Process for printing a substrate resistant to a heat of more than 220 degrees C.

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 paper or aluminum foils, are printed with sublimable dyes using binders and the auxiliary substrates thus printed are in turn used to print the textiles. Here, the auxiliary carrier with the printed side is placed on the textiles to be printed, after which the dyes are sublimed onto the textile material by heating the auxiliary carrier on the unprinted 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 heat-resistant fabrics which, as such, do not accept the sublimable dyes, such as wood, metals, certain plastics, glass, ceramic materials, natural and plastic products or the like, by the transfer printing process printing by providing such substrates with or before the transfer printing with a surface layer made of a thermoplastic material, which binds to the surface of the substrate and absorbs the sublimed disperse dyes. Thermoplastics have always been used as plastic coatings in these known processes.

It has now been found that such articles obtained in the transfer printing process do not have sufficient migration resistance, at least in certain applications, with the result that the dyes migrate in the surface layer on the substrate and blur the printed image or pattern. This disadvantage occurs particularly and particularly strongly when the printed substrate is exposed to short-term high temperatures or continuous heating during its later use.

This is the case with many household items, such as stove tiles, heating cladding, floor coverings in rooms with underfloor heating, stoves, cooking pots, kitchen machines of all kinds, etc. Especially in such applications, the previously known polytransfer processes are not suitable because they do not produce clear print images or cause the initially clear images to blur with time.

The object on which the invention is based was therefore to obtain a new method for printing on substrates which are stable when heated above 220 ° C., which leads to flawlessly clear printed images which also do not blur with time, not even with continuous heating or short-term heating by migration or be blurred and not yellowing either.

The method according to the invention for printing on a substrate that is resistant to heating above 220 ° C. after the transfer printing process by coating the substrate with a plastic that is affine to the printing inks, placing an auxiliary carrier printed with sublimable dispersion dyes on the plastic coating and transferring the dispersion dyes by dry heat treatment into the plastic coating characterized, that at least one crosslinked thermoset from the group of phenoplasts, aminoplasts, polyesters, polyphenylene sulfide resins, silicone resins, acrylate resins, alkyd resins, polyether sulfone resins, polyamideimide resins and / or unsaturated polyester resins is used as the plastic for coating the substrate.

Surprisingly, it has been found that the migration tendency of the dyes becomes practically negligible with this process, even if the printed substrates are exposed to relatively high temperatures during printing or after printing. The reduction in the migration tendency is due on the one hand to the three-dimensional crosslinking of the thermosets and on the other hand to the structure of the disperse dyes, which in turn leads to an unusually high sublimation temperature. There is also practically no discoloration or yellowing of the coating due to aging or heating.

Because of the surprisingly frozen migration tendency of the dyes according to the invention, the substrates printed by the process according to the invention can be exposed to shock temperature stresses above 220 ° C. and long-term permanent temperature stresses, for example to 150 ° C., without any dye migration being recognizable.

For this reason, many household items, such as saucepans, frying pans, electric kitchen appliances, rechauds, waffle irons, grills, toasters, coffee machines, oven tiles, heating panels, ashtrays and many other objects, can be printed true to the photograph for the first time in the sense of halftone or halftone technology, without the printing process or later the image is blurred.

The substrates can consist of metals such as aluminum or steel, glass, ceramic materials, natural or artificial stone products, heat-resistant plastic or the like. For example, ceramic tiles, which could previously only be decorated using the screen printing process, can now be printed using halftone technology with true-to-life images, and such tiles can be used even in heated areas, such as on hot tables, as stove tiles or as floor tiles in rooms with underfloor heating, without using Migration of the photographic print would be blurred. The ceramic tiles can consist of conventional tile materials such as clay, earthenware, stoneware, porcelain, chamotte or the like. However, the substrates can also be slabs made of natural stones, such as granite, marble, slate, dolomite or any other natural stone, or of a plastic material, made of wood or metal. Other substrates can be, for example, moldings made from phenolic resins reacted with organic di- and / or polyisocyanates, especially those made from foams according to DE-OS 2 542 900.

Other substrates that can be printed using the method according to the invention are materials in web form that can be coated and printed in strip form. These can in turn consist of metal, plastic or the like.

The method is also particularly suitable for printing on a wide variety of household appliances which are exposed to elevated temperatures temporarily or long-term, such as from _Kall kinds of tableware, toasters, hot plates, waffle irons, grills, thermos containers and heaters. All of these are coated at least on their visible sides with the thermosetting plastic or first with another plastic and finally with the thermosetting plastic before the decoration is printed on using the transfer printing process.

When we are talking about cookware, this includes all containers of any shape, with or without a handle or handle, as used in the home and kitchen. For example, there are saucepans, frying pans, quick-action pots, kettles, milk jugs, roasting pans, saucepans, bowls, each with or without a lid, and other containers which serve to heat food or beverages. Such cookware is usually made of metal, such as steel, aluminum, enamelled steel, but can also consist of ceramic material or, above all, of fireproof glass. According to the invention, the heating plates can be printed with decor on their heating surface, without this losing quality due to the heating. The thermal surface can be made of any thermally conductive material, such as steel or ceramic.

The thermos containers can be in the form of bottles, jugs, mugs, mugs or boxes or in other conventional forms for this purpose. They are generally used to store drinks or food in the home, but they can also be used for technical purposes.

Various designs of heating devices to be printed according to the invention with a housing and at least one visible side are known. For example, it can be oil ovens, gas ovens, coal ovens, electric ovens or heat stores. It is essential that all of these heaters have a housing which is generally essentially cuboid with at least one visible side. This housing is generally made of metal, but can also be covered or supplemented in certain areas with ceramic plates, plastic plates, wooden plates or the like.

The thermosets used according to the invention 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 silicone resins, especially 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 to use 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 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 can be stacked and processed further immediately. 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 irradiation.

In the process according to the invention, the procedure is usually that the substrate is first provided 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.

After the precursor of the thermosetting material has been applied, crosslinking or curing takes place in a manner known per se, a hard and resistant coating being obtained on the substrate. The printed subcarrier is now placed on this surface layer with the printed side facing this layer, whereupon the dispersion colors are transferred by sublimation to and into the thermosetting surface coating of the substrate by heating from the unprinted side of the subcarrier.

From the thermosets used according to the invention, those which have sufficient affinity for the dispersion dyes used in particular can easily be selected with a few preliminary tests. Such routine tests are within the skill of the average person skilled in the art.

The disperse dyes used are suitably those which sublime above 200, especially above 220 ° C. The disperse dyes used according to the invention expediently sublimate 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 only exceed 500 ° C., preferably not above 400 ° C. , sublimate.

The disperse dyes used are expediently high-molecular disperse dyes with molecular weights above 280, preferably above 340 and up to molecular weights of 1000. A preferred group of such disperse dyes are certain anthraquinone, monoazo and azomethine dyes, but the process according to the invention is not for these groups of dyes limited.

While in the dyes previously used for transfer printing processes, there are no ionic, highly water-solubilizing groups, such as -S0₃H or -COOH may be contained, such dyes can be used successfully in the process according to the invention. The number of non-ionic polar groups, such as NO₂, -CN, -S0₂R (R = alkyl), -OH, -NH₂ or -NHR (R = alkyl), higher than with the previously used dyes. 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, cyno groups are preferable to nitro groups, and fluorine atoms are more suitable than chlorine atoms. Trimethylsilyl groups can increase the vapor pressure in the azo dyes.

In summary, it can be said with regard to the useful disperse dyes that, in contrast to known transfer printing processes, so-called sublimation-resistant disperse dyes can now be used in the process according to the invention. Anthraquinone, monoazo and azomethine dyes are preferred, the molecules of which are heavily occupied by amino, alkoxy, oxalkyl, nitro, halogen and cyano groups. These dye groups are defined in Color Index, Volume 1, pages 1655 to 1742.

Preferred examples of dyes used in the present invention are those of the following formulas. These dyes were not usable in the previous transfer printing processes.

Blue dyes:<chemistry id="chem0001" num="0001"><img file="EP0014901A2_D0001.tif" /></chemistry><chemistry id="chem0002" num="0002"><img file="EP0014901A2_D0002.tif" /></chemistry><chemistry id="chem0003" num="0003"><img file="EP0014901A2_D0003.tif" /></chemistry>

Yellow dyes:<chemistry id="chem0004" num="0004"><img file="EP0014901A2_D0004.tif" /></chemistry><chemistry id="chem0005" num="0005"><img file="EP0014901A2_D0005.tif" /></chemistry><chemistry id="chem0006" num="0006"><img file="EP0014901A2_D0006.tif" /></chemistry><chemistry id="chem0007" num="0007"><img file="EP0014901A2_D0007.tif" /></chemistry><chemistry id="chem0008" num="0008"><img file="EP0014901A2_D0008.tif" /></chemistry>

Orange dye:<chemistry id="chem0009" num="0009"><img file="EP0014901A2_D0009.tif" /></chemistry>

Red dye:<chemistry id="chem0010" num="0010"><img file="EP0014901A2_D0010.tif" /></chemistry>

Purple dye:<chemistry id="chem0011" num="0011"><img file="EP0014901A2_D0011.tif" /></chemistry>

The subcarrier can be printed with these dyes continuously in gravure printing or discontinuously in offset printing, with images or patterns having to be printed in reverse. You can use the finest screening. Printing can also be done using the classic screen printing process or on rotary film printing machines.

The auxiliary carriers, such as transfer papers, should have a weight of at least 60 g / m², maximum weight of 12₀ own g / m. The tear length should be at 5000 m, the burst pressure at approx. 3 to 3.5 kg / cm², the absorption at 60 to 80 g water per square meter in 60 seconds (according to Kobb) and the porosity at 40 ml / sec. lie. In addition to paper, metal foils and possibly elastic but not dye-affine plastic foils can also be used as auxiliary carriers, provided they can withstand the transfer printing temperatures above 220 ° C.

With the method according to the invention one can work on continuous finishing lines for aluminum sheets at furnace temperatures of approx. 250 ° C. When the cooling zone is switched off, the aluminum sheet and transfer paper can be passed over a calender roll at the same time. The drying heat of 250 in the aluminum_C. enables the transfer onto the aluminum without additional energy supply.

In the drawing, three application examples of the method according to the invention are shown. In the drawing shows<ul id="ul0001" list-style="none"><li>1 is a perspective view of a tile or plate printed according to the invention made of ceramic material or metal,</li><li>2 is a perspective view of a metal web printed according to the invention,</li><li>Fig. 3 is a broken away enlarged section of the cross section of the tile or plate of FIG. 1 along the line III-III and</li><li>Fig. 4 is a perspective view of a hot plate printed on the thermal surface according to the invention.</li></ul>

In Fig. 1, a tile or plate is shown in perspective, which can be coated and printed as a single plate. The coating can be carried out by dipping processes, spraying processes or other known coating processes. The tiles can be plastic-coated on one side on the visible side or on both sides.

In _Fig. As an alternative, FIG. 2 shows a correspondingly printed strip-shaped metal web in roll form which is suitable for being coated with a strip.

Fig. 3 of the drawing shows the cross section of an object printed according to the invention using the example of the tile or plate of Fig. 1. The substrate 1 made of metal or another material common for tiles or plates, such as ceramic material, is on both sides with the plastic coating 2 and a thermosetting coating 4 provided. The thermoset coating 2 lies on the visible side of the tile or plate and lies directly on the substrate 1. Dyes 3 are embedded in the thermosetting coating 2 in such a way that they adjoin the free surface thereof, but in the illustrated case only extend over a limited part of the thickness of the thermosetting coating, the latter being free of dyes in its area directly adjacent to the substrate 1 .

The heating plate 7 shown in FIG. 4 of the drawing has a grip strip 6 at each of its two ends, between which the heating part 5 with the printed heating surface is located.

Examples

Comparative example

According to Example 7 of DE-OS 2 642 350, a steel sheet 0.5 mm thick was surface-coated with a thermoplastic polyester resin matted by titanium dioxide. With the help of a transfer paper, which was printed with the usual emulsion colors sublimed below 220 C, an image was printed on this polyester resin coating using the transfer printing process at 200 ° C for 30 seconds.

The product only showed pressure fidelity in the temperature range between 0 and 80 ° C. Significant dye migration occurred above 80 to 110 ° C, which was shown by blurring of the surface. Above 110 ° C the halftone fabrics migrated in the sense of trigromy or quadrogromy migrated to a gray value without figure.

example 1

An aluminum sheet was pretreated with an organic grease solvent to make its surface free of grease and other contaminants. Then the pre-cleaned aluminum sheet was first coated with a white primer layer with a layer thickness of 40 ± 10 µm using a spray process. The coating was then dried in a continuous oven at 180 ° C. for 10 minutes. Then a colorless clear lacquer layer based on silicone polyester was also applied by spraying with a layer thickness of 15 ± 10 µm. The Troc_k- Was carried out at 250 ° C. for 10 minutes.

The still hot coated sheets were brought into contact with a transfer printing paper which had been printed with dyes subliming above 220 ° C. using the offset process. The printing process was heated to 250 ° C.

The printed aluminum sheets obtained in this way were distinguished by very good heat resistance and service temperatures above 150 ° C. and by high resistance to all loads, such as occur in the household sector, for example.

Example 2

Biscuit tiles were first sprayed with a two-component polyurethane barrier primer, which was dry at room temperature, because the tiles were very absorbent. This pretreatment agent was based on aliphatic urethane acrylate.

A plastic coating made of polyacrylate was then applied in the casting process. The top coat layer was with a layer thickness of 50 + 10_/to be applied solvent-free. The crosslinking took place within fractions of a second at room temperature by electron beam curing. The coating had an exceptional scratch resistance and hardness for plastic surfaces.

The still hot coated tiles were brought into contact with a transfer printing medium which was printed with high-pressure printing with dyes sublimating above 220 ° C, the transfer printing was carried out at 240 ° C.

Example 3

Tinplate was coated directly by roll-coating with a coating system based on a saturated polyester and a self-crosslinking acrylic resin without any pretreatment. First, a white primer based on a saturated polyester was applied as a base coat in a layer thickness corresponding to 20 to 30 g / m, after which it was dried at 160 ° C. for about 8 minutes. Then a colorless clear lacquer layer based on a self-crosslinking acrylate resin was applied in a layer thickness corresponding to 10 to 20 g / m² applied. The drying took place within 10 minutes at 190 ° C.

The tinplate was later at 250 ° _C. with a transfer printing medium, which was screen-printed with dyes that sublime above 220 ° C, printed.

Example 4

Chipboard was first subjected to a sanding with a grain size of 80 to 120. The coating system consisted of a material based on an unsaturated polyester with a co-accelerator and organic peroxide as a catalyst.

A white primer coat in an amount of 400 g / m² was sprayed on with a cup gun at an air pressure of 3 to 3.5 bar and a nozzle size of 2 to 3 mm. Drying was carried out at room temperature until grindable for 4 to 6 hours or at a temperature of about 80⁰ C for 20 minutes. The grit was then sanded with 280 to 320 grit before the top coat.

Thereafter, a colorless clear coat was applied with the same cup gun in an amount of 150 to 300 g / m² applied. The drying was carried out at room temperature for 8 to 10 hours or at a temperature of about 80 ° C for 10 to 15 minutes.

At a later point in time, the chipboard coated in this way was printed with a transfer printing medium which was printed with dyes which sublimated above 220 ° C.

The printed products obtained in all four examples had excellent image clarity even after prolonged use and with temporary heating to 200 ° C. and with long-term heating to 150 for several hours⁰ C. Despite the heating, migration of the dyes was not noticeable and the printed images remained completely clear.