While people are talking about thermoplastic elastomers, we usually easily think of TPE.The injection molding process is adapted to TPEs rather readily. The various classes of TPEs will generally mold well. Historically, the thermoplatic urethanes were the exception due to their high viscosity, but in recent years TPU grades that injection mold well have been commercialized. In order to process TPEs, the key process variables, including melt temperature, melt viscosity, and shrink rate, have to be set to accommodate the particular properties of any given class of TPE.
The TPVs represent a special case since the structure does not consist of a single polymer type. TPVs have a cross-linked rubber phase dispersed in a thermoplastic phase. Some are highly tailored to injection molding and work extremely well. These molding grade TPVs work better in thin and difficult-to-mold parts. Typical injection molding parameters & typical temperature settings for commercial TPEs are in below Tables.
Typical Injection Molding Parameters for Commercial TPEs
| TPE Class | Typical Melt Temperature, °C | Typical Injection Pressure, MPa | Typical Shrinkage Rate, % |
|---|---|---|---|
| SBC | 190–200 | 1.0–5.5 | 0.3–0.5 |
| TPO blend | 175–205 | 1.0–10.0 | 0.8–1.8 |
| EPDM TPV | 190–230 | 1.0–10.0 | 0.5–4.7 |
| NBR TPV | 190–230 | 1.0–10.0 | 1.0–2.2 |
| MPR | 199–255 | 1.0–5.5 | 1.1–1.9 |
| TPU | 175–205 | 1.0–7.0 | 0.5–2.5 |
| COPE | 180–260 | 2.0–10.0 | 0.5–1.6 |
Typical Injection Molding Temperature Setting for Commercial TPEs
| TPE | SBS | TPO | TPV | MPR | TPU | COPE |
|---|---|---|---|---|---|---|
| Zone | Temperature, °C | Temperature, °C | Temperature, °C | Temperature, °C | Temperature, °C | Temperature, °C |
| Feed/Rear barrel | 120–150 | 185–200 | 170–190 | 171–177 | 160–182 | 200–215 |
| Center barrel | 170–182 | 190–210 | 170–190 | 171–177 | 177–199 | 205–235 |
| Front barrel | 185–195 | 200–220 | 170–190 | 171–177 | 188–210 | 210–235 |
| Nozzle | 190–200 | 200–220 | 170–210 | 171–177 | 190–210 | 215–240 |
| Melt | 190–200 | 207–216 | 185–205 | 171–177 | 185–210 | 220–245 |
| Mold | 22–32 | 10–50 | 10–80 | 21–49 | 38–60 | 20–50 |
There are many reasons to use “soft-touch” materials over rigid parts for industrial and consumer goods. Due to the property of elastomer, TPE we are widely used in overmolding.
Processing techniques such as co-injection, two-shot molding, and insert molding have been used with increasing frequency since they offer significant cost and performance advantages.
Two-shot injection molding provides the greatest adhesion between the rigid substrate and the soft TPE compound, but it is difficult to control and expensive. In this method the substrate and the TPE are injected simultaneously, and the TPE migrates into the proper position [201].
Two-shot injection molding uses a complex mold with several gates and activated slides. The rigid substrate is injected first, and then the mold is indexed to another barrel, and the TPE compound is injected onto the rigid substrate.
Anyway, for any further information, you can also contact Qiqiangsheng Moulds for more details about plastic injection molding services.
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