Thermoplastic Elastomers
Key Takeaways
- TPEs behave like rubber but process like thermoplastics, so they can be molded, extruded and reground.
- No curing or vulcanization step is needed, which removes a whole stage from the process.
- They suit overmolding and co-molding, and blend readily with other materials to tune feel and strength.
- Low surface energy makes them hard to print and bond, so pretreatment or specially formulated ink is usually required.
Thermoplastic Elastomers (TPE)
Thermoplastic elastomers are polymers that behave like vulcanised rubber in service but process like a thermoplastic — they can be injection moulded, extruded, reground and recycled, with no irreversible curing step. That combination comes from a two-phase morphology: rigid domains that act as physical crosslinks at room temperature, and soft flexible segments that supply the elasticity. Heat the material and the rigid domains soften, so it flows; cool it and they reform.
The Principal TPE Families
| Family | Abbreviation | Characteristics | Typical applications |
|---|---|---|---|
| Styrenic block copolymers | TPE-S (SBS, SEBS) | Soft, low cost, easy to overmould; SEBS has good UV and thermal stability | Grips, soft-touch overmoulds, seals |
| Thermoplastic polyolefin | TPO | Low density, good weathering, very low surface energy | Automotive bumpers, interior skins |
| Thermoplastic vulcanisate | TPV | Dynamically vulcanised rubber phase; strong compression set resistance | Weatherstrip, seals, gaskets, under-bonnet parts |
| Thermoplastic polyurethane | TPU | Outstanding abrasion resistance, toughness, oil resistance | Tubing, cable jacketing, wearables, footwear |
| Copolyester | COPE / TPC | High-temperature and chemical resistance | Bellows, couplings, industrial hose |
| Polyether block amide | PEBA | Low density, excellent flex fatigue, energy return | Medical tubing, catheters, sports equipment |
Hardness spans roughly Shore A 20 to Shore D 70 across the families, so specification usually starts with the required hardness and service temperature before narrowing to a chemistry.
Laser Marking Thermoplastic Elastomers
TPEs are among the more difficult materials to mark cleanly, for reasons that follow directly from what makes them useful:
- Low melting and softening points. The thermal window between forming a mark and melting or distorting the surface is narrow. Excess heat produces a smeared, glossy depression rather than a crisp mark.
- Elastic recovery. The material deforms and rebounds, so depth-based engraving gives poor definition. Contrast-based marking is the better strategy.
- Poor 1064 nm absorption in polyolefinic grades. TPO and many TPE-S grades are aliphatic and behave like polypropylene — they need a laser additive to mark at all with a fiber laser.
- Carbon black loading. Many TPEs are black, so a dark carbonized mark is invisible. A foamed light mark, best produced with a short-pulse MOPA laser, is usually the only legible option.
In practice, short pulses, low average power and high marking speed — delivering energy quickly and limiting accumulated heat — give the best results.
Bonding, Printing and Surface Treatment
Olefinic TPEs share polypropylene’s low surface energy, typically around 29–31 mN/m, and will not accept inks, adhesives or coatings without pretreatment. Atmospheric plasma and flame plasma both raise it into a workable range, though the soft surface demands gentler settings than a rigid moulding would tolerate. TPU and copolyester grades are more polar and generally easier to bond and print.
A further consideration in overmoulded assemblies: adhesion between the TPE and its rigid substrate depends on chemical compatibility between the two, not on surface treatment. TPE-S bonds well to styrenics, TPU to polycarbonate and ABS, and TPO to polyolefins. Mismatched pairs fail at the interface regardless of processing.
Surface Treatment Choices for TPE
TPEs combine low surface energy with mobile additives and a soft, heat-sensitive
surface, which rules out or complicates several pretreatments that work well on rigid
polymers. The practical comparison:
| Method | Suitability for TPE | Notes |
|---|---|---|
| Atmospheric plasma | Usually the best inline choice | Selective, robot-mountable and low thermal load. Standoff control matters more than on rigid substrates because the surface deforms. |
| Cold gas plasma | Best result, batch only | Reaches shadowed geometry on overmoulded assemblies and gives the most durable activation. Outgassing of oils extends pump-down time. |
| Flame plasma | Use with caution | Effective, but the thermal load can distort or gloss a soft surface. Traverse speed must be controlled tightly. |
| Corona | Films and sheet only | A web process. It does not address moulded or overmoulded TPE parts. |
| Chemical primer | Effective, with a cost | Still common on TPV and TPO. Adds a wet process, solvent handling and a cure step to the line. |
Whichever route is chosen, the treat-to-bond interval matters more on TPE than on any
other polymer family. Oils and plasticisers migrate back to the surface quickly, so
activation that would last days on a rigid polyolefin may last hours here.
Overmoulding and Two-Shot Considerations
Most TPE in production is overmoulded onto a rigid substrate, which makes bond strength a
moulding question before it is a surface question:
- Chemical compatibility governs the bond. A styrenic grade bonds
readily to polystyrene and ABS; a TPV bonds to polypropylene. Pairing a TPE with an
incompatible substrate produces a mechanical interlock at best, and specifying a bondable
grade is far cheaper than pretreating a mismatch. - Substrate temperature at the second shot is frequently the difference
between a bonded and a peelable part. A cold insert gives a poor bond regardless of the
TPE grade. - Design a mechanical lock anyway where the joint is structural. Through
holes, undercuts and dovetails carry load that a marginal chemical bond will not. - Mould release is the usual contaminant. On overmoulded assemblies the
release agent used on the rigid insert is the most common cause of adhesion failure at the
interface, and it is easy to overlook because it originates in an upstream process.
Troubleshooting TPE Marking, Printing and Bonding
| Symptom | Likely cause | Correction |
|---|---|---|
| Laser mark distorts or pits the surface | Low softening point — energy is deforming before it marks | Shorten pulse width on a MOPA source and raise speed. Long pulses are the wrong tool on soft grades. |
| No usable laser contrast on a natural grade | Polyolefinic TPE with poor 1064 nm absorption | A laser additive is effectively mandatory. Confirm it does not alter durometer beyond specification. |
| Ink adheres at first, peels within days | Plasticiser or oil migration into the ink layer | This is a material-selection problem, not a treatment problem. Specify a low-migration grade or an ink chemistry formulated for plasticised substrates. |
| Bond good on trial parts, poor in production | Longer treat-to-bond interval in the real line | Move the treatment station adjacent to bonding. Activation decay is faster on TPE than on rigid polymers. |
| Overmould peels cleanly from the substrate | Incompatible TPE and substrate pairing, or a cold insert | Check chemical compatibility first, then substrate temperature at the second shot. Pretreatment cannot rescue a mismatched pair. |
| Printed graphics crack in service | Ink film less elastic than the substrate | The substrate recovers elastically and the coating does not. Specify a flexible ink system rated for the strain the part actually sees. |
Related Terms and Reading
- Plastics laser marking solutions
- Polymer surface pretreatment
- Polyurethane
- Best practices for bonding semi-crystalline thermoplastics
- Adhesion failures
Applying this in production
The Sabreen Group provides independent engineering support for marking, bonding and pretreatment of thermoplastic elastomers. If you are specifying a process, qualifying a material or troubleshooting a production problem, our engineering services team can help. Contact us to discuss your application.
Frequently Asked Questions
What is a thermoplastic elastomer?
A class of polymers combining the elastic properties of rubber with the processability of thermoplastics. TPEs stretch and return to shape like traditional elastomers, but can be molded, extruded and reused like any other thermoplastic, which reduces waste.
How do TPEs differ from conventional rubber?
Conventional rubber requires curing or vulcanization, an irreversible chemical step. TPEs do not, so they can be reprocessed and regrind can be reused. That also makes them compatible with overmolding and co-molding onto rigid substrates.
Where are TPEs commonly used?
Soft-touch grips, seals and gaskets, medical tubing and device components, automotive interior and exterior parts, footwear soles and sports equipment, consumer electronics and flexible enclosures, plus toys, tools and household goods.
Are TPEs difficult to print on or bond?
Yes, typically. Like other low surface energy polymers they are hydrophobic and not naturally wettable, so inks and adhesives struggle to achieve intimate contact. Surface pretreatment or a purpose-formulated flexible ink is normally required.
Can TPE parts be laser marked?
They can, but as with most polymers they have little inherent near-infrared absorption. Laser-sensitive additives compounded into the material are what enable high-contrast marking, and short-pulse MOPA lasers help avoid thermal damage on soft substrates.
Why does ink peel from TPE weeks after it looked well adhered?
Usually migration. Oils and plasticisers in the elastomer move to the surface over time and into the ink layer, weakening the interface after the part has already passed inspection. Surface treatment does not fix this, because the problem originates in the bulk material. Specify a low-migration grade, or an ink chemistry formulated for plasticised substrates.
Which surface treatment suits moulded TPE parts?
Atmospheric plasma is usually the best inline choice — selective, robot-mountable and low in thermal load. Low-pressure cold gas plasma gives the most durable activation and reaches shadowed geometry on overmoulded assemblies, but is batch-only. Flame needs careful control because the thermal load can distort a soft surface, and corona is a web process that does not address moulded parts at all.
What actually determines overmould bond strength?
Chemical compatibility between the TPE and the substrate, and the substrate temperature at the second shot — both before any surface treatment is considered. A styrenic grade bonds to polystyrene and ABS, a TPV to polypropylene; a mismatched pair gives a mechanical interlock at best. Mould release on the rigid insert is the most common contaminant, and it originates upstream where it is easily overlooked.
