The process of digital pre-press for flexography is the series of steps and techniques to obtain engraved flexo plates that will be the input for another process called press or printing.
On the good execution of this process in each of its stages will depend to a great extent the results of the flexo prints.
Flexography has not been immune to changes due to new technologies, which have improved processes and optimized pre-press systems. Allowing this that the process of analog pre press would change to be a digital process.
What is digital prepress?
It is the series of processes before the press that through tools or digital process equipment (software and technological language equipment) support all stages from the creation of the graphic design to the flexographic plates.
This process differs from the analog process mainly because of the new generation of high-tech process equipment and software.
These solve problems of greater technical precision in the development of flexographic plates, the optimization of graphic resources, greater predictability in the printed result and a greater number of digital tools for control and measurement.
The digital prepress process
It is important to define first, what are the steps in the process of Pre-Press flexographic. It is a complex process, which below you will find in a simple and easy to understand each of its stages.
The beginning is the design
It is key to understand that graphic design for flexography is very different from that of other sectors.
Have you ever thought that you must have to start creating a design for flexo?
The first thing is to know the number of inks that the design must have, this information will depend largely on the printing capacity of the flexo machine.
The files must be created by graphic editing programs such as Illustrator, Photoshop, Corel Draw, Acrobat, among others. It is very important that the files have a configuration of CMYK color and not RGB.
Among other important features is the retouching of photographs, applied trapping, review of legal texts, color montage, elongations, among a number of variables that must be taken into account.
Within this stage, there must be computers with high graphic capacity, ample storage space and screens with special color settings.
Additionally, different software developers have designed various options that make the layouts audited and verified with automatic processes.
color test or color-proof
The color test or contract test is the color guide that the printer can have as a way of predicting the final print.
With a correct configuration of equipment and supplies, it is possible to obtain between a 95 % and 98 % closeness of color with the end print.
Some of the conditions for a correct and stable configuration are the following:
- Color proofing printer.
- Spectrophotometer that certifies at the end of printing is within the parameters.
- Certified paper that does not alter colors.
- Color software that allows accurate tonal values to be transmitted to the final print.
Control of finished files
While many of the digital prepress file processing software have automatic checks, in-depth quality control must be put in place on the finished files.
This review is prior to engraving on the CTP (computer to plate) and thoroughly review aspects such as elongation, trapping, weft angles, texts, assembly guides and special customer requirements.
In the digital pre-press process there are countless CTP equipments for engraving the final files on the plate.
The engraving is done through a laser that will copy the information contained in the finished files. This copying is so important, since the files are made up of very small shapes (pixels) that their size is measured in microns.
One of the equipment with the greatest technological advance today is the CTP with technology KODAK FLEXCEL NX which unlike the rest uses a unique square laser engraving of its technology (engraving square spot) that transfers the pixels of the design without any loss of information.
These technological advances and the different applications within digital engraving allow the performance of prepress printing to be better and better.
Advances such as specialized micro screens (DigiCap and Flexcel Nx Advantage) that allow ink transfer in an optimal and efficient way.
Exposure of the Plate to UV Light
After the plate recording process, either by a digital film or a carbon layer, the UV light exposure process is carried out to copy the image to the photopolymer plate.
This process works like a tracing on the polymer, since only where the UV light passes through, that will be the area that the plate will copy and will not remove in the washing process.
After this, another UV exposure is made in the lower part of the plate, which will determine the height of the floor of the same.
Through a machine designed to wash flexographic plates, it will be removed by means of friction with special brushes and a solvent, the polymer that was not exposed by UV light.
This process makes the plate have two levels, the floor or base, and the relief or copy area.
Drying of the plate
After having undergone a polymer removal process, either by means of a solvent or a mixture of water and soap, the iron is left with many of these components adhered.
By means of trays with controlled temperatures, the chemical residue that is left on the plate.
Completion and control of the plate
At the end of the oven time, a process called finalization is given that will leave the plate ready for use.
Lastly, and one of the steps that should have the most relevance, is the prepress quality control.
This process will ensure that each flexographic plate meets the necessary characteristics to meet the best performance on press.
The height of the relief and the floor should be checked if they are within the established range. On the other hand, the hardness must be measured, which is the surface tension of the plate, which must be correct to guarantee a good ink transfer.
Also through a bedside table or lamp The plates will be checked against the light to see any imperfections that the plates may have.
And proper packaging will prevent flexo plates from being damaged on their way to the printer.