CA1067280A - Fabrics and methods of making fabrics from synthetic tapes - Google Patents

Abstract

FABRICS AND METHODS OF MAKING
FABRICS FROM SYNTHETIC TAPES

Abstract of the Disclosure A supply roll of longitudinally oriented synthetic sheet is provided having alternating relatively thick longitudinal ribs and relatively thin longitudinal webs. The sheet is advanced, and selected webs are torn to separate the sheet into a plurality of tapes of a desired width. The tapes are then fed directly in line into a loom or knitting machine and woven or knitted into a fabric.

Description

- ~a~7~ Kim Case 14 This invention relates to new and improved fabrics and methods for making fabrics from synthetic tapes or ribbon mono-filaments, and particularly to fabrics and methods for making such fabrics by providing a synthetic sheet having longitudinal striations embossed therein forming alternating relatively thick longitudinal ribs and relatively thin webs, and tearing selected webs to separate the sheet into a plurality of tapes or ribbons of a deqired width and feeding the tapes or ribbons into a loom or knitting machine for fabrication into a woven or knitted fabric.
Heretofore, in the manufacture of fabrics from synthetic tapes or ribbon monofilaments, the tapes or ribbons have been pre-pared by either the (1) extrusion of plastic through a die con-taining a series of separate slits with dimensions such that after melt drawdown, quenching and orientation the tapes or ribbons have the width desired; or (2) extrusion of plastic through a die which profiles or scores the film so that it can be separated into tapes or ribbons such as described, for example, in U.S-. patents 3,594,870 and 3,527,859; or (3) extrusion of plastic through a wide slit die to form a flat sheet and either before or after or-ientation slitting the sheet to form tapes or ribbons of the de-sired wid*h such as shown, for example, in U.S patents 3,398,220 and 3,503,1~6. One of the drawbacks of the first and second meth-ods is that complicated dies with multiple openings, ridges or profiles are required. Furthermore, a different die is required to provide different widths of tapes or ribbons. A drawback of the third method is that even with the use of very sharp knives or cutters to effect-the slitting of the film, the width of the tapes is not uniform bPcause the film tends to follow lines of orienta-tion induced during melt drawdown or orientation after quenching~
These lines of orientation may vary somewhat from the linear or machine direction over long lengths of the sheet. Thus, the rib-bon monofilaments will not be uniform in strength or size. Be-cause of the lack of uniformity in strength, frequent breaks in the tapes or ribbons during production and use are encountered.

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z~o Additionally~ another is that very sharp knives must always be used to slit the film without tearing, and this requires frequent replacement and shapening of the slitting knives, necessitating shutdown of the production line. Furthermore, the knives cause nicks and notches in the edges of the slit tapes which initiate tear propagation across the tapes resulting in broken tapes.
Additionally, the slitters must be initial]y set up with great care and precision in order to attempt to accurately cut the film into uniform tapes. This is time-consuming and thus costly.
Ordinarily, when a flat film is slit or otherwise sep-arated into a plurality of tapes, the tapes are then wound either onto a beam for use as warp yarns, or onto suitable individual packages for subsequent use. In the subsequent weaving or knit-ting operations, the individual packages or beams have the tapes unwound therefrom and fed into the appropriate machine to form the woven or knitted fabric. The winding of the packages or beams and the unwinding therefrom is time-consuming and rela-tively costly. Additionally, the handling of individual packages as opposed to handling of a single, wide width film or sheet is relatively inefficient.
To overcome the aforementioned winding and handling prob-lems, a slit-knit technique has been developed, as shown, for ex-ample, in U.S. patent 3,214,943 wherein a sheet of flat film is slit directly in an in-line operation to feed a knitting machine with tapes of a predetermined width. Similarly, a slit-weave technique is known wherein woven fabrics are made from the in-line slitting of oriented flat film. However, continuity of oper-ation and uniformity of the knitted or woven fabrics are adversely affected by the factors previously mentioned, which result, among other things, in the need to change slitting knives frequently, line shutdowns due to tape breaks caused by tears which follow imperfections in the film or nicks or notches in the edges of the tapes, and imperfections in the knitted or woven fabrics due to non-uniformity of the slit tapes or ribbons.

~a67z80 According to the invention, there is provided a method of making fabrics from longitudinally oriented synthetic sheet material that is embossed with longitudinal striations providing longitudinal ribs of relatively thick material alternated with connecting areas occupied by relatively thin material, the said sheet material being provided on a supply roll, comprising the steps of advancing the sheet material from the supply roll, in-itially separating the leading edge of the sheet material into two or more tapes each having a desired width by a parting of at least one of the connecting areas, advancing each tape in a di-rection vertically divergent from that of the adjacent tape while maintaining longitudinal tension uniformly across the sheet mat-erial to continue the said parting along the said connecting area and thereby to tear the sheet material into separate tapes, and continuously feeding the separated tapes into a fabrication machine to form a fabric.
According to a preferred embodiment of the invention, designed to provide a more open woven or knitted fabric with greater porosity, the relatively thin material in the connecting areas of the sheet material on the supply roll are in the form of an open network structure of fibrils whereby the tearing of the connecting areas is accomplished by tearing the individual fibrils as the adjacent tapes are advanced in divergent directions.
Another aspect of the invention provides a woven fabric comprising a plurality of woven tapes, each tape having two or more longitudinally oriented ribs interconnected in uni-form spaced relationship by relatively thin polymeric material.
In one preferred embodiment, the relatively thin polymeric material interconnecting the longitudinal ribs is in the form of fibrils so that the woven fabric has a predetermined degree of porosity.

Other advantages of the present invention will be apparent from the following detailed description of the invention when considered in conjunction with the following detailed draw-ings. It is to be noted that the drawings illustrate only typical embodiments of the invention and are therefore not to be - 4a -i ~ l -o~

~.Q67Z~O

considered limiting 4f its scope, for the invention may admit to other equally effectlve embodiments.
FIq~ ~ is a perspective view illustrating a portion of a longitudinally striated sheet which can be formed into tapes or ribbons in accordance with the principles of this invention.
FIG. 2 is a view illustrating a roll of longitudinally striated sheet material and apparatus for tearing the sheet into tapes of desired width and feeding them into a loom or knitting machine in accordance with the principles of this invention.
FIG. 3 is a view illustrating an opened network having continuous longitudinal filaments and apparatus for tearing tapes of desired width from the network in accordance with the principles of this invention.
Referring now to FIG. 1, there is shown an embossed longitudinally striated film generally designated as 10 including a plurality of parallel continuous longitudinal ribs 11 intercon-nected by webs 12 of reduced thickness. The embossed sheet 10 may be prepared in a variety of different ways. A preferred method is to feed the molten plastic sheet coming from an extrusion die (not shown) into the nip of two counter-rotating rolls, one of the rolls having a ridged pattern formed therein and the other roll having either a smooth surface or also having a ridged pattern thereon. The longitudinal ribs may be formed on one side of the sheet or on both sides, or, alternatively, longitudinal main ribs may be formed on one side with transverse tie ribs formed on the other side as described in U.S. Patents-Nos. 3,922,329 and

3,914,365.
It is important that the longitudinal ribs 11 be formed parallel to the longitudinal axis of the sheet 10 so that endless tapes can be subsequently formed of uniform width. The spacing of the ribs 11 on the embossed s~heet may be as few as two ribs per inch or as many as 200 rihs per inch. The thickness of the webs 12 can range from about 5% to 25~ of the thickness of the ribs 11.
The cross-sectional shape of the webs 12 in the sheet may be 1(1~;~7;~80 varied and be, for example, "U" or "V;' shaped, or have other shapes. Likewise, the cross-sectional shape of the ribs 11 may he quite varied and may include, without limitation, circular, triangular, truncated or rectangular cross-sections.
The polymer during embossing of the ribs should be at a temperature considerably below the crystalline melting point in a case of a partially crystalline polymer like polypropylene, or below the softening point in the case of an amorphous polymer like polyvinyl chloride. For example, in the case of polypropylene, embossing roll temperatures between 15C. and 130C. are quite satisfactory, while with unplasticized polyvinyl chloride, temper-atures from room temperature to 50C. may be employed. The orien-tation by linear drawing of the embossed sheet may be effected by conventional methods for flat~plastic sheets and under conditions applicable to the polymer used. A typical method is by passing the embossed sheet over a series of heated rolls rotating at progressively higher speeds. The spacing between the draw rolls is preferably kept low to minimize transverse contraction or draw-down of the sheet. The extent of orientation will depend upon the characteristics of the polymer employed and the strength and elongation properties desired. Typically, the orientation may vary from 2X (doubling of the length) to lOX.
An annealing or heat treating step may be included after orientation. This heat treating step, the conditions of which will depend upon the polymer employed, decreases the amount of shrinkage of the tapes or fabrics prepared from them, on exposure to elevated temperatures during use.
After orientation and annealing, the oriented longitudin-ally striated sheet may be wound on a supply roll for subsequent splitting or tearing in a separate operation, or it may be split in line and the tapes or ribbons either wound on individual pack-ages or spools, or fed directly into a knitting machine or loom.

Furthermore, if desired, the sheet may be separated into tapes prior to orientation, and the tapes may be drawn subsequently to orient them in the longitudinal direction.
Referring to FIG. 2, the forming of tapes from the or-iented striated sheet 10 can be readily effected with excellent uniformity by using tearing facilities such as leasing rods 16, 17 and 18 or dull-edge comb guides (not shown) or the like, The sheet 10 is advanced by nip rolls 19 through the lease rods which split or tear the sheet 10 into tapes of a desired width contain-ing two or more ribs 11. The sheet 10 can easily be split into tapes of any desired width by initially cutting or tearing the leading end of the sheet 10 in the desired web areas and feeding adjacent tapes differently through the lease rods 16, 17 and 18 so that upon advancement of the sheet the lease rods direct the tapes in di~erging directions and tear the sheet into tapesO For example, tape lOa containing three ribs 11 interconnected by webs 12 is fed under lease rod 16, over lease rod 17 and under lease rod 18 while the adjacent strip lOb also having three ribs 11 per tape is fed over lease rod 16, under lease rod 17 and over lease rod 18. As strips lOa and lOb advance, the web between strips lOa and lOb is torn, thus forming uniform tapes of a desired width.
Careful alignment of the tearing facilities is not necessary as in the case of gang slitters since the sheet will tear only in the relatively thin webs 12 between the webs 11 of the sheet~ Further-more, since the leasing rods or comb guides do not have sharp edges, there is no tendency for them to cut the ribs 11 as would be the case if sharp knives or rotating cutters were usedc The tearing or splitting operation previously described preferably is carried out in line with a loom or knitting machine, in which case the oriented striated sheet is unwound from a roll, passed through selected guides or lease rods for effecting split-ting to the width desired, and fed into the loom at a rate coor-dinated with the weaving operation. An advantage of this method is that the tapes remain flat and do not twist or fold over, thus assuring maximum and uniform coverage in the woven fabric. When 1~67zt~o using individual packa~es of warp yarns that are fed into the loom, it is very difficult to avoid twist, thus adversely affect-ins coverage and uniformity. Similarly, yarns for introduction into multiple feed knitting machines may be prepared in line with the knitting machine by unwinding the oriented striated sheet from a roll, tearing selected webs to form tapes of a desired width using suitable guides or lease rods, and feeding the tapes into the knitting machines.
If it is desired to make a more open woven or knitted fabric with greater p~rosity than one that can be obtained by knitting or weaving flat tapes, it is possible to first open the embossed oriented striated film into a network structure gener-ally designated as 20, thereby separating the main ribs into indi-vidual main filaments 21 which are interconnected by fibrils or tie ribs 22 as shown in FIG. 3. The fibrils or tie ribs 22 uni-formly hold the main filaments 21 in parallel and uniformly spaced relationship to one another.
The amount of porosity desired in the finished knit or woven fabric will determine how much the network structure is to 20 be opened. After the sheet is opened into a network, the desired tape width is selected and the fibrils in the areas between ad-jacent tapes are split or torn by the lease rods or other facil-ities as previously described. The network structures may be formed by any method, such as, for example, by mechanical fibril-lation as described in U.S. patent 3,495,752 or by spontaneous fibrillation of sheets embossed on two sides which is described in the aforementioned U.S. Patents Nos. 3,922,329 and 3,914,365. The two-side embossing methods described in the aforementioned patent applications may be particularly desirable 30 for use in making open tapes for fabrics because the tie filaments on the opposite side of the sheet provide dimensional stability as well as strength. In the two~side embossing method, the sheet is embossed on one side to form a plurality of parallel main ribs in the longitudinal direction and on the opposite side to form a , ~0~'72~(~

~lurality of parallel tie ribs in a direction transverse to that of the main ribs. Preferably~ the ratio of the cross-sectional area of the main ribs to the tie ribs is at least 1,5 to 1, and the ratio of the height of the main ribs to the thickness of the webs between the main ribs is at least 3 to 1. Alternatively, the tie ribs can be formed in a discontinuous manner so that no substantial portion crosses over the opposite side of the main ribs, The direction of the tie ribs on the reverse side of the sheet should be transverse to that of the main ribs, but need not be perpendicular to it. Typically, any angle between 45 and 90 from the longitudinal direction of the main ribs is satisfactoryO
If two-side embossing is employed, the tapes produced are stiffer, i.e., more resistant to curling or overlapping, because of the presence of the tie filaments interconnecting the main filaments as illustrated in FIG. 3.
Conjugate or bicomponent plastic sheets may also be employed wherein two or more different polymers are extruded to-gether to form sheets containing layers of separate polymers.
One layer of the sheet typically has a component made of a rela-tively high melting point polymer with the remaining portion beingmade of a lower melting point polymer. A fabric made from such tapes can be easily bonded at the cross-over points by hot calen-dering or at intermittent points by use of hot embossed pressure rolls positioned at selected points. Such bonding can eliminate raveling and improve the dimensional stability of fabrics.
The subject methods are applicable to thermoplastic fiber-forming polymers generally. These include polyolefins such as low density polyethylene, high density polyethylene, polypropylene homopolymer, propylene random copolymer, propylene random copoly-mers containing up to 10% of another olefin, block copolymers ofpropylene containing up to 25~ of another olefin, polyamides such as nylon 6, nylon 66, polyesters such as polyethylene terephthal-ate and other high molecular weight thermoplastic polyesters, and polyvinyl chloride. Conjugate plastic sheets as described above _ 9 _ ~0~7'~80 are also applicable. Additionally, bicomponent plastic sheets in which a higher melting component is used to form the major por-tion of the main rib may be employed. Furthermore,-alloys, and mixtures of polymers may also be employed.

Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of making fabrics from longitudinally oriented synthetic sheet material that is embossed with longitudinal striations providing longi-tudinal ribs of relatively thick material alternated with connecting areas occupied by relatively thin material, the said sheet material being provided on a supply roll, comprising the steps of advancing the sheet material from the supply roll, initially separating the leading edge of the sheet material into two or more tapes each having a desired width by a parting of at least one of the connecting areas, advancing each tape in a direction vertically divergent from that of the adjacent tape while maintaining longitudinal tension uniformly across the sheet material to continue the said parting along the said connecting area and thereby to tear the sheet material into separate tapes, and continuously feeding the separated tapes into a fabrication machine to form a fabric.

2. A method of making fabrics as claimed in claim 1 in which the said relatively thin material in the connecting areas of the sheet material on the supply roll is in the form of an open network structure of fibrils whereby the tearing of the connecting areas is accomplished by tearing the individual fib-rils as the adjacent tapes are advanced in divergent directions.

3. A method as set forth in claim 1 wherein said tapes are torn by positioning relatively dull edged elements in the path of the selected advanc-ing webs.

4. A method as set forth in claim 1 wherein said sheet is opened into a network having longitudinal filaments interconnected by fibrils and selected fibrils are torn to separate the network into tapes.

5. A method as set forth in claim 1 wherein the ratio of the thickness of the ribs to the thickness of the webs is at least 3:1.

6. A woven fabric comprising a plurality of woven tapes each tape having two or more longitudinally oriented ribs interconnected in uniform spaced relationship by relatively thin polymeric material.

7. A woven fabric as claimed in claim 6 wherein the relatively thin polymeric material interconnecting the longitudinal ribs is in the form of fibrils so that the woven fabric has a predetermined degree of porosity.