Papermakers fabric with flat machine direction yarns

Abstract: An industrial fabric, for example a papermakers fabric, having a single layer of cross machine direction yarns 21a,21b (hereinafter CMD yarns) interwoven with a system of machine direction yarns 22,23 (hereinafter MD yarns). The weave of the fabric is such that alternate CMD yarns 21a are crimped to a significantly greater degree than the respective adjacent CMD yarns 21b. The crimped CMD yarns 21a have smaller diameter than the other CMD yarns 21b. The MD yarns 22,23 are flat monofilament yarns which are vertically stacked. The weave gives rise to a warp-fill in the range of 80-125%.

Description: The present invention relates to papermakers fabrics and in particular to fabrics comprised of flat monofilament yarns. BACKGROUND OF THE INVENTION Papermaking machines generally are comprised of three sections: forming, pressing, and drying. Papermakers fabrics are employed to transport a continuous paper sheet through the papermaking equipment as the paper is being manufactured. The requirements and desirable characteristics of papermakers fabrics vary in accordance with the particular section of the machine where the respective fabrics are utilized. With the development of synthetic yarns, shaped monofilament yarns have been employed in the construction of papermakers fabrics. For example, U.S. Patent No. 4,290,209 discloses a fabric woven of flat monofilament warp yarns; U.S. Patent No. 4,755,420 discloses a non-woven construction where the papermakers fabric is comprised of spirals made from flat monofilament yarns. Numerous weaves are known in the art which are employed to achieve different results. For example, U.S. Patent No. 4,438,788 discloses a dryer fabric having three layers of cross machine direction yarns interwoven with a system of flat monofilament machine direction yarns such that floats are created on both the top and bottom surfaces of the fabric. The floats tend to provide a smooth surface for the fabric. Permeability is an important criteria in the design of papermakers fabrics. In particular, with respect to fabrics made for running at high speeds on modern drying equipment, it is desirable to provide dryer fabrics with relatively low permeability. U.S. Patent No. 4,290,209 discloses the use of flat monofilament warp yarns woven contiguous with each other to provide a fabric with reduced permeability. However, even where flat warp yarns are woven contiguous with each other, additional means, such as stuffer yarns, are required to reduce the permeability of the fabric. As pointed out in that patent, it is desirable to avoid the use of fluffy, bulky stuffer yarns to reduce permeability which make the fabric susceptible to picking up foreign substances or retaining water. U.S. Patent No. 4,290,209 and U.S. Patent No. 4,755,420 note practical limitations in the aspect ratio (cross-sectional width to height ratio) of machine direction warp yarns defining the structural weave of a fabric. The highest practical aspect ratio disclosed in those patents is 3:1, and the aspect ratio is preferably, less than 2:1. U.S. Patent No. 4,621,663, assigned to the assignee of the present invention, discloses one attempt to utilize high aspect ratio yarns (on the order of 5:1 and above) to define the surface of a papermakers dryer fabric. As disclosed in that patent, a woven base fabric is provided to support the high aspect ratio surface yarns. The woven base fabric is comprised of conventional round yarns and provides structural support and stability to the fabric disclosed in that patent. U.S. Patent No. 4,815,499 discloses the use of flat yarns in the context of a forming fabric. That patent discloses a composite fabric comprised of an upper fabric and a lower fabric tied together by binder yarns. The aspect ratio employed for the flat machine direction yarns in both the upper and lower fabrics are well under 3:1. In use, papermakers fabrics are configured as endless belts. Weaving techniques are available to initially weave fabrics endless. However, there are practical limitations on the overall size of endless woven fabrics as well as inherent installation difficulties. Moreover, not all papermaking equipment is designed to accept the installation of an endless fabric. Flat woven fabrics are often supplied having opposing ends which are seamed together during installation of the fabric on papermaking equipment. Usually one end of the fabric is threaded through the serpentine path defined by the papermaking equipment and is then joined to its opposing end to form a continuous belt. A variety of seaming techniques are well known in the art. One conventional method of seaming is to form the machine direction yarns on each end of the fabric into a series of loops. The loops of the respective fabric ends are then intermeshed during fabric installation to define a channel through which a pintle is inserted to lock the ends together. For example, U.S. Patent Nos. 4,026,331; 4,438,789; 4,469,142; 4,846,231; 4,824,525 and 4,883,096 disclose a variety of pin seams wherein the machine direction yarns are utilized to form the end loops. In each of those patents, however, the machine direction yarn projects from the end of the fabric and weaves back into the fabric adjacent to itself. Accordingly, the loops inherently have a twist or torque factor and are not entirely orthogonal to the plane of the fabric. U.S. Patent 4,883,096 specifically addresses this problem. It would be desirable to provide a papermakers fabric with machine direction seaming loops which do not have torque and/or twist. US 2554034 describes the construction of a papermakers felt consisting of round non-woollen warp yarns and a mixture of round and flat weft yarns. The flat weft yarns are woven through the warp yarns in such a way that they become surface yarns on one surface or the other of the felt - usually alternating between the top surface and the bottom surface. In accordance with the present invention, there is provided an industrial fabric, for example a papermakers fabric, comprising a single layer of CMD yarns interwoven with a system of MD yarns wherein alternate CMD yarns are crimped to a significantly greater degree than the respective adjacent other CMD yarns in said single CMD layer characterised in that at least some of said MD yarns weave knuckles around each said alternate CMD yarns and all of said MD yarns weave in floats either over or under said other CMD yarns In an embodiment of the invention, said CMD yarns include yarns of at least two different diameters and are interwoven in a selected repeat pattern such that the CMD yarns having the relatively smaller diameter are crimped significantly more than the CMD yarns having the relatively larger diameter. Preferably said MD yarns are flat monofilament yarns having paired upper and lower yarns stacked in vertical alignment; and the actual warp fill of at least said upper MD yarns is in the range of 80%-125%. In order that the invention may be better understood, several embodiments thereof will now be described by way of example only and with reference to the accompanying drawings in which:- Figure 1 is a schematic diagram of a multi-layer papermakers fabric not being an embodiment of the present invention; Figure 2 is a cross-sectional view of the fabric depicted in Figure 1 along line 2-2; Figure 3a is a cross-sectional view of the fabric depicted in Figure 1 along line 3-3; Figure 3b is a cross-sectional view of a prior art weave construction; Figure 4a illustrates the yarn orientation in the fabric depicted in Figure 1 after the fabric is finished showing only two representative stacked MD yarns; Figures 4b, 4c and 4d are a series of illustrations showing the formation of a seaming loop for the papermakers fabric depicted in Figure 1. Figure 5 is a schematic view of an embodiment of a single layer fabric made in accordance with the present invention; Figure 6 is a cross-sectional view of the fabric depicted in Figure 5 along line 7-7; Figure 7 is a cross-sectional view of the fabric depicted in Figure 5 along line 8-8; Figure 8 is a perspective view of a portion of the fabric illustrated in Figures 5-7; Figure 9 illustrates the yarn orientation in the finished fabric depicted in Figure 5 showing the end loop formed by one of the MD yarns; Figure 10 is a top view of the opposing ends of a fabric constructed in accordance with Figure 5 just prior to pin-seaming the ends together. Referring to Figures 1, 2 and 3a, there is shown a papermakers dryer fabric 10 which is not an embodiment of the present invention. The fabric 10 comprises upper, middle and lower layers of cross machine direction (hereinafter CMD) yarns 11, 12, 13, respectively, interwoven with a system of MD yarns 14-19 which sequentially weave in a selected repeat pattern. The MD yarn system comprises upper MD yarns 14, 16, 18 which interweave with CMD yarns 11, 12 and lower MD yarns 15, 17, 19 which interweave with CMD yarns 12, 13. The upper MD yarns 14, 16, 18 define floats on the top surface of the fabric 10 by weaving over two upper layer CMD yarns 11 dropping into the fabric to weave in an interior knuckle under one middle layer CMD yarn 12 and under one CMD yarn 11 and thereafter rising to the surface of the fabric to continue the repeat of the yarn. The floats over upper layer CMD yarns 11 of upper MD yarns 14, 16, 18 are staggered so that all of the upper and middle layer CMD yarns 11, 12 are maintained in the weave. As will be recognised by those skilled in the art, the disclosed weave pattern with respect to Figures 1, 2 and 3a, results in the top surface of the fabric having a twill pattern. It will be recognised by those of ordinary skill in the art that the length of the float, the number of MD yarns in the repeat, and the ordering of the MD yarns may be selected as desired so that other patterns, twill or non-twill, are produced. As best seen in Figures 2 and 3a, lower MD yarns 15, 17, 19, weave directly beneath upper MD yarns 14, 16, 18, respectively, in a vertically stacked relationship. The lower yarns weave in an inverted image of their respective upper yarns. Each lower MD yarn 15, 17, 19 floats under two lower layer CMD yarns 13, rises into the fabric over one CMD yarn 13 and forms a knuckle around one middle layer CMD yarn 12 whereafter the yarn returns to the lower fabric surface to continue its repeat floating under the next two lower layer CMD yarns 13. With respect to each pair of stacked yarns, the interior knuckle, formed around the middle layer CMD yarns 12 by one MD yarn, is hidden by the float of the other MD yarn. For example, in Figures 1 and 3a, lower MD yarn 15 is depicted weaving a knuckle over CMD yarn 12 while MD yarn 14 is weaving its float over CMD yarns 11, thereby hiding the interior knuckle of lower MD yarn 15. Likewise, with respect to Figures 1 and 3a, upper MD yarn 18 is depicted weaving a knuckle under yarn CMD yarn 12 while it is hidden by lower MD yarn 19 as it floats under CMD yarns 13. The upper MD yarns 14, 16, 18, are woven contiguous with respect to each other. This maintains their respective parallel machine direction alignment and reduces permeability. Such close weaving of machine direction yarns is known in the art as 100% warp fill as explained in U.S. Patent No. 4,290,209. As taught therein (and used herein), actual warp count in a woven fabric may vary between about 80%-125% in a single layer and still be considered 100% warp fill. The crowding of MD yarns 14, 16, and 18 also serves to force MD yarns 15, 17, 19, into their stacked position beneath respective MD yarns 14, 16, 18. Preferably MD yarns 15, 17, and 19 are the same size as MD yarns 14, 16, and 18 so that they are likewise woven 100% warp fill. This results in the overall fabric of the preferred embodiment having 200% warp fill of MD yarns. Since the lower MD yarns 15, 17, 19 are also preferably woven 100% warp fill, they likewise have the effect of maintaining the upper MD yarns 14, 16, 18 in stacked relationship with the respect to lower MD yarns 15, 17, 19. Accordingly, the respective MD yarn pairs 14 and 15, 16 and 17, 18 and 19 are doubly locked into position thereby enhancing the stability of the fabric. As set forth in the U.S. Patent No. 4,290,209, it has been recognized that machine direction flat yarns will weave in closer contact around cross machine direction yarns than round yarns. However, a 3:1 aspect ratio was viewed as a practical limit for such woven yarns in order to preserve overall fabric stability. The present stacked MD yarn system preserves the stability and machine direction strength of the fabric and enables the usage of yarns with increased aspect ratio, in a preferred range of 2:1 to 6:1, to more effectively control permeability. The high aspect ratio of the MD yarns translates into reduced permeability. High aspect ratio yarns are wider and thinner than conventional flat yarns which have aspect ratios less than 3:1 and the same cross-sectional area. Equal cross-sectional area means that comparable yarns have substantially the same linear strength. The greater width of the high aspect ratio yarns translates into fewer interstices over the width of the fabric than with conventional yarns so that fewer openings exist in the fabric through which fluids may flow. The relative thinness of the high aspect ratio yarns enables the flat MD yarns to more efficiently cradle, i.e. brace, the cross machine direction yarns to reduce the size of the interstices between machine direction and cross machine direction yarns. For example, as illustrated in Figure 3b, a fabric woven with a single layer system of a flat machine direction warp having a cross-sectional width of 1.5 units and a cross-sectional height of 1 unit, i.e. an aspect ratio of 1.5:1, is shown. Such fabric could be replaced by a fabric having the present dual stacked MD yarn system with MD yarns which are twice the width, i.e. 3 units, and half the height, i.e. 0.5 units. Such MD yarns thusly having a fourfold greater aspect ratio of 6:1, as illustrated in Figure 3a. The thinner, wider MD yarns more efficiently control permeability while the machine direction strength of the fabric remains essentially unaltered since the cross-sectional area of the MD yarns over the width of the fabric remains the same. For the above example, illustrated by Figures 3a and 3b, the conventional single MD yarn system fabric has six conventional contiguous flat yarns over 9 units of the fabric width having a cross-sectional area of 9 square units, i.e. 6*(1u.*1.5u.). The thinner, wider high aspect ratio yarns, woven as contiguous stacked MD yarns, define a fabric which has three stacked pairs of MD yarns over 9 units of fabric width. Thus such fabric also has a cross-sectional area of 9 square units, i.e. (3*(0.5u.*3u.)) + (3*(0.5u.*3u.)), over 9 units of fabric width. In one example, a fabric was woven in accordance with Figures 1, 2 and 3, wherein the CMD yarns 11, 12, 13 were polyester monofilament yarns 0.6mm in diameter interwoven with MD yarns 14-19 which were flat polyester monofilament yarns having a width of 1.12mm and a height of 0.2mm. Accordingly, the aspect ratio of the flat MD yarns was 5.6:1. The fabric was woven at 48 warp ends per inch with a loom tension of 40 pounds per linear 2.54cm (1 inch) and 12.5 CMD pick yarns per 2.54 cm (1 inch) per layer (three layers). The fabric was heat set in a conventional heat setting apparatus under conditions of temperature, tension and time within known ranges for polyester monofilament yarns. For example, conventional polyester fabrics are heat set within parameters of 340°F-380°F temperature, 6-15 pounds per linear 2.54 cm (1 inch) tension, and 3-4 minutes time. However, due to their stable structure, the fabrics of the present invention are more tolerant to variations in heat setting parameters. The fabric exhibited a warp modulus of 6000 PSI (pounds per square inch) measured by the ASTM D-1682-64 standard of the American Society for Testing and Materials. The fabric stretched less than 0.2% in length during heat setting. This result renders the manufacture of such fabrics very reliable in achieving desired dimensional characteristic as compared to conventional fabrics. The resultant heat set fabric had 12.5 CMD yarns per inch per layer with 106% MD warp fill with respect to both upper and lower MD yarns resulting in 212% actual warp fill for the fabric. The finished fabric has a permeability of 83CFM as measured by the ASTM D-737-75 standard. As illustrated in Figure 4a, when the fabric 10 is woven the three layers of CMD yarns 11, 12, 13 become compressed. This compression along with the relatively thin dimension of the MD yarns reduces the caliper of the fabric. Accordingly, the overall caliper of the fabric can be maintained relatively low and not significantly greater than conventional fabrics woven without stacked MD yarn pairs. In the above example, the caliper of the finished fabric was 0.050 inches. It will be recognised by those of ordinary skill in the art that if either top MD yarns 14, 16, 18 or bottom MD yarns 15, 17, 19 are woven at 100% warp fill, the overall warp fill for the stacked fabric will be significantly greater than 100% which will contribute to the reduction of permeability of the fabric. The instant fabric having stacked MD yarns will be recognised as having a significantly greater percentage of a warp fill than fabrics which have an actual warp fill of 125% of non-stacked MD yarns brought about by crowding and lateral undulation of the warp strands. Although the 200% warp fill is preferred, a fabric may be woven having 100% fill for either the upper or lower MD yarns with a lesser degree of fill for the other MD yarns by utilizing yarns which are not as wide as those MD yarns woven at 100% warp fill. For example, upper yarns 14, 16, 18 could be 1 unit wide with lower layer yarns 15, 17, 19 being .75 units wide which would result in a fabric having approximately 175% warp fill. Such variations can be used to achieve a selected degree of permeability. Alternatively, such variations could be employed to make a forming fabric. In such a case, the lower MD yarns would be woven 100% warp fill to define the machine side of the fabric and the upper MD yarns would be woven at a substantially lower percentage of fill to provide a more open paper forming surface. The stacked pair MD weave permits the formation of orthogonal seaming loops within MD yarns. With reference to Figures 4a-d, after the fabric has been woven and heat set (Figure 4a), CMD yarns are removed leaving the crimped MD yarns 14, 15 exposed (Figure 4b). One of the yarns, for example, MD lower yarn 15, of the stacked pair is trimmed back a selected distance leaving the other exposed MD yarn 14 of the MD yarn pair and vacated space between the CMD yarns, as illustrated in Figure 4c. Upper MD yarn 14 is then backwoven into the space vacated in the weave pattern by lower MD yarn 15 such that a loop L is formed on the end of the fabric, as illustrated in Figure 4d. Preferably, between 1.27-12.7cm (0.5-5.0 inches) of upper layer yarn 14 is backwoven into the fabric to provide sufficient strength for the end loop and assure retention of the free end of MD yarn 14 within the weave of the fabric. The inverted image weave permits the crimp of the upper MD yarn 14 to match the space vacated by the lower MD yarn 15 which further enhances the strength of the end loop. As shown in phantom in Figure 4d, adjacent yarn pair 16, 17 is processed in a similar manner. However, when upper yarn 16 is looped back and backwoven in the fabric, it is pulled against the CMD yarns. When the upper MD yarns are woven 100% fill, the crowding of the yarns secure the orthogonal orientation of the seaming loops. To achieve a uniform seam for a fabric woven in accordance with the weave pattern depicted in Figure 1, each upper MD yarn 14 forms a loop and the other upper MD yarns 16, 18 are backwoven against the endmost CMD yarn of the fabric. Thus every third upper MD yarn defines a loop such that an array of loops is created on each end of the fabric. The seam is assembled by intermeshing the opposing arrays of loops and o inserting a pintle yarn between the intermeshed loops. Preferably, loop forming yarns 14 would all be backwoven approximately the same distance within the fabric to provide sufficient strength to prevent the loops from being pulled apart during normal usage. Non-loop forming yarns 16, 18, would preferably be backwoven a somewhat shorter distance since during usage no load is imparted to those yarns. For example, upper MD yarns 14 would be backwoven approximately 7.62cm (3 inches), MD yarns 16 would be backwoven approximately 5.08cm (2 inches) and MD yarns 18 would be backwoven approximately 2.54cm (1 inch). Respective lower layer yarns 15, 17, 19 would be trimmed to complement the backweaving of their respective MD yarn pair yarns 14, 16, 18. Referring to Figures 5, 6 and 7, there is shown a preferred embodiment of a fabric 20 made in accordance with the teachings of the present invention. Papermakers fabric 20 is comprised of a single layer of CMD yarns 21a, 21b interwoven with a system of stacked MD yarns 22-25 which weave in a selected repeat pattern. The MD yarn system comprises upper MD yarns 22, 24 which define floats on the top surface of the fabric 20 by weaving over three CMD yarns, under the next one CMD yarn 21a to form a knuckle, and thereafter returning to float over the next three CMD yarns in a continuation of the repeat. Lower MD yarns 23, 25 weave directly beneath respective upper MD yarns 22, 24 in a vertically stacked relationship. The lower MD yarns weave in an inverted image of their respective upper MD yarns. Each lower MD yarn 23, 25 floats under three CMD yarns, weaves upwardly around the next one CMD yarn 21a forming a knuckle and thereafter continues in the repeat to float under the next three CMD yarns. As can be seen with respect to Figures 5 and 7, the knuckles formed by the lower MD yarns 23, 25 are hidden by the floats defined by the upper MD yarns 22, 24 respectively. Likewise the knuckles formed by the upper MD yarns 22, 24 are hidden by the floats of the lower MD yarns 23, 25 respectively. The caliper of the fabric proximate the knuckle area shown in Figure 7, has a tendency to be somewhat greater than the caliper of the fabric at non-knuckle CMD yarns 21b, shown in Figure 6. However, the CMD yarns 21a around which the knuckles are formed become crimped which reduces the caliper of the fabric in that area as illustrated in Figure 7. Additionally, slightly larger diameter CMD yarns are preferably used for CMD yarns 21b, shown in Figure 6, which are not woven around as knuckles by the MD yarns to eliminate any difference in fabric caliber. Preferably the diameter of the larger CMD yarn 21b equals the diameter d of the smaller CMD yarns 21a plus the thickness t of the MD yarns. In one example, a fabric was woven in accordance with Figures 5-8, wherein the CMD yarns 21a, 21b were polyester monofilament yarns 0.6mm and 0.8mm, respectively, in diameter interwoven with MD yarns 22-25 which were flat polyester monofilament yarns having a width of 1.12mm and a height of 0.2mm. Accordingly, the aspect ratio of the flat MD yarns was 5.6:1. The fabric was woven at 48 total warp ends per 2.54cm (1 inch) with a loom tension of 40 PLI pounds per linear 2.54cm (1 inch) and 20 CMD total pick yarns per 2.54cm (1 inch). The permeability averaged 90 CFM in the resultant fabric. In another example, fabric was woven in accordance with Figures 5, 6 and 7, wherein the CMD yarns 21a, 21b were polyester monofilament yarns 0.7mm in diameter interwoven with MD yarns 22-25 which were flat polyester monofilament yarns having a width of 1.12mm and a height of 0.2mm. Accordingly, the aspect ratio of the flat MD yarns was 5.6:1. The fabric was woven at 22 CMD pick yarns per 2.54cm (1 inch). The fabric was heat set using conventional methods. The fabric exhibited a modulus of 6000 PSI. The fabric stretched less than 0.2% in length during heat setting. The resultant fabric had 22 CMD yarns per inch with 106% MD warp fill with respect to both upper and lower MD yarns resulting in 212% actual warp fill for the fabric. The finished fabric had a caliper of 0.122cm (.048 inches) and an air permeability of 60CFM. As best shown in Figure 8, the high aspect ratio yarns 22-24 effectively brace the CMD yarns 21a in the weave construction. This bracing effect can be quantified in terms of the degree of contact arc  and contact bracing area, CBA, as follows:- CBA = πd (  360 o )w where d = diameter of the CMD yarn  = the degree of arc over which there is contact between the MD and CMD yarns w = width of the MD yarn π = the constant pi. The degrees of arc over which MD yarns 22-25 are in contact with CMD yarns 21a is dependent upon the spacing of the CMD yarns within the weave. For the above example, employing alternating 0.6mm and 0.8mm diameter CMD yarns with 0.2mm thick MD yarns, the degree of contact arc can be maintained in a preferred range of between 60° to 180° by varying the pick count of the CMD yarns from 14 picks per inch to a maximum of 28.22 picks per 2.54cm (1 inch). In the preferred embodiment where the pick count is 20 picks per 2.54cm (1 inch), the degree of contact arc  is approximately 101°. This results in a bracking contact area of approximately 0.79mm 2 at each knuckle in the fabric. Applicant's use of high ratio aspect yarns, i.e. yarns having a width:thickness ratio of at least 3:1, provides for increased bracing contact of the flat MD yarns with the CMD yarns 21a. This is comparatively exemplified by modifying the equation for contact bracing area, CBA, to be defined in terms of the thickness of the MD yarns. Since the MD yarn width w equals the thickness t of the MD yarn multiplied by the aspect ratio, w > 3t for yarns having an aspect ratio greater than 3:1. Accordingly, fabrics made in accordance with the teachings of the present invention utilising high aspect ratio MD yarns exhibit enhanced bracing of the CMD yarns by the MD yarns such that: CBA = πd (  360 o )3t As best seen in Figure 9, seaming loops are formed by upper MD yarns 22. The respective lower MD yarns 23 are trimmed a selected distance from the fabric end and the upper MD yarns 22 are backwoven into the space vacated by the trimmed lower MD yarns 23. Upper MD yarns 24 are similarly backwoven into the space vacated by trimming back lower MD yarns 25. However, as best seen in Figure 9, upper MD yarns 24 are backwoven against the madness CMD yarn 21b. As illustrated in Figure 10, a series of seaming loops is formed on each of the opposing fabric ends 27, 28. When the fabric is installed on papermaking equipment, the respective end loops formed by MD yarns 22 are intermeshed and a pintle 30 is inserted therethrough to lock the intermeshed series of loops together. Since the seaming loops L are formed by backweaving MD yarns 22 directly beneath themselves, no lateral twist or torque is imparted on the loop and the loops are orthogonal with the plane of the fabric. This facilitates the intermeshing of the loop series of the opposing fabric ends 27, 28. The orthogonal loops are particularly advantageous where, as shown in Figure 9, the MD yarns 22, 24 are 100% warp fill and adjacent loops are separated by individual MD yarns of the same width as the loop MD yarns 22. Lateral torque or twist on the seaming loops make the seaming process more difficult particularly where the loop-receiving gaps between the loops of one fabric end are essentially the same width as the loops on the opposing fabric end and vice versa. With reference to the fabric depicted in Figures 5-10, the loop forming MD yarns 22 are preferably backwoven approximately 5.08cm (2 inches) while the non-loop forming MD yarns 24 are preferably backwoven 2.54cm (1 inch). A variety of other weave patterns employing the paired stacked weave construction of the instant invention may be constructed within the scope of the present invention. For example, in some applications it may be desirable to have MD yarn surface floats over six or more CMD yarns. Such fabrics are readily constructed in accordance with the teachings of the present invention.

Claims: An industrial fabric, for example a papermakers fabric (20), comprising a single layer of CMD yarns (21a,21b) interwoven with a system of MD yarns (22-25) wherein alternate CMD yarns (21a) are crimped to a significantly greater degree than the respective adjacent other CMD yarns (21b) in said single CMD layer characterised in that at least some of said MD yarns (22-25) weave knuckles around each said alternate CMD yarns (21a) and all of said MD yarns weave in floats either over or under said other CMD yarns (21b). A fabric according to claim 1 wherein said CMD yarns (21a,21b) include yarns of at least two different diameters and are interwoven in a selected repeat pattern such that the CMD yarns (21a) having the relatively smaller diameter are crimped significantly more than the CMD yarns (21b) having the relatively larger diameter. A fabric according to claims 1 or 2 wherein said: MD yarns (22-25) are flat monofilament yarns having paired upper and lower yarns stacked in vertical alignment; and the actual warp fill of at least said upper MD yarns (22,24) is in the range of 80% - 125%. A fabric according to claims 1 or 2 wherein CMD yarns (21a,21b) alternate between a first relatively larger diameter and a second relatively smaller diameter in said single CMD layer. A fabric according to claim 4 wherein said MD yarns (22-25) are flat monofilament yarns having a thickness t and said first diameter is approximately equal to said second diameter plus t. A fabric according to claim 4 wherein said first diameter is about 0.8mm, said second diameter is about 0.6mm, and said MD yarns (22-25) are flat monofilament yarns having a thickness of about 0.2mm. A fabric according to claim 1 wherein said MD yarns (22-25) repeat with respect to four of said CMD yarns (21a,21b) with a float of three such that first and third CMD yarns within the float are not the CMD yarns which have the significantly greater degree of crimp. A fabric according to claim 7 wherein the float of some of said MD yarns (22-25) is over three CMD yarns and the float of other of said MD yarns is under three CMD yarns within the fabric repeat. A fabric according to claim 8 wherein each of the MD yarns (23,25) which have floats under the CMD yarns (21a,21b) are disposed beneath at least one MD yarn (22,24) which has its float weaving over the CMD yarns. A fabric according to claims 1, 2, 7, 8 or 9 wherein said MD yarns (22-25) are flat monofilament yarns having an aspect ratio greater than 3:1.

Inventors: LEE HENRY J, LEE, HENRY J.
Applicants: ASTEN S C V, V.ASTEN S.C.
Application year: 1991
Main classification: D21F1
IPC codes: D21F7, D21F1