EP0558010A1 - Method and device for printing web material - Google Patents

Abstract

The invention relates to a method and a device for printing web material (2). The device consists of a back pressure cylinder (1) with an elastic support for guiding the web material (2) and of a forme cylinder (4) which is assigned a roll (6) of foamed material which is soaked with a thermoplastic ink, the forme cylinder (4) and the roll (6) of foamed material being arranged in a heating chamber (5). The intention of the invention is to provide a method and a device for printing web material, in which an uninterrupted operation is made possible and optimum utilisation of the available thermoplastic ink is achieved. A device according to the invention is characterised by a supply unit with which thermoplastic ink in the solid state can be supplied to the roll (6) of foamed material via an aperture (7) in the heating chamber (4), the temperature in the heating chamber (4) being selected such that the thermoplastic ink can be melted onto the roll (6) of foamed material when it comes into contact therewith. <IMAGE>

Description

The invention relates to a method for printing material webs, in which heated thermoplastic ink is transferred from a foam roller soaked in this color onto the cliché of a heatable cliché cylinder and then printed from the cliché onto the material web. The corresponding device consists of a housing with a heating chamber in which a plate cylinder and a foam roller associated therewith for the transfer of heated thermoplastic ink to a plate arranged on the plate cylinder are rotatably mounted, and an impression cylinder which is arranged such that a plate to be printed Material web between the impression cylinder and the plate cylinder can be passed.

Flexographic printing processes that work with flexible printing forms and liquid, solvent-based inks are preferably used for printing material webs. The corresponding device mainly consists of an impression cylinder for guiding the material web, a plate cylinder and an associated inking roller. The ink is usually fed to the inking roller by means of an immersion roller which is immersed in an ink pan. The ink is transferred to the cliché on the cliché cylinder via the combination of the dipping roller and the inking roller.

From DE 31 01 243 A1, a rotary printing method and a device for carrying out the method are known in which ink is fed to an immersion roller from an ink tray during the printing process. The ink on the dipping roller is then optionally transferred to an intaglio cylinder with the interposition of an anilox roller and from there to the web of material to be printed.

However, this device is unsuitable for the use of thermoplastic ink, which is in solid form at room temperature, since on the one hand only a little ink adheres to the surface of the immersion roller and on the other hand the ink on the surface of the immersion roller only in the areas of the gravure cylinder is passed on, which comes into contact with the grid plate arranged on the printing cylinder.

Signing devices are also known in which the required ink is supplied from a bottle placed on it, which is closed with a permeable membrane.

With these known printing devices, there is a risk that the ink will dry out when the business is interrupted, or that the viscosity of the ink may change during operation. The result is faulty or unusable print images. In addition, pigmented inks cannot be used when using membranes, e.g. for printing with white ink on a dark background. Should e.g. Material webs are printed in the form of plastic films, so it is often necessary to pretreat them by means of a corona discharge in order to achieve adequate adhesion of the color on the film.

Further disadvantages of these known printing devices are that long drying distances are required, particularly when printing on both sides.

To avoid these disadvantages, printing devices have been developed in which a heated metal plate on a plate cylinder transfers a thermoplastic ink previously applied to the plate to the material web to be printed. Such a printing device and an associated printing method have become known from EP 163 808 A2. The transfer of the thermoplastic ink to the metal cliché takes place from a foam rubber roller impregnated with this ink, which is used as an ink reservoir, whereby the aforementioned disadvantages can be largely avoided. For the transfer of the thermoplastic ink from the metal plate to a material web, an impression cylinder is provided, which presses the material web against the plate cylinder and thus enables printing on the material web.

With such a printing device, however, there is the disadvantage that only a substantially smaller part of the ink introduced into the foam roller can be removed. Furthermore, reuse, i.e. Soaking the used foam rubber rolls is uneconomical and therefore not useful. Due to the relatively low yield of the foam rolls impregnated with thermoplastic paint, the printing process for changing the foam rolls often has to be interrupted, or a greatly deteriorating print quality has to be accepted.

Furthermore, a device for handling adhesives has become known from US Pat. No. 2,877,763, in which adhesive in the form of a rod is tangentially fed to a melting device and is metered out under pressure from a nozzle. The melting device consists of a heated housing in which a chamber for receiving a rotatable melting and feeding roller is arranged. The surface of this roller is with transverse grooves provided that pull the supplied adhesive tangentially into the chamber and melt there.

However, this device is not suitable, in particular because of the tangential feed and the resulting high feed speed, for feeding thermoplastic ink to a printing device for printing on material webs.

The invention is therefore based on the object of providing a method and a device for printing on webs of material in which an uninterrupted printing process is made possible and optimal utilization of the available thermoplastic ink is achieved.

As a first solution to the problem, it is proposed in a method of the type mentioned at the outset that the foam roller is additionally supplied with thermoplastic ink by melting onto its surface during the printing process.

By melting onto the surface of the foam roller, the thermoplastic ink is evenly distributed on its surface and at the same time is distributed within the foam roller. This particularly simple process ensures constant pressure quality without any special effort.

In an expedient embodiment of the invention, the thermoplastic ink is supplied by melting it from an ink bar placed on the foam roller, so that this enables particularly easy handling of the ink. This color bar can also consist of a color powder.

As a second solution to the problem is proposed in a method of the type mentioned that the foam roll during the printing process, thermoplastic ink is additionally sprayed onto the surface of the ink.

This method is particularly suitable for applications in which the ink consumption is so great that the foam roller is not able to melt enough color from the ink bar. The solution is e.g. then advantageous when printing at high speeds, small repeats and large areas. The paint is heated, preferably in a paint tank, to such an extent that it becomes liquid and then sprayed onto the foam roller. This can happen depending on the color consumption.

To control the amount of ink applied, it is advantageous if the thermoplastic ink is supplied intermittently.

One of the first solution corresponding device of the type mentioned is characterized in that a feed unit is provided with the thermoplastic paint in the solid state at an opening in the heating chamber of the foam roller is feasible and the temperature in the heating chamber is selected so that the thermoplastic Color in contact with the foam roller can be melted onto it.

Due to the temperature of the heating chamber, the foam roller is warmed up so that the thermoplastic paint, which is in the solid state, is melted onto the rotating foam roller in contact with it.

In a preferred development of this solution, the thermoplastic paint is in the form of a paint bar which extends through the opening into the heating chamber and can be placed on the foam roller. This execution is characterized by good handling of the thermoplastic paint in solid form.

The feed unit expediently has a conveying device for conveying the ink bar in the direction of the foam roller. A metered melting of the ink bar on the foam roller can be achieved in a simple manner by the conveying device.

In particular, the feed unit can consist of a feed shaft which is connected to the foam roller via the opening in the heating chamber and is provided with the conveying device for conveying the ink bar.

In another embodiment of the device according to the first solution, it is provided that the conveying device has a clamping device which engages the end of the paint bar opposite the foam roller, and a drive with which the clamping device with the paint bar can be displaced towards the foam roller depending on the ink consumption is.

The clamping device can e.g. be connected to a spring-loaded half nut which is moved on a clockwise rotating threaded spindle in the direction pointing towards the foam roller. The spindle can be driven by an electromagnet using a rack, a gear and a freewheel. Furthermore, a limit switch can be provided at the lower end of the conveyor, which is actuated in the lower end position of the color bar and supplies a signal for inserting the next color bar. When the half nut is withdrawn, it is no longer in engagement with the spindle and can therefore be pushed back into the starting position in a simple manner.

A device according to the second solution mentioned above is characterized in that a spray device is provided is, with the thermoplastic paint in the liquid state from a paint tank through an opening in the heating chamber of the foam roller can be fed.

The particular advantages of the invention can be seen in the fact that on the one hand an exchange of used foam rolls is no longer necessary and on the other hand a continuous printing process with constant quality can be realized. This reduces the costs otherwise incurred to a minimum. The device can also be kept in readiness for printing without any subsequent possible reduction in quality when the printing is continued. Furthermore, the color used is used to the maximum. Finally, it is also an advantage of the invention that the ink supply to the foam roller can be carried out intermittently, so that control of the ink application to the foam roller is possible.

Fig. 1

ein Ausführungsbeispiel, bei dem ein Farbbarren durch einen Zuführschacht auf die Schaumstoffrolle aufgesetzt wird,

Fig. 2

ein Ausführungsbeispiel, bei dem ein Farbbarren mit Hilfe einer an dessen freiem Ende angreifenden Klemmvorrichtung auf die Schaumstoffrolle aufgesetzt wird,

Fig. 3

ein Ausführungsbeispiel, bei dem thermoplastische Farbe in flüssigem Zustand auf die Schaumstoffrolle aufgesprüht wird, und

Fig. 4

einen Schaltplan für das in Fig. 3 gezeigte Sprühverfahren.

Some embodiments of the invention are explained below with reference to the drawing. Show it:

Fig. 1

an embodiment in which a color bar is placed on the foam roller through a feed shaft,

Fig. 2

an embodiment in which a color bar is placed on the foam roller with the aid of a clamping device acting on its free end,

Fig. 3

an embodiment in which thermoplastic paint is sprayed onto the foam roller in the liquid state, and

Fig. 4

a circuit diagram for the spraying process shown in FIG. 3.

As can be seen from FIG. 1, the device for printing material webs 2 with a thermoplastic ink from a rubberized impression cylinder 1 has a cliché cylinder 4 mounted on its lateral surface a cliché 3 is attached. The distance between the impression cylinder 1 and the plate cylinder 4 is set so that the plate 3 rolls on the web of material 2 passed between the two cylinders and the ink on the plate 3 can be transferred to the web 2. Subsequent to the plate cylinder 4, a foam roller 6 is mounted at intervals. The distance between the foam roller 6 and the plate cylinder 4 is slightly less than the thickness of the plate 3, so that it rolls once on the foam roller 6 each time the plate cylinder 4 rotates. The color in the foam roller 6 is transferred to the plate 3 in accordance with the surface structure of the plate.

Since the material web 2 is to be printed with a thermoplastic ink, the cliché cylinders 4 and the foam roller 6 are accommodated in a heating chamber 5.

An opening 7 is provided in the heating chamber 5 above the foam roller 6, through which an ink bar 8 can be introduced into the heating chamber 5. For this purpose, a vertically arranged feed shaft 9 is fastened above the opening 7, the cross section of which corresponds to the dimensions of the color bar 8 to be fed. The opening 7 widens conically in the direction of the feed channel 9, which facilitates the insertion of the color bar 8. Faults caused by ink bars 8 which may jam or tilt in the opening 7 are thereby also avoided.

The opening 7 in the heating chamber 5 and the associated feed shaft 9 can also be arranged elsewhere in the heating chamber 5. So would be an oblique or horizontal one Arrangement conceivable. This does not affect the function described below.

If a paint bar 8 is now inserted into the feed shaft 9 and placed on the foam roller 6, paint melts, which is distributed on the foam roller 6 by the rotation thereof.

In order to achieve an optimal color distribution, a conveying device 10 is arranged within the feed shaft 9, with the aid of which the conveying of the ink bar 8 in the direction of the foam roller 6 can be controlled. The ink bar 8 is preferably fed intermittently. The ink supply is controlled by a preselection counter (not shown) depending on the number of prints. This allows the amount of paint supplied to be regulated and interrupted if necessary. This is e.g. then the case when the material web 2 must be exchanged for another material web 2. Since in this case the printing device has to be stopped, but the heating in the heating chamber 5 continues to operate, further paint would melt from the ink bar 8 if it remains on the foam roller 6. If the feed is stopped at this time, no paint can melt.

When the printing device is restarted, only the intermittent feeding of the color bar 8 then has to be continued.

To avoid an otherwise possible interruption of the ink supply, an empty indicator 11 is arranged in the lower region of the feed chute 9, which indicates when a new ink bar 8 is to be inserted. This empty detector 11 can consist, for example, of an optoelectronic sensor.

The device described above ensures the continuous printing of material webs 2. Through the constant and controllable ink supply through the feed chute 9 it is no longer necessary to replace the foam roller 6, or it is possible to use it much longer. Replacing the foam roller 6 is only necessary when it is mechanically worn or when the color changes. In addition, interruptions in operation due to technology are no longer detrimental to the quality of the printing result, since at the same time the ink is supplied by the ink bar 8 when the printing process is resumed.

In the exemplary embodiment shown in FIG. 2, the feed shaft of the device shown in FIG. 1 has been replaced by a conveyor device with a clamping device 12 for the ink bar 8. In practice, it has been shown that it makes sense to design the feed unit for ink bars 8 so that it has as little contact as possible with drive and guide elements. This is ensured in particular by the exemplary embodiment shown in FIG. 2.

As can be seen from FIG. 2, the ink bar 8 is held at its end opposite the foam roller 6 by the clamping device 12, into which it can be inserted. By means of a drive 13, the clamping device 12 is moved towards the foam roller 6 as a function of the ink consumption, so that the ink bar 8 can melt on its end face in contact with the foam roller 6 and soak it. In the clamping device 12 there is a spring-loaded half-nut, not shown in the drawing, which is moved downwards on a clockwise rotating threaded spindle 14. The threaded spindle 14 is driven by an electromagnet, not shown in the drawing, with the aid of a toothed rack, a toothed wheel and a freewheel. As soon as the color bar 8 reaches its lower end position, a limit switch is actuated, which supplies a signal for inserting the next color bar. When the half-nut is withdrawn, it is no longer engaged the threaded spindle 14 and can therefore be easily pushed back into the starting position.

In the exemplary embodiment shown in FIG. 3, thermoplastic paint is applied to the foam roller in the liquid state by a spray device. This exemplary embodiment is particularly suitable for prints at high speeds, small repeats and large areas in which it is no longer possible to melt off enough thermoplastic ink by contacting a color bar with the foam roller. For the extended field of application, the paint is therefore heated so far that it changes to the liquid state, and then sprayed onto the foam roller 6 in order to soak it. This can also happen depending on the color consumption.

The spray device for the thermoplastic paint operates according to the circuit diagram shown in FIG. 4.

As can be seen from this, mains air supplied from the outside is switched on and off by a three / two-way solenoid valve 15. With the aid of a pressure regulator 16 for the conveying air acting on the paint tank, the amount of paint emerging from the nozzle 17 can be regulated, which is intended to soak the foam roller 6. At the same time, the compressed air that is to atomize the paint is switched on via a controllable check valve 18. The pressure for this can be set on a pressure regulator 19 for the spray air. In addition, a post-spraying time can be set by means of a suitable device 20, which ensures that, after the ink supply has ended, any paint residues still emerging at the nozzle 17 are sprayed.

The spray air regulated by the pressure regulator 19 is then passed through a preheating chamber 21 to the spray device shown in FIG. 3. Via a line 22 it reaches an annular chamber 23 from which it closes a part emerges from an annular gap 24 and atomizes the paint conveyed through a nozzle 25 through the nozzle 17. The other part of the spray air emerges from two laterally arranged nozzles 26 and forms the paint cone into an oval cross section.

With the aid of the intermediate layers 27 shown in FIG. 3, the height of the spraying device in relation to the foam roller 6 can be changed so that the width in which the foam roller 6 is sprayed can be varied.

Reference symbol list

1

Impression cylinder

2nd

Material web

3rd

cliche

4th

Cliché cylinder

5

Heating chamber

6

Foam roll

7

opening

8th

Color bars

9

Feed chute

10th

Conveyor

11

Empty detector

12

Clamping device

13

drive

14

Threaded spindle

15

Solenoid valve

16

Pressure regulator

17th

jet

18th

check valve

19th

Pressure regulator

20th

Device for setting the post-spraying time

21

Preheating chamber

22

management

23

chamber

24th

Annular gap

25th

Color valve

26

jet

27

Liner

Claims (10)

Process for printing material webs, in which heated thermoplastic ink is transferred from a foam roller impregnated with this ink to the cliché of a heated cliché cylinder and then printed by the cliché onto the material web, characterized in that the foam roller additionally melts thermoplastic ink during the printing process is fed on their surface. A method according to claim 2, characterized in that the thermoplastic ink is supplied by melting from a paint bar placed on the foam roller. Process for printing material webs, in which heated thermoplastic ink from a foam wool impregnated with this color is transferred to the cliché of a heated cliché cylinder and is then printed by the cliché onto the material web, characterized in that the foam roller additionally thermoplastic ink in liquid during the printing process Condition is applied by spraying on the surface. Method according to one of claims 1 to 3, characterized in that the thermoplastic ink is supplied intermittently. Apparatus for carrying out the method according to claim 1 or 2, consisting of a housing with a heating chamber in which a plate cylinder and a foam roller associated therewith for the transfer of heated thermoplastic ink are rotatably mounted on a cliché arranged on the plate cylinder, and an impression cylinder which is arranged such that a material web to be printed can be passed between the impression cylinder and the plate cylinder, characterized in that a feed unit is provided with the thermoplastic ink in the solid state through an opening (7) in the heating chamber (5) of the foam roller (6) can be supplied and the temperature in the heating chamber (4) is selected so that the thermoplastic paint in contact with the foam roller (6) can be melted onto it . Apparatus according to claim 5, characterized in that the thermoplastic paint is in the form of a paint bar (8) which extends through the opening (7) into the heating chamber (5) and can be placed on the foam roller (6). Apparatus according to claim 6, characterized in that the feed unit has a conveyor device (10) for conveying the ink bar (8) in the direction of the foam roller (6). Apparatus according to claim 7, characterized in that the feed unit consists of a feed shaft (9) which is connected to the foam roller (6) via the opening (7) in the heating chamber (5) and to the conveying device (10) for conveying the color bar (8) is provided. Apparatus according to claim 6, characterized in that the conveying device comprises a clamping device (12) which on the end of the paint bar opposite the foam roller (6) (8) engages, and has a drive (13) with which the clamping device (12) with the ink bar (8) depending on the ink consumption to the foam roller (6) is displaceable. Apparatus for carrying out the method according to claim 3, consisting of a housing with a heating chamber in which a plate cylinder and a foam roller associated therewith for the transfer of heated thermoplastic ink to a plate arranged on the plate cylinder are rotatably mounted, and an impression cylinder arranged in this way is that a material web to be printed can be passed between the impression cylinder and the plate cylinder, characterized in that a spray device is provided with the thermoplastic ink in the liquid state from an ink tank through an opening (7) in the heating chamber (5) of the foam roller ( 6) can be fed.

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