JP7163363B2 - fiber sheet - Google Patents

Description

The present invention relates to a fiber sheet and a method for manufacturing a fiber sheet.

Fiber sheets made of fibers are known. Fibers include, for example, so-called nanofibers having nano-order diameters of several nanometers or more and less than 1000 nm, and so-called microfibers having micrometer-order diameters of several micrometers or more and less than 1000 micrometers.

As a fiber sheet, for example, in Patent Document 1, a plurality of nanofibers made of a thermoplastic resin (thermoplastic polymer) and lumps generated by adhesion of the nanofibers, and a lump satisfying a predetermined condition are disclosed. , a nanofiber sheet containing more than a predetermined amount per unit area. This nanofiber sheet has pores with a diameter of 5 μm or less formed between the nanofibers.

Such fiber sheets are actively being developed for use in various fields. Expected applications include, for example, filters, which include solid-gas separation filters that separate solids and gases, and solid-liquid separation filters that separate solids and liquids.

By the way, an electrospinning method is known as a method for manufacturing fibers such as nanofibers and fiber sheets. The electrospinning method is also called an electrospinning method, as described in Patent Document 1, and is performed using, for example, an electrospinning apparatus (also called an electrospinning apparatus) having a nozzle, a collector, and a power source. In this electrospinning apparatus, a voltage is applied between the nozzle and the collector by a power source, for example, the nozzle is negatively charged and the collector is positively charged.

When the raw material solution is ejected from the nozzle while a voltage is applied, a cone-shaped projection called Taylor cone formed from the solution is formed at the opening at the tip of the nozzle. When the applied voltage is gradually increased and the Coulomb force exceeds the surface tension of the solution, the solution is ejected from the tip of the Taylor cone to form a spinning jet. The spinning jet moves to the collector by Coulomb force, is collected as fibers on the collector, and forms a fiber sheet composed of fibers on the collector. The fiber sheet thus obtained is sometimes subjected to heat treatment, and Patent Document 1 also performs heat treatment.

JP 2016-199828 A

Filters are required to have filtration accuracy, which is separation performance, but the fiber sheet described in Patent Document 1 has insufficient filtration accuracy when used for filtration. In addition, the filter is required to have durability, but the fiber sheet described in Patent Document 1 may detach the fiber pieces when used for filtration.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a fiber sheet excellent in filtration accuracy and in which detachment of fiber pieces is suppressed, and a fiber sheet manufacturing method for manufacturing the fiber sheet.

The fiber sheet of the present invention is made of fibers and has pores. The average pore diameter of the pores is in the range of 6.1 μm or more and 20 μm or less. At least 90% of the pores have a pore diameter within the range of DA x 0.80 to DA x 1.20, where DA is the average pore diameter, and the fiber is a cellulose acetate polymer. Formed from pionate or cellulose acetate butyrate.

The angle between the fiber and the sheet surface of the fiber sheet is θ, and when 0°≦θ≦90°, θ is preferably 20° or less.

According to the present invention, it is possible to obtain a fiber sheet having excellent filtration accuracy and suppressing detachment of fiber pieces.

1 is a schematic perspective view of a fiber sheet that is one embodiment of the present invention; FIG. It is explanatory drawing of the angle (theta) to make. 1 is a schematic diagram of sheet material forming equipment; FIG. 1 is a schematic diagram of a sheet material forming device; FIG. 1 is a schematic diagram of a temperature control device; FIG. 1 is an SEM (Scanning Electron Microscope) image of the fiber sheet obtained in Example 1. FIG. 4 is an SEM image of the fiber sheet obtained in Comparative Example 2. FIG.

The fiber sheet 10 of this embodiment shown in FIG. 1 is formed of fibers 11 . However, the fiber sheet only needs to contain the fibers 11, and in addition to the fibers 11, other fibers made of different materials may be provided. In FIG. 1 , the XY plane is the film surface of the fiber sheet 10 and Z is the thickness direction of the fiber sheet 10 .

The diameter of the fiber 11 is approximately 1.8 μm in this embodiment, but is not particularly limited. When the fiber sheet 10 is used as a filter for solid-gas separation or solid-liquid separation, the diameter of the fiber 11 is preferably in the range of 0.1 μm or more and 5 μm or less. This is because detachment of the fiber piece is further suppressed. Suppression of detachment of the fiber pieces means that detachment of the fiber pieces from the fiber sheet 10 is suppressed, and suppression of detachment of the fiber pieces leads to excellent durability. In order to avoid complication of the drawing, FIG. 1 shows only a portion of one sheet surface side in the thickness direction Z of the fiber sheet 10 . Therefore, the fiber sheet 10 has a structure in which a large number of fibers 11 are stacked in the thickness direction Z. As shown in FIG.

The thickness of the fiber sheet 10 is preferably in the range of 5 μm to 5000 μm, more preferably in the range of 10 μm to 3000 μm, and even more preferably in the range of 20 μm to 1000 μm. In this example, the thickness is set to 50 μm.

The fiber sheet 10 has a plurality of holes 12 . The holes 12 are formed in the voids defined by the fibers 11 so as to pass through the fiber sheet 10 in the thickness direction Z. As shown in FIG. Therefore, some of the voids do not form the voids 12 penetrating in the thickness direction Z, but exist as spatial regions closed by the fibers 11 , for example, non-penetrating in the thickness direction Z. FIG.

Here, the average pore diameter of the plurality of pores 12 is DA (unit: μm). The average pore diameter DA is in the range of 2 μm or more and 20 μm or less. When the average pore diameter DA is 2 μm or more, compared with the case where the average pore diameter DA is less than 2 μm, when the fiber sheet 10 is used as, for example, a filtering filter, the throughput per unit time is increased. A high throughput per unit time means a high filtration efficiency. When the average pore diameter DA is 20 μm or less, detachment of fiber pieces is suppressed when used as a filtering filter, for example, compared to the case where the average pore diameter DA is larger than 20 μm. The average pore diameter DA is more preferably in the range of 3 µm or more and 15 µm or less, and further preferably in the range of 4 µm or more and 10 µm or less.

The average pore diameter DA can be obtained by the following method. First, a 5 cm square (5 cm×5 cm) is cut from the fiber sheet 10 to obtain a sample. After immersing this sample in GALWICK (manufactured by POROUS MATERIAL) having a surface tension of 15.3 mN/m, the average pore diameter DA was measured by the bubble point method using a perm porometer (manufactured by POROUS MATERIAL). can get.

Among the plurality of pores 12, the percentage of pores 12 having a pore diameter within the range of DA x 0.80 or more and DA x 1.20 or less (hereinafter referred to as a predetermined pore percentage) is at least 90%, that is, 90% That's it. As described above, since the pore size distribution of the pores 12 is very small, separation is achieved with excellent filtration accuracy when used as a filter for filtration. The predetermined pore ratio (unit: %) is more preferably 95% or more, more preferably 98% or more, and the closer to 100%, the more preferable.

The predetermined pore ratio was calculated from the sum (amount) of the pores 12 having DA×0.80 or more and DA×1.20 or less with respect to the pore size distribution obtained from a perm porometer (manufactured by POROUS MATERIAL). . Specifically, using the pore size distribution (correlation data between the pore size and the abundance of pores having the pore size) output by the perm porometer, the range of DA × 0.80 or more and DA × 1.20 or less The ratio of the amount of pores having a pore diameter to the total amount of pores was determined as the predetermined ratio of pores.

It is preferable that the fibers 11 are adhered to each other at portions where they overlap in the thickness direction Z and/or where they are in contact with each other in the sheet surface direction (in the XY plane) of the fiber sheet 10. there is Thus, the fibers 11 are fixed together. By this fixation, the fiber sheet 10 further suppresses detachment of the fiber pieces.

The fiber 11 is made of a polymer, more specifically a thermoplastic resin (polymer). The thermoplastic resin of this example is the cellulosic polymer 15 (see FIG. 3). The cellulosic polymer 15 is preferably cellulose acylate. Cellulose acylate is a cellulose ester in which some or all of the hydrogen atoms constituting the hydroxy groups of cellulose are substituted with acyl groups.

Cellulose acylate includes cellulose acetate propionate (hereinafter referred to as CAP, melting point Tm is 188° C. or higher and 210° C. or lower, glass transition point Tg is 147° C.) and cellulose acetate butyrate (hereinafter referred to as CAB, melting point Tm is 195° C. or higher and 205° C. or lower, glass transition point Tg is 141° C.) or cellulose triacetate (hereinafter referred to as TAC, melting point Tm is 290° C., glass transition point Tg is 200° C.) preferable. As a result, even under high temperature conditions of, for example, 100° C. or higher and 140° C. or lower, the filter can be used as a filter with high filtration accuracy and high durability.

2, fibers 11a, 11b, 11c, . . . extend in a direction along one sheet surface (hereinafter referred to as first sheet surface) 10A. The direction along the first sheet surface 10A may be extended with an in-plane component parallel to the first sheet surface 10A, and may be curved within the plane. The other sheet surface (not shown, hereinafter referred to as a second sheet surface) may be considered parallel to the first sheet surface 10A. Therefore, the fibers 11a, 11b, 11c, . . . also extend in the direction along the second sheet surface. The fibers 11a, 11b, 11c, .

The angle formed by the fiber 11 and the first sheet surface 10A is assumed to be θ (unit: °). However, the angle θ to be formed is defined within the range of 0° or more and 90° or less, that is, 0°≦θ≦90°. The angle θ formed is preferably 20° or less, and thus extends in the direction along the first sheet surface 10A. In FIG. 2, the angle .theta. is shown only for the fiber 11b in order to avoid complication of the drawing, but the other fibers 11b, 11c, . . . The angle θ formed is more preferably 15° or less, and even more preferably 10° or less.

The angle θ to be formed can be determined using a SEM (Scanning Electron Microscope) image, and is also determined by this method in this example. First, the fiber sheet 10 is cut in the thickness direction, and an SEM image is observed. When an image is observed, a portion of one fiber 11 in the longitudinal direction is observed as a line segment. Twenty such linear fiber portions are arbitrarily selected, and the angles θ1, θ2, θ3, . The average value of these 20 measured angles is obtained by the formula (θ1+θ2+θ3+ . It is preferable that the 20 fibers selected from the image have the largest possible angle θ among the fiber portions to be observed.

According to the above configuration, since the filtration accuracy is excellent and detachment of the fiber pieces is suppressed, it is suitable as a filter for separating or removing a target substance from a mixture of solid and liquid (solid-liquid mixture). can be used. Among such filters, filters that can be particularly preferably used are those for food (including beverages), medical, and ultra-high-precision filters that are concerned about contamination of fiber pieces and require high-precision separation performance. Filters for pure water and high-purity chemicals. Specific examples include filters for removing fine particles and/or microorganisms from beverages, filters for pretreatment of industrial pure water, and filters for inspection that collect specific cells from bodily fluids such as blood and saliva. . Examples of test filters include blood sugar test, urine sugar test, lifestyle disease test, gene test, tumor marker test, blood test, and the like.

The fiber sheet 10 is manufactured by a manufacturing method having a sheet material forming process and a fiber sheet forming process. The sheet material forming step forms the sheet material 16 (see FIG. 3). Sheet material 16 is a precursor of fiber sheet 10 . The fiber sheet forming step forms the fiber sheet 10 from the sheet material 16 .

The sheet material forming equipment 20 shown in FIG. 3 is for forming the sheet material 16 using an electrospinning method. The sheet material forming equipment 20 includes a solution preparing section 21 and a sheet material forming device 22 . The details of the sheet material forming device 22 are shown in another drawing, and only a part of the sheet material forming device 22 is shown in FIG.

The solution preparation section 21 prepares the solution 25 for forming the fiber 11 . The solution preparation unit 21 prepares the solution 25 by dissolving the cellulosic polymer 15 in the cellulosic polymer solvent 26 .

In this embodiment, a mixture of dichloromethane and methanol is used as solvent 26 . When cellulose acylate is used as the cellulosic polymer 15, the solvent 26 includes methanol, ethanol, isopropanol, butanol, benzyl alcohol, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, and methyl formate. , ethyl formate, hexane, cyclohexane, dichloromethane, chloroform, carbon tetrachloride, benzene, toluene, xylene, dimethylformamide, N-methylpyrrolidone, diethyl ether, dioxane, tetrahydrofuran, 1-methoxy-2-propanol and the like. These may be used alone or in combination, depending on the type of cellulose acylate.

In this example, the sheet material forming equipment 20 includes pipes 33a to 33c that connect the solution preparation unit 21 and the sheet material forming apparatus 22, and the sheet material forming apparatus 22 is provided with nozzles 36a to 36c that are spaced apart from each other. 36c. The pipes 33a-33c are for guiding the solution 25. As shown in FIG. Pipe 33a connects solution preparation section 21 and nozzle 36a, pipe 33b connects solution preparation section 21 and nozzle 36b, and pipe 33c connects solution preparation section 21 and nozzle 36c. Thereby, the solution 25 is discharged from each of the nozzles 36a to 36c. The solutions 25 exiting the nozzles 36a-36c form fibers 11, respectively. In the following description, the pipes 33a, 33b, and 33c are referred to as pipes 33 when not distinguished from each other. The nozzles 36a, 36b, and 36c are referred to as nozzles 36 when not distinguished from each other.

In this example, a long support member 37 is used for stacking the fibers 11 and supporting the sheet material 16, and the support member 37 is moved in the longitudinal direction. Although the details of the support 37 will be described later with reference to another drawing, the horizontal direction in FIG. 3 is the width direction of the support 37, and the depth direction of FIG. The nozzles 36a to 36c are arranged side by side in the width direction of the support 37 in this order. Although the number of nozzles 36 is three in this example, the number of nozzles 36 is not limited to this. A pump 38 for sending the solution 25 to the nozzle 36 is provided in each of the pipes 33a to 33c. By varying the number of revolutions of pump 38, each flow rate of solution 25 exiting nozzles 36a-36c is adjusted.

The nozzles 36a-36c are held by a holding member 41. As shown in FIG. A nozzle unit 42 of the sheet material forming device 22 is configured by the holding member 41 and the nozzle 36 .

The sheet material forming device 22 will be described with reference to FIG. FIG. 4 shows a case viewed from the nozzle 36a side of FIG. 3, and only the nozzle 36a is shown for the nozzles 36 in order to avoid complication of the drawing. The sheet material forming device 22 includes a spinning chamber 45, the aforementioned nozzle unit 42, a stacking section 50, a power source 51, and the like. The spinning chamber 45 accommodates, for example, the nozzle unit 42 and part of the collecting section 50, and is configured to be hermetically sealed to prevent the solvent gas from leaking to the outside. The solvent gas is the vaporized solvent 26 of the solution 25 .

The nozzle unit 42 is arranged in the upper part inside the spinning chamber 45 . The tip of the nozzle 36 from which the solution 25 exits is directed toward a collector 52 located below the nozzle 36 in FIG. When the solution 25 exits from an opening formed at the tip of the nozzle 36 (hereinafter referred to as tip opening), the solution 25 forms a generally conical Taylor cone 53 at the tip opening.

The stacking section 50 is arranged below the nozzle 36 . The stacking section 50 has a collector 52 , a collector rotation section 56 , a support supply section 57 , and a support winding section 58 . The collector 52 attracts the solution 25 coming out of the nozzle 36 and collects the formed fibers 11 as the sheet material 16. In this embodiment, it is collected on a support 37, which will be described later.

The collector 52 is composed of an endless belt made of a strip of metal. The collector 52 may be made of a material that is charged when a voltage is applied by the power source 51, such as stainless steel. The collector rotating section 56 is composed of a pair of rollers 61 and 62, a motor 60, and the like. The collector 52 is horizontally stretched over a pair of rollers 61 and 62 . A motor 60 arranged outside the spinning chamber 45 is connected to the shaft of one roller 61 to rotate the roller 61 at a predetermined speed. This rotation causes the collector 52 to move and circulate between the rollers 61 and 62 . In this embodiment, the moving speed of the collector 52 is set to 0.2 m/min, for example, but it is not limited to this.

A support 37 made of a strip-shaped aluminum sheet is supplied to the collector 52 by a support supply section 57 . The support 37 is for stacking the fibers 11 to obtain the sheet material 16 . The support supply section 57 has a delivery shaft 57a. A support roll 63 is attached to the delivery shaft 57a. The support roll 63 is configured by winding the support 37 around a winding core 64 . The support winding section 58 has a winding shaft 67 . The winding shaft 67 is rotated by a motor (not shown) to wind the supporting body 37 on which the sheet material 16 is formed on the set winding core 68 . Thus, the sheet material forming apparatus 22 has a function of forming the fibers 11 and a function of forming the sheet material 16, and the fibers and sheet material are produced by the electrospinning method. Note that the support 37 may be placed on the collector 52 and moved by the movement of the collector 52 .

The sheet material 16 may be formed by directly stacking the fibers 11 on the collector 52, but depending on the material forming the collector 52 or the surface condition of the collector 52, the fiber sheet 10 may stick to the collector 52. It may be difficult to remove. For this reason, it is preferable to guide the support 37 to which the sheet material 16 is less likely to stick onto the collector 52 and collect the fibers 11 on this support 37 as in the present embodiment.

Power supply 51 applies a voltage to nozzle 36 and collector 52, thereby charging nozzle 36 to a first polarity and collector 52 to a second polarity opposite to the first polarity. Department. By passing through charged nozzle 36, solution 25 is charged and exits nozzle 36 in a charged state. In this example, the holding member 41 and the nozzle 36 are electrically connected, and the voltage is applied to the nozzle 36 via the holding member 41 by connecting the power source 51 to the holding member 41 . is not limited to this. For example, a voltage may be applied to each nozzle 36 by connecting a power supply 51 to each nozzle 36 . In this embodiment, the nozzle 36 is positively (+) charged and the collector 52 is negatively (-) charged, but the polarities of the nozzle 36 and the collector 52 may be reversed. It should be noted that the collector 52 side may be grounded to set the potential to zero. The solution 25 is spouted from the Taylor cone 53 as a spinning jet 69 toward the collector 52 by being charged by voltage application. In this example, the solution 25 is charged by applying voltage to the nozzle 36 , but the solution 25 may be charged in the pipe 33 and the charged solution 2 may be guided to the nozzle 36 .

An appropriate value for the distance L between the nozzle 36 and the collector 52 varies depending on the type of the cellulose polymer 15 and the solvent 26, the mass ratio of the solvent 26 in the solution 25, etc., but it is preferably in the range of 30 mm or more and 500 mm or less. In this embodiment, it is 150 mm, for example.

The voltage applied to the nozzle 36 and the collector 52 is preferably 5 kV or more and 200 kV or less, and from the viewpoint of forming the fiber 11 thin, the voltage is preferably as high as possible within this range. In this embodiment, it is set to 40 kV, for example.

The operation of the sheet material forming equipment 20 will be described. A voltage is applied by a power supply 51 to the nozzle 36 and the circulating collector 52 . This causes the nozzle 36 to be positively charged as a first polarity and the collector 52 to be negatively charged as a second polarity. The nozzle 36 is continuously supplied with the solution 25 from the solution preparation unit 21 , and the support 37 is continuously supplied onto the moving collector 52 . The solution 25 is charged positively, which is the first polarity, by passing through each of the nozzles 36a to 36c, and exits from each tip opening of the nozzles 36a to 36c in the charged state.

The collector 52 attracts the solution 25 exiting the tip opening while being charged to the first polarity. As a result, a Taylor cone 53 is formed at the tip opening, and a spinning jet 69 is ejected from the Taylor cone 53 toward the collector 52 . The spinning jet 69, which is charged to the first polarity, splits into smaller diameters due to repulsion by its own electric charge and/or stretches to smaller diameters in a helical trajectory while heading toward the collector 52. Then, the fibers 11 are collected as the sheet material 16 on the support 37 (collecting step).

In this example, the solution 25 is sprayed toward the support 37 by ejecting it from the nozzle 36, but the solution 25 may be sprayed by a method that does not use the nozzle. For example, there are an electro-bubble spinning method, a wire fixed electrode method, and the like. The electro-bubble spinning method is a method in which a compressed gas is supplied to the solution 25 and a voltage is applied to the generated bubbles to cause the solution 25 to fly linearly from the surface of the bubbles to form the fibers 11. The method is introduced. The wire-fixed electrode method is a method of forming the fiber 11 by applying a solution to a wire whose both ends are fixed and applying a voltage between the wire and a collector. A fiber forming apparatus using this wire-fixed electrode method is sold, for example, by Elmarco.

A large amount of the solvent 26 is evaporated from the spinning jet 69 on the way to the collector 52 so that the fibers 11 on the support 37 do not adhere to each other even if they come into contact with each other, or, if they do adhere, the adhesive force is kept small. It is preferable to let

The collected fibers 11 are fed as a resilient sheet material 16 together with the support 37 to the support winding section 58 . The fiber sheet 10 is wound around the winding core 68 while overlapping the support 37 . After the winding core 68 is removed from the winding shaft 67 , the sheet material 16 is separated from the support 37 . The sheet material 16 obtained in this way is long, but may be cut into a desired size, for example, in this example as well, for example, by cutting into a circular shape.

The temperature control device 81 shown in FIG. 5 is for forming the fiber sheet 10 from the sheet material 16 . The temperature adjustment device 81 includes an accommodation section 82 and a temperature adjustment mechanism 83 . The accommodation portion 82 accommodates the sheet material 16 therein. Although the storage portion 82 of this example is provided with a mounting table 86 on which the sheet material 16 is placed, the configuration of the storage portion 82 is not particularly limited, and a commercially available constant temperature bath or the like may be used. The temperature control mechanism 83 adjusts the temperature inside the accommodation portion 82, thereby heating, cooling, or maintaining the sheet material 16 accommodated therein at a constant temperature. Note that, in the present embodiment, the temperature inside the storage portion 82 set by the temperature control mechanism 83 is regarded as the temperature of the sheet material 16 .

Fiber sheet 10 is formed from sheet material 16 in the following manner. First, the sheet material 16 is held by a frame (frame) 87 . The frame 87 is a tension imparting member that imparts tension to the sheet material 16 . A tension is applied to the sheet material 16 in the plane direction (the direction of the XY plane) (tension applying step). It is preferable that the tension is kept small enough to prevent wrinkles and slack in the sheet material 16 and that the area of the sheet material 16 (area of the surface along the XY plane) does not change as much as possible. The frame 87 has a circular shape and holds the sheet material 16 with the sheet material 16 exposed at the center. It is not limited to frame 87. However, the tensioning member preferably holds the entire perimeter of the sheet material 16 rather than a portion of the perimeter to more reliably prevent wrinkling and sagging during heating and cooling, which will be described later.

The sheet material 16 held by the frame 87 and being tensioned is stored in the storage portion 82 . The temperature control mechanism 83 heats the sheet material 16 through the storage portion 82 . The sheet material 16 is heated while being tensioned, and the fibers 11 are bonded to each other in the sheet material 16 whose temperature has risen, thereby obtaining the fiber sheet 10 (heating step). Thus, the tensioning step has a heating step.

By heating under tension, a fiber sheet 10 having an average pore diameter DA in the range of 2 μm or more and 20 μm or less and a predetermined pore ratio of 90% or more is obtained, and the formed angle θ is 20%. °. In addition, by bonding the fibers 11 to each other, detachment of the fiber pieces is suppressed during use such as filtration. It should be noted that the longer the heating process time, the smaller the angle θ formed. However, from the viewpoint of suppressing excessive melting of the fiber 11, the heating process time is preferably in the range of 10 seconds to 1200 seconds, more preferably in the range of 30 seconds to 900 seconds. preferable. The heating process time is the time during which the temperature of the sheet material 16 is maintained at the set temperature.

Here, the melting point of the cellulose-based polymer 15 is Tm (unit: °C), and the glass transition point is Tg (unit: °C). In the heating step, the sheet material 16 is preferably heated to a temperature between Tg and Tm. By heating to a temperature equal to or higher than Tg, the fibers 11 are softened compared to the case of heating to a temperature lower than Tg, making it easier for the fibers 11 to fuse together (bond by melting). Moreover, by heating to a temperature of Tm or less, compared with the case of heating to a temperature higher than Tm, excessive melting of the fiber 11 to form a film without voids or carbonization can be more reliably prevented. escape.

It is preferable that the tension applying step has a cooling step after the heating step. That is, it is preferable to cool the fiber sheet 10 obtained in the heating step (cooling step) while tension is applied. As a result, the predetermined pore ratio of the fiber sheet 10 can be easily maintained in the state immediately after the heating process. It is preferable to release the tension after the cooling step.

In this example, a circulating belt is used as the collector 52, but the collector is not limited to the belt. For example, the collector may be a fixed flat plate or a cylindrical rotating body. Even in the case of a flat or cylindrical collector, it is preferable to use a support 37 so that the sheet material 16 can be easily separated from the collector. When a rotating body is used, a cylindrical sheet material made of fibers is formed on the peripheral surface of the rotating body. Just cut it.

[Example 1] to [Example 7]
Using the sheet material forming equipment 20 and the temperature control device 81, the fiber sheets 10 were manufactured as Examples 1 to 7. The cellulosic polymer 15 used is described in Table 1 in the "Polymer" column. In Table 1, when the acyl group of the cellulose acylate used as the polymer is a propionyl group, it is described as "Pr", and when it is a butanoyl group, it is described as "Bu". The "acyl group content" (unit: % by weight) in Table 1 is the catalog value of Eastman Chemical Company.

The solvent 26 is a mixture of dichloromethane and methanol as described above, and the mass ratio of dichloromethane:methanol is 87:13. The concentration of the cellulosic polymer 15 in the solution 25 was set to 8% by mass. This concentration is determined by {M1/(M1+M2)}×100, where M1 is the mass of the cellulose-based polymer 15 and M2 is the mass of the solvent 26 .

A heating step was performed during the tensioning step. The temperature of the sheet material 16 set in the heating process and the time for which the temperature was maintained are described in the "Temperature" column and the "Time" column of the "Heating process" in Table 1. The average diameter of the fibers 11 was 1.8 μm. The average value of the diameters was obtained by measuring the diameters of 100 fibers 11 from an image taken with a scanning electron microscope and calculating the average value.

The obtained fiber sheet 10 was evaluated for filtration accuracy and detachment of fiber pieces. The evaluation method and evaluation criteria are as follows. Evaluation results are shown in Table 1. A SEM image of a cross section in the thickness direction of the fiber sheet 10 obtained in Example 1 is shown in FIG.

1. Filtration Accuracy 1% by mass of crosslinked acrylic polydisperse particles (manufactured by Soken Chemical Co., Ltd.) having an average particle size of 10 μm were dispersed in pure water, and filtered through a fiber sheet 10 . The particle size distribution of each liquid before and after filtration was measured using a particle size distribution analyzer (manufactured by BECKMAN COULTER Co., Ltd.). From the obtained particle size distribution before and after filtration, the capture rate of particles larger than the average pore diameter DA of the fiber sheet 10 is [{(number of particles before filtration)-(number of particles after filtration)}/(number of particles before filtration )]×100%, and evaluated according to the following criteria. A and B pass, C and D fail.
A: Capture rate is 85% or more.
B; Capture rate is 75% or more and less than 85%.
C; Capture rate is 65% or more and less than 75%.
D: Capture rate is 65% or less.

2. Separation of Fiber Pieces The fiber sheet 10 was attached to a stainless steel line holder (KS-47 manufactured by Advantech Co., Ltd.), and 1 L (liter) of pure water was filtered. The liquid after filtration (filtrate) was captured by a grid filter. The entire capture side surface of the grid filter was observed with a microscope, and the number of fiber pieces was counted and evaluated according to the following criteria. A and B pass, C and D fail. The results are shown in Table 1, "Detachment of fiber piece" column.
A; The number of fiber pieces was 0 or more and 5 or less.
B; The number of fiber pieces was 6 or more and 10 or less.
C; The number of fiber pieces was 11 or more and 20 or less.
D; The number of fiber pieces was 21 or more.

Furthermore, using the fiber sheet 10 obtained in Example 1, genetic testing was performed. Specifically, after filtering the human whole blood with the fiber sheet 10 obtained in Example 1, white blood cells remaining on the fiber sheet 10 are used, and paragraphs [0057] to [ 0061]. As a result, results similar to those of the example described in Japanese Patent No. 4058508 were obtained.

[Comparative Example 1] to [Comparative Example 4]
Comparative Examples 1 to 3 were obtained by not performing the heating process or changing the temperature of the sheet material 16 in the heating process. Moreover, Comparative Example 4 was carried out as a manufacturing method without a tension applying step.

Filtration accuracy and detachment of fiber pieces were evaluated by the same method and criteria as in the example. Evaluation results are shown in Table 1. A SEM image of the cross section in the thickness direction of the fiber sheet obtained in Comparative Example 2 is shown in FIG.

REFERENCE SIGNS LIST 10 fiber sheet 10A first sheet surface 11, 11a, 11b, 11c, . 33c Piping 36a to 36c Nozzle 37 Support 38 Pump 41 Holding member 42 Nozzle unit 45 Spinning chamber 50 Stacking unit 51 Power source 52 Collector 53 Taylor cone 56 Collector rotating unit 57 Support supplying unit 57a Sending shaft 58 Support winding unit 60 Motor 61, 62 Roller 63 Support roll 64 Winding core 67 Winding shaft 68 Winding core 69 Spinning jet 81 Temperature control device 82 Storage unit 83 Temperature control mechanism 86 Mounting table 87 Frame L Distance

Claims (2)

In a porous fiber sheet made of fibers,
The average pore diameter of the pores is in the range of 6.1 μm or more and 20 μm or less,
Where the average pore diameter is DA, the percentage of the pores having a pore diameter within the range of DA x 0.80 or more and DA x 1.20 or less is at least 90%,
The fiber is a fiber sheet made of cellulose acetate propionate or cellulose acetate butyrate. 2. The fiber sheet according to claim 1, wherein .theta. is 20.degree. or less, where .theta. is the angle between the fiber and the sheet surface of the fiber sheet, and 0.degree..ltoreq..theta..ltoreq.90.degree.

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