Computer to plate (CTP) – The process is a simple theory, photopolymer properties alter under exposure to UV light. A similar technology exists in the coating on aluminium lithographic printing plates, both are subjected to UV light by way of a a movie (negative or positive) as well as in the situation of’ positive’ litho plates the totally exposed area is washed away but in the case of photopolymer the unexposed material is washed away while the exposed part is hardened, thus film negatives are used.
Photopolymer can be bought in an assortment of forms and ctp machine in China with different characteristics, the principle feature for letterpress is the’ shore hardness’ which can vary from low 20 ‘s to around 85 for sure steel backed plates, the harder plates (60 upwards) being suitable for deeper impression work. There are specific problems to hold in your head – each and every component of the processing cycle is vital and any variable is essential. Each plate type as per it is own specification will require different exposure times, washout times & temperatures, oven temperatures for drying out and post exposure and drying times. It sounds difficult but it’s surprisingly straight forward.
A film negative features the preferred image or design being printed or’ letterpressed’. A percentage of photopolymer plate is cut corresponding to the image size and then placed in the exposure tray. The film negative is overlayed seeing to it the film (emulsion side down) is in contact that is good devoid of air bubbles or maybe pockets between the film and plate that’ll 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 product for several 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 extra water and placed in the drying device 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 no film is used at this point) and placed once more in to the dryer, the 2nd drying time is essential to make certain the plates are properly’ detacked’.
he plate is today finished and can be mounted on double sided adhesive ready to place holding a precision ground metal base on the press, the whole process taking around 30 – 40 minutes. For letterpress the preferred plates are’ foil’ (meaning plastic) backed rather than steel backed which are difficult to cut and work with, especially for multi-colour work. Of the foil backed plates sold the KF range by Toyobo is essentially 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 deeper plates like 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 heal or even harden the polymer.
Failure to perform this can lead to weak plates that do not survive the print run with high-quality details slowly disappearing from the inked impression. The plate must then be packed behind to compensate but this is problematic and not desirable. Even during well made plates you will discover limits into the level of fine detail achievable in ctp machine plates, lines below 0.3 pt could well not keep through the production process.
Important developments in technology have made the polymer plate system more doable in recent years at equally entry level and for big lithographic businesses both enjoying advancements towards a more’ computer to plate’ (CTP) process. In lithography this’s a slightly different process using a variation on the photopolymer plate device referred to as Flexography which focuses more on accurate halftones called for by modern presses. For both Flexography and Photopolymer for Letterpress, CTP is actually forwarded by the advancement of new polyester based films.
Developments in laser films do not seem to be effective because of this kind of high end work but inkjet films achieve consistent industry standard results with DMAX > 4 although it is important to employ a software RIP to do this. The achievements of the polyester films is based on the longer accuracy of modern inkjet printers (the minimum requirement would be an anhubg like the Epson 4900 which is still a relatively modest investment) and within the science of all the money taken in and most of the movie product.
We’ve tested an assortment but endorse the Folex product Reprojet P Hd available on thirty meter rolls or even slice sheets. The film runs not by holding sufficient ink being a dense black and so reach the DMAX target but by the filament in the structure of the film dealing with the ink to deflect light and cut it away on the polymer. We have discovered in testing that exposure times over needed can cause UV leakage (particularly if the ink is too light) but then plate makers must be working to the guide times specified by plate makers so this is not a problem.
The digital movie is going to hold an amazing amount of ink which together with the film ‘s properties provide excellent results. Trying to print movie with not a RIP as Waasatch, Efi or Filmgate just using the cron ctp will lead to floating (ink literally drifting on the surface) and wastage. These RIP’s are and also extra expense to small print stores but there is a less expensive choice in Accurip which we’ve tested running at droplet size thirteen 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 main task of taking control of how ink is laid down and also the amount 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 especially the artform side of this particular printing process, photpolymer plates have been in increasing need in the Uk and in certain plates that allow a deeper perception in to thick paper due to the luxury stationery market. Although polymer plates have already been out there for a while the KF152 for deep impression work has not been sent out in the Uk in recent times. There’s now a distributor and Lyme Bay Press are providing KF152 plates as the sole distributor and a plate making service together with technical support for all those with printing problems, encouraging brand new development in the letterpress community.