5.4 Films and plates recording

5.4.1 General characteristics

Illustrative transparencies were initially output in the recording sections of apparatuses called “color” scanners in accordance with the most important reproduction function which determined their wide use in printing practice [1.3; 1.10].

Later, in the mid-1970s, monochrome electronic devices, such as the Autocon 1000 of ECRM, appeared. They replaced b/w photomechanical reproduction, primarily in newspaper production. Halftones of CT originals were recorded at a given scale with the necessary sharpness and tone correction not only on the film, but also on photo paper. In combination with actively developed by the time the phototypesetting it had facilitated manual stripping of text-picture pages. The image could be positive, which, in contrast to the use of cameras, provided a double saving of expensive film in relation to the most common copying on positively sensitive litho plates [5.23].

As the integration processing of the text and illustrations the electronic phototypesetters and scanner recording sections were replaced by the universal film output device - imagesetter. Scanner in prepress began to be called only the device of image capturing, borrowing for this purpose the term used earlier for the corresponding peripheral device of computer technology. As coming further to computer-to-plate (CtP) concept the term “imagesetter” had, in turn, transformed to “platesetter”.

The main characteristics of recording devices are:

• format and dimensional accuracy of recorded matter;

• resolution;

- performance;

- type of light source used;

- precision stacking of the recorded lines and stability of exposure.

The large format allows for reproducing big-size calendars and posters while for particularly small products (playing cards, labels, postcards, etc.), the image is possible to obtain repeatedly over the entire press sheet. This excludes additional operations, costs and quality losses associated with the images multiplication in special equipment (see Fig. 4.7).

As the growth performance and the functionality of raster processors the large output format allowed for the recording in a press sheet size along with the register marks, test wedges and other proprietary information.

In addition to eliminating manual assembly of mechanicals the electronic imposition freed also from the necessity of scanning the plates prior their installation in the press. Previously, this was done on special auxiliary equipment to obtain information about the ink supply along the print sheet zones of its adjustment. Pre - installation of such adjustment significantly reduces the time and waste of paper in the “print-ready” process. With the electronic imposition, these data are already available in digital files, which structure is consistent in this regard with the parameters of various types of presses in the concept of CIP3 (Computer Integrated Prepress, Press, Postpress).

Speed of recording determines the performance and thus, to a large extent, the profitability of this expensive equipment. Resolution defines the quality of tone and color rendition as well as the available screen frequency. These device parameters and the characteristics of used materials depend in turn on the irradiation source properties.

However, the most characteristic common feature, which largely determines most of the above parameters, is the principle of construction of the output device. In this sense, there are distinguished the devices:

- fed from roll of material (capstan);

- with mounting the recorded substrate on the drum (on-drum);

- with fixing the substrate inside the drum or some caved surface (in-drum).