Most coatings consist of a binder matrix filled with solid particles, being pigments and/or fillers. The particles must be dispersed, stabilized and distributed in the paint. During film formation, when the wet paint transforms into a dry coating, the particles should stay uniformly distributed in the system.
Pigment Volume Concentration
The properties of a coating are governed by, amongst others, the loading of the system with solid particles. Some coatings contain a high amount of solid particles and other coatings, like clear coats, are free of particles. Particle loading is quantified by the Pigment Volume Concentration (PVC) of the system. The PVC of a system is defined as the volume percentage of solid particles in the system after film formation:
Vp : total volume of all pigments in the system.
Vf : total volume of all fillers in the system.
Vb : volume of the non-volatile part of the binders in the system.
Definition of Pigment Volume Concentration
The definition implies that the PVC of a system is calculated by leaving the volatile components, like water and solvents, out. The volumes of the non-volatile components should be used, implying that the weights of the solids must be transferred into volumes by using the density of each of the components.
A system of high PVC has a high loading and a system of low PVC contains a low amount of particles:
For the ease of calculation we forget about the additives. The total volume of solid particles in 100 grams of this system can be calculated by dividing the weight of TiO2, 25.20 grams, by its density. This gives: Vp = 6.00 cm3. The paint does not contain filler: Vf = 0.
Now we have to calculate the non-volatile part of the binder. We know the following:
- The alkyd resin is dissolved in organic solvent, de-aromated white spirit D-40, having a density of 0.80 g/cm3.
- We must use the non-volatile part of the binder in the PVC calculation.
- The density of the alkyd solution is 1.00 g/cm3; this is not the density of the alkyd resin.
The 54.67 grams of alkyd solution contains 32.80 grams of alkyd resin and 21.87 grams of D-40. From the density of D-40, it follows that the alkyd solution contains 27.34 cm3 of solvent. The rest of the volume of the alkyd solution is the non-volatile alkyd resin: Vb = 27.33 cm3. From this analysis it follows that the density of the alkyd resin is 1.20 g/cm3.
By inserting the volume of the solid particles and the volume of the non-volatile part of the binder in the equation, it follows that the PVC of this system is 18.0%.
To learn more about Pigment Volume Concentration, read “Effect of Pigment Volume Concentration on Coatings Properties – Part II” by expert Ron Lewarchik.
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