JP4676857B2 - Sea-island composite fiber for high toughness ultrafine fiber - Google Patents

Description

  The present invention relates to an ultrafine fiber that has an extremely large number of islands, has strength when the sea component is dissolved and removed, and has excellent diameter uniformity.

  Conventionally, many techniques for producing ultrafine fibers have been proposed. Typical production methods include direct spinning, sea-island type composite spinning, and electrospinning. In the direct spinning method, it is necessary to reduce the nozzle diameter at the time of spinning, which increases the extrusion pressure, and as a result, the extrusion state becomes unstable, causing problems such as yarn breakage and fluffing. Moreover, there was a limit to the diameter of the fiber that can be produced. In the sea-island type composite spinning method, Patent Documents 1 and 2 describe a method for obtaining ultrafine fibers from fibers obtained by blending sea-island polymers in a chip state. It is widely used because it can be easily manufactured by a conventional apparatus. However, the ultrafine fiber made from the sea-island type composite fiber obtained by using this method has a problem that the fiber diameter varies greatly.

  Further, Patent Document 3 describes a method for producing a fiber composed of an aggregate of fine polymer short fibers by forming a sea-island cross section using a composite polymer mixed with a static mixer as an island component. Due to the formation of island phases, the homogeneity is insufficient and the aggregate fiber is composed of fine fibrils, which causes a problem in toughness.

  Patent Document 4 describes a method for producing a sea-island structure fiber obtained by joining a melt flow of each of the sea-island polymers to form a joined flow, and dividing and joining the joined flow. As the number of islands varies, there are problems with toughness and product quality stability.

Electrospinning is an apparatus capable of producing a nonwoven fabric having a fiber diameter of several tens of nanometers. In this method, a high voltage is applied between the tip of the nozzle containing the polymer solution and the substrate, and the charged polymer solution is ejected and accumulated on the substrate. Recently, it has attracted particular attention because it can be easily produced in a small amount and a low concentration solution. However, the fiber diameter of the nonwoven fabric prepared using electrospinning varies considerably as described in Patent Document 5. In addition, the toughness is weak compared to ordinary fibers, and there is a limit in application. The manufacturing method also has a problem from the viewpoint of facility safety and environmental load, such as using solvents and high voltage.
From the above, high toughness ultrafine fibers that have a uniform fiber diameter and can be applied and developed are demanded.

Japanese Patent Laid-Open No. 3-113082 JP-A-4-126815 Japanese Patent Publication No. 60-28922 JP 2000-110028 A JP 2004-68161 A

  An object of the present invention is to overcome the above-mentioned problems and to provide a composite fiber for high toughness ultrafine fibers that can obtain a high toughness ultrafine fiber that has a uniform fiber diameter and can be applied and developed for various uses.

As a result of intensive studies to solve the above problems, the present inventors have reached the present invention. That is, according to the present invention, a sea-island type composite fiber having an easily soluble polymer as a sea component and a hardly soluble polymer as an island component, wherein the ratio of sea component: island component is 10: 90-60 based on weight. 40, and in the fiber cross section, when the fiber diameter (R) and the average diameter (r) of the island component are drawn through the center of the fiber cross section and four straight lines are drawn every 45 degrees, The average value (S) and maximum value (Smax) of the distance between the island components in a straight line satisfy the following relational expressions (I) and (II), and the toughness of the fiber after dissolution of the sea components is 20 or more. A sea-island type composite fiber for ultra-toughness ultrafine fibers is provided.
0.001 ≦ S / r ≦ 0.5 (I)
Smax / R ≦ 0.15 (II)

  The composite type composite fiber for high toughness ultrafine fibers of the present invention (hereinafter sometimes referred to as sea-island type composite fiber or composite fiber) is a sea-island type composite having a readily soluble polymer as a sea component and a hardly soluble polymer as an island component. It is a fiber, and the ratio of the sea component: island component should be in the range of 10: 90-60: 40, preferably in the range of sea component: island component 20: 80-40: 60, based on weight. When the proportion of the sea component is 60% or more, the amount of the solvent necessary for dissolving the sea component increases, which causes problems in terms of safety, environmental load, and cost. If it is less than 10%, the islands are easily stuck.

In the present invention, in the fiber cross section of the above-mentioned composite fiber, the fiber diameter (R) and the average diameter (r) of the island component, and four straight lines every 45 degrees through the center of the fiber cross section. The average value (S) and the maximum value (Smax) of the distance between the island components that are in a straight line when drawn are such that the following relational expressions (I) and (II) are satisfied. It is important that the toughness is 20 or more. Thereby, the high toughness which is the object of the present invention can be achieved.
0.001 ≦ S / r ≦ 0.5 (I)
Smax / R ≦ 0.15 (II)
Note that Smax is the maximum value of the interval between island components excluding sea components in the center of the fiber.

Here, when the value of S / r exceeds 0.5, or when the value of Smax / R exceeds 0.15, the high-speed spinnability deteriorates and the draw ratio cannot be increased. The high elongation property of the drawn yarn of the fiber is lowered, and the strength of the ultrafine fiber after the sea component is dissolved is lowered. When the value of S / r is less than 0.001, island components are easily stuck together. In order to obtain higher toughness, the following ranges are more preferable.
0.01 ≦ S / r ≦ 0.3
Smax / R ≦ 0.08

  Further, in the present invention, the average value (S) of the interval between the island components and the interval (So) between the island component closest to the fiber outer periphery and the fiber outer periphery when the four straight lines are drawn. The ratio So / S is preferably in the range of 0.1 to 2.0. When So / S exceeds 2.0, the strength and elongation properties of the drawn yarn of the composite fiber tend to decrease, and the strength of the ultrafine fiber after dissolution of the sea component tends to be low. Tends to stick together between island components.

  In the present invention, it is preferable that the sea-island composite fiber has a yield point due to the sea component breaking in the load-elongation curve at room temperature. The manifestation of the yield point is a phenomenon observed because the sea component is solidified faster than the island component, and the orientation of the island component is lowered due to the influence of the sea component. This yield point means the partial break point of the sea component, and after the yield point, the island component with low orientation extends. The sea-island component breaks at the breaking point of the load-elongation curve. These phenomena can also be explained from the fact that the yield point shifts to the initial stage (that is, the direction of elongation is 0%) as the spinning speed increases.

  In the present invention, the difference between the elongation (%) at the yield point and the breaking elongation (%) is particularly preferably 40% or more. When the difference between the elongation at the yield point and the elongation at break is 40% or less, the elongation is lower than when it is less than 40%, and therefore there is a tendency that the draw ratio does not increase and high toughness cannot be achieved. . The difference between the elongation (%) and the elongation at break (%) at a more preferable yield point is 50 to 200%.

  Next, the number of islands in the fiber cross section is particularly preferably 100 or more. The greater the number of islands, the higher the productivity when dissolving and removing sea components to produce ultrafine fibers, and the fineness of the resulting ultrafine fibers is also remarkable, expressing the softness and glossiness that are unique to ultrafine fibers. be able to. Here, when the number of islands is less than 100, an ultrafine fiber having a small fiber diameter cannot be obtained even if sea components are dissolved and removed. Further, if the number of islands is too large, not only the production cost of the spinneret is increased, but also the workability itself is liable to be lowered.

  Furthermore, in the present invention, it is desirable that the average diameter of the island component is 50 to 2000 nm, preferably 100 to 1000 nm. When the average diameter of the island component is less than 50 nm, the fiber structure is unstable and the physical properties and fiber form are unstable, which is not preferable. On the other hand, when the average diameter exceeds 2000 nm, softness and glossiness peculiar to ultrafine fibers are obtained. Not preferable.

  The combination of polymers constituting the sea-island composite fiber of the present invention preferably satisfies the following three points. That is, the three points are (1) the melt viscosity of the sea component at the time of melt molding is greater than the melt viscosity of the island component, (2) the dissolution rate of the sea component in the island component is 200 times or more, (3) the island component The residual elongation is greater than the sea component.

  When the melt viscosity of the sea component at the time of melt spinning is larger than the melt viscosity of the island component, the sea-island cross-section formability is improved. If this condition is satisfied, even if the composite weight ratio of the sea components is 50% or less, the islands will not adhere to each other and become different from the sea-island fibers. When the islands are stuck together, when sea components are dissolved and removed, not only ultrafine fibers but also irregular fibers are created, and problems such as dyed spots and pilling are likely to occur. A particularly preferred melt viscosity ratio (sea / island) is in the range of 1.1 to 2.0, particularly 1.3 to 1.5. If this ratio is less than 1.1, the island components are likely to stick together during melt spinning, whereas if it exceeds 2.0, the difference in viscosity is too large and the spinning tone tends to decrease. In the melt spinning, specifically, each melt viscosity measured at a temperature 10 to 40 ° C. higher than the melting point of the higher melting point polymer of the island component and the sea component (1 ) As long as the relationship is satisfied.

  When the dissolution rate of the sea component with respect to the island component is 200 times or more, the island separation property is improved. When the dissolution rate is less than 200 times, the island component of the separated fiber cross-section surface layer is dissolved because the fiber diameter is small while the sea component in the center of the fiber cross-section is dissolved. Despite being reduced in weight, the sea component at the center of the fiber cross-section cannot be completely dissolved and removed, causing problems such as the thickness of island components and the deterioration of strength due to solvent erosion, resulting in fluff and dyed spots. Occurs. Specifically, when the sea component is a polyester polymer, the dissolution rate is calculated by calculating the dissolution rate constant from the weight loss rate with respect to the weight loss time at 95 ° C. with a 4% NaOH aqueous solution. did. When the sea component is a polyamide-based polymer, it means a dissolution rate measured for 24 hours at 25 ° C. (room temperature) with 99% formic acid, and when the sea component is styrene at 60 ° C. with toluene. In the present invention, the hardly soluble polymer and the easily soluble polymer refer to a polymer based on the solubility in an organic solvent such as an alkaline aqueous solution, formic acid, or toluene.

  When the residual elongation of the island component is greater than that of the sea component, the island after sea dissolution can be made tough. If the residual elongation of the island component is smaller than the sea component, the draw ratio cannot be increased, so that the toughness value of the island after sea dissolution becomes low, and an ultrathin fiber that can be applied and developed cannot be created.

  The polymer constituting the sea component is preferably a polymer satisfying the above three points, and particularly preferred are polyester-based polymers, polyamide-based polymers, polystyrene-based polymers, and polyethylene-based polymers having good fiber-forming properties. For example, polylactic acid, an ultrahigh molecular weight polyalkylene oxide condensation polymer, and a copolymer polyester of 5-sodium sulfoisophthalic acid are optimal as the easily soluble polymer in an alkaline aqueous solution. Here, the alkaline aqueous solution refers to potassium hydroxide, sodium hydroxide aqueous solution and the like. Nylon 6 can be easily dissolved in formic acid, and polystyrene can be easily dissolved in an organic solvent such as toluene.

  Among the above polyester polymers, polyethylene having an intrinsic viscosity of 0.4 to 0.6 obtained by copolymerizing 6 to 12 mol% of 5-sodium sulfoisophthalic acid and 3 to 10 wt% of polyethylene glycol having a molecular weight of 4000 to 12000. A terephthalate copolymer polyester is preferred. Here, 5-sodium sulfoisophthalic acid contributes to improving hydrophilicity and melt viscosity, and polyethylene glycol (PEG) improves hydrophilicity. In addition, PEG has a hydrophilicity increasing action that is considered to be due to its higher-order structure as the molecular weight increases. However, since the reactivity becomes poor and a blend system is produced, problems arise in terms of heat resistance and spinning stability. there is a possibility. On the other hand, if the copolymerization amount is 10% by weight or more, there is an effect of decreasing the melt viscosity, which is not preferable. From the above, the above range is appropriate.

  The sparingly soluble polymer constituting the island component preferably satisfies the above-mentioned three points, and examples thereof include polyamide-based polymers, polystyrene-based polymers, and polyethylene-based polymers. Among these, polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, nylon 6, and nylon 66 are preferable for clothing. On the other hand, in industrial materials and medical applications, polystyrene, polyethylene and the like that are resistant to water, acid, and alkali are preferable in terms of durability. Furthermore, the island component is not limited to a round cross section, and may be an irregular cross section.

  The sea-island type composite fiber of the present invention described above can be easily produced, for example, by the following method. That is, a polymer having a high melt viscosity and an easily soluble polymer and a polymer having a low melt viscosity and a hardly soluble polymer are melt-spun using the former as a sea component and the latter as an island component. Here, the relationship between the melt viscosity of the sea component and the island component is important, and when the melt viscosity of the sea component is small, the island components may stick together.

  As the die used for melt spinning, an arbitrary one such as a hollow pin group or a fine hole group for forming an island component can be used. For example, a spinneret may be used in which an island component extruded from a hollow pin or a fine hole and a sea component flow that is designed to fill the gap between the island component are joined and compressed to form a cross section of the sea island. . Examples of spinnerets that are preferably used are shown in FIGS. 1 and 2, but are not necessarily limited thereto. In the cross section of the sea-island type composite fiber of the present invention, the fiber diameter (R), the average diameter (r) of the island component, and the average value (S) and the maximum value (Smax) of the interval between the island components are represented by the formula (I) and It is important to satisfy (II), and any base can be used as long as it can create a cross section that satisfies these equations. FIG. 1 shows a method in which a hollow pin is discharged into a sea component resin reservoir portion and is joined and compressed. FIG. 2 shows a method in which island components are formed by a fine hole method.

  Each figure will be described more specifically. In the spinneret 1 shown in FIG. 1, the melted island component polymer in the island component polymer reservoir 2 before distribution is in the island component polymer introduction passage 3 formed by a plurality of hollow pins. On the other hand, the molten sea component polymer is introduced into the pre-distribution sea component polymer reservoir 5 through the sea component polymer introduction passage 4. The hollow pin forming the island component polymer introduction passage 3 passes through the sea component polymer reservoir 5 and is located at the center of the entrance of each of the plurality of core-sheath type composite flow passages 6 formed thereunder. The part opens downward. The island component polymer flow is introduced from the lower end of the island component polymer introduction passage 3 into the central portion of the core-sheath type composite flow passage 6, and the sea component polymer flow in the sea component polymer reservoir 5 is Is introduced so as to enclose the island component polymer, and a core-sheath type composite flow having the island component polymer flow as a core and a sea component polymer flow as a sheath is formed. It introduce | transduces in the funnel-shaped confluence | merging channel | path 7, and in this confluence | merging channel | path 7, each sheath part adjoins each other, and a sea-island type compound flow is formed. The sea-island type composite flow gradually decreases in the horizontal cross-sectional area while flowing down in the funnel-shaped merge passage 7 and is discharged from the discharge port 8 at the lower end of the merge passage 7.

  In the spinneret 11 shown in FIG. 2, the island component polymer reservoir 2 and the sea component polymer reservoir 5 are connected to an island component polymer introduction passage 13 formed of a plurality of through holes. The molten island component polymer in the island component polymer reservoir 2 is distributed to the plurality of island component polymer introduction passages 13 and is accommodated in the sea component polymer reservoir 5 through the plurality of island component polymer introduction passages 13. It passes through the melted sea component polymer and flows into the core-sheath type composite flow passage 6 and flows down the central portion thereof. On the other hand, the sea component polymer in the sea component polymer reservoir 5 flows down into the core-sheath composite flow passage 6 so as to surround the island component polymer flowing down the central portion thereof. As a result, a plurality of core-sheath type composite flows are formed in the plurality of core-sheath type composite flow passages 6, and a plurality of core-sheath type composite flows are formed in the funnel-shaped join passage 6. In the same manner as in FIG. 1, it flows down while forming a sea-island type composite flow, further reduces its horizontal cross-sectional area, and is discharged from the discharge port 8.

The discharged sea-island type composite fiber is solidified by cooling air and wound up. The winding speed is not particularly limited, but is preferably 1000 to 5000 m / min. If it is less than 1000 m / min, the spinning property is poor. If it exceeds 5000 m / min, the spinning stability is poor.
The obtained undrawn yarn can be adjusted to desired strength, elongation and heat shrinkage characteristics. The stretching step may be any of a method such as a separate stretching step after winding, or a method of simultaneously spinning and performing winding after the stretching step. What is important here is that the preheating condition during stretching is 60 to 150 ° C. As a result, yarn irregularities and single yarn breakage can be prevented.

  The toughness of the ultrafine fiber after dissolution in the sea obtained in the present invention is preferably 20 or more. If it is more than this, application development is possible not only in textile products but in a wide range of fields. More preferably, it is 25 or more.

  FIG. 3 is a cross-sectional explanatory view of an embodiment (21) of the sea-island type composite fiber of the present invention, which is composed of a sea component 22 and a large number of island components 23 arranged separately from each other in the sea component 22. Yes. A method for measuring the interval between island components will be described with reference to FIG. In FIG. 3, when the four straight lines 25-1, 25-2, 25-3, and 25-4 are drawn on the cross section 21 through the center 24 at an angle of 45 degrees with respect to each other, The interval between the island components on the four straight lines is measured, and the maximum value Sm and the interval So between the island component closest to the fiber outer periphery and the fiber outer periphery are determined, and the average value S of these intervals is determined. calculate. In FIG. 3, four linear island components are drawn and described, and the description of the island components is omitted.

  The sea-island type composite fiber of the present invention, or the ultrafine fiber bundle obtained by removing sea components from the composite fiber, is a yarn, braided yarn, spun yarn, woven fabric, felt, using at least a part of them. It can be used as an intermediate product such as non-woven fabric and artificial leather.

  In addition, since the above-mentioned ultrafine fiber bundle has high toughness, the intermediate products include jackets, skirts, pants, underwear and other clothing, sports clothing, clothing materials, carpets, sofas, curtains, interiors, and car seats. Interior goods, cosmetics, cosmetic masks, wiping cloths, health goods, and other daily necessities, environment and industrial materials such as abrasive cloths, filters, harmful substance removal products, battery separators, sutures, scaffolds, artificial blood vessels, blood filters It can be used for a wide range of medical purposes.

  Furthermore, because the above-mentioned ultrafine fiber side has a large specific area, it has excellent adsorption and absorption characteristics.For example, it can adsorb drugs such as proteins and vitamins, health and beauty promoting drugs, anti-inflammatory agents, disinfectants, etc. Can be used. On the other hand, since it has regulability, it can be used for pharmaceutical and hygiene applications such as drug delivery systems.

Hereinafter, the present invention will be described more specifically with reference to examples. Each evaluation item was measured by the following method.
(1) Melt viscosity measurement The polymer after drying is set in an orifice set at the melter melting temperature at the time of spinning, melted and held for 5 minutes, and then extruded under several levels of load. The shear rate and melt viscosity at that time Plot. By gently connecting the plots, a shear rate-melt viscosity curve is created, and the melt viscosity when the shear rate is 1000 sec- ¹ is observed.

(2) Sea-island cross-section formation The sea-island state was observed using an optical microscope and evaluated in two stages.
○: No island sticking part ×: With island sticking part

(3) Dissolution rate measurement Yarn is wound at a spinning speed of 1000 to 2000 m / min with a 0.3φ-0.6L × 24H base of each of the sea and island components, and the residual elongation is in the range of 30 to 60%. To obtain a 75 de / 24 fil multifilament. The weight loss rate was calculated from the dissolution time and the dissolution amount at a bath ratio of 100 at a temperature at which the solvent was dissolved in each solvent.
In the table, the case where the sea-island dissolution rate difference was 200 times or more was marked with ◯, and the case where it was 200 times or less was marked with ×.

(4) Fiber diameter (R), average diameter (r) of island components, and the distance between island components in a straight line when four straight lines are drawn every 45 degrees through the center of the fiber cross section Average value (S) and maximum value (Smax)
Fiber cross-sectional photographs were taken and measured with a transmission electron microscope TEM at a magnification of 30000 times.

(5) Load-elongation curve The weight of 9000 m of the sea-island type composite fiber was measured three times to obtain the fineness from the average value. And the load-elongation curve was calculated | required as initial stage sample length of 100 mm and pulling speed of 200 m / min at room temperature. When the yield point corresponding to the partial breakage of the sea component appeared in the load-elongation curve, the difference between the intermediate yield point and the breaking elongation was obtained from the chart paper.

(6) Ultrafine fiber toughness after dissolution in sea The toughness is calculated from the following formula.
Toughness = Strength x (Elongation) ^1/2
The fineness of the ultrafine fiber was calculated from the fineness (D) and dissolution removal rate (RR) of the sea-island composite fiber obtained previously. The formula is as follows.
Fineness of extra fine fiber = D x (1-RR)
A cylindrical braid having a weight of 1 g or more is prepared using sea-island type composite fibers, and sea components are dissolved and removed. Thereafter, the cylinder was unwound and a load-elongation curve was obtained under the conditions shown in (5). The strength was obtained by dividing the load value at break by the calculated fineness, and the elongation was obtained from the elongation value at break.

(7) Uniformity of island component diameter By 30,000 times TEM observation of ultrafine fiber after dissolution and removal of sea component, the average fiber diameter is calculated for the ultrafine fiber in one composite fiber, and the maximum-minimum width is average. Smaller than 50% of the fiber diameter was marked with ◯, and larger was marked with x.

(8) Texture of ultrafine fibers A sensory test was conducted on seven monitors and evaluated in two stages.
○: 5 or more people who evaluated that there was a slimy feeling peculiar to ultrafine fibers ×: 5 people or less who evaluated that there was a slimy feeling peculiar to ultrafine fibers Using the polymers listed in Table 1 for the island and sea components, Sea-island type composite unstretched fibers having the number of islands shown in Table 1 were melt-spun at a spinning temperature of 285 ° C. and wound at the spinning speed shown in Table 1. The obtained undrawn yarn was subjected to roller drawing at a drawing temperature of 60 to 90 ° C. and the magnification described in Table 2, and then heat-set at 150 ° C. and wound up. At this time, the spinning discharge amount was adjusted so that the drawn yarn was 40 dtex / 10 fil. This drawn yarn was knitted in a cylinder, and the sea component ratio equivalent was dissolved with a solvent. The uniformity of the island components was determined by TEM observation of the fiber cross section. For the toughness of the island component, a load-elongation curve is obtained, the strength is a value obtained by dividing the load value at break by the calculated fineness, and the elongation is calculated by applying to the calculation formula as the elongation value at break. It was shown in 2.

[Example 1]
The island component was copolymerized with polyethylene terephthalate having a melt viscosity at 285 ° C. of 1200 poise, and the sea component was copolymerized with 4 wt% of polyethylene glycol having an average molecular weight of 4000 having a melt viscosity of 1400 poise at 285 ° C. and 8 mol% of 5-sodium sulfoisophthalic acid. The modified polyethylene terephthalate was spun at a ratio of island component: sea component = 60: 40 using a die having 500 islands, and wound at 1500 m / min. Here, the residual elongation of the island component was larger than that of the sea component, and the difference in alkali weight loss rate was 1000 times. In the unloading curve at room temperature, the yield point corresponding to the partial rupture of the sea component was expressed. The difference between the yield point and the breaking elongation was 60%. When the cross section of the raw yarn was observed by TEM, the sea-island cross-section formation was good. The fiber diameter (R) and the average diameter (r) of the island component, and the distance between the island components in this straight line when four straight lines are drawn every 45 degrees through the center of the fiber cross section, When the relationship between the average value (S) and the maximum value (Smax) was examined, S / r = 0.1 and Smax / R = 0.05. Further, the ratio So / S of the average value (S) of the interval between the island components and the interval (So) between the island component closest to the fiber outer periphery and the fiber outer periphery was 0.8. Furthermore, a tubular knitting was made using a drawn yarn obtained by drawing this at a draw ratio of 2.8 times, and the weight was reduced by 40% at 95 ° C. with a 4% NaOH aqueous solution. When the cross section of the fiber was observed, a group of ultrafine islands having a uniform island diameter was formed. The strength of the island component after sea weight loss was 3.1 cN / dtex, the elongation was 75%, the toughness was 30, and a high-toughness ultrafine fiber having a uniform fiber diameter and applicable development could be produced.

[Example 2]
The same sea-island polymer as in Example 1 was used at the same sea-island ratio, spun using the same die as in Example 1, and wound up at a spinning speed of 1000 m / min. In the unloading curve at room temperature, the yield point corresponding to the partial rupture of the sea component did not appear and was a normal unloading curve. Furthermore, the drawn yarn obtained by drawing this at a draw ratio of 4.5 times formed a sea-island cross section having a uniform island diameter. A cylindrical knitting was made using the drawn yarn, and the weight was reduced by 40% at 95 ° C. with a 4% NaOH aqueous solution. The results are shown in Table 1.

[Example 3]
The island component was copolymerized with polyethylene terephthalate having a melt viscosity at 285 ° C. of 1200 poise, and the sea component was copolymerized with 4 wt% of polyethylene glycol having an average molecular weight of 4000 having a melt viscosity of 1350 poise at 285 ° C. and 9 mol% of 5-sodium sulfoisophthalic acid. Using modified polyethylene terephthalate, spinning was performed using a die having 400 islands, and wound at the same spinning speed. In the unloading curve at room temperature, the yield point corresponding to the partial rupture of the sea component was expressed. The ratio So / S of the average value (S) of the interval between the island components and the interval (So) between the island component closest to the fiber outer periphery and the fiber outer periphery was 0.9. Table 1 shows the physical properties of the undrawn yarn, and Table 2 shows the difference between the yield point and the elongation. Further, a tubular knitting was made using a drawn yarn obtained by drawing this at a draw ratio of 3.9, and the weight was reduced by 10% at 95 ° C. with a 4% NaOH aqueous solution. When the cross section of the fiber was observed, a group of ultrafine islands having a uniform island diameter was formed. The results are shown in Table 1.

[Example 4]
Polyethylene terephthalate having a melt viscosity of 1150 poise at 285 ° C. is used as the island component, 3 wt% of polyethylene glycol having an average molecular weight of 4000 having a melt viscosity at 285 ° C. of 1300 poise is used as the sea component, and 10 mol% of 5-sodium sulfoisophthalic acid. The copolymerized modified polyethylene terephthalate was spun at a ratio of island component: sea component = 70: 30 using a die having 900 islands, and wound at 3500 m / min. Here, the residual elongation of the island component was larger than that of the sea component, and the alkali weight loss rate difference was 2000 times. In the unloading curve at room temperature, the yield point corresponding to the partial rupture of the sea component was expressed. The ratio So / S between the average value (S) of the interval between the island components and the interval (So) between the island component closest to the fiber outer periphery and the fiber outer periphery was 1.1. Table 1 shows the physical properties of the undrawn yarn, and Table 2 shows the presence or absence of the yield point and the difference between the yield point and the elongation. Further, a tubular knitting was made using a drawn yarn obtained by drawing this at a draw ratio of 2.3 times, and the weight was reduced by 30% at 95 ° C. with a 4% NaOH aqueous solution. The results are shown in Table 2.

[Comparative Example 1]
The same sea-island polymer as in Example 1 was used, and the number of islands was the same but spinning was carried out at the same sea-island ratio using different bases and wound at the same spinning speed. In the unloading curve at room temperature, the yield point corresponding to the partial rupture of the sea component did not appear and was a normal unloading curve. When the cross section of the raw yarn was observed by TEM, the sea-island cross-section formation was good. Table 1 shows the physical properties of the undrawn yarn, and Table 2 shows the difference between the yield point and the elongation. Despite winding at the same spinning speed, the draw ratio of the above-mentioned sea-island composite fiber was 2.1 times, a value lower than that of Example 1. A cylindrical knitting was made using the drawn yarn, and the weight was reduced by 40% at 95 ° C. with a 4% NaOH aqueous solution. The results are shown in Table 2.

[Comparative Example 2]
Using the same sea-island polymer as in Example 1, using the same die, spinning was performed at a sea-island ratio of sea: island = 70: 30, and wound at the same spinning speed. In the unloading curve at room temperature, the yield point corresponding to the partial rupture of the sea component did not appear and was a normal unloading curve. When the cross section of the raw yarn was observed by TEM, the sea-island cross-section formation was good. Table 1 shows the physical properties of the undrawn yarn, and Table 2 shows the difference between the yield point and the elongation. Since the sea ratio is as high as 70%, the physical properties of the sea components are reflected at the time of stretching, so the stretching ratio was as low as 1.7 times. A cylindrical knitting was made using the drawn yarn, and the weight was reduced by 70% at 95 ° C. with a 4% NaOH aqueous solution. Since it took time to reduce the sea part, the islands near the surface were excessively reduced and the island diameter became uneven. The results are shown in Table 1.

[Comparative Example 3]
The island component was copolymerized with polyethylene terephthalate having a melt viscosity of 1550 poise at 285 ° C., and the sea component was copolymerized with 3 wt% of polyethylene glycol having an average molecular weight of 4000 having a melt viscosity of 1100 poise at 285 ° C. and 3 mol% of 5-sodium sulfoisophthalic acid. The modified polyethylene terephthalate was spun at a ratio of sea: island = 30: 70 using a die having 500 islands and wound at 1500 m / min. Here, the residual elongation of the island component was larger than that of the sea component, and the difference in alkali weight loss rate was 500 times. Table 1 shows the physical properties of the undrawn yarn, and Table 2 shows the difference between the yield point and the elongation. In the unloading curve at room temperature, the yield point corresponding to the partial rupture of the sea component was expressed. Moreover, it was ratio So / S0.8 of the average value (S) of the space | interval of an island component, and the space | interval (So) of an island component nearest to a fiber outer periphery, and a fiber outer periphery. Further, a tubular knitting was made using a drawn yarn obtained by drawing this at a draw ratio of 2.2, and the weight was reduced by 30% at 95 ° C. with a 4% NaOH aqueous solution. When the cross section of the fiber was observed, a group of ultrafine islands having a uniform island diameter was formed. However, it has been difficult to increase the draw ratio. The results are shown in Table 2.

[Comparative Example 4]
The island component was copolymerized with polyethylene terephthalate having a melt viscosity at 285 ° C. of 1200 poise, and the sea component was copolymerized with 3 wt% of polyethylene glycol having an average molecular weight of 4000 having a melt viscosity of 1,500 poise at 285 ° C. and 5 mol% of 5-sodium sulfoisophthalic acid. The modified polyethylene terephthalate was spun at a ratio of sea: island = 40: 60 using a base having 700 islands, and wound at 1000 m / min. Here, the residual elongation of the island component was larger than that of the sea component, and the alkali weight loss rate difference was 100 times. When the cross-section of the raw yarn was observed with a TEM, the sea-island cross-section formation was good, but the difference in the alkali weight reduction rate of the sea component relative to the island component was 100 times, which was insufficient. Despite being considerably reduced due to its small size and the sea equivalent being reduced, most of the sea in the center of the fiber cross-section was not reduced, so the softness unique to ultrafine fibers could not be obtained. The results are shown in Tables 1 and 2.

[Comparative Example 5]
The same sea-island polymer as in Example 1 was used, and spinning was performed at sea: island = 30: 70 using a die having 25 islands, and wound at the same spinning speed. When the cross section of the raw yarn was observed with a TEM, the sea-island cross-section formability was good, the difference in the alkali weight loss rate of the sea component relative to the island component was sufficient, and the fiber cross-section after the alkali weight loss was observed to have a uniform island diameter. Although the island group was formed, since the diameter of the ultrafine fiber was as large as 3.2 μm, the characteristic unique to the ultrafine did not appear. The results are shown in Tables 1 and 2.

[Comparative Example 6]
The island component was copolymerized with polyethylene terephthalate having a melt viscosity at 285 ° C. of 1200 poise, and the sea component was copolymerized with polyethylene glycol having an average molecular weight of 4000 having a melt viscosity of 900 poise at 285 ° C. and 8 mol% of 5-sodium sulfoisophthalic acid. The modified polyethylene terephthalate was spun at a ratio of sea: island = 40: 60 using a die having 100 islands, and wound at 1500 m / min. When the cross-section of the raw yarn was observed by TEM, the sea-island cross-section formation was poor. Specifically, although islands exist independently on the fiber surface portion, a cross section is formed in the fiber center portion so that the sea component surrounds the joined island. Therefore, even if the amount was reduced, ultrafine fibers could not be formed. The results are shown in Tables 1 and 2.

[Example 5]
Using the same island polymer as in Example 1, using nylon 6 having a melt viscosity of 1350 poise at 285 ° C. as the sea component, spinning was performed using a base having 800 islands at a ratio of sea: island = 30: 70. , And wound up at 1000 m / min. Here, the residual elongation of the island component is larger than that of the sea component, and PET, which is the island component, does not substantially dissolve in formic acid. In the unloading curve at room temperature, the yield point corresponding to the partial fracture of the sea component did not appear. When the cross section of the raw yarn was observed by TEM, the sea-island cross-section formation was good. Table 1 shows the physical properties of the undrawn yarn. Further, a tubular knitting was made using a drawn yarn obtained by drawing this at a draw ratio of 2.9 times, and immersed in formic acid to dissolve and remove only the sea component. When the cross section of the fiber after formic acid treatment was observed, a group of ultrafine islands having a uniform island diameter was formed. The results are shown in Table 2.

[Example 6]
Nylon 66 having a melt viscosity of 1150 poise at 285 ° C. is used as the island component, and the modified PET used in Example 1 is used as the sea component, and the base has 1000 islands at a ratio of sea: island = 20: 80. And wound up at 1000 m / min. Here, the residual elongation of the island component is larger than that of the sea component, and Ny, which is the island component, does not substantially dissolve in the alkaline solution, so there is a sufficient difference between the dissolution rates of the sea islands. In the unloading curve at room temperature, the yield point corresponding to the partial fracture of the sea component did not appear. The ratio So / S between the average value (S) of the interval between the island components and the interval (So) between the island component closest to the fiber outer periphery and the fiber outer periphery was 1.0. Furthermore, a tubular knitting was made using a drawn yarn obtained by drawing this at a draw ratio of 3.1, and immersed in formic acid to dissolve and remove only the sea component. When the cross section of the fiber after formic acid treatment was observed, a group of ultrafine islands having a uniform island diameter was formed. The results are shown in Table 2.

[Example 7]
The island component was copolymerized with polyethylene terephthalate having a melt viscosity at 285 ° C. of 1000 poise, and the sea component was copolymerized with 6 wt% of polyethylene glycol having an average molecular weight of 4000 having a melt viscosity of 1200 poise at 285 ° C. and 8 mol% of 5-sodium sulfoisophthalic acid. Using modified polyethylene terephthalate, spinning was performed using a base having 950 islands at a ratio of sea: island = 60: 40, and wound at 1000 m / min. Here, the residual elongation of the island component was larger than that of the sea component, and the alkali weight loss rate difference was 2500 times. In the unloading curve at room temperature, the yield point corresponding to the partial fracture of the sea component did not appear. When the cross section of the raw yarn was observed by TEM, the sea-island cross-section formation was good. The results of undrawn yarn are shown in Table 1. The ratio So / S between the average value (S) of the interval between the island components and the interval (So) between the island component closest to the fiber outer periphery and the fiber outer periphery was 1.2. Further, a tubular knitting was made using a drawn yarn obtained by drawing this at a draw ratio of 2.7 times, and the weight was reduced by 60% at 95 ° C. with a 4% NaOH aqueous solution. When the cross section of the fiber was observed, a group of ultrafine islands having a uniform island diameter was formed. The results are shown in Table 1.

FIG. 2 is a partial cross-sectional explanatory view of an example of a spinneret used for spinning the sea-island type composite fiber of the present invention. FIG. 6 is a cross-sectional explanatory view of a part of another example of the spinneret used for spinning the sea-island type composite fiber of the present invention. It is a section explanatory view of one embodiment of the sea-island type composite fiber of the present invention.

Claims (8)

A sea-island composite fiber having an easily soluble polymer as a sea component and a hardly soluble polymer as an island component, wherein the ratio of sea component: island component is 10:90 to 60:40 based on weight, and the fiber cross section , The fiber diameter (R) and the average diameter (r) of the island components, and the distance between the island components in a straight line when four straight lines are drawn every 45 degrees through the center of the fiber cross section High toughness ultrafine fibers characterized in that the mean value (S) and the maximum value (Smax) satisfy the following relational expressions (I) and (II), and the toughness of the fibers after dissolution of the sea component is 20 or more Sea-island type composite fiber.
0.001 ≦ S / r ≦ 0.5 (I)
Smax / R ≦ 0.15 (II)   The sea-island composite fiber for high-toughness ultrafine fibers according to claim 1, wherein the load-elongation curve of the sea-island composite fiber has a yield point due to the breakage of the sea component.   The sea-island composite fiber for high toughness ultrafine fiber according to claim 2, wherein the difference between the elongation at yield point and the elongation at break is 40% or more.   The number of islands is 100 or more, the average diameter (r) of the island component is 50 nm to 2 μm, and the average value (S) of the interval between the island components and the fiber outer circumference in this straight line when drawing four straight lines The sea-island composite fiber for high toughness ultrafine fibers according to claim 1, wherein the ratio So / S between the distance between the island component and the fiber outer periphery (So) is in the range of 0.1 to 2.0.   The sea-island composite fiber for high toughness ultrafine fibers according to claim 1, wherein the melt viscosity of the sea component during melt spinning is higher than the melt viscosity of the island component.   At least one alkaline aqueous solution in which the sea component is selected from polylactic acid, ultrahigh molecular weight polyalkylene oxide condensation polymer, polyethylene glycol compound copolymer polyester, and polyethylene glycol compound and 5-sodium sulfoisophthalic acid copolymer polyester The sea-island composite fiber for high toughness ultrafine fibers according to claim 1, which is an easily soluble polymer and has a sea component weight reduction rate of 200 times or more with respect to the island component.   The sea-island type composite fiber for high toughness ultrafine fibers according to claim 1, wherein the sea component is polyethylene terephthalate copolymerized with 6 to 12 mol% of 5-sodium sulfoisophthalic acid and 3 to 10 wt% of polyethylene glycol having a molecular weight of 4000 to 12000. .   The sea-island type composite fiber for high toughness ultrafine fiber according to claim 1, wherein the sea component is nylon and soluble in formic acid.

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