Processing aids refer to additives used to improve the rheology and molding properties of plastics, usually with low viscosity or surface energy, with a certain lubricating effect; mainly including plasticizers and lubricants.
(1) Plasticizer
Plasticizers can increase the flexibility, extensibility, and plasticity of plastics because of their ability to weaken the van der Waals forces between polymer molecules, thereby increasing the mobility of polymer molecular chains, reducing the crystallinity of polymer molecular chains, and reducing plastic flow. Temperature and hardness are conducive to the molding of plastic products. Commonly used plasticizers include phthalates, sebacates, and chlorinated paraffins.
Plasticizers can be divided into two categories: primary plasticizers and secondary plasticizers: primary plasticizers are characterized by good compatibility with resins, high plasticizing efficiency, migration resistance, low volatility, and low oil (water) properties. ) Extractability, low temperature flexibility; the compatibility of the secondary plasticizer with the resin is poor, and it is mainly used together with the main plasticizer to reduce the cost.
(2) Lubricant
It can improve the friction and adhesion between the particles of each layer of plastic and the melt and the metal surface of the processing equipment, increase the fluidity of the resin, achieve the controllable resin plasticization time, and maintain continuous production. lubricant.
Lubricants can be divided into external lubricants and internal lubricants.
The main function of the external lubricant is to enable the polymer melt to smoothly leave the hot metal surface of the processing equipment. The compatibility between the external lubricant and the polymer is poor, and only a thin lubricant layer is formed at the interface between the polymer and the metal. The most commonly used external lubricant is stearic acid and its metal salts.
The internal lubricant has good compatibility with the polymer, which can reduce the cohesion between the polymer molecules, thereby helping the polymer flow and reducing the temperature rise caused by the heat of internal friction. The most commonly used internal lubricants are low molecular weight ones. Polyethylene etc.
(3) Release agent
A release agent is a functional substance between the mold and the finished product. The release agent is chemically resistant and does not dissolve in contact with different resin chemistries (especially styrene and amines). The release agent also has heat and stress properties, and is not easy to decompose or wear; the release agent adheres to the mold without being transferred to the part being processed, and does not interfere with painting or other secondary processing operations. Due to the rapid development of injection molding, extrusion, calendering, molding, lamination and other processes, the amount of mold release agent has also been greatly increased.
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