Irradiation crosslinking is an important link in the production of heat shrinkable tubes. The purpose of irradiation is to make the semi-finished products form a cross-linking network under the radiation of 60CoY ray or high energy electron beam of electric accelerator. That is to say, the material can obtain "shape memory effect" by irradiation processing.
Y radiation and beam radiation processing
Y-ray is a high-energy photon with strong penetration. It is often used for radiation processing of large-scale products and special-shaped parts. It is conveyed by stacking or hanging basket. However, the dose rate of Y source is low, the irradiation period is long, and the radiation oxidation is serious. Electron beam is a high-energy charged particle with limited penetration ability in the material. It is more suitable for the irradiation processing of thin tubes, sheets, membranes and other products. The dose rate of electron beam is high, the radiation is completed instantaneously, and the radiation oxidation is less. At present, with the continuous improvement of power, especially energy of industrial accelerators, electron beam radiation processing has been more and more widely used in the radiation production of heat-shrinkable products.
Crosslinking Degree and Performance
The degree of crosslinking determines the expansion process and shrinkage performance of heat shrinkable tubes. The crosslinking degree is too low to meet the requirement of improving material properties. It is difficult to ensure the uniformity of product size when stretching, and it can not completely restore the shape size before stretching when shrinking. Excessive crosslinking degree will make the product hard and brittle, and even crack in the process of expansion and tension. The optimal irradiation crosslinking degree of different materials can be determined only by dilatation and thermal shrinkage experiments.
The effect of high uniformity of crosslinking degree on the properties of products can not be neglected. Because of the low degree of crosslinking, low strength and poor temperature resistance, these areas are first stretched during expansion, which results in uneven or cracking of expansion, especially in large multiple expansion.
In order to ensure the quality of irradiation, in addition to the performance indicators of accelerator such as energy non-uniformity and scanning non-uniformity, it is necessary to study the technology and device under the accelerator beam. Accelerator pre-beam irradiation can take the following measures or processes for quality control: monitoring absorbed dose during irradiation; using "8" type irradiation for continuous irradiation of heat shrinkage tube; and rotating irradiation for intermittent heat shrinkage tube.