PVC ink must never be used directly on PETG, as it may cause film biting, ink layer cracking, and poor adhesion; in contrast, specialized PETG-specific PU ink can be applied to PVC, albeit at a higher cost. Additionally, there are universal inks available—let’s explore how to select appropriate printing inks for different shrink films.
-PVC shrink film ink: Main resin NC+PU, low cost with excellent adhesion to PVC. 2) Solvent: Ethyl acetate + isopropanol (a weak solvent); otherwise may corrode PVC, causing film whitening or perforation. 3) Film properties: Moderately hard; requires only a shrinkage rate of 50%–65%, with moderate requirements for tensile toughness. 4) Temperature resistance: Shrinkage temperature range 70–90°C; standard shrink-type inks are sufficient.
-PETG shrink film ink: High-tensile polyurethane (without nitrocellulose) cannot be formulated with conventional NC resin. PETG is a modified polyester; ordinary strong esters and ketone solvents can corrode the film surface, causing fogging, whitening, shrinkage, and wrinkling. Only weakly alcohol-soluble or low-erosive solvents should be used. The film exhibits extremely high toughness requirements: PETG may undergo lateral shrinkage of 70%–80%, necessitating high elasticity to prevent direct cracking or ink bleeding during thermal shrinkage. 4) Temperature resistance: With higher shrinkage temperatures (85–115°C), the ink must demonstrate superior heat resistance without losing adhesion at elevated temperatures.
To achieve dual membrane compatibility on a single machine: Prioritize using halogen-free universal shrinkable PU ink (alcohol-soluble) – it neither corrodes PVC nor fails to adhere firmly to PETG, accommodating both substrates without frequent ink changes. 2. Surface pre-treatment: – PVC: Typically requires only simple corona treatment (38–42 mN/m); – PETG: The corona value must reach 46–52 mN/m; otherwise, even the highest-quality ink will not provide adequate adhesion. 3. Surface printing/underlying printing: PETG underlying printing demands higher ink toughness; select an ink with greater elongation.
