Paper-based flexible packaging is increasingly considered as a sustainable alternative to polymer-based flexible packaging solutions.
Segment 3 in Greener’s Sustainability Series explores potential obstacles to forming and sealing paper-based materials on flow wrappers and vertical baggers and presents solutions for maintaining package quality and productivity with these new structures.
Paper-Based Flexible Packaging Materials
Characteristics
Four characteristics of paper affect its performance.
1. Sealability
First, paper is not sealable by itself. To be utilized in flexible packaging, paper must also include a cold seal adhesive or heat activated sealant layer.
Paper is also less thermally conductive than most polymer-based materials which may led to sealing problems.
2. Barrier
Paper alone does not provide adequate barrier protection and requires additional treatments to contain the product’s aroma and flavor and protect against outside contaminates.
3. Recyclability
To be considered recyclable, paper-based flexible packaging must contain at least 70-90% paper, depending on regional or national requirements.
This criterion limits the thickness of additional sealant and barrier layers and can affect their functionality.
4. Thickness and Stiffness
Paper-based materials also tend to be thicker and stiffer than traditional materials, with significantly less capacity for elongation.
Forming Issues
The characteristics of paper-based flexible packaging materials can make forming more difficult.
These thicker, stiffer materials require extra tension to draw them through the wrapper or bagger and can be easily buckled, wrinkled, and damaged by standard forming components, causing sealing problems and fractures to sealant and barrier coatings that leave them less effective.
These forming issues may not be readily apparent, so packages should be regularly tested.
Forming Solutions
Specialized Formers
Specialized formers designed for paper-based flexible packaging are often required to maintain even, consistent tracking that alleviates excess stress and damage.
Greener Corporation partners with Kenray Forming to provide these specialized forming solutions.
Power Film Drive
Wrappers and baggers without a power film drive may need this feature added, since relying exclusively on fin wheels or belts can magnify forming problems with paper-based materials.
Fin Wheels
On flow wrappers, customized fin wheel designs such as gripper grooves and Dura-Therm material may be needed to draw the thicker and stiffer material and prevent slippage.
Sealing Issues
Heat Sealing Problem
As explained in our previous Tech Bite, the effective seal range of a packaging material is defined as the difference between the seal initiation temperature and the distortion temperature.
With all materials, machine speeds are limited by the need to fit normal sealing jaw temperature cycles within the seal range.
Paper-based structures, with greater thickness, stiffness, lower thermal conductivity, and potentially thinner sealant layers, can require longer dwell times for heat from the sealing jaws to reach and activate the sealant. This reduces their seal range and may lead to sealing problems.
Reductions to machine speed may be necessary to seal the package and caulk off leaks.
Pressure
The heat transfer limitations of paper-based materials, along with their extra thickness and stiffness, can make it difficult to apply the sealing pressure required to produce quality seals—especially across gaps at the corners and at the fin or lap seal.
Sealing jaw setup and design become especially critical. The serrations must apply enough pressure to activate and help move the limited amounts of sealant into gaps to caulk off leaks, yet not exert excess pressure that crushes or splits these more easily damaged structures.
Sealing Solutions
Setup and Adjustments
Adjustments that work with traditional materials may need to be checked with carbon impressions and refined for greater accuracy.
Dura-Therm Sealing Jaws
Sealing Jaws made from Greener’s proprietary Dura-Therm alloy provide more responsive and consistent thermal conductivity to reduce temperature cycle fluctuations, helping to keep them within the paper-based material’s seal range and to maintain production speeds.
Sealing Jaw Serration Pattern
To provide the even, consistent heat transfer and sealing pressure that paper-based structures require, your sealing jaw serration pattern should be custom designed for your specific material, machinery, and conditions.
Easy Seal™️ FLEX Jaws
And Greener’s Easy Seal™️ FLEX Jaws further optimize sealing pressure by compensating for the extra layers of material at the fin seal.
Collaboration
Collaboration is a key component for successfully running paper-based flexible packaging materials.
Greener Corporation works with packagers, machine manufacturers, and material suppliers to provide material evaluations, setup and procedural changes, customized components, and technical service solutions.
Paper-based flexible packaging materials have been most widely implemented on cold seal applications for products with less stringent barrier requirements, such as some candy, and on secondary packaging for multi-packs of previously packaged items.
The ultimate goal is to enable the use of these and other sustainable materials for a wider variety of applications without sacrificing seal quality or productivity.
To learn more about running sustainable materials on flow wrappers and vertical baggers, contact Greener Corporation. We provide integrated parts and technical services worldwide.
