What are the differences between PP and PE label materials? Chemical structure + 5-dimensional comparison + 4-step selection guide
💡 💡 At a Glance
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Last week, a client in the cold-chain food business asked me: "My label needs to go into a -20°C freezer. Should I choose PP or PE?"
I said: "PE—its glass transition temperature is -100°C, making it more cold-resistant than PP at -10°C."
I said: "5-dimension comparison—structure + performance + temperature + application + cost, each with its own characteristics. This article doesn't discuss "which is better, PP or PE"—it covers the chemical structure of PP / PE + a 5-dimension comparison + 4-step selection + 3 typical applications + 5-step printing precautions."
2 Material Chemical Structures
PP (Polypropylene) Chemical Structure
3 Molecular Characteristics:
- Main chain: -CH2-CH(CH3)-n (with methyl side chain)
- Crystallinity: 50-70% (high)
- Glass transition temperature: -10°C
3 Structural Features:
- High C-C bond energy in the main chain (chemical stability)
- Methyl side chain provides hydrophobicity (water resistance)
- High crystallinity (good hardness)
PE (Polyethylene) Chemical Structure
3 Molecular Characteristics:
- Main chain: -CH2-CH2-n (simplest structure)
- Crystallinity: 50-80% (HDPE)
- Glass transition temperature: -100°C
3 Structural Features:
- Simplest main chain (flexible)
- No side chains (linear molecule)
- Extremely low glass transition temperature (most cold-resistant)
| Dimension | PP | PE |
|---|---|---|
| Chemical Structure | C-C main chain + methyl side chain (-CH3) | C-C main chain + hydrogen side chain (-H) |
| Density | 0.91 g/cm³ (light) | 0.92-0.96 g/cm³ (heavy) |
| Melting Point | 165°C (high) | 120-135°C (medium) |
| Temperature Resistance | -20 to 120°C | -50 to 80°C |
| Hardness | Relatively hard | Relatively soft |
| Chemical Resistance | Excellent (resistant to acid / alkali / oil) | Medium (resistant to acid / not resistant to alkali) |
| Transparency | Semi-transparent | Semi-transparent |
| Cost | 0.2-0.4 yuan / sheet | 0.25-0.5 yuan / sheet |
| Application | Medium hardness + chemical resistance | Flexibility + cold resistance |
Application 1: PP Labels (Mainstream 70%)
3 Application Categories:
- Cosmetics / daily chemicals (medium hardness + water resistance)
- Food / pharmaceuticals (chemical resistance + hygiene)
- Industrial / chemical (chemical resistance)
3 Advantages:
- Chemical resistance (resistant to acid / alkali / oil)
- Good hardness (conforms to product)
- Moderate cost (0.2-0.4 yuan)
Application 2: PE Labels (High-end 25%)
3 Application Categories:
- Cold chain food (-40°C frozen products)
- Northern outdoor (-30°C winter)
- Chemical drums (flexible bending)
3 Advantages:
- Cold resistance (-100°C glass transition temperature)
- Flexibility (bending conformance)
- Impact resistance (not easy to crack)
Application 3: Composite Materials (High-end 5%)
3 Application Categories:
- PP + PE composite (double layer)
- PP + aluminum foil (high barrier)
- PE + paper (eco-friendly)
3 Advantages:
- Double-layer performance superposition
- High barrier (moisture-proof + water-resistant)
- Customization (combination on demand)
Step 1: Clarify the Application Scenario
3 Operating Steps:
- Temperature (room temperature / low temperature / high temperature)
- Chemical (chemical resistance / water resistance / oil resistance)
- Flexibility (hard / soft)
Step 2: Select Material Type
Choose 1 of 3:
- PP (medium hardness + chemical resistance)
- PE (flexible + cold resistant)
- Composite material (double layer)
Step 3: Select Specific Model
3 Operating Steps:
- Thickness (30-100μm)
- Surface treatment (corona / coating)
- Special properties (barrier / UV resistance)
Step 4: Test + Order
3 Operating Steps:
- Labeling test (100 sheets)
- Environmental test (high / low temperature + chemical)
- Bulk order
Step 1: Corona Treatment
3 Key Points:
- Mandatory (PP / PE surface energy is low)
- Dyne pen ≥ 38 dyne / cm
- Print within 24 hours after treatment
Step 2: Ink Selection
3 Key Points:
- Special ink for PP / PE
- Strong adhesion (cannot be torn off by tape)
- Chemical resistance (water and oil resistant)
Step 3: Drying Temperature
3 Key Points:
- PP 60-80°C (medium temperature)
- PE 50-70°C (low temperature)
- Too high causes deformation (irreversible)
Step 4: Tension Control
3 Key Points:
- PP tension 5-10 N / m
- PE tension < 5 N / m (too tight causes stretching)
- Stable (avoid fluctuation)
Step 5: Printing Precision
3 Key Points:
- 300 DPI minimum
- After PP surface energy improvement
- PE requires corona treatment
Issue 1: Ink Falling Off
Symptom: Ink comes off when torn after printing
Cause: No corona treatment (ink does not adhere)
Solution: Corona treatment mandatory before printing
Issue 2: Label Deformation
Symptom: Deformation after labeling (bending / wrinkling)
Cause: Excessive drying temperature + over-tight tension
Solution: Control temperature + tension
Issue 3: Blurry Printing
Symptom: Unclear text
Cause: Unstable tension + improper ink
Solution: Adjust tension + switch to special ink
## 3 Real CasesCase 1: Cosmetic Bottle Body (PP)
Configuration:
- PP synthetic paper 80μm
- Corona treatment 38 dyne
Application: 500,000 sheets per month (cosmetics)
Case 2: Cold Chain Food (PE)
Configuration:
- PE synthetic paper 60μm
- Frozen adhesive
Application: 300,000 sheets per month (-20°C cold chain)
Case 3: Chemical Drum (PE)
Configuration:
- PE thick film 100μm
- Permanent acrylic
Application: 1 million sheets per year (chemicals)
If you want to learn about pressure-sensitive adhesive chemistry — refer to the basics of pressure-sensitive adhesive material chemistry, or directly contact a LeXiang Packaging consultant, material selection + test report delivered within 24 hours.
FAQ
What are the differences between PP and PE label materials?
PP and PE are the 2 most commonly used film label materials, 5-dimension comparison: (1) Chemical structure — PP (polypropylene) main chain C-C + side chain methyl (-CH3), PE (polyethylene) main chain C-C + side chain hydrogen (-H); (2) Physical properties — PP is harder (density 0.91 g/cm³, melting point 165°C), PE is softer (density 0.92-0.96, melting point 120-135°C); (3) Temperature resistance — PP -20 to 120°C, PE -50 to 80°C; (4) Applications — PP (medium hardness / chemical resistance), PE (flexible / low-temperature resistance); (5) Cost — PE slightly more expensive by 0.05-0.1 yuan per sheet (higher density). 3 core differences: (1) Hardness — PP is harder, PE is softer; (2) Melting point — PP higher at 165°C vs PE 120-135°C; (3) Transparency — PP semi-transparent, PE semi-transparent. 3 selection recommendations: (1) Chemical resistance + high temperature choose PP; (2) Flexibility + cold resistance choose PE; (3) For medium scenarios both are acceptable.
What are the characteristics of PP label materials?
4 core characteristics of PP labels: (1) Chemical resistance — propane main chain + methyl side chain (chemical stability) + acid/alkali/oil resistance; (2) High hardness — high crystallinity (50-70%) + tensile strength (30-50 MPa); (3) Temperature resistance — melting point 165°C (medium heat resistance) + suitable for -20 to 120°C; (4) Waterproof — hydrophobic methyl + non-absorbent + excellent waterproof. 3 molecular features: (1) Main chain -CH2-CH(CH3)-n (methyl side chain); (2) Crystallinity 50-70% (high); (3) Glass transition temperature -10°C (higher than PE). 3 typical applications: (1) Cosmetics / daily chemicals (medium hardness + waterproof); (2) Food / pharmaceutical (chemical resistance + hygiene); (3) Industrial / chemical (chemical resistance). 3 usage notes: (1) Poor cold resistance (< -20°C prone to brittleness); (2) Low transparency (not as good as PVC); (3) Corona treatment required before printing (to improve adhesion).
What are the characteristics of PE label materials?
4 core characteristics of PE labels: (1) Flexibility — linear main chain + hydrogen side chain (soft molecular chain) + good bendability; (2) Cold resistance — glass transition temperature -100°C (the most cold-resistant plastic) + suitable for -50 to 80°C; (3) Impact resistance — high impact strength (not easily broken) + tear resistance; (4) Chemical stability — polyethylene main chain + low polarity (acid/alkali resistance). 3 molecular features: (1) Main chain -CH2-CH2-n (simplest structure); (2) Crystallinity 50-80% (high-density HDPE); (3) Glass transition temperature -100°C (extremely cold resistant). 3 typical applications: (1) Cold chain food (-40°C frozen products); (2) Northern outdoor (-30°C winter); (3) Chemical drums (flexible bending). 3 usage notes: (1) Limited temperature resistance (< 80°C softens); (2) General transparency (semi-transparent); (3) Corona treatment required for printing (to improve ink adhesion).
How to choose between PP and PE?
4-step selection process: (1) Clarify the use scenario — room temperature / low temperature / high temperature / chemical resistance; (2) Choose material type — PP / PE / other; (3) Choose specific model — thickness (30-100μm) + surface treatment (corona / coating); (4) Test + order. 3 core selection factors: (1) Temperature — PP -20 to 120°C, PE -50 to 80°C; (2) Chemical — PP has good chemical resistance, PE is average; (3) Flexibility — PP hard, PE soft. 3 typical scenario selections: (1) Cosmetics / daily chemicals (room temperature + chemical resistance) — PP (mainstream 70%); (2) Cold chain / outdoor (low temperature + flexibility) — PE (30%); (3) Medium scenarios — both acceptable (depends on price). 3 recommendations: first check temperature + then chemical resistance + finally cost.
What should be noted when printing on PP and PE?
5 printing notes: (1) Corona treatment — must be done before printing (PP/PE surface energy is low, corona needed to increase adhesion); (2) Ink selection — choose PP/PE dedicated ink (ordinary ink has poor adhesion); (3) Drying temperature — PP 60-80°C vs PE 50-70°C (too high temperature causes deformation); (4) Tension control — PE tension < 5 N/m (too tight causes stretching deformation); (5) Printing accuracy — 300 DPI minimum (after PP surface energy improvement). 3 common problems: (1) Ink shedding — no corona treatment before printing; (2) Label deformation — drying temperature too high; (3) Blurry printing — unstable tension. 3 recommendations: (1) Corona treatment before printing (essential); (2) Choose dedicated ink (don't save on this); (3) Test before mass production. 3 testing tools: Dyne pen (measure surface energy) + tape peel test (measure adhesion) + rub tester (measure rub resistance).
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