PVC processing and products
the compatibility of ACR and PVC is good, can speed up the gelation after China's entry into wto, shorten melting plasticizing time, improve the melt strength and thermal extensibility. The amount of ACR - 1% 5% can greatly improve the processing properties of PVC. In addition to the ACR, chlorinated polyethylene, ethylene/vinyl acetate copolymer, methyl methacrylate/butadiene/styrene copolymer are also commonly used PVC processing modifier. The addition of the modifier and can greatly improve the impact toughness of PVC, thus also known as impact modifier.
PVC extrusion molding products has two kinds: one kind is soft products, generally use PVC resin with high relative molecular mass, with a single screw extruder can be smoothly molding, products mainly include film, hose, wire and cable, etc. With PVC coated wire and cable, the most widely used compared with rubber, the use of PVC wire and cable with flame retardant, oil resistant, good resistance to water and coloring. In addition to civil, also used in automobile, spacecraft, etc.
PVC resin is heat-sensitive, forming the intermediate thermal decomposition. Therefore, in addition to adding stabilizer, forming equipment should have avoided material is heated for a long time, easy to melt flow properties. Extrusion molding, deep screw slot screws used to prevent the strong shear caused material decomposition, screw length to diameter ratio of shoulds not be too large, to prevent material decomposed by heat for a long time. The nose section and melt contact surface should be smooth, no dead Angle, to prevent the material cause decomposition of stagnation.
when molding the general use of screw injection molding machine, screw the screw groove comparable with deep in the screw, the screw head conical, lest cause decomposition material stock too much, use rapid plasticizing and high-speed injection molding process. Reduce material in the stagnant time in the cylinder, the mould should be set on the vent and the discharge of HCI gas may be produced. Product design should avoid sharp corners, because it is easy to produce stress concentration and result in the crack of the products. Equipment, mould parts in contact with the PVC melt anticorrosive processing should be paid attention to.
in the processing, PVC melting speed is slow, low melt strength, easy cause melt flow defect, need to join processing modifier to overcome these disadvantages, speed up the resin gelation in the plasticizing process, improve the liquidity of the melt, reach the purpose of improving the product quality. ACR is a kind of acrylic ester copolymer, which is the most commonly used PVC processing modifier, with different structure and composition of different varieties, and can meet the processing requirements of different products.
PVC is amorphous polymer, when the molten material cooling, shrinkage rate is not big. The polarity of the PVC has the advantages of easy coloring and printing for light products can be added to a small amount of plastic blue and disperse violet coloring, yellow cover injection molding processing resin itself. Because PVC is multicomponent plastic, processing performance is closely associated with the preparation of the material. In front of the molding must be through the efficient mixed plastic refining equipment, reasonable process mixture dispersed evenly powder and granular materials, plastic paste, such as different state, again through the different processing method to produce a wide variety of PVC products.
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