How to prevent the aging of PVC heat shrinkable film?

In the process of processing, storage and use of PVC heat shrinkable film, under the action of light, heat and oxygen, aging phenomena such as fading, embrittlement and cracking will occur. In order to prevent the aging phenomenon of PVC heat shrinkable film, it is necessary to add stabilizers. Heat stabilizers are mainly used to prevent heat aging, antioxidants are mainly used to prevent oxidative aging, and light stabilizers are mainly used to prevent light aging, collectively referred to as stabilizers. At present, the most effective stabilizer for PVC heat shrinkable film is methyl tin heat stabilizer (181 for short), which has a good effect on the calendering, extrusion, injection molding and blow molding of rigid polyethylene (PVC). . Due to its high safety, it is also suitable for food packaging and high-definition rigid polyethylene products. At the same time, it is also widely used in plastic doors and windows, water supply pipes, decorative materials, etc., and can also replace other plastic heat stabilizers.

PVC heat shrinkable film is a white powder with an amorphous structure, with a small degree of branching, a relative density of about 1.4, a glass transition temperature of 77-90°C, and an initial decomposition temperature of about 170°C. It has poor light and thermal stability. When the temperature is higher than 100°C or exposed to sunlight for a long time, it will decompose to produce hydrogen chloride. Further active catalytic decomposition will cause discoloration, and the physical and mechanical properties will be sensitively decreased. In practice, in order to improve thermal stability and light stability, it is necessary to add stabilizers.

The molecular weight of industrially produced PVC is generally between 50,000 and 110,000, which has great polydispersity. The molecular weight increases as the polymerization temperature decreases. Without a fixed melting point, it starts to soften at 80-85°C, transforms into a viscoelastic state at 130°C, and transforms into a viscous flow state at 160-180°C. It has good mechanical properties, tensile strength is about 60MPa, impact strength is 5-10kj/m2, and excellent dielectric properties.