Note: Descriptions are shown in the official language in which they were submitted.
CA 02391955 2002-05-14
WO 01/53895 PCT/IL00/00031
LIQUID TONER AND METHOD OF PRINTING USING SAME
FIELD OF THE I~1VENTION
The present invention is related to the field of electrostaographic printing
and especially
to the field of printing using liquid toner.
BACKGROUND OF THE II~TVENTION
Modern liquid toner electrostatic imaging began with the invention of a new
class of
toners referred to herein as ElectroInk~ (which is a trademark of Indigo, N.V.
of The
Netherlands). This toner is characterized by its comprising toner particles
dispersed in a Garner
liquid, where the toner particles are comprised of a core of a polymer with
fibrous extensions
extending from the core. When the toner particles are dispersed in the Garner
liquid in a low
concentration, the particles remain separate. When the toner develops.an
electrostatic image the
concentration of toner particles increases and the fibrous extensions
interlock. A large number
of patents and patent applications are directed toward this type of toner and
charge directors
which are comprised in it. These include: US Patents 4,794,651; 4,842,974;
5,047,306;
5,407,307; 5,192,638; 5,208,130; 5,225,306; 5,264,312; 5,266,435; 5,286,593;
5,300,390;
5,346,796; 5,407,771; 5,554;476; 5,655,194; 5,792,584 and 5,5923,929, PCT
Patent
publication WO/92/17823 (equivalent to US Patent application 08/203,596) and
PCT patent
application PCT~IL99/00394, the disclosures of all of which are incorporated
herein by
reference.
It has been discovered that this type of toner allows for high quality offset
printing at
high speed. However, this type of printing is described inter alia in patents
and patent
application numbers 4,678,317; 4,860,924; 4,980,259; 4,985,732; 5,028,964;
5,034,778;
5,047;808; 5,078.504; 5,117,263; 5,148.222; 5,157,238; 5,166,734; 5,208,130;
5,231,454;
5,255,058; 5,266.435; 5,268,687; 5,270,776; 5,276,492; 5,278,615; 5,280,326;
5,286.948;
5,289,238; 5,315.321; 5,335,054; 5,337,131; 5,376,491; 5,380,611; 5,426,491;
5,436,706;
5,497,222; 5,508,790; 5,527,652; 5,552,875; 5,555,185; 5,557,376; 5,558,970;
5,570,193;
5,571,645; 5,572.274; 5,585,900; 5,592,269; 5,596,396; 5,610,694; 5,636,349;
5,655,194;
5,737,666; 5,745,829; 5,749,032; 5,793,490; 5,854,960; 5,864,353; 5,900,003;
5,915,152;
5,923,929; 5,935,754 and PCT publications (now US patent applications) WO
96/29633
(08/930.249); WO 96/35182 (08/945,415); WO 96/29633 (08/894,707); WO 97/07433
(09/011,634); WO 97/39385 (09/171,396); WO 98/55901 (09/445,035) and WO
99/454,433
and PCT applications PCT/IL98/00553 and PCT/IL99/00363, the disclosures of all
of which
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CA 02391955 2002-05-14
WO 01/53895 PCT/IL00/00031
are incorporated herein by reference. Systems incorporating various ones of
these patents are
sold under the names E-Print 1000~, Omnius~, TurbostreamTM and CardpressTM.
In the course of time various methods for development of latent electrostatic
images
have been developed for liquid toner, as described in the above referenced
patents and patent
applications. In addition, the speed of printing has increased. Printing is
performed on a large
number of materials. Other operating conditions have also changed.
In general, ElectroInk comprises a polymer or polymers (usually pigmented)
which
solvate the earner liquid at some temperature above room temperature (and
preferably above
normal storage temperatures of 30-40oC) and do not solvate the earner liquid
or dissolve
substantial amounts of it below that temperature. Above the solvation
temperature the polymer
adsorbs the earner liquid and is plasticized and softened by it. At elevated
temperatures the
toner material is thus soft enough to bond with a paper substrate. In
practice, the temperature
and pressure at which transfer to paper is made is controlled so that the
transfer is complete, the
transferred toner is fixed to the paper and the image is not squashed.
PCT publication WO 92/17823 (US Patent Application 08/203,596) discloses a
toner
comprising two components in which the viscosity vs. temperature
characteristics are specified.
In particular, it was found that toner based on a mixture of polymers having a
break-point on a
semi-logarithmic plot of viscosity vs. temperature at between 3x105 and 5x106
at a temperature
of below 65oC, when in a 40% by weight of toner polymer mixed with carrier
liquid, allowed
for good transfer and fixing of the image at relatively low transfer blanket
temperatures. This
weight percentage was chosen as a standard since it represented a proportion
believed to exist
during transfer of the toner to a paper substrate.
SUMMARY OF THE INVENTION
An aspect of some preferred embodiments of the invention is concerned with
liquid
toners comprising pigmented toner particles in a carrier liquid. Preferably,
the polymer in a
40% weight to weight mixture with earner liquid, has a break point on a semi-
logarithmic
viscosity vs. temperature curve at between 3.8x103 centipoise and a value
below 5.3x105
centipoise and a temperature of below 68°C, more preferably below 6~
°C. In preferred
embodiments of the invention, the toner particle polymer is comprised of two
or more
polymers.
Preferably one of the polymers comprises a first, relatively higher viscosity
material in
an amount of between 70 and 90 percent and a second polymer having a second,
relatively
lower viscosity in an amount of between ~ and 25 percent. In some preferred
embodiments of
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WO 01/53895 CA 02391955 2002-05-14 pCT/IL00/00031
the invention, a third polymer having a relatively low viscosity is comprised
in the toner
polymer in an amount between 2 and 10 percent. In preferred embodiments of the
invention, the
third polymer is reactive with components of a substrate on which the toner is
printed.
The present inventors have found that under conditions in which the amount of
pigment
~ in the toner is increased over that in prior art (and thus thinner layers of
toner are utilized)
and/or in which the amount of liquid is reduced by removing liquid from toner
prior to its
transfer, and/or in which the speed of the process is increased and the time
available for transfer
to the paper decreased, the optimum viscosity is reduced over that of toners
of the prior art.
An aspect of some preferred embodiments of the invention relates to a toner
including a
polymer material that is reactive with a substrate on which it is printed.
In general, printing with toner materials on paper is relatively
straightforward,
especially when transfer thereto is by heat and pressure, since the toner is
forced into the paper
and forms a good bond with it.
Thus, in a preferred embodiment of the invention the polymers utilized include
a minor
proportion of a first polymer having a relatively greater reactive affinity
for the paper and a
major portion of a second polymer having substantially no reactive affinity or
a relatively
smaller reactive affinity of the paper. In preferred embodiments of the
invention, the first
polymer comprises between 2-10% of the total amount of polymer in the toner
particles. In
some preferred embodiments of the invention, the second polymer is a mixture
of polymers.
In one preferred embodiment of the invention the first polymer has an
anhydride
functionality and is compatible (forms a homogeneous mixture) with the other
toner polymers
in the particles. The anhydride functionality is believed to form a bond, at
the fixing
temperature of about 70-90oC, with the cellulose in the paper. In particular,
it is believed that
the oxygen in the anhydride bonds with hydrogen in the cellulose. Thus, under
high speed
printing conditions, the anhydride (or other material with a high affinity for
paper) provides for
adequate boding of the toner to the paper, despite the relatively shorter
times available for
transfer of the toner to the paper and for fusing it thereto.
The first polymer may be in the form of a terpolymer containing an anhydride
functionality, such as malefic anhydride terpolymer or it may, for example, be
malefic anhydride
grafted linear low density polyethylene, malefic anhydride grafted
polypropylene copolymer,
malefic anhydride grafted linear ethylene acetate polymer. Other materials
with anhydride
functionality may also be used.
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WO 01/53895 CA 02391955 2002-05-14 pCT/1L00/00031
Other minor portion polymers believed to work in a similar manner include
polymers
having an epoxy functionality. It is believed that when activated by water or
hydroxyl
functionalities in the paper, the epoxy functionality bonds with hydroxyl
functionalities in the
paper.
While the second polymer may include any polymer or mixture of polymers having
suitable viscosity, solvation and other parameters for toner, some especially
suitable first
polymer materials include, ethylene methacrylic acid copolymers and their
ionomers, ethylene
acrylic acid copolymers and their ionomers, polyamides, etc., or mixtures
thereof. It should be
understood that some of these materials may have higher or low than optimal
viscosity and that
blends of the polymers may be required to provided a desired viscosity.
There is thus provided, in accordance with a preferred embodiment of the
invention, a
liquid toner comprising:
a carrier liquid; and
toner particles dispersed in the Garner liquid, said toner particles
comprising:
a polymer blend comprising:
a first polymer comprising a minor portion of said blend and having a
relatively higher chemical reactivity with paper; and
a second polymer comprising a major portion of said blend and having a
relatively lower or null chemical reactivity with paper.
Preferably, the polymer blend has, on a semi-logarithmic viscosity vs.
temperature
cooling curve, a transition at a temperature below about 65oC, wherein at
temperatures below
the transition temperature, the rate of change of viscosity with temperature
is higher than the
rate of change at temperatures above the transition temperature.
Preferably, at the transition temperature, the viscosity is below about 10~
centipoise.
Preferably, at the transition temperature, the viscosity is below about 2x105
centipoise.
Preferably, at the transition temperature, the viscosity is above about 104
centipoise.
In a preferred embodiment of the invention the second polymer comprises at
least two
polymers.
In a preferred embodiment of the invention, the polymer blend is substantially
insoluble
in the Garner liquid and wherein at least one of the polymers solvates the
Garner liquid at an
elevated temperature.
In a preferred embodiment of the invention, the proportion of the first
polymer in the
blend is between about 2% and about 10%, preferably about 5%.
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WO 01/53895 CA 02391955 2002-05-14
PCT/IL00/00031
In a preferred embodiment of the invention, the first polymer comprises a
polymer having an
anhydride functionality. The first polymer may include, in accordance with
various preferred
embodiments of the invention, one or more of malefic anhydride terpolymer,
malefic anhydride
grafted linear low density polyethylene, malefic anhydride grafted
polypropylene copolymer,
and malefic anhydride grafted linear ethylene acetate polymer.
In preferred embodiments of the invention, the second polymer comprises one or
more
of ethylene methacrylic acid copolymer; an ionomer of ethylene methacrylic
acid copolymer,
an ester of ethylene methacrylic acid copolymer, low molecular weight ethylene
acrylic acid
copolymer, an ionomer of low molecular weight ethylene acrylic acid copolymer,
an ester of
ethylene acrylic acid copolymer, and an acid modified ethylene vinyl acetate
terpolymer.
Preferably, the toner particles comprise at least one pigment.
There is further provided, in accordance with a preferred embodiment of the
invention, a
liquid toner comprising:
a Garner liquid; and
toner particles dispersed in the carrier liquid, said toner particles
comprising:
a polymer blend comprising at least first and second distinct polymers,
wherein
the polymer blend has, on a semi-logarithmic viscosity vs. temperature cooling
curve, a
transition at a temperature below about 65°C, wherein at temperatures
below the transition
temperature, the rate of change of viscosity with temperature is higher than
the rate of change at
temperatures above the transition temperature.
In a preferred embodiment of the invention, the transition temperature, the
viscosity is
below about 10~ centipoise. Preferably, at the transition temperature, the
viscosity is below
about 2x 1 O5 centipoise.
In a preferred embodiment of the invention, at the transition temperature, the
viscosity
is above about 104 centipoise.
In a preferred embodiment of the invention, the polymer blend is substantially
insoluble
in the carrier liquid and wherein at least one of the polymers solvates the
carrier liquid at an
elevated temperature.
In a preferred embodiment of the invention, the polymer blend comprises one or
more
of ethylene methacrylic acid copolymer, an ionomer of ethylene methacrylic
acid copolymer,
an ester of ethylene methacrylic acid copolymer, low molecular weight ethylene
acrylic acid
copolymer, an ionomer of low molecular weight ethylene acrylic acid copolymer,
an ester of
ethylene acrylic acid copolymer, or an acid modified ethylene vinyl acetate
terpolymer.
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WO 01/53895 CA 02391955 2002-05-14 PCT/IL00/00031
Preferably, the toner particles comprise at least one pigment.
There is further provided, in accordance with a preferred embodiment of the
invention, a
method of printing comprising:
providing an electrostatic image; and
developing the electrostatic image with a toner in accordance with any of the
preceding
claims.
Preferably, the method includes transfernng the developed image from a surface
on
which it is developed to a final substrate.
Preferably, the final substrate contains cellulose.
In a preferred embodiment of the invention, the developed image comprises
first
transferring the image to an intermediate transfer member and then transfernng
the image
therefrom to the final substrate.
In a preferred embodiment of the invention, transferring comprises fixing the
transferred
image to the final substrate.
1 S BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be more clearly understood from the following
description of
the preferred embodiments thereof, taken together with the following drawings,
in which:
Fig. 1 shows a semi log plot of viscosity in centipoise as a function of
temperature of a
melt viscosity cooling curve of two toners, in accordance with a preferred
embodiment of the
invention; and
Fig. 2 is a schematic drawing of a liquid toner printing system utilizing a
toner in
accordance with a preferred embodiment of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
NON-LIMITING EXAMPLES OF TONERS
A first exemplary toner, in accordance with a preferred embodiment of the
invention,
can be prepared by loading 1020 grams of Nucrel 699 resin (an ethylene
methacrylic acid
copolymer by Dupont), 120 grams of AC5120 resin (an ethylene acrylic acid
copolymer by
Allied Signal) with 60 grams of Lotadar 8200 (malefic anhydride terpolymer by
Atochem) and
1800 grams of Isopar-L (Exxon) an isopparaffinic hydrocarbon fraction in a
Ross double
planetary mixer, preheated by a heating bath, set to 150oC. The ingredients
are mixed for about
1.5 hours at speed control setting 3. The speed is increased to a speed
setting of 6 for 30
minutes, the heating is stopped and the mixer is cooled with a fan while
mixing is continued.
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W~ 01/53895 CA 02391955 2002-05-14
PCT/IL00/00031
The result is a pasty material. It is noted, for the reasons given in the
summary, that the malefic
anhydride has a higher affinity for paper than do the other polymers.
836.30 grams of the pasty material are loaded into a 1S attritor (Union
Process) with
3/16" chrome steel grinding media, together with 67.07 grams of Helliogen Blue
pigment 7080
(BASF), 7.45 grams of Helliogen Green pigment (BASF), 4.14 grams of aluminum
stearate
(Riedel de Haen) and 1384.07 grams of Isopar L. The material is ground at
40°C for 20 hours.
The result is discharged from the attritor and mixed with an amount of Isopar
L to form a
working dispersion. The toner is charged utilizing a charge director,
preferably a charge
director described in the above referenced US patent 5,346,796 and containing
30 parts by
weight lecithin, 30 parts by weight Basic Barium Petronate (BBP) and 6 parts
by weight
isopropylamine dodecylbenzesulfonate (ICI G3300B) as a stabilizer. The charge
director,
dissolved in Isopar-L is added in an amount of about 30-40 mg of solids of the
charge director
per gram of toner solids. A small amount of Marcol 82, such as 2% of the
earner liquid, may be
added to carrier liquid to form a mixed earner liquid, as described in the
above references.
The result is a cyan toner having a relatively high pigment concentration.
A second exemplary toner, in accordance with a preferred embodiment of the
invention,
can be prepared by loading 960 grams of Nucrel 699 resin (an ethylene
methacrylic acid
copolymer by Dupont), 240 grams of AC5120 resin (an ethylene acrylic acid
copolymer by
Allied Signal) 1800 grams of Isopar-L (Exxon) in a Ross double planetary
mixer, preheated by
a heating bath, set to 150oC. The ingredients are mixed for about 1.5 hours at
speed control
setting 3. The speed is increased to a speed setting of 6 for 30 minutes, the
heating is stopped
and the mixer is cooled with a fan while mixing is continued. The result is a
pasty material.
971.75 grams of the pasty material are loaded into a 1 S attritor (Union
Process) with
3/16" chrome steel grinding media, together with 55.66 grams of Helliogen Blue
pigment 7080
(BASF), 4.14 grams of Helliogen Green pigment (BASF), and 11.5 grams of
aluminum stearate
(Riedel de Haen) and 1257 grams of Isopar L. The material is ground at
58°C for about 1.5
hours, followed by continued grinding at 45oC for I0.5 hours. The result is
discharged from the
attritor and mixed with an amount of Isopar L to form a working dispersion at
about 2% solids.
The toner is charged utilizing a charge director, preferably a charge director
described in the
above referenced US patent 5,346,796 and containing 30 parts by weight
lecithin, 30 parts by
weight BBP and 15 parts by weight 63300 as a stabilizer. The charge director,
dissolved in
Isopar-L is added in an amount of about 30-40 mg of solids of the charge
director per gram of
toner solids.
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WO 01/53895 PCT/IL00/00031
The result is a cyan toner having a relatively high voltage stability, for use
in high speed
printing. For black toner an additional 2.5 mg/gm of stabilizer is added.
Fig. 1 shows viscosity as a function of temperature (cooling curves) for the
polymer
materials used in the two toners. Curve 1, is for the polymer material in the
first exemplary
toner and curve 2 is for the polymer materials in the second exemplary toner.
It is seen that
these materials have a break-point at about 45oC and 1.05x104 centipoise and
at about SSoC
and 104 centipoise, respectively, when mixed with Isopar-L in a 40% w/w
concentration.
In general, while, in the past toners with a higher viscosity at these
standard conditions
was desirable, the lower viscosity toners, as described herein, work well in
environments in
which the solids concentration is higher at transfer to the paper (for example
due to increased
evaporation of carrier liquid) or in which the time allotted for transfer is
greatly reduced.
It will be further understood that many variations of the toners according to
the
invention are possible and the toners that are defined by the claims may be
produced using a
wide variety of polymers. In particular, other ethylene methacrylic acid
copolymers and
ionomers and esters of ethylene methacrylic acid copolymers of various
molecular weights may
be used in place of Nucrel 699. In some preferred embodiments of the invention
low molecular
weight ethylene acrylic acid copolymers and/or their ionomers and esters
and/or other
terpolymers such as an acid modified ethylene vinyl acetate terpolymer (ELVAX)
may be
substituted for the specific AC 5120 resin indicated above. In some preferred
embodiments of
the invention the polymer having a relatively greater reactive affinity for
cellulose can be any
suitable polymer having an anhydride or epoxy functionality or other polymer
that strongly
bonds chemically to paper, preferably to hydrogen or to hydroxyl
functionalities of the
cellulose. Examples of materials with anhydride functionalities believed to be
suitable for use
in the present invention include a terpolymer containing an anhydride
functionality, malefic
anhydride grafted linear low density polyethylene, malefic anhydride grafted
polypropylene
copolymer, and malefic anhydride grafted linear ethylene acetate polymer.
Figure 2 shows a high speed printer for which the first exemplary toner is
designed.
This system is described in detail in PCT application PCT/IL98/00553. The
reader is referred to
that application for more details on the operation of the printer.
Printer 200 of Fig. 2, utilizes a single photoreceptor 102 and a single
intermediate
transfer member (ITM) 110. However, situated about photoreceptor 102 are a
plurality of
developers 108. Each developer develops an electrostatic image on
photoreceptor 102 with a
different color image. The images are transferred seriatim to an intermediate
transfer member
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WO 01/53895 PCT/IL00/00031
110. In a preferred embodiment of the invention, a sheet 48 on an impression
roller 42 rotates
once for each color and the different color images are transferred to the
sheet seriatim.
Preferably, photoreceptor 102 is large enough so that a plurality or all of
the individual color
images are developed during a single rotation of photoreceptor 102.
Alternatively, the images
are transferred seriatim to the intermediate transfer member and then
transferred together to the
sheet. In this type of one-shot transfer, the sheet travels at the process
speed, but is printed on
only once. The developer (which is preferably of the type described in WO
93/01531 or in WO
95/10801 ) and other components of the printing engine are described with
reference to Figs. 11
13 of the '553 application. Other printing engines, as for example those shown
in Figs. 2-5 of
the '553 application can also be used.
In the embodiment for which the first exemplary toner was described, the
process speed
is 122 cm/sec and the surface temperature of the intermediate transfer member
is between. 95
and 100°C. A fan optionally blows air on the image on the ITM to
increase the solids
concentration prior to transfer from the ITM. In order to assure good transfer
from the
1 ~ intermediate transfer member in the approximately 1 cm nip between the ITM
and the
impression roller the an exemplary pressure of about 6.4 kg/cm2 is applied. In
addition, to
assure transfer of the toner to the intermediate transfer member an exemplary
transfer voltage of
about 650 Volts is used.
The second exemplary toner is useful in conjunction with more conventional
systems as
described in the above referenced patents and applications, in which a same
conventional roller
developer is used for developing all of the separations and a low toner
particle concentration
liquid toner (such as 2%) is introduced in the space beriveen the developer
roller and the . In
this system, the process speed is about 61 cm/sec and the pressure is about 5
kg/cm2. The
transfer voltage is about 650 Volts. The interested reader is directed to
these publications for
further details.
It will be understood that, in view of the results presented herein and in WO
92/17823
(USSN 08/203,597), breakpoints in the standard cooling curve for useful toner
polymers , may
vary, depending on the printing conditions, occurring between 104 (or less)
centipoise to above
107 centipoise. Preferably, of course, the temperature is below 65°C,
more preferably 60°C or
below.
It will be understood that the particular materials and proportions of
materials are
provided for exemplary purposes only. As is well known in the art, the
proportions,
temperatures, mixing times and grinding times as well as the choice of charge
director can be
9
WO ~l/53895 CA 02391955 2002-05-14 pCT/IL00/~~031
varied substantially in the production of liquid toner. Furthermore, while a
number of different
embodiments have been shown, details of one embodiment of the invention may,
where
applicable, in other embodiments of the invention. Similarly, some details
shown in the
embodiments, while preferred, are not essential and some preferred embodiments
of the
~ invention may omit them.
As used herein, the terms "have", "include" and "comprise" or their
conjugates, as used
herein mean "including but not limited to".
