GB2423998A

GB2423998A - Charge-dissipating forming belt for making nonwovens

Info

Publication number: GB2423998A
Application number: GB0505056A
Authority: GB
Inventors: Michael Bodnar
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-03-11
Filing date: 2005-03-11
Publication date: 2006-09-13
Also published as: GB0505056D0

Abstract

A woven fabric for a belt for use in forming dry nonwoven sheets incorporates conductive yarns to dissipate electric charges and comprises a first set of sheet-side warps 301, a second set of machine-side warps 302 and at least one set of wefts (a sheet-side set 100 and a machine-side set 200 as shown) which may include binder wefts 4,8,12,16. The sheet-side warp set includes a conductive yarn 301 in each repeat which does not appear on the machine side and the machine-side warp set also includes a conductive yarn (308, Fig 9) which does not appear on the sheet side and the weft set(s) include(s) a conductive yarn 4 which contacts both the conductive warps. In further embodiments of the invention three sets of wefts are provided with the conductive weft (7, Figs 15-18 and 8, Figs 20-35)) belonging to the central set.

Description

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FORNIN(3 BELT FOR NONWOvEIq5 INCLUDING CONDUCTIVE YARNS

FIELD OF THE INVENTION

This invention relates to forming belts for dry forming processes for the manufacture of nonwovens, and in particular to forming belts wherein the amount of conductive materials for dissipation of static electricity from such belts is optimised.

BACKGROUND OF THE INVENTION

In the manufacture of nonwovens, the web is typically formed by one of three types of process, these being a wet process, a dry process or a melt process. Of these, dry processes can be carding or air-laying, and melt processes can be spun bonding or melt-blowing. For each of the processes of air-laying, spun bonding and melt-blowing, a high-speed operation is involved in the depositing of the constituent fibers on a forming belt.

A coimnon problem to each of these processes, and shared to some extent with many industrial processes involving high machine speeds, Particularly in controlled dry environments, is the accumulation of static electricity.

In the manufacture of nonwovens, this problem inhibits the optimum web formation, causes premature separation of the web from the forming belt, and creates risks of sparking, fire or explosion. The significance of this problem increases in proportion to the continuing development of machines capable of ever greater operational speeds. )

Various methods have been used or attempted in various industrial processes to dissipate such static electricity.

These include the application of coatings, as in US Patent No. 3,542,633, to Goldsmith; and application of a charge at a suitable location on a moving belt element, as in EP 950,744, to Weng et al. Further, static-dissipation can be provided to end-product fabrics, by coating, bonding of a suitable layer to the fabric, as in US Patent No. 4,307,144, to Sanders et al.; or adding raised portions to the fabric, in which a discharge yarn plied to a carrier yarn is included in the fabric, as in US Patent Nos. 4,557,968 to Thornton et al. and 4,606,968 to Thornton et al. It is also known to incorporate electrically conductive wires into the weave of various fabrics, for example as disclosed in US Patent No. 5,655,585 to Fry.

Similarly, attempts have been made in relation to the fabrics used in papermaking machines to reduce the problems of accumulation of static electricity, particularly in the dryer section, by various approaches to fabric construction.

For example, a conductive coating comprising an anti- static agent can be applied to a complete dryer fabric after weaving, for example as taught in US Patent No. 4,427,736, to Beacom et al. A base fabric having dissipation properties can be applied to filter fabrics, as in WO 027 4416 to Jarvinen et al. Alternatively, electrically conductive fibers can be included within the weave, as in DE 8606334, assigned to Carl Veit GinbH, and JP 9263688 to Toyohiko et al., in which a sheath of conductive material is applied to monofilament yarns for dryer fabrics; similarly, GB 2,346,387 to Jeffrey et al. discloses a transfer fabric having conductive yarns encapsulated in polymer.

Additionally, metal/polyester blends are known for use in the weaves of press felts or dryer fabrics.

However, each of these approaches is subject to the limiting factor that the coating or other additional material should interfere as little as possible with the desirable physical attributes and performance of the fabric as a whole derived from the properties of its component yarns. This is particularly significant in the somewhat related but specific environment of the industrial manufacture of nonwovens. As this process takes place in an entirely dry environment, static electricity creates the further hazard of interference with the initial sheet formation; and the solution to the problem must take into account the parameters of the sheet formation process selected.

Up to the present, the most effective approach has been to incorporate electrically conductive yarns into the weave of the forming belts. These can be similar to the yarns discussed above in relation to papermaking machine dryer fabrics, and can comprise metal wires, for example of stainless steel, bronze, brass, or various other alloys such as Invar. Alternatively, conductive particles can be incorporated within a polymer forming the outer layer of a yarn. For example, JP Patent No. 9263688 to Toyohiko et al., for dryer fabrics, suggests the use of carbon black, or whiskers of silver, copper, copper iodide or zinc oxide as suitable conductive materials.

The use of conductive yarns can be combined with other desirable features for such forming fabrics for nonwovens.

For example, US Patent No. 6,790,796 to Smith et al. discloses a belt including anti-slip, braided yarns, which can have suitable coating for static electricity dissipation. Further, WO 03038168 to Levine et al. and WO 03095740 to Monnerie et al. disclose the use of flat monofilament yarns which can be conductive. it is indicated that conductive warp or weft yarns can be included. However, there is no indication of the numbers of such yarns which should be used in proportion to the numbers of regular, non-conductive, yarns in such patterns, or the types of pattern for which this could be an effective approach, except that WO 03038168 indicates suitability for a pattern identified as a 4B weave.

Additionally, a belt has been disclosed comprising yarns of PEEK with conductive metal filaments in the wefts, which are said to be capable of withstanding higher temperature ranges than plastic monofilament, as noted in Paetow, H., Plastic Fabrics in the Nonwovens Industry, Nonwovens Conference and Trade Fair, published in Nonwovens World April 1998. /

These considerations of quantity and weave pattern suitability are significant, firstly in relation to economics and secondly in relation to performance. The cost of conductive yarns of any of these described types is relatively high in comparison with the regular yarns used in forming belts of this nature. Further, some types of conductive yarn may be incompatible with, or not possess the desirable functional attributes of, the optimum regular yarn materials for the specific application. For these and other reasons, it is therefore particularly desirable to use only the minimum number of conductive yarns which is necessary in order to achieve the required dissipation properties for the belt.

In multi-layer forming belts having at least two sets of warp yarns, additional problems are encountered in providing for effective dissipation of static electricity, where in the weave patterns of choice for the application the sheet side warp yarns are not exposed on the machine side, and the machine side warp yarns are not exposed on the sheet side. For such belts, the need to have conductive yarns exposed on both sides of the belt has been addressed by a combination of conductive warp and weft yarns. However, the suggestions in the references noted above suffer from the disadvantages of appearing to require a cost- prohibitive number of conductive yarns in proportion to the non- conductive yarns, and of being applicable only to a restricted number of weave patterns.

Up to now, it has been considered essential to provide for a relatively large number of conductive yarns in n proportion to the number of nonconductive yarns. For example, in a typical 12 x 16 weave pattern, it is usual to provide at least four conductive warp yarns and two conductive weft yarns for each repeat of the weave pattern.

However, it has now been found that weave patterns can be provided for such belts, particularly multi-layer belts, in which the number of conductive yarns used in each repeat can be substantially reduced, while maintaining the required level of static dissipation, thus enabling significant economies in the cost of materials, and the optimization of the physical properties of the regular non-conductive yarns, in a significantly greater variety of weave patterns. The patterns of the invention typically reduce the number of conductive weft yarns required by at least 50%.

The invention therefore seeks to provide a charge dissipating forming belt for use in a dry nonwoven sheet forming process, the forming belt (a) having a sheet side surface and a machine side surface and being woven according to a first repeating weave pattern requiring at least four sheds in the loom, and (b) comprising at least two sets of warp yarns and at least one set of weft yarns, wherein in each repeat of the first repeating weave pattern: i. each warp yarn of the first set interweaves with selected weft yarns to contribute to a second repeating pattern which comprises the weave pattern J) of the sheet side surface of the belt, but is not exposed on the machine side surface; ii. each warp yarn of the second set interlaces with selected weft yarns to contribute to a third repeating pattern which comprises the weave pattern of the machine side surface of the belt, but is not exposed on the sheet side surface; iii. one of the warp yarns of each set is comprised of an electrically conductive material; iv. one weft yarn is comprised of an electrically conductive material; and v. the electrically conductive warp yarn of the first set and the electrically conductive warp yarn of the second set is arranged so as to contact the one electrically conductive weft yarn.

The invention further seeks to provide a method of manufacture of a charge dissipating forming belt for use in a dry nonwoven sheet forming process, comprising the steps of (a) weaving a sheet side surface and a machine side surface according to a first repeating weave pattern requiring at least four sheds in the loom, and comprising at least two sets of warp yarns and at least one set of weft yarns; (b) providing in each repeat of the first repeating weave pattern one electrically conductive warp yarn in each set; and (c) providing in each repeat of the first repeating weave pattern one electrically conductive weft yarn which is in contact with each electrically conductive warp yarn.

The weaves of the invention can include additional sets of weft yarns, and some or all of these yarns can be woven as stacked groups of two or more yarns per group.

Additionally, a third set of weft yarns can be provided which act as binder yarns.

The conductive yarns of the invention are preferably constructed of polymer materials, such as nylon 6/6, having a conductive coating, such as particles of carbon black. Currently available coated polymer yarns preferably have a resistance which is in a range between 2 x 1O and 8 x 10 [power 4] ohms/cm. Yarns having a lower resistance, such as weft yarns constructed of suitable metals, can also be used.

Readily available conductive yarns typically have a circular crosssection. For example, Sanstat* available from Shakespeare Conductive Fibres, of 6111 Shakespeare Road, Columbia, South Carolina 29223, USA, has been found to be suitable. However, other yarns could also be suitable, and any configuration could be used which is compatible with the physical properties required for a particular application.

* Trade mark

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DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described with reference to the drawings, in which Figure 1 is a weave diagram of a first embodiment of the invention; Figures 2 to 13 show the paths of machine direction yarns in sequence in the embodiment of Figure 1; Figure 14 is a weave diagram of a second embodiment of the invention; Figures 15 to 18 show the paths of machine direction yarns in sequence in the embodiment of Figure 14; Figure 19 is a weave diagram of a third embodiment of the invention; and Figures 20 to 35 show the paths of machine direction yarns in sequence in the embodiment of Figure 19.

Referring to Figures 1 to 13, a first embodiment of the invention is shown. In Figure 1, the symbol X in a square indicates that the specific warp yarn passes over a weft yarn at that point, and a blank square indicates that the warp yarn passes under a weft yarn at that point. As can be seen from Figure 2, a forming belt 21 has a sheet side surface 22 and a machine side surface 24, and comprises a first set of weft yarns 100, a second set of weft yarns 200, and a set of warp yarns 300. In the weave diagram of Figure 1, the paths of the warp yarns 300 of this embodiment are shown vertically in the figure, and the warp yarns 300 are numbered individually as 1 to 12. The paths of the weft yarns 100 and 200 are shown horizontally

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in Figure 1, and the weft yarns 100, 200 are numbered individually as 1 to 16.

In each of Figures 2 to 13, the paths of each consecutive warp yarn in one set of warp yarns 300 is shown, corresponding to each of the twelve warp yarns identif led as 1 to 12 in Figure 1. Thus, warp yarn 301 in Figure 2 corresponds to warp yarn 1 in Figure 1, warp yarn 302 in Figure 3 corresponds to warp yarn 2 in Figure 1, and warp yarn 312 in Figure 13 corresponds to warp yarn 12 in Figure 1.

In each of Figures 2 to 13, it can be seen that some of the warp yarns 300 of this embodiment, i.e. warp yarns 301, 303, 304, 306, 307, 309, 310 and 312, interweave only with the first set of weft yarns 100, and are not exposed in the machine side surface 24. Others of the warp yarns 300 of this embodiment, i.e. warp yarns 302, 305, 308 and 311, interlace only with the second set of weft yarns 200, and are not exposed in the sheet side surface 22.

In each repeat of the weave patterns of the invention, at least one warp yarn 300 exposed in the sheet side surface 22 and at least one warp yarn 300 exposed in the machine side surface 24 is conductive. In this embodiment, the conductive warp yarns are 301 and 308.

The weft yarns 100 and 200 are numbered individually to correspond with the numbers shown in Figure 1. Four of the weft yarns, 4, 8, 12 and 16 are shown in Figures 2 to 13 as smaller than the remaining weft yarns 100, 200, the difference being exaggerated for ease of understanding.

These four weft yarns are each binder weft yarns, but in each repeat of the weave pattern, only one of them, weft yarn 4, is conductive.

Similarly, the machine side weft yarns 200 are shown as being larger than the sheet side weft yarns 100. However, the selection of relative sizes will be determined by the specific physical properties required for the belt.

Thus it can be seen that the first of the two conductive warp yarns, 301, interweaves only with the sheet side surface weft yarns 100, and in each repeat of the weave pattern Contacts the conductive weft yarn 4 without being exposed in the machine side surface 24. Similarly, the second of the two conductive warp yarns, 308, interlaces only with the machine side surface weft yarns 200, and in each repeat of the weave pattern contacts the conductive yarn 4, without being exposed in the sheet side surface 22.

Referring now to Figures 14 to 18, a second embodiment of the invention is shown, in which three sets of weft yarns are provided, i.e. weft yarns 120, 220 and 420. In Figure 14, the weave pattern of this embodiment is shown, the paths of the warp yarns 320 being shown in the vertical direction, the individual warp yarns being identified as 1 to 8. The paths of the weft yarns 120, 220 and 420 are together shown in Figure 14 in the horizontal direction, n the individual yarns being identified as 1 to 14. As in Figure 1, the symbol X in a square indicates that the specific warp yarn passes over a weft yarn at that point, and a blank square indicates that the warp yarn passes under a weft yarn at that point.

In Figures 15 to 18 the path of each consecutive warp yarn 320 in one set is shown, identified as the paths of warp yarns 321 to 328. In this embodiment, warp yarns 321, 323, 325 and 327 are exposed on the sheet side surface 22 and not the machine side surface 24, and warp yarns 322, 324, 326 and 328 are exposed on the machine side surface 24 and not the sheet side surface 22.

In this embodiment, the conductive warp yarns are 321 and 326, and the single conductive weft yarn is 7. Similarly to the first embodiment shown in Figures 1 to 13, the conductive weft yarn 7 and one of weft yarns 420, identified as 14, are shown as being smaller than the remaining weft yarns 120, 220 and 420. The difference in size has been exaggerated in Figures 15 to 18 for ease of understanding.

Thus it can be seen that the first of the two conductive warp yarns, 321, interweaves only with the third weft yarns 420 and the sheet side surface weft yarns 120, and in each repeat of the weave pattern contacts the conductive weft yarn 7 without being exposed in the machine side surface 24. Similarly, the second of the two conductive warp yarns, 326, interlaces only with the third weft yarns 420 and the machine side surface weft yarns 220, and in each repeat of the weave pattern contacts the Conductive yarn 7, without being exposed in the sheet side surface 22.

Referring to Figures 19 to 35, a third embodiment of the invention is shown, in which the weft yarns comprise three sets, 130, 230 and 430. Figure 19 shows the weave pattern of this embodiment, the paths of the warp yarns 330 being shown in the vertical direction, and the individual warp yarns being identified as 1 to 16. The paths of the weft yarns 130, 230 and 430 are shown together in the horizontal direction, the individual weft yarns being identified as 1 to 12. As in Figure 1, the symbol x in a square indicates that the specific warp yarn passes over a weft yarn at that point, and a blank square indicates that the warp yarn passes under a weft yarn at that point.

In Figures 20 to 35 the path of each consecutive warp yarn 330 in one set is shown, identified as the paths of warp yarns 331 to 346. In this embodiment, warp yarns 331, 332, 335, 336, 339, 340, 343, and 344 are exposed on the sheet side surface 22 and not the machine side surface 24, and warp yarns 333, 334, 337, 338, 341, 342, 345 and 346 are exposed on the machine side surface 24 and not the sheet side surface 22.

In this embodiment, the conductive warp yarns are 331 and 338, and the single conductive weft yarn, in the set of weft yarns 430, is 8. n

Thus it can be seen that the first of the two conductive warp yarns, 331, interweaves only with the third weft yarns 430 and the sheet side surface weft yarns 130, and in each repeat of the weave pattern contacts the conductive weft yarn 8 without being exposed in the machine side surface 24. Similarly, the second of the two conductive warp yarns, 338, interlaces only with the third weft yarns 430 and the machine side surface weft yarns 230, and in each repeat of the weave pattern contacts the conductive yarn 8, without being exposed in the sheet side surface 22.

In each of the embodiments of the invention as shown and described, the weave patterns, all requiring at least four sheds in the loom, provide a repeating weave pattern in which one conductive warp yarn is provided for each of two sets of warp yarns, one being exposed in the sheet side surface 22 and not the machine side surface 24, and the other being exposed in the machine side surface 24 and not the sheet side surface 22; and only one conductive weft yarn is provided, the weft yarn path for which results in the conductive weft yarn being in contact with each of the conductive warp yarns. This results in substantial economy over the prior art, in which the anti-static multi-layer weave patterns have required at least two conductive weft yarns in each repeat.

It should be noted that some or all of the weft yarns of each embodiment can be made of different dimensions from other weft yarns within a set or different sets, according to the performance requirements for the particular application for which the belt is to be used, for example the extent to which binder yarns are required to be smaller to provide for protection from external forces, such as machine side abrasion. The differences shown in the drawings are illustrative only, and different combinations of dimensions can be selected as appropriate.

The static electricity can be discharged from the belt by any suitable known means. Typically, a conductive element is provided on the machine which comes into contact with the belt at a suitable location, for example a grounded roll which discharges the electricity as the belt travels around the roll, or a suitable metal wire, such as copper, can be provided to contact the belt at an appropriate location.

Claims

1. A charge dissipating forming belt for use in a dry nonwoven sheet forming process, the forming belt (a) having a sheet side surface and a machine side surface and being woven according to a first repeating weave pattern requiring at least four sheds in the loom, and (b) comprising at least two sets of warp yarns and at least one set of weft yarns, wherein in each repeat of the first repeating weave pattern: (i) each warp yarn of the first set interweaves with selected weft yarns to contribute to a second repeating pattern which comprises the weave pattern of the sheet side surface of the belt, but is not exposed on the machine side surface; (ii) each warp yarn of the second set interlaces with selected weft yarns to contribute to a third repeating pattern which comprises the weave pattern of the machine side surface of the belt, but is not exposed on the sheet side surface; (iii) one of the warp yarns of each set is comprised of an electrically conductive material; (iv) one weft yarn is comprised of an electrically conductive material; and (v) the electrically conductive warp yarn of the first set and the electrically conductive warp yarn of the second set is arranged so as to contact the one electrically conductive weft yarn.

2. A charge dissipating forming belt as claimed in Claim 1 wherein (1) the weft yarns comprise at least a first set of weft yarns each contributing to the sheet side surface and a second set of weft yarns each contributing to the machine side surface; (ii) at least some of the first set of weft yarns are binder weft yarns; and (iii)the one electrically conductive weft yarn is a binder weft yarn.

3. A charge dissipating forming belt as claimed in Claim 1 or Claim 2 wherein at least some of the first set of weft yarns together with some of the second set of weft yarns comprise stacked groups in a plane substantially perpendicular to the sheet side surface.

4. A charge dissipating forming belt as claimed in Claim 1 wherein all the weft yarns comprise stacked groups in a plane substantially perpendicular to the sheet side surface.

5. A charge dissipating forming belt as claimed in Claim 3 wherein the stacked groups comprise pairs.

6. A charge dissipating forming belt as claimed in Claim 1 wherein each conductive warp yarn and each Conductive weft yarn has a resistance in a range between 2 x l0 and 8 x 10 [power 41 ohms/cm.

7. A charge dissipating forming belt as claimed in Claim 6 wherein each conductive warp yarn is constructed of a polymeric material having a conductive coating.

8. A charge dissipating forming belt as claimed in Claim 6 or Claim 7 wherein each conductive weft yarn is constructed of a material selected from metal and polymeric material having a conductive coating.

9. A method of manufacture of a charge dissipating forming belt for use in a dry nonwoven sheet forming process, comprising the steps of (a) weaving a sheet side surface and a machine side surface according to a first repeating weave pattern requiring at least four sheds in the loom, and comprising at least two sets of warp yarns and at least one set of weft yarns; (b) providing in each repeat of the first repeating weave pattern one electrically conductive warp yarn in each set; and (c) providing in each repeat of the first repeating weave pattern one electrically Conductive weft yarn which is in contact with each electrically conductive warp yarn.