Sumitomo Chemical Advanced Technologies developed and will commercialize new long-fiber thermoplastic (LFT) compounds with high-performance liquid crystal polymer (LCP) matrices reinforced with 13mm chopped carbon fiber or fiberglass. The materials are undergoing customer evaluations in several industries and developmental quantities of two grades, SUMIKASUPER SCG-379 with 30-50% fiber-weight fraction (FWF) E-glass and SUMIKASUPER SCG-420 with 30-40% FWF high-modulus carbon fiber are available to interested parties for testing. An LCP matrix and the option for carbon fiber reinforcement upgrade the thermal and mechanical performance available from LFT technology and the products are being targeted to replace alloys of aluminum and magnesium and steel.
The vast majority of all commercial LFT products feature fiberglass-reinforced polypropylene (PP), although higher temperature polyamide 6 and 6/6 (PA6, PA6/6) have been gaining market share in this segment. And commercial carbon fiber reinforced LFT grades are available in PP, PA, thermoplastic polyurethane (TPU), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), and polyethersulfone (PES).
LCPs are a family of polymers producing thermoplastic parts with unique processing characteristics and extremely high performance including the highest thermal stability of any thermoplastic which is why they are used to replace metals, ceramics, and polymer composites. Most commercial LCPs are aromatic polyesters characterized by high thermal and mechanical performance, excellent and inherent flame/smoke/toxicity (FST), good weatherability, excellent electrical insulation, high resistance to stress cracking, and chemical inertness. This makes them ideal for use in electrical and electronic components (including fiberoptic cables, printed circuit boards, chip carriers, connectors (conventional, radio-frequency (RF), and fiber-optic), and other surface-mount components), microelectromechanical systems (MEMS), pump components, coil forms, and sensors), plus components for chemical processing (including pumps, meters, and valves). Sumitomo Chemical introduced the industry’s first chemically soluble LCPs, specifically developed to produce films and coatings to protect flexible and rigid electronic components and speaker membranes.
Commonly processed by injection molding although the new LFT compounds also can be compression molded LCPs also can be melt-spun into fiber, extruded, or cast into thin sheets/films, and applied as coatings. Molded parts can be joined via thermoplastic welding techniques, especially ultrasonic and laser welding. Plating and adhesive bonding to LCPs are possible when a special additive package is used. Owing to the highly rigid structure of their molecular chains, the weak van der Waals forces between molecular chains, and their liquid crystalline nature which tend to be nearly linear and to occupy a stacked orientation maintaining order regardless of solid or liquid phase. LCP polymer chains align in the flow direction during molding and are highly anisotropic. This accounts for excellent flow-direction mechanical properties, resulting from the self-reinforcing orientation, but also for the high flow and molding productivity characterizing the materials, which cycle as fast as 5-10 seconds at low injection pressures.
Most thermoplastics and especially fiber-reinforced thermoplastics exhibit anisotropy after processing. Molded properties of LCPs can vary between flow and crossflow directions. Hence, care should be used when designing parts and molds for LCPs to take advantage of and avoid the challenges of this characteristic. High anisotropy means weld lines where flow fronts with different molecular orientations converge) are weaker and prone to warpage and thermal-expansion differentials. Hence, LCPs are typically reinforced with glass fiber and mineral fillers, not to increase stiffness and strength but to reduce anisotropy. Warpage also can be reduced with proper gate design in the mold. Because of their high performance, LCPs are priced accordingly as a premium product. However, given their high melt flow rates, fast setup times, and low thermal expansion in the direction of flow, LCPs can be formed into thin-wall parts with short molding cycles that deliver high performance at low mass and lower material usage — all of which help offset higher initial material costs. The thermal stability typical of LCPs enables processors to efficiently reuse regrind and recycle reject parts, which again reduces material losses and lowers effective part cost.