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, comprising: a printer frame comprising a base frame (2); a support carriage (5) mounted on the base frame (2) for supporting a card (19) to be printed; a printing station (9) mounted to the printer frame for inkjet printing on a top surface of the card (19), the printing station (9) comprising at least one print head (11); and an ion generator (30) mounted to the printer frame for emitting charged ions, which can be sent to the top surface of the card (19).

Description

Technical Field

[0001] This 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 Technology

[0002] As is well known, credit cards, smart cards, magnetic stripe cards, etc., typically bear logos, images, and trademarks that help users identify the purpose of the card and distinguish each card from others. US 6,478,485 discloses a process and apparatus for decorating articles that may be cards.

[0003] Furthermore, EP2658723, EP2658721, EP2658722 and EP2718109, which can be regarded as useful sources of information about the present invention, extensively and thoroughly disclose and illustrate some detailed features of an inkjet printer for printing on cards.

[0004] Figure 1 and Figure 2 An inkjet printer 1, known in the prior art for printing on cards, is shown. For example... Figure 1 and Figure 2 As shown, the inkjet printer 1 has a base frame 2. Preferably, a storage area 3 storing one or more cards 4 is arranged on the base frame 2. Preferably, the inkjet printer 1 may be provided with a support carriage 5, on which a plate-shaped tray 6 is mounted. The plate-shaped tray 6 receives the card to be printed from the storage area 3 and holds the card thereon. The plate-shaped tray 6 may be provided with a tray heater 7, which is embedded in the plate-shaped tray 6 and used to heat the card held thereon. The support carriage 5 is adapted to move the card held on the support carriage within the inkjet printer 1. More specifically, the support carriage 5 is arranged on a guide plate 20 mounted to the base frame 2 and adapted to be guided along the guide plate 20. More specifically, the support carriage 5 receives the card to be printed from the card storage area 3 by means of a pick-up station or extraction station 8 and moves the card held thereon along the guide plate 20. The guide plate 20 carries such a card to a printing station 9, where the card is inkjet printed by the printing station 9. Thus, the guide plate 20 and the support carriage 5 can also be used to bring the card to the inkjet station 10, where the card moves away from the inkjet printer 1 and is received in a suitable container.

[0005] The printing station 9 comprises at least one print head 11 for inkjet printing on the card. The printing station 9 comprises a drive system (not shown) adapted to move the print head 11 back and forth along a preset path, so that the print head 11 can inkjet the card during a series of steps regulated by a suitably configured regulating unit (not shown). Preferably, the print head 11 is slidably mounted on a support plate 12. In the preferred embodiment, the support plate 12 is transversal and in particular perpendicular to the movement path or guide 20 of the support carriage 5.

[0006] The extraction station 8 is adapted to extract the card 4 from the storage area 3. The extraction station 8 picks up one card 4 at a time from the storage area 3 and places it on the support carriage 5. Subsequently, the card 4 moves along the guide 20 to the printing station 9, where the inkjet printing action is performed by controlled ejection of ink onto the top surface of the card. After inkjet printing, the card 4 moves towards the ejection station 10. The ejection station 10 is configured to move the card 4 away from the support carriage 5 and preferably to drop it into a container.

[0007] The extraction station 8 is shown in more detail in Figure 3 and Figure 4 , Figure 4 is a cross-section according to the IV-IV line in Figure 3 . The extraction station 8 comprises at least one main roller 13, which can be in contact with the first card at the bottom of the stack of cards 4 in the storage area 3, for extracting the first card to be printed from the storage area 3, which becomes the picked card 19. Preferably, the main roller 13 is rotatably mounted to the base frame 2 below the storage area 3, so that the weight of the stack of cards 4 contributes to maintaining the first card in contact with the main roller 13. In the preferred embodiment, an auxiliary counterweight is placed on top of the stack of cards 4, so as to provide an additional component to the force that pushes the first card in contact with the main roller 13.

[0008] The extraction station 8 further comprises a plurality of auxiliary rollers 14, 15, 16, 17 and 18 mounted downstream of the main roller 13, so as to engage the picked card 19 that advances as a result of the interaction with the main roller 13, to make it drop on the plate-shaped tray 6 fitted on top of the support carriage 5. More precisely, the auxiliary rollers 14 to 18 are positioned to receive the picked card 19 from the main roller 13 and make it advance in the direction indicated by the arrow Fl in Figure 3 , allowing it to be processed for printing. In Figure 5 , it is shown that the picked card 19 has been placed on the support carriage 5 and can move along the guide 20 after having just left the auxiliary rollers 17 and 18 of the extraction station 8.

[0009] When the function of the extraction station 8 is to supply cards for printing, the auxiliary rollers 14 to 18 define a reference plane that is substantially parallel to the plane of the plate tray 6. Under certain conditions, the picked-up card 19 is not sent to the plate tray 6 mounted on the support carriage 5 for printing; instead, the auxiliary rollers 14 to 18 are moved by a suitable mechanism (not shown) such that the reference plane they define is tilted and the picked-up card 19 is along... Figure 4 The arrow F2 in the diagram indicates that the device moves towards the output. Figure 4 The structure of extraction station 8 shown in the illustration precisely refers to this auxiliary discharge function. However, Figure 4 The main purpose is to show in detail the position of the picked-up card 19 held by the auxiliary rollers 14 to 18.

[0010] During the extraction process, some friction occurs between the picked-up card 19 and the main roller 13 and auxiliary rollers 14 to 18. Due to the triboelectric effect, the extraction process can cause the picked-up card 19, which is typically made of a dielectric material, i.e., an electrically insulating material, to become charged. The generated charge cannot move freely on the top surface of the card; instead, the generated charge tends to adhere randomly to the picked-up card 19 in an unpredictable distribution on the top surface of the card.

[0011] Furthermore, the origin of triboelectric charging cannot be attributed solely to friction with the main roller 13 and auxiliary rollers 14 to 18. In fact, the simple treatment of the card 4, made of dielectric material, before loading the storage area 3 may also cause some unbalanced charge to appear on the top surface of the card. In short, when the picked-up card 19 is positioned on the support carriage 5 in preparation for printing (as... Figure 5 As shown), it is very likely that some unpredictable distribution of unbalanced charge has been created on the top surface of the picked-up card 19. Figure 6 A support carriage 5 is shown, which holds the picked-up card 19 and moves along a guide plate (not shown) toward the printing station 9 in the direction indicated by arrow P.

[0012] Printing station 9 performs the printing action using at least one printhead 11 slidably mounted on support plate 12. The printhead 11 is provided with multiple nozzles; all nozzles are electrically actuated in a controlled manner to generate ink droplets from predetermined nozzles, which are directed to predetermined positions on the top surface of the picked-up card 19. As is well known to those skilled in the art, during and after ejection, ink droplets may fragment into multiple smaller parts due to the dynamic nature of the ejection. This situation occurs in… Figure 7 As shown in, Figure 7In the example of figure 1, the nozzle 21 ejects a small amount of ink 22 contained in the print head 11 in the form of an ink drop 23. More commonly, there is a main drop 24, which is large at the front, heavy in mass and fast in speed, followed by a plurality of smaller and generally slower drops, usually referred to as satellites 25. Some satellites 25 are formed by a number of micrometric and sub-micrometric drops, which are very small in mass and low in speed, usually named aerosol 26. In short, each ejection out of a determined nozzle proves to be the generation of a plurality of ink drops with different masses and speeds.

[0013] It is easily understandable that the motion of the different ink drops can be affected differently by possible perturbations. In fact, the heaviest and fastest drops, i.e. the main drops 24, having a large momentum, are almost not disturbed and follow a trajectory almost not perturbed. On the contrary, the smallest and slowest drops, especially the aerosol 26, being small in momentum, are easily deviated from their path by any possible perturbation. In other words, the ink drops having a high momentum tend to hit the print medium, which means that the top surface of the picked-up card 19 is in the expected and predetermined position, while the ink drops having a low momentum are subjected to a stronger influence from the perturbations. In particular, the aerosol 26, consisting of the smallest ink drops having a very small speed and often scattering around under the perturbations, often reaches unpredictable positions on the top surface of the picked-up card 19, far from the predetermined landing point of the main drops 24 generated during the same ejection.

[0014] Among the possible perturbation factors, one common cause is the air flow. The presence of fans that can even reach the print area or simply the back and forth movement of the print head and of the supporting carriage can act as a perturbation factor, whose influence on the ink drops motion depends on the perturbation intensity and on the ink drops momentum.

[0015] Another important perturbation factor that can affect the motion of the ink drops is the electric field that can be present in the surroundings of the print head, where the trajectories of the ink drops are formed, and especially in the space between the nozzle and the print medium, i.e. the picked-up card. Depending on the polarity of the electric charge, the electric field acts on the picked-up card, which has a net electric charge, in the form of an attractive or repulsive force. Moreover, since matter comprises components with positive and negative electric charges, even if the net charge is zero, the electric field can displace the positive and negative charges of the matter in separate directions, thus inducing what is called polarization. It is well known to the person skilled in the art that a polarized matter can be subjected to a force from the electric field even if the net charge is zero, when the electric field has a non-zero gradient, i.e. when the electric field is not uniform in space.

[0016] In most cases, the liquid ink contained in the print head shows some electric conductivity and it can comprise electrically charged components that have some mobility within the liquid ink. Therefore, the liquid ink can be subjected to the action of an electric field and the motion of the ink drops can be affected by the electric field created in the space between the nozzle and the print medium, i.e. the picked-up card.

[0017] The electric field has different effects on the fragmented part of the ejected ink due to the different mass and charge distribution of the ink droplets. In particular, the motion of the aerosol is susceptible to strong influence of the electric perturbation due to the small mass of the tiny ink droplets of which it is composed.

[0018] Many attempts have been made to solve the problems due to the electric perturbation in inkjet printers, for example as shown in patents No. US 5774141 and No. US 7824008, in which the aggregation or repulsion of the charged stray ink droplets is performed by means of additional electric biasing means distributed in the vicinity of the print head and of the printing area. However, the printing defects that occur in a certain allegedly unpredictable manner during the printing of cards with inkjet printers are still an annoying drawback and require more specific handling.

[0019] In more detail, after printing, some cards appear dirty. In other words, there are scattered ink dots on the expected image. This means that small ink droplets have scattered around, away from the intended landing point. This effect, commonly referred to as fogging, is particularly severe and frequent at the border between a densely printed area and a sparsely printed area or even in areas completely free of printing. This situation is particularly critical in the case of printing of cards with a large number of images, such as bank cards, credit cards, loyalty cards, etc. Figure 8 a and Figure 8 b of the document Figure 8 a, in which the expected printed image 27 is compared with the actual printed image 28 in b of the document Figure 8 a, in which the expected printed image 27 is compared with the actual printed image 28 in b of the document

[0020] Observing the artifacts on the printed card at high magnification, they are mostly composed of very small ink dots, most likely generated by the aerosol deviating its trajectory. Moreover, there is evidence that the card is often electrically charged due to the extraction process and possibly also due to the previous card handling. The creation of some electric charges unevenly distributed on the top surface of the card can be shown using a suitable instrument, such as an electrometer. It therefore seems reasonable to attribute the appearance of ink dots on the card to the electric field.

[0021] On the other hand, the electrical conductivity of the ink seems to play a role in the most frequent distribution of artifacts at the border between a densely printed area and a sparsely printed area. In fact, when the ejected ink is still liquid on the top surface of the card, the charged components of the ink can be rearranged, reducing the local static charge on the top surface of the card to some extent. This effect can be more effective in densely printed areas, while the reduction effect is weaker in sparsely printed areas.

[0022] Without wishing to be bound by theory, it is believed that a strong gradient of the electric field, enhanced by the unevenness of the surface charge distribution, can create a deflection force with a significant component parallel to the surface. This unevenness can be created because of the different ink distribution, which has different effects in reducing the local charge. Along this line of thought, multiple ink droplets constituting the aerosol can easily be polarized and deflected by the unbalanced electric field, thus falling away from the intended location on the card.

[0023] To reduce the electrical disturbance, and in particular to reduce the strength of the electric field gradient, some neutralization of the effect of the electric charge can be considered. For example, the support carriage on which the card is placed during printing can be provided with a topmost grounded conductive layer with which the bottom surface of the card is in contact. However, due to the card thickness, this solution would not be so effective in shielding the electrostatic field at the top surface of the card, i.e. the ink landing surface. SUMMARY

[0024] To solve the above technical problem, the present invention provides an inkjet printer in which an ion generator is arranged to send additional electric charges, in particular some charged ions, directly onto the top surface of a card to be printed, so as to compensate for the effect of the previously existing electrostatic charge of the top surface of the card and to solve the problem of ink aerosol scattering at undesired locations on the card, thus eliminating the fogging problem.

[0025] In particular, the present invention provides an inkjet printer for printing on a card, comprising: a printer frame comprising a base frame; a support carriage mounted on the base frame for supporting a card to be printed; a printing station mounted to the printer frame for inkjet printing on a top surface of the card, the printing station comprising at least one printhead; and an ion generator mounted to the printer frame for emitting charged ions that can be sent to the top surface of the card. Preferably, the ion generator is actuated with variable duty cycle and variable intensity before and during printing.

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

[0027] Preferably, the polarity of the emitted charged ions is varied at predetermined time periods to prevent the positively and negatively charged ions from neutralizing each other before reaching the top surface of the card.

[0028] Preferably, the ion generator is a unipolar ion generator for emitting charged ions with a single polarity and the charged ions are able to reach the top surface of the card by diffusion.

[0029] Preferably, the unipolar ion generator comprises: an ion generator housing having an aperture for allowing the generated electrically charged ions to exit; a pair of electrodes housed within the ion generator housing; and a pair of electrical terminals for connection with an ion generator power module on the inkjet printer, one electrical terminal for one electrode.

[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 comprises a top frame, the top frame is connected with the base frame by side frames; and the ion generator is fixed to the top frame.

[0032] Preferably, the inkjet printer further comprises a guide plate; the support carriage is arranged 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 print head and a second position in which the support carriage faces the print head; the print station is movable transversely to the guide plate above the guide plate; and the ion generator is outside the movement path of the print station.

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

[0034] Preferably, the inkjet printer further comprises: a storage area for storing at least one card to be printed; and a pick-up station for picking up the card from the storage area to the support carriage.

[0035] According to the solution of the present application, the electrically charged ions emitted by the ion generator in the inkjet printer can be sent to the top surface of the card to be printed to compensate for the effect of the previously existing static charge on the top surface of the card, thus avoiding the significant presence of fog on the printing surface, i.e. avoiding the significant presence of false dots in the entire printed image. BRIEF DESCRIPTION OF DRAWINGS

[0036] Non-limiting and non-exhaustive embodiments of the present application will be described by way of example with reference to the accompanying drawings, in which:

[0037] Figure 1 A left side perspective view of an inkjet printer known in the prior art for printing on cards is shown.

[0038] Figure 2 A right side perspective view of the inkjet printer in Figure 1 is shown.

[0039] Figure 3 shows a perspective view of a storage area and a pick-up station of an inkjet printer in Figure 1

[0040] Figure 4 shows a cross-sectional view along the IV-IV line in Figure 3

[0041] Figure 5 shows a partial perspective view of a support carriage holding picked-up cards.

[0042] Figure 6 shows a perspective view of a print station of an inkjet printer in Figure 1

[0043] Figure 7 shows a sketch illustrating ink drops ejected by nozzles of a print head.

[0044] Figure 8 a of shows an intended printed image.

[0045] Figure 8 b of shows an actual printed image printed by an inkjet printer in Figure 1

[0046] Figure 9 shows a perspective view of an inkjet printer according to one embodiment of the present invention.

[0047] Figure 10 shows a perspective view of a unipolar ion generator in the inkjet printer shown in Figure 9

[0048] Figure 11 shows a top view of the inkjet printer shown in Figure 9 DETAILED DESCRIPTION

[0049] So that the above and other features and advantages of the present application can be

[0050] The present invention provides an inkjet printer in which an ion generator is arranged to send additional electric charges, in particular some charged ions, directly onto a top surface of a card to be printed in order to compensate for the effect of previously existing electrostatic charges on the top surface of the card.

[0051] Figure 9 ​​​​​​A perspective view of an inkjet printer 1 according to one embodiment of the present application is shown. The inkjet printer 1 is used for printing on a card such as a credit card, a smart card, a magnetic card. Preferably, the card comprises or is made of a thermoplastic material. In particular, the thermoplastic material can be selected from the group comprising: 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); polylactic acid (PLA). The laminated polyvinyl chloride is formed of a central layer of polyvinyl chloride filled with mineral fillers and a pair of transparent polyvinyl chloride films respectively applied on respective surfaces of the central layer. Also preferably, the card has a substantially plate-like shape having a substantially rectangular shape in plan view with two larger sides and two smaller sides.

[0052] As Figure 9 shown, the inkjet printer 1 comprises a printer frame comprising at least a base frame 2. In addition, although not shown and not essential, the printer frame can further comprise a top frame connected to the base frame 2 by side frames. In particular, lower ends of the side frames are connected to the base frame 2 and upper ends of the side frames are connected to the top frame, thereby forming an accommodation space in which various components of the inkjet printer 1 are accommodated.

[0053] As Figure 9 shown, 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 a top surface of the card, and the printing station 9 comprises at least one printhead 11 for ejecting ink droplets onto the top surface of the card as needed. The card supported on the support carriage 5 can be picked or extracted from a storage area 3 for storing at least one card to be printed by a pick-up station or extraction station 8, as described above with reference to Figures 1 to 6 As Figure 9 shown in the embodiment, the card supported on the support carriage 5 can also be referred to as a picked card 19. The support carriage 5 is mounted on the base frame 2. The support carriage 5 can be directly mounted on the base frame 2, i.e. the support carriage 5 can be fixed to the base frame 2. The support carriage 5 can also be indirectly mounted on the base frame 2. For example, in Figure 9In the illustrated embodiment, the support carriage 5 can be arranged on a guide plate 20 which in turn is mounted to the base frame 2. The support carriage 5 is guided by the guide plate 20 to move between a first position in which the support carriage 5 does not face the printhead 11 and a second position in which the support carriage 5 faces the printhead 11. It can be understood that the “first position” can also be referred to as an initial or receiving position for receiving the picked card 19 onto the support carriage 5; and that the “second position” can also be referred to as a printing position for performing inkjet printing on the top surface of the picked card 19. The printing station 9 is mounted to the printer frame. In particular, the printing station 9 is mounted to the support plate 12 which in turn is fixed to the base frame 2. The printing station 9 is further movable transversely, preferably perpendicularly, to the movement path of the support carriage 5 or the guide plate 20 above. In particular, the printhead 11 is slidably mounted on the support plate 12 which is transversely, and in particular perpendicularly, to the movement path of the support carriage 5 or the guide plate 20. Figure 9 In the illustrated embodiment, the printing station 9 is mounted to the support plate 12 which in turn is fixed to the base frame 2. The printing station 9 is further movable transversely, preferably perpendicularly, to the movement path of the support carriage 5 or the guide plate 20 above. In particular, the printhead 11 is slidably mounted on the support plate 12 which is transversely, and in particular perpendicularly, to the movement path of the support carriage 5 or the guide plate 20.

[0054] As mentioned above, when the picked card 19 is positioned on the support carriage 5 in preparation for printing, it is likely that some unpredictable distribution of unbalanced charges has already been created on the top surface of the picked card 19. To address or at least mitigate the unpredictable distribution of unbalanced charges on the top surface of the picked card 19, an ionizer 30 for emitting charged ions which can be sent to the top surface of the picked card 19 is provided in the inkjet printer 1. The ionizer 30 is mounted to the printer frame. The ionizer 30 can be directly mounted to the printer frame. For example, the ionizer 30 can be fixed to the top frame of the printer frame. The ionizer 30 can also be indirectly mounted to the printer frame. For example, the ionizer 30 is mounted to the printer frame by a mounting bracket 35 which is fixed to the base frame 2. In particular, the mounting bracket 35 comprises a vertical support 36 which is fixed to the base frame 2 and extends upwardly from the base frame 2, and a horizontal support 37 which is connected to an upper end of the vertical support 36 and extends substantially horizontally, wherein the ionizer 30 is fixed to the horizontal support 37.

[0055] As a first approach, an air ionizer that alternately emits positively and negatively charged ions can be used as the aforementioned ion generator 30. The negatively and positively charged ions emitted by the air ionizer can neutralize most of the pre-existing static charge on the top surface of the picked-up card 19 (because these static charges repel charged ions of the same polarity and attract charged ions of opposite polarity) until a certain charge balance is reached on the top surface of the picked-up card 19. In one embodiment, the positively and negatively charged ions are delivered to the top surface of the picked-up card 19 via a gas flow. The gas flow helps to push away either the positively or negatively charged ions before generating ions of opposite polarity, preventing the emitted alternating charged ions from neutralizing each other before reaching the top surface of the picked-up card 19. The gas flow can be an airflow; for example, a fan can be provided to provide airflow. Sometimes different gases can also be used to form the gas flow. Furthermore, the polarity of the emitted charged ions changes over a predetermined time period (typically a few seconds, e.g., 1 to 2 seconds) to allow the alternating stream of charged ions to adapt to the actual charge distribution on the top surface of the picked-up card 19, thereby further preventing the emitted alternating charged ions from neutralizing each other before reaching the top surface of the picked-up card 19. Such a long duration slows down the print volume of the inkjet printer 1. Moreover, the gas stream carrying alternating charged ions can represent a disturbance to the movement of ink droplets, regardless of the neutralization of charge on the top surface of the picked-up card 19, and therefore regardless of the compensation of the electric field on the top surface of the picked-up card 19.

[0056] As a more preferred embodiment, the inkjet printer 1 is provided with a unipolar ion generator (i.e., a unipolar ion generator) as ion generator 30 for emitting charged ions with a single polarity, which are capable of reaching the top surface of the picked-up card 19 by diffusion without the use of any gas flow. Figure 9 and Figure 10 As shown, the unipolar ion generator includes an ion generator housing 31, a pair of electrodes (not shown), and a pair of electrical terminals 33. The ion generator housing 31 has a hole 32 to allow the generated charged ions to escape and disperse into the surrounding space. The electrodes are housed within the ion generator housing 31. The two electrical terminals 33 (one terminal for each electrode) are connected to an ion generator power module (not shown) on the inkjet printer 1. The generated charged ions 34 with a single polarity can be positive (e.g., ...). Figure 10(As shown) or even negative, depending on the construction of the unipolar ion generator. Since the charged ions 34 have a single polarity, there is no risk of "ion neutralization." In this case, the charged ions 34 are able to reach the top surface of the picked-up card 19 by diffusion without the use of any gas flow; therefore, there is no disturbance caused by any gas flow.

[0057] Although the unipolar charged ions 34 are unlikely to generate a charge balance on the top surface of the picked-up card 19, thus neutralizing the pre-existing static charge, the generated charged ions 34 will have different impact rates point-to-point, depending on the distribution of the pre-existing static charge. For example, let's assume there is a non-uniform charge distribution on the top surface of the picked-up card 19. Specifically, let's assume there are positively charged and uncharged regions on the top surface of the picked-up card 19, and that the generated charged ions 34 are also positive. Due to the stronger electric field in the charged regions, the generated positive charged ions 34 are easily repelled when approaching the charged regions on the top surface of the picked-up card 19 (perhaps some of the generated charged ions 34 will reach the top surface of the picked-up card 19 at a very slow rate anyway); conversely, in the uncharged regions, the impact rate of the generated positive charged ions 34 will still be high, and the top surface of the uncharged regions tends to collect more and more of a certain positive charge. Since a lower positive charge density (fewer repelled ions) would result in a higher impact rate, the trend is towards reaching an equilibrium with a more uniform positive charge distribution on the top surface of the picked-up card 19. Alternatively, let's assume the presence of negatively charged and uncharged regions on the top surface of the picked-up card 19 and that the generated charged ions 34 remain positive. The generated charged ions 34 will have a higher impact rate on the negatively charged regions than on the uncharged regions (because they are attracted). Therefore, the negatively charged regions lose their negative charge faster than the uncharged regions accumulate positive charge. The end result is the same: some uniform positive charge will be created on the top surface of the picked-up card 19. It can be understood that reversing the polarity of the generated charged ions 34 will not affect the final uniformity of charge on the top surface of the picked-up card 19: simply put, the final result will be a uniformly negatively charged surface. In any case, the overall effect of these charged ions 34 is likely a reduction in the gradient value on the top surface of the picked-up card 19, although the net charge has not yet been offset. In other words, the emitted charged ions can generate a more uniform charge distribution on the top surface of the card, thus creating a more balanced electric field near the top surface of the card without making the card itself neutral. Therefore, the unipolar ion generator adapted in the inkjet printer 1 can be a positive ion generator or a negative ion generator without affecting the performance of the solution.

[0058] Figure 11 yes Figure 9 The image shows a top view of inkjet printer 1. Figure 11 It can be clearly seen that the ion generator 30 is located outside the movement path of the print station 9, thus preventing any mechanical interference with the moving print head 11 of the print station 9. Furthermore, when the picked-up card 19 is positioned in the print position, the orthogonal projection of the ion generator 30 in the base frame 2 falls outside the periphery of the picked-up card 19. Moreover, since the generated charged ions can cover a certain distance, the ion generator 30 does not need to be too close to the picked-up card 19, nor does it need to be aligned with the center of the picked-up card 19, in order to effectively perform its function, such as... Figure 11 As shown. Of course, preferably, when the support carriage 5 is in the second position, the orthogonal projection of the ion generator 30 in the base frame 2 coincides with the center of the orthogonal projection of the support carriage 5 or the picked-up card 19 in the base frame 2, because the symmetrical positioning of the ion generator 30 can produce a more uniform effect.

[0059] The ion generator 30 can be optionally actuated with a variable duty cycle and variable intensity before and during printing. According to an embodiment, when the ion generator 30 is actuated with a variable duty cycle, it is actuated during some printing sequences and not actuated during others. For example, in a multi-layer printing mode, the ion generator 30 can be active during the printing of all layers, or it can be actuated only during the printing of a subset of layers, depending on the geometry of the printer module, card material, ink composition, etc., to achieve maximum charge uniformity without causing electrostatic adhesion to the card due to excessive charge on the top surface of the card. As an example, during the printing of a card with only 4 layers, the duty cycle of the ion generator 30 can be 100%, i.e., the ion generator 30 is always on, while in the case of 16 layers, the duty cycle of the ion generator 30 can be in the range of 25% to 50%. For example, in the case of 16 layers, the ion generator 30 can be operated during the printing of the first layer in a set of four layers and turned off during the printing of the subsequent three layers; in this example, the sequence is repeated four times.

[0060] According to an embodiment, when the ion generator 30 is actuated, it generates an ion flux, which includes the generated charged ions 34. When the ion generator 30 is actuated with a variable intensity, the ion flux is variable, meaning the number of generated ions 34 varies over time. For example, depending on the card material 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 charged ions 34 generated on the top surface of the card. According to an embodiment, the ion generator 30 is mounted in a fixed position relative to the printer frame, thereby controlling the duty cycle and / or the intensity of the ion generator 30, i.e., the intensity of the ion flux, allowing adjustment of the operating conditions of the ion generator 30. For example, the intensity of the ion generator 30 can be adjusted by adjusting its power supply.

[0061] For example, if the ion generator 30 operates at 12 volts DC, the intensity of the ion flux can be changed by altering the power supply value. For instance, by reducing the power supply value to 6 volts DC, the ion generator 30 produces charged ions 34 with a lower intensity. According to embodiments, turning the ion generator 30 on or off can also be a way to change its intensity. According to embodiments, the variability of the ion generator 30 can be understood as the variability of the ion flux caused by adjusting the power supply of the ion generator 30. For example, turning the power supply of the ion generator 30 on or off results in variability of the ion flux. As another example, increasing or decreasing the power supply value of the ion generator 30 results in variability of the ion flux.

[0062] To quantify the variability of intensity 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) relative to the monitored charged plate. The monitored charged plate was set to 0 volts and then disconnected from any voltage source, meaning its voltage was left to float. In fact, the voltage on the plate was monitored using a high-impedance cable via an oscilloscope to minimize disturbance to the plate's electrical state. After waveform acquisition began, the ion generator 30 was turned on, thus generating negative ions in this experiment, with the power supply value maintained at a fixed value within the range of 6 to 12 volts. During the experiment, an increasing negative voltage was created on the monitored plate. Over a long period, the negative voltage tended to follow an asymptotic curve to a fixed negative value. The experiment was then reproduced with different power supply values ​​to examine whether this would induce a change in the time required to reach that negative value. In this experiment, the time required to reach specific voltage levels (-400 volts and -800 volts, respectively) based on the DC power supply level applied to the ion generator 30 was examined. The experiment shows 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 time taken is non-linear, as shown in the table below:

[0063] Direct current power supply -400 volts -800 volts 6 volts 1.4 seconds 26 seconds 8 volts 0.34 seconds 1.3 seconds 10 volts 0.18 seconds 0.54 seconds 12 volts 0.14 seconds 0.38 seconds

[0064] This experiment clearly demonstrates that the ion generator 30 has a very wide dynamic range of efficiency, and even fine-tuning depending on the printing mode can be achieved through small voltage adjustments to the power supply of the ion generator 30. Advantageously, the power supply value can be easily adjusted using simple circuitry such as a voltage divider or potentiometer.

[0065] As described below, the use of an ion generator 30 with a variable duty cycle and / or variable intensity can solve various technical problems, such as those encountered when printing on plastic cards with non-uniform charge distributions. Typically, in such applications, the surface of the plastic card can include different regions with different charges. In this example, the plastic card comprises two distinct regions, each with a different charge. According to embodiments, the ion generator 30 is configured to reduce the difference in charge between the two regions, thereby minimizing the charge gradient that causes the droplet deviation described previously. The elimination or at least a strong reduction of net charge 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 can strongly reduce or even eliminate the net charge of the card. In some cases, the charge polarity may even reverse over a long period if the ion flow continues. Conversely, if the polarity of the ions is the same as the charge of the card, the ion generator 30 can achieve equilibrium between the two regions of the card. However, in some cases, the ion flux may be gradually and increasingly repelled by the card's electric field. Therefore, in some cases, only a slow increase in net charge can occur over a long period of time, such as when many layers must be printed on the same card. Thus, using a variable duty cycle is a solution to overcome this drawback, particularly related 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, overcoming the technical problems caused by the variability of printing conditions.

[0066] The presence of a nearly uniform charge distribution and the resulting electric field is not inherently a drawback. In fact, during ink droplet ejection, the electric field can attract the charged components of the ink droplet with a specific polarity, which concentrate in the droplet head; the droplet breaks up into a large main droplet and is attracted toward the top surface of the card without any significant deflection, as is well known to those skilled in the art. On the other hand, due to the decrease in gradient, the tiny ink droplets at the tail (which constitute an aerosol with small mass and low velocity) are either repelled if they have the opposite polarity to the main droplet, or continue along their original trajectory if they are neutral.

[0067] It should be noted that effective charge homogenization will take approximately half a second or less, which is fully compatible with the print volume requirements of inkjet printers used for printing on cards. The solution of this invention allows inkjet printers to print hundreds of cards without even noticing the significant presence of fogging on the printed surface, i.e., no significantly erroneous ink dots throughout the printed image.

[0068] The above-mentioned technical features can be combined arbitrarily. Although not all possible combinations of the individual technical features are described, all combinations of these technical features should be considered within the scope described in this specification, provided they do not conflict.

[0069] Although the invention has been described in conjunction with embodiments, those skilled in the art should understand that the above description and drawings are merely illustrative and not restrictive, and that the invention is not limited to the disclosed embodiments. Various modifications and variations are possible without departing from the spirit of the invention.

[0070] List of reference numerals

[0071] 1 Inkjet printer

[0072] 2. Base Frame

[0073] 3 Storage Area

[0074] 4 cards

[0075] 5. Support carriage

[0076] 6. Plate-shaped trays

[0077] 7 Tray Heater

[0078] 8. Pickup Station

[0079] 9 Printing Stations

[0080] 10 Jet Stations

[0081] 11 Printhead

[0082] 12 Support Plates

[0083] 13 Main Roller

[0084] Auxiliary rollers 14, 15, 16, 17, 18

[0085] 19 The picked-up cards

[0086] 20 guide plates

[0087] 21 nozzles

[0088] 22 Ink

[0089] 23 Ink Drops

[0090] 24 Lord's Drop

[0091] 25 satellites

[0092] 26 Aerosols

[0093] 27 Expected Printed Image

[0094] 28 Actual printed images

[0095] 29. The Ink Spots of Error

[0096] 30 Ion Generator

[0097] 31 Ion generator housing

[0098] 32 holes

[0099] 33 electrical terminals

[0100] 34 Charged ions

[0101] 35 Mounting bracket

[0102] 36 Vertical support components

[0103] 37 Horizontal Support Components

Claims

1. An inkjet printer (1) for printing on cards, comprising: Printer frame, which includes a base frame (2); A support carriage (5) is mounted on the base frame to support the card to be printed; A printing station (9), which is mounted to the printer frame for inkjet printing on the top surface of the card, the printing station including at least one printhead (11). and An ion generator (30), mounted to the printer frame, is used to emit charged ions that can be sent to the top surface of the card. The ion generator is characterized in that it is actuated with a variable duty cycle and a variable intensity before and during printing.

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

3. The inkjet printer according to claim 2, wherein, The polarity of the emitted charged ions changes over a predetermined time interval to prevent the positively and negatively charged ions from neutralizing each other before reaching the top surface of the card.

4. The inkjet printer according to claim 1, wherein, The ion generator is a monopolar ion generator used to emit charged ions with a single polarity, and the charged ions can reach the top surface of the card by diffusion.

5. The inkjet printer according to claim 4, wherein, The unipolar ion generator includes: The ion generator housing (31) has a hole (32) for allowing the generated charged ions to exit. A pair of electrodes, which are housed within the ion generator housing; and A pair of electrical terminals (33) are connected to the ion generator power module on the inkjet printer, with one terminal for one electrode.

6. The inkjet printer according to any one of claims 1 to 5, wherein, The inkjet printer includes a mounting bracket (35) for mounting 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 also includes a top frame, which is connected to the base frame via side frames; and the ion generator is fixed to the top frame.

8. The inkjet printer according to any one of claims 1 to 5, wherein, The inkjet printer also includes a guide plate (20); the support carriage is arranged on the guide plate and guided by the guide plate to move between a first position and a second position, in the first position the support carriage is not facing the print head, and in the second position the support carriage faces the print head; The printing station is capable of moving laterally 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, When the support carriage is in the second position, the orthogonal projection of the ion generator in the base frame coincides with the center of the orthogonal projection of the support carriage in the base frame.

10. The inkjet printer according to any one of claims 1 to 5, wherein, The inkjet printer also includes: Storage area (3), which is used to store at least one card to be printed; and Extraction station (8) is used to extract the card from the storage area to the support carriage.

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