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

BACKGROUND ART

The traditional Fourdrinier papermaking process substantially includes three subsequent steps, carried out in corresponding sections of the papermaking machine: forming section, pressing section, drying section.

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

Hereinafter, as customary in the papermaking industry, the terms "machine direction" (abbreviated "MD") and "cross machine direction" (abbreviated "CMD") are used to indicate a direction aligned with the feeding direction of the forming fabric in the papermaking machine and a direction parallel to the surface of the fabric and crosswise (orthogonal) to the feeding direction, respectively. The direction or orientation of the warp and weft yarns of the forming fabric are also indicated with reference to machine direction and cross machine direction.

Furthermore, again as customary in the industry, 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 the opposite side facing the machine is ^' the bottom surface. This reference will be adopted also to describe the vertical spatial arrangement of the yarns in the forming fabric.

Some features of the papermaking fabrics are particularly important, such as the supporting capacity and the filtering capacity, especially in the forming section.

Furthermore, papermaking fabrics must have excellent stability also when moved at high speed, high permeability for reducing the amount of water withheld in the pulp when it is transferred to the pressing section and a low energy consumption for moving them.

Although various types of papermaking fabrics are known, in particular for use in the forming section, there still appears to be margin for improvement in the industry, e.g. in terms of mechanical strength, stability, durability, draining capacity and quality of the formed paper.

DISCLOSURE OF INVENTION

It is there-fore an object of the present invention to provide a papermaking fabric which has all these features in satisfactory measure, being in particular fully efficient, highly draining, strong and stable in time, and which ensures the formation of high quality paper.

The present invention therefore relates to a papermaking fabric as disclosed in essential terms in accompanying claim 1 and the additional features of which are disclosed in the dependent claims.

The present invention further relates to the use of such a fabric in a papermaking machine, and specifically in the forming section of the machine, as well as a papermaking process using such a fabric, as disclosed in accompanying claims 13 and 14, respectively.

BRIEF DESCRIPTION' OF THE DRAWINGS

The invention is further described in the following non-limitative embodiments, with reference to the accompanying figures, in which:

- figure 1 is a diagrammatic top plan view of a top layer of a fabric according to the invention (showing one fabric repeat unit) ;

- figure 2 is a diagrammatic top plan view of a bottom layer of the fabric in figure 1;

- figures 3a, 3b, 3c are section views taken along plotting planes Illa-IIIa, Illb-IIIb, IIIc-IIIc of figures 1 and 2, respectively.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to figures from 1 to 3 , reference numeral 100 indicates a papermaking fabric as a whole, in particular a forming fabric to be used in the forming section of a papermaking machine.

The fabric 100 is a triple sixteen harness fabric and comprises a top layer 101 and a bottom layer 102 formed, as customary, by corresponding repeat units which form together a fabric repeat unit 104; figures 1 and 2 show a single fabric repeat unit 104; it is understood that in commercial and industrial applications the unit 104, as the repeat units of the single layers 101, 102, may be repeated several times, both in machine direction and in cross machine direction, for forming a fabric 100 of suitable size for use on a papermaking machine .

In general, the fabric 100 is formed by longitudinal warp yarns which extend in machine direction (MD) and by crosswise weft yarns, substantially orthogonal to the previous yarns, which extend in cross machine direction (CMD) . Hereinafter (and as customary in the industry) , the longitudinal warp yarns which extend in machine direction will be named "MD yarns", and the crosswise weft yarns which extend in cross machine direction will be named "CMD yarns" for the sake of simplicity.

In the case in point, a fabric repeat unit 104 of the fabric 100 includes eight top MD yarns 1-8, three top CMD yarns P6, P10,P14, eight bottom MD yarns 9-16, three bottom CMD yarns MC5 , C9 , C13 , and four binding yarns L7 , L8 , Lll, L12 comprising corresponding support portions 115 and corresponding binding portions 116.

The interweaving or weave of these yarns for forming the fabric 100 is described in detail below.

The top layer 101 includes the top MD yarns 1-8 and the to CMD yarns P6,P10,P14, as well as the support portions 115 of the binding yarns L7 , L8 , Lll, 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 , Lll, 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 yarn 9-16. The binding yarns L7 , L8 , Lll , L12 bind the top MD yarns 1-8 to 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 alternatively, over and under consecutive pairs of top MD yarns, i.e. by passing over two adjacent top MD yarns and under the two following adjacent top MD yarns, and so forth. For example, as shown in figure 3a, the top CMD yarn P6 passes under the top MD yarns 1,2, over the top MD yarns 3,4, under the top MD yarns 5,6, over the top MD yarns 7,8 and so forth ("over-2/under-2" sequence with respect to the top MD yarns 1-8) .

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

Layers 101, 102 are joined and bound to one another to form the fabric 100 by means of binding yarns L7,L8,L11,L12.

Each binding yarn L7 , L8 , Lll , L12 in a fabric repeat unit 104 comprises a support portion 115, which is interwoven with the top MD yarns 1-8, 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. In particular, the binding yarns L7 , L8 , Lll , L12 are organized 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 binding yarn pair L11,L12 is arranged between the top CMD yarns P10,P14.

The binding yarns L7 , L8 , Lll , L12 comprise respective support portions 115 , which are interwoven with the top MD yarns (i.e. pass over the top MD yarns), and respective binding portions 116, which pass under the top MD yarns and bind the bottom MD yarns .

The binding yarns L7,L8;L11,L12 of each pair (despite being shown side-by-side, for the sake of clarity, in the diagrammatic view not in scale in figure 2) are interwoven and superimposed vertically so that the support portions 115 of a binding yarn of the pair is superimposed on the binding portions 116 of the other binding yarn of the pair and vice versa; the two binding yarns of a pair intersect at some of the top MD yarns 2- 8 which define corresponding transition MD yarns which pass over both binding yarns of the pair and under which the binding yarns of the pair cross and define the transition between the support portions 115 and the binding portions 116.

For the pair of binding yarns L7,L8, the transition yarns are the top MD yarns 3-4 and 7-8.

The binding yarns L7 , L8 , Lll , L12 of each pair are interwoven so that the support portions of one are arranged over the binding portion of the other.

As a whole, the two binding yarns L7 , L8 ; Lll , L12 of each pair pass over the. top MD yarns under which the adjacent top CMD yarn passes.

The binding yarns L7 , L8 , Lll , L12 pass alternatively over a pair of two adjacent top MD yarns 1-8 (defining the support portions 115) and under the following six adjacent top MD yarns 1-8 (defining the binding portions 116) .

Both the binding yarns L7,L8, Lll, L12 of the pair pass under the transition yarns.

Each binding yarn L7 , L8 , Lll , L12 passes, with its support portion 115, over the top MD yarns 1-8 under which the top CMD yarns P6,P10,P14 pass, and pass under the top MD yarns 1-8 over which the top yarns CMD P6,P10, P14 pass.

For example (figure 3b) , the support portion 115 of the binding yarn L7 passes over the top MD yarns 1,2, while the binding portion 116 passes under the top MD yarns 3,4,5,6,7,8; the binding yarn L8 (figure 3c) passes over the top MD yarns 5,6 with the support portion 115 thereof, while it passes under the top MD yarns 1,2,3,4,7,8 with the binding portion 116.

Both binding yarns L7 , L8 pass under the transition yarns 3 , 4 and 7,8.

In the fabric repeat unit 104, each binding yarn L , L8 , Lll , L12 bonds (passes over) a pair of two adjacent top MD yarns 1-8 and binds (passes under) a bottom MD yarn 9-16, in particular offset in cross machine direction by two or three portions with respect to the pair of bound top MD yarns; for example, the binding yarn L7 (figure 3b) passes over the top MD yarns 1,2 and under the bottom MD yarn 12, which is offset by two positions in cross machine direction with respect to the top MD yarn 2; the binding yarn L8 (figure 3c) passes over the top MD yarns 5,6 and under the bottom MD yarn 9, which is offset by three positions in cross machine direction with respect to the top MD yarn 6.

Each binding yarn L7 , L8 , Lll , L12 passes over two adjacent top MD yarns 1-8 and under the next two adjacent top yarns MD 1-8, and so on; and under a bottom MD yarn 9-16 and over all the following bottom MD yarns 9-16, and so on.

The other pairs of binding yarns are interwoven in similar manner although they are preferably offset in cross machine direction by one or more top MD yarns with respect to the pair of preceding binding yarns .

In this manner, the binding yarns L7,L8,L11,L12 and the top CMD yarns P6,P10,P14 form a broken reps weave pattern with the top MD yarns 1-8 (figure 1) .

With reference to figures 2-3, the bottom layer comprises the bottom MD yarns 9-16, the bottom CMD yarns MC5,MC9,MC13 and the binding portions of the binding yarns L7 , L8 , Lll , L12.

The bottom CMD yarns MC5,MC9,MC13 are interwoven with the bottom MD yarns 9-16 with a "over-l/under-3" sequence (figure 3a) . For example, as shown in figure 3a, the bottom CMD yarn MC5 passes over the bottom MD yarns 11 and 15 and under the bottom MD yarns 9-10, 12- 14 and 16.

The other bottom CMD yarns MC9,MC13 follow a similar "over-l/under-3" pattern 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 so as to form a four harness satin structure.

Each binding yarn L7 , L8 , Lll , L12 binds, in the fabric repeat unit 104, two top MD yarns 1-8 and a bottom MD yarn 9-16; in particular, each binding yarn L7,L8,L11,L12 binds a pair of adjacent top MD yarns 1-8 and a bottom MD yarn 9-16 which is offset by two positions in cross machine direction with respect to the pair of top MD yarns (specifically, with respect to the second top MD yarn of the pair) ; for example, the binding yarn L7 (figure 3b) passes over the top MD yarns 1,2 and under the lower MD yarn 12, which is offset by two positions in cross machine direction with respect to the top MD yarn 2; the binding yarn L8 (figure 3c) passes over the top MD yarns 5,6 and under the bottom MD yarn 9.

Each binding yarn L7 , L8 , Lll , L12 passes over a pair of adjacent top MD yarns and under the next six top yarns MD, and so on; and under a bottom MD yarn and over the following seven bottom MD yarns, and so on. The same pattern is followed by all the binding yarns L7 , L8 , Lll , L12 , but the binding yarns are offset in cross machine direction, precisely by two top MD yarns.

Seen as a whole, the binding yarns of each pair (e.g. the binding yarns L7,L8) therefore follow a "over- 2/under-2" sequence with respect to the top MD . yarns 1- 8, i.e. a sequence which is complementary (in addition to being equal) to the sequence of the top CMD yarns P6,P10,P14 with respect to the top MD yarns 1-8; and a "under-l/over-3" sequence with respect to the top MD yarns 9-16, i.e. a sequence complementary to the sequence of the bottom CMD yarn MC5,MC9,MC13 with respect to the bottom MD yarns 9-16 (which is a "over- l/under-3" sequence) .

The interweave of the yarns L7 , L8 , Lll , L12 with the top MD yarns 1-8 and the bottom MD yarns 9-16 may take different forms.

It can be seen that in the figures as a whole the repeat unit 104 of the fabric 100 are eight bottom MD yarns and eight top MD yarns .

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

It is defined as the ratio between weft yarns and warp yarns the ratio between the number of weft yarns which are repeated to form the fabric in cross machine direction and the number of warp yarns which are repeated in cross machine direction to form the fabric. In the fabric 100 there are four weft yarns for each warp yarn; this corresponds to the manufacturing method of the fabric: in the weaving on the loom, four weft yarns are inserted for each warp yarn.

Crosswise (i.e. perpendicularly to machine direction) , the fabric 100 therefore has a sequence of four weft yarns which are repeated in machine direction for each warp yarn (which is alternatively a top yarn or a bottom yarn according to the weaving with the weft yarns) .

In other words, the repeat unit 104 of the fabric is formed by a single warp yarn (MD yarn) for each four weft yarns (CMD yarn) : for each warp yarn (which may be a top MD yarn 1-8 or a bottom MD yarn 9-16, according to the weave with the warp CMD yarns) there are indeed a top CMD yarn (one of either P6,P10,P14), a bottom CMD yarn (one of MC5 , MC9 , MC13 ) and a pair of binding yarns (L7,L8; L11,L12) .

The warp yarns are diagrammatically shown in figures 3a, 3b, 3c in pairs to form two layers; in fact, the warp yarns assume this arrangement by effect of the weaving with the weft yarns, but only one warp yarn is repeated in cross machine direction.

The 4 : 1 ratio between the weft yarns and the warp yarns reflects the weaving method of the fabric 100; four consequent weft yarns are inserted at each ledge (or insertion) of the fabric forming loom on each weft yarn.

The fabric 100 therefore has one warp yarn every four weft insertions . Each top or bottom MD yarn is associated in each loom insertion or ledge, to a top CMD yarn, a bottom CMD yarn and a pair of binding yarns.

A person skilled in the art will recognize that the fabrics according to the present invention may take different forms.

For example, with respect to the description above, the number and/or the position of the pairs of binding yarns may be varied with respect to the number and/or position the top CMD yarns (e.g. there may be one binding yarn for every two or three top CMD yarns, or there may be two or three or more binding yarns for every top CMD yarn) .

Yarns of various shapes (e.g. with round _x or flat section) and sizes may be used.

The shape of the yarns used in the fabric of the invention may be varied according to the properties intended to be imparted to the end product. For example, the yarns may be monofilament yarns, flat monofilament yarns, multifilament yarns, twisted multifilament or monofilament yarns, yarns of any type, or any combination thereof. The materials with which yarns are made may be those commonly used in the field. For example, polyester, polyamide, polyamide/polyester yarns or the like may be used. A person skilled in the art may select the materials of the yarns also according to the specific application for which the end product is intended.

For example, the top MD yarns, the top CMD yarns and the binding yarns may have (reciprocally equivalent or different) diameter from approximately 0,10 to 0,35 mm; the bottom MD yarns may have diameter from approximately 0,12 to 0,30 mm; the bottom CMD yarns may have diameter from approximately 0,10 and 0,50 mm; it is understood that these sizes are only an example, and other sizes may be used according to specific needs. The mesh (i.e. the size of the mesh) of the fabric may also vary. For example, the mesh size of the top surface must be comprised between approximately 32x37 and 37x46 (warp yarns per cm x weft insertions per cm) and the total mesh size may vary from approximately 64x74 to 74x92 (warp yarns per cm x weft insertions per cm) .

A fabric with 4:1 ratio and four harness satin structure bottom layer according to the invention has the features shown in table 1.

TABLE 1

( ^* ) warp yarns per cm x weft mesh per cm

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

(a) preparing a papermaking fabric as described above ;

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

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

Such a process is for the rest substantially well known by a person skilled in the art and therefore further details with this regard are not necessary.

Moreover, it is understood that further changes and variations may be made to the description provided herein, without departing from the scope of the invention as defined in the appended claims.