Plastisol fusion

Plastisol Fusion—This property is a function of temperature, time, and solvating power of the plasticizer. This property may be measured by determining the clear point, that is, the temperature at which a clear solution is obtained when a low concentration of resin is suspended in a plasticizer and heated at a constant rate. 

Fusion Properties As with both flexible and rigid PVC, the higher the resin molecular weight, the slower the fusion. Plasticizer selection also plays a major role in plastisol fusion properties. PVC/vinyl acetate and other copolymer resin systems are sometimes used to speed fusion in plastisol systems. As the copolymer content increases, the rate of fusion increases. 

Dr Joseph Green, formerly with FMC, points out that the isopropylated triphenyl phosphates are distinct compared with TCPs in that they have high plastisol fusion... 

Both cold- and hot-dipped parts are fused as with powder coatings. There is much variation in industrial practice regarding plastisol fusion cycles. Glass bottles coated... 

A type of physical stabili2ation process, unique for poly(vinyl chloride) resias, is the fusion of a dispersion of plastisol resia ia a plastici2er. The viscosity of a resia—plastici2er dispersioa shows a sharp iacrease at the fusioa temperature. Ia such a system expansioa can take place at a temperature corresponding to the low viscosity the temperature can then be raised to iacrease viscosity and stabili2e the expanded state. 

Plastisols may also be semi-geUed for storage, ie, enough heat is imparted to convert the plastisol into a soHd but without the full development of tensile properties brought about by full fusion. 

Random copolymers of vinyl chloride and other monomers are important commercially. Most of these materials are produced by suspension or emulsion polymerization using free-radical initiators. Important producers for vinyl chloride—vinyUdene chloride copolymers include Borden, Inc. and Dow. These copolymers are used in specialized coatings appHcations because of their enhanced solubiUty and as extender resins in plastisols where rapid fusion is required (72). Another important class of materials are the vinyl chloride—vinyl acetate copolymers. Principal producers include Borden Chemicals Plastics, B. F. Goodrich Chemical, and Union Carbide. The copolymerization of vinyl chloride with vinyl acetate yields a material with improved processabihty compared with vinyl chloride homopolymer. However, the physical and chemical properties of the copolymers are different from those of the homopolymer PVC. Generally, as the vinyl acetate content increases, the resin solubiUty in ketone and ester solvents and its susceptibiUty to chemical attack increase, the resin viscosity and heat distortion temperature decrease, and the tensile strength and flexibiUty increase slightly. 

Plasticizers weaken the intermolecular forces in the PVC reducing crystallinity. A relatively stable suspension, called a plastisol, of finely divided PVC in a liquid plasticizer, can be poured into a mod and heated to about 175°C producing a solid flexible plastic as a result of fusion of the plasticizer in the PVC. 

Propellants. Satriana and Bracuti (Ref 30) claim the use of pyrolyzed urea as a ballistic modifier which when incorporated in a doublebase plastisol propint produces a burning rate plateau. Thus, PbSnC>3 (90) and urea, acet and w (10g) are sintered for one hr at 500—50°, cooled, screened, molded and cured for use in a plastisol proplnt contg 30% HMX. Leach (Ref 37) reports that ballistic and other test results indicate that there is no significant difference between M30 proplnt contg Nitroguanidine prepd by the urea/AN process and that prepd by the standard British fusion process. 

Because of the low level of emulsifiers and protective colloids, the suspension polymer types are most suitable for electrical applications and end uses requiring clarity, This form is also employed in the bulk of extrusion and molding applications. Cost is lower than for emulsion and solution forms. The emulsion or dispersion resins are employed mainly for organosol and plastisol applications where fast fusion with plasticizer at elevated temperature will occur as a result of the fine particle size of the resin. 

Foams are made by the addition of blowing agents to the plastisol. These may be continuously applied to a moving substrate which includes a pass at an elevated temperature where foaming occurs, followed by fusion of the plastisol. 

A considerable range of plasticizers is available but those used most commonly are phthalate esters such as dioctyl or dinonyl phthalate (DOP or DNP). If it should be necessary to reduce the temperature of fusion, or to increase the rate of fusion (as with some expandable plastisols) a fast-solvating plasticizer such as butyl benzyl phthalate may be employed. Besides primary plasticizers such as these, less efficient secondary plasticizers (like chlorinated paraffins) can be included with a view to reducing costs and improving flame retardance. 

So that the temperature of the web can be increased in stages the oven should be zoned in a minimum of three sections. Most pastes contain a volatile diluent and it is essential that the temperature in the first zone should be relatively low so that volatiles can be driven off before fusion occurs. Too rapid an application of heat leads to blistering of the coating as residual solvent escapes from the fused areas. In each of the zones careful control of the air temperature, velocity, and distribution is essential for uniform fusion across the full width and throughout the coating. Operating conditions for ovens for PVC plastisols were considered by A. C. Poppe.5... 

A layer of transparent lacquer or PVC plastisol may be superimposed as desired to protect print and to control the gloss of the finish. A vinyl-acrylic lacquer may be applied in tandem with colour printing or, say, a clear plastisol coating by screen printing, usually in the last stage as the material passes to the oven for fusion and expansion. 

J m dia and dried by spray-drying or coagulation, are used as plastisol resins. Plastisols are dispersions of PVC in plasticizer. Heat allows fast diffusion of plasticizer into the PVC particle, followed by fusion (gelation), to produce a physically cross-linked elastomer, where the physical cross-links are PVC crystallites. 

During processing, the plastisol is heated slowly. When the gel point is reached, the plastic absorbs the plasticizer. However, in a very soft compound, the plastic dissolves into the plasticizer. Because each plastic particle remains a separate particle, the resultant gel has no useful physical properties. But on further heating, the plasticized plastic partially melts and flows into the plasticizer this occurs at the fusion point or over the fusion range. On cooling, the material comprises the tough rubber compound known as a flexible vinyl. 

Kaolin has a use in plastisol formulations giving good rheological control. Calcium carbonate is also used in this area. An alternative to calcium carbonate, phyllite, has been evaluated. This material, which contains quartz, muscovite and kaolinite, was characterised on the basis of paste viscosity, gelation and fusion behaviour, and mechanical properties (70). 

In the manufacture of glass fiber insect screening, a typical process would involve coating the yarns with the plastisol dispersion weaving the yarns into a fabric and then heat setting to cause fusion of the yarns at the interstices. 

Plastisol products are normally supplied to a customer under pre-aranged specifications as to color, viscosity, fusion point, etc., therefore product specifications are not shown. 

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