This is a simple but very effective application of polyester heat shrink tubing
for masking areas during coating operations. One manufacturer requires a white coating
over a clear balloon, but the neck must remain uncoated so that a UV curable adhesive
can be used to bond it to the catheter. A piece of heat shrink tubing is applied
to the neck, then the balloon is dipped in the coating. After it dries, the heat
shrink is peeled away, leaving the neck uncoated. The key to this application is
the thinness of the polyester tubing. A thicker shrink tubing would leave a thick
edge of coating material on the balloon, unlike the ultra-thin wall polyester tubing.
Clear angioplasty balloons are shown after a white coating has been applied to one
end. Polyester shrink tubing was used to mask the small diameter ends to prevent
the balloon end from being coated. This enables the manufacturer to use a UV-curable
adhesive for bonding the ballon to the catheter. Top view shows coated balloon prior
to removal of the mask. The heat shrink tube is partially removed from the end of
the middle balloon. Bottom view shows shrink tubing has been completely removed,
thus leaving an uncoated clear neck ready for bonding.
Another manufacturer applies a slippery coating to a length of wire that has a fine
spring coil at the end. Polyester heat shrink tubing is used to mask the spring
to keep it from being coated during the dipping process. The low shrink temperature
permits the masking operation without heat distortion, and the tight shrink fit
prevents the coating from flowing into the spring. Afterwards, the polyester tubing
is easily peeled away.
The key properties of polyester heat shrink tubing in masking applications are:
- Very thin wall to prevent thick build up at edge
- Low shrink temperature allows application without heat distortion
- Easily removed
- Tight shrink fit on substrate
Removal of polyester heat shrink tubing:
- Heat shrink tube is easily removed by pulling or peeling and the mandrel is pulled
out of the catheter tube.
- The heat shrink tubing does not stick to most materials.
- If necessary, the tip may easily be trimmed using a razor blade.
- Observe the ultra, smooth glass-like surface finish of the taper produced using
this process.