We’re all familiar with shelf life as it relates to perishable food items. And for many perishables such as milk, meats, or bagged salad greens; a smell test or other visual evidence often verifies that the specified shelf life is a pretty accurate and obviously tested predictor of spoilage. But what about labels? They don’t provide the kinds of tangible signs we get from the food we eat. Shelf life for label materials is usually buried down near the end of specifications from plastic film converters from whom your label manufacturer gets these materials. Depending on type and vendor, shelf life typically varies between 1 and 2 years. But we still don’t know…what changes or goes bad?
What does label shelf life mean? What might I expect if the label has gone bad?
Label shelf life means the maximum length of time that a label can remain unused before exhibiting a performance decrease. For all practical purposes the specified shelf life is relevant to adhesive performance. Over time, particularly in poor storage conditions, moisture and air can penetrate through and between the release liner and adhesive layer with one or more of the possibilities that the adhesive can oxidize, ooze, lose tack, or cause the level of release exhibited of the liner protecting the adhesive to increase so that it becomes difficult to remove.
Don’t blindly throw your inventory away!
You’ve got current relabeling projects in the field, and you just realized that your label inventory is past the 1-2 year shelf life typically specified by the actual material converter/manufacturer! Should you trash all of your inventory? Stop work until new inventory can be received? Don’t panic.
First, the 1 to 2 year shelf life is a general specification that has been in the label material industry for a long time. Since then the use of chemically stable and highly oxidation resistant acrylic adhesives has become the industry standard for outdoor weatherable label materials. But the specified shelf life has not really evolved to reflect the more stable shelf life performance of these newer adhesives. I recently read of an independently conducted test study comparing adhesion of freshly manufactured label materials with an acrylic adhesive to 4 year old retain samples of same that demonstrated no statistical difference in adhesion.
Second, I know of no converters specifying a 1 to 2 year shelf life for plastic film base label materials using modern acrylic adhesives that can supply data indicating loss of adhesion after that period.
Third, I know from firsthand experience that the combined amount of time that some label materials sit in raw and finished goods form on the shelves and racks of material converters, label manufacturers, and end users routinely exceeds the typical 1 and even 2 year shelf life specifications; at no apparent detriment to adhesive performance. In short, a 1-2 year specified shelf life is overly conservative and is unsupported by real life performance.
This is all interesting, but where am I left in terms of practical guidance?
Glad you asked. Or actually, I guess I asked for you.
What’s most important is that everything here about shelf life, whether going with that specified by the converter or going with the more pragmatic reality, is predicated upon proper and best practice storage of materials. Proper condition specifications by converter vary, but in general this means in the range of 60°-75° F and ~ 50% R.H. Labels should also be stored flat in clean, dry, sealed poly bags, without heavy objects on top of them and in small stacks so as to minimize compressive weight on top of them. Don’t forget to monitor inventory that may be sitting around in the back of field service trucks. More than once I’ve wondered if poorly stored stray inventory sitting in tool bins in field trucks doesn’t become the source of reported issues that “My labels are bad and won’t stick!”, and are assumed to be representative of the rest of the inventory back at the warehouse store.
But specifications engineers like numbers; so I’m going to stick my neck out here and say that for plastic film type labels with acrylic adhesives, if proper storage conditions are observed, then shelf life can reasonably be considered to be 4 years. I can attest that I’ve seen rolls of raw material and finished goods labels sitting on shelves that are 4+ years old and which demonstrated no observable decrease in adhesive performance.
The practical guidance of a 4 year shelf life along with a FIFO rotation under modern inventory control, should insure that you will not find need to dispose of out-of-date inventory. But should you still find need to question whether your labels are still good you can conduct an easy and fast in-house test right in your warehouse. Simply adhere a few representative samples to a clean metal test panel or other surface representative of your field application. Temperatures should be ~60° F or greater to insure adequate adhesion conditions. Let the label remain for 24 hrs. Depending upon label material the sample should destruct or deform, and prove equally as difficult to remove as would a properly installed field label. If proper bond is demonstrated there will be no impact on service life because of some eventual affect that would have been caused by shelf life. There is no mystery. The labels either still adhere properly, or it will be apparent that shelf life has compromised adhesion. Once applied, the adhesive does not degrade or lose tack over time.
Electromark offers a variety of high performance, outdoor weatherable label film materials including vinyls, polyesters, acrylics, and various retro-reflective grades. All of these materials utilize acrylic or modified acrylic adhesives.