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highest practical aspect ratio disclosed in those patents PAPERMAKERS FABRIC HAVING STACKED is 3:1, and the aspect ratio is preferably, less than 2:1. MACHINE DIRECTION YARNS U.S. Pat. No. 4,621,663, assigned to the assignee of

the present invention, discloses one attempt to utilize This application is a continuation-in-part of copend- 5 high aspect ratio yarns (on the order of 5:1 and above) ing application Ser. No. 07/829,985 U.S. Pat. No. to define the surface of a papermakers dryer fabric. As 5,230,371, filed Feb. 3, 1992, entitled PAPERMAK- disclosed in that patent, a woven base fabric is provided ERS FABRIC HAVING DIVERSE FLAT MA- to support the high aspect ratio surface yarns. The CHINE DIRECTION YARN SURFACES, which in woven base fabric is comprised of conventional round turn was a continuation-in-part of application Ser. No. 10 yarns and provides structural support and stability to 07/534,164, filed Jun. 6, 1990, entitled PAPERMAK- the fabric disclosed in that patent. ERS FABRIC WITH STACKED MACHINE DI- U.S. Pat. No. 4,815,499 discloses the use of flat yarns RECTION YARNS U.S. Pat. No. 5,103,874; Ser. No. in the context of a forming fabric. That patent discloses 07/654,008, filed Feb. 14,1991, entitled PAPER MAK- a composite fabric comprised of an upper fabric and a ERS FABRIC WITH FLAT HIGH ASPECT 15 lower fabric tied together by binder yarns. The aspect RATIO YARNS U.S. Pat. No. 5,117,865; and Ser. No. ratio employed for the flat machine direction yarns in 07/567,974, filed Aug. 15,1990, entitled PAPERMAK- both the upper and lower fabrics are well under 3:1. ERS FABRIC WITH ORTHOGONAL MACHINE In use, papermakers fabrics are configured as endless DIRECTION YARN SEAMING LOOPS U.S. Pat. belts. Weaving techniques are available to initially No. 5,092,373. 20 weave fabrics endless. However, there are practical

The present invention relates to papermakers fabrics limitations on the overall size of endless woven fabrics and in particular to fabrics comprised of stacked ma- as well as inherent installation difficulties. Moreover, chine direction monofilament yarns. not all papermaking equipment is designed to accept the

„ . „„ „ „,,„, „ installation of an endless fabric.

BACKGROUND OF THE INVENTION 25 ^ WQven fabrfcs m often ... having oppos_

Papermaking machines generally are comprised of ing ends which are seamed together during installation

three sections: forming, pressing, and drying. Paper- of the fabric on papermaking equipment. Usually one

makers fabrics are employed to transport a continuous end of the fabric is threaded through the serpentine path

paper sheet through the papermaking equipment as the defined by the papermaking equipment and is then

paper is being manufactured. The requirements and 30 joined to its opposing end to form a continuous belt,

desirable characteristics of papermakers fabrics vary in A variety of seaming techniques are well known in

accordance with the particular section of the machine the art. One conventional method of seaming is to form

where the respective fabrics are utilized. the machine direction yarns on each end of the fabric

With the development of synthetic yarns, shaped into a series of loops. The loops of the respective fabric

monofilament yarns have been employed in the con- 35 ends are then intermeshed during fabric installation to

struction of papermakers fabrics. For example, U.S. Pat. define a channel through which a pintle is inserted to

No. 4,290,209 discloses a fabric woven of flat monofila- lock the ends together.

ment warp yarns; U.S. Pat. No. 4,755,420 discloses a For example, U.S. Pat. Nos. 4,026,331; 4,438,789;

non-woven construction where the papermakers fabric 4,469,142; 4,846,231; 4,824,525 and 4,883,096 disclose a

is comprised of spirals made from flat monofilament 40 variety of pin seams wherein the machine direction

yarns. yarns are utilized to form the end loops. In each of those

Numerous weaves are known in the art which are patents, however, the machine direction yarn projects

employed to achieve different results. For example, from the end of the fabric and weaves back into the

U.S. Pat. No. 4,438,788 discloses a dryer fabric having fabric adjacent to itself. Accordingly, the loops inher

three layers of cross machine direction yarns interwo- 45 ently have a twist or torque factor and are not entirely

ven with a system of flat monofilament machine direc- orthogonal to the plane of the fabric. U.S. Pat. No.

tion yarns such that floats are created on both the top 4,883,096 specifically addresses this problem,

and bottom surfaces of the fabric. The floats tend to It would be desirable to provide a papermakers fabric

provide a smooth surface for the fabric. with machine direction seaming loops which do not

Permeability is an important criteria in the design of 50 have torque and/or twist,

papermakers fabrics. In particular, with respect to fab- Additionally, the opposing sides of a papermakers

rics made for running at high speeds on modern drying fabric generally serve distinct functions. One side being

equipment, it is desirable to provide dryer fabrics with utilized to carry the aqueous paper web; the other side

relatively low permeability. being in contact with the various rolls and other mecha

U.S. Pat. No. 4,290,209 discloses the use of flat mono- 55 nisms of the papermaking machine. It would be desir

filament warp yarns woven contiguous with each other able to provide a true two-sided dual characteristic

to provide a fabric with reduced permeability. How- papermakers fabric designed to facilitate the distinct

ever, even where flat warp yarns are woven contiguous requirements for the opposing fabric sides,

with each other, additional means, such as stuffer yarns, „_.. m

are required to reduce the permeability of the fabric. As 60 SUMMARY AND OBJECTS INVENTION

pointed out in that patent, it as desirable to avoid the use The present invention provides a papermakers fabric

of fluffy, bulky stuffer yarns to reduce permeability having a system of flat monofilament machine direction

which make the fabric susceptible to picking up foreign yarns (hereinafter MD yarns) which are stacked to

substances or retaining water. control the permeability of the fabric. The present

U.S. Pat. No. 4,290,209 and U.S. Pat. No. 4,755,420 65 weave also provides for usage of high aspect ratio yarns

note practical limitations in the aspect ratio (cross-sec- as structural weave components. The system of MD

tional width to height ratio) of machine direction warp yarns comprises at least upper and lower yarns which

yarns defining the structural weave of a fabric. The are vertically stacked. Preferably, the upper MD yarns

20

define floats on the upper surface of the fabric and each upper MD yarn is paired in a vertically stacked orientation with a lower MD yarn. The lower MD yarns may weave in an inverted image of the upper MD yarns to provide floats on the bottom fabric surface or may 5 weave with a different repeat to provide a different surface on the bottom of the fabric.

The upper MD yarns may be flat monofilament yarns woven contiguous with each other to reduce the permeability of the fabric and to lock in the machine direction 10 alignment of the stacking pairs of MD yarns. A stacked, contiguous woven machine direction system provides stability and permits the MD yarns to have a relatively high aspect ratio, cross-sectional width to height, a greater than 3:1. Machine direction yarns further define *5 a series of orthogonal seaming loops on the opposing fabric ends. End segments of the lower MD yarns are removed and the upper MD yarn ends are looped back upon themselves and rewoven into the fabric end in the space vacated by the trimmed lower MD yarn end segments. The lower MD yarns may weave in an inverted image of the upper MD yarns such that the crimp of the upper MD yarns conformed with the lower MD yarn weave pattern space into which the 25 upper MD yarn ends are backwoven. This improves the strength of the seam.

Non-loop forming upper MD yarns are also preferably backwoven into the space vacated by trimming the respective lower MD yarns. The upper MD yarns may ^ be woven contiguous with each other to lock in the machine direction alignment of the stacking pairs of MD yarns and the orthogonal orientation of the end loops.

In a preferred embodiment, the same type of material 35 and the same geometric shape and size yarns are used throughout each layer of the machine direction yarn system. Additionally, at least one intermediate layer of MD yarns is provided and intermediate MD yarns are stacked between the upper and the lower MD yarns, 40 respectively.

It is an object of the invention to provide a papermakers fabric having permeability controlled with woven flat machine direction yarns.

It is a further object of the invention to provide a low 45 permeability fabric constructed of all monofilament yarns without the use of bulky stuffer yarns and without sacrificing strength or stability.

Other objects and advantages will become apparent from the following description of presently preferred 50 embodiments.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a papermakers fabric made in accordance with the teachings of the present 55 invention;

FIG. 2 is a cross-sectional view of the fabric depicted in FIG. 1 along line 2—2;

FIG. 3a is a cross-sectional view of the fabric depicted in FIG. 1 along line 3—3; 60

FIG. 3b is a cross-sectional view of a prior art weave construction;

FIG. 4a illustrates the yarn orientation in the fabric depicted in FIG. 1 after the fabric is finished showing only two representative stacked MD yarns; 65

FIGS. 4Z>, 4c, and 4d are a series of illustrations showing the formation of a seaming loop for the papermakers fabric depicted in FIG. 1;

FIG. 5a is a perspective view of a prior art MD yarn seaming loop;

FIG. 5b is a perspective view of an orthogonal MD yarn seaming loop made in accordance with the present invention;

FIG. 6 is a schematic view of a second embodiment of a fabric made in accordance with the present invention;

FIG. 7 is a cross-sectional view of the fabric depicted in FIG. 6 along line 7—7;

FIG. 8 is a cross-sectional view of the fabric depicted in FIG. 6 along line 8—8;

FIG. 9 is a perspective view of a portion of the fabric illustrated in FIGS. 6-8;

FIG. 10 illustrates the yarn orientation in the finished fabric depicted in FIG. 6 showing the end loop formed by one of the MD yarns;

FIG. 11 is a top view of the opposing ends of a fabric constructed in accordance with FIG. 6 just prior to pin-seaming the ends together;

FIG. 12 is a schematic view of a third alternate embodiment of a fabric made in accordance with the teachings of the present invention showing only one pair of stacked MD yarns;

FIG. 13 is a schematic view of a fourth alternate embodiment of a fabric made in accordance with the teachings of the present invention showing only one pair of stacked MD yarns;

FIG. 14 is a schematic view of a fifth alternate embodiment of a fabric made in accordance with the teachings of the present invention showing only one pair of stacked MD yarns;

FIG. 15 is a schematic view of a sixth alternate embodiment of a fabric made in accordance with the teachings of the present invention showing only one pair of stacked MD yarns;

FIG. 16 is a schematic view of a seventh alternate embodiment of a fabric made in accordance with the teachings of the present invention showing only one pair of stacked MD yarns;

FIG. 17 is a schematic view of a eighth alternate embodiment of a fabric made in accordance with the teachings of the present invention showing only one pair of stacked MD yarns;

FIG. 18 is a cross-sectional view of a ninth alternate embodiment of a fabric made in accordance with the teachings of the present invention which includes a layer of intermediate MD yarns stacked between the MD yarns of the upper and lower MD yarn layers.

FIG. 19 is a cross-sectional view of the fabric depicted in FIG. 18 along line 19—19;

FIG. 20 is a cross-sectional view of the fabric depicted in FIG. 18 along line 20—20; and

FIG. 21 is a cross-sectional view of a tenth alternate embodiment of a fabric made in accordance with the teachings of the present invention which includes a layer of intermediate MD yarns stacked between the MD yarns of the upper and lower MD yarn layers.

DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS

Referring to FIGS. 1, 2, and 3a, there is shown a papermakers dryer fabric 10 comprising upper, middle and lower layers of cross machine direction (hereinafter CMD) yarns 11,12,13, respectively, interwoven with a system of MD yarns 14-19 which sequentially weave in a selected repeat pattern. The MD yarn system comprises upper MD yarns 14, 16, 18 which interweave

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