Blog
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printing are here (outdated) and chamber blade printing.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.
here are some example products for you a better understanding:
Brown Flexo Printing Paper Box
Logistic Shipping Box Moving Box Packing Box
Digital Device Packing Box
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Contact Us
Contact: Eric Liu
Phone: +86 15000723435
Tel: +86-27 87850068
E-mail: eric@shpkg.com
Add: Building 3, 720 Lane XinSongjiang Road, Songjiang, Shanghai 201612.