Manufacturing Processing Guide

TPE Injection Molding

TPE injection molding is a manufacturing technique where TPE materials are melted and injected into a mold cavity to form specific shapes.

TPEs are a class of polymers that combine the flexibility and elasticity of rubber with the processability of thermoplastics. Unlike traditional rubber, which requires vulcanization, TPEs can be melted and reformed multiple times without losing their properties, making them ideal for injection molding.

Key properties include:

Excellent flexibility and elasticity: TPEs can stretch and return to their original shape, similar to rubber.
Resistance to heat, oils, and chemicals: They maintain performance in harsh environments.
Good colorability and transparency options: Allows for aesthetic customization.
Recyclability: TPEs can be reprocessed, reducing waste.
Cost-effectiveness: Compared to traditional rubbers, TPEs offer economic benefits in large-scale production.

TPE Injection Molding Process

TPE injection molding, also known as thermoplastic elastomer injection molding or TPE molding, is a manufacturing technique where TPE materials are melted and injected into a mold cavity to form specific shapes. TPEs are a class of polymers that exhibit both the elasticity of rubber and the processability of thermoplastics, making them suitable for applications requiring flexibility and durability. This process is widely used in industries such as automotive (e.g., seals, gaskets), consumer goods (e.g., soft-touch grips), and medical devices (e.g., tubing, seals) due to their versatility and recyclability.

The process begins with feeding TPE pellets into an injection molding machine, where they are heated to a molten state and injected under high pressure into a closed mold. After cooling, the finished part is ejected, and ready for use or further processing. This method is known for its high-volume production capabilities, with short cycle times enabled by the advanced properties of TPE compounds.

Benefits of Using TPE in Injection Molding

TPE injection molding offers several advantages, enhancing its appeal for manufacturers:

Efficient Production: TPEs have short cycle times, enabling rapid production rates. This is particularly beneficial for high-volume manufacturing.
Design Flexibility: TPEs can be molded into complex shapes, offering a range of hardness levels to meet diverse needs.
Sustainability: TPEs are recyclable, aligning with environmental goals. This is supported by findings that TPE production does not release harmful substances like dioxins.
Cost Savings: Compared to traditional rubber molding, TPE injection molding reduces costs, especially for large production runs, due to automated processes and material reusability.

Types of Thermoplastic Elastomers

TPEs are categorized into several types based on their chemical structure and properties, each offering unique advantages for specific applications. Below is a detailed breakdown:

Type	Description	Key Properties	Common Applications
TPE-S (Styrenic Block Copolymers)	Includes SBS (styrene-butadiene-styrene) and SEBS (styrene-ethylene/butadiene-styrene).	SEBS has better heat and chemical resistance than SBS.	Seals, gaskets, adhesives, footwear.
TPU (Thermoplastic Polyurethane)	Known for high abrasion resistance and flexibility.	Excellent wear resistance, flexibility, and toughness.	Automotive interiors, medical tubing, footwear.
TPO (Thermoplastic Polyolefin)	Blends of polypropylene and ethylene-propylene rubber.	Good weatherability, impact resistance.	Automotive exterior parts, building materials.
TPV (Thermoplastic Vulcanizate)	Made by dynamic vulcanization, offering high-temperature resistance.	High-temperature resistance, elasticity.	Under-the-hood automotive parts, industrial hoses.
TPC (Thermoplastic Polyester Elastomer)	Also known as copolyester elastomers, with good heat and chemical resistance.	Heat resistance, chemical resistance, electrical insulation.	Industrial applications, automotive hoses.
TPA (Thermoplastic Polyamide Elastomer)	High strength, based on polyester-amide or polyether-amide block copolymers.	High strength, fatigue resistance.	Aerospace components, high-performance parts.

TPE Injection Molding Design Guide

Designing parts for TPE injection molding is critical to ensure manufacturability and part quality. The following are essential guidelines

Wall Thickness: Maintain consistent wall thickness throughout the part to prevent warping or uneven shrinkage, given TPEs’ lower shrink rate compared to other materials. This consistency helps in achieving uniform cooling and reduces stress.
Undercuts: Avoid undercuts, as TPEs’ flexibility can make part removal difficult, potentially damaging the mold or part. Design parts to allow easy ejection.
Draft Angle: Incorporate a draft angle of at least 1 degree on each side to facilitate smooth ejection from the mold, reducing tool wear and cooling times, which can help control costs.
Venting: Ensure proper venting in the mold design to allow volatile organic compounds (VOCs) to escape, preventing defects like burns or voids. This is particularly important given TPEs may produce VOCs during molding.
Gate Placement: Strategically place gates to minimize stress concentrations and prevent warping. Proper gate design, such as using a standard main runner with a 3C draft angle, can enhance material flow and part quality.
Cooling: Control cooling rates, as TPEs cool slower than other materials like polypropylene, which can affect part dimensions and surface finish. Adjust mold temperature to ensure consistent quality, with higher mold temperatures potentially improving weld lines and appearance.

TPE Molding Process Guide

The production process for TPE injection molding involves several key parameters that must be carefully monitored to ensure part quality and production efficiency. The following details provide a comprehensive overview:

Temperature Control:

Barrel Temperature: Set between 160°C and 210°C, varying by TPE type and manufacturer recommendations. This range ensures the material melts uniformly without degrading.
Nozzle Temperature: Maintain at 180°C-230°C to facilitate smooth material flow into the mold, preventing premature solidification.
Mold Temperature: Adjust to prevent moisture condensation, typically higher than the condensation temperature of the injection zone. Higher mold temperatures can improve weld lines and part aesthetics but may extend cycle times.

Pressure Management:

Injection Pressure: Typically ranges from 150 psi to 450 psi, depending on part complexity and material viscosity. Soft TPEs require minimal pressure due to low viscosity, ensuring proper filling without flashing.
Holding Pressure: Applied to pack the mold and ensure part density, preventing voids or sink marks.

Speed and Timing:

Injection Speed: Control to fill the runner system rapidly, then slow down after the gate, maintaining speed until the part is 90% full, then reduce further to complete filling without flashing. TPEs are shear responsive, so increasing speed can help with filling thin walls.
Cooling Time: Monitor to ensure proper solidification, varying by part size, complexity, and TPE material. Proper cooling is essential for dimensional stability.

Material Preparation:

Drying: Dry TPE pellets to less than 5% moisture content, ideally between 2%-3%, using a vacuum drying oven at 60°C-70°C for 2 hours. Properly seal dried materials to prevent reabsorption of moisture, which can affect part quality.

Mold Design and Venting:

Ensure proper venting to manage VOCs and prevent defects. Gate design, such as using a standard main runner with a 3C draft angle, is critical for material flow. Monitor part weights to verify process stability and consistency, as gate size, location, and runner dimensions can affect properties.

Overmolding with TPEs

Overmolding enhances part functionality, such as adding grips to tools or seals to electronics, expanding TPE’s application scope. The process involves molding TPE over a substrate to create parts with combined properties, such as soft-touch surfaces or enhanced grip. It’s a significant application for TPEs, particularly in consumer and medical products.

Material Selection for TPE Overmolding

Substrate Material: Common substrates include polypropylene (PP), polyethylene (PE), ABS, and polycarbonate (PC). The choice affects adhesion and compatibility.
TPE Selection: Depends on desired properties like hardness and adhesion. Styrenic TPEs adhere well to polyolefins, while modified TPEs are needed for engineering plastics.

Design Considerations for TPE Overmolding

Adhesion: Ensure good bonding through chemical or mechanical means, such as textured finishes for mechanical interlocks.
Wall Thickness: The TPE layer should be thick enough to prevent delamination, with sufficient thickness for functionality.
Mold Design: Requires multiple cavities or alignment features to accommodate both substrate and TPE, ensuring precise overmolding.

Processing Parameters for TPE Overmolding

Temperature Control: Manage substrate and TPE temperatures for proper bonding, with high melt temperatures critical for adhesion.
Injection Speed and Pressure: Controlled to prevent substrate damage, with profiling to ensure uniform flow, as per industry practices.
Cooling Time: Sufficient to allow bonding, typically longer for overmolded parts, with cooling times of 35-40 seconds per 0.100″ wall thickness for overmolded sections.

Contact Us for TPE Injection Molding

TPE are relatively common injection molding plastic, the Thermoplastic Elastomer (TPE) material combines the benefits of both thermoplastics and elastomers. Erye Molding has the skills and know-how to support you from part design through prototyping and production. We have the expertise for your TPE injection molding project, contact us and request a quote today.