Granted Patent
Utility
US 4,428,775 · App. 06/233,663
Reinforced cement sheet product containing no asbestos for fabricating on hatschek machine
Inventors:
Robert M. Johnson, Elmer M. Melling
Patented Case
View Patent ↗
Granted: Jan 31, 1984
Filed: Feb 11, 1981
Inventors
Robert M. Johnson
Elmer M. Melling
Assignee (at issue)
National Gypsum Company
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.