PVC Resin
There are 4 types of PVC Resin grouped by polymerization method
1. Suspension Grade PVC
2. Emulsion Grade PVC
3. Bulk Polymerised PVC
4. Copolymer PVC
Suspension Grade PVC
The most widely prevalent type, Suspension grade PVC is made by polymerizing droplets of Vinyl Chloride monomer suspended in water. When Polymerisation is complete, the slurry is centrifuged and the PVC cake is gently dried by special heating systems so as not to subject the unstabilised resin to heat degradation. Particle size of the resin ranges from 50-250 microns and have porous popcorn like structures which readily absorbs Plasticisers. The structure of the PVC particles can be modified by selecting suitable suspending agents and Polymerisation Catalyst. Less porous types are extensively used for the high volume Rigid or Unplasticised PVC applications like PVC Pipes, Windows, Sidings, Ductings. Suspension grades of a coarser particle size and very porous structures absorb large quantities of Plasticiser forming a dryblend at temperatures as low as 80oC.The more porous types are used in Plasticised applications like Cables, Footwear, Soft Calendered Sheeting and Films etc.
Emulsion Grade PVC
Emulsion Polymerised PVC is what Paste Grade Resin is and this is almost exclusively used for Plastisols. Paste grade resin is a very 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 much more energy to produce and is considerably costlier than Suspension resin. The paste grade resin carries the emulsifying chemicals and catalysts 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 does not absorb much Plasticiser at room temperatures. Temperatures in excess of 160-180oC are needed to drive the plasticer into the Resin during curing. Paste grade Resin is extensively used 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 can have a tough semitransparent wear layer over printed and foamed layers which are sitting on top of highly filled base coats to build up the thickness. Many extremely attractive and rich effects are possible and these represent the higher end of Vinyl Flooring.
Bulk Polymerised PVC
Bulk Polymerisation gives the purest form of PVC resin as no emulsifying or suspending agents are used. They are mainly used in transparent applications. They are mainly made available in the lower K value groups, as Unplasticised PVC Foils for Blister Packaging and other Calendered/Extruded Transparent films are best processed from lower K Value grades. Refinements in Suspension resin technology has edged out Bulk PVC in the recent past.
Copolymer PVC
Vinyl Chloride is copolymerized with comonomers like Vinyl acetate give a range of resins with unique properties. PVAc or Copolymer of Vinyl Chloride and Vinyl acetate is the most important. The good solubility in solvents of PVAc makes it the prime choice for Vinyl Printing Inks and solvent cements. There is a very special application of PVAc in Floor tiling and it is the resin of choice for Vinyl Asbestos tiles. The Resin is actually a binder rather than the main ingredient. With Copolymer Resin it is possible to manufacture floor tiles with Fillers like Asbestos and Calcium Carbonate accounting for as much as 84% with the Copolymer and other compounding additives as low as 16%. Such high levels are not possible with Suspension resin as its melt viscosity is much higher and cannot coat and encapsulate such high levels of inert filler. Special callendering trains are required for Vinyl asbestos tiles. However with Asbestos falling out favour, such products have slowly died out.
Post time: Apr-07-2022