Extrusion process of CPVC pipe
Issuing time:2019-02-18 22:10
Chlorinated polyvinyl chloride (PVC) resin (hereinafter referred to as the CPVC) was founded in 1958 by American BFGoodrich company (BFGoodrich) is developed successfully, it is a product of polyvinyl chloride (PVC) resin chlorinated, after chlorination of PVC chloride content can be raised from 57% to 64% ~ 75%, with the increase of chloride content, the corresponding temperature tolerance, rigid, resistant to chemical corrosion, flame retardancy, smoke abatement to increase, but the CPVC resin melt viscosity increased, brittle, decreased the impact strength, thermal stability is reduced, a great difficulty for CPVC extrusion processing, At the same time, if the process control is improper, a large amount of HCl gas will be generated and the processing equipment and mold will be severely corroded. Therefore, the extrusion of CPVC resin has always been the focus of discussion. In the processing of CPVC resin, "plasticization" is the key, so how to get good plasticizing quality from the formula, equipment and process technology is the key to CPVC resin processing.
Formula for chlorinated polyvinyl chloride (PVC - C) pipes
1. Thermal stabilizer
CPVC resin is more easily decomposed than PVC in the processing process, so more heat stabilizer needs to be added than PVC. During the trial production, it can be added according to 1.5 ~ 2.5 times the amount of PVC, and then appropriately increased or decreased according to the trial production. The general principle is: heat stabilizer should not be added too much, otherwise it will affect the plasticization of CPVC resin. Basically, the processing of PVC heat stabilizer can processing CPVC, such as lead salt stabilizer and calcium zinc stabilizer and composite lead stabilizers, the metal liquid soap stabilizer and organic tin stabilizer, etc., in numerous heat stabilizer, when the special requirements of steel tubes with different is different on the selection, production and health level of CPVC pipes should choose non-toxic calcium zinc stabilizer or organic tin stabilizer; The use of liquid organotin stabilizer should be avoided as far as possible in the production of pipes with temperature resistance requirements. Calcium stearate is not added to produce high impact pipes.
Lubricant, and the effect of heat stabilizer is as important as the content of too little, can lead to processing difficulties, even can bring considerable damage to equipment, join the amount is too much, not only affects the quality of plasticizing, will also reduce the vicat softening temperature of the pipe, so how to grasp the addition amount of lubricant is the key, is also the design key of CPVC pipe formula, so far as to say that CPVC pipe formula design is part of a lubrication system design. CPVC resin has a high melt viscosity, at least twice that of PVC resin , so the amount of lubricant added is slightly more than that of PVC resin. When using different stabilizers, the ratio of internal and external lubricants is different. Generally speaking, the use of lead salt stabilizers requires more internal lubricants and an appropriate amount of external lubricants. The use of organic tin stabilizer, need to be configured with more external lubricants and an appropriate amount of internal lubricants; When using the compound stabilizer with lubricating system, the amount of inner and outer lubricants should be appropriately reduced. Stearic acid (HSt) can be used as the internal lubricant, while high temperature paraffin, PE wax or oxidized polyethylene wax should be used as the external lubricant of CPVC resin. In a word, if the ratio between inner and outer lubricants is well coordinated, this formula is not a mature one, at least in terms of extrusion molding.
3. Impact modifier and processing assistant
Because of CPVC resin chlorine content is higher, its shock resistance less than PVC resin, modification, impact resistant agent must be added to common impact resistant agent has: CPE, MBS, ABS and impact ACR, etc., in the machining process of CPVC pipes to join the CPE, toughening effect obviously, its content between 8 ~ 12 toughening effect is best, but to join CPE can significantly reduce the vicat softening temperature of the pipe; MBS and ABS have little effect on vicat's softening temperature, but they have poor weather resistance because their molecular chains contain unsaturated double bonds. Impact resistant ACR is an ideal impact resistant modifier, but its price is higher. Based on the above reasons, the author recommends to use the mixture of CPE/MBS as the impact modifier to meet the requirements of vekka softening temperature, impact resistance, weather resistance and price, etc. The ratio of the two is 1.5:1. The current domestic use of ACR processing aid mainly, it is the product of the mixed together several acrylic ester compounds, it can improve the plasticizing degree of resin, but because of its high melt viscosity, CPVC resin molecules between don't need to use other additives to increase the friction heat, it is more easy than PVC resin plasticizing, therefore in extrusion processing of CPVC pipes should add or not add less ACR coagulant.
4. Other additives
Other additives include fillers and colorants.
Adding the right amount of filler can not only reduce the cost, but also improve the processing performance. It can reduce the processing viscosity of CPVC resin, improve the dispersion of mixture, reduce the adhesion of equipment and mold during extrusion processing, at the same time, as a filler of rigid particles, but also can improve the impact resistance of CPVC pipes. The most commonly used filler is calcium carbonate. It is advisable to add no more than 5 parts, otherwise it will affect the properties of the product.
CPVC pipes are slightly darker than PVC pipes in color and appear grayish white. However, some colorants can be added as required. When adding colorants, a small amount of rutile type titanium dioxide should be added to cover up the gray color of CPVC pipes and reduce its influence on colorants.
Chlorinated polyvinyl chloride (PVC - C) pipe processing
Generally, parallel or conical twin screw extruders are used for extrusion processing of CPVC pipes. Considering that CPVC is easier to be plasticized than PVC, it is easier to control the extrusion production of CPVC pipes by using parallel twin screw extruders. If lead salt stabilizer is used in the formula, the extruder should have better plasticizing performance. If the formulation is organotin as stabilizer, the extruder screw compression ratio should not be too large.
2. Processing technology
2.1 mixing of materials
Mixed process of CPVC resin and PVC resin, need to be mixed high-speed and low-speed cooling mixing two process, usually high-speed mixing temperature should be controlled in 115 ~ 125 ℃, can't is too high, otherwise easy to mix yellow material, cause in the process of extrusion materials decomposition or appear "plasticizing" phenomenon. Slow cooling mixer temperature control in 40 ~ 50 ℃, also cannot too much, otherwise will mix the material with room temperature difference is too big, the relationship between materials absorb excess moisture in the air and influence the performance of the products.
2.2 extrusion temperature
The extrusion process of CPVC pipe focuses on the process temperature, which will directly affect the plasticizing quality of the pipe. General process temperature due to the difference of extruder plasticizing properties, and there is a big difference, the differences, sometimes there will be 20 ~ 30 ℃. In theory, the processing temperature is higher than PVC, CPVC material but in fact, based on our years of experience in processing, processing temperature of the CPVC to 5 ~ 8 ℃ lower than the PVC, it is because the CPVC melt viscosity is bigger than PVC, melt between molecules will produce a lot of friction heat, at this time if the extruder and then give it too much heat, it is easy to cause decomposition of the material.
In terms of process temperature setting, the curve should be kept flat as far as possible, which is conducive to the plasticizing quality of CPVC resin, and the curve going up and down is not conducive to the plasticizing of pipes. Generally, the curve of "U" shape is more appropriate. The whole process of temperature control in general can be divided into three parts: core barrel, confluence and mold, barrel temperature from the area began to decline, in turn confluence core temperature and slightly lower than the barrel temperature, in the mold temperature setting, it is worth noting that the mouth mould temperature and the temperature of the core mold, mold temperature should be lower than the barrel of the heating section temperature around 10 ℃, otherwise it will affect pipe longitudinal retraction rate, no request for longitudinal retraction rate of pipes is not affected by this limitation, the core mould heating can be normal after pulling out the pipe broken, CPVC melt in the heat and to the heat generated by the friction mandrel can maintain the temperature of the mandrel.
CPVC piping at home is a relatively new pipelines, but because of the particularity of CPVC resin, its processing continuous processing has brought certain difficulty, in particular, have many factories, make the pipes in the domestic promotion and application of some difficulties, my company production of CPVC pipes for five years, accumulated a lot of experience in production and processing, based on the two aspects of formulation and processing technology of CPVC of CPVC pipe production is presented, hope to manufacturer of the pipe and is about to introduce the pipe to draw lessons from, In order to make the pipe in xinjiang region can be rapid and healthy development.