Flexible packaging is all around us – whether in the form of snack pouches, medicine blister packs, or the labels on bottles and cartons. It is lightweight, versatile, and increasingly sustainable. Yet one persistent challenge shadows its success – inks simply don’t like to stick to plastic films. When adhesion fails, the consequences are visible and costly – smudged graphics, peeling labels, delamination, and even product recalls. For printers, converters, and brand owners, ensuring that inks bond reliably to these surfaces is a matter of both science and business.
Why films resist inks
Unlike paper, which absorbs ink into its porous structure, polymers such as polyethylene, polypropylene, and polyester are smooth, chemically inert, and water-repellent. Their low surface energy means that when ink is applied, it tends to bead up like water on glass rather than spreading evenly. Solvent-based inks have traditionally been used to overcome this, as the solvents lower surface tension and improve wetting. However, environmental pressures and stricter regulations are driving the industry toward alternatives.
Water-based inks, while safer and more sustainable, have higher surface tension and struggle to wet these non-porous substrates. Achieving good wetting is essential because adhesion depends on the ink drop flattening across the surface. If the angle of the droplet remains steep, the print will lack the intimate contact needed for bonding. Coated and treated films, which often measure in the range of 38–56 dynes per centimetre, require inks with even lower surface tension to spread spontaneously.
The invisible barriers
Beyond the natural chemistry of polymers, other factors interfere with adhesion. Additives used during film processing, such as slip or anti-block agents, can migrate to the surface and form an invisible, slippery layer that reduces surface energy. Contaminants from handling – fingerprints, dust, oils, and mold release residues – further obstruct bonding. Even when inks are designed with the right viscosity and colour strength, these surface conditions can sabotage performance.
Ink formulation itself is a balancing act. Solvent-based systems spread easily but raise safety and environmental concerns. Water-based systems are cleaner but dry more slowly and can fail on untreated plastics. To bridge this gap, chemists have introduced new polymers that reduce surface tension, crosslinking agents that strengthen resistance to heat and chemicals, and hybrid resins that combine adhesion with printability. The direction is clear: inks are evolving to grip more stubborn surfaces while remaining compliant with regulations.
Raising surface energy
If adhesion is all about contact, then raising the surface energy of films becomes the natural solution. Techniques such as corona discharge, flame treatment, and atmospheric plasma have become cornerstones of modern packaging production. By bombarding polymer surfaces with energetic ions, these treatments break molecular bonds and introduce polar groups, transforming a surface that repels inks into one that welcomes them.
Corona treatment is fast, effective, and easily integrated into high-speed converting lines. Plasma systems, though more sophisticated, offer precise control and can even clean the surface by burning away microscopic contaminants. Flame treatment remains useful for three-dimensional objects like bottles, while chemical primers are sometimes applied as an anchoring layer before printing.
The benefits of these treatments, however, diminish over time. Additives migrate back to the surface, and molecular chains relax, meaning treated films should be printed quickly or re-treated before use. Quality control tools such as contact angle measurement provide a more reliable indication of treatment success than traditional dyne pens, giving converters greater confidence in their processes.
Business and regulatory pressures
Adhesion is not merely a technical puzzle; it has commercial and regulatory dimensions as well. In sectors such as food and pharmaceuticals, inks must be low migration, ensuring that no harmful components pass through the packaging into the product. This has led to the development of next-generation ink systems formulated without restricted substances and designed to meet strict local and global regulations.
Toward best practices
Achieving consistent adhesion requires discipline across the entire chain – from material handling to final storage. Resin pellets should be properly dried to avoid moisture uptake that weakens bonding. Surfaces must be kept clean, free of oils and dust, and printing or lamination should occur soon after treatment. Packaging stored in unsuitable conditions risks additive migration, which undermines adhesion before it even reaches the press. In some cases, lightly texturing a surface can provide microscopic ridges and valleys that enhance mechanical anchoring for the ink film.
At the forefront of innovation in inks, adhesives, and coatings, GLS Speciality Chemicals has built a strong reputation as a partner of choice for converters and brand owners worldwide. With a deep commitment to sustainability, GLS develops next-generation water-based, solvent-less, and UV-curable solutions that not only ensure superior adhesion on challenging substrates but also align with global compliance and recyclability goals. By combining scientific expertise with state-of-the-art manufacturing and a customer-centric approach, GLS empowers packaging professionals to achieve vibrant, durable, and environmentally responsible results across food, pharma, and consumer packaging segments.
Looking ahead
The story of ink adhesion in flexible packaging is one of convergence between science and commerce. Advances in polymer chemistry are yielding inks that stick to surfaces once considered impossible. Surface treatment technologies are becoming smarter, cleaner, and more integrated into high-speed lines. Regulators and brand owners alike are insisting on solutions that are safer and more sustainable.
For converters and packaging professionals, the challenge is to bring all of these elements together, choosing the right ink, applying the right treatment, and maintaining the right process discipline. The reward is packaging that not only looks vibrant and professional but also stands up to the stresses of handling, transport, and shelf life.
In the end, adhesion is more than just chemistry – it is a reflection of trust. Brands rely on it to ensure their products are recognized and remembered. Consumers rely on it for safety and quality. And as the industry races toward a more sustainable future, ensuring that the printed message sticks has never been more important.
