Prepress

Prepress for gravure printing plays a huge role. For the print to look beautiful and seem to be created by a designer, it is necessary to carry out a number of specific works on preparing the layout. At the same time, it is necessary to take into account characteristics of a particular printing press and printing material. This requires experience of pre-press specialists and special technical equipment; we have all of these and we have extensive experience in preparing layouts for various industries and printing on various types of materials.

Our prepress department will provide you with professional services for processing your layouts.

Read more about Prepress and file requirements.

Blank preparation for gravure printing cylinders

The gravure printing form is a steel pipe of a certain thickness and diameter. The pipe ends have steel flanges having special slotted keys for fixing the cylinders on the printing machine.

The most important feature of high-quality workpieces is high bending strength – this is important because the force of pressing the printing cylinder to the rubberized shaft of the counter can reach 500 kg.

Also, blanks must pass the balancing stage on special equipment to reduce the beating, which is a key parameter determining the quality at print speeds above 150 m / min.

Applying a copper layer on a greasy preparation in a galvanic way.

A copper layer about 2 mm thick and a thin working layer (drawing jacket) 100 microns thick are applied on the steel, prepared surface of the workpiece in a special electroplating bath . For strong adhesion of the main copper layer to the surface of the steel cylinder by electroplating a thin nickel layer is created. Between the main layer and the working copper layer the thinnest (about 1 micron) separation electrically conductive layer is put.

The purity of the copper layer, its uniformity will determine the quality of the following engraving, the uniformity of printing of complex gradients especially in high tones and the stability of the cylinder to stress during printing.

Grinding the copper surface of the cylinder

The copper layer deposited on the steel blank is “dimensioned” on a precision lathe. This is an important stage since each subsequent cylinder (as they are located on the printing press) must be slightly larger than the previous one. It is necessary to create a uniform tension along the entire length of the printing press to compensate the inevitable stretching of the film during the printing process.

Grinding is performed in several stages with the obligatory control of the roughness of the copper surface of the cylinder. Proper selection of the roughness of grinding stones and grinding modes ensures an optimal mode of operation during printing of the doctor blade – a special thin metal plate that fits tightly to the printing cylinder and removes excess paint from its surface.

Engraving printing cylinder

The most important stage where on a prepared surface an engraving machine applies special-shaped indentations that will subsequently transfer paint to the surface to be printed.

Modern engraving equipment is controlled by a graphic station with specialized software. When using electromechanical technology of transferring images to a copper surface, a diamond-headed cutter is used. When engraving to change the tone, the volume of the printing element changes due to a change in both the depth and the area of ​​its working surface.

The printing elements have the shape of a regular tetrahedral pyramid, the base of which is located on the surface of the cylinder. The surface of the bevelled walls of the printing elements is smooth, which provides a better perception of ink by the film and eliminates the deposition of paint residues in the recesses of the printing elements. Illustrative and textual materials are engraved at the same time.

Chrome plating on the engraved surface of the cylinder.

To ensure a high runout resistance, the copper surface of the cylinder must be protected by a thin (5-7 mm) layer of chromium. This technological operation is performed in a special electroplating bath using settings preventing damage to the inner surface of the cells, which distorts the color reproduction during printing and also prevents chromium surface cracking.

Testing printing cylinders on a sample printing machine.

Ready-made printing cylinders are tested for defects possible during manufacture and the compliance of the text graphic parts of the design with the sample approved by the customer is also monitored. It is possible to produce it on a sample printing machine that simulates the operation of a cylinder on a real press. The result of this work will be a print which shows that the cylinders are manufactured correctly, and also allows to prepare an ink formulation that will significantly shorten the work on the printing machine.