A clear distinction: “High-pressure” vs. “Low-pressure” PE film! Low density = high pressure; high density = low pressure?

Preface 

Polyethylene ( PE ) In the field of thin films, “ High-pressure membrane “” Low-pressure membrane ” It’s a high-frequency term, but many beginners easily get confused: Why low density? PE The membrane is a high-pressure, high-density membrane. PE Is the membrane a low-pressure membrane? Are the only difference between the two their densities? How can we make the right selection during procurement to avoid mismatches? 

Actually “ High voltage “” Low pressure ” Originating from the production process, it directly determines. PE The density, structure, and performance of membranes significantly influence their application scenarios. This article breaks down these aspects—from core definitions and manufacturing processes to performance characteristics, applications, and selection criteria—helping you thoroughly understand the differences between the two and their respective areas of applicability. 

I. Basic Understanding: First, grasp the core definitions. —— High voltage = Low density, low pressure = High density 

PE of the membrane “ High voltage “” Low pressure ” It’s not the pressure itself that matters, but rather the pressure conditions during the polymerization process. This difference directly leads to variations in resin density and crystallinity, resulting in two films with markedly different properties. 

(1) High Voltage PE Membrane: Low-density polyethylene ( LDPE ) Thin film 

High voltage PE The membrane material is low-density polyethylene. LDPE ), due to production needs 100-300MPa High pressure, 150-300℃ Free-radical polymerization at high temperatures, commonly known as... “ High-pressure membrane ” It has many molecular branches and a high degree of crystallinity. 50%-60% , density 0.910–0.925 g/cm³ 。

(2) Low pressure PE Membrane: High-density polyethylene ( HDPE ) Thin film 

Low pressure PE The membrane material is high-density polyethylene ( HDPE ), using Ziegler - Natta catalyst, in 0.1-5MPa Low pressure, 60-100℃ Coordination polymerization at moderate temperatures, commonly known as... “ Low-pressure membrane ” It has few molecular branches and a regular arrangement, with high crystallinity. 80%-95% , density 0.941–0.965 g/cm³ 。

(3) Key distinction: Don't get confused. “ Process Name ” With “ Performance name ”

The core correspondence needs to be clearly defined to avoid confusion: 

• “ High voltage “” Low pressure ” It is a process characteristic corresponding to polymerization pressure; 
• “ Low density “” High density ” It is a material property corresponding to density and crystallinity; 
• Core correspondence: High-pressure process → Low density PE→ High-pressure membrane; low-pressure process → High density PE→ Low-pressure membrane. 

II. Core Difference: How Does the Production Process Determine Film Performance? 

High pressure and low pressure PE The differences in membrane performance stem from the distinct molecular structures resulting from variations in the polymerization process. The number of branches and the degree of crystallinity directly influence key properties such as flexibility and strength. Below, we’ll analyze these aspects in detail, linking process specifics to performance outcomes. 

(1) Comparison of Production Processes: The Core Difference Between High-Pressure and Low-Pressure Systems 

• Aggregation pressure High-pressure membrane required 100-300MPa , large equipment investment; low-pressure membranes only 0.1-5MPa Low equipment threshold; 
• Polymerization temperature High-pressure membrane 150-300℃ High-temperature polymerization; low-pressure membrane 60-100℃ Medium-temperature polymerization; 
• Catalyst and Reaction High-pressure membranes use free-radical initiators, which readily produce branched chains; low-pressure membranes use coordination catalysts, resulting in well-ordered molecular chains. 
• Molding process Both can be used for blow molding and cast film processes. High-pressure films are more suitable for blow molding (offering high transparency and high flexibility), while low-pressure films can be processed by both blow molding and cast film methods; cast film processing improves surface smoothness. 

(2) Key Performance Comparison: 8 See it clearly at a glance with a broad perspective. 

Performance differences determine application scenarios. 8 Comparison of Core Dimensions: 

• Flexibility and Hand Feel High-pressure membranes are flexible, soft, easily stretchable, and fold without leaving creases; low-pressure membranes are less flexible, relatively stiff and difficult to stretch, and leave creases when folded. 
• Tensile strength and puncture resistance High-pressure membrane tensile strength 10-20MPa Generally puncture-resistant; low-pressure membrane 20-40MPa Excellent puncture resistance and tear resistance; 
• Transparency and Glossiness High-pressure films have high transparency and good gloss; low-pressure films have poorer transparency and lower gloss, with some appearing slightly hazy. 
• Temperature resistance High-pressure membrane -60℃ To 80℃ , not resistant to high temperatures; low-pressure membrane -60℃ To 110℃ , bearable 80-90℃ Short-term sterilization; 
• Barrier property Both have moderate barrier properties; the low-pressure membrane, due to its higher crystallinity, is slightly superior to the high-pressure membrane. 
• Heat sealability High-pressure membrane heat-sealing temperature 105–120℃ Wide window, easy for high-speed heat sealing; low-pressure film. 125–140℃ The window is narrow and the difficulty is high; 
• Processing adaptability High-pressure membranes are easy to process and can be blown down to a thinness of: 0.01mm The following: Low-pressure membranes are difficult to process, and thin-specification products are not easy to form. 
• Cost Under the same thickness, the raw material cost of high-pressure membranes is slightly higher than that of low-pressure membranes. 

III. Application Scenarios: High-pressure Membranes and Low-pressure Membranes “ A place to put one's skills to use ”

Based on their performance differences, the two have different focuses in application scenarios; at the core is... “ Performance meets requirements ”：

(1) High Voltage PE Typical applications of membranes (low density) 

High-pressure films, with their high flexibility, high transparency, and excellent heat-sealing properties, are ideal for applications that demand both flexibility and superior aesthetics. 

• Food packaging Supermarket shopping bags, cling film, snack bags (inner layer), bread bags, fruit preservation bags, and more; 
• Daily chemical packaging Shampoo and body wash outer bags, inner lining films; 
• Industrial assistance Product surface protective film (low-tack), lightweight product wrapping film; 
• Other Agricultural microfilms (short-term), raw material films for disposable gloves. 

(2) Low pressure PE Typical applications of membranes (high-density) 

Low-pressure membranes, with their high strength, excellent puncture resistance, and good temperature tolerance, are suitable for applications that demand high strength and weather resistance. 

• Industrial packaging : ton bag liner film, carton liner film, electronic component film, high-strength wrapping film; 
• Food packaging Freezer food bags, rice bags, flour bags, feed bags; 
• Daily Chemicals and Building Materials Laundry detergent, outer bags for laundry powder, profiles / Pipe packaging film; 
• Other Agricultural thick-film (long-term), geomembrane (for impermeability). 

(3) Special Scenarios: Combined Modification of the Two Materials 

In complex scenarios, the two materials can be blended and blown into film—for example, adding them to high-strength shopping bags. 20%-30% Low pressure PE Enhanced tear resistance; added to highly transparent industrial films 10%-20% High voltage PE Improve transparency. 

IV. Procurement and Usage Selection Guide: Avoiding Common Pitfalls 

Procurement PE Membranes can easily lead to pitfalls due to confusion and misinterpretation. Below are selection guidelines and reminders about common misconceptions: 

(1) Core Principles for Model Selection 

• Requires high flexibility, high transparency, and easy heat sealing. → Select a high-pressure membrane; 
• Requires high strength, high puncture resistance, and excellent temperature resistance. → Choose low-pressure membranes; 
• Need to balance flexibility and strength. → Select blended membrane; 
• Cost-sensitive, with low performance requirements. → Priority low-pressure membrane (can be thinned to reduce costs). 

(2) Common Misconceptions to Be Aware Of 

• Misconception 1： “ High-pressure membranes are suitable for high-pressure environments. → Correction: High pressure is a production process and is unrelated to the operating pressure. High-pressure membranes have low strength and therefore cannot be used in high-pressure applications. 
• Misconception 2： “ The transparent ones are all high-pressure films. → Correction: Low-pressure membranes can be enhanced with antireflection coatings to improve transparency, but this approach comes at a high cost. For applications prioritizing low cost and high transparency, high-pressure membranes are the preferred choice. 
• Misconception 3： “ Low-pressure membranes must have low costs. → Correction: High-pressure films of the same thickness are slightly more expensive, but low-pressure films can be thinned to reduce overall costs—this needs to be calculated. 
• Misconception 4： “ All PE The membrane can be sterilized at high temperatures. → Correction: Only low-pressure membranes can withstand it. 80-90℃ Short-term high temperature, high-pressure membrane ultra- 80℃ Easily deformed. 

(3) Procurement Inspection Tips 

• Hand feel: soft and easy to stretch → High-pressure membrane; relatively hard and difficult to stretch. → Low-pressure membrane; 
• Folded: No creases / Easily recoverable → High-pressure membrane; obvious creases → Low-pressure membrane; 
• Transparent: Clear and high-gloss → High-pressure membrane; slightly hazy → Low-pressure membrane; 
• Stretchability: Greatly extensible and not easily broken. → High-pressure membrane; small stretchability, prone to breakage. → Low-pressure membrane. 

V. Industry Trends: High Voltage and Low Voltage PE The upgrade direction for membranes 

With the tightening of environmental policies and the upgrading of the market, high-pressure and low-pressure... PE Membranes are evolving toward high performance, environmental friendliness, and functionalization: 

• Environmentalization Development PBAT/PE Biodegradable films and single-material recyclable films are well-suited to the dual-carbon policy. 
• Functionalization Add antimicrobial, antistatic, and other additives to develop specialized functional films. 
• Process optimization High-pressure membranes improve equipment to reduce energy consumption; low-pressure membranes optimize catalysts to lower processing difficulty. 
• Scene Expansion High-pressure membranes are upgrading to high-end food packaging; low-pressure membranes are expanding into high-end industrial packaging. 

Conclusion 

High pressure and low pressure PE The core difference in membranes stems from the molecular structural variations caused by the manufacturing process, which ultimately manifest in their performance. Remember the key logic: “ High voltage = Low density = High flexibility, low pressure = High density = High intensity ”。

Membrane companies and purchasers don’t need to aim for the high end—what matters most is selecting the right membrane type precisely based on application requirements and cost considerations. As technology continues to advance, both sides will keep pushing boundaries and further expanding the scope of applications. 

You're at high pressure, low pressure. PE What challenges have you encountered when selecting membranes for procurement and use? What identification tips do you have? Feel free to share in the comments!