Water-based printing ink

The invention relates to a water-based oxidizing printing ink especially suited for flexographic printing. The ink comprises an epoxy ester resin, an inorganic and/or organic pigment, a drier, a cyclodextrin and water. Preferably, the ink also includes a drier activator such as 2,2'-bipyridyl and a wax.

FIELD OF THE INVENTION 
The invention relates to a water-based oxidizing printing ink. The ink has 
been found to be especially useful in flexographic printing processes. 
BACKGROUND OF THE INVENTION 
Water-based printing inks are well-known. Although such inks are preferred 
over solvent-based inks from an environmental point of view, they are 
disadvantageous from the standpoint that they are slow-drying as compared 
to solvent-based inks. 
For flexographic printing processes, oxidizing water-based printing inks 
generally require the use of driers such as a cobalt naphthenate. However, 
the incorporation of driers into water-based inks tends to destabilize the 
ink, particularly at the relatively high levels of driers which are 
required for flexographic printing processes. Moreover, water-based inks 
containing the requisite levels of driers required for flexographic 
printing processes have objectionable odors. 
SUMMARY OF THE INVENTION 
It has now been found that oxidizing water-based printing inks especially 
suitable for flexographic printing processes may be prepared with 
relatively low levels of driers, provided a cyclodextrin is incorporated 
in the ink. The resultant inks dry rapidly, are quite stable and have no 
objectionable odor. 
DETAILS OF THE INVENTION 
The oxidizing water-based printing inks of the invention comprise an epoxy 
ester resin; an inorganic and/or organic pigment; a drier; a cyclodextrin; 
and water. 
Preferably, the epoxy ester resin is present in an amount of about 15-40 
wt. %, preferably 20-35 wt. %, based on the weight of the ink, and 
comprises the reaction product of (i) about 65-75 parts per hundred of the 
ester obtained from the esterification of about 40-60 parts per hundred of 
an epoxy resin with about 60-40 parts per hundred of a drying oil 
partially conjugated unsaturated fatty acid having an iodine number of 
about 125-185, an acid number of about 180-210 and a degree of conjugation 
of about 20-25%, said ester having an acid number below about 10, and (ii) 
about 35-25 parts per hundred of a mixture of about 20-28% of one or more 
unsaturated monobasic acids having a polymerizable double bond and about 
80-72% of one or more reactive monomers having a polymerizable double 
bond, said epoxy resin comprising the condensation product of bisphenol A 
and epichlorohydrin and having an epoxide equivalent weight of about 400 
to 1100 and represented by the structure below wherein n has a value of 0 
to about 8, preferably a value of about 2.2: 
##STR1## 
The epoxy ester resin is typically utilized in a neutral form. Such neutral 
form may be readily obtained by neutralization of about 94 parts of the 
resin with 6 parts of an amine such as 3 parts of triethanolamine and 3 
parts of dimethylaminoethanol. 
Preferably, the drying oil partially conjugated unsaturated fatty acid is 
obtained from an oil selected from the group consisting of safflower oil, 
sunflower oil, tung oil, canola oil, tall oil, dehydrated castor oil, soya 
bean oil, oiticica oil, plukenetia oil, perilla oil, hemp-seed oil, walnut 
oil, tobacco seed oil and linseed oil. The monobasic acid is preferably 
selected from the group consisting of acrylic acid, methacrylic acid, 
crotonic acid and vinylacetic acid. The reactive monomer is preferably 
selected from the group consisting of styrene, vinyl toluene and the 
acrylic and methacrylic acid esters of C.sub.1 -C.sub.10 alcohols. 
Typically, 65-75 parts of the esterified epoxy resin is reacted with 35-25 
parts of the mixture of unsaturated monobasic acids and reactive monomers. 
The reaction between the resin and such mixture is carried over a 2 hour 
period at 120.degree.-150.degree. C. in the presence of about 1-6 wt % of 
a peroxide catalyst such as di-tert. butyl peroxide, benzoyl peroxide, 
cumene peroxide, tertiary butyl perbenzoate, tertiary butyl hydroperoxide, 
and the like. The resultant solution is then neutralized with an amine to 
a pH of about 5-9 to make it water dilutable. 
Resins of the type employed in the water-based printing inks of the present 
invention are well known and are usually utilized in the form of a 
solution wherein organic solvents are generally present in an amount such 
that the solvent content will be in the range of about 3-15 wt %, based on 
the weight of the finished ink. 
Useful organic solvents for dissolving the resin include glycol ethers and 
alcohols such as ethylene glycol monomethyl ether, ethylene glycol 
mono-n-propyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol 
mono-n-hexyl ether, ethylene glycol monophenyl ether, propylene glycol 
monomethyl ether, propylene glycol mono-n-propyl ether, propylene glycol 
mono-n-butyl ether, propylene glycol monophenyl ether, diethylene glycol 
monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol 
mono-n-butyl ether, diethylene glycol mono-n-hexyl ether, dipropylene 
glycol monomethyl ether, dipropylene glycol mono-n-propyl ether, 
dipropylene glycol mono-n-butyl ether, tripropylene glycol monomethyl 
ether, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl 
alcohol, sec-butyl alcohol, and mixtures thereof. 
Epoxy ester resins useful for the present invention may be prepared in 
accordance with the teachings of U.S. Pat. No. 4,166,054 to Charles J. 
Meeske et al. and assigned to Reichhold Chemicals, Inc., and incorporated 
herein by reference. These resins are commercially available; a useful 
example of such resin is Reichhold Chemicals' Epotuf.RTM. Epoxy Ester 
Resin 92-737 dissolved in a mixture of 15% ethylene glycol monobutyl 
ether, 6% ethylene glycol monobutyl ether and 9% sec-butyl alcohol. This 
solution contains 70.+-.2% non-volatiles, an acid number of 54-60 and a 
Gardner-Holdt viscosity of Z.sub.7 -Z.sub.8. 
The pigment is typically present in an amount of about 5-30 wt %, 
preferably 10-20 wt. %, based on the weight of the ink. Suitable pigments 
include CI Pigment Yellow 12, CI Pigment Yellow 42, CI Pigment Black 7, CI 
Pigment Black 11, CI Pigment Red 9, CI Pigment Red 17, CI Pigment Red 22, 
CI Pigment Red 23, CI Pigment Red 57:1, CI Pigment Red 67, CI Pigment Red 
146, CI Pigment Red 224, CI Pigment Green 7, CI Pigment Green 36, CI 
Pigment Blue 15:3, CI Pigment Violet 23 and CI Pigment Violet 32. 
The drier is present in an amount of about 0.1-5 wt. %, preferably 0.5-3 
wt. %, based on the weight of the ink. Suitable driers comprise the 
octoates, resinates, naphthenates, neodecanoates, tallates and linoleates 
and mixtures thereof of metals selected from the group consisting of 
calcium, cobalt, magnesium, manganese, zinc, cerium, zirconium and 
mixtures thereof. Desirably, a drier activator such as 2,2'-bipyridyl is 
incorporated in the ink in an amount of about 0.1-1 wt. %. 
The cyclodextrin is present in an amount of about 0.5-5 wt. %, preferably 
1-3 wt. %, based on the weight of the ink. Suitable cyclodextrins comprise 
.alpha.-cyclodextrin, .beta.-cyclodextrin, .gamma.-cyclodextrin and 
derivatives of such cyclodextrins such as 
hydroxypropyl-.gamma.-cyclodextrin, hydroxypropyl-.beta.-cyclodextrin, 
hydroxyethyl-.beta.-cyclodextrin, methyl-.beta.-cyclodextrin, 
triacetyl-.beta.cyclodextrin, maltoscyclodextrin, 
trimethyl-.beta.cyclodextrin, sulfated-.alpha.-cyclodextrin, 
sulfated-.beta.-cyclodextrin, sulfated-.gamma.-cyclodextrin, 
carboxymethyl-.beta.-cyclodextrin, and the like. For the purposes of the 
present invention, the preferred cyclodextrin comprises 
.gamma.-cyclodextrin. 
The printing ink of the invention desirably also contains a wax present in 
an amount of about 1-5 wt. %, based on the weight of the ink. Such wax may 
be a polytetrafluoroethylene wax, polyethylene wax, Fischer-Tropsch wax, 
silicone fluid and mixtures thereof. It is also desirable to incorporate a 
defoamer in the ink in an amount of 0.1-0.5 wt. %, based on the weight of 
the ink. 
The balance of the ink will consist of water. Typically, the water will be 
present in an amount of about 30-60 wt. %, based on the weight of the ink. 
The water-based inks of the invention will typically have a viscosity of 
about 25.+-.2 sec. as measured on a #2 Zahn cup at 20.degree. C. and may 
be printed at speeds of up to 200 m/min. The inks dry rapidly--typically 
the imprinted substrate will be cured in ovens of 5-6 meters in length at 
temperatures of 80.degree. to 180.degree. C. and a residence time of 0.1 
to 2 seconds. Thus a second color may be printed almost instantaneously 
upon a previously-printed color.

The following examples shall serve to illustrate the invention. Unless 
otherwise indicated, all parts and percentages are by weight. 
EXAMPLE 1 
For comparative purposes, a conventional water-based printing ink was 
prepared from the components indicated in Table I below; this ink 
contained no driers. 
TABLE I 
______________________________________ 
"Epotuf" 92-737, 70% solids 
28.6 
Triethylamine 0.9 
Dimethylaminoethanol 0.9 
CI Pigment Red 17 15.0 
Polyethylene Wax 3.3 
Silicone Emulsion 1.3 
Defoamer 0.2 
Water 49.8 
100.0 
Printability good 
Odor standard 
pH 12 Solution Resistance 
good 
1% Aqueous Ammonia Resistance 
none 
Gloss high 
Stability good 
______________________________________ 
Incorporation of a drier in the ink would improve the formulation by 
crosslinking the epoxy ester resin and provide excellent resistance 
properties. However, metallic driers often hydrolyze in water; thus their 
use would be altogether precluded or such usage would lead to instability 
problems or objectionable odors. Examples 2 and 3 set forth below 
illustrate the problems caused by the use of metallic driers in varying 
amounts. 
EXAMPLE 2 
A water-based printing ink was prepared from the components indicated in 
Table II below; this ink contained the drier cobalt naphthenate and the 
drier activator 2,2'-bipyridyl. 
TABLE II 
______________________________________ 
"Epotuf" 92-737, 70% solids 
28.6 
Triethylamine 0.9 
Dimethylaminoethanol 0.9 
CI Pigment Red 17 15.0 
Polyethylene Wax 3.3 
Silicone Emulsion 1.3 
Defoamer 0.2 
Cobalt Naphthenate, 5% 
0.8 
2,2'-Bipyridyl, 30% 0.3 
Water 48.7 
100.0 
Printability good 
Odor heavy 
pH 12 Solution Resistance 
very good 
1% Aqueous Ammonia Resistance 
very good 
Gloss high 
Stability unstable 
______________________________________ 
A water-based printing ink was prepared from the components indicated in 
Table III below; this ink contained the drier cobalt naphthenate and the 
drier activator 2,2'-bipyridyl. 
TABLE III 
______________________________________ 
"Epotuf" 92-737, 70% solids 
28.6 
Triethylamine 0.9 
Dimethylaminoethanol 0.9 
CI Pigment Red 17 15.0 
Polyethylene Wax 3.3 
Silicone Emulsion 1.3 
Defoamer 0.2 
Cobalt Naphthenate, 5% 
0.4 
2,2'-Bipyridyl, 30% 0.3 
Water 49.1 
100.0 
Printability good 
Odor moderate 
pH 12 Solution Resistance 
very good 
1% Aqueous Ammonia Resistance 
weak 
Gloss high 
Stability unstable 
______________________________________ 
EXAMPLE 4 
A water-based printing ink was prepared from the components indicated in 
Table IV below; this ink contained the drier cobalt naphthenate, the drier 
activator 2,2'-bipyridyl and .gamma.-cyclodextrin. Based on these results, 
it appears that cyclodextrins have the capability of forming inclusion 
complexes with metallic driers thus "protecting" them from hydrolysis. The 
resulting water-based printing ink exhibited superior properties in 
respect to stability, odor and printability. 
TABLE IV 
______________________________________ 
"Epotuf" 92-737, 70% solids 
28.6 
Triethylamine 0.9 
Dimethylaminoethanol 0.9 
CI Pigment Red 17 15.0 
Polyethylene Wax 3.3 
Silicone Emulsion 1.3 
Defoamer 0.2 
Cobalt Naphthenate, 5% 
0.4 
2,2'-Bipyridyl, 30% 0.3 
.gamma.-Cyclodextrin, 18% 
1.5 
Water 47.6 
100.0 
Printability good 
Odor slight 
pH 12 Solution Resistance 
very good 
1% Aqueous Ammonia Resistance 
excellent 
Gloss high 
Stability good 
______________________________________ 
The inks were tested by imprinting on a polyethylene polycoated board. The 
drying cycle was 15 seconds in an oven at 80.degree. C. 
The prints were tested after exposure to ambient temperature for 24 hours. 
Resistance to the high pH reagents was evaluated as follows. The prints 
were placed on a flat surface. The appropriate solution was applied to the 
surface of the printed stock. After the appropriate time had elapsed, the 
solutions were wiped 5 times in one direction with tissue paper using 
moderate pressure in order to absorb bleed and loose pigment affected by 
the treatment solution.