Composite forming fabric

Abstract

A composite forming fabric comprising a paper side layer having a paper side surface, a machine side layer having a bottom wear side surface, and a plurality of pairs of first and second interchanging yarns, wherein: the paper side layer and the machine side layer each comprise warp yarns and weft yarns woven together; said paper side layer and said machine side layer each having a predetermined repeat of the weave pattern in the cross-machine-direction; each pair of first and second interchanging yarns having at least two segments in the paper side layer within each repeat of the weave pattern, said segments providing an unbroken weft path in the paper side surface, with each succeeding segment being separated in the paper side surface of the paper side layer by at least one paper side layer transitional warp yarn; at least one pair of first and second interchanging yarns within each repeat of the weave pattern being binder yarn pairs, each binder yarn in each binder yarn pair binding together the paper side layer and the machine side layer, and at least one pair of first and second interchanging within each repeat of the weave pattern being top weft / binder yarn pairs for stiffening the fabric and binding together the paper side layer and the machine side layer of the fabric.

Description

FIELD OF THE INVENTION [0001] The present invention relates to fabrics with paired, interchanging yarns, and more particularly, to fabrics employed in web forming equipment, such as papermaking and non-woven web forming equipment. More particularly, the preferred fabrics of this invention are employed as forming fabrics in web forming equipment. BACKGROUND OF THE INVENTION [0002] Papermaking involves the forming, pressing and drying of cellulosic fiber sheets. The forming process includes the step of depositing an aqueous stock solution of the fibers, and possibly other additives, onto the forming fabric upon which the initial paper web is formed. The forming fabric may run on a so-called Gap Former machine in which the aqueous stock initially is dewatered, and the initial paper sheet is formed between two forming fabrics. [0003] An effective forming process typically produces a sheet with a very regular distribution of fibers and with a relatively high solids content, i.e., a high ...

AI Technical Summary

Benefits of technology

[0029] In accordance with certain embodiments of the invention at least some of the binder yarns in the pairs of first and second intrinsic, interchanging yarns float under at least two adjacent wear side machine direction yarns, and if desired, under at least three adjacent wear side machine direction yarns to provide enhanced binding of the paper side layer to the machine side layer.

[0030] In addition, by floating the interchanging yarns under two or more adjacent wear side machine direction yarns, the overall height and void volume within the fabric is reduced. This reduces the potential water carrying potential of the fabric; resulting in the formation of a dryer sheet on the fabric.

[0031] In an alternative structure for providing a thin fabric with minimal delamination tendency at least some of the binder yarns of the interchanging binder yarn pairs interlace with a number of single, non-adjacent wear side MD yarn within each repeat of the weave pattern.

[0032] In all embodiments of the invention disclosed herein all or some of the wear side and / or paper side warp yarns can be of a non-circular cross section but particularly of bi-nodal (e.g., dumbbell—or “figure 8” shaped) cross-section. The bi-nodal yarn(s) is (are) extruded with the bi-nodal cross section and thus require(s) no bonding process of the type employed in the prior art, where two adjacent, but separately-formed warp yarns have been woven to an identical weave repeat. Use of bi-nodal warps, with a vertical-to-horizontal aspect ratio of at least 1:1.25, allows a thinner fabric to be provided but with the same overall cross sectional area as prior art structures. This will reduce the water carrying capacity of the fabric, thereby resulting in the formation of a paper sheet with reduced moisture content in the forming section, which, in turn, reduces production costs. Furthermore, unlike the use of profiled and flat warp yarns employed in prior art forming fabrics, the bi-nodal yarns employed in this invention provide several benefits as follows: (1) each bi-nodal yarn provides a drainage channel along the center thereof to effectively direct water through the fabric; (2) the use of bi-nodal yarns avoids the single large surface of the prior rectangular and ovate yarns, which could directly or indirectly undesirably mark the sheet; (3) when used as a wear side warp the bi-nodal yarn is less likely to cause as severe a distortion of the interlacing weft yarn knuckles as a yarn of similar cross-sectional area but of a circular cross section to thereby potentially cause less strikethrough marking of a paper sheet formed thereon and (4) when used in the fabric paper side layer in the same number as prior art, circular cross-section yarns the bi-nodal yarn will double the MD orientated fiber support points of the fabric due to the two, generally circular, dumbbell shaped ends forming part of each bi-nodal yarn; thereby reducing, or minimizing the formation of undesired wire-marks in the formed paper sheet.

[0033] In accordance with another aspect of this invention, the binder position relative to the interlacings of the warp and weft yarns in the wear side layer of the fabric can be selected to facilitate a significant increase in fabric bending stiffness and thus the ability of the fabric to control sheet basis weight profiles in a desired manner.

[0038] A table showing preferred fabrics combinations and the required shafts is shown below. It can be seen that there are generally higher number of weave repeats when using the “high shaft” technique. This provides a significant benefit by allowing more randomness and flexibility in distributing binding points in composite fabrics and in distributing interchange points of interchanging yarn pairs employed in the fabric. In this way, a fabric with a reduced tendency to form undesired wiremarks in the formed paper sheet can be provided compared to the prior art. No. ofNo. ofRatioNo. ofNo. ofPapersideNo. ofWearsidePS:WSLoomPapersidePapersideWeaveWearsideWearsideWeaveWeaveShaftWarpsWeaveRepeatsWarpsWeaveRepeatsRepeats2010Plain(1 / 1)5104 / 122.50Prior Art2412Plain(1 / 1)6125 / 123.00Prior Art24122 / 14125 / 122.00Prior Art2814Plain(1 / 1)7146 / 123.502814Plain(1 / 1)7144 / 1 / 1 / 123.5030152 / 15154 / 131.673216Plain(1 / 1)8163 / 142.003216Plain(1 / 1)8167 / 124.003216Plain(1 / 1)8165 / 1 / 1 / 124.003618Plain(1 / 1)9185 / 133.0036182 / 16185 / 132.003618Plain(1 / 1)9188 / 124.5036182 / 16188 / 123.004020Plain(1 / 1)10204 / 142.504020Plain(1 / 1)10207 / 1 / 1 / 125.0040202 / 25209 / 122.5042212 / 17216 / 132.3348241 / 112247 / 134.0048242 / 18247 / 132.6748242 / 18245 / 1 / 1 / 132.6756281 / 114286 / 143.50

Problems solved by technology

Such localized penetration results in “wire marks” which actually is the result of fiber density variations throughout the sheet area.

Moreover, these basis weight variations can result in undesired variations in sheet absorption properties; a property very relevant to the functionality of quality graphical papers where a consistent uptake of print ink is necessary to produce a clear sharp image.

Other factors also cause the formation of undesired wire marks.

However, the use of thick yarns often causes undesirable wire marks.

The relatively high “void volume” is typically associated with sheet rewetting on the paper machine such that the sheet solids content at transfer to the press section may be undesirably low.

That is, the fibrous web formed on the papermaking fabric has an undesirably low fiber-to-weight ratio.

This can result in reduced papermaking machine performance through a higher amount of sheet breaks, reduced running speed and higher drying costs downstream of initial web formation.

However, fabrics formed in the above way have the disadvantage that an additional gluing process is required which adds to the manufacturing cost of the fabric.

Moreover, the results may not be permanent, in that the fabrics are susceptible to separation of the joined (glued or fused) yarns.

Additionally, the reduction in yarn mass, compared with prior art structures of the type disclosed in the U.S. Pat. No. 4,636,426, may result in reduced fabric stability.

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