High-Performance Charging Unit for Liquid Electrophotographic Presses

The HP Indigo presses dominate the commercial printing market with more than 50% market share using Liquid Electrophotography technology with superb print quality, high productivity and wide paper gamut. The new HP Indigo 7000 Digital Press introduced in Drupa08 runs at a marking speed of 2.15 m/s and places about three quarter of a billion dots on the paper per second. The new press incorporates many breakthrough improvements, including a new charging system featuring a charge roller. This unique charge roller unit is the first such technology used in a production digital press and supports by far the highest process speed of any offset-quality electrophotographic press. The single charge roller replaces the three scorotron units used in the previous generation Series II presses with improved charging uniformity and reduced cost per page. The charge roller is also much easier to maintain and is a "green" solution with minimal ozone generation. In this paper we discuss the multiple challenges that had to be overcome to meet or exceed the initial charge roller unit design objectives. This includes a useful life of over a half million impressions, which is far longer than other charge rollers.