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What is the CTP plate ?
Aug 29, 2017

What is the CTP plate.png

CTP plate means Computer-to-plate (CTP) is an imaging technology used in modern printing processes. In this technology, an image created in a Desktop Publishing (DTP) application is output directly to a printing plate.


This compares with the older technology, computer-to-film (CTF), where the computer file is output onto a photographic film. This film is then used to make a printing plate, in a similar manner to a contact proof in darkroom photography.



CTP methods differ according to the construction type of the imagesetter and the light source used to expose the plate surface. In terms of construction type there are three different kinds: internal drum, external drum and flat-bed imagesetters. The two main light sources used to expose the plate are ultraviolet light lamps and laser diodes. The wavelength and energy of the laser diodes depend on the type of plate that is used. This technology is mainly used in newspaper and magazine printing.


Internal drum imagesetters

In an internal drum image setter the plate is put into a cylinder, while the imaging head moves along the axis of the cylinder to expose the plate. The rotating mirror at the end of the imaging head rotates around its axis to beam the laser on the desired part of the fixed plate. The construction type makes it more difficult to use several lasers at the same time, but just using one laser also has advantages such as uniform beam intensity over the whole plate.


External drum image setters

The plate is wrapped around a drum that can rotate around its axis, while the imaging head that projects the image on the plate can move along this axis to focus the laser beam on the surface. The simple construction type makes it possible to arrange multiple image heads next to each other and use them simultaneously. This leads to a decrease of the imaging time needed to expose a whole printing plate.


Flat-bed image setters

The image is reproduced line by line on a fixed flat printing plate by a laser beam that is deflected by a rotating polygon mirror and then onto the printing plate. Because of the setup the laser beam becomes less accurate at the edges of the printing plate and is therefore mainly smaller formats or production with lower quality expectations.


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