EVOH Skin Film vs. Thermoforming Film: the Process Differences and Practical Breakthroughs in High-Barrier Packaging

In sectors like fresh meat, ready-to-eat meals, and aseptic medical packaging, Evoh (ethylene-vinyl alcohol copolymer) stands out with oxygen barrier properties up to 10,000 times better than polyethylene, making it a go-to material for advanced barrier packaging. However, its performance is highly influenced by the processing method—namely, Skin Film formed by vacuum differential pressure and Thermoforming Film shaped through mechanical mold pressing. These distinct techniques lead to different performance characteristics and application ranges.

 

1.The Fundamentals: Vacuum Forming vs. Mold Pressing — Two Paths to Molecular Orientation

1.1 EVOH Skin Film: Achieving Micron-Level Conformity through Vacuum Forming

The process involves a five-layer co-extruded cast film (PE / adhesive / EVOH / adhesive / PE) that’s softened at 110 °C using infrared heating, then vacuum-formed under a differential pressure of -0.08 MPa to create precise, tight conformity to the product shape.

 

1.2 EVOH Thermoforming Film: Supporting Deep Draws with Mold Pressing

This method uses a seven-layer co-extruded blown film (PP / adhesive / PA / EVOH / PA / adhesive / PP), which is thermo-pressed at 160 °C and formed into trays with a deep draw ratio of 3.5:1.

 

Performance Highlights:

By applying asynchronous biaxial stretching (machine direction 4:1, transverse direction 8:1), the PA layer achieves a tensile strength of 45 MPa and puncture resistance of 18 N.

 

Process Distinction:

Skin films depend on vacuum pressure to achieve micron-scale fitting, while thermoforming films require high-temperature molding to form complex deep structures. This difference drives specific EVOH grade choices and layer thickness designs.

 

2.Performance Comparison: Balancing Barrier Properties, Mechanical Strength, and Production Efficiency

 

2025 Moisture Resistance Breakthrough:

Thermoforming film production with Guangdong Jinming’s 650 mm die-head achieves thickness variation within ±1.5% at speeds of 45 m/min, surpassing Mitsubishi Heavy Industries’ ±2.5% benchmark.

 

3.Practical Applications: From Freshness Precision to High-Volume Efficiency

3.1 EVOH Skin Film: The Ideal Choice for Irregularly Shaped Fresh Products

For premium fresh displays, chilled beef steaks use a structure of PE / adhesive / EW-3201 (12 μm) / adhesive / PE, featuring:

 

Outer PE layer of at least 25 μm for puncture resistance

 

KE-3000 adhesive that maintains peel strength with less than 3% degradation after retort

 

Case in point: Freshippo’s chilled salmon packaged with a nano-bentonite composite film extends shelf life from 5 to 9 days at 4 °C.

 

3.2 EVOH Thermoforming Film: The Industrial Backbone for Ready Meal Sterilization

The innovative seven-layer structure (PP / adhesive / PA / EW-3801 / PA / adhesive / PP) with asynchronous biaxial stretching (MD 3:1 + TD 8:1) achieves:

 

Tensile strength of 45 MPa in the longitudinal direction

 

Puncture resistance of 18 N even at -40 °C frozen conditions (tested on pork knuckle bones)

 

Real-world example: Anjoy Foods’ ready-meal production line operates at a 1:3.5 draw ratio, producing 200 million packages annually with a 99.2% sterilization pass rate after 121 °C retort.

 

4.Advancing Compliance: Bio-Based Materials and Recycled Content Integration

In line with the EU PPWR 2035 regulation raising bio-based content requirements to 35% by 2030, processing advances include:

 

Skin Film: Solvent-free co-extrusion achieves near-zero VOC emissions and zero detection of SVHC substances like PAHs and DEHP.

 

Thermoforming Film: Chuanwei’s bio-based EVOH packaging (derived from castor oil) reaches 45% bio-content, reduces carbon footprint by 30%, and supports 30% recycled PE blending.

 

Additional Innovation: Incorporating plant essential oils (such as clove and rosemary) into EVOH films boosts antibacterial activity by 40%, with no loss in peel strength (validated by Labthink testing).

 

5.Frequently Asked Questions

Q1: How is EVOH barrier stability maintained under high humidity?

 

Skin Film: The EVA/EVOH/EVA multi-layer structure absorbs moisture stress, keeping oxygen transmission rate fluctuations within ±5% at 85% relative humidity.

 

Q2: Why is asynchronous biaxial stretching preferred for thermoforming films?

Synchronous stretching can cause uneven crystallization in EVOH polymer, leading to whitening and brittleness. Asynchronous stretching—stretching first in the machine direction, then transverse—allows better control of crystallinity, improving yield by around 15%.

 

Q3: How does EVOH layer thickness impact shelf life?

 

For Skin Film, an EVOH layer thickness of 12 μm or more ensures OTR ≤ 0.04 cc and shelf life up to 25 days for chilled meats (with total bacterial count under 6.0 log CFU/g).

 

For Thermoforming Film, a minimum EVOH layer thickness of 15 μm is required to prevent OTR increases over 20% after 121 °C sterilization in ready meals.

 

EVOH Skin Film leverages micron-level vacuum adsorption to enhance freshness preservation precision for irregular-shaped products, while Thermoforming Film employs industrial-scale deep drawing to meet the sterilization demands of ready meals. These distinct process routes represent the natural evolution of EVOH plastic’s high-barrier packaging potential across diverse application scenarios.