In flexible packaging printing, many factories face the issue of ink not dry even when dried at the correct temperature. The printed surface feels tacky, smears easily, and becomes unstable in color. This issue slows down the line and increases defect rates. The main challenge is finding out whether the cause comes from the ink formulation or the substrate itself.
DRYING MECHANISM & SIGNS OF INK NOT DRYING PROPERLY
How ink dries in common printing systems
The drying process varies between ink types. Solvent-based inks dry through evaporation and solvent release under hot airflow. Water-based inks dry through evaporation combined with moisture absorption into the substrate. UV inks dry through a curing reaction under light. Drying speed depends on heat, airflow, ink film thickness, and machine speed. If any of these factors shift, the ink layer may dry unevenly. Cases where the surface dries but the inner layer remains wet are common.
Signs that ink is not fully dry
When not fully dry, the printed surface feels sticky when touched. The color smears when rubbed or rewound. The print may look dull or transfer onto the next layer. Blocking between film layers is a typical sign. These signs often appear in areas with thick ink films or solid coverage. Many operators increase temperature when the issue appears. However, higher heat is not always effective if the root cause lies outside the dryer.
CAUSES – FROM ADDITIVES OR FROM THE SUBSTRATE?
Causes related to additives in the ink formulation
Using too much slow-evaporating solvent extends the drying time. Certain plasticizers soften the ink film and reduce thermal stability. Strong surfactants retain moisture and cause slow drying in some systems. When the ratio of resin, pigment, and additives is unbalanced, the ink surface may dry while the inner layer stays wet. This increases tack and smearing. Variations in additive batches may also create inconsistent results. Therefore, the ink not dry may originate from the formulation itself.
Causes related to the substrate and surface energy
PP or PE films with poor corona treatment reduce ink adhesion. Low adhesion creates a thicker ink layer that dries slowly. In this case, heat distribution becomes uneven and drying time increases. Some substrates contain anti-blocking wax or mineral oil residue. The ink slips on the surface and forms a thicker layer. This can cause ink not dry even when temperature increases.
QUICK METHODS TO IDENTIFY THE ROOT CAUSE
Small adjustments to the ink formulation
The operator can reduce retarder in a portion of the ink. Replace the additive batch or increase resin content within limits. After adjustment, reprint a short section to compare drying time. If drying improves, the cause likely lies in the additives. Rub-off testing also helps. A fully dried ink will not smear when wiped lightly. If smearing appears even at high temperature, the ink may have an imbalance in additives.
Assessing the substrate with simple tests
Dyne testing is essential. Substrates below the required dyne often cause ink not dry. The IPA wipe test checks for oil or wax residue. If the film changes color or feels slippery, the substrate has contamination. Comparing different rolls helps narrow down the cause. If one roll prints well and another shows defects, the issue is substrate-related. If all rolls show the same issue, the ink must be reviewed.
Observing the press and dryer conditions
Check actual dryer temperature using sensors. Many systems show a gap between set temperature and actual temperature. Airflow and direction also matter. If airflow is weak, solvent vapor cannot escape. This causes moisture retention even at the right heat. At high machine speeds, dwell time is shorter. Some factories increase heat to compensate. However, if the substrate is incompatible, higher heat still cannot ensure drying.
SOLUTIONS TO ENSURE CONSISTENT DRYING IN PRODUCTION
Adjusting the ink formulation for each printing system
Reducing slow-evaporating additives is a basic solution. Optimize surfactant levels to avoid moisture retention. Balancing resin and pigment helps stabilize the ink film. Some substrates require resins with higher compatibility.
Controlling substrate quality before printing
The substrate must meet the dyne standard for each ink type. Re-corona treatment helps when dyne is low. Avoid rolls with dust, oil, or wax particles. Proper substrate preparation helps reduce cases of ink not dry in production.
Optimizing dryer conditions and machine operation
Adjust crossflow, increase hot air volume, and maintain stable actual temperature. Control ink film thickness through print density. Maintain a machine speed that matches the ink and substrate. These factors help achieve the required drying level.
VICHEM – AUTHORIZED DISTRIBUTOR OF PRINTING INK ADDITIVES IN VIETNAM
Vichem is the authorized distributor of printing ink additives in Vietnam. We provide high-quality products along with international-standard technical service.
- Technical consulting: Support customers in selecting the right product for their application.
- Color-matching tests: Vichem’s specialists perform color-matching tests to ensure results meet design requirements.
- Application support: Assist customers during production integration to ensure optimal efficiency.
For more information, please contact us via:
📞 Hotline: 08 1790 1790
📧 Email: contact@vichem.vn
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🌐 Website: www.vichem.vn
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