EP1240368A2 - Improved process and apparatus for stretching slivers of animal fibres - Google Patents

Abstract

A method and apparatus for creating a transient equivalent of thermoplasticity in wool or animal fibres, such that they can be extended by substantial amounts without breaking and without requiring to be at high moisture regain or chemically treated to increase plasticity. In one version a process is provided for stretching sliver in which the sliver is passed in a substantially straight line path through a stretching zone from feed rollers to a single haul pulley unit. False twist generated by the haul pulley unit is freely propagated along the sliver uninhibited by contact with pulleys or other devices.

Description

IMPROVED PROCESS AND APPARATUS FOR STRETCHING SLIVERS OF

ANIMAL FIBRES

FIELD OF THE INVENTION The invention relates to animal fibre processing. More particularly, although not exclusively, the invention relates to an improved process and apparatus for modifying

the diameter, length and crimp of wool and animal fibres. The modifications may be

temporary or permanent depending on the process conditions selected.

BACKGROUND TO THE INVENTION

Stretching With Temporary Set

Fibres which have high shrinkage, usually 1 5 to 30%, have various applications

known to the textile industry. They are used as a component of 'high-bulk' yarns for

knitting, that is yarns which have an unusually large ratio of volume to mass. They are also used to make high shrinkage yarns which are mixed with yarns of low or zero shrinkage in woven fabrics to produce cockled effects, such as seersucker. They

may also be used to produce yarns of high shrinkage which form some of the tufts in

a pile fabric, such as carpet, so that the difference in shrinkage between the tufts of high and low shrinkage will produce high and low pile or long and short tufts in order to form a visual pattern. It is preferable that the potential shrinkage of fibres for these purposes can be realised by a simple and inexpensive process, such as steaming.

A method of producing fibre of high shrinkage potential, which is well known and

extensively used, is to stretch thermoplastic fibre while it is hot and relatively plastic, to cool it while it is still held in an extended state and thereby stabilise it. Since the fibre is not completely plastic but is visco-elastic during the hot-stretch process, some elastic strain energy is created within the molecular structure of the fibre, but

this energy is not sufficient to overcome the relative immobility of the structure after cooling and so cause shrinkage. When the fibre is subsequently heated, the structure

of the fibre becomes more mobile and the 'latent' elastic strain energy is enabled to cause shrinkage. The most common application of this method is in the production of high shrink acrylic fibres which are blended during textile processing with fibres of much lower shrinkage, usually also acrylic fibres, to produce knitting yarns of high

bulk due to a differential shrinkage effect When the blended yarn shrinks, fibres

having low shrinkage characteristics are caused to buckle or to form helices of increased radius in the twisted yarn structure so as to increase the volume of the yarn. Although the mass of a longitudinal element of the yarn is increased as a result

of the shrinkage, the volume is increased to a greater degree, thus causing the

desired increase in the ratio of volume to mass. Lighter weight garments can be

produced as a result of this technique.

The hot-stretching process used to create the high shrinkage potential is carried out

on the acrylic fibre while it is still in continuous filament form Techniques to stretch and temporarily set continuous filament tows are known to the industry. Here, the words 'temporarily set' refer to filaments which are stabilised in an extended condition such that the filament has a potential shrinkage which can be realised by a subsequent treatment such as steam relaxation. The word 'tow' refers to a

substantially twist-free bundle of parallel filaments, usually several thousand in number. The continuous filaments are then usually converted to discontinuous staple fibres for further textile processing into yarn. The difficulty of stretching and temporarily setting fibres such as wool, which do not occur in continuous filament form and are not thermoplastic, has until recently prevented the industry from applying the concept of stretch and temporarily setting to wool and animal fibres.

Consequently these fibres have been placed at a technological disadvantage and their use in high bulk yarns has been hampered. The principal factors disadvantaging wool

and animal fibres in this context are that:

1 . Such fibres are discontinuous and a strand comprised of wool fibres will normally attenuate by "drafting" de, fibres will slip in relation to their neighbours at much

lower applied attenuating force than is required to stretch the fibres themselves).

2. Such fibres are not thermoplastic de, they cannot normally, by control of temperature alone, be rendered plastic and capable of being substantially

stretched without breaking).

A number of attempts to stretch and set wool slivers are referred to in the following patents:

1 . Preventing drafting of a continuous twistless strand of wool fibres called a "sliver" by gripping the sliver using clamps at closely spaced intervals of distance (less than the length of most of the fibres) and causing the clamps to move apart during the process: UK patent 1 , 1 89,994.

2. Preventing the drafting of a wool sliver by gripping the sliver using rollers at closely spaced intervals of distance (less than the length of most of the fibres) and causing successive roller groups to increase progressively in surface speed: USP 5,459,902.

3. Twisting the sliver sufficiently to prevent drafting under the large applied attenuating forces required to stretch the fibres: UK patent 1 , 1 96,41 9.

4. Twisting the sliver temporarily while in the stretching process, known to the

industry in many other applications as "false twisting", although the twist is real but temporary, in order to prevent drafting: USP 4,961 ,307 (Cooke), and PCT

WO 91 /02835 and USP 5,758,483 (Phillips and Thomas) .

Most of the patents refer to the use of steam to effect temporary set de, temporary

stabilisation in the extended fibre condition). Here, the sliver is held in the extended

condition within an atmosphere of saturated steam, which is known to the industry to be an effective means of achieving temporary set. In most of these patents, some

degree of pre-plasticising of the wool fibres is described. This may be effected simply by the addition of water or may be an addition of an aqueous solution of a reducing

agent, such as sodium metabisulphite, both of which are known to the industry as methods of increasing the plasticity of wool. Reduction of the disulphide bonds in

wool fibres, followed by reformation of the bonds in water or steam is widely used, for example in the wool carpet industry for twist stabilisation.

Pre-treatment of the wool fibres with a reducing agent to plasticise them facilitates a more permanent setting or stabilisation of any imposed deformation of the fibre (twist, length extension or bending) . Thus the industry is familiar with such techniques for controlling the degree of set from very temporary to highly permanent. Despite the existence of the above patents, in some cases for more than two

decades, the techniques described have not led to widespread usage for provision of either temporarily or permanently set extended wool or animal fibres. The reasons are thought to be that the use of moving close-spaced clamps or the use of a twisting 5 process, followed by a stretching and setting process, followed by a de-twisting

process are not economically viable. Although false twisting is long-known to the

textile industry, patents describing its use in the context of stretching staple (wool)

fibres are relatively recent and these patents, PCT WO 91 /02835 and USP 5,758,483 describe processes which may be limited in their usefulness to the ι o industry because they require a relatively complex series of multiple pulleys,

significant process dwell times in steam and significant demand for energy to effect

substantial reductions in moisture regain in the wool.

Permanently-set Diameter and Curvature Changes

15 Finer wool fibres are generally valued more highly. They can be spun to finer yarns than coarser fibres, which permits lighter weight fabrics to be made, and they feel

softer to the touch. It is therefore not surprising that the patents described above in

the context of the stretch with temporary set, also provide methods of stretching with permanent set, in order to effect a reduction in fibre diameter which is

0 substantially unaffected by steam or water.

It is also not surprising that the above patents share similar chemical pre-treatments and post-treatments. Rendering wool fibres more plastic by breaking some of the disulphide bonds in the fibre using a reducing agent, usually sodium metabisulphite, is well known and widely practised by some sectors of the wool industry. Following

such reduction treatments, an after-treatment consisting of repeated aqueous rinsing

or rinsing in solutions of hydrogen peroxide is also well-known and practised as a means of encouraging re-formation of the disulphide bonds in the fibre and substantially eliminating metabisulphite residues in the fibre.

Examples of commercial processes using this reduce/process/re-oxidise chemistry are

the tape-scour and WRONZ/ADM Group Ltd Twist-set process described in the

following publications:

WRONZ Techline No. T1 . The WRONZ Chemset Yarn Processing System, October

1 988;

J Ince, Setting wool yarns for cut-pile carpets. Wool Science Review, 50, November

1 974, 2;

E A Forbes and J H Dittπch, JSDC, 96, 1 980, 10.; and

The Manufacture of Wool Carpets. Editor G H Crawshaw. The Textile Institute,

Manchester, 1 987, 29.

A treatment for stabilising wool carpet yarns and the subsequent hydrogen peroxide treatment of such yarns before beck or winch dyeing of cut-pile carpet is described in

the following publication: C T Page, P W Robinson, S A Edwards and W W Connelly,

Winch Beck Dyeing of Wool Carpets. Australasian Textiles, 10/2, March/April 1 990, 52. The use of fabric after-treatments with oxidising agents, including hydrogen peroxide, is also known to the industry for stabilising wool by increasing the permanence of reduction setting treatments employing sodium bisulphite or other

reducing agents, for example, see: A G de Boos, J Delmenico and M A White,

Permanent Press Effects in Wool, Part VII: Stabilising Set with Additives to the Wash Liquor. Journal of The Textile Institute, 62, 1 971 . 1 98.

In summary, the wool textile industry has available well-known technology based on chemical reduction of disulphide bonds within the fibre, followed by manipulation or

constraint of the textile material to the desired shape or configuration (eg, flat fabric, pleated fabric, twisted yarn) and finally followed by an oxidation treatment to reverse

the initial reduction cleavage of the disulphide bonds. These treatments are usually known in the wool textile industry as "permanent setting" treatments.

It is an object of the present invention to provide a process which overcomes or at

least ameliorates a number of the abovementioned disadvantages and to provide an improved process for stretching and temporary setting in the resulting extended condition of wool fibres with a simplified apparatus which offers a useful alternative choice.

It is a further object of the invention to identify processing conditions in which the

process will enable fibre curvature (crimp) to be modified. Ordinarily a stretching process would be expected to reduce the curvature of a wool fibre to a level which is less than that of the untreated fibre. Fibre curvature affects the processing

performance and end product characteristics and is a property of considerable

commercial significance. SUMMARY OF THE INVENTION

The invention provides for a method of creating a transient equivalent of

thermoplasticity in wool or animal fibres, such that they can be extended by substantial amounts without breaking and without requiring to be at high moisture

regain or chemically treated to increase plasticity.

In one aspect, the invention provides a process for stretching sliver in which the

sliver is passed in a substantially straight line path through a stretching zone from

feed rollers to a single haul pulley unit, such that false twist generated by the haul

pulley unit is freely propagated along the sliver uninhibited by contact with pulleys or

other devices.

In another aspect, the invention provides an apparatus for continuously stretching

and temporarily or permanently setting wool or animal fibres in sliver form,

comprising a single haul pulley unit imparting false twist to the sliver and providing in a stretching zone stretching traction, a microwave drier creating a drying zone which rapidly increases the temperature and reduces the regain of the false-twisted sliver

and a substantially straight line sliver path through the stretching and drying zone from feed rollers to the haul pulley unit.

The scope of the invention further includes:

(a) a version of the process which provides fibres which are stretched and temporarily set (ie, stabilised such that they remain stretched until exposed to

steam or water); (b) a version of the process which provides fibres which, by comparison with unprocessed fibre, are permanently set and have either:

• reduced diameter with reduced curvature (crimp)

• increased curvature substantially without change of diameter

• certain combinations of reduced diameter and restored or increased curvature.

Depending on the combination of diameter and crimp, the fibre length may be

increased or decreased and the lustre of the fibre may be increased.

TEMPORARILY SET STRETCH In a particular aspect, the invention provides for a process for stretching and

temporary setting of animal fibres comprising:

placing a microwave or radio frequency energy applicator in a stretching zone so

that a false twisted wool or animal fibre sliver can be substantially simultaneously

rendered adequately plastic for stretching at relatively low moisture regain and stretched

According to yet another aspect of the present invention there is provided an

improved process for continuously stretching and temporarily setting wool or other

animal fibres and thus providing fibres having high shrinkage potential, which can

conveniently be realised in a steam relaxation treatment or in a water relaxation treatment.

Preferably the processes further comprise the step of using a combined false twisting and traction providing haul pulley flyer downstream of the energy applicator and outside of the energy application zone such that the path of the sliver through the

energy applicator is substantially straight.

The process further comprises the application of microwave or radio frequency, but preferably microwave, energy, to heat the sliver throughout its thickness very rapidly.

For the production of temporarily set stretched fibre, preferably a moisture regain of

1 9 to 25 % , more preferably 20 to 23%, is used and is obtained by passing "dry" (ie, approximately in equilibrium with ambient air) sliver or top, through a steam tube so designed as not to deposit droplets of condensed steam on the fibre. Preferably a

reduction in moisture regain to 1 0 to 1 5 %, more preferably 1 2 to 1 4% is effected so

as to effect temporary setting.

The present invention also provides for a process for stretching and temporary setting

of animal fibres comprising achieving a mobile plastic fibre state at moderate, preferably 19 to 25%, moisture regain, by increasing the fibre temperature rapidly to

a level above the glass transition temperature at that level of regain by means of a

linear microwave or radio frequency heater located in a straight zone in which the sliver is plasticised, stretched and then progressively dried as it passes along the

straight zone.

In a further aspect, the present invention provides for a single modified haul pulley flyer adapted to cause a sliver to exit the flyer along the axis of rotation, and which is located downstream of a stretching and drying zone such that the sliver path is substantially straight from feed rolls to the flyer. The straight sliver path facilitates

use of a linear heater and equalisation of sliver torque throughout the stretch zone.

The microwave or radio frequency heating can be augmented by the passage of

warm air through the tubular cavity of the heater.

Further aspects of the invention which should be considered in all its novel aspects

will become apparent from the following descriptions which are given by way of

example only

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example only and with reference to

the accompanying figures in which:

• Figure 1 illustrates in graph form the glass transition temperature of wool as a

function of water content,

• Figure 2 illustrates an apparatus for creating false twist and at the same time providing hauling traction;

• Figure 3 illustrates the rope making industry's Spinning Jenny which embodies a haul pulley device similar to that in Figure 2;

• Figure 3a is the condenser and nipper;

• Figure 3b shows the direction of rotation of hauling capstans;

• Figure 4 illustrates in graph form the relationship between stretched sliver regain, degree of micron reduction and crimp curvature; and • Figure 5 illustrates a general arrangement for a stretch apparatus according to the

invention.

Prior art methods of heating include creating an atmosphere of steam around the sliver, as described in PCT WO 91 /0283. This requires much longer periods of time to heat the core of sliver which is in a twisted, tensioned and therefore dense

condition. Heat applied to the surface of such a strand requires substantial time to

diffuse to the core. It is possible therefore, by the use of a microwave or radio frequency heater, to create an environment within and throughout the radial extent of the twisted sliver of high temperature approaching or even exceeding 100 °C

together with a moisture content which has not yet substantially changed from its

original or input level. It has been found by extensive experimentation that a moisture

regain of 1 9 to 25 % but preferably 20 to 23% is adequate to permit high levels of

stretch, 40 to 60%, to be safely applied to wool sliver and that a reduction in moisture regain to 1 0 to 1 5 % but preferably 1 2 to 1 4% is adequate to effect

temporary setting.

The invention provides a process which enables the object of stretching and

temporary setting to be achieved with a regain change of only 7 to 10% which minimises energy consumption.

Without being bound by any particular theory, it is believed that this apparent

transient thermoplasticity in wool in the given conditions can be described as follows: Wool like most polymeric solids is subject to a temperature and moisture dependent

second-order transition from a glass-like stiff state to a more mobile, more plastic state. The transition from stiff to plastic states occurs as the temperature is increased through a temperature called the glass transition temperature. In wool, the glass transition temperature is highly moisture dependent, being relatively low when

the wool fibre moisture regain is high and appreciably higher when the fibre regain is relatively low (see Figure 1 ) . By providing in a stretch-set process wool fibre that is in

the relatively mobile plastic state characteristic of fibre that has a higher regain than

that at the glass transition boundary at that temperature, it is possible to take advantage of the plastic condition in order to achieve stretching without excessive

stress and to effect temporary setting by drying the wool in its stretched condition

until its moisture regain is on the dry side of the glass transition.

Alternatively and a preferred subject of the present invention, the mobile plastic state

can be achieved at moderate levels of moisture regain, 1 9 to 25%, by increasing the fibre temperature to a level above the glass transition temperature at that level of

regain. Most methods of heating reduce the regain by evaporation which increases the glass transition temperature. Microwave or radio frequency heating enables the

temperature in the dense false twisted sliver to be raised very rapidly and crucially

before significant evaporation and drying has occurred. Thus is created a transient state in which the wool sliver of moderate moisture regain is rendered plastic and amenable to high levels of stretch. The only known alternative means of achieving this state of plasticity in the interior of a twisted dense sliver under tension at such

low levels of moisture regain is to soak the twisted dense sliver in steam for a

lengthy dwell time. The present invention, by using microwave or radio frequency heating, permits the same state to be achieved very rapidly and in the absence of an externally applied steam atmosphere

The invention permits the wool sliver to pass in a substantially straight path, without

the need to pass around pulleys or guides, through the entire zone in which it is

plasticised, stretched, partially dried, cooled and temporarily set. This straight path

has three advantages:

1 . It facilitates passage of the sliver through a linear heating chamber containing the

microwave or radio frequency electrical fields and no problems require to be

addressed due to the presence of pulleys or guides in strong electrical fields.

2. It automatically provides for location of the extension at the optimum point or short zone along the sliver when it has achieved maximum plasticity or minimum tensile modulus as the sliver heats up. Because the sliver heats rapidly, the

temperature gradient along the silver is steep and the location at which stretch occurs is substantially static (ie, it does not advance and retreat by large

distances which would lead to irregular levels of set).

3. It automatically provides equal torque at all points along the sliver in the stretch-

set zone. Hence as the sliver stretches and becomes thinner, twist (ie, false

twist) is redistributed such that the thinner stretched sliver receives more twist than the earlier unstretched section of the sliver. By this means is avoided any

requirement to have additional apparatus to adjust twist level as the sliver stretches, such as those described in PCT WO 91 /02835. An exemplary embodiment of a process according to the invention will now be

described:

The stages of a process according to the present invention can be as follows:

1 . Supplying the process with a sliver of wool or other animal fibres, that is a

continuous strand of fibres resembling a twist-free rope, typically of 28 to 60

grams per metre linear density. This may be carded sliver or carded and gilled

sliver or combed sliver.

2. Adjusting the moisture regain of the sliver to the desired range 1 9 to 25 % but preferably 20 to 23%, by passing the sliver through a double-walled tube

supplied with live steam (ie, saturated steam at approximately atmospheric pressure) . This also serves to pre-heat the sliver. Alternatively, the sliver may be

pre-conditioned (stored) in an atmosphere which results in the same range of

regain. After adjustment of the regain, the sliver is supplied at a controlled rate by a pair of feed (nip) rolls which also serve as a twist block.

3. Twisting the sliver with sufficient twist substantially to prevent drafting (ie,

slippage of the fibres relative to their neighbours). The degree of twisting

required to prevent drafting may be specified in terms of twist factor, a parameter conventionally used in the textile industry to indicate degree of

twisting. Twist factor is defined as the twist in turns per metre multiplied by the square root of the sliver linear density in grams per 1 000 metres. A twist factor of 2000 to 3000 is likely to be adequate to prevent drafting, with the lower end of the range being appropriate for long fibres and the higher end of the range for shorter fibres. The process is not limited to this range of twist factors, which are

given by way of example. The twist inserted by the present invention is not permanent twist, but temporary twist. The sliver is in a twisted condition only during the time when it passes through the stage of the process when it is highly

tensioned and it is untwisted as it leaves this zone. This process of inserting

twist which exists in a textile strand temporarily and for the duration of the passage of the strand through a process zone or stage is known to the industry

as false twisting, despite the fact that the twist is real but temporary.

4. Stretching the sliver in the same zone of the process in which it is in a twisted state. The extension may typically be 40 to 60% for sliver which is to be

temporarily set and has not been pre-treated with a reducing agent.

5. The traction to effect the sliver stretching and the twist to prevent drafting of fibres during this stretching are both provided by a haul pulley flyer of the type

that is widely used in the rope, cordage, hard-fibre and bast fibre industries; D Himmelfarb, The Technology of Cordage Fibres and Rope. Leonard Hill (Books)

Ltd, London, 1 957, Figure 1 2 and pp 1 27-1 47; and A V Pπngle, The Mechanics of Flax Spinning. H R Carter Publications Ltd, Belfast, 1 954.

In these industries the twist inserted is usually required to be 'real' or permanent twist and this outcome is achieved by rotating the collection package (usually a large bobbin) with respect to the strand axis (see Figure 3) . In the present

invention the twist is not required to be 'real' or permanent but preferably to be 'false' or temporary and therefore the collection package downstream of the haul pulley flyer is not rotated with respect to the strand axis. An example of a modified haul pulley flyer is shown in the attached Figure 2. In Figure 2, the

apparatus for creating false twist consists of a framework E carrying capstans B and pulleys C. Pulleys C act only as guides to change the sliver direction The framework rotates (driven) about the centre line x-y. In use the sliver moving in the direction of the arrows shown has false twist at A and is substantially twist- free at D. The capstan rollers B are circumferentially grooved as are the guide

rollers or pulleys C. The capstan rollers B also rotate about their own axes in order to provide traction. This is an adaptation of a well known apparatus in the

public domain.

A further important feature of the process and apparatus is that only a single

haul pulley flyer unit is required, which reduces string-up time and this haul pulley

flyer unit is located downstream of the stretching zone and drying zone, such

that the sliver path is substantially straight from feed rolls to the flyer. In this straight zone is located a linear microwave or alternatively radio frequency

heater, but preferably a microwave heater, through which the sliver passes and is rapidly heated, plasticised, stretched and then progressively dried as it passes along the zone. The microwave (or radio frequency) heater is substantially the

only energy source for heating and then drying. An ancillary low volume warm airflow through the microwave heater tubular cavity is provided to remove the evaporated moisture which would otherwise eventually saturate the cavity.

While the sliver is twisted and extended, the cumulative drying effect of the heat input in the microwave field and of the hot sliver subsequently passing across an

air gap of at least 2 to 3 metres and then being rapidly rotated in air by the whirling haul puliey flyer, reduces the moisture regain sufficiently to effect temporary setting. The cooling effect of the air gap and whirling in air at the

haul pulley aids the setting effect. Experimentation has shown this to be achieved if the regain is less than 1 5%, but preferably 12 to 14%.

8. Collecting the sliver in a conventional can coiler, known to the industry. The can coiler is driven at a controlled speed just adequate to collect the delivered sliver, but not apply undue tension to it which might induce irregular drafting.

Alternatively, the stretched sliver may be collected as twisted (ie, having real

twist) sliver on a bobbin mounted within the haul pulley flyer (ie, by using the

flyer in the manner familiar to the rope industry and illustrated in Figure 3 where 8 is the chain sheet, 9 is the condenser and nipper, 1 0 is the twist pulley, 1 1 is

the hauling capstan, 1 2 is the flyer sprocket and 1 3 is the tension pulley). If this

option is used, then a subsequent process is required to untwist the sliver so that

it may be processed in the next stage of textile processing which may be gilling or opening and carding. In Figure 5 is shown a general arrangement of parts for an example of stretch apparatus. In this example a sliver 7 is supplied from a creel 1 to a pre-steamer 2 to

squeeze rollers 3. The sliver 7 then passes in a false-twisted state through

microwave dryer 4 to the haul pulley flyer 5. The sliver is then collected by any suitable collection means such as a can coiler 6. PERMANENTLY-SET STRETCH

A further application of the process and apparatus disclosed is to supply the stretch- set apparatus with sliver which has been pre-plasticised by a chemical reductive

treatment, known to the industry, such that a greater degree of permanence of set is

achieved. A further increase in degree of set can be achieved by increasing the distance between the microwave or radio frequency heater and the haul pulley flyer and optionally surrounding the sliver with a steam atmosphere. Yet a further increase in degree of set or permanence of stretch may be achieved by an oxidising after- treatment, for example with hydrogen peroxide solution, known to the industry for

this application, or a cross-linking treatment, for example with formaldehyde, known

to the industry for this application.

An exemplary embodiment of a process for producing permanently stretched fibre

according to the invention will now be described. The stages of a process according

to the invention can be as follows:

(a) Treat wool or animal fibre sliver or top with a chemical reduction agent such as

sodium metabisulphite solution for example in the following preferred conditions:

- sodium metabisulphite 1 0 to 30 g/l

- temperature 80 to 85°C

- time 1 .5 to 10 minutes

- pH 5 to 7.5

The higher concentrations of metabisulphite are combined with the shorter times

and vice versa.

(b) Reduce the sliver moisture regain to 45 to 60% by the use of squeeze rollers.

(c) Stretch the sliver substantially as described in Stages 3 to 6 of the process previously described for effecting temporary-set stretch, with the following important exception. The stretch or extension applied to the sliver is typically but

not necessarily exclusively 60 to 90% . (d) Select the input of microwave energy in order to control the regain of the sliver

or top after the exit of the stretching zone in order to select the level of crimp curvature and micron reduction in the processed sliver, according to the following

generalised parameters:

i. for minimum crimp curvature and maximum micron shift, use minimum sliver

regain, typically less than 10% for sliver treated with 10 g/l metabisulphite

and less than 20% for sliver treated with 20 g/l metabisulphite,

n. for maximum crimp curvature and minimum (or even zero) micron shift, use

high sliver regain, typically 30 to 60% and not more than 1 5 g/l metabisulphite pre-treatment,

in. for close to maximum micron shift, typically 90 to 100% of maximum micron shift and a crimp curvature typical of the stretched micron in natural

wools, use sliver regain in the range 20 to 40% for sliver treated with 10 to

1 5 g/l metabisulphite.

The generalised parameters for controlling crimp curvature and degree of micron

shift describe selected outcomes from a continuum illustrated in Figure 4, which

shows the effect of stretching wool over a range of sliver regains. Importantly these regain values are the regains at the exit of the stretching zone.

The following embodiments of the invention are given by way of example without restricting the application of the invention. Example 1

A sliver of 28.6 micron wool was treated with 1 0% sodium metabisulphite solution at 85°C and then squeezed in nip rolls as it entered the stretch zone of the process

such that the moisture regain was reduced to approximately 60% . It was stretched

by 65 % and at the same time dried as it passed through a tubular microwave oven, so that it emerged from the stretch zone with a moisture regain of approximately 8%.

The diameter and crimp curvature of the fibre after steam relaxation as measured by the OFDA method (Optical Fibre Diameter Analyser, IWTO Test Method 47) were as follows. The fibre length (Almeter method) and the yellowness (Y-Z) are also shown.

Diameter Curvature Fibre length Yellowness

(micron) (°/mm) (barbe mm) (Y-z), ^•;

Untreated 28.6 66 97 5.8

Stretched 24.2 29 1 1 8 3.2

The stretched fibre was finer and had lower crimp curvature, increased fibre length and reduced yellowness (ie, it had a whiter colour). Example 2 A sliver similar to that described in Example 1 was pre-treated with metabisulphite in the same conditions. It was squeezed and stretched in the same conditions as in Example 1 , with the important exception that less microwave power was supplied,

such that the moisture regain of the sliver after the stretch zone was approximately 35%. After steam relaxation of the sliver, the fibre diameter, crimp curvature, fibre length and yellowness were as follows. Diameter Curvature Fibre length Yellowness^*** (micron) (°/mm) (barbe mm) (Y-Z)

Untreated 28.6 66 97 5.8 Stretched 24.9 82 1 04 3.0

The stretched fibre was finer (although the diameter reduction was only 1 3% as compared to 1 5% in Example 1 ) . The crimp curvature and fibre length were increased and the yellowness was decreased.

Since the present invention is a process and apparatus for stretching wool, it is obvious that combination of a stretching process with permanent setting treatments

known to the industry will enable the industry to benefit from the invention in

providing a permanently set stretched fibre, as well as the temporarily set version

previously described.

Thus by the invention there is provided an improved process and apparatus for

stretching slivers of wool or animal fibres, which may advantageously be used either for the production of temporarily set stretched fibre having high shrinkage potential or for the production of permanently set stretched fibre having reduced diameter, increased length and modified crimp curvature.

Particular examples of the invention have been described and it is envisaged that

improvements and modifications can take place without departing from the scope of the attached claims.

Claims

1 . A process for stretching sliver in which the sliver is passed in a substantially

straight line path through a stretching zone from feed rollers to a single haul pulley unit, such that false twist generated by the haul pulley unit is freely propagated along the sliver uninhibited by contact with pulleys or other

devices.

2. A process as claimed in Claim 1 whereby false twist in the stretching zone is

automatically distributed within the stretching zone such that there is constant torque along the sliver and therefore greater twist (turns per metre) where it is needed at the stretched and thinner parts of the sliver.

3. A process as claimed in Claim 1 or Claim 2 in which rapid heating and drying

of the densely packed sliver is effected by passing the sliver through a microwave field which acts as a drier.

4. A process as claimed in Claim 3 wherein the microwave field is constrained in a tubular wave guide.

5. A process as claimed in Claim 3 or Claim 4 in which the substantially straight line path of the sliver without pulleys or guides enables the sliver to pass conveniently through the microwave field.

6. A process as claimed in any one of Claims 3 to 5 in which sliver which is to be temporarily set in a stretched state is plasticised to a small degree by passing through a steam tube situated before the feed rollers of the stretching zone, which increases the temperature of the sliver to approximately 100°C

and increases the sliver regain to at least 1 9°C and in which process the sliver

regain is subsequently reduced by the microwave drier to less than 14°C.

7. A process as claimed in Claim 6 in which the sliver is temporarily set using a

regain change of 7 to 1 0%

8. A process as claimed in any one of the preceding claims wherein the set provided to the fibres of the sliver is temporary set.

9. A process as claimed in any one of claims 1 to 9 wherein the set provided to the fibres of the sliver is permanent set.

10. A process as claimed in Claim 9 wherein greater permanence of set is achieved by chemical reduction of the fibres before stretching, such as with a

metabisulphite treatment.

1 1 . A process as claimed in Claim 9 or claim 1 0 wherein greater permanence of

set is achieved by either increasing the distance between the microwave drier and the haul pulley flyer or surrounding the sliver with a steam atmosphere.

1 2. A process as claimed in Claim 1 1 wherein yet a further increase in the degree of set is provided by either an oxidising aftertreatment or a cross-linking treatment.

1 3. An apparatus for continuously stretching and temporarily or permanently

setting wool or animal fibres in sliver form, comprising a single haul pulley unit imparting false twist to the sliver and providing in a stretching zone stretching

traction, a microwave drier creating a drying zone which rapidly increases the temperature and reduces the regain of the false-twisted sliver and a

substantially straight line sliver path through the stretching and drying zone from feed rollers to the haul pulley unit.

14. An apparatus as claimed in Claim 1 3 wherein the single haul pulley unit is adapted to cause a sliver to exit the flyer along the axis of rotation and which

is located downstream of the stretching and drying zone.

1 5. An apparatus as claimed in Claim 1 3 or Claim 1 4 wherein an air gap of at least 2 to 3 metres exists between an exit of the microwave drier and the haul pulley unit.

6. A continuously stretched and temporarily or permanently set sliver produced by a process as defined in Claims 1 to 1 2 or on an apparatus as defined in Claims 1 3 to 1 5.

7. A continuously stretched and temporarily or permanently set sliver as claimed

in Claim 1 6 formed from wool or animal fibres.