Working Process of Stack Flexo Printing Machine

Did you know that over 60% of all flexible packaging worldwide is produced using flexographic printing? Among the various types of flexographic machines, the stack flexo printing machine stands out for its versatility, precision, and ability to handle a wide range of substrates and print jobs.

As brands and manufacturers strive for faster turnaround times, higher printing quality, and reduced waste, understanding how a stack flexo printing machine works becomes essential. Whether you're a packaging company, print technician, or simply exploring printing technologies, this comprehensive guide will help you grasp the inner workings of this powerful equipment.

In this post, you'll learn everything from the key components of the stack flexo printing machine to its step-by-step working process, advantages, and how it compares to other technologies. We'll also include data-driven insights and a breakdown of each part's role in print quality and productivity.

Key Takeaway

A stack flexo printing machine uses a vertical stack configuration for its print stations, enabling precise multi-color printing on flexible substrates. It operates through a systematic process involving substrate feeding, ink application, image transfer, drying, and output. With fast setup times, reduced waste, and high-speed capabilities, it's ideal for packaging, labels, and large-scale print production.

Key Components of a Stack Flexo Printing Machine

Understanding the anatomy of a stack flexo printing machine is crucial to mastering its operation. Below we break down the core mechanical parts that contribute to its performance.

Print Stations – Vertical Stacking for Multi-Color Prints

The print stations in a stack flexo printing machine are arranged vertically, typically one above the other. Each station prints a specific color, allowing for multi-color designs. This configuration allows flexibility in print job setup and easy maintenance access.

Benefits:

• Supports 4 to 8 colors (or more) for complex graphics.

• Ideal for large-format printing on flexible packaging.

• Compact footprint compared to inline machines.

Anilox Rollers – Control Ink Transfer Precisely

The anilox roller is a critical component that controls the amount of ink transferred to the plate cylinder. It consists of a ceramic-coated roller engraved with thousands of microscopic cells.

Key Functions:

• Regulates ink volume.

• Ensures uniform ink distribution.

• Enhances print consistency.

Technical Insight: Anilox rollers are rated in cells per inch (CPI), and the depth of the cells determines the ink carrying capacity. Higher CPI = finer detail.

Plate Cylinders – Transfer Images onto the Substrate

The plate cylinder holds the flexible printing plates, which are usually made of photopolymer. These plates are imaged with the desired artwork and wrapped around the cylinder.

Functions:

• Transfers inked image to substrate.

• Works in conjunction with the impression roller.

• Replaced or changed during job setups.

Impression Rolls – Ensure Consistent Contact and Print Quality

The impression roll applies pressure to ensure proper contact between the substrate and the plate cylinder. It's vital for maintaining print clarity and registration.

Benefits:

• Maintains print consistency.

• Reduces substrate movement.

• Works with tension control systems.

Drying Systems – UV or Hot-Air Dryers for Quick Curing

Each color station is equipped with drying units that can be UV-based or hot-air systems. These units cure the ink before the substrate moves to the next color station.

Comparison of Drying Methods:

Web Handling System – Tension Control for Smooth Substrate Movement

The web handling system ensures the substrate moves smoothly through the machine. It includes unwind units, tension sensors, guide rollers, and rewind mechanisms.

Importance:

• Prevents substrate wrinkling or misalignment.

• Maintains precise registration.

• Supports high-speed operation.

Step-by-Step Working Process

The working process of a stack flexo printing machine involves synchronized steps that turn raw substrate into finished printed material.

Substrate Feeding

The process begins with substrate feeding from the unwind unit. The system can handle various substrates like plastic films, paper, aluminum foil, and nonwovens.

Key Features:

• Automatic tension control.

• Edge guiding systems for alignment.

• Roll diameter sensors for efficiency.

Ink Application

Next, ink is applied to the anilox roller via an ink fountain or chamber doctor blade system. From there, it transfers a measured amount of ink to the plate cylinder.

Modern Enhancements:

• Closed ink systems reduce evaporation.

• Real-time viscosity control for consistent ink quality.

Printing

The plate cylinder, carrying the image, comes into contact with the substrate with the help of the impression roller. Each color is applied in a separate station, and the substrate passes vertically from one unit to the next.

Highlights:

• Supports up to 10 colors.

• High-speed printing (up to 600 m/min).

• Suitable for both water-based and solvent-based inks.

Drying / Curing

After each color is printed, the ink is dried or cured using hot-air or UV dryers. This prevents ink smearing and enables faster production.

Drying Efficiency Tip: Using interstation UV dryers can significantly increase throughput.

Registration & Alignment

Advanced registration systems use cameras and sensors to ensure each color aligns perfectly with the previous one. This is essential for high-resolution graphics.

Technologies Used:

• Servo motors for micro-adjustments.

• Closed-loop feedback systems.

Finished Product Output

Once printing is complete, the substrate is rewound or cut into sheets, depending on the application. Inline slitting, perforation, or lamination can also be integrated.

Advantages of Stack Flexo Printing Machines

The stack flexo printing machine offers several benefits that make it the go-to choice for converters and packaging producers.

Key Advantages:

• High Versatility
  Can print on various substrates — from thin films to heavy paperboard.

• Excellent Color Reproduction
  Multiple print stations ensure vibrant, accurate colors.

• Compact Design
  Vertical stacking saves floor space and simplifies access.

• Easy Maintenance
  Separate print decks allow for isolated maintenance without stopping the whole machine.

• Cost-Effective for Long Runs
  Ideal for large-scale packaging and label production.

• Speed and Efficiency
  Modern machines can reach speeds of 500-600 meters per minute.

• Eco-Friendly Inks
  Compatible with water-based and UV-curable ink systems.

Comparison: Stack Flexo vs. Other Printing Technologies

Conclusion

The stack flexo printing machine remains a cornerstone in the world of flexible packaging and label production, thanks to its modular design, high printing speeds, and ability to handle a wide variety of substrates. From substrate feeding to drying, each step in the working process is optimized for speed, consistency, and print quality.

In an era where consumer expectations are rising and print runs are becoming more customized, the stack flexo system offers the right balance between traditional volume printing and modern-day flexibility.

Investing in the right flexo technology not only improves production efficiency but also supports sustainable practices with eco-friendly inks and minimal waste. As the industry evolves, expect further integration of AI-driven registration, automated web handling, and IoT-based diagnostics to further enhance the capabilities of stack flexo printing machines.

FAQs

Q1: What materials can be printed with a stack flexo printing machine?

A: It can handle paper, plastic films, aluminum foil, nonwoven fabrics, and more, making it extremely versatile.

Q2: What's the difference between stack and CI flexo printing machines?

A: Stack flexo printers have independent vertical print units, while CI (Central Impression) machines have all colors printed around a central drum. Stack machines offer better flexibility for multiple substrates.

Q3: How many colors can a stack flexo machine print?

A: Most commercial machines support 4 to 10 colors, depending on configuration and application.

Q4: Is UV printing supported in stack flexo machines?

A: Yes, many modern systems are equipped with UV drying systems for faster curing and better durability.

Q5: What industries use stack flexo printing machines?

A: Common industries include food packaging, pharmaceutical labels, industrial wraps, and retail bags.