Note: Descriptions are shown in the official language in which they were submitted.
~115334
ELECTROGI~APHIC EI.EMENT PROVIDED WITH
ELECTRICAL CONNECTION MEANS
BACKGROUND OF THE INV~r~TION
1. Field Of The Invention
This invention relates in general to electro-
photography and in particular to an electrographic element
provided with novel electrical connection means~ to a
method of forming such connection means, and to an electro-
graphic copier utilizing such electrographic element. More
10 specifically, this invention relates to an electrographic
element comprising an electrically insulating support, an
electrically conductive layer overlying the support, and
an electrically insulating photoconductive layer overlying
the conductive layer, and to a method of providing electrical
15 connection means within such element, which means are adapted
; to establish electrical connection between the conduc-
tive layer of the element and a grounding or biasing memDer
which engages a~surface of the element during use of the
element within the copier.
20 ? _ Description Of The Prior Art
A common type of electrographic element is an
element comprising an electrically insulating support, an
electrically conductive layer overlying the support, and an
electrically insulating photoconductive layer overlying the
25 electrically conductive layer. The photoconductive layer
contains a normally insulating material whose electrical
resistance varies with the amount of incident electromagnetic
radiation it receives during an imagewise exposure. A wide
variety of materials can be used as the support for such
30 elements, for example, the support can be composed of paper
or of a polymeric sheet material. The electrically conduc-
tive layer can be a separate layer or a part of the support
layer and can be formed from a wide variety of materials, such
as a thin metal foil, a vapor deposited metal layer, a dis-
35 persion of a semiconductor in a resinous material, or anelectrically conducting salt. The electrographic element can
be opaque or transparent, depending upon the intended mode
of use.
- ~ i
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334
In use, the electrographic element is first given
a uniform surface charge, generally in the dark after a
suitable period of dark adaptation. It is then exposed to
a pattern of actinic radiation which has the effect of dif-
5 ferentially reducing the potential of this surface chargein accordance with the relative energy contained in various
parts of the radiation pattern. The differential surface
charge or electrostatic latent image remaining on the electro-
graphic element is then made visible by contacting the surface
10 with a suitable electroscopic marking material. Such marking
material,or toner, whether contained in an insulating liquid
or on a dry carrier, can be deposited on the exposed surface
in accordance with either the charge pattern, or the absence
of charge pattern, as desired. Deposited marking material
15 can then be either permanently fixed to the surface of the
- element by known means such as heat, pressure, solvent vapor,
or the like, or transferred to a second element to which it
can similarly be fixed. Likewise, the electrostatic latent
image can be transferred to a second element and developed-
; 20 there.
The function of the electricall~ conducting layerin electrographic elements is to create a highly conducting
reference plane which ideally is held at or near ground poten-
tial. During charging of the photoconductive layer with a
25 corona charger, the potential of the conducting layer has a
tendency to build up with respect to ground if it is not
grounded. Typically, if the surface of the photoconductive
layer is charged to 600 volts, the potential of an ungrounded
conducting layer can vary from about 50 to about 450 volts or
30 more. Thus, the differential between the conducting layer and
the photoconductive layer may range from about 150 volts to
about 550 volts. In this situation, when the charging step
is completed and the surface of the element is exposed to a
pattern of actinic radiation, the photoconductive layer becomes
35 conducting in the light-struck regions and the potential of
the surface of the photoconductive layer in these areas approaches
that of the conducting layer. Because of the small difference
in potentials which may exist between areas struck by light and
those not struck, little or no latent image is produced.
111533~
Similarly poor results are obtained when the
conducting layer is inefficiently grounded. Conventional
grounding methods, such as metal strips, rollers, etc.
placed in electrical contact with the element may be satis-
5 factory in those systems where the element is charged whilestationary but are often ineffective when used in those
systems wherein the element is charged while in motion.
Direct electrical contact with the conducting layer for
gro~nding purposes is very difficult and inefficient when,
10 as is usually the case, it is extremely thin, e.g., a few
hundred ~ngstroms, and creates wear problems if the element
is contacted for grounding while in motion. Ideally, during
charging of the photoconductive layer, the electrically con-
ducting layer should be held at ground potential to insure
15 that the maximum charge be impressed and stored in the photo-
conductive layer.
Conducting lacquers such as those described in U. S.
Patent 3,639,121, issued February 1, 1972 to W. C. York, can
be used to aid in maintaining electrically conducting layers
at ground potential. However, these materials should be
applied directly to the electrically conducting layer, i.e.,
to an exposed portion of the layer. This is accomplished~by
either applying it to the edge of the element or, if the
conducting layer is set off so that a portion of its surface
is exposed, by applying the lacquer to the exposed surface.
Thus, the modes of application are somewhat limited, particu-
larly if the conducting layer is inaccessible.
An alternative approach to providing electrical
connection means in electrographic elements is that described
in U. S. Patent 3,684,503, issued August 15, 1972 to W. D.
Humphriss et al. In this method, a particulate electrically-
conducting material is imbibed into the element to form a dis-
persion extending from the surface of the element through the
overlying layer or layers and into contact with the electri-
cally conductive layer, thereby forming an electrical pathfrom the surface to tAe electrically conductive layer which
can be utilized in grounding the element. The method of U. S.
Patent 3,684,503 is very effective with many electrographic
elements but is limited in regard to the range of electro-
graphic elements to which it is applicable. Thus, for example,
33~
if the photoconductive layer overlying the conductive layeris thick, or if there are several contiguous photoconductive
layers, or if there are overcoat and/or subbing layers and/or
interlayers in addition to one or more photoconductive layers,
then the total thickness of material overlying the conductive
layer can be so great as to prevent the electrically-conductive
particulate material from being imbibed all the way from the
surface of the element to the conductive layer and thereby
render the method of U. S. Patent 3,684,503 inoperative.
Moreover, even though the total thickness of material over-
lying the conductlve layer may not be so great as to preclude
imbibition from the surface because of the depth of imbibition
needed, if one or more of the layers overlying the conductive
layer contains a tough polymeric binder which strongly resists
imbibition, then the method may again be rendered inoperative.
Other ~rocedures for the formation of electrical
connection means in electrographic elements are also known.
For example, British Patent No. 1,490,001, published October
26, 1977, describes a method in which electrical connection
means is provided by forming a hole in a non-image area of the
element extending from the outer surface to at least the
electrically conductive layer and inserting in the hole an
electrically-conductive composition comprising an adhesive
and a pigment in an amount sufficient to completely fill the
hole. Preferably, a piece of metallic foil is utilized to
cover the exposed adhesive composition in the hole and provide
a suitable surface for contact with an electrode. This patent
also discloses that a channel can be formed in place of the
hole and the electrically-conductive composition can be inserted
into the channel. A similar disclosure is provided in U. S.
Patent 3,743,410, issued July 3, 1973 to R. I. Edelman et al,
which describes an electrographic element adapted to be
grounded while in motion which includes a channel in the
photoconductive layer exposing the underlying conductive
layer and an electrically-conductive material that has been
inserted into the channel. In comparison with these procedures,
the method of this invention is much better suited to use in
production operations carried out on a commercial scale in
view of its simplicity and adaptability to high speed manu-
4 facturing operations.
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1115334
SUMMA~Y OF 'l`~IE INVENT:[ON
The present inve~tion provides improved electrical
connection means within an electrographic element, which means
are adapted to establish electrical connection between a con-
5 ductive layer of the element and a grounding or biasingmember which engages a surface of the element while the ele-
- ment is in motion. The electrographic element is comprised
of an electrically insulating support, an electrically con-
duc~ive layer overlying the support, and an electrically
10 insulating photoconductive layer overlying the conductive
layer and the electrical connection means comprises a region
of dispersed particulate electrically-conducting material
within a non-recording portion of the element which extends
from the surface of the element into contact with the conductive
15 layer. This region defines on the surface of the element an
elongated stripe which is longitudinally disposed in the direc-
tion of motion of the element and which encompasses an elongated
longitudinally disposed groove. To form the region of dispersed
particulate electrically-conducting material, an elongated groove
20 extending from the surface of the element at least to a position
proximate to the conductive layer is formed in the element and
an imbibable composition comprising the particulate material is
then applied to the surface of the element as an elongated stripe
which encompasses the groove. The groove serves to promote the
25 imbibition of the particulate material into contact with the
conductive layer so as to form an electrical path from the
conductive layer to the stripe on the surface of the element
and thus provide electrical connection with the grounding or
biasing member which engages the stripe.
The electrographic element of this invention is
adapted for use in an electrographic copier in which it is
moved through a plurality of processing stations including an
exposure station to form a visible image and in which the
copier includes a grounding or biasing member for applying a
35 reference potential to the conductive layer o~ the element
during movement of the element through the exposure station.
Means are provided within the copier for positioning the ele-
ment during movement of an image area thereof through the
exposure station to maintain effective contact between the
40 grounding or biasing member and the stripe on the surface Of
I the element, thereby connecting the reference potential to the
conductive layer.
. -5-
~llS334
BRIEF` DL~SCRIPTION OF T~IE DRAWINGS
.
FIG. 1 is a schematic representation of an
electrographic copying apparatus employing the improved
electrographic element of this invention.
FIG. 2 is a face view of a portion of an electro-
graphic element having electrical connection means in accor-
dance with this invention disposed along one edge thereof
and a row of perforations disposed along the opposite edge.
FIG, 3 is a face view of a portion of an electro-
graphic element having electrical connection means in accor-
dance with this invention disposed along both edges thereof.
FIG. 4-a is a cross sectional view taken along the
line 4-4 in FIG. 2 illustrating the electrical connection
means.
FIG. 4-b is a cross sectional view of an alterna-
tive embodiment of the electrical connection means.
FIG. 4-c is a cross sectional view of a further
alternative embodiment of the electrical connection means.
FIG. 5 is a cross sectional view illustrating the
electrical connection means of this invention in an alterna-
tive embodiment of the electrographic element.
FIG. 6 is a cross sectional view illustrating the
electrical connection means in contact with a grounding or
biasing member of an electrographic apparatus.
FIG, 7 is a schematic illustration of the cutting
of an elongated groove and formation of a conductive stripe
in an electrographic element in accordance with this invention.
~IG. 8 is a schematic illustration of an alternative
procedure for cutting the elongated groove in an electrographic
element.
DESCRIPTION OF THE PREFERRED E~BODIMEMTS
The present invention is characterized by the usein combination of an imbibable composition containing particu-
late electrically-conducting material and a groove which
extends from a surface of the electrographic element at least
into proximity with the conductive layer of the element. This
combination provides very effective electrical connection means
under a wide variety of circumstances. For example, the function
~l~S334
o~ the groove in promoting the imbibition of the particulate
material into contact with the conductive layer renders the
method effective with electrographic elements having one or
more layers overlying the conductive layer which together
are of such substantial thickness as to render it impossible
to imbibe the particulate material all the way from the sur-
face of the element to the conductive layer. Moreover, it
also enables the method to be used with electrographic
elements in which a photoconductive layer, or other layer
that overlies the conductive layer, is comprised of a tough
polymeric binder which is so resistant to imbibition of
particulate material as to render it impossible to imbibe
the particulate material all the way from the surface of
the element to the conductive layer. The method of the
present invention can be readily varied to render it
especially suitable for the particular electrographic element
involved. Thus, when the element is one which is moderately
susceptible to penetration by ~mbibition, the groove can be
relatively shallow as long as it is of sufficient depth to
enable the particulate material to make good contact with
the conductive layer. Under particular circumstances, it
may be desirable to form the groove with a depth such that
only a very slight thickness of mate~ial overlies the con-
ductive layer, or to form the groove with such a depth that
the conductive layer is exposed but not penetrated, i.e.,
all overlying material is removed, or to form the groove with
such a depth that it extends into the conductive layer or
through the conductive layer and into the underlying material.
Any of these techniques can be successfully utilized in
carrying out the present invention.
Turning now to FIG. 1, there is schematically
shown an electrographic copying apparatus 1 comprising an
electrographic element 2 in the form of an endless belt
configured for movement along an endless path past various
operative stations of the apparatus. As shown in FIG. 4,
the electrographic element 2 is a layered structure comprising
an electrically insulating support 3, an electrically conductive
layer 4 overlying support 3, and an electrically insulating
photoconductive layer 5 overlying conductive layer 4. The
conductive layer 4 is electrically connected to ground or
other selected reference potential source by engagement of
element 2 with metal bristle brush 6.
- -7-
l' .
5334
Operati~e stations of the apparatus 1 include
a primary charging station at which corona discharge device
7 applies an overall charge to the external surface of
photoconductive layer 5. After receiving the primary charge,
5 an image se~ment of electrographic element 2 advances past
the exposure station 8 where the segment is imagewise exposed
to light patterns of a document to be copied by xenon lamps
or other known imaging apparatus. Rollers 16 serve to con-
vey electrographic element 2 past the operative stations and
10 properly position it during movement of the image segment
through exposure station 8 to maintain effective contact
between brush 6 and the surface of electrographic element 2.
The electrostatic image residing on the image segment after
passage through exposure station 8 is next advanced over a
15 magnetic brush or other development station 9 where toner is
attracted to the charge pattern corresponding to dark image
areas of the document. The developed image is then advanced
to a transfer station 10 where the toner image is transf`erred
by the action of corona discharge device 12 to pap-er which is
20 fed from supply 11. The paper bearing the toner image is then
transported through a fixing station 13, for example, a roller
fusing device, to a bin 14. In the meantime, the segment from
which the toner is transferred advances past a cleaning station
15 in preparation for another copy cycle.
Referring now to FIG. 2, electrographic element 2
is shown to include a row of perforations 17 adjacent to one
side thereof and electrical connection means 18 adjacent to the
opposite side thereof. Electrographic element 2, provided
with perforations 17, is especially adapted for use in an
30 electrographic copying apparatus of the type described in
U. S. Patent 3,914,047 issued October 21, 1975 to W.`E. Hunt,
Jr, et al. The perforations 17 are utilized to generate
control timing signals for synchronizing machine functions
as described in detail in U. S. Patent 3,914,047. Electrical
35 connection means 18 comprises a region of dispersed particulate
electrically-conducting material, within a non-recording
; portion of electrographic element 2, which extends from th_
surface of electrographic element 2 and, as shown in FIG. 4,
reaches into contact with electrically conductive layer 4.
4 The dispersed particulate electrically-conducting material
can be any suitable material such as, for example, carbon
-8-
I
'
11~S334
black or graphite particles. The region of dispersed particu
late electrically-conducting material defines on the surface
of electro~raphic element 2 an elongated stripe 19 which is
longitudinally disposed in the direction of motion of electro-
5 graphic element 2 and which enco~passes an elongated longitu-
dinally disposed groove 20.
In the alternative embodiment of electrographic
element 2 which is shown in FIG. 3, there is provided a
second electrical connection means 21 comprising a region of
10 dispersed particulate electrically-conducting material which
extends into contact with electrically conductive layer 4 and
which defines an elongated longitudinally disposed stripe 22
which encompasses an elongated longitudinally disposed groove
23. In electrical connection means 21, contact of the dispersed
15 particulate electrically-conducting material with conductive
layer 4 is achieved both as a result of the presence of groove
23 and as a result of contact with the exposed edges of conduc-
tive layer 4 within each of perforations 17.
Referring now to parts (a), (b) and (c) of FIG. 4,
20 there are shown alternative embodiments of electrical connec-
tion means 18. In each of these embodiments groove 20 extends
frcm the exterior surface of electrographic element 2 at least
to a position proximate to conductive layer 4. In the embodi-
ment of part (a), groove 20 terminates a short distance above
25 the upper surface of conductive layer 4 and the dispersed
particulate electrically-conducting material has traveled by
a process of imbibition from the bottom of groove 20 into
contact with conductive layer 4. In the embodiment of part
(b), groove 20 is of a depth such as to expose conductive
30 layer 4, that is, it terminates at the upper surface of con-
ductive layer 4. Dispersed particulate electrically-conductive
material is in contact with conductive layer 4 at the bottom of
groove 20 and also as a result of its lateral movement into
photoconductive layer 5 by a process of imbibition. In the
35 embodiment o~ part (c), groove 20 extends completely through
conductive layer 4 and into support 3. Dispersed particulate
electrically-conductive material is in contact with conductive
layer 4 at its exposed edges 24 and 24' within groove 20 and
also as a result of its lateral movement into photoconductive
40 layer 5 by a process of imbibition.
334
FIG. 5 shows an alternative embodiment of electro-
graphic element 2 which includes a subbing layer 25 between
electrically conductive layer 4 and photoconductive layer 5
and a protective overcoat layer 26 over photoconductive layer i
5. In this embodiment, groove 20 extends from the surface of
electrographic element 2 through each of overcoat layer 26,
photoconductive layer 5, subbing layer 25, and electrically-
conductive layer 4,and into support 3. Dispersed particulate
electrically-conductive material is in contact with conductive
layer 4 at its exposed edges 24 and 24' within groove 20 and
also as a result of its lateral movement into subbing layer
25 by a process of imbibition.
As illustrated in FIG. 6, grounded metal bristle
brush 6 serves to engage stripe 19 as electrographic element
2 is conveyed past the operative stations of an electrographic
copying apparatus. Since there is an electrical path from
conductive layer 4 to the surface of electrographic element 2,
provided by the dispersed particulate electrically-conducting
material, this serves to ground conductive layer 4.
Electrographic elements provided with improved
electrical connection means in accordance with this invention,
can be formed using any of a wide variety of materials as the
support. Typical supports include cellulose triacetate film,
poly(vinyl acetal) film, polystyrene film, pol~(ethylene
terephthalate) film, polycarbonate film, paper, polymer-coated
paper, and the like. Most usually the support is a tough,
flexible, transparent, electrically insulating material such
as a poly(ethylene terephthalate) film.
The conductive layer in the electrographic elements
of this invention is a thin layer which is sandwiched between
the support and the photoconductive layer. It can be formed
from many different materials, as is well known in the electro-
graphic art. For example, it can be a thin sheet of a metal
such as aluminum, copper, zinc or brass, or a metal foil such
as an aluminum foil, or a vapor deposited metal layer of a
metal such as silver, aluminum or nickel, or a layer which is
a dispersion of a semi-conductor in a resin, as described for
example in U. S. Patent 3,245,833, or a layerOf an electrically-
conducting salt, as described for example in U. S. Patents
3,007,801 and 3,267,807. A further example of a useful con-
ductive layer is a layer comprised of a dispersion Gf carbonblack or graphite in a polymeric binder.
-10--
.
33~
The electrical connection means of this invention is
a region of dispersed particulate electrically-conducting
material which defines an elongated conductive stripe on the
. surface of the electrographic element. This stripe can be
located along the edge of the electrographic element, as
5 illustrated herein, or it can be spaced inwardly from the edge
at any desired location. Typically, it will be at the edge
or close to the edge of the element. In certain instances it
is desirable to provide two stripes, one adjacent each edge of
the element, as also illustrated herein. In this case, the
10 electrographic copying apparatus is, of course, provided with
means for engaging each of the stripes. Perforations can be
located within the region of one of the stripes, as illustrated
herein, or they can be located outside the stripe region. An
advantage of locating them within a stripe is that it is then
15 possible for them to assist in providing electrical connection
to the conductive layer. Whether one, or more than one stripe
is used, each such stripe will be located in a non-recording
portion of the electrographic element. To obtain the region of
dispersed particulate electrically-conducting material within
20 the element an imbibable composition comprising the particulate
material is applied to the surface of the element as an elongated
stripe and, with the aid of the elongated groove, imbibed into
contact with the conductive layer.The imbibable composition, as
hereinafter described in greater detail, advantageously contalns
25 a polymeric binder which will aid in bonding the particulate
material within the element and assist in providing a stripe
which ls durable and abrasion resistant. Any suitable form of
grounding or biasing member can be used to engage the conductive
stripe, for example, the member can be a metal bristle brush, as
30 illustrated herein, or a metal strip, or a metal Y~lle.r.
It is to be understood that the term "ground" as used
herein is relative and merely represents a relative potential
to which other positive or negative potentials are referred.
For example, in referring to the surface of the photoconductive
35 layer as being charged to 600 volts, it is intended to mean 600
volts above a reference ground potential. For convenience, ground
potential as used herein is arbitrarily assigned a value of zero
volts.
. 111.~334`
The dispersed par!iculate electrically-conductive
material which forms the electrical connection means of this
invention can be any finely-divided particulate material having
good electrical conducting properties. Typical conducting
materials include graphite, carbon black, nickel, silver, alumi-
num, copper, tin, etc. and mixtures thereof, all of which are
particulate and have good electrical conducting properties. The
particle size of these conducting materials can vary depending
on the particular material used but generally ranges from about
0.001~ to about 100~. Graphite has been found to be very satis-
factory based on its property of being a good lubricant as well
as a conductor. When graphite is used, less wear is encountered
in those non-recording regions of the element which are in
contact with the metal grounding devices.
In preparing the novel electrographic elements of this
invention, a liquid dispersion of the particulate electrically
conducting material in a solvent is applied to the surface of the
electrographic element. The solvent should be one which is capable
of impregnating (e.g., by swelling, cracking or dissolving) the
polymeric binder contained in a photoconductive layer or other
layer, such as a subbing layer, which is in direct contact with
the electrically conductive layer, and preferably one which is
capable of impregnating the binders in all layers overlying the
electrically conductive layer. Suitable solvents having these
characteristics include aliphatic alcohols having 1 to 8 carbon
atams such as methanol, ethanol, isopropanol, etc., ketones having
3 to 10 carbon atoms such as acetone, methylethyl ketone, etc.,
and chlorinated alkanes having l to 8 carbon atoms such as methyl-
ene chloride, propylene chloride, chloroform, etc. Mixtures of
3 these solvents may also be used. The particular solvent or mix-
ture employéd is somewhat dependent upon the polymer to be im-
pregnated and the selection of the optimum solvent to be used is
- apparent to those skilled in the art. A particularly useful sol-
vent which is capable of impregnating most of the more common
hyd~ophobic film-forming resin binders employed in the various
layers of electrographic elements, comprises a mixture of a ketone
such as acetone or methyl ethyl ketone with a chlorinated hydro-
carbon such as methylene chloride or propylene chloride.
The solvent and particulate electrically-
conducting material are thoroughly mixed, e.g., with
a ball mill or blender, so as to create a uniform
dispersion of the conducting material in the solvent.
ll~S334
.
Frequently, in order to obtain a uniform stable dispersion of
solids in liquid, it is necessary to employ a small amount of a
polymerlc binder. The added binder aids primarily in the creation
of a more uniform dispersion. When such a binder is employed,
5 the ratio Or conducting material to binder ranges from 0.5 to 10
parts by weight and preferably 1.5 to 2.5 parts by weight of
conducting materlal for each part by weight of binder. Enou~h
solvent is added to bring the solids content to at least 5%
and hOt more than 90% of the liquid dispersion. The binder
10 used in the imbibable composition can be any of a wide variety
Or polymeric materials. Suitable materials include styrene-
butadiene copolymers; silicone resins; styrene-alkyd resins;
silicone-alkyd resins; soya-alkyd resins; poly(vinyl chloride);
poly(vinylidene chloride); Uinylidene chloride-acrylonitrile
15 copolymers; poly(vinyl acetate); vinyl acetate-vinyl chloride
copolymers; poly(vinyl acetals) such as poly(vinyl butyral);
polyacrylic and methacrylic esters, such as poly(methylmethacrylate),
poly (n-butylmethacrylate), poly(isobutyl methacrylate), etc.;
polystyrene; nitrated polystyrene; polymethylstrene; polyesters
20 such as poly(ethylene terephthalate); phenolformaldehydè resins;
polyamides; polycarbonates, polythiocarbonates; poly(ethyleneglycol-
`co-bishydroxyethoxyphenyl propane terephthalate); copolyme~s
of vinyl haloarylates and vinyl acetate such as poly(vinyl-m-
bromobenzoate-covinylacetate); polyolefins such as polyethylene,
25polypropylene, etc.
The electrographic elements of this invention can be
composed of only three layers, namely, an electrically conductive
layer sandwiched between a support and a photoconductive layer.
However, they may include two or more contiguously disposed
3 photoconductive layers, each of which exhibits different
characteristics, and may include a variety of other layers such
as barrier layers, subbing layers, overcoat layers, and so forth.
The various layers making up the element typically vary greatly
in thickness. For example, the support may have a th~ckness of
35 about 100 microns and the photoconductive layer a thickness of
about 20 microns while each of the electrically conductive layer,
subbing layer and overcoat layer may have a thickness of less than
one micron. The electrographic element is typically utilized in
the form of a continuous belt but it may be employed in other
4 configurations such as for example in the form of a flat sheet
or in cylindrical form.
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.
! ~
1~533~a
.
The photoconductive layer in the electrographic element
of th~s invention can be prepared from a wide variety of materials.
In general, this layer is prepared by dispersing a photoconductor
in a resinous binder and coating the resultant dispersion on
5 the electrically conductive layer or on a subbing layer overlying
the electrically conductive layer. Binders useful for this
purpose include the same polymeric materials referred to above
as being useful as binders in the imbibable composition. Photo-
conductors suitable for use in the photoconductive layer include
10 inorganic, organic and organo-metallic materials. Typical
photoconductors which are useful include zinc oxide, titanium di-
oxide, organic derivatives of Group lVa and Va metals such as
those having at least one amino-aryl group attached to the metal
atom, aryl amines, polyarylalkaneshaving at least one amino
15 substituent~-and the like. The use of organic photoconductors
is preferred. Illustrative examples of organic photoconductors
are those described in U.S. patents 3,139,338; 3,139,339;
3,140,946; 3,141,770; 3,148,982; 3,155,503; 3,257,202; 3,257,203;
3,257,204; 3,265,496; 3,265,497; 3,274,000; and 3,615,414.
A sensiti7er for the photoconductor may optionally be
included in the photoconductive layer to change the elect~o~hoto-
sensitivity or spectral sensitivity of the element. Sensitizing
compounds useful in the photoconductive layers described herein
can be selected from a wide variety of materials, including such
25 materials as pyryliums, including thiapyrylium and selenapyrylium
dye salts, disclosed in U.S. Patent 3,250,615; fluorenes such
as 7,12-dioxo-13-dibenzo(a,h)fluorene, 5,10-dioxo-4a,11-
diazabenzo(b)fluorene, 3,13 -dioxo- 7 - oxadibenzo(b,g)fluorene,
and the like; aromatic nitro compounds of the kinds described
3 in U S. Patent 2,610,120; anthrones like those disclosed in U.S.
Patent 2,670,284; quinones, U.S. Patent 2,670,286; benzophenones
U S Patent 2,670,2~7; thiazoles U.S. Patent 2,732,301; mineral
acids; carboxylic acids, such as maleic acid, dichloroacetic
acid, and salicylic acid; sulfonic and phosphoric acids; and
35various dyes, such as cyanine (including carbocyanine), mercocyanine
diarylmethane, thiazine, azine, oxazine, xanthene, phthalei~,
acridine, azo, anthraquinone dyes and the like and mixtures
thereof. The sensitizing dyes preferred for use with this
invention are selected from pyrylium, selenapyrylium and thia-
4pyrylium salts, and cyanines, including carbocyanine dyes.
Where a sensitizing compound is employed with the binderand organic photoconductor to form a sensitized electrographic
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.
11~.tj33~
element, it is suitable to mix an amount Or the sensitizing
compound with the coating composition so that, after thorough
mixing, the sensitizing compound is uniformly distributed in
the coated element. Other methods of incorporating the sensitizer
5 or the effect of the sensitizer may, however, be employed
consistent with the practice of this invention. In preparing the
photoconductive layers, no sensitizing compound is required to
give photoconductivity in the layers which contain the photo-
conducting substances, therefore, no sensitizer is required in
10 a particular photoconductive layer. However, since relatively
minor amounts of sensitizing compound give substantial improvement
in speed in such layers, the sensitizer is preferred. The
amount of sensitizer that can be added to the photoconductive
layer to give effective increases in speed can vary widely. The
15 optimum concentration in any given case will vary with the
specific photoconductor and sensitizing compound used. In general,
: substantial speed gains can be obtained where an appropriate
sensitizer is added in a concentration range from about 0.0001
to about 30 percent by weight based on the weight of the film-
20 forming coating composition. Normally, a sensitizer is addedto the coating composition in an amount by weight from about
0.005 to about 5.0 percent by weight of the total coating
composition.
Solvents useful for preparing the photoconductive
25coating compositions include a wide variety of organic solvents
for the components of the coating composition. For example,
benzene; toluene; acetone; 2-butanone; chlorinated hydrocarbons
suoh as methylene chloride, ethylene chloride, and the like;
ethers, such as tetrahydrofuran and the like, or mixtures of
3such solvents can advantageously be employed in the practice
of this invention.
In preparing the coating compositions for the photo-
conductive layer, useful results are obtained where the photo-
conductive substance is present in an amount equal to at least
35about 1 weight percent of the coating composition. The upper
limit on the amount of photoconductive material present can be
widely varied in accordance with usual practice It is normally
required that the photoconductive material be present in an
amount ranging from about 1 weight percent of the coating
4composition to about 99 weight percent of the coating composition.
A preferred weight range for the photoconductive material in the
coating composition is from about 10 weight percent to about
60 weight percent.
! - -15-
.
.
33~a
Coating thicknesses of the photoconductive composi-
tion can vary widely. Norrnally, a wet coating thickness in the
range of about 0.01 to 2 millimeters is useful in the practice
of this invention. A preferred range of coating thickness is
5 from about 0.02 to 0.2 millimeters before drying, although
such thicknesses can vary widely depending on the particular
application desired for the electrographic element.
In the method of this invention an elongated longitudi-
nally disposed groove is formed in a non-recording portion of
10 the electrographic element. This groove extends from an exterior
surface of the elemént at least to a position proximate to the
electrically conductive layer. It is formed with a depth and
width adapted to promote the imbibition of the particulate
electrically-conducting material into contact with the elec-
15 trically conductive layer. The optimum depth and width willdepend upon numerous circumstances including the structure and-
composition of the electrographic element and the imbibing
characteristics of the composition containing the particulate
electrically-conducting material. As explained hereinabove, the
20 groove may terminate a short distance above the electrically
conductive layer, may terminate at the surface of the electrically
conductive layer, or may extend into or through the electrically
conductive layer. Typically~ a groove with a width of from about
0.2 millimeters to about 5 millimeters is suitable.
Imbibition of the composition containing the particulate
electrically-conducting material causes it to spread laterally
as well as to penetrate downwardly from the surface to which it
is applied. Since the composition is applied as a stripe which
encompasses the groove, it flows into the groove and spreads
3 laterally from the walls of the groove as well as penetrating
downwardly from the bottom of the groove. Even though the distance
it is capable of penetrating may be relatively small, since the
groove extends to a position at least proximate to the conductive
layer the resulting dispersion of particulate electrically-
35 conducting material will easily extend into effective contactwith the conductive layer and thereby provide an electrically-
conductive path from the conductive layer to the surface of the
element.
The groove can be formed in the electrographic element in
any suitable manner. One technique which is suitable for forming
I the groove is the use of a revolving knife blade which is rotated
at high speeds, such as speeds of several thousand revolutions
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.
33~ :
per minute. The blade is preferably made of a very durable
and wear resistant material, such as a stainless steel blade
or a steel blade with a diamond edge. An alternative technique
is to carry out a localized pyrolysis in which the material is ,
5, vaporized in a controlled manner along the desired path.'
Methods of accomplishing this include the use of a laser beam
or an electron beam.
In forming the groove by use of a laser, the action
of the laser beam serves to vaporize the material on which the
beam,is impinged and thereby generate a groove. Suitable lasers
for this purpose are well known. Laser beams having wavelengths
in theinfrared range are generally satisfactory. A C02 laser
is preferred because of its high efficiency characteristics.
me wldth of the laser beam wlll be selected in accordance
with the desired width of the groove. The laser beam can be
moved relative to a stationary substrate to form the groove
but it will usually be more convenient for the laser beam to
be fixed in position and the substrate to be moved at an
appropriate rate to form a groove of the desired depth.
' After the groove has been formed in the electrographic
element, the imbibable composition containing the particulate
electrically-conducting material is applied to the surface of
the élement as an elongated stripe which encompasses the gr,oove.
The stripe may be of any suita~le width, with the width ordinarily
25 being commensurate with the size of the grounding or biasing
member in the electrographic apparatus which is intended to
engage the stripe. Typically the stripe will have a width of
about 5 to about 25 millimeters and it will typically be about
5 to about 100 times as wide as the groove. The groove will
3 usually be located at or near the midpoint of the stripe but it
may be at any position wlthin the stripe, as desired.
Application of the imbibable composition to the surface
of the electrographic element can be carried out in any suitable
manner. For example,'it can be carried out by spraying or by
35 the use of a coating hopper such as a hopper of the extrusion
type. The imbibable composition flows into the groove and
penetrates into the material surrounding the groove. If the
groove dQes not extend all the way through the photoconductive
layer, the composition will be imbibed through the material
4 which lies between the bottom of the groove and the electrically
conductive layer. It will also spread laterally from the walls
of the groove by the process of imbibitlon into the photoconductive
-17- !
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.
11~533~
layer and into any subbing layer overlying the electrically
conductive layer. The imbibable composition is applied in an
amount sufficient to provide effective contact of the particulate
electrically~conducting material wlth the electrically conductive ;~
layer. The optimum amount to be used will depend on the
characteristics of both the imbibable composition and the
electrographic element as well as the method of application.
The amount used can be su~icient to completely fill the groove
and provide a level surface thereover. However, lesser amounts
can also be used. In any event, the result will be that the
groove will be at least partially filled with the particulate
electrically-conducting material.
The method of this invention is a simple, effective
and reliable procedure which is well adapted to use in a high
volume production operation. The steps of forming the groove
and applying the imbibable composition can be carried out as
independent operations or as sequential steps in a single
continuous process. If carried out independently, they can,
of course, be conducted at different speeds with the speed
chosen for each step being optimum for that particular
operation. When the groove-forming step and the step of
applying the imbibable composition are carried out as sequential
steps of a single continuous operation, the speed at which
the web is advanced can be selected within a broad range,
for example, a speed in the range of from about 5 to about
200 centimeters per second. The steps of forming the groove
and applying the imbibable composition can also be carried out
as part of a continuous process which involves other operations
such as coating o~ the various layers on the support, forming
3 the perforations, slitting, and so forth. After application
of the imbibable composition, it is pre~erred to impinge air
or other gaseous medium on the element and/or to heat the
element in order to drive off the solvent. Heating also serves
to promote the penetrating action of the imbibable composition
and thereby facilitate good contact with the electrically conduc-
tive layer. As explained hereinabove, the imbibable composition
preferably contains a polymeric binder. The binder promotes the
bonding of the particulate material within the element and assists
in forming a stripe which is durable and abrasion resistant
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.
111533"
and, accordingly, is able to resist being worn away by the
frictional contact with the grounding or biasing member.
In view of the long-wearing characteristics of the conductive
stripe, the electrographic element can be re-used a great
many times while still maintaining excellent electrical
contact with the grounding or biasing member.
Referring now to FIG. 7, there is shown a particular
embodiment of the method of this invention in which the
groove is formed in the electrographic element by the use of a
laser beam. In this method, electrographic element 2 is
unwound from supply roll 30 which is-mounted for rotation
about its axis on a suitable framework (not shown) and passes
around guide rollers 32 and 34, which maintain it under proper
tension,and over bac~ing roll 36. A laser 38 positioned
above electrographic element 2, opposite backing roll 36,
impinges a laser beam 40 onto electrographic element 2 as
it advances and thereby forms a groove 20. To assist in
removing vapors produced by vaporization of the material
on which laser beam 40 impinges, an exhaust duct 42 connected
to a vacuum source (not shown) is positioned closely adjacent
to the region of impingement. A spray nozzle 44 fed with the
imbibable composition from a suitable supply source (not
shown) directs a liquid spray 46 onto the surface of elect~o-
graphic element 2 to form a stripe 19 which encompasses
groove 20. After passing under spray nozzle 44, electro-
graphic element 2 is advanced into a drying chamber (notshown) in which warm air or other gaseous medium is directed
into contact with the stripe to remove solvent and promote
imbibition.
FIG. 8 illustrates an alternative embodiment of
3 thè method of this invention in which the groove is formed
in the electrographic elément by the use of a rotating knife
blade. In this method, electrographic element 2 is unwound
from supply roll 30 and passes around guide rollers 32 and 34
and over backing roll 36. A rotatable knife blade 48 driven
by a suitable drive means 50, such as a variable-speed motor,
engages the surface of electrographic elernent 2 as it passes
over backing roll 36 and thereby forms a groove 20. To
assist in the removal of dust formed by the cutting action
of knife blade 48, exhaust duct 42 is positioned closely
4 ad~acent to the region where cutting takes place. After
groove 20 has been cut, the advancing element passes under
-19- :
33~
- spray nozzle 41~, which direc~s liquid spray 46 onto its
surface and thereby forms stripe l9 encompassing groove 20,
and then passes through the drying chamber in which warm
air impinges on the stripe.
In either the embodiment of FIG. 7 or the embodiment
of FIG. 8,the web can be wound onto a take-up roll after
the stripe has been dried or it can be cut to appropriate
lengths, each of which will serve to form an endless belt
for use in an electrographic copying apparatus, or it can be
subjected to additional operations such as slitting.
In forming the groove in the electrographic
element, it is ordinarily desirable that it be made as narrow
as possible since this will involve the minimum removal of
material and therefor the minimum formation of vapors or
dust. It must, of course, be made wide enough to enable
the imbibable composition to enter the groove The most
appropriate width for the groove may be determined, at least
in part, by the choice of method used to form the groove,
for example, it may be determined by the minimum practical
thickness for knife blades used in forming the groove by a
cutting process. As previously indicated, there is a wide
degree of choice in regard to the depth of the groove. The
groove can be readily cut to a desired depth by, for example,
varying the pressure applied to a rotating knife blade or
varying the power output from a laser. It is a particular
advantage of the method of this invention that the groove does
not have to be cut to an exact predetermined depth and does not
have to be of exactly the same depth at all points along its
longitudinal extent. Since the imbibable composition is
capable of penetrating a gubstantial distance into the photo-
3 conductive layer, or other layer of the electrographic element,it is pnly necessary that the groove extend to a position at
least proximate to the electrically-conductive layer, that is,
to a position that is not so far away that the imbibable compo-
sition will not be able to reach the electrically-conductive
layer. It should be noted that while mechanical methods of
cutting the groove, such as a rotating knife blade, result in
the generation of dust, the use of a laser beam brings about a
vaporization of the solid materials. This vaporization is, of
course, accompanied by the generation of considerable heat and
4 the solid material is rendered molten and flowable. The groove
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334
will usually be somewhat jagged and irregular in appearance,
and considerable flow of the molten material will take place.
For simplicity~ no attempt has been made to illustrate this
in the drawings herein. With some polymeric binders, the
fused material formed by the laser beam may, upon subsequent
5 cooling, be converted to a crystalline state in which it is
quite resistant to penetration by imbibable compositions.
Under these circumstances, it may be necessary to control the
laser such that it cuts a groove which reaches or at least
very nearly reaches the electrically conductive layer or
10 which extends into the electrically conductive layer or
completely through it. Thus, if the electrically conductive
layer is exposed by removing all overlying material this
provides for contact between the particulate electrically-
conducting material and the electrically conductive layer at
15 the bottom of the groove. If the groove cuts into or through
the electrically conductive layer, there is opportunity for
contact between the particulate electrically-conducting
material and the edges of the electrically conductive layer
within the groove. In either instance, contact between the
20 particulate electrically-conducting material and the electrically
conductive layer is also provided as a result of the lateral
spreading of the imbibabLe composition. The lateral spreading
action which occurs is an important feature of the present
invention since it provides much more effective contact with
25 the electrically conductive layer than is achieved merely as
a result of contact at the bottom of a groove which exposes
the electrically conductive layer. Use of an eLectrically
conductive composition which is not capable of imbibition
would, of course, not provide the lateral spreading action and
30 thereby would give much less effective contact.
The combined use of a groove and an imbibable composi-
tion in accordance with this invention is useful with electro-
graphic elements of many different structural variations.
Thus, the method of this invention is applicable in any situation
35 where thereiS an inaccessible electrically conductive layer
sandwiched between other layers of an electrographic element.
It is particularly advantageous where the electrically conductive
layer is very thin and the overlying layers are very resistant
to imbibition.
Electrographic elements containing the novel
electrical connection means of this invention are useful in the
xerographic process. In this process, the electrographic element,
while held in the dark, is given a blanket electrostatic charge
by placing it under a corona discharge to give a uniform charge
45 to the surface of the photoconductive layer. During this charg-
-21-
ing step, the electricall" conducting layer is maintained at
ground potential by ~lcci rically connecting the conductive
stripe on the electrograpnic element to ground. In the absence
of grounding in this manner, the difference in potential
5 between the photoconductive layer and the conducting layer
is not large enough to produce a suitable latent image.
The charge is retained on the surface of the photoconductive
layer because of the substantial dark insulating property of
the layer, i.e., the low conductivity of the layer in the dark.
10 When using an element,containing electrical connection means
as described herein,that is charged while in motion, the
potential of the conducting layer is maintained at grounu
potential as efficiently as with an element that is charged
while stationary. In other words ? the electrical connection
15 means permits exceptionally good contact to be made between
the conducting layer and the grounding means while the element
is in motion. The electrostatic charge formed on the surface
of the photoconductive layer is then selectively dissipated
from the surface of the la~er by imagewise exposure to light
20 by means of a conventional exposure operation such as for
example, by a contact-printing technique, or by lens projection
of an image, or by reflex techniques and the like, to
thereby form a latent image in the photoconductive layer.
Exposing the surface in this manner forms a pattern of electro- ;
static charge by virtue of the fact that light energy striking
the photconductor causes the electrostatic charge in the light
struck areas to be conducted away from the surface in proportion
to the intensity of the i~lumination in a particular area.
The charge pattern produced by exposure is then de-
30 veloped or transferred to another surface and developed there,
i.e., either the charge or uncharged areas are rendered visible,
by treatment with a medium comprising electrostatically respon-
sive particles having optical density. The developing electro-
statically responsive particles can be in the form of a dust
35 or powder and generally comprise a pigment in a resinous carrier
called a toner. A preferred method of applying such a toner to
a latent electrostatic image for solid area development is by
the use of a magnetic brush. Methods of forming and using a
magnetic brush toner applicator are described in the following
40 U. S. Patents 2,786,439; 2,786,440; 2,786,441; 2,811,465j
2,874, o63; 2, 984,163; 3, 040,704; 3,117,884; and reissue Re.
25,779. Liquid development of the latent electrostatic image
may also be used. In liquid development the developing parti-
cles are carried to the image-bearing surface in an electrically
~1~5334
-22-
~l~S33~
insulating liquid carrier. Methods of development of this
type are widely known and have been described in the patent'
literature, for example, in U. S. Patent 2,297,691 and in
Australian Patent 212,315. In dry developing processes the
most widely used method of obtaining a permanent record is
5 achieved by selecting a developing particle which has as
one of its components a low-melting resin. Heating the powder
image then causes the resin to melt or fuse into or on the
element. The powder is, therefore, caused to adhere permanently
to the surface of the photoconductive layer. In other cases, a - '
10 transfer of the charge image or powder image formed on the
photoconductive layer can be made to a second support such as
paper which would then become the final print after developing
and fusing or fusing respectively. Techniques of the type
indicated are well known in the art and have been described in
15 a number of U. S. and foreign patents, such as U. S. Patents
2,297,691 and 2,551,5~2 and in "RCA Review", vol 15. It is
f'requently necessary during development to maintain the elec-
trically-conducting layer at a given potential in order to
obtain a clean background. The electrical connection means
20 provided in the elements of this invention enables one to easily
maintain the potential of the electrically-conducting layer at
a preselected level.
In a typical example of the practice of this invention,
an electrographic element comprised of a poly(ethylene tere-
25 phthalate) support with a thickness of 100 microns, a nickellayer with a thickness of less than 1 micron overlying the
support, and a photoconductive layer, comprised of an organic
photoconductor dispersed in a polycarbonate binder and having
a thickness of approximately 20 microns, overlying the nickel
30 layer, is grooved by the use of a rotating knife blade and then
spray coated to form the desired conductive stripe. The groove
is formed with a width of approximately 1 millimeter and a depth
of approximately 15 microns and is cut by a rotating stainless
steel knife blade driven by a motor at a speed of 6000 revolu-
35 tions per minute while the electrographic element is advancedat a speed of 30 centimeters per second. After the groove is
formed, a stripe with a width of 10 millimeters, which encom-
passes the groove, is applied by spraying the following imbibable
composition onto the surface of the element:
11~S334
Component Weight %
Polyvinylbutyral resin 3.3
Carbon black 6.5
Propylene chloride 41.2
5 Acetone 49.0
After formation of the stripe by the spray coating operation,
the solvent is removed by contacting the element with warm
air at a temperature of about 165F.
In a further typical example of the practice of
10 this invention, the electrographic element described above
is grooved by the use of a laser beam and then coated with
an imbibable composition to form the desired conductive
stripe. A suitable laser for this purpose is a 50-watt
C2 laser equipped with a 2.5 inch focal length lens. The
15 groove can be formed along only one edge of the element or,
by equipping the laser with two lenses and a beam splitter,
grooves can be simultaneously formed along both edges. The
element can be advanced at any suitable speed during the step
of forming the grooves with a laser beam, such as a speed of
20 30 centimeters pèr second. Preferably, the power output from
the laser is regulated so that the groove is cut completely
through the nickel layer of the element described above and
into the poly(ethylene terephthalate) support. Following
formation of the groove, an imbibable composition,as described
25 above,is applied in the form of a stripe which encompasses~the
groove by a suitable method of application such as spraying or
hopper coating.
The invention has been described in detail with
particular reference to preferred ernbodiments thereof, but
3 it will be understood that variations and modifications can
be effected within the spirit and scope of the invention.
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