Retro plastic cafeteria plates, vintage diner style divided meal tray plates

Set of six vintage plastic cafeteria plates with divided sections, 10 3/4" in diameter overall. These are marked Jones - Zylon Made in USA, 70s or 80s vintage?

They've been used but are in very good clean condition, nice and glossy, very little scratching. They're light and easy to carry, not as heavy as melmac.