Tips for problem-free cold foiling in sheet-fed offset printing
  Application technology tips for cold foiling in sheet-fed printing

In general, it can be said that every module requires its own specific settings. Universally-applicable basic settings do not exist, unfortunately.

 

Foil tension

This should be kept as low as possible, but not so low as to cause creasing.

 

Speed of application

Good transfer results can be achieved at speeds between 8000 and 12000 sheets/h. The results at higher speeds are very dependent on the substrate and design.

 

Rubber blankets

Standard rubber blankets can be used to apply the adhesive.

Mainly Superpress (glass bead blanket) or Irioblanket (white teflon coating) are used to apply the foil.

Quick release rubber blankets should be used for subsequent printing to prevent stripping of foil particles and adhesive.

 

Adhesive coat

The adhesive coat should be adjusted according to the substrate. As a rule, the coating weight will be approx. 2 - 3 g/m². In the case of adhesives for silver foil, an optical density of 0.3 - 0.35 (measured with the filter that gives the highest value) would be suitable; in the case of adhesives for gold foils, a suitable value would be 0.55 - 0.65 (measured with the blue filter).

 

Packing for the rubber blankets

The packing in a foil printing unit can be between 0.0 - 0.2 mm above the bearing rings. This variable can affect the circumference of the rubber blanket cylinder and therefore also the speed of the foil to the substrate.

 

Contact pressure

The following parameters can improve at a somewhat higher pressure: gloss, edge definition, raster print.

Compared to the printing impression adjustment required in printing units for normal printing, the printing impression adjustment for foil printing units should be somewhat thicker in order to achieve optimal foil transfer (surface coverage, gloss, edge definition).

 

Trouble-Shooting

Foil not transferred fully

  • Possible causes: Adhesive coat insufficient, contact pressure too low, rubber blanket in foil unit too soft, packing under rubber blanket not optimal, wrong foil

 

  • Solutions: Adjust adhesive coat, if necessary use new adhesive batch, increase the contact pressure, use harder rubber blanket, thicken the packing, replace the packing, check the foil

 

 

Pin holes in the surface

  • Possible causes: Adhesive coat insufficient, substrate too absorbent

 

  • Solutions: Adjust adhesive coat, if necessary use new adhesive batch, replace substrate with a non-absorbent one

 

 

Foil adhering to locations outside the design

  • Possible causes: Adhesive coat too high, adhesive "splashing” onto locations outside the design, rubber blanket in adhesive unit too soft

 

  • Solutions: Adjust adhesive coat, if necessary use new adhesive batch, use harder rubber blanket, if necessary check dampening

 

 

Foil breaking up

  • Possible causes: Angle of release incorrect, foil tension of unwind/rewind too high, adhesive weight too high, adhesive has emulsified the dampening agent

 

  • Solutions: Change the release angle, adjust the foil tension, after the adhesive weight, if necessary replace adhesive batch and check dampening

 

 

Surface is unlevel - cracks in transverse direction

  • Possible causes: Adhesive weight too high, contact pressure too high, rubber blanket in foil unit too soft, packing under rubber blanket not optimal

 

  • Solutions: Adjust adhesive weight, if necessary use new adhesive batch, adjust contact pressure, use harder rubber blanket, thicken packing, replace packing

 

 

Surface exhibits transverse cracks at start or end of sheet

  • Possible causes: Foil tension of unwind unit too high, setting of distributing rollers not OK.

 

  • Solutions: Adjust foil tension, adjust distributing rollers

 

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