Common Problems Related to Low Loop Tack and How to Solve Them

Introduction

Loop tack is a critical performance metric in pressure-sensitive PET films. When loop tack is too low, labels fail to adhere properly on first contact—causing production issues, aesthetic defects, and even brand damage. In this guide, we explore the most common problems associated with low loop tack, the loop tack failure causes, and practical adhesive PET troubleshooting strategies to restore or improve bonding performance. Whether you're experiencing full detachment or reduced grab, solving "why your PET film is not sticking" starts with identifying the root cause.

Problem 1: PET Film Not Sticking to the Substrate

One of the most reported issues in labeling is that the PET film is not sticking at all upon initial application. This is often caused by:

• Low surface energy substrates (e.g., HDPE, PP, coated metals)

• Improper surface preparation (dust, oil, release agents)

• Incompatible adhesive formulation

Solutions:

• Switch to a high-tack or rubber-based adhesive

• Use a primer or corona/plasma treatment to raise surface energy

• R&D a custom adhesive PET film with targeted wetting properties

Problem 2: Tack Degrades After Storage

Sometimes the adhesive initially performs well but loses its tack after days or weeks—especially in high-humidity or high-temperature storage. This delayed performance drop often leads to PET film not sticking during later stages.

Causes:

• Over-crosslinked adhesives

• Oxidation or contamination of the adhesive layer

• Improper roll storage (e.g., excessive heat or pressure)

Fixes:

• Store adhesive rolls between 15–25°C at 40–60% RH

• Test for shelf life and revalidate bonding via loop tack failure causes simulation

• Modify formulation to include antioxidants or softeners

Problem 3: Inconsistent Loop Tack Across the Roll

Inconsistency across a roll (some areas stick, others don’t) is a serious quality issue. These inconsistencies stem from:

• Uneven adhesive coating weight

• Inadequate mixing or dispersion of tackifiers

• Pressure damage during winding

What You Can Do:

• Use high-precision coating methods (e.g., slot-die or gravure)

• Calibrate machinery to reduce winding pressure

• Conduct quality checks across the full web width for adhesive PET troubleshooting

Problem 4: Loop Tack Fails Under Cold Conditions

In refrigerated or winter environments, some PET labels exhibit loop tack failure causes related to adhesive hardening. The film doesn’t wet the surface properly and bounces off instead of sticking.

Recommendations:

• Use cold-temp rated adhesives that stay flexible below 5°C

• Choose rubber-based adhesives with plasticizers for better low-temp flow

• Validate tack with cold chamber loop tack testing

Problem 5: Labels Lift at the Edges After Application

Edge lifting is subtle but damaging. Even if the center adheres well, poor edge performance ruins the product’s appearance and durability.

Root Causes:

• Low initial tack (not enough loop tack force)

• Curved or uneven surfaces not fully contacted

• Drying of adhesive before application (in linerless systems)

Remedies:

• Increase adhesive coat weight

• Use flexible film constructions

• Reengineer application method (angle, pressure, dwell time)

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