The main application for cold foiling in narrow web printing is plastic self-adhesive labels, mainly polyethylene or polypropylene labels. Paper labels, tube laminates and folding boxes are more and more often being finished with cold foil using the narrow web printing process.
The finishing technology
The process consists of a combination of printing and laminating. As a rule, foil transfer occurs inline as for sheet-fed printing and can be easily integrated into the printing process; the foil is applied as a "fifth color”, so to speak.
The radical curing UV adhesive is applied to the substrate in the desired design by means of a printing unit. The cold foil is then introduced into the process, and the adhesive-coated substrate and the cold foil are pressed together by means of a nip roller, i.e. the cold foil is laminated onto the substrate. Next the adhesive is cured by UV light through the cold foil. The carrier film of the cold foil is then removed (foil release), and the cured adhesive ensures that the optically active layers remain bonded to the areas to which adhesive was applied. As a rule, foil transfer is performed at the start of the printing process. The cold foil can then be easily overprinted in multiple colors in the subsequent printing units, thereby allowing a multitude of design effects to be achieved. It would, of course, also be possible to implement the cold foil application step at the end of the printing machine.
The majority of applications utilize UV flexographic printing. Cold foiling technology can, however, also be used with UV web-fed offset printing or UV web-fed letterpress printing. One reason why flexographic printing is the preferred method is its speed. Another is that it is especially suitable for cold foiling because it provides very good control of the adhesive application step. The adhesive is applied to the polymer flexographic printing plate by means of an anilox roller, and the plate then transfers it to the substrate. The necessary adhesive quantity for a particular substrate can be very easily adjusted by selecting an anilox roller with a suitable volume.