BACKGROUND OF THE INVENTION

Field of the Invention:

[0001] The invention concerns a woven fabric for use in a machine to produce a fiber web, preferably a tissue fiber web, the woven fabric having a machine direction and a cross machine direction, as well as a paper side and a machine side, wherein the paper side is. formed by warp yarns and by weft- yams which warp yarns and weft yams are interwoven with each other in a weave pattern, wherein the paper side comprises a plurality of twill lines, each twill, line being formed by a plurality of neighboring warp yarn flotations, wherein each warp yarn flotation of the weave pattern that contributes to the formation of the twill lines passes over a first weft yarn, wherein the first weft yarn passes over a first warp yarn that directly neighbors the warp yarn flotation on a first side and passes below a second warp yarn that directly neighbors the warp yam flotation on a second side, the second side being opposite the first side, wherein the warp yarn flotation also passes over a second weft yam that directly neighbors the first weft .yam.

[0002] Such woven fabrics are already known in commerce. One example of such a prior art fabric 10' is shown in Fig. 1 which illustrates a view onto the paper side of the fabric 10'. As can be seen the paper side is formed by a plurality of warp yarns interwoven with a plurality of weft yarns. For the sake of clarity only three warp yarns are provided with reference signs, namely WA1’,

WA’ and WA2’, and only five weft yarns are provided with reference signs, namely WET, WE2', WE3’, WE4' and WE5’. As in most cases, the fabric is flat woven meaning that the warp yarns extend substantially, but not necessarily exactly, in machine direction MD of the woven fabric 10', whereas the weft yarns extend in cross machine direction CD of the woven fabric 10'. The woven fabric

10’ is made endless by a seam, which is not illustrated here. In case the fabric is not flat woven but round woven - which is rather rare - the warp yams would correspond to .the weft yarns and vice versa. Generally speaking, according to the present invention the warp yarns shall refer to the yarns that extend in the machine direction MD of the fabric 10', whereas the weft yams shall refer to the yarns that extend in the cross machine direction CD of the fabric 10'.

[0003] In the illustrated prior art example each warp yarn forms several flotations on the paper side of the woven fabric 10’, wherein all- flotations have the same length. One of these flotations, or floats, is denominated with reference sign FL’ in Fig. 1 . This flotation FL’ is formed by warp yam WA’ which floats above the five weft yarns WE1 '-WE5'. The warp yarn WA’ that forms the flotation

FL' is neighbored by a first warp yarn WA1’ on a first side and by a second warp yarn WA2' on a second side opposite the first side, wherein the first warp yarn

WAT and the second warp yarn WA2’ form similar flotations on the paper side of the woven fabric 10' but with an offset. Thus, warp yarn WA1’ floats only above weft yarns WE4’ and WE5’ - and three further weft yarns without reference sign

- but not about weft yarns WE1 WE2’ and WE3'. The offset results in that directly neighboring flotations of warp yarns together form a diagonal twill line TL’ that extends substantially from the lower right side to the upper left side in Fig. 1 .

In fact, several such twill lines extend parallel to each other across the complete paper side of the woven fabric 10'. The distinctive diagonal twill lines are clearly separated from each other. In the present example between two neighboring twill lines there is some kind of plain weave structure, i.e. a woven structure which is free of any flotations.

[0004] Such a woven fabric with diagonal twill lines on its paper side is conducive to sheet building, especially when the sheet is transferred to it with a rush speed differential.

[0005] Having a doser look to the five weft yams WE1'-WE5’ which pass below the warp yarn WA’ to form the warp yarn flotation FL’, it can be seen that the weft yarn WE1' passes over the first warp yarn WA1’ and below the second warp yam WA2', whereas the weft yarn WE2’ passes below the first warp yarn WA1’ and below the second warp yam WA2’, the weft yarn WE3’ passes over the first warp yarn WA1' and over the second warp yam WA2', the weft yarn

WE4’ passes below the first warp yarn WA1’ and below the second warp yam

WA2’ and the weft yarn WE3' passes below the first warp yarn WA1’ and over the second warp yam WA2'.

[0006] Fig. 2 shows schematically a cross-sectional view through the fabric

10’ of Fig. 1 along the weaving path of the weft yarn WE3’. Due to the fact that the weft yam WE3’ forms some kind of a plain weave structure at the center of the warp yam flotation FL’ by passing over the first warp yarn WA1 below the warp yarn WA’ and then again over the second warp yarn WA2', there is created a pressure point at the warp yarn flotation FL'. This pressure point absorbs all of the compressive toad applied to the fabric 10’ and leads to short life due to monofilament yarn fibrillation. The pointed nature of the warp yam flotation FL' also makes it difficult to surface sand the fabric to the desired level of contact area on the paper side of the fabric 10' without removing excessive amounts of mass.

BRIEF SUMMARY OF THE INVENTION

[0007] It is accordingly an object of the invention to provide a woven fabric which overcomes the. above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which avoids, or at least. reduces, these problems. In particular the present invention aims to provide a woven fabric that has an enhanced lifetime and is less prone to wear. It is a further object of the present invention to provide, a fabric that can be surface sanded to a desired level of contact area at the paper side without removing excessive amounts of mass.

[0008] With the above and other objects in view there is provided, in accordance with the invention, a woven fabric for a paper making machine, for example for producing fiber webs, such as tissue paper. The woven fabric has a machine direction, a cross machine direction, a paper side and a machine side, and the fabric comprises: warp yarns and weft yarns interwoven with one another in a weave pattern; the paper side being formed with the warp yarns and the weft yarns and the paper side having a plurality of twill lines, each formed by a plurality of neighboring warp yarn flotations; each of the warp yam flotations of the weave pattern that contributes to a formation of the twill lines passing over a first weft yarn; the first weft yarn passing over a first warp yam that directly neighbors the warp yarn flotation on a first side and passes below a second warp yarn that directly neighbors the warp yarn flotation on a second side opposite the first side; the warp yarn flotation also passing over a second weft yarn that directly neighbors the first weft yam; and the second weft yam passing below the first warp yarn and over the second warp yarn.

[0009] In other words, the inventor has found that the problem can be solved by replacing the weft yarn with the plain weave structure - usually provided at the center of the warp yarn flotation - by two weft yams wherein one .of these two weft yarns is the first weft yarn passing over the first warp yarn and below the second warp yarn, whereas the other of these two weft yarns is the second weft yarn passing below the first warp yam and over the second warp yarn.

Thus, these two weft yarns together take over the function of the plain weave structure of the one weft yarn that they substitute, but without any of these two weft yarns in fact forming a plain weave structure. The result is that the fabric has the same number of weft knuckles but the point at the center of the warp yarn flotation is flattened and the pressure point is eliminated. [0010] A positive side effect of this solution is that the elimination of the plain weave structure also allows to drive the count of the woven higher which gives the advantage of lower air permeability and. leads to better and less fiber bleed through.

[0011] In a preferred embodiment the first weft yam passes below the warp yam flotation substantially in the center of the warp yarn flotation. In this context the word “substantially” means that either - if the warp yam flotation passes over an odd number of weft yarns - the first weft yarn should be in middle one of the odd number of weft yarns (e.g. the fifth weft yarn of nine such weft yarns), or - if the warp yarn flotation passes over an even number of weft yarns - the first weft yarn should be next to the middle of the even number of weft yams (e.g. the fifth or sixth' weft yarn of ten such weft yarns).

[0012] Preferably, all weft yarns that pass below the warp yarn flotation also pass below either one. or both of the first warp yam and the second warp yam. In other words, none of these weft yarns form a plain weave structure with the warp yarn of the warp yam flotation and the first and second warp yarns. Thus, the creation of a pressure point can be avoided.

[0013] In a preferred embodiment all warp yam flotations of the weave pattern that contribute to the formation of the twill lines have the same length.

The length of the warp flotations is preferably at least 5 and can be for example

9 or 10. [0014] Other features which are considered as characteristic for the invention are set forth in the appended claims.

[00151 Although the invention is illustrated and described herein as embodied in woven structured fabric with crossing twill lines, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be' made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

[0016] The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0017] Fig. 1 is a partial view of a prior art woven fabric in a plan view onto the paper side of the fabric;

[0018] Fig. 2 is a diagrammatic section taken along the weaveline of one of the weft yams in Fig. 1 , 'along the cross machine direction;

[0019] Fig. 3 shows a plan view on the paper side of a portion of a fabric according to a first embodiment of the present invention; and

[0020] Fig. 4 shows a view on' the paper side of a portion of a fabric according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] Referring now once more to the figures of the drawing in detail, a first embodiment of the present invention is shown in Fig. 3, which illustrates a view on the paper side of a portion of a woven fabric 10. The exemplary fabric is a forming fabric in a paper making machine and the fabric, or clothing, is suitable to form paper webs, such as tissue paper. The paper side, which is opposite the machine side, is formed by a plurality of warp yams interwoven .with a plurality of weft yarns. Since the woven fabric 10 is a single layer fabric the same warp yams and weft yams also form the machine side of the woven fabric 10. For the sake of clarity only three warp yams are provided with reference signs, namely

WA1 , WA and WA2, and only two weft yams are provided with reference signs, namely WE1 , WE2. The fabric is flat woven meaning that the warp yarns extend substantially, but not all necessarily exactly, in machine direction MD of the woven fabric 10, whereas the weft yams extend in cross machine direction CD of the woven fabric 10. The woven fabric 10 is made endless by a not shown seam.

In case the fabric is not flat woven but round woven the warp yarns would correspond to the weft yarns and vice versa.

[0022] Each warp yarn forms serval flotations, or floats, on the paper side of the woven fabric 10. The tong flotations that have a length of 11 in this exemplary embodiment are referred to as warp yarn flotations in the following.

Directly neighboring warp flotations form diagonal twill lines TL, or oblique twill lines TL, on the paper side of the fabric 10. [0023] One of. these warp yam flotations is designated with reference sign FL in Fig, 3. The warp yarn flotation FL is formed by warp yarn WA floating over eleven weft yams. The middle one of. these eleven weft yarns is referred to as first weft yarn WE1 in the following. The first weft yarn WE1 passes over a first warp yarn WA1 which first warp yarn WA1 directly neighbors the warp yarn. WA that forms the warp yarn flotation FL on a first side, namely on the left-hand side in Fig. 3. Furthermore, the first weft yam WE1 passes below a second warp yarn

WA2 which second warp yarn WA2 directly neighbors the warp yam WA that . forms the warp yarn flotation FL on a second side, namely on the right-hand side in Fig. 3.

[0024] The first weft yarn WE1 has a directly neighboring weft yam which is referred to as second weft yam WE2 in the following. Differently to the first weft yarn WE1 , the second weft yarn WE2 passes below the first warp yam WA1 and over the second warp yarn WA2,

[0025] None of the weft yarns that pass below the warp yarn flotation FL passes above both, the first warp yarn WA1 and the second warp yarn WA2.

[0026] Fig. 4 shows a view on the paper side of a portion of a woven fabric according to a second embodiment of the present invention. This embodiment is very similar to the first embodiment. The main difference is that the length of the warp yarn flotations that form diagonal twill lines is different. In this exemplary embodiment the length is ten, i.e., the respective warp yams float above 10 weft yams. Therefore, the same reference signs are used as in the first embodiment. With regard to the details of this second embodiment, reference is had to the description. of the first embodiment which largely also applies to the second embodiment. The first weft yam WE1 passes below the warp yarn flotation FL substantially at its center. In fact the precise middle would be between the first weft yam WE1 and its directly neighboring second weft yarn WE2.

[0028] The following is a summary list of reference, numerals and the corresponding structure used in the above description of the invention:

10 woven fabric

10' woven fabric (prior art)

CD cross machine' direction

FL warp yarn flotation

FL’ warp yarn flotation (prior art)

MD machine direction

TL diagonal twill line twill line (prior art)

WA1 - WA2 first and second warp yams WA1’ - WA2' first and second warp yams (prior art)

WA warp yarn (forming the warp yarn flotation. FL)

WA' warp yam (forming the warp yarn flotation FL') (prior art)

WE1 - WE2 first and second weft yarns

WE1'- WE5’ weft yams (prior art)