Coating apparatus – Immersion or work-confined pool type – Work-confined pool
Patent
1988-11-08
1991-05-28
Beck, Shrive
Coating apparatus
Immersion or work-confined pool type
Work-confined pool
118411, B05C 3132
Patent
active
050184784
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of coating a paper web utilizing a coating apparatus, having a pressurized coating chamber in communication with the web to be coated.
The invention also relates to an apparatus for coating a moving paper web, including a pressurizable coating chamber to be filled with a coating paste, substantially of a width equal to that of the web, and which chamber, in use, communicates with said web. The coating chamber is defined by the web, on the inlet side by the rear wall of the coating apparatus and on the outlet side by the front wall of the coating apparatus as well as by a wiper arranged at the upper part of the front wall for removing excess coating paste.
Coating apparatuses with a pressurized coating chamber, e.g. so called short dwell coaters, have an elongate opening through which the coating paste comes into contact with the web. The coating zone is sealed on the inlet side of the web by the rear wall of the coating apparatus or by some other sealing wall. At the outlet side of the web the wiping member prevents the free flow of the coating paste from the coating zone. The edges of the coating zone are sealed by edge seals or edge limiters in order to prevent the coating paste from flowing out from the edges of the apparatus.
The edge seals in the pressurized coating apparatuses cause problems. It has been found difficult to provide sealing devices which operate satisfactorily and reliably. Some of the coating paste remains on the edge zones, dries and causes running problems in the coating, breaks and cleaning operations. Additionally, the coated paper in the edge zones is of bad quality and cannot, therefore, be fully utilized.
The main direction of developments in attempting to deal with the problems has been to minimize the leakages of coating paste at the edge seals. For example, Finnish patent 72902 discloses a throttling member arranged to improve the sealing effect of the edge seal. As a consequence of this, the coating paste which has reached the coating zone does not immediately meet the edge seal, the result of which is that the coating pulp at the edge seal remains substantially stationary and the leak of coating paste through the edge seal is minimized.
Finnish patent application 854053 discloses an arrangement which tends to minimize the overflow of the coating paste with a two-piece edge seal. The overflow gap can thus be reduced to considerably less than 1.5-2 mm so that only little paste escapes from the overflow gap.
U.S. Pat. No. 4,354,452 discloses a soft edge seal, which eliminates or minimizes the overflow of the coating paste. The edge seal comprises a soft member, which when filled with air or liquid seals the end area of the coating zone.
The elimination of the problems has not been entirely successful in the above-mentioned mechanical constructions. The solutions have proved less successful in practice, while the basic problems, i.e. uneven coating at the edge areas and disturbances in the coating process still remain unsolved, because in the coating chamber, in the edge zone of the freely flowing coating paste and the slow coating paste at the edges, deposition of paste, thickening and drying take place.
The application of coatings to paper webs of different width has also been difficult.
One object of the present invention is to avoid or minimize the above-mentioned deficiencies and to provide even better coating conditions, by means of which the slowing down of the coating paste flow at the edge areas and problems caused by the slower, thicker paste are avoided or minimized.
Another object of the invention is to provide an improved coating apparatus with better operating qualities, wherein the coating paste flows optimally also at its edge zones.
Yet another object of the invention is to provide a coating apparatus which is applicable according to the width of the web and with which variations in the width of the web can be taken into account and the web can be optimally utilized.
Recently it has been discovered that too careful a s
REFERENCES:
patent: 4354452 (1982-10-01), Patterson
patent: 4398494 (1983-08-01), Alheid
patent: 4426412 (1984-01-01), Gebert et al.
patent: 4434194 (1984-02-01), Gebert et al.
patent: 4440105 (1984-04-01), Jelfema
patent: 4440809 (1984-04-01), Vreeland
patent: 4503804 (1985-03-01), Damrau
patent: 4836133 (1989-06-01), Wohrle
A. Ahlstrom Corporation
Beck Shrive
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