U.S. patent application number 11/895535 was filed with the patent office on 2007-12-27 for latex-based overcoat for ink-jet printing applications.
Invention is credited to Sivapackia Ganapathiappan, Kent Vincent.
Application Number | 20070296789 11/895535 |
Document ID | / |
Family ID | 33096903 |
Filed Date | 2007-12-27 |
United States Patent
Application |
20070296789 |
Kind Code |
A1 |
Vincent; Kent ; et
al. |
December 27, 2007 |
Latex-based overcoat for ink-jet printing applications
Abstract
Compositions, systems, and methods for protecting an ink-jet
produced image printed on a substrate are provided. The composition
can comprise a liquid vehicle and latex particulates dispersed in
the liquid vehicle, wherein the latex particulates have a surface
dielectric constant from 2.0 to 3.0 at room temperature, and a bulk
density from 0.90 g/cm.sup.3 to 1.10 g/cm.sup.3. An alternative
composition can comprise a liquid vehicle and latex particulates
dispersed in the liquid vehicle, wherein the latex particulates
have a reactive surfactant covalently attached thereto.
Inventors: |
Vincent; Kent; (Cupertino,
CA) ; Ganapathiappan; Sivapackia; (Los Altos,
CA) |
Correspondence
Address: |
HEWLETT PACKARD COMPANY
P O BOX 272400, 3404 E. HARMONY ROAD
INTELLECTUAL PROPERTY ADMINISTRATION
FORT COLLINS
CO
80527-2400
US
|
Family ID: |
33096903 |
Appl. No.: |
11/895535 |
Filed: |
August 23, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10404260 |
Mar 31, 2003 |
|
|
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11895535 |
Aug 23, 2007 |
|
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Current U.S.
Class: |
347/101 ;
106/287.35 |
Current CPC
Class: |
Y10T 428/24802 20150115;
B41M 7/0027 20130101; C09D 11/30 20130101; C09D 11/54 20130101 |
Class at
Publication: |
347/101 ;
106/287.35 |
International
Class: |
B41J 2/01 20060101
B41J002/01; C09D 107/02 20060101 C09D107/02 |
Claims
1. An overcoating composition for protecting a printed image on a
substrate, said composition comprising: (a) a liquid vehicle void
of colorant; and (b) latex particulates dispersed in the liquid
vehicle, said latex particulates having a surface dielectric
constant from 2.0 to 3.0 at room temperature, and a bulk density
0.1 g/cm.sup.3 less to 0.1 g/cm.sup.3 greater than the vehicle
density, wherein the latex particulates are core-shell or inverse
core-shell and have a glass transition temperature from 0.degree.
C. to 50.degree. C.
2. A composition as in claim 1, wherein the latex particulates are
present in the liquid vehicle at from 0.1 wt % to 20 wt %
solids.
3. A composition as in claim 1, wherein the latex particulates have
a bulk density of from 0.90 g/cm.sup.3 to 1.10 g/cm.sup.3 in liquid
vehicle that is predominantly water.
4. A composition as in claim 1, wherein the surface dielectric
constant is from 2.3 to 2.8.
5-9. (canceled)
10. A composition as in claim 1, said composition being
colorless.
11. A composition as in claim 1; wherein the liquid vehicle
includes a predominant amount of water, from 0 wt % to 45 wt %
cosolvent, and from 0 wt % to 5 wt % vehicle surfactant.
12. A composition as in claim 1, further comprising an ultraviolet
absorber.
13. (canceled)
14. A composition as in claim 1, said composition being jettable
from an ink-jet pen.
15-26. (canceled)
27. A system for producing waterfast and humidfast images,
comprising: (a) a media substrate; (b) an ink-jet ink including a
colorant, said ink-jet ink configured for being printed on the
media substrate; and (c) a coating composition including latex
particulates dispersed in a liquid vehicle, said coating
composition configured for overcoating the ink-jet ink on the media
substrate, said latex particulates having surfactant associated
with a surface of the latex particulates.
28. A system as in claim 27, wherein the surfactant is a reactive
surfactant covalently attached to the surface of the latex
particulates.
29. A system as in claim 27, wherein the latex particulates have a
surface dielectric constant from 2.0 to 3.0 at room temperature,
and a bulk density from 0.1 g/cm.sup.3 less to 0.1 g/cm.sup.3
greater than the vehicle density.
30. A system as in claim 29, wherein the surfactant is a
non-reactive surfactant adsorbed on the surface of the latex
particulates.
31. A system as in claim 27, wherein the latex particulates are
present in the liquid vehicle at from 0.1 wt % to 20 wt %
solids.
32. A system as in claim 27, wherein the colorant is a dye.
33. A system as in claim 27, wherein the colorant is a pigment.
34. A system as in claim 29, wherein the surface dielectric
constant is from 2.3 to 2.8.
35. A system as in claim 27, wherein a crosslinking agent is
polymerized in the latex particulates at from 0.1 wt % to 5 wt
%.
36. A system as in claim 27, wherein the latex particulates have a
glass transition temperature from 0.degree. C. to 50.degree. C.
37. A system as in claim 27, wherein the latex particulates include
at least one ring-containing monomer.
38. A system as in claim 27, said coating composition being
substantially colorless.
39. A system as in claim 27, wherein the liquid vehicle includes a
predominant amount of water, from 0 wt % to 45 wt % cosolvent, and
from 0 wt % to 5 wt % vehicle surfactant.
40. A system as in claim 27, wherein the media substrate is a
porous media substrate.
41. A system as in claim 27, wherein the coating composition is
configured to be printed at a greater drop weight that the ink-jet
ink.
42. A method for producing waterfast and humidfast images,
comprising: (a) jetting an ink-jet ink including a colorant onto a
media substrate; and (b) jetting a coating composition including
latex particulates dispersed in a liquid vehicle over the ink-jet
ink previously jetted on the substrate, said latex particulates
having surfactant associated with a surface of the latex
particulates.
43. A method as in claim 42, wherein the surfactant is a reactive
surfactant covalently attached to the surface of the latex
particulates.
44. A method as in claim 42, wherein the latex particulates have a
surface dielectric constant from 2.0 to 3.0 at room temperature,
and a bulk density from 0.1 g/cm.sup.3 less to 0.1 g/cm.sup.3
greater than the vehicle density.
45. A method as in claim 44, wherein the surfactant is a
non-reactive surfactant adsorbed on the surface of the latex
particulates.
46. A method as in claim 42, wherein the latex particulates are
present in the liquid vehicle at from 0.1 wt % to 20 wt %
solids.
47. A method as in claim 42, wherein a crosslinking agent is
polymerized in the latex particulates at from 0.1 wt % to 5 wt %,
and wherein the latex particulates have a glass transition
temperature from 0.degree. C. to 50.degree. C.
48. A method as in claim 42, said coating composition being
substantially colorless.
49. A method as in claim 42, wherein the media substrate is a
porous media substrate.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to the ink-jet
printing of durable images. More particularly, the present
invention relates to a latex coating composition that can be used
to overcoat ink-jet printed images.
BACKGROUND OF THE INVENTION
[0002] Computer printer technology has evolved to a point where
very high-resolution images can be transferred to various types of
media, including paper. One particular type of printing involves
the placement of small drops of a fluid ink onto a media surface in
response to a digital signal. Typically, the fluid ink is placed or
jetted onto the surface without physical contact between the
printing device and the surface. Within this general technique, the
specific method that the ink-jet ink is deposited onto the printing
surface varies from system to system, and can include continuous
ink deposit and drop-on-demand.
[0003] With regard to continuous printing systems, inks used are
typically based on solvents such as methyl ethyl ketone and
ethanol. Essentially, continuous printing systems function as a
stream of ink droplets that are ejected and directed by a printer
nozzle. The ink droplets are directed additionally with the
assistance of an electrostatic charging device in close proximity
to the nozzle. If the ink is not used on the desired printing
surface, the ink is recycled for later use. With regard to
drop-on-demand printing systems, the ink-jet inks are typically
based upon water and solvents such as glycols. Essentially, with
these systems, ink droplets are propelled from a nozzle by heat or
by a pressure wave such that all of the ink droplets ejected are
used to form the printed image.
[0004] There are several reasons that ink-jet printing has become a
popular way of recording images on various media surfaces,
particularly paper. Some of these reasons include low printer
noise, capability of high-speed recording, and capability of
multi-color recording. Additionally, these advantages can be
obtained at a relatively low price to consumers.
[0005] Though there has been great improvement in ink-jet printing
technology, as described previously, there is still improvement
that can be made in many areas. With respect to ink-jet ink
chemistry, the majority of commercial ink-jet inks are water-based.
Thus, their constituents are generally water-soluble, as in the
case with many dyes, or water dispersible, as in the case with
pigments. Furthermore, ink-jet inks have low viscosity (typically 5
cps or less) to accommodate high frequency jetting and firing
chamber refill processes common to ink-jet pens.
[0006] Ink-jet prints are often known for poor durability when
exposed to water or high humidity. This results from the use of
water-soluble and water dispersible colorants within the
water-based ink. There has been great improvement in the area of
water durability of ink-jet inks through incorporation of certain
ink-jet compatible latex polymers. When printed as part of an
ink-jet ink, a latex component of the ink can form a film on a
media surface, entrapping and protecting at least some of the
colorant within the hydrophobic print film. However, not all
colorant will necessarily be protected upon printing, as would be
optimal.
[0007] Polymers that form durable films are typically made from
copolymers having bulk densities on the order of 1.15 g/cm.sup.3 or
greater, which is appreciably greater than water, the primary
component of thermal ink-jet ink. As such, conventional latex
particles are normally designed to flocculate so that latex
precipitate may be easily shaken or stirred back into dispersion
without agglomeration. Such flocculation behavior is well known
with latex paints. Unfortunately, these conventional teachings do
not address the unique needs of ink-jet printing applications. For
example, the micro-channel ink feeds in ink-jet pens are easily
clogged with precipitant, particularly when a pen is stored or
otherwise unused for prolonged periods of time. Such precipitation
is not easily redispersed by pen shaking, as flow constriction
prohibits adequate mixing within micro-channels of pen
architecture. Additionally, micro-channels used for jetting can
house some of the ink over prolonged periods in preparation for
firing, and settled latex particulates can cause further
constricting of the micro-channels. This can result in ink-jet pen
failure due to clogging of the micro-channels. Further, the
micron-order settling distances found in the fluid channels of
thermal inkjet pens exacerbate the problem.
SUMMARY OF THE INVENTION
[0008] It has been recognized that it would be advantageous to
develop a latex-based overcoat for ink-jet printing applications.
Such latex-based overcoats can be applied as a protective coating
to dye-based and/or pigment-based ink-jet ink produced images.
[0009] Specifically, a composition for protecting an ink-jet
produced image printed on a substrate can comprise a liquid vehicle
void of colorant and having latex particulates dispersed in the
liquid vehicle. The latex particulates can have a surface
dielectric constant from 2.0 to 3.0 at room temperature, and a bulk
density from 0.90 g/cm.sup.3 to 1.10 g/cm.sup.3. Additionally, in
one embodiment, non-reactive surfactant can be adsorbed on the
surface of the latex particulates.
[0010] Alternatively, a composition for protecting an ink-jet
produced image printed on a substrate can comprise a liquid vehicle
void of colorant and having latex particulates dispersed in the
liquid vehicle, wherein the latex particulates have a reactive
surfactant covalently attached thereto.
[0011] Additionally, a system for producing waterfast and humidfast
images can comprise a media substrate, an ink-jet ink including a
colorant, and a coating composition. The ink-jet ink can be
configured for being printed on the media substrate. Further, the
coating composition can include latex particulates dispersed in a
liquid vehicle. The coating composition can also be configured for
overcoating the ink-jet ink on the media substrate. Further, the
latex particulates can have surfactant associated with the surface
of the latex particulates.
[0012] A method for producing waterfast and humidfast images is
also disclosed which can comprise steps of jetting an ink-jet ink
including a colorant onto a media substrate and jetting a coating
composition including latex particulates dispersed in a liquid
vehicle over the ink-jet ink previously jetted on the media
substrate. The latex particulates can have surfactant associated
the surface of the latex particulates.
[0013] Additional features and advantages of the invention will be
apparent from the detailed description that follows which
illustrates, by way of example, features of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0014] Before the present invention is disclosed and described, it
is to be understood that this invention is not limited to the
particular process steps and materials disclosed herein because
such process steps and materials may vary somewhat. It is also to
be understood that the terminology used herein is used for the
purpose of describing particular embodiments only. The terms are
not intended to be limiting because the scope of the present
invention is intended to be limited only by the appended claims and
equivalents thereof.
[0015] It must be noted that, as used in this specification and the
appended claims, the singular forms "a," "an," and "the" include
plural referents unless the context clearly dictates otherwise.
[0016] As used herein, "liquid vehicle" or "ink vehicle" refers to
the fluid in which colorants and/or latex particulates are added to
form solutions and/or solutions. Many liquid vehicles, as well as
specific vehicle components that can be used to formulate the
liquid vehicles, are known in the art. Typical ink vehicles can
include a mixture of a variety of different agents, such as
co-solvents, surfactants, buffers, biocides, sequestering agents,
viscosity modifiers, and water.
[0017] "Colorant" can include dyes and/or pigments that may be used
to impart color to an ink vehicle in accordance with embodiments of
the present invention. In accordance with the present invention,
colorant is typically used in ink-jet inks to be overcoated by the
latex particulate-containing coating compositions of the present
invention. This in not to say that the latex can not be present in
the colorant-containing ink-jet ink as well.
[0018] Concentrations, amounts, and other numerical data may be
expressed or presented herein in a range format. It is to be
understood that such a range format is used for convenience and
brevity, and thus, should be interpreted in a flexible manner to
include not only the numerical values explicitly recited as the
limits of the range, but also to include all the individual
numerical values or sub-ranges encompassed within that range as if
each numerical value and sub-range is explicitly recited. To
illustrate, a concentration range of "0.1 wt % to 5 wt %" should be
interpreted to include not only the explicitly recited
concentration of 0.1 wt % to 5 wt %, but also include individual
concentrations and the sub-ranges within the indicated range. Thus,
included in this numerical range are individual concentrations,
such as 1 wt %, 2 wt %, 3 wt %, and 4 wt %, and sub-ranges, such as
from 0.1 wt % to 1.5 wt %, 1 wt % to 3 wt %, from 2 wt % to 4 wt %,
from 3 wt % to 5 wt %, etc. This same principle applies to ranges
reciting only one numerical value. For example, a range recited as
"less than 5 wt %" should be interpreted to include all values and
sub-ranges between 0 wt % and 5 wt %. Furthermore, such an
interpretation should apply regardless of the breadth of the range
or the characteristics being described.
[0019] As used herein, "effective amount" refers to at least the
minimal amount of a substance or agent, which is sufficient to
achieve a desire effect. For example, an effective amount of a
"liquid vehicle" is at least the minimum amount required in order
to create an ink composition, while maintaining properties
necessary for effective ink-jetting.
[0020] The term "freqcel" denotes a reduction in ink drop ejection
velocity with increased pen firing frequency. The lowering of drop
velocity can be a problem as changes in the trajectory of the fired
drops can reduce drop placement accuracy on the print media.
Without being bound by one particular theory, freqcel may be
attributable to thermal shear stripping of surfactant from latex
near a pen firing chamber at the time of drop nucleation. As
surfactant is typically present in ink-jet inks to help separate
particles, a reduction in surface-adsorbed or surface-attracted
surfactant can promote greater inter-particle attraction. This can
result in increased ink viscosity. Greater pen firing energy can be
used to counteract this phenomenon, but bubble entrapment can be
exacerbated at these higher viscosities, which is known to worsen
freqcel performance.
[0021] The term "decel" denotes an increase in ink flow resistance
within pen micro-channels, which in turn, reduces ejected drop
volume. Such flow resistance can be caused by changes in ink
rheology or plugged channels, and is often responsible for ink
starvation within a pen firing chamber.
[0022] The term "decap" is a measure of how long a nozzle may
remain inactive before plugging and how many pen firings are
required to re-establish proper drop ejection.
[0023] The terms "surface dielectric constant" and "bulk dielectric
constant" as well as the terms "bulk density" and "glass transition
temperature" require a detailed explanation. Table 1 below
provides, by way of example, certain homopolymers values for
homopolymers that can be used to predict bulk or surface dielectric
constants, bulk densities, and glass transition temperatures of
latex copolymers in accordance with principles of the present
invention. Such predictions can be made in accordance with accepted
Bicerano correlations, reported in Predictions of Polymer
Properties, Bicerano, Jozef, Marcel Dekker, Inc., New York, N.Y.,
1996. Table 1 should not be construed as including all homopolymers
that can be used to make latex in accordance with principles of the
present invention. Additionally, not all of the homopolymers listed
in Table 1 are effective for use in making the latex particulates
in accordance with principles of the present invention. Table 1 is
merely provided to teach what is meant by the terms "surface
dielectric constant" or "bulk dielectric constant" as well as the
terms "bulk density" and "glass transition temperature."
TABLE-US-00001 TABLE 1 Homopolymer values Monomer W E.sub.coh1
V.sub.W N.sub.dc .epsilon. V .rho. T.sub.g n-octyl 198.31 69686
127.08 24 2.45 204.2 0.971 -20 methacrylate Styrene 104.15 39197
64.04 10 2.55 99.1 1.050 99.9 cyclohexyl 168.24 59978 99.86 24 2.58
153.2 1.098 103.9 methacrylate 2-ethylbutyl -- 59130 107.28 24 2.68
163.7 1.040 11 methacrylate hexyl 170.23 59804 106.70 24 2.69 168.5
1.010 -5.2 methacrylate isobutyl 142.20 48496 85.60 224 2.70 136.1
1.045 47.9 methacrylate t-butyl 142.20 46427 84.94 24 2.73 139.4
1.020 107 methacrylate sec-butyl 142.20 48872 86.92 24 2.75 135.2
1.052 57 methacrylate 2-ethylhexyl 198.31 77980 127.65 24 2.75
202.2 1.020 5.2 methacrylate n-butyl 142.20 49921 86.33 24 2.77
134.8 1.055 20 methacryalte n-butyl 128.17 46502 76.82 24 2.87 --
-- -54 acrylate benzyl 176.22 64919 98.40 24 2.90 149.4 1.179 --
methacryalte hexyl acrylate 156.23 65352 98.56 24 2.91 151.6 1.030
-57.2 ethyl methacrylate 114.15 40039 65.96 24 3.00 102.0 1.119
50.9 methyl 100.12 35097 54.27 24 3.10 85.6 1.170 104.9
methacrylate methyl 86.09 31678 44.76 24 3.28 70.6 1.220 8 acrylate
ethylene 198.22 88978 111.69 48 3.35 169.88 1.169 -- glycol di
methacrylate methacrylic 86.09 38748 45.99 24 3.52 70.6 1.219 187
acid hydroxyethyl 130.14 66502 69.44 36 3.74 -- -- 86 methacrylate
methacryloyl- 230.22 111243 116.06 72 3.84 177.4 1.298 58.3
oxyethyl succinate acrylic acid 72.06 35329 36.48 24 3.90 53.5
1.347 106 In Table 1 above, the abbreviations used are defined as
follows: W Monomer molecular weight (grams/mole) E.sub.coh1
Cohesive energy (joules/mole) V.sub.w Van der Waals volume
(cm.sup.3/mole) N.sub.dc Fitting parameter (cm.sup.3/mole)
.epsilon. Dielectric constant (no units) V Molar volume
(cm.sup.3/mole) .rho. Density (grams/cm.sup.3) T.sub.g Glass
transition temperature (Celsius)
[0024] From these values, the bulk or surface dielectric constant,
bulk density, and glass transition temperature of latex copolymers
formed by copolymerization of any combination of these monomers (or
other known monomers where these values are available) may be
predicted using the following Bicerano correlations and glass
transition temperature relationships: Dielectric constant
(.di-elect cons.)=1.412014+(0.001887E.sub.coh1+Nd.sub.c)/V.sub.w
Formula 1 .rho.=W/V Formula 2
[1/T.sub.g].sub.copolymer=.SIGMA.(w/T.sub.g).sub.n Formula 3
[0025] In the above Formulas 1 and 2, .di-elect cons. and .rho. are
the latex bulk or surface dielectric constant and bulk density,
respectively. The terms E.sub.coh1, N.sub.dc, V.sub.w, W, and V are
the molar fraction sum of the homopolymer cohesive energies,
fitting parameters, van der Waals volumes, molecular weights, and
molar volumes, respectively. The inverse latex glass transition
temperature, [1/T.sub.g].sub.copolymer, which is computed in Kelvin
as provided in Formula 3, is the sum (n) of the ratio of weight
fraction to homopolymer glass transition temperature of each
monomer in the latex copolymer.
[0026] With respect to latex that is polymerized or copolymerized
to be roughly uniform throughout, the terms "bulk dielectric
constant" and "surface dielectric constant" can be used
interchangeably. For example, the bulk dielectric constant
describes not only the core hydrophobicity, but also the surface
hydrophobicity, as the core and the surface are, on average, of the
same material. However, in embodiments where a core-shell, inverse
core-shell, or composite latex is formed, the bulk dielectric
constant will usually be different than the surface dielectric
constant, as the core of the latex will be of a different polymer
or copolymer than the shell. Thus, in core-shell, inverse
core-shell, and composite embodiments, it is primarily the
dielectric constant of the shell material, i.e., the surface
dielectric constant, which plays a role in surfactant adsorption.
As a result, when referring to dielectric constant values, surface
dielectric constant values will be used, as the surface dielectric
constant values account for both single material latex copolymers
as well as core-shell, inverse core-shell, and composite latex
copolymers.
[0027] Generally, the term "reactive surfactant" means any
surfactant, e.g., surfmer, non-migratory surfactant, etc., that has
the ability to fix itself onto the surface of a latex particulate,
such as, for example, by formation of a covalent bond. Typically,
the reactions between reactive surfactants and the latex particle
surface are sufficiently strong to prevent separation and migration
therebetween.
[0028] Generally, the term "non-reactive surfactant" includes
surfactants that are adsorbed (as opposed to fixed, reacted, or
bonded) onto the surface of the latex particle. During high-speed
printing operations, non-reactive surfactants are typically
desorbed or stripped off of the latex particle surface, unless the
latex particle surface exhibits favorable conditions, such as a low
dielectric constant. These surfactants can be adsorbed on the
surface of the latex by matching, within a reasonable range, the
surface dielectric constant of the latex and the hydrophobic moiety
of the surfactant.
[0029] The definition of reactive surfactant and non-reactive
surfactant can be more fully appreciated with reference to the
descriptions and examples contained hereafter.
[0030] The terms "latex-containing coating," "coating composition,"
"latex particulate-containing coating composition," and the like,
includes substantially colorless compositions including a liquid
vehicle having latex particulates dispersed therein. These
compositions typically are void of colorant, and can be used to
protect images printed by colorant-containing ink-jet inks. These
coating compositions can include 0.1 wt % to 20 wt % latex
particulate solids, dispersed in a liquid vehicle. In one
embodiment, the solids can be present in the liquid vehicle at from
4 wt % to 12 wt %.
[0031] With this in mind, it has been recognized that it would be
advantageous to develop compositions, systems, and methods for
printing waterfast and humidfast images. Specifically, latex
particulate-containing coating compositions can be used to overcoat
dye- and pigment-based ink-jet ink produced images.
[0032] In accordance with an embodiment of the present invention, a
composition for protecting an ink-jet produced image printed on a
substrate can comprise a liquid vehicle void of colorant and latex
particulates dispersed in the liquid vehicle. The latex
particulates can have a surface dielectric constant from 2.0 to 3.0
at room temperature, and a bulk density from 0.90 g/cm.sup.3 to
1.10 g/cm.sup.3.
[0033] Alternatively, a composition for protecting an ink-jet
produced image printed on a substrate can comprise a liquid vehicle
void of colorant and latex particulates dispersed in the liquid
vehicle, wherein the latex particulates have a reactive surfactant
covalently attached thereto.
[0034] Additionally, a system for producing waterfast and humidfast
images can comprise a media substrate, an ink-jet ink including a
colorant, and a coating composition. The ink-jet ink can be
configured for being printed on the media substrate. The coating
composition can include latex particulates dispersed in a liquid
vehicle, and can also be configured for overcoating the ink-jet ink
on the media substrate. Further, the latex particulates can have
surfactant associated with the surface of the latex
particulates.
[0035] A method for producing waterfast and humidfast images can
comprise steps of jetting an ink-jet ink including a colorant onto
a media substrate, and jetting a coating composition including
latex particulates dispersed in a liquid vehicle over the ink-jet
ink previously jetted on the media substrate. The latex
particulates can have surfactant associated with the surface of the
latex particulates.
[0036] As stated, the compositions for protecting ink-jet produced
images (or coating compositions) described herein include a liquid
vehicle and a dispersion of latex particulates. These coating
compositions can be overcoated on dye- and/or pigment-based ink-jet
ink produced images to form a coating lattice or protective film
that is typically clear, or substantially colorless. Print films
developed through incorporation of colorant with latex in a common
vehicle do not typically provide substantially complete
encapsulation of the colorant between the media substrate and the
film, particularly when the colorant is a dye. A fraction of the
colorant can invariably lie on top of or may only be partially
trapped by the latex. The use of a latex overcoat can provide a
definitive barrier between the colorant and the environment,
moisture, and/or smearing agents.
[0037] A latex overcoat can provide still further advantages. For
example, an overcoat can include a greater solids content of latex
a composition containing both a latex and a pigment (as both the
pigment and the latex must be considered when determining a total
solids amount in an ink-jet ink). This consideration is valuable as
the respective coating and ink can be limited in solids content due
to certain ink-jet imposed viscosity thresholds. The latex solids
content of an ink-jet ink can thus be compromised by the content of
pigment. As a result, by separating latex solids from pigment
solids, more latex can be used in a liquid vehicle, thereby
providing more latex since the total amount of solids does not have
to include pigment solids amounts.
[0038] The latex of the present invention can be prepared through
conventional free radical addition of a monomer mixture through
emulsion polymerization. Suitable monomers are included in U.S.
Pat. No. 6,057,384, which is incorporated herein in its entirety by
reference. The latex can be dispersion stabilized through
incorporation of a monomer or monomers that promote latex surface
charge, including those represented by acrylic acid, methacrylic
acid, vinyl benzoic acid, and methacryloyloxyethyl succinate. These
charge forming monomers typically are present in the copolymer at
from 0.5 wt % to 20 wt %. In another embodiment, the charge forming
monomers can be present at from 3 wt % to 10 wt % of the monomer
mix. These charge forming monomers can be neutralized after latex
polymerization to form salts. In one embodiment, the salts can be
formed through the reaction of a latex carboxylic acid with
potassium hydroxide.
[0039] Particle dispersion stability is also influenced by particle
density, which influences the ability of particles to settle within
pen microchannels. In accordance with embodiments of the present
invention, the latex can be generated or selected to have a bulk
density of 0.90 g/cm.sup.3 to 1.10 g/cm.sup.3. In a more detailed
embodiment, the bulk density can be from 1.02 g/cm.sup.3 to 1.05
g/cm.sup.3. This more narrow range results from the understanding
that the liquid vehicle of many aqueous ink-jet inks has a density
on the order of about 1.02 g/cm.sup.3.
[0040] In a more detailed embodiment, the bulk density range
provided can be modulated such that the bulk density is in a range
slightly above or below the liquid component density of the
predominantly water-based ink vehicle. By predominant, what is
meant is that water is present in an amount that is greater than
any other single vehicle component. Within a relatively narrow
density band above or below this level, Brownian energy can prevent
latex settling or floatation, respectively. As ink vehicle fluid
densities of predominantly water-based ink-jet inks are typically
about 1.02 g/cm.sup.3, bulk densities of latex particulates that
are approximately the same to slightly higher or lower can be
included with little to no settling over a period of years. Thus,
in this embodiment, in order to prevent latex particulate settling
or floatation, the density can be kept in a range slightly higher
or slightly lower than the density of an ink vehicle and within the
range that Brownian momentum exchange is effective. The rate of
settling can increase with the difference between the vehicle and
latex densities. However, if the liquid vehicle is other than about
1.02 g/cm.sup.3, bulk density ranges for latex particulates may be
desirable for use that are other than those ranges previously
enumerated.
[0041] One strategy that can be used to obtain appropriate bulk
density is to utilize low-density latex polymers having
incorporated therein at least one ring containing monomer. The ring
containing monomer can improve the print film durability of the
latex. In one embodiment, the latex according to this aspect of the
invention, can contain a blend of alkane, e.g., hexyl methacrylate,
and ring-based, e.g., styrene, monomers to adjust the thermal glass
transition temperature for print film formation at a given
temperature. The use of these or other similar polymers can provide
the above-mentioned benefits without a reduction in print film
durability.
[0042] The glass transition temperature of the polymer can fall in
the range of about 0.degree. C.<T.sub.g<50.degree. C. In an
alternative embodiment, the glass transition temperature range can
be from 10.degree. C.<T.sub.g<40.degree. C. These temperature
ranges can allow for room temperature film formation of an ink
without process or pen induced particle agglomeration. Higher glass
transition temperature ranges may be selected for use when latex
coagulation is accomplished at a higher than ambient temperature,
for example by heated fuser roller. When using a conjugated ring
structure, the .pi.-electrons of such ring structures can provide
strong adhesive forces without the added density typical of more
polar monomers. Additionally, a blend of alkane and ring-based
monomers can be used to adjust the thermal glass transition
temperature (T.sub.g) of the latex copolymer for print film
formation.
[0043] The latex can also be stabilized to protect from thermal
shear degradation by the incorporation of a crosslinking agent or
multimer, such as a dimer, into the copolymeric latex. For example,
from 0.1 wt % to 5 wt % of such a multimer can be present in the
latex particulates. Alternatively, from 1 wt % to 2 wt % of such a
multimer can be used. These crosslinking agents are capable of
forming crosslinks between polymer chains in the latex particle.
Examples of appropriate crosslinking agents that can be used
include ethylene glycol dimethacrylate, pentaerythritol
tetraacrylate, ethyleneglycol dimethacrylamide, divinyl benzene, or
other monomers with polymerizable di- or polyfunctional groups.
This relatively narrow range of crosslinking can aid in maintaining
the integrity of latex under the high thermal shear conditions that
occur during thermal ink-jet printing, while not adversely
impacting its room temperature film-forming properties.
[0044] Optionally, one or more ultraviolet absorber moieties can be
included in the coating composition of the present invention. For
example, an ultraviolet absorber can be dissolved or dispersed in
the liquid vehicle containing the latex particulates, or
alternatively, the ultraviolet absorber can be polymerized into the
latex particulates. Appropriate ultraviolet absorbers can include
blocking chromophore moieties, which can imparts lighffastness to
the polymer. A more detailed description of UV absorbers can be
found in U.S. Pat. No. 6,057,384, which was previously incorporated
herein by reference. Separating a colorant-containing ink-jet ink
from a latex-containing coating composition can also provide
advantages with respect to embodiments utilizing this ultraviolet
protection. For example, an overcoat can include ultraviolet
absorbers that protect entrapped colorant from photo degradation.
In general, it is not typically desirable to include ultraviolet
absorbers in inks, as the close proximity of colorant and
ultraviolet absorber can allow transfer of absorbed photon energy
to the colorant, accelerating photo-degradation. Thus, the presence
of an absorber in the ink, ironically, can increase the amount of
photon energy that would otherwise be absorbed by the ink. By
including these types of compositions in an overcoat, the
ultraviolet absorbed and colorant can be separated in different
print layers, thereby providing improved performance.
[0045] Copolymeric latexes having a surface dielectric constant
from 2.0 to 3.0 can also provide acceptable properties. In one
embodiment, the surface dielectric constant can be from 2.3 to 2.8.
Such dielectric constant ranges for latex copolymers provide
sufficient dielectric constant hydrophobicity to sufficiently
anchor non-reactive surfactants (if present) to the latex, thereby
protecting against substantial thermal shear stripping that can
occur in thermal ink-jet printing applications. A latex surface
dielectric constant as low as 2.0 can be achieved by incorporating
monomers having a very low dielectric constant. Examples of such
monomers include fluorosilicons or fluorocarbons. Alternatively,
reactive surfactants can be covalently attached to the surface of
the latex particulates. When this approach is followed, surface
dielectric constant becomes less of a consideration, as thermal
stripping is less likely to occur when reactive surfactant is
covalently attached to the latex particulates.
[0046] Generally, the latex particles of the present invention can
be prepared by mixing monomers together to form a monomer mixture.
A polymerization step can also be carried out to form the
particulates. Surfactant(s) can then be added to the monomer
mixture and sheared to form an emulsion. The surfactant(s) can
include a reactive surfactant, a non-reactive surfactant, or a
combination of reactive and non-reactive surfactants. In one
embodiment of the invention, non-reactive surfactants can be used
to form the latex particle, and reactive surfactants can be used,
either in concert or added in a second step. Alternatively,
polymerization can be carried out as a soap-free polymerization,
with a reactive surfactant being added near the end of
polymerization.
[0047] As described, dielectric constant values can be used as a
measure of hydrophobicity. Steric stabilizers, such as surfactants,
can be used to control the latex particulate size during
polymerization, and can also be selected to provide additional
particle dispersion stability. Such stabilizers can be adhered to
the particle surface to minimize thermal stripping under pen firing
conditions. This phenomenon can be prevented by matching the
hydrophobicity of the latex monomer set and the non-reactive
surfactant. The hydrophobic segments of conventional surfactants
typically comprise long branched or unbranched hydrocarbon chains,
e.g., from 5 to 50 atoms in length, at a first end, and branched or
unbranched long hydrophilic chains, e.g., from 5 to 100 atoms in
length, at the other end. An example of such an unbranched
surfactant is shown as Formula 4 below: ##STR1## wherein m can be
from 5 to 50, n can be from 5 to 100, and R can be H or CH.sub.3.
Formula 4 merely provides one exemplary surfactant that can be
used. Other known surfactants can also be used. As shown, the
hydrophobic moiety and the hydrophilic moiety can be bound together
by an acid, such as a phosphoric acid. Such an acid can add charge
to the surface of the latex, which compliments the charge that may
already be present on the surface. Further, the hydrophilic moiety
can add steric stabilization to the surface of the latex.
[0048] Hydrophobic moieties of the surfactant, if primarily
aliphatic, typically are expected to have dielectric constants of
about 2.3, as is nominal for polyolefins. Good adhesion of a
hydrophobic moiety of a surfactant to the surface of a latex
particulate can occur when the dielectric constants of the two are
matched as closely as can be achieved. Departure from optimal
adhesion is believed to be proportional to the dielectric constant
difference between a hydrophobic moiety of the surfactant and the
surface of the latex. As a result, it has been recognized that a
narrow range of latex surface dielectric constants, as well as bulk
densities, can be obtained by engineering latexes to meet these
criterion. By obtaining one or both of these properties, if a
non-reactive surfactant is desired to be adsorbed on the surface of
the latex, adequate surfactant adhesion can be obtained to minimize
or eliminate latex printability and dispersion related problems
often associated with latex-containing ink-jet inks. Further, such
formulations can prevent both latex floatation and settling within
an aqueous-based ink vehicle. In other words, upon adhesion of the
hydrophobic moiety of the surfactant to the surface of a latex
particulate, the hydrophilic moiety can extend from the surface in
a hair-like manner, providing properties to the hydrophobic latex
particulate that makes it useable in a predominantly water-based
ink-jet ink vehicle.
[0049] It is understood that the surface dielectric constant of a
latex particle is of primary concern in situations where a
non-reactive surfactant is being used to provide dispersion
stability. Thus, in alternative embodiments of the invention,
non-reactive surfactants having a dielectric constant closely
matched to the dielectric constant of the latex particle can be
used. Without being restricted to any particular theory, the
adsorption between the hydrophobic segment of the non-reactive
surfactant and the latex surface seems to improve as the dielectric
constants are more closely matched, thus making the non-reactive
surfactant less likely to strip off during jetting from a thermal
ink-jet pen.
[0050] Similar to non-reactive surfactants, reactive surfactants
are molecules that typically have a hydrophobic segment and an
ionizable and/or polar segment or group. The hydrophobic segment
preferentially absorbs onto the surface of the latex particle
during and following particle polymerization. The hydrophilic
segment extends into the normally aqueous solution phase and
thereby provides a steric barrier against particle coagulation.
Unlike their non-reactive counterparts, reactive surfactants
additionally contain a reactive group on a hydrophobic segment that
is capable of covalently bonding to the latex surface. In one
embodiment of the present invention, the reactive group is of the
same reactive species as that found in the latex monomer(s) so that
the surfactant reacts more readily into the latex surface during
the latex polymerization reaction. It is understood that the
reactive surfactant may also bind to the latex surface through
other and subsequent reaction means.
[0051] Suitable reactive surfactants for use with the present
invention include any surfactants having a reactive group on the
hydrophobic segment that are capable of covalently bonding to the
surface of a latex particle. The length and composition of the
hydrophobic segment of the reactive surfactant can be selected to
substantially correspond to the surface chemistry and the
rheological needs of the latex particle. One such representative
hydrophobic segment is a C.sub.10-20 alkyl chain. The hydrophilic
group may be anionic, cationic, or non-ionic. Suitable anionic
functional groups include, for example, sulfonate, phosphonate, and
carboxylate ions. Suitable cationic functional groups include, for
example, ammonium ions. Suitable non-ionic surfactants typically
include surfactants exhibiting ethoxy group hydrophilicity.
[0052] The reactive group can be selected based on the reactive
species of the latex monomer. For example, acrylate reactive groups
could be selected as reactive groups for use with lattices that are
polymerized via vinyl, acrylic and styrenic monomers. A
representative reactive surfactant for such a reaction is
MAXEMUL.TM. 6106 (available from Uniquema), which has both
phosphonate ester and ethoxy hydrophilicity, a nominal C.sub.18
alkyl chain with an acrylate reactive group. Other representative
reactive surfactants with phosphate ester functionalities suitable
for such reactions include, but are not limited to,
MAXEMUL.TM.6112, MAXEMUL.TM. 5011, MAXEMUL.TM. 5010 (all available
from Uniquema). Alternative reactive surfactants suitable for use
with various embodiments of the present invention include
polyoxyethylene alkylphenyl ether ammonium sulfate (available from
Montello, Inc. as HITENOL BC-10.TM., HITENOL BC-1025.TM., HITENOL
BC-20.TM., HITENOL BC-2020.TM., HITENOL BC-30.TM.), polyoxyethylene
alkylphenyl ether (available from Montello, Inc. as NOIGEN
RN-10.TM., NOIGEN RN-20.TM., NOIGEN RN-30.TM., NOIGEN RN-40.TM.,
and NOIGEN RN-5065.TM.), sodium allyloxy hydroxypropyl sulfonate
(available from Rhodia as SIPOMER COPS-1.TM.), alkenenyl-functional
nonionic surfmers, allyl methoxy triethylene glycol ether, sodium
methallyl sulfonates, sulfopropyl acrylate, vinyl sulfonate, vinyl
phosphate, monosodium ethylsulfonate monondodecyl maleate, sorbitol
acrylate, sorbitol methacrylate, perfluoro heptoxy
poly(propyloxy)methacrylate, phenoxyl poly(ethyleneoxy acrylate,
phenoxyl poly(ethyleneoxy)methacrylate, nonyl phenoxy
poly(ethyleneoxy)crotanate, nonyl phenoxy
poly(ethyleneoxy)fumarate, nonyl phenoxy poly(ethyleneoxy)acrylate,
nonyl phenoxy poly(ethyleneoxy)methacrylate, mono doecyl maleate,
and allylsulfosuccinate derivatives (such as TREM LT-40.TM.
(available from Henkel)). In particular embodiments of the
invention, where applicable, the reactive surfactant will include 1
to 40 ethyleneoxy or propyloxy units.
[0053] In another embodiment, the latex particulates of the present
invention can include a conventional core-shell or inverse
core-shell latex structure, or composite latex. Such a composite
latex can be prepared in accordance with principles of the present
invention, wherein the shell layer incorporates a monomer mix in
accordance with the properties described herein, e.g., surface
charge monomer, multimer, dielectric constant specifications, etc.
The shell layer, in this case, can provide thermal shear and
dispersion stabilizing properties independent of the properties of
the latex core. Additionally, the core and shell polymers
collectively can be configured to produce a latex particle having a
bulk density as defined previously with respect to non-composite
polymeric or copolymeric latexes. As is known in the art,
core-shell latexes can be prepared in a two-step process, where a
first latex particle is synthesized and forms a seed for
polymerization of shell monomers around the seed particle.
[0054] Whether using single copolymeric latex or a composite latex,
as long as the latex is prepared in accordance with the principles
described herein, problems associated with freqcel, decap, and
decel can be substantially improved. For example, freqcel can be
proportionately overcome by increased latex surface hydrophobicity.
A latex that is principally comprised of a methyl
methacrylate-hexyl acrylate copolymer, for example, can show
freqcel at 3 kHz, while a significantly more hydrophobic
styrene-hexyl methacrylate copolymer latex shows virtually no
freqcel through 12 kHz. More hydrophobic latex, however, when
stripped of its surfactant through dialysis, shows significant
freqcel at 3 kHz, as observed with the less hydrophobic latex.
Without being bound by any particular theory, the adhesion between
the hydrophobic segment of non-reactive surfactant and the latex
surface seems to improve as the dielectric constants are more
closely matched, thus making the surfactant less likely to strip
off during jetting from a thermal ink-jet pen. Reactive
surfactants, on the other hand, do not require such dielectric
matching, as reactive surfactants are typically covalently bound to
the surface of the latex.
[0055] A typical liquid vehicle formulation that can be used with
the latexes described herein can include water, and optionally, one
or more co-solvents present in total at from 0 wt % to 30 wt %,
depending on the pen architecture. Further, one or more non-ionic,
cationic, and/or anionic surfactant can be present, ranging from 0
wt % to 5.0 wt %. The balance of the formulation can be purified
water, or other vehicle components known in the art, such as
biocides, viscosity modifiers, materials for pH adjustment,
sequestering agents, preservatives, and the like. Typically, the
ink vehicle is predominantly water.
[0056] Classes of co-solvents that can be used can include
aliphatic alcohols, aromatic alcohols, diols, glycol ethers,
polyglycol ethers, caprolactams, formamides, acetamides, and long
chain alcohols. Examples of such compounds include primary
aliphatic alcohols, secondary aliphatic alcohols, 1,2-alcohols,
1,3-alcohols, 1,5-alcohols, ethylene glycol alkyl ethers, propylene
glycol alkyl ethers, higher homologs of polyethylene glycol alkyl
ethers, N-alkyl caprolactams, unsubstituted caprolactams, both
substituted and unsubstituted formamides, both substituted and
unsubstituted acetamides, and the like. Specific examples of
solvents that can be used include trimethylolpropane,
2-pyrrolidinone, and 1,5-pentanediol.
[0057] One or more of many surfactants can also be used as are
known by those skilled in the art of ink formulation and may be
alkyl polyethylene oxides, alkyl phenyl polyethylene oxides,
polyethylene oxide block copolymers, acetylenic polyethylene
oxides, polyethylene oxide (di)esters, polyethylene oxide amines,
protonated polyethylene oxide amines, protonated polyethylene oxide
amides, dimethicone copolyols, substituted amine oxides, and the
like. The amount of surfactant added to the formulation of this
invention may range from 0 wt % to 5.0 wt %. It is to be noted that
the surfactant that is described as being usable in the ink vehicle
is not the same as the surfactant that is described as being
adhered to the surface of the latex, though many of the same
surfactants can be used for either purpose.
[0058] Consistent with the formulation of this invention, various
other additives may be employed to optimize the properties of the
ink composition for specific applications. Examples of these
additives are those added to inhibit the growth of harmful
microorganisms. These additives may be biocides, fungicides, and
other microbial agents, which are routinely used in ink
formulations. Examples of suitable microbial agents include, but
are not limited to, Nuosept (Nudex, Inc.), Ucarcide (Union carbide
Corp.), Vancide (R.T. Vanderbilt Co.), Proxel (ICI America), and
combinations thereof.
[0059] Sequestering agents, such as EDTA (ethylene diamine tetra
acetic acid), may be included to eliminate the deleterious effects
of heavy metal impurities, and buffer solutions may be used to
control the pH of the ink. From 0 wt % to 2.0 wt %, for example,
can be used. Viscosity modifiers and buffers may also be present,
as well as other additives known to those skilled in the art to
modify properties of the ink as desired. Such additives can be
present at from 0 wt % to 20.0 wt %.
[0060] Colorant-containing ink-jet inks that can be overcoated with
the latex compositions of the present invention include any ink-jet
ink that is functional with a latex overcoating of the present
invention. Examples of such inks or ink-sets include those
available from Hewlett-Packard Company. Though ink-jet ink produced
images can be overcoated with the compositions of the present
invention, other printed images can also be coated, included laser
printer produced images, offset ink printed images, silver halide
photographic images, photo copier produced images, and the
like.
[0061] The present latex-containing coating can be printed through
a set of ink-jet nozzles that is separate from the nozzles used to
print the colored ink-jet ink. The coating can be printed
subsequent to the printing of the colored ink after any functional
time interval. For example, depending on the application, it may be
desirable to print the latex overcoating composition immediately
after application of the colorant-containing ink-jet ink, and in
other embodiments, it may be desirable to print the latex
overcoating after several seconds or even minutes. The overcoat
nozzles can be included in the same pen architecture as the ink-jet
ink, or can be included in separate pen architecture. In one
embodiment, a set of overcoat nozzles at both the leading end and
the trailing end of the collective colored ink-jet nozzles can be
used to allow for subsequent overcoat printing in a bi-directional
traversing pen printer. Further, the overcoat can be printed at a
higher drop weight than that of the colorant-containing ink-jet
ink. Higher drop weight is generally provided by larger nozzle
diameters, in addition to other pen geometry expansions. Higher
drop weight can also allow for a printed overcoat print dot to
spread beyond the boundary of the colored ink dot it protects with
greater print film thickness. This technique can provide greater
composite print film durability. Further, larger diameter nozzles
generally allow printing with less vehicle co-solvent, further
improving print film durability.
EXAMPLES
[0062] The following examples illustrate embodiments of the
invention that are presently known. Thus, these examples should not
be considered as limitations of the present invention, but are
merely in place to teach how to make the best-known compositions of
the present invention based upon current experimental data. As
such, a representative number of compositions and their method of
manufacture are disclosed herein.
Example 1
Preparation of Various Latexes
[0063] Nine latex copolymers were prepared using the same procedure
and total weight percents of monomers and additives, the only
difference being the individual monomers and weight percent for
each monomer selected. The monomer content for each copolymer is
set forth in Table 2 below: TABLE-US-00002 TABLE 2 Monomer content
for each of nine copolymers prepared Monomers (wt %) Copolymer MMA
Styrene BMA HMA EHMA HA MES MAA EGDMA 1 74 15 10 1 2 58 31 10 1 3
48 41 10 1 4 41 48 10 1 5 40 49 10 1 6 20 69 10 1 7 89 10 1 8 20 59
10 1 9 20 73 6 1 In Table 1 above, the abbreviations are defined as
follows: MMA methyl methacrylate BMA butyl methacrylate HMA hexyl
methacrylate EHMA 2-ethylhexyl methacrylate HA hexyl acrylate MES
methacrylolyoxy ethyl succinate MAA methacrylic acid EGDMA ethylene
glycol dimethacrylate
[0064] The procedure used to prepare each individual latex was as
follows. A 200 gram monomer mix consisting of three or four
monomers according to Table 2 was mixed into 70 ml of water. Each
mixture was emulsified with Rhodafac RS710 surfactant in 14.6 g of
water. The Rhodafac concentration for each copolymer preparation
was varied from between 1.5 wt % to 2.5 wt % to maintain a
collective particle size between 220 nm to 260 nm. A solution of
potassium persulfate (1 g) in water (50 ml) was added dropwise to a
reactor containing 90.degree. C. preheated water (650 ml). The drop
rate was adjusted to fully release the persulfate over a period of
24 minutes. Three minutes into the persulfate addition, the
emulsion was dropwise added to the reactor over a period of 20
minutes. The reaction was maintained at 90.degree. C. for 1.5 hour,
and then cooled to room temperature. The nine respective latex
polymers obtained were neutralized with potassium hydroxide
solution to bring the pH of each latex solution to about 8.5. Each
of the nine latex copolymers prepared were then filtered with a 200
mesh filter to particle sizes from about 220 to 260 nm.
Example 2
Performance of Latexes
[0065] The bulk or surface dielectric constant, bulk density, and
glass transition temperature of latex copolymeric particulates of
Example 1 can be predicted, provided certain information is known
about the monomers used in the latex particulate. Specifically, by
using the relationships described in Formulas 1-3 provided above,
and the homopolymer values shown in Table 1, the nine latexes
prepared in Example 1 were calculated to have the respective bulk
or surface dielectric constants and bulk densities shown in Table 3
below. All of the latex copolymers prepared had a glass transition
temperature that would be acceptable for use at room temperature.
Table 3 below shows the results of tests conducted with respect to
dispersion stability, freqcel, and printability, as follows:
TABLE-US-00003 TABLE 3 Bulk density and surface dielectric constant
compred to dispersion stability, freqcel, and printability Bulk
Surface Density Dielectric Dispersion Copolymer (g/cm.sup.3)
Constant Stability Freqcel Printability 1 1.16 3.12 Poor poor poor
2 1.13 3.09 Poor poor poor 3 1.12 3.07 Poor poor poor 4 1.11 3.06
Poor poor poor 5 1.04 2.86 acceptable acceptable acceptable 6 1.04
2.81 acceptable acceptable acceptable 7 1.04 2.80 acceptable
acceptable acceptable 8 1.04 2.77 acceptable acceptable acceptable
9 1.03 2.72 acceptable acceptable acceptable
[0066] With respect to dispersion stability shown in Table 3 above,
a portion of the latexes prepared in accordance with Example 1 were
each diluted to 0.25 wt % solids in water, each dilution filling a
standard test tube. The test tubes were placed vertical at rest in
a standard test tube rack and monitored for particle layering and
settling over an eight-month period. All latexes having a computed
density of over 1.10 g/cm.sup.3 showed particle precipitation
within three weeks, the severity of layering was proportional to
density. The latexes having densities less than 1.05 g/cm.sup.3
showed no layering or settling over the eight-month period.
[0067] With respect to the freqcel and printabilty (decel and
decap) observations provided in Table 3, each of the latexes
prepared in accordance with Example 1 were incorporated into a
standardized ink formulation and print tested for freqcel, decel,
and decap using a Hewlett-Packard thermal ink-jet pen. Latexes
having computed dielectric constant above 3.0 failed to print above
8 kHz drop frequency and showed poor printability as measured by
decel and decap metrics. The severity of freqcel, decel, and decap
problems increased proportionately as the latex dielectric constant
was increased. The latex having the highest dielectric constant
(3.12) failed to print at 3 kHz. Latexes having dielectric constant
below 3.0 showed significant improvement in freqcel, decel and
decap, with improvement appearing to be inversely proportional to
latex dielectric constant. Those latexes having dielectric constant
below 2.8 had an even better freqcel, decel and decap
performance.
Example 3
Preparation of Core-Shell Latex Particulates
[0068] A core-shell latex was synthesized using a seeded
polymerization process. The core, in this case, was a copolymer of
63 wt % methyl methacrylate and 37 wt % hexyl acrylate, having a
computed dielectric constant of 3.01. The shell was a copolymer of
53 wt % hexyl methacrylate, 6 wt % methyl methacrylate, and 1 wt %
diethyleneglycol dimethacrylate, having a computed dielectric
constant of 2.80. The shell was polymerized to encapsulate the
core. The core to shell weight ratio was about 40:60. The resultant
latex was then tested identically in accordance with Example 3. The
freqcel, decel and decap results compared favorably to those
latexes of roughly uniform copolymeric material having a bulk
dielectric constant of 2.80 described in Example 2.
Example 4
Preparation of Latex Particulates Having Non-Reactive Surfactant
Adsorbed Thereon
[0069] About 102.5 g of methyl methacrylate, 120 g of hexyl
acrylate, 25 g of mono-methacryloyloxyethyl succinate, 2.5 g of
ethylene glycol dimethacrylate, and 1 g of isooctylthioglycolate
were mixed together in an addition funnel to form a monomer
mixture. About 85 g of water and 20.8 g of 30% RHODAFACT.TM.
(non-reactive surfactant) surfactant were added to the monomer
mixture and sheared gently to form an emulsion. At the same time,
725 ml of water were heated to 90.degree. C. in a reactor. An
initiator solution was separately prepared by dissolving 0.87 g of
potassium persulfate in 100 ml of water. The initiator solution was
added dropwise to the reactor at a rate of 3 ml/min with stirring.
The monomer emulsion was simultaneously added dropwise to the
reactor, starting 3 minutes after the start of initiator addition
and over a period of 30 minutes. The reaction mixture was
maintained at 90.degree. C. for 2 hours with stirring following
addition of the additives. The reaction mixture was allowed to cool
to 50.degree. C. at which time 23 g of 17.5% potassium hydroxide
solution was added to bring the pH of the reaction mixture to 8.5.
The resultant latex had a particle size of 230 nm.
Example 5
Preparation of Latex Particulates Having Reactive Surfactant
Attached Thereto
[0070] About 102.5 g of methyl methacrylate, 120 g of hexyl
acrylate, 25 g of mono-methacryloyloxyethyl succinate, 2.5 g of
ethylene glycol dimethacrylate, and 1 g of isooctylthioglycolate
were mixed together in an addition funnel to form a monomer
mixture. About 105 g of water and 0.62 g of MAXEMUL.TM. 6106
(reactive surfactant) were added to the monomer mixture and sheared
gently to form an emulsion. At the same time, 725 ml of water were
heated to 90.degree. C. in a reactor. An initiator solution was
separately prepared by dissolving 0.87 g of potassium persulfate in
100 ml of water. The initiator solution was added dropwise to the
reactor at a rate of 3 ml/min with stirring. The monomer emulsion
was simultaneously added dropwise to the reactor, starting 3
minutes after the start of initiator addition and over a period of
30 minutes. The reaction mixture was maintained at 90.degree. C.
for 2 hours with stirring following addition of the additives. The
reaction mixture was allowed to cool to 50.degree. C. at which time
23 g of 17.5% potassium hydroxide solution was added to bring the
pH of the reaction mixture to 8.5. The resultant latex had a
particle size of 320 nm.
Example 6
Preparation of Ultraviolet Absorber-Containing Latex Particulates
Having Non-Reactive Surfactant Adsorbed Thereon
[0071] About 102.5 g of methyl methacrylate, 117.5 g of hexyl
acrylate, 2.5 g of ultraviolet absorber monomer Norbloc 7966, 25 g
of mono-methacryloyloxyethyl succinate, 2.5 g of ethylene glycol
dimethacrylate, and 1 g of isooctylthioglycolate were mixed
together in an addition funnel to form a monomer mixture. About 85
g of water and 20.8 g of 30% RHODAFAC.TM. (non-reactive surfactant)
surfactant were added to the monomer mixture and sheared gently to
form an emulsion. At the same time, 725 ml of water were heated to
90.degree. C. in a reactor. An initiator solution was separately
prepared by dissolving 0.87 g of potassium persulfate in 100 ml of
water. The initiator solution was added dropwise to the reactor at
a rate of 3 ml/min with stirring. The monomer emulsion was
simultaneously added dropwise to the reactor, starting 3 minutes
after the start of initiator addition and over a period of 30
minutes. The reaction mixture was maintained at 90.degree. C. for 2
hours with stirring following addition of the additives. The
reaction mixture was allowed to cool to 50.degree. C. at which time
23 g of 17.5% potassium hydroxide solution was added to bring the
pH of the reaction mixture to 8.5. The resultant latex had a
particle size of 230 nm.
Example 7
Preparation of Ink-Jettable Overcoat Composition
[0072] An ink-jettable coating composition was prepared by
dispersing 5 wt % solids of the composition of Example 4 in a
liquid vehicle. The liquid vehicle included 79 wt % water, 15 wt %
organic cosolvent, 0.5 wt % vehicle surfactant, and 0.5 wt %
biocide. The overcoat composition prepared provides good protection
to both pigment-based and dye-based ink-jet inks printed on porous
and other media.
Example 8
Preparation of Alternative Ink-Jettable Overcoat Composition
[0073] An ink-jettable coating composition was prepared by
dispersing 5 wt % solids of the composition of Example 5 in a
liquid vehicle. The liquid vehicle included 79 wt % water, 15 wt %
organic cosolvent, 0.5 wt % vehicle surfactant, and 0.5 wt %
biocide. The overcoat composition prepared was colorless and
provides good protection to both pigment-based and dye-based
ink-jet inks printed on porous and other media.
Example 9
Preparation of Ultraviolet Absorber-Containing Ink-Jettable
Overcoat Composition
[0074] An ink-jettable coating composition was prepared by
dispersing 5 wt % solids of the composition of Example 6 in a
liquid vehicle. The liquid vehicle included 79 wt % water, 15 wt %
organic cosolvent, 0.5 wt % vehicle surfactant, and 0.5 wt %
biocide. The overcoat composition prepared was colorless and
provides good protection to both pigment-based and dye-based
ink-jet inks printed on porous and other media.
[0075] While the invention has been described with reference to
certain preferred embodiments, those skilled in the art will
appreciate that various modifications, changes, omissions, and
substitutions can be made without departing from the spirit of the
invention. It is intended, therefore, that the invention be limited
only by the scope of the following claims.
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