In the last 6 months I’ve received more calls and questions on shelf life of label stock than I have in the past 5 years. They range from the request for information and data to the frenzied call that production discovered that their label stock ‘expired’ a month ago and the line will be shut down if I don’t do something. The entire concept of putting a shelf life on modern pressure sensitive label stock is a shaky and shadowy one at best, and I think its time to turn on the kitchen light and see which hole the cockroaches scurry to.
Lots of things need a shelf life; food would be a prime example. My Significant Other is a nutritional professional and I’ve had ‘perfectly good food’ snatched out of my hand and tossed in the garbage after it passed my ‘smell test’, but was past its expiration date. In the image above we illustrate a blatant disregard of any shelf life awareness at all. On a sea kayak trip on Lake Superior, the above gentleman discovered a can of what appeared to be beer that had been rolling around in Gitchee Gumee for so long that all the graphics were worn off the can. The guy in question is a Quality Professional at a Twin Cities medical device manufacturer which makes the story even better. Not knowing what kind of beer it was, how long it had been at the bottom of the lake, or if it even was beer, our hero opened the can and drank it. He said it tasted like crap but then it could have been a Lite beer. When I asked permission to use this photo, with the 50′s porn star black bar in place to protect his identity, I was required to mention that, “Surely you’ll make note that it was day 3 of very limited consumption (like only 2 beers per day). We were roughing it”. Nevertheless it is apparent that any shelf life considerations were ignored, even though this guy is the kind of fellow who would zealously monitor shelf life requirements on incoming parts and institute CAR’s, PAR’s, audits, fines, suspensions, and perhaps even a good Singapore style caning if said requirements were not met. It is also noteworthy that no ill effects, other than his normal character flaws, were noted after consumption.
But what about pressure sensitive labels, the kind we all use on terminally sterilized device packaging? Most paper label stock has a one year shelf life and most pressure sensitive films have a two year shelf life…..when stored at ambient temperature of course. But when does the countdown start on that year? When the adhesive is made? When its coated at the label stock converter? When we print and die cut it? Ship it? When its received at the device manufacturer? Clears inspection and hits the inventory shelf? That arbitrary year could be closer to two years in the case of some of the more lightly used materials. The real question is whether that date of one year, two years, has any basis in reality or can be supported by any sort of data that would indicate loss of properties after that amount of time. The answer to that question boys and girls, would be an emphatic hell no.
That one year shelf life time frame has been around for a long time, well before the widespread development and use of acrylic adhesives. My 1966 Ford Econoline van, a vehicle that always caused girlfriends parents to shudder, died a painful death at 115,000 miles. My 2003 VW Passat was sold to a friend when it had 200,000 miles on it and now has closer to 300m. I believe the reason for that was an improvement in technology. Pressure sensitive label adhesives have similarly improved over the years as well.
Advanced Web, with the help of one of our label stock vendors and at the request of a device manufacturer, did some studies on adhesion over time. We took some current paper label stock, laser material to be exact, with an acrylic emulsion adhesive and tested and compared it against 4 year old retains of the same material. We did peel, shear, and tack on 4 common substrates including PETG, Tyvek, SBS cartons, and a stainless steel control. There was statistically no difference in the numbers between the two materials. When I discussed this fact with the Technical Director at our vendor, he was not surprised at all. He even sent me a letter, on company letterhead, stating that, “In reality, nothing dramatic should change with a PS labelstock construction after one year. The acrylic adhesive is chemically stable and will not oxidize or loose tack. The silicone release liner should stay near the same level as well. In summary, the PS labelstock construction should retain its functional performance after one year. Likewise, after the label is applied,the adhesive does not degrade or lose tack over time…..” Many device companies have 5,7, and 10 year real time shelf life info on their products and I have not heard of one PS label failure in all of that real time testing.
So, does one year shelf life for PS label materials make any sense at all based on the evidence. Nope. Will this evidence and the informed opinions of technical folks involved in the industry make any dent in this beloved one/two year time frame? Nope. Is a shelf life date even necessary for most modern label stock, given reasonable inventory control, production cycles, and FIFO? Nope. So please forgive me if you hear a sigh, a cleansing breath, when you call me with your underwear on fire about 13 month old label stock, 13 months from some magical, arbitrary, ephemeral start date. I’ll probably calmly ask you what substrates your labels are being used on, send you that letter I received from our vendor, bust our production’s hind ends to get you some ‘fresh’ label stock, and maybe even attach this blog post to my delivery confirmation email. Given regulatory paranoia, I do not see any light at the end of this tunnel however, so we need to be content to wallow in and perhaps even enjoy non-value added time sucking activity. On the label shelf life issue, the mouse traps are carefully set as the elephants are stampeding through the front door.