GB1600063A

GB1600063A - Process for the production of a core and sheath yarn

Info

Publication number: GB1600063A
Application number: GB636078A
Authority: GB
Original assignee: Akzo NV
Current assignee: Akzo NV
Priority date: 1978-02-17
Filing date: 1978-02-17
Publication date: 1981-10-14

Description

(54) PROCESS FOR THE PRODUCTION OF A CORE AND SHEATH YARN (71) We, AKZO N.V, of IJSSEL LAAN 82, Arnhem, Netherlands, a body corporate organised under the Laws of the Netherlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a process for the production of a core and sheath yarn; more particularly, it relates to a process for the production of a core and sheath yarn in which the sheath component is wrapped round the core component alternately clockwise and anti-clockwise and to an apparatus for carrying out the process.

Processes and apparatus for the production of so-called core and sheath yarns are known. In German Offlenlegungsschrift No.

1,908,219, for example, a process is described for the production of a wool-like mixed yarn consisting of a core component and one or more sheath components, in which one or more multifilament yarns are delivered to a multifilament yarn forming the core component at right-angles or approximately at right angles to the axis of the latter multifilament yarn within the false twisting zone. The entire yarn may subsequently be subjected to a second heat treatment and then twisted.

In another known process, described in French Patent No. 1,251,346, two yarns in front of the heating device of a false twisting station were delivered at different velocities to a yarn guide eyelet which exactly determined the point at which the two yarns met, and from there, the yarns were passed together through the false twisting device.

This process, however, did not produce a core and sheath yarn. The two yarns brought together in front of the false twisting device lay strictly parallel to each other after leaving the device.

The technical problem to be obviated by the present invention involves producing a core and sheath yarn in which the core component is wrapped round the sheath component alternately in the clockwise and anticlockwise directions.

The present invention provides a process for the production of a core and sheath yarn wherein the sheath component loops round the core component alternately in the S- and the Z-direction, which comprises delivering multifilament sheath component to the multifilament core component from the side at an angle of at least 150 and with at least 10% overfeed at the inlet of a friction false twisting apparatus and passing the two components together over the false twistproducing friction surface which is moved substantially at right-angles to the general direction of movement of the components, the friction between the components and the friction surface periodically being reduced to less than 50% of the normal value momentarily. By "normal value" referring to the friction is meant that value which becomes established when the other parameters are maintained, but the measures for briefly reducing the friction are omitted.

The core and sheath yarn may subsequently be treated to produce the resistance to shifting and may then be wound. In a preferred embodiment of the process according to the present invention, the overfeed of the sheath component may amount to from 20 to 50%. The ratio of the number of reductions in friction per minute to the velocity of the core component in metres per minute is preferably from 10:1 to 350:1, although ratios of up to 600:1 may quite well be feasible, depending on the chosen velocity.

According to the present invention, the desired resistance to shifting may be produced by known means, such as the application of size, blow treatments which cause the individual filament to intermesh without forming loops and the method of winding a so-called cross-ply round the yarns.

According to a preferred embodiment of the present invention, the sheath component may be a textured yarn produced by cnmp- ing.

It may be advantageous to ensure that, between its discharge from the working surface of the friction false twisting apparatus and the treatment to increase the shifting resistance, the core and sheath yarn only comes into contact with yarn guide devices of the type the surface of which follows the movement of the yarn, such as yarn guide rollers.

An apparatus according to the present invention for carrying out the present process, based on known single spindle friction false twisting apparatus, is distinguished in that the working surface of the individual friction false twister has one or more notches on the circumference which comes into contact with the yarn. It has been found advantageous if that part of the working surface of the false twisting apparatus which is left unchanged amounts to at least 25% of the total surface. On the other hand, the notches should cover at least 25% of the total working surface which comes into contact with the yarn. According to a particular embodiment of the present invention, the notches are asymmetric in that they drop steeply on what is seen as the front edge when viewed in the direction of rotation and uniformly rise again to the level of the normal working surface at the rear end of the notch.

A very pronounced change in the character of the finished product is obtained as a result of the distance which is established between the points at which the direction of twist of the sheath component is reversed and of the intensity or density with which this sheath component is wrapped round the core component. It has been found that these properties may be influenced to a considerable extent both by the overfeed for the sheath component and by the component tension ratios. However, the amount of variation is fluid and depends upon several factors, such as the material used, the yarn titre and the individual titre, the individual filament count, the particular false twisting apparatus used and the number of notches on the circumference, so that the overfeed and component tensions necessary to produce the desired result may most easily be determined by experiments.

The effects of the measures according to the present invention was surprising. There was no doubt that the brief reduction in the component tension, optionally to 300, for example due to the component dropping into a notch, was responsible for the alternation in the direction of the spiral of the core component. At the same time, however, it was found that the distance between the points at which a change in the direction of the spiral takes place does not correspond to a simple relationship between the component velocity and the speed of rotation of the false twisting apparatus, but may vary very considerably as a result of a change in the other factors mentioned above. It seems probable, however, that the frequency of the change in component tension, based on the component velocity, represents a lower limit for the distances between the reversing points so that the number of reversing points occurring per unit time cannot be more frequent than, for example, the number of contacts per unit time between the component and the surfaces situated between the notches.

The present invention will now be illustrated with reference to the accompanying drawings, wherein Fig. 1 represents schematically the layout of an apparatus for carrying out the process according to the present invention; Fig. 2 represents a yarn produced according to the present invention; Fig. 3 is a top plan view of the working surface of a friction false twisting apparatus showing a notch; Fig. 4 is the same as Fig. 3, but with two notches; Fig. 5 is a longitudinal section through a known friction false twisting apparatus; and Fig. 6 is a longitudinal section through a friction false twisting apparatus according to the present invention.

Fig. 1 represents schematically the general layout of an apparatus for carrying out the process according to the present invention. The multifilament core component 2 is delivered from a supply spool 1 of stretched filaments and drawn off through a guide 3 and between a first delivery mechanism 4, 5 and then passed through a fixing device 6, a known single friction false twisting apparatus 7 and a second delivery mechanism 8, 9 to the winding spool 10 which is driven by the drive cylinder 11. A second multifilament component, which may already have a false twist crimp, is delivered to the core component 2 from a second supply spool 12 by way of a guide 13 and brake 14, and encounters this core component 3 at some point between the fixing device and the false twisting device and is then passed together with the core component through the false twisting device. The two components leave the friction false twister together in the form of a core and sheath yarn produced by the process according to the present invention, having a sheath 16 wound alternately in the S- and the Zdirection, and are wound in this form.

If desired, an apparatus for applying a size to render the yarns resistant to shifting, followed by a drying apparatus, may be arranged between the second delivery mechanism 8, 9 and the winding mechanism 10, 11. In some cases, depending on the density of the yarn leaving the false twister, the treatment with size may be replaced by a blow treatment to intermesh the individual filaments forming the yarn, in which case the knots of the intermeshing occur mainly at the points of reversal in the direction of the spiral of the sheath component.

To carry out the process according to the present invention, is is not absolutely necessary to use a supply spool 1 of already stretched filaments. The process may also be integrated with a stretch texturing process, but in that case a so-called sequential process should be employed so that the component leaving the first delivery mechanism 4, 5 is stretched. This first delivery mechanism 4, 5 may be designed as the delivery mechanism which stretches the component.

The friction false twisting apparatus 7 employed is a single spindle apparatus in which the component is passed over a friction surface which rotates in a plane preferably inclined at an angle to the general direction of movement of the component, in particular substantially of right-angle.

According to the present invention, this friction surface is formed so that one or more changes in component tension occur during one revolution of the friction surface. This may be achieved by means of notches on the friction surface, as indicated in Figs. 3, 4 and 6. Fig. 5 represents a known friction apparatus 7', while Fig. 3 represents the friction surface 26 of a false twist apparatus 7 which, according to the present invention, has a notch 21. The shaded area 21 (shading was used for the sake of clarity) represents the notch. It is produced by cutting a piece out of the friction surface 26 as indicated in Fig. 6. Although the edge 25 which lies in the direction of movement of the component is preferably slightly rounded off, it drops fairly steeply, but from the lowest point the notch gradually rises to the level of the working surface 26. The depth of the notches 21, 22 is not drawn to scale.

According to the present invention, the depth may be between 0.5 and 10 mm, and for components of higher titre even more, and it depends on the dimensions of the friction ring, particularly its height, external and internal diameter and surface radius measured in cross-section, as well as on the yarn titre.

Figs. 3 and 4 only represent the possibilities provided with one and with two notches 21, 22 on the circumference of the friction surface 26, but the number of notches may be larger and depends in particular on the size or diameter of the friction surface 26, the intended speeds of rotation in operation and the titres of the components used.

Fig. 2 represents a core and sheath yarn 16 produced by the process according to the present invention. The sheath component 28 is wrapped round the core component 27 with varying degrees of density and the direction of the sheath component round the core component changed from clockwise to anti-clockwise at irregular intervals. The reference numeral 17 in the Figure, for example, shows a zone in which the sheath component has a pronounced clockwise direction, while at 19 it takes an anticlockwise direction. A reversal point 18 is also clearly seen between these two zones.

Another point of reversal 18 may also be seen at the lower end of the piece of yarn, but here it has a relatively loose form.

The appearance of the yarn, particularly with regard to the intensity of wrapping the sheath round the core and the distance between the point of reversal may be influenced to a considerable extent, for example, by varying the component tensions, the number of notches arranged on the circumference of the friction surface, the speed of rotation of the friction apparatus, the depth of the notches and the component velocities.

It was, in any case surpnsing to find that such an effect is achieved by the particular form of the friction surface used according to the present invention for carrying out the present process.

WHAT WE CLAIM IS: 1. A process for the production of a core and sheath yarn wherein the sheath component loops round the core component alternately in the S- and the Z-direction, which comprises delivering multifilament sheath component to the multifilament core component from the side at an angle of at least 15 and with at least 10% overfeed at the inlet of a friction false twisting apparatus and passing the two components together over the false twist producing friction surface which is moved substantially at rightangles to the general direction of movement of the components, the friction between the components and the friction surface periodically being reduced to less than 50% of the normal value momentarily.

2. A process as claimed in claim 1 in which the core and sheath yarn is subsequently treated to produce sufficient resistance to shifting of the sheath component in relation to the core component and is wound.

3. A process as claimed in claim 1 or claim 2 in which the overfeed of the sheath component is from 20 to 50%.

4. A process as claimed in any of claims 1 to 3 in which the ratio of the velocity of the core component in metres per minute to the number of reductions in friction per minute is from 1:10 to 1:350.

5. A process as claimed in any of claims 1 to 4 in which, after leaving the false twisting zone, the core and sheath yarn is treated with a size which renders it resistant to shifting of the sheath component in relation to the core component, which size is dried

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. filaments forming the yarn, in which case the knots of the intermeshing occur mainly at the points of reversal in the direction of the spiral of the sheath component. To carry out the process according to the present invention, is is not absolutely necessary to use a supply spool 1 of already stretched filaments. The process may also be integrated with a stretch texturing process, but in that case a so-called sequential process should be employed so that the component leaving the first delivery mechanism 4, 5 is stretched. This first delivery mechanism 4, 5 may be designed as the delivery mechanism which stretches the component. The friction false twisting apparatus 7 employed is a single spindle apparatus in which the component is passed over a friction surface which rotates in a plane preferably inclined at an angle to the general direction of movement of the component, in particular substantially of right-angle. According to the present invention, this friction surface is formed so that one or more changes in component tension occur during one revolution of the friction surface. This may be achieved by means of notches on the friction surface, as indicated in Figs. 3, 4 and 6. Fig. 5 represents a known friction apparatus 7', while Fig. 3 represents the friction surface 26 of a false twist apparatus 7 which, according to the present invention, has a notch 21. The shaded area 21 (shading was used for the sake of clarity) represents the notch. It is produced by cutting a piece out of the friction surface 26 as indicated in Fig. 6. Although the edge 25 which lies in the direction of movement of the component is preferably slightly rounded off, it drops fairly steeply, but from the lowest point the notch gradually rises to the level of the working surface 26. The depth of the notches 21, 22 is not drawn to scale. According to the present invention, the depth may be between 0.5 and 10 mm, and for components of higher titre even more, and it depends on the dimensions of the friction ring, particularly its height, external and internal diameter and surface radius measured in cross-section, as well as on the yarn titre. Figs. 3 and 4 only represent the possibilities provided with one and with two notches 21, 22 on the circumference of the friction surface 26, but the number of notches may be larger and depends in particular on the size or diameter of the friction surface 26, the intended speeds of rotation in operation and the titres of the components used. Fig. 2 represents a core and sheath yarn 16 produced by the process according to the present invention. The sheath component 28 is wrapped round the core component 27 with varying degrees of density and the direction of the sheath component round the core component changed from clockwise to anti-clockwise at irregular intervals. The reference numeral 17 in the Figure, for example, shows a zone in which the sheath component has a pronounced clockwise direction, while at 19 it takes an anticlockwise direction. A reversal point 18 is also clearly seen between these two zones. Another point of reversal 18 may also be seen at the lower end of the piece of yarn, but here it has a relatively loose form. The appearance of the yarn, particularly with regard to the intensity of wrapping the sheath round the core and the distance between the point of reversal may be influenced to a considerable extent, for example, by varying the component tensions, the number of notches arranged on the circumference of the friction surface, the speed of rotation of the friction apparatus, the depth of the notches and the component velocities. It was, in any case surpnsing to find that such an effect is achieved by the particular form of the friction surface used according to the present invention for carrying out the present process. WHAT WE CLAIM IS:

1. A process for the production of a core and sheath yarn wherein the sheath component loops round the core component alternately in the S- and the Z-direction, which comprises delivering multifilament sheath component to the multifilament core component from the side at an angle of at least 15 and with at least 10% overfeed at the inlet of a friction false twisting apparatus and passing the two components together over the false twist producing friction surface which is moved substantially at rightangles to the general direction of movement of the components, the friction between the components and the friction surface periodically being reduced to less than 50% of the normal value momentarily.

before the yarn is wound.

6. A process as claimed in any of claims 1 to 4 in which the resistance to shifting of the sheath component in relation to the core component is produced by interlacing the individual filaments without the formation of loops mainly at the points of reversal in the direction of rotation.

7. A process as claimed in any of claims 1 to 6 in which a yarn which has been textured by a crimp treatment is supplied as sheath component.

8. A process as claimed in claim 1 substantially as herein described with particular reference to the accompanying drawings.

9. An apparatus for carrying out a process as claimed in any of claims 1 to 8 which comprises a single spindle friction false twisting apparatus, the friction surface of which being provided with one or more notches.

10. An apparatus as claimed in claim 9 in which the un-notched friction surface amounts to at least 25% of the total contact surface.

11. An apparatus as claimed in claim 9 or claim 10 in which the notches amount to at least 25% of the total contact surface of the friction surface.

12. An apparatus as claimed in any of calims 9 to 11 in which the notch or notches are asymmetric and drop steeply on that edge which is seen as the front edge in the direction of rotation and uniformly ascend to the level of the normal contact surface at the rear end of the notch.

13. An apparatus as claimed in claim 9 substantially as herein described with particular reference to the accompanying drawings.

14. A core and sheath yarn when produced by a process as claimed in any of calims 1 to 8.