The best dispersant dosage for aqueous pigment paste

The optimum dispersant concentration (ODC) is usually expressed as the amount of dispersant required per unit mass of pigment. The larger the surface area per unit volume of pigment, the higher the ODC. ODC is also related to the type of dispersant: Dispersant is a simple surfactant. Small molecule? Low molecular polymer? Or resin? In addition, the technical literature indicates that the ODCs of different dispersants will change, but they belong to the same species.

The latest publication called polymer dispersants "high molecular weight" (HMW), and other low molecular weight dispersants are called "traditional" dispersants. The exact molecular weight of commercial HMW dispersants is patented, and the literature focuses on the differences in the relative molecular mass of HMW dispersants and conventional dispersants.

Colored pigments can be directly dispersed into the paint, or they can be made into color paste before use for coloring the paint. The focus of this paper is on the preparation of colorants by dispersing colored pigments.

Pigment dispersion

Pigment dispersion is a process in which pigment aggregates (adsorbed from pigment particles) are broken up into individual pigment particles, wetting all surfaces of the pigment and keeping the pigment particles in separate states.

Dispersing pigment aggregates requires the use of equipment similar to ball mills, small media mills and high speed dispersers. Separating the pigment particles and separating the gas and liquid adsorbed on the surface of the pigment will produce a new pigment surface. Pigment wetting is achieved by the dispersant and the solvent adhering to the surface of the exposed pigment. The dispersant maintains the separation distance between the two pigment particles with a minimum safe distance between the two pigment particles. Usually, the distance is -10 nm when the dispersant is the resin, and -5 nm when the dispersant is the surfactant. When the distance between the pigment particles is less than the minimum safe distance, the cohesive force will cause the particles to aggregate and eventually flocculate. Flocculation results in significant changes in the properties of the pigments such as color strength, gloss and viscosity.

Dispersants maintain pigment dispersion by two mechanisms: electrostatic shielding stabilization and steric hindrance. Under electrostatic shield stabilization, each pigment particle surrounds a double layer of ionic charge. For example, a pigment first adsorbs anions [-] and then is surrounded by a cation [+] layer. When the two pigment particles are close to each other, the Coulomb repulsion force predominates, thereby changing their running trajectory to avoid closer. Static shielding requires polar solvents such as water. Water ionization is H 3 O + and OH − , which can replace conjugated ions, allowing cation [+]/anion [-] to dissociate. Under steric hindrance, a large number of dispersant chains acts as a barrier against close contact between the pigment particles. As the chains mix with each other, the osmotic pressure increases, driving the solvent between the chains. The steric hindrance mechanism can play a role in polar (such as water) and non-polar (such as petroleum ether) solvents.

Source: Ink Information