METHOD FOR PRINTING A LENTICULAR CARD, PRINTED LENTICULAR

CARD AND PRINTER FOR LENTICULAR CARD

This invention relates to a method for printing a lenticular card, a printed lenticular card and a thermal sublimation printer adapted for the printing of lenticular cards.

The invention is located in the area of identification documents with or without integrated circuits such as driving licences, identity cards, membership cards, access cards, passports, bankcards, electronic purses, multi-application cards and other secure documents. Due to the value and the importance of all these documents, they are often the subject of unauthorised copying, alterations, changes and counterfeiting. Until now, lenticules were only used for identification cards as a security element to display two different pieces of information depending on the degree of inclination of the card. However, lenticules have not yet been used over all or part of the surface of such cards, for example to display an image or photograph in three dimensions. Lenticular cards are generally made of large sheets or plates. Thus, at least one flat plate on which images are printed is fixed to a lenticular plate, with indexing holes provided in each plate in order to ensure proper registration between the images and the lenticules. After fixing the plates to each other, the cards are cut out. In general, the plates are printed by means of lithographic offset printing or screen printing.

Another method, described in patent application US2002/0187215, consists in printing at least one plate having indexing holes and then assembling that plate onto another transparent plate that also has indexing holes. A special tool is then used to form lenticules in the transparent plate, using the indexing holes to make sure that the image printed on the first plate is registered correctly with the lenticules to be made. The cards are then cut out.

With these existing methods, it is not possible to individualise the cards by printing personal data such as the photograph of their holder, for example, on each card.

In order to be able to individualise each lenticular card and offer different and personalised printing for each card, the idea of printing lenticular cards using a card- to-card method using thermal sublimation has been considered. Such a thermal sublimation process is better known by the acronym D2T2 (Dye Diffusion Thermal Transfer). This printing technique uses heat-sensitive inking ribbons that are divided into panels. At the time of printing, the dyes are sublimated, that is they go from the solid state to the gaseous state because of the action of a heated point, and are deposited on the substrate to print. The coloured panels pass fully on the document to print, and the inking panels can thus be used only once. For colour printing, four- colour ribbons called YMCK (Yellow, Magenta, Cyan, Black) ribbons are generally used. The printing is carried out in as many passes as there are colours to deposit on the document to print, with one additional pass to apply the protective coating.

However, such printing of lenticular cards using direct thermal sublimation does not allow high-quality printing, because of the poor registration between the printed images and the lenticules. The reason for that is that printing by direct thermal sublimation is very difficult, because the position of the lenticular card in relation to the printing head of the printer is not easy to adjust, leading to poor registration. In particular, that gives rise to a moire effect and a lack of sharpness in the printing.

Because of these drawbacks, the idea of printing the cards using the reverse thermal sublimation technique was envisaged. That involves a type of printing by transfer, where the image is first printed onto an intermediate retransfer film, which is then used to transfer the printed image onto the surface of the object to print. The technique is used to adjust the position of the intermediate retransfer film more finely in relation to the printing head of the printer. Figure 1 is a schematic drawing of a printer 10 using reverse thermal sublimation. The printer comprises a thermal printing head 11 that is used to print an image on an intermediate retransfer film 16 by heating a four-colour YMCK ribbon 12 that is fed out from a roll 17A. The intermediate film 16 printed in this way is fed out from a roll 17B. The card to print

20 is inserted in the printer so that the surface 22 to be printed, opposite to lenticules 21 , is located opposite the intermediate film 16 to be transferred. The intermediate film 16 is then pressed against the surface 22 of the card to be printed by means of a thermal roller 18 that hot laminates the intermediate film. The intermediate film used actually comprises two transparent layers. One of them, on which the image is printed, is designed to be fixed to the lenticular card by means of hot laminating, while the other 19 is designed to be removed after the image 23 is transferred to the card. The card printed in this way comes out of the printer, while the second transparent layer 19 of the intermediate film is wound onto a core 17C and then disposed of or recycled.

The first drawback of this printing method lies in the use of fully transparent transfer film, which calls for an additional subsequent stage where an opaque layer 24 is laminated in order to increase the opaqueness of the lenticular card to offer a background for the printed image 23. Another drawback lies in the fact that it is very difficult to register the image on the intermediate film in relation to the lenticules of the card.

To improve such registration, document US 6, 712, 536 proposes such a reverse thermal transfer printer adapted for printing lenticular cards. To allow correct registration between the lenticules and the image to print, a mark is made on the flat surface to be printed on the lenticular card. An optical sensor placed at the entry of the printer is used to detect the mark and then send a signal to a central command system so as to position the intermediate film in relation to the lenticules. The printer adapted in this way is expensive and complex to implement, because it requires means for sensing, analysis and processing before it can start any printing. As a result, printing requires a large number of stages, which extends the printing time and increases production costs.

That is why one of the technical problems addressed by this invention is to offer a printer using reverse thermal sublimation and an associated method, which would make it possible to print lenticular cards reliably, while providing correct registration between the image to print and the lenticules of the card, in order to obtain a high-quality three-dimensional image. The printer must also be simplified in its construction and inexpensive.

The solution to the technical problem posed is achieved according to this invention by the fact that the printer includes

- a feed roller designed to catch the lenticular card and set it into motion, the said roller having one ribbed surface, where the shape of the ribbing follows that of the convex lenticules of the lenticular card,

- a thermal roller designed to catch the intermediate film bearing the image to print and to set it into motion,

- the said feed and thermal rollers are placed opposite one another and work in synchrony so as to keep the lenticular card and the intermediate film bearing the image to print under pressure while fixing the said film by means of hot lamination and enabling the automatic mechanical registration of the image in relation to the lenticules.

Advantageously, the mechanical system comprises a feed roller with a ribbed surface, the shape of which follows that of the convex lenticules of the card. In that way, after it is inserted in the printer, the card is caught by the feed roller, making it possible to guide the card relatively to the intermediate printed film to transfer.

The feed roller is placed opposite a thermal roller, so that during the stage when the film bearing the image to print is laminated, the lenticular card is kept under pressure between the feed roller and the thermal roller. The film bearing the image to print is positioned in relation to the feed roller. The feed roller and the thermal roller function synchronously so as to register the image to print correctly in relation to the lenticules.

The associated printing method is remarkable in that it comprises the following stages: - the lenticular card is fed mechanically by means of a ribbed feed roller and, simultaneously, the intermediate film bearing the image to print is positioned relative to the lenticules by means of a thermal roller that functions synchronously with the card feed roller,

- the card and the intermediate film are held under pressure between the card feed roller and the thermal roller and

- the intermediate film bearing the image to print is applied and fixed by hot lamination on the flat surface of the lenticular card.

In that way, the card is fed by a fully mechanical system. The intermediate retransfer film bearing the image to print is positioned in relation to the mechanical feed system and not the card. Such positioning allows the reliable automatic registration of the image in relation to the lenticules, as the mechanical feed system makes it possible to guide the lenticular card relative to the intermediate film bearing the image to transfer.

Further, this card-to-card printing process makes it possible to personalise each card.

The invention further relates to a lenticular card printed using the method of reverse thermal sublimation method according to the invention.

Lastly, the invention relates to the intermediate retransfer film that is designed to be used for printing the surface of an object using reverse thermal sublimation, in order to obtain, in a single stage, a printed object such as a lenticular card with an opaque background so that there is no need for the further lamination of an opaque layer.

To achieve that, the intermediate film comprises a first opaque layer that supports the image and a second substrate layer on a surface of the opaque layer opposite the image. Advantageously, the second layer is dissociated from the opaque layer that bears the image during the hot lamination of the retransfer film that is designed to transfer the image onto the surface of the object to print.

In that way, thanks to structure of the retransfer film used, no subsequent additional lamination is required, because the printed image has an opaque background that gives it sufficient contrast.

Other particularities and benefits of the invention will become clear in the description below, provided as a non-limitative illustrative example, by reference to the figures attached, which represent:

- figure 1 , already described, is a sectional diagram of a reverse thermal sublimation printer according to the prior art,

- figure 2A is a sectional diagram of a reverse thermal sublimation printer according to the invention,

- figure 2B is a detailed diagram of the mechanical feed system of the printer in figure 2 A,

- figures 3A, 3B and 3C are a sectional view of a lenticular card during printing, a top view of an intermediate retransfer film and a perspective view of a lenticular card printed according to the invention respectively, and

- figures 4A, 4B and 4C, are schematic drawings of a lenticular card with the lenticules turned obliquely, a feed roller for such a card and a drawing illustrating the relative movement of the printer head in relation to the intermediate film to which the image that will then be printed on the lenticular card with oblique lenticules is transferred respectively.

Figure 2A is a schematic drawing of a reverse thermal sublimation printer 30 according to the invention. Like conventional printers, it includes feed rollers 37A and 37B respectively, a four-colour ribbon 32 of the YMCK type and an intermediate retransfer film ribbon 36. A thermal head 31 is used to locally heat the ink panels of the YMCK ribbon 32 and transfer them to the intermediate film 36 so that the image to print on the lenticular card 40 is first transferred to the intermediate film 36. The lenticular card 40 to print is inserted in the printer and set in motion by means of a first feed roller 34.

The printer further comprises a mechanical feed system 38 designed to catch the card, set it in motion, keep it under pressure at the time of printing and thus ensure proper registration of the intermediate film bearing the image to print in relation to the lenticules of the card. That mechanical system as illustrated in figure 2B comprises a feed roller 38 with a ribbed surface. The shape of the ribs 38A follows that of the convex lenticules 21 of the lenticular card. A thermal roller 39 is used to hot laminate the intermediate film 36 onto the flat surface 42 of the lenticular card 40 and thus fix the image to print on it. The feed roller 38 and the thermal roller 39 are placed opposite one another, on either side of the card to print.

Advantageously, the intermediate retransfer film 36 comprises lateral perforations 36C, of the cinema perforation type, on at least one of the two longitudinal edges of the film so that the film 36 is caught by sprockets or teeth placed on the lateral edges of the thermal roll 39 and the intermediate film 36 is correctly set in motion in relation to the lenticular card 40.

The feed roller 38 and the thermal roller 39, which synchronously and mechanically feed the intermediate retransfer film 36, are placed so as to function

synchronously in order to ensure the correct registration of the image to print in relation to the lenticules of the card. The feed roller 38 is opposite the thermal roller and they press against each other so as to hold the card correctly in position during the stage of lamination and fixing the image on its surface 42. As a result, thanks to that mechanical feed system, registration is completely controlled and automated.

The printed card 40 delivered by the printer has printing 43 on the side opposite the lenticules 41 and an opaque background 36A placed on the printing for obtaining better rendering and better contrast of the printed image. The printed image and the background are applied simultaneously when the intermediate film is laminated by using the special intermediate film described in greater detail below. In that way, there is no need for additional lamination to apply an opaque background on the printing, which reduces the time and cost of printing lenticular cards.

Further, doing away with the subsequent lamination of an opaque background avoids deforming the printed layer due to the heating involved in such additional lamination. Such deformation leads to defects, particularly a loss of sharpness of the image. Thanks to the printer and its associated method, the printing obtained is thus of high quality, with a true three-dimensional effect.

The lenticules 41 of the card are preferably directed parallel to the printing direction, that is they are placed in the direction of the length L of the card in the example in figures 2A to 3C. Such orientation advantageously makes it possible to better position the picture in relation to the lenticules and obtain high-quality sharp printing. That is because of the mechanical adjustment of the printing head 31 in relation to the feed rollers 38, 39 of the card and the intermediate film. The intermediate film 36 is unfolded perpendicularly to the printing head 31 , so that the printing lines on the film are parallel to the direction of movement of the intermediate film 36. The film is then positioned parallel to the lenticular card. In this case, all the play in the mechanical feeding of the various parties does not affect the alignment of the lenticular cards. As a result, if the card arrives with a shift of a few hundredths of a millimetre in the feed direction, that has no effect on the quality of the image. On the other hand, if the lenticules are placed perpendicular to the movement direction, it is necessary to be able to reposition the print head 31 in relation to the card shift, due to the play in the mechanical roller feed system. It would thus be

necessary in that case to provide a system for the vertical adjustment of the position of the printing head 31 of the figure 2A.

A lenticular card may also be made with the lenticules 41 oriented obliquely, that is neither parallel nor perpendicular to the printing direction. A schematic drawing of such a lenticular card has been provided in figure 4A. In that case, the feed roller 38 as shown in figure 4B comprises helically tilted notches or ribbing 38, so that it can follow the lenticules of the card. Besides, in order to be able to print the lenticular card and achieve optimum registration between the printed image and the oblique lenticules, a control system designed to control the movement of the printing head is required to adjust the position of the printing head in relation to the intermediate film while the image is being transferred to the intermediate film. In figure 4C, the movement direction of the printing head 31 is schematically shown by the double arrow T, whilst the movement direction of the intermediate film 36 is shown by the arrow F. The printing method used by the printer thus consists in positioning the intermediate film 36 bearing the image to print in relation to the ribbed feed roller 38. To do so, the intermediate retransfer film 36 comprises lateral perforations 36C, of the cinema perforation type, on at least one of the two longitudinal edges of the film so that it is caught by sprockets or teeth placed on the lateral edges of the thermal roller 39, and can thus be positioned in relation to the feed roller 38 of the card. When the film is positioned, the last stage consists in hot laminating the intermediate film onto the flat surface of the lenticular card in order to transfer the image to it.

Figure 2B is a more detailed perspective view of a lenticular card 40 when the retransfer film is laminated between the thermal roller 39 and the ribbed feed roller 38. The card is fed by the rollers in the direction indicated by arrow D. The lenticules of the card are turned in the lengthwise direction L of the card and are parallel to the movement direction of the card and the direction of the printing lines. The intermediate film is also fed in the same direction as the card, and when it is pressed against the flat surface of the card, between the feed roller 39 and the ribbed roller 38, it is simultaneously heated, so that the image to transfer is fixed onto the flat surface 42 of the card.

Figures 3A, 3B and 3C are schematic drawings of the card just before and just after the lamination of the intermediate film 36, bearing the image 43 to transfer to the card 40.

The intermediate film 36 used is in fact a multilayer film. It comprises a first opaque layer 36A and a second support layer 36B. Optionally, it also comprises a layer of glue or equivalent, which binds the first opaque layer to the second support layer and which is designed to disappear or change state when the two layers are separated by the thermal effect during the lamination. The image 43 to print on the card is transferred by means of a YMCK ribbon that is heated by the thermal head 31 of the printer, on the external side of the opaque layer 36A, opposite the support layer 36B. The second support layer 36B is made of material designed to be separated from the first opaque layer 36A containing the image, under the effect of heat, that is during the lamination stage. The lamination temperature is temperature that is typically used in the manufacture of cards, that is it ranges from 115 to 200 ⁰ C. As a result, the material that makes up the support layer must have a melting point sufficiently high to withstand that temperature.

The material that makes up the second support layer 36B may for example by polyethylene or paper or any other material with similar properties. The support layer 36B is dissociated from the first printed layer 36A during the lamination stage, then it is taken up on a core 37C for example. That wound up layer may be either recombined to form a new intermediate film or disposed of. The layer may be transparent or opaque.

As illustrated in figures 3A and 3B, the support layer 36B may be chosen so that it is wider than the opaque layer 36A, so that the lateral perforations 36C are only arranged on the lateral edges of the support layer 36B. In that way, the perforations disappear with the support layer 36B, when it is separated from the opaque layer during the lamination stage, and do not appear on the finished product.

The material that makes up the first layer 36A of the intermediate film 36 must for its part be opaque and resistant to the lamination temperature. It must be able to be glued at the lamination temperature on the flat surface 42 of the lenticular card 40. The material may for example be polyethylene terephthalate (PET) or

acrylonitrile butadiene styrene (ABS), with or without filler, or polycarbonate (PC) with opaquing filler or any other material with similar properties. The first layer 36A, the external surface 43 of which is printed, may for example be about 50μm thick.

According to a variant of embodiment, the opaque layer 36A may itself be made up of an assembly of several layers, one being designed to receive the image printed by the printing head and the second layer being designed to achieve opaqueness.

For its part, the lenticular card 40 has a transparent body made of polycarbonate, for example, or polyethylene terephthalate or polyvinylchloride or any other material with similar properties.