Gravure printing

Gravure printing or rotogravure printing is a method that belongs to the intaglio printing techniques. The printing plate is embossed and the printing areas are under the level of the non-printing areas.

The gravure printing predecessor called copperplate is dated back to the 15th century. At that time, motifs were manually engraved in the copper plates, but the rest of the process was virtually the same.  The gravure was invented by Karel Klíč, a Czech citizen, in 1890. He derived it from another of his inventions, so called heliogravure. Heliogravure is again based on the copperplate printing. Manual engraving is here replaced by a photochemical process. In the first step, a photographic negative with a motif is copied to a copper plate. It is coated with asphalt and gelatine layers that cover the surface except of the printing areas that are then etched using an acid. Printing areas with variable depths are created. The rest of the process is identical to the gravure.

Actually, the gravure printing principle is very simple. Printing areas that are embossed under the non-printing area level are filled with a thin, instant-drying ink. During the printing phase, the ink is transferred to the substrate. The most common substrate for gravure printing is paper. The ink is fixed to the substrate by evaporating of volatile solvents.

Gravure printing is most often based on two rollers/cylinders: a cylinder with printing plate (gravure cylinder) and an impression roller. The ink bearing cylinder rotates partially immersed in the ink fountain. The ink adheres to the cylinder. The excessive ink is then removed from the cylinder surface using a blade (cleaning doctor). This ensures that the ink remains only on the printing areas that are under the cylinder cover. Then the printing itself follows. The impression roller pushes the printing plate against the substrate that catches the ink. The gravure printing machines are almost solely rotary. This means that an "endless" paper runs between the roller and the printing plate so that printing is very fast.

Nowadays the printing plate consists only from the cylinder (gravure cylinder) and the printing pattern is engraved directly to this cylinder. Due to this a new cylinder must be prepared for each printing. Only the steel core can be re-used and the next steps must be repeated. Therefore the gravure printing is very expensive and this technique pays off only with high numbers of copies (impressions). 

The printing (forme) plate consists of a steel core on which is electrolytically coated with the other elements.  First the nickel layer is applied. It protects the core against corrosion and at the same time fixes the copper layer that is applied over it. As soon as these three layers are finished the printing image (pattern) must be created. It is made by etching and electromechanical (with a diamond needle) or laser induced engraving. As soon as the printing pattern is prepared the chrome plating step follows. A thin chromium layer is applied on the cylinder to increase resistance of the roller surface against abrasion. At the end, the cylinder is polished and prepared for using in the printing machine.

Gravure printing gives the highest quality of the tinted master copy prints. This is thanks to the printing screen. Each printing pattern is screened and only then the printing forme is embossed into the cylinder.

Gravure printing is divided in conventional, letterpress and semi-letterpress gravure. The differences are in the type of printing screens that is created in the printing (gravure) cylinder and enables colouring. The conventional gravure printing uses printing cells of the same size and varying depth. The light areas have the smallest depths of cells whereas dark areas have the deepest cells. Letterpress gravure uses printing cells of different sizes. The light areas have the smallest areas of cells whereas dark areas have the largest cells. Semi-letterpress gravure uses printing dots with varying depth and size. So it is a combination of both previous methods and nowadays it is the most common method.

As mentioned above, gravure printing is a printing method with very expensive pre-printing works and it pay off with high numbers of copies. However, it allows achieving a very high printing quality even on a low-quality paper and in some cases it substitutes offset as the most common printing technique. This technique is mostly used for printing of high numbers of copies printed on the less-quality substrates, e.g. catalogues, leaflets, magazines, and some covers.