01 January 2013
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Microcapsules in adhesive dispensing

These days, microcapsules appear in almost every industrial sector, where they take numerous roles.

However, dispensing these fragile materials can be a problem since clearly it is important that the microcapsules be undamaged by the dispensing process. In adhesive technology, microcapsules can fulfil several functions. For example, microcapsules may be an integral part of the control of reaction and curing processes. Some anaerobic threadlocking adhesives contain microcapsules.

After applying the adhesive to a screw, the action of screwing it into a thread bursts the capsules, releasing active materials which initiate the cure. The handling, application and dosing of these materials can present some big challenges. The material feed and dispensing onto the substrate must occur without any shear stress to prevent damage to the microcapsules.

Piston pumps may not be appropriate if they induce high pressure or pulsation which can harm the microcapsules. Gear pumps might not work either, because of the geometry involving physical interaction with the gears and high shear forces. An ideal dosing system must impart no shear stress on the material, and be highly precise.

Intertronics has introduced endless-piston technology from German company ViscoTec. The positive displacement, volumetric dispensing pumps will dispense or dose independent of input pressure, material viscosity and ambient temperature. The special geometry of the stator and rotor configuration works as a progressive cavity pump.

The rotor seals against the stator, forming a series of spaces or pockets, which translate along as the rotor rotates, keeping their form and volume. The pumped material is moved inside the pockets. In addition, the pockets are shaped such that they taper and overlap; the output is continuous, even and pulse free. Therefore it is possible to dose very shear sensitive and delicate materials without damaging them.

Paul Gay

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