|Antistatic, electrostatic dissipative (ESD) and conductive additives are in demand for plastics compounds used in several applications from packaging to automotive. Additive suppliers have introduced new migrating antistats, permanent antistats, and nanomaterials for this market.
Antistats are used widely in packaging such as film, thermoformed containers and PET bottles, in which they help surfaces separate during production and reduce dust attraction for short-term cosmetic improvement. Traditional migrating antistats include longchain alkyl phenols, ethoxylated amines, and glycerol esters like glycerol monostearate (GMS). Migrating antistats diffuse to the polymer surface over time, creating a thin layer that attracts water molecules that provide a conductive pathway that prevents build-up of static electricity. Antistatic additives reduce a polymer�s surface resistivity to the range of 1010 to 1012 ohms/ sq., providing a slow static decay rate that prevents charge accumulation. Migrating antistats are also being considered for static charge protection in plastic and wood-plastic composite decking, where thick sections can hold a large pool of antistat to provide longer-term protection. While migrating antistats offer cost-effective protection for short-term applications, other applications need longer-term protection or the lower resistivity required to prevent sparks and protect electronics from electrostatic dissipation. These applications can use permanent antistats or conductive additives such as carbon black, conductive fibres and nanomaterials.
Inherently dissipative polymers (IDPs) form a conductive polymer matrix or interpenetrating network within the base polymer, offering non-leaching, permanent static dissipation at a faster static decay rate than migrating antistats, typically 108 to 1012 ohms/sq. surface resistivity, depending on amount and dispersion of the additive in the polymer. Unlike migrating antistats, most IDPs operate nearly independent of relative humidity, although surface resistivity will be slightly higher (less conductive) at low moisture levels. IDPs are colourable and non-sloughing, giving them an advantage over carbon blacks. IDPs are taking some market share from migratory antistats, but that most growth applications are in different market segments requiring long-term, reliable ESD protection. For example, the growing use of electronics in many markets is driving increased demand for ESD protection during electronics production, packaging, shipment and use. Because of miniaturization, electronics are increasingly sensitive to particulate contamination and must be protected from lower levels of static charge. IDPs in trays, conveyor belts, and cases for electronic circuit production prevent static discharge that could destroy sensitive circuits. Even in packaging of electronics, more reliable ESD protection offered by permanent antistats is desired to protect the relatively expensive packaged product during shipping and handling, say suppliers. Other key applications include copiers and printers, where IDPs prevent charge build-up that might cause paper jams or mis-feeding. Industrial packaging is a new growth market for ESD additives in applications replacing metal and paper. ESD additives find application in flexible intermediate bulk containers (FIBC) that must be protected from static discharge, because a spark could lead to fire or dust explosion. Permanent anti stats are finding growing application in preventing charge build-up in artificial turf, particularly in Europe. Cost-performance of IDPs has improved over the last few years as global capacity expansions has brought down costs and product optimization has led to improved performance. As cost-performance of IDPs improves, they can find increasing application in aesthetic antistatic uses, eliminating dust attraction in cosmetic packaging, automotive interiors in new cars, appliance housings and window blinds.
Carbon blacks and conductive fibres, including graphite and metals, can be compounded into polymers to make them conductive, with resistivity ranging from 101 to 106 ohms/sq. Graphite particles are used mainly in applications that require both thermal conductivity and electrical conductivity. Products optimized to perform at lower fill levels are being developed, which should allow them to compete better with carbon black in electrically conductive applications.
Carbon nanotubes (CNTs) continue to grow in use as non-sloughing, conductive additives that also maintain or enhance physical properties. CNTs are used at very low loadings that reduce weight and do not interfere with polymer properties. They are getting more cost competitive as more players enter the market and as larger volume application demand comes in. CNTs are used in small volumes in space and sporting goods applications, but the largest volume use is automotive applications such as electrically conductive polyamide fuel lines. Emerging applications include under-the hood, electronics and electrostatically-painted body panels. CNTs are replacing carbon black or carbon fibre in electronics applications that have increasing requirements for minimal contamination and high, uniform ESD protection in complex moulded parts, particularly important in manufacture of hard disk drive and computer chip, where greater storage density and smaller feature diameter make devices smaller and more sensitive to ESD and contamination.
Multi-wall carbon nanotubes (MWCNTs) have been used commercially as conductive additives for plastics since the early 1990s. They are concentric graphitic rings about 10 nanometers in diameter. Poorly dispersed nanotube-based compounds perform no better than using carbon black or carbon fibre. Because CNTs are difficult to disperse, they are sold as a predispersed masterbatch to minimize variability and dispersion problems in the subsequent custom compounding step. Carbon nanofibres (CNF) have a larger diameter (10-100 nm) than MWCNTs. Fullerene nanotubes (or tubular fullerenes), including single wall carbon nanotubes (SWCNT), are still very new materials, available in significant commercial quantities for just 2 years. They have high growth potential in the transparent, conductive films market for electronics applications like touch panels and displays, as well as in high performance composites. Graphene sheets, which are essentially �unrolled� carbon nanotubes, are one of the most conductive materials � with a very high surface area (700 to 1000 m2/g). Graphene�s overlapping layers and high surface area allow high electron transfer at low loading levels. Because graphene has such a large surface in contact with the polymer, it improves mechanical properties even under extreme high or low temperatures. In under-the-hood (bonnet) parts, graphene offers high-temperature conductivity and inhibits solvent swelling.
(Extracted from Plastics Additives & Compounding article by Jennifer Markarian)