What is a flexo printing press?

 In-depth  Analysis of Inline, Central Impression, and Stack Flexographic Printing Technologies

Introduction

In the contemporary packaging and printing industry, flexographic printing technology has become a mainstream process in areas such as labels, flexible packaging, and corrugated boxes, owing to its environmental friendliness, high production efficiency, and broad substrate adaptability. Inline flexographic printing, central impression (satellite) flexographic printing, and stack printing, as three primary forms of flexo technology implementation, each possess unique technical characteristics and suitable application scenarios. This article provides a comprehensive and systematic comparative analysis of these three printing technologies from multiple dimensions, including mechanical structure, printing process, quality control, application fields, and economic benefits, offering professional reference for printing companies in their technology selection.

I. Differences in Mechanical Structure and Working Principles

Inline Flexo Press

Inline flexographic presses adopt a linear arrangement structure, with each printing unit sequentially arranged in a horizontal or vertical direction. Each printing unit is independently equipped with a plate cylinder, an impression cylinder, and an inking system, achieving synchronous operation through a central drive system or electronic shaft drive. ZONBON brand high-end inline equipment utilizes a "tower" design, with printing units arranged vertically, saving approximately 30% of floor space.

Technical Characteristics:

Modular design, allowing flexible configuration of 1-12 printing units

Typicolor group spacing is usually 800-1200mm

Utilizes a closed chambered doctor blade inking system, with ink transfer accuracy of ±0.5μm

Registration accuracy can reach ±0.05mm (with electronic shaft drive system)

Central Impression Flexo Press

The core feature of the central impression (CI) flexo press is the common impression cylinder structure, where all printing units are arranged in a satellite formation around a large central impression cylinder. ZONBON brand CI-type equipment uses a single-wall alloy steel impression cylinder with a diameter range of 800-2500mm, treated with dynamic balancing to achieve a radial run-out of ≤0.01mm.

Technical Characteristics:

Central impression cylinder surface temperature control accuracy of ±0.5℃

Compact color group spacing, typically 400-600mm

Utilizes a short ink path system, improving ink transfer efficiency by 15-20%

Registration accuracy can reach ±0.03mm (benefiting from the common impression surface)

Stack Flexo Press

Stack presses employ a vertically stacked structure, with printing units arranged one above the other, achieving synchronization through gear transmission. ZONBON brand stack equipment uses three-point floating bearing support, effectively reducing mechanical vibration to ≤0.005mm.

Technical Characteristics:

Compact structure, occupying only 40% of the floor space of an inline press

Vertical spacing between color groups is 500-800mm

Uses an open ink fountain or simple doctor blade system

Registration accuracy is generally ±0.1mm

Table 1: Comparison of Mechanical Parameters of the Three Flexo Press Types

Parameter                              Inline                        Central Impression      Stack

Color Unit                              Arrangement Linear  Satellite Vertical            Stack

Typical Color Unit Spacing  1000mm                     500mm                          600mm

Impression Method          Independent               Common                      Independent

Mechanical Accuracy           ±0.05mm                   ±0.03mm                    ±0.1mm

Floor Space                           Large                           Medium                        Small

II. Comparison of Printing Process Performance

Registration Accuracy Performance

CI presses, leveraging the advantage of the common impression surface, exhibit the best registration accuracy, especially suitable for precision printing on extensible materials (like PE film). Measured data shows that the ZONBON brand CI-450 CI press has a registration fluctuation of ≤0.03mm at 200m/min.

Inline presses, through optimization of electronic shaft drive and tension control systems, can achieve registration accuracy of ±0.05mm, meeting most packaging printing requirements. Stack presses, due to cumulative errors in mechanical transmission, have relatively lower registration accuracy, typically around ±0.1mm.

Ink Transfer Characteristics

The short ink path system of CI presses enables ink transfer efficiency of 85-92%, with dot gain controllable within 12%. The constant temperature ink chamber system (25±0.5℃) developed by ZONBON further ensures ink viscosity stability.

Inline presses use a closed inking system, with ink transfer efficiency of 80-88%, and dry-back density deviation for 8-color printing is ≤0.08. Stack presses, limited by the open ink fountain, have ink transfer efficiency of only 75-82%, requiring frequent ink adjustments.

Substrate Adaptability

CI: Particularly suitable for thin, easily stretched materials (12-250μm films), capable of handling high-temperature materials like 3-layer co-extruded PE, PP (maximum temperature resistance 150°C).

Inline: Most versatile, capable of handling papers, films, foils, and composite materials ranging from 30-500g/m²; ZONBON equipment configured with UV curing systems can UV inks.

Stack: Mainly applicable to rigid materials like cardstock and corrugated board ranging from 300-2000g/m².

Printing Speed Range

CI: 150-450 m/min (for films)

Inline: 100-300 m/min (general purpose)

Stack: 80-200 m/min (for paperboard)

III. Key Quality Control Technologies

Tension Control System

ZONBON inline equipment uses full closed-loop tension control, with segment control accuracy reaching ±0.5N. CI equipment benefits from the stable traction of the central impression cylinder, with tension fluctuation ≤0.3N. Stack equipment typically uses mechanical tension control, with an accuracy of ±1.5N.

Registration Control System

High-end inline and CI presses are equipped with CCD automatic registration systems, capable of detecting and correcting registration deviations of ±0.02mm in real-time. The ZONBON ACR system samples every 50ms, with a response time of <100ms.

Color Management System

Modern flexo presses are commonly equipped with online spectrophotometers. The ZONBON ICS system can achieve:

ΔE ≤ 1.5 (under standard illuminant D50)

Color difference automatic compensation response time < 30s

Support for ISO 12647-6 standard

IV. Application Fields and Economic Analysis

Typical Application Scenarios

CI: Food flexible packaging (60%), pharmaceutical packaging, label printing.

Inline: Carton packaging (45%), labels (30%), specialty packaging.

Stack: Corrugated box pre-print (70%), thick paperboard packaging.

Return on Investment Comparison

Table 2: Comparison of Economic Indicators for the Three Flexo Press Types (Example: 8-color press)

Indicator                                                Inline        Central Impression   Stack

Equipment Investment (10,000 RMB) 800-1200   1200-1800                  400-700

Energy Consumption (kW/h)               90-120       120-160                      60-80

Make-ready Time (min)                        25-40          15-25                         30-45

Waste Rate (%)                                      3-5              2-3                             5-8

ROI Period (months)                            18-24           24-36                         12-18

Comprehensive Operating Costs

Although CI presses have a higher initial investment, they yield the lowest unit cost in high-volume production. Calculations show:

When monthly output exceeds 800,000 linear meters, CI costs are 12-15% lower than inline.

For small and medium batch production (<200,000 linear meters), inline presses have a cost advantage.

Stack presses are suitable for economical production of low value-added products.

V. Technological Development Trends

Hybrid Printing Technology: ZONBON's latest generation equipment integrates flexo and digital printing units, enabling variable data printing.

Intelligent Maintenance Systems: Industry 4.0-based remote diagnostic systems can predict over 90% of mechanical failures.

Green Printing Technology: The adoption rate of environmentally friendly processes like solvent-free inks and LED-UV curing has reached 60%.

Ultra-Precision Printing: Laser-engraved ceramic anilox rolls (up to 1200 LPI) combined with high-definition flexo plates enable fine printing at 175 LPI.

Conclusion

Inline, central impression, and stack flexographic printing technologies each have their own technical advantages and suitable application areas. CI presses are irreplaceable for precision printing on film materials, inline presses serve as the mainstay for packaging printing due to their flexibility and versatility, while stack presses maintain a cost advantage in printing rigid materials like corrugated board. Printing companies should select the most appropriate technological solution based on factors such as product mix, quality requirements, order characteristics, and investment budget. Through continuous technological innovation, the ZONBON series of flexographic equipment provides specialized, differentiated printing solutions for customers with diverse needs, driving flexographic printing technology towards higher efficiency, greater precision, and enhanced environmental sustainability.

Precision Decision-Making: Technical Analysis and Selection Guide for Stack, Central Impression, and In-Line Flexographic Printing

In today's diverse, personalized, and increasingly demanding packaging printing market, flexographic printing has secured a pivotal position due to its environmental friendliness, efficiency, and versatility across substrates. However, faced with varying product requirements, order structures, and budget constraints, selecting the most optimal and economical solution among the mainstream in-line, central impression (CI), and stack flexographic printing technologies has become a critical challenge for every printing decision-maker. This article delves into the core principles, technical characteristics, and application scenarios of these three technologies, providing rigorous professional insights to inform your investment and production decisions.

1. Core Principles and Structural Differences: Similarities and Divergences in Technical Foundations

To make the right choice, it is essential to first understand the fundamental differences in their design philosophies and mechanical structures.

In-Line Flexographic Printing

Structural Features: Independent printing units arranged linearly or in a straight-line configuration. Each unit handles one color, with the substrate passing sequentially through each unit under a tension system to achieve multi-color registration.

Core Advantage: Modular design. This structure offers exceptional flexibility, allowing for easy integration of additional modules such as drying, cooling, surface treatment (e.g., corona), die-cutting, coating, and reversing, enabling "one-pass" inline processing and significantly expanding process possibilities.

Central Impression (CI) Flexographic Printing

Structural Features: All printing units are arranged circumferentially around a large-diameter central impression cylinder. The substrate adheres to the central cylinder, completing all color registrations in a single rotation.

Core Advantage: Unmatched registration accuracy and stability. Since the substrate remains fixed to the central cylinder throughout printing, material stretch, distortion, and path deviations are minimized, making it ideal for thin, deformable substrates.

Stack Flexographic Printing

Structural Features: Multiple printing units are stacked vertically on a central frame, each with its own impression cylinder. The substrate follows a "U" or vertical path between units.

Core Advantage: Compact footprint, cost-effectiveness, and ease of double-sided printing (achieved via a reversing mechanism). Simple operation and maintenance.

2. Comprehensive Performance Comparison: Multi-Dimensional Trade-offs Based on structural differences, the three methods exhibit distinct performance profiles.

                                                                In-Depth Analysis:

Registration King: CI flexo. Its "single-rotation" principle ensures unparalleled stability for products with stringent registration demands (e.g., thin films, pressure-sensitive labels), significantly reducing waste.

Flexibility Champion: In-line flexo. For manufacturers handling frequent job changes, diverse products (e.g., switching from film bags to carton boxes), or requiring complex inline finishing (e.g., laminating, die-cutting, creasing), its modular design offers unmatched adaptability.

Cost-Effective Choice: Stack flexo. Ideal for budget-conscious users with simpler product structures, short-to-medium runs, or double-sided printing needs, providing reliable quality at a lower investment.

3. Application Scenarios and Selection Guidelines

The choice ultimately hinges on core business needs.

Prioritize CI Flexo When:

Large-volume, single-material orders (e.g., beverage labels, hygiene product packaging, snack films).

Products demand extreme registration precision, especially with thin, deformable substrates.

Production requires uninterrupted, high-speed efficiency.

Prioritize In-Line Flexo When:

Product variety is vast, requiring frequent changeovers.

Processes are complex, needing integrated inline finishing (e.g., printing with immediate die-cutting, waste removal, stacking).

Substrates range widely (films to thick boards).

Future-proofing for new processes is a priority.

Prioritize Stack Flexo When:

Budget-sensitive startups or users seeking quick ROI.

Short-to-medium runs with common double-sided printing needs.

Space constraints necessitate compact equipment.

Supplementing existing capacity or handling specific tasks like proofing or spot-color printing.

4. ZONBON Brand Perspective: A Pragmatic Approach to Technical Selection

Guided by ZONBON’s ethos of professionalism and pragmatism, we recommend transcending mere equipment comparisons to engage in strategic reflection:

Market Positioning & Product Planning: Is your target market high-volume efficiency or small-batch customization? How will your product line evolve in 3–5 years? Align equipment with your strategic vision.

Total Cost of Ownership: Beyond upfront costs, evaluate consumables (plates, anilox rolls, inks), energy use, maintenance, training, and potential waste. A seemingly expensive machine may deliver greater long-term value through efficiency and lower waste.

Technical Fit & Talent Readiness: Advanced equipment requires skilled operators. Assess your team’s capabilities or plan for training/recruitment to ensure effective utilization.

Supplier Evaluation: Choose a mature, reliable supplier with robust after-sales support—critical for production continuity.

Conclusion

In-line, CI, and stack flexo technologies are not inherently superior or inferior—only more or less suited to specific needs. CI excels in precision and speed, in-line in flexibility and expandability, and stack in economy and practicality. Successful selection stems from deep business insight, technical understanding, and ZONBON’s forward-looking, pragmatic wisdom. Before deciding, conduct sample tests with actual production materials at supplier facilities, letting data and facts guide your final choice.