Granted Patent
Utility
US 4,880,667 · App. 07/110,636
Photochromic plastic article and method for preparing same
Inventor:
Cletus N. Welch
Patented Case
View Patent ↗
Granted: Nov 14, 1989
Filed: Oct 15, 1987
Inventor
Cletus N. Welch
Assignee (at issue)
PPG Industries, Inc.
This patent predates the USPTO's electronic file wrapper — prosecution documents from this era exist only in the Patent Office's paper records. A certified copy of the file history can be ordered from the USPTO's paper archives.