Platesetters

Platesetters are imaging devices used in offset printing prepress to expose printing plates directly from digital data. They form the image on plates by writing with a laser according to a digital file, enabling computer-to-plate workflows that bypass traditional film-based platemaking. The plates are typically aluminum with a photosensitive emulsion or a polymer substrate, and the output is controlled by a RIP that converts page descriptions into raster data for the plate.

Exposed plates then undergo a processing sequence appropriate to the plate type. Traditional photosensitive plates require chemical development, rinsing, drying, and gumming or baking before mounting on a press. Some modern plates are processless or require minimal processing, relying on press conditions to complete imaging. Platesetters can be integrated with loading and unloading systems and support for multiple plate sizes and thicknesses.

Technologies include thermal platesetters and violet/blue diode platesetters, each designed for specific plate chemistries. Thermal platesetters use a thermal laser to expose heat-sensitive emulsions and tend to offer high resolution and imaging stability but require compatible thermally activated plates. Violet or blue diode platesetters use visible light to expose violet-type plates, often at lower cost and with different performance characteristics. Infrared and other variants exist, each aligning with specific plate chemistry and processing requirements.

History and context: CtP systems emerged in the 1990s and 2000s, largely replacing film-based workflows in commercial, packaging, and newspaper prepress. They reduced makeready times, eliminated film costs, and lowered chemical usage, while requiring investment in compatible plates and maintenance.

Today platesetters remain a standard component of many offset prepress systems, supporting automated workflows and consistent plate imaging, though some segments experiment with hybrid or digital inkjet alternatives.