Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
BACKGROUND OF THE INVENTION
This invention relates to electrophotographic develop-
ment utiliæing magnetic toner particles which are applied from
magnetic brush to the electrostatic latent image without
use of a carrier material.
A vast majority of the electrographic copying pro-
cesses in use today involve creation on a suitable recording
medium of an electrostatic charge pattern corresponding to a
pattern of light and shadow to be reproduced and the development
of that pa~tern by deposition of marking material on the r~cord-
ing medium according to forces generated by such electrical
potential pattern. Xerography is the most widely known o~ these
techniques. The substrate may be photoconductive, such as in
the case of selenium as taught in Carlson's U. S. Patent 2,297,691,
or may be a conventional insulating substrate overlying a
photoconductor layer, as described in Watanabel U~ S. Patent
3,536,483, to name a few examples.
After creation the electrical potential pattern is
generally developed by means of a finely divided developer
powder thus giving form to the hitherto latent electrostatic
image. In a common technique a ~ine, insulating, electroscopic
powder is cascaded over the electrical potential pattern bearing
member. The powder i9, in the conventional use, triboelectrically
charged to a de~inite polarity and deposits preferentially in
regions o the surface where there is a preponderance of charge
of the opposite polarity. The triboelectric charge is caused
by presence of carrier beads in the powder mix. This technique
of development is called cascade development.
In another form of cascade development, called mag-
netic hrush development, magnetic carriers or magnetic tonersare employed. In this
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technique a magnetlc ~orce is used to provide adherence of the
toner-carrier mixture to a support member which is then presented
to the image bearing member. In comparison to cascade development,
magnetic brush development ~ills in solid areas better, is more
compact, and does nct depend on gravity to present the toner
to the surface, a factor which allows reedom in locating the
developer station.
In yet another form of electrostatic charge pattern
development, a conductive one-component toner is used by
bringing a conductive support member bearing a layer of fine
conductive toner powder into contact with the charge pattern
b~aring memker as in U. S. Patent 3,166,432 to Gu~dlach. In this
case the toner is held to the support member by van der Waal's
forces and the conductive support member is held at a bias
potential during development. This technique fills in solid
areas and requires only one component in the developer material.
A further method of developing an electrostatic charge
pattern is to e~ploy an electroscopic toner suspended in a
liquid. With the proper choice o~ materials, the toner becomes
charged to a definite polarity when dispersed in the liquid.
When the electrostatic charge pattern bearing memher is brought
into contact with the liquid suspension, the toners deposit
where there is a preponderance of charge o~ the opposite polarity
as in cascade development.
While all of the above techniques have certain
advantages in particular situations, each one suffers from dis-
advantages which impair their utility in actual machines.
~ In the conventional cascade development technique
- the toner-carrier combination has a definite charge polarity
and ls not reversible without changing the toner or the carrier.
Thus, positive and ne~ative developed images cannot easily be
made. Also the images are hollow and solid areas are not filled
in resulting in low-fidelity development compared to the or-
iginal charge pattern~ The triboelectric properties of the
toner, while necessary to development, cause severe problems.
Uneven charging of the tonexs causes backgrounding as do khe
uneven forces between carrier and toner result in varying
threshold levels from ~oner to toner. Also, since the toner
retains its charge for long periods of time, during cascading
some toners escape the development region and enter other
parts of the apparatus causing mechanical problems. These pro-
blems, coupled with the inherent problems of using a two-com-
ponent s~stem where only one component is depleted, de~initely
limit the utility of such techniques.
The magnetic brush development, as it also usas
carr:ier, suffers from some o~ the above mentioned disadvantages
although it overcomes others. As mentioned above, this tech-
nigue is less efficient but helps to fill in solid areas.
However, it still requires triboelectric toners, which have the
concomitant problems mentioned above. Also, due to the
mechanical ~rushing action and other electrical characteristics,
this technique usually results in high background deposition
and poor machine latitude.
The pxocess described in Gundlach, U. S. Patent 3,166,432,
has many advantages over the above mentioned cascade type
techniques. However, it suffers rom drawbacks which limit its
applicability. The van der Waal's forces, which act to adhere
the toner onto the conductive support member, are a counterforce
to the image producing electric force generated by the electro-
static charge~ pattern, and as such mu~t be selectively overcome
to have toner deposited. The van der Waal's forces are weak and
non-uni~orm from one toner to the next. Also high contrast is
dif~icult to achieve The fact that the van der Waal's forces
are not undar direct control but subject largely to the surface
properties of the materials involved makes the system highly
susceptible to alteration of developmant properties upon wearing
of the involved surfaces or variations in ambient conditions of
temperature and humidity.
In a liquid development technique most of the problems
of cascade development are present in addition to other unique
to a liquid system. The technique requires kriboelectric
charging, making image reversal dif~icult as explained above.
Also, as in the case of cascade development, the charge on a
given toner is not well controlled, resulting in high background
deposition, poor machine latitude, and a characteri~tic
splot~hiness in large dark or grey areas. The inherent problems
of the handling liquids, usually solvents, in a machine are also
present.
There have been suggested systems for magnetic develop-
ment not utilizing the carrier material. One such system
was described in U. S. 2,846,333 to Wilson. Wilson et al dis-
closed the use of magnetic brush to apply toner particles
formed of ~errites and resin material to develop electrostatic
latent images. The dif~iculty with this process was the con-
ductivity o the toner made electrostatic transfer di~ficult.
A further developmen~ o~ magnetic development without
carriers is illustrated by Kotz~ U. S. 3,909,258 wherein an
electrostatic development process utilizing a magnetic brush
without carrier i9 illustrated. A toner suitable for use in
the Kotz process is disclosed in U. S. 3,639,245 to Nelson wherein
a dry toner powder having specific electric conductivity is
disclosed. The toner o~ Nelson is ~ormed by blending magnetite
with the resin and then after blending pulverizing to a small
particle size. The particles are then mixed with conductive
carbon black which is imbedded in the surface of the particle
and then a small particle size SiO2 agent is mixed into the
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S~:~'7~
toner to improve the flowability. The toner of Nelson suffers
the disadvantage that it does not transfer well from a photo-
conductive substrate to plain bond paper.
Therefore there is a continuing need for toners
suitable for use in one component magnetic development systems.
There is a need for toners suitable for high speed develop
ment that also have good electrostatic transfer characteris
tics for transfer from a photoconductive surface to plain
b~nd paper.
SUMMARY OF THE INVENTION
It is an object of an aspect of this invention to
provide a toner overcoming the above noted deficiencies.
It is an object of an aspect of this invention to
provide a process of toner manufacture that overcomes the
lS deficiencies of the above noted processes.
It is an object of an aspect of the invention to
produce clear sharp images by magnetic brush development of
electrostatic images without using a carrier.
It is an object of an aspect of the invention to
produce a toner that will transfer electrostatically from the
photoreceptor to plain bond paper.
It is an object of an aspect of the invention to
form a toner suitable for high speed development by magnetic
brush system without carrier.
It is an objeck o an aspect of the invention to
produce a toner whose electrical resistivity is field dependent.
It is an object of an aspect of this invention to form
electrically field dependent toner by a simple process.
It is an object of an aspect of the invention to
form toners whlch after transferred to paper adhere sufficiently
well hy electrostatic forces that image disturbances (blurj
do not occur on handling prior to fusing.
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These and other objects of the invention are
generally accomplished by formation of a toner comprising
magnetically attractable material and a resin wherein khe
magnetically attractable particle is coated with à thin coat-
S ing of material compatible with the resin of the toner buthaving a strong affinity for the magnetite surface and com-
patible with the solvents used in the toner formation. The
toner of the invention is prefer~bly formed by spray d~ying
from a slurry solution.
In a specific embodiment in accordance with the
instant invention a stearic acid is neutralized with ammonium
hydroxide to form a watér soluble ammonium compound. Magnetite
pigment is added to the aqueous solution with agitation such
that the ammonium compound is deposited on the pigment surface
and then decomposed and converted back to the stearic acid by
heating. The material is filtered, washed and dryed and the
pigment is then dispersed in a solution of toluene and styrene-
but~lmethacrylate re~in and spray dryed. me magnetite may
be used in an amount of about 50 percent by weight of the
resin magnetite dispersion. The solvent forms abouttwo thirds
by weight of the total spray drying slurry solution. Magnetite
coated by other methods i5 also suitable for the instant
process . ,.
In accordance with one aspect o~ this invention
there is provided a single c~mponent, electrically field depend-
ent developer comprising toner particles, said particlescomprising a resin and magnetic particles coated with a
surfactant, the surfactant being present in an amount of
about 0.1 to about 10 weight percent of the magnetic material,
said magnetic material belng present at higher concentration
near the toner particle surface than in the interior of the
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particle, said toner being characterized by a field dependence
such that at low fields of less than 100 volt/cm the resist-
ivity is greater than 1012 ohm-cm and less than 1012 ohm~cm
at fields greater than 100 volt/cm, along a line of a slope
greater than 5 when log of powder resistivity is plotted
versus the log of the field in volt/cm.
In accoxdance with another aspect of thi-s invention
there is provided a single component electrically field dependent
dev~loper comprising toner particles, said particles com-
prising resin, and a surfactant coated magnetite wherein thesurfactant coating comprises a fatty acid or fatty acid
derivative and the toner is characterized by a field depend-
ence such that at low fields of less than 100 volt/cm the
resistivity is greater than 1012 ohm-cm and at some higher
field $hey exhibit a sharp drop to a resistivity of less
than lOa ohm-cm along a line of a slope greater than 5 when
log of powder resistivity is plotted versus the log of the
field in volt/cm.
In accordance with another aspect of this invention
there is provided a method of imaging comprl~sing ~orming an
electrostatic image, developing said electrostatic image
with a single component electrically field dependent developer
comprising toner part.iclesl said toner paxticles comprising
resin and magnetic pigment, said developing being conducted
at a f.ield strength such that the toner particles have a
resistivity of less than 1012 ohm-cm and electrostatically
: transferriny the thus developed toner image to plain paper
at a field strength less than 100 volt/cm at which the toner
: particles have a resistivi.ty greater th~n 1012 ohm-cm.
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'77
In accordance with another aspect of this invention
there is provided a single component, electrically field dependent
developer comprising toner particles said particles including
resin and magnetic pigment said toner exhibiting a substant-
ially constant resistivity greater than 1012 ohm-cm as the
field strength increases to a point where the resistivity
decreases at a slope greater than about 5 to a resistivity
less than about 1~8 ohm-cm when log of powder resistivity
in ohm-cm is plotted against field strength expressed as
log E volt/cm.
BRIEF DESCRIPTION OF TE[E DR~WINGS :
Figure 1 illustrates the res.istivity versus electrical
field strength of a toner of the instant invention.
Figure 2 illustrates the resistivity versus electrical
field strength o~ a non-humidity sensitive toner of the instant
invention.
Figure 3 illustrates the effect of varying the
amount of magnetite coating of toners of the invention.
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DESCRIPTION OF THE INVENTION
The toners o~ the instant invention generally have
resistivity that is dependent on the strength of the
electrical field. They are conductive during the high field
during develop~ant but have a powder resistivity of about 107
to 1017 ohm-cm at the low field during transer. The great field
dependent resis~ivity change o~ these ~oners allows transer o~
the toner by the customary electrostatic transfer processes
without use o specially treated paper or transfer techniques
such as pressure or use of adhesives. Further the toner is con-
ductive at high fields so as to easily deve?op by inductive
techniques. The toners o~ the instant invention have a resis-
tivity of greater than about 1012 ohm-cm at low ~ields o~ about 10
volt/cm which corresponds to about 1 log E volt/cm as used in
the drawings. It is pre~erred that the high resistivity of
greater than about 1012 ohm-cm be maintained at at least up to
a~out 100 volt/cm field strength which corresponds to about 2
log E volt~cm in the drawings to giva greater trans~er latitude~
The preferred initial resistivity is greater than 10 4 ohm-cm
which of course corresponds to about 14 log E ohm-cm on the
drawings as thls range allows good~ e~e~ o~ the electro-
static image. The toners o~ the invention display a substantially
stable resisti~ity as field strength increases and then have a
sharp break point where the resistivity rapidly decreases at a
~5 slope of greater than about 5 when plotted as the log of powder
resistivity (ohm-cm) versus log of the field in volt/cm. The
preferred slope lS yreater than about 10. Generally the slope
is about 10 to 20~ for toners o the invention. The slope greater
than about 10 is pre~erred as it results in excellent eIectro-
static trans~er and also good development.
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The toners and magnetic pigments the,rein o the instant
invention are referred to as magnetic because they are attracted
to a magnet. They are not themselves magnets. The toners are
held to a magnetic brush roller or belt by magnetic forces.
S The mag brush is biased to induce a charge, opposite to that
caxried by the photoreceptor, into the toner particles~ Then the
outer particles develop the electrostatic image as the electro-
static forces overcome the magnetic forces to deposit toner in
the image areas. The earlier referenced U. S. 3,909,258 has
illustrations o the forces present in the developing process
utilizing a magnetic brush system without a carrier.
The magnetic pigment utilized in the toners of the inven-
tion may be any suitable particle which will give the desired mag-
netic properties. Typical of such materials are ferrites, iron
particles and nickel alloys. Preferred for the instant process
are magnetite particles as they are black in color, low cost
and provide excellent magnetic properties. The magnetite parti-
cles may be o~ any shape and any size which results in a semi-
conductive ton~r particles with good trans~er properties. Generally
the particle size is between .02 micron and about 1 micron.
A preferred average particle size for the magnetite particles is
about 0.1 to 0.5 rnicron average particles size. ~he particles
may be a acicular or cubic shaped.
The trans~er efficiency of the toners of the instant
invention is greater than ahout 70 percent and generally reaches
, 85 percent in ordinary electrostatic transfer.
The coated magnetic pigment may be utilized in
any amount that forms a magnetic field depend~ ~ ~oner. A
suitable range has been found to be a magnetic~pIgment
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con~ent between about 40 and about 70 weight percent o~ coated
magnetic particle in the inished toner~ A preerxed range
is a coated magnetite content between about 45 and 55
weight percent of coated magnetite for good magnetic develop-
ment properties and good transfex.
The material coating the magnatic particle may be any
material which is compatible with the toner resin and maintains
a firm bond to the magnetic particle during mixing with a solvent
for the toner resin and spray dryinyO These materials generally
are surfactants. The magnetic particle coating suitably ~ s one
moiety displayin~ a~inity to the magnetite surface such as
carboxylicr sulfate, sulfonate, phosphate, ester, alcohol,
amine, amide groups and quarternary ammonium compounds, or com~
binations o~ the above and another moiety which displays
af~inity to the resin and the solvent such as long chain aliphatic
groups co~prisin~ rom 6 to 22 carbon atoms or aromatic
groups of about the same carbon content. Preferred are stearic
acid and stearic acid derivative materials which have been ~ound
to have good dispersion properties and result in desirable semi-
conductive toner properties that aid in transfer~ The amount o~
coating typically may vary between about .1 and 10 percent by
weight. A preferred ranye of coating material for magnetite is
C~9~l17about 1 to about ~ weight percent o the magnetite for good
insulative propertias at low ~ield~
The toner resins may be selected ~rom any suitable
toner resin material that is compatible with the coating of the
magnetite.
While~any suitable resin possessing the properties
as above described may be employed in the system o~ ~he present
invention. Typical o~ such resins are polyami~es, polyurethanes,
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epoxy, vinyl resins and polymeric esterification products of a
dicarboxylic acid and a diol comprising a diphenol. ~ny ~uitable
vinyl resin may be employed in the toners of the present
system including homopolymexs or copolymers of two or more vinyl
monomexs. Typical of such vinyl monomeric units include: styrene;
p-chloro~tyrene; vinyl naphthalene; ethylencally unsaturated
mono-olefins such as ethylene,propylene, butylene, isobutylene
and the like; vinyl esters such as vinyl chloride, Yinyl hromide,
vinyl ~luoride~ vinyl acetate, vinyl propionate, vinyl benzoateO
vinyl butyrate and the like; esters o~ alphamethylene ~iphatic
monocarboxylic acids such as methyl acrylate, ethyl acrylate, n-
butylacrylate, isobutyl acrylate, dodecyl acrylate, n-octyl
acrylate, 2-chloroethyl acrylate, phenyl acrylate, methyl-alpha-
chloroacrylate, methyl methacrylate, ethyl methacrylate, butyl
methacrylate and the like; acrylonitrile, methacrylonitrile,
acrylamide, vinyl ethers such as vinyl methyl ether, vinyl
- isobutyl ether, vinyl ethyl ether, and the like; vinyl ketones
such as vin~l methyl ketone, vinyl hexyl ketane, mothyl isopro-
penyl ketone and the like; vinylideno halides such as vinylidene
chloride, vinylidene chloro~luoride and ~he like, and N-vinyl
compounds such as ~-vinyl pyrrol, N-vinyl carbozole, N-vinyl in-
dole, N-vinyl pyrrolidene and the like; and mixtures thereo.
It is gen~rally found that toner resins containing
a relatively high ~ercentaye o styrene are preferred since greater
image definitlon and density is obtained with their use. The
styrene resin employed may be a homopolymer of styrene or styrene
homolo~s or copolymers o styrene with other monomeric groups
containing a single methylene group attached to a carbon atom
by a double bond. Any of the above typical monomeric units may
be copolymerized with styrene by addition polymerization. Styrene
~,
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resins may also be formed by the polymerization o mixtures o~
two or more unsaturated monomeric materials with a styrene
monomer. The addition polymerization technique employed embraces
known polymerization technique such as free radical, anionic and
cationic polymerization processes. Any o~ these vinyl resins may
be blended with one or more other resins if desired, preferably
other vinyl resins whLch insure good triboelectric properties and
uniform resistance against physical degradationO However, non-
vinyl type thermoplastic resins may also be em~loyed including
resin modified phenolformaldehyde resins, oil modiied epoxy resins,
polyurethane resins, cellulosic resins, polyether resins and mix-
tures thereo~.
Polymeric estexification products o a dicarboxylic
; acid and a diol comprising a diphenol may also be used as a
preferred resin material for the toner com~ositions of the instant
invention. The diphenol reactant has the general formula:
~ (OR')~ o ~ ~ R ~ ~ O (OR )n2
wherein R repreæents substituted and unsubstituted alkylene
radicals having ~rom 2 to 12 carbon atoms, alkylidena radicals
having from 1 to 12 carbon atoms and cycloalkylidene radicals
having from 3 to 12 carbon atoms; R' and R" represent sub-
stituted and unsubstituted alkylene radicals having from ~ to 12
carbon atoms, alkylene arylene radicals having rom 8 to 12
carbon atoms and arylene radicals; X and X' represents hydrogen
or an alkyl radical having from 1 to 4 carbon atoms; and nl
; 30 and n2 ar~ each at least 1 and thP avexage sum of nl and n2
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i~ less than 21. Diphenols wherein R represents an alkylidene
radical having from 2 to 4 carbon atoms and R' and R" represents
an alkyle~e radical having from 3 to 4 carbon atoms are preferred
because greater blocking resistance, increased definition of xero-
graphic characters and more complete transfer of toner images are
achie~ed. Qptimum results are obtai;~ h ~iols in which
R' is an isopropylidene radical and R' and R" are selected from
the group consisting of propylene and butylene radicals because
th resins formed from the~e diols possess higher aggl omeration
re~istance and penetxate extremely rapidly i~to paper receiving
sheets under fusing conditions. ~icar~oxylic ac~ds having ~rom
3 to 5 carbon atoms are preferred because the resultiny toner
re~in possesses greater resis~ance to film formation on reusable
imaging surfaces and resist the formation o fine~ under machine
operation conditions. Preferred results are obtained with alpha
.unsautrated dicarboxylic acids including fumaxic acid, maleic acid
: or maleic acid anhydride because maximum resistance to physical
degradation o the toner as well as rapid melting properties
are achieved. Any suitable diphenol which satisies the above
formula.may be employed. Typical such diphenols include: 2,~-bis
(4-beta hydroxy ethoxy phenyl)-propane, 2,2-bis(4-hydroxy isopropoxy
phenyl~ propane, 2,2-bis(4-beta hydroxy ethoxy phenyl) pentane,
2,2-bis(4-beta hydroxy ethoxy phenyl)-butane, ~,2-bis(~-hydroxy-
prop~xy-phenyl)-propane, 2,2-bis(4~hydroxy-propoxy-phenyl)
propane, I,l-bis(4-hydroxy-ethoxy-phenyl)-butane, 1,1-bis(4-
hydroxy isoprspoxy-phenyl) heptane, 2,~-bis(3-methyl-4-beta-
hydroxy ethoxy-phenyl) propane, 1,1-bis(4-beta hydroxy ethoxy
phenyl)-cyclohexane, 2,2'-bis~4~beta hydroxy ethoxy phenyl)-
norbornane, 2,2'-bis(4-beta hydroxy ethoxy phenyljnorbornane,
2,2-bis(4-beta hydroxy styryl oxyphenyl) propane, the poly-
oxyathylene ether o~ isopropylidene diphenol i~ which both
phenolic hydroxyl groups are oxyethylated and the a~erage
number of oxy2thylene groups per mole i~ 2.6, the polyoxy-
propylene ether o 2-butylidene diphenol in which both the -
----T. ~ r
j - 13 -
phenolic hydroxy groups are oxyalkylated and the average number
of oxypropylene groups per mole is ~.5, and the like. Diphenols
wherein R represents an alkylidena radical having from 2 to 4
carbon atoms and R' and R" represent an alkylene radical having
from 3 to 4 carbon atoms are pre~erred because greater blocking
re~istance~ increased de~inition o~ xerographic characters and
moxe complete transer of toner images are achieved. Optimum
results are obtained with diols in which R is isopropylidene
and R' and R" are selected from the group consisting of propy-
lene and butylene because the resins formed from these diols
possess higher agglomeration resistance and penetrate extremely
rapidly into paper receiving sheets under fusing conditions.
Any ~uitable dicarboxylic acid may be reacted with
a diol as described above to ~orm the toner compositions of
this invention either substituted or unsubstituted, saturated or
unsaturated, having the general srmula:
HOOC R'lln COOH
wherein R"' represents a substituted or unsubstituted alky].ene
radical haviny ~rom 1 to 12 carbon atoms, arylene radicals or
alkylene arylene radicals havi~g ~rom 10 ~o 12 carbon ~ oms and
n3 is less than 2. Typical such dicarboxylic acids including
their existing anhydrides are: oxalic acid, malonlc acid,
succinic acid, glutaric acid, adipic acid, pimeli- acid, suberic
aci.d, azelaic acid, sebacic acid, phthalic acid, mesaconic acid,
homophthalic acid, isophthalic acid, terephthalic acid, o-
phenyleneaceti~-beta-propionic acid, itaconic acid, maleic acid,
maleic acid anhydride, fumaric acid, phthalic acid anhydride,
traumatic acid, citraconic acid, and the like. Dicarbo~ylic
acids having ~rom 3 to 5 carbon atoms are preerred because the
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resulting toner resîns possess grea~er resistance to film
~ormation on reusable imaging surfaces and resist formation
o fines under machine operation conditions. Optimum
results are obtained with alpha unsaturated dicarboxylic acids
s including fumaric acid, maleic acid, or maleic acid anhydride
because maximum resistance to physical degradation o~ the
toner as well as rapid melting properties are achieved. The
polymerization esterification products may themselves be co-
polymerized or ble~ded with one or more other thermoplastic
io resins, preerab1y aromatic resins, aliphatic resins, or mix-
tures thereof. Typical thermoplastic resins include: xesins
modified phenolformaldehyde resin, oil modi~ied epoxy resi.ns,
polyurethane resins, cellulosic resins, vinyl type resins and
mixtures thereo. When the resin component of the toner con-
tains an added resin, the added component should be present
in an amount less than about 50 percent by weight based on
the total weight of the resin present in the toner. A
relatively high percentage o~ the polymeric diol and dicarboxy-
lic acid condensation product in the resinous component o~ the
toner i~ prefexred because a greater reduction o~ ~using tem-
peratures is achieved with a giverl quantity of additive material.
Further, sharper images and denser images are obtained when
a hiyh percen~age of the polymeric diol and dicarboxylic acid
condensation product is present in the toner. Any sui~able
blending techni~ue may be employed to incoxporate the added
resin into the toner mixture. The re~ lting resin blend is
substantially homogeneous and highly compatible with pigments
and dyes. Where suitable, the colorant may be added prior to,
simultaneously with or subsequent to the blending or polymeri-
zation step.
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Optimum electrophotographic results are achieved with
styrene-butyl methacrylate copolymers, styrene-vinyltoluene
copolymers, styrene-acrylate copolymers, polystyrene resins,
predominately styrene or polystyrene based resins as generally
described in u. S. Reissue 25,136 to Carlson and poly-
styrene blends as described in U. S. 2,788,288 to Rheinfrank and
Jones.
Any method of toner particle formation may be utilized
in the instant invention which results in toner o~ the desired
properties. Typical o~ such methGds are hot melt formation
and mastication ollowed by attrition to toner particle size.
The preferred method o~ the instant invention is forming a
solvent dispersion of the magnetite and toner resin and spray
drying the dispersion as this results in toner particles having
the magnetite concentrated at the sur~ace and results in toner
; of good magnetic and electrostatic properties for excellent
magnetic induction development and electrostatic transfer to
plain paper. While not wishing to be bound by any theory as to
; why the instant toners display their remarkable ield dependent
properties it is believed that the properties are somehow related
to the concentration of magnetic particles at the sur~ace of the
toner and that the coating o the magnetic pigment contributes to
this higher concentration that results ater spray dxying.
The solvent used ~or spray drying may be any material
capable of dissolving the toner resin without adversely
e~ecting the coating of the maynetite. Solvents ~or toner
.
resi~s are well known including hydrocarbons, alcohols, ketones,
esters, amides,~luorinated hydrocarbons, chlorinated hydrocarbons
and other well known solvents. Pre~erred solvents are toluene
for use with styrene polymer resins and styrene polymer
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blends as this resuIts in a toner that is solvent free
and the solvent is low cost and relatively non-toxic.
Chloroform has been found to be a preferred solvent for
use with polyester type toner resins as it is readily
available, non-flammable and results in a toner of low
residual solvent. Both chloroform and toluene also are
compatible with the preferred fatty acid and derivative
coatings for the magnetite. The solvent is generally
used in an amount such that the solids content of the
solvent slurry is 5-20% by weight. The term solidscontent
is used here to indicate the solid resulting from spray
drying which is the resin and magnetite plus any other
additives to the toner such as colorants.
An invention relating to the formation o magnet-
ite coated in a manner particularly suitable for use
in the instant invention has been perfected. Magnetite
coated by the inventive process is not humidity sensitive
which is an advantage in toner formation and further
readily is dispersed in solvents and resins without efect-
ing the properties of the coating. This process is gen-
erally performed by neutralizing a fatty acid of stearic
or a derivative of a fatty acid of a stearic acid with
ammonium hydroxide to form a water soluble ammonium compound.
The pigment preferably magnetite, is then added to the
a~ueous solution with agitation. Ammonium compound is
deposited on the pigment surface and then decomposed
and converted back to the fatty acid or derivative of
a fatty acid by heating. The aqueous dispersion is then
filtered, washed and dryed. The pigment coated by this
~ 30 process is hydrophobic and has good dispersion properties
- ln organic matrixes such as polymer resins and organic
solvents. Among suitabIe fatty acids and fatty acid
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~17-
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derivatives are myristic, pentadecanoic, palmitic, lauric,
margaric, oleic and linoleic aclds and mixtures thereof.
Preferred are stearic acids and mixtures of stearic acid
and other fatty acids of C14 to C18 to give good coating
and electrical properties.
Another toner forming method involves generally
spray drying a dispersion of resin and magnetite coated
with a fatty acid or derivative of a fatty acid to form
a toner. The dispersion of magnetite and fatty acid
in solvent generally is agitated or heated with reflux
and agitation for a time prior to addition of polymer
and spray drying.
In a specific embodiment fifty parts by weight
magnetite, 2 parts by weight stearic acid and 50 par~s
of toluene were mixed and heated to about 110C for about
1 hour with reflux and agitation. After heating the
mixture is blended with a polymer solution containing
a styrene polymer in toluene. The dispersion was then
- spray dryed to form a toner. The toner is found to have
a powder resistivity from 106 ohm-cm to 1017 ohm-cm
depending on field strength.
The agitation or agitation with heating oE the
magnetite and fatty acid or fatty acid derivative in
solvent may be carried out for any length of time resulting
in a toner having the desired field dependent properties
after spray drying. Generally the heating is carried
out with reflux for a period of about 30 minutes to 3
hoursO A preferred time of heating is about 1 hour with
reflux which results in a toner having the desired field
dependence without an overly long formation time period.
~ A temperature of reflux heating is selected dependent
; ; on the volatility of the solvent being used. The heating
~ -18-
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temperature of about lOn.to about 150C has been
fo~nd to be typical for common solvents.
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.
.
Other methods of coating the steari~ acid or stearic
acid derivatives onto magn~tite particles may also be utilized.
Among these processes are the direct coating onto magnetite
particles by tumbling with a fatty acid material possibly with
low heat. Another method o~ coating magnetite is to coat it with
Ci~ an ammonium stearate or other fatty acid ammonium and then heat
the coated particle so that the fatty acid coating particle is
recovered.
While the above discussion has not included the additicn
of additives to the solvant prior to spray drying ~or inclusion
in the toner it is encompassed in the invention that addikives
such as pigments, humidity control materials and dyes may be added
prior to toner formation~ The preferred magnetite materials are
black and there~ore suitable for the majority o~ electrophoto-
graphic reproduction uses without benefit of colorant additives.
However other less dark colored magnetic materials might require
pigment or dye additives to obtain a suitable toner color. Such
pigments and dyes are not needed to obtain the field sensitivity
required of the invention.
It is ~urth~r contemplated that after treatment processes
such as classi~ication might be necessary depending on the
particle size range achieved by the spray drying.
DESCRIPTION OF ~HE PREFERRED EMBODIMENTS
The ~ollowin~ Examples urther de~ine, describe and
compare methods o~ preparing toners of the instant invention
and of utilizing them in electrophotographic applications. Part3
and percentages are by weight unless otherwise indicated.
EX~MPLE I
100 grams o~ 65/35 styrene-butylmathacrylate resin is
dissolved in 500 grams toluene. After dissolving the resin with
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.: ~ ' , -. - ' ',' '' ' ' ' ' '' :
toluene lO0 grams Pfizer MO 4431 coated magnetite is added to a
Kady mill containing ~he solution and is milled ~or 30 minutes.
The Pfizer coated magnetite comprises acicular particles of about
.1 to about 1 micron length and .02 to .2 micron diameter~ They
are coated with stearate coating comprising a mixture of fatty
acids and calcium salts. The calcium salts are bel~ ved to be
hydrophilic resulting in a slightly humidity sensitive property~
After milling the dispersion is fed to a Bowen spray dryer at a
~eed rate of 200 milliliters per minute and at a temperature o
180-220F. Toner par~icles having an average size of about
15 microns and a range of from about 5 to about 30 microns
are recovered. These toners are found to be capable of rapid
development by using a magnetic system without carrier and are
successfully transferred by electrostatic transer at about
a 75 percent trans~er eficiency at low humidlty. Eowever,
the toner is somewhat moisture sensitive and has a slope of
Ci~
~j71 ~five at high humidity of 86%. The field resistivity
- of this toner is shown in Figure l at 17% relativa humidity.
E _ I
The process of Example I is repeated except 96 grams
o~ Piccolastic D-125 a polystyrene polymer i.s subs~itu~ed for the
polymer and 104 grams o~ coated magnetite is utilized. The toner
; displays excellent transfer properties. The properties are similar
to th~ Example I toner except it is more humidity sensitive.
~2
The process of Example I is repeated except that chloro-
form i5 substituted or the toluene and 100 grams of the polyester
resin is substituted~for the resin of E~ample I. This toner
also exhibits good electrical characteri~tics and transfers very
wèll. The properties are similar to the Example I toner.
" ` ~
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~X~MPLE IV
The process of Example I is repeated except 120 grams
of the coated magnetite are utilized and 80 grams of th~ resin.
The toner of this Example also displays excellent transfer pro-
S perties and good development characteristics. The properties are
similar to the Example I toner.
EX~MPLE V
The process of Example I is again repeated except
130 grams of the coated magnetite is utilized and 70 grams o
the resin. This tonex also exhibits good transfer and develop-
ment charackeristics. The properties are similar to the
Example I toner.
EX~MPLE VI
As a control, toner of Example A in U. S. 3,639,245
i5 fabricated. When utilized in electrostatic trans~er apparatus
this toner does not transfer efectively as only about 30 percent
o~ the toner is transferred.
EX~MPLE VII
-
Tha prvcess of Example I is repeated except 96 grams
of Piccolastics D-125 a polystyrene polymer is substituted
for the polymer and 104 grams of Cities Service Mapico ~lack
magnetite coated with stearic acid is substituted or the mag-
netite. The Mapicb Black magnetite comprises cubic particles
of about 0.02 to about 0.8 micron. The toner displays excellent
~5 development and trans~er characteristics.
~XaMPLE VIII
The above example is repeated except 70 grams of resin
and 130 grams of coated magnetite are utilized. The toner also
has excellent developrnent and transfer propextiesO
EX~MPLE IX
A dispersion of about 100 grams Pfizer magnetite
e ~ ks
-- 21 --
.
7~
Mo-4232, an uncoated magnetite, about 4 grams stearic acid and
about 100 grams of toluene are mixed and heated to about 100 C
for l hour with reflux and gentle agitation. This heating was
carried out in a three neck flask. After heating, the mixture is
blended with a polymer solution containing about 96 grams of
polystyrene resin (Pic~olastic D-125) in about 1000 grams of
toluene. The dispersion is then spray dryed to a toner of about
12~ avera~e particle size. ~he resulting toner had excellent field
dependent characteristics. As illustrated by Figure 2 the initial
resistivity was greater than 14 ohm~cm initially and at a certain
po~ t dropped rapidly in resisti~ity. This toner also as
illustrated by Figure 2 showed very little humidity sensitivity~
The toner was ound to be capable o rapid development using
a magnetic system without carrier and successully transerred
by electrostatic transfer at about a 75% rate of transfer
efficiency.
EXAMPLE X
G.~ A toner is prepared as in Example ~ except that about
f.lZq 17198 grams of a 35/65 styrene and butylmethacrylate resin
are substituted for the polystyrene resin o Example I. This
tonex is ound to produce excellent transer and have par-
ticularly desirable field dependent properties.
Resistlvity of this toner is given as line 2 of
Figuxe 3.
` EX~MPLE XI
The process of Example I is repeated except that
about 2 grams of stearic acid are utilized and about 98 parts
of the 65/35 styrene and butylmethacrylate of Example V.
This toner also is ound to produce desirable field dependent
properties. The resistivity o this toner is shown by line 1 of
Eigure 3 in the drawlngs.
-- 22 --
.
.
~$~
EX~MPLE XII
The process of Example I is repeated except
that about 6 grams of stearic acid are utilized and about
94 grams of a 65/35 styrene and butylmethacrylate resin
of Example v. This toner also has desirable resistivity
properties and is illustrated by line 3 of drawing Figure 3.
EXAMPLE XIII
As a contxol, a toner was formed by spray drying
a slurry of about 104 grams magnetite MO-4232 and 48%
Piccolastic*D-125 and about 400 grams ~oluene and when
tested over the same range as illustrated in Figure 2
the toner only varies ~etween about 1016 and 1017 ohm-cm.
The toners of the invention in contrast vary between
about 1014 ohm-cm at a low field strength of about 40 volts
and a resistivlty of about 10~ ohm-cm at a field strength
of about 8000 volts/cm.
The resistivity measurements for toner llsed
throughout this application are determined by the following
.
process. Measurements on powder are complicated by the
fact that the results are influenced by characteristics
of the powder particles shape and size in addition to
powder composLtion. Thereore, measurements were obtained
on powder rather than by molding the powder into a pellet
specimen in order to better xelate the properties to
; 25 the toner behavior in development. The measurements
were made using a two inch diameter electrode of a Balsbaugh
cell for measuring -the direc-t current restivity of the
.....
toner. The;gap distance is 0.05 inch. The toner is
pac]ced between the electrodes of the aell by vibration
... .
until a constant bed volumn 1s reached. The current
is measured as~a function of applied voltage at the 50
* trade mark
23- -
mil gap. The electrification time is 1 minute as recommended
by ASTM me~hod. After each measurement the sample is repacked by
.;
:
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vibration. ~esistivity is calculated according to Ohms law
and the data 2S ~resented in the figure~ is as a Log of resis-
Ci~L- tivity verses ield strength.
7 7
The transfer ef~iciency in thi~ application is
measured com~aring the weight of toner transferred to a paper
with the weight o toner remaining on the photoreceptor and
removed by an adhesive tape applied thereto after transfer to
paper is completed.
Although speci~ic materials and conditions were set
forth in the above exemplary processes in the formation and using
the toner of the invention these are merely intended as illustra-
tions of the present invention. Various other substituents and
processes such as those listed above may be substituted ~or those
in the examples with similar results. In addition to the
steps used by the toner of the present invention other steps or
modificakions may be used. For instance the toner could be
classified prior to utilization for developing and trans~er.
In addition other materials such as colorants could be added.
Other modifications o~ the present invenkion wi}l occur
to those skilled in khe art upon reading the present disclosure.
These are intended to be included within the scope o~ this
invention. For in~tance, the magnetic toner of this invention
could be utilized in conventional magnetic development onto zinc
oxide paper where trans~er did not take place. Further thè
toner o this invenkion could be utilized for processes requiring
development o~ magnetic images rather than electrostatic latent
images.
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