Viscosity of plastisols and organosols

Extrusion viscometer operated under high shear rates is used to determine viscosity of organosols and plastisols. A sample conditioned to proper temperature is placed in an extrusion chamber, and the extrasion pressure and the rate of flow through the orifice are measured and used for result calculations. The orifice has the inside diameter of 3.17 nun 

T viscosity, Pas R radius of orifice, cm P pressure, MPa D density of sample, g/ml T efflux time, s L orifice length, cm W weight of material effluxed, g. 

It should be noted that the ASTM method is different than ISO standard. Severs rheometers of two different geometries are specified by ISO standard. They have a radius of orifice of 1.5 mm and its height either 45 or 22.5 mm depending on the model (dimensions of orifice are totally different than specified in ASTM). The use of several pressures is suggested to determine rheological properties of plastisols, since viscosity must be determined at different shear rates. Calculations are done from the equation [3.8]. 

Viscosity can alternatively be measured by Brookfield viscometer according to ASTM D 1824 but results will differ because of the differences in shear rates and non-Newtonian properties of plastisols and organosols. 

Karl Fischer titration is specified for use in plasticizers. The method determines free and Itydration water in solid and liquid samples. In most cases, automatic titration is used and this is the main subject of standard but manual titration method is also included in the appendix. The sample containing a maximum of 100 mg of water is dissolved in a suitable solvent and titrated with Karl Fischer reagent which consists of iodine, sulfur dioxide, organic base, and solvent. The titration end-point is determined amperometrically. The ASTM method lists numerous substances in which the presence of water can be determined. There is also a list of substances which interfere with measurements. 

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ASTM D1824-95, Apparent viscosity of plastisols and organosols at low shear rates. 

The method and type of equipment used also vary with the type of adhesive. As an example, the viscosity of electrically conductive adhesives is measured according to ASTM D1824, Apparent Viscosity of Plastisols and Organosols at Low-Shear Rates by Brookfield Viscosity The viscosity of typical electrically conductive die-attach adhesives is measured with a Brookfield HBT viscometer with Spindle TB and Speed 5. For higher-viscosity conductive adhesives and for underfill adhesives, a Brookfield RVT or RVF viscometer is used with Spindles 6 or 7 at speeds of 4—10.4 rpm. Another Brookfield viscometer, the Cone-and-plate viscometer with a CP-51 spindle is used for low-to-intermediate viscosity adhesives. Finally, the Brookfield HAT and HBT instruments are used for the high-viscosity (1-2 million cP at 1 rpm) adhesives typically used in SMT applications. ... 

Standard Test Method for Apparent Viscosity of Plastisols and Organosols at Low Shear Rates by Brookfield Viscosity, ASTM D1824, Am Soc. Testing and Materials. 2002. 

The method and type of equipment used also vary with the type of adhesive. As an example, the viscosity of electrically conductive adhesives is measured aeeording to ASTM D1824, Apparent Viscosity of Plastisols and Organosols at Low Shear Rates by Broolfield ViscosityThe viseosify oftypieal electrically conductive die-attach adhesives is measured... 

For the relative viscosity of emulsions, in the absence of deformation and coalescence, Eqs 7.24-7.30 may also be used, provided that the intrinsic viscosity is calculated from Eq 7.50 and that the maximum packing volume fraction is treated as an adjustable parameter, dependent on the interphase. This pragmatic approach has been successfully used to describe [r]] vs. (() variation for such complex systems as industrial lattices (at various stages of conversion), plastisols and organosols. 

The 100% linearity of PX-316 imparts superior low temperature flexibility to vinyl compositions, and demonstrates excellent light and heat stability, as well as low volatility. Addition of PX-316 to plastisols and organosols lowers initial viscosity and leads to longer shelf life. 

Orapex 4.4 also provides vinyl plastisol and organosol formulations with low initial viscosity and extended viscosity stability by virtue of its low solvating action. 

Organosols are plastisols that contain a volatile diluent. The volatile component is usually selected from true nonsolvents for PVC resins such as the aliphatic hydrocarbons—the main purpose of the volatile ingredient is to lower the viscosity of the paste by contributing more liquid to the formulation. Very low plasticizer levels are then possible, and higher durometer hardness values are attainable (as compared to plastisols). 

For coating applications it is common practice to add solvent (diluent) to a plastisol to bring down viscosity. This mixture is referred to as organosol. It may be applied by various coating methods to form a film on a substrate and then is heated to bring about fusion, as in the case of plastisol. 

The organosols are a partial dilution of the plastisol with a mixture of solvent and nonsolvent. It is a way of lowering viscosity. Because this does introduce some volatile material, applications are limited to those in which the volatile matter can evaporate conveniently. This is still better, however, than using resin solutions where the solids content is very low (5-30 percent) and toxicity, flammability, cost, and handhng of the solvents may be detrimental to efficient use. Organosols typically have a 75-95 percent solids concentration. 

Plastisols are of considerable importance commercially. Tbey are converted into tougb, rubbery products by heating at about 160°C (gelation). Organosols are cbaracterized by the presence of a volatile organic diluent whose sole function is to reduce the paste viscosity. The diluent is removed after application and before gelling the paste. 

Coating materials composed of resins suspended in a hydrocarbon liquid. An organosol is plastisol with an added solvent, which swells the resin particles, thereby increasing viscosity. Applications include spray coating, dipping, and coatings for aluminum, fabrics, and paper. 

A plastisol may be regarded as an organosol in which the continuous phase is almost entirely liquid plasticizer (small amounts of solvent are used for viscosity adjustment). PVC plastisols are made from PVC powder, adipate and phthalate ester plasticizers and minor amounts of epoxy-type resin in solution to aid pigment dispersion and to help (with other additives) to keep the polymer stable to heat and oxidation. The resultant coating is nearly solvent-free and so can be applied in thick films (100-250 m) and stoved without disruption by escaping solvent. The plasticizer penetrates the particles, aiding sintering as the metal substrate reaches c. 200°C in 30-60 s. 

Organosol n A suspension of a finely divided resin in a plasticizer together with a volatile organic liquid (ASTM D 883). A somewhat tighter definition requires that the volatile liquid comprise at least 5% of the total weight of the suspension. The resin used is most frequently PVC, but the term applies to such suspensions of any resin. An organosols can be prepared from a plastisol merely by adding a volatile diluent or solvent that serves to lower viscosity and evaporates when the compound is heated. 

In cases where plasticizer content must be lower than 50 phr to reach a certain set of properties, it may be usefid to promote processing by addition of volatile organic additives to form an organosol. Hydrocarbons arc most commonly used because of their relatively low materials cost and suitability for solvent recovery operations. In plastisol compounds based on 25—50 phr ester plasticizer, the addition of 5-10 phr of a hydrocarbon diluent will lead to low and stable viscosity. Particular grades should reflect a flash point consistent with safe operations. The rate of evaporation of course decreases with increasing flash point, but the efficiency of solvent recovery increases. 

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