Understanding the Root Causes of Loop Tack Failure in PET Labels

Introduction

Loop tack is essential for PET labels to adhere instantly and effectively, especially in high-speed applications. When loop tack failure causes disrupt adhesion, the entire labeling operation can be compromised. Understanding what’s behind poor tack behavior—beyond the visible symptoms—is key to successful adhesive PET troubleshooting. This article explores common adhesive failures, material mismatches, and environmental triggers that explain why PET film is not sticking as expected.

What Is Loop Tack and Why Does It Fail?

Loop tack is the initial grab strength of an adhesive when no external pressure is applied. It reflects how “sticky” the label feels immediately upon contact. Failures occur when this tack is:

• Too weak to hold the label
• Inconsistent across the roll
• Lost over time due to environmental exposure

Each failure points to deeper adhesive PET troubleshooting issues.

Common Loop Tack Failure Causes

1. Incorrect Adhesive Rheology

If the adhesive is too viscous or too fluid, it won’t flow properly into the substrate's microtexture.

• Too viscous = poor wet-out
• Too fluid = adhesive spreads thin, reducing bonding

✅ Solution: Adjust polymer ratio and add wetting agents or tackifiers.

2. Surface Energy Mismatch

A high-energy adhesive won’t bond well to a low-energy surface like PE or PP.

• The label peels off or slides before adhering.
• PET film not sticking often starts here.

✅ Solution: Use primers or switch to adhesives compatible with the substrate's surface energy.

3. Environmental Conditions

Loop tack is highly sensitive to:

• Temperature: Cold stiffens adhesives.
• Humidity: Excess moisture dilutes tack over time.
• UV/Heat: Causes oxidation and aging.

✅ Solution: Test adhesives under actual storage and use conditions.

4. Contaminated Surfaces

Even a small amount of dust, oil, or silicone can cause failure.

• Labels won’t adhere evenly or lift at edges.
• Contamination is a leading silent killer of loop tack.

✅ Solution: Implement cleanroom standards or anti-static film handling procedures.

5. Improper Adhesive Coating

Adhesive layer may be too thin, uneven, or have skipped zones.

• Tack strength varies between labels.
• Tack fails even though the formulation is correct.

✅ Solution: Inspect coating thickness and apply uniform pressure during lamination.

PET Film Not Sticking: A Troubleshooting Checklist