Temperature extremes are one of the most common physical properties that can impact label adhesion. Most label adhesives have a minimum application temperature and then, once the adhesive bond is solidly made, a much broader ‘operating temperature’. Fortunately, this is usually a rather wide range with -20F to 176F being fairly typical. Transport testing of packages is usually at -20F on the cold side and 100F and 85%RH, and/or 140F and 30%RH for the heat (ISTA P2A, 2008). Accelerated aging of labeled packages is typically at 130F. Unfortunately, temperature is not all that easy to control and can do fun and crazy things when it decides to fluctuate.
Heat is usually the culprit that causes trouble with labels as well as me personally.
I’ll take -5F over 90F any day of the week, no matter how sick people think that is (take the poll!).
Heat can cause outgassing, plasticizer bleed, and also cause substrates to expand at rates different from the label that is stuck on them. In one incident, a polyprop case with a paper label passed the accelerated aging tests at 130F but failed the back-window-of-car-in-Arizona-in-July test, the BWCAJ test. The guidance doc for this test will be approved shortly, I’m sure. We also put together a package for a mechanical heart valve a few years ago. This project had me more excited than when I look at a ladder with its 37 “please don’t be an idiot” labels (thanks for that, plaintiff’s bar!). This package had tyvek lidding, paper tamper evident seals, a clear polyprop info wrap, a TTR imprinted PET label set that was used on the package and shelf carton, and a vinyl seal strip around the entire polycarb cylinder. This was an autoclavable package and everything worked fine in the testing but when some prototypes hit the field everything went to hell. Tyvek tranparentized, vinyl oozed, and the package looked really, really ugly. The culprit? Using a flash autoclave cycle rather than a regular cycle.
Its impossible to avoid all the pitfalls but there are a few things to keep in mind. First of all, try to stay around nominal on your adhesive temp range selections rather than at either ragged edge. 3M’s 467 or 468 adhesives, familiar to many as the product used on hardgoods nameplates,can’t be removed most of the time with dynamite and a chisel. At -40F however, it falls off so its probably a bad choice for your Alaskan Pipeline drill labeling needs. Think about the adhesive properties that will be critical for your app as well. The package that failed the BWCAJ test worked when an adhesive with low shear strength was used, allowing the label to move with the expansion and contraction of the package. Matching face stock and the substrate being labeled is a good idea as well. Not only does it make recycling easier but if you have a polyprop label on a polyprop package, the expansion coefficient is the same.
Having different materials causes an effect like a bi metal thermostat, where the different rates of expansion/contraction cause the metal sensor to actually bend one way or another. Finally, conditions that replicate the actual usage are a good idea. While most medical devices don’t sit in someones car window in a mall in Scottsdale in July, most do get shipped somewhere. Whether those devices are shipped to Bismarck, ND in January or Oxford, MS in July can most certainly make a difference in label performance.