Patent Application
20060075737
The present application claims priority under 35 U.S.C. § 119 of German Patent Application No. 10 2004 048 432.5 filed Oct. 5, 2004, the disclosure of which is expressly incorporated by reference herein in its entirety.
The present invention relates to industrial fabrics, and in particular, but not exclusively, to industrial fabrics such as paper maker's forming fabric. 2. Discussion of Background Information
The structure of forming fabric for use in paper making machines effects the web formation from the wet pulp and Therefore has a bearing on the quality of the paper produced. Conventionally, forming fabrics are manufactured from fabrics' produced by weaving single, cylindrical monofilament strands of polymer material or metal wires. The knuckles formed at the cross-over points of such woven fabrics however, impart a mark onto the paper surface, causing a reduction in smoothness. Also, such fabrics have been shown to demonstrate a poor sheet release.
In order to alleviate the above described drawbacks fabrics have been developed in which at least some of the individual yarns within the structure of the fabric are composed of a plurality of individual, joined, monofilament polymeric strands.
In U.S. Pat. No. 4,636,426 (Huyck Corporation) two adjacent, monofilament strands are glued together using a heat activated polymeric adhesive. The joined strands are utilized in either the machine direction (MD), the cross direction (CD) or both the MD and the CD of the fabric. The adhesive is also used to adhere the MD and CD yarns at their cross-over points. By this means the overall height of the knuckle is reduced.
In U.S. Pat. No. 5,591,525 (Shakespeare) and divisional thereof U.S. Pat. No. 5,597,646 (Shakespeare) the fabric is formed using yarns which have been formed by extruding, through a die, at least two individual filaments of polymer around a single axis, the swell of the material at the die fusing the filaments together. The single axis forms a central axis which can be either a filament or a void.
Fabrics formed using joined yarns however have the disadvantage that they are not particularly stable and are susceptible to separation of the so-called joined (glued or fused) yarns.
In U.S. Pat. No. 5,944,062 (Christini Forming Fabrics GmbH), the weave pattern of the fabric is such that adjacent MD or CD yarns are woven in, in side by side pairs so as to be mutually contacting. This has the drawback that the problem of separation of the yarns remains, together with the fact that two insertions of the loom are required during formation of the fabric in order to insert such pairs.
In U.S. Pat. No. 5,366,798 (Wangner Systems Corporation) a single system of warp yarns is woven with stacked triple weft yarns. The middle yarn of the triple weft has a cross-section which is of H-shaped, star-shaped, or X″ shaped configuration; which shaped cross-section forms upper and lower channels in which respective upper and lower wefts of the stack are received and supported. This helps prevent lateral shifting of the yarns within the stacked structure, which would lead to an alteration in the knuckle pattern presented on the support surface of the fabric and an alteration of the drainage properties;
U.S. Pat. No. 4,705,601 (Chiu-Kai) describes a three layer forming fabric in which warp yarns having an ovate cross-section are incorporated into the lowermost, that is machine-side layer. Ovate warp yarns have a greater tensile strength than the cylindrical yarns used in The uppermost, that is pulp side layer, which allows comparatively a fewer number of such ovate yarns than cylindrical yarns to be used. This gives rise to a lower density in the lowermost layer, which enables a greater water extraction because it is possible to apply a greater suction pressure to the lowermost layer. The ovate yarns however have the same vertical height as the cylindrical yarns, in order that the overall thickness of the fabric is not altered by using such yarns and in order that the surface of the uppermost layer is not changed.
The present invention provides a fabric in which the effect that the knuckle has on the product transported thereon is reduced and which overcomes or alleviates the above described drawbacks.
In accordance with one aspect of the present invention, a monofilament yarn is provided having a bi-nodal cross section.
The bi-nodal monofilament yarn may include two nodes, which are immediately adjacent, or the nodes may be separated by an integral linking bridge.
The bi-nodal yarns preferably have an aspect ratio of maximum width to maximum height ranging from 1.1 to 1.7, preferably from 1.3 to 1.6 and most preferably around 1.4.
The bi-nodal yarns may be symmetrical or non-symmetrical in respect to their longitudinal axis.
According to a further embodiment of the invention the nodes may be flat at one side of the yarn.
The bi-nodal yarns preferably are made of a polymeric material. The polymeric material preferably including alone or in combination PA, PE, PET.
In accordance with a second aspect of the invention there is provided an industrial fabric including at least some monofilament yarns having bi-nodal cross section.
By providing a yarn produced from a single filament the yarn has more structural integrity and is thereby more stable and less susceptible to separation when compared to a fused yarn, yarns joined during die swell or yarns simply laid side by side. The increase in stability further allows the use of thinner (when viewed vertically) yarns, thereby further reducing fabric thickness whilst maintaining or decreasing void volume. For example, a bi-nodal yarn could replace a yarn of thicker diameter, but with the same mass in order to reduce the fabric thickness.
As the mass remains the same, the void volume decreases. A decrease in void volume results in less water carry and so therefore reduces the likelihood of re-wet. This is particularly beneficial for forming fabrics. In terms of production this leads to a dryer sheet, which would mean energy savings or an ability to speed the paper machine up.
The consequential reduction in knuckle height leads to improved paper smoothness and easier sheet release. The channel between the nodes leads to improved water drainage. The nodes also provide point contacts with the product conveyed on the fabric, resulting in much finer wire marks. There is also a reduction in the time taken to weave the fabric, since the bi-nodal yarn takes the place of two separate yarns.
A fabric constructed with bi-nodal yarns also has improved stiffness which is beneficial on high speed gap formers with their enclosed forming zones. Stiffness equates to good sheet macro-formation due to reduction in streaks (density variations), caused by fabric with low stiffness not being able to withstand the hydraulic pressures.
According to a preferred embodiment of the invention the bi-nodal yarns are warp yarns and/or weft yarns of the fabric.
According to a further embodiment of the invention the fabric is a multi layer fabric including bi-nodal yarns on the paper side layer and/or wear side layer and/or on a middle layer of the fabric.
Bi-nodal yarns used on the paper side of the fabric lead to a reduction of knuckle height resulting in a smoother paper contacting surface with less tendency of wire marking. Bi-nodal yarns used on the wear side of the fabric preferably but not exclusively as CD yarns has the advantage that they enhance the scraping action of fibers from elements and reduce friction/drive load by trapping water, leading to an increase in the longevity of the fabric. Bi-nodal yarns when added to the middle or top layers of for example a triple-weft fabric can provide good stiffness, giving additional fiber support in the top layer.
Favorably all paper side layer warn yarns are provided with bi-nodal cross section.
Further it is advantageous if all wear side warp yarns are provided with bi-nodal cross section.
To increase the flatness of the paper side layer at least some of the bi-nodal yarns provided on the paper side layer having a flat side facing to the paper side.
To increase wear resistance of the wear side layer at least some of the bi-nodal yarns provided on the wear side layer having a flat side facing to the wear side.
According to a further aspect of the invention the bi-nodal yarns provided on the paper side layer having the same aspect ratio like the bi-nodal yarns provided on the wear side layer.
To get a fine and smooth paper side and a wear resistant wear side preferably at least some bi-nodal yarns provided on the paper side layer having a smaller total cross sectional area than the bi-nodal yarns provided on the wear side layer.
In accordance with a third aspect of the present invention there is provided a method of making an industrial fabric comprising the step of extrusion of a single filament yarn through a die to produce a monofilament bi-nodal yarn.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.
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, and wherein:
a and 2b are sectional side views of a single layer fabric woven with non-symmetrical bi-nodal yarns;
a is a sectional side view of a known single layer fabric employing mono-filament MD yarns:
b is a view similar to
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.
The bi-nodal yarns of the present invention are prepared by extrusion a single filament to form a bi-nodal yarn. Examples of the shapes of such bi-nodal yarns are shown in
a and 2b illustrate the use of the non-symmetrical bi-nodal yarns (c) and (d) in a single layer fabric 34 and 36. It is to be understood that the yarns can lie in either the MD or CD directions or both the MD and CD directions. Also, the yarns can be woven in position either way round with their flatter side facing (such as in
It is also to be understood that other types of bi-nodal yarns, such as (a) and (b) could be used in such a single layer weave. For example in
Furthermore, by forming the bi-nodal yarn from a single yarn it is possible to produce a yarn of increased structural integrity when compared to a paired, joined or ‘fused yarn. The increased stability allows the use of thinner yarns to reduce fabric thickness whilst maintaining or decreasing void volume. For example, a bi-nodal yarn could replace a cylindrical yarn of thicker diameter, but having the same mass to reduce the fabric thickness. As the mass remains the same, the void volume decreases. A decrease in void volume results in less water carry and so therefore reduces the likelihood of re-wet. This is particularly beneficial in forming fabrics leading to the production of a dryer sheet, which would mean energy savings or an ability to speed the paper machine up.
Furthermore, a channel for water drainage is provided between the two nodes, unlike a flat yarn, which has no ability to drain water. The nodes of the bi-nodal yarn also only present a point contact producing thereby a much finer wire mark, when compared to the broader contact provided by a flat yarn.
Other variations on the use of bi-nodal monofilament yarns will readily occur to those skilled in the art.
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. Changes 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 048 432.5 | Oct 2004 | DE | national |
