Gravure presses

The gravure printing presses has several basic element: gravure cylinder, ink fountain, impression roller. And substrate control

To the cylinder base is electroplate a layer of copper. Which has historically been –and continues to be –the dominant surface material for gravure cylinders –and is commonly electroplate to the base utilizing a sulfuric-acid electrolyte. On top of the copper, after engraving, is plated a thin layer of chrome, which is applied to protect the etched copper surface from the abrasion of the doctor blade during printing. After print runs the cylinder needs to be resurface.

The copper surface of the cylinder, prior to printing, is etched or engraved. A particular image printed in gravure is essentially a collection of many tiny cells that are etched with varying depths (dark regions of a print utilize deeper cells that can hold more ink, while lighter regions utilize shallower cells that hold less ink). This is why gravure-printed type look fuzzy when examined under magnification. But due to this printing mechanism, gravure can print halftones extremely well. Before the development of electromechanical engraving in the 1960s, most gravure cylinder etching was performed photochemically, using carbon tissue resister coating and ferric chloride etchants to chemically etch the image areas. Now, the art- work to be engraved is often placed before an optical scanning device, which uses photodiodes to receive the image, ning device, which uses photodiodes to receive the image, and the image is transformed into digital data, which is then used to drive an engraving head (typically a diamond stylus), which can produce as many as 5.000 cells per second. New developments in direct computer-to-engraving-head imaging are removing the need for a film positive from which to obtain the information to drive the engraving head.

One particular consideration with the gravure cylinder is ensuring that it is as close to perfectly round as possible(and that the circumference of the cylinder is large enough to carry the image to be printed). Total indicated runout (TIR) is use to indicate the roundness of the cylinder, and gravure cylinder are manufacture-and need to be kept-within strict tolerances.

Ink fountain. The inking system for a gravure press is far less complex than that used for offset lithography. The gravure cylinder is particularly submerged in a large pan of thin, highly fluid ink. (ink is pumped into the pain as needed from a sump, typically located below the fountain pain. As the cylinder rotates in the ink). Its surface becomes covered within ink, and the cell fill. A thin, flexible steel doctor blade, either alone or in tandem within with other pre-wiping devices, scrapes the excess ink from the surface of the cylinder before the inked cells cotact the subtrate. Some gravure inking fountain utilize a fountain roller, a cloth-covered roller that is partially submerged in the ink fountain and that contacts the surface of the gravure cylinder. In some con figuration. Ink is sprayed onto the surface of the cylinder by a nozzle.