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. The paper side is formed by warp yams and by weft yarns which warp yams and weft yams are interwoven with each other. The paper side comprises a plurality of twill lines, each twill line being formed by a plurality of neighboring flotations of warp yams. The twill lines comprise an MD vector component directed in the machine direction of the woven fabric and a CD vector component directed in the cross machine direction of the woven fabric. At least some twill lines are diagonal twill lines meaning that the CD vector component of these twill lines is unequal to zero.

Such woven fabrics are already known in the market. One example of such a fabric 10’ is shown in figure 1 which illustrates a view on of the paper side of the fabric 10’. As can be seen the paper side is formed by a plurality of warp yams interwoven with a plurality of weft yams. For the sake of clarity only three warp yams are provided with reference signs, namely WAT, WA2’ and WA3’, and only five weft yams are provided with reference signs, namely WET, WE2’, WE3’, WE4’ and WE5’. The fabric is flat woven which means that the warp yams extend substantially, but not 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 yams would correspond to the weft yams and vice versa.

In the shown example from the prior art each warp yam forms serval flotations on the paper side of the woven fabric 10’, wherein all flotations have the same length. One of these flotations is denominated with reference sign FL’ in figure 1 . This flotation FL’ is formed by warp yam WA2’ which floats above the five weft yams WET-WE5’. The neighboring warp yams WAT and WA3’ form similar flotations on the paper side of the woven fabric 10’ but with an offset. Thus, warp yam WAT floats only above weft yams WE4’ and WE5’ - and three further weft yams without reference sign - but not about weft yams WET, 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 figure 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. For the sake of clarity, it should be mentioned that the word “flotation” means that a yam floats about at least two other yams that are located next to each other.

The diagonal twill lines form a certain angle with the machine direction MD of the woven fabric 10’, which angle is not zero. If the direction of the twill line TL’ is described by an MD vector component MD-VC’ extending in the machine direction MD of the woven fabric 10’ and an CD vector component CD-VC’ extending in the cross machine direction CD of the woven fabric 10’, this means that the value of the CD vector component CD-VC’ is unequal to zero. In the present example the CD vector component CD-VC’ is directed against the cross machine direction CD of the woven fabric 10’ so that it has a negative sign. The ratio of the MD vector component MD-VC’ and the CD vector component CD-VC’ is characteristic for the angle formed by the diagonal twill line TL’ with the machine direction MD of the woven fabric 10’.

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. However, the strong diagonal twill lines make the fabric directional and difficult to guide on the paper machine.

It is an object of the present invention to avoid or at least reduce this problem. In particular the present invention aims to provide a woven fabric that is conducive to sheet building while at the same time it is easy to guide on the paper machine.

This object is achieved by a woven fabric according to the independent claim. Advantageous embodiments are the subject-matter of the dependent claims.

In particular the problem is solved by the generic woven fabric as described at the beginning wherein the plurality of diagonal twill lines consists of first diagonal twill lines and second diagonal twill lines, wherein the CD vector components of the first diagonal twill lines have an opposite sign to the CD vector components of the second diagonal twill lines, and wherein the sum of all CD vector components of the first diagonal twill lines is substantially balanced with the sum of all CD vector components of the second diagonal twill lines.

In this context the term “substantially balanced” means that the absolute value of the CD vector components of all first diagonal twill lines taken together corresponds to 80% to 120%, preferably to 90% to 110%, most preferably to 100%, of the absolute value of absolute value of the CD vector components of all second diagonal twill lines taken together.

Having diagonal twill lines extending in different directions on the paper side of the woven fabrics allows to guide the woven fabric easily on the paper machine.

Preferably, the woven fabric has only one layer. In such a case the warp and weft yarns that form the paper side at the same part also form the machine side of the woven fabric.

According to a preferred embodiment the number of the first diagonal twill lines substantially equals the number of the second diagonal twill lines. Furthermore, total length of all first diagonal twill lines can substantially equal the total length of all second diagonal twill lines.

The first diagonal twill lines preferably have all the same first CD vector component and the second diagonal twill lines preferably also have all the same second CD vector component. More preferably, the first CD vector component has the same absolute value than the second CD vector component. This can result in some kind of symmetry of the first diagonal twill lines and the second diagonal twill lines with respect to the machined direction of the woven fabric. This is especially true if additionally all diagonal twill lines have the same MD vector component.

Preferably the diagonal twill lines are formed from neighboring flotations of warp yams, wherein the flotations have a length of at least 3, more preferably of 5. Some of the weft yarns can have a different cross section than other weft yams. For example the cross sections can vary as to their size and/or as to their shape. However, additionally or alternatively these weft yams can differ from the other weft yams with respect to their material and/or type. With “type” is meant here that the weft yams are either monofilaments or multifilaments.

A very advantageous embodiment is characterized in that the weft yams that are situated in the middle of any one of the flotations that define the diagonal twill lines have a cross section which is smaller than the cross sections of the remaining weft yams that are not situated in the middle of any one of the flotations that define the diagonal twill lines. With such a configuration of different cross sections of the weft yams, it is possible to keep the knuckle height of the flotations relatively low, i.e. to control the knuckle height of the flotations.

Preferably the warp yams which form with their flotations the diagonal twill lines are interwoven with the weft yams in a plain weave structure between two successive flotations. In other words the corresponding sections of the warp yams are interwoven with the weft yams in such a way that the warp yam goes continuously above and below directly neighboring weft yams.

To achieve a more straight and less “stepped” twill line, it is advantageous if the flotations of the warp yams which define the diagonal twill lines themselves form an angle unequal to 0° with the machine direction of the woven fabric, wherein the sign of the angle corresponds to the sign of the MD vector component of the diagonal twill line that is formed by the corresponding flotation.

In a preferred embodiment at least some of the diagonal twill lines extend straight from one side of the woven fabric to the opposite side thereof. Additionally or alternatively at least some of the diagonal twill lines can end somewhere between opposite sides of the woven fabric. With “sides” of the fabric are meant the left and the right side of the fabric when looking into machine direction of the fabric.

Some diagonal twill lines can be broader than other diagonal twill lines. A broader twill line can be achieved for example by having two or more twill lines directly next to each other, i.e. without any separation e.g. a separation formed by a plain weave structure between them. Then these two or more twill lines can jointly form one broader twill line.

In some embodiments of the present invention the diagonal twill lines can be formed from neighboring flotations of warp yams, wherein the flotations have a length of 7 or even more.

To obtain a desired level of contact area on the paper side of the fabric without removing excessive amounts of warp yam material, it is proposed that the weft yams that are situated in the middle of any one of the flotations that define the diagonal twill lines pass over at least one adjacent warp yam on a first side of the corresponding flotation and pass under at least one adjacent warp yam on a second side of the corresponding flotation. Furthermore, it is proposed that the weft yams that are situated in the middle of any one of the flotations that define the diagonal twill lines each have one adjacent other weft yam which other weft yam passes over at least one adjacent warp yam on the second side of the corresponding flotation and passes under at least one adjacent warp yam on the first side of the corresponding flotation.

More preferably the weft yams that are situated in the middle of any one of the flotations that define the diagonal twill lines pass over exactly one adjacent warp yam on a first side of the corresponding flotation and pass under exactly two adjacent warp yams on a second side of the corresponding flotation, wherein the weft yams that are situated in the middle of any one of the flotations that define the diagonal twill lines each have one adjacent other weft yam which other weft yam passes over exactly one adjacent warp yam on the second side of the corresponding flotation and passes under exactly two adjacent warp yams on the first side of the corresponding flotation.

The weft yams that are situated in the middle of any one of the flotations that define the diagonal twill lines and their corresponding adjacent other weft yams can be equal to each other in view of at least one the following features: cross section, material, type, but may differ from other weft yams in the woven fabric in view of that feature.

Especially the weft yams of the pair of weft yams can have a smaller diameter than other weft yams of the woven fabric. In the following the present invention is explained in more detail with the aid of different exemplary embodiments shown in the following figures:

Figures 2 and 2a show a first embodiment of the present invention and a modification of the first embodiment, respectively;

Figures 3 and 3a show a second embodiment of the present invention, similar to the first embodiment, and a modification of the second embodiment, respectively;

Figures 4 and 4a show a third embodiment of the present invention and a modification of the third embodiment, respectively;

Figures 5 and 5a show a fourth embodiment of the present invention, similar to the third embodiment, and a modification of the fourth embodiment, respectively;

Figures 6 and 6a show the weaving pattern and the weaving card of the third embodiment of the present invention, respectively;

Figures 7a-7f show the weft yarn paths of the third embodiment;

Figures 8a-8c show the warp yam paths of the third embodiment;

Figures 9 and 9a show a fifth embodiment of the present invention, similar to the third embodiment, and a modification of the fifth embodiment, respectively;

Figures 10 and 10a show a sixth embodiment of the present invention and a modification of the sixth embodiment, respectively; and

Figures 11 and 12 show a seventh and an eighth embodiment of the present invention, respectively.

A first embodiment of the present invention is shown in figure 2 which illustrates a view on the paper side of a portion of a woven fabric 10. The paper side is formed by a plurality of warp yams interwoven with a plurality of weft yams. 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 , WA2 and WA3, and only five weft yams are provided with reference signs, namely WE1 , WE2, WE3, WE4 and WE5. The fabric is flat woven which means that the warp yams 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.

Each warp yarn forms serval flotations on the paper side of the woven fabric 10, wherein all flotations have the same length in the shown embodiment. One of these flotations is denominated with reference sign FL1 in figure 2. The flotation FL1 is formed by warp yarn WA1 which floats above the five weft yams WE1 -WE5. Another of these flotations is denominated with reference sign FL3 which is formed by warp yam WA3 which also floats above the five weft yams WE1-WE5. Yet another of these flotations is denominated with reference sign FL2 which is formed by warp yam WA2 floating weft yams WE1 and WE2 and three other weft yams but not weft yams WE3, WE4 or WE5. Flotation FL2 is directly neighboring both, flotation FL1 and flotation FL3, wherein the flotations FL1 and FL3 are not neighbored to each other.

All the flotations together form a plurality of twill lines on the paper side of the woven fabric 10. In figure 2 some twill lines extend in a direction which - roughly speaking - extends from the lower right side to the upper left side. These twill lines will be referred to as “first diagonal twill lines” in the following. The remaining twill lines extend - again roughly speaking - in a direction from the lower left side to the upper right side in figure 2. These twill lines will be referred to as “second diagonal twill lines” in the following. The first diagonal twill lines are all parallel to each other and spaced apart from each other by the same distance. Similarly, the second diagonal twill lines are parallel to each other and spaced apart from each other. However the distance between the second twill lines varies in this exemplary embodiment. To be more precise, there are two different distances between parallel second twill lines, wherein the two different distances alternate.

Thus, the first diagonal twill lines and the second diagonal twill lines cross each other in a substantially regular pattern. The woven fabric 10 comprises areas with a plain weave structure between the intersecting first and second diagonal twill lines. These areas define pockets on the paper side of the woven fabric 10, whereas the first and second diagonal twill lines define elevations on the paper side of the woven fabric 10. Thus, the woven fabric 10 is structured on its paper side wherein the structure is preferably adapted to impart a good visible pattern on a final fiber web, in particular final tissue fiber web, that is formed or transported in a wet form on the paper side of the woven fabric 10.

For the sake of clarity only one first diagonal twill line is denominated with reference sign TL1 in figure 2, and only one second diagonal twill line is denominated with reference sign TL2 in figure 2. The flotation FL1 contributes to the definition of the first diagonal twill line TL1 , the flotation FL3 contributes to the definition of the second diagonal twill line TL2, and the flotation FL2 contributes to the definition of both, the first and second diagonal twill lines TL1 and TL2. In other words, the flotation FL2 is situated at the crossing point of the two diagonal twill lines TL1 and TL2.

The first diagonal twill line TL1 forms a first angle with the machine direction MD of the woven fabric 10, which angle is not zero. The direction of the first diagonal twill line TL1 can be described by a first MD vector component MD-VC1 extending in the machine direction MD of the woven fabric 10 and a first CD vector component CD-VC1 extending in the cross machine direction CD of the woven fabric 10. The value of the first CD vector component CD-VC1 is unequal to zero.

The second diagonal twill line TL2 forms a second angle with the machine direction MD of the woven fabric 10, which angle is not zero. The direction of the second diagonal twill line TL2 can be described by a second MD vector component MD-VC2 extending in the machine direction MD of the woven fabric 10 and a second CD vector component CD-VC2 extending in the cross machine direction CD of the woven fabric 10. The value of the second CD vector component CD-VC2 is unequal to zero.

Like in the present embodiment it is preferable that the first MD vector component MD- VC1 is the same as the second MD vector component MD-VC2 in view of its direction and magnitude, whereas the first CD vector component CD-VC1 only corresponds to the second CD vector component CD-VC2 in terms of its magnitude but not in terms of its direction. In fact, the first CD vector component CD-VC1 is directed to the left in figure 2 and, thus, against the cross machine direction CD of the woven fabric 10, whereas the second CD vector component CD-VC2 is directed to the right in figure 2 and, thus, in cross machine direction CD of the woven fabric 10. In other words the first CD vector component CD-VC1 and the second CD vector component CD-VC2 have the same absolute value but opposite signs. Here the sign of the first CD vector component CD-VC1 is negative while the sign of the second CD vector component CD-VC2 is positive.

The ratio of the first MD vector component MD-VC1 and the first CD vector component CD-VC1 is characteristic for the first angle formed by the first diagonal twill line TL1 with the machine direction MD of the woven fabric 10. The ratio of the second MD vector component MD-VC1 and the second CD vector component CD-VC2 is characteristic for the second angle formed by the second diagonal twill line TL2 with the machine direction MD of the woven fabric 10. The first angle and the second angle also have the same magnitude but opposite signs.

Such a woven fabric with corresponding first diagonal twill lines TL1 and second diagonal twill lines TL2 on its paper side is not only conducive to sheet building, especially when the sheet is transferred to it with a rush speed differential, but can also be easily guided on the paper machine.

Notably, the flotations FL1 and FL3 themselves are inclined with respect to the machine direction MD of the woven fabric 10, wherein their inclination substantially corresponds to the inclination of the first diagonal twill line TL1 and the second diagonal twill line TL2 with the machine direction, respectively. In contrast to that, the flotation FL2 at the crossing point of the two diagonal twill lines TL1 and TL2 extends substantially parallel to the machine direction MD of the woven fabric 10.

Figure 2a shows a modification of the first embodiment from figure 2. The portion of a woven fabric in figure 2a has substantially the same weaving pattern as the weaving pattern of the portion of the woven fabric 10 shown in figure 2. However, in figure 2a weft yams with different diameter are applied. To be more precise, the weft yams that pass under the middle of any of the flotations of the warp yams on the paper side of the woven fabric have a smaller diameter than the remaining weft yams that do not pass under the middle of any of the flotations of the warp yams on the paper side of the woven fabric. This results in that the knuckles formed by the warp yam flotations on the paper side are not as high as in the first embodiment according to figure 2. Thus, the pattern imparted in the final fiber web can be positively influenced. In the modification according to figure 2a all warp yam flotations on the paper side of the woven fabric have the same length because they all pass over five consecutive weft yams. Furthermore, two consecutive weft yams having a larger diameter are followed by one weft yam having a smaller diameter and so on.

Figures 3 and 3a show a second embodiment of the present invention, similar to the first embodiment, and a modification of the second embodiment, respectively. In the following only the differences as to the first embodiment and its modification will be explained. For the rest, reference is made to the above description.

The second embodiment according to figure 3 and its modification according to figure 3a substantially only differ from the first embodiment according to figure 2 and its modification according to figure 2a, respectively, in that some second twill lines are broader then the remaining second twill lines and also than the first twill lines. In fact, broad second twill lines alternate with small second twill lines. The width of the twill lines can be adjusted by the number of warp yam flotations that contribute to their definition.

Figures 4 and 4a show a third embodiment of the present invention and a corresponding modification thereof, respectively. In the following only the differences as to the first embodiment and its modification will be explained. For the rest, reference is made to the above description.

The third embodiment according to figure 4 and its modification according to figure 4a substantially differ from the first embodiment according to figure 2 and its modification according to figure 2a, respectively, in that some first twill lines end when reaching a second twill line and vice versa. In the portion of the woven fabric shown in figure 4 only one first diagonal twill line really crosses one second diagonal twill lines. All other first and second diagonal twill lines end at another diagonal twill line in this shown portion. The two crossing diagonal twill lines divide the shown portion of the woven fabric into four sections, two of them having first diagonal twill lines extending parallel to each other, and two of them having second diagonal twill lines extending parallel to each other.

The third embodiment according to figure 4 is described in more detail with respect to figures 6 - 8c, wherein figure 6 shows the weaving pattern of the third embodiment, figure 6a shows the weaving card of the third embodiment, figures 7a-7f show the weft yam paths of the third embodiment, and Figures 8a-8c show the warp yarn paths of the third embodiment.

Figures 5 and 5a show a fourth embodiment of the present invention, similar to the third embodiment, and a modification of the second embodiment, respectively. In the following only the differences as to the third embodiment and its modification will be explained. For the rest, reference is made to the above description.

The fourth embodiment according to figure 5 and its modification according to figure 5a substantially only differ from the third embodiment according to figure 4 and its modification according to figure 4a, respectively, in that some first and second twill lines are broader then the remaining first and second twill lines. In fact, broad first and second twill lines alternate with small first and second twill lines, respectively.

All exemplary embodiments one to four with their respective modifications have in common that the flotations which form the diagonal twill lines each have a length of five. That means that the corresponding warp yams pass over five consecutive weft yams on the paper side of the woven fabric.

Furthermore, in all these embodiments one to four the weft yams that pass under the middle of any of the flotations of the warp yams on the paper side of the woven fabric are woven in a plain weave structure with the warp yams of the woven fabric. Thus, each third weft yam in these embodiments is woven in plain weave. In figures 7a-f referring to the third embodiment these weft yams correspond to weft yams 3, 6, 9 and so on. Moreover, these weft yams can be easily identified in figures 2a, 3a, 4a and 5a referring to the corresponding modifications, since these weft yams have a smaller diameter than the remaining weft yams that do not pass under the middle of any of the flotations of the warp yams on the paper side of the woven fabric.

Even though using weft yams with a smaller diameter results in that the warp yam flotations on the paper side are not as high as using weft yams with a larger diameter, there is still room for improvements. It is the merit of the inventor to have found out that a weft yam being up on either side at the center of every warp yam flotation creates a pressure point at the center of each flotation which restricts fabric life. The pointed nature of the warp yarn flotation also makes it difficult to surface sand the fabric to the desired level of contact area without removing excessive amounts of material of the warp yarns. In addition, the weft yams with the plain weave structure can make it difficult to drive the count high enough to reduce fabric permeability to a reasonable level.

To further improve the above described embodiments of the present invention, it is proposed to substitute each weft yam that passes under the middle of a flotation on the paper side of the woven fabric by a pair of adjacent weft yams that are not woven in a plain weave structure. To be more precise, it is preferred that one weft yam of the pair of weft yams passes over exactly one warp yam that is adjacent the flotation on a first side (e.g. on the left hand side) of the flotation and passes below exactly two warp yams that are adjacent the flotation on a second side (e.g. on the right hand side) of the flotation, while the other weft yam of the pair of weft yams passes over exactly one warp yam that is adjacent the flotation on the second side (e.g. the right hand side) of the flotation and passes below exactly two warp yams that are adjacent the flotation on the first side (e.g. the left hand side) of that flotation.

Modifying that way the third embodiment shown in figure 4 and its corresponding modification shown in figure 4a results in the fifth embodiment shown in figure 9 and its corresponding modification shown in figure 9a, respectively. In the fifth embodiment and its modification each flotation of the warp yams that form the diagonal twill lines has the length of seven, meaning that the corresponding warp yams float over seven consecutive weft yams on the paper side. Furthermore, each weft yam from the pair of weft yams passes over one warp yam and then under three warp yams instead of going up and down all the time as in the plain weave structure of the third embodiment. The result is that the woven fabric according to the fifth embodiment has the same number of weft knuckles compared to the third embodiment shown in figure 4 but the point at the center of the warp yam flotation is flattened. The resulting fabric has much higher natural contact area so that les surface sanding is required to achieve the desired level of contact area. The pressure points are also eliminated. Furthermore, the elimination of the plain weave also allows the count to be woven higher which gives the advantage of lower air permeabilities that leads to better sheet drying. A sixth embodiment of the present invention is shown in figure 10. Like in the fifth embodiment the warp yarn flotations forming the diagonal twill lines all have the length of seven. Furthermore, weft yams that are situated in the middle of any one of the flotations that define the diagonal twill lines pass over exactly one adjacent warp yarn on a first side of the corresponding flotation and pass under exactly two adjacent warp yams on a second side of the corresponding flotation, wherein the weft yams that are situated in the middle of any one of the flotations that define the diagonal twill lines each have one adjacent other weft yam which other weft yam passes over exactly one adjacent warp yam on the second side of the corresponding flotation and passes under exactly two adjacent warp yams on the first side of the corresponding flotation. Thus, this embodiment substantially exhibits the same advantageous like the previously described fifth embodiment.

Figure 10a shows a modification of the sixth embodiment from figure 10. The portion of a woven fabric in figure 10a has substantially the same weaving pattern as the weaving pattern of the portion of the woven fabric shown in figure 10. However, in figure 10a weft yams with different diameter are applied. To be more precise, the weft yams that are situated in the middle of any one of the flotations that define the diagonal twill lines and their corresponding adjacent other weft yams have a smaller diameter than the remaining weft yams that do not pass under the middle of any of the flotations of the warp yams on the paper side of the woven fabric. This results in that the knuckles formed by the warp yam flotations on the paper side are even less high compared in the sixth embodiment according to figure 10.

A seventh and an eighth exemplary embodiment are shown in figures 11 and 12 respectively. Differently to the previously described embodiments of the present invention, the flotations that form the diagonal twill lines have a length greater than 7 meaning that the corresponding warp yams pass over more than 7 consecutive weft yams. Furthermore, in these two embodiments the twill lines do not cross each other. Last but not least, the weft yams of the seventh embodiment according to figure 11 all have the same weaving pattern, meaning here that all weft yams pass over one warp yam and then under seven warp yams on the paper side of the fabric.

Many further modifications are thinkable within the scope and spirit of the present invention as defined in the independent claims. Finally it should be noted that the modified embodiments shown in figures 2a, 3a, 4a, 5a, 9a and 10a may additionally or alternatively differ from their corresponding basic embodiments according to figures 2, 3, 4, 5, 9 and 10, respectively, in that some weft yams are made from another material and/or are of a different type than other weft yams.

Reference signs woven fabric woven fabric (prior art)

CD cross machine direction

CD-VC1 first CD vector component

CD-VC2 second CD vector component

CD-VC’ CD vector component (prior art)

FL1-FL3 flotations flotation (prior art) machine direction

MD-VC1 first MD vector component

MD-VC2 second MD vector component

MD-VC’ MD vector component (prior art)

TL1 first diagonal twill line

TL2 second diagonal twill line

TL’ twill line (prior art)

WA1 - WA3 warp yarns

WA1 ’ - WA3’ warp yarns (prior art)

WE1 - WE5 weft yarns

WE1 ’ - WE5’ weft yams (prior art)