JP4960616B2 - Short fiber, method for producing the same, and precursor thereof - Google Patents

Description

  The present invention relates to a short fiber having a fiber diameter of 1 μm or less and a manufacturing method thereof, and more specifically, while the fiber diameter is 1 μm or less, the fiber diameter and the fiber length are almost uniform and can be arbitrarily determined. In addition, the present invention relates to a short fiber that can achieve a highly uniformly dispersed state when a fiber structure is manufactured by a papermaking method, a manufacturing method thereof, and an intermediate raw fiber.

  In recent years, ultrafine fibers with a fiber diameter of 1000 nm (= 1 μm) or less have attracted attention as research objects, as represented by nanofibers defined with a fiber diameter of 1 to 100 nm. Due to its specificity such as adsorptivity, it has been studied as a raw material for highly functional materials such as ultra-high performance filters, separators such as batteries and capacitors, or abrasives such as hard disks and silicon wafers. In the future, it will be necessary to arbitrarily control the fiber diameter, fiber dispersion state, and fiber density at the nano-order level in the materials and fiber structures that contain the fibers in order to develop new functions that have not existed in the past. Is done. For example, if two or more types of fibers with different fiber diameters at the nano level have a structure having a density gradient in the thickness direction of the nonwoven fabric, or if the density can be controlled by mixing short fibers of any fiber diameter and fiber length according to the purpose It is believed that more sophisticated and higher performance functions can be achieved with high performance filters and separators.

  It is described that it is possible to produce ultra-fine fibers in which 60% or more of the island component domains are in the range of 1 to 150 nm by a method of extracting the sea component of the fiber of the mixed spinning (see, for example, Patent Document 1). ). However, those having a fiber diameter in the range of 30 nm accounted for 70% of the total number of fibers, and the remaining 30% of the fibers had a broader fiber diameter distribution as they deviated from this. In addition, mixed spinning fibers are affected by the mixing ratio, melt viscosity difference, solubility parameter, etc. of the polymer constituting the sea component and the island component in controlling the fiber diameter. It is necessary to select, and it is very difficult to obtain an ultrafine fiber having a target fiber diameter arbitrarily even in consideration of spinnability and the like.

  In addition, a method for obtaining a nonwoven fabric using fibers having a fiber diameter of 50 to 500 nm obtained by mechanically beating fibrillated mixed spinning fibers of polyvinyl alcohol and polyacrylonitrile is described (for example, Patent Documents). 2). However, as a matter of course, there are many unbeaten non-fibrillar fibers, and it is almost impossible to arbitrarily control the fiber diameter.

On the other hand, even if the fiber diameter is made uniform, if the fiber length varies, a fiber structure with a uniform density cannot be obtained, and coarseness equal to chance occurs. The method of removing the sea component of the mixed spun fiber described in Patent Document 1 and the beating fibril fiber as in Patent Document 2 naturally cannot obtain a uniform fiber length. Means for removing sea components after cutting sea-island fibers to a predetermined length to obtain ultrafine fibers are disclosed (see, for example, Patent Documents 3 and 4). Although the sea component dissolved component is infiltrated also from the cut end and aims to efficiently remove the sea component, according to the study by the present inventors, the island component fiber can be cut even after being cut first. In the sea-island fiber having a diameter of 1 μm or less, it is difficult to remove the sea component at the center, and it is difficult to increase the yield of the ultrafine fiber. In addition, it is difficult to control the interval between the fibers of the island component, and it cannot be applied as it is. On the other hand, a method of cutting sea island-type fibers after removing sea components in a tow state is also described. However, in the case of sea-island fibers having an island component fiber diameter of 1 μm or less, the polymer constituting the sea component in the central portion is described. It is difficult to remove the fiber, and it is difficult to increase the yield of ultrafine fibers (for example, see Patent Document 5).
As described above, there were no ultra-fine short fibers having an ultra-fine fiber of 1 μm or less and a substantially uniform fiber diameter and fiber length.

JP 2004-169261 A JP 2003-129393 A JP 2003-105660 A Japanese Patent Laid-Open No. 7-331581 JP 2003-253555 A

  The present invention has been made against the background of the above prior art, and an object thereof is to provide a short fiber having a uniform fiber diameter of 1 μm or less with a small distribution of fiber diameter and fiber length.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have been able to precisely control the island component interval and have a polymer that constitutes an appropriate sea component so that the sea component extraction / removability is good. By selecting the polymer that constitutes the island component and performing precise archipelago sea-island composite spinning, cutting the undrawn yarn or drawn yarn to 50 to 1000 μm and then removing the sea component, the fiber diameter and fiber length are relatively The inventors have reached the invention of ultra-fine fibers that are uniform, have good dispersibility, and can arbitrarily control the structure of the fiber structure according to the purpose.

That is, the subject of this invention consists of a thermoplastic resin, the fiber diameter is 10-1000 nm, the fiber diameter variation coefficient (CVd) defined below is 0-15, the fiber length is 50-1000 μm, and the fiber length variation coefficient defined below. (CVl) is 0-20, and the aspect ratio (= fiber length / fiber diameter) is 100-2000, the short fiber is an easily soluble component as a sea component, A short fiber obtained from a sea-island composite fiber having an island component as a hardly soluble component, wherein the sea-island composite fiber is obtained by melt spinning, and a melt viscosity ratio (sea component) between the sea component and the island component at the melt spinning temperature. / Island component) is 1.1 to 2.0, the fiber diameter (Xd) of the island component in the cross section of the sea-island type composite fiber is 10 to 1000 nm, the number of islands is 100 or more, and the sea component between the island components Thickness (S) of 0.0 A sea fiber type composite fiber satisfying 1 ≦ S / Xd ≦ 0.5 is cut into a fiber length of 50 to 1000 μm, and then the sea component is extracted and removed to obtain the island component as a short fiber. It can be solved by the manufacturing method .
Fiber diameter variation coefficient (CVd) = σd / Xd × 100 (%)
[However, the fiber diameter is the average value of the major axis and minor axis in the fiber cross section, σd is the standard deviation of the fiber diameter distribution, and Xd is the average fiber diameter. ]
Fiber length variation coefficient (CVl) = σl / Xl × 100 (%)
[However, σl represents the standard deviation of the fiber length distribution, and Xl represents the average fiber length. ]

  According to the present invention, it is possible to obtain a short fiber having a uniform fiber diameter and fiber length and good dispersibility even though the fiber diameter is a superfine fiber having a fiber diameter of 1 μm or less. This is not possible with conventional ultra-fine fibers obtained by extracting sea components from mixed spun fibers or with ultra-fine fibers obtained by beating fibrillation.

Hereinafter, embodiments of the present invention will be described in detail.
The fiber of the present invention is made of a thermoplastic resin, has a fiber diameter of 10 to 1000 nm, and has a fiber diameter variation coefficient defined by the following formula of 0 to 15.
Fiber diameter variation coefficient (CVd) = σd / Xd × 100 (%)
However, the fiber diameter here refers to the average value of the maximum diameter and the minimum diameter of the fiber cross section, σd is the standard deviation of the fiber diameter distribution, and Xd is the average fiber diameter.

  If the fiber diameter is less than 10 nm, the influence of intermolecular force becomes strong, or the fiber structure itself is unstable and the fineness of individual ultrafine fibers is poor. At present, the ultrafine fibers are uniformly dispersed. It is difficult to obtain a fibrous structure. On the other hand, when the thickness exceeds 1000 nm, the fiber diameter deviates from the region of the fiber diameter where the unique physical properties aimed by the present invention are obtained. A particularly preferable range is 50 to 900 nm.

  Further, when the fiber diameter variation coefficient (CVd) is in the range of 0 to 15, preferably in the range of 0 to 10, when the CVd required as the fiber variation coefficient capable of nano-level structure control exceeds 15, It is difficult to design a fiber structure having a precise fiber composition gradient at the nano level.

Furthermore, the fiber of the present invention has a fiber length of 50 to 1000 μm, and has a fiber length variation coefficient defined by the following formula of 0 to 20.
Fiber length variation coefficient (CVl) = σl / Xl × 100 (%)
Here, σl represents the standard deviation of the fiber length distribution, and Xl represents the average fiber length.

  The fiber length is in the range of 50 to 1000 μm, preferably 100 to 500 μm. If the thickness is less than 50 μm, fiber dropout from the nonwoven fabric surface and sheet strength may be reduced. On the other hand, when the thickness exceeds 1000 μm, entanglement is likely to occur when the fiber is formed as an ultra-fine fiber, which causes defects such as bundling or pill-like shape, and inhibits the homogeneity of the structure.

Further, when the fiber length variation coefficient (CVl) is in the range of 0 to 20, preferably in the range of 0 to 10, when the CVl necessary as the fiber variation coefficient capable of nano-level structure control exceeds 20, It is difficult to design a fiber structure having a precise fiber composition gradient at the nano level. In order to set the average fiber length and the fiber length variation coefficient within a predetermined range, it is preferable to increase the accuracy of an apparatus for cutting fibers such as a guillotine cutter.

  The aspect ratio defined by the fiber length / average fiber diameter needs to be in the range of 100 to 2000, preferably in the range of 200 to 1500, and more preferably in the range of 300 to 1000. If the aspect ratio is less than 100, there is a great possibility that the fiber drop off from the nonwoven fabric surface and the sheet strength will decrease, and if it exceeds 2000, entanglement is likely to occur when short fibers are formed, resulting in defects such as bundling and hairballs, Impairs structure homogeneity. By selecting a fiber length having an appropriate aspect ratio according to the fiber diameter, a nonwoven fabric having both high uniformity and strength can be obtained.

  As a manufacturing method of the short fiber described above, after manufacturing a precise island-island type composite fiber having an island fiber diameter of 1 μm or less and an island number of 100 or more, the short fiber is cut into a predetermined fiber length. The method of taking out the short fiber which consists of an island component by eluting or decomposing | disassembling a sea component through a generating precursor is preferable. There is also a method of elution or decomposition of sea components in advance and supplying it to the papermaking process as short fibers, but in the state of sea island type composite short fibers, it is shipped to the nonwoven fabric manufacturer as a fiber generation precursor, and the papermaking process A method of removing the sea component by a sea component solvent or a decomposition accelerating chemical solution in the pre-process of the pulper or the pulper, or a method of removing the sea component after paper making in a precursor state may be employed.

  The method for forming the fiber web is not limited to the wet nonwoven fabric method (papermaking method), but the papermaking method is the most preferred means for more evenly dispersing short fibers of 1 μm or less. As a papermaking method, it can be formed by a conventionally known method, for example, a horizontal long net method, an inclined wire type short net method, a circular net method, or a long net / circular net combination method. In order to bind the short fibers, the wet nonwoven web after papermaking may be pressed using a calendar roller or an embossing roller depending on the application or purpose, or the fibers are entangled in the thickness direction with a water needle. Alternatively, heat bonding may be performed using a mixture of binder fibers or a chemical binder.

  A method for producing a sea-island composite fiber in the previous stage as a precursor for generating short fibers composed of the sea-island composite fiber will be described. The sea / island weight ratio is not particularly limited, but is preferably in the range of sea component: island component = 10: 90 to 60:40, and particularly preferably in the range of sea component: island component = 20: 80 to 40:60. If the proportion of the sea component exceeds 60% by weight, the amount of the solvent necessary for dissolving the sea component increases, the amount and time of the agent necessary for decomposition increase, and there are problems in terms of safety, environmental load, and cost. There is. Moreover, when it is less than 10% by weight, the island components may stick together.

  It is important that the number of islands is 100 or more. The higher the number of islands, the higher the productivity in producing fibers by dissolving and removing sea components, and it is relatively easy to obtain fibers having an island fiber diameter of 1 μm or less without extremely reducing the parent fiber diameter. 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. In particular, the number of islands is preferably 500 or more. The upper limit of the number of islands is not particularly limited, but it is preferably set to 1000 or less because not only the manufacturing cost of the spinneret increases, but also the processing accuracy itself tends to decrease.

  Further, the sea-island type composite fiber needs to have a thickness (S) of sea components between the island components of 0.001 ≦ S / Xd ≦ 0.5 (Xd is an average fiber diameter). If the S / Xd value is less than 0.001, the island components may stick together, making it difficult to separate the island components. Further, if the S / Xd value exceeds 0.5, the island component separation is improved, but the high-speed spinnability and the draw ratio cannot be increased, so that it becomes difficult to obtain a fiber having a target fiber diameter. In addition, the strength of the fiber after dissolution of the sea component may decrease, or the dissolution of the island component may progress while dissolving and removing the thick sea component, and the homogeneity between the island components may decrease.

  The requirements for the polymer constituting the sea component and the polymer constituting the island component that achieve the S / Xd value described above are such that the sea component has a high melt viscosity and is easily soluble in consideration of the extractability of the sea component. A polymer is used, and the island component is a low melt viscosity and hardly soluble polymer. In particular, the relationship between the melt viscosity of the polymer that constitutes the sea component and the polymer that constitutes the island component is important. When the melt viscosity of the polymer that constitutes the sea component is small, the island components may be stuck together. If the melt viscosity of the polymer that constitutes the sea component satisfies a larger relationship than the island component, even if the composite weight ratio of the sea component is 50% or less, the island components are mostly stuck together and the sea island fibers It will not be a different fiber. When island components are stuck together, not only ultrafine fibers but also irregular fibers are created when sea components are dissolved and removed, and short fibers having a uniform fiber diameter, which is the object of the present invention, cannot be obtained. A particularly preferred melt viscosity ratio (sea component / island component) 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.

  Here, the easily soluble component and the hardly soluble component are selected as a combination of polymers that dissolve or decompose one polymer and hardly dissolve or decompose the other polymer with respect to a certain solvent or drug. This means that the readily soluble component is selected as the sea component. Here, regarding the extractability of the sea component (elution or decomposability with respect to a certain solvent or drug), the island component separability is achieved by the fact that the dissolution rate of the polymer constituting the sea component in the island component is 200 times or more Becomes better. 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 at the center of the fiber cross-section is dissolved. Even though the amount is reduced, the sea component at the center of the fiber cross section cannot be completely dissolved and removed, leading to thick spots of the island component and solvent erosion of the island component itself. Short fibers with a fiber diameter cannot be obtained.

  The above describes the method for producing short fibers having a uniform fiber diameter, which is an object of the present invention, mainly from the viewpoint of removing sea components. When focusing on the spinning / stretching process as another viewpoint, the configuration of the die used for spinning, the type of polymer constituting the sea-island component, the melt viscosity, and the like are also important. The melt viscosity is as described above, and the polymer type is described below.

  The polymer constituting the sea component is a thermoplastic resin, and it is essential that the melt viscosity at the time of melt spinning is higher than the polymer constituting the island component, and the polymer constituting the island component for the solvent or degradable drug Any polymer may be used as long as the dissolution rate ratio is 200 or more, and polyesters, polyamides, and polyolefins such as polyethylene and polystyrene having particularly good fiber-forming properties can be mentioned as preferred examples. The polyamide is preferably an aliphatic polyamide. As specific examples, polylactic acid, ultra-high molecular weight polyalkylene oxide condensation polymer, polyoxyalkylene glycol compound and 5-sodium sulfoisophthalic acid copolyester are optimal as the alkaline aqueous solution-soluble polymer. However, the copolymerization component is not limited to these, and another copolymerization component may exist after the copolymerization thereof. Here, the alkaline aqueous solution refers to potassium hydroxide, sodium hydroxide aqueous solution and the like. In addition to this, formic acid for aliphatic polyamides such as nylon 6 and nylon 66, trichlorethylene for polystyrene and polyethylene (especially high pressure method low density) Examples thereof include hydrocarbon solvents such as hot toluene and xylene for polyethylene and linear low-density polyethylene), and hot water for polyvinyl alcohol and ethylene-modified vinyl alcohol polymers.

  Among copolyester polymers, an intrinsic viscosity of 0.4 to 0.6 dL / g 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 is used. Polyethylene 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, it is considered that the above range is appropriate.

  The polymer constituting the island component is a thermoplastic resin, and any fiber-forming polymer may be used as long as it is lower than the viscosity of the sea component at the time of melt spinning and has a dissolution rate ratio with the sea component as described above. . Among them, polyamides, polyesters, polyolefins and the like are preferable examples. Specifically, in applications where mechanical strength and heat resistance are required, in polyesters, polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate or the main repeating unit thereof, isophthalic acid or 5- Aromatic dicarboxylic acids such as metal salts of sulfoisophthalic acid, aliphatic dicarboxylic acids such as adipic acid or sebacic acid, hydroxycarboxylic acid condensates such as ε-caprolactone, or diethylene glycol, trimethylene glycol, tetramethylene glycol or hexamethylene glycol A copolymer with a glycol component or the like is preferred. Of the polyamides, aliphatic polyamides such as nylon 6 and nylon 66 are preferable. On the other hand, polyolefins are not easily attacked by acids, alkalis, etc., and have a characteristic that they can be used as binder components after being taken out as fibers due to their relatively low melting point. Preferred examples include high density polyethylene, linear low density polyethylene, isotactic polypropylene, ethylene propylene copolymer, and ethylene copolymer of vinyl monomer such as maleic anhydride. Furthermore, the island component is not limited to a round cross section, and may be an irregular cross section.

  In particular, polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene terephthalate isophthalate having an isophthalic acid copolymerization rate of 20 mol% or less, or aliphatic polyesters such as polyethylene naphthalate, or nylon 6, nylon 66, etc. Since aliphatic polyamides have heat resistance and mechanical properties due to a high melting point, they are more heat resistant than ultrafine fibrillated fibers made of polyvinyl alcohol / polyacrylonitrile mixed spun fibers as described in Patent Document 2. It is considered preferable because it can be applied to applications that require properties and strength.

  In addition, with regard to the polymer that constitutes the sea component and the polymer that constitutes the island component, organic fillers, antioxidants, thermal stability, as necessary, within a range that does not affect the physical properties of the spinning fiber and the short fibers after extraction. Various additives such as additives, light stabilizers, flame retardants, lubricants, antistatic agents, rust preventives, crosslinking agents, foaming agents, fluorescent agents, surface smoothing agents, surface gloss improvers, mold release improvers such as fluororesins, etc. It does not matter even if it contains an agent.

  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 in which an island component flow extruded from a hollow pin or a fine hole and a sea component flow that is designed to fill the gap between them are merged and compressed to form a sea island cross section. Good. Examples of spinnerets that are preferably used are shown in FIGS. 1 and 2, but are not necessarily limited thereto. In the sea-island type composite fiber cross section of the present invention, it is important that the relationship between the average fiber diameter (Xd) and the thickness (S) of the sea component between the island components satisfies 0.001 ≦ S / Xd ≦ 0.5. Any base can be used as long as it can create a cross section that satisfies the following formula. 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.

  The discharged sea-island type composite fiber is solidified by cooling air and taken up by a rotating roller or an ejector set at a predetermined take-up speed to obtain an undrawn yarn. The take-up speed is not particularly limited, but is preferably 200 m / min to 5000 m / min. Productivity is poor at 200 m / min or less. Also, spinning stability is poor at 5000 m / min or more.

  The obtained undrawn yarn may be subjected to the cutting process or the subsequent extraction process as it is depending on the use and purpose of the fiber obtained after extracting the sea component, and the intended strength, elongation and heat shrinkage characteristics Therefore, it can be subjected to a cutting step or a subsequent extraction step via a stretching step or a heat treatment step. The stretching process may be a separate stretching method in which spinning and stretching are performed in separate steps, or a straight stretching method in which stretching is performed immediately after spinning in one process may be used. The sea-island composite short fiber having a fiber length of 50 to 1000 μm is obtained by cutting the filament obtained by the above production method as it is or using a guillotine cutter or a rotary cutter as a tow bundled in units of tens to millions. Thus, a short fiber precursor can be obtained. The target short fiber can be obtained by dissolving and removing this sea component under appropriate conditions.

  Following the removal of the sea component, after neutralization and before the paper making process, as a fiber dispersant, a polyester ester, C8 sulfosuccinate, polyoxyethylene (POE) nonylphenol ether sulfate, Amine, POE nonylphenol ether sulfate sodium, POE nonylphenol, POE oleyl ether, fluorine-based activator, modified silicone and the like can be used. A dispersing agent is not limited to these, You may use multiple types. In addition, in order to increase the dispersibility of the pulp-like material, the entanglement between the pulp-like materials may be reduced by applying it to a pulper, refiner, beater, etc. in a wet state with dry, wet or dispersant added. Is possible.

  Although it is possible to make paper by a conventional method using only short fibers obtained by subjecting sea-island type composite fibers to an alkali weight loss treatment, depending on the purpose of the fiber structure, other compositions or polymers of the same composition It is also possible to mix short cuts made of

Hereinafter, the present invention will be described more specifically with reference to examples.
In addition, each item in an Example was measured with the following method.
(1) Melt viscosity measurement The polymer after vacuum drying at room temperature (about 25 ° C) for 24 hours is set in an orifice set to the melt temperature at the time of spinning, melted and held for 5 minutes, and then extruded under several levels of load. Plot the shear rate and melt viscosity at that time. The plot was gently connected to create a shear rate-melt viscosity curve. The melt viscosity described below indicates a value at a shear rate of 1000 sec- ¹ .

(2) Dissolution rate measurement Obtained by discharging the sea component and island component polymers from a die having a diameter of 0.3 mm and a length of 0.6 mm from a die having 24 holes and spinning at a spinning speed of 1000 to 2000 m / min. The undrawn yarn was drawn so that the residual elongation was in the range of 30 to 60% to prepare a multifilament of 83 dtex / 24 filament. Using this as a bath ratio of 100 at a predetermined solvent and dissolution temperature, the rate of weight loss was calculated from the dissolution time and the dissolution amount. 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 ×.

(3) Measurement of average fiber diameter and thickness (S) of sea component between island components Fiber cross-sectional photographs were taken at a magnification of 30000 times and measured with a transmission electron microscope TEM. Depending on the TEM machine, the length measurement function is used for measurement, and for a TEM that does not exist, the photograph taken may be enlarged and copied with a ruler after taking the scale into consideration. However, the fiber diameter was defined as the average value of the major axis and the minor axis in the fiber cross section. The thickness (S) of the sea component between the island components was defined as an average value obtained by randomly measuring 50 distances between the island components.

(4) Uniformity of average fiber diameter The average fiber diameter (Xd) and standard deviation (σd) in the fiber diameter data of 50 fibers randomly selected by 30,000 times TEM observation of ultrafine fibers after dissolution removal of sea components. The fiber diameter variation coefficient (CVd) defined below was calculated.
Fiber diameter variation coefficient (CVd) = σd / Xd × 100 (%)

(5) Fiber length Using a scanning electron microscope (SEM), the short fibers after dissolution and removal of sea components were placed on a base and measured at 20 to 500 times. Depending on the SEM machine, the length measurement function is used for measurement, and for the SEM that does not exist, the photograph taken may be enlarged and copied, and the scale taken into consideration, and measured with a ruler.

(6) Fiber length uniformity After randomly selecting 50 points from the measured fiber length data, and calculating the average value (Xl) and the standard deviation (σl) calculated from each measured data, The defined fiber length variation coefficient (CVl) was calculated.
Fiber length variation coefficient (CVl) = σl / Xl × 100 (%)

(7) Undispersed defect or entanglement A 100% fiber web of short fibers was prepared with a hand-drawing apparatus described in JIS P8222 so that the basis weight was 50 g / m2, and after drying for 30 minutes in a windless state at 130 ° C., 5 mm Cut into squares and place them gently on a scanning electron microscope (SEM) sample stage, observe this surface at 20 to 500 times, and visually check for unsatisfactory dispersion such as unopened bundles, pills (strings of yarn), etc. The number of things that could be confirmed and clarified was measured. When the dispersion failure was confirmed at 21 or more places in 5 mm square, it was judged as x (defect), and when it was 20 places or less, it was judged as ○ (good).

(8) Sea component extractability On the above-mentioned web, when the extraction and removal of the sea component is insufficient and 11 or more bundled fibers are confirmed, × (defect), and when 10 or less, ○ ( Good).

(9) Qualitative and quantitative analysis of copolymerization component of copolyester After dissolving fiber sample in deuterated trifluoroacetic acid / deuterated chloroform = 1/1 mixed solvent, JEOL Ltd., JEOL A-600 super A nuclear magnetic resonance spectrum ( ¹ H-NMR) was measured using conductive FT-NMR. Qualitative and quantitative evaluation was performed from the spectrum pattern according to a conventional method.

Moreover, the following methods were also used for the polyethylene glycol copolymerization amount and the like as required. That is, the fiber sample was sealed with an excess amount of methanol, and decomposed with methanol in an autoclave at 260 ° C. for 4 hours. The amount of the copolymerization component was quantitatively determined for the decomposition product using gas chromatography (HP6890 Series GC System, manufactured by HEWLETT PACKARD), and the weight percentage based on the measured polymer weight was determined. Qualitative evaluation was also performed by comparing the retention time with the standard sample.

[Example 1]
Polyethylene terephthalate having a melt viscosity of 120 Pa · sec at 285 ° C. for the island component, 4% by weight of polyethylene glycol having an average molecular weight of 4000 for the sea component, and 9 mol% of 5-sodium sulfoisophthalic acid, and a melt viscosity at 285 ° C. Using a modified polyethylene terephthalate of 135 Pa · sec, spinning is performed using a base having a shape shown in FIG. 1 with a weight ratio of sea component: island component = 10: 90, and a spinning speed of 1500 m / min. The undrawn yarn was obtained by taking-up. The difference in alkali weight loss between the sea component and the island component was 1000 times, and the sea component was quite easily decomposable in alkaline aqueous solution. This was stretched 3.9 times and then cut to 1000 μm with a guillotine cutter to obtain a short fiber precursor. When this was reduced 10% at 95 ° C. with a 4% NaOH aqueous solution, it was confirmed that short fibers having a relatively uniform fiber diameter and fiber length were produced. When the cross section of the short fiber precursor (sea-island composite short fiber) was observed with a TEM and the average fiber diameter (Xd) and the thickness of the sea component between the island components (S) were examined, S / Xd = 0.03, It was within the range described in claims 3 and 7. Also, as shown in Table 1, fiber diameter and its coefficient of variation, fiber length and its coefficient of variation, aspect ratio, undispersed defects or entanglement, and sea component extractability, both fiber diameter and fiber length are uniform, dispersibility, and extraction It was confirmed that the property was good.

[Examples 2 to 3, Comparative Example 1]
The results of changing only the cut length in Example 1 are shown in Table 1.

[Comparative Example 2]
Polyethylene terephthalate having a melt viscosity at 285 ° C. of 120 Pa · sec as the island component, polyethylene glycol having an average molecular weight of 4000 having a melt viscosity at 285 ° C. of 140 Pa · sec as the sea component, 4% by weight, and 5-sodium sulfoisophthalic acid. Using a modified polyethylene terephthalate copolymerized with 8 mol%, spinning was performed at a sea-island ratio of sea component: island component = 70: 30 using a base of 400 islands having the shape shown in FIG. 1, and at a spinning speed of 1500 m / min. The undrawn yarn was obtained by taking-up. This was stretched by 1.7 times and then cut to 500 μm with a guillotine cutter to obtain a short fiber precursor. When this was reduced by 70% at 95 ° C. with a 4% NaOH aqueous solution, it took time to reduce the sea component, so the island component near the surface was excessively reduced and the average fiber diameter became uneven. . When the cross section of the short fiber precursor was observed with a TEM, the average fiber diameter (Xd) and the thickness of the sea component between the island components (S) were examined, and S / Xd = 0.8. It was out of the range described in Item 7, and the homogeneity of the sea island was broken. Further, the fiber diameter and its variation coefficient, the fiber length and its variation coefficient, the aspect ratio, the undispersed defect or entanglement, and the sea component extractability are as shown in Table 1.

[Example 4]
Polyethylene terephthalate having a melt viscosity of 115 Pa · sec at 285 ° C. is used as the island component, and 3% by weight of polyethylene glycol having an average molecular weight of 4000 having a melt viscosity of 130 Pa · sec at 285 ° C. is used as the sea component. A modified polyethylene terephthalate copolymerized with 10 mol% of isophthalic acid was spun using a base having the number of islands of 900 (same type as in FIG. 1) at a weight ratio of sea component: island component = 30: 70, and taken up at 3500 m / min. An undrawn yarn was obtained. The alkali weight loss rate difference was 2000 times. This was stretched 2.3 times and then cut to 500 μm with a guillotine cutter to obtain a short fiber precursor. When this was reduced by 30% at 95 ° C. with a 4% NaOH aqueous solution, it was confirmed that short fibers having a relatively uniform fiber diameter and fiber length were produced. When the cross-section of the short fiber precursor (sea-island composite short fiber) was observed with a TEM and the average fiber diameter (Xd) and the thickness of the sea component between the island components (S) were examined, S / Xd = 0.22. It was within the range described in claims 3 and 7. Also, as shown in Table 1, fiber diameter and its coefficient of variation, fiber length and its coefficient of variation, aspect ratio, undispersed defects or entanglement, and sea component extractability, both fiber diameter and fiber length are uniform, dispersibility, and extraction It was confirmed that the property was good.

[Comparative Example 3]
The results of changing the cut length in Example 4 are shown in Table 1.

[Example 5]
Polyethylene terephthalate having a melt viscosity of 120 Pa · sec at 285 ° C. is used as the island component, and 3% by weight of polyethylene glycol having an average molecular weight of 4000 having a melt viscosity of 135 Pa · sec at 285 ° C. is used as the sea component. Using modified polyethylene terephthalate copolymerized with 9 mol% of isophthalic acid, spinning was performed using a base having the number of islands (same type as FIG. 1) at a weight ratio of sea component: island component = 30: 70, and 1000 m / min. The undrawn yarn was obtained. The alkali weight loss rate difference was 1200 times. This was stretched 22 times in a hot water bath at 80 ° C., then further passed 2.3 times in a dry heat state after passing through a heating roller at 90 ° C., cut to 100 μm with a guillotine cutter, and a short fiber precursor was obtained. Obtained. In order to dissolve and remove only the sea component, it was confirmed that a short fiber having a relatively uniform fiber diameter and fiber length was produced when the amount was reduced by 30% at 95 ° C. with a 4% NaOH aqueous solution. When the cross section of the short fiber precursor (sea-island composite short fiber) was observed with a TEM and the average fiber diameter (Xd) and the thickness of the sea component between the island components (S) were examined, S / Xd = 0.24. And within the ranges described in claims 3 and 7. Also, as shown in Table 1, fiber diameter and its coefficient of variation, fiber length and its coefficient of variation, aspect ratio, undispersed defects or entanglement, and sea component extractability, both fiber diameter and fiber length are uniform, dispersibility, and extraction It was confirmed that the property was good.

[Comparative Example 4]
Table 1 shows the result of changing the cut length in Example 5.

[ Reference Example 6 ]
Using polyethylene terephthalate having a melt viscosity at 270 ° C. of 60 Pa · sec as the island component and using polylactic acid having a melt viscosity of 175 Pa · sec at 270 ° C. and a purity of 99% as the sea component, : Island component = 20: 80 weight ratio, spinning using a 500 island cap (same type as in FIG. 1) and drawing at 1000 m / min to obtain an undrawn yarn. The alkali weight loss rate difference was 1000 times. After extending this 2.0 times, it cut | disconnected to 1000 micrometers with the guillotine cutter, and obtained the short fiber precursor. In order to dissolve and remove only the sea component, it was confirmed that short fibers having a relatively uniform fiber diameter and fiber length were produced when the amount was reduced by 20% at 95 ° C. with a 4% NaOH aqueous solution. When the cross section of the short fiber precursor (sea-island composite short fiber) was observed with a TEM and the average fiber diameter (Xd) and the thickness of the sea component between the island components (S) were examined, S / Xd = 0.29. And within the ranges described in claims 3 and 7. Also, as shown in Table 1, fiber diameter and its coefficient of variation, fiber length and its coefficient of variation, aspect ratio, undispersed defects or entanglement, and sea component extractability, both fiber diameter and fiber length are uniform, dispersibility, and extraction It was confirmed that the property was good.

[Example 7]
Nylon 6 having a melt viscosity of 115 Pa · sec at 285 ° C. is used as the island component, and polyethylene glycol having an average molecular weight of 4000 having a melt viscosity of 140 Pa · sec at 285 ° C. is used as the sea component. Using modified polyethylene terephthalate copolymerized with 8 mol% of isophthalic acid, spinning was performed using a base having the number of islands (same type as FIG. 1) at a weight ratio of sea component: island component = 20: 80, and 1000 m / min. The undrawn yarn was obtained. Here, since nylon 6 which is an island component does not substantially dissolve in an alkaline solution, there is a sufficient sea-island dissolution rate difference. This was stretched by 3.1 times and then cut to 500 μm with a guillotine cutter to obtain a short fiber precursor. In order to dissolve and remove only the sea component, it was confirmed that a short fiber having a relatively uniform fiber diameter and fiber length was produced when the amount was reduced by 30% at 95 ° C. with a 4% NaOH aqueous solution. When the cross section of the short fiber precursor (sea-island composite short fiber) was observed with a TEM and the average fiber diameter (Xd) and the thickness of the sea component between the island components (S) were examined, S / Xd = 0.27. And within the ranges described in claims 3 and 7. Also, as shown in Table 1, fiber diameter and its coefficient of variation, fiber length and its coefficient of variation, aspect ratio, undispersed defects or entanglement, and sea component extractability, both fiber diameter and fiber length are uniform, dispersibility, and extraction It was confirmed that the property was good.

  The fiber diameter distribution of the nanofibers shown in the examples of Patent Document 1 is that the number of fibers present in the average fiber diameter ± 15 nm is about 70%, so that the standard deviation is approximately 15 nm. No, it can be understood how uniform the short fiber of the present invention is compared with the prior art since the CVd is 18 to 31.

  According to the present invention, a short fiber having a uniform fiber diameter and fiber length and good dispersibility can be obtained even though the fiber diameter is 1 μm or less. This is not possible with conventional ultra-fine fibers obtained by island fiber extraction of mixed spun fibers or with ultra-fine fibers obtained by beating fibrillation. Since the ultra-fine short fiber of the present invention can arbitrarily control the fiber diameter and fiber length, in a fiber structure such as a wet nonwoven fabric, the structure control such as a density gradient layer structure at a fiber diameter of nanometer level is possible. It is possible to obtain ultra-thin paper with an unprecedented basis weight and thickness, and it is expected to contribute to technological innovations for downsizing and increasing the capacity of fuel cells and lithium batteries in separator applications. I am convinced that it will greatly contribute to the development of nanofiber structures in the future.

1 is a schematic view of a spinneret used for spinning a sea-island type composite fiber that is a precursor for generating short fibers according to the present invention. FIG. 4 is another schematic view of a spinneret used for spinning sea-island type composite fibers that are precursors for generating short fibers according to the present invention.

Explanation of symbols

1: Pre-distribution island component polymer reservoir part 2: Island component distribution introduction hole 3: Sea component introduction hole 4: Pre-distribution sea component polymer reservoir part 5: Individual sea component / island component = sheath / core structure forming part 6: Whole sea island Joint throttle part

Claims (11)

Made of a thermoplastic resin, the fiber diameter is 10 to 1000 nm, the fiber diameter variation coefficient (CVd) defined below is 0 to 15, the fiber length is 50 to 1000 μm, and the fiber length variation coefficient (CVl) defined below is 0 to A short fiber having an aspect ratio (= fiber length / fiber diameter) of 100 to 2000, wherein the short fiber has an easily soluble component as a sea component and a hardly soluble component as an island component. The sea-island type composite fiber is obtained by melt spinning, and the melt viscosity ratio (sea component / island component) between the sea component and the island component at the melt spinning temperature is 1. 0.1 to 2.0, and the fiber diameter (Xd) of the island component in the cross section of the sea-island composite fiber is 10 to 1000 nm, the number of islands is 100 or more, and the thickness (S) of the sea component between the island components is 0.001 ≦ S / Xd ≦ 0.5 After cutting a certain sea-island type composite fiber to fiber length of 50 to 1000 [mu] m, and wherein the obtaining the short fibers of the island component to extract and remove the sea component, the manufacturing method of the short fibers.
Fiber diameter variation coefficient (CVd) = σd / Xd × 100 (%)
[However, the fiber diameter is the average value of the major axis and minor axis in the fiber cross section, σd is the standard deviation of the fiber diameter distribution, and Xd is the average fiber diameter. ]
Fiber length variation coefficient (CVl) = σl / Xl × 100 (%)
[However, σl represents the standard deviation of the fiber length distribution, and Xl represents the average fiber length. ] The method for producing short fibers according to claim 1, wherein the thermoplastic resin is at least one thermoplastic resin selected from polyesters, polyamides, and polyolefins. At least one alkaline aqueous solution in which the sea component is selected from polylactic acid, ultra-high molecular weight polyalkylene oxide condensation polymer, polyalkylene glycol copolymer polyester, and polyoxyalkylene glycol copolymer polyester and 5-sodium sulfoisophthalic acid copolymer polyester method for producing a staple fiber according to claim 1 or claim 2, which is readily soluble polymer. According to any one of claims 1 to 3 sea component is polyethylene terephthalate-based copolyester obtained by polymerizing 3 to 10 wt% copolymer of polyethylene glycol of 5-sodium sulfoisophthalic acid 6-12 mol% and a molecular weight from 4,000 to 12,000 Of manufacturing short fibers. The thermoplastic resin is polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, nylon 6, nylon 66, high density polyethylene, low density polyethylene, or isotactic polypropylene. The manufacturing method of the short fiber of description. A sea-island type composite fiber having an easily soluble component as a sea component and a hardly soluble component as an island component, a short fiber generation precursor , the sea-island type composite fiber obtained by melt spinning, and a sea component at a melt spinning temperature The melt viscosity ratio (sea component / island component) between the island component and the island component is 1.1 to 2.0,
The fiber diameter (Xd) of the island component made of a thermoplastic resin in the cross section of the sea-island type composite fiber is 10 to 1000 nm, the fiber diameter variation coefficient (CVd) defined below is 0 to 15, and the fiber length of the island component is 50-1000 μm, the fiber length variation coefficient (CVl) defined below is 0-20, and the aspect ratio (= fiber length / fiber diameter) is 100-2000,
It is a sea- island type composite fiber having 100 or more islands, a sea component thickness (S) between the island components of 0.001 ≦ S / Xd ≦ 0.5, and a fiber length of the sea-island type composite fiber of 50 to 1000 μm. Characteristic short fiber generation precursor.
Fiber diameter variation coefficient (CVd) = σd / Xd × 100 (%)
[However, the fiber diameter is the average value of the major axis and minor axis in the fiber cross section, σd is the standard deviation of the fiber diameter distribution, and Xd is the average fiber diameter. ]
Fiber length variation coefficient (CVl) = σl / Xl × 100 (%)
[However, σl represents the standard deviation of the fiber length distribution, and Xl represents the average fiber length. ] At least one alkaline aqueous solution in which the sea component is selected from polylactic acid, ultra-high molecular weight polyalkylene oxide condensation polymer, polyalkylene glycol copolymer polyester, and polyoxyalkylene glycol copolymer polyester and 5-sodium sulfoisophthalic acid copolymer polyester The short fiber generation precursor according to claim 6 , which is a readily soluble polymer. According to claim 6 or claim 7 which is polyethylene terephthalate-based copolyester sea component are polymerized copolymer 3-10 wt% of polyethylene glycol of 5-sodium sulfoisophthalic acid 6-12 mol% and a molecular weight from 4,000 to 12,000 A short fiber generation precursor. The thermoplastic resin is polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, nylon 6, nylon 66, high-density polyethylene, low-density polyethylene, or isotactic polypropylene. The short fiber generation precursor described. The short fiber obtained by the manufacturing method of the short fiber of any one of Claims 1-5. The short fiber obtained by removing a sea component from the short fiber precursor of any one of Claims 6-9.

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