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Cold-foil transfer application tips

Applications: Under normal circumstances, any job that is printed on a flexo machine may use the cold-stamping process. However, the particular capabilities of the flexo machine must be taken into account, and for this, the customer should contact his machine supplier. During the cold-stamping process, the wet lamination technique requires printing, laminating and stripping stations. Using this new process, it is possible to print halftones to full tones depending on the adhesive, substrate, anilox roller and printing plate used.

Adhesives: There are numerous adhesives available on the market. You must carefully test the suitability of the adhesive for your particular job. The adhesive should be suitable for application over free-radical UV-curable inks/coatings in addition to being applicable over solvent- or water-based inks.

Substrates: Practically all substrates that are processed on flexo machines, such as polypropylene, polyethylene and nonabsorbent papers, can accept cold stamping. If there are adhesion problems, contact the adhesive supplier.

Anilox rollers: Depending on the design to be applied to the substrate, the right anilox roller must be chosen. First start with 120 lines/cm and 10 cm3/m2. For fine detail work, the ceramic anilox should have higher line counts. For broad areas, lower line counts are needed. For all nonabsorbent materials and plastics, the typical coating weight should be in the range of around 2 to 5 g/m2. This calls for the anilox roller to be 180 lines/cm and 6 cm3/m2. For more absorbent substrates, like paper, start with an anilox roller with 100 lines/cm and 14 cm3/m2.

Laminating station: For the application of cold-stamping foil to wet, UV adhesive, a silicone roller with 80 to 95 shore hardness is recommended. The tension of the foil unwinding and rewinding units should be as low as possible. Be careful, though, to avoid wrinkling. If you use a nip roller with too low a shore hardness, the result will be poor foil transfer.

UV lamps: For UV curing, medium- or high-pressure mercury lamps should be used. The UV lamp output should be adjustable to take into account operating speed. The higher the speed, the more UV lamp output is required. Typical outputs are in the range of 120 to 200 watts/cm. For colored cold foils, the UV lamp output must be set higher than for silver or light gold shades.

Speeds: Typical printing and application speeds are between 45 and 120 m/min.

Source: www.kurz.de

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