The "Ruffled Edge" Challenge of Thin Films: Understanding the Underlying Technical Logic—From Causes to Solutions, All in One Article

Preface 

In thin-film production and processing, “ Ruffled hem ”  It's a common yet tricky flaw. —— Wavy wrinkles appear at the edges of the film—seemingly minor, yet they can lead to issues such as slitting deviations, inaccurate print registration, and composite bubbles, directly increasing scrap costs. Whether it is PE 、 PET Whether it's general-purpose films, optical films, packaging films, or other functional films, they may all be affected by this issue. 

This article will explore from “ Defining cognition ”  Get your hands on it—dissect the root causes behind the ruffled edge—and then provide practical prevention and solutions to help you quickly master the approach to tackling this tricky craft challenge, ultimately boosting your production efficiency. 

I. Basic Understanding: What Is a Thin Film “ Ruffled hem ”？

1. Core Definition : During molding or processing, the edge regions of the film develop wave-like wrinkles extending along the length due to uneven stress and inconsistent shrinkage, often concentrated near the edges. 5–50 mm The area features a relatively flat central region. 

2. Typical characteristics ：

• Directionality: The folds are distributed along the length, forming either periodic or irregular wave-like patterns; 
• Regional: Appears only at the edges, as opposed to “ Full-width wrinkling ”  Distinguish; 
• Hazard: Affects downstream processes such as slitting, printing, and laminating, and in severe cases, leads to product scrap. 

3. High-incidence scenarios : Extrusion casting, film blowing, biaxial stretching ( BOPP/PET ) and subsequent slitting processes. 

II. Core Breakdown: Generated by the Ruffled Hem 4 Major dimensional reasons 

The essence of the ruffled edge is “ Localized Stress Imbalance ” Specifically, it can be analyzed from four dimensions: production process, material properties, equipment condition, and environmental factors. 

(1) Production Process: Improper parameter control is the primary cause. 

1. Extrusion Casting /  Film-blowing process: Initial molding plants hidden risks 

• Uneven die temperature : Temperature deviations across different areas of the die (e.g., edges higher than the center) lead to variations in the flow rate of the molten resin, resulting in uneven cooling and shrinkage after extrusion, making the edges prone to wrinkling. 
• Mismatch between extrusion and traction speeds : Excessive traction speed or inconsistent speeds at both ends can cause uneven stress on the film edges compared to the center, leading to wrinkles as stress is released during cooling. In the blown-film process, pressure imbalances between the two ends of the traction roller often trigger this issue. 
• Uneven cooling rate : The cooling rollers and air rings cause different cooling rates between the edges and the center (e.g., if the edges cool too quickly), leading to uneven shrinkage during shaping and subsequently generating stress. 

2. Two-way stretching process: Stress imbalance during the stretching phase 

• Vertical stretching ( MD ) Speed Deviation : Inconsistent speeds at both ends of the front and rear traction rollers (e.g., the left side faster than the right), or insufficient parallelism of the roller bodies, results in uneven edge tensile forces, leading to the formation of a lotus-leaf edge after cooling. 
• Horizontal stretching ( TD ) Uneven tension : The tension difference between the chain clamps on both sides of the stretching machine (one side higher, the other lower) causes uneven lateral expansion of the film, making the side with lower tension more prone to wrinkling. 

3. Slitting Process: Secondary Damage from Post-Processing 

• Slitting knife angle deviation :The cutting tool was not perpendicular to the film's running direction, causing uneven stress on the edges after slitting and resulting in irregular wrinkles. 
• Improper winding tension control : Excessive winding tension or uneven tension at both ends can flatten even the smallest wrinkles, or lead to inconsistent edge shrinkage during the winding process. 

(II) Material Properties: Inherent Raw Material Differences Lead to Issues 

1. Melt Index ( MI ) Inequality 

Between raw material batches MI Significant differences (such as in peripheral areas) MI High), leading to varying melt resin flowability, thickness deviations after extrusion, and uneven cooling shrinkage. 

2. Additive distribution is uneven. 

Insufficient mixing of antioxidants, slip agents, and other additives—such as an excess of edge slip agents—leads to differences in the coefficient of friction and thermal stability between the film edges and its center, exacerbating uneven shrinkage. 

3. Crystallographic Degree of Difference 

Crystalline materials ( PE/PP ) During cooling, the crystallinity differs between the edges and the center (edges cool faster and have lower crystallinity), leading to stress caused by the difference in shrinkage rates. 

(III) Equipment Status: The Hidden Impact of Hardware Failures 

1. Rolling equipment lacks sufficient precision. 

• Cooling rollers and traction rollers may exhibit barrel-shaped (bulging in the middle) or tapered (thicker at one end, thinner at the other), leading to uneven film contact pressure and causing imbalances in stretching and cooling. 
• The roll body's parallelism deviation (inconsistent distance between the two ends) causes greater stress on the film edges than in the middle. 

2. Die Head Precision Defect 

• Uneven lip gap (deviation between edge and center > 0.01mm ), leading to uneven extruded film thickness and significant shrinkage differences. 
• Die lip is blocked or material accumulates, leading to reduced local output and causing the film to thin, which in turn triggers wrinkling. 

3. Ribbon machine chain clamp malfunction 

Chain clamp wear, jamming, and improper closure lead to uneven clamping force, resulting in insufficient stretching of the film edges and the formation of wrinkles. 

(IV) Environmental Factors: Indirect Interference from External Conditions 

1. Temperature and humidity fluctuations 

The workshop experiences significant temperature fluctuations (e.g., high temperatures at the edges, low temperatures in the center), or humidity levels are slightly elevated (<|endofcontentisef. RH ＞ 70% ) This leads to condensation on the cooling rollers, both of which can cause uneven cooling rates. 

2. Dust pollution 

Dust particles in the air adhere to the roller surface, causing the film to have uneven local contact. This leads to an imbalance in cooling and stretching, making the edges prone to wrinkling. 

III. Practical Guide: Prevention and Solutions for Ruffled Edges 

(1) Preventive Measures: Reducing Risks at the Source 

1. Process Parameter Optimization 

• The die head features segmented temperature control, ensuring uniform temperature across the entire width. ≤2℃ ; Calibrate the temperature sensor. 
• The control extrusion-to-drawing speed ratio is 1:1.05–1:1.1 , ensure that the speed deviation at both ends of the traction roller is within acceptable limits. ≤0.5% 。
• The cooling roller is supplied with constant-temperature circulating water, resulting in wind ring wind speed deviation. ≤5%。

2. Material Control 

• Choose the same batch MI Deviation ≤0.1 g/10 min The raw materials; testing before mixing different batches MI 。
• Using a high-speed mixer 1000-1500r/min ) Mixed additives, time ≥30min , ensuring even distribution. 
• Crystalline materials can control the deviation in crystallinity between edges and the center by adjusting the cooling rate. ≤2%。

3. Equipment Maintenance 

• Monthly inspection of roll body runout ( ≤0.02mm ), calibrate parallelism quarterly (deviation ≤0.01mm ）。 
• Check the die lip clearance weekly, and disassemble and clean the die head monthly to remove accumulated material. 
• Daily inspection of chain clip clamping force (deviation: ≤5% ), clean and lubricate the tracks weekly. 

4. Environmental Control 

• Workshop with constant temperature and humidity (temperature 23±2℃ , Humidity 50±5% RH ), avoid setting workstations near windows or air vents. 
• Clean equipment and floors daily; the high-precision film workshop requires Class 10,000 cleanliness standards. 

(II) Mitigation Measures: Addressing Issues After They Arise 

1. Quick Troubleshooting Process 

• Observe the position of the ruffled edge: unilateral traction is present. / Chain clamp experiences unilateral pressure; bilateral appearance detected at the mold head. /  Cooling system. 
• Measuring film thickness: Deviation between edge and center > 5% , the die or extrusion speed needs to be adjusted. 
• Check equipment status: Detect roller runout and tension, and eliminate hardware malfunctions. 

2. Targeted Handling 

• Uneven die temperature : Reduce the edge temperature zone 1-2℃ , Observe 10-15 Minutes. 
• Uneven traction speed : Adjust the inverter parameters to reduce the speed difference between the two ends to ≤0.5% 。
• Uneven cooling : Cleaning condensation on the roller surface / Dust, adjust the wind ring's air velocity. 
• Material unevenness : Replace the uniformly mixed raw materials, or remix the additives. 
• Slitting Issue : Calibrate the slitting knife angle to reduce winding tension 10-15% 。

Conclusion 

Thin film “ Ruffled hem ”  Though small, it tests the ability to meticulously manage every step of the production process—from precisely controlling process parameters, to rigorously overseeing raw materials and equipment, and even maintaining stable environmental conditions. Each环节 plays a critical role in determining the film's flatness. 

As thin-film technology advances toward higher precision—such as electronic-grade films and optical films— “ Zero lotus-leaf edge ”  Will become a core competitive advantage. In the future, combined with AI Intelligent methods such as visual inspection and automatic parameter adjustment will enable more efficient solutions to the scalloped edge issue. We hope the analysis and proposed solutions in this article will help enhance your production practices, making film manufacturing more stable and highly efficient.