Paint is coated on the surface of the object to be protected or decorated, and can form a continuous film firmly attached to the object to be coated, its role is mainly four points: protection, decoration, masking the defects of the product and other special role to enhance the value of the product. The reason why there is such an important role, which is inseparable from the additives in the coating, today we will learn about the wetting and dispersing agent in the coating.
I. Principle of action.
1. In a mechanical way, the most basic purpose of dispersing pigments in the medium is to disperse the oleophilic cohesive particles that result from drying in the pigment manufacturing process. When the particle fineness becomes smaller, the exposed surface area increases and enhances the optical properties of the pigment, such as: coloring performance, gloss, brightness, covering power or transparency.
2. In general dispersant grinding systems, such as inks and coatings, resin is one of the components in the formulation, however, resin and dispersant will compete with each other in pigments. The adsorption ability of the dispersant on the surface of the pigment will also be affected by the resin, and the resin and the dispersant will compete with each other for the opportunity to adsorb on the surface of the pigment. But the difference between dispersant and resin is the fastness of dispersant adsorption on pigment surface, dispersant not only has extremely strong adsorption power on pigment, but also has good affinity to solvent. Resin on the surface of pigment, in reality, only plays a wetting role, it does not dip in the surface of pigment for a long time, after time, resin will slowly leave the surface of pigment and lead to flocculation, though, the presence of resin still hinders the anchoring of dispersant on the surface of pigment. Therefore, when choosing the resin, the film-forming function brought by the resin should be examined, and it is not necessary to choose another good wetting or grinding resin. In addition, the resin content in the grinding base material should be considered sufficient to maintain the stability of the formula.
3. The use of dispersant in the grinding base, compared with the traditional grinding base, the most critical adjustment of its formulation is the concentration of resin solution. The concentration of resin in traditional grinding media is high, and the amount of pigment that can be filled is low. Although reducing the resin concentration can make the viscosity of the dispersion medium itself lower and the pigment filling amount can be increased, such a dispersion system is not stable and cannot be used in actual production. If a good dispersant is used, the dispersion system can be stabilized at a lower resin concentration, thus the pigment filling in the grinding base material can be greatly improved. The space barrier created by the solventized chain of the dispersant in the medium reduces the suction between the particles and greatly reduces the grinding viscosity, which is one of the reasons why the pigment filling can be improved. Under the action of dispersant, the increase of pigment filling amount varies with different dispersing systems, but in the adjustment process, the grinding base material should be kept with moderate viscosity.
Second, the use method and dosage.
The dosage of wetting and dispersing agent should be determined according to the dispersed pigment, and the best dosage is based on the formation of a dense single-molecule adsorption layer on the surface of the pigment. If the dosage is too small, the dispersant cannot show its advantages, and too much dosage will affect the stability of grinding. This is mainly due to the fact that the overcrowded wetting dispersant on the pigment surface cannot fully stretch out the solventized chains of the dispersant, and in addition a large amount of free dispersant will have a negative impact on the coating film.
In the actual operation process, we can calculate the approximate amount of dispersant according to the theoretical rules, and then use it as the midpoint to float up and down, and observe the change of performance indexes such as viscosity, film gloss and coloring power of the dispersed system with the amount of dispersant, when the amount of dispersant is moderate, the viscosity of the dispersed system has obvious minimal value while the gloss and coloring power of the film has great value.