What you need to know about web offset printing
Offset printing is characterised by several distinctive features that enabled it to become the most widely used printing technology globally. One of the main distinctive features is the low-cost high-quality aluminium offset printing plate, which combines fast imaging and processing with the best image quality on the market.
Until the 80s of the previous century, offset printing was only used for printing on absorbent substrates, for products like newspapers, magazines, brochures, folding cardboard applications, and security documents. This changed with the development and maturation of energy-curing ink technologies like Electron Beam curing, UV curing, and more recently LED-UV curing.
The integration of energy curing systems in web offset presses allowed offset to enter the markets of non-absorbent substrates as are used for labels. Flexible packaging printing, however, requires easy and cheap repeat-length variability.
It was the successful development and introduction of the Variable Sleeve Offset Press technology, abbreviated as VSOP, by the team from DG press in 2003 that enabled VSOP web offset presses to enter and gain the significant share of the flexible packaging market that it has today and still growing.
How offset works
Inks for offset printing typically have a paste, high viscosity, and character. When offset inks pass from the ink fountain through the roller train towards the plate, the viscosity is lowered to a suitable level due to shear forces in the ink, temperature control, and the addition of a micro quantity of dampening water.
A set of three or more so-called form-rollers apply the ink-dampening water emulsion onto the surface of the offset printing plate. The micro quantity of dampening water in the ink is attracted to the hydrophilic non-image areas on an offset plate while the polymeric image areas take up the ink. In a second transfer step, the ink on the image areas of the offset plate is transferred to a printing blanket that is applied around the blanket cylinder. In the third and final step, the ink is transferred from the surface of the printing blanket to the substrate.
The low-cost offset plates and the fast plate imaging and processing make web offset the perfect printing technology for any short-run print production but especially for flexible packaging and labels. Change of a job on a web offset press only takes minutes and when using all the advantages of Extended Color Gamut the efficiency is even higher. Offset printing is also ideal for printing on paper and cardboard, where the compressible printing blanket has an advantage when printing substrates with an uneven surface.
Standardised printing process
Standardisation pushes productivity and efficiency and leads to a reduction of waste and defects. When it comes to standardisation in printing it is offset that can draw from the widest choice of standards for various substrates and applications ranging from magazines and brochures to labels and packaging. The applicable industry standards and specifications for offset printing can be obtained from ISO (12647), Fogra (PSO certification), Idealliance (GRACoL and G7), and ICC to mention a few.
Safe for food packaging
Web offset is suitable for safe food packaging printing as the paste inks make web offset ideally suited for wet-trap printing, which is a requirement for Electron Beam curing. EB curable inks do not contain photoinitiators, and EB curing is very robust and colour-blind providing a full cure of white inks and higher ink coverage.
Perfect for security printing
Due to its standardisation, wet-in-wet printing capabilities, and very fine screens offset printing is ideally suited and commonly used for security printing. Most security printing operations are typically characterised by a combination of different printing technologies in one, the so-called Hybrid printing press. The modular design of the DG-AUXO and the DG-Vision web offset press series make them ideally suited for inline combination with different printing technologies like letterpress, dry-offset, flexo, rotogravure, inkjet, and other digital technologies. Allowing the use of specialty inks and varnish for all kinds of security features.
Web offset printing is presumably the most sustainable printing technology as it doesn’t use solvents or VOCs, preventing high carbon footprint and Greenhouse gas emissions. Web offset consumes less energy than printing technologies that require hot-air drying for evaporation of solvents or water from the inks, like for example flexo and rotogravure
Download the Introduction to Web Offset Printing, a guide specifically designed to gain a deeper understanding of Web Offset Technology.
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