Note: Descriptions are shown in the official language in which they were submitted.
1~77;~;~5
BACI~ OUND OF '~ INvrJNr[lIoN
This invention relates in general to imaging systems
and more par~icularly to im~roved elec~rostatoyraphic developer
mixtures ~or use in such systems.
The formation and development of imayes on the surface
of photoconductive materials by electrostatograpl~ic means is
known. The basic elec-trostatographic process, as taught by
C. F. Carlson in U. S. Patent 2,297,691, involves placing a
uniform electrostatic charge on a photoconductive insulating
layer, exposing the layer to a light and shadow image to dissi-
pate the charge on the areas of the layer e~posed to the light,
and developing the resultant electrostatic latent image by
depositing on the image a finely-divided elec-troscopic 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. ~. Wise in U~ S. Patent 2,618,582, is
known as "easeade" development. In this method, developer
material comprising relatively large carrier particles having
finely-dividecl toner particles electrostatically elinging to
the surfaee of the carrier partieles in eonveyed to and rolled
or eascaded across the surface bearing the electrostatic latent
image. The charged portions of the surfaee have a eharge of
the same polarity as, but stronger than, the earrier particles.
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~0'77~'~5
Toncr and carrier particles havincJ opposi~e polarities are
selec-ted so that -the toner par~iclcs electros~a~ically cliny
to the carrier particlcs. In order to develop a ne~ativel~
charged electros-tatic latent image, a toner and carrier com~
bination are selected in which -the toner is triboelectrically
positive in relation to the toner. Conversely, to develop
a positively charged electrostatic 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 ascerlding
order 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
eascades 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
earrier 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
eommercial electrostatographic development technique.-~ A
general purpose office copying machine incorporating this
technique is described in U. S. Patent 3,099,943.
Another technique for developing electrostatic latent
images is the "magnetic brush" process as disclosed for e~ample,
in U. S. Patent 2,874,063. In this process, a developer material
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... ...
' ~ , , ' -
3~5
COn~aillillCJ tOllC'~ and ma~JnctiC carrier particles is a-ttracted
to an~ is carricd by a magnet. The magne-tlc Eield causcs align-
ment o~ the mac3netic particles in the brush-like con~iguration
when this ma~netic brush is brought into contact with an
electrostatic laten-t imaqe-bearing surface, the toner particles
are attracted from the carrier particles oE the brush to the
charged areas of the image-bearing sur~ace but no-t 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 electrosta-tic latent
images is disclosed in U. S. Patent 3,503,776 issued 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 sur-
face. 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 transported along its arcuate pa-th,
frictional contact between the developer and the imaging sur-
face in the contact zone circulates the developer in the bath
and brings developer material into developing configuration
with the imaged surface.
Many other methods, such as the "touchdown" develop-
ment method disclosed by C. R. Mayo in UO S. Patent 2,895,847,
are known for applying electroscopic particles to the electro-
static 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
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1(~77;~25
a~d throu~Jh the widcsprc~d availabili-ty and u~lliza-tion of
el~ctrost~togxaphic im~ing equipment.
In au-tomatic reproduction equipment, it is conventional
to employ as the imaging plate a photoconductor on a conductive
substrate in the form of a c~lindrical drum or a flexible belt
ich is continuously rotated through a cycle of sequential oper-
ations including charging, exposing, developing, transferring
and cleaning. The developer chamber i9 charged with 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 defici-
encies 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 electriflcation being governed in most cases by
the distance between their relative positions in the tribo-
electric series. ~owever, when otherwise compatible electro-
scopic powder and carrier materials are removed from each
other in the triboelectric series by too great a distance, the
resulting images are very faint because the attractive forces
between the carrier and toner particles compete with the
attractive forces between the electrostatic latent image and
the toner particles. Although the image density described
,
. . .
:~L(3'7732~i
in ~he immediately precedin~3 sentcnce may be improved by
increasing toner concen-tration in the cleveloper mixture, unde-
sirably high bac~round toner deposition as well as increased
toner impaction and agglomeration is encountered when the
developer mixture is over-toned. 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 particles.
Excessively high electrostatographic plate charges are not
only undesirable because of the high power consumption necessary
to maintain the electrostatographic plate at high potentials, but
also because the high potential causes the carrier particles to
adhere to the electrostatographic plate surface rather than merely
roll across and off the electrostatographic plate surface. Print
deletion and massive carry-over of carrier particles often occur
when carrier particles adhere to reusable electrostatographic
imaging surfaces. Massive carrier carry-over problems are particu-
larly acute when the developer is employed in solid area coverage
machines where excessive quan-tities of toner particles are removed
from carrier particles thereby leaving many carrier particles
substantially bare of toner particles. Further, adherence o~
carrier particles to reusable electrostatographic imaging surfaces
promotes the formation of undesirable scratches on the surfaces
during image transfer and surface cleaning operations.
It is, therefore, apparent that many materials which
otherwise have suitable properties for employment as carrier
particles are unsuitable because they possess too high a tribo-
electric value in addition uniform triboelectric surface
characteristics of many carrier surfaces are di~ficult to
achieve with Mass production techniques. Quality
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:::
~V 7 73~
images are, in some installces, allnost :impossible to obtain in
high speed automatic maci~ines when carriers having non-uniform
triboelectric properties are employed. Although it may be
possible to alter the triboelectric value of an insulating carrier
material by blending the carrier material with another insulating
material having a triboelectric value remote from the triboelectric
value of the original carrier material, relatively larger
quantities of additional material are necessary to alter the tri~
boelectric value of the original carrier material. 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 triboelec-tric properties of
carrier surfaces to accommodate the use of desirable toner
compositions while retaining the other desirable physical charac-
teristics of the carrier. The alteration o-f the triboelectric
properties of 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 pos-sible to employ materials previously not suitable as
a carrier. Thus, for example, a carrier 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. However, since most carrier coating materials are
deficient in one or more of the above areas, there is a continuing
need for improved electrostatographic carrier and developer
compositions and methods for forming the same.
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. . _ . . .
~773ZS
I~ is also apparc~ ~rom the description presented
above as well as in other development techniques, that the toner
is subjected to severe mechanical attrition which tends to break
down the particles into undesirable dus-t fines. The formation
of fines is retarded when the toner contains a tough, high
molecular weight resin which is capable of withstanding the
shear and impact forces imparted to the toner in the machine.
Unfortunately, many high molecular weight materials cannot be
employed in high spced automatic machines because they cannot
be rapidly fused during a powder image haat fixing step. On
the other hand, low molecular weight resins which are easily
heat fused at relatively low temperatures are usually undesir-
able because these materialstend to form thick films on reusable
photoconductor surfaces. These films tend to cause image de-
gradation and contribute to machine maintenance down time.
Many low molecular weight resins decompose when subjected 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 of-ten
offset to other adjacent sheets. Additionally, low molecular
weight resins are often extremely difficult or even impossible
to comminute in conventional grinding apparatus. Also, ihe
toner materials must bè capable of accepting a charge of the
correct polarity when brought into rubbing contact with the
surface of carrier materials in cascade or touchdown development
systems. Additionally, many toner materials cannot satisfactor-
ily be transferred by conventional electrostatographic develop-
ment systems from reusable imaging surfaces in automatic copy-
ing and duplicating machines. Since most polymeric toner
materials are deficient in one or more of the above areas, there
is a continuing need for improved toners and developers.
--8--
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:
~l(37~73~5
n accordance with one aspect of this invention there
is provided an electrostatographic developer composition for
use in developing electros-tatic latent images on a recording
surface, said developer composition comprising carrier particles
and toner particles, characterized in that at least either the
carrier or toner is a functionalized polymer obtained by the
systematic chemical alteration of the active hydrogen contain-
ing constituents of said polymer by silylation to provide
particles having controlled triboelectric charging properties.
In accordance with another aspect of this invention
there is provided an electrostatographic imaging process
comprising the steps of providing an electrostatographic
imaging member having a recording surface, forming an electro-
static latent image on said recording surface, and contacting
said electrostatic latent image with a developer mixture
- comprising finely-divided toner particles electrostatically
clinging to the surface of carrier particles having an average
particle diameter of between about 50 microns and about 1,000
microns, at least one of either the toner or the carrier com-
prising a functionalized polymer obtained by the systematic
chemical alteration of the active hydrogen containing constitu-
ents of said polymer by silylation to provide particles charac-
terized as having controlled triboelectric charging properties,
whereby at least a portion of said finely-divided toner
particles are attracted to and deposited on said recording sur-
face in conformance with said electrostatic latent image.
_g_
-' ' ~ - ~ '. ,
~(37~73~5
By way of added explanation, in accordance with an
dspect of this invention, chemical alteration of the tribo-
electric charging potential of functional polymers employed
as toner materials and carrier coating materials is
controlled. The controlled vaxiation of the tribo-
electric behavior of functional polymexs provides a means of
attaining optimum triboelectric responses of electrostatographic
developer materials for specifically defined applications. Thus, 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
active hydrogen containing materials such as alcohols, acids, phenols
mercaptans, amines, amides, imines and the corresponding silyl
derivatives. These relationships have been found to be extremely
helpful in designing new toners and carrier materials. Ey this
invention, the triboelectric charging properties of toner-carrier
pairs are controlled to enable optimum triboelectric relationships in
developer compositionsO
It is to be noted that, by itself, no material has
a triboelectric charge. The magnitude of a triboelectric charge
depends upon both the toner and the carrier material. Thus,
replacement of one of the components to optimize triboelectric
charging properties is generally necessary to provide the desired
triboelectric response. By so doing, greater latitude is available
for specific electrostatographic applications. In accordance with
this invention, it has been found that by varying the degree of
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~L~773~
chcmical moclification of pol~mcrlc matcrials Eor use as toner
materials and/or carrier coating materials, either stoichiometrically
or kinetically, the triboelectrie propcrties oE developer materials
can be controlled in a continuous manner.
In electrostatographic development of selenium photo-
conductor latent images, polymers which tend to take on a relatively
high positive eharge are gencrally satisfaetory for use as carrier
eoating materials and polymers whieh tend to take on a relatively
high negative eharge are generally satisfaetory for use as toner
materials;in electrostatographic development of other photoeonductor
latent images, for example, zine oxide, phthalocyanine, cadmium
sulfide and polyvinylearbazole-trinitroflurenone, the opposite is
true. 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 triboeleetrie
eharging seale determines the triboelectrie eharge between them,
their relative positions determine the sign of the triboeleetrie
eharge. Those materials low on the scale prefer to adopt a positive
eharge and those materials high on the scale prefer to adopt a
negative charge. Appropriate toner-carrier pairs ean be seleeted
based on their triboeleetrie eharging or triboeleetric series
relationship to satisfy a particular acceptable triboelectrie
eharging range requirement for a given electrostatographic machine
developer housing.
It has been found that triboelectrie behavior is a funetion
of molecular strueture whieh now allows the controlled and
progressive modification of the triboelectrie eharging properties
of ~oner and carrier compositions so as to obtain optimum
triboelectric eharging properties between toner and earrier pairs.
. ;.
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773'~
Thus, by this invelltion, adjustment o~ the tri~oelectric charging
properties of electrostatographic developer rnatcrials need not be
in stepwise fashion but may be accomplished in a continuous manner
providing a high degree of "fine tuning" of triboelectric properties
for developer materials.
In accordance with this invention, the triboelectric
charging properties of monomeric and polymeric compounds may be
modified by systematic chemical modification by means of silylation.
This chemical process leads to changes in the triboelectric behavior
of active hydrogen containiny materials. The process also allows
for controlled variation of triboelectric behavior of carrier
materials in a continuous fashion. Thus, silylation of hydroxyl
moieties of polymeric materials is a means of obtaining such effect.
Generally speaking, the passing of a silylating reagent in a stream
of inert gas through a solid bed of hydroxylic material accomplishes
silylation. The depth or amount of silylation will depend, to some
extent, on the permeability of the silylation reagent through solid.
For some toner and carrier material applications, surface reaction
may be sufficient. In addition, solution silylation of the solid
may be practiced. Silylation reactions in solution will generally
lead to more homogeneous reaction which may be advantageous for some
toner and/or carrier applications. In either case, the degree of
silylation may be controlled either stoichiome-trically or kinetically,
making available a continuous range of toner and carrier materials
having controlled various triboelectric properties. Further, this
invention is not limited to the silylation of hydroxyl moieties of
polymer materials, but extends as well to the silylation of other
active hydrogen containing compounds such as alcohols, carboxylic
acids, phenols, mercaptans, amines, amides, imines, selenols,
thiophenols, and the like. Thus, this invention provides a means of
1C3'7'73~5
ef~c~ing mon.i~ored si.li.con a~di~ions to pol~neric materials by
the addition of organic silicon moieties to effect desired an~
controlled triboelectric properties thereto. The si.Licon units may
be introduced either as terminal g.roups or as block copolymer
components. Therefore, this method affords a means for systemati-
cally varying the triboelectric charging relationship of toner-
carrier developer compositions by either surface treatment of the
materials or by chemical modification of toner and/or carrler
materials prior to their fabrication to provide controlled tribo-
electric behavior of such materials.
It has been further found that for aliphatic hydroxyls,
silylation causes the material to accept more negative tribo-
electric charge. Thus, for either a particular toner or carrier
material candidate, the desired negative triboelectric charge will
be improved. Some of the advantages here include the facile
reaction of solid hydroxylic substrates with gaseous silylation
reagents which occurs readily. In addition, the conversion of
hydroxyl moieties of silyl ether moieties may be controlled in a
continuous fashion thus allowing the "fine tuning" of triboelectric
properties of developer compositions. For materials containing
aromatic hydroxyls, silylation causes the material to accept more
positive, that is less negative, charge in triboelectric charging.
Thus, silylation will decrease the negative charge on toners or
carrier materials of such structure. Thus, the invention may be
employed to increase or decrease the net triboelectric charge to the
requisite level for toner-carrier pairs.
In general, any method such as for preparing silyl
ethers is wi~hin the scope of this invention. Any suitable silylating
agent may be employed to obtain the functionalized carrier materials
of this invention. Typical silylating agents include dimethlamino-
-13-
,
~L~'773;~5
trimcthylsil~ne, trimetllyL- and dimeth~l cl~lorosi:lalles and
polysiloxane~ witll reactive terminal moie~ies.
Further, ~he use of dilunctional silylating agents
may lead to crosslinkirlg which in some app~ications particularly
carriers and carrier co~tings would be advantageous.
The chemical modifica~ion oE such materials enables
the alteration of materials having optimum physical properties
in such a way as to improve their triboelectric properties for
electrostatographic use. This invention may serve as a guide
for the preparation of developer compositions having "finely-
tuned" triboelectric charging properties, and the capacity
for continuous control of such properties through variation in
extent of reaction may be employed for such purpose.
In regard to triboelectric response, particularly with
regard to carrier materials, it is to be noted that materials
such as those derived ~y silylation of styrene-methacrylate co-
polymers provide excellent carrier coatings, especially in view of
their crosslinkability. By the use of such materials, toners that
previously provided unacceptable triboelectric response with
conventional carriers now function properly. Thus, the coating
of carrier cores, for example, metallic beads, with functionaliæed
polymers containing a crosslinking agent provides carrier materials
which in addition to improved toughness, the triboelectric pro-
perties 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 hydroxy or amino
functionalized polymers and crosslinking these materials via re-
action of the pendant hydroxyl or amino moieties with a crosslinking
agent such as a di~unctional silylating agent provides a means of
continuous control of the trikoelectric properties of the coated
-14-
'
:1(33'7~7;~5
carriers. In ~cklition, tile use oE diEunctional silylating ayents
leads t:o crosslillkincJ whicll is advanta~eous as to the abrasion~
resisl:ant properties of th~ carrier coating material. It has been
found that as the degree of conversion increases, the capacity
for positive triboelectric charging deereases. In addition, the
degree of eonversion can be controlled stoichiometrically. ~hus
various hydro~yl or amino containing polymers exhibit similar
effects. It is to be noted that it is not necessary for the
polymer material to be crosslinked to observe a change in the
triboelectric charging properties since the change in triboelectrie
eharging is not due to molecular weight change. Monofunctional
reagents have been found to bring about similar changes. When a
earrier coating material of such structure is silylated, it will
eause a given toner material to acquire a lower negative charge
then the same unsilylated coated carrier.
Any suitable carrier coating material may be chemically
modified in accordance with this invention to control the trlbo-
electrie properties of the coated carrier. Typical carrier coating
materials include styrene-acrylate-organosilicon terpolymers,
polyvinyl alcohol, polyvinyl butyral, polyamides such as poly-
eaprolactam and polyhexamethylene adipamide; polyurethanes; thermo-
setting resins including phenolic resins such as phenol-iorma:Ldehyde,
phenol-furfural and resorcinol formaldehyde; amino resins such as
urea-formaldehyde and melamineformaldehyde; polymeric acids, alcohols;
and the like. Many of the foregoing and other typical carrier
eoating materials are described by L. E. Walkup in U. S. Patent
2,618,551; B. B. Jaeknow et al in U. S. Patent 3,526,533; and R. J.
Hagenbach et al in U. S. Patents 3,533,835 and 3,658,500.
Any suitable eleetrostatographic carrier coating thickness
may be emp~oyecl. However, a earrier coating having a thickness at
-15-
~_.
10~73Z5
lea;t suf~iciellt to ~orm a Lhill c~ntinuous film on thc carrier
particle is preerrecl because ~he carr;er COatinCJ will then
possess sufEicient thickness to resist abrasion and prevent pin-
holes which adversely afect the triboelectric properties of the
coatecl carri~r 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 ~n the weight of the
coated carrier particles. Preferably, the carrier coating should
comprise from about 0~1 percent to about 1.0 percent by weight
based on the weight of the coated carrier particles because maximum
durability, toner impaction resistance, and copy quality are
achieved. To achieve further variation in the properties of the
coated 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. An
ultimate coated carrier particle having an average diameter between
about 50 microns and about l,000 microns is preferred in cascade
systems because the carrier particle then possess sufficient density -
and inertia to avoid adherence to the electrostatic image during the
cascade development process. Adherence of carrier particles to an
electrostatographic drum is undesirable because of the formation
of deep scratches on the drum surface during the image transfer and
drum cleaning steps, particularly w~lere 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.
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 materials
include sodium chloride, ammonium chloride, aluminum potassium
chloriae, Rochelle salt, sodium nitrate, potassium chlorate,
-16-
- 10773ZS
~ranular zircon, granular silicon, mekhyl methacrylate, glass,
silicon dioxide, ~lintshot, iron, steel, ferrite, nickel,
Carborundum, and mixtures thereof.
Any suitable well-known toner material may be employed
with the coated carriers of this invention as well as the toner
materials prepared in accordance with this invention. Typical
toner materials include gum copal, gum sandarac, rosin,
cumaroneindene resin, asphaltum, gilsonite, phenolformaldehyde
resins, rosin modified phenolformaldehyde resins, methacrylic
resins, polystyrene resins, polypropylene resins, epoxy
resins, polyethylene resins, polyester resins, and mixtures
thereof. The particular toner material to be employed obviously
depends upon the separatlon of the toner particles from the coated
carrier in the triboelectric series and should be sufficient to
cause the toner particles to electrostatically cling to the carrier
surface. Among the patents describing electroscopic toner com-
positions are U. S. Patent 2,659,670 to Copley; U. S. Patent
2,753,308 to Landrigan; U. S. Patent 3,079,342 to Insalaco; U. S.
Patent Reissue 25,136 to Carlson and U. S. Patent 2,788,288 to
Rheinfrank et al. These toners generally have an average particle
diameter between about 1 and 30 microns.
Any suitable photoconductive materials may be used together
with the developer materials such as those disclosed in U. S. Patents
2,803,542 to Ullrich, U. S. Patent 2,970,906 to Bixby, U. S. Patent
~,121,006 to Middleton, U. S. Patent 3,121,007 to Middleton, and
U. S. Patent 3,151,982 to Corrsin.
~ he surprisingly better results obtained with the
electrostatographic coated carriers of this invention may be due
to many factoxs. For example, the coated carriers of this invention
possess smooth outer surfaces which are highly resistant to cracking,
-17-
~L~773Z5
cllippincJ, an~l fl~lkir~g. In c~scade clevelopmen~ syxtems, tlle smooth
suriace en~ances tlle rolling action oE the carrier particles across
the electrostatographic surfaces and reduce5 the tendency of carrier
particles to adhere to tlle electrostatographic imaging surfaces.
When these coated carriers are employed in electrostatographic
development systems, carrier liEe is unexpectedly extended
particularly with respect to toner impaction resistance. Additionally
the carrier coating materials of this invention appear to contribute
to the stability of the triboelectric properties of the coated carrier
over a wide relative humidity range. Because of their triboelectric
properties, these carrier materials may be employed in reversal
development of positively charged images. Further, the coa-ted
carriers of this invention provide more uniform triboelectric
characteristics than current carriers when employed in electrostato-
graphic development systems. In addition, the coated carriers of
this invention provide exceptionally good life performance,
durability, copy ~uality, quality maintenance, less carrier bead
sticking and agglomeration, and also provide improved abrasion
resistance thereby minimizing carrier chipping and fla~ing. Further,
the coated carriers of this invention provide triboelectric values
such that they can be used with a wide variety of presently available
toners in present electrostatographic processes, and retain a
predictable triboelectric value. Thus the improved coated carrier
particles of this invention have desirable properties which permit
their wide use in presently available electrostatographic systems.
With regard particularly to the toner compositions of
this invention, any suitable vinyl resin having a melting point of
at least about llO~F may be employed. 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
~77~25
~he polymeriza~ion o~ mi~ures o~ two or more of these~ unsaturated
monomers. ~le c~pression "addition polymerization" is intended
to include known polymerization techniques such as free radical,
anionic and cationic polymerization processes.
The combination o~ 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 4 poise at temperatures
up to about 450F. ~hen the toner is characterized by a bloc~ing
temperature less than about 110F, 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 ~uality.
Any suitable pigment or dye may be employed as the
colorant for the toner particles. Toner colorants are well-known
and include, for examp]e, carbon black, nigrosine dye, aniline blue,
Calco Oil Blue, chrome yellow, ultra marine blue, duPont Oil Red,
~uinoline Yellow, methylene blue chloride, phthalocyanine blue,
Malachite Green Oxalate, lamp black, Rose Bengal and mixtures thereof.
The pigment or dye should be present in the toner in a sufficient
quantity to render it highly colored so that it will form a clearly
visible image on a recording me~ber. Thus, for example, where
conventional electrostatographic copies of typed documents are
desired, the toner may comprise a b]ack pigment such as carbon
black or a blac~ 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 colorantemployed is a dye, substantially smaller quantities
of colorant may be used. However, since a number of the above
--19--
.
3~
pic~rnen~s usccl il~ elec'~:r~s~cl~oy~c~ ic toner compositions may
a~fect both tlle glass ~ran~ition and fusion temperatures o~
the toner compositions of ~his inven~ion, their concentratlon
preferably should not e~ceed about 10 percent by weight of the
colored toner.
The toner compositions of the present invention may
be prepared by any we]l-known toner mixing and comminution
technique. For example, the ingredients may be thoroughly
mixed by blending, mixing and milling the components and
thereafter micropulverizing the resulting mixture. Another
well-known technique for forming toner particles 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 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 addition to the carrier particles prepared in accord-
ance with this invention, any suitable coated and uncoated carrier
materials well-known in the art may be used. The carrier
particles comprise any suitable solid materials, provided that
the carrier particles acquire a charge having an opposite pol-
arity to that of the toner particles when brought in close con-
tact with the toner particles so that the toner particles adhere
to and surround the carrier particles. When a positive repro-
duction of the electrostatic images is desired, the carrier par-
ticle is selected so that the toner particles acquire a charge
havin~ a polarity opposite to that of the electrostatic image.
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~]'~ernatively, if a ~eversal reproduc~ion of the eleetrostatie
image is desired, the carrler is selected so tha~ the toner
particles acquire a charge having the same polarity as that of
the electrostatic image. ~lus the materials or the earrier
partieles are selected in accordanee with their triboeleetric
properties in respeet to the eleetroscopie toner so that when
mixed or brought into mutual eontaet, one component of the
developer is charyed positively if the other component is
below the first eomponent in the triboelectric series and
negatively if the other component is above the first component
in a triboelectric series. By proper seleetion of earrier
materials in aeeordanee with their triboeleetrie effeets, the
polarities of their eharge, when mixed, are such that the
eleetroscopic toner partieles adhere to and are eoated on the
surfaees of earrier particles and also adhere to that portion
of the electrostatic image-bearing surfaee having a greater
attraetion for the toner than the earrier partieles.
D~:SCRIPTION OF PREFERRED EMBODIMENTS
The following examples, other than the control
examples, further define, describe and compare preferred
methods of preparing and utilizing the toner materials and
coated earriers of the present invention in eleetrostatographie
applieations. Parts and percentages are by weight unless other-
wise indicated~
In the following, the relative triboelectrie values
generated by contact of earrier beads with toner particles
is measured b~ means of a caseade deviee. The deviee eomprises
a grounded metal plate set at an arbitrary but eonstant angle
of elevation to horizontal, for example, 30 degrees and a eup
at the bottom of the ineline. The eup is not attaehed to the
ineline and is thus not grounded; it is attaehed to an eleetrometer.
J
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.. . .
~L~773~5
~ e material ~o bc te~ c~d is coated onto a metallic sheet,
sucll as alulninum, and this is attached to the incline. I'hen
beads of tlle desirecl 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 ~uantity
is a direct measure of the triboelectric charging capacity of
the polymeric film. The measurement is done at constant relative
humidity and temperature Since triboelectric measurements
are relative, the measurements should, Eor comparative purposes,
be conducted under substantially identical conditions.
EXAMPLE I
About 82.3 grams of carrier beads having a particle
size of about 600 microns comprising flintshot coated with
ethyl cellulose were dried in vacuo for about 17 hours. In
a cascade triboelectric measurement as discussed above, these
beads were found to acquire a net charge of about +0.57
nanocoulombs per gram versus a film of a styrene-n-butyl
methacrylate copolymer having a 2.54:1.00 mole ratio respectively.
EXAMPLE II
About 10.0 ml. of dimethylaminetrimethylsilane was
passed on a stream of dry nitrogen through about 82.3 grams
of carrier beads having a particle size of about 600 microns
comprising flintshot coated wlth ethyl cellulose disposed iIl
a 1 x 6 inch cylindrical bed over a period of about 25 minutes.
After drying in vacuo for about 17 hours, in a cascade tribo-
electric measurement under substantially the same conditions
as in Example I, the treated carrier beads were found to
acquire a net charge of about +0.14 nanocoulombs per gram
versus a film of a styrene-n-butyl methacrylate copolymer
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7732~;
ha~ing a 2.~ 1.()0 molc ra~io as in Examl~le I. 'l'hus, it was
found that t~le triboelectric charcJing capacity oE the sil~la~ed
carrier beads is more negative after sil~lation thereof.
EXAMPLE I~I
About S.0 ml. of dimethylaminotrimethylsilane was
passed on a stream of dry nitrogen through about 60.0 grams
of carrier beads having a particle size of about 250 microns
coated with the aminolyzed polymer of a styrene-n-butyl
methacrylate copolymer containing hydroxyl moieties for about
90 minutes. The aminolyzed polymer was prepared by ester
group aminolysis of the styrene-n-butyl methacrylate copolymer
having a 2.54:1.00 mole ratio with an aminoalcohol resulting
in formation of hydroxyalkyl amide functions. Thus a mixture
of about 117.5 arams (0.289 mole of ester functions based on
elemental analysis) of the styrene-n-butyl methacrylate, about
41.0 grams (0.350 mole) of a 6-aminohexanol, and about 39.3 grams
(0.350 mole) of 1,4-diazabicyclo (2,2,2) octante was stirred
under dry nitrogen at about 180C (oil bath temperature 205C)
using an ambient air-cooled condenser to allow excape of the
n-butanol produced. The polymer was minolyzed to the extent
of about 25 mole percent. The polymer was purified by dissolving
in tetrahydrofuran and then 10% HCl was added. The li~uid
phase was decanted from the gummy polymer. This procedure
was repeated twice, followed by a fourth and fifth was using
5% methanolic HCl. The polymer was taken up in tetrahydrofuran
and precipitated by dropwise addition with rapid stirring to
10% HCl. After homogenization in a blender and filtration,
the process was repeated. The polymer in tetrahydrofuran
solution was then precipitated in like manner from deionized
water, and this process repeated. After a final precipitation
. .
773~5
from me~llLInol, t:he polymer was dried in vacuo. Gen~rally,
the polymer samplc was clissolv~d in about five times its
weigh~ oE tetrahydrofuran. Volumes of the precipitatiny solu-
tions were 6-]0 times those of the polymertetrahydrofuran
solution. 250 micron steel beads were coated with about
0.28 percent of the polymer by evaporation of solvent tetra-
hydrofuran from a tumbling mixture of the beads in a solution
of the polymer.
A portion of these coated beads, about 60.0 grams,
was placed in a 1 inch diameter column and 5 ml. of dimethylamino-
trimethylsilane was passed over the beads on a stream of dry
nitrogen over a 90 minute period.
After drying in vacuo for about 17 hours, in a
cascade triboelectric measurement under substantially the
same conditions as in Example I, the silylated coated carrier
beads were found to acquire a net charge of about +0.19
nanocoulombs per gram versus a film of a styrene-n-butyl
methacrylate copolymer having a 2.54:1.00 mole ratio.
Unsilylated carrier beads coated with the aminolyzed polymer
acquired a net charge of about +0O94 nanocoulombs per gram.
The carrier bead coating upon silylation was found to have
a lower capacity for positive triboelectric charging.
Although specific components t proportions and
procudures have been stated in the above description of the
preferred embodiments of the novel carrier compositions,
other suitable components, proportions and procedures as
listed above may be used with similar results. Further,
other materials and procedures may be employed to synergize,
enhance or otherwise modify the novel system.
Other modifications and ramifications of the present
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:1~'7'7~5
inventiol~ w:ill a~l)c,lr to tllosc: skilled in the axt upon the
readillg o:F t]lis clisclosure. These are intended to be includecl
within the scope of this invention.
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