Paper making and fiber liberation – Processes and products – With coating after drying
Reexamination Certificate
1999-08-26
2001-02-27
Fiorilla, Christopher A. (Department: 1731)
Paper making and fiber liberation
Processes and products
With coating after drying
C162S204000
Reexamination Certificate
active
06193840
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for producing surface-treated paper, in particular fine paper.
Further, the present invention relates to a dry end of a paper machine intended for the production of surface-treated paper which has a forward dryer section, also referred to as a “predryer section” or a “main dryer section”, and a subsequently arranged on-line or off-line finishing section.
BACKGROUND OF THE INVENTION
In the prior art, in multi-cylinder dryers of paper machines, twin-wire draw and/or single-wire draw is/are employed. Drying groups applying a twin-wire draw include two wires which press the web, one from above and the other one from below, against the heated cylinder faces of the drying cylinders. Between the rows of drying cylinders, which are usually horizontal rows, the web has free and unsupported draws. The free draws are susceptible to fluttering which may cause web breaks, in particular since the web is still relatively moist and, therefore, has a relatively low strength. For this reason, in recent years, increasing use has been made of a single-wire draw in which each group of drying cylinders has only one drying wire. The web runs on support of the single drying wire through the entire group so that the drying wire presses the web on the drying cylinders against the heated cylinder faces thereof, and whereas, on the reversing cylinders or rolls arranged between the drying cylinders, the web remains at the side of the outside curve. Thus, in a single-wire draw, the drying cylinders are placed outside the drying wire loop and the reversing cylinders or rolls are situated inside the drying wire loop.
In prior art normal groups having a single-wire draw, the heated drying cylinders are typically arranged in an upper row and the reversing cylinders are therefore arranged in a lower row, below the upper row. The upper row and lower row are generally horizontal and parallel to one another. The current assignee's Finnish Patent No. 54,627 (corresponding to the current assignee's U.S. Pat. No. 4,202,113, the specification of which is hereby incorporated by reference herein) describes an arrangement wherein normal groups having a single-wire draw and so-called inverted groups having a single-wire draw are arranged one after the other. In typical inverted groups, e.g., of the type shown generally in U.S. Pat. No. 4,202,113, the heated drying cylinders are arranged in the lower row and the reversing suction cylinders or rolls are arranged in the upper row. This arrangement utilizing normal and inverted groups enables a principle objective to be achieved, i.e., to dry the web symmetrically from both of its sides.
With respect to additional prior art, reference is made to published International Patent Applications WO 88/06204 and WO 88/06205 (assigned to Beloit Corp.) which describe dryer sections.
Accordingly, in the following description, the terms “normal (drying) group” and “inverted (drying) group” are used to denote the cylinder groups having a single-wire draw as described above, as such is accepted terminology to those skilled in the art. The expression “single-wire draw” is equivalent to the terms “single felting” and “single tier” which are interchangeably used in the art. Similarly, the expression “twin-wire draw” is synonymous with the expression “double felting” as used in the art. Also, in the following description, the term “wire” when used to denote a wire in the dryer section or finishing section encompasses other types of dryer section clothings such as fabrics, which are more common today than wires, and felts.
In dryer sections that comprise inverted and normal drying groups, various problems have occurred. The present invention is directed toward a resolution of these problems. For example, problems have been encountered in the runnability of the dryer section and in the threading of the web, problems arising from differences in the speeds of different wires, problems in the removal of broke especially in inverted groups, as well as problems related to the control of transverse shrinkage of the web. These problems tend to become worse as the running speed of the paper machine becomes higher. As to the problems of control of the transverse shrinkage of the web, the use of a single tier dryer section in general provides better control than a dryer section applying double felting.
With respect to prior art involved in and related to the present invention, reference is made to the following patent publications and articles published in journals:
W. Haessner, “Trocknungstechnik und deren Entwicklung”; Das Papier 44, 10A, 1990;
“The Valmet Sym-Run Concept”, Paper Asia, May/Jun 1992;
J. Yli-Kauppila, “Dryer Section for High Speed Paper Machines”, Proceedings of the Helsinki Symposium of Alternate Methods of Pulp and Paper Drying, Helsinki Jun. 4-7, 1991;
Sam Palazzolo, “No-draw drying”, Tappi Journal, September 1990;
W. Leitenberger, “Die Contirun-Trockenpartie fur schnellen, sicheren Bahnlauf”, Das Papier, Heft 6, 1992;
U.S. Pat. Nos. 3,753,298, 3,868,780, 4,602,439, 4,972,608, 4,982,513, 5,022,163, 5,065,529, 5,146,696, and 5,177,880;
V. Korhonen and A. Kuhasalo, “Ropeless tail threading from press to reel”, World Pulp & Paper Technology 1993;
H. Lepisto und P. Eskelinen, “Verbesserung der Lauffahighkeit schneller Papiermaschinen mit Hilfe neuer Ventilationseinrichtungen”, Das Papier 1985, Heft 10A;
Lindberg, Juppi, Eskelinen, “High Speed Dryer Section Developments for Sheet Stability”, 78th Annual Meeting, Technical Section CPPA, 1992.
With respect to the prior art closely related to the invention, reference is further made to the current assignee's Finnish Patent No. 91,900 (corresponding to U.S. patent application Ser. No. 07/808,161, now U.S. Pat. No. 5,416,980, the specification of which is hereby incorporated by reference herein), in which a method is described for drying a web in the dryer section of a paper machine, in particular for reducing the tendency of curling of the paper web. In the method described in FI '900, the paper web is dried on drying cylinders, against whose heated faces the paper web is pressed by means of a drying wire. In the dryer section, groups of drying cylinders are used, in which twin-wire draw and/or single-wire draw is/are applied. In this method, among other things, it has been considered inventive that in the dryer section, hot water vapor is fed substantially onto the entire width of the paper web. By means of this vapor, tensions that have been formed or that tend to be formed in the fiber mesh in the paper web are relaxed by means of heat and moisture in the area of their formation or substantially immediately thereafter.
In the prior art, a dryer section is known which is composed exclusively of the above drying groups with a single-wire draw. In these groups, between the contact-drying cylinders placed in the upper rows in the groups, normal small diameter suction rolls that are provided with inside (internal) suction boxes have been used. One particular prior art dryer section of interest is a dryer section supplied by, e.g., J. M. Voith GmbH, and situated at PM 1, Stora Feldmuehle, Reisholz, Duesseldorf, Germany which initially contained only single-tiered groups in the predryer section but later was modified to provide a double felted group as the last group in the predryer section.
A drawback of these small diameter suction rolls is the high requirement of negative pressure and suction energy because, owing to the small diameter of these rolls, high centrifugal forces arise on these rolls which tend to separate the web from the drying wire. By means of the curve sectors of small radius, the suction rolls also produce a rather large relative difference in speed between the drying wire and the web, which is in many respects unfavorable. Further drawbacks include the wear of the seals at the suction box inside the suction rolls and the repeated requirement of servicing of these seals as well as the high noise level. In this prior art paper machine, the over
Elijoki Seppo
Ilvespaa Heikki
Kerttula Reima
Kuhasalo Antti
Fiorilla Christopher A.
Steinberg & Raskin, P.C.
Valmet Corporation
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