Printing device for printing on objects and printing process

Abstract

The invention relates to a printing device (1) for printing on objects (2). The printing device (1) comprises a printhead (10) configured to generate a pressure jet (12) or droplet jet (12) containing magnetically alignable material particles (14) in the direction of an object (2) to be printed, in order to convey the magnetically alignable material particles (14) to the object (2). The printing device (1) further comprises an alignment unit (20) configured to align the magnetically alignable material particles (14). The printhead (10) has a printhead opening (15) through which the pressure jet (12) or droplet jet (12) passes during a printing process, and the printhead opening (15) has an opening diameter (d) greater than 80 µm (micrometers).

Description

[0001] The present invention relates to jet printing methods for color materials using magnetically alignable particles. In particular, the invention relates to a printing device for printing on objects and a printing method for printing on objects.

[0002] Inkjet printers are used in a wide variety of applications today. They work by directing a jet of ink from a nozzle onto the object to be printed, typically applying tiny droplets of ink to specific areas of the object to create a printed image. Generally, a distinction can be made between continuous inkjet printers and drop-on-demand printers. The latter are also known as DOD (Drop-on-Demand) printers, piezoelectric printers, or bubble-jet printers.

[0003] Banknote printing also utilizes inks with so-called effect pigments, which are applied to a substrate surface to produce angle-dependent changes in hue or gloss after application and, if necessary, further processing steps. However, the effect pigments of such inks have certain properties that complicate their precise application to the substrate. For example, the size and shape of these effect pigments limit the possibilities for applying effect pigment inks.

[0004] It is an object of the present invention to make the application of colors with magnetically alignable particles more efficient.

[0005] This problem is solved by the subject matter of the independent claims. Further features of the invention will become apparent from the dependent claims, the following description, and the figures.

[0006] According to one aspect, a printing device, for example an inkjet printer, is intended for printing on objects. The printing device comprises a printhead designed to generate a jet of print or droplet containing magnetically alignable material particles, directed towards the object to be printed, thus conveying the magnetically alignable material particles to the object. The printing device further comprises an alignment unit designed to align the magnetically alignable material particles. The printhead has a printhead opening through which the jet of print or droplet passes during a printing process. The printhead opening preferably has an opening diameter greater than 80 µm (micrometers).

[0007] The printing device according to the invention makes it possible to print objects, for example plastic or paper substrates, with effect pigment colors more efficiently. In particular, the printing device is able to generate a jet of print or droplet spray with high precision onto an object, even though the jet of print or droplet spray contains magnetically alignable material particles that, due to their size and shape, could not normally be printed using conventional jet printers.

[0008] A printhead opening with a nozzle diameter greater than 80 µm facilitates the passage of magnetically alignable material particles through the printhead opening, as the pigment sizes of such particles are typically larger than 1 µm. With a smaller opening diameter, the size and shape of these particles could cause them to become wedged together in the printhead, blocking or at least hindering their passage. This, in turn, would affect the resulting print or droplet jet. The print or droplet jet should exit the printhead opening with the highest possible accuracy to ensure the required precision in applying the magnetically alignable material particles to the object being printed.

[0009] The printhead can therefore be part of a color jet printing device, in particular an inkjet printing device, which generates the print jet or droplet jet through the printhead opening, so that the magnetically alignable material particles are conveyed onto the object to be printed by means of the print jet or droplet jet.

[0010] The printhead can deliver either a jet or a droplet jet. The jet can form a continuous stream of material containing the magnetically alignable material particles in a distributed form. The droplet jet can form a discontinuous stream of material, in which individual droplets are generated by the printhead and sequentially delivered to the object being printed, with the magnetically alignable material particles contained in a distributed form within each droplet.

[0011] The object to be printed can be a flat substrate, for example, a plastic, paper, or cardboard material, on which a printed layer is created by means of the impacting pressure jet or droplet jet. This layer contains magnetically alignable material particles in a distributed arrangement. Preferably, the object to be printed is a paper material suitable for banknotes.

[0012] The pressure jet or droplet jet can contain components other than the magnetically alignable material particles. For example, the magnetically alignable material particles can be distributed within a liquid carrier material or arranged movably within such a liquid carrier material, allowing the alignment unit to direct the magnetically alignable material particles onto the object to be printed before or after application.

[0013] The magnetically alignable material particles can have an elongated or plate-like shape, allowing color effects to be created by changing their orientation to produce angle-dependent changes in hue or gloss. In particular, once applied to and aligned with the object, the magnetically alignable material particles can produce changes in hue or gloss when the object is viewed from different angles. Such color effects can enhance counterfeit protection and can also be used to improve aesthetics.

[0014] The alignment unit can align the magnetically alignable material particles, that is, change their position, location, and / or orientation, in order to create a first subset of similarly or identically oriented material particles, a second subset of differently oriented material particles, and so on. In this way, the color effect described above can be achieved.

[0015] According to one embodiment, the printhead is designed to generate the print jet or droplet jet with magnetically alignable material particles that have a particle dimension greater than 1 µm (micrometer).

[0016] The magnetically alignable material particles are therefore not nanoparticles or colloids with dimensions smaller than approximately 1 µm. The printing device according to the invention is therefore suitable for jet printing, in particular inkjet printing, with magnetically alignable material particles, for example effect pigments, which have a minimum size of 1 µm.

[0017] According to one embodiment, the printhead is designed to generate the print jet or droplet jet with magnetically alignable material particles having a particle length of 20 µm (micrometers) to 30 µm (micrometers).

[0018] As explained above, the magnetically alignable material particles can have an elongated or plate-like shape, with a particle length of 20 µm to 30 µm along their longitudinal or greatest extent. The printhead opening diameter can be selected such that four magnetically alignable material particles fit side by side into the printhead opening, i.e., the nozzle opening. With a maximum pigment size of 30 µm (micrometers), the minimum printhead opening diameter can be 73 µm (micrometers). Preferably, the minimum printhead opening diameter is 80 µm (micrometers), as described above.

[0019] According to one embodiment, the printhead is designed to generate the print jet or droplet jet with magnetically alignable material particles, which at least partially comprise magnetically alignable effect pigments.

[0020] The magnetically alignable effect pigments are, for example, a component of a printing ink also known as OVMI (optically variable magnetic ink). Such color pigments with a magnetic moment can be printed onto the object to be printed using the printing device according to the invention. The effect pigments can have ferromagnetic material properties and / or metal oxide layers on their surfaces. The magnetically alignable effect pigments can, for example, also be in the form of gold pigments, which, after alignment in the printing layer on the object, can create a gold-colored gradient between light and dark for the viewer. Likewise, the magnetically alignable effect pigments can be in the form of colored ink with magnetic pigment, which, after application to the object to be printed, creates a shadow.

[0021] According to one embodiment, the printhead is designed to generate the print jet or droplet jet with magnetically alignable material particles that are in the form of non-colloidal particles.

[0022] The magnetically alignable material particles do not include nanoparticles or colloidal particles with maximum dimensions or sizes smaller than approximately 1 µm (micrometer). Rather, the magnetically alignable material particles used here have a minimum size of approximately 1 µm (micrometer).

[0023] According to one embodiment, the alignment unit is designed to align the magnetically alignable material particles of the pressure jet or droplet jet during the conveyance of the magnetically alignable material particles in the direction of the object.

[0024] The alignment unit can therefore be designed or positioned relative to the print jet or droplet jet in such a way that the magnetically alignable material particles can be aligned or pre-aligned before they even strike the object, i.e., already within the print jet or droplet jet. Such pre-alignment of the magnetically alignable material particles within the print jet or droplet jet can be facilitated by the aforementioned printhead opening diameter of greater than 80 µm.

[0025] According to one embodiment, the alignment unit is designed to align the magnetically alignable material particles after they have been conveyed to the object.

[0026] The alignment unit can therefore be used to align the material particles applied to the object immediately after printing, while the ink containing the magnetically alignable particles is still liquid. Subsequently, a binder in the ink can be cured, for example, using a UV irradiation device or a UV curing device, to fix the alignment of the particles or pigments. Alternatively, a hot air supply device can be used to cure the ink's binder with a stream of hot air. Similarly, an infrared irradiation device can be used to cure the ink's binder using infrared radiation. Furthermore, a microwave irradiation device can be used to cure the ink's binder, for example, a resin, using microwave radiation.

[0027] According to one embodiment, the printing device comprises a printing plate for receiving the object to be printed, wherein the alignment unit is provided in the area of ​​the printing plate to align the magnetically alignable material particles.

[0028] The alignment unit can be positioned partially or completely directly beneath the object to be printed and, after the magnetically alignable material particles strike it, align or orient them on the object. Alternatively, the alignment unit can also be positioned partially or completely above the object to be printed.

[0029] Alternatively, the alignment unit can also be arranged outside a printing area, whereby the object is transported out of the printing area of ​​the printing device after the application of the magnetically alignable material particles and into an alignment area where the alignment of the magnetically alignable material particles takes place.

[0030] According to one embodiment, the alignment unit is arranged at least partially or completely above the printing surface.

[0031] This has the advantage that the alignment unit can be integrated into the printing device together with the printhead and moved along with it. This allows the printhead, along with the alignment unit, to be moved over the object to apply the ink, thereby depositing the magnetically alignable material particles. As the printhead moves, the alignment unit also moves over the object, aligning the material particles. This enables a compact design, for example, by combining the printhead and the alignment unit into a single unit that can be moved back and forth over the object.

[0032] According to one embodiment, the alignment unit has at least one magnet which is designed to generate a magnetic field in order to align the magnetically alignable material particles on the object by means of the magnetic field.

[0033] The alignment unit can have several magnets arranged above and / or below the printing surface or the object. This allows the magnetically alignable material particles to be oriented differently in various areas of the object. The alignment unit can be configured to allow for the adjustment of at least one magnet, or an arrangement of several magnets, to selectively set different magnetic fields or field strengths in specific areas of the printed layer on the object. This can be achieved via a movement mechanism within the printing device, on which the magnet(s) are movably mounted. The at least one magnet can be a permanent magnet and / or in the form of a magnetic cylinder. In particular, the at least one magnet can magnetize the magnetically alignable material particles to align them.

[0034] For example, a magnet in the alignment unit can also be provided in the area of ​​the printhead to pre-align the material particles in the printhead or in the print jet or droplet jet exiting the printhead.

[0035] According to one embodiment, the alignment unit has at least one electromagnet designed to generate a magnetic field with variable magnetic field strength in order to align the magnetically alignable material particles on the object by means of the magnetic field with variable magnetic field strength.

[0036] The alignment unit can have several electromagnets arranged above and / or below the printing surface or the object. This allows the magnetically alignable material particles to be oriented differently in various areas of the object. The alignment unit can be configured to allow for the adjustment of at least one electromagnet, or an arrangement of several electromagnets, to selectively set different magnetic fields or field strengths in specific areas of the printed layer on the object. This can be achieved via a movement mechanism within the printing device, on which the electromagnet(s) are movably mounted.The at least one electromagnet can, in particular, set a magnetic field with a specific field strength in order to magnetize the magnetically alignable material particles within the magnetic field, so that they are aligned.

[0037] One example further illustrates the use of a printing device, as described herein, for producing at least a partially printed security feature for a security document. The security document could be, for example, a banknote, an identity card or passport, or a card-shaped data carrier such as a payment card or the like.

[0038] According to one aspect, a printing process, for example an inkjet printing process, is provided for printing on objects. In one step of the process, a print jet or droplet jet containing magnetically alignable material particles is generated by means of a print head having a print head opening with an opening diameter preferably greater than 80 µm (micrometers). In a further step, the print jet or droplet jet is conveyed towards the object to be printed. In a further step, the magnetically alignable material particles are aligned by an alignment unit. The process steps can be carried out in the aforementioned order.

[0039] The above-described material components of the printing device according to the invention can each be configured to perform the respective steps of the printing process.

[0040] Exemplary embodiments of the invention are explained in more detail below with reference to schematic drawings. Fig. Figure 1 shows a printing device with a first arrangement of an alignment unit for aligning magnetically alignable material particles. Fig. Figure 2 shows a printed layer applied to an object with magnetically aligned material particles. Fig. Figure 3 shows a printing device with a second arrangement of an alignment unit for aligning magnetically alignable material particles. Fig. Figure 4 shows a printing device with a third arrangement of an alignment unit for aligning magnetically alignable material particles. Fig. Figure 5 shows a flowchart for a printing process for printing on objects.

[0041] In the figures, identical or functionally equivalent elements are given the same reference symbols.

[0042] Fig. Figure 1 shows a printing device 1 with a printhead 10, which is configured to generate a pressure jet 12 or droplet jet 12 containing magnetically alignable material particles in the direction of an object 2 to be printed, in order to convey the magnetically alignable material particles to the object 2. The printing device 1 further comprises an alignment unit 20, which is provided in the printing device 1 according to a first arrangement. In the Fig. In the case shown in Figure 1, the alignment unit 20 comprises at least two alignment elements 21, 22, which are arranged above a printing surface 30 on which the object 2 to be printed is located. It should be noted that, in addition to the two alignment elements 21, 22 of the alignment unit 20, further alignment elements or only one alignment element may be provided, which may also be located above or below the printing surface 30. The printing surface 30 is configured to receive the object 2 to be printed. The printing surface 30 can be designed as a base, table, or platform.

[0043] The print surface 30 and the print head 10 can be moved relative to each other along the direction of movement 3 (indicated by arrows). For example, the print head 10 can be movable within the printing device 1, while the print surface 30 is fixed within the printing device 1. Conversely, the print head 10 can also be fixed within the printing device 1, while the print surface 30 is movable within the printing device 1. It can also be provided that the print head 10 is moved relative to the print surface 30 by means of a rotary movement. In this case, the print head 10 can be moved, for example, around the print surface 30 or around the object 2 to be printed. Such a rotary movement can be additional to or alternative to the movement described in the Fig. The relative movement shown in 1 will take place in 3.

[0044] The printhead 10 can be attached to a carrier unit 11 of the printing device 1, which ultimately moves the printhead 10 relative to the printing surface 30. The carrier unit 11 can also include a container or feeder for a colorant containing magnetically alignable material particles. By means of the pressure jet 12 or droplet jet 12 directed onto the object 2, a print layer 13, for example in the form of a printed image, can be created on the object 2.

[0045] The printhead 10 is configured to convey the print jet 12 or droplet jet 12 containing the magnetically alignable material particles from the printhead 10 onto a surface of the object 2 to be printed, so that the print layer 13 containing the magnetically alignable material particles is created on the surface of the object 2. Fig. 1 magnetically alignable material particles not shown can be magnetically aligned either during their transport in the pressure jet 12 or droplet jet 12, or only when they have come to rest within the pressure layer 13 on the object 2, i.e. after being transported onto the object 2.

[0046] The alignment elements 21, 22 of the alignment unit 20 can be provided in the form of magnets that generate a magnetic field, so that the magnetically alignable material particles can be aligned on the object 2 by means of the magnetic field.

[0047] The alignment elements 21, 22 of the alignment unit 20 can also be in the form of electromagnets that generate a magnetic field with variable magnetic field strength. This field allows the magnetically alignable material particles on the object 2 to be aligned. The generated magnetic field strength can be varied by changing the electric current applied to the electromagnet. In one example, the printing plate 30, along with the object 2, is moved along the direction of movement relative to the alignment elements 21, 22 (i.e., the electromagnets), so that the electromagnets are located over different areas of the object 2 or over the printing layer 13 at different times.By additionally varying the field strength over time, the magnetically alignable material particles can be aligned differently in certain areas or with varying intensity. The... Fig. Figure 2 shows an example of magnetically alignable material particles 14, which have been oriented differently in certain areas. The alignment elements 21, 22 can be moved by means of a rotational movement. For example, the alignment elements 21, 22 can be moved around the printing surface 30 or around the object 2 to be printed. In other words, the alignment elements 21, 22 can be moved around the object 2 to be printed, for example in a circular motion perpendicular to the direction of movement 3, in order to align the magnetically alignable material particles.

[0048] The magnetically alignable material particles used can be part of a paint or varnish material in which they are dispersed. These particles can have minimum dimensions of 1 µm (micrometer). For example, they can have maximum dimensions between 20 µm (micrometers) and 30 µm (micrometers). The paint material, including the magnetically alignable material particles, is applied to the object 2 by the pressure jet 12 or droplet jet 12. To generate a precise pressure jet 12 or droplet jet 12 that ultimately produces a sharp printed image on the object 2, the print head 10 or print nozzle can have an opening 15 with a diameter greater than 80 µm (micrometers).This prevents the magnetically alignable material particles of the specified size from becoming wedged or blocked in the printhead 10, while still ensuring a precise print jet 12 or droplet jet 12.

[0049] Based on the Fig. 1 shows Fig. 2 now the printed layer 13 applied to object 2 with the magnetically aligned material particles 14. In Fig. Figure 2 shows in particular an example of magnetically alignable material particles 14 which were oriented differently in certain areas by means of the alignment elements 21, 22 of the alignment unit 20. For this purpose, the alignment unit 20 can generate a differently oriented magnetic field and / or a different field strength over different areas of the printing layer 13. This can be achieved by relative movement of the printing surface 30 with respect to the alignment unit 20 along the direction of movement 3 (see Figure 2). Fig. 1) In a first area 131, the material particles 14 can, for example, be aligned obliquely to the surface of the object 2, in a second area 132, the material particles 14 can, for example, be aligned parallel to the surface of the object 2, in a third area 133, the material particles 14 can, for example, be aligned perpendicular to the surface of the object 2, and in a fourth area 134, the material particles 14 can, for example, again be aligned obliquely to the surface of the object 2.

[0050] Fig. Figure 3 shows a printing device 1 in which the alignment elements 21, 22 of the alignment unit 20 are provided according to a second arrangement. The alignment elements 21, 22, which can be in the form of permanent magnets or electromagnets, are rigidly coupled to the printhead 10, for example via the carrier unit 11, so that the alignment elements 21, 22 together with the printhead 10 can be moved along the direction of movement 3 relative to the printing surface 30 or to the object 2. It can be provided that the alignment elements 21, 22 are moved by means of a rotary movement. In this way, the alignment elements 21, 22 can be moved, for example, around the printing surface 30 or around the object 2 to be printed.In other words, the alignment elements 21, 22 can be moved around the object 2 to be printed, for example in a circular motion perpendicular to the direction of movement 3, in order to align the magnetically alignable material particles. Such a rotational movement can be used in addition to or as an alternative to the movement shown in . Fig. The relative motion shown in section 3 will take place. Regarding the further details in Fig. The explanations of the 3 components shown and their functions are based on the following: Fig. 1 referred.

[0051] It may be provided that, in addition to the printhead 10 and the alignment elements 21, 22, a drying unit (not shown) is also coupled to the carrier unit 11, so that the drying unit, together with the alignment elements 21, 22 and the printhead 10, can be moved along the direction of movement 3 relative to the print surface 30 or to the object 2. In this movement direction 3, the printhead 10 can be positioned first, followed by the alignment elements 21, 22, and only then the drying unit. In this way, the print layer 30, containing the magnetically alignable material particles 14, can first be applied to the object 2. As the carrier unit 11 moves in the direction of movement 3, the magnetically alignable material particles 14 contained in the print layer 30 can then be aligned by means of the alignment elements 21, 22, for example as shown in Fig. Figure 2 illustrates this. If the carrier unit 11 continues moving in direction 3, the drying unit can now dry and / or harden the printed layer 13 along with the previously aligned material particles 14, thus essentially freezing the alignment state of the material particles 14. Drying or hardening can be achieved using a UV irradiation device, a hot air supply device, an infrared irradiation device, and / or a microwave irradiation device. In particular, a binder of the ink or the printed layer 13 is hardened or dried. After drying, the previously aligned material particles 14 can no longer move within the printed layer 13 and retain their alignment, thus providing an optically variable effect, such as a viewing angle-dependent color change or gloss change, for a viewer of the printed object.

[0052] Fig. Figure 4 shows a printing device 1 in which the alignment elements 21, 22 of the alignment unit 20 are provided according to a third arrangement. The alignment elements 21, 22, which can be in the form of permanent magnets or electromagnets, are rigidly coupled to the printing surface 30, so that the alignment elements 21, 22 together with the printing surface 30 can be moved along the direction of movement 3 relative to the print head 10. Regarding the further details in Fig. The explanations of the four components shown and their functions are based on the following: Fig. 1 referred.

[0053] Fig. Figure 5 shows a flowchart for a printing process for printing on objects. The printing process can be, for example, one of the methods described in the Fig. 1, Fig. 3 and Fig.The printing process is carried out using the four printing devices 1 shown. In step S1, a magnetically alignable pressure jet 12 or droplet jet 12 containing material particles 14 is generated by a printhead 10, which has a printhead opening 15 with an opening diameter 15 greater than 80 µm (micrometers). In step S2, the pressure jet 12 or droplet jet 12 is directed towards an object 2 to be printed. In step S3, the magnetically alignable material particles 14 are aligned by an alignment unit 20.

Claims

[1] Printing device (1) for printing on objects (2), comprising: a print head (10) designed to generate a pressure jet (12) or droplet jet (12) containing magnetically alignable material particles (14) in the direction of an object (2) to be printed, in order to convey the magnetically alignable material particles (14) to the object (2); an alignment unit (20) designed to align the magnetically alignable material particles (14); wherein the printhead (10) has a printhead opening (15) through which the print jet (12) or droplet jet (12) passes during a printing process; wherein the printhead opening (15) has an opening diameter (d) greater than 80 µm. [2] Printing device (1) according to one of the preceding claims, wherein the printhead (10) is configured to generate the print jet (12) or droplet jet (12) with magnetically alignable material particles (14) having a particle dimension greater than 1 µm; and / or wherein the printhead is designed to generate the print jet (12) or droplet jet (12) with magnetically alignable material particles (14) having a particle length of 20 µm to 30 µm. [3] Printing device (1) according to one of the preceding claims, wherein the print head (10) is configured to generate the print jet (12) or droplet jet (12) with magnetically alignable material particles (14) comprising at least partially magnetically alignable effect pigments. [4] Printing device (1) according to one of the preceding claims, wherein the print head (10) is configured to generate the print jet (12) or droplet jet (12) with magnetically alignable material particles (14) which are in the form of non-colloidal particles. [5] Printing device (1) according to any one of the preceding claims, wherein the alignment unit (20) is configured to align the magnetically alignable material particles (14) of the pressure jet (12) or droplet jet (12) during the conveyance of the magnetically alignable material particles (14) in the direction of the object (2); and / or wherein the alignment unit (20) is designed to align the magnetically alignable material particles (14) after the magnetically alignable material particles (14) have been conveyed to the object (2). [6] Printing device (1) according to any of the preceding claims, comprising: a printing plate (30) to hold the object to be printed (2); wherein the alignment unit (20) is provided in the area of ​​the printing surface (30) in order to align the magnetically alignable material particles (14). [7] Printing device (1) according to claim 6, wherein the alignment unit (20) is arranged at least partially or completely above the printing surface (30). [8] Printing device (1) according to one of the preceding claims, wherein the alignment unit (20) has at least one magnet which is designed to generate a magnetic field in order to align the magnetically alignable material particles (14) on the object (2) by means of the magnetic field. [9] Printing device (1) according to one of the preceding claims, wherein the alignment unit (20) has at least one electromagnet which is designed to generate a magnetic field with variable magnetic field strength in order to align the magnetically alignable material particles (14) on the object (2) by means of the magnetic field with variable magnetic field strength. [10] Printing methods for printing on objects (2), comprising: Generating a magnetically alignable pressure jet (12) or droplet jet (12) containing material particles (14) by means of a printhead (10) having a printhead opening (15) with an opening diameter (15) greater than 80 µm (S1); Conveying the pressure jet (12) or droplet jet (12) towards an object to be printed (2, S2); Alignment of the magnetically alignable material particles (14) by an alignment unit (20, S3).

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