Yes, COPPERPLATE is a Scrabble word!

Letter values in Scrabble US: C 3, O 1, P 3, P 3, E 1, R 1, P 3, L 1, A 1, T 1, E 1.

Is it a valid word?

COPPERPLATE is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a graceful style of handwriting based on the writing used on copperplate engravings
a print made from an engraved copperplate
an engraving consisting of a smooth plate of copper that has been etched or engraved

Also: copperplate engraving.