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Criteria for Proper Selection of Developer Roller Material Bulk Resistivity in an Electrophotographic Printer

IP.com Disclosure Number: IPCOM000101978D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 3 page(s) / 104K

Publishing Venue

IBM

Related People

Baker, RW: AUTHOR [+2]

Abstract

Disclosed are criteria for the proper selection of bulk resistivity for the materials used in the developer roller (DR) of a monocomponent, non-magnetic, contact development electrophotographic printer. Figure 1 shows an end view of the roller. It consists of a metal shaft 1 onto which a compliant rubber layer 2 is molded. A thin coating 3 is then applied. Proper selection of the bulk resistivity (BR) of the rubber layer (BRr) and the coating (BRc) is crucial if high print quality over the entire environmental range is to be attained.

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Criteria for Proper Selection of Developer Roller Material Bulk Resistivity in an Electrophotographic Printer

       Disclosed are criteria for the proper selection of bulk
resistivity for the materials used in the developer roller (DR) of a
monocomponent, non-magnetic, contact development electrophotographic
printer.  Figure 1 shows an end view of the roller.  It consists of a
metal shaft 1 onto which a compliant rubber layer 2 is molded.  A
thin coating 3 is then applied.  Proper selection of the bulk
resistivity (BR) of the rubber layer (BRr) and the coating (BRc) is
crucial if high print quality over the entire environmental range is
to be attained.

      BRr is a key factor in the development process.  The
electrostatic field in the nip between the DR and the photoconductor
(PC) drum, which determines the amount of toner developed onto the
PC, is defined by the applied voltages, the nip residence time
(Tnip), BRr, and the capacitance of the nip (Cnip).  When an
electrical transient occurs in the development zone, such as the
passage through the nip of a discharged area on the PC, the voltage
on the surface of the DR first drops substantially in response to the
transient and then rises exponentially to the voltage applied to the
DR shaft as Cnip is charged through the rubber resistance.  The time
constant of this exponential rise (TAUnip) is given by:  TAUnip =
Rr*Cnip.  Rr is the rubber resistance and is related to BRr thus:  Rr
= BRr*Tr/Ar, where Tr is the rubber layer thickness and Ar is the
effective rubber layer cross-sectional area.

      If Tnip is small with respect to TAUnip, the effective
development field at the exit of the nip will be substantially less
than that predicted by the applied voltages.  Figure 2 shows the
percentage of applied voltage present at the nip exit as a function
of Tnip/TAUnip.  Four experimentally determined data points are also
shown.  If Tnip/TAUnip < 0.5, the effective development field will be
small.  This situation requires excessive power supply voltages to
achieve full development.  A...