First of all I apologize for the time between blog posts. I’ve been reminded of this fact a number of times by our Global Marketing Czarina (GMC but not the truck company), a relentless woman that actually threatened me with a device wired to my ignition system some morning if I didn’t get one out. Fortunately, there is no shortage of labeling topics these days, so I thought I would expand on the ‘affixed’ part of the FDA’s ‘affixed and legible’ exacta.
Affixed seems like a fairly black and white concept. Either it’s affixed or it’s lying on the floor of the warehouse. The big question however, is just how affixed is ‘affixed’. From what I’ve seen there really doesn’t seem to be any sort of consensus for just how tightly a label needs to be adhered to a surface. The most common measurement of how well a label sticks to a substrate is peel strength. Peel strength is the measure of the average force to part two bonded materials, for example a label and a shelf carton. Its measured in lbs/inch or gm/cm. Thankfully, I’ve not seen any numbers called out on any prints or specs as yet and I think that’s a very, very good thing. Peel strength, like the porosity and caliper of Tyvek, can and does vary.
The chart below has five different label stocks that have been in common usage for a number of years by five different medical device companies to label terminally sterilized packaging. The peel tests were done on a 90 degree peel apparatus at both 20 minutes and 24 hours. Substrate adhered to was Tyvek 1073B lidding material.
|Label Stock||20 minutes||24 hours|
|Device Co A||.7||.95|
|Device Co B||.74||.98|
|Device Co C||1.5||1.8|
|Device Co D||1.2||Fiber tear (label)|
|Device Co E||1.2||1.6|
Let’s think about an adhesion spec for a label test or qualification. Remember that all of these face stock/adhesive combinations have been in use on terminally sterilized devices, ETO and gamma, for over a decade. Do we want to have a firm number for a specification, let’s say 1.5 lb/sq”? I would definitely vote no on that. The variation in adhesive coat weight, caliper variation in the substrate itself, and having to inspect, measure, and verify each lot would prompt my negative ballot. Plus given the variation in the chart above, picking a fixed number would preclude a number of adhesives, remembering that all of these are currently functional qualified adhesives for terminally sterilized packaging. If we decided that fiber tear was the criteria then four of the five would be eliminated. In an IOPP survey that was conducted by the Labeling Subcommittee of the Medical Device Tech Committee a couple years back, only 13% of the respondents required fiber tear on any part of the packaging. Pass/fail is definitely the best way to specify label adhesion to the multiple substrates of a device package. So how do we determine the pass/fail criteria?
By far the most common method in current usage is to label the package and put it through its conditioning cycle. 93% of the respondents used ASTM F 1980, accelerated aging, as part of their conditioning cycle. Slightly fewer than 90% then used either ASTM 4169 or ISTA protocols for distribution simulation and then evaluated the labeled package. 87% of respondents just checked the package after the distribution cycle but over a quarter checked at multiple stages in the process.
There are really only three kinds of adhesive ‘failures’ to think about. Removing a label cleanly from a package is not considered a failure; it’s generally referred to as a removable adhesive. Technically if such an adhesive didn’t come off during the supply chain distribution cycle, then it is still indeed affixed. When attempting to break that adhesive/substrate bond we discussed above three things can happen. One is for the label stock to tear and partially remain on the substrate. The second is for the substrate to tear (especially corrugated and SBS cartons), and the last is for co-adhesive separation. This is where some of the adhesive stays on the label and some on the substrate. This is the operant principle behind a Tyvek lid/tray or peel pouch, fracturing of the adhesive itself.
Testing a label for adhesion is a pretty simple, tried and true process. Label the package, subject it to the hot/cold/moisture conditions it may encounter, test for shipping conditions it may encounter and if there is still a label on the package, affixed and legible as they say, you have a winner. The trend of course, is to have more and precise numbers, including peel, shear, and tack characteristics, paper strength numbers for machine and cross direction, and even opacity and brightness numbers. Not necessary people. As I’ve said before, these paper weights and specs can change in two months. Plus the converter, label supplier or device manufacturer can’t even measure them to verify. Even a minor change that results in a new cute name that the marketing gurus like, for example changing Transtherm from 1C to 2C, can result in chaos if we have to send you a C of C that calls out the exact material used. Paper companies can change branding in the time it takes for the average medical device package engineering department to think about thinking about initiating an ECR to document the measly and insignificant change. My advice would be to keep our collective’ eyes on the prize’, affixed and legible.
In just a few weeks the special Olympic edition of this blog will appear. In it we will list the bronze, silver, and gold medal winners of the Head Scratching Label Issue contest. Judges are ready, several potential winners are already in the clubhouse, and names have already been changed to protect the guilty.
Lastly, whoever can name the ‘package’ having its label peeled in the above photo and posts the answer in a comment will be eligible to win a (not!) valuable prize.