PVC Insulation Material: Halogen-Containing Insulation Materials Part I

PVC insulation material is a mixture of PVC powder with specific additives such as plasticizers, stabilizers, flame retardants, lubricants, and other agents. After several decades of production and use, PVC manufacturing, formulation adjustments, and processing technology have become highly mature. Due to its excellent processability and low cost, PVC-insulated cables are widely used in various fields, including household appliances, machinery, network communication, and building wiring. They exhibit significant performance characteristics:

1. Mature manufacturing technology, easy to shape and process. Compared to other cable insulation materials, PVC offers effective control over surface color, gloss, printing, processing efficiency, flexibility, conductor adhesion, mechanical and electrical properties.

2. Excellent flame retardancy, making it easy for PVC-insulated wires to achieve various fire-resistant grades as per standard requirements.

3. Generally used for rated voltages of up to 1000V AC and below.

However, PVC also has some inherent limitations that restrict its use, primarily as follows:

1. PVC emits a large amount of dense smoke, causing reduced visibility and releasing carcinogenic substances and HCl gas when burned, posing serious harm to the environment. With the development of low-smoke, halogen-free insulation material manufacturing technology, the gradual replacement of traditional PVC insulation has become an inevitable trend in cable development.

2. Ordinary PVC insulation has poor resistance to acids, alkalis, heat oils, and organic solvents. Due to the principle of chemical compatibility, PVC wires are prone to damage and cracking in specific environments.

To address these issues, material formulations can be optimized and improved through irradiation cross-linking processing. This transforms ordinary thermoplastic PVC into insoluble thermosetting plastics, stabilizing the molecular structure, enhancing insulation mechanical strength, and increasing the short-circuit temperature to as high as 250°C.

During PVC irradiation processing, excessive irradiation doses can lead to decomposition. Irradiating pure PVC molecules results in dehydrochlorination, chain breaking reactions, and discoloration, making it difficult to obtain valuable materials. Sensitizers containing multifunctional unsaturated monomers can reduce chain breaking and discoloration in PVC molecules, contributing significantly to the formation of cross-linked networks.

PVC, in the presence of sensitizers like TMPTM and TMPTA, exhibits remarkable improvements in properties at doses below 10 kGy. It can be used as an insulation material and for various fittings (e.g., producing flame-retardant cables with a heat resistance of 105°C). When compared to systems without sensitizers, systems containing sensitizers have a 5% to 10% higher gel content at the same radiation dose. To achieve the same gel content, systems with sensitizers require a lower radiation dose, reducing radiation dose by over 50%. Lower radiation doses help prevent defects caused by excessive temperature rise during irradiation. Currently, the development direction of PVC insulation materials mainly includes flexible cross-linked PVC cable compounds, transparent cable compounds, and lead-free PVC cable compounds.