Page 25 - Plastics News March 2019

FEATURES

Thermosets plastics have gained in popularity among Tablecredit: https://www.modorplastics.com/plastics-
manufacturers, who have switched to their use as a lower learning-center/thermoset-vs-thermoplastics/
cost replacement for metal components.
Type of Thermoset Materials
The benefits that thermoset plastics can offer over their
metal counterparts include: Thermosetting polymers are built from various types
of material that serve key roles and applications in the
• Available molded-in tolerances plastics fabrication industry. The two thermoset molding
• Choice of color and surface finishes compound processes are Reaction Injection Molding (RIM)
• High strength-to-weight ratio and performance and Resin Transfer Molding (RTM).
• Outstanding dielectric strength Composite thermoset materials consist of a matrix and a
• Low thermal conductivity and microwave transparency dispersed, fibrous, or continuous second phase. Casting
• Resistance to corrosion effects and water resins include a catalyst or hardener. Thermoset electrical
• Lower tooling/set-up costs resins and electronic-grade products are used in potting
• Reduced production costs over fabrication using or encapsulating compounds, conductive adhesives, and
metals dielectric sealants. 1
Disadvantages of Thermosets Thermal compounds are designed to form a thermally
conductive layer on a substrate, either between
There are certain disadvantages to the use of thermosets
whereas the material properties are not as developed as components or within a finished electronic product.
those of thermoplastics. Thermoset purging compounds are used to clean molding
machines between runs of different colors or compositions.
The low initial viscosity of materials results in flash and the Gap filling products are used to fill in gaps or spaces
need for secondary operations. Also, low tensile strength between two surfaces to be bonded or sealed. 1
and ductility tend to result in parts that require designs
with thick walls. The compounds used in thermosets Specific types of thermoset materials that are in use within
are reactive systems, which can impact the useful shelf the plastics fabrication industry include the following:
life. Batch processes may exhibit greater variation and RIM Thermosetting Plastics:
less consistency from lot-to-lot. High levels of some
filler in the materials may result in excessive tool wear. • pDCPD (polydicyclopentadiene)
The product quality is dependent upon the degree of • Polyurethanes
crosslinking established during the molding cycle. 2 • Polyureas
• Structural Foams
Table 1: Pros and Cons of Thermoset Materials RTM Thermosetting Plastics (Fiberglass-rein-
forced):
Thermoset Pros2 Thermoset Cons2
• Polyester
More Resistant against high Cannot be recycled.
temperature • Vinyl Ester
• Polyimides
Hard and rigid Much more difficult to surface Other Types of Thermosets and Thermoset
finish. Resins:
Excellent aesthetics finishes Cannot be remolded or • Epoxy
reshaped.
• Phenolics
High mechanical property Poor thermal conductivity for • Bismaleimide (BMI)
housing replacements. • Fluoropolymers

Cost-effective The rigidity of the material • Polytetrafluoroethylene (PTFE)
can result in product failure • Polyvinylidene fluoride (PVDF)
when used in high in vibration • Melamine
applications.
• Silicone
Excellent dimensional stability • Urea Formaldehyde

25 March 2019 Plastics News