CTP Platemaking: Thermal, Violet and the Digital Plate
What CTP is
Computer-to-plate exposes the printing plate directly from the digital file, skipping film entirely. The RIP sends a raster straight to a platesetter, a laser writes the image on the coated plate, and the plate goes to press. It is the standard prepress step for offset and letterpress plate production.
Thermal CTP
Thermal systems use an infrared laser. The energy either ablates a surface layer or triggers a thermal polymerisation of the image area, and the plate is then processed. Thermal plates are prized for robustness and long run length, with strong latitude on press and resistance to handling, which is why thermal dominates high-volume and large-format work.
- Infrared laser; ablative or thermal-polymer plates
- Strong run length and press robustness
- Common for high-volume and very-large-format (VLF) plates
Violet and UV CTP
Violet systems use a visible laser and photosensitive plates, typically imaging faster and with lower energy, and a visible-light path is easier to service. They suit high-throughput daily-news and commercial work where speed and turnaround matter most.
- Visible-laser, fast imaging, easier handling
- Strong fit for high-volume commercial and newspaper
- Tighter ambient-light discipline in the plate room
Plate chemistry and the chemistry-free trend
Plates come in negative and positive formulations, and the clear direction is toward chemistry-free and low-chemistry processing to cut waste and simplify the plate room. Processless plates go from imager to press with minimal or no wet step, which is increasingly the default for shops chasing lower operating cost and simpler compliance.
The CTP workflow
The digital chain is RIP to raster, expose on the platesetter, process and gum, then mount. Because there is no film, registration and repeatability improve and makeready drops; the bottleneck moves from the contact step to plate handling and press setup.
- RIP and imposition to raster
- Platesetter exposes the coated plate
- Processor or chemistry-free step, then press
Choosing thermal versus violet
Let run length and turnaround decide. Long runs, large formats and maximum robustness point to thermal; maximum imaging speed and high daily throughput point to violet; and if operating cost and compliance lead, weigh a chemistry-free or processless plate regardless of laser type.
McLantis in the plate room
McLantis thermal CTP platesetters are engineered for stability from commercial formats up to very-large-format plates, sharing the precision-motion and optical platform that also underpins its LDI and computer-to-screen lines — so a prepress team can standardise on one imaging philosophy across plate, screen and direct printing.