Reliable high performance drop generator for an inkjet printhead

Abstract

An inkjet drop ejection system comprises a combination of printhead components and ink, mutually tuned to maximize operating characteristics of the printhead and print quality and dry time of the ink. Use of a short shelf (distance from ink source to ink firing element), on the order of 55 microns, provides a very high speed refill. However, it is a characteristic of high speed refill that it has a tendency for being overdamped. To provide the requisite damping, the ink should have a viscosity greater than about 2 cp. In this way, the ink and architecture work together to provide a tuned system that enables stable operation at high frequencies. One advantage of the combination of a pigment and a dispersant in the ink is the resultant higher viscosity provided. The high speed would be of little value if the ink did not have a fast enough rate of drying. This is accomplished by the addition of alcohols or alcohol(s) and surfactant(s) to the ink. Fast dry times are achieved with a combination of alcohols, such as isopropyl alcohol with a 4 or 5 carbon alcohol or with iso-propyl alcohol plus surfactant(s). One preferred embodiment of a short shelf (90 to 130 microns), ink viscosity of about 3 cp, and surface tension of about 54 provides a high speed drop generator capable of operating at about 12 KHz. Reducing the shelf length to about 55 microns, in combination with rotating the substrate at an angle to the scan direction, permits maximum drop generator operation as high as about 20 KHz. As a consequence of employing pigment-based inks, high optical densities are realized, along with excellent permanence (no fade and better waterfastness), and good stability. The combination of preferred ink and pen architecture provides good drop generator stability.