EP0544019A1 - Process and apparatus for applying and incorporating dyes into a plastic-bearing substrate - Google Patents

Abstract

A process for applying a decoration of sublimable dyes to a substrate (10) provides that a medium (12) is placed on the substrate (10) and the dye is transferred onto the substrate by IR heating of the medium (10). In this case, the medium is heated to temperatures below 170 DEG C, depending on the plastic of the substrate, and the medium is pressed over its full surface area onto the substrate by means of electrostatic charging and a vacuum. The side of the substrate (10) to which the decoration is applied is heated to a lesser extent than the opposite side of the substrate. To improve the quality of the colour transfer from the medium onto or into the substrate, it is provided that the surface area of the medium (12) is subdivided into a plurality of segments (12a, 12b, 12c ...), for which a set temperature is specified in each case, an actual temperature is measured during heating and a heating device (34), effective for the segment concerned, is controlled in a manner corresponding to a comparison of set and actual temperatures. <IMAGE>

Description

The invention relates to a method and a device for applying and introducing dyes onto or into a plastic substrate, in which a color carrier is placed on the substrate and the color is transferred to the substrate by heating the carrier with infrared radiation.

Such a method is known from US-A 2 721 821. There, a colored decor is printed on a polyethylene substrate, heating to 120 to 185 ° C. The heating takes place with infrared radiation, which is radiated through the substrate onto the ink carrier, i.e. the ink carrier is heated on its side facing the substrate by means of IR radiation. It is provided that the ink carrier is designed to be reflective to the IR radiation on its surface not covered with dyes, so that this radiation is absorbed only where paint is applied.

GB-A 1 107 401 describes a process for colored printing on plastics, in which the plastic is heated in a heated glycerol bath at 175 to 180 °. The surface of the plastic is gelled.

EP 0 098 506 A2 discloses a method and a device for generating permanent images on substrates, in which a support with dye is arranged between the substrate and a heated matrix, which has raised sections, the shape of which corresponds to the image to be transmitted . After the transfer of the dyes to the substrate has taken place by means of this heated matrix, the substrate is heated so that the dye diffuses from an ink into the substrate.

DE 24 38 723 A1 describes a method for the dry transfer of organic compounds to webs, in which transfer temperatures between 100 and 200 ° C are provided.

GB 2 127 747 A1 describes a transfer printing process in which the transfer printing partners are positioned by means of electrostatic charging.

Furthermore, methods for applying decorations from dyes to plastic substrates are known from DE 37 08 855 C1 and DE 39 04 424 C1.

From DE patents 17 71 812, 23 37 798, 24 36 783 and from 24 58 660 it is known to print on textile fabrics with the so-called transfer printing process. Here, an ink carrier (also called auxiliary carrier) is printed with printed images (decors) made from sublimation printing inks. The ink carrier (auxiliary carrier) can in particular consist of paper. Printing takes place, for example, by means of offset or rotary printing processes. The print images are transferred by sublimation from the ink carrier to the textile to be colored (so-called transfer printing).

The printing inks mentioned are produced from sublimable disperse dyes using binders and oxidation additives. In the state of the art, the printed ink carriers (also called transfer papers) are placed with the color printed side on the textile side to be printed and heated by means of a printing plate heated to 170 to 220 ° C (using the cycle method) or by means of a rotating cylinder (using the continuous process). As soon as the temperature of approx. 170 to 220 ° C reaches the dyes, they sublime into the textiles made of synthetic fibers.

A known method of the type described (EP-A 0 014 615), which is primarily intended for decorating eyeglass frames, is carried out in such a way that an eyeglass frame with its surface to be decorated is placed on a base with each working cycle is arranged within a vacuum chamber and is movable up and down by means of a piston-cylinder unit. The vacuum chamber has a side opening for inserting the eyeglass frame, which can be closed with a door. On its upper side, the vacuum chamber has a horizontal, stationary frame which delimits a slot with a frame which is also arranged above it and is horizontal but can be moved up and down. A carrier film is inserted through the slot, which is rolled off a reel and is provided on the underside with the decor that is to be applied to the spectacle frame. The decor has, for example, been applied to the carrier film as a multicolor print or as a decal and consists of colors which can be sublimed at a temperature below the destruction temperature of the carrier film. As soon as an eyeglass frame has been inserted into the vacuum chamber and the door has been closed, the upper frame is lowered so that it clamps the carrier film between itself and the lower frame and the vacuum chamber is thereby sealed and can be evacuated. The carrier film is over the upper frame arranged heating device heated to the sublimation temperature of the decor and then the glasses frame by means of its raised and lowered within the vacuum chamber base on which it has been placed, moved up and pressed against the carrier film. The vacuum causes the carrier film to nestle tightly against the surfaces to be decorated on the front and in lateral areas of the spectacle frame. This state is maintained for a period of time sufficient for the colors forming the decor to transition away from the carrier film into the structure of the material of the spectacle frame. The vacuum is then released, the spectacle frame is lowered and thereby separated from the carrier film and finally removed from the vacuum chamber.

In this known method, the carrier film is greatly stretched in individual areas so that it nestles sufficiently against the spectacle frame. It is inevitable that the decor will be distorted in the particularly stretched areas of the carrier film. The distortions can be compensated to a certain extent by applying an appropriately corrected decor to the carrier film from the outset. In addition, distortions in objects such as spectacle frames, whose surfaces to be decorated are relatively narrow, are hardly noticeable. It is different with objects that are to be decorated over a large area. With such objects, disturbing distortions of the decor cannot always be avoided if the decor has been applied by the known method. In addition, as the size of the surface to be decorated increases, the risk that the decor will be affected by air pockets.

In another known method for applying decorations to objects (DE-A-32 28 096), the objects, for example tin cans, are first of all applied by a coating system led, which applies a layer of dye-affine, migration-preventing plastic on the outside of the objects. After the coating has been chemically or physically dried, the coated objects are fed to a labeling machine, in which decor carriers in the form of printed banderoles are removed from a stack or endless strips, placed around each object and fixed with an adhesive strip, glue line, electrostatic field or the like will. The objects are then heated, for example by means of hot air, to a temperature of 200 ° to 350 ° C., preferably 250 ° to 300 ° C. at these temperatures, which produce an extreme heat shock, the water contained in the banderoles evaporates suddenly, so that each banderole is shrunk onto the associated object in a fraction of a second and generates an autogenous pressure required for the transfer of the decoration from the banderole to the object . When heated further, the dyes that form the decor sublimate into the plastic coating underneath.

With this method it is of crucial importance that the relative movement inevitable when shrinking a banderole relative to the associated object is completed before the dyes which form the decoration are heated to such an extent that their migration into the plastic layer begins. If this difficult condition cannot be met, it must be expected that at least parts of the decor will be blurred on the object.

From US 4 178 782 a device for printing a textile web with sublimable dye is known, which is fed on a carrier film. The device has a drivable drum that can be heated from the inside, around the bottom of the carrier film with the dye layer turned radially outwards, and above it the textile web to be printed, and above this an endless pressure belt made of metal mesh guided over rollers to run. The region of the drum that is wrapped in this way can be covered by a hood, within which a negative pressure is maintained. In this way, when the ink is sublimed, gas released is sucked through the textile web to be printed and the pressure belt made of metal mesh lying thereon. The pressing forces exerted by the pressure belt on the textile web are generated exclusively by the mechanical tension of the pressure belt and somewhat reduced by the negative pressure inside the hood.

From DE 25 42 350 C1 the attempt has become known to also print certain plastic products in the transfer printing process, which had previously been used successfully with textiles, which poorly accept the sublimable dyes in question. Attempts have been made there to coat such bodies with thermoplastic films which absorb the dyes, and then attempts are made to print on the films using the transfer printing process explained above. However, the process has not proven itself, especially since the migration resistance of the dyes (that is, the spatial stability of the dyes after transfer printing) was only guaranteed for medium to high molecular dyes (with molecular weights between 300 and 1,000). Sublimation temperatures of over 180 ° C or 200 to 220 ° C for a period of at least 25 seconds have been used. At these relatively high temperatures, however, most thermoplastic films melt or they become so soft that the color substrates (paper etc.) used in transfer printing stick or damage the surfaces of the films so that the product did not meet the aesthetic requirements. The migration resistance of the dyes required for good image reproduction was also not achieved.

Therefore, noteworthy results in the sublimation printing transfer process have so far only been achieved in the prior art with thermosetting films and varnishes (FR-A 2 230, DE-A 24 24 949, GB-A-1 517 832). However, these methods did not lead to satisfactory reproducible results. Both the materials and the sublimation process are not described with sufficient precision. The results achieved left a lot to be desired, particularly due to yellowing and low migration resistance and color blurring.

Because of the extensive use of thermoplastic films and sheets, which are thermoformed into three-dimensional bodies, e.g. Components for interior fittings, furniture parts (especially fronts), household appliances, office machines, lighting fixtures, car molded parts, etc., can be molded, there has long been a need for a way to provide good quality thermoplastic substrates with colored decorations.

EP 0 014 901 describes an attempt to achieve constant, traceable and stable transfer printing results in that the molecular weights of the sublimable disperse dyes, the temperatures used and the composition and nature of the plastic substrates are specified in more detail. It has come to the conclusion that heating to temperatures of 220 ° C. and more is necessary for the application of the transfer printing process to plastics. This excludes a large number of thermoplastic materials. The process remained limited to certain thermosetting plastic coatings and certain substrates made of inorganic materials.

The prior art also teaches as a prejudice that the molecular weight of the dyes used is important in sublimation printing. The aforementioned EP 0 014 901 teaches the use of high molecular weight disperse dyes with molecular weights between 300 and 1,000, in particular with a view to the required resistance to migration.

The German patents 37 08 855 and 39 04 424 already mentioned at the outset bring progress in that they sublimation printing are based on the use of heated printing plates or heated cylinders and instead suggest heating with thermal radiation (infrared radiation). This prior art does not go into details of the materials used or of the sublimation temperatures.

From the unpublished European patent application 90 108 663.7, a method and a device for applying and introducing dyes onto or into a plastic substrate are known, in which the ink carrier on its side facing away from the substrate depending on the plastic of the substrate at temperatures is heated below 170 ° C, the ink carrier is brought into full-surface contact with the substrate by electrostatic charging and the substrate is heated so that the side of the substrate to which the dyes are applied or introduced is heated less than the opposite other side (back) of the substrate. The present invention is based on this not prepublished prior art.

The invention has for its object to develop the method known from EP application 90 108 663.7-2304 and the corresponding device so that the quality of the product produced is further improved.

According to the invention, this object is achieved in the method mentioned at the outset by dividing the surface of the ink carrier into a plurality of segments, for each of which a target temperature is specified, an actual temperature is measured when heated, and a heating device which is effective for the relevant segment is correspondingly corresponding a comparison of target and actual temperatures is controlled.

The heating is preferably carried out by means of a plurality of infrared emitters, individual infrared emitters each being assigned to a segment of the surface of the color carrier.

According to a further preferred embodiment of the invention, it is provided to measure the actual temperatures of the surface segments of the color carrier by means of one, preferably two, infrared cameras.

According to a further preferred development of the invention it is provided that the ink carrier is porous and is brought into contact with the substrate by air suction through the ink carrier, and that when the actual temperature at least one of the segments of the ink carrier by a predetermined Threshold deviates from a predetermined comparison temperature, an abrupt air suction is carried out.

• eine Vielzahl von unabhängig voneinander steuerbaren Heizeinrichtungen, von denen einzelne Heizeinrichtungen jeweils einzelnen Segmenten der Fläche des Farbträgers zugeordnet sind,
• eine Einrichtung zum Messen der Ist-Temperaturen der Flächensegmente des Farbträgers, und
• eine Steuereinrichtung zum Steuern der Heizeinrichtungen entsprechend einem Vergleich der Ist-Temperaturen mit vorgegebenen Soll-Temperaturen.

The device according to the invention for solving the problem is characterized by

• a plurality of heating devices which can be controlled independently of one another, of which individual heating devices are each assigned to individual segments of the surface of the ink carrier,
• a device for measuring the actual temperatures of the surface segments of the ink carrier, and
• a control device for controlling the heating devices in accordance with a comparison of the actual temperatures with predetermined target temperatures.

Infrared emitters are preferably provided as the heating device and one or two infrared cameras are preferably used as the device for measuring the actual temperatures.

It is already known from European application 90 108 663.7, which was not previously published, to use a plurality of infrared radiators for heating the color carrier, the individual infrared radiators being controllable at different temperatures.

According to this older proposal, a specific program for controlling the individual infrared emitters is therefore specified. This program is generated on the basis of the given color distribution of the decor to be transferred, and the individual infrared emitters are then set to specific, predetermined outputs in accordance with this once specified program. In this state of the art, the individual infrared emitters are thus invariably controlled in terms of time and location in accordance with a predetermined temperature pattern. However, it has been shown that a significantly improved quality of the product produced can be achieved if this control of the individual infrared emitters is optimally adapted to the conditions actually prevailing in transfer printing.

The actual instantaneous temperature at various points on both the substrate and the ink carrier depends very sensitively on the environmental conditions, in particular the instantaneous humidity, air flow etc. The plate thickness tolerances also go into the instantaneous temperatures at different locations on the substrates or ink carrier , ie the variation of the thickness of the substrate depending on the manufacturing conditions. The actual instantaneous temperature at a certain point on the substrate or the color carrier also depends on the degree of drying (moisture) of the substrate.

It has been shown that the above-mentioned influences influence the quality of the transfer print. The invention therefore teaches to continuously control the intensity of the individual infrared emitters over the entire area of the color carrier (and thus also of the substrate), in dependence on constantly, that is to say at regular time intervals in the seconds range or also shorter, measured instantaneous temperatures at a variety of locations on the ink carrier (or substrate). Then, due to the above-mentioned environmental influences, for example due to an air flow or the like, a local one occurs Deviation of the actual temperature of one or more segments of the surface of the ink carrier, then the infrared emitters assigned to these segments are immediately adapted to such a change in temperature, ie the infrared emitters are operated either more or less, depending on whether the measured Actual temperature is greater or less than a given setpoint. According to the invention, therefore, complete control loops are formed with respect to the heating of all segments of the color carrier. These temperature control circuits ensure that variations in the environmental conditions, which can cause local temperature fluctuations on the substrate or on the ink carrier, are compensated for with the least possible time delay.

Fig. 1

in Drauf- und Seitenansicht die Vorbereitung eines Substrates und eines Farbträgers für den Transferdruck;

Fig. 2 und 3

schematische Ansichten des Transferdruckes;

Fig. 4

Einzelheiten des Transferdruckes in stark vergrößertem Maßstab,

Fig. 5

eine Farbverteilung eines zu druckenden Bildes und eine zugehörige Steuerung der Intensität von Infrarot-Strahlern und

Fig. 6

schematisch eine Steuerung einer Vielzahl von Infrarot-Strahlern entsprechend einem Vergleich von Ist- und Soll-Temperaturen.

The invention is explained in more detail below with reference to the drawing. It shows:

Fig. 1

in top and side view the preparation of a substrate and an ink carrier for transfer printing;

2 and 3

schematic views of the transfer printing;

Fig. 4

Details of the transfer print on a greatly enlarged scale,

Fig. 5

a color distribution of an image to be printed and an associated control of the intensity of infrared emitters and

Fig. 6

schematically a control of a plurality of infrared emitters according to a comparison of actual and target temperatures.

A substrate 10 is to be decorated with an image of sublimable disperse dyes by transfer printing. The term substrate is intended in particular to encompass films, foils or plates, the films or foils having thicknesses of 25 to 1000 microns and the plates having thicknesses of 1 to 10 mm. The films, foils or plates can be made from a plastic granulate, Granulate mixtures and extruded from several types of plastic or mixtures. Inorganic particles (powder, flour) can also be mixed in, the proportion of plastics on the surface of the substrate preferably being more than 50%. The following plastics are particularly suitable for the application of the invention: PC (polycarbonates), ABS, PMMA, PET and PDT. The process parameters are set depending on the material used (see below).

The plastic films, sheets or foils can also be composed of several types and layers of plastic.

The method according to the invention is not only suitable for substrate surfaces that are smooth, but also for structured, porous, matt and rough surfaces. The substrate material can be clear or colored.

A substrate is also to be understood as a plastic layer that is applied in the form of lacquer to a material surface of e.g. Wood, ceramic or artificial stone is applied, if necessary with networking.

If plastics which are sensitive or are less resistant to chemical and mechanical stresses or to light are used, they can, after printing according to the invention, be coated with more resistant varnishes or coatings made of other types of plastics which are known per se.

The substrate 10 is printed in color with the aid of an ink carrier 12. For this purpose, the image to be transferred to the substrate is printed on the ink carrier 12 using sublimable disperse dyes. In particular, sheets of paper come into consideration as the ink carrier 12, on the one hand the one to be transferred Take a good picture of sublimable colors and, on the other hand, have sufficient air permeability so that air can be sucked through the ink carrier 12 during sublimation transfer printing. Good results are achieved with paper weights from 30 to 120 g. The paper surfaces can be of any size, in particular they can be 1 m² or larger.

Sublimable disperse dyes of a conventional type are processed into printing inks using binders and, if appropriate, oxidation additives. The images, patterns, individual colors or motifs with which the substrate 10 is to be provided are printed on the ink carrier 12 by means of offset, rotary, gravure, flexographic or screen printing processes.

According to FIG. 1, the substrate 10 which is to be printed is placed in a loading station 14 and an ink carrier 12 is placed on the substrate. As shown, the printed ink carrier 12 made of paper is substantially larger than the substrate 10, so that the ink carrier clearly overlaps the substrate on all edges. The overlapping area in the illustrated embodiment is at least 20%, preferably at least 30%.

In a first step, the substrate and ink carrier layers, which are superimposed in this way in a first step, are transferred to a station 16 for electrostatic charging. Here, the substrate 10 is so electrostatically charged with respect to the ink carrier 12 that the ink carrier 12 lies snugly over the entire surface of the substrate 10. This is achieved in the third step according to FIG. 1. In the fourth step, the arrangement of substrate 10 and ink carrier 12, which is glued to it, is conveyed to a sublimation station, which is shown in more detail in FIG.

A conveyor belt 18 transfers the arrangement of substrate 10 and ink carrier 12 produced as described above to a table 20 with a heating plate, which is provided with air-permeable vertical channels (not shown), so that air can be sucked through the table top from top to bottom is. For this purpose, a vacuum chamber 22 is provided under the table top, which is connected to a vacuum pump, not shown.

According to FIGS. 2 and 3, the substrate 10 is conveyed onto the table 20 with the ink carrier 12 firmly attached thereto, and then vacuum is applied in the chamber 22. Neither a cover film over the ink carrier 12 nor a base between the substrate 10 and the table 20 is required.

A housing 24 is arranged above the table 20, in which a multiplicity of infrared radiators 36 are accommodated side by side. The housing 24 with the infrared emitters 36 overlaps the entire area of the substrate 10 and the ink carrier 12. A temperature measuring device 26 measures the temperature on the surface of the substrate 10 facing the infrared emitters and on the side of the ink carrier 12 lying thereon with the sublimable ones Emulsion paints. A further temperature device 27 measures the temperature of the heating plate of the table 20 and thus the temperature on the surface of the substrate 10 which is directly against the table 20, that is to say the side of the substrate 10 which is not decorated.

The individual infrared radiators 36 in the housing 24 are controlled to different temperatures by means of a controller 28, as will be explained in more detail below with reference to FIG. 5.

As shown schematically in FIG. 3, air is sucked into the vacuum chamber 22 through the porous ink carrier 12, specifically through the channels (not shown) in the heated table top 20. The edge space 30 between the overlapping ink carrier 12, the substrate 10 and the table 20 pumped air-free, so that the ink carrier 12 attracts evenly over the entire surface of the substrate 10. There are no folds or warps in the ink carrier 12 and air or gas bubbles are removed. This applies in particular to heating during sublimation with the formation of steam.

In this state, the table 20 and the infrared radiators 36 are heated. The infrared radiation 32 generated by the infrared radiators 36 serves to heat the sublimable dyes arranged on the underside of the ink carrier 12, while the heating of the table 20 serves to heat the substrate 10 on the non-printed side. This heating of the substrate 10 not only has the purpose of achieving dimensional stability of the substrate, but also has a significant effect on the penetration of the color molecules into the substrate 10.

This is explained in more detail in FIG. 4, where the individual parts are shown in a strongly distorted magnification in order to illustrate the process of sublimation and the penetration of the color molecules into the substrate. As said, the air flow 34 from the outside through the ink carrier 12 and the air flow 36 below the ink carrier 12 produces a uniform, tension-free, bubble-free and saturated application of the ink carrier 12 on the substrate 10 The substrate 10 is heated with the table top 20 to a temperature which is higher than the temperature at the surface of the substrate 10 to be printed. In FIG. 4, an increasing temperature gradient is thus produced from top to bottom. This temperature gradient has the consequence that the dye molecules 40 penetrate relatively far into the substrate after sublimation. In FIG. 4, the area of the substrate 10 into which the molecules 40 penetrate is designated by 10b, while the area which is essentially free of dye molecules is designated by 10a.

The degree of heating on the surface of the substrate 10 and correspondingly on the lower surface of the ink carrier 12 (measured with the temperature measuring device 26 according to FIG. 2) depends on the material of the substrate 10. The heating is between 60 ° C (for e.g. ABS) and 150 ° C (for e.g. PBT). For PC, heating to 130 ° C has proven to be beneficial. The temperature on the lower surface of the substrate 10 (measured with the temperature sensor 27 according to FIG. 3) should in each case be about 3 to 30 ° C., in particular 5 to 15 ° C. higher, depending on the type and thickness of the material.

In particular, temperature values of 120 to 135 ° C in the sublimation area (ie on the substrate undersurface and substrate surface) have proven to be favorable for ABS, 90 to 100 ° C for ABS, 150 to 160 ° C for PBT and for PET 80 to 90 ° C.

The problem of back sublimation is solved by the relatively low temperatures used according to the invention.

Depending on the thickness of the substrate 10 and its material, the sublimation process is completed in 10 to 30 seconds.

The quality of the product produced can be further increased by controlling the intensity of the individual infrared emitters 36 as a function of which color is to be sublimed by the emitter in question. Different colors require different energies per unit area for sublimation. So the energy requirement increases (and accordingly the temperature to be generated by the infrared radiation) from yellow to red and cyan to black by about 20%. This is taken into account by individual control of the individual infrared emitters according to the predominant color component directly under the emitter. This results in uniform sublimation for all colors, and at the same time the surface of the substrate to be printed is heated sufficiently uniformly, which promotes image quality. 5 shows an example of an image to be printed on the ink carrier 12 on the left, lighter colors (increasingly from yellow to red) being provided in the outer regions 12a, 12b and 12c, while the image becomes increasingly darker towards the center until it is in the center Section has a black area. Correspondingly, FIG. 5 on the right schematically shows a view of the infrared radiators 36 in the housing 24 from below (for example with reference to FIG. 4), with 100% of a predetermined IR power in the middle area corresponding to the black area of the image Infrared emitters is generated, while the infrared power is reduced to the outside as indicated.

The ink carrier 12 is preferably blackened on its rear side.

The depth of penetration of the sublimable dye molecules into the substrate of 100 to 300 micrometers achieved with the above-described method does not cause the image to fade, but surprisingly, on the contrary, improves the image quality; the picture appears more intense and spatial. Migration is negligible. The product produced as described can be subjected to a brief shock heating of, for example, 200 to 300 ° C. for 2 to 3 minutes for the purpose of thermoforming without impairing the image quality. Continuous heating from 100 to 200 ° C is also possible (depending on the type of plastic, e.g. 145 ° C for PC and 200 ° C for PBT).

There is no damage to the substrate surface. The plastic surface retains its structure without any changes, regardless of whether the surface is polished to a high gloss, matt, semi-gloss, curved, coarse or finely structured. Due to the electrostatic attraction forces and the vacuum forces acting at the same time, the image quality is also good for coarse, rough and finely structured surfaces.

With the described method, relatively large amounts of dye can be transferred (10 to 20 g wet or 3 to 7 g dry). This and the large diffusion depth described enable thermoforming up to 250% expansion without fading or brightening of the colors.

FIG. 6 schematically describes the control of a large number of infrared emitters in accordance with a comparison of actual and target temperatures with respect to individual segments of the ink carrier.

In FIG. 6, those components which correspond to those previously described with reference to FIGS. 1 to 5 are provided with the same reference symbols.

In addition to the components described so far, the invention according to FIG. 6 uses two infrared cameras 44, 44 ', which are known as such (for example under the name "Thermovision" from AGEMA).

The entire surface of the color carrier 12 facing the infrared radiators 36 is fictionally divided into individual segments, for example into segments of 10 × 5 cm area. In a plan view, the surface of the color carrier 12 would be divided into gaps like segments.

As explained at the beginning, the temperatures in the individual segments of the ink carrier can vary depending on different conditions, e.g. of environmental conditions, such as moisture, air flow, etc., of fluctuations in the thickness of the substrate plates and also of the degree of drying (moisture) of the substrate plates. Furthermore, detailed studies have shown that the color density on the ink carrier 12 influences the air permeability of the ink carrier. This also allows variations in the temperature to occur over the surface of the ink carrier. The porosity of the paper of the ink carrier can also be inhomogeneous, so that there is an uneven air permeability, which can also result in variations in temperature. Finally, the infrared absorption in the ink carrier is dependent on the colors and therefore location-dependent.

If the control of the individual infrared emitters 36 of the device were now exclusively in accordance with a predefined temperature program, as was explained with reference to FIG. 5, the above-mentioned temperature variations would be insufficiently taken into account.

The arrangement according to FIG. 6 is suitable for eliminating undesirable temperature fluctuations in transfer printing. The temperatures are measured locally for the multiplicity of segments of the surface of the ink carrier 12 by means of the infrared cameras 44 44 '. The areas detected by the infrared cameras 44, 44 'are indicated by the marginal rays 46 and 46' in FIG. 6. The infrared cameras 44, 44 'supply the associated instantaneous temperatures for each individual segment of the surface of the ink carrier 12, which are entered into a computer 50 via lines 52, 54. The temperature control program for the individual infrared emitters is also stored in the computer 50. As explained with reference to FIG. 5 above, each infrared radiator 36 has a specific segment on it Assigned surface of the ink carrier 12. In other words: for example, the surface of the ink carrier 12 can be divided into 30 × 30 segments in a grid-like manner. Correspondingly, 30 x 30 infrared emitters can then be arranged above the surface of the ink carrier, each irradiating and heating that segment which is arranged directly below them.

A desired target temperature is stored in the computer 50 for each segment (corresponding to FIG. 5). At the same time, the instantaneous actual temperature of each of the segments of the surface of the ink carrier 12 is now measured by the infrared cameras 44, 44 'during operation of the infrared radiators and compared in computer 50 with the assigned target temperature of this segment. If there is a discrepancy between the actual and target temperatures (due to the imponderables regarding the environmental conditions, etc.), the associated infrared emitter is controlled in such a way that the discrepancy between the actual and target temperatures is as small as possible. The control signals from the computer 50 to the individual infrared radiators 36 are transmitted via the line 56.

A further refinement of the invention results from the following: With the transfer printing method described above, it can happen that "gas bubbles" are trapped between the paper of the ink carrier 12 and the substrate 10. Such local gas bubbles create problems with the transfer of the dyes from the paper to the substrate as well as with the diffusion in the substrate. Such gas bubbles also produce a marked temperature jump in the temperature of the ink carrier 12 at the affected point. The device according to FIG. 6 makes it possible to overcome the harmful effect of such gas inclusions between ink carrier 12 and substrate 10 in a large number of cases. By means of the infrared cameras 44, 44 ', such a temperature jump, which can be traced back to a gas inclusion, can be determined without further ado, namely if the Actual temperature of the point in question deviates by a relatively large value from the specified target temperature or a value typical during heating. In such a case, the printing process does not necessarily have to be interrupted and the substrate and the ink carrier removed as rejects. Rather, it is possible to remove the gas inclusion by a sudden "vacuum surge". The vacuum system is therefore operated suddenly (suddenly) in such a way that a suddenly greatly increased air intake takes place through the ink carrier 12, as a result of which there is a good prospect of removing the undesired gas inclusion. For this purpose, the vacuum system is preferably provided with a venturi pump, which enables good control of the suction power.

Claims (7)

Method for applying and introducing dyes or a decoration made of dyes onto or into a plastic substrate (10), in which a dye carrier (12) is placed on the substrate (10) and the dyes (40) are heated on or are transferred into the substrate (10),
characterized in that the surface of the ink carrier (12) is divided into a plurality of segments (12a, 12b, 12c ...), for each of which a target temperature is specified, an actual temperature is measured when heated and one for the relevant one Segment effective heating device (34) is controlled according to a comparison of target and actual temperatures. Method according to claim 1,
characterized in that the heating is carried out by means of a plurality of infrared emitters (36), individual infrared emitters each being assigned to one of the segments. Method according to one of claims 1 or 2,
characterized in that the actual temperatures of the surface segments of the ink carrier (12) are measured by means of at least one infrared camera divided into segments. Method according to one of the preceding claims,
characterized in that the ink carrier (12) is porous and is brought into contact with the substrate by air suction through the ink carrier, and in that when the actual temperature of at least one of the segments of the ink carrier by a predetermined threshold value of a predetermined comparison temperature deviates, a sudden air suction is carried out. Device for applying and introducing dyes or a decoration made of dyes onto or into a plastic substrate (10), in which an ink carrier (12) is placed on the substrate (10) and the dyes are heated on or into the substrate (10) are transmitted
characterized by - A plurality of independently controllable heating devices (36), of which individual heating devices (36) are each assigned to individual segments of the surface of the ink carrier (12), - A device (44, 45 ') for measuring the actual temperatures of the surface segments of the ink carrier (12), and - A control device (50) for controlling the heating devices (36) in accordance with a comparison of the actual temperatures with predetermined target temperatures. Device according to claim 5,
characterized in that infrared radiators (36) are provided as heating devices. Device according to one of claims 5 or 6,
characterized in that at least one infrared camera is provided as a device for measuring the actual temperatures of the surface segments of the ink carrier.

Images