25) is stopped and then restarted on the film (1), complementarily formed, interlocking irregularly serrated edges are formed , Method according to one of the preceding claims, characterized in that a supply roll (28) for a slide-type printing material is provided for a proofing. Use of the decorative film produced according to one of the preceding claims with an inkjet printer for coating a part of the surface of substrates which are otherwise coated with a decorative film produced by a different printing process, wherein the decorative film produced with the inkjet printer has the same appearance as that according to the other printing process produced decorative film. Use according to claim 12, characterized in that the other printing process is a gravure printing process. Use according to claim 12 or 13, characterized in that the decorative film is a decorative film for imitation of a wooden surface.

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