Patent Publication Number: US-6708732-B1

Title: Fabrics for web forming equipment

Description:
FIELD OF THE INVENTION 
     This invention relates to unique fabrics for use in web forming machines for making sanitary paper webs (e.g., tissue and towel stock) and other wet formed cellulosic sheets or nonwoven webs; most desirably patterned web products which are especially suitable for use in papermaking machines. Although the fabrics of this invention are particularly well suited for use as a forming wire in the forming section of a papermaking machine to make patterned sanitary paper products, it is within the scope of the broadest aspects of this invention to employ these fabrics for a variety of other applications in papermaking machine, e.g., as a transfer fabric or dryer fabric, particularly a through-air-dryer (TAD) fabric, as well as in nonwoven apparatus. For some applications one surface of the fabric is employed as the web-contacting, or engaging surface, whereas for other applications the opposed surface of the fabric may preferably be employed as the web-contacting, or engaging surface. 
     Reference throughout this application to a “web forming machine” includes both papermaking and nonwoven machines. 
     Reference throughout this application to a “web forming fabric” is not limited to use of the fabric in the forming section of a web forming machine, but includes uses in other areas of such web forming machines. 
     BACKGROUND OF THE INVENTION 
     Web forming fabrics employed to make patterned fibrous webs are commercially available and a number of such fabrics are disclosed in existing patents, e.g., U.S. Pat. No. 6,237,644 (Hay et al.), U.S. Pat. No. 5,429,686 (Chiu), U.S. Pat. No. 6,203,663 (Chiu) and Swedish Patent No. 427,053 (Gusums Bruk AB). It is important that these fabrics be capable of use in forming fibrous webs having a desired balance of strength, caliper and absorbency (including absorbency capacity and rate). 
     The inventors herein are two of the four inventors of the inventions forming the subject matter of Hay et al. U.S. Pat. No. 6,237,644. This latter patent discloses tissue forming fabrics, particularly single layer structures, employed to form fibrous webs having a useful combination of strength, caliper and absorbency. 
     There is a continuing desire to provide fabric constructions capable of use to form fibrous webs having enhanced, or increased, strength, caliper, absorbent capacity and/or absorbency rate. In particular, there is a continuing need to achieve a desired balance among these various properties. Generally, just improving the strength of the formed web tends to result in a denser structure that often does not provide the desired absorbency rate and/or capacity required in tissue products. 
     There also is a benefit and desire for web forming fabrics having opposed surfaces, each of which can constitute a web-engaging surface, depending upon the specific application of the forming fabric in the web forming machine. 
     Thus, a continuing need exists for web forming fabrics capable of use in forming fibrous webs, e.g., tissue products, having a desired balance of strength, caliper, absorbency rate and capacity, and that also is versatile in use. 
     SUMMARY OF THE INVENTION 
     The above and other objects of this invention are achieved in a web forming fabric having a machine direction of intended movement on a web forming machine and a cross-machine direction substantially normal to said machine direction, wherein said fabric includes machine direction yarns disposed generally in the machine direction and transverse yarns disposed generally transversely to the machine direction, said fabric including on one surface thereof first and second substantially linear arrays of systematically distributed areas of high drainage, said first and second substantially linear arrays being oriented at an acute angle to the machine direction and at an acute angle to each other. The boundaries of each of said systematically distributed areas are defined by two pairs of adjacent sides, the adjacent sides of one pair being angled segments of one transversely extending yarn and the adjacent sides of the other pair being angled segments of a second transversely extending yam contiguous to said one transversely extending yarn. 
     In preferred embodiments of this invention the systematically distributed areas of high drainage in the web forming fabrics of this invention include within their boundaries only machine direction yarns. 
     In accordance with the preferred embodiments of a web forming fabric of this invention, each systematically distributed area in the first substantially linear array is separated from contiguous systematically distributed areas on opposite sides thereof and in the same substantially linear array by spaced-apart angled segments of a pair of single transverse yarns that are contiguous to each other. 
     In one preferred embodiment of this invention the systematically distributed areas in the first substantially linear array are separated from adjacent systematically distributed areas in the same first substantially linear array by an angled segment of a single transverse yarn, and the systematically distributed areas in the second substantially linear array are separated from adjacent systematically distributed areas in the same second substantially linear array by an angled segment of a single transverse yarn. 
     In another embodiment of this invention, the systematically distributed areas in the first substantially linear array are separated from adjacent systematically distributed areas in the same first substantially linear array by an angled segment of a single transverse yarn and the systematically distributed areas in the second substantially linear array are separated from adjacent systematically distributed areas in the same second substantially linear array by a plurality of contiguous angled segments of contiguous transverse yarns, said contiguous angled segments of contiguous transverse yarns providing areas of drainage lower than that of the systematically distributed areas. 
     In accordance with the preferred embodiments of this invention the machine direction yarns on the side of the fabric opposed to the side including the systematically distributed surface areas, each include relatively long floats over a plurality of adjacent weft yarns; preferably over at least six adjacent weft yarns. Most preferably, each of the continuous machine direction floats of each machine direction yarn floats over at least the same three contiguous weft yarns as an adjacent machine direction yarn, with the continuous machine direction floats of adjacent machine direction yarns partially overlapping each other in the machine direction. 
     In one embodiment, each relatively long machine direction float is over seven adjacent weft yarns, with each continuous machine direction float of each machine direction yarn being over at least the same four contiguous weft yarns as an adjacent machine direction yarn and with the continuous machine direction floats of adjacent machine direction yarns partially overlapping each other in the machine direction. 
     The side of the fabric opposed to the side including the systematically distributed surface areas is well suited for engaging, or contacting the web being dryed in a dryer section of a web forming machine; preferably in a through-air-dryer section of a papermaking machine. In particular, the long, partially overlapping machine direction floats of adjacent machine direction yarns establish excellent adherence of the web to a creping cylinder (e.g., a Yankee dryer) in the machine direction to provide for very effective creping of the web being formed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view from one side of a web forming fabric in accordance with one embodiment of the invention; 
     FIG. 2 is a view of the surface of the web forming fabric opposite the surface shown in FIG. 1; 
     FIG. 3 is a photograph of the surface of the web forming fabric illustrated in FIG. 1; 
     FIG. 4 is a photograph of the surface of the web forming fabric illustrated in FIG. 2; 
     FIG. 5 is a weave diagram of the fabric illustrated in FIGS. 1 through 4, with the X&#39;s illustrating regions in which the machine direction yarns pass over the transverse direction yarns on the surface of the fabric illustrated in FIGS. 1 and 3; 
     FIG. 6 is a view of one side of an alternative embodiment of a fabric of this invention, which is believed to be the preferred embodiment of the invention; 
     FIG. 7 is a photograph of the surface of the fabric illustrated in FIG. 6; 
     FIG. 8 is a photograph of the surface of the web forming fabric opposite the surface shown in FIGS. 6 and 7; and 
     FIG. 9 is a weave diagram of the fabric illustrated in FIGS. 6 through 8, with the X&#39;s illustrating regions in which the machine direction yarns pass over the transverse direction yarns on the surface illustrated in FIGS.  6  and  7 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, a web forming fabric in accordance with one embodiment of the invention is shown generally at  10  in FIGS. 1-4, and the weave diagram for the fabric is shown in FIG.  5 . This fabric includes a 10 shaft repeat and a 10 step repeat. However, the weave pattern can be varied, so long as the structure described hereinafter is achieved. 
     Turning to FIGS. 1 and 3, a web-engaging surface or side  11  of the fabric  10  is illustrated. When the fabric  10  is employed in the web forming zone of a papermaking machine, the side  11  of the fabric  10  receives the papermaking slurry thereon, with the water being drained through the fabric by gravity, pressure or vacuum assist. 
     The difference between the illustration in FIG.  1  and the photograph in FIG. 3 is that the weft, or transverse yarn pattern is shifted by three yarns. That is, the fourth weft yarn from the top depicted in FIG. 1 ( 46 ) is the first full weft yarn from the top depicted in the photograph of FIG.  3 . 
     It should be understood that when the fabric  10  is flat woven, which is usually the method employed in the formation of forming fabrics for use in the forming zone of a web forming machine, the warp yarns are the machine-direction yarns, which are oriented in the machine-direction of movement of the fabric on the web forming machine, and the weft yarns are the cross-machine-direction yarns, which are oriented in the transverse direction to the direction of movement of the fabric on the web forming machine. 
     In a tubular weaving operation, which often is employed to form woven fabrics utilized in dryer fabrics, the weft yarns are the machine-direction yarns, which are oriented in the machine-direction of movement of the fabric on the web forming machine, and the warp yarns are the cross-machine-direction yarns, which are oriented in the transverse direction to the direction of movement of the fabric on the web forming machine. 
     For purposes of brevity, the description which follows is directed to flat woven fabrics of the invention, it being understood that in tubular woven fabrics the machine direction yarns will be weft yarns and the cross machine direction yarns will be warp yarns. 
     Referring to FIG. 5, the weave diagram, which depicts by X&#39;s warp yarns passing over weft yarns on the surface  11  of the fabric, illustrates certain interesting features of the fabric  10  of this invention. First, in each repeat pattern each of the ten (10) warp yarns passes over less than half of the ten (10) weft yarns, and in the preferred embodiment passes over only two (2) of the ten (10) weft yarns. This results in the formation of a single layer fabric that generally has identifiable sub-levels in the surface  11  of the fabric  10 , with the bottom level, as viewed from the surface  11  (FIGS.  1  and  3 ), being generally defined solely by machine-direction warp yarns. 
     Moreover, as will be described in greater detail later in this application in connection with FIG. 2, the preferred weave pattern of the fabric  10  results in each machine direction yarn having relatively long machine direction floats on the side of the fabric  11   a  opposed to side  11 , with the machine direction floats of adjacent machine direction yarns in this surface  11   a  partially overlapping each other in the machine direction. This arrangement makes the side  11   a  of the fabric  10  well-suited for use in the dryer section of a web forming machine, and in particular in a through-air dryer (TAD) section of a papermaking machine, as will be described in greater detail hereinafter. 
     Referring to FIGS. 1 and 3, the web forming fabric  10  employs a 10 shaft/10 step repeat pattern with the warp yarns  12 ,  14 ,  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28 ,  30  and  32  being in the machine direction of intended movement on a web forming machine and the weft yarns  40 ,  42 ,  44 ,  46 ,  48 ,  50 ,  52 ,  54 ,  56 ,  58 ,  60  being oriented generally in the cross-machine direction. It should be understood that the warp yarn  32  is in the identical orientation relative to the weft yarns as warp yarn  12 , and actually starts a second repeat. Likewise, the weft yarn  60  is in the identical orientation relative to the warp yarns as weft yarn  40 , and also starts a second repeat. 
     Referring to FIGS. 1 and 3, the fabric  10 , as viewed from the side  11  includes systematically distributed, high drainage areas  62  arranged in first and second substantially linear arrays, with each drainage area being located in each of said substantially linear arrays. 
     Referring to FIGS. 1 and 3, the first substantially linear arrays of high drainage areas  62  are depicted by the reference lines  64 , which pass generally through the centers thereof, and the second substantially linear arrays of high drainage areas  62  are depicted by the reference lines  66 , which pass generally through the centers thereof. As should be apparent from a study of the drawings, the first and second substantially linear arrays of high drainage areas are oriented at an acute angle to the machine direction (MD) and at an acute angle to each other. 
     The boundaries of each of said systematically distributed high drainage areas  62  are defined by two pairs of adjacent sides, e.g.,  68 — 68  and  70 — 70 , respectively. The adjacent sides  68 — 68  are angled segments of one transversely extending weft yarn, e.g.,  40 , and the adjacent sides  70 — 70  are angled segments of a second transversely extending weft yarn ,e.g.,  42 , contiguous to said one transversely extending weft yarn  40 . This relationship exists for all of the systematically distributed areas  62 , e.g., the systematically distributed area designated  62   a  (which is the same as the other systematically distributed areas  62  but is designated  62   a  for purposes of this discussion) is defined by two pairs of adjacent sides  72 — 72  and  74 — 74 , respectively; with the adjacent sides  72  being angled segments of weft yarn  54  and the adjacent sides  74  being angled segments of contiguous weft yarn  56 . 
     Still referring to FIGS. 1 and 3, the region within the boundaries of each of the systematically distributed areas  62  is provided solely by machine direction yarns, e.g., machine direction yarns  16 ,  18 ,  20 ,  22 ,  24  and  26  are the only yarns provided within the boundaries of the systematically distributed area designated  62   a.    
     Still referring to FIGS. 1 and 3, each of the systematically distributed areas  62  in each of the first substantially linear arrays defined by the reference lines  64  are separated from adjacent systematically distributed areas  62  in the same first substantially linear array by an angled segment, e.g.,  80  of a single transverse yarn, e.g.,  50  and the systematically distributed areas  62  in each of the second substantially linear arrays defined by the reference lines  66  are separated from adjacent systematically distributed areas  62  in the same second substantially linear array by a plurality of contiguous angled segments, e.g.,  84 ,  86  of contiguous transverse yarns, e.g.,  44 ,  46 . However, as can be seen in FIGS. 1 and 3, the sides defining the opposite boundaries of each of the systematically distributed areas  62  are provided by angled segments, e.g.,  92  of a pair of single transverse weft yarns that are contiguous to each other, e.g.,  48 ,  50 . 
     Still referring to FIGS. 1 and 3, contiguous transverse, weft yarns also include contiguous angled segments that are aligned generally along a line intermediate adjacent reference lines  64  and provide spaced-apart areas of drainage that are significantly lower than in the systematically distributed areas  62 . These spaced apart areas of low drainage are created by heavy twill lines (e.g., illustrated by adjacent segments  70 , 84 ;  84 , 86 ;  86 , 92 ), each extending continuously at an acute angle relative to the machine direction, from one side edge of the fabric  10  to the other. 
     The fibrous webs formed on the fabric  10 , when the fabric is employed in the forming section of a papermaking machine, tend to have low basis weight regions formed in these low drainage areas of the fabric, resulting in an adverse effect on the tensile strength of the fabric. However, for some applications the strength level may be acceptable; particularly in view of enhanced caliper and absorbency characteristics obtained in the formed web by use of the web forming fabric  10  of this invention. For example, it is possible that the fabric  10  may be acceptable either by itself, or as part of a multiply structure, e.g., multiply board structures. 
     FIGS. 2 and 4 illustrate the appearance of the fabric  10  as viewed from side  11   a  of the fabric, which is opposed to the side  11 . The weave pattern also can be understood by referring to FIG. 5, which illustrates, by clear, or blank, squares, the regions in which the machine direction yarns float over the weft yarns on the side  11   a  of the fabric. This side  11   a  is believed to be well suited for use as a web-contacting or web-engaging surface in dryer applications, and more preferably in through air dryer applications. In particular, the long machine direction floats provided by each machine direction yarn, accompanied by the fact that adjacent machine direction floats partially overlap in the machine direction, should provide excellent adherence of the web being formed to a Yankee dryer or other creping cylinder in the circumferential direction of creping from the dryer or cylinder. 
     Referring to FIGS. 2,  4  and the weave diagram of FIG. 5, it should be noted that in side  11   a  each of the machine direction yarns floats over seven contiguous weft yarns in each repeat, e.g., warp yarn  12  floats continuously over weft yarns  46 ,  48 ,  50 ,  52 ,  54 ,  56  and  58 ; warp yarn  14  floats continuously over weft yarns  40 ,  42 ,  44 ,  46 ,  48 ,  50  and  52 , etc. Moreover, each of the machine direction yarns in the side  11   a  floats continuously over four of the same weft yarns as each adjacent machine direction yarn, e.g., both machine direction yarns  12  and  14  float continuously over weft yarns  46 ,  48 ,  50  and  52 ; both machine direction yarns  14  and  16  float continuously over weft yarns  40 ,  42 ,  44  and  46 , etc. Thus each continuous float of each machine direction yarn in the side  11   a  partially overlaps in the machine direction with a continuous float of an adjacent machine direction yarn over a distance equal to the four contiguous weft yarns over which each of said adjacent yarns floats. 
     Referring to FIG. 9, a weave diagram of an alternate web forming fabric  100  (FIGS. 6-8) in accordance with this invention is shown. In fact, this is believed to be a more preferred embodiment than the web forming fabric  10 , because it does not provide the same heavy twill lines that are created in the fabric  10 . Thus, fibrous webs formed on the web forming fabric  100  may not have the same undesired lines of low basis weight that result from the formation of fibrous webs on the fabric  10 . By reducing, or minimizing, these low basis weight lines, the tensile strength of the formed webs should be enhanced. 
     The weave pattern shown in FIG. 9, although having an 8 shaft/8 step repeat pattern, does have similar features to the weave pattern of the web forming fabric  10 . In particular, in each repeat, each of the machine direction warp yarns  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  116  and  118  on one side  111  of the fabric passes over less than half of the weft yarns  120 ,  122 ,  124 ,  126 ,  128 ,  130 ,  132 ,  134  and  136 , and preferably passes over only two of the weft yarns in the repeat. This same feature exists on side  11  of the web forming fabric  10 . However, unlike the weave pattern in the web forming fabric  10 , each of the machine direction warp yarns passes over two adjacent transverse weft yarns on side  111 , e.g., warp yarn  102  passes over adjacent weft yarns  120  and  122 ; warp yarn  104  passes over adjacent weft yarns  126  and  128 , etc. In the web forming fabric  10  each of the machine direction warp yarns, on side  11 , passes over transverse weft yarns that are spaced from each other by one additional transverse weft yarn, e.g., warp yarn  12  passes over weft yarns  40  and  44 , but under  42 ; warp yarn  14  passes over weft yarns  54  and  58 , but under  56 , etc. 
     It should be noted that the warp yarns  102  and  118  have the same position and orientation with respect to all of the weft yarns because warp yarn  118  starts a new repeat. Likewise, the weft yarns  120  and  136  have the same position and orientation with respect to all of the warp yarns because the weft yarn  136  starts a new repeat. 
     Referring to FIGS. 6 and 7, the web forming fabric  100 , as viewed from side  111 , is illustrated. This forming fabric includes systematically distributed high drainage areas  140  in both first substantially linear arrays, one of which is defined by reference line  142  passing generally through the center thereof and in second substantially linear arrays, one of which is defined by reference line  144  passing generally through the center thereof. Each of the systematically distributed high drainage areas  140  in each first array is separated from adjacent systematically distributed areas  140  in the same first array by angled segments, e.g.,  146  of single transverse yarns, e.g.,  124  and  126 . Moreover, each of the systematically distributed areas  140  in each of the second substantially linear arrays defined by reference lines  144  is separated from adjacent systematically distributed areas in the same second array by angled segments, e.g.,  148  of single transverse yarns, e.g.,  126  and  128 . This results in each of the boundaries between adjacent systematically distributed areas  140  being provided by a yarn segment of only a single yarn, which eliminates the heavy twill lines provided by the web forming fabric  10 . This results in the regions of low drainage in the web forming fabric  100  being minimized relative to the web forming fabric  10  illustrated in FIGS. 1 and 3. 
     It is believed that the weave pattern included in the web forming fabric  100  may provide a more preferred construction than the weave pattern provided in the web forming fabric  10  by eliminating the heavy twill pattern formed by multiple, contiguous weft yarns. Such a heavy twill pattern can adversely effect the tensile strength properties of the fibrous webs formed on the fabric. 
     In particular, in the web forming fabric  10  illustrated in FIGS. 1 and 3, spaced-apart, heavy, angled twill lines are provided by multiple contiguous yarn segments located between the reference lines  64 . These heavy, angled twill lines result in the formation of angled low basis weight regions in the formed web, thereby creating, for many applications, an undesirably low tensile strength. This same deficiency does not exist in the fabric  100 . 
     Referring to FIGS. 8 and 9, it should be noted that in side  111   a  of the fabric  100  each of the machine direction yarns floats over six contiguous weft yarns in each repeat, e.g., warp yarn  102  floats continuously over weft yarns  124 ,  126 ,  128 ,  130 , 132  and  134 ; warp yarn  104  floats continuously over weft yarns  130 ,  132 ,  134 ,  136  ( 120 ),  122  and  124 , etc. Moreover, each of the machine direction yarns in the side  111   a  floats continuously over three of the same weft yarns as each adjacent machine direction yarn, e.g., both machine direction yarns  102  and  104  float continuously over weft yarns  130 ,  132  and  134 ; both machine direction yarns  104  and  106  float continuously over weft yarns  120 ,  122  and  124 , etc. Thus each continuous float of each machine direction yarn in the side  111   a  partially overlaps in the machine direction with a continuous float of an adjacent machine direction yarn over a distance equal to the three contiguous weft yarns over which each of said adjacent yarns floats. 
     Thus, the long machine direction floats in side  111   a  provided by each machine direction yarn, accompanied by the fact that the machine direction floats in adjacent machine direction yarns partially overlap in the machine direction, should provide excellent adherence of the web being formed to a Yankee dryer or other creping cylinder in the circumferential direction of creping from the dryer or cylinder. Thus the side  111   a  of the fabric  100  is believed to be well suited for use as the web contacting surface when the fabric  100  is employed in a through air dryer section and for then conveying the web dried in that section to the Yankee dryer or other cylinder for subsequent creping. 
     Without further elaboration, the foregoing will so fully illustrate my invention that others may, by applying current or future knowledge, readily adopt the same for use under various conditions of service.