Coating processes – With post-treatment of coating or coating material – Solid treating member or material contacts coating
Patent
1996-12-30
1999-02-09
Bell, Janyce
Coating processes
With post-treatment of coating or coating material
Solid treating member or material contacts coating
427356, 427428, 118106, 118108, 118123, 118207, 118244, B05D 312, B05C 1102
Patent
active
058691430
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a national phase application of PCT/EP95/02464 filed Jun. 24, 1995 and based, in turn, on German national application P4429964.8 filed Aug. 24, 1994 under the International Convention.
TECHNICAL FIELD
FIELD OF THE INVENTION
There are known processes and devices for the coating of paper or cardboard webs, which are based on the principle that at first an excess of coating material is applied to the web by means of a coating system and then the excess is wiped off by means of a doctor element, until the desired coating weight is reached.
BACKGROUND OF THE INVENTION
State of the Art
The coating systems for excessive application can use applicator rollers (DE C 36 23 402) and applicator chambers which are open towards the web (EP-C 0 051 698). The doctor elements are usually mechanical doctor elements, such as scraping blades (DE-C 36 23 402), wiper rods (DE-C 30 22 955), wiper bars (EP-C 0 109 520) and so-called air knives, which wipe off the excess with compressed air coming from a slotted nozzle (DE-A 40 14 463). In order to achieve higher production speeds, i.e. higher speeds of the web of material, in these known processes the web of material is guided around a backing roller while the coating material is applied in excess and while the excess is wiped off, and is therefore supported by the roller over its entire width during the coating process.
Practice has proven that with the coating using the known application and doctoring systems, it is very difficult to obtain an end product with an even, and therefore high-quality coating, when working with very high production speeds of over 1000 m/min. At high web speeds, irregularities occur in the finished coating, such as variations in the coating weight, stripes or streaks.
OBJECTS OF THE INVENTION
It is the object of the invention to provide an improved generic process and a generic device so that at very high web speeds a coating with an even finish can be achieved.
SUMMARY OF THE INVENTION
This object can be achieved based on the concept that errors in the finished coating after the excess is wiped off can be traced back to irregularities of the excess film, which have not been evened out during doctoring. Particularly in cases of coating at high web speeds, considerable centrifugal forces directed away from the web act upon the coating material, due to the convex web guidance, i.e. a web guidance which is curved towards the uncoated side, during the application and the removal of the excess material. The centrifugal forces cause the coating material to spray away and/or lead to the irregularities, e.g. to the formation of stress lines in the film of coating material reaching the doctoring device. According to the invention the web is concave, i.e. curved towards the coating side. This way the centrifugal forces act in the direction towards the web, so that not only are the above-mentioned negative effects avoided, but due to the centrifugal forces a uniformization of the film on the coating material is effected before dosage.
As a further advantage it can be mentioned that the negative effect exerted by the air incorporated in the coating material or entrained by the web is minimized. The air contained in the coating material or existing on the web can lead to errors in the finished coating, even to uncoated portions in the end product. The centrifugal forces directed towards the web push away the air from the web prior to dosage, so that it escapes, or at least accumulates on the side of the excess film facing away from the web. The complete coating of the web with coating material is insured even with air inclusion.
BRIEF DESCRIPTION OF THE DRAWING
The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:
FIGS. 1, 2, 3, 4, 5, 6 and 7 show in principle the invention with various application and doctoring systems in diagrammatic form;
FIG. 8 is a side el
REFERENCES:
patent: 3722465 (1973-03-01), Krautzberger
patent: 4537801 (1985-08-01), Takeda
patent: 4738877 (1988-04-01), Krautzberger
patent: 5028450 (1991-07-01), Naka et al.
patent: 5348768 (1994-09-01), Shibata et al.
patent: 5397600 (1995-03-01), Shibata et al.
patent: 5569494 (1996-10-01), Suzuki et al.
JP 1-231969 Japanese Patent Abstract C-665, 13 Dec. 1989, vol. 13, No. 562.
Becker Ingo
Knop Reinhard
Bell Janyce
Dubno Herbert
Jagenberg Papiertechnik GmbH
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