What is offset printing?

Offset printing is one of the best known and most widely used printing technologies. Therefore we use it for many projects: from leaflets and posters, through brochures, magazines and newspapers, all the way to carton packaging, wobblers and multipart forms. Moreover, this technology offers high quality while still providing excellent repeatability in larger print runs.

The high speed of offset presses translates into an attractive unit price. In addition, production runs smoothly, so many jobs are completed within a relatively short time. As a result, offset combines favourable economics with very good print quality.

How does the offset process work?

Image transfer via the blanket cylinder

In offset printing the image is transferred from the printing plate to the substrate with the help of an intermediate cylinder. This cylinder is covered with a blanket, often simply called the “rubber”. Therefore the ink does not go directly onto the paper. First the ink covers the plate cylinder, then the image is passed to the blanket cylinder, and only afterwards the blanket transfers it to the final material. Consequently, the process maintains high quality and very stable results throughout the run.

Types of offset printing

To keep things clear, it helps to remember that offset printing is usually divided into two main types. On the one hand there is sheetfed offset, and on the other hand web offset, also known as reel-fed offset. These technologies differ in how the substrate is fed, in production speed and in typical applications.

Sheetfed offset printing

In sheetfed offset the substrate is fed as sheets in a defined format. Therefore most printing houses in many markets work primarily on sheetfed presses. The sheet is printed with highly viscous offset inks that cure through absorption and polymerisation. Afterwards the printed sheets are delivered to the delivery pile, where they form an even stack.

Even when drying is supported, for example by IR units or anti-set-off powder, the stack still needs time to rest so that the ink can fully cure on the paper. In web offset this waiting time is almost eliminated, which is why the overall process can be much faster. Consequently, the choice of technology often depends on run length, deadline and product type.

Web offset printing (reel-fed)

In web offset the substrate is supplied as a continuous web on a reel. In this case different inks are used than in sheetfed offset. In addition, there are two main variants of web offset: coldset and heatset.

Coldset

Coldset offset, sometimes called “cold” web offset, relies mainly on ink absorption into the paper. Therefore this variant is ideal for very high volumes. However, it is usually used for jobs with lower quality demands, for example advertising leaflets or basic newspapers.

Heatset

Heatset offset, or “hot” web offset, uses very high temperature during printing. First the ink penetrates the paper, then solvents evaporate in the dryer. Moreover, heatset makes it possible to print on heavier stocks and to achieve clearly better quality. Therefore printing companies choose this technology for high-volume prestige magazines and catalogues.

Efficiency and cost advantages of web offset

Web presses can run even three to five times faster than sheetfed presses. Consequently, the cost per copy is often significantly lower. In addition, an in-line folding unit can deliver almost finished products directly at the end of the process. Cheaper reel stock is another important advantage of this technology. In heatset printing, calendered and coated papers are commonly used. In summary, the final product for the customer often costs clearly less than in sheetfed offset.

Web (Roll) Offset Printing

– the material is supplied in rolls (commonly called reels) and printed with inks different from those used in sheet-fed offset printing. There are two main types of web printing:

Coldset – as the name suggests, “cold” offset. The ink sets by being absorbed into the paper.

Heatset – “hot” offset. In this process, printing occurs at very high temperatures, where the ink both penetrates the paper and evaporates.

In short, coldset is typically used for high-volume but lower-quality jobs, such as advertising leaflets. Heatset, on the other hand, allows printing on thicker substrates with much higher quality. This technique is often used for high-volume, premium magazines and catalogs. Web presses can operate 3–5 times faster than sheet-fed machines, reducing production costs. Additionally, integrated folding systems can produce nearly finished products directly from the press. Using cheaper roll-stock paper, often calendered or coated, further lowers costs. Overall, the final product is significantly more affordable than in sheet-fed printing.

A short history: where did the breakthrough in printing come from?

Alois Senefelder (1771–1834)

If we go back to the ideas that later led to the development of offset printing, we soon arrive at Alois Senefelder. He was the son of an actor at the Royal Theatre, yet he studied law because his father had chosen this path for him. However, after his father’s death he made a different decision, so he broke off his studies and turned to the theatre, hoping for a successful stage career. Unfortunately, he quickly realised that acting was not his strength, therefore the stage did not become his place.

Printing costs and early experiments

Despite his lack of acting skills, he wrote plays whose popularity slowly grew. When he tried to distribute these scripts, he encountered a serious problem: printing generated high costs, while the income from sales stayed low. As a result, he began spending more time in printing houses and then decided to experiment on his own by engraving copper plates. Moreover, this work required a lot of time and precision, because he had to prepare a mirror image of the expected final result.

Laundry list, stone and observation

One day his mother asked him to write down a list of laundry. Since he had no sheet of paper, he wrote everything on a stone, using a mixture of soot, soap and wax. Then he noticed that water did not adhere to the areas covered with this substance, whereas the printing ink behaved differently. Therefore he started to draw on stone and later to transfer the image onto a printing forme. Consequently, he patented his invention and went down in history as the creator of lithography, derived from the Greek word “lithos”, meaning rock.