Polyethylene (PE) is one of the most commonly used films in self-adhesive label materials - especially for squeezable, curved, and flexible product packaging. However, many press operators and converters have reported a persistent challenge: face material curling during or after printing, especially on specific presses such as the Weigang ZX450.
This issue not only disrupts matrix stripping and die-cutting but can also lead to waste, misalignment, and compromised label quality. So, what causes PE curling, and how can converters optimize their setup to reduce or eliminate it?
In this article, we explore:
The nature of PE materials in printing applications
Common causes of curling on flexo presses like Weigang ZXC450
Mechanical and environmental factors affecting print quality
Best practices and material recommendations
Expert insights from Sinopack's technical support team
Let's dive in.
Understanding PE Face Materials in Label Applications
PE (Polyethylene) face materials are known for their softness, flexibility, and durability, making them a go-to option for labels used on:
Personal care products (e.g. shampoo, lotion bottles)
Household chemicals
Baby wipes
Health supplements
Squeezable containers
Unlike stiffer films like BOPP (Biaxially Oriented Polypropylene), PE can stretch and conform to irregular surfaces without breaking. However, that flexibility comes at a cost - dimensional stability.
Curling issues typically occur when the PE label is subjected to:
Excessive tension during printing
Uneven ink or varnish coverage
Incorrect drying/curing conditions
Incompatible adhesive-liner balance
What's Happening on the Weigang ZX450?
The Weigang ZX450 is a widely used narrow-web flexo press known for high-speed production and versatility. However, some users have reported that PE label stock curls when processed on this machine - particularly during longer runs or higher-speed jobs.
Let's examine the potential causes in more detail:
picture: weigang.com
1. Mechanical Factors: Press Settings & Tension Control
a. Tension Profile Misalignment
PE is a low-modulus material, meaning it stretches easily under pressure. Excessive web tension - especially between the unwinder and printing units - can cause the face stock to deform. If the liner and face stock stretch at different rates, curling becomes inevitable.
Solution:
Reduce web tension, especially at unwinding and infeed zones
Use tension zone separation to isolate stress
Ensure equal tension balance between face stock and liner
b. Drying Heat or UV Exposure
Many flexo setups use UV or IR drying units after each station. If the drying temperature is too high or unevenly applied, it can cause shrinkage on the printed side, leading to upward or downward curling depending on direction.
Solution:
Lower dryer temperature or increase airflow to dissipate heat
Apply UV curing in shorter bursts or use LED units for cooler drying
If possible, alternate curing between top and bottom layers to balance tension
2. Material-Driven Factors: Face Stock, Adhesive & Liner Imbalance
a. PE Face Stock Thickness
Thinner PE (below 60μm) is more prone to curling. Curling may also occur if the PE is not co-extruded with sufficient stiffness or lacks a dimensional stabilizer layer.
Solution:
Use co-extruded or reinforced PE films (e.g., layered with PP or PET)
Increase face stock thickness to 75μm+ for better layflat performance
Apply topcoat for added stiffness and ink adhesion
b. Adhesive Type and Coat Weight
An uneven or incompatible adhesive coat weight can result in curl due to differential contraction between adhesive and face stock.
Solution:
Opt for pressure-sensitive adhesives specifically formulated for flexible films
Test low-flow adhesives to avoid "pull-back" effect
Request TDS from your material supplier and check adhesive-liner compatibility
c. Liner Material
Glassine liners with high tension memory may shrink differently than the PE film, causing curling after printing and die-cutting.
Solution:
Use super-calendered glassine or PET liners with dimensional stability
Avoid mismatching thick adhesives with thin liners
Choose liners with anti-curling treatments
3. Design-Related Issues: Ink Coverage and Die-Cutting
a. Heavy Ink or Varnish Flood Coating
PE face materials tend to absorb heat during heavy ink or varnish coverage, which can lead to differential shrinkage.
Solution:
Use lightweight artwork or minimize flood coating
Use UV inks designed for film substrates with low shrinkage
Optimize anilox roll specs to control ink transfer
b. Die-Cut Pattern & Matrix Stripping Tension
Intricate die-cut shapes and aggressive matrix stripping can pull on the edges of the label, resulting in post-conversion curling.
Solution:
Adjust stripping angle and tension settings
Apply anti-curl edge perforation if needed
Modify die-cut layout to balance pull force
Sinopack's Technical Recommendations for PE Label Applications
As a supplier of premium self-adhesive label materials, Sinopack regularly works with printing partners to fine-tune material performance on specific equipment like the Weigang ZX450. Based on field feedback and lab testing, we recommend:
✅ Use 85μm matte PE face stock with surface coating for better ink control
✅ Match with a medium-flow hotmelt or emulsion acrylic adhesive
✅ Pair with FSC-certified super-calendered glassine liner
✅ Run tension tests at multiple stages (infeed, print zone, die-cutting)
✅ Request materials with anti-curling treatment or improved dimensional balance
Field Case Example: Converter in Southeast Asia
A narrow-web converter in Southeast Asia encountered severe curling issues with standard PE labels on their Weigang ZXC450, especially during high-volume body care label production.
🔍 Problem Identified:
Thin 55μ PE
High-tack adhesive with aggressive liner tension
Flood UV varnish on most labels
🛠 Solution Applied:
Switched to Sinopack 75μ coated PE face material
Balanced adhesive coat weight to match liner density
Recalibrated curing temperature & slowed press speed by 10%
Optimized matrix stripping tension at exit zone
📈 Result:
Curling eliminated
25% improvement in matrix stripping efficiency
Customer feedback: "More stable and reliable over long runs"
Conclusion: Collaboration is the Key to Curl-Free PE Labels
Curling in PE self-adhesive materials is a multi-variable issue - but it's also solvable. By taking a holistic view of your press settings, face stock properties, adhesive-liner match, and post-press processes, converters can achieve high-performance results, even on challenging presses like the Weigang ZX450.
At Sinopack, we're here to support your printing process with:
Custom material recommendations
Technical support for press troubleshooting
Sample rolls for testing and validation
Full TDS and safety data for PE label products
Need help solving label curling?
📩 Contact us for expert advice, sample kits, and tailored PE label materials designed for high-speed narrow-web flexo presses like the Weigang ZX450.