Granted Patent
Utility
US 6,281,172 · App. 09/287,903
Quaternary nitrogen containing amphoteric water soluble polymers and their use in drilling fluids
Inventors:
Brent Warren, Peter Marten Van Der Horst, Theodorus A. van't Zelfde
Patented Case
View Patent ↗
Granted: Aug 28, 2001
Filed: Apr 7, 1999
Inventors
Brent Warren
Peter Marten Van Der Horst
Theodorus A. van't Zelfde
Assignee (at issue)
AKZO NOBEL N.V.
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.