Offset printing

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.

The first rotary offset lithographic printing press was created in England and patented in 1875 by Robert Barclay.

[3] The offset cylinder was covered with specially treated cardboard that transferred the printed image from the stone to the surface of the metal.

Many printers, including Ira Washington Rubel of New Jersey, were using the low-cost lithograph process to produce copies of photographs and books.

[10] Many modern offset presses use computer-to-plate systems as opposed to the older computer-to-film work flows, which further increases their quality.

Waterless offset lithography employs a different method where a plate's non-image areas are protected via a layer of ink-repellent silicon.

These lasers are generally at a wavelength of 830 nm, but vary in their energy usage depending on whether they are used to expose or ablate material.

A lithographic ("litho" for short) press uses principles of lithography to apply ink to a printing plate, as explained previously.

In sheet-fed offset, "the printing is carried out on single sheets of paper as they are fed to the press one at a time".

They are able to print business forms, letterheads, labels, bulletins, postcards, envelopes, folders, reports, and sales literature.

Finally, the blanket and impression cylinders are used to transfer the image to the substrate running through the press.

[22] The delivery system is the final destination in the printing process while the paper runs through the press.

[23][verification needed] Web-fed refers to the use of rolls (or "webs") of paper supplied to the printing press.

[24] Offset web printing is generally used for runs in excess of five or ten thousand impressions.

In addition to the benefits of speed and quick completion, some web presses have the inline ability to cut, perforate, and fold.

A typical coldset configuration is often a series of vertically arranged print units and peripherals.

As newspapers seek new markets, which often imply higher quality (more gloss, more contrast), they may add a heatset tower (with a dryer) or use UV (ultraviolet) based inks which "cure" on the surface by polymerization rather than by evaporation or absorption.

In addition, waste sheets can be used for make-ready (which is the testing process to ensure a quality print run).

This allows for lower cost preparation so that good paper is not wasted while setting up the press, for plates and inks.

The speed of web-fed presses makes them ideal for large runs such as newspapers, magazines, and comic books.

[25] There are many types of paste inks available for utilization in offset lithographic printing and each have their own advantages and disadvantages.

Heat-set inks are the most common variety and are "set" by applying heat and then rapid cooling to catalyze the curing process.

Cold-set inks are set simply by absorption into non-coated stocks and are generally used for newspapers and books but are also found in insert printing and are the most economical option.

They require specialized equipment such as inter-station curing lamps, and are usually the most expensive type of offset litho ink.