Environmental-friendly soft polyvinyl chloride cable formulation design points

Selection of Resins The first issue in the formulation of cable materials with good processability and physical and mechanical properties is the selection of suitable PVC resins. The higher the degree of polymerization (molecular weight) of PVC, the higher the tensile strength, impact strength, and elastic modulus of the product, and the better the resistance to heat and cold, but the melt flowability and plasticity of the product decrease, and the processing temperature increases. Research and trials have shown that PVC resins with a degree of polymerization of about 1000 to 1300 (loose, K values ​​of 60 to 75) are more suitable for the preparation of cable materials.

Selection of Environment-Friendly Stabilizer PVC resin is extremely unstable to heat, and when it is heated, its temperature exceeds 90°C. It begins to decompose. When the temperature is higher than 120°C, it decomposes obviously, releasing a large amount of hydrogen chloride (HCl) gas, with the increase in the amount of escaped HCl. The color gradually darkens. Therefore, pure PVC resin without stabilizers cannot be processed and applied.

The stabilizers commonly used in PVC processing include lead salts and chromium salts, but stabilizers containing heavy metals such as lead salts and chromium salts cause serious heavy metal pollution to the environment. For this reason, the current use of stabilizers tends to be environmentally friendly. The first is the use of organotin stabilizers, which have the advantages of good stability and low dosage. They are mainly used in highly transparent hard and soft products, but organotins are mostly toxic, and most of them have special odors. The hue at the beginning of processing is good, but it will be discolored and appear dark spots later; the second is to use calcium stearate and zinc stearate together with chelating agent. However, domestic ordinary calcium/zinc stabilizers have too short thermal stabilization time and thermal stability cannot meet the requirements of the wire and cable industry. Selection of internationally renowned imported calcium/zinc stabilizer brands A, B, C, D, E, F, G, H, I, J, and thermal stability of cable materials produced using these stabilizers in accordance with GB8815-2002 The test results are shown in Table 1 (the amount of the other main raw materials is PVC: 100 phr, dioctyl phthalate: 50 phr, and calcium carbonate: 30 phr).

As can be seen from the data in Table 1, the thermal stability of stabilizers A, B, C, E, G, and I is better, while J, D, and H are a little worse. According to different product varieties GB8815-2002 standard soft PVC plastic heat stability time requirements between 50 ~ 180min. From the test data in Table 1, we can see that for the stabilization effect, the cable material series products using this stabilization system meet the requirements of soft PVC plastics for wire and cable, and the determination of specific stabilizer species can be determined according to the type of cable material produced.

Selection of plasticizers Soft PVC plastic compounds, the main plasticizer in the formula can be based on different temperature levels and use of phthalates, such as dioctyl phthalate, diheptyl phthalate, o-benzene Diisodecyl dicarboxylate; terephthalic acid, such as dioctyl terephthalate; trimellitic acid, such as trioctyl trimellitate. These main plasticizers for PVC plastics for wire and cable can be used alone or in combination with one another. In order to improve certain properties (such as anti-aging properties) of soft PVC cable, auxiliary plasticizers such as epoxidized soybean oil and epoxidized butyl oleate are also added.

Selection of fillers and other processing aids The fillers in soft PVC cable materials are mainly calcium carbonate and calcined clay. Calcium carbonate has little effect on the insulation properties of cable materials. It mainly plays a role in reducing the cost in the formulation of cable materials; calcined clay is the main additive for improving the insulation properties of cable materials, and the amount is generally 5 to 15 phr. The lubricant used is a lubricant commonly used in cable materials, such as polyethylene wax, and the amount thereof is generally 0-2.5 phr.