Flexographic printing uses a flexible plate to print onto a substrate, which may be a wood-pulp based, synthetic, or laminated material.
Such substrates may include:
Films such as polyester, OPP, nylon, and PE, Papers, Carton board, Non-woven textiles, Coated or un-coated liner board.
Today’s flexo printing presses use photopolymer printing plates containing a mirror relief image of the required print.
The raised areas on the plate have ink applied to them by an anilox roller and then transfer it onto the substrate.
There are three different structures of a flexographic printing machine, which is depending on the arrangement of the printing units,
and also may be called the printing decks: they are CI flexo printing machine or central impression printing machine, stack flexo printing
machine and the inline flexo printing machine.
Central impression printing machine, or CI, flexo printing machine means that decks are arranged around a single,
large-diameter impression cylinder.
In a modern flexographic press, each print unit comprises of:
Anilox roller: a cylinder of highly engineered metal and/or ceramic, which is laser engraved with minute cells of a given angle, line screen,
and volume to deliver the required fineness of print,
Chambered doctor blade system: a device that delivers a measured amount of ink to the cells of the anilox roller
Plate cylinder: which the printing plate is mounted upon
Impression cylinder: a sleeve that supports the substrate as the printing plate is pressed against it
Inking system: ink holding tank, ink pump with delivery and return ink lines, plus other elements to ensure the maintenance of ink supply and viscosity
Between the print units, driers may be installed so that subsequent colors can be applied to the substrate without merging into those previously printed.
These driers may utilize hot air, infrared or ultra-violet light, depending on the application.
During the printing process, the ink is pumped into the ink chamber of the doctor blade system. Two blades within the ink chamber, the barrier blade,
and the doctor blade, seal either end and confine the ink to the chamber while it is in contact with the anilox roller. As the anilox roller rotates, the cells
in contact with the doctor blade system collect ink, and then any surface excess is removed as the roller passes under the doctor blade. As the anilox rotates,
its surface comes into contact with the raised areas of the printing plates mounted on the plate cylinder, transferring the ink. The printing plate then rotates
and transfers the image onto the substrate.
CI Flexo Printing Machine Applications:
The applications of CI flexo printing include the manufacture of flexible and aluminum packaging, pre-print liners and labels, plastic and paper bags, heavy-duty
paper sacks, and shrink sleeves.
The flexo printing press offers users a number of advantages, not least that the most readily available inks are water-based and therefore easier to work with and
faster to dry.
The manufacture of flexo printing plates is relatively straightforward and the process is also easily adaptable to a wide range of substrates.
The high print quality and registration accuracy of CI (Central Impression) flexo printing are well established, while recent developments among in-line flexo printing presses have meant that flexographic presses are now able to compete against gravure and litho machines in areas such as fiber-board packaging manufacture.
Stack flexo printing machine means the decks are stacked one above the other.
The in-line flexo printing machine means the print units are laid out horizontally in a line.
The difference between CI flexo printing machine and Unit type flexo printing machine
Difference in machine structure：
The printing unit of the CI flexo printing machine is arranged around the center cylinder, and the printing is performed under the same tension. The tension is stable, the feeding path is short, and stable register printing.
The printing units of the unit type flexo printing are arranged in sequence and sequentially heated by the oven after and after printed, which will cause changes in the printing materials, Especially inaccuracy register printing caused by the tension fluctuate during the process of raising and lowering speed. Factors such as printing perimeter control and printing plate roll accuracy differences can cause printing instability.
Difference in register printing type：
The register printing of CI flexo machine is printing under the same tension. The principle of register printing is according to phase difference of each motor to perform register printing control , there is no effect on start-up, shutdown, acceleration, deceleration, and quality of printed labels.
The register printing of unit type is based on the detection of printed marks for register printing after printed and there is a lag adjustment. For start, stop, acceleration, deceleration, quality of the printed target, etc., there will be detection of printed marks to adjust and lag, causing waste.
Waste from printing clutch pressure：
The register printing of CI flexo printing dose not need to be adjusted under combined pressure and separation pressure, and the register printing accuracy is not affected.
But In the unit type, after the pressure is removed, there is no printing detection mark. the reading and detection of the mark after printing is wasteful.
Different finished product rates：
It is no need to operate the CI flexo printing machine after restarting, accelerating, and changing rolls. The waste of changing rolls is generally about 10 meters. But for the unit-type flexo printing machine, the printing marks will change after printing and changing rolls. After marking, there is waste in adjusting again, and the waste of changing rolls is generally more than 100 meters. The finished product rates of CI flexo printing machine is around 99.5%, while finished product rates of unit printing is around 97%.
Different production efficiency:
The printing unit of CI flex printing machine is heavy, generally about 25 tons, and ensure the stable high-speed printing. The printing process is that after the color ink is dried, it is finally entered into a large oven, and drying is more energy-saving. Printing speed is generally 260-320 m / min. The colors of unit type are arranged separately, and after each color is thoroughly dried, it enters the next color. The printing speed is generally 100-150 meters / minute.
The operation of CI flexo printing machine is easier. Register printing, pressure, roll changing are all automatic. The unit type flexo priting machine separate arrangement of each color makes the operation more difficult. Generally, operating CI flexo printing machine only needs two people, while the unit type flexo printing machine needs 3-4 people, and the operator needs “eyes and hands fast”, which has higher requirements.
Printing pressure stability
The central cylinder of the CI flexo printing machine adopts constant temperature control, and the printing pressure is relatively stable. For unit type flexo printing machine, the change of each printing bottom roller is different, and compared with CI flexo printing presses, the printing pressure constant is poor.
The inks of CI flexo printing machine are centralized, which is beneficial to ink management and reducing waste. The unit-type flexo printing machine inks are arranged in rows on the transmission side, which increases the difficulty of managing ink and wastes cleaning ink.
Order change time is different:
CI flexo printing machine are concentrated in the single station. The same personnel and the same number of printing groups, and order changing time is generally 20 minutes, while unit type flexo printing machine require 40 minutes. For non sleeve type flexo printing machine takes longer than 80 minutes. The CI flexo printing machine saves more than 50% on order change time.
Flexographic printing is a method of using rubber printing plates mounted on a cylinder of various repeat lengths which is inked by a roll carrying fluid ink. For every revolution of the printing plate cylinder an image is roduced.
Rotogravure printing is a newer technology that relies on engraved individual cylinders to produce the printed image.
Each option has certain advantages, (Flexographic is great for smaller quantity runs and generally is cheaper where Rotogravure produces better quality images) but recent advances in pre-press cylinder engraving technology has allowed us to deliver “gravure”quality at “flexo”prices.