What is the role of the morphological structure of pigments in coatings

With the development of industry and the improvement of living standards, pigments are more and more applied to the coating industry to give objects better performance. Coatings are mainly composed of film-forming substances, pigments and fillers, additives and solvents, and are widely used in our daily life. Coatings cannot protect the coated items, but can also decorate and impart some special functions to the coated items. . Pigment manufacturers

Pigments, unlike dyes, are usually insoluble in the medium used, and in most cases exist as aggregates. If the aggregates of the pigment structure remain stable, the tinting strength, hiding power, and chroma of the pigment are improved. If the pigment is not dispersed well, many defects may occur, such as: flocculation, loss of light, color shift, floating color, blooming, precipitation and other problems.

The structure of the pigment, and the role it plays when it is dispersed:

1. Pigment shape and particle size

Most pigments are used in coatings in a state of suspension. The particle size distribution of pigments is generally between 0.05 μm and 1 mm, but studies have shown that when the particle size of pigments is between 0.05 and 0.50 μm It has better tinting strength, gloss, hiding power and weather resistance.

The Z-small particles formed in the process of pigment manufacturing are called primary particles, which exist in the form of single crystals or a group of crystals with very small particle size. The agglomerates formed by the surface-to-surface connection between the original particles are called aggregates, and the aggregates are relatively compact, and it is difficult for general dispersing equipment to disperse them into original particles.

The original particles and aggregates are combined by van der Waals force, and the larger pigment granular agglomerates are formed, which are called agglomerates. It is dispersed into primary particles or aggregates by mechanical force.

In order to achieve the ideal state of the original particle suspension after the pigment is dispersed, at least the suspension between the aggregates and the original particles, but the trend of the system is to recover from the state to the state, so the pigments with fine particle distribution are easy to aggregate into flocs . Structurally, flocs are very similar to agglomerates, but the color in the flocs is the resin solution instead of air. The presence of dispersants will prevent or slow down the occurrence of flocculation.

2. Pigment dispersion process

The dispersion process of pigments is divided into three steps: wetting, dispersion and stabilization. During the wetting process, the air and water vapor on the pigment surface are replaced by the resin solution, and the solid and gas phases are converted into solid and liquid phases. In particular, low molecular weight wetting and dispersing additives can speed up the wetting process.

During the dispersion process, mainly relying on the action of mechanical energy, the agglomerated state of the pigment is broken into smaller particles and becomes a dispersed state. The third step is the stabilization process. The dispersant is used to maintain the stability of the dispersed state of the pigment, prevent uncontrolled flocculation, and promote the suspension to obtain a stable state according to the type and molecular structure of the binder adsorbed on the surface of the pigment. Dispersants, especially polymer dispersants, play a significant role in the stabilization of pigment particles.