EP4028261B1 - Method and device for print finishing - Google Patents

Description

The invention relates to improved methods and devices for print finishing.

Print finishing refers to changing the surface of a printing material such as paper, cardboard, etc. through an additional coating. This gives the paper either a certain shine, a structure or pre-defined effects that it does not have in its original, unprocessed form. Print finishing involves changing the paper surface, which, on the one hand, makes the print product as a whole more durable by protecting it from wear and, on the other hand, contributes to its sale or to the sale of the products or services depicted in it through a visual or tactile enhancement.

Finishing processes can be based on coating, joining, forming or separating the printing material. The processes in which finishing is carried out by joining include laminating, laminating and foil transfer. Film transfer includes finishing processes in which transfer layers are removed from a carrier film and transferred to the printing material. This group of processes includes hot foil stamping, cold foil transfer and foil transfer to toner realized as part of digital printing. In addition to the aesthetic enhancement of a product, special... Films (hologram films) can also be used to protect products and documents.

During hot foil stamping, under the effect of pressure, temperature and contact time, transfer layers of an embossing foil are transferred to the material using an embossing stamp, which simultaneously undergoes a permanent change in shape. Hot foil stamping takes place as flat stamping with a tool or relief stamping with a die and male die. Either flat embossing stamps or embossing rollers are used as embossing tools, which are heated for the foil transfer. The temperature depends on the embossing foil used, the printing material and the machine type and is between 80...220 °C.

The embossing foil consists of several layers. One or more transfer layers are either applied directly to a polyester carrier film, or the transfer layers are applied to a separating layer on the carrier film, which melts under the influence of heat and thus releases the transfer layers. The transfer layers include an optically active layer and an adhesive layer (reactivatable adhesive). The adhesive layer serves to create a permanent and smudge-proof connection between the optically effective layer and the printing material. Color pigments, metal pigments and plastics can be used for the optically effective layer, which leads to very different visual effects.

Cold foil transfer achieves similar visual effects to hot foil stamping, but without material deformation. By transferring a metallized A plastic layer that is removed from a carrier film and, if necessary, subsequent overprinting can be used to achieve a wide variety of metal effects.

In known processes, cold foil finishing is carried out, for example, with two additional printing units in an offset printing machine. In the first printing unit, a special adhesive is applied to the printing material using a standard printing form. Since the characteristics of offset printing come into play, small screen elements and fine line thicknesses can be transferred. A second printing unit is equipped with a film transfer device. The film is guided from the unwinding station into the printing gap between the blanket cylinder and the printing cylinder and brought into contact with the printing material.

The film consists of several layers that are located on a carrier film. The color is provided by an aluminum layer and a protective varnish layer, the coloring of which influences the color impression. By adhesion of an adhesive layer to the printed adhesive layer, the transfer layers remain adhered to the substrate. The carrier film is then wound up again.

The visual effect of cold foils is similar to that of embossing foils. However, there is no haptic effect because there is no deformation or noticeable surface change.

Cold foils are used in the production of various printed products, for example in label printing, on high-quality packaging or in commercial printing.

The cost advantage is the fact that finishing can be done inline in the printing press and, compared to other types of finishing, no special tools have to be produced. However, the prerequisite for cold foil transfer is two additional printing units and the foil transfer station.

US 2009/078364 A1 describes a printing press having a transfer device for transferring gold foil and the like. The transfer device contains a printing cylinder and a film transfer device. The impression cylinder receives sheets from a delivery cylinder. The film transfer device presses the transfer film onto the sheets to which a UV-curable resin varnish has been applied as an adhesive to transfer a gold foil or the like from the transfer film to the sheets. The transfer film is pressed onto the resin varnish over the sheets. Then lamps shine ultraviolet rays from above onto the pressed film to cure the resin varnish.

WO 2009/053316 A2 relates to a coating system for transferring imaging or covering layers from a transfer film to a printing material. For this purpose, at least one film application module is used in a sheet-fed rotary printing machine. The coated foil sheet can be dried from its back. The corresponding drying device is downstream of the film coating. Here, the film application should be carried out on film printing materials in conjunction with an offset printing machine with upstream or downstream varnish modules. Before or after application, additional printing and intermediate drying can be carried out, for example with Using a UV dryer. The use of heat-reduced UV dryer systems in conjunction with foil application can be used for cold foil lamination.

US 2015/343761 A1 describes a process for cold stamping on a three-dimensional object. The object is held by a holding device so that it can rotate about an axis of rotation. In a first step, an adhesive is applied to the object at a first work station. In a second step, a transfer film is pressed onto the object by a pressing device at a second work station. At the same time, the adhesive is hardened at the second work station.

One object of the present invention is to further develop and improve the known methods and devices for print finishing, in particular for cold foil transfer.

What is initially proposed for this is a method for print finishing, in which a printing material and a transfer film with a transfer layer are provided, the printing material is moved along a transport path at a transport speed, and a radiation-curing plastic is applied to the printing material during the movement of the printing material in a first section of the transport path is applied, after the radiation-curing plastic has been applied, the printing material is irradiated in a second section of the transport path, while at the same time the transfer film is pressed onto the printing material and moved with it along the transport path, and when leaving the second section of the transport path, the transfer film is removed from the printing material becomes.

The previously known methods of cold foil transfer use adhesives that are already sticky when they are applied to the printing material and therefore easily remove the transfer layer from the transfer foil when the carrier foil is removed from the printing material. In the method according to the invention, a radiation-curing plastic is used as the adhesive instead, which is initially present as a resin, i.e. liquid or pasty and has no or almost no adhesive strength. Only when this resin is irradiated with radiation of a specific wavelength does it become sticky and then harden. In this way, the transfer layer is removed from the transfer film in the areas in which the surface of the printing material has the resin of the radiation-curing plastic, while the transfer layer remains on the transfer film in the remaining areas. This brings significant advantages. For example, nozzles of a printing device that is used to apply the resin to the printing material can no longer become clogged because the irradiation of the resin applied to the printing material only takes place after printing.

The printing material is moved horizontally and the transfer film is guided in the second area of the transport path around a partial circumference of a pressure roller, which is pressed onto the printing material. This has particular advantages for the print finishing of printing materials in the form of individual sheets - in contrast to the roll-to-roll process. According to the invention, the printing material and the transfer film only touch each other in a very short area, as seen in the transport direction, so that a relative displacement occurs Due to different transport routes, they cannot have a negative impact on the result of the processing. For the same reason, it can advantageously be further provided in the proposed method that the pressure roller is moved in rotation at a peripheral speed that is equal to the transport speed of the printing material.

The pressure roller is pressed onto the transport path when a printing material is moved under it and is raised when no printing material is moved under it. This avoids a paper jam that can occur as a result of the printing material colliding with the pressure roller pressed onto the transport path.

It can also be particularly advantageously provided that the pressure roller is provided as a radiation-permeable hollow body and a radiation source is provided in the pressure roller. For a high-quality result, it makes sense that the transfer film is pressed onto the printing material. The irradiation can occur either beforehand, so that the curing process of the resin begins during the action of the pressure roller, or afterwards. However, if the pressure roller is a radiation-permeable hollow body in which a radiation source is arranged, the pressing of the film onto the printing material and the hardening of the resin of the radiation-curing plastic coincide, and the effect of the radiation takes place during the pressing of the pressure roller through the translucent hollow body.

The task is further solved by a device for Print finishing, which comprises the following: a transport device for moving a printing material along a transport path, a printing device for applying a radiation-curing plastic to the printing material in a first section of the transport path, a film feed device for feeding transfer film to a surface of the printing material in a second section of the transport path , and an irradiation device for curing the radiation-hardening plastic in the second section of the transport path, which comprises at least one radiation source.

The film feed device has at least one unwinder and one take-up reel as well as a pressure roller arranged between them, around which the transfer film is guided and which is pressed onto the printing material. The pressure roller is movable back and forth between a lower position in which it presses on the transport path and an upper position in which it is lifted off the transport path. This makes it possible for the pressure roller to be pressed onto the transport path when a printing material is moved under it and to be raised when no printing material is moved under it. This avoids a paper jam that can occur as a result of the printing material colliding with the pressure roller pressed onto the transport path.

The transport device can, for example, have a belt conveyor on which the printing material is transported lying down. The transport device advantageously has a suction belt conveyor on which the printing material is held by means of negative pressure. The Suction belt conveyors can, for example, have a perforated conveyor belt guided around deflection rollers, with a so-called suction box being arranged between the deflection rollers, in the interior of which a negative pressure is generated by means of a pump.

In a further embodiment, it can be provided that at least one tension roller is arranged between the unwinder and the pressure roller and/or between the pressure roller and the take-up roller in order to produce a constant web tension in the transfer film.

It can also be particularly advantageously provided that the pressure roller is designed as a radiation-permeable hollow body and that the at least one radiation source is arranged in the pressure roller. The pressing of the film onto the printing material and the hardening of the resin of the radiation-curing plastic coincide, and the effect of the radiation takes place during the pressing of the pressure roller through the translucent hollow body.

In a further embodiment of the proposed device, it can be provided that the irradiation device comprises, in addition to the at least one radiation source, at least one movably arranged aperture for directing the beam generated by the radiation source. This aperture can, for example, comprise a hollow cylindrical body with a slot-shaped aperture opening which is rotatably arranged inside the pressure roller about its longitudinal axis.

For process variants in which radiation curing is used Plastic that can be hardened by IR radiation is used, it is provided on the device side that the at least one radiation source emits IR radiation.

In process variants in which plastic that can be hardened by UV radiation is used as the radiation-curing plastic, it is provided on the device side that the at least one radiation source emits UV radiation.

The invention is explained in more detail below using an exemplary embodiment and an associated figure, which shows a device according to the invention.

At the beginning of a device according to the invention there is a sheet feeder 11 and at its end there is a sheet delivery 12.

A transport device 2 for moving a printing material 1 along a transport path, the beginning and end of which are each indicated by a horizontal arrow, is arranged between the sheet feeder 11 and the sheet delivery 12.

The transport device 2 has a suction belt conveyor 21 on which the printing material 1 is held by means of negative pressure. The suction belt conveyor 21 has a perforated conveyor belt guided around deflection rollers, with a suction box being arranged between the deflection rollers, in the interior of which a negative pressure is generated by a pump 22.

Above the transport device 2, in a first section of the transport path, there is a printing device 3 for applying a radiation-curing plastic to the Printing material 1 arranged. The printing device 3 is designed in the manner of an inkjet printer, in which instead of a printing ink, a resin of a radiation-curing plastic is applied to the surface of the printing material 1, while the printing material 1 is moved past under the printing device 3 by the transport device 2. By triggering the binding reaction, the adhesive is activated to achieve dimensional stability of the printed image (so-called “pinning”).

Downstream of the printing device 3, a film feed device 4 for feeding transfer film to a surface of the printing material 1 is arranged in a second section of the transport path, also above the transport device 2. The film feed device 4 comprises a uncoiler 41, a rewinder 43 and a pressure roller 42 arranged between the uncoiler 41 and the reel 43. The transfer film 6 is guided around the pressure roller 42 and pressed onto the printing material 1. Between the uncoiler 41 and the pressure roller 42 and between the pressure roller 42 and the take-up reel 43, an arrangement of two tension rollers 44 coupled to one another is arranged, which serves to produce a constant web tension in the transfer film 6.

The pressure roller 42 is moved back and forth by means of a yoke 45 and a pneumatic cylinder 46 acting on the yoke 45 between a lower position in which the pressure roller 42 presses on the transport path and an upper position in which the pressure roller 42 is lifted off the transport path movable.

The device further comprises a Irradiation device 5 with a UV lamp as a radiation source 51 for curing the radiation-curing plastic. The pressure roller 42 is designed as a radiation-permeable hollow body and the UV lamp 51 is arranged in the pressure roller 42. The irradiation device 5 also has a movably arranged aperture 52 for directing the beam generated by the radiation source 51, which is designed as a hollow cylindrical body with a slot-shaped aperture opening which is rotatable inside the pressure roller 42 about the longitudinal axis of the pressure roller 42.

Reference symbol list

1

printing material

11

Sheet feeder

12

Sheet delivery

2

Transport facility

21

Suction belt conveyor

22

pump

3

Printing facility

4

Film feeding device

41

Uncoiler

42

pressure roller

43

reel

44

tension roller

45

yoke

46

Pneumatic cylinder

5

Irradiation facility

51

Radiation source

52

cover

6

Transfer film

Claims (11)

1. Method for print finishing, in which

   • a printing material (1) and a transfer film (6) having a transfer layer are provided;

   • the printing material (1) is moved along a transport path at a transport speed;

   • during the movement of the printing material (1), a radiation-curing plastic is applied to the printing material (1) in a first section of the transport path;

   • following the application of the radiation-curing plastic, the printing material (1) is irradiated in a second section of the transport path while, at the same time, the transfer film (6) is pressed onto the printing material (1) and is moved along the transport path with the printing material (1), and

   • as it leaves the second section of the transport path, the transfer film (6) is removed from the printing material (1);

   wherein the printing material (1) is moved lying horizontally and, in the second area of the transport path, the transfer film (6) is led around a partial circumference of a pressure roll (42), which is pressed onto the printing material (1), and the pressure roll (42) is pressed onto the transport path when a printing material (1) is moved through underneath it and is raised when no printing material (1) is moved through underneath it.
2. Method according to Claim 1, in which the pressure roll (42) is moved in rotation at a circumferential speed which is the same as the transport speed of the printing material (1).
3. Method according to Claim 1 or 2, in which the pressure roll (42) is provided as a hollow body that is transmissive to radiation and a radiation source (51) is provided in the pressure roll (42).
4. Device for print finishing, comprising

   • a transport device (2) for moving a printing material (1) along a transport path;

   • a printing device (3) for applying a radiation-curing plastic to the printing material (1) in a first section of the transport path;

   • a film supply device (4) for supplying transfer film (6) to a surface of the printing material (1) in a second section of the transport path; and

   • an irradiation device (5), which comprises at least one radiation source (51), for curing the radiation-curing plastic in the second section of the transport path; wherein

   • the film supply device (4) has at least one unwinder (41) and a rewinder (43) and a pressure roll (42) arranged between them, around which the transfer film (6) is guided and which is pressed onto the printing material (1); and

   • the pressure roll (42) is movable so as to reciprocate between a lower position, in which it presses on the transport path, and an upper position, in which it is lifted off the transport path.
5. Device according to Claim 4, in which the transport device (2) has a suction belt conveyor (21), on which the printing material (1) is held by means of negative pressure.
6. Device according to Claim 4 or 5, in which at least one tension roll (44) for producing a constant web tension in the transfer film (6) is arranged between the unwinder (41) and the pressure roll (42) and/or between the pressure roll (42) and the rewinder (43).
7. Device according to one of Claims 4 to 6, in which the pressure roll (42) is designed as a hollow body that is transmissive to radiation and the at least one radiation source (51) is arranged in the pressure roll (42) .
8. Device according to one of Claims 4 to 7, in which the irradiation device (5), in addition to the at least one radiation source (51), comprises at least one movably arranged shutter (52) for steering the beam generated by the radiation source (51).
9. Device according to Claims 7 and 8, in which the shutter (52) comprises a hollow cylindrical body with a slit-like shutter opening which is arranged in the interior of the pressure roll (42) so as to be rotatable about the longitudinal axis of the latter.
10. Device according to one of Claims 4 to 9 in which the radiation-curing plastic is able to be cured by IR radiation and the at least one radiation source (51) emits IR radiation.
11. Device according to one of Claims 4 to 9, in which the radiation-curing plastic is able to be cured by UV radiation and the at least one radiation source (51) emits UV radiation.

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