Thermal ink jet printer with droplet ejection by bubble collapse

Claim 1

An ink jet printhead for use in a thermal ink jet printer to direct ink droplets on demand toward a movable recording medium comprising: an ink manifold for holding and maintaining a layer of ink having a predetermined thickness, the manifold having an elongated opening therein which confronts the recording medium and is spaced therefrom a predetermined distance, the width of the manifold opening being a dimension which causes a meniscus to be formed therein by the ink so that weeping of ink therefrom is prevented; a linear array of heating elements being formed on an internal surface of the manifold opposite the manifold opening, the heating element array being parallel to and aligned with said manifold opening; electrode means for directing current pulses to each individual heating element; means for selectively energizing each heating element by addressing the electrode means with current pulses of predetermined duration representative of digitized data signals, so that the ink contacting the heating elements is momentarily vaporized to form a vapor bubble; and upon collapse of each bubble, a fluid velocity in the ink layer is directed toward the heating elements and, through conservation of momentum, a quantity of ink is directed away from and in a direction substantially perpendicular to the heating element with a velocity sufficiently large to overcome the ink surface tension at the meniscus in the manifold opening, so that the quantity of ink is ejected therethrough as a droplet propelled toward the recording medium.