What is the effect of the shape and structure of the pigment in the paint?
What is the effect of the shape and structure of the pigment in the paint?
With the development of industry and the improvement of living standards, pigments are more and more applied to the paint industry, in order to give objects better performance. The coating is mainly composed of film-forming substances, pigments and fillers, additives and solvents. It is widely used in our daily life. The coating can not only maintain the coated articles, but also decorate and give some special functional effects to the coated articles.
Pigments are different from dyes. They are usually insoluble in the medium used. In most cases, they exist in the form of aggregates. If the aggregates of the pigment structure persist in stability, then the coloring power, covering power and chromaticity of the pigment will be improved. If the pigment is not well dispersed, it may produce many defects, such as flocculation, loss of light, color deviation, floating color, blooming, deposition and other problems.
The structure of the pigment and the effect when the pigment is loose:
1. Shape and particle size of pigment
Most pigments are used in paints in the condition of being made into suspension, and the particle size distribution of pigments is generally from 0.05 μ M to 1 mm, but it has been indicated that when the particle size of the pigment is between 0.05 and 0.50 μ M, it has better coloring power, gloss, covering power and weather resistance.
The smallest particle formed in the process of pigment manufacturing is called the original particle. It exists in the form of a single crystal or a group of crystals, and the particle size is very small. The clumps formed by the surface and surface structure between the original particles are called aggregates. The aggregates are relatively close. It is difficult for the general dispersing equipment to disperse them into the original particles.
The original particles and aggregates are combined by van der Waals force to form larger pigment granular agglomerates, which are called agglomerates. The agglomerate particles are in contact with each other by points, edges and corners. The effect force between particles is small, and can be dispersed into original particles or aggregates by mechanical force.
In order to achieve the desired original particle suspension after dispersion, at least the suspension between the aggregate and the original particle, but the trend of the system is to recover from the high-energy state to the low-energy state, so the pigment with fine particle distribution is easy to gather into a floccule. In terms of structure, the floc is similar to the agglomerate, but the color in the floc is resin solution rather than air. The existence of dispersant will prevent or slow down the formation of flocculation.
2. Dispersion process of pigment
The dispersion process of pigment is divided into three steps: moisture, dispersion and stability. In the wet process, the air and water vapor on the surface of the pigment are replaced by the resin solution, and the solid and gas phases are converted into solid and liquid phases. In particular, low-molecular type moisture dispersant can accelerate the moisture process.
In the process of laxity, relying mainly on the effect of mechanical energy, the gathering state of pigment is broken into smaller particles, becoming laxity. The third step is the process of stability. The dispersant is used to maintain the stability of the dispersion of the pigment, prevent uncontrolled flocculation, and promote the suspension to achieve stability according to the variety and molecular structure of the adhesive adsorbed on the surface of the pigment. The dispersant, especially the polymer dispersant, plays a great role in the stability of pigment particles.