Once again HealthPack, this year in Denver, was a fine way to augment your medical device packaging knowledge, both by listening to the presentations and by hanging out and exchanging info and BS with colleagues, customers, and suppliers. Because of heavy snowfall in the area this year and potential avalanche danger, two intrepid colleagues from an esteemed medical device manufacturer in the Philadelphia area and I decided to head up to the continental divide and make sure that the Healthpack event in Denver was safe from any potential avalanche issues. After extensively exploring and testing every chute and canyon in the area of the Eisenhower Tunnel on I-70 and analyzing the data at the Westbound & Down Brewpub in Idaho Springs, we determined that the attendees would be safe at the Denver Marriott. A number of them expressed relief that we had undertaken this dangerous and very altruistic task.
The last blog post was centered on ‘affixed’ half of the FDA Subpart 820 mantra of affixed and legible regarding pressure sensitive label stock on terminally sterilized device packages. Although legibility failure is not nearly as intermittent or puzzling as adhesive failure, it does exist and there do need to be some systems in place to prevent it. By legibility, we are not talking about using two-point type on a pill bottle to frustrate grandma when she dodders over in her walker to grab the bottle. A more focused definition of legibility in our industry is to ensure that the information both the label vendor and the device manufacturer print on their label remains in the same readable condition as it is in when the label is applied to the package. We label printers have a variety of inks including water based, solvent based, and UV cured and a fairly extensive choice of pigment durability to resist UV and fluorescent light degradation. Likewise, we can protect our printing with everything from press varnish to UV varnish to laminates. Typically, the ink system is not specified in engineering prints, but that is slowly changing with the UV / water based split at around 50-50 at this writing. Device manufacturers have graduated from the old school dot matrix printers and now use thermal transfer printers and laser printers almost exclusively for their variable data. Both have their advantages and disadvantages, which I discussed a previous blog post.
The main enemy of legibility is abrasion, rubbing or scraping the text, symbols, or graphics off the label. This can come from many sources but the main one is the package itself, typically white SBS shelf cartons, jostling around in a corrugated shipper. The wear can come from either the corrugated sides or the other cartons in the shipper that aren’t secured tightly enough. The starch in corrugated makes it not only difficult to adhere to at times, but also ramps up the abrasive quality considerably.
Typically, this issue is discovered after distribution when testing either ASTM or ISTA protocols, and can be avoided in a few different ways:
- The old standby has always been to shrink wrap the package, a solution that has been taking some heat from both the cost and unnecessary waste stream addition angles.
- In high abrasion situations, perhaps heavy parts like ortho implants (or even several small packages in a shipper), we can spot varnish our printing with a ‘slip’ varnish or UV cured varnish. This protects the flexographic printing that we do on the label and leaves the area to be thermal transfer or laser printed receptive to one of those two processes.
- We have found out over the years that wax thermal transfer ribbons are usually OK on shrink wrapped packages, but the device manufacturers need to go to the somewhat more expensive wax/resin combo ribbons for extra abrasion resistance.
A few years back, I got a call from a device manufacturer saying that the ribbons we had sold them were “not printing cleanly”. Sure enough, after looking at the shrink wrapped package, the Thermal Transfer Ribbon (TTR) printing appeared to be out of focus, like a person just had a shot of whiskey and a couple beers before looking at it. After some research, it was discovered that someone in manufacturing had not liked the look of the finished package and kicked up the heat a bit in the shrink tunnel. This caused the wax ribbon to partially melt to the shrink film and as soon as the film moved that out of focus effect occurred. Wax/resin combo ribbons are the best choice for packages with no shrink wrap.
As resin content increases, so does durability up to the point of some pure resin ribbons that have under hood automotive approval on polyester face stocks. We actually have a couple customers that like that combo for their device packages, the main reason being that a certain percentage of their products are autoclaved and that is the bulletproof combo for high temp and high humidity autoclave apps as well as gamma and ETO. Like most things, it seems to be a balancing act between cost, package aesthetics, and waste stream concerns. Laser printing does not typically have as many abrasion issues because of the natural abrasion resistance of the rough, uncontested paper label surface and the nature of laser toner, which fills those peaks and valleys in the paper sheet and is then fused with heat.
As mentioned above, the qualification and validation activities for legibility are typically visual examination of the package after one or more steps in a distribution testing protocol. The tried and true standard of standing 18″ away while looking for two seconds with the unaided human eye is usually ignored because people pore over the label, sometimes with magnification, to check for any potential smudging. In the end, however, the definition of legible straight out of Merriam-Webster is, “Capable of being read or deciphered”. Like most labeling-related issues, cost, function, aesthetics, and increased impact on the waste stream are the often competing factors that need to be balanced when choosing components for the labeling system. Good luck!
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