A mylar tape is originally known as BoPET tape which means Biaxially oriented polyethylene terephthalate. It is a polyester film made out of extended polyethylene terephthalate.
Its important properties are its high tensile strength, dimensional and chemical stability, reflectivity, transparency, gas and aroma barrier properties as well as electrical insulation properties. The molten polyethylene terephthalate is forced into a chill roll that transforms the fluid into an amorphous state. It is then drawn biaxially oriented where it is first drawn towards the machine direction with the help of heated rollers and later drawn in the slanting direction.
The film can also be drawn in both the directions at the same time using high-end machines. Next, the drawn film is subjected to heat in the oven to the temperature that is above 200 ˚C. This heating process prevents the film from getting back to its original shape and the molecular orientation in the film plane is arrested. This orientation of the polymer chains in the mylar tape is the reason for its high strength and firmness. The Young’s modulus, which is a measure of the stiffness of an isotropic elastic material, is about 4GPa.
Another important result of the molecular orientation found in mylar tape is that it stimulates the development of many crystal nuclei. The crystallites that develop in a high speed get to the boundary of adjacent crystallite and stay smaller than the wavelength of noticeable light. This results in high clarity of mylar tape regardless of its semi crystalline structure.
Generally the surface of the mylar type produced will be smooth and if it is not treated with any additives, the layers might stick to each other when the film is wound up. Hence, the tape is treated with microscopic inert inorganic particles to coarsen the surface of the tape. The tape is then given a metal finish through vapor deposition of a thin film evaporated metals like aluminum, gold or other suitable metals onto it. For applications related with food packaging the aluminized mylar tape can be laminated with a polyethylene film that offers good sealing as well as improves puncture withstanding. The surface of the polyethylene tape side looks dull while the PET side looks glossy.
Mylar tape is used in protecting food against oxidation and flavor loss and thus promotes extended shelf life. For example you can note the coffee powder packaging that involves foil tape packaging of pouches. The surface of the packages get the glossy or matte finish is obtained through BoPET or mylar tape. The white colored mylar tape is used in covering dairy products such as yoghurt. The clear mylar tape is used to cover fresh or frozen meals. It can resist high temperature and thus the foodstuffs ideal for reheating in the microwave oven with the seals.
The metal finish mylar tape is used for the book covers, T-shirts and other garments. It is also used as a protective cover over pins, buttons and badges and serves as a backing for sandpaper. It is also widely used to protect important documents like medical records.
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