Laser-safe PSA “Vinyl”: Proof of Concept

Mary’s ResMed AirSense 11 saves the data from every overnight breath she takes on an SD card, which she uploads to OSCAR once a week. I figured she needed an SD card to USB adapter / card reader of her very own:

PU PSA Vinyl test - installed
PU PSA Vinyl test – installed

The lurid green letters aren’t backlit, they’re cut from a PVC-free “vinyl” (really, polyurethane) sheet with adhesive on the back.

N.B.: Laser-cutting real vinyl, made from PVC, releases enough chlorine gas to corrode the guts of your machine and, with poor fume extraction, rot your lungs along with it.

The LightBurn layout is pretty much what you’d expect, with the letter inside the outline of the USB dingus on a tool layer to get the size right:

PU PSA Vinyl test - LB layout
PU PSA Vinyl test – LB layout

The red layer is a “kiss cut” through the vinyl (remember: polyurethane) that leaves the backing paper mostly undamaged:

PU PSA Vinyl test - dot mode cut detail
PU PSA Vinyl test – dot mode cut detail

The cut uses Dot Mode, with the laser firing at 10% power for 2 ms, spaced every 0.1 mm along the cut. I found 0.1 mm spacing produced a more-or-less continuous cut in the PETG sheet for the Tek Circuit Computer cursor hairline, but this picture shows it’s definitely running in pulsed mode. In any event, Dot Mode is the only way a 60 W CO₂ laser can make a kiss cut, as a normal vector cut can’t run fast enough to prevent cutting all the way through the backing paper, even at 10% power, around those letters.

The edges of the letters are slightly melted with a raised border, although they look pretty good if you’re not peering at them through a microscope.

I cut the rectangular outline with scissors, peeled the waste vinyl away, and weeded the ‘a’ with tweezers:

PU PSA Vinyl test - weeded
PU PSA Vinyl test – weeded

Stick a snippet of transfer tape on top:

PU PSA Vinyl test - transfer tape
PU PSA Vinyl test – transfer tape

In theory, the transfer tape sticks more firmly to the cut letters than the letters adhere to their backing paper, so peeling off the tape also peels the letters off the backing paper.

Which did not go well:

PU PSA Vinyl test - transfer tape - peeling
PU PSA Vinyl test – transfer tape – peeling

The two adhesions obviously require a delicate balance to work properly and I would be unsurprised to learn different transfer tapes behave differently on each type of vinyl sheet, with no way to know the results without trying every possible combination.

A few retries got the “r” back in position on the transfer tape, but a bit of kink remains in the “M”.

A third adhesion balance occurs between the transfer tape and the USB card reader, where the tape must stick to the letters slightly less than the letters stick to the reader. Burnishing the tape + letters to the reader encouraged the letters to stick and the tape pulled off without dislodging them.

We deemed the result good enough for the purpose and the process taught me a few lessons along the way. Next time, maybe it’ll work out better.

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