Note: Descriptions are shown in the official language in which they were submitted.
37Z6
B KGRO~ND OF THE INVENTION
This invention relates in general to imaging systems
and more particularly to improved electrostatographic developer
mixtures for use in such systems.
The formation and development of images on the surface
of photoconductive materials by electrostatographic means is
known. The basic electrostatQgraphic process, as taught by
C. F. Carlson in U.S. Patent 2,297,691, issued November 6,
1942 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 resultant
electrostatic latent image by depositing on the image a
finely-divided electroscopic material referred to in the
art as "toner". The toner is 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, usually electro-
statically, to a support surface such as paper. The
transferred image may subsequently be permanently affixed to
a support surface by heat or other suitable affixing means,
such as solvent or overcoating treatment may be used instead.
Many methods are known for applying the electroscopic
particles to the latent image to be developed. One development
method, as disclosed by E. N. Wise in U. S. Patent 2,618,582,
;i issued November 18, 1952 is known as "cascade" development. In
this method, developer material comprising relatively large
carrier particles having finely-divided toner particles
electrostatically clinging to the surface of the carrier
particles is conveyed to and rolled or cascaded across the
surface bearing the electrostatic latent image. The charged
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portions o~ the surface have a charge of the same polarity
as/ but stronger than, the carrier particles. Toner and
carrier particles having opposi~e polarities are selected so
that the toner particles cling to the carrier particles. In
order to develop a ne~atively charged electrostatic latent
image, a toner and carrier combination are selected in which
the toner is triboelectrically positive in relation to the
; toner. Conversely, to develop a positively charged electro-
static latent image, a toner and carrier combination wherein
the toner is triboelectrically negative in relation to
the carrier is used. The triboelectric relationship between
the toner and carrier depends on the relative positions of
the materials in the "triboelectric series". In this series,
materials are arranged in ascending ordQr of their ability
to take on a positive charge. Each material is positive
with respect to any material classified below it in the
series; and, negative with respect to any material above
it in the series. As the developer mixture cascades or rolls
across the image-bearing surface, the toner particles are
electrostatically attracted from the carrier to the charged
portions of the image-bearing surface, whereas they are not
; electrostatically attracted to the uncharged or background
portions of the image which they contact. The carrier particles
and unused toner particles are then recycled. The cascade ~.
development process is extremely good for the development
of line copy images, and is the most widely used commercial ; `~
electrostatographic development technique. A general
purpose office copying machine incorporating this technique
is described in U.S. Patent 3,099,943 to Eichorn et al
~ssued ~ugust 8, 1963.
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Another technique for developing electrostatic
latent images is the "magnetic brush" process as disclosed
for example, in U. S. Patent 2,874,063 to Princeton issued
February 17, 1959. In this process, a developer material
containing toner and magnetic carrier particles is attracted
~o and is carried by a magnet. The magnetlc field causes
alignment of the magnetic particles in a brush-like
configuration when this magnetic brush is brought into contact
with an electrostatic latent image-bearing surface, the-toner
particles are attracted from the carrier particles of the
brush to the charged areas of the image-bearing surface but
` not to the uncharged areas. Since the charged areas have
an imagewise configuration, the toner material clings to
` the surface in imagewise configuration, thus developing the
latent image.
Another method for developing electrostatic latent
images is disclosed in U.S. Patent 3,503,776 issued March 31,
1970 to R. W. Gundlach. In this method, images are formed
by transporting an electrostatic latent image-bearing surface
in a generally ascending arcuate path, and contacting only
the image in a contact zone with a bath of developer material
transported in a concave chamber adjacent the lower path of
the imaging surface. The contact zone extends from about
the lowermost point of the arcuate path to the uppermost
point of the arcuate path. As the imaging surface is trans-
ported along its arcuate path, frictional contact between
the developer and the imaging surface in the contact zone
circulates the developer in the bath and brings developer
- material into developing configuration with the imaged
surface.
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Many other methods/ such as the "touchdown"
development method disclosed`by C. R. Mayo in U. S. Patent
2,895,847, issued July 21, 1959 are known for applying
electroscopic particles to the electrostatic latent image
to be developed. The development process, as described
above, together with numerous modifications, are well-known
to the art through various patents and publications and
through the widespread availability and utilization of
electrostatographic imaging equipment.
; 10 In automatic reproduction equipment, it is
conventional
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to employ as -the imaging pla-te o-~ a photoconductor on a ccnduc-tive
subs-trate in the form o~ a cylindrical drum or a flexible belt
which is continuous]y rotated through a cycle of sequential
operations including charging, exposing, developing, transferring
and cleaning. The developer chamber is charged wlth a
developer mixture comprising carrier particles and enough toner
particles for hundreds of reproduction cycles. Generally, the
freshly charged developer mixtures contain between about 1.5
and 5% toner particles based upon the weight of the developer.
This initial concentration provides sufficient toner for many
reproduction cycles without causing undesirably high background
toner deposition.
While ordinarily capable of producing good quality
images, conventional developing systems suffer serious defi-
ciencies in certain areas. In the reproduction 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 relatively large; the
degree of such electrification being governed in most cases
by the distance between their relative ~ositions in the tribo-
electric series. However, when otherwise compatible electro-
scopic powder and carrier materials are removed from each other
in the triboelectric series by too grea-t a distance, the result-
ing 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
toner concentration in the developer mixture, undesirably high
background toner deposition as well as increased toner irnpaction
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and agglomeration is encountered when the developer mixture i5
overtGned. The initial electros-tatographic plate charge may be
inereased -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 partic]es. Excessivly high eleetrostatographic
plate charges ar-e not only undesirable because of the high
power consumption necessary to maintain the electrostatographic
plate at high potentials, but also because the high po-tential
causes the carrier particles tG adhere to the eleetros-tatographic ~ -~
plate surface rather than mer-ely roll across and off the electro-
statographic plate surface. Print dele-tion and massive carry-
over of carrier particles often occur when carrier particles
adhere to reusable electrostatographie imaging surfaees. Massive
earrier earry-over problems are partieularly acute when the
developer is employed in solid area coverage machines where
exeessive quantities of toner particles are removed from carrier
particles thereby leaving many carrier particles substantially
bare of toner particles. Further, adherenee of earrier partieles
to reusable eleetrostatographie imaging surfaees promotes -the
formation of undesirable scratches cn the surfaces during image
transfer and surface cleaning operations.
It is therefore apparent that many materials which
otherwise have suitable properties for employment as carrier
partieles are unsuitable beeause they possess too high or too ~- ;
low a triboeleetrie value. In addition, uniform triboelectric
surfaee characteristics of many carrier surfaces are difficul-t
to achieve with mass production techniques. Quality images
are, in some instances, almost impossible to oktain in high
speed automatic machines when carriers having non-uniform
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triboelectric proper-ties are employed. Although it may be
possible to alter the triboelec-tric vlaue of an insulating
carrier material by blending the carrier material with another
insula-t`ing material having a triboelec-tric value remote from
the triboelectric value o-f -the original carrier material,
relatively large quantities of additional material is
necessary to alter the triboelectric value of the original
carrier material. The addition of large quantities of material
tG the original carrier material to change the triboelectric
properties thereof requires a major manufacturing opera-tion 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
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carrier. The alteration of the triboelectric properties o-f a
carrier by applying a surface coating thereon is a particularly
desirable technique. With this technique, not only is it possible
to control the triboelectric properties of a carrier made from ;
materials having desirable physical characteristics, it is also
possible to employ materials previously not suitable as a carrier. :;
Thus, for example, acarrier having desirable physical properties
with the exception of hardness, can be coated with a material
having desirable hardness as well as other physical properties,
rendering the resultant product more useful as a carrier. How- -~
ever, since most carrier coating ma-terials are deficient in one
or more of the above areas, there is a continuing need for improved
electrostatographic carrier and developer composition and methods
for forming the same.
Further, it is apparent from the description presented
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above as well as in other development techniques, that the
toner is subjected to severe mechanical attrition which tends
to break down the par-ticles into undesirable dust fines. The
formation of fines is retarded when the toner contains a
tough, high molecular weigh-t resin which is capable of with-
standing the shear and impact forces imparted to the toner
in the machine. Unfortunately, many high molecular weight
materials cannot be employed in high speed automatic machines
because they cannot be rapidly fused during a powder image -
heat fixing step. On the other- hand, low molecular weight
resins which are easily heat fused at relatively low temper-
atures are usually undesirable because these materials tend
to form thick films on reusable photoconductor surfaces. ;
These films -tend to cause image degradation and contribute
to machine maintenance down time. Many low molecular weight
resins decompose when subjec-ted to fusing conditions in high
speed copying and duplicating machines. In addition, low
molecular weight resins tend to form tacky images on the
copy sheet which are easily smudged and often offset to other
adjacent sheets. Additionally, low molecular weight resins
are often extremely difficult or even impossible to comminute
in conventional $rindingapparatus. Also, the toner materials
must be capable of accepting a charge of -the correct polarity
when broughtinto rubbing contact with the surface of carrier
materials in cascade or touchdown development systems.
Additionally, many toner materials cannot satisfactorily be
transferred by conventianal electrostatographic development
systems from reusable imaging surfaces in automatic copying
and duplicating machines. Since mos-t polymeric -toner materials
are deficient in one or more of -the above areas, there is a
lV73~Zfi
continuing need for improved toners and developers.
In accordance with one aspect of this invention
there is provided an electrostatographic developer composition
~or use in developing electrostatic latent images on a recording
surface, the developer composition being comprised of a
toner material and a carrier material; the toner material
having an average particle diameter of less than about 30
microns and consisting essentially of a colorant and a polymer
having aromatic moieties selected from the group consisting
of styrene alkyl methacrylates and styrene alkyl acrylates;
the carrier material containing carrier particles having an ::
average particle diameter of between 50 microns and about
1,000 microns, each of the carrier particles comprising a
core surrounded by an outex coating in the amount of from
0.1 percent to about 10 percent by weight based on the
weight of the carrier particles, the outex- coating consisting
; essentially of a functionalized polymer selected from`the
group consisting of styrene alkyl methacrylates and styrene .
alkyl acrylates, the polymer ~or both the toner and the
~ 20 carrier being.obtained.by the systematic chemical alteration
of the aromatic moieties of the polymer by nitration, halo- :-
genation, acylation, or alkyl substitution to thereby provide
toner and carrier particles characterized as having closely
controlled triboelectric charging properties.
By way of added explanation, in accordance with an
aspect of this invention chemical alteration of the tribo-
electric charging potential of functional polymers employed ~ .
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as toner and carrier materials is controlled. The controlled ~,
variation of the triboelectric behavior of functional polymers
provides a means of attaining optimum triboelectric responses
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of electrostatograph:ic developer- materials for specifically
defined applica-tions. Ihus? in accordance with this invention,
monomeric and/or polymeric materials are systematically
chemically modified to provide structural effects which yield
structure~triboelectric property relationships among various
substituted aromatic moieties such as nitroaromatics,
haloaromatics, aromatic ethers, and alkylaromatics. These
relationships have been found to be extremely helpful in
designing new carrier and toner materials. By -this invention,
the triboelectric charging proper-ties of toner-carrier pairs
are controlled to enable optimum triboelectric relationships `
in developer compositions. ;
It is noted that, by itself, no material has a tribo- ;
electric charge. The magnitude of a triboelectric charge depends
upon both the toner and the carrier material. Thus, replace-
ment of one of the components to optimize triboelectric charg-
ing properties is generally necessary to provide the desired
triboelectric response. By so doing, greater latitude is avail~ -~
able for specific electrostatographic applications. In accord-
ance with this invention, it has been found that by varying the
degree of chemical modification of polymeric materials for use
as toner or carrier materials, the triboelectric properties ~
of developer materials can be controlled in a continuous manner. `
In electrostatographic developrnent of selenium photo-
conductor latent images, polymers which tend to take on a rela-
tively high positive charge are generally satisfactory for use `
as carrier coating materials and polymers which tend to take on
a relatively high negative charge are generally satisfactory for
use as toner materials. In electrostatographic developement of
other photoconductor latent images, for examp]e, zinc oxide,
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~737Z~
phthalocyanine, cadmium sulfide, polyvinylcarbazole-
trinitroflurenone. The reverse is true regarding charging
properties of carriers and toner. In accordance with this
invention, the triboelectric properties of developer materials
are correlated with their structural composition and thereby
predictably controlled. Since the distance between a given toner-
carrier pair on a trihoelectric charging scale determines the
; triboelectric charge between them, their relative positions
determine the sign of the triboelectric charge. Those materials
low on the scale prefer to adopt a positive charge and those
materials high on the scale prefer to adopt a negative charge.
Appropriate toner-carrier pairs can be selected based on their
triboelectric charging or triboelectric series relationship to
satisfy a particular acceptable triboelectric charging range re-
quirement for a given electrostatographic machine developer
housing.
It has been found that triboelectric behavior is a
function of molecular structure which now allows the controlled
and progressive modification of the triboelectric charging prop-
erties of developer compositions so as to obtain optimum tribo-
electric charging properties between -toner and carrier pairs.
Thus, by this invention, adjustment of the triboelectric charging
properties of electrostatographic developer materials need not be
in stepwise fashion but may be accomplished in a continuous
manner prcviding a high degree of "fine tuning" of triboelectric
properties f-or developer materials.
; In accordance with this invention, the triboelectric
charging properties of monomeric and polymeric compounds may
be modified by systematic chemical alteration of aromatic moieties
of monomers and polymers. Such alteration of a aromatic function-
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ality may be accomplished by methods Icnown -to the art, such as,
halogenation using the reaction of the aromatic polymer with
elemental bromine, alkylation or acylation using the well known
Friedel-Crafts reaction with alkyl halides and Lewis Acids, or
nitration, using nitric/sulfuric acids, special reagents, such
as cupric nitrate/acetic anhydride. Aromatic reactions on
polymers can not always be driven to completion and frequently
side reaction do occur. Under certain nitration conditions,
for example, it has been found that oxidation accompanies nitration
as manifested by the presence of hydroxyl moieties. Such side-
reactions are, however, quite reproducible and, thus, their
influence on -the triboelectric behavior of the resultan-t species
can also be reproduced with a high degree of precision. The
functional groups introduced by these processes may additionally
be employed for varied purposes including covalent bonding to
dyes having functional groups, the addition of triboelectric
charge modifiers, and bonding to substrates. Extensions of
these uses are numerous and obvious to the artisan.
Thus, -in accordance with this invention, there is
provided a method for the preparation of developer materials
having controlled triboelectric properties for electrostato-
graphic applications. The principle of this invention may be
practiced with any monomer, polymer, or copolymer containing -
an aromatic functionality. Therefore, this invention enables
the controlled alteration of the triboelectric properties of
materials having optimum physical properties to provide
developer materials (both toner and carrier) having improved
triboelectric properties for electrostatographic use while ~;
retaining their desirable physical properties.
It has been found that the -triboelectric charge ac-
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quired by -the nitrated aromatics is much more negative than the
non-nitra-ted polymer material. It is further noted that a
standard nitration procedure usually yields a polymer which
does not charge as negatively as a nitrated/oxidized material
even though the degree of nitration is comparable. Thus it
appears that the oxidation also increases the extent of negative
triboelectric charging property of polymeric materials. For
example, it has been fou~d that nitration of a styrene-n-
butylmethacrylate copolymer material yields a polymer whose
triboelectric charging potential enables its use as a carrier
material with various toners above it in the triboelectric
series including those that are usually referred -to as "reversal"
carriers.
The degree of nitration of nitration-oxidation can be
controlled either stoichiometrically or kinetically so as to ; ;
optimize salient physical and triboelectric properties. Typi-
cally, any suitable nitration process may be employed to provide
the chemically modified carrier materials of this invention.
Typical nitration processes include the use of a mild, non-
hydrolytic process employing reagents such as cupric nitra-te
and acetic anhydride, for example, when polymers are hydro-
lytically unstable under usual nitration conditions. Under
conditions using cupric ni-trate/acetic anhydride, oxidation
accompanies nitration. Thus, in one step a high work function
material with functional groups can be prepared. The use of`
such functional moieties enables the further addition of tribo-
electric charging moieties to the polymer.
Therefore, by this invention, desirable electros-tato
graphic properties are intrinsic to the polymer material and
need not depend upon external addi-tives. The prediction and
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11~737Z6
control of triboelectric characteristics for imaging materials
is now possible by this invention.
It has also been found that introduction of other -
electron withdrawing groups such as halogen, chlormethyl or
acyl, into the aromatic moieties of polymers such as polystyrene
and styrene-n~butyl methacrylate copolymers causes an increase
in their propensity for negative triboelectric charging. Con-
versely, introduction of electron releasing moieties such as
me-thyl, t-butyl, alkoxy, and alkylthio increases their propen-
sity for positive charging. Thus the triboelectric properties
of polymers containing aromatic moieties may be selectively ~ ~-
altered by chemical modification. The chemical modification
encompasses the attachment of functionality to the aromatic
nucleus. It is also possible to change the triboelectric
charging propensity of aromatic polymers by multi-step chemical
modification, however, the preferred approaches are one-step
transforma-tion such as nitration, hydroxylation, halogenation,
sulfonation, alkylation, and acylation. An alternative to ~-~
reactions of polymers in many applications is the polymerization
of aromatic monomers bearing the desired substituent. The
aforementioned techniques may be applied to many polymers ~ ~ ;
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including those disclosed above and their derivatives as well
as polyesters, styrene-alkyl methacrylates, styrene-alkyl
acrylates, terephthalate polyesters, and phenolformaldehyde
polymers.
The chemical modification of such ma-terials enables the
alteration of materials have optimum physical properties in such
a way as to improve their triboelectric properties for electro-
statographic use. This invention may serve as a guide for the
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~0737Z6
preparation of developer compositions having "finely-tuned"
triboelectric charging properties, and the capacity for continuous
control of such properties -through variation in extent of
reRction may be employed for such purpose.
In regard to triboelectric response, it is to be noted
that materials such as those derived by nitration of styrene-
methacrylate copolymers provide excellent carriers or carrier
coatings, especially in view of their crosslinkability. For
example, by the use of such materials, toners that previously
exhibited unacceptable triboelectric response with conventional ~;
carrier now function properly. Thus, the coating of carrier
cores, for example, metallic beads, with suitably function-
alized polymers containing a crosslinking agent provides carrier
materials which in addition to improved toughness, the
triboelectric properties thereof may be continuously varied
by means of controlling the amount of the crosslinking agent
in the coating composition.
The coating of metallic carriers with functionalized
polymers and crosslinking these materials, for example, via
reaction of pendant hydroxyl with a crosslinking agent such as
diisocyanate provides a means of continuous control of the
triboelectric properties of the coated carriers. It has been
found that as the degree of conversion increases, the capacity
for positive triboelectric charging decreases. In addition,
the degree of conversion can be controlled stoichiometrically. `-
Further, various typcs of crosslinking agents which are
reactive toward hydroxyl may be employed. In addition, various
amine or sulfhydroxyl containing polymers have been found to
exhibit similar effects.
Any suitable carrier material or carrier coating
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material may be chemically modified in accordance with this
invention to control the triboelectric properties. Typical
materials include styrene-acrylate-organosilicon terpolymers,
polyvinyls and polyvinylidenes such as polystyrene, polymethy-
lstyrene polyesters 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 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 issued November 18, 1952; B. B. Jacknow
et al in U. S. Patent 3,526,533 issued August 1, 1970; and
R. J. Hagenbach et al in U. S. Patents 3,533,835 issued
; November 13, 1970 and 3,658,500 issued August 25, 1972. ~ ~;
Any suitable electrostatographic carrier coating thick-
ness may be employed. However, a carrier coating having a thick-
ness at least sufficient to form a thin continuous film on the
` carrier particle is prefQrred because the carrier coating will
then possess sufficient thickness to resist abrasion and pre-
vent pinholes which adversely affect the triboelectric pro-
perties of th~ 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 ~rom about
0.1 percent to about 1.0 percent by weight based on the weight
of the coated carrier partic]es because maximum durability,
toner impaction resistance, and copy quality are achieved.
To achieve further variation in the properties of the coated
carrier particles, well-known additives such as plasticizers,
reactive and non-reactive polymersl dyes, pigments, wetting
agents and mixtures thereof may be mixed with the coating materials.
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An ultimate coated carrier particle having an average
diameter between about 50 microns and about 1,000 microns is
` preferred in cascade systems because the carrier particle
then possesses suf~icient density and inertia to avoid adherence
to the electrostatic image during the cascade development
process. ~dherence of carrier particles to an electrostato-
graphic drum is undesirable because of the ~ormation of
deep scratches on the drum surface during the image transfer
and drum cleaning steps, particularly where cleaning is
accomplishedby a web cleaner such as the web disclosed by
W. P. Graff, Jr., et al in U. S. Patent 3,186,838 issued
June 1, 1965.
` Any suitable well known coated or uncoated electro-
statographic carrier bead material may be employed as the core
of the beads of this invention. Typical carrier core matèrials
; include sodium chloride, ammonium chloride, aluminum potassium
chloride, Rochelle salt, sodium nitrate, potassium chlorate,
granular zircon, granular silicon, methyl methacrylate,
glass, silicon dioxide, flintshot, iron, steel, ferrite,
nickel, Carborundum, and mixtures thereof.
Typical resins that may be modified in accordance with
this invention for use as toners include those having a
melting point of at least about 110F such as, for example,
i vinyl resins including homopolymers or a copolymers cf two
or more vinyl monomers. Typical monomeric units which may
be employed to form vinyl polymers includeO styrene, p-
chlorostyrene; vinyl naphthalene; ethylenically unsaturated
mono-olefins such as ethylene, propylene, butylene, isobutylene
and the like; vinyl esters such as vinyl chloride, vinyl
b~omide, vinyl ~luoride, vinyl acetate, vinyl propionate,
vinyl ~enzoate, vinyl butyrate, and the like; esters o~
alphamethylene aliphatic monocarboxylic
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~0737Z6
acids such as me-thyl acrylate, ethyl acrylate, n-butyl acrylate,
isobutyl acrylate, dodecyl acrylate, n -octyl acrylate, 2-chloro-
ethyl acrylate, phenyl acrylate, methylalpha-chloroacrylate,
methyl methacryla-te, ethyl me-thacrylate, 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; vinylidene halides such as vinylidene chloride, vinylidene
chlorofluoride and the like; and N-vinyl compounds such as N-
vinylpyrrole, N-vinylcarbazole, N-vinylindole, N-vinylpyrrolidene
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. The resins may
be formed by the polymerization of mixtures of two or more of
these unsaturated monomers. The expression "addition
polymerization" is intended to include known polymerization
techniques such as free radical, anionic and cationic polymer-
ization processes.
The combination of the resin component and colorant
whether the resin component is a homopolymer, copolymer, or
blend, should have a blocking temperature of at least about
110F and a melt viscosity of less than about 2.5 x 10 poise
at temperatures up to about 450 F. When the toner is charac- .
-terized by a blocking temperature less than about 110 F, the
toner particles tend to agglomerate during storage and machine
operation and also form undesirable films on the surface of
reusable photoreceptors which adversely affect image quality.
` Any suitable pigment or dye rnay be ernployed as the
colorant for the toner particles. Toner colorants are well~
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known and include, ror example, carbon black, nigrosine dye,
aniline blue, Calco Oil Blue, chrome yellow, ultra marine
blue, duPont Oil Red, Quinoline Yellow, mekhylene blue chloride,
phthalocyanine blue, Malachite Green Oxalate, lamp black,
Rose Bengal and mixture 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 examp]e, where conventional
electrostatographic copies of typed documents are desired,
the toner may comprise a b1ack pigment such as carbon black
or a black dye such as Amaplast Black dye, available frGm 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
quantitiesof colorant may be used. However, since a number
of the above pigments used in electrostatographic toner compo-
sitions may affect both the glass transition and fusion temp-
eratures of the toner compositions of this invention, their
concentration preferably should not exceed about 10 percent
by weight of the colored toner.
The toner compositions of the present invention may
be prepared by any well-known toner mixing and comminution
technique. For example, the ingredients may be thorough~y
mixed by blending, mixing and milling the components and
thereafter micropulverizing 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.
When the toner materials of this invention are to
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be employed in a cascade development process, the toner should
have an average particle size less than about 30 microns and
preferably between about 4 and about 20 microns for optimum
results. For use in powder cloud development methods, particle
diameters of slightly less than 1 micron are preferred.
In the preparation of developer materials in accordance
with this invention, either a toner material having specifically
designed properties, a carrier material having specifically
designed properties or both may be used. If only a carrier in
10 accordance with this invention is used, any suitable well-known
toner material may be employed. Typical toner materials include
gum copal, gum sandarac, rosin, cumaroneindene resin, asphaltum~
gilsonite, phenolformaldehyde resins, rosin modified phenolfor-
maldehyde resins, methacrylic resins, polystyrene resins, poly-
propylene resins, epoxy resins, polyethylene resins, polyester
resins, and mixtures thereof. The particular toner material to
be employed obviously depends upon the separation of the toner ~ ;
particles from the coated carrier in the triboelectric series
and should be sufficient to cause the toner particles to elec- ?
20 trostatically cling to the carrier surface. Among the patents
describing electroscopic toner compositions are U. S. Patent
2,659,670 issued November 17, 1953 to Copley; U. S. Patent
2,753,308 issued July 3, 1956 to Landrigan; U. S. Patent
3,079,342 issued February 26, 1963 to Insalaco; U. S~ Patent
Reissue 25,136 issued March 13, 1962 to Carlson and U. S. Patent
2,788,288 issued April 9, 1957 to ~heinfrank et al. These toners
generally hav0 an average particle diameter between about 1 and
30 microns.
If only a toner in accordance with this invention is
30 used~ any suitable coated or uncoated carrier material well-known
in the art may be used in combination therewith. The carrier
particles comprise any suitable solid materials, provided that
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- 1~737Z6
the carrier particles acquire a charge having an opposite
polarity to that of the toner particles when brought in close
contact with the toner particles so that the toner particles
adhere to and surround the carrier particles. When a positive
reproduction of the electrostatic images is desired, the
carrier particle is selected so that the toner particles acquire
a charge having a polarity opposite to that of the electro-
sta-tic image. Al-ternatively, if a reversal reproduction of
the elec-trostatic image is desired the carrier is selected
so that the toner particles acquire a charge having the same
polarity as that of the electrostatic image. Thus -the
materials for the carrier particles are selected in accordance
with their triboelectric properties in respect to the elec-
troscopic toner so that when mixed or brought into mutual
contact, one component of the developer is charged positively
if the other component is below the first component in the
triboelectric series and negatively if the other component
is above the first component in a triboelectric series. By
proper selection of carrier materials in accordance with
their triboelectric effects, the polarities of their charge,
when mixed, are such that the electroscopic toner particles
adhere to and are coated on the surfaces of carrier particles
and also adhere to that portion of the electrostatic image- ~
bearing surface having a grea-ter attraction for the toner ~ -
than the carrier particles. Typical carriers include sodium
chloride, ammonium chloride, aluminum potassium chloride,
Rochelle salt, sodium nitrate, aluminum nitrate, potassium
chlorate, granular zircon, granular silicon, methyl methacry-
late, glass, silicon dioxide, nickel, steel, iron ferrites,
and the like. The carriers may be employed with or without
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iO~3~2~,
a coating. Many of the foregoing and other typical carriers
; are described by L. E. Walkup et al in U. S. Patent 2,638,416
and E. N. Wise in U. S. Patent 2,618,552 issued November 18,
lg52. An ultimate coated carrier particle diameter between
about 50 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 development process. Adherence of carrier beads
to electrostatographic drums is undesirable because of the
formation of deep scratches on the surface during the imaging
transfer and drum cleaning steps, particularly where cleaning
is accomplished by a web cleaner such as the web disclosed by
W. P. Graff, Jr., et al in U. S. Patent 3,186,838 issued June
1, 1965. Also print deletion occurs when carrier beads adhere
to electrostatographic imaging surfaces. Generally speaking, ` ~ ?
satisfactory results are obtained when about 1 part toner is `~
used with about 10 to 200 parts by weight of carrier.
The developer compositions of the instant invention
may be employed to develop electrostatic laten~ images on any
20 suitable electrostatic latent image-bearing surface including -~
conventional photoconductive surfaces. Well-known photo-
- conductive materials include vitreous selenium, organic or in-
organic photoconductors embedded in a non-photoconductive matrix~ i
organic or inorganic photoconductors embedded in a photoconduc-
tive matrix or the like. Representative patents in which
photoconductive materials are disclosed include U. S. Patent
2,903,542 issued September 8, 1959 to ~llrich, U. S. Patent
2,970,906 issued February 7, 1961 to Bixby, U. S. Patent
3l121,006 issued February 11, 1964 to Middleton, U. S. Patent
.
3,121,007 issued February 11, 1964 to Middleton, and UO S~
Patent 3,151,982 issued November 6, 1964 to Corrsin.
J 22
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~73t726
DESCRIPTION Ol~ PREFERRED EMBODIMENTS
The ~ollowing examples ~urther de~ine, describe,
and compare methods of preparing the developer materials o~ the
present invention and of utilizing them to develop electro-
static latent images. Parts and percentages are by weight
unless otherwise indicated.
In the following, the relative triboelectric va~ues
generated by contact of carrier beads with toner particles is
measured by means of a cascade device. The device comprises
a gounded metal plate set at an arbitrary but constant angle
of elevation to horizontal, for example, 30 degrees, and a
cup at the bottom of the incline. The cup is not attached to
the incline and is thus not grounded; it is attached to an
electrometer. The material to be tested is coated onto a
metallic sheet, such as aluminum, and this is attached to the
incline Then beads of the desired carri*r material are
cascaded down the film and into the electrometer cup, where
the charge acquired by the beads is measured. From this
quantity and the weight of the beads the charge to mass ratio
is calculated. This quantity is a direct measure of the
triboelectric charging capacity of the polymeric film. The
measurement is done at constant relative humidity and -temper-
ature. Since triboelectric measurements are relative, the
measurements should, for comparative purposes, be conducted
under substantially identical conditions.
EXAMPLE I
Correlation of molecular structure and tribo-
elec-tric behavior in polymeric systems is of practical
importance when considering toner candidates and such is
demonstrated herein. Thus, a polymeric system based on a
:
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~07~7~i
polystyrene series, chosen for accessibili-ty and simplicit~,
having the generic structure:
wherein X may be ~I, t-C4Hg, Br, CH2Cl, N02, and C~l3was
studied. Po]y(p-nitrostyrene), where X = N02, was synthesized
from polystyrene by nitration; poly(p bromostyrene), where
X = Br, was prepared from polystyrene by using bromine/thallium
acetate; poly(p-chloromethylstyrene), where X = CH2Cl9 was
prepared by polymerization of the corresponding monomer; and
poly~p-methylstyrene), where X = CH3was formed from the
polystyrene, X = CH2Cl by reductive dehalogenation with
lithium aluminum hydride. Films of the polymers were cast
onto aluminum sheets from tetrahydrofuran solution except
that poly(p-nitrostyrene) was cast from dimethylformamide.
The films were dried for about fifteen hours in vacuo at
about 60C and then transferred without exposure to moist ~,
air to a dry box maintained at zero relative humidity. Zinc
carrier beads were similarly dried for about fifteen hours
in vacuo at about 120C and transferred. Cascade triboelectric
measurements were conducted using an angle of about 30 C,
a drop height of about 1 cm, and a film length of about nine
inches. The humidity was raised to successive constant ~ ,
levels by use of saturated salt solutions. The films and
carrier beads were equilibrated at each relative humidity
condition for about twenty hours prior to triboelectric
charging measurement. The results indicate that with
:- :
increased electron withdrawing power of the substituent -there
is an accompanying increase in the amount of negative charge ~ -
- 24 -
: ' : . . . . ~ .
1~737;:2~
generated on the film. In the present examples the electron
withdrawing power of -the substituents increases in the
following order: t - C4Hg ~CH3 ~H ~CH2Cl <Br ~N02. Though
both carrier beads and films may be affected by moisture,
the slope of a line at a given relative humidity is a function
only of the materials since the same carrier is used for
each film. These results indicate a practical means of
predicting the relative triboelectric behavior of polymers
which are substituted in the aromatic moiety, such as pre-
dictably increasing the negative charging property of the
polymer. While the triboelectric charging property of mix-
tures and copolymers is not generally linear with composition
it is a linear function of the extent of reac-tion for chemical
modifications as shown in the following table.
Zinc Carrier Bead Charge In
_ X Nano-Coulombs/gram at ~3% Relative Humidity
t-C4H9 +0.13
CH3 +0.19
H +0.30
CH2Cl +0.70 -
~r +1.1
2 +4-7
'
EXAMPLE II
To a solution of about 40 ml of concentrated nitric
acid and about 40 ml of concentrated sulfuric acid were added
with stirring about 62.5 grams of a styrene-n-butyl methacrylate
copolymer (2.54:1.00 mole ratio) at such a rate that the tempera-
ture did not exceed 30 C. The mixture was then allowed to
stand for about 2 hours, then poured into water and fil-trated.
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~;373~Z6
The solid was washed wi-th water, dissolvecl in tetrahydrof`uran
and reprecipitated by dropwise addi-tion to water. This latter
step was repeated several times and then the solid was vacuum
dried. Elemental analysis showed about 42 percent nitration of
available phenyl groups. Films were cast from solution onto
aluminum plates and thorougly dried. 250 micron steel beads
acquired a charge of -~0.1 nano-coulombs/gram when cascaded down
this film. The starting copolymer causes these beads to acquire
about -0.29 nano-coulombs per gram. Therefore, nitration of
the polymer markedly increases its negative charging capacity.
EXAMPLE III
To a mixture of about 14.7 g of styrene-n-butyl meth-
acrylate copolymer (2.54:1.00 mole ratio) is about 250 ml -
of acetic anhydride was added with stirring about 53.0g
of Cu(N03)2. 3H20 at such a rate that the temperature did not
exceed 70 C. The mixture was heated momentarily on a steam bath
and then kept at about 70 C for about 1.5 hours. The mixture
was poured into water and filtered. ~he solid was washed with i
water and saturated sodium bicarbonate. It was dissolved in `~
tetrahydrofuran and precipitated into an aqueous solution of
ethylenedinitrilotetraacetic acid disodium salt. It was then ~
successively precipitated from tetrahydrofuran solution into `
aqueous sodium bicarbonate and several times into water. It
was then dried in vacuo. Elemental analysis indicated that ;
about 42 percent of the available phenyl groups were nitrated, ~;
while about 50 percent of the phenyl groups were oxidized. A
film was cast from solution onto an aluminum plate and dried
thorough-ly Against this film 250 micron steel beads acquired
a charge of about +2 nano-coulombs per gram. Steel beads (250
microrl) coated with chlorinated polypropylene, which is very
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'1.~737Z6
near the bottom of -the triboelectric series and hence with
most materials causes these beads to acquire very large negative
charges, e.g., with the starting styrene-n-butyl methacrylate
(2.54:1.00 mole ratio) copolymer about -2.2 nano-coulombs per
gram, take on a charge of abou-t +0.~ nano-coulombs per gram.
Thus, the nitrated/oxidized polymer acquires a much higher nega-
tive charge than the nitrated polymer and is even lower in the
triboelectric series than chlorinated polypropylene.
EXAMPLE IV
A mixture o-f' about 35.5 grams of styrene-n-butyl
methacrylate copolymer (2.54:1.00 mole ratio), about 9.06 grams
of thallic acetate sesquihydrate and about 200 ml carbon
tetrachloride was stirred for about 18 hours at about 25 . Then
about 38.8 grams of bromine was added over about 1.5 hours
with stirring. The mixture was stirred for about 6 hours and
then heated under reflux for about 12 hours. The mixture was
then poured into methanol and filtered. The dried polymer was
precipitated from tetrahydrofuran successively with aqueous
sodium bisulfite, twice from aqueous sodium bicarbonate, twice
from water and once from methanol and dried in vacuo. Elemental
analysis showed the presence of about 1.1 bromine atoms per
phenyl gro~p. A film was cast from solution onto an aluminum plate
and thoroughly dried. Using the cascade device 250 micron steel
beads acquired a charge of about +0.95 nano-coulombs per gram vs
this film. With the parent copolymer, 250 micron steel beads acquire
a charge of about -0.29 nano-coulombs per gram. Thus, the
.
bromination of the polymer substantially increases its propen-
sity for negative charging.
Although specific components, proportions and pro-
cedures have been stated in the above description of the
~ . .
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.
~737;2 ~
preferrecl embodiments of -the novel -toner compositions, other
suitable components, proportions and procedures as listed
above may be used with similar results. Further, other materials
and procuedures may be employed to synergize, enhance or other-
wise modify the novel system.
Other modifications and ramifications of the present
invention will appear to those skilled in the art upon the
reading of this disclosure. These are intended to be included
within the scope of this invention. ~ ,
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