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In the evolving world of product branding and part decoration, pad printing remains a reliable method for applying precise, durable images onto a wide range of plastic components. However, when it comes to printing on “difficult” substrates—such as polypropylene (PP), polyethylene (PE), nylon (PA), or thermoplastic elastomers (TPE)—even seasoned decorators can run into adhesion challenges.
These materials are prized for their chemical resistance, durability, and moldability—but these same properties make them inherently difficult to decorate using conventional ink systems. This article explores the technical factors at play when printing on low surface energy plastics, outlines best practices for ink selection and surface treatment, and introduces specialized ink systems developed to solve these specific challenges.
Most plastics that fall into the “difficult to print” category have one thing in common: low surface energy. Measured in dynes/cm, surface energy determines how well a liquid (in this case, ink) wets the surface. If the ink beads up or fails to spread evenly, it’s a clear sign that adhesion will be poor. Typical printing success requires a surface energy of at least 38–42 dynes/cm, yet untreated PE and PP surfaces often measure below 30 dynes/cm.
This low wettability prevents the ink from bonding properly, leading to poor adhesion, image flaking, or complete failure during durability testing (e.g., crosshatch, rub, or solvent resistance tests).
Before considering specialized ink systems, it’s important to explore surface treatment options that can increase the surface energy of the plastic part. The most common methods include:
Each treatment method has its benefits and limitations based on the part’s geometry, material, and production throughput.
While surface treatment is often essential, ink selection plays an equally critical role. The right ink system must be tailored to the material properties, part function, and durability requirements. Here’s a breakdown of popular substrate types and recommended ink chemistries:
These are two of the most common but challenging plastics. Inks for untreated PP/PE often require pre-treatment or a special adhesion promoter.
Nylon is hygroscopic and prone to variable adhesion due to its moisture content.
Soft-touch coatings and TPEs used in consumer goods or grips are notoriously difficult due to their oily or waxy surface feel.
Because plastic formulations can vary even within a single resin type, testing remains essential. Always perform adhesion validation using recognized industry standards:
Be aware that results may vary depending on print pad hardness, cliché depth, ink viscosity, and drying conditions.
Decorating low surface energy plastics may present challenges, but with the right combination of surface treatment, ink chemistry, and process control, pad printing can still deliver vibrant, permanent images across a wide range of difficult substrates. As materials evolve, ink technology continues to advance—providing more options than ever for meeting the durability, regulatory, and aesthetic demands of modern plastic products.
At Deco Technology Group, we’ve helped hundreds of companies overcome substrate-related print challenges with Swiss-engineered ink systems and technical guidance. Whether it’s medical devices, automotive parts, consumer electronics, or industrial components—we’re ready to help bring your pad printing goals to life.
If you're facing print failures on polypropylene, nylon, or other tough plastics, we can help. At Deco Technology Group, we offer Swiss-made Printcolor inks engineered specifically for low-energy substrates—plus hands-on technical support to get your process dialed in.
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