Inking apparatus of a printing press, printing press comprising the same and method of producing a vibrator roller

Abstract

There is described an inking apparatus of a printing press, in particular an offset or letterpress printing press, comprising at least one ink duct (11, 12) with an ink supply roller (13, 14), an ink roller train (30) comprising at least one inking roller (31) which receives ink from the at least one ink duct (11, 12), and at least one vibrator roller (15, 16) interposed between the ink supply roller (13, 4) and the inking roller (31), which vibrator roller (15, 16) is swung back and forth between the ink supply roller (13, 14) and the inking roller (31) and intermittently transfers ink from the ink supply roller (13, 14) to the inking roller (31). A circumference of the vibrator roller (15, 16) exhibits an ink-transfer 10 structure (15a, 16a) which reflects a desired inking profile of a printing plate to be inked by the inking apparatus and is designed to modulate a quantity of ink transferred by the vibrator roller (15, 16). The ink-transfer structure (15a, 16a) on the circumference of the vibrator roller (15, 16) is subdivided, in a circumferential direction (y) of the vibrator roller (15, 16), into an integer number 1 (r) of individual ink-transfer portions (15b, 16b) that are repeated with a determined circumferential period (?y) in the circumferential direction (y), each individual ink-transfer portion (15b, 16b) reflecting the desired inking profile of the printing plate to be inked by the inking apparatus. A contact length (CL) over which the vibrator roller (15, 16) runs in contact with the ink supply roller (13, 204) is equivalent to the determined circumferential period (?y) of the individual ink-transfer portions (15b, 16b) or to an integer multiple of the determined circumferential period (?y) of the individual ink-transfer portions (15b, 16b).

Claims

1. An inking apparatus of a printing press, in particular an offset or letterpress printing press, comprising: at least one ink duct with an ink supply roller; an ink roller train comprising at least one inking roller which receives ink from the at least one ink duct; and at least one vibrator roller interposed between the ink supply roller and the inking roller, which vibrator roller is swung back and forth between the ink supply roller and the inking roller and intermittently transfers ink from the ink supply roller to the inking roller, wherein a circumference of the vibrator roller exhibits an ink-transfer structure which reflects a desired inking profile of a printing plate to be inked by the inking apparatus and is designed to modulate a quantity of ink transferred by the vibrator roller, wherein the ink-transfer structure on the circumference of the vibrator roller is subdivided, in a circumferential direction of the vibrator roller, into an integer number of individual ink-transfer portions that are repeated with a determined circumferential period in the circumferential direction, each individual ink-transfer portion reflecting the desired inking profile of the printing plate to be inked by the inking apparatus, and wherein a contact length over which the vibrator roller runs in contact with the ink supply roller is equivalent to the determined circumferential period of the individual ink-transfer portions or to an integer multiple of the determined circumferential period of the individual ink-transfer portions.

2. The inking apparatus as defined in claim 1, wherein the integer number of individual ink-transfer portions that are repeated in the circumferential direction is lower or equal to 10.

3. The inking apparatus as defined in claim 2, wherein the integer number of individual ink-transfer portions that are repeated in the circumferential direction is within a range of 4 to 6.

4. The inking apparatus as defined in claim 1, wherein the ink-transfer structure on the circumference of the vibrator roller is a structured outer layer that is directly formed onto a circumference of a cylindrical core of the vibrator roller or a structured surface of an exchangeable plate or sleeve medium carried by a cylindrical body of the vibrator roller.

5. The inking apparatus as defined in claim 1, wherein the ink-transfer structure on the circumference of the vibrator roller is a relief structure exhibiting raised ink-transfer areas.

6. The inking apparatus as defined in claim 5, wherein at least the ink-transfer structure is a 3D-printed structure.

7. The inking apparatus as defined in claim 1, wherein the ink-transfer structure on the circumference of the vibrator roller is structured in such a way that the ink-transfer structure guarantees a continuous and uninterrupted circumferential support upon contacting the ink supply roller or the inking roller.

8. The inking apparatus as defined in claim 1, wherein the ink-transfer structure is subdivided, in an axial direction of the vibrator roller, into an integer number of individual ink-transfer sections that are repeated with a determined axial period the axial direction.

9. The inking apparatus as defined in claim 1, wherein the at least one ink duct is an ink fountain device comprising an ink fountain blade cooperating with the ink supply roller, which ink fountain blade is positioned with respect to a circumference of the ink supply roller to leave a selected spacing between the ink fountain blade and the circumference of the ink supply roller.

10. The inking apparatus as defined in claim 9, wherein the selected spacing between the ink fountain blade and the circumference of the ink supply roller is adjustable uniformly over an entire axial length of the ink supply roller.

11. The inking apparatus as defined in claim 1, comprising: a first ink duct with a first ink supply roller; a first vibrator roller interposed between the first ink supply roller and a first inking roller of the ink roller train, which first vibrator roller is swung back and forth between the first ink supply roller and the first inking roller and intermittently transfers ink from the first ink supply roller to the first inking roller; a second ink duct with a second ink supply roller; and a second vibrator roller interposed between the second ink supply roller and the first inking roller, which second vibrator roller is swung back and forth between the second ink supply roller and the first inking roller and intermittently transfers ink from the second ink supply roller to the first inking roller, wherein a circumference of the first vibrator roller exhibits a first ink-transfer structure which reflects a first part of the desired inking profile and is designed to modulate a quantity of ink transferred by the first vibrator roller, and wherein a circumference of the second vibrator roller exhibits a second ink-transfer structure which reflects a second part of the desired inking profile and is designed to modulate a quantity of ink transferred by the second vibrator roller.

12. The inking apparatus as defined in claim 1, comprising: a first ink duct with a first ink supply roller; a first vibrator roller interposed between the first ink supply roller and a first inking roller of the ink roller train, which first vibrator roller is swung back and forth between the first ink supply roller and the first inking roller and intermittently transfers ink from the first ink supply roller to the first inking roller; a second ink duct with a second ink supply roller; and a second vibrator roller interposed between the second ink supply roller and a second inking roller of the ink roller train, which second vibrator roller is swung back and forth between the second ink supply roller and the second inking roller and intermittently transfers ink from the second ink supply roller to the second inking roller; wherein a circumference of the first vibrator roller exhibits a first ink-transfer structure which reflects a first part of the desired inking profile and is designed to modulate a quantity of ink transferred by the first vibrator roller, and wherein a circumference of the second vibrator roller exhibits a second ink-transfer structure which reflects a second part of the desired inking profile and is designed to modulate a quantity of ink transferred by the second vibrator roller.

13. The inking apparatus as defined in claim 1, wherein the ink roller train includes at least one distribution roller oscillating in an axial direction.

14. The inking apparatus as defined in claim 1, wherein the ink-transfer structure on the circumference of the at least one vibrator roller is derived from prepress data of the relevant printing plate to be inked.

15. The inking apparatus as defined in claim 14, wherein the prepress data complies with the CIP3 Print Production Format.

16. A printing press comprising an inking apparatus as defined in claim 1.

17. The printing press as defined in claim 16, wherein the printing press is an offset printing press.

18. The printing press as defined in claim 17, wherein the printing press is an offset printing press for simultaneous recto-verso printing of security documents.

19. A method of producing a vibrator roller suitable for use as the at least one vibrator roller of the inking apparatus defined in claim 1, comprising the steps of: (a) providing a desired inking profile of the printing plate to be inked; and (b) forming, on a circumference of the vibrator roller, an ink-transfer structure which reflects the desired inking profile and is designed to modulate a quantity of ink transferred by the vibrator roller, wherein the ink-transfer structure on the circumference of the vibrator roller is subdivided, in a circumferential direction of the vibrator roller, into an integer number of individual ink-transfer portions that are repeated with a determined circumferential period in the circumferential direction, each individual ink-transfer portion reflecting the desired inking profile of the printing plate to be inked.

20. The method as defined in claim 19, wherein step (b) includes structuring an outer layer that is directly formed onto a circumference of a cylindrical core of the vibrator roller or structuring a surface of an exchangeable plate or sleeve medium to be carried by a cylindrical body of the vibrator roller.

21. The method as defined in claim 19, wherein the ink-transfer structure is formed as a relief structure exhibiting raised ink-transfer areas.

22. The method as defined in claim 21, wherein at least the ink-transfer structure is produced by 3D-printing.

23. The method as defined in claim 19, wherein step (a) includes deriving the desired inking profile from prepress data of the relevant printing plate to be inked.

24. The method as defined in claim 23, wherein the prepress data complies with the CIP3 Print Production Format.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages of the present invention will appear more clearly from reading the following detailed description of embodiments of the invention which are presented solely by way of non-restrictive examples and illustrated by the attached drawings in which:

(2) FIG. 1 is a schematic side view of a printing press designed for simultaneous recto-verso printing of sheets as typically used for the production of security documents, such as banknotes;

(3) FIG. 2 is a schematic partial side view of the printing group of the printing press of FIG. 1;

(4) FIG. 3 is a schematic side view of one of the inking apparatuses of the printing press of FIGS. 1 and 2, namely the uppermost (fourth) inking apparatus on the recto (front) side;

(5) FIG. 4 is a more detailed side view of the upstream end of the inking apparatus of FIG. 3;

(6) FIG. 5 is a schematic view of an illustrative printed sheet as used in the context of the production of security documents, such as banknotes;

(7) FIG. 6 is a partial view of individual illustrative imprints and of a corresponding ink zone subdivision;

(8) FIG. 7 is a view of a particular composite offset background of an illustrative banknote design as printable on a printing press of the type shown in FIGS. 1 and 2;

(9) FIG. 8 is an illustrative view of a portion of a printing plate used to print part of the composite offset background of FIG. 7;

(10) FIG. 9 is a schematic view illustrating a desired inking profile corresponding to the portion of the printing plate of FIG. 8 to be inked to produce the relevant part of the composite offset background of FIG. 7;

(11) FIG. 10 is an illustrative view of the desired inking profile of FIG. 9 which is repeated along the entire width of the printing plate to be inked;

(12) FIG. 11 is an illustrative view of a corresponding ink transfer structure to be provided on a circumference of one vibrator roller of the inking apparatus of the printing press in accordance with a first embodiment of the present invention, which ink transfer structure is representative of the inking profile of FIG. 10;

(13) FIG. 12 is a greyscale photographic illustration of a vibrator roller provided with an example of the ink transfer structure of the present invention;

(14) FIG. 13 is an illustrative view of the desired inking profile of FIG. 9 which is repeated along the entire width of the printing plate to be inked, which inking profile is subdivided in this example into first and second parts;

(15) FIG. 14 is an illustrative view of a corresponding, first, ink transfer structure to be provided on a circumference of a first one of the vibrator rollers of the inking apparatus of the printing press in accordance with a second embodiment of the present invention, which first ink transfer structure is representative of the first part of the inking profile of FIG. 13;

(16) FIG. 15 is an illustrative view of a corresponding, second, ink transfer structure to be provided on a circumference of a second one of the vibrator rollers of the inking apparatus of the printing press in accordance with the second embodiment of the present invention, which second ink transfer structure is representative of the second part of the inking profile of FIG. 13;

(17) FIG. 16 is a detailed side view of the upstream end of another inking apparatus that could be used in the context of the present invention in lieu of the inking apparatus shown in FIGS. 1 to 4; and

(18) FIGS. 17a and 17b are schematic cross-sectional views of distinct vibrator roller configurations that could be used in the context of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(19) The present invention will be described in the particular context of a sheet-fed offset printing press for simultaneous recto-verso printing of sheets as typically used for the production of security documents, such as banknotes, which printing press comprises individual vibrator-type inking apparatuses as already discussed in the preamble hereof with reference to FIGS. 1 to 4 (and 16). The invention is however applicable to any printing press that likewise relies upon the use of vibrator-type inking apparatuses, i.e. any printing press having at least one inking apparatus that comprises (i) at least one duct with an ink supply roller, (ii) an ink roller train comprising at least one inking roller which receives ink from the at least one duct, and (iii) at least one vibrator roller interposed between the ink supply roller and the inking roller, which vibrator roller is swung back and forth between the ink supply roller and the inking roller and intermittently transfers ink from the ink supply roller to the inking roller.

(20) As this will be appreciated from the following description of various embodiments of the invention, a key element of the invention resides in the provision, on the circumference of the vibrator roller, of an ink-transfer structure which reflects a desired inking profile of a printing plate to be inked by the inking apparatus, which ink transfer structure is designed to modulate a quantity of ink transferred by the vibrator roller.

(21) FIG. 7 schematically illustrates an illustrative example of a composite offset background forming an imprint P of a particular banknote design (recto/front side only) that is typically printable on a printing press of the type illustrated in FIGS. 1 and 2. It is to be understood that the particular banknote design includes another composite offset background that is printed on the verso/back side of the sheets (which occurs simultaneously to the printing of the recto side of the sheets in the example of FIGS. 1 and 2). Such a composite offset background typically consists of a multiplicity of individual offset prints that are printed in register with one another in different ink colours. With a printing press of the type illustrated in FIGS. 1 and 2, at least four distinct printing plates are used to print the recto (front) side of the sheets, which means that the particular composite offset background is formed in such case of four individual patterns that are printed in register with one another. As this has already been mentioned in the preamble hereof, an additional printing group could optionally be provided on top of the offset printing press of FIGS. 1 and 2, upstream of the main printing group, thereby increasing the number of printing plates (and accordingly the number of individual patterns) that are used to print the recto (front) side of the sheets (see in particular U.S. Pat. No. 6,101,939 and International (PCT) Publication No. WO 2007/042919 A2 which are also incorporated herein by reference in their entirety). In any event, the number of individual printing plates used to print a particular design is not as such important in the context of the present invention.

(22) It will further be understood that the composite offset background that is actually printed on the sheets consists of a repetition of the composite offset background illustrated in FIG. 7 in accordance with the particular matrix arrangement of m?n imprints P (as for instance shown in FIG. 5, where m=5 and n=8 by way of a non-limiting illustrative example).

(23) FIG. 8 illustrates one corresponding portion PP* of a printing plate PP used to produce part of the composite offset background of FIG. 7. This can be any suitable printing plate PP (whether for wet-offset or dry-offset printing) that is mounted on any one of the plate cylinder 115 (or 125 as the case may be) illustrated in FIGS. 1 to 3.

(24) In the particular example, such printing plate PP could be inked using a single one of the ducts 11, 12 or both ducts 11, 12, in which case two (or more) different inks are used to ink corresponding portions of the printing plate PP. For the purpose of the discussion of a first embodiment of the invention, it will be assumed that a single duct (e.g. duct 11 of FIG. 3) is used to ink the printing plate PP with a single ink. It will however be appreciated that the invention is applicable irrespective of the number of inks used to ink the relevant printing plate PP.

(25) FIG. 9 illustrates a desired inking profile IP* corresponding to the particular portion PP* of the printing plate PP to be inked shown in FIG. 8. FIG. 9 only illustrates the inking profile for one given imprint position along the axial direction x, but it will be appreciated that the desired inking profile of the entire printing plate PP is basically a repetition of the inking profile IP* of FIG. 9 an integer number m of times (m being equal to the number of columns of imprints P to be printed as shown in FIG. 5). This is schematically illustrated by FIG. 10 where the desired inking profile IP of the entire printing plate PP consists of a repetition of the inking profile IP* shown in FIG. 9 five times along the axial direction x in the particular example. It will be appreciated that the repetition period (or axial period) ?x of the inking profile IP corresponds to dimension L1 of the relevant imprint P.

(26) It shall be appreciated that the desired inking profile is a function of each particular design and that the desired inking profile IP*, IP shown in the Figures is accordingly to be regarded as a purely illustrative example. Advantageously, such an inking profile can be derived from typical prepress data of the relevant printing plate, such as for example prepress data complying with the CIP3 Print Production Format that is widely used in the art. In the context of the present invention, it suffices to understand that the desired inking profile IP is basically a representation of the relevant amount of ink that is required to ink any given printing plate PP, which quantity is dependent upon the particular design to ink on the printing plate PP. As schematically shown in FIG. 9, the desired inking profile IP typically exhibits peaks indicative of where a high amount of ink is required to ink the printing plate PP and depressions indicative of where a comparatively lower amount of ink is required to ink the printing plate PP.

(27) In accordance with the present invention, the printing plate PP is inked by means of an inking apparatus having basically the same configuration as known in the art, namely a vibrator-type inking apparatus as for instance shown in FIGS. 3 and 4. In contrast to the know solutions, the printing plate PP is however inked in such a way as to substantially match the desired inking profile IP of that particular printing plate PP.

(28) As already mentioned in the preamble hereof, the known inking apparatuses typically rely upon a so-called ink zone system with individual ink zones and adjustable ink keys having a certain specified width in the axial direction (e.g. 30 mmsee again FIG. 6), which means that a precise inking profile cannot be achieved. Furthermore, in the particular case of the production of security documents which are printed in the form of a matrix arrangement of imprints as shown in FIG. 5, each relevant column of imprints typically requires different ink key settings, which leads the operator to make compromises in the inking of the printing plate.

(29) In accordance with the present invention, each printing plate PP can be precisely inked in accordance with the desired inking profile IP of that relevant printing plate PP. This is achieved by using an inking apparatus of the aforementioned type where the circumference of the vibrator roller exhibits an ink-transfer structure which reflects the desired inking profile IP of the relevant printing plate PP to be inked by the inking apparatus, which ink-transfer structure is designed to modulate the quantity of ink transferred by the vibrator roller. In other words, according to the invention, the ink-transfer structure on the circumference vibrator roller is exploited to precisely define and modulate the quantity and distribution of ink to be supplied to the printing plate in dependence of the desired inking profile of that printing plate.

(30) FIG. 11 illustrates an example of an ink transfer structure that could be provided on the circumference of one of the vibrator rollers 15, 16 of the inking apparatus of FIGS. 3 and 4 in accordance with a first embodiment of the invention. The relevant ink transfer structure is generally designated by reference numeral 15a or 16a depending on whether the relevant structure is provided on the circumference of vibrator roller 15 or vibrator roller 16 and reflects the desired inking profile IP shown in FIG. 10. For the sake of the discussion, it will be assumed that only one ink duct is used for inking the relevant printing plate PP (i.e. either ink duct 11 or ink duct 12).

(31) The ink transfer structure 15a (16a) provided on the circumference of the vibrator roller 15 (16) is preferably a relief structure exhibiting raised ink-transfer areas (shown as grey areas in FIG. 11), which relief structure comes into contact with the typically smooth surface of the associated ink supply roller 13 (14). The ink transfer structure 15a (16a) could be any other suitable structure that can perform a selective transfer of ink upon contacting the circumference of the associated ink supply roller 13 (14), such as a structure having ink-accepting and ink-repelling zones. A photographic illustration of a vibrator roller 15 (16) provided with a relief structure acting as the ink transfer structure 15a (16a) is shown in FIG. 12.

(32) As schematically shown in FIG. 11, the ink-transfer structure 15a (16a) on the circumference of the vibrator roller 15 (16) is subdivided, in a circumferential direction y of the vibrator roller 15 (16), into an integer number r of individual ink-transfer portions 15b (16b) that are repeated with a determined circumferential period ?y in the circumferential direction y, each individual ink-transfer portion 15b (16b) reflecting the desired inking profile IP of the printing plate PP to be inked by the inking apparatus. In the illustrated example, six (r=6) individual ink-transfer portions 15b (16b) are repeated in the circumferential direction y, the determined circumferential period ?y being equivalent to the circumferential length of the vibrator roller 15 (16), i.e. ? times the relevant diameter of the vibrator roller 15 (16), divided by integer number r. Assuming for instance a vibrator roller 15 (16) having a nominal outer diameter of 60 mm, the circumferential period ?y is equivalent in the illustrated example to approximately 31.416 mm.

(33) In an extreme case, integer number r could be equal to 1, meaning that the relevant ink-transfer structure 15a (16a) on the circumference of the vibrator roller 15 (16) would include only one ink-transfer portion 15b (16b). In practice however, the number r of individual ink-transfer portions 15b (16b) is preferably greater than one. Integer number r may advantageously be lower or equal to 10, even more preferably in the range of 4 to 6.

(34) In accordance with the present invention, a contact length over which the vibrator roller 15 (16) runs in contact with the ink supply roller 13 (14) is equivalent to the determined circumferential period ?y of the individual ink-transfer portions 15b (16b) or to an integer multiple of the determined circumferential period ?y of the individual ink-transfer portions 15b (16b). This contact length is schematically illustrated in FIG. 11 as a horizontal band having dimension CL in the circumferential direction y. In the illustrated example, the contact length CL is selected to be equivalent to the determined circumferential period ?y.

(35) The desired contact length CL can be selected by operating the relevant ink supply roller 13 (14) so as to rotate intermittently with a specified rate (or sweep) corresponding to the desired contact length CL, the vibrator roller 15 (16) being driven into rotation by friction under the action of the relevant ink supply roller 13 (14) when both rollers are in contact with each other.

(36) Thanks to the above solution, and irrespective of the particular position on the circumference of the vibrator roller 15 (16) where the vibrator roller 15 (16) comes into contact with the associated ink supply roller 13 (14), the vibrator roller 15 (16) will carry and transfer a partial ink stripe that is modulated in dependence of the relevant ink transfer structure 15a (16a). More precisely, in the illustrated example where the contact length CL is equal to the circumferential period ?y, the vibrator roller 15 (16) will in each case take up a certain quantity of ink that precisely matches the relevant profile defined by each individual ink-transfer portion 15b (16b). Should the contact length CL be increased to e.g. twice the circumferential period ?y, then twice the amount of ink will be taken up by the vibrator roller 15 (16).

(37) The exact number r of individual ink-transfer portions 15b (16b) is selected on the basis of the particular inking requirements, it being to be understood that an increase in the number r of individual ink-transfer portions 15b (16b) means a shorter ink stripe and contact length CL (in the circumferential direction y), and therefore a decrease in the amount of ink taken up and transferred by the vibrator roller 15 (16).

(38) As shown in FIG. 11, the ink-transfer structure 15a (16a) is advantageously subdivided, in the axial direction x of the vibrator roller 15 (16), into an integer number m of individual ink-transfer sections 15c (16c) that are repeated with the determined axial period ?x in the axial direction x, i.e. five (m=5) times in the illustrated example, the ink-transfer structure 15a (16a) thus reflecting the particular distribution of columns of imprints P as for instance illustrated in FIG. 5. This is particularly advantageous in the context of the production of security documents as discussed above. Indeed, this axial subdivision of the ink-transfer structure 15a (16a) into individual ink-transfer sections 15c (16c) that match the particular distribution of columns of imprints P ensures that the vibrator roller 15 (16) takes up and transfers a precise amount of ink that is the same for each column of imprints P. If a single imprint P or single column of imprints P is printed (i.e. m=1), the ink-transfer structure 15a (16a) will evidently consist of a single ink-transfer section 15c (16c).

(39) In the preferred example where the ink-transfer structure 15a (16a) is designed as a relief structure exhibiting raised ink-transfer areas, it is particularly advantageous to structure the ink-transfer structure 15a (16a) in such a way that it guarantees a continuous and uninterrupted circumferential support upon contacting the ink supply roller 14 (15) or the inking roller 31. This can for instance be guaranteed by ensuring that the ink-transfer structure 15a (16a) exhibits at least one continuous support portion 15d (16d) extending in the circumferential direction y over the circumference of the vibrator roller 15 (16), thereby guaranteeing that any given portion of the ink-transfer structure 15a (16a) is always brought into contact with the circumference of the associated ink supply roller 13 (14). This ensures proper frictional engagement of the vibrator roller 15 (16) with the ink supply roller 13 (14) (and the inking roller 31) irrespective of the position where the two rollers get into contact with each other. In the illustrated example, five such continuous support portions 15d (16d) are formed, which continuous support portions 15d (16d) coincide with the highest position of the relevant inking profile IP.

(40) Alternatively, the various ink-transfer sections 15c (16c) could be offset one with respect to the other in the circumferential direction y so as to ensure a continuous and uninterrupted circumferential support. Proper frictional engagement of the vibrator roller 15 (16) with the ink supply roller 13 (14) could also be guaranteed by providing a suitable continuous support portion (e.g. annular sections acting as bearer rings) at both ends of the vibrator roller 15 (16), outside of the region of the ink-transfer structure 15a (16a), in which case the ink-transfer structure 15a (16a) could exhibit a discontinuous contact surface in the circumferential direction y.

(41) FIGS. 13 to 15 are illustrative of a further embodiment of the invention in which both ink ducts 11, 12 are used to ink a given printing plate PP with a desired inking profile IP. As shown in FIG. 13, the desired inking profile IP consists in such case of two parts IPa and IPb, each representing the relevant quantity and distribution of ink to be supplied by the first and second ink ducts 11 and 12 respectively. In essence, the inking principle is similar to that already described with reference to FIGS. 10 to 12, with the main difference that each vibrator roller 15, 16 exhibits on its circumference a corresponding ink-transfer structure 15a, 16a reflecting the first part IPa, respectively second part IPb of the desired inking profile IP as for instance illustrated in FIGS. 14 and 15.

(42) The subdivision of the desired inking profile IP into the first and second parts IPa, IPb and the resulting ink-transfer structures 15a, 16a obviously depend on the particular design to be printed with the printing plate PP and the relevant axial distribution of the two (or more) inks to be supplied to the printing plate PP via the first and second ink ducts 11, 12.

(43) In this latter example, so-called iris or rainbow effects can be produced by partial mixing of the inks in the axial direction x, which partial mixing can be achieved by providing the relevant ink roller train 30 (or 30*) with suitable distribution rollers 35 oscillating in an axial direction x as schematically illustrated in FIG. 3.

(44) Thanks to the invention, adjustment of the inking is improved in a substantial manner. Indeed, thanks to the invention, an adequate modulation and distribution of the quantity of ink is ensured by the relevant ink-transfer structure 15a, 16a provided on the circumference of the vibrator roller 15, 16. The overall amount of ink supplied by the inking apparatus can be adjusted easily by playing with several simple parameters such as (i) the frequency or rate at which the vibrator roller 15 (16) is brought into contact with the associated ink supply roller 13 (14), (ii) the number r of individual ink transfer portions 15b (16b), which impacts the corresponding circumferential period ?y and contact length CL, (iii) the actual contact length CL which can be equivalent to the circumferential period ?y or be an integer multiple thereof, and/or (iv) overall adjustment of the ink film thickness on the circumference of the ink supply roller 13 (14).

(45) In an extreme case, the inking apparatus could be greatly simplified by discarding the typical ink zone system of the known solutions. Indeed, thanks to the invention, adjustment of the inking in individual ink zones may not be necessary anymore as the necessary distribution of ink is ensured by the relevant ink-transfer structure 15a, 16a provided on the circumference of the vibrator roller 15, 16. In other words, each ink duct 11, 12 could be designed as very simple ink fountain devices comprising an ink fountain blade 11a, 12a cooperating with the ink supply roller 13, 14, however with a very simple adjustment system, namely such an adjustment system where the spacing between the ink fountain blade 11a, 12a and the circumference of the ink supply roller 13, 14 is adjustable uniformly over an entire axial length of the ink supply roller 13, 14, rather than by way of individual ink keys as in the known solutions. This being said, individual ink keys could still be of interest if one desires to provide the operator with further ability to individually control the amount of ink in the axial direction x.

(46) Different solutions may be adopted to form the ink-transfer structure of the present invention onto the circumference of the vibrator roller. One solution schematically illustrated by FIG. 17a may consist in structuring an outer layer 15e (16e), made e.g. of rubber, polymer or any other suitable material, that is directly formed onto a circumference of a cylindrical (e.g. metallic) core 15f (16f) of the vibrator roller 15 (16). Structuring could for instance be carried out by mechanical or laser engraving of the outer layer 15e (16e). In such case, the outer layer 15e (16e) could be removed after use and the cylindrical core 15f (16f) recoated with a new outer layer 15e (16e) and structured again for further use.

(47) An alternate solution schematically illustrated by FIG. 17b may consist in structuring a surface of an exchangeable plate or sleeve medium 15g (16g) to be carried by a cylindrical body 15h (16h) of the vibrator roller 15 (16). The exchangeable plate or sleeve medium 15g (16g) could in particular be produced in a manner similar to conventional relief or letterpress printing mediums. In this case, the exchangeable plate or sleeve medium 15g (16g) could be stored together with the associated printing plate PP for future use.

(48) The ink-transfer structure 15a (16a) could also be formed by means of 3D-printing techniques, in which case a suitable relief structure could for instance be formed directly onto a circumference of a cylindrical core or on a surface of an exchangeable plate or sleeve medium. As a matter of fact, a complete sleeve medium integrating the ink-transfer structure 15a (16a) could be formed, as a whole, by 3D-printing.

(49) The material used to produce the ink-transfer structure of the present invention should exhibit suitable properties to ensure proper ink-transfer. In that respect, it is preferable to use such a material that in particular exhibits suitable hardness properties. In the examples discussed above, the ink supply rollers 13, 14 are typically ceramic-coated rollers and the ink-transfer structures 15a, 16a on the circumference of the vibrator rollers 15, 16 should preferably exhibit a hardness of the order of 37?-40? Shore (A). The material of the ink-transfer structures 15a, 16a may be rubber, polymer or any other material exhibiting similar properties.

(50) Producing a vibrator roller suitable for use as the (at least one) vibrator roller 15, 16 of the inking apparatus of the invention basically involves the following steps:

(51) (a) providing a desired inking profile of the printing plate to be inked; and

(52) (b) forming, on a circumference of the vibrator roller, an ink-transfer structure which reflects the desired inking profile and is designed to modulate a quantity of ink transferred by the vibrator roller in accordance with the principle described above, namely by subdividing the ink-transfer structure on the circumference of the vibrator roller (in a circumferential direction of the vibrator roller) into an integer number r of individual ink-transfer portions that are repeated with a determined circumferential period in the circumferential direction, each individual ink-transfer portion reflecting the desired inking profile of the printing plate to be inked.

(53) Various modifications and/or improvements may be made to the above-described embodiments without departing from the scope of the invention as defined by the annexed claims.

(54) In particular, a twin-duct inking apparatus may be of the type illustrated in FIGS. 1 to 4 where both vibrator rollers 15, 16 cooperate with a same inking roller 31 of the ink roller train 30 or of the type illustrated in FIG. 16 where the vibrator rollers 15, 16 cooperate with distinct inking rollers 31*, 32* of the ink roller train 30*.

(55) In addition, while the illustrations of FIGS. 11, 12, 14 and 15 show ink-transfer structures 15a, 16a that are more or less directly mirroring the desired inking profile IP of the printing plate PP to be inked, one could opt for any other suitable ink-transfer structure reflecting the desired inking profile IP. In particular, the ink transfer structure could be a screened structure with zones gradually modulating the quantity of ink in dependence of the desired inking profile. In essence, any structure that can suitably modulate the quantity of ink between 0% and 100% of the desired ink quantity is possible.

(56) While the invention has been described in the context of the production of security documents, it should be appreciated that the invention is not limited to this particular application.

LIST OF REFERENCE NUMERALS USED THEREIN

(57) 10 inking apparatus of printing press 100 (four inking apparatuses on the recto side) 10* alternate embodiment of inking apparatus (FIG. 12) 20 inking apparatus of printing press 100 (four inking apparatuses on the verso side) 20* alternate embodiment of inking apparatus (FIG. 12) 11 (first) ink duct/ink fountain device 11a ink fountain blade of ink fountain device 11 12 (second) ink duct/ink fountain device 12a ink fountain blade of ink fountain device 12 13 (first) ink supply roller (duct roller) 14 (second) ink supply roller (duct roller) 15 (first) vibrator roller cooperating with ink supply roller 13 15a ink-transfer structure on circumference of vibrator roller 15 (formed of individual ink-transfer portions 15b) 15b individual ink-transfer portions which are repeated an integer number (r) of times in the circumferential direction y of the vibrator roller 15 15c individual ink-transfer sections which are repeated an integer number (m) of times in the axial direction x of the vibrator roller 15 15d continuous support portion of ink-transfer structure 15a extending in the circumferential direction y 15e structured outer layer of vibrator roller 15 that is directly formed onto a circumference of cylindrical core 15f and that is structured to form the ink-transfer structure 15a (first variantFIG. 17a) 15f cylindrical core of vibrator roller 15 supporting the outer layer 15e (first variantFIG. 17a) 15g exchangeable plate or sleeve medium of vibrator roller 15 whose surface is structured to form the ink-transfer structure 15a (second variantFIG. 17b) 15h cylindrical body of vibrator roller 15 carrying the exchangeable plate or sleeve medium 15g (second variantFIG. 17b) 16 (second) vibrator roller cooperating with ink supply roller 14 16a ink-transfer structure on circumference of vibrator roller 16 (formed of individual ink-transfer portions 16b) 16b individual ink-transfer portions which are repeated an integer number (r) of times in the circumferential direction y of the vibrator roller 16 16c individual ink-transfer sections which are repeated an integer number (m) of times in the axial direction x of the vibrator roller 16 16d continuous support portion of ink-transfer structure 16a extending in the circumferential direction y 16e structured outer layer of vibrator roller 16 that is directly formed onto a circumference of cylindrical core 16f and that is structured to form the ink-transfer structure 16a (first variantFIG. 17a) 16f cylindrical core of vibrator roller 16 supporting the outer layer 16e (first variantFIG. 17a) 16g exchangeable plate or sleeve medium of vibrator roller 16 whose surface is structured to form the ink-transfer structure 16a (second variantFIG. 17b) 16h cylindrical body of vibrator roller 16 carrying the exchangeable plate or sleeve medium 16g (second variantFIG. 17b) ?x (axial) period at which the individual ink-transfer sections 15c, 16c are repeated in the axial direction x ?y (circumferential) period at which the individual ink-transfer portions 15b, 16b are repeated in the circumferential direction y 30 ink roller train (embodiment of FIGS. 1 to 4) 30* ink roller train (alternate embodiment of FIG. 12) 31 inking roller of ink roller train 30 cooperating with vibrator rollers 15, 16 31* (first) inking roller of ink roller train 30* cooperating with vibrator roller 15 32* (second) inking roller of ink roller train 30* cooperating with vibrator roller 16 33* intermediate ink-transfer roller interposed between first and second inking rollers 31*, 32* 35 ink distribution rollers oscillating in the axial direction x 40 (optional) dampening unit 100 simultaneous recto-verso (Simultan) offset printing press 101 printing group of printing press 100 102 sheet feeder group of printing press 100 103a sheet transfer cylinder (one-segment cylinder) 103b sheet transfer cylinder (two-segment cylinder) 103c sheet transfer cylinder (one-segment cylinder) 104 drying/curing unit 110 (first) blanket cylinder (three-segment cylinder) 115 (four) plate cylinders (one-segment cylinders) 120 (second) blanket cylinder (three-segment cylinder) 125 (four) plate cylinders (one-segment cylinders) 150 pair of side frames supporting blanket cylinders 110, 120 151 (first) mobile inking carriage supporting inking apparatuses 10 152 (second) mobile inking carriage supporting inking apparatuses 20 160 sheet transporting system (with spaced-apart gripper bars) 180 sheet delivery station S printed sheet E effective printed area on printed sheet S P security (e.g. banknote) imprint within effective printed area E (composite offset background) L length of sheet S (typ. 700 mm) W width of sheet S (typ. 820 mm) L1 length of security imprint P (in the axial direction x) L2 length of security imprint P (in the circumferential direction y) PP printing plate carried by plate cylinder 115, resp. 125 A (first) pattern on security imprint P B (second) pattern on security imprint P IP desired inking profile of printing plate PP IPa first part of desired inking profile IP as formed e.g. by means of first vibrator roller 15 IPb second part of desired inking profile IP as formed e.g. by means of second vibrator roller 16 x axial direction (transverse to the path of the printed sheets) y circumferential direction (parallel to the path of the printed sheets)