EP0572686A1 - Use of a paper sheet for transferring coloured decoration to a plastic film - Google Patents

Abstract

The use of a paper for transferring colour to a plastic film (14) to be decorated provides for the following: - the plastic film (14) to be decorated is preheated before it is introduced into the calender, - the preheated plastic film (14) is guided on a heated transfer roll (10) of the calender, - the paper (16) which is provided with a coloured decoration on one side is guided over the plastic film (14) onto the heated transfer roll (10) of the calender such that its side provided with the coloured decoration faces the plastic film (14), - a buffer film (18) is guided over the paper (16) on the transfer roll (10), - a tensioning cover (20) which presses the plastic film (14), the paper (16) and the buffer film (18) towards the transfer roll (10) is laid externally over the buffer film (18), - the transfer roll (10), the plastic film (14), the paper (16), the buffer film (18) and the tensioning cover (20) are moved through the calendar synchronously with the same angular velocity and - after it has passed through the calendar, the plastic film (14') with coloured decoration is cooled under tension. <IMAGE>

Description

The invention relates to the use of a paper for applying color to a plastic film to be decorated.

It is known in the prior art to decorate plastic textiles in color by means of transfer printing. In this known method, calenders with a transfer roller are used, the transfer paper being placed on the bottom of the transfer roller and the textile web to be decorated in color. A stretch ceiling is stretched over the textile web so that the textile web and the transfer paper underneath are stretched radially in the direction of the transfer roller. The transfer roller is heated by means of a heating medium, for example a heating liquid arranged in the transfer roller.

So far, however, it has not been possible to use this process, which is successful for the colored decoration of textiles, even on smooth plastic films. When used on smooth plastic films (i.e. non-woven, knitted or otherwise made of fibers), considerable quality problems occurred in particular because the plastic film could not be moved through the calender completely synchronously and that there were uncontrolled shrinkages and the like is what caused the quality of the product to suffer.

From US-A-2 721 821 a method for applying a colored decoration to a substrate made of polyethylene is known, in which heating takes place to 120 to 185 ° C., a sublimation print being carried out from an ink carrier onto the substrate. 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.

Also known from DE-A-24 38 723 is a method in which dyes are transferred to a substrate in such a way that a color support is placed on the substrate and the color is transferred to the substrate by heating the support with infrared radiation by means of sublimation printing.

GB-A-1 107 401 describes a process for colored printing on plastics, in which the plastics are heated to 175 to 180 ° C. in a heated glycerol bath. 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.

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 58 669 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. The printing takes place e.g. 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 prior 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). Once the temperature of about 170 the dyes reach up to 220 ° C, they sublimate into the textiles made of synthetic fibers.

Another known method (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, which is arranged within a vacuum chamber and can be moved 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 passed 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 heated to the sublimation temperature of the decoration by means of a heating device arranged above the upper frame and then the spectacle frame is moved upwards by means of its base which can be raised and lowered within the vacuum chamber and on which it has been placed, and is 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 condition is maintained for a period of time is sufficient for a transition of the colors forming the decor 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. In the case of such objects, disruptive 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 passed through a coating system which applies a layer of dye-affine, migration-preventing plastic to the outside of the objects. After chemical and physical drying of this coating, 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 one object each and fixed with an adhesive strip, glue line, electrostatic field or the like. The objects are then, for example by means of hot air, to a temperature of 200 ° to 350 ° C., preferably Heated from 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 to run around the bottom of the carrier film with the radially outwardly facing dye layer and over it the textile web to be printed and over this an endless pressure belt made of metal mesh guided over rollers. 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 26 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 foils fuse or become so soft that the ink carriers (paper, etc.) used in transfer printing stick or damage the surfaces of the foils 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.

Minor problems occurred in the sublimation pressure transfer process in the prior art when using thermosetting films and lacquers (FR-A-2 230 794, DE-A 24 24 949, GB-A-1 517 832).

Because of the extensive use of thermoplastic films and sheets, which can be thermoformed into three-dimensional bodies, such as components for interior fittings, furniture parts (in particular fronts), household appliances, office machines, lighting elements, car molded parts, etc., there has long been a need a possibility 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 required 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 1000, 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.

EP-A-0 455 849 describes a method for applying and introducing dyes onto or into a plastic substrate, in which infrared radiation is directed inhomogeneously depending on the color distribution of the decoration onto a color support, so that the colors are sublimated - Transfer be transferred to the substrate.

Sublimation printing is complex and very sensitive to compliance with the process parameters if good results are to be achieved.

The invention has for its object to provide a method and an apparatus with which a color decor with good qualitative results can be applied to a plastic film in a simple manner. The process is said to have a high throughput, i.e. have a high decorating speed and the product should meet high demands with regard to its aesthetic and mechanical properties.

• a) die zu dekorierende Kunststoff-Folie wird vor ihrer Einführung in den Kalander vorgeheizt,
• b) die vorgeheizte Kunststoff-Folie wird auf eine geheizte Transferwalze des Kalanders geführt,
• c) das Papier, das auf einer Seite mit einem Farbdekor versehen ist, wird so über die Kunststoff-Folie auf die geheizte Transferwalze des Kalanders geführt, daß seine mit dem Farbdekor versehene Seite der Kunststoff-Folie zugekehrt ist,
• d) eine Pufferfolie wird über das Papier auf die Transferwalze geführt,
• e) eine die Kunststoff-Folie, das Papier und die Pufferfolie in Richtung auf die Transferwalze drückende Spanndecke wird außenseitig über die Pufferfolie gelegt,
• f) die Transferwalze, die Kunststoff-Folie, das Papier, die Pufferfolie und die Spanndecke werden synchron mit gleicher Winkelgeschwindigkeit durch den Kalander bewegt und
• g) nach Durchlaufen des Kalanders wird die farbig dekorierte Kunststoff-Folie unter Spannung gekühlt.

The solution to this problem according to the invention provides for the use of a paper for applying color to a plastic film to be decorated by means of a calender with at least the following steps:

• a) the plastic film to be decorated is preheated before being introduced into the calender,
• b) the preheated plastic film is passed onto a heated transfer roller of the calender,
• c) the paper, which is provided with a color decoration on one side, is guided over the plastic film onto the heated transfer roller of the calender in such a way that its side with the color decoration faces the plastic film,
• d) a buffer film is passed over the paper onto the transfer roller,
• e) a stretch ceiling pressing the plastic film, the paper and the buffer film in the direction of the transfer roller is placed on the outside over the buffer film,
• f) the transfer roller, the plastic film, the paper, the buffer film and the stretch ceiling are moved synchronously through the calender at the same angular velocity and
• g) after passing through the calender, the colored plastic film is cooled under tension.

Preferred embodiments of the use of a paper according to the invention are described in the dependent claims.

The invention is explained in more detail below using an exemplary embodiment.

The figure shows a device for applying color to a plastic film to be decorated by means of a calender.

The calender has a transfer roller 10 which can be heated by means of a heating medium 12.

A film 14 made of plastic is to be provided with a colored decoration.

The film 14 can in particular consist of acrylic, polyester, polycarbonate, polypropylene, PBT, polyethylene, polystyrene, ABS and mixtures thereof. As the above list shows, thermoplastics are particularly suitable for the process, which have so far largely been beyond colored decoration, especially when high quality requirements were involved.

The film 14 can have a thickness in particular in the range from 25 to 750 μm, thicknesses of around 500 μm are particularly suitable.

In addition to the film 14 to be decorated, a transfer film 16 made of paper and a buffer film 18 and a stretch ceiling 20 are used. These flat structures are placed in layers in the specified order over the transfer roller 10, as explained in more detail below.

The film 14 to be decorated is unwound from a drum 22 and, before being transferred to the transfer roller 10 of the calender, fed to a heating device (26a, 26b) in order to preheat the plastic film 14. The heating devices mentioned form a heating tunnel which applies heat to the plastic film both at the bottom and at the top, that is to say on both sides. Infrared radiators are preferably provided as heating devices, which cover the entire surface of the plastic film. The preheating takes place between the unwind drum 22 and a deflecting roller 28, the deflecting roller 28 being followed by a tensioning roller 30 so that the plastic film 14 in the heating device 26a, 26b is under mechanical tension.

The values of the tension, the preheating and the transfer speed of the film depend on the materials used, the thickness of the film, etc. The following transfer speeds can be achieved, for example: If the preheating device 26a, 26b is set to approximately 90% of its maximum output, then a feed can be achieved the plastic film 14 can be adjusted from about 15 m per minute. If, on the other hand, only 20% of the maximum output of the preheating is used, a feed rate of 5 m per minute can be set. The preheating is such that there are no shrinkage problems when subsequently decorating the film. The individual parameters are to be determined experimentally depending on the materials used, film thickness, rotation speeds, colored decorations etc.

The preheating under tension between the rollers 22 and 28 is carried out so that the film does not sag significantly.

The preheated plastic film 14 in the manner described is then guided over the tensioning roller 30 and a further deflection roller 32 onto the transfer roller 10. The finished decorated plastic film 14 'leaves the transfer roller 10 via the rollers 34 and 36 and arrives at a further roller 38, which at the same time causes cooling of the printed plastic film 14' and its mechanical tension (stretching). The finished plastic film 14 'in this way is then wound onto a further roller 24, so that the colored plastic film is available for further processing.

A paper film 16 is also wound on a roll and is fed to the transfer roller 10 via the deflection roller 32 in such a way that the paper film 16 comes to lie radially above the plastic film 14.

In the illustrated embodiment, a particularly suitable paper is used as the film 16, which paper consists practically of pure cellulose without the addition of binders or other chemicals. The paper was not deleted during its production, but instead was heavily calendered. The paper is preferably long-fiber with about 70 to 80 g / sqm. Such paper has advantages in terms of a relatively high temperature in transfer printing, a relatively high adjustable speed of the transfer roller 10 and thus a high production speed and in terms of the quality of the product produced. With papers other than those described above, it may happen that the papers leave traces on the thermoplastic material of the plastic film 14, in particular at the transfer temperatures used here in the range from 160 ° C. to 170 ° C. and higher.

The transfer printing is thus carried out at temperatures from 140 ° C to 170 ° C and the preheating takes place at temperatures which are lower than the transfer temperature, e.g. 10 to 40% lower.

The transfer film (in the illustrated embodiment, the printed paper) is provided on its side facing the plastic film 14 with a colored decoration, which is transferred from the transfer film 16 (paper) to the plastic film 14 to be decorated, during the common circulation of the films with the transfer roller 10.

To promote the transfer printing, that is to say the transfer of the colored decoration from the transfer film 16 to the plastic film 14, it is provided that a buffer film (18) is placed radially above the transfer film 16 (paper) on the transfer roller 10, specifically in such a way that that the buffer film 18 overlaps both the plastic film 14 to be decorated and the transfer film 16 axially on both sides.

The buffer film 18 is unwound from an unwinding roller 42 and passes over a roller 44 over the paper foil 16 onto the transfer roller 10. A paper is used as the buffer foil. The type of paper depends on the colors and materials used and is optimized experimentally in individual cases.

The buffer film 18 is also moved in synchronism with the above-mentioned films together with the transfer roller 10 at a fully synchronized angular speed and reaches a winding roller 48 via the rollers 34, 46.

The transfer film 16 (paper), from which the colored decoration has been transferred to the plastic film 14 ', passes over the rollers 34 and 46 to a take-up roller 40 The figure is the transfer film from which the colored decoration has largely been removed (ie transferred to the plastic film 14), indicated by the reference symbol 16 '.

A stretch ceiling 20 is placed over the buffer film 18 (paper), which is moved synchronously (at the same angular velocity) together with the transfer roller, the plastic film 14 and the transfer film 16 and the buffer film 18. The stretch ceiling 20 runs endlessly and is tensioned by means of a piston / cylinder unit 50. The stretch ceiling 20 is e.g. from a felt, in particular a polyester felt. The stretch ceiling 20 thus generates a radial force on all the foils (14, 16 and 18) underneath.

The above-mentioned problems of the prior art are overcome on account of the radial stratification of the various foils with different functions specified above.

In particular, the buffer film (in particular made of paper) causes a uniform force distribution, that is to say locally different force peaks of the felt of the stretch ceiling 20 are compensated for. Furthermore, the paper buffer film protects the stretch ceiling 20 from ink that has reached the transfer roller 10, in particular when the device is idling, that is to say when starting up.

The buffer film 20 circulates endlessly and can be used several times for transfer printing.

The method described above causes the dyes to diffuse into the thermoplastic material of the plastic film 14 on the transfer roller 10. The diffusion is such that the colored decoration of the plastic film 14 'makes high demands, particularly with regard to mechanical stability and is also sufficient in terms of print quality. The product is not disturbed by shrinkage or other local smearing or displacements.

With the above-mentioned device, transfer temperatures on the transfer roller in the range from 130 to 240 ° C. can also be used.

Claims (7)

Use of a paper for applying color to a plastic film (14) to be decorated by means of a calender with at least the following steps: a) the plastic film (14) to be decorated is preheated before being introduced into the calender, b) the preheated plastic film (14) is guided onto a heated transfer roller (10) of the calender, c) the paper (16), which is provided with a color decoration on one side, is guided over the plastic film (14) onto the heated transfer roller (10) of the calender in such a way that its side with the color decoration is provided with the plastic film (14) turned towards d) a buffer film (18) is guided over the paper (16) onto the transfer roller (10), e) a stretch ceiling (20) pressing the plastic film (14), the paper (16) and the buffer film (18) in the direction of the transfer roller (10) is placed on the outside over the buffer film (18), f) the transfer roller (10), the plastic film (14), the paper (16), the buffer film (18) and the stretch ceiling (20) are moved synchronously with the same angular velocity through the calender and g) after passing through the calender, the colored plastic film (14 ') is cooled under tension. Use of a paper according to claim 1,
characterized in that the film (14) to be decorated consists of a thermoplastic material. Use of a paper according to one of the preceding claims,
characterized in that the preheating according to step (a) is carried out with plastic film (14) under mechanical tension. Use of a paper according to one of the preceding claims,
characterized in that the preheating according to step (a) is carried out on both sides of the plastic film, in particular by means of IR radiation. Use of a paper according to one of the preceding claims,
characterized in that paper is used as the buffer film (18). Use of a paper according to claim 1,
characterized in that the paper is heavily calendered. Use of a paper according to claim 1,
characterized in that the paper has a mass of 70 to 80 g / m².

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