Material Thoughts: A TPV for car weather seals, a TPE for EPDM replacement

The mailbag this week brought news of a new thermoplastic vulcanizate introduced by ExxonMobil Chemical, plus a thermoplastic elastomer commercially introduced by Alliance Polymers & Services. The former material is being marketed for automotive parts such as glass encapsulated weather seals whereas the latter is of interest to processors seeking a cost-effective replacement for vulcanized rubber and EPDM in applications such as extruded glazing gaskets and seals for refrigerators, dishwashers and other appliances.

From ExxonMobil Chemical (Houston, TX) comes Santoprene M200 TPV for automotive parts such as glass encapsulated weather seals for quarter lights and side fixed glass applications, parts requiring a top appearance. According to the supplier, this thermoplastic vulcanizate (TPV) has a low dynamic viscosity, which results in enhanced flow over a wide range of shear. The result is molded seals with a high-end surface appearance and no flow marks.

When compared to other TPVs used in these applications, processability is improved, claims ExxonMobil Chemical, as the injection pressure can be reduced by about 30-40%, injection temperatures can be lowered by 10° C (50° F) and shorter cycle times are possible, depending on part size and wall thickness. The lower injection pressure also means the new TPV grades are less sensitive to flow direction during molding, so there is less risk of part warping.

The new grades have high gloss levels; processors can turn to mold graining to match the surface aspect of extruded profiles. These TPV grades' compression and tension set are comparable to EPDM rubber. They are available in two hardness levels, 60 Shore A and 75 Shore A, and can be used as a drop in replacement for existing materials.

New from thermoplastic elastomers (TPEs) distributor Alliance Polymers & Services (APS, Romulus, MI), is the Polymax Maxelast D-Series of TPEs for extrusion applications. They are billed as a cost effective replacement for vulcanized rubber and EPDM.

Applications targeted include not only the above-mentioned extruded glazing gaskets and seals for refrigerators, dishwashers and other appliances, but also pipe seals, ladder feet, water stops and blown compounds for low density seals. Additional applications include automotive and construction window and door seals, plus solar products - the Maxelast D01-011A grade has been used in solar panel seal applications. Quantities are available in 55 lb. (25 kg) bags up to truckloads.

The D-Series of Maxelast TPEs are available in natural, black or transparent grades in hardness ranges from 30 to 60 Shore A. When extruded or co-extruded into profiles, the new Maxelast grade can also be miter-cut and heat welded for corner fastening products and applications.  Depending on the grade, these TPEs also can be foamed to achieve a smooth surface or skin.