GB2247697A

GB2247697A - Improvements relating to apparatus for use in producing non-woven webs from thermo-plastic

Info

Publication number: GB2247697A
Application number: GB9115824A
Authority: GB
Inventors: Ian David Slack
Original assignee: Extrusion Systems Ltd
Current assignee: Extrusion Systems Ltd
Priority date: 1990-09-07
Filing date: 1991-07-23
Publication date: 1992-03-11
Also published as: GB9019580D0; GB9115824D0

Abstract

The present specification discloses a method and apparatus for use in producing non-woven webs from thermo-plastic polymer materials. The apparatus comprises a chamber (11) through which a movable conveyor (13) extends, the chamber (11) being connected to evacuation means (23) which can create a partial vacuum in chamber (11). A tapered duct (17) connects with chamber (11) above conveyor (13) and extends generally vertically upwardly from a position beneath a spinnerette (31). The upper end of duct (27) is open to the atmosphere and has a larger cross- sectional throughflow area than the lower end region thereof, which communicates with chamber (11). Thus evacuation means (23) in effect draws air into duct (27) so that the filaments produced by spinnerette (31) are entrained in the air flow and accelerated by the air flow along tapered duct (27). On entering the chamber (11) the air flow velocity reduces but the momentum of the filaments causes them to disperse randomly and be collected on conveyor (13). The non-woven web is subjected to heat bonding, calendering or needling process. <IMAGE>

Description

DESCRIPTION IMPROVEMENTS RELATING TO APPARATUS FOR USE IN PRODUCING NON-WOVEN WEBS FROM THERMO-PLASTIC POLYMER MATERIALS The present invention relates to apparatus for use in producing non-woven webs from thermo-plastic polymer materials.

Non-woven webs of thermo-plastic polymer materials are produced by the process of spinning fine denier fibres from molten polymer, stretching and accelerating the fibres to thus draw down the molten polymer fibres, and then, whilst the molten fibres are still under tension, cooling the fibres to cause them to solidify, thereby locking in the elongation to provide molecular orientation in the cooled fibre.

The fibres so produced are randomly projected onto a moving perforated conveyor belt to form a continuous web.

One known form of apparatus for completing the above process is disclosed in U.S. Patent Specification No. 4,405,297, this apparatus comprising a spinnerette which is arranged to produce molten fibres in a chamber which connects with a downwardly directed duct. Air under pressure is fed into the chamber to one side of the fibres, the majority of the air passing down the duct thereby stretching, accelerating and tensioning the fibres aS they pass along the duct. The remainder of the air cools the fibres and is extracted from the top region of the chamber, the fibres being collected on a moving, perforated, conveyor belt as they issue from the lower end of the duct into the ambient atmosphere.The main problem with this known construction is that air is introduced into the chamber under pressure and the pressure must be controlled as otherwise it will either be too great resulting in fibre breakage or too little, and the fibre will not have the desired dimensions and strength. Further as the fibres issue from the spinnerette in a closed chamber access to the spinnerette is not easy and also, it is not easy to observe any faults occurring due to blocked spinnerette capillaries, etc.

The aim of the present invention is to provide apparatus for use in producing non-woven webs from thermo-plastic polymer materials, wherein the above problems are obviated.

According to the present invention there is provided apparatus for use in producing non-woven webs from thermo-plastic polymer materials, said apparatus comprising a chamber through which a movable conveyor extends, the chamber being connected to evacuation means which can create a partial vacuum in the chamber, a tapered duct connecting with the chamber above the conveyor and extending generally vertically from a position beneath a spinnerette, the upper end region of the duct being open to the atmosphere and having a larger cross-sectional throughflow area than the lower end region of the duct, which communicates with the chamber.

Under working conditions air is evacuated from the chamber creating a partial vacuum within the chamber, which results in atmospheric air in the region of the spinnerette being drawn into the upper end region of the duct and accelerated along the duct due to the tapered construction of the duct. Molten filaments emerging from the spinnerette are carried by the flow of air down the duct and the frictional resistance of the moving air acting on the filaments, creates a tension in the filaments and accelerates the filaments with the flow of air. The flow of atmospheric air from the region around the spinnerette induces a current of air which flows between the individual filaments, thereby progressively cooling the filaments so that they solidify as they pass down the duct.As the air flow enters the chamber the air velocity decreases due to the expansion allowed and eddies and vortices are formed in the air flow.

However, whilst the air velocity decreases at this point the filaments continue at high speed by virtue of the kinetic energy imparted whilst passing through the narrow lower end region of the duct where air velocity is at a maximum. The eddy currents and vortices cause the individual cooled filaments to separate from one another and they are projected, in a random manner, through the chamber onto the surface of the conveyor belt where they are collected as a random laid web, the web constantly moving along with the conveyor and exiting the chamber.

In a preferred embodiment of the present invention the duct has aerofoil-shaped sides which cause the air to accelerate with substantially laminar flow along the duct, and to decelerate as the air flow enters the divergent area at the aerofoil-shaped sides at the lower end region of the duct.

Further, the conveyor preferably passes between sealing rollers to enter and exit the chamber with the conveyor being preferably perforated. In operation a pressure drop occurs across the perforated conveyor belt with the higher pressure being above the belt.

This pressure helps to maintain the web in contact with the conveyor belt and reduces the likelihood of the filaments moving about on the conveyor belt.

In practice any number of spinnerettes and tapered ducts may feed a single chamber and conveyor so that the production rate may be proportionately increased. Alternatively filaments of different cross-sectional shapes or different polymers may be produced at each spinnerette.

After the web emerges from the chamber it may be subjected to a heat bonding, calendering or needling process for compacting and interlacing the individual filaments from which it is composed. Further or alternatively, the web can be rolled up for storage or transportation.

The present invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 schematically illustrates in vertical cross-section, a preferred embodiment of the present invention; Fig. 2 schematically illustrates part of the embodiment of Fig. 1 feeding a hot bonding machine; Fig. 3 schematically illustrates part of the embodiment of Fig. 1 feeding a calendering machine; and Fig. 4 schematically illustrates part of the embodiment of Fig. 1 feeding a needling machine.

The preferred embodiment of the present invention shown in Fig. 1 of the accompanying drawings comprises a chamber 1 having a top wall 3, bottom wall 5, end walls 7 and 9, and side walls 11, only one of which is evident in the cross-sectional view of the accompanying drawing. A perforated conveyor 13 extends across the chamber 1, the conveyor 13 entering the chamber 1 between rollers 15, each of which rollers is sealed to the end wall 7 by sliding seals 17, and exiting the chamber 1 between rollers 19 each of which is sealed to end wall 9 by sliding seals 21.

Evacuation means in the form of a fan 23 located in exit duct 25, are provided in the bottom wall 5 of the chamber 1 and a tapered duct 27 opens into the chamber 1 via the top wall 3. Any other suitable evacuation means can, of course, be substituted.

The tapered duct 27 is formed by two aerofoilshaped sides 29 which are placed back-to-back, so that they define an elongated venturi-shaped duct 27.

Placed a distance above the centre line of the duct 27 is a spinnerette 31 connected to a source 33 of molten polymer. The bottom side of the spinnerette 31 is provided with capillaries which are spaced apart so that atmospheric air may freely pass between the filaments as they are drawn down from the spinnerette 31.

Under working conditions, the air is evacuated through duct 25 by fan 23 creating a partial vacuum within the chamber (1). Atmospheric air in the region of the spinnerette is drawn into the upper entrance of the duct 27 and the aerofoil shaped sides 29 cause the air to accelerate with substantially laminar flow through duct 27.

The molten filaments emerging from the spinnerette 31 are carried by the flow of air down the duct 27 and the frictional resistance of the moving air acting on the filaments creates a tension and accelerates the filaments with the flow of air.

The flow of atmospheric air from the region around the spinnerette induces a current of air to flow between the individual filaments, thereby progressively cooling them so that they solidify as they pass down the duct 27.

As the air flow enters the elongate divergent area 34 at the trailing edge of the aerofoil sides 29, the air velocity decreases as the air is allowed to expand, and eddies and vortices are formed in the air flow. Although the air velocity is decreasing at this point due to expansion, the filaments continue at high speed by virtue of the kinetic energy imparted whilst passing through the narrow section of duct 27 where air velocity is at a maximum. The eddy currents and vortices cause the individual cooled filaments 25 to separate from one another and they are projected, in a random manner, through the chamber 1 onto the surface of the conveyor belt 13 where they are collected as a random laid web 35, the web 35 constantly moving along with the conveyor 13 and exiting from the chamber 1 between rollers 17.

In operation, a pressure drop occurs across the perforated conveyor belt 13, with the higher pressure above the belt. This pressure helps to maintain the web 35, in contact with the conveyor belt 13 and prevents the filaments from moving about on the conveyor belt 13.

Whilst the illustrated embodiment shows a chamber (1) with a single duct 27 and a single spinnerette 31, it is envisaged that a machine with a single chamber having multiple inlet ducts and spinnerettes, would enable the production rate to be proportionately increased. Alternatively different polymers could be used at each position to provide webs of composite layers.

After the web 35 emerges from the apparatus, it can be subjected to a heat bonding (Fig. 2), calendering (Fig. 3) or a needling process (Fig. 4) for compacting and interlacing the individual filaments from which it is composed. Hot bonding (Fig. 2) is carried out by passing the web 35 between one or two heated rollers 37. Calendering (Fig. 3) is carried out by passing the web 35 around roller 39 and through press nips 41 and 43. Needling (Fig. 4) is carried out by passing the web 35 through a needling machine 45 which has a cyclically movable needle platen 47. Further or alternatively the web can be rolled up on a winder 49 for storage or transportation.

Claims

1. Apparatus for use in producing non-woven webs from thermo-plastic polymer materials, said apparatus comprising a chamber through which a movable conveyor extends, the chamber being connected to evacuation means which can create a partial vacuum in the chamber, a tapered duct connecting with the chamber above the conveyor and extending generally vertically from a position beneath a spinnerette, the upper end of the duct being open to the atmosphere and having a larger cross-sectional through flow area than the lower end region of the duct, which communicates with the chamber.

2. Apparatus as claimed in claim 1, in which the duct has aerofoil-shaped sides arranged back-to-back so that the duct gradually tapers from its upper end towards the narrowest part of the duct, which is nearer to the chamber than to the upper end of the duct, the duct then diverging before it opens into the chamber.

3. Apparatus as claimed in claim 1 or claim 2, in which the conveyor passes between sealing rollers to enter and exit from the chamber.

4. Apparatus as claimed in any one of claims 1 to 3, in which the conveyor is perforated.

5. Apparatus as claimed in any one of claims 1 to 4, in which two or more spaced apart ducts extend generally vertically upwardly from the chamber, each duct being located beneath a spinnerette.

6. A method of producing non-woven webs from thermo-plastic polymer materials comprising the steps of producing a number of filaments using a spinnerette, the filaments being directed generally vertically downwardly towards the open upper end of a tapered duct which leads to a chamber, producing a partial vacuum in said chamber so that air is drawn into the upper end of said duct, said air flow entraining and accelerating the filaments through the tapered duct, air flow velocity reducing as the air enters the chamber so that the moving fibres diverge from each other randomly and collect on a conveyor moving through the chamber, the web thus formed exiting the chamber on the conveyor.

7. A method as claimed in claim 6, in which air is extracted from the chamber from beneath the conveyor, the conveyor being perforated so that the air flow through the conveyor holds the filaments on the conveyor to thus form the web.

8. A method as claimed in claim 6 or 7, in which the web is subjected to a heat bonding, calendering or needling process for compacting and interlacing the individual filaments from which it is composed.

9. Apparatus for use in producing non-woven webs from thermo-plastic polymer materials, constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

10. A method of producing non-woven webs from thermo-plastic polymer materials substantially as hereinbefore described with reference to the accompanying drawings.