Many plastic materials, such as polyethylene and polypropylene, naturally have low surface energy. This means that paints, adhesives, inks, and metallic coatings often struggle to stick to them, which can cause issues with printing, assembly, painting, or metallization. To address this challenge, manufacturers use various techniques, like flame, plasma, or corona treatments, to temporarily boost surface energy and improve adhesion. Another effective approach is to use high performance gases, which can provide a more permanent increase in surface energy and make plastics much easier to work with.
This article explores how Inhance Technologies’ ModyFy™ process uses specialty gases to activate polymer surfaces for better performance in industrial applications.
To improve adhesion on hard-to-bond plastics, surface activation is typically achieved by introducing polar functional groups onto the surface. This creates a functionalized layer on the plastic, but only at the very surface—typically between 0.01 and 10 microns deep—so the core properties of the material remain unchanged.
ModyFy™ is highly controllable, and ensures a consistent, even activation across all surfaces—including complex shapes, deep grooves, curves, and edges—and makes it possible to treat large volumes efficiently.
Figure 1 Effect of ModyFy™ treatment on surface energy of different plastics
Thermoplastic polyolefins (TPOs) are widely used in the automotive industry thanks to their customizable properties. Traditionally, TPOs with high rubber content are compatible with solvent-based primers for decorative finishes. However, many TPO grades have lower rubber content, making them difficult to activate with conventional primers. ModyFy™ addresses this limitation by permanently activating both high- and low-rubber-content TPO panels, enabling reliable painting, adhesive bonding, and printing.
To validate performance, crosshatch paint testing (ASTM D3359) was performed on ModyFy™-treated TPO plaques (ADX 1310). The results showed perfect adhesion (SB rating) even after 10 weeks of storage prior to painting. Figure 2 presents these results, demonstrating consistent performance across various storage times.
Figure 2 Results of a crosshatch test on TPO (ADX 1310) after treatment and painting (left to right): A) Untreated TPO, B) Treated and stored for one week, C) Treated and stored for two weeks. D) treated and stored for four weeks and E) Treated and stored 10 weeks, prior to painting. Low VOC architectural paint was used in testing.
ModyFy™ treated polyethylene (PE), polypropylene (PP), and TPO panels can be bonded with traditional urethane or epoxy adhesives—without any special surface preparation. In a demonstration, two adhesives (Loctite Hysol U-09SFL for urethane and Loctite Hysol 907 for epoxy) were used to bond a metal component to activated PE, PP, and TPO surfaces. After 24 hours of curing, pull tests (ASTM D4541) revealed a sevenfold increase in the force required to separate the bonded parts compared to untreated surfaces. In every case, the failure occurred within the polymer substrate itself, indicating that the adhesive bond was stronger than the material. Figure 3 and Table 1 provide visual and numerical data from these tests.
Figure 3 Image showing cohesive failure of the substrate when tested with epoxy (clear) and urethane (white adhesive) on ModyFy™ treated TPO plaque.
Table 1 Defelsko test pull force results measured on Untreated and ModyFy™ treated samples.
Water-based adhesives are increasingly popular due to their lower environmental impact and cost, but they typically perform poorly on untreated polyolefins. ModyFy™ surface activation allows these adhesives to wet out the plastic surface evenly, eliminating issues like blistering and poor bonding. Figure 4 compares the performance of a water-based adhesive (3M ‘77’ low VOC adhesive) on untreated versus ModyFy™-treated TPO surfaces. The treated surface shows uniform adhesive coverage and excellent adhesion, while the untreated surface suffers from blistering and delamination.
Figure 4 Adhesive failure mode on untreated TPO plaque and cohesive failure on ModyFy™ treated plaque
In automotive interiors, soft-touch surfaces are often created by bonding urethane foams to rigid polyolefin substrates like TPO. ModyFy™ eliminates the need for tie-coats, primers, or boundary layers, enabling direct bonding with strengths that exceed the cohesive strength of the foam itself.
Chlorinated polyolefin (CPO) primers are commonly used in North America to enhance paint adhesion on exterior automotive plastics, but environmental concerns are driving the search for alternatives. In Europe, CPO primers have been largely replaced by technologies like flame, plasma, corona, and ModyFy™. ModyFy™ treated TPOs not only meet but often surpass OEM paint adhesion specifications, with improved resistance to delamination, scratching, and peeling over the life of the vehicle (see Table 2 below for comparative data).
Table 2: Effect of using ModyFy™ and CPO primers on adhesion of paint to TPO substrate
ModyFy™ surface technologies' versatility allows treatment to be tailored for any forms and shapes. Treatment conditions and equipment are fully customizable, ensuring that the process meets the specific requirements of each customer and application.
This flexibility translates into significant advantages for manufacturing design and operations. ModyFy™ supports both batch and continuous processing, enabling efficient surface activation for products of all sizes and complexities. Over the past four decades, Inhance Technologies has leveraged ModyFy™ to enhance the surface properties across several industries such as packaging, automotive, fuel systems, medical devices and more.
Contact us, to learn how we can enable reliable adhesion, printing, and coating on a wide variety of polymer materials, to continue to drive innovation and performance across multiple markets.