FWIW Department:


Scotch (adj.)
"of Scotland," 1591, contraction of Scottish. Disdained by the Scottish because of the many insulting and pejorative formations made from it by the English (e.g. Scotch attorney, a Jamaica term from 1864 for strangler vines). As a noun, elliptical for Scotch whisky, it is attested from 1778. Scotch-Irish is from 1876; more properly Scots-Irish (1972), from Scots (c.1352), the older adj., which is from Scottis, the northern variant of Scottish. Scotch Tape was said to be so called because at first it had adhesive only on the edges (to make it easier to remove as a masking tape in car paint jobs), which was interpreted as a sign of cheapness on the part of the manufacturers.

http://www.etymonline.com/index.php?term=Scotch.