JP6315691B2 - Method for evaluating electrospinning apparatus - Google Patents

Description

  The present invention relates to a method for evaluating an electrospinning apparatus.

  The electrospinning method (electrospinning method) is attracting attention as a technology that can relatively easily manufacture a nano-sized diameter fiber (hereinafter referred to as nanofiber) without using mechanical force or thermal force. In the electrospinning method that has been performed so far, a solution of a substance that is a raw material for nanofibers is filled in a syringe, a needle-like nozzle attached to the syringe, and a collection electrode facing the needle-like nozzle The operation of discharging the solution from the tip of the nozzle is performed under the condition that a high DC voltage is applied during the period. The discharged solution is stretched by Coulomb force, the solvent is instantly evaporated, and nanofibers are formed while the raw material is solidified. The nanofibers are deposited on the surface of the collecting electrode.

In order to increase the productivity of nanofiber manufacturing, many companies and research institutions have been developing technologies to improve the productivity of nanofiber manufacturing, and the shape of electrodes and nozzles of electrospinning equipment. Various ingenuity has been applied to materials and materials.
For example, in Patent Document 1, a metal ball having a small diameter, a metal spinning nozzle arranged with a small distance between the metal ball and the nozzle opening, and a path between the metal ball and the spinning nozzle opening are orthogonal to each other. A plurality of units consisting of high-speed air flow nozzles that inject high-speed air currents are arranged in parallel, and a high voltage is applied between the metal sphere and the spinning nozzle to generate nanofibers that are scattered from the plurality of units. A nanofiber manufacturing method is disclosed in which fibers are collected and collected by a nanofiber collecting section.

  Patent Document 2 discloses a nanofiber manufacturing apparatus having an outflow body in which a large number of outflow holes are provided on the side surface of a conductive cylinder having a diameter of 10 mm to 300 mm. Then, a voltage is applied between the effluent and an electrode provided with an insulator layer on the surface facing the effluent to form a nanofiber, and two collecting electrodes (attracting electrodes) having opposite polarity potentials. ) Attracts nanofibers and collects them on the material to be deposited. The thin insulator layer with a thickness of 0.2 mm can prevent the nanofiber from adhering to the electrode, and can change the charged state of the nanofiber and efficiently use the two collecting electrodes (attracting electrodes). Can collect.

However, the verification of the effect of the electrospinning device that devised the shape and material of the electrodes and nozzles was prepared by preparing a polymer solution in which a polymer and a solvent were mixed or dispersed as the raw material solution for spinning, and actually carrying out a spinning experiment. Is done by doing. That is, a nonwoven fabric composed of ultrafine fibers such as nanofibers obtained by actual spinning is sampled and directly observed with an electron microscope or the like, and the resulting fiber diameter, fiberization rate, appearance Etc. are generally used as indicators.
However, such a conventional effect verification method requires a lot of time and labor. For example, when observing with an electron microscope, since the field of view is narrowed because the observation is performed at a high magnification, the range that can be simultaneously observed or evaluated is limited. In order to evaluate, it is necessary to observe a wide and many places, and it takes an enormous amount of time.

JP 2012-107364 A JP 2010-59557 A

  Therefore, the subject of this invention is providing the evaluation method of the electrospinning apparatus which can evaluate the performance of an electrospinning apparatus simply.

  The present invention relates to a method for evaluating an electrospinning apparatus including a nozzle and an electrode, and supplies water to the nozzle while applying a DC voltage and forming an electric field between the electrode and the nozzle. Then, the dripped water is collected from the tip of the nozzle, and the dripped water is collected in a metal container, and the charge amount of the collected water is measured with a charge meter, and the measured value and the dripped or collected water are measured. The present invention provides an evaluation method for an electrospinning apparatus that calculates the amount of charge per unit mass of water from the mass and evaluates the electrospinning apparatus using the obtained amount of charge per unit mass of water as an index.

  According to the method for evaluating an electrospinning apparatus of the present invention, the performance of an electrospinning apparatus used for nanofiber production or the like can be easily evaluated.

FIG. 1 is a schematic diagram showing an example of an electrospinning apparatus for evaluating performance in an embodiment of the method for evaluating an electrospinning apparatus of the present invention and an example of an evaluation apparatus used in an embodiment of the present invention. Fig.2 (a) is a side view which shows the nanofiber manufacturing apparatus which is an example of the electrospinning apparatus of evaluation object, FIG.2 (b) is a front view in Fig.2 (a). FIG. 3 is a cross-sectional view showing an example of a nozzle structure in the nanofiber manufacturing apparatus shown in FIG. FIG. 4 is an exploded perspective view showing a nanofiber manufacturing apparatus which is another example of the electrospinning apparatus to be evaluated. FIG. 5 is a schematic diagram showing a cross-sectional structure of the nanofiber manufacturing apparatus shown in FIG. FIG. 6 is a schematic diagram showing another example of the electrospinning apparatus to be evaluated by the evaluation method of the present invention together with an example of the evaluation apparatus shown in FIG. FIG. 7 is a graph showing the relationship between the elapsed time from the start of water dripping and the integrated value of the charge amount. FIG. 8A is a scanning electron micrograph of a nanofiber manufactured by a nanofiber manufacturing apparatus with a low charge amount per unit mass of water, and FIG. 8B is a charge per unit mass of water. It is the scanning electron micrograph of the nanofiber manufactured with the nanofiber manufacturing apparatus with a high quantity.

The present invention will be described below based on preferred embodiments with reference to the drawings.
FIG. 1 shows an example of an electrospinning apparatus that evaluates performance in an embodiment of the method for evaluating an electrospinning apparatus of the present invention, and an example of an evaluation apparatus that is used in an embodiment of the present invention.
One embodiment of the present invention is an evaluation method of an electrospinning apparatus 10 including a nozzle 13 and an electrode 14 as shown in FIG. 1, and a DC voltage is applied as shown in FIG. Under the state where the electric field E was formed between the nozzle 13 and the metering liquid delivery device 2 such as a metering pump, water was supplied to the nozzle 13 and the water 4 was dropped from the tip of the nozzle and dropped. Water 4 is collected in a metal container 5. Then, the charge amount of the collected water (charged water) is measured by the charge amount measuring device 6. Then, the charge amount per unit mass of water is calculated from the measured value of the charge amount and the mass of the dropped or collected water. Then, the performance of the electrospinning apparatus 10 is evaluated using the obtained charge amount per unit mass of water as an index.

  An electrospinning apparatus for performing performance evaluation in one embodiment of the evaluation method of the present invention is, for example, a nanofiber manufacturing apparatus 10 shown in FIGS. 2 (a) and 2 (b). As shown in these drawings, the nanofiber manufacturing apparatus 10 basically employs a jet ESD method in which ESD (Electro-Spray Deposition) and a high-speed jet stream (jet) are combined. The manufacturing apparatus 10 includes a raw material injection unit 11 for injecting a raw material liquid for producing nanofibers. The raw material injection unit 11 includes a liquid feeding unit 12 and a nozzle 13. The nozzle 13 is erected at the tip of the liquid feeding unit 12. The nozzle 13 is open at the vertical upper end, and the raw material liquid can be injected through the opening. The nozzle 13 is made of a conductive material such as metal and has conductivity. The liquid feeding unit 12 includes a metering pump (not shown), and can inject the raw material liquid from the nozzle 13 in an amount determined per unit time.

  The nozzle 13 is composed of a needle-like straight pipe. A raw material liquid can be circulated in the nozzle 13. The inner diameter of the nozzle 13 is, for example, 200 μm or more and 3000 μm or less, preferably 300 μm or more and 2000 μm. The outer diameter of the nozzle 13 is, for example, preferably from 300 μm to 4000 μm, and preferably from 400 μm to 3000 μm. By setting the inner diameter and outer diameter of the nozzle 13 within this range, the raw material liquid containing a polymer and having viscosity can be fed easily and quantitatively, and the electric field is concentrated in a narrow area around the nozzle. The raw material liquid can be charged efficiently.

  An electrode 14 is disposed at a position separated from the nozzle 13. Specifically, the electrode 14 is disposed facing the opening of the nozzle 13 at a position immediately above the opening of the nozzle 13. The electrode 14 is plate-shaped and has two flat portions and four side portions. One of these two flat portions (the lower surface in FIG. 2) faces the nozzle 13. The direction in which the nozzle 13 extends and the plane portion of the electrode 14 are substantially orthogonal. The electrode 14 is made of metal or the like and has conductivity. The distance (shortest distance) between the tip of the nozzle 13 and the electrode 14 is preferably set to 20 mm or more, particularly 30 mm or more. If it is narrower than this, the raw material liquid sprayed from the tip of the nozzle 13 and in the form of a fiber tends to adhere to the electrode 14. The distance between the tip of the nozzle 13 and the electrode 14 is set to, for example, 20 mm or more and 200 mm or less, preferably 30 mm or more and 100 mm or less.

  A DC voltage is applied between the nozzle 13 made of a conductive material and the electrode 14 by the voltage generating means 101 via the earth 102 and the metal conductor 103. The nozzle 13 is grounded as shown in FIG. On the other hand, a negative voltage is applied to the electrode 14. Therefore, the electrode 14 becomes a cathode and the nozzle 13 becomes an anode, and a voltage is generated between the electrode 14 and the nozzle 13 to form an electric field. In order to generate an electric field between the electrode 14 and the nozzle 13, a positive voltage may be applied to the nozzle 13 and the electrode 14 may be grounded instead of applying the voltage shown in FIG. . However, it is preferable to ground the nozzle 13 rather than applying a positive voltage to the nozzle 13 because an insulation measure can be simplified. The voltage generated by the voltage generating means 101 is changed to a DC voltage as long as the electrode 14 is kept at the cathode and the nozzle 13 is kept at the anode, that is, as long as the nozzle 13 is kept at a higher potential than the electrode 14. It may be a fluctuating voltage in which a voltage is superimposed. From the viewpoint of keeping the charge amount of the raw material liquid constant and producing nanofibers of uniform thickness, the voltage is preferably a DC voltage.

  A known device such as a high voltage power supply device can be used for the voltage generating means 101. The potential difference applied between the electrode 14 and the nozzle 13 is preferably 1 kV or more, particularly 10 kV or more from the viewpoint that the raw material liquid can be sufficiently charged. On the other hand, this potential difference is preferably 100 kV or less, particularly 50 kV or less, from the viewpoint of preventing discharge between the nozzle 13 and the electrode 14. For example, it is preferably 1 kV to 100 kV, particularly preferably 10 kV to 50 kV. When the voltage applied by the voltage generating means 101 is a variable voltage, the time average of the potential difference generated between the electrode 14 and the nozzle 13 is preferably within the above range.

  The manufacturing apparatus 10 further includes an air flow injection means 15. The air flow ejecting means 15 can eject a primary high-speed air flow. The airflow ejecting means 15 is disposed at a position where an airflow can be ejected between the nozzle 13 and the electrode 14. The nanofiber formed from the raw material liquid is positively charged and tends to extend from the nozzle 13 serving as the anode toward the electrode 14 serving as the cathode. The airflow ejected from the airflow ejecting means 15 changes the traveling direction of the nanofibers and transports the nanofibers in a direction in which the capturing means is present (the right direction in FIG. 2A) and stretches the nanofibers. It contributes to that.

  As the air flow ejected from the air flow ejecting means 15, for example, one dried by a dryer or the like to a humidity of 30% RH or less can be used. The air flow is preferably maintained at a constant temperature so that the state of the manufactured nanofibers is maintained constant. The wind speed of the air flow is preferably 20 m / sec or more, particularly 25 m / sec or more, for example. If it is slower than this, it becomes difficult to change the traveling direction of the nanofiber to the direction in which the collecting means is present against the electric field between the nozzle 13 and the electrode 14. The upper limit of the wind speed is, for example, preferably 60 m / sec or less, particularly 53 m / sec or less. If the wind speed is faster than this, the air flow may cause the fiber to break. The wind speed is preferably 20 m / sec or more and 60 m / sec or less, and particularly preferably 25 m / sec or more and 53 m / sec or less.

  In addition to the air flow injection means 15, the manufacturing apparatus 10 also includes a second air flow injection means 16. The second airflow injection means 16 injects a secondary high-speed airflow that is an airflow slower than the primary high-speed airflow over a wide range so as to include the primary high-speed airflow from the airflow injection means 15. Is. By injecting a large amount of the secondary high-speed air flow so as to include the primary high-speed air flow, the disturbance of the primary high-speed air flow can be suppressed, and the nanofiber can be stably manufactured.

  In the manufacturing apparatus 10, a collection unit that collects the nanofibers is disposed at a position facing the air flow injection unit 15 and the second air flow injection unit 16. In particular, a collecting electrode (not shown) can be arranged as part of the collecting means. The collection electrode can be a flat plate made of a conductive material such as metal. The plate surface of the collecting electrode and the air flow injection direction are substantially orthogonal. Further, as will be described later, the collecting electrode can be coated on the substantially entire surface with a covering with a dielectric exposed, more preferably on the entire surface. Here, the substantially entire surface means a surface occupying an area of 90% or more of the total surface area of the surface. The entire surface means a surface that occupies 100% of the total surface area of the surface. In order to attract positively charged nanofibers to the collecting electrode, a lower (negative) potential is applied to the collecting electrode than the nozzle 13 serving as the anode. In order to make the attraction more efficient, it is preferable to apply a lower (negative) potential than the electrode 14 which is a cathode. The lower limit of the distance (shortest distance) between the collecting electrode (electrode surface) and the tip of the nozzle 13 is preferably 100 mm or more, and more preferably 500 mm or more. If it is narrower than this, the nanofiber may not be sufficiently solidified before reaching the collecting electrode. The upper limit is preferably 3000 mm or less, more preferably 1000 mm or less. If it is wider than this range, the electric attraction force by the collecting electrode is weakened, and the collection rate of the nanofiber is lowered. For example, it is preferably 100 mm or more and 3000 mm or less, and more preferably 500 mm or more and 1000 mm or less.

  Furthermore, in the manufacturing apparatus 10 of the present embodiment, a collector (not shown) in which nanofibers are collected between the collection electrode and the nozzle 13 so as to be adjacent to the collection electrode. Can also be arranged as a collecting means. As a collector, insulators, such as a film, a mesh, a nonwoven fabric, and paper, can be used, for example.

  Furthermore, in the manufacturing apparatus 10 of the present embodiment, air exhaust means (not shown) that exhausts the injected air flow is disposed so as to face the air flow injection means 15 and the second air flow injection means 16. You can also. The air exhaust means is preferably arranged on the back side (the side farther from the nozzle 13) than the collection electrode described above. As the air exhaust means, for example, a known device such as a suction box can be used.

  In the nanofiber manufacturing apparatus 10 shown in FIG. 2, the surface facing the nozzle 13 (the bottom surface of the electrode 14 in the drawing) of the planar portion constituting the plate-like electrode 14 is covered with a dielectric exposed on the surface. It is covered with a body 17. In the case of FIG. 2, the covering 17 is made of a single kind of dielectric. The surface facing the nozzle is the surface of the electrode that can face from the tip of the nozzle (opening through which the raw material liquid is jetted). The covering 17 having a dielectric exposed on the surface is a covering in which almost the entire surface (90% or more area) is composed of only a dielectric. It is preferable that the entire surface (100% area) of the covering 17 is made of only a dielectric. The covering is a covering in which a dielectric is exposed on the surface and no conductor such as metal is present on the surface. A typical example is a covering made up of a single type of dielectric, but the covering may be a composite of multiple types of dielectrics, or the surface may be made up of only a dielectric. For example, it may be a composite containing metal particles or a metal or air layer in the inside (portion not exposed on the surface). In particular, an air layer may exist at a part of the joint between the electrode and the covering, but it is preferable that the electrode and the covering are in close contact from the viewpoint of strengthening the bonding between the electrode and the covering. There is no object that further covers the surface of the covering.

  In the electrode 14 shown in FIG. 2, only the surface facing the nozzle 13 is covered with the covering 17. In addition to this, a part of the surface not facing the nozzle 13 is also covered with a dielectric exposed on the surface. It is preferably covered with the body 17. Furthermore, it is preferable that the entire surface that does not face the nozzle 13 is covered with a covering 17 having a dielectric exposed on the surface. Here, the surface that does not face the nozzle is the surface of the electrode that cannot be faced from the tip of the nozzle (opening through which the raw material liquid is sprayed). More specifically, it is the surface of the electrode surface excluding the surface facing the nozzle.

  Dielectric materials used for the covering 17 include ceramic materials such as insulating materials such as mica, alumina, zirconia, and barium titanate, bakelite (phenol resin), nylon (polyamide), vinyl chloride resin, polystyrene, polyester, and polypropylene. And resin materials such as polytetrafluoroethylene and polyphenylene sulfide. Among these, it is preferable to use at least one insulating material selected from alumina, bakelite, nylon, and vinyl chloride resin, and it is particularly preferable to use nylon. As the nylon, various polyamides such as 6 nylon and 66 nylon can be used. Moreover, a commercial item can also be used as nylon. As such a commercial item, MC nylon (trademark) is mentioned, for example. The dielectric used for the covering 17 can contain an antistatic agent. By containing an antistatic agent, when the charged raw material liquid, nanofiber, or the like adheres to the covering 17, the charging of the covering 17 can be reduced. As the antistatic agent, known commercial products can be used. For example, Peletron (Sanyo Chemical Industry Co., Ltd.), Electro Stripper (Kao Corporation), Electro Master (Kao Corporation), Riquemar (RIKEN Vitamin ( Co., Ltd.), Riquet Master (RIKEN Vitamin Co., Ltd.) and the like can be used.

  The covering body 17 preferably covers the electrode 14 with a uniform thickness. The thickness of the dielectric exposed on the surface constituting the covering 17 is preferably 0.8 mm or more, particularly 8 mm or more. In addition, the said thickness points out the thickness of the coating body 17 (equal to the thickness of the coating body 17), when the coating body 17 is comprised from the single type or multiple types of dielectric material. When the covering 17 is a composite containing metal particles or a layer of metal or air in the inside (portion not exposed on the surface), the thickness of the dielectric existing between the surface and the metal or air is set. Shall point to. The upper limit value of the thickness of the covering 17 is preferably 20 mm or less, particularly preferably 15 mm or less.

  In the manufacturing apparatus, in addition to or instead of disposing the covering 17 on the entire surface of the electrode 14 facing the nozzle 13, substantially the entire outer surface of the nozzle 13 is dielectrically formed on the surface. It is also preferred to coat with an exposed body covering. Specifically, as shown in FIG. 3, the outer surface of the nozzle 13 is covered with a covering body 107. The covering 107 extends beyond the tip 13 a of the nozzle 13. The extending portion 107 a of the covering body 107 has a cylindrical shape surrounding the nozzle 13 and has a hollow portion. This hollow portion communicates with the inside of the nozzle 13. The outer surface of the nozzle 13 is the inner surface of the nozzle 13 in contact with the raw material liquid flowing through the nozzle 13, the surface of the tip 13 a of the nozzle 13 to which the raw material liquid is injected, and the nozzle 13 on the opposite side. It is the surface excluding the end surface. The covering 107 is made of a single type of dielectric. The nozzle 13 preferably covers the entire outer surface (90% or more area) with the covering 107, and more preferably covers the entire outer surface (100% area) of the nozzle 13 with the covering 107. It is also preferable to extend the covering 107 beyond the tip 13 a of the nozzle 13. As the dielectric constituting the covering 107 that covers the nozzle 13, the same dielectric as that constituting the covering 17 that covers the electrode 14 can be used. The dielectric can contain the same antistatic agent as used in the covering 17. The thickness of the covering 107 can be the same as the thickness of the covering 17 that covers the electrode 14.

  In one embodiment of the evaluation method of the present invention shown in FIG. 1, the extending direction of the nozzle 13 is substantially horizontal in the nanofiber manufacturing apparatus 10 shown in FIGS. 2 and 3 as shown in FIG. Thus, the manufacturing apparatus 10 is subjected to an evaluation test. As shown in FIG. 1, evaluating the state in which the nozzle 13 and the electrode 14 are separated from each other in a substantially horizontal direction has a low risk that charged water approaches the liquid feeding unit 12 and the electrode 14 and is affected. To preferred. Further, as shown in FIG. 1, it is preferable from the viewpoint of workability to dispose the metal container 5 vertically below the tip of the nozzle 13 and collect the water 4 dripped from the nozzle 13.

  In the evaluation method of the present embodiment, a potential difference is generated between the electrode 14 and the nozzle 13 by using the voltage generating means 101 provided in the manufacturing apparatus 10, thereby the electric field E between the electrode 14 and the nozzle 13. Is forming. Therefore, it is not necessary to prepare a separate high voltage power supply device for performance evaluation. However, the direct-current voltage applied between the electrode 14 and the nozzle 13 is 10 kV or less in absolute value from the viewpoint of preventing the charged water from scattering or fogging and reducing the amount of water collected in the metal container 5. Preferably, the absolute value is 5 kV or less. The difference between the amount of water supplied to the nozzle 13 and the amount of water recovered in the metal container 5 is preferably as small as possible from the viewpoint of measurement accuracy. In addition, the DC voltage applied between the electrode 14 and the nozzle 13 is preferably 0.5 kV or more in absolute value and more preferably 1.0 kV or more in absolute value from the viewpoint of measurement accuracy.

  In the evaluation method of this embodiment, in the state where the electric field E is formed between the electrode 14 and the nozzle 13, water is supplied to the nozzle 13 and dropped from the tip of the nozzle 13, and the dropped water is dropped into a metal container. Collect in 5. The supply of water to the nozzle 13 can be performed using the liquid feeding section 12 of the raw material injection means 11 provided in the manufacturing apparatus 10 by using water instead of the raw material liquid. FIG. 1 shows a quantitative liquid feeding device 2 such as a quantitative pump provided in the liquid feeding unit 12. When carrying out the evaluation method of the present invention, the metering pump used in the actual spinning may be used as it is, or it may be replaced with another metering pump and used.

  The water supply speed to the nozzle 13 is preferably 10.0 g / min or less, more preferably 5.0 g / min or less, from the viewpoint of dropping the liquid delivered from the nozzle as water droplets instead of a continuous water flow. More preferably, it is 2.0 g / min or less. Further, the water supply speed to the nozzle 13 is preferably 0.2 g / min or more, more preferably 0.5 g / min or more, from the viewpoint of measurement accuracy. When a continuous water flow from the nozzle 13 to the metal container 5 is formed, electrical communication occurs through the water flow, making it difficult to measure the amount of water in the metal container 5.

Various charge amount measuring devices 6 can be used for measuring the charge amount of water collected in the metal container 5. As the charge amount measuring device 6, for example, a coulomb meter (NK-1001, 1002) manufactured by Kasuga Electric can be used.
Further, as shown in FIG. 1, the measurement of the amount of water in the metal container 5 can be performed by placing the metal container 5 in a Faraday cage 61 made of a conductive material. Is preferable from the viewpoint of measuring the charge amount with high accuracy. In FIG. 1, reference numeral 51 is charged water, and reference numerals 62, 63 and 64 are metal probe wires connected to the tip of the measurement probe, the measurement probe, and the ground.

  In the present embodiment, a DC voltage is applied between the nozzle 13 and the electrode 14, and water is fed to the nozzle 13 at a predetermined speed while the electric field E is formed. Spill from. The charged water is dropped substantially vertically downward by gravity. The charge amount of water accumulated in the metal container 5 within a predetermined time (for example, within a few minutes) is measured, and the measured value is divided by the mass of the accumulated water to obtain the charge amount per unit mass of water (nC / G). The mass of the water accumulated in the metal container 5 is measured by, for example, removing the metal container 5 from the Faraday cage 61 after the measurement of the charge amount of the accumulated water and transferring it to the chemical balance. In addition, when the quantitative liquid feeding device 2 having excellent quantitative properties is used, the liquid feeding amount (g / min) per unit time is multiplied by the liquid feeding time (minutes), and the value is determined as the predetermined value. It can also be used as the amount of water dripped from the tip of the nozzle within the time or the mass of water collected in the metal container 5.

  In the present invention, the charge amount per unit mass of water is calculated from the measured value of the charge amount of the collected water and the mass of the dropped or collected water, and the charge amount per unit mass of the obtained water. The electrospinning apparatus is evaluated using as an index.

In the evaluation, it is usually judged that the performance is higher when the amount of charge per unit mass of water is higher, and the performance is judged lower when the amount of charge per unit mass of water is lower.
As described above, the charge amount of the collected water may be measured only once by dropping the water from the nozzle for a predetermined time, and then the charge amount of the collected water may be measured only once. It is preferable that the amount is measured at a plurality of points in the process of increasing the amount of water in the metal container, and the charge amount per unit mass of water is calculated using the measured values at the plurality of points. For example, as shown in FIG. 7, the plurality of measured values are obtained every minute, with the amount of water accumulated in the metal container (or the elapsed time from the start of dropping proportional to the horizontal axis) being the horizontal axis and the amount of charge being the vertical axis. Is plotted, and the slope obtained by drawing an approximate straight line by the least-squares method passing through intercept 0 in the obtained graph is defined as the charge amount per unit mass.

Examples of water used in the present invention include ion exchange water, distilled water, and ultrapure water. In the case of using a spinning liquid such as a normal spinning raw material for evaluating an electrospinning apparatus, the charged liquid adheres to the electrode, making it difficult to achieve an accurate mass, or ultrafine fibers to the electrode. The contact may cause the charge to disappear or be charged to the opposite polarity. In addition, since the amount of charge varies greatly depending on the degree of evaporation, measurement in a dry state is desirable, but it takes time until it becomes dry and measurable, and the charged state is maintained while waiting for it to become dry. It is extremely difficult to keep in mind, and is not suitable for high-precision measurements.
In addition, the use of water means that water is readily available, inexpensive, that no preparation is necessary, that preparation and cleanup are easy, harmless to the body, and between devices. There are advantages such as easy comparison.

  4 and 5 show another example of an electrospinning apparatus that performs performance evaluation in one embodiment of the evaluation method of the present invention. In addition, regarding the manufacturing apparatus 18 illustrated in FIGS. 4 and 5, the description regarding the manufacturing apparatus 10 illustrated in FIGS.

  The manufacturing apparatus 18 includes an electrode 19 and a raw material liquid injection nozzle 20. The electrode 19 has a concave spherical shape as a whole, and particularly has a substantially bowl shape. A concave curved surface R is provided on the inner surface. The electrode 19 having the concave curved surface R has a planar flange portion 19a at the position of the opening end. As long as the inner surface of the electrode 19 is a concave curved surface R, the outer surface of the electrode 19 does not need to have a substantially bowl shape, and may have another shape. The electrode 19 is made of a conductive material and is generally made of metal. The electrode 19 is fixed to a base 30 made of an electrically insulating material. Further, as shown in FIG. 5, the electrode 19 is connected to a DC high voltage power supply 40 which is a voltage generating means, and a negative voltage is applied thereto.

When the concave curved surface R is viewed from the opening end side, the opening end is circular. This circle may be a perfect circle or an ellipse. As will be described later, from the viewpoint of concentrating the electric field on the tip of the nozzle 20, the open end of the concave curved surface R is preferably a perfect circle. On the other hand, the concave curved surface R is a curved surface at any position. The curved surface referred to here is (a) a curved surface that does not have a flat surface portion at all, or (b) a shape that can be regarded as a concave curved surface as a whole by connecting a plurality of segments having a flat surface portion. Or (c) one of the three axes orthogonal to each other is connected to a plurality of annular segments having a belt-like portion with no curvature, and has a shape that can be regarded as a concave curved surface as a whole. Say. In the case of (b), for example, a concave curved surface R is formed by connecting segments having flat portions of the same or different sizes, which are rectangular with a vertical and horizontal length of about 0.5 to 5 mm. It is preferable.
In the case of (c), for example, it is preferable to form the concave curved surface R by connecting annular segments composed of a plurality of flat cylinders having different radii and heights of 0.001 to 5 mm. In this annular segment, among the three axes orthogonal to each other, that is, the X-axis, Y-axis, and Z-axis, the X-axis and Y-axis including the cross section of the cylinder have a curvature, and Z is the height direction of the cylinder. The axis has no curvature.
The distance (shortest distance) between the tip 20a of the nozzle 20 and the concave curved surface R can be made the same as the distance (shortest distance) between the tip of the nozzle 13 and the electrode 14 in the manufacturing apparatus 10.

  It is preferable that the concave curved surface R has a value such that the normal line at an arbitrary position passes through the tip of the nozzle 20 or the vicinity thereof. In this respect, it is particularly preferable that the concave curved surface R has the same shape as the inner surface of the true spherical shell. As shown in FIGS. 4 and 5, the bottom surface of the concave curved surface R is open, and the nozzle assembly 21 is attached to the opening.

  The nozzle assembly 21 includes the nozzle 20 described above and a support portion 22 that supports the nozzle 20. The nozzle 20 is made of a conductive material, and is generally made of metal. On the other hand, the support portion 22 is made of an electrically insulating material. Therefore, the electrode 19 and the nozzle 20 described above are electrically insulated by the support portion 22. The nozzle 20 is grounded. The tip 20 a of the nozzle 20 is exposed in the electrode 19 having a concave curved surface R. The nozzle 20 passes through the support portion 22, and the rear end 20 b of the nozzle 20 is exposed on the back side of the electrode 19 (that is, the side opposite to the concave curved surface R). The nozzle 20 does not necessarily have to pass through the support portion 22, and the rear end 20 b of the nozzle 20 may be positioned in the middle of the raw material liquid supply through hole provided in the support portion 22. The through hole for supplying the raw material liquid provided in the rear end 20b of the nozzle 20 or the support portion 22 is connected to a supply source (not shown) of the raw material liquid. The nozzle assembly 21 constitutes a raw material injection means together with a raw material supply source.

  In the manufacturing apparatus 18, as shown in FIGS. 4 and 5, an air flow injection means 23 including a through hole is provided in the vicinity of the base portion of the nozzle 20 in the nozzle assembly 21. The airflow ejection means 23 is formed along the direction in which the nozzle 20 extends. Further, the airflow ejecting means 23 is formed so as to be able to eject an airflow toward the tip 20a of the nozzle 20. When viewed from the opening end side of the electrode 19, two airflow ejection means 23 are provided so as to surround the nozzle 20. The airflow ejecting means 23 is formed at a symmetrical position with the nozzle 20 in between. The air flow injection means 23 comprising a through hole has an opening on the rear end side connected to an air flow supply source (not shown). By supplying air from this supply source, air is jetted from around the nozzle 20. The jetted air is sprayed from the tip 20a of the nozzle 20 and the raw material liquid elongated by the action of an electric field is applied to a collecting electrode (not shown) disposed at a position facing the airflow jetting means 23. Transport toward. 4 and 5 show a state in which two airflow ejecting means 23 are provided, the number of airflow ejecting means 23 is not limited to this, but one or three or more. It may be. Furthermore, the shape (cross-sectional shape) of the through-hole forming the air flow injection means is not limited to a circle, but may be a rectangle, an ellipse, a double ring, a triangle, a honeycomb, or the like. From the viewpoint of obtaining a uniform air flow, an annular through hole surrounding the nozzle is desirable.

  In the manufacturing apparatus 18, a covering 207 with a dielectric exposed on the surface is arranged on the entire surface of the electrode 19 that is a cathode, on the entire surface facing the nozzle 20 and on a portion of the surface not facing the nozzle 20. ing. The electrode 19 and the covering 207 are in direct contact. The covering body 207 has a hollow convex portion 207a having a shape complementary to the electrode 19 made of the concave curved surface R. The top of the convex portion 207a is open, and the nozzle assembly 21 is fitted into the opening. The convex portion 207 a covers the surface of the electrode 19 that faces the nozzle 20. The covering 207 has a flange portion 207b extending in the horizontal direction from the open end of the hollow convex portion 207a. The flange portion 207b covers a part of the surface of the electrode 19 that does not face the nozzle 20 (flange portion 19a). In a state where the covering body 207 is fitted to the concave curved surface R of the electrode 19, the electrode 19 and the covering body 207 are passed through bolts through the through holes formed in the flange portion 19a of the electrode 19 and the flange portion 207b of the covering body 207. Fix by bolting.

  As the dielectric constituting the covering 207 used in the present embodiment, the same dielectric as that constituting the covering 17 covering the electrode 14 can be used. And it is easy to use a molded body obtained by melt-molding various thermoplastic resins. The dielectric can contain the same antistatic agent as used in the covering 17. Further, the thickness of the covering 207 covering the electrode 19 can be the same as the thickness of the covering 17 covering the electrode 14.

When the manufacturing apparatus 18 shown in FIGS. 4 and 5 is evaluated, as shown in FIG. 6, the manufacturing apparatus 18 is arranged so that the extending direction of the nozzle 20 is vertically downward, and the evaluation shown in FIG. Evaluation is performed as in one embodiment of the method. More specifically, under a state in which a DC voltage is applied and an electric field is formed between the electrode 19 and the nozzle 20, water is supplied to the nozzle 20 by the metering device 2 such as a metering pump, and the nozzle 20 The water 4 is dropped from the tip, and the dropped water 4 is collected in the metal container 5. Then, the charge amount of the collected water (charged water) is measured by the charge amount measuring device 6. Then, the charge amount per unit mass of water is calculated from the measured value of the charge amount and the mass of the dropped or collected water. Then, the performance of the electrospinning apparatus 18 is evaluated using the obtained charge amount of water per unit mass as an index. The evaluation method shown in FIG. 6 is the same as the evaluation method shown in FIG. 1 except that it is not particularly described, and the above description is appropriately applied.
In addition, the nanofiber manufactured by the manufacturing apparatuses 10 and 18 described above generally has a thickness of 10 nm to 3000 nm, particularly 10 nm to 1000 nm, when the thickness is expressed by a circle-equivalent diameter. The thickness of the nanofiber can be measured, for example, by observation with a scanning electron microscope (SEM).

  In addition, as a raw material liquid used for manufacturing nanofibers in the manufacturing apparatuses 10 and 18 described above, a solution in which a polymer compound capable of forming a fiber is dissolved or dispersed in a solvent or a melt obtained by heating and melting a polymer compound is used. Can be used. The electrospinning method using a polymer solution as a raw material liquid is sometimes called a solution method, and the method using a polymer melt is sometimes called a melting method. The solution or melt can be appropriately mixed with inorganic particles, organic particles, plant extracts, surfactants, oil agents, electrolytes for adjusting ion concentration, and the like.

  Generally, as a polymer compound for producing nanofiber, polypropylene, polyethylene, polystyrene, polyvinyl alcohol, polyurethane, polyethylene oxide, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, poly-m-phenylene terephthalate, poly-p-phenylene isofura Tate, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl chloride, polyvinylidene chloride-acrylate copolymer, polyacrylonitrile, polyacrylonitrile-methacrylate copolymer, polycarbonate, polyarylate, polyester carbonate, nylon , Aramid, polycaprolactone, polylactic acid, polyglycolic acid, collagen, polyhydroxybutyrate , Polyvinyl acetate, polypeptides and the like. The polymer compound to be used is not limited to one type, and any plurality of types can be used in combination from the exemplified polymer compounds.

  When a solution in which a polymer compound is dissolved or dispersed in a solvent is used as the raw material liquid, the solvent includes water, methanol, ethanol, 1-propanol, 2-propanol, hexafluoroisopropanol, tetraethylene glycol, triethylene glycol, Dibenzyl alcohol, 1,3-dioxolane, 1,4-dioxane, methyl ethyl ketone, methyl isobutyl ketone, methyl-n-hexyl ketone, methyl-n-propyl ketone, diisopropyl ketone, diisobutyl ketone, acetone, hexafluoroacetone, phenol, Formic acid, methyl formate, ethyl formate, propyl formate, methyl benzoate, ethyl benzoate, propyl benzoate, methyl acetate, ethyl acetate, propyl acetate, dimethyl phthalate, diethyl phthalate, dipropyl phthalate, Methyl chloride, ethyl chloride, methylene chloride, chloroform, o-chlorotoluene, p-chlorotoluene, carbon tetrachloride, 1,1-dichloroethane, 1,2-dichloroethane, trichloroethane, dichloropropane, dibromoethane, dibromopropane, bromide Methyl, ethyl bromide, propyl bromide, acetic acid, benzene, toluene, hexane, cyclohexane, cyclohexanone, cyclopentane, o-xylene, p-xylene, m-xylene, acetonitrile, tetrahydrofuran, N, N-dimethylformamide, pyridine, etc. Can be illustrated. The solvent to be used is not limited to one type, and a plurality of arbitrary types may be selected from the exemplified solvents and mixed.

  In particular, when water is used as a solvent, it is preferable to use the following natural and synthetic polymers having high solubility in water. Examples of natural polymers include pullulan, hyaluronic acid, chondroitin sulfate, poly-γ-glutamic acid, modified corn starch, β-glucan, gluco-oligosaccharide, heparin, keratosulfuric acid and other mucopolysaccharides, cellulose, pectin, xylan, lignin, glucomannan. Galacturonic acid, psyllium seed gum, tamarind seed gum, gum arabic, tragacanth gum, soy water soluble polysaccharide, alginic acid, carrageenan, laminaran, agar (agarose), fucoidan, methylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose and the like. Examples of the synthetic polymer include partially saponified polyvinyl alcohol, low saponified polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene oxide, and sodium polyacrylate. These polymer compounds can be used alone or in combination of two or more. Among these polymer compounds, from the viewpoint of easy preparation of nanofibers, natural polymers such as pullulan and synthetic polymers such as partially saponified polyvinyl alcohol, low saponified polyvinyl alcohol, polyvinyl pyrrolidone and polyethylene oxide should be used. Is preferred.

  Moreover, although it is not highly soluble in water, it can be insolubilized after formation of nanofibers, partially saponified polyvinyl alcohol that can be crosslinked after formation of nanofibers in combination with a crosslinking agent, partially saponified polyvinyl alcohol, poly (N-propanoylethyleneimine) ) Oxazoline-modified silicones such as graft-dimethylsiloxane / γ-aminopropylmethylsiloxane copolymer, acrylic resin such as twein (main component of corn protein), polyester, polylactic acid (PLA), polyacrylonitrile resin, polymethacrylic acid resin, etc. , High molecular compounds such as polystyrene resin, polyvinyl butyral resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polyurethane resin, polyamide resin, polyimide resin, and polyamideimide resin are also used. Door can be. These polymer compounds can be used alone or in combination of two or more.

As mentioned above, although this invention was demonstrated based on the preferable embodiment, this invention is not restrict | limited to the said embodiment. For example, in the manufacturing apparatus shown in FIG. 2, the nozzle 13 may be a curved pipe having a curvature. 4 and 5, it is preferable that the concave curved surface R of the electrode 19 has the shape of the inner surface of the hemispherical spherical shell. Instead, for example, the shape of the inner surface of the spherical shell of the spherical crown It is good. Moreover, in embodiment shown in FIG.4 and FIG.5, although the nozzle 20 was arrange | positioned in the bottommost part of the concave curved surface R, you may arrange | position the nozzle 20 in the position of other than that.
The electrospinning apparatus to be evaluated in the present invention is not particularly limited as long as it is an electrospinning apparatus including a nozzle and an electrode, and may be those described in Patent Document 1 and Patent Document 2. In the apparatus of Patent Document 2, an outflow body in which a large number of outflow holes are provided on the side surface of the conductive cylinder corresponds to the nozzle.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, “%” and “part” mean “% by mass” and “part by mass”, respectively.

[Example 1]
In the manufacturing apparatus 10 shown in FIG. 2, as the configuration of the raw material injection means 11, those adopting the nozzle length, the nozzle inner diameter, and the liquid feeding member quality shown in Table 1 are set as apparatuses A to H, and the respective apparatuses A to H are used. For H, an evaluation test was performed using water as a model raw material liquid, and the amount of charge per unit mass of water (hereinafter, also simply referred to as “charge amount”) was measured. The nozzle length is a length indicated by a symbol L in FIG.

The method for measuring the charge amount is shown below. The area of the flat portion of the electrode 14 (the surface facing the nozzle 13) was 81 cm ² (9 cm long × 9 cm wide), and the entire surface was covered with a covering 17 made of a dielectric. The thickness of the dielectric was 10 mm. The distance (shortest distance) between the tip of the nozzle 13 and the electrode 14 was 50 mm.

[Measurement method of charge amount]
With respect to the manufacturing apparatus 10, as shown in FIG. 1, the entire apparatus was rotated 90 degrees so that the extending direction of the nozzle 13 was substantially horizontal. Then, a DC voltage of -5 kV is applied between the nozzle and the electrode with a high voltage generator (HAR-60R1-LF manufactured by Matsusada Precision Co., Ltd.), and the cylinder 13 is used to feed the nozzle 13 at a speed of 1.0 g / min. Water was supplied and water was dropped from the nozzle 13 at the same speed. A water droplet dropped substantially vertically downward by gravity was received by a metal container 5 placed in a Faraday cage 61 (NQ-1400 manufactured by Kasuga Denki). Water was dripped from the nozzle 13 for 6 minutes, and the charge amount of the water accumulated in the metal container 5 was measured every minute with a coulomb meter (NK-1001, 1002 manufactured by Kasuga Electric), and the measured value was recorded. . The metal container 5 was made of stainless steel. No air flow was injected from the air flow injection means 15 and the second air flow injection means 16.
FIG. 7 shows an example of a graph drawn when the charge amount is obtained. The measured length L of the nozzle 13 is 15 mm for shape 1 and 50 mm for shape 2. The nominal diameter of the nozzle 13 is 16G. Plot the charge amount (integrated value) per minute with the elapsed time on the horizontal axis and the charge amount on the vertical axis, and draw an approximate straight line by the least squares method passing through the intercept 0 on the graph obtained there. Asked. After measuring the amount of charge after 6 minutes, the metal container 5 was taken out and the mass of the water accumulated inside was measured with an analytical balance. As a result, the mass P (g) of the water accumulated in the metal container 5 and the nozzle 13 were measured. Since there was a deviation from the estimated mass of 6.0 g from the water supply speed (appropriate speed of water from the tip of the nozzle 13), the reciprocal of their ratio (P / 6) in the aforementioned inclination ( 6 / P), and the value after correction was defined as the charge amount (charge amount per unit mass of water). The corrected values are shown in Table 1.

[Evaluation]
In the result of the charge amount shown in Table 1, the nanofiber was manufactured using the device A having the maximum value under the same conditions as the device D having the maximum value and the material A. A 15% aqueous solution of pullulan was used as the raw material liquid. The speed at which the raw material liquid was sprayed from the nozzle 13 was 1.0 g / min. The area of the flat portion of the electrode 14 (surface facing the nozzle 13) was 81 cm ² (length 9 cm × width 9 cm), and the entire surface was covered with a covering 17 made of bakelite. The thickness of the bakelite was 10 mm. An air flow having a flow rate of 200 L / min was injected from the air flow injection means 15, and no air flow was injected from the second air flow injection means 16. The distance (shortest distance) between the tip of the nozzle 13 and the electrode 14 was 40 mm, and a voltage of −30 kV was applied between the nozzle 13 and the electrode 14. The obtained nanofiber was photographed with a scanning electron microscope (SEM), a photograph of the nanofiber obtained by the apparatus A is shown in FIG. 8 (a), and a photograph of the nanofiber obtained by the apparatus D is shown in FIG. 8 (b). It was shown to. Moreover, the average fiber diameter was about 500 nm in FIG. 8A and about 200 nm in FIG. 8B.

According to the method for evaluating an electrospinning apparatus of the present invention, the nozzles of the electrospinning apparatus are replaced as described above, and an evaluation test as in Example 1 is performed for each of a plurality of apparatuses having different nozzles. By calculating the amount of charge per unit mass, it is possible to evaluate the performance of the nozzle of the electrospinning apparatus using the amount of charge.
In the electrospinning apparatus evaluation method of the present invention, instead of the nozzle, the electrode of the electrospinning apparatus is replaced, and each of a plurality of apparatuses having different electrodes is subjected to an evaluation test as in Example 1. You can also. Also in this case, by calculating the charge amount per unit mass of water for each of the plurality of devices, the performance of the nozzle of the electrospinning device can be evaluated using the charge amount. The different electrodes referred to here include not only the shape, material, and thickness of the electrode, but also the shape, material, thickness, and the like of the dielectric covering the electrode.

DESCRIPTION OF SYMBOLS 1 Evaluation apparatus 5 Metal container 6 Charge measuring device 10, 18 Nanofiber manufacturing apparatus (electrospinning apparatus)
DESCRIPTION OF SYMBOLS 11 Raw material injection means 12 Liquid feeding part 13,20 Nozzle 14,19 Electrode 15,23 Airflow injection means 16 2nd airflow injection means

Claims (6)

An evaluation method of an electrospinning apparatus including a nozzle and an electrode,
Under a state where an electric field is formed between the electrode and the nozzle by applying a DC voltage, water is supplied to the nozzle and dropped from the tip of the nozzle, and the dropped water is collected in a metal container. And
Measure the charge amount of the collected water with a charge meter, calculate the charge amount per unit mass of water from the measured value and the mass of dripped or collected water,
An evaluation method for an electrospinning apparatus, wherein the electrospinning apparatus is evaluated using the amount of charge per unit mass of water obtained as an index.   The evaluation method of the electrospinning apparatus according to claim 1, wherein a DC voltage applied between the electrode and the nozzle is set to 10 kV or less in absolute value.   The evaluation method of the electrospinning apparatus according to claim 1 or 2, wherein a supply rate of water to the nozzle is 5.0 g / min or less.   The charge amount of the collected water is measured at a plurality of points in the process of increasing the amount of water in the metal container, and the charge amount per unit mass of water is calculated using the measured values at the plurality of points. The evaluation method of the electrospinning apparatus of any one of Claims 1-3.   The nozzle of the electrospinning device is replaced, and the performance of the nozzle of the electrospinning device is evaluated by calculating the amount of charge per unit mass of water for each of a plurality of devices having different nozzles. The evaluation method of the electrospinning apparatus of any one of 1-4.   The charge amount per unit mass of water is calculated for each of a plurality of electrospinning apparatuses with exchanged electrodes, and the performance of the electrodes of the electrospinning apparatus is evaluated from the results. 2. The method for evaluating an electrospinning apparatus according to item 1.