JP2012092458A - Ultrafine fiber for binder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide ultrafine binder fibers that have a uniform fiber diameter notwithstanding ultrafine fibers, and are uniformly dispersed in the main fibers during paper making without hindering performance that the main fibers have, and also have a good adhesiveness.SOLUTION: There is provided ultrafine fibers for a binder, wherein the ultrafine fibers are made of a thermoplastic resin and simultaneously meets the following requirements:(1) an average fiber diameter Xd is 10 to 2000 nm; (2) a coefficient of variation in fiber diameter (CVd) represented by the following formula (I) is 0 to 25%: CVd=σd/Xd×100 (%) (I) (in the formula, the average fiber diameter represents an average value of the longest diameter and the shortest diameter in a fiber cross section, and σd represents a standard deviation of a fiber diameter distribution); and (3) a crystallinity Xc by a density method is 20% or less.

Description

  The present invention relates to an ultrafine fiber having a fiber diameter of 10 to 2000 nm made of a thermoplastic resin. More specifically, it has a uniform fiber diameter, excellent adhesion, and uniformly forms a fiber structure such as papermaking. The present invention relates to a possible fine fiber for a binder.

  In recent years, as typified by nanofibers, ultrafine fibers with a fiber diameter of 1000 nm or less have attracted attention due to their peculiarities such as hygroscopicity and low molecular weight substance adsorption, such as ultra-high performance filters, batteries and capacitors. Adoption is considered as a raw material for high-performance materials such as separators or abrasives such as hard disks and silicon wafers.

  These require precision separation and processing as well as uniform thickness and pores, and ultrafine fibers constituting the material must be uniform in diameter and length. Such ultrafine fibers can be produced by extracting the sea component of the mixed and spun fiber, extracting and removing the sea component from the sea-island type composite fiber, mechanically or chemically dividing the split type composite fiber. For example, Patent Document 1 proposes a synthetic paper using ultrafine fibers by extracting a sea component from a polymer alloy. Yes.

However, this method has a problem that it is difficult to control the fiber diameter of the island component of the two-component mixed fiber, and the dispersion of the fiber diameter becomes large.
In addition, Patent Document 2 exemplifies short-cut nanofibers made of sea-island type composite fibers, but the method for bonding the fibers is not described in detail, and the uniformity of separators, filters, etc. In addition, the use for which strength as a material is required is still insufficient.

JP 2005-264420 A JP 2007-107160 A

  The object of the present invention is to solve the above-mentioned problems of the prior art, have a uniform fiber diameter, excellent adhesion, and capable of uniformly forming a fiber structure such as papermaking, with a fiber diameter of 10 to 2000 nm. The object is to provide ultrafine fibers for binders.

  As a result of intensive studies in order to solve the above problems, the present inventors have found that the above problems can be solved by defining the uniformity of the fiber diameter and crystallinity, and have reached the present invention.

That is, according to the present invention, there is provided an ultrafine fiber for a binder which is made of a thermoplastic resin and satisfies the following (1) to (3) simultaneously.
(1) The average fiber diameter Xd is 10 to 2000 nm.
(2) The fiber diameter variation coefficient (CVd) represented by the following formula (I) is 0 to 25%.
CVd = σd / Xd × 100 (%) (I)
(However, the average fiber diameter is the average value of the longest diameter and the shortest diameter in the fiber cross section, and σd indicates the standard deviation of the fiber diameter distribution.)
(3) Crystallinity Xc by density method is 20% or less.

In this case, the ultrafine fiber for binder is a fiber obtained by eluting and removing the sea component from the sea-island composite fiber having the easily soluble component as the sea component and the hardly soluble component as the island component. It is desirable that the apparent draft at the time of formation is 10 to 1000.
Further, it is desirable that the binder ultrafine fibers have a ratio (L / Xd) of the average fiber diameter (Xd) to the fiber length (L) of 100 to 2500.

  According to the present invention, although it is an ultrafine fiber, it has a uniform fiber diameter, so that it is uniformly dispersed in the main fiber during papermaking, and does not interfere with the performance of the main fiber, and also has good adhesion. Ultra fine binder fibers can be obtained.

It is the schematic which shows one embodiment of the spinneret used in order to spin the sea-island type | mold composite fiber which is a generation | occurrence | production precursor of the ultrafine fiber for binders of this invention. It is the schematic which shows the other embodiment of a spinneret used in order to spin the sea-island type | mold composite fiber which is a generation | occurrence | production precursor of the ultrafine fiber for binders of this invention.

Hereinafter, embodiments of the present invention will be described in detail.
The fiber of the present invention is made of a thermoplastic resin, and its fiber diameter Xd is 10 to 2000 nm. If the fiber diameter is less than 10 nm, the fiber structure itself is unstable because the influence of intermolecular force is strong, and the fineness of the individual ultrafine fibers is reduced, so that the ultrafine fibers are uniformly dispersed. It becomes difficult to obtain a structure.

  On the other hand, when the fiber diameter exceeds 2000 nm, the fiber structure becomes non-uniform, the adhesive strength is also lowered, and the performance of the main ultrafine fibers is hindered, and it is difficult to obtain the intended physical properties of the present invention. Become. A particularly preferable range of the fiber diameter is 50 to 1500 nm.

  Further, the fiber diameter variation coefficient (CVd) of the binder fiber of the present invention needs to be in the range of 0 to 25%. When CVd exceeds 25%, the uniformity is greatly reduced, and when used as paper, its function and quality are greatly impaired. The preferred range is 0-20%, more preferably 0-15%.

  Further, the crystallinity of the binder fiber of the present invention needs to be 20% or less. When the degree of crystallinity exceeds 20%, the adhesiveness with the main fiber becomes poor at the time of paper making, the strength as paper is lowered, and the function is also impaired. The degree of crystallinity is preferably 15% or less, more preferably 10% or less. In order to improve the adhesion performance, it is preferable to lower the degree of orientation of the amorphous part in addition to the degree of crystallinity, and the higher the fiber elongation, the better. A preferable elongation is 100% or more.

  The ultrafine fiber of the present invention has a nano-level fiber diameter with little variation, and it is possible to design a product suitable for the application. For example, in the filter application, if a substance that can be adsorbed in the ultrafine fiber diameter is selected, the fiber diameter can be designed according to the application, and the product design can be performed very efficiently. Become.

  As a method for producing the ultrafine fiber for binder of the present invention, a conventionally known method can be exemplified, but a method of producing by removing sea components from a sea-island type composite fiber having a multi-island structure is most preferable. At that time, the draft which is the ratio of the speed of winding of the fiber and the speed per hour of the polymer discharged from the discharge hole as the sea-island type cross-sectional shape is preferably 10 to 1000, more preferably 10 to 500, The composite fiber is preferably not stretched or heat-treated. When the draft exceeds 1000, or when the fiber is stretched or heat-treated, the breaking elongation may decrease and the crystallinity may exceed 20%, which is not preferable because the adhesiveness as the binder fiber decreases.

  Further, the sea component polymer can be appropriately selected as long as it is a polymer having higher solubility than the island component polymer, but the dissolution rate ratio (sea / island) is particularly preferably 200 or more. When this dissolution rate ratio is less than 200, part of the island component of the fiber cross-section surface layer is dissolved while the sea component of the fiber cross-section center is dissolved, so the sea component is completely dissolved and removed. For this purpose, the island component is also reduced, and the strength of the island component due to the unevenness of the island component or solvent erosion may occur, thereby reducing the function as a binder having a uniform fine diameter.

  The dissolution rate ratio can be determined by spinning the polymer of the sea component and the island component alone and calculating the respective weight loss rates using a solvent capable of dissolving and reducing the sea component. For example, the sea component and the island component are each discharged from a die having a discharge hole having a hole diameter of 0.3 mm and a length of 0.6 mm, taken at a predetermined spinning speed, and this is set to a bath ratio of 100 at a predetermined solvent and dissolution temperature, and the dissolution time The rate of weight loss is calculated from the dissolved amount.

  Next, the greater the number of island components, the higher the productivity when producing ultrafine fibers by dissolving and removing sea components, and the resulting ultrafine fibers also become significantly finer, contributing to dispersion and uniformity during papermaking. Therefore, the number of island components is preferably 100 or more, more preferably 500 or more. If the number of island components is too large, not only will the production cost of the spinneret increase, but the processing accuracy of the spinneret itself tends to decrease, so the number of island components is preferably 1000 or less.

  Preferred examples of the polymer constituting the sea component include polyesters, polyamides, and polyolefins such as polyethylene and polystyrene, which are particularly good in fiber formation. The polyamide is preferably an aliphatic polyamide. As specific examples, polylactic acid, ultrahigh molecular weight polyalkylene oxide condensation polymer, polyoxyalkylene glycol compound and 5-sodium sulfoisophthalic acid copolyester are most suitable 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, as a combination of a polymer constituting a sea component and a solvent or degradable agent for dissolving the polymer, formic acid for aliphatic polyamide such as nylon 6, nylon 6, 6 or the like, trichloroethylene for polystyrene, or polyethylene (especially high pressure method) Hot water for hydrocarbon solvents such as hot toluene and xylene for low density polyethylene and linear low density polyethylene) and polyvinyl alcohol and ethylene-modified vinyl alcohol polymers can be given as examples.

  Among copolymerized polyester polymers, polyethylene terephthalate copolymer having an intrinsic viscosity of 0.3 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. Polymerized polyether 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, but it becomes a blend system due to poor reactivity, which causes problems in terms of heat resistance and spinning stability. there is a possibility. On the other hand, when 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 units 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. Other examples include polysulfone, polyimide, polyketones, polyarylate and the like.

Furthermore, the island component is not limited to a round cross section, and may be an irregular cross section. A small amount of other polymers, antioxidants, antistatic agents, pigments, fluorescent brighteners and other additives may be contained.
In addition, for the polymer constituting the sea component and the polymer constituting the island component, organic fillers, antioxidants, heat stabilizers, light, and so on, as long as they do not affect the spinning properties and physical properties after extraction. Contains various additives such as stabilizers, flame retardants, lubricants, antistatic agents, rust inhibitors, crosslinking agents, foaming agents, fluorescent agents, surface smoothing agents, surface gloss improvers, mold release improvers such as fluororesins, etc. You can leave.

  The sea-island type composite fiber composed of the sea component polymer and the island component polymer preferably has a polymer melt viscosity ratio (sea / island) in the range of 0.8 to 2.0. When the melt viscosity ratio is less than 0.8 times, when the composite mass ratio of the sea component is as low as less than 50%, the island components are easily joined to each other during melt spinning, while the melt viscosity ratio is 2. If it exceeds 0 times, the stability of the spinning process tends to decrease because the viscosity difference is too large.

Furthermore, the sea-island composite fiber of the present invention preferably has a composite mass ratio of sea components of less than 50%. The sea-island composite mass ratio (sea: island) is preferably in the range of 30:70 to 5:95. If it exists in the said range, the thickness of the sea component between island components can be made thin, the dissolution removal of a sea component will become easy, and the conversion to an ultrafine fiber of an island component will become easy. Here, when the proportion of the sea component exceeds 50%, the thickness of the sea component becomes too thick. On the other hand, when the proportion is less than 5%, the amount of the sea component becomes too small and the mutual connection occurs between the islands. It becomes easy.
The sea component and the island component are melted separately, combined into a sea-island shape in the base, and discharged. Then, after solidifying with cooling air or the like, it is taken up as undrawn fiber, preferably at a speed of 200 to 2000 m / min.

  As a die used for melt spinning, any 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. FIG. 1 shows a method in which a hollow pin is discharged into a sea component resin reservoir portion and is joined and compressed, and FIG. 2 is a method in which island components are formed by a fine hole method.

  The ultrafine fiber for a binder of the present invention is produced from the island component by eluting or decomposing the sea component after producing the island-island type composite fiber and then passing through the precursor of the short fiber cut into a predetermined fiber length. The method of taking out the short fiber which becomes is preferable. There is also a method in which sea components are eluted or decomposed in advance and supplied to the papermaking process as short fibers, but in the state of sea-island type composite short fibers, the form of the fiber generation precursor is taken, before the pulper or pulper in the papermaking process In the process, a method of removing the sea component by using a sea component solvent or a decomposition accelerating chemical solution, or a method of removing the sea component after paper making in a precursor state may be employed.

  In order to remove the sea component, it is preferable to treat with an aqueous solution of an alkali metal compound such as sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, among which sodium hydroxide and potassium hydroxide are particularly preferably used. The concentration, treatment temperature, and treatment time of the aqueous alkali solution vary depending on the type of alkali compound used, but the concentration is 10 to 300 g / L, the temperature is 40 ° C. to 180 ° C., and the treatment time is in the range of 2 minutes to 20 hours. Is preferred.

  Following the removal of the sea component, after neutralization and before the paper making process, as a fiber dispersant, 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 improve the dispersibility of the pulp-like material, the entanglement between the pulp-like materials may be reduced by applying to a pulper, refiner, beater, etc. in a wet state with dry, wet or dispersant added. Is possible.

  The filament obtained by the above production method is used as it is, or a tow bundled in units of several tens to several millions, and cut with a guillotine cutter or a rotary cutter to make a binder fiber particularly suitable for papermaking Can do. In order to obtain a uniform nonwoven fabric, the fiber length (L) is preferably such that the ratio (L / Xd) to the average fiber diameter (Xd) is 100-2500. If L / Xd is less than 100, fiber drop and sheet strength may be reduced. On the other hand, if L / Xd exceeds 2500, entanglement is likely to occur when the fiber is made of ultrafine short fibers, resulting in defects such as bundling and pilling, and hinders the uniformity of the structure. A preferable L / Xd range is 200 to 2000, and a particularly preferable range is 500 to 1500.

  The method of 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 the binder short fibers of 2000 nm 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. The binder fiber of the present invention is suitably used for a method of pressure-bonding and heat-bonding a wet nonwoven web after paper making using a calender roller or an embossing roller in order to bind to the main fiber.

  The binder fiber of the present invention may be of any structure and shape, such as a paper-like material, a cloth-like material, a wad-like material, a belt-like material, a string-like material, and a thread-like material. Absent. The woven fabric, knitted fabric, and non-woven fabric may be a composite material in which a plurality of types of fibers are mixed, mixed, woven, or knitted. Further, these textile products may be used. Applications include environmental and industrial material applications such as filters, hazardous substance removal products, battery separators, vehicle interiors such as car seats, interior products such as carpets, sofas, curtains, cosmetics, cosmetic masks, wiping cloths, health Examples include daily use such as goods, medical use such as abrasive cloths, sutures, scaffolds, artificial blood vessels, and blood filters, and clothing such as jackets, skirts, pants, and underwear, sports clothing, and clothing materials.

  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) Average fiber diameter Xd
Using a transmission electron microscope, 100 ultrafine fiber cross-section photographs were taken at a magnification of 30000 times, and the average value of the major axis and the minor axis in each fiber cross section was determined as Xd.

(2) Uniformity of average fiber diameter
The standard deviation (σd) was calculated from the value obtained for Xd, and the fiber diameter variation coefficient (CVd) was determined by the following formula (I) and evaluated.
CVd = σd / Xd × 100 (%) (I)

(3) Crystallinity Xc
A density gradient tube made of calcium nitrate was prepared, the density of the ultrafine fibers was measured at n = 3, and the average value was defined as ρ. Using this value, the amorphous density (ρa) of the thermoplastic resin constituting the ultrafine fiber, and the crystal density (ρc), the crystallinity (Xc) was calculated by the following formula (II).
Xc = (ρc / ρ) × (ρ−ρa) / (ρc−ρa) × 100 (%) (II)
Here, as ρa and ρc, known values described in the Polymer handbook and the like were used. For example, ρa = 1.335, ρc = 1.455 for polyethylene terephthalate, ρa = 1.08, ρ = 1.23 for nylon 6, ρa = 0.850, ρc = 0.936 for polypropylene, ρa = 0.85, ρc = 1.00 for polyethylene, ρa for polyethylene naphthalate = 1.32, ρc = 1.41, for polyphenylene sulfide, ρa = 1.32, ρc = 1.43 shall be used, and unless otherwise stated, values calculated by the method described in Chapter 4 of Propertires of Polymers (by DW Van Krevelen) .

(4) Fiber length L
With a scanning electron microscope, the side face of 100 ultrafine fibers was measured at 20 to 500 times, and the average value was obtained.

(5) Elongation of ultrafine fiber A tensile test was performed on the ultrafine fiber bundle under the conditions of a test length of 200 mm and a tensile speed of 200 mm / min to obtain the elongation at break (%).

(6) Melt viscosity After the polymer is dried, it is set in an orifice set to the melt temperature at the time of spinning and held in a melted state for 5 minutes, and then extruded under a predetermined level of load. Asked. The above operation was repeated under multiple levels of load, and the melt viscosity when the shear rate was 1000 sec- ¹ was estimated.

(7) Uniformity of paper made after mixing ultrafine binder fiber to 30 wt% with respect to the main fiber precursor, and then using a hand-drawing device described in JIS so that the basis weight is 20 g / m ^2. A web was prepared, dried for 2 minutes at 120 ° C. using a rotary dryer, and further subjected to pressure-bonding treatment at 70 kgf / cm between metal rollers to obtain paper. Cut out 3 squares of 5mm square from the obtained sample, observe this surface with scanning electron microscope at 20 to 500 times, and visually check for unsatisfactory dispersion such as unopened bundles, pills (strings of yarn) Number was measured. When the number of dispersion failures was confirmed at 21 or more locations in a 5 mm square, it was judged as x (defective), and when it was 20 locations or less, it was judged as ○ (good).
The vertical about the size of 20cm square of the paper, the thickness of the monitor 100 places the transverse each 2cm square per meter (manufactured Daiei Kagaku Seiki Mfg., Ltd., "PEACOCK model H") sample 1 cm ² per Use Measurement was performed with a load of 1.764 N (180 g) applied, the standard deviation σt was determined from the average value Xt, the thickness variation coefficient (CVt) was determined by the following equation, and the uniformity was evaluated.
CVt ＝ σDt / Xt × 100 (%)

(8) Adhesiveness of binder fiber The paper prepared in the uniformity evaluation was sampled in the vertical direction and the horizontal direction as test pieces having a width of 2 cm and a length of 9 cm, and the test pieces were gripped with a chuck, and the chuck interval was set to 5 cm. The film was stretched at a pulling speed of 5 cm / min, and the strength at break was determined as an average value in the vertical and horizontal directions, converted to a width of 1 cm and a sample weight per 100 g / m ² .

[Reference Example 1]
Polyethylene terephthalate with an intrinsic viscosity of 0.63 (35 ° C, in orthochlorophenol) as an island component, polyethylene with an intrinsic viscosity of 0.42 copolymerized with 9 mol% of 5-sodium sulfoisophthalic acid and 3 wt% of polyethylene glycol with a number average molecular weight of 4000 as a sea component After melting separately using terephthalate, merged by weight ratio of sea: island = 30:70 in the composite die, sea island with 900 islands with a discharge amount per single hole of 2.2 g / min from the die with a hole diameter of 0.5 mm It was discharged at a spinning temperature of 290 ° C. as a mold composite section. After the discharged yarn is taken up at a spinning speed of 1000 m / min, it is continuously drawn at a spinning roller temperature of 100 ° C. and a draw ratio of 4.0 times, and then wound after heat setting with a 120 ° C. roller to obtain a sea-island type composite drawn yarn. It was.
The melt viscosity of each of the sea component and the island component was 130 Pa · s and 115 Pa · s, and the melt viscosity ratio (sea / island) of the polymer was 1.1. Using the obtained sea-island type composite fiber, a tubular knitting was created, and when the weight was reduced in an alkaline solution at 70 ° C. and 3.5 g / l, only the sea component was eluted, the average fiber diameter of the island component was 690 nm, and the elongation was It was confirmed that 30% extra fine fibers were generated. This sea-island type composite fiber was used as the main fiber precursor a.

[Example 1]
The same polymer as in Reference Example 1 was used for both the island component and the sea component, and was discharged from a sea-island die having 400 islands in the same manner as in Reference Example 1, and wound up without stretching at a spinning speed of 1500 m / min. The draft at this time was 185. Using the obtained sea-island type composite fiber, a cylindrical knitting was made, and when weight reduction treatment was performed for 1 minute in an alkaline solution at 70 ° C. and 3.5 g / l, only the sea component was eluted, and the average fiber diameter as an ultrafine fiber It was confirmed that ultrafine fibers having Xd = 1060 nm, CVd = 13, density 1.342 g / cm ³ , crystallinity 6.3%, elongation 320% were generated.
This sea-island type composite fiber was cut to a length of 750 μm as an ultrafine fiber precursor A for binder, mixed with a main fiber precursor a cut to a length of 500 μm in Reference Example 1 at a weight ratio of 30:70, 70 ° C., 3.5 Each sea component is dissolved and removed with an aqueous NaOH solution of g / l, and a small amount of paper making aid (dispersant: Takamatsu Yushi Co., Ltd., YM-81, antifoaming agent: GE Toshiba Silicone, TSA-730) is added again. Dispersed in water and made paper. Table 1 shows the physical properties of the obtained paper together with the physical properties of the ultrafine fibers.

[Reference Example 2]
Using polyethylene naphthalate with an intrinsic viscosity of 0.62 as the island component and polyethylene terephthalate with an intrinsic viscosity of 0.49 copolymerized with 9 mol% of 5-sodiumsulfoisophthalic acid and 3% by weight of polyethylene glycol with a number average molecular weight of 4000 as the sea component Then, they were merged in the composite base, melt spun at a spinning temperature of 300 ° C. and a spinning speed of 1000 m / min with the same base and discharge amount as in Reference Example 1, and the sea-island type composite unstretched fiber was wound up.
The melt viscosity of each of the sea component and the island component was 283 Pa · s and 250 Pa · s, and the melt viscosity ratio (sea / island) of the polymer was 0.9. The obtained undrawn yarn was subjected to roller drawing at a drawing temperature of 130 ° C. and a draw ratio of 3.9 times, and then heat-set with a non-contact heater at 200 ° C. to obtain a sea-island type composite drawn yarn. Using the obtained sea-island type composite drawn yarn, a cylindrical knitting was made, and when the weight was reduced in an alkaline solution of 98 ° C. and 3.5 g / l, only the sea component was eluted, and the average fiber diameter of the island component was 672 nm, It was confirmed that ultrafine fibers having an elongation of 25% were generated. This sea-island type composite fiber was used as the main fiber precursor b.

[Example 2]
The same polymer as in Reference Example 1 was used for both the island component and the sea component, and was discharged from a sea-island die having 900 islands in the same manner as in Reference Example 1, and wound without stretching at a spinning speed of 1500 m / min. The draft at this time was 121. Using the obtained sea-island type composite fiber, a cylindrical knitting was made, and when weight reduction treatment was performed for 1 minute in an alkaline solution at 70 ° C. and 3.5 g / l, only the sea component was eluted, and the average fiber diameter as an ultrafine fiber It was confirmed that ultrafine fibers with Xd = 1273 nm, CVd = 12, crystallinity 10.1%, elongation 290% were generated.
This sea-island type composite fiber was cut to a length of 950 μm as an ultrafine fiber precursor B for binder, mixed with a main fiber precursor b cut to a length of 500 μm in Reference Example 2 at a weight ratio of 30:70, 70 ° C., 3.5 Each sea component was dissolved and removed with g / l NaOH aqueous solution, and paper was prepared in the same manner as in Example 1. Table 1 shows the physical properties of the obtained paper together with the physical properties of the ultrafine fibers.

[Comparative Examples 1-2]
In Example 2, a sea island type composite fiber having 200 islands was designated as Comparative Example 1, and the obtained sea island type composite fiber was designated as an ultrafine fiber precursor C. In Example 2, the obtained sea-island type composite fiber was roller-drawn at a drawing temperature of 130 ° C. and a draw ratio of 3.9 times, and then heat-set with a non-contact heater at 200 ° C. Body D. Table 1 shows these physical properties and the physical properties of paper prepared in the same manner as in Example 2 using these and the ultrafine fiber precursor b.

[Comparative Example 3]
In Example 2, the sea-island type was used in the same manner as in Example 2 except that 9 mol% of 5-sodium sulfoisophthalic acid and 3% by weight of polyethylene glycol having a number average molecular weight of 4000 were copolymerized and had an intrinsic viscosity of 0.35. A composite fiber was prepared and used as an ultrafine fiber precursor E.
The melt viscosity of each of the sea component and the island component was 110 Pa · s and 250 Pa · s, and the melt viscosity ratio (sea / island) of the polymer was 0.44. Table 1 shows the physical properties of the obtained ultrafine fibers and the properties of paper prepared in the same manner as in Example 2 using the ultrafine fiber precursor b.

  As shown in Table 1, in Examples 1 and 2, which are within the scope of the present invention, since the fiber has a uniform fiber diameter and good adhesiveness, a paper having excellent uniformity can be obtained. Can do. In Comparative Example 1 in which the fiber diameter was outside the range of the present invention and in Comparative Example 3 in which the fiber diameter variation coefficient was outside the range of the present invention, the uniformity was poor when paper was used. On the other hand, in Comparative Example 2 in which the sea-island fiber was stretched and heat-set and the crystallinity was outside the scope of the present invention, the paper was relatively uniform, but the adhesiveness was poor and the paper strength was poor. It became a thing.

  According to the present invention, a binder fiber having a thin fiber diameter of 10 to 2000 μm and a uniform fiber diameter is obtained. By using this fiber, it becomes possible to uniformly disperse when mixed with the ultrafine fiber as the main fiber, and because it has excellent adhesiveness, it is possible to obtain a paper with excellent uniformity and strength. it can. Therefore, there is a possibility that a thin paper with a low basis weight that has never been obtained can be obtained, and it becomes possible to achieve further high performance and downsizing as a microfiltration and separation material, and it can be applied to separator applications and filter applications. Be expected.

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 confluence throttle part

Claims (3)

An ultrafine fiber for a binder, which is made of a thermoplastic resin and satisfies the following (1) to (3) simultaneously.
(1) The average fiber diameter Xd is 10 to 2000 nm.
(2) The fiber diameter variation coefficient (CVd) represented by the following formula (I) is 0 to 25%.
CVd = σd / Xd × 100 (%) (I)
(However, the average fiber diameter is the average value of the longest diameter and the shortest diameter in the fiber cross section, and σd indicates the standard deviation of the fiber diameter distribution.)
(3) Crystallinity Xc by density method is 20% or less.   This is a fiber obtained by elution and removal of sea components from sea-island type composite fibers that have easy-dissolvable components as sea components and hard-dissolvable components as island components, and the apparent draft when forming sea-island type composite fibers is 10 to 1000 The ultrafine fiber for a binder according to claim 1, wherein the fiber is not stretched or heat set.   The ultrafine fiber for a binder according to claim 1 or 2, wherein the ratio (L / Xd) of the average fiber diameter (Xd) to the fiber length (L) is 100 to 2500.

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