Note: Descriptions are shown in the official language in which they were submitted.
7907
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~.TER~.BASED INK COMPOSITI~
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Descx~ptlon
Tech!nical Field
:
The present in~ention is concerned with aqueous ink
compositions which'exhibit ~ood water fastness without
requ~xing t~e presence of a resinous binder in the
compositi~n~ The'pres'ent invention is especially con-
cerned with'aqueous ~nk'compositions which are useful
as jet printing inks.
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B~ckground Art
The basic technique'employed in jet printing involve~
us~n~ at least one'~nk'~et nozzle assembly attached to
a pressurized source of ~nk. Each ink nozzle has a
small orifice gener~lly with'a diameter of about 0.0005
to about 0,0028 inches which'~s energized by an electro-
mechanical transducer to emit a continuous stream of
generally unifo~ ink droplets at a rate of about 20 to
about 200 kilohertz. The stream of droplets is directed
onto the sur~ace of a mo~ing writing ~edium, such as
. 20 paper. The stream. of droplets is controlled to form
the desired printed characters in response to video
signals der~ved from an electronic character generator
and in response to an electrostatic deflection system~
In particular, the jet printers are adapted for pro-
~iding a record on a writing medium by generating a
series of ink drops, applying a charge successively
on each o~ the ~nk drops in respon e to a signal which
is recei~ed by the'printex, The drops are then directed
along a path between two parallel conductive plates.
A deflect~on field, which is generated at a bias poten-
tial, is applied to these plates with the result that
the ink drops are deflected so that they reach the
writing medium. They provide a representation, charac-
teristic of the information contained in t~e signals.
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The general configuration of ink systems
employed with ~nk jet printers ~nclude an ink sump
whichstoresthe ink. The sump feeds a compressor
which in turn feeds a conduit, which is connected to
an ~nk jet nozzle, An electromechanical transducer
is ~mployed to ~ibxate the nozzle at some suitable
high frequency, which after the ink is injected
through an orifice of the nozzle in a stream, causes
the stream to bxeak into the individual drops. It
is desired for proper charging of the individual
drops that the breakup of the stream occur within the
chargin~ slot. The charging slot is the most desirable
point alony the path of the`stream for the actual
ch~rge of each ~ndividual drop to ~e placed.
To be suitable as an ink in ink jet printing
systems~ the ink must possess a number of important
characteristic~ or properties. For instance, the ink
must have a viscosity suitable for providing the pro-
per flow characteristics in the jet printing process.
Most ink jet printing inks have viscosities within
the rangeof about 1 to about 10 centipoise at 75F
and preferably about 2 to about 6 centipoise at about
75F. Of course, depending on the particular config-
urati~n of the des~red ink jet printing apparatus to
be employed, the viscosity of a particular composition
c~n vary somewhat.
Moreover, in view of the small orifice dia-
meters of the nozzle employed, nozzle clogging can
hecome ~ major concern. Therefore, an ink to be em-
ployed in an ink jet printing operation cannot containparticulate m~terial which could clog the orifice of
the nozzle. ~urthermore, the ink employed should not
be one which would dry and plug the orifice when the
system is not in operation. Another requirement for
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an ink jet printing ink is that it be electrically
con~uct~Ve. The ink should also have a rel~tively
fas~ drying time and sh~uld be resistant to smearing~
Since the ink should be resistant to smearing on
the writing medium, the ink must ha~e the property of
being readily absoxbèd into the writing medium.
At the present time, commercially available
ànk jet co~pos~tions contain an organic resin bondîng
agent to ix or bond the dye to the substrate. It has
been believed that the use of a synthetic resin binder
is necessary for such prupose. For instance, U.S.
Patent 4,136,076 to Daniels suggests an ink jet print-
ing camposition where~y the permanence and adhesion
to the target ~urface is improved by the presence of
certain p~lymers which conta~n unesterified free
carbonyl groups and certain multivalent metals to
provide ~ cross~linking of the polymer. Daniels
~urther su~gests the use of certain volatile bases
including ammonium hydroxide in order to render the
polymers soluble in water or alcohol required by
Daniels because of the presence of the polymer.
Moreover, U.S. Patent 3,891,581 to Argenio
suggests a water dilutable transfer ink composition
for use in flexographic and xotogravure heat transfer
printing processes which contain a thermoplastic resin
such as a polyester obtained by reacting a polyol
partially esterified rosin with maleic anhydride and/or
fumaric acid. These compositions can contain ammonium
hydroxide. The ammonium hydroxide is present so that
the composition has a pH of between about 8 and 9.
U.S. Patent 4,150!997 to Hayes also suggests
the presence of cert~in bases to ink compositions con-
taining a fluorescent pigment. The fluorescent pigment
is a mixture of a dye ~nd an organic resin which ap-
parently is cured (along theselines, see column 2,
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lin~s 2Q-23 and colu~n 3, lines 12 and 13), The
base ~s ~dded to solubilize the pigment~ For in-
stance, the base c~n be ammonium hydroxide which,
according to the disclosure of this patent, forms
a quaternary salt with the fluorescent pigment.
U.S. Patent 3,846,141 to Ostergren et al suggests
jet printing ink compositions which can contain a
base such ~s an alkanol a~ine, a monovalent hydrox-
ide suchas an alkali metal hydroxide, ammonium
hydrox~de or morpholine to provide a composition
having a pH above ~bout 9. The base is disclosed
as enabling the ink composition to be modi~ied by
the incorporation of a resinous system such as a
modi~ied styrene-maleic anhydride resln (see column 3,
lines 53 et seq.l.
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U~S. Patent 3,594,736 to Hertz et al is of generalintere$t~
Disclosure of Invention
The present invention, contrary to the suggestion in
the prior art, does not require the presence of
a resinous bonding agent in order to achieve water
fastness of the dye. According to the present
invention, the pH of the composition is ~djusted
by incorporating ammonium hydroxide which maintains
the dye dissolved while the ink is ln the bottle or
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container but evaporates after the ink is printed onto
the substrate thereby reducing the pH and thereby
rendering the ink insoluble on the paper, According
to the present invention, a resinous binder is not
necessary to achieve ~oth proper pH ~alance and water
fastness as previously ~elieved.
The present inVention is concerned with an
ink composition which consists essentially of an
a~ueous solution o~ an organic direct dye and ammonium
hydroxide, The ammonium hydroxide is present in the
composition in an amount sufficient to provide the
solution with a pH of at least about 9.5. In addi-
t~on, the ~queous solution is free from resinous
Binder components which are insoluble in water at a
pH of ~bout 7 or less.
Brief ~escription of Drawing
The drawing is a graph of water resistances of the inks
of ~xamples 6 and 7.
Best and Various Modes
~or Carrying Out Invention
According to the present invention, it is essential
that the pH of the aqueous solution be provided by the
addition of ammonium hydroxide as the basic material.
It has been noted, aswill be discussed hereinbelow,
that the use of other basic materials such as sodium
hydroxide and sodium carbonate have not provided the
de~ree of water fastness achieved by the present in-
vention when a synthetic resinous binder is not pre-
sent in the composltion. Also, the addition of other
volatile hases such as ammonium carbonate or morpholine
does not provide the same desired results achieved with
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ammonium hydroxide. The pH of the solution must be
at least about 9.5 and is preferably at least about 10.
Generally the pH o~ the solution is not greater than
ab~ut 12. The composition generally contains about
,05 to about 5% ~y ~eight of ammonium hydroxide and
preferahly ~bout 0,1 to 3% ~y weight in order to
achie~e the necessa~ pH level.
In addition~ the compos~tion must contain a coloring
material which ts an ~rganic direct dye or mixture of
such'dyes. The dyes employed should be soluble in
water at a pH o~ a~out 9.5 and/or higher but substan-
tially insoluble at a pH of 7 or less to achieve the
~esults obta,ined by the present invention. For in-
stance, dyes such as Direct ~lue 1 and Direct Black 80
which Are soluble at a pH o~ 7 or belowdid not exhibit
~ater fastness when formulated with ammonium hydroxide
~ithout a xesinous bonding agent.
The use of pigments or other forms of particular
matertal is not desirable since such materials tend
to clog up the ~rery small orifices of the jet printer.
Preferred dyes of the present invention are the com-
mercially available direct dyes which generally contain
an ionizable inor~anic salt, such as Glauber salts,
or sodium chloride which has been added during manufac-
ture in order to standardize the dye lot. The inorganic~aterial thus renders the dye conducti~e whereby the ink
drops are capable of b~ing deflected in an electro-
magnetic field during jet printing. Such direct dyes
are ~ell known to those skilled in the art and are
commercially available, as represented by the CI Direct
Black 38 dyes; Di~ect Black 19 dye; Amanil-P*dye;
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Di~ect Blue 106; Direct Black 163; and Food Black 2.
A particularly pre~erred dye is Direct Black 19 dye.
It has been noted that Direct Black 19, Direct Black
38~ and ~m~nil-P dye have exhibited excellent water
fast properties when employed with the ammonium
hydrox~de. Howevex, var~ous other of the direct
dyes, such as D~xect Blue 106, Direct Black 163, and
Food Black 2 have been ~ormulated along with ammonium
hydroxide but such, although exhibiting some degree
of improved watex fastness, have not shown the excep-
; tionally high degree ach~eved by the use of the above
three-mentioned dyes.
The dye is generall~ present in the composition in
amounts o~ about 0,5 to about 8% by ~eight, and
preferahl~ ~bout 2 to about 5% ~y weight. In addition,
it is noted that the water employed shbuld be distilled
water which do~s not contain any substantial amounts
of ions and can be considered deionized water.
The compositions can also contain auxiliary constituents
such as humectants, bioc~des, fungicides, and stabil-
izers or solubilizers.
Examples of some suitable humectants include gylcol
and glycol derivatives, such as the polyalkylene
glycols (such as polyethylene glycols and polypropylene
glycols], propylene glycol, lower alkyl ethers of
ethylene glycol, or diethylene glycol (such as ethylene
glycol monomethyl-ether, ethylene glycol monoethyl
ether, diethylene glycol monomethyl ether, diethylene
glycol monoethyl ether, and ethylane glycol monobutyl
ether); and glycerine. The humectant can generally be
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pre~ent in the co~position, when employed, in a~ounts
of ~out 5 to about 45% by weight. The hu~ectants are
employed to retard the dxying of the inks to prevent
prernature drying in the capillaries or other portions
of the jet printing apparatus.
Examples of some solub~lizing agents to insure that
the dye remains in solution include those mentioned
in U.S~ Patent 3,846,141, such as N~methyl-2-pyrroli-
done; ~ -dihydroxyethyl sulfide, N-vinyl pyrrolidone,
substituted pyrrolidone, such as Solvofen HM-Gaf,
4-methoxy-4 methyl pentanone-2 and tetrahydro~
furfuryl alcohol. The a~ount of solubilizing
agent generall~ employed is up to about 5% by weight
andpreferably ~out 0.5 to about 4% by weight based
upon the total weight o~ the ink composition.
Also, the ink composition may include a preservative
to inhibit the irowth of bacteria during storage,
particul~rly when the compositions are to be stored
for prolonged periods of time. The bacteria might
cloy the orifice of the jet printer if not prevented
from growing. Examples of some suitabie preservatives
are sodium omadine, and 6-acetoxy-2,4-dimethyl-m
dioxane. Such are usually employed in amounts of up
to about 1% by weight.
The composition ~ight also contain a chelating agent,
such as ethylenedia~ine tetraacetic acid, tetra-
sodium, generally xeferred to as EDTA. Chelating
agents are employed for complexing metal ions such as
ixon, Zinc, or magnesium present within the aqueous
composition in order to prevent the precipitation of
metal ions dissolved in the water or present along
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~7907
witll the dye The chelating agent is generally employed
in ~mounts up to about 5~ ~y weight and preferably
abollt 0.05 to about 0.5% by wei~ht.
It is desirable that the compositions of the present
invention have a viscosity of about 1.2 to about 10
centipoi~e at 75~ and prefera~ly about 2 to about 6
centipo~se at 75~F.
The compositions of the present invention can be pre-
pared by thbroughly mixing the constituents to insure
uniform mixin~ and complete dissolution of the dye and
then ~ilter;~ng the resulting composition to remove
any particulate contamination~ Filtration of the
composition after mixing the components is highly
desir~ble in oxder to remove from the composition
particulate matter~ such as contamination or undissolved
dye which mi~ht otherwise serve to clog or obstruct
the oxifices of a jet prlnter during use. It is gen-
erally pre~erred to filter the compositions of the
present invertion in order to remove particulate
matter having a diameter greater than about 2 microns,
and preferably greater than about 1 micron in order
to insure that the obstruction o~ the jet printed ~ill
be avoided.
In accordance with the preferred method of preparing
t~e compositions of the present invention, the water
vehicle, a~monium hydroxide, any humectants, if present,
and any solubilizing agent~ if employed, are first
thoroughtly mixed in a manner in which the introduc-
tion of air into the mixture or foaming is substantially
avoided. After ~ uniform mlxture is obtained, the
preserVative~ i~ employed~isslowly added and mixing
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i5 continued until ~ unifo~m mixture is obtained.
Afte~ this, the oxganic dye is slowly sifted into the
re~ulting mixture ~hile~a~itation is continued to
en ure substantially complete dissolution of the dye
S in the aqueous solution~ After dissolution of the
dye, the ink composition is filtered to remove any
particulate ~atter contained therein having a size
greater th~n the desired maximum particle size.
The following non~limiting examples are presented
wherein amounts are by weight unless the contrary is
stated.
Example 1
To about 857.5 grams of deionized water at 72~F are
added w~th stirring about 10 grams of a 30% solution
lS of ammonium hydroxide; about 100 grams of Carbowax*200
(i.e. poLyethylene glycol); and about 32.5 grams of
Direct Black 19 dye. This solution is stirred for
a~out 4 hours at room temperature and filtered
through a .45 micron membrane filter. This ink pro-
du~ed excellent water fast properties when printedon a wide variety of papers. The ink was applied by
a ink ~et technique.
Example 2
Example 1 is repeated except that the ink composition5 is formulated as follows:
Direct ~lack 19 Dye 8.0%
NH40H (30% solution) 4.5%
Carbowax 200 * 10.0%
H2O 77.5%0 The results ohtained are similar to thoseof Example 1.
*Trade Mark
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Example 3
Exa~ple 1 is repe~ted except that the ink composition
is ~'ormul~ted as follows:
Direct Black 19 Dye ,5%
NH40H (30~ solution) .5%
Carbowax 20010.0%
H2O 89.0% ,,
The results obtained are similar to those of Example 1.
Ex'ample 4
Example 1 i5 repeated except that the ink composition
i~ formulated as follows;
Direct Black 38 Dye 3.25
NH40H C30% solution) 1.1%
Car~owax 200 10.0-~
H2O 85.65%
The results obt~ined are similar to those of Example 1.
EXample' 5
Exa~ple 1 is repeated except that the ink composition
is formulated as ~ollows:
Amani;l-P Dye 3.25
(Am. Color & Chem.~
NH4OH (,30% solution~ 1.0%
Carbowax 200 10.0%
H2O 85.7S%
The results obtained are si~ilar to those of Example 1.
Example 6
Example 1 is repeated except that the ink composition
contains about 3.25% Direct Black 19 dye; about 10~
Carbowax 200; about 4% N-methyl-2-pyrrolidone; about
0,1% sodium omadine; and 0.2~ ethylenediamine tetra-
acetic acid, tetrasodium salt; and remainder deionized
water and ammonium hydroxide to provide a pH of 10.2
The results obtained are similar to those o~ Example 1.
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The dashed line on the ~raph shows the water resistance
by Use of a spectrophotometer by measuring the absor-
ban~e of material washed off of a pr~nted sheet ~ith
water. As noted, the ink lost pract~cally nothing in
the test.
Example 7
Example 6 is repeated except that about 0.15% of
sodium hydroxide and .1 to .2% of sodium carbonate
are employed in place of the ammonium hydroxide to
proyide the s~lution w~th a pH of 10.2. The solid
line in the graph shows the water resistance of this
ink~ A compaxison of the results shown in the graph
~or the ~nk of this example and that of example 6
clearly shows a significant difference in water spill
resistance of the two inks with that of the present
invention clearly being superior.
The tests for examples 6 and 7 were conducted at a
temperature of about 74F, relative humidity of about
39~, a jet diameter of about 1.29 mils, an ink drop
diameter of 2.48 mils, alambda (distance between drops)
of 6.10 mils; ~xequency of 100 kilohertz; pressure
of 32.2 ps~, and matrix spacing of 4.2 mils.
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