Page 252 - Engineering Plastics Handbook

214 Engineering Plastics

commercialized [29]. GETEK laminates offer superior thermal and elec-
trical performance. In 2003, the Polyclad Laminates division of Cookson
Electronics acquired the rights to GETEK copper-clad laminates.
In thermosets prepared via free-radical polymerization, the terminal
OH end group of PPE needs to be capped because the aromatic hydroxyl
will act to quench free radicals and inhibit the polymerization [30, 31].
Capping the OH with a reactive group facilitates incorporating the PPE
into the thermoset matrix [32].
In 2003, GE Advanced Materials introduced Noryl ETX resins, which
are designed to enhance the performance of thermoset resins.

Design

The successful use of engineering thermoplastics for end-use applica-
tions is dependent on important criteria such as

1. Selection of the proper resin grade that will give the desired per-
formance
2. Proper design of the part and associated tooling
3. Use of the correct molding parameters

Selection of an appropriate resin is aided by property data. Depending
on the application the data can be at ambient, low, and elevated tem-
peratures.
Designing plastic parts involves very specific expertise. There are basic
principles the designer follows for the best performance, e.g., minimum
stress in the part (where the stress load is as low as possible) and uniform
stress in the part (where the stress should be distributed uniformly).
Consistent wall thicknesses facilitate achieving low and uniform stress.
However, when the design requires varying thicknesses, then gradual
transitions are essential.
Designs can get complicated with multicavity tools or multiple gates
and hence weld lines or knit lines. Someone with plastic design experi-
ence is generally necessary for the correct design of plastic parts.
Proper molding conditions are another element for optimizing the
performance of plastic parts. Improper molding can result in high
molded-in stress and hence poor part performance.

Processing Modified PPE
Modified PPE grades cover a wide range of compositions. General guide-
lines on processing appear below. However, optimization of processing
parameters is dependent on many things, such as the resin, tool design,
and molding machine. The recommendations of the manufacturer for