Patent Application
20100096095
1. Field of the Invention
The invention relates to a method as well as to a device for the production of a fibrous web, especially a graphic paper web.
2. Description of the Related Art
Methods for paper drying are already known, whereby the moist paper is pressed by a wire belt via a pressure hood against a specially constructed steam-heated cylinder (refer for example to DE 10 2004 017 808 A1 and DE 10 2004 017 809 A1). With these methods which also include particularly the so-called BoosterDryer method a considerably higher drying rate can be achieved than with conventional methods. The cylinder shell which is optimized for a high heat flow, as well as the contact pressure of the wire belt, ensure a high thermal output. Due to the steam pressure occurring in the paper layers close to the cylinder the water is pressed into the enveloping wire belt in a partially non-evaporated state which results in considerable energy savings. The applicable technology was used predominantly for the production of liner.
The advantage of such a condensation drying concept consists in that the surface of a respective paper web side is significantly compressed and smoothed in that the lignin on the fibers is softened and set. The smoothing process is however only satisfactory in connection with a wood-containing furnish, especially GW (ground wood pulp), TGW (thermo ground wood pulp), and PGW (pressure ground wood pulp) where sufficient lignin is present on the fibers. The smoothing potential is excellent with these types of furnish. At the same time the fiber bonding and characteristics such as the so-called Scott-Bond which is important for example for the heat-set web-offset (HSWO) are significantly improved with paper drying methods of this type.
One problem, especially with paper drying methods of this type, however, consists in that in a relevant drying unit a smooth surface is produced on one side of the web, namely on the side facing the drying cylinder, while the surface of the other side—the side facing the wire belt—remains clearly rougher. Consequently, the application of one single drying unit operating according to the condensation drying concept is not suitable for twin-wire graphic papers, such as wood-free papers.
In the area of the classic wood-free papers which according to the definition of “CEPI” have a maximum content of mechanical fibrous pulp of 10% the development of new types continues. Various paper mills use a so-called high yield pulp such as for example BCTMP/CTMP and APMP (bleached mechanical pulp) for their fibrous material in their paper types. The BCTMP (bleached chemi-thermo-mechanical pulp) is a bleached refiner wood pulp under utilization of pressure and heat, as well as chemical action. CTMP (chemi-thermo-mechanical pulp) is a refiner wood pulp under utilization of pressure and heat, as well as chemical action, and the APMP (alkaline peroxide mechanical pulp) is a refiner wood pulp with preceding alkaline peroxide treatment for improved lignin solution. In some existing paper mills the pulp already contains 40 to 50% of these fibers, combined with kraft pulp. Future development could bring types having a content of up to 80 to 90% of BCTMP and APMP fibers.
The BCTMP/APMP pulps typically contain 12 to 19% lignin in LBKP pulp (LBKP=leaf bleached kraft pulp) and 19 to 27% lignin in NBKP pulp (NBKP=needle bleached kraft pulp). This amounts to approximately 70 to 85% of the entire lignin content of the mechanical pulp (GW, ground wood and TMP). The lignin adheres to the fibers. When the lignin softens and the fibers are “fused together” significantly improved mechanical strength properties result. These include for example the Scott-Bond, the tensile strength and the tear strength.
What is needed in the art is to create an improved method as well as an improved device of the type referred to at the beginning whereby especially the strength properties, for example the fiber bonding, and the surface smoothness are improved for the purpose of optimum coating of the fibrous web and energy is saved. A particular additional intent is to be able to construct a shorter paper machine, thereby achieving space savings.
The present invention provides a method of producing a fibrous web, especially a graphic paper web, from a pulp composition which consists of at least 20 weight % high yield pulp and a maximum 80 weight % wood free pulp (kraft pulp), whereby the moving fibrous web is dried in particular in a location in the drying section of the paper machine in question by way of a high-temperature drying device where said web has a moisture content of at least 10% at a temperature of >110° C.
The high yield pulp includes preferably fibrous pulp selected from the group which consists of BCTMP, CTMP, APMP and any desired combination thereof.
The web is subjected to a relatively high temperature during a relatively early stage where the moisture in the fibrous web is still relatively high, so that the lignin on the fiber surfaces is distinctly softened and a new bonding potential can be created. This results in a distinct improvement in the strength properties of the fibrous or paper web.
The high temperature drying device is utilized preferably in an area where the fibrous web has a moisture content of at least 20%, especially a moisture content of approximately 50%, and preferably a moisture content of approximately 55%.
The high temperature drying device can be utilized advantageously especially also in a location where the fibrous web has a moisture content in the range of approximately 10 to approximately 55% and preferably in the range of approximately 30 to approximately 55%.
The fibrous web is dried preferably by way of a high temperature drying device at a temperature of >120° C. and preferably >130° C.
It is also especially advantageous if the fibrous web is dried by way of a high temperature drying device at a temperature in the range of approximately 110 to 200° C. At higher temperatures the fibers could be damaged due to yellowing or scorching.
According to one preferred practical design the high temperature drying device includes at least one heated drying cylinder which is covered over a section of its outside circumference by at least one pressure hood which exerts pressure on the drying cylinder, whereby the fibrous web, together with at least one wire belt and one impermeable clothing is carried with the fibrous web that is located on the side of the drying cylinder between the drying cylinder and the pressure hood.
A high temperature drying device of this type is known for example from DE 10 2004 017 808 A1 and DE 10 2004 017 809 A1. Moreover, the high temperature drying device can be designed in particular as described in these documents.
In this context the operating temperature of the drying cylinder is advantageously selected to be >120° C., preferably >130° C. or in a range of approximately 110 to approximately 200° C.
Softening of the natural substances is dependent on the temperature as well as on the moisture. Consequently the greatest advantage can be gained from the process that produces an improved strength in the pre-drying section of the paper machine. According to a preferred design of the inventive method the high temperature drying device is therefore provided in the pre-drying section.
Utilization of just one such drying unit with one drying cylinder and a dedicated pressure hood results in a significant two-sidedness with regard to the roughness and the absorbing capacity in the paper sheet. For some products, for example single-sided release papers, printing papers, etc., such a single drying unit can be utilized directly. If however a sufficiently low roughness of for example approximately 10 to approximately 30% is to be produced—which is typical for raw paper for graphic coated papers—and a relatively low two-sidedness with regard to the absorbing capacity is to be ensured, the different solutions cited below are especially feasible.
Two high temperature drying devices, preferably immediately following each other in direction of web travel, can be advantageously utilized, whereby preferably one side of the fibrous web is brought into contact with the drying cylinder of the first and the other side of the fibrous web with the drying cylinder of the second high temperature drying device.
The operating temperature of the heatable cylinder of the at least second high temperature drying device, viewed in direction of web travel, is advantageously selected to be >120° C., preferably 130° C. or in a range of approximately 110 to approximately 200° C.
The operating temperature of the heatable cylinder of the first high temperature drying device, viewed in direction of web travel, is preferably lower than the drying cylinder of the second high temperature drying device. The operating temperature of the first cylinder can therefore be limited.
According to an additional practical embodiment of the inventive method only one high temperature drying device is utilized with existing two-sidedness of the supplied fibrous web relative to the roughness and/or the absorbing capacity and the fibrous web which is fed into said drying device is brought into contact with the drying cylinder of the high temperature drying device with its rougher side, that is the side having a greater absorbing capacity.
An asymmetric press concept—for example a DuoCentriNipcoFlex-Press plus conveyor belt—can be utilized to produce a significant two-sidedness in the press and a corresponding compensation can be provided for by the one-sided effective high temperature drying device which includes for example one drying cylinder with assigned pressure hood.
It is also especially advantageous if—for the compensation of an existing two-sidedness in the fibrous web with regard to roughness and/or the absorbing capacity—a pre-calender is utilized especially as a high temperature drying device, preferably at the end of the pre-drying section. Therefore, a pre-calender of this type may also particularly be utilized in place of a drying unit with a drying cylinder with assigned pressure hood.
A preferred pre-calender is a high temperature softnip-calender.
Alternatively a NipcoFlex shoe calender can specifically also be advantageously utilized as a pre-calender.
The pre-calender may be located before or after a pre-coater or pre-size press.
The pre-calendering process includes preferably steam pre-moistening. This helps to achieve that the fibers on the still rough side of the fibrous web are softened, thereby enabling a better smoothness.
According to an additional advantageous embodiment of the inventive method an existing two-sidedness of the fibrous web with regard to the roughness and/or the absorbing capacity is compensated in the coating section through the coating weight. A way can therefore especially be provided in order to compensate for an existing two-sidedness in the fibrous web with regard to the roughness and/or absorbing capacity through appropriate control and/or adjustment of the coating weight in the coating section.
Coating can occur for example by way of one to six coating units, either in single-sided application or simultaneous two-sided application. One or several layers can be applied simultaneously during the coating process in order to achieve the desired paper properties.
The fibrous web is advantageously coated in the coating section through a direct and/or indirect coating process and/or through blade coating and/or through film-coating and/or through spray coating and/or through curtain coating and/or through multi-curtain coating.
In an additional advantageous embodiment of the inventive method an existing two-sidedness of the fibrous web with regard to the roughness and/or the absorbing capacity is compensated especially in a final calendering process by way of an appropriately designed calender. A calender can be used here in particular which would provide a significant two-sidedness.
The advantages of utilizing especially the condensation drying concept, especially in the production of WF paper with 10 to 80% mechanical fiber pulp or wood pulp, half-mechanical bleached or non-bleached fiber pulp are amongst others:
The present invention further provides initially a device for the production of a fibrous web, especially graphic paper web, with a way to produce a pulp composition which consists of at least 20 weight % high yield pulp, including fibrous pulp, selected from the group which consists of BCTMP, CTMP, APMP and any desired combination thereof, and a maximum of 80 weight % wood free pulp (kraft pulp) and at least one high temperature drying device provided especially in one drying section for the purpose of drying the moving fibrous web at a temperature of >110° C. in a location where the arriving fibrous web has a moisture content of at least 10%.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one embodiment of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
Referring now to the drawings, and more particularly to
The fibrous web is produced based on a stock composition which consists of at least 20 weight % high yield pulp and contains a maximum of 80 weight % wood free pulp (kraft pulp).
The high yield pulp includes fibrous pulp which is selected preferably from the group which consists of BCTMP, CTMP, APMP and contains any desired combinations thereof.
The device 10 includes two high temperature drying devices 12, 14 for the purpose of drying the moving fibrous web which are located immediately following each other in direction of web travel L. Here, the fibrous web is dried by at least one of these high temperature drying devices 12, 14, preferably at least by the second high temperature drying device 14 at a temperature of >110° C. in a location where the incoming fibrous web has a moisture content of at least 10%. In the present example the two high temperature drying devices are located at the end of a pre-drying section 16.
As can be seen also especially from
The fibrous web is carried between the drying cylinder 18 and the pressure hood 20, together with at least one wire belt as well as with an impermeable clothing with the fibrous web located on the side of the drying cylinder 18.
The operating temperature of at least the second drying cylinder 14 is selected to be >120° C., preferably >130° C. or in a range of approximately 110 to approximately 200° C.
As can be seen in
The diagrams according to the
According to the diagram in
The influence of the moisture upon the vitrification temperature is illustrated in
While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 026 681.4 | Jun 2007 | DE | national |
This is a continuation of PCT application No. PCT/EP2008/056750, entitled “METHOD AND DEVICE FOR PRODUCING A FIBER WEB”, filed Jun. 2, 2008, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2008/056750 | Jun 2008 | US |
| Child | 12632264 | US |
