![Page 1: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/1.jpg)
Heat Sealing
Duncan Darby
Clemson University
![Page 2: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/2.jpg)
Common Method to Close / Shape Flexible Packages
• Supply thermal energy on outside of package
• Soften / “melt” sealant
• Also used in closure of semi‐rigid and rigid packages– Especially combinations with flexible, e.g. cups & lids, etc.
![Page 3: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/3.jpg)
What Is Needed to Make a Seal
• Two surfaces‐ thermoplastic “seal partners”
• Time, Temperature and Pressure??
• Actually time, energy and pressure– Different seal methods supply energy in different ways
![Page 4: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/4.jpg)
Heat Conduction
• Most common type of sealing is heated tooling– Often called hot bar, bar, constant temperature, heat sealing, etc.
• Depending on conduction through the materials
• Generally need higher melt point on outside than on inside
![Page 5: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/5.jpg)
Model of Conductive Heat SealingSeal Interface Temperature vs. Time
0.0
50.0
100.0
150.0
200.0
250.0
300.0
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
Time, sec
Tem
pera
ture
, F
Temperature @ Seal Interface vs. Time
0.0000
50.0000
100.0000
150.0000
200.0000
250.0000
300.0000
0.000 0.100 0.200 0.300 0.400 0.500 0.600
Time (s)
Tem
pera
ture
(F)
2 mil LLDPE sealed one side at 250 F
2 mil LLDPE sealed two sides at 250 F
![Page 6: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/6.jpg)
Model of Cooling of Heat SealCooling Curve for a Seal
0
50
100
150
200
250
300
0 2 4 6 8 10 12 14 16 18
Time, s
Tem
pert
ure.
F
Temp seal interface
2 mil LLDPE initially at 250 F
![Page 7: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/7.jpg)
To Understand Seal Mechanisms
• Separate:– The mechanism of creating the seal
– The mechanism of opening the seal
![Page 8: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/8.jpg)
3 Mechanisms of Making a Seal• Chain entanglement across seal interface
– Aka molecular intermingling, autohesion
– Molecular chains cross interface & entangle together
• Intermolecular bonding– Functional groups on one seal partner attracted to those on other seal partner
• Mechanical Seal– No real chemical compatibility involved
– Plastic flows into pores or around fibers of seal partner
![Page 9: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/9.jpg)
4 Opening Mechanisms• Destruct / Fusion ‐ Seal is stronger than something else, so something else breaks
• Adhesive (peelable)‐When opening, sealant comes away from seal partner
• Cohesive (peelable)‐ Sealant on one of the seal partners breaks within itself
• Interfacial / delamination (peelable)‐ Seal strong, but delamination built into structure allows for easier opening
![Page 10: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/10.jpg)
Relating Seal Mechanisms to Opening Mechanisms
• Chain entanglement– Typically destruct, cohesive, interfacial peel
– Blended sealants can result in cohesive or adhesive bonds
• Intermolecular bonding– Typically adhesive
• Mechanical– Typically destruct, cohesive
![Page 11: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/11.jpg)
Opening Mechanisms
AdhesiveCohesive
DestructInterfacial split
![Page 12: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/12.jpg)
Seal Curves
• Help to characterize / predict seal behavior of material
• Derived from seal test
• Y‐axis: Seal strength
• X‐axis: Energy (usually temperature)– Pressure, time could also be used
![Page 13: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/13.jpg)
Seal Test‐What To Expect
Typically, one of these will end up in the seal curve
![Page 14: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/14.jpg)
Example Seal Curve
![Page 15: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/15.jpg)
Risks of Using MST / SIT
• Can be arbitrary‐ different film companies use different “minimums”– ASTM specifies a number
• Different polymers / processing may give different shapes
• Best practice is to have entire curve
![Page 16: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/16.jpg)
Seal Curves with MST’s
![Page 17: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/17.jpg)
Hot Tack
• Seal curves measured when seal has cooled
• For some applications, seal when hot is important
• Seal may encounter impact or pressure when hot trying to push seal open– Vertical form fill seal machines
– Hot fill applications
![Page 18: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/18.jpg)
Measuring Hot Tack
• Make seal on device
• Immediately after seal jaw opens, measure seal strength
• The stronger the opening force when hot, the better the hot tack properties
![Page 19: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/19.jpg)
Heat Seal Defects: Poor Seals• Insufficient / Excess time, energy, pressure
• Incompatible layers
• Wrinkles in seal area
• Misalignment on packaging line
• Completely missed seal
• Tear / delaminate on opening
![Page 20: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/20.jpg)
General Seal Defects
![Page 21: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/21.jpg)
Causes of Leaking Seals
• Product in seal
• Insufficient (or excess) time, energy, pressure
• Gussets, fins, laps that go from one thickness to another– Sealant has to flow to prevent open channels
– “Caulking”
![Page 22: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/22.jpg)
Leaking Seals
![Page 23: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/23.jpg)
Product in Seal: Powders & Particulate
• May not melt at all
• If they do melt, probably not compatible with sealant
• Options– Prevent it from happening during fill
– Flush it out with lots of sealant
– Get sealant that seals through contamination
![Page 24: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/24.jpg)
Solid in Seals
![Page 25: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/25.jpg)
Product in Seal: Liquids & Grease• Low vaporization temperatures
– Vaporize & expand during seal, may break seal back open
• High vaporization temperatures– May not blow seal open, probably prevent seal
• Options– Prevent it from happening during fill
– Get sealant that seals through contamination
![Page 26: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/26.jpg)
Liquid in Seals
![Page 27: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/27.jpg)
Packaging Material Components in Seal: Slip Additive
• Added to promote machinability
• Some versions migrate to film surface: “bloom”
• Slick, powdery on surface & prevent good seals
• Options– Adjust slip additive to balance machinability and COF
– Use non‐migratory slip additives
![Page 28: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/28.jpg)
Packaging Material Components in Seal: Solvent‐free Adhesive
• Solvent‐free adhesives start as monomers / oligomers
• Small enough to migrate into and through film
• Interact with slip additive in high slip films to contaminate seal surface
• Options– Change slip package / concentration
– Change adhesive
![Page 29: 3.3 - joint2Kaas, Darby - TAPPI€¢ Mechanical Seal – No real chemical compatibility involved – Plastic flows into pores or around fibers of seal partner. 4 Opening Mechanisms](https://reader031.vdocuments.net/reader031/viewer/2022013014/5af9c5a67f8b9a5f588e87f7/html5/thumbnails/29.jpg)
Thank You