Troubleshooting PET Film Not Sticking: 5 Hidden Loop Tack Failure Causes

Introduction

A common challenge in pressure-sensitive label applications is poor initial adhesion—especially when PET film is not sticking as expected. This issue often stems from hidden loop tack failure causes not easily visible during production. When labels don’t bond instantly, it disrupts line efficiency, raises product rejection rates, and increases labor costs. In this article, we reveal lesser-known reasons for low loop tack and how effective adhesive PET troubleshooting can resolve these problems.

1. Improper Adhesive Surface Wetting

For loop tack to function properly, the adhesive must quickly wet and flow across the surface. When it doesn’t:

• The PET film peels off with minimal force.
• Tack feels low even if the formulation is correct.

Root Causes:

• Low surface energy on the target material (e.g., untreated plastic, silicone-coated surfaces).
• Overly viscous adhesive not flowing at ambient conditions.

Fix:

• Add surfactants or tackifier resins to improve flow.
• Use corona or plasma treatments on the substrate.

2. Under-Cured or Over-Cured Adhesive Layers

Manufacturing issues like incorrect UV curing or thermal setting can damage adhesive performance:

• Under-curing leads to incomplete polymer bonding.
• Over-curing creates brittle adhesives with low flexibility.

This directly impacts loop tack failure causes, especially under bending or light contact.

Fix:

• Review curing parameters (UV dose, temperature).
• Use FTIR or DSC analysis to confirm proper curing.

3. Storage Environment of Adhesive Rolls

Even high-quality adhesive PET can lose tack if stored improperly.

Indicators:

• Rolls feel “dry” to the touch.
• Adhesion fails on both test and production surfaces.
• Tack decreases over time.

Likely Causes:

• Heat/humidity causing adhesive oxidation or softener evaporation.
• Pressure from tight winding compressing adhesive.

Preventive Measures:

• Store between 15–25°C and 40–60% RH.
• Avoid stacking heavy rolls.
• Perform tack testing monthly if stored long term.

4. Incompatibility Between Adhesive and PET Film

Sometimes the PET film backing is not compatible with the adhesive layer due to:

• Release coating residue.
• Anti-blocking additives on the film surface.
• Mismatched shrink tension during lamination.

What to Do:

• Clean film surface or use a PET with no silicone transfer.
• Switch to an adhesive system with higher compatibility (e.g., acrylic blends or rubber-based).

5. Low Ambient Temperature at Application Point

Cold environments significantly reduce adhesive flow and surface wetting—especially for PSA labels.

• At 5°C and below, most acrylics stiffen.
• The result: tack failure on high-speed applicators or refrigerated products.

Adhesive PET Troubleshooting Tip:

• Choose low-temp-rated adhesives designed for cold flow.
• Store label rolls in the same environment where they’ll be applied.