High Speed Dispersion of Titanium Dioxide
Titanium dioxide (TiO2) is chemically inert and has exceptional opacity and whiteness. These properties have led to its widespread use in many industries.
Titanium dioxide is most commonly supplied in powder form but may also be predispersed in oil or aqueous systems. The diversity of applications leads to many different methods of processing, however process requirements are basically the same:
- TiO2 is usually supplied in powdered/premicronised form and particle size reduction (grinding) is not applicable in most cases.
- To maximise opacity and gloss properties, TiO2 must be fully dispersed and evenly distributed throughout the product.
- Dust/solvent emissions must be minimised.
The following problems can be encountered when using conventional mixers and agitators:
- On addition to the water, solvent, varnish or other media the particles tend to re-agglomerate.
- Conventional mixers cannot break these down effectively.
- Long mixing cycles are required to obtain uniform dispersion.
- Extended processing time contributes to solvent emissions.
- Powder has to be added under controlled conditions which can be time consuming and leads to increased dust emissions.
The high speed, high shear operation of a Silverson mixer provides the solution to these problems.
The rotor/stator workhead rapidly disperses the TiO2 particles into the surrounding liquid, leading to a more uniform product and shorter processing times.
This can be achieved using a batch mixer immersed in the processing vessel, or by the addition of a Silverson In-Line mixer to an existing process in a recirculation system as illustrated.
- The TiO2 is added to the aqueous or organic solvent at a much faster rate, reducing dust emissions.
- The rotor/stator workhead provides an intense shearing action capable of breaking down even hard agglomerates.
- Operation can be carried out in a closed system, reducing solvent emissions.
- A Silverson mixer is more energy efficient and economical.
- The shorter processing times required to obtain a uniform dispersion reduce wear and therefore downtime and maintenance costs.
The batch size, formulation, type of ingredients and the viscosity of the end product dictate which machine from the Silverson product range is best suited to individual processing requirements.
High Shear Batch Mixers
- Suitable for batch sizes up to 1000 litres
- Can be used on mobile floor stands
- Sealed units available to control solvent/dust emissions
High Shear In-Line Mixers
- Ideal for larger batches
- Aeration free
- Easily retrofitted to existing plant
- Can be used to discharge vessel
- Multistage units available
- Ideal for larger batches
- Capable of rapidly incorporating large volumes of powder
- Minimised aeration
- Minimised cleaning requirements
- Suitable for higher viscosity mixes
- Suitable for operation at higher temperatures
- Minimum operator input required
- Capable of rapidly incorporating large volumes of powders
- Excellent in-tank movement, even when processing high viscosity mixes
- The design is suitable for applications from aggressive chemical service to the most demanding hygienic standards and requirements
- Easy to clean - designed for Cleaning-In-Place
- Low maintenance - single-piece mixing head with no wearing parts or bushes
- Can be used in conjunction with a Silverson In-Line mixer where intense high shear is required