US3856612A - Non-woven structures - Google Patents

Abstract

Non-woven fabrics and webs of uniform thickness and width are prepared from conventional webs of randomly laid continuous filaments which fabrics and webs have non-uniform edges and are of non-uniform thickness by contacting the web with a folding guide and pneumatically folding the web followed by calendering of the folded web.

Description

United States Patent McGinnis, J r,

[ 1 Dec. 24, 1974 NON-WOVEN STRUCTURES Paul 111. McGinnis, .112, Kings Mountain, NC.

Celanese Corporation, New York, NY.

Filed: Aug. 2, 1971 Appl. No.: 168,293

Inventor:

Assignee:

US. Cl 161/108, 156/181, 156/202, 156/204,161/150, l61/152,161/170 that. Cl 1332b 3/04 Field of Search 161/102, 99, 104, 107, 161/108,151,152,150,156,169,170; 156/180, 181, 202, 204

References Cited UNITED STATES PATENTS 3/1942 Kerrihard 161/152 h am 2,980,570 4/1961 Cook et a1v 161/152 3,081,519 3/1963 Blades et a1. 3,148,101 9/1964 Allman, Jr. et a1." 3,652,377 3/1972 Helmick 161/166 Primary Examiner-William J. Van Balen Attorney, Agent, or Firm-Pamela D. Kasa ABSTRACT 8 Claims, 5 Drawing Figures PATENTED 3.85815 1 3 sum 1 or 2 lNl/E/VTGR PAUL H. MCGINNIS Jr.

W WWW A 7' TO/PA/E Y BACKGROUND OF THE INVENTION Non-woven fabrics, i.e., structures of fibers held together with a bonding material have been produced since about 1932, but have been of only limited commercial interest until recently. At present, there is a considerable interest in employing non-woven fabrics in a wide variety of products including wearing apparel, bed linens, surgical bandages, liquid and gas filters including tobacco smoke filters and innerliners.

Non-woven fabrics are generally prepared by depositing a fibrous material onto a surface followed by bonding the fibers into a coherent structure. Bonding may be achieved by spraying or saturating the web with a chemical adhesive or plasticizer, or by forming the web entirely or partially of thermoplastic fibers and then subjecting the web to heat and/or pressure to cause fusing of these thermoplastic fibers.

Because of their strength and ease of manufacture, very useful non-woven fabrics are prepared by randomly depositing continuous filaments onto a surface, at least about of the filaments being thermoplastic, and then subjecting the web to temperature and/or pressure conditions to fuse bond the thermoplastic filaments and thus produce a coherent structure.

Unfortunately, non-woven fabrics of randomly laid continuous filaments suffer from two undesirable structural features. First, random laying of the fibers produces a fabric having a randomly varying width, and thus non-parallel edges. Since a fabric having a uniform width is necessary for conversion into most end products, it is necessary to trim the edges of the product be fore further processing. Obviously, this additional step results in a corresponding increase in the cost of the fabric and a considerable waste of material, often amounting up to about 25% of the total product.

A second deficiency resides in the fact that these fabrics are significantly thicker at the center than at the edges since the random laying ofthe filaments tends to concentrate the greatest proportion of filaments at the center with a diminishing number of filaments going from the center to the edge, with the outer edges of the fabric being comprised of only a very few filaments. The distribution of a filamentary density tends toward the normal, i.e., about 67% of the filament weight lies in a range covering about the center 50% of the web width.

In order to appreciate the desirable features of nonwoven fabrics comprised of randomly laid continuous filaments, a means for overcoming the above defects is needed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide non-woven fabrics comprised of randomly laid continuous filaments having a uniform width and thickness.

Other objects are to provide improved apparatus and processes for preparing the aforesaid fabrics.

Additional objects, if not specifically set forth herein, will be obvious to the skilled artisan upon a reading of the present specification taken in conjunction with the drawings.

DRAWINGS FIG. 1 is a perspective view of an apparatus suitable for achieving the objects of the present invention.

FIG. 2 is a top view of said apparatus.

FIG. 3 is a detailed end view of a folding means comprising a part of the present apparatus.

FIG. 4 is an end view of a conventional web of randomly laid continuous filaments.

FIG. 5 illustrates an end view of the product of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Generally, the objects of the present invention are achieved by conveying a non-woven fabric of randomly laid continuous filaments under a slight longitudinal tension, subjecting the edges of the fabric to forces sufficient to fold said edges onto the main body of the fabric such that the edges are substantially coincident with the center of the fabric, and passing the web through the nip of calender rolls where the edges are firmly pressed into the main body of the web before recovering from the forces acting thereon.

The steps of a preferred embodiment of the present invention are set forth in the following description and are to be considered in conjunction with the appended drawings described generally hereinabove of an apparatus for use in the practice of the present invention.

For the sake of clarity, the following description will encompass production of the non-woven fabric as well as treatment of non-woven fabrics to produce the product of the present invention. It is to be understood, however, that the present invention resides in the treatment of conventional randomly laid non-woven fabrics of continuous filaments to improve its properties and does not reside in the production of these fabrics, per se.

In the embodiment illustrated in the drawings, an extruder 10 deposits a filamentary material 12 onto a suit able collector means 14 to produce a non-woven fabric comprised of randomly laid continuous filaments. In the drawing, extruder 10 is a spray spinning device of the type taught for example in US. Pat. No. 3,444,863 and is comprised of an extruder which conveys a thermoplastic filament-forming material in a molten condition to an extrusion nozzle which projects a stream of the thermoplastic material into the atmosphere. This stream is then attenuated by one or more air jets to form at least one highly attenuated continuous filament. Instead of using this device, other devices taught in the prior art for the production of randomly laid nonwoven fabrics may also be employed. For example, US. Pat. No. 3,148,101 describes the production of fabrics of this nature by extruding a plurality of continuous thermoplastic filaments from a conventional multi-hole spinnerette onto a moving conveyor surface parallel to the spinnerette face.

Depending upon the type of extruder employed, the filamentary material, and the resultant fabric, may be composed of one or more continuous filaments.

Collector 14, as shown in the drawings, is comprised of a pair of parallel rolls each preferably having a diameter of from about 2 to about 12 inches. These rolls normally ride against each other but are adapted to separate to a thickness of up to about 0.125 inch to provide a path for a non-woven fabric of a corresponding thickness. These rolls are usually positioned so that the central axis of the filamentary material being extruded against rolls I4 will intersect the nip thereof at a right angle.

As will be subsequently described in:greater detail, it is of importance in the present invention that the fabric is processed under a degree of tension. Accordingly, collector 14 has been found to be particularly useful since it securely holds the fabric and resists slippage thereof as downstream tension is applied. It is to be understood, however, that other collectors may be employed instead of collector 14. For example, one may use a single roll or drum of the type taught in U.S. Pat. No. 3,444,863 or a conveyor belt of the type taught in U.S. Pat. No. 3,148,101. These types of collectors are generally adequate to provide the required resistance of the tensioning forces. If desired, however, a pair of calender rolls or other friction means may be inserted after the collection means and before subsequent processing steps. This device serves as a fabric supply source for the later steps.

As shown in H0. 4, the random web exiting from collection means 14 is substantially thicker in the middle than at the edges and gradually tapers from the center to each edge. Webs prepared for most applications have a thickness of from about 5 to about 125 mils at the center and will gradually decrease in thickness to only a few filaments on each edge. In addition, the edges of the fabric tend to be uneven and non-parallel. Upon exiting from the web supply source, i.e., collection means 14, or calender rolls in certain other embodiments, the fabric is drawn under tension past folding guide 18 which lies in a plane parallel to the plane of the non-woven fabric and preferably within about mm of the fabric plane. Preferably, folding guide 18 has a thickness of from about 1 to about 5 mm. While folding guide 18 may be comprised of a single flat sheet, it is preferably comprised of two segments which are adjustable within the plane relative to each other. The length of folding guide 18 is preferably from about one to about three times its adjusted width. As will'become apparent, this length will also be from about one to about three times the width of the folded web. Instead of passing the entire web over one surface of folding guide 18, it is in fact, preferred to pass one side of the web over a first segment of folding guide 18 and the other side ofthe web under the second segment of folding guide 18. The advantage of passing the web in this manner will be apparent in the description of the next step.

As the non-woven fabric is conveyed under tension past folding guide 18, portions of the web are acted upon by folding means 20. In describing the action of folding means 20, reference will be made to the center and side portions of the web. As used herein, the center portion of the web comprises approximately one-half of the entire web and is constituted of portions of the web extended from the center line of the web to approximately one-halfthe distance from the center line to the edge of the web on either side. The side portions of the web are the outer portions; each side portion comprising approximately the outer one-fourth of the web. 1n the preferred embodiment, folding means 20 are comprised of air lances adapted to blow a stream of air or other suitable gas under a volumetric flow rate of from about 5 to about cu. ft./min. against the side portions ofthe fabric to fold each side portion in a 180 are about the folding guide and over onto the central portion of the fabric. Preferably, folding means 20 are located at a distance of from about V2 to about 3 inches from the outer edges of the segments of folding guide 18, are positioned at an angle of from about 10 to about 30 above or below the plane of folding guide 18 and are directed along the tangent of the edge of the folding guide opposite the surface over which the fabric first travels. Desirably, these air lances project air from a slot having a length of from about 25 to about percent of the length of folding guide 18. Air projected from folding means 20 bends the side portions of the fabric over the segments of folding guide 18 and onto the central portion of the fabric such that the edges of the fabric are placed at substantially the center of said fabric, i.e., approximately one-fourth of the fabric will be folding about each folding guide segment.

Preferably, moving web 12 is caused to move in a plane intersecting the plane formed by folding guide 18 at a slight angle along a line intermediate the two members comprising folding guide 18. Both edge portions of web 12 which extend beyond folding guide 18 are caused to rotate through a arc in a common, e.g., clockwise or counterclockwise, direction about their respective folding guide member. The movement of each edge is actuated by its respective folding means 20 which urge one of said edges in an upward direction and the other of said edges in a downward direction. By directing folding means 20 in this manner, turbulence is avoided, promoting increased uniformity of folding.

Immediately adjacent, i.e., within from about 0.1 to about 1.0 inches of the downstream ends of the segments of folding guide 18 are located calender rolls 22. At rest, these rolls are in contact, but are adapted to freely ride apart to the width of the final web desired, e.g., up to about 0.125 inch. Calender rolls 22 are adapted to travel at a linear speed of about 1 to 10 percent, and preferably from about 3 to about 5 percent greater than the speed of collector means 14, thus maintaining the fabric under tension during folding. Calender rolls 22 serve to draw the fabric through the folding device and firmly press the folded edges into the central portion of the fabric to produce a coherent fabric having uniform density and thickness across its width.

Upon exiting from collector rolls 22, the non-woven fabric comprising the product of the present invention is collected on roll 24 or may be directed to further processing.

As shown by P16. 5, the hereinbefore described process and apparatus is capable of producing a nonwoven fabric of randomly-laid continuous filaments which fabric has uniform width and thickness and is comprised of a coherent web having its side portions folded over onto and pressed against its center portion with the edges of the web extending to the central axis of the web. Preferably, one side portion of the web is folded onto a first face of the center portion and the other side portion is folded onto the opposite face. ln other words, the web is folded in the form of a compressed S. As a result of the process employed, the fabric is characterized by being free of mechanically cut fiber ends along its edges.

The polymers preferably employed in producing the fabric treated by the present invention are the polyolefins, such as polyethylene or polypropylene. The melt index of the polyolefins polymer prior to extrusion will ordinarily be from about 5 to 60 and preferably from about 15 to about 40. The intrinsic viscosity will be from about 1.0 to about 2.5 and preferably from about 1.0 to about 2.0. Instead of the polyolefins, one may also employ other thermoplastic melt extrudable fiberforming polymers such as the polyamides, polyesters, polyacetals, and cellulose esters, e.g., cellulose acetate or mixtures thereof. With some of the polymers, extrusion is aided by mixing the polymer with a melt depressant or plasticizer to facilitate melting without decomposition. Bicomponent filament structures also find utility in the practice of this invention.

lt is also understood that a multiplicity of extrusion jets may supply the primary web with spaced regions of different polymeric type. In one such embodiment, the edge portions of the web are formed from polymer A and the center portions of polymer B. If the edge portions are folded toward a common face, it is possible to prepare a web having differential faces A and B, respectively, of if the edges are folded to opposite faces each face will comprise adjacent segments A and B. In the former case, it is possible to prepare interesting tape or yarn structures by slitting or fibrillating the calendered web. Similarly, the surface of the calendered web may be combed, fluffed or fibrillated to produce non-woven blanket-like or wall covering structures. A structure having faces formed by different polymeric materials may also be desirably utilized as a secondary carpet backing wherein one face is adapted to grip the flooring, and the opposite face is adapted for adhesion to the primary backing containing the tufted material.

Obviously, in the event the folding were accomplished fully to the opposite edge of the web, rather than the center, sandwich structures of differential polymer character could be prepared and post-treated in like manner.

EXAMPLE Various non-woven fabrics for use in tobacco smoke filters were prepared using the hereindescribed process and apparatus. These fabrics had a width of from 4.5 to 6 inches and thicknesses of from 5 to mils and were composed of continuous polyolefin filaments prepared by spray spinning. These fabrics were of uniform density and thickness and the edges thereof were parallel to each other.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit and scope thereof.

What is claimed is:

l. A bonded non-woven fabric having parallel sides and being of substantially uniform thickness and density across its width comprising a randomly-laid continuous thermoplastic polymer filament web folded and pressed such that the randomly-laid edges are substantially coincident with the center of the web.

2. The fabric of claim l wherein said filaments are formed ofa polymer selected from. the group consisting of the polyolefins, polyamides, polyesters, and cellulose esters.

3. The fabric of claim I having a width of about 4.5 to about 6 inches; a thickness of from about 5 to about 15 mils; and a density of from about 1.0 to about 3.0 oz./sq. yd.

4. The fabric of claim 1, wherein said thickness and density have a coefficient of variation of less than 5 percent.

5. A bonded nonwoven fabric comprising a random array of continuous thermoplastic filamentary material composed of at least one organic synthetic polymer, said bonded non-woven fabric forming a single planar structure composed of at least two layers of said material calendered together such as to resist delamination, said layers being integrally connected at the outermost edges therefore, the calandered material comprising said portions folded over upon itself and extending across at least half of said folded fabric such that the edges are substantially coincedent with the center of the folded fabric.

6. The bonded nonwoven fabric of claim 5 wherein said structure comprises three layers, wherein the outermost layers extend in opposite directions to the center of the base layer, as in a compressed S.

7. The bonded non-woven fabric of claim 5 wherein the said planar structure has opposite faces composed of different polymeric material.

8. The ribbon of claim 7 wherein one face is com posed of a synthetic linear polyester, and the opposite face is composed of polypropylene.

Claims (8)

1. A BONDED NON-WOVEN FABRIC HAVING PARALLEL SIDES AND BEING OF SUBSTANTIALLY UNIFORM THICKNESS AND DENSITY ACROSS ITS WIDTH COMPRISING A RANDOMLY-LAID CONTINUOUS THERMOPLASTIC POLYMER FILAMENT WEB FOLDED AND PRESSED SUCH THAT THE RANDOMLY-LAID EDGES ARE SUBSTANTIALLY COINCIDENT WITH THE CENTER OF THE WEB.

2. The fabric of claim 1 wherein said filaments are formed of a polymer selected from the group consisting of the polyolefins, polyamides, polyesters, and cellulose esters.

3. The fabric of claim 1 having a width of about 4.5 to about 6 inches; a thickness of from about 5 to about 15 mils; and a density of from about 1.0 to about 3.0 oz./sq. yd.

4. The fabric of claim 1, wherein said thickness and density have a coefficient of variation of less than 5 percent.

5. A BONDED NON-WOVEN FABRIC COMPRISING A RANDOM ARRAY OF CONTINUOUS THERMOPLASTIC FILAMENTARY MATERIAL COMPOSED OF AT LEAST ONE ORGANIC SYNTHETIC POLYMER, SAID BONDED NONWOVEN FABRIC FORMING A SINGLE PLANAR STRUCTURE COMPOSED OF AT LEAST TWO LAYERS OF SAID MATERIAL CALENDERED TOGETHER SUCH AS TO RESIST DELAMINATION, SAID LAYERS BEING INTEGRALLY CONNECTED AT THE OUTERMOST EDGES THEREFORE, THE CALANDERED MATERIAL COMPRISING SAID PORTIONS FOLDED OVER UPON ITSELF AND EXTENDING ACROSS AT LEAST HALF OF SAID FOLDED FABRIC SUCH THAT THE EDGES ARE SUBSTANTIALLY COINCEDENT WITH THE CENTER OF THE FOLDED FABRIC.

6. The bonded non-woven fabric of claim 5 wherein said structure comprises three layers, wherein the outermost layers extend in opposite directions to the center of the base layer, as in a compressed S.

7. The bonded non-woven fabric of claim 5 wherein the said planar structure has opposite faces composed of different polymeric material.

8. The ribbon of claim 7 wherein one face is composed of a synthetic linear polyester, and the opposite face is composed of polypropylene.

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