How to Resolving Telescoping Issues in EVOH High-Barrier Film Rewinding

In premium packaging sectors such as food, medical devices, and pharmaceuticals, even minor visual imperfections in EVOH high-barrier film can impact brand perception. A roll of film that winds flat and smooth is more than an aesthetic goal—it’s a sign of quality and process control. Yet, telescoping, or bulging during rewinding, remains a common challenge. Beyond its appearance, this issue reflects uneven internal stress distribution, which may compromise barrier performance, shelf life, and product safety.

1.Understanding the Root Causes

1.1 Stress Imbalance: The Core Issue

Telescoping is typically the result of imbalanced residual stress within the film. EVOH, a material with strong viscoelastic behavior, accumulates internal stress during winding. These built-up forces, much like compressed springs, seek release over time. When stress release varies across layers, the imbalance causes visible deformations in the roll.

1.2 EVOH’s Sensitivity to Environmental Factors

EVOH polymer is particularly responsive to changes in humidity and temperature. Unlike PE or PP, its stress relaxation rate increases significantly in hot, humid conditions. If heat cannot dissipate efficiently within the roll, temperature gradients develop, and differential stress release can result in thermally induced telescoping. Its material memory and slow relaxation behavior must be considered when defining process parameters.

2.A Holistic Approach to Prevention

2.1 Precision Tension Control

Tension is the cornerstone of winding stability. For EVOH plastic, consistent and moderate tension is critical. Implementing a closed-loop tension control system with tapered adjustment—where tension gradually decreases as roll diameter increases—helps counter rising winding stress and maintains stability.

2.2 Ensuring Thickness Uniformity

Even minor, micron-level thickness deviations can accumulate layer by layer, leading to hard spots or bulges across the film width. Inline thickness monitoring systems, such as IR or beta-ray gauges coupled with auto-die controls, are essential to keeping variation within ±2%, ensuring smooth and even rolls.

2.3 Surface Treatment Uniformity

Non-uniform corona treatment or uneven distribution of slip agents (e.g., erucamide) can result in surface friction inconsistencies. During rewinding, sections with lower friction are more prone to interlayer slippage, which promotes buckling. To avoid this, ensure consistent surface treatment and use additives that are stable and compatible with EVOH material.

2.4 Controlled Rewinding Environment

EVOH's barrier properties and physical performance are closely tied to temperature and humidity. Insufficient cooling or poor ventilation inside the roll can cause temperature gradients that trigger stress release at different rates. Rewinding and initial storage should be conducted in climate-controlled environments (recommended: 23±2°C, 50±5% RH) to maintain consistent quality.

3.FAQ

Q1: How can we assess our production line’s risk for telescoping and plan improvements?

A: Start by collecting a week’s worth of operational data—tension, temperature, and thickness. Then use simulation tools or digital twin models to identify stress points and develop a tailored improvement plan.

Q2: Why does this issue occur when producing EVOH films, but not with PE under the same settings?

A: The difference lies in material behavior. PE relaxes stress more quickly and tolerates localized over-stress. EVOH resin, being stiffer, retains internal stress longer and is more sensitive to imbalance. Processes that work for PE may be too aggressive for EVOH, which requires more precise controls.

Q3: How do upstream processes like extrusion or casting affect winding quality?

A: Significantly. For instance, inconsistent melt temperatures during extrusion can create weak points in the film. Uneven cooling on chill rolls can lead to variable crystallinity. Both affect shrinkage behavior and internal stress, which manifest during winding as telescoping or bulging. Stable winding begins with a stable upstream process.

High-quality winding of EVOH film depends on the synergy between material behavior, equipment precision, process settings, and environmental control. To prevent telescoping, manufacturers must adopt a systematic approach—from extrusion to final winding. Only by addressing each contributing factor can they ensure flat, stress-balanced, and visually perfect rolls that meet the demanding standards of high-performance packaging applications.