SPINNERET FOR PREPARING ISLAND-IN-THE-SEA YARNS

Abstract

Disclosed is a spinneret for preparing island-in-the-sea yarns, wherein island ingredient supply channels are partitioned into a plurality of groups in a discharge portion. The island-in-the-sea yarns prepared using the spinneret can prevent aggregation of island portions in the center thereof, although the number of island portions is 500 or more. Accordingly, island-in-the-sea yarns are considerably advantageous for the preparation of microfibers, since 500 or more island portions can be disposed in one island-in-the-sea yarn and fineness of island portions can thus be reduced. In addition, the island-in-the-sea yarns have an advantage of considerably reduced production costs, since 500 or more microfibers can be produced from one island-in-the-sea yarn. Furthermore, the island-in-the-sea yarns render a specific color according to the ratio of sea portions to island portions and diameter of fibers, without adding chromogenic compounds such as dyes, and are thus applicable to photochromic fibers.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application Serial No. 10-2009-0012138, filed Feb. 13, 2009, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a spinneret for preparing island-in-the-sea yarns, and more specifically, to a spinneret for preparing island-in-the-sea yarns capable of preventing aggregation of island portions during spinning, although the island portions are high in number.

2. Background Art

An island-in-the-sea yarn is a yarn whose cross-section has a structure in which island ingredients are dispersed in a sea ingredient. When the sea ingredient is removed by elution or dissolution during post-processing after spinning, only the island ingredient remains. Accordingly, increased preparation costs and environmental problems disadvantageously occur due to waste of resins and the use of solvent to elute the sea ingredient. In spite of these problems, island-in-the-sea yarns enable preparation of microfibers, which cannot be obtained using conventional microfiber preparation methods, and are thus widely used as yarns for industrial materials such as artificial suede, filters and cleaning products.

Of conventional island-in-the-sea yarns, the term “sea ingredient” refers to an ingredient eluted or dissolved during post-processing after spinning, and the term “island ingredient” refers to an ingredient of fibers, left behind after removal of the sea ingredient. Processes for preparing suede fabrics from the island-in-the-sea yarns require a series of steps including weight-reduction, napping, dying, etc. Fineness uniformity and napping uniformity of micronized island-ingredient fibers are considerably important in stabilizing quality of fibers, and arrangement and structure of the cross-sections of island-ingredient fibers are thus core factors deciding quality.

Accordingly, in order to maximally utilize the island ingredient, island-in-the-sea yarns are prepared by conjugate-spinning an alkali-soluble polymer as a sea ingredient and a fiber-forming polymer as an island ingredient in the form of island-in-the-sea. The island-in-the-sea yarns are generally prepared for the purpose of obtaining microfibers. That is, the prepared island-in-the-sea yarns are treated with an alkali solution to elute the soluble polymer as the sea ingredient and thereby to obtain microfibers comprising only the island ingredient. As such, the method for preparing microfibers from the island-in-the-sea yarns advantageously exhibits superior spinning and drawing operation efficiencies and enables preparation of a higher fineness of microfibers, as compared to methods for preparing microfibers using direct-spinning, but requires a process for elution-removing the sea ingredient polymer with an organic solvent during post-processing after weaving or knitting. Improvement in quality of final products can be realized depending on the micronization level of island-ingredient fibers. Accordingly, a great deal of research and development are practically conducted to further micronize the fineness of island-ingredient fibers.

In accordance with conventional commercially available technologies to date, the number of island-ingredient fibers obtained is 37 or less and fineness of micronized island-ingredient fibers obtained is 0.05 deniers. Accordingly, there is a need to develop methods for preparing island-ingredient fibers with fineness of 0.04 deniers or less by increasing the number of island-ingredient fibers to 38 or more.

However, when the number of island-ingredient fibers is 38 or more, the cross-section structure thereof is very important and cross-sectional arrangement of island-ingredient fibers in island-in-the-sea yarns should be elaborately designed. Specifically, FIG. 1 is a top view illustrating a conventional spinneret for preparing island-in-the-sea yarns. More specifically, a spinneret for preparing island-in-the-sea yarns 1 includes a discharge portion 2, through which island-in-the-sea yarns are discharged, and a peripheral portion 3 surrounding the periphery of the discharge portion 2. The discharge portion 2 has a structure in which a plurality of island ingredient supply channels 5 are radially arranged based on one spinning core 4, and the number of island ingredient supply channels 5 may be varied depending on the desired number of island ingredients. A sea ingredient supply channel 6 is formed in the peripheral portion 3 surrounding the periphery of the discharge portion 2. When an island ingredient and a sea ingredient are injected through respective supply channels of the spinneret in FIG. 1, the sea ingredient supplied through the sea ingredient supply channel 6 in the spinneret is introduced into the discharge portion 2 and surrounds the island ingredient supply channel 5, while filling the discharge portion 2. Through this process, island-in-the-sea yarns wherein island portions are arranged in the sea ingredient can be prepared.

FIGS. 2 and 3 show cross-sections of conventional island-in-the-sea yarns (comprising 331 island portions) spun through the spinneret of FIG. 1. In FIG. 2, island portions 12 are concentrically arranged based on one spinning core 11 in island-in-the-sea yarns and the island portions take up 30 to 70% of the total cross-section of island-in-the-sea yarns. In FIG. 3, island portions 14 are also concentrically arranged based on one spinning core 13 in island-in-the-sea yarns and the island portions take up 30 to 80% of the total cross-section of island-in-the-sea yarns. This cross-sectional structure is normal, when island portions are small in number, while island portions adjacent to the spinning core 11 formed in the center of island-in-the-sea yarns are highly dense and may be aggregated during spinning, when island portions are large in number (about 300 or higher) or a cross-sectional area ratio of the island portions increases. That is, as the number of island portions in island-in-the-sea yarns increases, an undesired side-effect (island-conjugation) in which island portions present in the center of island-in-the-sea yarns are aggregated and lumped may readily occur. In this regard, application of the arrangement pattern of conventional island-in-the-sea yarns comprising 37 or less island portions cannot secure stable formation of fiber cross-sections. Accordingly, there is an increasing need for specific designs to suitably arrange island portions in the cross-sections of island-in-the-sea yarns.

SUMMARY 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 spinneret for preparing island-in-the-sea yarns, to prevent aggregation of island portions and obtain chromogenic island-in-the-sea yarns.

In accordance with the present invention, the above and other objects can be accomplished by the provision of a spinneret for preparing island-in-the-sea yarns including: a discharge portion, including a plurality of island ingredient supply channels to discharge island-in-the-sea yarns; and a peripheral portion arranged in the periphery of the discharge portion, the peripheral portion including a sea ingredient supply channel, wherein the island ingredient supply channels are partitioned into a plurality of groups in the discharge portion.

The discharge portion may further include one or more sea ingredient supply channels.

The island ingredient supply channels may be grouped based on two or more spinning cores.

The spinning cores may include one standard spinning core arranged in the center of the island-in-the-sea yarn and a plurality of peripheral spinning cores arranged based on the standard spinning core.

Preferably, distances between the standard spinning core and the peripheral spinning cores may be substantially equivalent.

The peripheral spinning cores may be spaced from one another by a uniform distance.

The peripheral spinning cores may be 3 to 20 in number.

The peripheral spinning cores may be 6 to 10 in number.

The number of island portions arranged with respect to one standard spinning core or one peripheral spinning core may be 10 to 300.

The sea ingredient supply channel may be interposed between the standard spinning core and the peripheral spinning core.

The total number of the island ingredient supply channels may be 38 to 1,500.

The total number of the island ingredient supply channels may be 500 to 1,500.

The total number of the island ingredient supply channels may be 1,000 to 1,500.

The island ingredient supply channel groups may have circular, oval, polygonal, or non-circular cross-sections.

The island ingredient supply channel groups may have identical or different shapes.

The spinning cores may be arranged based on the center of the discharge portion.

A sea ingredient supply channel may be arranged in the center of the discharge portion.

The spinning cores may be 3 to 20 in number.

The spinning cores may be 6 to 10 in number.

The sea ingredient supply channel may be arranged between the spinning cores.

The discharge portion may have a diameter of 15 to 50 mm.

The island ingredient supply channel may have a diameter of 0.1 to 0.3 mm.

The sea ingredient supply channel may have a diameter of 0.1 to 0.3 mm.

The discharge portion may be 2 to 20 in number.

A maximum distance between the centers of adjacent island ingredient supply channels present in one group may be smaller than a maximum distance between the centers of adjacent island ingredient supply channels present in two adjacent groups.

Hereinafter, a brief description will be given of the terms used herein.

Unless specifically mentioned, the term “spinning core” means a specific standard point at which island ingredient supply channels are grouped (partitioned) on an upper plate of a spinneret.

The term “standard spinning core” means a spinning core acting as a center and the term “peripheral spinning core” means a remaining spinning core arranged based on the standard spinning core, when the spinning cores are plural in number and are composed of one spinning core and other spinning cores arranged based on the one spinning core.

The expression “island ingredient supply channels are arranged such that they are grouped” means a state in which the island ingredient supply channels are arranged, based on one spinning core, such that they are partitioned in a predetermined shape, and for example, when two spinning cores are present in a spinneret, island ingredient supply channels are arranged in a predetermined shape, based on respective spinning cores and the island ingredient supply channels are thus divided into two groups in the island-in-the-sea yarns spun using the spinneret.

The term “photochromic fiber” means a fiber which does not render color through physical and chemical bonds of color-rendering substances such as dyes or pigments, but renders color using interference of light through structural and optical design of fibers.

The expression “fibers are birefringent” means that when light is irradiated to fibers having different refractive indices according to directions, the light incident to the fibers is refracted in two different directions.

The term “isotrope” means a property in which an object has a constant refractive index irrespective of a direction in which light passes through the object.

The term “anisotrope” means a property in which optical properties of an object are varied according to directions of light and an anisotropic object is birefringent and is the opposite of an isotrope.

The term “optical modulation” means a phenomenon in which irradiated light is reflected, refracted, or scattered, or intensity, cycle of wave motion or characteristics thereof are varied.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a top view illustrating a conventional spinneret for preparing island-in-the-sea yarns;

FIGS. 2 and 3 are electron micrographs illustrating the cross-section of island-in-the-sea yarns prepared using the spinneret of FIG. 1;

FIG. 4 is a top view illustrating a spinneret for preparing island-in-the-sea yarns according to one embodiment of the present invention;

FIG. 5 is a sectional view illustrating group-type island-in-the-sea yarns prepared using the spinneret of FIG. 4;

FIG. 6 is a top view illustrating a spinneret for preparing island-in-the-sea yarns according to another embodiment of the present invention;

FIG. 7 is an electron micrograph illustrating group-type island-in-the-sea yarns prepared using the spinneret of FIG. 6;

FIG. 8 is a top view illustrating a spinneret for preparing island-in-the-sea yarns according to another embodiment of the present invention;

FIG. 9 is a sectional view illustrating group-type island-in-the-sea yarns prepared using the spinneret of FIG. 8; and

FIG. 10 is a sectional view illustrating a passage of light emitted to the island-in-the-sea yarns prepared using the spinneret according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The island-in-the-sea yarns prepared using the spinneret for preparing island-in-the-sea yarns of the present invention are free of aggregation of island portions in the center thereof, although the number of island portions is 500 or more, because the island portions in the island-in-the-sea yarns are partitioned into two or more groups. Accordingly, island-in-the-sea yarns are considerably advantageous for the preparation of microfibers, since 500 or more island portions can be disposed in one island-in-the-sea yarn and fineness of island portions can thus be reduced. In addition, the island-in-the-sea yarns have an advantage of considerably reduced production costs, since 500 or more microfibers can be produced from one island-in-the-sea yarn.

Furthermore, the island-in-the-sea yarns render a specific color according to the ratio of sea portions to island portions and diameter of fibers, without adding chromogenic compounds such as dyes and are thus applicable to photochromic fibers. The photochromic fibers may render a variety of colors according to intensity of light, position and angle of observer.

Furthermore, island-in-the-sea yarns comprising island portions and sea portions exhibiting different optical properties enable formation of birefringent interfaces between the island portions and sea portions and can thus more considerably improve optical modulation efficiency, as compared to birefringent fibers, and are free of aggregation of island portions in the center thereof, although the number of island portions is 500 or more. As a result, the island-in-the-sea yarns maximize an optical modulation interface area and thus considerably improve optical modulation efficiency, as compared to conventional island-in-the-sea yarns comprising one spinning core. Accordingly, luminance-enhanced films comprising the island-in-the-sea yarns have superior optical modulation effects and exhibit considerably improved luminance, as compared to luminance-enhanced films comprising conventional birefringent fibers or island-in-the-sea yarns.

Hereinafter, the present invention will be illustrated in more detail.

The island-in-the-sea yarns prepared using the conventional spinneret for preparing island-in-the-sea yarns have a cross-sectional structure wherein island portions are concentrically arranged based on one spinning core, or island portions are randomly disposed without a spinning core. This cross-sectional structure is normal, when island portions are small in number, while island portions adjacent to the spinning core formed in the center of island-in-the-sea yarns are highly dense and may be aggregated during spinning, when island portions are large in number (about 300 or higher). That is, as the number of island portions in island-in-the-sea yarns increases, an undesired side-effect (island-conjugation) in which island portions present in the center of island-in-the-sea yarns are aggregated and lumped may readily occur.

Accordingly, in one embodiment, in an attempt to prevent aggregation of the island portions, the present invention provides a spinneret for preparing island-in-the-sea yarns comprising a discharge portion comprising a plurality of island ingredient supply channels to discharge island-in-the-sea yarns, and a peripheral portion, which is arranged in the periphery of the discharge portion and comprises a sea ingredient supply channel, wherein the island ingredient supply channels are partitioned into groups. More preferably, the problem can be solved by designing the island ingredient supply channels to be partitioned into groups based on two or more spinning cores. As a result, the phenomenon in which island portions are excessively concentrated on one spinning core can be prevented, microfibers can be prepared by forming 500 or more island portions in one island-in-the-sea yarn, and production costs can be reduced, since several hundred microfibers can be produced from one island-in-the-sea yarn.

FIG. 4 is a top view illustrating an upper plate of the spinneret for preparing island-in-the-sea yarns according to one embodiment of the present invention. A spinneret for preparing island-in-the-sea yarns 200 includes a discharge portion 210, through which island-in-the-sea yarns are discharged, and a peripheral portion 220 surrounding the periphery of the discharge portion 210. The discharge portion 210 has a structure in which a plurality of island ingredient supply channels 215 are partitioned into groups based on four spinning cores 211, 212, 213 and 214. The island ingredient supply channel groups are circular in the present invention, but are not limited thereto, and may have circular, oval or various non-circular shapes. The discharge portion 210 may further comprise a sea ingredient supply channel 216. The position of the sea ingredient supply channel 216 is not limited. However, the arrangement of the sea ingredient supply channel 216 between adjacent island ingredient supply channel groups is advantageous for preventing aggregation of island portions. Meanwhile, the number of the sea ingredient supply channel 216 may be one or more. Like conventional spinnerets for preparing island-in-the-sea yarns, the peripheral portion 220 comprises sea ingredient supply channels 221, 222, 223 and 224, and the number of the sea ingredient supply channels 221, 222, 223 and 224 is not limited and may be equivalent to the number of the spinning cores 211, 212, 213 and 214.

FIG. 5 is a longitudinal sectional view illustrating group-type island-in-the-sea yarns prepared using the spinneret of FIG. 4. Four spinning cores are arranged in an island-in-the-sea yarn 250 and island portions 255, 256, 257, 258 are grouped based on the spinning cores 251, 252, 253 and 254. That is, a plurality of island portions 255, 256, 257, 258 are partitioned based on the respective spinning cores 251, 252, 253 and 254 and the island-in-the-sea yarn 250 has a cross-sectional structure in which as many island portion groups as spinning cores are present. In this case, the groups of island portions 255, 256, 257, 258 arranged based on the spinning cores 251, 252, 253 and 254 may be deformed, while edges of cross-sections are swollen, due to a die swelling phenomenon during spinning of island-in-the-sea yarns, although the island ingredient supply channel groups of the spinneret in FIG. 4 have circular cross-sections. Accordingly, island portion groups of spun island-in-the-sea yarns may have semicircular, sector, circular, spheroidal, polygonal or non-circular cross-sections, and their shapes are not particularly restricted and may be identical or different. Meanwhile, in the drawings, each spinning core is represented by a thick black dot, which is shown for clearer description alone, and means one point acting as an actual center of the groups and the point may be either an island portion or sea portion. Furthermore, spaces present in the island-in-the-sea yarns may actually be filled with island portions, or only sea portions.

In a preferred first embodiment, one standard spinning core may be arranged in the center of the discharge portion 310 and a plurality of peripheral spinning cores are arranged based on the standard spinning core. Hereinafter, repeated description is omitted and only distinguishing characteristics of the first embodiment will be described. FIG. 6 is a top view illustrating an upper plate of a spinneret for preparing island-in-the-sea yarns. Specifically, the discharge portion 310 has a structure in which island ingredient supply channels are grouped based on one standard spinning core 311 arranged in the center thereof, and seven peripheral spinning cores 312, 313, 314, 315, 316, 317, 318 are arranged outwardly based on the standard spinning core 311. Sea ingredient supply channels 319, 320, 321, 322, 323, 324 and 325 are interposed between the standard spinning core 311 and respective peripheral spinning cores 312, 313, 314, 315, 316, 317 and 318. Like conventional spinnerets for island-in-the-sea yarns, sea ingredient supply channels 331, 332, 333, 334, 335, 336 and 337 may be formed in a peripheral portion 330 surrounding the periphery of the discharge portion 310, but the present invention is not limited thereto.

FIG. 7 is an electron micrograph illustrating group-type island-in-the-sea yarns prepared using the spinneret of FIG. 6. As shown in FIG. 7, one standard spinning core 351 is arranged in the center of the island-in-the-sea yarn, and seven peripheral spinning cores 352 to 358 are arranged based on the standard spinning core 351. In this case, preferably, the distances between the standard spinning core 351 and the plurality of peripheral spinning cores 352 to 358 may or may not be substantially uniform. When the longitudinal cross-section of the island-in-the-sea yarn is circular, aggregation of island portions is efficiently minimized if the distances between the standard spinning core 351 and the plurality of peripheral spinning cores 352 to 358 are substantially uniform. On the other hand, when the longitudinal cross-section of the island-in-the-sea yarn is spheroidal, it is preferred that the standard spinning core 351 and the peripheral spinning cores 352 to 358 be formed such that the distances between the standard spinning core 351 and the peripheral spinning cores 352 to 358 are long in a longer axis direction of the spheroid, but are short in a short axis direction thereof.

Meanwhile, the number of peripheral spinning cores may be preferably 3 to 20, more preferably, 6 to 10. As shown in FIG. 7, the most advantageous effects can be obtained when the number of peripheral spinning cores 352 to 358 arranged based on one standard spinning core 351 is 6 to 8 and the number of grouped island portions in the standard spinning core 351 and peripheral spinning cores 352 to 358 is 100 to 200 (Table 1).

In accordance with a preferred second embodiment of the present invention, the island-in-the-sea yarns comprise one or more spinning cores arranged based on the center of the discharge portion, and more preferably, the island-in-the-sea yarns may comprise no spinning core in the center thereof.

Hereinafter, repeated description is omitted and only distinguishing characteristics of the second embodiment will be described. FIG. 8 is a top view illustrating an upper plate of a spinneret for preparing island-in-the-sea yarns according to the second embodiment. Specifically, a discharge portion 410 comprises three spinning cores 411, 412, 413 arranged based on a center 430 thereof, and eight spinning cores 414, 415, 416, 417, 418, 419, 420, 421 are arranged outward of the spinning cores 411, 412, 413. At this time, both the three spinning cores 411, 412, 413 arranged at an inner region and the eight spinning cores 414, 415, 416, 417, 418, 419, 420, 421 arranged outward of the spinning cores are arranged based on the center 430 of the island-in-the-sea yarn. In this case, the number of the spinning cores may be 3 to 20, more preferably, 6 to 10, but the present invention is not limited thereto. Meanwhile, a sea ingredient supply channel 430 may be formed in the space between the spinning cores 411, 412 and 413, that is, in the center of the discharge portion 410, and a plurality of sea ingredient supply channels 422, 423, 424, 425, 426, 427, 428 and 429 may be formed between the three spinning cores 411, 412, 413 and the eight spinning cores 414, 415, 416, 417, 418, 419, 420, 421. Furthermore, the peripheral portion 440 may also comprise a plurality of sea ingredient supply channels 441, 442, 443, 444, 445, 446, 447 and 448. FIG. 9 is a longitudinal cross-sectional view illustrating the island-in-the-sea yarn spun using the spinneret of FIG. 8. Specifically, three spinning cores 452, 453, 454 are arranged based on a center 451 of the island-in-the-sea yarn, and eight spinning cores 455 to 462 are arranged outward of the spinning cores 452, 453, 454. At this time, both the three spinning cores 452, 453, 454 arranged at an inner region and the eight spinning cores 455 to 462 arranged outward of the spinning cores are arranged based on the center 451 of the island-in-the-sea yarn.

Meanwhile, the number of island ingredient supply channels present in the discharge portion may be 38 to 1,500, more preferably, 500 to 1,500 and most preferably, 1,000 to 1,500, when the number of island ingredient supply channels is suitably controlled. Furthermore, the number of the island ingredient supply channels arranged in each spinning core may be 10 to 300, more preferably, 100 to 150, although the present invention is not limited thereto. Consequently, the number of island ingredient supply channels arranged adjacent to each spinning core may be suitably controlled under the conditions that the island portions are not aggregated and fineness of island-in-the-sea yarns and island portions, fineness of desired microfibers and optical modulation efficiency, as mentioned below, are maximized. Meanwhile, the island ingredient supply channels may have a diameter of 0.1 to 0.3 mm, the sea ingredient supply channel may have a diameter of 0.1 to 0.3 mm. The island ingredient supply channel group may have a diameter of 8 to 15 mm, and the discharge portion may have a diameter of 15 to 50 mm. Meanwhile, like conventional spinnerets, the spinneret has a funnel-like shape wherein a lower plate, where island-in-the-sea yarns are practically discharged, has a smaller diameter than the diameter of an upper plate. Like conventional cases, the discharge portion in the lower plate may have a diameter of 0.1 to 0.6 mm. Meanwhile, the spinneret may have a maximum distance between the centers of adjacent island ingredient supply channels present in one group that is smaller than a maximum distance between the centers of adjacent island ingredient supply channels in two adjacent groups. That is, the spinneret has non-uniform distances between two adjacent groups, thus making the maximum distance between the centers of adjacent island ingredient supply channels forming the boundary between adjacent groups (the maximum distance between the centers of adjacent island ingredient supply channels present in two adjacent groups) larger than the maximum distance between the centers of adjacent island ingredient supply channels present in one group. As a result, island ingredient supply channels are not present in spaces between the groups and the spaces are empty, thus contributing to prevention of aggregation of island portions in the center.

Furthermore, one spinneret may comprise 2 to 20 discharge portions and in this case, 2 to 20 threads of island-in-the-sea yarns can be obtained through a single spinning operation.

The island-in-the-sea yarns prepared using the spinneret of the present invention will be sufficient, when they have a fineness comparable to single yarn fineness of common island-in-the-sea yarns and preferably have a single yarn fineness of 0.5 to 30 deniers. Of the island-in-the-sea yarns, island portions preferably have a single yarn fineness of 0.0001 to 1.0 deniers, in view of efficient accomplishment of objects of the present invention. Consequently, the group-type island-in-the-sea yarns enable arrangement of a maximum of island portions and are thus considerably useful for mass-production of microfibers.

Meanwhile, a luminance-enhanced film for LCDs can be fabricated using the island-in-the-sea yarns, whose sea portions are not eluted.

Conventional LCD devices do not necessarily have a high use efficiency of light emitted from a backlight. This is because 50% or more of the light emitted from the backlight is absorbed by a rear-side optical film. Accordingly, in order to increase the use efficiency of the backlight light in LCD devices, a luminance-enhanced film is interposed between an optical cavity and a liquid crystal assembly. However, conventional luminance-enhanced films are fabricated by alternately stacking flat sheet-shaped isotropic optical layers and flat sheet-shaped anisotropic optical layers, which have different refractive indices, and performing an extension process on the stacked structure so that the stacked layer has an optical thickness and a refractive index of the respective optical layers, which can be optimized for selective reflection and transmission of incident polarized light. Accordingly, this fabrication process had a disadvantage of complicated fabrication of the luminance-enhanced film.

In particular, since each optical layer of the luminance-enhanced film has a flat sheet shape, P-polarized light and S-polarized light have to be separated from each other in response to a wide range of incident angles of the incident polarized light. Accordingly, this film has a structure, in which an excessively increased number of optical layers are stacked, thus disadvantageously involving exponential increase in production costs and deterioration in optical performance due to optical loss.

Accordingly, the island-in-the-sea yarns prepared using the spinneret of the present invention are arranged to cause light emitted from a light source to be reflected, scattered and refracted on the birefringent interface between the island-in-the-sea yarns and an isotropic sheet, thereby inducing optical modulation and considerably improving luminance. Specifically, light emitted from an external light source may be largely divided into S-polarized light and P-polarized light. In the case in which only a specific polarity of light is required, the P-polarized light passes through a luminance-enhanced film without being influenced by the birefringent interface. However, the S-polarized light is modulated into randomly refracted, scattered or reflected wavelength, i.e., 5-polarized light or P-polarized light on the birefringent interface. If the modulated light is reflected and irradiated on the luminance-enhanced film again, the P-polarized light passes through the luminance-enhanced film, and the S-polarized light is scattered or reflected again. Through repetition of this process, desired P-polarized light can be obtained.

Accordingly, when a plurality of group-type island-in-the-sea yarns forming a birefringent interface with a sheet are arranged in the sheet, luminance can be considerably improved without using conventional stack-type luminance-enhanced films. The present inventors found that use of general birefringent fibers as a polymer having birefringent interfaces has an advantage of low production costs and easy production, but disadvantageously cannot improve luminance to a desired level and is thus unsuitable for industrial application, instead of the conventional stack-type luminance-enhanced films.

Accordingly, the afore-mentioned problem can be solved by using birefringent island-in-the-sea yarns as birefringent fibers having birefringent interfaces. More specifically, the case where birefringent island-in-the-sea yarns are used is found to provide considerably improved optical modulation efficiency and luminance, as compared to the case where conventional birefringent fibers are used. Of the constituent components of island-in-the-sea yarns, the island portions are anisotropic and sea portions partitioning the island portions are isotropic. This case, where the interfaces between a plurality of island portions and a plurality of sea portions constituting the island-in-the-sea yarns as well as the interfaces between the island-in-the-sea yarns and the sheet are birefringent, exhibits considerably improved optical modulation efficiency and is thus industrially applicable as an alternative to stack-type luminance-enhanced films, as compared to conventional birefringent fibers wherein only the interfaces between the sheet and birefringent fibers are birefringent. Accordingly, as compared to the case where common birefringent fibers are used, the case where birefringent island-in-the-sea yarns are used exhibits superior optical modulation efficiency and birefringent island-in-the-sea yarns which comprise island portions and sea portions exhibiting different optical properties, thus enabling formation of birefringent interfaces therein, can more considerably improve optical modulation efficiency. More specifically, in island-in-the-sea yarns comprising optically isotropic sea portions and anisotropic island portions, the levels of substantial equality and in-equality between refractive indexes along spatial axes X, Y and Z affect scattering of polarized light. Generally, scattering performance varies in proportion to the square of the difference in refractive index. Accordingly, as the difference in refractive index according to a specific axis increases, light polarized according to the axis is more strongly scattered. On the other hand, when the difference in refractive index according to a specific axis is low, a ray of light polarized according to the axis is weakly scattered. When the refractive index of sea portions at a specific axis is substantially equivalent to the refractive index of island portions, incident light that is polarized by an electric field parallel to this axis is not scattered, irrespective of the size, shape and density of a portion of the island-in-the-sea yarns, but may pass through the island-in-the-sea yarns. More specifically, FIG. 10 is a sectional view illustrating a passage in which light permeates birefringent island-in-the-sea yarns of the present invention. In this case, p waves (represented by lines) pass through island-in-the-sea yarns, independent from the interface between the outside and the birefringent island-in-the-sea yarns and the interface between island portions and sea portions present in birefringent island-in-the-sea yarns, while S waves (represented by dots) are affected by the interface between the sheet and the birefringent island-in-the-sea yarns and/or the interface between island portions and sea portions in the birefringent island-in-the-sea yarns and are thus optically modulated. As a result, the group-type island-in-the-sea yarns render a specific color according to the ratio of sea portions to island portions and diameter of fibers, without adding chromogenic compounds such as dyes and are thus applicable to photochromic fibers.

Meanwhile, it is preferred that the difference in refractive index in two axes is 0.03 or less and the difference in refractive index in the remaining axis is 0.05 or more. In this case, P waves pass through birefringent interfaces of island-in-the-sea yarns, while S waves undergo optical modulation. More preferably, when the difference in refractive index between sea portions and island portions in island-in-the-sea yarns in a longitudinal direction is 0.1 or more and, with respect to the remaining two axial directions, the refractive index of the sea portion is substantially equivalent to that of the island portion, optical modulation efficiency can be maximized.

Consequently, in order to maximize optical modulation efficiency of island-in-the-sea yarns, island portions and sea portions should exhibit different optical properties and an optical-modulation area should be wider. For this purpose, the number of island portions should be as large as possible. However, conventional island-in-the-sea yarns comprising 500 or more island portions have advantages of decreased optical-modulation interface area and deteriorated optical-modulation efficiency due to aggregation of island portions, although they comprise anisotropic island portions and isotropic sea portions. Accordingly, in the present invention, aggregation of island portions can be solved by two or more spinning cores, although 500 or more island portions are present. As a result, the island-in-the-sea yarns prepared using the spinneret of the present invention exhibit maximized optical modulation efficiency and luminance-enhanced films into which the island-in-the-sea yarns are incorporated also exhibit considerably improved optical modulation efficiency and luminance.

Any material for sea and/or island portions may be used so long as it is commonly used as a material for island-in-the-sea yarns, and examples of sea portions and/or island portions include polyethylene naphthalate (PEN), copolyethylene naphthalate (co-PEN), polyethylene terephthalate (PET), polycarbonate (PC), polycarbonate (PC) alloys, polystyrene (PS), heat-resistant polystyrene (PS), polymethylmethacrylate (PMMA), polybutylene terephthalate (PBT), polypropylene (PP), polyethylene (PE), acrylonitrile butadiene styrene (ABS), polyurethane (PU), polyimide (PI), poly vinyl chloride (PVC), styrene acrylonitrile (SAN) mixtures, ethylene vinyl acetate (EVA), polyamide (PA), polyacetal (POM), phenol, epoxy (EP), urea (UF), melanin (MF), non-saturated polyester (UP), silicon (Si), elastomers and cycloolefin polymers and combinations thereof. In view of efficient improvement in optical modulation, it is preferable to adopt materials for the island portions and the sea portions which have substantially identical refractive indexes in two axes, but have great difference in refractive index in one axis. However, it is more preferable that when polyethylene naphthalate (PEN) is used as a material for island portions in the birefringent island-in-the-sea yarns and a copolyethylene naphthalate and polycarbonate alloy alone or a combination thereof is used as a material for sea portions, luminance is greatly improved, as compared to birefringent island-in-the-sea yarns made of common materials. In particular, when the polycarbonate alloy is used as the sea portions, birefringent island-in-the-sea yarns with the most excellent optical modulation property can be prepared. In this case, the polycarbonate alloy may be preferably composed of polycarbonate and modified polycyclohexylenedimethylene terephthalate glycol (PCTG) and more preferably, use of the polycarbonate alloy consisting of the polycarbonate and modified polycyclohexylenedimethylene terephthalate glycol (PCTG) which are present in a weight ratio of 15:85 to 85:15 is effective for improvement in luminance. When polycarbonate is present in an amount less than 15%, polymer viscosity required for spinning performance is excessively increased and use of a spinning machine is disadvantageously impossible, and when the polycarbonate is present in an amount exceeding 85%, a glass transition temperature increases and spinning tension increases, after discharge from a nozzle, thus making it difficult to secure spinning performance.

Most preferably, use of the polycarbonate alloy consisting of the polycarbonate and modified polycyclohexylenedimethylene terephthalate glycol (PCTG) which are present in a weight ratio of 4:6 to 6:4 is effective for improvement in luminance. Furthermore, in view of efficient improvement in optical modulation efficiency, it is preferable to adopt materials for the island portions and the sea portions which have substantially identical refractive indexes in two axes, but have great difference in refractive index in one axis.

Meanwhile, methods for modifying isotropic materials into birefringent materials are well-known in the art and for example, polymeric molecules are oriented and materials thus become birefringent when they are drawn under suitable temperature conditions.

Consequently, the island-in-the-sea yarns prepared using the spinneret for preparing island-in-the-sea yarns of the present invention have a structure wherein island portions are partitioned into two or more groups, and are thus free of aggregation of the island portions in the center thereof, although the number of island portions is 500 or more. Accordingly, island-in-the-sea yarns are considerably advantageous for the preparation of microfibers, since 500 or more island portions can be disposed in one island-in-the-sea yarn and fineness of island portions can thus be reduced. In addition, the island-in-the-sea yarns have an advantage of considerably reduced production costs, since 500 or more microfibers can be produced from one island-in-the-sea yarn. Furthermore, the island-in-the-sea yarns render a specific color according to the ratio of sea portions to island portions and diameter of fibers, without adding chromogenic compounds such as dyes, and are thus applicable to photochromic fibers. When the island-in-the-sea yarns, whose sea portions are not eluted, are applied to luminance-enhanced films for LCDs, they can impart maximum optical-modulation effects thereto.

Hereinafter, the following Examples and Experimental Examples will be provided for a further understanding of the invention. These examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

Example 1

An isotropic PC alloy (nx=1.57, ny=1.57, nz=1.57) consisting of polycarbonate and modified polycyclohexylenedimethylene terephthalate glycol (PCTG) in a ratio of 5:5 was used as a sea ingredient and anisotropic PEN (nx=1.88, ny=1.57, nz=1.57) was used as an island ingredient. In order to obtain island-in-the-sea yarns having the cross-section shown in FIG. 7, island-in-the-sea yarns (wherein 130 island portions are arranged in one spinning core and a total number of island portions is 1040), were placed on a spinneret whose upper plate has the cross-section shown in FIG. 6. Under this composition, 150/24 undrawn yarns were spun at a spinning temperature of 305° C. and at a spinning rate of 1,500 M/min and then drawn 3-fold to obtain 50/24 drawn yarns. FIG. 7 is an electron micrograph of island-in-the-sea yarns spun using the spinneret of FIG. 6. As can be seen from FIG. 7, no aggregation of island portions was observed.

Comparative Example 1

The spinning was performed in the same manner as in Example 1 except that the island-in-the-sea yarns were spun using a spinneret wherein one spinning core is present and 334 island ingredient supply channels are arranged in the one spinning core, as shown in FIG. 1. FIG. 2 is an electron micrograph of island-in-the-sea yarns spun using the spinneret of FIG. 1. As can be seen from FIG. 2, aggregation of island portions was observed in the center of island-in-the-sea yarns.

The spinneret for preparing island-in-the-sea yarns of the present invention exhibits superior optical modulation performance without causing aggregation of island portions, and may thus be widely used for the preparation of island-in-the-sea yarns applicable to microfiber fields, optical devices such as cameras, cellular phones and high luminance-requiring LCDs.

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

1. A spinneret for preparing island-in-the-sea yarns comprising:

a discharge portion comprising a plurality of island ingredient supply channels to discharge island-in-the-sea yarns; and

a peripheral portion arranged in the periphery of the discharge portion, the peripheral portion comprising a sea ingredient supply channel,

wherein the island ingredient supply channels are partitioned into a plurality of groups in the discharge portion.

2. The spinneret according to claim 1, wherein the island ingredient supply channels are grouped based on two or more spinning cores.

3. The spinneret according to claim 2, wherein the spinning cores include one standard spinning core arranged in the center of the discharge portion and a plurality of peripheral spinning cores arranged based on the standard spinning core.

4. The spinneret according to claim 3, wherein the peripheral spinning cores are 3 to 20 in number.

5. The spinneret according to claim 3, wherein the peripheral spinning cores are 6 to 10 in number.

6. The spinneret according to claim 3, wherein the number of island ingredient supply channels arranged with respect to one standard spinning core or one peripheral spinning core is 10 to 300.

7. The spinneret according to claim 3, wherein the sea ingredient supply channel is interposed between the standard spinning core and the peripheral spinning core.

8. The spinneret according to claim 1, wherein the total number of the island ingredient supply channels is 38 to 1,500.

9. The spinneret according to claim 1, wherein the total number of the island ingredient supply channels is 500 to 1,500.

10. The spinneret according to claim 1, wherein the total number of the island ingredient supply channels is 1,000 to 1,500.

11. The spinneret according to claim 1, wherein the spinning cores are arranged based on the center of the discharge portion.

12. The spinneret according to claim 11, wherein a sea ingredient supply channel is arranged in the center of the discharge portion.

13. The spinneret according to claim 11, wherein the sea ingredient supply channel is arranged between the spinning cores.

14. The spinneret according to claim 11, wherein the discharge portion has a diameter of 15 to 50 mm, and the island ingredient supply channel or the sea ingredient supply channel has a diameter of 0.1 to 0.3 mm.

15. The spinneret according to claim 1, wherein the island ingredient supply channel group has a diameter of 8 to 15 mm.

16. The spinneret according to claim 1, wherein the discharge portion is 2 to 20 in number.

17. The spinneret according to claim 1, wherein the discharge portion further comprises one or more sea ingredient supply channels.

18. The spinneret according to claim 1, wherein a maximum distance between the centers of adjacent island ingredient supply channels present in one group is smaller than a maximum distance between the centers of adjacent island ingredient supply channels present in two adjacent groups.

19. An island-in-the-sea yarn spun using the spinneret according to claim 1.