Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF TIIE INVENTION
This invention relates in general to electro-
statographic imaging systems, and in particular, to
improved developer materials and their use.
The formation and development of images on
the surface of photoconductive materials by electro-
static means is well-known. The basic electrostato-
graphic process, as taught by C. F. Carlson in U. S.
Patent 2,297,691, involves placing a uniform electro-
static charge on a photoconductive insulating layer,
-exposing the layer to a light-and-shadow image to
dissipate the charge on the areas of the layer exposed
to the light and developing the resulting electrostatic
latent image by depositing on the image a finely-divided
electroscopic material referred to in the art as "toner".
The toner will normally be attracted to those areas of
the layer which retain a charge, thereby forming a toner
image corresponding to the electrostatic latent image.
This powder image may then be transferred to a support
surface such as paper. The transferred image may
subsequently be permanently affixed to the support
; surface as by heat. Instead of latent image formation -
by uniformly charging the photoconductive layer and
then exposing the layer to a light-and-shadow image,
one may form the latent image by directly charging the
layer in image configuration. The powder image may be
fixed to the photoconductive layer if elimination of
the powder image transfer step is desired. Other suit-
able fixing means such as solvent or overcoating treat-
ment may be substituted for the foregoing heat fixing
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Many methods are known for applying the
electroscopic particles to the electrostatic latent
image to be developed. One development method, as
disclosed by E. N. Wise in U. S. Patent 2,618,553 is
known as "cascade" development. In this method,
developer material comprising relatively large carrier
particles having finely-divided toner particles electro-
statically clinging to the surface of the carrier
particles is conveyed to and rolled or cascaded across
the electrostatic latent image-bearing surface. The
composition of the toner particles is so chosen as to
have a triboelectric polarity opposite that of the
carrier particles. In order to develop a negatively
charged electrostatic latent image, an electroscopic
powder and carrier combination should be selected in
which the powder is triboelectrically positive in
relation to the carrier. Conversely, to develop a
positively charged electrostatic latent image, the
electroscopic powder and carrier should be selected in
which the powder is triboelectrically negative in
relation to the carrier. This triboelectric relation-
ship between the powder and carrier depends on their
relative positions in a triboelectric series in which
the materials are arranged in such a way that each
material is charged with a positive electrical charge
when contacted with any material below it in the series
and with a negative electrical charge when contacted
with any material above it in the series. As the mix-
ture cascades or rolls across the imagebearing surface,
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the toner particles are electrostatically deposited and
secured to the charged portions of the latent image and
are not deposited on the uncharged or background portions
of the image. Most of the toner particles accidentlly
deposited in the background are removed by the rolling
carrier, due apparently, to the greater electrostatic
attraction between the toner and the carrier than
between the toner and the discharged background. The
carrier particles and unused toner particles are then
recycled. This technique is extremely good for the
development of line copy inages. The cascade develop-
ment process is the most widely used commercial electro-
statographic development technique. A general purpose
office copying machine incorporating this technique is
described in U. S. Patent 3,099,943.
Another technique for developing electrostatic
images is the "magnetic brush" process as disclosed,
for example, in U. S. Patent 2,874,063. In this method
a developer material containing toner and magnetic carrier
particles is carried by a magnet. The magnetic field
of the magnet causes alignment of the magnetic carriers
in a brush-like configuration. This "magnetic brush"
is engaged with an electrostatic latent imagebearing
surface and the toner particles are drawn from the
brush to the electrostatic image by electrostatic attrac-
tion. Many other methods such as "touchdown" develop-
ment as discLosed by C. R. May in U.S. Patent 2,895,847
are known for applying electroscopic particles to the
electrostatic latent image to be developed. The develop-
ment processes as mentioned above, together with numerous
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variations, are well-known to the art through various
patents and publications and through the widespread
availability and utilization of electrostatographic
imaging equipment.
In automatic electrostatographic equipment,
it is conventional to employ an electrostatographic
plate in the form of a cylindrical drum which is con-
tinuously rotating through a cycle of sequential opera-
tions including charging, exposure, developing, trans-
fer and cleaning. The plate is usually charged with
corona with positive polarity by means of a corona
generating device of the type disclosed by L. W. Walkup
in U. S. Patent 2,777,957 which is connected to a suit-
able source of high potential. After forming a powder
image is electrostatically transferred to a support
surface by means of a corona generating device such as
the corona device mentioned above. In automatic equip-
ment employing a rotating drum, a support surface to
which a powdered image is to be transferred is moved
through the equipment at the same rate as the periphery
of the drum and contacts the drum in the transfer posi-
tion interposed between the drum surface and the corona
ge~erating device. Transfer is effected by the corona
generating device which imparts an electrostatic charge
to attract the powder image from the drum to the support
surface. The polarity of charge required to effect
image transfer is dependent upon the visual form of the
original copy relative to the reproduction and the
electroscopic characteristics of a developing material
employed to effect development. For example, where a
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positive reproduction is to be made of a positive
original, it is conventional to employ a positive
polarity corona to effect transfer of a negatively
charged toner image to the support surface. When a
positive reproduction from a negative original is
desired, it is conventional to employ a positively
charged developing material which is repelled by the
charged areas on the plate to the discharge areas
thereon to form a positive image which may be trans-
ferred by negative polarity corona. In either case,
a residual powder image and, occasionally, carrier
particles remain on the plate after transfer. Before
the plate may be reused for a subsequent cycle, it
is necessary that the residual image and carrier
particles, if any, be removed to prevent ghost images
from forming on subsequent copies. In the positive-
to-positive reproduction process described above, the
residual developer powder, as well as any carrier
particles present, are tightly retained on the plate
surface by a phenomenon that is not fully understood
but believed caused by an electric charge. The charge
is substantially neutralized by means of a corona
generating device prior to contact of the residual
powder with a cleaning device. The neutralization of
the charge enhances the cleaning efficiency of the
cleaning device.
Typical electrostatographic cleaning devices
include the "web" type cleaning apparatus as disclosed,
for example, by W. P. Graff, Jr., et al in U. S. Patent
3,186,838. In the Graff, Jr., et al Patent, removal
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of the residual powder and carrier particles on the p,late is
effected by rubbing a web of fibrous material against the
imaging plate surface. These inexpensive and disposable webs
of fibrous material are advanced into pressure and rubbing or
wiping contact with the imaging surface and are gradually ad-
vanced to present a clean surface to the plate whereby sub-
stantially complete removal of the residual powder and carrier
particles from the plate is effected.
While ordinarily capable of producing good quality images,
conventional developing systems suffer serious deficiencies in
certain areas. In the reporduction of high contrast copies such
as letters, tracings and the like, it is desirable to select the
electroscopic powder and carrier materials so that their mutual
electrification is governed in most cases by the distance between
their relative positions in the triboelectric series. However,
when otherwise compatible electroscopic powder and carrier materials
are removed from each other in the triboelectric series by too
great a distance, the resulting images are very faint because the
attractive forces between the carrier and toner particles compete
with the attractive forces between the electrostatic latent image
and the toner particles. Although the image density described in
the immediately preceding sentence may be improved by increasing
the toner concentration in the developer mixture, undesirably
high background toner deposition as well as increased toner im-
paction and agglomeration is encountered when the toner concen-
tration in the developer mixture is excessive. The initial
electrostatographic plate charge may be increased to improve the
density of the deposited powder image, but the plate charge would
ordinarily have to be excessively high in order to attract the
electroscopic powder away from the carrier particle. Excessively
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high electrostatographic plate charges are not only undesirable
because of the high power consumption necessary to maintain the
electrostatographic plate at high potentials, but also because the
high potential causes the carrier particles to adhere to the
electrostatographic plate surface rather than merely roll across
and off the electrostatographic plate surface. Print deletion
and massive carryover of carrier particles often occur when
carrier particles adhere to reusable electrostatographic imaging
surfaces, Massive carrier carry-over problems are particularly
acute when the developer is employed in solid area coverage
machines where excessive quantities of toner particles are re-
moved from carrier particles thereby leaving many carrier particles
substantially bare of toner particles. Further, adherence of
carrier particles to reusable electrostatographic imaging surfaces
promotes the formation of undesirable scratches on the surfaces
during image transfer and surface cleaning operations. It is
therefore, apparent that many materials which otherwise have
suitable properties for employment as developer materials are
unsuitable because they possess unsatisfactory triboelectric
properties. In addition, uniform triboelectric surface charac-
teristics of many carrier surfaces are difficult to achieve with
mass production techniques. Quality images are in some instances
almost impossible to obtain in high speed automatic machines when
carriers having non-uniform triboelectric properties are employed.
Although it may be possible to alter the triboelectric value of an
insulating carrier material by blending the carrier material with
another insulating material having a triboelectric value remote
from the triboelectric value of the original carrier material,
relatively larger quantities of additional material is necessary
to alter the triboelectric value of the original carrier material.
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1(143149
The addition of large quantities of material to the original
carrier material to change the triboelectric properties thereof
requires a major manufacturing operation and often undesirably
alters the original physical characteristics of the carrier
material. Further, it is highly desirable to control the
triboelectric properties of carrier surfaces to accommodate
the use of desirable toner compositions while retaining the
other desirable physical characteristics of the carrier.
Another factor affecting the stability of the triboelectric
properties of developer materials is the susceptibility of
developer particles to "toner impaction". When developer
particles are employed in automatic machines and recycled
through many cycles, the many collisions which occur
between the carrier particles and other surfaces in the machine
cause the toner particles carried on the surface of the carrier
particles to be welded or otherwise forced onto the carrier
surfaces. The gradual accumulation of impacted toner material
on the surface of the carrier causes a change in the tribo-
electric value of the carrier and directly contributes to the
degradation of copy quality by eventual destruction of the
toner carrying capacity of the carrier.
Thus, there is a continuing need for a better developer
material for developing electrostatic latent images.
SUMMARY OF THE INVENTION
In accordance with one aspect of this invention there
is provided a classified electrostatographic toner material
comprising toner particles having a particle size number dis-
tribution with a fine index ratio of less than about 2.50,
a particle size volume distribution with a coarse index ratio of
less than about 1.50, and a particle size distribution wherein
less than about 30.0 percent by number of the particles have
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an average particle size diameter of less than about 5 micron
about 25 percent of the particles have a diameter between
about 8 microns and about 12 microns, and less than about 5
percent by number of the toner particles have an average
particle diameter greater than about 20 microns.
The classified high surface area carrier materials
desirably have a specific surface area of at least about 150
cm /gram. However, it is preferred that the carrier materials
have a specific surface area of at least about 165 cm2/gram
because developer life is improved such as to provide increased
copy quantity with the developer material in a high speed
electrostatographic reproduction apparatus while maintaining
low background levels and sustaining solid area development
density. ~ptimum results are obtained ~hen the carrier
materials of this invention have a specific surface area
of at least about 175 cm2/gram.
In accordance with another aspect of this invention
there is provided an electrostatographic developer mixture
comprising finely divided toner particles electrostatically
clinging to the surface of carrier particles, the toner
particles having the composition set forth above.
In accordance with another aspect of this invention ~-
there is provided an electrostatographic imaging process
comprising the steps of providing an electrostatographic
imaging member having a recording surface, forming an electro-
static latent image on the recording surface, and contacting
the electrostatic latent image with the developer referred to
above, whereby at least a portion of the finely divided toner
particles are attracted to and deposited on the recording
surface in conformance with the electrostatic latent image.
It has been found that the area ratios of carrier to
toner material in a high speed magnetic brush development system
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were such that the toner concentration could no-t be sufficiently
reduced to enable a charge level for minimal deposit of toner
material in background areas of an electrostatic latent image
during development thereof while retaining sufficient tonèr
concentration to provide satisfactory solid area density. By
providing the carrier materials of this invention having a
minimum specific surface area this problem has been overcome.
Thus, this invention now enables the use of a developer mixture
having a lower toner concentration per unit surface area of
carrier to provide a higher net electrical charge level. It
has been found that in the electrostatic copying process that
where any given carrier material is employed to provide a tribo-
electric charge to toner materials by contact charge transfer,
the area of carrier triboelectric charging surface is critically
important. The carrier charging surface area has been found to
relate to thë amount of toner material that, for a given toner
material, can be charged to a useful triboelectric potential or
level. Therefore, in accordance with this invention, it has
been found that the triboelectric charg1ng capacity of a carrier
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material is surL-ace area dependent and accordingly, this
invention may be employed to design optimum deve]oper materials
for any given electrostatographic development system
The term coarse index is defined as the ratio of the
volume distribution of particle size diameter of 84 percent
of the toner particles divided by the particle size diameter of
50 percent of the toner particles. Similarly, the term fine
index is defined as the ratio of the number distribution of
particle size diameter of 50 percent of the toner particles
divided by the particle size diameter of 16 percent of the
toner particles. Both the coarse index and fine index ratios
are calculated from the respective volume and number cumulative
frequency plots which are obtained from particle size analysis
performed on a Coulter Counter employing a 100 micron orifice.
The former value represents the median or average particle size
distribution by weight or volume of the toner particles and has
an important influence on the copy quality obtained in an electro-
statographic development system. The fine index is a measure of
the toner particles number average distribution, weighted on the
fine end, and has an important reflection on the measure of the
useful lifetime of the developer, the systems life, rate of
photoreceptor filming and rate of toner impaction on the electro-
statographic recording surface.
It has been found that the classified developer materials of this
invention provide satisfactory results when the particle size
number distribution fine index of the toner particles is less
than about 2.50. Improved results are obtained with, and it is
preferred, that the particle size number distribution fine index
thereof is less than about 2.00. Optimum results are obtained
when the particle size number distribution fine index of the
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classified toner materials is less than about 1.45. Similarly,
satisfactory results are ohtained with the classified developer
materials of this invention when the partlcle size volume
distribution coarse index of the toner particles is less than
about 1,50. However, it is preferred that the particle size
volume distribution coarse index thereof be less than about 1.45
because improved resolution and edye definition is obtained on
the copies. Optimum results are obtained when the particle size
volume distribution coarse index of the toner materials is less
than about 1,35.
In addition, it has been found that the classified
toner materials of this invention provide satisfactory results
when the particle size distribution thereof is such that less
than about 30.0 percent by number of the toner particles have
an average particle diameter of less than about 5 microns, about
25.0 percent by number of the toner particles have an average
particle diameter of between about 8 microns and about 12
microns, and less than about 5.0 percent by number of the toner
particles have an average particle diameter greater than about
20 microns. However, it is preferred that the particle size
distribution be such that less than abou' 20 percent by number
of the toner particles have an average particle diameter of
less than about 5 microns, about 45 percent by number of the toner
particles have an average particle diameter of between about 8
microns and about 12 microns, and less than about 5 percent by
number of the toner particles have an average particle diameter
greater than about 20 microns. Optimum results are obtained
when the particle size distribution is such that less than about
10 percent by number of the toner particles have an average par-
ticle diameter of less than about 5 microns, about 60 percent
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by numher of the toner particles have an average particle diameter
of between about 8 microns and about 12 microns, and less than
about 5 percent by number of the toner particles have an average
particle diameter greater than about 20 microns.
It has been found that the classified carrier materials
of this invention provide satisfactory results when the particle
size volume distribution geometric standard deviation thereof is
less than axout 1.3 and the volume average particle diameter is
less than about 100 microns. Improved results are obtained with,
and it is preferred, that the particle size volume distribution
geometric standard deviation thereof be less than about 1.2 and
the volume average particle diameter is less than about 90 microns.
Optimum results are obtained when the volume distribution geometric
standard deviation of the classified carrier materials of this
invention is less than about 1.15 and the volume average particle
diameter is less than about 85 microns. The term geometric
standard deviation as employed herein is defined as the deviation
encountered in a particle size analysis approximately measured
as the ratio of the particle diameter which is greater than that
of 84 percent of the sample to that of the particle diameter which
is greater than that of 50 percent of the sample. This value
represents the median or average particle size distribution by
weight or volume of the carrier particles and has an important
reflection on copy quality obtained in an electrostatographic
development system. Another measure of the geometric standard
deviation of the classified carrier materials of this invention
is the deviation encountered in a particle size analysis approxi-
mately measured as the ratio of the particle diameter which is
greater than that of 50 percent of the sample to that of the
particle diameter which is greater than that of 16 percent of the
sample. The 50 percent value represents the median or average
particle size by volume of the carrier particles and has an
important reflection on the measure of the useful lifetime of the
developer, In both cases, the y~ ueg obtained for the volume
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average particle diameter and the geometric standard deviation
are determined by size analysis performed by a sieve analysis
employing all U. S. Standard sieves from 325 mesh to 70 mesh.
Any suitable particle classification method may be
employed to obtain the classified toner materials of this in-
vention. Typical particle classification methods include air
classification, screening, cyclone separation, elutriation,
centrification, and combinations thereof. The preferred method
of obtaining the classified toner materials of this invention
is by centrifugal air classification. In this method, air or
some other gas flows inwards in a spiral path through a flat,
cylindrical chamber. particles contained in the air flow are
exposed to two antagonistic forces, viz., to the inwardly
directed tractive force of the air, and to the outwardly
directed centrifugal force of the particle. For a definite
size of particles, that is, the "cut size," both forces are
in equilibrium. Larger (heavier) particles are dominated by
the mass-dependent centrifugal force and the smaller (lighter)
particles by the frictional force proportional to the particle
diameter. Consequently, the larger or heavier particles fly
outwards as coarse fraction, while the smaller or lighter ones
are carried inwards by the air as fine fraction. The "cut size"
usually depends upon the gradient of the spiral, the peripheral
component, and the absolute dimension of the classifying chamber.
Adjustment of the "cut size" may be effected through variation
of the two factors first mentioned, while the range of the "cut
size" may be determined by the respective dimension of the classi-
fying chamber. Satisfactory centrifugal air classification results
may be obtained when employing an apparatus such as the Mikroplex
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Spiral Air Classifier Type 132Mp model available from the Alpine
(R)
American Corporation, Natick, Massachusetts, or an Acucut
Model B18 unit available from the Donaldson Company, Inc., Tulsa,
Oklahoma.
Any suitable particle classification method may be em-
ployed to obtain the high surface area carrier materials of this
invention. Typical particle classification methods include air
classification, screening, cyclone separation, elutriation,
centrification, and combinations ~hereof. The preferred method
of obtaining the high surface area carrier materials of this
invention is by screening or seiving.
Any suitable vinyl resin having a melting point of at
least about 110 F may be employed in the toner compositions.
The vinyl resin may be a homopolymer or a copolymer of two or
more vinyl monomers. Typical monomeric units which may be
employed to form vinyl polymers include: styrene, p-chloro-
styrene, vinyl naphthalene; ethylenically 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 alpha-
methylene aliphatic monocarboxylic acids such as methyl acry-
late, ethyl acrylate, n-butylacrylate, isobutyl acrylate,
dodecyl acrylate, n-octyl acrylate, 2 chloroethyl acrylate,
phenyl acrylate, methyl-alpha-chloroacrylate, methyl
methacrylate, ethyl methacrylate, butyl methacrylate and
the like; acrylonitrile, methacrylonitrile, acrylamide, vinyl
ethers such as vinyl methyl ether, vinyl isobutyl ether, vinyl
ethyl ether, and the like; vinyl ketones such as vinyl methyl
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ketone, vinyl hexyl ketone, methyl isopropenyl ketone and the
like; vinylidene halides such as vinylidene chloride, vinyl-
idene chlorofluoride and the like; and N-vinyl compounds such
as N-vinyl pyrrole, N-viny] carbazole, N-vinyl indole, N-vinyl
pyrrolidene and the like; and mixtures thereof. Generally,
suitable vinyl resins employed in the toner have a weight aver-
age molecular weight between about 3,000 to aho t 500,000.
Toner resins containing relatively high percentages
of a styrene resin are preferred. The presence of a styrene
resin is preferred because a greater degree of image definition
is generally achieved upon latent image development. Further,
denser images are obtained when at least about 25 percent by
weight, based on the total weight of resin in the toner, of a
styrene resin is present in the toner, The styrene resin may
be a homopolymer of styrene or styrene homologues or copolymers
of styrene with other monomeric groups containing a single
methylene group attached to a carbon atom by a double bond. Thus,
typical monometric materials which may be copolymerized with sty-
rene by addition polymerization include: P-chlorostyrene, vinyl
naphthalene; ethylenically unsaturated monoolefins such as they-
lene, propylene, butylene, isobuthlene 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 alpha-methylene aliphatic monocarboxylic acids
such as methyl acrylate, ethyl acrylate, n-butylacrylate, isobutyl
acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acry-
late, phenyl acrylate, methyl-alpha-chloroacrylate, methyl metha-
crylate, ethyl methacrylate, butyl methacrylate and the like;
acrylonitrile, methacrylonitrile, acrylamide, vinyl ethers such
as vinyl met~yl ether, vinyl isobutyl ether, vinyl ethyl ether,
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1~43~49
and the like, vinyl ketones such as vinyl methyl ketone,
vinyl hexyl ketone, methyl isopropenyl ketone and the
like; vinylidene halides such as vinylidene chloride,
vinylidene chlorofluoride and the like; and N-vinyl
compounds such as N-vinyl pyroole, N-vinyl carbazole, N-vinyl
indole, N-vinyl pyrrolidene and the like; and mixtures
thereof. The styrene resins may also be formed by the
polymerization of mixtures of two or more of these
unsaturated monomeric materials with a styrene monomer.
The expression "addition polymerization" is intended
to include known polymerization techniques such as free
radical, anionic and cationic polymerization processes.
The vinyl resins, including styrene type reins,
may also be blended with one or more other resins if
desired, When the vinyl resin is blended with another
resin, the added resin is preferably another vinyl
resin because the resulting blend is characterized by
especially good triboelectric stability and uniform
resistance against physical degradation. The vinyl
resins employed for blending with the styrene type or
other vinyl resin may be prepared by the addition
polymerization of any suitable vinyl monomer such
as the vinyl monomers described above. Other thermo-
plastic resins may also be blended with the vinyl
resins of this invention. Typical non-vinyl type
thermoplastic resins include: rosin modified phenol
formaldehyde resins, oil modified epoxy resins, poly-
urethane resins, cellulosic resins, polyether resins
and mixture thereof. When the resin component of the
toner contains styrene copolymerized with another un-
~aturated monomer or a blend of polystyrene and another
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resin, a styrene component of at least about 25 percent
by weiyht based on the total weight of thc resin
present in the toner is preferred because denser im-
ages are obtained and a greater degree of image
definition is achieved with a given quantity of toner
material.
It is to be understood that the specific
formulas given for the units contained in the resins
of the toner materials re-present the vast majority of
the units present, but do not exclude the presence
of monomeric units or reactants other than those
which have been shown. For example, some commercial
materials contain trace amounts of homologues or un-
reacted or partially reacted monomers. Any minor
amount of such substituents may be present in the
materials of this invention.
Any suitable pigment or dye may be employed
as the colorant for the toner particles. Toner color-
ants are well-known and include, for example, carbon
black, nigrosine dye, aniline blue, Calco Oil Blue,
chrome yellow, ultramarine blue, duPont Oil Red~
Qunioline Yellow, emthylene blue chloride, phtha-
locyanine blue, Malachite Green Oxalate, lamp black,
Rose Bengal and mixtures thereof. The pigment or dye
should be present in the toner in a sufficient quantity
to render it highly colored so that it will form a
clearly visible image on a recording member. Thus,
for example, where conventional electrostatographic
copies of typed documents are desired, the toner may
comprise a black pigment such as carbon black, for
example, furnace black or channel black, or a black
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dye such as Amaplast Black dye, available from the
National Aniline Products, Inc. Generally, the pig-
ment is employed in an amount from about 1 percent
to about 20 percent by weight based on the total
weight of the colored toner. If the toner colorant
employed is a dye, substantially smaller quantities of
colorant may be used. However, since a number of the
above pigments used in electrostatographic toner com-
positions may affect both the glass transition and
fusion temperatures of the toner compositions of this
invention, their concentration preferably should be
about 10 percent by weight of the colored toner.
The toner compositions may be prepared by
any well-known toner mixing and comminution technique.
For example, the ingredients may be thoroughly mixed
by blending, mixing and milling the components and
thereafter micropulverizing the resulting mixture.
Another well-known technique for forming toner particles
i5 to spray-dry a ball-milled toner composition com-
prising a colorant, a resin, and a solvent.
Any suitable coated or uncoated electro-
statographic carrier bead material may be employed
as the high surface area carrier material of this in-
vention. Typical cascade development process carriers
include sodium chloride, ammonium chloride, aluminum
potassium chloride, Rochelle salt, sodium nitrate,
aluminum nitrate, potassium chlorate, granular zircon,
granular silicon, methyl methacrylate, glass and silicon
dioxide. Typical magnetic brush development process
carriers include nickel, steel, iron, ferrites, and
the like. The carriers may be employed with or without
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a coating, Many of the foregoing and other typical
carriers are described by L. E. walkup, et al. in
U. S. patent 2,638,~16 and E. N. Wise in U. S. Patent
2,618,552. An ultimate coated carrier particle dia-
meter between about 30 microns to about 1,000 microns
is preferred because the carrier particles then possess
sufficient density and inertia to avoid adherence
to the electrostatic images during the cascade devel-
opment process. For magnetic brush development, the
carrier particles generally have an average diameter
between about 30 microns and about 250 microns. Gen-
erally speaking, satisfactory results are obtained
when about 1 part toner is used with about 10 to 200
parts by weight of carrier.
The high surface area carrier materials of
this invention may be coated with any suitable coating
material. Typical electrostatographic carrier particle
coating materials include vinyl chloride-vinyl acetate
copolymers, styrene-acrylate-organosilicon terpolymers,
natural resins such as caoutchouc, colophony, copal,
dammar, Drangon's Blood, jalap, storax; thermoplastic
resins including the polyolefins such as polyethylene,
polypropylene, chlorinated polyethylene, and chloro-
sulfonated polyethylene; polyvinyls and polyvinylidenes
such as polystyrene, polymethylstyrene, polymethyl
methacrylate, polyacrylonitrile, polyvinyl acetate,
polyvinyl alcohol, poly vinyl butyral, polyvinyl
chloride, polyvinyl carbazole, polyvinyl ethers, and
polyvinyl ketones; fluorocarbons such as polytetra-
fluoroethylene, polyvinyl fluoride, polyvinylidene
fluoride; and polychlorotrifluoroethylene; polyamides
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1043~ 9,9
such as polycaprolactam and polyhexamethylene
adipamide; polyesters such as polyethylene terephtha-
late; polyurethanes; polysulfides, poly carbonates;
thermosetting resins including phenolic resins such
as phenol-formalidehyde, phenol-furfural and resorcinol
formaldehyde; amino resins such as urea-formaldehyde
and melamineformaldehyde; polyester resins; epoxy
resins; and the like. Many of the foregoing and other
typical carrier coating materials are described by
L. E. Walkup in U. S. Patent 2,618,551; B. B. Jacknow,
et al. in U. S. Patent 3,526,433; and R. J. Hagenbach,
et al. in U. S. ~atents 3,533,835 and 3,658,500.
When the high surface area carrier materials
of this invention are coated, any suitable electro-
statographic carrier coating thickness may be employed.
However, a carrier coating having a thickness at least
sufficient to form a thin continuous film on the car-
rier particle is preferred because the carrier coating
will then possess sufficient thickness to resist
abrasion and prevent pinholes which adversely affect
the triboelectric properties of the coated carrier
particles. Generally, for cascade and magnetic brush
development, the carrier coating may comprise from
about 0.1 percent to about 10.0 percent by weight
based on the weight of the coated carrier particles.
Preferably, the carrier coating should comprise from
about .3 percent to about 1.5 percent by weight based
on the weight of the coated carrier particles because
maximum durability, toner impaction resistance, and
copy quality are achieved. To achieve further varia-
tion in the properties of the coated composite carrier
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lQ43~49
particles, well-known additives such as plasticizers,
reactive and non-reactive polymers, dyes, pigments,
wetting agents and mixtures thereof may be mixed with
the coating materials.
When the high surface area carrier materials
of this invention are coated, the carrier coating
composition may be applied to the carrier cores by
any conventional method such as spraying, dipping,
fluidized bed coating, tumbling, brushing and the like.
The coating compositions may be applied as a powder,
- a dispersion, solution, emulsion or hot melt. When
applied as a solution, any suitable solvent may be
employed. Solvents having relatively low boiling
points are preferred because less energy and time is
required to remove the solvent subsequent to applica-
tion of the coating to the carrier cores. If desired,
the coating may comprise resin monomers which are poly-
merized in situ on the surface of the cores or plastisols
gelled in situ to a non-flowable state on the surface
of the cores. Surprisingly, it has been found that for
a given inefficient coating process, carrier core
materials having the specific surface areas designated
in this invention results in increased effective area,
that is, triboelectric charging coated area per unit
weight. Thus, increased carrier active area increases
the net toner material triboelectric charge level for
a given toner concentration by weight in a developer
mixture. Therefore, where it is preferred to operate an
electrostatographic development system at a minimum
toner concentration as to provide solid area coverage
and at a toner concentration high enough to minimize
toner deposits in background areas of a developed
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.
. . . : . : . , ,
1~43~149
electrostatic latent image resulting from toner par-
ticles having a low or weak triboelectric charge, these
objectives may be attained hy employing the high sur-
face area carrier materials of this invention. In
accordance with this invention, the aforementioned
objectives are attained by operating at a decreased
toner concentration providing lower background deposits
and enabling longer developer life.
Any suitable organic or inorganic photocon-
ductive material may be employed as the recording sur-
face with the classified developer materials of this
invention. Typical inorganic photoconductor materials
include: sulfur, selenium, zinc sulfide, zinc oxide,
zinc cadmium sulfide, zinc magnesium oxide, cadium
selenide zinc silicate calcium strontium sulfide
cadmium sulfide, mercuric iodide, mercuric oxide,
mercuric sulfide, indium trisulfide, gallium selenide,
arsenic disulfide, arsenic trisulfide, arsenic tri-
selenide antimony trisulfide, cadmium sulfo-selenide
and mixtures thereof. Typical organic photoconductors
include: guinacridone pigments, phthalocyanine pig-
ments, triphenylamine, 2,4-bix(4,4'-diethylamino-phenol) -1,
3,4,-oxadiazol, N-isopropylcarbazol, triphenylpyrrol,
4,5-diphenyl-imidazolidinone, 4,5-diphenyl-imidazol-
idinethione, 4,5-bix-(4'-amino-phenyl)-imidazolidinone,
1,5-dicyanonaphthalene, 1,4-dicyanonaphthalene, amino-
phthalodinitrile, nitrophthalodinitrile, 1,2,5,6-
tetraazacyclooctatetraene-(2,4,6,8), 2-mercaptobenzo-
thiazole-2-phenyl-4-disphenylideneoxazolone, 6-hydroxy-
2,3-di(p-methoxyphenyl)-benzofurane, 4-dimethylamino-
benzylidene-benzhydrazide, 3-benzylidene-aminocarbazole,
-24-
. .
~(~43~49
polyvinyl carbazole, (2-nitro-benzylidene)-p-bromoaniline,
2,4-dip~enylquinazoline, 1,2,~-triazine, 5-diphenyl-3-
methyl-pyrazoline,2-(4'dimethylamino phenyl)-benzoxazole,
3-aminecarbazole, and mixtures thereof. Representative
patents in which photoconductive materials are dis-
closed include U. S. patents 2,803 542 to Ullrich, U. S.
patent 2,970,906 to Bixby, U. S. patent 3,121,006 to
Middleton, U. S. Patent 3,121,007 to Middleton, and
U. S. patent 3,151,982 to Corrsin.
DESCRIPTION OF PREFERRED EMBODIMENTS
; The following examples further define, des-
cribe and compare methods of preparing the developer
materials of the present lnvention and of utilizing them
to develop electrostatic latent images. Parts and
percentages are by weight unless otherwise indicated.
In the following examples, toner impaction
is measured by a spectrophotometric technique. In
general, a 3-5 gram sample of the developer is weighed
accurately. Next it is washed with an aqueous surfactant
solution to remove loose, non-impacted toner. A quan-
tity of the appropriate solvent is added aimed at dis-
solving the impacted toner polymer and suspending the
carbon black. The mixture of solution and suspended
carbon black is ultra-sonified to disperse the carbon
black. The resultant suspension is transferred to a
volumetric flask and diluted with additional solvent
to the mark. The apparent absorbance of the suspension
is measured in the visible region. ThiS is compared
to a standard curve derived from the virgin toner used
to prepare the developer, The concentration of im-
pacted toner is calculated from the absorbance of the
-25-
', ' ,, ' ',", ' ~ ,"'; ' ~" '
~43~9
sample dispersion. Generally it has been found most
useful to measure the rate of toner impaction through-
out any machine test. ~or practical considerations,
the number of measurements has to be limited and
very good results have been obtained based upon toner
impaction during the first 50,000 copies during any
test. The rate of toner impaction is calculated from
the milligrams of impacted toner polymer per gram of
developer per 1,000 copies.
Further, in the following examples, the
toner materials were classified employing an Acucut
Model B18 unit available from the Donaldson Company,
Inc., Tulsa, Oklahoma.
EXAMPLE I
A control developer mixture is prepared by
mixing a toner composition comprising a mixture of
about 90 parts by weight of a copolymer of about 58.0
percent by weight of styrene and about 42.0 percent
by weight of n~butyl methacrylate, and about 10 parts
by weight of a furnace carbon black with carrier
particles. The toner particles were determined to
have a particle size number distribution fine index
of about 1.70, a particle size volume distribution
coarse index of about 1.40, and a particle size distri-
bution wherein about 50 percent of the toner particles
had an average particle diameter of less than about 5
microns, about 23 percent by number of the toner
particles had an average particle diameter of between
about 5 microns and about 8 microns, about 15 percent
by number of the toner particles hadi an average particle
diameter of between about 8 microns and about 12 microns,
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.... . .. . ..
1~43~9~9
about 7 percent by number of the toner particles had
an average particle diameter of between ahout 12
microns and about 20 microns, and about 5 percent by
number of the toner particles had an average particle :
diameter of more than 20 microns. The carrier particles
comprised nickel-zinc ferrite coated with about 0.6%
by weight, based on the weight of the core material,
of a carrier coating composition comprising styrene,
a methacrylate ester, and an organosilicon compound
as disclosed in U. S. patent 3,526,533. The coated
ferrite carrier material is determined by seive analysis
to have a particle size distribution as follows:
: U. S. Seive % By Weight
70 mesh ( 210u) . o
80 mesh ( 177u) o
100 mesh ( 149u) . .1
120 mesh ( 125u) .1
140 mesh ( 105u) 7.2
170 mesh (88u) 30 4
200 mesh (74u) 30.7
230 mesh (63u) 25.5
270 mesh (54u) 5.7
325 mesh (44u) 0.2
pan
By calculation, the coated ferrite carrier material
is determined to have a specific surface area of about
128 cm2,/gram. About 1 part by weight of the toner
particles was mixed with about 100 parts by weight of
the carrier particles to form the developer mixture.
Copies of a standard test pattern were made with the
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. .
1(~43~49
developer rnixture in an electrostatographic copying
machine employing a rnagnetic brush development system.
It was found that the developer mixture failed after
about 100,000 copies. Developer failure was exper-
ienced in the form of high background, i.e., exceeding
the specified 0.0l background density level at 1.0
solid area density. A high level of photoreceptor
filming was observed as print-out on the copies occurred
at a frequency of about every 15 000 copy intervals
The rate of toner impaction was found to be about
0.0450.
EXAMPLE II
A developer mixture is prepared by mixing
about 1 part of the toner material employed in
~xample I with about 100 parts of the carrier material
employed in Example I except that the toner particles
were determined to have a particle size number distri-
bution fine index of about 2.07, a particle size
volume distribution course index of about 1.40, and
a particle size distribution wherein about 29 percent
of the toner particles had an average particle diameter
of less than about 5 microns, about 30 percent by
number of the toner particles had an average particle
diameter of between about 5 microns and about 8 microns,
about 25 percent by number of the toner particles had
an average particle diameter of between about 8 microns
and about 12 microns, about 11 percent by number of
the toner particles had an average particle diameter
of between about 12 microns and about 20 microns, and
about 5 percent by number of the toner particles had an
average particle diameter of more than 20 microns.
1~3~ 9
The carrier material was de~ermined by seive anal.ysis
to have the following particle size di.stribution:
;'
.
U.S. Seive /O By Wei~ht
70 mesh ( 210u) 0
80 mesh ( 177u) o
. 100 mesh ( 149u)
0.8
120 mesh ( 125u)
5.9
140 mesh ( 105u)
21.4
170 mesh ( 88u) 40.3
200 mesh ( 74u) 28.5
230 mesh ( 63u) 1.4
270 mesh ( 54u) 1.4
325 mesh ( 44u) 0.3
pan
By calculation, the coated ferrite carrier material
is determined to have a specific surface area of about
151 cm2/gram. The developer is used to develop an
electrostatic latent image under substantially the
same conditions as in Example I. It was found that
the developer mixture performed satisfactorily up to
about 225,000 copies. A lower level of photoreceptor
filming was observed as print-out on the copies at a
frequency of about every 25,000 copy intervals. The
rate of toner impaction was found to be about 0.0280.
EXAMPLE III
A developer mixture is prepared by mixing
about 1 part of the toner material employed in Example
I with about 100 parts of the carriqr material employed
in Example I except that the toner particles were
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~343~9
determined to have a particle size number distribution fine
index of about 2.60, a particle size volume distribution
coarse index of about 1.35, and a particle size distribution
wherein about 23 percent of the toner particles had an average
particle diameter of less than about 5 microns, about 18 per-
cent by number of the toner particles had an average particle
diameter of between about 5 microns and about 8 microns, about
35 percent by number of the toner particles had an average
particle diameter of between about 8 microns and about 12 microns,
about l9 percent by number of the toner particles had an average
particle diameter of between about 12 microns and about 20
microns, and about 5 percent by number of the toner particles
had an average particle diameter of more than 20 microns. The
carrier material was determined by seive analysis to have the
following particle size distribution:
U. S. Seive% By Weight
70 Mesh ( 210u) o
80 Mesh ( 177u) o
100 Mesh ( 149u) o
120 Mesh ( 125u) 0.16
140 Mesh ( 105u) 13.8
170 Mesh ( 88u) 35.1
200 Mesh ( 74u) 40.9
230 Mesh ( 63u) 7.59
270 Mesh ( 54u) 1.86
325 Mesh ( 44u) .53
pan 0,06
By calculation, the coated ferrite carrier material is determined
to have a specific surface area of about 160 cm2/gram The
developer is used to develop an electrostatic latent image under
-30-
1~43~9~9
substantailly the same conditions as in ~xample I. It was found
that the developer mixture performed satisfactorily up to about
375,000 copies. A lower level of photoreceptor filming was
observed as print-out on the copies at a frequency of about
every 35,000 copy intervals. The rate of toner impaction was
found to be about 0.0220.
EXAMPLE IV
A developer mixture is prepared by mixing about 1 part
of the toner ~aterial employed in Example I with about 100 parts
of the carrier material employed in Example I except that the
toner particles were determined to have a particle size number
distribution fine index of about 2.25, a particle size volume
distribution coarse index of about 1.35, and a particle size dis-
tribution wherein about 21 percent of the toner particles had an
average partacle diameter of less than about 5 microns, about
15 percent by number of the toner particles had an average
particle diameter of between about 5 microns and about 8 microns,
about 40 percent by number of the toner particles had an average
particle diameter of between about 8 microns and about 12 microns,
about 19 percent by number of the toner particles had an average
particle diameter of between about 12 microns and about 20 microns,
and about 5 percent by number of the toner particles had an
average particle diameter of more than 20 microns. The carrier
material was determined by seive analysis to have the following
particle size distribution:
-31-
,
1~43~9
U. S. Seive % By Weight
70 Mesh ( 210u) 0
80 Mesh ( 177u) 0
100 Mesh ( 149u) 0
120 Mesh ( 125u) 0
140 Mesh ( 105u) 5.7
170 Mesh ( 88u) 44,7
200 Mesh ( 74u) 34.9
230 Mesh ( 63u) 10.9
270 Mesh ( 54u) 3.7
325 Mesh ( 44u) .13
pan
By calculation, the coated ferrite carrier material is determined
to have a specific surface area of about 168 cm /gram. The
developer is used to develop an electrostatic latent image under
substantially the same conditions as in Example I. It was found
that the developer mixture performed satisfactorily up to 325,000
copies when the test was suspended. A lower level of photoreceptor
filming was observed as print-out on the copies at a frequency of
about every 50,000 copy intervals. The rate of toner impaction
was found to be about 0.0140.
EXAMPLE V
A developer mixture is prepared by mixing about 1 part
of the toner material employed in Example I with about 100 parts
of the carrier material employed in Example I except that the
toner particles were determined to have a particle size number
distribution fine index of about 1.70, a particle size volume
distribution coarse index of about 1.33, and a particle size
distribution wherein about 13 percent of the t-oner particles had
an average particle diameter of less than about 5 microns, about
12 percent by number of the toner particle had an average particle
diameter of between about 5 microns and about 8 microns, about
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. '
-
~6~43~9~9
50 percent by number of the toner particles had an average
particle diameter of between about 8 microns and abou~ 12
microns, about 20 percent by number of the toner particles
had an average particle di.ameter of between about 12 microns
and about 20 microns, and about 5 percent by number of the
toner particles had an average particle diameter of more than
20 microns, The carrier material was determined by seive
- analysis to have the following particle size distribution:
U. S. Seive % By_Weight
70 Mesh ( 210u) 0
80 Mesh ( 177u) .2
100 Mesh ( 149u) 1.7
120 Mesh ( 125u) 4.5
140 Mesh ( 105u) 7,5
170 Mesh ( 88u) 10.3
200 Mesh. ( 74u) 62,4
230 Mesh ( 63u) 2.6
270 Mesh ( 54u) 5.1
325 Mesh ( 44u) 5.1
Pan ,51
This distribution was reconstructed artificially and does not
satisfy a log-normal plot for a geometric standard deviation
calculation, By calculation, the coated ferrite carrier material
is determined to have a specific surface area of about 177 cm2/gram,
The developer is used to develop an electrostatic latent image
under substantially the same conditions as in Example I, It was
found that the developer mixture performed satisfactorily up to
400,000 copies when the test was suspended, A low level of photo-
receptor filming was observed as print-out on the copies at a
frequency of about every 135,000 copy intervals, The rate of
toner impaction was found to be about 0.0117,
; -33-
1~43~9
Thus, highly classified developer materials of this
invention are characterized as providing improved copy quality
experienced in reduced toner deposits in background areas. In
addition, developer materials of this invention are further
characterized as resulting in improved machine performance with
longer systems life, that is, these developer materials provide
substantially improved triboelectric charging properties of the
developer mixtures for substantially longer periods of time
thereby increasing the developer life of the developer mixtures
and decreasing the time intervals between replacement of the
developer materials. Further still, the developer materials of
this invention may be characterized as providing dense toner
images and are particularly useful in magnetic brush development
systems. ThUS, by providing the develop~r materials of this
invention, substantial improvements in systems life due to intrin-
sic developer life result upon the classification and use of
developer materials having teh specified physical characteristics.
In addition, the developer materials of this invention
may be further characterized as experiencing substantially reduced
impaction rates resulting in more stable triboelectric charging
properties of the developer mixtures for substantially longer
periods of time thereby increasing the developer life of the
developer mixtures and decreasing the time intervals between
replacement of the developer materials.
The expressions "developing material" and ~developer
mixture" as employed herein are intended to include toner material
or combinations of toner material and carrier material.
Although specific materials and conditions are set forth
in the above examples of making and using the developer materials
of this invention, these are merely intended as illustrations of
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~04319~9
the present invention, These and other high surface area carrier
materials, toner materials, substituents, and processes, such
as those listed above, may be substituted for those in the
Examples with similar results,
Other modifications of the present invention will
occur to those skilled in ~he art upon a reading of the present
disclosure. These are intended to be included within the scope
of this invention,
.
:,:
