More than 550 years ago, a certain Johannes Gutenberg started a media revolution: the printing press he invented enabled the production and dissemination of information on an unprecedented scale. Another 500 years after Gutenberg, the spread of the Internet ushered in another serious change in communication and information exchange.
The end of the print media has often been invoked, but reality is different. Print and digital exist side by side without being able to outdo their respective competitors.
In the area of marketing, companies can arouse the interest of potential customers on a number of tracks, QR codes in printed advertising even create a bridge between the printed product and the digital world. In contrast to many of its successors presented below, industrial planographic printing in particular is still an important medium.
1. High pressure
With this oldest mechanical printing process, the color is transferred directly from the printing form to the printing material. Either individual letters, entire lines of text or complete templates can be used as printing forms. Depending on the type of material used, they are divided into hard and elastic high-pressure forms.
For clichés, i.e. entire templates, brass alloys, zinc and steel, for example, are mainly used, while lead, wood or plastic can also be used for single letters. Depending on the degree of hardness and the durability of the materials, larger or smaller editions can be printed.
The nature of the material – rough, porous or smooth – also has an effect on the absorption and release of color. For example, copper plates give off a great deal of the ink they have absorbed into the substrate, whereas zinc and iron plates retain more ink.
The special feature of the printing forms is that the printing parts are significantly higher than the non-printing areas. As a result, only the raised – raised – areas are provided with color during printing and only they ultimately transfer this back onto the printing material.
Even if the process originates from the Gutenberg printing press, it is suitable for all three printing principles.
- Platen printing presses use the flat-against-flat principle and can be used up to a format of DIN A3.
- Stop cylinder high-speed presses consist of a flat printing medium and a cylinder on which the paper is stretched. However, the production speed is limited to only about 5,000 prints per hour and is therefore hardly ever used.
- Rotary printing machines are designed according to the round-against-round principle – the paper is printed between a plate cylinder, the printing medium and the impression cylinder. By connecting several plate cylinders in series, multi-colored prints can also be produced in one printing process, and the output of around 30,000 prints per hour is once again significantly higher than that of the high-speed presses.
Because of the high costs and the elaborate production, letterpress is hardly used in the modern printing industry, only for sophisticated print graphics or artistically designed books – which is what it was originally intended for.
2. Gravure printing
The way the gravure printing process works is the opposite of that of letterpress printing, in that the printing forms are basically designed in opposite directions: the elements to be printed are engraved in the form as indentations, as is the case with copperplate engravings, for example.
These are steel cylinders with a thin copper layer (base copper), onto which an even thinner layer of engravable copper or a thin Ballard skin that can later be peeled off is galvanized.
The tiny printing elements are the so-called cells, the non-printing parts are called bars. After the ink has been applied, the excess ink is removed from these using a squeegee, which is a kind of steel ruler the width of the printing cylinder, so that it only remains in the cells.
The printing machines with which the gravure printing process is implemented consist of the following parts:
- Impression cylinder and impression cylinder
- Ink tray and squeegee
- Drying system
For mass with class
During the printing process, the printing cylinder first picks up the ink from the ink tray, and the squeegee then removes the excess from the webs. The impression cylinder, in turn, has to generate sufficient pressure so that this ink is, as it were, sucked out of the cells and transferred to the printing material.
If the end result is to have several colors, it is necessary to dry the colors after each printing process, because gravure printing is not suitable for working wet-on-wet. However, it is very well suited for jobs with high print runs, i.e. of more than 300,000 copies. This includes mass printed matter, magazines, but also wallpapers and packaging.
Depending on the requirements, rotary machines – with an output of 60,000 prints per hour – or sheet-fed printing machines – as a supplement to offset printing – can be used.
3. Print through
The screen printing process, of which the most well-known representative is screen printing, is also a direct process. As with letterpress printing, the color is thus transferred directly from the printing form to the printing material. While, for example, high pressure is necessary for the transmission of information in letterpress printing, it is reduced to a minimum in screen printing.
This is due to the fundamentally different technology. The basis of the screen printing consists of a fine-meshed fabric, either textile, plastic or steel, which is stretched on a frame. The fineness of the fabric determines the permeability for the color – the more threads are used, the less the color is applied.
The stencils are applied to this sieve using different methods. However, the manual production of printing formes is now mainly limited to the artistic field, as well as the various techniques of photomechanical printing form production. A distinction is made between direct stencils and indirect stencils.
Slow but versatile
In either case, the applied coatings render parts of the screen impervious to paint. During printing, this is applied to the substrate through the open areas using a squeegee. As a result of the pressure applied, the stencil is pressed directly onto the substrate so that the contours are sealed when the paint is applied.
The process of printing through is comparatively slow – fully automatic printing machines can produce between 1,000 and 3,000 prints per hour – but it can be used on a wide variety of materials and shapes.
In addition to the classic substrates such as paper, textiles, plastics, ceramics, metal, wood or glass can also be printed in this way. Screen printing is therefore also used, for example, in the electronics industry for the production of circuit boards.
4. Planographic printing
Flat printing owes its name to the fact that printing and non-printing elements are not separated from one another by different height levels, as is the case with letterpress and gravure printing – they are rather on one level. In the printing industry, offset printing has established itself as a flat printing process based on the repulsion of water and (fat-rich) paint.
The printing form is therefore chemically prepared in such a way that the printing parts absorb the ink, whereas it rolls off the non-printing areas. Accordingly, the surfaces are divided into lipophilic (fat-loving) and hydrophilic (water-loving). The process itself is indirect, because after the ink has been applied to the printing form, it is first passed on to a so-called blanket cylinder before it reaches the printing material.
Color mode: CMYK and RGB
Apart from the special printing form, offset printing also differs from other processes in the colors used. In four-color printing, in contrast to digital photography, for example, the CMYK color mode is used. Orders to online printing companies therefore require, among other things, a corresponding adjustment of the data in this regard, as otherwise unwanted color shifts can occur during printing.
In the smaller CMYK color space, the number of colors that can be displayed is smaller than in the RGB color space customary in the digital sector. One of the things that makes offset printing an economically attractive printing process is the wide range of possible applications – from catalogs and packaging to books and brochures – with very high print runs in a short period of time. Up to 18,000 prints per hour can be achieved.
5. Digital printing
Everyone knows the digital printing process from their own households, because initially it means little more than that the templates can be put directly on paper without the need for special printing forms. The main choice here is between inkjet and laser printers.
Digital printing also has a place in the printing industry for various reasons. Working without printing forms is just as much a part of this as the possibility of sorting in the printing process or expanding the system to include cutting and binding facilities.
In the case of smaller runs, which are increasingly being used by the economy – keyword product variety and print-on-demand to avoid large stocks – the production costs are also below those of offset printing. It is also interesting that digital inkjet systems can also implement large formats.