Note: Descriptions are shown in the official language in which they were submitted.
~L157~)9
The present invention relates to an ink composition
for ink-jet recording and more particularly, the present
invention relates to an aqueous ink composition for ink-jet
recording process, wherein ink droplets are jetted from an
orifice of the print head by an impulsive decrease of the
volume of a pressure chamber thereof.
An ink-jet recording system of this kind is known~
Such a system is disclosed, for example, in U.S. Patent
3,946,398. According to this patent, the recording
process consists of the following two steps: a step
wherein the inner volume of the pressure chamber filled
with ink is suddenly decreased by the formation of an -
electrical driving pulse and an ink drop is jetted from
the orifice, thus a single drop of ink is transferred to
the recording paper by a single driving pulse, and a step
to return the entire system to its ori~inal state, thus
preparing the system for another ink-jetting process. An
.,
ink composition used for this type of ink-jet printing
- process, as is the case for any ink composition of other
ink-jet recording systems, requires that the ink not only
`;
;; causes no serious clogging at the orifice, to give a suffi-
cient contrast to a jetted image, no change in its physical
or chemical properties, no precipitation during storage
thereof, but also that the viscosity and the surface tension
thereof be maintained within an adequate range. Particularly,
the influence caused by the viscosity of the ink on ink-jet
printing performance is great and in the case when ink
having an improper viscosity value, which is normally pre-
determined according to the individual printing apparatus,
and the various electrical factors to be given to the
apparatus, is used, various troubles are likely to be caused
':~
A~
,
. .
.
~7~9
in the jetting and the returning steps and thus satisfactory
recording would become impossible. For example, if the ink
having a viscosity lower than the proper viscosity range is
used, it is impossible to compensate for the speed deviation
of each part of the ink column jetted from the orifice in
the jet process, and as a result two or more ink drops
having different speeds are jetted for a single electrical
driving pulse, which greatly deteriorates the print quality.
Further, in the returning step, there may be trouble. For
example, after an ink drop is jetted, the meniscus of the
ink drops for a while by reaction and thereafter, on
returning to its original position by the action of the
capillary force, if the viscosity of the ink is too low,
the damper action of the ink is small and therefore an ink
meniscus passes the orifice and is again returned by sur-
face tension, which causes the meniscus to vibrate and it
takes a long time for this vibration to settle down in the
original balanced position. On the other hand when the
viscosity is too high, suc~ type of vibration does not
appear. ~onetheless, when the ink is returned by a
capillary force, it takes a long time and in both cases,
the time required for the meniscus to return to the original
state is long and consequently the printing speed is lowered.
The proper viscosity range of the ink in the ink-jet system
of this kind in which no such troublesome phenomena influences
the viscosity of the ink needs be within 4 to 20 centipoises.
Similarly, the surface tension of the ink has a
big influence on the ink-jet recording system of this kind
and when an ink having a surface tension of improper value
is used, the same trouble happens in both the jetting process
and the returning steps and satisfactory recording becomes
'
3~9
difficult. For example, when an ink having a surface
tension that is lower than the proper value is used, the
shape of an ink drop is hard to be kept constant and, in ~i
some cases, two or more ink drops having different speeds
are jetted for a single electrical driving pulse (so-
called a satellite), and further in the returning process,
when the fallen ink meniscus is returned to its original
position by a capillary force after an ink drop is jetted,
the returning time becomes long due to the fact that the
capillary force becomes small and, consequently, the
frequency characteristic is worsened.
In the case where the surface tension is too high,
on the contrary, in the returning step by a capillary force,
the returning speed thereof is too high due to a big
capillary force and, consequently, the ink meniscus begins
to vibrate. Therefore, again, it takes a long time to
settle down to the original balanced position. The proper
range of the surface tension of the ink for the ink-jet
system of this kind within which no such troublesome
phenomena occurs is about 40 to 60 dyn/cm.
Heretofore, as an ink composition for this purpose,
various kinds have been proposed but nothing satisfies all the
above-mentioned requirements, although some of those require-
ments may be satisfied, and, therefore, the known ink
compositions have some drawbacks. For example, it has been
known that cellulose derivatives such as hydroxypropyl
cellulose, carboxymethyl cellulose, hydroxyethyl cellulose
and methyl cellulose, etc., or water-soluble thickeners
such as polyvinyl alcohol are added to the ink composition
in order to keep the desired viscosity, but such water-
soluble thickener changes its viscosity during storage
:
ilS;~6 :i~
thereof due to an interaction with water-soluble dye as a
colorant and, depending on the condition, a precipitate
may result. Thus the ink-jet recording system of this
kind has had some drawbacks from a practical point of view.
Furthermore, in the case where a fine orifice structure of
30-200 microns is employed in an ink-jet system of this
kind, which is usually the case, there have been such dis-
advantages that the orifice is often clogged due to the
precipitation of a solid component in the ink composition
by evaporation of solvent during storage of the ink inside
the orifice, the response of ink-jet by inner volume change
induced by an electrical driving pulse will be impeded and,
consequently, ink may not be jetted; or the jetting con-
dition changes as time elapses and, for one or more of the
above-mentioned reasons, a stable recording becomes im-
possible. Furthermore, it has been known that water-soluble
polyhydric alcohol is added to water-color ink composition
for the purpose of prevention of clogging of the orifice
as described in U.S. Patents Nos. 3,705,043 and 3,846,141,
Japanese Patent Publications Open to Public Inspection No.
72712/1975 and 95008/1975 and West German OLS Patent ~o.
2,258,804. All of these ink compositions consisting of
an aqueous solution comprising water-soluble dye and wetting
agent, in an amount less than 40 weight percent, such as
polyethylene glycol, polypropylene glycol, ethylene glycol,
propylene glycol, diethylene glycol and glycerol etc. as
its basic component, but even by the addition of such wetting
agent it is almost impossible to maintain the viscosity range
within 4-20 centipoises and the prevention of clogging in
the orifice and of penetration of the air bubbles into the
orifice can be achieved only imperfectly.
Ai
639
The object of the present invention is to
eliminate these drawbacks and to provide an ink composi-
tion for ink-jet recording, whereby no serious clogging
occurs at the orifice, no substantial changes in physical
and chemical properties or no precipitate will be caused
during storage, and recorded images can have sufficient
contrast and, therefore, stable and clear recording can
be maintained in the recording for a long period and even
after a long storage.
The present invention thus more specifically
relates to an ink composition for ink-jet recording con-
sisting of an aqueous solution comprising a water-soluble
acid or direct dye and a polyethylene glycol with a poly-
merization degree of 4 to 25, said composition having a
viscosity of 4 to 20 centipoises and a surface tension of
40 to 60 dyn/cm at 25C.
As the water-soluble acid and direct dye to be
used for the present invention, any of the ones having a
solubility of more than 0.5 weight percent can be used and
in the case of monochromatic recording, it is preferable to
use a black or blue dye to obtain a high contrast on the
recording paper. For example, C.I. Acid Blacks ~o. 2, 7,
24, 31, 52, 107, 118, 119, 156 and C.I. Direct Blacks No.
17, 32, 38, 51 can be used as black dyes and C.I. Acid
Blues No. 9, 62, 102, 104, 113, 117, 120 and C.I. Direct
Blues ~o. 1, 6, 15, 25, 71, 86 and 226 can be used as a
blue dye and such dye can be used independently or in any
combination of two or more kinds. The amount of the dyes
added is not necessarily an important factor in particular
when sufficient recording is obtained, however, in general,
0.5-8 weight percent is suitable in practice and 1.0-5 weight
t~
~1~7~3~
percent is more preferable.
As polyethylene glycol to be used for the present
invention, one with an optional average molecular weight
can be used as long as it has the aforesaid polymerization
degree and, for example, polyethylene glycol (molecular
weight 200), polyethylene glycol (molecular weight 300),
polyethylene glycol (molecular weight 400), polyethylene
glycol (molecular weight 600), and polyethylene glycol
(molecular weight 1000) can be mentioned. According to
the present invention these compounds may be used singly
or in any combination of two or more.
Such polyethylene glycols are all miscible with
water and due to their wetting, low volatility and thick-
ening properties, they play an important role in the ink
composition of the present invention. Regarding the poly-
merization degree of polyethylene glycol, the one with a
polymerization degree of 4 to 25 can be used and a poly-
merization degree of 4 to 10 is preferable. The amount of
such polyethylene glycol to be used may be decided depend-
ing on the predetermined viscosity, surface tension andshould be sufficient to prevent the clogging of the orifice
and the penetration of bubbles. Furthermore, the amount to
be used varies depending upon the polymerization degree of
polyethylene glycol but it can be optionally selected
within a wide range as long as the aforesaid conditions
are satisfied. An amount of 30-60 weight percent is general-
ly preferable.
In the present invention various kinds of
additives, if necessary, can be used. For example when
the composition has to be stored for a long time, it is
possible to add an antiseptic agent or an antimold to the
a~
7~3~
composition of the present invention to prevent or to
decrease the growth of bacteria or mold therein. It has
been known that various kinds of antiseptic agents are
useful for this purpose and Bacillat 35TM (1,3,5-hexahydro
triazine derivative) sold by Hoechst AG, for example, is
preferable. The amount of antiseptic agent or antimold
added is generally 1 weight percent or less based on the
total amount of ink composition and the range of 0.01-0.5
weight percent is especially preferable.
Furthermore, a surface active agent may be added
in order to change the surface tension of the ink composi-
tion or to improve the so-called "wetting" of the ink in the
ink passage. Preferred examples include polyoxyalkylene and
alkylethers thereof which are sold as siloxane-oxyalkylene
copolymer (L-5340) by Union Carbide Co., and fluorine
surface active agent (FC-430) sold by 3M, all of which are
non-ionic surface active agents. The amount of surface
active agents added is generally 1 weight percent or less
based on the total amount of the ink composition and the
range of 0.05 to 0.5 percent by weight is especially
preferable.
Furthermore, it is possible to add various kinds
of inorganic or organic buffersto prevent a pH change
caused mainly by the absorption of carbonic acid gas in the
air during storage of the ink in the container or during
the period of residence in the orifice. ~arbonates such as
sodium carbonate and potassium carbonate, for example, are
preferred, and 0.1 to 5 percent by weight based on the total
amount of the ink composition may be suitable and more
preferably 0.1 to 2 percent by weight is used.
Furthermore, it is possible to add various kinds of
~.~
3.~ 3~
chelating reagents to mask the metal and metallic ion of
the composition. For example, sodium gluconate, ethylene-
diamine tetra acetic acid (EDTA), disodium ethylenediamine
tetra acetate, trisodium ethylenediamine tetra acetate,
tetrasodium ethylenediamine tetra acetate and sodium salt
of diethylenetriamino penta acetic acid etc. can be
mentioned.
As stated above, the ink composition of the present
invention is useful because no change in physical and
chemical properties or no precipitate is caused during
storage, no serious clogging at the orifice occurs and
stable and clear recording can be maintained even for
recording for a long period of time and even after the
ink has been in the ink chamber for a long time.
It is surprising that the ink composition of the
present invention shows an excellent effect when it is
used for ink-jet recording, but when other polyalkylene
glycols that are similar to polyethylene glycol are used,
the effects obtained by the present invention will not be
attainable. For example, most of the polypropylene glycols
do not dissolve in water and even if they dissolve, their
viscosity becomes too high in practice and by utilizing a
polymethylene glycol, for example, a stable and clear record-
ing cannot be attained.
The present invention is illustrated hereinbelow
with reference to the following examples.
"~
~:157i~3~
Example 1:
Ink Composition % bY weiqht
C.I. Direct Black 17 2.5
Polyethylene glycol
(molecular weight: 200 and
average polymerization
degree: 4.1) 47.2
Distilled Water 50.1
Potassium Carbonate 0.2
Bacillat M (antiseptic
agent made by Hoechst AG) 0.1 .
The above components for an ink composition were -:
mixed under agitation to make a homogeneous aqueous solution
and this solution was then filtered through a filter having
a pore size of 1.0 micron.
The ink composition thus obtained had a viscosity
value of 7.8 c.p.s. and surface tension of 58 dyne/cm at
normal temperature (25C).
The ink composition thus prepared was used in the
ink-jet recording apparatus device disclosed in Figs. 1 to
3 of U.S. Patent 3,946,398 and ink-jet recording was con-
ducted under the conditions shown below.
Parameters for Ink-Jet Printing Operation:
Printing speed 1750 dots/sec
Static pressure 0.006 psi
Peak pressure of the pulse 5.74 psi
Pulse voltage 80 volts
Pulse width. 140 us
Diameter of the orifice 0.00~8 inches
As a result of this experiment it was found that a
clear and excellent print could be obtained by using the
'A
ink composition according to the present invention and the
quality of the printed image remained unchanged after con- '
tinuous recording operation for 24 hours and, furthermore,
even in operation, wherein the ink composition was stored
for one month in the device.
Example 2:
Ink Composition-% bY weiaht
C.I. Direct Black 32 4.0
Polyethylene glycol
(molecular weight: 400 and
average polymerization
degree 8.7) 47.7
Deionized Water48.0
EDTA-tetra sodium salt 0.2
Bacillat 35 (Hoechst AG) 0.1
Another aqueous ink composition consisting of the
above shown components was prepared in the same manner as in
Example 1. The viscosity and the surface tension of the ink
composition thus prepared were 11.0 c.p.s. and 56 dyn/cm at
normal temperature.
Using this ink, ink-jet recording was conducted
using the same device and in the same manner as in Example
1 and, similarly as in Example 1, good results were obtained.
Further, even after a long period of storage, no
growth of bacteria or mold was observed and no precipitation
occurred.
-- 10 --
7~,~
6~9
Example 3:
Ink Composition% by weiqht
C.I. Direct Blue 252.0
C.I. Direct Black 322.0
Polyethylene glycol
(molecular weight: 600 and
average polymerization
degree: 13.2) 45.0
Distilled Water 50.0
Sodium carbonate 0.2
EDTA-tertiary sodium salt 0.2
Bacillat M 35 (~oechst AG) 0.1
Another aqueous ink composition consisting of the ~ :
above components was prepared in the same manner as in
Example 1. The viscosity and the surface tensi~n of the
ink composition thus prepared were respectively 16.2 c.p.s.
and 59 dyn/cm at normal temperature (25C).
Using this ink the same experiments as in Example :
2 were repeated and similarly good results were obtained.
Example 4:
Ink Composition % bY weiaht
C.I. Acid Black 109 3.5
Polyethylene glycol
(molecular weight: 300 and
average polymerization
degree: 6.4) 40.0
Distilled Water 56.2
EDTA-tetra sodium salt 0.2
Bacillat 35 (Hoechst AG) 0.1
'~
. .
11~7~39
Another aqueous ink composition consisting of the
components shown above was prepared in the same manner as
in Example 1. The viscosity and the surface tension of
the ink composition thus prepared were 5.1 c.p.s. and
60 dyn/cm at normal temperature (25C).
Using this ink, ink-jet recording was conducted
in the same manner as Example 2, and similarly good results
were obtained.
