Intaglio (printmaking)

The gravure printing method is a printing technique in which the imaged elements are present as depressions in the printing plate. The entire printing plate is inked prior to printing, and the excess dye is then removed with a doctor blade or a wiper, so that the printing ink is only in the wells. A high contact pressure and the adhesion forces between paper and paint cause the ink transfer. The method is used both in the commercial gravure printing as well as in the artistic field.

Gravure

In the industrial area of gravure is used exclusively. The printing plates in gravure printing plates are not made, but made ​​of steel cylinders. In a four -color printing four separate pressure cylinders per order can be used. Own this gravure cylinder format caused a considerable weight and should be replaced with specific transport systems.

Platemaking

The production of printing plates in gravure defeated in the course of technological development significant changes. There are mainly two types of the cylinder assembly. The steel cylinder encased around a 2 mm thick copper layer, the basic copper is called. In this inner copper layer either engrave copper is electroplated with a coating thickness of about 100 microns or a so-called deductible Ballard is electroplated onto the copper base. Between this 100 micron thin Ballard and the basic copper is a separating layer. This allows the Ballard after printing simply remove and replace with a new one.

The grid in the gravure printing decomposes the image into tiny printed form elements, the cups are called, while the non-printing elements webs hot. The webs are required for the blade to wipe the excess ink from the cylinder. The squeegee consists of a length of the pressure cylinder corresponding steel ruler.

Conventional etching or photogravure

As the inventor of photogravure applies the Austrian Karl Klietsch, in 1879 linked the use of the pigment paper with the photographic transfer process. First, it was printed by copper plates to the use of high-speed presses in the commercial sector, the production of printing form cylinders necessitated.

The conventional etching of the pressure cylinder that was practiced until the mid- 1960s, took place via the pigment paper. In the area covered by a light-sensitive gelatin chromium layer paper, a uniform grid is first copied. In a second copy after exposing a photographic Halbtonpositivfilm on the grid. Thereafter, the paper pigment is adhered to the gelatin layer on the printing cylinder. Using warm water, the paper is carefully loosened and then removed the unexposed gelatin, until the cylinder leaving a negative, shaded relief gelatin.

Now the pressure cylinder is successively etched in several acid baths of ferric chloride and water, starting with the bathroom with the highest concentration. In the outer copper layer differently and creates deep, but the same size cups. The deeper the wells, the more color it can absorb the pressure and creates a correspondingly darker tone. This is called the " deep variable low pressure ". Finally, the remaining gelatin layer is washed off the cylinder and the contact pressure can occur.

Electromechanical engraving

Electromechanical engraving is one of the conventional methods and is used sporadically since about 1960 to the present. The company Hell in Kiel in 1966 brought the first electronically controlled engraving machine on the market, the " Helio- Klischograph ". Abtastzylinder and the plate cylinder to be engraved are interconnected via a shaft. On the Abtastzylinder A so-called opal film is with all the image information, text and line drawings. According to the brightness of the sensed image point on the opal film adequate amount of light is reflected and converted into an electrical signal. This output signal of the scanning head of the engraving is processed in the computer and used to control the engraving, which receives two pieces of information: First, the actual image signal along with position and, secondly, the signal for defining the screen frequency and screen angle. A diamond stylus cuts then a correspondingly large and deep wells physically in the copper layer the printing cylinder.

Instead of a Halbtondiapositivs as opal film also screened opal films are used as Graviervorlage. An economical method is the takeover of offset films, so print templates that were previously used for reasons of cost Offsetandruck. This method is called offset gravure conversion or OT- conversion. The scanning head is set such that the halftone films are integrally offset sampled and converted into corresponding continuous tone values ​​. The most important prerequisite for the OT- conversion is the de-screening of the originals, otherwise a moire would be built on the engraved gravure cylinder.

Electronic engraving

As of 1995, the gravure cylinder is mainly directly, without going through a opal film, engraved. The signals for the engraving come out of the digital data set for printing form description. Today, increasingly engraved with the laser beam, which enables higher engraving speeds. Depending on the method, a zinc surface or a thicker chromium layer instead of the copper is engraved. Experiments with a plastic coating had no success.

Wells are burned in the cylinder surface in principle, in the laser engraving, the thickness of the electronic signal comprises a function corresponding to a larger or smaller volume. The high write resolution of up to 2540 dpi (= 100 points per millimeter ) allows a very high sharpness. Therefore, the direct laser engraving is especially for printing of labels and packaging, typical for example for cigarettes, are suitable.

Another electronic method for platemaking is the modern etching process. Here, the cylinder is first coated with a lacquer or photoresists layer which is then exposed with a laser. Wherein the layer is removed at the points at which the cells are to appear later. The subsequent computer-monitored etching or electrolytic copper removal generates the final wells.

Engraved gravure forms tend to be so-called missing dots, which means lack of grid points, as some wells transferred too little color due to their shape on the paper. Based on the number of missing dots of professionals is the quality of gravure Products evaluated. This problem is addressed with electrostatic printing aids.

Gravure printing machines

The printing unit of a gravure printing machine consists essentially of the impression cylinder, the ink trough, the doctor, the impression roller and the drying system and works as follows: The pressure cylinder immersed in the thin liquid ink in the ink tray one. The wells in the plate cylinder are completely flooded with color. The doctor blade removes the excess ink, so that is just in the cups printing ink, the webs between the wells, however, are free from paint. The excess ink from flowing back into the paint tray. Then, the printing process. The impression ensures a high pressure to transfer the ink from the cells almost completely in the substrate. The impression roller is used in gravure printing to produce the necessary mechanical pressure for sucking the ink from the cells of the plate cylinder through the paper. For this, the impression roller presses the printing material against the mold cylinder and provides for the transport of the paper through the entire printing unit. In multi-color gravure printing must be dried after each print, because a wet-on -wet printing in the low-viscosity or low viscosity gravure inks is not possible.

There are both gravure presses and sheetfed presses. In rotary printing, especially high-volume products are made. Your print performance is currently at 60,000 impressions per hour, the equivalent of a paper web speed of around 16 m / s The less common sheet-fed gravure printing is mainly used in the printing of fluorescent colors, metallic inks and coatings (for example metallic, UV-activated, grobpigmentöse colors) as a special color to finished printed sheets from the offset.

In combination with the offset printing high quality and visually appealing print results are possible in sheet-fed gravure printing. Applications are mainly found in the cigarette industry, but also in perfume, cosmetics packaging, displays, security and safety and security printing. In rotogravure excellent results are achieved in commercial printing. A reproduced in gravure image comes very close to the original artwork.

Characteristics of the low- pressure

The most important feature in the gravure printing is the jagged edge or sawtooth effect to letters and line drawings, as not only images but also text and line drawings are rasterized. When deep variable low pressure drop under a magnifying glass on the same large, square dots that look often hollowed out in the lighter tones. In the deep and surface variable low pressure by an engraved printing plate, the grid points to a different size and color saturation.

All manually established artistic Intaglio prints - usually in sheet printing method - have a distinctive mark one caused by the pressure in the gefeuchtete paper plate boundary, called the facet that leaves an impression in the paper and results on the back of the printed paper a raise. Another feature is that different copies of a disk have small differences in measurement. Reason, the moisture of finished prints, which causes a minimum of differential shrinkage of the sheets during subsequent drying.

Managerial Applications

The gravure printing process is now used commercially for print jobs with long runs of more than 300,000 copies. The selection of the printing method is dependent on various criteria, such as the size or the number of the printing forme change. In gravure printing magazines such as Der Spiegel and star, TV magazines, newspaper and magazine inserts and catalogs are produced (for example, from the Otto-Versand, Quelle or IKEA ) in this printing process. Another great market is the packaging gravure, for example, the manufacture of folding cartons, Tetra Paks or foil packaging. Other applications include the decorative, textile, banknote and security printing. Is mainly print on absorbent paper with a smooth, satin finish. Gravure printing is competing for web offset printing.

Artistic gravure

As an artistic medium of low pressure gives the artist great aplomb with which his imagination can realize unhindered. In particular, the etching has been a special field visual artist since Rembrandt repeatedly.

The artistic gravure printing processes are divided into two groups: Once the manual, dry methods based on physical cold deformation of the pressure plate as drypoint, engraving, mezzotint ( mezzotint ), stone etching, and on the other the wet etching process in which chemical or electrochemical methods material is removed as Ätzradierung, aquatint, Vernis Mou ( Weichgrundätzung ) and partly in steel engraving.

In addition, many mixing techniques are used so that the strict separation between dry and wet processes can not be so limited. When called relief printing, relief printing, and also without color blind printing, metal plates are cut to shape, some sheets or wires are soldered or stamped parts of the plate or cut out.

Some eraser shape below the actual color display her stage character as a colorless reactive pressure in the copper printing handmade paper. The Carborundum is a combination of etching and relief printing, in which (in addition to etching ) on portions of the printing plate, a mixture of carborundum ( abrasive) or marble powder is applied with acrylic resin. The ink adheres to the grain interstices and gives the impression colored areas of high intensity. Joan Miró has created such works.

The photogravure emerged at the end of the 19th century with the noble printing process arose photosensitive coatings. It allows photographic reproductions. The end of the 20th century, a new method were added, which are produced with a clad on a smooth surface (typically photosensitive ) polymer film. Cerataryt is a print using sheets of wax or waxed materials.