Pharma glass defects - Part 28. Lehr sticker

Hello everyone – welcome to Part 28 of an ongoing series on cosmetic defects that may be present in pharmaceutical glass vials? Today’s defect is called a “Lehr Sticker”, which is also related to the “Adhered Glass”, “Spiticule”, and “Glass Stringer” defects (see Footnote 1).? In this case, the common theme is a piece of glass being stuck somewhere it’s not supposed to be – how it gets there and where it’s located is what distinguishes each defect type.? We’ve also covered “Belt Marks”, a defect that occurs when glass becomes too hot and begins sagging over the elements of the conveyor belt that transports vials through an annealing lehr.? As the name suggests, the Lehr Sticker defect also occurs in the annealer.? Glass vials that become too hot can become lightly stuck to each other if they are packed closely together to create glass-to-glass contact.? Unloading these vials from the conveyor belt breaks these fragile connections and creates the defect (see Footnote 2). ?The phrasing of Lehr Sticker seems to place emphasis on the material that has been accidentally transferred to a container.? However, that material has to come from somewhere, and so Lehr Stickers are really a combination of material simultaneously being removed from one region of a vial’s external surface and transferred to the external surface of a different vial.

A key feature of the Lehr Sticker is its vertical orientation owing to the line of contact between vials.? The simple illustration provided in Figure 1 is just showing a single Lehr Sticker defect, although in practice we can expect to see multiple vertical lines around the perimeter of a vial assuming the containers going through the lehr are closely packed together.? On a related point, we would expect to see multiple vials with Lehr Stickers within a given population given how the defect is formed.

Positive identification of the Lehr sticker defect requires the magnification provided by an eye loupe or optical microscope.? You’re not likely to confuse a Lehr Sticker with the aforementioned related defects (Spiticule, Stringer, etc.).? I would instead be watching out for other linear-shaped defects such as Airlines, Scratches, etc. and remember my comments about vertical orientation and the potential for observing multiple defects on a single vial.? Assuming that you have positively identified a Lehr Sticker, it is considered a Minor defect due to its aesthetic impact.?

Questions or comments?? Leave them below or feel free to directly contact me.

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Footnotes

1.?????? I’m deep enough into this series that I have to sometimes double check whether I have written about a particular defect or not.? Adhered Glass was covered in Part 6 of the series, but I still haven’t gotten around to discussing a Glass Stringer or Spiticule (a great word that doesn’t appear in the OED, Merriam-Webster, etc. – I unfortunately can’t use it to play Scrabble).

2.?????? The entry for Lehr Sticker in the PDA TR 43 defect lexicon for converted tubular vials also mentions the possibility of vials sticking together during depyrogenation.? If you compare the information available in my post on the viscosity of glass with typical depyrogenation schedules, you’ll probably conclude that this seems pretty unlikely to happen. ?The depyrogenation tunnel would have to be much hotter than usual for this defect to be created.? It’s interesting to note that the Lehr Sticker entry in the defect lexicon for molded glass vials does not mention depyrogenation as a potential root cause.? I’d be curious to hear from anyone who has actually experienced the creation of Lehr Sticker defects during depyrogenation.