Computer to plate (CTP) – The procedure is a theory, photopolymer properties alter under exposure to UV light. An equivalent technology prevails in the coating on aluminium lithographic printing plates, both are subjected to UV light through a digital movie (negative or positive) as well as in the case of’ positive’ litho plates the totally exposed area is flushed away but in true of photopolymer the unexposed material is washed away while the totally exposed part is hardened, thus film negatives are used.
Photopolymer can be purchased in a variety of forms and ctp machine in China with various characteristics, the principle feature for letterpress is the’ shore hardness’ that could range from low 20 ‘s to around 85 for some steel backed plates, the harder plates (sixty upwards) being ideal for much deeper impression work. There are certain issues to hold in mind – every single part of the processing cycle is essential and some varying is essential. Each plate style according to it is very own specification is going to require various exposure times, washout times and temperatures, oven temperatures for drying and post exposure and drying times. It sounds difficult but it is surprisingly straight forward.
A film negative features the preferred image or design to be printed or’ letterpressed’. A portion of photopolymer plate is cut corresponding to the picture size and then positioned in the exposure tray. The film negative is overlayed making sure the film (emulsion side down) is in contact that is good devoid of air bubbles or sections between the movie and plate which will cause UV leakage and also a blurry image. The vacuum blanket is rolled over the film and plate, drawer closed plus the time of exposure begins beginning the vacuum and UV lights.
After exposure the plate is put into the washout model for many minutes (depending on plate type) in water around 20c. Soft brushes rotate to wash away the plate and waste material is immediately dehydrated to get rid of excess water and placed in the drying device for the correct time at a temperature between 60c and 80c. After initial drying is complete plates are post exposed to UV light without the vacuum (as no movie is required only at that point) as well as placed once more in to the dryer, the second drying time is essential to make certain the plates are properly’ detacked’.
he plate is currently completed and may be mounted on double sided adhesive ready to place holding a precision ground metal platform over the press, the whole operation taking around 30 – 40 minutes. For letterpress the preferred plates are’ foil’ (meaning plastic) backed rather than steel backed that are tough to cut and work with, especially for multi-colour work. Of the foil backed plates sold the KF range by Toyobo is just about the most popular and popular and especially the KF95 (0.95mm plate) and the KF152 (1.52mm plate). It’s to be remembered that the deeper plates including the KF152 require extra length of exposure so the UV is able to penetrate to the floor of all the money taken in and most of the plate and properly cure or perhaps harden the polymer.
Failure to perform this can result in weak plates which don’t last the print run with great details slowly disappearing from the inked impression. The plate must then be loaded behind to compensate but this is problematic and not desirable. Even during well made plates there are limits into the amount of high-quality detail achievable in amsky ausetter lasers, lines below 0.3 pt might very well not hold through the creation process.
Important improvements in technology have made the polymer plate system far more feasible in the past few years at both entry level and also for large lithographic businesses both experiencing advancements towards a more’ computer to plate’ (CTP) process. In lithography this is a slightly different process using a variation of the photopolymer plate system also known as Flexography which focuses much more on accurate halftones needed by modern presses. For both Photopolymer and Flexography for Letterpress, CTP has been forwarded by the advancement of brand-new polyester based films.
Developments in laser movies don’t appear to be successful because of this kind of top quality work but inkjet films achieve constant industry standard results with DMAX > 4 though it is essential to use a program RIP to achieve this. The achievements of the polyester films lies in the more precision of modern inkjet printers (the minimum requirement will be an anhubg such as Epson 4900 which is still a fairly modest investment) and in the science around the movie product.
We’ve tested an assortment but endorse the Folex product Reprojet P Hd situated on thirty meter rolls or cut sheets. The film works not by holding enough ink to be a dense black and thus reach the DMAX goal but by the filament in the framework of the movie working with the ink to deflect light and cut it out on the polymer. We have discovered in tests that exposure times in excess of needed could cause UV leakage (particularly if the ink is too light) but then plate makers should be working hard to the guidebook times specified by plate manufacturers so this is not an issue.
The digital movie is going to hold a remarkable amount of ink which combined with the film ‘s properties give excellent results. Attempting to print movie that has no RIP like Waasatch, Efi or Filmgate just using the amsky uv ctp machine will result in floating (ink literally drifting on the surface) and wastage. These RIP’s are and also additional expense to small print stores but there’s a less costly option in Accurip which we have tested running at droplet size 13 out of fifteen and the results are excellent. We’ve in addition used EFI and are intending to test Waasatch. Any of these RIP’s perform the important task of taking command of the way ink is laid down as well as the level whereas onboard printer drivers will set up the ink down, in terms that are simple, too much too fast.
With the resurging interest in letterpress and particularly the artform aspect of this printing process, photpolymer plates have been in increasing need in the Uk and in particular plates that allow a deeper perception in to heavy paper due to the luxury stationery market. Though polymer plates are already out there for some time the KF152 for huge impression work hasn’t been distributed 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 program in addition to tech support for all those with printing problems, encouraging brand new progress in the letterpress community.