EP0454160A2

EP0454160A2 - Elastic core and sheath type composite filaments and textile structures comprising the same

Info

Publication number: EP0454160A2
Application number: EP91106833A
Authority: EP
Inventors: Yasuo Muramoto; Kiyoshi Yoshimoto; Masao Matsui; Masami Fujimoto; Yoshiaki Morishige; Tsutomu Naruse; Yoshinori Murafuji; Souichi Murakami
Original assignee: Kanebo Ltd
Current assignee: Kanebo Ltd
Priority date: 1990-04-27
Filing date: 1991-04-26
Publication date: 1991-10-30
Also published as: CN1058813A; EP0454160A3

Abstract

An elastic core and sheath type composite filament composed of a thermoplastic non-elastomer sheath component, such as polyamide, copolyester and polyolefin, and a crosslinked polyurethane core component, preferably predominantly allophanate-crosslinked, wherein a core/sheath conjugate ratio (X) and a crosslink density (Y µmol/g) of the polyurethane satisfy simultaneously the inequalities:

3 ≦ X ≦ 100,

Y ≧ 0 and

Y ≧ -8.7X + 52.

The filament of the invention free from tackiness and excellent in elastic stretch recovery, heat resistance, and workability in knitting or weaving, can provide textile structures of high quality, for example, high-stretchable, support type stockings with good appearance and tactile properties.

Description

The present invention relates to an elastic core and sheath type composite filament consisting of a sheath component of a fiber-forming thermoplastic non-elastomer and a core component of a polyurethane, and textile structures comprising such a composite filament.
Polyurethane elastomer yarns have hitherto been applied in diversified fields, with peculiar properties thereof being utilized. However, these polyurethane elastomer yarns, different from usual synthetic filament yarns, stick to each others due to tackiness inherent therein, whereby not only an excessive tensile force for drawing out from yarn packages is required but also great variations in tension occur when taken-up yarns are unwound.
Furthermore, since the polyurethane elastomer yarns elongate with a little tensile stress and also have a high coefficient of friction, the yarns are low in workability and difficult to handle in succeeding steps, so that they are followed about by problems of yarn breakages, uneven knitting, etc. even under a strict process control. One of measures to eliminate the above difficulties is application of an oiling agent (for example, an oiling agent predominantly comprising dimethyl silicone, admixed with a metallic soap, monoamines or the like: as disclosed in Japanese Patent Publications Nos. 40-5,557 and 46-16,312).
However, an effect of improvement by means of oiling, has been recognized to a certain extent but limited and not perfect. Namely, suppose the case of spinning and taking-up on a take-up roll, if the tackiness of the yarns are reduced, the take-up operation tends to be impossible to continue for a long time due to cobwebbing, yarn package collapsing, etc. This tendency becomes conspicuous with increase of the take-up speed (for example, to 500 m/min. or more) and with decrease of the diameter of the yarn package (for example, to 100 mm or less) during take-up.
Contrariwise, if the yarns are made to be tacky, a long time take-up operation will be able to be conducted, whereas a serious trouble in succeeding steps will occur due to difficulties in yarn unwinding.
Therefore, there have been problems such that a rewinding step must be introduced expressly, or the like, in order to mitigate such a difficulty. Namely, it is other present situation that an operability as good as that of other synthetic fibers, such as being attainable by completely eliminating the mutual sticking during spinning, yet allowing the take-up to be conducted for a long time and, besides, making yarn handling very easy in succeeding steps, can in no way be expected only with a delicate control by means of oiling.
As another measure to eliminate the difficulties, there have so far been proposed core and sheath type composite filament yarns, such as an elastic yarn consisting of concentric polyurethane core and polyurethane sheath composite filaments (for example, Japanese Patent Publication No. 61-14,245, proposed by the present inventors), and an elastic yarn consisting polyurethane core and polyolefin sheath composite filaments (for example, Japanese Patent Publication No. 61-194,221).
The above elastic, polyurethane-polyurethane type concentric composite filament yarn, since the sheath is composed of a polyurethane, has disadvantages in respects of tackiness inherent therein, a high-speed take-up ability at spinning step, workability at succeeding steps, tactile properties of goods formed therefrom, etc. Additionally, this yarn has a difficulty in blending with polyester yarns.
In the case of the polyurethane core and polyolefin sheath composite filament, it has disadvantages such that heat resistance is low and if the heat resistance is tried to be increased by increasing the hardness of the polyurethane core component, then the elastic stretch recovery as a composite filament decreases. Additionally, since a core/sheath conjugate ratio is rather small, the sheath largely affects and deteriorates the property of the yarn. Accordingly, such filament yarns have been put only to applications, mainly utilizing the tackiness thereof.
Furthermore, it has also been known that textile structures composed of polyurethane elastomer yarns have undesirable tactile properties such as hand or touch, and also are poor in dyeability and color fastness. Accordingly, the textile structures composed of a polyurethane elastomer yarn alone scarcely appear in the market, since production processes are accompanied by extreme difficulties.
In order to reinforce the polyurethane elastomer yarns to facilitate handling thereof, covering yarns comprising a polyurethane core yarn and a nylon plating yarn wound around the core yarn have been proposed and applied to many uses. However, the covering yarns have an increased thickness as compared with polyurethane bare yarns, due to the wound plate yarns, so that stockings knit with such yarns are heavy and lack transparency. Besides, processes for manufacturing such a yarn require a covering step, causing a different problem of an extremely low output rate.
Particularly in the stockings, importance is attached to stretching properties and particularly fittability to legs, so that in addition to the above covering yarns, there have been proposed crimp-potential composite filament yarns. For example, a crimped yarn consisting of eccentric polyurethane core and polycapramide sheath composite filaments, which allows the covering step to be omitted (Japanese Patent Publication No. 55-27,175) and an elastic yarn consisting of composite filaments comprising an eccentric core of a crosslinked polyurethane elastomer (Japanese Patent Publication No. 1-118,619) have been known.
Alternatively, the eccentric polyurethane core and polycapramide sheath composite filament yarn has drawbacks such that it requires a step of draw and relax treatment to develop a crimp recovering force and has a rather low modulus of stretch recovery as it is rendered by crimps. Further, it is necessary to give great care to uniformity of the crimps. Moreover, stockings composed of such a yarn have problems such as of lacking transparency, having a poor knit texture, providing undesirable appearance to the legs wearing them, or the like.
Further, polyurethane elastomer yarns have a hot water shrinkage at 100°C of at most 10-odd percent. As a process for increasing this value, there has been a hot or cold drawing process. When the polyurethane elastomer yarns are subjected to hot drawing, for example, a 2-3 times drawing at 120°C, a hot water shrink percentage becomes generally in the twenties to thirties. However, the drawn polyurethane elastomer yarns spontaneously shrink at room temperature before measurement of such a hot water shrinkage is conducted. Moreover, different from other synthetic filaments, the polyurethane elastomer yarns are hardly set and thereby very difficult to handle. Namely, during lying, the yarns spontaneously shrink even if they are not heated and thus present a further problem of dimensional instability.
As a process for improving the drawability, Japanese Patent Publication No. 55-9,093 proposes a process of conjugating a non-elastomer with a polyurethane polymer having an unreacted isocyanate group incorporated thereinto in an amount of 1-45 µg eg. per 1 g of polymer at the time of conjugate-spinning. However, this process has a difficulty such that the isocyanate group content in the polyurethane must be controlled on the above level until spinning, as well as a problem of a low elastic stretch recovery of the resulting composite filaments since a polyurethane having a melting point temperature of 200-235°C which has hard segments considerably increased is employed.
As a result of assiduous researches aiming at obviation of the above difficulties, we, the inventors, have achieved the present invention.
A first object of the present invention is to provide a novel elastic, composite filament yarn having an excellent elastic stretchability and an improved workability in spinning and take-up steps as well as in succeeding steps, owing to tackiness-free.
A second object of the present invention is to provide a polyurethane filament yarn having an excellent dyeability and exhibiting a high shrinkage through hot water treatment.
Further, a third object of the present invention is to provide novel textile structures, particularly ladies' hosiery, having novel properties entirely different from conventional textile structures comprising a polyurethane bare yarn, such as excellent elastic stretch, heat resistance, tactile properties when being put on, and transparency.
Namely, the filament according to the present invention to achieve the above objects is an elastic, core and sheath type composite filament characterized by consisting of a fiber-forming thermoplastic non-elastomer sheath component and a polyurethane core component, which is characterized in that a core/sheath conjugate ratio X and a crosslink density Y (µmol/g) of the polyurethane satisfy simultaneously the following inequalities:

$3 ≦ X ≦ 100,$

$Y ≧ 0 and$

$Y ≧ -8.7X + 52.$
The above non-elastomer, taking a balance with a melt viscosity of the polyurethane during spinning into consideration, is preferred to have an optimum melt-spinning temperature of at most 238°C.
A first embodiment of the present invention is the aforesaid filament wherein the non-elastomer is a polyamide having at least one of characteristics: a melting point determined with a differential scanning calorimeter (DSC) being within the range between 80°C and 220°C; and a relative viscosity determined at 25°C with a solution of 1 g polymer in 100 mℓ of 98% sulfuric acid being at most 2.3.
A second embodiment of the present invention is the aforesaid filament wherein the non-elastomer is a copolyester comprising polyethylene terephthalate as a principal constituent and 12-50 mol % of an isophthalate comonomer.
A third embodiment of the present invention is the aforesaid filament wherein the non-elastomer is a copolyester obtained from a dicarboxylic acid ingredient comprising 60-88 mol % terephthalic acid and 12-40 mol % isophthalic acid and a diol ingredient comprising 75-90 mol % ethylene glycol and 10-25 mol % of at least one glycol selected from the group consisting of diethylene glycol, triethylene glycol, neopentyl glycol and butanediol.
A fourth embodiment of the present invention is the aforesaid filament wherein the non-elastomer is a polyolefin selected from the group consisting of polyethylene, polypropylene, polystyrene and polybutene and the polyurethane has a crosslink density Y of at least 6 µmol/g, preferably at least 10 µmol/g.
The polyurethane core component of the present invention preferably comprises a polyurethane crosslinked by polyisocyanate, having a crosslink density Y of at least 6 µmol/g, preferably at least 10 µmol/g.
Such a crosslinked polyurethane is preferred to have predominantly an allophanate crosslinked structure.
The filament of the present invention is most preferred to have a cross-sectional shape wherein the core component and the sheath component have substantially a common center of gravity.
Further, the present invention includes a textile structure comprising the above elastic, core and sheath type composite filament.
Namely, the textile structure according to the present invention comprises an elastic, core and sheath type composite filament characterized by consisting of a fiber-forming thermoplastic non-elastomer sheath component and a polyurethane core component, which is characterized in that a core/sheath conjugate ratio X and a crosslink density Y (µmol/g) of the polyurethane satisfy simultaneously the following inequalities:

$3 ≦ X ≦ 100,$

$Y ≧ 0 and$

$Y ≧ -8.7X + 52.$
Such a textile structure of the present invention is preferably embodied in a ladies' hosiery whose non-elastomer is a polyamide.
In such a ladies' hosiery, the polyamide is most preferred to be nylon-12.
The above and other objects, features and advantages of the present invention will become more apparent from reading the following description of the preferred embodiments taken in connection with the accompanying drawings, wherein:
Fig. 1 is a schematical vertical sectional view of a spinneret to be employed in the manufacture of the filament of the present invention, in particular, showing a portion where flows of two molten components meet, of the spinneret.
On the outset, as a typical example of polyamides to be employed for the fiber-forming thermoplastic non-elastomer sheath component in the first embodiment of the present invention, mention may be made of, for example, nylon-6 and a modified nylon-66. Besides, homopolyamides such as nylon-8, nylon-9, nylon-10, nylon-11, nylon-12 or the like, copolyamides such as nylon-6/66, nylon-6/12 or the like, terpolyamides such as nylon-6/12/10 or the like, further multipolyamides and mixtures thereof, also can be preferably employed. Among the others, nylon-12 is particularly preferred for application to ladies' hosiery.
Taking a balance with a melt viscosity of a polyurethane during spinning into consideration, these non-elastomers preferably have an optimum melt-spinning temperature of not exceeding 238°C which is also the upper limit of the optimum melt-spinning temperature of polyurethanes. As a measure of the optimum melt-spinning temperature, relative viscosity or melting point temperature may be adopted. For example, as for nylon-6, it is particularly preferred to select those having a relative viscosity of at most 2.3, which is determined at 25°C with a solution of 1 g nylon sample in 100 mℓ of 98% sulfuric acid. Alternatively, nylons, such as a modified nylon-66, nylon-8, nylon-9, nylon-10, nylon-11, nylon-12, copolymers thereof, blend polymers thereof, or the like, having a melting point temperature determined with a differential scanning calorimeter (DSC) of 80-220°C are also preferred. If the melting point temperature exceeds 220°C, the melt-stability and resistance to heat of the polyurethane of the core component will lower to unbalance the melt-viscosity of the core component with that of the sheath component during conjugate-spinning and the resulting filaments will have a low modulus of stretch recovery, so that it is not preferred. A melting point temperature of less than 80°C is also not preferred, because the non-elastomer will have a poor fiber-formability and become tacky.
In the next place, in the second embodiment of the invention, polyesters to be applied to the sheath component are copolyester comprising polyethylene terephthalate as a principal constituent and 12-50 mol % of acid ingredients being isophthalic acid. If the isophthalic acid percent in the acid ingredient exceeds 50 mol %, polymer pellets may stick with each others to form bridging during drying or spun filament yarns may cause troubles such as sticking or the like, so that it is not preferred. Contrariwise, if the isophthalic acid percent is less than 12 mol %, the optimum melt-spinning temperature will increase to such an extent that the melt viscosity becomes hardly balanced with that of the core component during spinning, and so it is not preferred. Therefore, the range between 15 mol % and 45 mol % is preferred.
Particularly in order to increase the hot water shrinkage of the yarn, the third embodiment of the present intention is preferred, which comprises, as a sheath component, a copolyester obtained from a dicarboxylic acid ingredient comprising 60-88 mol % terephthalic acid and 12-40 mol % isophthalic acid and a diol ingredient comprising 75-90 mol % ethylene glycol and 10-25 mol % of at least one glycol selected from the group consisting of diethylene glycol, triethylene glycol, neopentyl glycol and butanediol. If the above diols other than ethylene glycol is less than 10 mol %, it is hard to lower the shrink commencement temperature, so that a preferable effet is hardly obtained. On the other hand, if such diols present in an amount of more than 25 mol %, the shrink commencement temperature will lower to such a great extent that there may arise a fear of inducing spontaneous shrink. If isophthalic acid as a dicarboxylic acid ingredient presents in an amount of less than 12 mol %, an improvement as expected of the heat shrinkage will not be attained, while isophthalic acid exceeding 40 mol % is not preferred, since polymer pellets tend to become tacky or aggregate, thereby causing a difficulty in biting of the pellets by screws of an extruder during spinning.
The copolyester to be employed in the present invention are preferred to have a glass transition temperature within the range between 55°C and 80°C. If it is less than 55°C, the shrink commencement temperature lowers to such a great extent that there will arise a fear of inducing spontaneous shrink. Alternatively, if it exceeds 80°C, the shrink commencement temperature will rise too much to obtain expected effects.
In the fourth embodiment of the present invention, the sheath component is composed of at least one polyolefin selected from the group consisting of polyethylene, polystyrene, polypropylene and polybutene. In this embodiment, the polyurethane of the core component has a crosslink density Y of at least 6 µmol/g, preferably at least 10 µmol/g. Since the sheath component is thermally very weak, if the crosslink density Y is less than 6 µmol/g, the composite filament yarns tend to exhibit a low heat resistance and a poor elastic stretch recovery.
Fiber-forming thermoplastic non-elastomers for the core component of the filament according to the present invention, may be admixed with known polymer-modifiers, such as delustrants, for example, titanium dioxide, antioxidants, electroconductive agents, antifungus agents, dyes, pigments or the like.
The polyurethanes for the core component of the composite filament according to the invention are not specifically limited insofar as they have fiber-formability. However, thermoplastic polyurethanes or crosslinked polyurethanes are preferred. The thermoplastic polyurethanes are melt-spinnable polymers which can be obtained by reacting a high molecular diol and an organic diisocyanate with a chain extender.
The high molecular diols are glycols having both terminal hydroxyl groups and a molecular weight of 500-5,000, for example, etheric polyols, such as polytetramethylene glycol, polypropylene glycol or the like, and esteric polyols such as polyhexamethylene adipate, polybutylene adipate, polycarbonate diol, polycaprolactone diol or the like. These may be used alone or in combination.
As a chain extender, mention may be made of 1,4-butane diol, ethylene glycol, propylene glycol, bis-hydroxyethoxy benzene or the like, which has a molecular weight of at most 500. Among the others, 1,4-butane diol and bis-hydroxyethoxy benzene are particularly preferred.
As an organic diisocyanate, mention maybe made of tolylene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), non-yellowing diisocyanates such as 1,6-hexane diisocyanate or the like, and mixtures thereof. Among the others, MDI is particularly preferred.
The polyurethanes are preferred to have a Shore A hardness within the range between 60 and 98. If the hardness is less than 60, undesirable problems will arise such that the resulting composite filament yarns exhibit a low elastic stretch recovery and spinning stability lowers. Alternatively, if the hardness exceeds 98, the polyurethane itself has such a low elastic stretch recovery that the stretch recovery of the yarn cannot be expected unless depending on a crimped structure and, further, there will arise an undesirable problem such that an optimum condition for melt-spinning polyurethanes having such a hardness is limited in a very narrow range. The preferred range of the hardness may be between 65 and 95.
Such a polyurethane may be admixed with known polymer-modifiers, such as dyes, pigments, UV stabilizers, UV absorbers, antifungus agents, or the like.
In the case where heat resistance, elastic stretch recovery, compatibility of the core component with the sheath component and the like are required to further increase of the composite filament yarns, a crosslinked polyurethane obtained by reacting the above polyurethane with a polyisocyanate may be arranged in the core component. As a crosslinking process, use may be made of the process described in Japanese Patent Publication No. 58-46,573 proposed by the present inventors, namely, a process wherein a molten thermoplastic polyurethane is admixed with a polyisocyanate and an allophanate crosslinkage is completed thereby during or after spinning.
The polyisocyanate is a compound consisting of a polyol component and an isocyanate component, having at least 2, preferably 2-3 isocyanate groups (NCO groups) in the molecule. As a polyol component, mixtures of a diol with a triol, having an average functionality of hydroxyl group of 2-3, or synthetic polyols having a functionality of 2-3, may be as suitably employed as the aforementioned diols having a molecular weight of 300-4,000 which are used for synthesis of polyurethanes. Alternatively, as an isocyanate component, may be employed the aforementioned diisocyanates to be used for synthesis of polyurethanes, trimers of an organic diisocyanate, reaction products of trimethylol propane with an organic diisocyanate, isocyanates having a functionality ranging 2-3 (for example, carbodiimide-modified isocyanate), etc. and mixtures thereof.
The reaction of both the above components can be conducted according to any known processes. However, it is preferred to conduct the reaction in such a manner that the content of the isocyanate group may be in excess, namely, the isocyanate group (NCO group) may be contained in an amount of 3-22% by weight in the reaction product. Needless to say, this amount depends upon the objective physical properties such as heat resistance, elastic stretch recovery or the like and polyols employed.
Loads of the polyisocyanate are preferably in the range of 6-40% by weight based on the polyurethane/polyisocyanate mixture to be used for the core component. The loads depend upon the NCO-group content and the kind of the isocyanate to be used. If the loads exceed 40% by weight, the spinning operation will be unstabilized due to uneven mixing or the resulting filament yarns will have unsatisfactory mechanical properties, and so it is not preferred. Alternatively, if the loads are less than 6% by weight, the resulting yarns will be deficient in heat resistance, and so it is also not preferred. A further preferable range is 10-30% by weight.
Thus, a crosslink structure predominantly comprising allophanate crosslinkages is formed in the polyurethane core component. Meanwhile, a crosslink structure formed mainly by biuret linkages is not preferred, as it will deteriorate spinnability to the utmost extent. Namely, since the biuret crosslinkages are formed at a larger rate than the allophanate crosslinkages, viscosity of the system will increase during spinning to such an extent that a stabilized spinning operation may be apt to be hardly performed.
In the next place, the core/sheath conjugate ratio will be explained.
The core/sheath conjugate ratio X is generally in the range of 3-100, preferably 5-90, more preferably 10-80, most preferably 20-70, as a cross-sectional area ratio. If the core/sheath ratio is less than 3, the filament yarn will be deficient in elastic recovery, stretch recovery at high temperatures and heat resistance. Alternatively, if this ratio exceeds 100, the sheath is apt to break or the filament is apt to be formed so as to expose the core component on the surface of the filament, whereby spinnability and light-stability will be badly affected.
In order to provide a composite filament with a sufficient performance, not only the above-mentioned conjugate ratio but also the crosslink density Y (µmol/g) of the polyurethane core component is important in the present invention. The core/sheath conjugate ratio X and crosslink density Y must be in the relation satisfying simultaneously the following inequalities:

$Y ≧ 0 and$

$Y ≧ -8.7 × X + 52.$

Namely, when the crosslink density is low, the conjugate ratio must be increased according to the above second inequality and alternatively, when the crosslink density is high, the applicable range of the conjugate ratio can be extended. Such a filament as being constituted not to satisfy the above second inequality is not preferred as it is inferior in performance as a composite filament, such as an elastic stretch recovery. Particularly, in the case where heat resistance is required for the filament, the crosslink density is preferred to be at least 6 µmol/g, preferably at least 10 µmol/g.
The crosslink density referred to in the present invention is to mean a crosslink density of a polyurethane in the core component which is determined by the following procedure:
In the case of a nylon sheath component, a sample of the polyurethane core is prepared by removing the nylon with a solvent such as formic acid or the like. In the case of a sheath component being other polymers, an appropriate solvent is selected to remove the sheath. Then, after dissolving at 23°C over 24 hours 1 g of this polyurethane into a dimethyl-sulfoxide solution containing about 200 µmol/g of n-butylamine, the n-butylamine remaining in the reaction system is back-titrated with a 1/100∼1/50 N-hydrochloric acid/methanol solution, using bromphenol blue as an indicator. The crosslink density Y (µmol/g) is found by the following equation:

wherein,

W₁ :: weight of solvent in sample dissolution (g),
W₂ :: weight of solution wherein sample is dissolved (g),
VO :: titer required for blank test (mℓ),
VS :: titer in sample dissolution (mℓ),
f-HCl :: titer (-), and
N-HCl :: concentration of normal solution (N).

There may be core components having a crosslink density too high to dissolve according to such a procedure as the above. However, it is needless to say that such a system can be suitably used insofar as it has a good spinnability.
As for a conjugation shape, the filament is preferred to have a cross-sectional shape wherein the core component and the sheath component have substantially a common center of gravity, from the viewpoints of spinning stability and yarn uniformity. Further, the cross-sectional shape of the composite filament according to the present invention may be circular or non-circular. Among the others, a concentric circular shape is particularly preferred.
Since the core is completely covered and has substantially a common center of gravity with the sheath, the composite filaments of the present invention have a very good spinnability, even if both the viscosities of the core and sheath components are somewhat unbalanced with each other. This is an outstanding feature of the present invention which is not seen in eccentric type composite filaments.
Next, the process for manufacturing the composite filaments of the present invention will be explained hereinafter.
On the outset, thermoplastic polyurethane pellets are fed from a hopper and heat-melted in an extruder. The suitable temperature for melting is in the range between 190°C and 230°C.
On the other hand, a polyisocyanate is melted at a temperature of 100°C or less in a supply tank and defoamed in advance. If the melting temperature is too high, the polyisocyanate is prone to denaturation. Accordingly, a lower temperature is desirable within a possible range for melting. Generally, a temperature between room temperature and 100°C is appropriately adopted.
The conjugate-spinning is preferably conducted with a melt-conjugate-spinning apparatus equipped with a means for melt-extruding a thermoplastic polyurethane provided with a polyisocyanate admixing means, a sheath component polymer melt-extruding means and a spinning head comprising a spinneret for core and sheath type conjugate-spinning. As the polyisocyanate admixing means, use may be made of known devices for metering a molten polyisocyanate with a metering pump, filtering the melt with a filter if required, and then incorporating it to a molten polyurethane at a core and sheath components meeting portion in the nose of the extruder. Alternatively, as the polyisocyanate admixing means, mixing devices having a rotary mixing element can be applied. However, more preferably employed is a mixing device having a static mixing element. As such a device, a known static mixer may be employed. Though the shape and number of the static mixing elements depend upon use conditions, they are important to be selected so as to allow a thorough mixing of the thermoplastic polyurethane and polyisocyanate to complete before entering the spinneret for conjugate-spinning. Generally, 20-90 elements are provided. The core component polyurethane thus admixed with the polyisocyanate is metered with a metering pump and introduced into the spinning head. The spinning head is preferred to be designed to reduce to a possible extent a dwell space for the mixture. After, if required, removing foreign matter with a metallic net, glass beads or the like in a filter layer provided in the spinning head, the mixture is introduced into the spinneret for core and sheath type conjugate-spinning, and conjugated with a sheath component, i.e., fiber-forming thermoplastic non-elastomer, which has been molten in another extruder. Thus conjugated melts are spun from the spinneret, air-quenched, oil-applied and then taken-up on a take-up roll. The take-up speed is generally 400-1,500 m/min.
Particularly, in order to increase the core/sheath conjugate ratio X, for example, to 15 or more, the structure of the core and sheath components meeting portion in the spinneret is preferred to be designed as shown in Fig. 1. Namely, in Fig. 1, the horizontal approach of the sheath component B is constructed to have a small depth D, for example, 2.0 mm, which is further decreased, for example, to 0.05-1.0 mm, near around the vertical conduit for the core component A. In this embodiment, the space H between the lower end of the upper vertical conduit 1 and the upper end of the lower vertical conduit 2 is smaller than the depth D.
The composite filament yarns immediately after spinning and taking-up, i.e., as-spun yarns, sometimes may be rather inferior in physical properties such as tensile strength, heat resistance or the like. However, after leaving to stand under room temperature for about 2 hours to 7 days, the physical properties remarkably improve, as well as elastic stretch recovery at high temperatures and compatibility of the core component with the sheath component. Further, heat-treatment after spinning by an appropriate means may promote the improvement of the yarn properties, thermal characteristics and compatibility of the core with the sheath.
The changes with time or heat-treatment, of the properties and thermal characteristics of the thus spun composite filaments, are caused by a reaction which is not yet completed and further progresses between the thermoplastic polyurethane used as a spinning material and the polyisocyanate admixed therewith. This reaction produces a polyurethane polymer branched or crosslinked by allophanate linking with the polyisocyanate, and further, the improvement of compatibility with the polyisocyanate is considered to be caused by a reaction between the polyisocyanate and reactive groups in the non-elastomer used, such as an amino, amide or carboxyl group in a polyamide based polymer.
The filament yarns according to the present invention can be used as an as-spun yarn or a drawn yarn. For example, if a composite filament of the invention which comprises a sheath component of a copolyester comprising diethylene glycol as a diol ingredient is left to stand and then hot- or cold-drawn 1.2-5.0 times its original length, the filament may increase hot water shrinkage. In this case, the draw ratio and heating temperature can be determined according to the aiming desired hot water shrinkage. However, generally, the higher these values are, the higher may be the shrinkage of the resulting yarns.
As explained above, since the sheath component is a fiber-forming thermoplastic non-elastomer and the core component is a polyurethane, the composite filament yarns of the invention have a good elastic stretch recovery. Namely, though the non-elastomer sheath component can in no way expect originally an elastic property, the filament yarns using a polyurethane as a core component and having a specified conjugate shape according to the present invention astonishingly exhibit a good elastic stretchability which is attributable not to a crimped structure but to yarns' own elastic property and, further, have an excellent performance such that a permanent strain at 100% elongation is small.
Furthermore, since the polyisocyanate is incorporated into the core component, not only the elastic stretch recovery and heat resistance but also compatibility of the core component with the sheath component improves due to a further reaction progress at boundary of these components.
Further features and advantages of the filament yarns according to the present invention are as follows:
The yarns of the invention are absolutely free from tackiness, as the core component is entirely enclosed in the non-elastomer sheath component. Therefore, in succeeding steps, the yarns can be very easily unwound from a yarn package, such as a bobbin, in the axial direction thereof, which could not be performed by conventional polyurethane yarns.
In the oil-application in spinning and take-up steps, a non-expensive emulsion oiling agent can be employed. Moreover, the yarn of the invention can be wound at a high speed, such as 1,000 m/min, on a bobbin or paper pirn of a small diameter.
The yarns of the invention have an advantage in a commercial production rate owing to the melt-spinning process applied.
The yarns of the invention is excellent in mildew resistance and operability in succeeding steps, such as knitting, weaving or the like.
The filament yarns comprising a polyamide or copolyamide sheath component according to the invention have an excellent dyeability.
The composite filament yarns according to the invention, since they have many excellent features as mentioned above, can be applied to fabrication of various textile structures, such as ladies' stockings, swimsuits, socks, foundation, or the like. Particularly, the stockings according to the invention have a good transparency, excellent appearance, desirable tactile properties or the like, as compared with conventional stockings.
The stockings referred to in this invention include all kinds of over-knee stockings, full-length stockings up to groin and panty stockings combining stocking portion with a panty portion, which are knit with the composite filament yarn of the invention, alone or in combination with an ordinary nylon yarn, a false-twisted yarn, a covering yarn comprising a polyurethane filament core yarn, or the like, by means of mix-knitting or blend-spinning.
The present invention will be explained more concretely hereinafter.

Examples 1-5

· Polyurethane:
Using a polycaprolactone diol having a molecular weight of 2,010, p,p'-diphenylmethane diisocyanate and, as a chain extender, 1,4-butane diol, a thermoplastic polyurethane having a hardness of 85 was synthesized according to a conventional process.
· Polyisocyanate:
A polycaprolactone diol having a molecular weight of 950 and a functionality of 2 was reacted with p,p'-diphenylmethane diisocyanate in such a manner that a percent NCO group might be 7.0% by weight, and a polyisocyanate was obtained.
· Polyamide:
A nylon-6/66 copolymer having a melting point of 199°C (the tradename: 5013B, manufactured by Ube Industries, Ltd.) was used.

The above thermoplastic polyurethane was melted in an extruder, the above polyisocyanate was incorporated at various feed rates into the molten polyurethane flow and then these polymers were thoroughly mixed with each other by a static mixer equipped with 35 mixing elements (manufactured by Kenics). On the other hand, the above nylon was melted in a separate extruder. The above two melts were severally metered and introduced into a spinneret for conjugate-spinning, having 8 orifices of a 0.5 mm diameter.
Varying the core/sheath conjugate ratio, a 40 denier monofilament yarn was spun at a spinning rate of 600 m/min (Examples 2-5 and Comparative Examples 1 and 2). Alternatively, a similar yarn was spun in the same manner except that the polyisocyanate was not incorporated (Example 1).
Properties of the yarns differing from each others in core/sheath conjugate ratio and crosslink density are shown in Table 1.
In Table 1, the elastic stretch recovery was found by the following equation, when a 100% stretch of the yarn at room temperature was repeated twice:

The larger the above value, the more excellent the elastic stretch recovery.
It is found from Table 1 that the filament having a core/sheath conjugate ratio as small as 2 (Comparative Example 1) is rather brittle and has a poor elastic stretch recovery, while the filament of Example 1 having a conjugate ratio of 10 is good in the both yarn properties. The yarn of Comparative Example 2 which does not satisfy the inequality: Y ≧ -8.7 X + 52, is inferior in elastic stretch recovery as well as the other yarn properties, while the yarn of Example 2 largely improves these properties. Further, it is also found from Examples 3-5 that the yarn properties and elastic stretch recovery are improved with increase of the core/sheath conjugate ratio.
Panty stockings were knit with the yarn of Examples 1∼4, using a four-feeder knitting machine. These stockings had an excellent transparency as well as good knit texture, stretchability, etc., as compared with conventional stockings.

Example 6

Spinning was conducted in the same manner as Example 1 except that the hardness of the polyurethane core component was varied, the core/sheath conjugate ratio was 15 and the crosslink density of the core component was 14 µmol/g.
The results are shown in Table 2.
From Table 2, it is found that either a too high or too low hardness of the polyurethane is not preferred, since it lowers the spinnability and elastic stretch recovery.

Example 7

The aforementioned thermoplastic polyurethane and polyamide were separately melted and metered, and then led to a spinneret for spinning composite filaments comprising the polyurethane as a core concentrically conjugated with the polyamide sheath. Conjugate-spinning was conducted at a spinning rate of 600 m/min. and a 20 denier, concentric core and sheath type composite monofilament having a core/sheath conjugate ratio in cross-sectional shape of 20 (Yarn-A) was obtained.
Alternatively, the thermoplastic polyurethane was melted in the extruder and the aforesaid polyisocyanate was incorporated into the polyurethane on the way to the spinneret for conjugate-spinning. The combined melts were thoroughly mixed by a static mixer having 35 mixing elements (manufactured by Kenics) and then a 20 denier composite monofilament (Yarn-B) was obtained in the same manner as the manufacture of Yarn-A. The polyurethane of Yarn-B had a cross link density of 29 µmol/g.
As Comparative Examples, the following 4 kinds of yarns were manufactured:

Yarn-C:: a 20 denier monofilament yarn spun from the thermoplastic polyurethane used in the manufacture of Yarn-A;
Yarn-D:: a 20/6 denier multifilament woolly nylon yarn that is a high bulky, false-twisted yarn;
Yarn-E:: a 20/2 denier crimped, eccentric core and sheath type composite filament yarn, comprising a polyurethane core having the same composition as the thermoplastic polyurethane of Example 1 and a hardness of 95, conjugated with a nylon-6 sheath having a relative viscosity of 2.1; and
Yarn-F:: a single covering yarn comprising Yarn-C, as a core yarn, wound therearound with a 13/3 denier multi-filament woolly yarn manufactured by false-twisting in an S- or Z-direction.

Using these yarns, 6 kinds of stockings were knit with a 4-feeder seamless stocking knitting machine at a knitting rate of 600 rpm. All 4 feeders were supplied with the same yarn, except that the covering yarn, Yarn-F, was supplied to 4 feeders alternately with a 13/3 denier multifilament flat yarn.
With regard to the thus obtained 6 kinds of yarns and stockings knit therewith, a test for physical properties of the stocking and a wear test by 30 persons were conducted.
The results are shown in Table 3.
In Table 3, the physical properties of the stockings are represented as follows:

· Elastic stretch recovery:
A 100% stretching of the calf portion of the stockings in the direction perpendicular to the length thereof was repeated 5 times, and the elastic stretch recovery is represented by a ratio of a tensile stress at 80% elongation to a contractile stress at 80% elongation in the final stretching, which is found by the following equation:
The larger this value, the higher the fit property.
· Transparency:
Stockings placed 10 cm in front of a 20 watt white lamp were stretched 100% in longitudinal and

The stockings using Yarn-A and Yarn-B according to the present invention had an elastic stretch recovery (fit property and support feel) on the same level as those of Yarn-C (polyurethane filament yarn) and improved tactile properties which are drawbacks of polyurethane filaments, so that the stockings of the invention had a very good wear property.
The stockings knit with Yarn-D, the woolly nylon yarn, lacked fit feel caused by stretch recovery and were not transparent. The stockings knit with Yarn-E, the eccentric sheath and core composite filament yarn, were poor in crimp uniformity. Alternatively, the stockings knit with Yarn-F, the convering yarn, had an inferior fabric texture and lacked transparency. Thus, the yarns other than the present invention respectively had such drawbacks that they could not provide stockings of high quality.
Light transmission was hindered by Yarn-E due to its crimp as well as by Yarn-F due to its bulkiness. On the contrary, Yarn-A and Yarn-B provided highly transparent stockings because of flatness of these yarns. Additionally, the yarns of the present invention provided a strong elastic power and an excellent fit feel when the stockings were stretched, not given by a spring stress of crimps but by making use of the yarns' own tensile stress.
The stockings according to the present invention, as seen from the results of the wear test, acquired excellent marks in the respective evaluation items and retained characteristics of polyurethane yarns. Moreover, it could be said that no stockings other than those of the invention had ever had such an extremely high quality and performance.

Example 8

Conjugate-spinning was conducted in the same manner as the manufacture of Yarn-B of Example 7, except that nylon-12 having a melting point on DSC of 178°C (the tradename: L1600, manufactured by Daicel-Huells) was employed. The obtained filament yarn was denoted as Yarn-G.
Hoses were knit with a one-feeder circular knitting machine, using Yarn-B and Yarn-C of Example 7 and Yarn-G. The properties of the hose after scouring and dyeing were investigated. The results are shown in Table 4.
In Table 4, the slipperiness was determined as follows:
An aluminum frame was inserted into a knit hose and placed in the horizontal position. Then, a disc of a 23 g weight and a 25 mm diameter was put on the hose and the aluminum frame was gradually inclined. The angle of inclination when the disc started to slip down represented the slipperiness of the hose fabric.
The smaller the angle, the better the slipperiness.
It is found from Table 4 that the hose knit with Yarn-G using nylon-12 for the sheath exhibits a good slipperiness. Stockings manufactured for trial with Yarn-G had a very good performance when they were put on.

Examples 9-13

· Thermoplastic polyurethane:
Using 14.6 moles of a polyhexamethylene adipate having a molecular weight of 1,950, 50.5 moles of p,p'-diphenylmethane diisocyanate and, as a chain extender, 34.9 moles of 1,4-butane diol, a polyurethane was synthesized according to a conventional process. The relative viscosity of the resulting polymer, determined at 25°C in a 1 g/100 mℓ dimethylformamide solution, was 2.11.
· Polyisocyanate:
Twenty-three and nine-tenth moles of a polycaprolactone diol having a number average molecular weight of 1,250 and 4.2 moles of a polycaprolactone triol having a number average molecular weight of 1,250 were reacted with 71.9 moles of p,p'-diphenylmethane diisocyanate to provide a viscous compound. The percent NCO group of this compound was 6.6% by weight.
· Copolyester:
Bis-hydroxyethyl terephthalate was adequately admixed with bis-hydroxyethyl isophthalate and polycondensed while stirring under vacuum in an autoclave (inside temperature: 270°C) and five kinds of copolyesters having isophthalate copolymerization ratios of 10, 20, 30, 50 and 60 mole %, respectively. These copolyesters were pelletized.

The above thermoplastic polyurethane was melted in an extruder, the above polyisocyanate was incorporated into the molten polyurethane flow and then these polymers were thoroughly mixed with each other by a static mixer equipped with 35 mixing elements (manufactured by Kenics).
On the other hand, the above copolyester was melted in a separate extruder. The above two melts were severally metered and introduced into a spinneret for concentric-conjugate-spinning, having 8 orifices of a 0.5 mm diameter.
Varying the core/sheath conjugate ratio over 10 to 70, 40 denier monofilament yarns were spun at a spinning rate of 600 m/min. In the spinning step, a 15% emulsion for polyester was applied as an oiling agent.
Operabilities of the above polyester in drying and conjugate-spinning steps are shown in Table 5.
When the isophthalate copolymerization ratio was 10 mol %, the melt-spinning temperature was required to be increased, so that the heat stability of the polyurethane was too much deteriorated to conduct conjugate-spinning. On the contrary, when this ratio was 60 mol%, the pellets aggregated due to tackiness thereof and formed bridging during drying and were not bitten by the screws of the extruder, so that spinning was impossible.
Then, the above thermoplastic polyurethane was employed in lieu of the copolyester as a sheath component and conjugate-spinning was conducted in the same manner as the above. In this case, as an oiling agent, dimethylsilicone in combination with 5% or 0.2% of an amino-modified silicone was used (Comparative Example 4 or 5). The yarn of Comparative Example 4 was free from tackiness.
In Table 6, the physical properties of the composite yarns are shown.
In Table 6, the evaluation items are determined as follows:

· Unwinding coefficient:
When a composite filament yarn wound on a bobbin is unwound at a rate of 50 m/min and taken-up on a take-up roll, the unwinding coefficient is represented by a surface speed ratio of the bobbin to the yarn package on the take-up roll, when the unwinding of the yarn becomes impossible due to sticking to the surface of the bobbin.
· Take-up continuable time:
The spinning and take-up continuable time means the period of time during which a composite filament yarn can be spun and taken-up at a take-up rate of 600 m/min. on a paper tube having an outside diameter of 83 mm, without cobwebbing or yarn package collapsing occurring.
· Heat resistance:
The heat resistance is represented by the temperature at which a composite filament yarn elongates 50% when the yarn loaded with a 12.5 mg/d weight is heated at a temperature increase rate of 70°C/min.
· High pressure dyeability:
The composite filament yarns in Table 5 were knit into hoses with a one-feeder circular knitting machine and dyed with a blue dye having a concentration of 2% owf, at 130°C for 60 min. Then, reduction washing was conducted at 70°C for 20 min. On the other hand, a standard polyester fabric was prepared by dyeing with the same bath as that used for dyeing the above hoses. The color difference between the above hoses and the standard fabric was measured. A color difference (△E) of 1.5 or less is denoted by ○ and that of 12 or more is denoted by ××.

From Table 6, it is found that the polyurethane-polyurethane type composite filament yarn (Comparative Example 4) is good in unwinding property but has difficulty in take-up property and, contrarily, if the yarn is made tacky as Comparative Example 5, the take-up property improves, while the unwinding property is deteriorated. It is also found that the yarns of Comparative Examples are low in high pressure dyeability.
Alternatively, in Examples of the present invention, it is found that the unwinding property, take-up property and high pressure dyeability are all excellent. It is also found from Examples 9 and 10 that the heat resistance largely depends upon whether or not crosslinkages are present in the core component. Further, it is also found from Examples 11-13 that if the core/sheath conjugate ratio increases, i.e., the sheath component ratio decreases, the physical properties approach to that of the polyurethane-polyrethane type composite filament.

Example 14

The yarn samples of the above Example 10 and Comparative Example 5 were buried underground for one month in spring. Then, after washing with water and drying, the yarn samples were measured for a strength retention. The results are shown in Table 7. From Table 7, it is found that the yarn of the invention is very excellent in strength retention.

Examples 15-17

· Copolyester:
From 85 mol.% of terephthalic acid, 15 mol.% of isophthalic acid, 85 mol.% of ethylene glycol and 15 mol.% of diethylene glycol, a polyester was synthesized according to a conventional process. This polyester had a glass transition temperature of 64°C.

The thermoplastic polyurethane of Example 9 was melted in an extruder, the isocyanate used in Example 10 was incorporated into the molten polyurethane flow and then these polyesters were thoroughly mixed with each other by a static mixer equipped with 35 mixing elements (manufactured by Kenics). On the other hand, the above copolyester was melted in a separate extruder. Those two polymer melts were severally metered and introduced into a spinneret for concentric-conjugate-spinning, having a 8 orifices of a 0.5 mm diameter. Varying the core/sheath conjugate ratio over 2 to 20, 40 denier monofilament yarns were spun at a spinning rate of 600 m/min. In the spinning step, a 15% aqueous emulsion was applied as an oiling agent. Alternatively, yarns having no polyisocyanate incorporated thereinto were spun in the same manner as the above.
The properties of these yarns are shown in Table 8.
From Table 8, it is found that yarns as Comparative Examples 6 and 7 which do not satisfy the inequality: Y≧-8.7X+52, are inferior in elastic stretch recovery and heat resistance. Further, it is also found from Examples 16 and 17 that the elastic stretch recovery improves with increase of the core/sheath conjugate ratio.
A filament yarn consisting of this sheath component polymer alone had tensile strength of 0.60 g/d, an elongation at break of 0% and an elastic stretch recovery of 0%, so that it is surprising that the present invention provides a yarn comprising such a polymer with an excellent stretchability.

Example 18

The yarns of Example 16 and Comparative Example 4 were drawn at 90°C 2 times their original length. Then, the yarns having an initial load of 1.0 mg/d attached thereto were soaked in hot water at 100°C for 30 min. and air dried. Then, the length L (mm) was determined. The heat shrinkage was found by the following equation:

wherein L₁ is the length before soaking in hot water. Let the original length be L_O, then L_O>L₁ in the case of spontaneous shrinking. This spontaneous shrinkage was found by the following equation:
From Table 9, it is found that the yarn of the invention has a low spontaneous shrinkage and a high hot water shrinkage, and the polyurethane-polyurethane composite filament yarn is not set by drawing.
Then, using the yarns of Examples 16 and 17, drawing was conducted at 120°C, varying the draw ratio, and the heat shrinkage was determined. The results are shown in Table 10. These yarns had a spontaneous shrinkage of 0.8% or less.
From Table 10, it is found that the heat shrinkage increases with increase of sheath component ratio or draw ratio.

Examples 19-21

Conjugate-spinning was conducted in the same manner as Example 16, except that a low density polyethylene having a melting point temperature of 100°C (the tradename: PE356, manufactured by Tosoh Corporation) was employed as the sheath component. The physical properties of the resulting yarns are shown in Table 11.
In Table 11, the physical properties were determined as follows:

· 190°C recovery:
A composite filament yarn elongated 30% at room temperature was heat-treated at 190°C for 1 minute in a hot air dryer and then returned to room temperature. The 190°C recovery is a recovery of the length after returning to room temperature, which is found by the following equation:

From Table 11, it is found that a yarn as Comparative Example 8 which has a crosslink density Y of not more than 10 µmol/g, or a yarn as Comparative Example 9 which does not satisfy the inequality: Y≧-8.7X+52, is inferior in elastic stretch recovery and heat resistance. Further, it is also found from Examples 20 and 21 that the elastic stretch recovery and heat resistance improve with increase of the crosslink density and, further from Examples 19 and 21 that both these properties improve with increase of the core/sheath conjugate ratio.
A filament yarn consisting of this sheath component polymer alone had a tensile strength of 0.12 g/d and a melting point temperature of 100°C, so that it is surprising that the present invention largely improves the tensile strength and heat resistance.

Example 22

With the yarn of Example 20 and the polyurethane-polyurethane composite filament yarn of Comparative Example 5, fastness to alkali was investigated.
Using an aqueous solution comprising 10% by weight of sodium hydroxide as an alkaline aqueous solution, the yarns under a tensionless condition were soaked in the solution and treated at 80°C or 100°C for 60 minutes. Thereafter, a strength retention was determined. The results are shown in Table 12.
From Table 12, it is found that the yarn of Comparative Example 5 which is a polyurethane-polyurethane composite filament yarn is remarkably embrittled at 100°C, while the yarn of the invention is very excellent in fastness to alkali.

Claims

An elastic, core and sheath type composite filament composed of a fiber-forming thermoplastic non-elastomer sheath component and a polyurethane core component, wherein a core/sheath conjugate ratio (X) and a crosslink density (Y) (µmol/g) of the polyurethane satisfy simultaneously the following inequalities:

$3 ≦ X ≦ 100,$

$Y ≧ 0 and$

$Y ≧ -8.7X + 52.$
The filament according to claim 1, wherein said non-elastomer has an optimum melt-spinning temperature of at most 238°C.
The filament according to claim 1, wherein said non-elastomer is a polyamide having at least one of characteristics: a melting point temperature determined with a differential scanning calorimeter being within the range between 80°C and 220°C; and a relative viscosity determined at 25°C with a solution of 1 g polymer in 100 mℓ of 98% sulfuric acid being at most 2.3.
The filament according to claim 1, wherein said non-elastomer is a copolyester comprising polyethylene terephthalate as a principal constituent and 12-50 mol % of an isophthalate comonomer.
The filament according to claim 1, wherein said non-elastomer is a copolyester obtained from a dicarboxylic acid ingredient comprising 60-88 mol % terephthalic acid and 12-40 mol % isophthalic acid and a diol ingredient comprising 75-90 mol % ethylene glycol and 10-25 mol % of at least one glycol selected from the group consisting of diethylene glycol, triethylene glycol, neopentyl glycol and butanediol.
The filament according to claim 1, wherein said non-elastomer is a polyolefin selected from the group consisting of polyethylene, polypropylene, polystyrene and polybutene, and the polyurethane has a crosslink density (Y) of at least 6 µmol/g.
The filament according to claim 1, wherein said polyurethane core component comprises a polyurethane crosslinked by polyisocyanate and having a crosslink density (Y) of at least 6 µmol/g.
The filament according to claim 7, wherein the crosslinked polyurethane has predominantly an allophanate crosslinked structure.
The filament according to claim 1, which has a cross-sectional figure wherein the core component and the sheath component have substantially a common center of gravity.
A textile structure which comprises an elastic, core and sheath type composite filament composed of a fiber-forming thermoplastic non-elastomer sheath component and a polyurethane core component, said filament having a core/sheath conjugate ratio (X) and a crosslink density (Y) (µmol/g) of the polyurethane satisfying simultaneously the following inequalities:

$3 ≦ X ≦ 100,$

$Y ≧ 0 and$

$Y ≧ -8.7X + 52.$
The textile structure according to claim 10, which is a ladies' hosiery of which the non-elastomer is a polyamide.
The textile structure according to claim 11, wherein said polyamide is nylon-12.