A production date may look sharp when it leaves a continuous inkjet (CIJ) printhead, yet smear during sealing, rub off during transport, or disappear after cold storage. For flexible packaging manufacturers, that failure can cause rejected batches and traceability problems. Improving CIJ ink adhesion on plastic film packaging requires more than increasing ink density. The film’s surface chemistry, ink formulation, drying conditions, and machine setup all influence whether a code remains readable. Understanding these factors helps packaging buyers choose suitable equipment and establish a reliable coding process.

Why CIJ Ink Fails to Adhere to PE, PP and PET Packaging Films

Unlike paper, most plastic films are non-porous, so ink cannot simply soak into the substrate. Polyethylene (PE) and polypropylene (PP), including some BOPP structures, often have relatively low surface energy. When the ink does not wet the surface adequately, droplets can spread unevenly or remain vulnerable to wiping and abrasion. PET may behave differently, especially when it has a functional coating, but material names alone cannot predict adhesion.

Surface condition can be just as important as polymer type. Slip additives, anti-fog coatings, silicone contamination, fingerprints, and residues from converting operations may interfere with bonding. Laminated pouches add another variable: the outward-facing printable layer may not match the material described in the overall packaging specification. The treated and untreated sides of the same film can also behave differently.

Consider a snack pouch that is coded correctly before filling but smears at the packing station. The problem may be insufficient drying time, a surface incompatible with the selected ink, or contact with a guide roller before the code has stabilized. Instead of automatically blaming the printer, identify exactly when the defect first appears.

For manufacturers operating high-speed pouch packaging lines, understanding how product movement and surface conditions affect printing is essential. The DAYSJET guide to continuous inkjet printing on flexible pouches explains additional factors affecting reliable date and batch coding.

Choose the Right CIJ Ink and Prepare the Film Surface

The first step is to obtain a representative sample of the actual film, including its coatings and printing-side information. Ask the film supplier whether corona or plasma treatment has been applied and whether the printable surface remains suitable at the time of coding. Surface-energy testing with appropriate dyne solutions can help investigate wetting, but it is not a universal pass-or-fail measurement. Treatment effects can change during storage, and adhesion still depends on the complete ink-and-substrate combination.

Next, select an ink formulated for the packaging material and operating conditions. A fast-drying ink may reduce smudging on a moving production line, while a high-adhesion formulation may be better suited to certain non-porous films. These benefits are not interchangeable: quick drying does not guarantee scratch resistance, and pigment ink is not automatically better than dye ink for transparent packaging.

The correct choice also depends on whether the package encounters refrigeration, moisture, heat sealing, or repeated handling. For food and pharmaceutical packaging, buyers must additionally confirm the approved application, print location, and applicable food-contact or migration requirements with the relevant suppliers.

As an industrial coding equipment manufacturer, DAYSJET provides CIJ printing solutions and ink-selection support for different production environments. The DAYSJET 1770-60 continuous inkjet printer is designed for industrial coding applications and supports various specialty ink options, including high-adhesion formulations.

With a 60-micrometer nozzle, 1–5-line printing capability, and flexible operating settings, this model is worth evaluating for date codes, batch numbers, and product identification on suitable packaging materials. However, customers should verify the selected ink’s compatibility with their actual PE, PP, or PET film before placing an equipment order.

Test Print Durability and Optimize the Packaging Line

Before purchasing equipment or changing an ink formulation, packaging manufacturers should conduct controlled trials using production-representative materials. Testing should reflect the actual message size, printing surface, line speed, and intended printhead distance. Record the ink type, substrate batch, surface treatment, operating conditions, and time between coding and the next mechanical contact.

Evaluate print quality at several stages. Check legibility immediately after printing, after the normal drying interval, and after pouch forming, stacking, or transport simulation. Depending on the application, practical inspections may include finger-rub checks, controlled abrasion testing, tape-adhesion testing, and exposure to moisture or cold. Define measurable acceptance criteria, including code readability and visible ink transfer, before testing.

Production-line setup is equally important. Keep the film moving consistently through the coding area, stabilize web tension or pouch position, and synchronize the print trigger with actual product movement. Rollers and guides should not contact freshly printed characters before the ink has reached the required handling resistance.

Operators should inspect the first coded product after each changeover and monitor print quality throughout the shift. For manufacturers experiencing repeated coding problems, it is useful to distinguish material adhesion failures from printhead alignment, triggering, and mechanical handling issues.

DAYSJET supports customers through equipment consultation, ink selection, installation guidance, and consumables supply. Packaging manufacturers can provide film samples, code specifications, expected line speeds, and handling requirements to help identify a suitable coding configuration. Its technical service and support resources also help customers evaluate their long-term operating and maintenance needs.

Conclusion

Reliable CIJ ink adhesion on plastic film packaging comes from matching the ink to the actual film, checking surface treatment, allowing sufficient drying time, and validating durability under production conditions. For PE, PP, PET, and laminated pouches, a structured testing process is more valuable than a generic claim of strong adhesion. With suitable equipment selection, technical support, and consistent inspection procedures, manufacturers can improve date-code readability, reduce avoidable rejects, and maintain reliable product traceability.