NZ553965A - Double layer forming fabric with high centre plane resistance - Google Patents

Abstract

Double layer forming fabrics, woven to an overall repeating weave pattern requiring at least 8 sheds in the loom, provide a low drainage area in a notional centre plane between the paper and machine side layers, to resist and retard initial impingement drainage. Transverse binder yarn pairs follow a single combined path interweaving with paper side layer and machine side layer yarns, with long internal floats under at least four paper side layer yarns between exchange points and interlacing points in the machine side layer. The members of the pairs are laterally displaced in relation to each other along the single combined path. The fabric has a total warp fill after heat setting of at least 100%. The drainage areas of the paper side layer and the machine side layers are between 25% and 50%, and the centre plane drainage area is between 8% and 20%.

Description

553965 Received by IPONZ 9 Sep 2010 DOUBLE LAYER FORMING FABRIC WITH HIGH CENTRE PLANE RESISTANCE Field of the invention.

The present invention relates to forming fabrics for use in papermaking machines. It is particularly concerned with double layer forming fabrics which are structured to provide a low drainage area in a notional centre plane between the paper 10 and machine side layers so as to resist and retard initial impingement drainage through the fabrics.

Background of the invention As used herein, the term "double layer forming fabric" refers to forming fabrics comprising two sets of yarns oriented in a first direction, one set located on the paper side and the other set located on the machine side of the fabric, and which are bound together by a single set of binder. 20 yarns oriented in a transverse direction and woven as pairs. The weave patterns of each of the paper and machine side surfaces, as determined by the overall fabric weave pattern, are either substantially the same or different. Further, as used herein, the term "transverse" refers to either the 25 machine direction or the cross machine direction of the fabric.

The binder yarns in the fabrics of this invention can be either weft yarns pairs, similar to those described, for 30 example, by Johnson in US 4,815,499, Barrett in US 5,544,678, or Seabrook et al. in US 5,826,627, or they can be warp yarn pairs such as are described in published US patent 1 553965 Received by IPONZ 9 Sep 2010 applications numbers 2003/0217782 by Nagura et al or US 2004/0020621 by Heger et al. , or any of US patents 5,152,326 to Vohringer, 4,605,585 to Johansson, 4,501,303 to Osterberg, and 6,223,780 to Kaldenhoff.

- In the double layer forming fabrics of the present invention, . all of the yarns oriented in the transverse direction as defined above comprise pairs of binder yarns, and the paper side layer and the machine side layer are each woven 10 to provide different, but related, weave patterns.

As used herein, the following terms have the following meanings: The term "binder yarn" refers to a yarn which occupies a 15 path in the paper side layer and which separately interlaces with a machine side layer yarn to occupy a path in the machine side layer. Either the warp yarns or the weft yarns in the fabric may be used as binder yarns. All of the yarns oriented in the transverse direction (as described above) in the 20 fabrics of this invention are binder yarns.

The term "drainage area", expressed as a percentage of the area of the fabric weave pattern repeat, refers to the proportion of that area not occupied by the yarns, both warp 25 and weft, used in weaving the fabric at a given substantially planar location within the fabric substantially parallel to the paper side surface and to the machine side surface of the forming fabric.

The term "fibre support index" or UFSI" refers to a calculation made according to the method described by Beran and summarized in Danby, R. & Perrault, J., ^Weaves of 2 553965 Received by IPONZ 9 Sep 2010 Papermaking Wires and Forming Fabrics", Montreal, QC, 90 th Annual PAPTAC Meeting, January 26-28, 2004/ page 2, and which provides a measure of the number of support points which are available to support the papermaking fibres on the paper side 5 surface of a given fabric weave pattern.

The term "flo.at" refers to that portion of a component yarn which passes over a group of other yarns in the fabric without interweaving or interlacing with them; the associated 10 term "float length" refers to the length of a float, expressed i as a number indicating the number of yarns passed over. A float length can be expressed in terms of numbers of paper side layer or machine side layer warp or weft yarns.

The term "frame" refers to the substantially rectangular ^ drainage area" defined' by the longitudinal axis of four interwoven yarns in the paper side surface of the paper side layer of a forming fabric. The number of frames per unit area is identified by the associated terms "frames/in2" or 20 " f rames / cm2" .

The term * interlace" refers to a locus at which a yarn forms at least, one knuckle with another yarn in the machine side layer.

The term "internal float" refers to that portion of a component yarn which passes between two sets of yarns; the associated term "internal float length" in relation to this invention refers to the length of an internal float, expressed 30 as a number indicating the number of PS yarns passed under. 3 553965 Received by IPONZ 9 Sep 2010 The term "interweave" refers to a locus at which a' yarn forms at least one knuckle with another yarn in the paper side layer.

. The term "machine direction", or "MD" refers to a line parallel to the direction of travel of the forming fabric when in use on the papermaking machine. The term "cross machine direction" or "CD" refers to a direction substantially perpendicular to the machine direction within the plane of the 10 fabric. In the fabrics of the present invention, either the first direction, or the transverse direction, may be parallel to the MD, depending on the construction of the fabric and whether the binder yarns are warp or weft yarns i.e. if the warp yarns are the binder yarns, the transverse direction is 15 parallel to the MD. The fabrics of the present invention are generally flat woven and seamed so that the warp yarns are oriented in the MD when the fabric is in use.

The term "paper side layer" refers to the layer in the 20 forming fabric onto which the stock is delivered from the head box slice. The term "machine side layer" refers to the layer in the forming fabric in contact with the support means in the papermaking machine. Thus each of these layers has a paper side surface ("PS") and a machine side surface ("MS"). In the 25 double layer fabrics of the invention, the machine side surface of the paper side layer is adjacent to the paper side surface of the machine side layer.

. The term "segment" refers to a portion of the single path 30 occupied by . a specific binder yarn in bne repeat of the overall weave pattern, and the associated term "segment length" refers to the length of a particular segment, and is 4 553965 Received by IPONZ 9 Sep 2010 expressed as the number of paper side layer yarns with which a member of a pair of binder yarns interweaves within the segment.

Forming fabrics are used in papermaking machines to retain and support the papermaking fibres in the stock, to allow ' water to drain from the stock so that an embryonic fibrous web may form and to convey that web to subsequent areas of the papermaking machine. Initially these fabrics were 10 woven from metal wire, typically phosphor bronze -or stainless steel; in recent times yarns created from thermoplastic resins have become the material of choice. Currently preferred resins \ include polyesters, polyamides and various polymer blends.

The simplest forming fabrics are woven as single layer structures. Although single layer fabrics, are known and used, they have several well documented disadvantages when used in certain papermaking conditions. i To overcome these disadvantages, double layer forming / fabrics have been developed which consist essentially' of two layers: these are a paper side layer which provides the surface on which an incipient paper web is formed, and a machine side layer which provides the surface that is in 25 contact with the static supporting surfaces of the paper making machine. As noted above, within the overall forming fabric weave pattern, either warp yarns or weft yarns can be used as binder yarns which serve to hold the layers of the double layer fabric together and may contribute to the 30 structure of one of the layers. It then follows that although the layers are bound together by the weaving process into a single fabric with a single overall repeating weave pattern, 553965 Received by IPONZ 9 Sep 2010 each of the layers is often constructed quite differently in terms of yarn sizes, yarn cross sectional shapes, yarn' count (in terms of numbers of yarns per unit length) , yarn fill (expressed as a percentage of the amount of yarns and their 5 : size relative to the total space available to accommodate them) and the thermoplastic polymer used in the yarns. It then also follows that at least the water handling capabilities, the wear resistance capabilities, and the strength capabilities of each layer, when considered 10 separately, are commonly quite different.

Modern forming fabrics are woven so as to provide a paper side layer which imparts, amongst other things, a minimum of ■fabric mark to, and provides adequate drainage of liquid from, 15 the incipient paper web. The paper side layer should also provide maximum support for the fibres and other papermaking solids in the paper slurry. The machine side layer should be' tough and durable, and provide a measure of dimensional stability to the forming fabric so as to minimize fabric 20 stretching and narrowing, or other distortions.

Weave patterns are known for double layer forming fabrics in which the warp yarns comprise pairs, alternately forming part of the paper side and the machine side weaves. In such 25 patterns, when one member of a pair passes from the paper side layer to the machine side layer, the second member of the pair passes from the machine side layer to the paper side layer, thus completing the weave pattern and while binding the two layers together. Examples of such patterns are found, for 30 example, in published US application Nos. 2003/0217782 of Nagura et al., 2004/0020621 of Heger et al., and in US patents 6 553965 Received by IPONZ 9 Sep 2010 ,152,326 to Vohringer, 4,605,585 to Johansson, 4,501,303 to Osterberg, and 6,223,780 to Kaldenhoff. Others are known.

Nagura et al. in US 2003/0217782 disclose a double layer 5 fabric in which warp pairs serve as binder yarns to interconnect the paper and machine side layer weft yarns. The yarns are arranged in the overall fabric pattern such that each warp yarn pair member replaces the other to complete the weave pattern of the opposite surface as the yarns exchange 10 locations between the surfaces.

Heger et al. in US 2004/0020621 disclose a double layer forming fabric likewise comprised of pairs of warp yarns which alternately interweave with the PS and exchange positions to 15 interlace with the MS and thus complete the weave pattern repeat of each of these two surfaces. The path taken by the two warp yarns as they enter into and exit from the PS is each different, and two warp of adjacent pairs must pass together under a common MS weft yarn.

Each of Vohringer, in US 5,152,326, Johansson in US 4,605,585 and Osterberg in US 4,501,303 discloses a forming fabric having first and second yarn systems interconnected by a third system comprising pairs of yarns which together form a 25 regular pattern on the paper side surface of the fabric.

Kaldenhoff discloses a similar construction but uses both warp and weft binder yarns.

One problem which is common to . all papermaking machines 30 and which can have an adverse effect on the formation properties of the web, and has not been significantly addressed by these known weave patterns, is the problem of 7 Received by IPONZ 9 Sep 2010 "impingement drainage" as will be discussed in greater detail below In the initial portion of either a single fabric or a 5 twin fabric forming section (either with or without an initial open surface portion) , an unsupported jet of highly aqueous stock is ejected at high speed from the head box slice onto the open surface of a moving forming fabric, or into the more or less convergent wedge shaped space between two moving 10 forming fabrics. The jet of aqueous stock will typically traverse a short distance before impinging the surface of the forming fabric, or fabrics, at the point of impingement. The angle of impingement formed between the' linear axis of the stock jet and the surface of the forming fabric, or fabrics, 15 on which paper is made is generally quite small, and typically is of the order of from about 4° to about 10°. Since the angle of impingement cannot be zero, which is to say tangential to the fabric surface, or fabric surfaces in a twin fabric paper making machine, at least in part because the stock jet widens 20 in the direction perpendicular to the fabric surface or surfaces in the space between the head box slice and the point of impingement, the pressure exerted by the stock jet onto the forming fabric or fabrics can be resolved into two components: a component essentially tangential to the fabric surface, and 25 a component essentially perpendicular to the fabric surface, both of which when combined have a considerable effect on impingement drainage rates. These forces are directly proportional to the speed at which the. forming fabric moves in the machine direction: as the machine speed increases so do 30 the impingement forces. 553965 8 553965 Received by IPONZ 9 Sep 2010 In. modern high speed papermaking machines in which the forming fabric (s) can be moving at speeds up to lOOkph, the minor pressure component vertical to the fabric surface exerts a significant level of force on the forming fabric, which can 5 cause excessive impingement derived drainage of the stock over the initial portion of the forming section. This minor pressure component (the "impingement pressure") and the turbulent forces created by stationary drainage elements, combined with the increased use of particulate fillers and 10 shorter papermaking fibres, have the effect of reducing first pass retention and increasing the embedment of the initial layers of the embryonic web into the paper side surface of the forming fabric.

It is well known that, on any papermaking machine under start up conditions and delivering a normal papermaking volume of water but without papermaking fibres from the headbox'slice onto the forming fabric-, this water will drain within a very short distance, approximately 12 inches (30 cm) , or less than 20' 1% of the • total available drainage length of the typical forming section. This indicates that, without fibres, all forming fabrics have far in excess of the drainage capacity required to make paper. However, as soon as papermaking fibres are introduced, drainage is retarded at a rate determined by 25 the length of the fibres, the quantity of fibres, the support characteristics of the papermaking surface of the forming fabric, and by the forces resisting and retarding impingement drainage. It was for this reason that the original forming boards installed on open surface fourdrinier type papermaking 30 machines were so successful. In more modern twin wire formers such as gap formers, the impingement shoe serves that function. 9 553965 Received by IPONZ 9 Sep 2010 It is known (from Johnson, Dale B., "Effect of Jet Impingement in Bel Baie Machines", Pulp and Paper Canada, 9385 (1992))that impingement drainage can cause sheet marking, low 5 retention by the forming fabric of papermaking fibres, fines and fillers (i.e. low first pass retention), and plugging (i.e. sheet sealing) of the paper side layer of the forming fabric- Unless the structure of the forming fabric is designed to allow it to better manage and control impingement drainage, 10 further increases in machine speed and/or paper making machine efficiency may be limited, or tied directly to improvement's in forming shoe or forming board construction.

None of the prior art discloses fabric constructions that 15 are specifically designed to retard the initial impingement drainage by means of long internal warp or weft floats which restrict the drainage area of the centre plane of the fabric. Although improved paper side layer surface uniformity can. be obtained by using weave patterns in which warp yarn pairs 20 together interweave with paper side layer weft yarns in sequence in a manner which provides a single unbroken warp path, known weave' patterns have not addressed the problem of impingement drainage. Specifically, there has not been any teaching of weave patterns which allow the 'binder yarns to 25 reside for greater lengths within the fabric as an internal float so as to close up this centre plane. Nor does the prior art address issues relating to fabric' stability and wear resistance arising from a fabric construction which is designed to retard the initial impingement drainage. Both of 30 these features are addressed in the present invention in ways which offer unexpected advantages as discussed herein. 553965 Received by IPONZ 9 Sep 2010 WO 2006/034576 PCT/CA2005/001473 It has how been found that the problems of impingement drainage can be significantly reduced, and the respective advantages of the preferred weave patterns for the paper side layer of these fabrics and the preferred weave patterns for 5 the machine side layer can be retained, by the use of weave patterns in which the fabric layers are bound together by pairs of binder yarns', where the members of each pair together form a single path in the paper side surface, and alternately interlace with the yarns of the machine side layer to 10 contribute to but not form a complete repeat of the machine side layer weave pattern; where the patterns further- provide for long internal floats of the binder yarns between the paper side layer . and the machine side layer, between successive interweaving and interlacing points. Such weave patterns 15 increase the resistance of the central plane of the fabric to the impingement drainage forces and fckereby provide numerous unexpected benefits, as will be discussed below.

Preferably the binder yarns- are warp yarns, but they may 20 also be weft yarns, depending on other physical attributes required for the weave pattern, based on the intended end use . of the fabric.

It has been found that such weave patterns enhance the 25 following fabric features in a manner not previously available .in the prior art.

Firstly, the paper side surface of the fabric offers good sheet support with reduced sheet marking, yet provides 30 sufficient drainage area to remove water to the interior of the fabric without 'entrapping fibres. This reduces, fibre 11 Received by IPONZ 9 Sep 2010 plugging or stapling, and so-called "sheet sealing" which makes removal of the embryonic web from the fabric difficult.

Secondly, the retardation of drainage in the area of the long internal floats of the binder yarns promotes good sheet formation and fines retention on the paper side surface of the fabric, with many of the same benefits to the sheet as are provided by the known forming boards and forming shoes.

Thirdly, the open drainage area of the paper side layer allows, for easy passage of air through the sheet top surface to the paper side surface of and thereafter through the forming fabric as the fabric and sheet together pass over the suction boxes and similar drainage devices in the forming section. This high air passage over the vacuum zones will result in the sheet leaving the forming zone in a dryer condition, which will" translate into greater efficiencies in both the press and drying sections of the paper machine.

Summary of the Invention The present invention seeks to provide a double layer forming fabric for use in either a single fabric papermaking machine, or a twin fabric paper making machine, which fabric provides improved resistance to impingement drainage in the initial portion of the forming section.

This invention further seeks to provide a double layer forming fabric in which all levels of the fabric contribute to the control of fluid flow through the fabric. The present invention relies on the use of pairs of yarns, preferably warp yarns, which are arranged so as to form long internal floats 12 553965 Received by IPONZ 9 Sep 2010 between the paper and machine side layers of the fabric, the yarns remaining within a notional centre plane for up to at least 80% of their paths, thereby reducing the drainage area through the centre plane in the fabric parallel to the paper 5 and machine side surfaces.

Although each pair of binder yarns follows a single combined path, the two members of each pair are adjacent and . thus necessarily laterally displaced from each other in the 10 paper side surface at the exchange points, where one member of the pair' leaves the paper side layer and the- other member enters the paper side layer. In the overall repeating weave patterns of the invention, .the long internal floats of the binder yarns, and the appropriate selection of the locations 15 at which each member of a pair interlaces with machine side layer yarns, results in the two members of each pair being somewhat' laterally displaced from each other along their lengths between the exchange points, which further restricts impingement drainage.

The effect of these features' of the arrangement of the yarns is that the drainage areas of both the machine and paper side layers are greater than that found at this notional centre plane. The reduced drainage area at the centre plane i resists the flow of fluid through the fabric so as to retard the very high initial impingement drainage that occurs at or near the point of impingement. This allows the initial web to form more gently and uniformly, with higher first pass retention and less sheet sealing and embedment. The overall 30 effect on the sheet is similar to that provided by the known .forming boards and forming shoes. 13 553965 Received by IPONZ 9 Sep 2010 In a first broad embodiment, the invention further seeks to provide a double layer forming fabric for a papermaking machine woven to an overall repeating weave pattern requiring at least 8 sheds in a loom and comprising in combination a paper side layer having a paper side surface, and a machine side layer, the fabric having at least (i) paper side layer yarns and machine side layer yarns each oriented in a first direction; and (ii) a set of yarns comprising only pairs of binder yarns interwoven with the paper side layer yarns and the machine side layer yarns in a direction transverse to the first direction, wherein: (a) in the paper side surface, each of the pairs of binder yarns occupies a single combined path; (b) the pairs of binder yarns are woven in the overall repeating weave pattern such that for each 10 pair: (A) in a first segment of the single combined path, a first member of the pair interweaves with selected ones of the paper side layer yarns at an interweaving location, and a second member of the pair interlaces with at least one of the machine side layer yarns at an interlacing location; (B) in a second segment of the single combined path, the second member of the pair interweaves 15 with selected ones of the paper side layer yarns at an interweaving location, and the first member of the pair interlaces with at least one of the machine side layer yarns; (C) lengths of the first and second segments are selected from equal and unequal; (D) between each adjacent segment the members exchange positions at an exchange point, and the members are laterally displaced in relation to each other along the single combined path at and between each consecutive exchange point; and (E) for each of the members of each of the pairs of binder yarns, between each of the interweaving locations and an immediately subsequent one of the interlacing locations, and between each of the interlacing locations and an immediately subsequent one of the interweaving locations, the member floats between the paper side layer yarns and the machine side layer yarns under at least four of the paper side layer yarns; (c) the machine side layer is woven to a repeating machine side layer weave pattern in which, for each of the pairs of binder yarns, in each repeat the first member and the second member alternately interlace with selected ones of the machine side layer yarns but do not form a complete repeat of the machine side layer weave pattern; and (d) the fabric has a total warp fill after heatsetting of at least 100%. 2769823_1.DOC 553965 Received by IPONZ 9 Sep 2010 In an embodiment, the invention seeks to provide a double layer forming fabric of the first broad embodiment, wherein (i) the paper side layer has a first drainage area, the machine side layer has a second drainage area, 5 and a centre plane within the fabric, defined as a notional plane substantially parallel to and located between the paper side layer and the machine side layer, has a third drainage area, wherein the first drainage area is the minimum open area unoccupied by yarns in the paper side layer, measured in a notional plane in the paper side layer and substantially parallel to the paper side surface, as a percentage of total area of the notional plane, the second drainage area is the 10 minimum open area unoccupied by yarns in the machine side layer, measured in a notional plane in the machine side layer and substantially parallel to the machine side surface, and the third drainage area is the minimum open area unoccupied by yarns in the centre plane; (ii) the first drainage area is between 25% and 50%; (iii) the second drainage area is between 25% and 50%; and 15 (iv) the third drainage area is between 8% and 20%.

There is also described herein a double layer forming fabric for a papermaking machine woven to an overall repeating weave pattern requiring at least 8 sheds in the loom and having a machine direction and a cross-machine direction and comprising in combination a paper side layer having 20 a first drainage area, a machine side layer having a second drainage area, and a centre plane within the fabric, defined as a notional plane substantially parallel to and located between the paper side layer and the machine side layer and having a third drainage area wherein (a) in one of the machine direction and the cross-machine direction, the fabric has a total fill 25 after heatsetting of at least 100%; (b) the first drainage area is between 25% and 50%; (c) the second drainage area is between 25% and 50%; and 2769823_1.DOC 553965 Received by IPONZ 9 Sep 2010 (d) the third drainage area is between 8% and 20%.

Preferably, the binder yams occupy at least 80% of the centre plane in each repeat of the overall repeating weave pattern, and preferably the third drainage area is between 8% and 15%. 2769823_1.DOC 553965 Received by IPONZ 9 Sep 2010 Preferably, the paper side layer yarns do not form stacked pairs over the machine side layer yarns, but are offstacked so that in a cross-section of the fabric in the-transverse direction, each paper side layer yarn is laterally 5 displaced from proximate machine side layer yarns. 17 553965 Received by IPONZ 9 Sep 2010 Preferably, in each repeat of the repeating weave pattern a ratio of the number of paper side layer yarns and the number of machine side layer yarns is selected from 3:1, 3:2, 2:1 and 5 1:1, but more preferably the ratio is 3:2.

In the fabrics of the invention, the binder yarns may comprise either warp yarns or weft yarns. Preferably, the binder yarns are warp yarns.

Preferably, the machine side layer is woven to a pattern selected from a 6-shed satin, a 12-shed satin, a twill and an N x 2N pattern, in which N is the number of sheds in the loom, and more preferably, the machine side layer is woven to an N x 15 2 N pattern.

Preferably, the paper side layer is woven to a pattern selected from a plain weave, a 3-shed twill, a 3-shed satin, a 4-shed twill and a 4-shed satin.

A wide range of overall repeating weave patterns is suitable for the fabrics of the invention, but preferably the overall repeating weave pattern requires 24 sheds.

Preferably, all the yarns for the fabrics of the invention are thermoplastic monofilaments. Preferably, the binder yarns are constructed of a monofilament material selected from polyethylene naphthalate and polyethylene terephthalate, and most preferably of polyethylene naphthalate. Preferably, the machine side layer yarns are constructed of a monofilament material selected from nylon, polyethylene terephthalate and a blend of polyethylene 18 553965 Received by IPONZ 9 Sep 2010 ■ terephthalate and polyurethane, such as described in US Patents Nos. 5,169,711 and 5,502,120, Brief Description of the Drawings The invention will now be described in more detail with reference to the attached drawings in which: i Figure 1 shows the paths of a pair"of warp yarns in one repeat 10 of the weave pattern of a first embodiment of the invention; Figure 2 shows the paths of a pair of warp yarns in one repeat of the weave pattern of a second embodiment of the invention; Figure'3 shows the paths of a pair of warp yarns in one repeat of the weave pattern of a third embodiment of the invention; Figure 4 is a photograph of the paper side surface of the embodiment of Figure 1; Figure 5 is a weave diagram of the embodiment of Figure 1; Figure 6 is a weave diagram of the paper side layer of the embodiment of Figure 1; Figures 7 and 8 are weave diagrams of , the embodiments of Figures 2 and 3 respectively; Figure 9 is a weave diagram of a fabric in a fourth embodiment 30 of the invention; 19 553965 Received by IPONZ 9 Sep 2010 Figure 10 is a weave diagram of a fabric in a fifth embodiment of the invention; Figure 11 is a photograph of a cross-section of an embodiment 5 of the invention; Figures 12 to 15 are computer generated' cross-sectional diagrams of a fabric of the invention; Figures 16 and 17 are photographs of the respective paper'side surface and machine side surface of a fabric of the prior art; Figures 18 and 19 are photographs of the respective paper side i surface and machine side surface of a fabric of the invention; 15 and Figure 20 is a graphical representation of the drainage areas of the fabrics of the invention.

Detailed Description Referring to Figures 1, 4 and 10, a first embodiment of the invention is shown. The fabric 100 has a paper side layer 52, having a paper side surface 54, on which the incipient 25 paper web (not shown) ' is carried, and is woven to a plain weave pattern with paper side layer weft yarns 60 and,pairs of' warp yarns 101a and 101b. The machine side layer 56 is woven to a different pattern, comprising an N x 2N weave, in which N quantifies the warp yarns 101a, 101b, and 2N quantifies the 30 weft yarns 62 in one repeat of the machine side layer weave pattern. • In the fabrics of the invention, N is an integer 553965 Received by IPONZ 9 Sep 2010 PCT/ CA2005/001473 greater than 3. This N x 2N pattern is described and claimed in US Patent No. 5,544,678.

In Figure 1, the paper side layer weft yarns 60 and the 5 machine side layer weft yarns 62 are individually identified by the appropriate numerals in sequence from 1 to 30.

Figures 1 and 10 show the path of a pair of typical warp yarns 101a and 101b in one repeat of the fabric weave pattern. 10 It can be seen that in a first segment 112, commencing at exchange point 102 under paper side layer weft yarn 8, warp yarn 101b interweaves with eight paper side layer weft yarns 10, 11, 13, 15, 16, 18, 20 and 21, at interweave location 104, while warp yarn 101a passes between the paper side layer 52 ' 15 and the machine side layer 56, under paper side layer weft yarns 8, 10, 11 and 13, interlaces with machine side layer weft yarn 14 at interlace location 108, and passes between the paper side layer 52 and the machine side layer 56, under paper ■ 1 side layer weft yarns 15, '16, 18, 20 and 21, meeting warp yarn 20 101b at exchange point 102 under paper side layer weft yarn 21.

In a second segment 114, after exchange point 102b, warp ' I yarn 101a interweaves with ten paper side layer weft yarns 23, 25 25, 26, 28, 30, 1, 3, 5, 6 and 8 at interweave location 106, _ while warp yarn 101b passes between the paper side layer 52 .and , the machine side layer 56, under paper side layer weft yarns 21, 23, 25, 26, 28 and 30, interlaces with machine side layer weft yarn 2 at interlace location 110, and then passes 30 between the paper side layer 52 and the machine side layer 56, under paper side layer weft yarns 3, 5, 6 and 8, meeting warp 21 553965 Received by IPONZ 9 Sep 2010 yarn 101a at a subsequent exchange point 102 under paper' side layer weft yarn 8.

It can thus be seen that between each interlacing 5 location 104, 106 and the immediately preceding and immediately subsequent exchange points 102, each of warp yarns 101a, 101b has long internal floats with a float length of at least 4, i.e. passing under at least four paper side layer weft yarns 60.

Figure 1 also shows that the number of paper side layer weft yarns 60 with which warp yarn 101a interweaves at each interweave location 104 (i.e. eight paper side layer weft yarns 60) is not the same as the number of paper side layer 15 weft yarns 60 with which warp yarn 101b interweaves at each interweave location 106 (i.e. ten paper side layer weft yarns 60). The weave pattern is thus asymmetrical.

Figure 4 is a photograph of the paper side surface 54 of 20 a fabric of the invention. All of the yarns shown vertically in the figure are pairs of binder yarns 101a, 101b, in the transverse direction to the paper side layer yarns 60. As described in relation to Figure 1, the members of each of these pairs of binder yarns exchange positions at exchange 25 points 102. In Figure 4, examples of such exchange points are shown as 102a, where a binder yarn 101a leaves the paper side layer 52 and its pair, binder yarn 101b, enters the paper side layer 52; and 102b, where a binder yarn 101b leaves the paper side layer 52 and its pair, • binder yarn 101a, enters the paper 30 side layer 52. At these exchange points, 102a and 102b, the lateral displacement of the members of the binder yarn pairs in relation to each other can be clearly seen. Further, as the 22 553965 Received by IPONZ 9 Sep 2010 binder yarns continue their single combined path following an exchange point 102a or 102b, the lateral displacement is also continued, so that the member leaving the paper side layer is not entirely under the member which commences interweaving ' 5 with the paper side layer yarns 60, and thus contributes to the restriction on impingement drainage: The weave pattern of the embodiment shown in Figure 1 is . described in Figures 5 and 6. Figure 6 shows the weave pattern • 10 of - only the' paper side layer 52 of the fabric 100. The numerals on the left side of the weave diagram correspond to the paper side layer weft yarns 60, with the numbers allocated in Figure 1. The numerals across the top of the weave diagram are of twelve consecutive pairs of warp yarns 101a, 101b. Thus 15 the paths of each of the warp yarns identified in Figure 6 corresponds to the paths of the illustrative warp yarns 101a, 101b in Figure 1. From these two figures, and the photograph of. the woven fabric in.Figure 4, it can be seen that each pair of warp yarns 101a, 101b together forms a single combined 20 warp path in the paper side surface 54 of the paper side layer 52. It can also be seen that both warp yarns 101a and 101b are required to complete the MS weave pattern; thus neither member of a warp yarn pair alone can form a complete repeat of. the' MS weave pattern. ■ However, as discussed above in relation to 25 Figure 4, the members of each pair are somewhat laterally displaced at and between the exchange points 102.

Figure 5 is a weave diagram of the complete fabric, i.e. the combined patterns of the paper side layer 52 and the 30 machine side layer 56, the numerals at the left of the drawing representing the thirty yarns comprising paper side layer weft yarns 60 and machine side layer weft yarns 62, and the 23 553965 Received by IPONZ 9 Sep 2010 numerals across the top of the diagram representing the twenty-four warp yarns of this pattern, comprising twelve consecutive pairs of warp yarns 101a, 101b.

Referring now to Figure 2, the paths of a pair of typical warp yarns 201a, 201b of a second embodiment are shown, in one repeat of the weave pattern. In Figure 2, the paper side layer weft yarns 60 and the machine side layer weft yarns 62 are individually identified by the appropriate numerals in sequence from 1 to 36.

As in the. embodiment of Figure 1, the two warp yarns 201a, 201b together form 'a single combined warp path in the paper side surface 54 (see Figure 4) of the paper side layer 52, while being somewhat laterally displaced at and between the exchange points 202. Similarly, the warp yarns 201a, 201b have long internal floats with a float length of at least 4 between each interlace location 208, 210 and the immediately preceding and immediately subsequent exchange point 202. In this weave pattern, in a first segment 212, warp yarn 201b interweaves at interweave location 204 with twelve paper side layer weft yarns 10, 12, 13, 15, 16, 18, 19, 21, 22, 24, 25 and 27, and in a 'second segment warp yarn 2 01a interweaves at interweave location 206 with twelve paper side layer weft ■yarns 28, 30, 31, 33, 34, 36, 1, 3, 4, 6, 7 and 9. It should be noted that although the path of warp yarn 201a in the paper side layer is identical to the path of warp yarn 201b in that layer, the paths of warp yarns 201a and 201b are not identical in the machine side layer 56, and neither of warp yarns 201a and 201b forms a complete repeat of the MS layer weave pattern. 24 553965 Received by IPONZ 9 Sep 2010 Referring to Figure 7, a weave diagram of the complete weave pattern of the fabric of the second embodiment of the invention is provided. As in the weave diagram of Figure 6, the numerals at the left side of the drawing represent the 5 thirty-six yarns comprising paper side layer weft yarns 60 and machine side layer weft yarns 62, corresponding to those shown in Figure 2. The numerals across the top of the drawing represent the twenty-four warp yarns of the pattern, comprising twelve consecutive pairs of warp yarns 201a, 201b.

Referring now to Figure 3, the paths of a pair of warp yarns 301a, 301b of a third embodiment are shown, in one repeat of the weave pattern. In Figure 3, the paper side layer weft yarns 60 and the machine side layer weft yarns 62 are 15 individually identified by the appropriate numerals in sequence from 1 to 48.

As in the embodiments of Figures 1 and 2, the two warp yarns 301a, 301b together form a single combined warp path in 20 the paper side surface 54 (see Figure 4) of the paper side layer 52, while being somewhat laterally displaced at and between the exchange points 302. Similarly, the warp yarns 301a, 301b have long internal floats with a float length of at least 4 between each first interlace location 308 and the 25 immediately preceding exchange point 302; and similarly between each second interlace location 310 and each subsequent exchange point 302. Further, between the two interlace locations 308, 310 for each of warp yarns 301a, 301b, there is a further long internal float with a float length of at least 30 4 between the paper side layer 52 and the machine side layer 56. In this weave pattern, in a first segment 312, warp yarn 301b interweaves at interweave location 304 with sixteen paper 553965 Received by IPONZ 9 Sep 2010 WO 2006/034576 PCT/CA2005/001473 side layer weft yarns 19, 21, 22, 24, 25, 27, 28, 30, 31, 33, 34, 36, 37, 39, 40 and 42; and in a second segment warp yarn 301a interweaves at interweave location 306 with sixteen paper • side layer weft yarns 43, 45, 46, 48, 1, 3, 4, 6, 1, 9, 10, 5 12, 13, 15, 16 and 18.

• It is apparent that the paths of the two warp yarns 3 01a, 301b of each pair follow an identical sequence in the paper •side layer 52 and the machine side layer 56. 1° Referring to Figure 8, a weave diagram of the complete weave pattern of the fabric of the third embodiment of the invention is provided. As in the weave diagrams of Figures 5 and 6, the numerals at the left of the drawing represent the 15 forty-eight yarns comprising paper side layer weft yarns 60 and- machine side layer weft yarns 62, corresponding to those shown in Figure 3. The numerals across the top of the drawing represent the twenty-four warp yarns of the pattern, comprising twelve consecutive pairs of warp yarns 301a, 301b.

It is possible to weave the fabrics of this invention in a broad number of shed patterns, other than the 24 shed patterns discussed above, while remaining within the scope of the invention. In the fabrics of this invention, each warp 25 yarn floats under at least four paper side layer weft yarns between each interweaving location and an immediately following interlacing location of that warp yarn with a machine side weft yarn; further, neither the first nor second warp yarns of a pair alone forms a complete repeat of the 30 second (machine side layer) repeating weave pattern. However, these two warp yarns together do form a complete repeat. In addition, due to the disclosed warp yarn arrangement in the I, jr 26 553965 Received by IPONZ 9 Sep 2010 fabrics of this invention, in the preferred embodiment two warp yarns will always pass together beneath each machine side layer weft yarn so as to form a "double warp knuckle" beneath the weft yarns. Alternatively, there may be 1 or 2 warp yarns 5 located between the two yarns forming the double warp knuckles. As a further alternative, the warp yarns may be arranged by means of the chosen weave pattern so that the warp yarns form only single knuckles beneath the weft yarns. As yet a further alternative, the weave pattern can provide for both 10 single and double knuckles in the machine side surface.

These double warp knuckles offer several advantages not previously available in fabrics woven using warp yarn pairs. First, the two warp yarns act together to more effectively 15 crimp the larger diameter machine side layer weft yarns, causing them to bow outwardly from the fabric surface so as to provide a wear plane on the machine side of the fabric which protects the warp yarns from abrasion, thereby increasing the service life of the fabric. Second, the double warp knuckles 20 allow for the use of relatively larger diameter weft yarns on the machine side surface of the fabric than would otherwise be available in fabric weave designs where only single warp knuckles are created in the weave pattern. Third, the use of these larger diameter machine side layer weft yarns enhances 25 both cross machine direction fabric stability and fabric stiffness, both properties which contribute significantly to overall fabric "runnability" (i.e., to resist creasing and similar fabric distortions when in use). We have found that these features, together with the other features of the 30 invention as described herein, can be provided in a number of different overall fabric weave designs requiring, for example, 12 sheds in the loom, or 16, 18, 20 sheds and more. 27 553965 Received by IPONZ 9 Sep 2010 The selection of suitable weave patterns for the fabrics of this invention from the broad number of available shed 'patterns will depend on the end use requirements and the physical 'restrictions of the loom on which they are woven. 5 Figures 8 and 9 provide examples of fabrics woven in accordance with the present invention which are arranged according to 16-shed patterns and which offer the features described above.

Referring now to Figure 9, a weave diagram of the complete weave pattern of a fourth embodiment of the fabric of the invention is provided, which is similar in aspects to that shown in Figures 8 and 3. As in the weave diagram of Figure 8, the numerals at the left side of the drawing represent the 15 48 weft yarns comprising the 32 paper side layer weft yarns 60 and the 16 machine side layer weft yarns 62 of this fabric (also as shown in cross-section in Figure 3). However, whereas the fabric illustrated in Figure 8 is woven according to a 24-shed pattern, requiring 24 warp yarns and 48 weft 20 yarns in the full repeat, the fabric of Figure 9 is woven according to a 16-shed pattern requiring 16 warp and 48 weft to construct. The yarn paths of the warp pairs in the fabric of Figure 9 are similar to those illustrated for typical, warp yarns 301a, 301b in Figure- 3. However, the 16-shed pattern 25 provides some benefits not available in the 24-shed construction. Most notably, it is possible in this 16-shed design to provide a long machine side layer weft yarn float which will take much of the abrasive wear to which the machine side surface is ejqposed. For example, inspection of Figure 9 30 shows that each of the machine side weft.yarns 2, 5, 8, 11, 14, 17 ... form a long machine side float of at least 12 warp yarns (see e.g. weft 5). For example, weft yarn 2 is 28 553965 Received by IPONZ 9 Sep 2010 interlaced only at the opposite ends of the repeat, i.e. with warp yarns 1 and 16. This causes the weft to bow outwardly from the fabric and provide a great deal of material for abrasive wear during use. Further, at certain locations on 5 the machine side of the fabric, two adjacent warp yarns pass together beneath a single weft (e.g. at weft 2, both warps 1 and 16 pass together beneath it). This tends to enhance the weft yarn crimp and recesses the warp yarns from abrasive wear at these locations. However, at most other locations, the 10 interlacing warps are separated from one another by one warp (e.g. at weft 11, the warps 1 and 3 are separated by warp 2. ■This tends to increase the overall stability of the machine side weave and thus the stability of the fabric.

Figure 10 is a weave diagram of a fifth embodiment of the invention, which is a fabric very similar to that shown in Figure 9. The main difference between these two fabrics is that the position of warp yarns 5 and 6, and 9 and 10 in the weave pattern have been exchanged.

The warp paths of the fabrics whose weave diagrams are shown in Figures 9 and 10 are substantially as shown in Figure 3 . Inspection of these weave diagrams in association with the warp profiles shows that between each interlacing location (at 25 machine side layer weft yarns 2, 11, 26 and 35) and the immediately preceding and immediately subsequent exchange points, each of the warp yarns has long internal floats between the paper side layer weft yarns 60 and machine side layer weft yarns 62 with a float length.of at least 4, i.e. 30 passing under at least four paper side layer weft yarns 60. 29 553965 Received by IPONZ 9 Sep 2010 Figure 9 also shows that the number of paper side layer weft yarns 60 with which each first warp yarn of a pair interweaves at each interweave location corresponding with interweave location 314 in Figure 3 (16 paper side layer weft 5 yarns) is the same as the number of paper side layer weft yarns 60 with which each second warp yarn pair member interweaves at each interweave location corresponding with interweave location 312 in Figure 3 (16 weft). The weave pattern is thus symmetrical, as shown in Figure 3, and is 10 different from that shown for example in Figure 1.

It should further be noted that although each of the warp yarns 101a, 101b, 201a, 201b, 301a and 301b contributes to the respective repeat weave pattern of the machine side layer 56, 15 no pair forms a complete repeat of such pattern.

Referring now to Figure 11, a photograph shows a cross-section in the MD of an embodiment of the invention. The paper side surface 54 of the paper side layer 52 is woven to a plain 20 weave pattern, in which (seen from the left of the figure) warp yarn 101a interweaves with selected paper side layer weft yarns 60 before exchanging positions with warp yarn 101b at exchange point 102, remaining between the paper side layer 52 and the machine side layer 56 before interlacing with a 25 selected machine side layer weft 62 at interlacing point 108. Similarly, warp yarn 101b interlaces with a selected machine side layer weft 62 at interlacing point 110, remains between the paper side layer 52 and the machine side layer 56, exchanges position with warp yarn 101a at exchange point 102, 30 and then interweaves with selected paper side layer weft yarns 60. From this micrograph, the long internal warp floats of the 553965 Received by IPONZ 9 Sep 2010 warp yarns 101a, 101b, which provide the desired restriction on impingement drainage, can clearly be seen.

Referring now to Figures 12 to 15, the effect of the 5 weave patterns of the invention can be seen. These four computer-generated figures depict what would be seen at notional planes at selected points within a fabric of the invention, as follows.

Figure 12 shows diagrammatically a top plane through the paper side layer 52 of the fabric 100 and substantially parallel to the paper side surface 54, and shows the drainage area of the paper side layer 52 as provided by the binder yarns 101a, 101b, as they interweave with the paper side layer 15 yarns 60. In this diagram, this first drainage area is approximately 32%.

Figure 13 shows diagrammatically the centre plane in the fabric, being a notional plane between, and substantially 20 parallel to, the paper side layer 52 and the machine side layer 56. This diagram shows the effect of the yarns occupying the space between the paper side layer 52 and the machine side layer 56 on the available drainage area. Careful inspection of this diagram shows that this third drainage area is 25 approximately 16%.

Figure 14 shows diagrammatically the bottom plane of the fabric, showing the drainage area of the machine side layer 56 as provided by the binder yarns 101a, 101b, as they interlace 30 with the machine side layer yarns 62. In this diagram, this second drainage area is approximately 28%. 31 553965 Received by IPONZ 9 Sep 2010 The drainage areas of each of these layers is shown graphically in Figure 20, which indicates the open area of a fabric of the invention at several points in relation to the depth into the fabric. It can be seen that at each of the 5 paper side surface 54 and the machine side surface 58, the drainage area is 100%. However, within the paper side layer 52, the first drainage area 122 can be seen ' to be approximately 31.9%, and within the machine side layer 56, the second drainage area 124 is approximately 27.7%. However, at 10 the centre plane between the paper side layer 52 and the machine side layer 56, the third drainage area 120 can be seen to be approximately 15.8%'.

Once the white water from the stock has passed through 15 the centre plane of a composite forming fabric, its rate of drainage has little impact on the paper quality unless it becomes too low, for example if the machine side layer of the composite forming fabric becomes plugged. The main purpose of the machine side layer is to provide adequate support for the I paper side layer, to provide adequate wear characteristics and to accommodate the stresses imposed on the forming fabric in use. ■ , In the fabrics of the invention, it is the drainage 25 capability - of the fabric 100 in the paper side layer 52 and at the centre plane between the paper side layer 52 and the machine side layer 56 combined which will determine the ability of the fabric to resist impingement drainage. This capability of the fabric 100 can be assessed diagrammatically 30 by combining Figures 12 and 13 to provide Figure 15. 7 32 553965 Received by IPONZ 9 Sep 2010 Careful inspection of Figure 15 shows that the resistance to impingement drainage comes from both the paper side layer 52 as shown. in Figure 12, and the centre plane as shown in Figure 13. When the drainage areas of these two contributing 5 features are combined, as shown., in Figure 15, the resulting drainage area is quite low, in this case approximately 16%. The' fabrics of the invention having these qualities therefore resist impingement drainage, and .allow better formation in the incipient paper web on the paper side surface 54 of the paper 10 side layer 52, because the combined first and third drainage areas,, i.e. in the paper side layer 52 and at the centre plane, will serve to slow down the rate of flow of the stock through the paper side layer 52.

Referring now to Figures 16 to 19, a comparison can be made between the fabrics of the invention and similar fabrics of the prior art.

Figures 16 and 17 are photographs showing the paper side 20 and machine side layers respectively of a fabric of the prior art. The high drainage areas of the fabric, comprised by the open areas 92, can be clearly seen.

Figures 18 and 19 are photographs showing the paper side 25 layer 52 and machine side layer 56 of a fabric of the invention. Each of these photographs shows dramatically that although the weave patterns appear similar from the surfaces of this fabric and the fabric shown in Figures 16- and 17, the fabric of Figures 18 and 19 has a substantially reduced 30 straight through drainage area of the fabric, as evidenced by the relatively few open areas 90. 33 553965 Received by IPONZ 9 Sep 2010 PCT/ CA2005/001473 It can thus be seen that the fabrics of this invention provide relatively little straight through drainage, due to the presence of the binder yarns in the centre plane of the fabric. These yarns fill the centre plane of the fabric so that ' drainage areas of from 8% to 20% are provided, in significant contrast to the higher drainage areas of the paper side layer and machine side layer. This tends to resist the initial impingement pressures of the stock jet, thus retarding drainage and providing improved formation.

Three samples of the fabrics of the invention were made, using warp binder yarns of polyethylene naphthalate (PEN), having a diameter of 0.12mm, 0.15mm and 0.15mm respectively, and a plain weave pattern for the paper side layer. The weft yarns for both the paper side layer and the machine side layer were of polyethylene teraphthalate (PET), of the dimensions indicated in the table below. The following characteristics were observed: Fabric 1 Warp yarns (mm.) 0.15 PEN PS weft yarns (mm.) 0.13 MS weft yarns (mm.) 0.25 Frames/in2 6,552 FSI 156 Elastic modulus (pli) 8,770 Caliper (in.) 0.0245 Fabric 2 0.15 PEN 0.13 0.25 6, 624 157 9,050 0.0276 Fabric 3 0.12PEN 0.13 0.22 10,800 200 7,000 0.025 The woven samples show that, as the warp yarn diameter is reduced from 0.15 to 0.12 mm, it is possible to increase the number of frames/in2 to as high as 10,800, which is very high 34 553965 Received by IPONZ 9 Sep 2010 especially when compared with more conventional triple layer fabric structures (e.g. those with intrinsic weft binder yarns) which normally will have about 8,000. frames/in2. The large number of frames provides rapid drainage of the sheet to 5 the interior of the fabric. This promotes good sheet formation and fines retention as well as easy passage of air through the paper side surface which improves the rate of drying of the sheet in the forming section. In addition, the high number of / frames is accompanied by a correspondingly high FSI value 10 which may be over 200, indicating good sheet support. This in turn reduces fiber "plugging" and sheet sealing, making the sheet easy to remove from the fabric at vthe pick-up point. Finally, the fabrics of this . invention can be woven so as to be very thin, in the range of about 0.025 in. (0.64 mm) 15 thickness (caliper) . This further promotes good sheet properties, and reduces the water carrying capacity of the fabrics, which in turn improves their cleanliness when used in a twin fabric forming environment, in that less water will be thrown off where the line of fabric travel is diverted from a 20 straight line run such as at a roll.

Those skilled in the 'art will realize that this invention is not limited to the paper and machine side layer weave' pattern combinations illustrated here.' Generally speaking, 25 the weave pattern of the paper side surface can be selected from: a plain weave, a twill, a broken twill or a basket weave woven using one of 2, 3, 4 or 5 sheds on the loom. The machine side weave can be a twill, broken twill, satin or an N x 2N pattern where N is the number of warp yarns in. the 30 pattern repeat and 2N. is the number of weft yarns, and N is > 3. Thus, suitable machine side weave patterns for use in the fabrics of this invention can be those woven according to 4, • 553965 Received by IPONZ 9 Sep 2010 , 6, 8, 10 and 12-shed patterns, but the invention is not so restricted.

Preferably, the fabrics of the invention are constructed 5 using a high modulus polymer monofilament material for the binder yarns, ' most preferably either polyethylene teraphthalate (PET) or polyethylene naphthalate (PEN). The paper side layer yarns are preferably of PET, and the machine side layer yarns are preferably of PET, nylon, or a blend of 10 PET and polyurethane as described in US Patents. Nos. 5,169,711 and 5,502,120. 1 The term "comprising" as used in this specification means "consisting at least in part of. When interpreting each statement in this specification that includes the term "comprising", features other than that or those prefaced by the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner. 36 553965 Received by IPONZ 9 Sep 2010

Claims (30)

WHAT WE CLAIM IS:

1. A double layer forming fabric for a papermaking machine woven to an overall repeating weave pattern requiring at least 8 sheds in a loom and comprising in combination a paper side layer having a paper side surface, and a machine side layer, the fabric having at least 5 (i) paper side layer yarns and machine side layer yarns each oriented in a first direction; and (ii) a set of yarns comprising only pairs of binder yarns interwoven with the paper side layer yarns and the machine side layer yarns in a direction transverse to the first direction, wherein: (a) in the paper side surface, each of the pairs of binder yarns occupies a single combined path; (b) the pairs of binder yarns are woven in the overall repeating weave pattern such that for each 10 pair: (A) in a first segment of the single combined path, a first member of the pair interweaves with selected ones of the paper side layer yarns at an interweaving location, and a second member of the pair interlaces with at least one of the machine side layer yarns at an interlacing location; (B) in a second segment of the single combined path, the second member of the pair interweaves 15 with selected ones of the paper side layer yarns at an interweaving location, and the first member of the pair interlaces with at least one of the machine side layer yarns; (C) lengths of the first and second segments are selected from equal and unequal; (D) between each adjacent segment the members exchange positions at an exchange point, and the members are laterally displaced in relation to each other along the single combined path at 20 and between each consecutive exchange point; and (E) for each of the members of each of the pairs of binder yarns, between each of the interweaving locations and an immediately subsequent one of the interlacing locations, and between each of the interlacing locations and an immediately subsequent one of the interweaving locations, the member floats between the paper side layer yarns and the machine side layer yarns 25 under at least four of the paper side layer yarns; (c) the machine side layer is woven to a repeating machine side layer weave pattern in which, for each of the pairs of binder yarns, in each repeat the first member and the second member alternately interlace with selected ones of the machine side layer yarns but do not form a complete repeat of the machine side layer weave pattern; and 30 (d) the fabric has a total warp fill after heatsetting of at least 100%. 2769823_1.DOC. 553965 Received by IPONZ 9 Sep 2010 -38-

2. A double layer forming fabric as claimed in Claim 1, wherein in a cross-section of the fabric in the transverse direction, each of the paper side layer yarns is laterally displaced from proximate ones of the machine side layer yarns.

3. A double layer forming fabric as claimed in Claim 1 or Claim 2, wherein in each repeat of 5 the repeating weave pattern a ratio of the number of paper side layer yarns and the number of machine side layer yarns is selected from 3:1, 3:2, 2:1 and 1:1.

4. A double layer forming fabric as claimed in Claim 3, wherein the ratio is 3:2.

5. A double layer forming fabric as claimed in Claim 1 or Claim 2, wherein the paper side layer yarns and the machine side layer yarns are wefts and the binder yarns are warps. 10

6. A double layer forming fabric as claimed in Claim 1 or Claim 2, wherein the paper side layer yarns and the machine side layer yarns are warps and the binder yarns are wefts.

7. A double layer forming fabric as claimed in any one of Claims 1 to 6, wherein the machine side layer is woven to a pattern selected from a 6-shed satin, a 12-shed satin, a twill and an N x 2N pattern, in which N is the number of sheds in the loom. 15

8. A double layer forming fabric as claimed in Claim 7, wherein the machine side layer is woven to an N x 2 N pattern.

9. A double layer forming fabric as claimed in any one of Claims 1 to 8, wherein the paper side layer is woven to a pattern selected from a plain weave, a 3-shed twill, a 3-shed satin, a 4-shed twill and a 4-shed satin. 20

10. A double layer forming fabric as claimed in any one of Claims 1 to 6, wherein the overall repeating weave pattern requires 24 sheds.

11. A double layer forming fabric as claimed in Claim 1, wherein the binder yarns are constructed of a monofilament material selected from polyethylene naphthalate and polyethylene terephthalate. 25

12. A double layer forming fabric as claimed in Claim 11, wherein the monofilament material is polyethylene naphthalate.

13. A double layer forming fabric as claimed in Claim 1, wherein the machine side layer yarns are constructed of a monofilament material selected from nylon, polyethylene terephthalate and a blend of polyethylene terephthalate and polyurethane. 30

14. A double layer forming fabric as claimed in claim 1, wherein 2769823_1.DOC 553965 Received by IPONZ 9 Sep 2010 -39- (i) the paper side layer has a first drainage area, and the machine side layer has a second drainage area, and a centre plane within the fabric, defined as a notional plane substantially parallel to and located between the paper side layer and the machine side layer, has a third drainage area, wherein the first drainage area is the minimum open area unoccupied by yarns in the paper side 5 layer, measured in a notional plane in the paper side layer and substantially parallel to the paper side surface, as a percentage of total area of the notional plane, the second drainage area is the minimum open area unoccupied by yarns in the machine side layer, measured in a notional plane in the machine side layer and substantially parallel to the machine side surface, and the third drainage area is the minimum open area unoccupied by yarns in the centre plane; 10 (ii) the first drainage area is between 25% and 50%; (iii) the second drainage area is between 25% and 50%; and (iv) the third drainage area is between 8% and 20%.

15. A double layer forming fabric as claimed in Claim 14, wherein in a cross-section of the fabric in the transverse direction, each of the paper side layer yarns is laterally displaced from 15 proximate ones of the machine side layer yarns.

16. A double layer forming fabric as claimed in Claim 14, wherein the binder yarns occupy at least 80% of the centre plane in each repeat of the overall repeating weave pattern.

17. A double layer forming fabric as claimed in any one of Claims 14 to 16, wherein in each repeat of the repeating weave pattern a ratio of the number of the paper side layer yarns and the 20 number of machine side layer yarns is selected from 3:1, 3:2, 2:1 and 1:1.

18. A double layer forming fabric as claimed in Claim 17, wherein the ratio is 3:2.

19. A double layer forming fabric as claimed in Claim 14 or Claim 16, wherein the paper side layer yarns and the machine side layer yarns are wefts and the binder yams are warps.

20. A double layer forming fabric as claimed in Claim 14 or Claim 16, wherein the paper side 25 layer yarns and the machine side layer yarns are warps and the binder yarns are wefts.

21. A double layer forming fabric as claimed in any one of Claims 14 to 20, wherein the machine side layer is woven to a pattern selected from a 6-shed satin, a 12-shed satin, a twill and an N x 2N pattern, in which N is the number of sheds in the loom.

22. A double layer forming fabric as claimed in Claim 21, wherein the machine side layer is 30 woven to an N x 2 N pattern. 2769823_1.DOC 553965 Received by IPONZ 9 Sep 2010 -40-

23. A double layer forming fabric as claimed in any one of Claims 14 to 22, wherein the paper side layer is woven to a pattern selected from a plain weave, a 3-shed twill, a 3-shed satin, a 4-shed twill and a 4-shed satin.

24. A double layer forming fabric as claimed in any one of Claims 14 to 20, wherein the

25. A double layer forming fabric as claimed in Claim 14 or Claim 16, wherein the third drainage area is between 8% and 15%.

26. A double layer forming fabric as claimed in Claim 14, wherein the binder yarns are constructed of a monofilament material selected from polyethylene naphthalate and polyethylene 10 terephthalate.

27. A double layer forming fabric as claimed in Claim 26, wherein the monofilament material is polyethylene naphthalate.

28. A double layer forming fabric as claimed in Claim 14, wherein the machine side layer yarns are constructed of a monofilament material selected from nylon, polyethylene 15 terephthalate and a blend of polyethylene terephthalate and polyurethane.

29. A double layer forming fabric as claimed in claim 1 and substantially as herein described with reference to any embodiment disclosed.

30. A double layer forming fabric for a paper making machine substantially as herein described with reference to any embodiment shown in figures 1 to 15 and 18 to 20 of the 20 accompanying drawings. 5 overall repeating weave pattern requires 24 sheds. ASTENJOHNSON, INC. By the authorised agents AJ PARK Per 2769823_1.DOC