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.
