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Nylon Plays Wider Role in Auto, Electronics and Packaging Sectors (Apr 26, 2006) Gordon Graff Introduction Comparing properties Automotive applications Electronics Packaging Conclusion Introduction Automotive, electronics and packaging applications are some of the fastest growing markets for engineering plastics. This growth is opening up new outlets for nylon plastics because of their high strength, high-temperature resistance, chemical resistance, as well as stiffness and abrasion resistance. Moreover, these properties can be extended with appropriate fillers and additives. At the same time, nylons, which fall under the polyamide category, are often less expensive than competing engineering thermoplastics. The ability of nylons to stand up to extremes is encouraging adoption of these materials in several markets. In automobiles, for example, engines are running at hotter temperatures than ever, requiring plastics that are heat resistant, especially in the presence of harsh automotive fluids. In electronics, connectors have higher pin densities and thinner walls than ever before, which requires resins with good flow and dimensional stability, two of nylon's outstanding characteristics. Elsewhere in electronics, the increased use of lead-free soldering - and consequently higher soldering temperatures - demands resins with exceptional heat resistance. In packaging, there is increased emphasis on plastics that can prolong shelf life of foods, while providing attractive, eye-catching enclosures. Nylon, with its good gas barrier properties, mechanical strength and easy printability, is therefore becoming a frequent choice for food packaging. Comparing properties Nylon 6,6 (PA 6,6) is the most popular form of nylon, followed by nylon 6 (PA 6). Other commercial products include nylon 4,6; nylon 6,12; nylon 11; and nylon 12. Nylons can be reinforced with carbon fibers and glass to add strength. Carbon fillers also give nylon electrical conductive and static dissipative properties. Minerals and flame retardants are other common additives to nylon. Nylons have a tendency to absorb moisture, which can degrade the processed polymer properties unless the resins are dried before processing. However, some types of nylon are less moisture-absorbing than others. Properties E-modulus (MPa), cond. PA12 PA11 PA612 PA66 PA6 PA46 1100 1100 1800 1700 1100 1100 Notched Impact Strength at 23° C (Charpy, kJ/m 2), cond. 7 14 6 12 20 Notched Impact Strength at -30° C (Charpy, kJ/m2), cond. 6 11 6 4 3 12 Melting Point (DSC,° C) 178 189 218 260 222 295 Heat Distortion Temp. HDT-B (0.45 MPa, ° C) 115 145 180 225 170 280 Moisture Absorption (23° C/50% rel.h. , %) 0.7 0.8 1.3 2.5 3.0 3.7 Density (dry, gm/cm3 ) 1.01 1.03 1.06 1.14 1.14 1.18 Table 1: Different commercial nylons exhibit a wide variety of properties. (Source: EMS-Grivory) 45 Nylon 6,6 has a good balance of strength, stiffness, heat resistance, resistance to hydrocarbons, lubricity and wear resistance. Nylon 6 has a better creep resistance but lower modulus than nylon 6,6; it processes at some 27° C lower than nylon 6,6, and with less mold shrinkage. Nylon 6 gives a lustrous surface, which is useful where appearance is a concern. However, nylon 6 absorbs moisture more readily than nylon 6,6. Nylon 4,6 has among the highest impact strengths of commercial grades of nylon, but its modulus is less than that of nylon 6,6. Nylon 4,6 has excellent resistance to wear and friction, and has outstanding flow characteristics, which makes it easy to process. However, the 4,6 material has a relatively high moisture absorption. Compared to other nylons, nylon 12 has a relatively low concentration of amide groups in the polymer chain, which gives it the lowest water absorption of any commercial nylon. It also has good to excellent resistance to oils, fuels, hydraulic fluids, solvents and salt. The material also resists stress cracking and abrasion. Nylon 6,12 is also fairly low in moisture absorption and has many properties similar to nylon 12. However, compared to nylon 12, the 6,12 polymer has a higher heat deflection temperature, and greater tensile and flexural strength. Nylon 11 is also relatively low in moisture absorption. It features a high degree of chemical resistance and the ability to accept high loadings of fillers. However, relative to other types of nylon , nylon 11 is higher in cost and less heat resistant. Automotive applications Automobile air intake manifolds were once made of metal, but today are often fabricated from 30-35% glass-reinforced nylon 6. Nylon 6,6 and 4,6 are also used in manifolds. According to an estimate by DSM, substituting metal in the manifolds with nylon reduces production costs by up to 30%, reduces the weight of the part by up to 50%, cuts system costs through parts integration and contributes to higher fuel efficiency. (For the intake manifold sector DSM supplies nylon 6 and a high-flow grade of nylon 6 under its Akulon trade-name.). Figure 1: Air intake manifolds are increasingly being fabricated from nylon 6 and nylon 4,6 (Source: DSM.) Nylon 4,6 is occasionally used for air intake manifolds, especially where a manifold is exposed to temperatures that exceed the capabilities of nylon 6 and nylon 6,6. According to DSM, which offers nylon 4,6 under its Stanyl label for intake manifold applications, replacing metals in manifolds with nylon 4,6 can cut costs by 10%. Engine covers are another frequent nylon 6 application. Compared to other types of nylon, the high-flow grades of nylon 6 are useful because they allow thinner walled designs, a better surface appearance, and a wider processing window due to better flow and lower injection pressures. Figure 2: Engine covers benefit from high-flow grade of nylon 6 (Akulon Ultraflow), which permits thinner walls and lower weight than standard nylons (Source: DSM.) Rocker valve covers are another place where nylon 6 is increasingly found in autos. For this application, industry claims that nylon 6 maintains strength and stiffness better over the life of the vehicle than nylon 6,6. It is also said to mold more easily than nylon 6,6, and to provide the best toughness for manufacturing and end-use conditions. In airbag containers, nylon 6 offers parts integration and reduced weight compared to metal containers. Containers made of nylon 6 do not splinter at low temperatures, as do some other polymers. Nylon 6 also possesses sufficient stiffness and strength to cope with high temperatures without failure. Figure 3: Good low-temperature performance and reliability are claimed assets of airbag containers made of nylon 6 (Source: DSM.) For a car's powertrain, plastic chain tensioner guides made of nylon 4,6 are being promoted by manufacturers. One reason is that nylon 4,6 is said to offer better wear performance than high molecular weight nylon 6,6. Nylon 4,6 in this application also reportedly enhances safety and reduces noise generated by the chain. Figure 4: Chain tensioner guides made of nylon 4,6 (Stanyl) are designed to offer improved wear over nylon 6,6, plus less noise generation (Source: DSM) Nylon 6,6 has found its way into automotive cooling systems, where it allows consolidation of various components once made of aluminum and plastics. Figure 5: Nylon 6,6 cooling system for Renault Mascott light truck consolidates header tank, inlet/outlet pipes, and radiator support brackets once made of different materials (Source: BASF.) Nylon 6,6 is also used in headlamp Bezels. According to DuPont, which supplies a heatresistant grade of its Zytel nylon 6,6 for this application, bezels made of nylon remain dimensionally stable even when the headlamps reach their operating temperature of 150° C. Nylon 6 also is being deployed in exterior automotive parts. These include door and tailgate handles, exterior mirrors, front-end grilles, fuel caps and lids, and wheel covers and trim. Elsewhere in the automotive world, nylon 12 is used in fuel lines, while nylon 6,12 is found in hydraulic clutch lines. Electronics Nylon 6,6 has long been a material of choice in electronic connectors. But this material is giving way to nylon 4,6 in this application because connectors are increasingly exposed to high temperatures. This is especially the case as lead-free soldering continues to advance in the industry. These high temperature soldering operations require connector materials that are stable to at least 230° C. Today's connectors have higher pin counts than in the past, requiring improved weld-line strength and better flow. There is also a finer pitch between pins, which necessitates connector materials with high flow, high mechanical strength, and exceptional weld-line strength. In many cases, nylon 4,6 meets all these requirements. Figure 6: Molding connectors with nylon 4,6 (Stanyl) led to less flash and less reworking than molding them with LCP, according to the manufacturer (Source: DSM.) Nylon filled with electrically conductive materials can provide antistatic, electrostatic discharge (ESD) and EMI/RFI shielding for electronic equipment, as well as for trays and conveyer systems used in the manufacture of semiconductor chips. Common fillers in this application include carbon fiber, carbon powder, nickel-coated carbon fiber, and stainless steel fiber. Just about any variety of nylon can be used in ESD and EMI/RFI protection. PolyOne, for instance, offers electrically conductive grades of nylon 6; 6,6; 12; and 6,12 under its Stat-Tech line of conductive polymers. Packaging In food packaging, nylon 6 films provide excellent barrier properties that keep oxygen out and seal aroma in. The films can be made by cast, blown or biaxially oriented polyamide (BOPA) processes. Foods commonly packaged with nylon 6 resins include meats, cheeses, dried foods, and chilled fruit juices. Oxygen permeability of the nylon films increases with temperature and humidity. Consumer packaging made of nylon 6 provides a good combination of strength, tear and puncture resistance. An example of this packaging is air cellular cushioning, which protects products from damage during shipment. In the medical field, nylon 6 is fabricated into tough, puncture-resistant packages for medical blister packs. Figure 7: Nylon 6 barrier properties make it useful for food packaging (left). It also finds uses as protective packaging for goods in transit (right). (Source: Honeywell.) Nanocomposites based on nylon 6 are also being developed for packaging applications. In these cases, the polymer is loaded with 2-8% of an organically treated mica-like clay mineral that is dispersed throughout the polymer in micron-size particles. According to RTP Co., which supplies nanocomposite compounds, films or sheets made of the nylon nanocomposites display a fourfold improvement in oxygen barrier properties over unfilled nylon 6 films. Compared to the unfilled nylon, the nylon nanocomposite also exhibit a 35° C improvement in heat deflection temperature, more than a third greater tensile strength, and a 50% improvement in flexural modulus. Recommended packaging applications of the nanocomposites include foods, cosmetics, medical products and electronic equipment Conclusion The unique properties of nylon resins, such as high strength, resistance to heat and chemicals, and dimensional stability, are giving these materials an advantage over other more costly engineering thermoplastics in three fast-growing end use markets: automotive, electronics and packaging. There are a broad range of polyamides included in the nylon class, each with their own property profiles. Additives and fillers are vital elements in extending the properties of nylon into new regimes, thereby opening up new markets to these materials. References: Website: Albis Plastics, Arkema, Asahi Thermofil, BASF, Degussa, Dow, DSM, DuPont, EMS-Grivory, Honeywell Plastics, PolyOne Corp., Rhodia, RTP Co., Solvay. Publication: Robert D. Leaversuch, "Strength and Beauty: New Nylons Bring Both to Under-Hood Parts," Plastics Technology, Jan., 2003. "Six Always Wins in Nylons Game," Modern Plastics, July, 2004. Joseph A. Grande, "New High-Performance Nylons for Automotive, Electronics, Packaging," Plastics Technology, May, 2005.