Wednesday, May 02, 2012

I'm that guy...

I'm that guy. The guy that everyone hates. The guy who made it so difficult to open your bag of potato chips.

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 some one 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 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 degree 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 feed 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 1/8th. A computer then decides which combination of 8 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 one of these 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.

Update September 18, 2012: I'm getting a lot of traffic today from one of the Motley
Fool discussion boards, one that unfortunately I can't access. Anybody feel like cluing me in about what is being said? Either add a comment or email me directly at john dot spevacek at aspenresearch dot com. Thanks

21 comments:

Miss MSE said...

I grew up in the Rocky Mountains, and I remember occasionally having bags of chips explode in the car on the way home from the store. I was happy when they stopped doing that, because it meant no more chips lost to the car, and no gunshot noises. So I don't blame you, I thank you.

Also, check the How It's Made archives: I'm pretty sure they've shown the VFSS machine in slow motion at least once.

John said...

We used to jokingly imagine truck drivers loosing an eye from a flying nacho chip when the bags opened or some such nonsense. Maybe there was some truth to that.

bradleyjx said...

Would this how it's made be a good look at that machine?

Anonymous said...

If you have trouble opening a bag of chips, then you don't deserve them.

Anonymous said...

Scissors anyone?

Trevor said...

I'm not sure about the feasibility of this, but why couldn't the bags just be shipped in a pressurized container?

John said...

I once pulled a bag of crisps (Walkers' Ready Salted) from a multi-pack to find it was simply a bag of air!

Mike said...

Video of VFFS, from the TV show How its Made: Potato Chips. http://www.youtube.com/watch?feature=player_detailpage&v=LkqBbr7Ewsw#t=241s

Anonymous said...

Trevor-

It'd be quite possible to ship bags in a pressurized container. The question is, why bother? Pressurized containers cost money to make, money to load, money to ship, and money to ship back when you're done. That money represents wasted effort, wasted manufacturing, wasted people-handling-boxes-time, and wasted gasoline, and results in less profit.

Anonymous said...

VFFS bagger with multiple heads (same machine as the How Its Made links, but more detail) https://www.youtube.com/watch?v=wR0oGNfY-fk

Ian Bicking said...

I assumed the bags were inflated as much as they are to protect from crushing. If you left enough room for expansion then you'd have enough room to crush the contents of the bag.

Anonymous said...

This video shows the multihead weigher pretty well.

http://www.youtube.com/watch?v=OyznL7W2L2I

Rickroll paranoia?
Google "Ishida weighers reduce giveaway for all products"

Ecron Muss said...

So the answer is... TURN THE BAG UPSIDE DOWN AND OPEN THE SOFTER BOTTOM SEAL!

Anonymous said...

Hi, does John/anyone know what the client was near the Rocky Mountains? I am doing some work for school, so I have limited research and do not wish to email directly for privacy/safety reasons. Thank you for any responses.

John said...

@Anonymous - 7PM

Oh that's an easy question. 20 years ago there was only 1 national chip company in the country, and they still are the biggest chip manufacturer today...

Robert Knieper said...

I am a packaging engineer that works for a major snacks company.

@Ian - you are correct, if you deflate the bag too much to allow for expansion due to elevation pressure changes, then you lose some product protection. You have to balance allowing for pressure expansion, strength of the seals, and the product protection need.

@Trevor/Anonymous - Quite right, the cost of shipping pressurized containers far exceeds the value of a $1.99 bag of potato chips. If the bag was filled with slicon semi-condutor chips then the value may be there.

@John - Time, temperature and pressure - but also seal jaws of the machine and inherent size and geometry can affect the overall strength of the bag system.

Anonymous said...

thanks john!

Anonymous said...

As an aside to some investment talk, there was some humorous discussion regarding opening a bag of chips. Someone posted a link to your site.

Anonymous said...

John, someone linked here from the Million Dollar Portfolio message boards as a response to one of our members joking:

"I'm still stumped by the plastic bags though. I was just trying to pull apart the top of a bag of potato chips. Ya have to pull with all of your might, and I ended up ripping the bag and shooting the chips all over the kitchen."

Cheers,
Jeremy

ericafitz said...

Hey John,

Can you explain why kettle chip bags are different than regular ship bags? They are thicker and have a white lining instead of the silver lining. Por Que?!?

Thanks!

John said...

@ericafitz,

The big thing that separates potato chips bags off from other chip bags (such as corn or tortilla chips) is that the potato chip bag doesn't allow in any light. I don't know the exact reaction but have always heard that the light will interact with the oils and make them bad. Why this only affects potato chips and not tortilla chips is not clear to me, but if it were possible to have a clear window to show off the product, someone would have done so.

Most companies go with the vapor coated aluminum option (giving you the silver interior), but white is also an option. You do need a pretty thick coat of white (usually a couple of coats) in order to achieve this.

So I don't think there is anything unique about kettle chips and especially their thickness having anything to do with the white coating instead of aluminum. It's a business and/or marketing decision.