US20030208886A1 - Fabric comprising shaped conductive monofilament used in the production of non-woven fabrics - Google Patents

Abstract

In an apparatus for the production of a non-woven web, structure, or article using a spun-bonding process in combination with a forming fabric which is woven having flat CMD yarns, flat MD yarns or both with some or all of such yarns being conductive so as to dissipate static electricity.

Description

FIELD OF THE INVENTION
• The present invention is directed towards a fabric used in combination with a melt-bonding apparatus to form, transport and bond a web into a non-woven fabric.[0001]
BACKGROUND OF THE INVENTION
• There presently exists apparatus for the production of spun-bond webs, structures or articles formed from filaments or fibers typically made from a thermoplastic resin. Such an apparatus is disclosed in U.S. Pat. No. 5,814,349 issued Sep. 29, 1998, the disclosure of which is incorporated herein by reference. These typically include a spinneret for producing a curtain of strands and a process-air blower for blowing process air onto the curtain of strands for cooling the same to form thermoplastic filaments. The thermoplastic filaments are then typically, aerodynamically entrained by the process air for aerodynamic stretching of the themoplastic filaments which are then, after passing through a diffuser, deposited upon a continuously circulating sieve belt for collecting the interentangled filaments and forming a web thereon. The web, structure or article, so formed, is then subject to further processing.[0002]
• Apparatus of this type, particularly for high-speed melt-bond web production are currently available from Reifenhäuser GmbH Co. Maschinenfabrik, Spicher Strabe D-53839 Troisdort, Germany and sold under the name Reicofil®. The latest generation of such high-speed spunbond lines is referred to as the Reicofil® 3 type system.[0003]
• Another manufacturer of such equipment is Nordson Corporation, 28601 Clemens Road, Westlake, Ohio 44145. Other manufacturers are STP Impianti, Rieter Perfojet, Kobelco, Ason and NWT.[0004]
• During the forming process, a high air flow volume is used to deposit the fibers on the forming fabric. This air volume is drawn through the forming fabric typically by vacuum boxes positioned thereunder. Oftentimes the area around the nip of the press rolls is rendered air tight to avoid any disturbance thereabout. Typically, four press rolls are involved which are a pair of top and bottom rolls through which the forming fabric with the web thereon passes. The air volume is provided between the successive nips.[0005]
• In high speed operations with high air flow, air leakage can occur between the top press roll and the forming fabric surface or through the fabric itself. Air leakage can result in undesired disturbance to the formation of the web. Excessive air carried by the fabric during web transportation may result in causing the web to flutter. The cause of such air being carried is divided between the fabric's permeability and the fabric roughness and raw material. The proportions are on the order of 80% to 20% air respectively.[0006]
• Accordingly, it is desirable to minimize air leakage particularly such leakage which is caused by the movement of the forming fabric.[0007]
• In addition, in a melt-bonding process (which incidentally can produce spun-bond or melt-blown or any combination of the two), there is a large amount of static electricity generated. Normally a negative charge builds up on the filaments or fibers as they are being processed. Successive layers of fibers, since they are the same polarity, tend to repel each other. Charged fibers tend to cling to the press rolls. They also tend to be repelled from the forming fabric, since it will develop a charge thereon during the processing of the charged fibers. This charge tends to accumulate.[0008]
• In European Patent Application No. EP 0 950 744 A1 it proposes using press rolls having a dielectric surface which is charged with a polarity that will repel the fibers. The forming fabric is also made from a dielectric material and charged such that it is opposite to that of the fibers, thereby attracting the fibers thereto.[0009]
• In summary, during the production of the non-woven web, structure or article provisions of some nature need to address the electric charges that are typically generated whether it be to dissipate them or use them in an advantageous fashion as disclosed in the aforesaid application.[0010]
SUMMARY OF THE INVENTION
• It is therefore a principal object of the invention to provide for the production of non-woven webs, structures or articles through, for example, the melt-bonding process, which minimizes air leakage, particularly that caused by the forming fabric.[0011]
• It is a further object of the invention to provide for a forming fabric for the production of non-woven webs, structures or articles that minimizes or eliminates web flutter.[0012]
• A yet further object of the invention is to provide for a forming fabric for use in the production of non-woven webs, structures or articles which provides for the effect of static electricity during production.[0013]
• These and other objects and advantages are achieved by the present invention. In this regard the invention is directed towards generally a forming fabric for use in the production of non-woven webs, structure or articles. The forming fabric comprises a woven structure having flat monofilament yarns in at least either the machine direction or cross machine direction. The use of the flat yarns in the forming fabric improve the fabric surface and decrease the empty volume in the fabric. The forming fabric may be single or multi-layered and is directed towards decreasing the disturbance caused by air whilst maintaining the desired permeability of the fabric. In addition, so as to address the static electricity problem, the flat monofilaments can be made of a conductive material which allows the dissipation of the static electricity on the web through the forming fabric to ground.[0014]
BRIEF DESCRIPTION OF THE DRAWINGS
• Thus by the present invention, its objects and advantages will be realized, the description of which should be taken in conjunction with the drawings wherein:[0015]
• FIG. 1 is a schematic representation of an apparatus for making a non-woven web, structure or article such as that implementing a melt-bond process;[0016]
• FIG. 2 is a side sectional schematic view of the nip of a press roll with a conventional forming fabric;[0017]
• FIG. 3 is a side sectional schematic view of the nip of a press roll with a forming fabric incorporating the teachings of the present invention;[0018]
• FIG. 4 is an enlarged sectional view of a conventional forming fabric taken along the machine direction of the fabric; and[0019]
• FIG. 5 is an enlarged sectional view of the forming fabric of the present invention taken along the machine direction of the fabric.[0020]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
• Turning now more particularly to the figures where like elements will be similarly numbered, FIG. 1 shows schematically an[0021]apparatus10 for forming a non-woven web, structure or article. Theapparatus10 is part of a melt-bond forming machine which forms a flat web or non-woven web, structure or article by a process other than weaving. Non-woven webs, structures or articles typically comprise fibers or filaments bonded together. In general, spun-bonding involves molten polymer which is extruded from a spinning head or spinneret which produces a curtain of strands. Illustrative of such an apparatus is that set forth in U.S. Pat. No. 5,814,349. A high flow of air is used to aerodynamically stretch, elongate or attenuate the strands which, after passing through a diffuser, are deposited on a formingfabric12. Presses are used to compress the deposit of filaments. As shown, by way of example, there are two presses, adownstream press14 and anupstream press16 each of which has a respectivetop press roll18 and20 andbottom press roll22 and24. The machine direction (MD) of thefabric12 is indicated byarrow26. Press16 presses against thefabric12 only while press14 presses against thefabric12 and the melt-bond web28 formed thereon.
• Intermediate the[0022]presses14 and16 is a melt-bonding apparatus30 which typically includes a spinneret, blower, attenuator and diffuser which produces and deposits the filaments onto formingfabric12. Air flow is indicated by arrow32. Beneathapparatus30 is a vacuum orsuction box34 which applies suction to the underside offabric12. The area betweenpresses14 and16 may be sealed which may be in a manner as set forth in U.S. Pat. No. 5,814,349 so as to avoid any disturbance.
• Air leakage can result in a disturbance of the web. As shown in FIG. 1, high air flow can result in air leakage (arrows[0023]36) between thetop press roll18 and thefabric12 surface or through the fabric thickness. Such air leakage is due to the excessive air carried by the fabric, the fabric surface roughness and fabric thickness. In this regard, reference is made to FIG. 2 which is a sectional view in the machine direction offabric12 andweb28 betweenrollers18 and22. Formingfabric12 is a single layer woven fabric havinground MD yarns38 and round cross machine direction (CMD)yarns40. Note that the particular weave (not shown) may vary depending upon the requirements for the particular application (i.e. permeability, etc.).
• As can be seen in FIG. 2, at a distance d[0024]₁between theMD yarns38 there exists a certain amount of empty space S₁. This empty space provides a receptacle to carry air by thefabric12. As the speed of the melt-bonding machine (and that of the fabric) increases, air carried by the fabric during web transportation can cause the web to flutter or to follow the press roll which is undesirable, in addition to increasing the air volume and air leakage. The amount of air carried by a typical fabric used in spun-bonding is about 80% due to fabric permeability and about 20% from fabric roughness, raw material and yarn shape.
• The present invention is directed towards providing in combination with a melt-bonding apparatus, a forming fabric which reduces the empty volume for carrying air and reduces the fabric roughness. In this regard, as shown in FIG. 3, is a cross section of the[0025]fabric12′ used in the present invention. Thefabric12′ shown is a single layer woven (weave not shown) using flatMD monofilament yarns38′ and/orflat CMD yarns40′ as a percentage of the weave. This can be all or part of the MD yarns, CMD yarns or both and may be included in a multi-layer fabric rather than the single layer shown. The flat yarns decrease the empty volume in thefabric12′. This decreases the amount of air carried by thefabric12′ into the forming area and in transporting theweb20 through the nip ofpress14. This reduced volume, in comparison to afabric12 made with all round monofilaments, can be seen by comparing the size of empty volume S₂for distance d₂(d₁=d₂) in FIG. 3 to S₁in FIG. 2.
• This can also be readily seen in comparing FIG. 4 to FIG. 5. In FIG. 4 there is illustrated a portion of[0026]fabric12 along the machine direction with round monofilaments illustrated for theCMD yarns40′. TheMD yarn38′ is shown and the empty volume is illustrated by S₃. In FIG. 5 thefabric12′ is also illustrated along the machine direction with flat monfilaments illustrated for theCMD yarns40′. TheMD yarns38′ may be flat monofilaments or a percentage of the machine direction yarns. As can be seen the empty volume illustrated by S₄compared to S₃is considerably smaller. Also, the fabric surface offabric12′ has a lesser degree of fabric roughness than that offabric12.
• Note that the flat yarns have been illustrated generally. The cross section of the yarns may vary, for example, the ratio between the thickness and the width could be from 1/1 to 1/5. Also, while shown as rectangular in shape (i.e. having parallel sides), they can be barrel-shaped (i.e. parallel sides with slightly curved top and bottom) or ellipitcal shape.[0027]
• As for the material used for the flat yarns, it can be any material suitable for the purpose. Note, however, as aforenoted during the operation of the melt-bonding machines, a large amount of static electricity builds up. In order to dissipate it, some of the yarns used in the fabric can be conductive. Accordingly, it is desirable that a portion of the flat CMD yarns and/or MD yarns be made of a conductive material or coated with a conductive material in order to dissipate the static electricity from the[0028]web28 to the ground, through thefabric12′.
• Accordingly, the[0029]fabric12′ of the present invention is a woven, single or multi-layer structure having flat CMD and/or MD with a portion of which are conductive. Such afabric12 reduces air disturbance during spun-bonding production whilst providing a desired permeability in the web production process.
• Although a preferred embodiment has been disclosed and described in detail herein, its scope should not be limited thereby; rather its scope should be determined by that of the appended claims.[0030]

Claims (12)

What is claimed is:

1. An apparatus for the production of a non-woven fabric produced by way of a melt-bonding process whereby fibers are deposited upon a forming fabric to create the non-woven web, article, or structure, the improvement comprising:

a forming fabric for use in combination with said apparatus which is woven and includes flat CMD yarns or flat MD yarns so as to reduce a volume or air in the forming fabric and improve surface roughness of the forming fabric in comparison to that of a forming fabric woven out of all round yarns.

2. The invention in accordance withclaim 1 wherein the forming fabric includes flat CMD yarns and flat MD yarns.

3. The invention in accordance withclaim 1 wherein said flat CMD yarns or flat MD yarns are conductive.

4. The invention in accordance withclaim 2 wherein said flat CMD yarns and flat MD yarns are conductive.

5. The invention in accordance withclaim 1 wherein said flat CMD yarns or flat MD yarns include parallel sides with a width to height ratio being from 1/1 to 1/5.

6. The invention in accordance withclaim 1 wherein said flat CMD yarns and flat MD yarns include parallel sides with a width to height ratio being from 1/1 to 1/5.

7. The invention in accordance withclaim 1 wherein said flat CMD yarns or flat MD yarns are barrel shaped or elliptical shaped.

8. The invention in accordance withclaim 1 wherein said flat CMD yarns and flat MD yarns are barrel shaped or elliptical shaped.

9. A method for the production of a non-woven fabric comprising the steps of:

providing a melt-bonding apparatus whereby fibers are deposited upon a forming fabric to create a non-woven web, structure, or article; and

using in combination with said apparatus a forming fabric which is woven and includes flat CMD yarns or flat MD yarns.

10. The method in accordance withclaim 9 wherein the forming fabric includes flat CMD yarns and flat MD yarns.

11. The method in accordance withclaim 9 wherein said flat CMD yarns or flat MD yarns are conductive.

12. The method in accordance withclaim 10 wherein said flat CMD yarns and flat MD yarns are conductive.

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