Flexographic Printing Introduction

1. What is flexographic printing?
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.

2. How many kinds of flexographic printing machines? 
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.

3. What are the differences from the 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.
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.
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.

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.

Process advantages
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.

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