Paint rheology

Optimizing Latex Paint Rheology with Associative Thickeners... 

Anwari Schwab Latex Paint Rheology b- Associative Thickeners 529... 

Modifying Latex Paint Rheology Through Blending... 

Anwari Schwab Latex Paint Rheology 6- Associative Thickeners 531... 

Problems with Blending. The principle of this approach to optimizing paint rheology is that two paints with the same Stormer viscosity will produce blends with the same Stormer viscosity. In practice, this result does not always occur. For example, a 50/50 HEUR/organoclay-thickened paint made from base paints at 100 KU each may have a Stormer viscosity of only 90 KU. This result often occurs when one of the base paints is very thixotropic. Also, a paint blend may have poorer flow and leveling than either of the base paints. Poor flow indicates that some flocculation may occur during the blending process. 

NW, Pigment Volume Content, and Latex. Pigment volume content (PVC) and latex type and grade are important for optimizing dry film properties. Percent NW is usually governed by the desired cost of the final product. The formulator usually does not use these variables to optimize paint rheology but should be aware of how they affect thickener efficiency. 

The basic formulating procedure to optimize latex paint rheology is as follows. 

If clear-liquid separation occurs, a third highly thixotropic, shear-thinning thickener can be incrementally blended in to determine the minimum amount required to stop the separation. Only small quantities of the third thickener should be used or the optimized paint rheology may change. 

Paint rheology may also be changed by varying other formulation ingredients however, possible changes in other paint properties may result. 

Two transient methods can be applied to study paint rheology [49] (i) Stress relaxation after sudden application of strain, (ii) Strain relaxation after sudden application of stress (creep measurements). In the stress relaxation case, a constant strain y is applied within a very short period (that must be much smaller than the relaxation time of the sample) and the stress a is followed immediately as a function of time. For a viscoelastic liquid (that is the case with many paint systems), the stress decreases exponentially with time t and reaches zero at infinite time. If the stress is divided by the applied constant strain, one obtains the stress relaxation modulus G(t) which is related to the instantaneous modulus by the following expression. 

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