APPARATUS TO PRODUCE NONWOVEN FABRIC

United States Patent 3824052

Process and apparatus to produce nonwoven fabric from a stream of liquid material having a high di-electric constant. The stream of liquid material is delivered past an air nozzle having a high electrical potential which attracts the liquid stream and shatters it into fine fibrous particles.

05/423332

07/16/1974

12/10/1973

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Deering Milliken Research Corporation (Spartanburg, SC)

425/7

264/441, 264/469, 264/483, 425/82.1

D04H1/56; D04H1/56; (IPC1-7): B29C13/00; B29D7/00

425/80-83,224 264

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3461943	PROCESS FOR MAKING FILAMENTARY MATERIALS	August 1969	Schile
3442633	METHOD AND APPARATUS FOR CONVEYING AND FOR TREATING GLASS FIBERS	May 1969	Perry
3338992	Process for forming non-woven filamentary structures from fiber-forming synthetic organic polymers	August 1967	Kinney
3276928	Reinforced mat construction and method of forming same	October 1966	Pearson et al.
3158668	Method and apparatus for mat forming	November 1964	Johnson
3020585	Process and apparatus for the manufacture of fiber linings or mats	February 1962	Berthon et al.
2466906	Method and apparatus for forming fibrous webs	April 1949	Miller
2382290	Manufacture of mineral wool	August 1945	Callander
2336745	Method and apparatus for making unwoven and composite fabrics	December 1943	Manning
2048651	Method of and apparatus for producing fibrous or filamentary material	July 1936	Norton

Spicer Jr., Robert L.

Armitage, Norman Petry William Marden Earle C. H. R.

This is a continuation of application Ser. No. 134,131, now abandoned, filed Apr. 15, 1971 which is a divisional application of pending prior application Ser. No. 11,725, filed Feb. 16, 1970, of James E. Fowler for Process and Apparatus to Produce Nonwoven Fabric.

That which will be claimed is

1. Apparatus to produce a nonwoven sheet of material comprising an extruder providing a flow of molten liquid, an air nozzle supported below and substantially perpendicular to the flow of molten liquid from said extruder, a high voltage potential means operably associated with said air nozzle to maintain substantially constant the horizontal distance between said air nozzle and the path of flow of molten liquid from said extruder, means supplying air under pressure to said air nozzle and means operably associated with said air nozzle to collect fibers formed by the action of air from said air nozzle on a stream of molten liquid from said extruder.

2. The structure of claim 1 wherein said means supporting said air nozzle includes a means to rotate said air nozzle partially around the path of flow of said air nozzle.

3. The structure of claim 2 wherein said means to rotate said air nozzle includes a parallelogram linkage.

4. The structure of claim 3 wherein said fiber collection means is an endless belt.

It is known to subject a liquid flow of polymeric material, such as a molten flow of thermoplastic polymer, to a high velocity fluid stream, such as air, to shatter the material into a plurality of discrete fibers or fibrils which may be suitably collected, such as on a moving screen or the like, to form a nonwoven web.

In such prior art processes, fiber forming polymeric material is extruded from a suitable extrusion orifice or die and subjected, while in liquid moldable form, to the action of a pressurized stream of gas which attenuates the polymeric stream and breaks it generally traversely to form a plurality of discrete particles or fibers. Since the physical characteristics of the fibers produced depend greatly upon the velocity and particular position of the pressurized gas stream relative to the moving flow of polymeric material, it has been quite difficult to control the size and uniformity of the fibrous particles produced due to the inherent wandering, erratic movement of the polymeric flow stream under influence of the pressurized attenuating gas.

It is therefore an object of the present invention to provide an improved process and apparatus for producing fibrous particles for use in the formation of nonwoven products by contacting a liquid flow of fiber forming material with a pressurized fluid stream to attenuate the same while accurately controlling the position of the flow of fiber forming material relative to the pressurized fluid stream to control the physical characteristics of the fibrous particles produced.

Other objects and advantages of the invention will become clearly apparent as the specification proceeds to describe the invention with reference to the accompanying drawings, in which:

FIG. 1 is a schematic representation of the new and improved process and apparatus;

FIG. 2 is a cross-section view through the extruder head and air nozzle apparatus;

FIG. 3 is a top view of the air nozzle; and

FIG. 4 is a top view of the air nozzle traverse linkage.

As discussed briefly, the invention is directed to shattering of a liquid stream which has a high di-electric constant and good electrical conductivity in the molten state. For purposes of this specification a liquid stream with a di-electric constant above 20 is one which has a high di-electric constant. In the preferred form of the invention a fiber forming polymeric material such as nylon 6 or nylon 6-6 is employed to form the shattered fibers and consequentially a nonwoven fabric.

Looking now to the drawings and especially to FIG. 1, the new and improved process and apparatus will be described. Briefly, a polymer such as nylon 6 is supplied in suitable form, such as pellets or discrete particles, into the hopper 10 of a conventional extruder 12. The polymer is brought to the molten state and extruded downwardly under pressure in a substantially vertical direction through a single orifice spinnerette 14. Located adjacent the downward path of flow of the extruded polymer 16 is a plurality of air nozzles 18 supplied with air under pressure from an air manifold 20 through a non-conductive air hose 22. The number of air nozzles 18 and spinnerettes 14 is dependent upon the width of nonwoven material to be made. Preferably, the air nozzles 18 are of a highly conductive material such as copper and are connected to a high voltage d.c. source through the cable 24 to provide the air nozzles 18 with a high electrical potential. To electrically isolate the charged air nozzles 18 from the support 25 a non-conductive air nozzle support 26 is provided.

As is known in the prior art, the high velocity air from the air nozzles 18 will shatter the polymer stream 16 into individual fibers and blow these individual fibers onto the continuously driven endless collection belt 28. The high electrical potential of the air nozzles 18 initially attracts the highly conductive polymer toward the nozzle and tends to maintain the stream a predetermined horizontal distance from the air nozzle opening 30 which aids in controlling the effective use of the air velocity to control the length and diameter of the shattered fibers. Also, since the electrical potential of the air nozzles 18 is high enough to create a corona discharge, the polymer stream and shattered fibers adjacent the nozzle rapidly take a charge which causes the fibers to repel one another as they travel to and impinge on the collection belt 28. The nonwoven web formed on the collection belt 28 is automatically moved upwardly and removed by an operator or a suitable automatic doffing apparatus.

As briefly described, the number of air nozzles 18 employed is dependent on the width of the ronwoven web material desired. In the embodiment described, two air nozzles 18 are shown and are mounted so that they can pivot back and forth to cover a certain preselected width of the conveyor belt 28 with shattered fibers. Preferably, the air nozzle 18 will pivot about a rotary path so that the horizontal distance between the end of the air nozzle and the polymer stream remains constant to maintain uniformity of the fibers being made and as much as possible the uniformity of the nonwoven web being made from such fibers.

To control the pivotal movement of the air nozzles 18 the linkage arrangement shown in a top view in FIG. 4 is employed. The T-shaped member 31 is rigidly secured to a suitable frame support (not shown) and supports a cross-bar 32 mounted on an upstanding portion 34 of the member 31. Pivotally connected to the cross-bar 32 at 36 and 38 are lever arms 40 and 42 which are pivotally connected to the long arms 44 and 46 of the parallelogram linkage at 48 and 50. Also pivotally connected to the ends of the arms 44 and 46 at 47 and 49 are the short arms 52 and 54 of the parallelogram linkage which are integral with the air nozzle support plates 56 and 58. Mounted to the upstanding portion 34 of the T-shaped member 31 is a pair of pulleys 60. Connected to each pivot point 49 is a wire or chain 62 wrapped around one of the pulleys 60 and then directed to a source of drive (not shown) which alternately pulls on one of the wires or chains 62 to cause the arms 44, 46, 52 and 54 to pivot about their pivot points to move the air nozzles 18 in an arc around the polymer scream 16 to blow shattered fibers across a predetermined width of the collection belt 28. Preferably, the air nozzle opening 30 is rectangular shaped to provide the most efficient use of the air on the polymer stream 16.

As set forth above, it is preferred to have a rectangular shaped nozzle opening 30. It is found that this shape of nozzle in conjunction with the proper air pressure provides the most consistent and efficient breaking of the fibers from the polymer stream. The selected air pressure normally will be one that will provide super sonic air velocities at the nozzle opening 30. The proper air velocity or as normally expressed, the mass flow rate, in conjunction with the viscosity of the polymer stream 16 is important in controlling the diameter of the fibers being produced. Normally, as the air pressure is lowered, the diameter of the fiber being produced, increases. It is preferred to provide smaller diameter fibers since the nonwoven web produced therefrom tends to be stronger, have better cover and much better cohesion between the fibers.

The following examples will illustrate the benefits obtained by applying a high electrical potential to the fluid nozzle used in shattering a molten polymer stream consisting of a material with generally a good di-electric constant and electrical conductivity in the molten state.

EXAMPLE 1

Nylon 6 polymer -- manufactured by Allied Chemical Company -- is processed through an extruder in a normal manner and expelled at a rate of 3.8 pounds per hour through a spinnerette consisting of a single 0.040 inch diameter orifice.

The fluid nozzle used is this example consists of a copper tube fitted with a throat section of 0.065 inch diameter, and a general configuration of an elliptical hyperboloid. The expanding gases are at least sonic at the nozzle exit. This particular nozzle had a flow rate of 6.6 scfm when operating at a pressure of 60 psig.

Placement of the fluid nozzle exit was 11/2 inches below the spinnerette orifice and approximately one-quarter inch away from and generally perpendicular to the molten polymer stream.

The following data is obtained from conditions where the only variable is the level of electrical charge applied to the fluid nozzle.

______________________________________ Average Fiber Diameter ______________________________________ No electric charge applied to fluid nozzle 25.2 microns 18,000 volts d.c. negative potential applied to nozzle 11.8 microns ______________________________________

The shattered filaments obtained by using the charged nozzle are considerably smaller for the same amount of compressed air consumed, thus resulting in a more economical operation. Furthermore, the smaller diameter fibers result in better cover, and a more uniform or homogeneous web.

EXAMPLE 2

A nylon 6 polymer spun in a manner similar to that outlined in Example 1 was processed at a rate of 2.6 pounds per hour through a 0.040 inch diameter spinnerette orifice. The nozzle was operated with compressed air at 47 psig. It was found again that whenever a charge was applied to the fluid nozzle smaller diameter filaments were obtained.

______________________________________ Average Fiber Diameter ______________________________________ No electrical charge applied 17.5 microns 10,000 volts electrical potential applied to nozzle 11.8 microns ______________________________________

EXAMPLE 3

A nylon 6 polymer spun in a manner similar to Example 1 was shattered with a nozzle consisting of a rectangular throat section with an exit area of 0.0029 square inches. Placement of the nozzle was 13/4 inches below the spinnerette orifice with the nozzle exit approximately one-half inch from the molten polymer stream, and generally perpendicular to the stream. The following table will illustrate the average fiber diameters obtained for several polymer flow rates, and the effect of a charged nozzle versus no electrical charge. The nozzle was operated at 50 psig.

______________________________________ Voltage Applied Polymer Flow Average Fiber to Nozzle Rate Diameter ______________________________________ 0 3.05 bm/hr. 32.1 microns 20,000 3.05 bm/hr. 14.9 microns 0 4.30 bm/hr. 27.2 microns 20,000 4.30 bm/hr. 20.3 microns 0 5.75 bm/hr. 19.8 microns 20,000 5.75 bm/hr. 16.3 microns 0 8.0 bm/hr. 32.4 microns 20,000 8.0 bm/hr. 24.2 microns ______________________________________

This table again reveals that smaller diameter fibers are obtained by using an electrical charge nozzle.

It can be readily seen that the application of a high voltage potential provides, under substantially the same conditions, fibers with a substantially reduced diameter as compared to fibers produced without the application of such voltage. As pointed out before, the charged air attracts the molten polymer stream and tends to maintain constant the distance between the air nozzle and molten stream. Furthermore, the corona discharge created by the high electrical potential allows the shattered fibers to readily pick up the charge of the air nozzle causing the fibers to repel one another to provide a better distribution of fibers on the collection belt.

Although I have described in detail the preferred embodiment of my invention, I contemplate that many changes may be made without departing from the scope or spirit of the invention and I desire to be limited only by the claims.