Computer to plate (CTP) – The procedure is a concept, photopolymer properties alter under exposure to UV light. A similar technology exists 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 case of’ positive’ litho plates the totally exposed area is washed away but in true of photopolymer the unexposed material is washed away while the exposed part is hardened, thus film negatives are used.
Photopolymer can be purchased in an assortment of forms and ctp machine with various features, the basic principle feature for letterpress is the’ shore hardness’ that can range from low 20 ‘s to around eighty five for some steel backed plates, the harder plates (60 upwards) being suitable for deeper impression work. There are particular situations to keep in your thoughts – every single part of the processing cycle is important and some varying makes a difference. Each plate type as per it is very own specification is going to require different exposure times, washout times and temperatures, oven temperatures for drying and also drying times and post exposure. It appears difficult but it’s surprisingly straight forward.
A film negative is made of the desired 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 ensuring the film (emulsion side down) is in good contact with no air bubbles or 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 exposure time begins beginning the vacuum and UV lighting.
After exposure the plate is positioned in the washout unit for a number of 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 get rid of excess water and placed in the drying unit for the proper 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 movie is required at this point) as well as placed once more in on the blow dryer, the next drying time is vital to make sure the plates are properly’ detacked’.
he plate is now done and may be mounted on double sided adhesive prepared to place holding a precision ground metal base along the press, the entire operation taking around 30 – forty minutes. For letterpress the preferred plates are’ foil’ (meaning plastic) backed instead steel backed which are hard to cut and work with, especially for multi-colour work. Of the foil backed plates sold the KF range by Toyobo is essentially the most popular and popular and especially the KF95 (0.95mm plate) and the KF152 (1.52mm plate). It’s to be remembered that the deeper plates which include the KF152 require more time of exposure so the UV can penetrate to the floor belonging to the plate and correctly cure or harden the polymer.
Failing to perform this could lead to weak plates that don’t survive the print run with wonderful 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 there are limits for the level of high-quality detail achievable in CTP machine parts, lines below 0.3 pt may well not keep through the production 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 enjoying advancements towards a more’ computer to plate’ (CTP) process. In lithography this’s a slightly different process using a variation of the photopolymer plate system called 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 continuing growth of brand-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 constant industry standard results with DMAX > four although it is important to employ a program RIP to achieve this. The success of the polyester films depends on the more 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 within the science around the film product.
We’ve tested a wide variety but endorse the Folex product Reprojet P Hd available on thirty meter rolls or slice sheets. The film works not by holding enough ink to be a dense black and thus get to the DMAX target but rather by the filament in the structure of the movie working with the ink to deflect light and cut it out from the polymer. We have discovered in tests that exposure times greater than required can result in UV leakage (particularly if the ink is too light) but then plate makers must be working to the guide times specified by plate companies so this’s not an issue.
The movie is going to hold an amazing level of ink which together with the film ‘s properties give unique results. Trying to print film without a RIP like Waasatch, Filmgate or Efi simply using the used CTP machine will result in floating (ink literally floating on the surface) and wastage. These RIP’s are and additional expense to small print shops but there’s a more affordable choice in Accurip which we’ve tested running at droplet size thirteen out of fifteen and the outcomes are superb. We have in addition used EFI and are intending to test Waasatch. Any of these RIP’s perform the important job of taking control of the way ink is laid down and also the quantity whereas onboard printer drivers will put the ink down, in terms that are simple, an excessive amount too quickly.
With the resurging interest in letterpress and especially the artform facet of this particular printing process, photpolymer plates have been in increasing demand in the Uk and in specific plates that permit a much deeper perception in to thick paper for the luxury stationery market. Although polymer plates are already out there for a while the KF152 for profound 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 program along with tech support for all those with printing problems, encouraging new growth in the letterpress community.