Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
_
Field of the Invention
The present invention relates to improved apparatus
and procedures for electrophoretic migration imaging systems
which use electrophotosensitivè marking particles and more
specifically to means and techniques for improving the
quality of images produced by such systems.
Background of the Invention
~ lectrophoretic migration imaging processes capable
of producing monochromatic or polychromatic images have been
extensively described in the patent literature. Early
publication of these processes occurred in a series of
patents by E. K. Kaprelian including U.S, Patent No. 2,940,847
issued June 14, 1960; U.S. Patent No. 3,100,426 issued
August 13, 1963; u.s. Patent No. 3,140,175 issued July 7,
1964 and U.S. Patent No. 3,143,508 issued August 4, 1964.
More recent publications relating to polychromatic, electro-
phoretic migration imaging processes include U.S. Patent No.
3,383,393 to Yeh issued May 21, 1968; U.S. Patent No.
3,384,565 to Tulagin and Carriera issued May 21, 1968 and
U.S. Patent No. 3,384,566 to Clark lssued May 21, 1968.
In a typical embodiment of a single-pass, poly-
chromatic, electrophoretic migration imaging system, images
are formed by providing a suspension of electrically photo-
sensitive particles of three different color types (each
type of particle being sensitive uniquely to a particular
color of light) between a transparent, electrically con-
ductive electrode (cornmonly termed the "in~ecting electrode")
and an electrode bearing an electrically insulating layer on
30 its outer surface (commonly termed the "blocking electrode").
An electric field is applied across the two electrodes "
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while simultaneously exposing the particles to multicolor
light image which is selectively absorbed by the particles
according to light color.
As these steps are completed, selective particle
migration takes place in image configuration producing
complimentary i~ages on both electrodes. While the theory
of image formation is not completely understood, it is
believed that the particles initially bear a charge in the
imaging suspension which causes them to be attracted to the
injecting electrode upon application of the electric field
between the blocking and in~ecting electrodes. Upon expo-
sure to actlvating electromagnetic radiation to which they
are sensitive (i.e., of a color absorbed), the exposed
particles adjacent the injecting electrode apparently under-
go a change in charge polarity by exchanging charge with the
injecting electrode. These particles, now bearing the same
charge polarity as the in~ecting electrode, are repelled by
it and migrate to the blocking electrode. The particles
which migrate to the blocking electrode are less able to
exchange charge with that e:Lectrode's insulating layer and
do not therefore readily recycle to the ln~ecting electrode.
As a result, an image is formed by particle subtraction on
the in~ectlng electrode, such image being typically a photo-
graphically positive image, and a complimentary image,
typically a negative or reversal image, is formed on the
blocking electrode. Electrophoretic migration imaging
systems of the type described above are commonly referred to
as PhotoElectroPhoretic processes or denoted by the acronym
PEP processes.
In U.S. Patent No. 3,976,485 another approach is
disclosed wherein electrically photosensitive particles,
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disposed between two spaced electrodes having predetermined
properties are sub~ected to an electric ~ield and imagewise
exposed to activating electromagnetic radiation and image
formation is achieved by immobilizing at least a portion Or
the exposed photosensitive particles and causing at least a
portion of the unexposed particles to undergo a net change
in charge polarity. In this approach, termed photoimmobilized
electrophoretic recording (PIER), one of the two spaced
electrodes has on its surface ad~acent the photosensitive
particles an amount of a dark charge exchange material
which provides a net change in charge polarity of the
photosensitive particles coming in electrical contact
therewith in the presence of a field and in the absence of
activating radiation. (This sur~ace is sometimes referred
to hereinafter as a dark charge exchange layer). The other
spaced electrode advantageously may have on its surface
ad~acent the photosensitive particles, a "blocking" layer,
i.e., a layer which under normal process imaging conditions
exhibits minimal charge exchange capablllty with either the
exposed or unexposed electrically photosensitlve particles.
In accord with various use~ul embodiments Or
either Or the above-described approaches, the electrically
photosensltive particles can be disposed between the spaced
electrodes in a liquid imaging suspension comprising an
electrically insulating liquid. Vpon being admixed in such
a liquid, the particles acquire an electrostatic charge Or a
positive or negative polarity, although it is not uncommon
~or the imaging suspension to contain a mixture of both
posltive and negative polarity particles.
In connection wlth the various known embodiments
of the above-described P~P processes, it has been proposed,
.
at one time or another, to modify the customary surface
characteristics of the so-called "in~ecting" electrode
and/or the "blocking" electrode. For example, in British
Patent 1,193,276 published May 28, 1970 in examples V-IX
thereof it is proposed to coat~extremely small amounts of a
"Lewis base" or a "Lewis acid", such as 2,4,7-trinitro-9-
fluorenone, on one or the other of the electrode surfaces
used in PEP processes to increase the photographic speed of
the PEP process. Similarly, in British Patent 1,347,162
10 published February 2~, 1974 it is proposed to coat a photo-
conductive layer on the surface of a PEP in~ecting electrode
in an attempt to modlfy various imaging characteristics of
conventional PEP processes, such as photographic speed,
DmaX , Dmin , image contrast, and spectral sensitivity. In
Weigl, U.S. Patent 3,616,390 issued October 26, 1971 and
Weigl U.S. Patent 3,723,288 issued March 27, 1973 it is
proposed to use as a conductive in~ecting electrode a pre-
illuminated photoconductive zinc oxide-binder coating
applied to a conductive substrate. In Welgl, U.S. Patent
20 3.,595,771 issued July 27, 1971, it iB proposed to use as the
"blocking electrode" of a PEP process a photoconductive
insulating coating such as a "charge transfer complex" of a
non-photoconductive aromatic polycarbonate polymer and a
"Lewis acid", such as 2,4,7-trinitro-9-fluorenone, in an
efrort to remove accumulated electrostatic charge which may
build up on a conventional highly insulating blocking
electrode. In Ota and Ota et al, U.S. Patents 3,689,399 and
3,689,400 issued September 5, 1972 it is suggested that one
can coat an insulating layer on the "inJecting" electrode as
well as the "blocking" electrode of a PEP image display
device. In addition, in British Patent 1,341,690 published
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December 28, 1971 it is proposed to coat on the surface of
an in~ecting electrode of a PEP process a photoconductive
layer, an electroluminescent layer over the photoconductive
layer, and a transparent conducting layer over the electro-
luminescent layer so that exposure may be effected by using
the photoconductive layer to selectively energize the
electroluminescent layer which in turn emits radiation to
expose the image-forming electrically photosensitive parti-
cles used in the process.
However, with regard to all of the above-described
processes, difficulty has existed in obtaining sufficiently
high density in the image formed for utilization, that is,
in causing a sufficient quantity of the photosensitive
pigment particles to migrate in the desired image pattern
onto the utilized electrode surface (the electrode surface
; on which the subsequently used image pattern is formed).
The exact cause(s) of this difficulty have not
been definitely determined; however, certain prior art
teachings theorize regarding them and propose improvement
solutions based on those theories.
For example, the disclosure of U.S. Patent Re. 28,260
proceeds on the assumption that some particles, bearing
charge causing them to be attracted to the in~ecting electrode,
do not obtain a sufficient charge exchange upon exposure and
thus remain on the in;ecting electrode due to small forces
bonding the particles to that electrode surface, e.g.,
Van der Waal's forces. The solution proposed is to provide
means for creating a dynamic stress on the weakly retained
particles to free them for migration. It is noted that the
dynamic stress can be created by a differential linear
velocity between a rolling and plate electrode at their
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imaging interface, and that the velocity differential should
not exceed 10~ of the velocity at which rolling electrode
translates.
U.S. Patent 3,595,772 theorizes that ~ulticolor
pigment particles of such imaging suspensions agglomerate
and that the inactivated particles of the bound together
mass restrain the activated particles therein from desired
image migration. The solution proposed is to prestress the
suspension to break up the agglomerates.
U.S. Patents 3,616,395; 3,737,310, 3,645,874 and
3,850,627 propose improvement of the process by precharging
the image suspension to make the particles unipolar and/or
to concentrate the particles near the injecting electrode
surface prior to the imaging operation.
U.S. Patents 3,676,313 and 3,477,934 disclose
techniques for precharging the suspension on one of the
electrodes to enhance the migration field or neutralize
charge which accumulates on one of the electrodes in a
continuous operation apparatus.
U.S. Patent 3,595,771 likewise is aimed towards
elimination of residual charge (from a previous imaging
operation) on an electrode and suggest constructing the
electrode of photoconductive lnsulative material and flood
exposing it between imaging sequences.
Thus it is evident there has been a generai
realization that image quality of photoelectrophoretic
migration imaging process could desirably be improved,
particularly as to resultant image density, and that a wide
variety of specific techniques for obtaining such improve-
ment have been proposed.
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_UMMARY OF THE INVENTION
The present invention likewise is aimed toward the
improvement of image quality in such processes and involves
unique approach, procedure and apparatus for providing such
improvement.
It is therefore a general objective of the present
invention to provide improved procedure and apparatus for
photoelectrophoretic migration imaging.
Another, more specific objective, is to provide
apparatus and methods for facilitating improved density and
background in an image resulting from such migration imaging
processes.
The above and other desirable results and features
are achieved in accordance with the present invention by the
provision of methods and means for providing an lmproved
operating environment for the imaged electrode of photo-
electrophoretic migration imaging apparatus. The term
"imaged electrode" as utilized above and throughout this
application refers to the surface on whlch marking particles
are accumulated for producing the image to be used. The
operatlng environment to which the imaged electrode is
sub~ected includes the imaging suspenslon and the non-imaged
electrode. The present invention, in one important aspect,
improves the operating environment by increasing the quantity
of marking particles presented to the development zone
dur-ing each of the successive stages of an imaging sequence.
In accordance with another important aspect the non-imaged
electrode surface, initially presented to the image electrode
is supplanted durlng each of the successive imaging sequence.
In accordance with another important aspect, light-activated
particles which have been attracted to the non-imaged
electrode are removed from the imaging zone berore furthrer
charge exchange and subsequent backmigration to the imaged
electrode can occur, thus eliminating their potential adverse
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effect as background on the ima~ed electrode. The above
aspects are accomplished in accordance with one embodiment
of the present invention by providing a layer containing a
controlled amount of imaging dispersion between the imaged
and the non-imaged electrode surfaces and controlling the
relative movement of the imaged and non-imaged electrodes,
during imaging~ to provide a substantially enlarged migration
environment to the imaged electrode. In this application
enlargement of migration environment refers to the ratio of
the non-imaged electrode surface presented at the imaging
zone during a complete development cycle to the imaged
electrode surface presented at the imaging zone during that
cycle. For example, in accordance with this terminology the
enlargement of prior art apparatus would be substantially
one (1.0).
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention are hereinafter
described with reference to the attached drawings which form
a part hereof and in which: ¦
Fig. 1 is a schematlc side view of exemplary prior
art apparatus for photoelectrophoretic migration imaging;
Fig. 2 is an enlarged schematic view of the
lmaglng zone of apparatus such as shown in Fig. l;
Fig. 3 is a schematic side view of one apparatus
embodiment f'or photoelectrophoretic imaglng ln accordance
wlth the present lnventlon;
~ig. 4 1s an end view of the Fig. 3 apparatus;
Flg. 5 ls a schematic side view of another apparatus
embodiment for practice of the present invention;
Fig. 6 ls a schematic side view of another apparatus
for practice of the present invention;
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Fig. 7 is a graph indicating results of a test
described in Example III;
Fig. 8 is a graph indicating results of another
test described in Example III;
Fig. 9 is a graph indicating the results of the
test described in Example IV;
Fig. 10 is a graph indicating the results of the
test described in Example V; and
Fig. 11 is a schematic end view of a web electrode
apparatus for practice of the present invention incorporating
an improved structure minimizing electrode rubbing;
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Before undertaking explanation of various embodi-
ments of the present invention, a slightly enlarged expla-
nation of the prior art on which it improves, is believed
appropriate. Fig. 1 illustrates a representative prior art
device for implementation of photoelectrophoretic migration
imaging. That device comprises a charge exchange electrode
1 and an image receiver electrode 2 which includes a con-
ductive roller 3 and an electrically insulative layer 4, itbeing assumed for our purposes that the layer 4 can be the
copy sheet to be utilized. As illustrated electrode 2 is
mounted for rotation about axis 6 and for translation in
rolling contact across electrode 1. An electrical potential
is provided by source 7 between the electrodes and as
electrode 2 rolls across electrode 1 a migration inducing
field is created across the gap between the proximate
surfaces thereof. A photoelectrophoretic dispersion 8 is
coated on electrode 1 and can comprise electrophotosensitive
pigment particles dispersed in an insulative carrier liquid.
A light image of an original 10 to be reproduced is in focus
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at the plane Or the dispersion in registration with the path
over which the insulative layer 4 will pass. The electrode
1 is substantially light transparent. Thus as the electrode
2 transverses electrode 1, pigment particles within the
development gap between the ele~trodes are believed to
become charged and thus attracted to charge exchange electrode
1. At the charge exchange electrode the exposed particles
change their polarity of charge and migrate to the oppo-
sitely biased insulative layer 4. The imaging sense (i.e.,
direct or reverse) of the image on layers 4 (and 1) will
depend on the mode of such migration imaging utilized. That
is, lf a conventlonal PEP system is utillzed, a reverse
sense image will form at electrode 4 with exposed particles
migrating thereto. If a PIER system is utllized, the image
on layer 4 will be direct in image sense, with unexposed
particles migrating thereto. As indicated in Fig. 1, an
essential feature of prior art devices is th~t ~he velocity
Vp of the peripheral surface of layer 4 is substantially equal
to the translational velocity Vt of the electrode 2 and in a
dlrection so that the relative velocity between surface 4
and the image ~f lO, at the traveling contact zone between
electrodes, is substantially zero, i.e., little or no slipping
occurs between the contacting electrode surfaces. Various other
optical arrangements have and can be implemented including e.g.,
scanning a movlng image at a rotating, but non-translatlng,
electrode nip, or translating the electrode 1 with an image
supported thereon past a rotating, but non-translating
roller. The critical constraint is that there be a sub-
stantially zero relatlve velocity between the light image
and the imaged electrode to obtain a sharp registration of
the image to be reproduced. Thls result can be obtained in
a variety of ways other than those mentloned above. However,
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as noted regarding Fig. 1, heretofore it has also been
presumed that there should exist an additional constraint,
viz. a minimum, or zero, relative velocity between the
electrode surfaces during imaging. Thus the enlargement Or
the migration environment is substantially 1.0 according
to the definition set forth above. As previously noted,
above, the teachings of U.S. Patent Re. 28,260 indicate that
a slight relative velocity may desirably exist between the
electrodes (to induce dynamic stress on particles); however,
the caveat is provided that the relative velocity should not
exceed 10% of the traversing velocity Or the roller to avoid
image destruction.
Fig. 2 is an enlarged schematic view of a portion
of the interface zone, or development gap, of the electrodes
1 and 2 of the Fig. 1 device and is provided to illustrate
phenomena which I theorize to exist under operation in such
prior art devices. In Fig. 2 it is assumed that all parti-
cles exhibit a positive polarity charge in the dispersion 8
and thus migrate to charge exchange electrode 1 because of
the electrostatic rorce Or attraction between the positively
charged particles and negatively biased charge exchange
electrode. Particles 21 exemplify those particles which
remain on charge exchange electrode 1 (if assuming a PEP
process) because they have not been activated by exposure to
radiation of wavelength to which they are sensitive (e.g.,
magenta and cyan particles during exposure to a blue image
light). Particle 22 represents a particle which has moved
to electrode 1, exchanged charge and migrated substantially
to electrode 2 (e.g., a yellow pigment exposed to the blue
image light~. It will be noted that at this stage of com-
pletion of the process for the lllustrated image portion, a
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substantial quantity of positive polarity pigment remains
very closely proximate the electrode 1. In actuality many
more particles are involved; and the number Or particles
shown in particular sta~es are not intended to be directly
proportional to the actual results. However, the differently
numbered particles are representative of different effects I
theorize to be present; and, in this regard, it is significant
to note particularly particles 23 and 24 whlch are assumed
to be yellow pigments. Particles 23 are shown bearing a
positive electrostatic charge and thus being attracted
toward electrode 1, where they should exchange charge and
migrate to electrode 2. However, it is theorized that one
or more effects may limit this and control or prevent
increased migration and density. First, the accumulation o~
unactivated particles 21 may present an electrical barrier
between the charge exchange electrode and exposed particles
and thus prevent or reduce charge exchange by particles 23.
Secondly, the accumulation of particles 21 may present an
optical barrier or scattering layer which deters efficient
activation of the particles 23.
Let us consider now particles 24 which also are
assumed to be yellow ones that have been blue-light acti-
vated, exchanged charge at electrode 1 and commenced migra-
tion to electrode 2. I theorize also that one or more
efrects may deter efficient migration of these partlcles.
For example, the accumulation of positively charged parti-
cles at electrode 1 and negatively charged particles (migrated)
at electrode 2, as the process progresses decreases the net
electric field which propels the negatively-charged particles
3o to the image electrode. Thus migration ls reduced. It will
be appreciated that the illustration Or Fig. 2 is at one
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intermediate stage of the mechanism occurring to image the
suspension segment shown. As the mechanism proceeds the
effects described can be envisioned to compound their
limitative effect, e.g., if a yellow particle 23 could not
exchange charge due to blockage from effective contact with
electrode 1, it would present a blue-light-absorbing barrier
to other yellow particles attracted toward the charge
exchange electrode. Also such yellow particles add color
contamination to the blue (magentacyan) image formed by the
unexposed particles.
Regardless of which one or more of the above
contribute or control the migration limiting mechanism, I
believe a limitation does exist as to maximum density which
can be obtained in accordance with prior art procedures such
as have been described. By the present invention I provide
means and method to significantly reduce such limitation(s).
Specifically, I have provided means and method to
substantially minimlze the limiting effects descrlbed
above. To do this I utilize means and procedure for in-
creasing the non-lmaged electrode surface, and in so~e
embodiments the quantity of suspension, presented to the
imaged electrode while the light image is being recorded
thereon. A remarkable aspect of the present invention is
that the foregoing can be accomplished by providing sub-
stantial relative movement between the electrodes' surfaces
during imaging and that, although the image on the non-
imaged electrode is elongated, the resulting image on the
image electrode is of higher density and not smeared. It is
to be noted that the non-imaged electrode envisioned in
accordance with the present invention can be formed of
materials known in the art as either in~ecting or blocking
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electrodes. However, other arrangements, e.g., ones in
which the non-imaged "electrode" function is performed by a
moving dispersion transport web which passes over a stationary
electrode could be devised and should be deemed equivalent
to the disclosed non-imaged electrode structures.
Referring now to Figs. 3 and 4, one simplified
embodiment for practice of the present invention is illus-
trated. The apparatus denoted generally 30 comprises a non-
imaged electrode 31 having an electrically conductive,
lC optically transparent support 32 and charge exchange layer
33. At least the portion 33 of the electrode 31 is longer
than the dimension shown, as indicated by the omitted sector,
for purposes hereinafter to be described. The imaged electrode
35 comprises a conductive roller portion 36 which can have
an electrically insulative surface coating (not shown) and
which supports a surface layer 37 which can be the copy
sheet. An optical system 38 images a light image of an
original 39 to be reproduced onto an image zone 40 within
the electrophotosensitive pigment particle suspension 41
between the electrodes. Spacers 42 can be provided to
maintain a gap between the electrodes. A source 45 of high
voltage potential is applied between the electrodes.
Electrode 35 is mounted for translation across the pro~ected
image at imaging zone 40 and for rotation in a clockwise
direction, the rate and direction of roller translative
velocity Vt and peripheral velocity Vp being such as to
provide substantially zero relative velocity, or slipping,
between the imaged electrode surface at the image zone and
the contiguous light image portion focused in the plane
within the suspension 41. Thus it can be seen that if as in
the prior art, electrode 31 and the supported suspension 41
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were stationary, no relative movement exists between them
and each successively imaged portion of electrode 35.
However, in accordance with the present invention,
at least the portion 33 of the non-imaged electrode 31 is
moved at a velocity Vs in the ~direction opposite Vt so that
substantial relative movement exists between the electrode
surfaces at their field defining interface thereby sub-
stantially increasing the enlargement of the migration
environment. That is, in the illustrated embodiment, the
movement of electrode 31 can be controlled according to the
criteria hereinafter described to simultaneously present
fresh non-imaged electrode surface and suspension at the
imaging zone, thus reducing the migration limiting effec~s
described above and enhancing image density on the imaged
electrode 35.
Fig. 6 discloses another embodiment of the present
invention adapted to provide such controlled movement to the
non-imaged electrode. The apparatus 30' is similar to that
described with respect to Figs. 3 and 4; however the non-
imaged electrode surface comprises a continuous belt 33'moved around a path over electrode support and contact plate
32'. A uniform layer of dispersion 41 ls supplied to the
belt from supply 47, which can be configured as a convention-
al emulsion coating hopper at lts outlet. Also a cleaning
brush 48 can be provided to aid in removal o~ residual
suspension from the electrode surface. The rate of movement
of electrode belt 33' is controlled by drlve motor 49 ln a
conventional manner. Imaged electrode 35 ls supported for
transversing and rotary movement by support rail 50 which
can include a geared groove rack 51 cooperating with a gear
configuration on the support shaft for electrode 35 to
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impart the desired transversing and rotary movement to theroller from Drive source 55.
Fig. 5 discloses an alternative embodiment for
implementing the present invention. In this apparatus 60,
imaged electrode 61 is supported ~or rotation on a fixed
axis 62. The non-imaged electrode 64 of this embodiment
comprises a cylindrical drum which includes an inner shell
65 of electrically-conductive optically-transparent material
and an outer shell 66 of transparent material. As shown
electrode 64 also rotates on a fixed axis and is located so
as to pass proximate electrode 61 in a manner defining an
imaging zone therebetween. A reservoir 67 of dispersion 68
is provided so that roller 64, in its lower path, obtains a
uniform layer of the suspension ~or transport to the i~aging
zone. Potential source 69 is connected to the electrodes to
provide a migration inducing electrical field in the vicinity
Or the nip formed by the roller electrodes, i.e., so that
the field extends throughout the imaging zone. A convention-
al scanning optical system, only a portion o~ which is
illustrated, directs successive portions Or the light image
to be reproduced via mirror 70 and lens 71 lnto focus at the
lmage zone. Such optical systems are conventional, e.g.,
such as shown and described in U.S. Patents No. 3,609,028
and 3,628,85~, and in operation provide a ~lowing sequence
Or discrete portions of the image to be reproduced at the
image zone. In the Fig. 5 embodiment the successive image
portions are pro~ected ln synchronization with the rotation
Or electrode 61, e.g., by tlmed movement Or the original or
Or scanning mirrors and lenses, i.e., there should be
substantially zero relative velocity between the portion Or
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the imaged electrode 61 at the image zone and the aerial
li~ht image projected thereon. However, the drive 74 for
non-imaged electrode 64 moves that electrode at a rate such
that its peripheral velocity is suDstantially in excess o~
the peripheral velocity of ele~ctrode 61, thereby providing
fresh electrode surface and dispersion during each suc-
cessive image segment development stage. It will be noted
that the movement of the electrode surfaces at their inter-
face is in the same direction~ in distinction to the em-
bodiments shown in Figs. 3, 4 & 6. In such a same-direction-mode
it is necessary- that the velocity of non-imaged electrode
surface be greater than in the opposed-direction-modes,
previously described, in order to obtain the equivalent en-
largement of the migration environment; however it should be -
pointed out that any of the foregoing embodiments can be
implemented in either the same direction or opposite direction
modes if relative velocity of the electrodes is selected to
present fresh electrode surface and dispersion at the proper ¦
rate. It is also to be noted that electrodes 61 and 64 can
be chosen o~ materials suitable in character ~or provlding
the reproductlon sense deslred as output on the lmaged
electrode for either the PEP or PIER systems.
Having now described various exemplary structures
for practlce of the present invention, description of varlous
speciric applications o~ such structures will be useful to a
further understanding of the invention and to provlde
teachlngs Or useful and preferred relatlve velocity ranges
~or the inventlon.
Example I
3o This test, which lllustrates the use of the
invention in a PIER system, was per~ormed using the followlng
materials and apparatus:
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A dark charge exchange surface was prepared by
coating Dispersion A given below, on the conductive surface
Or an electrode composed of a poly(ethylene terephthalate)
film support bearing a thin, electrically conductive~ sub-
stantially transparent, evaporated nickel overcoat having an
optical density of 0.4.
Dispersion A
50.25 gm 2,4,7-trinitro-9-fluorenone (TNF)
80.40 gm Le~an~ 145 Bisphenol-A polycarbonate
sold by General Electric
2010.00 gm 60/40 mixture by weight of dichloro-
methane/1,2-dichlorethane
6.5% total solids
Dispersion A was coated on the electrode at a
coverage of 0.325/gm/sq. ft. and dried. The dried coating
was coated again with the same dispersion at the same
coverage and dried to obtain a final dark charge exchange
layer thickness of 5-lO microns.
A multicolor liquid imaging suspension was pre-
pared by mixing together in equal volumes the following
pigment dispersions: ¦
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Cyan Pigment Dispersion
0.5 gm Cyan Blue GTNF (a trade name of the beta form of
copper phthalocyanine, C.I. No. 74160, available
from American Cyanine).
150 gm admixture of equal parts by weight of Piccotex
100~ (a trade name of a styrene-vinyl toluene
copolymer available from Pennsylvania Industrial
Chemical Corp.) and Isopar G~, an
isoparaffinic aliphatic hydrocarbon liquid sold
by Exxon Corp. of New Jersey.
Milling time - 30 days
~a~enta Pi~ment Dispersion
0.5 gm Watchung Red B, a barium salt of 1-4'
methyl-5'-chloro-aæobenzene-2'-sulfonic acid
2-hydroxy-3-naphthoic acid, C.I. No. 15865,
available from E.I. DuPont de Nemours and Co.
150 gm admixture of equal parts by weight of Piccotex
lOOm and Isopar Gl~.
~illing time - 30 days
Yellow Pigment Dispersion
0.6 gm Indofast Yellow (a trade name of a flavanthrone
pigment, C.I. No. 70600, available from Harmon
Colors Co.)
150 gm of an admixture composed of 2 parts by weight of
Piccotex lOO'n to 3 parts by weight of
Isopar'~.
Milling time - 81 days
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The pigment dispersions were individually ball milled
in 250 ml brown glass bottles each containing 635 gm of
0.32 cm diameter sta;nless steel balls. The milling rate was
about 33 cm/sec.
The dark cbarge exchange surface as prepared above ;
was used in a manual migration imaging apparatus similar to
that illustrated in Figs. 3 and 4. A dielectric paper
covered, aluminum roller electrode was used to receive the
unexposed migrated pigment particles and was spaced to a gap
of about 50 microns above the dark charge exchange surface by
inserting poly(ethylene terephthalate) film spacer strips at
the edges of the roller between the dark charge exchange
surface and the roller. The dielectric paper was a paper
support coated with an insulating layer, with a dry thickness
of about 10 microns, of poly (vinyl butyral) resin available
from Shawinigan Products Corp. under the tradename of
Butvarm B-76.
Imaging was accomplished by simultaneously moving the
paper covered roller electrode at a translational velocity of
about 1.0 cm/sec across the dark charge exchange surface
bearing a .001 inch to .002 inch thick layer of the multicolor
liquid imaging suspension while pulling the dark charge
exchange surface (by hand) in the opposite direction at a
velocity of approximately 1.0 cm/sec, thus providing a
migration environment of 2Ø At the same time an electrical
potential of + 1~6 Kv was applied to the roller and a 600
footcandle white light exposure was made through a positive
color transparency to the liquid imaging suspension.
Observations:
The multicolor positive image formed on the paper
covered roller electrode was of high density and good quality.
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l&~3~8
For comparison purposes, a control image was formed using
the identical imaging method with the exception that the
dark charge exchange surfaced electrode was held stationary.
Average optical density measurements ob~ained from the test
image and the control image arè tabulated below:
IMAGE RED DENSITY BLUE DENSITY GREEN DENSITY
. ~
Control .25 .35 .35
Test .50 .65 .75
Example II
A dark charge exchange surface was prepared as
described in Example I.
A cyan pigment dispersion was prepared from the
following formulation:
0.7 gm Cyan Blue GTNF
150 gm admixture of equal parts by
weight of Piccotex 100 and Isopar G~
Milling time - 28 days
The cyan pigment dispersion was ball milled in a
250 ml brown glass bottle filled with 625 gm of 0.32 cm
diameter stainless steel balls.
Imaging was accomplished as described in Example I,
except that the exposure was made through a red Kodak
Wratten Filter No. 2g.
Observations:
The test image formed on the paper covered roller
electrode was a positive and the measured average red density
was higher than the density of a control image formed by
holding the dark charge exchange surface-imaging electrode
stationary.
Imag~ Average Red Density
Control 0.45
Test -75
_ _ _
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. . .
`
Example III
This example was désigned to show that the density
of a PIER image is a function of the relative velocity
between the imaged and the non-imaged electrode surfaces.
A dark charge exchange sur~ace was prepared as
described in Example I. A bottle of cyan dispersion described
in Example I was prepared. ~o this dispersion about 5 ml of
Isopar ~ was added after the 30 day milling period to
reduce dispersion viscosity. Imaging was accompllshed using
a processing configuration similar to that shown in Fig. 6
except that the charge exchange electrode was ~ed from a
supply to a take-up roller in the same direction as the
translation of the imaged electrode, i.e., same direction
mode of operation. Also the dispersion was hand applied as
in Example I. The test object consisted of a 1 cm x 1.2 cm
black patch having clear background. A Carousel pro~ector
provided a 1200 rc light intensity at the plane of the test
ob~ect. The light exposure was 1200 fc (white tungsten)
through a red Kodak Wratten Filter No. 29, through a black
and white transparency and then through the 0.4 ND N1 support
of the dark charge exchange sur~ace. The roller receiver
was held at an electrical potential of about +1.5 KV.
A series o~ prints were made with a roller trans-
lational velocity and roller peripheral velocity Vp of about
0.71 cm/sec. Prints were made at dark charge exchange,
l.e., non-imaged electrode, lateral velocities Vs of 0,
- 1.65 cm/sec, 2.2 cm/sec, 2.3 cm/sec, 2.9 cm/sec, 3.3 cm/sec,
and 3.8 cm/sec.
Another series of prints using the above-mentloned
cyan dlsperslon diluted 1:1 by volume with Isopar ~ were
made at velocitles Vs o~ 3.4 cm/sec, 5.o8 cm/sec and 6.4 cm/sec.
For this series of images the roller translatlonal veloclty
Yt and perlpheral velocity Vp were 1~4 cm/sec.
___
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. . . _ _ , . .
3~
Observatlons:
The images formed on the paper covered
roller receiver electrode had the same image sense as the
original test ob~ect. The measured average image densities
of the block pattern image formed at each surface velocity
are tabulated in Table II for the .71 cm/sec roller veloclty
and in Table III for the 1.4 cm/sec roller velocity.
Table II
. I
Surface Velocity Avg. Red Density . .
10 1.65 cm/sec 0.75
2.2 ~ 1.00
2-3 0.90 .
2.9 1.1
3.3 1.20
3.8 1.40
3.8 1.45
Table III
Surface Velocit~ Avg. Red Densit~
3 4 1.10
5.1 1.55
5.1 1.60
6.4 1.80
The maximum density (DmaX) as a function of surface
velocity Vs for each roller translational velocity Vt is
plotted in Fig. 7. The maximum density as a function of
migration envlronment enlargement is plotted in Fig. 8.
Example IV
.
This example was designed to illustrate the
rormation of high density three color PIER images using
' ;
~ 23-
moving surface processing. The same apparatus described in
Example III was used but in opposed-direction-mode.
In this example the test ob~ect was a color trans-
parency which includes cyan, magenta, yellow, and neutral
patches. The exposure entering the test ob~ect was about
1500 fc originating from a Carousel projector.
A trimix liquid imaging suspension was prepared by
mixing together the following pigment dispersions:
Cyan Pigment Dispersion
4.0 gm of cyan particles composed of the beta form
of copper phthalocyanine, C.I. No. 74160, available from
American Cyanamid under the trade name of Cyan Blue GTNF.
450 gm of a mixture of a styrene-vinyl toluene
copolymer (available under the trade name of Piccotex 120
from Pennsylvania Industrial Chemical Corp.) and an iso-
paraffinic aliphatic hydrocarbon liquid sold under the trade
name Isopar ~ by Exxon Corp. of New Jersey. This 450 gm
admixture consists of the ratio 180/270 of Plccotex 120 and
Isopar ~.
The cyan pigment dispersion was ball milled for
about 6 weeks in 950 ml brown glass bottles half filled with
0.32 cm diameter stainless steel balls. The bottle surface
milling velocity was about 22.5 m/min.
Magenta Pigment Dispersion
1.0 gm magenta particles composed of Watchung Red
B, a barium salt of 1-4'-methyl-5'-chloro-azobenzene-2'-
sulfonic acid)-2-hydroxy-3-naphthoic acid, C.I. No. 15865,
available from E.I. DuPont de Nemours and Co.
150 gm mixture of Piccotex 100 and Isopar ~ con-
sisting of e~ual parts.
24-
3i3~8
The magenta pigment dispersion was ball milled for
about 4 weeks in 250 ml brown glass bottles filled with
635 gm of 0.32 cm diameter stainless steel balls. The
bottle surface milling velocity was about 22.5 m/min.
Yellow Pigment Dispersion
1.5 gm of yellow particles composed of a flavan-
throne pigment, C.I. No. 70600, available from Harmon Colors
Co. under the trade name of Indofast Yellow.
150 gm of 2 parts by weight of Piccotex 100 to 3
parts by weight of Isopar ~
The preparation was the same as the magenta
pigment dispersion except the dispersion was milled for 8
weeks.
The final trimix liquid imaging suspension was
prepared by mixing the above C, M, Y dispersions in the
ratio 1/1/1 by volume.
Observations:
The results of this example are summarlzed in Fig.
9. DmaX for the cyan, magenta, yellow and neutral patches
were plotted as a function of migration environment enlarge-
ment. For each color, the density increased with increasing
environment enlargement. It was also observed that improved
background (Dm1n) occurred using moving surface processing
compared to prints formed at an environment enlargement of
1.0 as used in prior art devices. In addition it was observed
that less exposure is required in moving surface processing.
Example V
This example was designed to illustrate the
utility of enlarged migration environment processing in PEP
migration imaging. This example utilizes a negatively
biased roller receiver which allows a positive image repro-
duction to be formed on the image electrode.
_
-25-
3~
.'
.
A cyan monocolor dispersion was prepared as follows:
Cyan Pigment Dispersion
0.5 gm Cyan Blue GTNF pigment particles
150 gm Isopar ~
It should be noted thàt no polymer is incorporated
in the carrier liquid as in the previous examples. The
dispersion was prepared as described for the magenta dis-
persion described in Example IV.
The non-imaged electrode comprised a poly(ethylene
terephthalate) film support bearing a thin, electrically
conductive, substantially transparent, evaporated nickel
overcoat having an optical density of 0.4.
Imaging was accomplished using the opposed-mode
processing and the apparatus configuration described in
Example IV. The test ob~ect consisted of a black-and-white
transparency having clear letter areas. A Carousel pro-
~ector provided a 2000 fc light intensity. The exposure was
filtered through a Kodak Wratten Fllter No. 29 and the
0.4 ND Ni support.
In thls example, the paper covered roller receiver,
image electrode, was held at an electrical potential of
about -1.5 KV, so that inltially positively charged particles
were flrst attracted to the image electrode.
A serles of prints were made with a roller velocity
of about 0.7 cm/sec at various lateral veloclties of the Ni
electrode. The procedure was similar to Example III.
Observatlons:
The cyan lmages formed on the paper covered roller
electrode had the same lmage sense as the original test
ob~ect. The measured average image densities of the roller
image formed at each surface velocity are plotted in Fig.
10. The data points showed scatter but the trend of the
_ _ _
-26-
3~
data shows higher image densities at higher relative velocities.
It is also significant to note that the present invention
serves to provide reduced background densities compared,
e.g., an enlargement environment of 1Ø This effect is
believed to be caused by the rèmoval of activated particles
by the non-image electrode before a second charge exchange
occurs.
Considering the foregoing Examples and my other
work with the present invention, it appears that image
density will increase in proportion to the increase in
enlargement of the migratlon environment. Optimum ranges of
such enlargement will depend to some extent on the image and
background densities desired from a system and upon other
system parameters such as the concentration of marking
particles in the image dispersion and thickness of the dis-
persion layer. In some applications an image density of 1.0
has been found acceptable; and in monocolor dispersions~
it has been shown above that an enlargement of about 1.5 can
provide this result. The slgnificant factor i9 that some
substantial enlargement be provided. For trimix dispersions
higher environment enlargements would normally be utilized
as can be seen from Fig. 9. In a system using dispersions
of concentrations such as described in the foregoing Examples,
I have found an enlargement of migration environment of
about 3 to be highly desirable for monocolor imaging while a
higher enlargement of about 5 to be preferred for tricolor
dispersions. The upper enlargement limit for practice of
the invention thus far appears to be only a matter of
machine construction.
For example, Fig. 11 illustrates an embodiment of
the present invention incorporating an improved feature for
[378
..
minimizing rubbing between electrodes in implementations
where such phenomenon occurs and is detrimental.
Specifically, it was observed that in certain
moving surface processing apparatus configurations consider-
able rubbing may occur during processing between the roller
receiver and the moving charge exchange electrode surface.
Since relative motion is required between both electrodes
for effective moving surface processing, the rubbing can
result in abraided and smeared images on the roller receiver.
The cause for such rubbing is believed to be the
electrostatic force of attraction between the oppositely
blased electrodes, l.e., an electrostatic force of attraction
between the positive biased roller receiver and the negative
biased charge exchange electrode pulls both electrodes
together resulting in rubbing.
The apparatus shown in Fig. 11 obviates this
problem by providing a counter force which reduces the force
of attraction between the electrodes. The counter force ls
provlded by applylng an electrostatlc voltage between the
semltransparent conductlng support layer 83 Or the movlng
charge exchange electrode 82 and an addltional semitrans-
parent conducting layer 84 positioned on a support 85 below
the glass support 81 Or layer 82. The polarity Or this
counter voltage 88 is chosen so that the addltional con-
ducting layer 84 is positive with respect to the charge
exchange electrode 82. In this manner an electrostatic
force Or attractlon exlsts between these two electrodes
whlch is dlrected opposite to the electrostatlc force exlsting
between the roller receiver and the charge exchange electrode.
Thus by ad~usting the counter voltage source a voltage is
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___
.
3C~
obtained above which no force of attraction is observed
between the roller and DCES during processing.
The invention has been described in detail with
particular reference to certain preferred embodiments thereof,
but it will be understood that `variations and modifications
can be effected within the spirit and scope of the invention.
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