“Plasticization” is a key in the process of processing from CPVC resin into finished or semi-finished products. Whether it is extrusion molding or injection molding, the quality of plasticization is directly related to the intrinsic quality and surface quality of the product. Therefore, how to obtain good plasticizing quality from the process, equipment and technology is the key to CPVC processing.
1. the molecular formula of CPVC
CPVC (PVC-C) is a chlorination product of PVC, which is a chlorination modification of polyvinyl chloride. The modified PVC can achieve two different purposes:
A. To increase the thermal deformation temperature, increase the rigidity, improve the chemical stability, and at the same time improve the weather resistance and flame retardancy, and reduce the smoke density. This product is usually used to make products for occasions with special requirements;
B. Improve the solubility of the material. This product, commonly known as perchloroethylene, is mainly used in the production of adhesives, coatings and polyvinyl chloride.
The chlorination process of CPVC is an aqueous phase suspension (slurry) chlorination process. Its molecular structure is: -CHCl-CHCl-CH2-CHCl-
The performance of CPVC is determined by two factors: the chlorine content and the distribution of chlorine on the CPVC molecular chain. Therefore, CPVC with the same chlorine content will have a large performance difference due to the different distribution of chlorine atoms.
Since the melt viscosity of CPVC is at least twice that of PVC, the processing temperature is high, and the release of hcl due to thermal decomposition during processing causes difficulty in processing and corrosion of equipment.
In the extrusion process, how to achieve the ideal “plasticization” of CPVC, a high-viscosity material (plasticization in place) is the key to CPVC processing technology.
Therefore, it has special requirements for the formula:
A. heat stabilizer requirements
Due to the high processing temperature of CPVC, the amount of heat stabilizer used in the formulation is much higher than that of PVC. Obviously, the use of the conventional three-salt, two-salt heat stabilizer is not suitable. At present, the more mature heat stabilizer is a composite lead series stabilizer with a lubricating system.
B. requirements for lubricants
Since CPVC has a high melt viscosity, particularly melt fracture in injection molding, it is not suitable to use only conventional paraffin, stearic acid and metal soap lubricating systems.
In the extrusion processing of CPVC, since CPVC has a metal surface which tends to adhere to the thermal post-processing equipment (especially the head and the mold), in order to eliminate such adhesion, an external lubricant must be added to the formulation. The external lubricant should be incompatible with the CPVC resin.
In the CPVC molding process (especially injection processing), under the action of pressure, the mutual friction between the CPVC resins generates frictional heat, which is unfavorable for the molding process and must be controlled. The internal lubricant can reduce the friction between the resin during the processing of CPVC. The internal lubricant should be compatible with the CPVC resin.
It should be noted that the balance of internal and external lubrication in the formulation is critical. Excessive internal lubrication will seriously affect the “plasticization”, which will deteriorate the quality of the product; excessive external lubrication will cause the lubricant to precipitate, and even the screw slip will seriously affect the normal production. The OP wax (brown coal ester wax) in the saponified wax is an ideal internal and external composite lubricant.
C. processing aids to improve the quality of plasticization
In the extrusion and injection molding processing of CPVC, processing aids must be used, the purpose of which is to improve the plasticizing quality and increase the low temperature impact resistance of the CPVC material and the toughness of the product.
In the case of CPVC, even at a viscous flow temperature (such as 195-205 ° C), its flow unit is still a primary particle, the interaction between the fine particles of the resin is poor, the heat transfer effect is poor, and melt fracture is easily generated. Poor quality.
ACR is a processing aid that promotes plasticization. It can be dispersed in CPVC melt into a network structure unit with a size of less than 0.01μm, and evenly distributed among CPVC fine particles, which is increased by shear force. The friction between CPVC particles promotes the heat and mass transfer of the molten system, increases the torque, accelerates the plasticization process, and improves the quality of plasticization.
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CTC: JANE SUN
This article is refer to bohanplastics.
Post time: May-15-2019