The actual process of breaking agglomerates (i.e., dispersion) occurs in three steps during the grinding process:
1. Wetting,
where air & other substances are displaced from the TiO2 surface by solvent,
dispersant & alkyd resin.
2. Grinding, in which the agglomerates of TiO2 particles are broken and separated
into an optimum particle distribution.
3. Stabilization, by which the optimally separated TiO2 particles are maintained
by either charge or steric stabilization.
Wetting agents will promote Steps 1 & 2 but do little to stabilize the separation of the TiO2 particles. Dispersants will promote Steps 1 & 2 and stabilize the separation of the TiO2 particles.
The dispersion of TiO2 in solvent-based alkyd resin depends on shear rate, mill base viscosity, mixing time, and degree of wetting provided by the vehicle. The alkyd resin is the sole wetting agent. A dispersant, formulated specifically for alkyd resins and solvent systems (such as Lorama LDA100 and LDA150 Polymeric Dispersants), is required for stabilization of the dispersed TiO2 particles. It is important to recognize that both the amount and the type of dispersant affect dispersion quality. Excess dispersant is self-defeating, particularly with ionic types, and should be avoided. The optimum amount varies with the particular dispersant used and the pigment.
Wetting Agents vs. Dispersants
Guidelines for modifying alkyd Enamels with LPRT
Methods of Lorama Polysaccharide Resin Technology Modification
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