JP6396771B2 - Method for producing ultrafine fiber nonwoven fabric - Google Patents

Description

  The present invention relates to an ultrafine fiber made of a polymer by allowing an air stream ejected from the outside of a polymer discharge hole to act to expand or reduce the diameter of the polymer and then effectively bringing a coagulating liquid into contact with the fiber to solidify the fiber. The present invention relates to a method for producing, and an ultrafine continuous fiber obtained by the method, and a nonwoven fabric having molding processability by heat treatment constituted by them.

Generally known methods for producing ultrafine fibers include a melt blow method, a sea-island type mixed spinning method, a flash spinning method, an electrospinning method, and an explosion spinning method.
The melt blow method and the sea-island type mixed spinning method are methods applied to polymers that can be melt-spun.

  The flash spinning method is applied to polymer solutions, and phase separation is performed before discharging a mixed solution of high-density polyethylene or polypropylene and a low-boiling solvent (such as chlorofluorocarbon) from the spinning hole. The low-boiling point solvent is rapidly gasified and expanded, and the polymer is solidified while being stretched to form a continuous continuous fiber made of fibrillated ultrafine fibers. It is a method of forming. However, the types of polymers to which this spinning method is applied are limited.

The electrospinning method can spin a polymer solution and is applied to an aramid polymer or the like (Patent Documents 1 and 2), but the productivity is generally lower than that of a melt blow method or the like.
In addition to these methods, a method for producing a yarn from a polymer solution by explosion spinning technology is known (Patent Document 3). This is a method in which spinning is performed by explosion of a polymer solution promoted by an air stream accelerated at high speed by a Laval tube, and its productivity is generally higher than that of electrospinning.

  In addition, the thermoplastic polymer is discharged from the polymer discharge hole, air is accompanied in parallel with the polymer melted from the outer periphery of the discharge hole, and high-speed cold air injected from an air slot away from the nozzle end surface is discharged. An apparatus for reducing the diameter of a polymer by acting on the polymer is disclosed (Patent Document 4).

  However, when the explosion spinning technology is used, or when the above-mentioned technology for thinning the thermoplastic polymer is applied to solution spinning using a polymer solution, particularly an aramid polymer solution, the polymer solution is discharged from the discharge hole and thinned. After that, when trying to solidify by contact with the coagulation liquid by dipping or steam spraying, a fiber breakage occurs at the time of contact with the coagulation liquid, and there is a problem that fibers with a large fiber diameter are scattered around is there. In addition, since the scattered fibers are collected at the same time when the nonwoven fabric is formed, the fiber diameter and the nonwoven fabric voids become large, and it is difficult to obtain an ultrafine fiber nonwoven fabric of excellent quality.

  In addition, the nonwoven fabric obtained in this way cannot be maintained in the shape after molding, or the polymer melts, even if it is subjected to hot-pressure molding treatment, etc. for molding into various members. Cannot be maintained, the shape of the pores is deformed, the predetermined function cannot be expressed, and it cannot be applied to various members.

Japanese Patent Laying-Open No. 2005-200779 JP 2006-336173 A US2004 / 00999981A1 US6013223

  The object of the present invention has been made in view of the above problems, and is composed of ultrafine fibers, and is used as a battery or capacitor separator, a fuel cell membrane material, a sound absorbing material, a heat insulating material, a flameproof material, a heat shielding material, Homogeneous and ultra-fine fiber nonwoven fabric that can be suitably used for applications such as protective clothing, adsorbents, moisture-permeable waterproof sheets, wallpaper, shoji, cleaners, adhesive tapes, filters, and the like, and its production It is to provide a method.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention discharged a polymer solution from a discharge hole having a small diameter, stretched or reduced in diameter, and solidified to form an ultrafine fiber. It has been found that a nonwoven fabric can be obtained. Furthermore, it has been found that it is effective to keep the degree of crystallinity of the fibers low in order to develop the molding processability by hot pressing, and the nonwoven fabric has a specific average fiber diameter, apparent density, and porosity. In addition, when using a nonwoven fabric in which the degree of crystallinity of the fiber constituting the nonwoven fabric obtained from X-ray diffraction is in a specific range, even if it has a thin shape that is not conventional, filters, separators for batteries, capacitors, etc. The present inventors have found that the moldability by hot-pressure treatment suitable for the present invention is exhibited, and have completed the present invention.

Thus, according to the present invention, a non-woven fabric comprising ultra-fine fibers and having molding processability by hot pressing, wherein the non-woven fabric satisfies all of the following (a) to (e): A nonwoven fabric is provided.
(A) The average fiber diameter of the fibers constituting the nonwoven fabric is 0.1 to 5 μm
(B) The average apparent density of the nonwoven fabric is 0.05 to 2.0 g / cm ^3.
(C) The average void diameter of the nonwoven fabric is 0.1 to 30 μm, the maximum void diameter is 50 μm or less. (D) The fiber large diameter portion / lumped portion amount is 10% or less in the nonwoven fabric. (E) The nonwoven fabric obtained from X-ray diffraction. The degree of crystallinity of the fibers constituting the fiber is 40% or less

  According to the present invention, a polymer solution is used as a raw material for fibers or non-woven fabrics, and spinning is carried out by a specific method, thereby forming a homogeneous and hot-pressure treatment composed of fibers having an ultrafine fiber diameter or ultrafine fibers. The nonwoven fabric which has the moldability by can be provided. Moreover, since the manufacture can suppress scattering of fibers due to yarn breakage, it can be performed with high productivity by suppressing process loss, and as a method for industrially manufacturing ultrafine fibers and nonwoven fabrics composed of them. It is valid.

It is the schematic of the cross section of the spinning nozzle and coagulation equipment used for the manufacturing method of the ultrafine fiber of this invention. It is the schematic of the lower surface of the spinning nozzle used for the manufacturing method of the ultrafine fiber of this invention.

The present invention is described in detail below.
The ultra-fine fiber nonwoven fabric of the present invention is a non-woven fabric composed of ultra-fine fiber and having molding processability by hot press treatment, wherein the nonwoven fabric satisfies the following (a) to (e), It has a homogeneous structure and can exhibit excellent performance as a separator for filters, adsorbents, batteries, capacitors, and the like. Hereinafter, the requirements (a) to (e) will be described in detail.

(A) In the present invention, the average fiber diameter of the ultrafine fiber is 0.1 to 5 μm. When the average fiber diameter is larger than 5 μm, the number of fiber components in the nonwoven fabric decreases, not only the density of the nonwoven fabric decreases, but also the space contained in the nonwoven fabric increases, and when used as a filter, fine dust is trapped. It cannot be collected and the collection efficiency is lowered. When a separator is used, it is difficult to reduce the thickness and improve the short circuit prevention. In addition, when the hot press molding process is performed by sandwiching it in a predetermined mold or the like, if the fiber becomes thick, the restoring force is large and it becomes difficult to maintain the molded shape. On the other hand, if the average fiber diameter is less than 0.1 μm, the strength obtained is significantly reduced and is easily damaged by physical impact, and the fiber may break or the nonwoven fabric may be damaged when subjected to hot pressing. It becomes easy to do. The average fiber diameter is preferably 0.3 to 4 μm, more preferably 0.4 to 3 μm.
In addition, the average fiber diameter of the continuous fibers constituting the nonwoven fabric of the present invention means the diameter of the fiber that can be confirmed by an electron micrograph of the nonwoven fabric surface, and arbitrarily select 100 fibers and measure the width. The average fiber diameter can be determined by averaging.

(B) The average apparent density of the nonwoven fabric is 0.05 to 2.0 g / cm ³ . When the apparent density of the non-woven fabric is less than 0.05 g / cm ³ , the dust collection efficiency is lowered in the case of a filter, and in the case of a separator, the tensile strength is small and the separator is broken in the production process. Further, when external pressure is applied, the thickness tends to decrease, and the handleability is poor. On the other hand, when the apparent density of the nonwoven fabric exceeds 2.0 g / cm ³ , the pressure loss increases in the case of a filter, so that clogging is accelerated, the life performance of the filter is shortened, and in the case of a separator, a short circuit is likely to occur. It is not preferable. Moreover, in order to obtain a desired thickness, it is necessary to increase the fiber accumulation amount, which is uneconomical. The average apparent density of the nonwoven fabric is preferably 0.075 to 1.5 g / cm ³ , more preferably 0.1 to 1.0 g / cm ³ .

The basis weight and thickness of the present invention are not particularly limited, but the basis weight is preferably 1 g / m ² or more and the thickness is preferably 2 μm or more. If the basis weight is smaller than 1 g / m ² and the thickness is smaller than 2 μm, the space contained in the nonwoven fabric is small, and a desired average apparent density and average void diameter described later tend to be difficult to obtain. On the other hand, in the case of a separator, it is preferably 1 g / m ² or more and a thickness of 2 μm or more. In the case of a filter, it is more preferable that the basis weight is 5 g / m ² or more and the thickness is 10 μm or more from the viewpoint of collection performance.

  (C) The nonwoven fabric has an average pore size of 0.5 to 30 μm and a maximum pore size of 50 μm or less. When the average void diameter is larger than 30 μm or the maximum void diameter is larger than 50 μm, the filter has poor performance for collecting fine dust, and in the case of a separator, a short circuit easily occurs, which is not preferable. On the other hand, when the average void diameter is less than 0.5 μm, in the case of a filter, the pressure loss increases, so clogging is quick, the life performance of the filter is shortened, and in the case of a separator, the porosity is reduced, It is not preferable. The average void diameter of the nonwoven fabric is preferably 0.75 to 20 μm, more preferably 1 to 10 μm, and the maximum void diameter of the nonwoven fabric is preferably 40 μm, more preferably 30 μm or less.

  (D) It is preferable that the fiber large diameter part and lump part amount contained in a nonwoven fabric are 10% or less in a nonwoven fabric. When the fiber large diameter part / lumced part amount contained in the nonwoven fabric is larger than 10%, even if the average fiber diameter is 0.1 to 5 μm, the large diameter part / lump part is an electrode when used in a separator or the like. Since the contact area increases, the internal resistance of the battery increases. The amount of the fiber large diameter part / lump part contained in the nonwoven fabric is preferably 8% or less, more preferably 6% or less.

  (E) The crystallinity χc of the fibers constituting the nonwoven fabric determined from X-ray diffraction needs to be 40% or less. In the present invention, by controlling the crystallinity χc to 40% or less, the molecular structure of the fiber is in an amorphous state, and when the hot-pressure treatment is performed later, the molecular structure is heat-set. This makes it easier to hold the shape. If the degree of crystallinity χc is greater than 40%, there are many crystallized parts in the molecular structure of the fiber, and the rigidity of the fiber becomes high. The shape of time cannot be retained over time. The crystallinity χc is preferably 30% or less, more preferably 20% or less, and still more preferably 18% or less.

  The ratio of the tensile strength in the longitudinal direction and the tensile strength in the lateral direction of the nonwoven fabric is preferably 0.2 to 5 times. When this ratio is larger than 5 times or smaller than 0.2 times, it indicates that the fibers constituting the nonwoven fabric are oriented in the longitudinal direction or the transverse direction, and the tensile strength In the direction of small, there is a tendency that the desired processability by hot pressing cannot be obtained. Preferably, it is 0.3 to 4 times, more preferably 0.4 to 3 times.

  In the present invention, the average fiber diameter is as described above, and it has molding processability by hot pressing, and by satisfying the above (a) to (e) at the same time, these effects are combined, and various members It can be molded when applied to a filter, a separator for an electricity storage device, an adsorbent, a sound absorbing material, a heat insulating material, a heat insulating material, a flameproof material, or a heat insulating material, a cleaner, protective clothing, wallpaper, or shoji paper It has been found that excellent filter performance, adsorption performance, separator performance, heat insulation performance, etc. are exhibited even in a state of being molded into an appropriate shape for various uses such as adhesive tape.

  In the present invention, as the ultrafine fiber, carbon fiber, glass fiber, ceramic fiber, asbestos fiber and other inorganic fibers, aramid fiber, vinylon fiber, polyarylate fiber, polybenzoxazole (PBO) fiber, polyphenylene sulfide fiber, aliphatic Examples include polyester fibers, wholly aromatic polyester fibers, polyamide fibers, polyolefin fibers, acrylic fibers, vinyl chloride fibers, polyketone fibers, cellulose fibers, and organic fibers such as pulp fibers. Can be used in combination.

  In the present invention, the melting point or thermal decomposition temperature of the ultrafine fiber is preferably 300 ° C. or higher, more preferably 350 ° C. or higher, and further preferably 400 ° C. or higher. The melting point or thermal decomposition temperature can be determined from a differential thermal analysis curve obtained by differential thermal analysis according to JIS K7121. As the ultrafine fiber, specifically, a fiber satisfying these can be selected from the above fibers, and among them, the aramid fiber is excellent in strength, resistance, flame resistance, chemical resistance, and insulation. It is particularly preferable because it exhibits high performance as a filter, a separator, a heat insulating material, a sound absorbing material, an adsorbing material, a flameproof material, and an adhesive tape.

The aramid polymer constituting the aramid fiber is a polymer in which one or two or more divalent aromatic groups are directly linked by an amide bond, and the aromatic group has two aromatic rings as oxygen, It may be bonded with a sulfur or alkylene group. In addition, these divalent aromatic groups may include a lower alkyl group such as a methyl group or an ethyl group, a halogen group such as a methoxy group, or a chloro group. Furthermore, these amide bonds are not limited and may be either para-type or meta-type.
As such an aramid polymer, polyparaphenylene terephthalamide, copolyparaphenylene-3,4'oxydiphenylene-terephthalamide, polymetaphenylene terephthalamide, polymetaphenylene isophthalamide and the like are preferably selected.

  In the present invention, by using the ultrafine fiber having the melting point or the thermal decomposition temperature, or the ultrafine fiber made of an aramid polymer, the filter or the adsorbent can be used from a garbage incinerator, a coal boiler, a metal blast furnace, or the like. The exhaust gas discharged reaches 150 to 200 ° C. and can exhibit high heat resistance that can withstand this. In addition, when used as a separator for an electricity storage device, for example, as a separator for a lithium ion battery, even when the electrolyte has a high liquid retaining property and the internal temperature of the battery reaches 200 ° C. or higher due to abnormal heat generation, the separator Without contraction, it is possible to prevent a short circuit between the electrodes due to contraction of the separator. Furthermore, when used for applications where moisture drying in activated carbon is important, such as for electric double layer capacitors, the element drying temperature can be raised, so that drying can be performed efficiently.

  In the present invention, the dry heat shrinkage of the nonwoven fabric at 200 ° C. is preferably 2% or less. As a result, in the case of a filter, in a high-temperature environment, the filter shrinks and restrains the collected dust, so that the removal performance does not decrease and the pressure loss does not increase, extending the filter life. it can. In the case of a separator, it is possible to prevent a short circuit between electrodes due to the shrinkage of the separator. In addition, when used in adsorbents, sound-absorbing materials, heat-resistant materials, flameproof materials, protective clothing, adhesive tapes, etc., the shape will not be significantly deformed even when exposed to high-temperature environments. In some cases, it is difficult for the adhesive part to be peeled off due to shrinkage, and it can be used continuously. The dry heat shrinkage rate at 200 ° C. of the nonwoven fabric is preferably 1.75% or less, more preferably 1.5% or less.

  In the present invention, the above ultrafine fiber is, for example, discharged from a discharge hole having a small diameter by a polymer solution obtained by a method described in detail later, stretched or thinned, and then solidified. It is preferable that it is the fiber which becomes. In addition, it is preferable that the polymer solution be discharged without bursting from the discharge holes because a homogeneous nonwoven fabric is obtained.

The nonwoven fabric manufacturing method described above can be effectively refined by improving the explosive spinning technology (described in WO02 / 052070) in which a polymer solution is bursted into fine fibers and the melt-blowing technology generally used for meltable polymers. Examples thereof include a fiberizing technique (US Pat. No. 6,013,223) and an electrospinning method disclosed in Japanese Patent Laid-Open No. 2005-200779.
Among them, a technique (US601223) that improves the melt-blowing technique performed with a meltable polymer and is effectively finer is preferable for producing the nonwoven fabric of the present invention. The polymer solution can be stretched and thinned by discharging the compressed air from the compressed air discharge holes installed on the concentric circles of the nozzle of the spinning device that discharges water, and the crystallinity can be controlled.

  Solvents that dissolve the aramid polymer include, for example, amides such as N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMF), dimethylimidazolidinone, and alkoxy-N-isopropyl-propionamide. Mention may be made of system polar solvents. Dimethyl sulfoxide (DMSO) is also used as a solvent. You may add solvents, such as toluene and acetone other than the said solvent, to such an extent that the solubility of a polymer is not impaired significantly. Among these, NMP and DMAc are preferable from the viewpoint of the stability of the aramid polymer solution.

In addition, an inorganic salt may be added to improve the spinnability. Examples of the inorganic salt that can be used in the present method include halides such as chloride or bromide having a cation selected from the group consisting of calcium, lithium, magnesium and aluminum, and calcium chloride or lithium chloride is particularly preferable. It is also possible to use mixtures of these salts.
Such inorganic salts may be added as necessary, but they may be inevitably produced by a solution preparation process (for example, a polymer production process). The content of the inorganic salt is 45% by weight or less, preferably 20% by weight or less, more preferably 10% by weight or less based on the aramid polymer.

The spinning polymer solution may contain water as long as the object of the present invention is not impaired. Here, the content of water is 70% by weight or less, preferably 50% by weight or less, more preferably 15% by weight or less, based on the weight of the polymer.
Specifically, as shown in FIG. 1, a polymer solution is supplied to a spinning nozzle 3 attached to a cavity 2 that has been adjusted to an appropriate temperature by a die 1. In this way, the polymer solution 10 that has passed through the nozzle inner tube 9 is effectively accelerated and thinned by the gas ejected from the gas ejection port 7 installed outside the polymer ejection hole.

Furthermore, the polymer solution 10 is solidified by being brought into contact with the coagulation liquid after being discharged from the polymer discharge hole, and becomes an ultrafine fiber.
Here, the discharge amount of the polymer solution and the discharge amount of compressed air for stretching and thinning the polymer solution can be appropriately selected depending on the nonwoven fabric shape such as the fiber diameter and the void diameter of the nonwoven fabric to be obtained. That is, when the fiber diameter of the fibers constituting the nonwoven fabric is reduced or the void diameter of the nonwoven fabric is reduced, the discharge amount of the polymer solution is decreased or the discharge amount of compressed air is increased, while the fibers constituting the nonwoven fabric are increased. When increasing the fiber diameter or increasing the void diameter of the nonwoven fabric, it is necessary to increase the discharge amount of the polymer solution or decrease the discharge amount of compressed air. As described above, it is necessary to set the manufacturing conditions appropriately balanced in order to obtain desired characteristics.

  In the present invention, the polymer solution is solidified by contact with the surrounding gas or contact with the coagulation liquid. As the coagulating liquid, for example, in the case of an aramid polymer, a poor solvent for the polymer is used, and examples thereof include water, a mixed solution of water / amide polar solvent, a mixed solution of water / alcohols, alcohols and the like. As the amide polar solvent contained in the water / amide polar solvent mixture, any solvent can be used as long as it dissolves the aramid polymer and is well mixed with water. DMF can be preferably used. Of these, in consideration of solvent recovery, the same kind as the amide polar solvent in the spinning polymer solution is preferable. Among the coagulating liquids, water, a water / NMP mixed solvent or a water / DMAc mixed solvent is preferable.

  The distance from the polymer solution discharge hole to the collection surface (hereinafter referred to as spinning distance) is preferably in the range of 100 to 800 mm. If the spinning distance is less than 100 mm, it is difficult to attach the coagulated water supply device. On the other hand, when the spinning distance exceeds 800 mm, the binding between the fibers on the spinning line becomes conspicuous, the rope-like fiber bundles increase in the nonwoven fabric, and the yarn and yarn when reaching the collecting surface The speed of the compressed air accompanying the strip is reduced, and the strength of the resulting nonwoven fabric is weak. The spinning distance is more preferably 200 to 700 mm, still more preferably 300 to 600 mm.

  The installation location of the coagulating liquid supply device used in the present invention is the same installation position height and the same coagulating liquid injection on both the web conveyance direction opposite side (upstream side) and the web conveyance direction side (downstream side). It is preferable to install them in pairs at an angle. This is because the coagulating liquid supply device is installed only at one location upstream or downstream in the web conveyance direction, or even if it is installed both upstream and downstream in the web conveyance direction, If the installation position height or the coagulating liquid injection angle is different, the flow direction of the yarn discharged from the nozzle is disturbed when supplying the coagulating liquid, thread breakage occurs, or the basis weight profile of the obtained nonwoven fabric deteriorates. This is not preferable because it causes

  Examples of the spray nozzle constituting the coagulation liquid supply apparatus used in the present invention include full cone pattern nozzles, holo cone pattern nozzles, knife jet pattern nozzles, and flat pattern nozzle sprays. In order to adjust the ratio between the tensile strength and the tensile strength in the short direction, it is preferable to use a flat pattern nozzle that can eject the coagulation liquid in a fan shape. In a knife jet pattern nozzle or the like in which the coagulation liquid is jetted in parallel with the web conveyance direction, the fibers constituting the nonwoven fabric are easily oriented in the longitudinal direction, and the tensile strength in the longitudinal direction of the nonwoven fabric is the tensile strength in the short direction. It becomes 5 times or more.

  The angle at which the coagulation liquid forms a fan shape, so-called spray angle, is preferably 30 to 140 degrees. A nozzle having an injection angle exceeding 140 degrees is difficult to manufacture, and if it is less than 30 degrees, fibers constituting the nonwoven fabric are easily oriented in the longitudinal direction. The spray angle of the coagulating liquid is more preferably selected from a flat pattern spray nozzle that is 40 to 140 degrees, more preferably 50 to 140 degrees.

  The spray nozzle of the coagulation liquid supply device is preferably installed at a position within 500 mm above or below the polymer solution discharge hole surface. When this position is above the nozzle surface, the distance is not particularly limited, but the coagulating liquid sprayed from the spray nozzle of the coagulating liquid supply device may adhere to the polymer solution discharge hole, When the polymer solution is discharged from the discharge hole, the polymer solution may solidify and solidify, resulting in a discharge failure of the polymer solution. On the other hand, when the spray nozzle of the coagulation liquid supply device is installed at a position exceeding 500 mm below the polymer solution discharge hole surface, the binding between the fibers on the spinning line becomes remarkable, and the rope-like shape is formed in the nonwoven fabric. The fiber bundle increases and the resulting nonwoven fabric becomes inhomogeneous.

  The spray nozzle of the coagulating liquid supply device is discharged and spun from the polymer solution discharge hole, is thinned by the air discharged from the surroundings, and extends in the width direction of the spinning line until it reaches the support for collection. In parallel, at least one or a plurality of the polymer solution discharge holes are arranged so that spraying can be performed uniformly at an appropriate angle between right angle and parallel to the spinning line. It is determined appropriately depending on the width, the type of spray nozzle, performance, and the like.

  The installation distance of the spray nozzle from the spinning line is preferably set in the range of 5 to 300 mm. When the distance from the spinning line is less than 5 mm, the compressed air sprayed from the spray nozzle of the spray spraying device strongly contacts and interferes with the yarn flowing on the spinning line, causing breakage of the yarn or the resulting nonwoven fabric. This is not preferable because the basis weight profile is deteriorated. On the contrary, if the distance from the spinning line exceeds 300 mm, the sprayed coagulating liquid is undesirably sprayed over a wide area on the spinning line. That is, in order to efficiently solidify the yarn, it is preferable to send liquid and air immediately after the yarn is sufficiently thinned to bring it into contact with the yarn, but the distance from the spinning line of the spray nozzle If the diameter exceeds 300 mm, the aqueous solution sprayed from the nozzle is sprayed loosely over a wide area on the spinning line, making it difficult to efficiently solidify the yarn, so it is necessary to increase the amount of coagulation liquid to be used Is not preferable.

By capturing the ultrafine fiber obtained in the present invention on a running belt, a homogeneous nonwoven fabric structure can be obtained. In that case, it can supplement directly on a sheet-like base material, and can also be set as a laminated body with a base material. The laminate thus obtained can be wound up once, and the aramid polymer ultrafine fiber can be captured again in the wound laminate so as to form a three-layer structure.
In the present invention, the basis weight of the nonwoven fabric is determined by the polymer solution discharge amount from the nozzle and the moving speed (belt speed) of the collecting surface, and can be appropriately adjusted depending on the purpose of use.

  After the spinning is completed, the obtained fibers and the nonwoven fabric constituted by them may be washed. As a method for washing fibers or non-woven fabrics, any means or equipment for removing the solvent and salt from the fibers may be used. For example, a method of immersing in a washing bath, a method of spraying a washing solution or steam, or a dryer Examples include a method of drying and removing. Among them, the method of immersing in a cleaning bath is preferable because of high cleaning efficiency.

  Subsequently, it is dried as necessary to remove moisture and residual solvent. The dried fiber or non-woven fabric may be subsequently heat-treated at a temperature of 100 to 500 ° C. in a heat treatment step. The heat treatment at this time may be performed under any conditions of a hot plate, a dry heat atmosphere, or a steam atmosphere. When a steam atmosphere is used, the steam may contain an amide polar solvent in addition to water. Here, the heat treatment temperature is preferably 100 to 500 ° C. More specifically, when the heat treatment temperature exceeds 100 ° C. higher than the glass transition temperature of the polymer, the crystallinity of the fiber is increased by heat setting, or the resulting fiber is severely deteriorated and colored, and in some cases There is a case to be threaded. On the other hand, when the temperature is lower than 100 ° C., the fiber may not be sufficiently relaxed. In addition, when heat-processing with a hotplate, Preferably it is 150-400 degreeC, More preferably, it is 150-350 degreeC, More preferably, it is preferable to implement at 150-195 degreeC. Moreover, in the case of the heat processing in a dry-heat atmosphere, Preferably it is 150-500 degreeC, More preferably, it implements at 150-400 degreeC. In the case of heat treatment in a steam atmosphere, it is preferable to carry out at 100 to 400 ° C., more preferably 100 to 300 ° C., and still more preferably 100 to 190 ° C.

  In the above spinning method, yarn breakage of the aramid polymer is unlikely to occur, and the resulting fiber is essentially continuous, and a non-woven fabric of ultrafine fibers with little fluff can be obtained. At the same time, the diameter can be reduced, and the average fiber diameter of the obtained fiber is 5 μm or less, preferably 3 μm or less, more preferably 2 μm or less. Moreover, the minimum with a preferable average fiber diameter of the fiber obtained is 0.01 micrometer, and a more preferable minimum is 0.05 micrometer.

  Hereinafter, the present invention will be described in more detail based on examples. However, the following examples do not limit the present invention. In addition, each physical-property value in an Example was measured with the following method.

<Fiber diameter (μm)>
The surface of the nonwoven fabric was observed with a scanning electron microscope JSM6330F (manufactured by JEOL) at a magnification of 1000 times, and 100 fibers were arbitrarily selected and measured.

<Weight per unit (g / m ² )>
Measurement was carried out according to the weight test method per unit area of JIS L 1906.

<Thickness (mm)>
Ono Sokki Using a digital linear gauge DG-925 (diameter of the measurement terminal part 1 cm), the thickness was measured at 20 arbitrarily selected locations, and the average value was obtained.

<Apparent density (g / cm ³ )>
The weight per unit volume was calculated from (weight per unit area) / (thickness).

<Cavity diameter (μm)>
As for the void diameter of the nonwoven fabric, the average void diameter and the maximum void diameter were determined by the bubble point method and the mean flow method described in STM-F-316. Each unit is μm.

<Melting point or thermal decomposition temperature (℃)>
In accordance with JIS K 7121 or JIS K 7120, from the temperature at the top of the melting peak of the DSC curve obtained by differential scanning calorimetry, or from the temperature at which the weight loss of the sample begins on the TG curve obtained from thermogravimetry Asked.

<Heat shrinkage (%)>
In accordance with JIS L 1906, the dry heat shrinkage of the nonwoven fabric after heat treatment at 200 ° C. for 15 minutes was determined in a no-tension state.

<Fiber diameter and lump amount (%) in nonwoven fabric>
With reference to the method described in Japanese Patent Application Laid-Open No. 2001-50902, the fiber large diameter portion and lump amount in the nonwoven fabric were determined as follows.
(1) Using an optical microscope (manufactured by Keyence, VHX-900), irradiate light from the light source to the object to be measured (nonwoven fabric sample), and photograph the object to be measured (nonwoven fabric sample) at a magnification of 50 times.
(2) In the image photographed by the above method, the reflected light reflected by the fiber large-diameter portion and the lump portion of the measured object having a fiber diameter and a lump size of 50 μm or more is irradiated by the light receiving element. Receives luminance information by receiving light.
(3) From the luminance information obtained in this way, the area of the fiber large diameter part and the lump part is obtained, and the fiber large diameter part and the lump part amount in the nonwoven fabric are calculated by the following formula.
Fiber large diameter portion and lump portion amount (%) in non-woven fabric = (area of fiber large diameter portion and lump portion / total area of photographed image) × 100
(4) The fiber large diameter part and lump part amount in the nonwoven fabric were measured at 10 arbitrarily selected locations, and the average value thereof was determined.

<Measurement of crystallinity χc>
Using an X-ray diffractometer (D8 DISCOVER with GADDS Super Speed, manufactured by Bruker AXS), measurement in the range of 2θ = 10 to 40 ° was performed. At this time, the profile in all directions of the sample was measured. According to the method of Hindeleh et al. (AM Hideleh and D. J. Johnson, Polymer, 19, 27 (1978)), peak separation was performed based on the omnidirectional diffraction curve of commercially available metaaramid, and the crystalline peak intensity after separation Was obtained from the ratio to the total peak intensity. The crystallinity peak was based on the peak position of the diffraction intensity curve of a commercially available aramid fiber or polyester fiber that is highly crystallized.

<Hot-pressure forming processability>
When the sample is cut into an A4 size in two directions, the longitudinal direction and the transverse direction of the nonwoven fabric, sandwiched between the concave and convex molds, heat treated at 100 ° C. for 1 minute, and then left at room temperature for 1 minute, Was measured with a protractor. If it was 90 to 120 degrees, the moldability was good, and if it exceeded 120 degrees, the moldability was x.

<Ratio of tensile strength in the longitudinal direction and tensile strength in the transverse direction of the nonwoven fabric>
Based on JIS P8113, the tensile strength test of the nonwoven fabric was performed, and the tensile strength in the longitudinal direction was divided by the tensile strength in the lateral direction to obtain a value.

[Example 1]
20 parts by weight of polymetaphenylene isophthalamide powder (manufactured by Teijin, 1.38 g / cm ³ ) having an intrinsic viscosity (IV) of 1.35 produced by an interfacial polymerization method according to the method described in Japanese Patent Publication No. 47-10863 Then, it was poured into 80 parts by weight of dimethylacetamide (DMAc) cooled to 0 ° C. to make a slurry, and then heated up to 40 ° C. and dissolved to obtain a polymer solution.
The above polymer solution was fed at 120 g / min to a spinning apparatus of US Pat. No. 6,013,223 using a gear pump, the spinning temperature was 40 ° C., and compressed air was fed at 10 m ³ / min for spinning. Here, in the spinning apparatus of US6031323, the hole diameter of the polymer solution discharge holes is 0.3 mm, and the polymer solution discharge nozzles are arranged in an array of 100 × 5 rows so that 500 pieces are equally spaced at a pitch of 5 mm. I used something.

The coagulation liquid supply device is positioned at a position 50 mm downward from the polymer solution discharge hole and 50 mm from the spinning line on both the web conveyance direction opposite side (upstream side) and the web conveyance direction side (downstream side). Using a flat spray nozzle (manufactured by Kyoritsu Alloy Manufacturing Co., Ltd., flat spray nozzle integrated type), the solid solution supply spray is applied to the polymer solution after discharge from the polymer solution discharge hole 200 mm below the spinning line. At the point, the spray angle of the spray nozzle was adjusted so that the thinned yarn and the coagulation liquid were in contact with each other.
Water whose temperature was adjusted to 30 ° C. was used as the coagulation liquid, and the water supplied to the pair of flat spray nozzles was 5 L / min.

The yarn discharged from the polymer solution discharge hole by the gear pump is immediately thinned and solidified along with the surrounding compressed air and coagulating liquid while flowing down toward the collecting surface in the downward direction on the spinning line, and 500 mm below the spinning device. On the collection belt installed in No. 1, the belt conveyance speed was set to 1.7 m / min while laminating continuous fibers, and the fiber configurations and fabric weights shown in Table 1 were obtained.
The obtained nonwoven fabric was heat-treated with a metal calender roll at a temperature of 150 ° C. and a set linear pressure of 50 kg / cm, and the clearance between the upper and lower rolls was arbitrarily adjusted to adjust the linear pressure. Got. Next, the average fiber diameter, apparent density, porosity, melting point of the fiber, dry heat shrinkage at 200 ° C., fiber large diameter and lump amount in the nonwoven fabric, degree of crystallinity of the nonwoven fabric fiber, longitudinal direction of the nonwoven fabric The ratio between the tensile strength and the tensile strength in the short direction, and hot press molding processability were evaluated, and the evaluation results are summarized in Table 2.

[Examples 2 to 7, Comparative Example 1]
Spinning was performed in the same manner as in Example 1 except that the spray angle of the coagulation liquid supply spray nozzle, the yarn-coagulation liquid contact position, and the amount of coagulation liquid were changed as shown in Table 1. A fabric with a basis weight was obtained. The obtained nonwoven fabric was heat-treated with a metal calender roll at a temperature of 180 ° C. and a set linear pressure of 50 kg / cm, and the clearance between the upper and lower rolls was arbitrarily adjusted to adjust the linear pressure. Got. Next, the average fiber diameter, apparent density, porosity, melting point of the fiber, dry heat shrinkage at 200 ° C., fiber large diameter and lump amount in the nonwoven fabric, degree of crystallinity of the nonwoven fabric fiber, longitudinal direction of the nonwoven fabric The ratio between the tensile strength and the tensile strength in the short direction, and hot press molding processability were evaluated, and the evaluation results are summarized in Table 2.

[Comparative Example 2]
A nonwoven fabric sample was prepared in the same manner as in Example 1 except that the nonwoven fabric was heat-treated with a metal calender roll at a temperature of 400 ° C. and a set linear pressure of 100 kg / cm. Next, the average fiber diameter, apparent density, porosity, melting point of the fiber, dry heat shrinkage at 200 ° C., fiber large diameter and lump amount in the nonwoven fabric, crystallinity of the fibers constituting the nonwoven fabric, longitudinal length of the nonwoven fabric The ratio between the tensile strength in the direction and the tensile strength in the short direction, and hot press molding processability were evaluated, and the evaluation results are summarized in Table 2.

[Comparative Example 3]
Short fibers made of polymetaphenylene isophthalamide fiber (Teijin Ltd., Conex) with a fiber length of 51 mm and a fiber diameter of 14 μm are spun with a card and subjected to a needle punching process with a needle density of 150 / cm ² and a thickness of 100 μm. The fiber structure which is a nonwoven fabric of 40 g / m < ² > of fabric weight was obtained. Next, the average fiber diameter, apparent density, porosity, melting point of the fiber, dry heat shrinkage at 200 ° C., fiber large diameter and lump amount in the nonwoven fabric, crystallinity of the fibers constituting the nonwoven fabric, longitudinal length of the nonwoven fabric The ratio between the tensile strength in the direction and the tensile strength in the short direction, and hot press molding processability were evaluated, and the evaluation results are summarized in Table 2.

  Further, as is apparent from Tables 1 and 2, in the present invention, the polymer solution discharged from the polymer solution discharge hole is thinned, and the coagulated liquid is compressed air with a spray nozzle toward the spinning line on which fibers are formed. By spraying together and solidifying without damaging the yarn, it is possible to obtain a non-woven fabric with no fiber breakage, few fiber large diameter parts and lump parts, and excellent hot press molding processability It was.

  The ultrafine continuous aramid fiber according to the present invention can provide a heat-resistant thin leaf material, and the heat-resistant thin leaf material is extremely useful as a material for a separator for a lithium ion battery, a separator base material for a capacitor, and a material for a filter, for example. is there. In addition, it can be used as a useful material for sound-absorbing materials, adsorbents, heat insulating materials, flameproofing materials, protective clothing, wallpaper, shoji paper, adhesive tape, and the like.

1: Die 2: Cavity 3: Spinning nozzle 4: Spinneret 5: Gas cavity 6: Intake port 7: Gas discharge port 8: Gas flow 9: Inner tube (capillary)
10: Polymer solution 11: Coagulating liquid supply nozzle 12: Coagulating liquid 14: Air 15: Polymer 16: Plate

Claims (6)

A method for producing a nonwoven fabric comprising ultrafine fibers and excellent in processability by hot-pressure treatment, wherein the ultrafine fibers discharge a polymer solution from discharge holes having a small diameter, and the polymer solution is discharged. The coagulation liquid is discharged using a flat pattern nozzle that can eject the coagulation liquid in a fan shape after discharging the pressure air from the pressure air discharge holes installed on the concentric circles of the nozzle of the device to expand or reduce the diameter of the polymer solution. Is a fiber obtained by solidifying this by forming the fan-shaped angle at 30 to 140 degrees and bringing it into contact with the coagulation liquid, and the nonwoven fabric satisfies all of the following (a) to (e): The manufacturing method of the ultrafine fiber nonwoven fabric to do .
(A) The average fiber diameter of the fibers constituting the nonwoven fabric is 0.1 to 5 μm
(B) The average apparent density of the nonwoven fabric is 0.05 to 2.0 g / cm ^3.
(C) The average void diameter of the nonwoven fabric is 0.1 to 30 μm, the maximum void diameter is 50 μm or less. (D) The fiber large diameter portion / lumped portion amount is 10% or less in the nonwoven fabric. (E) The nonwoven fabric obtained from X-ray diffraction. The degree of crystallinity of the fibers constituting the fiber is 40% or less 2. The method for producing an ultrafine fiber nonwoven fabric according to claim 1, wherein the nonwoven fabric has a tensile strength in the longitudinal direction of 0.2 to 5 times the tensile strength in the lateral direction. The method for producing an ultrafine fiber nonwoven fabric according to claim 1 or 2, wherein the ultrafine fiber has a melting point or thermal decomposition temperature of 300 ° C or higher. The method for producing an ultrafine fiber nonwoven fabric according to any one of claims 1 to 3, wherein the ultrafine fiber is a polymetaphenylene isophthalamide fiber. The method for producing an ultrafine fiber nonwoven fabric according to any one of claims 1 to 3, wherein the ultrafine fiber is a polyparaphenylene terephthalamide fiber or a copolyparaphenylene 3,4'-oxydiphenylene terephthalamide fiber. The method for producing an ultrafine fiber nonwoven fabric according to any one of claims 1 to 5, wherein the nonwoven fabric has a dry heat shrinkage rate of 2% or less at 200 ° C.

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