Coating apparatus – With heat exchange – drying – or non-coating gas or vapor... – Plural treatments
Patent
1996-03-21
1997-11-11
Pianalto, Bernard
Coating apparatus
With heat exchange, drying, or non-coating gas or vapor...
Plural treatments
118 68, 118115, 118117, 118118, 118119, 118123, 118126, 118202, 118203, 118222, 118223, 118249, 118255, 118419, 118427, B05C 1100
Patent
active
056859090
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a process for producing paper webs coated on both sides, in particular so-called LWC-papers, in a paper making machine. The invention additionally relates to an apparatus for carrying out such a process.
A process comprising coating one side of a dried paper web in a first application nip between a first application roll and a first opposing element, drying the coating, then coating the other side of the web in a similar second application nip and drying the coating is known from DE 43 02 437 A1. According to FIG. 1 of this publication, the paper web dried in the paper making machine is initially supplied via a smoothing or calendering unit to a first coating plant. In this, one side of the paper web is indirectly coated with a coating mass by means of a first application roll which together with a first opposing roll forms a first application, nip. This takes place by forming a coating film on the shell of the application roll by means of a nozzle application unit and the film is then transferred by the application roll onto the paper web. As a metering element, the coating plant has a roll doctor with a profiled shell surface. The paper web is then dried and supplied to a second coating plant in which the other side of the paper is also indirectly coated. After a further drying process, the finished paper web coated on both sides is rolled up.
A similar process is described in EP 0 596 365 A1 published after the priority date of the present invention.
In DE 43 02 437 A1 already cited, various problems are described which occur in the production of relatively thin paper webs containing recycled paper and intended to be coated on both sides. The present invention is also based on the same problems. However, the known process solves only a part of the described problems. In particular, the known process has not successfully produced a paper web coated on both sides that satisfies high standards, in particular with respect to a uniform smoothness which is as great as possible and with respect to a high gloss.
SUMMARY OF THE INVENTION
The invention is therefore based on the object of further developing the known process to the extent that paper webs coated on both sides can be produced with substantially greater smoothness and gloss values than before. It also forms part of this object to additionally provide an apparatus which is suitable for carrying out this process.
This object is solved by the combination of features of either metering the coating mass onto one of or both of the application rolls using in each case a smooth doctor element and then calendering the web after the second drying step, or as an alternative, calendering after at least partially drying both sides of the web while operating the process at a web speed of at least 900 m/min. The coating is applied to the application roll before the roll surface enters the application nip.
Amongst others, the recognition led to the invention that the use of a smooth doctor element to form the coating film on each of the application rolls in connection with a calendering of the paper web, coated on both sides, by means of at least one calendering unit leads to substantially higher smoothness and/or gloss values than before. It is presumed that this surprisingly good result is achieved in that the use of a smooth doctor element, compared with the commonly known profiled roll doctor, exerts a higher shearing effect on the coating color and that the plate-shaped pigment particles are aligned on account of this in such a manner that they lie flat on the paper surface from the outset. As a result of this, after the following calendering process, there is to a much lesser extent than hitherto the tendency that the surface of the finished paper has a matt characteristic.
The use of a coating blade as a doctor element is possible. However, the use of a smooth roll doctor is preferred because the transverse profile of the coating is capable of being more easily controlled with this, i.e. it succeeds wit
REFERENCES:
patent: 2970564 (1961-02-01), Warner
patent: 4548840 (1985-10-01), States et al.
patent: 5176955 (1993-01-01), Ejiri et al.
patent: 5271998 (1993-12-01), Duckett
Finnish Examiner's Official Action (and translation of same) dated 12 Sep. 1996.
FI-952004 (English equivalent is U.S. Patent Application No. 08/577,419 filed Dec. 22, 1995.).
German Search Report dated 20 Jan. 1995 (P 44 14 949.2).
JP 61-18467 A., In: Patents Abstracts of Japan, C-353, Jun. 13, 1986, vol. 10, No. 166.
Aksnes Fredrik
Berg Anette
Kustermann Martin
Reich Stefan
Riepenhausen Bernd
Pianalto Bernard
SCA Graphic Sundsvall AB
Voith Sulzer Papiermaschinen GmbH
LandOfFree
Device for producing paper webs coated on both sides does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Device for producing paper webs coated on both sides, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Device for producing paper webs coated on both sides will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1225540