The most common printing method today is offset printing. Naturally, in the area of offset printing there is also improvement of printing equipment for sheet and roll printing, modernization as well as the creation of new printing equipment and active introduction of new printing technologies. Let us take a look at some of the innovations for this method of printing, implemented in production.
Offset printing without dampening
Since ancient times it was known that offset (flat) printing is based on selective wetting of printing and non-printing elements located in one plane. In this case the non-printing elements before the printing process should be moistened, otherwise there will be rolling of ink across the whole surface of the printing plate. Only when wetted will the non-printing elements repel the ink from their surface, ensuring that it rolls onto the printing elements only and thus prints.
But after a long search in early 1982 the Japanese company Toray Industries created the technology of dry (waterless) offset, which does not require dampening of the non-printing elements and allows the press to work without dampening unit. According to this technology, silicone rubber is used to create an ink-repellent layer on the printing plate’s non-printing elements. Japan was the first country where this technology was first tried, and then it began to be used in Europe and other regions of the world, arousing great interest among printers.
We will not study in detail the rather thorny path of offset without dampening to printing companies. But we should note that this method has now become an industrial technology for which offset printing machines are created and modernized, there are special printing inks and papers, and numerous studies and recommendations on the optimum technology. The European Waterless Printing Association EWPA (European Waterless Printing Association) has been operating in Europe for more than 5 years and holds its annual meetings.
Wet offset has found its industrial application in both web and sheetfed printing. Various printing inks have been developed for it, including those with ultraviolet drying. Such inks have a rather complicated composition in comparison with ordinary offset inks. Suffice it to say that they contain up to 8 components. They consist of the pigment, binder system, rheological auxiliary agent, mineral oils or vegetable-based oils, wax, siccative, anticaking agent and other additives. In turn, the binder includes solid resins, mineral oils, vegetable-based oils, and auxiliaries for gelatinizing the binder.
Equipment is already available, as well as materials for the digital recording of information on special plate materials for offset without dampening. Among the pioneers in the introduction of this method in production we find digital printing machines Karat (KBA company), machines with direct digital recording of information on the plate material DI (Direct Imaging) of Heidelberger Druckmaschinen AG. Analog and digital plate materials for this method are produced by Presstek and Kodak Polychrome Graphics. The technical capabilities of the process already make it possible to use offset without dampening on web offset presses, including newspaper printing (KBA and MAN Roland).
It turned out that the many advantages of offset without dampening outweighed its economic disadvantages and the printing and technical difficulties that existed so far.
In more than 5 years of the EWPA work, a lot of experience has been accumulated in the work of printing companies with this technology, which makes it possible to offer certain practical recommendations. The main problem in non-wetting offset, as well as in standard offset, is maintaining a constant ink unit temperature which is why printing machines are equipped with ink unit and cylinder cooling devices, pumps with compressors providing heat supply in order to secure high quality of the product. In offset without dampening the need of reducing the surface temperature of rollers and blanket and offset cylinders to 24°C with very narrow tolerances is very important. Therefore special temperature maintenance equipment is required – this is the main focus of the EWPA. As a result of research and recommendations made by the Dutch company VIS-Sensorcontrol, special non-contact infrared sensors were created to automatically control each of the coloring machines of a multicolor machine and to regulate the temperature of each coloring machine.
In this way, offset without dampening is successfully making its way into the offset industry and, what’s more, is already being used successfully in a number of plants.
