Electrically conductive plastics continue to provide reliable EMI shielding in a wide variety of applications. Specifically, thermoplastics can overtake bulky metal enclosures due to their superior weight, EMI shielding capabilities, and simpler manufacturing process. However, before purchasing any thermoplastic, it is important to consider performance capabilities.
Single pellet vs multi-pellet dry blend
Electrically conductive thermoplastics are typically sold as a pellet blend of two or more components, made up from a variety of base polymers and stainless steel pellets. In small applications and sizes, these blends can generally be effective but are always bound to have consistency issues. In transportation and handling the stainless-steel pellets will settle to the bottom, resulting in an inconsistently shielded final product. This problem becomes more evident when molders run large quantities of parts and when they store the mix in large containers.
Selecting a one pellet plastic material, like Parker Chomerics PREMIER PBT 250-FR, eliminates this problem, since there is no mixing of pellets. Instead of having stainless steel pellets as a separate component, stainless steel fibers are pultruded into the plastic pellets to provide shielding. Single pellet thermoplastics can be sold in large quantities, unlike pellet mixes.
Different types of flame retardant ratings
Understanding the plastic’s UL 94 rating will help determine how it will perform under fire hazard conditions. In order to receive the UL 94 5VA certification, the plastic must stop burning after 60 seconds on a vertical plaque, with no drips or holes, according to the UL website. This rating, is the highest level of flammability resistance for any thermoplastic. The next rating down, UL 94 V-0, means the plastic can stop burning within 10 seconds on a vertical specimen and the drips are non-flammable. Most thermal plastics that are electrically conductive fall under the UL 94 V-0 rating and require an extra coating to be EMI shielded. But Parker Chomerics PREMIER PBT 250-FR earns a 5VA rating at 2.5 mm thickness without the need of a coating to achieve electrical conductivity.
Compared to metal enclosures
In addition, plastics can also be more cost effective than metal enclosures. Although metals are typically more cost effective initially, the secondary machining requirements of
many metal components can add significant cost and lead time. For example, many die cast parts require machining operations to drill and tap threads while most thermoplastics can be molded with pre-formed holes and use thread forming screws. Also, plastics are significantly lighter than metal enclosures, helping to better achieve light-weighting goals.
Parker Chomerics PREMIER PBT 250-FR, a single pellet UL 94 5VA electrically conductive thermoplastic, is known for its excellent performance where petrochemical exposure is common. Typical applications include retail fuel dispenser pumps, housings, dispensers and face plates, electronic payment terminal housings, security access points, and more.
This blog contributed by Page Ludl, marketing co-op, Chomerics Division.