Note: Descriptions are shown in the official language in which they were submitted.
1315091
DYES CONTAINING TETRAMETHYLAMMONIUM
CATIOh FOR INK-JET PRINTINC INKS
1 TECHNICAL FIELD
Tbe present invention relates to ink compoqitions for
ink-jet printers, and, more particularly, to ink compo i-
tions iD which the Qolubility of the dye i3 increased byreplacement of sodium cations.
BACKGROUND ART
The use of aqueous-based inks for ink-jet printers is
well-known. Such composition~ are relatively inexpensive
and easy to prepare; typically, the ink compriseq water
and a glycol ether, usually diethylene glycol (commonly
referred to as the vehicle), and a dye. Typically, the
water and glycol ether are present in generally the same
proportion ana the dye, for example, Food Black 2, is
present up to about 6~ of the total composition, depending
on tbe desired density of the print.
The prior art inks generally use exi~ting commercial
dye salt~ (cation plus dye anion) as formea, which are
aimply dis~olve~ in the ~ehicle and filtered to prepare
the in~. Such dyes, whicb generally contain a plurality
of sulfonate anion groups, are designea to form solids in
paper or cloth, employing cations guch as sodium cations,
which promote precipitation of the dye salt. Consequent-
ly, the dyes do not easily remain liquid ln the orifice of
an ink-Jet ~rinter.
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Thus, a persistent problem associated with aqueous-
based inks is their propensity to crust over a period of
time, eventually leading to plugging of the orifice in the
printer mechanism from which droplets of ink are expelled
in the printing operation. Crusting is the crystallization
of the ink around the orifice in the print head, causing
partial or full blockage of the orifice, leading to
misdirection of the drop (partial blockage) or prevention
of drop ejection (full blockage). The crusting problem
arises from the evaporation of the water from the ink
solvent (vehicle) and the consequent precipitation of the
dye salt which has become substantially insoluble as a
result of this water loss.
Attempts have been made to solve the crusting problem.
Hygroscopic agents have been added to reduce the rate of
water evaporation by their ability to pick up water vapor
from the air. Exemplary of such hygroscopic agents are
water-soluble polymers, alkanol amines, amides and
polyhydric alcohols.
While some improvement has been realizes with these
hygroscopic agents, a total solution to the crusting prob-
lems has not yet been achieved. Further, apparently no
methods are known to prevent crusting of the anionic dyes
in neutral to mildly acidic aqueous-based inks (pH 4 to 7).
Attempts are continuing to develop inks in which the
dye solubility is increased.
Other approaches include developing new dyes for ink-
jet inks. For example, U.S. Patent 4,557,761 discloses a
variety of sulfonate-containing dyes with cations such as
sodium, potassium, lithium, ammonium and amine salt cat-
ions.
However, as shown above, dyes with sodium cations have
~, certain deficiencies. Dyes with potassium cations also
suffer from certain deficiencies, notably evidencing
crusting. Dyes with ammonium cations, on the other hand,
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are not stable. Thus, the cations listed in U.S. Patent
4,557,761 cannot be considered to be equivalent.
Finally, many cations are not suitable for dyes
employed in inks used in thermal ink-jet printing. In
this instance, a problem known as kogation may occur.
Kogation is a coined term, unique to thermal ink-jet
printing, and describes the extent of decomposition of
the ink on the resistors of thermal ink-jet printers as
a consequence of heating. Such heating is used to form
droplets of ink, which are propelled toward the
substrate.
While sodium-containing dyes evidence crusting
problems, they also evidence superior kogation
properties. Dyes containing other cations which
evidence improved crusting also often evidence poor
kogation.
DISCLOSURE OF INVENTION
Accordingly, it is an object of an aspect of the
present invention to provide an ink composition
2~ evidencing increased dye solubility in the vehicle.
It is an object of an aspect of this invention to
provide an ink in which the crusting problem is minimal.
It is an object of an aspect of this invention to
provide an aqueous-based ink for ink-jet printers in
which kogation of the dye in the ink solvent (vehicle)
is not adversely affected by partial or total
replacement of sodium cations.
It is an object of an aspect of this invention to
provide an aqueous-based ink for ink-jet printers in
which the solubility of anionic dyes in mildly acidic to
mildly basic media is increased.
Various aspects of the invention are as follows:
An ink composition suitable for use in ink-jet
printers comprising:
(a) a vehicle comprising about 5 to 95% water and
the balance at least one glycol ether;
(b) a dye having at least one negatively charged
functional group per molecule, present in an amount up
to about 0.1 Molar of the vehicle composition, said dye
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3a
having a plurality of anionic sites, originally complexed
with sodium cations, at least a portion of said sodium
cations being replaced with tetramethylammonium cations,
said portion being in an effective amount to reduce
crusting of said ink without affecting kogation.
A process for increasing dye solubility without
adversely affecting kogation in an ink comprising a
vehicle and a dye, said vehicle comprising about 5 to 95%
water and the balance at least one member selected from
the group consisting of glycols and glycol ethers and
said dye having at least one negatively charged
functional group per molecule, said dye being present in
an amount up to about 0.1 Molar of the vehicle
composition and having a plurality of anionic sites,
originally complexed with sodium cations, said process
comprising replacing at least a portion of said sodium
cations with tetramethylammonium cations.
By way of added explanation, the ink composition of
the invention comprises a vehicle and an anionic dye
containing a plurality of sodium cations associated with
each dye molecule, at least about one-fourth of the
~odium cations being replaced by tetramethylammonium
~' ~IMA) cations.
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1 The dye containing TMA catlon~ evidence~ increa3ea
solubillty and reduced crusting ln inks commonly used in
ink-~et printing, yet ~how~ no tendency toward kogation.
~EST MODE(S) FOR CARRYING OUT THE INVENTION
The ink compositions of the invention comprise an
aqueous-based vehicle and a dye. The pH of the ink may be
maintained in the both the acidic and ba~ic regions,
ranging from about 4 to 9.
! The ~ehicle of the ink comprises water and at least
one of the glycols and glycol ethers commonly employed in
the ink~ used in ink-Jet printing. Example~ of suoh
compound~ include diethylene glycol, triethylene glycol
and polyethylene glycols. The water i9 pre~ent in an
amount ranging from about 5 to 95~, the balance being at
least one of the glycols and/or glycol etherq. Prefer-
ably, the vehicle comprises about 50~ water and the bal-
ance a glycol ether ~uch as diethylene glycol.
To the vehicle is added up to about 0.1 Molar of a
dye, preferably an anionic dye. The amount of the dye
added is a function of choi¢e, being largely dependent
upon the solubility of the dye in the vehicle (which
limits the upper range of dye ¢oncentration) and the
; 25 aesired density of the print achieved with the ink (which
limits the lower range of dye ¢oncentration - typically
about 0.005 Molar). Preferably, the concentration of the
dye in the ink composition is about 0.065 Molar. For Food
Bla¢k 2, a dye commonly used in ink-Jet inks, the corre-
sponding con¢entration in wt~ ranges from about 0.5 to
10~, with aDout 6~ being preferred.
The dye to which the invention is suitably applied is
an or~anic molecule having at least one negatively charged
functional ~roup per molecule. Since sulfonate (S03-)
; groups are espeoially Denefitted from the practice of the
invention, dyes having such group~ are preferrea. A don-
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1 venlent dye ln this regard is Food Black 2 (FB2), which
has a mixture of two, three and four sulfonate groups per
molecule. (The effective value ls about 3.2 sulfonate
groups per molecule for commercially available F82.)
The negative charge of the 3ulfonate group i~ most
commonly balancea by the presence of positively charged
sodium (~a'). Other anionic dyes may also be suitably
employed, since, aQ will be discussed in further detail
below, the solubility of the anionic dyes is increased in
acidic media by employing the teachings of the invention.
Example~ of other anionic dyes which may be employed
in the ink composition disclosed herein include Direct Red
9, Direct Red 227, Acid Yellow 23, Direct Yellow 86, Acid
Blue 9, Direct Blue 86, Direct Blue 199 and Acid Blue 185.
In accordance with the invention, an ink composition
suitable for use in ink-jet printers i9 provided, compris-
ing:
- ~ (a) a vehicle comprising about 5 to 95~ water
and the balance at least one glycol ether; and
(D) a dye having at lea~t one negatively charged
functional group per molecule, present ln an amount up to
0.1 Molar of the ink composition, the dye haYing a plural-
ity of anionic slte~, orlglnally complexed with sodium
cations, at least a portion of the sodium cations being
replaced wlth tetramethylammonium cations.
The presence of tetramethylammonium (T~A) cations
increase-~ the solubility of the dye in the vehicle without
adversely affecting ko~ation. The presence of TMA alqo
reduces crusting of the ink around the oriflces of the
~0 ink-~et printer, sucn crusting being caused by evaporation
of the water in the vehicle of the ink upon exposure to
air,
The partial or complete replacement of sodium cations
by TMA cations may be accomplished by a variety of meth-
ods, exemplary of which are ion exchange an~ reverseosmosis. In tne ion exchange reaction, the dye with
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1 ~odium cations l~ passed through an acid-loaaed lon ex-
1 change resin. The sodium catlons are replaced wlth hydro-
¦ gen cations. The lon-exchanged dye l~ then reacted wltn
tetramethylammonium hydroxide (TMA+ OH-). The TMA cations
replace the hydrogen cations, whlch react with the hydrox-
ide anions to form water.
Preferably, at least acout one-fourth of the sodium
cations muQt be replaced by the TMA cations ln order to
obtain the benefits disclosed herein. However, most pref-
erably, at least about one-half of the sodium cations are
replaced in order to obtain the best combination of pro-
perties.
It has been 4bserved that the more the TMA replace-
ment for sodlum, the better the color density achievable.
Further, low temperature start-up (an indication Or the
ability for the first drop of ink to fire when the printer
has been idle for a period of t$me) is improved.
The presence of T~A permits a concentration of dye up
to 0.100 Molar. Above thi~ level, the viscosity of the
inK is too high. For practical purposes and economy, the
maxlmum amount of TMA-dye i9 about 0.065 Molar; above this
level, the color den~ity is at its maximum ana increases
no further.
A ~light exces~ of TMA (about 5 to 10~) may be pre~-
ent ln the ink to provlde the manufacturer wlth a marginwhen maklng the TMA form of the dye.
INDUSTRIAL APPLICA~ILITY
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The TMA-substituted dyes provided in accordance with
the invention flnd u~e in inks u~ed in ink-jet printing,
particularly in thermal ink-jet printing.
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1 EXAhPLES
A ~erles of dyes were preparea, employing Food Black
2, which originally had all anionic sites complexed witn
sodium cations. The vehicle compri~ed diethylene glycol
(DEG) and water in the concentration~ given below. In the
inks listed in Ta~le I below, the dye concentration is
given in terms of millimolarity. Comparisons are made
with ~ubstitutions of sodium cations ranging from no re-
placement to partial replacement to full replacement bytetramethylammonium (TMA) cation. For comparison, full
i replacement by ammonium cation (NH4) and potassium (K) are
also given.
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TABLE I.
Example Cation S Na Replacement Concentration, mM
1 Na _- 39
- 2 TMA 50 39
3 TMA 100 39
4 TMA 100 52
TM~ 100 65
6 NH4 100 39
7 K 100 39
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The properties of solubillty, crustin~, room tempera-
ture (RT) and low temperature (LT) start-up, kogation,
storage and change in color den~ity (delta E) are listed
; in Table II below. The solubility is shown for two vehi-
cle concentrations: 50/50 DEG/H20 and 90/10 DEG/H20.
Start-up is measured for pens exposea for a period of
tlme to a temperature Lroom (RT) or 10C (LT)] at low
relative humiaity (RH) to determine whether water loss ha~
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1 been su~ficient to cause a signiflcant decrease ln the
quallty of drop eJections,
Storage referq to the stability of chemical and phy~-
ical properties during ~torage.
Delta E i9 a meaqure of color denqity. If the color
i~ measurea in CIELAB coordinateq, then E i9 given by
E = L(L2 - L1)2, (a2 - a1)2 1 (b2 - b1)2]1/2
where L, a and b are the coordinate~ of reference in
CIELAB space and 1 refer~ to the reference and 2 refers to
the sample. De}ta E = E - Eo~ where Eo is for the lowest
concentration ~tandard and E is for the sample.
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TABLE II.
Exam- Solubility Cru~t- Start-up Koga- Storage Delta
ple 50/50 90/10 ing RT LT tion
1 F F P G F G G F
2 G G G F
3 E E E E E G G F
4 E E G E G G G
E E G G G E
6 ' P
7 P F
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The foregolng relative observations are based on the
following scale, with the definitions of each observation
for each property as follows:
E ~ Excellent
G = ~ooa
F = Fair
P = Poor.
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1 A perusal of Table II above shows that solublllty lq
enhanc~d ln both 50/50 DEC/H20 and 90/10 DEG/H20 for
replacement of sodium cationq by tetramethylammonium cat-
ions. Further, kogation is not adversely affected by such
replacement. Other properties of the inks containing TMA-
replaced dyes, ~uch aq crusting, start-up, ~torage and
print quality are 3een to be at lea~t equlvalent to those
of ink~ containing ~odium cation~. Finally, compari~on
with replacement by other cations (K and NH4) point~ up
the improvement achievea with the sub~tition of tetrameth-
; ylammonium for ~odium.
Thu~, an ink compoqition for ink-jet printers ha~
been provided. The ink comprises an anionic dye in which
at least a portion of the a~sociated ~odium cations are
replaced with tetramethylammonium cations. Various
changes and modification~ will be readily apparent to
those of ordinary qkill in the art, and all ~uch changes
and modifications are con~idered to be within the scope of
this invention.
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