JP2010121221A - Nanofiber structure and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nanofiber structure having improved mechanical properties and a method for producing the same. <P>SOLUTION: The method for producing a nanofiber structure includes simultaneously performing a step of electrostatically spraying a sample solution by using a jet ESD (Electro-Spray Deposition) method to prepare a nanofiber and producing a nanofiber-containing nanofiber structure on a substrate and an electrostatic spray condition control step in which when the sample solution is electrostatically sprayed by the jet ESD method, the condition of the electrostatic spray is adjusted so as to adjust the physical properties of the nanofiber structure, so that the physical amount of joining part, which is made of the same material as the fiber and which joins at least a part of the nanofiber or at least a part of the substrate is controlled. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a nanofiber structure and a method for producing the same, and more particularly, to a nanofiber structure and a method for producing the nanofiber structure having greatly improved physical properties, that is, physical strength.

  In recent years, nanofiber structures produced from various synthetic polymers and biopolymers have begun to be used for various applications, and are expected to grow into a large industry in the near future. In the US, research on multifunctional special protective clothing worn by police officers, firefighters, doctors, and nurses has already begun, and a large market is expected. Military applications are military uniforms that are lighter than before and have unprecedented functions, and are a collection of nanometer units. Development of new laminated materials with different functions is advancing. In addition, high-performance air filters made from nanofibers have been put to practical use as engine filters, and ultra-lightweight high-functional defense clothing for biochemical hazard protection using nanofibers and regenerative medicine using nanofibers as a medium are also actively developed. Has been done. In Sweden, nanofiber structures are being put into practical use as “environmentally friendly packaging materials”.

  Nanofibers are generally defined as fibers having a diameter of 1 micron (= 1,000 nm) or less in diameter. As a nanofiber manufacturing method, a technique called an ESD (Electro-Spray Deposition) method or an electro-spinning method is the most noticeable technology. The two techniques are technically identical. In the ESD method, a high voltage is applied between the capillary and the substrate, and the sample solution (polymer solution) is sprayed as a charged fiber (fiber) from the nozzle at the tip of the capillary. The charged fiber exiting the capillary is drawn toward the substrate (electrode) in the electric field and is deposited on the substrate to form a thin fiber layer (thin film). Since the nanofibers formed in this way are in a “nonwoven fabric” form, they are expected to be used as nonwoven fabrics.

  On the other hand, several techniques obtained by improving the melt spinning method, which is a traditional spinning method, for nanofibers have been proposed. For example, a melt-blowing method, a flash spinning method, a derivative technique thereof, and the like (in this specification, such a nanofiber manufacturing technique other than the ESD method is referred to as a “traditional melt-spinning method”).

  A nanofiber structure produced by an ESD method or a traditional melt spinning method generally has a mechanical property of low mechanical strength and weakness against tensile force and friction. For example, improvement in mechanical strength such as peeling of the nanofiber layer is required.

Therefore, a technique for improving the mechanical strength by heat-treating nanofibers manufactured by the ESD method has been proposed (see Patent Document 1). Also in the traditional melt spinning method, a technique for improving the mechanical strength of the fiber has been proposed (see Patent Document 2).
Japanese Laid-Open Patent Publication No. 2008-013864 Japanese Laid-Open Patent Publication No. 2007-224460

  Some of the traditional melt spinning methods can produce nanofibers, but many can only produce fibers that are slightly below 1000 nm, and even if fibers of several hundred nm can be produced, the production conditions are severe. There are problems such as. On the other hand, manufacturing equipment using the ESD method has been widely available on the market for several years (Fuence) and is one of the most realistic options for producing nanofibers.

  However, the ESD method has a drawback that it is not suitable for mass production because the amount of spray from one capillary is very small. In the ESD method, although it varies depending on the compound and spray conditions, the spray rate from one capillary is usually said to be several μl per minute. Conventionally, a method of aiming for mass production with a simple configuration in which a large number of capillaries are installed and electrostatic spraying from a large number of capillaries has been adopted, and a manufacturing facility using such an ESD method with a large number of capillaries. Has also been used. However, such a method using a large number of capillaries is insufficient in quality and high in manufacturing cost as a mass production technique.

  Therefore, the present applicant has developed a technique (hereinafter, sometimes referred to as a jet ESD method) that can increase the discharge amount from one spray hole by several thousand times or more to cope with mass production (Japanese Patent Application No. 2007-). 289921).

  In a normal ESD method, depending on the conditions of electrostatic spraying (for example, a set voltage), the sample solution may not be made into fibers but may form ball droplets and adhere to the substrate (electrode or base fabric). is there. And the ball-shaped droplets envelop the resulting nanofibers, which may cause the surface area to be remarkably reduced or cause clogging, impairing the functionality of the nanofiber structure (for example, The filter performance may be reduced). That is, when used as a fiber, a droplet deposited in the fiber (more accurately, a ball-like substance in which the droplet is solidified) is like an impurity. The inventors of the present invention have been researching and searching for the optimum conditions for producing nanofibers using the jet ESD method. However, the research includes conditions where such droplets are not generated as much as possible.

  In such research activities, the present inventors have found that droplets and spherical substances (more precisely, a solid body in which droplets are solidified) deposited in fibers are actually It was found that the mechanical properties were greatly affected. In the jet ESD method, the inventors have found a technique for producing nanofibers with improved mechanical properties by controlling the physical quantity of droplets / dried spherical substances deposited in the fiber and deposited in the fibers.

  Accordingly, an object of the present invention is to provide a nanofiber structure with improved mechanical properties and a method for producing the same. That is, the object of the present invention is to make a mechanically strong material made from a synthetic polymer, a biopolymer, an organic polymer, an inorganic substance, etc. that solves the mechanical property of the nanofiber structure that is weak against tensile force and friction. It is to provide a nanofiber structure.

In order to solve the above-described problems, a method for producing a nanofiber structure according to the first invention includes:
Using a jet ESD method to electrostatically spray a sample solution to form nanofibers to produce a nanofiber structure comprising nanofibers on a substrate;
When the sample solution is electrostatically sprayed by the jet ESD method, in order to adjust the physical properties of the nanofiber layer, at least a part of the nanofibers and other nanofibers are adjusted by adjusting the conditions of electrostatic spraying. An electrostatic spray condition control step for controlling a physical quantity of a connecting portion made of the same material as the nanofiber, which connects (fixes or bonds) at least a part of the substrate or at least a part of the substrate;
Are performed simultaneously.

The method for producing a nanofiber structure according to the second invention
The electrostatic spray conditions are:
Including the discharge amount (flow rate) per hour of the sample solution to be electrostatically sprayed,
It is characterized by that.

Moreover, the method for producing the nanofiber structure according to the third invention is as follows.
The electrostatic spray conditions are:
Including the pressure of the airflow applied to the sample solution to be electrostatically sprayed,
It is characterized by that.

Moreover, the manufacturing method of the nanofiber structure according to the fourth invention is:
The electrostatic spray condition control step includes:
A layer direction physical property control step of controlling a physical quantity of the connecting portion in the thickness direction of the nanofiber layer by changing the electrostatic spraying condition while changing the electrostatic spraying condition;
It is characterized by that.
For example, in the initial stage of electrostatic spraying, if the physical quantity of the connecting portion is controlled to increase (the flow rate or voltage is increased or the jet pressure is decreased), the adhesion between the nanofiber layer and the substrate, peeling Resistance can be remarkably improved. That is, as the physical quantity is increased, the adhesion / peeling resistance between the substrate and the nanofiber layer is significantly improved. In addition, when the control is performed so that the physical quantity of the connected portion is not generated as much as possible except in the initial stage of electrostatic spraying (that is, after the intermediate stage), the characteristics (filter function, surface adsorption function, etc.) of the nanofiber layer are not impaired. . Or if the physical quantity of a connection part is set to an appropriate quantity, it will have a certain amount of mechanical strength, and can also maintain the characteristics (filter function, surface adsorption function, etc.) of a nanofiber layer. Thus, if the spraying conditions are changed according to the stage of electrostatic spraying, the physical quantity can be controlled in the thickness direction of the nanofiber layer.

Moreover, the method for producing a nanofiber structure according to the fifth invention is as follows:
The physical quantity is
It is at least one of the size of the connecting portion, the number per unit area, the mass per unit volume, the number, and the occupied volume.

The nanofiber structure according to the sixth invention is
It is the nanofiber structure manufactured by the invention in any one of 1st-5th.

The nanofiber structure according to the seventh invention is
A nanofiber structure manufactured by any one of the first to fifth inventions,
Adhesion between the nanofiber layer and the substrate is achieved by connecting (fixing) at least a portion of the nanofiber and at least a portion of the substrate with a connecting portion made of the same material as the nanofiber. Or peel resistance is given,
It is characterized by that.

The nanofiber structure according to the eighth invention is
The average remaining number of sections of the nanofiber layer when a crosscut test of 2 mm pitch is performed on the nanofiber layer using a mending tape is 50% or more.
It is characterized by that.

The nanofiber structure according to the ninth invention is
The base material is a mesh-like base material,
It is characterized by that.

The nanofiber structure according to the tenth invention is
A nanofiber structure in which a substrate and a nanofiber layer containing nanofibers are formed on the substrate,
By connecting (fixing) between at least a part of the nanofibers and at least a part of the substrate with a connecting part made of the same material as the nanofibers, the nanofiber layer and the substrate are in close contact with each other. Imparted or peel resistance,
It is characterized by that.

The nanofiber structure according to the eleventh invention is
The nanofiber structure was fabricated using a jet ESD method,
It is characterized by that.

A nanofiber structure according to the twelfth invention is
The average remaining number of sections of the nanofiber layer when a crosscut test of 2 mm pitch is performed on the nanofiber layer using a mending tape is 50% or more.
It is characterized by that.

  A nanofiber structure with increased mechanical strength can be produced, and can be applied to various applications. Furthermore, according to the present invention, post-treatment such as heat-treating the nanofiber structure is unnecessary, and further, it is not necessary to use a material different from the nanofiber for the adhesive, thereby increasing the mechanical strength. However, there is an advantage that the characteristics of the nanofiber structure are not impaired.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  The better the quality of the nanofiber structure (uniformity of fiber diameter and thickness, mixing of irregular droplets), the worse the adhesion to the substrate (substrate such as nonwoven fabric), and the nanofiber layer peels off. To do. In order to solve this problem, after creating the nanofiber structure, it is possible to attach it by some chemical method or hold it down by a physical method, but in these methods, the characteristics of the nanofiber structure can be considered. (For example, a filter function etc.) will be impaired. Therefore, in the present invention, focusing on the fact that the nanofiber structure is microscopically composed of nanofibers and fine droplets (connecting portions) of the same compound as the nanofibers, Electrostatic spraying is performed while controlling the size, ratio to nanofiber, mass per unit volume, number, occupied volume, and the like. That is, the present invention improves the mechanical strength by controlling the physical quantity of the microdroplet (connection portion) while electrostatic spraying simultaneously with the nanofiber and the microdroplet (connection portion) of the same compound as the nanofiber. This is a technique for obtaining a nanofiber structure. This makes it possible to produce a nanofiber structure with increased mechanical strength without impairing the functionality (typically filter performance) of the nanofiber.

<Jet ESD method>
Prior to the description of the present invention, the principle of the jet ESD method used in the present invention and a jet ESD electrostatic spraying device (an immobilization device, an electrostatic spray spinning device) capable of performing the jet ESD method will be described.

<Embodiment 1 of Jet ESD Electrostatic Spraying Device>
FIG. 1 is a conceptual diagram showing a basic configuration of a jet ESD electrostatic spraying apparatus. As shown in the figure, a syringe (container) 1 contains a sample solution 2. The sample solution 2 is, for example, a biopolymer solution such as protein, an organic polymer solution, or a polymer solution.

  Further, the sample solution in the syringe 1 is subjected to extrusion pressure by a plunger (discharge means) 3. The extrusion pressure is given by, for example, a stepping motor and a screw feed mechanism (not shown). The sample solution 2 that has been subjected to the extrusion pressure has its internal pressure increased in the syringe 1 and is discharged from the tip of the nozzle 4. As described above, by providing an adjustment mechanism (stepping motor and screw feed mechanism) that adjusts the speed at which the sample solution is discharged, it is possible to adjust the discharge speed to an appropriate level. Such adjustment makes it possible to obtain a dry deposit rather than a wet deposit formed at an excessive rate. That is, it is possible to adjust the discharge speed to a limit that does not cause wet deposits. Further, in order to cope with mass productivity, it is possible to operate for a long time by separately adding a sample solution tank and replenishing the sample solution from the tank. The atomization can be realized in the same manner regardless of whether the sample solution is a syringe as shown in FIG. 1, a tank as shown in FIG. 3, a capillary, or a box-shaped container. The nozzle 4 is made of metal, and a positive voltage is supplied from the high voltage power supply PS through the wire 5. The negative side of the high voltage power supply PS is connected to the counter electrode EL. By applying a voltage from a high voltage power source, a positive voltage is applied to the sample solution 2 via the nozzle 4 and the solution is positively charged. The polarity of the voltage applied to the sample solution 2 may be negative.

  The sample solution 2 discharged from the tip of the nozzle 4 collides with a high-speed air flow Af of compressed air (or compressed nitrogen) injected from the tube TB, and the sample solution 2 is atomized by the collision energy. It becomes a fine particulate material. The compressed air whose direction and speed are adjusted by an adjusting mechanism (not shown) collides with the sample solution 2 as an air flow (gas) having a constant kinetic energy. The sample solution itself also has a small amount of kinetic energy corresponding to the discharge speed and its specific gravity. The collision energy generated by the collision between the airflow having the kinetic energy and the sample solution causes the particles of the sample solution 2 to overcome the surface tension and jump out of the surface of the sample solution as particles (that is, fine particles and mist as fibers). It will be converted to Increasing the velocity of the compressed air increases this collision energy and reduces the particle size of the atomized droplets. As the speed of the compressed air is increased, the discharge amount of the solution can be increased. This means that a single deposit (such as a thin film, a microstructure formed of nanofibers or nanoparticles) can be produced in a short time, and the manufacturing cost can be reduced.

  At this time, the air flow Af emitted from the tube TB is usually one in which the atmospheric pressure (jet atmospheric pressure) is controlled using a pump or the like. Since the speed of the airflow correlates with the pressure of the airflow, it is preferable to adjust the pressure of the airflow with a valve (not shown) opening degree or the like. That is, by controlling the air pressure of the air flow, a stable air velocity and air flow can be obtained continuously, and therefore a deposit having the same properties (particle size, etc.) can be obtained. In addition, when the air flow Af is applied in the immediate vicinity of the sample solution 2, the particles can be more effectively formed. Therefore, it is preferable to bring the tip of the tube TB close to the nozzle 4 in the distance. When compressed air is sent by a pipe joint, an air nozzle, an air gun or the like instead of the tube TB, the gas flow can be concentrated, and the airflow Af having a stable direction of the airflow can be injected. In addition to compressed air, an inert gas, hot steam, or the like may be used depending on the application. The wire 5 is connected to the metal nozzle 4 at the tip of the syringe 1 as described above, and a positive voltage is applied from the external high voltage power source PS through the wire 5. Finally, a positive charge is transmitted to the sample solution 2 passing through the nozzle 4. In addition to the metal nozzle, the sample solution 2 can be charged with a conductive wire, a conductive thin film, a conductive mesh, or a device that emits charged ions. The negative terminal of the high voltage power supply PS is connected to the counter electrode EL that collects the atomized sample. In FIG. 1, the polarity of the high voltage power source PS is set to be positive for the sample solution 2 and the counter electrode EL is set to be negative. However, even if the polarity of the high voltage power source is changed, a deposit can be formed in the same manner.

  Alternatively, it may be simply grounded without applying a negative polarity voltage to the counter electrode. If the counter electrode is grounded, the potential of the deposit is further grounded, and the merit of being in an electrically neutral state can be eliminated, and the danger of electric shock to the person when the deposit is taken out can be eliminated. The counter electrode usually uses a large flat surface, but the deposit can be formed in that shape by changing it to a desired shape. Normally, the shape of the deposit is formed using a mask, which will be described later. However, if the shape of the counter electrode itself is changed, the setting can be handled easily and the deposit can be formed in any desired shape while easily increasing the collection efficiency. Can be formed.

  The particulate matter 6 atomized by the airflow Af flies in a charged state. Microscopically, the particulate matter can be viewed as an aggregate of particles having the same positive charge. That is, the particles having the same positive charge fly toward the counter electrode EL in a state where the particles have adhered to each other. Since the particles have the same charge, they repeatedly split while repelling each other, and gradually become finer fine particulate matter while being dried and attracted to the negative potential of the counter electrode EL, It is deposited on the substrate 7 supported by the support portion 8 and becomes a deposit 9 (or a specific micro pattern determined by a spot, a film, a thin film mask or the like). The support portion 8 has a role of supporting the two conductive materials of the substrate 7 and the counter electrode EL in a close contact state.

  According to the jet ESD electrostatic spraying apparatus, the sample solution can be atomized at a high speed, so that a thin film or a nanofiber structure (that is, deposit / deposit) can be formed at a very high speed. The deposited / fixed deposit 9 can also be adjusted to a uniform thickness. Moreover, drying of the atomized particulate matter 6 is further promoted by the high-speed airflow Af. In addition, since the sample can be collected at room temperature, it is possible to fix the sample without impairing the activity and / or functionality of the solution. Furthermore, even a highly viscous solution can be easily atomized by the pushing pressure of the plunger 3 and the high-speed airflow Af.

  As shown in FIG. 1, the place where the sample / particulate material accumulates is ahead of the direction in which the compressed air flows. However, by adding another large air flow generation means, the flight direction of the flying particulate material 6 can be changed. The location where the sample / particulate matter is deposited may be arbitrarily set. In this case, the target of the airflow of the two airflow generating means is different, and the airflow is concentrated on the tip of the nozzle and the target is focused on the particulate matter in flight. In this configuration, in order to adjust the temperature, a temperature control mechanism that controls (particularly warms) the temperature of the container such as a syringe, the airflow, and the counter electrode can be provided. By heating the container and airflow, it can be used for sample solutions that are unstable at low temperatures and easily lose their activity and functionality.

<Form 2 of Jet ESD Electrostatic Spraying Device>
FIG. 2 is a conceptual diagram showing a basic configuration of another jet ESD electrostatic spraying apparatus. Hereinafter, in each drawing, the same reference numerals are given to the same elements, and the description thereof is omitted. 1 differs from that of FIG. 1 in that the direction of the high-speed air flow Af is blown from right next to the nozzle, whereas in FIG. The direction of the airflow Af can be atomized in the same manner from diagonally above or directly above. In FIG. 2, avoiding the syringe 1, the air flow Af is collided with the sample solution 2 located at the discharge port EXT from above, and the sample is deposited on the horizontal substrate 7. By arranging in this way, the air flow Af can be applied to the tip of the nozzle 4 while avoiding the syringe 1, and thus the atomization of the air flow Af can be performed efficiently without being reduced. Further, the size of the apparatus increases when the air flow Af is applied from the side of the syringe 1, but in this configuration, the apparatus can be reduced in size by arranging the tube TB obliquely. Further, in this configuration, since the deposit is formed on a horizontal substrate, it is difficult for the deposit to be bent.

<Mode 3 of Jet ESD Electrostatic Spraying Device>
FIG. 3 is a conceptual diagram showing a basic configuration of still another jet ESD electrostatic spraying apparatus. The main difference between the apparatus of FIG. 3 and that of FIG. 1 is that a tank Ta is used instead of the syringe 1, and a discharge port EXT is provided on the bottom surface of the tank Ta instead of the nozzle. Further, an electrostatic induction device EI is provided to face the discharge port EXT provided on the bottom surface of the tank Ta. A positive potential is supplied to the electrostatic induction device EI. The electrostatic induction device (electrode or the like) EI can give a charge to the sample solution 2 without contacting the tank Ta or the sample solution. As described above, the electrostatic induction device EI is configured to indirectly charge the sample solution by electrostatic induction by placing a member such as an electrode applied with a high voltage in the vicinity of the nozzle 4.

  The sample solution is charged before spraying at the location of the discharge port EXT. Since the high-speed airflow Af is applied from the side, the counter electrode EL is also arranged in the extending direction of the airflow Af. In this configuration, since a container is used instead of a syringe, it is more suitable for mass production. Further, since the container has many flat portions, a plurality of discharge ports can be easily provided. Therefore, if the number of discharge ports is increased, it is possible to increase the number of deposits produced and the amount of production per hour.

<Form 4 of Jet ESD Electrostatic Spraying Device>
FIG. 4 is a conceptual diagram showing a basic configuration of still another ESD electrostatic spraying apparatus. The main difference between the apparatus of FIG. 4 and that of FIG. 3 is that the airflow Af is blown out from the direction directly beside the nozzle in FIG. 3, whereas the airflow Af is blown out obliquely from below in FIG. That is. Furthermore, the tank Ta is made conductive, and a wire 5 is connected to the tank Ta to give an electric charge to the sample solution 2 via the tank Ta. As described above, since the air flow Af is applied to the discharge port EXT from obliquely below, the kinetic energy of the air flow Af can be transmitted to the sample solution 2 more efficiently, so that the collision energy becomes higher. Therefore, the atomization speed and atomization efficiency are improved, and the droplets can be further refined.

<Embodiment 5 of Jet ESD Electrostatic Spraying Device>
FIG. 5 is a conceptual diagram showing a basic configuration of still another ESD electrostatic spraying apparatus. The difference between the apparatus of FIG. 5 and that of FIG. 3 is that the discharge port EXT of the tank Ta is arranged on the upper side. Since the discharge port is arranged on the upper side, there is an advantage that the discharge amount can be adjusted in a state where there is no dripping due to the weight of the liquid itself. Furthermore, in this aspect, hot steam is used instead of compressed air, and the hot airflow Af is used. Further, a heater HT is installed in the tank Ta, and the sample solution 2 is heated to be in a molten state. According to this configuration, even a solid or gel-like material can be sprayed and fixed at room temperature. Therefore, according to this structure, it becomes possible to produce a deposit using a substance or material that could not be used as a solvent or a sample.

<Form 6 of Jet ESD Electrostatic Spraying Device>
FIG. 6 is a conceptual diagram showing a basic configuration of still another ESD electrostatic spraying apparatus. The main difference between the apparatus of FIG. 6 and that of FIG. 5 is that in FIG. 5, the direction of the airflow Af is a blowout from diagonally above in FIG. Further, as shown in the figure, the entire apparatus is accommodated in the case CS, and the space where the atomization occurs is decompressed by the vacuum pump VAC. By depressurizing the space in which the atomization occurs, it is possible to further evaporate the solvent and increase the atomization speed, and to fix / deposit the sample with higher activity and functionality. Can do.

<Form 7 of Jet ESD Electrostatic Spraying Device>
FIG. 7 is a conceptual diagram showing a basic configuration of still another ESD electrostatic spraying apparatus. As shown, the apparatus comprises three atomizing units 10a, 10b, 10c. Thus, in this structure, it is possible to provide many atomization units and it is a structure suitable for mass production. Furthermore, in the seventh embodiment, a guide GD for guiding the airflow Af containing the sprayed sample solution / particulate matter to the substrate 7 is provided between the nozzle 4 and the substrate 7. The guide GD makes it possible to effectively guide the air stream Af (ie sprayed sample solution / particulate matter) to the intended deposition area.

<Eighth form of jet ESD electrostatic spraying device>
FIG. 8 is a conceptual diagram showing a basic configuration of an ESD electrostatic spraying device according to still another embodiment of the present invention. The main difference between the apparatus of FIG. 8 and that of FIG. 7 is that a discharge port EXT is provided on the bottom surface of the tank Ta instead of the nozzle, and the tank Ta is made conductive. As shown, the apparatus comprises three atomizing units 11a, 11b, 11c. Thus, this configuration can also be provided with a large number of atomization units, and is a configuration suitable for mass production.

<Form 9 of Jet ESD Electrostatic Spraying Device>
FIG. 9 is a conceptual diagram showing a basic configuration of yet another ESD electrostatic spraying apparatus. As shown in FIG. 9, in this configuration, the discharge port EXT is provided on the side surface of the tank Ta. Further, the sample solution is supplied by adjusting to a desired flow rate and a desired hydraulic pressure by a pump. The airflow Af of this configuration can adjust the flow rate and air pressure according to the type and viscosity of the solution. It is possible to easily adjust the atomization speed / fixation speed by combining these two adjustments. As shown, the apparatus comprises three atomizing units 20a, 20b, 20c. Thus, this apparatus can also provide many atomization units and can be used for mass production. In this configuration, a donut-shaped electrode 12a-c and a mask 13a-c are further provided as a guide mechanism / collecting means for collecting or guiding droplets. Two tanks of high voltage power supplies PS1 and PS2 are applied to the tank Ta-c. A voltage supplied from the high voltage power supply PS2 is applied to the donut-shaped electrode (collimator ring). Since the electrostatically sprayed particles are charged with a high voltage, they fly toward a counter electrode having a large potential difference from the particles themselves. When passing through the donut-shaped electrode ring in the middle, the atomized particles are further narrowed down to the center of the ring by the high voltage repulsive force of the donut-shaped electrode, and the collection efficiency of the atomized droplets is increased. Can be raised. Further, the mask 13a-c provided on the substrate 7a-c is hollowed out in the form of a desired deposition pattern with an insulator such as a fluororesin, and the sample is deposited in the desired pattern while increasing the collection efficiency. c can be deposited. By making the mask from an insulator, the mask is charged the same as the flying particles, and the flying particles are repelled from the mask and concentrated in the shape of the deposition pattern. And it deposits with the shape of the pattern. Therefore, collection efficiency can be increased. In any of the embodiments, as in the seventh embodiment, a cylindrical guide for guiding the airflow Af to the substrate 7 may be provided.

  FIG. 12 is a schematic diagram for explaining the principle of the jet ESD electrostatic spraying apparatus. FIG. 10 is a schematic diagram when atomization is attempted using only an air flow in the jet ESD electrostatic spraying apparatus. FIG. 11 is a schematic diagram when atomization is attempted using only voltage application in the jet ESD electrostatic spraying apparatus. In each figure, the sample solution Sn accommodated in the tank Ta is discharged from the discharge port EXT provided on the bottom surface of the tank Ta. In FIG. 12, the sample solution Sn in the tank Ta is given a positive charge by the high voltage power source PS. The air current collides with the sample solution Sn protruding from the discharge port EXT from the horizontal direction. The particles of the solution are atomized as particulate matter Pa1 by a synergistic action of the kinetic energy of the airflow (which can be regarded as collision energy) and the electrostatic force of the sample solution Sn. The particulate matter Pa1 is dried while flying toward the substrate SB (counter electrode EL).

  The atomized particulate matter Pa1 is reduced in particle size by drying, and electrostatic repulsion due to electric charges is further increased, and the division is repeated and further miniaturized. In addition, while the particulate matter Pa1 is flying toward the substrate SB (more precisely, the electrode EL on the other side of the substrate), the particulate matter Pa1 is further divided by the kinetic energy (collision energy) given by the airflow, and further miniaturized. Go. That is, as shown in FIG. 12, the particulate matter Pa1 has a small particle size and is deposited / adsorbed on the substrate SB as shown as the particulate matter Pa2 at a middle distance between the discharge port EXT and the substrate SB. Sometimes the particle size becomes even smaller, as shown as particulate matter Pa3. The deposited particulate matter Pa3 (deposit) is in a dry or almost dry state and does not lose its activity or functionality. In FIG. 12, a deposit of a microstructure made of nanoparticles is obtained. However, if a material that is easily fiberized is used as a sample, the deposit can be formed as a microstructure made of nanofibers (such as a non-woven sheet). it can.

  In FIG. 10, since the atomization is based only on the airflow, the droplets can be reduced in size only to the extent shown as the particulate matter Pa2. That is, only the amount of impact energy generated by the kinetic energy of the airflow and the kinetic energy of the sample solution Sn discharged from the discharge port EXT is used for atomization. Therefore, it is difficult to make the particle size of the atomized particulate material sufficiently fine so that the particulate material is sufficiently dried. Therefore, a sufficiently dry deposit cannot be formed on the substrate SB, and a solution layer L1 as shown in FIG. 10 is formed. That is, in the case of FIG. 10, the nanostructure is not formed, and the sample cannot be immobilized in a dry state. In this case, since the particulate matter is not charged, it is not attracted by the counter electrode EL. Therefore, the sample is wasted without being collected by the substrate SB.

  In FIG. 11, since electrostatic spraying is performed only by voltage application, when the diameter of the discharge port EXT is too large, it is difficult to atomize just by dropping the liquid as shown in the figure. Further, even if the diameter of the discharge port EXT is sufficiently small, if the discharge amount of the liquid is increased, the liquid simply falls as shown in the figure and cannot be atomized. Therefore, it is difficult to form a sufficient size / thickness / amount deposit on the substrate SB in a short time.

  On the other hand, FIG. 12 shows that the solution is atomized without dropping the liquid as shown in the figure even when the diameter of the discharge port EXT is large and the discharge amount is large. It is possible to produce a thickness / quantity deposit in a very short time.

  FIG. 13 is a schematic diagram for explaining the production principle of the nanofiber structure according to the present invention. The sample solution Sn stored in the tank Ta is discharged from the discharge port EXT provided on the bottom surface of the tank Ta. The sample solution Sn in the tank Ta is given a positive charge by the high voltage power supply PS. The air current collides with the sample solution Sn protruding from the discharge port EXT from the horizontal direction. Due to the synergistic action of the kinetic energy of this air stream (which can be regarded as collision energy) and the electrostatic force of the sample solution Sn, the particles of the solution mist as particulate matter Pa4 and nanofibers Fi1. It will become. The particulate matter Pa4 and the nanofiber Fi1 are dried while flying toward the substrate SB (counter electrode EL).

  The atomized particulate matter is reduced in particle size by drying, and electrostatic repulsion due to electric charges is further increased, and the division is repeated and further miniaturized. In addition, while the particulate matter is flying toward the substrate SB (more precisely, the electrode EL on the other side of the substrate), the particulate matter is repeatedly divided by the kinetic energy (collision energy) given to the airflow and further miniaturized. . Although the behavior of the nanofiber Fi1 in flight is not clearly clarified at present, it can be observed with an SEM photograph or the like after being deposited / fixed on the substrate SB. As shown in the figure, the particulate matter Pa5 and the nanofiber Fi2 are deposited on the substrate. The particulate matter Pa4 functions as a connecting portion that connects (fixes) the nanofiber Fi2 to the substrate SB. As described above, the particulate matter Pa5 significantly improves the mechanical strength as the nanofiber structure, in particular, the adhesion to the substrate and the releasability by connecting (fixing) the nanofiber Fi2 to the substrate SB. . Or it functions as a connection part which connects nanofibers like particulate matter Pa6. Even in the case of a particulate material (connecting portion) that does not contact the substrate SB like the particulate material Pa6, there is an effect of improving the mechanical strength as the nanofiber structure F1. For example, there is an effect of preventing and suppressing fuzz of nanofibers.

<Example 1>
As Example 1 of the present invention, a sample solution was electrostatically sprayed onto an aluminum foil by a jet ESD method under the following conditions to form a nanofiber structure (deposit / deposit). The deposit was observed with an SEM, the diameter of droplets that could be connected portions was measured, the number of droplets was counted, and the number per 1 cm ² was obtained. In order to check the adhesion and peel strength, it is used as a base material for nonwoven fabrics. However, if a nonwoven fabric is used, it is difficult to measure the number of droplets, size, particle size, etc. A foil was used.

<Conditions for Jet ESD Method>
Base material: Aluminum foil Material: PVA powder (polyvinyl alcohol powder)
Sample solution: PVA 10mass% aqueous solution Voltage: 25kV
Flow rate (discharge volume): 800, 1100μL / min
Electrostatic spray amount: 5mL
Jet air pressure: 0.1, 0.2, 0.3, 0.4, 0.5 MPa
Discharge port: 1 place

  FIG. 14 is a graph showing the correlation between the diameter of a droplet that can be a connecting portion of the nanofiber structure produced in Example 1 and the airflow pressure. As shown in this graph, it can be observed that the higher the air pressure, the smaller the diameter of the droplet that can be a connecting portion. It can be observed that the diameter of the droplet increases as the flow rate (discharge amount) of the sample solution to be electrostatically sprayed increases with the same airflow pressure. Further, in the present invention, the physical properties (droplet size, diameter, etc.) of the droplet that can be a connecting portion are adjusted by adjusting at least one of the airflow pressure and the discharge amount, preferably both. Thus, finally, it is possible to adjust the peel strength, peel resistance, and adhesion strength of the base material, the substrate, and the substrate.

  FIG. 15 is a graph showing the correlation between the number of droplets that can be connected to the nanofiber structure produced in Example 1 and the airflow pressure. As shown in this graph, it can be observed that the number of droplets that can be connected portions increases as the airflow pressure increases. Further, it can be observed that the number of droplets decreases as the flow rate (discharge amount) of the sample solution to be electrostatically sprayed increases with the same airflow pressure. That is, as shown in FIGS. 14 and 15, the physical properties such as the number of droplets, the particle size, and the size can be adjusted by the air flow pressure and the discharge amount. In the present invention, as described above, by adjusting at least one of the air flow pressure and the discharge amount, preferably both, the physical properties of the liquid droplets (unit area, number per unit volume, size, etc.) that can become the connecting portion are obtained. By adjusting, finally, it is possible to adjust the peel strength, peel resistance, and adhesion strength of the base material, the substrate, and the base.

  The SEM photograph of the nanofiber structure produced in Example 1 was observed, and the average diameter of the droplets and the number of droplets (around 1 cm 2) were counted. As described above, FIG. 14 shows the change in droplet size when the airflow pressure is changed, and FIG. 15 shows the change in the number of droplets when the airflow pressure is changed. 14 and 15, it can be seen that when the air pressure is high, the droplet size decreases and the number of droplets increases. Therefore, it is possible to control the size and number of droplets according to the purpose, and finally adjust the peel strength, peel resistance, and adhesion strength to the desired values and properties for the base material, substrate, and substrate. is there.

  16, 17 and 18 show SEM photographs (magnification 100 times) of the nanofiber structure produced in Example 1 at a flow rate of 1100 μL / min. FIG. 16 is an SEM photograph of the nanofiber structure produced under conditions of an airflow pressure of 0.1 MPa. FIG. 17 is an SEM photograph of the nanofiber structure produced under the condition of an airflow pressure of 0.3 MPa. FIG. 18 is an SEM photograph of the nanofiber structure produced under the condition of an airflow pressure of 0.5 MPa. As shown in these figures, it can be observed that the higher the airflow pressure, the smaller the droplet size and the number of the droplets.

<Examples 2 and 3>
As Example 2 and 3 of this invention, the sample solution was electrostatically sprayed on the nonwoven fabric base material by the jet ESD method on the following conditions, and the nanofiber structure (deposit / deposit) was formed. Example 2 is a nanofiber structure produced under conditions where the peel strength is improved, and Example 3 is a nanofiber structure produced under conditions where the peel strength is weakened. In order to compare the effects of adhesion, peel strength, and peel resistance of the nanofiber layer to the substrate according to the present invention, a nanofiber structure by a conventional ESD method was produced as Comparative Example 1.

<Example 2: Conditions of jet ESD method>
Base material: Non-woven fabric Material: PVA powder Sample solution: PVA 10mass% aqueous solution Voltage: 21kV
Jet air pressure: 0.5 MPa
Flow rate (discharge volume): 590μL / min
Electrostatic spray amount: 20mL
Base material size: Diameter 56cm
Discharge port: 1 location

<Example 3: Conditions of jet ESD method>
Base material: Non-woven fabric Material: PVA powder Sample solution: PVA 10mass% aqueous solution Voltage: 21kV
Jet air pressure: 0.5 MPa
Flow rate (Discharge rate): 160μL / min
Electrostatic spray amount: 20mL
Base material size: Diameter 56cm
Discharge port: 1 location

<Comparative Example 1: Conditions of ESD method>
Base material: Non-woven fabric Material: PVA powder Sample solution: PVA 10mass% aqueous solution Voltage: 15kV Flow rate (discharge amount): 5μL / min
Electrostatic spray amount: 0.5mL
Nozzle: 1

<Cross cut test>
A peel test (cross cut test) of the nanofiber structures of Examples 2 and 3 and Comparative Example 1 was performed in accordance with JIS5600-5-6. The difference between this embodiment and the standard is that JIS5600-5-6 uses an adhesive tape with a width of 25 mm. In this embodiment, a mending tape with a width of 18 mm (Askul, part number 599-486) is used. In other words, the adhesion between the nanofiber and the substrate was evaluated. In the peeling test, using a cutter on the surface of the film, 6 parallel vertical and horizontal parallel lines are drawn at intervals of 2 mm, and cuts in the shape of a base are made so that 25 square sections are formed in 1 cm ² . The tape is brought into close contact with the part of the base and peeled off, and the number of bases remaining (number of remaining parts) is counted. This was performed in five regions of each nanofiber structure.

  FIG. 19 is a drawing-substituting photograph after the peel test of the nanofiber structure according to Example 2. FIG. 20 is a drawing-substituting photograph after the peel test of the nanofiber structure according to Example 3. As shown in FIG. 19, the nanofiber structure of Example 2 has high peel strength, and as shown in FIG. 20, the nanofiber structure of Example 3 has weak peel strength. This indicates that it is possible to increase the mechanical strength (peeling strength), which is a physical property of the nanofiber structure, by adjusting the number and size of the microdroplets that function as connecting portions according to the present invention. It is. In FIG. 25, the table showing the result of the peeling test of the nanofiber structure of Examples 2 and 3 and Comparative Example 1 is shown. As shown in FIG. 25, the average number of remaining nanofiber structures of Example 2 was 12.6, and about half of the sections remained. The remaining number in Example 3 is 0 on average, and all the sections are peeled off. In Comparative Example 1, it was found that the nanofiber structure produced by the conventional ESD method had a remaining number of 0 in all, and the peel strength was extremely weak. Thus, the nanofiber structure produced by the conventional ESD method does not have sufficient peel strength. Even if the flow rate is adjusted, the ESD method is limited in terms of the maximum flow rate due to its principle, and it is estimated that sufficient peel strength to withstand practical use cannot be obtained.

  FIG. 21 is an SEM photograph (magnification 500 times) of the nanofiber structure produced in Example 2. FIG. 22 is an SEM photograph (5000 magnifications) of the nanofiber structure produced in Example 2. As shown in FIG. 21, a large number of microdroplets are distributed, and it can be observed that a large number of microdroplets are connected (fixed) between the 20-30 μm fiber of the nonwoven fabric and the nanofibers. . That is, in Example 2, it can be seen that there are a large number of microdroplets, and these function as connecting portions to obtain a sufficient peel strength.

  FIG. 23 is an SEM photograph (magnification 500 times) of the nanofiber structure produced in Example 3. 24 is an SEM photograph (5000 times magnification) of the nanofiber structure produced in Example 3. FIG. As shown in FIG. 23, although there are several micro droplets, it is not possible to observe the connection between the non-woven fiber and the nanofiber. That is, in Example 3, since the number of micro droplets is too small, it does not function sufficiently as a connecting portion, and it is understood that sufficient peel strength cannot be obtained.

  Although the present invention has been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications and corrections based on the present disclosure. Therefore, it should be noted that these variations and modifications are included in the scope of the present invention. For example, the functions included in each unit, each means, each step, etc. can be rearranged so as not to be logically contradictory, and a plurality of means, steps, etc. can be combined or divided into one. It is. Moreover, although PVA powder was used in the embodiment, it should be noted that any material that can be made into a fiber by the jet ESD method can be applied to the present invention.

  For example, general polymer materials, biopolymer materials, plastics, high-performance polymer materials, engineering plastics, and the like can also produce nanofiber structures by the technique according to the present invention. Below are some examples with SEM pictures.

  FIG. 26 is an SEM photograph (magnification 500 times) of a nanofiber structure using PAN. It is a nanofiber structure produced using a 12 mass% DMF (N, N-dimethylformamide) solution of PAN. This photo is a cross-sectional photograph, the upper part is a nanofiber layer of chitosan, the lower part is a base material, and the upper part (nanofiber) and the lower part (base material) are connected by a connecting part made of the same material as the nanofiber You can observe what is being done.

  FIG. 27 is an SEM photograph (500 times magnification) of a nanofiber structure using chitosan. It is a nanofiber structure produced using a 12 mass% chitosan aqueous solution (acetic acid 5 mass%, PEG 1 mass%). In this figure, it can be observed that the base material and the nanofiber are bonded together by a connecting portion made of the same material as the nanofiber.

  FIG. 28 is an SEM photograph (magnification 1000 times) of a nanofiber structure using nylon. In this figure, it can be observed that the base material and the nanofiber are bonded together by a connecting portion made of the same material as the nanofiber.

  FIG. 29 is an SEM photograph (100 × magnification) of a nanofiber structure using PAN (polyacrylonitrile). In this figure, it can be observed that the base material and the nanofiber are bonded together by a connecting portion made of the same material as the nanofiber.

  FIG. 30 is an SEM photograph (100 times magnification) of a nanofiber structure using PVA (polyvinyl alcohol). In this figure, it can be observed that the base material and the nanofiber are bonded together by a connecting portion made of the same material as the nanofiber.

  FIG. 31 is an SEM photograph (100 × magnification) of a nanofiber structure using PVDF (polyvinylidene fluoride). In this figure, it can be observed that the base material and the nanofiber are bonded together by a connecting portion made of the same material as the nanofiber.

  FIG. 32 is an SEM photograph (100 × magnification) of a nanofiber structure using PU (polyurethane). In this figure, it can be observed that the base material and the nanofiber are bonded together by a connecting portion made of the same material as the nanofiber.

  Thus, according to the present invention, the present invention is applied to various materials such as PAN (polyacrylonitrile), chitosan, polyurethane, PVA (polyvinyl alcohol), PVDF (polyvinylidene fluoride), PU (polyurethane), It is possible to produce a nanofiber structure with improved mechanical strength.

It is a conceptual diagram which shows the basic composition of a jet ESD electrostatic spraying apparatus. It is a conceptual diagram which shows the basic composition of another jet ESD electrostatic spraying apparatus. It is a conceptual diagram which shows the basic composition of another jet ESD electrostatic spraying apparatus. It is a conceptual diagram which shows the basic composition of another ESD electrostatic spraying apparatus. It is a conceptual diagram which shows the basic composition of another ESD electrostatic spraying apparatus. It is a conceptual diagram which shows the basic composition of another ESD electrostatic spraying apparatus. It is a conceptual diagram which shows the basic composition of another ESD electrostatic spraying apparatus. It is a conceptual diagram which shows the basic composition of another ESD electrostatic spraying apparatus. It is a conceptual diagram which shows the basic composition of another ESD electrostatic spraying apparatus. In a jet ESD electrostatic spraying device, it is a mimetic diagram at the time of trying atomization using only air current. In a jet ESD electrostatic spraying device, it is a mimetic diagram at the time of trying atomization using only voltage application. It is a schematic diagram for demonstrating the principle of a jet ESD electrostatic spraying apparatus. It is a schematic diagram for demonstrating the preparation principle of the nanofiber structure by this invention. 4 is a graph showing a correlation between a diameter of a droplet that can be a connecting portion of a nanofiber structure manufactured in Example 1 and an air pressure. 4 is a graph showing the correlation between the number of droplets that can be a connected portion of the nanofiber structure produced in Example 1 and the air pressure. It is a SEM photograph of the nanofiber structure produced on condition of air pressure 0.1MPa. It is a SEM photograph of the nanofiber structure produced on condition of air pressure 0.3MPa. FIG. 18 is an SEM photograph of the nanofiber structure produced under the condition of an airflow pressure of 0.5 MPa. 4 is a drawing-substituting photograph after a peel test of a nanofiber structure according to Example 2. FIG. 4 is a drawing-substituting photograph after a peel test of a nanofiber structure according to Example 3. FIG. 4 is a SEM photograph (magnification 500 times) of the nanofiber structure produced in Example 2. FIG. 3 is a SEM photograph (magnification: 5000 times) of the nanofiber structure produced in Example 2. 4 is an SEM photograph (magnification 500 times) of the nanofiber structure produced in Example 3. 4 is an SEM photograph (magnification: 5000 times) of the nanofiber structure produced in Example 3. It is a figure which shows the table showing the result of the peeling test of the nanofiber structure of Example 2, 3 and the comparative example 1. FIG. It is a SEM photograph (magnification 500 times) of the nanofiber structure using PAN. It is a SEM photograph (magnification 500 times) of the nanofiber structure using chitosan. It is a SEM photograph (magnification 1000 times) of the nanofiber structure using nylon. It is a SEM photograph (magnification 100 times) of the nanofiber structure using PAN. It is a SEM photograph (magnification 100 times) of the nanofiber structure using PVA. It is a SEM photograph (magnification 100 times) of the nanofiber structure using PVDF. It is a SEM photograph (magnification 30 times) of the nanofiber structure using PUF.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Syringe 2 Sample solution 3 Plunger 4 Nozzle 5 Wire 6 Particulate matter 7 Substrate 7a, 7b, 7c Substrate 8 Support part 9 Deposit 9a-c Deposit 10a, 10b, 10c Atomization unit 11a, 11b, 11c Atomization unit 20a , 20b, 20c Atomization unit 12a-c Donut-shaped electrode 13a-c Mask Af Airflow Ar1-3 Spot array CS Case EL Counter electrode EI Electrostatic induction device EXT Discharge port F1-3 Deposit GD Guide L1-L3 Position Pa1-5 Particulate matter PS, PS1, PS2 High voltage power supply SB Substrate SB1 Substrate SB11-13 Aluminum foil substrate Sn Sample solution SP Spot SPT Support part Ta Tank TB Tube VAC Vacuum pump Fi1, Fi2 Nanofiber F1 Nanofiber structure

Claims (12)

A method for producing a nanofiber structure,
Using a jet ESD method to electrostatically spray a sample solution to form nanofibers to produce a nanofiber structure comprising nanofibers on a substrate;
When the sample solution is electrostatically sprayed by the jet ESD method, in order to adjust the physical properties of the nanofiber layer, at least a part of the nanofibers and other nanofibers are adjusted by adjusting the conditions of electrostatic spraying. An electrostatic spray condition control step for controlling a physical quantity of a connecting portion made of the same material as the nanofiber, which connects at least a part of the substrate or at least a part of the substrate;
The manufacturing method of the nanofiber structure characterized by implementing simultaneously. In the manufacturing method of the nanofiber structure according to claim 1,
The electrostatic spraying conditions are:
Including a discharge amount per hour of the sample solution to be electrostatically sprayed,
The manufacturing method of the nanofiber structure characterized by the above-mentioned. In the manufacturing method of the nanofiber structure according to claim 1 or 2,
The electrostatic spraying conditions are:
Including the pressure of the airflow applied to the sample solution to be electrostatically sprayed,
The manufacturing method of the nanofiber structure characterized by the above-mentioned. In the manufacturing method of the nanofiber structure according to any one of claims 1 to 3,
The electrostatic spray condition control step includes:
A layer direction physical property control step of controlling a physical quantity of the connecting portion in the thickness direction of the nanofiber layer by changing the electrostatic spraying condition while changing the electrostatic spraying condition;
The manufacturing method of the nanofiber structure characterized by the above-mentioned. In the manufacturing method of the nanofiber structure according to any one of claims 1 to 4,
The physical quantity is
It is at least one of the size of the connecting portion, the number per unit area, the mass per unit volume, the number, and the occupied volume.
The manufacturing method of the nanofiber structure characterized by the above-mentioned.   The nanofiber structure manufactured by the manufacturing method of the nanofiber structure of any one of Claims 1-5. A nanofiber structure produced by the method for producing a nanofiber structure according to any one of claims 1 to 5,
By connecting at least a part of the nanofiber and at least a part of the substrate with a connecting part made of the same material as the nanofiber, adhesion between the nanofiber layer and the substrate or Peeling resistance is given,
Nanofiber structure characterized by that. The nanofiber structure according to claim 7, wherein
The average remaining number of sections of the nanofiber layer when a crosscut test of 2 mm pitch is performed on the nanofiber layer using a mending tape is 50% or more.
Nanofiber structure characterized by that. In the nanofiber structure according to any one of claims 6 to 8,
The substrate is a mesh-like substrate;
Nanofiber structure characterized by that. A nanofiber structure in which a substrate and a nanofiber layer containing nanofibers are formed on the substrate,
By connecting at least a part of the nanofiber and at least a part of the substrate with a connecting part made of the same material as the nanofiber, adhesion between the nanofiber layer and the substrate or Imparted peel resistance,
Nanofiber structure characterized by that. The nanofiber structure according to claim 10, wherein
The nanofiber structure was fabricated using a jet ESD method,
Nanofiber structure characterized by that. The nanofiber structure according to claim 10 or 11,
The average remaining number of sections of the nanofiber layer when a crosscut test of 2 mm pitch is performed on the nanofiber layer using a mending tape is 50% or more.
Nanofiber structure characterized by that.