Guide to the use of water-based inorganic pigment dispersants: Accurately control the key elements of addition

In the coating, ink, ceramic and other industries, water-based inorganic pigment dispersants are key additives to achieve uniform dispersion of pigments and improve product performance. However, if used improperly, not only can its advantages not be brought into play, but it may also affect product quality. From the precise calculation of the amount added to the choice of the timing and method of addition, every link is very important.

1. Scientifically determine the amount added: the golden ratio to meet the needs

The amount of water-based inorganic pigment dispersants added is not a fixed value. It is necessary to comprehensively consider factors such as pigment type, particle size, and system characteristics to achieve the best dispersion effect. Generally speaking, the amount added fluctuates between **0.5% - 5%** of the pigment weight.

Different types of pigments have obvious differences in the demand for dispersants. For example, due to the surface properties of iron oxide pigments, the addition amount is usually 1% - 3%; while for nano-sized titanium dioxide pigments with extremely small particle size and large specific surface area, in order to ensure that each particle can be effectively coated and dispersed, the addition amount may need to be increased to 3% - 5%. In addition, the formulation of the coating or ink system will also affect the addition amount. If the system contains more surfactants, the dispersant may need to be appropriately increased to avoid interference caused by competitive adsorption.

In actual production, the optimal addition amount is often determined by experiments. Using the gradient addition method, multiple experimental groups with different addition amounts are set up to compare and observe the fineness, stability, fluidity and other indicators of the pigment after dispersion. For example, when preparing exterior wall paint, paint samples with addition amounts of 1%, 2%, and 3% can be configured respectively, the pigment particle fineness can be measured by a scraper fineness meter, and its sedimentation stability can be evaluated by the static observation method. Finally, the addition amount with the best performance is selected as the production standard.

2. Grasp the timing of addition: key steps determine the dispersion effect

The timing of adding water-based inorganic pigment dispersants directly affects their dispersion efficiency and final product performance. There are mainly two ways of adding in the pre-dispersion stage and adding in the grinding stage.

Adding in the pre-dispersion stage is to pre-mix the dispersant with the pigment and water to form a uniform pigment slurry. This method is suitable for most conventional production scenarios. It can make the dispersant fully adsorbed on the surface of the pigment particles and reduce the agglomeration force between the pigment particles in advance. Taking ink production as an example, the water-based inorganic pigment dispersant and the pigment are first stirred and mixed at a low speed in a mixing barrel for 15-20 minutes to allow the dispersant to initially wet the pigment particles, and then other additives and resins are added. After subsequent grinding treatment, a uniformly dispersed ink system can be obtained.

For some special pigments or products with extremely high dispersion requirements, it is more suitable to add dispersants during the grinding stage. For example, when preparing high-gloss and high-transparency automotive topcoats, dispersants are slowly added in batches during the grinding process of a sand mill or a ball mill. In this way, under the mechanical force of grinding, the dispersant can be promoted to penetrate deeper into the pigment aggregates, further open the agglomerated pigment particles, and achieve a finer dispersion effect.

It should be noted that no matter when you choose to add it, you should avoid premature contact between the dispersant and other substances in the system that may produce chemical reactions to prevent flocculation, precipitation and other undesirable phenomena, which will affect the dispersion effect and product quality.

3. Select the addition method: Accurate operation of the adaptation process

The selection of the addition method needs to be combined with the production equipment and process characteristics. Common addition methods include direct addition, dilution and batch addition.

Direct addition is suitable for laboratory tests or small production scales with strong equipment stirring capacity. Pour the calculated dispersant directly into the reactor or mixing barrel, turn on the stirring equipment, and use the shear force generated by high-speed stirring to quickly mix the dispersant with the pigment and other materials. However, in this method, it should be noted that the addition speed should not be too fast to avoid excessive concentration of the dispersant in local areas and the formation of agglomeration.

Addition after dilution is to dilute the dispersant with an appropriate amount of water into a solution of a certain concentration, and then slowly add it to the system. This method can effectively avoid the problem of excessive local concentration of the dispersant, especially for large-scale production equipment or products with extremely high requirements for dispersion uniformity. For example, when producing architectural coatings, dilute the water-based inorganic pigment dispersant into a 10% - 20% aqueous solution, inject it into the stirring kettle at a constant speed through a metering pump, and keep the stirring equipment running stably to ensure that the dispersant is evenly dispersed in the entire system.

Batch addition is often used to deal with difficult-to-disperse pigments or processes with special requirements for the dispersion process. First, add some dispersants for preliminary dispersion. After the system reaches a certain uniformity, add the remaining dispersants to continue dispersing. For example, when preparing ceramic glazes, for some metal oxide pigments with unstable color, 60% of the dispersant can be added for pre-dispersion. After 10-15 minutes of stirring, the remaining 40% of the dispersant is added, and the ball mill is used to grind for 3-4 hours to finally obtain a glaze with stable dispersion and uniform color.

The correct use of water-based inorganic pigment dispersants is a technology that requires the combination of theory and practice. From accurately determining the amount of addition to grasping the appropriate time and method of addition, each link is closely related. With the continuous development of production processes and the emergence of new materials, the use method also needs to keep pace with the times.