Computer to plate (CTP) – The method is a theory, photopolymer properties alter under exposure to UV light. A comparable technology is present in the coating on aluminium lithographic printing plates, both are subjected to UV light by way of a a movie (positive or negative) and in the circumstances of’ positive’ litho plates the exposed area is washed away but in correct of photopolymer the unexposed material is washed away while the exposed part is hardened, therefore film negatives are used.
Photopolymer is available in a wide variety of forms and ctp machine in China with various features, the basic principle feature for letterpress is the’ shore hardness’ that could range from low 20 ‘s to around eighty five for many steel backed plates, the harder plates (60 upwards) being ideal for much deeper impression work. There are particular issues to keep in your thoughts – each and every element of the processing cycle is vital and any variable makes a difference. Each plate style according to it is very own specification is going to require various exposure times, washout times & temperatures, oven temperatures for drying and also post exposure and drying times. It sounds difficult but it is surprisingly straight forward.
A film negative features the preferred design or image to be printed or’ letterpressed’. A part of photopolymer plate is cut corresponding to the photograph size then put into the exposure tray. The film negative is overlayed ensuring the film (emulsion side down) is in contact which is good without any air bubbles or perhaps sections between the movie and plate which will cause UV leakage and a blurred image. The vacuum blanket is rolled over the movie and plate, drawer closed and the length of exposure begins beginning the vacuum and UV lights.
After exposure the plate is placed in the washout unit for many minutes (depending on plate type) in water around 20c. Soft brushes rotate to cleanse away the plate and waste material is right away dehydrated to take out extra water and placed 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 movie is used only at that point) and placed once more in towards the blow dryer, the next drying time is vital to ensure the plates are properly’ detacked’.
he plate is currently completed and can be installed on double sided adhesive prepared to place holding a precision ground metal platform on the press, the entire process taking around 30 – forty minutes. For letterpress the preferred plates are’ foil’ (meaning plastic) backed instead steel backed which are difficult to cut and work with, particularly for multi colour work. Of the foil backed plates available the KF range by Toyobo is one of the most well known and widespread and especially the KF95 (0.95mm plate) and the KF152 (1.52mm plate). It has to be remembered that the deeper plates such as the KF152 need extra exposure time so the UV is able to penetrate to the floor belonging to the plate and correctly heal or even harden the polymer.
Failure to perform this could lead to weak plates that do not last the print run with good details gradually disappearing from the inked impression. The plate should then be loaded behind to compensate but this is problematic and not desirable. Along with well made plates there are limits towards the level of great detail achievable in uv ctp lasers, lines below 0.3 pt might very well not keep through the creation system.
Important innovations in technology have created the polymer plate system more feasible in recent years at equally 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 by using a variation on the photopolymer plate application called Flexography which focuses more on accurate halftones needed by modern presses. For equally Photopolymer and Flexography for Letterpress, CTP has been forwarded by the development of new polyester based films.
Developments in laser films don’t seem to be effective due to this type of high end work but inkjet films achieve consistent industry standard results with DMAX > four though it’s essential to work with a software RIP to do this. The success of the polyester films depends on the longer precision of modern inkjet printers (the minimum requirement would be an anhubg including the Epson 4900 which is still a relatively modest investment) and also in the science on the film product.
We’ve tested an assortment but endorse the Folex product Reprojet P Hd situated on 30 meter rolls or perhaps trim sheets. The film works not by holding enough ink being a dense black and thus reach the DMAX target but by the filament inside the framework of the movie working with the ink to deflect light and cut it out from the polymer. We have found in tests that exposure times in excess of needed can cause UV leakage (particularly if the ink is too light) but then plate makers should be working hard to the manual times specified by plate manufacturers so this’s not an issue.
The movie will hold a remarkable level of ink which combined with the film ‘s properties provide unique results. Attempting to print movie without having a RIP as Waasatch, Filmgate or Efi simply using the ctcp machine will result in floating (ink literally drifting on the surface) and wastage. These RIP’s are and also additional expense to small print outlets but there’s a cheaper choice in Accurip which we have analyzed running at droplet size thirteen out of 15 and the outcomes are superb. We have additionally used EFI and are intending to test Waasatch. Any of these RIP’s perform the important task of taking control of the way ink is laid down as well as the quantity whereas onboard printer drivers will put the ink down, in terms which are simple, too much too fast.
With the resurging interest in letterpress and particularly the artform side of this printing process, photpolymer plates were in increasing demand in the Uk and in particular plates which allow a much deeper impression in to thick paper due to the luxury stationery market. Though polymer plates have been on the market for a while the KF152 for profound impression work has not been distributed in the Uk in recent times. There is now a distributor and Lyme Bay Press are providing KF152 plates as the main distributor and a plate making program in addition to tech support for all those with printing problems, encouraging new development in the letterpress community.