Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F1/00—Wet end of machines for making continuous webs of paper
  • D21F1/0027—Screen-cloths
  • D21F1/0036—Multi-layer screen-cloths
  • D21F1/0045—Triple layer fabrics
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F7/00—Other details of machines for making continuous webs of paper
  • D21F7/08—Felts
  • D21F7/083—Multi-layer felts

Definitions

• This invention relates to dewatering fabrics used in the press section of a papermaking machine. It is particularly concerned with a press section fabric including multiple distinct layers of flattened monofilament warp yarns configured to provide improved roll nip pressure uniformity, reduced paper marking, increased paper dewatering and enhanced compaction resistance.
• Pressure non-uniformity in a press nip can arise from two sources: a) the press rolls themselves, which may be grooved or drilled to provide void space for the water expressed from the web in the nip; and b) the press fabric itself, which, due to its woven structure (or other reasons) transmits press nip pressures unevenly.
• either of these two sources may be the dominant source of non-uniformity and hence of paper marking or low dewatering.
• the pattern of the grooves of the press roll can be seen clearly in the finished paper, while in other cases, the marks of the woven structure of the fabric can be seen. Sometimes both marks are present.
• a flattened monofilament warp yarn with a somewhat higher aspect ratio is used at a high fill factor, in a weave pattern which provides long exposed floats of flattened monofilament warp yarns on the paper side of the fabric.
• This weave construction provides a relatively flat, smooth, almost platform-like surface on the paper side of the fabric. This relatively flat surface transfers the meclianical loads imposed by the press section rolls from the press fabric to the paper web in a way that provides improved pressure uniformity.
• the maximum benefit of a Jackson press section fabric appears to be obtained in a weave design that includes a single layer of weft yarns.
• the maximum float length for the flat warp yarns can be achieved, thereby imparting the maximum smoothness and pressure uniformity to the fabric.
• This invention seeks to overcome these problems and to provide an improved fabric of the type described by Jackson which provides better roll cavity bridging characteristics and better pressure uniformity. Further, this invention also seeks to enhance the compaction resistance of the fabric. Additionally, this invention seeks to provide a fabric in which these improvements can be realised without losing the ability to have long exposed floats of flattened monofilament warp yarns on the paper side of the fabric.
• warp yarn is used to designate the warp on the weaving loom, that is the set of yarns that travel from the warp beam through the heddles of the loom, and which form the shed through which the weft yarn is passed. If a fabric of this invention is woven as an endless loop, the flattened monofilament warps lie in the cross- machine direction of the paper making machine. It is known to weave an endless loop incorporating a seam, or to insert a seam later, in order to facilitate installation in a press section.
• a fabric of this invention is woven as a "flat" fabric, as a continuous run, and then joined into the required endless loop with a suitable seam, the flattened monofilament warps lie in the machine direction of the paper making machine.
• this invention provides a woven dewatering fabric, for the press section of a papermaking machine, having a first side and a second side, one of which constitutes the paper side of the fabric, and the other of which constitutes the press roll side of the fabric, and having long exposed floats of flattened monofilament warp yarns on the first side of the fabric, wherein:
• the aspect ratio of the flattened monofilament warp yarns is at least 1.5:1;
• the fabric weave includes at least two distinct layers of warp yarns each including flattened monofilament warp yarns, one of which provides the exposed first side floats;
• the fabric weave further includes at least one layer of weft yarns; and
• the fill factor for each of the distinct layers including flattened monofilament warp yarns is at least 45%.
• the long exposed floats on the first side of the fabric satisfy a definition for 'float ratio* similar to the one given by Jackson, WO 91/04374, modified to fit the fabrics of this invention.
• the long exposed floats on the first side of the fabric satisfy a float ratio formula x/y, wherein:
• x represents the number of weft yarns in a weft yarn layer on the first side of the fabric in a single weave pattern repeat which are on the inside of the fabric with respect to a particular flattened monofilament warp yarn, and supporting that warp yarn;
• (iv) x is greater than one-half of y.
• a porous layer such as a fibrous batt
• a porous layer can be attached to the paper side, or to both the paper side and the press roll side, of the fabric.
• the flattened monofilament warp yarns making up each of the distinct layers of warp yarns are situated substantially vertically above one another in the woven fabric.
• Figures 1, 2 and 3 show a single weft yarn layer fabric
• FIGS 4 through 11 show alternative weave patterns
• Figures 12 and 13 show a weave pattern incorporating a binder tie yarn
• FIGS 14, 15 and 16 show fabrics carrying porous layers
• Figure 17 shows the face of a fabric.
• Figure 1 a single weft yarn layer fabric according to this invention.
• the fabric as shown includes three layers of yarns:
• Each set of warp yarns is woven at a fill factor of at least 45%, and preferably of about 85%.
• the combined fill factor for the two sets of warp yarns is greater than 90%, and preferably is about 170%.
• This high fill factor for the flattened monofilament warp yarns provides the improved pressure uniformity on the paper side, improved press roll cavity bridging on the press roll side, and enhanced compaction resistance of the fabric.
• Figures 2 and 3 show schematically the weave pattern for the fabric of Figure 1.
• three conventions are used; it can be seen that the yarns in Figure 1 are numbered to match Figures 2 and 3.
• Figure 2 a filled-in square indicates that at that point a warp yarn passes over a weft yarn.
• Figure 3 represents a cross section based on Figure 2 along the line of the warp yarn numbers given: thus in Figure 3 the warp yarns are numbers 1 & 2 from Figure 2, and the section in Figure 3 is the left-hand side of the diagram in Figure 2.
• Third, 'A' represents the first side and 'B' the second side, of the fabric. In all of these fabrics the side A includes the long exposed floats.
• SUBSTITUTE SHEET patterns for the two sets of warp yarns are mirror images of each other. This is not necessary, and the weave pattern adopted for the press roll side B can be different to that of the paper side A.
• the warp yarn weave pattern on the side A of the fabric preferably utilizes the long exposed float concepts described by Jackson in WO 91/04374. That is, the weave pattern includes long exposed floats of flattened monofilament warp yarns with an aspect ratio of at least 1.5:1 on the side A of the fabric but not necessarily on the side B of the fabric.
• These long exposed floats can be characterized by a "float ratio" expressed by the formula x/y as defined above.
• float ratio which is the point at which fabric integrity becomes questionable. For a fabric similar to that shown in Figure 1, this seems to occur at a float ratio of about 9/10. It also appears that if the values of x and y are both low, or if x is close to one half of y, then the dewatering properties of the fabric are impaired.
• the float ratio in a given fabric need not be constant either along a given flattened monofilament warp yarn, or for all of the flattened monofilament warp yarns in a given weave. Further, not all of the exposed floats of flattened monofilament warp yarns need have a float ratio in which
• SUBSTITUTE SHEET x is both greater than one, and greater than one half of y, although maximum benefit will be obtained if these restrictions are observed.
• Figure 17 which shows only the side A of the fabric, a fabric can be woven with varying float ratios. From the top downwards in Figure 17 the float ratios are 7/8, 5/8, 6/8, 4/8, 6/8, 3/8 and 5/8.
• the float length can be varied along a given flattened monofilament warp yarn, to provide in sequence a 1/2 unit, then a 5/6 unit, for example. In such a case the float ratio should be determined over the full length of the pattern repeat, and 1/2 combined with 5/6 in fact is 6/8.
• the warp yarn weave pattern on the side B of the fabric is not so restricted, as is shown in the weave designs of Figures 4 through 9. In each of these, whilst an adequate float ratio is maintained for -the set of warp yarns providing the side A long exposed floats, the path for the other warp yarns can be quite different.
• Figures 6 and 7 show a second fabric in which the warp yarn weave patterns are mirror images of each other, while in Figures 4, 5, 8 and 9 the patterns are quite different.
• the float ratio for side A of each of these weaves is: x y x y
• the warp yarn sets have differing path lengths. Designs of this type may require the use of two, or more, warp yarn beams, as is well known to those skilled in the art of weaving. The designs illustrated are all interwoven so that the result is a single fabric.
• Figures 10 and 11 illustrates a design using two layers of weft yarns, and three layers of flattened monofilament warp ya ⁇ ls 1, 2 and 3.
• the weave pattern for warp yarn 1, on the side A of the fabric and warp yarn 3, on the side B of the fabric are essentially similar, but this is not necessary: the pattern for warp yarn 3 can be different.
• the third layer of warp yarns, 2, is interlaced into the weft yarns between the other two. Due to the high fill factors used for each warp yarn, in the woven fabric the three warp yarns lie substantially above each other. In this fabric the float ratio is 5/6.
• Figures 12 and 13 illustrate a fabric in which the two distinct layers of flattened monofilament warp yarns weave separately into the two sets of weft yarns.
• One set of flattened monofilament warp yarns weaves into the side A set of wefts (the even numbered ones) and the other set of flattened monofilament warp yarns weaves into the side B set of wefts (the odd numbered ones).
• the weave patterns shown are essentially
• the pattern for side B need not be the same as that for side A.
• the float ratio is 5/6.
• These two layers are then joined together in the weave by the separate binder yarns Y.
• These separate binder yarns can be incorporated either in the warp yarn direction (as shown in Figure 13) or in the weft yarn direction (not shown).
• binder yarns are small relative to the warp yarns or weft yarns, often serving only to hold the fabric together during weaving and subsequent processing, until a fiber batt layer is attached by needling thus binding the entire structure together.
• the binder yarns are soluble yarns and are removed by washing after needling.
• the binder yarns are stronger and withstand use in the press section, to keep the two layers of the fabric from separating.
• the fabrics of this invention may also be used with porous layers attached thereto. If only one layer is used, generally it will be attached to the paper side of the fabric, such as the layer 70 attached to side A of the fabric, or the layer 80 attached to side B of the fabric, in Figures 14 and 15. Two porous layers, as at 70 and 80 in Figure 16 may be attached one to each side of the fabric. Again although this seemingly makes both faces of the fabric the same, it
• a porous layer 70, 80 comprises a staple fiber batt, which is generally attached to the fabric by needle punching.
• a batt is used, some thought should be given to the direction in which it is laid, since it is known that the batt fibers tend to be oriented substantially in the direction the batt is laid onto the base fabric. For the fabrics of this invention it is preferred that a batt is laid with a high degree of fiber orientation. There are, nevertheless, several options for the direction of orientation, relative to the direction of the long exposed floats in side A of the fabric, regardless of whether side A is or is not the paper side of the fabric.
• the orientation can be substantially parallel to, or substantially perpendicular to, the side A exposed floats.
• each batt independently can be substantially parallel to, or substantially perpendicular to, the side A exposed floats.
• both side A and side B batts oriented in the same direction, and either parallel or perpendicular to the side A exposed floats, or the side A and side B batts oriented substantially perpendicular to each other, and one of them - either side A or side B - parallel to the long exposed floats.
• SUBSTITUTE SHEET order to minimize the space between the flattened warp yarn support points, such as the distance Z in Figure 3.
• the purpose of this high weft yarn fill is to reduce the bending of the flattened monofilament warp yarns in a direction at right angles to their plane in the fabric under the influence of the very high pressures exerted on the fabric in the press.
• the material used for the flattened monofilament warp yarns a stiff material with a high elastic modulus deflects less than a soft one;
• a soft deformable weft yarn provides better support than a yarn which is hard and makes contact with the warp yarns along a thin line.
• weft yarn spacing should be less than 8 times the flattened monofilament warp yarn thickness, and is preferably less than 5 times.
• Generally press fabrics are constructed from nylon onofilaments, with a nylon staple fiber batt, although polyester and other materials are sometimes used. It is preferred to use nylon for this invention, but this invention is not so limited.
• the distinct warp yarn layers in the fabric of this invention are woven from flattened monofilament yarns. In these flattened monofilament warp yarns, the aspect ratio, that is the ratio of width to thickness, should be at least 1.5:1. If the thickness is made too low, the filament becomes too thin and too flexible, and tends to transmit both knuckle markings from the fabric weave and any pattern of cavities in the press rolls to the paper. A suitable lower limit for the thickness appears to be at about 0.1 mm.
• the aspect ratio is made too low it becomes difficult to control the weaving process and hence it is desirable that the aspect ratio be at least 1.5:1, and preferably at least 2.0:1.
• a desirable range for the aspect ratio is from about 4:1 to about 10:1.
• Currently available weaving equipment appears to be able to handle fibers with an aspect ratio of up to about 100:1.
• the fiber cross section also need not be simply substantially rectangular. It is also of advantage to use the grooved flattened monofilament warp yarns described by Jackson, WO 91/04374.
• a fabric according to this invention can be woven either as a closed endless loop, or as a continuous run of fabric which is then seamed in some way to provide the required loop.
• a closed loop fabric the flattened monofilament warp yarns He in the cross-machine direction, that is substantially at a right angle to the direction in which the paper web moves.
• the flattened monofilament warp yarns lie in the machine direction of the fabric substantially parallel to the direction of movement of the paper web.

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• 1991
  • 1991-07-12 MX MX9204090A patent/MX9204090A/es unknown
  • 1991-07-12 WO PCT/CA1991/000247 patent/WO1993001350A1/en not_active Ceased
  • 1991-07-12 CA CA002112124A patent/CA2112124A1/en not_active Abandoned
  • 1991-07-12 EP EP91911773A patent/EP0594617A1/de not_active Withdrawn
  • 1991-07-12 JP JP3511314A patent/JPH07500381A/ja active Pending
  • 1991-07-12 FI FI940134A patent/FI940134A7/fi unknown

Non-Patent Citations (1)

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