EP1392898A4

EP1392898A4 - A polyurethane type elastic fiber, and a process of preparing for the same

Info

Publication number: EP1392898A4
Application number: EP02718687A
Authority: EP
Inventors: Il-Cheon Kwon; Doo-Hyun Kim; Kyung-Hwan Ro
Original assignee: Kolon Industries Inc
Current assignee: Kolon Industries Inc
Priority date: 2001-04-19
Filing date: 2002-04-19
Publication date: 2007-08-29
Also published as: JP2004526069A; US20040121149A1; EP1392898A1; CN1509352A; WO2002086208A1; CN1270006C

Abstract

Disclosed a polyurethane elastic fiber and a method of producing the polyurethane elastic fiber. The method of producing the polyurethane elastic fiber is characterized in that polyol with high molecular weight and diisocyanate with excessive amount are mixed in a condition of a designated shear rate and prepolymerized to produce a prepolymer, the prepolymer is reacted with the chain extender and the chain terminator to produce a polymer, and an additive is added to the polymer and the final polymer is spun. The method of producing the polyurethane elastic fiber according to the present invention improves the stability of the polymer, has an excellent spinnability even in high-speed spinning, and remarkably reduces the generation of wave yarns. The polyurethane elastic fiber of the present invention is excellent in heat resistance, thermosetting efficiency and coherence strength between the monofilaments.

Description

A POLYURETHANE TYPE ELASTIC FIBER, AND A PROCESS OF PREPARING FOR THE SAME

TECHNICAL FIELD The present invention relates to a polyurethane elastic fiber and a process of preparing the same. More particularly, the present invention relates to a process of preparing a polyurethane elastic fiber, which improves the stability of polymer and has high-speed spinnablity, thereby remarkably reducing the generation of wave yarn. Further, the present invention relates to a polyurethane elastic fiber having excellent heat resistance, thermosetting efficiency and coherence between monofilaments.

Polyurethane polymer can be prepared by a one-staged polymerization, in which polyol with high molecular weight of 1, 600-2, OOOg/mol, diisocyanate with an excessive amount, and chain extender such as diol or diamine compound are simultaneously reacted. Alternatively, polyurethane polymer can be prepared by a two-staged polymerization comprising two steps, a first step of that polyol with high molecular weight of 1, 600-2, OOOg/mol and diisocyanate with the excessive amount are prepolymerized, thereby preparing a prepolymer, and a second step of that a chain extender and a chain terminator such as diol or diamine compound are simultaneously reacted with inputted the prepolymer. Compared with the one-staged polymerization, the two-staged polymerization produces a more regular structure and has a lower possibility in a bridged bond, thereby easily regulating the degree of polymerization. Most of the polyurethane elastic fibers are now prepared by the two-staged polymerization.

The first stage of the two-staged polymerization, i.e., the prepolymerization step, is that polyol with high molecular weight, i.e., diol compound, and diisocyanate with excessive amount are reacted and forms urethane bonds, thereby preparing a prepolymer, in which an isocyanate group is formed on both ends of polyol.

Generally, the molecular weight of polyol is approximately l,800g/mol, and the ratio of NCO/OH is about 1.5 to 1.8. The aforementioned prepolymerization is performed at the temperature of approximately 60 to 90 ^°C for 1 to 2 hours in a bulky condition without solvent. As the reaction temperature is higher, the reaction speed is also higher. If a solvent such as Dimethylacetamide (hereinafter, referred to as "DMAc") or Dimethylformamide (hereinafter, referred to as "DMF") is used, the reaction temperature is increased by the catalysis of the solvent. Thus, the reaction is finished at the temperature of 30 to 60 ^°C within 10 to 20 minutes.

The second stage of the two-staged polymerization, i.e., the chain extending step, is that the prepolymer and compound with active hydrogen in a low molecular weight such as ethylene diamine, propylene diamine, 1,4-butadiol are reacted, thereby increasing the degree of polymerization. Herein, this compound is used as the chain extender.

If the prepolymer is reacted with diamine, urea bonds are formed.

If the prepolymer is reacted with diol, urethane bonds are formed. The chain- extending step is faster than the preliminary step and is an exothermic reaction. Therefore, in order to uniformly form the reaction, a polar solvent such as DMAc or DMF is used.

BACKGROUND ART Korean Patent Publication No. 196651 discloses a method of preparing a polyurethane polymer, in which glycol and diisocyanate (reaction mole ratio: 1.5—1.64) are mixed in a static mixer at the temperature of 40— 50 ^°C and reacted, thereby preparing a first polymer with non-reacted diisocyanate of 4 mole%. After then, the first polymer is reacted with chain extender comprising ethylene diamine 74 to 80 mol%, 1,2-diaminopropane 19 to 25 mol% and diethyltriamine 0.2 to 0.8 mol , thereby preparing the polyurethane polymer.

However, the aforementioned prior art has many problems, as follows. The temperature of 40 to 50 ^°C is too broad not to uniformly mix glycol and diisocyanate. For example, the reaction of glycol and diisocyanate is very intensive. Therefore, at the temperature of more than 45 ^°C , a large amount of glycol and diisocyanate are reacted before being uniformly mixed. Thus, it is difficult to uniformly mix glycol and diisocyanate, and a large amount of glycol and diisocyanate are reacted before being uniformly mixed, thereby increasing the possibility of forming gel caused the reaction. In order to maintain the reaction temperature to be less than 42 ^°C , the supply temperature of glycol and diisocyanate must be predetermined to be less than 42 "C prior to being putted in the static mixer. However, when the temperature is deviated from 43-44 ^°C , impurity such as dimmer is rapidly increased within diisocyanate. Therefore, in order to maintain the reaction temperature to be less than 42 ^°C , a heat exchanger must be installed prior to the static mixer or an external jacket is attached to the static mixer, thereby controlling the temperature. Compared with a method, in which glycol and diisocyanate are mixed at the same temperature as the storage temperature (43-4 ^°C) of diisocyanate, this method is improper.

Further, the aforementioned prior art uses diethyltriamine (0.2-0.8 mol%) among chain extenders, thereby improving the heat resistance and thermosetting efficiency in a subsequent process. However, excessive bridged bonds are introduced within the polymer, thereby decreasing linearity of the polymer and phase transition of the polymer before spinning. Therefore, it is difficult to stabilize the polymer, thereby reducing the spinnability. Thus, this prior art cannot increase the spinning speed more than 650m/sec. Further, Japanese Laid-open Publication No. 4-100919 discloses a method, in which only ethylene diamine of 0.18 weight% is used as the chain extender, and triamine, tetramine, pentamine, and the like are added to the polymer prior to the spinning step. However, problems of this method are that viscosity of the polymer is very unstable before spinning, and the spinnability is low. Further, this method improves the heat resistance but decreases the thermosetting efficiency.

In U.S. Patent. No. 5,362,432, a compound comprising ethylene diamine 83-92 mol% and 1,2-diaminoρropane 8-17 mol% is used as the chain extender. However, in this method, ethylene diamine with a good filling characteristic is comparatively much used, thereby reducing the stability of viscosity of the polymer before spinning. Therefore, it is difficult to control the process. Further, this method deteriorates the thermosetting of the manufactured elastic fiber. Further, in U.S. Patent No. 5,981,686, a compound comprising ethylene diamine 10-65 mol% and 1,3-diaminopentane 35-90 mol% is used as the chain extender. In this patent, in order to provide a little bridge to the polymer, amines of three functional group such as diethyltriamine are selectively used as the chain extender or the chain terminator. However, the aforementioned patent did not apparently state the amount of the used diethyltriamine. Moreover, U.S. Patent No. 5,000,899 discloses a method, in which a compound comprising ethylene diamine 50-80 mol% and 2-methylpentamethylene diamine 20-50 mol% is used as the chain extender.

Among the chain extenders of U.S. Patent Nos. 5,981,686 and 5,000,899, 2-methylpentamethylene diamine and 1,3-diaminopentane have a longer chain than ethylene diamine and 1,2-diaminopropane, characteristics of an odd chain with 5 carbons, and characteristics of having bulky side chain such as methyl or ethyl. By these characteristics, the aforementioned U.S. Patents prevent an inner crystallization of the polymer or the elastic fiber, i.e., crystallization due to re-alignment of hard segment and soft segment by phase separation, thereby decreasing the heat resistance. The lower heat resistance reduces the maintenance of physical property in a subsequent processing step and removing specific characteristics of the elastic fiber.

DISCLOSURE OF THE INVENTION

Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a method of preparing a polyurethane elastic fiber, which improves the stability of viscosity of polymer and has an excellent spinnablity even in a high-speed spinning, thereby remarkably reducing the generation of wave yarn. Further, the present invention provides a polyurethane elastic fiber having excellent heat resistance, thermosetting efficiency and coherence between monofilaments. In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of a method of producing a polyurethane elastic fiber, characterized in that a prepolymer is produced using a continuous polymerizing tube in a cylinder pipe comprising a static mixer, a heat raiser, a reactor, and a cooler, as follows, and the prepolymer is reacted with a chain extender/ a chain terminator to produce a polymer, and an additive is then added to the polymer. as follows — [a process of producing the prepolymer]

(i) mixing polyol with high molecular weight and diisocyanate with excessive amount within the static mixer with the shear rate of more than 20sec^_1 without the inner mixing element,

(ii) first-reacting polyol with high molecular weight and diisocyanate with excessive amount within the heat raiser with the shear rate of more than 3sec^-1 without the inner mixing element, and

(iii) second-reacting the first-reacted compound within the reactor with the shear rate of more than O. lsec^"1 without the inner mixing element, thereby preparing a first prepolymer. In accordance with another aspect of the present invention, there is provided a polyurethane elastic fiber characterized in that coherence strength between monofilaments is more than 145mgf.

In order to provide the shear rate in preparing a prepolymer, the present invention employs a continuous polymerizing tube with a mixing element formed in a Kenics type or a Sulzer type on its inside. The continuous polymerizing tube is shaped in a cylinder pipe. The continuous polymerizing tube comprises a static mixer, a heat raiser, a reactor, and a cooler. The static mixer is designed so that the shear rate is more than 20sec^-1 without the inner mixing element. The heat raiser is designed so that the shear rate is more than 3sec^_1 without the inner mixing element. The reactor is designed so that the shear rate is more than O.lsec^-1 without the inner mixing element. First, polyol with high molecular weight and diisocyanate with excessive amount are mixed within the static mixer with the shear rate of more than 20sec^-1 without the inner mixing element, and reacted within the heat raiser with the shear rate of more than 3sec^-1 without the inner mixing element, and reacted within the reactor with the shear rate of more than O. lsec^-1 without the inner mixing element, thereby preparing a first prepolymer.

Herein, polytetramethyleneetherglycol with the number average molecular weight of 1,700-3,000 and 4,4'-methylenediphenyldi- isocyanate, which are generally used to produce a polymer for polyurethane elastic fiber, are used. Herein, the mole ratio of diisocyanate per glycol is properly about 1.5-1.75. During the process of preparing the prepolymer, three-dimensional bridged bonds are easily generated by the heterogeneous mixture and reaction. Therefore, is it very important to properly control the shear rate within the static mixer, the heat raiser, and the reactor.

Without the inner mixing element, the shear rate of the mixture for the prepolymer within the static mixer is more than 20sec^-1. If the shear rate is less than 20sec^-1, the monomers are not uniformly mixed, thereby forming much gel, and reducing the spinnability and the quality of the prepolymer.

Preferably, the mixing temperature of the static mixer is controlled to be 43-44 ^°C . If the mixing temperature is more than 45 ^°C , the reaction is considerably processed prior to the uniform mixing, thereby forming gel of three-dimensional bridged bonds. Components of gel are accumulated within the static mixer or moved into a next step.

Thereby, the replacement cycle of the static mixer is shortened or the quality of the prepolymer is deteriorated. Further, the gel influences the final spinning step, thereby reducing the spinnability, generating the wave yarn, and providing a bad effect to the physical property of the produced elastic fiber. If the mixing temperature is less than 43 ^°C , since the mixing temperature is lower than the storage temperature of diisocyanate, additional equipment is required.

Moreover, it is very important to set the shear rate within the heat raiser to be more than 3sec^-1 without the inner mixing element. If the shear rate is less than 3sec^-1, the heterogeneous reaction is increased and gel is increased within the prepolymer.

The raised temperature of the heat raiser and the final temperature of the raised prepolymer are also important factors. It is desired to prevent the rapid heat-raising and to set the final raised temperature of the heat raiser to be less than 90 ^°C . When the reaction temperature of the prepolymer is more than 90 ^°C , the side reaction is rapidly progressed, thereby increasing the possibility of generating the gel. Further, since the reaction of glycol and diisocyanate is an exothermic reaction, the exothermic reaction must be controlled by well regulating the heat raising time.

If the heat raising time is too fast, since it is difficult to control the generated heat during the reaction, the finally raised temperature of the prepolymer can be more than 90 ^°C . On the other hand, if the heat raising time is too slow, the equipment of the heat raiser is long with the same supplying amount of the raw material, thereby additionally installing the heat raiser.

Further, it is very important to set the shear rate within the reactor to be more than O.lsec^-1 without the inner mixing element. If the shear rate is less than O.lsec^-1, the heterogeneous reaction generates the formation of the gel. Herein, it is desirable to control the reaction temperature of the reactor to be less than 80-90 °C . If the reaction temperature is more than 90 °C , the side reaction is rapidly progressed, thereby increasing the possibility of generating the gel. The prepolymer manufactured by the aforementioned process comprises gels with a diameter of less than 20um. Herein, the number of these gels is 600/g. The gels improve the processing property and the quality of the final product. The number of the gels within the prepolymer is measured by a Coulter Counter.

Next, a chain extender and a chain terminator are added to and reacted with the prepolymer, thereby preparing the polyurethane polymer. More particularly, the prepolymer is solved by a N,N'- Dimethylacetamide (hereinafter, referred to as "DMAc") solvent, thereby forming a solution of the prepolymer. This solution is reacted with a N,N'-Dimethylacetamide solution (chain extender) comprising diamine and triamine, and a N,N'-Dimethylacetamide solution (chain terminator) comprising monoamine. Herein, as diamine used as the chain extender, ethylene diamine or 1,2-diaminopropane may be used. As triamine, diethyltriamine may be used.

For example of the chain extender solution, a solution comprising ethylene diamine of 60-75 mol%, 1,2-diaminopropane of 24.9-39 mol , and diethyltriamine of less than 0.1 mol% may be used. As monoamine used as the chain terminator, diethylamine may be used. Desirably, the chain extender of 96-98.5 equivalent% and the chain terminator of 4.5-7.0 equivalent% are used. The chain extender solution and the chain terminator solution may be separately provided, or may be simultaneously provided. The prepared polyurethane polymer (hereinafter, referred to as "final polymer") has a concentration of 36-38.5 weight% according to the amount of N,N'-Dimethylacetamide solution for solving the prepolymer, and a number average molecular weight of 30,000-50,000. The number average molecular weight can be measured by a- Gel Permeation Chromatography (GPC).

The polyurethane polymer and an additive are mixed within the static mixer without the inner mixing element at the condition of the shear rate of more than 0.13sec^-1, thereby forming a dope just before spinning. Preferably, the additive comprises triamine group compound.

More particularly, the additive may be selected from triamine group compound, a conventional antioxidant, an anti-yellowing agent, an ultraviolet stabilizer, a dyeing improving agent, a dulling agent, or a spinning-enhancing agent. More preferably, as the triamine group compound, diethylenetriamine is used.

In case that diethylenetriamine is not used as the chain extender but used as the additive, the bridged bonds are formed in high-speed spinning, thereby improving the heat resistance of the elastic fiber, preventing the precipitation due to re-agglutination of inorganic additives, and uniformly mixing the additive and the polymer.

At this time, the uniform mixture of the additive and the final polymer is very important. If the mixture of the additive and the final polymer is heterogeneous, components of the additive, which are not uniformly dispersed and the mixed, generates wave yarns from the spun elastic fiber, thereby cutting the yarn. Further, the coherence between the filaments is lowered, thereby causing the crack of the filament in a subsequent processing step, and deteriorating the processing property and the quality of the final processed fiber.

In order to uniformly mix the final polymer and the additive, a static mixer shaped in a cylinder pipe is used. The shear rate within the static mixer is more than 0.13sec^-1 without the inner mixing element. The storage temperature of the additive slurry mixed into the final polymer is very important. If the storage temperature of the additive slurry is more than 60 ^°C , factors of the raise and the discontinuance of the viscosity of the slurry are larger than factors of the lowering of the precipitation speed due to micro brown motion, thereby promoting the re -agglutination and the precipitation speed of the additive slurry, deteriorating the quality of the additive slurry and promoting the clogging cycle of a filter for the additive. Therefore, the quality and the production of the final polymer are influenced.

Further, if the storage temperature of the additive slurry is less than 40 ^°C , the relative viscosity of the additive slurry against the temperature is raised, thereby increasing the generation of the difference pressure and functioning as an unstable factor of the process. And, the micro brown motion is weak, thereby promoting the re- agglutination, improving the quality of the additive and shortening the clogging cycle of the filter. Therefore, it is preferable to maintain the storage temperature of the additive slurry to be ranged from 40 to 60 ^°C .

A designated amount of the formed dope is pushed into a spinning tub with the temperature of 180~280^°C using a gear pump. Thereby, the solvent included in the dope is evaporated, thus preparing the polyurethane elastic fiber. This method is referred to as a dry spinning method.

During the dry spinning process, as the final polymer (dope) comprising various additives is changed into a yarn state, the polymer is chemically changed via transamidation or aminolysis. By this chemical change, the dope is changed into the yarn state and its molecular weight is increased.

The number average molecular weight of the elastic fiber, which is prepared by the present invention, is about 40,000—70,000. The number average molecular weight of the elastic yarn can be also measured by the Gel Permeation Chromatography (GPC). It is proper to set the spinning speed of the present invention to be 800-1,200 m/sec.

The spinning dope produced by the present invention has low content of gel. The additives are uniformly mixed/dispersed within the spinning dope. Therefore, the spinning dope has an excellent spinnability and remarkably reduces the generation of wave yarn. In the polyurethane elastic fiber produced using the aforementioned spinning dope, a proper amount of triamine is used as the chain extender and the additive, thereby causing the three-dimensional bridged bonds, and improving the heat resistance, the thermosetting efficiency, and the coherence between the monofilaments. According to the heat resistance test, the strength maintenance rate is more than 54%, and the coherence between the monofilaments is more than 145mgf.

The number of gel particles of the prepolymer, the molecular weight of the final polymer and the elastic yarn, the stability of viscosity of the final polymer, the heat resistance, and the thermosetting efficiency of the final polymer are measured, as follows.

^• Number of gel particles of the prepolymer

The prepolymer is solved in 1% LiCl DMAc electrolyte by a 0.5% concentration. Then, the number of gel particles of the prepolymer is measured by the Coulter Counter (Coulter's product in England)

^• Stability of viscosity of final product The final product is stored in an oven at 50 ^°C . At this time, the viscosity of the final product is measured every two hours for 3 days, thereby measuring the rate of climb of viscosity of the final product. Herein, the viscosity of the final product is measured by a Brook Filter RV viscometer using a No. 7 spindle, which has a rotational

speed of lOrpm.

^• Molecular weight of final polymer and elastic yarn After the sample is solved in 0.05M LiCl DMF solution by a concentration of 0.05%, the molecular weights of the final polymer and the elastic yarn are measured by the Gel Permeation Chromatography (GPC). Herein, polyethylene oxide is used as a calibration standard material, and a Waters's product is used as the GPC.

^• Judgment of wave yarn

The sample with a length of 10cm is elongated at the speed of 500%/30sec until 500%, and is then left for 1 minute. And, the sample is also relaxed. If the produced yarn has at least 2 knobs, which are curved or winds, within a length of 10cm, this yarn is judged as a wave yarn. The judgment of the wave yarn is represented by the number of the wave yarns among 5,000 cheeses in percentage.

^• Heat resistance and thermosetting efficiency After elongating the sample with the length of 10cm until 15cm, the elongated sample is placed in a hot-blast oven at 195 °C for 70 seconds. Then, the sample is relaxed and cooled in a standard temperature and humidity condition for 2 hours and is treated in a boiled water at 100 °C for 30 minutes. The strength before treating, the strength after treating, and the change of the length are measured. The heat resistance is estimated by the strength maintenance rate and the thermosetting efficiency is estimated by the length change rate of the sample. The sample with the high strength maintenance rate has the good heat resistance, and the sample with the high length change rate has the excellent thermosetting efficiency. -_{. ^Λ} ■ -_. ._. ,_ns^ Strength of sample after treating . , __n

Strength maintenance rate(%)= „f- _^ — ~^ , , , — X 100

Strength of sample before

, , ,„ .. (Length of sample after treating - Length of sample before treating) X 200

Length change rate(%)=- ^§ - — „^& z- -z — - — . ^

Length ot sample before terating

^• Coherence between monofilaments

One strand of the monofilament is separated by a length of 5cm from the polyurethane elastic yarn comprising plural filaments. One end of the separated monofilament and one ends of other combined monofilaments are attached to an Instrung provided with a rod cell of less than 1kg so that a contact point between the separated monofilament and the non- separated monofilaments is disposed on the center of a cage of 5cm, and then elongated at the speed of 1000%/min, thereby measuring the shear strength of the separated monofilament and the non- separated monofilaments. A result is obtained by the average of the coherences, which are measured during elongation. Each sample are measured more than three times. BEST MODE FOR CARRYING OUT THE INVENTION Example 1

Polytetramethyleneetherglycol with a 1,800 molecular weight of lmol and 4,4'-diphenyldiisocyanate of 1.65mol were putted into the continuous polymerizing tube, which is shaped in the cylinder pipe. The continuous polymerizing tube comprises the static mixer with the shear rate of 20sec^-1 without the inner mixing element, the heat raiser with the shear rate of 3sec^-1 without the inner mixing element, the reactor with the shear rate of O.lsec^-1 without the inner mixing element, and the cooler. As the static mixer was maintained at 43.5 °C , the end of the heat raiser was maintained at 89 °C , and the reactor was maintained at 88 ^°C . Polytetramethyleneetherglycol and 4,4'-diphenyldiisocyanate were reacted for 110 minutes, thereby producing the prepolymer with isocyanate on both ends. The prepolymer was cooled to 40 ^°C, and 4,4' -dimethylacetamide was added, thereby producing a solution including the prepolymer of 45%. Then, as the polymer solution was cooled to 5 ^°C and severely mixed, the polymer solution was reacted with N,N' -dimethylacetamide solution of 98.5 equivalent%, which is used as the chain extender and comprises ethylene diamine of 59.9 mol%, 1,2-diaminopropane of 40 mol% and diethylenetriamine of 0.1 mol%, and N,N' -dimethylacetamide solution 6.5 equivalent%, which is used as the chain terminator and comprises diethylamine, thereby preparing the final polymer. The produced final polymer has the number average molecular weight of is 31,000 and the viscosity of 2,200 poise at 40°C , and comprises solid of 38.5%. The final polymer was uniformly mixed with the additive slurry comprising l,3,5-tris(4-t- buthyl-3-hydroxy-2,6-dimethylbenzene)-l,3,5-triazine-2,4,6- (lH,3H,5H)trion antioxidant of 1.2 weight%, l,l,l',l'-tetramethyl-4,4'- (methylene-di-p-phethylene)disemicarbazide waste gas stabilizer of 1.0 weight%, N-(4-etoxycarbonylphenyl)-N-methyl-N-phenylformamidine ultraviolet stabilizer of 1.5 weight%, titanium oxide of 2 weight%, blue pigment(ultra marine blue) of 0.01 weight%, and diethylenetriamine of 0.2 weight%, and being stored at 45 ^°C within the static mixer with the shear rate of 0.13sec^-1 without the inner mixing element, thereby producing the dope just before spinning. The dope is spun using the spinning tub with the temperature distribution between 260-200 ^°C by the dry spinning, thereby producing the polyurethane elastic yarn of 40 denier. Table 1 shows the measured results of the number of gel particles of the prepolymer, the rate of climb of viscosity of the final product, the frequency of generating the wave yarn, the heat resistance and the thermosetting efficiency of the produced elastic yarn, and coherence between monofilaments.

Example 2

The same method with that of the example 1 except for using a chain extender compound in which a mole ratio of ethylene diamine, 1,2- diaminopropane, and diethylenetriamine is 75-'24.9:0.1, and using the chain extender of 96.0 equivalent% and the chain terminator of 7.0 equivalent% was used to produce the polyurethane elastic yarn. The measured results of the number of gel particles of the prepolymer, the rate of climb of viscosity of the final product, the frequency of generating the wave yarn, the heat resistance and the thermosetting efficiency of the produced elastic yarn, and coherence between monofilaments were the same as the results of Table 1.

Example 3

The same method with that of the example 1 except for using diethylenetriamine of 0.1 weight% as the additive was used to produce the polyurethane elastic yarn. The measured results of the number of gel particles of the prepolymer, the rate of climb of viscosity of the final product, the frequency of generating the wave yarn, the heat resistance and the thermosetting efficiency of the produced elastic yarn, and coherence between monofilaments were- the same as the results of Table 1.

Example 4

The same method with that of the example 1 except for using diethylenetriamine of 0.3 weight% as the additive was used to produce the polyurethane elastic yarn. The measured results of the number of gel particles of the prepolymer, the rate of climb of viscosity of the final product, the frequency of generating the wave yarn, the heat resistance and the thermosetting efficiency of the produced elastic yarn, and coherence between monofilaments were the same as the results of Table 1.

Comparative Example 1

The same method with that of the example 1 except that the continuous polymerizing tube comprising the static mixer with the shear rate of 19sec^-1, the heat raiser with the shear rate of 2.8sec^-1, the reactor with the shear rate of 0.09sec^-1 without the inner mixing element, and the additive static mixer with the shear rate of O.lsec^-1 without the inner mixing element were used, and except that the temperature of the static mixer was 49 ^°C , the temperature of the raised prepolymer was 95 ^°C , the temperature of the reactor was 93 ^°C , and the storage temperature of the additive slurry was 65 ^°C , was used to produce the polyurethane elastic yarn. The measured results of the number of gel particles of the prepolymer, the rate of climb of viscosity of the final product, the frequency of generating the wave yarn, the heat resistance and the thermosetting efficiency of the produced elastic yarn, and coherence between monofilaments were the same as the results of Table 1. Comparative Example 2

The same method with that of the example 1 except for using a chain extender comprising ethylene diamine of 70 mol% and 2- methylpentamethylene diamine of 30 mol%, and using an additive without diethylenetriamine was used to produce the polyurethane elastic yarn. The measured results of the number of gel particles of the prepolymer, the rate of climb of viscosity of the final product, the frequency of generating the wave yarn, the heat resistance and the thermosetting efficiency of the produced elastic yarn, and coherence between monofilaments were the same as the results of Table 1.

Comparative Example 3

The same continuous polymerizing tube and the additive static mixer with those of the comparative example 1 was used. And, the same method with that of the example 1 except for using ethylene diamine as the chain extender and adding diethylenetriamine of 0.18 weight% to the solid of the polymer to produce the dope was used to produce the polyurethane elastic yarn. The measured results of the number of gel particles of the prepolymer, the rate of climb of viscosity of the final product, the frequency of generating the wave yarn, the heat resistance and the thermosetting efficiency of the produced elastic yarn, and coherence between monofilaments were the same as the results of Table 1. Comparative Example 4

The same continuous polymerizing tube and the additive static mixer with those of the comparative example 1 was used. And, the same method with that of the example 1 except for using a chain extender comprising ethylene diamine of 80 mol%, 1,2-diaminopropane of 19.8 mol%, and diethylenetriamine of 0.2 mol% was used to produce the polyurethane elastic yarn. The measured results of the number of gel particles of the prepolymer, the rate of climb of viscosity of the final product, the frequency of generating the wave yarn, the heat resistance and the thermosetting efficiency of the produced elastic yarn, and coherence between monofilaments were the same as the results of Table 1.

Table 1 The Results of Test

INDUSTRIAL APPLICABILITY

The elastic fiber of the present invention has excellent heat resistance (strength maintenance rate), thermosetting and coherence between the monofilaments, thereby being effectively used as a yarn for clothes. The present invention improves the stability of the polymer, has an excellent spinnability even in high-speed spinning, and remarkably reduces the generation of wave yarns.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

WHAT IS CLAIMED IS:

1. A method of producing a polyurethane elastic fiber, characterized in that a prepolymer is produced using a continuous polymerizing tube in a cylinder pipe comprising a static mixer, a heat raiser, a reactor, and a cooler, as follows, and the prepolymer is reacted with a chain extender/ a chain terminator to produce a polymer, and an additive is then added to the polymer. as follows — [a process of producing the prepolymer]

(i) mixing polyol with high molecular weight and diisocyanate with excessive amount within the static mixer with the shear rate of more than 20sec^-1 without the inner mixing element,

(ii) first-reacting polyol with high molecular weight and diisocyanate with excessive amount within the heat raiser with the shear rate of more than 3sec^-1 without the inner mixing element, and in) se.cond-reacting the first-reacted compound within the reactor with the shear rate of more than O.lsec^-1 without the inner mixing element, thereby preparing a first prepolymer.

2. The method of producing the polyurethane elastic fiber as set forth in claim 1, wherein the temperature of the static mixer is 43-44 °C .

3. The method of producing the polyurethane elastic fiber as set forth in claim 1, wherein the temperature of the heat raiser is less than

90 ^°C .

4. The method of producing the polyurethane elastic fiber as set forth in claim 1, wherein the temperature of the reactor is 80-90 ^°C .

5. The method of producing the polyurethane elastic fiber as set forth in claim 1, wherein in the chain extending/chain terminating reaction, the chain extender of 96-98.5 equivalent% and the chain terminator of 4.5-7.0 equivalent% are added.

6. The method of producing the polyurethane elastic fiber as set forth in claim 1, wherein the polymerized polyurethane polymer and the additive are mixed within the static mixer with the shear rate of more than 0.13sec^-1 without the inner mixing element.

7. The method of producing the polyurethane elastic fiber as set forth in claim 1, wherein the chain extender is a N,N'- dimethylacetamide solution comprising ethylene diamine of 60-75 mol%, 1,2-diaminopropane of 24.9-39 mol%, and diethylenetriamine of 0.1-1 mol%.

8. The method of producing the polyurethane elastic fiber as set forth in claim 1, wherein the additive comprises a triamine group compound.

9. The method of producing the polyurethane elastic fiber as set forth in claim 8, wherein the content of the triamine group compound is 0.1-0.3 weight% to solids of the polymer.

10. The method of producing the polyurethane elastic fiber as set forth in claim 8, wherein the triamine group compound is diethylenetriamine .

11. A polyurethane elastic fiber characterized in that coherence strength between monofilaments is more than 145mgf.