J1me 7, 1966
F. A. SCHWERTZ
3,254,998
INDUCTION IMAGE FORMATION
Filed April 2, 1962
INVENTOR.
FREDERICK A. SCHWERTZ
,3
QQQ
ATTORNEY
United States Patent 0 "
3,254,998
Patented June 7, 1966
l
2
3,254,998
radiation exposure of an original copy thus according
more ef?cient, expeditious image formation than known
Frederick A. Schwertz, Pittsford, N.Y., assignm- to Xerox
plate structures as an inducing member, the invention
INDUCTION IMAGE FORMATION
gorporation, Rochester, N.Y., a corporation of New
or r
‘
by the prior art. In addition by employing multiplying
accords increased speed sensitivity in the inducing of
electrostatic latent images onto an insulating rectifying
layer. The image thus induced may thereafter be utilized
in any of the conventional forms of xerography.
Accordingly, the instant invention has for an objective
10 the formation of electrostatic latent images on insulating
In the process of xerography, for example, as ?rst dis
rectifying layers simultaneous with an exposure of area
closed in Carlson patent 2,297,691, issued October 6,
of a photo-responsive member adjacent and across said
1942, a zerographic plate comprising a layer of photo
layer. In accordance with this objective, images formed
Filed Apr. 2, 1962, Ser. No. 184,326
8 Claims. _(CI. 96-11)
This invention relates to xerography and in particular‘
to improved method and apparatus for charge deposition.
conductive insulating material on a conductive backing
employing high speed multiplying xerographic plates are
is given a uniform electric charge over its surface and is 15 induced into an adjacent insulating rectifying layer and
then exposed to the subject matter to be reproduced, usual
there preserved for further processing.
ly by conventional projection techniques. This exposure
It is a further object of the invention to provide im
discharges the plate areas in accordance with the radia
proved method and apparatus for induction formation
tion intensity that reaches them, and thereby creates an
of image patterns on insulating rectifying layers.
electrostatic latent image on or in the photoconductive 20
It is a further object of the invention to provide im
layer. The latent image thus formed may thereafter be
proved novel method and apparatus for induction for
utilized, as for example, by being developed with an elec
troscopic powder which may be af?xed to the xerographic
mation of image patterns on insulating rectifying layers
during exposure.
plate, or optionally transferred to a secondary support
It is a further object of the invention to form induced
surface on which it is affixed, or the latent image may be 25 charge patterns on insulating rectifying layers from pat
utilized without development as though sensing or for
terns of activating radiation having a lower radiation in
transfer to other surfaces by techniques known in the
tensity than was required for image formation by method
and apparatus known heretofore.
art.
Various means of charge deposition are known in the
It is still a further object of the invention to device
art of xerography including corona charging and a form 30 novel apparatus and method to induce charges on insulat
of induction charging as disclosed, for example, in the
above-cited Carlson patent for depositing charge onto a
xerographic plate. After depositing a charge uniformly
onto a xerographic‘plate, it is usual to discharge the plate
selectively on exposure to radiation of predetermined
intensity as to form an electrostatic latent image.
Recently there has been discovered a novel method of
inp rectifying layers in predetermined pattern con?gura
tionr formed substantially simultaneously with exposure
of a high speed xerographic plate.
Embodiments of the invention are illustrated in the
following drawings in ‘which:
FIG. 1 is a sectional view of an embodiment of ap
paratus in accordance with the invention; and,
FIG. 2 is a sectional view of an embodiment of a
depositing electrostatic ‘charge onto insulating surfaces
continuous automatic apparatus in accordance with the
by principles of induction wherein the chargeable mem
ber comprises an insulating layer of current insulating 40 invention.
Referring to FIG. 1, there is illustrated apparatus in
rectifying material that preferentially conducts one polar
cluding support means 10 to support original copy 11 to
ity of charge carrier and like a diode, conducts in one
be reproduced. Copy 11 is exposed through a conven
direction only. This prior method ?rst charges or al
tional objective lens 12 supported in a suitable light-tight
ternatively charges and exposes a xerographic plate con
ventionally, which charge is then employed to correspond 45 housing 13 enclosing the radiation and light sensitive mem
bers utilized for image formation. Supported in the focal
ingly charge the insulating rectifying layer.
plane of the lens is a photoconductive member, gen
In the art of xerography, most plate members when
erally designated 14, that may comprise, for example, a
charged respond to radiation in a manner such that each
xerozgraphic plate having a p‘hotoconductive layer 15 of
the plate surface produces less than one charge carrier 50 vitreous selenium overlying a conductive member which
unit of radiation energy, such as a photon, exposed to
_to dissipate the charge. There are also known plate mem
bers which result in multiplication effects. These effects
are attributed to solid state qualities that cause a multi
in this embodiment is transparent and may comprise a
transparent coating 16 such as tin oxide on an insulating
glass transparent base 17.
'
The induced image ‘is to be formed on an insulating
plication of charge carriers so that the plate exhibits in
creased speed sensitivity when exposed to the same unit 55 rectifying plate, designated 22, that may, for example,
comprise ‘a vitreous selenium layer 23 supported on an
interfacial layer 24 such as copper oxide, in turn overly
ing a conductive backing member 25.
intensity of radiation as compared to conventional plates,
A potential from a source 30 is applied across the
or contra, effects more rapid dissipation on exposure at
the same level of radiation intensity. These multiplying 60 sandwich as shown for a predetermined programmed
period controlled by a suitable timing device 31 to form
plates, however, although exhibiting greater sensitivity
an induced electrostatic latent image on the surface of
‘than conventional plates, are also characterized by high
of radiation energy. This then results in an equivalent
charge dissipation of the plate on exposure to a lower
or rapid dark decay properties.
That is, these multi
plying plates are unable to retain an applied charge in the
layer 23. On energizing of the timer, there is applied
a potential between the conductive layers while simultane
absence of radiation, such that images of charge formed 65 ously, through relay 32, lamps 33 are energized from a
during exposure decay too rapidly to be developed.
Now in accordance with the instant invention, there is
110 volt source to illuminate the pattern of copy 11.
As
the copy pattern is illuminated, the light image-of the
copy renders layer 15 selectively conductive in pattern
con?guration corresponding to the light areas of the copy
provided novel improved method and apparatus for in
ducing charge into insulating rectifying layers. By means
70 to form an electrostatic latent image on the interface sur
of the invention, electrostatic latent images are induced
face of layer 15. The pattern thus formed at the interface
onto the insulating rectifying layer simultaneous with a
3,254,998
3
4 .
is effective to induce on the surface of layer 23, an op
67 at an erase station 74.
posite polarity charge in position in adjacent areas across
mechanism, plate power supply, and erasure mechanism
may be placed in inoperative condition and the apparatus
the areas of charge on surface 15 and conforming also
to the configuration of the pattern of copy 11. After
run as a copy duplicator.
Alternatively, the exposure
That is, following movement
separating the plate 22 from plate 14, the electrostatic
of drum 35 past the image forming station 50, there
latent image induced on the surface of layer 23 can be
utilized for development, as in the process of xerography,
can be used to subsequently induce image patterns onto
exists on the drum surface an induced image pattern of
secondary insulating rectifying layers to be described, or
insulating rectifying layer is supplied from a supply spool
can be used for such other utilization purposes known
to those in the art. Thus, following the application of
a selective ?eld pattern of an original image, there is in
duced a charge pattern on the insulating rectifying layer
conforming in con?guration to the pattern of copy 11.
charge. This pattern is advanced to induction image
stations 51 and 52 whereat a web member 53 having an
70 and moves around a roller 71 which, as illustrated in
this embodiment, is maintained at ground potential.
Speed of movement of members 53 is synchronized
with the speed of rotation of drum 35 and as the drum
surface contacts the surface of web 53, charge patterns
The image formed on layer 15 will remain on its surface 15 previously induced on the‘ drum surface cause re-induc
for a period depending on the decay rate property of
tion onto the surface of plate members 53. The insulat
the photoconductor used. If layer 15 has a low decay
ing rectifying layer of web 53 may in this embodiment
rate, the image can be reused for subsequent induction
comprise a layer of zinc oxide in an insulating binder
charging without the necessity of reg-exposing under an
applied ?eld. On the other hand, even with a low decay
rate characteristic, if it is not desired to reuse this image,
overlying a conductive backing such as foil or paper in a
conductive condition or the like. With a positive charge
pattern on the surface of drum 35, negative charge pat
it can be erased by \a uniform illumination of light from
terns conforming in con?guration to the image pattern
lamps 34 under control of a suitable On-Off switch.
projected will be formed on the surface of members 53
Reference is not had to FIG. 2 in which is illustrated
at the charge induction stations 51 and 52.
an embodiment of an automatic apparatus employing the 25
Following image induction at stations 51 and 52,
instant invention. An insulating rectifying layer in the
members 53 are advanced out of contact with the surface
form of a cylindrical drum, generally designated 35, in
of drum 35 and are advanced through processing sta
accordance with the invention may comprise, for example,
tions 72. At the process stations, the charge patterns on
a vitreous selenium layer 40 overlying a copper oxide
the surface of 53 may be developed and fused to form
interlayer 41 on a conductive aluminum base 42 and 30 duplicate hard copy or may be otherwise utilized as, for
which drum is mounted for rotation about a shaft 43
example, through scanning or the like to create electrical
that is driven continuously by a motor M—l. Drum 35
' signals for utilization as for display on cathode-ray tubes
is driven in the direction indicated by the arrow and
or the like. Following passage through the process sta
moves ?rst through an image forming station 50, to be
tions, members 53 are advanced onto takeup spools 73.
described, and next to image induction stations 51 and 35 As is well known in the art, these webs may be cut into
52 whereat the induced image formed at station 50 is
appropriate lengths and stacked rather than fed to take
utilized for forming secondary induction images on plate
members 53 having an insulating rectifying layer of op
posite polarity characteristics to that of drum 35 as will
be understood.
'
Original copy that is to be reproduced may, for ex
ample, be contained on a continuous micro?lm web,59
although any conventional copy source and projection
technique known in the art of xerography or photography
can be employed in the alternative. The ?lm web is
continuously advanced by means of a motor M—2 from
a supply reel 60 to a takeup reel 61 inbetween which it
passes an illumination source comprising, for example,
a lamp 62 and a condenser lens 63. The image pattern
up spools as shown.
Alhough two charge induction stations are shown, it
should be realized that in the concept of the instant in
40 vention the image on drum 35 is in no way affected while
the charge is induced into an adjacent member such as
web 53. Accordingly, any number of stations may be
positioned around the charge inducing member, which in
this instance is drum ,35, to induce charge into adjacent
members substantially any number of times. After pass
ing the induction stations, drum 35 is advanced through
an erase station 74 whereas the insulating rectifying layer,
which is also photoconductive, may be illuminated with
light to erase the charge pattern from its surface and
is optically projected by an objective lens 64 which may, 50 thus prepare'the drum for recycling.
if desired, have a focal length adapted to effect projection
In each of the described embodiments, it has been
at a desired magni?cation ratio. The light image is pro
considered that the insulating rectifying material is
jected downward in this embodiment through a projection
chosen on exposure to generate .a range of charge carries
slit 65 onto an advancing p‘hotoconductive member 66,
sufficient to‘operate as described. Where the circum
that may be constructed similarly as member 14 of FIG; 55 stances require, the range may be enhanced by applying
I, and
continuously energized from a power source
selective levels of heat or radiation as by employing
69. Drum 35 moves at a synchronous rate with the rate
a transparent substrate 25 through which light can be
of the projected image and member 66 is driven through
applied in conjunction with the exposure step. Thus
a suitable gear-Wheel 68 from motor M—l at a linear rate
identical with the peripheral rate of drum 35. For il
lustrative purposes, member 66 is shown of ?nite length
which will necessitate its being returned to a leftmost
starting position between exposures out of physical con
it was found thatwhen using a 11/2 mil zinc oxide plate
formed of a zinc oxide photoconductor in a silicone
'binder on an aluminum substrate, spaced opposite a
NESA (tin oxide) backed vitreous selenium plate on a
transparent glass substrate, a satisfactory image was in
tact with drum 35 if the latter continues to rotate. Al
duced on the zinc oxide surface. The air gap between
ternatively, member 66 can be constructed of ?exible ma 65 the two surfaces was believed to be less than about ?ve
terial or connected rigid segments and made endless for
microns in thickness and as uniform as possible. The
continuous recycling. In the latter instance there will
image was formed of a photographic negative placed on
the glass substrate of the selenium and rear illumination
illumination (not shown) to eliminate unwanted patterns
from a high intensity light source of about 4500 ang
remaining on surface 15 after utilized for induction, and 70 stroms effectively placed a shadow image on the selenium
means to offset the endless member after image formation
surface. Simultaneously, a potential on the order of ap
around‘the projection path as to avoid interfering with
proximately 600 volts was connected to the substrates
be required an image erasure means, such as a source of
the image being projected.
Operation of the unit can be continuous with drum 35
with the negative pole being connected to the aluminum
substrate and the positive pole connected to the NESA.
being constantly recycled after erasure by an erase unit 75 The voltage was applied for a period of approximately
3,254,998
5
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30 seconds after which the two electrodes were shorted
since a ?ow of positive charge through the zinc oxide
binder layer would be required. In this latter instance, a
out and the plates separated. After separation, a nega
tive voltage of greater than 200 volts was found to have
been induced onto the zinc oxide surface. This charge,
which constituted a latent electrostatic pattern of the
p-type semiconducting storage or insulating rectifying
layer would be necessary to achieve a similar result.
In general, the induction of a positive electrostatic im
negative image, was developed by well-known techniques
age from the photoconductor requires a semiconducting
of xerography and resulted in a sharp, dense image as is
storage layer or insulating rectifying layer in which the
commonly associated with a large negative charge. An
available current carrier is the electron. Conversely, for
opposite positive charge was formed on the selenium
the induction of negative electrostatic images from the
surface.
10 photoconductor, the available current carrier must be the
Brie?y ‘as understood, there are basically two forms
positive hole. Therefore, with a proper selection of appro
of insulating rectifying materials, those which are pref
priate materials, a latent image having a polarity of choice
erentially conductive with a majority of charge {carriers
opposite the photoconductor may be induced and subse
for positive charge carriers (holes), are termed “p” type,
quently utilized as is conventional in the xerographic proc
and those conductive for negative charge carriers (elec 15
ess.
trons) are termed “11” type.
While zinc oxide had been prominently mentioned as
the rectifying layer with which the process of the invention
Some materials may re
spond in varying degrees to either form of charge carrier
but being substantially insulators as all insulating rectify
ing layers contain virtually no intrinsic charge carriers
but rather possesses only those charge carriers injected 20
therein from an external source or generated therein by
may be carried out, other semiconductors which will form
highly rectifying contacts to a conducting support, and
which need not be inherently photoconductive, would also
form suitable storage or insulating rectifying layers. In
other Words, it is essential that current flow into the semi
the activity of activating radiation. The zinc oxide bind~
er layer has the apparent property of being “it” type. In
conductive layer or insulating rectifying layer only when
any event negative charges attracted to the selenium
biased in the forward direction by the electrostatic image
charge are injected from the binder layer substrate, pass 25 being formed on the photoconductive surface that is ef
through the binder layer, and 1are trapped at the ‘binder
fective to induce the image on the surface of the insulat
layer top surface. These immobilized charges on the
ing rectifying layer.
binder layer become ?xed when the binder plate and the
The insulating rectifying layers may contain the de
selenium plate are separated in the dark. The binder
sired properties for use in the instant invention or they
layer, therefore, being an insulating rectifying layer, has 30 may be so rendered. Thus Where the insulating layer is it
self insufficiently rectifying, i.e., conducts both polarities
equally or is only slightly p-type or n-type, recti?cation
come trapped near or at the top surface. The potential
may be supplied by forming a highly rectifying barrier
thus induced on the insulating recti?er layer can be com
layer between the insulating layer and the conductive
parable to normal xerographic potentials since it is known 35 backing which injects charge carriers into the insulator
that the series capacitance of the insulating recti?er layer
or alternatively, the layer may be doped. As stated above,
during the photoconductor exposure, while biased in the
zinc oxide is strongly n-type so that modi?cation of the
conductive direction, is effectively in?nite. The actual
material either by doping or by the interposition of a bar
capacitance of the insulating recti?er layer, which be
rier layer between the zinc oxide and the conductive
the property that application of a small electrostatic ?eld
causes charges to be injected from the substrate to be
comes etfective on dis-assembly, can be made comparable 40 electrode are unnecessary for utility herein.
with the capacitance of normal xerographic plates.
Therefore in accordance with the invention, semi-con
ductive ?lms orrinsulating rectifying layers have been
found for which the conductivity differs substantially de
pending upon the direction of the impressed electric ?eld.
As shown by the above example, plates comprising a ?lm
Vitreous
selenium is p-type and commercial xerographic plates on
an aluminum backing may be used as describedéherein.
However, as a properly prepared selenium layer is only
slightly p~type, the use of such unmodi?ed layers results
in moderately long charging times. By the addition of
a rectifying barrier layer such as cuprous oxide between
the vitreous selenium and the conductive backing, the
found to sustain a negative surface charge and are known
charging time ‘may be reduced to the order of 1 or 2
to sustain negative surface charge many times longer than
seconds. Alternatively, the selenium may be doped to
'they will support a positive surface charge. In other 50 either render it highly p-type or even to reverse the polar
words, this ?lm can be made to serve as a resistor-diode
ity of the major charge carriers to render the material n
conducting electrons from the base to the surface at a
ty-pe. Thus, as disclosed in U.S. 2,863,768, when alloyed
much greater, rate than in the opposite direction under
with arsenic trisul?de, selenium becomes highly n-type
‘an equal but. opposite ?eld. Further, such conduction
while still being an elfective photoconductive insulator. .
of zinc oxide in ‘a binder coated on aluminum have been
will take place Without light exposure but only because 55 Tellurium is also a suitable additive to selenium to render
of the applied ?eld. The distribution of negative charges ,
induced on the zinc oxide surface is a mirror image of
a vitreous selenium layer n-type. The selenium may also
be rendered more highly p-type by the inclusion of very
the positive electrostatic image formed on the selenium
minor amounts of halogen. In the case of doping with a
surface. These negative charges remain on the zinc oxide
halogen, care must be taken to prevent the inclusion of
surface and form a negatively charged electrostatic latent 60 too much impurity which would render the material too
image. When the separation is carried out in air, some
conductive for use as a photoconductive insulator.
air breakdown has been found to occur causing the nega
As should be apparent, substantially all known photo
tively induced image to be of a reduced magnitude than
conductive insulating layers can be employed in connection
that formed on the selenium plate. Where separation is
with this invention, either intrinsically or as modi?ed ac
carried out in a vacuum or with a controlled potential, 65 cording to the teaching herein, and included Within this
this presents no problem. That is, a control potential may
group, for example, are semiconductive materials cooled
‘be provided between the rbases during separation as, for
below the temperature necessary for thermal generation
example, disclosed in copending application Serial vNo.
of charge carriers therein which thus act as insulators.
747,542, ?led July 9, 1958, now U.S. Patent No. 3,057,
Therefore in the instant invention, it is essential that
719, in the names of Walkup and Byrne.
70 the charge inducing member induce a developable charge
density on the insulating rectifying layer. To accomplish
Thus in the zinc oxide binder layer, electric current is
carried by electrons and holes make no appreciable contri
this, there must be a su?icient magnitude of potential avail
bution to the current. If the latent image on the selenium
able from a potential source and the intensity level of the
> activating radiation must be sufficiently high to render
surface were composed of negative charges, the process
described above ‘would not work as well with Zinc oxide, 75 the charge inducing member sufficiently and selectively
3,254,998
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conductive in an allotted charging time. Most photocon
ductors employed in xerography, such as vitreous seleni
um, have a quantum e?iciency of somewhat less than unity.
This means that, at best, for each photon of light which
Pressure exerted on the backs of the respective plates
has found to reduce the air ?lm thickness to accord in
duced potentials of higher order. Also the use of insulat
ing liquids of high speci?c conductive capacitance in place
strikes a xerographic plate, one “electron” or “hole” is
of the air ?lm has also been found to increase the gap
removed.
capacitance.
By obtaining charge-carrier multiplication
.
.
whereby each absorbed photon will produce- many charge
carriers within the plate, there results quantum e?iciency
greater than unity. In other words, by carrier multiplica
The advantages of the invention should be instantly
apparent in that it accords expeditious induction of elec
trostatic latent images on insulating rectifying layers si
tion is meant causing ?ow of more than one electronic 10 multaneous with exposure while according increased sensi
charge (in excess of dark current) by the action of each
tivity of response to radiation by the use of multiplying
photon of light energy incident on a light sensitive medium.
plates as the charge inducing member. At the same time
This phenomenon of multiplying plates and their struc
by means of the invention, “wear and tear” on the delicate
tures are disclosed in copending application, Serial No.
surface of the inducing photoconductive insulator is large—
714,929, ?led February 12, 1958 in the name of J. Bardeen 15 ly eliminated. That is, since the necessity for developing
and now Patent US. 3,041,166.
the image on the inducing photoconductor, transferring
The instant invention when used with multiplying plates
of the type described in the above referred to Bardeen
the developed image and cleaning off the residual powder
is eliminated, physical damage to a fragile surface such
patent captures the image while preserving speed. It is
knownthat the time necessary to induce a charge onto the 20
surface of an insulating recti?er layer to a potential within
as vitreous selenium is at an absolute minimum.
In the above description, there is disclosed a novel
method and apparatus for induction-charging of an in
l/e of its ?nal value, is the product of the resistivity of
sulating rectifying layer. From the discussion of the in
the material, measured in the conductive direction, times
vention in connection with the drawings, there will be
the dielectric constant of the material expressed in MKS
units. Because of this factor, it is necessary to either main 25 suggested obvious modi?cations and variations to those
skilled in the art and such variations and modi?cations
tain contact for an adequate time to effect desired charge
are intended to be included in the scope of this invention
density or to provide a greater charge density in the
and, it is intended to cover the invention broadly within
charge inducing member and allow charge to be induced
for less time as required for equilibrium, to result in a
the claims. For example, in FIG. 2, a ?at plate could
charge deposit on the insulating rectifying layer equal to 30 be substituted for drum 35. Also, for a full frame ex
what is desired. Now however, in accordance with the
instant invention, the induction time may be decreased
posure, a ?at plate could be stopped momentarily during
exposure instead of a continuous slit exposure as illus
by utilizing multiplier photoconductors as charge induc
ing members having a quantum e?iciency greater than
trated.
What is claimed is:
unity.
'
35
1. A method of forming an electrostatic latent image
The multiplying e?ect is produced when using photo
of original copy by induction on a ?rst plate comprising
conductors such as cadmium sul?de and cadmium selen
an insulating rectifying layer supported on a conductive
ide. Therefore, in the instant invention, the photocon
substrate and capable of allowing ?ow of current in a
tive layer designated 15 can be constituted of a pho
?rst direction and substantially insulating in the reverse
toconductive material such as cadmium sul?de to achieve 40
a desired quantum multiplication. With such an arrange
ment, less light is required to achieve the desired charge
direction including:
(a) placing a second plate comprising a photoconduc
tive insulator overlying a conductive radiation trans
density on the surface of plate'23. By this means the
mitting substrate with the surface of the insulator
rate of induced image formation, especially in automatic
in closely spaced substantially contiguous relation
machines, can be increased dependent on the multiplica
ship to the surface of a ?rst plate on which an image
tion effect available with the photoconductor employed.
Thus, the handicap of high dark decay characteristics
associated with these multiplying plate structures is im
is to be formed;
(b) connecting a charging potential between the sub
strates of said plates; and,
(c) while said potential is connected exposing said sec
ond plate to an activating radiation image of original
material in the instant invention in which it is not neces
sa'ry that the charge formed on the surface of the induc
ing member be developable. Rather, in accordance with
the invention, retention of charge by the inducing mem
ber may totally be unnecessary beyond being utilized to
copy for a time period su?icient to inducev a charge
pattern of the copy on the surface of the ?rst plate.
2. The method according to claim 1 in which said sec
induce an image pattern onto an insulating rectifying
ond plate comprises a material having a quantum e?icien
layer. Therefore in ‘accordance with the instant inven 55 cy greater than unity.
tion, utilizing simultaneous application of ?eld and ex
_ 3. A method of forming an electrostatic latent image
posure, a photoconductor having a quantum ef?ciency of
of original copy by induction on a ?rst plate comprising
greater than unity may be utilized to advantage to in
an insulating rectifying layer supported on a conductive
duce charge patterns on insulating rectifying layers in
substrate and capable of allowing ?ow of current in a
place of other photoconductors usually used in commer 60 ?rst direction and substantially insulating in the reverse
cial xerography.
Since the highest possible image potential or charge
on the insulating rectifying layer is the desired goal, the
direction including:
(a) placing a second plate comprising a photoconduc
space between surfaces ‘during the induction formation
should be as small as possible. Since the induction image 65
should faithfully represent the original image, all capaci
In the case of an air ?lm, this means
(b) connecting a charge potential between the sub
that the presence of dust particles could constitute a criti~
cal factor, and should therefore consciously be excluded. 70
Also ‘preferably, although not necessarily, the insulating
rectifying layer, the photoconduc-tor layer or both should
be su?iciently ?exible to conform to the irregularities of
strates of said plates;
‘
v
(c) while said potential is connected exposing said
second plate through the transparent substrate to an
activating radiation image of original copy for a
time period su?icient to induce a charge pattern of
the copy on the surface of the insulating rectifying
the other surface as to minimize the extent of interference
caused by occasional dust particles or the like.
spaced substantially contiguous relationship to the
insulating rectifying layer surface of a ?rst plate on
which an image is to be formed;
tance should preferably be uniform throughout the entire
area of interest.
tive insulator overlying a conductive transparent sub
strate with the surface of the insulator in closely
75
layer; and,
'
3,254,998
9
10
(d) separating said plates in a manner to produce an
induced charge pattern of original copy on the sur
face of said ?rst plate developable with eiectroscopic
powder deposition.
copy on the surface of the insulating rectifying layer
of said ?rst plate; and,
(d) placing said induced image bearing surface into
4. The method according to claim 3 in which said
second plate comprises a material having a quantum. effi
ciency greater than unity.
period su?icient to induce. a charge pat-tern of the
1
5. A method of forming an electrostatic latent image
of original copy by induction on a ?rst plate comprising
an insulating rectifying layer supported on a conductive 10
closely spaced relationship with the surface of an
insulating rectifying layer of a third plate whereby
a charge pattern of original copy is induced on the
surface of the insulating rectifying layer of said third
plate.
7. The method according to claim 6 in which the in
substrate and capable of allowing ?ow of current in a ?rst
sulating rectifying layers of said ?rst and third plates
direction and substantially insulating in the reverse direc
are predominantly conductive in the direction of current
tion more predominantly with one polarity of current than
?ow to current of opposite polarities.
the other including:
8. In the method of Xerography in which developable
(a) placing a second plate comprising a photoconduc 15 electrostatic latent images are formed on a support sur
tive insulator overlying a conductive transparent sub
face, the improvement comprising a method of forming an
strate with the surface of the insulator in closely
electrostatic latent image of original copy by induction
spaced substantially contiguous induction charging
on the surface of a ?rst plate comprising an insulating
relation to the surface of an insulating rectifying
rectifying layer supported on a conductive substrate and
layer of a ?rst plate on which an image is to be 20 capable of allowing ?ow of current in a ?rst direction and
formed;
_
(b) connecting opposite poles of a DC. charging po
tential between the substrates of said plate with the
pole connected to the substrate of the ?rst plate
being of the same polarity as the corresponding pre 25
dominance of its conductivity;
(c) while said potential is connected exposing an ac
tivating radiation image of original copy through the
transparent substrate of the second plate for a time
period sufficient to induce a charge pattern of the 30
copy on the surface of the insulating rectifying layer
of the ?rst plate; and,
(d) separating said plates whereby said induced charge
pattern of original copy is retained on said insulating
rectifying layer and is developable with electroscopic
powder deposition.
6. A method of forming an electrostatic latent image
of original copy by induction on a ?rst plate comprising
an insulating rectifying layer capable of allowing ?ow of
substantially insulating in the reverse direction including:
(a) placing a second plate comprising a photoconduc
tive insulator overlying a conductive transparent sub
strate with the surface of the insulator in closely
spaced substantially contiguous relationship to the
surface of an insulating rectifying layer on a ?rst
plate on which an image is to be formed;
(b) connecting a charging potential between the sub
strates of said plates;
(0) 'while said potential is connected simultaneously
exposing said second plate through the transparent
substrate to an activating radiation image of original
copy for a time period su?icient to induce a charge
pattern of the copy on the surface of the insulating
rectifying layer; and,
(d) separating said plates whereby the insulating rec
tifying layer retains an induced charge pattern of
original copy developable with electroscopic powder
deposition.
current in a ?rst direction and substantially insulating in
References Cited by the Examiner
the reverse direction and supported on a conductive sub
strate including:
(a) placing a second plate comprising a photoconduc
tive insulator overlying a conductive transparent sub
strate ‘with the surface of the insulator in closely
2,817,277
2;833,648
5/1958
spaced substantially contiguous relationship to the
2,853,383
9/1958
Keck ___________ __ 95——1.7 X
insulating rectifying layer surface of a ?rst plate on
which an image is to be formed;
2,937,943
2,962,374
5/1960
11/1960
Walkup _________ __ 95—-——1.7 X
Dessauer ________ __ 95--—1.7 X
UNITED STATES PATENTS
12/1957 ‘BOgdOHOff _________ __ 95—-1.7
Walkup _________ __ 95-17 X
(b) connecting a D.‘C. charging potential between the
substrates of said plates;
50 NORMAN G. TORCHIN, Primary Examiner.
(c) concomitant with connection of said potential, ex
EVON C. BLUNK, Examiner.
posing the substrate of said second plate to an ac
tivating radiation image of original copy for a time
D. D. PRICE, Assistant Examiner.