Patent Application
20080257513
1. Field of the Invention
The present invention relates to an apparatus for treating a fibrous web, in particular for producing a tissue paper web, with at least one crêping nip which is limited on the one side by a crêping belt and on the other side by a web supporting face formed in particular by a mating roll and through which the fibrous web can be passed, whereby a relative speed is provided between the crêping belt and the web supporting face.
2. Description of the Related Art
The technology for producing tissue paper webs is known in principle. For example, a tissue paper web is mechanically pressed in a press nip, whereby the tissue paper web is carried by a roll face at a first speed. The web is picked up by a permeable, woven belt with a structured surface at a second speed, whereby the second speed is lower than the first speed. The objective is to create a high-bulk tissue paper web by means of a crêping effect. Here the press nip thus forms a crêping nip. However, crêping without pressing force and only with a relative speed in the crêping nip is also possible. What is needed in the art is to achieve a good crêping effect while reducing the crêping belt wear.
The present invention provides an apparatus the surface of the web supporting face and/or the material forming the web supporting face are selected with a view to little crêping belt wear caused by operation of the apparatus, in particular with a view to a small coefficient of friction.
Up to now the material and surface of the web supporting face were selected solely with a view to achieving a good crêping effect. An influence on the crêping belt wear was not known up to now. In connection with the invention it was discovered namely that the crêping belt in the crêping nip is not separated from the web supporting face but that the crêping belt or at least the humps of a structured and rough belt are thrust against the web supporting face in spite of the fibrous web lying in between. The reason is that on the one hand the fibrous web is relatively thin and light, namely approximately 15 g/m2 to approximately 40 g/m2, and that on the other hand the humps push the fibers of the fibrous web aside on account of the crêping operation. These problems are resolved by the present invention.
Preferably the web supporting face is formed by a soft material. Through this measure the relative speed between the crêping belt and the web supporting face is reduced in that the soft material in the crêping nip is elastically deformed. Downstream from the crêping nip the deformation is reversed. Hence there is no negative effect on the speed difference between the crêping belt and the fibrous web and therefore none on the crêping effect. The crêping belt wear is reduced as the result of the smaller speed difference
Preferably the hardness of the material forming the web supporting face equals approximately 20 to approximately 120 Pussey & Jones. This range of values has proven to be particularly advantageous.
According to one embodiment of the present invention, the web supporting face is formed by a roll comprised of two materials, namely an inner material selected for the roll's strength and an outer material selected for little crêping belt wear. Particularly good adaptation to the requirements with regard to a good crêping effect and little wear on the one hand and stability of the roll on the other hand can be achieved as the result. Preferably steel or stainless steel is provided as the inner material. Particularly stable rolls can be formed therewith. Above all PTFE, meaning polytetrafluoroethylene, can be used as the external material. Particularly good results can be achieved therewith.
According to another embodiment of the present invention, hardness and thickness of the outer material are selected to achieve a desired deformation of the roll. By way of the hardness and thickness it is possible to achieve in suitable manner a desired deformation and hence reduction of the speed difference.
According to another embodiment of the present invention the web supporting face has a rough structure, in particular a macro-roughness. The friction between the web supporting surface and the crêping belt can be reduced as the result. It is preferred for the structure of the web supporting face to correspond to the structure of the crêping belt or for it to be at least similar. Particularly little friction can be achieved therewith. It is preferred in particular for the structure of the web supporting face to have raised regions and, in between these, particularly soft transitional regions. The combination of a structure with raised regions and soft transitional regions in between has the advantage that when the raised regions of the crêping belt slide over the rough surface, the contact is interrupted periodically and the friction reduced as the result.
According to another embodiment of the present invention, the surface of the web supporting face is highly polished. This results in a micro-roughness, as the result of which the abrasion effect and hence the crêping belt wear are reduced.
According to a particular embodiment of the present invention, the web supporting face is formed by a roll which is comprised of steel or stainless steel and/or has a hardened surface layer or a hard covering. Such a surface can be constructed to be particularly smooth, as the result of which particularly little friction and hence crêping belt wear results. A press nip can be positioned upstream from the crêping nip. Said press nip can be constructed as a longitudinal nip, a shoe press nip, a roll nip or simply a felted nip. The production process can be improved further as the result. The crêping belt is comprised in particular of structured fabric such as TAD fabric or spiral-linked fabric. Such material has proven to be particularly advantageous for the crêping effect. In addition, the crêping belt can be permeable or non-permeable, and be made of woven or non-woven material. Advantages can be drawn likewise therefrom. Arranged downstream from the crêping nip there can be a drying cylinder, in particular a Yankee cylinder, and/or a crêping nip can be constructed on a drying cylinder, in particular a Yankee cylinder. Through the use of a drying cylinder, the crêping effect can be improved further.
According to another embodiment of the present invention there can be constructed on the drying cylinder, in particular by means of a mating roll, a press nip through which the fibrous web is passed together with the crêping belt. Again, the crêping process can be improved further as the result. The contact area between the crêping belt and the drying cylinder and/or between the crêping belt and the mating roll is preferably between approximately 20% and approximately 70%, more preferably between approximately 25% and 50% and still more preferably approximately 30%. Very little wear and very good quality of the tissue paper web can thus be obtained. Through the small contact area, pockets in which the high-bulk crepe material is protectively received are created in the regions lying in between. Nevertheless, good pressing of the fibrous web and good tensile strength are achievable through the use of the drying cylinder. The press nip on the drying cylinder can be formed by a suction press roll, a press roll or a shoe press roll with an extended roll nip. Good results can be achieved therewith. The crêping nip can be formed furthermore without mechanical pressing means or with mechanical pressing means. Also, it is possible for different crêping nips to be combined with each other. In this way production can be improved further. A soft press roll, a hard press roll or a belt press can be provided as mechanical pressing means. Such pressing means are particularly suited for the intended purpose. In the event of using a belt press, the belt has preferably a tensile strength of at least 40 kN/m, preferably at least 50 kN/m and more preferably at least 60 kN/m. The required pressing force can thus be achieved.
The present invention is used preferably for fibrous webs with a mass of approximately 15 g/m2 to approximately 40 g/m2. With such thin and light fibrous webs the problem of wear on the crêping belt is particularly great, and so are, therefore, the advantages achieved by the current invention. On the side of the crêping belt opposite the mating roll, provision can also be made for a crêping roll or a suction press roll. The rolls can have the following properties:
Mating roll:
Crêping roll/suction press roll:
The mating roll or surface of the mating roll it can be constructed from polyester, modified polyester, high-temperature polyamide, phnapphlape-based polyester, phnapphlape-based polymer, or a polyethylene naphtalate polymer. As material for the crêping belt it is also possible to provide: Polyurethane, silicone rubber and the materials previously listed for the mating roll. Furthermore, the crêping belt can be comprised of embossed material. Provision can also be made for a coating with nanoparticles in order to increase the wear resistance of all the materials.
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
Downstream from press nip 5 in the web running direction I, crêping belt 13, which is transported over deflecting rolls 14, rests against soft roll 4. Hence between crêping belt 13 and soft roll 4 there is a created crêping nip 15 which is limited on the one side by surface 4a of soft roll 4 and on the other side by crêping belt 13. Provided on the exit side of crêping nip 15 are doctor blade 16 and suction apparatus 17. Doctor blade 16 is not used here for crêping but for cleaning soft roll 4.
Arranged in the loop of crêping belt 13 there is also roll 18 which together with drying cylinder 19, in particular a Yankee cylinder, forms another press nip 20. Downstream from press nip 20 in the web running direction there is arranged drying hood 21 on drying cylinder 19.
As is shown in
The material and/or surface 4a of roll 4, which forms the web supporting face for fibrous web 1 in crêping nip 15, and the surface of crêping belt 13 are selected with a view to reducing the wear of crêping belt 13. In particular the selection is undertaken such that a small coefficient of friction between the crêping belt 13 and the surface 4a of the roll 4 results. For example the hardness of the material forming the web supporting face equals between approximately 20 and 120 Pussey & Jones. In particular PTFE, meaning polytetrafluoroethylene, is possible as a material for surface 4a of roll 4. Crêping belt 13 can be comprised of TAD fabric or spiral-linked fabric. Furthermore it can be permeable or impermeable, woven or non-woven.
Press nip 20 on drying cylinder 19 can be constructed likewise as a crêping nip. A relative speed then exists between drying cylinder 19 and crêping belt 13. Press nip 20 on drying cylinder 19 can also be constructed as a shoe press nip, and mating roll 18 can also be constructed as a suction press roll. Unlike crêping nip 15, crêping nip 20 is constructed as a press nip. Mating roll 18 can be constructed in addition as a soft pressing roll or as a hard pressing roll. However, it is also possible for crêping nip 15 to be constructed as a belt press nip. Then crêping belt 13 has preferably a tensile strength of at least 40 kN/m, in particular at least 50 kN/m and more preferably at least 60 kN/m. Fibrous web 1 has moreover preferably a mass of approximately 15 g/m to approximately 40 g/m2.
Using the apparatus of the present invention it is possible to achieve a good crêping effect with a simultaneously low level of wear on crêping belt 13.
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 2005 060 378.5 | Dec 2005 | DE | national |
This is a continuation of PCT application No. PCT/EP2006/068277, entitled “DEVICE AND METHOD FOR TREATING A WEB OF FIBROUS MATERIAL, IN PARTICULAR FOR PRODUCING A WEB OF TISSUE PAPER”, filed Nov. 9, 2006, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2006/068277 | Nov 2006 | US |
| Child | 12138506 | US |
