I'm The Guy Who Made Snack Bags So Impossible To Open

I'm that guy. The guy that everyone hates. The guy who made it so difficult to open your bag of potato chips. And this is the story of how, when and why I did it.

It was my first job right out of school. I was working for Hercules Chemical, a company that no longer exists, although you have to blame that on someone else. I was in the Packaging Films Group, making multilayer polypropylene films for food packaging. The film had a heat-seal adhesive on one side of the polypropylene base. One of our larger clients used our films to make potato chip bags. The problem they had with our existing films was that the they seal was too weak. The client's chip-making plants were located west of the Rocky Mountains, so when trucks would drive their chips out to California, some of the seals would open up due to the pressure difference between the high altitude air and the air sealed inside the bag. And so they needed a stronger seal from us, which was then passed down to me.

Other options besides a stronger seal are technically possible but not economically feasible. Potato chip bags are made on a vertical form-fill-seal(VFFS) machine. The preprinted film is unrolled and shaped to form a tube. A seal is made along the tube forming the back of the bag, and a seal is also made at 90 degrees to this back seal, pinching the tube and forming the bottom of the bag. The chips are then added to the bag. This is actually a very cool process that is more complicated than you might imagine. The chips are fed to a number of weigh-pans located just above the bag opening. Each pan has a fraction of the total weight to be added, say one-eighth. A computer then decides which combination of eight pans are to be dumped into the bag so as to most closely match the desired value. While it would be much cheaper to have a single pan machine, having the additional pans very quickly pay for themselves. All of this is done at high speed. I would love to post a video of a VFFS machine, but I've not ever found one that really shows the process very well to someone who's not seen one.

The point here is that while technical options exist to prevent premature opening of the bag, such as reducing the initial air pressure in the bag, attempting to add this to the existing processing equipment would be a nightmare. So it was necessary to increase the seal strength.

In a heat seal, you are attempting to melt the adhesive polymer and get it to flow into the other layer. Upon cooling, the two layers are now entangled and show adhesion. The strength of a heat-seal depends on three and only three variables: time, temperature and pressure. Increasing any of this will increase the strength of the bond, but most manufacturing engineers are really only open to increasing pressure. Increasing sealing time slows the entire process, and increase the sealing temperature also slows the process since it takes longer to heat the adhesives to the higher temperature, that adds to the time as well. The best option was to develop an adhesive that sealed at a lower temperature, something that was successfully accomplished, or so I'm led to believe from all the complaints that colleagues pile on me now that they know I'm that guy.

Republished from It's The Rheo Thing with kind permission from John Spevacek.


Comments

    US chip bags must be different to ours...
    I've never had a problem opening chips! (Maybe I'm just overly experienced)

      Ah, explained in the article had I bothered to read before commenting!
      Australia is so flat (even in our mountainous areas by world standards), the pressure difference is probably negligible.

        And having worked with VFFS machines myself, I heartily agree that they're cool!

          I thought I'd better jump in before you commented on your own comments one more time and created some sort of infinite StevoTheDevo loop!

      They probably are. I noticed when I went to the US in 2002, their M&Ms bags had a more papery feel to them than the ones that were in Australia then.

      Also, as explained downthread, Australia doesn't have the issues with pressure differences, because not only do we have less difference in altitude between the production plants and the highest altitude destinations, but more of our transportation is able to be done by land based methods.

      So yeah, interesting article, just lacking a bit in the localisation department.

        M&M bags in the US are different to the chip packets.

        One would assume that the reason a chip packet is pressurised is to protect the form of the chip. If you had no air at all in the bag, the chips would simply crumble when transported.

        M&M's and skittles are a different beast. they are a hard candy that holds it shape. As a result, the pressure needed in these packets would be much much lower. This is why an American M&M packet is made of paper coated with (presumably) a thin plastic film to ensure freshness. This means that you dont need to open a packet in the same way you open chips, all you need to do is rip the top and it opens easily.

        Thats the way i see it anyway. While I am not a packaging expert, I have opened a few of them in my time. :)

          So if it's not an issue of preserving the shape, then why aren't our M&M packets the same as theirs?

          Methinks you may have missed the point of his bringing up the M&Ms :P

    ... Im assuming this isnt an Australian article, as I, nor anyone I know, have EVER had a problem opening a packet of chips... Other packaging, sure some are a pain in the arse to open, but potato chips? People must be retarded if they cannot open them.

    Given the size of your average american, I think they should make them even harder to open...

      Haha, oh you

      Funnier when one considers our obesity rate in Australia is higher.

        Percentage maybe, actual number of people, no.

    Yeah, I've never had a problem eith opening the bags. I open the bags by placing it gently on the ground, then jumping on top. It's then a simple process of eating the chips off the ground. No problem.

    Now for the guy that makes the plastic clamshell packaging that require a stanley knife to cut open - his time will come....

      use a can opener - true story, actually works

      yesssss he has some answering to do
      There's the only solution of risking your object (fragile or brittle) and high force sharp tool application damage !

    skittle and m&m packages are still pretty hard to open, like trying to open it at an end like you would a chip bag.
    but usually its like: if you cant open it by pulling the sides, you can rip the side off using the jagged end things...
    yeah, this conversation makes me laff

    Great, now I want chips. THANKS FOR NOTHING!

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