Thermoplastic Polyurethane (TPU) and Thermoplastic Elastomer (TPE) parts combine rubber-like feel with plastic-like processing, but that versatility comes at a cost: low surface energy that causes adhesives to bead up rather than bond. Plasma and corona treatments are the two industrial technologies that consistently solve this without resorting to aggressive chemical etching.
Why TPU and TPE Resist Bonding
Surface energy determines how well a liquid — an adhesive or ink — spreads across and interacts with a solid. When substrate surface energy falls well below adhesive surface tension, the adhesive beads up the way water does on a waxed car. TPU and TPE are formulated with plasticizers, flame retardants, and UV stabilizers that migrate to the surface over time, creating a weak boundary layer even after an initial clean. Historically, manufacturers leaned on chemical primers and solvent etching, but those methods carry real drawbacks: high VOC emissions, worker exposure risk, inconsistent manual application, and ongoing consumable cost.
How Corona Treatment Works
Corona treatment applies a high-voltage, high-frequency electrical discharge between an electrode and a grounded surface, ionizing the surrounding air. The ionized air’s reactive species clean organic contaminants off the part and deposit polar oxygen-containing groups — hydroxyl and carbonyl — that raise surface energy and improve wetting. It’s fast, low-cost, and easy to integrate into extrusion or web-handling lines, which is why it dominates film and packaging applications. Its limitation shows up on complex 3D geometries: the discharge is hard to control in deep recesses, and the dyne level it achieves decays over time, so bonding has to follow shortly after treatment.
How Plasma Treatment Works
Plasma is the fourth state of matter — a mixture of ions, electrons, and neutral particles created by energizing a gas. When plasma strikes a TPU or TPE surface, it micro-etches away contaminants and creates a high density of functional sites for covalent bonding, often producing a bond stronger than the elastomer itself. Atmospheric plasma uses a nozzle mounted on a robotic arm to treat a specific bond line on an assembly line; vacuum plasma treats an entire part inside a sealed chamber, delivering uniform coverage on complex geometries that a nozzle can’t reach precisely.
Choosing Between the Two
Corona fits large flat areas or continuous film processing where throughput speed and lower capital cost matter most. Plasma is the better choice for complex 3D parts, safety-critical bond strength requirements, robotic-integrated automation, and situations where only a specific localized area should be activated without affecting the rest of the part’s surface finish. Both technologies can be tuned by adjusting power, gas flow, or treatment-head distance to suit substrates ranging from a soft 30 Shore A TPE to a rigid 80 Shore D TPU.
Verifying the Treatment Before Bonding
Repeatability is the real advantage plasma and corona hold over manual solvent wiping. Dyne pens give a fast pass/fail check — if the test ink beads up, the surface energy is too low to proceed. Contact angle measurement with a goniometer gives a more precise reading; a low contact angle confirms high surface energy and good wettability. Because activated surfaces undergo “hydrophobic recovery” as reactive groups rotate back into the bulk material or react with ambient humidity, best practice is bonding as soon as possible after treatment — ideally within minutes, not hours. Logging the elapsed time between treatment and bonding on each line, not just the treatment settings themselves, catches the drift that a purely visual inspection will miss. For adhesive selection that pairs correctly with a plasma-activated surface, Email Us with your treatment parameters and target bond strength.
Where This Matters Most
Consumer electronics assemblies — waterproof seals, overmolded tool grips — benefit from the thinner bond lines plasma activation allows, since higher bond strength per unit area means less adhesive surface is needed for a compact design. Automotive weatherstripping and soft-touch dashboard components need bonds that survive years of vibration and thermal exposure without delaminating, which plasma-treated interfaces demonstrably outperform on. Renewable-energy equipment housings using TPE gaskets for weatherproofing see the same benefit: a properly activated surface resists the humidity cycling that outdoor installations experience over a multi-year service life.
Incure’s UV-curable adhesive lines are formulated to work in tandem with plasma-activated TPU surfaces, providing near-instantaneous, high-strength bonds once the surface energy has been raised. Moving away from solvent-based primers toward physical surface activation is also a genuine sustainability improvement — eliminating VOC-heavy chemistry reduces both scrap rates and workplace exposure risk while producing a more consistent bond.
For related background on adhesive selection and bond-line design, see UV glue vs. epoxy for heavy-duty repairs and how CTE mismatch causes adhesive bond failure. If you’re evaluating plasma or corona equipment for a TPU/TPE production line, Contact Our Team to discuss which fits your part geometry and volume.
Visit www.incurelab.com for more information.