Method and apparatus for producing embossed structures in radiation-curing materials

Abstract

For the production of embossed microstructures in radiation-curing materials, use is made of a micro embossing form fixed to a reflective or scattering cylinder surface. Via a press nip, the micro embossing form comes into contact with the substrate guided over a cylinder or a deflection roller. The radiation-curing material is acted on in one or both pockets, before or after the press nip, with radiation which penetrates into the press nip by reflection or scattering.

Claims

1. A method of producing embossed structures in radiation-curing material, the method comprising: applying an embossing form to a surface of a cylinder or a sleeve and causing the embossing form to come into contact with the radiation-curing material in a linear press nip; and irradiating the radiation-curing material with UV radiation for curing in a pocket following the press nip downstream in a transport direction of the radiation-curing material; and wherein the surface of the cylinder or of the sleeve is reflective and/or scattering in a wavelength range of the UV radiation used for curing.

2. The method according to claim 1, wherein the embossing form is a micro-embossing form and a material of the micro-embossing form is transparent to radiation in a wavelength range of the radiation used for the curing.

3. The method according to claim 1, which comprises: providing a first radiation source in a pocket upstream of the press nip in the transport direction of the radiation-curing material, wherein the first radiation source is dimensioned with respect to the wavelength and/or the power of the radiation such that the radiation-curing material is only partially cured and remains deformable as it enters the press nip; and providing a second radiation source in the pocket following the press nip downstream in the transport direction of the radiation-curing material, wherein the a power and/or wavelength of the second radiation source is dimensioned such that the radiation-curing material is completely and thoroughly cured after having traversed the press nip.

4. The method according to claim 1, wherein the radiation-curing material is a web product and the method further comprises coating the web product with liquid media.

5. The method according to claim 1, which comprises embossing and curing security labels, printed electronics, optically readable codes or holograms.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 shows a narrow-strip web-fed press, sectioned vertical-longitudinally in a simplified schematic representation;

(2) FIG. 2 shows a simplified, highly enlarged, representation of the region around the cylinders 10 and 11 in the flexographic printing unit 8 of the press of FIG. 1;

(3) FIG. 3 is a similar view of an embodiment of the invention that is modified slightly in comparison with FIG. 2;

(4) FIG. 4 is a similar view of yet a further exemplary embodiment of the invention modified in comparison with FIG. 2;

(5) FIG. 5 shows a further enlarged representation of the region 20 from FIG. 4; and

(6) FIG. 6 is a schematic diagram of an alternative exemplary embodiment of the invention in a sheet-fed press.

DETAILED DESCRIPTION OF THE INVENTION

(7) Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown a narrow-strip web-fed press with a machine frame that is open toward the side of the viewer. A material webpaper or filmdesignated by 3 is guided over a multiplicity of deflection rollers. Numeral 2 designates the web roll from which the material web 3 is unwound, and 4 designates the roll onto which the material web 3 is wound up again after the material web 3 has been printed, varnished and finished in many ways and has been provided with micro embossings in a manner still to be described.

(8) A plurality of printing and/or finishing units 5, 6, 7 and 8, past which the material web 3 is guided, are accommodated one after another in the machine frame. As a result of the modular construction of the machine, printing units operating in accordance with quite different printing methods can be used. Thus, 5 designates an offset printing unit, 6 a gravure printing unit, 7 a screen printing unit and 8 a flexographic printing unit. A machine having this construction is offered, for example, by the company Gallus Ferd. Resch AG, Harzbchelstrae 34, 9016 St. Gallen, Switzerland under the designation RCS 330-HD.

(9) The flexographic printing unit 8 has now been converted, as described in FIG. 2, into an embossing unit for impressing microstructures such as holograms into a UV varnish layer previously applied to the material web 3. For this purpose, the cylinder 10 has been provided with a sleeve 110, on the outer side of which a metal layer 14 that reflects UV radiation has been applied. The material of the layer 14 can be, for example, aluminum or stainless steel or chromium. The reflective surface 14 in turn carries a micro embossing form 13 made of silicone rubber. The material silicone rubber is transparent in the wavelength range between 300 and 400 nm, in which UV varnishes are normally cured. The micro embossing form can be produced, for example, by being de-molded from a nickel shim, i.e. a thin nickel sheet produced by electroplating and having the embossing structures as a punch. It has a thickness of typically 2 mm and carries on its surface the microstructures de-molded from the shim. Because of its soft, flexible consistency and the low surface energy of silicone rubber, it is particularly well suited for the embossing of structures into still moist or only slightly dried ink or varnish layers.

(10) The material web 3 guided over the deflection cylinder 11 carries on its surface the freshly printed image elements 12a, illustrated greatly exaggerated, which, in the course of the web movement, run through the press nip between the cylinder 10 or the sleeve 110 and the deflection roll 11.

(11) Instead of already applying the ink or the varnish which the microstructure embossing is intended to carry to the printing material before the latter runs through the press nip, it may also be expedient to use the micro embossing form 13 as a varnishing blanket, so to speak, and thereon to apply the varnish or ink layer to the substrate 3 to be printed via an applicator roll, for example the roll 9 of the web-fed press illustrated in FIG. 1, while said substrate is running through the press nip, in which the micro embossing takes place at the same time.

(12) In the pocket Z1 located downstream in relation to the movement of the material web 3, after the press nip between the two cylinders 10 and 11, a UV emitter 15 is installed over the entire width of the material web 3. This can be, for example, an array of UV-emitting diodes or UV laser diodes, which emit their radiation aimed at the press nip. The UV radiation emitted penetrates the silicone rubber of the micro embossing form 13, is reflected and scattered at the rough mirrored surface 14 of the sleeve 110, and the scattered radiation penetrates through the silicone rubber of the micro embossing form 13 again and then strikes the ink or varnish layer of the printed image element 12a just passing through the press nip, which layer is thus cured as it passes through the press nip and in the surface of which the depressions of the micro embossing form 13 are, so to speak, frozen in in this way, as can be seen schematically at a microstructure element designated by 12b.

(13) In order to stop scattered UV radiation getting into the surroundings, the two pockets Z1 and Z2 downstream and upstream of the press nip are each partitioned off by a scattered light screen 17b and 17a.

(14) In order to increase the effectiveness of the UV curing process in the press nip, as illustrated in the exemplary embodiment according to FIG. 3, a focusing reflector 18 is connected upstream of the UV emitter designated by 25 there. This reflector has a high efficiency, since it concentrates the UV radiation with strip-like incidence in a linear focus 21 directly above the reflective layer 14 of the sleeve 110, from where the diffusely reflected UV radiation 16 reaches the press nip through the silicone layer of the micro embossing form 13.

(15) In the alternative exemplary embodiment according to FIG. 4, the focusing reflector mirror 18 is left out. Instead, optical fibers 19 are placed on the light exit windows of the UV diode array designated by 35, which fibers guide the emitted UV light in the pocket located downstream after the press nip until entirely in the press nip. Immediately in front of the press nip, the UV radiation emerges from the fiber ends, passes through the UV-transparent micro embossing form 13 and is scattered into the press nip at the roughly mirrored surface 14 of the sleeve 110.

(16) In a quite similar exemplary embodiment, illustrated only as a detail in FIG. 5, mirroring of the sleeve 110 is omitted. Instead, the micro embossing form 13 consists of a material such as silicone having embedded metal particles, which reflects or scatters the UV radiation for the curing of the moist ink or varnish layer of the printed image element 12a, in particular on the rear side. This is achieved, for example, by means of a two-layer structure of the silicone micro embossing form 13 having a high proportion of metal particles on the rear side and a metal-free structure of the silicone layer on the embossing side. If necessary, the micro-rough surface of the cylinder or cylinder cover or sleeve 110, on which the micro embossing form 13 rests, also ensures diffuse reflection of the UV radiation at this point in the direction of the fluid of the printed image element 12a to be cured in the press nip. Since the optical fiber 19 leads the UV radiation up very close to the press nip, and thus a considerable part of the UV radiation is coupled into the UV-transparent silicone micro embossing form 13 and thus reaches the press nip, effective thorough curing of the ink or varnish layer of the printed image element 12a in the press nip or directly thereafter can also be achieved in this way.

(17) In the above-described exemplary embodiments, the UV emitter is in each case located in the pocket Z1 located downstream after the press nip. However, it is also possible, in particular when use is appropriately made of ink or varnish systems operating with a curing delay, to arrange the UV emitters in the pocket Z2 located upstream before the press nip.

(18) Furthermore, it is possible to operate with UV emitters in both pockets, as is described in the following exemplary embodiment according to FIG. 6. In FIG. 6, 111 designates a double-size impression cylinder of a sheet-fed press. Said cylinder has two cylinder channels 112a and 112b, in which gripper bars 113a and 113b are accommodated, by which the sheet 103 running through is held until it is conveyed onward by the next following transport cylinder 121. In addition, in FIG. 6, the freshly printed image elements are again designated by 12a and, following their embossing with microstructure elements, are designated 12b.

(19) The embossing cylinder 10 has only the single diameter as compared with the cylinder 111 and likewise has a channel 130, in which a plate 120, which is wound around the cylinder and once more carries a micro embossing form 113 on its outer side, is held by clamping devices, not specifically illustrated.

(20) In the pocket Z2 located upstream of the press nip, there extends over the entire cylinder length, behind a screen 117b, a UV lamp 115b, the wavelength and output of which are matched to the UV ink or the UV varnish of the printed image element 12a in such a way that the ink or the varnish has only been pre-cured before the passage through the press nip to such an extent that, although it is firm, it is still soft and flexible. Thus, the microstructure can be impressed thereon in the press nip without it immediately losing the embossed structure again after emerging from the press nip. In the pocket Z1 placed downstream there is a second UV light source 115a, the wavelength and output of which are now chosen such that the ink or varnish layer is finally thoroughly cured there following passage through the press nip.

(21) The method described here is suitable in particular for cationic curing or for UV material systems, that is to say inks and varnishes, which cross-link via cationic initiators.

(22) The desired two-stage curing can be achieved in that about 20 to 40% of the radiated power for the UV lamp 115a is expended for the UV lamp 115b. Suitable inks and varnishes for such a two-stage curing process are offered, for example, by the company Weilburger Graphics GmbH in Gerhardshofen, Germany, under the designations Senolith-UV-Glanzlack 360049 (radical) and Senolith-UV-Hochglanzlack 365010 (cationic), and by Heidelberger Druckmaschinen AG, Heidelberg, Germany, under the designation Saphira UV-Coating HG FB U8730 (radical).

(23) The invention has been described above by using an in-line printing system. However, the method can also be used in all installations which are suitable for coating substrates with liquid media. Furthermore, the method according to the invention can be used in printing systems of any type, including inkjet or electro-photographic printing systems, and in print further processing if in the further processing appliance, such as a punch, a stapler or a folding box gluing machine, for example, the product processed there is once more intended to be provided directly with a micro embossing in-line.

(24) In addition to the embossing of microstructures onto flat substrates such as paper film, web or roll products, the method can also be implemented in filling installations and in packaging machines.

(25) The micro embossing form can also be designed very differently, as a metal or metal structure, as a plastic film, possibly reinforced with metal or plastic fabric, etc.

(26) Furthermore, it is possible to provide the micro embossing form with an anti-adhesive layer. Particularly suitable for this purpose is the silicone rubber that is transparent in the ultraviolet spectral range and is marketed under the name Sylgard 184 by Dow Corning GmbH in Wiesbaden, Germany.

(27) The invention has been described above in conjunction with UV-curable inks and varnishes. However, it is also possible to use inks and varnishes that cure in the visible wavelength range or in the infrared range, and to provide appropriate emitters for the curing of the microstructures.

(28) Finally, the method can be extended still further in that the micro embossing form is provided in a further production step with a varnish to protect the micro embossing structure located underneath or with a varnish layer matched in terms of refractive index to the embossed varnish or the embossed ink. This further layer can be applied either to the entire area or in a screened manner.

(29) By using the method according to the invention, it is possible to comply with high security standards during the production of printed products, since the production of the security feature can now also be carried out directly at the end of the production chain and does not necessarily have to be supplied as a label. In addition, the expenditure for producing and changing the embossing form is significantly more beneficial than in the methods known in the prior art.