Papermachine fabric

Abstract

The invention relates to a papermachine fabric, in particular a press felt, having a carrier layer on which, at least in some sections, fibers with exposed fiber ends are arranged, the fibers forming a contact surface with which a paper web can be brought into contact, and wherein the contact surface is substantially formed by the exposed fiber ends.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 10 2004 056 319.5 filed on Nov. 22, 2004, the disclosure of which is expressly incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a papermachine fabric, in particular a press felt for the press section of a paper machine.

2. Discussion of Background Information

In U.S. Pat. No. B2-6,605,188 a trasport belt for a paper machine is disclosed which, on its paper-side surface, has a layer comprising at least two fibers with different surface properties. This paper-side layer has hydrophilic and hydrophobic regions, in order to improve the separation properties of the belt from the paper web. The additional surface having the at least two different fibers is ground flat in a suitable way, the fibers being to some extent exposed on the surface and therefor creating what is known as a specific micro roughness. Such a transport belt, for example, constitutes a papermachine fabric.

Fabrics of this type normally have fibers on their paper-side surface which, for example, form loops on the surface or are exposed flat on the surface. Loops of this type or fibers lying flat can impair the quality of the paper produced in the paper machine because of indentations in the paper, in particular if these indentations or impressions lead to missing dots on the paper later when the paper is printed, for example in the gravure printing process. It is precisely in the case of permeable dewatering structures, such as for example a dryer fabric, which are preferably used in the press section of a paper machine, that imprints on the paper surface are to be avoided, however. At the same time, in particular in high-speed paper machines for graphic papers, good separation of the fabric from the paper web is to be possible.

Furthermore, U.S. Pat. No. 4,772,504 discloses apress felt for use in a press section of a paper machine which has a dense surface layer in order to avoid renewed wetting and in order to avoid blowing effects.

SUMMARY OF THE INVENTION

The invention is based on the object of providing a papermachine fabric of the type mentioned at the beginning with which a high paper quality can be achieved and in which, in particular, imprints on the paper web are prevented. A further object of the invention is to produce a papermachine fabric having improved paper removal properties.

The generic papermachine fabric, which in particular can be a press felt, has a carrier layer on which, at least in some sections, fibers with exposed fiber ends are arranged. In this case, the fibers form a contact surface with which a paper web can be brought into contact.

The papermachine fabric according to the invention is distinguished by the fact that the contact surface is substantially formed by the exposed fiber ends.

In this case, it is advantageous that, by means of a papermachine fabric of this type, the contact surface on an even and flat level with respect to the paper web is increased and the dimensions of each individual contact point between the fabric on the paper web are kept as small as possible. Overall, the result is thus a high number of contact or supporting points on the paper-side surface of the fabric which do not press into the paper web, precisely because of their large number and respectively small area. As previously mentioned, fiber indentations or impressions normally constitute a reason that printed dots are missing in the finished product, for example in a graphic paper such as a newspaper page printed in the gravure printing process, which can be attributed to the incompletely even structure of the paper web. As a result of the large number of relatively small contact points, the result is thus a very even and uniform surface of the papermachine fabric, that is to say for example a press felt, and therefore a likewise uniform surface of the paper web, which therefore has a very high quality.

Furthermore, as a result of the high number of relatively small contact points of the contact surface coming into contact with the paper web, the ability to remove the paper web simply from the papermachine fabric, for example when transferring the paper web to another fabric, is improved considerably.

The carrier layer advantageously has a surface in relation to which the fibers extend at an angle (α) between 45 and 90°.

According to a further advantageous embodiment, the fibers extend substantially perpendicular to the surface of the carrier layer.

According to an advantageous development of the invention, a binder layer, in which the fibers are partly embedded, is arranged on the surface of the carrier layer.

The carrier layer has a binder layer on its paper-side surface, and the fibers are embedded in the carrier layer, preferably by means of needling, and the binder layer is arranged to be penetrated completely. The binder system is used to anchor the fibers and, at the same time, can contribute to the papermachine fabric overall having the required permeability or in general the desired technical properties, such as resistance to compaction, durability, chemical resistance or void volume. This can be done by using additional substances or materials which have a lower melting point than, for example, the carrier layer and/or the fibers. This can also be done by adding a liquid/suspension-type binder system.

For the purpose of additional anchoring of the fibers, it may be expedient if these are additionally embedded in the carrier layer by means of needling and penetrate the binder layer completely.

According to a particularly preferred development of the invention, the ends of the fibers project beyond the surface of the carrier layer or the binder layer by less than 1 mm, preferably less than 0.5 mm, more preferably less than 0.3 mm and more than 15 μm. From this, it follows that the ends of the fibers ultimately project outward slightly beyond the surface of the fabric, that is to say toward the paper web. As a result of the large number of fiber ends, the result is thus numerous contact points for the paper web on the fabric, that is to say for example on the press felt, so that ultimately a surface of the papermachine fabric which is to a certain extent “hedgehog-like” is produced. In any case, the indentations of the cross section of each exposed fiber end are smaller than indentations from fibers lying flat

According to another development to the invention, the ends of the fibers project beyond the surface of the carrier layer or the binder layer by less than ten times the fiber diameter, preferably less than five times, particularly preferably less than three times the fiber diameter. This relation can also be important for reducing indentations on sides of the paper web. Viewed generally, in order to reduce indentations, the relation between the extent of the projection of the fibers beyond the surface of the fabric relative to the fiber diameter and to the flat resting of the fibers in the case of the prior art can be decisive. According to the invention, this relationship is decisively important for fiber diameters >3 dtex. Fibers with a fineness index <3 dtex do not have to follow this relationship because of the fact that they cannot cause any indentations on the paper web which influence the subsequent printing of the paper.

Advantageously, in the case of fibers with a fineness index of 3.3 dtex, 250,000 to 325,000 fibers per cm² and, in the case of fibers with a fineness index of 6.7 dtex, 125,000 to 200,000 fibers per cm² are arranged in the carrier layer or the binder layer. This illustrates once more what a large quantity of contact points the papermachine fabric formed in accordance with the invention has.

In the case of fiber mixtures, the result of what has been stated above is accordingly a number of contact points corresponding to the mixture ratio of the fibers in the fiber mixture.

According to another development of the invention, the binder layer is softer than the fiber material and preferably formed from a thermoplastic elastomer. This ensures flexibility, which also contributes to reducing indentations on the paper. However, it is also possible for the binder layer to be similarly hard or harder than the fiber material, depending on the construction of the complete structure of the papermachine fabric.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings.

Embodiments of the subject matter of the invention will be explained in more detail in the following by using the drawing, all the features described and/or illustrated pictorially, on their own or in any desired combination, forming the subject matter of the present invention, irrespective of their combination in the claims or their back reference. In the drawing:

FIG. 1 shows a schematic perspective partial view of a papermachine fabric; and

FIG. 2 shows a schematic perspective partial view of the papermachine fabric on a highly enlarged scale.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.

In FIG. 1, a papermachine fabric 1, in particular but not exclusively a press felt for the press section of a paper machine not specifically shown, is shown schematically in a perspective partial view.

The x axis shown in FIG. 1 extends in the longitudinal direction of the papermachine fabric 1, also called the fabric in the following text, the y axis extends in the transverse direction of the fabric and the z axis extends in the direction of the height or the thickness of the fabric. The x axis therefore corresponds to the machine running direction, also called the machine direction, the y axis corresponds to the cross machine direction.

The papermachine fabric 1 can also be what is known as a smoothing belt or an impermeable transport belt, for example having the desired separation properties from the paper web, not specifically shown.

The papermachine fabric 1 has a carrier layer 2, in which fibers 3 are embedded, for example needled. Likewise provided to anchor the fibers 3 is a binder layer 6, in which the fibers are partly embedded. With their exposed fiber ends 5, the fibers 3 form a contact surface 7 for a paper web, not shown.

According to the invention, the contact surface 7 is formed by the exposed fiber ends 5 of the fibers 3. The present embodiment shows that the fibers extend substantially at right angles to the surface 4 of the carrier layer 2 and to the fabric 1.

As already indicated previously, the papermachine fabric 1 can have a permeable dewatering structure and therefore, in particular, constitute a press felt. The carrier layer 2 can be, for example, what is known as a woven or nonwoven base substrate which has the required mechanical properties, such as sufficient tensile strength in the machine running direction and transversely thereto. See also the x, y axes in FIG. 1.

The fibers 3 can have a uniform or different diameter and a uniform or different shape, identical or different chemical, thermal and mechanical properties.

It is also possible for fibers which are not exposed on the surface 4 to be provided.

For better clarity, only a few fibers are shown in FIG. 1. It is clear that, in practice, the papermachine fabric 1 has numerous fibers and likewise numerous fiber ends 5 projecting substantially vertically. This is illustrated in a perspective schematic partial view of the papermachine fabric 1 in FIG. 2, which ultimately results in a densely packed, somewhat “hedgehog-like” surface structure of the fabric.

The ends 5 of the fibers usually project beyond the surface 4 of the carrier layer 2 or the binder layer 6 by less than 1 mm, preferably less than 0.5 mm, particularly preferably less than 0.3 mm and more than 15 μm. Furthermore, it has proven worthwhile for the ends 5 of the fibers to project beyond the surface 4 of the carrier layer 2 or the binder layer 6 by less than ten times the fiber diameter, preferably less than five times, more preferably less than three times the fiber diameter.

The dense arrangement of the individual fiber ends beside one another also results from the fact that, in a preferred embodiment of the invention, in the case of fibers with a fineness index of 3.3 dtex, 250,000 to 325,000 fibers per cm² and, in the case of fibers with a fineness index of approximately 6.7 dtex, 125,000 to 200,000 per cm² are arranged in the carrier layer or the binder layer.

The aforementioned binder layer 6 is normally softer than the fiber material and preferably formed of a thermoplastic elastomer.

The sections of the fibers exposed above the desired projection height, such as fiber loops, for example, can be removed from the surface of the fabric by mechanical, thermal or chemical methods. A possible mechanical method is, for example, grinding or cutting off the projecting fiber ends 5.

The separation properties of the relevant papermachine fabric from the paper web, not specifically shown, can be adjusted by modifying the fiber diameter and by a mixture of different fiber diameters. In another method for the removal of fiber sections projecting further than desired, the fibers are treated in such a way that they are not electrically conductive. The ends are then charged up statically, so that they stand approximately vertically. This process could also be carried out during the application of the binder layer. As previously mentioned, the carrier layer can have what is known as a binder layer. However, it is also possible for the fabric to have only one carrier layer.

A papermachine fabric is therefore created in which indentations in the paper web on account of the structure and the surface of the fabric are effectively prevented. By using the papermachine fabric according to the invention, a paper with a very high quality can therefore be produced.

It should also be noted that the term papermachine fabric is also intended to be understood to be a fabric for the production of tissue paper, board or chemical pulp.

It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Charges may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.

Claims

1. A papermachine fabric, comprising a carrier layer on which fibers with exposed fiber ends are arranged, the fibers forming a contact surface with which a paper web can be brought into contact, wherein the contact surface is substantially formed by the exposed fiber ends.

2. The papermachine fabric as claimed in claim 1, wherein the carrier layer has a surface in relation to which the fibers extend at an angle (α) between 45 and 90°.

3. The papermachine fabric as claimed in claim 1, wherein the fibers extend substantially perpendicular to the surface of the carrier layer.

4. The papermachine fabric as claimed in claim 1, wherein a binder layer is arranged on the surface of the carrier layer in order to hold the fibers.

5. The papermachine fabric as claimed in claim 4, wherein the fibers are embedded in the carrier layer by means of needling and penetrate the binder layer.

6. The papermachine fabric as claimed in claim 4, wherein the ends of the fibers project beyond at leat one of the surface of the carrier layer and the binder layer by less than 1 mm.

7. The papermachine fabric as claimed in claim 4, wherein the ends of the fibers project beyond at least one of the surface of the carrier layer and the binder layer by less than ten times the fiber diameter.

8. The papermachine fabric as claimed in claim 4, wherein the fibers having a fineness index of 3.3 dtex, 250,000 to 325,000 fibers per cm2 are arranged in at least one of the carrier layer and the binder layer.

9. The papermachine fabric as claimed in claim 4, wherein the binder layer is softer than the fiber material and formed of a thermoplastic elastomer.

10. The papermachine fabric as claimed in claim 4, wherein the ends of the fibers project beyond at leat one of the surface of the carrier layer and the binder layer by less than 0.5 mm.

11. The papermachine fabric as claimed in claim 4, wherein the ends of the fibers project beyond at leat one of the surface of the carrier layer and the binder layer by less than 0.3 mm and more than 15 μm.

12. The papermachine fabric as claimed in claim 4, wherein the ends of the fibers project beyond at leat one of the surface of the carrier layer and the binder layer by less than 1 mm and more than 15 μm.

13. The papermachine fabric as claimed in claim 4, wherein the ends of the fibers project beyond at least one of the surface of the carrier layer and the binder layer by less than five times the fiber diameter.

14. The papermachine fabric as claimed in claim 4, wherein the ends of the fibers project beyond at least one of the surface of the carrier layer and the binder layer by less than three times the fiber diameter.

15. The papermachine fabric as claimed in claim 4, wherein the fibers having a fineness index of 6.7 dtex, 125,000 to 200,000 fibers per cm2 are arranged in at least one of the carrier layer and the binder layer.