Note: Descriptions are shown in the official language in which they were submitted.
7~
The present invention is generally directed to an improved
apparatus and an improved proeess for causing the development of images in
an electrostatographic imaging system. More specifically, the present
invention is directed to an improved self-agitated development apparatus
5 and development process wherein a two component insulating developer
composition is contained and transported in a highly agitated development
zone encompassed by an imaging member and a transporting member,
thereby allowing for the continual development of high quality images,
including the efficient development of solid areas.
10The development of images by electrostatographic means is well
known, including the development of latent images employing toner parti-
cles, as described for example in U. S. Patent 3,618,552, cascade develop-
ment; U. S. Patents 2,874,063, 3,251,70~, and 3,357,402 magnetic brush
development, U. S. 2,217,776 on powder cloud development, and U.S.
153,166,432 on touchdown development. In one magnetic brush system
developer material comprised of toner and magnetic carrier partieles, is
transported by a magnet, which magnet is the source of a magnetic field
that causes alignment of the magnetic carrier into a brush like configura-
tion. The resulting magnetic brush is brought into close proximity to the
20 electrostatic latent image bearing surface causing the toner particles to be
attracted from the brush to the electrostatic latent image by electrostatic
attraction.
While many processes are in existence for causing the develop-
ment of images, difficulties continue to be encountered in the design of a
25 simple, inexpensive and reliable two-component insulative developer system,
which provides a high solid area development rate, low background deposi-
tion and long term stability. Thus for example, the present magnetic brush
systems are sometimes inefficient since only a small fraction of the toner
transported through the development zone is accessible for deposition onto
30 the image bearing member. ~or insulative developer, the solid area
deposition is limited by a layer of net charged carrier particles resulting
from toner deposition on a precharged imaging member. Since the develop-
er entering the development zone has a neutral charge, deposition of
charged toner onto the imaging member produces a layer of oppositely
35 charged developer which opposes further toner deposition. The net electr~
static force due to the charged image member and the net-charged
_
`:
- --2--
developer layer becomes zero for that toner between the developer and the
electrostatic latent image of the imaging member. The 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
5 neutralize the image charge. Image field neutrali~ation can occur, however,
if there is a sufficiently high developer flow rate and multiple development
rollers. Image field neutralization is herein defined to occur 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.
10 In the absence of a bias on the development roller, image neutralization
produces a zero development electric field. Since a toner layer is of finite
thickness, the charge density of the toner layer is less than the image
charge density for the condition of image field neutrali~ation. The
difference in charge density depends on the relative thicknesses of the
15 imaging member and toner layer. If the thickness of the charged toner layer
is much less than the imaging member, image field neutralization occurs
when the toner charge density neutralizes the image charge density.
When magnetic brush development is accomplished with conduc-
tive developer materials, the solid area deposition is not limited by a layer
20 of net-charged developer near the imaging member, since this charge is
dissipated by conduction ~o the development roller. The solid area deposi-
tion is, however, limited by image field neutralization, provided there is
sufficient toner available at the ends of the developer brush, while the toner
supply is limited to the ends or tips of the bristles, since toner cannot be
25 extracted from the bullc of the developer where the high developer conduc-
tivity collapses the electric field within the developer, at any location, and
confines it to the region between the latent image and the developer. For
either insulative or conductive developer, the solid area deposition is limited
by toner supply at low toner concentrations. The toner supply is limited to a
30 layer of carrier material adjacent to the image bearing member since the
magnetic field stifens the developer and hinders developer mixing in the
development zone.
Numerous improved types of toner materials, apparatus, and
processes have been envisioned for the purpose of producing line copies of
35 high resolution, however, difficulties continue to be encountered in produc-
ing consistently high quality copies of line and solid areas, in view of for
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example the breakdown in the trihoelectric relationship between the carrier
particles and the toner particles, inefficient and incomplete removal of
sufficient toner from the carrier particles, the inability of the toner
particles to transfer from one carrier bead to another carrier bead in the
5 development zone, thereby depleting the amount of toner available at the
surface of the image to be developed; and the like. While many of the
electrophotographic machines now currently in use employ two-component
developer mixtures of toner and carrier materials, solid area development is
limited, particularly with magnetic brush systems utilizing insulative devel-
10 oper materials, by for example, either electric field eollapse or inadequatetoner supply as explained hereinbefore.
There continues to be a need for apparatus and processes which
will improve the quality of images produced, particularly in electrophoto-
graphic systems, such as xerographic imaging systems, which are simple and
15 economical to operate; and which result in reproducible high quality images
including both line copy quality and solid area image development. Addi-
tionally, it would be desirable to provide an apparatus and a process where
background development is substantially eliminated, and where the life of
the developer is increased. In the systems discussed hereinbefore, there
20 continues to exist the problem of achieving uniform development for both
the fine line image areas as well as the larger solid areas of the
electrostatic latent image, while maintaining a minimum background densi-
ty.
In accordance with the present invention there is provided an
25 improved apparatus and an improved development process wherein toner
particles are made continuously available immediately adjacent to a flexible
imaging surface, in that toner particles transfer from one layer of carrier
particles to another layer of carrier particles in a development zone,
thereby increasing the amount of toner available at the surface of the image
30 bearing member. In accordance with the present invention, this is generally
accomplished by establishin~ a develop~.ent zone encompassed by a transport-
ing member or development roll and a flexible image bearing member the
distance between the members being from about 0.05 millimeters to about
1.5 millimeters, and preferably from about 0.4 millimeters to about 1.0
35 millimeters, the development zone containing therein insulating toner
--4--
particles and insulating carrier particles. The toner migration rate depends yeneral-
ly on the amount of developer agitation, the magnitude of the elec~rical
~ield applied to the development zone, the lengkh o~ the develcpment zone,
and/or the amount or degree of deflection of the flexible imaging member.
5 The magnitude of the electric field is inversely proportional to the develop-
er thickness, and directly proportion~l to the difference in potential
between the charged imaging member and the bias on the development
roller. Thus for example, for a typical image potential of about 400 volts, a
background potential of about 50 volts, and a roll bias of about 100 volts to
10 suppress background deposition, the electric field potential is about 300
` volts across the developer layer. For a preferred thickness of 0.5 mm
(millimeters), the development electric field is 300 volts across 0.5 mm; i.e.,
600 V/mm. Also the degree of developer agitation is proportional to the
shear rate and development time, thus for a particular process speed and
15 development roll speed, increased developer agitation is obtained when the
developer layer is thin, for example, one layer of toner particles and the
development zone is long, which 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
20 are accomplished.
Improved developer agitation and hence solid area development
is obtained with the improved apparatus, and improved process of the
present invention when a low magnetic field is present in the development
zone, since with such a field, the developer does not stiffen but is fluid-like
25 under agitation and/or shearing. The magnetic field is generally less than
150 gauss and preferably less than 20 gauss. If desired, ferromagnetic
material such as steel can be used to shape and reduce the magnetic field in
the development zone.
A development system based on a self-agitated development
30 zone has a number of advantages over conventional systems, for example,
solid area and line development is at its maximum, since the toner charge
neutralizes the fields from the image charge; and development, limited by
image field neutralization enables the present system to develop in one
embodiment low voltage images associated with thin image bearing mem-
35 bers. For a particular image potential the amount of toner deposited on theimaging bearing member is substantially independent of the spacing between
the development roll, and the image bearing member, within the range of
0.05 millimeters to 1.5 millimeters.
In one specific preferred embodiment, the present invention is
directed to an apparatus and a process for causing the development of
5 electrostatic latent images on a flexible imaging member, characterized in
that the improvement resides in the provision of a development zone,
encompassed by a flexible imaging member moving at a speed of from about
5 cm/sec to about 50 cm/sec, and a transporting member, moving at a speed
of from about 6 cm/sec to about lOO cm/sec, the imaging member and
10 transporting member having a distance therebetween of from about O.OS
millimeters to about 1.5 millimeters, the movement of said members causing
a shearing action in said development zone, adding an insulating developer
composition to the development zone, the developer composition being
comprised of insulating toner particles and insulating magnetic carrier
15 particles, introducing a high electric field in the development zone, the
insulating toner particles being caused to migrate from one layer of carrier
particles to another layer of carrier particles contained in the development
zone as a result of said shearing action, and said high electric field, the
carrier particles rotating in one direction than subsequently in an opposite
20 direction, wherein the toner particles are continuously made available i~-
diately adjacent the imaging member~ While developer agitation occurs in
the presence of a small magnetic field, the absence of a magnetic field is
preferred. As indicated, for example, with reference to Figure 5, the
flexible imaging member is deflected in an arc by the developing composi-
25 tion, which deflection acts as a pressure force so as to cause agitation ofthe developer particles..
The process of the present invention is particularly adaptable in
an electrophotographic imaging apparatus which comprises another feature
of the present invention, the apparatus containing an imaging means, a
30 charging means, an exposure means, a development means, a transfer
means, and a fusing means, characterized in that the improvement resides in
the development means consisting essentially of a transporting means
moving at a speed of from about 6 cm/sec to about 100 cm/sec, a flexible
imaging means moving at a speed of from about S cm/sec to about 50
35 cm/sec, said transporting means and said flexible imaging means having a
distance therebetween of from about 0.05 millimeters to about 1.5 milli-
.
- ~ .î t~:3~
--6--
meters, said movement causing a shearing action which
in combination with a high electrical field causes
insulating toner particles contained in the development
means to migrate from the insulating carrier particles
contained in the development means, migration being in
the direction of the flexible imaging means, said
migration resulting from the rotation of carrier
particles in one direction and subsequently in an
opposite direction as a result of said shearing action
and said electric field wherein said toner particles
are made continuously available immediately adjacent to
the imaging means.
Various aspects of the invention thus can be
listed as follows:
An improved process for causing the development of
electrostatic latent images on an imaying member,
- comprising providing a development zone ranging in
length of from about 0.5 centimeters to about 5
centimeters, which development zone is encompassed by a
tensioned deflected flexible imaging member and a
transporting member wherein the flexible imaging member
is comprised of a supporting substrate, a
: photogenerating layer, and a transport layer, causing
the deflected 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 deflected
flexible imaging member and said transporting member
moving at different speeds, the ratio of the velocity
of the transporting member to the flexible imaging
member being greater than zero and less than 1,
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 insulating magnetic
carrier particles, the flexible imaging member being
deflected by the electrically insulating developer
E
-6a-
particles, wherein the deflection of the flexible
imaging member caused by the insulating developer
particles contained in the development zone is in the
form of an arc, 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 and subsequently in another direction
whereby toner particles are continuously made available
immediately adjacent the deflected flexible imaging
member, said process being accomplished in the absence
of a magnetic field.
lS 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; and the means
for imaging and the means for tran.sporting having a
distance therebetween of from about 0~05 millimeters to
about 1.5 millimeters.
An electrostatographic imaging apparatus comprised
in operative relationship of a tensioned deflected
flexible imaging member, a transporting roller means
containing magnets therein attached to the transporting
roIler core, said roller containing thereon insulative
developer particles comprised of electrically
~ .
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' ' " ': ~
'
7:~
-6b-
insulating toner particles, and electrically insulating
magnetic carrier particles, whereby toner particles are
transferred to the deflected flexible imaging member
with the further provision that there is provided a low
magnetic field means in a developmen-t zone encompassed
by the deflected flexible imaging member, and the
transporting roller means, and high magnetic fields at
the entrance and exit regions of said development zone.
An electrostatographic imaging method which
comprises forming an electrostatic image on a tensioned
deflected flexible imaging member contained in 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 cmtsec to about lO0 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
caused by electrically insulating developer particles
comprised of electrically insulating toner particles,
0 and electrically insulating magnetic carrier particles
situated in a development zone encompassed by said
de.flected flexible imaging member means, and said
transporting means, said deflection and said relative
movement of the deflected flexible imaging member means
and transporting means providing sufficient force so as
to cause agitation of said developer particles, means
for introducing a high electric field into the
development means, wherein said electrically insulating
toner particles migrate from said electrically
.....
7~
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insulating magnetic carrier particles, the migration
being in the direction of the deflected flexible
imaging member means, said migration resulting ~rom the
rotation of the electrically insulating carrier
particles in one direction and subsequently in another
direction, whereby said electrically insulator toner
particles are made continuously available immediately
adjacent the deflected flexible imaging member means,
and wherein agitation and the presence of an electrical
field in the development zone causes toner particles to
migrate and deposit on the electrostatic latent image,
followed by transferring the developed image to a
substrate, and permanently fixing the image thereto.
For a better understanding of the present
invention, and further features thereof, reference is
made to the following detailed description of various
preferred embodiments wherein:
Figure 1 is a partially schematic cross-sectional
view of the development system of the present
invention. Figures lA, lB, and lC illustrate the
transfer of toner particles from carrier particles to
the imaging member, and the transfer of toner particles
from one carrier particle bead to another carrier bead;
such transfer of toner particles occurring primarily as
a result of agitation.
Figure 2 is a partially schematic cross-sectional
view of a conventional development zone wherein
two-component insulative developer material is
employed.
Figure 3 is a partially schematic cross-sectional
view of a conventional development zone wherein
conductive developer is employed.
Figure 4 illustrates an electroded cell for
measuring the electrical and development properties of
developer.
Figure 5 illustrates a preferred embodiment of the
development system of the present invention that
incorporates the features of a thin long and low
magnetic field development zone, as well as a high
.~ `~
3 7
-6d-
magnetic field at the entrance and exit regions of the
development zone.
Figure 6 illustrates a comparison between (1) the
solid area development characteristic of the
self-agitated development system of the present
invention as illustrated in Figures 1 and 5; and (2)
the development characteristics of a conventional
magnetic brush development system as illustrated in
Figure 2.
Figure 7 illustrates another preferred embodiment
of a self-
,~ ~
. ., 1~,.
--7--
agitated development system that incorporates an idler rolL
Figure 8 illustrates the use of the process and device of the
present invention in an electrophotographic imaging system.
Illustrated in Figure l is a development system of the present
5 invention designated lO, which is comprised of a positively charged image
bearing member l, negatiely charged toner particles 2, attached to positive-
ly charged carrier particles 3, a developer transporting member 4, which
also serves as a development electrode, toner depleted layer D, which layer
has carrier particles containing a positive charge, this layer having less
lO toner on the carrier than the adjacent carrier layers, ~, B, and A, a biased
voltage source 6, and a toner developed layer 7. A, B, C, and D designate
layers of developer comprised of carrier and toner particles. The image
bearing member l, and developer transporting member 4, in this embodiment
are moving in the direction shown by the arrows 5 and Sa. In this
15 illustration the transporting member 4 is moving at a greater speed than the
image bearing member l. It is this difference in speed between these two
members which causes a shearing action in the development zone, thereby
causing agitation of the carrier and toner particles, wherein movement of
the carrier particles causes toner particles to transfer from one layer of
20 carrier particles, such as layer B, to another layer OI carrier particles, such
as layer A. It is not intended to be limited to the method of operation
shown, nor to be limited to any theory of operation; thus other methods of
operation are envisioned by this invention. For e~ample the speed of the
imaging member l can be greater than the speed of the transporting member
25 4, and movement can be in the opposite direction to that which is shown.
Also although the carrier particles 3 are shown in ordered layers7 in actual
operation they can be distributed randomly in size and position. The shape of
the carrier particles is not necessarily completely spherical as shown, that
i9, most carrier particles are non-spherical with surfaces that can be jagged
30 or textured. Further, 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 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,
35 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 Figures lA-lC. This movement or agitation,
which results in improved development of images, is caused primarily by the
movement of the imaging member 1, and developer transporting member 4,
as indicated herein.
In one m ethod of operation, as indicated hereinbefore, the
development electrode 4 is moving at a surface speed which is faster than
the speed of the imaging member 1, both the development electrode and the
imaging member moving in the same direction. This relative motion
between the development electrode 4 and imaging member 1, causes the
developer which is comprised of toner particles 2, and carrier particles 3, to
be agitated by a shearing action. When the speed of the image bearing
member 1, is less than the speed of the electrode 4, as shown in Figure 1, the
shearing action c~uses movement of the carrier particles 3, that is, the
carrier particles move in both a clockwise and counterclockwise direction,
- 15 but on the average tend to move in a counterclockwise direction. Thedeveloper agitation the development electric field, and deflection of the
flexible imaging member allow toner particles 2 adhering to the carrier
particles 3 to migrate towards the imaging member 1. The toner particles
closest to the imaging member 1 are deposited on the imaging surface,
therefore the carrier particles adjacent the imaging surface lose 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 mentioned hereinbefore.
Maximum agitation, which is preferred, is obtained when the magnetic field
in the development zone is low, and the developer layer is thin, that is,
ranging in thickness 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 image bearing member is positively charged an elec-
trostatic 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
~9
under normal conditions to overcome the toner adhesion, and thus the toner
particles are retained on the carrier particles 3. However, when agitation is
supplied to the developer, that is, toner particle plus carrier particles, the
toner which remains between two carrier particles can easily transfer when
5 the surfaces involved are separated, by a rolling or a sliding action. The rate
of electric field assisted toner migration towards the image bearing member
is therefore increased in comparison to when agitation is not utilized. As
illustrated in Figure l, toner migration results in a toner depleted layer D
and although the toner depleted carrier is positively charged, the effect of
10 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-
15 agitated tw~component insulative development system, and when theelectrostatic 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 is defined by the product of
the shear rate and development time. The average shear rate is equal to the
20 absolute value of the difference in the development roller or electrode
velocity, VR, and imaging member velocity, VI, divided by the developer
thickness, L, i.e., the average shear rate equals I VR - Vl ~/L. The
development time is equal to the development zone length, W, divided by
the absolute value of the development roller speed, ~ VR ¦ ; i.e., the
25 development time equals W/ i VRI . Thus the degree of developer agitation
is equal to ( I VR - Vl I /L) x (W/ I VR I ) or [ 11- l/V I ] where V is equal to
VR/VI 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 I l - l/V 1, is typically near a
30 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 l 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
35 mm to l.0 mm, the developer agitation ranges from 2 to lO00 units and
preferably from 10 to 50 units.
--10--
There is shown in some detail in Figure lA, lB, and lC, what is
occurring at eaeh 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
5the identical components as described with reference to Figure 1, with the
addition that Z represents an area or zone of the carrier particles which
have been depleted of toner particles. In Figure lA there is ilustrated a
carrier partiele 3, of layer A, which is depleted by toner particles 2, in the
area or zone Z; while Figure lB, 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 earrier particle 3, layer B.
In this Figure lB, 8 represents the interface area between carrier particles.
Likewise toner particles 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 Figure lB, come into contact with
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
~ no toner particles are present, since the electrical fields transferred the
toner from the carrier beads, for example the carrier beads of layer A, to
the imging member 1. This is caused primarily because of the rocking
motion of the carrier beads 3, which motion further causes a positive charge
to be contained on the carrier particles.
More specifically, with reference to Figures lA, lB and lC, as the
carrier beads rotate as a result of agitation in accordance with the method
of 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 fromthe carrier bead of layer
A, and the 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
3~7~
--11--
greater than the force from the carrier bead of layer B, the toner particles
beeome detached from the carrier particles of layer B and attach to the
carrier particles of lflyer A during bead rotation, reference ~igure lB. This
action replaced the toner particles on the carrier particles of layer A but
5 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 illustrated in Figure lC,
however, an additional layer of carrier particles is shown, namely layer C.
lO Thus the carrier particles of la~er 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 simultan-
eously throughout the development zone, and as a result toner particles are
continually available on the carrier particles immediately adjacent the
15 imaging member, while the carrier particles near the transporting member 4
contain thereon 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
20 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 Figure 5.
Developer mixing in the developer sump charges the added toner by
25 triboeleetric 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 even when the developers have a rather
low toner concentration in comparison to the developers used in convention-
30 al systems. The minimum toner concentration for acceptable solid areadevelopment depends on several factors inclllding the ratio of the develop-
ment roll speed to photoreceptor speed and the degree of developer
agitation which depends on the magnetic field strength, the development
zone length and the spacing between the imaging member and the develop-
35 ment roll. Thus for example for a developer containing o.a5 percent byweight of toner, mixed with about 0.75 percent by weight of 100 um
tj~3~
--12--
diameter steel carrier beads, the solid area development is 0.5 mg/cm2 for a
development voltage of 300 volts7 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 Figure 2 is a conventional magnetic brush develop-
ment 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 Figure 2 is comprised of an
imaging member l, negatively charged toner particles 2, positively charged
carrier particles 3, development electrode 4, developed toner layer 7, irnage
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 Figure l.
The magnetic field causes 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, as no agitation is occurring
with the other developer particles, transfer of toner from the carrier
particles does not result, thereby in effect rendering these other developer
20 particles substantially useless. The charge density on the developer layer A
is equal to the negative of the toner charge density 7 on the image bearing
member, divided by the ratio of the development roll 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
25 interface. This electric field becomes zero despite the fact that the image
charge is not neutralized by toner eharge. 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
30 concentration is low and the stiffening of developer by the magnetic field
aids in limiting the supply of toner.
Illustrated in Figure 3 is an enlarged view of a development zone
containing conductive developer. In this Figure, l represents the imaging
member, 2 represents negatively charged toner particles, 3 represents
35 positively charged carrier particles, 4 is a development electrode, 6
represents the voltage source, 7 represents the developed toner layer. As
~ j
--13--
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 are not transferred from
one layer of carrier particles, such as B to another layer of carrier particles
such as A, and thus no development will occur after a short period of time.
Thus toner development onto the imaging member only occurs from the first
10 bead layer 1. In both the systems as described in Figures 2 and 3, the
amount of toner transferred from one layer of carrier particles to another
layer of carrier particles is substantially zero, whereas with the system of
the present invention, toner particles are being constantly replenished to the
first layer of carrier particles, which replenishment is important for
15 efficient solid area development, and efficient development of lines.
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 Figure 4, which represents an electroded cell for
2U measuring the development properties of developer under controlled condi-
tions. 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 bias is applied to the de~eloper tray
25 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 subjecting the assembly to an
air jet for the purpose of removing loose toner particles. Using the device
shown in Figure 4, in one embodiment, the toner weight per unit area was
30 0.23 mg/cm2 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/cm2. The larger
35 developed toner mass for magnetic field free conditions is attributed to
increased developer agitation. In a situation where an operable development
;9~ ,'h
-14-
system is used the toner weight developed on the imge bearing member is
proportional to the ratio of the development roll speed to 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 mgtcm2 would be obtained on
5 the image bearing member. This would result in an acceptable reflective
optical density of ( ¦).
When similar development data is obtained with a thinner
developer layer of 0.5 mm the solid area development increases since the
development electric field is higher. With a 450 gauss magnetic field
10 applied across the developer, the developed toner density is 0.28 mg/cm2
compared to the 0.09 mg/cm2 obtained for a developer thickness of 1.5
millimeters. For magnetic field free conditions, the developed density
increases to 0.80 mg/cm2 compared to the 0.23 mg/cm2 obtained when the
developer thickness is 1.5 mm. The increase in solid area development for
15 the magnetic field-free case is ude to a high agitation of the thin developerlayer. The agitation increases the toner supply and displaces the developer
net-charge towards the development electrode. Increased solid area devel-
opment is thus obtained by making the developer layer lthin and the
development zone magnetic field free.
Self-agitation of developer in the development zone requires
relative motion between the developer transporting electrode member and
the image bearing member. When the electrode is brought into contact with
the developer without lateral movement, a small quantity of toner is
transferred to the electrode when a voltage is applied and the electrode is
25 removed. When the electrode is displaced while in contact with the
developer, increased development occurs since the developer is agitated by
the relative motion, the degree of agitation depending 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 roller is typically moving at a speed faster than the
35 image bearing member, developer will tend to accumulate at the entrance
to the magnetic field free zone. To ensure good developer flow, a strong
~.
-15 -
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, and prevents scavaging of the toner in solid areas, since as the
5 electrode spacing increases the fields in the solid areas decreases.
Illustrated in Figure 5 is a development system that incorporates
the features of a thin and low magnetic field development zone, as well as a
high magnetic field at the entrance and exit regions of the development
zone. In this figure, there is represented a flexible development roller 15,
10 containing magnets tnerein, 16 attached to a core or "keeper" 17. The roller
15 obtains developer 18 (toner and carrier~ when it passes through the
development sump 19. Metering blade 20 is used to control the thickness of
the developer material. As the deflected flexible image bearing member 1
moves in the direction shown it comes into contact with the development
15 roll 15, whereby toner particles are transferred to the imaging member 1. At
this point there is a low magnetic field region 21. There are high magnetic
field regions located at the entrance 22 and the exit 23 of the system.
~egion (21) allows developer to remain on the roller 15, while region 22
insures good developer flow and region 23 prevents developer from contact-
20 ing the latent image surface as the electrode spacing increases.
In this embodiment developer agitation occurs in the region oflow magnetic field, and the image bearing member can be a belt photo-
receptor or an electroreceptor (charge patterns generated by electric~l
means; such as electronic printers), both OI which can be partially wrapped
25 around the developer-covered development roll. The developer layer
provides the spacing between the development roll and image bearing
member. Steel shunting inside the development roll is used to reduce the
magnetic field between the magnetic poles at the entrance and exit regions.
Designating v as the ratio of the development roll velocity and imaging
30 member velocity, good developer flow is obtained when the value of v is
greater than zero and less than -1. If v is greater than -1, but less than zero
inadequate developer flow results in the development zone.
A thin layer of developer is applied to the development roll with
the aid of a metering blade 20, closely spaced -from the development roll.
35 The uniformity of the developer thickness is determined by the run-out in
the roll and the straightness of the matering blade. When the metering
.
.
.
-16-
blade is positioned where the magnet;c field is in a radial direction
~perpendicular to the development roll), the developer layer thickness is
approximately equal to the metering blade gap setting, while when 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 redueed 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 metering 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.
Figure 6 is a graph of data displaying the solid area development
characteristics of the self-agitated development system depicted in Figure
5. This figure also includes data obtained with a conventional single
development roll magnetic brush development system. In Figure 6, the curve
G represents data obtained for self-agitated development with a 0.4 mm
gap, (distance between imaging member and transporting member) while
curve H represents data obtained with a conventional magnetic brush
system, 1.5 mm gap. The same developer with a toner concentration of 2.7
percent and polymer coated ferrite beads coated with a fluoropolymer was
used for both systems operating at a speed ratio of 2. Increased develop-
ment with the self-agitated system, curve G, is attributed to the thin
developer layer (0.4 mm), low magnetic field (20 gauss) and long develop-
ment zone (3 cm). For the conventional system, curve H, the gap between
the photoreceptor and development roll is maintained at 1.5 mm. The
magnetic field is 500 gauss over the development zone length of 0.5 cm. At
a development potential of 200 volts, the reflection image density, curve G
is greater than 1, 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 development roll and image bearing member is deter-
mined by the developer layer thickness. As indicated this spacing typically
ranges from about 0.05 millimeters to about 1.5 millimeters and preferably
from about 0.4 millimeters to about 1.0 millimeters. The magnetic field
within the central area of the development zone is generaly less than 150
gauss and preferably less than 20 gauss, while the magnetic field at the
."
;
, . . . .
g7~i
-17--
entrance and exit regions of the development zone is ra~ially directed and
typically 300 to 800 gauss, with magnetic poles being like polarity. The
magnetic field profile is obtained by a suitable choice of permanent
magnets, thus steel shunting inside the development roll can provide
5 magnetic field shaping at the surface of the development rolL
The length of the development zone depends on the configuration
of the image bearing member and developer transport member. In a
preferred embodiment, the image bearing member is a ~elt partially
wrapped around a development roll with a diameter which is typically 3.8
10 cm to 6.4 cm. The length of contact between the developer and image
bearing member ranges from 0.5 cm to 5 cm. The preferred length is 1 cm
to 2 cm. Idler rolls positioned against the backside of the belt can be used
to alter the belt path.
Figure 7 illustrates one example of a self-agitated development
15 system design that incorporates the use of 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 electrophotographic or similar apparatus. In this
Figure the numerical designations 15, 16, 17, 19, 21, 22 and 23 represent the
same components as described in Figure 5. In Figure 7 the idler roll in the
region 22is designated 24. Itis understood that a second idler roll could be
placed near the region 23 to alter the path of the imaging member without
causing a change in the operation of the development sys~em. The system
shown in Figure 7 is operating in a mode in which the development roller and
25 imaging member are moving in opposite directions.
The apparatus and process of the present invention is useful in
many systems including electronic printers and electrophotographic copy
machines, such as those employing xerographic apparatus well known in the
art. In Figure 8 there is illustrated an electrophotographic printing machine
employing an 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
transport layer containing small molecules of N,N,N',N'tetraphenyl-[l,l'-
biphenyl~ 4-4'-diamine, or similar diamines (m-TBD) dispersed in a polycar-
': ,
' '` ' `
--18--
bonate and a generation layer of trigonal selenium. Imaging member 1moves 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
5 entrained about a sheet-stripping roller 28, tensioning system 299 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.
10 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 Figure 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 2q. Roller 30 is coupled to
15 motor 33 by suitable means such as a belt drive. sheet-stripping roller 28 isfreely 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
20 generally by the reference numeral 34, charges the photoconductive surface
of imaging member 1 to a relatively high, substantially uniform potential.
Next, the charged portion of the photoconductive surface is
advanced through exposure station I. An original document 35 is positioned
face down upon transparent platen 36. Lamps 3~ flash light rays onto
25 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 corres-
30 ponds to the informational areas contained within original document 35.
Thereafter, imaging member 1 advances the electrostatic latentimage 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
35 contact with the electrostatic latent image. The self-agitated development
system 39 includes a developer roller 40 which transports a layer of
.
,
--19-
developer material comprising magnetic carrier particles and toner particles
into contact with imaging member 1. As shown in Figure 1, 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
5 configuration of the developer materi~l. The electrostatic latent image
attracts the toner particles from the carrier granules forming a toner
powder image on the photoconducitve surface of member 1. The develop-
ment 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 Figures 1, lA, lB, lC, 5 and 7.
Imaging member 1 then advances the toner powder image to
transfer station R. At transer 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
15 (not shown). Preferably9 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 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
20 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
25 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 assernbly, indicated generally
by the reference numeral 50, which permanently affixes the transferred
30 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
35 catch tray for subsequent removal from the printing machine by the
operator.
`~
~ " , ~ .
.
-20-
Invarlably, after the sheet o~ support material is
separated from the photoconductive surface or imaging
member 1 some residual particles remain adhering
thereto. These residual particles are removed from the
photoconductive surface at cleaning .sta~ion 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 flexible image
bearing member 1, include inorganic and organic
photoreceptor materials such as for example amorphous
selenium, selenium alloys, including alloys of
selenium-tellurium, selenium arsenic, selenium
antimony, selenium-tellurium-arsenic, cadmium sulfide,
zinc oxide, polyvinylcarbazole, layered organic
photoreceptors, such as those containing as an
injecting contact, carbon dispersed in a polymer,
overcoated with a transport layer, which in turn i5
overcoated with a generating layer, and finally an
overcoating of an insulating organic resin, such as
those described in U.S. Patent 4,251,612, on Dielectric
Overcoated Photoresponsive Imaging Member and Imaging
Method.
Thus, as disclosed in U.S. Patent 4,251,612, the
flexible image bearing member may be comprised of a
layered organic photoresponsive device comprised of a
substrate overcoated with a hole injecting material
which, in turn, is overcoated with a hole transport
~ ~ .
7~
-20a-
layer overcoated with a charge generating layer in
contact with an electrically insulating resin.
Alternatively, as disclosed in U.S. Patent 4,251,612,
the flexible image bearing member ma~v be comprised of a
substrate, a hole transport layer and a charge
generating layer.
As specifically disclosed in U.S. Patent
4,251,612, the photogenerating layer may be comprised
of vanadyl phthalocyanine, metal phthalocyanines or
metal free phthalocyanines and the transport layer may
be comprised of electrically active diamine molecules
dispersed in an inactive resinous binder, the diamine
molecules being of the formula
~N
wherein X is selected from the group consisting of
(ortho) CH3, (meta) CH3, (para) C~3, (ortho) Cl, (meta)
Cl, (para) Cl.
Other organic photoreceptor materials include
4-dimethylaminobenzylidene, benzhydrazide; 2-benzyl
idene-amino-carbazole, 4-dimethylamino-benzylidene,
benzhydrazide; 2-benzylidene-amino-carbazole, polyvinyl
carbazole; (2-nitro-benzylidene)p-bromo-aniline; 2,4-
diphenyl quinazoline, 1,2,4-triazone; 1,5-diphenyl-3-
methyl pyrazoline 2-(4'-dimethylamino phenyl) benzox-
azole; 3 amino-carbazole; polyvinylcarbazole-trinitro-
30fluorenone charge transfer complex; phthalocyanines and
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 the development roll provides
.
~ 6~
--21--
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, etc.
The developer material is comprised of a toner resin, colorant or
pigment, and a suitable insulatin~ 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. In one embodiment thus the
range of development times is calculated as follows:
Longest Time W = 5 cm =~second
-~ ~"Fi' cm/sec
Shortest time 10~ r~n/sec = 5 10 seconds
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
20 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 naphtha-
lene, ethylenecally unsaturated mono olefins such as ethylene, propylene,
25 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
acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, phenyl
30 acrylate, methyl alphachloroacrylate, methyl methacrylate, ethyl methacry-
late, butyl methacrylate and the like; acrylonitrile, rnethacrylonitrile,
acrylamide, vinyl ethers 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 isopropenyl ketone and the like; vinylidene
35 halides such as vinylidene chloride, vinylidene chlorofluoride and the like;
and N-vinyl indole,N-vinyl pyrrolidene and the like; and mixtures thereof.
A~,
.
-22-
Generally toner resins containing a relatively high
percentage of styrene are preferred since greater image
dPfinition and density is obtained with their use. The
styrene resin employed may be a homopolymer of styrene or
styrene homologs of copolymers of styrene with other
- 5 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 polymerizationO 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 techique employed embraces known polymerization
techiques such as free radical, anionic and cationic
polymerization processes. Any of these vinyl resins may
be blended with one or more resins if desired, preerably
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. Patent
3,655,374, the diphenol reactant being of the formula as
shown in column 4, beginning at line 5 of this patent and the
dicarboxylic acid being of the formula as shown in column 6
of the above patent. The resin is present in an amount so
that the total of all ingredients used in the toner total
about 100 percent, thus when 5 percent by weight of the
alkyl pyridinium compound is used and 10 percent by weight
of pigment such as carbon black, about 85 percent by weight
of resin material is used.
Optimum electrophotographic resins are achieved with
styrene butylmethacrylate copolymers, styrene vinyl toluene
-23-
copolymers, styrene acrylate copolymers, polyester resins,
predominantly styrene or polystyrene based resins as
generally described in U. S. Reissue 24,136 to Carlson and
polystyrene blends as described in U. S. Patent No. 2,788,2~8
to Rheinfrank and Jones.
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.
Any suitable pigment or dye 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, chrome yellow, ultramarine
blue, DuPont oil red, methylene blue chloride, 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 docu-
ments are desired, the toner may comprise a black pigment
such as carbon black or a black dye such as Amaplast* black
dye available from the National Aniline Products Inc. Pre-
ferably the pigment is employed in amounts from about 3 per-
cent to about 20 percent by weight based on the total weight
of toner, however, if the toner color employed is a dye,
- 25 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 includes quaternary
ammonium compounds as described in U. S. Patent 3 t 970,571, and
alkyl pyridinium halides such as cetyl pyridinium chloride.
Any suitable insulating magnetic carrier material
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 negative polarity, to that of the
*trade mark
'
-23a-
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 ~errites,
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. Patents 3,847,604 and 3,767,538 can be
employed, provided they are rendered insulating in accordance
with the process defined herein, these
--24--
carriers being nodular carrier beads of nickel characterized by surface of
reoceurring recesses and protrusions providing particles with a relativel~J
lar~e external area. Preferably the carrier particles, or their cores are of
materials that are sufficiently conducting but yet insulating to dissipate net
5 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 1000 microns, thus allowing the carrier to possess
sufficient density and inertia to avoid adherene to the electrostatic images
during the development proeess.
The carrier may be employed with the toner coMposition in any
suitable combination, however, best results are obtained when about 1 part
per toner is used and about 10 to about 4000 parts by weight of carrier.
Other modifications of the present invention will occur to those
skilled in the art based upon a reading of the present disclosure. These are
15 intended to be included within the scope of the present invention.
