EP0546483B1 - Device for coating a substrate with a substance - Google Patents

Description

The invention relates to a device for coating a substrate with a substance, in particular a film with an adhesive, the substance being applied via a loading head by perforating a template onto the substrate in cooperation with a counter-pressure roller or the like within a coating gap, the counter-pressure roller has a screen jacket with holes and a radially oriented suction flow is generated in an area in and / or after the coating gap in the counter-pressure roller.

Such devices are known in many forms and designs. For example, reference is made here to DE-OS 39 05 342, which shows a perforated cylinder in cooperation with a counter-pressure roller, between which a substrate is passed and coated with a substance. As a rule, the substance, which can be a thermoplastic, for example, is melted beforehand, so that they are applied to the substrate in the liquid state.

Such devices are used not only for coating textile substrates, but also for example for coating films with an adhesive or the like. All of these application options are intended to be encompassed by the present invention.

The coating of foils, in particular, poses considerable problems. The foils are usually very thin webs that are passed between the stencil and the counter-pressure roller. It is not enough that the film is guided in the coating gap, but it should also be subjected to a certain tensile stress so that it does not deform during the coating process. It is particularly important to take into account that heat is applied to the film in the coating gap, since the template is heated due to the melted substance.

This is a reason that the film is not pulled directly out of the coating nip, but that it remains on the counter-pressure roller after the coating nip and is only lifted off the counter-pressure roller after a certain circumferential area. As a result, the film is already cooled so that it can be subjected to higher tensile forces again. This is particularly important because the force with which the substrate is held on the counter-pressure roller results from the web or tensile stress after the counter-pressure roller and the friction of the substrate on the counter-pressure roller. If, for example, no tensile stress is exerted, the frictional force as a guide for the film is also lost. However, the stencil exerts considerable attraction on the film. The template, usually a metal cylinder, has perforations, the inner surface is usually a multiple of the area with which the substance to be applied is connected to the substrate. These perforations cause very high adhesive forces, so that a considerable force has to be used to pull the substance out of the perforation by means of the substrate. If the film on the counter-pressure roller does not have sufficient hold, ie if there is no sufficient tension and no sufficient friction, the film remains on the template or forms a trailing belly.

Furthermore, DE-A 29 43 894 discloses a device for the intermittent transport of preferably air-impermeable webs of goods. There two exemplary embodiments are described with which, for example, a web of material can be coated by means of a screen carriage and a roller. Furthermore, a device is shown that works with a roller as a suction roller and a pressure cylinder, between which the web is guided. The suction roller is provided with a suction segment to at least partially fix a web to the roller.

The present invention has for its object to provide a device of the above. To develop a way of ensuring that the substrate adheres to the counter-pressure roller and thus reliably pulls the substrate off the stencil.

To achieve this object, the suction flow is eliminated in a draw-off area for the coated substrate and compressed air flows out of the holes for lifting off the coated substrate.

This means that a vacuum is built up inside the screen jacket, at least in a partial area, which through the holes causes the substrate to contact the screen jacket is dressed. The question of tension or web tension is no longer of crucial importance, since the vacuum built up increases the friction of the substrate on the counter-pressure roller considerably. The effect is also independent of whether the film is warm after the coating gap and thus loses tensile strength. In any case, it is ensured that the film remains on the counter-pressure roller, ie the substance is pulled out of the perforation of the template immediately after the coating gap.

It should be emphasized that within the scope of the present invention the design of the counter-pressure roller and template is of secondary importance. It is also within the scope of the invention that, for example, the stencil and / or counter-pressure roller runs as an endless belt over rollers, so that a flat coating gap is formed for the substrate. All of these configurations are intended to be encompassed by the present inventive concept.

As a rule, it should be sufficient for the suction flow to be applied to the substrate only in a partial peripheral region of the counterpressure roller. This mainly depends on the holding forces that should be exerted on the substrate.

Since the substrate is to be pulled off the counterpressure roller after a certain circumferential area, it has proven advisable to release the vacuum at least in this area so that the removal of the substrate from the counter roller is facilitated. This lifting can also be supported in that, for example, compressed air is applied in this area through the holes in the screen jacket, which supports lifting of the substrate.

So that vacuum or compressed air is not applied to the entire counter-pressure roller or to a too large sub-area, it should be advisable to provide a ring inside the screen jacket, which is divided into chambers at least in some areas. These chambers are delimited by chamber walls, on which the screen jacket is then guided. The chamber walls can either be firmly connected to the screen jacket and sweep past an inner roller when the screen jacket is rotated. Another possibility is to insert the chamber walls into an inner roller so that the screen jacket runs on the chamber walls. There are certainly other configurations here as well conceivable, which should also be encompassed by the inventive concept.

Since a wide coating gap is preferably formed between the counter-pressure roller and the stencil, as is already described in DE-OS 39 05 342, the chamber walls should be designed to be elastic, at least in the area of this coating gap, since the screen jacket of the stencil lies in this coating gap. As a result, both the coating of the substrate and its guidance are significantly improved.

• Fig. 1 einen schematisch dargestellten Querschnitt durch eine erfindungsgemäße Vorrichtung zum Beschichten eines Substrates;
• Fig. 2 einen vergrößert dargestellten Teilbereich des Querschnitts aus Fig. 1;

Further advantages, features and details of the invention result from the following description of preferred exemplary embodiments and from the drawing; this shows in

• 1 shows a schematically illustrated cross section through an inventive device for coating a substrate;
• FIG. 2 shows an enlarged partial area of the cross section from FIG. 1;

A device P according to the invention for coating a substrate 1, in particular a film, has, according to. Fig. 1 a template 2, which cooperates with a counter-pressure roller 3. In the template 2 there is a loading head 4, via which a melted substance, not shown, is applied to the substrate 1 through perforations 5. For this purpose, the feed head 4 is provided with corresponding channels and a nozzle mouth 6, a further embodiment of the feed head 4, provided that it is known, is not to be described in more detail here.

In the present case, the template 2 is designed as a preferably metallic cylinder, the perforations 5 being formed in this metallic cylinder, and this metallic cylinder rotating in the direction z about an axis of rotation A. Corresponding drive elements for the template 2 are also neglected for the sake of clarity. However, it has a radius r which is so large that the feed head 4 can be accommodated in any case.

The counter-pressure roller 3 interacts with the template 2 and rotates about its axis B in the direction z 1. The counter-pressure roller 3 has a jacket 7, which is designed as a sieve, i.e. also perforated. The radius r 1 denotes the radius of the counter-pressure roller 3, i.e. the distance of the axis of rotation B from the screen jacket 7.

In the present exemplary embodiment, the axis of rotation A of the template 2 is arranged below the axis of rotation B of the counter-pressure roller 3. Of course, the concept of the invention also includes an inverted arrangement. Preferably, however, the axis of rotation A should maintain a distance a from the axis of rotation B which is less than the sum of the two radii r and r 1. This causes, as is shown in particular in FIG. 2, that the screen jacket 7 in a certain area b when interacting with the template 2 of this template 2 and in this way an extended coating gap 8 is formed. In the area of this coating gap 8, the substrate 1 is guided between the template 2 and the counter-pressure roller 3.

In the present exemplary embodiment, a ring 9 is formed within the counter-pressure roller 3 and is divided into chambers 10. For this purpose, chamber walls 11 are provided. In Fig. 2 it can be seen that 10 holes 12 are provided in the screen jacket 7 in the region of the chambers, through which either air can be sucked into the chambers 10 or air can be blown out of the chambers 10. The meaning of air intake or air blowing is described below.

How the chambers 10 are produced is said to be of minor importance. It is contemplated, for example, to design the interior of the counter-pressure roller 3 as a rubberized roller 13, in the rubber jacket 14 of which the chamber walls 11 are embedded as strips of material, for example made of sheet metal. The screen jacket 7 is then pushed onto this sheet metal strip and rotates in the direction z 1.

However, it is also conceivable that the chamber walls 11 are connected to the screen jacket 7 and graze along the roller 13. However, if the area b described above is formed, within which the screen jacket 7 of the stencil 2 rests over a wider coating gap 8, it must be ensured in any case that the chamber walls or their holder yields. This is indicated in Fig. 2 and can be solved with the rubber jacket 14 of the rubberized roller 13 in a simple manner, the chamber walls 11 then being inclined in the direction of rotation.

In the present exemplary embodiment, the substrate 1 is guided over a roller 15 before it enters the coating gap 8. The substrate 1 of the counter-pressure roller 3 then lies against it and is guided over a substantial part of the circumference of the counter-pressure roller 3 before it lifts off from the counter-pressure roller 3 and is fed to further processing or recycling.

The method of operation of the present device according to the invention for coating a substrate is as follows:

As is known and indicated above, the substance to be applied is pressed out of the feed head 4 through the nozzle mouth 6 into a perforation 5 and comes into contact with the substrate 1. However, the contact area 16 is relatively small in relation to the area with which the substance is in contact with the template 2 within the perforation 5. That is, the adhesive forces of the perforations 5 are very high. The result of this is that the substrate 1 tends to adhere to the template 2, so that further options must be sought so that the substrate 1 can be removed from the template 2 after coating the substance can be lifted off together with the coating.

For this purpose, on the one hand, the substrate 1 wraps around the counter-pressure roller 3 to a large extent. The force that holds the substrate 1 on the counter-pressure roller 3 results from the web tension when the substrate 1 is pulled off the counter-pressure roller 3 and the friction of the substrate 1 on the counter-pressure roller 3. If, for example, the web tension approaches zero, the friction of the Substrate on the counter-pressure roller 3 towards zero. As a result, the force that holds the substrate 1 on the counter-pressure roller 3 is absent and the substrate 1 remains on the template 2 for an undesirably long time, and considerable bulges can form.

If, for example, very thin foils, such as diaper foils, are to be coated with a substance, these foils cannot be subjected to a high web or tensile stress that would actually be required to hold the foil on the counter-pressure roller 3. In addition, the film is warmed up within the coating gap 8 and thereby loses tensile strength again. Therefore, it has not been possible to coat such thin films with a normal stencil and counter-pressure roller.

According to the present invention, however, a vacuum is generated in the chambers 10 in the region b of the coating gap 8 and thereafter so that radially directed forces act on the substrate 1 and hold this substrate 1 firmly on the counter-pressure roller 3. It is sufficient in itself if only a few chambers in and after the coating area are subjected to a vacuum, practice showing how many such chambers are necessary within the counter-pressure roller 3. It goes without saying that the more chambers are subjected to vacuum become, the more firmly the substrate 1 is held on the counter-pressure roller 3.

In the present example, the ring 9 is divided into chambers 10 as a whole. This should only be understood as an example, since only one or a few chambers after the coating gap 8 can suffice. However, it is also contemplated that in order to lift the substrate from the counter-pressure roller 3, the vacuum is not only released, if any, in the chambers provided there, but that the corresponding chamber or chambers are pressurized with compressed air in this extraction area 17, so that the substrate 1 is virtually blown off from the counter-pressure roller 3 from the inside.

Another positive feature can be seen in the fact that the counter-pressure roller 3 is preferably cooled, so that this alone increases the tensile strength of the substrate 1. This should be understood as an improved embodiment.

Claims (5)

1. Apparatus for coating a substrate with a substance, more especially a film with an adhesive, the substance being applied to the substrate via a feed head through perforations in a template in co-operation with a counter-pressure roller or the like internally of a coating gap, the counter-pressure roller (3) comprising a filter cover (7) with openings (12), and a radially aligned suction stream being produced in a region in and/or after the coating gap (8) in the counter-pressure roller, characterised in that the suction stream is removed in a discharge region (17) for the coated substrate (1), and compressed air flows from the openings (12) to raise the coated substrate (1).
2. Apparatus according to claim 1, characterised in that the counter-pressure roller (3) comprises a ring (9) radially communicating with the filter cover (7), said ring being divided, at least partially, into chambers (10).
3. Apparatus according to claim 2, characterised in that the chambers (10) are formed from chamber walls (11) which are connected to the filter cover (7).
4. Apparatus according to claim 2, characterised in that the chambers (10) are formed from chamber walls (11) which sit in a cover (14) of an internal roller (13), while the filter cover (7) is slipped over the chamber walls (11) and rotates above said walls.
5. Apparatus according to claim 3 or 4, characterised in that the chamber walls (11) are resiliently mounted and follow a yielding of the filter cover (7).

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