Computer to plate (CTP) – The procedure is a concept, photopolymer properties alter under exposure to UV light. A similar technology is present in the coating on aluminium lithographic printing plates, both are subjected to UV light through a digital movie (negative or positive) and also in the case of’ positive’ litho plates the totally exposed area is flushed away but in correct of photopolymer the unexposed material is washed away while the exposed part is hardened, therefore film negatives are used.
Photopolymer can be bought in an assortment of forms and computer to plate making machine with various features, the basic principle feature for letterpress is the’ shore hardness’ that could vary from low 20 ‘s to around 85 for some steel backed plates, the harder plates (60 upwards) being suitable for deeper impression work. There are particular problems to keep in mind – each and every element of the processing cycle is essential and some varying is important. Each plate type according to it’s own specification is going to require different 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 portion of photopolymer plate is lower corresponding to the image size then placed in the exposure tray. The film negative is overlayed seeing to it the film (emulsion side down) is in good contact with no air bubbles or maybe pockets between the movie and plate which will cause UV leakage and a blurred image. The vacuum blanket is rolled over the film and plate, drawer closed and the length of exposure begins starting the vacuum and UV lights.
After exposure the plate is placed in the washout unit for several minutes (depending on plate type) in water around 20c. Soft brushes rotate to clean away waste material and the plate is right away dehydrated to take out excess water and positioned in the drying unit for the appropriate 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 required only at that point) and also placed once more in towards the hair dryer, the next drying time is important to make certain the plates are properly’ detacked’.
he plate is now finished and may be mounted on double sided adhesive prepared to place on a precision ground metal base on the press, the entire operation taking around 30 – forty minutes. For letterpress the preferred plates are’ foil’ (meaning plastic) backed instead steel backed that are difficult to cut and work with, particularly for multi-colour work. Of the foil backed plates sold the KF range by Toyobo is essentially the most well known 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 time of exposure so the UV is able to penetrate to the floor of all the money taken in and most of the plate and correctly heal or perhaps harden the polymer.
Failing to do this can lead to weak plates that don’t last the print run with wonderful details slowly disappearing from the inked impression. The plate should then be loaded behind to compensate but this’s tricky and not desirable. Along with well made plates there are limits to the level of fine detail achievable in ctp machine plates, lines below 0.3 pt might well not hold through the production system.
Important improvements in technology have made the polymer plate system much more feasible in recent years at both entry level and for big lithographic businesses both having advancements towards a more’ computer to plate’ (CTP) process. In lithography this is a slightly different process using a variation of the photopolymer plate device generally known as Flexography which focuses more on accurate halftones required by modern presses. For both Photopolymer and Flexography for Letterpress, CTP is actually forwarded by the development of new polyester based films.
Developments in laser movies do not seem to be successful because of this type of top quality work but inkjet films achieve constant industry standard results with DMAX > four though it’s necessary to employ a software RIP to achieve this. The good results of the polyester films is based on the longer precision of contemporary inkjet printers (the minimum requirement would be an anhubg like the Epson 4900 which is still a fairly modest investment) and in the science of all the money taken in and most of the film product.
We have tested a wide variety but endorse the Folex product Reprojet P Hd situated on thirty meter rolls or trim sheets. The film runs not by holding enough ink being a dense black and thus get to the DMAX goal but instead by the filament in the framework of the movie dealing with the ink to deflect light and cut it out through the polymer. We have found in testing that exposure times over required can cause UV leakage (particularly if the ink is just too light) but then plate makers must be working on the manual times specified by plate makers so this is not an issue.
The movie is going to hold an amazing amount of ink which together with the film ‘s properties provide unique results. Trying to print film with not a RIP as Waasatch, Filmgate or Efi just using the used CTP machine will bring about floating (ink literally floating on the surface) and wastage. These RIP’s are and added expense to small print outlets but there is a less costly option in Accurip which we have analyzed running at droplet size 13 out of 15 and the outcomes are superb. We’ve in addition used EFI and are about to test Waasatch. Any of these RIP’s perform the important task of taking control of the way ink is laid down and also the total amount whereas onboard printer drivers will set up the ink down, in terms that are simple, an excessive amount too quickly.
With the resurging interest in letterpress and particularly the artform facet of this printing process, photpolymer plates were in increasing need in the Uk and in certain plates which allow a much deeper impression in to thick paper towards the luxury stationery market. Although polymer plates have been available for a while the KF152 for intense impression work hasn’t been distributed in the Uk of late. There is now a distributor and Lyme Bay Press are providing KF152 plates as the single distributor and a plate making program along with tech support team for all those with printing problems, encouraging new growth in the letterpress community.