Film printing doesn’t happen in a climate-controlled laboratory — it happens in workshops where summer brings both heat and humidity, and winter brings dry air and static. The film absorbs moisture, the ink changes viscosity, the solvent evaporates at the wrong rate. Adapting to seasonal shifts isn’t optional — it’s how you keep the press running when the weather changes.
Film: Moisture Is the Enemy
In high temperature and high humidity, plastic film absorbs moisture from the air. The absorbed water interferes with ink drying — the ink film won’t set, forcing the operator to increase dryer temperature. That overcompensation produces poor gloss and dull color. Nylon (BOPA) film is the worst case — its amide groups actively pull moisture from the air, making it the most climate-sensitive substrate in flexible packaging.
The simplest defense: use recently manufactured film that hasn’t been sitting in storage absorbing humidity. Pay attention to how the film is packaged — rolls left exposed in humid conditions will absorb moisture before they reach the press. The fresher the film, the less accumulated moisture.
Ink: Drying Speed Is Climate-Dependent
Ambient conditions are the single largest external influence on ink drying — more than the ink formulation itself. In summer heat, the top surface of the ink film skins over while the inner layer dries slowly, trapping solvent underneath. In cool, dry conditions, the entire film dries uniformly. The response isn’t just temperature adjustment — it’s solvent reformulation.
Use nationally certified solvents to blend fast-, medium-, and slow-drying thinners matched to the climate. Maintain the pressroom at approximately 25°C and 65–75% RH. These are target values, not aspirational ones — ink behavior changes measurably outside this range.
Pigments: Not All Colors Respond Equally
Different pigments absorb water at different rates. Red pigment powder absorbs moisture more readily than other colors — which means red ink thickens faster in humid conditions. When the ink thickens, transfer drops, color shifts, and the print drifts off specification.
Countermeasures for humid conditions: use a semi-enclosed ink pan with a covered doctor blade assembly to limit air contact. If water droplets form on the ink surface — and they will, in high humidity — wick them out with a sponge immediately and top up with fresh ink. When the press stops, drain the ink pan and seal the ink container. Do not let ink sit exposed to humid air.
Solvent Quality: The Hidden Variable
Many converters use surface-print ink as a substitute for lamination-grade ink — the two are chemically different and require different solvent systems. If the solvent doesn’t meet the national standard, its composition is uncontrolled: water content varies, evaporation rates are inconsistent, and impurities react with the pigment over time.
Water in the solvent is absorbed by the pigment powder during circulation, causing phase separation and swelling of the pigment particles. The downstream consequences: residual odor after lamination, bubbles in the laminate, and poor bond strength. For surface printing, an overly thick ink layer combined with substandard thinner produces primary and secondary blocking — the print sticks to itself, then sticks again after further processing.
Solvent quality isn’t a purchasing decision — it’s a print quality decision. Test every incoming batch.
References
- Wikipedia: Hygroscopy: Mechanisms of moisture absorption in polymer films and pigments, and the effects of humidity on material properties in printing.
- Wikipedia: Solvent: Solvent chemistry, purity specifications, and evaporation behavior relevant to ink drying under varying climate conditions.
- Wikipedia: Flexible Packaging: Overview of film printing including substrate handling, ink systems, and environmental control requirements.
- Wikipedia: Nylon 6 (BOPA): Polyamide chemistry and moisture absorption properties relevant to nylon film printing in high-humidity environments.
- Flexible Packaging Association (FPA): Industry resource covering climate-adaptive printing practices, solvent management, and quality control.