Computer to plate (CTP) – The procedure is a theory, photopolymer properties alter under exposure to UV light. A comparable technology exists in the coating on aluminium lithographic printing plates, both are subjected to UV light through a film (negative or positive) and in the situation of’ positive’ litho plates the exposed area is flushed away but in true of photopolymer the unexposed material is washed away while the exposed portion is hardened, therefore film negatives are used.
Photopolymer is available in a variety of forms and computer to plate making machine with different features, the basic principle feature for letterpress is the’ shore hardness’ which can range from low 20 ‘s to around 85 beyond doubt steel backed plates, the harder plates (sixty upwards) being suitable for much deeper impression work. There are certain situations to keep in your thoughts – every component of the processing cycle is vital and any varying makes a difference. Each plate type according to it’s own specification is going to require various exposure times, washout times and temperatures, oven temperatures for drying and also drying times and post exposure. It may sound difficult but it’s surprisingly straight forward.
A film negative features the preferred design or image to be printed or’ letterpressed’. A percentage of photopolymer plate is lower corresponding to the image size and then positioned in the exposure tray. The film negative is overlayed seeing to it the film (emulsion side down) is in contact that is good with no air bubbles or perhaps pockets between the movie and plate which will cause UV leakage and a blurry image. The vacuum blanket is rolled over the movie and plate, drawer closed and the exposure time begins beginning the vacuum and UV lights.
After exposure the plate is put into the washout unit for many minutes (depending on plate type) in water around 20c. Soft brushes rotate to wash away the plate and waste material is right away dehydrated to remove excess water and positioned in the drying product for the proper time at a temperature between 60c and 80c. After initial drying is complete plates are post exposed to UV light without the vacuum (as absolutely no film is needed only at that point) and also placed once more in to the hair dryer, the next drying time is crucial to make sure the plates are properly’ detacked’.
he plate is today done and may be installed on double sided adhesive prepared to place holding a precision ground metal base along the press, the whole operation taking around thirty – 40 minutes. For letterpress the preferred plates are’ foil’ (meaning plastic) backed instead steel backed that are difficult to cut and work with, especially for multi colour work. Of the foil backed plates sold the KF range by Toyobo is one of the most widely used and popular and especially the KF95 (0.95mm plate) and the KF152 (1.52mm plate). It has to be remembered that the greater plates which include the KF152 need extra time of exposure so the UV can penetrate to the floor on the plate and correctly cure or harden the polymer.
Failure to accomplish this can lead to weak plates which do not survive the print run with good details gradually disappearing from the inked impression. The plate must then be packed behind to compensate but this is tricky and not desirable. Even in well made plates there are limits on the amount of wonderful detail achievable in uv ctp lasers, lines below 0.3 pt may well not keep through the creation system.
Important improvements in technology have made the polymer plate system much more feasible in the recent past at equally entry level and also for big lithographic businesses both experiencing advancements towards a more’ computer to plate’ (CTP) process. In lithography this’s a slightly different process using a variation of the photopolymer plate device known as Flexography which focuses much more on accurate halftones called for by modern presses. For both Photopolymer and Flexography for Letterpress, CTP is actually forwarded by the continuing growth of brand-new polyester based films.
Developments in laser movies do not seem to be effective due to this kind of top quality work but inkjet films achieve constant industry standard results with DMAX > 4 although it’s essential to use a software RIP to achieve this. The success of the polyester films lies in the longer precision of contemporary inkjet printers (the minimum requirement will be an anhubg just like the Epson 4900 which is still a fairly modest investment) and also within the science on the film product.
We’ve tested a variety but endorse the Folex product Reprojet P Hd situated on 30 meter rolls or slice sheets. The film runs not by holding sufficient ink being a dense black and so reach the DMAX target but by the filament within the framework of the movie working with the ink to deflect light and cut it away on the polymer. We have discovered in tests that exposure times over required can cause UV leakage (particularly if the ink is simply too light) but then plate makers should be working hard on the guidebook times specified by plate manufacturers so this’s not a problem.
The film will hold a remarkable level of ink which combined with the film ‘s properties provide exceptional results. Attempting to print film without a RIP as Waasatch, Efi or Filmgate simply using the ctcp machine will bring about floating (ink literally drifting on the surface) and wastage. These RIP’s are and also added expense to small print shops but there is a cheaper alternative in Accurip which we have tested running at droplet size 13 out of fifteen and the outcomes are superb. We’ve additionally used EFI and are about to test Waasatch. Any of these RIP’s perform the main task of taking command of how ink is laid down and also the level whereas onboard printer drivers will set up the ink down, in terms that are simple, a lot too fast.
With the resurging interest in letterpress and especially the artform side of this particular printing process, photpolymer plates have been in increasing demand in the Uk and in particular plates which allow a deeper opinion in to thick paper towards the luxury stationery market. Although polymer plates have already been on the market for a while the KF152 for serious impression work hasn’t been sent out in the Uk in recent times. There is now a distributor and Lyme Bay Press are providing KF152 plates as the single distributor and a plate making service along with tech support for those with printing problems, encouraging new expansion in the letterpress community.