Granted Patent
Utility
US 4,730,057 · App. 06/817,564
Phthalide derivatives useful as colorless chromogenic material
Inventors:
Nobuo Kanda, Naoki Yonese, Mitsuru Kondo
Patented Case
View Patent ↗
Granted: Mar 8, 1988
Filed: Jan 10, 1986
Inventors
Nobuo Kanda
Naoki Yonese
Mitsuru Kondo
Assignee (at issue)
Kanzaki Paper Manufacturing Co., Ltd.
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.