Yes, BINDER is a Scrabble word!

Letter values in Scrabble US: B 3, I 1, N 1, D 2, E 1, R 1.

Is it a valid word?

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

a machine that cuts grain and binds it in sheaves
something used to bind separate particles together or facilitate adhesion to a surface
holds loose papers or magazines
something used to tie or bind

Also: reaper binder, ring-binder.