Not a 'thermal' printer...
it used sparks to blast the silver conductive film off... there was a distinct smell of ozone when using one...
Just had pointy bits that were pulled across the paper on a continuous loop of wire and the printer discharged where each 'pixel' was...
https://en.wikipedia.org/wiki/Spark_printing
https://en.wikipedia.org/wiki/Sinclair_ZX_Printer