EP0119548A2 - Process for printing on supports by the transfer process - Google Patents

Abstract

An article having a substrate with a synthetic resin surface that has an affinity for printing inks is printed with a laser-induced hot print method. A transfer medium, printed on a face side with an image formed of sublimable dyes is faced against the synthetic resin surface, and a laser beam is made to impinge upon the unprinted back of the transfer medium. The laser beam is of sufficient intensity to cause the dyes to sublimate and penetrate at least partially into the synthetic resin surface of the substrate.

Description

The invention relates to a method for printing a substrate with a plastic surface affecting the printing inks after the transfer printing process by placing an auxiliary carrier printed with dyes that can be sublimated under the process conditions on the plastic surface and transferring the dyes into the plastic surface.

For example from DE-OSen 1 771 812, 2 337 798, 2 436 783 and 2 458 660 it is known to print on textile fabrics according to the so-called transfer printing process, in that auxiliary substrates, in particular made of paper or aluminum foil, are printed with sublimable dyes using binders and the subcarriers printed in this way in turn are used for printing on the textiles. In this case, the auxiliary carriers are placed with the printed side on the textiles to be printed, after which the dyes are sublimed onto the textile material by heating the auxiliary carrier on the non-printed side to about 160 to 220 ° C. If the textile material consists of cotton fabric, according to the publications mentioned special measures are used to bind the dyes on the cotton.

From DE-OS 2 642 350 it is also known to print heat-resistant fabrics which, as such, do not accept the sublimable dyes, such as wood, metals, certain plastics, glass, ceramic materials, plastic products or the like, by the transfer printing process by before or at the same time as the transfer printing, such substrates are provided with a surface layer made of a thermoplastic which bonds to the surface of the substrate and absorbs the sublimable dyes. Similar processes are known from FR-PS 2 230 794 and GB-PS 1 517 832, in which the substrate is coated with an epoxy resin or a hardened unsaturated polyester resin. According to EP-OS 14 901, the substrate is coated with a cross-linked thermoset from the group of phenoplasts, aminoplasts, polyesters, polyphenylene sulfide resins, silicone resins, acrylate resins, alkyd resins, polyethylene sulfide resins and / or unsaturated polyester resins, and high-molecular dispersion dyes with molecular weights are used as sublimable dyes 340 and 1000 used.

It is characteristic of all these known processes that the transfer of the dyes by sublimation from the auxiliary carrier to and into the surface of the substrate was carried out with the aid of heat radiation which was supplied by an external heat source. This is disadvantageous insofar as expensive and space-consuming heating devices were required, in particular if continuous work was to be carried out, such as tunnel ovens or the like. The residence times of the auxiliary carrier on the substrate required by the prior art were relatively long, so that high transfer printing speeds could not be achieved in a continuous manner.

The object underlying the invention was now to be able to carry out the transfer printing process without the use of thermal radiation and with the shortest possible residence times of the auxiliary carrier on the substrate.

Surprisingly, it has now been found that the transfer of sublimable dyes into the plastic coating of a substrate can also be achieved with electromagnetic waves, with short dwell times being sufficient to enable the transfer printing process to be operated in a continuous manner at a high throughput speed.

According to the invention, the method described at the outset is characterized in that the unprinted back of the auxiliary carrier is treated with a laser beam of an intensity delt, which is sufficient to let the dyes penetrate at least partially into the plastic coating of the substrate. It is expedient to use a laser beam of such an intensity and to treat it so long that the subcarrier receives a temperature below its flash point or decomposition point, but as close as possible to it.

This process considerably reduces the outlay on equipment and the space required for the transfer printing devices, in particular in the case of continuous operation at high throughput speeds, since in these cases tunnel ovens or other space-taking systems were required in order to bring the rapidly moving substrates to the required temperature. Even in the event that preheating which supports the laser beam effect is used in the method according to the invention, the outlay on equipment required for this is in no relation to the outlay on previously required preheating devices.

If, on the other hand, known processes were used without preheating the substrate and only heating the auxiliary support from the back, considerable heating times were required, which prohibited working at high throughput speeds. Compared to such processes, the present process has the advantage that it is possible to transfer printing at high throughput speeds in a continuous manner.

The method according to the invention does not require any preheating treatment, but depending on the nature of the substrate surface, it may be advantageous to preheat it before the laser beam treatment to a temperature below the sublimation temperature of the dyes, in order to facilitate the penetration of the subliming dye molecules into the surface layer of the substrate. The preheating can be carried out in a simple manner, for example with the aid of infrared radiators.

The laser beam strikes the dyes of the subcarrier printing with high intensity and penetrates the subcarrier from the rear, displacing the dye molecules le in thermal motion sufficient to instantly sublimate the dye molecules onto the surface of the substrate. Since the laser beam simultaneously sets the surface layer of the substrate, which consists of an organic plastic, in molecular motion without allowing it to soften so that it sticks to the auxiliary carrier, the dye molecules do not remain on the surface of the substrate, but penetrate into it Plastic existing surface layer of the substrate, where they are anchored against abrasion.

The processes take place in a very short time, and, as mentioned, the penetration of the dye molecules into the substrate surface can be facilitated by preheating the substrate surface, so that the residence times of the auxiliary carrier on the substrate surface can be kept very short. Broadly speaking, it can be said that the residence time is between 0.001 and 10 seconds, preferably between 0.001 and 1 seconds and especially between 0.01 and 0.1 seconds.

When reference is made to substrates with a plastic surface in connection with this invention, these can be objects which are made entirely of plastic, such as, for example, those made of polymethacrylate, in which the dyes penetrate into the surface area. However, the substrates can also consist of any other materials, such as metal, wood, glass, porcelain, ceramics or the like, and can then be provided with a surface coating of a plastic that is affinity to the printing inks. Examples of this are steel plates, household appliances made of steel or aluminum, beverage cans made of aluminum, ceramic tiles, chipboard, plywood, but also non-woven fabrics or woven or active substances, natural stones or foam blanks. The process can also be used well for printing on continuous steel.

The surface coating of such substrates can be carried out with the aid of thermoplastics known for this purpose or with the aid of cross-linked thermosets. Examples of both art substance classes can be found in the publications cited at the beginning.

Examples of thermoplastics for surface coating include polyacrylonitrile, polyacrylates, polyesters, polyurethanes, cellulose derivatives, epoxy resins, polyamides and others. Among them, nonlinear polyurethanes and polyesters are preferred.

Examples of crosslinked thermosets are epoxy resins, phenoplasts, aminoplasts, crosslinked polyesters, polyphenylene sulfide resins, silicone resins, crosslinked acrylate resins, alkyd resins, polyethylene sulfide resins, polyether sulfone resins and crosslinked unsaturated polyester resins.

The thermosets used can be crosslinked in different ways. Crosslinking agents are used which are capable of converting the linear molecular chains of the precursor of the crosslinked thermoset, which has reactive centers, onto the substrate by forming intermolecular bridges into networks of three-dimensional structure. The crosslinking agents can either themselves be built into the network as intermolecular bridges or activate a direct combination of reactive centers from chain to chain.

For example, the network can be formed by polyaddition reactions or polycondensation reactions, but also by radical, peroxide-catalyzed polymerization.

Accelerators such as cobalt octanoate, dimethylaniline or peroxides can be added to influence the hardening of the thermosets.

A particularly favorable group of thermosets is that of the silicone resins, particularly those with _"methyl, ethyl and phenyl substituents, such as methylphenyl silicone resins. Depending on the substituents, they are water-repellent and flame-retardant, show good dimensional stability at high temperatures and have good surface hardness in addition to excellent affinity for the disperse dyes to be used. Silicone polyester resins are also very suitable.

Another means of crosslinking the thermosets is by using crosslinking radiation, such as infrared rays, ultraviolet rays or ionizing radiation, such as gamma rays, X-rays or electron beams. This method is known per se and is described, for example, in "defazet Deutsche Farben-Zeitschrift" 1977, pages 257 to 264 and in "Maschinenmarkt", Würzburg, 84 (1978), 64, pages 1249 to 1252. The advantages of this networking method are the very high production speed and the uniformity of the networking. The curing or crosslinking takes place at room temperature. Pigmented and unpigmented systems can be used equally.

During electron radiation, the wet paint film is covered with a protective gas. Good inerting combined with high ionization density due to the electron radiation leads to a high degree of cross-linking of the thermoset molecules. After a hardening time of approx. 0.2 seconds, the products are immediately stackable and can be processed further. This technology enables greater surface hardness, increased abrasion resistance, increased density, improved resistance to chemicals, good dye affinity, reduced flammability and high throughput speeds.

Unsaturated acrylate resins and unsaturated polyester resins, as described, for example, in the above article "defazet", the content of which is included here, are particularly suitable for this crosslinking method by radiation.

In the process according to the invention, the usual procedure is to first provide the substrate with a precursor of the crosslinked thermosetting plastic at least on the surface to be printed. This can be done by dipping, brushing, spraying, brushing on or rolling on a solution or dispersion of the precursor of the thermoset. Instead, it can also be applied without solvent by extrusion, lamination or powder coating.

Certain substances such as pigments can already be added to the precursor of the thermoset. Instead, an intermediate layer suitable for achieving colored effects or for improving the surface quality, such as a pigmented intermediate layer, can also be applied under the precursor coating.

Dispersions are preferably used as dyes, which sublimate more than 80% only above 200, especially above 220 ° C. The disperse dyes used according to the invention expediently sublimate more than 90% above 250 ° C., preferably above 300 ° C., particularly above 350 ° C. For reasons of equipment, however, it is expedient to select such dyes that do not first exceed 500 ° C., preferably not sublimate only above 400 ° C.

While the dyes previously used for transfer printing processes should not contain any ionic, highly water-solubilizing groups such as -S0 ₃ H or -COOH, such dyes can be used successfully in the process according to the invention. The number of non-ionic polar groups, such as -NO ₂ , -CN, -So R (R = alkyl), -OH, -NH ₂ or -NHR (R = alkyl), can be higher than in the dyes previously used . In addition to alkyl-substituted amino groups, such as isobutylamino groups, linear residues can also be present, which has hitherto been avoided in the transfer printing process. In the case of azo dyes, cyano groups are the Nitro groups are preferable, and fluorine atoms are better than chlorine atoms. Trimethylsilyl groups can increase the vapor pressure in the azo dyes.

A preferred group of the disperse dyes used according to the invention are certain anthraquinone, monoazo and azomethine dyes, but the process according to the invention is not restricted to these groups of dyes.

Anthraquinone, monoazo and azomethine dyes are particularly preferred, the molecules of which are heavily occupied with amino, alkoxy, oxalkyl, nitro, halogen and cyano groups. These dye groups are defined in Color Index, Voluem l, pages 1655 to 1742.

In many cases it can be useful to pretreat before the surface coating of the substrate with a primer, which can consist of a thermoplastic with titanium dioxide or zinc oxide and is referred to as a clear lacquer. Thermoplastics that can be used for this are, for example, polyacrylonitrile, polyesters, polyurethanes, cellulose derivatives, such as cellulose 21/2 acetate, cellulose triacetate, nitrocellulose, polyamides, such as polycaprolactam, polyundecanamide or polyhexamethylene adipamide, and in particular nonlinear polyurethanes and polyesters.

Papers are usually used as auxiliary carriers, especially those that have no plastic coating where possible. The papers can also be siliconized or teflonized. Plastic films or other film materials can also be used as auxiliary carriers. The printing on the subcarriers can be done with all known printing processes in the sense of trichromatic or quadrochromic, such as in rotogravure or offset processes. The greatest printing accuracy and image quality can be achieved with several thousand different colors.

In general, the transfer printing process increases in size Outer surface patterns must be transferred so that the diameter of the laser beam, which can be, for example, 16 to 18 mm, is not sufficient to treat the entire surface to be printed. For this reason, it is expedient to fan out the laser beam with respect to its original diameter, such as 16 to 18 mm, to a larger diameter and / or to have the laser beam swept over the surface of the auxiliary carrier to be irradiated.

The fanning out to a larger diameter of the beam can take place in a known manner with the aid of optical lenses. In this way, for example, the laser beam can be brought to a diameter of 15 to 20 cm in order to treat, for example, the entire surface of a rotating aluminum beverage can without deflecting the laser beam.

Coating of larger areas in particular, such as when printing on metal plates, can be done by deflecting the laser beam with the aid of a swivel mirror, a so-called wobbler. Such a swiveling mirror can, for example at a power of 500 Hz, at a distance of 1 m from the substrate, a surface with a diameter of 50 cm, at a distance of 2 m, a surface with a diameter of 100 cm and at a distance of 4 m Brush surface with a diameter of 200 cm. Of course, the methods of fanning out and deflecting the laser beam can be combined.

Particularly when using a fixed, ie not deflected, laser beam, it is advisable to use a laser beam that has the smallest possible difference in intensity across its cross-section, since otherwise there is a risk that the auxiliary carrier will be heated to very different degrees, so that it is already in certain areas burns while it is still insufficiently heated in other areas in order to transfer the dyes sufficiently and to make the surface layer of the substrate receptive to the dyes. In the case of the deflection method this is not of decisive importance, since the rapid change of location of the point of impact of the laser beam on the auxiliary carrier compensates for differences in intensity in the cross section of the laser beam.

Laser beams of different origins, different intensities and different wavelengths can be used. The wavelength will generally be in the range between 500 and 50,000 nm, preferably in the range from 1000 to 20,000 nm, particularly preferably in the range from 2500 to 15,000 nm and very particularly in the range from 8000 to 12,000 nm. For example, a laser beam from a Co 2 gas laser with a wavelength of 10 600 nm can advantageously be used.

The intensity or continuous output power of the laser beam is usually in the range from 50 to 15,000 watts, preferably in the range from 100 to 1000 watts, particularly preferably in the range from 200 to 800 watts, very particularly in the range from 300 to 600 watts. For example, a laser beam with an output power of 400 to 500 watts can be used with advantage.

The laser beams used according to the invention can come from a wide variety of lasers, such as solid-state lasers, semiconductor lasers, dye lasers, gas lasers, liquid lasers and chemical lasers. The use of laser beams from gas lasers, preferably from CO ₂ gas lasers, is preferred.

• Fig. 1 eine Draufsicht auf eine Vorrichtung zur Durchführung des erfindungsgemäßen Verfahrens zum Bedrucken von zylindrischen Dosen,
• Fig. 2 eine Seitenansicht einer anderen Vorrichtung zur Durchführung des Verfahrens nach der Erfindung, ebenfalls zum Bedrucken von Dosen,
• Fig. 3 eine Seitenansicht einer weiteren Vorrichtung zur Durchführung des Verfahrens nach der Erfindung zur Bedruckung eines Flachkörpers beispielsweise aus Polymethacrylat und
• Fig. 4 eine seitliche Darstellung noch einer weiteren Vorrichtung zur Durchführung des Verfahrens nach der Erfindung zum Bedrucken von Glasflaschen.

The invention is further illustrated by the drawing using four exemplary embodiments. In this means

• 1 is a plan view of an apparatus for performing the method according to the invention for printing on cylindrical cans,
• Fig. 2 is a side view of another device for performing the method according to the invention, just if for printing on cans,
• Fig. 3 is a side view of another device for performing the method according to the invention for printing a flat body, for example made of polymethacrylate and
• Fig. 4 is a side view of yet another device for performing the method according to the invention for printing on glass bottles.

In the device according to FIG. 1, the cans 1 are guided through a preheating cabinet 2 with infrared radiators 3. They then arrive in a screw conveyor 4, which transfers them to the transport star 5 (stepped transmission-controlled), with which the cans are first passed past further infrared radiators 6 and preheated further. Then they are brought into position 7 by means of the preferred cylinder 11 in contact with the printed auxiliary carrier 13, which is unwound from the center spool 8 and wound onto the winding spool 9, which is controlled by the photocell 10. In position 7, the auxiliary carrier is treated with the aid of the laser sublimator 14 with a laser beam which transfers the dyes into the plastic coating of the cans.

After this transfer printing, the cans reach the discharge station 12 with the aid of the transport star 5.

In the system shown in FIG. 2, tin cans come from the hopper 15 onto the transport device 16 and from there through a preheating cabinet 17 with infrared emitters 18. In the ionization station 19, the cans are charged electrostatically and then with the aid of a schematically shown Maltese cross on the sheet unit 20 passed, which electrostatically adheres a sheet of the printed auxiliary carrier to each can. The can is then guided past the laser 21 with the aid of the Maltese cross, which transfers the dyes into the plastic surface coating of the tinplate can. Then the can passed through the sheet suction station 22, where the electrostatic charge is removed and the auxiliary carrier is sucked out of the can. Finally, the can arrives at the discharge device 23 and from there out of the machine.

In the device shown in FIG. 3, a flat body made of polymethacrylate 24, for example, is placed on the timing belt 25, which advances the flat body in time. The flat body passes the laser sublimator 26, while at the same time the auxiliary carrier 27 comes into contact with the flat body 24. The auxiliary carrier 27, printed on its underside, is unwound from the spool 28 via the synchronous advance 30 and wound onto the spool 29 after transfer printing.

In the system shown in FIG. 4, glass bottles are coated in the coating station 31 with a coating of a dye-affine plastic. The glass bottles 32 coated in this way reach a positioning unit 38 via a conveyor device 39 with the help of the clock generator 37, in which they come into contact with a label tape 34 which is unwound from a spool 35 and wound onto a spool 36 after transfer printing. In the same position in which the label band is in contact with the bottle, a laser beam from the laser sublimator 33 strikes the back of the label band, as a result of which the label is printed onto the glass bottle.

The invention is further illustrated by the following examples.

example 1

Aluminum beverage cans, which are seamlessly drawn from an aluminum blank using the deep-flow method, are given an internal coating in the conventional sense and are coated on the outside with an epoxy resin coating system, which is specific to the dye, and polymerized over heat siert. The further treatment takes place in a system according to FIG. 1 of the drawing.

The pretreated beverage cans are fed into a preheating cabinet of the laser sublimation system via conventional conveyor belts and brought into rhythm with the transfer printing system via a screw.

From there, the beverage cans are taken over by a Maltese cross, preheated to 200 ° C using infrared emitters and fed to the point where the rotating can comes into contact with endless transfer label paper.

In the contact zone, the transfer material is hit by a laser beam, which is distorted in the width of the respective can, and the sublimation of the dye takes place in less than a second. The printed transfer label paper is wound up and later fed to the recycling process, while the printed beverage cans are fed to the standardized palletizing.

Example 2

Seamless tinplate cans drawn in multiple stages using the deep-flow process are painted on the inside as usual and painted on the outside with an acrylic-based paint system. The further treatment takes place in a system according to FIG. 2 of the drawing. The ready-to-print material is fed into the discontinuously operating laser sublimation machine via a dosing system (storage) and heated to approx. 200 ° C in a preheating cabinet using infrared radiators.

Finally, the beverage can is charged electrostatically, guided past the sheet feeder via a Maltese cross, and labeled.

In the next cycle station, the rolling can with the laser beam of 500 kW and a spread width appears _D osenbreite set in contact. The transfer takes place in less than a second. The electrostatic field is then neutralized by ionization and the transfer paper is directed into the sheet suction station by vacuum.

The edruckten to ^g cans are as standardized palletizing fed.

Example 3

The new laser sublimation method has made it possible to thermally transfer cast or extruded polymethacrylate and then to deform it in a rubber-elastic state under vacuum or with compressed air. The transfer printing takes place in a system according to FIG. 3 of the drawing.

The polymethacrylate plates run into the laser sublimation machine via a synchronized conveyor belt. In a transfer printing zone, they are brought into contact with continuous paper running synchronously, on which decorations with disperse dyes are rotogravure printed.

The transfer printing area is swept by a laser beam, which is brought into defined vibrations via special lenses and an electromagnetic system. The energy should not be less than 500 kW. The preference is synchronized with the laser transfer speed. The transferred transfer decor paper is rewound and sent to the recycling process.

Example 4

Beverage bottles made of glass are completely or partially surface-coated in a system according to FIG. 4 of the drawing via a painting station with a dye-affine coating system, with special attention to an adhesion promoter. The glass bottles run in a heat oven for the polymerisation of the finishing layer and are over a clock system brought into contact with an endless labeling tape which is printed with disperse dyes.

Laser radiation occurs at the contact points between the paper and the rotating can, whereby the transfer printing takes place thermally in less than a second.

The decorated glass bottle runs into the packaging station while the transfer paper is continuously being wound up for recycling.

The same system is able to decorate beer and other beverage glasses, for example, after a small changeover.

Claims (11)

l. Process for printing a substrate with a plastic surface affinity to the printing inks by the transfer printing process by placing an auxiliary carrier printed with dyes sublimable under the process conditions on the plastic surface and transferring the dyes to the plastic surface, characterized in that the unprinted back of the auxiliary carrier is laser beamed treated at an intensity sufficient to allow the dyes to at least partially penetrate the plastic surface of the substrate. 2. The method according to claim 1, characterized in that one preheats the substrate surface before the laser beam treatment to a temperature below the sublimation temperature of the dyes. 3. The method according to claim 2, characterized in that preheating the substrate surface with infrared rays. 4. The method according to any one of claims 1 to 3, characterized in that the laser beam is fanned out to a larger diameter compared to its original diameter and / or the laser beam is allowed to sweep over the surface of the auxiliary carrier to be irradiated. 5. The method according to any one of claims 1 to 4, characterized in that the laser beam with an intensity or output power of 50 to 15,000 watts, preferably from 100 to 1000 watts, particularly preferably from 200 to 800 watts, particularly from 300 to 600 Watts, used. 6. The method according to any one of claims 1 to 5, characterized ge indicates that a laser beam with the smallest possible intensity differences across its cross-section is used. 7. The method according to any one of claims 1 to 6, characterized in that a laser beam with a wavelength in the range from 500 to 50,000 nm, preferably from 1000 to 20,000 nm, particularly preferably from 2500 to 15,000 nm, particularly from 8000 up to 12,000 nm. 8. The method according to any one of claims 1 to 7, characterized in that the auxiliary carrier 0.001 to 10 seconds, preferably 0.001 to 1 seconds, particularly preferably 0.01 to 0.1 seconds, treated with the laser beam. 9. The method according to any one of claims 1 to 8, characterized in that the surface to be irradiated of the auxiliary carrier is coated by deflecting the laser beam by means of a pivoting mirror. 10. The method according to any one of claims 1 to 9, characterized in that one uses a laser beam from a gas laser, preferably a CO 2 gas laser. 11. The method according to any one of claims 1 to 10, characterized in that it is treated with a laser beam of such intensity and for so long that the auxiliary carrier is heated to below its flash point or decomposition point.

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