EP0032215B1 - Bicomponent fibres and filaments having improved crimp stability against mechanical stress - Google Patents

Abstract

1. Bicomponent fibres and threads of two components A and B, consisting of different acrylonitrile polymers arranged eccentrically to each other, having permanent three-dimensional crimp, characterised in that they consists of a more highly shrinkable component A, which consists of a polymer or a polymer mixture having a comonomer content of not more than 2% by weight, and a component B with lower shrinkage, which consists of a polymer having a comonomer content of 4-15% by weight, and in that they have a recovery power in the cold which enables them to still retain, after mechanical stress of 1 cN/dtex, at least 30% of the crimp which they had prior to the stress.

Description

The invention relates to bicomponent fibers made from two different eccentrically arranged thread-forming acrylonitrile polymers with permanent three-dimensional crimp, which recovers particularly well at room temperature after strong mechanical loads.

It has been shown in the past that bicomponent fibers with round, three-dimensional crimp were obtained by simultaneously spinning and stretching two differently shrinking acrylonitrile polymers. Great efforts have been made to produce articles from such fibers. which, in addition to the known advantages for synthetic fibers, such as Ease of care, lightfastness and improved mechanical values, also achieve the advantages such as high volume, good grip, dimensional stability and elasticity of the articles, as they are known for wool. Although progress has been made, the crimping of previously known bicomponent fibers does not adequately withstand the mechanical stresses that occur during yarn production, so that the volume in the yarns cannot develop fully.

An improvement was achieved by using components with different degrees of swelling, so that through wet, thermal treatment during dyeing or steaming, the yarn structure was loosened and, after drying, a volume development corresponding to that of wool could take place.

Such a crimp which is not stable under the influence of water has the disadvantage that articles lengthen or become matted in the moist state and require drying at elevated temperature (ie not at air temperature) in order to achieve their initial length.

The invention was therefore based on the object of producing bicomponent fibers consisting of acrylonitrile polymers which have a permanent, three-dimensional crimp, which is still present with as large a portion as possible even after strong mechanical loads and which is used for volume development, dimensional stability and elasticity in the knitted piece and for increased pressure stability in polar articles and carpets.

Bicomponent fibers and filaments consisting of two components A and B, which are formed from different acrylonitrile polymers arranged eccentrically to one another, have now been found which, even after a strong mechanical load of over 1 cN / dtex, still over 30%, for coarser titers of over 6.0 dtex even show more than 50% of their crimp before exercise because of their good cold recovery ability. This crimp then contributes to increased bulk, increased shape stability and elasticity in the knitted piece and increased pressure stability in the pile article. The present invention therefore relates to such fibers and threads.

Bicomponent fibers with such crimp stability are obtained if a polymer or a polymer mixture which has a comonomer fraction of at most 2% by weight is used as the more shrinking component A and a polymer which has a comonomer fraction of 4 to 15 is used as the weaker shrinking component , preferably 4-8 wt .-%. Component A advantageously also differs from component B in that it has at least 10% greater cold recovery capacity after an elongation of 10%. It is further preferred if component A can store at least 15% more elastic energy than component B.

• Abb. 1 zeigt die Abhängigkeit des Streckbandkochschrumpfes von dem Ausmass der Verstrekkung, wenn man die zum Aufbau der erfindungsgemässen Bikomponentenfasern verwendeten Polymeren A (Kurve A) und B (Kurve B) jeweils für sich alleine verspinnt.
• Abb. 2 zeigt ein typisches Kraft-Dehnungsdiagramm, aus dem sich die Aufnahme von elastischer Energie durch Integration von 0% Dehnung bis Dy ergibt. Ey entspricht der Dehnung im Punkt y, d.h. dem Punkt an dem die Kraft-DehnungsKurve abflacht.
• Abb. 3 zeigt in der Kurve 1 das Einkräuselungsverhältnis in % in Abhängigkeit von der mechanischen Belastung von erfindungsgemässen Fasern. Kurve 2 zeigt die gleiche Abhängigkeit für handelsübliche Bikomponentenfasern.
• Abb. 4 entspricht der Abb. 3, stellt jedoch die beschriebene Abhängigkeit für Fasern höheren Titers dar.

In the figures used to further explain the invention, the following is shown:

• Fig. 1 shows the dependence of the stretching band boil shrinkage on the extent of the stretching if the polymers A (curve A) and B (curve B) used to build up the bicomponent fibers according to the invention are spun individually.
• Fig. 2 shows a typical force-strain diagram, from which the absorption of elastic energy results through integration from 0% strain to Dy. Ey corresponds to the elongation at point y, ie the point at which the force-elongation curve flattens.
• Fig. 3 shows in curve 1 the crimping ratio in% as a function of the mechanical load of fibers according to the invention. Curve 2 shows the same dependency for commercially available bicomponent fibers.
• Fig. 4 corresponds to Fig. 3, but shows the described dependency for fibers of higher titer.

Acronitrile homopolymers and copolymers which have a comonomer content of at most 2% by weight are suitable as component A of the fibers according to the invention, which shrinks more. Those polymers which have a higher molecular weight are particularly preferred. A measure of the molecular weight are the times that defined amounts of solution need to pass through a capillary. The time tp that a 0.5% polymer solution in dimethylformamide (DMF) takes to pass through the capillary at 20 ° C. is compared with the time t _o that pure DMF takes to pass through the same capillary at the same temperature. Polymers that obey the relationship t _P ≥ 2.1 t _D are polymers for component A. particularly suitable. Preferably tp is 2.1 to 2.5 times tp.

Comonomers which are customary in this technology are monomers which can be copolymerized with acrylonitrile, such as acrylic or methacrylic acid esters, such as the particularly preferred methyl acrylate, ethyl acrylate, methyl methacrylate, methyl methacrylate, vinyl ester, such as vinyl acetate, allyl or methallylsulfonic acid or their alkali metal sulfate acid or their alkali metal sulfate acid in question.

If these polymers are preferably spun dry, washed and stretched using customary techniques, they have a stretching belt boil shrinkage which, depending on the stretching, has approximately the course shown in FIG. 1 with curve A.

The polymers forming the weaker shrinking component B with a comonomer content of at least 4% by weight can contain the same comonomers as those mentioned for component A. The comonomers for component B should be selected such that after spinning, washing and drawing under the same conditions as for component A, a stretching tape is obtained depending on the drawing, as is shown by the curve in Fig. 1 B is shown.

Particularly preferred polymers for component B are those which have a viscosity which allows them to obey the relationship tp <2 to. tp and t _o are defined here as well as specified for component A. Viscosities are preferred which give rise to the relationship tp = 1.7-2.0 tp.

For a good curl stability against mechanical stress, it has been shown to be advantageous, as already mentioned, if component A shows a 10% higher cold recovery than component B after an elongation of 10% at 20 ° C. Cold recovery b is complete Equation (3) defined below.

Furthermore, it is advantageous for the crimp stability if 15% more elastic energy can be stored in component A than in component B. The elastic energy that can be stored in a fiber is obtained by absorbing a force-strain Diagram according to Fig. 2. The diagram shows the elastically stored energy component by integration up to Dy

The polymers A and B are spun into bicomponent fibers according to the usual techniques, so that the polymers are arranged eccentrically to one another in cross section. The dry spinning process is particularly preferred. The solvents known for dry spinning are suitable as spinning solvents, e.g. Dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, but preferably dimethylformamide.

The spinning solutions from the two polymers A and B are prepared in such a way that spinning solutions with approximately the same viscosity preferably result.

The bifilar nozzles from which the polymers are spun according to the usual technologies are preferably constructed such that a channel with polymer solution A and a channel with polymer solution B lead to each nozzle hole. The solutions are pumped through these channels to the nozzle holes so that each fiber contains at least 30% of each of the two components.

After spinning, the threads are treated according to the usual technologies. The threads are combined into tapes of about 2 million dtex, the residual solvent is removed, the threads are then drawn, dried, crimped and packaged as a cable or cut and steamed to produce fibers after crimping.

The threads and fibers according to the invention have mushroom-shaped, lip-shaped, trilobal and / or dumbbell-shaped cross sections. Which cross-sectional shape predominates depends on the selected spinning conditions. Mushroom-shaped and lip-shaped cross sections preferably occur.

wobei die Zahl der Kräuselbögen nach einer Standardvorschrift (entsprechend Strecker, B.F.: Faserkräuselung Chemiefasern 1974, Seite 852) ermittelt wurde.In addition to a balanced and stable crimp, the bicomponent threads and fibers according to the invention show good fiber properties such as raw tone, tear resistance, elongation at break and good dyeability. They preferably have an irreversible crimp, because articles made of fibers with reversible crimp lose their bulky and voluminous character when exposed to moisture and tend to felt, since the crimp of these fibers disappears or is strengthened when exposed to moisture. The curl reversibility Ac.pc was determined according to US-A-3 038 236.

the number of crimped sheets was determined according to a standard specification (according to Strecker, BF: fiber crimping chemical fibers 1974, page 852).

• 1. Eine Faser wird mit 10-³ cN/dtex belastet, und ihre Länge I₁ wird bestimmt.
• 2. Die gleiche Faser wird mit 0,3 cN/dtex belastet, und ihre Länge 1₂ wird bestimmt.
• 3. Die gleiche Faser wird 30 Sekunden mit 0,6 cN/dtex belastet, 30 Sekunden zur Erholung entlastet, und die Faserlänge 1₃ wird gemessen.
• 4. Die gleiche Faserlänge I₄ wird unter einer Belastung von 0,3 cN/dtex gemessen.
• 5. Die gleiche Faser wird 30 Sekunden mit 1 cN/dtex belastet, 30 Sekunden zur Erholung entlastet, und die Faserlänge I₅ wird gemessen.
• 6. Die Faserlänge I₆ wird unter einer Belastung von 0,3 cN/dtex gemessen.
  usw.

Cables and fibers are then processed into dyed yarns, for example, according to the process steps customary for worsted spinning, using both strand dyeing and crimped dyeing or flock dyeing and damping of the finished yarns. Fibers made from such yarns according to the invention now show outstanding and surprising crimp stability against mechanical stress, which can also be called cold recovery. The determination of the crimp stability compared to mechanical Stress can be carried out as follows:

• 1. A fiber is loaded with 10- ³ cN / dtex and its length I ₁ is determined.
• 2. The same fiber is loaded with 0.3 cN / dtex and its length 1 ₂ is determined.
• 3. The same fiber is loaded with 0.6 cN / dtex for 30 seconds, relieved for 30 seconds for recovery, and the fiber length 1 ₃ is measured.
• 4. The same fiber length I ₄ is measured under a load of 0.3 cN / dtex.
• 5. The same fiber is loaded with 1 cN / dtex for 30 seconds, relieved for 30 seconds for recovery, and the fiber length I ₅ is measured.
• 6. The fiber length I ₆ is measured under a load of 0.3 cN / dtex.
  etc.

wobei für

• i = 2 die Belastung 0,6 cN/dtex
• i = 3 die Belastung 1,0 cN/dtex
• i = 4 die Belastung 1,5 cN/dtex
• i = 5 die Belastung 2,0 cN/dtex gewählt wurde.

The cold recovery b depends on the load

being for

• i = 2 the load 0.6 cN / dtex
• i = 3 the load 1.0 cN / dtex
• i = 4 the load 1.5 cN / dtex
• i = 5 the load 2.0 cN / dtex was chosen.

The process was repeated until the fibers broke. The fibers according to the invention, which were prepared from finished yarns, now had the cold recovery shown in FIG. 3 as a function of the load (curve 1). It has now been shown that fibers with larger titers show higher back crimps after loading than fibers with lower titers. For this reason, only those with the same titer were selected in Fig. 3 for comparison for fibers with lower crimp ratios (curve 2). The corresponding curves for higher titers were shown in Fig. 4 (curve 1 for crimps that crimp back heavily after exposure, curve 2 for crimps that crimp back less after exposure).

Studies on several commercially available bicomponent fibers always showed only measured values in curve 2 in FIGS. 3 and 4 and never the excellent crimp stability against mechanical stress due to good cold recovery, as was observed on the fibers according to the invention.

Fibers are subjected to high mechanical loads in the course of further processing into yarns. When processing into worsted yarn, they go through the following path, for example: The fibers are delivered as flakes in the bale and entered into a card. The carding belt runs through two sections and reaches the pitcher chair. The belt is then refined to two subsequent sections, passes through a controlled section and two high-speed machines for further refinement. The so-called roving is spun and wound on cops. Several individual yarns are then twisted to the raw yarn, coiled, strand dyed and dried.

On fibers according to the invention with a titer of 3.3 dtex and comparative fibers according to Example 2, the crimp, which is reduced as a result of the mechanical stress on the fibers, was measured after individual process steps. Table 1 shows the result.

• Eine Einzelkapillare wird wie unter A mit 10-³ cN/dtex vorgespannt. Diese Vorspannung ist so gering, dass die Länge I_A der gekräuselten Kapillare gemessen werden kann, ohne dass die Kräuselung nennenswert beeinträchtigt wird. Anschliessend wird die Kapillare mit 0,3 cN/dtex gespannt. Unter dieser Vorspannung wird die Kapillare entkräuselt. Die Länge I_B der entkräuselten Faser wird bestimmt.

The crimp was determined as follows:

• A single capillary is prestressed as in A with 10- ³ cN / dtex. This pretension is so small that the length I _{A of} the crimped capillary can be measured without the crimp being appreciably impaired. The capillary is then tensioned at 0.3 cN / dtex. The capillary is uncurled under this pretension. The length I _{B of} the crimped fiber is determined.

The crimp is calculated as follows:

• a) Bezüglich des Griffs war das Garn aus den erfindungsgemässen Fasern etwas kerniger, fülliger und elastischer.
• b) Bezüglich der Optik wird das Garn aus den erfindungsgemässen Fasern fülliger, trotz einer geschlossenen Oberfläche.
• c) Der Bausch der Garne wurde objektiviert durch die Messung des spezifischen Gewichtes der Garne.

On the yarns from the fibers according to the invention and from the comparison fibers, the feel, appearance and bulk were compared.

• a) With regard to the handle, the yarn made from the fibers according to the invention was somewhat robust, fuller and more elastic.
• b) With regard to the appearance, the yarn made from the fibers according to the invention becomes fuller, despite a closed surface.
• c) The bulk of the yarns was objectified by measuring the specific weight of the yarn.

For this purpose, pieces of yarn were hung in a frame, which was pushed into a slide projector. The yarns were projected onto a screen and the yarn diameters were measured in different places.

The values were averaged and the true yarn diameter was calculated using the magnification factor. The volume V of 1 m of yarn was determined using the yarn diameter. Then 50 pieces of 1 m long yarn strands, the length of which was determined under a load of 10 ^-3 cN / dtex, were cut out, weighed and their average weight G was determined. The specific weight of the yarn is calculated as follows:

When comparing yarns made from fibers according to the invention with yarns made from comparison fibers, the yarns made from the fibers according to the invention had a lower specific weight, with specific weights being achieved which also occur for wool yarns.

If yarns from the fibers according to the invention were used in comparative tests in the carpet sector and in the pile sector, it was found that carpets and pile articles made from the fibers according to the invention have a higher pressure stability than carpets and pile articles made from comparison fibers.

The following examples serve to explain the invention in more detail. Unless otherwise noted, parts and percentages relate to weight.

example 1

Polymer solution A: An acrylonitrile copolymer mixture with tp = 2.13 t _o from 85% acrylonitrile homopolymer and 15% acrylonitrile copolymer with tp = 1.92 t _o from 91% ACN, 5.6% AME and 3.4% Na-MS were at 100 ° C dissolved in DMF, so that a 24.5% solution was formed.

Polymer solution B: An acrylonitrile copolymer with tp = 1.89 to from 93.6% acrylonitrile (ACN), 5.7% methyl acrylate (AME) and 0.7% sodium methallylsulfonate were dissolved at 80 ° C in dimethylformamide (DMF), see _above that a 29.5% solution (amount of PAN based on the amount of solution) was formed.

Both solutions were fed to a bifilar nozzle so that each nozzle hole was served with the solutions in a 1: 1 ratio, and bicomponent fibers were spun dry side by side. The spun material was combined into a cable of 2 million dtex, stretched 1: 4.0 times at 95 ° C., washed at 95 ° C., prepared, dried under tension at 120 ° C. for 45 seconds, crimped, cut and over 1.5 Minutes fixed in steam. The fibers had a titer of 3.3 dtex, a mushroom-shaped cross section and a fibrillated surface, a moisture of 2% and a preparation order of 0.35% (extracted with methanol). They had a tenacity of 2.5 cN / dtex and a maximum tensile elongation of 40%. The maximum loop tension of the fiber was 55% of the fiber strength and the maximum loop extension was 15%. The fibers had a freezing temperature of 89 ° C in air and 48 ° C in water. They had a density before cooking of 1.18 g / cm and a density after cooking of 1.17. Their crimp was E = 25.9% and a crimp number of n ₁₀₀ = 102 was determined. The fibers showed a crimp reversibility of Δc.pc of 0.07. The values for the crimping ratio after the load b were:

In further processing in the worsted spinning mill, the fibers had the crimping values given in Table 1 for the fibers according to the invention. The yarn (Nm 16/4) from the fibers had a soft, pleasant wool-like feel, a closed yarn surface with a clear thread structure and a high bulk. It had a specific weight of = 0.075 g / _cm3 .

If polymer solution A was spun alone and aftertreated under the same conditions as above, it was found that the cable had a boiling shrinkage after stretching Showed 24%. The fibers from this polymer had a longitudinal swelling of 1.8% and they shrink or recover after an elongation of 10% at 20 ° C. by 59% of the elongation at this temperature. According to the force-strain diagram, up to point Y: E _el = 0.43 · 10 ^-5 joules of elastic energy per dtex and 100 mm fiber length can be stored.

If the polymer solution B was spun alone and aftertreated under the same conditions as above, it was found that the cable had a cooking shrinkage of 210% after the stretching. The fibers from this polymer had a longitudinal swelling of 1.6% and they shrink or recover after an elongation of 10% at 20 ° C by 46% of the elongation at this temperature. According to the force-elongation diagram, elastic energy per dtex and 100 mm fiber length can be stored up to the point YE _el = 0.26 · 10 ^-5 joules.

Example 2 (comparative example)

Polymer solution A: An acrylonitrile copolymer with tp = 1.9 t _d of 90.3% acrylonitrile, 9% AME and 0.7% Na-MS was dissolved in dimethylformamide at 80 ° C., so that a 29.5% solution was obtained .

Polymer solution B: as in Example 1

The two solutions were spun as in Example 1 and the spinning material was also post-treated as in Example 1. The fibers had a mushroom-shaped cross section and a fibrillated surface, a moisture of 2% and a preparation order of 0.36%. They had a tenacity of 2.4 cN / dtex and a maximum tensile elongation of 42%. The maximum loop tension of the fibers was 60% of the fiber strength and the maximum loop extension 16%. The fibers had a freezing temperature in air of 75 ° C and 37 ° C in water. Their crimp was 16% and their crimp number n ₁₀₀ = 82. The fibers show a crimp reversibility of Ac.pc = 0.09. The values for the crimp ratio after the load b: were:

In further processing in the worsted spinning mill, the fibers had the crimping values given in Table 1 for the comparison fibers. The yarn (Nm 16/4) from the fibers had a soft feel, but the yarn was severely crushed and unsightly at individual points on which it had been in the dyeing apparatus. In addition, its bulk was not sufficient because it had a specific weight of ß = 0.13 g / cm ³ .

If the polymer solution alone was spun and aftertreated under the same conditions as in Example 1, it was found that the cable had a boiling shrinkage of 21%. The fibers from this polymer had a longitudinal swelling of 1.4% and they shrink or recover after an elongation of 10% at 20 ° C. by 48% of the elongation at this temperature. The elastically storable energy fraction was E _el = 0.39 · 10 ^-5 joules per dtex and 100 mm fiber length.

Example 3

The same solutions A and B as in Example 1 were spun and aftertreated, but the amount of solution per spinning hole was doubled compared to Example 1. The fibers had a titer of 6.2 dtex, again a mushroom-shaped cross section and a fibrillated surface, a moisture content of 2.4% and a preparation order of 0.33%. They had a tenacity of 2.6 cN / dtex and a maximum tensile elongation of 40%. Loop values, freezing temperature and density corresponded to the values as in Example 1. The number of crimps was n ₁₀₀ = 75, the crimp was 20% and the crimp reversibility was Ac.pc 0.08. The values for the crimp ratio after the load were:

Yarns from the fibers with the coarser titers are usually somewhat fuller than yarns with titers of 3.3 dtex. These yarns have a somewhat more robust feel. With these fibers it was possible to produce very elastic dyed yarns which had a specific weight p = 0.065 g / cm ³ .

Example 4 (comparative example)

The same solutions A and B as in Example 2 were spun and aftertreated, but compared to Example 2 the amount of solution per spin hole was doubled again. The fibers had a titer of 6.7 dtex and again roughly the same fiber data as in Example 2. However, they had a crimp of E = 14% and a crimp number of n ₁₀₀ = 78. The crimp reversibility had a value of 0.1. The values for the crimp ratio after the load were:

After the strand dyeing, the yarns were flattened again in some places and had a higher specific weight of g = 0.12 g / c _m3 .

Example 5

Polymer Solution A: An acrylonitrile copolymer with tp = 2.12 t _o from 99.3% ACN and 0.7% Na-MS were dissolved at 100 ° C in DMF, so that a 24.5% strength solution.

Polymer Solution B: Another acrylonitrile copolymer with tp = 1.89 t _o of 93.6% of acrylonitrile (ACN), 5.7% Na and 0.7 AME-MS was dissolved at 80 ° C in DMF to form a 29, 5% solution was created.

The solutions were spun and treated as in Example 1. The fibers had a titer of 3.3 dtex, a lip-shaped cross section, a moisture of 3% and a preparation order of 0.35%. They had a fine strength of 2.4 cN / dtex and a maximum tensile elongation of 39%. Their crimp was 18% and the number of crimps was determined to be n ₁₀₀ = 82. The fibers showed a crimp reversibility of Ac.pc = 0.1. The values for the crimp ratio after the load were:

A hand-knitting yarn made of these fibers (Nm 16/4) had a soft wool-like feel, a closed yarn surface with a clear thread structure and a high bulk. It had a specific weight of p = 0.87 g / cm ³ . If polymer solution A alone was spun and aftertreated under the same conditions as in Example 1, it was found that the cable had a shrinkage of 23% after stretching. The fibers from this polymer had a longitudinal swelling of 1.6% and they shrink or recover after an elongation of 10% at 20 ° C by 59% of the elongation at this temperature. According to the force-displacement diagram can be stored up to the point YE = 0,39.10- ⁵ joules of elastic energy per dtex and 100 mm fiber length.

Example 6 Polymer solution A; as in example 1 Polymer solution B: An acrylonitrile copolymer with tp = 1.92 t _o 91% ACN, 5.6% DMF and 3.4% Na-MS was dissolved at 80 ° C in DMF, so that a 28.5% solution was .

The solutions were spun and treated as in Example 1. The fibers had a titer of 6.9 dtex, a mushroom-shaped cross-section, a moisture of 1.2% and a preparation order of 0.5%. They had a tenacity of 2.6 cN / dtex and a maximum tensile elongation of 36.3%. Their crimp was 26% and the number of crimped sheets n ₁₀₀ = 124. The fibers showed a crimp reversibility of Δc.pc = 2.9. The values for the crimp ratio after the load were:

A hand knitting yarn made of these fibers (Nm 8/3) had a soft wool-like feel, a closed yarn surface with a clear thread structure and a high bulk. It had a spec. Weight of e = 0.75 g / cm ^{3. However,} it lengthens under the influence of moisture by about 15% and must be brought back into its attractive form in dry heat. If the polymer solution B was spun alone and aftertreated under the same conditions as Example 1, it was found that the cable had a shrinkage of 21% after stretching. The fibers from this polymer had a longitudinal swelling of 3.7%, and they shrink cold or recover by 48% of the elongation after an elongation of 10% at 20 ° C. According to the force-elongation diagram, elastic energy per dtex and 100 mm fiber length can be stored up to the point YE _el = 0.5 · 10 ^-5 joules.

Claims (6)

1. Bicomponent fibres and threads of two components A and B, consisting of different acrylonitrile polymers arranged eccentrically to each other, having permanent three-dimensional crimp, characterised in that they consists of a more highly shrinkable component A, which consists of a polymer or a polymer mixture having a comonomer content of not more than 2% by weight, and a component B with lower shrinkage, which consists of a polymer having a comonomer content of 4-15% by weight, and in that they have a recovery power in the cold which enables them to still retain, after mechanical stress of 1 cN/ dtex, at least 30% of the crimp which they had prior to the stress.

2. Bicomponent fibres and threads according to Claim 1, characterised in that the viscosity of the component A obeys the relationship tp≥2.1 to and the viscosity of the component B obeys the relationship t_p≥2 to, tp being the time which a 0.5% polymer solution in dimethylformamide requires to flow through a capillary tube at 20°C, whereas to is the time which pure dimethylformamide requires to flow through the same capillary at the same temperature.

3. Bicomponent fibres and threads according to Claims 1 and 2, characterised in that component A exhibits a recovery power in the cold after an elongation of 10% at 20°C which is at least 10% higher than that of component B.

4. Bicomponent fibres and threads acording to Claims 1 to 3, characterised in that at least 15% more elastic energy can be stored in component A than in component B.

5. Bicomponent fibres and threads according to Claims 1 to 4, characterised in that neither of components A or B occupies a proportion of the cross-sectional area of the fibres of threads of less than 30%.

6. Bicomponent fibres and threads according to Claims 1 to 5, characterised in that they have titres of 1.6 to 30 dtex.

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