The issue of the ideal shelf life is a debate that likely will never be settled. The reason for the debate and the complicating factors is that in order to address this issue, some device manufacturers have instituted a ‘remaining shelf life’ requirement. In effect, this is a non-negotiable requirement stating that any component with less than X% of remaining shelf life upon receipt will be rejected. This brings us full circle to the root issue of when the shelf life actually begins.
Does it begin when the adhesive is coated at our converter? When its received at AWT? When it’s manufactured at AWT? Shipped? When it’s received at the device manufacturer?
Perhaps the way to solve this issue is to adopt the current system many companies use: shelf life begins upon receipt.
Unfortunately, this does not always the consensus. Anyone that has added a shelf life requirement for packaging materials over the past few of years seems to go for the date of manufacture – a date easily tracked since that is the date shown on the core or package labels. The challenge is dealing with blanket order, minimum/maximum, and kanban type orders. These are all good methods to lower cost and ensure quick delivery. They are very poor methods if the ‘remaining shelf life’ scheme is implemented.
On orders of this type, choosing to run somewhere between a quarter and semi-annual quantity would make the most sense. Semi-annual would mean that last shipment would only have 50% of that year shelf life left, which would not be acceptable under some of the requirements listed. The easiest way to be compliant would be to buy smaller runs of label stock at a higher cost and then revert back to the venerable run and ship – no matter what the quantity. Costs would go through the roof of course, but maybe that’s okay for something as critical as shelf life . . .
Of course it’s not okay. It’s a non-solution to what ought to be a non-issue. The best way to deal with this potential headache is to generate some data proving that the shelf life of modern water-based acrylic emulsion adhesives is about 4-6 times what the legal department of big label stock converters say it is. AWT performed this testing for one of our customers and discovered statistically insignificant differences between the 4 year-old product and the new label stock.
Since device manufacturers need to generate their own data, it stands to reason that some side-by-side testing of old and new material on 3 or 4 common substrates would be adequate. Peel, shear, and tack are the three measures of label adhesion to a substrate, and all have standard tests, whether they are ASTM, FINAT, or other standards. Since most of the warehouse and storage areas of device companies are climate controlled (or ideally should be; label stock can get really hot and tends to ooze badly), the need for any hot and cold conditioning would seem to be precluded.
Four year old stock is generally readily available from AWT archives or our vendor retainers, both of which are documented and traceable. While package engineering time is at a premium, this would seem to have intern or entry level engineer written all over it. Cost justification would be not only perfectly good label stock scrapped, but additional costs per unit of the above run and ship scenario. Double or triple that year of shelf life, and the cost of administering the shelf life conundrum would drop precipitously as well.
If a company could find the time to generate the data, this could waylay much of the potential issues down the road. The shelf life debate, however, is likely far from over anytime soon.