CA2870463A1

CA2870463A1 - Method for manufacturing a value document

Info

Publication number: CA2870463A1
Application number: CA2870463A
Authority: CA
Inventors: Alexander Bornschlegl; Christoph Mengel; Andreas BAADER; Gunter Olschewski
Original assignee: Giesecke and Devrient GmbH
Current assignee: Giesecke and Devrient Currency Technology GmbH
Priority date: 2012-05-29
Filing date: 2013-05-14
Publication date: 2013-12-05
Anticipated expiration: 2033-05-14
Also published as: WO2013178325A2; ZA201408152B; HK1201234A1; MX2014014369A; CN104321199A; DE102012010534A1; MX359340B; WO2013178325A3; EP2888112B1; CN104321199B; BR112014029183A2; EP2888112A2; CA2870463C

Abstract

The invention relates to a method for manufacturing a value document, comprising: a) printing a value document substrate with an oxidatively drying printing ink; b) treating the printed value document substrate with UV
radiation or with ozone; and c) drying the printed value document substrate, which was treated with UV radiation, at room temperature or increased temperature.

Description

Method for manufacturing a value document [0001] The invention relates to a method for manufacturing a value document, such as a bank note, a deed or an identity document.

[0002] Upon the manufacturing of value documents the printing operation is mostly effected in several printing steps, in which diverse consecutive printing and refining processes can be employed. One of the first steps is here normally a single-colored or multicolored background print by offset and/or letterset method.
The print equipment employed therefor may strongly vary and depends on the following parameters:
¨ the employed security inks or security pigments;
¨ the type of the employed value document substrate (e.g. substrates on the basis of cotton fibers; substrates based on mixed fibers; substrates on the basis of plastic foils);
¨ the provision of substrates to be printed, which have an inhomogeneous structure (e.g. paper substrates furnished with a foil element; partly preprinted substrates);
¨ the provision of substrates to be printed, which at various places have a different pH-value and/or a different paper moisture.

[0003] While production faults leading to a visible deterioration of the printing result can be discovered and compensated already at the printing machine (e.g.

inking), with production faults which have an effect on the drying of the substrate and/or the extensions of the substrate there exists the danger of these strongly delaying the further production process and additionally increasing the spoilage amount. The different print equipments required for the printing have, moreover, a strong influence on the behaviour of the print sheets in the further printing steps.
Print steps which supply heat lead to substrate shrinkages. In printing steps which are effected under a high mechanical pressure dimensional changes (in particular dimension enlargements) appear at the substrate. Most of all the intaglio printing which is widely used in value document printing and security printing especially stresses substrate and ink layers, so that a sufficient drying is essential.

[0004] When the dimensional changes at the substrate exceed certain tolerance limits, there often only remains the reprint with a changed print equipment.
Alternatively, the print equipment of the subsequent printing steps can be adapted, which entails high expenditure and high costs.

[0005] The deficient drying of a printed value document substrate as a result of a problematic ink recipe or as a result of a non-absorbent substrate can be partially accelerated by supplying heat. However, the heating of printed products often leads to a hardly controllable change of the extensions of the printed substrate.
This is the case in particular with cellulose, cotton and further paper substrates, in which the heat input leads to a loss of humidity. As a result, the registration often cannot be maintained in the subsequent printing steps. Also when plastic substrates or hybrid substrates (e.g. multilayer foil/paper/foil substrates, as they are known from WO 2004/028825 A2) are used, the effect occurs. A further disadvantage is that the setting-off of printing ink within a stack of value documents cannot be substantially improved in this way. The setting-off of printing ink herein refers to the occurrence of the still wet printing ink being imaged onto the next print sheet and disturbing the printing result there.

[0006] The drying of a printed value document substrate can additionally be accelerated by adding metal-containing dry substances. Oxidatively drying printing inks (i.e. printing inks which do not belong to the UV inks or UV
lacquers) normally contain a dry substance or siccative. Dry substances are in particular organic salts of certain metals such as cobalt (e.g. cobalt octoate, cobalt naphthenate), manganese, calcium (e.g. calcium octoate), zirconium or cerium.
Metal-containing dry substances take their effect only in the presence of oxygen.
On condition that storage and transport are effected largely in the absence of air, a dry substance can be worked into the ink already ex factory. The disadvantage with these dry substances is, however, that the employment of (heavy) metal compounds is problematic for reasons of work-related safety and health hazards.
A low applied concentration would thus be desirable, which leads to long drying times, however.

[0007] The drying of a printed value document substrate can moreover be accelerated by adding peroxide-containing substances, such as inorganic or organic peroxides. Upon decaying, these release radical oxygen and thus accelerate the oxidative drying of the ink layer. This also works at places at which there prevails an air or oxygen deficiency, therefore also with non-absorbent substrates and in high or large-area value document stacks. It is of disadvantage, however, that peroxide-containing substances of the ink may be added only relatively shortly before the print, because the ink cannot be stored over a longer time period because of the chemical reaction which starts with the adding of the peroxide.

[0008] The drying of a printed value-document substrate can moreover be accelerated by using UV-drying background inks or hybrid UV systems instead of oxidatively drying systems. Such inks, however, are distinctly more expensive, often possess sensitizing properties and possibly have a poor overprintability.
Moreover, as a ready-made ink it has an only limited durability. This similarly also applies to novel hybrid ink formulations which contain conventional, oxidatively drying ink components as well as UV-curing ink components.

[0009] The present invention is hence based on the object of providing a method improved in view of the drying of printed value document substrates.

[0010] The method should cause in particular one or more of the following technical effects:

¨ the adaptation of the shrinkage of the print sheet to the needs of the subsequent printing steps;
¨ the remediability of problems with the ink recipe (e.g. the content of dry substances), preferably also after the effected print;
¨ the shortening of the drying time, so as to enable in this way a shorter production time and a reduction of the storage area.

[0011] This object is achieved by the feature combinations according to the independent claims. The dependent claims represent preferred embodiments.
Summary of the invention

[0012] A first aspect of the invention relates to a method for manufacturing a value document, comprising:
a) printing a value document substrate with an oxidatively drying printing ink;
b) treating the printed value document substrate with UV radiation; and c) drying the printed value document substrate, which was treated with UV
radiation, at room temperature or at an increased temperature.

[0013] It is preferred, that in step b) the treatment of the value document substrate is effected with UV radiation and additionally with ozone. The additional treatment with ozone is preferably effected by exposing the value document substrate to ozone in indoor air with a concentration in a range of 1 to 15 ppm.

[0014] Furthermore, it is preferred, that in step b) the treatment with UV
radiation is effected by a (simultaneous) printing machine equipped with a UV
drying system, preferably a UV dose rate of 10 mJ/cm2 to 200 mJ/cm2 per side being chosen. A UV dose rate of 15 mJ/cm2 to 80 mJ/cm2 per side is in particular preferred. The measurement of the UV dose can be effected by means of a photochromatic film, e.g. by means of a measuring strip "tesag UV Strip" sized 70 mm x 19 mm of the company Dr. Honle AG.

[0015] In step c) the drying is effected preferably at room temperature.
Furthermore, it is preferred to carry out the drying of the value documents in the form of a value document stack, the value document stack having in particular 200 to 10 000 print sheets, preferably 5000 to 7000 print sheets.

[0016] A second aspect of the invention relates to a method for manufacturing a value document, comprising:
a) printing a value document substrate with an oxidatively drying printing ink;
b) treating the printed value document substrate with ozone; and c) drying the printed value document substrate, which was treated with ozone, at room temperature or at an increased temperature.
Detailed description of the invention

[0017] The first aspect of the invention is described hereinafter with reference to preferred embodiments.

[0018] The method according to the invention is applicable with all the usual value document substrates, in particular with paper substrates, polymer substrates and so-called hybrid substrates, which are understood to be foil-composite substrates which either have a core on the basis of paper and outer layers on the basis of polymers or a core of a plastic material and outer layers on paper-basis. It is preferred to employ substrates on the basis of cotton fibers.

[0019] The substrate can have certain coatings, impregnations or also prints and/or security elements or foil elements. In the case of a polymer substrate or of a composite substrate with a core made of paper and outer layers on the basis of polymers it is expedient to apply one or several coatings on the polymer material, which coatings ensure the adhesion of the print to be applied on the respective substrate. This layer applied on the polymer material is usually referred to as ink-receiving layer. In the case of a paper substrate, ink-receiving layers are normally dispensable, but the paper substrate can be wholly or partly coated, in order to equip it with certain properties, e.g. luminescent properties due to applied luminescence substances.

[0020] Oxidatively drying printing inks comprise (or consist of the following components): oxidatively drying film formers, (color) pigments, fillers, solvents and additives. Corresponding to DIN 55 945 the film former is that component of the binder, which is essential for the film being accomplished (see also:
Thomas Brock: "Lehrbuch der Lacktechnologie", 2nd edition, Curt R. Vincentz Verlag, 2000, page 190). Film formers are in particular macromolecular organic substances. Corresponding to this standard, the binder is understood to be the non-volatile portion of a coating substance without pigment and filler, but including softeners, dry substances and other non-volatile auxiliary agents. The term "non-volatile portion" is herein understood to be the non-volatile portion according to ISO 4618.

[0021] With respect to the oxidatively drying film former employable for the oxidatively drying printing ink, film former molecules are preferred which are linkable to aliphatic double bonds through the action of atmospheric oxygen via oxygen bridges. In particular oxidatively drying alkyd resins, urethane alkyds, epoxy resin esters with unsaturated fatty acids, oil-modified phenolic resins, as well as natural or synthetic triglycerides with at least partly unsaturated fatty acid residues are preferred as film formers.

[0022] The oxidatively drying printing ink can preferably have dry substances or siccatives in particular organic salts of certain metals such as cobalt (e.g. cobalt octoate, cobalt naphthenate), manganese, calcium (e.g. calcium octoate), zirconium, cerium, zinc or iron. For building the organic salts there can be employed organic acids, in particular long-chain fatty acids such as linseed oil fatty acid or tall oil fatty acid, resin acids, naphthenic acid or 2-ethylhexanoic acid. With oxidatively drying film formers the dry substances catalyze the oxygen transfer from the air by redox reactions and accelerate the film formation by polymerization.

[0023] The oxidatively drying printing ink is in particular a background printing ink.

[0024] The step of treating the printed value document substrate with UV
radiation is expediently effected by using UV drying systems, which can be based in particular on medium pressure mercury UV radiators or iron- or gallium-doped medium pressure mercury UV radiators. The radiator power per lamp lies in the range of 120 W/cm to 250 W/cm, preferably at 180 W/cm. Suitable radiator systems are for example the units BLK-5 or BLK-2 of the company 1ST METZ
GmbH.

[0025] In the case of a (simultaneous) printing machine equipped with a UV
drying system, the method is expediently effected at a print speed of 8000 to 12000 sheets/h, in particular 10000 sheets/h, and at an adjustment of the dose rate of a single radiator within a range of 4 mJ/cm2 to 100 mJ/cm2. With respect to avoiding shrinkage of the print sheet it is preferred to adjust the radiator power within a range of 4 mJ/cm2 to 60 mJ/cm2, the range of 10 mJ/cm2 to 40 mJ/cm2 being in particular preferred.

[0026] The step of drying the printed value document substrate, which was treated with UV radiation, is effected at room temperature or at an increased temperature. Room temperature is understood to be herein a temperature of 20 C.
The drying at an increased temperature can be effected in particular at a temperature in a range of 35 C to 40 C.

[0027] For avoiding the shrinkage of the value document substrate, it is preferred to carry out the step of drying the value documents in the form of a value document stack. The value document stack can have in particular 200 to 000 print sheets, preferably 5000 to 7000 print sheets. A value document stack with about 6000 print sheets is in particular preferred for the drying.
Furthermore, it is preferred that the stack core temperature does not exceed a temperature of 40 C. The drying of the value documents in the form of a value document stack is preferably effected at room temperature.

[0028] The second aspect of the invention is described hereinafter with reference to preferred embodiments.

[0029] With respect to the steps a) and c) of the method according to the second aspect of the invention, reference is made to the preferred embodiments described in connection with the first aspect of the invention.

[0030] The step b) of treating the printed value document substrate with ozone is expediently effected by exposing the value document substrate to ozone in indoor air with a concentration in a range of 1 to 15 ppm, a concentration of about ppm being particularly preferred. Furthermore, it is preferred that the generation of the ozone is carried out directly in the immediate proximity of the paper surface, for example by the UV radiation emitted by the UV radiators in the presence of (air) oxygen.

[0031] Further embodiment examples as well as advantages of the invention will be explained hereinafter in connection with the Figures.
There are shown:
Fig. 1 the results of the test series according to embodiment example D, which were obtained on the basis of a carbon black pigment without dry substance;

Fig. 2 the results of the test series according to embodiment example E, which were obtained on the basis of a carbon black pigment with dry substance;
Fig. 3 the results of the test series according to embodiment example F, which were obtained on the basis of an organic colored pigment with dry substance.

[0032] In the embodiment examples there was employed a simultaneous printing machine suitable for printing with conventionally drying printing inks with subsequently fitted UV drying system of the company 1ST Metz ("BLK-5", two radiators per side with a radiator power of 180 W/cm each).
Embodiment example A:

[0033] Cotton vellum paper was printed in a simultaneous sheet printing machine on both sides, each side with one offset and two letterset inks. The inks contained 3 % by weight dry substance on a cobalt/manganese-salt-basis. The print speed was 8000 sheets/h. The print sheets were dried at room temperature in stacks of 6000 sheets each and could be further processed by intaglio printing method after 48 hours at the earliest. After switching on two UV units (company 1ST Metz, model "BLK-5") per side with 40 % of the maximum power and subsequent drying at room temperature in stacks of 6000 sheets each, further processability by intaglio printing method could be achieved already after 20 hours.

[0034] It could be shown, that the paper substrate is not changed in a noticeable way in its dimension or spatial extension by the UV doses required for reducing the drying time to less than 20 hours, whereas a higher heat input by hot air in fact leads to a higher shrinkage of the substrate. In case that an increased shrinkage is desired, the power of the UV radiator can be increased.
Embodiment example B:

[0035] Cotton vellum paper was printed in a simultaneous sheet printing machine on both sides, each side with three letterset inks. The inks contained 3 %
by weight dry substance on a cobalt/manganese-salt-basis. The print speed was 10000 sheets/h. The print sheets were dried at room temperature in stacks of sheets each until further processing. After one hour from each the upper side of the stack, the center of the stack and the bottom side of the stack five sheets were removed from the stack, measured and the average of the measured values was determined.

[0036] With a radiation power of 90 % of the maximum power there was noted an average shrinkage of the substrate in a range of 1.5 mm to 1.9 mm. A
further processing after 20 hours by intaglio printing was possible without problems.
The dimension enlargement of the substrate caused by the intaglio printing was in the same order of magnitude, so that with the described method a substantial dimension neutrality could be achieved.
Embodiment example C:

[0037] Cotton vellum paper having foil elements applied in partial regions was printed in a simultaneous sheet printing machine on both sides, each side with one offset and two letterset inks. The inks contained 3 % by weight dry substance on a cobalt/manganese-salt-basis. The print speed was 8000 sheets/h. In particular the foil regions which were printed with the wet offset ink were not sufficiently dried upon arranging the printed sheets in stacks, so that a strong setting-off in the stack onto the respectively next sheet back was observed. After switching on two UV
units (company 1ST Metz, model "BLK-5") per side with 50 % of the maximum power the problem of setting off did no longer occur. Therefore, the UV
radiation effected a distinct curing of the ink surface already within a few minutes.

[0038] The further embodiment examples D, E and F were carried out at laboratory printing units. The elementary procedure was as follows:

[0039] At a test print device of the company IGT Metz a test print with an applied amount of printing ink of 1 g/m2 on cotton vellum paper was carried out.
After drying under the stated conditions the printed side was placed on an unprinted piece of paper of the same size and this interconnection jointly compressed. The amount of ink transferred to the previously unprinted paper was used as a measure of the drying. This method reflects the real production conditions well, because here too the printed sheets have to withstand a similar stress in the next processing step.
Provision of the reference samples:

[0040] The printed strips were dried open in the indoor air at a temperature of 20 C for four hours.
Carrying out the drying by means of UV radiation:

[0041] The printed strips were irradiated with the stated UV dose rate directly after the printing in a continuous UV belt dryer. As UV radiators there are used normal medium pressure mercury UV radiators (company 1ST, type CK
spectrum) as well as iron-doped medium pressure mercury UV radiators (company 1ST, type CK-II spectrum). The printed strips moreover were fixed on a metal carrier for a fast heat dissipation. The temperature of the printed strips achieved room temperature again already after 5 to 10 seconds after the passage through the dryer. The strips were then dried for four hours next to the reference strips.
Carrying out the drying by means of heat:

[0042] The printed strips were dried directly after the printing in a drying cabinet free of circulating air at 35 C for one, two or three hours. After the respective time the strips were removed from the drying cabinet and dried further at room temperature next to the reference strips for the remaining time until the total drying time of four hours.

Carrying out the drying by means of ozone:

[0043] The printed strips were gassed at room pressure under the stated conditions in a chamber with a mixture of atmospheric air and ozone directly after the printing. After expiry of the stated time the strips were removed from the chamber and dried further at room temperature next to the reference strips for the remaining time until the total drying time of four hours. The connected ozone generator was operated with dried indoor air and worked with a corona discharge.
Embodiment example D (test series):

[0044] A black letterset ink on the basis of a carbon black pigment without dry substance was applied onto cotton vellum substrate with an applied amount of 1 g/m2 and dried in various ways:
Reference: four-hour drying at room temperature.
UV 1: irradiation with a UV dose rate of 70 mJ/cm2, with subsequent four-hour drying at room temperature.
UV 2: irradiation with twice the UV dose rate of UV 1, with subsequent four-hour drying at room temperature.
UV 3: irradiation with three times the UV dose rate of UV 1, with subsequent four-hour drying at room temperature.
Heat 1: one-hour drying at 35 C with subsequent three-hour further drying at room temperature.
Heat 2: two-hour drying at 35 C with subsequent two-hour further drying at room temperature.
Heat 3: two-hour drying at 35 C with subsequent one-hour further drying at room temperature.

[0045] Figure 1 shows the ink amount transferred to the unprinted substrate by the compressing. The greater this amount the worse was the drying of the ink at the time of the offset.

[0046] Usually, at room temperature an ink without dry substance must dry at least a week or longer until the print sheets can be further processed.
Therefore, no industrial production is possible. Also the drying in the heat cabinet requires a relatively long drying period and moreover changes the extension of the paper substrate. Also in embodiment example D there is thus shown that a three-hour heat input cannot achieve a significant effect compared to the reference. The UV
radiation, however, achieves already a measurable effect.
Embodiment example E (test series):

[0047] A black letterset ink on the basis of a carbon black pigment with 3 %
by weight of a dry substance on a cobalt-salt-basis was applied onto a cotton vellum substrate with an applied amount of 1 g/m2 and dried in various ways:
Reference: four-hour drying at room temperature.
UV 1: irradiation with a UV dose rate of 70 mJ/cm2 with subsequent four-hour drying at room temperature.
UV 2: irradiation with twice the UV dose rate of UV 1 with subsequent four-hour drying at room temperature.
UV 3: irradiation with three times the UV dose rate of UV 1 with subsequent four-hour drying at room temperature.
Heat 1: one-hour drying at 35 C with subsequent three-hour further drying at room temperature.
Heat 2: two-hour drying at 35 C with subsequent two-hour further drying at room temperature.

Heat 3: two-hour drying at 35 C with subsequent one-hour further drying at room temperature.

[0048] Figure 2 shows the ink amount transferred to the unprinted substrate by the compressing. The greater this amount the worse was the drying of the ink.

[0049] It is thus clearly shown, that the UV radiation can achieve effects, compared to the reference, in an order of magnitude as these can otherwise be caused only by heat.
Embodiment example F (test series):

[0050] A red letterset ink on the basis of an organic colored pigment was applied onto a cotton vellum substrate with an applied amount of 1 g/m2 and dried in various ways. The ink contained 3 % by weight of dry substance:
Reference: four-hour drying at room temperature.
UV 1: irradiation with a UV dose rate of 70 mJ/cm2 with subsequent four-hour drying at room temperature.
UV 2: irradiation with twice the UV dose rate of UV 1 with subsequent four-hour drying at room temperature.
UV 3: irradiation with three times the UV dose rate of UV 1 with subsequent four-hour drying at room temperature.
Heat 1: one-hour drying at 40 C with subsequent three-hour further drying at room temperature.
Heat 2: two-hour drying at 40 C with subsequent two-hour further drying at room temperature.
Heat 3: two-hour drying at 40 C with subsequent one-hour further drying at room temperature.

Ozone 1: . one-minute exposure to ozone in indoor air with a concentration of about 10 ppm with subsequent four-hour further drying at room temperature.

[0051] Figure 3 shows the ink amount transferred to the unprinted substrate by the compressing. The greater this amount the worse was the drying of the ink.

[0052] It is thus clearly shown, that the UV radiation can achieve effects, compared to the reference, in an order of magnitude as these can otherwise be caused only by heat. Ozone, too, shows an advantageous effect.

[0053] In combination tests it could be shown, that ozone still further intensifies the effect of the UV radiation.

[0054] The effect of a UV treatment of a duration of under one second with subsequent four-hour further drying at room temperature has shown, e.g. with a tested ink containing a normal siccative, a similarly high effect as the four-hour drying at a temperature of 35 C. Particularly interesting is the additional observation that the UV irradiation in the case of inks without siccative likewise shows an effect, whereas the exposure to heat within the observed time period has not effected any appreciable drying.

Claims

1. A method for manufacturing a value document, comprising:
a) printing a value document substrate with an oxidatively drying printing ink;
b) treating the printed value document substrate with UV radiation; and c) drying the printed value document substrate, which was treated with UV radiation, at room temperature or at an increased temperature.

2. A method for manufacturing a value document, comprising:
a) printing a value document substrate with an oxidatively drying printing ink;
b) treating the printed value document substrate with ozone; and c) drying the printed value document substrate, which was treated with ozone, at room temperature or at an increased temperature.

3. The method according to claim 1, wherein in step b) the treating of the value document substrate is effected with UV radiation and additionally with ozone.

4. The method according to any of claims 1 or 3, wherein in step b) the treating with UV radiation is effected by a (simultaneous) printing machine equipped with a UV drying system, in which at a print speed of 10000 sheets/h a UV
dose rate of 10 mJ/cm2 to 40 mJ/cm2 per radiator is chosen.

5. The method according to any of claims 1 to 4, wherein in step c) the drying at room temperature is effected in particular in a stack.

6. The method according to claim 5, wherein the drying of the value documents is carried out in the form of a value document stack and the value document stack has in particular 1000 to 10 000 print sheets, preferably 5000 to 7000 print sheets.

7. The method according to claim 2, wherein the step b) of treating the printed value document substrate with ozone is effected by exposing the value document substrate to ozone in indoor air with a concentration in a range of 1 to 15 ppm.