Drawn polymer compensation film

Polymers with flexible chains are isotropic because of the random orientation of the chains. They become, however, anisotropic when they are drawn (stretched) because the chains tend to align parallel to the drawing [49]. Now we consider the orientational order and birefringence induced by drawing. 

In some liquid crystal displays, however, biaxial compensation films are needed. These can be made by drawing polymer films in the two directions in the film plane [50]. They can also be made by drawing uniaxial liquid crystal polymer films in the direction perpendicular to the uniaxial axis [52,53]. 

---

When a polymer film is drawn uniaxially, the induced birefringence is usually uniaxial. The produced compensation film is a positive a plate. The drawing can be carried out by the machine in a roll-to-roll process, as shown in Figure 15.18 [50]. The stretching rate can be adjusted by changing the relative speed between the feed rolls and the stretching rolls. 

---