Role Of Pigments In Morphological Structure Of Coatings
Pigment is increasingly being used in the paint industry to give items a better presentation, says pigment orange 16 manufacturer. Paint is mainly composed of film-forming substances, pigments, auxiliaries and solvents, which are widely used in our daily life.
Unlike dyes, pigments are usually insoluble in the medium they are used in, and in most cases exist in the form of aggregates. If the aggregates of the pigment structure remain stable, the pigment’s coloring power, hiding power and chromaticity are improved. If the pigment is not well dispersed, many defects may occur, such as: flocculation, loss of light, color shift, floating color, blooming, precipitation and other problems.
The structure of pigment, and the role of pigment dispersion
Morphology and particle size of pigment
Most of the pigments are made into suspension and used in paints. The particle size of pigments is generally distributed from 0.05 μm to 1 mm, but some researches show that when the particle size of pigments is between 0.05 ~ 0.50 μm, they have better coloring power, gloss, covering power and weather resistance.
The smallest particle formed in the process of pigment manufacturing is called the original particle, which exists in the form of single crystal or a group of crystals with very small particle size. The agglomerates formed between the primitive particles by surface-to-surface bonding are called aggregates, which are relatively compact and difficult to be dispersed into primitive particles by general dispersing equipments.
The original particles and aggregates are combined together by van der Waals force, and the larger pigment granular clumps formed are called agglomerates. The particles of the agglomerates are in contact with each other by points, edges and corners, and the inter-particle force is small, which can be dispersed into the original particles or aggregates by the force of machinery.
To achieve the ideal state of suspension of original particles after pigment dispersion, at least the suspension between aggregates and original particles, but the tendency of the system is to recover from high-energy state to low-energy state, so the pigments distributed by microfine particles can be easily aggregated into flocculent. Structurally, flocs are very similar to agglomerates, but the color in the floc is a resin solution rather than air. The presence of dispersant will prevent or slow down the occurrence of flocculation.
Dispersion process of pigment
The dispersion process of pigment is divided into three steps: wetting, dispersion and stabilization.
In the process of wetting, the air and water on the surface of pigment are replaced by resin solution, and the solid and gas phases are converted into solid and liquid phases. Especially the low molecular wetting and dispersing agent can speed up the wetting process.
In the process of dispersion, mainly relying on mechanical energy, the agglomerate state of pigment is broken into smaller particles and becomes dispersed state.
The third step is the process of stabilization, the dispersant is used to keep the pigment dispersed state stable, to prevent uncontrolled flocculation, and according to the type of binder adsorbed on the surface of the pigment and the molecular structure, to promote the suspension to obtain a stable state. The dispersant, especially the polymer dispersant, plays a great role in the stabilization of pigment particles.