The dispersion technology of silica in coatings is a key process, which is directly related to the performance and quality of coatings. The following is a detailed study of the dispersion technology of silica in coatings:

1. Dispersion principle

Silica dispersant is a chemical additive that can improve the dispersion performance of silica particles in liquid media. The basic principle is to reduce the surface tension of silica particles, making them easier to disperse in liquid, thereby improving the stability and uniformity of the entire system. Specifically, silica dispersants usually contain some molecules with special chemical structures, which can be adsorbed on the surface of silica particles to form a stable protective film. This protective film can not only reduce the attraction between particles and prevent particle agglomeration, but also increase the compatibility between particles and liquid media, so that particles can be better dispersed in liquid.

2. Dispersion method

Use dispersant:

Ionic dispersant: adsorbed on the surface of silica through electrostatic action, so that silica particles carry the same charge, thereby generating electrostatic repulsion to prevent particle agglomeration. For example, anionic dispersants such as sodium dodecylbenzene sulfonate have a good dispersing effect on silica in aqueous systems. Cationic dispersants such as hexadecyltrimethylammonium bromide can also be used in certain specific systems, but their scope of use is relatively narrow.

Nonionic dispersants: mainly achieve the dispersion of silica through steric hindrance effect. They form a stable adsorption layer on the surface of silica to prevent the particles from approaching each other. Nonionic dispersants such as polyethylene glycol and sorbitan fatty acid esters are used in a variety of systems.

Polymer dispersants: have a long molecular chain and a special structure, can provide electrostatic repulsion and steric hindrance effects at the same time, and have a more significant dispersing effect on silica.

Surface modification: Silane coupling agent is used to modify the surface of silica. One end of the silane coupling agent molecule can react with the hydroxyl group on the surface of silica, and the other end can combine with the polymer matrix, thereby improving the compatibility of silica with the matrix and improving the dispersibility.

Titanate coupling agent can also be used for surface treatment of silica. It can form chemical bonds with the surface of silica, reduce surface energy, and make it easier to disperse in polymers.

High-speed stirring and grinding:

Using high-speed stirring equipment or grinder to mix silica and matrix materials can increase the dispersion of silica. High-speed stirring can generate strong shear force to break the agglomeration of silica and make it evenly dispersed in the matrix.

For some high-viscosity systems, three-roll grinders and other equipment can be used for grinding to further improve the dispersion effect.

Ultrasonic treatment:

Using the cavitation effect and mechanical vibration of ultrasound, silica can be better dispersed in the matrix. Ultrasonic treatment can destroy the agglomerates of silica and promote its mixing with the matrix.

Batch addition:

During the processing, silica is added to the matrix material in batches instead of all at once. This can reduce the agglomeration of silica and improve the dispersion effect.

3. Dispersion equipment

Different dispersion equipment can be used according to the viscosity of different coating dispersion systems, the volatility of solvents, the production method and the final dispersed particle size, for example:

Kneading type: such as kneading machine, planetary mixer, etc., which are often used for the dispersion of hard pastes with high raw material viscosity and high shear force.

Compression shear type: such as three-roller grinder and double-roller grinder, which are dispersion equipment that exerts a large pressure in the gap between the rollers to generate large shear stress, suitable for materials with high viscosity and high adhesion.

Stirring and mixing type: such as colloid mill, Kady mill, etc., rely on a high peripheral speed agitator to generate high shear speed.

Grinding shear type: such as sand mill and ball mill, which are equipment that disperses by the impact and shear stress of balls or sand (or beads).

4. Dispersion stability mechanism

Generally, the dispersion of carbon black (which can be compared to silica here) in the coating needs to go through the following three processes: carbon black is wetted by the paint, carbon black is dispersed, and carbon black particles are stabilized. Among them, the stabilization of carbon black particles is mainly achieved in the following two ways:

Electrostatic repulsion: stabilize the dispersion. After the carbon black surface adsorbs the dispersant, the potential of the particle surface increases, and it carries the same charge, so the repulsion between the particles increases, making the dispersion stable.

Three-dimensional protection (encapsulation) effect: stabilize the dispersion. Because the resin and dispersant overlap on the surface of the carbon black particles after adsorption, the osmotic pressure of the surface increases and the entropy value decreases, and the repulsion between the particles also increases, making the dispersion stable.

5. Application and Challenges

The application of silica in coatings can significantly improve the stability, fluidity and adhesion of the coating, make the coating more evenly distributed on the surface of the coated object, and improve the covering power and durability of the coating. However, with the enhancement of environmental awareness and the promotion of green production concepts, the environmental performance requirements for silica dispersants are also getting higher and higher. In the future, the research and development of more environmentally friendly, efficient and low-toxic silica dispersants will become an important direction for the development of the industry.

In summary, the dispersion technology of silica in coatings involves many aspects, including dispersion principle, dispersion method, dispersion equipment, dispersion stability mechanism, application and challenges. By continuously optimizing these technologies, the performance and quality of coatings can be further improved to meet market demand.