GB2204886A

GB2204886A - Improved apparatus for the production of nonwoven fabrics

Info

Publication number: GB2204886A
Application number: GB08806118A
Authority: GB
Inventors: Roberto Zanferrari
Original assignee: Neuberger SpA
Current assignee: Neuberger SpA
Priority date: 1987-04-10
Filing date: 1988-03-15
Publication date: 1988-11-23
Anticipated expiration: 2008-03-15
Also published as: GB8806118D0; IT8767297A0; IT1207385B; GB2204886B

Abstract

Apparatus for the production of a non-woven fabric from a web of continuous filaments by extrusion and spinning of thermoplastic resins and comprises a spinning head 11 having staggered spinnerets 14, 15 for producing bundles of filaments and arranged obliquely to the direction of a moving suction applied apron 25 on which the web is formed, cooling chambers 17 for each filament bundle, bundle acceleration nozzles 22 having a venturi tube structure and inclined relative to the spinning axis of the head 11, bundle widening fixed blades 26 arranged obliquely to the axial plane of the cooling chambers 17 and inclined relative to the plane of apron 25, and bundle distributing blades 28 inclined relative to the plane of apron 25 and oscillatable in synchronism by rods 30, 30' to form a homogeneous web on apron 25. The web is consolidated by hot calendering using rolls 33, 34. The bundles are subjected to cooling and aerodynamic acceleration of the filaments at a speed ratio of between 500 and 3500. <IMAGE>

Description

"IMPROVED APPARATUS FOR THE PRODUCTION OF NONWOVEN FABRICS" This invention relates to apparatus for the production of nonwoven fabrics.

More particulary, the invention relates to apparatus for the production of nonwoven fabrics by spinning thermoplastic resins and formation of a web of continuous filaments (according to the so-called "spunlaid" process).

This process substantially comprises the steps of extruding the molten polymer through a spinneret, cooling and accelerating the filaments thus formed, spreading the bundles of filaments and depositing them on an advancing movable apron and finally mechanically consolidating the web thus formed.

There are several variations to the spunlaid process and various solutions are known for the practical execution of the process steps and for optimizing the quality of the product. For example, U.S. Patent No. 3,736,211 to Allied Chemical Corp. discloses an apparatus comprising a biplanar fixed baffle arranged at the exhaust end of a suction nozzle from which the filaments are ejected before being deposited on an underlying apron. The biplanar baffle has the function of widening the filaments and distributing them at random on the underlying surface to form a uniform nonwoven fabric.

British Patent No. 1,473,270 to Hoechst AG discloses an apparatus for the production of nonwoven fabrics, likewise comprising an inclined baffle arranged at the outlet end of a nozzle for drawing and accelerating the continuous filaments coming from a spinning head or bobbins formed previously.

To improve the distribution of the filaments on the underlying collecting apron, the baffle is arranged for rotation around a vertical axis so as to impart to the filaments a helical path.

European Patent No. 94,993 to Toray Industries, Inc., describes an apparatus for the production of non-woven fabrics comprising a pair of appropriately inclined baffles arranged at the outlet end of the accelerating nozzle. These baffles may be fixed or arranged for rotation around a vertical axis, again for the purpose of improving the distribution of the filaments on the underlying collecting apron.

It is the main purpose of the present invention to provide an apparatus for producing a high quality nonwoven web having superior mechanical characteristics and a high uniformity of these characteristics in the end product obtained.

This and other objects and advantages of the invention, which will become apparent from the following description, are achieved according to the invention by an apparatus comprising a spinning head with a plurality of spinnerets staggered in two parallel rows and arranged obliquely relatively to the normal plane of the direction of advance of an underlying collecting apron, a series of cooling chambers for the bundles of produced filaments, a series of accelerating nozzles for the produced filaments, a widening device formed by a series of fixed blades arranged obliquely at the discharge end of the accelerating nozzles, a device for distributing the filaments of the bundles on the apron advancing therebelow and a device for consolidating the formed web to obtain a nonwoven fabric.

The improvement provided by the present invention consists in that each of- the accelerating nozzles is arranged obliquely relative to the axis .of spinning and the device for distributing the filaments is substantially formed by an array of movable blades arranged in parallel and inclined relative to the plane of the collecting apron, these blades being arranged obliquely to the normal plane of the direction of advance of the apron and obliquely relative to each of the accelerating nozzles, each of the movable blades being further arranged for oscillation around an axis coinciding with its upper edge and being provided with means for connection to all the other blades for synchronized oscillation of all the movable blades of the array.

The succession of the various steps of the process that can be carried out by the apparatus according to the invention is indicated by the block diagram of Fig. 1. In step 1 of the preparation of the bundles of filaments, a fluid mass of thermoplastic resin that has previously been heated is fed to a series of spinnerets for extrusion therethrough. The spinnerets produce an array of staggered bundels of filaments that are gradually cooled in step 2 in chambers arranged therebelow to stabilize the physical characteristics thereof and to prevent them from adhering by contact to one another and will remain separated from one another until the formation of the web. The cooling in step 2 is produced by a flow of air at a controlled temperature, directed perpendicularly to the direction of the bundles and fed at a low differential pressure.In the subsequent step 3 the bundles of filaments are thinned out by acceleration.

By "acceleration", as used herein, the operation 3 is intended which consists in drawing out the filament that has just been formed and therefore is still in a plastic state. This operation is intended to remove the filament that is still in a fluid state from the spinneret for thinning it out. This operation is carried out by applying to the filament an aerodynamic drawing force by means of a flow of air at high speed, directed parallel to the filament after the latter has been cooled and inclined away from its original direction, i.e.

direction of formation. Speed ratios of between 500 and 3500 as expressed by the ratio between the final speed of the filaments and the speed of extrusion are used. The accelerating member is inclined so that the filaments forming the bundle will find a point of contact and will remain separated from one another and substantially parallel to the axis of acceleration. The final speed of the filaments is determined substantially by the speed of the drawing air, taking into account the slip on the filament and the friction on the apparatus; normally it may be between 2500 and 6000 m/min.

Step 4 of widening and distributing the bundle of filaments on the advancing surface, on which the web is formed, is carried out by a succession of impacts of the bundles of filaments independently of one another by appropriate means. During these impacts the filaments dissipate their kinetic energy by producing a counter pressure of air which causes a sudden widening of the bundles and the consequent increase of the spacing of the individual filaments from one another. These impact means are arranged according to a particular geometry for the purpose of producing a highly homogeneous distribution of the filament on the advancing surface on which the nonwoven web is formed, after which follows the step 6 of final consolidation.

In effect, the oblique arrangement relative to the normal plane of the direction of advance of the array of bundles over their entire extension, the spreading of the bundles on an impact area that is inclined relative to the plane of the advancing surface, and the distribution with a reciprocating movement of the filaments of each individual bundle through a further impact area defined by a fan type oscillating means that is likewise inclined relative to the plane of the advancing surface and likewise constitutes an oblique array relative to the normal plane of the direction of advance, compensate and level the heaps of filaments produced by the dead centers of overlapping of the bundles on the advancing surface to form a web that is highly homogeneous in structure and mechanical properties.The array of fixed and movable blades forming the widening and distributing devices is arranged obliquely relative to the normal plane of the direction of advance of the depositing apron at an angle identical to the angle defined by the obliquity of the spinning head, so that no torsion of the bundles of filaments will occur between the spinning head and the widening and distributing devices.

The invention will now be further described with reference to the accompanying drawings which illustrate, by way of example, a preferred embodiment of the invention. In the drawings: Fig. 1 is a block diagram showing the individual steps of the process that can be carried out by the apparatus according to the invention; Fig. 2 is a diagrammatic plan view of apparatus for the production of nonwoven fabrics according to the invention; Fig. 3 is a diagrammatic side elevational view of the apparatus of Fig. 2; Fig. 4 is a diagrammatic front elevational view of part of the apparatus of Fig. 2; Fig. 5 is a diagrammatic perspective view of the apparatus according to the invention, and Fig. 6 is an exploded perspective view of a detail of a spinning head according to the invention.

Referring to Fig. 2, denoted by 11 is a spinning head which is shown diagrammatically and comprises an array of spinnerets aligned in two rows 12 and 13, with spinnerets 14 of one row staggered relative to spinnerets 15 of the other row. The two rows 12 and 13 are fed independently with molten polymer in a manner not shown, as this is known in the art. The polymer is formed by thermoplastic resin such as polyolefin, polyamide, polyester or the like and can be mixed with appropriate dyes independently in the two rows to impart to the final product the desired coloring. The independent feed of the spinnerets arranged in the two rows 12 and 13 also permits the spinnerets 14 and 15 to be fed with different polymers.

Each spinning unit substantially comprises the members shown in the exploded view of Fig. 6, i.e. a distributor 7 provided with a hole of inverted funnel shape for conducting the molten polymer, a first filter 8 and a preliminary spinneret 9 for subdividing the mass of molten polymer, and a second filter 10 located above the spinneret 14. The spinnerets 14 and 15, as the preliminary spinnerets, have a special geometry conceived to produce each two separate bundles of filaments. Therefore, the spinnerets comprise two substantially elliptical areas 16 and 23 in which the holes are located through which the polymer is extruded.

The staggered arrangement of the spinnerets 14 and 15 in the two rows 12 and 13 and the production of a double bundle of filaments in each individual spinneret permits the formation of an array of relatively continuous bundles of filaments, in which the bundles are spaced from one another at a relatively reduced distance which, however, permits separate treatment of the bundles in the devices located downstream of the spinning head until the formed filaments are ejected with a very regular distribution onto an underlying movable apron 25 which advances in the direction of the axis X, still referring to Fig. 2. According to a characteristic of the present invention, the spinning head 11 - and all the devices located therebelow - are arranged obliquely relative to the normal plane Y of the axis of advance X so as to form an angle a.

Considering also Figs. 3 and 4, the bundles of filaments that have just been formed traverse a series of cooling chambers 17, one for each bundle of filaments and thus two for each spinneret 14 or 15. Each cooling chamber 17 is formed by an upper parallelepiped portion 18, provided on one side with a grid 20 to permit cooling air to enter in the direction of the arrows A in Fig. 3, and by a lower troncopyramidal portion 19 from the bottom of which the cooling air and the bundle of filaments are discharged in the direction of the arrows B.

The bundles leaving the cooling chambers 17 are then conducted through a series of accelerating nozzles 22 having a cylindrical geometry with an axis forming an angle b relative to the axis of the cooling chambers (or the spinning axis) and the mouth positioned at the end of the cooling chambers 17. Each accelerating nozzle is formed by an upper portion 23, in which the apertures for the entry of low pressure accelerating air in the direction of the arrows C are provided, and by a discharge conduit 24 of reduced diameter in which the air is accelerated by a Venturi tube effect.The acceleration that is produced here consists of an aerodynamic pull exerted on the filament which has already substantially solidified as it has already been subjected to cooling, but the effect of this pull is more evident upstream of the accelerating nozzle, i.e. in the area between the spinnerets and the cooling chambers 17 where the filament is still in a plastic state. Thus, by imparting a certain speed to the cooling air by appropriately dimensioning the nozzles 22 and adjusting the amount of air that is introduced, the final speed of the filaments is determined from the ratio of which relative to the speed of extrusion the accelerating ratio is obtained which is between 500 and 3500. In the case of polypropylene resin this accelerating ratio normally is between 900 and 1500, but it may vary within the range indicated above when other thermoplastic resins are used.

The inclination of the nozzles at the angle b has the purpose of creating a point of contact between the filaments and the mouth of the nozzles to prevent the filaments from twisting in the nozzles, which would render it difficult to spread out the bundle of filaments.

Arranged between the accelerating nozzles 22 and the apron 25 are the devices for widening and distributing the bundles, which are shown in Figs. 3, 4 and 5.

The device for widening the bundles is formed substantially by an array of fixed blades 26 arranged obliquely relative to the axial plane of the cooling chambers and of the accelerating nozzles and inclined at an angle c relative to the plane of the movable apron 25. These fixed blades 26 are mounted in a support structure, not shown, as it is obvious to one skilled in the art, considering also the diagrammatic character of the drawings. The fixed blades 26 are interposed between the pairs of nozzles 22 in a position adjacent their transverse direction, i.e. between the transversely adjacent pairs of nozzles, so that each of the fixed blades is in a position below a pair of accelerating nozzles which ejects onto the blade a pair of bundles of filaments (fig. 3).

In effect, each bundle of filaments leaving an accelerating nozzle, in addition to having acquired its final characteristics, retains its kinetic energy due to its mass and to its speed and moreover is immersed in a flow of accelerating air which is exhausted but still has a residual energy of its own. In the apparatus according to the invention, these energies are utilized for separating the individual filaments forming the bundle and for distributing them on a plane to form the web.

Thus, on each blade 26 an impact area is formed for the bundles and the accelerating air jet coming from the conduits 24, giving rise to a counter pressure of air which causes widening of the bundles and a subdivision of the individual filaments forming the thread. Due to the inclined arrangement of the blades 26 relative to the axial plane of the accelerating nozzles 22, the widened bundles of filaments are thrown by the blades 26 against the distributing device which is formed substantially by an array of blades 28 which are pivotally mounted upwardly at 29 and given an oscillating movement by a pair of rods 30 and 30' mounted for reciprocating movement in the direction of the arrow D in Figs. 4 and 5 and connecting the blades at their opposed flanks.The blades 28 act as movable baffles for the filaments which, due also to the residual energy of the air still conducting them, are deposited and uniformly distributed in fan fashion on the movable carpet 25 advancing in the direction X. Uniformity of the distribution is obtained due to the scheme of depositing with a high level of casualness of the filaments on the apron, which in turn depends on the orientation and attitude imparted to the array of bundles of filaments along their entire path of travel from the spinning head 11 to the final depositing surface 25 or, with regard to the apparatus, by the geometrical characteristics and reciprocal arrangement of the various components of the apparatus according to the invention.

The movable collecting apron 25 is mounted on a vacuum box, not shown, and has a permeable structure, for example net structure, so that the vacuum below will keep the filaments, which by now have been deposited in the form of a web, adhering together until they are consolidated. The apron may be made to operate either in an open or a closed cycle provided that it ensures a good continuity of the characteristics determining the loss of load so that no significant variations will occur in the regularity of the end web.

The web thus produced is then consolidated by hot calendering through a pair of heated rolls 33 and 34 before leaving the apparatus at the position where the apron returns over a roll 35 (Fig. 5).

The nonwoven web obtained by the apparatus according to the invention is characterized by superior mechanical characteristics distributed very uniformly in each direction thereof.

Claims

CLAIMS:

1. Apparatus for the production of a nonwoven web by spinning continuous filaments, comprising a spinning head (11) with a plurality of spinnerets staggered (14, 15) in two parallel rows (12, 13) and arranged obliquely relative to the normal plane of the direction of advance of an underlying collecting apron (25), a series of cooling chambers (17) for the bundles of produced filaments, a series of accelerating nozzles (22) for the produced filaments, a widening device formed by a series of fixed blades (26) arranged obliquely at the discharge end of said accelerating nozzles (22), a device for distributing said filaments of said bundles on said apron (25) advancing therebelow and a device (33, 34) for consolidating the formed fleece to obtain a nonwoven fabric, characterized by the improvement wherein each of said accelerating nozzles (22) is arranged obliquely relative to the axis of spinning, and said device for distributing said filaments is substantially formed by an array of movable blades (28) arranged in parallel and inclined relative to the plane of said collecting apron 25), said blades being arranged obliquely to the normal plane of the direction of advance of said apron (25) and obliquely relative to each of said accelerating nozzles (22), ech of said movable blades (28) being further arranged for oscillation around an axis (29) coinciding with its upper edge and being provided with means (30, 30') for connection to all the other of said blades (28) for synchronized oscillation of all of said movable blades (28) of said array.

2. Apparatus as claimed in claim 1, wherein said connection means (30, 30') of said movable blades (28) is formed by at least one rod connected to the flanks of said blades and arranged to be actuated with a reciprocating movement.

3. Apparatus as claimed in claim 1, wherein said array of movable blades (28) is oriented parallel to said spinning head (11).

4. Apparatus as claimed in claim 1, wherein each of said spinnerets (14, 15) comprises two separate areas (16, 23) of extrusion holes.

5. Apparatus for the production of a nonwoven web by spinning continuous filaments substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.