Incremental printing of symbolic information – Thermal marking apparatus or processes
Reexamination Certificate
1999-10-14
2001-06-19
Le, N. (Department: 2861)
Incremental printing of symbolic information
Thermal marking apparatus or processes
Reexamination Certificate
active
06249297
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process for continuously printing a flat plastic film, flocked or not, the device for practicing the process and the printed plastic film obtained by this process.
The invention also relates to a process for continuously printing a colored or uncolored motif on a flat plastic film, flocked or not, adapted to be thermoformed to a predetermined non-planar surface, as well as the flat printed plastic film and the thermoformed plastic film obtained by this process.
Transfer printing by sublimation is already known as such and consists, in the first instance, in printing on a support paper designs from inks constituted by sublimable coloring agents which are adapted to vaporize at a certain temperature and to be fixed permanently on synthetic materials, for example polyester or polyamide polymers, the printing process of the support paper being adapted to be anything at all, for example offset printing, heliographic or flexographic printing, or again serigraphic printing by flat plate or rotary plate. Then, in the second instance, the designs in sublimable coloring agents, preliminarily imprinted on the support paper, are transferred by sublimation, by placing in contact, under a regulated pressure and at a predetermined temperature, generally with the aid of hot rolls, the pre-printed paper with the textile support to be printed, generally for a duration of 5 to 40 seconds. The hot rolls can comprise, in the case of printing in formats, a hot press with horizontal plates, or in the case of continuous printing from rolls of printed paper and of synthetic material to be printed, a rotating heated cylinder associated with a belt rolling under tension.
However, transfer printing by sublimation is not adapted to print plastic films, for the following reasons:
plastic films, and more particularly extruded films, have errors of flatness, which renders difficult their continuous printing, from a roll of plastic film,
plastic films, and more particularly plastic films adapted to be thermoformed, such as polyvinyl chloride (PVC) films or polystyrene films, have a thermal sensitivity such that they melt and thus lose all cohesion, when they are subjected to impression by transfer by sublimation at a temperature of about 200° C., which gives rise to random dimensional fluctuation of the plastic film during printing whilst the pre-impregnated impression paper undergoes no deformation, thereby giving rise to blurred and irregular printing,
the melting of the plastic film during printing also gives rise to sticking of the plastic film on the conveyor belt of the printing machine,
the melting of the non-flocked plastic film also leads to sticking of the plastic film to the pre-printed printing paper.
This printing process by transfer by sublimation can be used to print certain plastic materials, if there is first applied a layer of glaze on the plastic material to be printed, or first treating the pre-printed printing paper so as to render it non-adhesive. This printing method is particularly used to print pieces of plastic that are injected or shaped, such as bottles, skis, pens, helmets, and in this case, the printing is carried out by means of a heating tool matching the shape of the plastic piece to be printed.
Another direct printing method for plastic films consists in using known processes of the flexographic or serigraphic type, but in this case, the ink does not penetrate the plastic material, such that the printing designs have low resistance to scraping and friction. Moreover, these printing processes do not permit obtaining the most detailed graphic effects, for example for color printing of the photographic type.
Still another known method to print plastic films consists in thermobonding on the surface to be printed of the plastic film a pre-printed support, for example polyester film printed by heliography, then hot counter-adhered to the plastic film at the outlet of the extruder.
On the other hand, when plastic films to be printed are adapted to be thermoformed, for example to form protective blocks, pieces for the automobile industry, elements for packing, printed designs on the flat plastic film subject the deformation of the plastic film on a non-planar surface, giving rise to a modification of the contours and of the configuration of the printed design, as well as a variation of the shade of the colors, because of the stretching of the plastic film during its thermoforming. When the design which must be given to the non-flat thermoformed surface is a geometric design, letters or numerals, the deformations of the design can be unacceptable.
SUMMARY OF THE INVENTION
The invention has for its first object to provide a continuous printing process of a plastic film, flocked or not, with transfer by sublimation, whilst having high quality, detail and sharpness of printing, for example of the four-color type, and avoiding any sticking between the plastic film and the conveyor belt or the pre-printed printing paper.
A second object of the invention is to provide a printing process for design on a flat plastic film, flocked or not, adapted to be thermoformed into a predetermined non-planar surface, which permits compensation for the deformations of the design and/or the variations of shade of the colors on the non-planar thermoformed surface.
To achieve the first-mentioned object, the invention has for a first object a continuous printing process of a plastic film, flocked or not, characterized in that it consists in:
applying on the back of the plastic film a temporary anti-adherent support, for example of paper,
heating the assembly of the plastic film and of the temporary support to a temperature such that the plastic film reaches its softening point to stick temporarily to the temporary support, such that this latter ensures the dimensional stability of the plastic film during the following thermal printing step,
transferring by sublimation a design constituted by a sublimable ink pre-printed on a printing paper, by contact under pressure and at a predetermined temperature with the front of the plastic film thermo-held on the temporary support,
cooling the assembly of the plastic film thus printed and of the temporary support to a temperature permitting the unsticking of the temporary support.
Preferably, the temperature to thermo-stick the plastic film to the temporary support is comprised between 100 and 200° C., preferably between 170 and 180° C. The temperature for transfer by sublimation can be comprised between 170 and 230° C. The temperature at which the assembly of the printed plastic film and the temporary support is cooled can be of the order of 20 to 30° C.
In one embodiment, the process of the invention consists, for a non-flocked plastic film, in pre-printing the printing paper with an ink containing sublimable coloring agents, with a low content of softening or anti-adherent agents, to avoid sticking between the plastic film and the impression paper, during the printing step by transfer by sublimation. The agents can be selected from silicones, organic fatty acids and chromium stearates.
In another embodiment, the process consists in preparing a flocked plastic film, by applying to the front of the plastic film an adhesive layer and flocking fibers of white color on said adhesive layer. Preferably, the adhesive layer is a polymer resin in aqueous emulsion or organic solution, and the flocks are preferably polyamide or polyester fibers, with a length comprised between 0.3 and 3.0 mm and a titre comprised between 0.5 and 20 Dtex (0.5 and 20.10
−7
Kg.m
−1
).
The plastic film can be a calendered, extruded or co-extruded film, selected from polymer resins of polyvinyl chloride base, polystyrene, polypropylene, acrylic butyl styrene (ABS), polyurethane, polyester, polycarbonate, polyamide or any mixture of these latter.
The printing paper can be printed by offset, flexographic, heliographic, serigraphic printing or by ink jet.
The invention also relates to the device for practicing the process described ab
Feggins K.
Le N.
Societe d'Enduction et de Flockage
Young & Thompson
LandOfFree
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