How to control the softness and hardness of PVC material? Why can't the engineering department make arbitrary changes once confirmed? The softness and hardness of PVC wire insulation material: plasticizers are the primary determining factor, while the rest are secondary factors
Phr: The number of parts added for every 100 parts of PVC resin
1 Plasticizer (core)
Principle: Inserting between PVC molecular chains weakens the strong polar forces between PVC molecules, lowers the glass transition temperature Tg, and turns hard PVC into flexible insulation material
Dosage: The higher the pH of the plasticizer, the softer the material and the lower the Shore A hardness; The conventional insulation of wires is 40-50 phr; The sheath is generally higher (50-60phr)
Type (difference in plasticizing efficiency)
DOP and DBP: high plasticizing efficiency, with less addition at the same hardness
DOTP, DINP, TOTM: slightly lower efficiency, better heat resistance, currently no ortho benzene wire material mainstream
DOA/DOS: Low temperature plasticization, suitable for cold resistant cables
Epoxy soybean oil ESO: auxiliary plasticizer+stabilizer, with a small amount of main plasticizer, slightly improves softness
Attention: The migration and volatilization of plasticizers in the later stage can cause the finished wire to harden after long-term use.
2 PVC resin powder (matrix)
Represented by K value/degree of polymerization:
The higher the K value (the higher the degree of polymerization): the longer the molecular chain, the stronger the intermolecular forces, and under the same plasticizer conditions, the material tends to be harder; Strong oil absorption (absorption of plasticizers) ability, commonly used for making high flexibility materials with high polymerization degree resins
The commonly used K value for wire insulation materials is 65-70 (with a polymerization degree of about 1000)
3 Inorganic fillers (calcium carbonate, ATH aluminum hydroxide, etc.)
The more fillers there are, the harder and less elastic the material becomes, which will offset the softening effect brought by plasticizers
Heavy calcium/light calcium: most commonly used to improve hardness and reduce costs; When the filling amount is large, the insulation material feels noticeably hard and easily brittle
ATH (flame retardant filler): used for flame retardant PVC insulation, which also increases hardness
Formula design logic: In order to maintain the target Shore A, adding more fillers requires synchronously increasing the plasticizer pH compensation.
4 Modified additives (with minor adjustments)
Powdered Nitrile Rubber (NBR): Blending modification improves low-temperature toughness and elasticity, providing a more flexible feel under the same hardness, without simply reducing hardness
Stabilizers (calcium zinc, lead salts), internal and external lubricants: basically do not change the basic hardness, mainly affecting processing and thermal aging; After aging and degradation, PVC molecular chains break and the material becomes hard and brittle
The softness and hardness are primarily determined by the type and amount of plasticizer added; Secondly, the K value of PVC resin and the filling amount of inorganic fillers are adjusted; Stabilizers and lubricants hardly affect the initial hardness, but they can affect the tendency to harden after aging.
