Overview of Virtual Flexo Plant
The lithographic printing process is a planographic technique, meaning that the image and nonimage areas are, for all practical purposes, in the same geometric plane. The image area of a plate is made of a material having an ink-receptive oleophilic (oil-loving) surface, while the nonimage area is made of a water-receptive, or hydrophilic, material. In printing, a thin film of water based solution (fountain, or dampening, solution) is applied to the plate and wets the nonimage area. Then ink is applied to the plate, where it adheres to the image area. On modern lithographic presses, the printing plate is attached to a cylinder and the ink on the plate is transferred, or offset, to a rubber-covered blanket, which in turn transfers the ink to the paper. Thus, the term "offset" is used to describe these types of presses. One revolution of the printing plate cylinder is referred to as an impression.
In full-color printing, color originals such as photographs are reproduced using only four inks--yellow, magenta, cyan, and black. Sometimes, special colors called pantone matching system inks or overprint varnishes or coatings may be used. One printing unit is needed for each color of ink.
The major subsystems of a press are the paper handling system, the dampening system, the inking system, and the drying system.
There are two types of paper handling systems to the offset lithographic press: sheetfed, where individual sheets are fed successively into the press, and web, where a continuous roll of paper, or web, is fed into the press. Typically, heatset lithographic printing presses are web. Paper (stock) is divided into two broad categories: coated and uncoated. Both are available in many grades, weights, and finishes. Coatings are principally composed of clay, calcium carbonate, or titanium dioxide dispersed in a suitable binder, usually starch or latex.