JP7440650B2 - Nonwoven fabric, nonwoven fabric manufacturing method, liquid filter - Google Patents

Description

The present invention relates to a nonwoven fabric, a nonwoven fabric manufacturing method, and a liquid filter.

Nonwoven fabrics made of fibers are known. Nonwoven fabrics are used in various applications such as filters. Electrospinning is known as a method for producing nonwoven fabrics. The electrospinning method, also called electrospinning method, applies a voltage between a collector and a solution in which a fiber material is dissolved in a solvent, and the solution is ejected to the collector, thereby depositing the formed fiber on the surface of the collector. This is a method of collecting nonwoven fabrics.

Further, as a filter for blood, the following Patent Document 1 is known. In Patent Document 1 listed below, by varying critical wettable surface tension (CWST) on the front and back sides of a filter, it is attempted to both improve filtration performance and shorten filtration time.

International Publication No. 2017/141752

However, the filter of Patent Document 1 has a problem in that the pores are collapsed due to pressure loss and the thickness of the filter is reduced, resulting in a decrease in filtration life and filtration performance.

The present invention has been made in view of the above background, and aims to provide a nonwoven fabric, a nonwoven fabric manufacturing method, and a liquid filter that can improve filtration life and filtration performance.

In order to solve the above problems, the nonwoven fabric of the present invention has an intertwined structure in which fibers are entangled, and the average linearity of the fibers is within the range of 0.1 μm or more and 5.0 μm or less. , the thickness is within the range of 0.1 mm or more and 50 mm or less, the porosity is at least 90%, the average pore diameter is within the range of 0.5 μm or more and 50 μm or less, and when a pressure of 30 kPa is applied. When the thickness is H30 and the thickness under no load is H0, H30/H0 is in the range of greater than 0.1 and less than or equal to 0.5.

When H0.5 is the thickness when a pressure of 0.5 kPa is applied, it is preferable that H30/H0.5 is in the range of 0.25 or more and 0.75 or less.

Preferably, the fibers are formed from cellulosic polymers.

Preferably, the cellulose-based polymer is cellulose acylate.

Preferably, the fiber contains a thermosetting polymer.

Preferably, the thermosetting polymer is an epoxy resin.

It is preferable that the critical wet surface tension is 70 mN/m or more.

In addition, in order to solve the above problems, the nonwoven fabric manufacturing method of the present invention applies a voltage between a collector and a solution in which a fiber material is dissolved in a solvent, and then sprays the solution from a nozzle. In a nonwoven fabric manufacturing method that collects on the surface of a collector,
an addition step of adding a thermosetting polymer to the solution;
and a curing step of thermosetting the thermosetting polymer.

Preferably, the fiber material is a cellulosic polymer.

Preferably, the cellulose-based polymer is cellulose acylate.

Preferably, the solvent is a mixture of multiple compounds.

Preferably, the solvent includes dichloromethane and methanol.

It is preferable to have a saponification step of saponifying and making it hydrophilic.

It is preferable to include a hydrophilization step. In the hydrophilization step, a method of hydrophilization by saponification treatment or a method of adding a hydrophilization agent is used.

It is preferable to include a drying step of freezing and drying.

Furthermore, in order to solve the above problems, the liquid filter of the present invention uses the above-mentioned nonwoven fabric.

According to the present invention, it is possible to provide a nonwoven fabric, a nonwoven fabric manufacturing method, and a liquid filter that can improve filtration life and filtration performance.

It is an explanatory view showing a part of the 1st surface side of a nonwoven fabric. FIG. 1 is a schematic diagram of nonwoven fabric manufacturing equipment. FIG. 1 is a schematic diagram of nonwoven fabric manufacturing equipment.

The nonwoven fabric 10 of this embodiment shown in FIG. 1 is formed of fibers 11. The nonwoven fabric 10 has an entangled structure in which the fibers 11 are intertwined with each other, and this entangled structure extends from one surface (hereinafter referred to as the first surface) 10A side to the other surface (hereinafter referred to as the first surface) in the thickness direction Z of the nonwoven fabric 10. 2 surface) continues to the 10B side. In other words, when multiple nonwoven fabrics manufactured by multiple spinning processes are stacked (laminated) to form a single nonwoven fabric, the above-mentioned entangled structure is interrupted between the layers of the nonwoven fabrics (the first surface 10A and the second surface The intertwined structure becomes intermittent with 10B). On the other hand, the nonwoven fabric 10 has an intertwined structure that is continuous from the first surface 10A to the second surface 10B, unlike a layered nonwoven fabric.

In addition, in FIG. 1, in order to avoid complication of the drawing, only a part of the first surface 10A side of the nonwoven fabric 10 is drawn, and the illustration of the second surface 10B side is omitted. Therefore, the nonwoven fabric 10 has a structure in which the fibers 11 are further continuous on the lower side (second surface 10B side) in FIG. 1 in the thickness direction Z. Note that the nonwoven fabric 10 only needs to include the fibers 11, and in addition to the fibers 11, it may include other fibers made of different materials.

The fiber 11 is formed to have a generally constant wire diameter. The average wire diameter (hereinafter referred to as average wire diameter) is within the range of 0.1 μm or more and 5.0 μm or less. When the average wire diameter is 0.1 μm or more, detachment of the fiber pieces is suppressed compared to the case where the average wire diameter is less than 0.1 μm. Suppression of detachment of fiber pieces means that detachment of fiber pieces from the nonwoven fabric 10 is suppressed, and suppressing detachment of fiber pieces leads to excellent durability as the nonwoven fabric 10. . By having an average wire diameter of 5.0 nm or less, the nonwoven fabric 10 has the same volume ratio of air (hereinafter referred to as porosity) compared to a case where the diameter is larger than 5.0 nm. It becomes softer. In addition, since the average wire diameter is 5.0 nm or less, the porosity of the nonwoven fabric 10 becomes larger than that of a case where the diameter is larger than 5.0 nm, even if the softness is the same, and as a result, the sound absorption When used as a material or heat insulating material, the sound absorption performance and heat insulation performance are improved, and when used as a filter, the filtration throughput is increased.

Note that the average wire diameter is more preferably within the range of 0.15 μm or more and 4.0 μm or less, and even more preferably within the range of 0.2 μm or more and 3.0 μm or less. The average wire diameter can be determined by measuring the wire diameters of 100 fibers 11 from images taken with a scanning electron microscope and calculating the average value.

As described above, the fibers 11 are intertwined, and the nonwoven fabric 10 has a plurality of voids 14 defined by the fibers 11 as spaces where air exists. When the plurality of voids 14 are connected in the thickness direction Z of the nonwoven fabric 10, they form voids penetrating the nonwoven fabric 10 in the thickness direction Z. When the nonwoven fabric 10 is used, for example, as a filter, these pores function as pores of the filter.

The average pore diameter of the pores (voids 14) functioning as the pores of the filter is within the range of 0.5 μm or more and 50 μm or less. Note that the average pore diameter is preferably within the range of 1.0 μm or more and 40 μm or less, and more preferably within the range of 2 μm or more and 30 μm or less. The average pore diameter is determined by first cutting out a 5 cm square (5 cm x 5 cm) sample from the nonwoven fabric 10, and applying this sample to a liquid (GALWICK (1,1,2,3,3,3- hexafluoropropene (manufactured by POROUS MATERIAL)) and then measured by the bubble point method using a palm porometer (manufactured by POROUS MATERIAL).

The volume ratio of voids 14 (hereinafter referred to as porosity) in nonwoven fabric 10 is 90% or more (that is, at least 90%). In addition, the porosity is preferably within the range of 90% or more and 99.8% or less, more preferably within the range of 95% or more and 99.6% or less, and within the range of 97% or more and 99.4% or less. It is more preferable that By increasing the porosity in this way, that is, by allowing a large amount of air to be contained inside, it is possible to broaden the range of uses. For example, it can be used as a sound absorbing material and a heat insulating material because it exhibits superior sound absorption and heat insulation performance compared to a case where the porosity is less than 90%. Furthermore, when made into a filter, it exhibits greater filtration performance than when the porosity is less than 90%. The filtration performance refers to the throughput per unit time and/or the sustainability of the state in which clogging is suppressed.

The porosity (unit: %) is expressed as follows: The weight of the nonwoven fabric 10 is W (unit: g/m ² ), the thickness is H (unit: mm), and the specific gravity of fiber 11 is ρ1 (unit: kg/m ³ ). When doing so, it can be determined by [1-{(W/1000)/(H/1000)}/ρ1]×100. The weight W is determined by cutting the nonwoven fabric 10 into 5 cm x 5 cm, measuring the mass using an electronic balance (manufactured by Mettler Toledo Co., Ltd.), and converting the measured value to 1 m ² . In this example, the thickness H is measured using a non-contact laser displacement meter (LK-H025 manufactured by Keyence Corporation).

The nonwoven fabric 10 has a thickness of 0.1 mm or more and 50 mm or less, where H30 is the thickness when a pressure of 30 kPa is applied, and H0 is the thickness when no load is applied. Note that the thickness H0 is preferably within the range of 0.2 mm or more and 40 mm or less, and more preferably within the range of 0.3 mm or more and 30 mm or less.

Moreover, H30/H0 of the nonwoven fabric 10 is within a range of greater than 0.1 and less than or equal to 0.5. The fact that the value of H30/H0 is within this range indicates that the nonwoven fabric 10 has good performance when used as a filter, particularly as a liquid filter. In other words, the pressure of 30 kPa is a large pressure close to the upper limit of the pressure expected to be applied to a liquid filter, and considering that the porosity of the nonwoven fabric 10 is 90% or more, the nonwoven fabric 10 has a pressure of 30 kPa. Even when a large pressure is applied, the voids 14 remain, indicating that the function as a filter is not lost (performance is good).

In addition, it is preferable that H30/H0.5 of the nonwoven fabric 10 is within the range of 0.25 or more and 0.75 or less, where H0.5 is the thickness when a pressure of 0.5 kPa is applied. . The fact that the value of H30/H0.5 is within this range indicates that the nonwoven fabric 10 deforms flexibly when subjected to a relatively small pressure such as 0.5 kPa. On the other hand, as described above, the nonwoven fabric 10 deforms only to the extent that the voids 14 remain even when subjected to a large pressure such as 30 kPa (does not deform flexibly). In other words, H30/H0 is within the range of greater than 0.1 and less than or equal to 0.5, and H30/H0.5 is within the range of greater than or equal to 0.25 and less than or equal to 0.75. The nonwoven fabric 10 shows that the relationship between the magnitude of the applied pressure and the amount of deformation is not linear (proportional) but nonlinear; more specifically, as long as the pressure is small, it deforms relatively flexibly. However, this shows that even if the pressure is increased, the deformation does not exceed a certain level.

For H30 and H0.5, attach a force gauge (manufactured by Imada Co., Ltd., ZTS-50N) to a manual stage (manufactured by Imada Co., Ltd., SVH-1000N), apply a load to the nonwoven fabric 10, and measure the predetermined load (H30). When measuring H0.5, the pressure is 30 kPa; when measuring H0.5, it is 0.5 kPa).

The critical wettable surface tension (CWST) of the nonwoven fabric 10 is preferably 70 mN/m or more. The critical wet surface tension was measured (evaluated) using an aqueous calcium chloride solution, an aqueous sodium hydroxide solution, and a water-ethanol mixture. Specifically, 10 drops of each of the above-mentioned aqueous solutions having different surface tensions are gently placed on the horizontal surface 10A of the nonwoven fabric 10, and left to stand for 10 minutes.If 9 or more of the 10 drops become wet, the nonwoven fabric 10 It is determined that the nonwoven fabric 10 is wetted by the solution having that surface tension, and if 2 or more drops out of 10 drops are not wetted by the solution having that surface tension, it is determined that the nonwoven fabric 10 is not wetted by the solution having that surface tension. Of the surface tensions of the solutions determined to be wet, the one closest to the surface tension of the solutions determined not to wet, and the surface tension of the solutions determined to be non-wet, to be determined to be wet. The average value of the surface tension closest to the surface tension of the solution obtained was defined as the critical wet surface tension of the nonwoven fabric 10.

As shown in FIGS. 2 and 3, the nonwoven fabric manufacturing equipment 15 of the present invention is for forming fibers 11 and manufacturing the nonwoven fabric 10 using an electrospinning method, and uses the solution shown in FIGS. 2 and 3. A preparation section 23 (addition process), a nonwoven fabric production section 24, and a heating section 40 (curing process), a saponification section 42 (saponification process), and a drying section 44 (drying process) shown in FIG. 3 are provided.

The solution preparation section 23 is for preparing a solution 23a for forming the fiber 11. The solution preparation unit 23 dissolves the material of the fiber 11 (fiber material 16) in the solvent 17 and adds the thermosetting material 18 to generate (prepare) a solution 23a. A hydrophilic agent may be added at this time. The hydrophilizing agent is not particularly limited, but polyvinylpyrrolidone, polyethylene glycol, carboxymethylcellulose, and hydroxypropylcellulose are preferably used.

As the fiber material 16, resin (polymer) can be used. As the polymer, it is preferable to use a polymer that can be made into a solution by dissolving in the solvent 17, and more preferably a polymer that can be made into a solution by dissolving in an organic solvent. Specifically, cellulose polymers, cycloolefin polymers (COP, etc.), polymethyl methacrylate (PMMA), polyester, polyurethane, polyethylene (PE), polypropylene, elastomer, polylactic acid (PLA), polystyrene, polycarbonate, polyacrylonitrile. (PAN), acrylic resin, polyvinyl alcohol (PVA), gelatin, polyimide, polyether ether ketone (PEEK), liquid crystal polymer (LCP), fluororesin, and the like.

Note that among the above polymers, it is preferable to use cellulose polymers. Furthermore, when using a cellulose polymer, it is preferable to use cellulose acylate. Cellulose acylate is a cellulose ester in which some or all of the hydrogen atoms constituting the hydroxyl groups of cellulose are substituted with acyl groups. Further, the cellulose acylate is preferably one of cellulose acetate propionate (CAP), cellulose triacetate (TAC), and cellulose diacetate (DAC).

The solvent 17 may be composed of one type of compound, or may be composed of two or more types of compounds. However, since the solvent 17 has the function of adjusting the evaporation rate in addition to dissolving the fiber material 16, from the viewpoint of adjusting the evaporation rate, it is preferable that the solvent 17 is a mixture composed of two or more types of compounds. . Specific examples include a mixture of dichloromethane (DCM) and methanol (MeOH), chloroform (CHCl ₃ ), water, and dimethylformamide (DMF). Further, as the solvent 17, ethanol (EtOH), isopropanol, butanol, benzyl alcohol, methyl ethyl ketone, cyclohexanone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl formate, ethyl formate, hexane, cyclohexane, carbon tetrachloride, benzene , xylene, N-methylpyrrolidone, diethyl ether, dioxane, 1-methoxy-2-propanol, toluene, acetone, tetrahydrofuran, and the like can be used. These may be used alone or in combination of two or more.

The thermosetting material 18 is a material that has the property of being hardened by heating. The thermosetting material is a thermosetting polymer, more specifically, a urethane resin, an epoxy resin, a phenol resin, a melamine resin, a urea resin, an amino resin, a silicone material, etc. Furthermore, a combination of multiple types of thermosetting materials may be used. The amount (weight) of the thermosetting material 18 to be added can be freely set, but it is preferably within the range of 10% or more and 50% or less of the weight of the solution 23a.

Note that in this embodiment, the solution 23a is generated by simultaneously mixing the fiber material 16, the solvent 17, and the thermosetting material 18, but the present invention is not limited thereto. The solution 23a may be generated by adding the thermosetting material 18 to a solution obtained by dissolving the fiber material 16 in the solvent 17. Alternatively, the solution 23a may be generated by dissolving the fiber material 16 using a solvent (solvent) in which the thermosetting material 18 is added to the solvent 17.

The nonwoven fabric manufacturing section 24 includes a nozzle unit 25, an accumulation section 26, and a power source 27. The nozzle unit 25 is formed to be long in the width direction of the support body 30, which will be described later (see FIG. 2). In the nozzle unit 25, a plurality of (three in this embodiment) nozzles 25a are arranged side by side along the longitudinal direction of the nozzle unit 25 (that is, the width direction of the support body 30) (see FIG. 2). A solution 23a prepared by the solution preparation section 23 is supplied to each nozzle 25a, and the solution 23a is discharged from each nozzle 25a toward the accumulation section 26. Note that the number of nozzles 25a provided in each nozzle unit 25 may be two or less, or four or more. Further, as described above, a plurality of nozzle units 25 that are long in the width direction of the support body 30 may be arranged in a row along the longitudinal direction (conveyance direction) of the support body 30.

The accumulation section 26 includes a collector 52, a support supply section 57, and a support winding section 58. The collector 52 is for attracting the solution 23a discharged from the nozzle 25a and collecting the formed fibers 11 to obtain the nonwoven fabric 10. In this embodiment, the fibers 11 are placed on a support 30 (described later). Collect. The collector 52 is constituted by an endless belt made of a metal strip and formed into an annular shape, and is stretched around rollers 61 and 62, and circulates as the rollers 61 and 62 rotate.

In FIG. 2, illustration of the support supply section 57, support winding section 58, and rollers 61 and 62 is omitted to avoid complication of the drawing. In addition, in the present embodiment, an example in which the fibers 11 are collected on the support 30 has been described, but a configuration in which the fibers 11 are collected directly on the collector 52 without (or abolished) the support 30 is described. You can also use it as Further, in this embodiment, an example has been described in which the fibers 11 are collected on an endless belt stretched between two rollers, that is, an example in which the collector is an endless belt, but the present invention is not limited to this. . For example, the fibers 11 may be collected on the circumferential surface of a rotating drum, that is, the collector may be a rotating drum.

A voltage is applied by a power source 27 between the collector 52 and the nozzle unit 25 (nozzle 25a). As a result, one of the collector 52 and the nozzle 25a is charged positively (+), and the other is charged negatively (-). By doing so, the solution 23a is attracted toward the collector 52 and is ejected from the nozzle 25a toward the collector 52. The collector 52 may be made of a material that is electrically charged when a voltage is applied by the power source 27, and is made of stainless steel, for example. In this embodiment, the nozzle 25a is charged to (+) and the collector 52 is charged to (-), but the polarities of the nozzle 25a and the collector 52 may be reversed. Alternatively, one of the collector 52 and the nozzle 25a may be grounded to set the potential to zero.

The support supply unit 57 supplies the support 30 made of, for example, a strip-shaped aluminum sheet to the collector 52. The support body 30 moves with the movement of the collector 52 and passes below the nozzle unit 25 . During this time, the fibers 11 ejected from the nozzle 25a are collected one after another on the support 30 to form the band-shaped nonwoven fabric 10. Thereafter, the support 30 is peeled off from the nonwoven fabric 10 and wound up on the support winding section 58.

On the other hand, the nonwoven fabric 10 from which the support body 30 has been peeled off is sequentially conveyed to a heating section 40, a saponification section 42, and a drying section 44. In the heating unit 40, the nonwoven fabric 10 is heated by, for example, a heater (not shown), and the nonwoven fabric 10 (thermosetting material 18 included in the nonwoven fabric 10) is cured. In addition, in the saponification section 42, for example, an alkaline solution containing isopropyl alcohol or the like is applied to the nonwoven fabric 10 by spraying, showering, coating, dipping, etc. By saponifying the nonwoven fabric 10, the nonwoven fabric 10 is made hydrophilic. Further, in the drying section 44, the nonwoven fabric 10 is dried, for example, by freeze drying using liquid nitrogen. In addition, in this embodiment, although the heating part 40, the saponification part 42, and the drying part 44 were provided in this order from the upstream side in the conveyance direction, the arrangement order of each of these steps can be changed as appropriate.

In the manner described above, the nonwoven fabric 10 is formed. The nonwoven fabric 10 thus formed has a thickness due to the intertwined structure in which the fibers 11 intertwine with each other without interruption from the first surface 10A to the second surface 10B, and has a plurality of voids 14. (See Figure 1). In addition, since the nonwoven fabric 10 includes the hardened thermosetting material 18, it has suitable performance when used as a filter (particularly a liquid filter), such as not being deformed beyond a certain level even when pressure is increased. .

Hereinafter, the results of verifying the effects of the present invention will be explained. The verification was performed by comparing the nonwoven fabrics of Examples 1 to 5 in which the present invention was implemented with Comparative Examples 1 and 2. In Examples 1 to 5, nonwoven fabrics 10 were manufactured using the nonwoven fabric manufacturing equipment 15 shown in FIGS. 2 and 3, and in Comparative Examples 1 and 2, nonwoven fabrics were manufactured without using the nonwoven fabric manufacturing equipment of the present invention. Specifically, the nonwoven fabric was manufactured without adding the thermosetting material 18.

Manufacturing method of Examples 1 to 5 and Comparative Examples 1 and 2 (addition amount of fiber material 16, solvent 17, thermosetting material 18), and manufactured nonwoven fabric (average wire diameter, porosity, basis weight, thickness (H0), thickness ratio (H30/H0 and H30/H0.5), and filtration life) are as shown in Table 1. In Example 6, as a hydrophilization step, instead of saponification, hydrophilization was performed by adding 5% by mass of polyvinylpyrrolidone to the solid component.

Regarding the filtration life, the nonwoven fabric was attached to a stainless steel line holder (KS-47 manufactured by Advantech Co., Ltd.), and an aqueous solution in which crosslinked acrylic polydisperse particles with an average particle diameter of 10 μm were dispersed in pure water at 0.1% by mass was filtered. . A pressure gauge (manufactured by Keyence Corporation) was attached in front of the stainless steel line holder to set the primary filtration pressure, and the amount of filtration that could be processed until the primary filtration pressure exceeded 30 kPa or until the melon burst was measured. The evaluation is "A (pass)" when the filtration capacity is 200 ml or more, "B (pass)" when it is 150 ml or more and less than 200 ml, and the evaluation is "B (pass)" when it is 100 ml or more and less than 150 ml. The evaluation was ``C (pass)'', and the evaluation in the case of less than 100 ml was ``D (fail)''.

As shown in Table 1, Comparative Examples 1 and 2 have a small H30/H0 value and do not function as a filter when large pressure is applied (low filtration performance (performance related to filtration life)). , Examples 1 to 5 have a large H30/H0 value and function effectively as a filter even when a large pressure is applied (high filtration performance (performance related to filtration life)), that is, the present invention was implemented. It was confirmed that by doing so, a nonwoven fabric 10 with good performance could be obtained.

10 Nonwoven fabric 10A First surface 10B Second surface 11 Fiber 14 Gap 15 Nonwoven fabric manufacturing equipment 16 Fiber material 17 Solvent 18 Thermosetting material 23 Solution adjustment section (addition process)
23a Solution 24 Nonwoven Fabric Manufacturing Department 25 Nozzle Unit 25a Nozzle 26 Accumulating Part 27 Power Supply 30 Support 40 Heating Part (Curing Step)
42 Saponification department (saponification process)
44 Drying section (drying process)
52 Collector 57 Support supply section 58 Support winding section 61, 62 Roller

Claims (11)

In a nonwoven fabric in which the intertwined structure of fibers is continuous in the thickness direction,
The average linearity of the fiber is within the range of 0.1 μm or more and 5.0 μm or less,
The thickness is within the range of 0.1 mm or more and 50 mm or less,
the porosity is at least 90%,
The average pore diameter is within the range of 0.5 μm or more and 50 μm or less,
When the thickness when applying a pressure of 30 kPa is H30, and the thickness when no load is H0, H30/H0 is within a range of greater than 0.1 and less than or equal to 0.5,
the fiber is formed of a cellulosic polymer;
the fiber contains a thermosetting polymer;
The thermosetting polymer is an epoxy resin,
The nonwoven fabric , wherein the thermosetting polymer content is at least 10 PHR . The nonwoven fabric according to claim 1, wherein H30/H0.5 is in the range of 0.25 or more and 0.75 or less, where H0.5 is the thickness when a pressure of 0.5 kPa is applied. The nonwoven fabric according to claim 1 or 2 , wherein the cellulose-based polymer is cellulose acylate. The nonwoven fabric according to any one of claims 1 to 3 , having a critical wet surface tension of 70 mN/m or more. A nonwoven fabric manufacturing method in which a voltage is applied between a solution in which a fiber material is dissolved in a solvent and a collector, and fibers formed by ejecting the solution from a nozzle are collected on the surface of the collector,
an addition step of adding a thermosetting polymer to the solution;
a curing step of thermosetting the thermosetting polymer ;
the fiber is formed of a cellulosic polymer;
the fiber contains a thermosetting polymer;
The thermosetting polymer is an epoxy resin,
The method for producing a nonwoven fabric , wherein the content of the thermosetting polymer is at least 10 PHR . 6. The nonwoven fabric manufacturing method according to claim 5 , wherein the cellulose-based polymer is cellulose acylate. The nonwoven fabric manufacturing method according to claim 5 or 6 , wherein the solvent is a mixture of a plurality of compounds. The nonwoven fabric manufacturing method according to claim 7 , wherein the solvent includes dichloromethane and methanol. The nonwoven fabric manufacturing method according to any one of claims 5 to 8 , further comprising a saponification step, which is a step after the curing step, of saponifying the fibers to make them hydrophilic. The nonwoven fabric manufacturing method according to any one of claims 5 to 8 , further comprising a drying step of freezing and drying the fibers, which is a step after the curing step . A liquid filter using the nonwoven fabric according to any one of claims 1 to 4 .

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