Method for printing a surface of an electronic chip card
The method of inkjet printing with varnish application and UV polymerization addresses the uneven texture and gloss issues in smart cards, achieving a uniform surface finish by smoothing and stabilizing the ink and varnish layers.
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- IDEMIA FRANCE SAS
- Filing Date
- 2025-11-19
- Publication Date
- 2026-06-17
AI Technical Summary
Inkjet printing on electronic smart cards results in uneven surface texture and varying glossiness due to differences in ink deposition, with dark areas being thicker and shinier than light areas, leading to a non-uniform appearance.
A method involving inkjet printing followed by varnish application, a pause period, and UV polymerization to smooth the surface and uniformize the thickness and gloss, using controlled varnish deposition and UV radiation to stabilize the ink and varnish.
The method achieves a uniform surface texture and consistent glossiness across light and dark areas, reducing the thickness variation to less than 0.010 µm and ensuring a smooth, homogeneous finish.
Smart Images
Figure IMGAF001_ABST
Abstract
Description
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 design on at least one of its opposite sides, forming a decoration and allowing identification, for example, of the supplier or the intended use of the card.
[0005] A process for manufacturing a printed smart card with a raised visual effect is known from US patent 7,455,235 B2. This process involves applying metallic ink to a smart card surface, followed by partially coating the metallic ink with a varnish, thus creating a three-dimensional-looking inscription. The metallic ink and varnish are applied to the smart card surface using a screen-printing process. The varnish, applied in a viscous state, is cured using ultraviolet radiation.
[0006] The whole 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 issuer. 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 design on the surface of a digital smart card by implementing an inkjet printhead printer,
[0009] This is known as print-on-demand ( Drop on Demand(or DoD in Anglo-Saxon terminology).
[0010] Inkjet printing allows for 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 that 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 an uneven feel, with more ink being deposited to print the dark coloured portions of the pattern than that deposited to print the light coloured portions of the pattern.
[0013] Therefore, the dark colored portions are thicker and form an extra thickness compared to the light colored portions.
[0014] For example, we can observe 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 µm, which can reach 0.025 µm. DESCRIPTION OF THE INVENTION
[0015] The present invention aims to remedy all or part of the drawbacks 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] According to the invention, the printing process comprises the following steps: printing by inkjet printheads to form a colour pattern on the surface of the card; printing of a varnish by a printhead on said surface of the card; implementation of a pause period; and polymerization of the ink and varnish by application of ultraviolet radiation to the surface of the card.
[0018] Applying varnish to the surface of the card helps to at least partially erase the raised areas created on the surface of the card by inkjet printing.
[0019] The pause period allows the varnish to flow across the surface of the card into the holes or gaps created within the printed colour pattern, thus smoothing the surface of the card.
[0020] In practice, the colour pattern includes at least two distinct colour portions.
[0021] The varnish fills the gaps created between distinct color areas, that is, between areas printed with lighter ink and adjacent areas printed with darker ink. The varnish also spreads over the lighter-colored printed areas, which are thinner than the darker-colored printed areas.
[0022] In practice, the pause period is at least 0.5 seconds, and preferably greater than 0.8 seconds.
[0023] According to an advantageous feature, during the varnish printing stage, a uniformly distributed quantity is applied by the print head to the surface of the card.
[0024] The layer of varnish thus applied allows the creation of a uniform deposit over the entire surface of the card, before the varnish creeps to fill the gaps between the printed areas of different colors.
[0025] 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.
[0026] The Plaintiff 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.
[0027] According to an advantageous feature, the printing process further includes a pre-polymerization step of the ink before the said varnish printing step, by applying ultraviolet radiation to the colour pattern formed on the surface of the card.
[0028] The pre-polymerization step prevents the ink from spreading on the surface of the card and helps to limit the mixing of colors in order to obtain a sharp edge of the images or text of the printed color design.
[0029] In practice, the power of the ultraviolet radiation in the ink pre-polymerization stage is less than the power of the ultraviolet radiation in said ink and varnish polymerization stage.
[0030] During the polymerization stage, the radiation power is increased in order to obtain homogeneous drying and complete curing of the ink and varnish.
[0031] As an example, the power of the ultraviolet radiation of said ink and varnish polymerization step is approximately equal to 16 W.
[0032] In comparison, the power of the ultraviolet radiation in the ink pre-polymerization stage is less than 2 W, and preferably between 0.05 and 0.10 W.
[0033] 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.
[0034] 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 µm.
[0035] The texture of the printed surface of the card is thus uniform, with very limited embossing effects. In addition, the card surface with a varnish layer has a more uniform glossy finish, both for the light and dark areas of the printed design. BRIEF DESCRIPTION OF THE FIGURES
[0036] Other features and advantages of the invention will become apparent from the following non-limiting description.
[0037] The attached drawings are given as non-exhaustive examples: there figure 1 is an algorithm illustrating the steps of a printing process according to an embodiment of the invention; the figure 2 is a simplified diagram of an inkjet printing machine adapted to implement the printing process according to the invention; and the figure 3, figure 4 and figure 5schematically illustrate examples of electronic smart cards having on a surface a pattern printed by the printing process according to the invention. DETAILED DESCRIPTION OF THE INVENTION
[0038] We will first describe, with reference to the figure 1 an embodiment of an inkjet printing process for printing a pattern on the surface of an electronic smart card.
[0039] The term "electronic smart card" in the following description refers to any type of smart card, such as GSM (Global System for Mobile communications) cards, bank cards, access cards, etc. The present invention relates both to smart cards using contacts or magnetic strips to communicate with card reading terminals, and to those communicating by radio frequency waves, known as "contactless" smart cards.
[0040] The printing process described below is particularly well suited to printing designs customized according to the cardholder and / or provider.
[0041] Inkjet printing allows for the printing of a personalized design (text, image, diagram) on the surface of the card.
[0042] This is referred to as DoD printing (abbreviation of the Anglo-Saxon terminology). Drop on Demand ) for inkjet printing, from a digital data file configured according to the custom pattern to be printed.
[0043] The use of inkjet printing is well known and does not need to be described in detail here.
[0044] In particular, it is implemented using a printhead machine that allows edge-to-edge printing (E2E for " Edge to Edge(In Anglo-Saxon terminology), meaning that the printing extends to the very edges of the card, without leaving any white margins. This printing technique is also called borderless printing.
[0045] As illustrated in the figure 1 The printing process first includes an S1 printing step by inkjet print heads to form a colour pattern on the surface of the card.
[0046] The color pattern may include at least two, and usually multiple portions of distinct colors.
[0047] The portions of the pattern to be printed can be in black and white with different levels of grey, or in colours of various shades.
[0048] By referring to the figure 2 , an inkjet printing machine 20 is schematically illustrated, with four print heads 21.
[0049] 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 different colored ink reservoir. Each print head 21 is also heated to a temperature of approximately 60°C.
[0050] Inkjet printing, typically using CYMK printheads, is employed. This technology relies on spraying tiny droplets of ink onto a substrate, in this case the surface of the card, to reproduce images and text in color.
[0051] CYMK is an acronym for the four ink colors used: Cyan, Yellow, Magenta, and Key (black). These inks are precisely blended to create a wide range of colors. The 21 printheads contain numerous micro-nozzles that project the ink droplets. Each nozzle is individually controlled to regulate the volume and placement of the droplets, enabling detailed and accurate reproduction of color shades and gradients.
[0052] 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.
[0053] Each value on this numerical scale from 0 to 255 represents a certain amount of ink projected per pixel.
[0054] 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).
[0055] This print driver allows precise control of the size and density of ink droplets deposited on the media, which is crucial for achieving accurate colors and image details.
[0056] The printing stage of an S1 image is thus controlled by software, which translates the digital information of the pattern to be printed into ink levels to be applied, and sends corresponding commands to each print head via the print driver.
[0057] 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.
[0058] 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.
[0059] This S2 pre-polymerization step is implemented to solidify and / or partially dry the ink immediately after it is deposited on the surface of the card.
[0060] This process is also called "pinning" in Anglo-Saxon terminology and allows 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.
[0061] As illustrated in the figure 2 , the inkjet printing machine 20 includes an ultraviolet radiation lamp 22 to perform this pre-curing of the ink on the surface of the card.
[0062] The ultraviolet radiation lamp 22 is of low power or intensity, sufficient to slightly fix the ink but without polymerizing or drying it completely.
[0063] 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.
[0064] 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 linear adjustment between 0 and 2 W.
[0065] The value of 10, corresponding to 20 / 255 W, or 0.078 W, can therefore be selected.
[0066] The processing time is also relatively short to prevent the ink from fully curing on the card. The pre-polymerization stage is very brief and allows the ink to dry through localized drying on the card surface.
[0067] In practice, the card is moved continuously under ultraviolet radiation which is localized over a very small width.
[0068] The S2 pre-polymerization step prevents the ink from spreading and the colors from mixing, in order to maintain sharper edges of the printed pattern.
[0069] The printing process also includes an S3 printing step of a varnish by a print head onto the surface of the card.
[0070] The S3 varnish printing step is implemented after the S2 ink pre-polymerization step.
[0071] As illustrated in the figure 2, a varnish print head 23, similar to the print heads 21 for inkjet, is implemented in the inkjet printing machine 20.
[0072] The varnish print head 23 is also controlled by a print driver in the same way as the inkjet print heads 21.
[0073] 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.
[0074] 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.
[0075] In practice, during the S3 varnish printing stage, a uniformly distributed quantity is applied by the varnish print head 23 to the surface of the card.
[0076] Thus, the same amount of varnish is sprayed for each pixel of the pattern printed on the card.
[0077] In practice, the selected value is at least equal to 155, and preferably greater than 175, for each pixel of the printed pattern.
[0078] This selection thus corresponds roughly to the projection of at least 2.5 drops of varnish per pixel.
[0079] This minimal amount of varnish allows for a uniform distribution of the varnish on the surface of the card and prevents 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.
[0080] 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.
[0081] This maximum threshold value of 255, corresponding to 4 drops of varnish, limits the total amount of varnish on the card's surface, thus minimizing the varnish overspray and, consequently, the overall thickness of the card after printing. This maximum threshold value also helps limit the additional production costs associated with using varnish.
[0082] As an example, the varnish used may be a varnish marketed by the American company Entrust ®< for DoD printing.
[0083] In general, a varnish with a viscosity between 1 and 5 cP (centipoise) is suitable for this step of printing an S3 varnish.
[0084] Spray varnish compensates for the raised areas created when printing a design using inkjet technology and evens out the gloss of the printed surface.
[0085] 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).
[0086] 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.
[0087] The sprayed varnish makes it possible to compensate for the differences in thickness between the light and dark colors of the pattern created by inkjet printing.
[0088] In order to achieve this homogenization at the surface level of the card, the printing process includes a step of implementing a pause period S4.
[0089] This pause period allows the varnish to spread over the surface of the card, at a speed that depends on its viscosity.
[0090] Typically, a varnish used in inkjet printing must have a fairly low viscosity to ensure good fluidity and good passage through the printing nozzle 23.
[0091] Typically, the viscosity of the varnish used can range from 1 to 20 cP (centipoise) and may vary depending on the varnish's chemical composition. Preferably, a varnish with a viscosity between 1 and 5 cP is suitable for a dwell time of less than 2 seconds.
[0092] Preferably, the pause period during the implementation step of a pause period S4 is at least 0.5 seconds, and preferably greater than 0.8 seconds.
[0093] The minimum threshold value of 0.5 seconds allows the varnish to spread over the surface of the card and fill the gaps existing at the level of the distinct colour portions printed in the design.
[0094] Preferably, to avoid slowing down card printing production, this pause period should be less than 2 seconds. Indeed, extending the pause period has no noticeable effect on the uniformity and spreading of the varnish beyond a certain duration and slows down the production rate without improving the varnish's homogenization on the card.
[0095] Finally, the printing process includes an S5 polymerization step of the ink and varnish by applying ultraviolet radiation to the surface of the card.
[0096] The S5 polymerization step is implemented by a high-power ultraviolet lamp 24 as schematically shown in the printing machine of the figure 2 .
[0097] The power of the ultraviolet radiation from the high-power ultraviolet lamp 24 implemented in this S5 polymerization step of the ink and varnish is approximately equal to 16 W.
[0098] The ultraviolet radiation power must be sufficient to allow for homogeneous drying and complete curing or polymerization of the ink and varnish printed on the surface of the card.
[0099] The use of ultraviolet rays allows the inks and varnish applied to the card surface to dry almost instantly. The inks dry through a photopolymerization process when exposed to ultraviolet light.
[0100] The S5 polymerization step ensures good adhesion of the ink and varnish to the surface of the card and limits scratches or alteration of the design by abrasion during use.
[0101] In particular, the power of the ultraviolet radiation in the S5 polymerization step of the ink and varnish is greater than that applied during the pre-polymerization step of the ink.
[0102] The high-power ultraviolet lamp beam 24 is also wide enough to cover the entire surface of the printed card and thus polymerize all points on the surface of the card.
[0103] As illustrated in the figure 2 , the printing machine 20 may further include a scrolling conveyor 25 which, when implementing the printing process as described above, allows the electronic smart card to be scrolled past the various print heads 21, 23 and ultraviolet lamps 22, 24 in a continuous card printing process.
[0104] 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 conveyor belt 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.
[0105] We have illustrated as examples electronic smart cards having on a surface a pattern printed by a printing process conforming to the printing process described previously.
[0106] On the figures 3 to 5 , each card 30, 40, 50 has a pattern printed on its surface 30a, 40a, 50a.
[0107] We have illustrated very schematically, and for purely illustrative purposes, a 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.
[0108] 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 µm.
[0109] Thickness variation, 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.
[0110] This thickness difference is generally on the order of 0.020 µm, sometimes reaching 0.025 µm after the inkjet printing stage of the pattern.
[0111] The printing process described above, with the printing of a varnish by a print head 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.
[0112] The thickness difference is therefore less than 0.010 µm. The surface texture of the card and the gloss appearance are thus uniformized.
[0113] The thickness difference is smaller when the amount of varnish deposited by the print head is greater.
[0114] This was illustrated, by way of comparison to figures 3 to 5 , a card 30, 40, 50 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).
[0115] The results are summarized below. Adjusting the amount of varnish Maximum thickness (µm) Minimum thickness (µm) Thickness difference (µm) Map 30 255 0.82 9 0.82 7 0. 002 Map 40 200 0.82 2 0.81 9 0. 003 Card 50 175 0.83 5 0.82 9 0. 006
[0116] Thus, the thickness difference, 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 µm.
[0117] Of course, the examples of implementation given above are by no means exhaustive, particularly with regard to examples of dimensions or materials.
[0118] In particular, the printing process may not include a pre-polymerization step.
[0119] In addition, each electronic smart card can have a pattern printed on its two opposite sides.
Claims
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 coloured pattern includes at least two distinct coloured portions.
3. A printing method according to claim 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 thatIn the varnish printing step (S3), a uniformly distributed quantity is applied by the print head (23) onto the surface of the card.
5. Printing method according to claim 4, characterized in that In the varnish printing step (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 a quantity of varnish deposited by said print head (23) for each printed pixel, the quantity 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 thatIt also includes 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. Printing method according to claim 6, characterized in that the power of the ultraviolet radiation of the pre-polymerization step (S2) of the ink is less than the power of the ultraviolet radiation of said polymerization step (S5) of the ink and varnish.
8. 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 approximately equal to 16 W.
10. Electronic smart card having on one 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 µm.