U.S. patent application number 09/968206 was filed with the patent office on 2002-03-21 for two component dispersant for wet milling process.
Invention is credited to Hertler, Walter Raymond, Ma, Sheau-Hwa.
Application Number | 20020035173 09/968206 |
Document ID | / |
Family ID | 24735921 |
Filed Date | 2002-03-21 |
United States Patent
Application |
20020035173 |
Kind Code |
A1 |
Ma, Sheau-Hwa ; et
al. |
March 21, 2002 |
Two component dispersant for wet milling process
Abstract
A process for preparing an aqueous dispersion by wet milling an
aqueous carrier medium, a particulate solid, and a polymeric
dispersant; wherein the polymeric dispersant is a combination of at
least 50% by weight of a block copolymer; and a random copolymer;
and wherein the block and random copolymers are prepared from
substantially the same monomers. This invention provides an easy
dispersion process for particulate solids, in particular colorants
such as pigments or disperse dyes, at higher loadings, and a
reduction of dispersion time which improves the productivity.
Resulting dispersions have particular utility as inks for ink-jet
printers.
Inventors: |
Ma, Sheau-Hwa; (Chadds Ford,
PA) ; Hertler, Walter Raymond; (Kennett Square,
PA) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY
LEGAL DEPARTMENT - PATENTS
1007 MARKET STREET
WILMINGTON
DE
19898
US
|
Family ID: |
24735921 |
Appl. No.: |
09/968206 |
Filed: |
October 1, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09968206 |
Oct 1, 2001 |
|
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|
08681586 |
Jul 29, 1996 |
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Current U.S.
Class: |
523/160 ;
523/161 |
Current CPC
Class: |
C08L 2666/02 20130101;
C08L 53/00 20130101; C09B 67/009 20130101; C09D 17/001 20130101;
C08L 53/00 20130101; C09D 11/326 20130101; C09B 67/0022
20130101 |
Class at
Publication: |
523/160 ;
523/161 |
International
Class: |
C03C 017/00; C09D
005/00 |
Claims
What is claimed is:
1. A process for preparing an aqueous dispersion comprising wet
milling an aqueous carrier medium, a particulate solid, and a
polymeric dispersant consisting essentially of a mixture of at
least one block copolymer and at least one random copolymer
wherein: (i) the block and random copolymers are prepared from
substantially the same monomers; and (ii) the random copolymer is
present in the amount of 1 to 100 parts by weight per 100 parts by
weight of the block copolymer.
2. The process of claim 1 wherein the copolymers have a number
average molecular weight less than 20,000.
3. The process of claim 2 wherein the block copolymer is selected
from the group consisting of AB, BAB, and ABC polymers.
4. The process of claim 3 wherein the particulate solid is a
colorant and the aqueous carrier medium comprises water and at
least one water soluble organic component.
5. The process of claim 4 wherein the wet milling is accomplished
in a media mill.
6. The process of claim 4 wherein the wet milling is accomplished
by passing the aqueous carrier medium, particulate solid and the
polymeric dispersant through a plurality of nozzles within a liquid
jet interaction chamber under a liquid pressure of at least 1000
psi.
7. An aqueous dispersion containing an aqueous carrier medium, a
particulate solid, and a polymeric dispersant consisting of a
mixture of at least one block copolymer and at least one random
copolymer wherein: (i) the block and random copolymers are prepared
from substantially the same monomers; and (ii) the random copolymer
is present in the amount of 1 to 100 parts by weight per 100 parts
by weight of the block copolymer.
8. The dispersion of claim 7 wherein the copolymers have a number
average molecular weight less than 20,000.
9. The dispersion of claim 8 wherein the block copolymer is
selected from the group consisting of AB, BAB, and ABC
polymers.
10. The dispersion of claim 9 wherein the particulate solid is a
colorant and the aqueous carrier medium comprises water and at
least one water soluble organic component.
11. The dispersion of claim 10 wherein the copolymers have a number
average molecular weight less than 20,000.
12. The dispersion of claim 11 particularly adapted for use as an
ink for ink-jet printers.
13. An ink particularly adapted for use with an ink-jet printer,
said ink consisting essentially of: (a) approximately 25 to 99.8%
of an aqueous carrier medium comprising water and at least one
water soluble organic component; (b) approximately 10 to 60% of a
particulate colorant having a particle size less than 15 microns;
and (c) approximately 0.1 to 30% of a polymeric dispersant
consisting of a mixture of at least one AB, BAB, or ABC block
copolymer and at least one random copolymer wherein: (i) the block
and random copolymers are prepared from substantially the same
monomers; and (ii) the random copolymer is present in the amount of
1 to 100 parts by weight per 100 parts by weight of the block
copolymer; wherein said percentages of components (a), (b) and (c)
are of the total ink composition.
14. The ink of claim 13 wherein the copolymers have a number
average molecular weight less than 20,000.
15. The ink of claim 13 wherein component (c) is present in the
amount of 0.1 to 15% by weight, has a number average molecular
weight below 10,000, and the ratio of block copolymer to random
copolymer in the range of 100 to 1 parts block copolymer per 1 part
random copolymer, by weight.
16. The ink of claim 15 wherein component (a) is present in the
amount of 70 to 96% and contains a water-soluble organic
solvent.
17. The ink of claim 15 wherein said block copolymer and random
copolymer are anionic.
18. The ink of claim 15 wherein said block copolymer and random
copolymer are cationic.
Description
FIELD OF THE INVENTION
[0001] This invention relates to an improved wet milling dispersion
process using a unique combination of a block copolymer and a
random copolymer of similar composition as the dispersant. The
process provides higher loading of particulate solids, with smaller
particle size and shorter processing times. The dispersions are
particularly suited for preparing pigmented inks for ink-jet
printers.
BACKGROUND OF THE INVENTION
[0002] Water-based pigment dispersions are well known in the art,
and have been used commercially for applying films, such as paints,
to various substrates. The pigment dispersions generally are
prepared by a dry method, such as 2-roll or 3-roll milling, or a
wet method, such as media milling. The dry milling method includes
a milling step wherein the dispersant and the pigment are
intimately mixed and milled utilizing mechanical forces to cause
particle size reduction and adsorption of the polymer to the
pigment surface; a grinding step wherein the pigment dispersion is
reduced to small chips; and an inversion step where the chips are
dissolved in an aqueous carrier medium. In the wet milling method,
particle size reduction and dispersion stabilization are conducted
in one step in the presence of the aqueous carrier medium.
[0003] The dispersant used in a wet milling process must
effectively wet the pigment surface and achieve a stable pigment
dispersion. Random copolymer dispersants have been disclosed for
this purpose, wherein the resulting aqueous dispersion is used as
an ink-jet printer ink, in U.S. Pat. No. 4,597,794 (Ohta et al.)
assigned to Canon. Block copolymer dispersants, having a
hydrophobic block that links to the pigment particles and a
hydrophilic block, also are disclosed for this purpose in U.S. Pat.
No. 5,085,698 (Ma et al.) assigned to DuPont.
[0004] Block copolymer dispersants offer improved dispersion
stability (compared to random polymer dispersants) because they
provide both a charge double layer and steric stabilization. The
block copolymers are difficult to manufacture, however, and tend to
form stable micelles in the dispersion due to their structure.
These micelles, with the hydrophobic pigment-binding segments
buried in the core, do not wet the pigment surface as effectively
as may be desired. Also, the block copolymers tend to have a high
viscosity, which hinders the milling process and requires a
reduction in pigment loading for successful milling to occur.
[0005] Surfactants may be added to facilitate pigment wetting and
to reduce dispersion viscosity, thereby addressing the problems
discussed above. The addition of surfactants, however, tends to
change other physical properties of the dispersion (such as surface
tension), and may render the dispersion unsuitable for a desired
application. For example, the surfactant may adversely affect
dispersion stability; and/or, when the resulting dispersion is used
as an ink, the ink tends to have a low surface tension that causes
image feathering and general poor print quality.
[0006] Accordingly, a need continues for an improved dispersion
process for preparing aqueous dispersions in general, and in
particular for preparing aqueous pigmented inks that are
particularly suited for use in ink-jet printers and contain
high-loading levels of small pigment particles.
SUMMARY OF THE INVENTION
[0007] It now has been found that the presence of certain random
polymers in aqueous particulate dispersions having a block
copolymer dispersant enhance wetting of the particles, and enable
the particulate loading to be increased without adversely affecting
physical properties such as surface tension. Accordingly, in one
aspect the invention provides a dispersion having an aqueous
carrier medium, at least one particulate solid, and a polymeric
dispersant that is a mixture of a block copolymer and a random
copolymer, wherein (i) the block and random copolymers are prepared
from substantially the same monomers; and (ii) the random copolymer
is present in the amount of 1 to 100 parts by weight per 100 parts,
by weight, of the block copolymer.
[0008] In another aspect, the invention provides a process for
preparing an aqueous dispersion by wet milling an aqueous carrier
medium, at least one particulate solid, and a polymeric dispersant
that is a mixture of a block copolymer and a random copolymer,
wherein (i) the block and random copolymers are prepared from
substantially the same monomers; and (ii) the random copolymer is
present in the amount of 1 to 100 parts by weight per 100 parts, by
weight, of the block copolymer. The process achieves high loadings
of the particulate solid (e.g., a pigment or disperse dye) during a
short time, which improves productivity.
DETAILED DESCRIPTION OF THE INVENTION
[0009] The invention provides a unique mixture of a block copolymer
to provide the dispersion stability, and a random copolymer of
substantially the same composition to enhance the wetting of the
surface of the particulate solid. This unique mixture of
dispersants allows a higher loading of particulate solid for higher
productivity, without adversely affecting the physical properties
of the dispersion such as surface tension. For example, the
resulting dispersion may contain up to 50% or 60% dispersed solids,
based on total weight of the dispersion. This loading of
particulate solids is up to twice the amount that can be achieved
when the block dispersants are used alone. Resulting pigment
dispersions are particularly suited for use with ink jet printers
in general, and thermal ink jet printers in particular.
Aoueous Carrier Medium
[0010] The aqueous carrier medium is water or a mixture of water or
at least one water soluble organic component. Deionized water is
commonly used. The organic component may be an organic solvent,
polymeric binder, thickener, thixotropic agent, coating aid,
etc.
[0011] For ink jet inks, the aqueous carrier medium is typically a
mixture of water and at least one water-soluble organic solvent.
Representative examples of water-soluble organic solvents are
disclosed in U.S. Pat. No. 5,085,698. Selection of a suitable
mixture of water and water soluble organic solvent depends upon
requirements of the specific application, such as desired surface
tension and viscosity, the selected pigment, desired drying time,
and the type of media substrate onto which the coating or ink will
be printed. A mixture of diethylene glycol and deionized water is
preferred as the aqueous carrier medium for ink jet inks, with the
composition typically containing between 30% and 95% (preferably
60% to 95%) water by weight, based on the total weight of the
mixture.
[0012] The amount of aqueous carrier medium in the ink is in the
range of approximately 70 to 99.8%, preferably at least 94%, based
on the total weight of the ink when the particulate solid is an
organic pigment, and approximately 25 to 99.8% when the particulate
solid is an inorganic pigment.
Particulate Solids
[0013] The particulate solid may be an insoluble colorant (such as
a pigment or disperse dye), colloidal silver halide, metallic
flake, a herbicide, an insecticide, or biomaterials (such as drugs)
depending upon the particular application of the dispersion. For
example, if the intended use is in an ink or a paint, the
particulate solid is an aqueous carrier medium insoluble colorant
such as a pigment, disperse dye, or a mixture thereof.
[0014] The particulate solid selected must be capable of binding
with the hydrophobic portion of the block copolymer. Preferably,
the particulate solids have "binding sites" that permit binding
with the polymer. Most of the above-mentioned particulate solids
have very specific functional groups on their surfaces.
[0015] For example, all carbon blacks have chemisorbed oxygen
complexes, primarily acidic in nature (e.g. carboxylic, quinonic,
lactonic or phenolic groups) on their surfaces to varying degrees,
depending on the conditions of manufacture. These acidic groups
provide binding sites for dispersants having basic functional
groups, such as amine groups. Other pigments have basic surfaces.
The pigment itself may contain functional groups, or the surfaces
may be modified by compounds containing functional groups such as
sulfonic acid, phosphoric acid, and carboxylic acid groups or
amine-type of basic groups. All are equally useful for this
invention. Furthermore, almost all of the organic color pigments
and many of the surface treatment compounds have aromatic features
in their structures, providing sites for additional aromatic
interactions with the dispersant. Examples of pigments that may be
used to form the composition include azo, anthraquinone,
thioindigo, oxazine, quinacridone, lakes and toners of acidic or
basic dye stuffs, copper phthalocyanine and its derivatives, and
various mixtures and modifications thereof.
[0016] The particle size has an influence on the dispersion
stability. Brownian motion of minute particles helps prevent
flocculation and settling. The particle size thus should be
selected to optimize the stability of the dispersion, consistent
with the other requirements of the intended application for the
dispersion.
[0017] For example, in ink jet ink applications, the pigment
particles need to be sufficiently small to permit free flow of the
ink through the ink jet printing device, especially at the ejecting
nozzles that usually have a diameter in the range of 10 to 50
microns. In addition, it also is desirable to use small particles
for maximum color strength and gloss. The useful range of particle
size is approximately 0.005 micron to 15 micron. Preferably, the
pigment particle size should range from 0.005 to 1 micron.
[0018] Also in the case of pigments, the selected pigment may be
used in dry or wet form. For example, pigments are usually
manufactured in aqueous media and the resulting pigment is obtained
as water-wet presscake. In presscake form, the pigment is not
aggregated to the extent that it is in dry form. Thus, pigments in
water-wet presscake form do not require as much deaggregation in
the process of preparing the inks as dry pigments. Representative
commercial dry and presscake pigments that may be selected to
advantage are disclosed in the aforementioned U.S. Pat. No.
5,085,698.
[0019] Fine particles of metal or metal oxides (such as copper,
iron, steel, aluminum, silica, alumina, titania, and the like) may
be used in the preparation of magnetic ink jet inks and other
coating applications for the electronic industries.
Dispersants
[0020] A mixture of at least one block copolymer and at least one
random copolymer is used as the dispersant to effectively wet the
surface of the particulate solid and to stabilize the
dispersion.
Block Copolymer
[0021] The block copolymers suitable for practicing the invention
include AB, BAB, and ABC structures. They may be anionic, cationic
or non-ionic. These block copolymers must contain hydrophobic and
hydrophilic blocks and balanced block sizes to contribute to the
dispersion stability. Functional groups can be built into the
hydrophobic (pigment binding) block for stronger specific
interactions between the pigment and the polymer dispersant to
provide improved dispersion stability. Preferred AB and BAB block
copolymers, and their process of preparation, are disclosed in U.S.
Pat. Nos. 5,085,698 and 5,272,201. ABC block copolymers, and their
methods of preparation, are disclosed in U.S. Pat. No. 5,219,945
and European Patent Application 0 556 649 A1 published Aug. 28,
1993.
[0022] In ABC block copolymers, the B block is a hydrophobic
homopolymer or random copolymer that serves to bind with the
pigment. The A block is a hydrophilic homopolymer or random
copolymer or salt thereof, which S is solvated by the aqueous
carrier medium and serves to stabilize the dispersion by steric
and/or double charge layer mechanisms. The C block is commonly an
alkylated poly(oxyethylene) substituted (meth)acrylate that is
compatible with common organic water-miscible solvents. The C block
provides additional dispersion stability.
[0023] The preferred structure of the C block monomer is:
CH.sub.2:CRC(O)O(CH.sub.2CH.sub.2O).sub.nR.sub.1
[0024] wherein R=--H or --CH.sub.3; R.sub.1=CaH.sub.2a+1 where
a=0-4; n=1-20. Examples of these monomers are ethoxyethyl
methacrylate, butoxyethyl methacrylate, and
ethoxypolyethyleneglycol methacrylate (polyoxyethylene of
MW=44-1000).
[0025] The block copolymer is present in at least 50% by weight,
preferably 50 to 98% by weight, and more preferably 75 to 98% by
weight, based on the total weight of the polymeric dispersant
combination of block copolymer and random copolymer.
Random Copolymer
[0026] The random copolymer is prepared using substantially the
same monomers as those used in preparation of the block copolymers,
and should have substantially the same or similar composition as
the block copolymer. This means either exactly the same set of
monomers or structurally related monomer sets should be used, and
about the same percentage per each type of monomers. The ionic
character, (anionic, cationic or nonionic) accordingly will be
compatible with that of the block copolymer to avoid flocculation.
Furthermore, it is preferred that the molecular weight of the
random copolymer be close to that of the block copolymer.
[0027] The random copolymers may be prepared by any of a number of
polymerization methods well known in the art. It is preferred that
monomers containing the free acids or free amines of the ionic
moieties be polymerized, and the moieties then converted to their
salt form after the polymer structure is formed. Exemplary
polymerization methods include free radical solution, emulsion,
suspension, bulk polymerization and the like (using a chain
transfer agent, if necessary). Other polymerization methods include
anionic and group transfer polymerization as described in U.S. Pat.
No. 4,508,880. Polymers so prepared have precisely controlled
molecular weight and very narrow molecular weight distribution.
[0028] The random copolymer is present in the range of
approximately 0.5 to 50% by weight, preferably 2 to 25%, based on
the total weight of the polymeric dispersant combination of block
copolymer and random copolymer.
[0029] Suitable anionic polymers have a backbone prepared from
ethylenically unsaturated units and at least one, and preferably
more than three, pendant ionic moieties derived from an anionic
unit on the monomer and having the general formula:
--CO.sub.2Z or --SO.sub.3Z
[0030] wherein Z is selected from conjugate acids of organic bases,
alkali metal ions, ammonium ion, and tetraalkylammonium ions. The
number of pendant ionic moieties should be sufficient to make the
anionic polymers soluble in the aqueous carrier medium and will
vary depending on the molecular weight. For the block copolymers,
these pendant ionic moieties are mostly concentrated in the
hydrophilic block.
[0031] Suitable cationic polymers have a backbone prepared from
ethylenically unsaturated units and at least one, and preferably
more than three, pendant ionic moieties derived from a cationic
unit on the monomer and having of the general formula: 1
[0032] wherein A is N, P, or S; R.sub.1, R.sub.2 and R.sub.3
independently are H, alkyl of 1 to 20 carbon atoms, alkyl ether of
1 to 20 carbon atoms, or aryl of 1 to 9 carbon atoms, or alkylaryl
of 1 to 9 carbon atoms, with the proviso that R.sub.3 is not
present when A is S; and wherein X is an anion selected from the
group consisting of halides, conjugate bases of organic acids, and
conjugate bases of inorganic acids. The cationic polymers
containing phosphonium and sulfonium moieties preferably are made
by reacting a halogenated copolymer (e.g., polymer containing
2-bromoethyl methacrylate) with tri-substituted phosphines (e.g.,
triphenylphosphine) or di-substituted sulfides (e.g.,
dimethylsulfide). The number of pendant ionic moieties should be
sufficient to make the cationic polymer soluble in the aqueous
carrier medium and will vary depending on the molecular weight of
the polymer. For the block copolymers, these pendant ionic moieties
are mostly concentrated in the hydrophilic block.
[0033] Strong interaction of a pigment with a dispersant polymer is
obtained when the dispersant has one or more attached structures
which are the same as the pigment. A common way that this may be
accomplished is through general hydrophobic attraction between the
polymer and the pigment surface. The pigment often is pretreated
with substances that render the surface hydrophobic. A polymer with
hydrophobic sites can bind to such a surface through hydrophobic
interactions.
[0034] A second way in which a dispersant polymer can bind to a
solid particulate is through aromatic interactions. If the solid
particulate contains aromatic or aromatic-like groups, or if its
surface has been pretreated with an aromatic substance, then the
aromatic groups in the hydrophobic site can further improve the
binding force to the solid particulate.
[0035] A third way in which a dispersant polymer can bind to a
solid particulate is through ionic bonds. For example, a solid
particulate containing sulfonic acid groups can bind strongly to a
polymer having basic groups, such as amine groups. Similarly, a
pigment containing quaternary ammonium groups can bind to a polymer
through acid groups.
[0036] Covalent bonding provides a fourth, and especially strong,
mode of binding a dispersant polymer to a solid particulate. For
example, a solid particulate with carboxylic groups will react with
a polymer containing epoxy groups to form ester linkages. Thus, a
polymer containing glycidyl methacrylate groups in the hydrophobic
site will form strong links to a carboxylic acid-containing solid
particulate.
[0037] The amount of the dispersant selected depends on the
structure, molecular weight, and other properties of the polymers,
and upon the pigment type and other components in the pigment
dispersion. The dispersant polymers (i.e., both the block and
random copolymer components) have a number average molecular weight
below 20,000, preferably below 10,000, and typically in the range
of 1,500 to 6,000. The polymeric dispersant mixture of block and
random copolymers is present in the range of approximately 0.1 to
30% by weight, preferably 0.1 to 15%, based on the total weight of
the pigment dispersion composition. If the amount of the dispersant
polymers becomes too large, the viscosity will increase and hinder
the dispersion process. If too little is present, the dispersion
stability is adversely affected. The ratio of block copolymer to
random copolymer is in the range of 100 to 1 by weight block
copolymer per part random copolymer, preferably 50 to 2.5 parts
block copolymer per part random copolymer, based on the weight. The
optimal ratio depends on the specific block copolymer and random
copolymer that is selected.
Dispersion Process
[0038] The dispersion process is a wet milling process. Wet milling
means the entire process of deflocculation, size reduction of the
particulate solid, and stabilization of the dispersion is carried
out in the presence of an aqueous carrier medium. Usually, the
selected block and random copolymers are first
neutralized/dissolved in the aqueous carrier medium to prepare a
polymer solution at about 10 to 25% solids. The block and random
copolymer solutions may be prepared separately and combined before
use, or a solution of both polymers can be prepared directly. The
selected particulate solid is added to the polymer solution,
preferably with agitation to prepare a premix.
[0039] The deflocculating (i.e., dispersing) step may be
accomplished using a conventional media mill with a wide range of
media including pebbles, stainless steel beads, glass beads,
zirconium beads, plastic particles such as polycarbonate, etc. The
type and size of the media selected is determined by the properties
of the particulate solid (e.g. the hardness, ease of fracturing the
agglomerates), and the desired particle size for the intended use.
The conventional mills (including the horizontal mill, ball mill,
or attritor) operate mechanically by agitating the media to produce
collision and shearing forces among the media. The particulate
solid is ground by the media, with new surfaces being generated as
the size of the particles are reduced. The dispersant polymers are
adsorbed onto these newly generated surfaces, preventing the
particles from flocculating together, and thereby stabilizing the
dispersion. Alternatively, this step may be accomplished without
using media by passing the premix through a plurality of nozzles
within a liquid jet interaction chamber, under a liquid pressure of
at least 1000 psi, to produce the required collision and shearing
forces among the particles to achieve particle size reduction and
adherance of the polymeric dispersant onto the newly generated
surfaces. Commercial units of this type are available from
Microfluidics Corp., Watham, Mass.
[0040] Loading of the particulate solid may be as high as 60%, but
will generally be in the range of approximately 10 to 50% by
weight, based on the total weight of the dispersion. The loading
for an inorganic pigment, having a specific gravity higher than the
typical organic pigments, may be as high as 75% by weight based on
the total weight of the dispersion. Optimal loading of the selected
particulate solid for the desired application, and the optimal
ratio of the particulate solid to the polymer, is determined by the
viscosity of the dispersion and is determined by routine
experimentation.
Additives
[0041] Depending on the the specific application, various types of
additives can be used to modify the properties of these
dispersions. Examples include organic cosolvents, coalescing
agents, polymeric binders, thickeners, thixotropic agents,
surfactants, coating aids, biocides, sequestering agents, and the
like.
[0042] For ink jet ink applications, anionic, cationic, nonionic,
or amphoteric surfactants may be present in the amount of 0.01 to
5%, and preferably 0.2 to 2%, based on the total weight of the ink.
Biocides such as Dowicides.RTM. (Dow Chemical, Midland, Mich.),
Nuosept.RTM. (Huls America, Inc., Piscataway, N.J.), Omidines (Olin
Corp., Cheshire, Conn.), Nopcocide.RTM. (Henkel Corp., Ambler,
Pa.), Troysans.RTM. (Troy Chemical Corp., Newark, N.J.), and sodium
benzoate; sequestering agents such as EDTA; and other known
additives, such as humectants, viscosity modifiers and other
polymers may also be added to improve various properties of the ink
compositions.
[0043] In a preferred embodiment, the dispersion is employed as an
ink for ink jet ink printers. The preferred formulation for this
application is:
[0044] (a) aqueous carrier medium: approximately 70% to 96%,
preferably 80% to 96%, based on total weight of the ink when an
organic pigment is selected; approximately 25% to 96%, preferably
70% to 96%, when an inorganic pigment is selected;
[0045] (b) pigments: up to approximately 30% pigment by weight for
organic pigments, but generally in the range of approximately 0.1
to 15%, preferably 0.1 to 8%, by weight of the total ink
composition; with inorganic pigments (which have higher specific
gravities), higher concentrations are employed, and may be as high
as 75% in some cases;
[0046] (c) dispersant polymer combination: approximately 0.1 to 30%
preferably 0.1 to 8%, by weight of the total ink composition.
[0047] Many ink performance features such as the drop velocity,
separation length of the droplets, drop size, and stream stability
are greatly affected by the surface tension and the viscosity of
the ink. Pigmented ink jet inks suitable for use with ink jet
printing systems typically have a surface tension in the range of
about 20 to 70 dyne/cm, preferably 30 to 70 dyne/cm, at 20.degree.
C. Acceptable viscosities are no greater than 20 cP, and preferably
in the range of about 1.0 cP to about 10 cP, at 20.degree. C.
[0048] The invention will now be further illustrated, but not
limited, by the following examples.
EXAMPLES
[0049] The random and block copolymers were prepared using the
following procedures:
[0050] A double slash in the copolymer name indicates a separation
between the blocks and a single slash indicates a random copolymer.
The values recited in parenthesis represent the degree of
polymerization for each monomer.
[0051] Preparation I: Random copolymer,
poly(ethoxytriethyleneglycol methacrylate-co-benzyl
methacrylate-co-methacrylic acid), ETEGMA/BzMA/MAA, (4/15/12)
[0052] To a solution of 58.6 g (0.253 mol) of
1,1-bis(trimethylsiloxy)-2-m- ethyl-propene and 2.5 g of tetrabutyl
ammonium m-chlorobenzoate (1.0M solution in acetonitrile) in 1120 g
tetrahydrofuran (dried by passing it through a column of alumina)
was slowly added a mixture of 478.8 g (3.03 mol) trimethylsilyl
methacrylate, 666.4 g (3.78 mol) of benzyl methacrylate (dried over
molecular sieves), and 251.4 g (1.02 mol) of
ethoxytriethyleneglycol methacrylate (dried over molecular sieves),
in 50 minutes, under nitrogen atmosphere. The temperature rose from
25.4.degree. C. to 73.5.degree. C. during the course of the
addition. The mixture was stirred overnight. It was quenched with
250 g of methanol. The mixture was distilled until 1410 g of
volatiles were collected and 1440 g of 2-pyrrolidone were added to
yield 2857 g of a 42% polymer solution.
[0053] The random polymer was neutralized using the following
procedure: 476.2 g of the polymer were mixed with 59.6 g of
potassium hydroxide solution (46.4% in deionized water) and 1464.2
g of deionized water until a homogeneous 10 polymer solution was
obtained.
[0054] Preparation II: Block copolymer, poly(methacrylic
acid-b-benzyl methacrylate-b-ethoxytriethylene glycol
methacrylate), MAA//BzMA//ETEGMA (12//15//4) To a solution of 146.5
g (0.63 mol) of 1,1-bis(trimethylsiloxy)-2-methyl-1-propene and 3.5
g of tetrabutyl ammonium m-chlorobenzoate (1.0 M solution in
acetonitrile) in 3000 g THF was slowly added, 1197.3 g (7.58 mol)
of trimethylsilyl methacrylate, in 25 minutes, under nitrogen
atmosphere. The temperature rose from 22.3.degree. C. to
51.1.degree. C. during the course of the addition. When the
temperature fell to 41.0.degree. C., 70 minutes later, 0.5 mL of
tetrabutyl ammonium m-chlorobenzoate was added and no exotherm was
detected. To the reaction mixture was then slowly added 1666.1 g
(9.46 mol) of benzyl methacrylate (dried over molecular sieves) in
45 minutes. The temperature rose to 61.8.degree. C. during the
course of the addition. When the temperature fell to 28.3.degree.
C., about 100 minutes later, 0.5 mL of tetrabutyl ammonium
m-chlorobenzoate was added and no exotherm was detected. To the
reaction mixture was then added 628.6 g (2.56 mol) of
ethoxytriethyleneglycol methacrylate (dried over molecular sieves)
over 20 minutes. The temperature rose to 31.8.degree. C. The
reaction mixture was stirred for 2.5 hours. It was quenched with
525 g of methanol and stirred overnight. The mixture was distilled
until 2600 g of volatiles were collected, and 1700 g of
2-pyrrolidone were added. Further distillation removed 924.2 g of
volatiles, and another 2351.9 g of 2-pyrrolidone were added to
yield a 39% polymer solution.
[0055] The block polymer was neutralized using the following
procedure: 131 g of the polymer were mixed with 17.6 g of potassium
hydroxide solution (46.4% in deionized water) and 482.8 g of
deionized water until a homogeneous 10% polymer solution was
obtained.
[0056] Preparation III: Block copolymer, poly(methacrylic
acid-b-benzyl methacrylate-b-ethoxytriethylene glycol
methacrylate), MAA//BzMA//ETEGMA (12//18//4)
[0057] The polymer was prepared using a procedure similar to that
described in Preparation II. A polymer solution of
MAA//BzMA//ETEGMA (12//18//4) composition at 39.6% solid in
2-pyrrolidone was obtained.
[0058] The block polymer was neutralized using the following
procedure: 350 g of the polymer were mixed with 38.3 g of potassium
hydroxide solution (45.6% in deionized water) and 536.5 g of
deionized water until a homogeneous 15% polymer solution was
obtained.
Control 1
[0059] A pigment dispersion was prepared using the polymer of
Preparation II as the sole dispersant polymer. The polymer solution
from Preparation II, 131.0 g, was mixed with 17.63 g of potassium
hydroxide solution (46.4% in deionized water), and 482.8 g of
deionized water in a high speed disperser Dispermat.RTM. FE
(BYK-Gardener, Inc., Silver Spring, Md.) for an hour to completely
dissolve the polymer. To the polymer solution was added 112.5 g of
FW18 carbon black (Degussa Corp., Allendale, N.J.), 6.1 g of
Proxel.RTM. G (Zeneca Inc., Wilmington, Del.) as biocide, and 150.0
g of deionized water. The mixture at 155% pigment loading was too
viscous to process in the high speed disperser. Deionized water was
added to dilute the pigment loading to 12.5%. At this
concentration, the mixture became a gel. After stirring for about
15 minutes, the viscosity decreased, and the mixture was stirred at
about 5000 rpm in the high speed disperser for an additional hour.
The mixture was then dispersed in a microfluidizer (Microfluidics
Corp., Watham, Mass.) by passing it through the interaction chamber
5 times under a liquid pressure of about 7,000 psi. The resulting
pigment dispersion had 12.5% pigment concentration with an average
particle size of 122 nm as determined by Brookhaven BI-90 particle
sizer. The final pH was 8.54.
Example 1
[0060] A pigment dispersion was prepared using a blend of polymers
prepared as described in Preparations I and II, in the ratio of
10:90 by weight.
[0061] The polymer solution from Preparartion II, 117.9 g (39% in
2-pyrrolidone), and 51.0 g (10% in deionized water)) of the
pre-neutralized polymer solution of Preparation I were mixed with
14.29 g of potassium hydroxide solution (46.4% in deionized water),
and 328.2 g of deionized water in a high speed disperser
Dispermat.RTM. FE (BYK-Gardener, Inc., Silver Spring, Md.) for an
hour to completely dissolve the polymer. To the polymer solution
was added, 112.5 g of FW18 carbon black (Degussa Corp., Allendale,
N.J.) and 6.1 g of Proxel.RTM. G (Zeneca Inc., Wilmington, Del.).
The mixture at 22% pigment loading was stirred at about 5000 rpm in
the high speed disperser for an hour. The mixture was then
dispersed in a microfluidizer (Microfluidics Corp., Watham, Mass.)
by passing it through the interaction chamber 5 times under a
liquid pressure of about 7,000 psi. The resulting pigment
dispersion had 22% pigment concentration with an average particle
size of 107 nm as determined by Brookhaven BI-90 particle sizer.
The final pH was 8.15.
[0062] With the polymer blend as the dispersant, the dispersion was
more easily processed at a higher pigment loading, and the
resulting particle size was smaller compared to the control.
Example 2
[0063] A pigment dispersion was prepared using a blend of polymers
prepared as described in Preparation I and II in the ratio of 5:95
by weight.
[0064] The polymer solution from Preparartion II, 124.5 g (39% in
2-pyrrolidone), and 25.55 g (10% in deionized water) of the
pre-neutralized polymer solution of Preparation I were mixed with
15.08 g of potassium hydroxide solution (46.4% in deionized water)
and 284.9 g of deionized water in a high speed disperser
Dispermat.RTM. FE (BYK-Gardener, Inc., Silver Spring, Md.) for an
hour to completely dissolve the polymer. To the polymer solution
was added, 112.5 g of FW18 carbon black (Degussa Corp., Allendale,
N.J.) and 6.1 g of Proxel.RTM. G (Zeneca Inc., Wilmington, Del.).
The mixture was too viscous to process. It was diluted to 18.9%
pigment loading with deionized water. The mixture was stirred at
about 5000 rpm in the high speed disperser for an hour. It was then
processed in a microfluidizer (Microfluidics Corp., Watham, Mass.)
by passing it through the interaction chamber 5 times under a
liquid pressure of about 7,000 psi. The resulting pigment
dispersion had 18.9% pigment concentration with an average particle
size of 106 nm as determined by Brookhaven BI-90 particle sizer.
The final pH was 8.17.
[0065] With the polymer blend as the dispersant, the dispersion was
more easily processed at a higher pigment loading, and the
resulting particle size was smaller compared to the control.
Control 2:
[0066] A pigment dispersion was prepared using the polymer of
Preparation III.
[0067] 133.3 g (15% solution) of the pre-neutralized polymer
solution of Preparation III, were stirred with 226.7 g of deionized
water and 40 g of FW18 carbon black (Degussa Corp., Allendale,
N.J.) in a high speed disperser Dispermat.RTM. FE (BYK-Gardener,
Inc., Silver Spring, Md.) at about 6000 rpm for an hour. The
mixture at 10% pigment loading was viscous. It was forced through
the microfluidizer (Microfluidics Corp., Watham, Mass.)
continuously for 90 minutes. No reduction in either particle size
or viscosity was accomplished.
Example 3
[0068] A pigment dispersion was prepared using a blend of polymers
prepared as described in Preparations I and III, in the ratio of
10:90 by weight. 20 g (10% solution) of the pre-neutralized polymer
solution of Preparation I, and 120 g (15% solution) of the
pre-neutralized polymer solution of Preparation III were mixed with
40 g of FW18 carbon black (Degussa Corp., Allendale, N.J.) and 220
g of deionized water in a high speed disperser Dispermat.RTM. FE
(BYK-Gardener, Inc., Silver Spring, Md.). The mixture was stirred
at about 6000 rpm for an hour. The mixture was then processed in a
microfluidizer (Microfluidics Corp., Watham, Mass.) by passing it
through the interaction chamber under a liquid pressure of about
7000 psi. It became viscous first, then with further processing the
viscosity gradually decreased. The mixture was passed through the
interaction chamber 15 times until an average particle size of 114
nm was obtained. The resulting pigment dispersion has a 10%
concentration.
[0069] The addition of the random copolymer of Preparation I made
this mixture processable.
Example 4
[0070] A pigment dispersion was prepared using a blend of polymers
prepared as described in Preparations I and III, in the ratio of
15:85 by weight.
[0071] 30 g (10% solution) of the pre-neutralized polymer solution
of Preparation I, and 113.3 g (15% solution) of the pre-neutralized
polymer solution of Preparation III were mixed with 40 g of FW18
carbon black (Degussa Corp., Allendale, N.J.) and 216.7 g of
deionized water in a high speed disperser Dispermant.RTM. FE
(BYK-Gardener, Inc., Silver Spring, Md). The mixture was stirred at
about 6000 rpm for an hour and 10 minutes. The mixture was then
easily processed with a microfluidizer (Microfluidics Corp.,
Watham, Mass.) by passing it through the interaction chamber 8
times under a liquid pressure of about 7000 psi. The resulting
pigment dispersion had 10% pigment concentration with an average
particle size of 115 nm as determined by Brookhaven BI-90 particle
sizer.
[0072] The dispersion process was significantly improved by the
presence of the random copolymer.
Example 5
[0073] An ink was prepared and tested using the following
procedure: The pigment dispersion concentrate of Example 1 was
letdown with a vehicle solution to give the following
composition.
1 INGREDIENT WEIGHT % Carbon Black, FW18, (Degussa Corp.,
Allendale, 2.75 NJ) Blend of polymers prepared as described in 1.25
Preparations I and II (10/90). 2-Pyrrolidone, Aldrich Chemical Co.,
Milwaukee, 5.0 WI Liponic .RTM. EG-1, Lipo Chemicals Inc.,
Paterson, NJ. 4.25 N-Methylpyrrolidone, Aldrich Chemical Co., 2.0
Milwaukee, WI Zonyl .RTM. FSA (DuPont Co., Wilmington, DE) 0.05
Proxel .RTM. G (Zeneca Inc., Wilmington, DE) 0.15 Deionized water
84.6
[0074] The ink was filled into a thermal ink jet pen and 15 printed
with a Hewlett Packard DeskJet ink jet printer (Hewlett Packard
Co., Palo Alto, Calif.) on Gilbert bond paper (25% cotton, Mead
Co., Dayton, Ohio.). It printed smoothly and the print had an
extremely high optical density of 1.50 and sharp edges. The print
was waterfast immediately after drying.
[0075] The ink stability was determined by measuring the particle
size change by Brookhaven BI-90 particle sizer (Brookhaven
Instrument Corp., Holtsville, N.Y. 11742) after the ink sample had
been subjected to 4 temperature cycles, each consisting of 4 hours
at -20.degree. C. and 4 hours at 70.degree. C. The above ink showed
no significant change.
Example 6
[0076] Example 5 was repeated with the following exception: the
pigment dispersion concentrate of Example 3 was used instead of the
pigment dispersion concentrate of Example 1.
[0077] The ink was filled into a thermal ink jet pen and printed
with a Hewlett Packard DeskJet ink jet printer (Hewlett Packard
Co., Palo Alto, Calif.) on Gilbert bond paper (25% cotton, Mead
Co., Dayton, Ohio.). It printed smoothly and the print had an
extremely high optical density of 1.55 and sharp edges. The print
was waterfast immediately after drying.
[0078] The ink appears to be stable. No flocculation was detected
after the temperature cycle test.
Example 7
[0079] Example 5 was repeated with the following exception: the
pigment dispersion concentrate of Example 4 was used instead of the
pigment dispersion concentrate of Example 1.
[0080] The ink was filled into a thermal ink jet pen and printed
with a Hewlett Packard DeskJet ink jet printer (Hewlett Packard
Co., Palo Alto, Calif.) on Gilbert bond paper (25% cotton, Mead
Co., Dayton, Ohio.). It printed smoothly and the print had an
extremely high optical density of 1.59 and sharp edges. The print
was waterfast immediately after drying.
[0081] The ink appears to be stable. No flocculation was detected
after the temperature cycle test.
* * * * *