US3441468A - Process for the production of non-woven webs - Google Patents

Description

April 29, 1969 E. SlGGEL ET AL PROCESS FOR THE PRODUCTION OF NON-WOVEN WEBS Filed Dec. 20, 1965 T 5 R OGN T G T MQMM v V d m R RE m MU RA EW km R Y W m B TQE United States Patent 27,435 Int. Cl. B29f 3/01; B32h 5/02 US. Cl. 161-469 12 Claims ABSTRACT OF THE DISCLOSURE Production of a non-woven, felt-like web of synthetic thermoplastic polyamide and polyester filaments by extruding continuous filaments of the individual molten polymers into a gaseous stream, using steam at a temperature of 320340 C. and a velocity of 70250 meters/ second for the polyamide while using air or another inert gas at a temperature of 30035'0 C. and a velocity of 70-250 meters/second for the polyester, the individual gas streams intercepting and directing their respective filaments outwardly from a spinning nozzle toward a collecting surface, collecting the filaments onto a moving surface as a web of intermingled substantially non-shrinkable polyamide filaments and shrinkable polyester filaments, and subsequently shrinking the polyester filaments in the web.

This invention relates to a process or method of forming non-woven webs, fabrics, sheets, bands or similar textile products of synthetic polymer filaments, and more particularly to the formation of a non-woven, felt-like textile web composed of polyamide and polyester filaments.

It is quite well known that animal fibers such as wool are capable of being felted to form a non-woven, felt-like web or fleece because these natural fibers have a unique surface structure. Spun fibers of synthetic thermoplastic polymers, such as polyamides and polyesters, do not have this property or tendency of felting. It has therefore been extremely diflicult to develop satisfactory techniques for the formation of non-woven webs or textile fabrics from these synthetic fibers.

In order to felt these synthetic polymer fibers, it is generally essential to coemploy shrinkable fibers which are capable of producing a felt-like effect when incorporated in a web or batt of non-shrinkable fibers. For example, the web can be formed on cards or garnetts or else with the aid of so-called air-lay machines from a mixture of staple fibers containing a certain proportion of shrinkable fibers. The resulting web is then bonded by means of a needle loom in which barbed needles engage individual fibers and draw them through the web, thereby interlocking groups of fibers and providing a mechanical bond. Finally, the non-woven web is subjected to a treatment in which the shrinkable fibers contract. The web formation can also be accomplished by depositing or wet-laying relatively short staple fibers from an aqueous dispersion onto a screen, a procedure which corresponds closely to the manufacture of paper. The resulting wetlaid web can then be further processed to achieve the desired fiber shrinkage or contraction as described above or by similar techniques. However, this wet process is usually considered to be better adapted to the production of hard surfaced paper-like products rather than soft and relatively voluminous felt-like products.

In all of the known processes, it is the usual practice to first produce the fibers in accordance with known methods wherein continuous filaments of the thermoplastic polymer are melt spun and then cut or torn into 3,441,468 Patented Apr. 29, 1969 ICC staple lengths. The non-woven web is then formed from the staple fibers in a process step which is both spatially and temporally separate from the melt spinning of the filaments. In some cases, attempts have been made to improve non-woven textiles by using staple fibers with special crimping effects, and some crimping or curling is considered to be advisable. Also, methods have been developed for fibrillating synthetic polymers in order to form so-called fibrids which are quite short in length and are primarily useful in the wet process as a means of holding the web together until it can be bonded by other means. Such methods require relatively expensive spinning and/or subsequent treatment of the fibers before they can be formed into a non-woven web.

One object of the present invention is to provide a new method of producing a non-Woven web of synthetic polymer filaments which does not require any intermediate steps between the spinning of the filaments and formation of the non-woven web and which nevertheless is highly effective in forming a relatively soft, felt-like textile material.

Another object of the invention is to provide a process for the production of a non-woven web of polyamide and polyester filaments wherein the extruded or melt spun continuous filaments can be directed at various angles onto a collecting surface, preferably so as to provide a selective orientation of the shrinkable fibers and a corresponding selective contraction in length and width of the web together with a change in the web thickness.

Still another object of the invention is to provide a process for the formation of a synthetic polymer non-woven web which does not require the fibrous material to be mechanically worked, as in the usual carding, needle punching or felting methods and which also does not require special bonding agents or other expensive additives.

Yet another object is to provide a textile product in the form of a non-woven web of synthetic polymer filaments produced in accordance with the process of the invention.

It has now been found that these and other objects and advantages are achieved, in accordance with the invention, by extruding a molten, fiber-forming, synthetic polyamide into a stream of steam which has a temperature of approximately 320 C. to 340 C. and a velocity of about 70 to 250 meters/second, while also extruding a molten, fiber-forming, synthetic polyester into a stream of an inert gas such as air which has a temperature of approximately 300 C. to 350 C. and a velocity of about 70 to 250 meters/second, and collecting these two types of filaments as they are extruded onto a moving surface in the form of a web intermingled polyamide and polyester filaments. The resulting non-Woven web then contains nonshrinkable polyamide filaments which are tangled or intermeshed with shrinkable polyester filaments, and the latter can then be shrunk in a conventional manner, preferably without any tension or pressure on the web, in order to yield the desired textile product.

The following detailed description of the invention should be considered in conjunction with the accompanying drawing wherein:

FIG. 1 is a cross-sectional view of a jacketed nozzle suitable for extruding and directing both the polyamide and polyester filaments onto a collecting surface in forming the non-woven web;

FIG. 2 is a schematic perspective view of a web-forming apparatus including a cylindrical collecting surface on which the filaments can be formed into a non-woven web and nozzles corresponding to that shown in FIG. 1;

FIG. 3 is a schematic perspective view of a web-forming apparatus which is identical to FIG. 2 except for the placement of the nozzles; and

FIG. 4 is a schematic perspective view of another webforming apparatus in which the collecting surface is a continuous screen, belt or band on which the filaments are deposited by suitable nozzles.

As illustrated in FIG. 1, the individual filaments or fibers are produced by means of the jacketed nozzle 1 in which the molten polymer introduced from the threaded conduit 2 is pressed through a tubular channel 3 which issues into the conical extrusion tip 4 provided with a number of orifices or openings 5 through which the molten polymer is extruded in the form of continuous filaments. The lower end of the tube 3 is surrounded by a jacket 6 which is connected to a lateral feed conduit 7 for the introduction of steam or air. In order to produce the required gas velocity of about 70 to 250 meters/second, a collar or ring 8 is mounted on the tube 3 just above the conical tip 5 at the outlet end of the nozzle, thereby providing a narrow annular gap space 9 spaced radially outwardly from the tube 3 and directly above the cone 4. The end of the jacket 6 is extended downwardly past the orifices 5 a short distance, but preferably not beyond the tip of the cone, so that the high velocity annular gas stream is directed downwardly to intercept and guide the extruded filaments without contact of these filaments with the jacket wall or with each other during this initial extrusion and gas stream guidance near the outlet end of the nozzle.

The proposed construction of the nozzle is thus particularly advantageous in that, on the one hand, the separately extruded filaments are not immediately recombined into a single strand or into an overly matted or coarse bundle and, on the other hand, the filaments can be rapidly spun and directed by the gas stream so as to be deposited in tangled form on a moving collecting surface over an adjustable area.

Various effects can be achieved depending upon the exact construction of the nozzle, the size and number of the orifices, the rate at which the melt is spun, the temperature and velocity of the gas, and other factors such as the speed and direction of movement of the collecting surface and the angle at which the filaments are directed onto the surface on which the web is being formed. For example, the diameter or denier of the filaments can be varied within wide limits by changing the temperature and velocity of the gas as well as the size of the spinning orifices. Especially desirable results are achieved when the filaments are formed into a non-woven web with an individual filament titer in the web itself of about 0.3 to 15 denier. With the nozzle illustrated in FIG. 1, it is thus preferable to employ orifices or nozzle openings with a diameter of about 0.3 to 0.6 millimeter.

The polyamide filaments should consist essentially of nylon, i.e. one of the well known fiber-forming polyamides characterized by recurring carbonamide groups (NHCO) separated by an alkylene chain of at least two carbon atoms and especially polyhexamethylene adipamide or polycaprolactam. The polyester is preferably polyethylene terephthalate or modified forms thereof which are capable of exhibiting a relatively high shrinkage capacity. Of course, it is also feasible to coemploy still other natural or synthetic filaments or fibers preferably in relatively small amounts of not more than 5 or 10% by weight, with reference to the total weight of the fibrous content of the non-woven web. It will be recognized that such use of other filaments or fibers does not alter the basic concept of the invention but merely serves to modify the properties of the textile product.

By extruding the polyamide melt into a stream of steam under the prescribed conditions of temperature and gas velocity of the invention, continuous filaments are produced which exhibit very little or no capacity to shrink. This result is obtained independently of other process conditions such as the extrusion pressure on the melt, the size of the filaments, the rate of extrusion or the exact manner in which the continuous filaments are directed toward and collected on a supporting surface.

Continuous filaments of the polyester are obtained if the molten polymer is spun into an air stream maintained at a temperature of about 300 C. to 330 C. and having the prescribed gas velocity. At temperatures above 330 C., continuous filaments can still be produced provided that the velocity or flow speed of the air is not too high. The resulting filaments or fibers exhibit an extremely high shrinkage capacity. Instead of air, any other inert gas may be employed as a means of applying the polyester filaments to the non-woven web, the term inert being used herein to denote the fact that the gas is not capable of causing any substantial shrinkage of the filaments in addition to the fact that the gas should have no tendency to deteriorate or impair the polyester filaments by a chemical reaction.

In general, because of the decreasing viscosity of the polymer melts as they are spun at higher temperatures, it will be apparent that lower gas velocities are required in order to form and convey continuous filaments with the gas stream. While some experimentation may be required to determine these parameters for any desired product, this can easily be accomplished by a number of preliminary tests with each type of filament in order to establish its particular properties. Any specific combination of temperature and velocity of the steam or air stream can then be selected in order to combine the polyamide and polyester filaments into a non-woven Web.

The ratio by weight of polyamide: polyester filaments combined in the non-woven web can be varied from about 90:10 to 20:80, preferably about :20 to 60:40.

The separately spun polyamide and polyester filaments are collected or gathered together on any suitable moving surface structure, preferably one which has both longitudinal and reciprocal transverse movement with reference to the points at which the filaments are extruded and directed by their respective gas streams toward this surface. For example, as the collecting surface on which the filaments can be laid to form an intermingled web, there can be used a rotating and axially reciprocating cylinder or drum as shown in FIGS. 2 and 3. The drum 10 with its axial spindle 11 can be mounted in any conventional manner, e.g. with the spindle 11 being journalled for both rotation and axial shifting in the supported bearing members 12 and 13 on either side of the drum, a suitable drive mechanism (not shown) being employed to rotate and axially reciprocate the drum 10 beneath the nozzles 1. By regulating the circumferential speed of the drum and providing various speeds and/ or distances of the lateral or traversing motion of the drum, the filaments or fibers can be collected in any desired state of disorder or intermingling during formation of the web. A higher circumferential velocity and/or a slower traverse stroke of the drum leads to a selective orientation of the filaments in the longitudinal direction of the web.

As indicated in FIG. 4, it is also possible to direct the spun filaments onto a substantially fiat collecting surface in the form of an endless or continuous moving belt, band or screen 14 carried by the end rollers 15 and 16, both of which can be rotatably mounted to move the belt in a longitudinal direction as well as being mounted for axial reciprocation to move the belt transversely in a regular pattern.

Of course, one can employ two or more nozzles for each type of filament, either adjacently or successively, so as to more rapidly form the web over a given area of the collecting surface. Alternatively, two or more drums or endless belts can be arranged together with suitably spaced nozzles to achieve a continuous web formation. In this way, the thickness of the web as it is formed can be adjusted to any desired extent, and many variations in the combination of the nozzles and collecting surface will be readily apparent to those skilled in this art. For example, it is also feasible to mount the nozzles for reciprocating transverse movement with reference to the longitudinal direction of the web as it is formed on the drum or on an, endless belt.

The polyamide and polyester can be initially melted and placed under pressure with any suitable extrusion device, e.g. a continuous screw extruder, as employed in a conventional melt spinning apparatus. The jacketed nozzles provided with a gas inlet are simply substituted in place of the conventional spinning nozzles.

After the filaments have been collected as a non-woven web on the moving surface, the web can be withdrawn and subjected to a shrinking treatment, preferably without placing any tension or pressure on the web. This shrinkage can be accomplished in any conventional manner as known for polyester filamets and fibers, e.g. by subjecting the web to the action of steam at about 100 C. to 120 C. As the polyester filaments shrink, the web contracts in its longitudinal and lateral dimensions While the thickness of the web increases, all in proportion to the ratio of polyester filaments contained in the web. Of course, the amount of shrinkage can also be influenced by the choice of fluid shrinking agents other than steam and/ or the conditions under which shrinkage takes place. In general, the shrinkage temperature should fall substantially below the melting point of the filaments, since excellent results are achieved without selectively melting one of the filaments.

The extent to which the length and width of the nonwoven web shrinks during the after-treatrnent with steam or a similar shrinking agent can be further influenced by the angle at which the polyester filaments are sprayed or directed at the collecting surface. For example, if both of the spinning nozzles are arranged such that the gas streams carry the filaments radially onto the cylindrical collecting surface as shown in FIG. 2, then the web will exhibit about equal shrinkage in length and width. On the other hand, if the polyamide filaments are directed radially against the drum surface but the polyester filaments fall tangentially thereon as illustrated in FIG. 3, then the web will exhibit a greater shrinkage in the longitudinal direction. As indicated in FIG. 4, the nozzle from which the polyester emerges can also be arranged at various angles with the flat planar collecting surface of the endless belt, i.e. so that the air stream is directed perpendicularly to the moving surface or at an acute angle with reference to the angle formed by a line corresponding to the gas stream and its projection onto the collecting surface. Regardless of the arcuate or fiat shape of the collecting surface, it will be recognized that a greater lateral or transverse orientation of the polyester filaments can be developed by increasing the reciprocal speed of transverse motion of the gas stream with reference to the longitudinal speed of the collecting surface. Thus, the degree of shrinkage in the width and length of the web can be readily adjusted by the angle of the nozzles and also by the speed of longitudinal and transverse motion as the web is formed. These adjustments can be easily carried out during the course of the process, or else they can be predetermined by a few routine tests.

The invention is further illustrated by but not restricted to the following examples.

Example 1 A nylon melt consisting of polycaprolactam heated in a conventional extruder to a temperature of 285 C. is spun through a nozzle with nine openings as shown in FIG. 1. Each opening in the nozzle cone or tip has a diameter of 0.5 mm. Steam is introduced into the jacket portion of the nozzle so as to flow therethrough at a velocity of 70 meters/second and at a temperature of 330 C. The amount of nylon extruded in the form of continuous filaments is about 150 grams/hour.

In the same manner, a polyethylene terephthalate melt heated to a temperature of 290 C. is spun through a second nozzle with four openings, each having a diameter of 0.4 mm., into a stream of air having a velocity of 70 meters/second and a temperature of 340 C. About 68 grams/hour of the polyester are extruded in the form of continuous filaments.

The two nozzles are arranged over a cylinder or drum collecting device as shown in FIG. 2 such that the nylon and polyethylene terephthalate filaments are directed approximately radially onto the drum surface. The distance of each nozzle from the surface of the drum is 40 cm. The drum has a diameter of 65 cm. and a width of 50 cm. and is rotated at a circumferential viscosity of about 10 meters/ minute. At the same time, the drum is transversely reciprocated at the rate of 1.5 strokes per revolution of the drum about its axis.

The filaments are deposited in a disordered or tangled state to form an even fleece on the drum surface, and the resulting web contains about 30% polyester filaments and 70% polyamide filaments intermingled with each other. The thickness of the web is 1.20 mm. The web is then subjected to a shrinkage treatment while completely free of tension by the application of steam at about C. for one minute. There occurs a very nearly uniform surface shrinkage in both longitudinal and transverse directions of the Web of 25-30%, and the thickness of the Web increases to 3.06 mm.

Several additional tests were carried out under the same conditions and with the same nozzle and drum arrangement as described above, except that the ratio of polyester to polyamide was varied and the velocity of the air stream in the polyester nozzle was also varied. The results of these experiments are summarized in the following table.

TAB LE Air velocity in the polyester nozzle 70 m.lsec. mJsec.

Ratio of polyester: polyamide Thickness of the web 1 Surface shrinkage approximately uniform in both length and width.

Example 2 The process is repeated under exactly the same conditions as described in Example 1 except that the polyamide filaments are directed radially against the drum surface while the polyester filaments are directed tangentially onto the surface as shown in FIG. 3. With an air velocity in the polyester nozzle of 70 meters/second and a ratio of polyester to polyamide of 30:70, there is obtained a non-woven web which has a thickness of 1.35 mm. before shrinkage and 5.76 mm. after shrinkage. The surface shrinkage of the web amounts to 40-45% in the longitudinal direction (corresponding to the circumference of the drum) and 25-30% in the transverse direction (corresponding to the width of the drum).

Similar results can be achieved by depositing the continuous polyamide and polyester filaments onto a moving endless belt, thereby producing a continuous non-woven web in the longitudinal direction of the supporting surface, the width of the web corresponding to the reciprocating transverse movement of this surface with reference to the position of the nozzles. However, it is also feasible to form a continuous non-woven web using one or more cylindrical drums and/or a plurality of nozzles for each type of filament. In all cases, one obtains a felt-like, nonwoven, synthetic filamentary textile product which has undergone a surface shrinkage of as high as 60% and an increase of thickness of up to about 10 times that prior to the shrinkage treatment.

The process of the invention does not require any expensive intermediate steps in the formation of staple fibers or so-called fibrids nor is it necessary to use special bonding agents, adhesives, needle punching, fabric backings or similar means of ensuring a coherent fleece or web. Of course, such additional techniques can be adopted in combination with the invention in order to obtain special effects or to use the non-woven web of the invention in the fabrication of various textile products, e.g. as linings or interlinings for clothing, blankets, sleeping bags and the like.

The invention is hereby claimed as follows:

1. A process for the production of a non-woven web of synthetic polymer filaments comprising:

extruding molten filaments of a fiber-forming synthetic thermoplastic linear polyamide into a stream of steam which has a temperature of about 320 C. to 340 C. and a velocity of about 70 to 250 meters/ second to provide filaments of substantially no shrinkage capacity;

extruding molten filaments of a fiber-forming synthetic thermoplastic linear polyester consisting essentially of polyethylene terephthalate into a stream of an inert gas which has a temperature of about 300 C. to 350 C. and a velocity of about 70 to 250 meters/second to provide filaments having a high shrinkage capacity;

collecting the filaments as they are extruded onto a moving surface in the form of a web of intermingled substantially non-shrinkable polyamide filaments and shrinkable polyester filaments with a weight ratio of polyamidezpolyester of about 90:10 to 20:80; and shrinking the polyester filaments in the web.

2. A process as claimed in claim 1 wherein said inert gas is air.

3. A process as claimed in claim 1 wherein the extruded filaments of said polyamide and said polyester are directed approximately perpendicularly toward said moving surface on which they are collected.

4. A process as claimed in claim 1 wherein said collecting surface has both longitudinal and reciprocal trans verse movement relative to the points at which said filaments are extruded and directed toward said surface.

5. A process as claimed in claim 1 wherein said extruded polyamide and polyester filaments are directed by their respective streams of steam and an inert gas toward a rotating and axially reciprocating cylindrically-shaped collecting surface.

6. A process as claimed in claim 5 wherein said polyamide and said polyester filaments are directed substantially radially onto said collecting surface.

7. A process as claimed in claim 5 wherein said polyamide filaments are directed substantially radially onto said collecting surface and said polyester filaments are directed substantially tangentially onto said collecting surface.

8. A process as claimed in claim 1 wherein said extruded polyamide and polyester filaments are directed by their respective streams of steam and an inert gas toward a substantially fiat collecting surface which has both longitudinal and reciprocal transverse movement relative to the points at which said filaments are extruded and directed toward said surface.

9. A process as claimed in claim 8 wherein said polyamide filaments are directed substantially perpendicularly onto said collecting surface and said'polyester filaments are directed at an acute angle onto said collecting surface.

10. The non-woven web of synthetic polymer filaments obtained by the process of claim 1.

11. A process as claimed in claim 1 wherein the weight ratio of polyamidezpolyester is about :20 to 60:40.

12. A process as claimed in claim 1 wherein the polyester filaments are shrunk by treating said web with steam at a temperature of about C. to C. while maintaining the web substantially free of compression and tension.

References Cited UNITED STATES PATENTS 2,336,743 12/ 1943 Manning 264-171 X 2,411,659 11/1946 Manning. 2,411,660 11/1946 Manning 156-183 X 2,437,263 3/1948 Manning 264-181 X 2,508,462 5/ 1950 Marshall. 2,522,527 9/1950 Manning. 2,571,457 10/ 1951 Ladisch 264-12 X 2,644,779 7/ 1953 Manning 156-167 2,689,199 9/1954 Pesce. 3,096,225 7/1963 Carr et al 156-181 3,117,055 1/1964 Guandigue et al. 3,156,752 11/1964 Cope 264-345 3,309,734 3/ 1967 Bynum et al. 3,338,992 8/1967 Kinney.

JULIUS FROME, Primary Examiner.

J. H. WOO, Assistant Examiner.

U.S. Cl. X.R.

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