1. A preparation method of composite spandex is characterized by comprising the following steps:

1) uniformly mixing 10-50 wt% of polyurethane urea, 45-85 wt% of thermoplastic polyurethane and 0.5-5.0 wt% of dipropylene glycol dibenzoate in dimethylacetamide to obtain a polyurethane solution A;

2) uniformly mixing 65-85 wt% of polyurethane urea, 10-30 wt% of thermoplastic polyurethane and 0.5-5.0 wt% of dipropylene glycol dibenzoate in dimethylacetamide to obtain a polyurethane solution B;

3) and respectively enabling the polyurethane solution A and the polyurethane solution B to pass through a skin feed port and a core feed port of the skin-core composite assembly, and preparing the composite spandex by a dry spinning technology.

2. The method for preparing composite spandex according to claim 1, wherein the diethylamine termination rate of the polyurethaneurea is 2.5% -5.5%, and free-NH is present in the solution of diethylamine and polyurethaneurea₂The molar ratio of (a) to (b) is 1:1 to 8: 1.

3. The method for preparing composite spandex according to claim 1, characterized in that the diethylamine end capping rate is calculated according to formula (1),

the end capping rate of diethylamine is C/D100% (1)

Wherein C is the molar amount of diethylamine and D is the molar amount of-NCO in the diisocyanate.

4. The method for preparing spandex composition according to claim 1, wherein said polyurethane solution a and said polyurethane solution B have the same solids content and kinematic viscosity.

5. The method for preparing composite spandex according to claim 4, characterized in that the solid content is 20-40% and the value of the kinematic viscosity at 40 ℃ is 1000-4000 poise.

6. The preparation method of composite spandex according to claim 1, characterized in that the weight ratio of the polyurethane solution A to the polyurethane solution B fed through the sheath-core composite component is 1: 1-1: 9.

7. The preparation method of composite spandex according to claim 1, wherein the aspect ratio of cylindrical guide holes in a spinneret plate of the sheath-core composite component is 4: 1-8: 1, and the aspect ratio of micropores is 2: 1-5: 1.

8. The composite spandex of claim 1, wherein the cross section of the composite spandex has no skin-core interface under an optical microscope, and the composite spandex has a single area and has a uniformity of less than or equal to 2.5%.

Background

The weft knitted fabric is formed by mutually nesting coils formed by the same yarn along the weft direction of the fabric, based on the special structure, the weft knitted fabric has bidirectional raveling property, not only can ravel along the reverse knitting direction, but also can ravel along the knitting direction, yarn breakage or coil structure damage is often caused by scratching, cutting, repeated stretching and the like in the wearing, using or washing processes of the fabric, so that fibers are caused to ravel from the breakage part along the longitudinal direction, the appearance and the uniformity of the fabric are seriously influenced, the fabric is finally damaged and discarded, meanwhile, the weft knitted fabric also has the phenomena of edge curling and silk hooking, particularly for the weft knitted flat fabric containing spandex, the phenomenon is more remarkable, and the spandex has high elasticity. In order to improve the above phenomenon, spandex having excellent thermal adhesiveness, which can provide a large number of network bonding points to a fabric, thereby suppressing the unraveling, curling and snagging phenomena of the fabric, has been required.

There have been many reports on spandex having the above-mentioned functions. CN1957125 and CN1723307 mainly describe the preparation of highly fusible spandex with melting point of 180 ℃ or lower by melt spinning technology, and at the same time, the strength retention rate after 150 ℃ dry heat treatment for 45 seconds in 100% elongation state is more than 50%, specifically the melt spinning preparation of the polymer obtained by the reaction of isocyanate-terminated prepolymer obtained by the reaction of polymer diol and diisocyanate and hydroxyl-terminated prepolymer obtained by the reaction of polymer diol, diisocyanate and low molecular weight diol. JP patent open 2007-177359 reports that thermoplastic polyurethane with a softening point of 50-140 ℃ is added to polyurethane urea in an amount of 5-60% of the total amount of the fiber, and after the polyurethane urea is uniformly mixed, spandex is prepared by a dry spinning technique, and the thermal bonding peel stress of the mutually crossed spandex after dry heat treatment is 0.2cN/dt or more. CN101484620 discloses a spandex having high recovery, heat resistance and function of preventing the off-line of clothing products, which contains a special polyurethane compound 5% -40% of the weight of the fiber, the polyurethane compound has a low hard segment ratio, and the hard segment structure is loose, the crystallinity is not high, i.e. the rapid melting of the hard segment at a specific temperature will not occur to cause the rapid change of the fiber structure, and good performance can be maintained. Both melt spinning and dry spinning have the same problems of spandex prepared by the above-mentioned techniques, i.e., heat resistance and thermal adhesiveness are difficult to be obtained, and the subsequent wide application of the product is limited.

One effective solution to the above problems in the industry is to use a skin-core composite structure, relying on the skin to provide special performance requirements such as thermal adhesion, and the core to provide basic performance support such as heat resistance to solve the above-mentioned contradictions. CN102257195A, CN102257198A, CN105431579A, CN102257194A, CN106222795A disclose a sheath-core composite spandex prepared by a dry spinning technique, the cross section of which at least comprises a sheath region and a core region, and a well-defined boundary is provided between the two regions, the sheath region at least contains fusible polyurethane with low melting point, and the core region at least contains polyurethane or polyurethane urea with high melting point, the spandex has a steam setting efficiency of more than 50% and a fusion strength of more than 0.15CN/dt, but due to the obvious change of the sheath and core structures, the great difference of the elasticity of the sheath and the core is brought, so that the sheath and the core of the cross section of the fiber are separated, and the fiber shows a spiral filament phenomenon on a macroscopic scale, which seriously affects the uniformity and stability of the product, and limits the mass production and the wide use of customers.

Disclosure of Invention

The technical problem is as follows: in order to solve the problems in the prior art, the invention aims to provide composite spandex, which is prepared by the process method disclosed by the invention and has excellent uniformity and stability, no spiral filament phenomenon and a single area, and the cross section of the composite spandex has no skin-core interface when observed under an optical microscope.

The technical scheme is as follows: the preparation method of the composite spandex comprises the following steps:

1) uniformly mixing 10-50 wt% of polyurethane urea, 45-85 wt% of thermoplastic polyurethane and 0.5-5.0 wt% of dipropylene glycol dibenzoate in dimethylacetamide to obtain a polyurethane solution A;

2) uniformly mixing 65-85 wt% of polyurethane urea, 10-30 wt% of thermoplastic polyurethane and 0.5-5.0 wt% of dipropylene glycol dibenzoate in dimethylacetamide to obtain a polyurethane solution B;

3) and respectively enabling the polyurethane solution A and the polyurethane solution B to pass through a skin feed port and a core feed port of the skin-core composite assembly, and preparing the composite spandex by a dry spinning technology.

Wherein the content of the first and second substances,

the diethylamine end capping rate of the polyurethane urea is 2.5-5.5%, and the diethylamine and free-NH in the polyurethane urea solution₂The molar ratio of (a) to (b) is 1:1 to 8: 1.

The diethylamine blocking rate is calculated according to the formula (1),

the end capping rate of diethylamine is C/D100% (1)

Wherein C is the molar amount of diethylamine and D is the molar amount of-NCO in the diisocyanate.

The polyurethane solution A and the polyurethane solution B have the same solid content and dynamic viscosity.

The solid content is 20-40%, and the value of dynamic viscosity at 40 ℃ is 1000-4000 poise.

The weight ratio of the polyurethane solution A to the polyurethane solution B fed through the skin-core composite component is 1: 1-1: 9.

The length-diameter ratio of the cylindrical guide hole in the spinneret plate of the sheath-core composite component is 4: 1-8: 1, and the length-diameter ratio of the micropore is 2: 1-5: 1.

The cross section of the composite spandex is observed under an optical microscope to form a single area without a skin-core interface, and the uniformity is less than or equal to 2.5 percent.

The melt index of the thermoplastic polyurethane is 10cm at a temperature of 180 ℃ and a pressure of 5kg³/10min～50cm³The melt index test standard is defined in accordance with ASTM D1238, American Society for Testing and Materials (ASTM).

The heatThe melt index of the plastic polyurethane is 10cm at the temperature of 180 ℃ and under the pressure of 5kg³/10min～50cm³The melt index test standard is defined in accordance with ASTM D1238, American Society for Testing and Materials (ASTM).

Has the advantages that: compared with the prior art, according to the preparation method of the composite spandex, the skin layer solution and the core layer solution have excellent compatibility through post-polymerization capability and mass and heat transfer processes. Therefore, the composite spandex of the invention has no skin-core interface at the cross section when observed under an optical microscope, presents a single area, has no spiral yarn phenomenon, has excellent uniformity, and is widely applied to the fields of silk stockings, seamless underwear and the like.

Drawings

Fig. 1 is a schematic cross-sectional view of a guide hole and a micro hole of a spinneret plate. Among them are: spinneret guide holes 1 and micropores 2.

Detailed Description

The preparation method of the composite spandex comprises the following steps:

1) uniformly mixing 10-50 wt% of polyurethane urea, 45-85 wt% of thermoplastic polyurethane and 0.5-5.0 wt% of dipropylene glycol dibenzoate in dimethylacetamide to obtain a polyurethane solution A;

2) uniformly mixing 65-85 wt% of polyurethane urea, 10-30 wt% of thermoplastic polyurethane and 0.5-5.0 wt% of dipropylene glycol dibenzoate in dimethylacetamide to obtain a polyurethane solution B;

3) and respectively enabling the polyurethane solution A and the polyurethane solution B to pass through a skin feed port and a core feed port of the skin-core composite component, and preparing the composite spandex by a dry spinning technology.

The polyurethane urea is prepared by polymerizing diisocyanate, oligomer polyol and mixed amine, wherein the mixed amine consists of a chain extender and a chain terminator, and the chain terminator at least contains diethylamine.

The polyurethane urea has a diethylamine blocking rate of 2.5-5.5%, and the molar ratio of diethylamine to the excess-NH 2 in the polyurethane urea solution is 1: 1-8: 1.

The melt index of the thermoplastic polyurethane is 10cm at a temperature of 180 ℃ and a pressure of 5kg³/10min～50cm³The melt index test standard is defined in accordance with ASTM D1238, American Society for Testing and Materials (ASTM).

The polyurethane solution A and the polyurethane solution B have the same solid content and dynamic viscosity, the solid content is 20-40%, and the value of the dynamic viscosity at 40 ℃ is 1000-4000 poise.

The weight ratio of the polyurethane solution A to the polyurethane solution B fed through the skin-core composite component is 1: 1-1: 9.

The length-diameter ratio of the cylindrical guide hole in the spinneret plate of the sheath-core composite component is 4: 1-8: 1, and the length-diameter ratio of the micropore is 2: 1-5: 1.

The dry spinning technology is that polyurethane solution is extruded by a spinneret plate, passes through a high-temperature channel, solvent is volatilized, strand silk is solidified and formed, and then drafting, false twisting, oiling and winding are carried out to prepare spandex.

To further illustrate the present invention, the following examples are provided to describe the specific procedures of the present invention in detail, but these examples should not be construed as limiting the invention in any way. It should also be understood that various modifications of the invention can be made by those skilled in the art after reading the teachings herein, and that such equivalents are within the scope of the invention as defined by the claims.

In the following examples and comparative examples, the cross-sectional morphology, spiral yarn, uniformity, etc. of the composite spandex were evaluated as follows.

(1) Cross-sectional morphology: the cross-sectional morphology of the composite spandex was observed by an XSP-9CE type microscope.

(2) Spiral wire: one end of the composite spandex with the length of 30mm is fixed, the other end of the composite spandex naturally droops, and the obvious bending phenomenon of the silk thread can be observed.

(3) Uniformity: the composite spandex is unwound by 3 times of drafting, the tension (gf) change in the process of unwinding the spandex of 1000 meters is tested by a tension device system, the variation coefficient of the tension value reflects the uniformity, and the smaller the numerical value, the better the uniformity.

Example 1:

preparation of the polyurethaneurea solution: 10kg of PTMEG with a molecular weight of 1810 and 2.52kg of 4, 4' -MDI were reacted at 70 ℃ for 120min to give an isocyanate-terminated prepolymer, DMAC was then added to dissolve it completely, and when cooling to 12 ℃ a mixed amine solution containing 203.0g of ethylenediamine, 62.6g of propylenediamine, 45.0g of diethylamine and 5902.0g of DMAC was then slowly added to carry out the chain extension reaction, and finally 35.7g of 2-methylpentanediamine was added.

Preparation of polyurethane solution a (skin layer stock solution): uniformly mixing 23 wt% of polyurethane urea, 75 wt% of thermoplastic polyurethane and 2 wt% of dipropylene glycol dibenzoate in a DMAC solution to form a skin layer stock solution with the solid content of 35% and the dynamic viscosity of 3900 poise at 40 ℃.

Preparation of polyurethane solution B (core stock solution): the polyurethane urea with the weight percentage of 83 percent, the thermoplastic polyurethane with the weight percentage of 15 percent and the dipropylene glycol dibenzoate with the weight percentage of 2 percent are evenly mixed in the DMAC solution to form the core layer stock solution with the solid content of 35 percent and the dynamic viscosity of 3900 poise at the temperature of 40 ℃.

The sheath layer stock solution and the core layer stock solution pass through a sheath-core composite assembly according to the weight ratio of 3:7, wherein the length-diameter ratio of a cylindrical guide hole in a spinneret plate of the sheath-core composite assembly is 4:1, the length-diameter ratio of a micropore is 3:1, a dry spinning technology is adopted, a solvent is volatilized and cured to form a strand, and then the composite spandex is prepared through drafting, false twisting, oiling and winding.

The melt index of the thermoplastic polyurethane described in this example was 19.4cm³/10min。

The composite spandex in the embodiment has no spiral yarn phenomenon, the cross section has no skin-core interface, and the uniformity is 1.22%.

Example 2:

composite spandex was prepared in the same manner as in example 1, except that the aspect ratio of the cylindrical guide holes in the spinneret of the sheath-core composite assembly was 8:1 and the aspect ratio of the micropores was 2: 1.

The composite spandex in the embodiment has no spiral yarn phenomenon, the cross section has no skin-core interface, and the uniformity is 1.05%.

Example 3:

composite spandex was prepared in the same manner as in example 1, except that polyurethane solution a was obtained by uniformly mixing 20% polyurethaneurea, 79% thermoplastic polyurethane, 1% dipropylene glycol dibenzoate in DMAC solution; the core layer stock solution is obtained by uniformly mixing 79% of polyurethane urea, 20% of thermoplastic polyurethane and 1% of dipropylene glycol dibenzoate in a DMAC solution.

The composite spandex in the embodiment has no spiral yarn phenomenon, no skin-core interface on the cross section and 1.68 percent of uniformity.

Example 4:

preparation of the polyurethaneurea solution: 10kg of PTMEG with the molecular weight of 1810 and 2.42kg of 4, 4' -MDI are reacted for 120min at 70 ℃ to obtain isocyanate end-capped prepolymer, then DMAC is added to be completely dissolved, when the temperature is cooled to 12 ℃, mixed amine solution containing 172.5g of ethylenediamine, 70.9g of propylenediamine, 20.0g of diethylamine, 22.0g of monoethanolamine and 4951.3g of DMAC is slowly added to carry out chain extension reaction, finally 14.3g of 2-methylpentanediamine is added to be uniformly stirred, and polyurethane urea solution with the solid content of 35 percent is obtained.

Preparation of polyurethane solution a (skin layer stock solution): uniformly mixing 20 wt% of polyurethane urea, 79 wt% of thermoplastic polyurethane and 1 wt% of dipropylene glycol dibenzoate in a DMAC solution to form a skin layer stock solution with the solid content of 35% and the dynamic viscosity of 3900 poise at 40 ℃.

Preparation of polyurethane solution B (core stock solution): the polyurethane urea with the weight percentage of 79 percent, the thermoplastic polyurethane with the weight percentage of 20 percent and the dipropylene glycol dibenzoate with the weight percentage of 1 percent are evenly mixed in the DMAC solution to form the core layer stock solution with the solid content of 35 percent and the dynamic viscosity of 3900 poise at the temperature of 40 ℃.

The sheath layer stock solution and the core layer stock solution pass through a sheath-core composite assembly according to the weight ratio of 3:7, wherein the length-diameter ratio of a cylindrical guide hole in a spinneret plate of the sheath-core composite assembly is 4:1, the length-diameter ratio of a micropore is 5:1, a dry spinning technology is adopted, a solvent is volatilized and cured to form a strand, and then the composite spandex is prepared through drafting, false twisting, oiling and winding.

The melt index of the thermoplastic polyurethane described in this example was 19.4cm³/10min。

The composite spandex in the embodiment has no spiral yarn phenomenon, the cross section has no skin-core interface, and the uniformity is 2.03%.

Comparative example 1:

preparation of the polyurethaneurea solution: 10kg of PTMEG with the molecular weight of 1810 and 2.32kg of 4, 4' -MDI are reacted for 120min at 70 ℃ to obtain isocyanate end-capped prepolymer, then DMAC is added to completely dissolve the prepolymer, when the prepolymer is cooled to 12 ℃, mixed amine solution containing 266.4g of ethylenediamine, 88.8g of propylenediamine, 30.0g of diethylamine and 4892.5g of DMAC is slowly added to carry out chain extension reaction, finally 28.6g of 2-methylpentanediamine is added to be uniformly stirred, and polyurethane urea solution with the solid content of 33.5 percent is obtained.

Preparation of polyurethane solution a (skin layer stock solution): uniformly mixing 25 wt% of polyurethane urea and 75 wt% of thermoplastic polyurethane in a DMAC solution to form a skin layer stock solution with a solid content of 33.5% and a dynamic viscosity of 3600 poise at 40 ℃.

Preparation of polyurethane solution B (core stock solution): uniformly mixing 85% of polyurethane urea and 15% of thermoplastic polyurethane in percentage by weight in a DMAC solution to form a core layer stock solution with the solid content of 35% and the dynamic viscosity of 3900 poise at 40 ℃.

The sheath layer stock solution and the core layer stock solution pass through a sheath-core composite assembly according to the weight ratio of 3:7, wherein the length-diameter ratio of a cylindrical guide hole in a spinneret plate of the sheath-core composite assembly is 3:1, the length-diameter ratio of a micropore is 8:1, a dry spinning technology is adopted, a solvent is volatilized and cured to form a strand, and then the composite spandex is prepared through drafting, false twisting, oiling and winding.

The thermoplastic polyurethane described in this comparative example had a melt index of 19.4cm³/10min。

The composite spandex in this comparative example had a severe spiral phenomenon, with a clear sheath-core interface at the cross-section, with a uniformity of 5.35%.

Fig. 1 shows a schematic cross-sectional view of a guide hole and a micropore of a spinneret plate, and a polyurethane solution A and a polyurethane solution B respectively pass through a skin feed port and a core feed port of a skin-core composite component, are combined above a guide hole 1 of the spinneret plate, and are extruded through a micropore 2 for solidification and forming, and finally, composite spandex is formed.

The invention has been described in terms of detailed embodiments and specific examples. It will be apparent to persons skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.