Pigment Paste Preparation-Effect of Pigment Specific Surface Area on Dispersant Selection

In the dispersion preparation of pigment paste, it will be found that the amount of dispersant added for organic pigments is higher than that of inorganic pigments. The specific surface area of organic pigments is several times that of inorganic pigments, or even higher. Some people may say that carbon black is an inorganic pigment. In fact, carbon black has always been considered an organic pigment in color paste preparation. When testing dispersants for organic pigments, carbon black is often tested as a reference.

 

Pigments exist in aggregate form, thus reducing the aggregate surface area. This is also a process of transition to a lower energy state. The function of the dispersant is to prevent this aggregation by forming an adsorption layer on the surface of the pigment.

 

Some people would think that the longer the pigment paste grinding time, the better the fineness of the pigment paste. In fact, this idea is wrong. Because grinding destroys aggregates, the dispersant is adsorbed on the pigment surface. When the aggregates are completely destroyed to the original particle size, no matter how long the grinding time is, it is a waste of resources. The adsorption of dispersant on the pigment surface becomes the physical basis of the dispersion process.

 

The larger the specific surface area of the pigment, the more dispersant is required. The smaller the particle size of the pigment, the greater the specific surface area. High-pigment carbon black has a very large specific surface area. so it’s why the amount of dispersant added for organic pigments and carbon black is several times that of inorganic pigments.

 

A good dispersant, even one that is chemically neutral, can disperse all types of carbon black. There are also titanium dioxide and inorganic pigment dispersants, and practice has proven that acidic groups are not necessarily necessary. Neutral dispersants can still disperse pigments well, and can also avoid the side effects of acidic groups on coating films. In actual preparation, pigments are regarded as inert particles, and their particle size and specific surface area are mainly considered. In this way, a good pigment paste product can be prepared.

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