Digital printer, method for performing production of workpiece and printing to workpiece, and system for supplying workpiece on which printing is performed

Abstract

To provide a digital printer which can extend an interval of cleaning operations which should be performed in order to maintain the function of a printing head.SOLUTION: A digital printer 1 includes a printing head substrate 2, on which a printing head 3 for discharging ink droplets in a printing direction 11 and a drying unit 4 for hardening the ink droplets are attached, the printing head and a drying unit define an operation space 22, in an operation space a printing image is applied onto the outer side surface of the workpiece by the printing head and the printing image on the workpiece is dried, the drying unit is configured so as to supply electromagnetic waves to be used for photochemical polymerization of the ink droplets, the drying unit has a radiation source 18, and the radiation source 18 is constituted so as to supply electromagnetic waves having the maximum intensity value at the wavelength of 395 nm, preferably at the wavelength of 385 nm, in particular, at the wavelength of 365 nm.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a digital printing apparatus, a method for manufacturing a workpiece and printing on the workpiece, and a system for supplying the printed workpiece.

Background Art

[0002] In European Patent No. 3473446, a digital printing apparatus is known. This digital printing apparatus has a print head module and an ink unit. The ink unit is configured to supply printing ink to the print head module. The print head support has a support interface, and the support interface is configured to be connected to the print head interface. The print unit holder, the print unit interface, the ink unit, the print head interface, the support interface, and the print head module form a columnar assembly arranged along the printing direction. At least one ink storage portion and a drying module are arranged in a portion disposed below the workpiece plane in the vertical direction.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a digital printing apparatus, a method for manufacturing a workpiece and printing on the workpiece, and a system for supplying the printed workpiece, which enable an extension of a cleaning interval in which a cleaning operation for maintaining the function of the print head must be performed.

Means for Solving the Problems

[0005] This problem can be solved, from a first perspective, by a digital printing apparatus that prints on a workpiece. In this case, the digital printing apparatus is equipped with a print head support, on which a print head that ejects ink droplets in the printing direction and a drying unit that hardens the ink droplets are attached, and the print head and the drying unit define a working space, in which the print head applies a printed image to the outer surface of the workpiece and the drying unit dries the printed image on the workpiece, and the drying unit is configured to supply electromagnetic waves used for the photochemical polymerization of the ink droplets, and it is assumed that the drying unit has a radiation source, and the radiation source is configured to supply electromagnetic waves having a maximum intensity at a wavelength of 395 nanometers, preferably at a wavelength of 385 nanometers, and particularly at a wavelength of 365 nanometers.

[0006] In this type of digital printing apparatus, it is assumed that the workpiece is positioned in a fixed location in the workspace for a limited period of time and undergoes rotational motion, with the axis of rotation of the workpiece aligned perpendicular to the printing direction. This allows for the creation of a large-area print image on the outer surface of the workpiece. Typically, the print head has at least one row of ink nozzles, which have multiple ink nozzles arranged in a straight line and spaced at equal intervals, with each ink nozzle configured to eject ink droplets individually in the printing direction. Therefore, the rotational motion of the workpiece ejects multiple rows of ink droplets aligned parallel to each other onto the outer surface of the workpiece, thereby creating a print image. Consequently, the print image can have an area many times larger than the line width of the ink droplet rows ejected from the ink nozzles of the print head.

[0007] The rotation of the workpiece causes relative motion of the printing area with respect to the drying unit, so that ink droplets applied to the outer surface of the workpiece reach the range of the drying unit's electromagnetic waves, and as a result, the appropriately adjusted printing ink is cured by photochemical polymerization.

[0008] As a general rule, the drying unit is assumed to be located on the opposite side from the print head. This is because it can provide a beneficial shielding effect from the electromagnetic waves supplied by the drying unit by the workpiece placed in the workspace. Advantageously, the central beam of the drying unit's radiation source is aligned parallel to and opposite to the printing direction of the ink droplets. Particularly advantageous is that the central beam and the printing direction are coaxial with each other.

[0009] Therefore, in principle, electromagnetic waves supplied from the drying device can reach the print head, which can lead to unwanted hardening of the printing ink and, consequently, blockage of the ink nozzles of the print head. In practice, the drying unit is operated such that electromagnetic waves are emitted only when the workpiece is placed within the workspace and the presence of the workpiece blocks the optical path between at least one radiation source and the printing nozzles of the print head.

[0010] Of course, in many workpieces made from materials with a certain degree of photoconductivity, unwanted propagation of electromagnetic waves from the radiation source to the print head can occur, which can lead to unwanted hardening of the printing ink at the print head.

[0011] Therefore, according to the present invention, it is assumed that the drying unit is equipped with at least one radiation source, in particular multiple radiation sources, that supplies electromagnetic waves having a maximum intensity at a wavelength of 395 nanometers. By using radiation sources whose electromagnetic radiation corresponds to the ultraviolet light range, the propagation of electromagnetic radiation in a workpiece that can act as a certain type of optical conductor based on its shorter wavelength compared to longer wavelength light is reduced or blocked.

[0012] Therefore, since the print head does not generate a radiation intensity that could cause the printing ink to harden, this means significantly reduces the risk of ink nozzle blockage due to unwanted hardening of the printing ink. As a result, the cleaning interval, which represents the time interval between the two cleaning processes of the print head, can be extended compared to other drying units that supply longer-wavelength electromagnetic waves.

[0013] An advantageous development of the present invention is the subject of the dependent claims.

[0014] Advantageously, the radiation source is provided as a light-emitting diode (LED) having a semiconductor composed of aluminum nitride (AIN), aluminum gallium nitride (AlGaN), aluminum gallium indium nitride (AlGalnN), and diamond (C), and the semiconductor is configured to supply monochromatic electromagnetic waves. In principle, the light-emitting diode having the aforementioned semiconductor is configured to emit monochromatic light, provided that the wavelength spectrum supplied from the LED is broadened based on the interaction between the light supplied by the semiconductor and the surrounding material.

[0015] In one advanced form of the present invention, the radiation source is configured to supply electromagnetic waves at 50% of its maximum radiant intensity with wavelength intervals smaller than 13 nanometers, and / or to supply electromagnetic waves at 25% of its maximum radiant intensity with wavelength intervals smaller than 20 nanometers. This means that the radiation source emits electromagnetic waves having a narrowband wavelength distribution, and thus supplies electromagnetic waves with extremely low intensity, especially longer waves, starting from the wavelength that determines the maximum intensity of the radiation source, which in the case of a light-emitting diode corresponds to the wavelength of monochromatic light emitted from the semiconductor. Therefore, in conjunction with the use of appropriately adjusted printing inks, polymerization of the printing ink is induced only when irradiated with short-wave electromagnetic waves, and in view of the situation in which electromagnetic waves do not propagate through the workpiece based on short wavelengths, direct drying of the ink at the print head is avoided.

[0016] In another embodiment of the present invention, it is assumed that a short-pass filter, particularly configured as an absorption filter or a dichroic filter, is placed between the radiation source and the workspace, having a cutoff wavelength greater than 400 nanometers, preferably greater than 390 nanometers, and especially greater than 370 nanometers. With such a short-pass filter, electromagnetic waves with wavelengths greater than the cutoff wavelength of the short-pass filter are absorbed by the filter material (absorption filter) or reflected by the filter (dichroic filter), depending on the type of short-pass filter, and therefore do not reach the workpiece and, consequently, the print head. Preferably, the cutoff wavelength of the short-pass filter is assumed to be several nanometers greater than the wavelength at which the radiation source has its maximum intensity. For example, it is assumed that a radiation source with a maximum intensity of 365 nanometers is combined with a short-pass filter having a cutoff wavelength of 390 nanometers, preferably 370 nanometers.

[0017] A appropriately tuned short-pass filter blocks, at least in general terms, preferably almost completely, and especially completely, wavelengths emitted from a radiation source and guided from the workpiece to the print head, thereby increasing the design freedom of the workpiece. This design freedom relates particularly to material selection, because when using this type of short-pass filter, there is little need to pay attention to ensuring that the workpiece itself absorbs unwanted wavelengths. This is especially important with plastic materials, where otherwise, appropriate absorbers must be provided, which can result in both increased costs and changes in the material properties of each plastic material.

[0018] Advantageously, the print head support is fixed to the machine frame, and the machine frame is equipped with a workpiece transport device, particularly a workpiece turntable rotatably supported on the machine frame, the transport device being configured to supply workpieces to the workspace and to rotate the workpieces within the workspace about a rotation axis aligned transversely to the printing direction. This provides a digital printing apparatus that can be used to print on a large number of workpieces in a short time. In this case, the print head support is preferably fixed in place on the machine frame, and the machine frame may optionally be equipped with a series of other work stations, such as another print head support and / or equipment for pre-processing or post-processing workpieces before and after the execution of the printing process.

[0019] Preferably, the conveying device is configured to convey workpieces along a linear or arc-shaped conveying path, in which case it is assumed that a step motion is performed for each workpiece, that is, a series of movements of the workpiece during the processing stages, particularly during printing, and between the processing stages.

[0020] Therefore, it is assumed that the workpiece remains in the workroom each time, rotating around a rotation axis, with the rotation axis aligned perpendicular to the printing direction. This means that, for example, printing can be performed at least partially on the annular outer surface of a workpiece that is arranged coaxially with respect to the rotation axis.

[0021] The object of the present invention is a method for manufacturing a workpiece made of a transparent or translucent material and for printing on the workpiece, comprising the following steps: supplying the workpiece to the working space of a digital printing device; ejecting ink droplets from a print head onto a printing area on the outer surface of the workpiece; creating a printed image on the outer surface by rotating the workpiece about a rotation axis; curing the ink droplets by irradiating at least a partial area of the printed image with electromagnetic waves having a wavelength of 395 nanometers, preferably a wavelength of 385 nanometers, and particularly 365 nanometers, and having a maximum intensity supplied by a radiation source. This object is solved by the method.

[0022] In an improved form of the method, it is envisaged that the workpiece is made of a glass material having an optical transmittance of less than 25%, preferably less than 15%, and particularly less than 5% in a wavelength range of less than 400 nanometers. In this case, the workpiece itself acts in the form of a short-pass filter, thereby assisting other means for avoiding the propagation of long-wave electromagnetic waves to the print head.

[0023] In another form of the method, the workpiece is made of plastic, where the plastic is assumed to have an absorber of ultraviolet radiation selected from the group consisting of 2-(2-hydroxyphenyl)-2H-benzotriazole, (2-hydroxyphenyl)-s-triazine, hydroxybenzophenone, oxanilide, titanium dioxide, iron oxide, zinc oxide, cadmium stearate. This type of workpiece ensures that electromagnetic waves of a longer wavelength that can reach the print head based on the photoconductivity of the workpiece are absorbed by the workpiece, thus preventing unwanted drying of the ink at the print head.

[0024] In a further developed form of the method, it is envisaged that when rotating the workpiece about a rotation axis, the distance between the outer surface of the workpiece on which the printed image is provided and the print head is constant.

[0025] Preferably, it is assumed that the workpiece is rotationally symmetrically configured at least in the area of the printed image. Particularly preferably, it is assumed that the entire workpiece is rotationally symmetric and is particularly configured in the form of a cylindrical sleeve.

[0026] The problem of the present invention is solved by a system for supplying a printed workpiece, which system comprises a digital printing device according to the present invention and a workpiece, where the workpiece is made of a glass material having a light transmittance of less than 25%, preferably less than 15%, particularly less than 5% of electromagnetic waves in a wavelength range of less than 400 nanometers and / or is made of plastic.

[0027] Advantageous embodiments of the present invention are illustrated.

Brief Description of the Drawings

[0028] [Figure 1] Shown is a highly schematic side view of a digital printing device having a print head support, a print head, a drying unit, and a workpiece held on a rotatably supported spindle. [Figure 2] Shown is a highly schematic front view of the digital printing device shown in FIG. 1, in which the print head support is not shown.

Embodiments for Carrying Out the Invention

[0029] The digital printing device 1 shown highly schematically in FIGS. 1 and 2 has a print head support 2 shown only schematically, on which a print head 3 and a drying unit 4 shown only schematically are fixedly attached. The print head support 2 is coupled to a machine frame 5 shown only schematically as well, and the machine frame 5 is fixedly placed on the floor plate of the manufacturing site not shown in a form not shown in detail.

[0030] A workpiece turntable 6, indicated only by symbols, is pivotally supported on the machine frame 5 so as to rotate around a rotation axis 9. In this case, the workpiece turntable 6 may actually be formed in the shape of a disc, for example, and has a plurality of main spindles radially aligned on its circumferential surface located radially outward, of which only one main spindle 7 is shown exemplarily in Figure 13. The main spindle 7 is held on the workpiece turntable 6 so as to rotate around a rotation axis 10 and is formed in the shape of a cylinder, as merely an example. The main spindle 7 is used to hold a workpiece 8, which is formed in the shape of a circular sleeve, as merely an example, and the workpiece 8 may be, for example, a plastic container made from a transparent or translucent plastic material.

[0031] The print head 3 is located on its lower surface 20, facing the outer surface 12 of the workpiece 8, behind a plurality of ink nozzles (not shown). The ink nozzles are arranged at equal pitches along a straight line, in this case, aligned parallel to the axis of rotation 10. Each ink nozzle can be individually controlled by a control device for the print head 3 (not shown), thereby enabling the ejection of ink droplets (not shown) in the printing direction 11. As merely an example, the spindle 7 (together with the workpiece 8 held therein) and the print head 3 are aligned with each other during the execution of the printing process such that the printing direction 11 is identical to the surface normal of the outer surface 12 of the workpiece 8. The arrangement of the ink nozzles (not shown) allows the print head 3 to eject a freely selectable number of ink droplets onto the outer surface 12 of the workpiece 8 along a straight line oriented parallel to the axis of rotation 10. Therefore, in order to create a printed image on the outer surface 12, the workpiece 8 is rotated around the rotation axis 10, and as a result, it is assumed that a printed image can be created by multiple ink droplets positioned side by side. The area of ​​the outer surface 12 of the workpiece 8 that can be printed by the print head 3 is also called the printing area 15 and has the shape of a part of a cylindrical surface.

[0032] As can be seen particularly from the drawing in Figure 2, the drying unit 4 is located on the side opposite to the print head 3. The drying unit 4, together with the print head 3, defines the workspace 22. Within the workspace 22, the spindle 7, on which each workpiece 8 is mounted, is rotatable by the rotation of the workpiece turntable 6 around the rotation axis 9. To this end, the workpiece turntable 6 performs a rotational step motion, and a continuous rotational motion and a stationary phase are assumed. During the stationary phase, printing is performed on the workpiece 8, and in this stationary phase, the workpiece 8 is moved relative to the print head 3 by the rotation of the spindle 7 around the rotation axis 10.

[0033] The drying unit 4 has a housing 16, the housing 16 is provided with a recess 17, and a plurality of radiation sources 18, configured as light-emitting diodes as just one example, are arranged in the recess 17. In this case, each of the radiation sources 18 is provided to supply electromagnetic waves having a spectral wavelength distribution in which the maximum intensity is at a wavelength of 395 nanometers, preferably 385 nanometers, and particularly 365 nanometers. Preferably, all radiation sources 18 are configured identically and, accordingly, each has the same spectral wavelength distribution.

[0034] The radiation sources 18 are configured such that the central beam 21 of each radiation source 18, which indicates the spatial direction in which the radiation source 18 has maximum intensity, is aligned parallel to and particularly coaxially with respect to the printing direction 11 of the ink nozzle located on the opposite side, and are positioned within the recess 17.

[0035] The recess 17 in the housing 16 is covered by a filter 19 whose optical properties are selected so as to block, at least almost completely, wavelengths of electromagnetic waves supplied from the radiation source 18 that exceed a predetermined cutoff wavelength. This is achieved by absorption or reflection of electromagnetic waves, depending on the configuration of the filter 19. As just one example, the cutoff wavelength of the filter 19 is assumed to be several nanometers greater than the wavelength at which the radiation source 18 has its maximum intensity.

[0036] The workpiece 8 is preferably made from an optically transparent or optically translucent material, particularly glass, plastic, or a composite of glass and plastic, and therefore has the property that visible light can pass through the workpiece 8 with low loss. Thus, the workpiece 8 forms waveguides for electromagnetic waves in the wavelength range of 380 nanometers to 780 nanometers. In order to avoid having to abandon the transparency or translucency of the workpiece 8, and to prevent electromagnetic waves supplied from the drying unit 4 to the outer surface 12 of the workpiece 8 for drying ink droplets from traveling to the print head 3, the workpiece 8 is configured, by appropriate material selection, such that the propagation of electromagnetic waves having wavelengths smaller than 400 nanometers, preferably smaller than 390 nanometers, and particularly smaller than 370 nanometers, is at least essentially hindered.

[0037] These properties can be achieved by using an appropriate absorbent when glass is used as the material for the workpiece 8. Preferably, the absorbent has properties such that it does not change or only slightly changes other properties of the glass material used. Similarly, when plastic is used for the workpiece 8, an absorbent suitable for each plastic material can be used.

[0038] Therefore, considering the printing apparatus 1 and the workpiece 8 together, a printing system 30 is obtained. Based on the characteristics summarized below, the printing system 30 enables printing on transparent or translucent workpieces using an inkjet printing method, which ensures long cleaning intervals for cleaning the print head.

[0039] The ink droplets ejected from the print head 3 through an inkjet nozzle (not shown) into the printing area 15 of the workpiece 8 in the printing direction 11 are configured to polymerize with electromagnetic waves having a wavelength less than 400 nanometers, preferably less than 390 nanometers, and particularly less than 370 nanometers.

[0040] The workpiece 8 is manufactured from a transparent material, in particular glass and / or plastic, in which case the material used therefor ensures at least partial absorption of electromagnetic waves with wavelengths smaller than 400 nanometers, preferably smaller than 390 nanometers, and particularly smaller than 370 nanometers, by a corresponding absorbent.

[0041] At least one radiation source 18 is configured to supply electromagnetic waves having a maximum intensity at a wavelength of 395 nanometers, preferably 385 nanometers, and particularly 365 nanometers.

[0042] Furthermore, it is assumed that a filter 19 is positioned between at least one radiation source 18 and the working space 22 defined by the print head 3 and the drying unit 4, and that the filter 19 is configured as a short-pass filter having a cutoff wavelength greater than 400 nanometers, preferably greater than 390 nanometers, and particularly greater than 370 nanometers.

Claims

1. A digital printing apparatus (1) for printing on a workpiece (8), comprising a print head support (2), on which a print head (3) for ejecting ink droplets in a printing direction (11) and a drying unit (4) for curing the ink droplets are attached. The print head (3) and the drying unit (4) define a working space (22). In the working space (22), application of a printed image onto the outer surface (12) of the workpiece (8) by the print head (3) and drying of the printed image on the workpiece (8) by the drying unit (4) are performed. The drying unit (4) is configured to supply electromagnetic waves used for photochemical polymerization of the ink droplets. In the digital printing apparatus (1), the drying unit (4) has a radiation source (18), and the radiation source (18) is configured to supply electromagnetic waves having a maximum intensity value at a wavelength of 395 nanometers, preferably at a wavelength of 385 nanometers, particularly at a wavelength of 365 nanometers. A digital printing apparatus (1) characterized by this.

2. The radiation source (18) is provided as a light-emitting diode having a semiconductor selected from the group consisting of aluminum nitride, aluminum gallium nitride, aluminum gallium indium nitride, and diamond, and the semiconductor is configured to supply monochromatic electromagnetic waves. The digital printing apparatus according to claim 1, characterized by this.

3. The radiation source (18) is configured to supply electromagnetic waves at 50% of the maximum radiation intensity with a wavelength interval smaller than 13 nanometers, and / or at 25% of the maximum radiation intensity with a wavelength interval smaller than 20 nanometers. The digital printing apparatus according to claim 1, characterized by this.

4. Between the radiation source (18) and the working space (22), there is arranged a short-pass filter (19) which has a cut-off wavelength greater than 400 nanometers, preferably greater than 390 nanometers, particularly greater than 370 nanometers, and which is configured in particular as an absorption filter or as a dichroic filter. The digital printing apparatus according to claim 1 is characterized in this.

5. The print head support (2) is fixed to the machine frame (5), and on the machine frame (5), there is arranged a transport device for the workpiece, in particular a workpiece turntable (6) which is rotatably supported on the machine frame (5). The transport device is configured to supply the workpiece (8) to the working space (22) and to rotate the workpiece (8) about a rotational axis (10) which is aligned transversely to the printing direction (11) within the working space (22). The digital printing apparatus according to claim 1 is characterized in this.

6. A method for manufacturing a workpiece (8) made of a transparent or translucent material and for printing on the workpiece, comprising: supplying the workpiece (8) to the working space (22) of the digital printing apparatus (1); discharging ink droplets from the print head (3) onto a printing area (15) of the outer surface (12) of the workpiece; creating a printed image on the outer surface (12) by rotating the workpiece (8) about the rotational axis (10); hardening the ink droplets by irradiating at least a partial area of the printed image with electromagnetic waves having a wavelength of 395 nanometers, preferably a wavelength of 385 nanometers, particularly 365 nanometers, and having a maximum intensity value, supplied from the radiation source (18); A method characterized by having the above steps.

7. The method according to claim 6, characterized in that the workpiece (8) is manufactured from a glass material having an optical transmittance of less than 25%, preferably less than 15%, particularly less than 5% in a wavelength range less than 400 nanometers.

8. The workpiece (8) is made of plastic, and in this case, the plastic has an ultraviolet radiation absorber selected from the group consisting of 2-(2-hydroxyphenyl)-2H-benzotriazole, (2-hydroxyphenyl)-s-triazine, hydroxybenzophenone, oxanilide, titanium dioxide, iron oxide, zinc oxide, and cadmium stearate. The method according to claim 6, characterized in that.

9. When rotating the workpiece (8) about the axis of rotation (10), the distance between the outer surface (12) of the workpiece (8) where the printed image is provided and the print head (3) is constant. The method according to claim 6, 7, or 8, characterized in that.

10. A system for supplying a workpiece (8) on which printing has been performed, The digital printing apparatus according to any one of claims 1 to 5, A workpiece (8) manufactured from a glass material having a light transmittance of less than 25%, preferably less than 15%, particularly less than 5% of electromagnetic waves in a wavelength range smaller than 400 nanometers, and / or a workpiece (8) manufactured from plastic having an ultraviolet radiation absorber consisting of the group consisting of 2-(2-hydroxyphenyl)-2H-benzotriazole, (2-hydroxyphenyl)-s-triazine, hydroxybenzophenone, oxanilide, titanium dioxide, iron oxide, zinc oxide, and cadmium stearate, A system comprising.

Images