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Injection Molding for Thermoplastic Elastomers
Mar 20, 2020

Injection Molding for Thermoplastic Elastomers

 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

Overmolding

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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