INTRO TO UV PRINTING
Business form printers, financial printers, book and manual printers, direct mail printers and even some commercial web printers often times use wet offset web printing presses, employing “oxidizing inks”, that is, inks that dry upon exposure to air. However, there are limitations with cold set printing including:
Conventional Oxidizing Inks Exhibit 5 Major Problems for Non Heat-Set Printer:
- Speed - Press speed depends on the rate of evaporation of water and solvent from the ink and absorption of ink into the paper.
- Tracking - Heavy, dense inks do not dry before the web goes through the next print unit resulting in ink on the downstream blanket & tracking on the web.
- Converting In-Line - Since inks are still semi-wet when web leaves press, problems occur in folding unit, bindery and other converting operations.
- Heat from laser printers - When cut sheet or roll forms go through the laser printer, it softens conventional oxidizing ink and deposits ink on rollers in laser printer. Forms and stationery printed with oxidizing inks are unacceptable for cut-sheet work.
- Paper Stock - Because oxidizing inks depend on absorption of ink into the paper, the printer is limited to printing on uncoated stocks which absorb inks, the printer is unable to print on:
- Coated Paper
- Foil Laminated Paper
- Plastic Films and Cards
- Thermal Coated Paper
Heat Set Inks Exhibit 3 Major Problems for The Heat-Set Printer:
- Heat-set solvent inks or heat-set water base inks contain carrier solvents. These VOC emissions require after-burners, and depending on locality may not meet the requirements of the Clean Air Act.
- Heat-set inks can resoften when exposed to heat in a thermal printer or laser printer.
- Heat-set inks require dryer tunnels that rob the web of moisture, shrink the printed product, change and alter the composition of the substrate. This limits the variety of substrates that heat-set printers can use.