FR2784619A1 - Transfer-printing and thermoforming of pattern into plastic film, exploits computer to control registration, anamorphosis and color density to arrive at desired pattern and color vibrance in geometric embossments - Google Patents

Abstract

For each elementary zone (a selected, simple geometric shape delimiting an embossment) of the film, the local degree of stretching during thermoforming into a non-planar surface is determined. For each elementary zone, a pre-deformed pattern (140a-d) to be printed on the surface of the flat film is determined. For each elementary zone (a selected, simple geometric shape delimiting an embossment) of the film, the local degree of stretching during thermoforming into a non-planar surface is determined. For each elementary zone, a pre-deformed pattern (140a-d) to be printed on the surface of the flat film is determined. The pre-deformed pattern is defined by anamorphosis (a generally non-linear transformation) from the elements of the finally-intended pattern (141a-d) to appear on the non-planar, thermoformed surface. Account is taken of the degree of local stretching, in passing from the deformed, to the final pattern (141). The deformed pattern (140), as defined by its components obtained from the previous stage, is printed onto the surface of the film be thermoformed (114). An Independent claim is also included for film embossed and printed as described. Preferred features: The shade of coloring for each elementary zone is determined in terms of the final required shade, in each part of the pattern, following deformation (stretching generally weakening the color). Marks (31, 32) are printed for precise registration of the delimited zone being thermoformed; they comprise a longitudinal line (31) and a transverse stroke (32). A known sublimation transfer technique employing a supportive paper substrate temporarily hot-adhered to the film is used to print the pattern onto the film, which is cooled and re-separated. The film is printed directly from a paper transfer using inks with additives preventing adhesion between transfer paper and film. In an alternative, a white fibrous flocking is first applied to the film for printing ( known processes further described and illustrated in the disclosure). The printed film is thermoformed using a tool (50), in registration.

Description

METHOD OF CONTINUOUSLY PRINTING A PLASTIC FILM
PLAN, TO BE THERMOFORMED IN A NON-PLANAR SURFACE
AND THERMOFORMED FILM OBTAINED BY THIS PROCESS
The invention relates to a continuous printing process of a flat plastic film, flocked or not, the device for its implementation and the printed plastic film obtained by this process.

 The invention also relates to a continuous printing process of a colored or non-colored pattern on a flat plastic film, flocked or not, intended to be thermoformed into a determined non-flat surface, as well as the printed flat plastic film and the film. thermoformed plastic obtained by this process.

 Sublimation transfer printing is already known as such and consists, in a first step, in printing on a paper support patterns from inks made up of sublimable dyes which are capable of vaporizing from a certain temperature and to be fixed permanently on synthetic materials, for example polymers of polyester or polyamide, the printing process of the backing paper being able to be arbitrary, for example offset printing, heliographic or flexographic printing, or else a screen printing with a flat or rotating frame. Then, in a second step, the patterns in sublimable dyes previously printed on the backing paper are transferred by sublimation, by bringing into contact, under a regular pressure and a determined temperature, generally using a thermal calender, paper pre-printed with the textile support to be printed, generally for a period of 5 to 40 seconds. The thermal calender may include, in the case of printing in formats, a heating press with horizontal plates, or in the case of continuous printing from rolls of printed paper and of synthetic material to be printed, a heating cylinder rotary associated with a treadmill under tension.

However, sublimation transfer printing is not suitable for printing plastic films, for the following reasons:
the plastic films, and more particularly the extruded films, have flatness defects, which makes it difficult to print them continuously, from a roll of plastic film,
plastic films, and more particularly plastic films intended to be thermoformed, such as polyvinyl chloride (PVC) or polystyrene films, have a thermal sensitivity such that they melt and thus lose all cohesion, when they are subjected to sublimation transfer printing at a temperature close to 200
C, which causes an anarchic dimensional fluctuation of the plastic film during printing while the pre-printed printing paper does not undergo any deformation, thus causing a fuzzy and irregular printing,
-the fusion of the plastic film during printing also causes the plastic film to stick to the conveyor belt of the printing machine,
the fusion of the non-flocked plastic film also leads to the gluing of the plastic film to the pre-printed printing paper.

 This sublimation transfer printing process can be used to print certain plastics, provided that a layer of varnish is applied to the plastic to be printed, or that the preprinted printing paper is treated beforehand. make it non-stick. This printing method is used in particular for printing injected or formed plastic parts, such as bottles, skis, pens, helmets, and in this case, the printing is carried out by means of a heating tool conforming to the shape of the plastic part to be printed.

 Another method of direct printing of plastic films consists in using known methods of the flexographic or screen printing type, but in this case, the ink does not penetrate into the plastic, so that the printed patterns have a low resistance to scratching. and friction. In addition, these printing methods do not make it possible to obtain the finest graphic effects, for example four-color printing of the photographic type.

 Yet another known method for printing plastic films, consists in fusing on the printing surface of the plastic film a previously printed support, for example a polyester film printed in photogravure, then hot-laminated on the plastic film leaving the extruder.

 On the other hand, when the plastic films to be printed are intended to be thermoformed, for example to form protective shims, parts for the automobile industry, conditioning and packaging elements, the patterns printed on the plastic film plane undergo the deformation of the plastic film into a non-planar surface, causing a modification of the contours and the configuration of the printed pattern, as well as a variation of the color tones, due to the stretching of the plastic film during its thermoforming. When the motif which must appear on the thermoformed non-planar surface is a geometric design, letters or numbers, the distortions of the motif may become unacceptable.

 The primary object of the invention is to propose a continuous printing process for a plastic film, flocked or not, by a sublimation transfer printing process, while having a quality, fineness and sharpness of high printing, for example of the four-color type, and avoiding any sticking between the plastic film as well with the conveyor belt as with the pre-printed printing paper.

 A second object of the invention is to propose a method of printing a pattern on a flat plastic film, flocked or not, intended to be thermoformed into a determined non-planar surface, which makes it possible to compensate for the deformations of the pattern and / or variations in color tones on the non-planar thermoformed surface.

To achieve the above-mentioned first object, the invention has as its first object a continuous printing process of a plastic film, flocked or not, characterized in that it consists in:
-apply a temporary non-stick support, for example paper, on the back of the plastic film,
-heating the entire plastic film and the temporary support to a temperature such that the plastic film reaches its softening point to temporarily bond to the temporary support, so that the latter ensures the dimensional maintenance of the plastic film during step d successive thermal printing, -transfer by sublimation a pattern consisting of a sublimable ink pre-printed on a printing paper, by contact under a pressure and a temperature determined with the front of the plastic film thermobonded to the temporary support, -cooling the whole plastic film thus printed and the temporary support at a temperature allowing the temporary support to detach.

 Advantageously, the temperature for fusing the plastic film to the temporary support is between 100 and 200 ° C., preferably between 170 and 180 ° C. The temperature for the sublimation transfer can be between 170 and 230 ° C. The temperature at which 1 ' all 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 method of the invention consists, for a non-flocked plastic film, of preprinting the printing paper with an ink containing sublimable dyes, with a low content of softening or non-sticking agents, to avoid bonding between the plastic film and the printing paper, during the sublimation transfer printing step. These agents can be chosen from silicones, organic fatty acids and chromium stearates.

 In another embodiment, the method consists in preparing a flocked plastic film, by applying an adhesive layer to the front of the plastic film and by flocking white fibers on said adhesive layer. Preferably, the adhesive layer is a polymer resin in aqueous emulsion or in organic solution, and the flocks are preferably fibers of polyamide or polyester, with a length between 0.3 and 3.0 mm and a titer between 0.5 and 20 Dtex (0.5 and 20.10-7 Kg. M-1).

 The plastic film can be a calendered film, extruded or co-extruded, chosen from polymer resins based on polyvinyl chloride, polystyrene, polypropylene, butadiene-styrene acrylic (ABS), polyurethane, polyester, polycarbonate, polyamide or any mixture thereof.

 The printing paper can be printed by offset, flexographic, heliographic, screen printing, or inkjet printing.

The invention also relates to the device for implementing the method described above, characterized in that it comprises:
an unwinding station, comprising a reel for a strip of plastic film, flocked or not, and a reel for a strip of temporary support,
-a heating station at the entrance of which the temporary support strip is applied against the back of the plastic film strip, the assembly consisting of said superimposed strips coming into contact with the temporary support strip against a driven heating drum in rotation, in order to deliver at the output a composite strip consisting of the plastic film heat-bonded to the temporary support,
-a heat-printing machine, comprising a conveyor belt under tension which comes into contact with the temporary support of said composite strip, a heating calender driven in rotation, and at least one reel for a strip of paper pre-printed with a pattern made of sublimable ink, said strip of pre-printed paper being applied to the front of the plastic film of said composite strip, upstream of the heating calender, so that the conveyor belt can press said composite strip under a determined pressure covered with preprinted paper against the heating calender, for sublimation transfer of the sublimable ink onto the front of the plastic film, the printing paper being separated from the composite strip printed downstream of the heating calender,
a cooling station for cooling the printed composite strip to a temperature such that the temporary support strip can be detached from the printed plastic film strip,
a winding station at the entrance of which the temporary support strip is peeled off from the printed plastic film strip, each strip being wound on a respective reel which is rotated.

 Advantageously, the cooling station comprises two double-envelope cylinders, each cylinder comprising a circulation of a cooling agent, for example water, in the double-envelope, so that said printed composite strip comes into contact with the first cylinder. by its temporary support strip, then with the second cylinder by its printed plastic film strip.

 The invention also relates to a strip of printed plastic film, characterized in that it is directly obtained by the aforementioned method.

To achieve the second above-mentioned object, the invention has as a second object a process for continuously printing a pattern, colored or not, on a flat plastic film, flocked or not, intended to be thermoformed into a determined non-planar surface , characterized in that it consists of:
-dividing geometrically into elementary zones the portion of the flat plastic film to be thermoformed,
-determine, for each elementary area of the film, the local stretching rate of the film during its thermoforming in the non-planar surface,
-determine, for each elementary zone of the film, the part of deformed pattern to be printed on the surface of the flat plastic film, this part of deformed pattern being defined by transformation by anamorphosis of the final pattern to appear on the non-planar thermoformed surface, taking account of the local stretching rate of the plastic film by which one passes from the part of the deformed pattern to the part of the final pattern,
-printing, on the surface of the portion to be thermoformed with the flat plastic film, the deformed pattern defined by all of the deformed pattern parts determined in the previous step.

 Advantageously, the method consists in determining, for each elementary area of the film, the color tint of the part of the deformed pattern, as a function of the desired color tint of the final pattern and of the local stretching rate of the film through which one is passing. from the distorted pattern part to the final pattern part.

 According to another characteristic, the method consists in simultaneously printing on the portion of the flat film other than that to be thermoformed, a mark to precisely locate the portion to be thermoformed of the flat plastic film. Said mark to be printed may include a line extending along an edge of the flat plastic film and a line extending transversely from this line.

Preferably, the aforementioned printing step of the flat plastic film consists in:
- apply a temporary non-stick support to the back of the flat plastic film,
-heating all of the flat plastic film and the temporary support to a temperature such that the plastic film reaches its softening point to temporarily stick to the temporary support, so that the latter ensures the dimensional maintenance of the plastic film during the step successive thermal printing,
transferring by sublimation the deformed pattern pre-printed upside down with a sublimable ink on a printing paper, by contacting under a pressure and a determined temperature of said printing paper with the front of the plastic film heat-bonded to the support provisional,
cool the entire flat plastic film thus printed and the temporary support to a temperature allowing the temporary support to peel off.

 In one embodiment, the method of the invention consists, for a non-flocked plastic film, of preprinting the printing paper with an ink containing sublimable dyes, with a low content of softening or non-sticking agents, to avoid bonding between the plastic film and the printing paper, during the sublimation transfer printing step. These agents can be chosen from silicones, organic fatty acids and chromium stearates.

 In another embodiment, the method consists in preparing a flocked plastic film, by applying an adhesive layer to the front of the plastic film and by flocking white fibers on said adhesive layer. Preferably, the adhesive layer is a polymer resin in aqueous emulsion or in organic solution, and the flocks are preferably fibers of polyamide or polyester, with a length between 0.3 and 3.0 mm and a titer between 0.5 and 20 Dtex (0.5 and 20.10-7 Kg. M-1).

 The plastic film can be a calendered film, extruded or co-extruded, chosen from polymer resins based on polyvinyl chloride, polystyrene, polypropylene, butadiene-styrene acrylic (ABS), polyurethane, polyester, polycarbonate, polyamide or any mixture thereof. The printing paper can be printed by offset, flexographic, heliographic, screen printing, or inkjet printing.

 In a subsequent step, the method of the invention consists in positioning laterally and transversely the surface portion to be thermoformed of the flat plastic film on the surface of which the deformed pattern is printed, opposite the shape of the tool. thermoforming, by means of the aforementioned printed mark, and to thermoform with said thermoforming tool only said portion in a non-planar surface on which the desired final pattern appears. Advantageously, the method consists in optically detecting the longitudinal line of the mark to laterally guide the flat plastic film and the transverse line of the mark to stop, in the longitudinal direction, the flat plastic film with its portion to be thermoformed opposite the shape of the thermoforming tool. Preferably, the method consists in calculating the parts of the deformed pattern by computer and in pre-printing the printing paper by an inkjet printing machine controlled by said computer. Inkjet printing enables digital printing to be carried out under optimal conditions, since there is no need to produce specific printing tools, such as cylinders, offset plates, screen printing frames, and where inkjet printing can be directly controlled by the computer equipped with software for calculating the deformations of the pattern.

 The invention also relates to the printed plastic film with a non-planar thermoformed surface, characterized in that it is directly obtained by the aforementioned process.

Other objects, details, characteristics and advantages of the invention will be described in more detail in the detailed description which follows of a particular currently preferred embodiment of the invention, given solely by way of illustration and not limitation, in reference to the appended schematic drawings, in which:
FIG. 1 is a schematic elevation view of an exemplary embodiment of the device for implementing the continuous printing process, in accordance with the first object of the invention;
FIG. 2 is a partial plan view of a strip of paper pre-printed with an upside-down pattern, colored or not, consisting of a sublimable ink, intended to be used in the process according to the first object of the invention;
FIG. 3 is a partial plan view of a strip of plastic film printed by sublimation transfer from the strip of pre-printed paper of FIG. 2;
FIG. 4 is a cross-sectional view along line IV of FIG. 5, showing the thermoforming of the strip of plastic film printed in FIG. 3 in a thermoforming tool with a spherical cavity;
FIG. 5 is a partial view from above according to arrow V in FIG. 4, showing the strip of thermoformed plastic film with a deformed pattern on its spherical surface;
FIGS. 6 and 7 are views similar to FIGS. 2 and 3 respectively, but with a preformed pattern for thermoforming, in accordance with the second object of the invention; and
FIGS. 8 and 9 are views similar to FIGS. 4 and 5 respectively, with an undeformed pattern on the strip of thermoformed plastic film.

 A particular embodiment of the device for implementing the continuous printing process of a plastic film by sublimation transfer will now be described with reference to FIG. 1.

 This device comprises an unwinding station 1 which rotatably supports a reel 2 from which is unrolled a temporary support strip 3 for example made of paper, and above the reel 2, a reel 17 from which is unrolled a strip of plastic film 4, ilocked or not. The temporary support is made of a material that is not very sensitive to heat, in order to ensure dimensional stability of the plastic film, during the subsequent sublimation operation, this material having a non-stick characteristic at room temperature, to facilitate the detachment of the film. plastic after thermal printing, as well as an ability to adhere hot with the plastic film when the latter undergoes fusion, during subsequent heating and sublimation transfer operations.

 The aforementioned strips 3 and 4 then pass through a heating station 5 which has three guide rollers 6, arranged upstream of a rotary heating drum 7, which is rotated clockwise indicated by the arrow F in the figure 1.

 At the entrance to the heating station 5, the strips 3 and 4 pass under a first roll 6, the front of the strip of plastic film 4 coming into contact with the roll 6 and the temporary support strip 3 coming into contact with the back of said strip 4. The set of strips 3 and 4 thus superimposed is conveyed horizontally to a second roller 6 against which the front of the strip of plastic film 4 always rests, said strips 3 and 4 performing a 90 turn around this second roller 6. Then, the superimposed strips 3 and 4 make a 180 turn around the third roller 6 which is located near the heating drum 7, so that the temporary support strip 3 comes into contact with the heating cylinder 7, to avoid sticking by softening of the plastic film on the heating drum 7. The set of bands 3 and 4 is wound around the heating drum 7, at an angle of about 270, of way that the tape plastic film 4 is brought to a temperature of about 200 C when the assembly leaves the heating drum 7. At the outlet of the heating drum 7, the strip of plastic film adheres, due to its fusion, to the support strip temporary 3 which provides dimensional support to said strip of plastic film 4, the assembly thus forming a composite strip 18, the two layers of which are temporarily bonded together.

 Said composite strip 18 is routed horizontally downstream of the heating drum 7 to a thermal printing machine 8. This thermal printing machine 8 comprises at its input a guide roller 9 against which the temporary support of the composite strip is supported. Then, the composite belt is conveyed by a conveyor belt 10 around a rotary heating calender 11 which is rotated counterclockwise in FIG. 1. The conveyor belt 10 consists of an endless belt which rolls around a plurality of rollers 12, some of these rollers being movable to adjust the tension of the belt 10 and therefore the pressure exerted by the belt 10 against the heating calender 11. The composite belt comes into contact with the conveyor belt 10 by its temporary support, to avoid any sticking between the plastic film and the carpet.

 The machine 8 further comprises at least one reel 13, for example two reels, from which is unrolled a strip 14 of pre-printed paper with a pattern consisting of a sublimable ink. The strip of pre-printed paper 14 is guided by a roller 15 upstream of the belt 10 and the heating calender 11. The machine 8 comprises two other coils 16 arranged downstream of the heating calender 11 and the conveyor belt 10, on which reels 16 is wound paper 14, after the sublimation transfer of the ink onto the plastic film of the composite strip. The pre-printed paper 14 is sandwiched between the heating calender 11 and the front of the plastic film of the composite strip which is pressed under pressure by the conveyor belt 10 against the heating calender 11. The pattern consisting of a sublimable ink is pre-printed on the side of the paper 14 which is intended to come into contact with the front of the plastic film of the composite strip, in order to allow the transfer by sublimation. By way of example, the sublimation transfer takes place around the heating calender 11, over an angular travel of approximately 300, at a temperature between 180 and 230 C, under a regular pressure generally less than 40 kPa exerted by the conveyor belt 10, and for an approximate duration of 5 to 40 s.

 When the plastic film used is not flocked, the sublimable ink of the pre-printed paper 14 contains softening or non-sticking agents, to avoid sticking of the pre-printed paper 14 on the plastic film. On the other hand, when the plastic film has a flocked surface intended to be printed, it is not necessary to provide such agents.

 The structure of the printing machine 8 will not be described in more detail, because it is known per se. On this machine 8, two reels 13 and two reels 16 are provided for the pre-printed paper 14, in order to avoid any interruption of the process, when one of the reels is completely unwound, the other thus taking over for replacement of the fully unwound reel.

 On leaving the machine 8, the printed composite strip 19 is conveyed to a cooling station 20 which comprises two rotary cylinders 21 and 22 offset vertically relative to one another.

The upper cylinder 21 is driven in clockwise rotation, while the lower cylinder 22 is driven in a counterclockwise direction. In a manner known per se, each cylinder 21 or 22 has a double envelope on its side wall, to circulate inside this double envelope of water, for example at 10 ° C., in order to cool the printed composite strip 19 , up to a temperature generally between 20 and 30 C.

 The composite strip first passes around the upper cylinder 21, coming into contact through its temporary support, in order to prevent the plastic film printed against this cylinder from sticking. Then, the already cooled composite strip passes around the lower cylinder 22, on the side of its printed plastic film, which no longer risks sticking to the cylinder 22. The path of the composite strip around the two cylinders 21 and 22 has a configuration substantially in form of S. At the outlet of the cooling station 20, the previously printed plastic film no longer adheres to the temporary support strip, due to the non-stick properties of the latter.

 Finally, the two superimposed strips pass through a winding station 23 which comprises a reel 24 around which the strip of printed plastic film 104 is wound and a reel 25 around which the temporary support strip 3 is wound. entrance to the winding station 23, the two superimposed strips 3 and 104 pass between two rollers 27 downstream of which the two strips are separated in the direction of their respective spools. The coils 24 and 25 and the rollers 27 are rotated.

 The operation of the device of FIG. 1 will now be briefly described.

 The temporary support strip 3 is first unwound from the reel 2 along the entire path inside the device to the winding reel 25, over a total length of about 20 to 30 meters. Then, the plastic film strip 4 is unwound from the reel 17, over a length of about 2 to 3 meters to the heating drum 7, because from this point the plastic film strip 4 adheres to the strip temporary support 3, which allows it to be driven through the entire device. It may be noted that the temporary support strip 3 which is wound on the reel 25, can be reused for the subsequent printing of a new strip of plastic film.

 In FIG. 2, a checkerboard pattern 30 is pre-printed on the strip of printing paper 14, the checkerboard pattern 30 comprising in its central square an equilateral triangle the apex of which is directed to the left. On this strip of printing paper 14, is also printed a mark consisting of a longitudinal line 31 and a transverse line 32, to locate on said strip 14 the pre-printed pattern 30.

 With the device illustrated in FIG. 1, it is possible to obtain at the outlet a strip of printed flat plastic film 104 comprising a checkerboard pattern 130 which is exactly the reverse image of the pattern 30 of the preprinted paper 14, the top of the triangle equilateral now being turned to the right in Figure 3.

 In Figure 4, there is shown a step of thermoforming a portion of this strip of printed plastic film 104, in a thermoforming tool 50 having a c connected to an external suction system, which allows to press the film plastic 104 softened by heating on the walls of the tool 50, this thermoforming tool being known per se, we have not shown the heating punch, the shape of which can be combined with the cavity 51. A flat portion of the strip of plastic film 104 is heated, then thermoformed into a spherical non-planar surface 114 by the thermoforming tool 50, this deformation causing a stretching of the checkerboard pattern 131, as visible in FIG. 5.

 The transformation of several elementary areas 130a to 130d of the flat plastic film into deformed elementary areas 131a to 131d on the thermoformed spherical surface 114. has been indicated in FIG. 4 by dotted arrows. The set of deformed elementary areas thus forms the distorted pattern 131 visible in FIG. 5.

 To compensate for this undesirable deformation of the pattern to appear on the thermoformed portion of the plastic film, it is determined, by reverse transformation, by anamorphosis, the preformed pattern 40 which is pre-printed upside down on a portion 114 of the printing paper. 14, this portion 114 corresponding to the portion intended to be thermoformed, as visible in FIG. 6. This deformation is calculated by computer using suitable software.

 The strip of plastic film 104 is printed with the preformed pattern 140 by not sublimation transfer of the preformed pattern 40 from the printing paper 14 as visible in FIG. 7.

 During the thermoforming of the portion 114, as illustrated in FIG. 8, each elementary zone 140a to 140d of the planar portion of the plastic film is transformed into an elementary zone 141a to 141d on the non-planar surface 114 obtained by thermoforming, as indicated by the dotted arrows in Figure 8.

 There is thus obtained on the portion 114 of the strip of thermoformed plastic film a pattern 141 which corresponds to the desired pattern, without final deformation.

 During the step of thermoforming the strip of printed plastic film 104, said strip is conveyed sequentially above the thermoforming cavity 51, so as to precisely position the portion to be thermoformed 114 above said cavity 51. The precise positioning of the portion 114 is obtained by optical reading of the longitudinal and transverse position of this portion 14, using the aforementioned references 31 and 32.

 Although this is not visible in the drawings, the deformation by thermoforming of the portion 114 is also accompanied by a variation in the color shades as a function of the local stretching rate of the plastic film, which also necessitates precompensating these color variations, when preprinting the printing paper 14.

 Although the invention has been described in connection with a particular embodiment, it is obvious that it is in no way limited thereto and that it includes all the technical equivalents of the means described as well as their combinations if these are within the scope of the invention.

Claims (12)

 1. A method of continuously printing a pattern, colored or not, on a flat plastic film (4), flocked or not, intended to be thermoformed into a specific non-planar surface, characterized in that it consists in:  dividing geometrically into elementary zones (140a-d) the portion (114) of the flat plastic film to be thermoformed,  -determine, for each elementary area of the film, the local stretching rate of the film during its thermoforming in the non-planar surface,  -determine, for each elementary zone of the film, the part of deformed pattern (140a-d) to be printed on the surface of the flat plastic film (4), this part of deformed pattern being defined by transformation by anamorphosis of the final pattern (141) to appear on the non-planar thermoformed surface, taking into account the local stretching rate of the plastic film by which one passes from the part of the deformed pattern to the part of the final pattern (14 la-d),  -printing, on the surface of the portion to be thermoformed (114) of the flat plastic film, the deformed pattern (140) defined by all of the deformed pattern parts determined in the previous step.  2. Method according to claim 1, characterized in that it consists in determining, for each elementary zone (140a-d) of the film, the tint of the colors of the part of the deformed pattern, as a function of the desired color tint of the final pattern and the local stretch rate of the film by which one passes from the deformed pattern part to the final pattern part.  3. Method according to claim 1 or 2, characterized in that it consists in simultaneously printing on the portion of the flat film other than that to be thermoformed, a mark (31,32) to precisely locate the portion to be thermoformed (114) of the flat plastic film.  4. Method according to claim 3, characterized in that the mark to be printed comprises a line (31) extending along an edge of the flat plastic film and a line (32) extending transversely from this line .  5. Method according to one of claims 1 to 4, characterized in that the aforementioned printing step of the flat plastic film consists in:  -apply a temporary non-stick support (3) on the back of the flat plastic film (4),  -heating the entire flat plastic film and the temporary support to a temperature such that the plastic film reaches its softening point to temporarily stick to the temporary support, so that the latter ensures the dimensional maintenance of the plastic film during the step successive thermal printing,  transferring by sublimation the deformed pattern (40) pre-printed upside down with a sublimable ink on a printing paper (14), by contacting under a pressure and a determined temperature of said printing paper with the front plastic film heat sealed to the temporary support,  cooling the entire flat plastic film thus printed (104) and the temporary support to a temperature allowing the temporary support to detach.  6. Method according to claim 5, characterized in that it consists, for a non-flocked plastic film, in pre-printing the printing paper (14) with an ink containing sublimable dyes, with a low content of softening or anti-softening agents -adherent, to avoid sticking between the plastic film and the printing paper, during the sublimation transfer printing step  7. Method according to claim 5, characterized in that it consists in preparing a flocked plastic film, by applying to the front of the plastic film (4) an adhesive layer and by flocking white fibers on said adhesive layer.  8. Method according to one of claims 1 to 7, characterized in that the plastic film (4) is a calendered film, extruded or co-extruded, chosen from polymer resins based on polyvinyl chloride, polystyrene, polypropylene, acrylic butadiene-styrene (ABS), polyurethane, polyester, polycarbonate, polyamide or any mixture thereof.  9. Method according to claim 3 or 4, characterized in that it consists, in a subsequent step, in positioning laterally and transversely the surface portion (114) to thermoform flat plastic film (104) on the surface of which is printed the deformed pattern (140), opposite the shape (51) of a thermoforming tool (50), by means of the aforementioned printed marker (31,32), and to be thermoformed with said thermoforming tool only said portion (114) in a non-planar surface on which the desired final pattern (141) appears.  10. Method according to claim 9, characterized in that it consists in optically detecting the longitudinal line (31) of the mark to laterally guide the flat plastic film (104) and the transverse line (32) of the mark to stop, in the longitudinal direction, the flat plastic film with its portion to be thermoformed (114) opposite the shape (51) of the thermoforming tool (50).  11. Method according to one of claims 5 to 7, characterized in that it consists in calculating the parts of pattern deformed by computer and in pre-printing the printing paper by an ink jet printing machine controlled by said computer.  12. Printed plastic film (104) with a non-planar thermoformed surface (114), characterized in that it is directly obtained by the process according to claim 9 or 10.