METHOD OF FORMING FILAMENT WEBS, AND APPARATUS FOR CARRYING OUT THE METHOD

Abstract: Method for forming filament webs which employs a granular polymer held in storage containers and provides the following operational steps in succession: - automatic supply of polymer granules to feed a silo, - compression and melting of the polymer granules in an extruder fed by the silo, - feed of the molten material (11) to a spinning assembly (12), - spinning of the material to produce a plurality of bundles of filaments, - cooling (13) of the bundles of filaments, - aerodynamic drafting (15) and conveying of the bundles of filaments, - aspiration (21) of the bundles of filaments in correspond­ ence with a conveyor belt (20), and - removal of web of filaments thus formed for the subsequent consolidating operations. Machine for forming filament webs according to the above method.

Description: This invention concerns a method to form non-woven fabrics. To be more exact, the invention concerns a method suitable to treat polymer granules so as to produce a plurality of manmade filaments, which are deposited in a uniform and ordered manner on a movable conveyor belt so as to form the non-woven fabric (see US-A-4496508). The method according to the invention provides for polymer granules to be taken automatically from storage containers and delivered to a silo. The silo feeds an extruder unit in which the polymer granules are compressed and brought to a molten condition. For this purpose the present applicant has found advantageous a pressure in the range of 70 to 100 atmospheres and a temperature in the range of 280°C to 310°C. While in the molten condition, the material is sent to and distributed among a plurality of spinning units, each of which comprises a spinneret. Suitable pump means arrange to extrude the material through the holes of each spinneret, thereby obtaining a set of filaments descending freely in a vertical line. These filaments are cooled during their vertical descent with controlled volumes of air, the temperature of which is also controlled. The filaments coming from each spinneret are introduced into an ejector unit positioned below the relative spinneret and fed with air circulating downwards from above. The number of ejector units is the same as the number of spinning units. The filaments in the ejector units are drafted by aerodynamic action and are drawn downwards until they leave the ejector units. The applicant has found by trials that drafting in the range of 200% to 300% is advantageous. The filaments which have left their respective ejector units and have been drawn farther downwards by the flow of air flowing from the ejector units cooperate with a distributor means capable of oscillating in a direction crosswise to the axis of the filaments. This distributor means, the extent of oscillation of which is advantageously between 1 mm. and 10 mm., provides for the orderly depositing of the filaments cooperating with it on a horizontal conveyor belt below the distributor means. The conveyor belt, which is driven at a suitable speed coordinated with the spinning speed, is positioned at an angle to the line of depositing of the plurality of the filaments on the conveyor belt. The combined action of the oscillatory motion of the distributor means and of the motion of forward movement of the conveyor belt obtains depositing of the filaments in successive layers on the conveyor belt as each layer tends to be superimposed on the neighbouring layer in the direction of movement of the conveyor belt. Contiguous layers are deposited at the same time across the conveyor belt in a number the same as the number of spinning units comprised in the plant or working in the plant. Aspiration means to fix the material on the surface of the conveyor belt while the material is still in the deposition phase are included at the lower surface of the conveyor belt. The material thus deposited has a fibrous structure with isotropic characteristics. Thereafter the material with the fibrous structure has to be thermoset and then calendered and wound on appropriate supports. The invention is therefore obtained with a method according to the characterization of Claim 1 and the dependent claims. The attached figure, which is given as a non-restrictive example, shows a diagram of a plant to produce non-woven fabrics which employs the method according to the invention. A polymer brought to a molten state in an extruder connected to a feeder silo (not shown in the figure) enters at 11 a spinning assembly 12 of a plant 10 that spins and forms non-woven fabrics. The spinning assembly 12 consists of spinning units of a rectangular type positioned parallel to each other; the number of the spinning units is coordinated with the width of the non-woven fabric to be produced. Each spinning unit comprises a distribution head, a false spinneret and a spinneret, the latter being provided with a row of holes arranged lengthwise in it. The molten polymer is fed to the spinneret by a metering pump and is forced through the holes thus arranged lengthwise, thus forming a plurality of parallel filaments descending freely towards the lower part of the plant 10. Each spinning unit is advantageously a modular unit which can be installed in or removed from the spinning assembly 12. The filaments are cooled below the spinning assembly 12 in a cooling assembly 13 in which the temperature and volume of cold air are controlled continuously. In this example the cooling assembly consists of a set of parallel diffusers connected to a cold-air generation system and to an assembly of ducts 14 to convey the air, the diffusers being positioned between the rows of holes in the spinnerets of the spinning units. During their descent the cooled filaments from each spinneret cooperate with a drafting assembly 15 consisting of ejectors 16, which are positioned parallel in a number the same as that of the spinnerets of the spinning assembly 12. The ejectors 16 have an intake of a length, in the lengthwise direction, coordinated with the length of the corresponding spinnerets. Each ejector 16 of the drafting assembly 15 consists advantageously of two parallel metallic walls extending vertically so as to form a conduit holding the filaments of the respective spinneret. The present applicant has found advantageous a distance between 800 cms. and 1200 cms. from the spinneret to the intake of the ejector 16. The parallel metallic walls of the ejector 16 near its intake comprise a horizontal slit; each slit is connected to a duct 17 communicating with a manifold conveying air under pressure, the manifold being connected in turn to suitable means for the production of compressed air. The horizontal slit in the walls constitutes in itself the throttled passage of a Venturi tube, and therefore the air under pressure entering through the slits into the interior of the metallic walls and flowing downwards produces the required drafting action on the filaments and at the same time causes the filaments to be conveyed towards the outlet of the ejectors 16. The filaments leaving each ejector 16 cooperate with a distributor means 18 capable of alternating motion on a horizontal plane. The extent and frequency of the oscillation of the distributor means 18 can be adjusted as required. The distributor means 18 consists substantially of a frame divided into segments, each segment in its inactive position being positioned in correspondence with the outlet of each ejector 16. Each segment consists of two parallel guide surfaces suitable to contain and guide laterallly the filaments leaving each ejector 16. The oscillatory movement of the distributor means 18 together with the action of the air leaving each ejector 16 and drawing with it the plurality of filaments produces an orderly, homogeneous distribution of the bundles of filaments on a conveyor belt 20 located below the distributor means 18. In this example the conveyor belt consists of an endless belt 20, which is formed of a mesh having a pre-determined ratio of empty spaces to solid portions. The conveyor belt 20 is driven advantageously by a speed change unit and cooperates with a suction box 21 having a width the same as that of the belt 20. The non-woven fabric thus formed and anchored to the mesh of the belt 20 is taken by the latter to a subsequent thermosetting station. The depositing of the layers of filaments on the conveyor belt 20 takes place, not orthogonally to the direction of advance of the belt 20, but according to a line suitably angled in relation to that direction of advance since the spinning assembly 12, cooling assembly 13, drafting assembly 15 and distributor means 18 are positioned in that manner in relation to the conveyor belt 20.

Claims: Method to form non-woven fabrics, which employs a granular polymer held in storage containers and comprises at least the following operational steps in succession: automatic supply of polymer granules to feed a silo, compression and melting of the polymer granules in an extruder fed by the silo, feed of the molten material (11) to a spinning assembly (12) consisting of a plurality of spinning blocks placed side by side, parallel and able to move, spinning of the material to produce a plurality of bundles and substantially parallel filaments, each bundle being arranged in a linear manner, cooling (13) of the bundles of filaments, aerodynamic drafting (15) and conveying, with ejectors (16), of the bundles of filaments into a distributor means (18) together with delivery to, and depositing on, a conveyor belt (20), aspiration (21) of the bundles of filaments deposited on the conveyor belt (20), and removal of the non-woven fabric thus formed for the successive finishing operations, the method being characterized in that the distributor means (18) comprises a frame divided into a plurality of parallel segments, placed side by side, with vertical sidewalls, each segment with its sidewalls cooperating with the respective bundles of filaments leaving the relative spinning blocks so as to contain and guide those bundles laterally, the lengthwise axis of the bundles of linearly arranged filaments being positioned at an angle to the lengthwise axis of the forward movement of the conveyor belt (20), the distributor means (18) being capable of a movement of lateral oscillation. Method as in Claim 1, in which the relative movement of lateral oscillation of the distributor means (18) is between 1 mm. and 10 mm. Method as in Claim 1 or 2, in which the width of the non-woven fabric formed on the conveyor belt (20) can be changed by inserting or removing spinning blocks. Method as in any claim hereinbefore, in which the aerodynamic drafting of the filaments leaving the ejector assembly is contained within a range between 200% and 300%.

Inventors: GERIN, UMBERTO, LANCEROTTO, FABIO, MERONI, ROBERTO, STOIA, JOHN
Applicants: NON WOVENS TECHNOLOGY S.P.A.
Application year: 1988
Main classification: D04H3
IPC codes: D04H3