U.S. patent application number 11/043850 was filed with the patent office on 2006-07-27 for pigments modified with surface counter-ions.
Invention is credited to Alexey S. Kabalnov, Hakan Wennerstrom.
Application Number | 20060162612 11/043850 |
Document ID | / |
Family ID | 36282603 |
Filed Date | 2006-07-27 |
United States Patent
Application |
20060162612 |
Kind Code |
A1 |
Kabalnov; Alexey S. ; et
al. |
July 27, 2006 |
Pigments modified with surface counter-ions
Abstract
The present invention relates to inkjet ink pigments having
surface counter-ions replaced with other counter-ions with larger
size and/or hydrophobicity. The effect of the replacement is to
decrease pigment-ink-vehicle-separation in the inkjet ink printing
process.
Inventors: |
Kabalnov; Alexey S.;
(Corvallis, OR) ; Wennerstrom; Hakan; (Lund,
SE) |
Correspondence
Address: |
HEWLETT PACKARD COMPANY
P O BOX 272400, 3404 E. HARMONY ROAD
INTELLECTUAL PROPERTY ADMINISTRATION
FORT COLLINS
CO
80527-2400
US
|
Family ID: |
36282603 |
Appl. No.: |
11/043850 |
Filed: |
January 25, 2005 |
Current U.S.
Class: |
106/31.6 ;
106/31.75; 106/400; 106/401; 106/493; 106/499 |
Current CPC
Class: |
C09D 11/322 20130101;
C09D 11/326 20130101 |
Class at
Publication: |
106/031.6 ;
106/031.75; 106/400; 106/401; 106/493; 106/499 |
International
Class: |
C09D 11/00 20060101
C09D011/00; C04B 14/00 20060101 C04B014/00; C08K 5/00 20060101
C08K005/00 |
Claims
1. A surface-modified pigment comprising: an outer surface; ionic
groups chemically grafted to the outer surface; and replacement
counter ions bound to the ionic groups, wherein the replacement
counter ions replace original counter ions bound to the ionic
groups, the replacement counter ions being larger in size, more
hydrophobic, or both larger in size and more hydrophobic than the
original counter ions in aqueous solution.
2. The surface-modified pigment of claim 1, wherein the ionic
groups chemically grafted to the outer surface of the pigment are
anionic groups and the replacement counter-ions are cationic
counter-ions.
3. The surface-modified pigment of claim 1, where the ionic groups
chemically grafted to the outer surface of the pigment are cationic
groups and the replacement counter-ions are anionic
counter-ions.
4. The surface-modified pigment of claim 3, wherein the anionic
counter-ions are alkyl sulfates.
5. The surface-modified pigment of claim 1, wherein the replacement
counter ions are hydrophobic cations or non-sodium alkali metal
cations.
6. The surface-modified pigment of claim 1, wherein the replacement
counter ions are combinations of at least two of the group
consisting of hydrophobic cationsand alkali metal cations.
7. The surface-modified pigment of claim 1, wherein the replacement
counter ions are selected from the group consisting of Li, K,
NH.sub.4.sup.+, N(CH.sub.3).sub.4.sup.+,
N(C.sub.2H.sub.5).sub.4.sup.+, N(C.sub.3H.sub.7).sub.4.sup.+,
N(C.sub.4H.sub.9).sub.4.sup.+.
8. The surface-modified pigment of claim 1, wherein the replacement
counter ions are a combination of at least two of the group
consisting of Li, Na, K, NH.sub.4.sup.+, N(CH.sub.3).sub.4.sup.+,
N(C.sub.2H.sub.5).sub.4.sup.+, N(C.sub.3H.sub.7).sub.4.sup.+, and
N(C.sub.4H.sub.9).sub.4.sup.+.
9. The surface-modified pigment of claim 1, wherein the replacement
counter ions are quaternary amines, quatemary phosphines, quatemary
arsines or combinations thereof.
10. An ink composition comprising a liquid vehicle and a
surface-modified pigment, wherein the surface-modified pigment
comprises a pigment with an outer surface, ionic groups chemically
grafted to the outer surface; and replacement counter ions bound to
the ionic groups, wherein the replacement counter ions replace
original counter ions bound to the ionic groups, the replacement
counter ions being larger in size, more hydrophobic, or both larger
in size and more hydrophobic than the original counter ions in
aqueous solution.
11. The ink composition of claim 10, wherein the ionic groups
chemically grafted to the outer surface of the pigment are anionic
groups and the replacement counter-ions are cationic
counter-ions.
12. The ink composition of claim 10, wherein the ionic groups
chemically grafted to the outer surface of the pigment are cationic
groups and the replacement counter-ions are anionic
counter-ions.
13. The ink composition of claim 12, wherein the anionic
counter-ions comprise alkyl sulfates.
14. The ink composition of claim 10, wherein the replacement
counter ions are hydrophobic cations or non-sodium alkali metal
cations.
15. The ink composition of claim 10, wherein the replacement
counter ions are combinations of at least two of the group
consisting of hydrophobic cations and alkali metal cations.
16. The ink composition of claim 10, wherein the replacement
counter ions are selected from the group consisting of Li, K,
NH.sub.4.sup.+, N(CH.sub.3).sub.4.sup.+,
N(C.sub.2H.sub.5).sub.4.sup.+, N(C.sub.3H.sub.7).sub.4.sup.+,
N(C.sub.4H.sub.9).sub.4.sup.+ and combinations thereof.
17. The ink composition of claim 10, wherein the replacement
counter ions are a combination of at least two of the group
consisting of Li, Na, K, NH.sub.4.sup.+, N(CH.sub.3).sub.4.sup.+,
N(C.sub.2H.sub.5).sub.4.sup.+, N(C.sub.3H.sub.7).sub.4.sup.+, and
N(C.sub.4H.sub.9).sub.4.sup.+.
18. The ink composition of claim 10, wherein the replacement
counter ions are quaternary amines, quaternary phosphines,
quaternary arsines or combinations thereof.
19. A method of making a surface-modified pigment comprising a
pigment with an outer surface; ionic groups chemically grafted to
the outer surface; and replacement counter ions bound to the ionic
groups, the replacement counter ions replacing original counter
ions, the replacement counter ions being larger in size, more
hydrophobic or both larger in size and more hydrophobic than the
original counter ions in aqueous solution; the method comprising
the steps of: converting the pigment outer surface ionic groups
into acidic form by ion-exchanging with hydrogen proton as
counterion; mixing the pigment having outer surface ionic groups in
acidic form with replacement counter ions in basic form, the
replacement counter ions replacing the original counter ions.
20. The method of claim 19, wherein the ionic groups chemically
grafted to the outer surface of the pigment are anionic groups and
the replacement counter-ions are cationic counter-ions.
21. The method of claim 19, wherein the ionic groups chemically
grafted to the outer surface of the pigment are cationic groups and
the replacement counter-ions are anionic counter-ions.
22. The method of claim 21, wherein the anionic counter-ions
comprise alkyl sulfates.
23. The method of claim 19, wherein the replacement counter ions
are hydrophobic cationsor non-sodium alkali metal cations.
24. The method of claim 19, wherein the replacement counter ions
are combinations of at least two of the group consisting of
hydrophobic cationsand alkali metal cations.
25. The method of claim 19, wherein the replacement counter ions
are selected from the group consisting of Li, K, NH.sub.4.sup.+,
N(CH.sub.3).sub.4.sup.+, N(C.sub.2H.sub.5).sub.4.sup.+,
N(C.sub.3H.sub.7).sub.4.sup.+, N(C.sub.4H.sub.9).sub.4.sup.+ and
combinations thereof.
26. The method of claim 19, wherein the replacement counter ions
are a combination of at least two of the group consisting of Li,
Na, K, NH.sub.4.sup.+, N(CH.sub.3).sub.4.sup.+,
N(C.sub.2H.sub.5).sub.4.sup.+, N(C.sub.3H.sub.7).sub.4.sup.+, and
N(C.sub.4H.sub.9).sub.4.sup.+.
27. The method of claim 19, wherein the replacement counter ions
are quaternary amines, quaternary phosphines, quaternary arsines or
combinations thereof.
28. A method of using a surface-modified pigment to decrease
separation of ink vehicle and pigment particles in an inkjet
printhead, the modified pigment comprising: a pigment with an outer
surface; ionic groups chemically grafted to the outer surface; and
replacement counter ions bound to the ionic groups, the replacement
counter ions replacing original counter ions, the replacement
counter ions being larger in size, more hydrophobic, or both larger
in size and more hydrophobic than the original counter ions in
aqueous solution; the method comprising the steps of: converting
the pigment outer surface ionic groups into acidic form by
ion-exchanging with hydrogen proton as counterion; mixing the
pigment having outer surface ionic groups in acidic form with
replacement counter ions in basic form, the replacement counter
ions replacing the original counter ions; suspending the
surface-modified pigment in liquid vehicle to make ink, and
printing the ink onto a medium with an inkjet printhead.
29. The method of claim 28, wherein the ionic groups chemically
grafted to the outer surface of the pigment are anionic groups and
the replacement counter-ions are cationic counter-ions.
30. The method of claim 28, wherein the ionic groups chemically
grafted to the outer surface of the pigment are cationic groups and
the replacement counter-ions are anionic counter-ions.
31. The method of claim 30, wherein the anion counter-ions comprise
alkyl sulfates.
32. The method of claim 28, wherein the replacement counter ions
are hydrophobic cations or non-sodium alkali metal cations.
33. The method of claim 28, wherein the replacement counter ions
are combinations of at least two of the group consisting of
hydrophobic cations and alkali metal cations.
34. The method of claim 28, wherein the replacement counter ions
are selected from the group consisting of Li, K, NH.sub.4.sup.+,
N(CH.sub.3).sub.4.sup.+, N(C.sub.2H.sub.5).sub.4.sup.+,
N(C.sub.3H.sub.7).sub.4.sup.+, N(C.sub.4H.sub.9).sub.4.sup.+ and
combinations thereof.
35. The method of claim 28, wherein the replacement counter ions
are a combination of at least two of the group consisting of Li,
Na, K, NH.sub.4.sup.+, N(CH.sub.3).sub.4.sup.+,
N(C.sub.2H.sub.5).sub.4.sup.+, N(C.sub.3H.sub.7).sub.4.sup.+, and
N(C.sub.4H.sub.9).sub.4.sup.+.
36. The method of claim 28, wherein the replacement counter ions
are quaternary amines, quaternary phosphines, quaternary arsines or
combinations thereof.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to inkjet ink pigments
modified with counter-ions that are larger and/or more hydrophobic
than the original counter ions, the modification resulting in
decreased pigment-ink vehicle separation.
BACKGROUND OF THE INVENTION
[0002] There is a considerable interest in using pigments in ink
jet inks. Pigments, as opposed to dyes are present in the inks in
the form of particles. As a result, pigmented inks have improved
edge definition for text and line art, better waterfastness and
smudge-fastness and better print durability (lightfastness,
ozonefastness and humidfastness), compared to dyes. The downside of
pigmented inks however is that they are less reliable. Thus,
pigmented inks tend to have worse idle (or decap) times, as defined
below. When the ink is not printed, the pigments tend to clog the
firing chamber by retracting away from the nozzle
SUMMARY OF THE INVENTION
[0003] The present invention relates to a surface-modified pigment
comprising: [0004] an outer surface; [0005] ionic groups chemically
grafted to the outer surface; and [0006] replacement counter ions
bound to the ionic groups, [0007] wherein the replacement counter
ions replace original counter ions bound to the ionic groups, the
replacement counter ions being more hydrophobic and/or larger in
size than the original counter ions in aqueous solution.
[0008] The present invention further relates to an ink composition
comprising a liquid vehicle and a surface-modified pigment, wherein
the surface-modified pigment comprises [0009] a pigment with an
outer surface, [0010] ionic groups chemically grafted to the outer
surface; and [0011] replacement counter ions bound to the ionic
groups, [0012] wherein the replacement counter ions replace
original counter ions bound to the ionic groups, the replacement
counter ions being more hydrophobic and/or larger in size than the
original counter ions in aqueous solution.
[0013] In addition, the present invention relates to a method of
making a surface-modified pigment comprising [0014] a pigment with
an outer surface; [0015] ionic groups chemically grafted to the
outer surface; and [0016] replacement counter ions bound to the
ionic groups, the replacement counter ions replacing original
counter ions, the replacement counter ions being more hydrophobic
and/or larger in size than the original counter ions in aqueous
solution;
[0017] the method comprising the steps of: [0018] converting the
pigment outer surface ionic groups into acidic form by
ion-exchanging with hydrogen proton as counterion; [0019] mixing
the pigment having outer surface ionic groups in acidic form with
replacement counter ions in basic form, the replacement counter
ions replacing the original counter ions.
[0020] Furthermore, the present invention relates to a method of
using a surface-modified pigment to decrease separation of ink
vehicle and pigment particles in an inkjet printhead, the modified
pigment comprising: [0021] a pigment with an outer surface; [0022]
ionic groups chemically grafted to the outer surface; and [0023]
replacement counter ions bound to the ionic groups, the replacement
counter ions replacing original counter ions, the replacement
counter ions being more hydrophobic and/or larger in size than the
original counter ions in aqueous solution;
[0024] the method comprising the steps of: [0025] converting the
pigment outer surface ionic groups into acidic form by
ion-exchanging with hydrogen proton as counterion; [0026] mixing
the pigment having outer surface ionic groups in acidic form with
replacement counter ions in basic form, the replacement counter
ions replacing the original counter ions; [0027] suspending the
surface-modified pigment in liquid vehicle to make ink, and [0028]
printing the ink onto a medium with an inkjet printhead.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0029] In U.S. Pat. No. 6,585,818 of Thakkar and Sun, which is
herein incorporated by reference, the inventors describe ink
compositions, containing a hydrophilic carbon black, organic
solvents and water. As the inventors point out: "As water
evaporates from the ink, the percentage of organic components in
the ink formulation increases so that the ink becomes less
hydrophilic. As the ink becomes less hydrophilic, the
self-dispersed pigment which is strongly hydrophilic is pulled back
into the bulk of aqueous phase." (U.S. Pat. No. 6,585,818, column
2, lines 7-11)
[0030] Tools are needed that can finely tune the degree of the
pigment retraction in an effective and economical manner. In this
application, pigment retraction will be called `pigment-ink vehicle
separation`, and abbreviated as PIVS. Specifically, the need
remains to finely adjust the rate of the pigment retraction.
[0031] As pigmented ink dries in an inkjet printhead, a quick
pigment-ink-vehicle separation (PIVS) may take place, which results
in the ink channel leading to the nozzles being substantially
devoid of the colorant. While the rapid rate of PIVS is undesirable
because of the idle (or decap) time being too short, the very slow
rate of PIVS may be beneficial for the printhead functioning, in
particular, when the printhead is stored for a prolonged time
either in uncapped or in capped position.
[0032] In order to alleviate the problem of PIVS, the inkjet
printers force the printhead to spit onto a special absorbing pad,
or `spitoon`, on a regular basis after the period of idle time. The
rate of spitting is substantially controlled by the rate of PIVS.
Very frequent spits are highly undesirable, because the inks are
consumed during spitting and printing is slowed down. On the other
hand, PIVS is beneficial for the longer-time storage of the
printhead either capped or uncapped, because it prevents the
irreversible clogging of the nozzles. From the printer
functionality standpoint, therefore, the best performance occurs
with a system that shows very slow PIVS, on the time-scale of
hours.
[0033] PIVS originates as ink sits in the ink channels and the
water in the ink evaporates. As the water evaporates, pigment
particles in the ink normally tend to move in the ink channel
towards the nozzles unless they exhibit incompatibility with the
solvent. Thus the pigment particles have two separate forces
pulling them independently in different directions, one force based
on the evaporation of the water in the ink and one force based on
the incompatibility of the pigment particles with the solvent. This
two-way movement of the pigment particles in the ink feed channel
creates a colorant band, or focusing point, which results in an
increased pigment concentration in the middle of the ink feed
channel. Over time this colorant band or focusing point gradually
moves toward the standpipe and away from the nozzle. Eventually the
colorant band can be completely pushed into the standpipe or it can
stop at some place in the ink channel before it reaches the
standpipe.
[0034] As described above, it has been found that pigment
counter-ions, bound to the ionic groups chemically grafted to the
surface of the pigment, play a major role in whether PIVS occurs or
not. The likely reason is because the change in the pigment
counter-ions changes the solvation energy of the pigment particle
as a whole. Following from this, pigments carrying the surface
replacement counterions which are larger and/or more hydrophobic
than the original counter-ions on the pigment surface cause less
PIVS.
[0035] The present invention relates to pigments having larger
and/or more hydrophobic surface cations, inks having such pigments
and methods of making and using such pigments. The degree of PIVS
is controlled in such pigments with counter-ions on the pigment
surface that are larger and/or more hydrophobic than the original
surface counterions.
[0036] In one embodiment of the present invention, counter-ions
that are larger and/or more hydrophobic replace the original
counter-ions that are bound to ionic groups chemically grafted to
the outer surface of the pigment particles. Such chemical grafting
of ionic groups can be done in several ways. Non-limiting examples
of such methods include: reacting carbon black particles with a
diazonium salt of aromatic carboxy- or sulfo-acid as set out in
Belmont et al., U.S. Pat. No. 5,571,311; and, alternatively,
introducing ionic surface groups by an oxidation reaction with
sodium hypochlorite as set out in Parker, U.S. Pat. No. 3,347,632.
The methods of chemical grafting described in these patents are
incorporated herein by reference.
[0037] It needs to be mentioned that the size of cations in aqueous
solution is in certain situations different from their atomic
radius. This is the result of the effect of hydration. Therefore,
lithium ion has a smaller crystallographic radius than sodium,
sodium being the usual first counter-ion of the pigment surface
before it is modified according to the present invention. However,
lithium-containing inorganic salts have smaller diffusivity in
water and smaller electrical conductivity in water than the
corresponding sodium salts, two characteristics that are found in
counterions which are actually larger in size (in terms of their
atomic radius) than sodium, such as K, NH.sub.4.sup.+,
N(CH.sub.3).sup.4+ (tetramethyl amine)(TMA),
N(C.sub.2H.sub.5).sub.4.sup.+ (tetraethyl amine)(TEA),
N(C.sub.3H.sub.7).sub.4.sup.+(tetrapropyl amine)(TPA), and
N(C.sub.4H.sub.9).sub.4.sup.+ (tetrabutyl amine)(TBA). The above
two conductivity characteristics make lithium ions, like the other
counter ions above, larger than sodium ion when each of the ions
are hydrated.
[0038] As non-limiting examples of such larger and/or more
hydrophobic replacement counter-ions on the pigment particles, the
counter-ions can include hydrophobic cations, non-sodium alkali
metal cations, or mixtures thereof. For example, replacement
counter-ions can include such groups as quatemary amines,
phosphines or arsines. As a further non-limiting example, the
replacement counter-ions can include: Li, K, NH.sub.4.sup.+,
N(CH.sub.3).sup.4+ (TMA), N(C.sub.2H.sub.5).sub.4.sup.+ (TEA),
N(C.sub.3H.sub.7).sub.4.sup.+(TPA), and
N(C.sub.4H.sub.9).sub.4.sup.+(TBA).
[0039] In another embodiment of the present invention, a mixture of
two or more kinds of counter-ions that are larger and/or more
hydrophobic replaces the original counter-ions on the pigment
particles. As a non-limiting example, such replacement counter-ions
on the pigment particles can include a combination of hydrophobic
cations and non-sodium alkali metal cations. For example, such a
combination can include such groups as quatemary amines, phosphines
or arsines. As a further non-limiting example, the replacement
counter-ions can include a combination of at least two of the
following: Li, Na, K, NH.sub.4.sup.+, N(CH.sub.3).sup.4+ (TMA),
N(C.sub.2H.sub.5).sub.4.sup.+ (TEA),
N(C.sub.3H.sub.7).sub.4.sup.+(TPA),
N(C.sub.4H.sub.9).sub.4.sup.+(TBA) and combinations thereof. In the
examples below, the chemical modification is conducted on anionic
pigments, that is, on pigments having anionic groups grafted to
their surface with cations as counter-ions. However, an alternative
implementation is also possible, with cationic groups grafted to
the surface of the pigment and anions as counter-ions. For anions
to be used as counter ions, one could use e.g., alkyl sulfates of
variable alkyl chain length (methylsulfate, ethylsulfate,
propylsulfate, etc). In the case of both cations and anions used as
counter-ions, proper adjustment of the hydrophobicity of the
counter-ion can be made by the selection of the right alkyl
length.
[0040] A non-limiting example of the method of making pigments
having counter-ions with larger and/or more hydrophobic cations is
as follows. A self-dispersed anionically-modified pigment is
converted into acidic form by using an ion exchange resin, and then
ion-exchanged by a base, or a mixture of bases, where the cation of
the base is the one that is going to be introduced on the
pigment.
[0041] In the examples below, the experimentation was conducted
with the LEG-1 solvent (Liponics), which is a polyethoxylated ether
of glycerol. The scope of the invention is however not limited to
this solvent and other ink-jet solvents can be used, such as
oligo-ethyleneglycols, alkylglycols, 2-pyrrolidone, etc.
EXAMPLES
Example 1
Ink Preparation
[0042] Commercial carbon black pigment CaboJet 200 (Cabot) was used
as the basis for the experiments. The pigment contains d.about.110
nm pigment particles of carbon black, with phenylsulfonic groups
chemically attached to the surface. The pigment is supplied as a 20
wt % solution, with sodium ion as the counter-ion.
[0043] In order to prepare different ionic forms of the pigment,
the stock solution was ion-exchanged into the sulfo-acid form by
mixing 200 g 20% aqueous pigment stock with 7g of Dowex-5W ionite
in acid form overnight with filtration. The procedure was repeated
4 times to ensure completeness of the exchange. For each of the
inks, the acid form was then converted into pH-neutral form by
ion-exchange using at least one of the bases: lithium, potassium,
ammonium, tetramethylammonium, tetraethylammonium,
tetrapropylammonium, and tetrabutylammonium hydroxides. The final
inks were formulated at two different pigment loadings: 4% and 0.1%
(Table 1). All the inks were formulated with the same solvent,
LEG-1 (Liponics), which was present at 10 wt %. The solvent
represents a polyethoxylated ether of glycerol.
[0044] Table 2 below demonstrates the degree of conversion of the
sodium form of the pigment to the other ionic forms. Table 3 lists
the pH and conductivities of some of the final inks. TABLE-US-00001
TABLE 1 Compositions of inks studied Ink name Pigment LEG-1 water
Na 4% 4% 10% balance K 4% 4% 10% balance Li 4% 4% 10% balance
NH.sub.4.sup.+ 4% 4% 10% balance TMA 4% 4% 10% balance TEA 4% 4%
10% balance TPA 4% 4% 10% balance TBA 0.1% 4% 10% balance Na 0.1%
0.1% 10% balance K 0.1% 0.1% 10% balance Li 0.1% 0.1% 10% balance
NH.sub.4.sup.+ 0.1% 0.1% 10% balance TMA 0.1% 0.1% 10% balance TEA
0.1% 0.1% 10% balance TPA 0.1% 0.1% 10% balance TBA 0.1% 0.1% 10%
balance
[0045] TABLE-US-00002 TABLE 2 Elemental composition of the inks,
containing 4 wt % of CaboJet pigments in different ionic forms Na
Sample ID: K, mmol/L Li, mmol/L Na, mMol/L impurities, % Li form
0.6 32.9 2.0 5.75% K form 31.8 2.3 6.64% NH4 form 0.6 1.9 TMA form
0.5 1.7 TEA form 0.7 1.8 TPA form 0.5 1.8 TBA form 0.5 1.8
[0046] TABLE-US-00003 TABLE 3 pH and conductivity of the inks,
containing 4 wt % of CaboJet pigments in different ionic forms, and
10% LEG-1 Conductivity of 4 wt % ink, Counter-ion pH of 4 wt % ink
.mu.S/cm Li 6.28 821 Na 6.88 946 K 5.9 1161 NH.sub.4.sup.+ 6.97
1215 TMA 7.6 871 TEA 7.52 752 TPA 9.46 628 TBA 6.81 540
Example 2
Observation of Pigment Retraction from the Nozzles (PIVS)
[0047] The inks were filled into empty printheads similar to HP
hpc4812a which have a transparent orifice plate, so that the
pigment retraction could be monitored by looking through the
orifice plate. PIVS measurements were done by using a Nikon
microscope equipped with a digital camera and taped on a regular
VCR. The `time zero` moment was set by doing a wipe of a printhead
with a dry blotter. The experiments were made at ambient humidity,
which was 30-60%. For each system, the time of PIVS was defined as
the time needed for the pigment front to cross the middle of
circular islands in the end of the ink feed channel from the moment
of the wipe. The time of PIVS showed a surprisingly good
reproducibility despite the variations in external relative
humidity, with the typical scatter of about 10%.
[0048] In Table 4, it can be clearly seen that there is a strong
counter-ion dependence of PIVS. The following counter-ion sequence
of PIVs was observed with the rate decreasing from left to right:
TMA>Na.about.NH4+>Li>>TPA>>TBA. Thus, at 4%
pigment loading, for TMA, the rate of PIVS was about 3.5 minutes.
It took twice as much for TEA, and about .times.10-100 longer for
TPA. For the 4% dispersion, the
[0049] TBA form showed a negligibly slow rate of PIVS. By combining
these counter-ions in a blend, the range of PIVS timescale would be
covered, from minutes to hours, as demonstrated by the last example
of Table 4. The concentration of pigment also affects the rate of
PIVS: at higher pigment concentration, the rate was slower,
although the order of cation effect was conserved. TABLE-US-00004
TABLE 4 Time of PIVS as the function of the counter-ion nature Time
of PIVS, minutes Time of 0.1% PIVS, 4% pigment pigment Ion load
load Li 3.9 9.5 Na 2.4 4.6 K 2.8 4.8 NH4+ 2.9 6.1 TMA 2.3 3.5 TEA
3.3 6.6 TEA-TPA 1:1 4.4 No data mixture TPA 7.4 No PIVS TBA 60.0 No
PIVS
[0050] While several embodiments have been described in detail, it
will be apparent to those skilled in the art that the disclosed
embodiments may be modified. Therefore, the foregoing description
is to be considered exemplary rather than limiting.
* * * * *