Flexographic printing is a versatile and cost-effective technique widely used in the packaging industry.
At the core of flexography lies platemaking, the process of preparing image carriers for printing.
Advances in plate technology have revolutionized flexographic printing, improving print quality, plate sizes, and reducing dot gain.
There are several types of image carriers used in flexographic printing, including rubber plates, photopolymer plates, and laser-engraved rubber plates or rollers.
Each plate technology offers unique advantages and applications.
Rubber Plates
Rubber plates have a long-standing tradition as the primary image carriers in flexographic printing.
They are created by duplicating an original plate, often comprising various type elements like hand-set foundry type, Monotype or Linotype, and zinc plates for line and halftone images.
The process involves molding a heat-setting matrix material against the original plate using a hydraulic press.
The resulting rubber stereo serves as the printing plate. Rubber plates are commonly used for line work and in situations requiring unique solvents in inks.
Advantages
- Tradition and familiarity in the printing industry.
- Suitable for line work and unique ink solvents.
Limitations
- Limited resolution for halftone images.
- Less appropriate for complicated designs.
Photopolymer Plates
Photopolymer plates have gained significant popularity in flexographic printing due to their ease of use and high-quality results.
These plates are directly created from photographic negatives, utilizing light-sensitive photopolymers.
When exposed to UV light through a photographic negative, the photopolymer polymerizes and becomes resistant to the washing-out medium.
The non-image areas are then removed, leaving behind the printing plate.
Photopolymer plates are available in various thicknesses, hardness levels, and with different backing materials.
Advantages
- High-quality results with fine details and halftone reproduction.
- Ease of use and convenience in plate creation.
Recent Advancements
- Thinner plates with reduced dot gain.
- Environmentally friendly wash-out solvents and water-washable solid plates.
Laser-Engraved Rubber Plates or Rollers
Laser engraving offers a unique method of preparing image carriers for flexographic printing.
It allows for the engraving of rubber plates or rollers using laser techniques.
Laser engraving can reproduce precise line work and halftone images from black and white positive copy or screened negatives/positives.
Advantages
- Precision in reproducing fine details and complex designs.
- Well-suited for continuous design printing.
Plate Mounting
Plate mounting is a pivotal step in the flexographic printing process.
Various methods are used, including the use of two-sided self-adhesive material. Pre-registering the plates in position on specialized equipment is essential to minimize unproductive time on the printing machine.
The use of a "cushion-back" adhesive layer can compensate for plate or press inaccuracies.
Using the thinnest possible adhesive tape ensures accurate printing by minimizing thickness variations.
Control of Flexographic Printing
Achieving optimal print quality in flexographic printing requires careful control of various factors.
This includes managing ink viscosity and its temperature dependence, understanding the role of the anilox roller, and adjusting pigment concentration with a medium.
Different applications may require specific ink viscosities and ink lay to control dot gain in halftone printing.
Waste reduction and make-ready time optimization efforts are crucial to improving efficiency and productivity in the flexographic printing process.
Conclusion
plate technology plays a critical role in the flexographic printing process, influencing the quality and versatility of printed materials.
Advancements in plate technology have led to improved print quality, larger plate sizes, and reduced dot gain, making flexographic printing a competitive and cost-effective printing method in various applications, especially in packaging
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