The flexographic process is a widely used printing method that employs relief printing to create images.
This article explores the various aspects of flexography, including the inks used, printing units, anilox rollers, press configurations, and recent developments.
Flexographic Process Overview
Flexography utilizes a relief printing technique where the printing image stands up in relief.It primarily uses liquid inks, which can be solvent-based, water-based, or UV-cured systems. The process relies on low printing pressure due to combination of fluid inks and soft, flexible printing plates.
These characteristics enable fast printing speeds on non-absorbent materials like films and foils.
Flexography also offers the ability to change or repair individual plates easily and obtain proofs.
The Printing Unit
The printing unit consists of three main parts: the inking unit, plate cylinder, and impression cylinder.The inking system's role is to apply a controlled film of liquid ink to the printing plate's surface.
It typically includes an ink trough, a rubber-covered fountain roller, and a screened (Anilox) inking roller engraved with cells.
The ink is transferred from the cells of the inking roller to the printing plates.
The plate cylinder, usually made of steel, holds the printing plates securely with self-adhesive material.
The impression cylinder, also made of steel, generates light printing pressure by passing the substrate between the plate and impression cylinders.
Anilox Roller and Ink Supply
The anilox roller is a critical component in achieving high-quality flexographic printing. It determines the ink supply to the plate.Anilox rollers can be made of ceramic or chrome-plated materials, each with different ink release characteristics.
Ceramic rollers, especially those laser-engraved, offer greater durability and control over screen ruling, cell shape, and profile.
The number and size of cells on the anilox roller regulate the volume of ink transferred.
Ink film thickness can be further regulated by adjusting the surface speed of the fountain roller, pressure between the fountain roller and screened roller, and the hardness of the rubber covering on the fountain roller.
Press Configurations
There are three basic types of flexographic press configurations: stack, common-impression, and in-line.The stack press features two or three integral printing units arranged vertically.
This configuration is commonly used for paper printing but less suitable for films.
The common-impression machine consists of multiple printing units arranged around a large cylinder.
This configuration allows for precise register between colors, making it ideal for multi-color work on extensible films.
The in-line machine has printing units arranged horizontally, with the impression cylinder below the web.
It is suitable for printing on lightweight board and less flexible materials.
Winding and Finishing
Flexographic printing often requires reel-form products for further processing.Machines used for flexography offer versatile winding equipment.
The printed web can be chopped into sheets in register, and manual or automatic splicing and infeed control options are available.
Ink drying systems , such as hot air or heated drums, ensure rapid drying to prevent set-off and sticking.
Rewinding equipment employs either a center or surface winding principle.
These features contribute to the efficiency and productivity of the flexographic process.
Recent Developments in Flexography
Flexography is constantly evolving, adapting to new requirements and technological advancements.It has been adapted for newspaper printing, and electronic pre-setting and control systems have been introduced.
New types of inks, including water-based and UV-cured systems, are being utilized. Inking systems are also undergoing improvements.
These developments have expanded the capabilities of flexographic printing and opened up opportunities for high-quality and diverse applications.
Conclusion
Flexography is a versatile printing process with distinct features, including the use of liquid inks, soft printing plates, and low printing pressure.
The printing units, anilox rollers, and press configurations contribute to the overall quality and efficiency of flexographic printing.
Ongoing developments in the industry continue to enhance the process, offering improved print quality, control, and capabilities.
With its adaptability and advancements, flexography remains a vital printing technique in various industries.
The printing units, anilox rollers, and press configurations contribute to the overall quality and efficiency of flexographic printing.
Ongoing developments in the industry continue to enhance the process, offering improved print quality, control, and capabilities.
With its adaptability and advancements, flexography remains a vital printing technique in various industries.
7