It seems that the patches I buy for fixing inner tubes come in one of 2 types. Both have metal foil on the stick-to-tube side. One has paper on the other side, the other plastic.
With the paper ones I can peel off the foil, glue them down, wait a minute, then split the paper from the centre and tear it off.
I can't do this with the plastic backing - any attempt to remove it seems to lift the edges.
Am I supposed to leave the plastic on, remove it before I glue the patch, or what?
The Rema Tip-Top patches that I use--which sound similar to those which the questioner describes--come with instructions in each plastic box. The package that I have shows the instructions pictorally in seven steps.
Here is the product that I use: http://www.artscyclery.com/descpage-79002.html
In step 7, the manufacturer distinctly recommends that the user remove the plastic backing.
I usually remove this cellophane backing myself. It sometimes is a little finnicky--if your patch isn't totally set it will seem to pull up the patch. Just use your thumb to set the patch more carefully. In the package's Step 6, the manufacturer uses a totally unidentifiable rectagular object to smooth out the patch before removing the cellophane. I use my thumb, personally, and it works just fine.
If one side of the cellophane won't seem to come off without removing the patch, you didn't put down enough vulcanizing fluid. Try the other side. If the patch is reasonably centered, this shouldn't be a problem.
The answer about leaching chemicals is news to me--though I admit freely that I never looked farther than the instructions in the box for advice.
Once in a moment of frustration, I left the cellophane on and put it into the tire--no problems so far. I had some concern there would be a problem if the cellophane were stuck between the rim and the bead but this doesn't seem to have been a problem for Anthony K or Darren Cope.
It looks as though it doesn't matter, but the manufacturer of Rema patches recommends removing it. I say remove it carefully. This is best done if you are generous with the vulcanizing fluid and careful to press the patch into place.
I followed the advice of leaving the plastic film on. After a few days the tire went flat again. Inspection revealed that the tube was puckered around the patch because the plastic film does not stretch in the same way as the tube and the patch. The new leak was coming from under the patch. Therefore from now on I am going to try to take the plastic off.
If the edges are lifting when you're removing the plastic, that is a strong indicator that the glue you used is not of a pedigree suitable for this type of repair. The adhesive is not melting into the rubber and not vulcanizing, but only providing a superficial tack, like the back of a scotch tape.
The edges will stick quite well to the inner tube if the glue is good.
However, even if the adhesive is good, to avoid "tempting fate", what I do is peel the plastic backing from the centre out. Before even gluing the patch on, I score a small X crosshatch cut in the center of the plastic backing with a sharp tool (but gently, without damaging the patch, obviously).
When the patch has set (I give it 12-24 hours, clamping the tube between two wooden blocks with a wood clamp), I then peel the plastic backing from its center cut out toward the edges. That direction reduces the tendency to lift.
Another important aspect is that there must be a decent amount of glue there all the way to the edges of the patch, and at least a millimeter beyond. When I'm applying the patch, I wiggle it around in a circular motion to get the glue spread to a slightly larger area than the patch, but still mostly within the limits of the plastic backing sheet (to avoid adhesion to the clamping blocks, and an overall tidy job).
At "peel time", you notice a big difference between the behavior of cheap rubber cement and proper tube repair contact cement: with the good adhesive, the extra glue squeezed out of the patch, caught between the plastic backing and the tube, is almost completely tack-free and releases the plastic backing easily. The poor type of adhesive remains more of a sticky, gooey mess, indicating a product that is for temporary paste-up jobs that allow repositioning. If your glue is like that, of course the edges lift, because in fact the whole patch will lift easily.
Park Tool's instruction guide on YouTube for their patch kit says leave the clear plastic top layer on. They've got loads of really good how to guides on YouTube. Worth a look.
I've learnt the hard way over 30 years of applying patches to inner tubes and I'm still not convinced I can get it right each time. One of the problems with new tubes being manufactured in Asia is that the production process leaves ridges along the length of the inner tube. These can comprise the patch and so should be reduced as far as possible when roughing up the tube before applying the rubber glue. Incidentally don't be in a rush to apply the patch over the glue as the curing process can take between 2 to 5 minutes depending on temperature. Also leaving the repaired tube 24 hours before reuse is a very good idea. As for the cellophane or clear plastic film, it must be removed to ensure the patch sits properly inside tyre. Peeling from the centre of the patch seems to be the best way to remove the film but this will require cutting an "X" in the centre............... Save the environment (and some money !!)......patch your inner tubes and if they can't be patched because the valve has pulled out they can still be used for many other applications such as bungee straps washers, lagging etc...
You should leave the plastic backing on, and the paper ones as well. The backing stops chemicals from the patch and glue working their way into the tire at the location directly in contact with the patch. I do not know if this leaching weakens the tire at all, but in many cases it will cause a dark "patch" to appear on the tire sidewall after an amount of time, which can look unsightly. After a long period of time (months) the plastic and paper will disintegrate by themselves so you don't have to worry about removing them.
There are two types of plastic backings. One has a weak line in the middle, another doesn't.
The one that has a weak line in the middle, the one you could buy from Rema TipTop until recently, you just stretch the patch along with the plastic backing. Stretching the patch doesn't lift the edges. However, the weak line develops into a crack, allowing you to pull the plastic backing away from the middle of the patch when cut to two pieces.
If the patch you use doesn't have a weak line (like I think Rema TipTop these days due to cost saving during manufacture), this won't work. However, if you carry a small razor blade in your patch kit (wrapped in disposable paper towel to prevent it from puncturing your spare tube -- which you obviously could put inside an old sock), you can make the crack in the middle of the plastic backing yourself. Then when you have initiated the crack, stretching it fully develops the crack, allowing you to peel it from the middle.
The razor blade has other uses too. For example most tubes have seams, and the razor blade can be used to cut the seam away if you need to patch close to a seam.
Don't believe the answers that say if the patch lifts, the glue is bad or that you didn't use enough glue. With best possible glue you can find, used in proper amounts, the patch still lifts. It's supposed to. A glue takes a day to dry. You patch a tube after few minutes of waiting. The patch will lift if you pull the plastic backing improperly, and not pulling the plastic backing prevents the glue from drying. Due to the glue not drying before a day of wait, you should never use a recently patched tube unless you're forced to. Carry a spare tube. When patching, the patched tube becomes the new spare tube. Then you have to use a recently patched tube only if you suffer more than one puncture in a day. Not following these instructions mean the patched tubes develop slow leaks.
