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about flexo printing

Author: Elena Ruan, sales manager of shanghai custom packaging Email: elena.ruan@shpkg.com

Flexo Printing is a direct high-pressure process.
It is a web-fed printing process in which flexo printing plates made from photopolymer or rubber, and low viscosity inks can be used. As high-pressure process, the raised areas of the printing plate are image supporting while the printing unit structure is simple and the intaglio printing process is similar. At the beginning of aniline dyes were used, by which was the flexo one of the high-quality printing process. Today it is characterized by its diverse application areas of, for flexographic printing can print on many materials that are to be printed be prohibited or restricted in other printing processes.
Contents
1 Application
2 The printing unit construction
2.1 The dipping roller printing unit
2.2 The chambered doctor blade system
3. printing form
4.The anilox roller 4
5 The ink
5.1 Solvent and water-based paints
5.1.1 Two-component paints
5.2 UV inks
6. The machine assembly
7. features
8. History and Development
9. References
10. journals
11. Web Links
12. References

Range
The main application is the printing of packaging materials made from plastics (such as PE, PET, PVC, PS, PP, PC, metallized film), paper and cardboard. The printability of plastic film is diminished by pretreatment of the printing material (usually Corona treatment for increasing the surface tension) allows, and the wetting properties of the low viscosity flexographic ink. Other possible uses include adhesive films, insulating paper, beverage containers, napkins, Carbon Copy, wallpaper and latex balloons. The Zeitungs flexo printing represents another field of application. In the US, Italy and UK newspapers are produced in Flexo Printing. However, the dominant on the world market newspaper printing processes is the offset.

The printing unit assembly
The sink roll printing unit
The chamber doctor blade system
In general, the flexographic printing unit includes an anilox roller, over which the printing plate is inked, called a printing cylinder, and plate cylinder on which the printing plate is mounted, and an impression cylinder which carries the printing material. Deviations in the design produced by various methods of coloring the anilox roller. Differences dipping roller printing are here (outdated) and chamber blade printing.

The dipping roller printing

In the dipping roll printing unit is delivered via the fountain roller ink to the screen roller. The excess paint can be with the aid of a doctor blade, which is steeply against the screen roller, stripped. The anilox roller has an open or closed doctor blade system.
The chamber doctor blade system
When chambered doctor blade system or open doctor blade system, the excess ink is also stripped with a doctor blade of the anilox roller surface. However, the ink is pumped into a chamber in this method, with which air pressure pushes close to the screen roller and the doctor blade contains. Doctor blades are usually made of steel, variants are plastic squeegee and ceramic coated steel blade.

Printing form
There are two different types of printing forms: produced by laser engraving rubber plates and photopolymer plates from UV-sensitive plastic. The latter are produced by exposure of the printing and subsequent washing out of the non-printing elements. The printing form, with the next line and text and halftones can be simulated by a scan is excited after their production to the printing cylinder. For mounting adhesive sheets are used, which significantly influence by their compressibility ink transfer. While incompressible films suitable for the printing of solid, compressible films are advantageous for the screen printing. Not only the properties of the adhesive films, but also the thicknesses even affect the printing process. Usually thin thicknesses for screen printing and thick are used for surface pressure. For thick substrates (for example, corrugated) and thick plates are used, since these changes in thickness can compensate for the printing material. Both rubber and now from photopolymer can cleavable in specific manufacturing processes and seamless printing forms are made for continuous printing.

The anilox roller
The anilox roller is used for the ink metering. Its surface consists of either chromium or ceramic (the most common) and is engraved by Moulette, YAG or CO2 laser. Accessible depending on the application are engravings from 60 to 500 cells per centimeter. Is the Rasterwalzenrasterung too rough, this can lead to undesirable tapering (fouling) of the smallest dots. In the wells formed by engraving the color is stored in the printing process. The wells are then partially emptied on the printing plate. It remains always at least half of the color as the remainder in the pan. Influence on the transferable ink volume have cell geometry and web content. The cups of the raster roller are arranged orthogonally or generally hexagonal. Alternatively, there is line-engraved anilox rolls. However, these are not in the flexo, but used in gluing units or short inking units of offset printing.

The ink
According to the wide variety of substrates and a variety is used in low-viscosity inks in flexographic printing. These can be divided into solvent-based, water-based and UV-curing inks. A special form of solvent-based inks represent the two-component colors.

Solvent and water-based inks
These colors are made up of
Solvent (ethanol or water in water-based paints) for regulating the viscosity,
Colored pigments,
Binders (soluble resins or acrylates for fixing the pigments)
and additives (waxes for abrasion resistance, flexibility and sliding properties of the ink film or blend to correct hue and color strength).
Such inks dry physically by driving off the solvent or evaporation of water play. This evaporation process is conveyed into drying boxes behind Farbwerken by fans. Supportive to IR radiation units are used. Since solvents and their vapors are flammable, they must be sucked in a closed air circuit. When using water-based inks, however, the viscosity and the pH must be controlled and regulated during long print jobs.

Two-component paints

When printing on transparencies can, usually the primer, a special two-component color are used. In addition to the solvent-based ink systems hardener are mixed, which enter into a prolonged chemical reaction with the binder of the color. The paint dries initially normal by evaporation of the solvent, while the complete curing process can take several days. The advantages over a normal color on these substrates are higher seal resistance, scratch resistance and better adhesion properties.

UV inks
UV inks are made in addition to a high content of binder of color pigments, additives and photoinitiators. Dry in a photochemical process, by photoinitiators a curing of the binder contained is triggered under the influence of UV radiation. Immediately behind the inking unit and the run through the radiator, the color is almost completely fixed. When handling of UV inks, it is important to avoid direct skin contact, as they can cause skin irritation and allergies. In addition, the radiation units must be completely sealed off, as direct contact with the UV radiation changes of the skin cells (especially in the eye) caused.

The machine assembly
Flexo printing in line construction
Satellite or central cylinder construction
compact design
Today flexographic presses usually have between four and ten printing units. These are arranged in series construction, satellite construction (central cylinder) or multi-cylinder compact design. Unlike the two alternatives, the satellite design has only one central impression cylinder in order to arranged the individual works. Since the web is held on the impression cylinder during the entire printing process, achieved this type of machine the maximum register accuracy and high production speed, there are up to 800 m / min. [1] An additional advantage over the line construction is the low space requirement. A disadvantage is the difficult accessibility of the individual printing units. In all constructions are located after each printing unit drying facilities. While the web of material the series construction thus the drying path can be extended and deflected, this is not possible in the satellite configuration. The short path and the high rate of production do not allow complete drying between the printing units. Other necessary equipment components are off and rewinder, ink pumps and web edge control. Moreover, there are ways to incorporate additional components such as cutting or punching, varnishing, corona treatment plant as well as measurement and monitoring systems.
The largest flexo presses are Zeitungsflexodruckmaschinen. In Italy are central cylinder machines, double width with a capacity of up to 96 pages 4/4-color. The currently largest Zeitungsflexodruckmaschine stands in London. It consists of eight rotations with a total of 320 pressure points. [2]

Features
Just as prints, which are produced in high-pressure processes, prints Flexo Printing may have pinched edges. These occur at too high a pressure on the pressure in zone using photopolymer plates. Most of this nuisance is accompanied by a tone value. If the pressure between the impression cylinder and the impression cylinder on the other hand too low, there is the risk of bubble formation between the printing form and the substrate, which can lead to uneven wetting of the printing medium with color. Unlike other high-pressure processes no shades can be recognized in flexographic printing.
When Zeitungs flexodruck low viscosity, color-rich, water-based inks are used. The result is a firmer abrasion and odor poorer pressure than in coldset. The newspaper reader after reading no printing ink on the fingers as the offset.