Granted Patent
Utility
US 4,020,056 · App. 05/566,851
Di-vinyl phthalides color formers
Inventor:
Sheldon Farber
Patented Case
View Patent ↗
Granted: Apr 26, 1977
Filed: Apr 10, 1975
Inventor
Sheldon Farber
Assignee (at issue)
NCR Corporation
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.