Dispersion resins plastisol viscosity

Another very important property of plasticizers for PVC resins is the ability to act as a dispersing medium for polyvinyl chloride plastisols. The performance of the particular plasticizer in a plastisol application depends to a great extent on a property known as its viscosity stability. The stability of the plastisol to viscosity build up is the manifestation of the solvating effects of the plasticizer, and thus, those materials with higher solvating efficiency tend to display an increase in plastisol viscosity on standing. Figure 3 is the plot of the viscosity stability of PVC o-phthalate ester plastisol compositions and, in essence, compares the alcohol-derived plasticizers with that of the olefin-derived plasticizer. The data show that... 

Extender resin or filler polymer—a PVC grade of spherical form, made by the suspension process and therefore cheaper than dispersion resin, which is used to reduce cost and viscosity of the plastisol (43,44). 

Air Reiease The air release properties of a dispersion PVC resin are governed by both the formulation and the surface coating on the plastisol resin. Air release is facilitated by low plastisol viscosity at low shear rates and a reduced surface tension. Coatings on the dispersion resin particle siuface can have a significant effect on viscosity and surface tension, as can other additives. Resin particle size can also play a role in air release, with larger particle sizes yielding improved air release. 

Generally, as the level of a given surface coating increases on the resin particle surface, the plastisol viscosity decreases. Small resin particles with a narrow uni-modal particle size distribution will also yield higher viscosities than will resin particles with a broad unimodal or multimodal distribution. This is one of the reasons that larger-particle-size blending resins are often used in conjunction with smaller-particle-size dispersion resins to reduce plastisol viscosity. 

As the plasticizer levels of a plastisol formulation decrease, the resulting viscosity of the plastisol will increase. Higher levels of surfactant on the dispersion resin will normally help to reduce the viscosity of plastisol formulations containing low levels of plasticizer. Another common practice to reduce plastisol viscosity is the use of blending resins. 

If all the resin particles are the same size, the plasticizer must occupy the free volume between the resin particles as well as coat the resin particles in order to permit fiow. If smaller resin particles are able to occupy much of this free volume instead of the plasticizer, more plasticizer is available to coat the resin particles and aid in flow. Through the use of blending resins, one creates a multimodal particle size distribution, which in turn helps to reduce plastisol viscosity. Depending on the particle size distributions of the blending and dispersion resins, there will be an optimum ratio of blending resin to dispersion resin to yield a minimum viscosity. In most resin systems, the ratio of dispersion resin to blending resin fliat yields the minimum viscosity typically ranges between 30 70 and 70 30. ... 

The pastes used are plastisols—finely divided polymer dispersed in plasticizer. They are mobile mixtures which may range in viscosity from liquids that can be poured readily to thick pastes—the viscosity depending essentially on the type of resin and the amount and type of plasticizer involved. Such mixtures can be applied to substrates by coating or by techniques akin to printing after application they are converted into homogeneous flexible vinyls by heating to temperatures in the range 175 to 200 °C, when the dispersed particles of resin dissolve in the plasticizer and are fused into a continuous structure.1... 

ISO 3219. 1993 (75], covers polyester resins as liquids, emulsions, or dispersions using a rotational viscometer, coaxial cylinder viscometer, and cone and plate system. ISO 2555 (76] refers to the Bookfield viscometer. ASTM D1824 [77] covers the use of this instrument for the measurement of apparent viscosity of plastisols and organisols at low shear rates. For high shear rates. ASTM D1823 (78] describes a method using a Burrell Severs A-120 viscometer. ISO 1628 (79] covers determinations of viscosity number and limiting viscosity for PVC, polyolefins, polycarbonate, thermoplastic polyester, and methyl methacrylate polymers, in parts 2 to 6 respectively. 

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. 

Uses Wetting agent, dye solvent, wax plasticizer, stabilizerfor textile, household, and cosmetic appiics., iipsticK rewetting dried skins secondary plasticizer, lubricant, and processing aid for vinyl resins grinding medium for pigment dispersions Features Recommended for low viscosity and non-exudation in PVC plastisols ... 

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