EP0655030B1 - Process and device for moistening a moving printed then thermally dried web of material - Google Patents

Abstract

PCT No. PCT/DE93/00715 Sec. 371 Date Feb. 16, 1995 Sec. 102(e) Date Feb. 16, 1995 PCT Filed Aug. 7, 1993 PCT Pub. No. WO94/04364 PCT Pub. Date Mar. 3, 1994A process and device are disclosed for moistening a moving web of material (10), in particular for moistening again a printed then dried printed material. As soon as possible after the thermal drying process is concluded, preferably in the area of the cooling cylinders, a moistening agent is pressed on one or both sides of the web of material (10) by an applicator (12) by means of a smooth cylinder (15), against a guiding element (11).

Description

13. The invention relates to a method and a device for moistening a printed and then thermally dried, moving material web according to the preamble of claims 1 and 13 respectively.

When processing and processing flat, in particular sheet-like materials, it is often necessary for the material to be processed to be moistened before a further processing step. Especially with printed and then thermally dried substrates, such as. B. paper or fabric webs, rewetting is required.

In web offset printing, for example, paper webs are printed at high speed and then subjected to a thermal drying process for drying and solidifying the printing inks. It is necessary moisten the printed paper web before final processing to ensure the original paper moisture and thus the elasticity and dimensional stability of the paper required for the final processing. This is necessary because dry paper is very brittle and therefore easily breaks or tears when folded or cut. In addition, dry paper expands when it absorbs moisture from the air. B. comes with glued magazines or the like to an unsightly curl of the finished magazines and to an uneven "outgrowth" of the individual pages in the cutting areas.

In a known method for moistening web-like material (DE 31 15 958 C2), a material web is subjected to a corona treatment before a dampening solution is applied to it in a moistening station, as a result of which a large number of adhesive adhesion centers are created for the adhesion of the dampening solution particles should. A dampening solution bath or a spray device (not described in detail) is used as the moistening station.

In another known device for moistening moving material webs, in particular paper webs (DE 38 23 739 A1), the paper web is guided with its one side in contact with an endless belt, the top of which carries a high-voltage conductive coating. A conductive atomizer is provided to form dampening solution aerosols and is arranged on the other side of the paper web at a distance from it. Between the atomizer and the conductive coating a strong electric field is built up, through which the aerosols are polarized and then accelerated so that they not only wet the paper web, but also penetrate into its pores.

A disadvantage of this known device is that high voltages in the range of 50 kV have to be used at relatively high powers, so that the humidification device is very sensitive to fluctuations in air humidity, since spark discharges can occur if the air humidity is too high and damage the paper web cause. In addition, complex shielding measures must be provided for safety reasons. Another disadvantage is that this known device requires a relatively large amount of space, so that it cannot be retrofitted to existing printing machines or other processing machines.

In another known device (DE 40 21 296 A1), an applicator roller is provided for applying a dampening solution to a material web, which roller is wetted by a scoop roller immersed in a dampening solution bath. To moisten a web of material, the application roller is pivoted against a web of material or paper so that it deflects it out of its transport path. This ensures that the material web moving over the application roller more or less grinds off the dampening solution film located thereon.
Since in this device the material web lies unevenly on the application roller, it is necessary to press the dampening solution evenly through a printed surface of the material web not possible. In addition, the exact dosage of the dampening solution required cannot be achieved.

From CH-A 467 159 a method and a device is known by which a transfer of a dampening solution to the printed side of a material web is accomplished in a similar manner. Here, the material or paper web is first thermally dried after printing, then cooled and guided over a cooled guide element in the form of a rotating cooling roller. During the cooling phase, the paper web on a flat side of the web is wetted with a dampening solution or water film for rewetting the web. For this purpose, the water film is first applied to a transfer roller of a roller arrangement and then rolled onto the circumference of the cooling roller by the latter. For this purpose, the paper web wraps around the cooling roller under its own tension in such a way that a large part of its roller circumference is exposed for unrolling the transfer roller.

In addition, the transfer roller is moistened by means of a roller arrangement which draws the water from a water trough.

The invention has for its object to rewet thermally dried and printed material webs, in particular paper webs, at a very high transport speed or in minimal time from their flat side of the web, in order to reduce the moisture loss caused by the drying process with all its disadvantages for the further processing of the material web (folding and folding largely compensate for paper webs).

Starting from a method and a device of the known type described above, this object is achieved by the characterizing features of method claim 1 and device claim 13.

According to the invention, therefore, a material web, after it has been dried, is wetted on at least one side with dampening solution, which is pressed into the web at the same time. The dampening solution is applied and pressed in at the earliest possible point in time, during the cooling phase, i.e. as soon as the printing ink is so solid that it no longer smears when the dampening solution is pressed in, thus preventing the printed image from being impaired. When the dampening solution is applied during the cooling phase, the absorption of the dampening solution into the material web, which is in particular a paper web, is supported by its cooling behavior.

From US A 30 66 046 it is known to apply a dampening solution to a material web by means of a pair of rollers forming a nip, but the pressure exerted in the gap is used for fine metering of the dampening solution. The application roller is equipped on the circumference with an absorbent rubber layer, onto which a textile fabric is applied, the threads of which are non-absorbent. The water used for moistening is stored in the rubber layer and, when the paper web is pressed against the applicator roller, pressed out of it to wet the paper web, for this purpose it is displaced into the spaces between the fabric threads.

From US-A 3,647,525 a method and a device are known, in which likewise for the application of a dampening solution to the material web, the latter is passed through a nip which is variable in width and thereby the dampening solution is metered into this.

The penetration of the dampening solution into the material web can advantageously be supported in that, according to claim 2, the material web wetted with the dampening solution is then passed through an electrical high-voltage field and is thus electrostatically charged. In particular, the dampening solution film, which after application can still have certain irregularities, is compensated in such a way that it is uniform over the entire width of the material web and adheres well to the material web. As a result, small fountain solution droplets are prevented can release from the dampening medium applied to the material web, even if the material webs, such as paper webs in web offset printing, are moved at high transport speeds.

This is particularly advantageous in the case of web offset printing, since it is necessary here to rewet a printed and then dried paper web into which the dampening solution can penetrate relatively slowly due to the coating with dried and possibly quenched printing ink. The uniform distribution and adherence of the dampening solution film to the paper web has the consequence that the printed image is not impaired by the dampening solution film and that the dampening solution has sufficient time to penetrate through the printing ink into the paper web.

Since the dampening is carried out at a point in time at which the printing ink already has a certain resistance to the pressing of the dampening solution but has not yet reached its final strength, the dampening solution can penetrate the relatively warm paper better through the printing ink. As a result, the paper already has improved elasticity during the subsequent treatment.

It is advantageous to design the electrostatic charge of the material web according to claim 3.

To form the dampening solution film, it is advantageous to proceed according to claim 4.

Further possible method steps for moistening the material web are shown in claims 5 to 7.

Furthermore, in particular in order to influence the electrical properties of the dampening solution, it may be advantageous to use water for this purpose, if appropriate with additives, as listed in claim 9.

According to an embodiment of the invention according to claim 10, the electrostatic charging is advantageously carried out with a high voltage below 50 kV. Only low electrical power is required, so that, carried out with high voltages, no undesirable spark discharges are to be feared, even with fluctuating air humidity. Because of the low currents required for the electrostatic charging, only relatively simple shielding measures are required for the parts carrying the high voltage, without the safety for a maintenance person being impaired thereby.

In the case of an embodiment of the method according to claims 11 and 12, the penetration behavior of the dampening solution can be additionally influenced and kept constant for a given dampening solution. This enables good and even rewetting to be achieved.

The method according to the invention can advantageously be carried out using a device according to claim 13, claims 14 to 16 relating to expedient embodiments of this device. Such a device for moistening a material web can be retrofitted in a particularly favorable manner into an already existing material web processing machine, since already existing transport and guide rollers can be used for the device according to the invention in this machine.

For example, in a web offset press, the cooling rollers, over which the printed and dried paper web is guided after drying to quench the printing ink, can be used as guide elements of the device according to the invention without major changes to the cooling station being necessary to install the device according to the invention can.

By designing the charging device according to claim 17, the device according to the invention can be made extremely space-saving.

Developments of the invention according to claims 18 and 19 enable a particularly precise and uniform adjustment of the amount of dampening solution in relation to the size of the web surface to be wetted. This is necessary in particular when remoistening or moistening printed and dried paper webs, since approximately 0.5 to 6 ml must be applied uniformly to 1 m ^{2 of} web of material to moisten the web of material. It is necessary to observe this amount of dampening solution per area very precisely, since too much dampening solution can lead to stains or other damage to the printed surface, while the brittleness of the dried paper web is not adequately eliminated if the dampening solution is introduced too little.

The uniform formation of the dampening solution film and its transfer to the material web surface can be achieved particularly well by designing the device according to claims 20 to 25.

For the specifically controlled and / or uniform spraying of the dampening solution to form the dampening solution film, the configurations according to claims 26 and 27 are expedient. It is further advantageous that at increased transport speeds of the material web, for the cooling of which an increased number of cooling rollers is then required, more cooling rollers are also available, on which devices for dampening according to the invention can be arranged.

Figur 1

eine schematische Darstellung einer Vorrichtung zum Anfeuchten einer bewegten Materialbahn,

Figur 2

eine schematische vereinfachte Darstellung einer Kühlwalzenanordnung einer Rollenoffsetmaschine mit daran angeordneten Vorrichtungen nach Fig. 1,

Figur 3

eine schematische, vereinfachte Draufsicht auf eine Feuchtmittelaufsprühvorrichtung mit zugeordneter Walze, wie sie in der Vorrichtung nach Fig. 1 verwendet wird,

Figur 4

einen Drehteller für die Aufsprühvorrichtung nach Fig. 3, und

Figur 5

eine schematische Teildarstellung eines Aufladestabes für die Vorrichtung nach Fig. 1.

The invention is explained in more detail below, for example with reference to the drawing; in this shows:

Figure 1

1 shows a schematic representation of a device for moistening a moving material web,

Figure 2

1 shows a schematic, simplified representation of a cooling roller arrangement of a web offset machine with devices arranged thereon according to FIG. 1,

Figure 3

2 shows a schematic, simplified top view of a dampening solution spraying device with an associated roller, as is used in the device according to FIG. 1,

Figure 4

a turntable for the spray device of FIG. 3, and

Figure 5

2 shows a schematic partial illustration of a charging bar for the device according to FIG. 1.

Corresponding components in the various figures of the drawing are identified by the same reference symbols.

As is shown schematically in FIG. 1, a material web 10 to be moistened is guided over an electrically conductive, preferably driven roller 11 serving as a guide element and thereby moved in the direction of arrow B. Arranged radially next to the roller 11 is an application device 12 for applying a dampening solution film to the material web 10, which has a spraying device 13 and a roller arrangement with a first and a second roller 14 and 15, respectively.

In the direction of movement B of the material web 10 behind the application device 12, a charging rod 16 of a charging device is arranged, which extends parallel to the longitudinal direction of the electrically conductive roller 11 and interacts with it in the manner of a capacitor in order to electrostatically charge the material web 10 after it has reached the area of the Application device for the dampening solution has left. For this purpose, the charging rod 16 is connected to a high voltage source U and the electrically conductive roller 11 to ground.

As indicated in FIG. 3, the spraying device 13 has a multiplicity of turntables 17 which are arranged next to one another in a row parallel to the first roller 14. As shown in FIG. 4, the turntables 17 are attached to a preferably lower end of a drive shaft 18 and have a central pot area 19, which is adjoined by a flat spray flange 20 which extends radially outwards. To drive the turntable 17 their respective drive shafts 18 are connected to a motor 21 in a suitable manner, not shown in detail.

In order to define a defined spray area for each turntable 17 of the spraying device 13, an aperture 22 is arranged between the turntables 17 arranged in series and the first roller 14 of the application device 12, which has a passage opening 23 in the area of each turntable 17 for spraying onto the first roller 14 Has dampening solution. The turntable with the assigned aperture areas form individual sectors, which are advantageously individually controllable, so that different sections of the material web can be rewet in the desired manner depending on the requirements.

In order to ensure that the dampening solution sprayed onto the first roller 14 forms a required uniform or specifically adjusted dampening solution film on the roller surface thereof, the first roller 14 is provided with a water-friendly, that is to say well wettable, surface. Suitable materials for the surface of the first roller 14 are e.g. Glass, ceramics and chrome. Here, however, chromium is preferably used because the roller 14 must be designed for very high speeds.

The second roller 15, which is in engagement with the first roller 14 in order to take over the dampening solution film applied to the first roller 14 and to transfer it to the material web 10, is via a bracket arrangement 24 about the longitudinal axis 25 of the roller which is perpendicular to the plane of the drawing 14 pivotally arranged. Around the roller 15, which has a ground surface and is made of rubber or a rubber-elastic plastic, with a force F To press against the material web B guided over the roller 11, a pneumatic cylinder arrangement 26 or another suitable pressing force generating device acts on the bracket arrangement 24.

The material of the rubber roller (15) has a Shore hardness of 30 ° to 70 ° Shore, in particular about 50 ° Shore. The force F is then chosen so that a surface contact pressure of about 0.9 to 2.5 dN / cm ² , in particular 1.7 dN / cm ² results.

The charging bar 16 of the charging device, which extends parallel to the conductive roller 11, has, as shown in FIG. 5, a plurality of needle electrodes 27 which are arranged in a row at a distance from one another. The needle electrodes 27 are preferably aligned in the radial direction to the roller 11 and thus perpendicular to the material web plane or to the tangential plane to the material web.

The moistening of a moving material web is carried out with the described device as follows:

First, a constant temperature dampening solution, for example water or water mixed with surfactants or other chemical substances, is supplied to the pot area 19 of the turntable 17 of the application device 13. To spray droplets of dampening solution, the turntable 17 is rotated at a high speed, for example at 5000 rpm. with a turntable diameter of approximately 80 mm. As a result of the resulting high peripheral speed and depending on the surface tension of the dampening solution and the wettability of the turntable material, dampening solution droplets become or aerosols with a diameter of about 50 microns to 75 microns, preferably from 60 microns to 65 microns, flung from the edge of the turntable. These aerosols are sprayed onto the first roller 14 and form a precisely meterable dampening solution film there, which is removed from the second roller 15 and transferred to the moving material web 10 rotating around the conductive roller 11. When the dampening solution film is transferred from the rubber-elastic roller 15 to the material web 10, the dampening solution film is divided between the material web 10 and the roller 15. After moistening or wetting the material web 10 with dampening solution, it runs under the charging rod 16, whereby the wetted material web 10 is charged. This electrostatic charge initially causes the wetted material web 10 to lay tight and smooth against the conductive roller 11. At the same time, the electrostatic charge causes an equalization of the dampening solution film applied to the material web 10, so that the dampening solution film adheres securely to the material web even at very high transport speeds and can penetrate the material web evenly.

The device described for rewetting a printed paper web in web offset printing can be used in a particularly advantageous manner.

In web offset printing, a continuous paper web is drawn off from supply rolls at very high speeds, for example at speeds in the range of 5-8 m / s, and printed in four consecutive printing units in four-color printing, for example. Then the printed paper web is in a drying station at temperatures dried at approx. 200 ° C to solidify the printing inks so that they can no longer be damaged in the subsequent processing. The drying process is then followed by cooling of the printed paper web, which serves to quench the heated and dried printing inks.

As a result of the drying process for the printing inks, the paper web is also dried out, so that it only has a low residual moisture of approx. 3-5% after drying.

As a result of this very low residual moisture in the paper, the paper web is relatively brittle, so that it is difficult to process in the subsequent operations, such as folding, cutting and stapling, and tends to be damaged. In addition, uncontrolled changes in the dimensions of the paper web being processed occur when the paper absorbs moisture from the environment after the final processing operations. This leads to poor quality or unattractive printed products.

In order to give the printed and dried paper web its initial moisture again before the final processing, the device for moistening a moving material web described with reference to FIG. 1 can be arranged in a cooling station of a web offset printing press. For this purpose, as shown in FIG. 2, application devices 12 for applying dampening solution are arranged on at least one or preferably on two or more cooling rollers 11 of a cooling station of the printing press, of which only the first four cooling rollers 11 of, for example, a total of eight cooling rollers are shown. When using two applicators 12 for dampening solution are assigned to these two cooling rollers, each of which brings about an opposite deflection of the paper web 10, so that both surfaces of the paper web 10 are moistened one after the other.

The application devices 12 are therefore preferably arranged on the inlet-side cooling rollers 11 in order to achieve rewetting of the paper web as soon as possible after drying. In a cooling station with e.g. four cooling rollers, the first application device can e.g. be arranged on the second cooling roller 11, as shown in dashed lines in FIG. 2.

The arrangement of the application devices 12 on the input side enables the use of a constant temperature dampening solution, which has a lower temperature than the paper web in this area, e.g. 15 ° C, additional cooling of the printed paper web.

In order to prevent an uncontrolled change in the dimensions of the paper web 10, in particular in the width direction after moistening, 12 spreader rollers 28 can subsequently be provided on an application device, as shown in broken lines in FIG. 2, in order to avoid shrinking of the paper web in the transverse direction.

Although no such spreader rolls are shown in FIG. 2 following the last cooling roll 11 shown there in the direction of movement B of the paper web 10, these can also be provided there if required.

A major advantage of the device described is that it can be easily converted into a device Finished cooling station can be installed, the cooling rollers 11 being used as conductive rollers, which interact with the respective charging bar 16 and the second roller 15 of the roller arrangement.

Claims (27)

1. Process and device for moistening a moving printed then thermally dried web of material (10), especially a paper web that is cooled after drying and is guided during the cooling phase over a cooled guide element (11) while being wetted, on a least one face, with a moistening film which is applied on a roller (15) of a roller arrangement (14, 15) in contact with the guide element (11) and is transferred from the latter to the web (10),
   characterised in that
   the moistening film, which is produced by spraying and is applied onto the roller (15) in metered quantities, is pressed at a defined pressure into the web of material (10), while the latter is still hot and dry, by rolling it onto the web as the latter passes between the guide element (11) and the roller (15).
2. Process according to claim 1, characterized in that the web (10), after having been wetted with the moistening agent, is then passed through an electric high-voltage field, being thus electrostatically charged.
3. Process according to claim 2, characterized in that electrostatic charging of the web (10) trough the electrically conductive guide element (11) occurs before the web leaves the guide element and within the area of application of the moistening agent.
4. Process according to any of the preceding claims, characterized in that for forming a moistening film a moistening agent is sprayed onto another roller (14) of the roller arrangement (14, 15).
5. Process according to any of the preceding claims, characterized in that the web 10) is wetted with a moistening agent on both faces.
6. Process according to claim 5, characterized in that the two faces of the web (10) are wetted one after the other.
7. Process according to any of the preceding claims, characterized in that the moistening agent is applied on the web (10) in several successive steps.
8. Process according to any of the preceding claims, characterized in that the moistening agent is pure water or water containing admixtures.
9. Process according to claim 8, characterized in that the admixtures added to the water are tensides or other chemical substances that influence the surface tension and/or the diffusion properties or the electric characteristics of the water.
10. Process according to any of the preceding claims 2 to 9, characterized in that electrostatic charging is effected with a positive or, preferably, a negative high voltage in the range of 10 kV to approximately 45 kV.
11. Process according to any of the preceding claims, characterized in that the moistening agent is maintained at a constant temperature before being applied on the web (10).
12. Process according to claim 12, characterized in that the moistening agent is maintained at a temperature of between 15° C and 50° C.
13. Device for carrying out the process according to any of the preceding claims, having a moistening agent application device (12) comprising cooled guide elements (11) for guiding the web of material (10), a moistening agent spray device (13) and at least one roller (15) of a roller arrangement that acts upon the guide element (11) at a defined pressure, wherein a moistening film, that is to be applied in metered quantity onto the roller (15), can be produced by means of the moistening agent spray device (13) and the moistening film produced by the moistening agent spray device can be pressed at a defined pressure into the web of material, while the latter is still hot and while it passes between the cooled guide element (11) and the roller.
14. Device according to claim 13, characterized in that the guide element is a driven cooling roller (11).
15. Device according to claim 13 or 14, characterized in that the roller (15) of the moistening agent application device (12) coacts with another roller (14) being in direct engagement therewith, for transferring the moistening film, that has been sprayed onto its surface by the moistening agent spray device (13).
16. Device according to any of the preceding claims 13 to 15, characterized in that a charging device is arranged behind the moistening agent spray device (12), in the direction of movement (B) of the web (10), for electrostatically charging the wetted web of material (10).
17. Device according to claim 16, characterized in that the charging device comprises a charging electrode arrangement (16, 27), connected to a high-voltage source (U), which is arranged opposite the wetted surface of the web (10) and coacts with the electrically conductive guide element and/or cooling roller (11), which latter is preferably connected to ground.
18. Device according to claim 16 or 17, characterized in that the charging device comprises a charging bar (16), which is connected to the high-voltage source (U) and carries a plurality of spaced needle electrodes (27) extending substantially perpendicularly relative to the guided web (10).
19. Device according to claim 17 or 18, characterized in that the charging electrode arrangement (16, 27) is arranged at a distance of 20 mm to 40 mm from the guide element and/or the cooling roller (11).
20. Device according to any of the preceding claims 15 to 19, characterized in that the other roller (14) has a hydrophilic surface.
21. Device according to any of the preceding claims 15 to 20, characterized in that the other roller (14) has a ceramic surface or, preferably, a chromium surface.
22. Device according to any of the preceding claims 11 to 21, characterized in that the roller (15) of the moistening agent application device (12) is made from rubber or a rubber-elastic plastic material.
23. Device according to claim 22, characterized in that the Shore hardness of the roller (15) is between 30 and 70° Shore, preferably between 45 and 55° Shore, especially 50° Shore.
24. Device according to any of the preceding claims 13 to 23, characterized in that the roller (15) is pressed upon the surface of the web of material, in the area of the guide element (11), in such a way that the resulting surface pressure is in the range of 0.9 dN/cm² to 2.5 dN/cm², preferably in the range of 1.4 dN/cm² to 2.0 dN/cm², especially 1.7 dN/cm².
25. Device according to any of the preceding claims 15 to 24, characterized in that the roller (15) and the other roller (14) of the moistening agent application device (12) have ground surfaces.
26. Device according to any of the preceding claims 13 to 25, characterized in that the moistening agent spray device (13) comprises several sectors distributed over the width of the web of material (10), that preferably can be controlled individually.
27. Device according to any of the preceding claims 13 to 26, characterized in that a rotary-plate spray device is provided as moistening agent spray device (13).

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