Granted Patent
Utility
US 4,634,767 · App. 06/771,920
Method for preparing spiro(indoline)-type photochromic compounds
Inventors:
Charles H. Hoelscher, Douglas S. McBain
Patented Case
View Patent ↗
Granted: Jan 6, 1987
Filed: Sep 3, 1985
Inventors
Charles H. Hoelscher
Douglas S. McBain
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.