Computer to plate (CTP) – The process is a concept, 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 movie (negative or positive) and also in the circumstances of’ positive’ litho plates the exposed area is flushed away but in correct of photopolymer the unexposed material is washed away while the uncovered portion is hardened, therefore film negatives are used.
Photopolymer is available in a variety of forms and ctp machine price with different features, the idea feature for letterpress is the’ shore hardness’ that could vary from low 20 ‘s to around eighty five for many steel backed plates, the harder plates (sixty upwards) being perfect for deeper impression work. There are particular issues to hold in your mind – each component of the processing cycle is vital and some varying is essential. Each plate type as per it’s own specification is going to require various exposure times, washout times & temperatures, oven temperatures for drying out as well as drying times and post exposure. It appears complicated but it is surprisingly straight forward.
A film negative features the preferred image or design to be printed or’ letterpressed’. A portion of photopolymer plate is lower corresponding to the picture size then placed in the exposure tray. The film negative is overlayed making sure the film (emulsion side down) is in contact which is good without any air bubbles or perhaps pockets between the movie and plate that’ll cause UV leakage and a blurry image. The vacuum blanket is rolled over the film and plate, drawer closed plus the exposure time begins starting the vacuum and UV lighting.
After exposure the plate is put into the washout unit for several minutes (depending on plate type) in water around 20c. Soft brushes rotate to cleanse away the plate and waste material is immediately 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 movie is required only at that point) and placed once more in towards the dryer, the next drying time is vital to make sure the plates are properly’ detacked’.
he plate is now completed and may be installed on double sided adhesive prepared to place on a precision ground metal platform over the press, the entire process taking around 30 – forty 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 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 has to be remembered that the deeper plates such as KF152 need to have extra exposure time so the UV is able to penetrate to the floor belonging to the plate and properly cure or harden the polymer.
Failing to perform this can result in weak plates which do not survive the print run with high-quality details gradually disappearing from the inked impression. The plate must then be loaded behind to compensate but this is tricky and not appealing. Even in well made plates you will discover limits into the level of good detail achievable in CTP machine parts, lines below 0.3 pt could very well not hold through the production system.
Important innovations in technology have made the polymer plate system more doable in the past few years at both 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 using a variation on the photopolymer plate system known as Flexography which focuses much more on accurate halftones called for 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 high end work but inkjet films achieve constant industry standard results with DMAX > four though it is necessary to use a program RIP to achieve this. The achievements of the polyester films is based on the greater precision of contemporary inkjet printers (the minimum requirement will be an anhubg just like the Epson 4900 which is still a fairly modest investment) and also within the science on the film product.
We’ve tested an assortment but endorse the Folex product Reprojet P Hd available on 30 meter rolls or even cut sheets. The film runs not by holding enough ink being a dense black and so get to the DMAX objective but instead by the filament within the structure of the movie working with the ink to deflect light and cut it out through the polymer. We’ve discovered in testing that exposure times in excess of required can lead to UV leakage (particularly if the ink is too light) but then plate makers must be working to the manual times specified by plate makers so this’s not a concern.
The film will hold a remarkable level of ink which combined with the film ‘s properties give unique results. Attempting to print movie that has no RIP as Waasatch, Efi or Filmgate just using the used CTP machine will result in floating (ink literally floating on the surface) and wastage. These RIP’s are and also added expense to small print outlets but there is a less expensive option in Accurip which we’ve tested running at droplet size 13 out of 15 and the outcomes are excellent. We have also 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 as well as the quantity whereas onboard printer drivers will set up 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 were in increasing demand in the Uk and in specific plates which allow a deeper perception in to heavy paper for the luxury stationery market. Though polymer plates have been available for some time the KF152 for serious impression work hasn’t been distributed in the Uk in recent times. There is now a distributor and Lyme Bay Press are providing KF152 plates as the lone distributor and a plate making system along with technical support for all those with printing problems, encouraging brand new progress in the letterpress community.