[0001] This invention relates to an electrostatographic toner composition comprising a colorant
and a resin.
[0002] In the development of electrostatographic images, a toner composition is mixed with
a carrier composition in order to impart the proper charge characteristics to the
toner particles and also for the purpose of carrying the toner particles by a physical
means to the surface which contains the latent electrostatic image. The carrier particles
are generally much larger in particle size than that of the toner varying from perhaps
5 to 100 times larger depending upon the particular developer being employed. The
toner is thus subjected to large forces in the development housing and in transit
toward the imaging surface, which forces result in the particle size reduction of
the toner particles. This creates problems because it not only provides a source for
dirt made up of the fine toner particles but also changes the triboelectric character
of the toner particles because of the reduction in size thereof and the impaction
and adhesion to the carrier particles. On the other hand, for economic reasons it
is desired to use customary particle size reduction techniques to achieve the desired
particle size of the colorant filled resinous materials. Uniformity in particle size
can be achieved subsequent to size reduction by standard classification methods. A
problem encountered because of these objectives is that particle size reduction will
also occur in the electrostatographic apparatus because the conditions therein are
similar to that encountered in the size reduction apparatus.
[0003] Thus, brittle failure of the toner particles together with size reduction occurs
in the electrostatographic process. This size reduction during the electrostatographic
process results in changes in both the triboelectric and charging characteristics
of the toner particles with respect to the particular carrier materials employed in
the process. That is, as the particle size reduction of the toner particles occurs,
the charge to mass ratio on the particles increases thereby increasing the forces
holding the size reduced toner particles to the carrier particles. This results in
even more harsh impacts between the large size carrier particles and the toner particles
either causing further reduction in the particle sizes or flattening of the particles
out in a pancake fashion which tightly adhere to the surface of the carrier particles
eventually resulting in reduction in the triboelectric characteristics.
[0004] Representative prior art patents include U.S. 3,391,082, issued July 2, 1969, U.S.
3,941,898, June 20, 1967, and U.S. 3,965,021, issued June 20, 1967. For example US
3391082 discloses a xerographic toner wherein the resin has a second order glass transition
temperature of 30° to 65°C and a limiting viscosity of 0.15 to 0.35, while US 3941898
patent teaches the preparation of a xerographic developer wherein the toner is a cross-linked
vinyl polymer or copolymer of a controlled molecular weight prepared by polymerizing
in the presence of a cross-linking agent a material capable of controlling the molecular
weight. Monomers disclosed include vinyl chloride, dimethyl maleate, diethyl maleate
and dibutyl maleate. US 3965021 is directed to a toner wherein the resinous material
is a blend of at least two polymers the first having a glass transition temperature
of -20°C and the second having a glass transition temperature of at least 5°C lower
than that of the first polymer.
[0005] The toner composition of the present invention is intended to have improved and long-lasting
mechanical and electrical properties, and is characterised in that the resin is a
copolymer of vinyl chloride present in an amount of from 65 to 75 mole percent, and
a lower alkyl maleate of fumarate, present in an amount of from 25 to 35 mole percent,
which copolymer has a number average molecular weight of from 15,000 to 25,000 and
a weight average molecular weight of from 45,000 to 55,000. The molecular weights
enumerated are determined by Gel Permeation Chromatography.
[0006] These particular copolymers exhibits extraordinary toughness and long life in the
development of electrostatic latent images and at the same time offer extremely good
fusing characteristics and excellent blocking characteristics during storage, shipping
and in the development procedure of the electrostatographic machine.
[0007] The colorant is employed in an amount of from about two weight percent to about 15
weight percent, based on the weight of the toner and preferably from about four percent
to about ten percent. A particular advantage achieved using the vinyl polymer in accordance
with this invention is that sharp, dark images are obtained using 5 percent by weight
carbon black which is only about one-half the amount used in commercially available
compositions.
[0008] In the practice of this invention, any suitable vinyl chloride-lower alkyl maleate
or lower alkyl fumarate copolymer in the quantities set forth above, may be used in
the preparation of the copolymer such as, for example, the C
2 to C
4 esters of maleic acid and fumaric acid such as ethyl, diethyl, propyl, isopropyl,
dipropyl, diisopropyl, butyl, isobutyl, tertiary butyl, dibutyl diisobutyl, ditertiary
butyl and the like. Ethyl maleate and diethyl maleate are the preferred monomers for
copolymerization with vinyl chloride.
[0009] The copolymers used in the preparation of toner compositions in accordance with this
invention are generally prepared by suspension polymerization techniques which are
well known in the art. In this method, the monomers are mixed together with a suitable
catalyst, such as benzoyl peroxide, lauroyl peroxide, azo- isobutyrylnitrile and the
like and dispersed with agitation as droplets (discontinuous phase) in an aqueous
medium (continuous phase) which contains stabilizers, emulsifiers and the like.
[0010] The polymer should have a suitable molecular weight such that when toner size particles
are prepared, they will have sufficient toughness to withstand the vigorous environment
within an electrostatographic apparatus, and at the same time exhibit the rheological
properties that prevent blocking under storage and transport conditions but can be
readily fixed to paper substrates by normal fusing conditions.
[0011] The toughness of the toner size particles can readily be determined by simulating
conditions in an electrostatographic machine. This can be done in a roll mill wherein
the resin powder is rolled with a carrier material over a period of time and by visual
observation of the toner particles under a scanning electron microscope.
[0012] The blocking characteristics of the resin can be determined by measurement of the
second order glass transition temperature. This generally should be as high as possible
without interfering with the fusing requirements. This second order glass transition
temperature should preferably be from about 41 to 65°C and preferably from about 54°C
to about 63°C at a heating rate of 10°C per minute in a Differential Scanning Calorimeter.
[0013] The fusing characteristics can be determined simply by placing particles of the toner
size, using particles on a glass slide, in an oven preheated to 135°C for two minutes.
The particles, if satisfactory for toner, will coalesce within this time.
[0014] In a specific test for toughness of the resin, six grams of resin powder made up
of resin particles having a size of from about 10 to 15 micron are rolled in a glass
jar of 473 cubic centimeters at a rate of 27.5 linear meters per minute with 500 grams
of 250 micron coated glass beads having a density of about 4.2 grams per cubic centimeter,
which are uniformly coated to a thickness of from 0.25 to 1 micron with a copolymer
of about 48 mol percent chlorotrifluoroethylene and about 52 mol percent of vinyl
chloride sold by Firestone Plastics Company under the designation FPC 461. Samples
are withdrawn periodically and the resin powder is blown off the coated glass beads
with an airstream at a pressure of 4.57 kilograms per cubic centimeter.
[0015] The blown off powder is viewed under a scanning electron microscope and a comparison
is made with the original particles. The longer the rolling test can be conducted
without a difference being observed, the tougher is the resin. That is, one viewing
the resin particles after the rolling test should be unable to detect any substantial
number of particles which have cracks or have been reduced in particle size because
of brittle failure caused by impaction with the high density glass beads.
[0016] The rolling test, set forth above can also be used in conjunction with a test for
resin powder concentration and charge to mass ratio. In this test, the rolled resin
particles and carrier particles are placed in a Faraday Cage and dry compressed air
is blown through the cage under a pressure of 4.57 kg/cm
2 in order to remove all of the resin particles capable of being removed from the coated
glass beads. A Faraday Cage is a device which consists of a brass cylinder having
a diameter of 2.54 cm and a length of 2.54 cm. A 100 mesh screen is positioned at
each end of the cylinder. The cylinder is weighed, charged with 0.5 grams of the above
stated mixture and connected to ground through a capacitor and an electrometer connected
in parallel. In addition to the determination of the resin concentration or the weight
loss by impaction on the glass carrier beads, this device also is used to determine
the charge on the particles in microcoulombs per gram of resin powder. The weight
loss of the resin sample can occur by two modes of resin particle failure, either
of which will be determined by the tests set forth above. First, the particles can
fail by brittle fracture, thereby causing the attrition of the resin particles with
the accompanying reduction in the mass of the resulting particles. This reduction
in mass corresponds to an increase in the charge to mass ratio, thereby increasing
the attractive forces between the coated glass beads and the size reduced resin particles.
As the charge to mass ratio on the resin powder particles increases above 40 microcoulombs
per gram, the attractive forces between the particles become so great that the resin
particles and the glass bead particles become inseparable due to the action of the
high pressure air passed through the Faraday Cage.
[0017] Secondly, the resin particles can fail because of ductile deformation. In this mode
of failure, the resin particles become flattened against the surface of the larger
high density glass beads in a pancake type formation. In such action, the particles
literally become welded to the surface of the glass beads thus preventing blowoff
and recovery of the toner particles. It can be seen that the tests indicated above,
that is, the visual observation of the toner particles by scanning electron microscope
and also the measurement of the recoverable toner after blowoff gives a precise test
for determining whether a resin material will have the proper physical characteristics
to withstand the forces involved in the normal operation of an electrostatographic
apparatus.
[0018] In the practice of this invention, any suitable blend of esterified polymers as described
above may be used in the preparation of toner par- tides by combining with a suitable
colorant. The toner may be prepared by dissolving the resinous material and a coloring
agent such as a dye or a pigment or by dissolving the resin and dispersing the colorant,
should it be insoluble, in a suitable solvent and spray drying to achieve uniformly
sized toner particles. The toner size may vary from about 1 micron to about 20 microns
and preferably from about 10 to about 15 microns. The toner particles should be of
substantially uniform size because of the nature of the spray drying operation.
[0019] In the preparation of the toner material, any suitable colorant may be employed such
as, for example, pigments or dyes including, 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 Oxylate, lamp black,
Rose Bengal and other pigments and dyes set forth in the Color Index, Vols. I and
II, Second Edition. Should a magnetic toner be desired, the colorant may be a magnetic
material such as iron particles, iron oxide, nickel, ferrite, magnetite or mixtures
of magnetic particles and colorant.
[0020] In the preparation for spray drying, the resinous material employed in the colorant
is dissolved in any suitable solvent such as, for example, chlorinated solvents including
trichloroethane, methylene chloride, tetrachlor- ethane, methylene dichloride, chloroform,
aromatic solvents such as toluene, benzene, naphthalene, xylene, ketones such as,
for example, methylethyl ketone, acetone, esters such as ethylacetate, amylacetate,
mixtures thereof and the like. The solvent should be chosen in order to assure that
all the resin components are soluble.
[0021] The spray drying operation is conducted in a suitable spray drying apparatus such
as, for example, the Bowen Laboratory spray dryer manufactured by Bowen Engineering
Corporation, North Branch, New Jersey. This unit is a lab size conical dryer with
concurrent airflow and has an interchangeable atomizing head mounted near the top
of the drying chamber. Any suitable atomizing head may be employed such as, rotating
disks, high pressure nozzles and the like. In order to achieve uniformity in size
of the particles, it may be desirable to classify the particles by any suitable classification
techniques well known in the classification art.
[0022] The toners of this invention can be mixed with a suitable carrier to form electrostatographic
developers. Any suitable carriers having a particle size of from about 30 microns
to about 1,000 microns may be employed such as, for example, glass beads, sand, particles
of ferromagnetic materials such as iron, cobalt, nickel, alloys thereof, ferrites,
and the like. Resinous materials such as methylmethacrylate, styrene and any suitable
resinous materials in particle sizes set forth above. The carriers may be employed
with or without a coating. Many suitable resinous coating materials may be employed
such as polyolefins, such as polyethylene polymethyl styrene, polymethylmethacrylate,
polyacrylonitrile, polyvinylacetate, polyvinyl alcohol, polyvinyl carbazole, fluorocarbons,
such as poly- tetrafluorethylene, polyvinylidene fluoride, polyamides, polyurethanes,
polycarbonates and the polymers set forth in U.S. Patent 3,526,533. Many of the foregoing
and other typical carriers are described in U.S. Patent Numbers 2,638,416; 2,618,552
and 4,075,391. The carrier should be chosen in order that the charge to mass ratio
of the blown-off toner is from about 10 to about 40 micro coulombs/gram and preferably
from about 10 to 30 micro coulombs/gm.
[0023] The toner composition generally comprises from about 0.1 ,to about 15 percent by
weight of the total toner carrier weight. Preferably, the toner is present in an amount
of from about 0.5 to 5 percent by weight based on the total weight of the developer
mixture.
[0024] In addition to the presence of toner and carrier, because the toner particles are
prepared by spray drying, it is generally preferred to add a flow agent to the developing
mixture in order to obtain the optimum flow characteristics of the toner in the electrostatographic
system. Any suitable flow agent such as, for example, colloidal silica, aluminum oxide,
titanium dioxide, talc and the like may be employed. These flow aids are sub-micron
in size and preferably from about 50 A to about 500 A. The flow agents are added in
an amount of from about 0.05 to about 1% based on the weight of the toner, and preferably
from about 0.1 to about 0.5%.
[0025] The invention is further illustrated by the following examples in which parts and
percentages are by weight unless otherwise specified.
Example I
[0026] A copolymer of about 70 mol percent vinyl chloride and about 30 mol percent ethyl
maleate having a second order glass transition temperature (Tg) of 57°C, a number
average molecular weight of about 21,750 and a weight average molecular weight of
about 51,350 by Gel Permeation Chromatography and marketed by Firestone Plastics under
the grade designation FPC-471 is spray dried from a chloroform solution in a Bowen
Laboratory Spray Dryer to obtain copolymer resin particles of from about 10 to 15
microns.
[0027] A small quantity of the resin particles are sprinkled onto a glass slide and placed
in an oven preheated to 135°C for two minutes. Upon removal, visual observation readily
indicates that the particles coalesce.
[0028] Six grams of the spray dried particles are subjected to the roll mill test previously
described herein. After 500 hours, the particles are viewed under a scanning electron
micro-I scope. No particle failure can be observed. Substantially 100% of the particles
are recovered after blow-off.
Example II
[0029] A solution of the copolymer of Example I in chloroform having 5% carbon black dispersed
therein is spray dried to form toner particles having a volume average particle size
of about 13 microns and a number average particle size of about 4 to 5 microns and
a resin content of about 95 percent and carbon black content of about 5 percent. About
0.25 percent of hydrophobic fumed silica sold as Aerosil R972 by DeGussa Incorporated
is blended into the toner in a Lodige Blender.
[0030] An electrostatic developer is prepared by mixing 1 percent of the above mixture with
a carrier material of 100 micron ferrite particles coated with 1.2 percent, based
on the weight of the ferrite, of a polystyrene resin having a number average molecular
weight of about 160,000 and a weight average molecular weight of about 360,000. The
polystyrene resin contains about 25% acetylene black. The coating is applied to the
carrier core in a Wurster Spouting Fluidized Bed manufactured by Dairy Equipment Company,
Madison, Wisconsin. The ferrite core is prepared in accordance with Example II of
U.S. Patent 4,075,391.
[0031] This developer is used in an electrostatographic copier having a magnetic brush development
system. After 250,000 copies, no change is visible in copy quality or in the character
of the toner particles viewed under a scanning electron microscope. Further, throughout
the test, the charge to mass ratio on the toner and the toner concentration after
blow-off remain substantially constant, the former being about 30 microcoulombs per
gram.
Example III
[0032] A copolymer of 72 mol percent vinyl chloride and 28 mol percent dibutyl maleate is
prepared by suspending about 100 parts of the monomers in the stated ratio and about
5 parts of lauroyl peroxide in about 500 parts by volume of a 1.25 percent polyvinyl
alcohol- water solution which is agitated at 3000 r.p.m. for 30 seconds in a Waring
Blender equipped with a Polytron mixing head to produce a droplet dispersion, the
droplets having an average droplet size of about 12 microns. The reaction is continued
at about 70°C with stirring at 80 r.p.m. for about six hours.
[0033] The polymer particles are separated by pouring the reaction mass into a large quantity
of water and then centrifuging. The supernatant liquid is decanted and the reaction
product is washed three times with water.
[0034] The polymer thus formed is used in the procedure of Example II to prepare toner particles
and developer.
[0035] This developer when used in an electrostatographic machine equipped with a magnetic
brush development system gives excellent results over many copy cycles.
Example IV
[0036] The procedure of Example III is repeated using diethyl maleate in place of dibutyl
maleate. The resulting developer exhibits long life in a xerographic copier.
[0037] It is to be understood that the examples herein are by way of illustration and that
other suitable copolymers as indicated above may be used throughout for those specifically
employed.
1. Elektrostatografische Tonerzusammensetzung, umfassend ein Färbemittel und ein Harz,
dadurch gekennzeichnet, daß das Harz ein Copolymer aus Vinylchlorid, das in einer
Menge von 65 bis 70 Mol% vorliegt, und einem Niederalkylmaleat oder-fumarat, das in
einer Menge von 25 bis 35 Mol% vorliegt, ist, wobei das Copolymer ein zahlenmittleres
Molekulargewicht von 15,000 bis 25,000 und ein gewichtsmittleres Molekulargewicht
von 45,000 bis 55,000 besitzt.
2. Elektrostatografische Tonerzusammensetzung nach Anspruch 1, dadurch gekennzeichnet,
daß das zahlenmittlere Molekulargewicht des Copolymerharzes 22,000 und das gewichtsmittlere
Molekulargewicht des Copolymerharzes 51,000 beträgt.
3. Elektrostatografische Tonerzusammensetzung nach Anspruch 1 oder 2, dadurch gekennzeichnet,
daß das Niederalkylmaleat Athylmaleat, Propylmaleat oder Butylmaleat ist.
4. Elektrostatografische Entwicklerzusammensetzung, umfassend die Tonerzusammensetzung
nach mindestens einem der Ansprüche 1 bis 3 und Trägerteilchen, wobei die Tonerteilchen
an der Oberfläche der Trägerteilchen haften.