Computer to Plate

The term Computer to Plate (CTP ) or German Digital printing plate exposure (DDB ) is a procedure in the pre-press, in which the printing plates are imaged directly from the PC in the platesetter. CTP also still referred to at the time (2009) in the early development located Exposure technology computer -to-press, in which the printing page contents are sent directly to the pressure cylinder so that even any pressure plate change in the printing press is not required.

In contrast to the indirect imaging over conventional film exposure method computer -to-film (CTF ) CTP saves considerable installation and material costs. At the same time can be customized with directly imaged printing plates produce higher quality print results, since the edge definition of the grid points is higher and smaller grid points can be generated. Another advantage of this method is a reduction by various mechanical influences on the printing plate, such as incorrect exposure, dust and scratches. Various platesetters have a so-called online development method that makes a development of the printing plate in an external development machine unnecessary. Thus further degradation mechanisms are limited. The data format usually TIFF G4 is used in the CTP process today.

Technology

CTP is a generic term for a wide range of imaging of offset printing plates. The CTP recorders differ according to their construction in inner drum, outer drum or flatbed platesetter and regarding the used light sources in violet and thermal laser and UV light sources, as well as the plate coating and the development of the exposed plate. Most of the laser light sources are in the range of visible light. This means for each plate material that the processing is done by complementary light. The most agreeable likely to be the processing of thermal plates in daylight, and the creation of violet plates, under yellow safelight.

UV exposure in flatbed

The light of a UV lamp, is directed via an optical system on the pressure plate and projected at every exposure operation rasterized sub-images on the flat-lying plate. The exposure head is guided horizontally and vertically over the plate and sets the partial images together into an overall picture.

Imaging with visible light

The technique of laser exposure with laser diodes has now enforced. This uses either red light diodes in the spectral range 633-670 nm for small-format flatbed scanners or violet diodes in the range of 400 to 410 nm, which are usually used in CTP with internal drums. The photopolymer and Silverhalogenideplates be fixed in a vacuum, and exposed with a single beam with a very fast rotating polygon. The cost of a platesetter with violet diodes are inexpensive relative to other setters relatively low, one reason why assert themselves platesetter with violet diode increasingly on the market.

Thermal imaging

Most common are now the infrared diodes for thermal plates. During the thermal imaging printing plates in a physical change of special thermal plates is generated. Here dissolve polymeric constituents of the coating and are washed in a subsequent development process. In thermal CTP digital thermal plate is clamped onto a rotating outer drum. Is illuminated with multi-beam laser diodes in the spectral range from 830 nm through elaborate design of the external drum, these are more expensive than internal drum. However, the method offers a high degree of process stability on exposure and development. Established on the market still have thermal CTP external-drum design, which today have a market share of over 60 percent.

CTP printing plates

For recorders with violet diode light-sensitive plates are used on silver halide or photopolymer base. Both have proven themselves in exposure systems that work with visible light between 488 nm and 670 nm. Silverhalogenideplates have high resolution capability and allow runs up to 350,000 prints. However, an additional branding to increase the number of copies is not possible. Photopolymer plates have a high process stability and guarantee a circulation of 200,000 impressions. To increase the circulation of up to one million prints and the use of UV inks baking is required. The imaging of the silver halide plates are made in positive functioning by the non-printing areas of the image are imaged while the photopolymer plates work negatively, ie takes place imaging of the printed image parts.

Thermal printing plates are also differentiated by type by negative or positive way of working. When negative process, crosslinking of the polymers in the printed areas of the image that is generated by the high energy of the laser beam. A subsequent heating of the entire plate reinforces the primary networking before the non-crosslinked polymers dissolved in the development process and the aluminum is exposed to the non-printing areas. In the positive mode of operation is due to the high energy of the laser beam is a destruction of the crosslinked polymers in the non-printing areas of the image that will be removed in an alkaline development process. This eliminates the additional heating of the plate. By baking the finished imaged and developed plate is suitable for long runs of one million prints and more. Thermal plates are preferably used in newspaper printing.

The latest printing plate generation, environmentally friendly Ablationsplatten, do not need more development machines. Here plates distinguish between chemical and process-free. In the chemistry-free plates, the exposed layer is drawn off at exposure, the minimum remaining fine dust removed the dampening unit in the printing machine from the disk. The process- free plates come without reworking from the CTP system in the press, where they are stripped when starting up the machine. General Ablationsplatten need a higher power or longer exposure time during imaging. The Ablationsplatten need less dampening and quicker ink-water balance. They have the same resolution and quantity stability, a slightly faster freewheeling behavior than normal printing plates, but are somewhat more sensitive to the treatment.

History of Computer to Plate

The inventor of this technology called Thomas Kälin from the Canton of Schwyz, Switzerland. The pre-press developed in the 1980s and 1990s by the pure analog increasingly digital artwork. At the same time the computing and EBV plants reached a performance that allowed a comprehensive data processing in the precursor. A first step was the use of computer -to-film (CTF ), and thus the output of a full-page, and later full-sheet film. Another condition was the development of thermally -sensitive lithographic printing plate coatings, suitable lasers and laser diodes for illumination, and optical- electronic controls and laser guidance systems that come from the defense.

At the fairs of the printing industry in the respective state of the art is very easy to recognize. Thus, the first CTP was at IPEX 1993, the second largest fair after drupa presented. At drupa 1995, the hundredth CTP system was sold. On the IMPRINTA 1997, there was the news that now the world 600 CTP were used. Drupa 2000, as a special innovation from the violet laser. In early 2001 there were, according to a survey conducted worldwide around 6000 CTP equipment. At drupa 2004, a new generation of CTP systems was presented, which were more efficient, high-quality and even cheaper than their predecessors. At drupa 2008, the eco-friendly Ablationsplatten were presented.