Patent Application
20180126766
This application claims the benefit, under 35 U.S.C. § 119, of German Patent Application DE 10 2016 221 855.7, filed Nov. 8, 2016; the prior application is herewith incorporated by reference in its entirety.
The present invention relates to a method for operating a UV curing device in a printing machine, in which a UV-curing fluid has been applied to a printing material that is moved in a direction of transport and has a printing material width, and the fluid is cured by UV radiation emitted by at least one fluid-cooled first UV LED emitter of the device at least in the effective range thereof.
The technical field of the invention is the field of curing printing fluids on substrates, in particular polymerizable printing ink or varnish on paper, cardboard, or plastic foil. Curing is achieved by applying electromagnetic radiation, in particular ultraviolet (UV) radiation, to the applied fluid. In that process, the fluid, at least its polymerizable portion, is polymerized.
The curing may be done over the entire surface or in sections. If the format of the substrate has a small width, curing over the entire surface results in unnecessarily high energy consumption. In addition, the radiation may be scattered outside the format width in an undesired way. European Patent EP 1 302 735 B1, corresponding to U.S. Pat. No. 6,857,368, discloses irradiation in accordance with the printed image. However, that document relies on infrared radiation to cure the printing fluid, i.e. heat is applied to the printing fluid, resulting in solvent evaporation. The document does not deal with cooling the device that is used for curing or the components thereof.
The curing process may be temporarily interrupted. European Patent Application EP 2 907 527 A1, corresponding to U.S. Pat. No. 9,281,093, discloses a UV emitter, for instance for curing varnish, adhesives, or plastics. In order to avoid damage to the substrate, the emitter may be switched off when the manufacturing process is interrupted. In order to be able to quickly restart the emitter after such an interruption, the temperature of the emitter is controlled during the interruption by using a heating element. In addition, the document describes cooling the emitter by air.
Known UV LED emitters for curing printing fluids include a plurality of modules that may individually be actuated and are jointly fluid-cooled. During operation of such a device, it may be necessary to switch some modules off. For instance, when smaller-format substrates are printed on, modules on the sides, i.e. outside the printing material, are switched off. Since such modules that have been switched off continue to be fluid-cooled together with the modules that are still in operation, water, e.g. moisture from the ambient air, may condense on the cooled modules. If such modules are restarted at a later time, there may be another problem: the modules may have an insufficient curing effect or may even be damaged.
It is accordingly an object of the invention to provide a method for operating a UV curing device in a printing machine, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known methods of this general type and which allows individual UV LED emitters in a UV curing device to be operated in a non-curing mode to avoid condensation-related problems.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for operating a UV curing device in a printing machine, in which a UV-curing fluid has been applied to a printing material that is moved in a direction of transport and has a printing material width, and the fluid is cured by UV radiation emitted by at least one fluid-cooled first UV LED emitter of the device at least in the effective range thereof. The first UV LED emitter is operated in a curing mode at a first power and at least one fluid-cooled second UV LED emitter is operated in a temperature control mode different from the curing mode and at a second power lower than the first power and different from zero. The second power and consequently the temperature of at least one LED array of the second UV LED emitter is selected in such a way that the LED array is free from condensate.
In accordance with the invention, undesired or even damaging water condensation, e.g. from the ambient air, may be prevented by operating the device in a temperature-control mode, allowing the UV curing process to be carried out in an unimpeded and thus advantageous way. Although it may initially seem contradictory, the second UV LED emitter is thus cooled (with a liquid) while at the same time its temperature is controlled (electrically), in particular, the second UV LED emitter is warmed up or heated.
The method of the invention may be used in production machinery and coating lines in general, in particular in lithographic offset printing presses (UV printing inks and varnishes) and in inkjet printing machines (UV inks and varnishes).
Another preferred development of the invention is distinguished in that the temperature of at least one LED array of the cooled second UV LED emitter is above the dew point temperature.
A further preferred development of the invention may be distinguished in that the first UV LED emitter is disposed in a first position in a transverse direction perpendicular to the direction of transport and parallel to the direction of the printing material width and the second UV LED emitter is disposed in the transverse direction in a second position different from the first position.
An added preferred development of the invention may be distinguished in that the first position is inside the format region corresponding to the printing material width and the second position is outside the format region.
An additional preferred development of the invention may be distinguished in that the first position is inside an image area corresponding to the printed area on the printing material and the second position is outside the image area.
Another preferred development of the invention may be distinguished in that the device is operated with a first group of at least two first UV LED emitters and a second group of at least two second UV LED emitters and in that the decision as to which LEDs of the device are to be assigned to the first group and which LEDs of the device are to be assigned to the second group is made as a function of the format region.
A further preferred development of the invention may be distinguished in that the cooling power is the same in the curing mode and in the temperature control mode.
An added preferred development of the invention may be distinguished in that the second output is selected as a function of the cooling power.
An additional preferred development of the invention may be distinguished in that the first UV LED emitter and the second UV LED emitter are jointly cooled, i.e. are connected to the same coolant circuit. A separate cooling device (including additional control valves) for the individual emitters may advantageously be dispensed with. Alternatively, it is possible for the first UV LED emitter and the second UV LED emitter to be cooled separately, in particular to be connected to a coolant circuit by using respective individually controllable valves.
Another preferred development of the invention may be distinguished in that the second power ranges between 5% and 30%, preferably between 10% and 20%, of the first power.
A concomitant preferred development of the invention may be distinguished in that at least one further fluid-cooled UV LED emitter is operated in a temperature control mode different from the curing mode and at a second power that is lower than the first power and different from zero. The further UV LED emitter may be offset from the first and/or second UV LED emitter/s, e.g. in the direction of transport and/or perpendicular to the direction of transport.
The invention and the preferred further developments thereof will be described in more detail below with reference to the drawings and based on a preferred exemplary embodiment. For reasons of clarity, mutually corresponding elements in the drawings bear the same reference symbols and reference symbols that are merely repetitive have in part been omitted.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for operating a UV curing device in a printing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
Referring now to the figures of the drawings in detail and first, particularly, to
The UV curing device 2 includes a number of UV LED emitters. The emitters are disposed next to one another, covering at least the format region 8, preferably the entire width of the printing machine or the maximum format region. The curing device is disposed to be substantially parallel to the transverse direction. The curing device includes first UV LED emitters 10a to 10d (emitter 10a in position 6a) having a configuration which corresponds to the image area 7 (or, conversely, emitters that correspond to the image area are referred to as first emitters). The curing device further includes second UV LED emitters 11a to 11d (emitter 11b in position 6b), which are disposed outside the format region. Finally, the curing device includes further second UV LED emitters 12a and 12b, which are outside the image area but inside the format region 8. In the illustrated example, the first UV LED emitters 10a to 10d are active and the second UV LED emitters 11a to 11d and 12a and 12b are practically inactive, i.e. substantially not in a curing mode. Thus, the only UV LED emitters that are actively curing the fluid 4 on the printing material are the first UV LED emitters 10a to 10d. In other words, the first UV LED emitters 10a to 10d are operated in a curing mode M1, whereas the further UV LED emitters are not operated in a curing mode. In accordance with the invention, they are instead operated at a temperature control mode M2 that is different from the curing mode. If the format of the substrate and/or the print job (and consequently the image) changes, a first LED may become a second LED and vice versa.
The UV LED emitters 10a to 10d that are operated in a curing mode M1 form an active first group 10′ operated in a curing mode and the UV LED emitters 11a to 11d and 12a and 12b that are operated in a temperature control mode M2 form a virtually inactive second group 11′ and 12′. When a print job requires maximum format sheets and the image extends over the entire format width, all emitters may be active, i.e. in the curing mode M1. If the print job is different from such a job, at least one emitter will be practically inactive, i.e. in the temperature control mode M2. For smaller formats than the maximum format, these are the emitters in the marginal regions of the device 2.
The curing device 2 may include more than the illustrated UV LED emitters, for instance more than 20. The first and second groups 10′, 11′ and 12′ of such a curing device may include any desired number of UV LED and may extend over any desired width of the curing device. That is to say that the curing device construction shown in
For reasons of clarity, the side view of the curing device shown in
Each one of the two UV LED emitters 10a and 11b is fluid-cooled. For this purpose, a fluid-type cooling device 20 is provided. The boards 16 are disposed on cooling bodies 21 that are connected to a coolant circuit 22. Unlike the illustrated construction, the boards may be disposed on a common cooling body. A control device 25 controls the cooling power of the coolant circuit 22, e.g. through the through-put of coolant per unit of time.
A control device 23 supplies power to the boards 16. The control device may actuate every board individually. In accordance with the invention, the first UV LED emitter 10a is operated in a curing mode M1. For this purpose, it is operated at a (relatively) higher (curing) power by the control device. The second UV LED emitter 11b is operated in a temperature control mode M2 and is therefore operated at a (relatively) lower power different from zero by the control device. in accordance with the invention, the second UV LED emitter, which is virtually inactive, i.e. is not used for curing in a current print job, is not operated at zero electric power but at a power (above zero but below the curing power) corresponding to the temperature control mode M2. This power ensures that the second UV LED emitter has a temperature and is in particular heated to substantially prevent condensation, in particular of air moisture, on the components thereof, in particular on the LED array 13, lenses 17, or cover 18 thereof.
A computer 24, which may, for instance, be provided on a control panel of a printing machine 1, is connected to the two control devices 23 and 25 for electric control or actuation of the cooling device. The computer may ensure that a temperature control power sufficient to avoid condensation is set at a given cooling power. The computer may also be connected to a (non-illustrated) sensor for measuring air moisture and may take the corresponding measurements thereof into consideration when adjusting the device.
The diagram shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2016 221 855.7 | Nov 2016 | DE | national |
