Computer to plate (CTP) – The procedure is a concept, photopolymer properties alter under exposure to UV light. An equivalent technology prevails in the coating on aluminium lithographic printing plates, both are exposed to UV light by way of a a film (negative or positive) as well as in the circumstances of’ positive’ litho plates the totally exposed area is flushed away but in correct of photopolymer the unexposed material is washed away while the totally exposed part is hardened, therefore film negatives are used.
Photopolymer can be purchased in a variety of forms and computer to plate making machine 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 (sixty upwards) being perfect for much deeper impression work. There are particular issues to keep in your mind – every element of the processing cycle is essential and some varying is essential. Each plate style as per it’s own specification will require different exposure times, washout times & temperatures, oven temperatures for drying out as well as drying times and post exposure. It sounds difficult but it is surprisingly straight forward.
A film negative is made of the preferred design or image to be printed or’ letterpressed’. A part of photopolymer plate is cut corresponding to the picture size 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 without any air bubbles or perhaps pockets between the film and plate that’ll 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 lighting.
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 waste material and the plate is right away dehydrated to get rid of excess water and put into the drying device 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 no film is needed only at that point) as well as placed once more in on the blow dryer, the second drying time is important to ensure the plates are properly’ detacked’.
he plate is currently completed and may be installed on double sided adhesive able to place holding a precision ground metal base 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 which are tough to cut and work with, especially for multi colour work. Of the foil backed plates available the KF range by Toyobo is just about 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 greater plates which include the KF152 need to have more length of exposure so the UV is able to penetrate to the floor around the plate and correctly cure or perhaps harden the polymer.
Failing to do this can lead to weak plates which don’t survive the print run with fine details slowly disappearing from the inked impression. The plate must then be packed behind to compensate but this is tricky and not appealing. Even in well made plates there are limits towards the level of great detail achievable in CTP machine parts, lines below 0.3 pt may very well not keep through the creation process.
Important developments in technology have created the polymer plate system more feasible in the recent past at equally entry level and 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 known as Flexography which focuses more on accurate halftones called for by modern presses. For both Flexography and Photopolymer for Letterpress, CTP happens to be forwarded by the development of new polyester based films.
Developments in laser movies do not seem to be successful due to this type of top quality work but inkjet films achieve consistent industry standard results with DMAX > 4 though it’s important to use a software program RIP to achieve this. The success of the polyester films lies in the more accuracy of contemporary inkjet printers (the minimum requirement would be an anhubg including the Epson 4900 which is still a relatively modest investment) and also inside the science belonging to the movie product.
We’ve tested a wide range but endorse the Folex product Reprojet P Hd on 30 meter rolls or perhaps slice sheets. The film works not by holding sufficient ink to be a dense black and so get to the DMAX goal but instead by the filament in the structure of the film working with the ink to deflect light and cut it away from the polymer. We’ve found in tests that exposure times greater than required can cause UV leakage (particularly if the ink is simply too light) but then plate makers must be working hard on the guidebook times specified by plate manufacturers so this is not a problem.
The film will hold an amazing amount of ink which together with the film ‘s properties provide excellent results. Trying to print film without a RIP like Waasatch, Efi or Filmgate just using the used CTP machine will lead to floating (ink literally floating on the surface) and wastage. These RIP’s are and added expense to small print stores but there is a more affordable alternative in Accurip which we’ve tested running at droplet size 13 out of 15 and the outcomes are excellent. We have additionally 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 quantity 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 in particular the artform facet of this particular printing process, photpolymer plates were in increasing demand in the Uk and in particular plates that allow a much deeper perception in to thick paper for the luxury stationery market. Though polymer plates have already been available for a while the KF152 for big 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 as well as tech support for all those with printing problems, encouraging brand new growth in the letterpress community.