Device with irradiator for curing UV-curable fluid on substrate

Abstract

The invention relates to a device for curing a UV-curable fluid on a printing substrate, such as a printing color or ink, the device having an irradiator, wherein the irradiator (5) comprises a flash lamp (6), characterized in that the irradiator (5) comprises at least two flash lamps (6) arranged in an array (10). The invention advantageously enables uniform / homogeneous and also environmentally friendly and cost-effective curing of the UV-curable printing fluid.

Description

Technical Field

[0001] The invention relates to a device having a radiator for curing a UV-curable fluid on a printing substrate. Background Art

[0002] The technical field to which the invention belongs lies in the field of the graphics industry and in particular in the field of curing preferably polymerizable fluids (such as pigments, varnishes, primers and / or liquid inks) on substrates / printing materials in the form of sheets, webs, films or labels, preferably made of paper, cardboard, kraft paper, plastic, metal or composite materials. In this case, the curing is achieved by subjecting the applied fluid to electromagnetic radiation, in particular by ultraviolet radiation (UV). In this case, the fluid (or at least its polymerizable parts) polymerizes.

[0003] In order to produce printed products in a printing press, the substrate (such as paper, cardboard or film) can be printed with different fluids. These fluids are usually printing pigments, inks, varnishes or combinations thereof. After applying these fluids, the printed substrate can be dried and / or cured in the printing press. A common group of fluids is dried by removing the solvent (usually water). Infrared dryers and hot air dryers are usually used in printing presses. Another common group of fluids is cured under the action of UV radiation or electron radiation. These fluids are usually compositions based on acrylates or other unsaturated compounds, which are partially polymerized under the action of ultraviolet or electron radiation in the presence of one or more photoinitiators and thus cured.

[0004] The curing process of UV-curable fluids in the printing press is usually divided into two stages. In the first step, only the initial curing Radiation-curable fluids (such as UV inks, UV varnishes or UV printing pigments). This preliminary curing is also called pinning. For this purpose, the radiation-curable fluid is usually irradiated with a relatively small dose of UV radiation with a longer wavelength shortly after it has been applied to the printing substrate. This fixes the printed image sufficiently so that it can be transported further through the machine and printed with other colors of fluid without undesired changes. In the prior art, LED radiators are usually used to achieve preliminary curing.

[0005] In the second step, usually at the end of the printing process, after all the pigments have been printed and the printed substrate has been finished with UV varnish if necessary, a final curing takes place. In the final curing, mercury vapor lamps emitting high-intensity ultraviolet rays with a particularly short wavelength are usually used in the prior art. In this way, the curing reaction in the initially cured radiation-curable fluid is completely or almost completely completed. The result is a cured print (such as a printed package, poster or brochure) that can be used in the usual way without blocking or fading.

[0006] In the printing industry there is a need for technical solutions for curing which are cost-effective and sufficient without the use of mercury vapor lamps.

[0007] Xenon flash lamps are in principle suitable for fully curing free-radical-curing pigment systems, since they have a broad spectrum that also includes the radiation fraction from UV-A to UV-C. Xenon flash lamps are available in different designs, of which the classic variant with an elongated glass tube is the most common, since this design offers the highest optical power.

[0008] DE 2019270 A1 describes a method and a device for curing a layer applied to an object, wherein a xenon pulse tube is used as the light source.

[0009] Xenon flash lamps with glass tubes can cover the format width of the printing press. However, in the direction transverse to the tube (i.e. in the printing direction or the conveying direction of the printing press), areas of the printed material may be irradiated with different intensities due to the periodic irradiation with the flash. But format-wide flash lamps are difficult to control and operate. In addition, the complexity of controlling the power of xenon flash lamps increases with the size (or position / length) of the lamp. This also applies to the build space for the power control. Summary of the invention

[0010] The object of the present invention is therefore to provide a technical solution which is improved compared to the prior art and which in particular allows uniform / homogeneous and yet environmentally friendly and cost-effective curing of UV-curable printing fluids.

[0011] This object is achieved according to the invention by a device.

[0012] Advantageous and therefore preferred developments of the invention are apparent from the preferred embodiments and from the description and the drawings.

[0013] According to the invention, a device for curing a UV-curable fluid on a printing substrate is provided, the device having an irradiator, wherein the irradiator comprises a flash lamp, characterized in that the irradiator comprises at least two flash lamps arranged in an array.

[0014] The invention advantageously enables UV-curable printing fluids to be cured uniformly / homogeneously and yet environmentally friendly and cost-effectively.

[0015] The flash lamp is preferably a gas discharge lamp in which the gas discharge does not occur continuously but in short pulses. During such a pulse, a preferably previously charged energy store, such as a capacitor, is discharged in a very short time through the flash lamp. The flash lamp can preferably be designed in a tubular shape and can then be referred to as a flash tube or pulse tube.

[0016] The UV light of the flash lamp is preferably unfocused in order to avoid excessively high energy densities that could damage the fluid and / or the printing substrate and / or to prevent problems of uneven curing when the printing substrate vibrates.

[0017] The respective power of the radiator and / or of the individual flash lamps is preferably controllable or adjustable, in particular controllable or adjustable in such a way that an optimal curing is achieved.

[0018] The individual flash lamps of the radiator can be replaced in an advantageous manner (for example in the event of a malfunction). In this case, the radiator itself can, for example, remain in the device.

[0019] Advantageously, one or more radiators can be constructed using flash lamps of identical construction. This increases the number of components and reduces the complexity and costs associated therewith.

[0020] It can be provided that at least two of the flash lamps are operated in a clocked / periodic manner (for example in flash mode) and that at least one other of the flash lamps is operated in a continuous mode (for example in CW mode).

[0021] The fluid is a printing fluid, preferably a pigment, a varnish, a primer and / or a liquid ink.

[0022] The printing substrate is preferably a printing material in the form of a sheet, strip, film or label, for example made of paper, cardboard, kraft paper, plastic, metal or a composite material (ie essentially two-dimensional or flat); alternatively, it is a three-dimensional object, for example made of plastic.

[0023] The following describes a preferred expansion scheme of the present invention (hereinafter referred to as expansion scheme).

[0024] An extension can be characterized in that the radiator comprises at least two flash lamps arranged in another arrangement, or a further radiator is provided, which comprises at least two flash lamps arranged in another arrangement. In this way, the radiation intensity can be adjusted. Alternatively or additionally, the radiation intensity can be adjusted by a variable conveying speed of the printing substrate. It can preferably be provided that the flash lamps of the first arrangement only preliminarily cure ("nail") the fluid, while the flash lamps of the second arrangement finally cure the fluid. Areas of high fluid density on the printing substrate can preferably be cured by irradiating these areas multiple times with ultraviolet light (preferably with ultraviolet light from multiple flash lamps) in the conveying direction of the printing substrate.

[0025] One development can be characterized in that the flash lamps are designed as tubes and each have a longitudinal axis in the direction of the tube.

[0026] A feature of an extended solution may be that the flashlights in the arrangement and / or the flashlights in the other arrangement are adjacent to each other and the adjacent flashlights do not overlap each other. A further development may be characterized in that the longitudinal axes of the flash lamps are coaxial with each other. A further development may be characterized in that the longitudinal axes of the flash lamps are located on a straight line in the direction of the arrangement. The straight line may preferably be perpendicular to the conveying direction of the printing substrate. A further development may be characterized in that the flash lamps are spaced apart from each other.

[0027] A feature of an extended solution may be that the flashlights in the arrangement and / or the flashlights in the other arrangement are adjacent to each other and the adjacent flashlights are arranged in an overlapping manner. A feature of an extended solution may be that the longitudinal axis of each second (i.e., every other) flashlight of these flashlights is located on a first straight line in the arrangement direction, and the longitudinal axis of each other flashlight of these flashlights is located on a second straight line in the arrangement direction, wherein the two straight lines are parallel and spaced apart from each other. These straight lines may preferably be perpendicular to the conveying direction of the printing substrate. A feature of an extended solution may be that the flashlights on the first straight line have a spacing from each other, and the flashlights on the second straight line have the same spacing from each other. A feature of an extended solution may be that the flashlights on the second straight line are arranged centrally relative to the gaps between the flashlights on the first straight line. A feature of an extended solution may be that a device for control or regulation is provided, and the device for control or regulation sets the spacing by means of a motor so that the fluid achieves a predetermined solidification. The overlapping method can preferably be selected in such a way that a uniform solidification is achieved.

[0028] The spacing of the flash lamps (both for the “no overlap” variant and for the “overlap” variant) can advantageously be selected such that the fluid on the printing substrate is irradiated essentially homogeneously, in particular in a direction perpendicular to the transport direction of the printing substrate.

[0029] An extended solution can be characterized in that the longitudinal axis of the flash lamp is arranged obliquely relative to the direction of the arrangement. The inclined flash lamp advantageously increases the duration of the irradiation of the fluid with ultraviolet light. This is particularly advantageous when the conveying speed of the printing substrate is high. An extended solution can be characterized in that the inclination is adjustable or settable. An extended solution can be characterized in that the inclination can be adjusted or set by a motor. An extended solution can be characterized in that a device for control or regulation is provided, which sets the inclination by means of a motor in such a way that a predetermined curing of the fluid is achieved, for example even in the case of printing substrates of different specifications / formats. That is to say, the adjustable inclination of the flash lamp can be used in an advantageous manner to adapt the radiator to different formats of the printing substrate.

[0030] Page-wide or format-wide radiators can preferably be constructed by arranging a plurality of flash lamps (in particular flash tubes) in an array. In this way, radiators for different formats can be constructed using a plurality of identical flash lamps. In this case, the device for controlling the radiator can be constructed from a plurality of identical sub-devices and the available construction space can thus be used more efficiently (in other words: a plurality of "small" control units instead of one "large" control unit). This building block system ("small" tubes with "small" control unit) can be used in an advantageous manner to construct radiators for different printing presses (i.e. for printing presses for different formats). In this case, the flash lamps can be arranged with or without overlap and / or with or without tilt.

[0031] The number of flash lamps that are active during curing (both for the "no overlap" variant and for the "overlap" variant as well as for the "inclined" variant) can be varied by individually controlling the flash lamps and in this way adapted to different formats of the print substrate. In the case of smaller formats, the flash lamps at the beginning and end of the array can advantageously be switched off depending on the format.

[0032] One development can be characterized in that the longitudinal axes of the flash lamps are parallel to one another and are preferably arranged in a non-coaxial manner. One development can be characterized in that the longitudinal axes of the flash lamps are perpendicular to a straight line in the arrangement direction (or more generally, form an angle with it that is not equal to 0° and 180°). The straight line can preferably be parallel to the conveying direction of the printing substrate. One development can be characterized in that the flash lamps are spaced apart from one another in the conveying direction.

[0033] The printing substrate is advantageously conveyed at a distance from one or more radiators, preferably in a range of 35 mm to 75 mm, for example 55 mm. The printing substrate is advantageously conveyed at a predetermined or variable conveying speed, for example, and the flashes (or: pulses) of the flash lamp are generated in a controlled, clocked manner so that the fluid on the printing substrate is irradiated substantially homogeneously, in particular in a direction parallel to the conveying direction of the printing substrate.

[0034] An extended solution may be characterized in that a plurality of radiators are arranged in a curved plane. An extended solution may be characterized in that a plurality of arrangements are arranged in a curved plane. An extended solution may be characterized in that the curved plane is formed by a carrier for the radiators and / or the arrangements. An extended solution may be characterized in that the curvature of the plane and / or the carrier can be changed (for example by means of a flexible carrier). The curvature can be adjusted in this way, for example, depending on the curvature of a roller that holds and / or transports the printing substrate. An extended solution may be characterized in that the curvature of the plane can be changed by a motor. An extended solution may be characterized in that a device for control or regulation is provided, which sets the curvature by means of a motor in such a way that a predetermined solidification of the fluid is achieved.

[0035] One development can be characterized in that the flash lamp is designed as a gas discharge lamp. One development can be characterized in that the flash lamp is designed as a xenon flash lamp and / or a krypton flash lamp. Xenon flash lamps advantageously have a broad UV spectrum and are also mercury-free.

[0036] One development may be a printing press designed for transferring and curing a UV-curable fluid onto a print substrate, characterized in that the printing press has at least one of the above-described devices.

[0037] One development can be characterized in that the printing press is a printing press that prints with offset printing ink. One development can be characterized in that the printing press is a printing press that prints with ink. One development can be characterized in that the printing press is a printing press that prints on essentially two-dimensional and / or essentially three-dimensional printing substrates (objects). One development can be characterized in that the printing press is a printing press that prints on sheets or webs of printing material.

[0038] One development can be characterized in that the sheets or webs are transported in the printing press essentially in a conveying direction and the device is arranged in the printing press in a transverse direction transverse to the conveying direction. One development can be characterized in that the arrangement is arranged transverse to the conveying direction. One development can be characterized in that the flashlights of the device, in particular their longitudinal axes, are arranged in the transverse direction.

[0039] An extended solution may be characterized in that the sheets or webs are transported in the printing press essentially in the conveying direction and the device is arranged in the conveying direction. An extended solution may be characterized in that the arrangement is arranged parallel to the conveying direction. An extended solution may be characterized in that the flashlights of the device (in particular the longitudinal axes of these flashlights) are arranged in a transverse direction transverse to the conveying direction. An extended solution may be characterized in that the device is constructed in a modular manner and at least two modules, each having at least one flashlight, are arranged spaced apart from each other. An extended solution may be characterized in that three or more modules are provided. An extended solution may be characterized in that at least one module is arranged in the discharger of the sheet printing press or (in the conveying direction) directly before the discharger of the sheet printing press.

[0040] One development can be characterized in that at least one further module is arranged in the discharger or (in the conveying direction) before the discharger, or in a printing mechanism or between two printing mechanisms. One development can be characterized in that at least one module is arranged before the varnishing mechanism or before the location for applying varnish. One development can be characterized in that at least one module is arranged before the printing mechanism for yellow pigment or ink or before the location for applying yellow pigment or ink.

[0041] One embodiment can be characterized in that at least one flash lamp has an actual tube length or effective tube length which is equal to or greater than the printed width of the printing substrate to be cured. The effective tube length is preferably the length of the section on the printing substrate which is parallel to the longitudinal axis of the tube and is irradiated for curing. Machine operators refer to such flash lamps in a simplified manner as "page width" or "format width".

[0042] Preferably, each flash lamp has a fixed interaction length (in the transport direction of the printing substrate) on the printing substrate (in particular between 0.1 m and 0.3 m, for example 0.2 m). The spacing of the flash lamps from one another (in the transport direction of the printing substrate) is preferably an integer multiple of the interaction length or, when all flash lamps are pulsed simultaneously, an integer multiple of the interaction length divided by the number of pulses. The same applies to inclined flash lamps.

[0043] As long as the printed substrate is in the region of the interaction length of the flash lamp or the radiator with the flash lamp, the number of pulses required for curing should preferably be achieved. A numerical example of this follows: for 4 pulses with a switch-on time of 2.5 ms each, this is possible at a substrate speed of 1 m / s when the flash lamps are operated at a frequency of 20 Hz.

[0044] One development can be characterized in that the device generates a substantially homogeneous UV distribution in the transverse direction. One development can be characterized in that the device generates a substantially homogeneous UV distribution in the transport direction.

[0045] Any combination of the features and feature combinations disclosed in the technical field, summary and developments above and in the exemplary embodiments below represents further advantageous developments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figures 1 to 8 The preferred embodiments of the present invention and the expansion scheme are shown. Corresponding features are indicated by the same reference numerals in the drawings. For the sake of clarity, repeated reference numerals in the drawings are partially omitted. Among them:

[0047] Figure 1 A preferred embodiment of the device according to the invention is schematically shown in a side view;

[0048] Figure 2 A preferred embodiment of the device according to the invention is schematically shown in a top view;

[0049] Figure 3A further preferred embodiment of the device according to the invention is schematically shown in a top view;

[0050] Figure 4 A further preferred embodiment of the device according to the invention is schematically shown in a top view;

[0051] Figure 5 A further preferred embodiment of the device according to the invention is schematically shown in a top view;

[0052] Figure 6 A further preferred embodiment of the device according to the invention is schematically shown in a top view;

[0053] Figure 7 A further preferred embodiment of the device according to the invention is schematically shown in a top view; and

[0054] Figure 8 A further preferred embodiment of the device according to the invention is shown schematically in a top view. DETAILED DESCRIPTION

[0055] Figure 1 A preferred embodiment of an apparatus 4 according to the invention is schematically shown in a side view. A printing press 1 is shown for printing a flat printing substrate 2, for example paper, by means of a UV-curable fluid 3, for example offset printing ink.

[0056] The printing press 1 comprises a device 4 for UV curing according to the invention, which comprises, by way of example, a plurality of radiators (one radiator 5 and at least one further radiator 5'). Each radiator comprises at least one flash lamp 6. These flash lamps 6 can be designed as tubes 6a, for example as gas discharge tubes and, for example, xenon flash lamps. These flash lamps 6 generate UV radiation 6b for curing the printing fluid 3. The radiators are arranged, by way of example, along a curved plane 7 of a carrier 7a. The curvature of this plane 7 is preferably adjustable (and thus adaptable to different printing substrates 2 or transport rollers), for which purpose a motor 17 and an associated control or regulation device 18 can be provided to control or regulate the curvature of the carrier 7a.

[0057] Figure 2 A preferred embodiment of a device 4 according to the invention is schematically shown in a top view. The printing press 1 and a print substrate 2 with a print image 2a printed by a printing fluid 3 and the device 4 according to the invention are shown.

[0058] The device 4 comprises at least one radiator 5. Five different radiators 5 are shown by way of example. However, the device 4 preferably comprises only radiators of identical construction. It can be seen that the flash lamps 6 of the radiator 5 can be arranged and / or oriented in different ways; for example, coaxially (from top to bottom), offset to one another, inclined at different angles or parallel to one another. Details of this are shown in the following figures.

[0059] The radiators 5 are preferably oriented transversely to the transport direction 8 (of the printing substrate 2 ), ie in the transverse direction 9 .

[0060] Figure 3 A further preferred embodiment of a device 4 according to the invention is schematically shown in a top view. A single flash lamp 6 is shown by way of example in the upper part of the figure, showing its longitudinal axis 13. A plurality of flash lamps 6 are shown below. The flash lamps 6 are arranged coaxially with respect to one another in an arrangement 10. The direction 11 of the arrangement 10 is parallel to the transverse direction 9. The longitudinal axes 13 of the flash lamps 6 lie on a straight line 12 in the direction of the arrangement 10. Another arrangement 10' of the radiators 5 is shown by way of example.

[0061] Figure 4 A further preferred embodiment of a device 4 according to the invention is schematically shown in a top view. A plurality of flash lamps 6 are shown. These flash lamps 6 are arranged offset to one another in an arrangement 10. The arrangement 10 has a direction 11 parallel to the transverse direction 9. The longitudinal axes 13 of the flash lamps 6 are located in the direction of the arrangement 10 on two straight lines 12 parallel to the direction 11. It can be seen that the offset flash lamps 6 of the two straight lines 12 have an overlap 14 with one another. It can also be seen that the flash lamps 6 of the respective straight lines 12 have spacings 15 (or gaps) with one another. Finally, it can be seen that the flash lamps 6 on one of the straight lines 12 are arranged centrally with respect to the corresponding gaps between the flash lamps on the other straight line 12.

[0062] Figure 5 A further preferred embodiment of a device 4 according to the invention is schematically shown in a top view. A plurality of flash lamps 6 are shown. These flash lamps 6 are each arranged obliquely in an arrangement 10, i.e., they each have an inclination 16 (or an angle different from both 0° and 180°) relative to a straight line 12. The arrangement 10 has a direction 11 parallel to the transverse direction 9. It can be seen that the inclination 16 is adjustable. For this purpose, a motor 17 is provided, which has a control or regulation device 18 for controlling or regulating the motor 17 or the inclination 16.

[0063] Figure 6 A further preferred embodiment of the device 4 according to the invention is schematically shown in a top view. Figure 5It can be seen that the flash lamps 6 have different inclinations 16 .

[0064] Figure 7 A further preferred embodiment of the device 4 according to the invention is schematically shown in a top view. It can be seen here that the flash lamps 6 (or their longitudinal axes 13 ) are oriented parallel to the conveying direction 8 .

[0065] Figure 8 A further preferred embodiment of the device 4 according to the invention is schematically shown in a top view. In this embodiment, the arrangement 10 of the radiators 5 (or the associated straight line 12) extends parallel to the transport direction 8 of the printing substrate 2, and the longitudinal axis 13 of the flash lamp 6 extends perpendicularly to the transport direction 8 (or parallel to the transverse direction 9). By way of example, a plurality of modules 4a of the device 4, each with a (page-wide) flash lamp 6, are arranged in the printing unit and / or varnishing unit 1a of the printing press 1, while a module 4a with a (page-wide) flash lamp 6 is arranged in the outfeed 1b of the printing press 1.

[0066] Reference numerals list

[0067] 1 Printing press

[0068] 1a Printing mechanism, varnishing mechanism

[0069] 1b Discharger

[0070] 2 Printing substrate

[0071] 2a Printing image

[0072] 3 Fluid

[0073] 4 Equipment

[0074] Module 4a

[0075] 5 Radiator

[0076] 5' Another radiator

[0077] 6 Flash

[0078] 6a Tube

[0079] 6b UV radiation

[0080] 7 Bending plane

[0081] 7a Vector

[0082] 8 Conveying direction

[0083] 9 Horizontal direction

[0084] 10 Arrangement

[0085] 10' Another row

[0086] 11 Direction

[0087] 12 Straight Line

[0088] 13. Vertical axis

[0089] 14 Overlap

[0090] 15 Interval, gap

[0091] 16 degrees of inclination

[0092] 17 Motor

[0093] 18 Equipment for control or regulation

Claims

1. A printing press, comprising: at least one printing unit configured to print a UV-curable fluid onto a web or sheet of a printing substrate, wherein the web or sheet is transported along a conveying direction in the printing press; at least one device for curing a UV-curable fluid on a printing substrate, the device being arranged in the printing press along a transverse direction transverse to the conveying direction and being configured to generate a substantially homogeneous UV light distribution; The at least one device for curing a UV-curable fluid comprises: an irradiator arranged to irradiate a UV-curable fluid on a printing substrate, the irradiator comprising a plurality of flash lamps arranged in a first arrangement and a plurality of flash lamps arranged in a second arrangement, or wherein the other irradiator comprises a plurality of flash lamps arranged in the second arrangement; The flash lamps are configured as tubes having respective longitudinal axes in a tube direction, and the tubes in the first arrangement and the second arrangement are arranged adjacent to each other and overlap each other between adjacent flash lamps; wherein the longitudinal axis of every other flash lamp is located on a first straight line in the arrangement direction, and the longitudinal axis of every other flash lamp is located on a second straight line in the arrangement direction, and the first straight line and the second straight line are parallel to each other and spaced apart from each other; wherein the flash lamps on the first straight line are spaced apart from each other at given intervals to form gaps therebetween, and the flash lamps on the second straight line are spaced apart from each other at given intervals to form gaps therebetween; and The flash lamps are arranged offset with respect to one another, wherein the flash lamps on the second straight line are arranged in the center of a corresponding gap between the flash lamps on the first straight line.

2. The printing press according to claim 1, It is characterized in that The device is configured to generate a substantially homogeneous UV light distribution in the transport direction.

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