CH688231A5 - A process for printing by sublimation substantially rigid objects, and heat-shrinkable sleeve for the implementation of said method. - Google Patents

Description

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Description

The present invention relates to the printing of objects by sublimation of at least one sublima-ble ink. The term "impression" must be understood in a broad sense within the scope of the invention, that is to say encompassing all types of figurative drawings, inscriptions, signs, used to decorate and / or personalize an object, as well for aesthetic than informative purposes. In the following text, the generic term "motif" will be used to designate these various types.

When it comes to objects whose shape is stable, whether rigid, or even deformable (such as bottles used in the field of cosmetics, or other bottles), a direct printing technique can be used. of the object (for example by pad printing, serigraphy, offset), or an indirect printing technique, according to which a plane support previously printed with the desired pattern is fixed on the object. The indirect printing technique is subdivided into two families, the first encompassing labeling techniques in which the support is printed on its external face and fixed on the object by its internal face, and the second using an essentially transparent support printed on its internal face by which said support is fixed on the object, which has the advantage of protecting the printed pattern against external aggressions. It is known in particular to use for this second family of sleeves made of heat shrinkable plastic printed flat by rotogravure, flexography or serigraphy.

Transfer techniques can also be used, such as decalcomania, using a printed film and transfer varnish, or even hot transfer, either by knurling if the pattern is in a strip, or by wrapping if the pattern is cir-conference (using a paper support printed upside down and a hot-melt adhesive, the support being wrapped on the object, then heated to transfer the pattern).

In all these techniques, either the object carries the support of the printed pattern, or said object is printed on its outer surface.

Printing specialists are increasingly seeking to rationalize the techniques used, in order to obtain printing methods on an industrial scale which make it possible to obtain patterns that are both detailed and fine, and which resist external aggressions, both mechanical and chemicals.

This is how research is currently being carried out on mass printing techniques, in particular sublimation printing. According to this technique, a pattern printed on a support using at least one sublimable ink is transferred hot to a predetermined area of an object by penetrating deep into the material of the object: the solid components are vaporized by heat, and penetrate into the molecular network of the object's material, achieve an impression or a coloration by condensing it. This naturally assumes that the material of the object is compatible with this penetration, which therefore excludes certain materials such as metals or glass, unless a prior coating made of a compatible material is provided.

The sublimation technique was especially developed for the printing of textile materials, in the field of clothing: the transfer is in this case relatively easy to implement using heated rollers between which the fabric and the support for an associated motif, said motif generally being pre-printed on the support with an ink which has the property of being sublimated at atmospheric pressure at temperatures between 140 ° C. and 180 ° C. The ink is then printed by a wet offset process if the support of the pattern is paper, or by screen printing if the support is a deformable knitted fabric or aluminum foil.

When, on the other hand, we are dealing with objects that can be described as "essentially rigid", that is to say rigid, semi-rigid, or deformable objects, with a stable shape, specialists collide to significant difficulties in using this sublimation technique, because the precise application of the support becomes very delicate, and this a fortiori if the object has a complex shape, because the support wrinkles and deforms the pattern before it is transferred to the object, and the application of uniform pressure is complex to implement.

The most recent technique consists in using as a pattern support a very deformable knitted fabric, and in placing the object thus wrapped between two elastic membranes between which a vacuum is created, the whole being placed for several minutes in an enclosure in which flows air at 200 = C.

This technique makes it possible to obtain a relatively regular pressure and temperature over the entire surface of the object to be printed, thanks to the elastic membranes, but it has the disadvantage of being essentially manual and not automatable, and therefore expensive and ill-suited. industrial production. In addition, the systematic exposure of the object to a high temperature for a time which is generally at least ten minutes de facto limits the types of objects concerned so as not to have any risk of deformation said object. Finally, the fabric used to support the pattern inevitably reveals a trace of mesh on the surface of the object, so that the sharpness of the impression is never perfect.

The object of the invention is precisely to propose a technique for printing essentially rigid objects by sublimation which does not have the aforementioned drawbacks and limitations.

The object of the invention is therefore to provide a process for printing such objects by sublimation allowing an easily automated implementation, with a result of excellent quality both for the clarity of the transferred pattern and for the precision of the positioning of this pattern. on the object.

It is more particularly a process for printing essentially rigid objects by sublimation, according to which a pattern printed on a support using at least one sublimable ink is transferred hot to a predetermined area of the object by penetrating deep into the material of the object, characterized in that one uses as

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support a sleeve of heat-shrinkable plastic essentially oriented in the transverse direction, on the internal surface of which is printed the pattern to be transferred, and in that the sleeve threaded on the object is heated to retract said sleeve and thus press the pattern against the predetermined area of the object, and the shrunk sleeve is heated to bring it to the sublimation temperature of the ink or inks forming the pattern and effect the transfer of said pattern.

According to a first embodiment of the method, the sleeve is threaded flat on the object before being retracted on said object.

It can then be provided that the heating of the sleeve is carried out with a gradual rise in temperature, in a single step, until the sublimation temperature is reached. In particular, the retracted sleeve is maintained for a predetermined period at the sublimation temperature, until the complete transfer of the pattern onto the object. As a variant, it is possible to provide that the sleeve is previously retracted on the object in a first step, then in a subsequent heated step with an almost immediate rise in temperature so as to be brought very quickly to the sublimation temperature.

According to a second embodiment of the method, a homothetic template of the object is used, the dimensions of which are slightly greater than those of said object, and the sleeve is threaded flat on this template and then heated to be retracted thereon. ci, then hot removed from said template, which makes it possible to produce a thermoformed sleeve which is subsequently threaded onto the object and then heated to be retracted on said object and brought to sublimation temperature.

Advantageously then, the thermoformed sleeve threaded onto the object is heated, in a single step, with an almost immediate rise in temperature to be brought very quickly to the sublimation temperature.

When using an almost immediate rise in temperature, it is advantageous to provide that the sleeve, possibly thermoformed, is heated to a temperature appreciably higher than the sublimation temperature, and that this sleeve is maintained at this temperature for a short time. predetermined, until the complete transfer of the pattern on the object.

It may be advantageous to use a template having a pointed end, so that the thermoformed sleeve has an end tail or chimney making it possible to print a possible end part of the object not covered by the retracted sleeve.

It is also possible to provide that the sleeve is removed from the object after completion of the transfer of the pattern on said object.

The sleeve can then be removed hot, immediately after completion of the transfer of the pattern on the object, or alternatively be removed cold, always after completion of the transfer of the pattern on the object, by pulling a tear tab in the longitudinal direction initially provided on said sleeve.

The invention also relates to a sleeve of heat-shrinkable plastic essentially oriented in the transverse direction, specially intended for the implementation of the above-mentioned sublimation printing process, said sleeve carrying on its internal surface a pattern which has been printed using at minus a sublimable ink.

According to a particular embodiment, the sleeve is in the form of a thermoformed homothetic sleeve of the object onto which the pattern is to be transferred, the dimensions of which are slightly greater, for example a few tenths of a millimeter, than those said object.

It is then possible to provide that said sleeve has an extension, for example a gripping tail, intended to facilitate its positioning and / or its hot removal, or possibly to print the terminal part of the object.

It is also possible to envisage that the sleeve has a tearing tab in the longitudinal direction, disjoined from the printed pattern, intended to facilitate the cold removal of said sleeve.

Other characteristics and advantages of the invention will appear more clearly in the light of the description which follows and the attached schematic drawings, illustrating particular modes of implementation, with reference to the figures where:

- fig. 1 illustrates an object to be printed and the sleeve printed with a pattern to be transferred (here diagrammed by an S);

- fig. 2a and 2b illustrate, in elevation and in top view, the object coated with its sleeve threaded flat;

- fig. 3a and 3b likewise illustrate the retraction of the sleeve followed by the transfer of the pattern on the object, with heating carried out in a tunnel with continuous passage of objects;

- fig. 4 illustrates the printed object stripped of its sleeve;

- fig. 5a and 5b illustrate a printed sleeve with tearing tab, respectively before being put on the object and after shrinking on said object (before being removed from it);

- fig. 6 illustrates a template homologous to the object to be printed and the sleeve printed with a pattern to be transferred, such a template being used in the context of a variant of the method according to the invention;

- fig. 7a and 7b respectively illustrate the aforementioned template, coated with the printed sleeve threaded flat, and the retraction of this sleeve on said template;

- fig. 8 illustrates the thermoformed sleeve thus obtained, here equipped with a gripping tail;

- fig. 9 and 10 illustrate the object coated with the aforementioned thermoformed sleeve, respectively before and after its retraction on said object, and FIG. 11 illustrates the printed object after hot removal of the shrunk sleeve;

- fig. 12a, 12b schematically illustrate, respectively in the open position and in the closed position, two heating jaws which can be used to carry out an almost immediate rise in temperature capable of bringing very quickly

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the sleeve, thermoformed or not, at the sublimation temperature, making it possible to operate in just a few seconds the transfer of the pattern on the object;

- fig. 13a, 13b illustrate in a similar manner two multiple heating jaws capable of printing several objects simultaneously (here four objects) by virtue of a duplication of the method according to the invention.

Fig. 1 illustrates an object to be printed 10, produced here in the form of a body of revolution, said object being essentially rigid. A predetermined area 12 of its outer surface 11 is intended to receive a predetermined pattern which will be transferred from a support produced in the form of a heat-shrinkable sleeve, by sublimation of the ink or inks constituting said pattern. There is such a cylindrical sleeve 15, the internal face of which has a pattern 16, here in the form of an S seen by transparency, printed flat. In accordance with an essential characteristic of the invention, the pattern 16 is therefore printed with at least one sublimable ink capable of hot transfer of said pattern onto the predetermined area 12 of the object 10. The sleeve

15 is made of heat-shrinkable plastic essentially oriented in the transverse direction. It is therefore a sleeve similar to that which is already used for the indirect printing of essentially rigid objects by heat-shrinking a transparent sleeve, with the essential difference that the printed pattern is here produced using minus a sublimable ink.

Figs. 2a and 2b illustrate the aforementioned sleeve 15 threaded flat on the object 10, with a positioning of said sleeve organized in such a way that the pattern to be transferred 16 is located exactly opposite the predetermined zone 12 of the object 10.

Figs. 3a and 3b illustrate the heating of the sleeve 15 threaded onto the object 10 to retract said sleeve and thus press the pattern 16 against the predetermined area 12 of the object, then the heating of the retracted sleeve to bring it to the sublimation temperature the ink (s) forming the pattern

16 and carry out the transfer of said pattern on the object 10. In FIG. 3b, two heating plates have been shown diagrammatically at 50, for example infrared plates, forming part of a tunnel through which the objects to be printed pass, as shown diagrammatically by the arrow 100. In such an embodiment of the method, the the sleeve 15 is heated with a gradual rise in temperature, in a single step, until the sublimation temperature of the ink or inks constituting the pattern to be transferred is reached. More specifically, a first heating step consists in first retracting the sleeve on the object, this retraction being perfect when a temperature which can be of the order of 120 ° C. is reached, after which the sleeve is heated to a higher temperature to reach the sublimation temperature of the ink or inks constituting the pattern, for example a temperature of the order of 160 ° C. The first phase of this rise in temperature thus achieves the plating of the pattern to be transferred against the surface of the object, while the second phase of rise in temperature no longer corresponds to any deformation of the sleeve on the object, but to a contribution heat and at an application pressure exerted on the pattern to be transferred, which makes it possible to obtain the sublimation of the pattern by maintaining it for a predetermined period at the sublimation temperature, until the complete transfer of the pattern onto the object. By way of example, a maintenance phase may be provided at 160 ° C. for a time of the order of 12 to 20 minutes. This naturally presupposes that the material constituting the object is capable of withstanding such heat treatment without exhibiting significant deformation of its wall. We will see later that in this case the transfer of the pattern can still be done via a thermoformed sleeve on a homothetic template.

Although this is in no way compulsory, provision will generally be made to remove the sleeve once the pattern has been transferred to the object produced, the printed object stripped of its sleeve being shown in FIG. 4.

If this removal is carried out immediately after completion of the transfer of the pattern, that is to say hot, this operation is easily carried out insofar as the wall of the sleeve is still relatively soft and adheres weakly to the object. It is however preferable to carry out a removal of the cold sleeve after completion of the transfer of the pattern on the object. In this case, it is difficult to extract as it is the cooled sleeve which then adheres against the wall of the object. It is then advantageous to provide, as illustrated in FIGS. 5a and 5b, that the sleeve 15 is equipped with a tongue 17 for tearing in the longitudinal direction, one end 18 of which serves as a gripping end for tearing the sleeve by simple pulling on said end, which then makes it possible to easily carry out the cold withdrawal of the shrunk sleeve by a simple peeling. As shown in FIG. 5b, it goes without saying that the positioning of the sleeve must then be such that the tongue 17 is disjoined from the printed pattern 16, so as not to affect the surface particles of the transferred pattern.

If the material constituting the object is not suitable for withstanding an exposure of ten minutes at a temperature of 160 ° C. for the transfer of the pattern by sublimation, it is possible to provide that the printing is carried out in two successive times. In this case, the sleeve 15 is retracted first on the object 10 in a first step, without exceeding the temperature necessary for obtaining perfect shrinkage of the sleeve on the object, that is to say ie for example a temperature of 120 ° C. Then, in a subsequent step, heating is then provided with an almost immediate rise in temperature to bring the shrunk sleeve very quickly to the sublimation temperature, which makes it possible to limit to a short duration, for example a few tens of seconds at maximum, the exposure of the object to the high temperature necessary to effect the transfer of the pattern on the object.

This almost immediate rise in temperature can for example be achieved using

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pairs of heating jaws, such as the jaws 30 illustrated in FIGS. 10a and 10b which are capable, when closed (fig. 10b) of applying a temperature of the order of 300 ° C to the outer surface of the sleeve. A very rapid heating of the wall of the object is thus obtained, which is favorable to the good transfer of the pattern thereon, but which cannot yet initiate the beginning of deformation of the wall of said object. In place of the simple jaws of Figs. 10a and 10b, it is possible to use multiple jaws such as the jaws 30 'illustrated in FIGS. 13a and 13b, in order to simultaneously process a plurality of conveyed objects (the conveying direction is again noted 100 in these figures).

In accordance with an advantageous variant of the process of the invention, provision is made to produce a printed sleeve which is thermoformed in a preliminary step, a sleeve whose internal surface is homologous with that of the object to be printed, but with slightly larger dimensions. to those of said object, for example a few tenths of a millimeter. Such a variant is particularly advantageous for obtaining perfect sublimation contact, and total control of the anamorphism of the pattern during the retraction of the sleeve on the object to be printed.

As illustrated in FIG. 6, a homothetic template 20 of the object to be printed is then used, the dimensions of which are slightly greater than those of said object. In this case, the template 20 has a pointed end 21, which makes it possible to obtain a tapered end of the associated sleeve 15 after retraction of the latter on said template.

As illustrated in fig. 7a, the preceding sleeve 15 is then threaded onto the template 20, sleeve on the internal surface of which the pattern 16 to be transferred has already been printed using at least one sublimable ink. Then, the sleeve 15 is heated to cause it to shrink on the template 20 as illustrated in FIG. 7b. The sleeve thus retracted can be easily removed hot from the template, and one thus obtains a thermoformed sleeve 15.1 (shown in Fig. 8) which has already undergone a shrinkage capable of bringing it to a shape very close to the shape that it will occupy finally after retraction on the object to be printed. The release of the thermoformed sleeve 15.1 out of the template 20 is in this case greatly facilitated due to the presence of the extension 19, here being in the form of a gripping tail, obtained by means of the tapered end 21 of the template 20. A reserve of thermoformed sleeves 15.1 can thus be produced in advance, ready to be placed on the objects to be printed.

It then suffices to thread the thermoformed sleeve 15.1 onto the object 10 (fig. 9), for example using the gripping tail 19, then to complete the retraction of this sleeve on said object (fig. 10), by exerting , in a single step, heating the sleeve with an almost immediate rise in temperature, so that said sleeve is brought very quickly to the sublimation temperature. It is then possible to use for this the heating jaws such as the jaws 30 of FIGS. 12a, 12b, or the jaws 30 'of FIGS. 13a and 13b. By bringing the thermoformed sleeve 15.1 to a temperature appreciably higher than the sublimation temperature, for example a temperature of 300 ° C., it will generally suffice for a few seconds to achieve, in the same pass, the end of the retraction of the sleeve and the transfer of the pattern on the object. The duration of the maintenance of this high temperature will naturally depend on the pattern to be transferred, depending on whether a more or less significant depth of penetration of said pattern into the material of the object is desired. It is then easy to understand that the exposure of the object for ten seconds to this high temperature will mostly eliminate any risk of initiating a deformation of the wall of the object, which would not have been the case with prolonged exposure to a temperature comparable to that of the sublimation temperature.

The thermoforming of such an intermediate sleeve on a template allows total control of the anamorphosis of the impressions. In addition, the suitability for the external surface of the object makes it possible to have perfect sublimation contact over the entire periphery of the object, which guarantees a regular and precise transfer of the pattern on said object. This technique naturally assumes that the shape of the object has a substantially rectilinear profile, or curved with a regular concavity.

The fact of providing a tail or a chimney at the end of the thermoformed sleeve can also prove to be very advantageous for perfecting the impression of a terminal part of the object not covered by the retracted sleeve: in fact, with sublimation, the part of the pattern which is adjacent (without actually contacting it) to this terminal part of the object is transferred by a gravity deposition process, which avoids having a localized printing defect.

When the pattern has been transferred, it is possible, as previously, to carry out a removal of the retracted sleeve, either hot at the end of the transfer process, for example using the gripping tail 19, or cold, then providing for a tearing tab in the longitudinal direction as previously described (variant not shown). The printed object, thus freed from its retracted preformed sleeve 15.1, is shown in FIG. 11.

The invention is applicable to the printing of objects of very diverse types, both in shape and in their constituent material. If the constituent material is unsuitable for the penetration of ink vapors during sublimation, for a deep transfer into the wall of the object, the difficulty can be overcome by providing for a preliminary lacquering of the object to be printed, which lacquering is made of a material capable of undergoing the sublimation transfer of the pattern to be printed.

We thus managed to achieve a process of printing essentially rigid objects by sublimation, allowing an easily automated implementation, with a result of excellent quality both for the sharpness of the transferred pattern and for the precision of the positioning of this pattern. on the object.

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The method is particularly advantageous for printing plastic objects, although other materials are naturally possible.

The invention is not limited to the embodiments which have just been described, but on the contrary encompasses any variant incorporating, with equivalent means, the essential characteristics set out above.

Claims (16)

Claims 1. A method of printing essentially rigid objects by sublimation, according to which a pattern printed on a support using at least one sublimable ink is transferred hot to a predetermined area of the object by penetrating deep into the material of the object. object, characterized in that a sleeve (15; 15.1) of heat-shrinkable plastic essentially oriented in the transverse direction is used as support, on the internal surface of which the pattern to be transferred (16) is printed, and in that the sleeve (15; 15.1) threaded on the object (10) is heated to retract said sleeve and thus press the pattern (16) against the predetermined zone (12) of the object, and the sleeve shrunk for bring to the sublimation temperature of the ink or inks forming the pattern and carry out the transfer of said pattern. 2. Method according to claim 1, characterized in that the sleeve (15) is threaded flat on the object (10) before being retracted on said object. 3. Method according to claim 2, characterized in that the heating of the sleeve (15) is carried out with a gradual rise in temperature, in a single step, until the sublimation temperature is reached. 4. Method according to claim 3, characterized in that the retracted sleeve (15) is maintained for a predetermined period at the sublimation temperature, until the complete transfer of the pattern (16) on the object (10). 5. Method according to claim 2, characterized in that the sleeve (15) is previously retracted on the object (10) in a first step, then in a subsequent heated step with an almost immediate rise in temperature to be brought very quickly at the sublimation temperature. 6. Method according to claim 1, characterized in that a template (20) homothetic of the object (10) is used, the dimensions of which are slightly greater than those of said object, and in that the sleeve (15) is threaded flat on this template (20) then heated to be retracted thereon, and finally removed hot from said template, which makes it possible to produce a thermoformed sleeve (15.1) which is subsequently threaded onto the object (10) then heated to be retracted on said object and to be brought to the sublimation temperature. 7. Method according to claim 6, characterized in that the thermoformed sleeve (15.1) threaded on the object (10) is heated, in a single step, with an almost immediate rise in temperature to be brought very quickly to the temperature of sublimation. 8. Method according to claim 5 or claim 7, characterized in that the sleeve (15) or the thermoformed sleeve (15.1) is heated to a temperature above the sublimation temperature, and it is maintained at this temperature for a period short predetermined, until complete transfer of the pattern to the object. 9. Method according to claim 6 or claim 7, characterized in that a jig (20) having a pointed end (21) is used, so that the thermoformed sleeve (15.1) has an end tail or chimney ( 19) allowing to print a possible end part of the object not covered by the retracted sleeve. 10. Method according to one of claims 1 to 9, characterized in that the sleeve (15; 15.1) is removed from the object after completion of the transfer of the pattern on said object. 11. Method according to claim 10, characterized in that the sleeve (15; 15.1) is removed hot, immediately after completion of the transfer of the pattern (16) on the object (10). 12. Method according to claim 10, characterized in that the sleeve (15; 15.1) is removed cold after completion of the transfer of the pattern (16) on the object (10), by pulling on a tear tab (17) in the longitudinal direction initially provided on said sleeve. 13. Sleeve made of heat-shrinkable plastic essentially oriented in the transverse direction, on the internal surface of which is printed a pattern for the implementation of the sublimation printing process according to one of claims 1 to 12. 14. Sleeve according to claim 13, characterized in that it is in the form of a thermoformed sleeve (15.1) homothetic to the object (10) onto which the pattern (16) is to be transferred, the dimensions of which are greater, for example by a few tenths of a millimeter, than those of said object. 15. A sleeve according to claim 14, characterized in that it has an extension, for example a gripping tail (19), intended to facilitate its positioning and / or its hot removal, or possibly to print the terminal part. of the object (10). 16. Sleeve according to claim 13 or claim 14, characterized in that it has a tongue (17) for tearing in the longitudinal direction, disjoined from the printed pattern (16), intended to facilitate its cold removal. 5 10 15 20 25 30 35 40 45 50 55 60 65 6