Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
B~C~GROUND O~ TIIE INVENTION
~ c prcsent invcntion rclates in gcncral to liquid
devclopmcnt of electrostatic char~e ima~cs ;ln~ more particu1;1rly
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to a method and app.lratlls cmploying a rotat.lble dcveloplllent
electrodc for carrying elcctrographic toncr into contact with
the charge images to be dcveloped.
DESCRIPTION OF TIIE PRIOR ART
llerctofore~ electrostatic charge images on the charge
retentive surface of the recording web have been developed with
liquid electrographic ~oner. In SUC]l systems, the development
station included a rotating cylindrical drum-shaped development
electrode. The drum-shaped electrode was mounted adjacent the
10: large image bearing surface of the recording medium. The lower
portion of the drum dipped into a bath of liquid toner so as to
pick up toner on the smooth surface of the drum and carry it
~nto contact with the charge images on the charge retentive
surfaces to ~e developed. The drum was rotated with sufficient
angular velocity~such that the peripheral speed of the drum
exceeded the speed of the web being developed so as to establish
a ~ead of liqui~d toner between the outer surface of the rotating
drum and the charge retentive surface to be developed. Such a
devel~pment station is disclosed in U.S. Patent 3,367,791 issued
20: February 6, 1968.
~Yhile suc~ a development station is suitable for developing
images moving at a relatively slow speed it is generally
unsatisfactory for developing images on charge retentive surfaces
of recording webs traveling at relatively high speeds, such as
; faster than two inches per second, because the angular and
peripheral velocity of the developmcnt electrode must be
relatively high to provide the necessary amount of toner to the
images being developed, particularly when the images include
relatlvely large dark areas ~hicll are to be developed with a
3Q. uniform degree of darkness.
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It has also been proposed, in the prior art, to utilize a
porous or perforated drum-shaped development electrode with
means inside the electrode for forcing elec,$rographic liquid
toner through the porous walls of the drum against the charge
retentive surface of the recording web to be developed. In one
embodiment, the drwn was rota~ed at the same speed as the speed
of the recording web ~eing developed. Such a device forms the
subject matter of U.S. Patent 3,618,567 issued November 9, 1971
and assigned to t~e same assignee as the present invention. In ;~
la another such device, a perforated development electrode drum
was rotated at a sufficient angular velocity such that the
surface of the drum adjacent the charge retentive surface being
de'yeloped was approximately up to ten times the speed of the image ~ ,
bearing we~ ~eing developed. This higher differential speed
allowe'd the drum to disturb the bounda~y laye~ of liquid toner
~hich'~ould ordinarily form adjacent the surface of the moving
j recording we~ to be developed. This boundary layer interferes
~ith complete 'development ~ecause it soon becomes depleted of
the electrographic toning paTticles. This depleted layer is
20: preferably removed so as to allow fresh electrographîc toner
to contact t~e charge image to be developed. This latter
differential speed perforated development electrode forms the
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subject matter and is claimed in u~S. Patent 3,952,702, issued
April 27, 1976, and assigned to the same assignee as ~h~
present invention.
While such perforated or porous development electrode drums
are capable of developing relatively large areas at relatively
high speeds, such as tens of inc~es per second, they are
cumbersomc assemblies and are relatively difficult to abricate
and tllUS are more costly than impcr~orate drumsO
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Thus it would be dcsiral~lc to provide an impro~ed rotat<lble
developmcnt electrode which is capable of operating at relatively
high wcb speeds, which is easy to -fabricate and assemblc, and whic h
does not have ~o be driven at such hig}l angular velocity as here-
tofore encountered with smooth imperforate development drums.
SV~RY OF T~IE PRESr:NT INVENTION
The principal object of the present invention is the
provision of an improved method and apparatus for liquid
development of electrostatic charge images.
lQ In one feature of the present invention, the development
~tation includes a cylindrical developmen~ electrode having a
rough outer surface to be rotated adjacent the charge retentive
surface of tHe recording medium being developed. This rough
surface serves to facilitate the carrying of liquid toner to
the charge images being developed and to disrupt the boundary
layer of liquid toner other~ise tending to form adjacent the
charge i~ages to be developed, ~hereby improved liquid
electrographic development ;s o~tained.
In another feature of the present invention,`liquid
; 20: electrographic toner is applied to the rough surface of a
cylindrical development electrode by directing a stream of liquid
develu~ment toner against the outer rough surface of the
; development electrode. The toner is preferably applied to a
region of the rotatable development electrode which is moving
toward the charge image bearing surface to be developed.
In another feature of the present invention, the outer
surface of a cylindrical development electrode includes an
array of lands and grooves such lands and grooves being
elongated and running transverse to the direction of rotation
of the developmcnt elcctrode.
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In accordance with the foregoing features,
there is more par~icularly provided:
In a method of developi.ng electrostatic latent
charge images on charge retentive surfaces the steps of:
mounting an electrically conductive development
electrode with a rough outer cylindrical surface thereof for
rotation about i~s axis of revolution;
passing the charge retentive surface of a recording
medium, bearing a latent charge image thereon to be developed,
adjacent said rough surface of the cylindrical development
electrode;
rotating said cylindrical development electrode with
an angular velocity such that the rough surface of said
development electrode is moving at a different speed than
that o the charye retentive surfaces to be developed; and
supplying liquid electrographic development toner,
having electroscopic toner particles suspended in a dielectric
liquid, to the rough surface of said development electrode
so that the toner liquid is brought into contact with the
charge images to be developed for developing same.
There is also provided:
In an apparatus for developing electrostatic images
on a charge retentive surface:
development electrode means having a rough
cylindrical surface comprising a plurality of discrete pro~
jecting surface portions, separated from one another by a
plurality of recessive surface portions;
means for mounting said development electrode means
for rotation about its axis of revoulution;
means for passing the charge retentive surface of a
~ recording medium, for bearing latent charge images thereon
:~ to be developed, adjacent said rough surface of said development .
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electrode and contiguous with said projectlng surface portions
thereof;
means for rotating said development electrode means
with an angular velocity such that said rough surface of said
development electrode moves at a differellt speed than that of . .
the adjacent charge retentive surface to be developed; and
means for supplying liquid electrographic development
toner, having electroscopic toner partic:Les suspended in a
d~electric liqu~d, to t~e rough surface of said development ~ :
electrode so t~a~ the toner liquid is carried into contact
wi~h the charge images on the charge retentive surface to be
developed for developing same, said liquid toner being carried
within said recessive surface portions, said projecting
surface portions serving to wipe liquid toner from said charge
retentive s~rface, whereby said charge retentive surface
undergoes a plurality of successive development operations,
each o said operations being followed by a wiping operation~
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Otller ic;lturcs ~n~l adv;llltllgcs Or the prcscnt invcntion will
becomc ~pl~aren~ upon a per~lsal of the ~ollowing spccificcltion
takcn in connection with the accompanying drawings wherein:
~RIEF D~JSCR~PTION OF TIIE DRAWINGS
Fig. 1 is a transversc sectional view of a liquid
electrographic developmcnt station incorporating features of
the present invention, and
Fig. 2 is an enlarged detail view of a portion of the
structure of Fig. 1 delineated by line 2-2.
DESCRIPTION OF T~IE PRE~ERRED E,~BODIMENTS
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Referring now to Fig. 1 there is shown a liquid electrographi
development station 1 incorporating features of the present
invention. Electrographic recording paper 2 is pulled through
the development sta~ion 1 by passing through the nip of a pair
af rollers 3 and 4~ Roller 4 is a squeegee roller having a
compressible layer 5 on the outer surface thereof and such layer
~eing compressed against the other roller 3, as of stainless
steel, to provide a frictional drive for the paper web 2 sand-
wlched ~etween the two rollers 3 and 4. The squeegee roller 4
2Q' is driven in the clockwise direction via any one of a number of
conventional drive means, such as a gear train or V-belt, not
shDwn ~
The electrograp~ic recording paper 2 is threaded between an
idler roller 5, as of stainless steel, and a development electrod
roller 6, as of aluminum. Rollers 3 and 5 are positioned relativ
to the development roller 6 so as to cause the electrographic
recording web 2 to be pressed into nominal engagement with a
portion of the surface of tlle developmcnt ~le~rOde 6. A V-belt
power take of of ~he squeegee roller 4 is passed over an idler
pulley 8 which in-turn drives the developmcllt roller 6 via a
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second V-bcIt ~Irivc ~. 'I'he pu]ley ratios are chosen so that t~.e
peripheral spocd of the development electrode 6 is within the
rangc of 2 to S times thc speed of the electrographic recording
web 2 which is to be developed. Any one of a number of drive
means, such as gear trains9 etc., ~.ay be employed as an alternati e
to the V-belt drives 7 and 9.
Liquid electrographic toner is applied to the development
drum via a spray pipe ll which directs a stream 12 of liquid
toner against the outer cylindrical su~face 13 of the
development electrode 6 in a region where the direction of
movement of the development electrode 6 is toward the
electrographic web 2 to be developed. The liquid electrographic
toner comprises a dielectric liquid vehicle having a suspension
of charged pigmented toner particles therein. The toner is drawn
from a reservoir 14 and supplied to the spray pipe ll via a pump
15 and conduit 16. A spray shield 17 is interposed between the
spray pipe 11 and the electrographic web 2 to prevent unwanted
spraying of the electrographic toner directly OTltO the web 2.
The electrographic recording web 2 includes a conductive
` 20 paper backing having a dielectric insulative layer coated thereon
`~ to form a charge retentive surface. Charge images to be
developed are deposited upon the charge retentive surface and
carried by the web 2 into the development station 1. The charge
retentive layer is disposed -facing the development drum 6.
Rollers 3 and 5 make electrical contact to the conductive side
of the web and the development electrode drum 6 may be operated
at a floating potential relative to the potentials applicd to
rollers 3 and 5 or the development drum 6 may be operated at a
suitable development potential relative to the potentials applie
to rollers 3 and S.
Referring now to ~i~. 2 there is shown the surface detail of
the dcvclopmcnt electrode drum 6. The outer surface l3 o~ the
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drum 6 is rough, and in a prc~erre(l cmbodiment comprises an array
of relatively thln longitudinally directed lands 21 separated by
wider groove portions 22. In a typical example, the~ lands 21
have a height of approximately 0.050 :inch relative to the bottom
of the groove portions 22. In operat:ion, the land portions 21
serve as wipers for wiping the depleted boundary layer
of toner from tlle charge retentive surface of the recording web 2.
The groove regions 22 between adjacent lands 21 serve to carry
- fresh toner into contact with the charge images to be developed
lQ.'. on th.e recording web 2.
In addition, the ~ottom surface of the grooves 22 serves the
function of the development electrode, namely, to provide a
conductive surface operating at a different potential than that
of the ch.arge images to be developed so that the field lines will
extend betwe'en` the' charge images and the adjacent surface of the
development elec'trode 6. In this manner the electric fields in
the electrograph.ic toner region between t~e development electrode
: 6 and the charge retentive surface are relatively high to
pedite transfer of toner particles from the electrographlc
20 . toner liquid to the charge images to be developed. In a
' preferred embodiment, the groove portions 22 are wikhin 0.100 inc
or less of the charge image ~eing developed. The land regions 21
;~ should be relatively narrow relative to the groove region 22 so
that nominal contact is established between the upper surfaces
of the lands 22 and the charge retentive surface so as to
:` efficiently disrupt the.boundary layer of'depleted toner adjacent
the web 2.
In addition, the lands 21 should have a slight pitch relative
to the axis of revolution of the development electrode 6 so that
the paper web 2, particularly in the case of a fan-fold
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elcctrograpllic web, ~loes not get c~ught and torn by the more
rapidly moving peripllcral surfacc of the ~leveloprnent electrode 6.
The spiral pitC]I o~ the lands is suff:icient iE the pitch has
advanced by one angular land period over the length of the
development electrode 6. Furthermore, the surface 13 of the
development electrode should be free of surface detail which is
invariant in the direction of rotation of the development electrod e
to prevent streaking and patterning of the developed image.
As an alternative to a surface roughness detai:L consisting
of lands and grooves, the surface of the development electrode may
be roughened ~y sand ~lasting, photoetching, or knurling.
Generally speaking, the rough surface 13 should have surface
detail thereon ~aving mean peak-to-peak amplitude variations of
between q.005 and 0.100 inch.
In an alternative embodiment oE the present invention, the
development electrode drive can be arranged for driving the
develop~ent electrode in a direction counter to the direction
; of ~oYement of the electrograp~ic we~ 2O In such an embodiment,
~; the Y-belt ta~e of drive 7 is moved to the back up roller 3 so20: a~ to drive the development electrode 6 in the counter-clockwise
I direction. In this latter embodiment, the spray pipe 12 is
preferably moved to a region adjacent the first quadrant of the
developmént electrode so that the electrographic toner is
sprayed onto the roughened surface o-f the surface 13 of the drum
in a region moving toward the charge retentive surface to be
de~eloped.
Although the surface roughening feature of the developmen~
electrode is, in a preferred embodiment, applied to an
imperforate development electrode drum 6 this is not a
requirement. It may be also used to advantage with perforated
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or porous dcvcloplllcnt olcctrodc drums whcreirl thc electrograp}lic
toner is pumpcd througll the pcr:forated wall of the dcvelopment
drum into contact Wit]l the charge retentive surface of the
record.ing medium to be dcveloped. In the case of the perforated
development electrode drum, the lands function in ~he same
manner as previously described wit.h regard to the embodiment of
Fig. 1 wherein the lands 21 serve to disrupt the boundary layer
of depleted toner adjacent the charge retentive sur~ace of the
recording web 2.
The differential speed between the speed o~ the recording
web 2 and that of the periphery of the development electrode 6
is preferably at least twice the speed of the web 2.
An advantage of the spray method of supplying liquid toner
to the development electrode, as contrasted with the method of
dip~ing the lower part of the rotating drum in :Liquid toner, is
that the spray tends to scrub away depleted toner from the
surface of the drum due to its turbulent impact with the drum.
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