The Design Principle Of the Basic Formula Of PVC

Polyvinyl chloride, abbreviated as PVC (Polyvinyl chloride) in English, is a vinyl chloride monomer (VCM) in peroxides, azo compounds and other initiators; or under the action of light and heat according to the free radical polymerization reaction mechanism Polymers formed by polymerization. Vinyl chloride homopolymer and vinyl chloride copolymer are collectively referred to as vinyl chloride resin.
 

PVC is a white powder with an amorphous structure. The degree of branching is small, the relative density is about 1.4, the glass transition temperature is 77~90℃, and it starts to decompose at about 170℃. The stability to light and heat is poor, above 100℃ or over a long period of time. Sun exposure will decompose to produce hydrogen chloride, which will further autocatalyze the decomposition, causing discoloration, and the physical and mechanical properties will also decline rapidly. In practical applications, stabilizers must be added to improve the stability to heat and light.

The molecular weight of industrially produced PVC is generally in the range of 50,000 to 110,000. It has a large polydispersity. The molecular weight increases with the decrease of the polymerization temperature; there is no fixed melting point, and it starts to soften at 80-85°C, and becomes viscoelastic at 130°C. , 160～180℃ begin to transform into viscous fluid state; it has good mechanical properties, the tensile strength is about 60MPa, the impact strength is 5-10kJ/m2, and it has excellent dielectric properties.

PVC used to be the world's largest production of general-purpose plastics, and it has a wide range of applications. It is widely used in building materials, industrial products, daily necessities, floor leather, floor tiles, artificial leather, pipes, wires and cables, packaging films, bottles, foaming materials, sealing materials, fibers, etc.

1. According to physical properties and cost requirements, select material components. Mainly the choice of modifier and filler. Generally stretch, impact resistance notch, notch tear, flexibility, ring stiffness.

2. According to the material components, consider the selection of process additives. Individuals generally regard stabilizers and lubricating systems as the main system of additives, which are chosen for the sake of the process. The stabilizer generally only considers the thermal stability and the influence on the melt. Lubrication system, melting point, flow, demoulding. Also consider the dispersion of the review system and the overall impact on the melt.

3. Make a simple judgment on the authenticity of the raw materials used and the authenticity of the factory data. The main purpose is to prevent fraud, which is also the weakness of many small and medium-sized enterprises. Especially the composite series stabilizer, the composite stabilizer is the main component of the basic process formula. Among the companies visited, 99% of them did not know that their confidants used stabilizer formulations. This means that 99% of small and medium-sized enterprises do not know the real basic crafting recipes used by their enterprises at all! This is also the biggest weakness of domestic technicians at present, and it is almost a joke to say that a master recipe master is almost a joke.

4. Understand the equipment, and have a preliminary understanding of the screw's shear capacity, compression ratio and lead. Generally asked about heavy calcium or light calcium, high calcium screw or low calcium screw. Understand the expected output required by the equipment. Understand the mold feed resistance, the approximate release ratio of the mold bin, and the effective straight length of the die. If the particles have to consider the loss of reprocessing.

5. According to the overall comprehensive consideration, according to the raw material composition, consider the stability, fluidity, dispersibility and the superiority of the melt. Design the initial formula system, and make reasonable adjustments to the formula according to the equipment and melt performance, and the judgment of the initial performance of the product.

Example 1:

Light calcium deposits have a large volume and only a small amount of filling is used. When the high filling volume is too large, the lead backflow causes uneven lead compression, melt fracture, partial decomposition, and uncontrollable production current.

Example 2:

CPE has high melt dilution and softness, high viscosity and increased shear heat. Therefore, when the amount of CPE is increased, the fluidity of the formula system is felt to be particularly poor, and a lot of lubrication is needed to control it. If lubrication is controlled by wax and acid, the interface bonding of the melt becomes worse. It is easy to enter the CPE to increase the lubrication and heighten the product's toughness. When the rubber elastomer is extruded into the die, if the formula body cannot well control the expansion, it will easily cause the melt performance to decrease.

Example 3:

When using heavy calcium, reduce the amount of stearic acid as much as possible. The interfacial tension of stearic acid to heavy calcium is too large, and it is easy to produce an isolation layer between PVC and calcium powder. It can be used to wrap free water. The influence of the mutual affinity of the melt is very obvious.

Example 4:

The higher the shearing section, the greater the amount of lubrication used in the early stage, but the lower the lubrication consumption in the middle stage. Such as Tongda threading pipe equipment. The lubrication system is not adjusted well at high speed, and the quality will obviously decrease when the speed increases.

Example 5:

The larger the mold silo, the higher the thermal stability relative to use. Otherwise, it will have a significant impact on the plasticizing and overall melt effect. That is to say, the general use system of the mold warehouse is high stability and low lubrication.

Example 6:

With the same formula, the faster the running speed of the vertebral twin-screw, the higher the amount of lubrication required, and the lower the amount of heat stabilizer, otherwise it will affect the speed and outlet mold expansion rate.