Computer to plate (CTP) – The method is a theory, 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 by way of a a digital movie (positive or negative) and in the case of’ positive’ litho plates the exposed area is flushed away but in the case of photopolymer the unexposed material is washed away while the exposed portion is hardened, thus film negatives are used.
Photopolymer can be purchased in an assortment of forms and ctp machine price with different characteristics, the basic principle feature for letterpress is the’ shore hardness’ which could range from low 20 ‘s to around eighty five for sure steel backed plates, the harder plates (sixty upwards) being ideal for much deeper impression work. There are specific issues to keep in mind – each part of the processing cycle is essential and some varying is essential. Each plate style according to it is very own specification will require different exposure times, washout times and temperatures, oven temperatures for drying and also drying times and post exposure. It sounds complicated but it is surprisingly straight forward.
A film negative is made of the preferred design or image to be printed or’ letterpressed’. A percentage of photopolymer plate is lower corresponding to the picture size then positioned in the exposure tray. The film negative is overlayed making sure the film (emulsion side down) is in contact that is good devoid of air bubbles or perhaps sections between the movie and plate that’ll cause UV leakage and also a blurry image. The vacuum blanket is rolled over the movie and plate, drawer closed plus the time of exposure begins beginning the vacuum and UV lights.
After exposure the plate is positioned in the washout model for several minutes (depending on plate type) in water around 20c. Soft brushes rotate to wash away waste material and the plate is immediately dehydrated to remove extra water and put into the drying product 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 virtually no film is used at this point) and also placed once more in on the hair dryer, the second drying time is crucial to make sure the plates are properly’ detacked’.
he plate is today done and may be mounted on double sided adhesive prepared to place holding a precision ground metal base along the press, the entire process taking around thirty – 40 minutes. For letterpress the preferred plates are’ foil’ (meaning plastic) backed rather than steel backed that are tough to cut and work with, especially for multi colour work. Of the foil backed plates sold the KF range by Toyobo is just about the most well known and widely used and particularly the KF95 (0.95mm plate) and the KF152 (1.52mm plate). It’s to be remembered that the greater plates such as KF152 need to have more time of exposure so the UV can penetrate to the floor of all of the plate and properly cure or perhaps harden the polymer.
Failing to perform this can lead to weak plates that don’t survive the print run with good details gradually disappearing from the inked impression. The plate must then be loaded behind to compensate but this’s problematic and not appealing. Even in well made plates you will discover limits on the level of wonderful detail achievable in amsky ausetter lasers, lines below 0.3 pt might well not hold through the production process.
Important improvements in technology have made the polymer plate system far more feasible in the past few years at both entry level and for large lithographic businesses both enjoying advancements towards a more’ computer to plate’ (CTP) process. In lithography this’s a slightly different process by using a variation of the photopolymer plate system also known as Flexography which focuses more on accurate halftones required by modern presses. For both Flexography and Photopolymer for Letterpress, CTP is actually forwarded by the advancement of brand-new polyester based films.
Developments in laser movies do not appear to be successful for this type of high end work but inkjet films achieve consistent industry standard results with DMAX > 4 although it is necessary to employ a program RIP to do this. The success of the polyester films is based on the greater accuracy of modern inkjet printers (the minimum requirement will be an anhubg such as the Epson 4900 that’s still a fairly modest investment) as well as inside the science of all the money taken in and most of the film product.
We’ve tested a variety but endorse the Folex product Reprojet P Hd on 30 meter rolls or even trim sheets. The film runs not by holding enough ink to be a dense black and thus reach the DMAX target but rather by the filament in the structure of the film working with the ink to deflect light and cut it out from the polymer. We’ve found in tests that exposure times greater than required can lead to UV leakage (particularly if the ink is just too light) but then plate makers should be working on the guide times specified by plate makers so this’s not a concern.
The film will hold an amazing level of ink which combined with the film ‘s properties provide unique results. Attempting to print film without using a RIP like Waasatch, Efi or Filmgate simply using the uv ctp plate making machine will result in floating (ink literally drifting on the surface) and wastage. These RIP’s are and added expense to small print shops but there’s a cheaper choice in Accurip which we’ve analyzed running at droplet size thirteen out of 15 and the outcomes are excellent. We’ve in addition used EFI and are about to test Waasatch. Any of these RIP’s perform the important job of taking command of how ink is laid down as well as the level whereas onboard printer drivers will install the ink down, in simple terms, a lot too fast.
With the resurging interest in letterpress and particularly the artform aspect of this printing process, photpolymer plates have been in increasing need in the Uk and in particular plates that permit a much deeper impression in to thick paper for the luxury stationery market. Though polymer plates have been out there for a while the KF152 for serious impression work hasn’t been sent out in the Uk of late. There is now a distributor and Lyme Bay Press are providing KF152 plates as the main distributor and a plate making program together with tech support team for those with printing problems, encouraging new growth in the letterpress community.