Offset Printing – Definition and Process
Offset printing is one of the main forms of flat printing. The process involves transferring an image from a flat printing plate onto a printing surface, such as paper. This transfer occurs through an intermediate cylinder covered with rubber, known as a blanket. Thanks to this technique, the print remains sharp and durable.
Types of Offset Printing
Offset printing is divided into several categories:
Sheet-fed offset – the substrate is individual sheets of paper.
Web offset – the substrate is a continuous roll of paper.
Coldset – “cold” offset, where ink sets by absorbing into the paper.
Heatset – “hot” offset, where ink sets both by absorption and by passing through a high-temperature drying tunnel before folding.
Coldset and heatset are commonly used for high-volume prints such as newspapers, magazines, and telephone books. The substrates are typically calendered and coated papers.
Water and Waterless Offset
Water-based offset uses a dampening solution. On the plate, hydrophilic areas are moistened by water, while hydrophobic areas accept ink. Maintaining a proper water–ink balance is essential, as the solution typically contains 85–95% water with additives like isopropyl alcohol (IPA). However, modern practices aim to reduce IPA use in favor of ecological buffers.
Waterless offset eliminates the dampening solution. It uses special silicone plates and high-surface-tension inks. This technique avoids issues such as ink emulsification or paper wetting. Moreover, it allows a thicker ink layer (above 3.5 µm) compared to traditional offset. However, due to higher costs and technical challenges, waterless offset remains a niche method.
Offset Plate Development
The development process removes the coating layer from the non-printing areas of a plate by dissolving it in a developer. As a result, the plate becomes ready for the printing process.
History of Offset Printing
The origins of offset printing date back to the 18th century with the invention of lithography by Alois Senefelder, son of a Royal Theater actor. Although he initially studied law, financial struggles led him to experiment with new printing methods. His discovery that greasy substances repel water became the foundation of lithography. Senefelder’s further experiments, such as transferring drawings from paper to limestone plates, allowed more precise reproductions. For this, he is recognized as the father of lithography.
Although lithography spread quickly, it had limitations, particularly the slow speed caused by heavy flat stones. It was gradually replaced by typography, where cylindrical plates made from zinc or aluminum improved efficiency. However, the direct contact of plate and paper caused wear. Later, an accidental discovery by an American papermaker revealed that transferring ink via a rubber blanket produced clearer prints. This innovation extended plate life and gave rise to modern offset printing.
The use of photography in lithography led to halftone glass plates and, later, full-color offset printing using process inks. Industrial production of presensitized offset plates in Kraków and beyond opened the door to mass-scale printing, which remains essential today.
To sum up, offset printing has a rich history and multiple forms, from sheet-fed to waterless. Its versatility ensures it continues to be the foundation of professional packaging and publishing. If you want to explore the advantages of offset printing for your own projects, simply contact our team and we will be happy to assist you.