The Ultimate Guide to Label Application & Problem Solving

To ensure your labels achieve perfect application and long-lasting performance, we present this comprehensive Ultimate Guide. Covering everything from fundamental principles to complex troubleshooting, this guide is designed to help you optimize your production process and enhance your product's image.

1. Environment Control is the Foundation of Success

   Optimal Labeling Environment: 15-24°C, 40-60% RH. Under these conditions, adhesive flow is optimal for the best wetting.

   Label Storage Conditions: Store in the same environment (15-24°C, 40-60% RH). Avoid high temperature/humidity or extreme dryness. The adhesive shelf life for unopened raw materials is typically one year.

2. The Science of Surface Preparation

   Cleanliness: Surfaces must be free of dust, oil, silicone, moisture, or any contaminants. Even invisible fingerprints can affect adhesion.

   Surface Energy: Ensure the substrate's surface tension is above 36 dynes/cm. Low surface energy materials (e.g., some PE, PP plastics) may require corona treatment or use of special ultra-aggressive adhesives.

   Physical State: Avoid using standard labels on severely uneven, porous, or very rough surfaces, which require special adhesives and face materials.

3. How Pressure-Sensitive Adhesives Work & Curing Process

   What "Pressure-Sensitive" Means: The adhesive does not air-cure; it must be pressed against the substrate to achieve intimate contact and develop tack.

   Initial Tack: The immediate adhesion upon application, preventing the label from shifting.

   Final Adhesion: After application, the semi-solid adhesive gradually flows over 24 hours, penetrating the micro-imperfections of the substrate surface, maximizing contact area and reaching its ultimate designed bond strength. Avoid abrasion, movement, or testing during this period.

1. Squeegee Selection & Application Science

   Types:

   Spring Steel (0.3mm/0.5mm): Provides rigid support, suitable for flat or regular curved surfaces.

   Spring Steel + High-Elasticity Sponge: The best all-around option; sponge absorbs uneven pressure, adapting to minor surface irregularities.

   Brushes: Suitable for easily scuffed materials or highly uneven surfaces, but may cause uneven pressure.

   Silicone/Rubber Squeegees: Soft texture, friendly to labels and protective films.

   Angle & Pressure: The ideal angle between the squeegee and the container is 30-45 degrees. Apply pressure evenly and consistently in a single, smooth motion, avoiding skipping or repeated strokes.

1. Bubbles

   Causes: Uneven squeegee pressure or incorrect angle; contaminants, pits, or unevenness on the substrate surface; plasticizer migration from plastic bottles reacting with the adhesive; excessive ambient humidity causing the face material to expand.

   Solutions: Use a sponge-backed squeegee and apply pressure in one smooth, continuous motion; thoroughly clean and inspect the substrate surface; select a specialty adhesive resistant to plasticizer migration for plastic bottles; control ambient humidity or switch to waterproof face materials like PE or PP.

2. Wrinkling

   Causes: Skipped areas during application due to an unsteady hand or machine; mismatch between labeling machine and conveyor belt speeds; excessive label length before application (leading to pre-wrinkling); excessive squeegee pressure or a substrate that is too soft (leading to post-wrinkling); incorrect label stiffness for the container's shape.

   Solutions: Ensure the application is continuous and covers the entire label surface; recalibrate machinery for speed synchronization; adjust the label dispensing length; reduce squeegee pressure or select a more flexible face material; choose low-stiffness materials for curved containers.

3. Lifting / Flying Off

   Causes: Incorrect adhesive selection (the most common cause); condensation, oil, or low surface energy on the container; excessive label stiffness causing rebound force on curved surfaces that exceeds adhesive strength; insufficient application pressure, leaving edges and corners poorly adhered; different thermal contraction rates between the label and substrate in low temperatures.

   Solutions: Select a specialized adhesive based on the container material (e.g., glass, PET, HDPE) and shape (curved, flat); ensure containers are completely dry and clean before application, using ultra-aggressive adhesives for low-surface-energy plastics; use ultra-soft film materials (like PE) with aggressive adhesives for small-diameter curved bottles; check and increase application pressure to ensure edges and corners are fully adhered; choose adhesives with excellent performance in low-temperature environments.

4. Hazing / Whitening

   Causes: Condensation forms on cold containers in humid environments, trapping moisture under the label after application, creating a white, hazy appearance.

   Solutions: Use air knives or warm air systems immediately before labeling to thoroughly dry and slightly warm the containers, eliminating all moisture.

5. Mis-feeding / Breaking

   Causes: Die-cutting is too deep, damaging the liner or causing adhesive to bleed into the cuts; excessive core tension or winding tension; a worn applicator plate that scratches the liner; mismatch between the liner release level and the adhesive's peel force.

   Solutions: Adjust die-cutting pressure to a "kiss-cut" (through the face material but not the liner); reverse the roll to relieve tension or adjust machine tension; replace or repair the worn applicator plate; consult our technical team to select the proper liner and adhesive combination.

6. Poor Ink Adhesion

   Causes: Insufficient UV lamp power or excessive curing speed; inadequate surface treatment (e.g., corona); the ink used is incompatible with the face material; unsuitable temperature or humidity in the printing environment.

   Solutions: Calibrate UV power and reduce printing speed accordingly; check the material's surface tension and apply corona treatment if necessary; conduct pre-press testing to ensure ink compatibility; strictly control the temperature and humidity in the pressroom.

7. Die-cutting Waste Removal Issues

   Causes: Insufficient die-cutting depth; overly complex label shapes; inappropriate liner release level; low ambient temperature.

   Solutions: Adjust the die-cutting pressure to the proper depth; optimize label design to avoid shapes that are difficult to matrix strip, such as sharp corners; select a liner with an appropriate release level; ensure the processing environment is at an adequate temperature.