Formula composition of chlorinated polyvinyl chloride (PVC-C) pipes - 2

2. Lubricants

The role of lubricants and heat stabilizers are equally important.

Adding too little, will cause processing difficulties, and even bring considerable damage to the equipment; adding too much, not only affect the quality of plasticization, but also reduce the Vicat softening temperature of the pipe. Therefore, how to balance the dosage of lubricant is the key, but also the key to the design of CPVC pipe formulations, or even that the design of CPVC pipe formulations is actually the design of the lubrication system.

CPVC resin melt viscosity is large, at least twice as much as PVC resin, so the dosage of lubricants added than PVC to be a little more.

Similar to the processing of PVC, when using different stabilizers, the formulation of the internal and external lubricant ratio is different.

Generally speaking, the use of organotin stabilizers, the need to configure more external lubricants and the appropriate amount of internal lubricant; the use of composite stabilizers with lubrication system, the amount of internal and external lubricants should be appropriately reduced. Internal lubricant can choose stearic acid (HSt), the external lubricant needs to choose high temperature paraffin wax, PE wax or oxidized polyethylene wax, general paraffin wax should not be used alone as the external lubricant of CPVC resin.

In short, the coordination of the internal and external lubricant ratio between the relationship, then the formula can not be said to be a mature formula, at least in the extrusion molding will not have any problems.

3. Impact modifier and processing aids

Due to the high chlorine content of CPVC resin, its impact resistance is worse than PVC resin, they must be added to modify the impact capability, commonly used impact modifiers are: CPE, MBS, ABS and Acrylic impact modifiers.

CPVC pipe processing in the addition of CPE, the toughening effect is very obvious, the amount of additions between 8 to 12 toughening effect is the best, but the addition of CPE will significantly reduce the pipe Vicat softening temperature; MBS, ABS on the Vicat softening temperature. 

MBS, ABS on the Vicat softening temperature has less effect, but because of their molecular chain contains unsaturated double bonds, weather resistance is poor; 

ACR impact modifiers is a more ideal impact modifier, but the price is higher.

For the above reasons, we recommend you to use CPE/MBS mixture as impact modifier, which can take into account the requirements of Vicat softening temperature, impact resistance, weather resistance and price, etc. The ratio of the two is around 1.5:1.

At present, China's domestic use of processing aids are mainly acrylic impact modifier, it is several acrylate compounds mixed together in the product, it can improve the degree of plasticization of the resin, but CPVC resin due to the melt viscosity is larger, the molecules do not need to increase the friction heat with the help of other additives, it is easier to plasticize than PVC resin, therefore, in the extrusion processing of CPVC pipe ACR impact modifiers should be added less or not added.

4, other additives

Other additives include fillers and coloring agents.

4.1 Filler

Add an appropriate amount of filler can not only reduce costs, but also improve processing performance. It can reduce the processing viscosity of CPVC resin, improve the dispersion of the mixture, reduce the adhesion of extrusion processing on the equipment and molds, at the same time, as a filler for rigid particles, but also to improve the impact resistance of CPVC pipe. The most commonly used filler is calcium carbonate, add as little as possible, not more than 5 parts is appropriate, otherwise it will affect the performance of the product.

4.2 Coloring agent

CPVC pipe is slightly darker than PVC pipe, grayish-white, but according to the need, add some coloring agent, add a small amount of titanium dioxide at the same time coloring agent should be added to cover up the gray of CPVC pipe to reduce its impact on the coloring agent.

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