The chlorinated polyvinyl chloride resin was successfully developed by BF Goodrich in 1958. It is a chlorinated product of polyvinyl chloride resin (PVC). The chlorine content of chlorinated PVC can be increased from 57% to 64. %~ 75%, with the increase of chlorine content, the corresponding temperature resistance, rigidity, chemical resistance, flame retardancy, smoke elimination, etc. are enhanced, but the melt viscosity of CPVC resin increases, brittleness increases, impact strength Decrease, lower thermal stability, and bring great difficulty to the extrusion processing of CPVC. At the same time, if the process is improperly controlled, a large amount of HCl gas will be generated and the processing equipment and the mold will be seriously corroded. Therefore, the problem of extrusion processing of CPVC resin has been It is the focus of discussion. In the processing of CPVC resin, 'plasticization' is the key. Therefore, how to obtain good plasticizing quality from formula, equipment and process technology is the key to CPVC resin processing.
I. Formulation of chlorinated polyvinyl chloride (PVC-C) pipe
1, heat stabilizer
CPVC resin is easier to decompose than PVC in the process of processing. Therefore, it is necessary to add more heat stabilizer than PVC. When trial production, it can be added according to the amount of PVC added 1.5~2.5 times, and then increase or decrease according to the trial production conditions. The principle is: heat stabilizer should not be added too much, otherwise it will affect the plasticization of CPVC resin. Basically, the heat stabilizer for processing PVC can process CPVC, such as lead salt stabilizer, calcium zinc stabilizer, composite lead stabilizer, Metal soap stabilizers and liquid organotin stabilizers. Among the many heat stabilizers, when the pipes have different special requirements, there are some differences in the selection. When producing sanitary CPVC pipes, non-toxic ones should be used. Calcium-zinc stabilizer or organotin stabilizer; when producing pipes with temperature resistance requirements, liquid organotin stabilizer should be avoided as much as possible; when producing high-impact tubing, calcium stearate is not added.
2, lubricant
The role of the lubricant is as important as the function of the heat stabilizer. If the amount is too small, it will cause processing difficulties, and even cause considerable damage to the equipment. Too much addition will not only affect the quality of plasticization, but also reduce the quality of the pipe. Vicat softens the temperature, so how to master the amount of lubricant added is the key, and it is also the key to the design of CPVC pipe formulation. It can even be said that the design of CPVC pipe formulation is actually the design of lubrication system. CPVC resin has high melt viscosity, at least It is twice the '1' of PVC resin, so the amount of lubricant added is slightly more than that of PVC resin. When different stabilizers are used, the ratio of internal and external lubricants in the formulation is different. Generally speaking, Use lead salt stabilizer, need to configure more internal lubricant and appropriate amount of external lubricant; use organotin stabilizer, need to configure more external lubricant and appropriate amount of internal lubricant; use compound stabilizer with lubrication system When used, the amount of internal and external lubricants should be appropriately reduced. Stearic acid (HSt) can be used for internal lubricants. High temperature paraffin, PE wax or oxidized polyethylene wax should be used for external lubricants. Generally, paraffin wax should not be used alone as CPVC resin.
3, impact modifiers and processing aids
Due to its high chlorine content, CPVC resin has better impact resistance than PVC resin. It must be modified with anti-impact agent. Common anti-impact agents are: CPE, MBS, ABS and impact-resistant ACR, etc., in CPVC pipe The addition of CPE in the processing has obvious toughening effect. The toughening effect is best between 8 and 12 parts, but the addition of CPE will significantly reduce the Vicat softening temperature of the tube; the effect of MBS and ABS on the Vicat softening temperature Smaller, but because of their unsaturated double bonds in the molecular chain, the weather resistance is poor; impact-resistant ACR is an ideal impact modifier, but the price is higher. For the above reasons, I recommend using CPE/MBS As an impact modifier, the mixture can meet the requirements of Vika softening temperature, impact resistance, weather resistance and price. The ratio of the two is 1.5:1. The current domestic processing is suitable. The additive is mainly ACR, which is a product of several acrylate compounds mixed together, which can improve the plasticization degree of the resin, but the CPVC resin has a larger melt viscosity, and the molecules do not need to be added by other additives. Friction heat, it is easier than PVC resin
4, other additives
Other additives include fillers and colorants.
4.1 filler
Adding the right amount of filler not only reduces the cost, but also improves the processing properties. It can reduce the processing viscosity of CPVC resin, improve the dispersion of the mixture, reduce the adhesion to the equipment and the mold during extrusion processing, and at the same time, as a rigid particle. The filler can also improve the impact resistance of CPVC pipe. The most commonly used filler is calcium carbonate, and the addition amount should not exceed 5 parts, otherwise it will affect the performance of the product.
4.2 coloring agent
CPVC pipe is slightly darker than PVC pipe, it is grayish white, but some coloring agent can be added according to need. A small amount of rutile titanium dioxide should be added at the same time as adding coloring agent to cover the gray of CPVC pipe and reduce its coloring agent. Impact.
Second, the processing technology of chlorinated polyvinyl chloride (PVC-C) pipe
1, extruder
Extrusion processing CPVC pipe usually uses parallel or conical twin-screw extruder. In view of the fact that CPVC is more plasticized than PVC, it is easier to control the extrusion production of CPVC pipe by using parallel twin-screw extruder. Lead salt stabilizers require extruders to have better plasticizing properties; if the formulation uses organotin as a stabilizer, the compression ratio of the extruder screw is not too large.
2, processing technology
2.1 Mixing of materials
The mixing process of CPVC resin is the same as that of PVC resin. It requires two processes of high-speed mixing and low-speed cooling. Generally, the high-speed mixing temperature should be controlled at 115~125°C. It should not be too high. Otherwise, the yellow material will be easily mixed. During the extrusion process. Causes the decomposition of materials or the phenomenon of 'over plasticization'. The temperature of low-speed cooling and stirring is controlled at 40~50°C, and it should not be too high. Otherwise, the mixed materials will have too much relationship with the room temperature, so that the materials are absorbed too much. The moisture in the air affects the performance of the product.
2.2 Extrusion temperature
The extrusion process of CPVC pipe is focused on the process temperature, which will directly affect the plasticizing quality of the pipe. The general process temperature will vary greatly depending on the plasticizing performance of the extruder, and sometimes there will be 20~ 30 ° C. In theory, CPVC material processing temperature is higher than PVC, but in fact, according to our many years of processing experience, CPVC processing temperature is 5 ~ 8 ° C lower than PVC, because CPVC melt viscosity is larger than PVC, A large amount of frictional heat will be generated between the molten molecules, and if the extruder supplies too much heat to it, it will easily cause decomposition of the material.
In the process temperature setting, the curve should be kept as gentle as possible, which is beneficial to the plasticizing quality of CPVC resin. The curve is not conducive to the plasticization of the pipe. The general curve is 'U' shape is more suitable. The whole process The temperature control can be roughly divided into three parts: barrel, merging core and mold. The temperature of the barrel is decreasing from one area, and the temperature of the combined core is slightly lower than the temperature of the barrel. In the temperature setting of the mold, it is worthwhile. Note that the temperature of the die and the temperature of the mandrel, the temperature of the die should be about 10 °C lower than the temperature of the heating section of the barrel, otherwise it will affect the longitudinal retraction rate of the pipe, and the pipe with no requirement for the longitudinal retraction rate. Without this limitation, the mandrel heating can be disconnected after the pipe is normally pulled out, and the heat of the CPVC melt and the heat generated by the friction of the mandrel can completely maintain the temperature of the mandrel.
Third, the conclusion
CPVC pipe is a relatively new pipe in China, but due to the particularity of CPVC resin, it has brought certain difficulties to its processing, especially continuous processing, which has made many manufacturers discouraged, so that the pipe is promoted and applied in China. To some difficulties, our company has been producing CPVC pipes for five years and has accumulated a lot of experience in production and processing. This paper introduces the production of CPVC pipes through the formulation and processing technology of CPVC, hoping to produce this. The pipe and the manufacturer who is about to introduce the pipe can learn from it, so that the pipe can get rapid and healthy development in my Xinjiang area.