EP0060953A1

EP0060953A1 - Textured yarn usable as a crepe yarn

Info

Publication number: EP0060953A1
Application number: EP81306200A
Authority: EP
Inventors: Hardev Singh Bahia
Original assignee: Courtaulds PLC
Current assignee: Akzo Nobel UK PLC
Priority date: 1981-01-02
Filing date: 1981-12-31
Publication date: 1982-09-29
Also published as: JPS5831135A

Abstract

A crepe yarn (12) comprises a core component (1) of continuous thermoplastic filaments and a sheath component (2) of continuous thermoplastic filaments false-twisted around the core component (1) in a sequence of spiral windings of changing hand with filaments of the sheath component (2) adhering to filaments of the core component (1). Such a yarn may be made by a process which comprises taking a yarn (8) in which a sheath component (2) of continuous thermoplastic filaments having an extensibility of at least 60 percent is combined with a core component (1) of continuous thermoplastic filaments having an extensibility at least 30 per cent below that of the sheath component (2), the said components also having a difference of softening temperature, feeding the yarn (8) under tension through a false twist texturising unit (11) employing rotary friction discs at a D/Y ratio in the range 1.39 to 4.0 to false twist the yarn, whereby the sheath component (2) is twisted about the core component (1) in a sequence of spiral windings of changing hand, and heating the false-twisted yarn to a temperature at which the filaments of only one of said components soften, whereby filaments of the sheath component (2) become adhered to filaments of the core component (1). Preferably the filaments of the yarn components are polyester or polyamide filaments.

Description

Conventional crepe yarn is a highly twisted yarn of high torque. The twisting process is comparatively slow and expensive, and the torque in the yarn makes it difficult to process. The present invention is concerned to provide a novel crepe yarn by a new process which is more economic than the conventional one.
According to this invention, a crepe yarn is characterised by a core component of continuous thermoplastic filaments and a sheath component of continuous thermoplastic filaments false-twisted around the core component in a sequence of spiral windings of changing hand with filaments of the sheath component adhering to filaments of the core component.
Preferably one or both of the core component and the sheath component comprises polyester or polyamide filaments.
The invention includes a process for making a crepe yarn which is characterised by taking a yarn in which a sheath component of continuous thermoplastic filaments having an extensibility of at least 60 per cent is combined with a core component of continuous thermoplastic filaments having an extensibility at least 30 per cent below that of the sheath component, the said components also having a difference of softening temperature, feeding the yarn under tension through a false-twist texturising unit employing rotary friction discs at a D/Y ratio in the range 1.39 to 4.0 to false-twist the yarn, whereby the sheath component is twisted about the core component in a sequence of spiral windings of changing hand, and heating the false-twisted yarn to a temperature at which the filaments of only one of said components soften, whereby filaments of the sheath component become adhered to filaments of the core component.
The crepe yarn of the invention has a low level of torque because the sequence of spiral windings of changing hand produces a substantial balance in torque. The form of these spiral windings is maintained because sheath component filaments are adhered to core component filaments. The resulting yarn has the characteristic handle and appearance of a crepe yarn.
The false-twist process of the invention can be carried out at speeds greatly in excess of those used in twisting processes and is more economic. Standard machines can be used with the rotary friction disc texturising units in common use, including those made by Barmag A.G., Ernest Scragg & Sons Ltd., and F.A.G. These usually comprise stacks of friction discs mounted on spindles arranged at the corners of a triangle so that the discs intermesh to provide a tortuous yarn path between them. Preferably the friction rims of the discs comprise or are coated with a ceramic material.
For the process of the invention the sheath component is required to have an extensibility which is at least 60 per cent and which is greater than that of the core component. Yarns suitable for the sheath component include undrawn yarns and partially orientated yarns (POY); particularly of polyamide or polyester filaments.
The core component may comprise a substantially fully orientated yarn produced directly by high speed spinning or by subsequent drawing of POY or undrawn yarn. POY may also be used for the core component in the process of the invention providing it exhibits an extensibility at least 30 per cent below that of the sheath component. Preferably the extensibility is no greater than about 110 per cent and polyester POY spun at 3,500 metres per minute or more will usually satisfy this condition.
As well as the difference in extensibility, the sheath and core components used in the process of the invention are required to have a difference in softening temperature so that the false-twisted yarn may be heated up to a temperature at which one component softens and sticks to the other component whilst that other component does not soften. Preferably there is a difference of at least 10°C between the respective softening temperatures, and this is usually achieved given the required difference in extensibility.
The rotary friction discs false-twist the yarn with the effect that the more extensible sheath component is stretched more than the core component by the induced tension and so becomes wound around the core filaments as a sheath. High-speed photography of the disc and yarn in motion during processing shows a phenomenon associated with this in which the more extensible sheath component is separated from the core component at the rim of the disc and forms an outflung loop.
Excess rotational speed of the friction discs tends to cause breakage of filaments of the more extensible component thereby producing a spun-like yarn rather than the crepe yarn of the invention. Too low a speed can give rise to yarn breakages because of excess tensions and poor control. For these reasons it has been found necessary to use a D/Y ratio in the range 1.39 to 4.0 in the process of the invention. The D/Y ratio is a well-known and used parameter for friction disc texturising and is the ratio of the surface speed of the friction disc to the yarn 'speed at the disc. The optimum value of the D/Y ratio for a given feedstock yarn can be determined by experiment. It is dependent upon the tension which it is desired to apply to the yarn being false-twisted and this tension is usually expressed in terms of the draw ratio applied to the yarn. The draw ratio is the ratio of the surface speed of draw rollers drawing the yarn away from the texturising unit to the surface speed of the feed rollers feeding the yarn to that unit. In general, within the specified range, the D/Y ratio is reduced as the draw ratio is increased.
The draw ratio used depends largely upon the extensibility of the core component. In order to produce a stable product yarn of minimum shrinkage higher draw ratios are used with more extensible core components. A suitable range for the common spectrum of nylon and polyester drawn yarns and POY is 1.02:1 to 1.3:1.
Then in the process of the invention the false-twisted yarn is heated to a temperature at which the filaments of one of the components soften. When both components comprise the same polymer then the component with the lower softening point will be the one with the higher extensibility, i.e. the sheath component. For example, at a yarn speed of 170 metres per minute undrawn nylon 6 yarn begins to soften at about 155°C whereas fully drawn yarn can be processed without softening at temperatures in excess of 190°C. The same is broadly true of polyethylene terephthalate yarn although in that case the undrawn yarn starts to soften at a slightly higher temperature around 160°C.
The conventional heaters used on texturing machines, including contact and radiant heaters, may be used for heating the false-twisted yarn.
The product yarn may be collected as a side-wound package. The adhesion of the filaments makes it unnecessary to insert true twist.
The invention is illustrated by the accompanying drawing in which

Figur 1 is a schematic elevation of one station of a friction false-twist texturing machine, and
Figure 2 is a representation of the crepe yarn of the invention.

Referring to Figure 1, a core component yarn 1 and a sheath component yarn 2 of extensibility greater than 60 per cent are withdrawn overend from cheese packages 3 and 4 respectively by feed rolls 5 of the 'Casablanca' apron type. The core component yarn 1 passes through the tube 6 on which the cheese of sheath component yarn is wound so that the sheath component yarn 2 is lightly wrapped around the core component yarn 1 as they pass together through the guide 7. This is not essential to the invention and the component yarns can be passed through the guide 7 side by side.
The combined yarn 8 is then forwarded between the feed rolls 5 and the draw rolls 9 (also of the 'Casablanca' apron type) and is put under the required degree of tension by regulating the relative speeds of the draw and feed rolls. Prior to the draw rolls, the yarn 8 passes successively through a heater 10 and a friction false-twisting unit 11. The friction false-twisting unit 11 is shown digrammatically as having intermeshing stacks of rotating friction discs. A suitable commercial unit is that made by Barmag A.G. using three stacks, each having three discs, mounted at the corners of a triangle. The discs are preferably ceramic at least at the rims where they contact the yarn. The frictional action of the rotating discs on the yarn passing over their rims is to false-twist it with the effect that in the product yarn 12 the sheath component yarn 2 is twisted around the core component yarn 1 in a sequence of spiral windings of changing hand. This is shown in Figure 2, where a sequence of 'S' twist changes to a sequence of 'Z' twist at the null point 15. This form is stable because the heat applied to the false-twisted yarn by the heater 10 causes filaments of the component with the lower softening point, usually the sheath, to soften and adhere tu filaments of the other component.
The product yarn 12 is collected as a side-wound package 13.
The invention is further illustrated by the following Examples in which equipment as illustrated in the drawing was used with a Barmag texturising unit having ceramic discs. The yarns are identified by decitex and number of filaments in the usual way, for example 44/10. The polyester yarn is a poly(ethylene terephthalate) yarn.

Example 1

Sheath component yarn - 60/5 undrawn nylon 6 spun at 1,000 m/min. (Extensibility of 370 per cent).
Core component yarn - 44/10 fully drawn nylon 6 (2.9:1 draw ratio; (Extensibility of 35 per cent).
Feed rolls speed (m/min) - 167
Draw rolls speed (m/min) - 173
Take-up speed (m/min) - 164
Draw ratio - 1.04
Heater temperature (°C) - 188
D/Y ratio - 2.67
Spindle speed of Barmag unit (rpm)- 2950
Yarn tension (T₁) at entry to
Barmag unit (g) - 7-5
Yarn tension (T₂) at exit from
Barmag unit (g) - 10.0

The product yarn was 100 per cent nylon 6 and had the handle and appearance of a crepe yarn. Its properties were measured and are as shown below.

Properties

Decitex - 100.8
Breaking load (CN) - 140
Breaking extension (per cent) - 34.7
Tenacity (CN/Tex) - 13.9
Initial modulus
(CN/Tex 100 per cent extension) - 28.8
Boiling water shrinkage (per cent) - 11.6
Snarl level (turns per cm) - 1 to 1.5

The yarn also gave 100 per cent recovery up to 10 per cent stretch. When weft knitted in an interlock construction, it produced an attractive crepe fabric with good stretch recovery.

Example 2

Sheath component yarn - 150/25 undrawn polyester spun at 1,200 m/min. (Extensibility of 200 per cent).
Cure component yarn - 78/24 a semi-matt fully drawn nylon 6. (Extensibility uf 35 per cent).
Feed rolls speed (m/min) - 230
Draw rolls speed (m/min) - 250
Take-up speed (m/min) - 250
Draw ratio - 1.09
Heater temperature (°C) - 179
D/Y ratio. - 3.3
Spindle speed of Barmag unit(rpm)- 5300
Yarn Tension (T₁) at entry to Barmag unit (g) - 10.0
Yarn tension (T₂) at exit from
Barmag unit (g) - 12.0

The product yarn was weft knitted in a plain construction to give a crepe fabric with good stretch recovery.
The fabric was dyed with an aqueous dye liquor containing 0.5 per cent by weight of the disperse dye Palanil Blue NB (Colour Index No. Disperse Blue 56) at 50:1 liquor : goods ratio. The fabric was entered into the dye bath at a liquor temperature of 50°C, and then the temperature of the liquor was raised to the boil and held there for 30 minutes. The dyed fabric was rinsed with water, hydro-extracted and dried. The polyester sheath component was dyed blue and the nylon 6 core component was undyed so that the fabric had a marl appearance.

Example 3

Sheath component yarn - 150/25 undrawn polyester spun at 1,200 m/min. (Extensibility of 200 per cent).
Core component yarn - 80/50 POY polyester spun at 3500 m/min. (Extensibility of 120 per cent).
Feed rolls speed (m/min) - 200
Draw rolls speed (m/min) - 250
Take-up speed (m/min) - 245
Draw ratio - 1.25
Heater temperature (°C) - 179
D/Y ratio - 3.14
Spindle speed of Barmag unit(rpm)- 5000
Yarn tension (T₁) at entry to
Barmag unit (g) - 12.0
Yarn tension (T₂) at exit from
Barmag unit (g) - 14.0

The product yarn was 100 per cent polyester yarn with the characteristic handle and appearance of crepe yarn.

Claims

1. A crepe yarn characterised by a core component (1) of continuous thermoplastic filaments and a sheath component (2) of continuous thermoplastic filaments false-twisted around the core component (1) in a sequence of spiral windings of changing hand (15) with filaments of the sheath component (2) adhering to filaments of the core component (1).

-2. A crepe yarn as claimed in claim 1 characterised in that at least one of the sheath and core components (1, 2) comprises polyester or polyamide filaments.

3. A process for making a crepe yarn characterised by taking a yarn (8) in which a sheath component (2) of continuous thermoplastic filaments having an extensibility of at least 60 per cent is combined with a core component (1) of continuous thermoplastic filaments having an extensibility at least 30 per cent below that of the sheath component (2), the said components also having a difference of softening temperature, feeding the yarn (8) under tension through a false twist texturising unit (11) employing rotary friction discs at a D/Y ratio in the range 1.39 to '4.0 to false twist the yarn, whereby the sheath component (2) is twisted about the core component (1) in a sequence of spiral windings of changing hand, and heating the false-twisted. yarn to a temperature at which the filaments of one but only one of said components soften, whereby filaments of the sheath component become adhered to filaments of the core component.

4. A process as claimed in claim 3, characterised in that at least one of the sheath and core components (1,2) comprises polyester or polyamide filaments.

5. A process as claimed in claim 3 or 4, characterised in that the sheath component (2) comprises a partially orientated yarn or an undrawn yarn.

6. A process as claimed in any of claims 3 to 5, characterised in that the core component (1) comprises a partially orientated yarn or a substantially fully orientated yarn.

7. A process as claimed in any of claims 3 to 6, characterised in that the core component (1) has an extensibility which is at most 110 per cent.

8. A process as claimed in any of claims 3 to 7, characterised in that the difference in softening temperature between the sheath and core components (1, 2) is at least 10°C.

9. A process as claimed in any of claims 3 to 8, characterised in that the yarn (8) being false twisted is subjected to a draw ratio in the range 1.02:1 to 1.3:1.

10. A nylun, polyester or mixed polyester/nylon crepe yarn characterised by being produced by a process as claimed in any uf claims 4 to 9.