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Achieving bubble-free mixing

Peter Swanson, managing director of Intertronics, explains the benefits of planetary centrifugal mixers and whether an atmospheric or vacuum type mixer is needed.

There are many industrial processes which require fast mixing of liquids, pastes and powders, and where the uniformity and homogeneity of these mixes is vital.  These include adhesives, inks, cosmetics, pharma-ceuticals, sealants, LED phosphors, nanoparticles, dental materials and more. Planetary centrifugal mixers can be suitable when working with materials that are difficult to mix — such as liquids or pastes with differing viscosities, or powders which are difficult to wet. Moreover, avoiding or removing entrapped air is often very important.

Planetary centrifugal mixers can mix, disperse and degas materials in seconds to minutes, in the user’s own product container. The planetary mixing action combines rotation and revolution ― the material container rotates at a 45-degree angle while it revolves in a set radius. The technology results in a fast, fully homogenous mix and, unlike machines which rely on the insertion of paddles or impellers into the material, no air is introduced; in fact, there is a tendency for any entrapped air to be removed.

The mixers are suitable for materials with very low viscosity to very high viscosity ― from water-like up to 100 million centipoise. Manufacturers use this type of equipment for small to large amounts of many materials, including silicones, conductive pastes, chemical materials and more.

Thinky planetary mixers have two standard modes, “mixing” and “defoaming”. In mixing mode the materials are under an acceleration of up to 400G, which results in a very fast uniform mix, even of substances of very different viscosities. The defoaming or degassing mode imparts a more centrifugal type force onto the materials, for dedicated air removal. This is normally followed by another period of mixing mode to recombine the materials evenly.

Planetary centrifugal mixers can bring numerous benefits to manufacturers. Because the process does not have to use dedicated containers and is non-contact (there are no mechanical stirrers in the materials), cleaning requirements are much reduced and the risk of cross-contamination is minimal. 

Precise and repeatable control of the process makes it possible to improve formulation quality, eliminate human error and reduce variations that occur due to operator skill. It is effective in controlling shear, so as not to damage your materials — unlike the use of rollers, mixing blades or propellers.

Choose your type

The combined mixing and degassing modes of the standard Thinky mixers, which operate under ambient pressure, will usually mix materials so that there is no visible sign of bubbles.

In applications where even micro-bubbles (perhaps on the order of 100μm diameter) cannot be tolerated, manufacturers may want to consider a mixer with an integral vacuum to achieve more thorough degassing. Mixing under vacuum will ensure that there is no air entrapment, even of very small bubbles. Highly viscous materials are more readily degassed under vacuum. Users of specialist optical materials or potting compounds for very high voltage applications cannot accept micro-bubbles in their critical projects. The use of a vacuum mixer will often preclude the need for a separate vacuum degassing process.

Case in point

One example of a company using a vacuum mixer is LED manufacturer Plessey Semiconductors, which transitioned from manufacturing development to full production by employing automated mixing and dispensing technologies. The company opted for a Thinky ARV-310 LED benchtop mixer to remove air while homogenously mixing heavy fillers into liquids, including phosphor.

Mixing is required for a broad range of applications and materials, but each one requires a carefully considered approach. By working with an experienced adhesives supplier, you can select the most appropriate equipment for your process.

 

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