WO2005090496A1

WO2005090496A1 - Rheologically unique intaglio printing inks

Info

Publication number: WO2005090496A1
Application number: PCT/US2005/008399
Authority: WO
Inventors: Solomon J. Nachfolger; David Fleming; Joseph Malanga; Caspar Lee
Original assignee: Sun Chemical Corporation
Priority date: 2004-03-12
Filing date: 2005-03-14
Publication date: 2005-09-29
Also published as: MXPA06010396A; EP1723207A4; AU2005224096A1; EP1723207A1; CN101107332A; BRPI0508118A; CA2559557A1

Abstract

Intaglio printing inks with unique rheological properties have been discovered. The intaglio printing inks are extremely dependent on temperature and almost independent of shear. The intaglio printing inks preferably are low in volatile organic components. The intaglio printing inks, because of the unique rheological properties exhibited, are excellent for intaglio printing on Tyvek and paper, for example, in the printing of security documents such as currency, postage stamps, stock certificates, bank notes and the like. It is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader quickly to ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the appended issued claims. 37 CFR ξ 1.72(b).

Description

RHEOLOGICALLY UNIQUE INTAGLIO PRINTING INKS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of U.S. Provisional Application Serial No. 60/552,681, which was filed on March 12, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0002] The present invention relates generally to intaglio printing inks, and to intaglio printing methods.

2. Description of Related Art

[0003] In intaglio printing, a rotating metal printing cylinder, usually steel or copper, is engraved with a pattern or image to be printed. A special ink is supplied by an inking cylinder to the printing cylinder, and the ink from the inking cylinder is transferred to the printing cylinder. Subsequent to inking, any excess of ink on the plain surface of the printing cylinder is wiped off by a rotating wiping cylinder. The ink remaining in the engraving of the printing cylinder is then transferred under pressure onto the substrate to be printed. [0004] The printing of security documents, for example paper currency, postage stamps, stock certificates, bank notes and the like, requires an outstanding printing quality and particular measures to prevent counterfeiting and forgery of the printed documents. Such security documents are preferably printed by the intaglio printing process.

[0005] Intaglio printing inks for the printing of security documents must satisfy a number of requirements, among them:

1 ) Improved rheological properties at the moment of ink transfer from the inking cylinder to the printing cylinder;

2) Improved rheological properties on the printing cylinder, at the moment of printing;

3) Improved rheological properties on the substrate right after printing; and

4) Easy wiping/removal of the excess ink from the plain surface of the printing cylinder.

[0006] As is also well known in the art, once the intaglio ink has been printed on the substrate, the printed substrate generally must be dried in order to allow subsequent processing. Drying time is, thus, a variable affecting the overall duration of the process. [0007] There is always a need in the art to discover new intaglio printing inks that improve one or more of the foregoing properties. Accordingly, it was an object of the present invention to discover new intaglio printing inks that satisfy this need.

SUMMARY OF THE INVENTION

[0008] This object and other objects were met with the present invention, which relates in a first embodiment to an intaglio printing ink exhibiting the following rheological properties at a constant shear rate of 100/sec: a) a first viscosity at a temperature that is the same as an ambient temperature surrounding the ink prior to a point in time that the ink contacts an intaglio printing cylinder; b) a second viscosity at a temperature that is the same as an operating temperature of the intaglio printing cylinder; and c) a third viscosity at a temperature that is the same as an ambient temperature surrounding the ink after a point in time that the ink has been pressed from the intaglio printing cylinder onto the substrate; wherein the first viscosity is greater than the second viscosity by at least 45 Pas; and the third viscosity is greater than the second viscosity by at least 45 Pas.

[0009] The present invention relates in a second embodiment to an intaglio printing ink, the intaglio printing ink comprising: a) a pigment; b) a vehicle; and c) optionally a modifier; the intaglio printing ink having a solids content between about 92% to about 100%.

[0010] The present invention relates in a third embodiment to an intaglio printing method, the printing method comprising the following steps: a) supplying an intaglio printing ink according to the invention to an engraved printing cylinder; b) wiping excess intaglio printing ink from the printing cylinder; and c) transferring the printing ink from the printing cylinder onto a substrate to be printed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0011] The invention will now be described in greater detail with reference to the drawings, wherein:

Figure 1 is a graph depicting the results of viscosity versus time program that starts at 26°C, continues to 58°C and returns to 26°C, at a constant shear rate of 100/s, and compares the viscosity changes undergone by a Green Tyvek Ink according to the present invention compared to a known BEP Black Ink;

Figure 2 is another graph depicting the results of viscosity versus time program that starts at 26°C, continues to 58°C and returns to 26°C, at a constant shear rate of 100/s, and compares the viscosity changes undergone by a Green Tyvek Ink according to the present invention compared to a Black Tyvek Ink also according to the present invention;

Figure 3 is another graph depicting the results of viscosity versus time program that starts at 26°C, continues to 58°C and returns to 26°C, at a constant shear rate of 100/s, and shows the viscosity changes undergone by the Tyvek Ink varnish alone;

Figure 4 is another graph depicting the results of viscosity versus time program that starts at 26°C, continues to 58°C and returns to 26°C, at a constant shear rate of 100/s, and compares the viscosity changes undergone by a Green Tyvek Ink according to the present invention compared to a Black Tyvek Ink also according to the present invention; and

Figure 5 is another graph depicting the results of viscosity versus time program that starts at 26°C, continues to 58°C and returns to 26°C, at a constant shear rate of 100/s, and compares the viscosity changes undergone by a Black Tyvek Ink according to the present invention compared to a similar ink lacking carnauba wax and to a similar wax having a high melting PTFE wax instead of the carnauba wax.

[0012] It is understood that the references to the drawings herein are meant to be exemplary of the preferred embodiment(s) described herein, and that neither the drawings themselves, nor the reference numerals on the drawings are meant to be limiting of the invention in any respect. DETAILED DESCRIPTION OF THE INVENTION

[0013] Conventional intaglio inks usually are formulated with high amounts of solvents to keep the viscosity of the inks low when the ink is on the printing cylinder, which is customarily operated at about 80°C. The amount of solvent in conventional intaglio inks can be 10% by weight or more, based on the total weight of the ink. Conventional intaglio inks also contain waxes, which melt at this temperature, and help to lower the viscosity of the ink from its initial value prior to contacting the printing cylinder. However, the presence of the solvents in the inks at this initial value means that the viscosity at this initial value is still relatively low. The viscosity of these conventional intaglio inks can be seen in this way to be relatively independent of temperature due to the presence of the solvent, in that there is a relatively small change in viscosity as the ink is taken from an initial value at ambient temperature before the ink contacts the printing cylinder, to a second value when the ink contacts the printing cylinder operating at about 80°C. Due to the presence of the wax, these conventional intaglio inks will regain most or all of the initial viscosity as the wax component solidifies once the ink has been transferred from the printing cylinder to the substrate, and, thus, cools to ambient temperature. A plot of the viscosity of conventional intaglio inks, as a function of temperature, will normally reveal a relatively flat curve (e.g., the BEP Black ink depicted in Figure 1), as the ink is manipulated from a first viscosity at ambient temperature prior to contacting the printing cylinder, through a second viscosity at about 80°C when the ink is in contact with the printing cylinder, to a third viscosity again at, for example, ambient temperature after the ink has been pressed from the printing cylinder onto the substrate. [0014] Surprisingly, a new class of intaglio printing inks have been discovered, which are extremely dependent upon temperature and also independent of shear. A plot of the viscosity of a member of this new class as a function of temperature at ambient temperature, then at printing cylinder temperature, then at ambient temperature again will reveal a U-shaped curve at constant shear. In other words, at ambient temperature prior to contacting the printing cylinder, the inventive inks will exhibit an extremely high viscosity, which will lower to an optimum viscosity for printing while the ink is in contact with the printing cylinder, and, then, the ink will quickly regain its high initial viscosity once the ink has been pressed from the printing cylinder onto the substrate, and the substrate moves away from the heated printing cylinder and the ink cools.

[0015] As a result of these new and completely unexpected rheological properties, the inventive inks are ideally suited for intaglio printing, for example, security documents, such as currency, postage stamps, stock certificates, bank notes and the like, onto Tyvek and paper substrates. Because the inventive inks recover their initial high viscosity almost immediately after being pressed from the printing cylinder and the heat associated therewith, the inventive inks remain fixed in the engraving's shape and do not feather or run. This results in a final print that is much sharper than it has been possible to obtain previously.

[0016] On the other hand, because the viscosity of the inventive inks falls to conventional viscosity levels on the printing cylinder at print temperature, the inventive inks are just as easy to wipe from the plain areas of the printing cylinder as are the conventional intaglio inks. Yet, from a practical standpoint, the combination of sharper prints and easy wiping, makes the inventive inks far superior to the conventional intaglio printing inks.

[0017] As noted above, the present invention relates in a first embodiment to an intaglio printing ink exhibiting the following rheological properties at a constant shear rate of 100/sec: a) a first viscosity at a temperature that is the same as an ambient temperature surrounding the ink prior to a point in time that the ink contacts an intaglio printing cylinder; b) a second viscosity at a temperature that is the same as an operating temperature of the intaglio printing cylinder; and c) a third viscosity at a temperature that is the same as an ambient temperature surrounding the ink after a point in time that the ink has been pressed from the intaglio printing cylinder onto the substrate; wherein the first viscosity is greater than the second viscosity by at least 45 Pas; and the third viscosity is greater than the second viscosity by at least 45 Pas. In a preferred embodiment, the first viscosity is greater than the second viscosity by at least 60 Pas, and/or the third viscosity is greater than the second viscosity by at least 60 Pas. In a particularly preferred embodiment, the first viscosity is greater than the second viscosity by at least 75 Pas, and/or the third viscosity is greater than the second viscosity by at least 75 Pas. In an especially preferred embodiment, the first viscosity is greater than the second viscosity by at least 85 Pas, and/or the third viscosity is greater than the second viscosity by at least 85 Pas. [0018] In one preferred embodiment, the first viscosity is at a temperature ranging from about 23 °C to about 28°C. In an especially preferred embodiment, the first viscosity is at a temperature about 26°C.

[0019] In one preferred embodiment, the second viscosity is at a temperature ranging from about 75°C to about 85°C. In an especially preferred embodiment, the second viscosity is at a temperature about 80°C.

[0020] In one preferred embodiment, the first viscosity, second viscosity and third viscosity are at constant shear. In an especially preferred embodiment, the first^' viscosity, second viscosity and third viscosity are at a shear of 100/s.

[0021] In a particularly preferred embodiment, the intaglio printing ink is one that exhibits the following rheological properties at a constant shear rate of 100/s: a) a first viscosity at a temperature of 26°C; b) a second viscosity at a temperature of 80°C; and c) a third viscosity at a temperature of 26°C; wherein the first viscosity is greater than the second viscosity by at least 70 Pas; and the third viscosity is greater than the second viscosity by at least 70 Pas.

[0022] In one preferred embodiment, these unique rheological properties can be brought about by manipulating the solids content of the ink. As noted above, the present invention relates in a second embodiment to an intaglio printing ink comprising: a) a pigment; b) a vehicle; and c) optionally a modifier; wherein the intaglio printing ink has a solids content between about 92% to about 100%. In a preferred embodiment, the solids content ranges between about 96% to about 100%.

[0023] This means that the inventive inks contain little or no volatile organic components (NOC), for example, organic solvents. The amount of NOC in the inventive inks is less than 8% by weight, preferably less than 4% by weight, based on the total weight of the ink.

[0024] The useful pigments are all those customarily used in the art of intaglio printing. For printing security documents, preference is given to inorganic and organic pigments, for example, 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. In general, the amount of pigment in the ink ranges from about 0.1 to about 40 % by weight, preferably from about 10 to about 30 % by weight, again based on the total weight of the ink.

[0025] Likewise, the useful vehicles are all those customarily used in the art. Preference is given to those containing alkyd resins (air-curable or isocyanate curing,) for example, those sold under the name SYΝOLAC, thermosetting acrylics (e.g. SYNACRYL), urethanes (thermosetting,) for example, those sold under the name UNITHANE, and polyesters (thermosetting,) for example, those sold under the name SYNOLAC. In general, the amount of vehicle in the ink ranges from about 40 to about 99.9 % by weight, preferably from about 40 to about 70 % by weight, again based on the total weight of the ink.

[0026] A modifier is optional, but, when present, can be selected from all those customarily used in the art, including driers, fillers, waxes, surfactants and the like. Preferably, one or more of driers, fillers, waxes and/or surfactants are included in the ink composition. 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, for example, 2,21-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. Suitable waxes include carnauba waxes, polytetrafluoroethylene (PTFE) waxes, polyethylene waxes, Fischer-Tropsch waxes, silicone fluids and mixtures thereof. Among the surfactants, non-ionic surfactants are especially preferred. Exemplary non-ionic surfactants suitable for use in the compositions according to the present invention include primary amines such as cocamine (available as Adagen 160D (TM) from Witco) and alkanolamides such as cocamide MEA (available as Empilan CME (TM) from Albright and Wilson), PEG-3 cocamide, cocamide DEA (available as Empilan CDE (TM) from Albright and Wilson), lauramide MEA (available as Empilan LME (TM) from Albright and Wilson), lauramide MIPA, lauramide DEA, and mixtures thereof. In general, the total amount of modifiers in the ink, when present, ranges from about 0.1 to about 40 % by weight, preferably from about 0.1 to about 30 % by weight, again based on the total weight of the ink.

[0027] Other customary ingredients can be added to the inventive ink formulations, provided that the solids content closely adheres to the foregoing values, and the resulting ink displays the unique rheological properties previously discussed. Whether the resulting ink displays the unique rheological properties previously discussed is easily ascertained in the manner previously described, i.e., by plotting the viscosity as a function of temperature at constant shear, and determining a U-shaped curve as the temperature is increased constantly from ambient temperature through 80°C and then decreased from 80°C to ambient temperature again.

[0028] The invention will now be described in greater detail by way of the following, non-limiting, examples:

EXAMPLES

[0029] A series of printing inks were prepared and designated "Tyvek inks" only because they were intended to be printed onto Tyvek substrate. However, these inks were suitable for printing onto other substrates, especially paper. The compositions of these Tyvek inks are shown below:

Green Tyvek 11 Intaglio Ink

Ingredients Wt.-%

Alkyd DP80/100 17.5

Empilan CDE 5.3

Unithane E20165 23.1

Micronized Carnauba 4.0

Brytomya M 29.9

Sturcal F 8.0

Green GN-C 1.7

Yellow BAW 1.2

Raven Black 1255 1.0

Tioxide RHD-2 7.3

R518/21 1-0314 Silicone 0.1

Cobalt 8% 0.2

Manganese 10% 0.35

Zirconium 0.35

Total 100.00

Solids Content 5.1

Black Tyvek 12 Intaglio Ink

Ingredients Wt.-%

Alkyd DP80/100 15.7

Empilan CDE 4.8

Unithane E20165 20.8

Micronized Carnauba 3.6

Brytomya M 23.4

Sturcal F 5.4

Raven Black 1255 1.1

R518/211-0314 Silicone 0.1

BASF Black 345 23.9

Blue LGLD 0.3

Irgalite Red RBS 0.1

Cobalt 8% 0.18

Manganese 10% 0.31

Zirconium 0.31

Total 100.00

Solids Content 4.6 Green Tyvek 50 Intaglio Ink

Ingredients Wt.-%

Alkyd DP80/100 17.4

Empilan CDE 2.7

Unithane E20175 23.0

SA100 [Surfac SDBS80] 2.7

Micronized Carnauba 4.0

Brytomya M 30.1

Sturcal F 8.0

Green GN-C 1.7

Yellow BAW 1.2

Raven Black 1255 1.0

Tioxide RHD-2 7.3

R518/211 -0314 Silicone 0.1

Cobalt 8% 0.2

Manganese 10% 0.30

Zirconium 0.30

Total 100.00

Solids Content 5.1

Black Tyvek 12 Intaglio Ink

Ingredients Wt.-%

Alkyd DP80/100 15.8

Empilan CDE 2.4

Unithane E20175 20.8

SA100 [Surfac SDBS80] 2.4

Micronized Carnauba 3.6

Brytomya M 23.4

Sturcal F 5.4

Raven Black 1255 1.1

R518/211 -0314 Silicone 0.1

BASF Black 345 23.9

Blue LGLD 0.3

Irgalite Red RBS 0.1

Cobalt 8% 0.18

Manganese 10% 0.31

Zirconium 0.31

Total 100.00

Solids Content 4.6 Green Tyvek 56 Intaglio Ink

Ingredients Wt.-%

Alkyd DP80/100 16.5

Empilan CDE 2.5

Unithane E20175 21.7

SA100 [Surfac SDBS80] 2.5

Micronized Carnauba 3.6

Brytomya M 29.5

Sturcal F 8.1

R518/211 -0314 Silicone 0.1

Phthalo Green 72-25 2.3

Yellow Iron Oxide 28-121 11.7

Blue, 52-107 0.1

Carbazole Violet, 60-47 0.1

Black, Elftex 8, 90-129 0.9

Cobalt 8% 0.1

Manganese 10% 0.2

Zirconium 0.2

Total 100.00

Solids Content 4.6

Black Tyvek 57 Intaglio Ink

Ingredients Wt.-%

Alkyd DP80/100 15.8

Empilan CDE 2.4

Unithane E20175 20.8

SA100 [Surfac SDBS80] 2.4

Micronized Carnauba 3.6

Brytomya M 20.4

Sturcal F 5.4

R518/211 -0314 Silicone 0.1

Black Iron Oxide 27.0

Black, Elftex 8, 90-129 1.8

Cobalt 8% 0.1

Manganese 10% 0.2

Zirconium 0.2

Total 100.01

Solids Content 4.4 Comparison Formulation:

Bank of England Intaglio Ink

Ingredients Wt.-%

Unithane 20157 21.1

Alkyd DP80/100 13.4

Empilan CDE 4.0

Wax Paste SA104 3.0

Micronized Carnauba 2.5

Exxsol D80 1.5

Paraset 32H 1.0

Organic Pigment 5.8

Brytomya M 22.7

Sturcal F 23.0

Bentone 1.0

Cobalt 8% 0.2

Manganese 10% 0.35

Zirconium 0.35

Total 100.00

Solids Content 12.2

[0030] A Haake rheology on the Tyvek Green 11 and Black 12 inks was made. The study showed just how close the green and black inks were to one another — almost superimposable. The precision of the test is +/- 3%, and the instrument was calibrated with a standard fluid medium immediately prior to the test as being at +1.9%. For comparison, a conventional black intaglio printing ink, BEP Black, obtained from BEP, was included in the study.

[0031] Viscosity of each of the inks at 26°C as a function of sheer was studied. The results are reported in Table 1 below: Table 1

[0032] In Table 1, the more significant results are highlighted in bold. The inventive Tyvek inks have very high viscosity at 100/s and exceedingly high maximum tau stress. This usually translates as pulling much higher amperage during wiping and causing lower wiper cylinder life. However, this problem was not observed. Without adding extra solvent which could deform the Tyvek ink, the viscosity can be brought down by adding varnish. Pumping problems can likewise be solved by this method.

[0033] When the critical shear rate drops below 100/s, printability usually suffers. However, again, no such problem was observed.

[0034] Cylinder temperature [80°C] times viscosity curves at 100/s were also run with the results reported in Table 2: Table 2

The 2 sec. initial reading in bold for Tyvek Black 12 is an anomaly and is not significant.

[0035] Haake rheology studies for the foregoing inks were plotted, and a plot of the results for Tyvek Green 11 versus BEP Black is shown in Figure 1. A plot of the results for Tyvek Green 11 versus Tyvek Black 12 is shown in Figure 2.

[0036] The data prove the inventive Tyvek inks to be extremely dependent upon temperature and almost independent of shear.

[0037] In an effort to ascertain whether the varnish was responsible for the results obtained, a Haake rheology study was made of the varnish alone. A plot of these results is shown in Figure 3. It should be clear that the Tyvek varnish by itself does not show the same degree of temperature dependency.

[0038] A Haake rheological study comparing the rheological properties of Tyvek Green 56 and Tyvek Black 57 is shown in Figure 4. Both inks were stable, and the viscosity for each @ 100/sec is about 230 Pas. This compares favorably to about 90 Pas for both Tyvek Green 11 and Tyvek Black 12 at ambient temperature. In both cases, the viscosity for the inventive black inks fall to about 10 Pas at 58°C, and that for the inventive green inks fall to about 15 Pas at the same temperature.

[0039] In an effort to ascertain whether the wax was responsible for the results obtained, Tyvek Black 56 inlc, which contained 3.6% Carnauba wax, was compared to (a) Tyvek Black ink without wax and (b) Tyvek Black containing 3.6% of PTFE (high melting) wax. The respective inks were formulated as shown in Table 3 below:

Table 3

[0040] The results are shown in Figure 5. Basically, no difference in the shape of the curves could be ascertained, which suggests that the unique rheological properties demonstrated herein are not due to the presence of a wax component, in and of itself.

[0041] Summarizing the foregoing, the rheology of the inventive Tyvek inks differs from "conventional intaglio" as follows: 1. Higher viscosity at low shear rates (poorer flow at room temperature.) 2. Higher viscosity at high shear rates (room temperature.) [0042] It should be understood that the preceding detailed description of the invention is merely a detailed description of one preferred embodiment or of a small number of preferred embodiments of the present invention and that numerous changes to the disclosed embodiment(s) can be made in accordance with the disclosure herein without departing from the spirit or scope of the invention. The preceding detailed description of the invention, therefore, is not meant to limit the scope of the invention in any respect. Rather, the scope of the invention is to be determined only by the appended issued claims and their equivalents.

Claims

WHAT IS CLAIMED IS:

1. An intaglio printing ink exhibiting the following rheological properties at a constant shear rate of 100/sec: a) a first viscosity at a temperature that is the same as an ambient temperature surrounding the ink prior to a point in time that the inlc contacts an intaglio printing cylinder; b) a second viscosity at a temperature that is the same as an operating temperature of the intaglio printing cylinder; and c) a third viscosity at a temperature that is the same as an ambient temperature surrounding the ink after a point in time that the ink has been pressed from the intaglio printing cylinder onto the substrate; wherein said first viscosity is greater than said second viscosity by at least 45 Pas; and said third viscosity is greater than said second viscosity by at least 45 Pas.

2. The intaglio printing ink according to claim 1, wherein said first viscosity is greater than said second viscosity by at least 60 Pas, and/or said third viscosity is greater than said second viscosity by at least 60 Pas.

3. The intaglio printing ink according to claim 2, wherein said first viscosity is greater than said second viscosity by at least 75 Pas, and/or said third viscosity is greater than said second viscosity by at least 75 Pas.

4. The intaglio printing ink according to claim 3, wherein said first viscosity is greater than said second viscosity by at least 85 Pas, and/or said third viscosity is greater than said second viscosity by at least 85 Pas.

5. The intaglio printing ink according to claim 1 , wherein the first viscosity is at a temperature ranging from about 23 °C to about 28°C.

6. The intaglio printing ink according to claim 5, wherein the first viscosity is at a temperature about 26°C.

7. The intaglio printing ink according to claim 1 , wherein the second viscosity is at a temperature ranging from about 75°C to about 85°C.

8. The intaglio printing ink according to claim 7, wherein the second viscosity is at a temperature about 80°C.

9. The intaglio printing ink according to claim 1 , wherein a plot of the viscosity of the ink as a function of time, and at a constant rate of temperature change, produces a viscosity-temperature profile from the first viscosity through the second viscosity to the third viscosity as depicted in Figure 4.

10. An intaglio printing ink according to claim 1 , which exhibits the following rheological properties at a constant shear of 100/s: a) a first viscosity at a temperature of 26°C; b) a second viscosity at a temperature of 80°C; and c) a third viscosity at a temperature of 26°C; wherein said first viscosity is greater than said second viscosity by at least 70 Pas; and said third viscosity is greater than said second viscosity by at least 70 Pas.

11. An intaglio printing ink, said intaglio printing ink comprising: a) a pigment; b) a vehicle; and c) optionally a modifier; said intaglio printing ink having a solids content between about 92% to about 100%.

12. The intaglio printing ink according to claim 11, which has a solids content between about 96%) to about 100%.

13. An intaglio printing method, said printing method comprising the following steps: a) supplying an intaglio printing ink according to claim 1 to an engraved printing cylinder; b) wiping excess intaglio printing ink from said printing cylinder; and c) transferring the printing ink from the printing cylinder onto a substrate to be printed.

14. An intaglio printing method, said printing method comprising the following steps: a) supplying an intaglio printing inlc according to claim 11 to an engraved printing cylinder; b) wiping excess intaglio printing ink from said printing cylinder; and c) transferring the printing ink from the printing cylinder onto a substrate to be printed.