Paper making and fiber liberation – Processes and products – With coating after drying
Reexamination Certificate
2002-04-15
2004-03-02
Griffin, Steven P. (Department: 1731)
Paper making and fiber liberation
Processes and products
With coating after drying
C162S205000, C162S125000, C162S358100, C162S358200, C162S358300, C162S361000
Reexamination Certificate
active
06699362
ABSTRACT:
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
The invention relates to a method for the manufacture of paper, in particular of fine paper, and to paper machine lines therefor.
In this description, by fine paper is meant uncoated fine paper and coated fine paper. The basis weight of uncoated fine paper is usually 40 to 230 g/m
2
, that of coated fine paper 60 to 250 g/m
2
. Typical pulp for the manufacture of fine paper comprises chemical fibres: short fibres which are obtained, for example, from birch and eucalyptus, and a long-fibre material obtained from softwood trees is generally added to this. The proportion of mechanical pulp is generally below 10%. About 15 to 30% of filler is added to the pulp, and the filler may be calcium carbonate, kaolin and/or other suitable mineral pigments. Recently, in the manufacture of fine paper, increasing use has also been made of recycled fibres.
The essential quality properties of coated woodfree fine paper include gloss, smoothness, bulk, opacity, and brightness, typically:
gloss is >70% (Hunter),
smoothness PPS
10
<1.1, bulk >0.8 cm
3
/g
opacity >92%, and
brightness >80%.
However, all of these quality values are seldom achieved at the same time on fine paper machines according to the state of the art.
In paper or board machines known in prior art, the short circulation and other stock systems are most commonly built such as to mix fibres, fillers, fines and additives to form a stock that is as homogeneous as possible in order to be supplied into a headbox of a paper machine. In multi-layer web forming, it is also known to use several different stock systems for feeding different fibre suspensions into the headbox. In prior art there are also known a short circulation and a headbox allowing layering of additives, fillers and/or fines. One stock feed arrangement of this kind advantageously applied in the invention is disclosed in FI patent application 934793. Fillers, fines and additives can also be supplied only in the headbox itself. One arrangement of this kind is described in EP patent publication 0 824157.
Quite recently, a novel type of short circulation arrangement has been developed, marketed by Metso Paper, Inc. under the trademark OptiFeed™, which is described, among other things, in the magazine article
Ein Neuer Ansatz für das Management der Nasspartie, Wochenblatt für Papierfabrikation
, vol. 19, No. 20, October 1998. By using the OptiFeed™ arrangement, the stock volumes of the short circulation are minimized, which enables, among other things, a quick grade change.
The headbox spreads the formed pulp suspension evenly onto a wire section, in which dewatering and couching of the web begin. In prior art there are known several different types of wire sections, or formers, known in themselves to a person skilled in the art; fourdrinier formers, hybrid formers, and gap formers. In recent years, in the manufacture of fine paper, a gap former has become common in which a slice jet produced by a headbox is fed between two wires and the bulk of the water is removed between said wires in two directions. One advantageous gap former arrangement has been described in the paper read by L. Verkasalo:
Efficient Forming at High Speeds, XI Valmet Paper Technology Days
1998. In the arrangements known in prior art, the fibre and filler distribution in the thickness direction of the web can be controlled to a limited degree, for example, by means of placement and vacuums of the dewatering elements of the former. The fillers often accumulate on the surfaces of the web in dewatering stages.
In prior art there are also known multi-layer headboxes, one of them having been described, for example, in the paper read by M. Odell:
Multilayering, Method or Madness?, XI Valmet Paper Technology Days
1998 and in FI patent 92 729, and one of them having also been described in the paper read by P. Ahonen:
Challenges for Digital Printing Paper, XI Valmet Paper Technology Days
1998. Multi-layer headboxes allow desired layer structures to be produced in the web by feeding stock in layers between wires.
The web is passed from the wire section to a press section where water is removed from the web by pressing it against one or two felts. A skilled person knows several different press arrangements from prior art, for example, a press based on roll nips, marketed by Metso Paper, Inc. under the trademark SymPress II™. Recently, instead of roll nips, in the case of all paper and board grades ever-increasing use has been made of an extended nip known in itself in prior art because of its higher dewatering capacity and/or its ability to retain the bulk of the web.
The dryer section in fine paper machines known in prior art has most commonly been formed of a dryer section which uses conventional single- and/or twin-wire draw and in which drying takes place mainly as cylinder drying while the wire presses the web against a heated cylinder surface. At high running speeds, single-wire draw through the entire dryer section has become common in recent years. As the most recent arrangement, for example, the patent application PCT/FI98/00945 has proposed combining impingement drying with cylinder drying in order to provide a higher evaporation rate and a shorter dryer section.
In several fine paper machines known in prior art, the paper web is passed from the dryer section to a precalender, which in known arrangements may be a calender with hard or soft nips, in which the paper web is passed through the nip between rolls to provide smoothness to the surface of the paper web. Recently, also in the case of fine paper, a so-called soft calender has become common which comprises a soft coated roll and a hot hard-faced thermo roll. In the precalender, loose fibres and other stock components are also fixed to the surface of the web, but, at the same time, differences in density may also be caused in the base paper and some of the bulkiness of the web important to many grades may be lost.
After that, in the fine paper machines known in prior art there is precoating, for example, a surface sizing or pigmenting unit. In surface sizing, the surfaces of the web are treated with a starch or pigment solution in a film size press, for example, by means of an applicator device marketed by Metso Paper, Inc. under the trademark SymSizer™. Surface sizing, pigmenting, or coating is performed at this stage typically on both sides of the web at the same time, but the surfaces of the web can also be treated separately in successive units. After that, the paper web is dried by using infrared dryers and airborne web-dryers as well as a subsequent cylinder group or groups, and the paper web is reeled by means of a machine reel-up.
After that, in the manufacturing process of fine paper according to prior art there is an unwind stand, from which the web is passed to an off-machine coating station. Different coating devices are known in prior art, such as, for example, coating devices of the blade coating, jet, film transfer or spray type. A coating agent is transferred by means of the coating device freely to the surface of the web either as a continuous jet (jet) or as drops (spray) or the coating agent is applied by a roll. In one known arrangement, one side of the paper web is precoated first, after which there is a dryer section, and after that the other side of the paper web is precoated, which is followed by a dryer section. The coating of the thus produced precoated web is completed by coating it with other coating layers and, after that, the web is dried, and wound up. The dryer part of the coating station typically comprises first a unit which is not in contact with the web, for example, an infrared dryer, and a cylinder group located after that. In the end, the web is unwound and calendered by means of a supercalender, which imparts a desired level of smoothness and gloss to the web. Reeling ends the fine paper machine line. One reel-up known in prior art is the reel-up marke
Griffin Steven P.
Halpern Mark
Metso Paper Inc.
Stiennon & Stiennon
LandOfFree
Method for the manufacture of paper, and paper machine line does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for the manufacture of paper, and paper machine line, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for the manufacture of paper, and paper machine line will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3246733