Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
This invention is generally directed to new developer compositions
and the use of such developers for causing the development of images in
an electrophotographic system. More specifically, the present invention
is directed to positively charged toners comprised of styrene-butadiene
copolymer type resins, which toners have broad temperature fusing latitudes,
low minimum fix temperatures, and are particularly useful with hot roll
fusing systems contained in electrophotographic imaging devices.
The electrophotographic process, and in particular, the xero-
graphic process is well-known as described in numerous prior art references
including many patents. In one sequence of the xerographic process the
latent electrostatic image formed on the photoconductive surface is devel-
oped with a variety of pigmented resin materials specifically made for
this purpose, such as toner. Many processes are used for applying the electro-
scopic particles or toners to the electrostatic latent image to be developed
such as for example, the development method described in U.S. Patent
3,618,552, cascade development, U.S. Patent 2,874,063, and 3,357,402,
magnetic brush development, U.S. Patent 2,221,776, powder cloud develop-
ment, and U.S. Patent 3,166,432, touchdown development.
There are instances where it is desirable in electrophotographic
systems to produce a reverse copy of the original, thus, for example, it
may be desirable to produce a negative copy from a positive original, or
a positive coW from negative original. This is referred to in the art as
image reversal, and in electrostatic printing such image reversal can be
accomplished by applying to the image a developer powder which is repelled
by the charged areas of the image and adheres to the discharged areas.
Specifica~ly, toners possessing positive charges are found to be more useful
and effective in electrophotographic reversal systems, and in particular,
in electrophotographic systems employing organic photoreceptors, which
in many instances are initially charged negatively rather than positively,
thus necessitating the need for a positively charged toner. Reversal de-
velopers are, for example, described in U.S. Patent 2,986,521.
In U.S. Patent 3,893,935 there is described the use of certain
quaternary ammonium salts as useful charge control agents for electro-
static toner compositions. According to the disclosure of this patent,
certain quaternary ammonium salts when incorporated into toner materials
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were found to provide a particulate toner composition, which exhibited
relatively high uniform and stable net toner charge when mixed with a
suitable carrier vehicle, and which toner also exhibited a minimum amount
of toner throw-off. U.S. Patent 4,079,041 contains a similar teaching with
the exception that a different charge control agent is used, namely a diazo
type compound.
Several patents are in existence which disclose the use of styrene
butadiene resins for use as toners in development systems, however, such
patents do not teach the use of such resins of a particular composition
and molecular weight for positively charged toners, and in particular for
positive toners which have broad fusing latitudes for example. The patents
involved include U.S. Patent 3,326,848 which discloses a toner of styrene
butadiene copolymer, U .S. Patent 3,960,737 which discloses a liquid devel-
oper of a mixture of styrene butadiene with an acrylate, U.S. Patent 3,766,072
~, which discloses a developer containing at least two type~of particles, one
of which can be a styrene butadiene type resin, (Pliolite S5D), Japanese
Patent Publication 109483 and U.S. Patents 3,090,755 and 3,965,022.
Many of the above-described toners and developers do not have
a broad fusing temperature latitude, described in detail hereinafter, nor
a combination of low minimum fix temperatures and broad fusing temperature
latitudes, without causing a decrease in the blocking temperature. Further
some of the above-described developers have a tendency to lose their positive
charge over a period of time, are difficult to prepare and in view of this
the quality of the image that is to be developed is adversely affected.
Also the use of charge control agents and developers as described in U.S.
Patent 3,893, 935 are soluble in water causing them to be leeched to the
toner surface by moisture thereby adversely affecting the machine en-
vironment and the copy quality.
Accordingly, there is a need for developers which have broad
fusing latitude temperature ranges, which toners can be used in hot roll
fusing systems, these toners containing positive charges thereon and having
low minimum fixing temperatures, that is, from about 250F to about 300F,
and high blocking temperatures of from about 105 F to about 135 F.
SUMMARY OF THE INVENTION
It is an object of~this l~nvent~on to provide a toner which overcomes
the above-noted disadvantages.
e
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It is an object of an aspect of this invention
to provide a toner which has a broad fusing latitude
temperature and can be used in hot roll fusing electrophoto-
graphic systems.
An object of an aspect of this invention is
the provision of a developer which contains positively
charged toner comprised of a styrene butadiene copolymer
resins.
An object of an aspect of this invention is
to provide a developer which contains positively charged
toner and a carrier material.
An object of an aspect of this invention is
to provide toners which will develop electrostatic latent
images containing negative charges on the photoreceptor
surface and which will transfer effectively electrostatically
from such a photoreceptor to plain bond paper without
causing blurring or adversely affecting the quality
of 'he resulting image.
An object of an aspect of the present invention
is to provide a toner resin having additional fuse to
hot offset temperature latitudes by increasing the resin
molecular weight distribution.
An aspect of this invention is as follows:
An improved dry electrophotographic toner
composition useful in electrophotographic imaging systems
employing hot roll fusing, the toner composition consisting
essentially of a colorant, a charge enhancing additive
for imparting a positive charge to the toner composition,
and an improved styrene butadiene copolymer resin having
a weight average molecular weight of from between about
60,000 and about 180,000, and a molecular weight
distribution of from about between 5 and 15, the
percentage by weight of styrene present ranging from
about 80 percent to about 95 percent, with the percentage
by weight of butadiene present ranging from about 5
percent to about 20 percent, such toner having a minimum
fixing temperature of from about 250 degrees Fahrenheit,
r~ ~'`~
~ to about 300 degrees Fahrenheit, a fusing temperature
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latitude of from about 105 degrees Fahrenheit to about
250 degrees Fahrenheit, and a blocking temperature of
from about 105 degrees Fahrenheit to about 135 degrees
Fahrenheit.
The percentage of styrene plus butadiene should
total about lO0 percent, thus, when 90 percent of styrene
is present in the copolymer resin, lO percent of butadiene
is present. Preferred are styrene/butadiene resins
containing 90 percent styrene and lO percent butadiene.
Many of the styrene/butadiene resins useful in the present
invention include those commercially available from
Goodyear Chemical Company, and known as Pliolite*, such
as Pliolite S5A-E. Also embraced within the scope of
the present invention are copolymers of vinyl toluene,
with butadiene, the percentage of butadiene being present
ranging from about 80 percent to about 95 percent, with
the percentage of other monomer, (vinyl toluene) being
from about 5 percent to about 20 percent.
* trade mark
il3~6f~:
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The amount of styrene butadiene copolymer resin present in
the toner formulation ranges from about 80 percent to about 95 percent,
and preferably from about 88 percent to about 94 percent based on the
weight of toner, while the amount of colorant present ranges from between
about 5 percent to about 20 percent and preferably from about 6 percent
to about 12 percent. Thus, for example, when 85 percent of the styrene
butadiene copolymer resin is present, 15 percent of the colorant is present.
By minimum fuse temperature is meant the temperature at
which the toner is sufficiently melted, coalesced, and attached to a substrate,
such as paper, so as to withstand conventional handling, filing, smearing,
smudging, and/or loss of information, while the hot offset temperature,
is the temperature at which the toner image splits internally with some
of the toner remaining on the fuser roll. The fusing temperature
latitude is the difference between the hot offset temperature, and the
minimum fuse temperature, as reported in Example I.
Numerous suitable dyes or colorants may be employed together
with the styrene butadiene resins for formulating the toner particles, such
materials being well-known and including various types of carbon blacks,
Nigrosine dye, aniline blue, chrome yellow, ultramarine blue, duPont oil
red, phthalocyanine blue, and mixtures thereof with the preferred material
being carbon black. The colorant should be present in the toner in sufficient
quantity to render it highly colored so that it will form a visible image
on the recording member. For example, where conventional xerographic
copies of documents are desired the toner may comprise a black pigment
such as carbon black. Also a black dye such as commercially available from
National Aniline Products Inc. can be employed. Preferably the colorant
is employed in amounts of from about 5 percent to about 20 percent by
weight based on the total weight of toner.
As an additional ingredient there can be included in the toner
composition of the present invention various additives, especially materials
such as nigrosine and charge control additives, such as alkyl pyridinium
compounds of the following formula:
A~ or ~ ~ A~ 2
R R
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wherein R is an aliphatic radical such as methyl, ethyl, propyl, butyl, hexyl,
octyl, nonyl and the like, and A is an anion such as chloride, bromide, fluoride,
sulfate, sulfonate, phosphate, borate, and the like. The preferred additive
is cetyl pyridinium chloride. The purpose of the charge control additive
is to impart a positive charge to the toner resin.
The additive is present in amounts of from about 0.25 percent
to about 4 percent, and preferably from about 0.5 percent to about 3 percent.
Several methods may be employed for producing the toner of
the present invention, one such method involving melt blending the resin
and the pigment followed by mechanical attrition. Other methods including
those well-known in the art such as spray drying, melt dispersion and dis-
persion polymerization. For example a solvent dispersion of resin and colorant
are spray dryed under controlled conditions to result in the desired toner.
Such a toner produced in this manner results in a positive charged toner
in relation to the carrier materials which are present when a developer
is formulated, and these toners exhibit the improved properties as mentioned
hereinbefore.
Any suitable carrier material can be employed with the toner
of the present invention as long as such particles are capable of triboelec-
trically obtaining a charge of opposite polarity to that of the toner particles.Toner plus carrier is referred to in the art as developer. In one embodiment
in the present invention that would be a negative polarity to that of the
toner particles which are positively charged so that the toner particles
will adhere and surround the carrier particles. Accordingly, the carriers
can be selected so that the toner particles require a charge of positive
polarity and include inorganic materials, organic materials, as well as
coated carriers, including for example, sodium chloride, ammonium chloride,
ammonium potassium chloride, aluminum nitrate, granular zinc, granular
silicone, methyl methacrylate, glass, steel, nickel, iron ferrite, silicone
dioxide, and the like. Coated carriers that may be used include the above-
mentioned carriers coated for example with organic materials such as
fluorinated polymers including polyvinylidene fluoride. Many of the carriers
that can be used are described in U.S. Patents 2,618,441; 2,638,416; 3,591,503;
3,533,835 and 3,526,533. Also nickel berry carriers as described in U.S.
Patents 3,847,604 and 3,767,598 can be employed. These carriers being
nodular beads of nickel characterized by surfaces of recurring recesses
and protrusions, provide particles with a relatively large external area.
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The diameter of the coated carrier particle is from about 50 to about 1,000
microns thus allowing the carrier to possess sufficient density and inertia
to avoid adherence to the electrostatic images during the development
process.
The carrier may be employed with the toner composition in
any suitable combination, however, best results are obtained when about
1 part per toner is used and about 10 to about 200 parts per weight of carrier.
Toners of the present invention may be used to develop electro-
static latent images on any suitable electrostatic surface capable of re-
10 taining charge including conventional photoconductors, however, the
toners of the present invention are best utilized in systems wherein a neg-
ative charge resides on the photoreceptor and this usually occurs with organic
photoreceptors. Illustrative examples of such photoreceptors include poly-
vinyl carbazole, 4-dimethylamino benzylidene, benzhydrazide, 2-benzyli-
15 deneamino-carbazole, 4-dimethylamino-benzylidene, benzhydrazide, 2-
benzylidene-amino-carbazole, polyvinylcarbazole substituted materials,
(2-nitrobenzylidene~p-amino aniline, 2,4-diphenyl-quinazoline, 1,2,4-tri-
azine, 1,5diphenyl-3-methyl pyrazoline, 2-(4'-dimethyl amino phenyl~benz-
oxazole, 3-amino carbazole, polyvinyl carbazole-trinitrofluorenone charge
20 transfer complexes, phthalocyanines and mixtures thereof.
The following examples are being supplied to further define
the species of the present invention, it being noted that these examples
are intended to illustrate and not limit the scope of the present invention.
Parts and percentages are by weight unless otherwise indicated.
Minimum fix was evaluated by subjecting the image to be tested
which has a fused solid area optical density of 1.2--0.1, as measured by
a Macbeth Model RD517 optical densitometer, to ten cycles of abrasive
action on a Teledyne Tabor Abrader Model 503, using #10 wheels and a
load of 1,000 grams of weight. The abraded images were then compared
30 to standard images representing various degrees of fix to assess fix on
a letter scale from A (best) to D (worst), based on the visual comparison
of the image relative to the standard. The standard images were derived
from a survey taken with Xerox 9200 images intentionally fused to a range
of levels. Fix for the PlioliteR resins was excellent (A) while the fix for
35 the polyester resins, reference Example I, were not of high quality, (C).
Also, in the following examples, hot offset temperature was
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measured by attaching a trailing piece of white paper to the image so that
any toner offset to the fuser roll would print back on the trailing sheet
on the subsequent roII revolution. Offset was defined as the appearance
of toner anywhere on the trailing sheet.
Temperatures on the fuser roll were measured using an iron
constantan thermocouple in contact with the fusing surface and confirmed
using a Barnes infared radiometer.
Images using the toner resins of the following examples were
made using a Xerox Model DR flat plate apparatus and a steel carrier.
10 These images were then evaluated for minimum fix and hot offset on a
test fixture comprised of a 3 inch diameter internally heated silicone rubber
coated fuser roll and a 3 inch diameter TeflonR coated back up roll. The
rolls were loaded to form a nip of 0.21 inches and operated at a surface
speed of 10 inches/sec. The silicone rubber coating the fuser roll was a
15 high temperature vulcanized silicone rubber 70 mils thick.
Toner mechanical requirements for minimum fix and hot offset
are incompatible in one respect; a good toner from a fix standpoint is one
that softens rapidly with increasing temperature, and flows readily under
relatively low pressures (40 to 200 PSI (pounds per square inch) ) encounter-
20 ed in the fusing nip, while a good toner for hot offset is one that is relatively
temperature insensitive with respect to softening, and one that can support
the stresses during release from the fuser roll (7 to 70 PSI), without failing
internally and creating hot offset. Thus, the ideal toner exhibits a high
modulus at room temperature ( > 400 PSI), which decreases rapidly with
25 increasing temperature to the range of 14-140 PSI (where minimum fix
occurs), and which abruptly levels off to form a plateau region where the
modulus becomes relatively temperature insensitive. Such plateau is known
in the art as the "rubbery plateau" region and it should extend over as broad
a temperature range as possible for maximum latitude.
Another toner mechanical requirement concerns the rate of
softening of the toner from room temperature to about 130 F. While rapid
softening of the toner is desirable for low minimum fix temperatures, it
is also desirable that the toner remain rigid at temperatures below 130 F
to prevent caking during transport and storage. The temperature where
35 caking appears within a twenty four hour period is called the blocking tem-
perature and is correlated to the glass transition temperature, a well known
rheological property. It has been experimentally observed (see "The Viscosity
11 -8-
of Polymers and Their Concentrated Solutions", by G. C. Berry and T. G.
Fox in Advances in Polymer Science, Volume 5, Pages 261-357, (1968)),
that for a given glass transition temperature, polymer families exhibiting
the lowest polarity exhibit the lowest viscosity at elevated temperatures
and thus might be expected to have the lowest minimum fix temperatures.
By this criteria, styrene butadienes are excellent resins for toners because
of their low polarity relative to other toner resins, such as the styrene
methacrylate family.
One object of the present invention is to obtain a broad molecular
weight distribution to extend the fusing latitude through an extension of
the rubbery plateau. A broad molecular weight distribution can be obtained
either during polymerization or by blending two or more resins after poly-
merization. Typically, a polymer will have a molecular weight distribution
(Mw) in the range of 2-4, where Mw = weight average molecular weight
(Mn) Mn number average molecular weight.
The styrene butadiene copolymers of the present application have molecular
weight distributions in the range of 5 to 15, thereby resulting in the im-
proved toners of the present application. Better fusing behavior would
be achieved using still broader molecular weight distributions but the prep-
0 aration of such materials becomes increasingly difficult for molecular
weight distributions above about 10.
EXAMPLE I
A toner was prepared comprising 10 percent of a carbon black,
e commercially available as Raven~5250, and 90 percent of a styrene buta-
diene copolymer comprised of 90 percent styrene and 10 percent butadiene,
having a weight average molecular weight of 163,000 (MMW = 8.9), and
commercially available from Goodyear Corporation as Pliolite S5A, by
melt blending followed by mechanical attrition. Other toners were prepared
in a similar manner, and these toners were subjected to fusing experiments
using a conformable fuser roll with the following results.
f r.6
11346~X,
g
Toner Minimum Fuse Hot Offset Fusing Blocking
Temp. Temp. Temp Temp.
Pliolite* 290F > 540F > 250F 120F
S5A
10% Raven
5250
Pliolite* 300 F 455 F 155 F 120 F
S5E
10% Raven
5250
Pliolite* 300F 420F 120F 115F to
10 Vinyl 120 F
Toluene
Copolymer
10% Raven
5250
*Commercially available from Goodyear Chemical Company.
15 Comparative experiments were also accomplished with a con-
formable fuser roll using toners from different resins that is, resins other
than styrene butadiene with the following results:
Toner Minimum Fuse Hot Offset Fusing Blocking
Temp. Temp. Temp. Temp.
Latitude
20 Linear 280 p 302 F 20 F 110 F
Polyester
Resin
+10% BPL*
Branched 270 F 350 F 80 F 110-115 F
Polyester
Resin
25 +10% BPL*
Branched 290 F 265 F 75 F 105-110 F
Polyester
Resin
+10% BPL*
Styrene/ 350 F 450 F 100 F 120 F
n-butyl
30 Methacrylate
Copolymer resin
65/35, 82% carbon
Black, 9%
Polyvinylbutyral, 9%
*BPL = Black Pearls (carbon black) commercially available
EXAMPLE II
There was prepared by melt blending followed by mechanical
attrition a toner comprised of 89.5 percent of Pliolite S5E, commercially
- lo -
available from Goodyear Chemical, and containing 90 percent styrene, l0
percent butadiene; 0.5 percent nigrosine, and 10 percent of carbon black,
Raven 420, commercially available from Citgo. This toner after being sub-
jected to the minimum fix and hot offset tests in accordance with Example
I resulted in the following:
Minimum fix temperature 275 F
Hot offset temperature 415 F
Fusing latitude temperature 140 F
Blocking temperature 115 F
The quality of fix was excellent, and on a scale of from A (best)
to D (worst), the level of fix was A.
EXAMPLE III
The procedure of Example n was repeated with the exception
that the Pliolite resin used was comprised of 89 percent styrene, ll percent
15 butadiene. The toner of this example had a minimum fix temperature of
300 F, a hot offset temperature of 380 F, a fusing latitude temperature
of 105 F, and a blocking temperature of 120 F.
EXAMPLE IV
The procedure of Example II was repeated with the exception
20 that 88 percent of the Pliolite resin of Example III, was mixed with 10 percent
of the carbon black and two percent Nigrosine. The toner of this example
had a minimum fix temperature of 260F, a hot offset temperature of 375F,
and a fusing latitude temperature of U5 F.
EXAMPLE V
Each of the toner resins of Examples I-IV, l part by weight, were
mixed with 50 parts by weight of a steel carrier, resulting in developing com-
positions.
These developer compositions when used in a xerographic imaging
fixture, the Xerox Model D flat plate apparatus, produced acceptable images.
30 as defined herein.
Other modifications of the present invention will occur to those
skilled in the art upon a reading of the present invention. These are intended
to be included within the scope of this invention.
