Complete Process of Self-adhesive Label Printing: Flexo, Digital & Screen Printing – Troubleshooting & Tips

Self-adhesive labels, widely used in food, cosmetics, electronics, and logistics industries, rely on precise printing processes to achieve both functional performance and aesthetic appeal. Among the various printing technologies, flexographic (flexo), digital, and screen printing stand out as the most mainstream methods, each with unique workflows tailored to different production demands. This article details the complete printing process of self-adhesive labels, focusing on the characteristics, operational steps, and application scenarios of these three core technologies.

1. Pre-Printing Preparation: The Foundation of Quality Labels

Pre-printing preparation is a critical phase that determines the efficiency of subsequent processes and the final quality of labels. It involves material selection, design optimization, and process planning, laying the groundwork for seamless printing operations.

1.1 Material Selection: Matching Performance to Requirements

Self-adhesive label materials consist of three core components: face material (printing surface), adhesive (bonding layer), and release liner (protective base paper). The selection of materials must align with the label’s application environment, such as resistance to moisture, high temperature, or chemicals, as well as printing technology characteristics.

• Face Material: Common options include paper-based and film-based materials. Paper materials like coated paper (for vibrant colors and smooth surfaces) and kraft paper (eco-friendly, rustic texture) are suitable for general packaging and promotional labels. Film materials such as PET (tear-resistant, high-temperature resistant), PVC (waterproof, oil-proof), and PP (lightweight, chemical-resistant) are ideal for electronics, cosmetics, and outdoor labels. Special materials like镭射 paper (anti-counterfeiting) and fragile paper (tamper-proof) cater to specific functional needs .
• Adhesive: Classified by bonding performance, options include permanent adhesives (for long-term bonding on product packaging), removable adhesives (for temporary labels like promotional stickers), and special adhesives (freezer-resistant for frozen food, high-temperature-resistant for automotive parts) .
• Release Liner: Typically made of glassine paper or kraft paper coated with silicone, it ensures easy peeling of the label while protecting the adhesive’s viscosity during storage and printing .

Key principle: High-quality materials are essential—expired or substandard materials may cause printing defects like ink bleeding or poor adhesion, increasing overall production costs despite lower initial procurement prices .

1.2 Design Optimization & Pre-Press Processing

This stage converts customer design requirements into printable files, requiring close collaboration between designers and printing technicians to avoid process conflicts.

• Design File Standardization: Customers should provide vector files (AI, EPS) or high-resolution PDFs (≥300 DPI) to ensure clear, non-pixelated printing. For flexo and screen printing, color separation is required (CMYK or spot colors), while digital printing supports direct use of RGB files with RIP (Raster Image Processor) conversion .
• Plate Making (for Flexo & Screen Printing): Flexo printing uses flexible photopolymer plates with raised image areas, which are wrapped around printing cylinders—their elasticity enables adaptation to various substrate surfaces . Screen printing requires fabric stencils (nylon or polyester) where the design area is porous (allowing ink passage) and non-design areas are blocked . Digital printing eliminates plate making, significantly reducing setup time .
• Proofing & Approval: Physical or digital proofs are provided to confirm color accuracy, text clarity, and process feasibility. This step prevents costly rework caused by design deviations, especially for large-batch orders .

2. Core Printing Processes: Flexo, Digital & Screen Printing

The three printing technologies differ significantly in principle, equipment, and workflow, making them suitable for distinct production scenarios. Below is a detailed breakdown of each process.

2.1 Flexographic Printing: The Mainstream for Mass Production

As the most widely used self-adhesive label printing method—accounting for 40-50% of the European market and over 90% of the U.S. market—flexo printing is a rotary relief printing technology known for high speed, versatility, and cost efficiency . It is particularly suitable for large-batch orders (≥100,000 labels) such as food and beverage packaging.

2.1.1 Printing Principle

Ink is transferred from anilox rollers (which control ink volume via micro-holes) to the raised image areas of flexible plates, then directly pressed onto the moving substrate (roll-to-roll feeding). Each color requires a dedicated plate and printing unit, enabling multi-color overprinting .

2.1.2 Key Workflow

1. Roll Loading: The self-adhesive material roll is mounted on the unwinding unit, and tension is adjusted to ensure stable feeding without wrinkling.
2. Ink Application: Water-based, solvent-based, or UV-curable inks are applied to anilox rollers. UV inks are preferred for environmental friendliness and fast curing .
3. Color Overprinting: The substrate passes through multiple printing units sequentially, with each unit applying one color. Modern flexo presses achieve high precision (registration error ≤0.1mm) through automated cylinder alignment.
4. UV Curing: After each color printing, UV lamps cure the ink instantly, preventing smudging and ensuring color stability .

2.1.3 Advantages & Limitations

Advantages: High printing speed (up to 300m/min), wide substrate adaptability (paper, film, foil), cost-efficient for large batches, and support for eco-friendly inks . Limitations: Time-consuming setup (plate installation, color adjustment) makes small-batch production costly; fine text reproduction is slightly inferior to digital printing .

2.2 Digital Printing: The Leader in Flexibility & Personalization

Digital printing, a plate-free technology that directly transfers digital files to substrates via inkjet or laser, has become the preferred choice for small-batch, personalized labels. It excels in scenarios requiring variable data (e.g., QR codes, serial numbers) and fast turnaround, such as e-commerce, limited-edition cosmetics, and pharmaceutical labels .

2.2.1 Printing Principle

Inkjet digital presses eject tiny ink droplets onto the substrate to form images; laser digital presses use electrostatic adsorption to transfer toner, which is then fused to the surface via heat. The entire process is controlled by RIP software, enabling real-time adjustments to designs .

2.2.2 Key Workflow

• File Import: Design files (including variable data) are imported into RIP software, which optimizes color and resolution for printing.
• Substrate Feeding: Supports both roll-to-roll (for continuous production) and sheet-fed (for small-batch special materials) feeding, with automated tension control.
• Direct Printing: The press prints the full-color image in one pass, eliminating the need for color-by-color overprinting. Variable data is automatically updated for each label (e.g., unique serial numbers).
• Instant Drying: UV inkjet or thermal fusion ensures immediate drying, allowing for on-demand post-processing .

2.2.3 Advantages & Limitations

Advantages: No plate setup (saves 2-3 days of preparation time), low minimum order quantity (even 100 labels are cost-effective), high flexibility for design modifications, and precise variable data printing . Limitations: Higher unit cost for large batches compared to flexo printing; some special films may require pre-coating for better ink adhesion .

2.3 Screen Printing: The Specialist for Special Effects

Screen printing, characterized by thick ink layers and strong three-dimensional effects, is a versatile technology suitable for almost all substrates—including plastic, metal, and glass. It is commonly used for labels requiring special effects like embossing, matte textures, or luminous patterns, such as electronic product logos and luxury wine labels .

2.3.1 Printing Principle

A stencil-mounted screen is pressed against the substrate. Ink is scraped across the screen with a squeegee, passing through the porous design areas to form thick, opaque images on the label surface. Each color requires a separate screen, and UV inks are typically used for quick curing .

2.3.2 Key Workflow

• Screen Preparation: Emulsion is coated on the screen, and the design is exposed to light to form a stencil (non-design areas harden, blocking ink).
• Substrate Fixing: The self-adhesive material is secured on the printing table to prevent movement during scraping.
• Ink Scraping: Ink is poured onto the screen, and a squeegee applies uniform pressure to transfer ink through the stencil to the substrate.
• UV Curing: The printed ink is cured with UV lamps to enhance durability and texture .

2.3.3 Advantages & Limitations

Advantages: Thick ink layers (30-100μm) for strong texture, excellent opacity (suitable for covering existing information), and compatibility with special inks (luminous, conductive, tactile) . Limitations: Low printing speed (mostly semi-automatic), limited precision for multi-color overprinting, and high labor costs for small batches .

3. Post-Printing Processing: Shaping the Final Label

Post-printing processing enhances the label’s functionality (e.g., durability, ease of use) and aesthetics. For efficiency, modern label presses integrate most processes inline; complex effects may require offline processing.

3.1 Surface Finishing: Protection & Aesthetics

• Coating/Glossing: Applying water-based or UV varnish increases scratch resistance and waterproofing. Local UV coating creates contrasting glossy/matte effects .
• Laminating: Covering the label with a transparent BOPP or PET film provides enhanced protection against moisture and tearing, suitable for outdoor or high-wear labels .
• Hot Stamping: Using heated metal plates to transfer gold, silver, or镭射 foil onto the label, creating a premium metallic effect for luxury products .

3.2 Forming Processing: From Roll to Finished Label

• Die-Cutting: The most critical step—using a circular or flat die to cut through the face material and adhesive layer without damaging the release liner, shaping the label into the desired form (round, rectangular, custom shapes). Circular die-cutting (inline with flexo/digital presses) achieves high speed and precision .
• Waste Stripping: Removing the excess face material (webbing) around the die-cut labels, leaving only the finished labels on the release liner .
• Slitting/Rewinding: Slitting large rolls of labels into smaller rolls of specified widths (for automatic labeling machines) or rewinding them into compact rolls for manual use .

3.3 Special Processing

For functional labels: Perforation (for easy tearing of coupon labels), embossing (creating 3D textures for blind labels), and die-cutting through release liner (for single-label dispensing) .

4. Quality Control & Packaging: Ensuring Consistency

Quality control runs through the entire process to avoid defective products. Key inspection items include:

• Printing Quality: Checking color consistency (using colorimeters), registration accuracy, and absence of defects like smudges or missing ink .
• Die-Cutting Precision: Ensuring label edges are smooth, no incomplete cutting, and waste stripping is clean .
• Functional Performance: Testing adhesive strength (peel test), water resistance, and scratch resistance of surface finishes .

Qualified labels are packaged in moisture-proof, pressure-resistant cartons or plastic film, with labels indicating product specifications, batch numbers, and storage conditions to ensure integrity during transportation .

5. Process Selection Guide: Matching Technology to Needs

Choosing the right printing process depends on order quantity, design requirements, and application scenarios. The following table provides a quick reference:

Criteria	Flexo Printing	Digital Printing	Screen Printing
Order Quantity	Large batches (≥10,000)	Small batches (100-10,000)	Small to medium batches
Turnaround Time	3-7 days (setup time)	1-2 days (no setup)	2-5 days (screen making)
Key Advantages	High speed, cost-efficient	Personalization, variable data	Special effects, thick ink layers
Typical Applications	Food/beverage labels, logistics labels	Limited-edition cosmetics, e-commerce labels	Electronic logos, luxury wine labels

Conclusion

The self-adhesive label printing process is a systematic project integrating material science, printing technology, and post-processing. Flexo printing dominates large-scale production with efficiency and cost advantages; digital printing leads the way in personalized and short-run orders with flexibility; screen printing excels in special effects to meet high-end aesthetic needs. By understanding the characteristics of each process and matching them to specific requirements, enterprises can achieve optimal balance between label quality, production efficiency, and cost control—creating labels that not only convey information but also enhance brand value.