Which printer is heated on chemically treated paper to form an image or a character?

A thermal printer, much like the cash register receipts you get that run a list of items in a heart beat. The image is burned on to the chemically coated paper. The same paper will darken when exposed to excessive sunlight/heat. The paper is one sided and usually very thin. It use to be that the old fax machines used roll paper that was chemically coated and usually a page of typing would take a very short period of time to completely print out.