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Mixing technologies for preparing adhesives

May 5, 2013

The goal of every industry is to produce high quality products in the most efficient way. When preparing adhesives it is all about how the mixing is performed. Recently there are many new technologies that are being used in manufacturing plants. There are new designs to be considered which may be the solution to many of the challenges mixing presents.

Many previously used mixers used a low speed turbine that churned the mixture. They were reliant on the added solvents to soften the polymers. This was a very time consuming process. Making a batch could take anywhere from 12 to 24 hours. Even then there was a problem with dissolving the resin, especially if it was in slab or pellet form. Several hours of mixing was devoted to just dissolving the resin.

To help speed up the process it is recommended that a high shear mixer be used. It uses a rotor containing four blades and rotates at a high speed. Using high shear it mechanically passes them through the stator openings. As the material is being pressed out, more is being pulled in. The substance is circulated through this process as particles become smaller and smaller which makes them dissolve much easier. The high shear mixer is excellent at dissolving solids into liquids and useful to prepare emulsions. Just switching from the traditional low speed mixing system to the high shear machine drastically reduces mixing time as well as saving power.

There are many advantages for using a solids liquids induction system as well. Pressure is used to force ingredients to a high shear zone to be mixed into a liquid stream. One advantage for using the solids liquids induction system for preparing emulsions is that is uses lower temperatures to process. It also provides an increased solids loading capability and works virtually dust free.

If the four bladed mixer is not able to significantly reduce particle size an ultra high shear mixer is advised. There are some issues with these homogenizers that makes them less attractive to lab techs. They can require a lot of general maintenance as well as consume a lot of time to clean up. And switching to this type of mixer can be quite costly initially. However, they are effective at reducing particle size for mixing. Actually they can produce very small particles in just one round.

In general, the solvent and bonding agent work together within the adhesive to provide for proper application. Adhesives which contain high-solids cannot be mixed in traditional mixers. This is when a multi-shaft mixer is used. They have two or three separate agitators which work in tandem. An anchor (low-speed) is used in conjunction with two high shear devices. This process helps to move the product through the device so that heat is transferred evenly.

The multi-shaft mixer is a closed system and offers the options of either vacuum or pressure mixing. Vacuum mixing helps produce a higher density adhesive. It also helps rid the product of voids that agitators can cause. It can also save by reducing other processing such as de-aeration.

Possibly the best choice is a planetary mixer. They far exceed multi-shaft mixers. It moves the batch through the vessel using far different methods than the limited multi-shaft types. It shifts the temperature zone to closer proximity of the disperser. With agitators that rotate and move throughout the vessel it carries the batch away from the walls and does a more thorough job of mixing. Rather than using a solid stream of liquid it starts with the solids and gradually adds the liquids.

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