Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
This invention relates in general to electrostato-
graphic imaging systems, and, in particular, to improved
developer materials and their use.
The formation and development of images on the
surface o~ photoconductive materials by electrostatic means
i9 well-known. The basic electrostatographic process, as taught
by C. F. Carlson in U.S. Pat. No. 2,297,691, involves placing
a uniform electrostatic 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 electros-tatic latent image
by depositing on the image a finely divided electroscopic
material referred to in the art as "toner".
One technique for developing an electrostatic latent
image is the "magnetic brush" process as disclosed, for example,
in U.S. Pat. No. 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 maynetic carriers in a brush-like configuration. This
magnetic brush is engaged with an electrostatic latent image-
bearing surface and the toner particles are drawn from the
brush to the electrostatic image by electrostatic attraction.
Many other methods such as "touchdown" development as dis-
closed by C. R. May in U.S. Pat. No. 2,895,847 are known for
applying electroscopic particles to the electrostatic latent
image to be developed. The development processes as mentioned
above, together with numerous variations, are well-known to
the art through various patents and publications and through the
widespread availability and utilization of electrostatographic
imaging equipment.
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While ordinarily capable o~ producing good quality
images, conventional developing systems suffer serious
deficiencies in certain areas. In the reproduction of high
contrast copies such as letters, tracings and the like, it
S is desirable to select the electroscopic powder and carrier
materials so that their mutual electrication is gcverned in
most cases by the distance between their relative positions
in the triboelectric series~ However, when otherwise com-
patible 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. ~lthough the image
density may be improved by increasing the toner concentration
in the developer mixture, undesirably high background toner
deposition as well as increased toner impaction and agglomera
tion is encountered when the toner concentration in the
developer mixture is excessive. The initial electrostato-
graphic 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 high electrostatographic plate charges are not
only undesirable because of the high power consumption neces-
sary 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 electro-
statographic plate surface. Print deletion and massive
carryover oE carrier particles often occur when carrier
particles adhere to reusable electrosta~ographic imaying
surfac~s. Massive carrier carry-over problems are particu-
larly acute when the developer is employed in solid area
S coverage machines where excessive quantities of toner particles
are removed from carr ier particles thereby leaving many
carrier particles substantially bare of toner particles.
Further, adherence of carrier particles to reusable electro-
statographic 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 properties. In addition, uniform
triboelectric surface characteristics 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. 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 compositlons while
retaining the other desirable physical characterist'ics of
the carrierO Another factor affecting the stability of the
triboelectric properties of developer materials is the sus-
ceptibility of developer particles to "toner impaction".
~ 7~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 chan~e in the triboelectric value of the carrier and
directly contribu~es to the degradation of copy quality
by eventual destruction of the toner carrying capacity of
the carrier.
PRIOR ART
In U.S. Patent 3,942,979, there is disclosed a
developer mixture comprising classified toner materials having
a particle size distribution wherein less than about 30% by
number of the toner particles have an average particle size
diameter of less than about 5 microns, about 25% oE the parti-
cles have a diameter between about 8 microns and about l~
microns, and less than about 5% by number of the toner particles
have an average particle diameter greater than about 20 microns.
The high surface area carrier materials have a specific sur-
face of at least about 150 cm2/gram. It is also indicated therein
that for cascade and magnetic brush development, the carrier
particles generally have an average diameter between about
30 microns and 1000 microns, and between about 30 and about
250 microns, respectively.
Present commercial magnetic brush development
systems generally employ carrier particles that are approxi-
mately 100 microns in diameter. Toner particles employed
with these carrier particles typically have a distribution
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of particle sizes that vary from l to 30 microns. Experience
with the aforementioned developer materials reveals degra-
dation of copy quality as reflected by blurred and mottled
prints having poor edge acuity and resolution.
Thus, there is a continuing need for better devel-
oper materials for developing electrostatic latent images.
UMM~RY OF THE INVENTION
It is, therefore, an object of an aspect of this
invention to provide developer materials which overcome
the above noted deficiencies.
It is an object of an aspect of this invention to
provide developer materials having more stable electrostato-
graphic properties.
It is an object of an aspect of this invention to
provide developer materials which have a longer useful life.
It is an object of an aspect of this invention to
provide developer materials which are less susceptible to
toner impaction.
It is an object of an aspect of this invention to
provide developer materials which are more resistant to
film formation on electrostatographic recording surfaces.
It is an object of an aspect of this invention to
provide developer materials which enable the attainment of
copied images having greatly improved quality.
It is an object of an aspect of this invention to
provide developer materials having improved triboelectric
properties.
An object of an aspect of this invention is to
provide developer materials which exhibit improved elec-
trical and mechanical properties useful in an electro-
statographic apparatus employing magnetic brush develop~
ment apparatus.
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An object of an aspect of this invention is to
provide improved developer materials having physical and
chemical properties superior to those of known developer
materials.
Various aspects of this invention are as follows:
An electrostatographic developer mixture comprising
finely-divided toner particles electrostatically clinging to
the surface of carrier particles, said toner particles con-
sisting essentially of particles having a diameter of
between about 3 microns and about 15 microns, and said
carrier particles consisting essentially of particles having
. a diameter of between about 15 microns and about 65 micxons.
An electrostatographic imaging process compris-
ing the steps of providing an electrostatographic imaging
member having a recording surface, forming an electro-
static latent image on said recording surface, and con-
tacting said electrostatic latent image with a developer
mixture comprising finely-divided toner particles electro-
statically clinging to the surface of carrier particles,
said toner particles consisting essentially of particles
having a diameter of between about 3 microns and about 15
microns, and said carrier particles consisting essential-
ly of particles having a diameter of between about 15
microns and about 65 microns, whereby at least a portion
of said finely-divided toner particles are attracted to
and deposited on said recording surface in conformance
with said electrostatic latent image.
Even better results are obtained when, and it is
preferred that, the toner materials have a particle diameter
in the range of between about 3 microns and about 10
microns and the carrier materials have a particle diameter
in the range of between about 10 microns and about 40
microns. Optimum results are obtained when the toner
materials have a particle diameter in the range of
between about 3 microns and about 8 microns and the
carrier materials have a particle diameter in the range
of between about 8 microns and about 24 microns.
It has now been found that the removal from
toner materials of toner particles which are below about
3 microns will provide a developer mixture having
improved carrier life, background deposits are minimized,
and photoreceptor cleaning is greatly facilitated.
More particularly, toner particles having a diameter
below 3 microns usually encompass free colorant
such as carbon black, and unpigmented
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platelets which are undesirable since they inhibit proper
triboelectric charging and reduce the active carrier sur~ace
area resulting in high background deposition of such particles.
By considering the particle size of toner particles
relative to copy quality, a particle size range of 3 to 15
microns with a mean particle size of about 2 microns has been
found to provide maximum copy quality. Apparently, toner
particles having a diameter below 3 microns are tribo-
electrically charged too highly and they tend to not be
developed as easily as the larger particles and also prevent
the larger particles from being charged high enough. These
lower charged larger particles are difficult to control in
a developer mixture and will usually undesirably develop
onto the background areas of an electrostatic latent image.
It has also been found that the removal from toner
materials of toner particles having a diam~ter larger than
15 microns will provide improved copy quality since such
particles have been found to produce observable blur in biased
transfer roll systems.
It has also been found that conventional 100 micron
siæe carrier particles are very quickly impacted with
toner particles thus reducing the useful life of such developer
mixtures. Thus, in accordance with this invention, by
employing toner particles having a diameter between 3 and 15
microns with carrier particles having a diameter of between
15 and 65 microns, this carrier size range increases the
surface area of the carrier material to acccmmodate the toner
material as described above and generates lower impaction
energies The net result of the developer mixtures of this
invention is the provision of prints produced by the electro-
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statographic process wherein the printed image now has
improved edge acuity, high resolution, and sharp, crisp
characters. Where an occasional toner particle deposits
in background areas, due to the smaller size of the toner
particles employed, the background deposit is not perceivable
by the naked eye. Likewise, due to the smaller size of the
carrier particles employed in the developer mixtures of this
invention, it is now possible for the carrier particles to
carry sufficient toner particles to enable development of large
solid areas without employing excessively high toner concentra-
tions which previously led to unacceptably high image background
deposits.
Pursuant to this invention, the enhanced surface/
volume ratio of the developer mass provides increased toner
carrying capacity and consequently improved toner concentra-
tion latitude. In addition, the developer materials of this
invention provide improved insulation between adjacent carrier
beads when the carrier particles are made of a conductive metal
and the carrier particles do not contain a coating of an
insulating material. This is due to the increased popwlation
of toner particles between contacting carrier particles which
improves the resistance to shorting between conductive carrier
particles and the photoreceptor thus allowing for higher bias
field latitudeO As indicated, the carrier material should
preferably be conductive to realize the virtual electrode
effect for maximum development and to prevent build-up of
net electrical charge. The combination of developer materials
of this invention has been found to provide prints of out-
standing high quality which is not discernible from offset
prints.
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It has further been found that the developer composi-
tions of this invention provide developed imayes having a more
uni~orm and lower pile height than achieved with conventional
electrostatographic developer compositions. For example, when
employing conventional developer compositions in a high speed
electrostatographic copying/duplicating machine, such as the
Xerox 9200, the developed, unfused image toner pile height is
between about 45 and SS microns. ~owever, when employing the
novel developer compositions of this invention in the same
machine, the developed, unfused image toner pile height is
only about 18 microns. In both instances, the image density
is about 1.3 but the lower toner pile height obtained with
the compositions of this invention is due to their greater
covering power; that is, a greater number of toner particles
are packed closer together, occluding more ima~e area,
absorbing more reflected light, and therefore the perceived
image density is the same in both cases yet the toner pile
height is much less with these new developer materials.
This finding is significant since there has conventionally
been a substantial disparity in toner pile height between
developed, unfused solid image areas and developed, unfused
line image areas. However, with the developer co~positions
of this invention, the toner pile height of developed, unfused
solid image areas and that of developed, unfused line image
areas is substantially the same. Thus, with uniform toner
pile hei~hts in both the solid imaye areas and the line image
areas, it is now possible to obtain a transferred and fused
image having a more uniform output density and a greatly
improved physical appearance. This is due to greatly improved
toner image transfer to a permanent substrate such as paper
since, in conventional transEer systems, toner particle size
and toner pile height affect transEer efficiency. That is,
excessively small toner particles were previously left behind
on the pnotoreceptor during transfer resulting in wasted toner,
a non-uniform transferred image was obtained, and photoreceptor
cleaning problems were aggravated. ~owever, with efficient
transfer of developed, unfused solid and line image areas
having uniform and lower toner pile heights, fusing of the
toner material is more efficient, more uniform, and requires
substantially less energy. Also, since less fusing energy
is required, copy paper degradation problems such as curling,
reduced moisture content, resistivity, and paper transport
problems are minimizèd.
Any suitable particle classification method may be em-
ployed to obtain the toner materials of this invention. Typical
particle classification methods include air classification,
screening, cyclone separation, elutriation, centrification,
and combinations thereof. The preferred method of obtaining
the 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 anta-
gonistic 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 particlesJ 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 frac-
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tion, while the smaller or lighter ones are carried inwards
by the air as fine frac-tion. The "cut size" usually depends
upon the gradient o~ 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
classifying chamber. Satisfactory centrifugal air classifi-
cation results may be obtained when employing an apparatus
1 ~ such as the Mikroplex Spiral Air Classifier Type 132MP model
available from the Alpine American Corporation, Natick,
Massachusetts, or an Acucut Model B18 unit available from ~k
the Donaldson Company, I~c., Tulsa, Oklahoma.
Any suitable particle classification method may be
employed to obtain the carrier materials of this invention.
Typi~al particle classification methods include air classi-
fication, screening, cyclone separation, elutriation,
centrification, and combinations thereof. The preferred
method of obtaining the carrier materials of this invention
is by screening or seiving.
Any suitable vinyl resin having a melting point of
at least about 110F 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
7~rdJQ ,~
alphamethylene aliphatic monocarboxylic acids such as methyl
acrylate, e~hyl acrylate, n-butylacrylate, isobutyl acrylate,
dodecyl acrylate, n octyl acrylate, 2-chloroethyl acrylate,
phenyl acrylate, methyl-alpha-chloroacrylate, methyl meth-
acrylate, 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 ketone, vinyl hexyl ketone, methyl isopropenyl ketone
10. and the like; vinylidene halides such as vinylidene chloride,
vinylidene chlorofluoride and the like; and N-vinyl compounds
such as N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole,
N-vinyl pyrrolidine and the like, and mixtures thereof.
Generally, suitable vinyl resins employed in the toner have
a weight average molecular weight between about 3,000 to
about 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 defini-
tion 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
tonerl 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 monomeric
materials which may be copolymeriæed with styrene by addition
polymerization include: P-chlorostyrene, vinyl naphthalene,
ethylenically unsaturated monoolefins such as ethylene,
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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 mono-
carboxylic acids such as methyl acrylate, 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 ketone, vinyl
hexyl ketone, methyl isopropenyl ketone and the like; vinyli-
dene halides such as vinylidene chloride, vinylidene chloro-
fluoride and the like; and N-vinyl compounds such as N-vinyl
pyrrole, N-vinyl carbazole, N-vinyl indole, N-vinyl pyrrolidine
and the like; and mixtures thereof. The styrene resins may
also be formed by the polmerization 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 resins, 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 poly-
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,.
3 ~
merization of any suitable vinyl monomer such as the vinyl
monomers described above. Other thermoplastic re~ins 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, polyurethane resins, cellulosic resins, polyether
resins and mixtures thereof. When the resin component of
the toner contains styrene copolymerized with another
unsaturated monomer or a blend of polystyrene and another
10- resin, a styrene component of at least about 25 percent by
weight based on the total weight of the resin present in
the toner is preferred because denser images are obtained
and a greater degree of image definition i5 achieved with a
given quantity of toner material.
lS It is to be understood that the specific formulas
given for the units contained in the resins of the toner
materials represent 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. E'or
example, some commercial materials contain trace amounts of
homologues or unreacted or partially reacted monomers. Any
minor amount of sucb 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 colorants are
well-known and include, for example, carbon black, nigrosine
dye, aniline blue, Calco Oil Blue, chrome yellow, ultramarine
blue, duPont Oil Red, Quinoline Yellow, methylene blue
chloride, phthalocyanine blue, Malachite Green Oxalate, lamp
b~ack, Rose Bengal and mixtures thereof. The pigment or dye
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should be present in the toner in a quantity sufficient to
render it highly colored so that it will form a clearly visible
image on a recording member. Thus, for example, where conven-
tlonal 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
dye such as Amaplast Black dye, available from the National
Aniline Products, Inc.. Generally, the pigment 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
compositions may affect both the glass transition and fusion
temperatures of the toner compositions of this invention,
their concentration preferably should be less than about
10 percent by weight of the colored toner. Representative
patents in which toner and developer materials are disclosed
include U.S. Patent 2,788,288, U.S. Patent 3,079,342, U.S.
Reissue Patent 25,136, U.S. Patent 3,577,3~5, U.S. Patent
3,653,893, U.S. Patent 3,590,000, U.S. Patent 3,655,374, U.S.
Patent 3,720,617, and U.S. Patent 3,819,367. Especially pre-
ferred for use in the present invention are those compositions
disclosed in U.S. Reissue Patent 25,136 and U.S. Patent
3,079,342 containing a copolymer of styrene and alkyl meth-
acrylate; the compositions disclosed in U.S. Patent 3,590,000
comprising a solid, stable hydropholic metal salt of a fatty
acid such as zinc stearate, and a polymeric esterification
product of a dicarboxylic acid and a diol comprising a diphenol;
and the compositions disclosed in U.S. Patent 3,819,367 con-
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.,
7:~3~
taining a minor proportion of submicroscopic silican dioxide
additive particles.
The toner compositions may be prepared by an
well-known toner mixing and comminution technique. For
example, the ingredients may be thoroughly mixed by blending,
mixing and milling the components and thereafter micro-
pulverizing the resulting mixture. Another well-known
technique for forming toner particles is to spray-dry a
ball-milled toner composition comprising a colorant, a resin,
and a solvent.
Any suitable coated or uncoated electrostatographic
carrier bead material may be employed as the carrier material
of this invention. Typical 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, and are preferred in the compositions of
this invention. The carriers may be employed with or
without a coating. Many of the foregoing and other typical
carriers are described by L. E. Walkup, et al in U.S. Pat.
No. 2,638,416 and E. N. Wise in U.S. Pat. No. 2,618,552.
Additionally, it is preferred that the carrier materials
have semi-conductive to conductive properties. Where
desired, the carrier materials o~ this invention may be
coated with àny suitable insulating material. Typical
electrostatographic carrier particle coating materials
include vinyl chloride-vinyl acetate copolymers, styrene-
acrylate-organosilicon terpolymers, natural resins such as
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~L7~9;~:
caoutchouc, colophony, copal, dammar~ jalap, storax; thermo
plastic resins including the polyolefins such as polyethylene,
polypropylene, chlorinated polyethylene, and chlorosulfonated
polyethylene; polyvinyls and polyvinylidenes such as poly-
styrene, polymethylstyrene, polymethyl methacrylate, poly-
acrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl
butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl
ethers, and polyvinyl ketones; fluorocarbons such as poly-
tetrafluoroethylene, polyvinyl fluoride, polyvinylidene
fluoride; and polychlorotrifluoroethylene; polyamides such
as polycaprolactam and polyhexamethylene adipamide; poly-
esters such as polyethylene terephthalate; polyurethanes;
polysulfides, polycarbonates, thermosetting resins including
phenolic resins such as phenol-formaldehyde, phenol-furfural
and resorcinol formaldehyde; amino resins such as urea-
formaldehyde and melamine-formaldehyde; 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. Pat. No. 2,618,551; B. B. Jacknow, et al.
in U.S. Pat. No. 3,526,433; and R. J. Hagenbach, et al. in
U.S. Pat. Nos. 3,533,835 and 3,658,500.
When the carrier materials of this invention are
coated, any suitable electrostatographic carrier coating
thickness may be employed~ However, a carrier coating having
a thickness of at least sufficient to form a thin film on the
carrier particle is preferred because the carrier coating will
then possess sufficient thickness to resist abrasion and
prevent pinholes which adversely affec~ the triboelectric
properties of the coated carrier particles. Generally, for
cascade and magnetic brush development, the carrier coating
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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
0.3 percent to about 1.5 percent by weight based on the
weight of the coated carrier particles because maximum
durability, toner impaction resistance, and cop~ quality
are achieved. To achieve further variation in the proper-
ties of the coated composite carrier 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 and the
coating may be continuous or discontinuous.
When the 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 application of the coating to the carrier cores.
I~ desired, the coating may comprise resin monomers which are
polymerized 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, increased carrier active area increases
the net toner material triboelectric charge lev~l for a given
toner concentration by weight in a developer mixture. There-
fore, where it is preferred to operate an electrostatographic
development system at a minimum toner concentration as to
.
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71~Z
provide solid area coverage and at a toner concentration high
enough to minimize toner deposits in background areas of a
developed electrostatic latent image resulting from toner
particles having a low or weak triboelectric charge, these
objectives may be attained by employing the developer materials
of this invention. In accordance with this invention, the
aforementioned objectives are attained by operating at an
increased toner concentration yet providing lower background
deposits and enabling longer developer life.
Any suitable organic or inorganic photoconductive
material may be employed as the recording surface with the
developer materials of this invention. Typical inorganic
photoconductor materials include: sulfur, selenium, zinc
sulfide, zinc oxide, zinc cadmium sulfide, zinc magnesium
oxide, cadmium selenide, zinc silicate, calcium strontium
sulfide, cadmium sulfide, mercuric iodide, mercuric oxide,
mercuric sul~ide, indium trisulfide, gallium selenide,
arsenic disulfide, arsenic trisulfide, arsenic triselenide,
antimony trisulfide, cadmium sulfo-selenide and mixtures
thereof. Typical organic photoconductors include: quin-
acridone pigments, phthalocyanine pigments, triphenylamine,
2,4-bis(4,4'-diethylamino-phenol)-1, 3,4-oxadiazol, N-iso-
propylcarbazole, triphenylpyrrole, 4,5-diphenylimidazolidinone,
4,5-diphenyl-imidazolidinethione, 4,5-bis(4'-amino-phenyl)-
imidazolidinone, 1,5-dicyanonaphthaLene, 1,4-dicyanonapthalene~
aminophthalodinitrile, nitrophthalodinitrile, 1,2,5,6-tetra-
azacyclooctatetracene-(2,4,6,8), 2-mercaptobenzothlazole-2~
phenyl-4-bisphenylideneoxazolone, 6-hydroxy-2 t 3-di(p-methoxyphenyl)-
benzofurane, 4-dimethy~aminobenzylidene-benzhydrazide, 3 benzyli-
dene-aminocarbazole, polyvinyl carbazole, (~-nitrobenzylidene)-
-20~
.
p-bromoanile, 2,4-diphenylquinazoline, 1,2,4-triazine,
5-diphenyl-3-methyl-pyrazoline, 2-(4'dimethylaminophenyl)-
benzoxazole, 3-aminocarbazole, and mixtures thereof.
Representative patents in which photoconductive materials are
disclosed include U.S. Pat. No. 2,803,542 to Ullrich, U.S. Pat.
No. 2,970,906 to Bixby, U.S. Pat. No. 3,121,006 to Middleton,
and U.S. Pat. No. 3,151,982 to Corrsin.
DESCRIPTION OF PREFERRED EMBODIMENTS
The ~ollowing examples further deEine, describe and
compare methods of preparing the developer materials of the
present invention and of utilizing ~hem to develop electro-
static latent images. Parts and percentages are by weight
unless otherwise indicated.
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 of between 8 and 30 microns. The carrier
particles comprised 100 micron nickel-zinc ferrite coated with
about 0.6 percent by weight, based on the weight o~ the core
material, of a carrier coating composition comprising styrene,
a methacrylate ester, and an organosilicon compound as dis-
closed in U.S. Pat. No. 3,526,533. The coa~ed ferrite carrier
material was determined to have a specific surface area of
about 151 cm2/gram.
About 1 part by weight of the toner particles was
mixed with about 100 parts by weight of the carrier particles
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to form the developer mixture~ Copies of a standard test
pattern were made with the developer mixture in an electro-
statographic copying machine employing a magnetic brush
development system. It was found that the developer mixture
failed after about 300,000 copies. Developer failure was
experienced in the form of high background, i.e, exceeding
the specified 0.01 background density level at 1.0 solid area
density. A high level of photoreceptor filming was observed
as print-out on the copies which occurred at a frequency of
about every 60,000 intervals. The rate of toner impaction
was found to be about 8 mg/g. The copies produced were
found to have blurred images, with poor edge acuity. Grey
scale and half-tone reproduction quality was poor. Copy
resolution was less than 7 line pairs per millimeter and the
presence of hollow characters was substantial.
EXAMPLE II
A developer mixture was prepared by mixing about
3 parts of the toner material employed in Example I with about
100 parts of carrier material except that the toner particles
were selected to have a particle size of between about 3 and
10 microns. The carrier particles were selected to comprise
35 micron nickel powder. The nickel powder was determined to
have a specific surface area of about 450 cm2/gram.
The developer mixture was used to develop an electro-
static latent image under substantially the same conditions as
in Example I. It was found that the developer mixture performed
satisf2ctorily up to about 300,000 copies after wh1ch the test
was suspended. No photoreceptor filming was observed as print-
out on the copies. The rate of toner impaction was insigniEicant
and not measurable using existing techniques.
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71~Z
The copies produced contained images free of blur
and edge acuity was excellent7 Grey scale and half-tone
reproduction quali~y was excellent. Copy resolution was
about 10 11ne pairs per miIlimeter and no hollow characters
were evident.
EXAMPLE III
A developer mixture was prepared by mixing about 3
parts by weight of a toner composition comprising a mixture of
about 88.5 parts by weight of a polymeric esterification product
of a dicarboxylic acid and a diol comprising a diphenol, and
about 11.5 parts by weight of a carbon black as disclosed in U~S.
Patent 3,590,00~ with about 100 parts by weight of carrier
particles. The toner particles were selected to have a particle
size of between 3 and 10 microns. The carrier particles com-
prised 35 micron nickel powder. By calculation, the nickel
powder was determined to have a specific surface area of about
450 cm /gram.
The developer mixture was used to develop an electro-
static la~ent image under substantially the same conditions as
2~ in Example I. It was found that the developer mixture performed
satisfactorily up to about 300,000 copies after which the test
was suspended. No photoreceptor filming was observed as print-
out on the copies. The rate of toner impaction was insignifi-
cant and not measurable using existing techniques,
The copies produced contained images free of blur
and edge acuity was excellent. Grey scale and half-tone
reproduction quality was excellent. Copy resol~tiQn was about
10 line pairs per millimeter and no hollow characters were
evident.
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71~Z
EXAMPLE IV
A developer mixture was prepared by mi~ing about 3
parts of the toner material employed in Example III with about
100 parts of the carrier material employed in Example III
except that about 0.65 parts by weight of submicroscopic silicon
'~
B dioxide particles tAerosil R-972) based on the weight o~ the
toner particles as described in U.S. Patent 3,819,367 was added
to the developer mixture.
The developer mixture was used to develop an electro-
static latent image under substantially the same conditions as
in Example I. It was found that the developer mixture performed
satisfactorily up to about 300,000 copies after which the test
was suspended. No photoreceptor filming was observed as print-
out on the copies. The rate of toner impaction was excellent
and not measurable using existing techniques.
The copies produced contained images free of blurand edge acuity was excellent. Grey scale and half-tone
reproduction quality was excellent. Copy resolution was about
10 line pairs per millimeter and no hollow characters were
evident.
EXAMPLE V
A developer mixture was prepared as in Example IV
except that about 0.35 parts by weight of zinc stearate based
on the weight of the toner particles as described in U.S. Patent
3,590,000 was added to the developer mixture.
The developer mixture was used to develop an electro-
static latent image under substantially the same c~nditions as
in Example I. It was found that the developer mixture performed
satisfactorily up to about 300,000 copies after which the test
3~ was suspended. No photoreceptor filming was observed as print-
JQ ~n~
--24--
L92
out on the copies. The rate of toner impaction was insigni~i-
cant and was not measurable using existing techniques.
The copies produced contained images free of bl~r
and edge acuity was excellent. Grey scale and half-tone
reproduction quality was excellent. Copy resolution was about
10 line pairs per millimeter and no hollow characters were
evident.
EXAMPLE VI
A developer mixture was prepared by mixing about 3
parts by weight of a toner composition comprising a mixture of
about 80 parts by weight of styrene, about 20 parts by weight
of isobutyl methacrylate, and about lO parts by weight of a
carbon black with about 100 parts by weight of carrier particles.
The toner particles were determined to have a particle size of
between 3 and 10 microns. The carrier particles comprised 35
micron nickel powder.
The developer mixture was used to develop an electro-
static latent image under substantially the same conditions as
in Example I. It was found that the developer mixture performed
satisfactorily up to about 300,000 copies after which the test
was suspended. No photoreceptor filming was observed as print-
out on the copies. The rate of toner impaction was insignifi-
cant and not measurable using existing techniques~
The copies produced contained images free of blur
and edge acuity was excellent. Grey scale and half-tone
reproduction quality was excellent. Copy resolution was about
lO line pairs per millimeter and no hollow characters were
evident.
3C
-25-
EXAMP_ VII
A developer mixture was prepared by mixiny about 3
parts by weight of a toner composition comprising a mixture of
about ~0 parts by weight of styrene, about 20 parts by weight of
isobutyl methacrylate, about 15 parts by weight of diphenyl iso-
phthalate, and about 10 parts by weight of a carbon black with
about 100 parts by weight of carrier particles. The toner par-
ticles were determined to have a particle size o between 3 and
10 microns. The carrier particles comprised 35 micron nickel
powder.
The developer mixture was used to develop an electro-
static latent image under substantially the same conditions as
in Example I. It was found that the developer mixture performed
satisfactorily up to about 300,000 copies after which the test
was suspended. No photoreceptor filming was observed as print-
out on the copies. The rate of toner impaction was insignificant
and not measurable using existing techniques.
The copies produced contained images free of blur and
edge acutity was excellent. Grey scale and half-tone reproduc-
tion quality was excellent. Copy resolution was about 10 line
pairs per millimeter and no hollow characters were evident.
Thus, the developer materials of this invention are
characterized as providing substantially improved copy
quality in the development of electrostatic latent images.
It is believed that developed image resolution is improved
due to the toner particle size range. The improved edge
acuity'is believed to result from less edge raking~by the
smaller carrier particles in the present developer mixtures~
The reduced mottle appearance and absence of hollow charac-
ters of copied images obtained appears to result from more
uniform latent image development and image transfer due to
- ,3~c
32
mo~e uniform triboelectric charge of the developer materials.
Improved grey scale and half-tone reproduction obtained with
the developer materials of this inventlon appears to be due
to the high developability of these smaller toner particles
and the virtual electrode effect at the photoreceptor surface
of the smaller conducti~e carrier particles. 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 images and are particularly useful in magnetic brush
development systems. Thus, by providing the developer
materials of this invention, substantial improvements in
systems life and copy quality result upon the use of developer
materials having the specified physical characteristics.
In addition, the developer materials of this
invention may be further characterized as experiencing sub-
stantially 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 deve~oper
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.
~1~7~
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 the present invention. These and other carrier
materials, toner materials, substituents, and processes, such
as those listed above, may be substitute~ for those in the
examples with similar results.
Other modifications of the present invention will
occur to those skilled in the art upon a reading of the present
disclosure. These are intended to be included within the
scope of this invention.
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