FABRIC WITH STAIR-CASE WEFT ARRANGEMENT TO GENERATE TOPOGRAPHY

Abstract

A forming fabric for a papermaking machine woven according to a repeating pattern. The fabric includes a PS layer having a PS surface, with the PS layer including PS warps and first PS wefts, second PS wefts, and binder PS weft pairs interwoven in a first repeating pattern, and a MS layer having a MS surface, with the MS layer including interwoven MS warps and MS wefts. The binder PS weft pairs are interwoven with the PS warps and the MS warps to bind the PS and MS layers together. The first PS wefts have a larger diameter than the second PS wefts, the second PS wefts have a larger diameter than the binder PS weft pair, and in each repeat, the first PS wefts, the second PS wefts, and the binder PS wefts are inserted sequentially, preferably from large to small, forming a stair step topography.

Description

FIELD OF THE INVENTION

The invention concerns forming fabrics for use in forming the initial embryonic web in a papermaking process. It is particularly concerned with composite forming fabrics comprised of two independent woven layers interconnected by pairs of binder weft yarns.

BACKGROUND OF THE INVENTION

Forming fabrics are known which have weave designs having two independent woven layers which are interconnected during weaving by a plurality of binder weft yarns. The binder yarns are woven as pairs such that, while a first pair member forms (or completes) the continuous unbroken weave pattern of the of non-binding weft yarns in the paper side (PS) layer, the second member interlaces with at least one warp yarn from the machine side (MS) layer so as to bind that layer to the PS layer. The pair members then exchange position (being directed during weaving from one layer to the other) so that the second member then continues the PS layer weave pattern so that it is unbroken and continuous while the first interlaces with a second, different warp yarn from the MS layer. Each exchange forms a segment of the continuous unbroken PS weave pattern. Such fabrics are known and have been described in U.S. Pat. No. 5,826,627 (Seabrook et al.) and others. Each binder yarn is said to be “intrinsic” in that it contributes to and is part of the PS surface pattern; additionally, each contributes to the interconnection of the PS and MS layers. Fabrics of this type are known as “SSB” or “sheet support binder” type forming fabrics in the papermaking arts.

While satisfactory in many respects, there is always a desire to improve on what has been done previously. The present invention is directed to an arrangement to increase bulk and topography for the paper sheet being formed.

SUMMARY

A forming fabric for a papermaking machine woven according to a repeating fabric weave pattern is provided. The fabric includes a PS layer having a PS surface, with the PS layer including PS warps and first PS wefts, second PS wefts, and binder PS weft pairs interwoven in a repeating pattern, and a MS layer having a MS surface, with the MS layer including interwoven MS warps and MS wefts. The binder PS weft pairs are interwoven with the PS warps and the MS warps to bind the PS and MS layers together in the forming fabric, and each interchanges between the layers. The first PS wefts have a larger diameter than the second PS wefts, the second PS wefts have a larger diameter than the binder PS weft pair, and the first PS wefts, the second PS wefts, and the binder PS wefts are inserted sequentially in each repeat of the repeating pattern, preferably from large to small, forming a stair step topography.

The PS warps, the PS wefts, the binder PS yarn pairs, the MS warps, the MS wefts are preferably polymeric yarns made from at least one material selected from PET, PA, PBT, PEN, PPS or PEEK.

Fabrics made in accordance with the teachings of the invention will be heatset, processed, seamed, and finished in a manner using techniques and equipment similar to that used with other known SSB type fabrics.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary as well as the following detailed description will be best understood when read in conjunction with the appended drawings. In the drawings:

FIG. 1 is a photograph of the PS of a forming fabric according to the invention, and

FIG. 2 is a photograph of the MS of the forming fabric shown in FIG. 1.

DETAILED DESCRIPTION

Certain terminology is used in the following description for convenience only and is not limiting. “PS” refers to a paper support side of a papermaking fabric. “MS” refers to a machine side of a papermaking fabric. “Warps” and “wefts” refers to yarns that are interwoven together to form a fabric. These terms originate based on the yarn positions in a loom used for weaving the fabric but are used for convenience only in identifying these yarns in a weave pattern, and the resulting woven product is not limited by the actual loom position of the yarns, and “warp” and “weft” merely refer to the orthogonally located yarn systems in the resulting woven fabric. In one arrangement, the warps extend in the machine direction (MD) and the wefts extend in the cross direction (GD). The yarns may be monofilaments or multi-filaments. The terms “about” and “approximately” encompass + or −10% of an indicated value unless otherwise noted. A reference to a list of items that are cited as “at least one of a, b, or c” (where a, b, and c represent the items being listed) means any single one of the items a, b, or c, or combinations thereof. The terminology includes the words specifically noted above, derivatives thereof and words of similar import.

FIGS. 1 and 2 show PS and MS layers 110, 120, respectively, of a SSB forming fabric 100 according to the invention.

Referring to FIG. 1, the PS layer 110 includes PS warps 112 interwoven with PS wefts 114, 116, 118 in a PS repeating pattern. The PS wefts include first PS wefts 114, second PS wefts 116, and binder PS weft pairs 118. The binder PS weft pairs 118 connect the PS layer 110 to the MS layer 120 by weaving under the MS warps 122 of the MS layer at connection points 130 (see FIG. 2) as noted in detail below. The yarns in the binder PS weft pair 118 exchange positions as they interweave with the MS layer so that the path of the binder PS weft pairs 118 on the paper support surface of the PS layer 110 in effect travel along a single yarn path, in a manner known to those of ordinary skill in the art.

In order to enhance bulk and form a desired topography in the sheet being formed on the first PS wefts 114 have a larger diameter than the second PS wefts 116, and the second PS wefts 116 have a larger diameter than the binder PS weft pair 118, and the first PS wefts 114, the second PS wefts 116, and the binder PS wefts 118 are inserted sequentially in a repeating pattern, preferably from large to small, giving a “stair step” topography. This provides a specific topography as based on the weft sizes as well as the specific arrangement in order to increase pocket size (area and volume) and depth. This stair step is characterized by a non-symmetrical appearance due to the drop off between the binder PS weft pair 118 to the first PS weft 114. Rush drag (the difference between slice velocity and forming fabric speed) on the papermaking machine can be used to manipulate the surface effect provided by this topography.

In the illustrated embodiment shown in FIG. 1, the PS weft yarns 114, 116, 118 are woven in a 2 over, 1 under, 2 over, 1 under twill pattern with the PS warps 112. Here the binder PS wefts 118 form a single yarn path with this weave pattern. Those skilled in the art will recognize that other weave patterns could be provided, such as the weft yarns 114, 116, 118 being woven in a 3 over, 1 under repeat, or various other weave patterns using the stair step spacing.

In one preferred embodiment, the first PS weft yarns 114 have a diameter of about 0.15 to 0.30 mm, and preferably 0.18 mm, the second PS weft yarns 116 have a diameter of about 0.12 to 0.25 mm, and preferably 0.15 mm, and the PS binder weft yarns 118 have a diameter of about 0.08 to 0.20 mm, and preferably 0.11 mm. The PS warps have a diameter of about 0.08-0.25 mm, and preferably 0.11 mm.

Referring to FIG. 2, the MS layer 120 includes MS warps 122 interwoven with MS wefts 124 in a MS repeating pattern. As can be seen from FIG. 2, in particular, each of the MS warps 122 forms one or more MS warp knuckles 126 over single ones of the MS wefts 124. All of the MS warp knuckles 126 are shown as single warp knuckles and do not extend over more than 1 MS weft 124. However, double warp knuckles could be provided. The MS wefts 124 form MS weft floats 128 over the MS warps 122, with floats over 3 MS warps being shown. However, the float size could vary. The MS warp knuckles 126 are preferably arranged in a twill or broken twill. The connection points 130 are located where the PS weft binder yarns 118 wrap under the MS warps 122.

The MS warps 122 and the MS wefts 124 preferably have a diameter in a range from about 0.10 to 0.40 mm.

The PS warps 112, the PS wefts 114, 116, 118, the MS warps 122, and the MS wefts 124 are preferably polymeric yarns made from at least one material selected from PET, PA, PBT, PEN, PPS or PEEK.

Having thus described the present invention in detail, it is to be appreciated and will be apparent to those skilled in the art that many physical changes, only a few of which are exemplified in the detailed description of the invention, could be made without altering the inventive concepts and principles embodied therein. It is also to be appreciated that numerous embodiments incorporating only part of the preferred embodiment are possible which do not alter, with respect to those parts, the inventive concepts and principles embodied therein. The present embodiment and optional configurations are therefore to be considered in all respects as exemplary and/or illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all alternate embodiments and changes to this embodiment which come within the meaning and range of equivalency of said claims are therefore to be embraced therein.

Claims

1. A forming fabric for a papermaking machine woven with a fabric weave pattern, the forming fabric comprising: a PS layer having a PS surface, with the PS layer including PS warps and first PS wefts, second PS wefts, and binder PS weft pairs interwoven in a repeating pattern;a MS layer having a MS surface, with the MS layer including interwoven MS warps and MS wefts;the binder PS weft pairs are interwoven with the PS warps and the MS warps to bind the PS and MS layers together in the forming fabric, and each binder yarn of the binder PS weft pairs interchanges between the layers;the first PS wefts have a larger diameter than the second PS wefts, the second PS wefts have a larger diameter than the binder PS weft pair; andthe first PS wefts, the second PS wefts, and the binder PS wefts are inserted sequentially in each repeat of the repeating pattern to form a stair step topography.

2. The fabric according to claim 1, wherein the first PS wefts, the second PS wefts, and the binder PS wefts are inserted sequentially from large to small in the repeating pattern.

3. The fabric according to claim 1, wherein the PS warps, the PS wefts, the binder PS weft pairs, the MS warps, and the MS wefts are polymeric yarns made from at least one material selected from PET, PA, PBT, PEN, PPS or PEEK.

4. The fabric according to claim 1, wherein the first PS weft yarns have a diameter of about 0.15 to about 0.30 mm.

5. The fabric according to claim 4, wherein the second PS weft yarns have a diameter of about 0.12 to about 0.25 mm.

6. The fabric according to claim 5, wherein the PS binder weft yarns 118 have a diameter of about 0.08 to about 0.20 mm.

7. The fabric according to claim 6, wherein the PS warps have a diameter of about 0.08-about 0.25 mm.

8. The fabric according to claim 7, wherein MS warps and the MS wefts have a diameter of about 0.10 to about 0.40 mm.