An undesired adhesion between touching layers of material caused by moderate pressure and/or temperature change. The extent to which damage to at least one surface is visible upon their separation.
Causes:
– Ink not drying on substrate;
– Ink skinned – Trapping solvent;
– Web rewound too warm;
– Excessive rewind pressure;
– Film treated on both sides, especially if treatment is different between each side;
– Plasticisers in film subjects to migration e.g. some vinyl films;
– Surface moisture on web;
– Excessive weight in stack;
– Pre-applied coating softens.
Solutions:
– Adjust solvent balance, use faster solvents. Check dryers;
– Use less heat initially. Reduce viscosity which reduces film thickness. Check dryers;
– Reduce web temperature by chilling to within 5°C of ambient. Instant chill rollers or reduce dryer temperature;
– Reduce web tension;
– Avoid excess pressure on re-reeling, use a non blocking varnish over inks. Best solution is to ensure film specification is correct at start;
– Avoid excess pressure, use non blocking overprint varnish. Use inks with non migratory pigments;
– Avoid over chilling especially in humid conditions where moisture condenses on cooled web;
– Reduce stack height;
– Change to solvents that do not attack prior coatings.
