GB2418675A

GB2418675A - Papermaking fabric

Info

Publication number: GB2418675A
Application number: GB0421779A
Authority: GB
Inventors: Dale Bernard Johnson; Richard Stone
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-09-30
Filing date: 2004-09-30
Publication date: 2006-04-05
Also published as: GB0421779D0; GB0508445D0

Abstract

A composite forming fabric comprises a paper side layer and a machine side layer. All of the warp yarns comprise pairs of binder yarns 110, each pair occupying in the paper side surface a single unbroken warp path in a repeating weave pattern. In a first segment 112, a first member 110b, of the pair interweaves with paper side layer weft yarns, and the second member 110a interlaces at an interlacing point with at least one machine side layer weft yarn. After an exchange point, in a second segment 114 the second member of the pair interweaves with paper side layer weft yarns, and the first member interlaces at an interlacing point with at least one machine side layer weft yarn. For each warp yarn, between each interlacing point and an adjacent exchange point, the yarn floats between the two layers under at least four paper side layer weft yarns. The fabrics of the invention provide reduced impingement drainage, improved paper sheet support and resultant paper sheet quality. After heat-setting the fabric has a total warp fill of at least 100%.

Description

241 8675

WARP DOUBLETS FORMING FABRIC

The present invention relates to woven composite forming fabrics for use in papermaking machines. As used herein, the term "composite forming fabrics refers to a double layer or extra support double layer forming fabric comprising two sets of weft yarns, 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 warp yarns woven as pairs. Each of these layers is woven to a repeating pattern, and the two patterns used may be substantially the same or they may be different. Such fabrics are distinct from those described, for example, by Johnson in US 4,815,499, Barrett in US 5,544,678, or Seabrook et al. in US 5,826, 627, which require binder yarns, in particular weft yarns, to interconnect the paper and machine side layers. In the composite forming fabrics of this invention, the paper side layer and the machine side layer are each woven to different, but related, weave patterns, and are interconnected by means of a single set of warp yarns woven in pairs.

As used herein, the following terms have the following meanings: The term "unbroken warp path" refers to the path in the paper side layer, which is visible on the paper side surface of the fabric, of the pairs of intrinsic warp yarns comprising all of the warp yarns, and which is occupied in turn by each member of the pairs making up the intrinsic warp binder yarns. l

The term paper side layers refers to the layer in the composite forming fabric onto which the stock is delivered from the head box slice. The term Machine side layers refers to the layer in the composite forming fabric in contact with the support means in the papermaking machine. Thus each of these layers has a paper side surface and a machine side surface. In a two layer composite fabric the machine side surface of the paper side layer is adjacent to the paper side surface of the machine side layer.

The term Machine directions, or nMDn 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 directions or 'CRUDE refers to a direction substantially perpendicular to the machine direction within the plane of the fabric.

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 ninterlacen refers to a locus at which a yarn forms at least one knuckle with another yarn in the machine side layer.

The term "binder yarns refers to a yarn which occupies a 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. All of the warp yarns in the fabrics of this invention are binder yarns.

The term "segment.' refers to the portion of the unbroken warp path occupied by a specific warp yarn, and the associated term "segment length'' refers to the length of a particular segment, and is expressed as the number of paper side layer wefts with which a member of a pair of warp yarns interweaves within the segment.

The term n float n 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 term float length refers to the length of a float, expressed 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 n internal floats refers to that portion of a component yarn which passes between two sets of yarns; the associated term n internal float length. in relation to this invention refers to the length of an internal float, expressed as a number indicating the number of PS yarns passed under.

The term Reframes 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 term "frames/in2.

The term n fiber support index or FSI refers to a calculation made according to the method described by Reran and summarized in Danby, R. & Perrault, J., Weaves of Papermaking Wires and Forming Fabrics., Montreal, QC, Both Annual PAPTAC Is Meeting, January 26-28, 2004, page 2, and which provides a measure of the number of support points available in a given fabric weave pattern.

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, the incipient paper web. The paper side layer should also provide maximum support for the fibers and other paper making solids in the paper slurry. The machine side layer should be tough and durable, provide a measure of dimensional stability to the composite forming fabric so as to minimize fabric stretching and narrowing, or other distortions.

IS Weave patterns are known for composite forming fabrics in which the warp yarns comprise pairs, alternately forming part of the paper side and the machine side weaves. In such 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 tying the two layers together. Examples of such patterns are found in published US application NOs. 2003/0217782 of Nagura et al., 2004/0020621 of Heger et al., and in US patents 5,152,326 to Vohringer, 4, 605,585 to Johansson, 4,501,303 to Osterberg, and 6,223,780 to Kaldenhoff.

However, although improved paper side layer surface uniformity can be obtained by using weave patterns in which the warp yarn pairs together interweave with the 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, discussed below.

One problem which is common to all papermaking machines 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 Impingement drainages. In the initial portion of either a single fabric open surface fourdrinier type forming section, or a twin fabric forming section, either with or without an initial open surface portion, an unsupported jet of aqueous stock is ejected from the head box slice onto the open surface of a single moving forming fabric, or into the more or less convergent wedge shaped space between two moving forming fabrics. The jet of aqueous stock will typically traverse a short distance before impinging the surface of the forming fabric 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 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, at least in part because the stock jet widens in the direction perpendicular to the fabric surface 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 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 the impingement l forces. Thus, impingement drainage is a fabric characteristic which may limit further increases in machine speed and/or efficiency unless it can be better managed and controlled.

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 cause excessive impingement derived drainage of the stock over the initial portion of the forming section. It is well known that, on any papermaking machine under start up conditions and delivering a normal papermaking volume of water but without papermaking fibers 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 1% of the total available drainage length of the forming section. This indicates that, without fiber, all forming fabrics have far in excess of the drainage capacity required to make paper. However, as soon as papermaking fibers are introduced, drainage is retarded at a rate determined by the fiber length, the quantity of fiber, 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 machines were so successful. In more modern twin wire farmers such as gap farmers, the impingement shoe serves that function.

Impingement drainage may cause sheet marking, low 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.

Most commonly for double layer forming fabrics, a plain weave pattern is used in the paper side layer, as this produces the greatest amount of effective fiber support and will provide the most Closed ups weave pattern, resulting in the greatest drainage resistance, rather than the more open patterns such as a l x 2 or l x 3 weave pattern, which have a greater amount of drainage area than a plain weave. However, there is a physical limitation to how closed up a plain weave can be. It can be shown by calculation that the lower limit of the drainage area is 25%, without an undesirable mechanical deformation of the yarns.

The desirable characteristics of the machine side surface of double layer forming fabrics include stability and resistance to abrasion. To achieve this, the machine side surface of such fabrics is typically not woven according to a plain weave pattern; generally, patterns which offer long weft floats on the machine side surface are preferred. Such patterns are generally more open, and provide more drainage area than the usual paper side surface weave structure.

It has now 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 the machine side layer can be retained, by the use of weave patterns in which the fabric layers are bound together by pairs of warp yarns, where the members of each pair together form an unbroken l warp path in the paper side surface, and alternately interlace with the weft yarns of the machine side layer to contribute to but not form a complete repeat of the machine side layer weave pattern and which provides for long internal warp floats between the paper side layer and the machine side layer, between successive interweaving and interlacing points.

It has been found that such weave patterns provide several advantages 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 sufficient drainage area to remove water to the interior of the fabric without entrapping fibers. This reduces fiber 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 warp yarns promotes good sheet formation and fines retention, with many of the same benefits as the known forming boards.

Thirdly, the high 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. l l

The invention therefore seeks to provide a composite forming fabric for a papermaking machine comprising in combination a paper side layer having a paper side surface, a machine side layer, a first set of waft yarns comprising paper side layer weft yarns, a second set of weft yarns comprising machine side layer weft yarns, and a set of warp yarns, wherein (i) all of the warp yarns comprise pairs of warp binder yarns which bind together the paper side layer and the machine side layer; (ii) in the paper side surface, each pair of warp binder yarns occupies a single unbroken warp path in a first repeating weave pattern; (iii) the pairs of warp binder yarns are woven in the first repeating weave pattern such that for each pair: (a) in a first segment, a first member of the pair interweaves with selected paper side layer weft yarns at an interweaving location, and a second member of the pair interlaces with at least one machine side layer weft yarn at an interlacing location; (b) in a second segment, the second member of the pair interweaves with selected paper side layer weft yarns at an interweaving location, and the first member of the pair interlaces with at least one machine side layer weft yarn; (c) the length of the first and second segments may be equal or unequal; and (d) for each member of each pair of warp yarns, between each interweaving location and an immediately subsequent interlacing location, and between each interlacing location and an immediately subsequent interweaving location, the member floats between the paper side layer weft yarns and the machine l side layer weft yarns under at least four paper side layer weft yarns; tiv) in the machine side layer, for each pair of warp binder yarns, the first member and the second member alternately interlace with selected machine side layer weft yarns in each repeat of the second repeating weave pattern but do not form a complete repeat of the second repeating weave pattern; and (v) the fabric has a total warp fill after heatsetting of at least 100%.

The invention will now be described in more detail with reference to the attached drawings in which: Figure 1 shows the paths of a pair of warp yarns in one repeat 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 shows a scanning electron micrograph of the paper side surface of a fabric 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; and Figures 7 and 8 are weave diagrams of the embodiments of Figures 2 and 3 respectively.

Referring to Figures 1 and 4, a first embodiment of the S invention is shown. The fabric 100 has a paper side layer 52, having a paper side surface 54, on which the incipient 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 lOla and lOlb. The machine side layer 56, is woven to a different pattern, comprising an N x 2N weave, in which N quantifies the warp yarns lOla, lOlb, and 2N quantifies the weft yarns 62 in one repeat of the machine side layer weave pattern. In the fabrics of the invention, N is an integer 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 machine side layer weft yarns 62 are individually identified by the appropriate numerals in sequence from 1 to 30.

Figure 1 shows the path of a pair of typical warp yarns lOla and lOlb in one repeat of the fabric weave pattern. It can be seen that in a first segment 112, commencing at exchange point 102 under paper side layer weft yarn 8, warp yarn lOlb interweaves with eight paper side layer weft yarns 10, 11, 13, 15, 16, 18, 20 and 21, at interweave location 104, while warp yarn lOla passes between the paper side layer 52 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 side layer weft yarns 15, 16, 18, 20 and 21, meeting warp yarn lOlb at exchange point 102 under paper side layer weft yarn 21.

In a second segment 114, after exchange point 102b, warp yarn lOla interweaves with ten paper side layer weft yarns 23, 25, 26, 28, 30, 1, 3, 5, 6 and 8 at interweave location 106, while warp yarn lOlb 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 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 yarn lOla at a subsequent exchange point 102 under paper side layer weft yarn 8.

It can thus be seen that between each interlacing location 104, 106 and the immediately preceding and immediately subsequent exchange points 102, each of warp yarns lOla, lOlb 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 lOla 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 weft yarns with which warp yarn lOlb interweaves at each interweave location 106 (i.e. ten paper side layer waft yarns 60). The weave pattern is thus asymmetrical.

The weave pattern of the embodiment shown in Figure 1 is described in Figures 5 and 6. Figure 6 shows the weave pattern 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 lOla, lOlb. Thus the paths of each of the warp yarns identified in Figure 6 corresponds to the paths of the illustrative warp yarns lOla, lOlb 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 lOla, lOlb together forms an unbroken warp path in the paper side surface 54 of the paper side layer 52. It can also be seen that both warp yarns lOla and lOlb 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.

Figure 5 is a weave diagram of the complete fabric, i.e. the combined patterns of the paper side layer 52 and the 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 numerals across the top of the diagram representing the twenty-four warp yarns of this pattern, comprising twelve consecutive pairs of warp yarns lOla, lOlb.

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. l l

As in the embodiment of Figure 1, the two warp yarns 201a, 201b together form an unbroken warp path in the paper side surface 54 of the paper side layer 52. 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 201a interweaves at interweave location 206 with twelve paper side layer waft 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.

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 5, the numerals at the left side of the drawing represent the thirty six yarns comprising paper side layer waft 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 individually identified by the appropriate numerals in sequence from 1 to 48. s

As in the embodiments of Figures 1 and 2, the two warp yarns 301a, 301b together form an unbroken warp path in the paper side surface 54 of the paper side layer 52. 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 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 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 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 waft yarns 43, 45, 46, 48, 1, 3, 4, 6, 7, 9, 10, 12, 13, 15, 16 and 18.

It is apparent that the paths of the two warp yarns 301a, 301b of each pair follow an identical sequence in the paper side layer 52 and the machine side layer 56.

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 Figure 5 and 6, the numerals at the left of the drawing represent the 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 should further be noted that although each of the warp yarns lOla, lOlb, 201a, 201b, 301a and 301b contributes to the respective repeat weave pattern of the machine side layer 56, no pair forms a complete repeat of such pattern.

Three samples of the fabrics of the invention were made, using warp 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 Fabric 2 Fabric 3 Warp yarns (mm.) 0.15 PEN 0.15 PEN 0. 12PEN PS weft yarns (mm.) 0.13 0.13 0.13 MS weft yarns (mm.) 0.25 0.25 0. 22 Frames/in2 6,552 6,624 10,800 FSI 156 157 200 Elastic modulus (pli) 8,770 9,050 7,000 Caliper (in.) 0.0245 0.0276 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 especially when compared with more conventional triple layer S 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 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 which may be over 200, indicating good sheet support. This in term reduces fiber plugging and sheet sealing, making the sheet easy to IS remove from the fabric at the 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) 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 straight line run such as at a roll.

Preferably, the fabrics of the invention are constructed using a high modulus polymer material for the warp yarns, most preferably either polyethylene teraphthalate (PET) or polyethylene naphthalate (PEN). The paper side layer weft yarns are preferably of PET, and the machine side layer weft yarns are preferably of PET, nylon, or a blend of PET and polyurethane as described in US Patent No. 5,502,120. r

Claims

Claims 1. A composite forming fabric for a papermaking machine comprising

in combination a paper side layer having a paper side surface, a machine side layer, a first set of weft yarns comprising paper side layer weft yarns, a second set of weft yarns comprising machine side layer weft yarns, and a set of warp yarns, wherein (i) all of the warp yarns comprise pairs of warp binder yarns which bind together the paper side layer and the machine side layer; (ii) in the paper side surface, each pair of warp binder yarns occupies a single unbroken warp path in a first repeating weave pattern; IS (iii) the pairs of warp binder yarns are woven in the first repeating weave pattern such that for each pair (a) in a first segment, a first member of the pair interweaves with selected paper side layer waft yarns at an interweaving location, and a second member of the pair interlaces with at least one machine side layer weft yarn at an interlacing location; (b) in a second segment, the second member of the pair interweaves with selected paper side layer weft yarns at an interweaving location, and the first member of the pair interlaces with at least one machine side layer weft yarn; (c) the length of the first and second segments may be equal or unequal; and (d) for each member of each pair of warp binder yarns, between each interweaving location and an immediately subsequent interlacing location, and between each interlacing location and an immediately subsequent interweaving location, the member floats between the paper side layer weft yarns and the machine side layer weft yarns under at least four paper side layer weft yarns; (iv) in the machine side layer, for each pair of warp binder yarns, the first member and the second member alternately interlace with selected machine side layer weft yarns in each repeat of the second repeating weave pattern but do not form a complete repeat of the second repeating weave pattern; and (v) the fabric has a total warp fill after heatsetting of at least 100%.
2. A composite forming fabric as claimed in Claim 1 wherein the first repeating weave pattern is selected from the group consisting of a plain weave, twill, broken twill, basket weave; and the second repeating weave pattern is selected from the group consisting of twill, broken twill, and an N x 2N pattern wherein N quantifies the warp yarns in one repeat of the second weave pattern and 2N quantifies the waft yarns in one repeat of the second weave pattern, and N is greater than 3.
3. A composite forming fabric as claimed in Claim 2 wherein the first repeating pattern is a plain weave and the second repeating weave pattern is an N x 2N pattern.
4. A composite forming fabric as claimed in Claims 1 or 2 wherein the total fabric warp fill is at least 105%.
5. A composite forming fabric as claimed in Claims 1 or 2 wherein the total fabric warp fill is at least 110%.
6. A composite forming fabric as claimed in Claims 1 or 2 wherein the total fabric warp fill is at least 120%.
7. A composite forming fabric as claimed in Claim 1 wherein the ratio of paper side layer weft yarns to machine side layer weft yarns is selected from the group consisting of 2:1, 3:2 and 1:1.
8. A composite forming fabric as claimed in any of Claims 1 to 7, wherein the warp binder yarns are constructed of a high modulus polymer material.
9. A composite forming fabric as claimed in Claim 8, wherein the polymer material is selected from polyethylene teraphthalate and polyethylene naphthalate.