Surfactants in the manufacture of paint materials

It was shown earlier in [192] that liquid suspensions of natural chalk with a mean particle size of about 50 pm at a content of 70 - 75% in water can be obtained using additives of nonionic and ionic surfactants of a certain structure. Without surfactant additives, the suspension becomes non-liquid at a chalk content of 50-55%. The experimental data on the effect of surfactants on the electrokinetic potential of chalk particles in suspension indicate a substantial role of the electrostatic factor in securing the liquefying action of anionic additives. 

Kaolin and alumina suspensions are also, in some cases, included in water paint formulations. It has been shown in [193] that a maximum shear yield stress is observed with AKP-30 alumina suspensions of a mean primary particle diameter of ca. 0.3 pm at pH 9, independent of the particle volume fraction between 0.2 - 0.3. For kaolin suspensions, the maximum shear yield stress is observed at pH 6 independent of the solid volume fraction. A direct correlation with the electrokinetic potential is observed. Thus, the pair-wise particle interaction is due to the electrostatic interaction which allows to control the stability of these suspensions. 

The t -potential and the surface charge of pigment particles in a polymer solution has a direct effect on the suspension stability [194]. Ultra-fine pigment particles ( 0.05 pm) were formed during dispersion, which both adsorb on larger pigment particles and are included in the latex structure. Here, a steric factor increases the sedimentation stability of the suspensions additionally. 

The effect of the surface tension on the quality of coatings is studied in [200]. When a coating is applied to a curved substrate, surface tension gradients are produced in the comers as result of diffusion of water-soluble surfactants. Hence, the coating thickness reduces at the circumference and increases in the centre. It is shown that an optimum surfactant concentration as well as an optimum method of coating application are important. 

The dispersion stability can be increased due to thickeners added, e.g. ethoxylated urethanes, which are able to form associates with the film forming latex [201]. At the same time, the dispersion contains a certain amount of surfactants these is free surfactant present in the latex, and added surfactant to disperse pigments and fillers. Stability is achieved by varying interaction with the two dispersed phases - latex particles associated with the thickener, and pigment particles. 

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