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Commercial Presses

Offset printing (or lithography) has been used for close to a century and is based on the simple idea that oil and water don’t mix. Offset printing is an indirect process through which an image is transferred, or offset, from one surface to another. A printing plate mounted on a cylinder transfers images to a rubber blanket mounted on another cylinder. The image is then transferred from the blanket cylinder to the substrate (or printing surface) as it passes between the blanket cylinder and an impression cylinder. The image on the plate is “right reading,” and when the image is transferred to the blanket it becomes “wrong reading.” When the image is transferred to the printing surface, it becomes right reading again. This process is called “offset” because the image isn’t transferred directly from plate to paper, but to a blanket first before finally printing. Because offset printing does not allow for variable repeats in one machine, offset presses are best used in high volume applications such as the printing of newspapers.

Types of offset printing

Sheet-fed – Images are printed on single sheets of paper as they are individually fed into the press. Print quality and sheet-to-sheet registration are often better than web-fed printing, however large runs may be more economical on web presses because of higher running speeds.

Web-fed – The press prints images on a continuous web of paper fed from a large roll. After printing, the paper is perforated or cut into individual sheets.

Waterless Printing (Eco Friendly Offset) – Offset printing can be made more environmentally friendly by removing water from the printing process. The waterless process uses the lithographic (offset) system while eliminating the fountain solution, or dampening system. Instead of conventional metal, paper or plastic printing plates, waterless offset printing uses a multi-layered silicone covered plate and special ink. This process still provides high quality and efficiency with low dot gain for enhanced detail, better color saturation and faster make readies. Without a dampening system, waterless printing requires temperature controls for the ink rollers and more frequent cleaning of the blankets. The plate chemistry is solvent based and requires special handling. Because of the solvents used, inks in waterless printing have a higher VOC content than the ones used in conventional lithography.

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