GB2069556A - Core yarns - Google Patents

Abstract

A core yarn fibrous sheath is spun about a core in the form of a flat ribbon or tape.

Description

SPECIFICATION Improvements in or relating to core yarns and a method of producing same This invention relates to core yarns.

Core yarns, which may be of any suitable material either natural or synthetic, are wellknown and consist generally of a central core around which a fibrous sheath is wound. The core is generally in the form of a continuous filament, which may be either monofilament or multifilament, although it could be a spun yarn which is produced in a spinning process prior to the spinning process in which the final core yarn is produced. In all cases the core, whether monofilament or multifilament, is of generally circular cross-section having a generally smooth exterior surface in the axial direction. The sheath fibres are wound around the central core in the form of a multiplex helix. Accordingly, in the finished core yarn the core extends axially within the yarn surrounded by the helically wound sheath.

The production of such core yarns is described in British Patent No. 1, 518, 771 which discloses a spinning machine incorporating two perforated suction drums located close to each other so as to form a nip therebetween. The drums are arranged to rotate in the same direction. The core material is fed into the nip of the two spinning drums in a direction parallel to the axes of the drums. At the same time, carded fibre produced from a sliver is blown into the nip of the rotating spinning drums by means of an air jet. The fibres are fed into the nip in a direction substantially tangential to the cooperating surfaces of the drums. The rotational movement of the spinning drums results in the fibres being twisted around the central core by a mechanical rolling-off action. The formed yarn is then drawn away from the forming zone by delivery rollers and wound on bobbins.

Such previously proposed core yarns have been found to be useful in practice but have suffered from certain disadvantages. For example, the core, whether monofilament or multifilament, is substantially smooth in the axial direction and consequently there is a tendency for relative axial movement to take place between the core and the sheath so that the core can become bared easily.

Furthermore, when core-less or multifilament core yarn is used as a weft yarn in woven secondary backing fabrics, e.g. for carpets, there is a tendency for a reduction in width of the woven fabric to take place during weaving.

An object of the present invention is to obviate or mitigate the aforesaid disadvantages.

According to the present invention there is provided a core yarn including a core comprising a flat ribbon or tape, and a fibrous sheath spun about said core.

Preferably, the flat ribbon or tape forming the core is deformed e.g. by twisting.

According to a further aspect of the present invention there is provided a method of producing a core yarn comprising feeding a flat ribbon or tape to a forming zone to form the core of the core yarn, and spinning a fibrous sheath around said flat ribbon or tape at said forming zone to form the core yarn.

Preferably the flat ribbon or tape is deformed at the forming zone e.g. by twisting prior to the fibrous sheath being spun about the core.

By the expression "ribbon or tape" as used herein is meant an elongated material which is essentially flat. British Standard 461 1; 1976 defines a tape yarn as "flat yarn having a high ratio of width to thickness, manufactured by film or spinnaret extrusion processes." Such yarns are normally monofilaments composed of synthetic resinous materials e.g. polypropylene. The core however can be of any other suitable flat ribbon or tape material such as a cellulosic material.

Normally the ratio of width to thickness would be at least 3:1.

Embodiments of the invention will now be described by way of example.

A core yarn is produced on a spinning machine of the type described in British Patent No.

1,518,771 and which includes a pair of perforated spinning or suction drums mounted adjacent each other with their axes parallel to each other in a horizontal plane. The drums are mounted for rotation in the same direction and so as to define a nip therebetween.

A continuous monofilament in the form of a flat fibrillated ribbon or tape of polypropylene, i.e. a tape yarn, is fed into the nip between the two spinning drums in a direction substantially parallel tp the axes of the drums. A polypropylene tape having an approximate width of 2.1 mm and an approximate depth of 0.03 mm has been found satisfactory but it will be appreciated that sudh dimensions are capable of substantial variation.

Simultaneously a plurality of single polypropylene fibres produced from a carded silver are fed into the nip between the spinning drums with the support of an air jet. The area over which the fibres contact the axially moving ribbon or tape constitutes a forming zone in which the ribbon or tape becomes the core of the final product and the fibres are wound in substantially helical fashion around the outer periphery of the core to form the sheath of the final product. During formation of the core yarn in the forming zone, the core ribbon or tape is deformed by the action of the spinning rollers so that it assumes an irregular crosssection due to the ribbon or tape being twisted and possibly crushed by the action of the spinning drums. Alternatively the core ribbon or tape could be fed to the forming zone in a pre-twisted or precrushed state.

The core yarn thus produced is led off over delivery rollers and wound on to bobbins.

A satisfactory product has been obtained utilizing polypropylene tape of 64 tex or 78 tex.

In an alternative embodiment in accordance with the invention, the tape or ribbon used to form the core is fibrillated prior to its passage to the core yarn forming zone of the spinning machine.

Such fibrillation takes the form of a plurality of spaced slits in the ribbon or tape and normally extending longitudinally thereof. Particularly on deformation of the ribbon or tape by twisting or crushing, the edges of the slits tend to separate from each other and add to the irregular exterior surface of the core. This provides edges additionai to the peripheral edges of the core tape or ribbon to assist in preventing relative longitudinal movement between the core and the spun sheath.

As previously indicated the core and sheath materials can be of any suitable natural or synthetic composition, e.g. acrylic or nylon.

It has been found that core yarns in accordance with the present invention provide an arrangement in which the sheath fibres adhere more satisfactorily to the core tape than is the case with core yarn produced using a multifilament core of generally circular cross-section which has a smooth exterior surface in the axial direction.

Accordingly, there is less tendency for relative axial movement to take place between the sheath and the core, presumably due to the irregular crossection of the core. It has also been found that if predetermined heat shrinkage properties are built into the tape which is to form the core, then these heat shrinkage properties tend to be imparted to the final yarn.

A secondary advantage of the present invention is that flat tapes of the type described above are less expensive than multifilament yarn.

Core yarn in accordance with the invention has been found to be particularly suitable in the production of woven fabrics e.g. for use as secondary backing materials for carpets or sack manufacture. During the weaving of such fabrics wherein the core yarn of the invention is used as the weft, it has been found that the use of such core yarns cause much less reduction in width during weaving as compared to other yarns such as core-less or multifilament yarns. It has been found, in the weaving or such fabrics, that the use of a polypropylene core having a colour different from the fibres of the covering sheath tends to give the finished woven fabric a more natural texture or appearance.

Although in the above described embodiment, the flat ribbon or tape forming the core is preferably deformed as by twisting, it is thought that some of the advantages at least of the invention will be obtained using merely a flat ribbon or tape which is not deformed.

Claims (16)

1. A core yarn including a core comprising a flat ribbon or tape, and a fibrous sheath spun about said core.

2. A yarn as claimed in claim 1, in which the flat ribbon or tape is deformed to produce an exterior surface to the core which is irre'gular in the axial direction.

3. A yarn as claimed in claim 2 in which the deformation is produced by the ribbon or tape having been twisted about its longitudinal axis or crushed.

4. A yarn as claimed in any preceding claim in which the ribbon or tape is a tape yarn (as hereinbefore defined).

5. A yarn as claimed in any preceding claim in which the ribbon or tape is a monofilament.

6. A yarn as claimed in any preceding claim in which the ribbon or tape is fibrillated.

7. A yarn as claimed in any preceding claim, in which the ribbon or tape has a width to thickness ratio of at least 3:1.

8. A method of producing a core yarn comprising feeding a flat ribbon or tape to a forming zone to form the core of the core yarn, and spinning a fibrous sheath about said flat ribbon or tape at said forming zone to form the core yarn.

9. A method as claimed in claim 8, comprising deforming the flat ribbon or tape prior to the fibrous sheath being spun about the core in order to produce an exterior surface to the core which is irregular in the axial direction.

1 0. A method as claimed in claim 9, in which the deformation is effected prior to or during the formation of the core yarn.

11. A method as claimed in claim 10, in which the deformation is effected by twisting the ribbon or tape about its longitudinal axis or by crushing.

12. A method as claimed in any of claims 8 to 11, in which the ribbon or tape is a tape yarn (as hereinbefore defined).

13. A method as claimed in any of claims 8 to 12, in which the ribbon or tape is fibrillated.

14. A method as claimed in any of claims 8 to 13, in which the ribbon or tape has a width to thickness ratio of at least 3:1.

15. A core yarn as claimed in claim 1, substantially as hereinbefore described. -

1 6. A method of producing a core yarn as claimed in claim 8, substantially as hereinbefore described.

1 7. A woven fabric comprising at least in the weft direction core yarn as claimed in any of claims 1 to 7 and 1 5.