In consumer goods markets, there are countless applications for clear plastics such as copolyesters, acrylic, SAN, amorphous nylon and polycarbonate. However, as new applications call for materials that can deliver durability, design flexibility and easy processing, existing plastics can fall short. Eastman Tritan copolyester is a new amorphous thermoplastic aimed at filling this gap. Uptil now, copolyesters have often been limited by their low heat resistance. The new material overcomes this hurdle with significantly increased heat resistance and toughness, offering exceptional clarity, low haze, high gloss and consistent color, as well as the potential for faster molding with lower levels of residual stress. This unique balance of performance and processability is well suited to bridge the gap between previous copolyester families and other clear plastics such as polycarbonate. Designed with a higher glass-transition temperature (Tg) than traditional copolyesters, the material delivers greater heat resistance without sacrificing the chemical resistance and low internal stress found in copolyesters.
Products molded have less residual stress than ones molded in other types of thermoplastics, such as polycarbonate. Combined with its superior chemical resistance, this lower residual stress level can significantly reduce the risk of product failure from environmental stress cracking (ESC). In molded polycarbonate products, ESC is often controlled through an annealing process or significant design modifications�compromises that can be largely eliminated through its use. Produced from a new, patented monomer, it is the first of a new family of materials. Thus far, it has been shown to be suitable for injection molding, injection-blow and stretch-blow molding, sheet and flat film extrusion, and thermoforming. It is available in commercial quantities and in several grades designed for different markets. The grades differ in Tg, melt flow rate, and incorporation of mold release.
The material offers many benefits for commercial and residential kitchenware and small kitchen appliances, including reusable food containers, sports bottles, mugs, pitchers, and containers for food processors and blenders. These products often require extremely versatile designs and shapes, exceptional clarity for vivid aesthetics and dishwasher durability�one of the biggest challenges to kitchenware design. Dishwashers in homes and professional kitchens expose kitchenware to a harsh combination of heat, hydrolytic and chemical attack, and applied stress. In some cases, kitchenware is exposed to the dishwasher dozens of times per week. Withstanding these environmental conditions was a major design goal in the development of the new copolyester. Products exposed to dishwashers must withstand heat, humidity, detergent chemicals, food, in-mold stress and abrasion from overpacking, along with hydrolytic attack. Commercial dishwashers reach peak temperatures of about 85 degree C and cycle for 1 to 2 minutes. Residential units reach peak temperatures around 70 degree C and have cycles of up to 2 hours. Also, kitchenware used in restaurants and commercial kitchens can be washed several times a day.
Although Tritan is a copolyester, it is similar to polycarbonate in many important respects. For example, polycarbonate has a reputation for high heat resistance and toughness. In notched Izod testing with 1/8-in. bars, polycarbonate can withstand impact of 14 ft-lb/in. with a partial break, as opposed to less than 5 ft-lb/in. for traditional copolyesters. In the same test, Tritan can resist an impact of 15.9 ft-lb/in. without breakage. Products molded in polycarbonate are at greater risk of ESC, particularly in more intricate shapes. This is because polycarbonate parts may experience significantly higher levels of residual stress than parts molded of Tritan.
The new copolyester is good news for OEMs, designers, and consumers, and also provides substantial benefits to molders. It can reduce costs by eliminating production steps and lowering material use, shipping weights, and inventory volumes. It can also deliver faster molding cycles than many other transparent plastics. Its melt flow is generally similar to that of polycarbonate, and its similar shrinkage allows it to be used in the same molds. It molds well with hot runners and small gates. It also thermoforms well with deep draws. Tritan can be injection molded faster than polycarbonate in thick sections without concern for residual stresses. The lower stress levels eliminate the need for an additional annealing step after molding (requiring expensive annealing ovens), thereby reducing energy use and overall processing time, lowering costs, and increasing production rates. And with a 2% lower density than polycarbonate, Tritan also yields more parts per pound of resin, which can contribute to material savings. For both extruded sheet applications and molded products, Tritan does not require predrying before thermoforming. Products can be thermoformed faster and at lower temperatures than polycarbonate sheet. The result is superior material distribution and increased design flexibility when using decorative paints and inks.