Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...
Reexamination Certificate
1994-11-21
2001-01-30
Hastings, Karen M. (Department: 1731)
Paper making and fiber liberation
Apparatus
Running or indefinite length product forming and/or treating...
C139S3830AA, C162S900000, C442S270000, C428S398000
Reexamination Certificate
active
06179965
ABSTRACT:
This invention relates to papermakers fabrics and, in particular, to wet press felts for use in the press section of a papermaking machine.
BACKGROUND OF THE INVENTION
Wet press felts are used in the press section of papermaking machines to transport and dewater an aqueous paper web which is being made into a desired paper product. The dewatering process conventionally entails transporting the aqueous web through a series of pressure nips.
It is well known in the art to employ press felts comprised of a base fabric with fibrous batt material needled thereto. The fibrous batt generally provides a smooth paper carrying surface and a resilient structure to assist in the dewatering of the aqueous paper web. Any irregularities in the wet felt can result in undesirable marking of the aqueous paper web since it is highly deformable at this stage of the papermaking process.
A wide variety of base fabric constructions are known in the art. For example, the base fabric may be comprised of a single layer or multiple layers of machine direction yarns, having a relatively large diameter to provide machine direction strength, interwoven with smaller diameter cross machine direction yarns.
Even though the base fabric is covered with batt material, the yarns which predominate the paper carrying side of the base fabric can cause marking on the aqueous paper web. In particular, the yarns which predominate on the paper carrying side of the base fabric can lead to problems with marking of the aqueous sheet. Such problems may not be initially apparent. However, they can occur after the fabric has been used on papermaking equipment since the batt materials becomes matted and/or compacted through use. This tends to augment the effect of the base fabric on the aqueous web.
Additionally, base fabrics have been designed to enhance the overall resiliency of the press felt to assist in the dewatering process. U.S. Pat. No. 4,537,816, assigned to the assignee of the present invention, discloses a wet felt having a selectively configured base fabric structure which is designed with void areas to enhance the resiliency and dewatering ability of the wet felt.
Another example of a base fabric designed to enhance the overall resiliency of press felt is disclosed in U.S. Pat. No. 4,883,097, assigned to the assignee of the present invention, wherein a compressible, resilient knit yarn is incorporated into the weave of the base fabric structure.
Additionally, U.S. Pat. No. 4,414,263, discloses the use of flat cross machine direction (CMD) yarns to decrease the prominence of CMD yarn knuckles in the base fabric of a wet press felt to avoid problems with marking.
Hollow synthetic monofilament yarns are known in the papermaking arts. Such yarns are disclosed in U.S. Pat. No. 4,251,588, for the manufacturer of a dryer fabric having improved dimensional stability. As noted therein, such conventional, hollow monofilament yarns have a core void of about 3% to 15% of their cross-sectional area to avoid flattening.
In the context of a dryer fabric application, applicant's assignee has experimented with using hollow monofilament yarns having a core void in excess of 30%. In such application, the wall thickness of the yarns is designed to become flattened in the weave to reduce the permeability of the dryer fabric.
Other uses of hollow yarns are known in the art. For example, U.S. Pat. No. 2,132,252, discloses the use of hollows metal wires in the creation of a forming fabric. However, such forming fabrics are not subjected to pressure nips and accordingly do not demand the resiliency of a press fabric. Additionally, U.S. Pat. No. 4,569,883, employs hollow fibers in the composition of spun yarns and/or to comprise the fibrous batt material for a wet press felt.
SUMMARY OF THE INVENTION
Present invention employs the use of hollow synthetic monofilament yarns in the construction of a base fabric for a papermakers wet press felt. The synthetic hollow monofilament yarns have selected compressibility and resiliency characteristics.
The hollow monofilament yarns are interwoven with other yarns to form a woven base fabric with the hollow monofilament yarns predominating, such as by defining CMD knuckles or floats, oil at least the paper carrying side of the base fabric. The weaving and finishing of the base fabric results in the hollow monofilament yarns retaining a substantially unflattened cross-section Accordingly, substantially unflattened portions of the hollow monofilament yarns predominate the paper carrying side of the base fabric thereby providing-a cushioning surface which is compressibly resilient to assist in the dewatering of the aqueous paper web as it is transported through a press nip during the manufacture of the paper.
In the preferred embodiment, the weaving and heat setting of the base fabric results in the hollow monofilament yarns varying in dimension from a substantially round cross-section to a partially flattened cross-section. Partial flattening occurs at the contact areas between the crossovers where warp and weft yarns interweave, such as at base fabric knuckles. Accordingly, partially flattened portions of the hollow monofilament yarns increase the contact area of the paper carrying side of the base fabric.
As the press felt carries an aqueous paper web through a press nip of a papermaking machine, the hollow monofilament yarns which predominate the paper carrying side of the base fabric become fully flattened within the nip. Accordingly, the base fabric's paper carrying surface exhibits a contact area significantly higher than fabrics which use conventional round monofilament cross machine direction yarns. Additionally, due to the resiliency of the hollow monofilament yarns, improved dewatering and avoidance of rewetting of the web is exhibited as the base fabric is compressed within the nip and rebounds as it exits the nip.
It is possible to use flat cross machine direction yarns to achieve a high contact area on the paper carrying side of the base fabric. However, such flat monofilament yarns do not exhibit the improved dewatering and avoidance of rewetting, since they lack resiliency. Additionally, flat yarns are problematic in weaving and are extremely difficult to bobbin rewind without twisting.
The hollow monofilament yarn is easily bobbin wound and woven in the same manner as conventional round yarns of similar diameter. The wet press felt is preferably woven endless such that the hollow monofilament cross machine direction yarns are warp yarns in the loom and are in the cross machine direction in use. However, the hollow monofilament yarns weave equally well as weft yarns which are thrown by a shuttle during weaving.
Preferably, hollow monofilament CMD yarns are interwoven with one or more layers of multifilament, twisted monofilament and/or monofilament nylon MD yarns to define the base fabric. Hollow nylon monofilament yarns having approximately 16%-25% internal core void have been found to exhibit the desired compressibility and resiliency characteristics.
Preferably a fibrous batt is needled to the base fabric to finish the wet press felt.
It is an object of the present invention to provide an improved wet press felt through the combination of enlarging the contact area of the yarns which predominate on the paper carrying side of the base fabric in the nip while increasing the resiliency of the base fabric.
Other objects and advantages of the present invention will become apparent from the following description of a presently preferred embodiment.
REFERENCES:
patent: 2132252 (1938-10-01), Weber
patent: 4107367 (1978-08-01), Fekete
patent: 4142557 (1979-03-01), Kositzke
patent: 4251588 (1981-02-01), Goetemann et al.
patent: 4259394 (1981-03-01), Khan
patent: 4290209 (1981-09-01), Buchanan et al.
patent: 4351874 (1982-09-01), Kirby
patent: 4379735 (1983-04-01), MacBean
patent: 4414263 (1983-11-01), Miller et al.
patent: 4461803 (1984-07-01), Booth et al.
patent: 4537816 (1985-08-01), Booth et al.
patent: 4569883 (1986-02-01), Renjilian
patent: 4883097 (1989-11-01), Dufour
patent
Cunnane, III Francis J.
Sanders H. Thomas
AstenJohnson, Inc.
Hastings Karen M.
Volpe & Koenig PC
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