What is Flexographic Printing and How It Works?

Flexographic printing, commonly known as flexo printing, is a high-speed, roll-feed web printing process that has become essential in producing high volumes of labels, flexible packaging, and various specialty items. With the capability to achieve speeds of up to 2000 linear feet per minute, flexography stands out for its efficiency and versatility.

Applications of Flexographic Printing

Flexography is predominantly used for printing on a variety of materials such as:

Labels
Flexible packaging
Folding cartons
Corrugated packaging
Gift wrap
Tissue paper
Napkins
Shopping bags
Envelopes
Ice cream cartons
Disposable plates and cups

Additionally, narrow-web flexographic printing presses have diversified into producing smaller packages like pouches, shrink sleeves, sachets, and snack wrappers.

How Flexographic Printing Works

The process involves several key components and steps:

The Photopolymer Plate: A flexible, photopolymer plate is wrapped around a rotating cylinder for each colour. Similar to letterpress printing, only the raised areas of the plate are inked and pressed onto the substrate.
The Rollers: A typical flexographic press includes four types of rollers:
- Fountain Roller: Delivers ink from an ink pan to the anilox roller.
- Anilox Roller: A steel or ceramic roller with finely engraved cells that transfer a uniform thickness of ink to the plate cylinder.
- Plate Cylinder: Holds the photopolymer plate and transfers the ink to the substrate.
- Impression Cylinder: Applies the necessary pressure to transfer the ink from the plate to the substrate.
Ink Transfer: First, the fountain roller delivers ink to the anilox roller. Next, the ink moves from the anilox roller to the plate cylinder. Finally, the ink transfers onto the substrate as it passes between the plate cylinder and the impression cylinder.
Drying Units: After applying each color, the drying units using hot air, infrared, or ultraviolet light fully dry the ink before the next color is applied.
Types of Presses:
- Stack Press: The printing decks stack vertically, which allows printing on both sides of the material.
- Central Impression (CI) Press: The printing decks position around a single, large impression cylinder, ensuring excellent registration.
- In-line Press: The printing decks align in a straight line, making it suitable for heavier substrates.

Inks Used in Flexographic Printing

Flexography accommodates various types of inks, including:

Water-based inks: Commonly used for printing on corrugated packaging.
Solvent-based inks: Used for printing on plastic shopping bags and industrial films.
Energy-curable inks: UV or electron beam (EB) curing systems quickly cure these inks, used for food packaging outer wraps.

Substrates

Flexographic presses can print on a wide range of substrates, such as:

Uncoated or coated papers
Carton board
Liner board
Aluminium foil
Various plastic films (e.g., LDPE, PP, BOPP, PET)
Non-woven fabrics
Laminates (multi-layered materials providing barrier layers for flexible packages)

Prepress, Platemaking, and Press Set-Up

Flexographic printing demands expertise in preparing artwork, images, and plates to ensure high print quality and minimise waste. Factors affecting print quality include plate types, image elongation, dot gain, and registration accuracy. Modern advancements have introduced digital photopolymer plates and automated prepress and platemaking processes, enhancing efficiency and reducing errors.

Post-Press and Finishing Processes

You can integrate post-press processes like die-cutting, cold foil stamping, and varnishing into in-line presses. Additional equipment like slitting machines, folders, gluers, and die-cutters transform printed rolls into finished products.

Technological Advances

Flexographic technology continues to evolve with advancements aimed at improving automation, environmental sustainability, and reducing waste. Hybrid flexo/inkjet systems, extended colour gamut systems, and sophisticated colour quality-control systems are examples of ongoing innovations.

Conclusion

Flexographic printing remains a cornerstone of the packaging industry due to its speed, versatility, and adaptability. As technology advances, flexography continues to evolve, meeting the growing demands for high-quality, efficient, and sustainable printing solutions.

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