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WEATHERABLE RESIN FOR INJECTION MOULDING WITH OPAQUE, MOULDED-IN-COLOUR
GE Advanced Materials has expanded its Lexan SLX weatherable copolymer resin line with two new opaque grades specifically designed for injection moulding. The new materials – Lexan SLX EXRL0124 and Lexan SLX EXRL0125 resins – were developed to address environmental issues and costs associated with painting plastic parts in applications that require long-term retention of colour and gloss in demanding outdoor use. Polycarbonate (PC) provides outstanding impact strength, good stiffness at lightweight, the ability to maintain mechanicals over a broad temperature range, high gloss, excellent tintability and paintability, option for water-clear transparency, and excellent mouldability. In challenging outdoor applications, however, scientists have traditionally needed to use UV additives to help stabilize the polymer, and tints, pigments, or paint to mask colour shift. Hardcoat technology has been employed to improve scratch and chemical resistance, and alloying and blending has been used to expand the chemical resistance for uncoated PC components. Lexan SLX resin effectively improves the weatherability of polycarbonate. The new material is a copolymer technology that has been derived from polyester carbonates and resorcinol arylates. When exposed to UV light, the new copolymer undergoes a photo-fries rearrangement and produces a new structure that is inherently a UV screener, essentially making the resin self-protecting. The Lexan SLX resin technology was initially deployed by GE Advanced Materials in a high-gloss film for use with in-mould decorated parts for the automotive industry. Comprised of a clear cap layer over a coloured layer (flat or metallic), the film maintains dimensional stability over a broad temperature range and can be back-moulded onto a variety of substrates to create a Class A surface. This technology provides excellent weathering, outstanding chemical and scratch resistance, plus excellent gloss and depth of image (DOI), which are all necessary to meet the automotive industry’s demanding aesthetic requirements. Lexan SLX film is now available from GE Advanced Materials in multiple gauges. In June 2003, GE introduced the first, injection-moulding grades of this copolymer, which are transparent and, in laboratory testing, demonstrate excellent weathering (seven+ years), high light transmission (>83%), and low haze (<1%), with performance and processing much like standard polycarbonate materials. Depending on weathering conditions, the new materials offer five-to-10 times better gloss, colour, and light transmission retention than standard UV-stabilized polycarbonate. After a slight initial colour shift, the transparent grades of Lexan SLX resin offer a longer lifetime of UV stability and clarity vs.traditional UV-stabilised polycarbonate. This makes the transparent grades of Lexan SLX resin an ideal candidate for lighting applications, including covers, refractors, and lenses. Now, GE Advanced Materials has expanded the Lexan SLX resin technology still further with two new opaque grades that are high gloss and can be pre-coloured in a range of hues for paint-replacement in injection-moulded parts. Lexan resin grades offer higher chemical, thermal, scratch, and weathering resistance. Post-weathered ductility is high, while most other physical, mechanical, processing, and shrinkage properties are very similar to standard PC grades. The new Lexan SLX materials are being positioned for use in components for sporting goods, automobiles, recreational vehicles, agricultural equipment, and telecommunications enclosures. “When exposed to UV light over time, traditional weatherable polymers can lose gloss, where this exceptionally tough copolymer technology can withstand the rigors of long-term outdoor use virtually unscathed,” says Kurt Schuering, global Lexan product manager, GE Advanced Materials. Key to this is the product’s unique ability to actually become a UV absorber, potentially extending the service life of the part by protecting both surface appearance and physical properties. Due to their outstanding performance, gloss retention, and colour stability, these new grades potentially hold the answer to the many challenges that outdoor equipment manufacturers in several areas have had to deal with for a long time,” Schuering said. Some of the first commercial applications for the new opaque grades of Lexan SLX resin include industrial backhoe fenders and the housing for a wireless infrastructure product from NexGen City. In both cases, the material was selected after testing revealed it met customer requirements for chemical resistance, weatherability, thermal stability (-40 to 77C), impact resistance, processability, and knit-line/flow characteristics. In the case of the backhoe fenders, Lexan SLX resin offered better design flexibility, weatherability, and ductility than painted dicylopentadiene (DCPD). For the NexGen City communications housing, the material replaces painted steel at lower weight and better design flexibility. No other thermoplastic tested by the customer passed the long-term impact and gloss retention requirements. According to Dave Meitzen, NexGen City, chief operating engineer, “We're very pleased to be using GE’s Lexan SLX resin for NexGen City’s wireless infrastructure product, which we are currently deploying in a 60-square-mile area around Garland, Texas. Once complete, this system will serve as the wireless backbone for the city’s first-responder – fire, EMT, and police – emergency personnel. This is a proven, leading-edge technology and a huge homeland security application for us, and Lexan SLX resin helped play a major role in its development,” Meitzen said.
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