Flexographic printing (often simply called flexography or flexo) is a modern and highly versatile relief printing technique. It is primarily used in the packaging industry to print self-adhesive labels, packaging films, corrugated cardboard, paper bags, and even napkins or wallpaper.
A characteristic feature of flexography is the use of flexible printing plates and fast-drying inks (water-based, solvent-based, or UV-cured).
Main stages of the flexographic printing process
- Design preparation (Prepress)
- The graphic design is prepared digitally, taking into account the specific requirements of flexography (e.g., compensation for material stretching or allowances for color registration).
- The image is prepared using color separation (typically CMYK plus Pantone spot colors or special whites).
- Imaging of printing forms (Flexographic plates)
- Printing forms are usually made of flexible photopolymer, either as flat plates or seamless sleeves.
- This process is most commonly carried out using a digital method (Computer-to-Plate / CTP):
- A laser ablates the mask layer on the photopolymer plate where the image is to be formed.
- Subsequently, the plate is exposed to UV light, and the uncured areas are washed away (or thermally removed), creating a raised relief (the printing pattern).
- Mounting the printing plates on the press
- The finished flexible photopolymer plates are precisely mounted (adhered using double-sided tape) onto the plate cylinders of the flexographic press. Modern presses utilize vision systems to ensure perfect color registration.
- Printing process (Flexography principle)
- Flexographic presses typically operate in an inline configuration or as central impression (CI) presses. The printing process itself proceeds in several steps at each color station:
- Ink pickup: The anilox roller, covered with microscopic cells, picks up ink from the reservoir.
- Metering: A doctor blade (a specialized blade) removes excess ink from the anilox roller, leaving a precisely defined amount within the cells.
- Transfer to the plate: The anilox roller transfers ink to the raised elements of the printing plate (photopolymer).
- Impression on the substrate: The printing plate presses the substrate (e.g., film, paper, or cardboard) against the impression cylinder, permanently applying the image.
- Flexographic presses typically operate in an inline configuration or as central impression (CI) presses. The printing process itself proceeds in several steps at each color station:
- Inter-station drying
- Since flexography involves high-speed printing on non-absorbent materials (e.g., plastic films), advanced drying systems (UV lamps, LEDs, or hot-air dryers) are installed between the individual printing stations and at the end of the line.
- In-line finishing and die-cutting
- Many modern flexographic presses allow for additional operations to be performed during a single pass of the material, such as:
- Varnishing (e.g., with UV varnish),
- Lamination (bonding multiple layers of film),
- Die-cutting (cutting out finished label or box shapes).
- Many modern flexographic presses allow for additional operations to be performed during a single pass of the material, such as:
Advantages and disadvantages of flexographic printing
- Substrate versatility: Ability to print on flexible, smooth, or uneven substrates, as well as thick corrugated board (which would be damaged in offset printing).
- High speed and productivity: An ideal technology for high-volume production (e.g., millions of labels or linear meters of film).
- Quick-drying inks: Allow for immediate rewinding of the material into rolls and further processing.
- Sustainability: Increasing use of water-based inks and safe UV/LED inks.
- Time-consuming and costly setup: The production of polymer plates and precise machine calibration can make short print runs unprofitable.
- Limitations regarding detail: Although modern flexography achieves excellent quality, it may still lag behind rotogravure or advanced offset printing when it comes to very fine details and precise tonal transitions.