CA 02352898 2001-07-11 1007-340 WARP TRIPLET FORMING FAHRICS KITH OPTIONAL WEFT BINDER YARNB. FTFT,D OF THE_ INVENTION The present invention relates to woven forming fabrics for use in papermaking machines. The forming fabrics of this invention consist essentially of at least two layers or sets of weft yarns, one in the paper side layer of the fabric and the other in the machine side layer of the fabric, which are held together by one set of warps, which includes both warp non-binder yarns and warp binder yarns in sets of three or triplets. In a further modification, the forming fabric can also include a second set of paired weft binder yarns, which also serve to hld together the paper side layer and the machine side layer. Thus although visually the fabrics of this invention contain at least two layers, these are not separate, interconnected woven structures, and cannot be separated into two distinct self- sustaining woven structures. RArKCROL1N1~' OF THE INVENTION The known composite forming fabrics comprise two essentially separate woven structures, each of which includes its own sets of warps and wefts, and each of which is woven to a pattern selected to optimise the properties of the layer. The paper side layer provides, amongst other things, a minimum of fabric wire mark to, and adequate drainage of liquid from, the incipient paper web. The machine side layer should be tough and durable, provide a measure of dimensional stability to the forming fabric so as to minimize fabric stretching and narrowing, and be sufficiently stiff to minimize curling at the fabric edges. Numerous fabrics of this type have been described, and are in industrial use. 1 CA 02352898 2001-07-11 The two layers of the known composite forming fabrics are interconnected by means of either additional binder yarns, or intrinsic binder yarns. Additional binder yarns serve mainly to bind the two layers together intrinsic binder yarns both contribute to the structure of the paper side layer and also serve to bind together the paper and machine side layers of the composite forming fabric. The paths of the binder yarns are arranged so that the selected yarns pass through both layers of the fabric, thereby interconnecting them into a single composite fabric. In these known composite fabrics, additional weft binder yarns were generally preferred over intrinsic weft binder yarns, as they were believed to cause fewer discontinuities in the paper side surface of the composite fabric. Recently, both single and paired intrinsic warp or weft binder yarn arrangements have been proposed. However, intrinsic weft binder yarns have been found to cause variations in the cross-machine direction mesh uniformity. Composite fabrics in which intrinsic weft binder yarns are incorporated have been found to be susceptible to lateral contraction under the tensile load placed upon them in a papermaking machine. These intrinsic weft binder yarns have also been found to be susceptible to internal and external abrasion, leading to catastrophic delamination of the composite fabric. It has also been proposed to use intrinsic warp binder yarns in pairs, so as to overcome at least some of these disadvantages. The use of pairs offers the advantages that the two warp binder yarns can be incorporated in sequence in successive segments of an unbroken warp path in the paper side surface, and that there is flexibility of choice for the locations at which each member of the pair interlaces with the machine side layer wefts. It is 2 CA 02352898 2001-07-11 thus possible to optimise the paper side surface to some extent, for example by reducing marking of the incipient paper web, and to improve the machine side layer wear resistance of the fabric, essentially by increasing the amount of material available to be abraded away before catastrophic failure, usually by delamination, occurs. More recently, it has been proposed to intrinsic warp binder yarns in triplets, in much the same way as the earlier pairs. These fabrics using triplet sets offer more or less the same advantages as the paired binder yarn fabrics, but are somewhat easier to weave. In the following discussion of this invention, it is to be understood that in a notation such as "2x2" the first number indicates the number of sheds required to weave the pattern, and the second number indicates the number of wefts in the pattern repeat. Thus a 2x2 pattern requires two sheds, and there are two wefts in the pattern repeat. It has now been discovered that it is possible to weave a fabric having acceptable paper making properties by utilizing triplets of warp yarns so that each member of the triplets interweaves separately in sequence with the paper side layer wefts, and so that the members of the triplets interlace in pairs with the machine side layer wefts, and by including at least one non-binding warp yarn in between each adjacent set of triplet warp binder yarns. Additionally, it has now been discovered that when non- binding warp yarns are included in between triplet sets of warp binder yarns, it is also possible to include paired weft binder yarns in the fabric construction, thus improving the level of 3 CA 02352898 2001-07-11 attachment of the fabric layers to each other without any loss of product quality. Accordingly, this invention seeks to improve upon the known fabrics in which triplet sets of warp binder yarns are used. The present invention seeks to provide a forming fabric having reduced susceptibility to cross-machine direction variations in the paper side layer mesh uniformity than comparable fabrics of the prior art. Additionally, this invention seeks to provide a forming fabric that is resistant to lateral contraction. Furthermore, this invention seeks to provide a forming fabric that is less susceptible to dimpling of the paper side surface. In a preferred embodiment, this invention seeks to provide a forming fabric having a lower void volume than a comparable forming fabric utilizing intrinsic weft binder yarns. This invention additionally seeks to provide a forming fabric that is resistant to delamination. siIMMARY OF THE INVENTION In a first broad embodiment the present invention seeks to provide a forming fabric, having at least a paper side layer and a machine side layer, which comprises weft yarns interwoven with warp yarns, including both non-binding warp yarns and triplet sets of warp binder yarns, according to a repeating pattern wherein: (a) each member of each triplet set of warp yarns interweaves with the paper side layer weft yarns to occupy in 4 CA 02352898 2001-07-11 sequence segments of at least one unbroken warp path in the paper side layer; (b) each segment in the unbroken warp path is separated by at least one paper side layer weft yarn; (c) each member of each triplet interlaces with at least one machine side layer weft yarn; (d) the members of each triplet interlace in pairs together with a single machine side layer weft yarn; and (e) each triplet set of warp binder yarns is separated by at least one non-binding warp yarn from the adjacent triplet sets of warp binder yarns. In a second embodiment, this invention seeks to provide a forming fabric, having at least a paper side layer and a machine side layer, which comprises weft yarns interwoven with warp yarns, including both non-binding warp yarns and triplet sets of warp binder yarns, and further comprising both non-binding weft yarns and paired sets of weft binder yarns, according to a repeating pattern wherein: (i) each member of each triplet set of warp yarns interweaves with the paper side layer weft yarns to occupy in sequence segments of an unbroken warp path in the paper side layer; (ii) each segment in the unbroken warp path is separated by at least one paper side layer weft yarn; (iii) each member of each triplet set interlaces with at least one machine side layer weft yarn; (iv) the members of each triplet set interlace in pars together with a single machine side layer weft yarn; (v) each triplet set of warp yarns is separated by at least one non-binding warp yarn from the adjacent triplet set of warp binder yarns; CA 02352898 2001-07-11 (vi) each member of each paired set of weft binder yarns interweaves with the paper side layer warp yarns to occupy in sequence sections of an unbroken weft path in the paper side layer; (vii) each section in the unbroken weft path is separated by at least one paper side layer warp yarn; (viii) each member of each paired set interlaces with at least one machine side layer warp yarn; and (ix) each paired set of weft binder yarns is separated by at least one non-binding weft yarn from the adjacent paired sets of weft binder yarns. Preferably, the forming fabric includes two layers of weft yarns, the first in the paper side layer, and the second in the machine side layer. Alternatively, the fabric includes three layers of weft yarns, the first in the paper side layer, the second in the machine side layer, and the third in an intermediate layer. Preferably, the members of each triplet set occupy a single unbroken weft path in the paper side layer. Preferably, the members of each paired set occupy a single unbroken warp path in the paper side layer. Preferably, the forming fabric as woven and prior to heat setting has a warp fill of from 100 to 125. Preferably, after heat setting the forming fabric has a warp fill of from 100 to 140$. 6 CA 02352898 2001-07-11 It is a requirement of this invention that the paper side layer warp yarns include triplet sets of warp binder yarns; each member of each triplet in turn occupies a portion of at least one unbroken warp path in the paper side surface weave pattern. Within the forming fabric overall weave pattern, all of the members of the triplets of warp yarns pass in pairs into the machine side layer to interlace with the same machine side layer weft, so as to form a single coherent fabric. The interlacing locations are knuckles formed by the interlacing of two members of each of the triplets with a single machine side layer weft yarn, so that within the weave pattern repeat all three members of each triplet interlace at least once with a machine side layer weft. The location of interlacing points is largely determined by the weave pattern chosen for the machine side layer. It can thus be seen that in the fabrics of this invention only the paper side layer contains any conventional warp yarns which interlace only with paper side layer weft yarns. In the fabrics of this invention, a first group of wefts in the paper side layer, and a second group of wefts in the machine side layer, are held together within the overall weave repeating pattern by sets of triplet warp yarns, which therefore contribute to both the structural integrity and the properties of both layers. The non-binder warp yarns contribute only to the structure of the paper side layer. If desired, a third group of wefts can be present which are paired sets of intrinsic weft binder yarns, located essentially between the first and the second groups of weft yarns. The length of the segments in the paper side surface unbroken warp path occupied in sequence by each member of the triplets of warp yarns, and the number of segments within one 7 CA 02352898 2001-07-11 weave pattern repeat, is open to a wide range of choices, such as a weave pattern with six segments, in which the path occupied in the weave pattern repeat by each member of the triplets is essentially similar, or a weave pattern with four segments, in which the path occupied in the weave pattern repeat of two members of the triplet is essentially similar, and the path occupied by the third member of the triplet is quite different. In the unbroken warp path in the paper side layer each segment will generally occur more than once, for example at least twice, within each complete repeat of the forming fabric weave pattern. Similarly, the length of the sections in the paper side surface unbroken weft path occupied in sequence by each member of the paired sets of weft binder yarns, and the number of sections within one weave pattern repeat, is open to a wide range of choices. In the unbroken weft path in the paper side layer each section will generally occur more than once, for example at least twice, within each complete repeat of the forming fabric weave pattern. Preferably, each segment in the unbroken warp path in the paper side surface of the paper side layer is separated from an adjacent segment by either 1, 2 or 3 paper side layer weft yarns. Preferably, each segment in the unbroken warp path in the paper side surface of the paper side layer is separated from an adjacent segment by one paper side layer weft yarn. Alternatively, each segment in the unbroken warp path in the paper side surface of the paper side layer is separated from an adjacent segment by two paper side layer weft yarns. Preferably, each section in the unbroken weft path in the paper side surface of the paper side layer is separated from an 8 CA 02352898 2001-07-11 adjacent section by either 1, 2 or 3 paper side layer warp yarns. Preferably, each section in the unbroken weft path in the paper side surface of the paper side layer is separated from an adjacent section by one paper side layer warp yarn. Alternatively, each section in the unbroken weft path in the paper side surface of the paper side layer is separated from an adjacent segment by two paper side layer warp yarns. Preferably, within the paper side layer weave pattern, the total segment length or lengths occupied by each member of a triplet of warp yarns occupying the unbroken warp path are identical. Alternatively, the total segment length or lengths occupied by two members of a triplet of warp yarns occupying the unbroken warp path are identical, and the total segment length or lengths occupied by the third member of a triplet of warp yarns is different. Preferably, within the paper side layer weave pattern, the total section length or lengths occupied by each member of a paired set of weft yarns occupying the unbroken weft path are identical. Alternatively, the total section length or lengths occupied by each of the members of a paired set of weft yarns occupying the unbroken warp path are different. Preferably, within the fabric weave pattern the interlacing points between the warp yarns with the machine side layer wefts are regularly spaced, and are the same distance apart. Alternatively, within the fabric weave pattern the interlacing points between the warp yarns with the machine side layer wefts are not regularly spaced, and are not the same distance apart. 9 CA 02352898 2001-07-11 Preferably, within the fabric weave pattern the interlacing points between the weft yarns with the machine side layer warps are regularly spaced, and are the same distance apart. Alternatively, within the fabric weave pattern the interlacing points between the weft yarns with the machine side layer warps are not regularly spaced, and are not the same distance apart. Preferably, the weave design of the fabric is chosen to incorporate at least one feature chosen from: (1) the first, second and third segment lengths in the paper side layer are the same, and the interlacing points between the warp yarns with the machine side layer wefts are regularly spaced: or (2) the first, second and third segment lengths in the paper side layer are the same, and the interlacing points between the warp yarns with the machine side layer wefts are not regularly spaced, and are not the same distance apart: or (3) the first and second segment lengths in the paper side layer are the same, and are different from the third segment length, and the interlacing points between the warp yarns with the machine side layer wefts are regularly spaced: or (4) the first and second segment lengths in the paper side layer are the same, and are different from the third segment length, and the interlacing points between the warp yarns with the machine side layer wefts are not regularly spaced: or (5) the section lengths in the paper side layer are the same, and the interlacing points between the weft yarns with the machine side layer warps are regularly spaced; or (6) the first and second section lengths in the paper side layer are not the same, and the interlacing points between CA 02352898 2001-07-11 the weft yarns with the machine side layer warps are not regularly spaced. Preferably, the paper side layer weave pattern is chosen from a 2x2, 3x3, 3x6 or 4x8 weave design. More preferably the paper side layer weave is chosen from a plain 2x2 weave: a 3x3 weave: and a 4x4 weave. Preferably, the weave design of the machine side layer is chosen from a 4x4, 4x8, 5x5, 6x6 or 6x12 weave design. More preferably the weave design of the machine side layer is chosen from a 3x3 twill, a 6-shed broken twill, or an N x 2N design such as is disclosed by Barrett in US 5,544,678. Alternatively, the paper side layer may be combined with a machine side layer woven according to a satin, twill, or broken twill design. Some exemplary combinations are shown in Table 1: others are possible. 11 CA 02352898 2001-07-11 PSL PSL MSL MSL Total Weave Sheds, P Weave Sheds, Sheds M 2x2 6 6x6 18 18 2x2 6 6x12 18 18 3x3 9 6x12 18 18 3x6 9 6x12 18 18 2x2 6 4x4 12 12 2x2 6 4x8 12 12 3x3 9 4x4 12 36 4x4 12 4x4 12 12 4x4 12 4x8 12 12 4x8 12 4x4 12 12 4x8 12 4x8 12 12 4x8 12 4x8 12 12 2x2 6 5x5 15 30 3x3 9 5x5 15 45 5x5 15 5x5 15 15 In the headings to Table 1, "PSL" indicates paper side layer, P is the number of sheds required to weave the paper side layer, "MSL" indicates machine side layer number, M is the number of sheds required to weave the machine side layer, and "Total Sheds" indicates the minimum number of sheds required to weave the fabric. In the preferred embodiments of this invention, either a 2x2 plain weave, or a 3x3 twill weave is used for the paper side layer, combined with a 6-shed twill, a 6-shed broken twill, or a Barrett Nx2N weave design for the machine side layer. The 12 CA 02352898 2001-07-11 combination of a 2x2 plain weave with a 6x6 twill will require a total of 18 sheds: the 6x6 twill will require 18, and the 2x2 plain weave will require 6 in order to fit onto the 6x6 twill. Because all of the triplets of warp yarns are utilized to interlace in pairs with machine side layer weft yarns, this interlacing pattern improves fabric modulus, thus making the fabric more resistant to stretching and distortion, while reducing lateral contraction and any propensity for fabric layer delamination. The incorporation of paired weft binder yarns also improves fabric stability, and further reduces any propensity for fabric layer delamination. An important distinction between prior art fabrics and those of the present invention is the total warp fill, which is given by warp fill = (warp diameter x mesh x 100)x. Warp fill can be determined either before or after heat setting, and, for the same fabric, is generally somewhat higher after heat setting. In all prior art composite fabrics, prior to heat setting, the sum of the warp fill in the paper side and machine side layers combined is typically less than 95~. The fabrics of this invention prior to heat setting can have a total warp fill that preferably is greater than 100$, and is typically from 105$ to about 125. After heat setting, the fabrics of this invention have a total warp fill that can be greater than 105, and is typically from about 105 to about 140$. This possibility to achieve this level of warp fill makes them unique. In the context of this invention certain definitions are important. 13 CA 02352898 2001-07-11 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 triplets of warp yarns, and which is occupied in turn by each member of the triplets making up the warp 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 weft yarns with which a member of a triplet of warp yarns interweaves within the segment. The associated terms "section" and "section length" are defined in the same way, the length being determined by the number of paper side layer warp yarns with which each member of a paired set of intrinsic weft binder yarns interweaves. The term "float" refers to a yarn which passes over a group of other yarns without interweaving 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. The term "interlace" refers to a point at which a specific paper side yarn wraps about a machine side yarn to form a knuckle, and the associated term "interweave" refers to a locus at which a paper side yarn forms at least one knuckle with another paper side yarn along a portion of its length. BRTEF DESCRIPTION OF THE DR_AWINOS. The invention will now be described by way of reference to the drawings, in which: 14 CA 02352898 2001-07-11 Figures 1 - 4 are cross sectional views showing typical paths for one triplet of warp yarns in one repeat of the forming fabric weave pattern; Figure 5 shows the fabric of Figure 1 including paired sets of binder weft yarns; Figure 6 shows the weft binder paths for the fabric of Figure 5; Figure 7 shows the paper side surface of a fabric of Fig. 5 including additional non-binder warps between the triplet sets; and Figure 8 shows the paper side surface of the fabric of Figure 5 including both paired weft binder yarns and non-binding warp yarns. In each of the schematic cross sectional views of Figures 1 - 4, the paired weft binder yarns are omitted for clarity; one or more of the paper side layer wefts shown can be replaced with a pair of binder wefts. In Figs. 1-4, within the pattern repeat the cut weft yarns shown are numbered from 1, starting with the first machine side layer weft at one side, and finishing with the last paper side layer weft at the other. The arrows A, B, C and D indicate the length of the pattern repeat in Figures 1 - 4 respectively. Also, in Figures 1 - 8 the three members shown of one triplet warp set are labelled X, Y and Z. The same weave pattern continues in each direction away from the cross section shown along the length of the fabric. The weave pattern also continues across the width of the fabric, but will be moved laterally so that the interlacing locations with the machine side layer wefts are not always with the same weft. CA 02352898 2001-07-11 nFTATLED DESCRIPTION OF THE FIGURES. In Figure 1 the paper side layer of the fabric is a 3x3 weave, and the machine side layer is a 6x12 weave according to the Nx2N designs in Barrett, US 5,544,678. The unbroken warp within the paper side layer includes the following four segments: - triplet Z interweaves with wefts 2,6, and 11, passing under the intervening paper side layer wefts - triplet X interweaves with only weft 15; - triplet Y interweaves with wefts 20, 24, and 29, passing under the intervening paper side layer wefts: and - triplet X interweaves with only weft 33. In the machine side layer there are two interlacing points: - triplets X and Y together interlace with machine side layer weft 4: and - triplets X and Z together interlace with machine side layer weft 25. The fabric of Figure 1 is woven in 18 sheds; it could also be woven in 36. It is thus apparent that all three members X, Y and Z of the triplet occupy in sequence segments of the unbroken warp path in the paper side layer which are separated by two paper side layer wefts, and all three members interlace in two pairs with machine side layer wefts. This relatively simple weave also shows several other features of this invention. Inspection of the paper side layer shows that although the triplets Y and Z follow the same path, with Z shifted along the pattern relative to Y, the triplet X 16 CA 02352898 2001-07-11 follows a quite different path. The two segments occupied by triplets Y and Z are the same length, and the two occupied by triplet X are also both the same length, but a different length to the other two. Further, within the four segments, triplets Y and Z occupy one segment each, and triplet X occupies the other two. Due to the differing warp path length of triplet X compared to Y and Z, the fabric of Figure 1 is woven using two warp beams, one for triplet X and the other for Y and Z. If this is not done it is likely that fabric distortion and unequal warp tensions will occur thus impairing the usefulness of the fabric as a forming fabric. It can also be seen that there are two paper side layer wefts between each segment. Inspection of the machine side layer shows that triplets X and Y interlace at one point, and triplets X and Z at the other: triplets Y and Z do not interlace together with the machine side layer wefts. Further, the interlacing points are not regularly spaced along the pattern: there are six and four machine side layer wefts between them. When taken together, these features indicate a significant level of flexibility in weave diagram choices. At least some of these factors are utilised in the more complex weave pattern of Figure 2. In Figure 2, the paper side layer is a simple 2x2 weave, with only one weft between succeeding segments. In this weave there are six segments: - triplet X interweaves with wefts 2, 5, 8, 11 and 14; - triplet Z interweaves with weft 17; - triplet Y interweaves with wefts 20, 23, 26, 29 and 32; - triplet X interweaves with weft 35; - triplet Z interweaves with wefts 38, 41, 44,47 and 50; and 17 CA 02352898 2001-07-11 - triplet Y interweaves with weft 53. The machine side layer is a 6 shed twill weave, in which there are three interlacing points which are regularly spaced with five machine side layer wefts between each: - triplets Y and Z together interlace with weft 4~ - triplets X and Z together interlace with weft 22~ and - triplets X and Y together interlace with weft 40. This fabric is also woven in 18 sheds, and can also be woven in 36. This more complex weave shows further features of this invention. Within the six segments, the first, third and fifth are all the same length, and although the second, fourth and six are the same length, the length is different to that of the other three segments: the segments are essentially in two sets of three, with the same length within each set. Since each triplet occupies one longer and one shorter segment, each triplet occupies the same overall length within the unbroken weft path. It can also be seen that the paths for triplets X and Y are the same, and that of Z is different. Closer inspection shows the path for triplet Z is the path for X and Y reversed: for X and Y the longer segment comes first, and the shorter one second, and for Z the shorter one comes first, and the longer one second. It can thus be said that all three triplets occupy essentially the same path. Unlike the fabric of Figure 1, this design can be woven using a single warp beam as the path lengths of each of the triplets is essentially the same. Inspection of the machine side layer shows that in addition to the interlacing points being regularly spaced, all three possible pairings of the triplets are used. In both of these weave diagrams it can be seen that at the interlacing points the pairs of triplets can be recessed to an extent from the wear plane of the fabric by the machine side 18 CA 02352898 2001-07-11 layer float exposed on the machine side of the fabric, thus potentially increasing fabric life. As the exposed weft float length in the machine side layer weave pattern becomes shorter, e.g. from 5 wefts to 3, the interlacing points are recessed to a lesser degree. Wear at these locations can thus be minimised by choosing a machine side layer weave pattern that will provide long exposed weft float lengths at the desired points. It is also apparent from these diagrams that although the three members of each triplet occupy in sequence the segments of the unbroken warp path, on the paper side surface, the weave pattern does not include any gaps since the pattern continues along the fabric without any breaks. In the fabric of Figure 3, the paper side layer is a 3x3 twill with two wefts between succeeding segments. In this weave there are six segments: - triplet X interweaves with weft 2; - triplet Y interweaves with wefts 6, 11 and 15; - triplet Z interweaves with weft 20; - triplet X interweaves with wefts 24, 29 and 33; - triplet Y interweaves with weft 38; and - triplet Z interweaves with wefts 42, 47 and 51. The machine side layer is a 6 shed broken twill. There are three interlacing points, which are regularly spaced, with five machine side layer wefts between each: - triplets X and Z together interlace with weft 10; - triplets Y and Z together interlace with weft 28; and - triplets X and Y together interlace with weft 46. This weave is similar to that shown in Figure 2 in that it utilises six segments of differing lengths in two sets of three, together with regularly spaced interlacing points. In this weave pattern, the paths of all three warps are the same. 19 CA 02352898 2001-07-11 The fabric of Figure 3 is woven in 18 sheds, and can also be woven in 36 sheds. A more complex weave design is shown in Figures 4A and 4B combined for clarity there is some overlap between these two parts of Figure 4. In this fabric although both the paper side layer and the machine side layer are each relatively simple patterns, the paper side layer is a 3x3 twill, and the machine side layer is the same 6x12 design used in Figure 1, the pattern repeat requires nine segments: - triplet Y interweaves with wefts 108, 5,9 and 14~ - triplet X interweaves with weft 18; - triplet Z interweaves with wefts 23, 27 and 32; - triplet X interweaves with wefts 36, 41, 45 and 50; triplet Z interweaves with weft 54: - triplet Y interweaves with wefts 59, 63 and 68~ - triplet Z interweaves with wefts 72, 77, 81 and 86~ - triplet Y interweaves with weft 90s and - triplet X interweaves with wefts 95, 99 and 104. In the machine side layer there are six interlacing points which are regularly spaced in a repeating sequence of 6 and 4 wefts between each: - triplets X and Z together interlace with weft 4~ - triplets X and Y together interlace with weft 25; - triplets Y and Z together interlace with weft 40; - triplets X and Z together interlace with weft 61~ - triplets X and Y together interlace with weft 76~ and - triplets Y and Z together interlace with weft 97. Inspection of Figure 4 shows further features of this invention. In Figures 1, 2 and 3 the number of segments is twice the number of interlacing points: for Figure 1 the numbers are CA 02352898 2001-07-11 4 and 2, and for both of Figures 2 and 3 the numbers are 6 and 3. In Figure 4 this ratio is different, with 9 segments and 6 interlacing points. The segments lengths again are not the same, with a repeating sequence of 4 wefts, 1 weft, and 3 wefts within the pattern repeat. It can also be seen that each member X, Y and Z of the warp triplet occupies a essentially the same path within the weave pattern. In Figure 5 the cross section of Figure 1 is reproduced for a fabric which also contains paired weft binder yarns. Two pairs of weft binder yarns are shown, and are identified as 100, 101 and 102, 103. The paths of one of these pairs of yarns 100,101 within the weave pattern are shown in Figure 6. Each member of the weft binder pair shown interweaves with the paper side layer warps, and also interlaces with two machine side layer warps. In the weave pattern shown, each section is the same length, and there is one paper side layer warp between succeeding sections occupied in sequence by the wefts 100 and 101. In Figure 7 the paper side surface of the paper side layer of a fabric utilising the triplet warp binder arrangement of Figure 1 is shown. In this fabric, the paper side layer is a 2x2 plain weave, and the machine side layer is the 6x12 weave used in Figure 1. Figure 7 illustrates the use of non-binding warp yarns the segments of the segments of the unbroken warp path er identified as X, Y and Z. The non-binding warp yarns 10 - 19 are inserted as shown between the triplet sets, and are interwoven so as to continue the pattern of the paper side layers these non- binding warp yarns are not interlaced into the machine side layer. One, two, three or more non-bonding warp yarns may be inserted between any adjacent pair of triplets these yarns will continue the weave pattern. 21 CA 02352898 2001-07-11 In Figure 8 the paper side surface of the paper side layer of another fabric utilising the triplet warp binder arrangement is shown. The segments of the unbroken warp path occupied by one triplet are identified as X, Y and Z. The non-binding warps are numbered from 10 - 14. It is to be noted that there is one non- binding warp between each triplet set of warp binder yarns. This fabric also includes paired weft binder yarns, occupying the sections S and T of the unbroken weft path. In Figure 8, the paired binder weft yarns are separated by three non-binding weft yarns: the paired weft binder yarns cen be separated by one, two three or more non-binding weft yarns. The number. of intervening yarns will depend upon the amount of interlayer binding strength desired, and the paper side layer properties desired in the final fabric. It is also possible to reverse the manner in which the binder yarns are inserted so as to reduce the size of a portion of the mesh openings. As shown, where the pair of binder yarns pass by each other at the section ends, section T is nearer to the bottom edge of Figure 8: this can be reversed, so that section S is in this position. A proportion of the paired weft binder yarns can be reversed in this fashion. This technique is described by Ward, US 5,967,195. As has been previously discussed, the weave structure of the paper side layer must "fit" onto the weave structure of the machine side layer. There are at least three reasons for this. First, the locations at which a pair of yarns from a triplet of warp yarns interlaces with a machine side layer weft yarn must coincide with the interweaving location with the paper side layer 22 CA 02352898 2001-07-11 of the third member of the triplet. The weave structures of each layer must therefore be such that this may occur without causing any undue deformation of the paper side layer paper side surface. Second, the paper side layer and machine side layer weave structures should fit such that the locations at which a pair of yarns from a triplet interlace together with a machine side layer weft is as far removed as possible from the ends of the segment in the paper side layer weave pattern occupied by the third member of the triplet. This will reduce dimpling and any other surface imperfections caused by bringing the third member of the triplet down from the paper side layer into the machine side layer. Third, the locations at which the pairs of warp yarns from each triplet interlace with the machine side layer weft yarns should be recessed into the machine side layer as much as possible from the wear plane of the machine side layer, so as to extend the fabric service life. This may be accomplished by making the exposed machine side layer float between two successive interlacing points as long as possible. The length of a machine side layer weft float will increase with the number of sheds used to weave the machine side layer pattern. Thus it is generally preferred that the machine side layer of the fabrics of this invention be woven according to patterns requiring at least 4 sheds, and preferably at least 6. Similar considerations apply to determining the weave structure and the location of the interlacing points for the paired weft binder yarns when these are used. 23 CA 02352898 2001-07-11 Selection of appropriate warp and weft yarn diameters for use in the fabrics of this invention will depend on many factors, including the grade of paper product which the fabric will be used to produce and will affect the air permeability of the resulting fabric. Selection of appropriate yarn diameters will be made in accordance with the intended end use of the fabric. Several other options are available in the design and construction of the fabrics of this invention. During the weaving process, it is possible to alter the order in which the warp yarn comprising the warp triplet sets are woven. for example, in the fabric design of Figure 8, the sequence of warp yarns in the warp triplet sets is always X, Y, Z. It is possible to use the other possible sequence X, Z, Y for some of the triplet sets in the same fabric. A porous surface coating cam also be applied to the paper side surface of the fabric, so as to enhance the uniformity of the surface: for example a photopolymerisable resin can be exposed through a mask, thus defining both pore size and location. Alternatively, a polymeric resin containing a soluble particulate substance can be used, as described by Gass in US 6,017,583 and in US 6,057,255. The fabrics of this invention show improved printability characteristics in comparison with known forming fabrics. 24