Supercritical fluid processes

Abstract

A process for the preparation of toner additive wax particles which comprises the micronization of said particles from a supercritical solution.

Description

This invention is generally directed to processes, and more specifically, the present invention relates to processes for the preparation of small, and submicron particles, for example wherein small is from about 0.001 to about 4 microns, or submicron of from about 0.05 to about 1.0 micron in average particle diameter, wherein undesirable solvents can be avoided, and wherein a supercritical fluid or compressed liquid, such as carbon dioxide, ethane, propane, butane, isobutane, pentane, chlorodifluoromethane or trifluoromethane is selected as the solvent. The present invention in embodiments relates to a process for the preparation of submicron particles, such as toner wax particles, which comprises the micronization and spraying of these particles from a supercritical solution. Of importance with respect to the present invention is the generation of dry wax particles comprised of small, or submicron ultrafine particle sizes and which particles are not believed to be presently availab...

AI Technical Summary

Benefits of technology

Another object of the present invention resides in the provision of simple processes for the preparation of submicron toner additives.

After the wax / material to be precipitated has dissolved, it is applied to the expansion chamber sufficient to maintain the temperature at or above the critical temperature of the solution being fed, for example from about 30.degree. C. to about 500.degree. C. A valve from the source of the solvent that is at a higher, for example from about 35 to about 805 bar, pressure than the vessel pressure is then opened to initiate fluid flow through the precipitation orifice. Upon establishment of a steady flow pattern, a valve V1 to the vessel is opened and valve V2 is subsequently closed. This pressurization of the expansion chamber prior to flow from the pressure vessel is selected primarily to prevent precipitation of wax upstream of the expansion nozzle and subsequent plugging of the orifice. The precipitated wax product is then collected via a downstream filtration device.

Problems solved by technology

Few polymers are soluble in carbon dioxide, and are, therefore, not suitable for RESS in carbon dioxide.

However, many fluoropolymers, including, poly(1,1,2,2-tetrahydroperfluorodecylacrylate), and silicones exhibit substantive solubility.

An additional difficulty is that, unless the material to be granulated can be fed to the vessel continuously under pressure, the solution conditions change as the expansion across the nozzle depletes the material inside.

This change in pressure can cause premature precipitation of the material being granulated inside the vessel, and the orifice can plug as a result.

Additionally, the energy savings of heating the expansion nozzle alone to above the critical temperature and not the entire vessel can be substantial.

One difficulty with this process that arises is adhesion of the toner to the fuser and not the paper, a phenomenon known as hot offset.

Many waxes, however, are not thermodynamically miscible with toner resins.

Therefore, the dispersion of wax is not uniform throughout an individual toner particle, nor is the weight fraction of wax in the toner uniformly distributed among the toner particles.

One drawback to the use of compatibilizer, however, is that the propensity of the wax to flow to the interfacial area is reduced.