Printing technology

Printing Technology Useful on the topic   

100 years of offset printing Printing process More about Gutenberg

General pressure:

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Printing refers to all reproduction processes for duplicating print templates. Correctly or reversed print templates are used depending on the printing process. These are first coated with a dye and then pressed onto a substrate. The dye is transferred from the artwork to the substrate. As a rule, the print template can be used several times.

There are the following imperative factors that are required for printing: Pressure hull (the printing machine) Printing ink Printing form Substrate

Printing principles   

A distinction is made between three printing principles: Surface against surface Cylinder against surface (round against flat) Cylinder against cylinder (round against round)

Printing process According to the relationship between the printing elements and the printing form, such as in Plano graphic printing, letterpress and gravure printing, as well as through printing. According to this feature, the printing processes are also differentiated in DIN 16500 into the main printing processes: letterpress (image areas of the printing form are higher than non-image areas, e.g. letterpress, flexographic printing), flat printing (see also lithography (image areas and non-image areas of the printing form are (approximately) on one level) ( Offset printing)), gravure (image areas of the printing form are deeper than non-image areas) and through printing (image areas of the printing form consist of a stencil on a color-permeable stencil carrier (screen made of plastic or metal threads), non-image areas are color-impermeable (screen printing)).

Printing process The four main printing methods are:

High pressure: A printing process that has been widespread since Johannes Gutenberg, known as classic letterpress, in which the printing elements are raised on the printing form (printing with movable letters). High-pressure printing plates can be designed as crucibles (flat printing plates) and cylinders and can print on both sheets of paper and paper from rolls. 

One type of letterpress is flexographic printing; A photopolymer plate is used as the printing form. The main areas of application for flexographic printing are packaging films. Flexographic printing is in close competition with copper gravure printing. Gravure printing achieves better results, but is more expensive for small and medium-sized print runs due to its high up-front printing costs.

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A further development to increase the efficiency in flexographic printing consists in the use of prefabricated continuous printing forms. These are rubber mixtures specially developed and adapted to the intended use (solvent inks, water colors or UV inks). After vulcanization on the carrier sleeve, the print motif is engraved into the surface using a laser.

Gravure printing: Printing process in which the printing elements are designed as a recess in the printing form. These depressions (cells) are filled with ink during the printing process, which is then transferred back to the printing material. The cells can be achieved, for example, by etching or engraving. Rotogravure printing (gravure printing with cylindrically designed printing forms) is now economical, especially for mass printed matter and magazines in very large editions, since the high costs of the printing form are offset by low costs in production printing.

Flat printing: (Stone printing and offset printing) - Offset printing is gaining more and more market share; modern offset machines are fast and today they are superior to rotogravure printing in terms of quality. In the future, it can be assumed that the share of digital printing will grow at the expense of offset printing.

Print through (stencil printing): (Stencil printing) - A universal print through process; the template is usually attached photochemically to the fine mesh made of synthetic fiber or even steel wire. Screen printing can be used in many ways to print flat objects of all formats .

Printing process: Pad printing: Pad printing is a kind of combination of stamp printing and transfer printing. The template is transferred from one surface to the other with the help of a tampon (made of silicone rubber) and can be applied to the recess of an ashtray or cup, for example. So it is not surprising that pad printing is used particularly in the production of promotional gifts and packaging, as well as in the fine printing of model railways.

Digital printing Digital printing is a printing process in which the print image is transferred directly from a computer to a printing machine. The printing system is usually an electro photographic printing system, such as a laser printer, which is designed for high numbers of copies. Other NIP processes are also used. In addition, the printing system can have further devices for cutting and binding. For large-format digital printing, electrographic processes or inkjet printers are used.

Digital printing is cheaper than offset printing for smaller print runs. In contrast to offset printing, for example, no fixed printing template is required, so that each sheet can be printed differently. A document consisting of several pages can be printed in the correct order without collating (sorting). Personalized data, such as invoices, credit card statements, account statements or advertising specifically tailored to the recipient, can be printed easily and inexpensively. Even with large print runs, there is no longer any cost advantage for offset printing.

The transition between a high-performance copier and a digital printing system is fluid. Digital printing systems often still have options for saving the artwork. They print with higher image quality and are more reliable than copiers. In digital color printing, the accurate color reproduction of templates or certain standardized color tones is also supported much more extensively. In order to achieve a high level of accuracy, there are usually complex settings and calibrations, so-called color management.

Digital printing also offers more ways to control how the pages of a document are arranged on the sheet. Several smaller pages can be arranged on one large sheet. Folding and binding the prints to the finished product are prepared in this way. Trimming is made easier by additionally printed cutting marks and suitable margins.

Offset printing Offset printing is a flat printing process that is widely used in commercial printing, packaging printing and newspaper printing. It emerged from the stone printing and is based on the different wetting behavior of different substances .

The printing areas on the printing plate are fat-friendly (lipophilic) and water-repellent (hydrophobic), so they accept the printing ink. The non-printing areas, on the other hand, repel the ink (lipophobic), but accept the water (hydrophilic). The non-printing areas are first wetted by the dampening system with a thin dampening solution film. Then the printing ink is applied to the printing areas by the inking rollers of the inking unit. The print image is first delivered to a rubber cylinder, from which it is transferred to the printing material. It is therefore also known as an indirect printing process. sheet fed offset and web offset are differentiated according to the format of the paper fed in. sheet fed offset is suitable for small and medium runs and is therefore mainly used in commercial and letterpress printing. With web offset, the paper comes straight from a large roll. It is mainly used for large and very large print runs, such as newspaper, catalog and telephone book printing.

In the past, offset printing plates were only copied from exposed films (as an intermediate carrier), but direct imaging (direct imaging) of the printing plate or CTP (computer to plate) has now established itself almost completely. With a laser (thermal or optical) the printing plate is exposed and developed in tiny dots (resolution up to 1,000 dots per centimeter) - today it is also chemical-free.

Screen printing: The artisanal-industrial screen printing, the (textile) film printing and the (artistic) serigraphy belong to the 4th group of printing processes, the so-called through-printing process. The printing form of the screen printing consists of a frame and a fabric, which is stretched over the frame. Using the fabric geometry (fabric thickness) and the theoretical color transmission volume of the stretched fabric and the coating thickness of the fabric, a defined layer thickness is achieved and guaranteed with repeatability. Parts of the fabric are covered (the barrier layer consists of an exposed, photosensitive layer). The printing parts are open, so they form the passage. This is then referred to as a stencil, printing screen or printing form.

The printing form is fixed in a device above the printing material. The printing medium is applied to the screen fabric on a non-motif area. During the printing process, the printing medium (e.g. a color) is coated into the printing form fabric ("pre-doctoring"). This is done with the flood squeegee.

The transfer of the printing medium to the substrate to be printed then takes place with the printing squeegee, which is guided over the screen in a line with a defined contact pressure. The jump is overcome by pressing downwards (distance between the substrate to be printed and the screen mesh). The pressure squeegee generates a shear force under which the pressure medium at the pressure squeegee edge maintains a lower viscosity. The rheological behavior of the printing medium - it becomes liquid due to a shear force and solidifies again when the shear force subsides - plays an important role in screen printing. If the viscosity builds

up again immediately after the shear force is removed, this is referred to as structural viscosity. If, on the other hand, the increase in viscosity is delayed (hysteresis), then one speaks of thixotropic.

The print medium now flows through the screen mesh and is absorbed by the print material. Immediately behind the pressure edge of the printing squeegee, the printing screen is released again from the substrate by the screen jumping off. The viscosity of the transferred printing medium increases again after the transfer due to the absence of the shear force. The higher-viscosity printing medium therefore does not run on the printed substrate and does not drip from the screen when it is pre-doctored. The printed image is clean and clear.

CMYK color model Mostly the CMYK color model (cyan, magenta, yellow (yellow), key (black = black)) is used, whereby a printing plate is required for each color. A large part of the colors of the color space can be printed with these four colors. For colors that cannot be printed with CMYK colors (gold, silver, reflective colors) or should not be printed (such as those of a company logo), there are also various standardized color palettes, such as HKS color fans or Pantone (solid colors). Different sizes of grid (extremely small dots that are not individually visible to the eye) result in a huge number of color nuances that are visible to the eye from four printing inks.

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