#### Introduction

In Part I of this article, expert Jochum Beetsma discussed the definition of PVC, including examples of PVC calculations and the PVC of various types of coatings. In Part II, we will discuss Critical Pigment Volume Concentration (CPVC), pigment oil absorption (OA), and the impact that pigment shape and density have on coatings properties.

#### Critical Pigment Volume Concentration

As the PVC increases, many properties of a coating change abruptly. These changes occur at the CPVC. CPVC can be defined as the point at which there is just sufficient binder to provide a completely absorbed layer on the pigment surface as well as all the interstitial spaces between the pigment particles in a close-packed system.

#### Diagram of Paint at CPVC

The CPVC for a pigment combination can be calculated from the oil absorption (OA) provided that the OA value is based on a non-flocculated dispersion. OA is expressed as grams of linseed oil per 100 grams of pigment. **ρ** is the density of the pigment(s), and 93.5 is 100 times the density of linseed oil (EU). Both OA and CPVC are expressed as percentages and not as fractions. The definitions of both OA and CPVC are based on close-packed pigment-binder with just sufficient binder to absorb at the pigment’s surface and fill all the interstices between the pigment particles. An example of the calculation of CPVC of a white alkyd (EU) finish using rutile titanium dioxide (EU) with an oil absorption value of 20 (# of grams of linseed oil/100 grams of pigment) and a pigment density of 4.2 g/cc follows: As the pigment density and/or the OA increases, the CPVC decreases. Above the CPVC, air voids are present (film density decreases) and below the CPVC, the pigment particles are separated. The dramatic and abrupt change in the behavior of paint that occurs when passing through the CPVC can be used to determine the CPVC. The abrupt changes in properties include: physical (adhesion, tensile strength/elongation and paint density), durability (resistance to moisture, rust, moisture penetration, blistering, wet adhesion, stain resistance), and appearance (hiding, gloss, tint strength). Other factors that effect water and oxygen permeation include particle shape and particle size. Pigment particles vary in size and shape. Some of the terms used to describe pigment particle structure in increasing order that they depart from sphericity to an increasing degree are as follows: Pigments with platelet shaped particles can reduce permeability especially if they are aligned parallel to the coating surface. Mica (EU), micaceous iron oxide (EU) and metal flakes (EU) are a few examples of such pigments. The smaller the average pigment particle size, the more resistant pigments are to dense packing. For example, the dense packing factor for fine (precipitated) calcium carbonate (EU) is on the order of half that of coarser calcium carbonate. The surface area of a unit weight of pigment varies inversely with the particle diameter. This relationship is especially true for most pigment particles that do not vary greatly in shape from a sphere, nodule or rectangle. Thus, for a given weight of pigment particles, halving the diameter doubles the surface area, and the greater the surface area for a given pigment, the greater the vehicle demands.

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Please provide a copy of Part #1 of this FINE informative presentation

We are glad you enjoyed the article. Here is the link to the Part 1. https://knowledge.ulprospector.com/832/pc-pigment-volume-concentration-1/

Excelent presentation, I expect to read II part.

It is possible calculate pigment density in a mixture of 2 or more pigments, but can you tell me how calculate OA (absortion oil) in a mixture of 2 or more pigments?

Dear Pilar,

The OA of a blend of two or more pigments can be calculated using the following equation:

OA = Mass of oil in grams/total mass of pigment X 100

So if the mass of a blend of two pigments is 100 and it requires 50 grams of oil (normally linseed oil) is absorbed, the OA is = 50

Thank you for reply. I suppose that you refer that it is necessary to measure experimentally the OA of pigments blend and then use the equation.

But my question is if there is some way of calculating OA of pigments blend theoretically. I have understood that it is possible to calculate OA of a blend theoretically by as following equation: OAblend= 1/∑xi / OAi; xi= weight fraction (over 1) of pigment i in blend; OAi= OA pigment i.

But I do not know how this equation is obtained and if the result is the same that Ronald’s equation.

i asked that PVC and CPVC for alkyd binder only or for all resin such as epoxy resin

Muchas gracias por compartir la información y lograr así formarnos en la formulación correcta de pinturas. Excelente presentación

Yes this is very simple suppose you want to calculate OA of blend of three pigments

1) Titanium Di oxide

2) Chrome pigment

3) Oxide pigments

Suppose the % age of these three pigment in you product formula is given by

Titanium Di oxide =50%

Chrome pigment =30%

Oxide pigments =20%

Take 10 gram of pigment blend according to individual pigment %age

Titanium =10*50% =5 gms

Chrome pigment =10*30% =3 gms

Oxide Pigment =10*20% =2 gms

Total pigment blend =10 gms

Now take this 10 gms pigments blend and obtain its oil absorption through linseed oil absorption method

Suppose 10 gram pigment mix takes 20 gms linseed oil

Then the oil absorption of the pigment blend per 100 gms will be

20*10=100

i hope you will understand

What if it is a mixture of Titanium and Aluminium paste? how to calculate OA since Aluminium does not have an OA value?

Dir sir

thank you for this article, it is very useful for the producers and chemists, I have a question for oil absorption. how I know that the pigment absorbs the oil and stopped at the limited point that no absorb above it, by notice or something else ??