Go with the Flow 20105

June 27, 2005

3 Min Read
Go with the Flow

When it comes to injection molding resins, flow is good. New high-flow plastics can fill more intricate features and thinner wall sections than possible with more viscous grades of the same plastics, opening up new design possibilities. And improving flow can improve the economics of injection molding—by reducing cycle times, allowing for smaller molding equipment, and eliminating filling-related defects such as short shots. For these reasons, plastics suppliers often try to tweak their proven materials to bump up the flow lengths. Here's a look at a trio of plastics that have recently received a flow upgrade:

High-Flow PEEK

Victrex has introduced a new family of polyaryletherketone (PEEK) compounds that more than doubles the flow length of the company's standard products. The flow improvement allows the material to work in molding sections as thin as 0.2 mm, which may allow it to compete with low-viscosity polymers such as LCP, PPS, and thermoset epoxy. By enabling better fiber wet-out, the viscosity improvement also allows fiber loadings up to 60 wt%, double what would be practical with standard grades. Applications for the new material, which has a HDT of 599F, include micro-fluid handling components and a variety of electrical connectors—particularly those made from plastics that have trouble with the high temperatures of lead-free soldering processes. For more information, visit http://rbi.ims.ca/4393-537.

HPX Series Polycarbonate

Intended for medical applications, these new polycarbonate-based copolymers from GE Advanced Materials offer a 15 to 25 percent increase in spiral flow lengths. That attribute alone comes in handy when making medical parts, which often require thin wall sections or small features. But this material does a lot more than flow well. According to Katherine Glasgow, who develops Lexan polycarbonate for GE, the material exhibits improved mold release characteristics, which allows engineers to put less draft on parts. For example, she has seen standard polycarbonate parts that have trouble releasing with 1.5 degrees of draft release easily with just a half degree of draft when molded in the new copolymer. Even more important, the new material significantly extends the number of autoclave cycles that a polycarbonate can withstand without sacrificing impact performance. GE notched izod tests show a tenfold improvement in the number of autoclave cycles when measuring impact with notched izod methods. The same material offers a fifty-fold improvement in Dynatup impact tests. The only property trade-off with HPX involves a slight increase in haze—but only less than 2 percent at thickness of 0.125 inches. For more information, visit http://rbi.ims.ca/4393-535.

Ultradur High-Speed PBT

This high-speed version of polybutylene terephthalate from BASF offers twice the flow length of standard PBT grades. To get such a dramatic improvement, BASF scientists employed a nanoscale additive whose tiny—50 to 300 nm—particles reduce the material's viscosity by about 50 percent without changing other physical or mechanical properties. Now in trials in Europe, the material has shown a significant impact on cycle times. In one application—a 1.5 gm plug-in connector for laptop computers—the material cut cycle times by more than 20 percent. It also slashed reject rates because difficulties filling the connector's thin ribs with conventional PBT had driven up scrap rates. The new material, which targets electrical and automotive applications, currently comes in two versions: Ultradur B4300 G4 with a 20 percent glass filling and B4300 G6 with 30 percent glass. For more information, visit http://rbi.ims.ca/4393-536.

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