EXTRUSION PROCESS FOR TONERS WITH IMMISCIBLE, LOW AND HIGH VISCOSITY COMPONENTS
Original Publication Date: 1991-Feb-28
Included in the Prior Art Database: 2004-Apr-05
Xerox Disclosure Journal
An extrusion process for the preparation of xerographic toners with both immiscible low and high viscosity components is disclosed. Certain xerographic toners may contain intermediate molecular weight, linear polymers, low molecular weight waxes, and a high molecular weight cross-linked polymer. In combination, these materials may be immiscible and difficult to disperse with an extruder. Core dispersion of the cross-linked resin or wax can cause copy quality or other subsystem problems. Typically, when mixing xerographic toner materials of different viscosities, it is more difficult to mix the higher viscosity material in the formulation if it is the minor component. For example, in a toner formulation containing about 60% of a resin of intermediate viscosity, that is, with a low melt flow index of 29 g/10 min at 150°C and 2.16 kg, and about 20% of a cross-linked polymer with a higher viscosity, for example, 15 - 40% gel, melt flow index of less than 1 g/10 min at 150°C and 2.16 kg, and about 5% by weight wax with a low viscosity, for example, 40 cp at 188°C. If the initial mixing does not involve the wax component, then a superior dispersion of the two aforementioned polymers are achieved. Thus, a pre-blend feed to the melt extruder should not contain the wax component into the first kneading blocks. The wax component is fed into the extruder subsequently to the first kneading blocks, where it can be mixed with the polymer-blend of intermediate viscosity. It is known in the art that increasing the temperature of extrusion improves the blending of polymers of mixed viscosities and that decreasing the temperature improves the blending of a wax component with polymeric materials. Additionally, fines or other toner reclaim can be fed into the extruder at the same time as the wax component is mixed to help disperse it macroscopically and to maintain lower temperatures. Such a dispersion process results in improved dispersion of components and improved copy quality and subsystem performance.