One of 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 and the PVC cake is gently dried by special heating systems so as to not 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 dwelling of your PVC particles might 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 your coarser particle size and extremely porous structures absorb vast amounts of Plasticiser forming a dryblend at temperatures only 80oC.The greater porous types are utilized in Plasticised applications like Cables, Footwear, Soft Calendered Sheeting and Films etc.
Emulsion Polymerised PVC is really what Paste Grade Resin is which is almost exclusively utilized for Plastisols. Paste grade resin is definitely a fine particle size PVC manufactured 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 generate and is considerably costlier than Suspension resin. The paste grade resin carries the emulsifying chemicals and catalysts by using it. It is actually 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 more than 160-180oC are needed to drive the plasticer in the Resin during curing. Paste grade Resin is extensively employed 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 which are sitting along with 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 Polymerisation allows the purest method of soft pvc granule as no emulsifying or suspending agents are utilized. They can be mainly employed in transparent applications. They can be mainly provided inside the lower K value groups, as Unplasticised PVC Foils for Blister Packaging and other Calendered/Extruded Transparent films are the best processed from lower K Value grades. Refinements in Suspension resin technology has edged out Bulk PVC not too long ago.
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 important. The best solubility in solvents of PVAc makes it the prime choice for Vinyl Printing Inks and solvent cements. There is a special application of PVAc in Floor tiling which is the resin preferred by Vinyl Asbestos tiles. The Resin is actually a binder rather than the main ingredient. With Copolymer Resin it is actually possible to manufacture floor tiles with Fillers like Asbestos and Calcium Carbonate accounting for just as much as 84% using the Copolymer and other compounding additives as little as 16%. Such high levels usually are not possible with Suspension resin as its melt viscosity is quite a bit higher and cannot coat and encapsulate such high levels of inert filler. Special callendering trains will be required 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 in the molecular weight and amount of polymerization.
• K70-75 are high K value resins which supplies best mechanical properties but are harder 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 that are the most favored. They have a good balance of Mechanical properties and processibility. UPVC (Unplasticised or Rigid PVC) is constructed from the less porous grades while Plasticised Applications would be best made from the greater number of porous grades. There is lots of grade choice because they serve the vast majority of PVC applications. Simply because of its sheer volume this family of PVC resins cost the cheapest.
• 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 produced from the reduced K value ranges. Prices are higher 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 that are 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 may be absorbed in large quantities. In special cases around 140-150 PHR of Primary plasticiser could be gelated into PVC for super soft products. The majority of Plasticisers are liquids and really need to 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 merely used when high Plasticiser levels are needed.
There is a huge selection of Primary plasticizers for pvc compound. This discussion will likely be limited to the most common, the Phthalate Esters. Phthalic acid is reacted with various alchohols to manufacture a household of Phthalate plasticizers in which Di Octyl Pthalate (DOP) is considered the most popular. Other important Primary Plasticisers are DOA & DOS (for low temperature applications), Trimellitates (for top temperature applications and Polymeric Plasticisers (High permanence).