What is offset prepress?

The pre-press phase of any print job is essential to achieve a satisfactory result

Prepress processes are those that take place between the creation of the design for a label, flexible packaging or brochure, for example, and the final print. On offset presses, they include the manufacture of the printing plate and the preparation of images and text for high-quality printing. Nowadays, these processes are digitised.

The documents with the files to be printed arrive at the pre-press shop, where they are converted into film negatives and then transferred to the plates using the same process used to develop photographs. The light passing through the negatives and hitting the printing plates produces the chemical reaction that activates the ink receptive coating and allows the image to be transferred.

Different plates are used; one for each primary colour (black, cyan, magenta, and yellow), a different plate is used. These plates can be made of different materials, although the one that offers the highest quality (and is therefore the most expensive) is aluminium.

Tasks that are part of the pre-press processes

The spectrum of processes involved in prepress is very broad, ranging from typesetting to substrate selection. Let’s take a look at some of them:

  • Typesetting: until not so long ago, this task was performed manually by typesetters. Today, the process by which textual stuff is presented graphically on paper or other media is digitised.
  • Editing and proofreading are also part of the pre-press work.
  • Press-accurate proofs consists of the creation of an identical facsimile of the job to be printed before production begins, in order to obtain the customer’s approval. Once the pdf files are ready for printing a high-resolution print proof is carried out and, with the customer’s approval, the imposition proof is carried out at the printer’s to check and adjust the offset press.
  • Projection and setting of a continuous tone of images, and imposition or combination of many pages in a single signature form.
  • Separation or specification of images or text to be placed on the plates by applying individual print media (inks, varnishes, etc.) to a common print.
  • Manufacture of plates: it is necessary to use material suitable for the needs of the printing method and the required quality of the job. Typically, these materials are rubber, plastic and aluminium, as well as the film that configures the photomechanical exposure and the processing of the light-sensitive emulsion into a printing plate.
  • Preparing the pdf file with the high-quality document, and choice of the printing substrate, an essential step in prepress work.

ROTATEK’s modular offset presses are equipped with the state-of-the-art technology that saves time and costs.. Thanks to the possibility of carrying out all processes inline, they optimise pre-press tasks and provide the best quality in finishes.