Water-based ink compositions comprising water, a pigment, a nonionic surfactant having a solubility in water of less than about 0.5 wt. % and a solubilizing agent sufficient to solubilize substantially all of the nonionic surfactant.

This invention relates to water-based ink compositions. These ink 
compositions are especially useful for publication gravure; these inks may 
be used in place of conventional publication gravure printing inks which 
are typically based on hydrocarbon solvents. The ink compositions of the 
present invention contain water, a pigment, a particular type of nonionic 
surfactant and a solubilizing agent. 
BACKGROUND OF THE INVENTION 
Safety and environmental considerations are forcing changes in printing ink 
formulations. Solvent-based printing inks are now regarded as being 
undesirable from several points of view and are being tolerated only 
because effective water-based printing ink compositions have not been 
developed to the point where they can replace solvent-based inks in terms 
of ease of use, printability and economy. This is particularly true for 
publication gravure printing inks which are generally based on toluene or 
mixtures of toluene and aliphatic hydrocarbons. Such solvents are 
hazardous (explosions at publication gravure printing plants have occurred 
in recent years) and require expensive solvent recovery units to limit air 
effluents (toluene and toluene/aliphatic hydrocarbon mixtures are very 
volatile, particularly at the temperature and air flow conditions normally 
present in printing press driers). 
As a result of heightened environmental and safety concerns, water-based 
inks are being introduced to replace solvent-based inks. However, prior 
art water-based inks have proven to be expensive and prone to printability 
problems, especially for publication gravure. Examples of such 
printability problems include poor transfer from the gravure cells and 
spreading behavior on paper. These printability problems typically 
manifest themselves as skipped dots in the tone areas and a generally 
"wormy" appearance and nonuniformity in the solids. U.S. Pat. No. 
4,954,556 relates to water-based ink compositions comprising emulsion 
polymers and rewetting agents. This patent alleges that the ink 
compositions described therein can be printed at high speed without 
permanent drying in the cells of a gravure cylinder, transfer of the ink 
composition to the substrate is not adversely affected and the inks dry 
quickly without causing paper curling. Although such qualities are most 
desirable, the ink compositions described in this patent are nevertheless 
disadvantageous because they contain extremely high (i.e. 10-50 wt.%) 
amounts of surfactant(s). Such high surfactant content leads to trapping 
problems on the paper, foaming problems during printing and, most 
importantly, very high cost. Unless these latter problems can also be 
overcome, there would be very little incentive for a printer to change 
from a solvent-based ink to such a water-based ink.

DETAILS OF THE PRESENT INVENTION 
It has now been discovered that it is possible to provide a water-based ink 
composition that overcomes the disadvantages of the ink composition of 
U.S. Pat. No. 4,494,556, while retaining its advantages. The ink 
compositions of the present invention thus may be readily substituted for 
traditional solvent-based inks, especially for publication gravure 
printing, thereby achieving the goals of safety and protection of the 
environment without any undue printing problems while maintaining an 
attractive cost. 
The water-based ink compositions of the invention comprise: 
(a) water; 
(b) a pigment; 
(c) a nonionic surfactant having a solubility in water of less than about 
0.5 wt. % and being present in an amount effective to lower the dynamic 
surface tension of the ink composition to a level in the range of about 25 
to 40 dynes/cm; and 
(d) a solubilizing agent sufficient to solubilize substantially all of the 
nonionic surfactant. 
Preferably, the dynamic surface tension of the ink composition will be in 
the range of 25 to 30 dynes/cm. This preferable range may be readily 
achieved by utilizing a nonionic surfactant (or mixtures of nonionic 
surfactants) having the lowest solubility in water and by adjusting the 
quantity. The nonionic surfactants preferably have a diffusivity in the 
range of 0.1-1.times.10.sup.-9 m.sup.2 /second, preferably 
0.3-0.6.times.10.sup.-9 m.sup.2 /second and a solubility in water of less 
than 0.5 wt. % and are employed in amounts of about 1 to 4 wt. %, 
preferably 3 to 4. 
Preferably the nonionic surfactant is selected from the group consisting of 
acetylenic diols containing 8 to 14 carbon atoms, acetylenic carbinols 
containing 8 to 14 carbon atoms and block copolymers of propylene oxide 
and ethylene oxide having a hydrophilic/lipophilic balance ("HLB") in the 
range of about 3 to 8 and a propylene oxide to ethylene oxide ratio of 8:1 
to 3:1. 
The ink composition of the invention also includes a solubilizing agent. 
The solubilizing agent is necessary in order to solubilize substantially 
all of the nonionic surfactant(s) present in the ink composition. It has 
been found that only those nonionic surfactants having a solubility (in 
water) of less than about 0.5 wt. % will produce the requisite lowering of 
the dynamic surface tension to a level of about 25 to 40 dynes/cm without 
using excessive amounts. Such level of dynamic surface tension assures 
that printability problems will not be encountered. The solubilizing agent 
is utilized in an amount that is sufficient to solubilize the nonionic 
surfactant(s) and therefore the amount of solubilizing agent will vary 
depending on the choice and amount of nonionic surfactant. In general, the 
solubilizing agent will be employed in an amount in the range of about 0.1 
to 5 wt. %, preferably 2 to 4 wt. %. 
Preferably the solubilizing agent is selected from the group consisting of 
the ammonium, potassium, or sodium salt of 
8[5-Carboxy-4-Hexyl-Cyclohex-2-enyl]Octanoic Acid, the ammonium, 
potassium, or sodium salt of a C.sub.8 -C.sub.13 dialkyl sulfosuccinic 
acid having a critical micellar concentration in the range of about 0.08 
to 0.12, phosphate ester surfactants, such as the condensation products 
resulting from the reaction of polyphosphoric acid and a compound having 
the formula R(CH.sub.2 CH.sub.2 O).sub.x H, wherein x is an integer of 1 
to 20 and R is either an alkylphenoxy group, the alkyl radical of which 
contains 5 to 10 carbon atoms, or is a C.sub.10 -C.sub.18 alkoxy group, 
and mixtures thereof. 
The ink composition of the invention will typically contain about 30 to 80 
wt. %, preferably 50 to 70 wt. %, water and about 3 to 15 wt. %, 
preferably 5 to 10 wt. %, of a pigment. The pigment may be any of those 
typically found in solvent-based publication gravure inks such as carbon 
black, phthalocyanine blue, phthalocyanine green, diarylide yellows, 
lithol rubine, red lake C, barium lithol, and the like. 
The ink composition of the invention may also contain the usual adjuvants, 
including solid binders such as acrylic and methacrylic resins, 
styrene-acrylic resins, rosin salts, etc.; waxes such as polyethylene 
waxes, polytetrafluoroethylene waxes, silicones, etc; and the usual 
corrosion inhibitors and biocides, if desired. In addition, it is usually 
beneficial to add 10 to 14 wt. %, preferably 15 to 30 wt. % of one or more 
emulsion polymers, i.e. aqueous addition polymers such as acrylic or vinyl 
emulsion polymers. Such polymers are well known in the prior art and are 
prepared from monomers such as acrylic or methacrylic acid esters of 
polyhydric alcohols acrylic acid or methacrylic acid esters, methyl 
methacrylate, styrene, vinyl styrene, vinyl toluene, vinyl acetate, vinyl 
chloride, vinylidene chloride and the like. 
The water-based ink compositions of the invention are further illustrated 
by the following non-limiting examples in which all parts are by weight, 
unless otherwise indicated. 
EXAMPLE 1 
A water-based. flexographic new ink was formulated from the following 
components: 
______________________________________ 
Component Wt. % 
______________________________________ 
Carbon Black 13 
Lignin 5 
Acrylic Emulsion Resin 8 
Dipropylene glycol 3 
Urea 3 
Phosphate Ester Surfactant 
0.5 
Clay 2 
Anti Foam 1 
Solubilizing Agent + Nonionic Surfactant* 
0.5 
Water 64 
______________________________________ 
*The solubilizing agent employed in this example was sodium diethylhexyl 
sulphosuccinate and the nonionic surfactant was 
24-7-9-tetramethyl-5-decyn-4, 7diol; the ratio of agent to surfactant was 
1:4 by weight. 
When the above formulation was used in a trial, it was found that the usual 
benefits of flexography were present, i.e. greatly reduced paper waste, 
rapid drying with little ink rub-off, strike-through of the paper by oil 
is eliminated and excellent dot resolution was obtained. However, it was 
also found that the usual problems associated with water-based 
flexographic new inks were not present in respect to this formulation, 
i.e. this formulation exhibited improved color development, better lay and 
less fill-in than prior art flexographic new inks. 
EXAMPLE 2 
Two black publication gravure inks were formulated as follows: 
______________________________________ 
Component Wt. %, Ink A 
Wt. %, Ink B 
______________________________________ 
Black Pigment Base* 
30 30 
Clay Base** 15 15 
Acrylic Emulsion Resin 
12 12 
Nonionic Surfactant*** 
2 2 
Solubilizing Agent**** 
1.5 0 
Water 39.5 41 
______________________________________ 
*The Black Pigment Base consisted of 30% Carbon Black in an acrylic resin 
solution vehicle 
**The Clay Base consisted of 60% Clay in a StyreneMaleic Anhydride Resin 
solution vehicle 
***2-4-7-9-tetramethyl-5-decyn-4,7-diol 
****Potassium Salt of a C.sub.21 Dicarboxylic Acid 
When Inks A and B were trialed on a commercial press, the trap of black 
over red as well as the lay-down of Ink B was inferior to that of Ink A, 
illustrating the need for the solubilizing agent. 
EXAMPLE 3 
A blue water-based publication gravure ink was formulated as follows: 
______________________________________ 
Component Wt. % 
______________________________________ 
Blue Pigment Dispersion* 
20 
Clay Base from Example 2 
25 
Acrylic Emulsion Resin 
18.5 
Antifoaming Agent 0.5 
Water 32 
Nonionic Surfactant** 
2 
Solubilizing Agent*** 
1 
Solubilizing Agent**** 
1 
______________________________________ 
*50% Phthalocyanine Blue Pigment in acrylic solution vehicle 
**2-4-7-9-tetramethyl-5-decyn-4,7-diol 
***sodium diethylhexyl sulphosuccinate 
****potassium salt of 8[5 (6)carboxy-4-hexyl-cyclohex-2-enyl]octanoic aci 
 
The blue water-based ink exhibited excellent printability when trialed on a 
publication gravure press; it was also noted that this ink readily 
transferred from the cells of the press. 
EXAMPLE 4 
A red publication gravure ink was formulated as follows: 
______________________________________ 
Component Wt. % 
______________________________________ 
Lithol Rubine Pigment Dispersion* 
30 
Acrylic Emulsion Resin 
14 
Clay Base from Example 2 
10 
Urea 4 
Dipropylene Glycol 2 
EO/PO Copolymer Surfactant** 
2 
Water 38 
______________________________________ 
*40% Lithol Rubine Pigment in acrylic solution vehicle 
**The copolymer had an ethylene oxide:propylene oxide ratio of 1:4 and a 
HLB of 7. 
The ink was trialed on a commercial press running at 1300 feet per minute; 
the ink quality was comparable to that of conventional publication gravure 
inks.