Introduction
Thermoplastic Elastomer—TPE —combines the best of two worlds. It feels like rubber but processes like plastic. It stretches and returns to shape. It grips comfortably in your hand. It seals against moisture and dust.
But TPE is not like rigid plastics. It behaves differently. It flows differently. It cools differently. Manufacturers who treat TPE like ABS or polypropylene face problems: inconsistent results, mold design failures, and quality issues.
This guide covers everything you need to know about TPE injection molding: material properties, process parameters, mold design, quality control, and applications.
What Makes TPE Unique?
TPE is a family of materials that behave like rubber at room temperature but can be processed like thermoplastics when heated. It offers elasticity, flexibility, and durability in one material.
Key Properties
| Property | Typical Range | Significance |
|---|---|---|
| Elongation at break | 100% – 600% | Stretches and recovers without breaking |
| Tensile strength | 10 – 30 MPa | Holds together under load |
| Compression set | <30% (after 22h at 70°C) | Maintains seal over time |
| Shore hardness | 30A (soft) to 80D (hard) | Versatile for different applications |
| Low-temperature flexibility | Down to -40°C | Stays flexible in cold conditions |
| Continuous use temperature | Up to 120 – 150°C | Withstands heat in service |
Chemical and Wear Resistance
TPE resists oils, water, and mild solvents. Some grades resist fuels, making them suitable for automotive components. Abrasion resistance is excellent—some TPEs outperform rubber in wear tests.
Medical-grade TPEs meet ISO 10993 standards for biocompatibility, used in syringe plungers and medical tubing.
How Do You Injection Mold TPE?
Key Process Parameters
Melt Temperature
TPE melts at 160°C to 230°C . Softer grades (lower Shore hardness) process at the lower end. A 50 Shore A TPE runs at 170°C to 190°C . A 70 Shore D grade may need 200°C to 220°C .
Injection Speed and Pressure
Moderate injection speed—30 to 60 mm/s —prevents shear heating that can degrade TPE. Injection pressure ranges from 500 to 1200 bar . Complex parts with thin sections require higher pressure.
Cooling Time
TPE has lower thermal conductivity than rigid plastics. Cooling time is shorter—typically 5 to 30 seconds . Total cycle times range from 15 to 60 seconds , making TPE efficient for high-volume production.
The table below summarizes parameters:
| Parameter | Range | Notes |
|---|---|---|
| Melt temperature | 160 – 230°C | Softer grades lower, harder grades higher |
| Injection speed | 30 – 60 mm/s | Moderate to avoid shear degradation |
| Injection pressure | 500 – 1200 bar | Higher for complex parts |
| Cooling time | 5 – 30 seconds | Shorter than rigid plastics |
| Cycle time | 15 – 60 seconds | Efficient for high volume |
Material Handling
TPE absorbs moisture. Dry to below 0.05% moisture content . Drying conditions: 60°C to 80°C for 2 to 4 hours . Poor drying causes voids and surface defects.
Store in humidity-controlled environments—below 50% relative humidity —to prevent reabsorption.
How Should Molds Be Designed for TPE?
Venting
TPE’s low viscosity requires proper venting to release trapped air. Vent depth: 0.01 to 0.02 mm . Vent width: 5 to 10 mm . Place vents at flow path ends and around sharp corners.
Cooling Channels
Even cooling prevents warpage. Position channels 8 to 12 mm from the cavity surface. Maintain a 1:1.5 ratio of channel diameter to distance from cavity. Use turbulent flow (Reynolds number > 4000) for better heat transfer.
Draft Angles and Surface Finish
Minimum draft angle: 1° per side . For textured surfaces, increase to 2° .
Surface finish: Ra 0.8 μm or better . A polished surface reduces sticking and improves part appearance.
Mold Materials
P20 steel is standard for TPE molds—good machinability and durability. For high-volume runs, H13 steel with chrome plating (0.001 to 0.002 mm thick) enhances wear resistance.
Hot runner systems work well for TPE. They reduce material waste and improve consistency. Use valve gates for better flow control.
What Defects Occur and How to Prevent Them?
| Defect | Cause | Solution |
|---|---|---|
| Warpage | Uneven cooling or wall thickness | Optimize cooling channels; design uniform walls (max 2:1 thickness ratio) |
| Sink marks | Excessive shrinkage in thick sections | Increase packing pressure; add fillets to thick areas |
| Flash | Mold mismatch or low clamping force | Check mold alignment; increase clamp force by 10–15% |
| Voids | Moisture in material or poor venting | Improve drying; add more vents |
| Sticky surface | Overheating or low-quality material | Lower melt temperature by 10–15°C; use high-purity TPE |
Quality Control Measures
Statistical Process Control (SPC): Monitor melt temperature and injection pressure. Keep variations within ±5% .
Mechanical testing: Test tensile strength and hardness on 1 in 500 parts .
Dimensional inspection: Use CMMs to ensure tolerances—typically ±0.1 mm for small parts.
Where Is TPE Used?
Automotive Components
TPE’s weatherability and chemical resistance suit exterior and interior applications:
- Door seals
- Grommets
- Steering wheel covers
Medical Devices
Biocompatible TPE meets ISO 10993 standards:
- IV connectors
- Catheter tips
- Syringe plungers
Consumer Products
TPE’s soft touch and durability are valued:
- Toothbrush handles
- Phone cases
- Toy parts
Footwear
TPE provides cushioning and slip resistance:
- Shoe soles (60–80 Shore A)
- Insoles
What Post-Processing Options Exist?
Ultrasonic Welding
Joins TPE parts quickly—0.5 to 2 seconds —with minimal heat. Use 20 to 40 kHz frequencies. Ideal for medical devices where heat-sensitive components are involved.
Painting and Coating
Clean surfaces with isopropyl alcohol before painting. Use acrylic or urethane paints for good adhesion.
Machining
Trim flash with sharp blades—HSS or carbide—at low speeds (1000 to 2000 RPM ) to avoid melting.
What Does a Real-World Example Look Like?
A medical device manufacturer needed a syringe plunger with a soft, biocompatible tip. The plunger body was rigid plastic. The tip needed flexibility for a tight seal.
The solution was overmolding TPE onto the rigid plastic plunger body. The mold was designed with valve gates for precise flow control. TPE was processed at 180°C with 40 mm/s injection speed.
The result: a seamless bond between materials. The TPE tip provided a leak-proof seal. The plunger passed all biocompatibility tests. Production cycle time was 25 seconds, meeting volume targets.
Conclusion
TPE injection molding combines rubber-like properties with plastic processing efficiency. The material offers elasticity (100% to 600% elongation), durability (10 to 30 MPa tensile strength), and low compression set (<30% after 22 hours at 70°C).
Processing requires moderate temperatures (160°C to 230°C), moderate injection speeds (30 to 60 mm/s), and proper drying to below 0.05% moisture. Mold design must account for TPE’s low viscosity—proper venting, even cooling channels, and polished surfaces.
Applications span automotive, medical, consumer products, and footwear. Post-processing options include ultrasonic welding, painting, and machining.
When material, mold, and process align, TPE injection molding delivers consistent, high-quality parts that feel like rubber and perform like engineered plastic.
FAQ
How does TPE differ from TPU in injection molding?
TPE offers broader hardness ranges and better low-temperature flexibility—down to -40°C. TPU provides higher abrasion resistance and tensile strength. TPE is often easier to process with lower melt temperatures. Choose TPE for soft-touch applications and flexibility. Choose TPU for high-wear applications like industrial components.
Can TPE be overmolded onto other plastics?
Yes. TPE bonds well to polypropylene (PP), polyethylene (PE), and ABS. Ensure proper mold temperature—40°C to 60°C —and select compatible TPE grades for strong adhesion. Surface preparation and material compatibility are critical for bond strength.
What causes TPE parts to have a sticky surface?
Overheating during processing causes surface stickiness. Excess plasticizers in low-quality TPE can also migrate to the surface. Solutions: lower melt temperature by 10°C to 15°C, use high-purity TPE grades, and verify drying conditions.
What are the drying requirements for TPE before molding?
Dry TPE at 60°C to 80°C for 2 to 4 hours . Target moisture content below 0.05% . Poor drying causes voids and surface defects. Store in humidity-controlled environments (below 50% RH) to prevent reabsorption.
What Shore hardness should I choose for my application?
30–50 Shore A: Very soft, like rubber bands. Good for grips, soft-touch surfaces.
50–80 Shore A: Medium soft, like shoe soles. Good for seals, gaskets.
80 Shore A – 50 Shore D: Firm, like flexible plastics. Good for structural parts with some flexibility.
50–80 Shore D: Hard, like rigid plastics. Good for wear-resistant components.
Contact Yigu Technology for Custom Manufacturing
At Yigu Technology , we specialize in TPE injection molding. Our experience spans automotive, medical, consumer, and footwear industries.
We help you select the right TPE grade for your application. Our molds are designed with proper venting, cooling, and surface finishes for TPE’s unique properties. We optimize process parameters to prevent defects and ensure consistency.
From overmolding to single-component parts, we deliver high-quality TPE components.
Contact Yigu Technology today to discuss your TPE injection molding project.
