EP0326919B1 - Process and device for producing coatings on substrates - Google Patents

Abstract

Process and apparatus for the production of rapidly curing coatings on surfaces of wood, woodworking materials, cured or uncured, woven or unwoven substrates which may be impregnated with an impregnating resin and consist of paper, cardboard, nonwoven or woven fabric and metal foils or plastic films by applying a liquid coating material containing plastics or synthetic resins, and if necessary diluents, plasticisers, flatting agents, fillers, colour-imparting substances and additives, a predried layer of an aqueous, solvent-free and substantially pollutant-free dispersion of a binder having a high film formation temperature above 60<o>C, into which waxes or paraffins have been incorporated in a concentration - based on the solids content of the dispersion - of 3 to 10% or more by precipitation at a high temperature, being fused together to form a film by a brief thermal shock at a temperature considerably exceeding the film formation temperature. <IMAGE>

Description

The invention relates to a method for producing quick-curing coatings on surfaces of wood, wood-based materials, hardened or unhardened, optionally impregnated with impregnating resin, woven or non-woven carrier materials made of paper, cardboard, nonwoven or woven fabric, and of foils made of metal or plastic by application a liquid coating agent containing plastics or synthetic resins and, if necessary, diluents, plasticizers, matting agents, fillers, coloring substances, additives and additives, and a device for carrying out this process.

A problem in the production of fast-curing coatings of the type described above are, on the one hand, the relatively long drying times and the pollutants which occur during processing, such as, for example, formaldehyde or skin-damaging solvents, such as must be used, for example, in UV-curable systems. With UV-curable systems that still manage with relatively short drying times, photoinitiators are needed, which are carcinogenic on the one hand and also lead to yellowing of the coating layer. Inadequately hardened surfaces often gas out unpleasant smelling vapors for months, which is why the previously known systems cannot satisfy for this reason either. In addition, in the case of all of them, the remaining residues during processing are special waste, which has to be disposed of in a complex manner. The problems with solvents or other pollutants can be significantly reduced if - as proposed in European Patent 62245 - aqueous dispersions are used. However, the dispersions proposed there, in which acrylate polymer and at least one unsaturated polyester resin were used, do not allow short curing times, which, for example, allow an immediate winding of a film which has been provided with such a coating. In addition, this creates thermoset coatings which are no longer thermally softenable and therefore neither re-calenderable nor transferable.

The invention is therefore based on the object of designing a process of the type mentioned in such a way that, with the aid of simple, pollutant-free starting materials, in a process which also takes place without adverse health conditions and residues, regardless of the carrier material used and the type of application of the coating crystal-clear, durable and both abrasion-resistant and moisture-resistant coatings are created, the drying time of which is extremely short, so that even at the highest processing speeds, roller machines running without additional drying plugs to be installed allow immediate winding.

To achieve this object, the invention provides that a predried layer of an aqueous, solvent-free and pollutant-free dispersion is provided on the carrier a binder as a coating agent with a high film-forming temperature above 60 ° C, into which waxes or paraffins with a concentration - based on the solids content of the dispersion - of more than 10% have been incorporated by hot precipitation, by a brief temperature shock with a Film formation temperature significantly exceeding temperature is melted into a thermoplastic film.

In extensive tests on which the present invention is based, it has been found that such binders with a high melting point or high minimum film-forming temperature (MFT), which can be applied in a conventional manner, for example by rolling, knife coating, spraying, filling, pouring or electrostatic spraying , when they are exposed to a very high temperature, are suddenly subjected to a melting process and thereby form a coherent film. This film formation under the temperature shock eliminates course disturbances, such as "orange peel effect", "roller marks", "squeegee strips", "raster effect", etc., which are very often due to the most careful recipe design and viscosity controls when applying liquid or pasty Do not let coating materials be avoided.

Due to the high melting temperature or the high MFT, the film formed in the melting process also solidifies immediately after leaving the temperature zone, so that immediately after the temperature shock the stackability, blocking resistance, windability etc. as well as the resistance of the resulting surface against mechanical and chemical effects are given.

It has proven to be particularly advantageous that self-crosslinking and / or externally crosslinkable and / or pre-crosslinked dispersions, e.g. based on acrylates, methacrylates, and their esters, nitriles, amides, vinyl acetate, styrene, butadiene, vinyl propionate, isobutene, polyurethane, vinylidene.

Hard resins that are water-soluble or that are made water-soluble by amination are preferably used. Reactive resins that can be diluted with water or are dispersed / emulsified in water by means of suitable emulsifiers can, in conjunction with the corresponding catalysts, promoters, accelerators (possibly latent adjustments), contribute to the improvement of the resistance to mechanical and chemical effects as part of thermal curing .

Hard resins are, for example, copolymers of styrene and acrylic acid, while reactive resins, e.g. systems capable of polycondensation (melamine-urea resins), polymerizable resins (polyester, acrylate resins) or polyaddition-capable resins (polyurethane compounds) with the corresponding catalysts or reactants.

If latent hardener systems are used, the production of 1-component materials is possible. The prerequisite here is that the light-off temperature is above 100 ° C.

Water-thinnable liquids with reactive groups, which are included in the chemical reaction as binder components, can help to reduce the viscosity with a high solids content. they can also have a clearly positive influence on hardening and film properties. Examples of such reactive diluents are polyols, polyethers, polyetherols and epoxides, each with at least two reactive groups. Film formers (polyvinyl alcohol), plasticizers, wetting agents, defoamers, matting agents, etc. can be used as recipe components to influence the processing and film properties.

The short temperature shock according to the invention - the short-term heating also has the advantage that only the coating that is actually to be melted into a film is heated, and not, for example, the carrier material, if the layer has been applied directly to the carrier material - can be done in various ways, for example also by radiant heat. However, it is preferably provided that the predried layer is melted together in direct contact with a surface which is approximately 100 to 200 ° C. and serves as an energy source, the thermoplastic film being additionally advantageous if the film is located directly behind the heating device leading to its formation is cooled. According to the preferred contact heating, either on a press surface or preferably on a heated calender roll, the possible cooling of the film after the film-forming heating device should possibly also be carried out by a cooled calender roll. Instead of or in addition, contact-free nozzle cooling can also be provided.

In the method according to the invention, the hot precipitation of high concentrations of wax or paraffin is of considerable importance, since in addition to an extremely fine distribution of the wax or Paraffins a kind of coating effect of the individual dispersion particles by wax particles takes place. This results in a significant improvement in the rheological properties and, as a result, very uniform application layers, regardless of the type of application of the layer. Added to this is the fact that in melt flow hardening, because of this coating of the dispersion particles by wax, there is a very rapid, uniform melting together, in which chemical reactions, which have obviously not been investigated in detail, also occur, since the layers formed in this way, in addition to high mechanical hardness, are also extremely resistant against liquids. It has been shown that even after days, liquids have not yet passed through such a layer, which, for example, plays a very significant role in the coating of wood-based materials with regard to the liquid resistance of tables or the like.

In addition, the proportion of preferably hot waxes or paraffins enables a very simple transfer process, such that the film is first formed on a roller or an endless belt and is transferred from there to the actual carrier. By means of this transfer process according to the invention, porous surfaces in particular, which are rough in their surface structure, can be provided with a smooth coating layer without excessive amounts of dispersing agent having to be used, since the agent does not have to be applied wet to the porous surface and therefore also not can penetrate to a high degree.

While the hot precipitation of waxes produces particularly good results, it is not an essential requirement For a usable result, a relatively high percentage of wax in the order of at least 3 to 10% or even more is of particular importance. In addition, it has proven to be useful to combine wax and emulsifier in the wax precipitation.

The following waxes have proven to be particularly suitable for the purposes of the invention: montan waxes (montanic acid or montan ester waxes), polyethylene waxes, polymer dispersions, natural waxes, ethylene / vinyl acetate copolymers in combination with suitable emulsifiers.

Not only the type of wax or paraffin used, but also the selected emulsifier system have a decisive influence on essential processing and surface properties (level, gloss, separation effect, hardness, resistance). By adding appropriate emulsifiers, e.g. the detachment from the plastic tape can be completely prevented, so that you can get an excellent laminating adhesive in this way.

The hardness, the viscosity and the gloss are also very strongly influenced by the respective emulsifier (on a combination of different emulsifiers), with an emulsifier amount of approximately 2 to 6% based on the overall recipe having proven to be very useful.

Finally, the following substances have proven particularly suitable as emulsifiers: oleic acid ethoxylate, fatty alcohol ethoxylate, oleic acid alkynolamide or - preferably - castor oil ethoxylate.

The transfer process also allows structured films to be produced very easily by using the Roller or the belt has a corresponding surface structuring, which is then retained accordingly after the transfer to the actual carrier.

The transfer process should be carried out with particular advantage in such a way that the actual film formation, i.e. the film formed from a predried dispersion layer is melted together with the transfer.

It is also within the scope of the invention to transfer several layers of different materials to form a multilayer film, the top layer, for example, being a binder layer in order to achieve particularly good adhesion to the respective carrier. In addition, for example, a special separating layer could also be provided so that the film detaches better from the roller or the belt, although this is generally not necessary because of the high wax or paraffin content and the special type of incorporation. With this wax portion, with a few exceptions, a film according to the invention can be removed very well from a smooth calender roll or a smooth steel or plastic belt in order to be transferred to a carrier, for example a paper web, a wooden plate or the like.

In a further development of the invention, the method according to the invention and the substances used thereby also enable a completely new form of printing on carriers, namely by first applying and at least predrying a film-forming layer onto a transfer belt or transfer roller onto which the individual Color layers printed on , followed by transfer to the actual carrier with the film-forming layer to be located on top, and possibly the formation of the film by melt flow hardening. This type of printing obviously allows printing on any surface, including rough porous surfaces that could not have been printed at all with conventional printing processes. In addition, it does not matter at all how thick and rigid the actual carrier is, since it does not have to be passed through a printing press which is usually matched to paper or foil sheets and therefore, for example, not simply for printing on Chipboard could be used, even if the surface condition would have allowed it.

In this transfer printing of supports, the top printing layer is preferably an adhesive or adhesion promoter layer to improve the adhesion on the support and to compensate for surface defects on the support.

Another advantage of the transfer printing process according to the invention is that the transfer carrier, i.e. the belt or the roller on which the actual coating film is formed or pre-formed and finally melted together during the transfer, is printed by means of a web printing machine and the layer is transferred to individual sheets can. This makes it possible to use the existing, much simpler and trouble-free web printing machines also for printing sheets. However, this sheet printing is especially for one of the main branches for which coating is required today, namely the coating of foil sheets or cardboard sheets for the production of packaging boxes is necessary.

In order to carry out the transfer method according to the invention, a device in a further embodiment of the invention is characterized by an endless transfer belt made of plastic or metal and rotating on the return path between a drying device and a transfer station with heatable transfer rollers and an inlet and outlet for the carrier to be coated an application device passes from the transfer station.

The preferred transfer process can also be carried out with the aid of a roller, to which the dispersion layer is first applied and pre-dried in order to be transferred from it to the actual carrier. In practice, however, a transfer belt is generally advantageous simply because of its longer length. The greater length of a belt enables a problem-free arrangement of a large number of application stations and an independent predrying of the melt contact hardening, so that in practice a transfer device using a roller can only be used advantageously in special cases.

Although the film according to the invention formed by melt flow hardening can be removed from the transfer belt or the transfer roller quite easily - any loose particles are automatically removed by the nozzle cooling - in some cases it may nevertheless be useful to arrange a cleaning device for the transfer belt in front of the application device, in order also remove any remaining coating parts or layers on the transfer belt in the event of any malfunctions, so that they do not interfere with those subsequently formed Film to be incorporated. The application devices for intermediate layers, for example an already mentioned adhesion promoter layer or a color primer layer or the like, are arranged downstream of the drying device, the use of a transfer belt instead of a transfer roller again having structural and procedural advantages.

In addition to the use of cooled cooling rollers or a nozzle cooling, which immediately follow the heatable transfer rollers in order to ensure a particularly sudden cooling of the film formed by melt flow hardening and thus a completely unproblematic further processing of the coated carrier, it can also be provided in a further development of the invention that a detour of the transfer belt relative to the substrate to be coated is provided between successive transfer rollers. As a result of this detour, both joints of the strip and small surface defects cannot have a decisive impact on the quality of the finished film, since such defects are no longer arranged at the same point on the coating in the region of two successive rolls.

The transfer and, if necessary, cooling rolls can be designed particularly simply as multiple calenders, in which the extremely smooth surfaces of the calender rolls result in additional smoothing of the film, which is already very smooth and coherent due to the melt flow hardening itself. The use of a transfer ribbon instead of a transfer roller also has the advantage that the transfer printing can take place in a much simpler manner and using commercially available web printing machines. For this purpose the transfer belt simply guided between the drying device and the transfer station by a commercially available web-fed printing press, ie commercially available web-fed printing machines can be supplemented to form such a transfer printing device.

Fig. 1 bis 5

verschiedene Ausführungsbeispiele erfindungsgemäßer Vorrichtungen zum Herstellen schnellhärtender Überzüge, wobei das Dispersionsmittel unmittelbar auf den zu beschichtenden Träger aufgebracht und zu einem Film schmelzgehärtet wird,

Fig. 6

eine Walzen-Transfervorrichtung, bei der ein vorgebildeter Film von einer Walze auf den eigentlichen Träger übertragen wird,

Fig. 7

eine schematische Darstellung einer erfindungsgemäßen Band-Transferiervorrichtung,

Fig. 8

eine vergrößerte Detaildarstellung zweier übertragungswalzen mit einer dazwischen angeordneten Umwegführung des Transferbandes,

Fig. 9

eine Darstellung einer Druckvorrichtung mit direkter Bedruckung von Rolle zu Rolle unter Aufbringung einer erfindungsgemäßen Filmdeckschicht, und

Fig. 10

eine schematische Darstellung einer Transferdruckvorrichtung, und

Fig. 11

eine schematische Darstellung eines abgewandelten Kalanders mit zusätzlichem Umlaufband.

Further advantages, features and details of the invention result from the following description of some exemplary embodiments and from the drawing. Show:

1 to 5

Various exemplary embodiments of devices according to the invention for producing quick-curing coatings, the dispersing agent being applied directly to the support to be coated and melt-hardened into a film,

Fig. 6

a roller transfer device in which a pre-formed film is transferred from a roller to the actual carrier,

Fig. 7

1 shows a schematic illustration of a belt transfer device according to the invention,

Fig. 8

an enlarged detail view of two transfer rollers with an intermediate detour of the transfer belt,

Fig. 9

an illustration of a printing device with direct printing from roll to roll with application of a film cover layer according to the invention, and

Fig. 10

a schematic representation of a transfer printing device, and

Fig. 11

a schematic representation of a modified calender with an additional conveyor belt.

Before the various devices for carrying out the coating process according to the invention shown in the drawings are to be discussed in detail, a few recipe examples for suitable prepared dispersion are listed, with the aid of which - as extensive tests on which the present invention is based - very good results can be achieved .:

For all recipe examples, it is advantageous to enter the last three positions as melted wax (95 - 100 ° C) in the previously completely perfectly dissolved template with vigorous stirring in a thin stream.

The simplest device for carrying out the coating method according to the invention is shown in FIG. 1. 1 shows the support to be coated, which of course does not have to be a tape as shown schematically, but of course could also be a sequence of tracks, plates or the like. This carrier 1 is coated with the aid of a coating device 2, which comprises a transfer roller 3 and a dispersion application roller 4, directly with the aqueous dispersion layer, which is then predried in a drying device 5. This drying device can be, for example, a nozzle dryer or an IR section. After this predrying, the actual melt flow hardening follows, which is already the simple one shown in FIG. 1 Embodiment is equipped as an interval contact hardening with a plurality of heated contact rollers 6. With 7 counter-contact rollers are designated. Instead of heating all three successive rollers 6, it could of course also be provided that, for example, only the first two are heated and the last is cooled, in order in this way to cool the film formed in contact with the heated rollers 6 on the carrier 1 in a particularly rapid manner to reach. The heating of the contact rollers 6 should be considerably above 100, up to 200 ° C in order to ensure sufficient heating of the predried dispersion layer to values which are considerably above the MFT, even at a high throughput speed of the carrier 1 and the resultant short contact time guarantee.

2 shows an embodiment in which, instead of a calender roller arrangement for curing the predried film, contact curing is carried out using a double belt machine 8. In the schematic exemplary embodiment according to FIG. 3, the coating of the carrier 1 takes place partly directly with the aid of the application device 2, partly indirectly with the aid of coating devices 2 'and 2' 'working on the belt 9 of the double belt machine. A modified contact hardening is also shown in this exemplary embodiment, which is illustrated schematically by the press with the jaws 10 and 11. These heated press jaws 10 and 11 also effect the transfer of the films of the coating devices 2 ′ and 2 ″ onto the carrier 1 with the contact hardening.

4 schematically shows a device with a plurality of stations, such as, for example is suitable for the opaque pigmented coating of chipboard, hardboard or MDF. It comprises a plurality of application devices 2, 2 ', 2''and2''' and correspondingly a plurality of dryers 5, 5 ', 5''and5''' as well as a schematically arranged printing machine 12.

5 schematically shows a device for contact hardening for the surface finishing of molded parts in connection with the pressing process. The double-roll coating device 2 applies a dispersion layer to the flat plates arriving on the transfer web 1, which in turn is predried in a known manner in the dryer 5 at temperatures between 30 and 100 ° C. The plates are placed on an intermediate stack 13 and then processed into molded parts in a molding press 14, the melt flow hardening of the dispersion layer initially only predried on the surface of the flat plates being carried out with the pressing into the desired shape. In a corresponding manner, other shaped bodies such as e.g. Manufacture party plates and cups from simple cardboard, because the coatings according to the invention - despite the use of aqueous emulsions as the starting material - are extremely waterproof after melt hardening.

6 schematically shows one possibility of how a conventional calender can be converted for the transfer coating according to the invention. The layer applied to the hot calender roll 20 at the top with the aid of the coating devices 2, 2 ′ is transferred to the belt 16 to be coated in the transfer process, with cooling to improve the detachment of the layer adhering to the belt 16 from the calender. To this end serves the cooling belt 40, which is cooled by the nozzle cooling device 41, so that it lies cold in the outlet area of the belt 16 from the calender roll 20 on the underside of this belt 16 and thus results in such a strong cooling that a much better separation effect between the transfer layer the band 16 and the calender surface is given.

A preferred embodiment of an apparatus according to the invention for forming film coatings is shown in FIGS. 7 and 8. This is a transfer device in which the film is applied from a transfer belt 15 to the actual carrier belt 16 to be coated. This carrier tape 16 is only to be understood schematically, since it does not have to be a tape which is wound from a roll 17 onto a roll 18. Instead of this, a sequence of sheets could of course also be provided with a coating using the transfer coating device according to FIG. 7 instead of a band 16. The transfer coating device comprises the actual transfer station 19 with heated calendar rolls 6 and counter-pressure rolls 7 as well as cooled calender rolls 6a and counter-pressure rolls 7a as well as the drying device 5, which in addition to a controllably heatable deflection roll 20 within a hood 29 can also comprise radiation heating devices indicated schematically by arrows. The transfer belt 15, which can be a plastic or metal belt with an extremely smooth surface, runs between the transfer station 19 and the deflection roller 20. An aqueous dispersion according to the invention, which is predried in the dryer 5, is applied to this belt with the aid of an application device 2, which is again only indicated schematically, in a manner known per se, that is to say by knife coating, spraying or the like. This dispersion can only be used with the help of a A further layer, for example an adhesion promoter layer, can be applied schematically indicated further application device 2 ', which can also comprise different stages. These two layers, i.e. the pre-dried film layer 21 and the adhesion promoter layer 22 - which are shown schematically in dashed lines in FIG. 7 - are transferred from the calender rolls 6, which are heated to temperatures between 100 and 200 ° C., to the carrier 16, or one other carrier entering the inlet 23, pressed on and thereby heated so quickly and abruptly to a temperature above its minimum film formation temperature MFT by the high temperature of the rollers 6, 7 that the only predried dispersion layer suddenly melts into a film which - favored by the Adhesion layer 22 - adheres firmly to the carrier 16. The film thus formed is cooled again by the cooled calender rolls 6a, 7a as quickly as it has been heated up, so that it can be wound onto the roll 18 immediately after it leaves the transfer station 19. The cooling additionally favors the detachment of the film according to the invention from the transfer belt 15, the actual smooth, abrasion-resistant film 21 now being present as the top cover layer, which is particularly firmly connected to the carrier 16 by the adhesive layer 22 underneath. In addition to the cooling rolls 6a, 7a, a nozzle cooling section 41 is also provided in FIG. 7, wherein this nozzle cooling section may also completely replace the cooling rolls 6a, 7a. In any case, it has been found useful, if not necessary, to provide cooling in such a transfer method after transfer to the belt to be coated, in order to achieve a much smoother, cleaner detachment from the transfer belt.

Between the cooling rollers 6a and the application device 2, a cutting and gluing device 30, indicated only schematically as a box, is provided, so that when the transfer belt 15 needs to be changed periodically, it can first be cut open, in order to glue a new transfer belt to the leading end, in order to then Pulling the tape through the device then finally connect the ends of the new tape section together. The cutting and gluing device 30 should be designed so that the tapes are cut obliquely at the joint, the bevel cut should be made so that it runs from top to bottom against the direction of travel, so that when coating material is applied to the transfer belt this cannot be pressed into the cut by the rollers and could possibly form beads. If the material is suitable, it is advisable in any case to provide as seamless a weld as possible instead of simply gluing the transfer belt.

The lifting device indicated schematically at 31 enables a very simple adaptation to different belt speeds. In the illustrated extended position with the transfer belt 15 wrapping around the foremost of the rollers 6, there is a relatively long contact time with the heated rollers 6, so that very high belt speeds are possible. At lower belt speeds, the wrap must be correspondingly lower so that the temperature in the layers 21, 22 does not become too high. This is achieved in that the lifting device 31 is adjustable, for example in the dashed position 31 ', in which there is only a very short contact distance with the calender roller 6 and thus also a correspondingly shorter period of time in spite of the low rotational speed is achieved, so that ultimately the desired actual heating of the layers 21, 22 can be controlled in this way at constant temperatures of the rollers 6.

In Fig. 8 a detour of the transfer belt 15 between the calender rolls 6 is indicated in order to compensate for the effect of any shocks or surface defects of the transfer belt. Between the two hot calender rolls 6 - the counter rolls have been omitted in this figure for the sake of simplicity - a nozzle cooling section 41 is again arranged in front of the lifting roll 42 in order to achieve this detour in order to in turn lift the transfer belt 15 from the belt 16 to be coated to achieve clean and smooth.

FIG. 9 shows a schematic printing device in which a coating according to the invention is also applied to the printing layers at the same time. The paper or foil tape 16 unwound from the roll 17 is printed in the schematic printing stations 25 and 26, although more than two can of course also be provided, and then each dried with the aid of dryers 5. A dispersion according to the invention is then applied to the printed strip surface in the application station 27 and again predried in the third dryer 5. With the help of the heated calender roll 6, the predried dispersion film is melted into a film and then the paper web 16, which is printed in this way and at the same time is protected on the surface by a film according to the invention, is wound onto a roll 18. According to the cooling belt in FIG. 6, a cooling belt 40 with a nozzle cooling section 41 is also provided in the arrangement according to FIG. 9 in order to prevent that the smooth film layer formed by the wrapping of the heated calender 6 on the belt 16 must be torn hot off the calender surface. The heat of the calender 6 is practically not impaired by the cooling belt 40, so that the heat of the calender comes through this cooling belt in the same way as if the cooling belt were not present. The film layer formed is now between the belt 16 and the cooling belt 40, so that when leaving the calender surface this film layer is still between the two belts. The belts 40 and 16 are only separated after passing through the cooling section 41. At this stage, however, this is now possible without any problems, since the cooling section also cools down the layer formed by melt flow between the two belts to such an extent that the separation no longer causes problems.

10 finally shows a transfer printing device in which, in a commercially available web printing press comprising the various printing units 25, 26 and 28, instead of printing on the actual carrier, preferably a paper web, a transfer belt 15 made of metal or plastic is printed onto which first with the aid of an application device 2, an aqueous dispersion has been applied and predried in a dryer 5. The three printed layers indicated by the application units 25, 26 and 28 are thus printed on the predried dispersion layer which, after passing through the printing press D, enters a transfer device 19. In this the melting of the dispersion into a film takes place with simultaneous transfer of this film and that printed on it and after it Transfer of printing layers lying below it to the carrier 16.

In the exemplary embodiment shown in FIG. 10, the transfer device 19 again contains two hot calender rolls 6 with corresponding counter-pressure rolls 7, in front of and behind which lifting rolls 31 and 31 'are arranged, which serve to change the wrap angle of the calender rolls 6 in accordance with the running speeds of the belts 15 and 16 in order in this way to be able to set the desired heating of the preheated dispersion layer and thus the exact temperature at which the film according to the invention is formed by melt flow hardening. At high belt speeds, the lifting rollers 31, 31 'are arranged in such a way that the course of the transfer belt 16 shown in FIG. 10 results. At very low belt speeds, at which the belt should not be in contact with the hot calender rolls 6 so that the layer is not heated too much, the lifting rolls 31, 31 'are in the respective dashed position so that also the dashed position of the transfer belt 16 results. In this case too, the actual transfer station is in turn followed by a nozzle cooling section 41 in order to achieve a clean separation of the transfer belt and the coated belt 16 with the film adhering to it from the melt flow. This separation is further favored by the fact that the air blown into the nozzle cooling device 41 is also blown in between the separating belts at 44, thus making it even easier to lift them apart.

The modified calendering device shown in FIG. 11 is special for existing calenders thought. After a direct coating of either the endless belt 1 or of individual sheets transported on the belt 1 with the aid of a coating device 2 according to FIGS. 1 to 3 and a predrying by a dryer 5, the belt 1 runs under a conventional calender 6 of an existing calendering machine which is in accordance with the invention is supplemented by an additional circumferential band 32 made of metal or plastic. With the aid of an adjustable lifting device 33, 33a, which can also take the position 33 ', 33a', this belt 32 enables the contact path to be adapted to the production speed, with a downstream nozzle cooling 34 after the melt flow hardening of the application layer on belt 1 or sheets transported on it ensure rapid cooling, so that extremely high production speeds are possible. Cutting and gluing devices are again indicated at 35 in order to be able to periodically change the tape 32. Such a cutting and gluing device is especially intended when using plastic tapes 32, while metal tapes, which also have a longer service life anyway, are to be replaced as a whole and prefabricated tape, but this usually causes difficulties in terms of machine technology (roller bearings on both sides).

The invention is not restricted to the exemplary embodiments shown. It would also be conceivable, in particular with regard to the transfer process described above, that the dispersion according to the invention not only runs pre-dried into the web printing press, but has already been formed by melt contact hardening before it enters the web printing press, which film is then applied together with those Printing layers and an adhesive layer in the transfer station 19 of FIG. 10 is applied to the actual substrate 16 to be printed. In this case, the transfer station 19 is not used for film formation at the same time.

In addition, it would also be possible, for example, to provide air nozzles (cold air knife) coming from below in the outlet of the device according to FIG. 7, in order to provide a clean air cut in the case of flaky sheets in which the coating layer extends over the sheets, with an uncoated edge then remaining, of course to be able to achieve by slightly lifting the sheets. Additional blowers acting from above and below can ensure that the overlapping bow ends are not lifted too far by the cold air knife, but only to such an extent that a sharp, clean air cut is achieved.

Claims (24)

1. Process for producing rapidly hardening coatings on surfaces of wood, wood materials, hardened or unhardened, optionally impregnated with resin, textured or untextured substrate materials composed of paper, cardboard, non-woven or woven fabric, and foils composed of metal or plastics material, by the application of a liquid, plastics- or artificial resin-containing coating agent, as well as, optionally, thinners, softeners, frosting agents, fillers, colouring substances, and additives, characterised in that, as a coating agent, a predried layer consisting of an aqueous, solvent- and toxin-free dispersion of a binder with a high film-forming temperature of more than 60°C, into which waxes or paraffins with a concentration - relative to the solid particle content of the dispersion - of 3 to 20% or more are worked by hot dropping, is melted down, by a brief temperature shock at a temperature considerably exceeding the film-forming temperature, to form a thermoplastic film.
2. Process according to claim 1, characterised by the use of dispersions which are capable of cross-linking with themselves and/or other substances, and/or which are already cross-linked, e.g. with a base of

   - acrylates, methacrylates, and their esters, nitriles, amides,

   - vinyl acetate,

   - styrene,

   - butadiene,

   - vinyl propionate,

   - isobutylene

   - polyurethane,

   - vinylidene.
3. Process according to claim 1 or 2, characterised by the use of reactive thinners with a base of

   - polyols,

   - polyethers,

   - polyetherols or

   - epoxy resins

   with at least two reactive groups in each case.
4. Process according to one of claims 1 to 3, characterised by the use of waxes with a base of

   - montan waxes (montan acid waxes, montan ester waxes),

   - polyethylene waxes,

   - polymer dispersions,

   - natural waxes,

   - ethylene/vinyl acetate copolymers in combination with suitable emulsifiers.
5. Process according to claim 4, characterised in that, as emulsifiers,

   - oleic acid ethoxylate,

   - fatty alcohol ethoxylate,

   - oleic acid alkynolamide

   or, preferably, castor oil ethoxylate are used.
6. Process according to one of claims 1 to 5, characterised in that the predried layer is melted down to a thermoplastic film in direct contact with a surface at approx. 100 - 200°C acting as an energy source.
7. Process according to one of claims 1 to 4, characterised in that the film is cooled directly behind the heating device that brings about its formation.
8. Process according to claim 7, characterised in that the film is subjected to contact cooling on cooled calendering rollers.
9. Process according to one of claims 1 to 8, characterised in that the predried layer is formed on a roller or an endless belt and is transferred thence to the substrate proper with the formation of the thermoplastic film.
10. Process according to claim 9, characterised in that the roller or belt has surface texturing.
11. Process according to claim 9 or 10, characterised in that a plurality of layers of different materials are layered one above another to form a multi-layer film.
12. Process for printing on substrates according to claims 9 to 11, characterised in that a film-forming layer is first applied to a transfer belt or transfer roller, on which the individual colour layers are printed, and is at least predried, and in that then the coating is then transferred to the substrate proper with the uppermost, film-forming layer, and the thermoplastics film is then formed by fused mass hardening.
13. Process according to claim 12, characterised in that a cement or adhesive layer is applied to the uppermost printed layer to improve adhesion to the substrate and to even out surface detects in the substrate.
14. Process according to claim 12 or 13, characterised in that the transfer belt or transfer roller is printed by means of a web-fed printing press, and the layer is transferred on to individual sheets.
15. Apparatus for carrying out the process according to one of claims 9 to 14, characterised by an endless, plastics or metal transfer belt (15), which revolves between a dryer (5) and a transfer bay (19) with heatable transfer rollers (6, 7) and an inlet and outlet for the substrate (16) to be coated and which passes through a coating device (2) on the return section from the transfer bay (19).
16. Apparatus according to claim 15, characterised in that a cleaning device for the transfer belt (15) is disposed in front of the coating device (2).
17. Apparatus according to claim 15 or 16, characterised by the coating devices (2') for middle layers (22) located downstream of the dryer (5).
18. Apparatus according to one of claims 15 to 17, characterised in that cooled cooling rollers (6a, 7a) are disposed behind the heatable transfer rollers (6, 7).
19. Apparatus according to one of claims 15, to 18, characterised in that a detour guide of the transfer belt (15) combined with a cooling section is provided opposite the substrate to be coated (16) between consecutive transfer rollers (6).
20. Apparatus according to one of claims 15 to 19, characterised in that the transfer rollers (6, 7; 6a, 7a) are formed as multiple calendars.
21. Apparatus according to one of claims 15 to 20, characterised in that the dryer (5) has, in addition to a heatable reversing roller (20), heaters positioned opposite the transfer belt upper face which switch on automatically.
22. Apparatus according to one of claims 15 to 21, characterised by a lift-off device (33, 33a; 33', 33a') for controlling the contact time at different transfer belt speeds by varying the speed of the calendering roller (6).
23. Apparatus according to one of claims 15 to 22, characterised by a cold air shearing blade connected in series to the cooling device (6a, 7a) for separating the film passing through in the case of overlapping sheets.
24. Apparatus according to one of claims 15 to 23, characterised in that, for transfer printing, the transfer belt (15) is guided through a web-fed printing press between the dryer (5) and the transfer bay (19).

Images