How to select the appropriate ink for printing shrink film ?

Step 1: Select the appropriate film substrate (the most critical factor, as it directly determines the ink resin system). Different films require specific inks; mixing them may cause ink bleeding, film adhesion issues, or ink detachment.

Film Material | Main Resin Systems | Key Limitations

PVC shrink film | NC nitrocellulose (basic version)/NC + small amount of PU | Suitable only for weak esters + alcohol solvents; ketones and strong esters may cause corrosion and whitening; the ink film has moderate toughness, suitable for shrinkage rates ≤65%.

PETG high-shrinkage film | Alcohol-soluble PU polyurethane (without NC) | Strong solvents are prohibited to prevent white film fogging; must exhibit high elasticity with lateral shrinkage of 70%–80% without cracking; heat-resistant up to 85–115°C

OPS shrink film | Modified PU ink | Moderately solvent-resistant, balancing adhesion and ductility

POF polyolefin membrane | Chlorinated PP + elastic PU | The membrane surface exhibits extremely low polarity; corona treatment must meet specifications to ensure stable adhesion with conventional inks

Step 2: Select a printing process and match the ink category

• Gravure printing (the preferred choice for large-scale beverage packaging labels)

1. Solvent-based (high production volume, vibrant colors)

-PVC: NC nitrocellulose shrink face印/backprint ink (most cost-effective option)

1. PETG/OPS: Alcohol-soluble PU elastic shrink ink (low-erosive solvent, non-corrosive to films)   2. Water-based gravure printing (meets food industry and low-VOC environmental requirements)

– PVC: Water-based nitrocellulose ink

-PETG: Water-based polyurethane PU ink; conventional acrylic ink exhibits insufficient adhesion.

• Softcover printing (suitable for small to medium orders; environmentally friendly production process)

Solvent flexography: NC+PU hybrid resin

Water-based flexographic printing: Water-based PU shrink ink

-UV flexography: High-elasticity shrinkage-specific UV ink (standard rigid UV inks crack upon shrinkage)

• UV curing (solvent-free, no dry plate required, high-speed production)

-PVC: Can be cured with standard free-radical UV radiation

-PETG/OPS: High elongation elastic UV resin; premium grades utilize cationic UV resin, offering superior temperature resistance and reduced cracking tendency

Step 3: Distinguish between surface printing and interior printing (to determine ink viscosity grade)

1. For surface printing (where patterns are printed on the outer layer), which involves significant contact friction, prioritize ink with wear resistance and anti-rehesion properties; moderate elasticity is sufficient. 2. For interior printing (the mainstream method for sleeve labels, where patterns are printed on the inner side of the film): The ink layer is enclosed by the film and subjected to greater compression, requiring high-ductility ink; under identical shrinkage conditions, the interior printing ink grade must be one level higher than that for surface printing, otherwise cracking is highly likely.

Step 4: Select the ink elasticity grade based on the shrinkage rate (the primary factor for crack prevention). The higher the shrinkage rate, the greater the elongation required for the ink film.

1. Low shrinkage (≤45%, PVC standard cylindrical bottles): Standard shrinkage ink with a fracture elongation of ≥50% is sufficient. 2. Medium shrinkage (50%–65%, conventional labeling applications): Medium elastic PU-modified ink. 3. High shrinkage (70%–80%, PETG-shaped or curved bottles): High elastic PU must be used with a fracture elongation of ≥150%; the ink layer should be as thin as possible, as thicker layers are more prone to cracking.

Step 5: Verify the operating environment (resistance indicators)

1. Room-temperature beverages: Only adhesion and anti-re黏ing properties are required.
2. Ice water and chilled beer: Must be resistant to ice water and condensation to prevent ink detachment when soaked.
3. High-temperature steam shrinkage furnace (≥100°C): The ink must exhibit enhanced heat resistance, remaining non-malleable and non-adhesive at elevated temperatures.
4. Food packaging: Select halogen-free, low-residue solvent-based inks compliant with food contact standards.

Step 6: Confirm the corona value (a prerequisite for adhesion; even high-quality ink requires pretreatment).

– PVC：38～42 dyn

-PETG: 46–52 dyn (ink will definitely flow out due to insufficient corona pressure)

– POF：42～48 dyn —

1. The Most Simple Ink Combination Schemes for Four Main Types of Membranes

Solution 1: PVC film (standard mineral water packaging label, mass-produced for cost efficiency) – Process: gravure printing – Ink: NC nitrocellulose solvent-based shrinkage ink – Diluent: ethyl acetate + isopropanol (free of cyclohexanone and strong butyl ester) – Maximum shrinkage limit: ≤65%

Option 2: PETG film (for irregular-shaped bottles and high-shrinkage labels) – Process: gravure printing – Ink: alcohol-soluble elastic PU-specific shrink ink – Diluent: alcohol + weak ester; strong solvents are prohibited – Requirements: elongation ≥150%, heat shrinkage resistance at 110°C without ink bleeding

Solution 3: A single production line prints both PVC and PETG simultaneously (dual-purpose machine). It uses a universal alcohol-soluble PU shrink ink that is non-corrosive to PVC, provides excellent adhesion to PETG, eliminates the need for frequent ink tray cleaning, and is compatible with both substrates.

Option 4: Environmentally friendly, VOC-free (for food factories – solvent emissions prohibited). Full transition to:   – Flexography: Water-based PU shrink ink   – High-speed lines: Elastic shrink UV ink (standard rigid UV ink prohibited)

Precautions for in-machine testing of contraction membrane:

Essential acceptance tests (conduct a preliminary test before actual implementation)

1. Adhesion: When the 100-mesh adhesive tape is torn, no ink is released;
2. Heat shrinkage test: Place in the corresponding temperature oven and observe after completion of shrinkage; no cracks or peeling should be observed.
3. Anti-adhesion: After 24 hours of storage, the ink surface does not adhere to the reverse side.
4. Water resistance test (for refrigerated products): Soak in cold water for 2 hours; the ink should not peel off or turn white.

The following points are often overlooked during factory operation:

1. Use only resin compatibility matching while ignoring solvent effects: Strong ester/ketone solvents will corrode PETG into white mist; even qualified ink resins prove ineffective. 2. Using standard NC ink for high-shrinkage PETG: The resin is too brittle, causing complete ink bleeding during shrinkage. 3. Employing low-grade surface printing ink for interior printing: Label shrinkage and compression typically result in cracks exclusively in interior print jobs. 4. Excessively thick ink layer: Abundant white ink accumulation will cause even high-quality elastic inks to crack; apply thin ink layers through multiple printing passes.