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Print Process Descriptions: Printing Industry Overview: Gravure

Because copper is so soft the image areas quickly wear. Cylinders that are used for press runs of a million impressions or more are chromium plated. Some gravure printers "Double Chrome" cylinders in order to run them even longer. When the chromium begins to wear or the image is no lit is stripped off and the cylinder is re-chromed. This is much cheaper (and environmentally responsible) than etching a new cylinder. Once the cylinder has degraded or the image is no longer needed the image can be stripped off and the base cylinder can be reused for other printing jobs unlike other printing processes.

Gravure Cylinder Imaging:

  • Chemical Etching
  • Electromechanically Engraved
  • Direct Digital Engraving.

There are three processes used for making gravure cylinders. The first is for conventional gravure using chemical etching that produces cells of the same size or area with varying depths. The second is Electromechanically engraved cylinders.

In electromechanically engraved cylinder making, the image or copy is wrapped around a scanning cylinder. The scanning head moves across the scanning cylinder which sends impulses to a computer. The computer signals a pneumatic head, which contains a diamond stylus, when and where to make a cell in the copper cylinder. The diamond stylus cuts an inverted pyramid shaped cell into the copper cylinder. Engraved cells may be up to 200 microns wide and up to 50 microns deep.

Chemical etching is hardly used now, but the process involves applying iron chloride solution of varying strengths over carbon tissue that has been sensitized to light by submerging it in a bath of potassium bichromate and water. The carbon tissue is a water-sensitive, fibrous paper that has been coated with a smooth gelatin resist.

In summary the gelatin resist is made to adhere to the cylinder. The cylinder is then exposed to UV light to harden the gelatin resist and then rinsed with plain water. Finally the etching technician applies the ferric chloride etchant which creates the printing cells on the cylinder.

Electromechanically engraved cells hold a lot less ink, yet print quality is equal to or better than chemically etched cylinders. In fact, an Electromechanically engraved cell holds approximately 30% less ink than a chemically engraved cell.

Recently direct digital engraving has become widespread. With this process the image can be created and manipulated using an image handling computer. Therefore, the steps of creating, copying, and rescanning film, and the loss of quality inherent in these steps, can be avoided (GAA 1991).

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