Originally Posted by
Spld cyclist
Do patches get old and fail to properly adhere? I ask because lately I've had a couple that didn't seem to hold. They were a couple patches that I got out of an old kit because I needed larger ones. Could have been operator error, but my patch jobs usually hold.
I ask because a box of 100 Rema patches would probably take 15 years for me to use up. The ones that seemed not to work were probably 10 years old, although they were probably not the highest quality to begin with.
The layer of rubber that contacts the tube is a mixture of unvulcanized rubber and one of a few suitable vulcanization ultra-accelerators. There's an activator in the glue, which activates the ultra-accelerator. The patch then vulcanizes itself to the tube. Patches can fail from age if the vulcanization gets kicked off, which can happen with high temperature, and which might ahppen at slow rate with time. There are probably failures where the ultra-accelerator breaks down and doesn't do its job.
Also, the point of sanding the surface of the tube isn't just to clean it, it's to provide a textured area, which gives the glued bond a lot more surface area, and makes it much stronger. Sand paper or emery cloth work much better than a cheese grater.