Computer to plate (CTP) – The process is a simple theory, photopolymer properties alter under exposure to UV light. An equivalent technology exists in the coating on aluminium lithographic printing plates, both are subjected to UV light by way of a a digital movie (positive or negative) as well as in the situation of’ positive’ litho plates the uncovered area is washed away but in true of photopolymer the unexposed material is washed away while the uncovered portion is hardened, therefore film negatives are used.
Photopolymer can be bought in a variety of forms and ctp machine in China with various characteristics, the idea feature for letterpress is the’ shore hardness’ which can range from low 20 ‘s to around eighty five for certain steel backed plates, the harder plates (60 upwards) being suited for deeper impression work. There are specific situations to hold in your mind – each and every element of the processing cycle is important and any varying is important. Each plate type according to it is own specification is going to require different exposure times, washout times and temperatures, oven temperatures for drying out as well as drying times and post exposure. It may sound complicated but it is surprisingly straight forward.
A film negative features the desired image or design being printed or’ letterpressed’. A percentage of photopolymer plate is cut corresponding to the image size then positioned 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 maybe sections between the movie and plate that’ll cause UV leakage and a blurred image. The vacuum blanket is rolled over the movie and plate, drawer closed plus the exposure time begins beginning the vacuum and UV lights.
After exposure the plate is placed in the washout unit for several minutes (depending on plate type) in water around 20c. Soft brushes rotate to wash away the plate and waste material is right away dehydrated to take out extra water and positioned in the drying unit 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 needed at this point) as well as placed once more in towards the hair dryer, the 2nd drying time is vital to make certain the plates are properly’ detacked’.
he plate is today completed and may be mounted on double sided adhesive prepared to place holding a precision ground metal platform along the press, the whole process taking around thirty – forty minutes. For letterpress the preferred plates are’ foil’ (meaning plastic) backed rather than steel backed which are difficult to cut and work with, particularly for multi colour work. Of the foil backed plates sold the KF range by Toyobo is essentially the most widely used and widely used and especially the KF95 (0.95mm plate) and the KF152 (1.52mm plate). It has to be recalled that the deeper plates such as KF152 require extra time of exposure so the UV can penetrate to the floor belonging to the plate and properly heal or harden the polymer.
Failing to do this could lead to weak plates that do not last the print run with great details slowly disappearing from the inked impression. The plate should then be loaded behind to compensate but this is tricky and not appealing. Along with well made plates you will discover limits on to the level of wonderful detail achievable in ctp machine plates, lines below 0.3 pt might very well not keep through the creation process.
Important developments in technology have created the polymer plate system far more feasible in recent years at both entry level and for large lithographic businesses both having advancements towards a more’ computer to plate’ (CTP) process. In lithography this is a slightly different process using a variation of the photopolymer plate device often known as Flexography which focuses much more on accurate halftones required 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 films don’t seem to be effective due to this type of top quality work but inkjet films achieve constant industry standard results with DMAX > four although it’s essential to work with a software RIP to do this. The good results of the polyester films is based on the greater precision of contemporary inkjet printers (the minimum requirement would be an anhubg just like the Epson 4900 which is still a fairly modest investment) and also within the science of the movie product.
We have tested a variety but endorse the Folex product Reprojet P Hd situated on 30 meter rolls or slice sheets. The film runs not by holding sufficient ink to be a dense black and thus get to the DMAX objective but rather by the filament inside the structure of the movie dealing with the ink to deflect light and cut it away through the polymer. We have discovered in testing that exposure times greater than 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 an issue.
The film is going to hold an amazing level of ink which together with the film ‘s properties give unique results. Trying to print film without using a RIP as Waasatch, Filmgate or Efi simply using the ctcp machine will lead to floating (ink literally floating on the surface) and wastage. These RIP’s are and extra expense to small print stores but there’s a less costly alternative in Accurip which we have tested running at droplet size thirteen out of fifteen and the results are excellent. We’ve also used EFI and are intending to test Waasatch. Any of these RIP’s perform the main task of taking command of the way ink is laid down as well as the amount whereas onboard printer drivers will install the ink down, in terms which are simple, a lot too fast.
With the resurging interest in letterpress and in particular the artform aspect of this printing process, photpolymer plates were in increasing need in the Uk and in certain plates which allow a much deeper perception in to thick paper because of the luxury stationery market. Though polymer plates have been available for some time 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 lone distributor and a plate making service as well as technical support for those with printing problems, encouraging new progress in the letterpress community.