Pigment Volume Concentration (PVC)
Variations in the ratio of binder to pigment volume significantly affects the final product.
Pigment volume concentration (PVC) is a number that represents the volume of pigment compared to the volume of all solids. PVC = Volume of Pigment/Volume of all Solids. This is expressed as a ratio of pigment to binder. For example, if a coating has a PVC of 30, then 30% of the total binder/pigment blend is pigment, and 70% is binder solids. (see fig. 2)
A high PVC paint could be defined as one at 50 PVC or higher. A high PVC paint (more pigment, less binder) would be flat in finish, generally less adhesive, and likely more porous.
A low PVC paint (less pigment, more binder) is expected to be glossier, more adhesive, and less porous. Technically, the PVC is called the “Critical PVC” or “CPVC” when the pigment and binder blend begin to create air interfaces or voids that increase porosity.
Levels of Pigmentation
As stated above, the point at which there is just enough binder to wet pigment particles is called the critical pigment volume concentration (CPVC). Pigment particles are entirely surrounded by binder below CPVC, and are not above CPVC. As pigment volume concentration increases above CPVC, void space and porosity increase while tensile properties decrease.
A film below the CPVC has excess resin and may exhibit a smooth surface that specularly reflects light (i.e. gloss paint); this light is perceived as gloss. Above the CPVC there is less vehicle present, and if the pigment particles protrude through the surface and the surface roughness increases, the light that is diffusely reflected will not be perceived as gloss and the paint will be a semi-gloss. When the volume of pigment is increased sufficiently, scattering also increases due to greater volume of air/pigment interfaces, and the paint appears flatter.
From fig. (3), you can see that both blistering and gloss decrease as CPVC is reached. Permeability, however, increases as CPVC is reached. Above CPVC, voids in the paint are filled by air and the paint becomes discontinuous. Other properties that rise and fall above and below CPVC are tensile strength, scrub resistance, enamel holdout, rusting, and contrast ratio.
CPVC can be calculated using the equation below:
||QA x p
OA = oil absorption value: grams of oil to wet
100 grams of pigment. It can either be determined experimentally
(ASTM D 281), or obtained from literature.
p = Density (g/ml)
CPVC (when several pigments are incorporated) = (V1 x CPVC1) + (V2 x CPVC2) + (V3 x CPVC3) + (V4 x CPVC4) + (Vn x CPVCn)