Chapter 11 - Oriented film technology

Abstract

This chapter focuses on the oriented film technologies. The majority of oriented plastic films are biaxially oriented, the characteristics of which ideally meet the demands on modern flexible packaging. The biaxial orientation results in a significant increase in the mechanical properties such as Young's modulus and tensile strength, a considerable improvement in the optical properties such as haze and gloss, as well as the barrier properties. The overall improved barrier properties are attained due to the orientation of the molecule chains. Stretching in machine direction is normally done by means of a machine direction orienter (MDO) via rolls with increasing speed. For all transverse oriented films, the stretching process takes place by means of a transverse direction orienter (TDO), where the film is fixed on both ends and, upon passing through an oven at various temperatures, is stretched in a transverse direction. Biaxial orientation, in the machine and transverse direction, can be done either sequentially or simultaneously. In the sequential process, an MDO and a tenter frame are successively utilized. In sequential orientation, the stretching process occurs in two steps and a relatively small process window in terms of temperatures and stretching ratios is available. With a worldwide consumption of over 6 million tons, biaxially oriented polypropylene (BOPP) films constitute by far the largest share in biaxially oriented film. The applications are very diverse and can basically be split into packaging applications, not only in the food but also in the nonfood sector. Biaxially oriented polyester films (BOPET), with approximately 2 million tons per year, are the second most common oriented film following BOPP.