Mylar Film- Biaxially Oriented Polyester Films.
Mylar films are thin plastic films. They are PET (polyethylene terephthalate) films that are used in various applications like making cages of insect, food packaging etc. They are actually Biaxially Oriented polyester films, Mylar is their trade name.Mylar films are thin plastic films. They are PET (polyethylene terephthalate) films that are used in various applications like making cages of insect, food packaging etc. They are actually Biaxially Oriented polyester films, Mylar is their trade name. Mylar film has great tensile strength which is an intensive property of any material and is the measure of the total pull required to tear that material apart. They are chemically and dimensionally stable and transparent plastic like films. The PET films came into market in mid 50''s. The major industries responsible for their launch were DuPont and Imperial Chemical industries. NASA was the first organization to use Mylar films in the design of their Echo satellites.
The Manufacturing Process
A film of polyethylene terephthalate is taken and extrusion is applied to it. The process of extrusion is done on a chilled role. The function of chilled role is to quench the film and bring it to an amorphous state. Drawing is applied to orient it biaxially. The whole process is done in a sequential way. After the completion of Drawing crystallization under tension is applied within the oven. The operating temperatures are above 200 °C. The importance of this step is that it helps in preventing the shrinking back of the film to its original shape by locking the molecular orientation of the film. It is this orientation of the molecules only that provides stiffness and high tensile strength to the film. Another significant effect of this orientation is that it is responsible for forming of various crystal nuclei. These crystal nuclei migrate to the boundary and combine with the neighboring crystal nuclei which give transparency and clarity to the film as a property.
The film is usually manufactured with certain additives like inert inorganic particles that give roughness effect to the film. If no additives are added to the film at the time of manufacture then the original film would have such smoothness that the layers would stick to one another at the time of piling or winding together.
Film can also be aluminized by subjecting it to a vapor of thin aluminum metal. Such films find great use in food packaging. This process decreases the permeability of the film to various gases making it reflect almost up to 90% of light falling on it. The sealability feature that is required in films used in packaging is provided by laminating the film by a layer of polyethylene.