Addressing Stretch Deformation in EVOH Films: Mechanism Analysis and Tension Control Strategies

In the high-barrier packaging industry, EVOH films are widely used due to their outstanding oxygen barrier properties and mechanical strength. They are essential in applications such as cold-chain food packaging, sterile medical device pouches, and moisture-sensitive electronics. As the demand for recyclable, high-performance films continues to grow, EVOH is increasingly adopted in sustainable multilayer film structures. However, stretch deformation during production—such as film narrowing or thinning—remains a recurring issue. One of the main contributors to this problem is improper tension control during film processing.

1.Understanding the Relationship Between Tension and EVOH Film Deformation

1.1 Material Sensitivity to Tension

EVOH (ethylene-vinyl alcohol copolymer) offers excellent mechanical properties and barrier performance, but is more tension-sensitive than traditional materials like PE or PP. EVOH polymer has a higher elastic modulus, requiring finer control during processing. In addition, its mechanical behavior is affected by humidity—moisture absorption lowers the modulus, increasing the risk of deformation under normal operating tension.

1.2 Deformation Mechanism and Typical Issues

During machine direction (MDO) or transverse direction (TDO) stretching, exceeding the material’s yield strength causes permanent deformation. This may appear as film width reduction (due to under-stretching or recoil in the transverse direction) or inconsistent thickness (from over-stretching longitudinally). These issues are more likely in high-temperature processing zones, where EVOH softens, increasing its susceptibility to over-stretching when tension is not properly managed.

1.3 Environmental Influences

Fluctuations in temperature and humidity significantly affect how tension interacts with the material. In humid environments, EVOH resin absorbs moisture, softens, and requires lower tension to prevent deformation. In contrast, dry conditions may allow for higher tension settings. Temperature shifts can also alter thermal shrinkage behavior, influencing tension stability and film performance.

2.Best Practices for Tension Management in EVOH Film Production

2.1 Tension Parameters and Setup Guidelines

Production data from 2024 suggest that optimal processing tension for EVOH film ranges between 1.2 and 3.5 kgf, depending on resin type and film thickness. A gradual transition in tension between the pre-heating and stretching zones is critical to avoid abrupt changes that can lead to film distortion or breaks. Start-up tension should remain within 15–20% of the material’s yield strength, while winding tension is typically 10–15% higher than unwind tension.

2.2 Intelligent Tension Control Systems

Many industry leaders now use AI-driven predictive control systems that monitor real-time parameters such as film temperature, ambient humidity, and tension feedback. These systems dynamically adjust processing settings, maintaining tension within a ±0.5% accuracy range, even under varying environmental conditions. Automatic compensation based on roll diameter ensures consistent winding quality throughout the production cycle.

2.3 Managing Environmental Conditions

To ensure stable production, workshops should maintain controlled environments at 23 ± 2°C and relative humidity of 50 ± 5%. In dry conditions, tension may be slightly increased. In humid conditions, it should be reduced accordingly and dehumidification measures implemented. A stable ambient environment helps ensure consistent film characteristics and improved yield.

3.Frequently Asked Questions

3.1 Q: Why is tension control so critical in EVOH film production?

A: EVOH plastic is more sensitive to tension than other common films. Improper settings can lead to irreversible deformation such as film narrowing or thinning, which affects final product quality, roll uniformity, and line efficiency. Proper tension control ensures better dimensional stability, consistent thickness, and reduced waste.

3.2 Q: What makes EVOH different from PE or PP in terms of tension control?

A: EVOH material requires tighter tension tolerances and more responsive adjustments. Its tension window is narrower (typically 1.2–3.5 kgf) and it reacts more strongly to humidity and temperature variations. Additionally, winding tension decay must be carefully managed, with a recommended taper ratio of 0.6–0.8, to avoid core over-tightening or outer-layer loosening.

3.3 Q: How can I tell if my tension settings are correct?

A: Three key indicators include:

Thickness tolerance within ±1.5%,

Uniform roll appearance without defects like “star patterns” or “flowering”,

Minimal film breaks or stretching inconsistencies during production.

Ideal initial tension should be 15–20% of the yield strength, with dynamic taper control during winding based on roll diameter.

As smart manufacturing and IoT technologies become more integrated into film production, the industry is shifting toward intelligent, real-time process optimization. EVOH packaging film deformation issues can often be resolved through tension control improvements. We recommend:

Routine calibration of tension sensors and pneumatic systems,

Maintaining detailed tension-setting profiles for each film batch,

Implementing closed-loop monitoring systems to automatically adjust processing conditions in real time.

With the right combination of materials knowledge, processing expertise, and advanced control systems, manufacturers can achieve both high-performance and high-stability EVOH high barrier film production.