Process and device for curing UV printing ink

Abstract

The invention concerns a process and a device for curing a UV curing printing ink ( 14 ) on a printed material ( 9 ), wherein the printing ink ( 14 ) is irradiated with UV light from a UV radiation source ( 8 ). A low pressure gas discharge lamp ( 7 ) is proposed as UV radiation source ( 8 ). The device in accordance with the invention is characterized in that it comprises a stationary reflector ( 5 ) having, in particular, a special reflecting layer with diffuse reflecting material based on silicone rubber having diffuse reflecting particle imbedded therein.

1 . Process for curing a UV curing printing ink ( 14 ) on a printed material ( 9 ), wherein the printing ink ( 14 ) is irradiated with UV light from a UV radiation source ( 8 ), 
 characterized in that,    a low pressure gas discharge lamp ( 7 ) is utilized as the UV radiation source ( 8 ) which has a spectral radiation flux integrated over the UV-B and UB-C region of more that 50% of the UV radiation flux, preferentially more than 75% of the UV radiation flux.    
     
     
         2 . The process of    claim 1   , characterized in that the maximum of the spectral radiation distribution of the low pressure gas discharge lamp ( 7 ) lies in the V-B or UV-C region.  
     
     
         3 . The process of    claim 1    or    2   , characterized in that the integrated spectral UV radiation flux, in particular the UV-C radiation flux, of the low pressure gas discharge lamp ( 7 ) above a wavelength of 190 nm, in particular above 240 nm, is in excess of 50%, preferentially more that 75%, of its UV radiation flux, in particular of its UV-C radiation flux.  
     
     
         4 . The process of one of the preceding claims, characterized in that the integrated UV radiation intensity, in particular the integrated UV-B and UV-C radiation intensity or, in particular, the UV-C radiation intensity, is between 1 and 100 mW/cm 2 , preferentially between 10 and 50 mW/cm 2 .  
     
     
         5 . The process of one of the preceding claims, characterized in that the printing ink ( 14 ) is not heated above 40° C. during the UV curing.  
     
     
         6 . The process of one of the preceding claims, characterized in that the printing ink ( 14 ) has high reactivity at room temperature.  
     
     
         7 . The process of one of the preceding claims, characterized in that the time duration of irradiation for curing the printing ink ( 14 ) is less than two seconds, preferentially less than one second.  
     
     
         8 . The process of one of the claims  1  through  7 , characterized in that the printing ink ( 14 ) comprises the following components: 
 a) one or more cycloaliphatic epoxy resins as curable fixing agent, and  
 b) one or more arylsulfonium salts as photo-initiator.  
 
     
     
         9 . The process of    claim 8   , characterized in that component b) contains a mixture of differing arylsulfonium salts.  
     
     
         10 . Device for curing a UV curing printing ink ( 14 ) on a printed material ( 9 ), by means of which the printing ink ( 14 ) is irradiated with UV light from a UV radiation source ( 8 ), in particular for carrying out the process according to one of the claims  1  through  9 , characterized in that the UV radiation source ( 8 ) comprises a low pressure gas discharge lamp ( 7 ) having a spectral radiation flux integrated over the UV-B and UB-C region of more that 50% of the UV radiation flux, preferentially more than 75% of the UV radiation flux.  
     
     
         11 . The device of    claim 10   , characterized in that the maximum of the spectral radiation distribution of the low pressure gas discharge lamp ( 7 ) lies in the UV-B or UV-C region.  
     
     
         12 . The device of    claim 10    or    11   , characterized in that the integrated UV radiation flux, in particular the Uv-C radiation flux, of the low pressure gas discharge lamp ( 7 ) above a wavelength of 190 nm, in particular above 240 nm, is in excess of 50%, preferentially more that 75%, of its UV radiation flux, in particular of its UV-C radiation flux.  
     
     
         13 . The device of one of the preceding claims, characterized in that it comprises a plurality, in particular more than four and preferentially more than eight, of low pressure gas discharge lamps ( 7 ).  
     
     
         14 . The device of    claim 13   , characterized in that it comprises low pressure gas discharge lamps ( 7 ) having mutually differing emission spectra.  
     
     
         15 . The device of one of the preceding claims, characterized in that the electrical power consumption of the low pressure gas discharge lamps ( 7 ) is between 0.2 and 2.5, preferentially between 0.5 and 1.0 watts per centimeter of wavelength.  
     
     
         16 . The device of one of the preceding claims, characterized in that the homogeneity of the UV radiation intensity on the printed material ( 9 ), in particular the UV-B and/or the UV-C intensity, in the region effective for curing the printing ink ( 14 ) is sufficiently high that the irradiation intensity deviates from an average value by less than 30%, preferentially by less that 20%.  
     
     
         17 . The device of one of the preceding claims, characterized in that it comprises a plurality of mutually adjacent low pressure gas discharge lamps ( 7 ), wherein the separation between the low pressure gas discharge lamps ( 7 ) is not more then 30%, preferentially is not more than 20%, of the diameter of the low pressure gas discharge lamp ( 7 ) bulbs ( 16 ).  
     
     
         18 . The device of one of the preceding claims, characterized in that it comprises a plurality of U-shaped low pressure gas discharge lamps ( 7 ) disposed in mutual adjacency at the parallel lengthwise sides of the U-shape, wherein the low pressure gas discharge lamps ( 7 ) are disposed in alternating opposite directions.  
     
     
         19 . The device of one of the preceding claims, characterized in that the separation between the low pressure gas discharge lamps ( 7 ) and the printed material ( 9 ) is less than 5 cm and/or more than 1 cm.  
     
     
         20 . The device of one of the preceding claims, characterized in that the low pressure gas discharge lamp ( 7 ) is a mercury vapor lamp or an amalgam lamp.  
     
     
         21 . The device of one of the preceding claims, characterized in that it comprises a reflector ( 5 ) to reflect the UV light emitted from the low pressure gas discharge lamps ( 7 ) onto the curing printing ink ( 14 ).  
     
     
         22 . The device of    claim 21   , characterized in that the reflector ( 5 ) is stationary.  
     
     
         23 . The device of    claim 21    or    22   , characterized in that the reflector ( 5 ) comprises a dielectric mirrored layer and/or a reflecting layer made from an optically diffuse reflecting material ( 1 ).  
     
     
         24 . The device of    claim 23   , characterized in that the optically diffuse reflecting material ( 1 ) comprises a matrix of transparent matrix material consisting essentially of a curable silicone rubber in which diffuse reflecting particles are imbedded.