Grooved-shape monofilaments and the fabrics made thereof

Abstract

A monofilament with longitudinally oriented grooves and fabrics made thereof having reduced air permeability, wherein the reduced permeability is achieved without using additional coatings or stuffer yarns. Bicomponent monofilaments made from these grooved monofilaments using solution or wire coating have improved coating adhesion and may also include a conductive coating.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to industrial fabrics. More specifically, the present invention relates to using yarns with longitudinally oriented grooves to reduce fabric permeability without the need of an additional coating or stuffer yarns. These yarns can also be bicomponent yarns with improved coating adhesion.

[0003] 2. Description of the Prior Art

[0004] During the papermaking process, a cellulosic fibrous web is formed by depositing a fibrous slurry, that is, an aqueous dispersion of cellulose fibers, onto a moving forming fabric in the forming section of a paper machine. A large amount of water is drained from the slurry through the forming fabric, leaving the cellulosic fibrous web on the surface of the forming fabric.

[0005] The newly formed cellulosic fibrous web proceeds from the forming section to a press section, which includes a series of press nips. The cellulosic fibrous web passes through the press nips supported by a press fabric, or, as is often the case, between two such press fabrics. In the press nips, the cellulosic fibrous web is subjected to compressive forces which squeeze water therefrom, and which adhere the cellulosic fibers in the web to one another to turn the cellulosic fibrous web into a paper sheet. The water is accepted by the press fabric or fabrics and, ideally, does not return to the paper sheet.

[0006] The paper sheet finally proceeds to a dryer section, which includes at least one series of rotatable dryer drums or cylinders, which are internally heated by steam. The newly formed paper sheet is directed in a serpentine path sequentially around each in the series of drums by a dryer fabric, which holds the paper sheet closely against the surfaces of the drums. The heated drums reduce the water content of the paper sheet to a desirable level through evaporation.

[0007] It should be appreciated that the forming, press and dryer fabrics all take the form of endless loops on the paper machine and function in the manner of conveyors. It should further be appreciated that paper manufacture is a continuous process which proceeds at considerable speeds. That is to say, the fibrous slurry is continuously deposited onto the forming fabric in the forming section, while a newly manufactured paper sheet is continuously wound onto rolls after it exits from the dryer section.

[0008] Contemporary papermaking fabrics are produced in a wide variety of styles designed to meet the requirements of the paper machines on which they are installed for the paper grades being manufactured. Generally, they comprise a<woven base fabric. The base fabrics may be woven from monofilament, plied monofilament, multifilament or plied multifilament yarns, and may be single-layered, multi-layered or laminated. The yarns are typically extruded from any one of the synthetic polymeric resins, such as polyamide and polyester resins, used for this purpose by those of ordinary skill in the paper machine clothing arts.

[0009] The woven base fabrics themselves take many different forms. For example, they may be woven endless, or flat woven and subsequently rendered into endless form with a woven seam. Alternatively, they may be produced by a process commonly known as modified endless weaving, wherein the widthwise edges of the base fabric are provided with seaming loops using the machine-direction (MD) yarns thereof. In this process, the MD yarns weave continuously back-and-forth between the widthwise edges of the fabric, at each edge turning back and forming a seaming loop. A base fabric produced in this fashion is placed into endless form during installation on a paper machine, and for this reason is referred to as an on-machine-seamable fabric. To place such a fabric into endless form, the two widthwise edges are brought together, the seaming loops at the two edges are interdigitated with one another, and a seaming pin or pintle is directed through the passage formed by the interdigitated seaming loops.

[0010] Further, the woven base fabrics may be laminated by placing at least one base fabric within the endless loop formed by another, and by needling a staple fiber batt through these base fabrics to join them to one another. One or more of these woven base fabrics may be of the on-machine-seamable type. This is now a well known laminated press fabric with a multiple base support structure.

[0011] In any event, the woven base fabrics are in the form of endless loops, or are seamable into such forms, having a specific length, measured longitudinally therearound, and a specific width, measured transversely thereacross.

[0012] Turning now to the yarns used heretofore, particularly for dryer fabrics, monofilament yarns have typically been extruded with a simple circular cross-section. More recently, monofilaments with shaped cross-section have been produced. These shaped monofilaments have been used in woven fabrics to modify the fabric surface texture or density, or in particular, to control the fabric air permeability. In this connection, for example, U.S. Pat. No. 5,361,808 (Bowen) discloses using finned or T-shaped monofilaments as weft, or stuffer, yarns to reduce air permeability. As another example, U.S. Pat. No. 5,998,310 (Bowen) shows a tri-lobal stuffer used to reduce permeability. “Y” and “X” and “T” shaped monofilaments are also described. Fabric stability at permeabilities of 200 CFM or greater using the shaped cross-machine-direction yarns is maintained. None of the prior art however, uses shaped yarns as functional yarns which reduce air permeability without using a coating and without using stuffer yarns. Nor does any of the prior art used shaped monofilaments for improved coating adhesion and for producing bicomponent monofilaments.

SUMMARY OF THE INVENTION

[0013] The present invention uses shaped functional yarns to reduce air permeability without the need to use a coating or stuffer yarns. The shaped monofilaments are also used for improved coating adhesion and for producing bicomponent monofilaments. More specifically, groove-shaped monofilaments and the fabrics made thereof are disclosed herein. When the fabrics are coated or laminated, the adhesion strength, tear-resistance and other properties are improved through an interlocking mechanism regardless of the particular coating chemistry. Bicomponent monofilaments made from these grooved monofilaments using solution or wire coating have improved delamination resistance and may also include a conductive coating.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a cross-sectional view of the grooved monofilament according to the present invention;

[0015] FIG. 2 is a typical design for a die used to make the grooved monofilament in FIG. 1;

[0016] FIG. 3 shows a typical “tensile stress” vs. “strain” plot for the grooved monofilaments;

[0017] FIGS. 4(b) and 4(d) are optical photomicrographs of the sheet surfaces of sample fabrics with grooved monofilaments; and

[0018] FIGS. 4(a) and 4(c) are the sheet surfaces of typical prior art fabrics with circular monofilaments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] A preferred embodiment of the present invention will be described in the context of a papermaking dryer fabric. However, it should be noted that the invention is applicable to the fabrics used in other sections of a paper machine, as well as to those used in other industrial settings where surface smoothness and planarity, and controlled permeabilities to water and air are of importance. Some examples of other fabric types to which the invention is applicable include papermaker's forming and press fabrics, through-air-drying (TAD) fabrics and pulp forming fabrics. Another example is of fabrics used in related-to-papermaking processes such as sludge filters and chemiwashers. Yet another example of a fabric type to which the invention is applicable is engineered fabrics, such as fabrics used in making non-woven textiles in the wetlaid, drylaid, meltblown and/or spunbonding processes.

[0020] Fabric constructions include woven, spiral wound, knitted, extruded mesh, spiral-link, spiral coil, and other nonwoven fabrics. These fabrics may comprise monofilament, plied monofilament, multifilament or plied multifilament yarns, and may be single-layered, multi-layered or laminated. The yarns are typically extruded from any one of the synthetic polymeric resins, such as polyamide and polyester resins, used for this purpose by those of ordinary skill in the industrial fabric arts.

[0021] A preferred embodiment of the grooved functional monofilament 1 of the present invention is illustrated in FIG. 1 (cross-sectional view) The monofilaments 1 are incorporated in a fabric as functional yarns as compared to stuffer yarns. The surface 2 of the monofilament 1 has a plurality of grooves 3 running along the length thereof. The grooves 3 may be provided during the extrusion of the monofilament 1. Each groove 3 has a C-shaped cross-section. The “open angle”, which is defined as the angle centering at the origin of the “C” and facing its outlet, is much less than 180 degrees.

[0022] It is an important characteristic that the grooves 3 have a “C”-shape but not a “U”-shape cross-section. In the preferred embodiment, the grooved monofilament 1 is made of a particularly tough and strong polymer such as polyester (PET), or alternatively, polyamide (PA). However, the grooved monofilament 1 can consist of another filament/fiber forming thermoplastic polymer material such as poly(phenylene sulfide) (PPS), polyetheretherketone (PEEK), poly(aryletherketone) (PEK), polyethylene (PE) or polypropylene (PP). Groove-shaped PET monofilaments are typically made through melt spinning using a die (sometimes referred to as a “spinneret”), and the die design is an important factor in shape extrusion. One typical die 4 is shown in FIG. 2. Note that the cross-section of the capillary 5 is roughly circular with five projections 6 into the interior area of the capillary 5. The projections 6 have a circular shape. The inlet angle 7, which is defined as the angle centering at the origin of the projection circular shape and facing into the interior area of the capillary 5, is over 250 degree. The diameter of the capillary 5 is about three times the size of the monofilaments to be produced. The ratio of length to diameter of the capillary 5 is about 3:1. Table 1 shows an example of the processing conditions for making the PET grooved monofilaments using this die 4. Note that processing conditions depend on the particular fiber-forming material used. 1 TABLE I Processing Conditions for Preparing Grooved PET Monofilaments. Draw & Extruder Die Spin Pump Melt & Quench Relax Throughput Resin Single Screw As Shown Size: 10 cc Melt: 550-555° F. Draw 5 × 5.28 Crystar Screw Size: 1.5″ In Speed: 3 rpm Quench: 144° F. @ 375° F. lbs./hr from Screw Design: D- Relax 0.12 Dupont S. Barrier, 3D, @ 400° F. .95 IV High Work

[0023] Tensile properties of the grooved PET monofilaments, prepared under the conditions in Table 1, were characterized using an Instron machine, with a crosshead speed of 10 inches per minute, and gage length of 10 inches. FIG. 3 shows a typical “tensile stress” vs. “strain” plot for these grooved PET monofilaments, and their tensile properties are detailed in Table 2. 2 TABLE 2 Physical and Mechanical Properties of the PET Grooved Monofilaments. Shrinkage Denier Break @ Loop (gm/ Diameter Tenacity Elong. 200° C. Strength 9000 m) (mm) (GPD) (%) (%) (GPD) 1669 0.55 3.64 25.0 11.0 2.87

[0024] The tensile properties of the grooved PET monofilaments indicated in Table 2 are comparable to those of PET monofilaments having other types of shapes. Further, by varying the processing conditions for making the grooved monofilaments, their physical and mechanical properties can be optimized for different applications.

[0025] A sample fabric was produced, being made partially of the grooved monofilaments and was woven using a monoplane weave, forcing the CD yarn (the grooved filaments) to the sheet side. Measurements taken from the sample fabric and from a typical prior art fabric having conventional circular monofilaments show that the weavability of the sample fabric was the same as the prior art fabric. FIGS. 4(b) and 4(d) are the optical photomicrographs of the sheet surfaces of the sample fabrics with the grooved monofilaments on top. FIGS. 4(a) and 4(c) are the surfaces of prior art fabrics with circular monofilaments on top. The symmetric surface of the fabric with grooved monofilaments on top was found to “look” and “feel” better than that of the fabric with circular monofilaments on top. Further, the sample fabric with grooved monofilaments on top exhibited considerably lower air permeability, e.g., 60 CFM, compared to a permeability of 103 CFM for the same style fabric with circular monofilaments on top. Advantageously, this reduced permeability is achieved without using a coating and without using stuffer yarns. 3 TABLE 3 Air Permeability Testing. filling loom H/S cal. filament weave (mm) loc. tension Perm. (in.) grooved 960 0.40 TMB 650 60 .061 circular 960 0.40 TMB 650 103 .059

[0026] In addition to demonstrating reduced permeability, fabrics woven partially or completely with the grooved monofilaments exhibit improved adhesion to coatings, and to laminate substrates which would be mechanically coupled together by way of, for example, a flow of thermoplastic material from a thermoplastic laminate substrate which is heated. For example, the laminate substrate may comprise bicomponent yarns which upon heating causes the melting of a portion of such yarns which flows into the grooves and which upon setting mechanically secures the laminate substrate to the grooved monofilaments. Tear resistance is also improved. These improvements are achieved through the mechanism of mechanical interlocking and surface roughening. Moreover, these improvements are effected regardless of the coating chemistry since it includes a mechanical interlock rather than solely a chemical bonding of the coating to the monofilament. Yet a further advantage is provided in that bicomponent monofilaments can be made from these grooved monofilaments using solution or wire coating. Compared to typical prior art sheath-core monofilaments, it is believed that the bicomponent monofilaments will have much better delamination-resistance because of mechanical interlock. One specific application of this type, for example, is the creation of conductive monofilaments made by coating the grooved core monofilaments with a conductive coating.

[0027] Modifications to the above would be obvious to those of ordinary skill in the art, but would not bring the invention so modified beyond the scope of the present invention. The claims to follow should be construed to cover such situations.

Claims

1. A fabric comprising a plurality of uncoated functional monofilaments having a grooved-shaped cross-section and having reduced air permeability compared with a fabric not having said monofilaments.

2. The fabric of claim 1 wherein a surface of each respective monofilament has a plurality of grooves formed thereon.

3. The fabric of claim 2 wherein each groove is C-shaped.

4. The fabric of claim 2 wherein each groove has an open angle less than 180 degrees.

5. The fabric of claim 1 wherein the fabric is a forming, press, dryer, TAD, pulp forming, sludge filter, chemiwasher, or engineered fabric.

6. A monofilament having a plurality of longitudinal grooves formed in its surface.

7. The monofilament of claim 6 wherein each groove is C-shaped.

8. The monofilament of claim 6 wherein each groove has an open angle less than 180 degrees.

9. The monofilament of claim 6 wherein coating adhesion is improved.

10. The monofilament of claim 6 wherein the grooved monofilament is made of a material selected from the group consisting essentially of polyester, polyamide, poly(phenylene sulfide), polyetheretherketone, poly(aryl ether ketone), polyethylene, and polypropylene.

11. A fabric comprising a plurality of grooved-shaped functional monofilaments and having improved adhesion to coatings compared with a fabric not having said grooved-shaped monofilaments.

12. The fabric of claim 11 wherein said fabric has improved adhesion to lamination substrates mechanically interlocked by way of a flow of thermoplastic material.

13. The fabric of claim 11 wherein the improved adhesion is achieved due to mechanical interlock regardless of the coating chemistry.

14. The fabric of claim 11 wherein the improved adhesion is achieved by an interlocking mechanism between the coating and the yarns in the fabric.

15. The fabric of claim 11 wherein the fabric is a forming, press, dryer, TAD, or engineered fabric.

16. A bicomponent monofilament made from a coated grooved-shaped monofilament.

17. The bicomponent monofilament of claim 16 having improved delamination resistance compared with a bicomponent monofilament not made from a coated grooved-shaped monofilament.

18. The bicomponent monofilament of claim 16 wherein the bicomponent monofilament is made using solution coating.

19. The bicomponent monofilament of claim 16 wherein the bicomponent monofilament is made using wire coating.

20. The bicomponent monofilament of claim 16 wherein said bicomponent monofilament has a conductive coating.

21. A die used for extruding groove-shaped monofilaments and having a capillary cross section with a plurality of projections oriented towards an interior of the capillary, wherein an angle centering at the origin of a respective projection and facing into said interior is over 250 degrees, and the open angle defined as the angle centering at the origin of a C and facing its outlet is much less than 180 degrees.

22. The die of claim 21 wherein a diameter of the capillary is approximately three times the size of the monofilaments to be produced.

23. The die of claim 21 wherein the ratio of length to diameter of the capillary is approximately 3:1.

24. The die of claim 21 wherein the monofilaments to be produced are made of PET.

25. The die of claim 21 wherein the monofilaments are extruded according to a melt spinning process.