JP2556649B2 - Latent elastic conjugate fiber, method for producing the same, and method for producing a fiber structure having stretch elasticity - Google Patents

Description

TECHNICAL FIELD The present invention relates to a conjugate fiber having excellent elongation recovery elasticity.
Especially, a part of the elongation recovery elasticity of the former is restrained by the latter by combining a fiber forming polymer having excellent elongation recovery elasticity and a fiber forming polymer which is inferior in elongation property and easily soluble in water or an alkaline aqueous solution. And a method for producing the same, and a method for exhibiting excellent elongation recovery elasticity by subjecting a fiber structure such as a yarn, a cloth, and a secondary product thereof made of such a composite fiber to water treatment or alkali treatment. In the description of this document and the appended claims, "water-soluble" means a property of being substantially dissolved by hot water and an alkaline aqueous solution, and "alkali-soluble" is soluble in an alkaline aqueous solution but hot water. Means a property that is hardly soluble or insoluble. It should be understood that "water treatment" includes "alkali aqueous solution treatment".

BACKGROUND ART Polyurethane elastic yarns have been used in various applications due to their excellent physical properties, but due to their properties such as stickiness, high elongation and low modulus, they can be wound up during spinning, processed into various yarns,
There are problems in handleability and operability of yarns in the post-process such as knitting and weaving.

In order to improve the stickiness, countermeasures are mainly taken from oil agents. For example, a method of adding metal soap or monoamines to an oil agent mainly containing dimethyl silicone is disclosed in JP-B-40-.
It is proposed in Japanese Patent No. 5557 and Japanese Patent Publication No. 46-16312. In addition, as another method of preventing sticking,
In JP-A-5-1993, a method for producing a core-sheath polyurethane-based composite elastic yarn in which urethane is arranged in the sheath and polyurethane cross-linked in the core is proposed.

Further, as another method for improving the handleability in the subsequent step, there is a method of reducing the elongation of the polyurethane elastic yarn. For example, there is a method of covering with nylon or the like, or performing hot drawing or cold drawing treatment. Furthermore, Japanese Patent Publication No. 55-8606 discloses polybis (propoxy).
Disclosed is a composite fiber in which a water-soluble polyamide containing ethaneadipamide as a main component and a polyurethane are compounded and which has latent rubber-like elasticity that can exhibit rubber-like elasticity by water treatment.

Of these, the improvement from the oil solution has some effects, but it is not complete and limited. That is, when considering the case of spinning and winding, if the sticking of the yarn is reduced, it is likely that the winding for a long time becomes impossible due to twilling or collapse. This tendency becomes more remarkable as the winding speed increases (eg, 500 m / min or more) and the diameter of the bobbin during winding decreases (eg, diameter 100 mm or less). On the contrary, if the yarn is stuck to the yarn, the yarn can be wound for a long time, but the yarn cannot be unwound in the subsequent process, which causes a serious trouble. In this way, it is often impossible to deal with the problem by just finely controlling the oil agent.

On the other hand, in the case of the urethane-urethane type core-sheath composite elastic yarn, at the time of spinning, it is possible to wind at high speed and for a long time on a small-diameter bobbin, and to carry out the stretchability and the stretchability which are usually carried out with nylon or polyester yarn. There was a difficulty in handling the yarn in the subsequent process.

On the other hand, the method of stretching the polyurethane elastic yarn to reduce the elongation has a problem that it needs to be carried out by a special method or machine because it cannot be stretched by an ordinary stretching machine. Further, in the case of hot drawing, the friction of polyurethane elastic yarn is high in the contact type, so that yarn breakage easily occurs. Therefore, there is a problem in operation unless the non-contact type is used. Furthermore, in order to heat set the polyurethane elastic yarn, it is necessary to apply considerably severe conditions such as high temperature or large elongation. In this case, the physical properties of the polyurethane elastic yarn itself may be deteriorated by the time it is passed to the subsequent step, and the performance as a product may be impaired.

The method of covering the polyurethane elastic yarn with nylon or the like requires the use of a special device and has a problem that the production speed is extremely slow.

Furthermore, the composite elastic fiber having a water-soluble polyamide as a sheath component and a polyurethane as a core component has a low yield in the synthesis of a diamine having an ether bond, which is a raw material of the polyamide, and has a thermal stability of the obtained polyamide. Since the melt stability is unstable and spinning is difficult, it has not been put to practical use.

In addition, the production rate of polyurethane elastic yarn is inferior to other general-purpose polymers such as nylon and polyester at present. For example, the spinning speed of polyurethane is limited to about 500 m / min in the melt spinning method. This is because, as described in Textile Society of Japan VOL.47, p.581 (1991), as the spinning speed is increased, molecular orientation becomes easier and the yarn becomes harder, and the elongation of the yarn increases the winding. This is because it is difficult to take them. Breakthroughs have not yet been made to achieve speeding up beyond the low modulus inherent in polyurethane fibers.

Further, Japanese Patent Publication No. 6286/1989 proposes a composite fiber containing hot water-useable copolyester as one component and capable of easily obtaining ultrafine fibers or special modified cross-section yarn by removing hot water. However, this fiber obtained by removal of hot water is not elastic and is outside the concept of latent elastic fiber intended by the present invention.

DISCLOSURE OF THE INVENTION Therefore, the object of the present invention is to make a fiber structure such as a yarn, a fabric, a fiber secondary product, etc. in the same manner as a general synthetic fiber such as nylon, and further, for example, for scouring, dyeing process, etc. It is an object of the present invention to provide a novel latent elastic conjugate fiber which can almost completely recover the properties as a polyurethane elastic yarn by a water treatment step or an alkali treatment step.

Another object is to provide a method for industrially advantageously and inexpensively producing a polyurethane elastic yarn which can be wound at a speed equivalent to that of general synthetic fibers such as nylon and has a low modulus. There is.

The present inventors have completed the present invention as a result of earnest studies for achieving the above object.

That is, the latent elastic conjugate fiber of the present invention is a polyurethane / polyester composite in which the crosslinked polyurethane mainly having an allophanate crosslinked structure and a Shore A hardness of 75 to 98 and the water-soluble or alkali-soluble polyester are in the range of 1/1 to 90/1. A single fiber that is uniformly extended and joined along the longitudinal direction with a ratio (volume ratio), the polyester is exposed on the fiber surface in the cross-section of the fiber, and the polyurethane (the water-soluble or alkali-soluble) is used. After the treatment for dissolving and removing the polyester) is independently performed, the tensile strength of 1.0 to 5.5 g / d, the elongation at break of 350 to 1200% and the excellent elongation recovery elasticity are exhibited.

Most preferably, the engagement form of the composite fiber is a core / sheath type in which polyurethane is the core component and the polyester is the sheath component.

The crosslink density of the allophanate crosslinked structure is preferably at least 6 μmol / g, more preferably at least 10 μmol / g.

The polyurethane / polyester composite ratio is preferably
It is in the range of 1/1 to 50/1, and more preferably in the range of 1/5 to 5/1. Generally, the preferred value of the tensile strength of the polyurethane single yarn after the hot water shrinkage is in the range of 2.5 to 4.5 g / d, but if the composite ratio is in the range of 1/1 to 5/1, it is generally 1.8 to 5.5 g. / d
The tensile strength of the fiber in the range is guaranteed.

 The breaking elongation is preferably 400 to 800%.

Preferable specific examples of the water-soluble polyester include aromatic dicarboxylic acid having a sulfonate as an acid component and / or its ester-forming derivative (component A) in an amount of 5 to 20.
55% by mole or more of aromatic dicarboxylic acid and / or its ester-forming derivative (component B) excluding the component A, and alicyclic dicarboxylic acid and / or its ester-forming derivative (component C) and alicyclic A dicarboxylic acid and / or an ester-forming derivative thereof (component D) and the above-mentioned components C and D are represented by the following formula: 0 mol% ≦ C + 4 × D ≦ 40 mol% (wherein C and D are C component or D respectively) The molar ratio of the component to the total acid component) is satisfied, and the glycol component is ethylene glycol.
It consists of 50 mol% or more.

Further, as a preferred embodiment of the alkali-soluble polyester, a copolyester composed of terephthalic acid, isophthalic acid, and a dicarboxylic acid having a sulfonate as a dicarboxylic acid component and ethylene glycol as a diol component can be mentioned.

The water-soluble or alkali-soluble polyester preferably has a glass transition temperature of 35 to 80 ° C.

The latent elastic composite fiber of the present invention is manufactured by melting thermoplastic polyurethane having a Shore A hardness of 75 to 98 and water-soluble or alkali-soluble polyester respectively, and adding and mixing polyisocyanate to the melted polyurethane. , A polyurethane / polyester composite ratio of 1/1 to 90/1 (volume ratio), and a composite spinning of both melts with a relational arrangement such that the polyester is exposed on the fiber surface in the cross section of the fiber, and 300 to 3000 m / min. It is characterized by winding at a winding speed.

Furthermore, the method for producing a fiber structure having elongation recovery elasticity according to the present invention, a fiber structure is formed by using the latent elastic composite fiber, and water treatment or alkali treatment under heating,
It is characterized in that the polyester is substantially dissolved and removed.

BRIEF DESCRIPTION OF THE DRAWINGS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. In the accompanying drawings, FIG. 1 is a cross-sectional view showing an example of a preferable composite form of the conjugate fiber of the present invention, and FIG. 2 is a core-sheath type suitable for spinning the conjugate fiber of the present invention. It is a vertical sectional view showing an example of a mouthpiece.

BEST MODE FOR CARRYING OUT THE INVENTION The polyurethane constituting the fiber of the present invention refers to a crosslinked polyurethane derived from a thermoplastic polyurethane. Thermoplastic polyurethane is a melt-spinnable polymer obtained by reacting a polymeric diol with an organic diisocyanate and a chain extender.

Examples of the polymer diol include ether polyols having hydroxyl groups at both ends and having a molecular weight of 500 to 5000, such as polytetramethylene glycol and polypropylene glycol, polyhexamethylene adipate diol, polybutylene adipate diol, polycarbonate diol, and polycaprolactone diol. Such glycols as ester-based polyols, etc., or a mixture thereof may be used.

Examples of the chain extender include 1,4-butanediol having a molecular weight of 500 or less, ethylene glycol, propylene glycol and bishydroxyethoxybenzene.

Organic diisocyanates include tolylene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI) or non-yellowing diisocyanates such as 1,6-hexanediisocyanate, and mixtures thereof.

In the present invention, a thermoplastic polyurethane polymerized from these components by a known method has a JIS-Shore A hardness of 75-9.
The range of 8 applies. When the hardness is less than 75, problems such as poor elastic recovery of the obtained composite yarn and lack of practical heat resistance tend to occur. On the contrary, if the hardness exceeds 98, the elastic recovery of the polyurethane itself is poor, and the elastic recovery of the composite yarn cannot be expected unless the crimped structure is used, and the range of optimum spinning conditions of the polyurethane is narrow. The range of 82 to 95 is suitable.

To the polyurethane applied to the present invention, known titanium oxide, ultraviolet stabilizer, ultraviolet absorber, antibacterial agent and the like can be added as required.

In order to give the polyurethane further heat resistance and further elastic recovery as fibers, a polyisocyanate is reacted with the thermoplastic polyurethane, and a crosslinked polyurethane having an allophanate crosslinked structure is mainly used.
As a method for producing crosslinked polyurethane, Japanese Patent Publication No. 58-46573
The method proposed by us in the publication, that is, a method of adding and mixing a polyisocyanate to a molten thermoplastic polyurethane to complete allophanate cross-linking during or after spinning may be used.

This polyisocyanate is composed of a polyol component and an isocyanate component, and is a compound having 2 or more, preferably 2 to 3 isocyanate groups in the molecule. As the polyol component, in addition to the above-mentioned diol having a molecular weight of 500 to 4000 used for the synthesis of polyurethane, a mixture of diol and triol to have an average functionality of 2-3, or a synthetic polyol having a functionality of 2-3 is also available. It can be preferably used. On the other hand, as the isocyanate component,
The above-mentioned diisocyanate used in polyurethane synthesis, a trimer of an organic diisocyanate, a reaction product of trimethylolpropane and an organic diisocyanate, or
Isocyanates having a functionality in the range of 2-3, for example,
Carbodiimide-modified isocyanate and the like can be used alone or as a mixture.

The above-mentioned two components can be reacted by a known method, but in this case, it is preferable to react them so that the isocyanate group content becomes excessive. Of course, this amount is appropriately selected depending on the desired physical properties such as heat resistance and recoverability, and the polyol used.

The amount of polyisocyanate added varies depending on the NCO group content and type of the polyisocyanate used, but is usually preferably in the range of 5 to 40% by weight based on the mixture of polyurethane and the polyisocyanate. 40 added
If it exceeds 5% by weight, the mixing tends to be non-uniform and the spinning tends to be unstable, and the mechanical properties of the yarn tend to be unsatisfactory, which is not preferable. On the contrary, if it is less than 5% by weight, it is difficult to obtain the desired heat resistance, which is not preferable. It is preferably in the range of 10 to 30% by weight.

In this way, a crosslinked structure mainly composed of allophanate crosslinks is formed in the polyurethane. At this time, when the polymer contains a urea bond, biuret bonds are formed and the spinnability is extremely deteriorated, which is not preferable. That is, since the production rate of biuret cross-linking is higher than that of allophanate cross-linking, the viscosity of the system during spinning increases and stable spinning tends to be impossible.

The crosslink density in the crosslinked polyurethane is preferably at least 6 μmol / g, which is measured after dissolving the water-soluble or alkali-soluble polyester component constituting the composite system. This is because if it is less than 6 μmol / g, it is difficult to obtain heat resistance as a composite yarn, that is, heat resistance in practical use.
More preferably at least 10 μmol / g. On this occasion,
In such a method, a polyurethane component having a crosslink density such that the sample does not dissolve is naturally conceivable, but such a system can of course be suitably used if it has good spinnability. The method for measuring the crosslink density of the crosslinked polyurethane was as follows. After dissolving the polyester component in the solvent, 1 g of the polyurethane was first stirred in a dimethylsulfoxide / methanol mixed solution at 23 ° C to 100 ° C for 12 hours, and then in a dimethylsulfoxide solution containing about 200 µmol / g of n-butylamine at 23 ° C. , Dissolve for 24 hours. After that, 1 /
The crosslink density was determined by back titrating n-butylamine in the reaction system with 100 to 1/50 N hydrochloric acid-methanol solution using bromphenol blue as an indicator.

On the other hand, the water-soluble polyester used in the present invention is
For example, it is a water-soluble copolymer which is easily soluble in hot water of about 50 ° C. or higher, but is extremely difficult to dissolve in water at room temperature or to cause tackiness. This copolymer preferably has the following composition. That is, terephthalic acid, isophthalic acid,
It is a copolymer of a dicarboxylic acid having a sulfonate and / or an ester derivative thereof, and an alicyclic dicarboxylic acid, and ethylene glycol, neopentylene glycol, diethylene glycol or the like as a diol component.

In a preferred embodiment, the aromatic dicarboxylic acid having a sulfonate and / or its ester-forming derivative (component A) has an alkali metal sulfonate such as 4-sulfoiiphthalic acid, 5-sulfoisophthalic acid, sulfo. Terephthalic acid, 4-sulfophthalic acid,
4-sulfonaphthalene-2,7-dicarboxylic acid, 5- [4
An alkali metal salt such as -sulfophenoxy] isophthalic acid or an ester-forming derivative thereof is used.
-Sulfoisophthalic acid sodium salt or its ester-forming derivatives are particularly preferred. The dicarboxylic acid having a sulfonate group and / or its ester-forming derivative is in the range of 5 to 20 mol%, preferably 6 to 10 mol% based on the total dicarboxylic acid component from the viewpoint of water solubility and water resistance.
A range of 12 mol% is good. If this amount is less than 5 mol%, the water solubility will be poor, and if it exceeds 20 mol%, problems during polymerization and poor operability during chipping will occur, and the polymer obtained will be easy to handle. It is not preferable because it may adversely affect the thermoplasticity.

As the aromatic dicarboxylic acid and / or its ester-forming derivative (component B) excluding the component A, there are terephthalic acid and / or its ester-forming derivative (component B1).
And isophthalic acid and / or its ester-forming derivative (B2 component) are preferred from the viewpoint of availability of raw materials, industrialization and good mechanical properties. Furthermore, this amount is at least 55 mol in all dicarboxylic acids. % Is preferable. If it is less than 55 mol%, the physical properties of the polymer to be obtained, in particular the melt heat stability and heat resistance, tend to be inferior, which is not preferable. Furthermore, the molar ratio of this B1 component / B2 component is 2/8.
-8/2, preferably 3 / 7-7 / 3 is preferable from the viewpoint of polymer amorphization and water solubility.

Examples of the alicyclic dicarboxylic acid and / or its ester-forming derivative component (C component) include 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid and 1,2
-Cyclohexanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 4,4'-bicyclohexyldicarboxylic acid and the like, or ester-forming derivatives thereof are used. Further, the linear aliphatic dicarboxylic acid or its ester-forming derivative may be used within the range of 10 mol% or less of the total dicarboxylic acid component. Examples of such dicarboxylic acid components include adipic acid, pimelic acid, suberic acid,
Examples thereof include aliphatic dicarboxylic acids such as azelaic acid and sebacic acid, and ester-forming derivatives thereof. If the amount of the above-mentioned linear aliphatic dicarboxylic acid component is too large, not only blocking tends to occur but also water resistance becomes poor, which is not preferable. That is, in a preferred embodiment of the readily water-soluble polyester, the linear aliphatic dicarboxylic acid and / or its ester-forming derivative component (D component) and the C component are represented by the following formula: 0 mol% ≤ C + 4 x D ≤ 40 mol% (However, C and D represent the mole fraction of the C or D component with respect to the total acid component) It is desired not only to prevent blocking of the polymer obtained but also from the viewpoint of water resistance.
This is because when the D component is, for example, 20 mol% and the C component is 0 mol%, and the above relationship is not satisfied, the glass transition temperature of the obtained polymer is about room temperature and the handling property is poor, and the polymer is poor. This is because the physical properties of are likely to be inferior.

In the present invention, aromatic dicarboxylic acid or its ester-forming derivative may be used as a dicarboxylic acid component other than the above within a range of 30 mol% or less of the total dicarboxylic acid component. Examples of these dicarboxylic acid components include:
Examples thereof include aromatic dicarboxylic acids such as phthalic acid, 2,5-dimethylterephthalic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid and biphenyldicarboxylic acid, or ester-forming derivatives thereof.

On the other hand, as the diol component, ethylene glycol is used in an amount of 50 mol% or more based on the total glycol component from the viewpoint of spinnability of the polyester copolymer. In addition to ethylene glycol as a glycol component, 1,4-butanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene are used as long as they do not adversely affect mechanical properties, heat melting stability, etc. Glycol and polyethylene glycol may be used in combination.

Suitable examples of the water-soluble polyester thus obtained include (A) 5 to 15 mol% of a dicarboxylic acid having a sulfonate group and / or its ester-forming derivative with respect to the total dicarboxylic acid component, (B) A mixture of terephthalic acid and / or its ester-forming derivative (terephthalic acid component) and an isophthalic acid and / or its ester-forming derivative (isophthalic acid component) in a molar ratio of 30/70 to 70/30 is completely dicarboxylic acid. For the acid component,
55 to 80 mol% (C) of all dicarboxylic acid components, 5 to 30 mol% of alicyclic dicarboxylic acid and / or its ester-forming derivative was polymerized with at least four acid components and a glycol component. Examples thereof include polyester copolymers.

The above-mentioned polyester used in the present invention has a high water-solubility, but the high water-solubility referred to in the present invention is not strictly physicochemical, and is a substance which is substantially dissolved and / or finely dispersed in water. Including. For example, when immersed in boiling water at 95 ° C. and a bath ratio of 100 for 3 minutes, all the fibers are dissolved and dispersed.

As such a water-soluble polyester, one having a glass transition temperature in the range of 35 to 110 ° C. is preferable. If this temperature is lower than 35 ° C., the handleability of the obtained composite yarn tends to be poor, which is not preferable, and if it exceeds 110 ° C., the solubility in water is insufficient, which is not preferable. Within the above range, for example, it is easily soluble in hot water at a temperature of 50 ° C. or higher, but extremely difficult to dissolve in water at a temperature of less than 50 ° C. or less likely to cause tackiness, resulting in good handleability. Glass fiber temperature is measured by Rigaku Co., Ltd. thermal analyzer (TAS100)
Then, the temperature is once raised to 180 ° C. at a rate of 10 ° C./min in a nitrogen stream, then cooled to −150 ° C. and then again raised to measure.

Among the copolyesters obtained as described above, for example, in order to be hardly soluble in water at a temperature of 30 ° C. or lower,
The glass transition temperature is also an important factor, in this case 40-60 ° C.
It is preferable to select the composition and the ratio thereof so that the glass transition point is obtained at the above temperature.

Further, as the alkali-soluble polyester, a dicarboxylic acid having a terephthalic acid, an isophthalic acid, and a sulfonic acid salt as a dicarboxylic acid component, and a copolymerized polyester made of ethylene glycol as a diol component can be mentioned. For example, copolymers of isophthalic acid / terephthalic acid / ethylene glycol with 2.5 mol% or more, preferably 3.3 mol% or more of 5-sulfoisophthalic acid or a metal salt thereof, or with 6 wt% or more of polyethylene glycol. Is mentioned.

Further, the water-soluble or alkali-soluble polyester is
It is preferable that it is a fiber-forming linear polymer and melt-spinnable, for example, it shows fluidity in the range of 180 to 300 ° C. and foams,
It is desirable that spinning be possible without decomposition. The water-soluble polyester copolymer applied to the present invention has thermal stability,
When a water-based spinning oil agent used in a normal melt-spinning method that is excellent in spinnability is used, sticking occurs, unwinding tension becomes large at the time of stretching, and the drawing operability may decrease, so a non-aqueous spinning oil agent is used. Is preferred.

Further, well-known additives such as a matting agent, an antioxidant and a lubricant may be blended with the water-soluble or alkali-soluble polyester.

As the method for polymerizing the copolyester used in the present invention, various ordinary methods can be used. For example, transesterification reaction of dimethyl ester of dicarboxylic acid and glycol, after distilling methanol, gradually reduced pressure under high vacuum, polycondensation method, or esterification reaction of dicarboxylic acid and glycol After distilling the produced water, the pressure is gradually reduced and polycondensation is performed under high vacuum, or when dimethyl ester of dicarboxylic acid and dicarboxylic acid are used as raw materials, dimethyl ester of dicarboxylic acid and ester of glycol. There is a method in which, after the exchange reaction, a dicarboxylic acid is further added to carry out an esterification reaction, and then polycondensation is carried out under high vacuum. As the transesterification catalyst, manganese acetate, calcium acetate, zinc acetate and the like can be used, and as the polycondensation catalyst, known ones such as antimony trioxide, germanium oxide, dibutyltin oxide and titanium tetrabutoxide can be used. Further, phosphorus compounds such as trimethyl phosphate and triphenyl phosphate and hindered phenol compounds such as Irganox 1010 may be used as the stabilizer. However, various conditions such as the polymerization method, the catalyst and the stabilizer are not limited to the above examples.

The polyurethane and polyester components have been described above. Next, the composite ratio will be described.

The composite ratio of polyurethane / polyester is the volume ratio of both components, that is, the yarn cross-sectional area ratio is 1/1 to 90/1, preferably 1/1 to 50.
/ 1, more preferably 1/1 to 5/1.

More preferably, the range of 4/1 to 20/1 is preferable. If the composite ratio is less than 1/1, the yarn quality is likely to be very brittle, and the handling becomes worse in the post-process such as stretching, and the amount to be dissolved is large, which is economically disadvantageous. . On the other hand, if this ratio exceeds 90/1, the spinnability tends to be poor, and especially in the case of the core-sheath type composite, the sheath component is likely to break, which is not preferable.

Next, as the composite form, any form may be used as long as the water-soluble polyester is exposed on the fiber surface in the cross-sectional shape of the fiber. For example, various known shapes such as a core-sheath type and a cross type shown in FIG. 1 can be used. Among them, in the concentric circular composite form, it is preferable that the center of gravity of both components of the core and the sheath are the same, from the viewpoints of spinning stability, uniformity of the obtained yarn, and handleability of the yarn. On the other hand, in the cross shape of FIG. 1 as well, by dissolving and removing the polyester component,
Polyurethane ultrafine yarn, which is difficult to produce by dry spinning or wet spinning, is easily obtained, which is preferable. In this case, a yarn of 2 denier or less per filament, for example, 0.2 denier can be easily obtained. On the other hand, the cross-sectional shape of the composite yarn may be circular or irregular.

Next, a method for producing a core-sheath type composite yarn having a crosslinked polyurethane as a core among the yarns of the present invention will be described.

The composite spinning is a spinning having a portion where a polyisocyanate is added and mixed in a portion where a thermoplastic polyurethane is melt extruded, a portion where a water-soluble or alkali easily-soluble polyester of a sheath component is melt-extruded, and a known core-sheath type composite spinneret. It can be preferably carried out by a melt-composite spinning apparatus equipped with a head.

It is possible to use a kneading device having a rotating part in a portion where polyisocyanate is added to and mixed with a molten polyurethane during spinning, but more preferable is a mixing having a static kneading element known per se. Is to use the device. The shape and number of static kneading elements differ depending on the conditions of use, but it is important to select so that the thermoplastic polyurethane and polyisocyanate are sufficiently mixed before flowing into the composite spinneret. Yes, usually 20 to 90 elements are provided. In this way, the molten polyurethane as the core component mixed with the polyisocyanate and the easily water-soluble polyester as the sheath component melted by another extruder are introduced into the core-sheath composite spinneret and spun and wound. The composite yarn of is obtained.

Further, in the design of the core / sheath composite mouthpiece in the case where the core / sheath composite ratio is, for example, 15/1 or more, the structure of the portion where the flow paths of the sheath component and the core component meet is as shown in FIG. ) Make the groove depth (d) of the introduction path shallow, for example, 2 mm or less. Core component (a)
The interval (h) between the lower part of the introduction hole (internal orifice flow path) 1 and the upper part of the core-sheath composite final discharge nozzle hole 2 is 0.05 to 1.
It is preferable to take measures such as making it as small as 5 mm.

As a winding method, for example, a winding machine capable of producing a speed of about 8000 m / min may be used to wind at a speed of about 300 m / min or more and about 3000 m / min or less. When ordinary polyurethane fibers are produced at such a rate, the elongation is reduced and the stress becomes very high, whereas in the case of the present invention, one component is polyester, so that it is wound at such a high speed. However, since the elongation of the urethane component is suppressed and the molecular orientation is disturbed, it is considered that such an adverse effect is unlikely to occur.

As a method of reducing the elongation at the stage of the raw yarn, any one of a method of reducing the elongation by optimizing conditions such as a polymer, a composite ratio and a spinning speed during spinning, a method of performing a stretching treatment after spinning, or Both can be used. Of these, the method of fixing the elongation during spinning is preferable, and the so-called spin draw method is particularly preferable. That is, the composite fiber during spinning is drawn by the draw roller 1.
By hot or cold drawing in the range of 3 to 6.5 times, the polyester of the sheath component is easily oriented and fixed, and the yarn is set because it is the core component, and the handleability as a yarn becomes very easy. The elongation of the final composite fiber after the spinning and / or drawing step is about 150% or less, especially 2
It is preferably in the range of 0 to 100%. Further, the strength is preferably 0.5 g / d or more from the viewpoint of workability.

The fiber of the present invention is a continuous filament or is cut and processed into staples, or is knitted, woven or mixed with other natural fibers or synthetic fibers to be a web-like cloth, or a fiber secondary product, etc. It does not require any special equipment when processing into various fiber structures and has very good workability. In particular, the latent elastic conjugate fiber of the present invention can be cut into staples and used as a mixed yarn with other fibers. Furthermore, even in a tricot using a polyurethane elastic yarn, it is not necessary to use a complicated warper dedicated to the polyurethane elastic yarn, and a warper used for an ordinary yarn, such as nylon, may be used. It has been considered extremely difficult with conventional elastic yarns. Furthermore, there is no case where a polyurethane elastic yarn having heat resistance and an ultrafine yarn, for example, a yarn having a fineness of 0.2 d / f, has been obtained so far.

In order to produce a fiber structure having stretch elasticity according to the present invention, the fiber of the present invention is processed into a fabric such as a yarn, a woven or knitted fabric or a non-woven fabric, or a fiber secondary product, and water treatment is applied to remove the sheath component. A dissolution method may be used. The water treatment step can also be performed by utilizing an aqueous treatment in the scouring and dyeing steps. In particular, when the sheath component is easily soluble in alkali, it is also possible to use a known alkali weight reduction processing method which is often used for polyester fibers.

As described above, the yarn of the present invention has the following advantages because the sheath component is water-soluble or alkali-soluble polyester and the core component is polyurethane.

-Polymerization of the sheath component is easy and the thermal melt stability is good.

-The elongation of the resulting composite yarn can be adjusted freely.

-It has excellent windability during spinning, and has almost no sticking, and so-called vertical movement is possible.

・ Even when spinning and winding, an inexpensive emulsion oil can be used, and it can be wound up on a small-diameter bobbin at a high speed of 1000 m / min. Furthermore, it is possible to wind up by high speed spinning of 3000 m / min.

-The polyurethane elastic yarn remaining after the dissolution has a strength of, for example, 4 g / d and a breaking elongation of 300% or more, which is surprisingly unthinkable with ordinary polyurethane fibers. Thus, it is quite unexpected that the polyurethane fiber obtained by dissolving and removing the polyester component of the conjugate fiber of the present invention exhibits a large tensile strength as compared with the polyurethane fiber obtained by the conventional single spinning of polyurethane. This is a remarkable effect that cannot be obtained. Further, the elastic recovery rate of this polyurethane elastic yarn shows a value of about 80 to 90% in the case of polyester polyurethane and about 88 to 95% in the case of polyether polyurethane.

・ It is possible to easily obtain ultrafine yarn of about 0.2 denier, which is not possible with conventional polyurethane elastic yarn.

-Since it is a melt spinning method, it has the advantage of being advantageous in industrial production.

Since it has excellent features as described above, it can be used for various purposes. For example, when it is used for a swimsuit, a product having a shortened process and excellent operability can be suitably used for socks, innerwear and pantyhose. Particularly in the case of ultrafine yarn, a product having unprecedented softness and texture can be obtained if used for such purposes.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited thereto.

Example 1 Thermoplastic Polyurethane Using 3500 parts by weight of polytetramethylene glycol having a molecular weight of 1000, 1220 parts by weight of p, p'-diphenylmethane diisocyanate, and 245 parts by weight of 1,4 bis (β-hydroxyethoxy) benzene as a chain extender. It was synthesized by a conventional method.
The relative viscosity of this polymer at a concentration of 1 g / 100 ml measured at 25 ° C. in dimethylformamide was 2.12.

Polyisocyanate A viscous compound was obtained by reacting 850 parts by weight of polytetramethylene glycol having a molecular weight of 850 with 500 parts by weight of p, p'-diphenylmethane diisocyanate. NCO of this compound
The weight percent was 6.2 weight percent.

Water-soluble polyester copolymer dimethyl terephthalate 38.74 parts by weight, dimethyl isophthalate 31.95 parts by weight 5-sulfoisophthalic acid dimethyl sodium salt 10,34 parts by weight, ethylene glycol 54.48 parts by weight, calcium acetate monohydrate 0.073 parts by weight, acetic acid After transesterification 0.024 parts by weight of manganese tetrahydrate under a nitrogen stream at 170 to 220 ° C. while distilling off methanol, trimethyl phosphate 0.05 parts by weight, and antimony trioxide 0.04 parts by weight and 1 as a polycondensation catalyst. Esterification was carried out by adding 17.17 parts by weight of 4,4-cyclohexanedicarboxylic acid and distilling off a theoretical amount of water at a reaction temperature of 220 to 235 ° C. After that, the pressure inside the reaction system is further reduced and the temperature is raised, and finally at 280 ° C and 0.2 mmHg, 2
Time polycondensation was performed. Then, polymerization was performed in the same manner with the composition ratio shown in Table 1.

 The obtained polymer was evaluated by the following methods.

Glass transition temperature: Thermal analyzer (TAS100) manufactured by Rigaku Co., Ltd.
Then, the temperature was once raised to 180 ° C. at a rate of 10 ° C./min in a nitrogen stream, then cooled to −150 ° C. and then again raised to measure.

Water-soluble: Add 425 g of water to 75 g of polyester copolymer, and add 9
It evaluated by stirring at 5 degreeC for 3 hours.

Spinning of only these polymers was performed. Nozzle temperature
230 ° C., nozzle diameter 0.5 mm, winding speed 500 m / min, dimethyl silicone-based oil was applied as the oil, and a 40-denier 1-filament yarn of the brand was sampled. The results are shown in Table 1.

From Table 1, the polymer from Comparative Example 1-1 had poor handleability when dried, and the yarn obtained from this had a large degree of sticking, so the elongation was not measured. Comparative Example 1
-2 contained less than 5 mol% of 5-sulfoisophthalic acid dimethyl sodium salt, and this polymer was insoluble in water. The yarn from Comparative Examples 1-3 was very brittle and poor in handleability. In Comparative Example 1-4, the glass transition temperature was close to room temperature because the diol component was 100% diethylene glycol. In addition, spinning was not performed because drying was extremely difficult and handling was poor.

 Next, an example in which a composite yarn is used will be described.

The above thermoplastic polyurethane was melted by an extruder, 15% by weight of the above polyisocyanate was added in the middle of the melt flow, and they were sufficiently kneaded by a 35-element static mixer (manufactured by Kenix).
-1 water-soluble polyester is melted by another extruder,
These were individually lightened and led to a concentric 4-hole compound mouthpiece (nozzle diameter 0.5 mm). This is usually 150 with a winding machine.
40d / 1f yarn was taken at a speed of 0 m / min. In the spin draw method, the first godet roller of the winding machine is fixed at 500 m / min, and the second drawing godet roller (draw roller) is changed to 2 to 3 times the speed of the first godet roller to wind it. A yarn having a fineness of 40d / 2 filament was obtained. In addition, a polyurethane elastic yarn of 40d / 1 filament having no sheath component was spun (Comparative Example 1-7).

In the above spinning, an oil agent mainly composed of dimethyl silicon was used.

The results are shown in Table 2. In addition, Example 1-5
-The yarns of Example 1-7 and Comparative Example 1-6 were not drawn.

From Table 2, in the case of a normal winding machine, the strength decreases as the core-sheath composite ratio decreases, and especially when the composite ratio is 1/6, the strength is extremely low at 0.06 g / d and yarn breakage occurs. Therefore, it was difficult to send it to the stretching step. On the other hand, looking at the case of the yarn by the spin draw method, it can be seen that the elongation decreases as the draw ratio during spinning increases, and the elongation is about the same as that of a normal yarn such as nylon. With a composite ratio of 2/1,
When comparing the ordinary winding machine and the yarn obtained by the spin draw method, it can be seen that the latter is superior in strength and elongation. Further, the yarns of Examples were excellent in long-time winding, unwinding property, and warpability.

Using the yarn of Example 1-7, it was subjected to warping by using a normal warping machine at the time of manufacturing nylon tricot. Further, the yarn of the present invention, which has been warped with 50d / 12f nylon as a front yarn, is subjected to a knitting process as a back yarn. Further processing was performed, but there was no problem.

Example 2 Next, Examples 1-4, 1-7, and Comparative Example 1-7.
The yarn was applied with a load of 1 mg / d for 30 minutes under hot water at 100 ° C. and air dried. Table 3 shows the hot water shrinkage ratio (hereinafter abbreviated as heat absorption) and the physical properties after the hot water treatment. In addition, Example 1-7
The yarn had a completely dissolved sheath component after heat absorption. still,
The heat flux was calculated by the following formula.

Heat balance (%) = (original length-length after air drying) x 100 / original length From Table 3, it is quite unexpected that the strength of the yarn of the present invention is much higher than the strength of ordinary urethane elastic yarn of 1.4 g / d. Further, in the case of the stretched polyurethane elastic yarn, so-called natural shrinkage occurs in which the yarn shrinks before the heat absorption measurement, but the yarn of the example is fixed, and such a phenomenon was not observed. Further, this yarn was drawn at 150 ° C. under a double condition. At this time, the heat flux showed a very high value of 70%.

Example 3 The water-soluble polyester used in Example 1 and the crosslinked polyurethane described in Example 1 were used (the composite ratio in this case was 1 /
2), the cross-shaped composite spinning as shown in FIG. At this time as well, the same apparatus as in Example 1 was used to spin at a draw ratio of 2.5 by the spin draw method to obtain a yarn of brand 40d / 20f. The results are shown in Table 4.

From Table 4, it can be seen that the latent elastic yarn of the present invention has a small elongation and is comparable to a yarn such as nylon. Further, from this example, a thin yarn of 1.3 denier per filament was easily obtained. The yarn was stretched at room temperature for 30 and then heat-treated in a hot air dryer at 190 ° C for 1 minute. After that, the return yarn was relaxed to room temperature, and the elongation recovery by the following formula was calculated.

Elongation recovery (%) = (1.3 x original length-set length) x 100 / (1.3 x original length-original length) As a result, the yarn is neither melt cut nor recoverable.
It is 23% and it can be seen that there is sufficient heat resistance. This yarn was useful not only for clothing but also for medical purposes such as artificial blood vessels.

Example 4 In Examples 1 to 3, the core / sheath composite ratio was changed to 8/1, the polyurethane core was placed concentrically, the water-soluble polyester side was placed in the sheath, and the winding speed was increased by a normal winding machine. Spinning was performed in the same manner except that the value was changed. For comparison, a polyurethane single yarn containing a polyisocyanate was similarly wound up.
The brand was 40d / 1 filament. The results are shown in Table 5.

From Table 5, as the spinning speed is increased, the strength increases and the elongation decreases, but as compared with the yarn of Comparative Example 1, the spinning speed is 3000.
It can be seen that even at a high speed yarn such as m / min, the elongation is surprisingly large and the heat absorption value is low, and it is a very soft yarn. On the other hand, without compounding as in this embodiment,
It can be seen that when the spinning speed is simply increased (Comparative Example 2), the hardness becomes extremely high.

Example 5 Thermoplastic Polyurethane was synthesized by a conventional method using 14.6 mol% of polyhexamethylene adipate having a molecular weight of 1950, 50.5 mol of p, p'-diphenylmethane diisocyanate, and 34.9 mol% of 1,4-butanediol as a chain extender. . The relative viscosity of this polymer at a concentration of 1 g / 100 cc measured at 25 ° C. in dimethylformamide was 2.15.

-Polyisocyanate: 23.9 mol% of polycaprolactone diol having a molecular weight of 1250 and a functionality of 2.0, 4.2 mol% of polycaprolactone triol having a molecular weight of 1250 and a functionality of 3, and 71.9 mol% of p, p'-diphenylmethane diisocyanate are viscous. The compound was obtained. The NCO weight% of this compound was 6.6 weight%.

Water-soluble polyester copolymer dimethyl terephthalate 38.74 parts by weight, dimethyl isophthalate 31.95 parts by weight, 5-sulfoisophthalic acid dimethyl sodium salt 10.34 parts by weight, ethylene glycol 54.48 parts by weight, calcium acetate-water salt 0.073 parts by weight, manganese acetate 0.024 parts by weight of tetrahydrate in a nitrogen stream at 170 ° C to 220 ° C
After performing the transesterification reaction while distilling off methanol with trimethyl phosphate, 0.05 parts by weight of trimethyl phosphate, 0.04 parts by weight of antimony trioxide as a polycondensation catalyst, and 17.17 parts by weight of 1,4-cyclohexanedicarboxylic acid are added at 220 to 235 ° C. Esterification was carried out by distilling off almost the theoretical amount of water at the reaction temperature. After that, the pressure inside the reaction system is further reduced and the temperature is raised, and finally at 280 ° C and 0.2 mmHg, 2
Time polycondensation was performed. When the obtained copolymer was analyzed, the intrinsic viscosity was 0.45.

The thermoplastic polyurethane was melted by an extruder, and the polyisocyanate was added in an amount of 18% by weight in the middle of the melt flow.
These were sufficiently kneaded with a static mixer of 35 elements (manufactured by Kenics Co., Ltd.), while the above polyester was melted by another extruder, and these were separately weighed, and a concentric 8-all composite spinneret (nozzle diameter 0.5 mm). A spinning speed of 600 m / min was used to obtain a morofilament having a fineness of 40d. Further, the yarn in which no polyisocyanate was added was also spun in the same manner. A 15% water emulsion was used as a spinning oil at this time. On the other hand, the sheath component was changed to the above-mentioned thermoplastic polyurethane, and the same composite spinning was performed.
As the oil agent at this time, a dimethyl silicone living oil agent containing 5% by weight and 0.2% by weight of amino-modified silicone as an isocyanate group deactivator was used (Comparative Example 5-1, respectively).
5-2).

 The results are shown in Table 6.

In Table 6, the unwinding coefficient means the yarn wound on the bobbin.
When unwinding at a speed of 50 m / min, it represents the ratio of the bobbin surface speed to the surface speed of the winding roller when the unwinding of the yarn becomes impossible due to the sticking of the bobbin surface. Long-term windability is the diameter
When rolled up on a 85 mm paper tube at a spinning speed of 600 m / min, it represents the time taken for winding without causing twilling or collapse.

It can be seen from Table 6 that the yarn of the present invention is excellent in long-term winding property and retrieving property, while the urethane composite elastic yarn has good unwinding property even if it has a sticking property. (Comparative Example 5-2), on the contrary, when the adhesive-free adhesive is used as in Comparative Example 5-1, the unwinding property is improved but long-time winding is impossible. The yarn of Comparative Example 5-2 could not be used in the subsequent step without taking measures such as rewinding.

Example 6 Table 7 shows the results of changing the composite ratio of the core-sheath.

It can be seen that the elongation and recoverability are improved as the ratio of the sheath component decreases from the above. However, when the composite ratio of the core / sheath was 100/1, the unwinding coefficient fluctuated greatly and the vertical movement was not possible. In this case, upon careful observation, the sheath component was broken and the core component was exposed. Conversely, this ratio is 1 /
At 2, the physical properties were very poor, and thread breakage occurred at the time of hitting.

Example 7 Next, the yarns of Example 5-2 and Comparative example 5-2 were subjected to a load of 1 mg / d, treated for 30 minutes in hot water at 100 ° C., and air-dried. The physical properties of this treated yarn are shown in Table 8.

The recoverability in Table 8 is the degree of recoverability when 100% elongation was repeated twice at room temperature, and is a value calculated by the following formula. The larger this value is, the better the recoverability is.

From Table 8, the yarn of the present invention is recoverable by hot water treatment,
You can see that the elongation is coming out.

Further, using the yarn of Example 5-2, a tubular knit fabric was made with a bite knitting machine. At this time, there was no problem in operability. On the other hand, the yarn made of only the polyurethane of Comparative Example 5-2 could not be knitted without adding special oil. Next, the tubular knit fabric was immersed in hot water at 100 ° C. for 30 minutes. The results are shown in Table 9.

Before the immersion, the tubular knitted fabric of this example hardly expanded, while the comparative example had a stretch ratio of 65%.

Example 8 The yarn (Example 5-2) in which polyurethane cross-linked to the core component was arranged in Example 5 was cold-drawn at a draw ratio of 2 times. It was warped and warped like the nylon thread. The polyurethane elastic yarn of Comparative Cooling 5-2 was used after being rewound, but in the warping, the warp was large and warping was impossible unless the positive feeding mechanism was used.

The adjusted beam yarn of Example 5-2 was used as a back yarn, and a nylon 50 denier / 12 filament yarn was used as a front yarn. Then, knitting a 28-gauge half tricot with a compound needle at a speed of 1300 rpm.
The operability was extremely good. The greige was scoured at 90 ° C for 5 minutes and heat set at 190 ° C. Next, the product dyed in the color of navy blue was a product that could be used as a swimsuit without any warp or fine defect. By the way, in the back composite yarn, the sheath was completely dissolved. When this was sewn into a swimsuit, the stretchability was sufficient.

Example 9 The thermoplastic polyurethane used in Example 5 is a polyether polyurethane (P2060: hardness 86, manufactured by Dainichiseika Co., Ltd.).
Further, the sheath component was replaced with the following alkali-soluble polyester, and the same composite spinning was performed.

-Alkali-soluble polyester A polyester was synthesized from 70 mol% of terephthaldimethyl, 30 mol% of isophthalic acid, 5 mol% of sodium 5-sulfoisophthalate, and 100 mol% of ethylene glycol by a conventional method to obtain chips.

 The intrinsic viscosity of this product was 0.52.

 The results are shown in Table 10.

From Table 10, it can be seen that the larger the composite ratio, the more elastic the yarn is, and that the yarn of the present invention has very good unwindability and warpability.

When the yarn of Example 9-1 was treated with alkali in boiling water for 20 minutes at a concentration of 1% of sodium hydroxide, the elastic elasticity and the recoverability were remarkably improved, and this yarn could be mixed with polyester.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hoho Matsutomi 3409 Higashi, Akiho-cho, Yoshiki-gun, Yamaguchi Prefecture (72) Inventor Shozo Fujimoto 1380-2 Shiomi-cho, Shimomatsu City, Yamaguchi Prefecture Inventor Yoshiaki Morishige, Naguchi Island, Yamaguchi City, Yamaguchi Prefecture 1418-3 (56) Reference JP 62-41316 (JP, A) JP 62-268818 (JP, A)

Claims (13)

(57) [Claims] 1. A polyurethane / polyester composite ratio (volume ratio) in which the crosslinked polyurethane mainly having an allophanate crosslinked structure and having a Shore A hardness of 75 to 98 and water-soluble or alkali-soluble polyester are in the range of 1/1 to 90/1. Is a single fiber uniformly extended along the longitudinal direction and joined, the polyester is exposed on the fiber surface in the fiber cross section, and the polyurethane alone has a tensile strength of 1.0 to 5.5 g / d and 350 A latent elastic composite fiber having a breaking elongation of ˜1200% and an excellent elongation recovery elasticity. 2. A core / sheath type composite fiber comprising the polyurethane as a core component and the polyester as a sheath component.
Composite fiber. 3. The composite fiber of claim 1, wherein the allophanate crosslinked structure has a crosslink density of at least 6 μmol / g. 4. The allophanate crosslinked structure is at least
The composite fiber of claim 1, having a crosslink density of 10 μmol / g. 5. The polyurethane / polyester composite ratio is
The composite fiber according to claim 1, which is in the range of 1/1 to 50/1. 6. The polyurethane / polyester composite ratio is
The composite fiber according to claim 1, which is in the range of 1/1 to 5/1 and has a tensile strength of 1.8 to 5.5 g / d. 7. The composite fiber according to claim 1, wherein the tensile strength is 2.5 to 4.5 g / d. 8. The breaking elongation is 400 to 800%.
Composite fiber. 9. The water-soluble polyester contains 5 to 20 mol% of an aromatic dicarboxylic acid having a sulfonate as an acid component and / or its ester-forming derivative (component A).
55 mol% or more of aromatic dicarboxylic acid and / or its ester-forming derivative (component B) excluding the components, and alicyclic dicarboxylic acid and / or its ester-forming derivative (component C) and alicyclic dicarboxylic acid and / or The ester-forming derivative (D component), and the above C component and D component are of the formula: 0 mol% ≤ C + 4 x D ≤ 40 mol% (where C and D are the C component or the total acid component of the D component, respectively). The above-described composite fiber according to claim 1, wherein the glycol component is 50 mol% or more of ethylene glycol. 10. The composite fiber according to claim 9, wherein the readily water-soluble polyester has a glass transition temperature of 35 to 80 ° C. 11. The composite fiber according to claim 1, wherein the readily water-soluble polyester is a copolyester composed of a dicarboxylic acid having terephthalic acid, isophthalic acid and a sulfonate as a dicarboxylic acid component and ethylene glycol as a diol component. 12. A thermoplastic polyurethane having a Shore A hardness of 75 to 98 and a water-soluble or alkali-soluble polyester are respectively melted, and a polyisocyanate is added to and mixed with the melted polyurethane, and then a polyurethane / polyester composite ratio of 1 is obtained. Composite spinning of both melts in a relationship of 1/1 to 90/1 (volume ratio) and such that the above polyester is exposed on the fiber surface in the cross section of the fiber, and winding at a winding speed of 300 to 3000 m / min. And a method for producing a composite fiber. 13. A polyurethane / polyether composite ratio (volume ratio) in which the crosslinked polyurethane having a Shore A hardness of 75 to 98 having an allophanate crosslinked structure and the water-soluble or alkali-soluble polyester are mainly in the range of 1/1 to 90/1. Is a single fiber that is evenly extended and joined along the longitudinal direction with the polyester exposed on the fiber surface in the fiber cross section, and the polyurethane alone is 1.0 to 5.5 g /
d to form a fibrous structure with latent elastic composite fibers having a tensile strength of 350 to 1200% and a breaking elongation of 350 to 1200% and an excellent elongation recovery elasticity, and subjecting the polyester to substantially water treatment or alkali treatment under heating. A method for producing a fiber structure having stretch elasticity, which comprises dissolving and removing.