A SEA-ISLAND TYPE COMPOSITE FIBER FOR RAISED WARP KNIT FABRIC, AND A PROCESS OF PREPARING FOR THE SAME

Abstract: The present invention relates to a sea-island type composite fiber and a process for preparing the same. In accordance with the present invention, a sea-island type composite fiber used in raised warp knitting which is prepared by the direct spin draw method by using alkali soluble copolymer polyester as a sea component and polyester mainly consisting of polyethylene terephthalate of more than 90 mole% as an island component, wherein the process is characterized in that: the melt viscosities of the island component polymer and the sea component polymer are controlled so that the difference ( DELTA MV9,000) in melt viscosity between the of island component polymer and sea component polymer at a shear rate of 9,000 (1/s) is 20% SIMILAR 70% of the difference ( DELTA MV500) in melt viscosity between the of the island component polymer and the sea component polymer at a shear rate of 500(1/s). A sea-island type composite fiber according to the present invention, is characterized in that: the melt viscosity ( DELTA MV9,000) of sea-island type composite fiber (filament) at a shear rate of 9,000(1/s) is 20 SIMILAR 60% of the melt viscosity ( DELTA MV500) of the sea-island type composite fiber (filament) at a shear rate fo 500(1/s). With respect to the yarn of the present invention, the decline of physical properties of the yarn are minimized in the dissolution of sea components or in the raising process for thereby preparing a raised warp knit fabric with good appearance and touch.

Description: A SEA-ISLAND TYPE COMPOSITE FIBER FOR RAISED WARP KNIT FABRIC, AND A PROCESS OF PREPARING FOR THE SAME BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a sea-island type composite fiber used in warp knitting and a process for preparing the same. More particularly, the present invention relates to a sea-island type composite fiber used in warp knitting and a process for preparing the same which improve the quality of raised warp knit, an end product, because of its excellent physical properties of yarnGsland component) after dissolving a sea component. Description of the Related Art In a warp knitting process for preparing a warp knit by using a sea-island type composite fiber, the property of yarn of a high quality, particularly, the property of smoothness of yarn is required because of a high knitting speed. In addition, the post processing process for preparing a warp knit requires a large number of complex steps such as weight loss, raising, dyeing and the like, it is necessary to control the sea component dissolubility, section forming property and raising property of yarn appropriately. Specifically, to enhance the touch and raising property of raised warp knit, it is very important to improve the sea or island component forming property and the island component division property during the dissolution of a sea component by controlling the melt viscosity of each of the sea component and island component. The sea-island type composite fiber is prepared by using alkali soluble polymer as a sea component and fiber forming polymer as an island component and by conjugated-spinning them into a sea-island type, which is produced mainly for the purpose of preparing a fine denier fiber. In other words, after preparing a sea-island type composite fiber, a sea component, alkali soluble polymer, is dissolved by treating the sea- island type composite fiber with an alkali solution, thus to prepare a fine denier fiber composed of only island ^ components. In this way, the method for preparing a fine denier fiber from a sea- island type composite fiber is advantageous in that a finer denier fiber of an excellent workability of spinning and drawing can be obtained as compared to the method for fabricating a finer denier fiber by direct spinning, while it requires a process for dissolving and removing a sea component polymer, with an organic solvent in the treatment process after weaving or knitting. Generally, as the sea component polymer used for the sea-island type composite finer used in warp knitting, alkali soluble copolymerized polyester is mainly used. The reason of which is because it is' possible to dissolve a sea component from an alkali solution and weight loss facilities widely applied in the weight loss processing of general polyester fabric without using a special apparatus and an organic solvent requiring a high recovery cost. If the island component polymer is nylon, the dissolution ,speed of the sea component is not so important because the extent that the nylon is penetrated by the alkali solution is very low in dissolving the sea component. While, if the island component is polyester, the sea component is penetrated before the sea component is completely dissolved in a case that the dissolution speed of the sea component is low because the polyester is weak to alkali, for thereby sharply degrading the physical properties of yarn after the dissolution. Resultantly, the raising property becomes defective and it is difficult to express the appearance and touch of an end product. On the other hand, if the dissolution speed of the sea component is high, the occurrence of the above problems can be prevented and the alkali density and the dissolution temperature and time can be reduced, thereby decreasing the dissolution cost and increasing the productivity. To increase the dissolution speed of the sea component, the constant weight of a copolymerized compound should be increased. However, if the constant weight of the copolymerized compound is excessively increased, the sea component becomes an amorphous polymer with no melting point but only softening point while the dissolution is improved, thus making spinning difficult. The prior art techniques for preparing alkali soluble polyester used in preparing a sea-island type composite fiber includes the following methods: 1) the method for copolymerizing dimethylisophtha- late sulfonate salt(hereinafter, " DMIS" ) or polyalkyleneglicol (hereinafter, " PAG" ) of a low molecular weight in a polyester polymerization process! 2) the method for blending polyester with PAG of a high molecular weight; and 3) the method for blending polyester polymer with PAG of a high molecular weight. In the case of preparing a sea-island type composite fiber by spinning, drawing and false-twisting the above-described alkali soluble polyester as the sea component and the polyester as the island component, the flat property of yarn is degraded and the knitting property becomes poor. More specifically, since a false-twisted yarn is bulky, the knitting property is degraded in a high speed warp knitting. In addition, since the thermal shrinkage property of yarn is bad, the raising property is degraded and the appearance and quality of a raised warp knit fabric becomes worse in the subsequent raising process after the warp knitting. SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a sea-island type composite fiber which is useful particularly for yarns used in warp knitting because of its yarn property (hereinafter, " flat property" ), by which a process-through property becomes, better due to a small friction between a needle of a warp knitting machine and yarn, and its excellent sea component dissolubility. It is another object of the present invention to provide a process for preparing a sea-island type composite fiber which is suitable particularly as yarn used in warp knitting. To achieve the above object, there is provided a process for preparing a sea-island type composite fiber for a raised warp knit fabric according to the present invention, in preparing a sea-island type composite fiber used in raised warp knitting by the direct spin draw method by using alkali soluble copolymer polyester as a sea component and polyester mainly consisting of polyethylene terephthalate of more than 90 mole% as an island component, wherein the process is characterized in that: the melt viscosities of the island component polymer and the sea component polymer are controlled so that the difference (ΔMN9,ooo) in melt viscosity between the island component polymer and sea component polymer at a shear rate of 9,000(l/s) is 20%~70 of the difference (ΔMV500) in melt viscosity between the the island component polymer and the sea component polymer at a shear rate of 500(l/s). In addition, there is provided a sea-island type composite fiber for a raised warp knit fabric according to the present invention, which is a sea-island type composite fiber used in raised warp knitting by the direct spin draw method by using alkali soluble copolymer polyester as a sea component and polyester mainly consisting of polyethylene terephthalate of more than 90 mole% as an island component, wherein the sea-island type composite fiber is characterized in that: the melt viscosity (ΔMVg,ooo) of a sea-island type composite fiber (filament) at a shear rate of 9,000(l/s) is 20-60% of the melt viscosity (ΔMV500) of the sea-island type composite fiber (filament) at a shear rate of 500(l/s). A preferred embodiment of the present invention will now be described in detail. Firstly, in the present invention, alkali soluble copolymerized polyester as a sea component and polyester mainly consisting of ■ polyethylene terephthalate of more than 90 mole% as an island component are used, and they are conjugated-spinned by a commonly used conjugated spinning spinneret 1. In the present invention, the raising property and cross section - forming property of composite fiber are improved by properly adjusting the melt viscosity of the sea component and island component: Generally, a shear flow is occurred to fiber by a pressure applied to a spinneret from an extruder during a spinning process, and the flow rate and shear rate are low in the extruder while they are very high in the spinneret. The shear stress according to such a shear rate is called the melt viscosity (MV), which is different according to polymer properties. However, with respect to the sea-island type composite fiber prepared by conjugated spinning more than two kinds of polymers, since the melt viscosities of sea and island components are different from each other, there occurs a difference between their shear stresses, resultantly affecting the sea and island shaping of the composite fiber and the physical properties of yarn. Therefore, to obtain the physical properties required for a uniform sea-island cross section formation and use, it is necessary to select sea-island component polymer having a proper melt viscosity. Particularly, in the case of a raised warp knit product, in order to express the raising property and the appearance and touch of finer yarn, it is necessary that polymers used for the sea-island type composite fiber keep their relative viscosity, rather than their melt viscosity. In the present invention, the difference (hereinafter, " ΔMVg.ooo" ) in melt viscosity between the island component polymer and the sea component polymer at a shear rate of 9,000(l/s) is 20-70% of the difference (hereinafter, " ΔMV5 00 " ) in melt viscosity between the island component and the sea component at a shear rate of 500(l/s). That is, the value of ΔMV at the spinneret should be smaller than he value of ΔMV at the extruder. In other words, the difference (ΔMV) in melt viscosity between the island polymer and the sea component polymer resulting from an increase of the shear rate should be reduced. Otherwise, the orientation property of the island component is decreased, the knitting property is degraded because a sufficient drawing is difficult, and raised fibers are entangled with one another in warp knit. Fig. 3 is a graph illustrating a change in ΔMV according to an increase of a shear rate. In Fig. 3, it is found that the difference in melt viscosity between the island component and the sea component is decreased gradually as the shear rate is increased. In addition, it is preferred that the melt viscosity (hereinafter, " MVs" ) of the sea component at a shear rate of 500-9, 000(l/s) is lower than the melt viscosity (hereinafter, " MVi" ) of the island component (MVs < Mvi). Fig. 3 is a graph illustrating the correlation between the melt viscosity and shear rate for each component. If the melt viscosity (MVs) of the sea component is larger than the melt viscosity of the island component polymer, cross section shaping property of the sea-island type fiber might be difficult. This causes a decrease in number of island components or the wreck of uniform formation of island components, and thusly the raising property becomes defective in warp knit raising and it is made difficult to express the appearance and touch of an end product. Moreover, it is preferred that the difference in melt viscosity (hereinafter, " ΔMV" ) between the sea component and the island component is lower than 1,000 poise. If the difference (ΔMV) in melt viscosity between the sea and island components is more than 1,000 poise, the island components become adhesive to one another during spinning and there may be generated unseparated fibers in which the island components are not separated even after the dissolution. Due to this, there is a risk that the fiber raising state becomes non-uniform in warp knit raising, the appearance becomes unclean, the lighting effect becomes weak and the touch becomes rough. Furthermore, it is preferred that the melt viscosity (MVi) of the island component polymer of the present invention is 850-1400 poise at a shear rate of 500(l/s) and it is 300-700 poise at a shear rate of 9,000(l/s). If the melt viscosity of the island component is too low, island components might not be formed or the number of them might be smaller. On the contrary, if the melt viscosity of the island component is too high, the island components become adhesive to one another and resultantly the cross section shaping property of composite fiber becomes defective, thus making it difficult to obtain an raised warp knit having a preferable appearance and touch. Furthermore, it is preferred that the melt viscosity (MVi) of the sea component polymer of the present invention is 350-850 poise at a shear rate of 500(l/s) and it is 150-300 poise at a shear rate of 9,000(l/s). If the melt viscosity of the sea component is too low, the sea components can be allowed to be adhesive to one another during spinning so that the cross section shaping of the island component cannot be maintained. On the contrary, if the melt viscosity of the sea component is too high, the cross section shaping of the island component is inhibited to thus decrease the number of the island components or make the thickness thereof non-uniform, resultantly making the cross section shaping property of composite fiber defective. Due to this, there is a risk that the fiber raising state becomes non-uniform in warp knit raising, the appearance becomes unclean, the lighting effect becomes weak and the touch becomes rough. The melt viscosity of the sea component polymer and island component polymer can be adjusted by properly controlling a polymerization temperature, the pressure of a polymerization tube, a polymerization detention time, the type and constant weight of copolymer and the like. As an example of adjusting the melt viscosity of the sea component polymer, DIMS of 3-15 mole is copolymerized into polyethylene terephthalate, to which polyethyleneglicol of 4-20 weight % having a number average molecular weight more than 8,000 can be added. Continuously, in the present invention, the sea-island type composite fiber is prepared by drawing a spinned yarn while passing the spinned yarn through the first Godet roller 2 and the second Godet roller 3 and winding up the same by a winder 4. In other words, in the present invention, the sea-island type composite fiber is prepared by the direct spin draw method in which spinning and drawing are performed in the same process. As compared to the method for preparing a bulky sea-island type composite fiber by the spin-draw-false twist method, the present invention can prepare yarns having a flat property, so it is more advantageous in high speed warp knitting. The sea-island type composite fiber (filament) used in warp knitting of the present invention which is prepared and wound by the direct spin draw method has a melt viscosity (MVg.ooo) at a shear rate of 9,000(l/s) which is 20-60% of the melt viscosity (MV50 0 ) at a shear rate of 500Q/s). If the melt viscosity MVg.ooo) at a shear rate of 9,000(l/s) has a value less than 20% of the melt viscosity (MV50 0 ) at a shear rate of 500(l/s), a detention time becomes longer during spinning or a carbonization phenomenon is occurred and thus it is likely to make the shaping of the island component impossible or form a non-uniform island component due to curved yarn. On the contrary, if the melt viscosity (MVg.ooo) at a shear rate of 9,000(l/s) has a value more than 60% of the melt viscosity (MV500) at a shear rate of 500(l/s), the flowability of the sea component polymer in the spinning spinneret becomes strong and thus it is more likely to prevent the shaping of cross section 'of island component. Due to this, it is difficult to express the appearance and touch in warp knit. Furthermore, it is preferred that the melt viscosity of the sea- island type composite fiber (filament) of the present invention is 350-1400 poise at a shear rate of 500(l/s) and it is 150-700 poise at a shear rate of 9,000(l/s). if the melt viscosities are too low or too high, it is likely to make the shaping of the sea component impossible or form non-uniform island components. . Due to this, it is difficult to, express the appearance and touch in warp knit. In the present invention, the melt viscosity, cross section forming property of sea and island comonent and raising property are evaluated by the following method. • melt viscosity The melt viscosity of the sea component polymer and island component polymer according to a shear rate is measured by applying a shear stress to a sample (chip) by using a capillary rheometer (spec: L=25.38mm, D=0.762mm, L/D=33.31) of INSTRON. At this time, the melt viscosity of polymer is 290°C, the shear rate is continuously changed in the ranges from 500 to 9,000(l/s), and the drying condition of the island component polymer (chip) and sea component polymer (chip) is set to 150°C x 5 hours in the vacuum state. Meanwhile, the melt viscosity of the sea-island type composite fiber (filament) according to a shear rate is measured by applying a shear stress to a sample [sea-island type composite fiber (filament) with a length of 1cm] by using a capillary rheometer (spec: L=25.38mm, D=0.762mm, L/D=33.31) of INSTRON. At this time, the melt viscosity of the sample [sea-island type composite fiber (filament)] is 290°C, the shear rate is changed in the ranges from 500 to 9,000(l/s), and the drying condition of the sample [sea-island type composite fiber (filament) ] is set to 150°C x 1 hour in the vacuum.state. • sea-island cross section shaping property 500 samples are prepared by sampling a composite fiber cross section, and the uniformity and seperation state of a sectional form are observed and evaluated by a microscope. Specifically, if the sectional form is uniform and the number of unseparated island components is two or less, the shaping property, is evaluated to be excellent, if the sectional form is not uniform and the number of unseparated island components is two or less, the shaping property is evaluated to be good, if the sectional form is uniform and the number of unseparated island components is 3-4, the shaping property is evaluated to be moderate, and if the number of island components is five or more, the sectional form is evaluated to be poor. • raising property The raising property is measured by dyeing a raised warp knit fabric and then observing the number of occurrence of defective portions per square meter (e.g., raised fiber aggregation, raised fiber release and the like). Specifically, if the number of occurrence of defective portions per square meter is two or less, the raising property is evaluated to be excellent. If the number of occurrence of defective portions per square meter is 3, the raising property is evaluated to be good. If the number of occurrence of defective portions per square meter is 4-6, the raising property is evaluated to be moderate. If the number of occurrence of defective portions per square meter is seven or more, it is evaluated to be poor. BRIEF DESCRIPTION OF THE DRAWINGS The above objects, features and advantages of the' present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a schematic view of a process of the present invention; Fig. 2 is a graph illustrating the correlation between the melt viscosity and shear rate for each component constituting a sea-island type composite fiber of the present invention; and Fig. 3 is a graph illustrating a change in the difference ,(ΔMV) in melt viscosity between sea component polymer and island component polymer according to a shear rate according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Hereinafter, the present invention will be described in more detail through examples and comparative examples, but it is not limited thereto. Example 1 Alkali soluble polymer having a melt viscosity (MV500) of 700 poise at a shear rate of 500(l/s) and having a melt viscosity (MVg,ooo) of 300 poise at a shear rate of 9,000 is prepared by ' blending polyethyleneglycol of 8 weight% having a number average molecular weight of 8,500 with copolymer polyester in which dimethyl-5- sulfoisophthalate sodium of 4 mole% is copolymerized. The prepared alkali soluble polymer is used as sea component polymer during conjugated spinning. The alkali soluble polymer (sea component polymer) is prepared by the batch polymerization method under the condition in which a polymerization temperature is 280°C, a polymerization tube pressure is less than 0.9 torr, and a polymerization tube detection time is 8 hours. Meanwhile, polyethylene terephtalate (MVsoo : 1,200 poise, MVg,ooo : 500 poise) having a intrinsic viscosity of 0.65 used as an island component polymer is prepared by the continuous polymerization method under the condition in which a polymerization temperature is 290°C, a polymerization tube pressure is less than 0.9 torr, and a polymerization tube detection time is 9 hours. The island component polymer and sea component polymer are spun by a sea-island type conjugated spinning spinneret having 36 island components at 288°C. Continuously, the spun yarn is drawn between a the first Godet roller of 80°C and the second Godet roller of 125°C at a drawing ratio of 2.9 times. Then, it is wound up at a winding speed of 4,300m/min, thereby preparing a sea-island type composite fiber having 5 24 filaments with 75 deniers. A warp knit fabric having a density of 23 strips/CM is prepared by using the sea-island type composite fiber as yarn of a surface structure and using copolymer polyester yarn (highly shrinkage yarn) having a fineness of 5 deniers and a boiling shrinkage ratio of 28% as yarn of a 10 back structure. At this time, the use ratio of the yarn used for the back structure is set to 26 weight% with respect to the total weight of warp knit. The thusly prepared warp knit raw fabric is raised so that it can shrink by 50% and then a finished warp knit fabric is prepared by 15 preliminary setting (190°C) → dissolving sea components (NaOH concentration 1% O.W. S, 98°C x 30 minutes) → dyeing (disperse dye) → buffing → final setting (180°C). Table. 2 shows the result of evaluating sea island cross section shaping property of the sea-island type composite fiber, the raising 20. property of the raised wrap knit fabric and the melt viscosity of the sea- island type composite fiber (filament) by the above-described evaluation method. Examples 2 and 3 and Comparative Examples 1 and 2 Except that the preparing conditions are changed as shown in 25 Table 1, the sea-island type composite fiber of 24 filaments having a denier of 75 and the raised wrap knit fabric are prepared under the same process and conditions as those in Example 1. Table. 2 shows the result of evaluating sea island cross section shaping property of the sea- island type composite fiber, the raising property of the raised wrap knit fabric and the melt viscosity of the sea-island type composite fiber (filament) by the above-described evaluation method. [Table 2] Results of Physical Properties INDUSTRIAL APPLICABILITY In the present invention, the appearance and touch of a product are excellent since a loss of a yarn strength caused by the dissolution of sea components or the raising process is minimized. In addition, in the present invention, it is easy to shape cross section of sea-island type fiber and dissolve sea components, and the raising property are good.

Claims: WHAT IS CLIMED IS: 1. A process for preparing a sea-island type composite fiber used in raised warp knitting by -the direct spin draw method by using alkali soluble copolymer polyester as a sea component and polyester mainly consisting of polyethylene terephthalate of more than 90 mole% as an island component, wherein the process is characterized in that: the melt viscosities of the island component polymer and the sea component polymer are controlled so that the difference (ΔMVg,ooo) in melt viscosity between the island component polymer and sea component polymer at a shear rate of 9,000(l/s) is 20%~70% of the difference (ΔMV500) in melt viscosity between the the island component polymer and the sea component polymer at a shear rate of 500(l/s). 2. The process of claim 1, wherein the melt viscosity (MVs) of the sea component at a shear rate of 500-9, 000(l/s) is controlled so that it does not exceed the melt viscosity (MVi) of the island component at a shear rate of 500-9,000(l/s). 3. The process of claim 1, wherein the difference (ΔMV) in melt viscosity between the island component polymer and the sea component polymer is controlled so that it is lower than 1,000 poise. 4. The process of claim 4, wherein the melt viscosity (MVi) of the island component polymer is controlled so that it has a value of 850-1,400 poise at a shear rate of 500(l/s) and it has a value of 300-700 poise at a shear rate of ,9,000(l/s). 5. The process of claim 1, wherein the melt viscosity (MVi) of the sea component polymer is controlled so that it has a value of 350-850 poise at a shear rate of 500(l/s) and it has a value of 150—300 poise at a shear rate of 9,000(l/s). 6. A sea-island type composite fiber used in raised warp knitting by the direct spin draw method by using alkali soluble copolymer polyester as a sea component and polyester mainly consisting of polyethylene terephthalate of more than 90 mole% as an island component, wherein the sea-island type composite fiber is characterized in that: the melt viscosity (ΔMVg,ooo) of a sea-island type composite fiber (filament) at a shear rate of 9,000(l/s) is 20-60% of the melt viscosity (ΔMV500) of the sea-island type composite fiber (filament) at a shear rate of 500(l/s). 7. The sea-island type composite fiber of claim 6, wherein the melt viscosity (ΔMV5 00 ) of the sea-island type composite fiber (filament) at a shear rate of 500(l/s) is 350-1,400 poise. 8. The sea-island type composite fiber of claim 6, wherein the melt viscosity (ΔMVgooo) of the sea-island type composite fiber (filament) at a shear rate of 9,000(l/s) is 150-700 poise. 9. A warp knit fabric which is made from the sea-island type composite fiber of claim 6.

Inventors: HWANG YOUNG-NAM, HWANG, YOUNG-NAM
Applicants: HWANG YOUNG NAM, KOLON INC, HWANG, YOUNG-NAM, KOLON INDUSTRIES, INC
Application year: 2001
Main classification: D01D5
IPC codes: D01D5, D01F8