Creating a region of heat sealed Tyvek where that sealed region has become “transparent” or “Transparentizing Tyvek” is characterized as an oversealed area or region of Tyvek.  Excerpted from ASTM F 1886-98:

“X1.4. Oversealed Areas–A combination of too much heat, pressure, or dwell time may cause oversealing to the point that it may cause packaging componenets to melt and become brittle and susceptible to cracking. When Tyvek sppunbonded polyolefin or a similar porous material is one of the substrates, this condition often is seen as a transparent or translucent seal where the material fibers are fused. This may become evident through an evaluation for pinholes or cracks along the seal. Another result of oversealing may be a spotty or incomplete looking seal, where, in this case, the heat seal adhesive is overheated an flows into the porous fiber structure of the material.”

The functional effect of oversealing Tyvek is to create potentially weakened transitional regions within the Tyvek structure.  That is, a potentially weakened region is formed in the transition area between the sealed and non-sealed areas of the Tyvek structure.  The transition area between sealed and unsealed region can be weakened, brittle and more prone to physical integrity compromises resulting from the fusing and embrittlement of the Tyvek structure.  Of course, any physically compromised area of a sterile barrier package increases the risk level for loss of physical package integrity which compromises sterile barrier integrity.

Oversealing is not a positive attribute and should be avoided by means of good sealing process development and sealing process control.  A Design of Experiments is a useful tool in developing sealing parameters which avoid oversealing your Tyvek structure.

I am not aware of any industry accepted procedures or best demonstrated practices for measuring finished packages internal vacuum or pressure.  I contacted Mr. Heinz Wolf, general manager, at PTI Industries, Packaging Technologies and Inspection, for some suggested measurement insight, as they are leaders in non destructive leak testing  Depending on your starting package vacuum, their nondestructive leak testing equipment can be utilized to derive an internal package vacuum by observing the pressure value on their equipment at the moment that the evacuated package starts to “expand” as additional vacuum is pulled on the already evacuated package.

The greatest vacuum that can be applied to the evacuated package is absolute vacuum at 29.93 in Hg. If your packages are very close to absolute vacuum (resulting from your vacuum sealing process) then no method is viable for determining internal package vacuum as insufficient pressure differential exists in order to measure vacuum.

 This method requires PTI Industries equipment or similar equipment with sophisticated pressure transducer systems for accurate pressure and negative pressure generation and measurement.

If your foil pouch seal strength is yielding a steep peel strength curve, perhaps you can consider whole package, in-process BURST testing to monitor your sealing process output. Although there is no demonstrable correlation between burst and peel strength the objective would be to develop control limits on your pouch burst strength values and routinely measure and monitor your seal integrity through burst testing data.

You can create control charts for your burst testing values for your package and establish upper and lower control limits based on your sealer operational capabilities and validated sealing parameters. Burst testing can discern a breach in the seal integrity. Furthermore, once you establish upper and lower control limits from your control charting activities, you can use your routine burst values to determine when you are trending outside your control limits and further evaluate the seal quality and integrity of the pouch to ensure you are producing acceptable seals.

I would recommend performing restrained burst testing and use a defined restraining fixture and defined headspace between pouch and fixture when performing the test to provide as much test method consistency as possible.

Here are some suggested practices for executing a time study or labor evaluation:

1. Develop a protocol or work instruction and seek review and approval from a few key stakeholders.  Those include professionals with industrial engineering experience, manufacturing, cost accounting, and package engineering responsibilities.

2.  Make sure all of the packaging personnel are trained.  Review/re-read (if needed) the SOP.

3.  Have all of the components readily available; this includes applicable labeling.  If gel packs or dry ice will be used, ensure that they’ve been preconditioned, as required and specified.

4.  Possibly set up a miniproduction line, unless one person packs out the shippers from beginning to end.  I might suggest that a miniproduction line would be more efficient, because if an operator is performing the pack out from beginning to end, they may be taking gloves on and off, doing transactions on a computer, and possibly generating labels.

5.  Test in live conditions.  For example, if they’re in an uncontrolled warehouse in Minneapolis in the winter or Phoenix in the summer, replicate those conditions.

6.  Evaluate several personnel, or a good representative population from the potential operator “pool.”  This may point out those who are really good and efficient and those who require more training.  You generate a bell curve of performance and determine how to optimize or maintain performance excellence.

7.  Perform the evaluation, several times, over the course of a rolling 12 months to determine variations over time and/or possibly adjust the labor standard.  You can set the standard at time “X.” However, a few more data points may compel you to more accurately adjust the labor standard.

Check out Greenbox at www.greenboxsystems.com. According to the company, Greenbox components are 100% organic-based materials, and phase-change material is nontoxic and fully biodegradable. Unlike EPS boxes that ship once and are then tossed into a landfill, Greenbox is designed for reuse. Studies show that Greenbox phase-change materials suffer no thermal degradation after more than 20,000 uses. I can not find any information on R-values on the Web site, so I believe you will have to call Greenbox to inquire about the PCMs and their R-values.

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