A common form of seam is achieved by extending selected longitudinal (machine direction) warp yarns of the fabric beyond the last transverse (cross direction) weft yarn, to form a loop, the end of which is back-woven into the fabric. The non-selected machine direction warp yarns are looped about the last cross direction weft yarn and the end back-woven into the fabric. Such a structure is described in GB-A-1488815, which discloses two patterns of weaving back the looped yarns, and cutting short of certain other MD yarns to provide space for the back woven loop ends.

Normally all the warp yarns have the same thickness or width, so that as a result when using only half the warp-yarns to form the loops, to afford space for interdigitation of the corresponding loops of the opposite end of the fabric, the tensile strength of the seam is relatively poor and there is a higher propensity in the seam region for marking of the paper sheet due to the greater open area in the seam region, as about 50% of the total width of the fabric is open space.

One approach to solving this problem is to use more than 50% of the warp yarns to form the loops. An example of this is WO 92/15743 wherein

the problem of obtaining space for interdigitation of loops where more than 50% space is used by the loops of each side, is tackled by crossing adjacent loops over each other. However the use of more than 50% warp yarns, and the crossing of the looped yarns makes the already complicated, prolonged and expensive seaming process take even longer to carry out.

A object of the invention is to provide a fabric structure which enables seaming to be carried with more than 50% of the warp yarn width, thus attaining lower open space in the seam, leading to a reduced propensity to marking of the paper sheet.

According to the invention a woven fabric structure comprises an array of warp yarns interwoven with an array of substantially orthogonally extending weft yarns, characterised in that said warp yarns comprise relatively wide warp yarns arranged in groups of one or more alternatively with relatively thin warp yarns arranged in groups of one or more.

The fabric is preferably for papermachine clothing, such as a dryer fabric, a forming fabric, extended nip press belt, press sleeve, basecloth, or for a filter belt or conveyor belt.

The warp yarns may be arranged in groups comprising alternating pairs of relatively wide yarns and pairs of relatively thin yarns. The alternating groups of warp yarns may each comprise single yarns, or any other number, and need not comprise the same number of wider and thinner yarns in the respective groups.

In seaming the fabric, in order to effect a loop and pintle wire joining seam between the opposite ends of the fabric, the thinner yarns are preferably looped around the last weft yarn (extending parallel to the edge, across the width of the fabric), and the wider yarns are preferably extended beyond the last weft yarn to form loops which may be interdigitated with similar loops of the opposing fabric end, and joined by a pintle wire passed through the tunnel formed by the interdigitated loops.

The loops will, being provided by the wider yarns, comprise more than 50% of the width of the fabric.

The fabric may comprise a single layer woven construction, with all weft yarns in a single tier, however multi layer, or multi-weft tier fabrics may also be used.

The warp yarns, at least the wider yarns, are preferably flat yarns.

The thinner yarns may also be flat yarns. However either or both the wider and thinner warp yarns may be of other cross-sectional profiles, such as triangular or semi-circular.

The invention also provides a method of seaming a woven fabric for forming the fabric into an endless belt characterised in that the fabric is formed with an array of longitudinally extending warp yarns, the warp yarns comprising relatively wide yarns arranged in groups of one or more alternatively with relatively thin warp yarns arranged in groups of one or more, said relatively thin warp yarns being looped about a last weft yarn of

the fabric edge, and the relatively wide warp yarns being formed into extended loops extending in the plane of the fabric beyond said last weft yarn.

Preferably the seam is completed by interdigitating said loops with corresponding loops on an opposed end of the fabric, and passing a pintle a wire through said interdigitated loops.

The invention further provides an endless fabric formed by seaming by the method according to the invention, or comprising a fabric including a woven fabric structure according to the invention.

A preferred embodiment of fabric structure according to the invention, seam, seaming method and endless fabric according to the invention will now be described by way of example with reference to the accompanying drawings wherein:- Figure 1 is a fragmentary enlarged detail view of part of a seam edge region of a woven papermachine fabric, showing part of the weave structure of the fabric of the seam formation; Figures 2a to 2c are cross-sectional views of yarn cross-sections used in the fabric; and Figure 3 is a diagram of an endless belt formed by the seamed fabric of the invention.

In Fig. 1, a woven fabric for a papermachine or other belt comprises

an array of cross-machine direction weft yarns 10, extending parallel to an edge of the fabric, and including a last weft yarn 10a, defining the edge.

An array of warp yarns is woven through the weft yarns 10 substantially orthogonally to the weft yarns of and in the machine direction of the belt.

The warp yarns comprise wide yarns 12 and thin yarns 13.

In the embodiment shown, the wide yarns 12 are grouped in side-by- side pairs, and the thin yarns 13 are also grouped in pairs between the pairs of wide yarns 12. The thin yarns 13 are looped around the last weft yarn 10a, and back woven into the fabric. The wide yarns however are extended beyond the last weft yarn 10a, to form seaming loops 14, and then back-woven into the fabric.

In the seaming process, the seaming loops 14 are interdigitated with loops 14'on an opposed fabric edge, and a pintle wire or binding yarn 15 is threaded through the interdigitated loops 14,14'to effect joining of the fabric edges. This produces a seam 16 as illustrated in Fig. 3, to form an endless belt 17.

The fabric weave of the invention enables a seam to be formed with loops 14 on each end to be joined which comprises more than 50% of the width of the fabric, so that the difference between the warp cover in the body of the fabric and the warp cover in the seam region is less than usual, typically 80% cover in the seam region compared with 100-120% warp cover in the body of a typical dryer fabric.

The wider and thinner yarns may be grouped in numbers other than pairs, from single yarns up, and the groups of wider and thinner yarns may comprise different numbers of yarns, e. g. 1 and 2, or 2 and 3.

In an example similar to Fig 1, a seam with 75% cover, ie 25% open area was made using flat warp (MD) yarns measuring 0.27x39mm and 0.27 (height) xO. 75mm (width). For every set of 4 warp yarns, two are wide, and are used to form seam loops 14. The seam strength was measured at 43kg/cm, compared with 32kg/cm for a fabric containing 56% warp cover if 4 narrow warp yarns are used in each set. These figures apply to a fabric with a warp density of 188 ends per 10 cm, woven to allow 6% reed width, and following heat setting has a warp density of 200 ends/10cm.

As shown in Fig. 2, the yarns, particularly the wider yarns 12 may have any of a number of cross-sectional profiles, such as flattened (Fig. 2a), circular (Fig. 2b) or elliptical (Fig. 2c).

The weave structure and seamed fabric belt of the invention can be in any appropriate application as papermachine clothing, as a filter belt, or conveyor belt or the like. The fabric may constitute a base for a further layer or layers such as fibrous non-woven batts etc, filtration coatings etc, depending upon the intended use of the belt.

The narrow yarns 11, may be of equal height to the yarns 12, as shown in Fig. 2a to form a mono-planar sheet support surface, or may be

of the same proportions, and thus lower than the wide yarns as in Figs. 2b and 2c. This latter arrangement is desirable when a ribbed dryer fabric is required, such ribs may be provided on the sheet side or the machine side of the fabric. The ribs and grooves in one end of the fabric are preferably aligned with these on the other end the fabric on the opposite side across the seam. Ribbed fabrics can also be used to emboss the sheet, for example as a tissue forming or drying fabric, or to provide yarns standing proud to provide extra resistance to wear.

The seam construction can be used to make an endless forming fabric or press felt, or base cloth.