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Efficacy of dispersant in coatings

Principle of the dispersing process:
1. The most basic purpose of dispersing pigments in the medium is to disperse the oil-friendly condensed particles caused by drying in the process of pigment manufacture. When the particle fineness becomes smaller, its exposed surface area increases and improves the optical properties of pigments, such as coloring properties, gloss, brightness, shading power, or transparency.
2. In general dispersant grinding system, such as ink, paint, resin is one of the components of the formula, but resin and dispersant in the pigment will compete. The adsorption ability of dispersant on pigment surface will also be affected by resin, resin and dispersant will compete with each other to adsorb on pigment surface. However, the difference between dispersant and resin is that dispersant adsorbs pigment surface fastness. Dispersant not only has strong adsorption ability to pigment, but also has good affinity to solvent. The resin actually only plays a wetting role on the pigment surface. It does not stick to the pigment surface for a long time. The resin will slowly leave the pigment surface and cause flocculation. However, the existence of resin still hinders the anchoring of dispersant on the pigment surface. Therefore, in the selection of resin, the film forming function brought by the resin should be considered as well, there is no need to choose another better resin with wetting or grinding ability. In addition, it is necessary to consider whether the resin content in the grinding base material is sufficient enough to maintain the stability of the formula.
3. As for the use of the dispersant in the grinding base, compared with the traditional grinding base,  the concentration of resin solution is the most important when it comes to the adjustment of the formula. The resin concentration in traditional grinding medium is higher and the amount of pigment can be filled less. Although the viscosity of the dispersion medium and the amount of pigment filling can be increased by reducing the resin concentration, the dispersion system is unstable and can not be used in actual production. If a good dispersant is used, the dispersion system can be stabilized at a lower resin concentration, thus greatly increasing the amount of pigment filling in the grinding substrate and reducing the suction between particles by the solvation chain of dispersant in the medium. This is one of the reasons for the increase of pigment filling. Under the action of dispersant, the increase of pigment filling is different with the dispersion system, but in the process of adjustment, the grinding base should be kept with moderate viscosity.
4. There are two mechanisms: electrostatic stability and potential stability when it comes to the stability of pigment dispersion, the two mechanisms must absorb onto the surface of the pigment.

The usage and dosage of dispersant:
The amount of dispersant should be determined according to the dispersed pigment, the optimum dosage is to form a dense monolayer adsorption layer on the surface of the pigment. Too little dispersant can not show its advantages, too much dosage will also affect the stability of grinding. This is mainly because the overcrowded dispersant can not fully extend the solvent chain of the dispersant on the pigment surface, a large number of free dispersants will have a negative effect on the coating film. In the process of practical operation, the approximate amount of dispersant can be calculated according to the theoretical rules, and then floating up and down at the midpoint to observe the relationship between the viscosity, film gloss and coloring power of the dispersion system and the amount of dispersant.

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