How to disperse a matting agent?

While staying on the topic of matting agents they can be divided into two groups: (i) stir in products, and (ii) products that have to be dispersed together with pigments and fillers. In regards to the second group handing is not difficult. It is a matter of dispersing a sufficient quantity of the agent in combination with pigments and fillers using the right equipment (high speed dissolver, pearl mill, etc...).

Figure 1 :

The dispersion of stir in matting agents based on silicas, waxes or organic products can be done in three different ways: via concentrates (masterbatch); directly during the production process of paints; or at the end of the paint production process in order to adjust the matt degree according the user’s request.

There are positive and negative aspects related to masterbatch production. The positive is the very easy handling of the concentrates, and also that they can be incorporated using stirrers at a low agitation speed. The negatives are, firstly, that the matting agent content of the concentrates are usually not high, and secondly, the stability of the matting-pastes can be reduced during storage due to evaporation of the solvents from the concentrate surface. This causes a build-up of semi-dry lumps, which are difficult to disperse in the final paint. Finally, if the paste contains resin it cannot be used universally.

Incorporation during the production process of the paints is a common method way of adding matting agents. Fluffy products should be incorporated in a low viscosity binder solution, via a stirrer or dissolver. Most matting agents are designed for an easy dispersion process. For example, dispersing with a pearl mill will result in a greater reduction of the particle size, which leads to a higher level of gloss, and therefore higher dosings of matting agents are necessary to adjust the required matt degree. To adjust the final matt degree through the incorporation of matting agents, it requires stir in products which can be easily dispersed using a simple stirrer. It is necessary, however, to ensure that there is enough space in the vessel so that the matting agent can be poured on the top and the vessel can be closed in order to avoid dust.

Periphery speed m/sec

Speed per min-1 Diameter dissolver disc mm Circumference mm 1000 1500 2000 2500 5000 Periphery speed m/sec 30 94 1.5 2,4 3,1 3,9 7,9 40 126 2,1 3,1 4,2 5,2 10,5 60 189 3,1 4,7 6,3 7,9 15,7 80 251 4,2 6,3 8,4 10,5 20,9 100 314 5,2 7,9 10,5 13,1 26,2

How to control the quality of matting agents dispersion?

When we use fillers as matting agents it is advisable to measure Grindometer or Hegmann value in order to receive information about the dispersing degree. Second, we can control the gloss degree at an angle of 60°.

For the other above mentioned product groups the main parameter should be the control of gloss behavior. However, in order to get an extensive understanding about the matt degree of the paint it is necessary to take measurements at angles of 60° and 85°. Sometimes here Grindometer values can be determined, too. As long as there is no rule that is comparable with common paint systems, it is to accept. Values higher than 25 microns are usual e.g. by using silica-matting agents. If we reduce this Grindometer value we will also reduce the matt effect and increase the gloss. Viscosity and transparency (for clear, sensitive applications) should be compared to a standard.