PVC / SBS blend modified bellows
DATE：2022/5/23 8:50:42 / READ： / SOURCE：This station
PVC / SBS blend modified bellows
With the rapid development of urban and rural construction market, the market sales volume of PVC bellows for construction is also increasing. This kind of pipe has the structure of corrugated annular groove, and has both the rigidity of UPVC pipe and the flexibility of hose. Therefore, it is rigid and flexible. It can replace the traditional steel pipe and plastic pipe for conveying liquid and gas and as the embedded wire sleeve. Moreover, it has a large length ratio per kilogram, so it is called "economical" pipe by the construction industry. However, the pipe produced by PVC alone has poor low-temperature performance, and the pipe fracture often occurs during construction in winter. If the additive is added to the formula, the strength of the pipe will be affected or the oxygen index will be reduced and the flame retardant effect will not be achieved. SBS modified PVC is used to produce bellows, so that this kind of pipe can not only bear certain pressure and bend freely in high and cold climate, but also has the effect of flame retardant. PVC transverse heat shrinkable film production line www.handern.com com1. Material selection and formula design (1) main raw material characteristics
1) Properties and characteristics of polyvinyl chloride (PVC). The flame retardant fire with 56% (mass fraction) chlorine content in the molecular structure of PVC, that is, the wire bushing made of PVC material, has the effect of wire combustion. PVC is a weakly polar polymer with good electrical properties; It has the characteristics of high volume electricity and breakdown voltage, as well as excellent chemical stability. However, PVC has many advantages, but it has some disadvantages, such as poor impact resistance, low temperature, poor thermal stability and so on. PVC is sensitive to the change of temperature. When the ambient temperature of the product changes from high to low, it will show brittleness. At this time, if external force is applied, even small deformation will destroy the product.
2. The material body is a styrene butadiene styrene triblock polymer obtained by copolymerization of butadiene and styrene.
① Molecular structure of SBS. The central segment of SBS molecular structure is polybutadiene (rubber), which is a continuum, and the two ends are polystyrene (plastic), which is a dispersion. At room temperature, SBS has an incompatible two-phase structure, and the separated polyethylene gathers together (also known as micro zone). At this time, PS plays a reinforcing role in the Pb segment of the rubber. The polystyrene segment is glassy and very hard at room temperature, and the end of the polybutadiene segment providing elasticity is fixed to form a physical cross-linked network structure. As a result, SBS presents the characteristics of elastomer at room temperature. When the temperature rises above the glass transition temperature Tg of PS, the micro region formed by PS melts and the physical crosslinking point is released, resulting in plastic flow. Therefore, it can be formed by the molding method of thermoplastic plastics. PVC transverse heat shrinkable film production line www.handern.com com
② SBS performance. SBS has higher strength and elasticity of raw rubber, and the permanent deformation is much smaller than that of plastic, but slightly larger than that of vulcanized rubber. When the temperature increases, the tensile strength and hardness of SBS decrease and the plasticity increases, which is conducive to molding processing. SBS also has better electrical insulation performance than ordinary hard plastics and air permeability of PE and PVC.
3) Original formula structure. The original formula structure is: 100kg polyvinyl chloride (SG-5), 2kg tribasic lead sulfate, 1.5kg dibasic lead phosphite, 1.5kg lead stearate, 1kg barium stearate, 2kg chlorinated polyethylene, 3kg calcium carbonate, 1.5kg stearic acid and 10kg impact modifier. The pipes produced with this formula can only withstand very small external pressure at low temperature. In order to change this situation, the new formula uses PVC / SBS as the main raw material, and the auxiliary materials are composed of stabilizer, lubricant, modifier, solubilizer, flame retardant, smoke suppressant, filler and pigment. PVC transverse heat shrinkable film production line www.handern.com com
(2) Although the composition of auxiliary raw materials PVC has many excellent properties, it also has disadvantages such as poor thermal stability and processability. Therefore, the selection of appropriate auxiliary raw materials will have a direct impact on the production cost and quality of products.
1) Selection of stabilizer. Because the melting temperature of PVC exceeds its decomposition temperature, it brings great difficulties to the molding process. In order to prevent thermal decomposition in the forming process, heat stabilizer must be added in production and processing.
The stabilizers usually used for PVC are tribasic lead sulfate, dibasic lead phosphite and metal soap stabilizers, so as to achieve the purpose of stability. Through the comprehensive comparison of the characteristics of metal soap stabilizer and lead salt stabilizer, it is determined to use the composite barium cadmium lead produced by Guangzhou Donghua chemical plant. The stabilizer is characterized by low dosage (1 / 3 ~ 1 / 4 of the usual dosage), high thermal stability, good compatibility with PVC, low volatility and non migration.
2) Selection of lubricants. In order to reduce the mutual friction between PVC and processing machinery and its internal molecules, so as to improve the processability of plastics and improve the performance of products, some lubricants must be added appropriately. Therefore, chlorinated paraffin with low volatility, good thermal stability and good dispersion was selected as lubricant. Chlorinated paraffin not only has lubricity, but also has certain flame retardancy and low price.
3) Selection of solubilizer. SBS and PVC have poor compatibility, so SBS and PVC cannot be directly modified by blending. In order to improve the impact resistance and low-temperature brittleness of PVC, methyl methacrylate butadiene styrene graft copolymer (MBS) is selected as the solvent, and the comprehensive properties of PVC can be greatly improved by SBS / PVC blending modification. PVC transverse heat shrinkable film production line www.handern.com com
4) Fillers and pigments. In order to ensure the market competitiveness of bellows with high quality and low price, add an appropriate amount of calcium carbonate (CaCO). This not only reduces the production cost, but also improves the strength of bellows and the stability of processing size. An appropriate amount of phthalocyanine blue pigment is used to color the appearance of the pipe, which adds a bit of brilliance to the appearance of the pipe.
5) Selection of toughening agent. The chlorine content in chlorinated polyethylene (CPE) has a great influence on the toughening effect. The chlorine content is too low, the crystallinity is high, the toughness is poor, the glass transition temperature is high, the compatibility with PVC is poor, and the toughening effect is not good; When the chlorine content is too high, CPE has strong cohesion, which is difficult to disperse into PVC, and the toughening effect is not good. Therefore, the chlorine content of CPE is 30% ~ 40%. Because CPE has good compatibility with PVC, it has good flame resistance after blending. This is because both PVC and CPE contain a large proportion of chlorine atoms in their macromolecular structures. CPE mixed in PVC can effectively stabilize the plasticization and toughening. Therefore, CPE is selected as the appropriate toughening agent, and the general dosage (mass fraction, the same below) is about 6% ~ 12%.
6) Selection of flame retardants and smoke suppressants. PVC is a flame retardant plastic, which has good flame retardancy. However, after adding other additives, it is necessary to add some flame retardant antimony trioxide (sbz03) appropriately in order to prevent the decline of flame retardancy of bellows. Such products will produce antimony oxychloride gas heavier than air after combustion to isolate the air, so as to achieve the purpose of flame retardant. The general dosage is 5% - 10% of the resin. PVC transverse heat shrinkable film production line www.handern.com com
The addition of a small amount of molybdenum trioxide (MoO3) can reduce the smoke emission of corrugated tube combustion by about 45%,. Molybdenum compounds also have dual functions of flame retardants and smoke inhibitors.. Molybdenum compounds. The dosage can be about 1% ~ 1.5%.
2. Preparation process
(1) add 110 (stop heating), add 1 / measurement of aluminate coupling agent DL-411-A, stir at high speed for 4min, then add the remaining 1 / 2 coupling agent, continue to stir at high speed for 6min, add an appropriate amount of stearic acid, stir at high speed for 30s ~ 1min, and then discharge the material.
(2) Mix BS quickly to make it loose, heat it to 60 ℃ (stop heating), add an appropriate amount of naphthenic oil, continue mixing at high speed for 4 ~ 6min, add CaCO3 with surface treatment, stir and heat it at high speed to 80, cool it, and continue mixing for 6 ~ 8min to discharge.
(3) Vcsbs kneading: firstly, the PVC is kneaded, and then the kneaded SBS is added. At the same time, the solubilizer MBS is added, kneaded at high speed for 4 ~ 8min, and the material is discharged.
(4) The fluidity of molten material is poor when PVC is out of molding, so temperature control is very important. The optimum forming and processing temperature of PVC is 160 ~ 180 ℃, and too high temperature in the feeding section will cause feeding fluctuation, so it is appropriate to control it at 145 ~ 160 ℃; The increase of the temperature in the compression section can increase the smoothness of the product surface. The temperature in the compression section is set at 165 ~ 175 ℃, the temperature in the metering section is set at 175 ~ 185 ℃, and the temperature of the machine head is set at 175 ~ 200 ℃; If the temperature of the die is too high, the product will have Coke marks, and if the temperature is too low, the surface of the product will not be smooth. Therefore, the die temperature should be 175 ~ 200 ℃.
(5) Inflation pressure the inflation pressure of bellows directly affects the quality of product molding. The pressure is too low, and the edges and corners of the pipe are not clear enough after forming; The pressure is too high and the pipe cannot be formed continuously, so the inflation pressure should be controlled at about 015mpa. Another factor affecting the forming quality is the temperature of the mold. Due to the long-time continuous operation friction and the increase of the surface temperature during pipe forming, the mold is easy to cause the phenomenon of "sticking mold". Therefore, the mold temperature should be controlled at 40 ~ 60 ℃, so as to facilitate the basic shaping of the products before opening the mold and avoid the lengthening of corrugated pitch during coiling.
(6) The traction speed is too fast, which is easy to cause the bellows to break due to the thin pipe wall; If the traction speed is too slow, it will increase the wall thickness or cause local "accumulation" in the pipe. Therefore, the traction speed is generally controlled at 6 ~ 10m / min.
3. Recycling method of waste products
The waste bellows produced in the processing process can be broken by a plastic crusher, and then the broken material can be ground into 40 ~ 60 mesh powder by a powder mill, which can be mixed with new ingredients. The dosage of the recycling department and new ingredients is: 25kg of new ingredients and 5 ~ 7kg of recycled materials.
Author：admin