Sequential stretching involves two steps: the first uses a machine direction oriented (MDO ) to stretch the material in the machine direction over a series of rollers, effectively increasing the length and decreasing the thickness of the web. In the second step, a transverse direction oriented (TDO) stretches the film or sheet perpendicular to the MDO stretching in the transverse (cross) direction on a tenter, increasing the width of the web and further decreasing its thickness. These steps are usually undertaken in-line one after the other following extrusion and casting of the web.
Sequential stretching Advantage
Sequential stretching is most often used in the production of materials such as BOPA, BOPP, BOPET. The primary advantage of this method is that it provides a lot of flexibility in process conditions (e.g. MD and TD stretch ratios) and a high production rate. It is also relatively cost-effective.
First Step: MDO
Machine direction oriented
Second Step: TDO
Transverse direction oriented