New TPEs are developed on a daily basis, for many reasons: new polymer technologies offered by our suppliers, evolving consumer preferences, or the newest government regulation. Depending on your application or end-use environment, you may already know if you need an SBC compound versus a TPV, but how do you choose the right grade?
TPEs can be custom-formulated to fit an extremely wide range of performance requirements, so choosing the right TPE can be tricky – even for the experts!
We always start with an outline of the application’s requirements, and then translate them into material requirements.
Use This Checklist to Guide You Through This Process
1. Intent for TPE Selection: New Grade or Material Replacement
It’s important to understand what material is currently being used, for example PVC or silicone rubber, or even another TPE and where improvements are needed or if there’s a price target.
If this is a brand new application for a TPE, note any functional or performance requirements.
2. Manufacturing Process: Formulating for Processability
Consider how the part will be manufactured and assembled. TPE formulations are adjusted based on how the material is processed, and can be tailored for injection molding, extrusion, or blow molding.
Specialty high-flow TPEs have been developed for complex parts with thin and thick sections or severe undercuts.
If the TPE will be over-molded or co-extruded onto another material, that substrate material is important to know. A TPE that bonds well to nylon won’t necessarily adhere to polycarbonate.
3. Cost Targets: Balancing Price & Performance
Quite often, there are cost targets involved in material selection, either defined in cost per pound or cost per part. Even having an estimate in mind will aid in making the decision.
4. Environmental Conditions: Use and Exposure
Will the product be used indoors, or outdoors, or both? What temperatures will it be exposed to and is chemical resistance required? If the TPE is used in a seal, for example, will it be under load or repeatedly flexed?
Consider these end-use conditions to determine if additives or specialty ingredients are needed:
- Temperature Requirements: Minimum and maximum constant use temperature, time exposed to extreme temperatures
- Exposure to UV or extreme weather conditions
- Chemical exposure: Is splash resistance required or will the part be submerged? Temperature during the exposure? Chemical type: acid, base, oil, cleaning solution, etc.?
- Usage: Is the part under load, or will it be repeatedly flexed or extended?
5. Regulatory Concerns: Industry and Market
Whether you’re designing a medical device or a pipe seal, there are rules and regulations that apply, depending on the industry and world region. Certifications or additional testing may be required, and may effect the choice of ingredients used in the TPE.
Consider the following:
- Electrical/Wire & Cable - UL certification or listing may be required, REACH SVHC compliance
- Automotive - OEM material specification approval
- Consumer Products, Housewares, Toys – compliance with the FDA for food contact in the US, or European directives for Food Contact (EU 1935/2004 and PIM 10/2011) and Toy Safety: 2009/48/EC and EN-71-3
- Medical & Healthcare - ISO 10993-5 compliant recipes for biocompatibility
- Building & Construction - NSF 51 and NSF 61 certification for use with potable water
6. Aesthetics & Surface Appearance: Determine Look & Feel
TPEs can be tailored to meet specific aesthetic requirements and are typically characterized by feel, finish, and color:
- Surface Feel/Haptics:
- High surface friction or “grippy” to the touch
- Dry feel or silicone-like
- Silky-smooth or lubricious
- Surface Finish
- Glossy (able to mimic high gloss levels of PVC)
- Matte (low gloss, rubber-like look & feel)
- Color
- In their “natural” form, TPEs can be clear like Plexiglas, translucent, or opaque, depending on the formula
- TPEs can also be supplied in custom colors, or can be colored on-line during processing. Some TPEs accept colors better than others.
7. Material Performance: Property Prioritization
The physical and thermal properties of a TPE are directly related to its composition and method of manufacture. If there are specific requirements for properties like hardness or performance like tear strength, those should be noted early in the material selection process.
Consider these factors to start:
- Hardness – Although the Shore A scale is most often used, TPEs can be measured on Shore OO, A, or D scales, and can range from a super soft gel (think shoe inserts) to a hard plastic like polypropylene.
- Stretch and Bounce-Back – By definition, a TPE can be stretched to twice it’s length and return back to it’s original shape. How a TPE stretches and “bounces back” is indicated by it’s tensile and elongation properties.
- Compression Set – Will the TPE part be under load, or expected to hold a seal over a long period of time? Under what conditions; elevated or low temperatures? Compression set requirements will determine what family of TPEs to choose.
- Abrasion Resistance or Resistance to Wear - Is this a disposable product, or something that needs to withstand repeated use over a long period of time? The “toughness” of the TPE depends on its chemistry.
- Tear Strength or Puncture Resistance - Consider how the product will be used, for example, for baby products, you’ll want a TPE with resistance to biting and tear. Tear strength can be measured, and TPEs can be optimized for maximum tear and puncture resistance.
- Resistance to Bending - Will the TPE be bent or flexed during use? This may translate into a flexural modulus requirement., which measures the TPE’s tendency to bend.
- Adhesion to Other Materials – Will the TPE be over-molded onto a rigid plastic like polycarbonate, like in a power tool handle? Will it be co-extruded with polypropylene to create a hard/soft seal? The substrate material is important when selecting the appropriate TPE.
- Special Requirements - Consider any special characteristics or attributes that may be needed for the TPE. Some examples:
- energy absorption for acoustic dampening
- recycled content
- mineral reinforced
- anti-microbial for hot, wet environments
A little context: Most often it’s at the point of engineering transfer that I talk with brand managers, industrial designers and design engineers as they evaluate material options to hone in on a specific grade. They’re pleased and surprised to learn the breath of TPE formulation possibilities available to them – or how easily a grade can be customized.
Looking for an easy to use guide for choosing the right TPE? Download this handy worksheet to simplify your next project.
