Hot Seal or Spot Seal?
How to Eliminate Gusset Seal Failures in Pouch Manufacturing
If you manufacture flexible pouches, you already know this: the gusset fold is one of the most common—and frustrating—failure points.
At this point in the structure, your material transitions from four layers down to two, creating an uneven sealing surface and a high risk for leaks.
Figure 1: The gusset fold creates a 4-layer to 2-layer transition, forming a high-risk leak zone. Spot sealing targets this area directly without overheating the full seal.
The Problem: Uneven Sealing at the Gusset
As shown in Figure 1, the gusset fold introduces a non-uniform sealing interface.
The thicker the material:
- The larger the potential gap
- The harder it is to achieve a hermetic seal
Your sealant layer must compensate for this.
⚠️ Key Insight
The sealant acts as “caulk.” If there isn’t enough of it, no machine setting will fix your leaks.
Why Overheating Makes It Worse
A common reaction to leaks is increasing:
- Temperature
- Dwell time
This may temporarily improve seals—but it creates bigger problems.
Overheating leads to:
- Crystallization
- Brittleness
- Seal cracking
- Delamination
And downstream, you’ll see:
- Fuzzy cuts
- Blade sticking
- Poor punch performance
⚠️ Common Mistake
Fixing leaks with heat often damages areas that were already sealing correctly.
A Better Approach: Spot Sealing
Instead of applying more energy everywhere, focus it where it’s needed most—the gusset fold.
Spot sealing works by:
- Targeting the failure zone directly
- Reducing thermal stress on the rest of the seal
- Improving consistency across production
As illustrated above, this localized approach eliminates the need to overprocess the entire seal.
✅ Best Practice
Control the problem area—not the whole seal.
Recommended Spot Seal Setup
For consistent results:
- Install a zipper crushing tool after the final cross seal
- Match the tool width to the cross seal
- Use a 70-durometer silicone rubber anvil
- Apply minimal pressure and stroke
Because the sealant is already activated, additional heat is often unnecessary.
If needed, prioritize heat over pressure to avoid visible defects.
No Spot Seal Station? Try This
If your machine doesn’t allow an additional station, you can still improve seal integrity.
Teflon Tape Method:
- Apply 3–5 layers of adhesive-backed Teflon tape
- Position it directly over the gusset fold
- Use it on the final cross seal
This creates a localized pressure point that improves sealing where it matters most.
Final Takeaway
If you’re chasing leaks by increasing heat and dwell, you’re solving the wrong problem.
Focus your process on the gusset fold—the true failure point—and you’ll see:
- Better seal consistency
- Stronger material integrity
- Fewer downstream issues
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