Probably the most widely prevalent type, pvc granule is made by polymerizing droplets of Vinyl Chloride monomer suspended in water. When Polymerisation is done, the slurry is centrifuged and the PVC cake is gently dried by special heating systems in order never to subject the unstabilised resin to heat degradation. Particle dimensions of the resin ranges from 50-250 microns and also have porous popcorn like structures which readily absorbs Plasticisers. The structure from the PVC particles could be modified by selecting suitable suspending agents and Polymerisation Catalyst. Less porous types are extensively employed for the top volume Rigid or Unplasticised PVC applications like PVC Pipes, Windows, Sidings, Ductings. Suspension grades of any coarser particle size and also porous structures absorb large quantities of Plasticiser forming a dryblend at temperatures as little as 80oC.The more porous types are used in Plasticised applications like Cables, Footwear, Soft Calendered Sheeting and Films etc.
Emulsion Polymerised PVC is really what Paste Grade Resin is and this is practically exclusively utilized for Plastisols. Paste grade resin is definitely a fine particle size PVC made by spray drying an Emulsion of PVC in Water similar to how milk powder is produced. Paste grade resin needs far more energy to create and is also considerably costlier than Suspension resin. The paste grade resin carries the emulsifying chemicals and catalysts along with it. It is therefore less pure than Suspension Polymerized or Bulk Polymerized PVC. The Electrical properties of Paste grade resin plastisols are therefore much poorer than Suspension Resin Compounds. Clarity is poorer than Suspension or Bulk PVC. Paste grade resin is compact in structure, and is not going to absorb much Plasticiser at room temperatures. Temperatures greater than 160-180oC are needed to drive the plasticer in the Resin during curing. Paste grade Resin is extensively utilized for Cushion Vinyl Floorings of wide widths. Different layers of specially formulated pastes are coated either over a suitable substrate (Direct Coating) or on Release Paper (Transfer coating). The layers are fused continuously in long ovens and rolled up after release paper is stripped off. The rolled good flooring may have a tough semitransparent wear layer over printed and foamed layers that happen to be sitting in addition to highly filled base coats to formulate the thickness. Many extremely attractive and rich effects are possible and these represent the larger end of Vinyl Flooring.
Bulk Polymerisation gives the purest method of upvc compound as no emulsifying or suspending agents are utilized. They are mainly utilized in transparent applications. They may be mainly provided within the lower K value groups, as Unplasticised PVC Foils for Blister Packaging along with other Calendered/Extruded Transparent films work best processed from lower K Value grades. Refinements in Suspension resin technologies have edged out Bulk PVC in the recent past.
Vinyl Chloride is copolymerized with comonomers like Vinyl acetate give an array of resins with unique properties. PVAc or Copolymer of Vinyl Chloride and Vinyl acetate is the most important. The excellent solubility in solvents of PVAc makes it the prime option for Vinyl Printing Inks and solvent cements. There exists a very special use of PVAc in Floor tiling and it is the resin of choice for Vinyl Asbestos tiles. The Resin is really a binder as opposed to the main ingredient. With Copolymer Resin it is actually easy to manufacture floor tiles with Fillers like Asbestos and Calcium Carbonate accounting for around 84% using the Copolymer as well as other compounding additives as low as 16%. Such high levels are certainly not possible with Suspension resin as its melt viscosity is significantly higher and cannot coat and encapsulate such high amounts of inert filler. Special callendering trains are essential for Vinyl asbestos tiles. However with Asbestos falling out favour, such products have slowly died out.
PVC Resins are classified by their K-Value, an indicator of the molecular weight and standard of polymerization.
• K70-75 are high K value resins that gives best mechanical properties but are more challenging to process. That they need more plasticizer for same softness. High end Cable insulations in Suspension resin and tough coatings for Conveyor belts, Industrial Flooring and other top quality applications in Paste grade are a handful of popular application. It is the costliest.
• K65-68 are medium K value resin what are the most in-demand. There is a good balance of Mechanical properties and processibility. UPVC (Unplasticised or Rigid PVC) is constructed from the less porous grades while Plasticised Applications work best made out of the greater porous grades. There is lots of grade choice since they focus on the vast majority of PVC applications. Because of its sheer volume this group of PVC resins cost the best.
• K58-60 are low K-value ranges. Mechanical properties are lowest, but processing is easiest. Many tough to process applications like injection moulding, blow moulding and Clear Calendered packaging film are made from the low K value ranges. Costs are greater than Medium K Value Resins.
• K50-55 are special resins which dexopky06 personalized for a few demanding applications. Interesting ones are Battery Separator Resins and Blending resins used along withPaste Grade resin to reduce costs. Processing is easiest.
As PVC is 56% Chlorine, it is probably the few Polymers that happen to be self extinguishing, as Chlorine can be a strong Flame inhibitor.
Plasticisers make the hard PVC resin softer. Primary plasticizers have good compatibility with PVC resin and may be absorbed in big amounts. In special cases up to 140-150 PHR of Primary plasticiser may be gelated into PVC for super soft products. Virtually all Plasticisers are liquids and must be absorbed in Suspension resin in heated mixers. High Speed mixers (which generate frictional heat while mixing) are the most famous varieties of dryblending equipment. Heated Ribbon blenders and Sigma mixers are only used when quite high Plasticiser levels are needed.
You will discover a vast array of Primary plasticizers for pvc compound. This discussion will likely be limited by the most popular, the Phthalate Esters. Phthalic acid is reacted with various alchohols to produce a family group of Phthalate plasticizers which Di Octyl Pthalate (DOP) is the most popular. Other important Primary Plasticisers are DOA & DOS (for low temperature applications), Trimellitates (for high temperature applications and Polymeric Plasticisers (High permanence).