Offset printing

Adapted from Wikipedia: http://en.wikipedia.org/wiki/Offset_printing

Offset printing is a widely used printing technique where the inked image is transferred (or "offset") from a plate to a rubber blanket, then to the printing surface. When used in combination with the lithographic process, which is based on the repulsion of oil and water, the offset technique employs a flat (planographic) image carrier on which the image to be printed obtains ink from ink rollers, while the non-printing area attracts a film of water, keeping the non-printing areas ink-free.

Offset printing advantages

Advantages of offset printing compared to other printing methods include:

• Consistent high image quality. Offset printing produces sharper and cleaner images and type than letterpress printing because the rubber blanket conforms to the texture of the printing surface.
• Quick and easy production of printing plates.
• Longer printing plate life than on direct litho presses because there is no direct contact between the plate and the printing surface.

Photo offset

The most common kind of offset printing is derived from the photo offset process, which involves using light-sensitive chemicals and photographic techniques to transfer images and type from original materials to printing plates.

In current use, original materials may be an actual photographic print and typeset text. However, it is more common -- with the prevalence of computers and digital images -- that the source material exists only as data in a digital publishing system.

Offset litho printing on to a web (reel) of paper is commonly used for printing of newspapers and magazines for high speed production.

Sheet-fed litho

Offset litho printing on to single sheets of paper or board. Commonly used for printing of short run magazines, brochures, letter headings, general commercial (jobbing) printing.

Present day

Offset printing is the most common form of high-volume commercial printing, due to advantages in quality and efficiency in high-volume jobs. While modern digital presses (Indigo Digital Press, for example) are getting closer to the cost/benefit of offset for high-quality work, they have not yet been able to compete with the sheer volume of product that an offset press can produce. Furthermore, many modern offset presses are using computer to plate systems as opposed to the older computer to film workflows, which further increases their quality.

In the last two decades, flexography has become the dominant form of printing in packaging due to lower quality expectations and the significantly lower costs in comparison to other forms of printing.