Method for operating a UV curing device in a printing machine

Abstract

A method for operating a UV curing device in a printing machine includes providing a printing material to which a UV-curing fluid or UV printing ink or varnish is applied. The printing material is paper or foil moving in a transport direction and having a width. The fluid is cured by UV radiation emitted by a fluid-cooled first UV LED emitter of the device at least in an effective range thereof. The first UV LED emitter is operated in a curing mode and at a first power, and a fluid-cooled second UV LED emitter is operated in a temperature control mode different than the curing mode and at a second power lower than the first power and different than zero. The second power and the temperature of an LED array of the second UV LED emitter is selected to cause the LED array to be free from condensate.

Claims

1. A method for operating a UV curing device in a printing machine, the method comprising the following steps: providing a printing material being moved in a direction of transport and having an applied UV-curing fluid and a printing material width; curing the fluid by UV radiation emitted at least in an effective range of at least one fluid-cooled first UV LED emitter of the device; operating the at least one fluid-cooled first UV LED emitter in a curing mode at a first power; operating at least one fluid-cooled second UV LED emitter in a temperature control mode different than the curing mode and at a second power lower than the first power and different from zero; selecting the second power and consequently the temperature of at least one LED array of the at least one fluid-cooled second UV LED emitter to cause the LED array to be free from condensate; and selecting the temperature of at least the LED array of the at least one fluid-cooled second UV LED emitter to be above a dew point temperature.

2. A method for operating a UV curing device in a printing machine, the method comprising the following steps: providing a printing material being moved in a direction of transport and having an applied UV-curing fluid and a printing material width; curing the fluid by UV radiation emitted at least in an effective range of at least one fluid-cooled first UV LED emitter of the device; operating the at least one fluid-cooled first UV LED emitter in a curing mode at a first power; operating at least one fluid-cooled second UV LED emitter in a temperature control mode different than the curing mode and at a second power lower than the first power and different from zero; selecting the second power and consequently the temperature of at least one LED array of the at least one fluid-cooled second UV LED emitter to cause the LED array to be free from condensate; placing the at least one fluid-cooled first UV LED emitter in a first position in a transverse direction perpendicular to the direction of transport and parallel to a direction of the printing material width and locating the first position within a format region corresponding to the printing material width; and placing the at least one fluid-cooled second UV LED emitter in the transverse direction in a second position different than the first position and locating the second position outside the format region.

3. The method according to claim 2, which further comprises locating the first position inside an image area corresponding to a printed area on the printing material, and locating the second position outside the image area.

4. A method for operating a UV curing device in a printing machine, the method comprising the following steps: providing a printing material being moved in a direction of transport and having an applied UV-curing fluid and a printing material width; curing the fluid by UV radiation emitted at least in an effective range of at least one fluid-cooled first UV LED emitter of the device; operating the at least one fluid-cooled first UV LED emitter in a curing mode at a first power; operating at least one fluid-cooled second UV LED emitter in a temperature control mode different than the curing mode and at a second power lower than the first power and different from zero; selecting the second power and consequently the temperature of at least one LED array of the at least one fluid-cooled second UV LED emitter to cause the LED array to be free from condensate; operating the device with a first group of at least two of the fluid-cooled first UV LED emitters and a second group of at least two of the fluid-cooled second UV LED emitters; and deciding which LED emitters of the device are assigned to the first group and which LED emitters of the device are assigned to the second group as a function of a size of a format region corresponding to the printing material width.

5. The method according to claim 1, which further comprises applying an identical cooling power in the curing mode and in the temperature control mode.

6. The method according to claim 5, which further comprises selecting the second power as a function of the cooling power.

7. The method according to claim 1, which further comprises cooling the at least one fluid-cooled first UV LED emitter and the at least one fluid-cooled second UV LED emitter together.

8. The method according to claim 7, which further comprises connecting one coolant circuit to the at least one fluid-cooled first UV LED emitter and the at least one fluid-cooled second UV LED emitter.

9. The method according to claim 1, which further comprises cooling the at least one fluid-cooled first UV LED emitter and the at least one fluid-cooled second UV LED emitter separately.

10. The method according to claim 9, which further comprises connecting the at least one fluid-cooled first UV LED emitter and the at least one fluid-cooled second UV LED emitter to a coolant circuit through respective individually controllable valves.

11. The method according to claim 1, which further comprises selecting the second power to be in a range of between 5% and 30% of the first power.

12. The method according to claim 1, which further comprises selecting the second power to be in a range of between 10% and 20% of the first power.

13. The method according to claim 1, which further comprises operating at least one further fluid-cooled UV LED emitter in a temperature control mode different than the curing mode at a second power being lower than the first power and different than zero.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a fragmentary, diagrammatic, partially-sectional, top-plan view of a curing device and a substrate;

(2) FIG. 2 is a partially-sectional, side-elevational view of a curing device; and

(3) FIG. 3 is a diagram indicating a curing mode and a temperature-control mode.

DETAILED DESCRIPTION OF THE INVENTION

(4) Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a section of a printing machine 1 including a curing device 2. The curing device is used to cure a printing material or substrate 3 having a printing material width 3. A fluid 4 has been applied at least to parts of the printing material, preferably in accordance with a print image. The fluid is a UV cured fluid such UV printing ink or UV varnish. The printing material is moved through the printing machine in a direction of transport 5. A direction referred to as a transverse direction 6 extends in a direction perpendicular to the direction of transport 5 and parallel to the direction of the printing material width 3. The printing material has a format region 8, which corresponds to the printing material width 3. The printing material further includes an image area 7, which corresponds to the regions or zones (extending in the direction of transport) to which fluid has been applied. The printing machine has a minimum and a maximum printable format region. An average format range is shown.

(5) 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.

(6) 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.

(7) 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 FIG. 1 is only to be viewed as a single example.

(8) For reasons of clarity, the side view of the curing device shown in FIG. 2 is limited to two UV LED emitters 10a and 11b, of which the emitter 10a will be described below by way of example. The illustrated emitter 10a includes an LED array or LED line 13 for generating UV radiation 14. In a different example, an LED array may alternatively include only a single LED. The UV radiation generated by the LED array defines an effective range 15 of the UV LED emitter. The UV LED emitter has a board 16 including the respective LED array. The UV LED emitter likewise includes a number of optical lenses 17 that are disposed in front of the LED array and shape the UV radiation. A UV-transparent cover 18, e.g. made of glass, is disposed in front of the lenses. The UV radiation of every UV LED of the respective LED array passes through a respective lens and the cover to reach the substrate 3 in an effective range.

(9) Each one of the two UV LED emitters 10a and 11 b 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. FIG. 2 shows that the two cooling bodies in the coolant circuit are connected in parallel. In the illustrated example, the two cooling bodies may only be jointly cooled. However, individually controllable valves may be provided in the circuit to allow every coolant body 21 to be cooled individually, for instance between 0% and 100%.

(10) 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.

(11) 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.

(12) The diagram shown in FIG. 3 illustrates both the curing mode M1 and the temperature control mode M2. As shown, the first UV LED emitter 10a is operated at a first curing power P1. It is also shown that the second UV LED emitter 11b is operated at a second (temperature control) power P2, which is lower than the first power. A power threshold P, which is between the two powers P1 and P2, forms the threshold between the curing mode M1 and the temperature control mode M2. The first power P1 is above the power threshold and the second power P2 is below the power threshold.

(13) FIG. 3 further indicates temperatures. A temperature T1 corresponds to the temperature of the (second) LED array of the temperature-controlled second UV LED emitter 11b. A temperature T2 corresponds to the dew point temperature of the LED array and a temperature T3 corresponds to a cooling temperature of the fluid-type cooling device 20. The temperature T1 of the second UV LED emitter 11b is above the dew point temperature T2. In accordance with the invention, the second UV LED emitter 11b, which is virtually inactive, is supplied with (electric) power P2 to heat it to a temperature T1 above the dew point temperature to prevent the second UV LED emitter from cooling down to a temperature T3 below the dew point temperature T2, avoiding undesired condensation or condensed moisture 30. The temperature T4 of the first UV LED emitter 10a or rather of the associated (first) LED array 13 is above T1.