EP0777785B1 - Method and device for coating continuous strips of material, in particular paper or cardboard - Google Patents

Abstract

PCT No. PCT/EP95/02464 Sec. 371 Date Dec. 30, 1996 Sec. 102(e) Date Dec. 30, 1996 PCT Filed Jun. 24, 1995 PCT Pub. No. WO96/06226 PCT Pub. Date Feb. 29, 1996A process for coating a web of material includes the steps of displacing the web along a path in a travel direction, applying a coating material at an application located along the path to forming a curved segment of the web, and wiping off the excess of the coating material.

Description

Technical field

There are various methods and for coating paper or cardboard webs Devices known that work on the principle that first by means of a Application system Coating material applied in excess to the running web and then the excess by means of a metering element except for the desired line weight is doctored off.

State of the art

Application rollers (DE-C 36 23 402) and application chambers open to the material web (EP-C 0 051 698) are known as application systems for the excess application.
As metering elements, it is known to use mechanical doctor elements such as doctor blades (DE-C 36 23 402), doctor rods (DE-C 30 22 955), doctor blades (EP-C 0 109 520) and so-called air knives, which strip off the excess with compressed air from a slot nozzle (DE-A 40 14 463). In order to be able to achieve higher production speeds, that is to say higher web speeds, in this known method the material web is usually guided in excess when applying the coating material and by scraping off the excess around a counter roller and is thus supported by the latter over its entire width during the coating process.

When coating with the well-known application and dosing systems, the Practice has shown that at very high production speeds of more than 1000 m / min is very difficult, an end product with a uniform and therefore to produce high quality line art. At high web speeds there are irregularities in the line pattern in the form of line weight fluctuations, Streaks or streaks.

Presentation of the invention

The invention is based, a generic method and a task Generic device to improve so that at very high web speeds a coating with a uniform line pattern is achieved.

This object is achieved with the features of patent claims 1 and 7, respectively.

The invention is based on the knowledge that errors in the line drawing after Scraping off the excess due to unevenness of the excess film that are no longer compensated for during dosing. Especially when Coating at high web speeds work due to the convex, i.e. H. web guide curved towards the uncoated side between application and scraping the excess of significant centrifugal forces onto the coating material a, which are directed away from the web. The centrifugal forces lead to Spraying of coating material and / or to an irregularity, e.g. B. to form tension lines of the film reaching the dosing element Coating material. According to the invention, the track is concave, that is to say coated Curved side. The centrifugal forces thus act in the direction of the path, so that not only the negative effects listed above are avoided, but even by the centrifugal forces an equalization of the film Coating material is effected before dosing.

Another advantage is that the negative effects of in the coating material air trapped or entrained by the web is reduced will. Air in the coating material or on the web can lead to errors in the line drawing lead to uncovered places on the end product. The one to the train Executed centrifugal forces force the air off the web before dosing away, so that it escapes or at least accumulates on the side facing away from the train Side of the excess film, which is then doctored off. The complete wetting of the web with coating material is even with air pockets guaranteed.

The subclaims contain preferred, since particularly advantageous, configurations The drawing serves to explain the invention in a simplified manner illustrated embodiments.

Brief description of the drawing

Figures 1 to 7 show in principle the invention with various orders and Dosing systems.

FIG. 8 shows a concrete embodiment in a side view.

Ways of Carrying Out the Invention

All coating devices shown in the figures have an application system 1 and in the running direction of the paper or cardboard web 2 arranged behind a metering system 3 with a dosing element. Application system 1 uses coating color as Coating material applied in excess to the paper or cardboard web 2 and then from the dosing element of the dosing system 3 to the desired one Line weight scraped off again.

Known application systems are used to apply the coating color: the Embodiments according to Figures 1, 2, 5, 6, 7 and 8 are roller applicators with an applicator roller 6 scooping from an ink pan 4, the roller or driven in the opposite direction to the web 2, the excess film 7 is applied thereon.

The embodiment according to FIG. 3 shows a so-called short dwell coater a nozzle chamber 8 open towards the web 2, the coating color in excess and with increased pressure is supplied. The application chamber 8 is on its outlet side of the dosing element, e.g. B. a doctor knife 9, completed.

To strip off the excess film 7 to the desired coating weight also known metering systems used: In the embodiments according to Figures 1, 2, 4, 6, 7 and 8 contain the metering systems 3 a scraper 9 as Dosing element. The scraper knife 9 is in one with the foot to the web 2 movable back in a scraper beam 10 clamp beam 11 attached. The scraper knife 9 of a support bar 12 supported, which is adjustable on the top of the doctor bar 10 is attached. The scraper bar 10 is around the metering line (= contact line the scraper knife tip on the track 2) is pivotally suspended in a frame. With this construction, the contact pressure of the doctor knife 9 can be the web 2 by moving the scraper knife base with the clamping bar 11 set without the one set by pivoting the scraper bar 10 To change the angle between the scraper knife tip and the web 2.

In the embodiment according to FIG. 4, a short dwell applicator is used with a Scraper knife 9 is used to place a pre-metered excess film 7 on the web 2 to apply. The final dosing is done with a blade dosing system that also has a scraper knife 9 as a final metering element. The embodiment according to figure 5 contains a roller applicator 1 and a metering system 3 with an air knife as Dosing element. The air knife consists of an over the width of the web 2nd extending slot nozzle 13 which is connected to a compressed air supply. Out a jet of compressed air is directed against the excess film 7 to the slot nozzle 13 to strip off the excess to the desired coat weight.

An essential feature of the invention is the course of the web 2 between the Applying the excess film 7 and dosing with the dosing element 9 or 13 to the desired coat weight. At least on a section between the Applying and dosing the web 2 is curved towards the coated side (= concave). On the concave section, the track 2 is curved so that the axis of curvature parallel to the web 2 and transverse to the web running direction on the Coating side runs at a distance from this. The web 2 is preferred on the the entire distance between application and dosing is concavely curved (Figure 1). If the route is concave only on part of this route, the track will 2 - as shown in Figure 2 - when applying the excess and / or when dosing preferably led straight. Following the concave path, the path 2 up to dosing straight or only slightly convex, i. e. for the uncoated Curved side, guided, so that the positive effects of the concave web guide cannot be undone or only to a non-disturbing extent. A slight convex curvature can have the advantage that the Metering element 9 does not spray scraped material against the web 2. Because the concave curved section compensates for irregularities in the excess film 7, it is possible under certain circumstances, the web 2 in front of the concavely curved Leg, e.g. when applying the excess film 7, convexly curved lead without errors in the line diagram after dosing.

Figures 6 and 7 show two ways of realizing the concave path:

In the embodiment according to FIG. 6, the paper or cardboard web 2 is two guide rollers 14, 15 arranged parallel to one another at a distance. Between the Application system 1 and the metering system 3, the web 2 by means of an air guide nozzle 16 concavely curved. Compressed air from the air guide nozzle 16 is coated against Side of the web 2 passed, the web tension is set so that the sets the desired curvature. The outlet-side guide roller 15 also supports the Lane 2 when dosing against the contact pressure of the doctor knife 9. In addition The curvature can be due to or instead of an overpressure on the coated web side the web 2 also causes a vacuum on the uncoated side will.

Figure 7 shows the principle of a preferred embodiment, in which the coated and thus sensitive web 2 during the concave guidance of a corresponding curved guide surface is supported on the uncoated side, preferred with a circumferential support band 17. That preferably from an elastic Support belt 17 made of material is also deflected by the two deflecting the web 2 Guide rollers 14, 15 deflected. One or both idlers 14, 15 are preferred only the inlet-side idler 14 are driven. The drive only on the inlet side Guide roller 14 has the advantage that the strand 2 supporting the strand 18 under is less voltage and can therefore be curved more easily concave. The curvature of the strand 18 is caused by a vacuum between the two Runs and / or by an overpressure acting from the outside against the coated side causes, e.g. to that described in the embodiment according to FIG Wise. Instead of a circumferential support band 17, concavely curved ones can also be used mechanical guide surfaces are used against which the web 2, z. B. with compressed air, is pressed.

The coating device shown in principle in FIG. 7 is shown in FIG. 8 shown in more detail:

The coating device has 2 frame parts on both long sides of the web 5 19, in which the two are formed as backup rollers at a distance from one another Guide rollers 14, 15, the application system 1 and the metering system 3 are suspended. Both support rollers 14, 15 are of the endless, over the working width of the Circumferential device extending support band 17 made of an elastic material.

The support belt 17 is at the web speed of the web 2 from the support roller 14 driven, which is connected to a rotary drive, not shown. The application system 1 contains an application roller 6, which is wrapped around the web 2 Area against the support roller 14 is adjustable. The preferably co-moving to Counter roller 14, that is to say in the opposite direction of rotation, driven application roller 6 draws from a paint tray 5 and is together with this on a swivel lever 20 can be raised and lowered.

That in the web running direction at a distance behind the applicator in the area of the support roller The dispensing system 3 arranged in 15 is in principle in the explanation of FIG. 1 described. The scraper bar 10 with the scraper knife 9 carrying Clamping bar 11 is between two side parts 21 around the doctor knife tip hung pivotably. The side parts 21 themselves are with the scraper bar 10 pivoted, e.g. B. to perform a change of the doctor knife 9 to be able to. The of the circumference of the support rollers 14, 15 and the free strand 18 the support band 17 limited space 22 is sealed and can be subjected to negative pressure, around the desired concave curvature of the web 2 supporting To be able to adjust trums 18. So that the web 2 rests securely on the strand 18 and thus, even at high speeds whose curvature follows, is the coated one Side of the web 2 between the applicator roller 6 and the metering element 9 with Compressed air can be applied. For this purpose, the space 23 between the application roller 6 and the metering element (scraper knife 9) with sealing elements with the exception of the Lane 2 open side sealed and connected to a compressed air supply. The Lane 2 is thus pressed without contact against the guide surface formed by the strand 18.

When coating, the web 2 is first of all from the inlet-side support roller 14 deflected, it lies on the outside on the support belt 17. From the application roller 6 coating color is applied in excess to the web 2, which then, from supported the strand 18 of the support band 17, concavely curved to the second Back-up roller 15 is guided. The scraper knife 9 is in the run-up area of the web 2 arranged on the support roller 15 so that the support roller 15 the web 2 against the Pressure of the doctor blade tip is supported before this from the support roller 15 in such a way largely convex that negative effects such as paint splashing, Stress ring formation etc. occur.

Claims (12)

1. A method for coating continuous strips (2), in particular of paper or cardboard where, typically, an initial excess amount of the coating substance is applied to the moving strip (2) by an application device and the excess coating substance is subsequently removed by a doctor device to produce the required coating thickness where the strip of material (2) is curved in a concave manner along part or all of the path between the application and doctor devices in such a way that the axis of curvature runs parallel to the strip of material (2) and across the line of travel of the strip on its coated side and at a distance from it.
2. A method as disclosed in Claim 1 where the strip of material (2) is guided along a concave, curved path between the application and doctor devices.
3. A method as disclosed in Claim 1 where the strip of material (2) follows a straight or only slightly convex path, i.e. curved away from the coated side, after the concave section of its path and as far as the doctor device.
4. A method as disclosed in one of the Claims 1 to 3 where the strip of material (2) is supported along its concave path on its uncoated side by a suitably curved guiding surface, in particular an endless moving support belt (17).
5. A method as disclosed in Claim 4 where the strip of material (2) is pressed against the guiding surface by means of compressed air.
6. A method as disclosed in one of the Claims 1 to 5 where the concave curvature of the strip of material (2) is caused by underpressure on the uncoated side and/or overpressure on the coated side.
7. A device for coating continuous strips (2), in particular of paper or cardboard using an application system (1) which initially applies an excess amount of the coating substance to the moving strip (2) and a doctor device (9, 13) which subsequently removes the excess coating substance where the strip of material (2) is curved in a concave manner along part or all of the path between the application and doctor devices in such a way that the axis of curvature runs parallel to the strip of material (2) and across the line of travel of the strip on its coated side and at a distance from it.
8. A device as disclosed in Claim 7 where the strip of material (2) follows a concave, curved path for the entire distance between the application (1) and dosing (9, 13) devices.
9. A device as disclosed in Claim 7 where the strip of material (2) follows a straight or only slightly convex path, i.e. curved away from the coated side, after the concave section of its path and as far as the doctor device (9, 13).
10. A device as disclosed in one of the Claims 7 to 9 where the strip of material (2) is supported along the concave section of its path on its uncoated side by a suitably curved guiding surface, in particular an endless moving support belt (17).
11. A device as disclosed in Claim 10 where contactless means (16, 23) are provided within the concave section of the path on the coated side in order to shape the strip of material (2) to the guiding surface.
12. A device as disclosed in one of the Claims 7 to 11 where means are provided within the concave section of the path on the uncoated side in order to generate underpressure and/or on the coated side in order to generate overpressure.

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