AU2008274799A1 - Printing device - Google Patents

Description

WO 2009/006749 Al PRINTING DEVICE The invention relates to a printing device with a printing forme for transferring a visually detectable information item onto a medium which is to be printed by means of a printing fluid such as, for example, a printing ink, in which printing device a printing surface of the printing forme has a first structure which is intended to transfer the printing fluid in a predefined manner to a printing substrate, and a first structure of which is provided for transferring a first visually detectable information item onto the printing substrate. Various printing processes are known from the field of reproduction technology. All these printing processes have the common goal of duplicating visually detectable information. In this case, in particular visually directly detectable information should be produced, i.e. such information which can be detected and evaluated by an observer with the naked eye, i.e. without the assistance of a device such as, for example, a microscope or an imaging sensor. Information can in particular be data in written form or graphical images. A printing forme is always used in such printing processes, by which means predefined information is transferred onto the medium to be printed, for example, paper or cardboard. The printing forme usually contains the information in identical or laterally reversed form. The information is transferred from the printing forme by means of the printing ink onto the medium to be printed and imaged. These per se previously known printing processes are known, for example, as intaglio printing, letterpress printing, flat screen printing, silk screen printing (screen printing), halftone process etc. Furthermore, the printing processes are distinguished as to whether the information is transferred directly from the printing forme onto the medium to be printed or indirectly via a subcarrier onto the medium to be printed. Examples of - 2 indirect printing processes in which the printing medium is firstly transferred from the printing forme onto the subcarrier and then from the subcarrier onto the medium to be printed are flexographic printing and photogravure. All these printing processes named in a non-definitive listing are suitable for the present invention. Diffractive structures are used in many fields of the technology, i.e. structures which produce diffraction effects under incidence of light of at least specific optical frequencies. Such structures are provided for various purposes, in particular as decorative elements or as security elements. As decorative elements they are intended to achieve pleasing or striking visual effects, for example, as packaging films or as product labels by which means the attention of customers can be directed onto the corresponding product provided with such a decorative element. As security elements which are visible with the naked eye or invisible, on the other hand, they are intended to guarantee the authenticity of products, money, money substitutes, credit cards and the like. In order to check the authenticity of objects secured with such security elements, it is determined whether the respective security elements have specific properties or contain specific visually detectable information. Grating structures having grating distances in the region of about 200 nm to 1500 nm are required, for example, to produce diffraction effects. Such diffractively active structures are usually mass-produced industrially by initially producing so-called master shims with the aid of photolithographic or laser-interferometric processes. Production shims are then produced from the master shims by means of galvanic processes and these are used to emboss the grating structures in suitable substrates such as, for example, hot stamping foils. The hot stamping foils can be -3 configured, for example, as labels so that the diffraction optically active patterns can be applied to any substrates. Apart from diffractively acting structures, other ultrafine structures which are provided as a security feature are also known, for example, microprints or guilloches. Unlike diffractively acting structures, the surface structures required to produce microprints and guilloches are at least a factor of 10 larger than the longest wavelength in the visible light spectrum. This makes it easier to produce such structures. In the prior art, the requisite high expenditure can de regarded as disadvantageous if a substrate is to be printed both with information and also provided with a security feature. In addition, the restricted variability and flexibility in the colouring cannot be satisfactory in such processes. In order to make a specific design appear in specific (primary) colours, it is necessary to stock foils having these colours. In addition, the applicability of the methods from the prior art is substantially restricted to those substrates in the surface of which a grating structure can be embossed. It is therefore the object of the invention to provide a possibility by which means a substrate can be provided with a security element or a decorative element which is based on very small surface structures, in particular on diffractively acting structures with the greatest possible flexibility in the colour selection regardless of the embossability of the substrate. The object is achieved according to the invention by a printing device of the type specified initially, the printing surface of which, in addition to a first surface structure for transferring a first visually detectable information item, has a second surface structure which is -4 arranged at least partially in the region of the printing surface in which the first structure is located, wherein the structuring of the second surface structure is smaller than or more finely structured than the structuring of the first surface structure and the second surface structure contains detectable/ascertainable information or a detectable/ascertainable information item can be produced with the second surface structure. The object is additionally achieved by a method according to patent claim 15 and by a printed substrate according to claim 12. The invention thus provides a multi-scale structuring of the printing surface which, in addition to larger structures, also includes very small structures having pre determined geometrical properties which are superposed on these. The second smaller and therefore finer surface structure can advantageously be suitable for use inter alia in connection with security elements and can be produced on a substrate by printing. The second structure should be arranged at least partially in those regions of the printing surface in which the first structure is located. According to the invention, these second structures can be arranged in the surfaces of the printing medium, i.e. in the visible side of the ready printed substrate. Since in conventional printing processes, the aim is usually to obtain the smoothest possible printing surfaces, the invention provides a measure which is diametrically opposed to the prior art. Also it is still the case that methods exist which include printing but attempt to produce a surface structure by embossing. This previously known surface structure, which differs from the surface structure according to the invention, is achieved by plastically deforming the substrate to be printed itself. In connection with the invention, the first surface structure preferably produces an optical information item at least substantially without diffraction effects, the - 5 content of which can preferably be detected with the naked eye or only by optical character recognition (OCR) or image processing. The information reproduced by the second surface structure, in particular its shape and colour (s) , can be detected and interpreted either with the naked eye or, however, by machine. The said diffractively acting second surface structure is advantageously produced on the substrate by means of a printing process, i.e. printing in which a printing medium, in particular a printing ink, is applied to a printable substrate. In this case, as in other embodiments of the invention, it is preferred if, at the same time as applying the second surface structure having the said very small structures, the visually detectable first information is also applied to the same surface section of the substrate to be prinLed, which information differs from the second information but preferably is at least partially superposed thereon. The visually detectable information of the first surface structure can, for example, be a relief, surfaces or lines which reproduce the detectable information without optical diffraction. The visually detectable information of the second surface structure, on the other hand, preferably uses the effect of optical diffraction in particular of different light diffraction orders in order to reproduce the optical information contained therein. The latter can, for example, contain different colour effects and/or a tilt-angle-dependent reproduction of characters, graphics and the like. A particularly favourable embodiment of the invention provides that the first and the second surface structure are contained in a single printing forme and are superposed or combined. In contrast to other solutions, a precisely fitting superposition of both information items from the first and the second surface structure is hereby always ensured. This applies even if the substrate should warp - 6 during the printing process. Furthermore, with this embodiment according to the invention, the entire printing can be carried out with only one printing forme which limits the expenditure in connection with the printing process despite the technically demanding, preferably diffractively acting surface structure and in particular despite the precisely fitting arrangement of both information items. In another preferred embodiment, the second structure is provided for producing an information item which is detectable with the naked eye and/or machine readable. This can be understood, for example, as embossed, very fine barcodes which are detected both with the naked eye as a diffraction effect and also contain machine-readable information. In this case, the information of the first structure should also remain detectable for the naked eye without substantial impairments. If, for example, the first information is a text printed with the first structure, this should remain readable although, for example, barcodes can be printed in its surface which can be detected both with the naked eye, for example as a colour-changing pattern, and can also be read out by machine. For the latter purpose, a reading device known per se can preferably be guided over the printed substrate, wherein the reading device reads out the information of the second surface structure printed on the substrate preferably using printing inks. In a preferred exemplary embodiment, an electrically conductive printing fluid which can be cured by ultraviolet radiation, from Conductive Ink Technology, Cambridge is used. This is used, for example, to print a line having a width of, for example, 1 mm and a length of, for example, 50 mm which is visible with the naked eye and forms a first pattern according to the invention. This pattern has a one dimensional barcode as a second pattern on its surface, whose stripes are formed by rectangular indentations of different width, wherein the width of these indentations is, for example, either 300 nm or 600 nm and wherein the indentations are, for example, 1 mm long and are perpendicular to the long axis of the protruding first pattern, and wherein the centre of two successive indentations has a constant spacing of, for example, 1200 nm. Such a barcode can be read out with a capacitive laser head as presented by the company JVC for reading out capacitive image plates, the capacitor used for this purpose having a gap of, for example, 200 nm width which detects the indentations. It is furthermore feasible for the protruding first pattern to be illuminated with a collimated laser beam which is diffracted by the previously described second pattern at different angles, depending on the distance of the protruding barcode stripes. It is also feasible for the first pattern to be produced with a magnetic printing fluid in such a manner that the protruding strips can be read out by a miniaturised read head. Regardless of the mode of action (optical, electrical, magnetic etc.) of the second structure or its physical principle of action for producing information, this can either be detected without aids or (only) with technical aids such as, for example, readers, receivers, devices for resistance measurement, etc. An example of structures whose information can only be detected using aids are machine readable codes in the manner of barcodes, e.g. the "glyphs" proposed by Xerox for coding paper documents. Insofar as such aids are required or are only helpful, the corresponding printing device, the printed substrate and the aids as a whole or parts thereof can be configured as a mutually matched information system according to the invention.

- 8 The printing device provided for producing printed substrates according to the invention with visually detectable information of the aforesaid second type can have a diffractive structure at least in a partial region of its surface. The latter is preferably arranged in a region or at the same place which is provided for receiving printing medium. This at least one region should either alone or in combination with other regions of the printing device also serve to transfer a non-diffractive optical information item to the substrate. The non-diffractive optical information can result from the printing medium, in particular from its colour(s) and geometrical form(s). The additional optical information as a result of the diffractive effect on the other hand results from the grating structure applied permanently to the printing medium, in particular imaged on said medium. Since the surface of the printing medium provided with the diffractive structure forms a visible side of the printing medium applied to the substrate, both optical information items are detectable after the printing process. Compared to conventional methods for producing diffractive structures, the invention makes it possible to produce such structures rapidly and cost-effectively. This applies particularly when the diffractive structure is integrated in a non-diffractive optical information item which should also be produced independently of the diffractive structure as can be the case, for example, in a packaging design. Due to the invention, it is for example possible to dispense with labels having diffractive security elements and nevertheless provide such security elements on packagings. In principle, any printing method can be used in connection with the present invention, in which a printing forme, for example, in the manner of a printing plate is used for printing with a printing medium, on the surface whereof a diffraction-optically active grating structure or another - 9 predetermined ultrafine structure can be applied. In the printing process the printing ink should wet all the structures of the printing surface of the printing forme and after the forming onto the substrate to be printed, should permanently retain its structuring taken over from the printing surface. Such a printing process is, for example intaglio printing as well as letterpress printing, in particular flexographic printing. In the latter, it is expedient if the printing ink cures at least partially in the printing line. The second structure, in particular a diffractively acting second structure can in particular include a security feature which is used for identification or for demonstrating the authenticity of a product, means of payment or similar. The printed-on security feature can in this case be visible with the naked eye or be configured as a hidden feature which can only be detected with the aid of technical aids such as, for example, microscopes or profilometers. Further preferred embodiments of the invention are obtained from the claims, the description and the drawings. The invention is explained in detail with reference to exemplary embodiments shown purely schematically in the figures: in the figures: Fig. 1 shows a perspective view of a printing device according to the invention; Fig. 2 shows an exemplary embodiment of a printed substrate which was produced using the printing device from Fig. 1; Fig. 3 shows a partial cross-sectional view of a printing device according to the invention in the - 10 region of a first and a second surface structure superposed therein; Fig. 4 shows another partial cross-sectional view of a printing device according to the invention in the region of a first and a second surface structure superposed therein. The printing device according to the invention shown purely schematically in Fig. 1 comprises a cylinder 1 of an intaglio printing device, the surface of which, apart from a printing pattern occupying a part of the cylinder surface, is smooth-surface and can thus be designated as a smooth surface. The surface or the cylinder is preferably elastic. The printing pattern 4 which is rectangular in its development and is visible and evaluatable with the naked eye corresponds to a first optical information item, for example, the rectangle shown in Fig. 1. The printing pattern has a plurality of extremely small receptacles which are incorporated as indentations in the region of the printing pattern 4 on the surface of the cylinder 1. Such surface structures are previously known per se and since they usually have size dimensions in the direction parallel to the directions of extension of the surface in the region of 10 pm to 150 pm, can be designated as micrometre-scale. Such receptacles of the printing form are frequently designated as saucers in screened intaglio printing. In other variants of intaglio printing, for example, so-called die stamping, these receptacles are usually executed as a graphical element, e.g. as entire, one-to-one printable letters or strokes. The surfaces of the at least approximately concavely shaped receptacles (saucers) themselves have a pre-determined structuring 3, the elements 5 of which are at least one order of magnitude, preferably about three orders of magnitude smaller than the dimensions of the receptacles 2.

- 11 This second surface structure can therefore be designated as "nanometre-scale". "Second surface structure" should furthermore be understood as higher and lower elements whose height differences can be in the region of 5 pm to 50 nm. In the exemplary embodiment, these comprise grating lines whose elevated elements (lines) can have a width of 0.05 pm - 5 pm and whose recessed elements (troughs) can have a width of 0.05 pm - 5 pm. If the spacings lie in the range of the wavelengths of visible light (about 400-700 nm), effects which can be detected with the naked eye are caused in incident ambient light. The properties of the attainable diffraction effects can be influenced by a suitable choice of further parameters of the structures known, for example, from hologram embossing such as, for example, the azimuth angle. The grating structures of an individual or preferably of a plurality of receptacles 2 can produce a detectable information item, for example, readable characters such as letters or numbers, a graphic and the like. Figures 3 and 4 show cross-sections of a part of a printing forme such as, for example, the printing cylinder 1 from Fig. 1. The depicted section of Fig. 3 shows a receptacle 2 in the printing surface of the printing forme which is part of the first surface structure. The receptacle 2 can be part of an intaglio relief incorporated in the printing surface and configured as an intaglio saucer. As depicted schematically here, the surface of the receptacle 2 is not smooth-surfaced but substantially provided with its own predetermined surface structure 3 over its entire receptacle surface. This microstructure of the second surface structure is therefore provided inside the intaglio relief. The second surface structure 3 is provided as a diffraction-optically active or active structure which in particular can have a frequency from a range of 20 lines/mm to 3000 lines/mm, preferably of 800 lines/mm to 2000 - 12 lines/mm, wherein the height differences between these structures are preferably less than or equal to 2 im, preferably less than or equal to 1 pm and particularly preferably from a range between 200 nm and 600 nm. The surface structure can be configured as a continuous or discontinuous linear grating or cross-grating structure. Such nanometre-scale structures can be produced using different production methods, for example, by holographic interferometric lithography, in particular laser interferometry, e-beam lithography and/or by photolithographic processes. Figure 4 shows another possible embodiment of the first and second surface structures in schematic view. In this exemplary embodiment, the first surface structure has both an intaglio relief (receptacle 2) and a letterpress relief 9 in its surface structure which can be incorporated in the printing surface by engraving. Both the recessed structures and also the elevated structures are provided with second surface structures 3 on their surface which in turn are diffraction-optically active as a result of their predetermined structuring. In addition to the nanometre-scale surface structure of the receptacles, regions between the receptacles having a nanometre-scale surface structure (3) can also be provided. The individual sections of the surface structured in this manner produce one or more additional detectable information items. This additional detectable optical information can either be a completely independent further information item different from the previously described information items or however can complement this information. In the exemplary embodiment, the further information is an additional independent information item, i.e. a diffractively active barcode configured as an additional security element. This or its information can be detected by machine, for example, by a reader which - 13 preferably checks automatically whether specific properties are present in the security feature. The second optical information is superposed on the first optical information, the rectangle of the exemplary embodiment. The smooth surface of the printing cylinder (i.e. the surface of the printing cylinder which lies outside the receptacles) - and therefore also the second structure of the printing surface - is in this case so constituted that an intaglio doctor blade can slide on the printing surface. The printing surface and its structure can additionally be configured so that they are suitable for printing and possibly associated embossing processes. Figure 2 also shows highly schematically a substrate 8 printed with the printing device from Fig. 1, for example, formed from a polymer film. This comprises a preferably multicoloured, first visually detectable information item which was produced by printing a number of receptacles 2, only one single receptacle being shown in Fig. 2. A nanoscale pattern 7 is formed as second optical information by printing inside the surface of the first optical information. In order to produce the printed substrate with a printed image 6 of the receptacles 2 and the second surface structure, the printing device from Fig. 1 is used with a printing method according to the invention which can proceed as follows: - the printing cylinder 1 is provided with ink in an ink duct, which is preferably wiped; - the substrate is guided between 1 and another so-called pressure cylinder, not shown, wherein the pressure cylinder presses the substrate along the printing line onto the printing cylinder; - 14 - pressure cylinder and/or printing cylinder 1 are preferably designed to be transparent in such a manner that UV light can be irradiated from inside the cylinder through its surfaces into the printing lines, thus effecting a partial curing of the ink. This facilitates release of the ink from the printing forme whilst retaining the casting of the second surface structuring in the printing ink. A formulation provided with photoinitiators and curable with ultraviolet light can be used as printing ink. The second surface structure is imaged in the printing ink of the printed substrate and is contained permanently therein as a result of the curing effect which prevents any deliquescence of this structure. In another embodiment, a nanoscale structure can preferably be introduced into the smooth surface of 2, as shown in Fig. 1. Such a structure is likewise printed onto the substrate 8 according to the above method. The surface structure of the printing device can be produced by selective removal of the printing forme provided with the first structure; however, it can also take place additively by providing the printing forme with a soft stamp with the second structure.

- 15 REFERENCE LIST 1 Printing cylinder 2 Receptacle 3 Nanometre-scale surface structure 4 Printing pattern 5 Element of 3 6 Printed image of 2 7 Printed image of 3 8 Substrate 9 Letterpress relief

Claims (19)

1. A printing device with a printing forme for transferring a visually detectable information item onto a medium which is to be printed by means of a printing fluid such as, for example, a printing ink, in which printing device a printing surface of the printing forme has a first structure which is intended to transfer the printing fluid in a predefined manner to a printing substrate, and a first structure of which is provided for transferring a first visually detectable information item onto the printing substrate, characterised by a second surface structure of the printing surface which is arranged at least partially in the region of the first structure, wherein the structuring of the second surface structure is smaller than the structuring of the first surface structure and the second surface structure contains a detectable information item or a detectable information item can be produced with the second surface structure.

2. The printing device according to claim 1, characterised in that the second surface structure has structuring elements whose size in at least one direction of extension running at least approximately parallel to the printing surface is in the region of less than or equal to 10 pm.

3. The printing device according to claim 1 or 2, characterised in that the first and the second structures are provided in the same printing forme and are superposed on one another.

4. The printing device according to at least one of the preceding claims, characterised in that the second - 2 surface structure is provided for producing an optical or opto-electronic information item.

5. The printing device according to any one of the preceding claims, characterised in that the second surface structure is provided for producing a magnetically effective structure.

6. The printing device according to any one of the preceding claims, characterised in that the second surface structure is provided for producing a visually detectable information item.

7. The printing device according to claim 6, characterised in that the surface structure is diffraction-optically active and in particular contains a lens structure in the form of a diffraction-optically active grating structure.

8. The printing device according to at least one of the preceding claims, characterised by a plurality of receptacles of the first surface structure for the temporary arrangement of the printing fluid on the printing forme, wherein at least a part of the surface of at least some of the receptacles is provided with the second surface structure, which is provided for reproducing or producing the second information items.

9. The printing device according to at least one of the preceding claims, characterised in that the printing forme, in particular the printing surface, contains an elastic material.

10. The printing device according to at least one of the preceding claims, characterised by a means for curing the printing fluid. - 3

11. The printing device according to claim 9, characterised in that the curing means are arranged in or behind the printing forme, whereby radiation, in particular UV radiation, can be introduced with the curing means through the printing forme into the printing fluid.

12. A printed substrate, to which a printing medium, in particular a printing ink, is applied to produce a detectable information item, characterised in that on the substrate, at least in sections, the printing medium reproduces a first optical information item and in the same section in which the first optical information item is present, the printing medium is provided with a surface structure which reproduces a second optical information item.

13. The printed structure according to claim 12, characterised in that the surface structure is diffraction-optically active.

14. The printed structure according to claim 12 or 13, characterised by the surface structure, the predetermined structuring surface elements of which have a size at least in a direction of extension running substantially parallel to the surface of the printing medium, which is less than or equal to 10 pm and which are provided for reproducing or producing the second optical information item.

15. A method for printing a substrate in which a printing medium such as, for example, a printing ink is applied to the substrate and by using a printing device provided with a printing forme, a visually detectable first information item is transferred to a surface section of the substrate, characterised in that a diffraction-optically active surface structure is produced with the printing device in the printing medium, at least in sections, which structure is applied to the same surface section which contains the first visually detectable information item.

16. The method according to claim 15, characterised in that predetermined surface elements are produced which at least in a direction of extension running substantially parallel to the surface of the printing medium, have a size which is less than or equal to 10 pm and which are provided for reproducing or producing the second optical information item.

17. The method according to claim 15 or 16, characterised in that at the same time as applying the first information item to the printing substrate, the second information item is also applied to the printing substrate.

18. The method according to at least one of claims 15 to 17, characterised in that the second information item is applied at least in sections in a region of the printing substrate in which the first information item is also applied.

19. The method according to at least one of claims 15 to 18, characterised in that radiation is introduced onto the printing fluid located in the printing forme for curing said printing fluid.