Overview of pigment additives and introduction of their performance (2)

5. Deposition

In extreme cases, deposition is also referred to as agglomeration, meaning that solids (usually pigments) or some of the solids in the coating are separated from the coating base and land on the bottom of the container. When the situation is not serious, these deposits are easily agitated and re-dispersed in the base material. This is called "mild deposition"; if it is difficult to redistribute, it is called "caking". To improve these conditions, some thickeners may be added, of which aluminum stearate is the most commonly used.

6. Crusting and drying

When the coating is exposed to air, it forms a layer of skin on the surface, which is usually due to drying, ie oxidation and polymerization. The most effective way to eliminate this phenomenon is to add antioxidants, commonly called anti-skinning agents. In contrast to crusting, which is dry, in fact, some coating systems that do not require desiccants can be dried by evaporation, such as spray paint and many grout coatings. The drying process is oxidation or polymerization, or both, and usually requires the addition of a desiccant, typically a metallic soap. There is a 1,10-phenanthroline containing no soap, but they are very effective on their own and are often used with cobalt and manganese soap desiccants. Metal ions of the metal soap may be cobalt, calcium, manganese, lead, iron, and zirconium, and naphthenic acids and high-oil fatty acids are important acids used to react with metals to form soaps. These soaps must be soluble in oil to act as a desiccant.

Cobalt soaps are the most powerful desiccants in paints. They mainly accelerate the oxidation of the film and have little effect on the polymerization. Lead is not an effective oxidation catalyst, but it is a very good catalyst for accelerating the polymerization of thin films. So cobalt and lead add up to produce a completely dry film. Calcium desiccants are almost non-toxic, so cobalt and calcium can be used to make non-toxic desiccants and cobalt-lead desiccants cannot be used.

7. Aging is lost

The so-called "aging loss" refers to the fact that the paint is dried very well during the initial manufacturing but is aged in the container after storage and loses its drying rate. This loss process can be very slow, sometimes over several months or more, but sometimes it may take only two to three weeks to lose dryness.

In pigments such as carbon black, Persian blue, titanium dioxide, certain organic reds, and other pigments, the initial drying conditions are satisfactory, but after a few weeks or months the drying properties are lost, making the original 4 hours dry. Coatings are not dry even for more than 4 days. To eliminate this problem, so-called "desiccant absorption" methods can be used, based on the principle that these pigments tend to absorb desiccants. However, when the coating contains a certain concentration of non-reactive metal, the absorption of the desiccant by the pigment is suppressed, and the reason for this is still unclear. A suitable lead compound is one of the effective desiccants that slowly dissolves in the coating and simultaneously releases lead.

8. Foaming phenomenon

Foaming or foaming generally occurs in water-based paints, but this is also a serious problem in certain solvent-based paints, especially during the final processing stage of the process. The so-called foaming means that stable foaming bubbles generate air bubbles at the air-liquid interface due to agitation, absorption of air, boiling, and other reasons. Defoaming sometimes takes several days or even several months. After the paint is made, it can be saved in the paint pot for 2~3 days to solve this problem, but this will seriously affect the production plan of the factory. Low-viscosity coatings will reduce foaming, and elevated temperatures will also help remove blisters. However, the most practical method is to use defoamers. Defoamers have the effect of lowering the surface tension and can quickly eliminate foam in the paint.

9. Grinding of pigments

In addition to the bead mills, the pigments are milled with little or no particle size, but rather the particles are agglomerated and separated into smaller pieces, ideally as a single particle, which is easily wetted by the binder.

The coating base wetting the pigment is to destroy the adhesion between the pigment particles and help the base material to wet each single particle, so that the pigment and the base material are in close contact with each other, and the adhesion between the pigment particles is reduced at the same time. Avoid forming agglomerates again. Additives can improve the grinding properties, improve the wetting characteristics of the base material, and make the original poorly wetted base material become a base material with excellent wettability. These additives can also increase the amount of pigment added, thereby increasing the yield.