Irradiation cross-linking is an important link in the production process of heat shrinkable tubing. The purpose of irradiation is to make the semi-finished product form a high-resolution cross-linked network under the irradiation of 60CoY rays or high-energy electron beams from an electric accelerator, that is, to obtain the "shape memory effect" of the material through irradiation processing. The following is the editor's summary of the radiation process of heat shrinkable tubes.
Y radiation and electron beam radiation processing
Y-rays are high-energy photons with powerful penetrating capabilities. They are usually used for radiation processing of large products and special-shaped parts, using stacking or hanging baskets to transport the radiation. However, the dose rate of the Y source is low, the irradiation time is long, and the accompanying radiation oxidation is serious. Electron beam is a kind of high-energy charged particles, and its penetration ability in matter is limited. It is more suitable for irradiation processing of thin tubes, thin plates, films and other products. The electron beam dose rate is high, the irradiation is completed instantly, and the accompanying radiation is less oxidized. At present, with the continuous improvement of the power, especially energy, of industrial accelerators, electron beam radiation treatment is more and more widely used in the radiation production of heat shrinkable products.
Cross linking degree and performance
The degree of cross linking determines the expansion processing performance of the heat shrinkable tube and the shrinkage performance of the product. If the degree of cross linking is too low, the requirements for improving material properties cannot be met. It is difficult to ensure the uniformity of the product size during expansion and stretching, and it cannot be completely restored to the outer size before expansion and stretching during contraction. Too high a degree of cross-linking will make the product hard, brittle or even cracked during expansion and stretching. For different materials, the best radiation cross linking degree must be determined through expansion, stretching and heat shrinkage experiments.
The influence of the uniformity of the high degree of cross linking on the product performance cannot be ignored. Since the parts with a low degree of cross linking have low strength and poor temperature resistance, these parts will expand and contract first during expansion and contraction, resulting in uneven expansion and contraction, especially cracks in large multiple expansion and contraction.
In order to ensure the radiation quality, in addition to the performance index requirements such as uneven accelerator energy and uneven scanning, it is also necessary to study the technology and equipment of the accelerator beam. Accelerator electron beam irradiation can take the following measures or processes for quality control: the absorbed dose should be monitored during the irradiation process; for continuous irradiation of heat shrinkable tubes, "8" type irradiation can be used, for intermittent heat shrinkable tubes , You can use rotating irradiation.