Method for using hard magnetic carriers in an electrographic process

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(11)

EP 1 156 375 A3

(12)	EUROPEAN PATENT APPLICATION

(88)	Date of publication A3:
	21.08.2002 Bulletin 2002/34

(43)	Date of publication A2:
	21.11.2001 Bulletin 2001/47

(21)	Application number: 01111258.8

(22)	Date of filing: 16.05.2001

(51)	International Patent Classification (IPC)⁷: G03G 9/107, G03G 15/09, G03G 9/083, G03G 9/113

(84)	Designated Contracting States:
	AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU MC NL PT SE TR
	Designated Extension States:
	AL LT LV MK RO SI

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Priority:

17.05.2000 US 204941
17.05.2000 US 572988
17.05.2000 US 572989

(71)	Applicant: Heidelberger Druckmaschinen Aktiengesellschaft
	69115 Heidelberg (DE)

(72)	Inventors:
	Alexandrovich, Peter Steven Rochester, New York 14617 (US) Göbel, Wilhelm K. Rochester, New York 14607 (US) Lambert, Patrick Rochester, New York 14617 (US) Stelter, Eric C. Pittsford, New York 14534 (US)

(74)	Representative: Franzen, Peter et al
	Heidelberger Druckmaschinen AG, Kurfürsten-Anlage 52-60 69115 Heidelberg 69115 Heidelberg (DE)

(54)	Method for using hard magnetic carriers in an electrographic process

(57) Methods for development of an electrostatic image are disclosed that utilize developer compositions with hard magnetic carrier compositions which can provide improved development efficiencies and reduced amounts of image carrier pick-up. The methods utilize hard magnetic carrier particles that are modified to have specific levels of resistivit, such as, for example, of from about 1x10⁵ ohm-cm to about 1x10¹⁰ ohm-cm, and a carrier charge-to-mass of greater than about 1.0 µC/g, which carriers can provide greater development speeds without unacceptable levels of image carrier pick-up. In embodiments, the hard magnetic materials are doped, i.e., bulk substituted, with multi-valent metals to adjust resistivity, while in other embodiments, the hard magnetic materials are coated with at least one multi-valent metal oxide.

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