By far the most widely prevalent type, pvc compound is manufactured by polymerizing droplets of Vinyl Chloride monomer suspended in water. When Polymerisation is done, the slurry is centrifuged along with the PVC cake is gently dried by special heating systems so as to not subject the unstabilised resin to heat degradation. Particle size of the resin ranges from 50-250 microns and get porous popcorn like structures which readily absorbs Plasticisers. The dwelling of your PVC particles may be modified by selecting suitable suspending agents and Polymerisation Catalyst. Less porous types are extensively utilized for our prime volume Rigid or Unplasticised PVC applications like PVC Pipes, Windows, Sidings, Ductings. Suspension grades of a coarser particle size and very porous structures absorb vast amounts of Plasticiser forming a dryblend at temperatures only 80oC.The greater number of porous types are employed in Plasticised applications like Cables, Footwear, Soft Calendered Sheeting and Films etc.
Emulsion Polymerised PVC is what Paste Grade Resin is and this is virtually exclusively utilized for Plastisols. Paste grade resin is certainly a fine particle size PVC produced by spray drying an Emulsion of PVC in Water very much like how milk powder is produced. Paste grade resin needs considerably more energy to make which is considerably costlier than Suspension resin. The paste grade resin carries the emulsifying chemicals and catalysts by using it. It can be 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 does not absorb much Plasticiser at room temperatures. Temperatures in excess of 160-180oC are necessary to drive the plasticer into 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 on 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 are sitting in addition to highly filled base coats to build up the thickness. Many extremely attractive and rich effects are possible and they represent the higher end of Vinyl Flooring.
Bulk Polymerisation allows the purest form of soft pvc granule as no emulsifying or suspending agents are utilized. They can be mainly employed in transparent applications. They may be mainly provided in the lower K value groups, as Unplasticised PVC Foils for Blister Packaging along with other Calendered/Extruded Transparent films would be best processed from lower K Value grades. Refinements in Suspension resin technology has edged out Bulk PVC in the recent past.
Vinyl Chloride is copolymerized with comonomers like Vinyl acetate give a variety of resins with unique properties. PVAc or Copolymer of Vinyl Chloride and Vinyl acetate is the most essential. The great solubility in solvents of PVAc makes it the prime choice for Vinyl Printing Inks and solvent cements. You will find a very special use of PVAc in Floor tiling and is particularly the resin preferred by Vinyl Asbestos tiles. The Resin is really a binder as opposed to the main ingredient. With Copolymer Resin it can be easy to manufacture floor tiles with Fillers like Asbestos and Calcium Carbonate comprising up to 84% together with the Copolymer and also other compounding additives only 16%. Such high levels will not be possible with Suspension resin as the melt viscosity is a lot 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, a warning sign of your molecular weight and amount of polymerization.
• K70-75 are high K value resins which gives best mechanical properties but are tougher to process. They want more plasticizer for same softness. High end Cable insulations in Suspension resin and tough coatings for Conveyor belts, Industrial Flooring and similar high end applications in Paste grade are a couple of popular application. It will be the costliest.
• K65-68 are medium K value resin what are the most in-demand. These people have a good balance of Mechanical properties and processibility. UPVC (Unplasticised or Rigid PVC) is manufactured out of the less porous grades while Plasticised Applications work best produced from the greater number of porous grades. There is lots of grade choice as they meet the needs of nearly all PVC applications. Simply because of its sheer volume this family of PVC resins cost the smallest.
• K58-60 are low K-value ranges. Mechanical properties are lowest, but processing is easiest. Many difficult to process applications like injection moulding, blow moulding and Clear Calendered packaging film are manufactured from the low K value ranges. Pricing is more than Medium K Value Resins.
• K50-55 are special resins which dexopky06 tailor made for many demanding applications. Interesting ones are Battery Separator Resins and Blending resins used along withPaste Grade resin to lower costs. Processing is easiest.
As PVC is 56% Chlorine, it is among the few Polymers which can be self extinguishing, as Chlorine is actually a strong Flame inhibitor.
Plasticisers make your hard PVC resin softer. Primary plasticizers have good compatibility with PVC resin and might be absorbed in big amounts. In special cases around 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 typically the most popular kinds of dryblending equipment. Heated Ribbon blenders and Sigma mixers are simply used when high Plasticiser levels are needed.
There is a wide array of Primary plasticizers for pvc compound. This discussion will probably be limited to typically the most popular, the Phthalate Esters. Phthalic acid is reacted with assorted alchohols to produce a family 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 top temperature applications and Polymeric Plasticisers (High permanence).