Development process and apparatus

The present invention is directed to an electrostatographic imaging apparatus, and an electrostatographic imaging method utilizing such apparatus, wherein the apparatus is comprised of an imaging means, a charging means, an exposure means, a development means, and a fixing means, the improvement residing in the development means comprising in operative relationship a tensioned deflected flexible imaging means; a transporting means; a development zone situated between the imaging means and the transporting means; the development zone containing therein electrically insulating toner particles, and electrically insulating magnetic carrier particles, means for causing the flexible imaging means for causing the transporting member to move at a speed of from about 5 cm/sec, to about 50 cm/sec; means to move at a speed of from about 6 cm/sec to about 100 cm/sec, the means for imaging and the means for transporting moving at different speeds; and the means for imaging and the means for transporting having a distance therebetween of from about 0.05 millimeters to about 1.5 millimeters.

BACKGROUND OF THE INVENTION 
This invention generally relates to a process, and an apparatus for causing 
the development of images in electrostatographic systems. More 
specifically, the present invention is directed to an improved process, 
and an improved apparatus for accomplishing the development of 
electrostatic latent images, by providing a development zone encompassed 
by a moving deflected flexible imaging member, and a moving transporting 
member. The flexible imaging member is deflected by electrically 
insulating developer particles, comprised of insulating toner particles, 
and insulating magnetic carrier particles contained in the development 
zone, which deflection, together with the relative movement of said 
members, is primarily responsible for the agitation and movement of the 
developer particles. Such as process, and apparatus allows the continual 
development of high quality images, including the efficient and effective 
development of solid areas. 
The development of images by electrostatographic means is well known. 
Generally in these systems, toner particles are applied to an 
electrostatic latent image by various methods including cascade 
development, reference U.S. Pat. No. 3,618,552, magnetic brush 
development, reference U.S. Pat. Nos. 2,874,063, 3,251,706, and 3,357,402, 
powder cloud development, reference U.S. Pat. No. 2,217,776, and touchdown 
development, reference U.S. Pat. No. 3,166,432. Cascade development and 
powder cloud development methods have been found to be especially well 
suited for the development of line images common to business documents, 
however, images containing solid areas are not faithfully reproduced by 
these methods. Magnetic brush development systems, however, provided an 
improved method for reproducing both line images, and solid areas. 
In magnetic brush development systems, it is usually desirable to attempt 
to regulate the thickness of the developer composition, which is 
transported on a roller, by moving the roller past a metering blade. The 
adjustment of the metering blade is important, since in the development 
zone the flow of developer material is determined by a narrow restrictive 
opening situated between the transport roller and the imaging surface. 
Accordingly, in order to provide sufficient toner particles to the imaging 
surface, it is generally necessary to compress the developer bristles, 
thereby allowing toner particles adhering to the carrier particles near 
the ends of the bristle to be available for development. Any variation, or 
non-uniformity in the amount of developer metered onto the transport 
roller, or into the spacing between the transport roller and imaging 
member can result in undesired developer flow, and non-uniform image 
development. Non-uniform development is usually minimized by carefully 
controlling developer runout on the transport roller, and on the imaging 
member, and by providing a means for side-to-side adjustment in the 
relative positions of the metering blade, development roller and imaging 
member. 
Moderate solid area development with magnetic brush is usually achieved by 
transporting the developer composition on a roller at a speed that exceeds 
the process speed of the image bearing member. At high process speeds the 
development-transport roller speed is limited by centrifugal forces, which 
forces cause the developer material to be removed from the roller. Thus, 
in order to obtain moderate solid area development at high process speeds, 
the use of multiple development rolls is necessary for increased 
developability. 
The developer materials presently used in magnetic brush development differ 
widely in their electrical conductivity, thus at one extreme in 
conductivity, such materials can be insulating, in that a low electrical 
current is measured when a voltage is applied across the developer. Solid 
area development with insulating developer compositions is accomplished by 
metering a thin layer of developer onto a development roll, which is in 
close proximity to an image bearing member, the development roll 
functioning as an electrode, and thus increasing the electrostatic force 
acting on the toner particles. In these systems, the spacing between the 
image bearing member, and the development roller must be controlled to 
ensure proper developer flow, and uniform solid area development, the 
minimum average spacing generally being typically greater than 1.5 
millimeters. 
Insulating developer compositions can be rendered conductive by utilizing a 
magnetic carrier material which supports a high electric current flow in 
response to an applied potential. Generally, the conductivity of developer 
compositions depends on a number of factors including the conductivity 
properties of the magnetic carrier, the concentration of the toner 
particles, the magnetic field strength, the spacing between the image 
bearing member and the development roll, and developer degradation due to 
toner smearing on the carrier particles. Also, when insulative toner 
particles are permanently bonded to a conductive carrier, the conductivity 
decreases to a critical value below which solid area development becomes 
inadequate, however, within certain limits the process and material 
parameters can be adjusted somewhat to recover the decrease in solid area 
developability. 
When employing conductive developer materials in electrostatographic 
imaging systems, the development electrode member is maintained at a close 
effective distance from the image bearing member, and a high electrostatic 
force acts only on those toner particles which are adjacent to the image 
bearing member. Accordingly, since the electrostatic force for development 
in such systems is not strongly dependent on the developer layer 
thickness, the uniformity of solid area development is improved despite 
variations in the spacing between the image bearing member and the 
development roller member. More specifically, for example, in magnetic 
brush development systems utilizing conductive developer materials, solid 
area deposition is not limited by a layer of net-charged developer near 
the imging member, since this charge is dissipated by conduction to a 
development roller. The solid area deposition is, however, limited by 
image field neutralization; provided there is sufficient toner available 
at the ends of the developer brush, which toner supply is limited to the 
ends or tips of the bristles, since toner cannot be extracted from the 
bulk of the developer mixture; wherein high developer conductivity 
collapses the electric field within the developer at any location, and 
confines it to a region between the latent image and the developer. For 
either insulative or conductive developer, solid area deposition is 
limited by toner supply at low toner concentrations, and the toner supply 
is limited to a layer of carrier material adjacent to the image bearing 
member, since the magnetic field stiffens the developer, and hinders 
developer mixing in the development zone. 
In the above-described systems, undesirable degradation or deterioration of 
the developer particles results. This is generally caused by a variety of 
factors, including for example, the frequency of collisions between 
adjacent carrier particles contained in the developer composition, which 
collisions adversely affect the developer conductivity, and the 
triboelectric charging relationships between the toner particles and 
magnetic carrier particles. Thus, for example, a decrease in the 
triboelectric charge on the toner particles causes an increase in solid 
area development, and an increase in the amount of toner particles that 
are deposited in the background, or normally white areas of the image, 
accordingly, in order to maintain the original image quality in such 
situations, the triboelectric charge on the toner particles is increased, 
by reducing the concentration of such particles in the developer 
composition mixture. Also, when the toner charge, and toner concentration 
decreases, the developer material must be replaced in order to obtain 
images with acceptable solid areas and decreased background. 
While several improved types of toner and carrier materials, as well as 
processes have been developed for the purposes of developing images, 
difficulties continue to be encountered in the design of a simple, 
inexpensive, and reliable two-component development system which will 
provide a high solid area development rate, low background deposition, and 
long term stability. The present magnetic brush systems are inherently 
inefficient primarily since only a small fraction of the toner transported 
through the development zone is accessible for deposition onto the image 
bearing member. For insulative developer, the solid area deposition is 
limited by a layer of net-charged carrier particles produced by toner 
development onto a precharged imaging member. Since the developer entering 
the development zone has a neutral charge, deposition of charged toner 
onto the imaging member produces a layer of oppositely charged developer 
which opposes further toner deposition. Also, the net electrostatic force 
due to the charged image member, and the net-charged developer layer 
becomes zero for that toner between the developer and the electrostatic 
latent image of the imaging member, and a collapse in the electrostatic 
force, or the electric field acting on the charged toner, occurs even 
though the toner charge deposited on the photoreceptor does not neutralize 
the image charge. Image field neutralization can occur, however, if there 
is a sufficiently high developer flow rate, and multiple development 
rollers. Image field neutralization results when the potential due to a 
layer of charged toner deposited on the imaging member is equal but 
opposite to the potential due to the charged imaging member. In the 
absence of a bias on the development roller, image neutralization produces 
a zero development electric field, and since the toner layer is of finite 
thickness, the charge density of the toner layer is less than the image 
charge density. Should the thickness of the charged toner layer be much 
less than the imaging member, image field neutralization occurs when the 
toner charge density neutralizes the image charge density. 
Accordingly, there continues to be a need for apparatus and processes which 
will improve the quality of the images produced, particularly in 
electrostatographic systems, such as xerographic imaging systems, which 
are simple and economical to operate; and which result in reproducible 
high quality images, including both line copy and solid area image 
development. Additionally, there continues to be a need for the provision 
of an apparatus, and process wherein background development is 
substantially eliminated, and where the life of the developer composition 
is increased. 
SUMMARY OF THE INVENTION 
It is therefore a feature of the present invention to provide a development 
process, and development apparatus which overcomes the above-noted 
disadvantages. 
It is a further feature of this invention to provide a self-agitated 
development apparatus, and process which allows for the production of 
images of high quality. 
Another feature of the present invention is the provision of an improved 
development apparatus, and process, which employs two-component insulative 
developer materials, and a deflected flexible imaging member. 
A further feature of the present invention is the provision of a 
self-agitated, two-component insulative development system, wherein low 
magnetic field development is accomplished. 
An additional feature of the present invention is the provision of a 
self-agitated development apparatus and process, whereby toner particles 
are continuously available immediately adjacent to the imaging surface, 
thus allowing full development of the image involved, including 
development of all solid areas. 
It is yet another feature of this invention to provide a development 
process for efficiently developing a low voltage image bearing member. 
In a further feature of the present invention there is provided development 
apparatus, and process which extends the life of the developer. 
These and other features of the present invention are accomplished by 
providing a self-agitated, two-component, insulative development process, 
and apparatus wherein toner is made continuously available immediately 
adjacent to a flexible deflected imaging surface, and toner particles 
transfer from one layer of carrier particles to another layer of carrier 
particles in a development zone. In one embodiment, this is accomplished 
by bringing a transporting member, such as a development roller, and a 
tensioned deflected flexible imaging member, into close proximity, that 
is, a distance of from about 0.05 millimeters to about 1.5 millimeters, 
and preferably from about 0.4 millimeters to about 1.0 millimeters, in the 
presence of a high electric field, and causing such members to move at 
relative speeds. Agitation of the developer particles contained in the 
development zone, depends primarily on the arc of degree of deflection of 
the flexible imaging member, and the relative speeds of, and the distance 
between the flexible imaging member and the transporting member, while 
migration of the toner particles depends primarily on the magnitude of the 
electric field in the development zone. The electric field utilized is 
inversely proportional to the developer thickness, and directly 
proportional to the difference in potential between the deflected charged 
imaging member, and the bias on the transporting member. At a typical 
image potential of about 400 volts, a background potential of about 50 
volts, and a transporting member bias of about 100 volts to suppress 
background deposition, the solid area development potential is about 300 
volts across the developer layer. For a preferred developer thickness of 
0.5 mm (millimeters), the development electric field is 300 volts across 
0.5 mm; i.e., 600 V/mm. 
The degree of developer agitation is proportional to the shear rate, and 
the development time, thus, at a particular process speed and at a 
particular transporting member speed, increased developer agitation is 
obtained when the developer layer is thin, and the development zone is 
long. The development zone length ranges from 0.5 cm to 5 cm with a 
preferred length being between 1 cm and 2 cm. However, lengths outside 
these ranges may be used providing the objectives of the present invention 
are accomplished. 
More specifically, the present invention in one embodiment is directed to a 
process for causing the development of electrostatic latent images on an 
imaging member, comprising providing a development zone, encompassed by a 
tensioned deflected flexible imaging member and a transporting member, 
causing the flexible imaging member to move at a speed of from about 5 
cm/sec to about 50 cm/sec, causing the transporting member to move at a 
speed of from about 6 cm/sec to about 100 cm/sec, said flexible member and 
said transporting member moving at different speeds, maintaining a 
distance between the flexible imaging member and the transporting member 
of from about 0.05 millimeters to about 1.5 millimeters, adding insulating 
developer particles to the development zone, which particles are comprised 
of electrically insulating toner particles, and electrically magnetic 
carrier particles, the flexible imaging member being deflected by the 
electrically insulating developer particles contained in the development 
zone, introducing a high electric field in the development zone, wherein 
the developer particles contained in the development zone are agitated, 
and the insulating toner particles migrate from one layer of carrier 
particles to another layer of carrier particles in the development zone, 
the carrier particles rotating in one direction then subsequently in 
another direction, whereby toner particles are continuously made available 
immediately adjacent the flexible imaging member, said process being 
accomplished in the absence of a magnetic field. 
In another embodiment, the present invention is directed to a self agitated 
development apparatus comprised of a deflected flexible imaging member 
means moving at a speed of from about 5 cm/sec to about 50 cm/sec, a 
transporting means moving at a speed of from about 6 cm/sec to about 100 
cm/sec, said flexible imaging member means, and said transporting means 
moving at different speeds, a development zone means containing insulating 
developer particles and situated between the deflected flexible imaging 
member means and the transporting member means, said flexible imaging 
member means being deflected by said developer particles in an arc of from 
about 10 degrees to about 50 degrees, wherein toner particles transfer 
from one layer of carrier particles to another layer of carrier particles 
in the development zone, causing the toner particles to be made 
continuously available immediately adjacent the flexible imaging member. 
In one further embodiment, the present invention is directed to an 
electrostatographic imaging apparatus comprised of an imaging means, a 
charging means, an exposure means, a development means, and a fixing 
means, the improvement residing in the development means comprising in 
operative relationship a tensioned deflected flexible imaging means; a 
transporting means; a development zone situated between the imaging means 
and the transporting means; the development zone containing therein 
electrically insulating toner particles, and electrically insulating 
magnetic carrier particles, means for causing the flexible imaging means 
to move at a speed of from about 5 cm/sec, to about 50 cm/sec; means for 
causing the transporting means to move at a speed of from about 6 cm/sec 
to about 100 cm/sec, the means for imaging and the means for transporting 
moving at different speeds; the means for imaging and the means for 
transporting having a distance therebetween of from about 0.05 millimeters 
to about 1.5 millimeters. 
In another embodiment, the present invention is directed to an 
electrostatographic imaging apparatus comprised of an imaging means, a 
charging means, an exposure means, a development means, a transfer means, 
and a fixing means, the improvement residing in the development means 
comprised in operative relationship of a deflected flexible imaging means, 
and a transporting means, means for causing the transporting means to move 
at a speed of from about 6 cm/sec to about 100 cm/sec, means for causing 
the deflected flexible imaging member means to move at a speed of from 
about 5 cm/sec to about 50 cm/sec, the means for transporting and the 
means for imaging moving at different speeds, said deflected flexible 
imaging member means and said transporting means having a distance 
therebetween of from about 0.05 millimeters to about 1.5 millimeters, the 
deflection of the flexible imaging member means being caused by 
electrically insulating developer particles comprised of electrically 
insulating toner particles, and electrically insulating magnetic carrier 
particles situated in a development zone encompassed by said deflected 
flexible imaging member means and said transporting means, said 
deflection, and the relative movement of the deflected imaging member 
means and transporting means providing sufficient force so as to cause 
agitations of said developer particles, means for introducing a high 
electric field in the development means, wherein said electrically 
insulating toner particles migrate from said electrically insulating 
carrier particles, the migration being in the direction of the deflected 
flexible imaging member means, said migration resulting from the rotation 
of the electrically insulating carrier particles in one direction, and 
subsequently in another direction, whereby said electrically insulating 
toner particles are made continuously available immediately adjacent to 
the deflected flexible imaging member means. 
In another illustrative embodiment, the present invention is directed to an 
electrostatographic imaging apparatus comprised of an imaging member 
means, a charging means, an exposure means, a development means, a 
transfer means, and a fixing means, the improvement residing in the 
development means comprised of a magnetic member means, containing magnets 
therein, a deflected flexible imaging means, means for causing movement of 
the magnetic member means, means for causing movement of the deflected 
flexible imaging means, the magnetic means and imaging means moving at 
different speeds, a developer reservoir means containing developer 
particles comprised of electrically insulating toner particles, and 
electrically insulating carrier particles, which developer particles are 
attracted to and maintained on the magnetic means, high magnetic field 
regions at the entrance and exit region in a development zne encompassed 
by the magnetic member means, and the deflected flexible imaging member 
means, and low magnetic field means in the development zone, wherein 
insulating toner particles are attracted to and deposited onto the 
deflected flexible imaging member. 
One important feature of the present invention, which together with the 
relative movement of the flexible imaging member, and the transporting 
member is primarily responsible for the agitation of the developer 
particles contained in the development zone, resides in the deflected 
flexible imaging member, this imaging member being deflected in an arc of 
from about 10 degrees to about 50 degrees, with respect to the 
transporting member. This deflection is caused primarily by the pressure 
exerted on the tensioned flexible imaging member by the developer 
particles contained in the development zone. As a result of the presence 
of these particles, there is exerted on the tensioned flexible member a 
pressure of from about 0.01 pounds per squared inch to about 2 pounds per 
squared inch, and preferably from about 0.1 pounds per squared inch, to 
about 1 pound per square inch. The pressure exerted on the flexible 
imaging member is also dependent on the tension and arc radius of the 
imaging member, thus the pressure P is obtained by dividing the belt 
tension, T, expressed in a force per unit width of the deflected imaging 
member, by the arc radius, R of the imaging member, as represented by the 
equation P=T/R. 
The flexible imaging member, in contrast to a rigid imaging member, 
provides a normal or downward force on the developer particles, in 
perpendicular relationship thereto, and such member also exerts a 
frictional force in parallel relationship to the deflected flexible 
imaging member and the transporting member, which frictional force causes 
agitation of the developer particles. As a result of agitation, the 
carrier particles move or rotate, allowing toner partiles to migrate from 
one layer of carrier particles to another layer of carrier particles in 
the presence of a high electrical field, as indicated hereinbefore. 
Agitation, and thus rotation of the carrier particles is not accomplished 
with a rigid imaging member, since such a member exerts substantially no 
frictional force, and provides a substantially zero normal force. 
Accordingly, the toner particles will not migrate from one layer of 
carrier particles to another layer of carrier particles in accordance with 
the process and apparatus of the present invention. This lack of movement 
of the toner particles will adversely effect image quality, especially 
with regard to the development of solid areas. 
The frictional force exerted by the flexible imaging member is dependent on 
a number of factors, including the degree of deflection of the imaging 
member, the tension in the imaging member, the coefficient of friction 
between the imaging member, and the insulating developer particles, and 
the normal force. Thus the frictional force exerted is the product of the 
coefficient of friction between the flexible imaging member, and the 
developer particles, and the normal force. The normal force exerted on one 
developer particle is the product of the normal pressure and the projected 
area of the developer or carrier particle. 
By flexible imaging member as used herein is meant deformed or deflected, 
such as the photoconductive materials, as described in U.S. Pat. No. 
4,265,990. In contrast, a rigid imaging member cannot be easily deflected, 
such members being stiff or hard, like amorphous selenium which has not 
been deposited on a flexible substrate. Improved developer agitation in 
the development zone, and hence better solid area development is obtained 
when a low magnetic field or substantially no magnetic field is present in 
such a zone, as the developer does not stiffen, reference for example FIG. 
2, but is fluid like under agitation and/or shearing. In accordance with 
the present invention, the magnetic field is generally less than about 150 
gauss, and preferably less than 20 gauss. 
The process of the present invention can be employed in electrostatographic 
systems as illustrated, for example, in FIG. 8. Such a development system, 
utilizing a flexible deflected imaging member results in a number of 
advantages over conventional imaging systems, including for example, 
agitation of the developer particles as described herein, maximum solid 
area and line development is at its maximum since the charge on the toner 
particles neutralizes the fields emanating from the image charge, and 
development, limited by image field neutralization enables the development 
of low voltage images associated with thin image bearing members, having a 
thickness of from about 10 to about 30 microns. Furthermore, for a 
particular image potential, the amount of toner particles deposited on the 
flexible image bearing member can be, within certin limits, substantially 
independent of the spacing between the transporting member and the 
flexible imaging member.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Illustrated in FIG. 1 is one embodiment of the development system of the 
present invention designated 10, which is comprised of a positively charge 
deflected flexible image member 1, negatively charged toner particles 2, 
attached to positively charged insulating carrier particles 3, a developer 
transporting member 4, which can also function as a development electrode, 
toner depleted layer D, which layer has carrier particles containing a 
positive charge, this layer having less toner on the carrier than the 
adjacent carrier layers, C, B, and A, a biased voltage source 6, and a 
toner developed layer 7. A, B, C, and D designate layers of insulating 
developer comprised of carrier and toner particles. The deflected flexible 
image bearing member 1, and developer transporting member 4, in this 
embodiment are moving in the direction shown by the arrows 5 and 5a. Also, 
in this illustration the transporting member 4 is moving at a more rapid 
rate of speed than the image bearing member 1, which difference in speed 
contributes to agitation, and a shearing action in the development zone, 
thereby causing agitation of the carrier and toner particles, wherein 
movement of the carrier particles in the presence of an electrical field 
causes toner particles to transfer from one layer of carrier particles, 
such as layer B, to another layer of carrier particles, such as layer A. 
It is not intended, however to be limited to the method of operation 
shown, nor to be limited to any theory of operation. 
The speed of the imaging member 1 can be greater than the speed of the 
transporting member 4, and movement can be in the opposite direction to 
that which is shown. Also although the carrier particles 3 are shown in 
ordered layers, in actual operation they can be distributed randomly in 
size and position. Further the shape of the carrier particles is not 
necessarily completely spherical as shown, that is, most carrier particles 
are non-spherical, with surfaces that can be jagged or textured. In 
certain embodiments the toner particles 2, can be charged positively, and 
the carrier particles 3, can be charged negatively. Such a developer would 
be useful in systems where the deflected flexible image bearing member is 
charged negatively. 
The arrows within the carrier particles 3, indicate that such particles are 
moving in both directions, first in one direction, for example, slightly 
to the right than in another direction, slightly to the left. While moving 
in one direction, then another, the particles are also rotating as more 
clearly illustrated in FIGS. 1A-1C. This movement or agitation, which 
results in improved development of images, is caused primarily by the 
frictional force exerted by the tensioned deflected flexible imaging 
member, which force would not be exerted by a rigid imaging member, and 
the relative movement of member 1, and member 4, as indicated herein. 
In one method of operation, as indicated hereinbefore, the transporting 
member 4 is moving at a surface speed which is faster than the speed of 
the flexible imaging member 1, with the development member and the 
deflected flexible imaging member moving in the same direction. This 
relative motion between the member 4, and the deflected flexible imaging 
member 1, is a contributing factor in causing the developer composition, 
which is comprised of toner particles 2, and carrier particles 3, to be 
agitated by a shearing action. When the speed of the flexible image 
bearing member 1, is less than the speed of the member 4, as shown in FIG. 
1, the shearing action causes movement of the carrier particles 3, that 
is, the carrier particles move in both a clockwise and counterclockwise 
direction, but on the average tend to move in a counterclockwise 
direction. The developer agitation and the development electric field 
allow toner particles 2 adhering to the carrier particles 3 to migrate 
towards the imaging member 1. The toner particles closest to the deflected 
flexible imaging member 1 are deposited on the imaging surface, therefore 
the carrier particles adjacent the imaging surface loose some of the toner 
particles adhering thereto, which toner particles must be replaced in 
order to continue to achieve high quality development, and in particular, 
solid area development. In order for this to occur, toner particles must 
be transferred from adjacent carrier layers, and this transfer is caused 
on a continual and constant basis by the shearing action, and an 
electrical field as indicated hereinbefore. Maximum agitation, which is 
preferred, is obtained when the magnetic field in the development zone is 
low, and the developer composition layer contained in the development zone 
is thin, that is, ranging in thickness of from about 0.05 millimeters to 
about 1.5 millimeters, and preferably from about 0.4 millimeters to 1.0 
millimeters. By low magnetic field it is meant that the field strength is 
generally less than 150 gauss. 
When the deflected flexible image bearing member is positively charged, an 
electrostatic force directed towards the imaging member acts on all of the 
negatively charged toner particles 2, which are near the image-carrier 
interface, and the carrier-carrier interfaces. In the absence of developer 
agitation, the electrostatic force on the toner particles is not 
sufficient under normal conditions to overcome toner adhesion, and thus 
the toner particles are retained on the carrier particles 3. However, when 
agitation is supplied to the developer, in the presence of an electric 
field, the toner which remains between two carrier particles can easily 
transfer when the surfaces are separated by a rolling or a sliding action. 
The rate of electric field assisted toner migration towards the flexible 
image member is therefore increased significantly, in comparison, to when 
agitation is not utilized. 
As illustrated in FIG. 1, toner migration results in a toner depleted layer 
D, and although the toner depleted carrier is positively charged, the 
effect of this charge layer on the toner motion in the bulk of the 
developer is small due to the proximity of the layer to the development 
roll. Thus, both solid area and line development will cease when the 
charge on the imaging member is essentially neutralized with charged 
toner. Accordingly, the availability of toner for solid area development 
is enhanced for a self-agitated two-component insulative development 
system, and when the electrostatic force and development agitation are 
sufficient, nearly all of the toner in the developer bulk will deposit on 
the image bearing member. 
The degree of developer agitation can be defined as the product of the 
shear rate and development time. The average shear rate is equal to the 
absolute value of the difference in the development roller or electrode 
velocity, V.sub.R, and imaging member velocity, V.sub.I, divided by the 
developer thickness, L, i.e., the average shear rate equals 
.vertline.V.sub.R -V.sub.I .vertline./L. The development time is equal to 
the development zone length, W, divided by the absolute value of the 
developer roller speed, .vertline.V.sub.R .vertline.; i.e, the development 
time equals W/.vertline.V.sub.R .vertline.. Thus the degree of developer 
agitation is equal to (.vertline.V.sub.R -V.sub.I 
.vertline./L).times.(W/.vertline.V.sub.R .vertline.) or 
[.vertline.1-1/V.vertline.] where V is equal to V.sub.R /V.sub.I and is 
positive or negative when the development roller or electrode moves in the 
same or opposite direction to the image bearing member respectively. It is 
assumed that the quantity .vertline.1-1/.vertline.V, is typically near a 
value of 1 in which case the degree of developer agitation is approximated 
by W/L, i.e., the ratio of the developer zone length to the developer 
layer thickness. When the development zone length ranges from 0.5 cm to 5 
cm (W) with a preferred length of 1 cm to 2 cm and the developer layer 
ranges in thickness of from about 0.05 mm to 1.5 mm (L) and preferably 
about 0.4 mm to 1.0 mm, the developer agitation ranges from 2 to 1,000 and 
preferably from 10 to 50. 
There is shown in some detail in FIGS. 1A, 1B, and 1C, what is occurring at 
each of the different layers of developer, designated A, B, and C when 
employing the imaging process and apparatus of the present invention. In 
these Figures the numerical and letter designations illustrate the 
identical components as described with reference to FIG. 1, with the 
addition that Z represents an area or zone of the carrier particles which 
have been depleted of toner particles. In FIG. 1A there is illustrated a 
carrier particles 3, of layer A, which are depleted by toner particles 2, 
in the area or zone Z; while FIG. 1B, illustrates the transfer of toner 
particles 2, from carrier particle 3, of layer B, to carrier particle 3, 
of layer A, resulting in a toner depleted area or zone Z, on carrier 
particle 3, layer B. In FIG. 1B, 8 represents the interface area between 
carrier particles, the toner particle 2 transfer from carrier particles 3 
of layer C, to carrier particles 3, of layer B, and there results a toner 
depleted layer or zone Z, on carrier particle 3, layer C. In essence thus 
the carrier particles of layers A, and B for example, reference FIG. 1B, 
contact each other, forcing the toner particles 2 between the carrier 3 of 
layers A and B, to in effect decide what carrier particles to remain with, 
those of layer A, or those of layer B. In view of the agitation system of 
the present invention the toner particles move from the carrier particles 
of layer B, to the carrier particles of layer A, thereby replacing the 
depleted toner particles on the carrier of layer A in order that such 
particles will be available to deposit on the imaging member, and cause 
development. In zone Z electrical fields transfer the toner particles from 
the carrier beads, for example the carrier beads of layer A, to the 
imaging member 1. This is caused primarily because of the rocking motion 
of the carrier beads 3, due to, for example, the frictional force exerted 
by the tensioned flexible imaging member, which motion further causes a 
positive charge to be contained on the carrier particles. 
More specifically, with reference to FIGS. 1A, 1B and 1C, as the carrier 
beads rotate in accordance with the present invention, some of the toner 
particles, 2 on the carrier bead of layer A, transfer to the image bearing 
member. The toner particles between the carrier particles of layer A, and 
the carrier particles of layer B, are being acted upon by two opposing 
forces that from the carrier bead of layer A, and the electrostatic force 
from the charged imaging member, and that from the carrier bead of layer 
B. As the force from the carrier bead of layer A, and the imaging member 
is greater than the force from the carrier bead of layer B, the toner 
particles become detached form the carrier particles of layer B and attach 
to the carrier particles of layer A during bead rotation, reference FIG. 
1B. This action replaces the toner particles on the carrier particles of 
layer A but leaves the carrier particles of layer B, with less toner 
particles. The carrier particle of layer A now has a net electrical charge 
of zero, whereas the carrier particle of layer B has a net positive 
electrical charge. The same transfer of toner particles and electrical 
forces is ilustrated in FIG. 1C, however, an additional layer of carrier 
particles is shown, namely layer C. Thus the carrier particles of layer B, 
obtains toner particles from the carrier particles of layer C by the 
methods described herein. This transfer of toner particles across the 
different carrier interfaces actually occurs simultaneously throughout the 
development zone, and as a result toner particles are continually 
available on the carrier particles immediately adjacent the imaging 
member, while the carrier particles near the transporting member 4 contain 
an excess of positive charges, in view of the loss of toner particles to 
the next layer of carrier particles. After a short period of time, the 
charge on the carrier particles near the member 4, become neutralized as a 
result of the high electrical field between the carrier particles and the 
imaging member. Subsequently, the carrier, and toner particles contained 
thereon are allowed to pass through a development sump in order that 
neutral toner particles from a toner dispenser can replenish those toner 
particles that have been used for developing images, reference FIG. 5. 
Developer mixing in the developer sump charges the added toner by 
triboelectric charging. 
When the apparatus and process of the present invention are employed in an 
imaging system, there is provided increased line and increased solid area 
development, which increases also result in those situations where the 
developer composition has a rather low toner concentration, in comparison 
to the developer compositions used in conventional systems. The minimum 
toner concentration for acceptable solid area development depends on 
several factors including the ratio of the transporting member speed to 
imaging member speed, and the degree of developer agitation which depends, 
for example, on the magnetic field strength, the development zone length, 
and the spacing between the imaging member and the development roll. Thus 
for example for a developer containing 0.25 percent by weight of toner, 
mixed with about 0.75 percent by weight of 100 um diameter steel carrier 
beads, the solid area development is 0.5 mg/cm.sup.2 for a development 
voltage of 300 volts, a speed ratio of 3, a magnetic field less than 20 
gauss, a development zone length of 3.3 cm, and a developer layer 
thickness of 0.5 mm. 
Illustrated in FIG. 2 is a conventional magnetic brush development system, 
wherein two component insulative developer material is used, this 
illustration being provided in order to more clearly point out the 
advantages of the present invention in some respects over conventional 
magnetic brush systems. The imaging system of FIG. 2 is comprised of an 
imaging member 1, negatively charged toner particles 2, positively charged 
carrier particles 3, development electrode 4, developed toner layer 7, 
image developer interface 9, and a biased voltage source 6. The developer, 
that is, toner plus carrier is a two-component insulative developer as 
described with reference to FIG. 1. 
The magnetic field casues the developer to form bead chains or bristles, 
which are rigid or stiff. Thus developer agitation is limited to a region 
near the image developer interface 9, and as no agitation in occurring 
with the other developer particles, transfer of toner from the carrier 
particles does not result, thereby in effect rendering these other 
developer particles substantially useless. The charge density on the 
developer layer A is equal to the negative of the toner charger density 7 
on the image bearing member, divided by the ratio of the development 
electrode speed to imaging member speed. The electric field from the layer 
of charged developer A is highly effective in reducing the net electric 
field at the image developer interface. This electric field becomes zero 
despite the fact that the image charge is not neutralized by toner charge. 
Solid area development with insulative developers is limited by field 
collapse even though a sufficient supply of toner might be contained 
within the first layer of developer A. Furthermore, the solid area 
development rate decreases when the toner concentration is low and the 
stiffening of developer by the magnetic field aids in limiting the supply 
of toner. 
Illustrated in FIG. 3 is an enlarged view of a development zone containing 
conductive developer. In this Figure, 1 represents the imaging member, 2 
represents negatively charged toner particles, 3 represents positively 
charged carrier particles, 4 is a development electrode, 6 represents the 
voltage source, 7 represents the developed toner layer. As illustrated in 
this Figure, the charged image bearing member induces an opposite charge 
in the layer of developer adjacent to the image. Toner in the developer 
(within the layer of developer) is inaccessible since the electric field 
is zero, because the high developer conductivity, and the magnetic field 
stiffens the developer, and reduces the migration of toner to the image 
bearing member, that is, toner particles usually do not transfer from one 
layer of carrier particles, such as B, to another layer of carrier 
particles such as A, as is the situation with the process and apparatus of 
the present invention. 
The conditions which make possible a self-agitated development zone for the 
improvement of solid area development efficiency is more clearly 
appreciated by describing measurements on a well defined system. This is 
illustrated in FIG. 4, which represents an electroded cell for measuring 
the development properties of developer under controlled conditions. In 
this Figure, the developer is located in a conducting tray 11, that can be 
biased with a voltage supply. The upper electrode 12 is coated with an 
insulating material such as a polyester or photoreceptor layer 13, which 
is contacted with the developer 14, when a bis is applied to the developer 
tray 11. Movement of the electrode as indicated by the arrow causes 
agitation of the developer layer. The toner density developed onto layer 
13 is measured by weighing the electrode assembly before, and after 
subjecting the assembly to an air jet for the purpose of removing toner 
particles. Using the device shown in FIG. 4, in one embodiment, the toner 
weight per unit area was 0.23 mg/cm.sup.2, which was deposited on an 
insulating overcoated electrode 12 under the following conditions: a 
developer bed thickness of 1.5 mm, an applied voltage of 600 volts, and an 
electrode displacement of 1.9 cm. When a magnetic field of 450 gauss was 
applied perpendicular to the cell electrodes, the developed toner mass 
decreased to 0.09 mg/cm.sup.2. The larger developed toner mass for 
magnetic field free conditions is attributed to increased developer 
agitation. Also, the toner weight developed on the image bearing member is 
proportional to the ratio of the transporting member and the imaging 
member speed. Thus when this ratio is 2, and under the conditions stated 
herein, the toner weight per unit area of 0.46 mg/cm.sup.2, would be 
obtained on the image bearing member. This would result in an acceptable 
reflective optical density of 1.1. 
When similar development data is obtained with a thinner developer layer of 
0.5 mm, the solid area development increses since the development electric 
field is higher. With a 450 gauss magnetic field applied across the 
developer, the developed toner density is 0.28 mg/cm.sup.2 compared to the 
0.09 mg/cm.sup.2 obtained for a developer thickness of 1.5 millimeters. 
For magnetic field free conditions, the developed density increases to 
0.80 mg/cm.sup.2 compared to the 0.23 mg/cm.sup.2 obtained when the 
developer thickness is 1.5 mm. The increase in solid area development for 
the magnetic field-free case is due to a high agitation of the thin 
developer layer. The agitation increases the toner supply and displaces 
the developer net-charge towards the development electrode. Increased 
solid area development is thus obtained by making the developer layer thin 
and the development zone magnetic field free. 
Self-agitation of the developer in the development zone requires relative 
motion between the developer transporting member and the deflected 
flexible image bearing member as indicated herein. When the transporting 
member is brought into contact with the developer without lateral 
movement, a small quantity of toner is transferred to the member when a 
voltage is applied and the member removed, while when the member is 
displaced while in contact with the developer, increased development 
occurs since the developer is agitated by the relative motion. The degree 
of agitation depends, for example, on the magnitude of the relative 
displacement, which is the product of the relative speed and displacement 
time. 
In a practical development system based on insulative developer a high 
solid area development rate is achieved when the development zone is thin, 
magnetic field free, and long, such development systems containing a means 
of flowing fresh developer through the development zone. Since the 
developer transporting member is typically moving at a speed faster than 
the image bearing member, developer will tend to accumulate at the 
entrance to the magnetic field free zone. To ensure good developer flow, a 
strong magnetic field at the zone entrance helps to establish proper 
developer flow through a low magnetic field region. A strong magnetic 
field at the exit region of the developer zone reduces carrier adhesion to 
the image bearing member, reference FIG. 5, and prevents scavaging of the 
toner in solid areas, since as the electrode spacing increases the fields 
in the solid areas decreases. 
Illustrated in FIG. 5 is another embodiment of the present invention 
wherein there is utilized a thin low magnetic field development zone, and 
a high magnetic field at the entrance and exit regions of the development 
zone. More specifically, there is illustrated in FIG. 1 a deflected 
flexible imaging member 1, which imaging member is subjected to a 
tensioning means, not shown, developing and transporting roller 15, 
magnets 16 attached to core 17, insulating developer particles 18, 
comprised of toner particles and carrier particles, developer reservoir 
19, metering blade 20, low magnetic field region 21, high magnetic field 
regions 22 and 23, the arrows indicating the direction of movement. 
Agitation of the carrier particles and movement of the toner particles as 
indicated hereinbefore occurs in a zone defined by the deflected imaging 
member 1 and roller 15. In operation, the developer particles 19, are 
intitially transported on roller 15, subsequent to metering by blade 20, 
which metering controls the thickness of the developer layer, the 
particles maintaining their position on roller 15 in view of the high 
magnetic fields 22 and 23, and the toner particles being caused to migrate 
to the imaging member 1, in low magnetic field region 21. 
Developer agitation is caused by the frictional force exerted by the 
flexible imaging member and the relative movement between the imaging 
member and magnetic roller as indicated herein, while the thickness of the 
developer layer, usually one layer of developer particles establishes the 
distance between the imaging member and the magnetic roller. Steel 
shunting inside the roller 15 is utilized to reduce the magnetic field 
between the magnetic poles at the entrance and exit regions. For 
achievement of good developer flow, the ratio, V of roller 15 velocity to 
flexible imaging member velocity, is greater than zero and less than -1. 
Inadequate developer flow usually results when V is greater than -1, that 
is -1/2 and the like. 
The magnetic field within the central area of the development zone is 
generally less than 150 gauss and preferably less than 20 gauss, while the 
magnetic field at the entrance and exit regions of the development zone is 
radially directed and is typically from about 300 to about 600 gauss. The 
magnetic field profile is obtained by a suitable choice of permanent 
magnets and steel shunting inside the roller 15 can provide magnetic field 
shaping at the surface of this roller. Also the magnetic poles are of like 
polarity in the embodiment illustrated. 
A thin layer of developer is applied to the roller 15 with the aid of a 
metering blade 20, closely spaced from the development roll. The 
uniformity of the developer thickness is determined by the runout in the 
roll and the straightness of the metering blade. When the metering blade 
is positioned where the magnetic field is in a radial direction 
(perpendicular to the development roll), the developer layer thickness is 
approximately equal to the metering blade gap setting. If the metering 
blade is located where the magnetic field is tangential to the roll, the 
developer layer thickness is approximately 0.4 of the metering gap 
setting. A reduced developer layer thickness is obtained because the 
developer bead chains tangential to the development roll are magnetically 
attracted to the mass of developer peeled away by the metering blade. 
Developer matering in a tangential magnetic field enables one to obtain a 
thin developer layer of approximately 0.5 mm when the metering gap is set 
at 1.2 millimeters. 
FIG. 6 is a graph of data comprising the solid area development 
characteristics of the self-agitated development system depicted in FIG. 
5, curve G; with the characteristics of a conventional magnetic brush 
system, curve H. As illustrated, line curve G, reveals an increased or 
higher optical density, as compared to line curve H. Therefore, increased 
toner deposition on the flexible imaging member results, curve G. 
With specific reference to FIG. 6, line G represents data obtained for the 
development system of the present invention with a 0.4 millimeter gap, 
(distance between the imaging member, and the transporting member) while 
curve H represents data obtained with a conventional magnetic brush 
system, 1.5 millimeter gap. A developer composition comprised of toner 
particles, in a 2.7 percent concentration consisting of a styrene 
n-butylmethacrylate copolymer and carbon black, and carrier particles 
containing a flouropolymer coating on a ferrite core was employed in both 
systems; and the speed ratio of the imaging member to the transport member 
was two for each system. Increased toner deposition, and thus increased 
development with the system of the present invention, curve G, is 
attributed to, the utilization of a deflected flexible imaging member, a 
thin developer layer (0.4 mm), a low magnetic field (20 gauss) and long 
development zone (3 cm). In the conventional system, the magnetic field is 
500 gauss, and the development zone length is 0.5 cm. Thus, for example, 
at a development potential of 200 volts, the reflection image density, 
curve G is greater than 1, indicating excellent toner deposition and 
superior development, while for conventional systems at 200 volts the 
reflection image density, curve H, is less than 0.2. 
For the self-agitated development system described herein, the spacing 
between the transporting or development member and the deflected flexible 
image bearing member is determined primarily by the developer layer 
thickness, that is, the amount of toner and carrier particles contained in 
the developer zone. As indicated this spacing typically ranges from about 
0.05 millimeters to about 1.5 millimeters and preferably is from about 0.4 
millimeters to about 1.0 millimeters. 
The length of the development zone depends , for example, on the 
configuration of the image bearing member, and the configuration of the 
developer transport member. In a preferred embodiment, the image bearing 
member is a belt partially wrapped or arced around a development roll, 
which roll has a diameter which is typically from about 3.8 cm to about 
6.4 cm. In this configuration, the length of the development zone, and 
contact between the developer and flexible imaging member ranges from 
about 0.5 cm to about 5 cm, with a preferred length being from about 1 cm 
to about 2 cm. Idler rolls positioned against the backside of the belt can 
be used to alter the belt path. 
FIG. 7 illustrates one example of a self-agitated development system design 
that incorporates an idler roll. Although not shown more than one idler 
roll can be used. The purpose of the idler roll, or rolls, is to allow 
freedom in the position of the zones, such as the paper transport zone for 
example in an electrostatographic or similar apparatus. In this Figure the 
numerical designations 15, 16, 17, 19, 21, 22, and 23 represent the same 
components as described in FIG. 5, while the idler roll is designated 24. 
It is understood that a second idler roll could be placed near region 23 
to alter the path of the imaging member without causing a change in the 
operation of the development system. The system shown in FIG. 7 is 
operating in a mode in which the development roller and imaging member are 
moving in opposite directions. 
The apparatus and process of the present invention is useful in many 
systems including electronic printers, and electrostatographic copying 
machines, such as those employing xerographic apparatus well known in the 
art. In FIG. 8 there is illustrated an electrophotographic printing 
machine employing a deflected flexible imaging member 1 having a 
photoconductive surface deposited on a conductive substrate, such as 
aluminized Mylar, which is electrically grounded. The imaging member 1, or 
the photoconductive surface can be comprised of numerous suitable 
materials, as described herein for example, however, for this illustration 
the photoconductive material is comprised of a photogenerating layer of 
trigonal selenium, or vanadyl phthalocyanine, overcoated with a transport 
layer containing small molecules of N,N,N',N'-tetraphenyl-[1,1'-biphenyl] 
4,4'-diamine, or similar diamines dispersed in a polycarbonate. Deflected 
flexible imaging member 1 moves in the direction of arrow 27 to advance 
successive portions of the photoconductive surface sequentially through 
the various processing stations disposed about the path of movement 
thereof. The imaging member is entrained about a sheet-stripping roller 
28, tensioning means 29, and drive roller 30. Tensioning system 29 
includes a roller 31 having flanges on opposite sides thereof to define a 
path through which member 1 moves. Roller 31 is mounted on each end of 
guides attached to the springs. Spring 32 is tensioned such that roller 31 
presses against the imaging belt member 1. In this way, member 1 is placed 
under the desired tension. The level of tension is relatively low 
permitting member 1 to be relatively easily deformed. With continued 
reference to FIG. 8, drive roller 30 is mounted rotatably and in 
engagement with member 1. Motor 33 rotates roller 30 to advance member 1 
in the direction of arrow 27. Roller 30 is coupled to motor 33 by suitable 
means such as a belt drive. Sheet-stripping roller 28 is freely rotatable 
so as to readily permit member 1 to move in the direction of arrow 27 with 
a minimum of friction. 
Initially, a portion of imaging member 1 passes through charging station H. 
At charging station H, a corona generating device, indicated generally by 
the reference numeral 34, charges the photoconductive surface of imaging 
member 1 to a relatively high, substantially uniform potential. 
The charged portion of the photoconductive surface is then advanced through 
exposure station 1. An original document 35 is positioned face down upon 
transparent platen 36. Lamps 37 flash light rays onto original document 
35. The light rays reflected from original document 35 are transmitted 
through lens 38 forming a light image thereof. Lens 38 focuses the light 
image onto the charged portion of the photoconductive surface to 
selectively dissipate the charge thereon. This records an electrostatic 
latent image on the photoconductive surface which corresponds to the 
informational areas contained within original document 35. 
Thereafter, imaging member 1 advances the electrostatic latent image 
recorded on the photoconductive surface to development station J. At 
development station J, a self-agitated development system, indicated 
generally by the reference numeral 39, advances a developer material into 
contact with the electrostatic latent image. The self-agitated development 
system 39 includes a developer roller 40 which transports a layer of 
developer material comprising magnetic carrier particles and toner 
particles into contact with the deflected flexible imaging member 1. As 
shown, developer roller 40 is positioned such that the brush of developer 
material deforms imaging member 1 in an arc, such that member 1 conforms 
at least partially, to the configuration of the developer material. The 
electrostatic latent image attracts the toner particles from the carrier 
granules forming a toner powder image on the photoconductive surface of 
member 1. The development roller 40 returns the developer material to the 
sump of development system 39 for subsequent re-use. The detailed 
structure of the development system 39 has been described herein, 
reference FIGS. 1, 1A, 1B, 1C, 5 and 7. 
Imaging member 1 then advances the toner powder image to transfer station 
K. At transfer station K, a sheet of support material 44 is moved into 
contact with the toner powder image. The sheet of support material 44 is 
advanced to transfer station K by a sheet feeding apparatus (not shown). 
Preferably, the sheet feeding apparatus includes a feed roll contacting 
the uppermost sheet of a stack of sheets. The feed roll rotates so as to 
advance the uppermost sheet from the stack into a chute. The chute directs 
the advancing sheet of support material into contact with the 
photoconductive surface of member 1 in a timed sequence so that the toner 
powder image developed thereon contacts the advancing sheet of support 
material at transfer station K. 
Transfer station K includes a corona generating device 46 which sprays ions 
onto the backside of sheet 44. This attracts the toner powder image from 
the photoconductive surface to sheet 44. After transfer, sheet 44 moves in 
the direction of arrow 48 onto a conveyor (not shown) which advances sheet 
44 to fusing station L. 
Fusing station L includes a fuser assembly, indicated generally by the 
reference numeral 50, which permanently affixes the transferred toner 
powder image to sheet 44. Preferably, fuser assembly 50 includes a heated 
fuser roller 52 and a back-up roller 54. Sheet 44 passes between fuser 
roller 52 and back-up roller 54 with the toner powder image contacting 
fuser roller 52. In this manner, the toner powder image is permanently 
affixed to sheet 44. After fusing, a chute guides the advancing sheet 44 
to a catch tray for subsequent removal from the printing machine by the 
operator. 
After the sheet of support material is separated from the photoconductive 
surface or imaging member 1 some residual particles remain adhering 
thereto, which particles are removed from the photoconductive surface to 
cleaning station M. Cleaning station L includes a rotatably mounted 
fibrous brush 56 in contact with the photoconductive surface. The 
particles are cleaned from the photoconductive surface by the rotation of 
brush 56 in contact therewith. Subsequent to cleaning, a discharge lamp 
(not shown) floods photoconductive surface 12 with light to dissipate any 
residual electrostatic charge remaining thereon prior to the charging 
thereof for the next successive imaging cycle. 
It is believed that the foregoing description is sufficient for purposes of 
the present application to illustrate the general operation of an 
electrophotographic printing machine incorporating the features of the 
present invention therein. 
Illustrative examples of the deflected flexible image bearing member 1, 
include inorganic and organic photoreceptor materials. Examples of 
inorganic materials, which are deposited on a flexible substrate, include 
amorphous selenium, selenium alloys, including alloys of 
selenium-tellurium, selenium arsenic, selenium antimony, 
selenium-tellurium-arsenic, cadmium sulfide, zinc oxide, and the like. 
Examples of flexible organic materials include layered organic 
photoreceptors, such as those containing as an injecting contact, carbon 
dispersed in a polymer, overcoated with a transport layer, which in turn 
is overcoated with a generating layer, and finally an overcoating of an 
insulating organic resin, such as those described in U.S. Pat. No. 
4,251,612, incorporated herein by reference, and overcoated photoreceptor 
devices comprised of a substrate, a transport layer and a generating layer 
such as those described in U.S. Pat. No. 4,265,990. 
Examples of other flexible imaging member materials include organic 
photoreceptor materials such as polyvinyl carbazole, 
4-dimethylamino-benzylidene, benzhydrazide; 2-benzylidene-amino-carbazole, 
2-benzylidene-amino-carbazole, polyvinyl carbazole; 
(2-nitro-benzylidene)-p-bromo-aniline; 2,4-diphenyl quinazoline; 
1,2,4-triazine; 1,5-diphenyl-3-methyl pyrazoline 2-(4'-dimethyl-amino 
phenyl) benzoxazole; 3amino-carbazole; 
polyvinylcabazole-trinitrofluorenone charge transfer complex; 
phthalocyanines, mixtures thereof, and the like. 
Illustrative examples of the transporting member 4 include virtually any 
conducting material made for this purpose, such as stainless steel, 
aluminum and the like. Texture in member 4 provides traction necessary for 
good developer transport from the developer sump and through the 
development zone. The development roll texture is obtained by one of 
several methods involving flame-spray treating, etching, knurling, and the 
like. 
The developer material is comprised of an electrically insulating toner 
resin, colorant or pigment, and a suitable insulating magnetic carrier 
material. By insulating as used throughout the description, is meant 
non-conducting, that is, for example charge does not tend to flow from the 
transport member to the ends of the carrier particles nearest the image 
bearing member within a time that is less than the development time. 
Considering the range of the development zone length, 0.5 centimeters to 5 
centimeters, and the speed of the transporting member, the range of 
development times is calculated as follows: 
##EQU1## 
While any suitable material may be employed as the toner resin in the 
system of the present invention, typical of such resins are polyamides, 
epoxies, polyurethanes, vinyl resins and polymeric esterification products 
of a dicarboxylic acid and a diol comprising a diphenol. Any suitable 
vinyl resin may be employed in the toners of the present system including 
homopolymers or copolymers of two or more vinyl monomers. Typical of such 
vinyl monomeric units include: styrene, p-chlorostyrene vinyl naphthalene, 
ethylenecally unsaturated mono-olefins such as ethylene, propylene, 
butylene, isobutylene and the like; vinyl esters such as vinyl chloride, 
vinyl bromide, vinyl fluoride, vinyl acetate, vinyl propionate, vinyl 
benzoate, vinyl butyrate and the like; esters of alphamethylene aliphatic 
monocarboxylic acids such as methyl acrylate, ethyl acrylate, 
n-butylacrylate, isobutyl arylate, dodecyl acrylate, n-octyl acrylate, 
2-chloroethyl acrylate, phenyl acrylate, methylalphachloroacrylate, methyl 
methacrylate, ethyl methacrylate, butyl methacrylate and the like; 
acrylonitrile, methacrylonitrile, arylamide, vinyl esters such as vinyl 
methyl ether, vinyl isobutyl ether, vinyl ethyl ether, and the like; vinyl 
ketones such as vinyl methyl ketone, vinyl hexyl ketone, methyl 
isopropenylketone and the like; vinylidene halides such as vinylidene 
chloride, vinylidene chlorofluoride and the like; and N-vinyl indole, 
N-vinyl pyrrolidene and the like; and mixtures thereof. 
Generally toner resins containing a relatively high percentage of styrene 
are preferred since greater image definition and density is obtained with 
their use. The sytrene resin employed may be a homopolymer of styrene or 
styrene homologs of copolymers of styrene with other monomeric groups 
containing a single methylene group attached to a carbon atom by a double 
bond. Any of the above typical monomeric units may be copolymerized with 
styrene by addition polymerization. Styrene resins may also be formed by 
the polymerization of mixtures of two or more unsaturated monomeric 
materials with a styrene monomer. The addition polymerization technique 
employed embraces known polymerization techniques such as free radical, 
anionic and cationic polymerization processes. Any of these vinyl resins 
may be blended with one or more resins if desired, preferably other vinyl 
resins which insure good triboelectric properties and uniform resistance 
against physical degradation. However, non-vinyl type thermoplastic resins 
may also be employed including resin modified phenolformaldehyde resins, 
oil modified epoxy resins, polyurethane resins, cellulosic resins, 
polyether resins and mixtures thereof. 
Also esterification products of a dicarboxylic acid and a diol comprising a 
diphenol may be used as a preferred resin material for the toner 
composition of the present invention. These materials are illustrated in 
U.S. Pat. No. 3,655,374, totally incorporated herein by reference, the 
diphenol reactant being of the formula as shown in column 4, line 5 of 
this patent and the dicarboxylic acid being of the formula as shown in 
column 6 of the above patent. 
The toner resin particles can vary in diameter, but generally range from 
about 5 microns to about 30 microns in diameter, and preferably from about 
10 microns to about 20 microns. 
Various suitable pigments or dyes may be employed as the colorant for the 
toner particles, such materials being well known and including for 
example, carbon black, nigrosine dye, aniline blue, calco oil blue, 
phthalocyanine blue, and mixtures thereof. The pigment or dye should be 
present in sufficient quantity to render it highly colored so that it will 
form a clearly visible image on the recording member. For example, where 
conventional xerographic copies of documents are desired, the toner may 
comprise a black pigment such as carbon black or a black. Preferably the 
pigment is employed in amounts from about 3 percent to about 20 percent by 
weight based on the total weight of toner, however, if the toner color 
employed is a dye, substantially smaller quantities of the color may be 
used. 
Also there can be incorporated in the toner (resin plus colorant) various 
charge control agents primarily for the purpose of imparting a positive 
charge to the toner resin. Examples of charge control agents include 
quaternary ammonium compounds as described in U.S. Pat. No. 3,970,571, and 
alkyl pyridinium halides such as cetyl pyridinium chloride. 
Numerous suitable electrically insulating magnetic carrier particles can be 
employed as long as such particles are capable of triboelectrically 
obtaining a charge of opposite polarity to that of the toner particles. In 
the present invention in one embodiment that would be a negative polarity, 
to that of the toner particles which are positively charged so that the 
toner particles will adhere to and surround the carrier particles. Thus, 
the carriers can be selected so that the toner particles acquire a charge 
of a positive polarity and include materials such as steel, nickel, iron 
ferrites, magnetites and the like. The carriers can be used with or 
without a coating, examples of coatings including fluoropolymers such as 
polyvinylidene fluoride, methyl terpolymers and the like. Also nickel 
berry carriers as described in U.S. Pat. Nos. 3,847,604 and 3,767,598 can 
be employed, these carriers being nodular carrier beads of nickel 
characterized by surface of reoccuring recesses and protrusions providing 
particles with a relatively large external area. Preferably the carrier 
particles, or their cores are of materials that are sufficiently 
conducting to dissipate net charge accumulation from the development 
process such as for example steel shot carriers. The diameter of the 
coated carrier particle ranges from about 50 to about 1,000 microns, thus 
allowing the carrier to possess sufficient density and inertia to avoid 
adherence to the electrostatic images during the development process. 
While preferred embodiments have been specified for the speed of movement 
of the members involved, it is to be appreciated that these members may 
have speeds outside the ranges disclosed, providing the objectives of the 
present invention are accomplished. Thus, for example, the flexible imging 
member can be caused to move at a speed of from about 5 cm/sec to about 80 
cm/sec, and the transporting member can be caused to move at a speed of 
from about 6 cm/sec to about 180 cm/sec. 
Other modifications of the present invention may occur to those skilled in 
the art based upon a reading of the present disclosure. These are intended 
to be included within the scope of the present invention.