TRIPLE PAPERMAKING FABRIC

Abstract

A papermaking fabric has a fabric repeating unit that comprises eight top MD yarns and eight bottom MD yarns that extend in machine direction; three top CMD yarns interwoven only with the top MD yarns; three bottom CMD yarns interwoven only with the bottom MD yarns; and two pairs of binding yarns interwoven with both the top MD yarns and the bottom MD yarns; the binding yarns of each pair cross each other under respective transition yarns; the binding yarns of each pair, together, leave exposed on a top surface of the fabric only single isolated transition yarns, all separated from each other in cross machine direction by a plurality of adjacent top MD yarns.

Description

TECHNICAL FIELD

The present invention relates to a papermaking fabric, in particular intended for use as a forming fabric in a forming section of a papermaking machine.

BACKGROUND ART

The traditional fourdrinier papermaking process mainly provides three successive steps, carried out in the corresponding sections of the papermaking machine: forming section, pressing section, drying section.

In the forming section, an aqueous pulp of cellulose fibers (and any possible other components) is arranged on a so-called forming fabric or canvas, which is tape-shaped closed in a loop and supported by rollers. The removal of water from the pulp through the forming fabric leads to the progressive formation of a wet paper material tape, with a relatively high water content still remaining. A further removal of water takes place in the pressing section, in which the paper material is pressed by passing through one or more pairs of rollers. The paper material is then sent to the drying section for final moisture removal. The paper thus formed is ready for the subsequent finishing and packaging steps.

In the following, as customary in the field of papermaking and related fabrics, the terms “machine direction” (abbreviated “MD”) and “cross machine direction” (abbreviated “CMD”) are used to indicate respectively a direction aligned with the feed direction of the forming fabric in the papermaking machine, and a direction parallel to the fabric surface and crosswise (perpendicular) to the feed direction. Also direction or orientation of the warp and weft yarns of the forming fabric are indicated with reference to the machine direction and cross machine direction.

It is also intended, again as customary in the industry, that the surface of the forming fabric in contact with the cellulose pulp (i.e. with the paper material being formed) is the top surface of the fabric; and that the opposite surface facing the machine is the bottom surface. This reference is also adopted to describe the vertical spatial arrangement of the yarns in the forming fabric.

Some characteristics of the papermaking fabrics are of particular importance, such as the support capacity and filtration capacity, especially in the forming section.

Furthermore, the papermaking fabrics should show excellent stability even when moved at high speeds, a high permeability to reduce the amount of water retained in the pulp when transferred to the pressing section, and a reduced energy consumption for the handling thereof.

Although various types of papermaking fabrics are known, in particular for use in the forming section, margins of improvement in this field still seem to be possible, for example in terms of mechanical strength, stability, life span, draining capacity and quality of the formed paper.

For example, WO2014/091410 describes a papermaking fabric having a top layer formed by top CMD yarns interwoven only with top MD yarns; a bottom layer formed by bottom yarns CMD interwoven only with bottom MD yarns; binding yarns are interwoven with both the top and bottom MD yarns, therefore binding the top and bottom layer.

On the other hand, it is known that even small changes of the structure can unpredictably affect the fabric performance and therefore, the properties of the paper manufactured from said fabric. It is well known in the field that apparently even very similar structures can behave in a completely different manner.

In fact, the fabric structure has a direct impact on the quality of the paper sheet being formed on the fabric, intimately in contact with the same: but the way in which structural changes to the fabric may affect the quality of the paper is not predictable.

DISCLOSURE OF INVENTION

It is therefore an object of the present invention to provide a papermaking fabric that maintains these characteristics to a satisfactory extent, resulting in particular, fully effective, high drainage, resistant and stable in time, and ensuring the formation of high quality paper.

The present invention therefore relates to a papermaking fabric as defined, in essential terms, in the appended claim 1 and, in its additional characters, in the dependent claims.

The present invention also relates to the use of said fabric in a papermaking machine, and specifically in the forming section of the machine, as defined in the appended claim 18.

The invention provides a papermaking fabric which, as some known fabrics, has a two layer structure, each of which is formed by independent weft and warp yarns, and a binding system formed by pairs of binding yarns; however, the invention is distinguished by the specific fabric structure which allows a fully effective fabric to be obtained, high drainage, resistant and stable in time, and capable of ensuring the formation of high quality paper.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described in the following non-limiting examples of embodiments, with reference to the accompanying figures wherein:

FIG. 1 is a schematic top plan view of a top fabric layer according to the invention, of which a fabric repeating unit is shown;

FIG. 2 is a schematic top plan view of a bottom fabric layer of FIG. 1;

FIGS. 3a, 3b, 3c are sectional views according to the trace planes IIIa-IIIa, IIIb-IIIb, IIIc-IIIc of FIGS. 1 and 2, respectively;

FIG. 4 is a schematic top plan view of an alternative of the top fabric layer according to the invention;

FIG. 5 is a schematic top plan view of a bottom fabric layer of FIG. 4;

FIGS. 6a, 6b, 6c, 6d are sectional views according to the trace planes VIa-VIa, VIb-VIb, VIc-VIc, VId-VId of FIGS. 4 and 5, respectively;

FIG. 7 is a view in machine direction (warp) of a detail of the fabric of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIGS. 1-3, the number 100 denotes as a whole a papermaking fabric, in particular a forming fabric for use in the forming section of a papermaking machine.

The fabric 100 is a triple 16 harness fabric and comprises a top layer 101 and a bottom layer 102 formed, as usual, by respective repeat units which together form one fabric repeating unit 104; in FIGS. 1 and 2 a single fabric repeating unit 104 is shown; it is understood that in commercial and industrial applications the unit 104, as well as the repeat units of the individual layers 101, 102, may be repeated several times, both in machine direction and in cross machine direction, to form a fabric 100 having suitable sizes for use on a papermaking machine.

In general, the fabric 100 is formed by longitudinal warp yarns that extend in machine direction (MD) and cross weft yarns, substantially orthogonal to the preceding ones, which extend in cross machine direction (CMD). In the following (and as usual in the field), the longitudinal warp yarns that extend in machine direction will be indicated, for brevity, as “MD yarns”, and cross weft yarns which extend in cross machine direction as “CMD yarns”.

In this case, a repeat unit 104 of the fabric 100 comprises eight top MD yarns 1-8, three top CMD yarns P6,P10,P14, eight bottom MD yarns 9-16, three bottom CMD yarns MC5,MC9,MC13, and four binding yarns L7,L8,L11,L12 comprising respective support portions 115 and respective binding portions 116.

The top layer 101 comprises the top MD yarns 1-8 and the top CMD yarns P6,P10,P14, as well as the support portions 115 of the binding yarns L7,L8,L11,L12.

The bottom layer 102 comprises the bottom MD yarns 9-16 and the bottom CMD yarns MC5,MC9,MC13, as well as the binding portions 116 of the binding yarns L7,L8,L11,L12 which extend to bind the bottom MD yarns 9-16.

The top CMD yarns P6,P10,P14 are interwoven only with the top MD yarns 1-8, and the bottom CMD yarns MC5,MC9,MC13 are interwoven only with the bottom MD yarns 9-16. The binding yarns L7,L8,L11,L12 bind the top MD yarns 1-8 with the bottom MD yarns 9-16.

The top MD yarns 1-8 and the top CMD yarns P6,P10,P14 are interwoven so that each top CMD yarn P6,P10,P14 passes over three adjacent top MD yarns and under a following top MD yarn, and so on. For example, as shown in FIG. 3a, the top CMD yarn P6 passes under the top MD yarn 1, over the top MD yarns 2,3,4, under the top MD yarn 5, over the top MD yarns 6,7,8 and so on.

The same pattern is followed by all the top CMD yarns P6,P10,P14, but the top CMD yarns are offset in cross machine direction, by one or two top MD yarns, specifically.

In particular, the top CMD yarn P10 is offset by a top MD yarn with respect to the preceding top CMD yarn P6 (then passing under the top MD yarns 2, 6 and over the remaining top MD yarns 1,3,4,5,7,8), and the top CMD yarn P14 is offset by two top MD yarns with respect to the preceding top CMD yarn P10 (then passing under top MD yarns 4,8 and over the remaining top MD yarns 1,2,3,5,6,7).

The layers 101, 102 are joined and bound together to form the fabric 100 by means of the binding yarns L7,L8,L11,L12.

Each binding yarn L7,L8,L11,L12 comprises, in a fabric repeating unit 104, a support portion 115, which is arranged over the top MD yarns 1-8 and is interwoven with the same, and a binding portion 116, which is arranged under the top MD yarns 1-8 and is interwoven with the bottom MD yarns 9-16.

The binding yarns L7,L8,L11,L12 are arranged in pairs between pairs of adjacent top CMD yarns P6,P10,P14. Each pair of binding yarns L7,L8 and L11,L12 is arranged between two adjacent top CMD yarns P6,P10,P14.

In particular, the pair of binding yarns L7,L8 is arranged between the top CMD yarns P6,P10, and the pair of binding yarns L11,L12 is arranged between the top CMD yarns P10,P14.

The binding yarns L7,L8; L11,L12 of each pair (though represented side by side, for clarity, in relation to the out of scale schematic views of FIGS. 2 and 3) are interwoven together and are vertically overlapped, so that the support portions 115 of a binding yarn of the pair are overlapping the binding portions 116 of the other binding yarn of the pair, and vice versa; the two binding yarns of a pair cross each other along some of the top MD yarns 1-8 which define respective transition yarns T, which pass over both the binding yarns of the pair and under which, the binding yarns of the pair cross each other, which define the transition between the support portions 115 and the binding portions 116.

The binding yarns L7,L8; L11,L12 of each pair, together, leave exposed (on the top surface of the fabric 100) only single isolated transition yarns T. For each pair of binding yarns L7,L8; L11,L12 each transition yarn T is separated from the other transition yarns T in cross machine direction by a plurality of other top MD yarns; in other words, the transition yarns T are all separated from each other in cross machine direction by a plurality of other top MD yarns. There are, therefore, only individual transition yarns T (not adjacent to one another), regularly spaced from one another in the cross machine direction by a plurality of other top MD yarns. There are, instead, no adjacent transition yarns T. In particular, the transition yarns T are separated from each other by other three adjacent top MD yarns.

For the pair of binding yarns L7,L8 the transition yarns T are the top MD yarns 4 and 8; for the pair of binding yarns L11,L12 the transition yarns T are the top MD yarns 3 and 7. The transition yarns T of each pair of binding yarns L7,L8; L11,L12 are spaced by three adjacent top MD yarns; the transition yarns T of the two pairs of binding yarns L7,L8; L11,L12 are offset by one top MD yarn.

Each of the binding yarns L7,L8,L11,L12 passes over three adjacent top MD yarns 1-8 (defining a supporting portion 115) and under the following five adjacent top MD yarns 1-8 (defining a binding portion 116).

The binding yarns L7,L8; L11,L12 of each pair are interwoven so that the support portions 115 of one are arranged over the binding portions 116 of the other.

The two binding yarns L7,L8; L11,L12 of each pair, together, pass over three adjacent top MD yarns, under a following top MD yarn and so on, following the same pattern (i.e. the same interlacing) of the top CMD yarns P6,P10,P14. The pairs of binding yarns L7,L8; L11,L12, however, are offset with respect to adjacent top CMD yarns (between which the pair of binding yarns is arranged), so as to pass over the top MD yarns that are left exposed by the adjacent top CMD yarns.

Both binding yarns L7,L8,L11,L12 of a pair pass under the transition yarns T.

For example (FIG. 3b), the binding yarn L7 passes over the top MD yarns 1,2,3 with its own support portion 115 and passes under the top MD yarns 4,5,6,7,8 with its own binding portion 116; the binding yarn L8 (FIG. 3c) passes over the top MD yarns 5,6,7 with its own support portion 115, as it passes under the top MD yarns 1,2,3,4,8 with its own binding portion 116. Both binding yarns L7, L8 pass under the transition yarns T defined by the top MD yarns 4 and 8.

In the fabric repeating unit 104, each binding yarn L7,L8,L11,L12 binds (passes over) a tern of adjacent top MD 1-8 yarns and binds (passes under) a bottom MD yarn 9-16, in particular being offset in the machine cross direction by an even number of positions (for example, two positions or four positions) with respect to the tern of top bound MD yarns.

For example, the binding yarn L7 (FIG. 3b) passes over (i.e. binds) the top MD yarns and under 1,2,3 (i.e. binds) the bottom MD yarn 15, which is offset by four positions in cross machine direction with respect to the top MD yarn 3; the binding yarn L8 (FIG. 3c) passes over the top MD yarns 5,6,7 and under the bottom MD yarn 9, which is offset by two positions in cross machine direction with respect to the top MD yarn 7.

In the other pair of binding yarns L11,L12, the binding yarn L11 passes over (i.e. binds) the top MD yarns 1,2,8, and under the top MD yarns 3,4,5,6,7 and passes under (i.e. binds) the bottom MD yarn 14, which is offset by four positions in cross machine direction with respect to the top MD yarn 2; the binding yarn L12 passes over the top MD yarns 4,5,6, under the top MD yarns 1,2,3,7,8 and under the bottom MD yarn 10, which is also offset by four positions in cross machine direction with respect to the top MD yarn 7.

Ultimately, each binding yarn L7,L8,L11,L12 passes over three adjacent top MD yarns 1-8 and under the following five adjacent top MD yarns 1-8, and so on; and under one bottom MD yarn 9-16 and over all the following bottom MD yarns 9-16, and so on.

In this way, the binding yarns L7,L8,L11 L12 and the top CMD yarns P6,P10,P14 form a four satin structure (four harness satin) with the top MD yarns 1-8 (FIG. 1).

The bottom layer 102 (FIG. 2) comprises the bottom MD yarns 9-16, the bottom CMD yarns MC5,MC9,MC13 and the binding portions 116 of the binding yarns L7,L8,L11,L12.

The bottom CMD yarns MC5,MC9,MC13 are interwoven with the bottom MD yarns 9-16 with a “over-2/under-6” sequence. For example, as shown in FIG. 3a, the bottom CMD yarn MC5 passes over the bottom MD yarns 10,11 and under the bottom MD yarns 9 and 12-16.

The other bottom CMD yarns MC9,MC13 follow a similar pattern “over-2/under-6” with respect to the bottom MD yarns 9-16, but each is offset with respect to the adjacent bottom CMD yarn in cross machine direction (in particular by one position) so as to form an interrupted six harness twill structure.

The bottom layer 102 comprises, furthermore, the binding portions 116 of the binding yarns L7,L8,L11,L12.

As already described, each binding yarn L7,L8,L11,L12 binds, in the fabric repeating unit 104, three adjacent top MD yarns 1-8 and one bottom MD yarn 9-16; in particular, each binding yarn L7,L8,L11,L12 binds (by passing over) a tern of adjacent MD yarns 1-8 and (by passing over) one bottom MD yarn 9-16 which is offset by two or four positions in cross machine direction with respect to the tern of top MD yarns (specifically, with respect to the third and last top MD yarn of the tern).

For example, the binding yarn L7 (FIG. 3b) passes over (i.e. binds) the top MD yarns 1,2,3 and passes under (i.e. binds) the bottom MD yarn 15, which is offset by four positions in cross machine direction with respect to the top MD yarn 3; the binding yarn L8 (FIG. 3c) passes over the top MD yarns 5,6,7 and under the bottom MD yarn 9, which is offset by two positions in cross machine direction with respect to the top MD yarn 7.

Each binding yarn L7, L8, L11, L12 passes over a tern of adjacent top MD yarns and under the following five top MD yarns, and so on; and under one bottom MD yarn, and over the following seven bottom MD yarns, and so on.

The binding yarns L7,L8; L11,L12 of each pair, together, with respect to the top MD yarns 1-8, follow a sequence identical to the sequence of the top CMD yarns P6,P10,P14 with respect to the top MD yarns 1-8. In particular, the binding yarns L7,L8,L11,L12 of each pair follow an “over-3/under-1” sequence with respect to the top MD yarns 1-8, which is, specifically, the same sequence of the top CMD yarns P6,P10,P14 with respect to the top MD yarns 1-8.

Again, the binding yarns L7,L8; L11,L12 of each pair, together, follow an “under-1/over-5” sequence (pair of binding yarns L7,L8), or an “under-1/over-3” sequence (pair of binding yarns L11,L12), with respect to the bottom MD yarns 9-16.

Alternatively, the two pairs of binding yarns L7,L8; L11,L12 can follow the same sequence (and in particular one of the two indicated), preferably being offset by one position in cross machine direction with respect to one another.

The interweave of the yarns L7,L8,L11,L12 with the top MD yarns 1-8 and bottom MD yarns 9-16 can however assume other shapes.

As can be seen, as a whole, from the figures in the repeat unit 104 of the fabric 100 there are eight bottom MD yarns and eight top MD yarns.

The fabric 100 has a ratio between weft and warp yarns of 4:1.

It is intended as ratio between the weft and warp yarns the ratio between the number of weft yarns that are repeated to form the fabric in machine direction and the number of the warp yarns that are repeated in cross machine direction to form the fabric.

In the fabric 100 there are four weft yarns for each warp; this corresponds to the manufacturing mode of the fabric: in the weaving on a loom, four weft yarns are inserted for each warp yarn.

In cross section (section perpendicular to the machine direction), the fabric 100 thus has a sequence of four weft yarns that are repeated in machine direction for each warp yarn (that is alternately a top or bottom yarn depending on the weaving with the weft yarns).

In other words, the fabric repeating unit 104 is formed by a single warp yarn (MD yarn) every four weft yarns (CMD yarn): for each warp yarn (which can be a top MD yarn 1-8 or a bottom MD yarn 9-16, depending on the weave with the weft CMD yarns), there is in fact one top CMD yarn (one of P6,P10,P14), one bottom CMD yarn (one of MC5,MC9,MC13) and a pair of binding yarns (L7,L8; L11,L12).

In FIGS. 3a, 3b, 3c of the warp yarns are schematically shown overlapped in pairs to form the two layers; in reality, the warp yarns are thus arranged due to the interweaving effect with the weft yarns, but in cross machine direction there is only one warp yarn which is repeated.

The ratio between weft and warp yarns of 4:1 reflects the weaving mode of the fabric 100; at each beat (or insertion) of the fabric forming frame, on each warp yarn four consecutive weft yarns are inserted.

The fabric 100 has, therefore, a warp yarn every four weft insertions. Each top or bottom MD yarn is associated, in every frame insertion or beat, with a top CMD yarn, a bottom CMD yarn and a pair of binding yarns.

Those skilled in the art will recognize that the fabrics, according to the present invention, can take various shapes.

For example, with respect to what has been previously described, the number and/or the position of the binding yarn with respect to the number and/or the position of the top CMD yarns can be varied (for example there can be a binding yarn every two or three top CMD yarns, or there can be two or three or more binding yarns for each top CMD yarn).

Also the number of the top and bottom CMD yarns of the fabric repeating unit can vary with respect to what is described and illustrated purely by way of example.

Moreover, all the weaving patterns or structures described for the layers 101, 102 can be different from those illustrated and described; for example, the top surface of the fabric does not necessarily need to be formed by a four harness satin structure as shown, but can be like canvas, twill, broken twill, etc.; and the bottom surface of the fabric doesn't need to be a six harness broken twill structure, but can have another shape, such as a broken satin, plain structure (canvas), a broken twill, a twill, etcetera. Again, further alternative structure patterns may be used in the fabric according to the present invention.

Yarns of various shapes (for example having a rounded or flattened section) and size.

The shape of the yarns used in the fabric of the invention can vary, also depending on the properties to impart to the final product. For example, the yarns may be monofilament yarns, flat monofilament yarns, multifilament yarns, multifilament or monofilament interwoven yarns, yarns of any kind, or any combination thereof. The materials of which the yarns are made of, can be those commonly used in the field. For example polyester, polyamide, polyamide/polyester yarns, or the like can be used. The technician skilled in the art will be able to select the materials of the yarns also as a function of the specific application for which the final fabric is intended to be used.

For example, the top MD yarns, the top CMD yarns and the binding yarns can have a diameter (equal or different from one another) comprised between about 0.10 and 0.25 mm; the bottom MD yarns can have a diameter between about 0.12 and 0.30 mm; the bottom CMD yarns can have a diameter between about 0.10 and 0.35 mm; these are purely exemplary dimensions, and yarns of other sizes can be used depending on specific needs. The knit also (i.e. the knit size) of the fabric may also vary. For example, the knit size of the top surface can be between about 34×38 and 37×48 (warp yarns per cm×weft insertions per cm) and the total knit size may vary between about 66×74 and 78×96 (warp yarns per cm×weft insertion per cm).

A fabric with a ratio of 4:1 and with the bottom layer having an six harness interrupted twill structure, produced according to the invention, has, for example, the characteristics shown in Table 1.

TABLE 1
YARN               Dimensions
top MD             0.12 mm
bottom MD          0.12 mm
binding            0.11 mm
top CMD            0.11 mm
bottom CMD         0.18 mm
mesh (top surface) 37 × 44 *
mesh (total)       74 × 88 *
* warp yarns per cm × weft insertions per cm

In FIGS. 4-6, wherein the details similar or identical to those already described are indicated with the same reference numbers, an alternative of the fabric 100 of the invention is shown.

As shown in FIGS. 4 and 6a, the top layer 101 still has a four satin structure: the top CMD yarns, of which only a pair of adjacent yarns P14,P2 are represented, are in fact interwoven with the top MD yarns 1-8 with a sequence “over-3/under-1” (each top CMD yarn passes over three adjacent top MD yarns and under a following top MD yarn, and so on).

As shown in FIGS. 5 and 6b, the bottom layer 102 has a structure: the bottom CMD yarns, of which only a pair of adjacent yarns MC13,MC1 are represented, are interwoven with the bottom MD yarns 9-16 with a sequence “over-3/under-1” (each bottom CMD yarn passes over one bottom MD yarn and under the following three adjacent bottom MD yarns, and so on).

FIGS. 4, 5, 6c and 6d show a pair of binding yarns L15, L16, which together have the same interlacing as described above:

each binding yarn L15, L16 binds (passes over) a tern of adjacent top MD yarns 1-8 and binds (passes under) a bottom MD yarn 9-16, in particular offset in the cross direction by an even number of machine positions (for example, four positions) with respect to the tern of bound top MD yarns.

The binding yarn L15 (FIG. 6c) passes over (i.e. binds) the top MD yarns 1,2,3 and passes under (i.e. binds) the bottom MD yarn 15, which is offset by four positions in cross machine direction with respect to the top MD yarn 3; the binding yarn L16 (FIG. 6d) passes over the top MD yarns 5,6,7 and under the bottom MD yarn 11, which is also offset by four positions in cross machine direction with respect to the top MD yarn 7.

In all embodiments of the invention, it is possible to bind the top layer 101 and the bottom layer 102, as well as by means of the binding yarns extending in cross machine direction (i.e. in the weft direction) as above described, also in machine direction (i.e. in the warp direction).

For this purpose, as shown in FIG. 7, in the fabric repeating unit 104 at least a pair of overlapped MD yarns, i.e., one top MD yarn and one bottom MD yarn overlapping one another (belonging to the top layer 101 and to the bottom layer 102, respectively), as for example the top MD yarn 6 and the bottom MD yarn 14 located directly under the top MD yarn 14, cross each other in machine direction, i.e. in the warp direction, so as to define a pair of warp binding yarns MD6, MD14, while maintaining the weaving patterns of both the top layer 101 (example: four satin), and of the bottom layer 102 (example: interrupted six twill structure).

The warp binding yarns MD6, MD14 of each pair are arranged directly one over the other, and cross each other maintaining the same basic structure (four satin). Each top MD yarn 1-8 and each bottom MD yarn 9-16 then maintains its weaving position even if acting as a warp binding yarn between the top layer 101 and the bottom layer 102.

In the fabric repeating unit 104 the warp binding yarns MD6, MD14 cross each other only once.

In the unit 104 several pairs of overlapped MD yarn may cross each other, even all the pairs, to define respective pairs of warp binding yarns: preferably, adjacent pairs of warp binding yarns cross each other, in offset positions, in machine direction.

It is understood that the binding in machine direction (warp) applies to all the embodiments of the invention and to all the weaving patterns of the fabric 100 mentioned above and others, that furthermore, fall under the invention.

According to an aspect of the invention, the fabric 100 described above is used in a papermaking process, in particular in the forming section of a papermaking machine. The process comprises the steps of:

(A) providing a papermaking fabric as described above;

(B) arranged on the top surface of the fabric an aqueous pulp of cellulose and/or a paper material to be formed; and

(C) removing water from the pulp and/or from the paper material to be formed.

Said process is, essentially known and well understood by those skilled in the art, therefore further details in this respect are not necessary.

It remains understood that, with what has been described and illustrated herein further modifications and alternatives can be applied which do not depart from the scope of the invention as defined in the appended claims.

Claims

1. A triple papermaking fabric (100), having at least one fabric repeating unit (104) that comprises: wherein: the fabric being characterized in that:

a set of warp yarns or machine direction (MD) yarns (1-16), that extend in machine direction (MD) and subdivide in eight top MD yarns (1-8) and eight bottom MD yarns (9-16);

a set of weft yarns or cross machine direction (CMD) yarns (P6,P10,P14; MC5,MC9,MC13; L7,L8,L11,L12), that extend in cross machine direction and specifically comprise: three top CMD yarns (P6,P10,P14), three bottom CMD yarns (MC5,MC9,MC13) and two pairs of binding yarns (L7,L8,L11,L12) comprising respective support portions (115) and respective binding portions (116);

the top CMD yarns (P6,P10,P14) are interwoven only with the top MD yarns (1-8) to form a top fabric layer (101);

the bottom CMD yarns (MC5,MC9,MC13) are interwoven only with the bottom MD yarns (9-16) to form a bottom fabric layer (102);

the binding yarns (L7,L8,L11,L12) are interwoven with both the top MD yarns (1-8) and the bottom MD yarns (9-16) so as to bind the top layer (101) with the bottom layer (102);

the binding yarns (L7,L8,L11,L12) are arranged in pairs between pairs of adjacent top CMD yarns (P6,P10,P14); and the binding yarns (L7,L8,L11,L12) of each pair intersect with each other under respective transition yarns (T), which pass over both the binding yarns of the pair;

the binding yarns (L7,L8; L11,L12) of each pair, together, leave exposed on a top surface of the fabric (100) only single isolated transition yarns (T), all separated from each other in cross machine direction by a plurality of adjacent top MD yarns (1-8); and

the transition yarns (T) defined by a first pair of binding yarns (L7,L8) are offset by one top MD yarn with respect to the transition yarns (T) defined by a second pair of binding yarns (L11,L12).

2. The fabric according to claim 1, wherein the transition yarns (T) of each pair of binding yarns (L7,L8,L11,L12) are separated from each other by terns of adjacent top MD yarns (1-8).

3. The fabric according to claim 1 or 2, wherein the sequence of the two binding yarns (L7,L8; L11,L12) of each pair, together, with respect to the top MD yarns (1-8) is the same as the sequence of the top CMD yarns (P6,P10,P14) with respect to the top MD yarns (1-8).

4. The fabric according to claim 1, wherein the two binding yarns (L7,L8; L11,L12) of each pair, together, pass over three adjacent top MD yarns (1-8) and under the following top MD yarn, and so on.

5. The fabric according to claim 1, wherein each binding yarn (L7,L8,L11,L12) passes over three adjacent top MD yarns (1-8) and under the following five adjacent top MD yarns (1-8), and so on; and under one bottom MD yarn (9-16) and over all the following bottom MD yarns (9-16), and so on.

6. The fabric according to claim 1, wherein the pairs of binding yarns (L7,L8; L11,L12) are offset with respect to the adjacent top CMD yarns (P6,P10,P14) so, as to pass over the top MD yarns (1-8) which are instead left exposed by the adjacent top CMD yarns (P6,P10,P14).

7. The fabric according to claim 1, wherein each binding yarn (L7,L8,L11,L12) binds, i.e. passes over, a tern of adjacent top MD yarns (1-8) and binds, i.e. passes under, one bottom MD yarn (9-16) which is offset in cross machine direction by an even number of positions with respect to said tern of top MD yarns.

8. The fabric according to claim 7, wherein each binding yarn (L7,L8,L11,L12) binds a tern of adjacent top MD yarns (1-8) and one bottom MD yarn (9-16) which is offset by two or four positions in cross machine direction with respect to the third and last top MD yarn of the tern.

9. The fabric according to claim 1, wherein each top CMD yarn (P6,P10,P14) passes over three adjacent top MD yarns (1-8) and under the next top MD yarn (1-8), and so on.

10. The fabric according to claim 9, wherein the top CMD yarns (P6,P10,P14) are offset in cross machine direction by one or two top MD yarns (1-8).

11. The fabric according to claim 9, wherein the fabric repeating unit (104) there is a first, a second and a third top CMD yarns (P6,P10,P14); the second top CMD yarn (P10) being offset by one top MD yarn with respect to the preceding first top CMD yarn (P6) and the third top CMD yarn (P14) being offset by two top MD yarns with respect to the preceding second top CMD yarn (P10).

12. The fabric according to claim 1, wherein the binding yarns (L7,L8,L11,L12) and the top CMD yarns (P6,P10,P14) form a four harness satin structure with the top MD yarns (1-8).

13. The fabric according to claim 1, wherein the bottom CMD yarns (MC5,MC9,MC13) are interwoven with the bottom MD yarns (9-16) with an “over-2/under-6” sequence.

14. The fabric according to claim 13, wherein each bottom CMD yarns (MC5,MC9,MC13) is offset by one position in cross machine direction with respect to the preceding bottom CMD yarn.

15. The fabric according to claim 1, wherein the fabric (100) has a ratio between weft and warp yarns of 4:1.

16. The fabric according to claim 1, wherein the top layer (101) and the bottom layer (102) are also bound in machine direction, i.e. in the warp direction.

17. The fabric according to claim 16, wherein in the fabric repeating unit (104) at least a pair of directly overlapped MD yarns (MD6,MD14), i.e. a top MD yarn and a bottom MD yarn directly overlapping one another, cross each other in machine direction, i.e. in the warp direction, so as to define a pair of binding warp yarns (MD6,MD14) maintaining the weaving patterns of both the top layer (101) and the bottom layer (102).

18. Use of a fabric (100) according to claim 1 in a papermaking machine for conveying a cellulose pulp and/or a paper material to be formed.