Inkjet printer for printing on cards

Abstract

The present invention relates to the field of inkjet printing technology. The present invention provides an inkjet printer (1) for printing on cards, said inkjet printer (1) comprising a printer frame comprising a base frame (2), a support carriage (5) mounted to the base frame (2) for supporting a card (19) to be printed, a print station (9) mounted to the printer frame and comprising at least one printhead (11) for inkjet printing on a top surface of the card (19), and an ion generator (30) mounted to the printer frame for emitting charged ions which can be directed to the top surface of the card (19).

Description

Field of the Invention

[0001]

[0001] The present invention relates to the field of inkjet printing technology, and more particularly to an inkjet printer for printing on cards, and more specifically to an inkjet printer for printing on cards made of plastic materials such as credit cards, smart cards, magnetic cards, etc. Background of the Invention

[0002]

[0002] As is known, credit cards, smart cards, magnetic cards, etc. usually have logos, images, trademarks that help the user identify the purpose of the card and distinguish each card from other cards. U.S. Patent No. 6,478,485 discloses a process and apparatus for decorating articles that can be cards.

[0003]

[0003] Furthermore, European Patent No. 2,658,723, European Patent No. 2,658,721, European Patent No. 2,658,722, and European Patent No. 2,718,109, which can be considered useful sources of information regarding the present invention, disclose and exemplify some detailed characteristics of inkjet printers for printing on cards extensively and thoroughly.

[0004]

[0004] Figures 1 and 2 show an inkjet printer 1 for printing on cards known in the prior art. As shown in Figures 1 and 2, the inkjet printer 1 has a base frame 2. Preferably, a storage zone 3 for storing one or more cards 4 is located on the base frame 2. Preferably, the inkjet printer 1 may be provided with a support carriage 5 to which a plate-shaped tray 6 is attached. The plate-shaped tray 6 receives cards to be printed from the storage zone 3 and holds the cards on it. The plate-shaped tray 6 may be provided with a tray heater 7 embedded in the plate-shaped tray 6 and used to heat the cards held on the tray. The support carriage 5 moves the cards held on it within the inkjet printer 1. More specifically, the support carriage 5 is located on a guide plate 20 attached to the base frame 2 and is guided along the guide plate 20. More specifically, the support carriage 5 receives cards to be printed from the card storage zone 3 by an extraction station or drawer station 8 and moves the cards held on it along the guide plate 20. The guide plate 20 moves such cards to the printing station 9 so that they can be inkjet printed by the printing station 9. The cards can then also be carried to the ejection station 10 using the guide plate 20 and the support carriage 5, where they are moved away from the inkjet printer 1 and received in a suitable container.

[0005]

[0005] The printing station 9 comprises at least one print head 11 for inkjet printing onto a card. The printing station 9 comprises a drive system (not shown) configured to move the print head 11 back and forth along a predetermined path, thereby enabling the print head 11 to eject ink onto the card during a series of steps adjusted by a appropriately configured adjustment unit (not shown). Preferably, the print head 11 is slidably mounted on a support plate 12. In a preferred embodiment, the support plate 12 is lateral, and in particular perpendicular, to the movement path of the support carriage 5 or the guide plate 20.

[0006]

[0006] The drawer station 8 is configured to draw cards 4 from the storage zone 3. The drawer station 8 removes cards 4 one by one from the storage zone 3 and places them on the support carriage 5. The cards 4 are then moved along the guide plate 20 to the printing station 9, where an inkjet printing operation is performed by controlled ejection of ink onto the top surface of the cards. After inkjet printing, the cards 4 are moved toward the ejection station 10. The ejection station 10 is configured to move the cards 4 away from the support carriage 5 and, preferably, to land the cards 4 in a container.

[0007]

[0007] The drawer station 8 is shown in more detail in Figure 3 and Figure 4, which is a cross-section along line IV-IV in Figure 3. The drawer station 8 comprises at least one main roller 13 that can contact the first card at the lower end of a stack of cards 4 in the storage zone 3 in order to draw the first card out of the storage zone 3 to become a drawn card 19 to be printed. Preferably, the main roller 13 is rotatably mounted to the base frame 2 below the storage zone 3 so that the weight of the stack of cards 4 helps to keep the first card in contact with the main roller 13. In a preferred embodiment, an auxiliary weight is placed at the upper end of the stack of cards 4 to give an additional component to the force pushing the first card in contact with the main roller 13.

[0008]

[0008] The drawer station 8 further comprises several auxiliary rollers 14, 15, 16, 17 and 18 mounted downstream of the main roller 13 to engage with the extracted card 19 as it moves forward due to its interaction with the main roller 13, and to land it on a plate tray 6 mounted on the upper end of the support carriage 5. More precisely, the auxiliary rollers 14-18 receive the extracted card 19 coming from the main roller 13 and are positioned to move the extracted card 19 forward in the direction indicated by arrow F1 in Figure 3 so that the card can be processed for printing. Figure 5 shows that the extracted card 19 is already positioned on the support carriage 5 and movable along the guide plate 20 immediately after it exits the auxiliary rollers 17 and 18 of the drawer station 8.

[0009]

[0009] The auxiliary rollers 14-18 define a reference plane substantially parallel to the plane of the plate tray 6 when the function performed by the ejection station 8 is to supply cards for printing. Under certain conditions, the ejected card 19 is not sent to the plate tray 6 attached to the support carriage 5 for printing, in which case the auxiliary rollers 14-18 are moved by a suitable mechanism (not shown) so that the reference plane defined by the auxiliary rollers is inclined, and the ejected card 19 is moved toward output along the direction indicated by arrow F2 in Figure 4. The configuration of the ejection station 8 shown in Figure 4 refers precisely to this auxiliary ejection function. However, Figure 4 is primarily intended to detail the position of the ejected card 19 held by the auxiliary rollers 14-18.

[0010]

[0010] During the pull-out process, some friction occurs between the pulled-out card 19 and the main roller 13 and auxiliary rollers 14-18. Due to the triboelectric effect, the pull-out process can cause the pulled-out card 19, which is generally made of a dielectric material, i.e., an electrically insulating material, to become charged. The generated charge cannot move freely across the entire top surface of the card, but rather tends to adhere randomly to the pulled-out card 19 with an unpredictable distribution across the entire top surface of the pulled-out card 19.

[0011]

[0011] Furthermore, the source of triboelectric charging is not solely attributable to friction with the main roller 13 and auxiliary rollers 14-18. In fact, even a brief handling of the card 4, made of dielectric material, before loading it into the storage zone 3 can generate some unbalanced charge on the top surface of the card. In summary, as shown in Figure 5, when the extracted card 19 is placed on the support carriage 5 and ready for printing, it is very likely that an unbalanced and unpredictable distribution of charge has been established across the entire top surface of the extracted card 19. Figure 6 shows the support carriage 5 holding the extracted card 19 and moving along a guide plate (not shown) toward the printing station 9 in the direction indicated by arrow P.

[0012]

[0012] The printing station 9 performs the printing operation by at least one print head 11 slidably mounted on a support plate 12. The print head 11 is provided with a plurality of nozzles, all of which are electrically actuated in a controlled manner to produce the ejection of ink droplets from predetermined nozzles, and the ink droplets are directed toward predetermined positions on the upper surface of the removed card 19. As is well known to those skilled in the art, during and after ejection, ink droplets may undergo fragmentation into a plurality of smaller parts due to the dynamics of ejection. This situation is shown in Figure 7, in which case nozzle 21 ejects a small portion of the ink 22 contained in the print head 11 in the form of ink droplets 23. More frequently, there is a large main droplet 24 with a large mass and a considerable velocity, followed by a plurality of smaller, often slower droplets, often called ancillaries 25. Some of the ancillaries 25 are made up of many micrometer and submicrometer droplets, with very small mass and low velocity, and are often called aerosols 26. Simply put, each ejection from the determined nozzle will produce multiple ink droplets with different masses and velocities.

[0013]

[0013] It is easy to understand that the movement of different ink droplets can be influenced in various ways by possible perturbations. In fact, the heaviest and fastest droplets, i.e., the main droplets 24 with high momentum, follow a trajectory that is hardly disturbed and hardly perturbed. In contrast, the smallest and slowest droplets, especially the aerosol 26, tend to deviate from their paths easily due to some possible perturbations because of their low momentum. In other words, ink droplets with high momentum tend to hit the printing medium, which means the top surface of the removed card 19 at an expected predetermined position, while ink droplets with low momentum are more strongly affected by perturbations. In particular, the aerosol 26, which consists of the smallest ink droplets that have very low velocities and often scatter all around under perturbations, frequently reaches unpredictable positions on the top surface of the removed card 19, away from the predetermined landing points of the main droplets 24 generated during the same ejection.

[0014]

[0014] Among the possible perturbants, the most frequent cause is airflow. The presence of a fan, whose effect may even reach the printing area, or simply the back-and-forth motion of the print head and support carriage, can act as a perturbant, and its effect on ink droplet motion depends on the perturbation strength and the amount of ink droplet motion.

[0015]

[0015] Another important perturbant that can affect the movement of ink droplets is the electric field that may exist around the print head, particularly in the space between the nozzle and the printing medium, i.e., the removed card, and this electric field creates the trajectory of the ink droplets. The electric field acts on the removed card, which has a net charge, either attractively or repulsively, depending on the polarity of the charge. Furthermore, because the material contains positively and negatively charged components, even if the net charge is zero, the electric field can displace the positive and negative charges of the material in different directions, causing so-called polarization. As is well known to those skilled in the art, if the electric field has a non-zero gradient, i.e., if the electric field is spatially non-uniform, the polarized material may experience a force from the electric field even if the net charge is zero.

[0016]

[0016] In most cases, the liquid ink contained in the print head exhibits some conductivity and may contain charged components that have some mobility within the liquid ink. Thus, the liquid ink may be subject to the action of an electric field, and the movement of the ink droplets may be affected by the electric field established in the space between the nozzle and the printing medium, i.e., the removed card.

[0017]

[0017] The electric field has different effects on the fragmented parts of the ejected ink due to the diverse mass and charge distribution between the ink droplets. In particular, the motion of the aerosol tends to be strongly influenced by electrical perturbations due to the small mass of the small ink droplets it comprises.

[0018]

[0018] For example, as shown in U.S. Patent No. 5,774,141 and U.S. Patent No. 7,824,008, many attempts have been made to solve the problem of electrical perturbations in inkjet printers, in which the collection or ejection of charged stray ink droplets is performed by further electrically biased parts distributed near the print head and printing area. However, printing defects that occur in some unpredictable way during card printing using an inkjet printer remain a troublesome drawback that requires more specific handling.

[0019]

[0019] More specifically, after printing, some cards appear smudged. That is, ink spots are spread across the entire intended image. This means that small ink droplets have scattered around the predetermined points of impact. This effect is often called mist and is particularly severe and frequent at the boundaries between densely and loosely printed areas, or even in areas that are not printed at all. This situation is illustrated in Figures 8a and 8b, where the intended printed image 27 in Figure 8a is compared to the actual printed image 28 in Figure 8b, and the actual printed image 28 shows false ink spots 29 outside the intended image boundary.

[0020]

[0020] When artifacts on printed cards are observed at high magnification, it can be seen that most of them consist of very small spots of ink, which are likely to be generated by aerosol deflection from their trajectory. Furthermore, there is evidence that the cards are often charged, due to the drawing process and possibly due to previous card handling. The establishment of some charge, which is unevenly distributed across the entire top surface of the card, can be shown using appropriate equipment such as a static meter. Thus, it seems reasonable to consider that the cause of the ink spots on the card is due to an electric field.

[0021]

[0021] On the other hand, the conductivity of the ink appears to play a role in the most frequent distribution of artifacts at the boundary between densely printed and sparsely printed areas. In fact, while the ejected ink is still liquid on the top surface of the card, the charged components of the ink are rearranged, thereby somewhat mitigating the localized static charge on the top surface of the card. Such an effect may be more effective in densely printed areas, but the mitigation is insufficient in sparsely printed areas.

[0022]

[0022] While we do not wish to be bound by theory, it is conceivable that a strong gradient of the electric field, heightened by the non-uniformity of the surface charge distribution, could generate a deflection force with a significant component parallel to the surface. Such non-uniformity can be established due to different local charge relaxation effects resulting from different ink distributions. According to this idea, multiple small ink droplets constituting an aerosol could be easily polarized and deflected by a non-uniform electric field, landing far from predetermined positions on the card.

[0023]

[0023] In order to mitigate electrical perturbations, and in particular to reduce the intensity of the electric field gradient, some form of neutralization of the charge effect should be assumed. For example, a support carriage on which a card is placed during printing may have an uppermost grounded conductive layer in contact with the bottom surface of the card. However, this solution is not very effective in shielding the electrostatic field on the top surface of the card, which is the ink-impact surface, due to the thickness of the card. [Overview of the project]

[0024]

[0024] In order to solve the above technical problems, the present invention provides an inkjet printer in which an ion generator is positioned to deliver additional charges, specifically some charged ions, directly onto the top surface of the card to be printed, in order to compensate for the effects of previous existing static charges on the top surface of the card and to solve the problem of ink aerosols scattering at undesirable locations on the card, thereby eliminating the problem of mist.

[0025]

[0025] Specifically, the present invention provides an inkjet printer for printing on a card, the inkjet printer comprising a printer frame having a base frame, a support carriage attached to the base frame for supporting the card to be printed, a printing station attached to the printer frame for inkjet printing on the upper surface of the card and comprising at least one print head, and an ion generator attached to the printer frame for emitting charged ions that can be sent to the upper surface of the card. Preferably, the ion generator is operated before and during printing with a variable duty cycle and variable intensity.

[0026]

[0026] Preferably, the ion generator is an air ionizer that alternately emits positive charged ions and negative charged ions.

[0027]

[0027] Preferably, the polarity of the emitted charged ions changes in a predetermined time period so that the positive charged ions and the negative charged ions are not neutralized with each other before reaching the upper surface of the card.

[0028]

[0028] Preferably, the ion generator is a unipolar ion generator for emitting charged ions having a specific polarity, and the charged ions can reach the upper surface of the card by diffusion.

[0029]

[0029] Preferably, the unipolar ion generator comprises an ion generator case having an opening allowing the generated charged ions to flow out, a pair of electrodes housed in the ion generator case, and a pair of electrical terminals, one for each electrode, connected to an ion generator power module mounted on the inkjet printer.

[0030]

[0030] Preferably, the inkjet printer comprises a mounting bracket for mounting the ion generator, and the mounting bracket is fixed to the base frame.

[0031] Preferably, the printer frame further includes a top frame connected to the base frame by a plurality of side frames, and the ion generator is fixed to the top frame.

[0032] Preferably, the inkjet printer further includes a guide plate, the support carriage is disposed on the guide plate and guided by the guide plate to move between a first position where the support carriage does not face the printer head and a second position where the support carriage faces the printer head, the printing station can move horizontally with respect to the guide plate above the guide plate, and the ion generator is out of the moving path of the printing station.

[0033] Preferably, the orthographic projection of the ion generator on the base frame coincides with the center of the orthographic projection of the support carriage on the base frame when the support carriage is in the second position.

[0034] Preferably, the inkjet printer further includes a storage zone for storing at least one card to be printed and a withdrawal station for withdrawing the card from the storage zone to the support carriage.

[0035] According to the solution of the present invention, charged ions released by an ion generator in an inkjet printer are sent to the upper surface of the card to be printed to compensate for the influence of previous existing static charges on the upper surface of the card and avoid a significant presence of mist on the printed surface, that is, avoid a significant presence of false ink spots across the entire printed image.

[0036] Non-limiting and non-exhaustive embodiments of the present invention will be described by way of example with reference to the following drawings.

Brief Description of the Drawings

[0037] [Figure 1]The left-hand schematic perspective view shows a conventional inkjet printer for printing on cards. [Figure 2] Figure 1 shows a schematic perspective view of the right side of the inkjet printer. [Figure 3] Figure 1 shows a schematic perspective view illustrating the storage zone and drawer station of the inkjet printer. [Figure 4] Figure 3 shows a cross-sectional view along line IV-IV. [Figure 5] A partial schematic perspective view is shown, illustrating the support carriage that holds the removed card. [Figure 6] Figure 1 shows a schematic perspective view of the printing station for the inkjet printer. [Figure 7] This diagram shows a schematic representation of ink droplets ejected by the printhead nozzles. [Figure 8a] Shows the intended print image. [Figure 8b] Figure 1 shows an actual printout image printed by an inkjet printer, where false ink spots exist outside the intended print image boundary. [Figure 9] A schematic perspective view of an inkjet printer according to one embodiment of the present invention is shown. [Figure 10] Figure 9 shows a schematic perspective view of a unipolar generator in an inkjet printer. [Figure 11] Figure 9 shows a top view of the inkjet printer. Detailed description of the embodiment

[0038]

[0049] To further clarify the above and other features and advantages of the present invention, the invention will be described in conjunction with the following accompanying drawings. It should be understood that the specific embodiments of the present invention are illustrative and not limiting.

[0039]

[0050] The present invention provides an inkjet printer in which an ion generator is positioned to directly deliver additional charges, specifically some charged ions, onto the top surface of a card to be printed on, in order to compensate for the effects of any prior existing static charges on the top surface of the card.

[0040]

[0051] Figure 9 shows a schematic perspective view of an inkjet printer 1 according to one embodiment of the present invention. The inkjet printer 1 is used for printing on cards such as credit cards, smart cards, and magnetic cards. Preferably, the card contains or is formed from a thermoplastic material. In particular, the thermoplastic material may be selected from the group including polyvinyl chloride (PVC), polyvinyl chloride (PVC) filled with mineral fillers, laminated polyvinyl chloride (PVC), acrylonitrile-butadiene-styrene (ABS) terpolymer, polyethylene terephthalate (PET), glycol-modified polyethylene terephthalate (PET-G), and polylactic acid (PLA). Laminated polyvinyl chloride is formed by a core layer of polyvinyl chloride filled with mineral fillers and a pair of transparent polyvinyl chloride films attached to each surface of the core layer. Furthermore, the card preferably has a substantially plate-like shape and, in plan view, has a substantially rectangular shape with two large sides and two small sides.

[0041]

[0052] As shown in Figure 9, the inkjet printer 1 includes a printer frame comprising at least a base frame 2. Furthermore, although not shown and not required, the printer frame may further include a top frame connected to the base frame 2 by a plurality of side frames. Specifically, the lower ends of the plurality of side frames are connected to the base frame 2, and the upper ends of the plurality of side frames are connected to the top frame, thereby forming a housing space in which various components of the inkjet printer 1 are housed.

[0042]

[0053] As shown in Figure 9, the inkjet printer 1 further comprises a support carriage 5 for supporting a card to be printed, and a printing station 9 for inkjet printing on the top surface of a card, the printing station 9 having at least one print head 11 for ejecting ink droplets onto the top surface of the card as needed. A card supported on the support carriage 5 can be removed or pulled out from a storage zone 3 for storing at least one card to be printed by a removal station or pull-out station 8, as described above in relation to Figures 1 to 6. Thus, in the embodiment shown in Figure 9, a card supported on the support carriage 5 can also be referred to as a removed card 19. The support carriage 5 is mounted on a base frame 2. The support carriage 5 may be mounted directly on the base frame 2, i.e., the support carriage 5 may be fixed to the base frame 2. The support carriage 5 may be mounted indirectly to the base frame 2. For example, in the embodiment shown in Figure 9, the support carriage 5 may be positioned on a guide plate 20 mounted on the base frame 2. The support carriage 5 is guided by the guide plate 20 and moves between a first position in which the support carriage 5 does not face the printer head 11 and a second position in which the support carriage 5 faces the printer head 11. The “first position” may also be called the initial position or receiving position for receiving the ejected card 19 onto the support carriage 5, and the “second position” may also be called the printing position for inkjet printing on the upper surface of the ejected card 19. The printing station 9 is mounted on the printer frame. Specifically, in the embodiment shown in Figure 9, the printing station 9 is mounted on a support plate 12 which is fixed to the base frame 2. The printing station 9 may also move laterally, preferably perpendicularly, with respect to the guide plate 20 or the movement path of the support carriage 5 above the guide plate 20. Specifically, the print head 11 is slidably mounted on the support plate 12 which is laterally, particularly perpendicular, to the movement path of the support carriage 5 or the guide plate 20.

[0043]

[0054] As mentioned above, when the removed card 19 is placed on the support carriage 5 in a ready-to-print state, there is a very high probability that an unbalanced and unpredictable distribution of charge has been established across the entire top surface of the removed card. To resolve or at least mitigate this unbalanced and unpredictable distribution of charge across the entire top surface of the removed card 19, an ion generator 30 is provided in the inkjet printer 1 to release charged ions that can be sent onto the top surface of the removed card 19. The ion generator 30 is mounted on the printer frame. The ion generator 30 may be mounted directly to the printer frame. For example, the ion generator 30 may be fixed to the top frame of the printer frame. Alternatively, the ion generator 30 may be mounted indirectly to the printer frame. For example, the ion generator 30 may be mounted to the printer frame by a mounting bracket 35 fixed to the base frame 2. Specifically, the mounting bracket 35 comprises a vertical support 36 fixed to the base frame 2 and extending upward from the base frame 2, and a horizontal support 37 connected to the upper end of the vertical support 36 and extending substantially horizontally, and the ion generator 30 is fixed to the horizontal support 37.

[0044]

[0055] As a first approach, an air ionizer that alternately emits positively charged and negatively charged ions can be employed as the ion generator 30. The negatively charged and positively charged ions emitted by the air ionizer can neutralize most of the existing static charge on the top surface of the extracted card 19, as the top surface of the extracted card 19 rejects charged ions of the same polarity and attracts charged ions of the opposite polarity until some charge balance is reached on the top surface of the extracted card 19. In one embodiment, the positively charged and negatively charged ions are delivered to the top surface of the extracted card 19 via a gas stream. The gas stream can help push the positively charged or negatively charged ions apart before ions of the opposite polarity are generated, preventing the emitted alternative charged ions from neutralizing each other before reaching the top surface of the extracted card 19. The gas stream may be an air stream, and for example, a fan may be provided to provide the air stream. In some cases, different gases may be used to form the gas stream. Furthermore, the polarity of the emitted charged ions changes over a predetermined period, usually a few seconds, for example, 1-2 seconds, so that alternative charged ions can flow to match the actual charge distribution on the top surface of the removed card 19, thereby further preventing the emitted alternative charged ions from neutralizing each other before reaching the top surface of the removed card 19. Such a long period can reduce the print yield of the inkjet printer 1. Moreover, despite the neutralization of the charge on the top surface of the removed card 19, and thus compensation of the electric field on the top surface of the removed card 19, the gas flow carrying the alternative charged ions can represent a perturbation of the ink droplet behavior.

[0045]

[0056] A more preferred approach is to provide a unipolar ion generator, i.e., a single-polarity ion generator, as the ion generator 30 in the inkjet printer 1, for releasing charged ions with intrinsic polarity that can reach the top surface of the card 19 extracted by diffusion without using a gas flow. As shown in Figures 9 and 10, the unipolar ion generator comprises an ion generator case 31, a pair of electrodes (not shown), and a pair of electrical terminals 33. The ion generator case 31 is provided with an opening 32 to allow the generated charged ions to spread and flow out into the surrounding space. The electrodes are housed within the ion generator case 31. Two electrical terminals 33, one for each electrode, are connected to an ion generator power module (not shown) mounted in the inkjet printer 1. The generated charged ions 34, with their intrinsic polarity, can be positive (as shown in Figure 10) or even negative, depending on the configuration of the unipolar ion generator. Because the charged ions 34 have intrinsic polarity, there is no risk of "ion neutralization". In this situation, the charged ions 34 can reach the upper surface of the card 19, which has been extracted by diffusion without the use of a gas flow, and therefore there is no perturbation caused by a gas flow.

[0046]

[0057] The charged ions 34, each possessing a unique polarity, can hardly bring about a charge balance on the top surface of the removed card 19. Instead, they neutralize the previously existing static charge on the top surface of the removed card 19. However, the generated charged ions 34 have different collision velocities from point to point, depending on the distribution of the previously existing static charge. For example, suppose there is a non-uniform charge distribution across the entire top surface of the removed card 19. Specifically, suppose there are positively charged and uncharged regions across the entire top surface of the removed card 19, and the generated charged ions 34 are also positive. Because the electric field is stronger in the charged regions, the generated positively charged ions 34 are easily rejected when approaching the charged regions on the top surface of the removed card 19 (some of the generated charged ions 34 may reach the top surface of the removed card 19 at a very slow speed). In contrast, in the uncharged regions, the collision velocities of the generated positively charged ions 34 remain high, and the top surface of the uncharged regions tends to gradually acquire a positive charge. If the positive charge density is low (fewer ions are rejected), the collision velocities are expected to be higher, so the tendency is to reach a balanced state with a more uniform positive charge distribution across the entire top surface of the extracted card 19. Alternatively, assume that there are negatively charged and uncharged regions across the entire top surface of the extracted card 19, and that the generated charged ions 34 are still positive. The generated charged ions 34 have higher collision velocities in the negatively charged region than in the uncharged region (because they are attracted to it). Thus, the negatively charged region loses negative charge more rapidly than the uncharged region accumulates positive charge. The final result is the same, with some uniform positive charge established across the entire top surface of the extracted card 19. It can be understood that reversing the polarity of the generated charged ions 34 does not affect the final uniformity of charge on the top surface of the extracted card 19, and the final state is simply a uniform negatively charged surface. In any case, the overall effect of these charged ions 34 is likely to be a reduction in the gradient value across the entire top surface of the removed card 19, even though the net charge is not neutralized.In other words, the released charged ions can generate a more uniform charge distribution on the top surface of the card, and therefore a more uniform electric field near the top surface of the card, without neutralizing the card itself. Thus, the unipolar ion generator attached to the inkjet printer 1 may be either a positive ion generator or a negative ion generator, without affecting the efficiency of the solution.

[0047]

[0058] Figure 11 is a top view of the inkjet printer 1 shown in Figure 9. As is clearly visible from Figure 11, the ion generator 30 is positioned away from the movement path of the printing station 9, thereby preventing any mechanical interference with the moving print head 11 of the printing station 9. Furthermore, the orthographic projection of the ion generator 30 within the base frame 2 is offset from the periphery of the extracted card 19 when the extracted card 19 is placed in the printing position. Moreover, since the generated charged ions can cover a certain distance, the ion generator 30 does not need to be too close to the extracted card 19 or coincide with the center of the extracted card 19 in order to effectively perform its function, as can be seen from Figure 11. Naturally, it is preferable that the orthographic projection of the ion generator 30 onto the base frame 2 coincides with the center of the orthographic projection of the support carriage 5 or the extracted card 19 within the base frame 2 when the support carriage 5 is in the second position. This is because the symmetrical positioning of the ion generator 30 provides a more uniform effect.

[0048]

[0059] The ion generator 30 can optionally be operated before and during printing with a variable duty cycle and variable intensity. According to one embodiment, when the ion generator 30 is operated with a variable duty cycle, the ion generator 30 is operated during some printing sequences and not during others. For example, in multilayer printing mode, the ion generator 30 may be active during the printing of the entire layer, or only during a subset of the layers, depending on the geometric layout of the printer module, the card material, the ink composition, etc., in order to obtain maximum charge uniformity without causing electrostatic adhesion of the card due to an excessive amount of charge on the top surface of the card. As an example, during printing of a card with only 4 layers, the duty cycle of the ion generator 30 can be 100%, meaning the ion generator 30 is always on, while with 16 layers, the duty cycle of the ion generator 30 can be in the range of 25% to 50%. For example, in a 16-layer design, the ion generator 30 can operate during the printing of the first layer of a group of four layers, and is turned off during the subsequent three layers. This sequence is repeated four times in this example.

[0049]

[0060] According to one embodiment, when the ion generator 30 is activated, it generates an ion flux, which includes the generated charged ions 34. When the ion generator 30 is operated at a variable intensity, the ion flux is variable, i.e., the number of ions 34 generated changes over time. For example, depending on the material of the card and / or the properties of the ink and / or the number of layers to be printed, it may be advantageous to adjust the intensity of the ion generator 30 to optimize the effect of the generated charged ions 34 on the top surface of the card. According to one embodiment, the ion generator 30 is mounted at a specific fixed position relative to the printer frame, and the operating conditions of the ion generator 30 can be adjusted by controlling the duty cycle of the ion generator 30 and / or the intensity of the ion generator 30, i.e., the intensity of the ion flux. For example, the intensity of the ion generator 30 can be adjusted to adjust its power supply.

[0050]

[0061] For example, if the ion generator 30 operates on a 12-volt DC power supply, the intensity of the ion flux can be changed by changing the power supply value. The ion generator 30 generates lower intensity charged ions 34 by, for example, lowering the power supply value to 6 volts DC. According to one embodiment, switching the ion generator 30 on or off may also be a way to change its intensity. According to one embodiment, the variability of the ion generator 30 can be understood as variability of the ion flux due to adjustment of the power supply of the ion generator 30. For example, switching the power supply of the ion generator 30 on or off leads to variability in the ion flux. In another example, increasing or decreasing the power supply value of the ion generator 30 leads to variability in the ion flux.

[0051]

[0062] To quantify the intensity fluctuations when the power supply value is adjusted, an experiment was conducted in which the ion generator 30 was placed at a fixed distance (10 cm in this experiment) from the monitored charged plate. The monitored charged plate was set to 0 volts and then disconnected from any voltage source, i.e., its voltage remained substantially a floating voltage. In fact, the voltage to the plate was monitored with an oscilloscope using a high-impedance cable to avoid disturbing the electrical state of the plate as much as possible. After waveform acquisition began, the ion generator 30 was switched on to generate negative ions in this experiment, and the power supply value was maintained at a specific fixed value within the range of 6 volts to 12 volts. During this experiment, an increasing negative voltage was established on the monitored plate. For a long time, the negative voltage tended to remain fixed at a negative value according to an asymptotic curve. Next, this experiment was reproduced with different power supply values ​​to check whether this induced a change in the time required to reach this negative value. This experiment investigated the time required to reach a certain voltage level (-400 volts and -800 volts, respectively) corresponding to the DC power supply level applied to the ion generator 30. This experiment showed that the higher the applied power supply voltage, the shorter the time required to reach the predetermined voltage level. The relationship between the power supply value and the required time is nonlinear, as shown in the table below.

[0052] [Table 1]

[0053]

[0063] This experiment clearly demonstrates that the dynamic range of the ion generation efficiency 30 is very large, and that fine adjustments can be obtained by small voltage adjustments to the power supply of the ion generator 30, even depending on the printing mode. Preferably, the power supply value can be easily adjusted using a simple circuit such as a voltage divider or a potentiometer.

[0054]

[0064] As will be described later, the use of an ion generator 30 having a variable duty cycle and / or variable intensity makes it possible to solve various technical problems, for example, when printing on plastic cards that have a heterogeneous charge distribution. Typically, in this use case, the surface of the plastic card may contain different regions having different charges. In this example, the plastic card contains two different regions, each having a different charge. According to one embodiment, the ion generator 30 is configured to reduce the difference in charge between the two regions and also minimize the charge gradient that causes the aforementioned droplet displacement. Net charge elimination or at least a significant reduction can be achieved by the ion generator 30. Furthermore, if the polarity of the emitted ions is opposite to the charge of the card, the ion generator 30 makes it possible to significantly reduce or even eliminate the net charge of the card. In some situations, if the flow of ions continues, it is even possible that the polarity of the charge may reverse over time. Conversely, if the polarity of the ions is the same as the charge of the card, the ion generator 30 makes it possible to reach a balance between the two regions of the card. Nevertheless, in some situations, the ion flux can be increasingly rejected by the card's electric field. Therefore, in some situations, for example, when many layers must be printed on the same card, the increase in net charge can be slow over a long period of time. Thus, the use of a variable duty cycle is a solution to overcome this drawback, particularly in relation to the number of layers applied during printing. The ability to adjust the operating conditions of the ion generator 30 using a variable duty cycle and / or variable intensity increases the number of degrees of freedom of the ion generator 30 to overcome the technical problems caused by the variability of printing conditions.

[0055]

[0065] The presence of a nearly uniform charge distribution and the resulting electric field does not in itself represent a disadvantage. In fact, during ink droplet ejection, the electric field can attract the charged component of ink droplets having a specific polarity, which concentrates at the head of the droplet, the latter becoming a larger main droplet after fragmentation, and is attracted toward the top surface of the card without significant deflection, as is known to those skilled in the art. On the other hand, small ink droplets at the tail, which constitute the aerosol with low mass and low velocity, are rejected if they have the opposite polarity to the main droplet, or if they are neutral, in which case they can continue along their original trajectory to ease the electrical gradient.

[0056]

[0066] It should be noted that effective charge uniformity requires approximately 1 / 2 second or less, which perfectly meets the print yield requirements of inkjet printers for printing on cards. The solution of the present invention can enable an inkjet printer to print hundreds of cards without even noticing the significant presence of mist on the printed surface, i.e., without the significant presence of false ink spots throughout the printed image.

[0057]

[0067] The various technical features described above can be combined in any way. While not all possible combinations of these technical features are described, all such combinations should be considered to fall within the scope described herein, provided they are not contradictory.

[0058]

[0068] Notwithstanding the description of the present invention in combination with embodiments, as will be apparent to those skilled in the art, the above description and drawings are illustrative and not limiting, and the present invention is not limited to the disclosed embodiments. Various modifications and variations are possible without departing from the concept of the present invention. [Explanation of Symbols]

[0059] 1. Inkjet printer 2 Base Frame 3. Storage Zone 4 cards 5. Support Carriage 6. Flat tray 7 Tray Heater 8 Drawer Station 9 Printing Station 10 Discharge Stations 11 Printheads 12 Support plate 13 Lord Laura 14, 15, 16, 17, 18 Auxiliary rollers 19. Cards that were removed. 20 Guide Plates 21 nozzles 22 Ink 23 Inkdrops 24 Main drop 25. Ancillary bodies 26 Aerosols 27 Intended print image 28 Actual printed image 29 Fake Ink Spots 30 Ion Generators 31 Ion Generator Case 32 openings 33 Electrical terminals 34 Charged Ions 35 Mounting bracket 36 Vertical supports 37 Horizontal support

Claims

1. In an inkjet printer (1) for printing on cards, A printer frame comprising a base frame (2), A support carriage (5) attached to the base frame to support the card to be printed, A printing station (9) is mounted on the printer frame and includes at least one print head (11) for inkjet printing on the upper surface of the card, An ion generator (30) attached to the printer frame for releasing charged ions sent to the upper surface of the card, Equipped with, The ion generator is operated before and during printing with a variable duty cycle and variable intensity. Inkjet printer.

2. The inkjet printer according to claim 1, wherein the ion generator is an air ionizer that alternately emits positively charged ions and negatively charged ions.

3. The inkjet printer according to claim 2, wherein the polarity of the emitted charged ions changes at a predetermined time period such that the positively charged ions and the negatively charged ions do not neutralize each other before reaching the upper surface of the card.

4. The inkjet printer according to claim 1, wherein the ion generator is a unipolar ion generator for releasing charged ions having a specific polarity, and the charged ions can reach the upper surface of the card by diffusion.

5. The aforementioned unipolar lion generator, An ion generator case (31) having an opening (32) that allows the generated charged ions to flow out, A pair of electrodes housed within the ion generator case, The ion generator power supply module mounted on the inkjet printer is connected to a pair of electrical terminals (33) one for each electrode, The inkjet printer according to claim 4, comprising:

6. The inkjet printer according to any one of claims 1 to 5, wherein the inkjet printer comprises a mounting bracket (35) for attaching the ion generator, and the mounting bracket is fixed to the base frame.

7. The inkjet printer according to any one of claims 1 to 5, wherein the printer frame further comprises a top frame connected to the base frame by a plurality of side frames, and the ion generator is fixed to the top frame.

8. The inkjet printer according to any one of claims 1 to 7, wherein the inkjet printer further comprises a guide plate (20), the support carriage is positioned on the guide plate and guided by the guide plate to move between a first position in which the support carriage does not face the printer head and a second position in which the support carriage faces the printer head, the printing station is able to move laterally relative to the guide plate above the guide plate, and the ion generator is outside the movement path of the printing station.

9. The inkjet printer according to claim 8, wherein the orthographic projection of the ion generator on the base frame coincides with the center of the orthographic projection of the support carriage on the base frame when the support carriage is in the second position.

10. A storage zone (3) for storing at least one card to be printed, A withdrawal station (8) for drawing the card from the storage zone to the support carriage, An inkjet printer according to any one of claims 1 to 9, further comprising the above.

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