Intaglio printing ink

Abstract: The invention relates to a printing ink especially suited for the intaglio printing of security documents such as postage stamps, stock certificates and the like. The ink comprises: a) an epoxy resin ester reacted with an unsaturated monobasic acid and a reactive monomer, b) a glycol and/or glycol ether, c) a pigment, d) a monoalkanolamine, e) a drier and f) water.

Description: The invention relates to a heatset printing ink for the printing of documents by intaglio printing, i.e, engraved steel die printing. The ink has been found to be especially useful for the printing of security documents such as stamps, checks, stock certificates, bank notes, tickets, etc. The term "intaglio printing" refers to a printing process wherein a printing cylinder or printing plate carries the engraved pattern and the engraved recess is filled with printing ink to be transferred to the printing substrate in order to create the document. In this type of printing, typically a rotating engraved cylinder (usually manufactured from steel or nickel and plated with chromium) is supplied with ink by one or more template inking cylinders by which a pattern of inks of different color is transferred to the printing cylinder. Any excess ink on the surface of the cylinder is then wiped off by a rotating wiper cylinder covered by a plastisol, using a dilute aqueous solution of sodium hydroxide and sulfonated castor oil as an emulsifying medium for the wiped-off excess ink. Thereafter, the printing pattern is transferred, under a pressure of up to 105 kg/cm 2 , to the substrate. The most widespread process for printing security documents, especially currency, is sheetfed non-heatset intaglio. Sheetfed non-heatset intaglio inks are based on oxidizable resins and alkyds and are very slow drying. Typically, one side of the currency is printed first and after 24-48 hours, the other side is printed. The typical printing speed of sheetfed intaglio is about 45-75 m/min. US-A-4,966,628 discloses sheetfed intaglio inks suitable for printing of security documents. Recently, patents disclosing heatset intaglio printing inks suitable for printing of security documents have been issued, e.g. see US-A-5,100,934 and US-A-5,367,005. Both patents describe printing ink formulations which have proven to provide excellent performance in respect to the heatset intaglio printing of currency. However, the inks disclosed in both patents exhibit either relatively high percentages of volatile organic compounds ("VOC") or are able to tolerate only small amounts of water. Until the present invention, efforts to reduce the VOC content of the heatset intaglio inks have failed. Reducing the content of volatile solvents or substituting water for part of the volatile solvents have resulted in incompatibility problems because of the nature of the resins present in such inks. Thus, it is the object of the present invention to overcome these drawbacks. This object has been achieved by the surprising finding that it is possible to replace part of the VOCs in heatset intaglio printing inks with water, thereby dramatically reducing the VOC content of such inks, while at the same time avoiding incompatibility problems which would otherwise occur because of the presence of water in such inks. The solution to this problem is that a monoalkanolamine is employed in the inks of the present invention, instead of the diamine curing agents employed in the inks disclosed in US-A-5,100,934. As will be apparent from the examples set forth below, the tolerance of the heatset intaglio printing inks for water is significantly improved as a result of the presence of the alkanolamine. The intaglio printing inks of the present invention comprise: a) a resin present in an amount of about 15 to 40 wt.%, preferably 20 to 35 wt.%, based on the weight of the ink, comprising 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 n has an average value of about 2.2: b) at least one glycol and/or glycol ether present in an amount of about 10 to 30 wt.%, preferably 15 to 25 wt.%, based on the weight of the ink; c) at least one inorganic and/or organic pigment present in an amount of about 3 to 30 wt%, preferably 5-28 wt.%. based on the weight of the ink; d) a monoalkanolamine having 2 to 8, preferably 2 to 5 carbon atoms, wherein the amino group is primary, secondary or tertiary, preferably primary; the monoalkanolamine is present in an amount of about 0.1 to 10 wt.%, preferably 1 to 3 wt.%, based on the weight of the ink; e) at least one drier, present in an amount of about 0.1 to 5 wt.%, preferably 0.5 to 4 wt.%, based on the weight of the ink; and f) water, present in an amount of about 5 to 20 wt.%, preferably 10 to 20 wt.%, based on the weight of the ink. Drying oil partially conjugated unsaturated fatty acids which are useful for esterifying the epoxy resin are those available from 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. Typically the esterification of the epoxy resin with the drying oil partially conjugated unsaturated fatty acid is carried out at a temperature of about 220°-240°C and continued until an acid number below 10 is obtained. The ester is then dissolved in a glycol ether such as ethylene glycol monobutyl ether to a concentration of 60% non-volatile and a Gardner-Holdt viscosity of K-N. The 60% non-volatile solution of the esterified epoxy resin is thereafter reacted with a mixture of 20-28% of one or more unsaturated monobasic acids having a polymerizable double bond and 80-72% of one or more reactive monomers having a polymerizable double bond. Suitable monobasic acids include acrylic acid, methacrylic acid, crotonic acid and vinylacetic acid. Suitable reactive monomers include styrene, vinyl toluene and the acrylic and methacrylic acid esters of C 1 -C 10 alcohols such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl and 2-ethylhexyl. Typically, 65-75 parts of the esterified epoxy resin will be reacted with 35-25 parts of the mixture of unsaturated monobasic acids and reactive monomers. The reaction between the esterified epoxy resin and such mixture may be carried over a two hour period at a temperature of about 120 to 150°C in the presence of about 1-6 wt% of a peroxide catalyst such as di-tertiary butyl peroxide, benzoyl peroxide, cumene peroxide, tertiary butyl perbenzoate, tertiary butyl hydroperoxide, and the like. The resultant solution is then typically neutralized with an amine to a pH of about 5 to 9 to make it water dilutable. Resins of the type employed in the intaglio printing inks of the present invention are well known and may be prepared in accordance with the teachings of US-A-4,166,054. These resins are commercially available; a useful example of Resin a) is Reichhold Chemicals' Epotuf® Epoxy Ester Resin 92-737 dissolved in a suitable solvent such as diethylene glycol monobutyl ether and is hereinafter referred to as "Varnish 90-164". This varnish contains 70±2% non-volatiles, has an acid number of 54-60 and a Gardner-Holdt viscosity of Z 7 -Z 8 . Suitable glycols and glycol ethers include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butylene glycol, octylene glycol, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether and propylene glycol monophenyl ether, and mixtures thereof. The pigment may be any desired inorganic and/or organic pigment suitable for heatset intaglio printing such as CI Pigment Yellow 12, CI Pigment Yellow 42, CI Pigment Black 7, CI Pigment Black 11, CI Pigment Red 9, 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. Suitable monoalkanolamines include ethanolamine (which is preferred), 3-amino-1-propanol, 4-amino-1-butanol, 5-amino-1-pentanol, 6-amino-1-hexanol, 2-(methylamino) ethanol and N,N-dimethylaminoethanolamine. Suitable driers are the heavy metal salts of complex fatty acids, present singly or as mixtures. Examples of useful driers are the octoates, resinates, naphthenates, neodecanoates, tallates and linoleates and mixtures thereof of metals such as cobalt, magnesium, manganese, zinc, cerium, zirconium and mixtures thereof. If desired, a small amount, e.g. 0.1-1.0 wt.%, based on the weight of the ink, of a drier activator may be included in order to enhance the activity of the drier; a suitable drier activator is 2,2'-bipyridyl. Preferably, the ink will contain one or more fillers in an amount of about 1 to 35 wt.%, based on the weight of the finished ink. Suitable fillers include china clay, calcium carbonate, calcium sulfate, talc, silica, corn starch, titanium dioxide, alumina and mixtures thereof. The ink may also contain about 1 to 5 wt.%, based on the weight of the finished ink, of a wax to improve scuff resistance. Suitable waxes include polytetrafluoroethylene waxes, polyethylene waxes, Fischer-Tropsch waxes, silicone fluids and mixtures thereof. The finished inks will typically have a viscosity in the range of 0.2 to 3 Pa.s (2 to 30 Poise) at 40°C and 100 second -1 shear rate 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 to 180°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. EXAMPLES 1-5 Five Intaglio printing inks having the colors set forth in Table I were prepared by combining the indicated ingredients and thereafter grinding the mixture on a 3-roll mill until a 4/2 grind was obtained. The properties of the five inks are shown in Table II.

Claims: An intaglio printing ink comprising: a) a resin present in an amount of 15 to 40 wt.%, based on the weight of the ink, comprising the reaction product of (i) 65-75 parts per hundred of the ester obtained from the esterification of 40-60 parts per hundred of an epoxy resin with 60-40 parts per hundred of a drying oil partially conjugated unsaturated fatty acid having an iodine number of 125-185, an acid number of 180-210 and a degree of conjugation of 20-25%, said ester having an acid number below 10, and (ii) 35-25 parts per hundred of a mixture of 20-28% of one or more unsaturated monobasic acids having a polymerizable double bond and 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 400 to 1100 and represented by the structure below wherein n has a value of 0 to 8: b) at least one glycol and/or glycol ether present in an amount of 10 to 30 wt.%, based on the weight of the ink; c) at least one inorganic and/or organic pigment present in an amount of 3 to 30 wt%, based on the weight of the ink; d) at least one monoalkanolamine having 2 to 8 carbon atoms, wherein the amino group is a primary, secondary or tertiary amino group, said monoalkanolamine being present in an amount of 0.1 to 10 wt.%, based on the weight of the ink; e) at least one drier, present in an amount of about 0.1 to 5 wt.%, based on the weight of the ink; and f) water, present in an amount of 5 to 20 wt.%, based on the weight of the ink. The ink of claim 1 wherein the monoalkanolamine is ethanolamine, 3-amino-1-propanol, 4-amino-1-butanol, 5-amino-1-pentanol and/or 6-amino-1-hexanol. The ink of claim 1 or 2 wherein the drying oil partially conjugated unsaturated fatty acid is obtainable from 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/or linseed oil. The ink of any of claims 1 to 3 wherein the monobasic acid is acrylic acid, methacrylic acid, crotonic acid and/or vinylacetic acid. The ink of any of claims 1 to 4 wherein the reactive monomer is styrene, vinyl toluene and/or the acrylic or methacrylic acid esters of C 1 -C 10 alcohols. The ink of any of claims 1 to 5 wherein the glycol and/or glycol ether is ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butylene glycol, octylene glycol, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether and propylene glycol monophenyl ether or a mixture thereof. The ink of any of claims 1 to 6 wherein the pigment is CI Pigment Yellow 12, CI Pigment Yellow 42, CI Pigment Black 7, CI Pigment Black 11, CI Pigment Red 9, 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/or CI Pigment Violet 32. The ink of any of claims 1 to 7 including a filler present in an amount of 1 to 35 wt.%, based on the weight of the ink, said filler being china clay, calcium carbonate, calcium sulfate, talc, silica, corn starch, titanium dioxide, alumina or a mixture thereof. The ink of any of claims 1 to 8 including a wax present in an amount of 1 to 5 wt.%, based on the weight of the ink, said wax being polytetrafluoroethylene waxes, polyethylene waxes, Fischer-Tropsch waxes, silicone fluids or a mixture thereof. The ink of any of claims 1 to 9 wherein the drier is selected from octoates, resinates, naphthenates, neodecanoates, tallates and linoleates and mixtures thereof of cobalt, magnesium, manganese, zinc, cerium, zirconium or a mixture thereof.

Inventors: MALANGA JOSEPH, NACHFOLGER SOLOMON J, MALANGA, JOSEPH, NACHFOLGER, SOLOMON J.
Applicants: SUN CHEMICAL CORP, SUN CHEMICAL CORPORATION
Application year: 1996
Main classification: C09D11
IPC codes: C09D11, C08L63