CAB-O-SPERSE® PG series dispersions are specialty fumed metal oxide dispersions designed for use in microporous coatings for inkjet media. The CAB-O-SPERSE PG series dispersions may be used as the main component of a microparticulate coating composition for inkjet media. This type of media includes paper, resin-coated paper (e.g., polyethylene-coated paper) and film (e.g., polyethylene terephthlate, polyester). It may be used in single layer coatings or as part of a multiple coating system to provide fast drying, high image quality and good gloss to inkjet prints.

A typical coating formulation would be made of a CAB-O-SPERSE® PG series dispersion with a binder, such as poly vinyl alcohol, at a dry fumed metal oxide to dry binder ratio of between 3:1 and 10:1. Other water-soluble polymers may also be used as binders. Optionally, other additives, such as dye-fixing agents and optical brighteners, can be used at low concentrations. All additives can be easily mixed with CAB-O-SPERSE PG dispersions by adding water-based solutions or dispersions with low to moderate speed mixing. It is necessary to maintain the pH of the composition at or above neutral to prevent premature coagulation of the silica particles due to loss of electrostatic charge.

The size of the particle in the CAB-O-SPERSE® PG series dispersions are small enough to enable glossy coatings. The actual gloss level attainable from the coating depends on both on the base material that is used and the coating process. Higher gloss products will generally be obtained from film or resin-coated paper coatings rather than similar coatings on paper. Likewise, it is generally known that certain coating processes are capable of providing higher gloss than the same materials used in other coating processes.

The aggregated structure of fumed metal oxide particles enables coatings with relatively high pore volume and fast drying characteristics to be obtained. It is well known, however, that the pore volume decreases as the amount of binder in the formulation increases. The optimum binder concentration for a particular formulation is therefore a balance between maximizing adhesion and coating durability, and minimizing the loss in absorptivity.