Why Adhesives Matter in Cement Bags
Adhesives are the invisible but critical component that holds cement bags together. In paper valve sack production, adhesives seal the bottom, attach the valve, bond paper layers, and close side seams. A bag’s strength is only as good as its adhesive bonds — a weak glue joint can cause catastrophic bag failure during handling.
The adhesive system accounts for only 5–10% of total bag material cost but has a disproportionate impact on bag quality and durability.
Adhesive Application Points
Types of Adhesives for Cement Bags
Hot Melt Adhesive (HMA)
| Property | Detail |
|---|---|
| Base | EVA (ethylene vinyl acetate) or polyolefin |
| Application Temp | 150–180°C |
| Setting Time | 2–5 seconds |
| Bond Strength | Medium–High |
| Cost | $1.50–$3.00/kg |
| Usage per Bag | 3–8 grams |
Advantages: Fast setting, clean application, no drying needed, high-speed compatible Disadvantages: Bond weakens at high temperature, lower long-term durability
PVA (Polyvinyl Acetate) Adhesive
| Property | Detail |
|---|---|
| Base | Polyvinyl acetate emulsion |
| Application Temp | Room temperature |
| Setting Time | 30–90 seconds |
| Bond Strength | High |
| Cost | $1.00–$2.00/kg |
| Usage per Bag | 5–12 grams |
Advantages: Strong permanent bond, low cost, water cleanup Disadvantages: Long setting time (limits line speed), moisture-sensitive before curing
Starch-Based Adhesive
| Property | Detail |
|---|---|
| Base | Modified corn/potato starch |
| Application Temp | Room temperature or warm |
| Setting Time | 10–30 seconds |
| Bond Strength | Medium |
| Cost | $0.50–$1.50/kg |
| Usage per Bag | 8–15 grams |
Advantages: Lowest cost, biodegradable, renewable source Disadvantages: Weakened by moisture, limited to paper-on-paper bonds
Chemical Adhesive (Synthetic Resin)
| Property | Detail |
|---|---|
| Base | Modified PVA, polyurethane, or acrylic |
| Application Temp | Room temperature |
| Setting Time | 10–60 seconds |
| Bond Strength | Very High |
| Cost | $2.00–$4.00/kg |
| Usage per Bag | 3–8 grams |
Advantages: Strongest bond, moisture-resistant after curing, best for heavy-duty bags Disadvantages: Higher cost, requires careful mixing/preparation
Adhesive Applications in Bag Production
Where Adhesive Is Used
| Application | Preferred Adhesive | Reason |
|---|---|---|
| Tube side seam (tuber) | Hot melt | Fast setting at high speed |
| Bottom sealing (bottomer) | Hot melt or chemical | Balance of speed and strength |
| Valve attachment | Hot melt | Quick bond for valve insertion |
| Paper layer bonding | Starch or PVA | Paper-to-paper economy |
| Reinforcement patches | Chemical adhesive | Maximum strength needed |
| PP woven lamination | PE extrusion | Thermal bond, not adhesive |
Glue System Components
A typical adhesive system on a bottomer machine includes:
- Glue tank — Heated reservoir (for hot melt) or stirred tank (for PVA/chemical)
- Pump — Delivers adhesive to applicators
- Applicators — Nozzles, rollers, or slot dies that apply adhesive to paper
- Temperature controller — Maintains optimal adhesive temperature
- Filter — Removes debris that could clog nozzles
Cost Analysis
Cost per Bag
| Adhesive Type | Usage/Bag | Cost/kg | Cost/Bag |
|---|---|---|---|
| Hot melt | 3–8g | $2.00 | $0.006–$0.016 |
| PVA | 5–12g | $1.50 | $0.008–$0.018 |
| Starch | 8–15g | $1.00 | $0.008–$0.015 |
| Chemical | 3–8g | $3.00 | $0.009–$0.024 |
Monthly Cost (1,000,000 bags/month)
| Type | Monthly Adhesive Cost |
|---|---|
| Hot melt only | $6,000–$16,000 |
| PVA system | $8,000–$18,000 |
| Starch system | $8,000–$15,000 |
| Chemical system | $9,000–$24,000 |
How to Choose the Right Adhesive
Decision Matrix
| Factor | Hot Melt | PVA | Starch | Chemical |
|---|---|---|---|---|
| Line Speed >100 bags/min | ✅ | ❌ | ⚠️ | ⚠️ |
| Heavy-duty bags (50kg) | ⚠️ | ✅ | ❌ | ✅ |
| Budget priority | ⚠️ | ✅ | ✅ | ❌ |
| Humid climate | ⚠️ | ❌ | ❌ | ✅ |
| Export quality | ⚠️ | ✅ | ❌ | ✅ |
| Eco-friendly | ❌ | ⚠️ | ✅ | ❌ |
✅ Best choice | ⚠️ Acceptable | ❌ Not recommended
Common Combinations
Many production lines use two adhesive systems:
- Hot melt for speed-critical applications (tube seam, valve insertion)
- Chemical/PVA for strength-critical applications (bottom seal, reinforcement)
Storage and Handling
Hot Melt
- Store in cool, dry area (below 40°C)
- Shelf life: 12–24 months
- Avoid overheating (charring degrades adhesive)
PVA/Chemical
- Store above 5°C (freezing damages emulsion)
- Shelf life: 6–12 months
- Stir before use if stored for extended periods
Starch
- Store in sealed containers (absorbs moisture)
- Shelf life: 3–6 months (mixed), 12+ months (dry powder)
- Mix fresh batches daily for consistent performance
Troubleshooting Common Issues
| Problem | Likely Cause | Solution |
|---|---|---|
| Weak bond | Wrong temperature or expired adhesive | Check temp, replace old stock |
| Stringing | Hot melt too hot | Reduce temperature by 5–10°C |
| Clogged nozzles | Debris or charred adhesive | Clean nozzles, add filter |
| Bubbling | Moisture in adhesive | Dry adhesive, check storage |
| Slow setting | Low temperature or wrong formulation | Increase temp or switch type |
Frequently Asked Questions
Can I use the same adhesive for paper and PP bags? No. Paper bags use water-based or hot melt adhesives. PP woven bags use heat sealing (thermal welding) or specialized PP-compatible adhesives. Standard PVA does not bond to PP surfaces.
How much does adhesive affect bag strength? Significantly. The adhesive bond is often the weakest point in a bag. A well-bonded bag will tear through the paper before the glue joint fails. A poorly bonded bag will peel apart at seams, causing cement spillage.
What is the ideal hot melt application temperature? Most EVA-based hot melts perform best at 160–175°C. Too low (below 145°C) causes weak bonds. Too high (above 190°C) causes charring and degradation. Always follow the manufacturer’s recommended temperature range.
Learn more about bag production in our Equipment Guides or use the Cost Calculator to see how adhesive costs affect your total production cost.