Achieving bubble-free mixing

There are many industrial processes in the pharmaceutical industry that require the fast mixing of liquids, pastes and powders, during which blend uniformity and homogeneity is vital

Here, Peter Swanson, Managing Director of adhesives specialist Intertronics, explains the benefits of planetary centrifugal mixers and whether an atmospheric or vacuum type mixer is needed.

Planetary centrifugal mixers play an important role when working with materials that are difficult to mix — such as liquids or pastes with differing viscosities, or powders that 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 as the material container rotates at a 45° angle while it revolves in a set radius.

The technology results in a fast, fully homogenous mix and, unlike machines that 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 to very high viscosities ― 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.

Mixing it up

Peter Swanson

“Our Thinky planetary mixers, for example, have two standard modes: mixing and defoaming. In mixing mode, the materials are under an acceleration of up to 400 G, which results in a very fast uniform mix, even with 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,” says Peter.

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 owing to operator skill. “It’s also an effective way to control shear,” says Peter, preventing material damage — unlike the use of rollers, mixing blades or propellers.”

Choose your type

“The combined mixing and degassing modes of our standard Thinky mixers, which operate under ambient pressure, will usually mix materials so that there is no visible sign of bubbles,” adds Peter. In applications in which even microbubbles (100 μm in 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 microbubbles in their critical projects. The use of a vacuum mixer will often preclude the need for a separate vacuum degassing process.

In conclusion, Peter comments: “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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