The shift towards domestic televisions with large, flat screens illuminated by plasma or liquid crystals (FTVs), together with the demands of a public sensitized to safety and environmental issues, are changing requirements for the types of thermoplastics required for housings.
For its latest wide-screen FTVs, Philips Electronics wanted a thermoplastic for the housing that incorporates a halogen-free flame retardant to meet consumer requirements that are strongest in Europe. The material also needed to meet legal requirements regarding fires that start inside the TV, while also not contributing to any fire started by an external source. (UL94 V-1 is the minimum requirement in the U.S. for flat TVs, slightly less strict than the V-0 for traditional TVs with cathode-ray tubes, which have higher voltages.)
Furthermore, Philips needed a material with a higher temperature resistance than the polystyrenes normally used for CRT TVs because of the higher temperatures generated by the electronics in FTVs. The housings of plasma screens in particular are subjected to very high temperatures during prolonged use.
Philips ultimately chose a new polycarbonate/ABS blend developed specifically for electrical enclosures by Bayer Polymers (Bayblend FR 2010) and Dow Plastics (Emerge 7560). Both of these grades are certified V-0 at 1.5 mm. Both also use additives free of antimony, as well as chlorine and bromium, thus meeting all the requirements for environment-friendly labels such as the German Blue Angel and the Swedish TCO 1999.
To determine a maximum permissible temperature for plastics in long-term service, the relative thermal index (RTI) has been defined to UL 746 B. The RTI value for Bayblend FR 2010 is 85C at 1.5 mm (mechanical loading with and without impact). At this long-term service temperature, good dimensional stability is ensured, even at the maximum operating temperatures of flat screen units, Bayer claims. Dow said in December it would have results back from its UL tests in January.
Bayer says the Bayblend grade''s good flow properties mean that there is a broad processing window for injection molding. "The plastic also has outstanding coatability and coating adhesion, making it possible to obtain an excellent surface finish," it reports, adding that there are numerous options for post-treating parts. Color fading is within limits set out in ASTM D 4459.
Dow for its part claims Emerge 7560 has flow properties better than any other PC/ABS blend currently available, "allowing it to easily fill large, thin-walled part molds while maintaining good practical toughness." And it notes the grade''s "excellent colorability and superior consistency" make it suitable for customized aesthetics and special effects when used with Dow''s Promatch self-coloring service.
At Philips Consumer Electronics'' high-end TV development center in Brugge, Belgium, Simon Van Hille says company strategy is to have at least two suppliers for each of its materials to ensure continuity of supply, and that Philips is looking for global availability. The company also wants processors to be able to reduce the diversity of materials they use so they can buy in bulk and reduce costs. Bayer Polymers, Leverkusen, Germany +49 214 30 25363; www.bayerpolymers.com. Dow Europe, Horgen, Switzerland +41 1 728 2108; www.dow.com
SBS for injection molding is tough and clear
BASF''s third-generation range of Styrolux styrene/butadiene/styrene (SBS) polymers, launched three years ago, has been extended with 3G 33, said to show three improvements over conventional SBS grades: highest transparency, even on thick-walled moldings; good impact strength and stiffness, thanks to a modified molecular morphology; and guaranteed good melt flow, enabling faster cycling times and greater output. It is aimed at medical applications, displays, and cosmetics packaging products, as well as toys and household articles. BASF AG, Ludwigshafen, Germany +49 621 60 43348; www.basf.com
PPE/PPS alloys take high temperatures
Xyron DG grades from Asahi Kasei have thermal stability, stiffness, flame retardance, and chemical resistance comparable to polyphenylene sulfide, while the polyphenylene ether component provides dimensional stability, reduces density, and tendency to flash. Already available in Japan, the grades are used for such applications as car radio components (replacing metal versions), gears for ink-jet printers, and parts in an LCD projector (replacing a more expensive liquid crystal plastic, LCP). Grades are highly filled, with 40% glass or combinations of glass and mineral filler (40% and 60%). Asahi Thermofil Europe SA, Brussels, Belgium +32 2 5260502; www.thermofil.fr
PS/PPE for freezer-to-microwave packs
Noryl PKN resin has high stiffness at higher temperatures, reducing the risk of hot food spills. It also reportedly has higher impact resistance at freezer temperatures than rival polypropylene-based materials.
Supplier GE Plastics says its good processability makes it a lower system-cost alternative to PP and crystalline PET. The PKN portfolio currently includes six commercial grades, transparent and opaque, covering a wide heat-resistance range. One grade, PKN4717, is specifically developed for foamed applications. GE Plastics BV, Bergen Op Zoom, the Netherlands +31 164 292911; www.geplastics.com
Wax offers right adhesion
Clariant''s Pigments and Additives division has come out with a polypropylene wax grafted with maleic anhydride, which is intended to aid processing of natural-fiber reinforced plastics. The reactive anhydride in Licomont AR504 forms stable bonds between the two materials and acts as both a coupling agent and compatibilizer. According to the producer, the wax''s low viscosity enables it to fully impregnate wood and other natural fibers. It can also have a positive effect on mechanical properties such as elasticity and toughness compared to additive-free formulations. Clariant GmbH, Sulzbach, Germany +49 6196 7578130; www.pa.clariant.com
Nanotechnology comes to rapid prototyping
NanoForm 15120 composite material is said to represent the first use of nanotechnology in rapid prototyping with stereolithography. DSM Somos introduced it in December at Euromold 2003, and is beginning beta testing. NanoForm is part of the company''s new ProtoComposites range.
The material, which contains ceramic nanofillers, is said to exhibit many properties similar to fused deposition and glass-filled nylon sintering materials, while providing the accuracy, precision, and surface finish inherent in stereolithography. Modulus is more than 5000 MPa, and deflection temperature under load is greater than 132C. DSM Somos says the composite technology of NanoForm also contributes to "exceptional dimensional stability, low shrink, and low coefficient of thermal linear expansion."
The company describes ProtoComposites as complex materials in which two or more distinct, complementary substances—especially metals, ceramics, glasses, or polymers—combine to produce functional properties not possible using individual components.
DSM Somos launched the ProtoComposites range last year with ProtoTool 20L (June 2003 MP/MPI). Both it and NanoForm 15120 contain a ceramic filler, but while the former requires modified processing equipment, Nanoform 15120 "can be used on any machine and by anyone," according to marketing and sales manager Ty Bacon.
"The Grail for stereolithography developers is materials that perform just like the engineering plastics they visually mimic," explains Bacon. "Current acrylate epoxies have reached their limits. We need a whole new technology."
He says researchers throughout DSM are working towards introduction of such a technology around the end of this year. DSM Somos, New Castle, DE, USA +1 302-326-8112; www.dsmsomos.com