VMA-GETZMANN - innovator of laboratory & pilot plant dispersing

BYK-Gardner, the sole representative of VMA-Getzmann in North America, supplies rotor stators, rotor-stators, high shear mixers, laboratory dispersers and pigment disperser technology for laboratories and pilot plants.

Pigment dispersing takes fine solid particles and mechanically dissolves them into a liquid vehicle. The mixing dispersing process requires sufficient energy to breakdown the pigment agglomerates and aggregates to their primary particle size. High shear milling blades are commonly used to disperse inorganic pigments used in paint formulations. For organic pigment dispersions the use of grinding media or ball milling is necessary.

Grinding media can consist of steel shot, glass beads, and a variety of ceramic materials. The diameter size is important to the final dispersion result. Typically the smaller the bead diameter the finer the particle size grind result.

The dispersion results are directly related to the amount of mechanical power transferred from the disperser/mixer to the mill base. The greater the mechanical power the finer the dispersion result in a faster period of time. The disperser’s motor horse-power rating is not the only factor in assessing the mechanical power. The motor’s torque and shaft speed are also important parameters.

The Dispersion process has three fundamental steps: Wetting out the pigment particles using an additive or appropriate resin system Applying shear force energy to breakdown the agglomerated or aggregated particles to their primary particle size Stabilizing the dispersed particle to prevent flocculation

Dispersion Equipment

There are two broad classes of dispersion equipment available. One class uses impeller blades or rotor-stator assembly rotating at high speeds to achieve the shear force energy. The rotational speed should be greater than 2,000 revolutions per minute (rpm) for laboratory size dispersers. The tip speed or peripheral speed of the impeller blade should be optimized between 3500 to 5000 feet/minute. The tip speed depends upon the diameter of the impeller blade and the rotational speed. The best dispersion results are obtained by achieving a “doughnut” flow pattern. This pattern is illustrated in the website video. The doughnut flow is indicative of the proper flow of the mill base onto the impeller blade edges. This class of equipment will be described as high shear mixers, dispersers, vertical dissolvers, rotor-stators, and Cowles mixers.

The second class of dispersion equipment uses media grinding material. The grinding media is moved by an agitator that causes collisions and friction of the media. The pigment particles get caught between the media causing them to breakdown. The amount of media used by volume is 50% to 80% of the mill base volume. The high concentration of grinding media in a confined space creates billion of collisions to occur. This constant bombardment can breakdown the most difficult agglomerated organic pigments. The most common dispersion equipment is the horizontal bead mill. The mill consists of a chamber with an internal agitator. The chamber is filled up to 80% of grinding media. The mill base is introduced into the chamber when the agitator is rotating between 500 to 6,000 rpms. Most horizontal bead mills will allow for multiple passes of the material through the milling chamber. A second milling system, the basket-mill is becoming a popular media disperser. The grinding media is contained in a basket shaped chamber. The basket-mill is lowered into a container of mill base. The basket-mill uses an impeller below the basket chamber to circulate the mill base into the basket. There is a sieve filter at the bottom of the basket to separate the media from the mill base. The mill base is circulated multiple times through the basket-mill until the final dispersion result is achieved.

BYK-Gardner has represented the VMA-Getzmann laboratory dispersers for more than 25 years in North America. The Dispermat product line offers the most comprehensive and flexible choices on the market. From the small bench top dissolvers to the floor mounted basket-milling systems are available. Based on the mill base volume, viscosity, and material type, the proper Dispermat is selected. For applications that need high shear mixing to media grinding the Dispermat line has accessory selections to perform both dispersing functions on one instrument.

How to Select the Appropriate Disperser Some questions you need to answer when selecting a disperser are “Does my application require a disperser or mixer?”, “What is the particle size needed for the application?” and “What size Dispermat is required?” Find out more about how to select the correct disperser and some other considerations. More Info ››

Application Notes Learn more about the use of the High-Shear Dispermat in combination with basket-mill technology. Review the process of the pre-dispersion followed by media grinding dispersion. There are applications for inks and coatings. More Info ››