JP2008101315A - Porous body and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new porous body composed of a porous support body and dispersed nanofibers in the pores of the support body, and having a reduced pressure drop and a high collection efficiency. <P>SOLUTION: The porous body with communicating micropores having a three-dimensional network structure of the nanofibers with a number average diameter of 1 to 500 nm dispersed in the pores of the supporting body, wherein the porous body of the network structure has a maximum pore size of 10 μm or less and a pressure drop of 300 Pa or less. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a porous body in which a nanofiber dispersion is three-dimensionally arranged in a hole of a support and a method for producing the same.

  Filters using fiber base materials are widely used in daily life applications such as masks, industrial applications such as air filters and liquid filters, and medical applications such as blood filters. There are two major performance requirements for such a filter. The first is the trapping efficiency of fine particles (filtered material), and the second is the pressure loss when gas or liquid that is to be filtered flows through the filter. is there.

  First, it is known that the trapping efficiency of fine particles generally increases as the pore size of innumerable micropores is reduced. For this reason, the use of thinner fibers has been studied.

  However, if the fine pore diameter is reduced by using finer fibers, the object to be filtered such as gas or liquid will not easily pass through the filter or will be clogged immediately, and the initial pressure of the filter will be reduced. There is a fatal problem as a filter that the amount of filtration per unit time is suppressed due to the increase in loss, or the life of the filter is significantly shortened due to a significant increase in pressure loss over time.

  For this reason, various studies have been made to suppress the pressure loss of the filter while the micropore diameter is uniform and the micropore diameter is made smaller. In addition, it has been studied to make the filter network structure three-dimensional instead of two-dimensional so as to improve the amount of collected filter and prevent clogging. For example, there is a method in which a three-dimensional skeleton is assembled with thick fibers, and ultrafine fibers are three-dimensionally arranged between the skeleton fibers.

As a specific example of the above-described method, as a technique for obtaining a structure in which nano-level fibers made of a thermoplastic polymer are arranged in a mesh in the holes of a support, after a nanofiber dispersion is attached to a porous support, There is a method of drying and removing the dispersion medium (Patent Document 1). According to this method, the nanofibers can be arranged in a mesh in the pores in the support. However, when the dispersion medium is removed by drying, the nanofibers are migrated together with the dispersion medium onto the wall surfaces of the pores to support the nanofibers. A network structure may not be generated at the center of a hole having a large hole diameter in the body, and a uniform three-dimensional network structure may not be formed. That is, a portion having a large pore diameter may be formed, and when used as a filter, there is a possibility that the portion having a large pore diameter becomes a defect that cannot capture fine particles. Further, if the nanofiber adhesion amount is increased so that such a portion having a large micropore size is not generated, the micropore size of the network structure becomes too small as a whole, and the pressure loss becomes too large. It was.
On the other hand, a method (Patent Document 2) has been proposed in which cellulose is produced by acetic acid bacteria to form a structure in which cellulose nanofibers are arranged on a polyester ultrafine fiber nonwoven fabric, but this method has low productivity. Therefore, industrial use was difficult.
JP 2005-330639 A WO97 / 23266 pamphlet

  An object of the present invention is to provide a porous body in which nanofiber dispersions are three-dimensionally arranged in the pores of a support and fine pores having high particulate collection efficiency and high air permeability communicate with each other.

  In order to solve the above-mentioned problems, the present invention mainly comprises the following constitution, that is, the present invention is a uniform network structure in which nanofibers having a number average diameter of 1 nm to 500 nm are three-dimensionally dispersed in the holes of the support. The present invention provides a porous body in which fine pores having low pressure loss and high collection efficiency are communicated. Further, the nanofibers having a number average diameter of 1 nm to 500 nm are dispersed in a dispersion medium to form a nanofiber dispersion, which is attached to a support, and the dispersion medium is removed by lyophilization. It is a manufacturing method of a porous body.

  Since the porous body in which the micropores according to the present invention are in communication has a three-dimensional structure, the micropores are uniform and small, and the pressure loss is small, so that it can be used as a high-performance and long-life filter.

  Below, the porous body with which the micropore based on this invention is connecting is demonstrated in detail with desirable embodiment.

  The porous body in which the micropores of the present invention communicate with each other has fine pores (hereinafter sometimes referred to as micropores. The pore diameter of micropores is also referred to as micropore diameter) inside the three-dimensional structure. It is a structure in which the micropores are continuously penetrated.

  The nanofiber referred to in the present specification is a single fiber having a diameter in the range of 1 nm to 1000 nm (1 μm), and there is no limitation on the fiber length, the cross-sectional shape, and the like.

  In the present invention, it is particularly important that the number average diameter of the nanofiber is 1 nm to 500 nm. As a result, the absolute strength required as a fiber can be obtained, and because the fiber is easily dispersed in the structure, it is easy to obtain a porous body in which micropores are communicated (hereinafter sometimes referred to as a continuous microporous body). There is. For example, when a continuous microporous material using nanofibers is used as a filter, the fine pore diameter is sufficiently reduced or the specific surface area is remarkably increased while suppressing the fiber from being cut even if the filtrate collides with it. The trapping performance of the fine particles can be improved. The number average diameter of the nanofiber is preferably 1 nm to 200 nm, more preferably 30 nm to 100 nm. The fiber length and cross-sectional shape of the nanofiber are not limited.

  In the present invention, the number average diameter of the nanofibers can be determined as follows. That is, the surface, transverse section or longitudinal section of the continuous microporous body is observed at a scanning electron microscope (SEM) magnification of 10,000 times, and the 150 nanofiber single fibers randomly extracted in the same plane in the fiber section direction. The length is the diameter and the number average is calculated.

In addition, the nanofiber used in the present invention corresponds to the nanofiber in the present specification in which the diameter of a single fiber is larger than 500 nm and is 1000 nm (1 μm) or less, but the fiber ratio of relatively coarse fibers is It is preferable that it is 3 weight% or less. Here, the fiber ratio of coarse fibers means the ratio of the weight of coarse single fibers (diameters greater than 500 nm to 1 μm or less) to the total weight of the nanofibers having a diameter greater than 1 nm and 1 μm or less. To calculate. That is, a single fiber diameter of each nanofiber single fiber and di, the square of the sum ^{(d1 2 + d2 2 + ··} + dn 2) = Σdi calculates ² (i = 1~n). Further, the fiber diameter of each nanofiber having a diameter greater than 500 nm is set to Di, and the sum of squares (D1 ² + D2 ² +... + Dm ² ) = ΣDi ² (i = 1 to m) is calculated. By calculating the ratio of ΣDi ² to Σdi ² , the cross-sectional area ratio of coarse fibers relative to all nanofibers, that is, the weight ratio can be obtained.

  The nanofibers used in the present invention preferably have a fiber component ratio of 3% by weight or less, more preferably 1% by weight or less, and still more preferably 0.1% by weight in the diameter range of 500 nm to 1 μm in diameter. % Or less. That is, this means that the presence of coarse nanofiber monofilaments exceeding 500 nm is close to zero.

  When the number average diameter of the nanofibers is 200 nm or less, the fiber composition ratio of the nanofiber single fiber having a diameter of more than 200 nm is preferably 3% by weight or less, more preferably 1% by weight or less, and still more preferably 0.8. 1% by weight or less. When the number average diameter of the nanofibers is 100 nm or less, the fiber constituent ratio of single fibers having a diameter of more than 100 nm is preferably 3% by weight or less, more preferably 1% by weight or less, and further preferably 0.1% by weight. % Or less. By these, while being able to fully exhibit the function of the porous body of the present invention, quality stability of a product can also be made good.

  Nanofibers of the present invention, nanofiber single fibers are divided into pieces, most of the single fibers may be in a form that is not agglomerated in bundles, the nanofiber single fibers are in a completely disjointed state, Or most of what is partly bonded has a form such as a disjointed state, which means a fiber-like form at the so-called monofilament level, and the nanofiber monofilaments are bundled It is important that the nanofiber is in the form of a nanofibril (hereinafter, an aggregate in which nanofiber monofilaments are not bundled but separated into pieces is sometimes referred to as a nanofiber dispersion). By using such a nanofiber dispersion, the surface area of the nanofiber can be increased, and when used in a filter, high performance can be exhibited.

  In addition, the “three-dimensional network structure” of the present invention refers to a structure in which the nanofiber dispersion is not a two-dimensional network but is uniformly distributed in three dimensions to form a network and form a network. The porous body of the invention has a network structure in which nanofibers are uniformly dispersed three-dimensionally into the hole in the support. The micropores formed by the three-dimensional network structure of the nanofibers formed in the holes of the support are also communicated.

  As an example of the porous body of the present invention, an SEM photograph of the porous body obtained in Example 1 described later is shown in FIG. Thus, in the porous body of the present invention, the nanofiber single fibers do not aggregate and form a uniform three-dimensional network structure as the nanofiber dispersion, so that the fine pore diameter formed between the nanofiber single fibers is uniform. Have fine pores.

  In the porous body of the present invention, it is important that the fine pores formed by the nanofibers, that is, the maximum pore diameter of the network formed by the nanofibers is 10 μm or less. By setting the maximum pore size to 10 μm or less, it is possible to efficiently collect fine particles and components to be captured when the porous body of the present invention is used for a filter. Specific examples of the measurement of the maximum pore diameter of the porous body will be described in detail in Examples described later, but can be determined as follows. That is, an SEM photograph with a magnification of 1000 times is taken from the porous body, and the area of the micropores in a square range with one side being 50 mm is analyzed on the SEM photograph by commercially available image processing software, and the diameter in terms of a circle is obtained It can be obtained by detecting the maximum value.

  The maximum pore diameter of the micropores is more preferably 5 μm or less, and further preferably 1 μm or less. The lower limit of the number average fine pore diameter is not particularly limited, but is preferably 100 nm or more from the viewpoint of reducing the pressure loss when flowing a gas or liquid that is an object to be filtered through the filter when used in a filter or the like. .

  It is important that the porous body of the present invention has a pressure loss of 300 Pa or less. When the pressure loss is within the above range, when used for a filter or the like, the flow rate when a gas or liquid, which is an object to be filtered, is passed through the filter is increased, and excellent performance is exhibited.

  In the present invention, the pressure loss ΔP (unit: Pascal) can be determined as follows. That is, using an apparatus according to JIS B9908 (2001) format 3, dust is fine particles (0.3 to 0.5 μm) in the atmosphere in the test chamber, and the air velocity passing through the filter is 4 m / min. The downstream pressure is measured and obtained from the difference between the upstream pressure and the downstream pressure.

  In order to reduce the pressure loss while reducing the micropore diameter, it is natural to use a support having a large hole and a small pressure loss, but the apparent density of the network structure of the nanofibers in the hole of the support is reduced. It is important to make it smaller. In other words, the nanofibers are not two-dimensionally arranged with a high-density network structure like paper, but are three-dimensionally shaded in the holes of the support or on the support so that the apparent density is small and the porosity is low. By making the structure high, the fine pore diameter and pressure loss can be achieved.

  The nanofiber used in the present invention is preferably made of a thermoplastic polymer. Thereby, since nanofiber can be manufactured using a melt spinning method, productivity can be made very high and joining of nanofiber single fibers can also be easily performed by thermal bonding. Further, when a thermoplastic polymer is used for the support, the same thermoplastic polymer as that of the nanofiber is preferable because it is easy to recycle at the time of disposal after the porous body of the present invention is used as a filter.

  The thermoplastic polymer as used in the present invention refers to polyethylene terephthalate (hereinafter sometimes referred to as PET), polybutylene phthalate (hereinafter sometimes referred to as PBT), and polylactic acid (hereinafter sometimes referred to as PLA). ), Polyester such as nylon 6 (hereinafter sometimes referred to as N6), polyamide such as nylon 66, polyolefin such as polystyrene (hereinafter sometimes referred to as PS) and polypropylene (hereinafter sometimes referred to as PP). , Polyphenylene sulfide (hereinafter sometimes referred to as PPS), and the like, but polycondensation polymers represented by polyesters and polyamides are preferred because many have high melting points. It is preferable that the melting point of the polymer is 165 ° C. or higher because the heat resistance is good. For example, the melting point is 170 ° C for PLA, 255 ° C for PET, and 220 ° C for N6. Further, the polymer may contain additives such as particles, a flame retardant, and an antistatic agent. Further, other components may be copolymerized as long as the properties of the polymer are not impaired. Furthermore, a polymer having a melting point of 300 ° C. or less is preferable because of ease of melt spinning.

  In the present invention, the support means that a large number of holes communicate with each other, and the communication means that it is continuously connected from one surface to the other surface (in this specification, the porous structure of the present invention is used). A large number of communicating holes in the support, which is the body skeleton material, are indicated as “holes”, and micropores in the porous body are indicated as “holes”. As this support, non-woven fabric, paper, woven fabric, knitted fabric, porous film, a material in which a large number of voids such as sponge are communicated, and a composite thereof can be used. The type of the support can be selected in consideration of performance such as pressure loss, strength, elastic modulus, shape stability, and nanofiber support. This support supports the nanofibers and can maintain the network structure formed by the nanofibers, so that the strength, elastic modulus, and shape stability that cannot be satisfied only with nanofibers with micropores are not possible. Performance can be supplemented. In addition, when using as a filter, select a thicker one to increase the amount of fine particles to be collected in order to maintain performance for a long time, or create a void to be collected in the thickness direction to prevent clogging. It is preferable to do. Moreover, there is no restriction | limiting in particular in the material of a support body, However, It is preferable to select so that the form stability of a support body may not deteriorate with a nanofiber dispersion liquid. As described above, it is preferable that the support is composed of the same thermoplastic polymer as the nanofiber because recycling is facilitated at the time of disposal.

  In the present invention, the method for producing nanofibers is not particularly limited, and as an example of a production method for obtaining nanofibers by a melt spinning method, for example, a known method described in JP-A-2004-162244 is adopted. Can do. Further, as described in JP-A-2005-273067, nanofibers can also be obtained by electrospinning.

  In the present invention, the nanofiber dispersion may be a dispersion in any state. Hereinafter, a nanofiber dispersion in which a nanofiber single fiber is dispersed in a dispersion medium is referred to as a nanofiber dispersion. . As will be described later, since the porous body of the present invention is preferably produced from the nanofiber dispersion, a method for adjusting the nanofiber dispersion will be described next.

  The nanofibers obtained as described above are cut to a desired fiber length with a guillotine cutter or a slicing machine. In order to improve the dispersibility of the nanofiber single fiber in the dispersion, even if the fiber length is too long, the dispersibility will be poor, or if the fiber length is too short, the nanofiber single fiber will be entangled when it is made porous As a result, the strength of the network structure formed by the nanofibers is reduced. From the viewpoint of improving these, the fiber length is preferably cut to 0.2 to 30 mm. The fiber length is more preferably 0.5 to 10 mm, and still more preferably 0.8 to 5 mm.

  In addition, as described in JP-A No. 2004-162244, after obtaining a polymer alloy fiber that is a nanofiber precursor and then dissolving a sea polymer that is an easily soluble polymer, the state of the polymer alloy fiber After cutting to a desired fiber length, the sea polymer may be dissolved to obtain cut nanofibers. When the sea polymer is dissolved and then cut, the island polymers may be fused with each other due to the shear heat generated at the time of cutting, and physical impact such as beating is applied, or the fused part is melted with a solvent. Although it is necessary to separate, according to this method, since the sea polymer exists between the island polymer and the island polymer at the time of cutting, the island polymers are not fused by shear heat generated at the time of cutting. Therefore, the island polymer after the sea polymer is dissolved, that is, the cut nanofibers are not fused at all or hardly, and it is easy to disperse up to one fiber, which is more preferable.

  Next, the obtained cut nanofiber is dispersed in a dispersion medium at a single fiber level. As a dispersion medium, considering not only water but also affinity with nanofibers, hydrocarbons such as hexane and toluene, halogenated hydrocarbons such as chloroform and trichloroethylene, alcohols such as ethanol and isopropyl alcohol, and ethyl ether And ethers such as tetrahydrofuran, ketones such as acetone and methyl ethyl ketone, esters such as methyl acetate and ethyl acetate, polyhydric alcohols such as ethylene glycol and propylene glycol, amines and amides such as triethylamine and N, N-dimethylformamide A general organic solvent such as a system solvent can be preferably used, but water is preferably used in consideration of safety and environment.

  As a method of dispersing the cut nanofibers in the dispersion medium at the single fiber level, a stirrer such as a mixer or a homogenizer may be used. In the case where the single fibers in the cut nanofibers are strongly aggregated or fused, it is preferable to beat in a dispersion medium as a pretreatment step of dispersion by stirring, a Niagara beater, a refiner, a cutter, Shear force can be applied with a laboratory grinder, biomixer, household mixer, roll mill, mortar, PFI beating machine, etc., and each fiber can be dispersed and administered into a dispersion medium.

  In order to make the dispersibility of the nanofiber monofilaments uniform in the nanofiber dispersion or to improve the mechanical strength of the structure when it is formed as a continuous microporous body, the fiber concentration in the dispersion is It is preferable to set it as 0.001 to 30 weight% with respect to the total weight. In particular, since the mechanical strength of the structure greatly depends on the existence state of the nanofiber single fiber in the dispersion, that is, the distance between the fibers, it is preferable to control the concentration of the nanofiber single fiber in the dispersion within the above range. The concentration of the nanofiber single fiber in the dispersion is more preferably 0.01 to 10% by weight, further preferably 0.05 to 5% by weight, and most preferably 0.05 to 1% by weight.

  Moreover, you may use a dispersing agent as needed in order to suppress the re-aggregation of a nanofiber single fiber. For example, when used in an aqueous system, the type of dispersant is selected from anionic systems such as polycarboxylates, cationic systems such as quaternary ammonium salts, and nonionic materials such as polyoxyethylene ethers and polyoxyethylene esters. It is preferable. The molecular weight of the dispersant is preferably 1000 to 50000, and more preferably 5000 to 15000.

  The concentration of the dispersant is preferably 0.00001 to 20% by weight, more preferably 0.0001 to 5% by weight, and most preferably 0.01 to 1% by weight, based on the total dispersion. Thus, a sufficient dispersion effect can be obtained.

  Next, the manufacturing method of the porous body of this invention is demonstrated.

  In the present invention, it is important that a nanofiber dispersion liquid in which nanofibers having a number average diameter of 1 to 500 nm are dispersed in a dispersion medium at a single fiber level is first attached to a support.

  The nanofiber dispersion obtained as described above is adhered to the support, and here, the nanofiber dispersion is adhered to the support means the following state.

  That is, the nanofiber dispersion is in contact with the support surface and inside. At this time, an interaction may or may not work between the nanofiber and the support. That is, the nanofiber dispersion may simply be placed on the support, van der Waals force, hydrogen bond, ionic interaction, or the like may be working, or a chemical bond may be generated.

  There is no restriction | limiting in particular in the method of attaching nanofiber dispersion liquid to a support body, According to the objective, it can select suitably.

  For example, as a first method, a nanofiber dispersion is sprayed onto a support. The nanofibers used in the present invention contain almost no coarse fibers with a single fiber diameter exceeding 500 nm, so they can be sprayed without clogging even from a fine nozzle such as spray or spray, and the nanofiber dispersion is supported in the form of a mist. Can be attached to the body. This method is effective when forming a network structure with nanofibers in pores near the surface of the support or when it is desired to make the network structure with nanofibers very thin. It is also effective when it is desired to further form a network structure of nanofibers on the support. The thickness of the nanofiber layer can be adjusted to 1 μm or less by adjusting the concentration of the nanofiber dispersion or the spraying time.

  As a second method of attaching the nanofiber dispersion to the support, a method of immersing the support in the nanofiber dispersion can be mentioned. As a dipping method, there is a method in which the support is completely submerged in the nanofiber dispersion or only the surface is dipped. This method is effective when the nanofiber dispersion is easily exhausted into the support, and the nanofiber network structure is formed three-dimensionally into the interior of the support. For exhausting the nanofiber dispersion into the support, it is more effective to add a drawing process such as mangle. Furthermore, since the nanofiber dispersion can be uniformly attached to the support, there are advantages such as suppression of defects such as pinholes even when wide processing or continuous processing is performed, and further, the uniformity of the network structure by nanofibers is high. Alternatively, the nanofiber dispersion may be immersed only from one side of the thick support. According to this method, the nanofibers in the nanofiber dispersion can be gradually filtered by the support, and the nanofiber concentration can be graded in the thickness direction of the support. This method is effective when it is desired to give a gradient to the apparent density of the network structure of nanofibers.

  As a third method of attaching the nanofiber dispersion to the support, there is a method of coating the nanofiber dispersion on the support. When the concentration of nanofibers in the nanofiber dispersion is increased or the viscosity of the nanofiber dispersion is increased by using a thickener, etc., and coated with a knife coater, etc., the nanofiber is uniformly formed to a desired thickness. Since there is an advantage that a fiber layer can be formed, it is effective in forming a network structure with nanofibers in the holes on the surface of the support and further forming a network structure with only nanofibers. As a specific coating method, a coating method using various known means such as a die coater, a roll coater, a rod coater, a blade coater, and an air knife coater, and then a drying method or a laminating method can be used.

  A method of simply sprinkling the nanofiber dispersion on the support can also be employed.

  Since the nanofibers used in the present invention contain almost no coarse fibers having a single fiber diameter exceeding 500 nm, the nanofibers are uniformly dispersed in the dispersion medium, and it is easy to form a solution in which the nanofibers are dissolved in the dispersion medium. When the nanofiber dispersion is attached by dipping or coating, the nanofibers can be uniformly attached to the support.

It is important to freeze the nanofiber dispersion after attaching the nanofiber dispersion to the support in this manner. By freezing the nanofiber dispersion, the nanofibers in the dispersion are fixed, that is, the nanofibers do not move, and the dispersion medium can be removed while maintaining the dispersed state during subsequent drying (sublimation). When dried without freezing, the nanofiber monofilaments dispersed in the dispersion medium move as the dispersion medium evaporates, and concentrate and aggregate, resulting in the formation of large pores. However, a uniform network structure cannot always be formed. Therefore, it is important to freeze the dispersion before drying (sublimation) of the dispersion medium.
There are no particular restrictions on the method of freezing the nanofiber dispersion, including exposure to an atmosphere below the temperature at which the dispersion medium freezes, such as a low-temperature freezer, or exposure to a low-temperature liquid such as liquid nitrogen. The method of instant freezing is preferable because the nanofiber single fibers can be immobilized while maintaining the dispersion state of the nanofiber single fibers in the dispersion. Also, increase the viscosity by adding a thickener to the dispersion, etc., and suppress the change in dispersion state and dispersion failure of the nanofiber single fiber in the dispersion, then take several hours to several days with a low temperature freezer etc. Slow freezing is preferable because the frozen dispersion is difficult to break. After that, the dispersion medium is dried (sublimated) by vacuuming. However, since only the dispersion medium is removed while the dispersion state of the nanofiber single fiber is fixed, the nanofiber is uniformly distributed in the pores of the support. A three-dimensional network structure can be obtained. In addition, since the nanofiber dispersion is not concentrated in the drying process, it is possible to obtain a continuous microporous body having a low apparent density and a high porosity. At this time, if the fiber concentration of the nanofiber dispersion liquid is reduced, the apparent density of the continuous microporous material obtained by freeze-drying the nanofiber dispersion liquid is reduced, the porosity is increased, and the pressure loss can be reduced.

  The nanofiber dispersion is freeze-dried to improve the strength and shape stability of the network structure with nanofibers in the support, such as acrylic resin, silicone resin, fluororesin, polyester resin, polyurethane resin, melamine resin, alkyl silicate resin, etc. A binder may be included and freeze-dried. Moreover, if the nanofiber to be used is a thermoplastic polymer, it can be made into a strong network structure by performing high temperature treatment with dry heat or wet heat and thermally bonding the nanofiber single fibers or the nanofiber and the support.

  The support to which the nanofiber dispersion is attached is a post-treatment such as pressure loss, strength, elastic modulus, and shape stability of the continuous microporous material formed by freeze-drying the nanofiber dispersion later, and pleatability. The selection may be made in consideration of the workability and reactivity. A porous sheet that has been pleated in advance can also be used. In this way, it is important to form a network structure with nanofibers in the holes using a support, and strength and elasticity, shape stability, performance and processing that can not be achieved only with a network structure with nanofibers alone Property, reactivity and the like can be imparted.

  Since the porous body obtained by the production method of the present invention has fine pores, it is suitable for filter applications by taking advantage of its network structure, and from the use of life materials such as masks to industrial applications such as air filters and liquid filters. And can be used for medical applications such as blood filters. For example, air filters for clean rooms, automobiles, exhausts for factories and incinerators, houses, etc., liquid filters for chemical processes, foods, medicines and medicines, fields where HEPA and ULPA filters are applied, etc. It is done. In particular, it is suitable for HEPA filters, ULPA filters and blood filters using a network structure.

  Hereinafter, the present invention will be described in detail with reference to examples. In addition, the measuring method in an Example used the following method.

A. Polymer melt viscosity The polymer melt viscosity was measured with a Capillograph 1B manufactured by Toyo Seiki Seisakusho. The polymer storage time from sample introduction to measurement start was 10 minutes.

B. Melting | fusing point The peak top temperature which shows melting | dissolving of a polymer by 2nd run using DSC-7 made from Perkin Elmaer was made into melting | fusing point of a polymer. At this time, the rate of temperature increase was 16 ° C./min, and the sample amount was 10 mg.

C. Worcester spots of polymer alloy fibers (U%)
Measurement was performed in the normal mode at a yarn feeding speed of 200 m / min using a USTER TESTER 4 manufactured by Zerbegger Worcester.

D. SEM Observation Platinum was vapor-deposited on the sample and observed with an ultrahigh resolution electrolytic emission scanning electron microscope at magnifications of 1000 and 10,000.
SEM device: UHR-FE-SEM manufactured by Hitachi, Ltd.
E. Observation of cross section of nanofiber by TEM Using a nanofiber bundle before dispersion, an ultrathin section was cut in the cross section direction of the nanofiber, and the cross section of the nanofiber was observed by TEM at a magnification of 40000 times. Moreover, metal dyeing | staining was given as needed.
TEM apparatus: H-7100FA type manufactured by Hitachi, Ltd. Number average diameter of fibers The number average diameter of fibers is determined as follows.

  The nanofibers contained in the porous body were measured by measuring the length in the fiber cross-sectional direction as a diameter from an SEM photograph of 10,000 times magnification of the above D term, and obtaining a simple average value thereof. In addition, the nanofibers that are the raw materials for the continuous microporous material described in the examples are calculated by converting the single fiber diameter of the fiber into a circle using image processing software (WINROOF) from a photograph obtained by TEM observation, and a simple average value thereof. Asked. At this time, the diameters of 150 fibers randomly extracted in the same cross section were analyzed and used for calculation.

G. Fiber composition ratio Using diameter analysis of 150 fibers in F above, let each single fiber diameter in the fiber dispersion be di, and sum of squares (d1 ² + d2 ² +... + D150 ² ) = Σdi ² (i = 150) is calculated. Further, each fiber diameter in the fiber dispersion having a diameter larger than 500 nm is set to Di, and the sum of the squares (D1 ² + D2 ² +... + Dm ² ) = ΣDi ² (i = 1 to m) is calculated. By calculating the ratio of ΣDi ² to Σdi ² , the cross-sectional area ratio of coarse fibers to all fibers, that is, the weight ratio of coarse fibers was obtained.

H. Mechanical properties At room temperature (25 ° C.), an initial sample length = 200 mm, a tensile speed = 200 mm / min, and a load-elongation curve was obtained under the conditions shown in JIS L1013 (1999). Next, the load value at the time of breaking was divided by the initial fineness, which was taken as the strength, the elongation at the time of breaking was divided by the initial sample length, and a strong elongation curve was obtained as the elongation.

I. Pressure loss Using an apparatus according to JIS B9908 (2001) type 3, dust is fine particles (0.3 to 0.5 μm) in the atmosphere in the test chamber, air velocity passing through the filter is 4 m / min, upstream of the filter and The pressure on the downstream side was measured, and the difference between the pressure on the upstream side and the pressure on the downstream side was taken as the pressure loss.

J. et al. Collection efficiency Using an apparatus according to JIS B 9908 (2001) type 3, dust is fine particles (0.3 to 0.5 μm) in the atmosphere in the test chamber, air velocity passing through the filter is 4 m / min, particle counter KC- The value obtained by 01D (manufactured by Rion Co.) was evaluated by calculating with the following formula.
Collection efficiency (%) = (1-C2 / C1) × 100
Here, C1: number of dust on the upstream side of the filter (0.3 to 0.5 μm) C2: number of dust on the downstream side of the filter (0.3 to 0.5 μm)

K. Maximum pore diameter of micropores The maximum pore diameter of micropores formed between fibers in the porous body is determined as follows. A square frame with a side of 50 mm is drawn on an arbitrary place on the SEM photograph of 1000 times magnification in the D section. Further, the fiber image in the frame was taken into image processing software (WINROOF), the micropores on the taken image were calculated in terms of a circle to obtain the diameter, and this maximum value was detected.

[Production Example 1 of Dispersion]
Melt viscosity 57 Pa · s (240 ° C., shear rate 2432 sec ⁻¹ ), melting point 220 ° C. N6 (20 wt%) and weight average molecular weight 120,000, melt viscosity 30 Pa · s (240 ° C., shear rate 2432 sec −1), melting point 170 ° C. poly-L lactic acid (optical purity of 99.5% or higher) (80% by weight) was melt-kneaded at 220 ° C. with a biaxial extrusion kneader to obtain a polymer alloy chip. Here, the weight average molecular weight of poly L lactic acid was determined as follows. That is, THF (tetrahydrofuran) was mixed with the sample chloroform solution to obtain a measurement solution. This was measured at 25 ° C. using water permeation gel permeation chromatography (GPC) Waters 2690, and the weight average molecular weight was determined in terms of polystyrene. The melt viscosity of N6 at 262 ° C. and a shear rate of 121.6 sec ⁻¹ was 53 Pa · s. Further, the melt viscosity of this poly L lactic acid at 215 ° C. and a shear rate of 1216 sec ⁻¹ was 86 Pa · s. The kneading conditions at this time were as follows.

    Polymer supply: N6 and copolymerized PET were weighed separately and supplied separately to the kneader.

Screw type: Fully meshed in the same direction Double thread Screw: Diameter 37mm, Effective length 1670mm
L / D = 45
The kneading part length was located on the discharge side from 1/3 of the effective screw length.

Temperature: 220 ° C
Vent: 2 places This polymer alloy chip was melted at a melting portion of 230 ° C. and led to a spin block having a spinning temperature of 230 ° C. The polymer alloy melt was filtered with a metal nonwoven fabric having a limit filtration diameter of 15 μm, and then melt-spun from a die having a die surface temperature of 215 ° C. At this time, a die having a die hole diameter of 0.3 mm and a hole length of 0.55 mm was used, but the ballast phenomenon was hardly observed. And the discharge amount per single hole at this time was 0.94 g / min. Furthermore, the distance from the base lower surface to the cooling start point (the upper end of the chimney) was 9 cm. The discharged yarn is cooled and solidified with a cooling air of 20 ° C. over 1 m, and is supplied with an oil supply guide installed 1.8 m below the base, and then passed through an unheated first take-up roller and second take-up roller. Winded up. This was subjected to a stretching heat treatment with the temperature of the first hot roller being 90 ° C. and the temperature of the second hot roller being 130 ° C. At this time, the draw ratio between the first hot roller and the second hot roller was 1.5 times. The obtained polymer alloy fiber showed excellent properties of 62 dtex, 36 filament, strength 3.4 cN / dtex, elongation 38%, U% = 0.7%. Further, when a cross section of the obtained polymer alloy fiber was observed with a TEM, poly-L-lactic acid showed a sea and N6 showed an island-island structure, and the number average diameter of the island N6 was 55 nm, and N6 was very finely dispersed. A polymer alloy fiber, which is a precursor of the converted N6 nanofiber, was obtained.

  The polymer alloy fiber obtained was immersed in a 5 wt% sodium hydroxide aqueous solution at 95 ° C for 1 hour to hydrolyze and remove 99% by weight or more of the poly-L lactic acid component in the polymer alloy fiber, and neutralized with acetic acid. Then, it was washed with water and dried to obtain a fiber bundle of N6 nanofibers. As a result of analyzing this fiber bundle from a TEM photograph, the number average diameter of the N6 nanofibers was 60 nm, which is an unprecedented thinness, and the fiber composition ratio of the single fiber diameter larger than 100 nm was 0 wt%.

  The obtained fiber bundle of N6 nanofiber was cut into 1 mm length to obtain a cut fiber of N6 nanofiber. A test Niagara beater (manufactured by Kumagaya Rikyu Kogyo Co., Ltd.) was charged with 10 L of water and 30 g of the previously obtained cut fiber, preliminarily beaten for 5 minutes, and then the excess water was removed to collect the fiber. The weight of this fiber was 250 g, and its water content was 88% by weight. 250 g of water-containing N6 nanofibers are directly charged into an automatic PFI mill (manufactured by Kumagaya Rikyu Kogyo Co., Ltd.) and beaten for 6 minutes at a rotation speed of 1500 rpm and a clearance of 0.2 mm (hereinafter referred to as seed). Got). 4.2 g of seed in an oster blender (manufactured by oster), 0.5 g of Charol (registered trademark) AN-103P (manufactured by Daiichi Kogyo Seiyaku Co., Ltd .: molecular weight 10,000) as an anionic dispersant as a dispersant, water 500 g was charged and stirred at a rotational speed of 13900 rpm for 30 minutes to obtain N6 nanofiber dispersion 1 having a N6 nanofiber content of 0.1 wt%.

[Production Example 2 of Dispersion]
Dispersion Production Example 1 was the same as Dispersion Production Example 1 except that N6 (45 wt%) having a melt viscosity of 212 Pa · s (262 ° C., shear rate 121.6 sec ⁻¹ ) and a melting point of 220 ° C. was used. The polymer alloy chip was obtained by melt-kneading. Next, this was melt-spun and stretched and heat treated in the same manner as in Production Example 1 of the dispersion to obtain a polymer alloy fiber. The obtained polymer alloy fiber exhibited excellent properties of 67 dtex, 36 filaments, strength 3.6 cN / dtex, elongation 40%, U% = 0.7%. Moreover, when the cross section of the obtained polymer alloy fiber was observed with a TEM, as in dispersion production example 1, poly L lactic acid was the sea and N6 was the island-island structure, and the number average diameter of the island N6 was A polymer alloy fiber having a thickness of 110 nm and ultra-dispersed N6 was obtained.

  The obtained polymer alloy fiber was hydrolyzed and removed 99% by weight or more of the poly-L lactic acid component in the polymer alloy fiber in the same manner as in Production Example 1 of the dispersion, neutralized with acetic acid, washed with water, dried, and N6 nanofibers Fiber bundles were obtained. As a result of analyzing this fiber bundle from a TEM photograph, the number average diameter of N6 nanofibers is 120 nm, which is an unprecedented thinness, and the fiber composition ratio of single fiber diameter larger than 500 nm is 0% by weight, and the single fiber diameter is 200 nm. The larger fiber composition ratio was 1% by weight.

  The obtained fiber bundle of N6 nanofiber was cut into 1 mm length to obtain a cut fiber of N6 nanofiber. This was preliminarily beaten in the same manner as in Production Example 1 of the dispersion to obtain N6 nanofibers having a water content of 88% by weight, and further beaten in the same manner as in Production Example 1 of the dispersion, and an anionic dispersant as a dispersant. Is stirred in the same manner as in Production Example 1 of the dispersion using Charol (registered trademark) AN-103P (manufactured by Daiichi Kogyo Seiyaku Co., Ltd .: molecular weight 10,000), and the content of N6 nanofibers is 0.1 wt. % N6 nanofiber dispersion 2 was obtained.

[Production Example 3 of Dispersion]
An N6 nanofiber dispersion 3 was obtained in the same manner as in Production Example 2 of the dispersion except that the content of N6 nanofibers was 1.0% by weight.

[Production Example 4 of Dispersion]
In Dispersion Production Example 1, N6 nanofiber dispersion 4 was obtained in the same manner as Dispersion Production Example 1 except that no dispersant was used.

[Dispersion Production Examples 5 and 6]
N6 nanofibers were prepared in the same manner as in Production Example 1 of the dispersion, except that the cut length of N6 nanofibers was 0.5 mm in Dispersion Production Example 5 and the cut length of N6 nanofibers was 5 mm in Dispersion Production Example 6. N6 nanofiber dispersions 5 and 6 having a content of 0.1% by weight were obtained.

[Production Example 7 of Dispersion]
Polystyrene (PS) copolymerized with 22 wt% of PBT (polybutylene terephthalate) having a melt viscosity of 120 Pa · s (262 ° C., 121.6 sec ⁻¹ ) and a melting point of 225 ° C. and 2 ethylhexyl acrylate was used, and the content of PBT was 20 The mixture was melt-kneaded in the same manner as in Production Example 1 of the dispersion at a kneading temperature of 240 ° C. to obtain a polymer alloy chip. At this time, the melt viscosity at 262 ° C. and 121.6 sec ⁻¹ of the copolymerized PS was 140 Pa · s, and the melt viscosity at 245 ° C. and 1216 sec ⁻¹ was 60 Pa · s.

  This was melt-spun in the same manner as in Production Example 1 of the dispersion at a melting temperature of 260 ° C., a spinning temperature of 260 ° C. (die surface temperature of 245 ° C.), and a spinning speed of 1200 m / min. At this time, a die having a discharge hole diameter of 0.7 mm and a discharge hole length of 1.85 mm provided with a measuring portion having a diameter of 0.3 mm above the discharge hole was used. The spinnability was good and the yarn breakage was 1 in 1 t spinning. The discharge rate per single hole at this time was 1.0 g / min. The obtained undrawn yarn was drawn and heat treated in the same manner as in Production Example 1 of the dispersion at a drawing temperature of 100 ° C., a draw ratio of 2.49 times, and a heat setting temperature of 115 ° C. The obtained drawn yarn was 161 dtex, 36 filaments, and the strength was 1.4 cN / dtex, the elongation was 33%, and U% = 2.0%. When the cross section of the obtained polymer alloy fiber was observed by TEM, the copolymer PS showed the sea, the PBT showed the island-island structure, the number average diameter of the PBT was 70 nm, and the PBT was nano-sized and uniformly dispersed. A polymer alloy fiber was obtained.

  By immersing the obtained polymer alloy fiber in trichlene, 99% by weight or more of copolymer PS as a sea component was eluted and dried to obtain a fiber bundle of PBT nanofibers. As a result of analyzing this fiber bundle from a TEM photograph, the number average diameter of the PBT nanofiber is 85 nm, which is an unprecedented fineness. The fiber composition ratio of the single fiber diameter larger than 200 nm is 0% by weight, and the single fiber diameter is 100 nm. The larger fiber ratio was 1% by weight.

  The obtained fiber bundle of PBT nanofibers was cut into 1 mm length to obtain cut fibers of PBT nanofibers. This was preliminarily beaten in the same manner as in Production Example 1 of the dispersion to obtain PBT nanofibers having a water content of 80% by weight, and further beaten in the same manner as in Production Example 1 of the dispersion. 2.5 g of this beaten seed, 0.5 g of Neugen (registered trademark) EA-87 (Daiichi Kogyo Seiyaku Co., Ltd .: molecular weight 10,000), which is a nonionic dispersant as a dispersant, and 500 g of water (Oster blender) And stirred for 30 minutes at a rotational speed of 13900 rpm to obtain a PBT nanofiber dispersion 7 having a PBT nanofiber content of 0.1% by weight.

[Production Example 8 of Dispersion]
PTT (polytrimethylene terephthalate) having a melt viscosity of 220 Pa · s (262 ° C., 121.6 sec ⁻¹ ) and a melting point of 225 ° C. and copolymer PS (polystyrene) (“Estyrene” KS-18, manufactured by Nippon Steel Chemical Co., Ltd.) Methyl methacrylate copolymer, melt viscosity 110 Pa · s, 262 ° C., 121.6 sec ⁻¹ ), PTT content 25 wt%, kneading temperature 240 ° C. A polymer alloy chip was obtained. The copolymer PS had a melt viscosity of 76 Pa · s at 245 ° C. and 1216 sec ⁻¹ .

  This was melt-spun in the same manner as in Production Example 1 of the dispersion at a melting temperature of 260 ° C., a spinning temperature of 260 ° C. (die surface temperature of 245 ° C.), and a spinning speed of 1200 m / min. At this time, a spinneret having a diameter of 0.23 mm and a discharge hole diameter of 2 mm and a discharge hole length of 3 mm was used as the base. The spinnability was good and the yarn breakage was 1 in 1 t spinning. The single-hole discharge rate at this time was 1.0 g / min. The obtained undrawn yarn was stretched 2.6 times in a 90 ° C. hot water bath. When the cross section of this was observed with a TEM, the copolymer PS showed sea and PTT showed an island-island structure. The number average diameter of PTT was 75 nm, and PTT was nano-sized and uniformly dispersed. Obtained. Further, this was a single fiber fineness of 3.9 dtex, a strength of 1.3 cN / dtex, and an elongation of 25%.

  In the same manner as in Production Example 7 for dispersion, the obtained polymer alloy fiber was eluted and dried with 99% by weight or more of the PS component in the polymer alloy fiber to obtain a PTT nanofiber fiber bundle. As a result of analyzing this fiber bundle from a TEM photograph, the number average diameter of the PTT nanofibers is 95 nm, which is an unprecedented fineness. The fiber composition ratio of the single fiber diameter larger than 200 nm is 0% by weight, and the single fiber diameter is 100 nm. The larger fiber composition ratio was 3% by weight.

  The obtained fiber bundle of PTT nanofibers was cut into 1 mm length to obtain cut fibers of PTT nanofibers. This was preliminarily beaten in the same manner as in Production Example 1 of the dispersion to obtain PTT nanofibers having a water content of 80% by weight, and further beaten in the same manner as in Production Example 1 of the dispersion. 2.5 g of this beaten seed, 0.5 g of Neugen (registered trademark) EA-87 (Daiichi Kogyo Seiyaku Co., Ltd .: molecular weight 10,000), which is a nonionic dispersant, are used as a dispersant, and 500 g of water. And agitated at a rotational speed of 13900 rpm for 30 minutes to obtain a PTT nanofiber dispersion 8 having a PTT nanofiber content of 0.1 wt%.

[Dispersion Production Example 9]
Similar to Dispersion Production Example 1 except that N6 in Dispersion Production Example 1 was changed to PP (polypropylene) (23 wt%) having a melt viscosity of 350 Pa · s (220 ° C., 121.6 sec ⁻¹ ) and a melting point of 162 ° C. And kneaded to obtain a polymer alloy chip. The melt viscosity of poly L lactic acid at 220 ° C. and 121.6 sec −1 was 107 Pa · s. This polymer alloy chip was melt-spun at the melting temperature of 230 ° C., the spinning temperature of 230 ° C. (the base surface temperature of 215 ° C.), the single-hole discharge rate of 1.5 g / min, and the spinning speed of 900 m / min. went. The obtained undrawn yarn was drawn and heat treated in the same manner as in Production Example 1 of the dispersion at a drawing temperature of 90 ° C., a draw ratio of 2.7 times, and a heat setting temperature of 130 ° C.

  The polymer alloy fiber thus obtained was immersed in a 5% by weight aqueous sodium hydroxide solution at 98 ° C. for 1 hour to hydrolyze and remove 99% by weight or more of the poly-L lactic acid component in the polymer alloy fiber, and neutralized with acetic acid. Then, it was washed with water and dried to obtain a fiber bundle of PP nanofibers. As a result of analyzing this fiber bundle from a TEM photograph, the number average diameter of N6 nanofibers was 240 nm, and the fiber ratio of single fiber diameters larger than 500 nm was 0% by weight.

  The resulting PP nanofiber bundle was cut into 1 mm lengths to obtain PP nanofiber cut fibers. This was preliminarily beaten in the same manner as in Production Example 1 of the dispersion to obtain PP nanofibers having a water content of 75% by weight, and further beaten in the same manner as in Production Example 1 of the dispersion. 2.0 g of this beaten seed, 0.5 g of Neugen (registered trademark) EA-87 (Daiichi Kogyo Seiyaku Co., Ltd .: molecular weight 10,000), which is a nonionic dispersant as a dispersant, and 500 g of water, Oster blender (Oster) And agitation at a rotational speed of 13900 rpm for 30 minutes to obtain a PP nanofiber dispersion 9 having a PP nanofiber content of 0.1% by weight.

[Dispersion Production Example 10]
Biaxially, under the following conditions, PET having a melt viscosity of 280 Pa · s (300 ° C., 1216 sec ⁻¹ ) is 80 wt% and polyphenylene sulfide (PPS) having a melt viscosity of 160 Pa · s (300 ° C., 1216 sec ⁻¹ ) is 20 wt%. Melt kneading was performed using an extrusion kneader to obtain a polymer alloy chip. Here, the PPS used was a linear type and the molecular chain terminal was replaced with calcium ions.

Screw L / D = 45
The kneading part length is 34% of the effective screw length
The kneading part was dispersed throughout the screw.

There are two backflow parts on the way. Polymer supply PPS and PET were weighed separately and supplied separately to the kneader.

Temperature 300 ° C
No vent The polymer alloy chip obtained here was guided to a spinning machine in the same manner as in Production Example 1 of the dispersion to carry out spinning. At this time, the polymer alloy melt was filtered with a metal nonwoven fabric having a spinning temperature of 315 ° C. and a limit filtration diameter of 15 μm, and then melt-spun from a die having a die surface temperature of 292 ° C. At this time, as the base, a nozzle having a discharge hole diameter of 0.6 mm provided with a measuring portion having a diameter of 0.3 mm above the discharge hole was used. And the discharge amount per single hole at this time was 1.1 g / min. Furthermore, the distance from the base lower surface to the cooling start point was 7.5 cm. The discharged yarn is cooled and solidified over 1 m with a cooling air of 20 ° C., and after the process oil agent mainly composed of fatty acid ester is supplied, it is 1000 m / min through the non-heated first take-up roller and the second take-up roller. It was wound up. The spinnability at this time was good, and there was no yarn breakage during continuous spinning for 24 hours. This was subjected to a stretching heat treatment with the temperature of the first hot roller being 100 ° C. and the temperature of the second hot roller being 130 ° C. At this time, the draw ratio between the first hot roller and the second hot roller was 3.3 times. The obtained polymer alloy fiber showed excellent properties of 400 dtex, 240 filament, strength 4.4 cN / dtex, elongation 27%, U% = 1.3%. Moreover, when the cross section of the obtained polymer alloy fiber was observed by TEM, PPS was dispersed uniformly as an island with a diameter of less than 100 nm in PET, which was a sea polymer. Moreover, when the circle-equivalent diameter of the island was analyzed by the image analysis software WINROOF, the average diameter of the island was 65 nm, and polymer alloy fibers in which PPS was ultra-dispersed were obtained.

  The obtained polymer alloy fiber is immersed in a 5% by weight sodium hydroxide aqueous solution at 98 ° C. for 2 hours to hydrolyze and remove 99% by weight or more of the PET component in the polymer alloy fiber, neutralized with acetic acid, and washed with water. And dried to obtain a fiber bundle of PPS nanofibers. As a result of analyzing this fiber bundle from the TEM photograph, the number average diameter of the PPS nanofibers was 60 nm, which is an unprecedented fineness, and the fiber ratio of the single fiber diameter larger than 100 nm was 0% by weight.

  The obtained fiber bundle of N6 nanofibers was cut into a length of 3 mm to obtain cut fibers of PPS nanofibers. This was preliminarily beaten in the same manner as in Production Example 1 of the dispersion to obtain PPS nanofibers having a water content of 80% by weight, and further beaten in the same manner as in Production Example 1 of the dispersion. 2.5 g of the beaten fiber, 0.5 g of Neugen (registered trademark) EA-87 (Daiichi Kogyo Seiyaku Co., Ltd .: molecular weight 10,000), which is a nonionic dispersant, are used as a dispersant, and 500 g of water is used as an oster blender (Oster). And stirred for 30 minutes at a rotational speed of 13900 rpm to obtain a PPS nanofiber dispersion 10 having a PPS nanofiber content of 0.1 wt%.

[Dispersion Production Example 11]
The polymer alloy fibers of Production Example 2 of the dispersion were cut into 1 mm lengths to obtain polymer alloy cut fibers. The obtained polymer alloy cut fibers were hydrolyzed to remove 99% by weight or more of the poly-L lactic acid component in the polymer alloy fibers in the same manner as in Production Example 1 of the dispersion, neutralized with acetic acid, washed with water and dried. Nanofiber cut fibers were obtained. This was carried out in the same manner as in Production Example 3 of dispersion to obtain N6 nanofiber dispersion 11 having a N6 nanofiber content of 1.0% by weight.

[Dispersion Production Example 12]
An N6 nanofiber dispersion liquid 12 having an N6 nanofiber content of 1.0 wt% was obtained in the same manner as in Production Example 11 of the dispersion liquid except that the cut length of the polymer alloy fiber was 0.2 mm.

[Dispersion Production Example 13]
A seawater component of 60% by weight of an alkali-soluble copolymer polyester resin, an island component of 40% by weight of N6 resin, 100 islands by melt spinning, and a polymer array composite fiber of 5.3 dtex (hereinafter referred to as composite fiber) ) Was stretched 2.5 times to obtain a 2.1 dtex conjugate fiber. The composite fiber had a strength of 2.6 cN / dtex and an elongation of 35%. Thereafter, the composite fiber was treated with a 3 wt% aqueous sodium hydroxide solution at 98 ° C. for 1 hour to hydrolyze and remove 99% by weight or more of the polyester component in the composite fiber, neutralized with acetic acid, After washing with water and drying, N6 ultrafine fibers were obtained. When the average single yarn fineness of the obtained ultrafine fibers was analyzed from the TEM photograph, it was 0.02 dtex (average fiber diameter of 1.4 μm). The obtained N6 ultrafine fiber was cut into 1 mm length to obtain a cut fiber, and then 50 g of this cut fiber and Charol (registered trademark) AN-103P (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) which is an anionic dispersant as a dispersant. : 0.5 g of molecular weight 10,000) and 500 g of water were charged in an oster blender (manufactured by oster Co., Ltd.) and stirred at a rotational speed of 13900 rpm for 30 minutes to obtain a fiber dispersion 13 having a N6 ultrafine fiber content of 0.1% by weight. Obtained.

<Example 1>
Using Nanofiber Dispersion 1 obtained in Production Example 1 of the dispersion, non-woven fabric PS150 manufactured by Japan Vilene Co., Ltd. was used as the support, and the support was immersed in the dispersion to obtain a length of 12 cm, a width of 12 cm, and a thickness. 43.2 g of dispersion 1 was impregnated on a 3 mm support, placed on a stainless steel bat, the stainless bat was cooled with liquid nitrogen, and the dispersion 1 impregnated on the support was frozen, and then −40 It was left still for 30 minutes in an ultra-low temperature freezer at 0 ° C.
The frozen sample was freeze-dried at a vacuum degree of 1 Pa with a freeze dryer (TF20-85TTNNN) manufactured by Takara Manufacturing Co., Ltd. to obtain a porous body.

  When the obtained porous body was observed with an SEM, the number average diameter of the nanofibers was 60 nm, the fiber ratio of single fibers having a single fiber diameter of greater than 200 nm was 0% by weight, and the single fiber diameter was greater than 100 nm. The fiber ratio was 0% by weight, the network structure composed of the nanofiber dispersion was three-dimensionally and uniformly formed in the holes of the support, and the maximum pore diameter was 4.83 μm. Moreover, the pressure loss of the porous body was 73 Pa, and the collection efficiency was 60.8.

<Examples 2 to 12>
For Examples 2 to 12, the nanofiber dispersions 2 to 12 obtained in Production Examples 2 to 12 of the dispersion were used and freeze-dried in the same manner as in Example 1 to obtain continuous microporous materials. Table 2 shows the number average diameter, the fiber ratio, the maximum pore diameter of the fine pores, the pressure loss, and the collection efficiency of the nanofibers.

<Comparative Example 1>
Using the ultrafine fiber dispersion 11 obtained in Production Example 11 of the dispersion, freeze-drying was performed in the same manner as in Example 1 to obtain a continuous microporous material. Table 2 shows the number average diameter, the fiber ratio, the maximum pore diameter of the fine pores, the pressure loss, and the collection efficiency of the nanofibers.

<Comparative example 2>
In Example 3, the support was impregnated with the fiber dispersion, and then dried at 70 ° C. for 5 hours using a hot air dryer without freezing to obtain a porous body.

  When the obtained continuous microporous material was observed with an SEM, the nanofibers aggregated in the fiber portion forming the support and were present near the wall surface of the pores of the support. Further, there are many portions where the nanofibers are not present near the center of the pores, that is, there are many portions with large micropores formed between the nanofibers. Table 2 shows the number average diameter, the fiber ratio, the maximum pore diameter of the fine pores, the pressure loss, and the collection efficiency of the nanofibers.

<Comparative Example 3>
The continuous porous body obtained in Comparative Example 2 was further impregnated with 43.2 g of the fiber dispersion 3 and dried at 70 ° C. for 5 hours using a hot air dryer without freezing to obtain a porous body.

  When the obtained porous body was observed by SEM, there were fewer portions where nanofibers were not present than in Comparative Example 3, but there were many portions with large fine pores formed between the nanofibers. Table 2 shows the number average diameter, the fiber ratio, the maximum pore diameter of the fine pores, the pressure loss, and the collection efficiency of the nanofibers.

<Comparative Example 4>
The porous material obtained in Comparative Example 3 was further impregnated with 43.2 g of the fiber dispersion 3, and dried at 70 ° C. for 5 hours using a hot air dryer without freezing to obtain a porous material.

  When the obtained porous body was observed with an SEM, the pores of the support were filled with the nanofiber network structure, and there were no large portions of micropores formed between the nanofibers, but the micropore diameter was reduced. The pressure loss was 678 Pa or more. The number average diameter of nanofibers, the fiber ratio, the maximum pore diameter of the fine pores of the porous body, and the collection efficiency were as shown in Table 2.

<Example 13>
The dispersion 1 used in Example 1 was diluted 10 times to obtain an N6 nanofiber dispersion having an N6 nanofiber content of 0.01% by weight. Got. Table 2 shows the number average diameter, the fiber ratio, the maximum pore diameter of the fine pores, the pressure loss, and the collection efficiency of the nanofibers.

<Examples 14 to 26>
For Examples 14 to 26, the porous bodies obtained in Examples 1 to 13 were treated with 120 ° C. steam for 5 minutes in an autoclave. The steam-treated porous body was cut into 5 cm square, and the weight at that time was defined as W1. The porous body cut out in 5 cm square was immersed in water at room temperature for 5 minutes, and then treated at 100 ° C. for 5 hours using a hot air dryer, and the weight dried was designated as W2. When the weight loss rate (%) = (W1-W2) / W1 × 100 was calculated, it was less than 0.5% in all the porous bodies of Examples 14 to 26, and nanofibers were hardly dropped from the porous bodies. It was confirmed.

  Since the porous body of the present invention has fine pores, it is suitable for filter applications by taking advantage of its network structure, from daily use materials such as masks to industrial applications such as air filters and liquid filters, and medical devices such as blood filters. Can be used for applications. For example, air filters for clean rooms, automobiles, exhausts for factories and incinerators, houses, etc., liquid filters for chemical processes, foods, medicines and medicines, fields where HEPA and ULPA filters are applied, etc. It is done. In particular, it is suitable for various high-performance filters and blood filters using a network structure.

It is a figure which shows the observation result by SEM of the porous body of Example 1. FIG. It is a figure which shows the observation result by SEM of the porous body of the comparative example 2.

Claims (7)

Nanofibers having a number average diameter of 1 nm to 500 nm have a three-dimensional network structure in the holes of the support, the fine pores of the network structure communicate with each other, and the maximum pore diameter of the fine pores of the network structure is 10 μm or less A porous body having a pressure loss of 300 Pa or less. The porous body according to claim 1, wherein the nanofiber is made of a thermoplastic polymer. The porous body according to claim 1 or 2, wherein the nanofiber has a fiber ratio of 3% by weight or less of a single fiber having a diameter greater than 500 nm and not greater than 1000 nm. The filter using the porous body in any one of Claims 1-3. A porous body characterized in that nanofibers having a number average diameter of 1 nm to 500 nm are dispersed in a dispersion medium to form a nanofiber dispersion, which is adhered to a support and the dispersion medium is removed by freeze-drying. Manufacturing method. The method for producing a porous body according to claim 5, wherein the nanofiber is made of a thermoplastic polymer. The method for producing a porous body according to claim 5 or 6, wherein the nanofiber has a fiber constituent ratio of a single fiber having a diameter of more than 500 nm and not more than 1000 nm of 3% by weight or less.