Computer to plate (CTP) – The process is a simple 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 digital movie (negative or positive) and also in the circumstances of’ positive’ litho plates the exposed area is flushed away but in true of photopolymer the unexposed material is washed away while the uncovered portion is hardened, thus film negatives are used.
Photopolymer is available in a variety of forms and ctp machine price with various characteristics, the basic principle feature for letterpress is the’ shore hardness’ that may range from low 20 ‘s to around 85 for certain steel backed plates, the harder plates (60 upwards) being suited for much deeper impression work. There are certain situations to keep in your thoughts – every element of the processing cycle is vital and some varying is essential. Each plate type based on it’s own specification will require various exposure times, washout times and temperatures, oven temperatures for drying as well as post exposure and drying times. It appears difficult but it is surprisingly straight forward.
A film negative is made of the desired image or design being printed or’ letterpressed’. A percentage of photopolymer plate is cut corresponding to the picture size then positioned in the exposure tray. The film negative is overlayed ensuring the film (emulsion side down) is in contact which is good with no air bubbles or maybe sections between the film and plate which will cause UV leakage and also a blurred image. The vacuum blanket is rolled over the movie and plate, drawer closed and the exposure time 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 clean away waste material and the plate is immediately dehydrated to remove excess water and put into the drying unit 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 absolutely no movie is needed at this point) and placed once more in towards the blow dryer, the next drying time is essential to make sure the plates are properly’ detacked’.
he plate is currently finished and can be mounted on double sided adhesive prepared to place holding a precision ground metal base over the press, the entire operation taking around 30 – 40 minutes. For letterpress the preferred plates are’ foil’ (meaning plastic) backed rather than steel backed that are hard to cut and work with, particularly for multi colour work. Of the foil backed plates sold the KF range by Toyobo is one of the most popular and widely used and especially the KF95 (0.95mm plate) and the KF152 (1.52mm plate). It’s to be recalled that the greater plates just like the KF152 need to have extra length of exposure so the UV is able to penetrate to the floor of the plate and properly cure or harden the polymer.
Failure to perform this can result in weak plates which don’t survive the print run with great details gradually disappearing from the inked impression. The plate must then be loaded behind to compensate but this is tricky and not desirable. Along with well made plates there are limits on the degree of high-quality detail achievable in CTP machine parts, lines below 0.3 pt could very well not hold through the creation system.
Important developments in technology have created the polymer plate system far more feasible in the past few years at equally entry level and for large lithographic businesses both enjoying advancements towards a more’ computer to plate’ (CTP) process. In lithography this is a slightly different process using a variation on the photopolymer plate device also known as Flexography which focuses more on accurate halftones needed by modern presses. For equally Flexography and Photopolymer for Letterpress, CTP is actually forwarded by the advancement of new polyester based films.
Developments in laser movies don’t seem to be effective because of this kind of top quality work but inkjet films achieve consistent industry standard results with DMAX > four although it is essential to employ a software RIP to achieve this. The achievements of the polyester films lies in the more precision of contemporary inkjet printers (the minimum requirement will be an anhubg just like the Epson 4900 which is still a relatively modest investment) and also in the science on the movie product.
We’ve tested a mix but endorse the Folex product Reprojet P Hd on 30 meter rolls or even cut sheets. The film runs not by holding sufficient ink being a dense black and so reach the DMAX goal but instead by the filament inside the structure of the movie dealing with the ink to deflect light and cut it away from the polymer. We’ve found in testing that exposure times over needed could result in UV leakage (particularly if the ink is too light) but then plate makers should be working to the manual times specified by plate companies so this’s not a concern.
The movie will hold a remarkable level of ink which combined with the film ‘s properties provide exceptional results. Trying to print film without having a RIP as Waasatch, Filmgate or Efi simply using the amsky uv ctp machine will lead to 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 tested running at droplet size 13 out of 15 and the outcomes are superb. We’ve also used EFI and are intending to test Waasatch. Any of these RIP’s perform the main job of taking command of the way ink is laid down as well as the quantity whereas onboard printer drivers will install the ink down, in terms which are simple, an excessive amount too fast.
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 specific plates which allow a deeper opinion in to heavy paper towards the luxury stationery market. Though polymer plates are already on the market for a while the KF152 for huge 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 single distributor and a plate making service as well as technical support for those with printing problems, encouraging new progress in the letterpress community.