Method for printing on the surface of an electronic smart card

Abstract

The invention relates to an inkjet printing method for a design on the surface of an electronic smart card, comprising a printing step (S1) using inkjet printheads to form a colored design on the card surface; a varnish printing step (S3) using a printhead on said card surface; a pause step (S4); and a polymerization step (S5) of the ink and varnish by applying ultraviolet radiation to the card surface. Use for creating personalized designs printed on an electronic smart card. Figure 1 for the abstract

Description

Title of the invention: Method for printing on the surface of an electronic smart card. TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a method of inkjet printing a pattern on a surface of an electronic smart card.

[0002] It also relates to an electronic smart card having a pattern printed according to the printing process according to the invention. STATE OF THE ART

[0003] The present invention finds its application in the field of electronic smart cards, such as bank cards, access cards, etc. It relates to both smart cards using contacts to communicate and those communicating by radio frequency waves.

[0004] Such an electronic smart card usually has a printed pattern on at least one of its opposite faces, forming a decoration and allowing identification, for example, of the supplier or the intended use of the card.

[0005] A method for manufacturing a printed smart card with a raised visual effect is known from US patent 7,455,235 B2. This method comprises a step of applying metallic ink to a surface of the smart card, followed by partially coating this metallic ink with a varnish, thereby creating a three-dimensional-looking inscription. The metallic ink and varnish are applied to a surface of the smart card using a screen-printing process. The varnish, applied in a viscous state, is polymerized using ultraviolet radiation.

[0006] The assembly is then covered with an overlay layer which, when laminated, preserves the shiny metallic parts and transforms the varnish into a dull surface, contributing to the relief effect.

[0007] However, it is often desired that the electronic smart card be customizable according to its use, the cardholder, or the card provider. For example, for a bank or payment card, the issuing bank may request the printing of a personalized logo. For an access card to a secure building, an image or text can be printed at the customer's request to facilitate recognition of the access card and its intended use.

[0008] In order to meet these needs for personalization of a printed design, it is known to implement inkjet printing techniques, which allow, from a digital file containing the data of the design to be printed, the creation of a specific pattern on the surface of a digital smart card through the implementation of an inkjet printhead printer,

[0009] This is referred to as print on demand (Drop on Demand or DoD in Anglo-Saxon terminology).

[0010] Inkjet printing allows the printing of personalized designs unlike mass printing techniques such as offset printing or screen printing.

[0011] However, inkjet printing has the disadvantage of creating a pattern on the surface of the electronic smart card which is more or less shiny depending on the color printed: the light colored parts have a more matte appearance than the dark colored parts which shine more.

[0012] In addition, the printed surface of the electronic smart card has a non-uniform feel, the amount of ink deposited to print the dark coloured portions of the pattern being greater than that deposited to print the light coloured portions of the pattern.

[0013] Consequently, the dark coloured portions are thicker and form an overthickness compared to the light coloured portions.

[0014] For example, a difference in thickness between the highest point and the lowest point (in a direction perpendicular to the surface of the map) of the order of 0.020 pm, which can reach 0.025 pm, can be observed. Description of the invention

[0015] The present invention aims to remedy all or part of the disadvantages of the prior art mentioned above.

[0016] To this end, the invention relates to a method of inkjet printing a pattern on a surface of an electronic smart card.

[0017]

[0018] According to the invention, the printing process comprises the following steps:

[0019] - printing by inkjet print heads to form a pattern in color on the surface of the map;

[0020] - printing of a varnish by a print head on said surface of the card;

[0021] - implementation of a pause period; and

[0022] - polymerization of ink and varnish by application of ultraviolet radiation on the surface of the map.

[0023] The printing of varnish on the surface of the card makes it possible to erase at least in part the reliefs created on the surface of the card by the inkjet printing.

[0024] The pause period allows the varnish to flow over the surface of the card towards the holes or interstices created within the printed colour pattern and thus to unify the surface of the card.

[0025] In practice, the colour pattern comprises at least two distinct colour portions.

[0026] The varnish thus fills the gaps created between the distinct color areas, that is, between the areas printed with lighter colored ink and the adjacent areas printed with darker colored ink. The varnish also spreads over the lighter colored printed areas, which are thinner than the darker colored printed areas.

[0027] In practice, the pause period is at least equal to 0.5 seconds, and preferably greater than 0.8 seconds.

[0028] According to an advantageous feature, in the varnish printing step, a uniformly distributed quantity is applied by the print head onto the surface of the card.

[0029] The layer of varnish thus applied allows the creation of a uniform deposit over the entire surface of the card, before finishing the varnish to fill the gaps between the areas printed with different colors.

[0030] In practice, at the varnish printing stage, the print head is controlled by a print driver from a level value selected on a scale of levels between 0 and 255 corresponding respectively to a quantity of varnish deposited by said print head for each pixel printed, the quantity of varnish deposited varying linearly between 0 drops at level 0 and 4 drops at level 255 and the selected level value being at least equal to 155, and preferably greater than 175.

[0031] The Applicant found that a level value of at least 175 was well suited to obtain a sufficient quantity of varnish to compensate for the reliefs created on the surface of the card by the inkjet printing of a pattern.

[0032] According to an advantageous feature, the printing process further comprises a pre-polymerization step of the ink before said varnish printing step, by applying ultraviolet radiation to the colour pattern formed on the surface of the card.

[0033] The pre-polymerization step prevents the ink from spreading on the surface of the card and limits the mixing of colors in order to obtain a sharp edge of the images or text of the printed color pattern.

[0034] In practice, the power of the ultraviolet radiation of the ink pre-polymerization step is less than the power of the ultraviolet radiation of said ink and varnish polymerization step.

[0035] At the polymerization stage, the power of the radiation is greater in order to obtain homogeneous drying and total curing of the ink and varnish.

[0036] By way of example, the power of the ultraviolet radiation of said ink and varnish polymerization step is substantially equal to 16 W.

[0037] In comparison, the power of the ultraviolet radiation of the ink pre-polymerization step is less than 2 W, and preferably between 0.05 and 0.10 W.

[0038] According to a second aspect, the present invention relates to an electronic smart card having on a surface a pattern printed by a printing process according to the invention.

[0039] According to the invention, the difference in thickness of the pattern printed on the surface of said card, between a highest point and a lowest point of said pattern, is less than 0.010 pm.

[0040] The texture of the printed surface of the card is thus uniformized, with very limited relief effects. In addition, the surface of the card with a varnish layer has a more uniform glossy finish, both for the light and dark portions of the printed design. BRIEF DESCRIPTION OF THE FIGURES

[0041] Other features and advantages of the invention will become apparent from the following non-limiting description.

[0042] To the attached drawings, given by way of non-limiting example:

[0043] - [Fig. 1] is an algorithm illustrating the steps of a printing process according to a method of implementing the invention;

[0044] - [Fig.2] is a simplified diagram of an inkjet printing machine adapted to implement the printing process according to the invention; and

[0045] - Figures [Fig. 3], [Fig. 4] and [Fig. 5] schematically illustrate examples of maps an electronic chip comprising on a surface a pattern printed by the printing process according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0046] We will first describe, with reference to [Fig.1], an embodiment of an inkjet printing process for a pattern on a surface of an electronic smart card.

[0047] In the following description, the term "electronic smart card" refers to any type of smart card, such as GSM (Global System for Mobile communications) cards, bank cards, access cards, etc. The present invention also relates to smart cards using magnetic contacts or strips to communicate with card reading terminals, such as those communicating via radio frequency waves, known as "contactless" smart cards.

[0048] The printing process described below is particularly well suited to printing designs customized according to the cardholder and / or supplier.

[0049] Inkjet printing allows a personalized design (text, image, diagram) to be printed on the surface of the card.

[0050] We thus speak of DoD printing (abbreviation of the Anglo-Saxon terminology Drop on Demand) for inkjet printing, from a digital data file parameterized according to the personalized pattern to be printed.

[0051] The use of inkjet printing is well known and does not need to be described in detail here?

[0052] In particular, it is implemented using a printing head machine that allows edge-to-edge (E2E) printing, meaning that the printing extends to the edges of the card, without leaving any white margins. This printing technique is also called borderless printing.

[0053] As illustrated in [Fig.1], the printing process first includes an SI printing step by inkjet print heads to form a colour pattern on the surface of the card.

[0054] The colour pattern may include at least two, and generally multiple portions of distinct colours.

[0055] The portions of the pattern to be printed may be in black and white with different levels of grey, or in colours of various shades.

[0056] With reference to [Fig.2], an inkjet printing machine 20 is schematically illustrated, with four print heads 21.

[0057] Each print head 21 contains a set of very fine nozzles through which the ink is expelled. Each print head 21 is connected to a reservoir of ink of a different color. Each print head 21 is further heated to a temperature of approximately 60°C.

[0058] Inkjet printing using CYMK printheads is typically used. This technology relies on spraying tiny droplets of ink onto a substrate, in this case the surface of the card, to reproduce color images and text.

[0059] CYMK is an acronym for the four ink colors used: Cyan, Yellow, Magenta, and Key (for black). These inks are precisely mixed to create a wide range or shades of color. The print heads 21 contain numerous micro-nozzles that project the ink droplets. Each nozzle is individually controlled to regulate the volume and placement of the droplets. allowing for a detailed and precise reproduction of color nuances and gradients.

[0060] Preferably, the print heads 21 are controlled by a print driver from a level value selected on a level scale between 0 and 255. This level scale allows control of the amount of ink deposited by each print head.

[0061] Each value on this numerical scale from 0 to 255 represents a certain amount of ink projected per pixel.

[0062] The levels from 0 to 255 represent a range of ink quantities. A value of 0 means that no ink is deposited (white), while a value of 255 means that a maximum amount of ink is applied (black or solid color).

[0063] This print driver allows precise control of the size and density of ink droplets deposited on the substrate, which is crucial for obtaining accurate colors and image details.

[0064] The printing step of an SI image is thus controlled by software, which translates the digital information of the pattern to be printed into ink levels to be applied, and by sending corresponding commands to each print head via the print driver.

[0065] In the embodiment described below, the setting on the digital scale is made between 0 (0 drops) and 255 (4 drops), the quantity of ink projected for each value from 0 to 255 varying linearly between 0 and 4 drops.

[0066] The printing process then preferably includes a pre-polymerization step S2 of the ink, by applying ultraviolet radiation to the colour pattern formed on the surface of the card.

[0067] This pre-polymerization step S2 is implemented to solidify and / or partially dry the ink immediately after its deposition on the surface of the card.

[0068] This process is also called "pinning" in Anglo-Saxon terminology and makes it possible to stabilize the ink droplets, preventing their diffusion or excessive mixing on the support, which could compromise the sharpness and precision of the printed pattern.

[0069] As illustrated in [Fig.2], the inkjet printing machine 20 includes an ultraviolet radiation lamp 22 to perform this pre-baking of the ink on the surface of the card.

[0070] The ultraviolet radiation lamp 22 is of low power or intensity, sufficient to slightly fix the ink but without polymerizing or drying it completely.

[0071] In practice, the power of the ultraviolet radiation during the S2 pre-polymerization step of the ink is less than 2 W, and preferably between 0.05 and 0.10 W.

[0072] The ultraviolet radiation lamp 22 is for example a lamp with a maximum power of 2W, with a digital adjustment over a range of values ​​between 0 (0 W) and 255 (2 W), allowing a linear adjustment between 0 and 2 W.

[0073] The value of 10, corresponding to 20 / 255 W, i.e. 0.078 W, can thus be selected.

[0074] The processing time is also relatively short to avoid complete cooking ink on the card. The pre-polymerization stage takes very little time and allows the ink to dry through localized drying on the surface of the card.

[0075] In practice, the card is moved continuously under ultraviolet radiation which is localized, over a very small width.

[0076] The pre-polymerization step S2 prevents the ink from spreading and the colors from mixing, in order to maintain sharper edges of the printed pattern.

[0077] The printing process also includes an S3 printing step of a varnish by a print head on the surface of the card.

[0078] The step of printing a varnish S3 is implemented after the pre-polymerization step of the ink S2.

[0079] As illustrated in [Fig.2], a varnish print head 23, similar to the print heads 21 for inkjet printing, is implemented in the inkjet printing machine 20.

[0080] The varnish print head 23 is also controlled by a print driver in the same way as the inkjet print heads 21.

[0081] In practice, the varnish print head 23 is controlled by a print driver from a level value selected on a scale of levels between 0 and 255 corresponding respectively to a quantity of varnish deposited by the print head 23 for each pixel printed.

[0082] As before, the selected value varies linearly between 0 drops (value 0) and 4 drops (value 255) deposited for each pixel of the printed pattern.

[0083] In practice, at the S3 varnish printing stage, a uniformly distributed quantity is applied by the varnish print head 23 onto the surface of the card.

[0084] Thus, the same amount of varnish is projected for each pixel of the pattern printed on the card.

[0085] In practice, the selected value is at least equal to 155, and preferably greater than 175, for each pixel of the printed pattern.

[0086] This selection thus corresponds substantially to the projection of at least 2.5 drops of varnish per pixel.

[0087] This minimum quantity of varnish allows for a uniform distribution of the varnish on the surface of the card and avoids the appearance of lines (or in Anglo-Saxon terminology, streakings) which correspond to a printing defect, making the images or texts of the design less sharp and homogeneous.

[0088] In practice, the selected value can be between 175 and 255, corresponding to the projection of 2.5 to 4 drops of varnish per pixel.

[0089] This maximum threshold value of 255, corresponding to 4 drops of varnish, limits the total amount of varnish on the card surface, thus reducing the varnish over-application and therefore the overall thickness of the card after printing. The maximum threshold value also limits the additional production costs associated with the use of varnish.

[0090] For example, the varnish used may be a varnish marketed by the American company Entrust® for DoD printing.

[0091] Generally, a varnish with a viscosity between 1 and 5 cP (centipoise) is suitable for this step of printing an S3 varnish.

[0092] The sprayed varnish makes it possible to compensate for the reliefs created during the printing of a pattern by inkjets and to homogenize the gloss of the printed surface.

[0093] Indeed, depending on the colors of the pattern printed by inkjet, the rendering of the printed surface is more or less matte (light colors) or glossy (dark colors).

[0094] In addition, since the hue of the printed color depends on the amount of ink projected by inkjets, the amount of ink projected is greater for dark colors, which thus form a greater thickness on the surface of the card compared to light colors, which require less amount of ink projected.

[0095] The sprayed varnish makes it possible to compensate for the differences in thickness between the light and dark colors of the pattern produced by inkjet printing.

[0096] In order to obtain this homogenization at the level of the surface of the card, the printing process includes a step of implementing a pause period S4.

[0097] This pause period allows the varnish to spread over the surface of the card, at a speed depending on its viscosity.

[0098] Typically, a varnish used in inkjet printing must have a sufficiently low viscosity to ensure good fluidity and good passage through the printing nozzle 23.

[0099] Typically, the viscosity of the varnish used can be within a range of 1 to 20 cP (centipoise) and may vary depending on the chemical composition of the varnish. Preferably, a varnish with a viscosity between 1 and 5 cP is suitable for a pause time of less than 2 seconds.

[0100] Preferably, the pause period during the step of implementing a pause period S4 is at least equal to 0.5 seconds, and preferably greater than 0.8 seconds.

[0101] The minimum threshold value of 0.5 seconds allows the varnish to spread over the surface of the card and to fill the gaps existing at the level of the distinct colour portions printed in the pattern.

[0102] Preferably, in order not to slow down the card printing production, this pause period is less than 2 seconds. Indeed, lengthening the pause period has no noticeable effect on the uniformity and spreading of the varnish beyond a certain duration of the pause period and slows down the production rate without any benefit to the homogenization of the varnish on the card.

[0103] Finally, the printing process includes a polymerization step S5 of the ink and varnish by application of ultraviolet radiation to the surface of the card.

[0104] The polymerization step S5 is implemented by a high-power ultraviolet lamp 24 as schematically shown in the printing machine of [Fig.2].

[0105] The power of the ultraviolet radiation from the high-power ultraviolet lamp 24 implemented in this polymerization step S5 of the ink and varnish is substantially equal to 16 W.

[0106] The ultraviolet radiation power must be sufficient to allow homogeneous drying and complete curing or polymerization of the ink and varnish printed on the surface of the card.

[0107] The use of ultraviolet rays allows the inks and varnish applied to the surface of the card to dry almost instantaneously. The inks then dry by a photopolymerization process when exposed to ultraviolet light.

[0108] The S5 polymerization step allows good adhesion of the ink and varnish to the surface of the card and limits scratches or alteration of the pattern by abrasion during its use.

[0109] In particular, the power of the ultraviolet radiation of the S5 polymerization step of the ink and varnish is greater than that applied during the pre-polymerization step of the ink.

[0110] The beam of the high-power ultraviolet lamp 24 is also wide enough to cover the entire surface of the printed card and thus proceed to the polymerization of all points on the surface of the card.

[0111] As illustrated in [Fig. 2], the printing machine 20 may further comprise a scroll belt 25 enabling, during the implementation of the printing process as described above, the electronic smart card to be scrolled in a screw fashion. screws of the different print heads 21, 23 and ultraviolet lamps 22, 24 in a continuous card printing process.

[0112] The distance between the varnish printing head 23 and the high-power ultraviolet lamp 24 on the one hand, and the speed of movement of the scrolling mat 25 on the other hand, are determined relative to each other so as to ensure the pause period of at least 0.5 s, and preferably 0.8 s, between the varnish printing step S3 and the polymerization step S5.

[0113] Figures 3 to 5 illustrate, by way of example, electronic smart cards having on a surface a pattern printed by a printing process conforming to the printing process described above.

[0114] In figures 3 to 5, each card 30, 40, 50 has a pattern printed on its surface 30a, 40a, 50a.

[0115] A very schematically illustrated, purely for illustrative purposes, pattern comprising an elliptical image, formed of dots or pixels printed in dark or black color, and a triangular image, formed of dots or pixels printed in light color.

[0116] Typically, after the inkjet printing step of such a pattern, the thickness difference between the points of the darkest portions and the points of the lightest portions of the printed pattern is at least 0.015 pm.

[0117] The thickness difference, in micrometers, is defined as the difference between the highest thickness formed by the ink deposited on the surface of the card, obtained for the darkest points of the printed pattern, and the lowest thickness formed by the ink deposited on the surface of the card, obtained for the lightest points of the printed pattern.

[0118] This thickness difference is generally on the order of 0.020 pm, sometimes reaching 0.025 pm after the inkjet printing step of the pattern.

[0119] The printing process described above, with the printing by a print head of a varnish and the polymerization of the ink and varnish after a pause period, makes it possible to uniformize the thickness formed by the pattern printed on the surface of the card, and to limit the thickness variation.

[0120] The thickness difference is thus less than 0.010 pm. The surface texture of the card and the gloss appearance are thus uniformized.

[0121] The thickness difference is smaller the greater the amount of varnish deposited by the print head.

[0122] A card 30, 40, 50 has been illustrated as follows, by way of comparison to figures 3 to 5, after the implementation of the printing process described above, in which the quantity of varnish at the varnish printing step S3 varies between 175 and 255 (corresponding to a linear variation between approximately 2.5 and 4 drops of varnish per pixel).

[0123] The results are summarized below. Varnish Quantity Adjustment Maximum Thickness (pm) Minimum Thickness (pm) Thickness Difference (pm) Card 30 255 0.829 0.827 0.002 Card 40 200 0.822 0.819 0.003 Card 50 175 0.835 0.829 0.006

[0124] Thus, the thickness deviation, that is to say the difference in thickness of the pattern printed on the surface of each card 30, 40, 50, between a highest point and a lowest point of the pattern, is less than 0.010 pm.

[0125] Of course, the examples of implementation given above are by no means limiting, particularly with regard to examples of dimensions or materials.

[0126] In particular, the printing process may not include a pre-polymerization step.

[0127] In addition, each electronic smart card may have a pattern printed on its two opposite sides.

Claims

Demands

1. A method for printing a pattern on a surface of an electronic smart card by inkjet printing heads (21) to form a pattern in color on the surface of the card; - printing a varnish (S3) by a printing head (23) on said surface of the card; - implementation of a pause period (S4); and - polymerization (S5) of the ink and varnish by application of ultraviolet radiation to the surface of the card.

2. A printing method according to claim 1, characterized in that the colour pattern comprises at least two distinct colour portions.

3. A printing method according to one of claims 1 or 2, characterized in that the pause period is at least equal to 0.5 seconds, and preferably greater than 0.8 seconds.

4. A printing method according to any one of claims 1 to 3, characterized in that at the varnish printing step (S3), a uniformly distributed quantity is applied by the print head (23) onto the surface of the card.

5. A printing method according to claim 4, characterized in that at the step of printing a varnish (S3), the print head (23) is controlled by a print driver from a level value selected on a scale of levels between 0 and 255 corresponding respectively to an amount of varnish deposited by said print head (23) for each pixel printed, the amount of varnish deposited varying linearly between 0 drops at level 0 and 4 drops at level 255 and the selected value being at least equal to 155, and preferably greater than 175.

6. A printing method according to any one of claims 1 to 5, characterized in that it further comprises a pre-polymerization step (S2) of the ink before said varnish printing step (S3), by applying ultraviolet radiation to the colour pattern formed on the surface of the card.

7. A printing method according to claim 6, characterized in that the power of the ultraviolet radiation of the ink pre-polymerization step (S2) is less than the power of the ultraviolet radiation of said polymerization step (S5) of the ink and varnish.

8. A printing method according to claim 7, characterized in that the power of the ultraviolet radiation of the pre-polymerization step (S2) of the ink is less than 2 W, and preferably between 0.05 and 0.

10.

9. A printing method according to any one of claims 1 to 8, characterized in that the power of the ultraviolet radiation of said polymerization step (S5) of the ink and varnish is substantially equal to 16 W.

10. Electronic smart card having on a surface a pattern printed by a printing process according to any one of claims 1 to 9, characterized in that the difference in thickness of the pattern printed on the surface of said card, between a highest point and a lowest point of said pattern, is less than 0.010 pm.

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